The Use of Sterically Bulky Phosphine Ligands in Iron and Ruthenium Dinitrogen Chemistry
A thesis submitted in partial fulfilment of the requirements for admission to the degree of
Doctor of Philosophy
by
Ryan James Gilbert-Wilson
School of Chemistry The University of New South Wales Australia PLEASE TY!'E Tli~ UNIVERSITY OF NeW SOUTH W.li..ES Tll.. l a/Dlsaemotlon Sh"t 5umame 01 fam~ name: GilllM·Wi~On
Ftrat name. Ry•n 01her namm JameO
AbbreYlllfon tor d Sdlb Tille: The Uoe Ol Sto~t<~lly Bulky Pho~~nlnc l l!iOridsln lrun ana Rlltllentum Olnltnlgflll Cll Ab$traet350 .,.,_ muimum: (PLEASE TYPE) This ll;esls Is pmranly oonc:emoa with 111• dovalopmenl of new muHidcnlQto photphlnellgands, the synthesis anc unodlona ol tron and ruthenium compl=s ot ~e llgllllds, With a •pec:illc toc:w on tho comp!eXoo wnl<:h IMOIJ)Orate 1 dlnlltogellllgano~ All mettl COfi!Piexea wo1o cf1araderlzlld DY ml{ltlnU Tho synl!losls anc dlamCIDiiilillo~ of the ktndered tnpodel phMphlne ligand P(CH,CH,CI'IJP'Pr1)-o (P'P/") Is dosct,oed, oloi\Q wltn lh• •ynlhoala and oha111ctell The oynthestS 8nd ohorJ<:te rtu~OII ol tno extremely hinder«! phosphine llgollda1 P(CH1CH,P'eu,), (P'P>'""), PhP(C:H,CH,P'Ilu,), (PhP'Pi''l. and P(CH,Cf1,CH,P'eu,)J (P'P,""') aro 6Cs0tlbe(j, atong wrl!llhe syntllos Ttll#lrnont at RuCI1(P'P,-., \!Mh • ••rtety ot hydride transfer agents ollorde The synthM1s c.t a Htlea Of tron ana tVlhtmum complfutei 'Mih "'" tlg-n(l P~.or. (P{CH,Ct'I;~PCy2}J) l$ Qft$ctlbttG lh61tOn(U). ru.thfUltutn(O), and tron(l) dlnltrogen tQITIPteus f'e(N,}(P7P,••), Ru(N,)(P'P..,), 2nd lft(N,)(P'p,<>jj" •nd tile !UIIIInlum(l) ohlcnl ccmplex RuC~P'P,") wota -synl!leiiZed "tfeductlon ~n The synl!le$1S and onara«ertzatlon ollh& ~m9n centered pod and ligand precumr "C'P,., Is ducnbed. A mol!lod tor tile lonnot~n ol "'lhenlum hydnde compleXes w1tn carn Ooolal'lt!OI' f'O!lltlng to I heroby g11111t to 1111 University ot New Soutll W"los or II• "ffORis IIIII rtghl to an:h!vo one to mar.. IMIIIIbla my thesis or dr818rti!Mn In wholo or'" panln tne University libranoa In all rorm• ol m~dla, now or llere aner knO\Yfl, subjoclto I~• provfslono of Inc Copyrighj 1\Q 11168 I reloln • II ~tliPOIIY ttg~tt . >UCh •• oatontrt~~nta. l•lso totoln tnc ~~gntto vse In Mu"' we I o!so oulhor1sc Unlu.mty Mlorofilms to usc tho 350 WOld ob1~ct of my lhlffialn 016o /~ .A .... ~~;3 '.)J...... --~ ~ ·--·- ~ -- ~~ Wltna.. lo.ta l'lle Umversrly 'I!GOQ"""'•thatlll•"' may be """"pl•oo•l circumstances reQlllnnr;ll!SJtldiQns on ~pflng or condtUons on use, Reqoosta tor mtlfr:t.an f~r • ponoo or up to 2 years 111ust ca nr8de m wrtung . ll,quuw for a longer petloct uf tellr(ctJon may be consldel'l!d 1~ excuptttmel circumstances and IMUire till a""""""l ol the Oeon .ol Graduate Resoardl FOR OFl'fCE"USii ONLY Oats or completion of rnqullt!llt~nft for Award THIS S~EET IS TO BE GLUED TO lll£ INSlDE FRONT COVER Of llll: lllESIS COPYRIGHT STATEMENT 'I hereby g1rant lhe Unlvernfty of New South Wales or Its agents the right to archive and t.o make available my lhesls or dlsse111!tlon In whole or part In the University nbraries In all forms of media, now or hBrB after known, Sllbject to the provisions t•f lhe Copyright Act 1968. I retain all proprfetary rights, SlJCh as patent rights. I also relafn lhe right to use In future worl AUniENTliCITY STATEMENT 'I Cl!rtil)t lhat the Llbrary deposit digital copy is a direct equivalent or the final o~ally approved version of my thosls. No emendation or contentllas oc:cu:rred and If ther'e am any mtnor var1aUo11s ln formatting, they are the result of the c;onverslon to digital formaL' Signed .... ~~····--~~·~··· "··.. ··" Date ,,, ';?,.~.j-3 /1.3 ...... ,.... , ...... Certificate of Originality 'I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.' Signature: I Preface This thesis is a report of original research undertaken by the author and is submitted for admission to the degree of Doctor of Philosophy at the University of New South Wales. The work was completed in the School of Chemistry at the University of New South Wales during the period March 2009 to August 2012. The work and results presented in this thesis are those of the author, unless otherwise acknowledged. Sections of this work have been published: 1. Ruthenium Hydride Complexes of the Hindered Phosphine Ligand Tris(3-diisopropylphosphinopropyl)phosphine. Bhadbhade, M. M., Field, L. D., Gilbert-Wilson, R., Guest, R. W. and Jensen, P. Inorganic Chemistry, 2011, 50, 6220-6228. t 2. New Super-hindered Polydentate Polyphosphine Ligands P(CH2CH2P Bu2)3, t t PhP(CH2CH2P Bu2)2, P(CH2CH2CH2P Bu2)3 and their Ruthenium (II) Chloride Complexes. Gilbert-Wilson, R., Field, L. D. and Bhadbhade, M. M. Inorganic Chemistry, Accepted January 2012. Sections of this work have been presented at Scientific Conferences: 1. Iron and ruthenium hydride complexes of the novel phosphine ligand Tris(3- diisopropylphosphinopropyl)phosphine. R. Gilbert-Wilson, L. D. Field II 16th Reactive Organometallics Symposium, University of New South Wales, Sydney, June 2009. Oral Presentation. 2. The use of steric factors in the quest for nitrogen fixation by Group 8 metals with phosphine ligands. R. Gilbert-Wilson, L. D. Field 5th Australian Organometallics Meeting, (OZOM 5), University of New South Wales, Sydney, January 2010. Poster Presentation. 3 iPr 3. Iron and ruthenium hydride complexes of the novel phosphine ligand P P3 . R. Gilbert-Wilson, L. D. Field 17th Reactive Organometallics Symposium, Australian National University, Canberra, June 2010. Oral Presentation. 4. Dihydrogen Route to Ruthenium Dinitrogen Complexes. R. Gilbert-Wilson, L. D. Field 6th Australian Organometallics Meeting, (OZOM 6), University of Tasmania, Hobart, January 2011. Oral Presentation. 5. Novel sterically bulky phosphines on ruthenium: Effects on dinitrogen coordination. R. Gilbert-Wilson, L. D. Field, M. M. Bhadbhade III 1st European Association for Chemical and Molecular Sciences Inorganic Chemistry Conference (EICC-1), University of Manchester, Manchester, UK, 11th -14th April 2011. Poster Presentation. 2 Cy 6. Iron and ruthenium nitrogen complexes of ligand P P3 and initial studies of ligand 2 Cy C P3 on ruthenium. R. Gilbert-Wilson, L. D. Field, 19th Reactive Organometallics Symposium, Australian National University, Canberra, June 2011. Oral Presentation . 7. Cracking the Nirtrogen triple Bond: Iron and Ruthenium Dinitrogen Chemistry. R. Gilbert-Wilson, L. D. Field The Faculty of Science Postgraduate Research competition for Excellence in Postgraduate Research, University of New South Wales, Sydney, 4th August 2011. Combined Poster and Oral Presentation. 8. Novel Iron and Ruthenium Dinitirogen Complexes with Cyclohexyl-Substituted Phosphine Ligands. R. Gilbert-Wilson, M. M. Bhadbhade, L. D. Field 11th Inorganic Conference of the Royal Australian Chemical Institute and the New Zealand Institute of Chemistry, (IC-11), University of Western Australia, Perth, 4th-8th December 2011. Oral Presentation. 9. Three and a Half Years of Sterically Bulky Phosphines: The Highlights Reel. IV R. Gilbert-Wilson, L. D. Field Reactive Organometallics Symposium 21, Australian National University, Canberra, ACT, Australia, 22nd June, 2012, Oral Presentation. 10. Sterically Bulky Phosphine Ligands on Iron and Ruthenium: Dinitrogen, Iron(I) and Ruthenium(I) Complexes. R. Gilbert-Wilson, L. D. Field Gordon Research Seminar on Organometallic Chemistry, Salve Regina University, Newport, Rhode Island, USA, 7th-8th July, 2012, Poster Presentation 11. Sterically Bulky Phosphine Ligands on Iron and Ruthenium: Dinitrogen, Iron(I) and Ruthenium(I) Complexes. R. Gilbert-Wilson, L. D. Field Gordon Research Conference on Organometallic Chemistry, Salve Regina University, Newport, Rhode Island, USA, 8th-13th July, 2012, Poster Presentation V Acknowledgements A number of people have made direct and indirect contributions to this work, without the people I've had around me the last three and a half years wouldn't have been such a fantastic experience, so thank you. First thanks go to my supervisor Professor Les Field. My deepest gratitude for the advice, support, guidance, chemistry knowledge, catchphrases, stories and laughs you have given me throughout this work. But most of all I want to thank you for showing me how it’s possible to be a successful academic with a wonderful family who enjoys their life, which even makes up for the waiting on paper drafts, so thank you. Without the efforts of both Dr. Hsiu Lin Li and Dr. Alison Magill this PhD might have happened but it would have been genuinely awful, both in quality and as an experience for me so thank you both. Hsiu Lin for being a fantastic co-supervisor, even before you were one officially, for all the amazing proofreading, for keeping me on track, teaching and advising me through the whole process. Thanks also for constantly feeding me, though I feel sorry for Liem that so much of his childhood chocolate went to me. Alison for knowing everything, fixing everything, being a source of great ideas and especially for the evening chats looking over the village green. You taught me a lot about how to think like a chemist and talked me through some of the hardest bits, so thank you. VI I’ve had the pleasure of sharing our lab with some great students over the last couple of years, unfortunately none of them for as long as I would have liked, but thanks go to Susan de Boer, Tim Shearer, Tanya Tan and Peter Jurd for their camaraderie. To my co-supervisor at the start of this project Dr. Guy Clentsmith, thanks for the help and advice at the inception of this project. I want to thank all the other academics in the UNSW School of chemistry for always being helpful and giving me great advice when I’ve needed it. Special thanks to Professor Barbara Messerle, Dr. Graham Ball and Associate Professor Stephen Colbran. All of the staff at the NMR facility have my utmost gratitude, not just for employing and teaching me over the last three years, but also for being incredibly welcoming, fixing my problems, and making the NMR work in this thesis what it is. So thanks go to Dr. Jim Hook, Dr. Don Thomas, Dr. Adelle Amoore, Dr. Doug Lawes and Hilda To my crystallographer Dr. Mohan Bhadbhade, we had some great times and some not so great times, but above all we had a lot of times. Throughout them all you were always filled with a boundless enthusiasm for crystallography which rubbed off on me, so thank you. The unfortunate geographical isolation of our lab from the rest of the school meant I didn’t get to see as much of my fellow PhD students as I would have liked, but when I did it was always fun and great to know we were all in it together. Special mention to Giulia Mancano for all the early morning runs and the after work rants, and to Sam Furfari for being a great conference buddy. VII I want to thank Alice Lang for two amazing years, you are going to conquer the world someday and I’m a better person for the time we spent together, so thank you. Getting involved in debating at UNSW changed my life, significantly for the better, and one of the best parts has been the amazing people I met through it. Mariel Barnes for being the best of friends, be it netball, debating, trivia and just life in general, you have been there, been there for me and been awesome and I don’t tell you it enough. To Anthony Morris, Vincent Wang, Kristyn Glanville, Stephen Garofano and David Ong, for the debating, the trivia and the karaoke but mostly for the interesting discussions and arguments, you’ve been a wonderful group of people I’ve been privileged to know. There are too many other debaters to thank individually who given me so much fun and kept me sane through my PhD. I do want to thank Sean Lawson, Dave Maher and Ben Williams all the great if slightly drunken discussions. A big thanks also to Angela Kintominas for the African adventures and general awesomeness, may we continue to reunite in exotic foreign locales long into the future. I owe an enormous amount to Daniel Kluger-Wynne and Elina Levinsky, for kick starting my life in Sydney, great weekends away in Canberra and providing constant fun, friendship and cards through the last three and a half years. I love you both, you’re awesome and I couldn’t be more excited you’re getting married. Moving from Melbourne to Sydney meant I left a lot of great friends there, but I’ve been lucky enough that they welcomed me with open arms whenever I was back in Melbourne VIII and even came up visited me up in Sydney. So thank you Sarah Freeman, Nikki Rubenstein, Joe Osborn, Hugh Sheppard, Roisin Briscoe, Or Cain and Dave Riglar, I love you guys. Thank you to Lindsay Bloch for being an great roommate over the last two and half years, it has been a lot of fun. I gratefully acknowledge the financial support I have received over the past four years from the Australian Government and the University of New South Wales. Last and definitely not least I have to thank my wonderful family, Mum, Dad and my little sister Hilary. You made me who I am, helped me when I needed it, advised me when I needed it, deflated my ego when I needed it and provided a wonderful home to holiday/return to. I love you all more than you can ever know. Ryan Gilbert-Wilson August 2012 IX List of Abbreviations 1D one dimensional 2D two dimensional approx. approximately atm atmosphere(s) br broad (NMR or IR) b.p. boiling point Bu butyl C6D6 deuterated benzene ca. circa COSY correlations spectroscopy Cy cyclohexyl į chemical shift (ppm) d deutero d doublet (NMR) DCM dichloromethane dd doublet of doublets (NMR) ddd doublet of doublet of doublets (NMR) ddq doublet of doublet of quartets (NMR) ddt doublet of doublet of triplets (NMR) dtd doublet of triplet of doublets (NMR) ESI electrospray ionisation Et ethyl EtOH ethanol FID free induction decay X h heptet (NMR) HOMO highest occupied molecular orbital HRMS high resolution mass spectrometry HSQC heteronuclear correlation through single quantum coherence Hz hertz (s-1) iPr isopropyl IR infrared J scalar coupling constant LRMS low resolution mass spectrometry LUMO lowest unoccupied molecular orbital m multiplet m meta M metal m/z mass to charge ratio Me methyl min. minute(s) MS mass spectrometry n normal NMR nuclear magnetic resonanance o ortho p para p pentet (NMR) Ph phenyl ppm parts per million q quartet (NMR) XI R alkyl group ref. reference s singlet (NMR or IR) t triplet (NMR) tBu tertiary-butyl THF tetrahydrofuran w/v weight by volume w/w weight by weight Ligand convention used in this work All ligands have the abbreviation X n R Y Pm Where X = non arm substituent on central phosphine Y = central coordinating atom of ligand n = number of methylene units separating the central coordinating atoms from the coordinating atoms on the arms of the ligand. m = number of ligand arms. R = type of substituent on the arm phosphines. 3 iPr i P P3 P(CH2CH2CH2P Pr)3 2 tBu t P P3 P(CH2CH2P Bu)3 3 tBu t P P3 P(CH2CH2CH2P Bu)3 2 tBu t PhP P2 PhP(CH2CH2P Bu)2 2 Cy P P3 P(CH2CH2PCy)3 H 2 Cy C P3 HC(CH2CH2PCy)3 XII Table of Contents 1 Introduction ...... 1 1.1 Nitrogen Fixation ...... 1 1.2 Haber - Bosch process ...... 2 1.3 Biological Nitrogen Fixation ...... 4 1.4 Chemistry of Dinitrogen Complexes ...... 5 1.4.2 Dinitrogen-Metal Binding ...... 6 1.4.3 Dinitrogen Complex Synthesis ...... 8 1.4.3.1 Displacement of a weakly bound ligand by N2 ...... 8 1.4.3.2 Spontaneous co-ordination of dinitrogen at a vacant co-ordination site ...... 10 1.4.3.3 Reduction of metal complexes leading to low-valence metal fragments that bind and activate dinitrogen...... 10 1.4.4 Catalytic Dinitrogen Fixation ...... 11 1.4.5 Nitrogen fictionalization on iron ...... 15 1.4.5.1 Conversion of dinitrogen to ammonia and hydrazine on iron ...... 15 1.4.5.2 Other functionalization of dinitrogen on iron...... 20 1.4.6 Coordination chemistry of reduced dinitrogen species on iron ...... 24 1.4.6.1 Iron intermediates along the alternating pathway ...... 24 1.4.6.2 Iron intermediates along the distal pathway ...... 27 1.4.7 Ruthenium dinitrogen complexes and nitrogen fixation intermediates...... 30 1.4.8 Protonation side reactions ...... 35 1.5 Aims of this work ...... 36 1.6 Structure of this Thesis ...... 37 1.7 References ...... 39 2 Ruthenium hydride complexes containing the hindered phosphine ligand 3 iPr Tris(3-diisopropylphosphinopropyl)phosphine P P3 ...... 47 2.1 Introduction ...... 47 2.2 Synthesis of Tris(3-diisopropylphosphinopropyl)phosphine, i 3 i P(CH2CH2CH2P Pr2)3, P P3 Pr (1) ...... 48 3 iPr + 2.3 Synthesis and characterization of [RuCl(P P3 )] (4) ...... 50 3 iPr + 2.3.1 X-ray Crystallography of [RuCl(P P3 )] (4) ...... 50 3 iPr + 2.3.2 NMR analysis of [RuCl(P P3 )] (4) ...... 53 XIII 3 iPr 2.4 Synthesis and characterization of RuH2(P P3 ) (5) ...... 57 3 iPr 2.4.2 X-ray Crystallography of RuH2(P P3 ) (5) ...... 57 3 iPr 2.4.3 NMR Analysis of RuH2(P P3 ) (5) ...... 59 3 iPr 2.5 Synthesis and Characterization of [Ru(H2)(H)(P P3 )][BPh4], (6[BPh4]) ...... 61 Scheme 2.5 ...... 61 3 iPr 2.5.2 X-ray Crystallography of [Ru(H2)(H)(P P3 )][BPh4], (6[BPh4]) ...... 61 3 iPr 2.5.3 NMR Analysis of [Ru(H2)(H)(P P3 )][BPh4], (6[BPh4]) ...... 64 2.6 Conclusions ...... 67 2.7 References ...... 69 t 3 New Super-hindered Polydentate Polyphosphine Ligands P(CH2CH2P Bu2)3, t t PhP(CH2CH2P Bu2)2, P(CH2CH2CH2P Bu2)3 and their Ruthenium(II) Chloride Complexes ...... 72 3.1 Introduction ...... 72 3.2 Preparation and characterization of phosphine ligands ...... 73 t 2 tBu 3.2.1 Synthesis of P(CH2CH2P Bu2)3, P P3 (10), ...... 73 3.2.1.1 Di(tert-butyl)chlorophosphine, ((CH3)3C)2PCl (9) ...... 74 3.2.1.2 Di(tert-butyl)phosphine, ((CH3)3C)2PH (7) ...... 75 3.2.1.3 Trivinylphosphine, (12) ...... 76 t 2 tBu 3.2.1.4 P(CH2CH2P Bu2)3, P P3 (10) ...... 76 t 2 tBu 3.2.2 Synthesis of PhP(CH2CH2P Bu2)2 (PhP P2 , 14) ...... 77 3.2.2.2 Divinylphenylphosphine (15) ...... 78 t 2 tBu 3.2.2.3 PhP(CH2CH2P Bu2)2 (PhP P2 , 14) ...... 79 t 3 tBu 3.2.3 Synthesis of P(CH2CH2CH2P Bu2)3, (P P3 , 16); ...... 79 3.3 Preparation and characterization of ruthenium chlorido complexes ...... 80 2 tBu 3.3.1 Synthesis of Ru(P P3 )Cl2 (18) ...... 80 2 tBu 3.3.2 NMR characterization of RuCl2(P P3 ) (18) ...... 81 2 tBu 3.3.3 Synthesis of RuCl2(PhP P2 ) (19): ...... 83 2 tBu 3.3.4 X-ray Crystallography of RuCl2(PhP P2 ) (19) ...... 83 2 tBu 3.3.5 NMR characterization of RuCl2(PhP P2 ) (19) ...... 85 3 tBu 3.3.6 Synthesis of RuCl2(P P3 ) (20) ...... 87 3 tBu 3.3.7 X-ray Crystallography of RuCl2(P P3 ) (20) ...... 87 3 tBu 3.3.8 NMR characterization of RuCl2(P P3 ) (20) ...... 90 XIV 3.4 Solid state NMR analysis ...... 91 3.5 Conclusions ...... 94 3.6 References ...... 95 4 Ruthenium Tris(3-di(tert-butyl)phosphinoethyl)phosphine hydride complexes .. 99 4.1 Introduction ...... 99 2 tBu 4.2 Treatment of RuCl2(P P3 ) with hydride reagents...... 101 2 tBu 4.2.1 Synthesis and characterization of RuHCl(P P3 ) (21) ...... 101 2 tBu 4.2.2 Synthesis and characterization of RuH(BH4)(P P3 ) (22) ...... 105 2 tBu 4.2.3 Synthesis and characterization of RuH(AlH4)(P P3 ) (23) ...... 111 2 tBu 4.3 Further reactions of Ru(H)(AlH4)(P P3 ) (23) ...... 115 2 tBu 4.3.1 Synthesis and characterization of K[Ru(H)3(P P3 )] (24) ...... 115 2 tBu 4.3.2 Synthesis and characterization of RuH2(CO)(P P3 ) (25) ...... 119 2 tBu 4.4 RuH2(N2)(P P3 ) (26) and related complexes ...... 123 2 tBu 4.4.1 Synthesis and characterization of RuH2(N2)(P P3 ) (26) ...... 123 15 2 tBu 15 4.4.1.2RuH2( N2)(P P3 ) ( N2-26) ...... 127 2 tBu 4.4.2 Synthesis and characterization of RuH2(H2)(P P3 ) (27) ...... 128 2 tBu 4.5 Small molecule adducts of RuHCl(P P3 ) (21) ...... 129 2 tBu 4.5.1 Synthesis and characterization of RuHCl(CO)(P P3 ) (28) ...... 129 2 tBu 4.5.2 Synthesis and characterization of RuHCl(N2)(P P3 ) (29) ...... 132 4.6 Nitrogen complex reactivity ...... 135 4.7 Conclusions ...... 136 4.8 References ...... 138 5 Iron and Ruthenium Dinitrogen Complexes of 2 Cy Tris(2-dicyclohexylphosphinoethyl)phosphine (P P3 ) ...... 140 5.1 Introduction ...... 140 5.2 Ligand ...... 141 5.3 Metal complexes ...... 142 5.4 Dinitrogen complexes ...... 144 2 Cy 2 Cy 5.4.1 Synthesis of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34)...... 144 2 Cy 2 Cy 5.4.2 NMR of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34)...... 145 15 2 Cy 5.4.3 N studies of Ru(N2)(P P3 ) (34)...... 146 XV 2 Cy 2 Cy 5.4.4 X-ray crystallography of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34)...... 147 5.5 Iron(I) and ruthenium(I) complexes ...... 152 2 Cy 5.6 FeH2(P P3 ) (37) ...... 161 5.7 Reactivity of dinitrogen complexes ...... 166 5.8 Conclusions ...... 173 5.9 References ...... 175 2 Cy 6CP3 Synthesis and Complexes ...... 179 6.1 Introduction ...... 179 H 2 Cy 6.2 Synthesis of tris[2-(dicyclohexylphosphino)ethyl]methane) ( C P3 , 46) ...... 181 6.2.1 Preparation of [(methoxycarbonyl)methylene]triphenylphosphorane (41) ... 181 6.2.2 Preparation of 3-(2-Hydroxyethyl)pentane-1,5-diol (43) ...... 183 6.2.3 Preparation of 3-(2-Chloroethyl)-1,5-dichloropentane (44) ...... 183 H 2 Cy 6.2.4 Preparation of tris[2-(dicyclohexylphosphino)ethyl]methane) ( C P3 , 46) 183 2 Cy 6.3 Synthesis and characterization of ruthenium complexes with the C P3 ligand. 185 6.3.1 Previous CP3 complex synthesis...... 185 6.3.2 CP3 complexes from ruthenium dihydrides precursors...... 186 6.3.3 Synthesis of suitable ruthenium dihydride precursors ...... 186 2 Cy 2 Cy 6.3.4 RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) ...... 187 2 Cy 2 Cy 6.3.4.1 Synthesis of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) ...... 187 2 Cy 2 Cy 6.3.4.2 X-ray crystallography of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) ...... 189 2 Cy 2 Cy 6.3.4.3 NMR spectroscopy of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) 193 2 Cy 6.3.4.4 Attempted reactions of RuH(N2)(C P3 ) (49) ...... 195 2 Cy 6.4 Attempted synthesis and characterization of iron complexes with the C P3 ligand...... 197 6.5 Conclusions ...... 199 6.6 References ...... 200 7 Summary, Conclusions and Future Work ...... 209 3 iPr 7.1 Ruthenium hydride complexes containing P P3 , (1)...... 209 2 tBu 2 tBu 7.2 Super-hindered Polydentate Polyphosphine Ligands P P3 (10), PhP P2 , 3 tBu (14), P P3 (16) and their Ruthenium(II) Chloride Complexes...... 211 2 tBu 7.3 Ruthenium P P3 (10) hydride complexes ...... 212 XVI 2 Cy 7.4 Iron and Ruthenium Dinitrogen Complexes of P P3 (30) ...... 214 H 2 Cy 7.5 C P3 (46) Synthesis and Complexes ...... 215 7.6 Future directions ...... 216 7.6.1 Ligand design ...... 216 7.6.2 Nitrogen complex reactivity ...... 218 7.6.3 Solid state NMR ...... 219 8 Experimental ...... 220 8.1 General Procedures ...... 220 8.1.1 Solvent Purification ...... 220 8.1.2 Reagent Sources ...... 220 8.1.3 Acid/base titration ...... 221 8.1.4 Software ...... 221 8.1.5 Infrared Spectra ...... 221 8.1.6 Microanalysis ...... 222 8.2 NMR Spectroscopy ...... 222 8.2.1 Deuterated Solvent Purification ...... 222 8.2.2 Referencing NMR Spectra ...... 222 8.2.3 Air sensitive sample preparation ...... 223 8.2.4 NMR Spectrometers ...... 223 8.2.5 NMR Spectroscopy with in machine photolysis ...... 223 8.3 Mass Spectrometry ...... 224 8.4 X-ray Crystallography ...... 224 8.5 Chapter 2 Experimental ...... 225 i 3 iPr 8.5.1 Synthesis of P(CH2CH2CH2P Pr2)3, P P3 (1) ...... 225 8.5.1.1P(CH2CH2CH2Br)3 (2)...... 225 i 8.5.1.2LiP Pr2 (3)...... 226 3 iPr 8.5.1.3P P3 (1)...... 226 3 iPr 8.5.2 Synthesis of [RuCl(P P3 )][BPh4] (4[BPh4])...... 227 3 iPr 8.5.3 Synthesis of Ru(P P3 )H2 (5)...... 229 3 iPr 8.5.4 Synthesis of [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4])...... 230 8.6 Chapter 3 Experimental ...... 231 t 8.6.1 Synthesis of Di(tert-butyl)phosphine, Bu2PH (7) ...... 231 XVII 8.6.1.1Tert-butylmagnesium chloride, tBuMgCl (8) ...... 231 t 8.6.1.2Di(tert-butyl)chlorophosphine, Bu2PCl (9) ...... 232 t 8.6.1.3Di(tert-butyl)phosphine, Bu2PH. (7) ...... 233 8.6.2 Synthesis of tris(2-di(tert-butyl)phosphinoethyl)phosphine, t 2 t P(CH2CH2P Bu2)3, P P3 Bu. (10)...... 234 8.6.2.1Vinylmagnesium bromide, CH2CHMgBr. (11) ...... 234 8.6.2.2Trivinylphosphine, P(CHCH2)3. (12) ...... 235 8.6.2.3Lithium Diisopropylamide, LiN(CH(CH3)2)2. (13) ...... 236 t 8.6.2.4Tris(2-di(tert-butyl)phosphinoethyl)phosphine, P(CH2CH2P Bu2)3, 2 tBu P P3 . (10) ...... 236 t 2 t 8.6.3 Synthesis of PhP(CH2CH2P Bu2)2 PhP P2 Bu (14) ...... 237 8.6.3.1Divinylphenylphosphine, PhP(CH=CH2)2. (15) ...... 237 t 2 tBu 8.6.3.2PhP(CH2CH2P Bu2)2 PhP P2 . (14) ...... 238 t 3 tBu 8.6.4 Synthesis of P(CH2CH2CH2P Bu2)3, P P3 . (16)...... 239 8.6.4.1LiP(C(CH3)3))2. (17) ...... 240 t 3 t 8.6.4.2P(CH2CH2CH2P Bu2)3, P P3 Bu. (16) ...... 240 2 tBu 8.6.5 Synthesis of RuCl2(P P3 ), (18)...... 241 2 tBu 8.6.6 Synthesis of RuCl2(PhP P2 ) (19)...... 242 3 tBu 8.6.7 Synthesis of RuCl2(P P3 ) (20)...... 243 8.7 Chapter 4 Experimental ...... 245 2 tBu 8.7.1 Synthesis of RuHCl(P P3 ) (21)...... 245 2 tBu 8.7.2 Synthesis of RuH(BH4)(P P3 ) (22)...... 246 2 tBu 8.7.3 Synthesis of RuH(AlH4)(P P3 ) (23)...... 247 2 tBu 8.7.4 Synthesis of K[RuH3(P P3 )] (24)...... 248 2 tBu 8.7.5 Synthesis of RuH2CO(P P3 ) (25)...... 249 2 tBu 8.7.6 Synthesis of RuH2(N2)(P P3 ) (26)...... 250 15 2 tBu 15 8.7.6.1Synthesis of RuH2( N2)(P P3 ) ( N2-26)...... 251 2 tBu 8.7.7 Synthesis of RuH2(H2)(P P3 ) (27)...... 252 2 tBu 8.7.8 Synthesis of RuHCl(CO)(P P3 ) (28)...... 253 2 tBu 8.7.9 Synthesis of RuHCl(N2)(P P3 ) (29)...... 254 8.8 Chapter 5 Experimental ...... 255 XVIII 8.8.1 Synthesis of Tris(2-di(cyclohexyl)phosphinoethyl)phosphine, 2 Cy P(CH2CH2PCy2)3, P P3 . (30) ...... 255 2 Cy 8.8.2 Synthesis of [FeCl(P P3 )][BPh4] (31[BPh4])...... 256 2 Cy 8.8.3 Synthesis of [RuCl(P P3 )][Cl] (32[Cl])...... 256 2 Cy 8.8.3.1[RuCl(P P3 )][BPh4] (32[BPh4])...... 257 2 Cy 8.8.4 Synthesis of Fe(N2)(P P3 ) (33)...... 257 2 Cy 8.8.5 Synthesis of Ru(N2)(P P3 ) (34) ...... 258 15 2 Cy 15 8.8.5.1Ru( N2)(P P3 ) ( N2-34)...... 259 2 Cy 8.8.6 Synthesis of [Fe(N2)(P P3 )][BPh4] (35[BPh4])...... 260 2 Cy 8.8.7 Synthesis of RuCl(P P3 ) (36)...... 260 2 Cy 8.8.8 Synthesis of FeH2(P P3 ) (37)...... 261 2 Cy 8.8.9 Synthesis of [FeH(N2)(P P3 )][BF4] (38[BF4]) ...... 262 2 Cy 8.8.10 Synthesis of [RuH(N2)(P P3 )][BF4] (39[BF4])...... 263 8.9 Chapter 6 Experimental ...... 265 8.9.1 Synthesis of Tris[(2-dicyclohexylphosphino)ethyl]methane, H 2 Cy HC(CH2CH2PCy2)3 C P3 , (46) ...... 265 8.9.1.1[(Methoxycarbonyl)methyl]triphenylphosphonium Bromide, [Ph3PCH2CO2Me]Br, (40) ...... 265 8.9.1.2[(Methoxycarbonyl)methylene]triphenylphosphorane, Ph3P=CHCO2CH3, (41) ...... 266 8.9.1.33-(Methoxycarbonyl)methylpent-2-enedioate, CH3O2CCHC(CH2CO2Me)2, (42) ...... 267 8.9.1.43-(2-Hydroxyethyl)pentane-1,5-diol, CH(CH2CH2OH)3, (43) ...... 267 8.9.1.53-(2-Chloroethyl)-1,5-dichloropentane, CH(CH2CH2Cl)3, (44) ...... 268 H 2 Cy 8.9.1.6Tris[(2-dicyclohexylphosphino)ethyl]methane, C P3 (46) ...... 269 8.9.2 Synthesis of RuH2(N2)(PPh3)3, (47) ...... 270 2 Cy 8.9.3 Synthesis of RuH(CO)(C P3 ) (48)...... 271 2 Cy 8.9.4 Synthesis of RuH(N2)(C P3 ) (49)...... 272 8.10 References ...... 274 Appendix A1 Crystallography Data ...... A-1 Appendix A2 Ruthenium Dinitrogen Complexes ...... A-3 Appendix A3 Publications ...... A-11 Appendix A4 EPR Simulations ...... A-28 XIX List of Figures 1 Introduction ...... 1 Figure 1.1 Distal and alternating mechanisms for the fixation of dinitrogen...... 3 Figure 1.2 Core structure of the molybdenum-iron cluster in the Azotobacter vinelandii nitrogenase protein...... 5 Figure 1.3 Bonding between dinitrogen and a metal center involves both ı and ʌ components...... 6 Figure 1.4 The catalytic Chatt cycle for the reduction of dinitrogen...... 12 Figure 1.5 Schrock's N2-fixation catalyst, Mo(N2)[(HIPT)N3N] ...... 13 Figure 1.6 [Mo(N2)2(PNP)]2(μ-N2) ...... 14 Figure 1.7 Ruthenium DPB binds a number of substrates of nitrogen fixation importance.69a ...... 31 2 Ruthenium hydride complexes containing the hindered phosphine ligand 3 iPr Tris(3-diisopropylphosphinopropyl)phosphine P P3 ...... 47 Figure 2.1 ORTEP plot (50% thermal ellipsoids) of A) 3 iPr [RuCl(P P3 )][BPh4].THF (4[BPh4]) and for comparison B) i 2a [RuCl(P(CH2CH2P Pr2)3)][BPh4]. Only one of the two complex cations in each asymmetric unit in shown. Selected hydrogen atoms, tetraphenylborate anions and THF solvate have been omitted for clarity...... 51 Figure 2.2 Variable temperature 31P{1H} NMR spectra for 3 iPr [RuCl(P P3 )][BPh4] (4[BPh4]) (242.95 MHz, methylene chloride-d2)...... 55 Figure 2.3 ORTEP plot (50% thermal ellipsoids) of one of the two 3 iPr [RuH2(P P3 )] (5) units within the asymmetric unit. Selected hydrogen atoms have been removed for clarity...... 58 1 Figure 2.4 Selected high field region of H NMR (600 MHz, benzene-d6) 3 iPr RuH2(P P3 ) (5) with coupling tree...... 60 Figure 2.5 ORTEP plot (50% thermal ellipsoids) of the complex cation of 3 iPr [Ru(H2)(H)(P P3 )][BPh4].EtOH (6[BPh4].EtOH. Selected hydrogen atoms have been removed for clarity...... 62 31 1 Figure 2.6 P{ H} NMR spectrum (242.9 MHz, THF-d8) of 3 iPr [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) at 298 K, 244 K and 215 K ...... 65 1 31 Figure 2.7 H2 and/or HD resonance in the H{ P} NMR spectrum (700 MHz, THF-d8) of partially deuterated XX 3 iPr [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) at 200 K with resolution enhancement...... 66 t 3 New Super-hindered Polydentate Polyphosphine Ligands P(CH2CH2P Bu2)3, t t PhP(CH2CH2P Bu2)2, P(CH2CH2CH2P Bu2)3 and their Ruthenium(II) Chloride Complexes ...... 72 Figure 3.1 Variable temperature 31P{1H} NMR spectra (243 MHz, Solvent: 2 tBu CD2Cl2) of RuCl2(P P3 ) (18) with spectra at (from front) 174 K, 188 K, 204 K, 220 K, 236 K, 252 K, 268 K and 284 K...... 82 2 tBu Figure 3.2 ORTEP plot (50% thermal ellipsoids) of RuCl2(PhP P2 ) (19), selected hydrogen atoms have been omitted for clarity...... 84 Figure 3.3 Variable temperature 31P{1H} NMR spectra (243 MHz, Solvent: 2 tBu CD2Cl2) of RuCl2(PhP P2 ) (19) with spectra at (from front) 179 K, 184 K, 195 K, 211 K, 226 K, 226 K, 243 K, 259 K, 275 K, and 300 K...... 86 3 tBu Figure 3.4 ORTEP plot (50% thermal ellipsoids) of RuCl2(P P3 ) (20), hydrogen atoms have been omitted for clarity...... 88 3 tBu Figure 3.5 Overlay of structural data for the two isomers of RuCl2(P P3 ) (20) in the solid state (hydrogen atoms have been omitted for clarity)...... 90 Figure 3.6 Solid state 31P{1H} NMR (121 MHz, 25 kHz MAS, 295 K) of 2 tBu 2 tBu 3 tBu RuCl2(P P3 ) (18), RuCl2(PhP P2 ) (19) and RuCl2(P P3 ) (20) ...... 92 4 Ruthenium Tris(3-di(tert-butyl)phosphinoethyl)phosphine hydride complexes ...... 99 Figure 4.1 Dinitrogen dihydride and metal diazene complex comparison...... 100 2 tBu 2 tBu Figure 4.2 RuCl2(P P3 ) (18) and RuH2(N2)(P P3 ) (26) ...... 100 2 tBu Figure 4.3 ORTEP plot (50% thermal ellipsoids) of RuHCl(P P3 ) (21), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 103 2 tBu Figure 4.4 ORTEP plot (50% thermal ellipsoids) of RuH(BH4)(P P3 ) (22), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 106 2 tBu Figure 4.5 RuH(BH4)(P P3 ) (22) ...... 109 2 tBu 1 Figure 4.6 Hydride region of RuH(BH4)(P P3 ) (22); A. H NMR spectrum at 298K; B. 1H NMR spectrum at 220K; C. 1H{31P} NMR spectrum at 220K; D. 1H NMR spectrum at 192K; E. XXI 1H{31P} NMR spectrum at 192K; F. 1H{11B} NMR spectrum 192K...... 110 2 tBu Figure 4.7 ORTEP plot (50% thermal ellipsoids) of RuH(AlH4)(P P3 ) (23), within each asymmetric unit. Selected hydrogen atoms and tert-butyl methyl groups of have been omitted for clarity...... 112 2 tBu Figure 4.8 ORTEP plot (50% thermal ellipsoids) of K[Ru(H)3(P P3 )] (24). Selected hydrogen atoms, and tert-butyl groups have been omitted for clarity...... 117 2 tBu Figure 4.9 ORTEP plot (50% thermal ellipsoids) of RuH2(CO)(P P3 ) (25), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 121 2 tBu Figure 4.10 ORTEP plot (50% thermal ellipsoids) of RuH2(N2)(P P3 ) (26), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 124 2 tBu Figure 4.11 ORTEP plot (50% thermal ellipsoids) of RuHCl(CO)(P P3 ) (28), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 131 2 tBu Figure 4.12 ORTEP plot (50% thermal ellipsoids) of RuHCl(N2)(P P3 ) (29), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 133 5 Iron and Ruthenium Dinitrogen Complexes of 2 Cy Tris(2-dicyclohexylphosphinoethyl)phosphine (P P3 ) ...... 140 2 Cy Figure 5.1 ORTEP plot (50% thermal ellipsoids) of [RuCl(P P3 )][BPh4] within each asymmetric unit. Hydrogen atoms, tetraphenylborate anion and THF solvate in the asymmetric unit have been omitted for clarity...... 143 31 1 15 2 Cy Figure 5.2 P{ H} NMR spectrum (162 MHz, C6D6) of Ru( N2)(P P3 ) 15 ( N2-34) ...... 146 Figure 5.3 ORTEP diagram (50% thermal ellipsoids, non-hydrogen atoms) 2 Cy of Fe(N2)(P P3 ) (33) excluding benzene solvate...... 148 Figure 5.4 ORTEP plot (50% thermal ellipsoids, non hydrogen atoms) of 2 Cy RuN2(P P3 ) (34) within each asymmetric unit. Pentane solvate has been omitted for clarity...... 150 Figure 5.5 ORTEP diagram (50% thermal ellipsoids, non-hydrogen atoms) 2 Cy of [Fe(N2)(P P3 )][BPh4] (35[BPh4])...... 154 Figure 5.6 ORTEP diagram (50% thermal ellipsoids, non-hydrogen atoms) 2 Cy of RuCl(P P3 ) (36), pentane solvate omitted for clarity...... 156 XXII 2 Cy + Figure 5.7 EPR spectrum of [Fe(N2)(P P3 )] (35) (77K). (gx, gy, gz) = (2.225, 2.040, 1.999). Lower curve is a simulation...... 159 2 Cy Figure 5.8 EPR spectrum of RuCl(P P3 ) (36) (77K). (gx, gy, gz) = (2.104, 2.064, 2.0005). Lower curve is a simulation...... 160 2 Cy Figure 5.9 ORTEP plot (50% thermal ellipsoids) of FeH2(P P3 ) (37) within each asymmetric unit. Selected hydrogen atoms and second complex in the asymmetric unit have been omitted for clarity...... 162 31 1 2 Cy Figure 5.10 Variable temperature P{ H} NMR spectra of FeH2(P P3 ) (37) with spectra at (from front) 190, 210, 225, 240, 254, and 315 K...... 164 Figure 5.11 Variable temperature high field 1H NMR spectra of 2 Cy FeH2(P P3 ) (37) with spectra at (from front) 190, 200, 210, 225, 240, 254, 271 and 285 K...... 165 Figure 5.12 ORTEP plot (50% thermal ellipsoids) of 2 Cy [FeH(N2)(P P3 )][BF4] (38[BF4]) within each asymmetric unit. Hydrogen atoms, tetrafluoroborate counter ion and THF solvate have been omitted for clarity...... 169 Figure 5.13 ORTEP plot (50% thermal ellipsoids) of 2 Cy [RuH(N2)(P P3 )][BF4] (39[BF4]) within each asymmetric unit. Hydrogen atoms, tetrafluoroborate counter ion and THF solvate have been omitted for clarity...... 171 2 Cy 6 C P3 Synthesis and Complexes ...... 179 H 2 Cy Figure 6.1 Tris[2-(dicyclohexylphosphino)ethyl]methane ( C P3 , 46) 180 H 2 Cy Figure 6.2 ORTEP plot (50% thermal ellipsoids) of C P3 (46). Selected hydrogen atoms have been omitted for clarity...... 184 2 Cy Figure 6.3 ORTEP plot (50% thermal ellipsoids) of RuH(CO)(C P3 ) (48) within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 189 2 Cy Figure 6.4 ORTEP plot (50% thermal ellipsoids) of RuH(N2)(C P3 ) (49) within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity...... 191 2 Cy Figure 6.5 1H NMR of RuH(CO)(C P3 ) (48), hydride region...... 194 2 Cy Figure 6.6 1H NMR of RuH(N2)(C P3 ) (49), hydride region...... 195 XXIII List of Tables 1 Introduction ...... 1 Table 1.1 Selection of N2 complexes and related species with binding mode and N-N bond lengths...... 7 2 Ruthenium hydride complexes containing the hindered phosphine ligand 3 iPr Tris(3-diisopropylphosphinopropyl)phosphine P P3 ...... 47 Table 2.1 Selected bond lengths (Å) and angles (º) for 3 iPr [RuCl(P P3 )][BPh4].THF (4[BPh4]) ...... 52 3 iPr Table 2.2 Selected bond lengths (Å) and angles (º) for [RuH2(P P3 )] (5) ...... 59 Table 2.3 Selected bond lengths (Å) and angles (º) for ...... 3 iPr [Ru(H2)(H)(P P3 )][BPh4].EtOH (6[BPh4]) ...... 63 t 3 New Super-hindered Polydentate Polyphosphine Ligands P(CH2CH2P Bu2)3, t t PhP(CH2CH2P Bu2)2, P(CH2CH2CH2P Bu2)3 and their Ruthenium(II) Chloride Complexes ...... 72 Table 3.1 Selected bond lengths (Å) and bond angles (º) for 2 tBu RuCl2(PhP P2 ) (19) ...... 85 3 tBu Table 3.2 Selected bond lengths (Å) and bond angles (º) for RuCl2(P P3 ) (20) ...... 89 4 Ruthenium Tris(3-di(tert-butyl)phosphinoethyl)phosphine hydride complexes ...... 99 2 tBu Table 4.1 Selected bond lengths (Å) and bond angles (º) for RuHCl(P P3 ) (21) ...... 104 2 tBu Table 4.2 Selected bond lengths (Å) and angles (°) for RuH(BH4)(P P3 ) (22) ...... 107 Table 4.3 Selected bond lengths (Å) and bond angles (°) for 2 tBu RuH(AlH4)(P P3 ) (23) ...... 113 Table 4.4 Selected bond lengths (Å) and bond angles (º) for 2 tBu K[Ru(H)3(P P3 )] (24) ...... 118 Table 4.5 Selected bond lengths (Å) and bond angles (º) for 2 tBu RuH2(CO)(P P3 ) (25) ...... 122 XXIV 2 tBu Table 4.6 Selected bond lengths (Å) and angles (º) for RuH2(N2)(P P3 ) (26) ...... 125 Table 4.7 Selected bond lengths (Å) and bond angles (º) for 2 tBu RuHCl(CO)(P P3 ) (28) ...... 132 Table 4.8 Selected bond lengths (Å) and bond angles (º) for 2 tBu RuHCl(N2)(P P3 ) (29) ...... 134 5 Iron and Ruthenium Dinitrogen Complexes of 2 Cy Tris(2-dicyclohexylphosphinoethyl)phosphine (P P3 ) ...... 140 Table 5.1 Selected bond lengths (Å) and angles (º) for 2 Cy [RuCl(P P3 )][BPh4] ...... 144 2 Cy Table 5.2 Selected bond lengths (Å) and angles (º) for Fe(N2)(P P3 ) (33) ...... 149 2 Cy Table 5.3 Selected bond lengths (Å) and angles (º) for RuN2(P P3 ) (34) ...... 151 Table 5.4 Selected bond lengths (Å) and angles (º) for 2 Cy [Fe(N2)(P P3 )][BPh4] (35[BPh4])...... 155 2 Cy Table 5.5 Selected bond lengths (Å) and angles (º) for RuCl(P P3 ) (36)...... 157 2 Cy Table 5.6 Selected bond lengths (Å) and angles (º) for [FeH2(P P3 )] (37) ...... 163 Table 5.7 Selected bond lengths (Å) and angles (º) for 2 Cy [FeH(N2)(P P3 )][BF4] (38[BF4]) ...... 170 Table 5.8 Selected bond lengths (Å) and angles (º) for 2 Cy [RuH(N2)(P P3 )][BF4] (39[BF4]) ...... 172 2 Cy 6 C P3 Synthesis and Complexes ...... 179 2 Cy Table 6.1 Selected bond lengths (Å) and angles (º) for RuH(CO)(C P3 ) (48) ...... 190 2 Cy Table 6.2 Selected bond lengths (Å) and angles (º) for RuH(N2)(C P3 ) (49) ...... 192 XXV Abstract This thesis is primarily concerned with the development of new multidentate phosphine ligands, the synthesis and reactions of iron and ruthenium complexes of these ligands, and a specific focus on the complexes which incorporate a dinitrogen ligand. The synthesis and characterisation of the novel hindered tripodal phosphine ligand i 3 iPr P(CH2CH2CH2P Pr2)3 (P P3 ) (1) is described, along with the synthesis and characterization of ruthenium chloro and hydrido complexes of 1. Complexes 3 i 3 i 3 iPr [RuCl(P P3 Pr)][BPh4] (4[BPh4]), RuH2(P P3 Pr) (5), and [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) were characterized by crystallography. Complex 4 is fluxional in solution, and low temperature NMR spectroscopy of the complex correlates well with two dynamic processes, an exchange between stereoisomers and a faster turnstile-type exchange within one of the stereoisomers. The synthesis and characterization of the extremely hindered phosphine ligands, t 2 tBu t 2 tBu P(CH2CH2P Bu2)3 (P P3 , 10), PhP(CH2CH2P Bu2)2 (PhP P2 , 14), and t 3 tBu P(CH2CH2CH2P Bu2)3 (P P3 , 16) are described, along with the synthesis and 2 tBu 2 tBu characterization of ruthenium chloro complexes RuCl2(P P3 ) (18), RuCl2(PhP P2 ) (19) 3 tBu 2 tBu 3 tBu and RuCl2(P P3 ) (20). The bulky P P3 (10) and P P3 (16) ligands are the most sterically encumbered PP3-type ligands so far synthesized and in all cases, only 3 2 tBu phosphorus donors are able to bind to the metal centre. Complexes RuCl2(PhP P2 ) (19) 3 tBu and RuCl2(P P3 ) (20) were characterized by crystallography. Low temperature solution 31 1 2 tBu and solid state P{ H} NMR were used to demonstrate that the structure of RuCl2(P P3 ) XXVI 2 tBu (18), is probably analogous to that of RuCl2(PhP P2 ) (5) which had been structurally characterized. 2 tBu 2 tBu t Treatment of RuCl2(P P3 ) P P3 = P(CH2CH2P Bu2)) with a variety of hydride transfer 2 tBu 2 tBu agents afforded the hydride complexes RuHCl(P P3 ) (21), RuH(BH4)(P P3 ) (22), 2 tBu 2 tBu RuH(AlH4)(P P3 ) (23), and the ruthenium (II) trihydride K[Ru(H)3(P P3 )] (24). The 2 tBu ruthenium complexes with small molecule donors RuH2(CO)(P P3 ) (25), 2 tBu 2 tBu 2 tBu RuH2(N2)(P P3 ) (25), RuH2(H2)(P P3 ) (27), RuHCl(CO)(P P3 ) (28) and 2 tBu 15 RuHCl(N2)(P P3 ) (29) were also synthesized. The N analogue of 26, 15 2 tBu 15 15 1 RuH2( N2)(P P3 )] ( N2-26) was also synthesized and characterized by N{ H} NMR spectroscopy. Complexes 21, 22, 23, 24, 25, 26, 28, and 29 were characterized by crystallography. 2 Cy The synthesis of a series of iron and ruthenium complexes with the ligand P P3 , P(CH2CH2PCy2)3 (30) is described. The iron(0), ruthenium(0), and iron(I) dinitrogen 2 Cy 2 Cy 2 Cy + complexes Fe(N2)(P P3 ) (33), Ru(N2)(P P3 ) (34), and [Fe(N2)(P P3 )] (35), and the 2 Cy ruthenium(I) chloro complex RuCl(P P3 ) (36) were synthesized by treatment of the 2 Cy + 2 Cy + iron(II) and ruthenium(II) cationic species [FeCl(P P3 )] and [RuCl(P P3 )] with 2 Cy potassium graphite under a nitrogen atmosphere. The iron(II) complex Fe(H2)(P P3 ) (37) 2 Cy + was also synthesized and characterized. The cationic dinitrogen species [Fe(N2)H(P P3 )] 2 Cy + (38) and [Ru(N2)H(P P3 )] (39) were prepared by treatment of 33 and 34, respectively, with one equiv of a weak organic acid. Complexes 32[BPh4], 33, 34, 35[BPh4], 36, 37, 38[BF4], and 39[BF4] were characterized by X-ray crystallography. XXVII The synthesis and characterization of the carbon centered podand ligand precursor H 2 Cy C P3 (46) is described. A method for the formation of ruthenium hydride complexes with carbon centered podands is developed, utilizing a reaction of between ruthenium H 2 Cy dihydride complexes with the ligand precursor. C P3 (46). This method is used to 2 Cy 2 Cy produce the ruthenium complexes RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) which are both characterized by multinuclear NMR spectroscopy and crystallography. The 2 Cy reaction chemistry and properties of with a variety of reagents RuH(N2)(C P3 ) (49) are also described. XXVIII 1 Introduction 1.1 Nitrogen Fixation Many chemicals essential for life, such as nucleic acids, proteins and most other biomolecules contain nitrogen.1 Though our atmosphere is 78 percent nitrogen gas by volume,2 this chemically inactive dinitrogen gas cannot be used by most life forms to synthesize these key biochemicals. It is necessary that the nitrogen undergo a process of ‘fixation', or conversion into a different chemical form so that it becomes bioavailable. This importance extends to the industrial sphere with ‘fixed’ nitrogen being a component of many synthetic materials, such as polymers, acrylics, dyes, explosives, resins and man-made fertilizers. In 2008 an estimated 48% of the world's population was fed by crops grown with man-made nitrogen fertilizers.3 This statistic gives some idea of the importance of ‘fixed’ nitrogen in agriculture today and therefore to the world. Dinitrogen is an extremely inert, non-polar molecule with a negative electron affinity.4 It has a large enthalpy of dissociation (945 kJ mol-1)2 and an ionization enthalpy (15.58 eV) comparable with that of the noble gas argon (15.75 eV).4 Dinitrogen has an extremely strong N-N triple bond with a bond dissociation energy of 942 kJ molí1 which results in most reactions involving dinitrogen being endothermic.2 The strength of the triple bond does not, by itself, explain the inertness of dinitrogen. The triple bond dissociation energy in acetylene (963 kJ molí1) is similar to that of dinitrogen, and for carbon monoxide is even higher (1072 kJ molí1), yet both these molecules participate in multiple chemical reactions that are unknown for dinitrogen. The discrepancy can best be explained in terms of the energies required for consecutive cleavage of each of the three bonds in the triply bound molecules. Dissociation of the first of the three bonds 1 References begin on page 39. í1 of N2 requires more than 419 kJ mol and corresponds to ca. half of the total triple bond energy, a characteristic that is unique to dinitrogen. In contrast, the splitting bond energy for the first of the three bonds in acetylene (222 kJ molí1) is the smallest.5 In addition, dinitrogen has a large HOMO-LUMO gap making it resistant to simple electron transfer redox processes and its low polarizability discourages formation of the highly polar transition states often involved in electrophilic and nucleophilic displacement reactions.6 Thus the development of an efficient catalytic cycle for the reduction of dinitrogen to a useful organic species at ambient conditions is a difficult task that has challenged scientists for decades. 1.2 Haber - Bosch process The Haber-Bosch process is currently used industrially to convert molecular nitrogen into ammonia. Chemist Fritz Haber developed the process, which was realised by the construction of a chemical plant designed by chemical engineer Carl Bosch. Such was this achievement, in the as yet unchartered waters of large scale high pressure technology, that it won both men a Nobel Prize.6 In the Haber - Bosch process, ammonia is produced from nitrogen and hydrogen gases at high temperature (400- 500qC) and pressure (102-103 atm) using heterogeneous iron- or ruthenium-based catalysts (Equation 1.1).7 Fe or Ru catalyst NN(g) + 3H2(g) 2NH3(g) (1.1) 102 -103 atm 400 - 500oC There are two mechanisms currently used to describe dinitrogen fixation in organometallic chemistry, distal (otherwise known as the Chatt mechanism) and alternating (Figure 1.1).8 2 References begin on page 39. Dinitrogen M NN Diazenido M NNH Distal Alternating NH M N NH Hydrazido (2-) M NNH2 H M Diazene NH NH3 NH Nitrido NM H M Hydrazido (1-) M NNH2 NH2 NH2 H Imido M NH 2 M Hydrazine M NNH2 NH2 NH3 Amido M NH2 Ammine M NH3 NH3 Figure 1.1 Distal and alternating mechanisms for the fixation of dinitrogen. The Haber-Bosch process is thought to occur through a modified distal mechanism where metal nitrides are formed through the reaction of nitrogen gas with an iron or ruthenium surface. The high temperature is required to overcome the kinetic inertness of dinitrogen whilst the pressure is needed to overcome the thermodynamic effect of an unfavorable equilibrium constant at the elevated temperature.6 The Haber-Bosch process accounts for over one percent of the world’s energy consumption due to its 3 References begin on page 39. energy intensive nature.9 Such energy usage provides ample incentive in terms of both cost and environmental impact to develop a system capable of reducing dinitrogen under significantly milder conditions, like those used by biological fixation. 1.3 Biological Nitrogen Fixation It has been known for over 100 years that biological systems are capable of nitrogen fixation.10 In nature, dinitrogen is ‘fixed’ to the biologically available form, ammonia, by a small but nonetheless diverse group of diazotrophic microorganisms which contain enzymes known as nitrogenases.11 These microorganisms live in the root nodules of legumes, maintaining a symbiotic relationship with plants like soybeans, peanuts and alfalfa. There are three distinct kinds of nitrogenase named after the metals present in the active sites, molybdenum-iron (MoFe), vanadium-iron and iron-iron.12 The most common and widely studied nitrogenases are those of the molybdenum-iron type. Molybdenum-iron nitrogenases are comprised of two component proteins, the Fe- protein and the FeMo-protein, with the former acting as a specific reductant for the latter in a reaction that requires the hydrolysis of two equivalents of MgATP (ATP = adenosine triphosphate) per electron transferred. The MoFe-protein contains two types of metal clusters, namely, the P-cluster, which mediates electron transfer from the Fe- 11 protein, and the MoFe-cofactor, which binds and reduces N2. A representation of the core structure of Azotobacter vinelandii nitrogenase, which falls into the molybdenum- iron category, is shown in Figure 1.2.13 4 References begin on page 39. S S Fe3 Fe7 S O O Cys-S Fe1 S Fe4 S Fe5 S Mo N-His X - CH2CH2CO2 S Fe2 Fe6 S - O CH2CO2 S Figure 1.2 Core structure of the molybdenum-iron cluster in the Azotobacter vinelandii nitrogenase protein. Crystallographic studies have determined that the central ligand, shown here in blue, is either carbon, nitrogen, or oxygen.13-14 Despite significant theoretical and experimental analysis an answer to the atom type of X is yet to be completely determined,15-16 though the most recent crystallographic analysis is heavily favoring a central carbon atom.17 Debate over the binding and reduction mechanism of dinitrogen by the nitrogenase enzyme is ongoing. The current literature supports the theory that nitrogen binds to a single iron (Fe6) of the iron molybdenum cluster at the active site.14 The issue of whether biological nitrogen fixation at the FeMo nitrogenase follows an alternating or distal route has yet to be decided, but current evidence supports the alternating mechanism due to the ability of the nitrogenase enzyme to use both hydrazine and diazene as a substrate for ammonia synthesis.14, 18 1.4 Chemistry of Dinitrogen Complexes 2+ 19 Since the discovery of the first dinitrogen complex [Ru(NH3)5(N2)] in 1965, chemists have sought to catalyze the reduction of dinitrogen by using metal complexes capable of binding and thereby activating this relatively inert molecule. 5 References begin on page 39. 1.4.2 Dinitrogen-Metal Binding The binding between dinitrogen and a metal center involves both ı bonding and ʌ back- bonding components as illustrated in Figure 1.3. 1S*g 3Vg NMN Figure 1.3 Bonding between dinitrogen and a metal center involves both ı and ʌ components. The dinitrogen acts a Lewis base by donating electron density from its HOMO into an empty metal d-orbital. Conversely, it acts as a Lewis acid accepting electron density from a filled metal d-orbital of appropriate symmetry into a degenerate 1ʌ*g orbital. As a result of the symmetry of the dinitrogen molecular orbitals and the degeneracy of the 1ʌ*g orbitals, dinitrogen can coordinate to metal centers via several different modes, the most common being end-on binding.20 Donation of electron density into the ʌ*-orbitals by the metal center weakens or ‘activates’ the triple bond and this weakening is characterized by an increase in bond length. Activation results in an increase in electron density on the terminal nitrogen, which renders it more nucleophilic in nature. Hence, dinuclear nitrogen-bridged complexes are relatively common. Table 1.1 illustrates the range of dinitrogen complexes, binding modes and levels of dinitrogen activation in the literature. 6 References begin on page 39. Table 1.1 Selection of N2 complexes and related species with binding mode and N-N bond lengths. Binding Compound N-N bond ref. Mode length(Å) 21 - NNgas 1.0975 1.255 22 - NN H H 1.460 21 - NN H H + 23 End-on P 1.13(3) P H Fe Mononuclear P N P N + 24 End-on Me2P 1.127(2) H P PMe2 Fe Dinuclear N P N Me 2 Fe Me P P 2 PMe2 PMe2 25 i i Pr Pr 1.239(4) End-on t K t Bu i Bu iPr Pr N N Dinuclear Fe N N Fe N N i i tBu Pr Pr tBu K i iPr Pr Side-on 1.088(12) 26 N Sm Sm Dinuclear N SiMe - SiMe 3 3 27 Side-on N 1.379 N N Me3Si N SiMe 3 Dinuclear Ti Ti Me3Si N N N SiMe 3 N SiMe 3 SiMe3 7 References begin on page 39. Table 1.1 (continued) Selection of N2 complexes and related species with binding mode and N-N bond lengths. i Me Si Pr2 2 P i 28 Side-on Pr 2P 1.548(7) N N Cl Me Si Zr Dinuclear 2 Zr SiMe2 N Cl N i Pr 2P PPri 2 SiMe2 Ph Ph 1.319(6) 29 Side-on Ph N H P Me Si H End-on 2 N aT Ta N SiMe2 SiMe Me Si 2 2 N N Dinuclear P N Ph Ph Ph In most compounds containing bound dinitrogen, the dinitrogen is only weakly í1 activated, typically exhibiting a ȞNŁN stretching frequency decrease of 200-300 cm and a NɁN bond length (~1.12 Å) that is only marginally elongated relative to the corresponding values for free dinitrogen (2331 cmí1 and 1.079 Å, respectively).20, 30 Despite showing only minimal spectroscopic evidence of NɁN bond weakening, the modestly activated dinitrogen molecule may, in some compounds, undergo reactions such as protonation, though, more commonly, substitution of the nitrogen ligand or no chemical reactivity is observed.20 1.4.3 Dinitrogen Complex Synthesis Dinitrogen complexes may be synthesized by three general routes:31 1.4.3.1 Displacement of a weakly bound ligand by N2 The iron complexes FeH2(N2)(PR3)3 (PR3 = PEtPh2, PBuPh2) shown in Scheme 1.1 are generated by the spontaneous reaction of the dihydrogen precursors FeH2(H2)(PR3)3 under one atmosphere of nitrogen.32 8 References begin on page 39. N H2 N N R3P PR3 2 Fe R3P PR3 R P H Fe 3 H H R3P H PR3 = PEtPh2, PBuPh2 Scheme 1.1 The displacement of dihydrogen by dinitrogen has been used extensively to synthesize a large range of nitrogen complexes, especially on iron, which can be sensitive toward other methods such as reduction.33 + The manganese complex [Mn(CO)(dppe)2(N2)] (where dppe = Ph2PCH2CH2PPh2) is an example of a coordinated V-bond being displaced by a dinitrogen molecule (Scheme 1.2). + + N H H N Ph2 Ph2 Ph2 Ph P P +N2 P P Mn Mn P P -N P P Ph Ph 2 Ph CO 2 Ph2 CO 2 Scheme 1.2 Here the electron deficient carbonyl complex is stabilized by two agostic interactions with protons on the phenyl rings of the dppe ligands. In solution, under an atmosphere of dinitrogen, the compound is in equilibrium with the six co-ordinate nitrogen complex.34 9 References begin on page 39. 1.4.3.2 Spontaneous co-ordination of dinitrogen at a vacant co-ordination site t t A mixed valence uranium (III)/(IV) dimer ([N3N ]U)2(μ-Cl) (where N3N = t N(CH2CH2NSi BuMe2)3) can be synthesized by reduction of the monomeric chloride t t [N3N ]UCl with potassium. Sublimation of this dimer affords [N3N ]U which, when placed under an atmosphere of dinitrogen, is converted completely to the nitrogen bridged dimer as illustrated in Scheme 1.3. N R N R NU N N R R NU +N2 R N R N N R R N -N2 N R NU N N t R=SiBuMe2 Scheme 1.3 The activation of the bridged dinitrogen is slight with an N-N bond length of 1.109(7) Å, essentially that of free dinitrogen. Application of a vacuum easily removes the dinitrogen in this reversible reaction. Highlighting the importance of the ligand t structure, it is interesting to note that replacing Si BuMe2 with SiMe3 results in a complex that is unreactive towards dinitrogen, whereas, the SiPh2Me analogue leads to a series of unidentifiable products.35 1.4.3.3 Reduction of metal complexes leading to low-valence metal fragments that bind and activate dinitrogen. 2 iPr 2 iPr Iron(0) and ruthenium(0) dinitrogen complexes Fe(N2)(P P3 ) and Ru(N2)(P P3 ) 2 iPr i (P P3 = P(CH2CH2P Pr2)3) can be synthesized by the reaction of the 10 References begin on page 39. 2 iPr 2 iPr [FeCl(P P3 )][BPh4] and [RuCl(P P3 )][BPh4] with potassium graphite (KC8) under a nitrogen atmosphere.36 N Cl N PiPr PiPr Pr PFe 2 2 i 2 iPr2PFe Na(C10H8) PiPr 2 PiPr2 Si THF Si N2 Scheme 1.4 An interesting new area of nitrogen activation chemistry is that derived from the iron(I) iPr dinitrogen complexes reported by the group of Jonas Peters. Fe(N2)(SiP 3), shown in iPr Scheme 1.4 has been generated by treatment of the chloride precursor FeCl(SiP 3) with an equivalent of sodium naphthalenide under an atmosphere of dinitrogen.37 This Ph complex and the analogous compound Fe(N2)(SiP 3) are the first reported iron(I) -1 dinitrogen complexes. These complexes show a level of activation (ȞNŁN = 2008 cm -1 iPr Ph and 2041 cm for Fe(N2)(SiP 3) and Fe(N2)(SiP 3) respectively) intermediate to the average activation levels of Fe(0) and Fe(II) dinitrogen complexes, with greater activation that Fe(II) but less than Fe(0).38 1.4.4 Catalytic Dinitrogen Fixation Treatment of [W(N2)2(PPhMe2)4] with excess acid produces nearly 2 mol of ammonia per tungsten center. Chatt et al. studied this process and identified a number of intermediates in a potential catalytic cycle that relies on the presence of an external 11 References begin on page 39. source of protons and electrons.31, 39 This cycle is known as the Chatt cycle and is illustrated in Figure 1.4. N N P (0) P NH +N2 M +H+ L +e- P P N NH3 P P P P M(0) M(I) L L P P P P +H+ +H+ +e- +e- NH2 NH2 N P P (I) P (II) P M NH3 M L L P P P P + + +H +H NH3 +e- NH N P P P (II ) P M(II) M L L P P N P P P (III) P +e- +H+ M +e- L P P Figure 1.4 The catalytic Chatt cycle for the reduction of dinitrogen. Since the discovery of the Chatt cycle there have been three systems in which molybdenum has been shown to act as a catalyst for the conversion of dinitrogen to ammonia under ambient conditions. 12 References begin on page 39. In 2003, the molybdenum(III) dinitrogen complex [(HIPT)N3N](N2)Mo (where i 3- [(HIPT)(N3N)] = [N(CH2CH2N(3,5-(2,4,6- Pr3C6H2)2C6H3))3] ) (Figure 1.5) was shown to catalytically produce ammonia from dinitrogen.40 iPr iPr iPr iPr N HIPT N HIPT N N Mo HIPT iPr iPr N N N i HIPT = 3,5-(2,4,6- Pr3C6H2)2C6H3 Figure 1.5 Schrock's N2-fixation catalyst, Mo(N2)[(HIPT)N3N] Evidence that this catalytic process follows a ‘Chatt-like’ cycle comes from the eight - intermediates which were characterized, namely, the Mo(III)-N2, [Mo(IV)-N2] , + + + Mo(IV)-N=N-H, [Mo(VI)=N-NH2] , Mo(VI)ŁN, [Mo(VI)=NH] , [Mo(IV)(NH3)] and 40a, 41 Mo(III)(NH3) species. Using decamethylchromocene as the external electron source and (2,6- F F lutidinium)[BAr 4] (Ar = 3,5-(CF3)2C6H3) as the proton source under an atmosphere of dinitrogen, the complexed dinitrogen was reduced to ammonia and the catalyst regenerated. Yields give a catalyst efficiency of around 65%, with direct reaction of reductant with proton source to generate hydrogen believed to be the primary cause for efficiency loss.40b Unfortunately, the turn over number for the ammonia generation was not very high (up to eight based on the Mo atom).42 The steric morphology of this ligand is noteworthy. [(HIPT)(N3N)] is a tripodal tetradentate amido amine which complexes to form trigonal bipyramidal molybdenum complexes. The bulkiness of the aromatic groups serves a dual purpose: the prevention 13 References begin on page 39. of dimerisation through a bridging dinitrogen ligand; and the formation of an approximately trigonal pocket in which dinitrogen, or its reduced products, are located and afforded a high degree of protection. The second system involves the work of Shilov, who has shown that dinitrogen can be reduced to a mixture of hydrazine and ammonia (10:1). The Mg[Mg2Mo8O22(OMe)6(MeOH)4] complex, becomes a good catalyst after being supported on a sodium amalgam surface using a surfactant (phosphatidylcholin or polyethylene glycol) with triphenylphoshine present in methanol solution. It has been proposed that dinitrogen is bound and reduced to hydrazine between two metal centers, but evidence for the exact mechanism of this reaction has yet to be established and no intermediates have so far been isolated.43 A third molybdenum-based system for the catalytic conversion of dinitrogen to ammonia has been recently identified by Nishibayashi et al.44 This system uses a molybdenum(0) dinitrogen dimer [Mo(N2)2(PNP)]2(μ-N2) complex with a PNP-type pincer ligand (PNP = 2,6-bis(di-(tert-butylphosphino)methyl)pyridine) (Figure 1.6). N N P N P N N Mo N N Mo N PN N P N N t P =PBu2 Figure 1.6 [Mo(N2)2(PNP)]2(μ-N2) 14 References begin on page 39. Using 2,6-lutidinium trifluoromethanesulfonate ([LutH]OTf) as the proton source and cobaltocene (CoCp2) as the source of external electrons, ammonia could be obtained from the reaction mixture under a nitrogen atmosphere. This catalytic system yielded 23 equiv. of ammonia per equivalent of catalyst (12 equiv. of ammonia per molybdenum atom in the catalyst) before the catalyst was exhausted and only free ligand remained in the reaction solution. The slightly higher turnover rate and the ability to use a slightly less reducing electron source (CoCp2 (-1.15 eV) vs. CrCp*2 (- 1.35 eV))44 makes the PNP system the most successful ambient-condition catalytic process to date. While not as sterically bulky as Schrock's [(HIPT)N3N] ligand, the PNP ligand still incorporates sterically bulky substituents. The tert-butyl groups on the terminal phosphines create a tight steric pocket in which the sensitive nitrogen fixation intermediates can reside and be afforded protection. Based on the results of catalytic and stoichiometric reactions of [Mo(N2)2(PNP)]2(μ-N2), the elucidated reaction pathway for this catalytic reduction of dinitrogen to ammonia is essentially the same as the Chatt cycle. 1.4.5 Nitrogen fictionalization on iron 1.4.5.1 Conversion of dinitrogen to ammonia and hydrazine on iron The nature of the nitrogenase active site, as well as the use of an iron catalyst in the Haber-Bosch process, has led to a large amount of interest in iron nitrogen complexes and their potential for nitrogen fixation.45 The first report of the functionalization of a dinitrogen at a single iron center was the production of ammonia derived from an iron(0) dinitrogen complex by Leigh et al in 1991.46 In this work, the iron (II) complex [FeH(N2)(dmpe)2][BPh4] (dmpe = Me2PCH2CH2PMe2) was deprotonated with base to 15 References begin on page 39. give the iron(0) complex Fe(N2)(dmpe)2 in situ which, upon treatment with acid, gave yields of ammonia up to twelve percent (Scheme 1.5). P P Cl N P N P P base P HCl Fe Fe N N Fe +NH3 P H P P P P P Cl Scheme 1.5 Subsequent work showed that similar complexes with other phosphine ligands such as bidentate depe (Et2PCH2CH2PEt2) and tetradentate P(CH2CH2PPh2)3 also produced low yields of ammonia (up to twenty percent).47 No mechanism for this reduction to ammonia has been proposed although analysis suggests the reduction power to produce ammonia is derived from the formal two electron oxidation of the metal center. It is noteworthy that Komiya et al.48 were unable to replicate the production of ammonia when treating a purified depe iron(0) dinitrogen complex with acid. In this work the iron(0) dinitrogen complex was derived directly from the iron(II) dichloride by treatment with sodium-naphthalenide under an atmosphere of nitrogen. The cause for this differing behavior is yet to be established definievely. In an analogous reaction, hydrazine was produced in 22% yield with a very small amount of ammonia by treatment of the iron(0) dinitrogen complex Fe(N2)(NP3) (NP3 = 49 N(CH2CH2PPh2)3) with hydrobromic acid in dichloromethane (Scheme 1.6). In this work, the iron(0) dinitrogen complex Fe(N2)(NP3) was synthesized by treatment of the hydride precursor [FeH(N2)(NP3)][BPh4] with n-butyl lithium. The [FeH(N2)(NP3)][BPh4] precursor complex was prepared by reaction of 50 [FeCl(NP3)][BPh4] with sodium borohydride in ethanol under dinitrogen. 16 References begin on page 39. + PPh PPh2 2 HBr Ph2 N n-BuLi N N 22% N2H4 P N Fe Fe II N H N Fe products CH2Cl2 PPh2 PPh2 PPh2 Scheme 1.6 Tyler et al. were also able to observe ammonia upon protonation of an iron(0)-N2 51 + complex. The dinitrogen hydride complex, trans-[Fe(DMeOPrPE)2(N2)H] (DMeOPrPE = 1,2-(bis(dimethoxypropyl)phosphino)ethane), was synthesized by + substitution of N2 for H2 in trans-[Fe(DMeOPrPE)2(H2)H] . Of particular note is that this dihydrogen complex was generated directly from H2 and trans-Fe(DMeOPrPE)2Cl2, instead of a hydride transfer reagent such as sodium borohydride, making H2 the ultimate source of electrons for the reduction of dinitrogen to ammonia (Scheme 1.7). While the six-coordinate hydride species is unreactive toward protonation,52 the reduced form Fe(DMeOPrPE)2(N2) is protonated with 1M triflic acid to produce 15% NH3 and 51 2% N2H4. 17 References begin on page 39. + Cl H P P 2 H2 Fe P P P P Fe Cl Base P P H N2 + P KOtBu P N2 Fe N P P P 2 Fe P P P H O O H+ P P + + = NH4 [N2H5] P P n+ 2+ Fe 2H2[PP] O O Scheme 1.7 Recently the direct synthesis of an iron nitride through the reaction of an iron complex, potassium and dinitrogen has been demonstrated by Holland et al.53 The nitride complex reacts with acid and H2 to give substantial yields of N2-derived ammonia. [LFe(μ-Cl)]2 (L is MeC[C(Me)N(2,6-MeC6H3)]2) reacts with two equivalents of potassium, generating the tetra iron bis(nitride) complex shown in Scheme 1.8. Treatment of this tetra iron complex with excess HCl or H2 generated ammonia in yields of 82% and 43% respectively. This experiment is particularly instructive because it is thought to be a possible model of the mechanism of the Haber-Bosch cycle, with the similar elements including a range of iron oxidation states, the presence of iron nitrides, reaction with H2 and the presence of potassium. 18 References begin on page 39. N N Ar 2equiv N Cl N N Cl Fe N KC8 K Fe Fe Fe N N Fe N K N Cl N 2 N Cl Fe N Ar N N Ar = 2,6-dimethylphenyl H2 25 °C Toluene N H N Fe Fe +2NH3 +2KCl N H N Scheme 1.8 Hydrazine is another target of nitrogen fixation as it is easily converted to ammonia or other nitrogen containing chemicals. Hydrazine was generated by the protonation of an iron (I) dinitrogen complex utilizing a silicon centerd tripodal ligand system. Using a - novel class of tripodal ligand, [Si(1,2-C6H4PPh2)3] , Peters et al. synthesized an Ph iron(I)-N2 (FeN2(SiP 3)) complex that generated hydrazine on exposure to a strong acid 37 (Scheme 1.9). The complex produced 17% hydrazine on reaction with HBF4, with the hydrazine yield increased to 47% through addition of a one-electron reducing agent (CrCl2). Further reduction of the iron(I)-N2 complex to the iron(0)-N2 complex resulted í1 in increased activation of the N2 (Ȟ(NŁN) = 1967 cm ), yet no reduction of dinitrogen 19 References begin on page 39. was observed under identical acidic conditions. This result and the evidence that an i - iron(I) complex with the analogous [Si(1,2-C6H4P Pr2)3] ligand had a much lower yield of hydrazine upon protonation led the authors to propose that increased reducing ability of complexes which leads to greater nitrogen activation, also results in favored H+ reduction to produce H2 over N2 reduction. This implies that a balance between strength of the acid and level of nitrogen activation is necessary for optimizing this reaction, rather than just high levels of both. N N PPh2 HBF4 Ph2PFe 47% N2H4 PPh2 Si CrCl2 Scheme 1.9 1.4.5.2 Other functionalization of dinitrogen on iron. The fixation of nitrogen does not solely involve the creation of N-H bonds. N-X bond formation from dinitrogen is a desirable method of directly accessing nitrogen containing molecules with N-C bond formation being particularly desirable due the vast range of useful chemicals containing this bond. Steps have been taken toward this type of chemistry using iron with the demonstrated formation of N-Si from two different classes of iron dinitrogen complexes as well as an example of N-C bond formation for a third iron dinitrogen system. 20 References begin on page 39. iPr iPr i - The first of these compounds is (FeN2(SiP 3)) (SiP 3 = [Si(1,2-C6H4P Pr2)3] ), Ph 54 analogous to the (FeN2(SiP 3)) complex discussed in section 1.4.5.1 above. Treatment iPr of (FeN2(SiP 3)) with chlorotrimethylsilane and sodium/mercury amalgam formed the iPr stable diazenido complex (SiP 3)Fe(N2SiMe3). This same diazenido complex can also be formed by the reaction of the analogous Fe(0) dinitrogen complex iPr [Na(THF)3][FeN2(SiP 3)] with chlorotrimethylsilane (Scheme 1.10). The solid state iPr structure of (SiP 3)Fe(N2SiMe3) reveals bond length changes relative to its precursor iPr [Na(THF)3][FeN2(SiP 3)] which indicate greater reduction of the N2 unit (N-N bond distance elongated from 1.147(4) Å to 1.195(3) Å, Fe-N bond distance shortened from 1.763(3) Å to 1.695(2) Å). This is supported by the infrared spectrum which gives an N-N stretching frequency of 1748 cm-1, which is much lower than those for all other known iron dinitrogen complexes.38 SiMe3 N Na(THF)3 N2 N N2 i i P Pr i Na/Hg P Pr2 i 2 P Pr2 i Pr2PFe iPr PFe Pr2PFe Me3SiCl 2 Me3SiCl i i PiPr P Pr2 P Pr2 2 Si THF Si THF Si -NaCl -NaCl Scheme 1.10 The second is the recent report of a series of silylated products using a new iron metallaboratrane framework in which iron is complexed with the TPB ligand (TPB = tris[2-(diisopropylphospino)phenyl]borane).55 The dinitrogen complex [Na][(TPB)Fe(N2)] could be treated with chlorotrimethylsilane to produce the diazenido derivative (TPB)Fe(N2SiMe3) in a similar fashion to that observed for the 21 References begin on page 39. iPr [Na(THF)3][FeN2(SiP 3)] complex discussed above. Unlike the above complex, further reduction can take place when given sufficient reducing agent and the coordinative flexibility of the TPB ligand. Treatment of (TPB)Fe(Br) with excess sodium/mercury amalgam in the presence of either chlorotrimethylsilane or 1,2- bis(chlorodimethylsilyl)ethane under a nitrogen atmosphere generated the respective hydrazido complexes [(TPB)Fe(N2SiMe3)][Na(THF)] (where the sodium cation is tightly ion paired with the hydrazido ligand) and (TPB)FeŁN-N(SiMe2CH2CH2SiMe2) (Scheme 1.11). This demonstrates the potential of iron dinitrogen complexes to go through a variety of nitrogen oxidations states which are intermediates in the dinitrogen reduction pathway. While N-Si bond formation is interesting and demonstrative of the type of mechanisms and reactions that can be used to form N-X, the direct formation of N-C is highly desirable because of the prevalence of N-C bonds in widely used chemicals. Direct N-C bond formation was achieved on iron using the iron dinitrogen complex i [(PhBP Pr3)Fe(N2)][MgCl-(THF)2] which through treatment with methyl tosylate gave i 56 the neutral [(PhBP Pr3)Fe(N=N-Me)] complex (Scheme 1.12). 22 References begin on page 39. Si Si N - Na+ N Br N2 i i i P Pr Si Si P Pr P Pr2 iPr PFe 2 iPr PFe 2 iPr PFe 2 Cl Cl 2 2 i i i P Pr2 P Pr2 xs Na/Hg P Pr 2 B B B xs Na/Hg 1atmN2 1atmN2 xs Na/Hg xs Me3SiCl Me3SiCl 1atmN2 SiMe3 SiMe3 N N THF N Na N PiPr PiPr Fe 2 iPr PFe 2 xs Na/Hg 2 i i P Pr2 P Pr2 B B i P Pr2 Scheme 1.11 MgCl(THF)2 Me N N N N Fe PiPr MeOTs Fe PiPr i 2 i 2 Pr2P i Pr2P i P Pr2 P Pr2 THF B B Ph Ph Scheme 1.12 23 References begin on page 39. 1.4.6 Coordination chemistry of reduced dinitrogen species on iron The sections above demonstrate that: (i) iron and ruthenium complexes readily bind dinitrogen, and (ii) some iron–dinitrogen complexes have the ability to reduce dinitrogen to ammonia, similar to the reactivity observed in nitrogenase enzymes. For both the synthetic ammonia-producing systems as well as in biological systems, the mechanism of dinitrogen reduction is still not apparent. Thus a burgeoning area of work has involved the synthesis and analysis of possible intermediates for both the distal pathway (metal nitride intermediates) and the alternating pathway (metal diazene (N2H2) and hydrazine (N2H4) intermediates) (Figure 1.1). 1.4.6.1 Iron intermediates along the alternating pathway The alternating dinitrogen-reduction pathway, which involves both diazene and hydrazine intermediates is currently the favored mechanism for nitrogen fixation by nitrogenase.14, 57 Both diazene and hydrazine are substrates for nitrogenase, and spectroscopic data of trapped intermediates have been obtained.18, 58 A theoretical study of the possible intermediates in the production of ammonia from Fe(0)-dinitrogen complexes such as observed in the work of Leigh46 and Tyler51 has demonstrated the alternating pathway to be the most likely mechanism.59 This study used density functional theory to compare the intermediates of three possible mechanisms. A Chatt- like mechanism, involving the stepwise addition of protons to the terminal nitrogen, was found to be the least favorable. A second pathway involving dimerisation of the Fe(dmpe)2N2 complex, followed by the stepwise addition of protons leading to hydrazine, was found to be energetically favorable; however many of the dimeric intermediates prefer to dissociate into monomers. A third mechanism proceeding 24 References begin on page 39. through diazene and hydrazine intermediates, formed by alternating protonation of each nitrogen atom, was found to be the most energetically favorable. 2í Synthetic iron complexes containing parent diazene (N2H2), hydrazido (N2H2 ), and hydrazine (N2H4) ligands can therefore provide insight into the alternating mechanism of nitrogen fixation on single iron centers and also provide data that can be compared with nitrogenase data to help elucidate mechanistic details of this process. The first iron diazene complexes were successfully synthesized by Sellmann et al. using iron sulfur scaffolds to make a number of bridging Ș1-diazene complexes.60 Starting with the iron hydrazine complex shown in Scheme 1.13 it was possible to oxidize the terminal hydrazine ligand to a bridging diazene with N–N bond distance of 1.30 Å using oxygen from air. Scheme 1.13 (μ-N2H2)[Fe(“NHS4”)] synthesis The first monomeric iron diazene complexes were synthesised from iron–phosphine scaffolds, although the assignment of the N2H2 ligands as true diazene (HN=NH) rather 2- than hydrazido (N2H2 ) is not yet definitive. Reaction of Fe(PP)2N2 (where PP =DMPE61 or DMeOPrPE52) with hydrazine results in the formation of an iron(0) Ș2- diazene complex and loss of H2. The crystal structure of cis-Fe(DMPE)2(N2H2) was obtained and showed trans-diazene coordinated in an Ș2-geometry. These iron(0)- 25 References begin on page 39. diazene complexes can also be synthesised by an alternative route, viz. reaction of the 2 2+ Fe(PP)2(Ș -N2H4) complex with a strong base such as potassium tert-butoxide, which 2 resulted in the deprotonation of the coordinated hydrazine to form the Ș -N2H2 complex.52, 62 These monomeric complexes of iron can be represented as either an iron(0) diazene complex or an iron(II) hydrazido(2-) complex. Charge decomposition analysis calculations favor the iron(0) diazene form, but analysis of the N–N bond length and chemical shifts of the nitrogen bound protons suggest the iron(II) hydrazido(2-) form.62 Use of an excess of an extremely strong base such as Schlosser’s base (KOtBu and t- BuLi) results in production of dinitrogen from the hydrazine ligand of cis- 2+ 15 [Fe(DMPE)2(N2H4)] . N labelling studies have shown that the dinitrogen ligand comes from the hydrazine ligand, but to this point the mechanism of this conversion 62 remains unknown. Treatment of the diazene complex cis-Fe(DMPE)2(N2H2) with the weak organic acid lutidinium triflate resulted in the resynthesis of the hydrazine 2+ complex cis-[Fe(DMPE)2(N2H4)] with continuing acid treatment resulting in the slow + + 62 production of NH4 as well as the ammine complex cis-[Fe(DMPE)2Cl(NH3)] . These results shows that diazene and hydrazine on simple iron diphosphine scaffolds can be converted into ammonia by acid and to dinitrogen by base, strengthening the case that these are likely intermediates in the process of acid-mediated nitrogen fixation by inorganic iron complexes. All the above diazene complexes have diazene in the trans arrangement; the first cis diazene complexes on iron was identified used the 63 tris(phosphino)borate ligands PhB(CH2PR2)3 (R = Cy, Ph) (Scheme 1.14). Similar to the Sellman complexes,, these involved bridging Ș1-diazene complexes and were prepared by the oxidation of a coordinated hydrazine, either by other ligands in the case of PhB(CH2PCy2)3 or by an external oxidant (Pb(OAc)4) in the case of PhB(CH2PPh2)3. 26 References begin on page 39. Scheme 1.14 1.4.6.2 Iron intermediates along the distal pathway As the distal pathway has been observed in synthetic Mo and W systems, it is possible that the protonation of iron nitrogen complexes to produce ammonia is occurring in a similar fashion. While there is also more evidence for nitrogenase acting through an alternating pathway, it is by no means definitive and a distal pathway cannot be ruled out. Iron nitrides would be a key intermediate in the distal pathway. A large range of iron nitrides have been synthesized56, 64 but only those most relevant to nitrogen fixation will be discussed. An iron nitride complex bearing phenyltris(1-mesitylimidazol-2-ylidene)borate as a ligand was produced through reaction of the chloride precursor with sodium azide 65 followed by irradiation to induce loss of N2. This reaction generated a four-coordinate iron(IV) nitrido complex that was then treated with TEMPO-H (TEMPO-H= 1- hydroxy-2,2,6,6-tetramethylpiperidine), resulting in yields of ammonia up to 74% (Scheme 1.15). Initial N–H bond formation was proposed to occur through hydrogen atom transfer, making this reaction the first ammonia producing reaction on iron in which both the protons and electrons come from the same source. 27 References begin on page 39. Scheme 1.15 Recently, this chemistry has been extended using the analogous phenyltris(1-tert- butylimidazol-2-ylidene)borate ligand.66 Using this ligand, it was possible to isolate the first thermally stable iron(V)–nitrido complex, the structure of which was confirmed by X-ray analysis. The reaction of the iron(V)–nitrido complex with three equivalents of cobaltocene as a reducing reagent and 15 equivalents of water as a proton source at -78 °C in tetrahydrofuran afforded ammonia in 89% yield, together with the formation of an iron(II) complex (Scheme 1.16). Lower yields of ammonia were obtained when less than three equivalents of cobaltocene were used for the reduction, indicating that sequential reduction is an essential part of the mechanism. Generally, nitrido ligands bonded to iron complexes are extremely unreactive, and harsh reaction conditions, such as strong acids, are required for their chemical transformation. This reaction sequence is the first successful example of the formation of ammonia by reduction of nitrido complexes under mild reaction conditions, though the reaction mechanism for the formation of ammonia from the iron(V)-nitrido complex has not yet been clarified. The resulting iron(II) product which remains after ammonia production has also not been fully characterized, though it is known the iron is in oxidation state II and that the phenyltris(1-tert-butylimidazol-2- ylidene)borate ligand is still coordinated. 28 References begin on page 39. Scheme 1.16 Another interesting iron nitride is obtained using the tris((diphenylphosphino)methyl)borate ligand PhB(CH2PPh2)3. This nitride complex was generated using sodium azide followed by reduction with sodium mercury amalgam (Scheme 1.17). Conversion of nitride to ammonia proceeded in good yield (80–95%) upon exposure of the bridged nitride complex to three equivalents of HCl. For the iron nitride complex i with the PhB(CH2P Pr2)3 ligand, coupling of the terminal nitride species to produce a bridging dinitrogen complex was observed.56, 64f This nitride coupling reaction represents the microscopic reverse of the dinitrogen cleavage reaction; with the only system able to produce iron nitrides from dinitrogen being that of Holland et al.53 which was discussed above and detailed in Scheme 1.8. 29 References begin on page 39. Scheme 1.17 1.4.7 Ruthenium dinitrogen complexes and nitrogen fixation intermediates. Though ruthenium complexes have not yet been shown to reduce bound dinitrogen to ammonia, there is still considerable interest in complexes of ruthenium that bear potential dinitrogen fixation intermediates as ligands. This is because ruthenium, like iron, is an important catalyst component in some industrial processes for the synthesis 67 of ammonia, as well as because ruthenium is often able to bind dinitrogen and N2Hx species more strongly than iron, hence allowing better characterization of reaction intermediates.31, 68 There is a large range of ruthenium-dinitrogen complexes (Appendix A2), but few have any potential application in nitrogen fixation chemistry. Described here will be the chemistry of ruthenium complexes that share a connection to nitrogen fixation and its possible intermediates. Use of the ligand DPB (DPB = diporphyrinatobiphenylene tetraanion) (Figure 1.7)69 on ruthenium has been shown to have application in the electrocatalytic reduction of another diatomic small molecule, dioxygen.70 When applied to dinitrogen, the system did not act as a nitrogen reduction catalyst but could be used to isolate and characterize a range of expected intermediate species in a dinuclear reduction of dinitrogen at two metal centers. 30 References begin on page 39. N N Im* N N Ru Ru N N N N N N N N Ru Ru N N N Im* N Im* Im* Im* Im* Ru Ru Ru Ru N HN H2N H3N N NH NH2 NH3 Ru Ru Ru Ru Im* Im* Im* Im* Figure 1.7 Ruthenium DPB binds a number of substrates of nitrogen fixation importance.69a 71 The initial ruthenium porphyrinate forms as the 5-coordinate complex [Ru2DPB], in which the two ruthenium centers are linked by a metal-metal bond. Treatment of [Ru2(DPB)] with 1-tert-butyl-5-phenylimidazole (*Im) under argon forms [(Ru(*Im))2(DPB)], which, when exposed to dinitrogen, rapidly forms the desired 31 References begin on page 39. í1 69a dinitrogen-bridged complex [(Ru(*Im))2(DPB)(ȝ-N2)] (ȞNN 2112 cm ). With excess ammonia or hydrazine [(Ru(*Im))2(DPB)(ȝ-N2)] forms bis-ammonia and bridged hydrazine complexes, respectively, by displacement of the dinitrogen ligand. The diazene complex [(Ru(*Im))2(DPB)(ȝ-HNNH)] can be prepared via oxidation of the hydrazine species, with further oxidation regenerating the dinitrogen complex. The bridging complex [(Ru(*Im))2(DPB)(ȝ-N2)] is remarkably stable, being air-stable indefinitely in the solid state and for hours in solution. Furthermore, there is no measurable loss of dinitrogen during five cycles of freeze-pump-thaw. However, the dinitrogen ligand is slowly replaced by competing axial ligands such as pyridine or carbon monoxide.69b As mentioned previously, hydrazine and diazene complexes are believed to be important intermediates in nitrogen fixation at the nitrogenase active site, but few complexes have been identified due to the inherent instability of diazene. The first reported side-on bound diazene and hydrazine complexes of ruthenium were reported in 72 2010 by Field et al. The reaction of cis-[RuCl2(PP)2] (PP = depe, dmpe) with hydrazine afforded end-on-bound ruthenium(II) hydrazine complexes (Scheme 1.18). Treatment of the hydrazine complexes with strong base afforded the side-on bound 2 2 ruthenium(0) diazene complexes cis-[Ru(Ș -NH=NH)(PP)2]. Treatment of cis-[Ru(Ș - NH=NH)(depe)2] with weak acid under chloride-free conditions afforded the side-on 2 bound hydrazine complex cis-[Ru(Ș -N2H4)(depe)2]2. The interconversion between the ruthenium diazene and the ruthenium hydrazine by acid-base treatment was reversible. 32 References begin on page 39. P P + H2 P Cl P N NH2 Ru Ru P Cl P Cl P P acid, Cl- base 2+ P P P P NH NH2 base Ru Ru P NH P NH 2 acid P P P = depe, dmpe P Scheme 1.18 A range of ruthenium hydrazine complexes, both end on bound73 and bridging74 have been reported but as these complexes have no obvious direct link to dinitrogen chemistry, either through reactions with the coordinated hydrazine or as models of dinitrogen fixation mechanism they will not be further discussed here. Ruthenium nitrides are thought to be important intermediates in the process of industrial nitrogen fixation on solid ruthenium catalysts, where they presumably form on the ruthenium surface and then react with hydrogen. A process analogous to this reactivity has been characterized by Holthausen, Schneider and co-workers for a ruthenium– t 75 nitrido complex bearing a PNP-type pincer ligand (PNP = N(CH2CH2P Bu2)2). The ruthenium nitride was prepared from the reaction of the corresponding ruthenium-chloro complex with an azide reagent (Scheme 1.19). 33 References begin on page 39. t t P Bu2 P Bu2 [PPN]N3 N Ru Cl N Ru N -N2 t t P Bu2 -[PPN]Cl P Bu2 H2 (1 atm) THF, 50 °C t P Bu2 H N RuH + NH KOtBu 4 3 t P Bu2 Vacuum Cl t t P Bu2 P Bu2 H i) 2 eq. HCl N Ru Cl N RuH3 ii) Vacuum t t P Bu2 60 °C P Bu2 PPN = Bis(triphenylphosphine)iminium Scheme 1.19 Hydrogenation of the nitrido complex under an atmosphere of dihydrogen at 50 °C for 48 h gave the corresponding ruthenium–hydrido complex together with the formation of ammonia in 80% yield. Confirmation of this reduction was obtained by the reduction of the 15N-labeled nitrido complex, successfully demonstrating the first example of hydrogenation of a ruthenium–nitrido complex to form ammonia. The final ruthenium– hydrido complex can be converted back into the starting ruthenium–chloro complex via three steps — dehydrogenation, protonation and deprotonation. As a result, ammonia is 34 References begin on page 39. pseudo-catalytically produced from azide and molecular dihydrogen in the presence of the ruthenium complex. 1.4.8 Protonation side reactions While there has been some success in protonating the dinitrogen ligand in iron (0) and iron (I) complexes, this type of reactivity remains rare and the systems are usually very sensitive to changes in protonation agent or even solvent. A more robust system in which an iron nitrogen complex can be converted into ammonia or hydrazine by a variety of protic reagents and with defined products would be desirable. To better define iron dinitrogen complexes which would meet the above criteria, it would be necessary to investigate the competing protonation processes and products which prevent protonation of the dinitrogen ligands, so that complexes can be designed to avoid these problems. 2 iPr 2 iPr Iron(0) and ruthenium(0) dinitrogen complexes Fe(N2)(P P3 ) and Ru(N2)(P P3 ) 2 iPr i (P P3 = P(CH2CH2P Pr2)3) have been shown to undergo protonation on the metal center rather than on the dinitrogen ligand when treated with a proton source.36 Treatment with one equivalent of a weak organic acid led to the iron(II) and 2 iPr + 2 iPr + ruthenium(II) dinitrogen hydride species [Fe(N2)H(P P3 )] and [Ru(N2)H(P P3 )] . The nitrogen ligands within these complexes have a lower level of activation than their precursors, and further protonation of these hydrido nitrogen complexes does not result in a reaction with the dinitrogen ligand. It is also of note that Peters' iron(I)-dinitrogen complexes, discussed in Section 1.4.5, + demonstrated a competing reaction with reduction of H to H2 at the iron center. It appears that if access of the solution protons to the metal center were restricted 35 References begin on page 39. sufficiently, then protonation on the dinitrogen ligand would then be a more preferred reaction and hence the desired protonation on nitrogen would be more likely. 1.5 Aims of this work The primary aims of the work described in this thesis are to generate new iron and ruthenium dinitrogen complexes with tripodal phosphorus ligands with high levels of steric bulk on the terminal phosphines. The project requires the design of synthetic routes to both new and known phosphine ligands, followed by the development of routes to new iron and ruthenium complexes, with an emphasis on the synthesis and characterization of dinitrogen complexes and their chemistry with a variety of reagents. The specific aims of this work were to: 3 iPr i. Investigate the ability of the ligand P P3 (1) to form iron and ruthenium complexes and the subsequent formation of dinitrogen complexes of iron and 3 iPr ruthenium with P P3 (1). ii. Synthesize and characterize a number of tripodal phosphine ligands with t-butyl groups on the terminal phosphines. iii. Investigate the potential of these new t-butyl group ligands to form new iron and ruthenium complexes, with an emphasis on formation of novel dinitrogen complexes. iv. Synthesize and characterize dinitrogen complexes of iron and ruthenium with 2 Cy the P P3 (30) ligand and investigate reactions with acids and other reagents with the aim of forming N-X bonds. v. Synthesize and characterize a carbon centered podand ligand with sterically bulky groups on the terminal phosphines as well as ruthenium complexes of the new ligand. 36 References begin on page 39. 1.6 Structure of this Thesis Chapter 1 Introduction to nitrogen fixation, dinitrogen metal complexation and a review of dinitrogen chemistry when bound to iron and ruthenium. Chapter 2 3 iPr Synthesis of tris(3-diisopropylphosphinopropyl)phosphine (P P3 ) (1). Synthesis and 3 iPr characterization of ruthenium hydride complexes of P P3 . Chapter 3 Design and synthesis of new ligands tris(2-di(tert-butyl)phosphinoethyl)phosphine 2 tBu 3 tBu (P P3 ) (10), tris(3-di(tert-butyl)phosphinopropyl)phosphine (P P3 ) (16) and bis(2- 2 tBu di(tert-butyl)phosphinoethyl)phenylphosphine (PhP P2 ) (14). Synthesis and 2 tBu 3 tBu 2 tBu characterization of the ruthenium chloride complexes of P P3 , P P3 and PhP P2 . Chapter 4 2 tBu Synthesis and characterization of a range of ruthenium hydride complexes of P P3 2 tBu including a dinitrogen dihydride complex RuH2(N2)(P P3 ) (26). Chapter 5 Synthesis and characterization of iron (0), iron (I) and ruthenium (0) dinitrogen 2 Cy complexes of tris(2-dicyclohexylphosphinoethyl)phosphine (P P3 ) (30), and investigation into their reactions with an organic acid. Chapter 6 37 References begin on page 39. Synthesis and characterization of the carbon centered podand precursor H 2 Cy HC(CH2CH2PCy2)3 ( C P3 ) (46) as well as ruthenium hydrido carbonyl and hydrido dinitrogen complexes of the ligand. Chapter 7 Summary, conclusions and further work. Chapter 8 Experimental Appendix A1 X-ray Crystallographic Data (Cifs in CD format) Appendix A2 Ruthenium Dinitrogen Complexes Table Appendix A3 Publications Arising from this Work. Appendix A4 EPR Simulation Data 38 References begin on page 39. 1.7 References 1. Kim, J.; Rees, D. C., Biochemistry 1994, 33, 389-97. 2. 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Chem. 1999, 38, 109-114; (e) Jahncke, M.; Neels, A.; Stoeckli-Evans, H.; Suss-Fink, G., J. Organomet. Chem. 1998, 565, 97-103; (f) Sellmann, D.; Rohm, C.; Moll, M., Z. Naturforsch., B: Chem. Sci. 1995, 50, 1729-38; (g) Matsumoto, K.; Uemura, H.; Kawano, M., Chem. Lett. 1994, 1215-18; (h) Hough, J. J.; Singleton, E., J. Chem. Soc., Chem. Commun. 1972, 371-2; (i) Chatt, J.; Leigh, G. J.; Paske, R. J., J. Chem. Soc. A 1969, 854-9. 45 References begin on page 39. 75. Askevold, B.; Nieto, J. T.; Tussupbayev, S.; Diefenbach, M.; Herdtweck, E.; Holthausen, M. C.; Schneider, S., Nat. Chem. 2011, 3, 532-537. 46 References begin on page 39. 2 Ruthenium hydride complexes containing the hindered phosphine 3 iPr ligand Tris(3-diisopropylphosphinopropyl)phosphine P P3 . 2.1 Introduction Polydentate phosphines have become important ligands for controlling the stereochemistry 1 of coordination complexes and have also been used to solubilize metal catalysts. PP3 ligands such as P((CH2)nPR2)3 (n= 2, 3; R= Me, Ph) form metal complexes with a range of applications, especially for complexes of iron and ruthenium. Applications have ranged from stabilization of complexes containing K2-dihydrogen to the formation of stable dinitrogen complexes with iron and ruthenium in both the 0 and +2 oxidation states.2 The PP3-type ligand provides a strong coordination environment, and is able to coordinate to the metal at up to four points through the four phosphine donors. Binding to form complexes with octahedral, trigonal bipyramidal and also square-pyramidal geometry is possible with PP3-type ligands. In an octahedral system, coordination of PP3-type ligands leaves two free coordination sites for other ligands and these remaining sites are geometry-constrained by the ligand to be in a cis arrangement. It is known that a cis arrangement of two ligands is a necessity for some parts of common catalytic mechanisms such as migratory insertion and 3 reductive elimination. Thus PP3-type complexes often have higher catalytic activity compared to complexes with mono or bidentate ligands, which can form inactive isomers where the two reactive ligands are in the unreactive trans arrangement.4 47 References begin on page 69. The encapsulating nature of PP3 ligands and the presence of sterically bulky groups on the terminal phosphines of PP3 ligands also has the propensity to restrict access to the metal centre and enhance chemical reaction at any of the non-PP3 ligands. There is now an expanding range of sterically-encumbered, polydentate ligands available,5 and in this chapter the synthesis of the hindered tripodal tetradentate phosphine ligand i 3 iPr P(CH2CH2CH2P Pr2)3 (P P3 ) is described. This ligand is a more hindered version of the PP3-type ligand skeleton, P(CH2CH2CH2PR2)3 which is known with either ethyl or methyl substituents on the terminal phosphine donors.6 A reasonable synthetic route to the hindered ligand is described as well as the formation and characterization of the ruthenium chloro and hydrido complexes. Characterization of these complexes allows analysis of the geometry around the metal centre as well as providing an initial assessment of the chemistry of these metal complexes. 2.2 Synthesis of Tris(3-diisopropylphosphinopropyl)phosphine, i 3 i P(CH2CH2CH2P Pr2)3, P P3 Pr (1) Syntheses of other PP3-type ligands with propylene-bridges between the apical and terminal phosphines have usually involved the radical-initiated addition of a dialkylphoshine (R2P- H) across the double bond of triallylphosphine. Syntheses of both P(CH2CH2CH2PMe2)3 6e and P(CH2CH2CH2PEt2)3 have been reported using this general approach. It is however not an ideal synthesis, due to the long reaction time required and the tendency to form 1,3-bis(dimethylphosphino)propane as a reaction side product.7 So, while i P(CH2CH2CH2P Pr2)3 (1) could possibly be synthesized by this approach, a synthesis without these described problems would be desirable. 48 References begin on page 69. 3 iPr P P3 (1) can be synthesized more efficiently using an alternative approach, via nucleophilic substitution of the halide in tris(3-bromopropyl)phosphine with a dialkylphosphide (Scheme 2.1).8 Tris(3-hydroxypropyl)phosphine was brominated using phosphorus tribromide to give the unstable tris(3-bromopropyl)phosphine (2). Tris(3-bromopropyl)phosphine tends to form a mixture of oligomeric and polymeric products on standing, probably by intramolecular or intermolecular nucleophilic attack of the central phosphine on a brominated Ȗ-carbon, to form an insoluble solid mass within a few hours. Tris(3-bromopropyl)phosphine was used immediately in the next step of the i 3 iPr sequence without further purification. P(CH2CH2CH2P Pr2)3, P P3 (1) was prepared in moderate yield (51% from tris(3-hydroxypropyl)phosphine) by the nucleophilic i substitution of bromide in the reaction of lithium diisopropylphosphide, (LiP Pr2, 3) with tris(3-bromopropyl)phosphine (Scheme 2.1).6e 3 OH Br 3 iPr P P 2 PBr3 Li P OH P Br P PiPr THF 2 HO Br i 51% Pr2P 2 Yield 1 Scheme 2.1 31 1 i 3 iPr In the P{ H} spectrum of P(CH2CH2CH2P Pr2)3, P P3 (1), two resonances are observed at 1.9 ppm and -34.7 ppm and these are assigned to the terminal phosphines and the central phosphine, respectively. Both resonances are singlets with no discernable coupling between the two phosphine environments and this is consistent with data reported for other 49 References begin on page 69. 3 P P3-type ligands incorporating propylene bridges between the apical and terminal phosphines.6e Tripodal phosphorus ligands of the P((CH2)nPR2)3 (n= 2, 3) type are well established as 9 3 iPr good ligands at ruthenium centres and, in this work, the P P3 ligand 1 was successfully employed in the synthesis of the five-coordinate chloro complex of ruthenium 3 iPr + [RuCl(P P3 )] (4). 3 iPr + 2.3 Synthesis and characterization of [RuCl(P P3 )] (4) Following the method detailed by Dr Ruth Guest,8 addition of sodium tetraphenylborate to 3 iPr a tetrahydrofuran (THF) solution of P P3 (1) and RuCl2(PPh3)3 afforded 3 iPr [RuCl(P P3 )][BPh4] (4[BPh4]) as a pink solid (Scheme 2.2). i Pr2 + P PB PC RuCl2(PPh3)3 + Cl P PiPr Ru 2 P D PA i Pr2P 1 4 Scheme 2.2 3 iPr + 2.3.1 X-ray Crystallography of [RuCl(P P3 )] (4) 8 A crystal structure of 4[BPh4] was reported prior to the work of this thesis. Analysis of this structure is included in this work to allow comparison with the information obtained about complex 4 from variable temperature NMR analysis reported below (Figure 2.1, Table 2.1). 50 References begin on page 69. 3 iPr Figure 2.1 ORTEP plot (50% thermal ellipsoids) of A) [RuCl(P P3 )][BPh4].THF i 2a (4[BPh4]) and for comparison B) [RuCl(P(CH2CH2P Pr2)3)][BPh4]. Only one of the two complex cations in each asymmetric unit in shown. Selected hydrogen atoms, tetraphenylborate anions and THF solvate have been omitted for clarity. The two structures within the asymmetric unit of 4[BPh4] are sufficiently similar that the crystallographic data of only one of the configurations, namely Ru1, is detailed here. Each asymmetric unit within the crystal structure contains one THF molecule, giving half a THF solvate for each metal complex. 3 iPr + The geometry of [RuCl(P P3 )] (4) is a distorted square-based pyramid with atoms Cl1, P1, P2 and P4 making up the base and P3 at the apex. The structure has a IJ value of 0.13, where IJ is a geometric parameter indicative of 5-coordinate complex geometry where IJ = 0 is perfect square pyramidal geometry and IJ = 1 is perfect trigonal-bipyramidal geometry.10 In this instance, the PB-Ru-PB angle, P1-Ru1-P4, at 156.51(2)º is appreciably closer to that of a square-based pyramid (180º) than a trigonal bipyramid (120º). In addition, the Ru-PB bond length, Ru1-P3, at 2.2536(6) Å is significantly shorter than the Ru-PA and Ru-PC bond 51 References begin on page 69. lengths Ru1-P1 and Ru1-P4 (2.4629(6) and 2.3892(7) Å, respectively) and this is characteristic of square-based pyramid geometry. One of the isopropyl methyl groups fills and blocks the void under the base of the pyramid probably through an anagostic (pseudo- agostic) interaction (d(Ru-H) = 2.637 Å (Ru1) and 2.369 Å (Ru2); M-H-C = 127.75Û (Ru1) and 131.18Û (Ru2)).11 3 iPr Table 2.1 Selected bond lengths (Å) and angles (º) for [RuCl(P P3 )][BPh4].THF (4[BPh4]) Ru1-Cl1 2.4351(7) Ru1-P2 2.2618(7) Ru1-P1 2.4629(6) Ru1-P3 2.2536(6) Ru1-P4 2.3892(7) Cl1-Ru1-P2 165.53(2) Cl1-Ru1-P1 89.28(2) Cl1-Ru1-P3 103.06(2) Cl1-Ru1-P4 83.51(2) P2-Ru1-P1 89.20(2) P2-Ru1-P3 91.38(2) P2-Ru1-P4 92.25(3) P1-Ru1-P3 99.40(2) P1-Ru1-P4 156.51(2) P3-Ru1-P4 104.00(2) There are three structures of ruthenium with the analogous tripodal tetradentate ligand 12 (P(CH2CH2CH2PMe2)3), however, these are all six-coordinate complexes with approximate octahedral geometry around the metal centre. The only comparative structure of a five-coordinate complex of ruthenium with a tripodal i 2a tetradentate phosphine ligand is that of [RuCl(P(CH2CH2P Pr2)3)][BPh4], which can be approximated to a distorted square-based pyramid in the same way as 4 (included in 52 References begin on page 69. i Figure 2.1 for comparison). In a similar fashion to 4, [RuCl(P(CH2CH2P Pr2)3)][BPh4] also has one of the isopropyl methyl groups filling and blocking the sixth coordination site under the base of the pyramid. The metal-to-donor atom lengths of 4 are equivalent to, or longer than, the analogous i + lengths in [RuCl(P(CH2CH2P( Pr)2)3)] . The P-Ru-P bond angles are all greater in 4 and i + the Cl-Ru-P bond angles are all more acute than in [RuCl(P(CH2CH2P( Pr)2)3)] . Thus in i + [RuCl(P((CH2)nP( Pr)2)3)] complexes with n= 2, 3, the complex with 3-carbon straps is a less strained complex and shows relaxation of the ligand bite angles and a lengthening of the metal to donor atom bond lengths. 3 iPr + 2.3.2 NMR analysis of [RuCl(P P3 )] (4) 31 1 In the P{ H} NMR spectrum of 4[BPh4] at room temperature, the signal for the three terminal phosphines PA/B/C, appears as a very broad resonance at 25.7 ppm while the signal for the central phosphine PD, signal appears as a sharp quartet at 14.2 ppm with a splitting of 36.4 Hz. A modest increase (25 K) in the temperature of the NMR experiment resulted in an appreciable sharpening of the resonances of the terminal phosphines. These spectra i 2a are analogous to those of [RuCl(P(CH2CH2P Pr2)3)][BPh4] and the broadness can be rationalized by the facile exchange of the terminal phosphine environments. It is interesting to note that the central phosphine PD resonance in 4[BPh4] appears to high field with respect to the terminal phosphine PA/B/C signals. In the analogous compound with i 31 1 two-carbon straps [RuCl(P(CH2CH2P Pr2)3)][BPh4], the P{ H} NMR spectrum shows the central phosphine as a quartet at 142.9 ppm (splitting 15.2 Hz) to low field of the three terminal phosphines, displayed as an exchange-broadened singlet at 72.1 ppm. The 53 References begin on page 69. i reversal in relative chemical shifts from 4 to those of [RuCl(P(CH2CH2P Pr2)3)][BPh4] is rationalized by the five-membered ring effect in phosphorus metallocycles. The five-membered ring effect is well documented and describes how phosphorus nuclei involved in five member metallocycles are significantly shifted to downfield compared to their four, six and seven member metallocycle analogues.13 This effect is magnified for the i + central phosphorus PC in [RuCl(P(CH2CH2P( Pr)2)3)] since the central P is effectively part of three five-membered metallocycles and this rationalizes why the two complexes, while chemically and structurally similar, have 31P chemical shifts for the central P atom which differ by almost 130 ppm. 31 1 As the temperature of the P{ H} NMR spectrum of 4[BPh4] is decreased, the spectra at first broaden and then sharpen. (Figure 2.2) At 243 MHz, as the temperature decreases to 220 K, the single broad resonance for the terminal phosphines separates into three distinct resonances representing the terminal phosphines individually, giving four distinct resonances representing the four different phosphine environments. At still lower temperatures, each of the resonances eventually splits into two resonances of comparable intensity (1:0.8) to give a total of eight resonances, which may be attributed to two isomers of 4[BPh4]. The chloride ligand resides either trans to the apical phosphorus or trans to a terminal phosphorus (Isomer-1 and Isomer-2). 54 References begin on page 69. P + P + P B1 P B2 C1 Cl C2 Ru Ru P P D1 PA1 D2 PA2 Cl Isomer-1 Isomer-2 31 1 3 iPr Figure 2.2 Variable temperature P{ H} NMR spectra for [RuCl(P P3 )][BPh4] (4[BPh4]) (242.95 MHz, methylene chloride-d2). In this system, there are two exchange processes operating: one that exchanges the terminal phosphorus environments, and one that interchanges Isomer-1 and Isomer-2. At 199 K, the 2 three resonances of the terminal phosphines of Isomer-2 (PA2, PB2, PC2) resolve with JP-P coupling observed, while in Isomer-1 the terminal phosphine resonances remain broad with 55 References begin on page 69. no defined coupling. All of the resonances eventually sharpen at 178 K to display similar coupling patterns. K1 + PB1 PC1 P P Cl B1 B1 Ru PD1 P P Cl P Cl A1 A1 C1 PA1 HA1P Cl PB1 K1 K1 A B P P Isomer-1 C1 C C K K K P + 2 2 2 P B2 C2 PB2 PB2 Cl Ru PD2 P A2 PA2 Ru PC2 PA2 Ru Cl PA2 Ru PB2 Cl D Cl E PC2 F PC2 Isomer-2 Scheme 2.3 The fact that the resonances of one isomer sharpen while the resonances of the other remain broad, suggests that the exchange of the terminal phosphines is faster in one isomer (Isomer-1) than the other (Isomer-2). The pattern and sequence of coalescences in the variable temperature NMR spectra can be rationalized by a model where exchange between the terminal phosphines in Isomer-1 (k1) is fast compared to the interchange between the isomers (k2, Scheme 2.3). We suggest that Isomer-1 is that in which chloride is trans to the central phosphines since the exchange of the terminal phosphines then involves simply a turnstile-type process, with exchange of the terminal phosphines between adjacent coordination sites. 56 References begin on page 69. 14 31 1 3 iPr Simulation of the exchange-broadened P{ H} NMR spectrum of [RuCl(P P3 )][BPh4] (4[BPh4]) was consistent with an exchange process where k1 § 3.5k2, and at 199 K, -1 -1 -1 -1 k1 § 385 sec and k2 § 110 sec , and at 210 K with k1 § 2135 sec and k2 § 610 sec . 3 iPr 2.4 Synthesis and characterization of RuH2(P P3 ) (5) 3 iPr Reaction of the ruthenium chloro complex [RuCl(P P3 )][BPh4] (4[BPh4]) with two 3 iPr equivalents of K[BEt3H] afforded the dihydride complex RuH2(P P3 ) (5) as a white crystalline solid (Scheme 2.4). P + P P B 2 Eq. KBEt H P T C Cl 3 E H Ru Ru P PC D PA PE Toluene H 5 4 Scheme 2.4 3 iPr 2.4.2 X-ray Crystallography of RuH2(P P3 ) (5) Crystals suitable for structural analysis were grown by slow evaporation of a toluene solution of 5 under nitrogen (Figure 2.3) and selected bond angles and lengths are given in Table 2.2. 57 References begin on page 69. 3 iPr Figure 2.3 ORTEP plot (50% thermal ellipsoids) of one of the two [RuH2(P P3 )] (5) units within the asymmetric unit. Selected hydrogen atoms have been removed for clarity. 3 iPr The geometry of RuH2(P P3 ) (5) is a distorted octahedron with the two hydrides in mutually cis coordination sites. There are eight previously reported structures of ruthenium(II) tetraphosphine dihydrides of which four have defined and refined hydrides.12c, 15 The Ru-H bond lengths of 1.62(5) Å, 1.69(5) Å sit comfortably within the ranges provided by the other four structures, with Ru-H bond lengths of 1.51 to 1.77 Å. Similarly the H-Ru-H bond angle of 91(2)º sits within the range of previously reported structures with bond angles between 77 to 93º. 58 References begin on page 69. 3 iPr Table 2.2 Selected bond lengths (Å) and angles (º) for [RuH2(P P3 )] (5) Ru1 -H1 1.62(5) Ru1 –H2 1.69(5) Ru1 –P1 2.2785(13) Ru1 –P2 2.3162(12) Ru1 –P4 2.3502(12) Ru1 –P3 2.3032(12) H1-Ru1-P2 71.7(17) H1-Ru1-P1 85.1(19) H1-Ru1-P3 75.4(17) H1-Ru1-P4 176.7(18) H2-Ru1-P2 88.4(15) H2-Ru1-P1 175.7(16) H2-Ru1-P3 85.0(15) H2-Ru1-P4 90.7(16) P2-Ru1-P1 89.45(4) P2-Ru1-P3 146.44(4) P2-Ru1-P4 105.33(4) P1-Ru1-P3 94.75(4) P1-Ru1-P4 93.42(4) P3-Ru1-P4 107.62(4) H1-Ru1-H2 91(2) 12c The structure of 5 is analogous to that of [RuH2(P(CH2CH2CH2PMe2)3)], which contains the related tetradentate phosphine ligand with methyl groups on the terminal phosphines rather than isopropyl groups. The average of the Ru-P bond lengths, 2.312 Å is slightly longer than for [RuH2(P(CH2CH2CH2PMe2)3)] for which the average Ru-P bond length is 2.286 Å. This is probably due to the steric bulk of the isopropyl substituents when compared to the methyl substituents, which results in elongation of the core Ru-P bonds. 3 iPr 2.4.3 NMR Analysis of RuH2(P P3 ) (5) 31 1 3 iPr In the P{ H} NMR spectrum of RuH2(P P3 ) (5), the signal for the two equivalent terminal phosphines PE appears as a doublet of doublets at 49.2 ppm, the signal for the 59 References begin on page 69. terminal phosphine PT is a doublet of triplets at 28.5 ppm and the central phosphine PC signal appears as a doublet of triplets at 0.4 ppm. 1 3 iPr Figure 2.4 Selected high field region of H NMR (600 MHz, benzene-d6) RuH2(P P3 ) (5) with coupling tree. The 1H NMR resonances for the two hydrido ligands of 5 both appear as doublets of triplets of doublets of doublets at -9.43 and -12.50 ppm due to coupling to the four phosphorus nuclei in three different environments, and to each other (Figure 2.4). The coupling 60 References begin on page 69. 2 constants JH-P are 59.6 Hz, 24.2 Hz and 18.8 Hz for the resonance at -9.43 ppm, and 2 63.2 Hz, 34.0 Hz and 15.0 Hz for the resonance at -12.50 ppm, with the JH-H coupling constant between the two hydrides of 6.2 Hz. The two hydrides are referred to as HA and HB, with HA being trans to a terminal phosphine PT and HB being trans to the central phosphine PC. The resonance at -9.43 ppm was assigned as HB because the coupling to three almost equivalent phosphines with a larger coupling to a single phosphine fits with being cis to the three terminal phosphines and trans to the central phosphine. Therefore the resonance at -12.50 ppm is assigned as HA which fits with the coupling to three distinct phosphorus environments. 3 iPr 2.5 Synthesis and Characterization of [Ru(H2)(H)(P P3 )][BPh4], (6[BPh4]) A solution of LiAlH4 (~1.5 M) in THF was added dropwise to a THF solution of 4[BPh4] to the point where the colour change from pink to colorless was complete. Ethanol was 3 iPr added and the resulting orange suspension worked up to afford [Ru(H2)(H)(P P3 )][BPh4] 6[BPh4] as an orange crystalline solid in poor yield (33%) (Scheme 2.5). P + 1. LiAlH P + P T 4 P T E Cl 2. EtOH E H Ru Ru PC P THF PC P E HH E 4 6 Scheme 2.5 3 iPr 2.5.2 X-ray Crystallography of [Ru(H2)(H)(P P3 )][BPh4], (6[BPh4]) Crystals suitable for structural analysis were grown from a THF/pentane solution of 6[BPh4] (Figure 2.5) and selected bond angles and bond lengths are given in Table 2.3. 61 References begin on page 69. 3 iPr + The geometry of [Ru(H2)(H)(P P3 )] (6) is a distorted octahedral with the hydride and dihydrogen ligands in mutually cis coordination sites. There is no element of symmetry in the cation, as the two mutually trans phosphines are not equivalent due to puckering of the six-membered metallocyclic rings. Figure 2.5 ORTEP plot (50% thermal ellipsoids) of the complex cation of 3 iPr [Ru(H2)(H)(P P3 )][BPh4].EtOH (6[BPh4].EtOH. Selected hydrogen atoms have been removed for clarity. There are two other structures of dihydrogen hydrido ruthenium complexes where the hydrido and dihydrogen ligands are in a mutually cis arrangement with four other 16 + 17 phosphine donors; [Ru(H2)(H)(PPh2Me)4] and [Ru(H2)(H)(P(CH2CH2PPh2)3)] . In both 62 References begin on page 69. of these complexes, the dihydrogen ligand was not refined. There have, however, been examples of ruthenium cis hydride dihydrogen complexes with all ligands refined including i 18 the dihydrogen ligand, and these include [Ru(H)(H2)(X)(P Pr3)2] (X= benzoquinoline) and i 19 [RuH(H2)(o-C6H5py)(P Pr3)2][BArF]. 3 iPr Table 2.3 Selected bond lengths (Å) and angles (º) for [Ru(H2)(H)(P P3 )][BPh4].EtOH 6[BPh4] H2 –H3 0.66(6) Ru1 –H1 1.59(3) Ru1 –H2 1.62(6) Ru1 –H3 1.75(4) Ru1 –P1 2.2890(9) Ru1 –P2 2.3756(9) Ru1 –P3 2.4270(8) Ru1 –P4 2.3591(9) H1-Ru1-H2 75(2) H1-Ru1-H3 97.4(18) H2-Ru1-H3 23(2) H1-Ru1-P1 86.3(12) H1-Ru1-P2 75.1(12) H1-Ru1-P3 178.7(12) H1-Ru1-P4 74.1(12) H2-Ru1-P1 161(2) H2-Ru1-P2 89(2) H2-Ru1-P3 106(2) H2-Ru1-P4 79(2) H3-Ru1-P1 175.4(14) H3-Ru1-P2 89.2(13) H3-Ru1-P3 89.2(13) H3-Ru1-P4 90.1(13) P1-Ru1-P2 89.15(3) P1-Ru1-P3 92.36(3) P1-Ru1-P4 93.56(3) P2-Ru1-P3 104.61(3) P2-Ru1-P4 148.79(3) P3-Ru1-P4 106.33(3) 63 References begin on page 69. The Ru1-H1 bond length for 6 (1.59(3) Å) is comparable to that of 1.54(4) Å for i i [Ru(H)(H2)(X)(P Pr3)2] and 1.528(20) Å for [RuH(H2)(o-C6H5py)(P Pr3)2][BArF]. Likewise the dihydrogen bond distances Ru1-H2 and Ru1-H3 for 6 of 1.62(6) and 1.75(4) Å, respectively, are similar but slightly elongated compared to those for i i [Ru(H)(H2)(X)(P Pr3)2] (1.57(5) and 1.68(4) Å) and [RuH(H2)(o-C6H5py)(P Pr3)2][BArF] (1.564(20) and 1.547(21) Å). This elongation is probably caused by the differences in the i donor atom in the coordination site trans to dihydrogen, with [Ru(H)(H2)(X)(P Pr3)2] being i carbon and [RuH(H2)(o-C6H5py)(P Pr3)2][BArF] being nitrogen as opposed to phosphorus in 6. 3 iPr 2.5.3 NMR Analysis of [Ru(H2)(H)(P P3 )][BPh4], (6[BPh4]) From observation of both the 31P{1H} NMR spectrum and the 1H NMR spectrum 3 iPr [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) is clearly fluxional in solution at room temperature. The 31P{1H} NMR spectrum at low temperature (215 K) shows four resonances for the coordinated phosphines (at 30.3, 21.3, 13.7 and 4.3 ppm, Figure 2.6). The appearance of four resonances is consistent with the solid-state structure where the two mutually trans phosphines are not equivalent due to puckering of the six-membered metallocyclic rings. At low temperature, the two mutually trans phosphines (PB and PC) exhibit a large resolved coupling (about 180 Hz). As the temperature is raised to 244 K, the resonances for PB and PC broaden and coalesce and this is probably due to ring-flipping of the ligand backbone. At higher temperatures (above 298 K), there is mutual exchange of all three of the terminal phosphines (a turnstile-type exchange) and the signals for the terminal phosphines are averaged to a single broad resonance. Modelling of the exchanges at 244 K indicates that the exchange of magnetism between the mutually trans phosphines (ring flip) occurs at a 64 References begin on page 69. rate of about 3000 s-1 and that the turnstile exchange of the terminal phosphines occurs at a significantly slower rate (about 300 s-1). 31 1 3 iPr Figure 2.6 P{ H} NMR spectrum (242.9 MHz, THF-d8) of [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) at 298 K, 244 K and 215 K 1 At 298 K, the H NMR resonances the hydrido and dihydrogen ligands of 6[BPh4] appear as a single broad resonance at -8.57 ppm, indicating fast exchange between the hydrido and dihydrogen ligands. At 195 K, the signal resolves to a broad two-proton resonance at -7.44 ppm, assigned to the dihydrogen ligand and a phosphorus-coupled doublet of triplets 2 at -10.3 ppm ( JH-P coupling constants of 57 Hz and 32 Hz) for the hydrido resonance. Further evidence for this assignment comes from the T1 values for these two high field resonances at 180 K at on a 600 MHz spectrometer, with the dihydrogen resonance having 65 References begin on page 69. a T1 of 68 ± 3 ms and the hydrido resonance a T1 of 594 ± 12 ms. It is characteristic of dihydrogen hydrido metal complexes that the dihydrogen ligand has a significantly shorter relaxation time than the hydrido ligand.6a Under an atmosphere of deuterium gas, the dihydrogen ligand exchanges for D2, partially incorporating deuterium into the metal-bound hydrogens. In the 1H NMR spectrum at 200 K, the dihydrogen (or hydrogen deuteride) resonance at about -10 ppm appears as a superimposition of signals (Figure 2.7) due to the different isotopomers. 1 31 Figure 2.7 H2 and/or HD resonance in the H{ P} NMR spectrum (700 MHz, THF-d8) of 3 iPr partially deuterated [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) at 200 K with resolution enhancement. The two three-line resonances corresponding to the species with coordinated H-D can be resolved and the JHD coupling of 31 Hz extracted. JHD greater than 15 Hz is considered to 66 References begin on page 69. be characteristic of dihydrogen complexes,20 clearly confirming the presence of K2-coordinated H-D in this species. Using the most recent interrelationship between H-H bond distance (dHH) and H-D coupling(JHD) of dHH = 1.47 - 0.0175JHD Å determined by 21 Gusev, dHH is determined to be 0.927 Å. This is longer than the value determined from 3 iPr the crystal structure of [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) of 0.66(6) Å, but expected as crystallographic techniques are notorious for giving foreshortened dHH because of rapid H2 rotation/vibration.20 3 iPr [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) is remarkably stable and survives unchanged under a nitrogen atmosphere indefinitely without substitution of the H2, even after several freeze-pump-thaw cycles. The lack of ready N2 substitution probably reflects the fact that 3 iPr steric crowding from the bulky P P3 ligand makes binding the smaller H2 more preferable than the bulkier N2. 3 iPr Treatment of [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) with potassium tert-butoxide in d8-THF 3 iPr results in clean deprotonation and formation of RuH2(P P3 ) (5). Conversely, treatment of - 5 with triflic acid in d8-THF in the presence of BPh4 results in formation of 6[BPh4] and this acid/base behavior is consistent with that observed for other hydrido and dihydrido complexes of ruthenium and iron.22 2.6 Conclusions 3 iPr The sterically hindered, tripodal tetradentate ligand P P3 (1) was synthesized and used in the synthesis of a series of stable ruthenium compounds. The five-coordinate chloro- 3 iPr + complex [RuCl(P P3 )] (4) was synthesized by multinuclear NMR spectroscopy, with low temperature 31P{1H} NMR spectroscopy being used to explore the exchange mechanisms 67 References begin on page 69. between its various isomers. Complex 4 was reduced with potassium triethylborohydride to 3 iPr produce RuH2(P P3 ) (5). Complex 4 was also reduced with lithium aluminium hydride, followed by reaction with ethanol to produce the stable hydrido dihydrogen species 3 iPr + [Ru(H2)(H)(P P3 )] (6). Complexes 5 and 6 were both characterized crystallographically and by multinuclear NMR spectroscopy. 3 iPr The bulky P P3 ligand is amongst the most sterically encumbered PP3-type ligands so far 3 iPr synthesized. While the P P3 ligand forms stable tetradentate five- and six-coordinate complexes with ruthenium, the complexes are hindered and they are fluxional in solution. This behaviour is typical of many complexes where the metal-phosphorus bonds are weakened because the bulky ligand substituents restrict the phosphorus donors from gaining optimal access to the metal centre. 68 References begin on page 69. 2.7 References 1. Mayer, H. A.; Kaska, W. C., Chem. Rev. 1994, 94 1239-72. 2. (a) Field, L. D.; Guest, R. W.; Vuong, K. Q.; Dalgarno, S. J.; Jensen, P., Inorg. Chem. 2009, 48 2246-2253; (b) Bianchini, C.; Perez, P. J.; Peruzzini, M.; Zanobini, F.; Vacca, A., Inorg. Chem. 1991, 30 279-287. 3. Masters, C., Homogeneous Transition-metal Catalysis. University Press, Cambridge: 1981. 4. Sung, K.-M.; Huh, S.; Jun, M.-J., Polyhedron 1998, 18 469-479. 5. Pascariu, A.; Iliescu, S.; Popa, A.; Ilia, G., J. Organomet. Chem. 2009, 694 3982- 4000. 6. (a) Bampos, N.; Field, L. D., Inorg. Chem. 1990, 29 587-8; (b) Bampos, N.; Field, L. D.; Messerle, B. A., Organometallics 1993, 12 2529-35; (c) Field, L. D.; Bampos, N.; Messerle, B. A., Magn. Reson. Chem. 1991, 29 36-9; (d) Antberg, M.; Frosin, K. M.; Dahlenburg, L., J. Organomet. Chem. 1988, 338 319-27; (e) Antberg, M.; Prengel, C.; Dahlenburg, L., Inorg. Chem. 1984, 23 4170-4. 7. Bampos, N. PhD Thesis. University of Sydney, Sydney, Australia, 1993. 8. Guest, R. Synthesis and Reactions of Iron and Ruthenium Dinitrogen Complexes. University of New South Wales, 2008. 9. (a) Bianchini, C.; Bohanna, C.; Esteruelas, M. A.; Frediani, P.; Meli, A.; Oro, L. A.; Peruzzini, M., Organometallics 1992, 11 3837-3844; (b) Bianchini, C.; Meli, A.; 69 References begin on page 69. Peruzzini, M.; Frediani, P.; Bohanna, C.; Esteruelas, M. A.; Oro, L. A., Organometallics 1992, 11 138-45; (c) Field, L. D.; Messerle, B. A.; Smernik, R. J., Inorg. Chem. 1997, 36 5984-5990; (d) Field, L. D.; Messerle, B. A.; Smernik, R. J.; Hambley, T. W.; Turner, P., Inorg. Chem. 1997, 36 2884-2892. 10. Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C., J. Chem. Soc., Dalton Trans. 1984, 1349-1356. 11. Brookhart, M.; Green, M. L. H.; Parkin, G., P. Natl. Acad. Sci. U.S.A. 2007, 104 6908-6914. 12. (a) Antberg, M.; Dahlenburg, L., Inorg. Chim. Acta 1986, 111 73-6; (b) Antberg, M.; Dahlenburg, L., Acta Crystallogr., Sect. C: Cryst. Struct. 1986, C42 997-9; (c) Dahlenburg, L.; Frosin, K. M., Polyhedron 1993, 12 427-34. 13. (a) Garrou, P. E., Inorg. Chem. 1975, 14 1435-1439; (b) Garrou, P. E., Chem. Rev. 1981, 81 229-66. 14. Reich, H. J. WinDNMR: Dynamic NMR Spectra for Windows, J. Chem. Educ. Software: 1998. 15. (a) Nicasio, M. C.; Perutz, R. N.; Walton, P. H., Organometallics 1997, 16 1410- 1417; (b) Mebi, C. A.; Frost, B. J., Inorg. Chem. 2007, 46 7115-7120. 16. Lough, A. J.; Morris, R. H.; Ricciuto, L.; Schleis, T., Inorg. Chim. Acta 1998, 270 238-246. 70 References begin on page 69. 17. Bianchini, C.; Masi, D.; Peruzzini, M.; Casarin, M.; Maccato, C.; Rizzi, G. A., Inorg. Chem. 1997, 36 1061-1069. 18. Matthes, J.; Grundemann, S.; Toner, A.; Guari, Y.; Donnadieu, B.; Spandl, J.; Sabo- Etienne, S.; Clot, E.; Limbach, H.-H.; Chaudret, B., Organometallics 2004, 23 1424-1433. 19. Toner, A. J.; Gründemann, S.; Clot, E.; Limbach, H.-H.; Donnadieu, B.; Sabo- Etienne, S.; Chaudret, B., J. Am. Chem. Soc. 2000, 122 6777-6778. 20. Morris, R. H., Coord. Chem. Rev. 2008, 252 2381-2394. 21. Gusev, D. G., J. Am. Chem. Soc. 2004, 126 14249-14257. 22. (a) Baker, M. V.; Field, L. D.; Young, D. J., J. Chem. Soc., Chem. Commun. 1988, 546-8; (b) Doi, T.; Fukuyama, T.; Horiguchi, J.; Okamura, T.; Ryu, I., Synlett 2006, 721-724; (c) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D., J. Am. Chem. Soc. 2005, 127 10840-10841. 71 References begin on page 69. 3 New Super-hindered Polydentate Polyphosphine Ligands t t t P(CH2CH2P Bu2)3, PhP(CH2CH2P Bu2)2, P(CH2CH2CH2P Bu2)3 and their Ruthenium(II) Chloride Complexes 3.1 Introduction The multihapticity, strong donor ability and lipophilicity of alkyl-substituted polydentate phosphines make them good ligands for controlling the stereochemistry of coordination 1 complexes and solubilizing metal catalysts. Ruthenium and iron complexes of PP3-type i ligands P((CH2)nPR2)3 (n = 2, 3 ; R = Me, Et, Pr) have been used in a wide variety of applications including the formation of stable dinitrogen complexes (in a range of oxidation states) and in the C-H activation and the stabilization of K2-dihydrogen complexes.2 The PP3-type ligands provide a strong coordination environment and they generally coordinate up to four points through the four strong phosphine donors. The geometry of coordination is constrained by the ligand, thus when all four of the phosphines are bound, an octahedral complex must have the remaining two coordination sites geometry constrained a cis arrangement (in adjacent coordination sites). The cis stereochemistry often results in higher catalytic activity for processes like migratory insertion or reductive elimination where a cis arrangement of the two non phosphine ligands is essential.3 Additionally, bulky phosphines have been particularly good ligands to enhance the catalytic activity of transition metal systems in a range of applications e.g. tri(cyclohexyl)phosphine enhances the activity of Grubbs' catalyst,4 and the tertiary-butyl groups on phosphine ligands such as tri(tert-butyl)phosphine have also afforded particularly active catalysts.5 72 References begin on page 95. There is now an expanding range of sterically encumbered, polydentate ligands available,6 but to this point, the bulkiest groups employed on the terminal phosphines of PP3-type i 2h polydentate phosphine ligands have been either isopropyl groups (P(CH2CH2 Pr2)3 and i 2g 7 P(CH2CH2CH2 Pr2)3 (1)) or cyclohexyl groups (P(CH2CH2Cy2)3) . The work described in this paper explores the effect of increasing steric bulk on polydentate phosphines by investigating tetradentate PP3 ligands with tertiary-butyl groups as substituents on the terminal phosphines. We report here the synthesis of the hindered tripodal tetradentate t 2 tBu t 3 tBu phosphine ligands P(CH2CH2P Bu2)3 (P P3 , 10) and P(CH2CH2CH2P Bu2)2 (P P3 , 16) t 2 tBu as well as the hindered tridentate phosphine ligand PhP(CH2CH2P Bu2)2 (PhP P2 , 14). This work reports the synthetic routes to the hindered ligands as well as the formation and characterization of their ruthenium chlorido complexes. Characterization of the complexes allows an analysis of the binding mode of this new series of bulky ligands and the behavior of the complexes, both in solution and the solid state. 3.2 Preparation and characterization of phosphine ligands t 2 tBu 3.2.1 Synthesis of P(CH2CH2P Bu2)3, P P3 (10), 2 R There are currently two methods for the preparation of P P3 type ligands. The first of these is the radical addition of a secondary phosphine across the unsaturated bonds of trivinylphosphine (12) with an example of this being the addition of dimethylphosphine 2 Me 8 across trivinylphosphine (12) to produce P P3 , as illustrated in Scheme 3.1. 73 References begin on page 95. PMe2 hQ P +3HP P AIBN Me2P PMe2 12 Scheme 3.1 2 R P P3 type ligands have also been prepared by the base-mediated addition of a secondary phosphine to trivinylphosphine 12 in a method modified from that of Morris et al7 used in the synthesis of analogous tripodal tetradentate phosphine ligands. This method has been 2 Me 9 used to synthesize a variety of tetradentate phosphine ligands including P P3 , and 2 iPr 2h P P3 . The primary advantage of the base-mediated method is the quicker reaction time and the lack of unwanted byproducts as formed in the radical reaction caused by competing radical coupling reactions and fragmentation of the 1,2-diphosphine intermediates.10 Base- 2 tBu mediated addition was the route used to synthesize the ligand P P3 (10) used in this work. 3.2.1.1 Di(tert-butyl)chlorophosphine, ((CH3)3C)2PCl (9) Di(tert-butyl)chlorophosphine (9) was prepared by the nucleophilic substitution of phosphorus trichloride by the Grignard reagent tert-butylmagnesium chloride following the method of Hofmann et al.11 (Scheme 3.2). The phosphorus signal for 9 appears in the 31P{1H} NMR spectrum as a single sharp resonance at 146.6 ppm. The protons of the tert-butyl groups appear in the 1H NMR spectrum as a doublet with a coupling constant of 12 Hz to phosphorus at 1.18 ppm. 74 References begin on page 95. 2 + PCl ClP Cl Mg 3 8 9 Scheme 3.2 3.2.1.2 Di(tert-butyl)phosphine, ((CH3)3C)2PH (7) Di(tert-butyl)phosphine (7) was prepared by the treatment of di(tert-butyl)chlorophosphine (9) with lithium aluminium hydride following a modified method by Timmer et al.12 (Scheme 3.3). Cl P + LiAlH4 HP 9 7 Scheme 3.3 Distillation afforded di(tert-butyl)phosphine (7) as a colorless liquid showing a singlet at 20.3 ppm in the 31P{1H} NMR spectrum. The 1H NMR spectrum of 7 shows a broad doublet at 3.14 with a coupling constant of 200 Hz which represents the phosphine proton, in addition to a sharp doublet at 1.16 ppm with a coupling constant of 11 Hz representing the tert-butyl protons. 75 References begin on page 95. 3.2.1.3 Trivinylphosphine, (12) Trivinylphosphine (12) was synthesized by the addition of trimethyl phosphite to a tetrahydrofuran (THF) solution of vinylmagnesium bromide at 0°C in a method modified from that of Maier et al., (Scheme 3.4).13 MeO P OMe + 3 MgBr P OMe 11 12 Scheme 3.4 Trivinylphosphine was isolated by distillation as a mixture with THF, directly from the crude reaction mixture and this solution was used in further reactions as quickly as possible after preparation to avoid polymerization. t 2 tBu 3.2.1.4 P(CH2CH2P Bu2)3, P P3 (10) LDA PtBu PtBu tBu tBu 2 2 P + 3 P P H THF/Hexane tBu P 12 7 2 10 Scheme 3.5 2 tBu P P3 (10) was prepared by the base-induced (lithium diisopropylamide, LDA, 13) addition of di(tert-butyl)phosphine (7) to trivinylphosphine (12) in a method modified from 7 31 1 2 tBu that of Morris et al. (Scheme 3.5). In the P{ H} NMR spectrum of P P3 (10), two resonances are observed at 34.1 and -15.3 ppm in a ratio of 3:1, assigned to the three 76 References begin on page 95. terminal phosphines and the central phosphine respectively. As is typical in PP3-type 3 ligands with ethylene bridges, coupling between the terminal and central phosphines ( JP-P = 24.9 Hz) is observed even before coordination to the metal center. t 2 tBu 3.2.2 Synthesis of PhP(CH2CH2P Bu2)2 (PhP P2 , 14) Tridentate ligands with a central phenylphosphine moiety have been synthesized a number of different ways. These include irradiation of phenylphosphine and donors with an unsaturated arm14 (Scheme 3.6), reaction of dilithium phenylphosphide with terminal donors containing a halogenated arm14 (Scheme 3.7), and base mediated addition of a secondary phosphine across the unsaturated bonds in divinylphenylphosphine (15) (Scheme 15 2 tBu 3.8). Base-mediated addition to divinylphenylphosphine (15) was the route to PhP P2 (14) used in this work. H hv H H + 2 N H N P N P H H H H Scheme 3.6 + 2 Cl P P P P P Li Li Scheme 3.7 77 References begin on page 95. KOtBu P + 2 HP P P P Scheme 3.8 3.2.2.2 Divinylphenylphosphine (15) The literature methods13 for the synthesis of divinylphenylphosphine (15) from dichlorophenylphosphine by reaction with vinylmagnesium bromide (11) are low yielding. Divinylphenylphosphine (15) was synthesized by an alternative approach by reaction of two equivalents of vinylmagnesium bromide (11) with one equivalent of diethoxyphenylphosphine (Scheme 3.9) in a method analogous to that of King et al. which used di(n-butoxy)phenylphosphine instead as the starting substrate.16 The phosphorus signal for 15 appears in the 31P{1H} NMR spectrum as a single sharp resonance at 16.1 ppm. + 2 BrMg P P O O 11 15 Scheme 3.9 78 References begin on page 95. t 2 tBu 3.2.2.3 PhP(CH2CH2P Bu2)2 (PhP P2 , 14) 2 tBu PhP P2 (14) was prepared by the base-induced (lithium diisopropylamide, LDA, 13) addition of di(tert-butyl)phosphine (7) to divinylphenylphosphine (15) in a method similar 2 tBu to that described eariler (Section 3.2.1.4) for the synthesis of P P3 (10) (Scheme 3.10). In 31 1 2 tBu the P{ H} NMR spectrum of PhP P2 (14) two resonances are observed at 34.0 and -16.9 ppm in a ratio of 2:1, and these are assigned to the two terminal phosphines and the 31 3 central phosphine respectively. Coupling between the P nuclei ( JP-P = 27 Hz) is observed even before coordination to the metal center. tBu tBu LDA + 2 P H THF/Hexane P t P t 7 Bu2P P Bu2 15 14 Scheme 3.10 t 3 tBu 3.2.3 Synthesis of P(CH2CH2CH2P Bu2)3, (P P3 , 16); 3 tBu P P3 (16) was prepared by the nucleophilic substitution of bromide in the reaction of t lithium di(tert-butyl)phosphide, (LiP Bu2, 17), with tris(3-bromopropyl)phosphine (2) (Scheme 3.11), in a method analogous that used for the synthesis of a related tripodal i 2g tetradentate phosphine ligand P(CH2CH2CH2P Pr2)3 (1) described in Chapter 2. In the 31 1 3 t P{ H} NMR spectrum of P P3 Bu (16), two resonances are observed at 26.2 and -35.5 ppm in a ratio of 3:1 assigned to the terminal phosphines and the central phosphine respectively. Both resonances are singlets with no discernible coupling between the two 79 References begin on page 95. 3 phosphine environments, and this is consistent with data reported for other P P3-type ligands incorporating propylene bridges between the apical and terminal phosphines.2b, 2g 17 OH Br 3 tBu P 2 PBr3 P P OH P Br Li t P P Bu2 HO Br THF t Bu2P 2 16 Scheme 3.11 3.3 Preparation and characterization of ruthenium chlorido complexes 2 tBu 3.3.1 Synthesis of Ru(P P3 )Cl2 (18) 2 tBu 2 tBu Addition of P P3 (10) to a THF solution of RuCl2(PPh3)3 afforded RuCl2(P P3 ) (18) as a tan solid which was isolated by filtration (Scheme 3.12). PT THF P + 2 tBu E Cl RuCl2(PPh3)3 P P3 Ru PC Cl 10 18 PF 2 tBu t P P3 =P(CH2CH2P( Bu)2)3 Scheme 3.12 80 References begin on page 95. 2 tBu 3.3.2 NMR characterization of RuCl2(P P3 ) (18) 31 1 2 tBu In the P{ H} NMR spectrum of RuCl2(P P3 ) (18) at room temperature, the two bound terminal phosphines PE/PT appear as a single very broad resonance (W1/2 = 55 Hz at 162 MHz; CD2Cl2 solution) centred around 91.4 ppm. The central phosphine PC appears as a 3 2 doublet of triplets at 106.2 ppm with a JP-P coupling constant of 37 Hz to PF, and a JP-P coupling constant of 17.5 Hz to PE/PT respectively. The resonance at 34.3 ppm is assigned to the pendant phosphine PF (not bound to the metal center) because (i) displays no coupling to the other terminal phosphines PE and PT; and (ii) PF has a chemical shift very close to the chemical shift observed for the terminal phosphines in the free ligand (34.1 ppm). 31 1 2 tBu When the P{ H} NMR spectra of RuCl2(P P3 ) (18) were collected at lower temperatures (systematically down to about -100°C, Figure 3.1) the PE/PT resonance broadened into the baseline before resolving and sharpening into two separate resonances at 132 and 50 ppm. This behaviour can be ascribed to the two bound, terminal phosphines, PE and PT, being in fast exchange at room temperature – probably associated with the degenerate isomerisation of the chloro ligand in the coordination sphere (Scheme 3.13). 17 31 1 2 tBu Simulation of the exchange-broadened P{ H} NMR spectrum of RuCl2(P P3 ) (18) gives rates for the exchange process where at 174 K, k § 800 sec-1 and 220 K, k § 100,000 sec-1. There is no evidence for the presence of a third stereoisomer (18a) where the vacant coordination site is trans to PC (the central phosphine). 81 References begin on page 95. PT PT PT PE Cl P Cl PE Ru E Ru Ru P P C Cl PC C Cl Cl P Cl P F PF F 18a Scheme 3.13 31 1 Figure 3.1 Variable temperature P{ H} NMR spectra (243 MHz, Solvent: CD2Cl2) of 2 tBu RuCl2(P P3 ) (18) with spectra at (from front) 174 K, 188 K, 204 K, 220 K, 236 K, 252 K, 268 K and 284 K. 82 References begin on page 95. 2 tBu 3.3.3 Synthesis of RuCl2(PhP P2 ) (19): 2 tBu Addition of a THF solution of RuCl2(PPh3)3 to a THF solution of PhP P2 (14), followed 2 tBu by stirring overnight and addition of hexane, afforded RuCl2(PhP P2 ) (19) as a yellow solid (Scheme 3.14). Crystals suitable for structural analysis were grown by slow diffusion of pentane into a dichloromethane solution of 19 (Figure 3.2) and selected bond angles and lengths are given in Table 3.1. PT PE Cl THF Ru 2 tBu PC Cl RuCl2(PPh3)3 + PhP P3 14 19 2 tBu t PhP P2 =PhP(CH2CH2P( Bu)2)2 Scheme 3.14 2 tBu 3.3.4 X-ray Crystallography of RuCl2(PhP P2 ) (19) 2 tBu The geometry of RuCl2(PhP P2 ) (19) is a distorted square-based pyramid with atoms Cl1, Cl2, P2 and P3 making up the base and P1 at the apex. The structure has a IJ value of 0.29, where IJ is a geometric parameter indicative of 5-coordinate complex geometry where IJ = 0 is perfect square pyramidal geometry and IJ = 1 is perfect trigonal-bipyramidal geometry.18 One of the tertiary-butyl methyl groups fills and blocks the void under the base of the pyramid, through an anagostic (pseudoagostic) interaction (d(Ru-H) 2.34(3) Å and ෳ(Ru-H- C) 111(2)°).19 83 References begin on page 95. 2 tBu Figure 3.2 ORTEP plot (50% thermal ellipsoids) of RuCl2(PhP P2 ) (19), selected hydrogen atoms have been omitted for clarity. 2 tBu The structure of RuCl2(PhP P2 ) (19) is comparable to that of 20 21 RuCl2(PhP(CH2CH2CH2PCy2)2), and RuCl2(PhP(CH2CH2PPh2)2), both of which are 5- n R coordinate complexes with similar PhP P2 ligands on ruthenium and two chloro ligands arranged in cis coordination sites. RuCl2(PhP(CH2CH2CH2PCy2)2) (IJ = 0.50) and RuCl2(PhP(CH2CH2PPh2)2) (IJ = 0.37), are both more significantly distorted towards a trigonal bipyramidal character than 19 but neither to the extent that they would be classified as trigonal bipyramidal geometry. There is also a difference in the way the tridentate ligand 84 References begin on page 95. is bound geometrically. The central phosphorus atoms of both complexes RuCl2(PhP(CH2CH2CH2PCy2)2) and RuCl2(PhP(CH2CH2PPh2)2) are located at the apex of the square based pyramids whilst for complex 19 it is located within the base of the pyramid with a terminal phosphine at the apex. There is a trend toward lengthening of the Ru-P bonds as the steric bulk on the terminal phosphines increases from phenyl (Ru-P = 2.198(2), 2.260(2), 2.280(2) Å) to cyclohexyl (Ru-P = 2.211(1), 2.276(1), 2.306(1) Å) to tert-butyl, (Ru-P = 2.265(1), 2.275(1), 2.385(1) Å). 2 tBu Table 3.1 Selected bond lengths (Å) and bond angles (º) for RuCl2(PhP P2 ) (19) Ru1 –Cl1 2.4257(10) Ru1 –Cl2 2.4628(10) Ru1 –P1 2.2748(11) Ru1 –P2 2.2652(11) Ru1 –P3 2.3849(11) Cl1-Ru1-Cl2 85.65(4) P1-Ru1-Cl1 96.06(4) P1-Ru1-Cl2 101.59(4) P1-Ru1-P2 82.00(4) P1-Ru1-P3 111.66(4) P2-Ru1-P3 81.96(4) P2-Ru1-Cl1 103.86(4) P2-Ru1-Cl2 169.52(4) P3-Ru1-Cl1 152.26(4) P3-Ru1-Cl2 87.56(4) 2 tBu 3.3.5 NMR characterization of RuCl2(PhP P2 ) (19) 31 1 2 tBu The P{ H} NMR spectrum of RuCl2(PhP P2 ) (19) has the two bound terminal phosphines PE/PT as a very broad resonance at 92.3 ppm (W1/2 = 75 Hz at 162 MHz; CD2Cl2 solution, 298 K). The central phosphine PC appears as a triplet at 94.4 ppm, with a 2 31 1 JP-P coupling constant of 12.6 Hz to PE/PT. P{ H} NMR spectra were also collected at decreased temperatures down to about -90°C (Figure 3.3). As the temperature descended 85 References begin on page 95. the PE/PT resonance broadened into the baseline before resolving into two separate 2 tBu resonances at 128 and 52 ppm. As observed for RuCl2(P P3 ) (18), the resonances for PE and PT are in fast exchange at room temperature and the NMR data is consistent with a fluxional 5-coordinate complex with the exchange similar to that depicted in Scheme 3.13. This assignment is also consistent with the structural data from the x-ray crystal structure. 31 1 Figure 3.3 Variable temperature P{ H} NMR spectra (243 MHz, Solvent: CD2Cl2) of 2 tBu RuCl2(PhP P2 ) (19) with spectra at (from front) 179 K, 184 K, 195 K, 211 K, 226 K, 226 K, 243 K, 259 K, 275 K, and 300 K. 86 References begin on page 95. 3 tBu 3.3.6 Synthesis of RuCl2(P P3 ) (20) 3 tBu While, RuCl2(P P3 ) (20) could be prepared in a similar manner to the syntheses of 2 tBu 2 tBu RuCl2(P P3 ) (18) and RuCl2(PhP P2 ) (19) (by the direct reaction of RuCl2(PPh3)3 with 3 tBu 3 tBu P P3 ligand (16)), the separation of RuCl2(P P3 ) (20) from the triphenylphosphine 3 tBu byproduct was difficult. A better route to RuCl2(P P3 ) (20) was by reaction of a toluene 3 tBu 3 tBu solution of P P3 (16) with di-μ-chlorobis[(p-cymene)chlororuthenium]. RuCl2(P P3 ) (20) was isolated cleanly as a green solid and crystals suitable for structural analysis were grown by slow evaporation of a toluene solution (Figure 3.4). Selected bond angles and lengths are given in Table 3.2. 3 tBu 3.3.7 X-ray Crystallography of RuCl2(P P3 ) (20) 3 tBu The geometry of RuCl2(P P3 ) (20) is a distorted square-based pyramid with the central phosphorus PC occupying the apical position. Only two of the three terminal phosphines PE are bound to ruthenium and they are in mutually trans positions. The two chloride ligands are also in mutually trans positions, with the two terminal phosphines making up the base of the pyramid (IJ = 0.15). 87 References begin on page 95. 3 tBu Figure 3.4 ORTEP plot (50% thermal ellipsoids) of RuCl2(P P3 ) (20), hydrogen atoms have been omitted for clarity. There are six previously reported structures of ruthenium(II) triphosphine dichloride complexes of similar geometry with linked phosphines donors in a meridional arrangement.22 The only other reported structure in which all three of the phosphine donors are part of the one ligand is [bis-1-(1'-diphenylphosphinoferrocenyl)phenylphosphine]dichlororuthenium(II),22a which has shorter Ru-P bond distances to the terminal phosphines (2.332(1) and 2.369(2) Å) than those observed in 20 (2.411(4) and 2.408(4) Å) probably due to the larger steric bulk of the 88 References begin on page 95. tertiary butyl groups in 20, but otherwise the structure has very similar bond lengths and angles. 3 tBu Table 3.2 Selected bond lengths (Å) and bond angles (º) for RuCl2(P P3 ) (20) Ru1 –Cl1 2.416(3) Ru1 –Cl2 2.467(3) Ru1 –P1 2.411(4) Ru1 –P2 2.195(4) Ru1 –P3 2.408(4) Cl1-Ru1-Cl2 164.11(13) P1-Ru1-Cl1 88.96(13) P1-Ru1-Cl2 89.57(14) P1-Ru1-P2 93.59(16) P1-Ru1-P3 172.88(17) P2-Ru1-P3 93.20(16) P2-Ru1-Cl1 114.45(15) P2-Ru1-Cl2 81.43(14) P3-Ru1-Cl1 90.18(13) P3-Ru1-Cl2 89.32(14) 3 tBu The structure of RuCl2(P P3 ) (20) has a P222 space group indicating there are no mirror planes within the unit cell. There is only a single isomer of 20 within the crystal, that being 3 tBu the isomer depicted in Figure 3.4. A second crystal of RuCl2(P P3 ) (20) was also used for structural analysis through single crystal X-ray diffraction and this afforded only low quality diffraction data due to the small crystal size. However, the solution was sufficient to determine that the structure was of a second isomer in which the ligand arm of the pendant phosphine PF is bent in the opposite direction to the original isomer. This difference can be clearly observed in an overlay of the two structures (Figure 3.5). 89 References begin on page 95. 3 tBu Figure 3.5 Overlay of structural data for the two isomers of RuCl2(P P3 ) (20) in the solid state (hydrogen atoms have been omitted for clarity). 3 tBu 3.3.8 NMR characterization of RuCl2(P P3 ) (20) 31 1 3 tBu In the P{ H} NMR spectrum of RuCl2(P P3 ) (20), the central phosphine PC appears as a 2 triplet at 60.8 ppm with a JP-P coupling of 35 Hz to PE. The two bound terminal phosphines PE appear as a doublet at 31.1 ppm and the pendant phosphine PF appears as a singlet at 25.5 ppm. The resonance at 25.5 ppm is assigned as a pendant phosphine not bound to the metal center for two reasons. Firstly PF displays no coupling to the bound phosphines and secondly because PF has a chemical shift at high field in the spectrum, very close to the chemical shift observed for the terminal phosphines in the free ligand (26.2 2 tBu ppm). In contrast to the fluxional behaviour observed in RuCl2(P P3 ) (18), and 90 References begin on page 95. 2 tBu RuCl2(PhP P2 ) (19) where there are ethylene bridges between the central and terminal 31 1 3 tBu phosphorus atoms, the P{ H} NMR spectrum of RuCl2(P P3 ) (20), where there are propylene bridges between the phosphine donors, is sharp at room temperature and 3 tBu unchanged by variation in temperature. The presence of the longer arms in the P P3 ligand probably results in a more stable framework with less backbone strain and a higher barrier to reorganisation and isomerisation of the coordination sphere of the metal. 3.4 Solid state NMR analysis Solid state 31P{1H} NMR spectra can be used for characterization of metal phosphine complexes in the solid state, and comparison with 31P{1H} NMR spectra of complexes for which X-ray crystallographic data is available provides additional structural information.22e, 23,3, 24 2 tBu We have, so far, been unable to grow crystals of RuCl2(P P3 ) (18) suitable for diffraction studies, however solid state NMR provides some level of structural characterization of complex 18, by comparison with the solid state NMR spectra of 2 tBu 3 tBu RuCl2(PhP P2 ) (19) and RuCl2(P P3 ) (20) for which both solid-state NMR and x-ray data are available. 31 1 2 tBu The solid state P{ H} NMR spectrum of RuCl2(PhP P2 ) (19) shows the presence of a 31 single species with three P resonances at 129, 88 and 47 ppm which we assign to PE/T, PC, PE/T respectively (Figure 3.6). These shifts correspond to those observed in solution-state at low temperature (Figure 3.3). 31 1 3 tBu The solid state P{ H} NMR spectrum of RuCl2(P P3 ) (20) shows the presence of two species each with three resonances. Species A' with resonances at 63, 32 and 31 ppm (masked by the PE signals for both species) corresponding to PC, PE, and PF respectively 91 References begin on page 95. and species B' with resonances at 62, 31 and 13 ppm corresponding to PC, PE, and PF respectively (Figure 3.6). The two species probably correspond to the two polymorphs of this compound identified by x-ray crystallography. 31 1 2 tBu Figure 3.6 Solid state P{ H} NMR (121 MHz, 25 kHz MAS, 295 K) of RuCl2(P P3 ) 2 tBu 3 tBu (18), RuCl2(PhP P2 ) (19) and RuCl2(P P3 ) (20) 31 1 2 tBu The solid state P{ H} NMR spectrum of RuCl2(P P3 ) (18) was initially obtained on material precipitated directly from a THF solution. These spectra displayed upwards of five different species in varying proportions, all with very similar chemical shifts and this probably indicates why it has been difficult to obtaining diffraction-quality crystals for this 92 References begin on page 95. 2 tBu compound. When RuCl2(P P3 ) (18) was recrystallized from dichloromethane, the solid state 31P{1H} NMR spectrum indicated the presence of only two species present in approximately equal amounts. In the 31P{1H} NMR spectrum of (18), both species have four 31P resonances: species A with four resonances at 136, 109, 51 and 35 ppm corresponding to PE/T, PC, PE/T and PF respectively, and isomer B with four resonances at 136, 107, 51 and 38 ppm corresponding to PE/T, PC, PE/T and PF respectively (Figure 3.6). The most significant difference in chemical shifts between the isomers appears to be in the two PF resonances, with a smaller, but still significant, difference in the PC resonances. The difference between the two isomers is likely to be the result of the pendant phosphine of the complex being able to adopt two different positions in the unit cell, as was observed in the 3 tBu structure of RuCl2(P P3 ) (20) (Figure 3.5). The chemical shifts for PC, PE and PT of complex 18 and 19 are very similar, with differences in chemical shift for the two metal-bound phosphines PE/T of only 4 and 7 ppm. Given that the length of the straps and the substituents on the terminal phosphines are the same for complexes 18 and 19, the fact that the observed shifts for 18 are closely aligned with 19 is indicative that the geometric arrangement of the coordinated phosphines in 18 are probably facially coordinated (as in 19). If 18 was to be meridionally coordinated the pattern of resonances would be expected to be like that of 20 even though the strap length of the ligands would result in differences in the actual chemical shifts.25 93 References begin on page 95. 3.5 Conclusions t 2 tBu The new sterically hindered, tridentate ligands P(CH2CH2P Bu2)3 (P P3 , 10), t 2 tBu t 3 tBu PhP(CH2CH2P Bu2)2 (PhP P2 , 14), and P(CH2CH2CH2P Bu2)3 (P P3 , 16) were synthesized and used in the synthesis of the corresponding ruthenium dichloride 2 tBu 2 tBu 3 tBu compounds RuCl2(P P3 ) (18), RuCl2(PhP P2 ) (19) and RuCl2(P P3 ) (20). Complexes 18, 19 and 20 were all characterized by multinuclear NMR spectroscopy, with low temperature 31P{1H} NMR spectroscopy being used to explore the dynamic processes of exchange present in complexes 18 and 19 in solution. Complexes 19 and 20 were both characterized crystallographically. 2 tBu 3 tBu The bulky P P3 (10) and P P3 (16) ligands are the most sterically encumbered PP3-type ligands so far synthesized. These ligands appear to be so sterically encumbered that they can only bind to ruthenium through three of the four phosphine donors leaving one of the terminal phosphines as a free pendant arm. All three ligands 10, 14 and 16 provide a highly sterically constrained ligand environment around the metal and this restricts the nature of the other groups that can bind to the metal centre. 31 1 2 tBu 2 tBu Solid-state P{ H} NMR spectroscopy of RuCl2(P P3 ) (18), RuCl2(PhP P2 ) (19) and 3 tBu 2 tBu RuCl2(P P3 ) (20) was used to gain insights into the solid state structure of RuCl2(P P3 ) (18) which could not be characterized crystallographically. Comparative solid-state NMR 2 tBu analysis also indicate that the solid state structure of RuCl2(P P3 ) (18) is analogous to 2 tBu that determined by X-ray crystallography for RuCl2(PhP P2 ) (19). 94 References begin on page 95. 3.6 References 1. Mayer, H. A.; Kaska, W. C., Chem. Rev. 1994, 94, 1239-72. 2. (a) Antberg, M.; Frosin, K. M.; Dahlenburg, L., J. Organomet. Chem. 1988, 338, 319-27; (b) Antberg, M.; Prengel, C.; Dahlenburg, L., Inorg. Chem. 1984, 23, 4170- 4; (c) Bampos, N.; Field, L. D., Inorg. Chem. 1990, 29, 587-8; (d) Bampos, N.; Field, L. D.; Messerle, B. A., Organometallics 1993, 12, 2529-35; (e) Field, L. D.; Bampos, N.; Messerle, B. A., Magn. Reson. Chem. 1991, 29, 36-9; (f) Bemi, L.; Clark, H. C.; Davies, J. A.; Drexler, D.; Fyfe, C. A.; Wasylishen, R., J. Organomet. Chem. 1982, 224, C5-C9; (g) Bhadbhade, M. M.; Field, L. D.; Gilbert-Wilson, R.; Guest, R. W.; Jensen, P., Inorg. Chem. 2011, 50, 6220-6228; (h) Field, L. D.; Guest, R. W.; Vuong, K. Q.; Dalgarno, S. J.; Jensen, P., Inorg. Chem. 2009, 48, 2246- 2253; (i) Osman, R.; Pattison, D. I.; Perutz, R. N.; Bianchini, C.; Casares, J. A.; Peruzzini, M., J. Am. Chem. Soc. 1997, 119, 8459-8473; (j) Bianchini, C.; Perez, P. J.; Peruzzini, M.; Zanobini, F.; Vacca, A., Inorg. Chem. 1991, 30, 279-87. 3. (a) Bemi, L.; Clark, H. C.; Davies, J. A.; Fyfe, C. A.; Wasylishen, R. E., J. Am. Chem. Soc. 1982, 104, 438-445; (b) Komoroski, R. A.; Magistro, A. J.; Nicholas, P. P., Inorg. Chem. 1986, 25, 3917-3925. 4. Schwab, P.; Grubbs, R. H.; Ziller, J. W., J. Am. Chem. Soc. 1996, 118, 100-110. 5. Hundertmark, T.; Littke, A. F.; Buchwald, S. L.; Fu, G. C., Org. Lett. 2000, 2, 1729-1731. 6. Pascariu, A.; Iliescu, S.; Popa, A.; Ilia, G., J. Organomet. Chem. 2009, 694, 3982- 4000. 95 References begin on page 95. 7. Jia, G.; Drouin, S. D.; Jessop, P. G.; Lough, A. J.; Morris, R. H., Organometallics 1993, 12, 906-916. 8. Bampos, N.; Field, L. D.; Messerle, B. A.; Smernik, R. J., Inorg. Chem. 1993, 32, 4084-8. 9. Tronoff, A. B., PhD Thesis2008, Ph.D. 10. Bampos, N.; Field, L. D.; Hambley, T. W., Polyhedron 1992, 11, 1213-1218. 11. Eisentrager, F.; Gothlich, A.; Gruber, I.; Heiss, H.; Kiener, C. A.; Kruger, C.; Ulrich Notheis, J.; Rominger, F.; Scherhag, G.; Schultz, M.; Straub, B. F.; Volland, M. A. O.; Hofmann, P., New J. Chem. 2003, 27, 540-550. 12. Timmer, K.; Thewissen, D. H. M. W.; Marsman, J. W., Recl. Trav. Chim. Pays-Bas 1988, 107, 248-55. 13. Maier, L.; Seyferth, D.; Stone, F. G. A.; Rochow, E. G., J. Am. Chem. Soc. 1957, 79, 5884-9. 14. Uriarte, R.; Mazanec, T. J.; Tau, K. D.; Meek, D. W., Inorg. Chem. 1980, 19, 79-85. 15. King, R. B.; Kapoor, R. N., J. Amer. Chem. Soc. 1969, 91, 5191-2. 16. King, R. B.; Kapoor, P. N., J. Am. Chem. Soc. 1971, 93, 4158-4166. 17. Reich, H. J. WinDNMR: Dynamic NMR Spectra for Windows, J. Chem. Educ. Software: 1998. 18. Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C., J. Chem. Soc., Dalton Trans. 1984, 1349-1356. 96 References begin on page 95. 19. Brookhart, M.; Green, M. L. H.; Parkin, G., Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 6908-6914. 20. Jia, G.; Lee, I.-m.; Meek, D. W.; Gallucci, J. C., Inorg. Chim. Acta 1990, 177, 81- 88. 21. Albinati, A.; Jiang, Q.; Ruegger, H.; Venanzi, L. M., Inorg. Chem. 1993, 32, 4940- 4950. 22. (a) Butler, I. R.; Griesbach, U.; Zanello, P.; Fontani, M.; Hibbs, D.; Hursthouse, M. B.; Abdul Malik, K. L. M., J. Organomet. Chem. 1998, 565, 243-258; (b) Iizuka, Y.; Li, Z.; Satoh, K.; Kamigaito, M.; Okamoto, Y.; Ito, J.-i.; Nishiyama, H., Eur. J. Org. Chem. 2007, 2007, 782-791; (c) Cotton, F. A.; Matusz, M., Inorg. Chim. Acta 1987, 131, 213-216; (d) Steenwinkel, P.; Kolmschot, S.; Gossage, R. A.; Dani, P.; Veldman, N.; Spek, A. L.; van Koten, G., Eur. J. Inorg. Chem. 1998, 1998, 477- 483; (e) MacFarlane, K. S.; Joshi, A. M.; Rettig, S. J.; James, B. R., Inorg. Chem. 1996, 35, 7304-7310; (f) Cowley, A. R.; Dilworth, J. R.; Maresca von Beckh W., C. A., Acta Crystallogr. Sect. Sect. E: Struct. Rep. Online 2005, 61, m1237-m1239. 23. Eichele, K.; Nachtigal, C.; Jung, S.; Mayer, H. A.; Lindner, E.; Ströbele, M., Magn. Reson. Chem. 2004, 42, 807-813. 24. (a) Maciel, G. E.; O'Donnell, D. J.; Greaves, R., Adv. Chem. Ser. 1982, 196, 389- 408; (b) Kroto, H. W.; Klein, S. I.; Meidine, M. F.; Nixon, J. F.; Harris, R. K.; Packer, K. J.; Reams, P., J. Organomet. Chem. 1985, 280, 281-7; (c) Fyfe, C. A.; Davies, J. A.; Clark, H. C.; Hayes, P. J.; Wasylishen, R. E., J. Am. Chem. Soc. 1983, 97 References begin on page 95. 105, 6577-84; (d) Clark, H. C.; Davies, J. A.; Fyfe, C. A.; Hayes, P. J.; Wasylishen, R. E., Organometallics 1983, 2, 177-80. 25. Garrou, P. E., Chem. Rev. 1981, 81, 229-266. 98 References begin on page 95. 4 Ruthenium Tris(3-di(tert-butyl)phosphinoethyl)phosphine hydride complexes 4.1 Introduction Metal hydrides and metal dinitrogen complexes have a long association, with metal hydrides having been exploited extensively for the synthesis of dinitrogen complexes, predominantly through displacement of dihydrogen by dinitrogen.1 The products of these reactions, and of some protonation experiments on Ru(0) and Fe(0) dinitrogen 2 complexes, are often metal dinitrogen hydride complexes [MLnH(N2)]. Interest in dinitrogen hydride complexes has also been driven by the discovery that paramagnetic iron hydrides are some of the key intermediates in the nitrogen fixation mechanism used by the enzyme nitrogenase.3 An area of dinitrogen hydride metal complexes which has been little explored is that of neutral iron or ruthenium dinitrogen dihydride complexes. The first to be reported in 4 1968 was RuH2(N2)(PPh3)3, yet little investigation has been undertaken on this class of compounds, especially in the field of nitrogen activation. While there have been other compounds of this type synthesized and characterized, like RuH2(N2)(dtbpmp) (dtbpmp 5 iPr iPr = 1,3-bis(di-tert-butylphosphinomethyl)benzol) and FeH2(N2)( PNP) ( PNP = 2,6- i 6 ( Pr2PCH2)2(C5H3N))), the only example to be structurally characterized is 7 RuH2(N2)(Cyttp) (Cyttp = C6H5P(CH2CH2CH2PCy2)2) (Cy = cyclohexyl). These dihydride dinitrogen complexes are interesting in that they are structural isomers of ruthenium(0) and iron(0) diazene complexes, which have been identified as possible 99 References begin on page 138. intermediates in the process of nitrogen fixation at an iron or ruthenium metal centre (Figure 4.1).8 H MNN M H HN NH Dinitrogen dihydride Metal diazene complex complex Figure 4.1 Dinitrogen dihydride and metal diazene complex comparison. t t Bu2P t P Bu2 H t Bu2P P P Bu2 P Ru Cl Ru P H P Cl t N tBu Bu2 2 N 18 26 2 tBu 2 tBu Figure 4.2 RuCl2(P P3 ) (18) and RuH2(N2)(P P3 ) (26) It was is my aim to expand the number of known dihydride dinitrogen complexes and further explore their chemistry. This work describes the synthesis of a diydride 2 tBu dinitrogen compound from RuCl2(P P3 ) (18). A range of different hydride reagents 2 tBu were employed in various attempts to synthesize RuH2(N2)(P P3 ) (26) from the 2 tBu dichloride RuCl2(P P3 ) (18), but the extremely sterically encumbered nature of the 2 tBu phosphine ligand P P3 results in the stabilisation of a range of novel ruthenium hydride complexes. The differing products of these reactions are detailed and 2 tBu characterized in addition to the synthesis and characterization of RuH2(N2)(P P3 ) (26). 100 References begin on page 138. 2 tBu 4.2 Treatment of RuCl2(P P3 ) with hydride reagents. 2 tBu P P3 (10) acts as a very sterically bulky tridentate phosphine ligand, binding to ruthenium through only three of the four phosphorus donors. To synthesize the desired dinitrogen dihydride complex, it was necessary to substitute the two chloro ligands of 2 tBu RuCl2(P P3 ) with two hydride ligands. A variety of hydridic reagents was investigated, yielding the following complexes. 2 tBu 4.2.1 Synthesis and characterization of RuHCl(P P3 ) (21) 2 tBu Stirring a suspension of RuCl2(P P3 ) and potassium hydride in THF at room temperature afforded two different species by NMR spectroscopy. Both species have three 31P{1H} resonances and a single resonance in the 1H spectrum located well into the region hydrides are observed (§ -30 ppm). The two species show similar 31P{1H} and 1H NMR spectra with the same coupling patterns between the respective peaks for each complex, indicating they are likely isomers. After initial reaction an isomer with a more shielded 1H hydride (G -30.61) resonance was in excess (Isomer A). Over time the proportion of this isomer decreased in line with subsequent formation of an isomer with a slightly less shielded hydride 1H hydride resonance (G -30.47) (Isomer B), this process of conversion being accelerated by heating. These complexes are probably kinetic (Isomer A) and thermodynamic (Isomer B) 2 tBu isomers of RuHCl(P P3 ) (21). Heating of the reaction mixture at 60 °C for six hours resulted in full conversion to Isomer B (Scheme 4.1). All further description and characterization was carried out on the thermodynamic isomer of 21. 101 References begin on page 138. P P T P Cl F KH F ' PF H P Cl PC PE P P C Ru Ru C Ru E PE Cl THF P H THF E PE Cl 18 Isomer A-21 Isomer B-21 Kinetic isomer Thermodynamic isomer Scheme 4.1 Crystals suitable for structural analysis were grown by evaporation of a 1:1 THF/toluene solution of complex 21 (Figure 4.3) with selected bond angles and lengths given in Table 4.1. 2 tBu The geometry of RuHCl(P P3 ) (21) is extremely distorted square based pyramidal, with the three phosphine donors and the chloride ligand forming the base of the pyramid and the hydrido ligand at the apex. IJ = 0.14, (where IJ = 0 is perfect square pyramidal geometry and IJ = 1 is perfect trigonal-bipyramidal geometry).9 The significant distortion comes from the large difference in apex to base bond angles between the extremely tight P2-Ru1-H1 bond angle of 72(2)° as opposed to the wide Cl1-Ru1-H1 angle of 134(2)° which are on opposite sides of the pyramid. The location of hydrides in X-ray crystallography is not always precise due to the low level of electron density, so no definitive conclusions can be drawn from this irregular geometry. 102 References begin on page 138. 2 tBu Figure 4.3 ORTEP plot (50% thermal ellipsoids) of RuHCl(P P3 ) (21), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. The three other reported structures of five-coordinate ruthenium hydrido chloro complexes with three phosphine donors include 10 RuHCl(R,R-1,2-bis-(diphenylphosphinamino)cyclohexane)(PPh3), 11 5 RuHCl(bis(phosphaadamantyl)propane)(PPh3), and RuHCl(PCy3)(Fe(Ș - 12 C5H4PPh2)2). All of these complexes share a similarity in that they possess sterically bulky phosphine donors which prevent the coordination of a fourth phosphine donor. 2 tBu This is consistent with the sterically bulky nature of P P3 , leading to the formation of 103 References begin on page 138. 2 tBu RuHCl(P P3 ) (21) as a five-coordinate complex. Complex 21 has considerably different geometry to the other listed compounds of this type. While these other hydrido chloro complexes are also square pyramidal, they have a phosphine donor located at the apex and hydrido and chloro ligands trans to each other in the base of the pyramid. 2 tBu Table 4.1 Selected bond lengths (Å) and bond angles (º) for RuHCl(P P3 ) (21) Ru1 –Cl1 2.4488(13) Ru1 –H1 1.73(6) Ru1 –P1 2.3393(12) Ru1 –P2 2.1776(12) Ru1 –P3 2.3305(12) Cl1-Ru1-H1 134(2) P1-Ru1-Cl1 97.93(4) P2-Ru1-Cl1 153.45(5) P3-Ru1-Cl1 97.95(4) P1-Ru1-H1 84(2) P2-Ru1-H1 72(2) P3-Ru1-H1 79.2(19) P1-Ru1-P2 85.41(4) P1-Ru1-P3 161.96(5) P2-Ru1-P3 84.22(4) 31 1 2 tBu The P{ H} NMR spectrum of RuHCl(P P3 ) (21) shows the central phosphine PC as a doublet of triplets at 120.8 ppm coupled to the pendant terminal phosphine PF and both of the bound terminal phosphines PE. The signal for PE is a doublet at 86.4 ppm 2 3 1 with JPE-PC = 14 Hz and PF as a doublet at 33.7 ppm with JPF-PC = 30 Hz. The H NMR 2 tBu spectrum of RuHCl(P P3 ) (21) contains the resonance due to the hydride proton to high field with a chemical shift of -30.47 ppm as a doublet of triplets, indicating 104 References begin on page 138. coupling to PE and PC. The extremely shielded nature of the hydride proton may be a product of the distorted geometry of the complex. 2 tBu Despite using an excess of potassium hydride in the reaction mixture RuHCl(P P3 ) (21) was the only hydride species formed under the reaction conditions. 2 tBu 4.2.2 Synthesis and characterization of RuH(BH4)(P P3 ) (22) 2 tBu Treatment of RuCl2(P P3 ) (18) with sodium borohydride in methanol resulted in the precipitation of a yellow solid. Filtration of the yellow solid afforded the hydrido 2 2 tBu borohydride complex RuH(ț -BH4)(P P3 )(22) (Scheme 4.2). Crystals suitable for structural analysis were grown by evaporation of a toluene solution of 22 (Figure 4.4) with selected bond angles and lengths given in Table 4.2. PF PT H P PC P F P NaBH4 Ru E C Ru Cl P H P Cl MeOH E H E B H H 18 22 Scheme 4.2 105 References begin on page 138. 2 tBu Figure 4.4 ORTEP plot (50% thermal ellipsoids) of RuH(BH4)(P P3 ) (22), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 2 tBu The geometry of RuH(BH4)(P P3 ) (22) is distorted octahedral with the three phosphine donors binding in a meridional arrangement around the ruthenium centre. The remaining three coordination sites are occupied by a hydride and two bridging hydrides of a tetrahydridoborate ligand. Of these three sites, one is trans to the central phosphorus donor, and the other two are mutually trans. These two mutually trans sites will hereby be referred to as the syn site as it is syn to the free arm and the anti site as it 106 References begin on page 138. is anti to the face of the complex with the free phosphine arm. The syn site is sterically less hindered than the anti site as the tertiary-butyl groups from the two bound arms are closer together around the anti site (Scheme 4.3). 2 tBu Table 4.2 Selected bond lengths (Å) and angles (°) for RuH(BH4)(P P3 ) (22) Ru1 –B1 2.281(8) Ru1–H1 1.55(5) Ru1 –H2 1.99(5) Ru1 –H3 1.79(5) Ru1 –P1 2.3467(17) Ru1 –P2 2.2118(15) Ru1 –P3 2.3474(17) H1-Ru1-H2 166(2) H1-Ru1-H3 100(3) H2-Ru1-H3 66(2) P1-Ru1-P2 83.69(6) P1-Ru1-P3 160.00(6) P2-Ru1-P3 84.64(6) P1-Ru1-H1 79.0(19) P1-Ru1-H2 98.2(14) P1-Ru1-H3 95.9(17) P2-Ru1-H1 79.7(18) P2-Ru1-H2 113.9(15) P2-Ru1-H3 179.6(18) P3-Ru1-H1 79.0(19) P3-Ru1-H2 101.4(14) P3-Ru1-H3 95.8(17) tBu t 2 Bu2P P P anti M X syn P tBu 2 Scheme 4.3 107 References begin on page 138. In the structure of complex 22 the syn site and the site trans to the central phosphine (P2) are occupied by the bridging tetrahydridoborate hydrides H2 and H3 respectively. The more sterically crowded anti site is occupied by a hydrido ligand (H1). The 2 tBu 13 structure of RuH(BH4)(P P3 ) (22) is analogous to that of RuH(BH4)(PMe3)3, which has the same donor atoms and geometry and only varies in the identity of phosphine donor. The ruthenium hydride bond distance between the two structures is comparable with a value of 1.55(5) Å for 22 against 1.49(4) Å for RuH(BH4)(PMe3)3. Comparison of the bond distances between ruthenium and the bridging borohydride hydrogens shows Ru1-H3 = 1.79(5) Å and Ru1-H2 = 1.99(5) Å bond lengths for complex 22 when compared to the essentially equal bond lengths 1.81(3) and 1.85(4) Å for RuH(BH4)(PMe3)3. Although the differences in bond lengths could be due to the fact H3 is trans to P2 and H2 is trans to hydride H1, the analogous H atoms in RuH(BH4)(PMe3)3 are also trans to phosphorus and hydride respectively. The longer Ru1-H2 bond distance is therefore likely to be due to the different steric environment 2 tBu produced by the bulky P P3 ligand when compared to the less bulky PMe3 ligands. 31 1 2 tBu The P{ H} NMR spectrum of RuH(BH4)(P P3 ) (22) displays three distinct resonances, a doublet of triplets at 118.5 ppm, a doublet at 97.7 ppm and a doublet at 35.5 ppm. These correspond to the central phosphine PC, the two bound terminal 1 phosphines PE, and the free phosphine PF, respectively. The H NMR spectrum of 2 tBu RuH(BH4)(P P3 ) (22) displays alkyl ligand resonances as well as resonances assigned to the various hydride ligands (Figure 4.5). The signal for the ruthenium hydride is a 2 doublet of triplets at -19.18 ppm due to JH-P coupling. The tetrahydridoborate hydride resonances consist of a broad resonance at 5.29 ppm corresponding to the terminal 108 References begin on page 138. hydrides and a second broad resonance at -6.26 ppm for the bridging hydrides. This broadness indicates exchange within the two bridging hydride environments and within the two terminal hydride environments, at a rate faster than the NMR timescale. P F H P A P C Ru E P H E H B C B HD1 HD2 22 2 tBu Figure 4.5 RuH(BH4)(P P3 ) (22) 1 1 31 2 tBu Low temperature H and H{ P} NMR spectra of RuH(BH4)(P P3 ) (22) enable further resolution of the bridging dihydride resonances (Figure 4.6). When the temperature was decreased to 220K, the two terminal hydrides of the borohydride remain as a single resonance at 5.29 ppm but the two bridging hydrides resolved into two separate resonances, a doublet at -6.14 ppm with a coupling constant of 2 JH-P = 40 Hz to PC, and a singlet at -6.32 ppm, representing the bridging hydrides HB 1 1 31 and HC respectively. H and H{ P} NMR spectra at 192K don't show any resolution of the two terminal hydrides of the borohydride but the signals for those hydrides (HD) and the bridging hydrides (HB and HC) all show a lopsided coupling pattern consistent with boron coupling at this low temperature. The coupling was shown to be to boron by 11 1 11 2 tBu B decoupling H{ B} NMR spectrum of RuH(BH4)(P P3 ) (22). 109 References begin on page 138. 2 tBu 1 Figure 4.6 Hydride region of RuH(BH4)(P P3 ) (22); A. H NMR spectrum at 298K; B. 1H NMR spectrum at 220K; C. 1H{31P} NMR spectrum at 220K; D. 1H NMR spectrum at 192K; E. 1H{31P} NMR spectrum at 192K; F. 1H{11B} NMR spectrum 192K. 2 tBu RuH(BH4)(P P3 ) (22) appears to be stable over time to a range of conditions including exposure to methanol and gentle heating, and does not lose BH3 to give the desired dihydride complex. 110 References begin on page 138. 2 tBu 4.2.3 Synthesis and characterization of RuH(AlH4)(P P3 ) (23) 2 tBu Slow addition of a THF solution of LiAlH4 to RuCl2(P P3 ) in THF, decolorized the 2 tBu solution and afforded the hydrido aluminiumtetrahyride complex RuH(AlH4)(P P3 ) (23) (Scheme 4.4). Crystals suitable for structural analysis were grown from a concentrated benzene-d6 solution of 23 (Figure 4.7) and selected bond lengths and angles are included in Table 4.3. P F H P PT LiAlH C PE PF 4 Ru PC Ru Cl P H THF E H PE Cl Al H H 18 23 Scheme 4.4 2 tBu The geometry of RuH(AlH4)(P P3 ) (23) is distorted octahedral around ruthenium with the three phosphine donors in a meridional arrangement. The three other coordination sites are occupied by hydrides, two of which are part of the tetrahydridoaluminate ligand. The ruthenium centers are bridged through their tetrahydridoaluminate ligands, with H4 of each monomer bonding tightly to the Al of the other monomer with a bond distance of 1.86 Å. This is the first structure of a ruthenium complex with a coordinated tetrahydridoaluminate ligand, dimerized or otherwise. 111 References begin on page 138. 2 tBu Figure 4.7 ORTEP plot (50% thermal ellipsoids) of RuH(AlH4)(P P3 ) (23), within each asymmetric unit. Selected hydrogen atoms and tert-butyl methyl groups of have been omitted for clarity. 14 The structure of the binuclear ruthenium species Cp*2Ru2(μ-Ph2PCH2PPh2)(μ-AlH5) 2- in which an AlH5 fragment bridges two ruthenium(II) centres has been reported, although the usefulness of this structure for structural comparison is limited due to the presence of only a single aluminate in the bridge. The complexes 2 15 16 [Cp*2ZrH(μ -H2AlH2)]2 and [(dmpe)2MnH2AlH2]2 contain the same dimerised tetrahydridoaluminate bridge between two metal centres as 23 and these hydroaluminate 112 References begin on page 138. bridges share similar bond lengths and geometries to that observed for the structure of 23. 2 tBu Table 4.3 Selected bond lengths (Å) and bond angles (°) for RuH(AlH4)(P P3 ) (23) Ru1 –Al1 2.4702(6) Ru1 –H5 1.58(2) Ru1 –H1 1.66(2) Ru1 –H2 1.66(2) Ru1 –P1 2.3399(5) Ru1 –P2 2.2619(5) Ru1 –P3 2.3362(5) Al1 –H1 1.86(2) Al1 –H2 1.75(2) Al1 –H3 1.54(2) Al1 –H4 1.60(2) Al1 –H4a 1.86(2) H1-Ru1-H2 93.4(10) H1-Ru1-H5 87.1(10) H2-Ru1-H5 177.9(9) P1-Ru1-P2 83.980(18) P1-Ru1-P3 151.612(19) P2-Ru1-P3 84.658(19) P1-Ru1-H1 94.2(7) P1-Ru1-H2 103.1(7) P1-Ru1-H5 78.9(7) P2-Ru1-H1 171.8(7) P2-Ru1-H2 94.8(7) P2-Ru1-H5 84.8(7) P3-Ru1-H1 93.4(7) P3-Ru1-H2 103.7(7) P3-Ru1-H5 74.2(7) 31 1 2 tBu The P{ H} NMR spectrum of RuH(AlH4)(P P3 ) (23) displays a similar three resonance pattern, previously observed for complexes 21 and 22. The resonance for the bound terminal phosphines PE is observed as a doublet at 113.5 ppm, the central 113 References begin on page 138. phosphine PC resonance as a doublet of triplets at 111.7 ppm, and the unbound terminal 1 2 tBu phosphine PF doublet at 35.1 ppm. In the H NMR spectrum of RuH(AlH4)(P P3 ) 2 2 (23) a doublet of triplets of doublets (due to JH-P and JH-H coupling) located at -13.54 ppm is assigned to the ruthenium hydride. Three distinct resonances assigned to the terminal and bridging hydrides of the tetrahydridoaluminate ligand were also observed. A broad resonance at 2.81 ppm was assigned to the hydrides attached solely to aluminium, whilst the doublet of triplets at -10.13 ppm and the broad singlet at -10.20 ppm were assigned to the two hydrides that bridge the ruthenium and aluminium centres. The appearance of a single broad resonance for the terminal aluminohydride nuclei indicates that the bridged structure observed in the crystal structure described above may not be present in solution, as the presence of the bridge in solution would 2 tBu differentiate the chemical shifts for H3 and H4. RuH(AlH4)(P P3 ) (23) may be a 2 tBu monomer in solution similar to the structure observed for RuH(BH4)(P P3 ) (22) (Figure 4.4) and forms a dimer when crystallized in the solid state as seen in the crystal structure of 23 (Figure 4.7). Alternatively there may be a rapid exchange process in solution which scrambles H3 and H4. 2 tBu While stable for periods of time up to several hours, RuH(AlH4)(P P3 ) (23) decomposes upon extended (overnight) exposure to a nitrogen atmosphere, both in solution or solid state, with one of the multiple decomposition products identified as 2 tBu 2 tBu RuH2(N2)(P P3 ) (26). RuH(AlH4)(P P3 ) (23) is also unstable to elevated temperatures in solution; heating a benzene or toluene solution of 23 results in the formation of multiple unidentified decomposition products. 114 References begin on page 138. 2 tBu 4.3 Further reactions of Ru(H)(AlH4)(P P3 ) (23) 2 tBu Although RuH(AlH4)(P P3 ) (23) decomposes in solution and in the solid state to give 2 tBu small amounts of RuH2(N2)(P P3 ) (26), clean separation of this desired product from the remaining starting material and the resulting aluminum salts was not possible. It was however, possible to accelerate this decomposition by treatment of 2 tBu RuH(AlH4)(P P3 ) (23) with ethanol. This reaction resulted in complete conversion of 2 tBu 2 tBu RuH(AlH4)(P P3 ) (23) to RuH2(N2)(P P3 ) (26) but also produced aluminum salts as byproduct which were difficult to remove, hindering purification. Two other strategies 2 tBu 2 tBu were also attempted to convert RuH(AlH4)(P P3 ) (23) to RuH2(N2)(P P3 ) (26), through treatment with potassium tert-butoxide and treatment with methanol. 2 tBu 4.3.1 Synthesis and characterization of K[Ru(H)3(P P3 )] (24) Potassium tert-butoxide was used in an attempt to use the oxophilicity of aluminum to 2 tBu displace aluminum hydride to give RuH2(N2)(P P3 ) (26). Addition of excess 2 tBu potassium tert-butoxide to a benzene solution of RuH(AlH4)(P P3 ) (23) and 2 tBu subsequent work up afforded K[Ru(H)3(P P3 )] (24) as a white powder (Scheme 4.5). P F H P P P K C E F H Ru t P P P H KO Bu C Ru E E H Al PE H H THF H H 24 23 Scheme 4.5 115 References begin on page 138. Crystals suitable for structural analysis were grown by slow evaporation of a toluene solution of 24 under N2 (Figure 4.8) and selected bond lengths and angles are included in Table 4.4. Trihydrido ruthenate complexes are uncommon, with this being the first example with an alkyl phosphine ligand instead of aromatic phosphine ligands.17 A mechanism has been proposed which is driven by the formation of thermodynamically stable aluminium-oxygen bonds. This mechanism involves the aluminate being displaced from coordination with the ruthenium centre through reaction with tert-butoxide and is shown in Scheme 4.6. - K+ 2 H - K+ 2 H 2 H P Ru H 2 H P Ru H P Ru H H P Ru H H Al H H H Al OtBu H -OtBu H Al H H H t +[AlH2(O Bu)]2 2 tBu Scheme 4.6 Proposed mechanism of reaction of RuH(AlH4)(P P3 ) (23) with 2 tBu potassium tert-butoxide to afford K[Ru(H)3(P P3 )] (24). 116 References begin on page 138. 2 tBu Figure 4.8 ORTEP plot (50% thermal ellipsoids) of K[Ru(H)3(P P3 )] (24). Selected hydrogen atoms, and tert-butyl groups have been omitted for clarity. 2 tBu The geometry of K[Ru(H)3(P P3 )] (24) is distorted octahedral around ruthenium with the three phosphine donors in a meridional arrangement, and the three other coordination sites occupied by hydrides. Each metal centre is part of a dimer, with interactions between the two hydrides and two potassium ions forming a bridge between the two metal centers. 117 References begin on page 138. 2 tBu Table 4.4 Selected bond lengths (Å) and bond angles (º) for K[Ru(H)3(P P3 )] (24) Ru1 –H1 1.67(3) Ru1 –H2 1.74(3) Ru1 –H3 1.66(3) Ru1 –P1 2.3129(10) Ru1 –P2 2.2261(10) Ru1 –P3 2.3170(10) Ru1 –K1 3.5438(8) P1-Ru1-P2 84.27(4) P1-Ru1-P3 161.92(4) P2-Ru1-P3 82.35(4) P1-Ru1-H1 85.5(10) P2-Ru1-H1 86.5(11) P3-Ru1-H1 81.6(10) P1-Ru1-H2 94.0(10) P2-Ru1-H2 173.3(10) P3-Ru1-H2 97.9(10) P1-Ru1-H3 97.3(11) P2-Ru1-H3 100.6(12) P3-Ru1-H3 97.1(11) H1-Ru1-H2 86.9(15) H1-Ru1-H3 172.5(17) H2-Ru1-H3 86.0(16) The only reported structure of a trihydrido ruthenate is that of [K(18-crown- 6)][H3Ru(PPh3)3] which is formed through the treatment of RuHCl(PPh3)3 with 2 equiv. 17 K[BBu3H]. The most marked difference between the two structures is the facial geometric arrangement of the hydrides and phosphines of [K(C12H24O6)][H3Ru(PPh3)3] when compared to the meridional binding in 24. However, the bond lengths around ruthenium are similar with ruthenium-phosphorus bond lengths of 2.338(4), 2.312(3), and 2.318(3) Å for [K(18-crown-6)][H3Ru(PPh3)3] compared to 2.3129(10), 2.2261(10), and 2.3170(10) Å for 24. The ruthenium hydride bond lengths of 1.60(9), 1.59(8), and 1.70(9) Å compared to 1.67(3), 1.66(3), and 1.74(3) Å for 118 References begin on page 138. [K(18-crown-6)][H3Ru(PPh3)3] and 24 respectively are also comparable. The potassium cations in both complexes are stabilised within the crystal structure by proximity to three electron rich hydrides, with distances of 2.57(8), 2.66(8), and 3.13(9) Å, compared to 2.55(4), 2.61(3), and 2.77(3) Å for [K(18-crown-6)][H3Ru(PPh3)3] and complex 24 respectively. Additional stabilisation is provided in [K(18-crown-6)][H3Ru(PPh3)3] by the common alkali metal stabilising ligand 18-crown-6 ether where in 24 the same role is performed by a solvating benzene molecule. The tert-butyl groups on the coordinated terminal phosphines forming steric pockets around the potassium ions probably contributes to further stabilisation of the potassium ion. 31 1 2 tBu The P{ H} NMR spectrum of K[Ru(H)3(P P3 )] (24) displays the signal for the two 2 terminal phosphines PE as a doublet at 131.6 ppm with a JP-P = 19 Hz coupling constant to PC. The signal for the central phosphine PC is a broad resonance at 121.1 ppm and the 3 pendant phosphine PF signal appears as a doublet at 35.2 ppm with a JP-P = 31 Hz 1 2 tBu coupling constant to PC. The H NMR spectrum of K[Ru(H)3(P P3 )] (24) displays three high field resonances at -9.10, -10.59 and -13.70 ppm in a ratio of 1:1:1 which are assigned to ruthenium hydrides. 2 tBu 2 tBu K[Ru(H)3(P P3 )] (24) could also be prepared by the treatment of RuH2(H2)(P P3 ) (27) with potassium hydride in THF overnight. 2 tBu 4.3.2 Synthesis and characterization of RuH2(CO)(P P3 ) (25) 2 tBu RuH2(CO)(P P3 ) (25) was observed as the major product of the reaction of 2 tBu RuH(AlH4)(P P3 ) (23) with methanol (Scheme 4.7), and this is not unexpected as 119 References begin on page 138. ruthenium phosphine complexes have previously been shown to act as alcohol dehydrogenation agents, producing ruthenium carbonyl complexes from methanol.18 Obtaining an analytically pure sample of 25 was difficult using the above synthesis, thus an alternative route was needed. O P P F H F C PC PE P P Ru MeOH C Ru E P H P H E H E H A Al B H H 25 23 + unidentified products Scheme 4.7 2 tBu Reaction of a THF solution of RuH2(N2)(P P3 ) (26) (See section 4.4.1) with carbon 2 tBu monoxide afforded RuH2(CO)(P P3 ) (25) as an off white powder (Scheme 4.8). Crystals suitable for structural analysis were grown by slow evaporation of a toluene solution of 25 under an atmosphere of N2 (Figure 4.9) and selected bond lengths and angles are included in Table 4.5. N O PF PF N CO C PC P P P Ru E C Ru E PE HA PE HA HB HB 26 25 Scheme 4.8 120 References begin on page 138. 2 tBu Figure 4.9 ORTEP plot (50% thermal ellipsoids) of RuH2(CO)(P P3 ) (25), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 2 tBu The geometry of RuH2(CO)(P P3 ) (25) is distorted octahedral about ruthenium with the three coordinated phosphine donors binding in a meridional arrangement and the two hydrido ligands in a mutually cis arrangement, with one hydride (H2) trans to the 19 carbonyl ligand. The structure of 25 is best compared to that of RuH2(CO)(PPh3)3, which displays the same ligand set and geometry but for the nature of the phosphine donors. The Ru-P and Ru-H bond lengths are all very similar, with less than 0.03 Å 121 References begin on page 138. difference between the two structures. The biggest difference between the structures comes from the differing bond angles between the three coordinated phosphines which are smaller in 25 than in RuH2(CO)(PPh3)3. This can be ascribed to the natural bite 2 tBu angle of the P P3 (18) as a ligand when compared with the monodentate PPh3 ligand. 2 tBu Table 4.5 Selected bond lengths (Å) and bond angles (º) for RuH2(CO)(P P3 ) (25) Ru1–C1 1.889(3) Ru1–H1 1.69(3) Ru1–H2 1.62(3) Ru1–P2 2.2804(7) Ru1–P1 2.3333(8) Ru1–P3 2.3358(8) C1–O1 1.138(5) C1-Ru1-P1 102.42(10) C1-Ru1-P2 114.01(13) C1-Ru1-P3 99.82(10) P1-Ru1-P3 157.68(3) P2-Ru1-P1 85.31(3) P2-Ru1-P3 83.93(3) C1-Ru1-H2 165.5(11) P2-Ru1-H2 80.5(11) P1-Ru1-H2 77.3(10) P3-Ru1-H2 81.6(10) C1-Ru1-H1 81.0(11) P2-Ru1-H1 165.0(11) P1-Ru1-H1 91.5(11) H1-Ru1-H2 84.6(15) P3-Ru1-H1 93.8(11) O1-C1-Ru1 175.2(4) 31 1 2 tBu The P{ H} NMR spectrum of RuH2(CO)(P P3 ) (25) displays the signal for the two 2 terminal phosphines PE as a doublet due to JP-P coupling to PC at 122.3 ppm, the signal 2 for the central phosphine PC as a doublet of triplets due to JP-P coupling to PF and PE respectively at 98.8 ppm, and the pendant phosphine PF signal as a doublet at 30.8 ppm. 122 References begin on page 138. 1 2 tBu The H NMR resonances for the two hydrido ligands of RuH2(CO)(P P3 ) (25) are located to high field. The resonance due to HA at -7.68 ppm is a doublet of triplets of doublets corresponding to coupling to PC, PE, and HB, with coupling constants of 83 Hz, 19 Hz and 2 Hz respectively where the large coupling to PC identifies HA as the hydride trans to PC. The second resonance, attributed to HB at -11.38 ppm, is a doublet of triplets, corresponding to coupling to PE and PC with coupling constants of 20 Hz and 19 Hz, respectively. The expected 2 Hz coupling to HA is not observed due to a slight broadening of the resonance assigned to HB. 2 tBu 4.4 RuH2(N2)(P P3 ) (26) and related complexes 2 tBu 4.4.1 Synthesis and characterization of RuH2(N2)(P P3 ) (26) 2 tBu Treatment of RuCl2(P P3 ) with potassium graphite in THF afforded some 2 tBu RuH2(N2)(P P3 ) (26) but again isolation from other concurrently formed biproducts proved difficult. The best method for synthesizing 26 was found to be treating 2 tBu RuCl2(P P3 ) with sodium in liquid ammonia. N PT PF PF N P Cl N P P C Ru 2 C Ru E PE Cl PE HA Na/NH3 H 18 B 26 Scheme 4.9 123 References begin on page 138. 2 tBu Like all other methods used to produce 26, a small amount of RuH2(H2)(P P3 )(7) was 2 tBu produced during the reaction which was converted to RuH2(N2)(P P3 ) (26) by reducing the volume of a pentane extract under a stream of nitrogen until a yellow 2 tBu precipitate of RuH2(N2)(P P3 ) (26) formed (Scheme 4.9). Crystals suitable for structural analysis were grown by slow evaporation of a toluene solution of 26 under an atmosphere of N2 (Figure 4.10) and selected bond lengths and angles are included in Table 4.6. 2 tBu Figure 4.10 ORTEP plot (50% thermal ellipsoids) of RuH2(N2)(P P3 ) (26), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 124 References begin on page 138. 2 tBu The geometry of RuH2(N2)(P P3 ) (26) is distorted octahedral with the three phosphine donors in a meridional arrangement, two hydrides in mutually cis coordination sites and the dinitrogen trans to one of the hydrides (H2). 2 tBu Table 4.6 Selected bond lengths (Å) and angles (º) for RuH2(N2)(P P3 ) (26) Ru1–N1 1.978 (3) Ru1–H1 1.65 (4) Ru1–H2 1.60 (4) Ru1–P2 2.2771 (7) Ru1–P1 2.3281 (7) Ru1–P3 2.3266 (7) N1–N2 1.111 (4) N1-Ru1-P1 99.60 (8) N1-Ru1-P2 111.12 (9) N1-Ru1-P3 102.25 (8) P1-Ru1-P3 157.99 (3) P2-Ru1-P1 84.10 (3) P2-Ru1-P3 85.64 (3) N1-Ru1-H2 170.8 (13) P2-Ru1-H2 77.5 (13) P1-Ru1-H2 77.8 (12) P3-Ru1-H2 81.0 (13) N1-Ru1-H1 86.7 (14) P2-Ru1-H1 162.2 (14) P1-Ru1-H1 92.4 (13) H1-Ru1-H2 84.7 (18) P3-Ru1-H1 91.5 (13) N2-N1-Ru1 175.2 (3) 7 The most analogous structure in the literature is that of RuH2(N2)(Cyttp) (Cyttp = C6H5P(CH2CH2CH2PCy2)2), which shares the same geometry and ligand arrangement, with the differences being solely related to the phosphine ligand. The Ru-H bond lengths of the two compounds are similar (all between 1.60 Å and 1.65 Å) as are the 125 References begin on page 138. Ru-N bonds (2.005(6) Å compared to 1.978(3) Å for 26). The only major discrepancy between the two structures is the P-Ru-P bond angles, which are around 10° smaller in 26. This can be attributed to the different bite angles of the ligands. 31 1 2 tBu The P{ H} NMR spectrum of RuH2(N2)(P P3 ) (26) contains the signal for the two terminal phosphines PE as a broad resonance at 121.7 ppm, the signal for the central phosphine PC is a multiplet at 97.1 ppm and the pendant phosphine PF signal as a doublet at 35.1 ppm. The 1H NMR resonances for the two hydrido ligands of 2 tBu RuH2(N2)(P P3 ) (26) are located at the high field end of the spectra. The resonance due to HA at -7.13 ppm is a doublet of triplets of doublets corresponding to coupling to PC, PE, and HB, with coupling constants of 90 Hz, 20 Hz and 4 Hz, respectively, where the large coupling to PC indicates that HA is trans to PC. The second resonance corresponding to HB at -17.03 ppm is a triplet of doublets of doublets, corresponding to coupling to PE, PC and HA with coupling constants of 24 Hz, 21 Hz and 4 Hz respectively. 2 tBu -1 The infrared spectrum of RuH2(N2)(P P3 ) (26) shows a sharp absorbance at 2115 cm which is assigned to the nitrogen-nitrogen triple bond stretch Ȟ(NŁN). The Ȟ(NŁN) is a measure of the degree of activation of the N-N triple bond when bound to a metal centre with frequencies generally found between the frequency for free dinitrogen at 2331 cm-1 and that for a diazene derivative PhN=NPh at 1442 cm-1.20 Ruthenium nitrogen complexes have Ȟ(NŁN) absorbances in the range 2029-2220 cm-1 (Appendix 2 tBu A2) so in comparison RuH2(N2)(P P3 ) (26) has an average level of nitrogen activation. The complex displays an intermediate level of activation for a ruthenium 126 References begin on page 138. dihydride dinitrogen complex where Ȟ(NŁN) for two previously reported complexes of 4 7 this type, [RuH2(N2)(PPh3)3] and [RuH2(N2)(cyttp)] are observed at 2147 and 2100 cm-1 respectively. 15 2 tBu 15 4.4.1.2 RuH2( N2)(P P3 ) ( N2-26) 15 2 tBu Addition of 1.5 atmospheres of N2 gas to a degassed solution of RuH2(N2)(P P3 ) 15 2 tBu 15 15 1 (26) in THF-d8 afforded a solution of RuH2( N2)(P P3 ) ( N2-26). The N{ H} 15 2 tBu 15 NMR spectrum of RuH2( N2)(P P3 ) ( N2-26) displays two broad resonances at -44.6 ppm and -65.7 ppm corresponding to Nȕ and NĮ respectively as well as a resonance at - 15 71.5 ppm corresponding to free N2 in solution. The broadness of the signals prevents 2 the observation of any JN-P coupling, indicating a process of exchange which averages any coupling. The exchange is also evident as there is no evidence for coupling between the metal hydrides and the 15N of the coordinated dinitrogen.. There is only a 2 slight broadening of the HB resonance at -17.03 ppm, preventing the observation of JH- 15 2 2 H coupling in this resonance of N2-26. The averaging of JN-P and JN-H couplings is evidence that the dinitrogen ligand is in a constant state of exchange with other dinitrogen molecules at a rate faster than that of the NMR timescale in these experiments. This suggests the dinitrogen ligand is only weakly bound in the complex 2 tBu RuH2(N2)(P P3 ) (26) and hence is not highly activated toward reaction. 127 References begin on page 138. 2 tBu 4.4.2 Synthesis and characterization of RuH2(H2)(P P3 ) (27) 2 tBu Addition of 1.5 atmospheres of H2 gas to a degassed solution of RuH2(N2)(P P3 ) (26) in THF-d8 resulted in a color change from yellow to colorless and afforded a solution of 2 tBu RuH2(H2)(P P3 ) (27) (Scheme 4.10). N P P F H F N P P P P H C E C Ru E 2 Ru P H PE H E A N H H HB 2 26 27 Scheme 4.10 2 tBu 2 tBu RuH2(H2)(P P3 ) (27) was also produced during the synthesis of Ru(H)2(N2)(P P3 ) (26) and addition of hydrogen gas during the work up of 26 resulted in the formation of 2 tBu 1 RuH2(H2)(P P3 ) (27). H NMR observation of the behavior of both 2 tBu 2 tBu RuH2(N2)(P P3 ) (26) and RuH2(H2)(P P3 )(27) under atmospheres of H2 and N2 respectively gives some idea of the relative binding preferences of the different small 2 tBu molecules to ruthenium in these complexes. RuH2(N2)(P P3 ) (26) is converted quantitatively into 27 under a H2 atmosphere, yet it takes multiple cycles of placing a 2 tBu solution of RuH2(H2)(P P3 )(27) under vacuum and refilling with a N2 atmosphere to get complete conversion back to 26. The 16 electron ruthenium dihydride core preferentially binds H2 over N2. 31 1 2 tBu The P{ H} NMR spectrum of RuH2(H2)(P P3 ) (27) contains the signal for the two 2 terminal phosphines PE as a doublet at 123.3 ppm with a JP-P = 8 Hz coupling constant to PC. The signal for the central phosphine PC is a doublet of triplets at 109.2 ppm and 128 References begin on page 138. the signal for the pendant phosphine PF signal appears as a doublet at 35.9 ppm with a 3 1 2 tBu JP-P = 35 Hz coupling constant to PC. The H NMR spectrum of RuH2(H2)(P P3 ) (27) displays the signals due to the alkyl groups of the ligand and a single broad resonance at -8.45 ppm in the high field region assigned to the ruthenium hydrides and bound dihydrogen. On lowering the temperature to 200K, the hydride resonance broadens further then resolves to two broad peaks at -6.94 ppm and -12.83 ppm with an integration ratio of three to one. Where at room temperature all four of the ruthenium hydride and hydrogen ligands were in fast exchange, at low temperature one of the ruthenium hydrides separates from the other three hydrogen atoms that its distinct resonance can be observed, whilst the other hydride and the dihydrogen ligand are still in a state of rapid exchange. It is likely that it is the hydride trans to the bound dihydrogen which is the one that separates, while the hydride bound cis to the dihydrogen continues in fast exchange. 2 tBu 4.5 Small molecule adducts of RuHCl(P P3 ) (21) 2 tBu Given RuHCl(P P3 ) (21) was a 5-coordinate complex it seemed possible that under the right conditions it would be possible to form a 6-coordinate hydrido chloro dinitrogen complex by the addition of a nitrogen ligand. To test this theory the 2 tBu synthesis of the carbonyl adduct of RuHCl(P P3 ) (21) was first attempted. 2 tBu 4.5.1 Synthesis and characterization of RuHCl(CO)(P P3 ) (28) 2 tBu Reaction of a THF solution of RuHCl(P P3 ) (21) with 1.5 atmospheres of carbon monoxide resulted in a color change from orange to colorless, which upon removal of 129 References begin on page 138. 2 tBu volatiles under reduced pressure afforded RuHCl(CO)(P P3 ) (28) as a beige powder (Scheme 4.11). Crystals suitable for structural analysis were grown by slow evaporation of a toluene solution of 28 under an atmosphere of N2 (Figure 4.11) and selected bond lengths and angles are included in Table 4.7. P P H F H F P P PC PE C E Ru CO Ru P Cl PE Cl E C O 21 28 Scheme 4.11 2 tBu The geometry of RuHCl(CO)(P P3 ) (28) is distorted octahedral with the three phosphine donors binding in a meridional arrangement. The chloro ligand is trans to the central phosphine and the hydrido and carbonyl ligands trans to each other and the carbonyl ligand occupying the sterically less hindered syn site (see Scheme 4.3). The 21 22 previously reported complexes RuHCl(CO)(PPh3)3, RuHCl(CO)[P(C6H5)2CH2OH]3, 23 24 RuHCl(CO)(PPh2Me)3, RuHCl(CO)(PPh3)(dppf), and 25 RuHCl(CO)(PPh3)2(F2P(O)C3H5) display the same geometry as 28 which is distorted octahedral with three meridional phosphorus ligands and the carbonyl ligand trans to the hydride. 130 References begin on page 138. 2 tBu Figure 4.11 ORTEP plot (50% thermal ellipsoids) of RuHCl(CO)(P P3 ) (28), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 31 1 2 tBu The P{ H} NMR spectrum of RuHCl(CO)(P P3 ) (28) contains the central phosphine PC as a doublet of triplets at 113.8 ppm coupled to the pendant terminal phosphine PF and both of the bound terminal phosphines PE. The signal for PE is observed as a 2 3 doublet at 99.6 ppm with JPE-PC = 7 Hz and PF as a doublet at 34.0 ppm with JPF-PC = 1 2 tBu 33 Hz. The H NMR spectrum of RuHCl(CO)(P P3 ) (28) contains the resonance due to the hydride proton to high field with a chemical shift of -7.39 ppm as a doublet of triplets, indicating coupling to PE and PC. 131 References begin on page 138. 2 tBu Table 4.7 Selected bond lengths (Å) and bond angles (º) for RuHCl(CO)(P P3 ) (28) C1–O2 1.147(2) Ru1–C1 1.9056(18) Ru1–H1 1.64(2) Ru1–Cl1 2.4987(4) Ru1–P1 2.3464(5) Ru1–P2 2.2433(4) Ru1–P3 2.3862(4) C1-Ru1-H1 177.5(7) C1-Ru1-Cl1 85.72(5) Cl1-Ru1-H1 93.6(7) P1-Ru1-P2 85.748(16) P1-Ru1-P3 150.410(16) P2-Ru1-P3 85.433(15) P1-Ru1-H1 74.4(7) P1-Ru1-C1 103.26(5) P1-Ru1-Cl1 93.595(16) P2-Ru1-H1 83.1(7) P2-Ru1-C1 97.53(5) P2-Ru1-Cl1 176.747(16) P3-Ru1-H1 76.5(7) P3-Ru1-C1 93.625(16) P3-Ru1-Cl1 105.88(5) Ru1-C1-O1 177.85(15) 2 tBu 4.5.2 Synthesis and characterization of RuHCl(N2)(P P3 ) (29) 2 tBu Various attempts were made to incorporate dinitrogen into RuHCl(P P3 ) (21). Higher pressures or long term exposure of solutions to nitrogen were ineffective, however extremely slow evaporation (§1 month) of a 2:1 hexane/THF solution of 2 tBu RuHCl(P P3 ) (21) under a nitrogen atmosphere (Scheme 4.12) yielded red crystals of 132 References begin on page 138. 2 tBu RuHCl(N2)(P P3 ) (29) suitable for structural analysis (Figure 4.12) with selected bond lengths and angles given in Table 4.8. Slow crystallisation P PF H F H P P under N2 PC PE C Ru E Ru P Cl P N E E Cl N 29 21 Scheme 4.12 2 tBu Figure 4.12 ORTEP plot (50% thermal ellipsoids) of RuHCl(N2)(P P3 ) (29), within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 133 References begin on page 138. 2 tBu Table 4.8 Selected bond lengths (Å) and bond angles (º) for RuHCl(N2)(P P3 ) (29) N1 –N2 0.998(5) Ru1 –N1 2.045(5) Ru1 –H1 1.62(4) Ru1 –Cl1 2.5757(10) Ru1 –P1 2.3743(8) Ru1 –P2 2.3009(8) Ru1 –P3 2.3750(8) N1-Ru1-H1 93.6(14) N1-Ru1-Cl1 89.04(15) Cl1-Ru1-H1 177.2(13) P1-Ru1-P2 84.17(3) P1-Ru1-P3 157.30(3) P2-Ru1-P3 83.15(3) P1-Ru1-H1 81.5(14) P1-Ru1-N1 94.00(10) P1-Ru1-Cl1 99.24(3) P2-Ru1-H1 78.5(14) P2-Ru1-N1 172.09(15) P2-Ru1-Cl1 98.84(3) P3-Ru1-H1 77.6(14) P3-Ru1-N1 95.99(10) P3-Ru1-Cl1 101.26(3) Ru1-N1-N2 170.9(6) Complex 29 was unstable in benzene and THF solutions, preventing NMR characterization. 2 tBu The geometry of RuHCl(N2)(P P3 ) (29) is distorted octahedral with the three phosphine donors binding in a meridional arrangement with the dinitrogen ligand trans to the central phosphine. The hydrido and chloro ligands are mutually trans with the chloro ligand occupying the less sterically hindered syn site (Scheme 4.3). The only 2 tBu structure in the literature with similar components to RuHCl(N2)(P P3 ) (29)is 134 References begin on page 138. 18 RuHCl(N2)(2,6-bis-(di-tert-butylphosphinomethyl)pyridine). The complex also features very similar geometry with a meridional tridentate ligand and the hydride and chloride ligands mutually trans in a distorted octahedral arrangement. This similarity extends to most of the Ru-X bond lengths (Ru-P, 2.3743(8) Å and 2.3750(8) Å for 29 vs 2.344(1) Å and 2.337(1) Å, Ru-Cl, 2.5757(10) Å vs 2.588(1) Å, Ru-H, 1.62(4) Å vs 1.59(3) Å) with the exception being Ru-N, (2.045(5) Å for 29 vs 1.925(3) Å) implying an extremely weakly coordinated dinitrogen in 29 which is consistent with the experimental observations on the instability of 29. The geometry of 2 tBu 2 tBu RuHCl(N2)(P P3 ) (29) differs from that of RuHCl(CO)(P P3 ) (28) in that the carbonyl ligand is bound trans to the hydride while the dinitrogen ligand is bound trans to the central phosphine. Carbonyl ligands are used to model dinitrogen ligands due to their similar size, molecular weight and electron density, but they usually generate complexes of greater stability.26 However in this case the geometry and properties of the dinitrogen complex could not be predicted by synthesis and analysis of the carbonyl analogue. 2 tBu The instability of RuHCl(N2)(P P3 ) (29) implies an extremely labile dinitrogen ligand which is only stable within the coordination sphere when the complex is in the solid state. 4.6 Nitrogen complex reactivity 2 tBu A variety of reactions involving RuH2(N2)(P P3 ) (26) were examined in an effort to 2 tBu functionalize the dinitrogen ligand. A solution of RuH2(N2)(P P3 ) (26) in THF-d8 was irradiated by a UV lamp for periods of thirty minutes and three hours in an attempt 135 References begin on page 138. to observe reaction between dinitrogen and hydride ligands. No apparent reaction had occurred by analysis of the NMR spectra after both irradiations. After 3 hours there was some decomposition of the complex as the solution turned murkier and dark precipitate started to form. There was no indication in the NMR spectrum that any product had formed. 2 tBu RuH2(N2)(P P3 ) (26) was treated with a variety of proton sources. Reaction with 2,6- lutidinium tetrafluroborate resulted in the generation of a number of unidentified 15 2 tBu 15 products. Repetition of this experiment using RuH2( N2)(P P3 ) ( N2-26) and 15 15 15 subsequent N NMR spectroscopy revealed only N2 as the sole N-containing species in solution, indicating any products resulting from the protonation reaction probably result in displacement of the N2 rather than by reaction at N2. 2 tBu RuH2(N2)(P P3 ) (26) was also treated with 1M HCl in diethyl ether, which produced no identifiable products indicative of reaction at N2. 4.7 Conclusions 2 tBu The sterically hindered, tridentate ligand P P3 was used in the synthesis of a series of 2 tBu novel ruthenium hydride compounds. The reaction of RuCl2(P P3 ) with potassium 2 tBu hydride, sodium borohydride and lithium aluminium hydride produced RuHCl(P P3 ) 2 tBu 2 tBu (21), RuH(BH4)(P P3 ) (22) and RuH(AlH4)(P P3 ) (23) respectively. Further reaction of complex 23 with potassium tert-butoxide and methanol formed 2 tBu 2 tBu K[Ru(H)3(P P3 )] (24) and RuH2(CO)(P P3 ) (25) respectively. The original target 2 tBu 2 tBu complex RuH2(N2)(P P3 ) (26) and its dihydrogen analogue RuH2(H2)(P P3 ) (27) 2 tBu were synthesized by reaction of RuCl2(P P3 ) with sodium in liquid ammonia and 136 References begin on page 138. 2 tBu work up under a nitrogen or hydrogen atmosphere respectively. RuHCl(CO)(P P3 ) 2 tBu (28) and RuHCl(N2)(P P3 ) were also produced by the addition of the appropriate gas 2 tBu to RuHCl(P P3 ) (21). Complexes 21-28 were characterized by multinuclear NMR spectroscopy, with complexes 21, 22, 23, 24, 25, 26, 28, and 29 also structurally characterized by X-ray 2- crystallography. To my knowledge, 23 is the first reported structure with an Al2H8 bridge on ruthenium, and 24 is the second structurally characterized ruthenium(II) trihydride anion and the first with alkyl rather than aryl phosphines. The stability of these usually unstable ruthenium hydride geometries is attributed to the protective nature of the sterically bulky phosphine ligand. Complex 26 is also the second ruthenium dinitrogen dihydride to be structurally characterized, In the dinitrogen complexes synthesized. The N2 is only weakly coordinated and reactions of 26 appeared to displace the coordinated dinitrogen rather than react with it. 137 References begin on page 138. 4.8 References 1. Ballmann, J.; Munha, R. F.; Fryzuk, M. D., Chem. Commun. 2010, 46 1013-1025. 2. Field, L. D.; Guest, R. W.; Vuong, K. Q.; Dalgarno, S. J.; Jensen, P., Inorg. Chem. 2009, 48 2246-2253. 3. Dance, I., Biochemistry 2006, 45 6328-40. 4. Knoth, W. H., Jr., J. Am. Chem. Soc. 1968, 90 7172-3. 5. Prechtl, M. H. G.; Ben-David, Y.; Giunta, D.; Busch, S.; Taniguchi, Y.; Wisniewski, W.; Goerls, H.; Mynott, R. J.; Theyssen, N.; Milstein, D.; Leitner, W., Chem.--Eur. J. 2007, 13 1539-1546. 6. Trovitch, R. J.; Lobkovsky, E.; Chirik, P. J., Inorg. Chem. 2006, 45 7252-7260. 7. Jia, G.; Meek, D. W.; Gallucci, J. C., Inorg. Chem. 1991, 30 403-10. 8. Field, L. D.; Li, H. L.; Dalgarno, S. J., Inorg. Chem. 2010, 49 6214-6221. 9. Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C., J. Chem. Soc., Dalton Trans. 1984, 1349-1356. 10. Abdur-Rashid, K.; Lough, A. J.; Morris, R. H., Organometallics 2001, 20 1047- 1049. 11. Hadzovic, A.; Lough, A. J.; Morris, R. H.; Pringle, P. G.; Zambrano-Williams, D. E., Inorg. Chim. Acta 2006, 359 2864-2869. 12. Jung, S.; Brandt, C. D.; Wolf, J.; Werner, H., Dalton Transactions 2004, 375-383. 13. Statler, J. A.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1984, 1731-1738. 138 References begin on page 138. 14. Lin, W.; Wilson, S. R.; Girolami, G. S., Organometallics 1997, 16 2987-2994. 15. Etkin, N.; Hoskin, A. J.; Stephan, D. W., J. Am. Chem. Soc. 1997, 119 11420- 11424. 16. Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B., J. Am. Chem. Soc. 1983, 105 6752-6753. 17. Chan, A. S. C.; Shieh, H.-S., J. Chem. Soc., Chem. Commun. 1985, 1379-1380. 18. Zhang, J.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.; Milstein, D., Organometallics 2004, 23 4026-4033. 19. Junk, P. C.; Steed, J. W., J. Organomet. Chem. 1999, 587 191-194. 20. Fryzuk, M. D.; Johnson, S. A., Coord. Chem. Rev. 2000, 200-202 379-409. 21. Snelgrove, J. L.; Conrad, J. C.; Yap, G. P. A.; Fogg, D. E., Inorg. Chim. Acta 2003, 345 268-278. 22. Kayaki, Y.; Shimokawatoko, Y.; Ikariya, T., Inorg. Chem. 2007, 46 5791-5797. 23. Motevalli, M.; Hursthouse, M. B.; Barron, A. R.; Wilkinson, G., Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 1987, 43 214-216. 24. Santos, A.; Lopez, J.; Montoya, J.; Noheda, P.; Romero, A.; Echavarren, A. M., Organometallics 1994, 13 3605-3615. 25. Gilje, J. W.; Schmutzler, R.; Sheldrick, W. S.; Wray, V., Polyhedron 1983, 2 603- 606. 26. Hidai, M.; Tominari, K.; Uchida, Y., J. Amer. Chem. Soc. 1972, 94 110-14. 139 References begin on page 138. 5 Iron and Ruthenium Dinitrogen Complexes of 2 Cy Tris(2-dicyclohexylphosphinoethyl)phosphine (P P3 ) 5.1 Introduction The first dinitrogen complexes were first identified in 1965,1 and these have proliferated since that time with a wide variety of transition metal dinitrogen complexes being successfully synthesized.2 Many of those complexes which undergo interesting reaction chemistry, contain a sterically-hindered ligand environment around the metal to stabilize and protect the reactive metal centre.3 There is now an expanding range of sterically-encumbered, polydentate ligands available and we report here the use of the 2 Cy 4 hindered tripodal tetradentate phosphine ligand P P3 (P(CH2CH2PCy2)3) to produce iron 2 Cy and ruthenium dinitrogen complexes. The P P3 ligand is a hindered version of the PP3 5 6 7 ligand skeleton, P(CH2CH2PR2)3, which is known with phenyl , methyl , isopropyl, and tert-butyl8 substituents on the terminal phosphine donors. There are examples in the literature where iron(0) dinitrogen complexes such as 9 3b Fe(N2)(dmpe)2 (dmpe = Me2PCH2CH2PMe2), Fe(N2)(NP3) (NP3 = N(CH2CH2PPh2)3), 10 and Fe(DMeOPrPE)2(N2) (DMeOPrPE = 1,2-(bis(dimethoxypropyl)phosphino)ethane), react with acid to give "fixed" dinitrogen in the form of NH3 and N2H4. To this point, this sort of reactivity has not been observed with iron(0) complexes of PP3-type ligands. When 2 iPr 2 iPr 7 2 Me 2 Me Fe(N2)(P P3 ) (P P3 = P(CH2CH2PiPr2)3, and Fe(N2)(P P3 ) (P P3 = 11 P(CH2CH2PMe2)3, are reacted with acid the result, is the protonation of the metal center to give the iron(II) hydrido nitrogen complexes rather than reaction at the dinitrogen ligand. Increasing the steric bulk on the PP3-type ligand has the potential to provide greater 140 References begin on page 175. protection of the reactive metal center and promote subsequent reaction at the coordinated dinitrogen. Thus, as part of our ongoing work investigating the chemistry of coordinated dinitrogen, 2 Cy we have studied the synthesis and reactions of dinitrogen complexes with the P P3 ligand. In this work I describe the synthesis and characterization of the iron(0), ruthenium(0), and 2 Cy 2 Cy iron(I) dinitrogen complexes Fe(N2)(P P3 ) (33), Ru(N2)(P P3 ) (34), and 2 Cy + [Fe(N2)(P P3 )] (35) with the structural characterization of 35 being the first report of a 2 Cy cationic dinitrogen complex of iron(I). The isolation and structure of RuCl(P P3 ) (36), the first stable ruthenium(I) monomeric complex with a neutral ligand is also discussed and the protonation reactions of the various dinitrogen species are also investigated. 5.2 Ligand LDA PCy PCy Cy Cy 2 2 P + 3 P P H THF/Hexane Cy P 12 2 30 Scheme 5.1 2 Cy P(CH2CH2PCy2)3, P P3 , (30) was prepared by the base-induced (lithium diisopropylamide, LDA, 13) addition of dicyclohexylhosphine to trivinylphosphine (12) in a method first used by Morris et al. (Scheme 5.1).12 In the 31P{1H} NMR spectrum of 2 Cy P P3 (30), two resonances are observed at 0.0 and -16.7 ppm in a ratio of 3:1, assigned to the three terminal phosphines and the central phosphine respectively. As is typical in 141 References begin on page 175. PP3-type ligands with ethylene bridges, coupling between the terminal and central 3 phosphines ( JP-P = 22 Hz) is observed even before coordination to the metal center. 5.3 Metal complexes 2 Cy The iron and ruthenium chloride complexes, [RuCl(P P3 )][BPh4] (32[BPh4]), 2 Cy 2 Cy [RuCl(P P3 )][Cl] (32[Cl]) and [FeCl(P P3 )][BPh4] (31[BPh4]), were synthesized 4 2 Cy following the method of Morris et al. [FeCl(P P3 )][BPh4] (31[BPh4]) was produced by 2 Cy combining P P3 (30) and FeCl2 in ethanol, followed by the addition of NaBPh4 resulting 2 Cy in the precipitation of the desired compound. [RuCl(P P3 )][Cl] (32[Cl]) was produced by 2 Cy combining RuCl2(PPh3)3 and P P3 (30) and washing away the produced PPh3 with ether. 2 Cy [RuCl(P P3 )][BPh4] (32[BPh4]) could be produced by an anion exchange from 2 Cy [RuCl(P P3 )][Cl] (32[Cl]). 2 Cy 4 While [RuCl(P P3 )][BPh4] (32[BPh4]) has been previously synthesized by Morris et al, characterization of the complex did not include any structural analysis. Crystals suitable for structural analysis were grown by vapour diffusion of pentane into a tetrahydrofuran (THF) 2 Cy solution of [RuCl(P P3 )][BPh4] under nitrogen (Figure 5.1) and selected bond angles and lengths are given in Table 5.1. 142 References begin on page 175. 2 Cy Figure 5.1 ORTEP plot (50% thermal ellipsoids) of [RuCl(P P3 )][BPh4] within each asymmetric unit. Hydrogen atoms, tetraphenylborate anion and THF solvate in the asymmetric unit have been omitted for clarity. 2 Cy + The geometry of [RuCl(P P3 )] is a distorted square-based pyramid with atoms Cl1, P1, P2 and P4 making up the base and P3 at the apex. The structure has a IJ value of W = 0.21 where IJ is a geometric parameter indicative of 5-coordinate complex geometry where IJ = 0 is perfect square pyramidal geometry and IJ = 1 is perfect trigonal-bipyramidal geometry.13 The geometry of the complex is similar to other ruthenium chloro complexes of PP3-type i + 7 i + 14 ligands [RuCl(P(CH2CH2P Pr2)3)] , and [RuCl(P(CH2CH2P Pr2)3)] . 143 References begin on page 175. 2 Cy Table 5.1 Selected bond lengths (Å) and angles (º) for [RuCl(P P3 )][BPh4] Ru1 –Cl1 2.4235(12) Ru1 –P1 2.2253(13) Ru1 –P2 2.3798(14) Ru1 –P3 2.2524(14) Ru1 –P4 2.3617(14) Cl1- Ru1-P1 166.02(5) Cl1- Ru1-P2 91.52(4) Cl1- Ru1-P3 110.65(5) Cl1- Ru1-P4 96.31(5) P1- Ru1-P2 82.93(5) P1- Ru1-P3 82.93(5) P1- Ru1-P4 83.48(5) P2- Ru1-P3 98.31(5) P2- Ru1-P4 153.45(5) P3- Ru1-P4 102.51(5) 5.4 Dinitrogen complexes 2 Cy 2 Cy 5.4.1 Synthesis of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34). 2 Cy 2 Cy The iron(0) and ruthenium(0) dinitrogen complexes Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) 2 Cy (34) were synthesized by treatment of a THF solution of [FeCl(P P3 )][BPh4] (31[BPh4]) 2 Cy or [RuCl(P P3 )][Cl] (32[Cl]), with potassium graphite under an atmosphere of nitrogen 2 Cy (Scheme 5.2). After workup, Fe(N2)(P P3 ) (33) was obtained as a orange/red solid, and 2 Cy 2 Cy Ru(N2)(P P3 ) 34 as an yellow solid. In the synthesis of Fe(N2)(P P3 ) (33), a side product was also formed in variable amounts in addition to the desired nitrogen complex. The side 2 Cy 2 Cy product was identified as the iron hydride FeH2(P P3 ) (37). The amount of FeH2(P P3 ) (37) was decreased by shorter reaction times, but it was still necessary to use fractional 2 Cy crystallization to obtain Fe(N2)(P P3 ) (33) of sufficient purity for analysis. 144 References begin on page 175. + PE P N + - E 2KC /N N LutH BF4 P [MCl(P2P Cy)]+ 8 2 T N N 3 M M THF P C PC H PE PE PE M=Fe,Ru 33 M=Fe 38 M=Fe 34 M=Ru 39 M=Ru 2 Cy P P3 =P(CH2CH2PCy2)3 Scheme 5.2 2 Cy 2 Cy 5.4.2 NMR of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34). 2 Cy 2 Cy The iron(0) species Fe(N2)(P P3 )(33), unlike its iron(II) precursor [FeCl(P P3 )][BPh4] (31[BPh4]), is diamagnetic and has a characteristic splitting pattern in the 31P{1H} NMR spectrum for a trigonal bipyramidal complex containing a tripodal tetradentate phosphine 2 Cy ligand. The resonance of the central phosphine PC of Fe(N2)(P P3 ) (33) appears at low field at 175.3 ppm and appears as a quartet with coupling to the three equivalent terminal phosphines PE with a coupling constant of 37 Hz. The three equivalent terminal phosphines 31 1 PE appear as a doublet at 84.2 ppm with splitting due to PC. In the P{ H} NMR spectrum 2 Cy of the ruthenium(0) species Ru(N2)(P P3 )(33), the resonances of the central phosphine PC and the three equivalent terminal phosphines PE appear as a quartet at 160.7 ppm 2 ( JP-P = 22 Hz) and a doublet at 73.9 ppm, respectively, with the signal intensity in a ratio 31 1 2 Cy of 1 : 3. The signals in the P{ H} NMR spectrum of RuN2(P P3 ) 34 are sharp, suggestive of a trigonal bipyramidal structure in solution. 145 References begin on page 175. 15 2 Cy 5.4.3 N studies of Ru(N2)(P P3 ) (34). PE 34 PE 2 15 J P-P 15N N 15N -34 Ru 2 2 PC J P-P PE PE 2 J P-N 3 J P-N PC 34 2J P-P 15 N2-34 2 J P-N 2 J P-P 3 J P-N 31 1 15 2 Cy 15 Figure 5.2 P{ H} NMR spectrum (162 MHz, C6D6) of Ru( N2)(P P3 ) ( N2-34) 15 2 Cy 15 Synthesis of Ru( N2)(P P3 ) ( N2-34) was performed through addition of 1.5 15 2 Cy atmospheres of N2 gas to a degassed solution of RuN2(P P3 ) (34) in benzene-d6. 146 References begin on page 175. The resolution-enhanced 31P{1H} NMR spectrum of the 15N-labeled ruthenium(0) species 15 2 Cy 15 Ru( N2)(P P3 ) ( N-34) (Figure 5.2) clearly shows additional splitting due to the 15 coordinated N2 ligand. The spectrum is clearly a mixture of the complex with and without 15N labeling approximately 20% 34: 80% 15N-34. The resonance of the central phosphorus 15 PC of N2-34 appears as a doublet of quartets of doublets at 160.8 ppm and that of the terminal PE phosphines as a doublet of doublet of doublets at 74.0 ppm. The assignment of 31 15 2 the P- N coupling constants is based on the assumption that the absolute value of the JP- 3 15 2 N coupling is larger than that for the JP-N coupling. The JP-N coupling constant of the PC 2 resonance (31 Hz) is significantly greater than the JP-P coupling constant (22 Hz) and an 3 order of magnitude greater than the JP-N coupling constant (3 Hz). The order of magnitude 2 3 difference between JP-N and JP-N trans coupling constants has been previously noted across the ruthenium center of a pyrazolyl phosphine complex, namely 7, 16 chloro-(triphenylphosphine)bis[bis(1-pyrazolyl)methane]ruthenium(II) chloride. In 31 15 2 contrast, the P- N coupling constants between PE and the coordinated dinitrogen ( JP-N 3 and JP-N) are 5 and 2 Hz, respectively. 2 Cy 2 Cy 5.4.4 X-ray crystallography of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34). 2 Cy Orange crystals of Fe(N2)(P P3 )(33) suitable for analysis by X-ray diffraction were grown by evaporation of a benzene solution of 33 (Figure 5.3). Selected bond lengths and bond angles are listed in Table 5.2. 147 References begin on page 175. Figure 5.3 ORTEP diagram (50% thermal ellipsoids, non-hydrogen atoms) of 2 Cy Fe(N2)(P P3 ) (33) excluding benzene solvate. 2 Cy The geometry around the metal centre of Fe(N2)(P P3 ) (33) approximates well to a trigonal bipyramid as demonstrated by a IJ value of W = 0.91, where IJ is a geometric parameter indicative of 5-coordinate complex geometry where IJ = 0 is perfect square pyramidal geometry and IJ = 1 is perfect trigonal-bipyramidal geometry.13 The N-N triple bond length of 1.134(3) Å indicates modest activation compared to the N-N triple bond length for free dinitrogen (1.10 Å).17 148 References begin on page 175. 2 Cy Table 5.2 Selected bond lengths (Å) and angles (º) for Fe(N2)(P P3 ) (33) N1 –N2 1.134(3) Fe1 –N1 1.812(2) Fe1 –P1 2.1430(9) Fe1 –P2 2.2105(9) Fe1 –P3 2.2301(12) Fe1 –P4 2.1991(8) N1- Fe1-P1 178.90(7) N1- Fe1-P2 93.84(8) N1- Fe1-P3 97.18(9) N1- Fe1-P4 95.06(8) P1- Fe1-P2 85.06(4) P1- Fe1-P3 83.42(5) P1- Fe1-P4 85.51(4) P2- Fe1-P3 124.14(3) P2- Fe1-P4 118.72(4) P3- Fe1-P4 114.55(4) Fe1- N1-N2 178.9(2) Two iron(0) dinitrogen complexes with four phosphorus donors have previously been 2 iPr 2 iPr 7 structurally characterized, the analogous Fe(N2)(P P3 ) (P P3 = P(CH2CH2PiPr2)3, and 18 Fe(N2)(depe)2 (depe = Et2PCH2CH2PEt2). The three structures are all comparable with 2 iPr Fe(N2)(P P3 ) and Fe(N2)(depe)2 having N-N bond distances of 1.1279(16) and 1.14(1) Å respectively, compared with a N-N distance of 1.134(3) Å for 33. These three complexes also have similar trigonal bipyramidal geometry, the only difference being that Fe(N2)(depe)2 has the dinitrogen ligand located in an equatorial position rather than the 2 iPr axial position of dinitrogen as in both 33 and Fe(N2)(P P3 ). 2 Cy Crystals of Ru(N2)(P P3 ) (34) suitable for structural analysis were grown by cooling a saturated pentane solution in the freezer (-20 °C) (Figure 5.4) with selected bond angles and lengths given in Table 5.3. 149 References begin on page 175. 2 Cy Figure 5.4 ORTEP plot (50% thermal ellipsoids, non hydrogen atoms) of RuN2(P P3 ) (34) within each asymmetric unit. Pentane solvate has been omitted for clarity. 2 Cy The geometry about the metal center of RuN2(P P3 ) (34) is effectively a perfect trigonal 2 Cy bipyramid (IJ = 1.0) with the three arms of the P P3 ligand being equivalent by symmetry. This is the second structurally characterized ruthenium(0) dinitrogen complex with the first 2 iPr 2 iPr i 7 being the analogous Ru(N2)(P P3 ) (P P3 = P(CH2CH2P Pr2)3) . Both have similar ruthenium phosphine bond distances and similar levels of dinitrogen ligand activation, as evidenced by the N-N bond lengths of 1.097(2) Å for 34, versus 1.109(4) Å for 150 References begin on page 175. 2 iPr Ru(N2)(P P3 ). These N-N distances are similar to the bond length for free dinitrogen (1.10 Å)17 demonstrating minimal overall activation. This lack of activation of the dinitrogen ligand suggests weak coordination, and this is consistent with the observed facile 15 exchange of this ligand with N2. 2 Cy Table 5.3 Selected bond lengths (Å) and angles (º) for RuN2(P P3 ) (34) N1 –N2 1.097(2) Ru1 –N1 2.0033(17) Ru1 –P1 2.2172(5) Ru1 –P2 2.3299(5) Ru1 –P3 2.3302(5) Ru1 –P4 2.3227(5) Ru1-N1-N2 179.8(2) P1-Ru1-N1 179.92(5) P2-Ru1-N1 96.28(5) P3-Ru1-N1 96.84(4) P4-Ru1-N1 96.03(4) P1-Ru1-P2 83.720(17) P1-Ru1-P3 83.227(17) P1-Ru1-P4 83.905(17) P2-Ru1-P3 118.866(17) P2-Ru1-P4 118.374(17) P3-Ru1-P4 119.102(17) 2 Cy -1 The infra red spectrum of Fe(N2)(P P3 ) (33) displays a sharp absorbance at 1996 cm which is assigned to the nitrogen-nitrogen triple bond stretch Ȟ(NŁN). The Ȟ(NŁN) stretch is a measure of the degree of activation of the N-N triple bond when bound to a metal centre, with frequencies usually found between the frequency for free dinitrogen at 2331 cm-1 and that for a diazene derivative PhN=NPh at 1442 cm-1.2a Monomeric iron(0) dinitrogen complexes have been identified with Ȟ(NŁN) absorbances in the range 1830-2141 cm-1.19 In comparison to other iron(0) dinitrogen complexes, 33 has an average 151 References begin on page 175. level of nitrogen activation, sitting slightly below the level of nitrogen activation observed 20 -1 10 -1 for Fe(dmpe)2(N2) (1975 cm ) and Fe(DMeOPrPE)2(N2) (1966 cm ) which have both displayed the ability to convert the bound dinitrogen to ammonia when treated with an appropriate proton source. 2 Cy -1 The infra red spectrum of Ru(N2)(P P3 ) (34) displays a sharp absorbance at 2083 cm assigned to the nitrogen-nitrogen triple bond stretch Ȟ(NŁN). The higher value when 2 Cy compared to that of Fe(N2)(P P3 ) (33), highlights the lower level of dinitrogen activation in ruthenium complexes when compared to those of iron complexes. The Ȟ(NŁN) value is comparable to that observed for other ruthenium(0) dinitrogen complexes such as i -1 7 Ru(N2)(P(CH2CH2P Pr2) (2083 cm ). 5.5 Iron(I) and ruthenium(I) complexes 2 Cy The iron(I) dinitrogen complex [Fe(N2)(P P3 )][BPh4] (35[BPh4]), was synthesized by 2 Cy treatment of a THF solution of [FeCl(P P3 )][BPh4] with one equivalent of potassium graphite under an atmosphere of nitrogen (Scheme 5.3). After workup, 35[BPh4] was obtained as a deep red solid. [BPh ] PCy2 4 1equiv.KC /N N 2 Cy 8 2 N [FeCl(P P3 )][BPh4] Fe(I) THF P PCy2 PCy2 6[BPh ] 4 Scheme 5.3 152 References begin on page 175. Attempting a similar reaction to produce the ruthenium(I) dinitrogen complex was 2 Cy unsuccessful. Reacting one equivalent of potassium graphite with [RuCl(P P3 )][BPh4] in 2 Cy THF resulted in a mixture of the starting material and Ru(N2)(P P3 ) (34). Using the 2 Cy 2 Cy chloride salt [RuCl(P P3 )][Cl] (32[Cl]) in the place of [RuCl(P P3 )][BPh4] (32[BPh4]) under the same reaction conditions resulted in the synthesis of the ruthenium(I) chloro 2 Cy complex RuCl(P P3 ) (36) as a blue solid after workup (Scheme 5.4). PCy2 1equiv.KC /N 2 Cy 8 2 Cl [RuCl(P P3 )][Cl] Ru(I) THF P PCy2 PCy2 5X7 Scheme 5.4 Until recently there were no stable ruthenium(I) complexes known. The few that had been identified were unstable species, often produced by electrochemical methods and these were unable to be isolated. Ru(dppp)2Cl (dppp = 1,3-bisdiphenylphosphinopropane) was the first of Ru(I) complex described in the literature and it was proposed that the presumed lability of the chloro ligand opened decomposition pathways through disproportionation.21 A longer lived complex Ru(PP3)Cl (PP3 = P(CH2CH2PPh2)3) was later identified but again was not successfully isolated.22 The first stable ruthenium(I) compounds were isolated iPr - iPr - - when anionic ligands of the type (SiP 3) ((SiP 3) = (2-iPr2PC6H4)3Si ) were applied in place of neutral multidentate phosphine ligands. The extra stability imparted by a non-labile charge stabilizing anionic ligand rather than a labile chloride resulted in the iPr iPr 23 2 Cy isolation of [(SiP 3)Ru(N2)] and [(SiP 3)Ru(PMe3)]. Our synthesis of RuCl(P P3 ) (36) 153 References begin on page 175. demonstrates that it is indeed possible to generate stable ruthenium(I) complexes with labile chloro ligands. The increased stability probably stems from the increased steric bulk of the neutral phosphine ligand, which may inhibit the disproportionation interaction between ruthenium(I) centers which is the proposed mode of their decomposition. 2 Cy Crystals of [Fe(N2)(P P3 )][BPh4] (35[BPh4]) suitable for structural analysis were grown by vapour diffusion of pentane into a THF solution of 35[BPh4] (Figure 5.5) with selected bond angles and lengths given in Table 5.4. Figure 5.5 ORTEP diagram (50% thermal ellipsoids, non-hydrogen atoms) of 2 Cy [Fe(N2)(P P3 )][BPh4] (35[BPh4]). 154 References begin on page 175. 2 Cy Table 5.4 Selected bond lengths (Å) and angles (º) for [Fe(N2)(P P3 )][BPh4] (35[BPh4]). N1 –N2 0.987(6) Fe1 –N1 1.878(6) Fe1 –P1 2.1870(16) Fe1 –P2 2.3010(16) Fe1 –P3 2.2760(17) Fe1 –P4 2.2981(16) N1- Fe1-P1 177.80(16) N1- Fe1-P2 95.88(16) N1- Fe1-P3 97.29(16) N1- Fe1-P4 94.16(16) P1- Fe1-P2 83.90(6) P1- Fe1-P3 84.72(6) P1- Fe1-P4 83.97(6) P2- Fe1-P3 118.56(6) P2- Fe1-P4 114.93(6) P3- Fe1-P4 123.48(6) Fe1- N1-N2 178.2(7) 2 Cy + The geometry of [Fe(N2)(P P3 )] (35) is distorted trigonal bipyramidal with atoms P2, P3, and P4 making up the equatorial plane and P1, and N1 at the two apexes (W = 0.91).13 This is the first structurally characterized iron(I) dinitrogen cation, with the previous three iPr Ph structurally characterized iron(I) dinitrogen complexes [Fe(SiP 3)(N2)], [Fe(SiP 3)(N2)] R - 24 i (SiP 3 = [(R2PC6H4)3Si] ) and [2-[2,6-( Pr)2PhN=C(CH3)]-6-[2,6-(iPr)2PhN- 25 CH=CH2](C5H3N)]Fe-N2 having had anionic ligands resulting in neutral complexes. iPr [Fe(SiP 3)(N2)] has a similar level of distortion from trigonal bipyramidal (W = 0.88) as Ph whereas [Fe(SiP 3)(N2)] is rigorously trigonal bipyramidal (W = 1.00). The distortion away from trigonal bipyramidal is probably due to the steric influence of the bulkier isopropyl and cyclohexyl groups and the way they pack against each other, rather than the innate geometrical preferences of an iron(I) center. 155 References begin on page 175. 2 Cy + -1 The infra red spectrum of [Fe(N2)(P P3 )] (35) shows a sharp absorbance at 2059 cm assigned to the nitrogen-nitrogen triple bond stretch Ȟ(NŁN). This is less activated than the previously identified iron(I) dinitrogen complexes for which IR data is known iPr -1 Ph -1 [Fe(N2)(SiP 3)] (2003 cm ) and [Fe(N2)(SiP 3)] (2041 cm ) as lower stretching wavenumbers indicates a weaker bonds.24 It does however lie to the lower end of the range for iron(II) complexes which have been identified between 2040-2145 cm-1.19 Figure 5.6 ORTEP diagram (50% thermal ellipsoids, non-hydrogen atoms) of 2 Cy RuCl(P P3 ) (36), pentane solvate omitted for clarity. 156 References begin on page 175. 2 Cy Crystals of RuCl(P P3 ) (36) suitable for structural analysis were grown by slow evaporation of a concentrated pentane solution of 36 (Figure 5.6) with selected bond angles and lengths given in Table 5.5. 2 Cy Table 5.5 Selected bond lengths (Å) and angles (º) for RuCl(P P3 ) (36). Ru1 –Cl1 2.486(2) Ru1 –P1 2.356(2) Ru1 –P2 2.332(2) Ru1 –P3 2.345(3) Ru1 –P4 2.196(2) Cl1- Ru1-P1 95.44(8) Cl1- Ru1-P2 99.61(8) Cl1- Ru1-P3 95.90(8) Cl1- Ru1-P4 176.34(9) P1- Ru1-P2 108.14(9) P1- Ru1-P3 142.53(9) P1- Ru1-P4 83.28(9) P2- Ru1-P3 104.95(9) P2- Ru1-P4 84.05(9) P3- Ru1-P4 83.15(9) 2 Cy The geometry of RuCl(P P3 ) (36) lies around halfway between trigonal bipyramidal and square based pyramid, which is attested to by the value of Wfor the structure being close to 0.5 (W = 0.56).13 This is due to the P1-Ru1-P3 angle (142.53(9)º) being much larger than the angles between the other equatorial phosphine donors P1-Ru1-P2 and P2-Ru1-P3 (108.14(9)° and 104.95(9)°) respectively, however not close enough to 180º for square- 2 Cy based pyramid geometry. The Ru1-Cl1 bond length of RuCl(P P3 ) (36) (2.486(2) Å) is 2 Cy longer than that of the Ru-Cl bond in the ruthenium(II) precursor [RuCl(P P3 )][BPh4] (2.4235(12) Å) as identified crystallographically (Appendix A2). This is likely due to the 2 Cy decreased charge on the ruthenium and indicates that the chloro ligand in RuCl(P P3 ) (36) 2 Cy is probably more labile that the chloro ligand in [RuCl(P P3 )][BPh4]. The increased 157 References begin on page 175. 2 Cy stability of RuCl(P P3 ) (36) over previously identified ruthenium(I) chloro complexes is therefore not likely to be due to a decrease in chloro ligand lability and can proabably best be attributed to the increased steric bulk preventing interaction between ruthenium(I) centers which ultimately leads to decomposition through disproportionation. There are only two other structurally characterized monomeric Ru(I) complexes iPr iPr 23 [(SiP 3)Ru(N2)] and [(SiP 3)Ru(PMe3)], both of which utilize the silicon centered ligand iPr - iPr - - (SiP 3) ((SiP 3) = (2-iPr2PC6H4)3Si ). Both of these structures are closer to having 2 Cy trigonal bipyramidal geometry (Wvalues of 0.76 and 0.86 respectively) than RuCl(P P3 ) (36), but are still significantly distorted from the trigonal bipyramidal geometry. This indicates 5-coordinate ruthenium(I) complexes prefer a geometry which is neither a square pyramidal geometry like ruthenium(II) nor a trigonal bipyramidal geometry like ruthenium(0) but something halfway between the two, in line with the intermediate oxidation state. 2 Cy 2 Cy Although complexes [Fe(N2)(P P3 )][BPh4] (35[BPh4]) and RuCl(P P3 ) (36) are formally Fe(I) and Ru(I) complexes, the possibility of a ligand-centered radical cannot be excluded based on structural studies alone, especially in light of the growing recognition of redox non-innocence of many auxiliary ligands.26 To investigate the distribution of spin density in 35 and 36, EPR spectra were obtained at 77 K in THF glass (Figure 5.7 and Figure 5.8) and Appendix A4. Each spectrum exhibits rhombic features with hyperfine coupling due to the phosphorus atoms of the ligand. In assessing metal radical character, the anisotropy of the g values (g being a constant of proportionality, whose value is the property of the electron in a certain environment) 158 References begin on page 175. (ǻg=gmax-gmin) is particularly noteworthy, since a large ǻg value has been noted as a crude indication of metalloradical character for S=1/2 systems,27 though there are some examples of ligand centered radicals with large ǻg.28 Proven ligand centered radicals have lower ǻg in the range of .0575,29 and 0.0779,30 and proven metal centered radicals having larger ǻg in the realm of 0.197, and 0.252.31 2 Cy + Figure 5.7 EPR spectrum of [Fe(N2)(P P3 )] (35) (77K). (gx, gy, gz) = (2.225, 2.040, 1.999). Lower curve is a simulation. Experimental parameters; Microwave power, 0.1978 mW; microwave frequency, 9.4915 GHz; modulation amplitude, 12 G; gain, 10000 Simulation parameters: Ȟ = 9.4915 GHz; gx = (31P) 2.225, gy = 2.040, 31 31 gz = 1.999; For one P atom Ax( P) = 70 MHz, Ay( P) = 130 MHz, 31 14 14 14 Az( P) = 130 MHz; For one N atom Ax( N) = 45 MHz, Ay( N) = 65 MHz, 14 31 31 Az( N) = 65 MHz; For two P atoms, Ax( P) = 45 MHz, Ay( P) = 65 MHz, 31 Az( P) = 65 MHz; Linewidth, Wx = 50 G, Wy = 80 G, Wz = 55 G. 159 References begin on page 175. 2 Cy Figure 5.8 EPR spectrum of RuCl(P P3 ) (36) (77K). (gx, gy, gz) = (2.104, 2.064, 2.0005). Lower curve is a simulation. Experimental parameters; Microwave power, 0.1963 mW; microwave frequency, 9.4915 GHz; modulation amplitude, 4 G; gain, 1000 Simulation parameters: Ȟ = 9.4915 GHz; gx = (31P) 2.104, gy = 2.064, 31 31 gz = 2.0005; For one P atom Ax( P) = 373 MHz, Ay( P) = 385 MHz, 31 Az( P) = 430 MHz; For one Ru atom Ax(Ru) = 45 MHz, Ay(Ru) = 25 MHz, 31 31 Az(Ru) = 40 MHz; For two P atoms, Ax( P) = 0 MHz, Ay( P) = 34 MHz, 31 Az( P) = 0 MHz; Linewidth, Wx = 65 G, Wy = 28 G, Wz = 65 G. 2 Cy + The ǻg value for [Fe(N2)(P P3 )] 35 of 0.226 is indicative of a clearly metal centered 2 Cy radical, while RuCl(P P3 ) (36), with a ǻg value of 0.103 is less diagnostic. Although g values alone cannot be used as a quantitative measure of spin density, the simulated EPR parameters also support 35 and 36 being metalloradicals. 160 References begin on page 175. 2 Cy 5.6 FeH2(P P3 ) (37) 2 Cy 2 Cy FeH2(P P3 ) (37) was first generated as a side product of the synthesis of FeN2(P P3 ) (33). Because it was formed alongside 33, and the similar solubility of the two complexes in various solvents make separation non-trivial, an alternative synthetic method was sought 2 Cy to enable characterization of 37. FeCl(P P3 )][BPh4] was reacted with potassium triethylborohydride (KBEt3H) in toluene to give 37 (Scheme 5.5). Crystals suitable for structural analysis were grown by evaporation of a toluene solution of complex 37 (Figure 5.9) with selected bond angles and lengths given in Table 5.6. PE 2 equiv. KBEt H P 3 T H [FeCl(P2P Cy)][BPh ] Fe 3 4 P Toluene C H PE 2 Cy P P3 =P(CH2CH2PCy2)3 37 Scheme 5.5 2 Cy The geometry of FeH2(P P3 ) (37) is distorted octahedral, with the two hydrides in a mutually cis arrangement. The distortion away from octahedral is due to P-Ru-P bond angles > 90º and H-Ru-P bond angles < 90º. 161 References begin on page 175. 2 Cy Figure 5.9 ORTEP plot (50% thermal ellipsoids) of FeH2(P P3 ) (37) within each asymmetric unit. Selected hydrogen atoms and second complex in the asymmetric unit have been omitted for clarity. Three other iron dihydride complexes with phosphine ligands have been characterized 32 32a crystallographically previously with FeH2(Ph2PCH2CH2PPh2)2 and 32b FeH2[(PhP(OC2H5)2]4 both having mutually cis hydrides also. 2 Cy FeH2(Ph2PCH2CH2PPh2)2, FeH2[(PhP(OC2H5)2]4, and FeH2(P P3 ) (37) all share similar distorted octahedral geometry with much smaller P-Fe-H bond angles than P-Fe-P bond angles. These compressed angles can be attributed to the small size of the hydride ligands, 162 References begin on page 175. which allows the bulkier phophines to move away from each other and toward the hydrides. The small differences observed in bond lengths and angles can be attributed to the different denticity of the ligands in all three complexes causing different steric demands on the final structure. 2 Cy Table 5.6 Selected bond lengths (Å) and angles (º) for [FeH2(P P3 )] (37) Fe1 –H1 1.44(3) Fe1 –H2 1.47(3) Fe1 –P1 2.1108(8) Fe1 –P2 2.1776(8) Fe1 –P4 2.1766(8) Fe1 –P3 2.2036(8) H1- Fe1-P2 94.9(12) H1- Fe1-P1 177.6(12) H1- Fe1-P3 94.5(11) H1- Fe1-P4 89.9(12) H2- Fe1-P2 65.6(11) H2- Fe1-P1 91.2(11) H2- Fe1-P3 173.1(11) H2- Fe1-P4 75.7(11) P1- Fe1-P2 86.85(3) P2- Fe1-P3 107.76(3) P2- Fe1-P4 140.77(3) P1- Fe1-P3 86.35(3) P1- Fe1-P4 87.75(3) P3- Fe1-P4 110.61(3) H1- Fe1-H2 88.1(15) 31 1 2 Cy The P{ H} NMR spectrum of FeH2(P P3 ) (37) contains only two sharp resonances at 315K, a quartet at 174.4 ppm assigned to the central phosphine PC and a doublet at 102.3 31 31 ppm assigned to the terminal phosphines PE/T in a 1:3 ratio, with a P- P coupling constant of 18 Hz (Figure 5.10). This spectrum is consistent with fast exchange occurring between the terminal phosphorus environments, PE and PT. At 240 K the exchange is slowed down causing significant broadening of the PE/T resonance. As the temperature is lowered further 163 References begin on page 175. to 190 K, two distinct broad resonances emerge at G 96.8 and G 113.7 for the two PE and one PT phosphine atoms respectively (Figure 5.10). PE P T H Fe P C H PE 37 31 1 2 Cy Figure 5.10 Variable temperature P{ H} NMR spectra of FeH2(P P3 ) (37) with spectra at (from front) 190, 210, 225, 240, 254, and 315 K. 1 2 Cy The H NMR spectrum of FeH2(P P3 ) (37) shows a similar exchange with process the two hydride signals in fast exchange at 285 K (Figure 5.11) giving rise to a single sharp resonance at -12.84 ppm. At 240 K, the hydride resonance was broadened to the point 164 References begin on page 175. 2 where JH-P coupling can no longer be observed. At 210 K two broad resonances appeared at -7.95 and -17.71 ppm, with these resonances becoming significantly sharper at 190 K (Figure 5.11). 1 2 Cy Figure 5.11 Variable temperature high field H NMR spectra of FeH2(P P3 ) (37) with spectra at (from front) 190, 200, 210, 225, 240, 254, 271 and 285 K. 2 Cy The iron dihydride FeH2(P P3 ) (37) has a faster rate of exchange than that observed for 2 Me 2 Me 6b the analogous dihydride FeH2(P P3 ) (P P3 = P(CH2CH2PMe2)3). This supports previous discussion that the mechanism of exchange for iron dihydrides with tetradentate phosphine ligands was most likely a process of temporary detachment of one of the bound phosphines to give a five coordinate complex which could undergo facile pseudorotation before recoordination of the fourth phosphine. This process would be accelerated by 165 References begin on page 175. increased steric bulk on the terminal phosphines as the steric repulsion between the terminal phosphines would increase, lowering the barrier for detachment. 5.7 Reactivity of dinitrogen complexes 2 Cy Treatment of the iron(0) and ruthenium(0) dinitrogen species Fe(N2)(P P3 ) (33) and 2 Cy Ru(N2)(P P3 ) (34) with one equivalent of the weak organic acid, 2,6-lutidinium tetrafluoroborate, results in protonation of the metal centers to give the iron(II) and 2 Cy + ruthenium(II) dinitrogen hydride complexes [FeH(N2)(P P3 )] (38) and 2 Cy + 2 Cy + [RuH(N2)(P P3 )] (39), respectively (Scheme 5.2). [FeH(N2)(P P3 )] (38) could also be 2 Cy generated by the treatment of FeH2(P P3 ) (37) with one equivalent of 2,6-lutidinium tetrafluoroborate under a nitrogen atmosphere, and it was this synthetic method which was 2 Cy + used to synthesize samples for characterization purposes. [FeH(N2)(P P3 )] (38) and 2 Cy + [RuH(N2)(P P3 )] (39) are both stable with respect to further protonation by 2 Cy 2 Cy 2,6-lutidinium tetrafluoroborate. Reaction of Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34) with an excess of stronger acids such as hydrochloric acid and triflic acid resulted in protonation of the phosphine ligand, and no identifiable products of reaction at the coordinated nitrogen. 2 Cy Treatment of [Fe(N2)(P P3 )][BPh4] (35[BPh4]) with a one equivalent of acid, either 2,6- lutidinium tetrafluoroborate or fluoroboric acid, resulted in the very slow synthesis of 2 Cy + [FeH(N2)(P P3 )] (38) most likely through acid assisted disproportionation. 2 Cy + [FeH(N2)(P P3 )] (38) is analogous to the known iron(II) dinitrogen hydride species 2 Me + 2 Me 6b, 33 2 iPr + 2 iPr [FeH(N2)(P P3 )] (P P3 = P(CH2CH2PMe2)3), and [FeH(N2)(P P3 )] (P P3 = 7 2 Cy + P(CH2CH2PiPr2)3), and [RuH(N2)(P P3 )] (39) is analogous to the known ruthenium(II) 166 References begin on page 175. 2 iPr + 7 dinitrogen hydride species [RuH(N2)(P P3 )] . These dinitrogen hydride complexes could also be formed through attack of a weak acid at the appropriate iron(0) and ruthenium (0) dinitrogen complex. The 31P{1H} NMR spectra of complexes 38 and 39 exhibit the three characteristic resonances of octahedral species with tripodal tetradentate phosphine ligands. The central 2 Cy + phosphine PC signal of [FeH(N2)(P P3 )] (38) at the relatively low field shift of 160.7 ppm is observed as a doublet of triplets with coupling constants of 28 and 24 Hz to PT and PE, respectively. The two equivalent terminal phosphines PE exhibit a resonance at 79.8 ppm which appears as a doublet of doublets and has twice the intensity of the other signals for PC and PT. The coupling constant of PE to PT is 11 Hz. The resonance of PT appears as a well resolved doublet of triplets at 70.3 ppm. The metal-bound hydride of 38 appears as a 1 triplet of doublets of doublets at -14.62 ppm in the H NMR spectrum, coupling to PE, PT, PC with coupling constants of 69 Hz, 53 Hz and 25 Hz respectively. 31 1 2 Cy + The P{ H} NMR spectra of [RuH(N2)(P P3 )] (39) displays the central PC signal at the low field shift of 140.7 ppm as a doublet of triplets with a coupling constants of 11 and 11 Hz to PT and PE, respectively. The two equivalent terminal phosphines PE appear as a resonance at 63.8 ppm which is observed as a doublet of doublets and has twice the intensity of the signals for PC and PT. The coupling constant of PE to PT is 11 Hz. The resonance of PT appears as a well resolved doublet of triplets at 51.4 ppm. The metal-bound hydride of 39 appears as a double of triplets of doublets at -11.26 ppm in the 1H NMR spectrum, coupling to PT, PE and PC with coupling constants of 72 Hz, 26 Hz and 23 Hz respectively. 167 References begin on page 175. 2 Cy + The infrared spectrum of [FeH(N2)(P P3 )] (38) displays a sharp absorbance at -1 2 Cy + 2107 cm , and the spectrum of [RuH(N2)(P P3 )] (7) displays a similar absorbance at 2172 cm-1, both of which are assigned to the dinitrogen stretch Ȟ(NŁN) for the respective complexes. These high values of Ȟ(NŁN) indicate the lower level of dinitrogen activation when bound to an Fe(II) or Ru(II) center when compared to the Fe(0), Ru(0), and Fe(I) 2 Cy 2 Cy 2 Cy + dinitrogen complexes Fe(N2)(P P3 ) (33), Fe(N2)(P P3 ) (34) and [Fe(N2)(P P3 )] (35) discussed above. For the iron complexes the level of dinitrogen activation appears to vary in an approximately linear fashion with oxidation state, with the Fe(0) complex 2 Cy -1 Fe(N2)(P P3 ) (33) having the greatest activation with an absorbance at 1996 cm , 2 Cy + -1 followed by the Fe(I) complex [Fe(N2)(P P3 )] (35) at 2059 cm and finally the Fe(II) 2 Cy + -1 complex [FeH(N2)(P P3 )] (38) at 2107 cm . 2 Cy + 2 Cy + Crystals of [FeH(N2)(P P3 )] (38) and [RuH(N2)(P P3 )] (39) suitable for structural analysis were grown by vapour diffusion of pentane into THF solutions of 38[BF4] (Figure 5.12) and 39[BF4] (Figure 5.13) with selected bond angles and lengths given in Tables 5.7 and 5.8 respectively. 168 References begin on page 175. 2 Cy Figure 5.12 ORTEP plot (50% thermal ellipsoids) of [FeH(N2)(P P3 )][BF4] (38[BF4]) within each asymmetric unit. Hydrogen atoms, tetrafluoroborate counter ion and THF solvate have been omitted for clarity. 169 References begin on page 175. 2 Cy Table 5.7 Selected bond lengths (Å) and angles (º) for [FeH(N2)(P P3 )][BF4] (38[BF4]) N1 –N2 1.028(7) Fe1 –N1 1.859(6) Fe1 –P1 2.2723(15) Fe1 –P2 2.3033(17) Fe1 –P3 2.2481(15) Fe1 –P4 2.1752(16) Fe1 –H1 1.69(10) Fe1-N1-N2 179.7(7) N1- Fe1-P1 94.27(15) N1- Fe1-P2 98.06(17) N1- Fe1-P3 93.50(15) N1- Fe1-P4 176.87(17) N1- Fe1-H1 103(3) P1- Fe1-P2 102.88(6) P1- Fe1-P3 148.12(6) P1- Fe1-P4 84.56(5) P1- Fe1-H1 77(4) P2- Fe1-P3 106.55(6) P2- Fe1-P4 85.04(6) P2- Fe1-H1 159(3) P3- Fe1-P4 86.02(6) P3- Fe1-H1 71(4) P4- Fe1-H1 74(3) 170 References begin on page 175. 2 Cy Figure 5.13 ORTEP plot (50% thermal ellipsoids) of [RuH(N2)(P P3 )][BF4] (39[BF4]) within each asymmetric unit. Hydrogen atoms, tetrafluoroborate counter ion and THF solvate have been omitted for clarity. 171 References begin on page 175. 2 Cy Table 5.8 Selected bond lengths (Å) and angles (º) for [RuH(N2)(P P3 )][BF4] (39[BF4]) N1 –N2 1.069(4) Ru1 –N1 2.042(3) Ru1 –P1 2.4213(7) Ru1 –P2 2.3496(7) Ru1 –P3 2.3599(7) Ru1 –P4 2.2408(8) Ru1 –H1 1.65(4) Ru1-N1-N2 177.1(3) N1-Ru1-P1 99.84(7) N1-Ru1-P2 94.56(7) N1-Ru1-P3 96.40(7) N1-Ru1-P4 177.21(7) N1-Ru1-H1 93.8(15) P1-Ru1-P2 103.98(3) P1-Ru1-P3 100.29(3) P1-Ru1-P4 82.92(3) P1-Ru1-H1 166.2(15) P2-Ru1-P3 151.17(3) P2-Ru1-P4 84.42(3) P2-Ru1-H1 76.1(15) P3-Ru1-P4 83.36(3) P3-Ru1-H1 76.7(15) P4-Ru1-H1 83.4(15) 2 Cy + 2 Cy + The geometry for both [FeH(N2)(P P3 )] (38) and [RuH(N2)(P P3 )] (39) is distorted octahedral with the dinitrogen ligand located trans to the central phosphine of the phosphine ligand and the hydrido ligand located trans to one of the arm phosphines. The short N-N bond lengths of 1.028(7) Å for 38 and 1.069(4) Å for 39 indicate no activation when compared with free dinitrogen of the nitrogen triple bond, in agreement with the observations from the IR data. 172 References begin on page 175. 2 Cy + Reaction of [FeH(N2)(P P3 )] (38) with potassium tert-butoxide in THF results in the 2 Cy regeneration of FeN2(P P3 ) (33). A similar result was observed for tert-butoxide treatment 2 Cy + 2 Cy of [RuH(N2)(P P3 )] (39) in THF, with Ru(N2)(P P3 ) (34) being regenerated. The 2 Cy 2 Cy + protonation of FeN2(P P3 ) (33) to give [FeH(N2)(P P3 )] (38) is readily reversible. + PE P N + - E N LutH BF4 P T N N M M P C PC H PE PE KOtBu PE 33 M=Fe 38 M=Fe 34 M=Ru 39 M=Ru P2P Cy =P(CH CH PCy ) 3 2 2 2 3 Scheme 5.6 5.8 Conclusions 2 Cy The iron(0) and ruthenium(0) dinitrogen complexes of the P P3 ligand were successfully synthesized, but the increased steric bulk doesn't significantly change the reactivity of these 2 iPr complexes when compared to that of their less sterically bulky analogues M(N2)(P P3 ) (M 2 Me = Fe, Ru) and Fe(N2)(P P3 ). Treatment with acid resulted in generation of the hydrido 2 Cy + 2 Cy + nitrogen species [FeH(N2)(P P3 )] (38) and [RuH(N2)(P P3 )] (39) rather than reacting with the coordinated dinitrogen ligand. A possible explanation for metal center protonation would be that the increased steric bulk of the terminal phosphines consequently increases the rate that the phosphine arms disassociate from the complex, leaving the iron(0) or ruthenium(0) centre still exposed to 2 Cy protonation. Analysis of the exchange rates of the FeH2(P P3 ) (37) complex showing a 173 References begin on page 175. faster rate of exchange between isomers in solution than the less sterically bulky analogue FeH2(PP3) (PP3 = P(CH2CH2PMe2)3). The complexes with bulkier ligands are stereochemically more labile. 2 Cy The extra steric bulk of the P P3 ligand allowed the generation of stable iron(I) and 2 Cy + 2 Cy ruthenium(I) species [Fe(N2)(P P3 )] (35) and RuCl(P P3 ) (36), analogues of which with less bulky phosphines had not previously been identified or had not characterized as stable species. The extra steric bulk conveys additional stability, probably by preventing the disproportionation pathways which usually decompose iron(I) and ruthenium(I) species. 174 References begin on page 175. 5.9 References 1. Allen, A. D.; Senoff, C. W., Chem. Comm. 1965, 621-2. 2. (a) Fryzuk, M. D.; Johnson, S. A., Coord. Chem. Rev. 2000, 200-202 379-409; (b) Hidai, M., Coord. Chem. Rev. 1999, 185-186 99-108; (c) MacKay, B. A.; Fryzuk, M. D., Chem. Rev. 2004, 104 385-401. 3. (a) Laplaza, C. E.; Cummins, C. C., Science 1995, 268 861-3; (b) George, T. A.; Rose, D. J.; Chang, Y.; Chen, Q.; Zubieta, J., Inorg. Chem. 1995, 34 1295-8; (c) Yandulov, D. V.; Schrock, R. R., J. Am. Chem. Soc. 2002, 124 6252-6253; (d) Betley, T. A.; Peters, J. C., J. Am. Chem. Soc. 2004, 126 6252-6254; (e) Fryzuk, M. D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T. F., J. Am. Chem. Soc. 2001, 123 3960-3973. 4. Jia, G.; Drouin, S. D.; Jessop, P. G.; Lough, A. J.; Morris, R. H., Organometallics 1993, 12 906-16. 5. (a) Bianchini, C.; Laschi, F.; Peruzzini, M.; Zanello, P., Gazz. Chim. Ital. 1994, 124 271-5; (b) King, R. B.; Kapoor, R. N.; Saran, M. S.; Kapoor, P. N., Inorg. Chem. 1971, 10 1851-60; (c) Stoppioni, P.; Mani, F.; Sacconi, L., Inorg. Chim. Acta 1974, 11 227-30. 6. (a) Field, L. D.; Messerle, B. A.; Smernik, R. J.; Hambley, T. W.; Turner, P., Inorg. Chem. 1997, 36 2884-2892; (b) Field, L. D.; Messerle, B. A.; Smernik, R. J., Inorg. Chem. 1997, 36 5984-5990. 7. Field, L. D.; Guest, R. W.; Vuong, K. Q.; Dalgarno, S. J.; Jensen, P., Inorg. Chem. 2009, 48 2246-2253. 175 References begin on page 175. 8. Gilbert-Wilson, R.; Field, L. D.; Bhadbhade, M. M., Inorg. Chem. 2012, 51 3239- 46. 9. Leigh, G. J.; Jimenez-Tenorio, M., J. Am. Chem. Soc. 1991, 113 5862-3. 10. Gilbertson, J. D.; Szymczak, N. K.; Tyler, D. R., J. Am. Chem. Soc. 2005, 127 10184-10185. 11. Field, L. D.; Messerle, B. A.; Smernik, R. J., Inorg. Chem. 1997, 36 5984-5990. 12. Jia, G.; Drouin, S. D.; Jessop, P. G.; Lough, A. J.; Morris, R. H., Organometallics 1993, 12 906-916. 13. Addison, A. W.; Rao, T. N.; Reedijk, J.; Vanrijn, J.; Verschoor, G. C., J. Chem. Soc. Dalton 1984, 1349-1356. 14. Bianchini, C.; Laschi, F.; Peruzzini, M.; Zanello, P., Gazz. Chim. Ital. 1994, 124 271-5. 15. Donovan-Mtunzi, S.; Richards, R. L.; Mason, J., J. Chem. Soc. Dalton 1984, 469- 474. 16. Otting, G.; Messerle, B. A.; Soler, L. P., J. Am. Chem. Soc. 1997, 119 5425-5434. 17. Sutton, L. E., Tables of Interatomic Distances and Configuration in Molecules and Ions. The Chemical Society: London, 1958. 18. Komiya, S.; Akita, M.; Yoza, A.; Kasuga, N.; Fukuoka, A.; Kai, Y., J. Chem. Soc., Chem. Comm. 1993, 787-788. 19. Hazari, N., Chem. Soc. Rev. 2010, 39 4044-4056. 176 References begin on page 175. 20. Hughes, D. L.; Leigh, G. J.; Jimenez-Tenorio, M.; Rowley, A. T., J. Chem. Soc., Dalton Trans. 1993, 75-82. 21. Zotti, G.; Pilloni, G.; Bressan, M.; Martelli, M., J. Electroanal. Chem. and Interfacial Electrochem. 1977, 75 607-612. 22. Bianchini, C.; Laschi, F.; Peruzzini, M.; Zanello, P., Gazz. Chim. Ital. 1994, 124 271-5. 23. Takaoka, A.; Gerber, L. C. H.; Peters, J. C., Angew. Chem. Int. Ed. 2010, 49 4088- 4091. 24. Mankad, N. P.; Whited, M. T.; Peters, J. C., Angew. Chem. Int. Ed. 2007, 46 5768- 5771. 25. Scott, J.; Vidyaratne, I.; Korobkov, I.; Gambarotta, S.; Budzelaar, P. H. M., Inorg. Chem. 2008, 47 896-911. 26. (a) Lu, C. C.; Bill, E.; Weyhermüller, T.; Bothe, E.; Wieghardt, K., J. Am. Chem. Soc. 2008, 130 3181-3197; (b) Harkins, S. B.; Mankad, N. P.; Miller, A. J. M.; Szilagyi, R. K.; Peters, J. C., J. Am. Chem. Soc. 2008, 130 3478-3485; (c) Adhikari, D.; Mossin, S.; Basuli, F.; Huffman, J. C.; Szilagyi, R. K.; Meyer, K.; Mindiola, D. J., J. Am. Chem. Soc. 2008, 130 3676-3682. 27. (a) de Bruin, B.; Hetterscheid, D. G. H., Eur. J. Inorg. Chem. 2007, 2007 211-230; (b) Ghumaan, S.; Sarkar, B.; Patra, S.; van Slageren, J.; Fiedler, J.; Kaim, W.; Lahiri, G. K., Inorg. Chem. 2005, 44 3210-3214. 28. Miyazato, Y.; Wada, T.; Muckerman, J. T.; Fujita, E.; Tanaka, K., Angew. Chem. 2007, 119 5830-5832. 177 References begin on page 175. 29. Büttner, T.; Geier, J.; Frison, G.; Harmer, J.; Calle, C.; Schweiger, A.; Schönberg, H.; Grützmacher, H., Science 2005, 307 235-238. 30. Cataldo, L.; Choua, S.; Berclaz, T.; Geoffroy, M.; Mézailles, N.; Avarvari, N.; Mathey, F.; Le Floch, P., J. Phys. Chem. A 2002, 106 3017-3022. 31. Sarkar, B.; Kaim, W.; Fiedler, J.; Duboc, C., J. Am. Chem. Soc. 2004, 126 14706- 14707. 32. (a) E.B.Lobkovskii, M. Y. A., A.P.Borisov, V.D.Makhaev, K.N.Semenenko, Yu.T.Struchkov, Koord. Khim. 1980, 6 1267; (b) Guggenberger, L. J.; Titus, D. D.; Flood, M. T.; Marsh, R. E.; Orio, A. A.; Gray, H. B., J. Am. Chem. Soc. 1972, 94 1135-1143; (c) Gao, Y.; Holah, D. G.; Hughes, A. N.; Spivak, G. J.; Havighurst, M. D.; Magnuson, V. R.; Polyakov, V., Polyhedron 1997, 16 2797-2807. 33. Field, L. D.; Guest, R. W.; Turner, P., Inorg. Chem. 2010, 49 9086-9093. 178 References begin on page 175. 2 Cy 6CP3 Synthesis and Complexes 6.1 Introduction 1 Podand ligands, such as the Sacconi ligands, [X(CH2CH2PR2)3] (X = N, P), provide rigid and well-defined coordination geometries, which can impose interesting chemical properties and reactivity patterns on their metal complexes.2 Pincer complexes share similar properties and have been studied much more extensively than podand complexes, due to their extensive catalytic properties. There is considerable potential to discover new catalytic complexes by studying the complexes of podand ligands. Little work has been devoted to the study of complexes containing podand ligands in which the apical donor is an anionic Group 14 element (i.e. C, Si, Ge, Sn and Pb)2-3 where there is effectively a covalent metal-element bond between the apical donor and the metal centre. Metal complexes with podand ligands with an anionic Group 14 apical donor typically have a strong bond between the apical donor and the metal, and this serves as a concrete anchor point for the ligand. Much of the work on anionic group 14 centered podands has been recent, with silicon centered podand complexes showing interesting new applications, especially with regard to dinitrogen chemistry. Iron complexes containing the SiP3-type ligands (SiP3 = - 4 [Si(o-C6H4PR2)3] , (R = Ph or iPr)) ligand, first reported by Hendriksen et al. and Joslin and Stobart5 have been shown by the Peters group to activate bound dinitrogen toward terminal protonation and silyation.6 179 References begin on page 200. Though sharing similar properties, carbon-centered podands have not yet been investigated to the same extent, largely because of the greater synthetic challenges encountered when compared to their silicon centered analogues. Reports on the carbon- centered podand ligand are, however, growing with recent work describing the synthesis 7 of a C3-symmetric palladium(II) complex derived from a CP3 podand, as well as work from Field et al. demonstrating a number of ruthenium complexes with carbon-centred 8 podand ligand derived from HC(CH2CH2PPh2)3. Another impetus for research into carbon-centered podands comes from studies of the active site of the nitrogenase enzyme, used in nature to achieve nitrogen fixation. Recent crystallographic analysis of the nitrogenase active site is heavily favoring a central carbon atom within the iron sulfur cluster.9 The nitrogen binding site on the iron cluster is trans to the central carbon atom with three sulfur atoms making up the remainder of the coordination sphere around the iron center. The development of iron podand complexes with a central anionic carbon located trans to a dinitrogen ligand is of particular interest as mimics for the nitrogenase active site. P H C P P 46 H 2 Cy Figure 6.1 Tris[2-(dicyclohexylphosphino)ethyl]methane ( C P3 , 46) 180 References begin on page 200. In this chapter, the synthetic approach to metal complexes containing new anionic CP3 H 2 Cy ligand from tris[2-(dicyclohexylphosphino)ethyl]methane ( C P3 , 46) is reported. H 2 Cy 6.2 Synthesis of tris[2-(dicyclohexylphosphino)ethyl]methane) ( C P3 , 46) To generate the desired metal complexes with a new sterically bulky CP3-type ligand it H 2 Cy was first necessary to synthesize the ligand precursor C P3 (46). A synthetic procedure similar to that reported by Field et al.8 for the synthesis of the analogous tris[2-(diphenylphosphino)ethyl]methane was employed. The approach to 46 was to assemble the organic framework of the tripod with halogens as substitueants at the ends of the three -CH2CH2- arms. The final step in the synthesis was a 3-fold nuclophilic substitution to replace the halogens with the required phosphine donors. The organic backbone of the tripod was assembeld in stages from dimethyl 1,3-acetonedicarboxylate (Scheme 6.1). 6.2.1 Preparation of [(methoxycarbonyl)methylene]triphenylphosphorane (41) It was necessary to prepare [(methoxycarbonyl)methylene]triphenylphosphorane (41) for use in the subsequent Wittig reaction which produced the hydrocarbon backbone of H 2 Cy C P3 (46). Triphenylphosphine was reacted with methylbromoacetate in ethyl acetate to produce [(methoxycarbonyl)methyl]triphenylphosphonium bromide (40) through the conversion to a quaternary phosphine (Scheme 6.1). 40 was then converted to the desired [(methoxycarbonyl)methylene]triphenylphosphorane (41) through treatment with sodium hydroxide. The base deprotonates the carbon alpha to the 181 References begin on page 200. quaternary phosphine, resulting in the formation of the P=C double bond and giving the desired triphenyl phosphonium ylide (Scheme 6.1). PPh O 3 Br- O Br Ph P+ O 3 O 40 OH- O O O O O O O O O Ph3P O O O O 41 42 LiBH4 OH OH SOCl2 Cl Cl CH CH HO Cl 44 43 Scheme 6.1 182 References begin on page 200. 6.2.2 Preparation of 3-(2-Hydroxyethyl)pentane-1,5-diol (43) 3-(2-Hydroxyethyl)pentane-1,5-diol (43) furnishes the carbon skeleton of the desired H 2 Cy ligand precursor C P3 (46). A Wittig reaction between [(methoxycarbonyl)methylene]triphenylphosphorane (41) and dimethyl 1,3-acetonedicarboxylate gave 3-(methoxycarbonyl)methylpent-2-enedioate (42) (Scheme 1) with the elimination of triphenylphopsphine oxide. Reduction of 42 using lithium borohydride afforded the desired triol 3-(2-Hydroxyethyl)pentane-1,5-diol (43) in 89% yield. This reaction reduces the esters of 42 to alcohols in addition to reducing the alkene in the backbone to an aliphatic chain in the same step (Scheme 6.1). 6.2.3 Preparation of 3-(2-Chloroethyl)-1,5-dichloropentane (44) To attach the terminal phosphines it was necessary to exchange the alcohol groups on the triol 43 for another functional group which is a better leaving group for substitution. 10 Previously both the trichloride CH(CH2CH2Cl)3 (44) produced using thionyl chloride, 11 and the tribromide CH(CH2CH2Br)3 produced using phosphorus tribromide and HBr have been used for this purpose. In this case the thionyl choride route to the trichloride 44 was exploited as despite the 26% yield, it was still found to be higher yielding than the equivalent route to the tribromide (Scheme 6.1). H 2 Cy 6.2.4 Preparation of tris[2-(dicyclohexylphosphino)ethyl]methane) ( C P3 , 46) This compound was prepared via a nucleophilic substitution of 3-(2-chloroethyl)-1,5- dichloropentane10 with lithium dicyclohexylphosphide, prepared in situ from the 183 References begin on page 200. 8 H 2 Cy secondary phosphine and n-BuLi (Scheme 6.2). C P3 (46) was obtained as a colourless solid, which was purified by recrystallisation from a THF/methanol mixture. 45 3 Equiv. P PCy2 Cl Cl Li H CH C Cy2P PCy2 Cl 44 46 Scheme 6.2 H 2 Cy Figure 6.2 ORTEP plot (50% thermal ellipsoids) of C P3 (46). Selected hydrogen atoms have been omitted for clarity. 184 References begin on page 200. H 2 Cy Crystals of C P3 (46) suitable for structural analysis were grown by slow evaporation of a toluene solution under nitrogen (Figure 6.2). 2 Cy 6.3 Synthesis and characterization of ruthenium complexes with the C P3 ligand. 6.3.1 Previous CP3 complex synthesis. The only previous use of a CP3-type ligand was by Field et al. utilizing the ligand 8 precursor CH(CH2CH2PPh2)3 to synthesize ruthenium complexes. Reaction of the ligand precursor CH(CH2CH2PPh2)3 with RuCl2(PPh3)3 in refluxing mesitylene dehydrogenated the CP3-ligand backbone to give the complex Ru(C(CH2CH2PPh2)2(=CHCH2PPh2))Cl2, an octahedral complex coordinated by two chloride ligands, the three phosphine donors and the double bond of the CP3-ligand backbone (Scheme 6.3). Treatment with hydride in the presence of a neutral donor ligand produced various ruthenium complexes, with the central carbon ı-bonded to the ruthenium center (Scheme 6.3). Attempts to replicate this approach to introducing the podand ligand by refluxing H 2 Cy C P3 (46) with RuCl2(PPh3)3 in toluene or in mesitylene were unsuccessful with no isolation of any identifiable complexes. By 31P{1H} NMR, the reaction mixture showed the presence of a range of complexes where it appeared that there had been only partial displacement of the PPh3 ligands in the metal precursor. It appeared that there was only partial displacement of the triphenylphosphine ligands resulting in a large range of complexes, none of which could be isolated or characterized. Reacting RuHCl(PPh3)3 185 References begin on page 200. H 2 Cy with C P3 (46), both at room temperature and in refluxing toluene, also failed to result in any identifiable complexes that could be isolated. PPh PPh 2 Ph2 2 ' P Cl H Ru C RuCl (PPh ) Cl Ph P PPh 2 3 3 2 2 PPh2 - 1Equiv.H 2Equiv.H- L L PPh PPh Ph2 2 Ph2 2 P P Cl L Ru Ru C L C H PPh2 PPh2 Scheme 6.3 6.3.2 CP3 complexes from ruthenium dihydrides precursors. While to this point unpublished, it has been previously observed within the Field group that the reaction of a CP3-ligand precursor with a RuH2(L)(PPh3)3 forms a ruthenium 12 hydrido complex with an ı-bound CP3-ligand. Complexes of the type 2 Cy H 2 Cy RuH(L)(C P3 ) have been synthesized by the reaction of C P3 (46) with RuH2(L)(PPh3)3. 6.3.3 Synthesis of suitable ruthenium dihydride precursors 2 Cy To synthesize ruthenium complexes of the type RuH(L)(C P3 ) it was necessary to prepare ruthenium precursors RuH2(L)(PPh3)3 (L = CO, N2). RuH2(CO)(PPh3)3 was prepared though the method of Ahmad et al.13 by Dr. Alison Magill and generously 186 References begin on page 200. provided to assist this project. Multiple methods have been utilised in the literature to synthesize RuH2(N2)(PPh3)3 (47). These have included: treatment of RuCl2(PPh3)3, 14 15 with Et3Al, treatment of RuCl2(PPh3)3 with Et3N under hydrogen, and the treatment 16 of RuCl2(PPh3)3 with an alkali metal borohydride under a nitrogen atmosphere. The most successful method was found to be the reaction of NaBH4 with RuCl2(PPh3)3 to 17 produce RuH2(N2)(PPh3)3 by the a modification of method of Morton et al. This modification involved extended exposure to a nitrogen atmosphere to achieve greater conversion of the initially produced RuH4(PPh3)3 to the desired RuH2(N2)(PPh3)3 than was achieved following the previous method (Scheme 6.4). PPh3 Ph P NaBH4 3 N N Ru RuCl2(PPh3)3 H H C6H6/MeOH PPh3 47 . Scheme 6.4 2 Cy 2 Cy 6.3.4 RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) 2 Cy 2 Cy 6.3.4.1 Synthesis of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) 2 Cy RuH(CO)(C P3 ) (48) was successfully synthesized by reaction of RuH2(CO)(PPh3)3 H 2 Cy 2 Cy with C P3 (46) in refluxing toluene (Scheme 6.5). RuH(CO)(C P3 ) (48) is a white solid which displays no or very limited solubility in either pentane or methanol, but a low level of solubility in benzene, toluene and THF. The solubility is significantly higher on warming. 187 References begin on page 200. ' P PCy2 E P RuH2(CO)(PPh3)3 T C O H Ru C C Toluene H Cy2P PCy2 PE 48 Scheme 6.5 This is the second report of a ruthenium hydrido carbonyl complex with a CP3 ligand, 8 the first being RuH(CO)(C(CH2CH2PPh2)3). Ruthenium dinitrogen complexes utilizing CP3-type ligand are so far unknown. They therefore represent an attractive synthetic target to explore the effect the new ligand has on the coordination strength and activation of the dinitrogen ligand. The similarity 2 Cy between the hydrido nitrogen complex and RuH(CO)(C P3 ) (48) synthesis meant a similar synthetic procedure was used. P PCy2 E PT N RuH2(N2)(PPh3)3 N H Ru C C THF H Cy2P PCy2 PE 49 Scheme 6.6 H 2 Cy Stirring RuH2(N2)(PPh3)3 (47) with C P3 (46) in THF at room temperature overnight 2 Cy produced a high yield (89%) of RuH(N2)(C P3 ) (49) after workup (Scheme 6.6). 188 References begin on page 200. 2 Cy 2 Cy RuH(N2)(C P3 ) (49) displayed similar solubility properties to RuH(CO)(C P3 ) (48) with the best solubility being observed in warm aromatic solvents. 2 Cy 2 Cy 6.3.4.2 X-ray crystallography of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) 2 Cy Figure 6.3 ORTEP plot (50% thermal ellipsoids) of RuH(CO)(C P3 ) (48) within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 2 Cy Crystals of RuH(CO)(C P3 ) (48) suitable for structural analysis were grown by slow evaporation of a toluene solution under nitrogen (Figure 6.3) and selected bond angles 2 Cy and lengths are given in Table 6.1. Crystals of RuH(N2)(C P3 ) (49) suitable for 189 References begin on page 200. structural analysis were grown by slow evaporation of a toluene solution under nitrogen (Figure 6.4) and selected bond angles and lengths are given in Table 6.2. 2 Cy Table 6.1 Selected bond lengths (Å) and angles (º) for RuH(CO)(C P3 ) (48) C2 –O1 1.160(12) Ru1 –C1 2.290(12) Ru1 –C2 1.881(12) Ru1 –P1 2.326(4) Ru1 –P2 2.283(4) Ru1 –P3 2.367(4) Ru1 –H1 1.59(2) Ru1-C2-O1 178.9(12) C1-Ru1-C2 177.6(5) C1-Ru1-P1 83.4(3) C1-Ru1-P2 83.1(3) C1-Ru1-P3 81.6(3) C1-Ru1-H1 90(3) C2-Ru1-P1 95.6(4) C2-Ru1-P2 96.5(3) C2-Ru1-P3 100.7(4) C2-Ru1-H1 88(3) P1-Ru1-P2 143.09(16) P1-Ru1-P3 103.88(12) P1-Ru1-H1 68(3) P2-Ru1-P3 107.89(16) P2-Ru1-H1 78(3) P3-Ru1-H1 169(3) 2 Cy 2 Cy The geometries of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) are isostructural. Both structures are distorted octahedrons with the hydride and small molecule ligand (carbonyl or nitrogen) in mutually cis coordination sites, and the small molecule ligand trans to the central carbon of the CP3-type ligand. There is only one other structure of a ruthenium complex with a ı-bound CP3-type ligand, t 8 Ru(C(CH2CH2PPh2)3)(H)(CN Bu). The Ru-CCP3 bond length of 48 is significantly 190 References begin on page 200. longer than that of 49, 2.290(12) and 2.215(5) Å respectively. The bond length difference indicates that the nature of the trans ligand has a significant effect on the strength of the ruthenium carbon ı-bond. 2 Cy Figure 6.4 ORTEP plot (50% thermal ellipsoids) of RuH(N2)(C P3 ) (49) within each asymmetric unit. Selected hydrogen atoms have been omitted for clarity. 191 References begin on page 200. 2 Cy Table 6.2 Selected bond lengths (Å) and angles (º) for RuH(N2)(C P3 ) (49) N1 –N2 1.106(6) Ru1 –C1 2.215(5) Ru1 –N1 1.976(5) Ru1 –P1 2.3122(15) Ru1 –P2 2.3003(15) Ru1 –P3 2.3781(15) Ru1 –H1 1.63(5) Ru1-N1-N2 178.7(5) C1-Ru1-N1 177.64(19) C1-Ru1-P1 84.19(15) C1-Ru1-P2 83.29(14) C1-Ru1-P3 82.27(15) C1-Ru1-H1 78(2) N1-Ru1-P1 95.58(13) N1-Ru1-P2 95.71(13) N1-Ru1-P3 100.06(14) N1-Ru1-H1 100(2) P1-Ru1-P2 147.40(6) P1-Ru1-P3 103.79(5) P1-Ru1-H1 75(2) P2-Ru1-P3 104.17(6) P2-Ru1-H1 73(2) P3-Ru1-H1 160(2) 2 Cy The 1.106(6) Å NŁN bond length of RuH(N2)(C P3 ) (49) demonstrates mildly increased activation of the NŁN bond when compared to the bulk of other ruthenium(II) dinitrogen species which have been structurally characterized (see Appendix A2). Mild -1 activation is also confirmed by the 2098 cm ȞNŁN stretch in the IR spectrum of 2 Cy RuH(N2)(C P3 ) (49) which is toward the more activated end of the range of NŁN stretches that have been reported for Ru(II) dinitrogen complexes (Appendix A2). 192 References begin on page 200. 2 Cy 2 Cy 6.3.4.3 NMR spectroscopy of RuH(CO)(C P3 ) (48) and RuH(N2)(C P3 ) (49) 31 1 2 Cy The P{ H} NMR spectrum of RuH(CO)(C P3 ) (48) displays two phosphorus signals, the first as a 2-phosphorus doublet at 69.4 ppm representing the equivalent terminal phosphines of the PE arms and the second as a 1-phosphorus triplet at 56.1 ppm 2 representing the single terminal phosphine of the PT arm, with a mutual JP-P coupling constant of 17 Hz. The metal-bound hydride of 48 appears as a doublet of triplets at 1 -10.31 ppm in the H NMR spectrum, coupling to PT and PE with coupling constants of 77 Hz and 28 Hz, respectively (Figure 6.5). The 13C{1H, 31P} NMR spectrum of 48 displays resonances associated with the carbonyl carbon and the CP3 ligand central carbon as singlets at 203.4 ppm and 66.3 ppm respectively. This information confirms the structure observed in the x-ray crystallography is persistent and stable in solution. 31 1 2 Cy The P{ H} NMR spectra RuH(N2)(C P3 ) (49) displays two phosphorus signals, the first as 2-phosphorus doublet at 61.0 ppm representing equivalent terminal phosphines of the PE arms and the second as a 1-phosphorus triplet at 47.4 ppm representing the 2 single terminal phosphine of the PT arm, with a JP-P coupling constant of 16 Hz between them. The metal-bound hydride of 49 appears as a doublet of triplets at 1 -9.89 ppm in the H NMR spectrum, coupling to PT and PE with coupling constants of 82 Hz and 28 Hz, respectively (Figure 6.6). This information confirms the structure observed in the X-ray crystallography is persistent and stable in solution. 193 References begin on page 200. PE P O 48 T C Ru C H P 2 E JH-PT =77Hz 48 2 JH-PE =28Hz 2 Cy Figure 6.5 1H NMR of RuH(CO)(C P3 ) (48), hydride region. 194 References begin on page 200. PE 49 P N T N Ru C H 2 PE JH-PT =82Hz 49 2 JH-PE =28Hz 2 Cy Figure 6.6 1H NMR of RuH(N2)(C P3 ) (49), hydride region. 2 Cy 6.3.4.4 Attempted reactions of RuH(N2)(C P3 ) (49) 2 Cy RuH(N2)(C P3 ) (49) is a ruthenium(II) complex and therefore has a low overall level of nitrogen activation when compared to ruthenium(0), iron(0), or even iron(II) complexes. The generation of a ruthenium(0) dinitrogen complex utilizing a CP3 ligand is desirable because it would be expected that the dinitrogen activation would be increased by being bound to an electron rich ruthenium(0) complex (see Chapter 5). Any ruthenium(0) complex would also likely be a negatively charged ruthenate 195 References begin on page 200. 2 Cy - complex because of the negative charge on [C P3 ] , requiring a positively charged cation. Work by Peters et al.18 has previously shown that negatively charged iron(0) complexes have significantly increased nitrogen activation, which is assisted by coordination of the alkali metal cation to the terminal nitrogen of the dinitrogen ligand, decreasing the N-N bond length. Two approaches were attempted to synthesize such a ruthenium(0) species from 2 Cy RuH(N2)(C P3 ) (49); (i) deprotonation of the coordinated hydride; and (ii) direct reduction. A number of highly basic reagents were used in an attempt to deprotonate the coordinated hydride, which would result in a formal two electron reduction of the ruthenium center. This base driven reduction has been previously exploited by Field et 19 2 Cy al. to generate iron(0) nitrogen complexes. Treatment of RuH(N2)(C P3 ) (49) with potassium tert-butoxide resulted in no reaction the starting material was unchanged. Treatment with Bu-Li resulted in yellowing of the solution, with the main species by 2 Cy NMR continuing to be RuH(N2)(C P3 ) (49) (Scheme 6.7). PE P T N N Bu-Li Ru No Reaction C H Toluene PE 49 Scheme 6.7 196 References begin on page 200. 2 Cy Direct reduction of RuH(N2)(C P3 ) (49) was attempted by treatment with metallic reducing agents, specifically two equivalents of potassium graphite, or an excess of sodium naphthalenide. In both reactions the starting material persisted in significant amounts and there was no product formed at a level that would allow characterization (Scheme 6.8). PE KC8 P T N N Ru No Reaction C H PE Sodium Naphthalenide 49 Scheme 6.8 2 Cy 6.4 Attempted synthesis and characterization of iron complexes with the C P3 ligand. - 2 Cy Multiple attempts were made to coordinate the C P3 ligand to an iron center, but none were successful in generating a compound which could be fully characterized. 2 Cy A method analogous to that used to produce RuH(N2)(C P3 ) (49) was attempted, and this approach required the synthesis of FeH2(N2)(PPh3)3. While there are descriptions 20 of the synthesis of FeH2(N2)(PPh3)3 within the literature the level of characterization is generally quite poor, rarely extending beyond an IR spectrum as proof of synthesis. Using the method of Borod'ko et al.20a, an amount of the complex previously identified as FeH2(N2)(PPh3)3 was synthesized, through the reaction of FeCl2.4H2O and PPh3 with LiBH4. This complex was unstable in solution, and degraded over time even when 197 References begin on page 200. stored as a solid under nitrogen. This instability prevented the desired reaction with H 2 Cy C P3 (46) from being carried out, as the degradation occurred at a faster reaction rate H 2 Cy than any reaction with C P3 (46) could be observed. Due to this instability it was also not possible to clearly identify whether the complex was indeed FeH2(N2)(PPh3)3 beyond matching the IR signal. - 2 Cy Other approaches to coordination of C P3 to iron revolved around the formation of an H 2 Cy adduct between FeCl2 and C P3 (46) which could then be treated with other reagents H 2 Cy in an attempt to induce complex formation. Stirring FeCl2 and C P3 (46) in THF overnight produced a colourless adduct which was soluble in THF and toluene. This iron-phosphine-adduct was paramagnetic and has not been determined in a crystalline form suitable for structural analysis. At this stage, this material is an adduct of FeCl2 H 2 Cy and C P3 (46) without future characterization. Treatment of the iron-phosphine-adduct with LiAlH4 resulted in precipitation of Fe(s) as a black powder and free ligand precursor, both at room temperature and at -85 °C. Treatment of the iron-phosphine-adduct with two equivalents of K[BEt3H] resulted in precipitation of Fe(s) as a black powder and free ligand precursor at room temperature. Performing the same reaction at -85 °C gave a yellow solution in which the color persisted till the solution was warmed to room temperature at which point precipitation of Fe(s) as a brown powder and ligand precursor were again observed. Treatment of the iron-phosphine adduct with NaBH4 in a mixture of THF and EtOH resulted in precipitation of a colourless solid. This colourless solid then degraded to 198 References begin on page 200. Fe(s) and ligand precursor when an attempt was made to dissolve it toluene. Treatment of the iron-phosphine-adduct with one equivalent of MgMe2 does result in the formation of a colourless product, which has yet to be further characterized. Treatment of the iron-phosphine-adduct with the strong base potassium tert-butoxide gave no reaction. 6.5 Conclusions In this chapter, the new sterically hindered, tripodal tetradentate ligand precursor H 2 Cy C P3 (46) was synthesized and used in the synthesis of a series of ruthenium 2 Cy - compounds utilizing the [C P3 ] ligand. It was found that complexes of the type 2 Cy RuH(L)(C P3 ) (L = CO (48), N2 (49)) could be synthesized by reacting the ligand H 2 Cy precursor C P3 (46) with ruthenium dihydride complexes of the type Ru(H)2(L)(PPh3)3 (L = CO, N2 (47)). This approach provides a new method for direct synthesis of carbon centred podand complexes. Complexes 48 and 49 were characterized by both crystallographically and by multinuclear NMR spectroscopy. Both 48 and 49 proved unreactive in attempts to convert ruthenium to a lower oxidation state, through either direct reduction or through using a strong base to react with the 2 Cy - metal-bound hydride ligand. Attempts to produce iron complexes with the [C P3 ] H 2 Cy ligand through various reactions using the ligand precursor C P3 (46) have so far proved unsuccessful. 199 References begin on page 200. 6.6 References 1. Stoppioni, P.; Mani, F.; Sacconi, L., Inorg. Chim. Acta 1974, 11 227-230. 2. Kuzu, I.; Krummenacher, I.; Meyer, J.; Armbruster, F.; Breher, F., Dalton Trans. 2008, 5836-5865. 3. (a) Barth, A.; Huttner, G.; Fritz, M.; Zsolnai, L., Angew. Chem. 1990, 102 956- 8; (b) Vogel, S.; Barth, A.; Huttner, G.; Klein, T.; Zsolnai, L.; Kremer, R., Angew. Chem. Int. Ed. 1991, 30 303-304; (c) Janssen, B. C.; Asam, A.; Huttner, G.; Sernau, V.; Zsolnai, L., Chem. Ber. 1994, 127 501-6; (d) Janssen, B. C.; Sernau, V.; Huttner, G.; Asam, A.; Walter, O.; Buechner, M.; Zsolnai, L., Chem. Ber. 1995, 128 63-70; (e) Seitz, T.; Asam, A.; Huttner, G.; Walter, O.; Zsolnai, L., Z. Naturforsch., B: Chem. Sci. 1995, 50 1287-306; (f) Urtel, K.; Frick, A.; Huttner, G.; Zsolnai, L.; Kircher, P.; Rutsch, P.; Kaifer, E.; Jacobi, A., Eur. J. Inorg. Chem. 2000, 33-50; (g) Mautz, J.; Heinze, K.; Wadepohl, H.; Huttner, G., Eur. J. Inorg. Chem. 2008, 1413-1422; (h) Mautz, J.; Huttner, G., Eur. J. Inorg. Chem. 2008, 1423-1434. 4. Hendriksen, D. E.; Oswald, A. A.; Ansell, G. B.; Leta, S.; Kastrup, R. V., Organometallics 1989, 8 1153-1157. 5. Joslin, F. L.; Stobart, S. R., J. Chem. Soc., Chem. Commun. 1989, 504-505. 6. (a) Takaoka, A.; Mendiratta, A.; Peters, J. C., Organometallics 2009, 28 3744- 3753; (b) Whited, M. T.; Mankad, N. P.; Lee, Y. H.; Oblad, P. F.; Peters, J. C., Inorg. Chem. 2009, 48 2507-2517; (c) Mankad, N. P.; Whited, M. T.; Peters, J. 200 References begin on page 200. C., Angew. Chem. Int. Ed. 2007, 46 5768-5771; (d) Lee, Y.; Mankad, N. P.; Peters, J. C., Nat. Chem. 2010, 2 558-565. 7. Ciclosi, M.; Lloret, J.; Estevan, F.; Lahuerta, P.; Sanau, M.; Perez-Prieto, J., Angew. Chem. Int. Ed. 2006, 45 6741-6744. 8. Allen, O. R.; Field, L. D.; Magill, A. M.; Vuong, K. Q.; Bhadbhade, M. M.; Dalgarno, S. J., Organometallics 2011, 30 6433-6440. 9. Spatzal, T.; Aksoyoglu, M.; Zhang, L.; Andrade, S. L. A.; Schleicher, E.; Weber, S.; Rees, D. C.; Einsle, O., Science 2011, 334 940. 10. Baumeister, J. M.; Alberto, R.; Ortner, K.; Spingler, B.; Schubiger, P. A.; Kaden, T. A., J. Chem. Soc., Dalton Trans. 2002, 4143-4151. 11. Alberto, R.; Angst, D.; Ortner, K.; Abram, U.; Schubiger, P. A.; Kaden, T. A., New J. Chem. 2007, 31 409-417. 12. Magill, A. M.; Field, L. D., University of New South Wales: 2011. 13. Ahmad, N.; Levison, J. J.; Robinson, S. D.; Uttlky, M. F.; Wonchoba, E. R.; Parshall, G. W., Complexes of Ruthenium, Osmium, Rhodium, and Iridium Containing Hydride Carbonyl, or Nitrosyl Ligands. In Inorg. Synth., John Wiley & Sons, Inc.: 2007; pp 45-64. 14. (a) Ito, T.; Kitazume, S.; Yamamoto, A.; Ikeda, S., J. Amer. Chem. Soc. 1970, 92 3011-16; (b) Knoth, W. H., Jr., J. Amer. Chem. Soc. 1968, 90 7172-3. 15. Eliades, T.; Harris, R. O.; Zia, M. C., J. Chem. Soc. D 1970, 1709. 201 References begin on page 200. 16. Harris, R. O.; Hota, N. K.; Sadavoy, L.; Yuen, J. M. C., J. Organometal. Chem. 1973, 54 259-64. 17. Morton, D.; Cole-Hamilton, D. J.; Utuk, I. D.; Paneque-Sosa, M.; Lopez- Poveda, M., J. Chem. Soc., Dalton Trans. 1989. 18. Mankad, N. P.; Whited, M. T.; Peters, J. C., Angew. Chem., Int. Ed. 2007, 46 5768-5771. 19. Field, L. D.; Guest, R. W.; Turner, P., Inorg. Chem. 2010, 49 9086-9093. 20. (a) Borod'ko, Y. G.; Broitman, M. O.; Kachapina, L. M.; Shilova, A. K.; Shilov, A. E., Zh. Strukt. Khim. 1971, 12 545-6; (b) Sacco, A.; Aresta, M., Chem. Commun. 1968, 1223-1224. 202 References begin on page 200. 7 Summary, Conclusions and Future Work The primary aim of this work was to examine whether a sterically bulky ligand set would enhance the reactivity of dinitrogen complexes of ruthenium and iron towards reaction of the coordinated N2. During the course of this work, a number of new and established sterically bulky multidentate phosphine ligands were produced and their complexes with iron and ruthenium extensively probed. While nitrogen complexes and their chemistry were the main target of this work, the pursuit of new complexes resulted in the production of a range of other novel compounds, including a number of interesting ruthenium hydrides. A suite of iron and ruthenium dinitrogen complexes were produced, but the theory that increased steric bulk on the phosphine ligands would restrict access to the metal centre and enhance reactivity at coordinated dinitrogen was disproven for the specific classes of compounds examined. 3 iPr 7.1 Ruthenium hydride complexes containing P P3 , (1). i 3 iPr The sterically hindered, tripodal tetradentate ligand P(CH2CH2CH2P( Pr2))3, P P3 (1) was synthesized and used in the synthesis of a series of stable ruthenium compounds. 3 iPr + The 5-coordinate chloro-complex [RuCl(P P3 )] (4) was characterised crystallographically and by multinuclear NMR spectroscopy, and low temperature 31P{1H} NMR spectroscopy was used to explore the exchange mechanisms between its various isomers. Complex 4 was reduced with potassium triethylborohydride to 3 iPr produce RuH2(P P3 ) (5). Complex 4 was also reduced with lithium aluminium hydride, followed by reaction with ethanol, to produce the stable hydrido dihydrogen 203 3 iPr + species [Ru(H2)(H)(P P3 )] (6). Complexes 5 and 6 were both fully characterized crystallographically and by multinuclear NMR spectroscopy. + PiPr P Pr iPr i + 2 i 2 2 PT Pr2 iPr Pr P i 2 i 2 Pr2 P H P H PE Cl Ru Ru P PiPr Ru P H P H 2 i H PC PE Pr2 i PiPr PiPr2 Pr2P 2 1 4 5 6 3 iPr The bulky P P3 ligand is amongst the most sterically encumbered PP3-type ligands 3 iPr so far synthesised. While the P P3 (1) ligand, forms stable tetradentate 5- and 6-coordinate complexes with ruthenium, the complexes are hindered and they are fluxional and hemilabile in solution. This behaviour is typical of many complexes where the metal-P bonds are weakened because the bulky ligand substituents restrict the phosphorus donors from gaining optimal access to the metal centre. 3 iPr The synthetic approach to the P P3 (1) ligand is generic and it therefore possible to introduce a range of substituents on the terminal phosphorus using this method. Other bulkier and tailored substituents may permit the chemistry of PP3 metal complexes to be tuned as hemilabile ligands to access catalytic reactivity not possible with stronger phosphine ligand sets. 2 tBu 2 tBu 7.2 Super-hindered Polydentate Polyphosphine Ligands P P3 (10), PhP P2 , 3 tBu (14), P P3 (16) and their Ruthenium(II) Chloride Complexes. t 2 tBu The new sterically hindered ligands P(CH2CH2P Bu2)3 (P P3 , 10), t 2 tBu t 3 tBu PhP(CH2CH2P Bu2)2 (PhP P2 , 14), and P(CH2CH2CH2P Bu2)3 (P P3 , 16) were 204 synthesized and used in the synthesis of the corresponding ruthenium dichloride 2 tBu 2 tBu 3 tBu compounds RuCl2(P P3 ) (18), RuCl2(PhP P2 ) (19) and RuCl2(P P3 ) (20). Complexes 18, 19 and 20 were all characterized by multinuclear NMR spectroscopy, and low temperature 31P{1H} NMR spectroscopy was used to explore the dynamic processes of exchange present in complexes 18 and 19 in solution. Complexes 19 and 20 were both characterized crystallographically. t t P Bu2 P Bu2 P tBu P PtBu t P 2 2 Bu2P tBu P PtBu P P 2 2 t Bu2 10 14 16 t t P Bu2 t tBu P Bu2 tBu P Bu2 2 P 2 Cl P Cl Ru Ru P P Cl P Cl Cl PtBu Ru 2 tBu P t 2 Ph Bu2P Cl 18 19 20 2 tBu 3 tBu The bulky P P3 (10) and P P3 (16) ligands are the most sterically encumbered PP3-type ligands so far synthesized. These ligands appear to be so sterically encumbered that they can only bind to ruthenium through three of the four phosphine donors leaving one of the terminal phosphines as a free pendant arm. All three ligands 10, 14 and 16 provide a highly sterically constrained ligand environment around the metal and this restricts the nature of the other groups that can bind to the metal centre. 205 31 1 2 tBu 2 tBu Solid-state P{ H} NMR spectroscopy of RuCl2(P P3 ) (18), RuCl2(PhP P2 ) (19) 3 tBu and RuCl2(P P3 ) (20) was used to gain insights into the solid state structure of 2 tBu RuCl2(P P3 ) (18) which could not be characterized crystallographically. Comparative 2 tBu solid-state NMR analysis also indicate that the solid state structure of RuCl2(P P3 ) 2 tBu (18) is analogous to that determined by X-ray crystallography for RuCl2(PhP P2 ) (19). 2 tBu 7.3 Ruthenium P P3 (10) hydride complexes 2 tBu The sterically hindered, tridentate ligand P P3 (10) was used in the synthesis of a series of new ruthenium hydride compounds in attempting to synthesize the targeted 2 tBu 2 tBu RuH2(N2)(P P3 ) (26) complex. The reaction of RuCl2(P P3 ) with potassium 2 tBu hydride, sodium borohydride and lithium aluminium hydride produced RuHCl(P P3 ) 2 tBu 2 tBu (21), RuH(BH4)(P P3 ) (22) and RuH(AlH4)(P P3 ) (23) respectively. Further reaction of complex 23 with potassium tert-butoxide and methanol formed 2 tBu 2 tBu K[Ru(H)3(P P3 )] (24) and RuH2(CO)(P P3 ) (25) respectively. The original target 2 tBu 2 tBu complex RuH2(N2)(P P3 ) (26) and its dihydrogen analogue RuH2(H2)(P P3 ) (27) 2 tBu were successfully synthesized by reaction of RuCl2(P P3 ) with sodium in liquid ammonia and work up under a nitrogen or hydrogen atmosphere respectively. The 2 tBu 2 tBu complexes RuHCl(CO)(P P3 ) (28) and RuHCl(N2)(P P3 ) were also produced by the 2 tBu addition of the appropriate gas to RuHCl(P P3 ) (21). 206 t t P Bu2 Bu2P H t P P Bu2 P Ru P Cl tBu P PtBu t 2 2 Bu2 10 21 - tBu P H tBu P H K+ t 2 2 Bu2P H P PtBu P PtBu P PtBu Ru 2 Ru 2 Ru 2 P H P H P H tBu H tBu H t 2 2 Bu2 H B H Al H H H 22 23 24 O N t t tBu P H H Bu2P C Bu2P N 2 P PtBu P PtBu P PtBu Ru 2 Ru 2 Ru 2 P H P H P H t t tBu H Bu2 H Bu2 H 2 25 26 27 O t t Bu2P C Bu2P Cl P PtBu P PtBu Ru 2 Ru 2 P Cl P N t t N Bu2 H Bu2 H 28 29 Complexes 21-28 were characterized by multinuclear NMR Spectroscopy, with complexes 21, 22, 23, 24, 25, 26, 28, and 29 also structurally characterized by X-ray 2- crystallography. To my knowledge, 23 is the first reported structure with an Al2H8 bridge to be observed on ruthenium, and 24 is the second structurally characterized ruthenium(II) trihydride anion and the first with alkyl rather than aryl phosphines. The stability of these usually unstable ruthenium hydride geometries is attributed to the protective nature of the sterically bulky phosphine ligand. Complex 26 is also the second ruthenium dinitrogen dihydride to be structurally characterized, however any 207 further reactions of 26 appeared to displace the coordinated dinitrogen rather than react with it. 2 Cy 7.4 Iron and Ruthenium Dinitrogen Complexes of P P3 (30) 2 Cy The iron(0) and ruthenium(0) dinitrogen complexes of the P(CH2CH2PCy2)3 (P P3 (30)) ligand could be successfully synthesized, but the increased steric bulk doesn't appear to change the reactivity of these complexes when compared to that of their less 2 iPr 2 Me sterically bulky analogues M(N2)(P P3 ) (M = Fe, Ru) and Fe(N2)(P P3 ). Treatment 2 Cy + with acid generated the hydrido nitrogen species [FeH(N2)(P P3 )] (38) and 2 Cy + [RuH(N2)(P P3 )] (39) rather than forcing reaction with the coordinated dinitrogen ligand. + + PCy2 PCy PCy2 Cy2 2 P Cl Cl Ru P Fe P P Cy2P PCy2 PCy PCy2 PCy2 2 30 31 32 + PCy2 PCy2 PCy2 PCy2 N N N N N N Cl Fe Ru Fe Ru P P P P PCy2 PCy2 PHCy2 PCy2 PCy2 PCy2 PCy2 PCy2 33 34 35 36 + + HCy PCy2 PCy PCy 2 Cy2 2 Cy2 2 P P N P N H N N Fe Fe Ru P H P H P H PCy 2 PCy2 PCy2 37 38 39 208 The increased steric bulk of the terminal phosphines probably increases the rate that the phosphine arms disassociation from the complex, leaving the iron(0) or ruthenium(0) 2 Cy centre exposed to protonation. Analysis of the exchange rates of the FeH2(P P3 ) (37) complex showing a faster rate of exchange between isomers in solution than the less sterically bulky analogue FeH2(PP3) (PP3 = P(CH2CH2PMe2)3), lends support to this theory. 2 Cy The extra steric bulk of the P P3 ligand allowed the generation of stable iron(I) and 2 Cy + 2 Cy ruthenium(I) species [Fe(N2)(P P3 )] (35) and RuCl(P P3 ) (36), analogues of which with less bulky phosphines had not previously been identified or had not been stable. The extra steric bulk likely conveys additional stability by inhibiting the disproportionation pathways which usually decompose iron(I) and ruthenium(I) species. H 2 Cy 7.5 C P3 (46) Synthesis and Complexes The new sterically hindered, tripodal tetradentate carbon-centred ligand precursor H 2 Cy C P3 (46) was synthesized and used in the synthesis of a series of ruthenium 2 Cy - 2 Cy compounds utilizing the [C P3 ] ligand. Complexes of the type RuH(L)(C P3 ) (L = H 2 Cy CO (48), N2 (49)) were synthesized by reacting the ligand precursor C P3 (46) with ruthenium dihydride complexes of the type Ru(H)2(L)(PPh3)3 (L = CO, N2 (47)). This approach provides a new method for direct synthesis of carbon centred podand complexes. Complexes 48 and 49 were characterized by both crystallographically and by multinuclear NMR spectroscopy. Both 48 and 49 proved unreactive in attempts to convert ruthenium to a lower oxidation state, through either direct reduction or through using a strong base to react with the metal-bound hydride ligand. Attempts to produce 209 2 Cy - iron complexes with the [C P3 ] ligand through various reactions using the ligand H 2 Cy precursor C P3 (46) have so far proved unsuccessful. Cy PCy Cy PCy PCy2 2 2 2 2 P O P N C N H Ru Ru C C H C H Cy2P PCy2 PCy2 PCy2 46 48 49 7.6 Future directions 7.6.1 Ligand design Further development of PP3-type ligands for use in iron and ruthenium dinitrogen complexes would best focus on PP3-type ligands with substituents on the terminal phosphines other than alkyl or aryl groups. With the addition of this work, there is now a library of PP3-type ligands with alkyl substituents with a variety of different steric properties which can be accessed. Thus moving to change the electronic properties of the complexes by using substituents such as methoxy or ethoxy groups would be more likely to lead to nitrogen complexes with new properties (Figure 7.1 A). PR2 P(OR)2 PR2 H C H P Si R2P PR2 (RO)2P P(OR)2 R2P PR2 A B C Figure 7.1 Proposed future ligand architectures. 210 Other ligand development which would be promising would be to incorporate non-phosphorus donors as the donor trans to the dinitrogen ligand, because the level of nitrogen activation is most influenced by the donor trans to the nitrogen ligand. The work on CP3 type ligands developed in Chapter 6, can be extended to incorporate H 2 Cy the ligand precursor C P3 (46) onto iron centres and form a wider range of ruthenium complexes. Other mixed donor podand ligands which would give desirable iron and ruthenium dinitrogen complexes would be CP3 complexes incorporating aryl ligand backbones (Figure 7.1 B) and SiP3 complexes incorporating alkyl ligand backbones (Figure 7.1 C). Both of these ligand systems have not yet been developed and would have ligand precursors that should be easier to deprotonate and hence provide a more direct route metal complexes than was observed for the alkyl CP3 systems described in Chapter 6. 7.6.2 Nitrogen complex reactivity 2 Cy Fe(N2)(P P3 ) (33) is the most activated dinitrogen complex produced within this thesis and so remains the most likely complex on which dinitrogen functionalization could be achieved. 2 Cy 2 Cy 2 Cy + While Fe(N2)(P P3 ) (33) and Ru(N2)(P P3 ) (34) convert to [FeH(N2)(P P3 )] (38) 2 Cy + and [RuH(N2)(P P3 )] (39) when treated with a weak proton source like lutidinium tetrafluroborate, they both pass through an intermediate complex which is yet to be characterized. These intermediate complexes form and are quickly converted to dinitrogen hydrides at room temperature but persist at temperatures below -50 ºC. The ruthenium intermediate complex is green, while the iron complex is a bright purple. 211 Further work to characterize these complexes could yield a better understanding of the protonation process and why interaction with the metal center seems to be preferential in these complexes. Other reactions with dinitrogen complexes which may yield interesting results would 2 Cy 2 Cy + include reacting Fe(N2)(P P3 ) (33) or [Fe(N2)(P P3 )] (35) with an organic azide to observe the reactivity and see if nitride formation can be observed and characterized. + PCy2 PCy2 PCy2 N N N N N N Fe Ru Fe P P P PCy2 PCy2 PHCy2 PCy2 PCy2 PCy2 33 34 35 7.6.3 Solid state NMR Solid state 31P NMR, as utilized in Chapter 3 would be useful in characterizing metal phosphine complexes used as catalysts bound to solid supports. The use of solid-state NMR was only examined briefly in this thesis but clearly has an emerging role in the characterisation or organometallic complexes. Traditional homogeneous catalysts are increasingly being tethered to surfaces to assist in purification and catalyst retrieval. A significant impediment to this process is characterizing these complexes as solution NMR is no longer available when working with a tethered complex. An extension of the basic solid-state NMR analysis used in this work would be to develop an effective 2D phosphorus-phosphorus spin diffusion experiment. A P-P spin diffusion experiment, calibrated against known complexes would potentially provide information about the distances between different phosphorus 212 atoms. With enough P-P distances measured it would be possible to glean information about the geometry of the metal complex when it is tethered to a surface. 213 8 Experimental 8.1 General Procedures All manipulations were carried out using standard Schlenk and glovebox techniques under a dry atmosphere of nitrogen. 8.1.1 Solvent Purification Solvents were dried and distilled under nitrogen or argon using standard procedures1 and stored in glass ampoules fitted with teflon taps. Benzene and hexane were dried over sodium wire before distillation from sodium/benzophenone. Ethanol was distilled from diethoxymagnesium and acetone was distilled from calcium hydride. Tetrahydrofuran (THF, inhibitor free), diethyl ether, toluene, dichloromethane and pentane were dried and deoxygenated using a Pure Solv 400-4-MD (Innovative Technology) solvent purification system. 8.1.2 Reagent Sources Starting materials were obtained from Aldrich and/or Merck and used without further purification unless stated otherwise. Tris(3-hydroxypropyl)phosphine (80%) was purchased from Strem Chemicals and used as supplied. lutidinium tetrafluoroborate,2 Dichlorotris(triphenylphosphine)ruthenium(II),3 trivinylphosphine,4 diethoxyphenylphosphine and diisopropylphosphine 5 were prepared by literature methods. Potassium graphite,6 and potassium triethylborohydride,7 were prepared by literature methods by Dr. Hsiu Lin Li (University of New South Wales) and generously provided for 8 use in this work. RuH2(CO)(PPh3)3, was prepared by literature methods by Dr. Alison Magill (University of New South Wales) and generously provided for use in this work. 220 References begin on page 274. LiAlH4 was purchased from Aldrich and a concentrated solution in THF prepared by soxhlet extraction. Phosphorus tribromide, phosphorus trichloride and tert-butyl chloride were purchased from Aldrich and freshly distilled prior to use. Potassium hydride was purchased from Aldrich and the oil washed out with hexane prior to use. Magnesium was purchased from Aldrich and burnished prior to use by vigorous stirring by a magnetic stirrer bar overnight under vacuum. The bulk compressed gases argon (>99.99%) and nitrogen (99.5%) were obtained from the British Oxygen Company (BOC) and used without further purification. 8.1.3 Acid/base titration Measurement of the concentration of grignard reagents was performed through acid/base titration. A 3 mL aliquot of the grignard to be measured was added very slowly to a flask containing mixture of diethyl ether (10 mL) and water (10 mL). The resulting solution was then titrated against a standard solution of HCl, using phenolphthalein as an indicator. 8.1.4 Software Dynamic NMR simulations were performed using WinDNMR: Dynamic NMR Spectra for 9 Windows. T1 calculations were performed using the curve fitting applications of Origin 8.1 by OriginLab.10 8.1.5 Infrared Spectra Infrared spectra were recorded using a Nicolet Avatar 360 FT-IR E.S.P or an Avatar 320 FT-IR spectrometer with samples prepared as a fluorolube mull. 221 References begin on page 274. 8.1.6 Microanalysis Microanalyses were carried out at the Campbell Microanalytical Laboratory, University of Otago, New Zealand. 8.2 NMR Spectroscopy 8.2.1 Deuterated Solvent Purification Deuterated solvents were purchased from Aldrich, Merck and Cambridge Isotope Laboratories. THF-d8 and benzene-d6 were dried over and distilled from sodium/benzophenone. Acetone-d6 was dried and distilled from calcium sulfate and stored over activated molecular sieves. Dichloromethane-d2 was dried and distilled from activated molecular sieves and stored over molecular sieves. Chloroform-d1 and D2O were used as received. All deuterated solvents, excepting chloroform-d1 and D2O, were vacuum distilled immediately prior to use unless otherwise stated. 8.2.2 Referencing NMR Spectra All NMR spectra were recorded at 298 K, unless stated otherwise. 1H and 13C{1H} NMR spectra were referenced to residual solvent resonances. 31P{1H} NMR spectra were referenced to external neat trimethyl phosphite at 140.85 ppm. Solid state 31P{1H} NMR spectra were referenced to external ammonium dihydrogen phosphate (ADP) (į = 1.0 ppm). 15N{1H} and 15N NMR spectra were referenced to external neat aniline at 56.5 ppm. 222 References begin on page 274. 8.2.3 Air sensitive sample preparation Air sensitive NMR samples were prepared in an argon- or nitrogen-filled glovebox or on a high vacuum line by vacuum transfer of solvent into an NMR tube fitted with a concentric Teflon valve. 8.2.4 NMR Spectrometers 1H, 13C{1H} and 31P{1H} spectra were recorded on Bruker DPX300, Avance III 400, Avance III 500, Avance III 600 or Avance III 700 NMR spectrometers operating at 300.3, 400.13, 500.13, 600.13, and 700.13 MHz for 1H, 100.61 or 150.92 MHz for 13C{1H}, 121.49, 161.98, 202.49, and 242.95 MHz for 31P{1H}, and 40.6 MHz for 15N{1H}, respectively. All NMR spectra were recorded at 298 K, unless stated otherwise. Solid state NMR, 31P{1H} and PDSD spectra were recorded on an Avance III 300 Bruker NMR spectrometer equipped with an Oxford 300 Magnet and a 2-channel 2.5 mm probe head. Samples were spun at 25 kHz MAS at the temperatures described. 8.2.5 NMR Spectroscopy with in machine photolysis NMR photolysis was performed with the assistance of Dr. Graham Ball (University of New South Wales) and his experimental set up which is described below. When monitoring the photolysis with NMR spectroscopy, the light source was a 248 nm KrF excimer laser (GAM EX5-500, GAM Laser Inc. Orlando, FLA). The light from the laser is directed horizontally via two prisms in an optics box to a point above the centre of the bore of the magnet of the 600 MHz NMR instrument. At this point, a long focal length (ca 1 m) lens focuses the beam via a third prism that directs the light vertically down the bore of the magnet on to the top of a 9 cm long, 4 mm OD quartz pipe. This pipe directs the light into 223 References begin on page 274. the top of the NMR solution contained in a short screw-cap NMR tube fitted with an O-ring around the quartz pipe. The design is similar to that of Hore and co-workers.11 8.3 Mass Spectrometry High resolution mass spectrometry was carried out at the Bioanalytical Mass Spectrometry Facility within the Analytical Centre of the University of New South Wales on an Orbitrap LTQ XL (Thermo Fisher Scientific, San Jose Ca, USA) ion trap mass spectrometer using a nanospray ionization source. 8.4 X-ray Crystallography Single crystal X-ray analyses were performed by either Dr Mohan Bhadbhade of the Mark Wainwright Analytical Facility at The University of New South Wales or by the author, with the majority of structures being a collaborative effort between the two. Excepting those structures obtained at the Australian Synchrotron, the following procedure was followed. Single crystals were attached, with Exxon Paratone-N, to a short length of fiber supported on a thin piece of copper wire inserted in a copper mounting pin. The crystal was quenched in a cold nitrogen gas stream from an Oxford Cryosystems Cryostream. A Bruker kappa APEXII area detector diffractometer employing graphite monochromated Mo-KĮ radiation generated from a fine focus sealed tube was used for the data collection. The data integration and reduction were undertaken with APEX2,1212 and subsequent computations were carried out with the X-Seed1313 graphical user interface. The structures were solved by direct or Patterson methods with SHELXS-9714 and extended and refined with SHELXL-97.1414 The non-hydrogen atoms in the asymmetric unit were 224 References begin on page 274. modeled with anisotropic displacement parameters. A riding atom model with group displacement parameters was used for the hydrogen atoms. All calculations were performed using the crystallographic and structure refinement data summarized in Appendix A1. The following sections outline the specific experimental procedures undertaken in this work. 8.5 Chapter 2 Experimental i 3 iPr 8.5.1 Synthesis of P(CH2CH2CH2P Pr2)3, P P3 (1) i Pr2 3 iPr P P P3 (1) was prepared by the nucleophilic substitution of bromide in i P P Pr2 tris(3-bromopropyl)phosphine with lithium diisopropylphosphide i Pr2P following a modified version of the method reported by Guest.15 1 8.5.1.1 P(CH2CH2CH2Br)3 (2). Br Phosphorus tribromide (4.5 mL, 0.048 mol) was added drop wise to a P Br stirring suspension of tris(3-hydroxypropyl)phosphine (7.2 g, 0.035 mol) Br in DCM (30 mL) under nitrogen. The reaction mixture was stirred at 2 room temperature for 18 hours. Saturated aqueous sodium carbonate solution (approx. 30 mL) was added to the reaction mixture until all effervescence ceased. The organic layer was separated and dried over anhydrous sodium sulfate. The solution was filtered and the solvent was removed under reduced pressure to give tris(3-bromopropyl)phosphine (2) as a clear liquid (10.0 g, 73%). The crude P(CH2CH2CH2Br)3 was used immediately in the next step without further purification. 225 References begin on page 274. 31 2 P NMR (162 MHz, benzene-d6): G -34.1 (1P, h, JP-H = 7 Hz). 1 31 H{ P} NMR (400 MHz, benzene-d6): į 2.99 (6H, m, CH2Br); 1.56 (6H, m, PCH2); 1.06 (6H, m, CH2CH2CH2). 13 1 3 C{ H} NMR (101 MHz, benzene-d6): į 34.7 (d, JC-P = 14 Hz, CH2Br); 29.4 (d, 1 2 JC-P = 16 Hz, PCH2); 25.5 (d, JC-P = 15 Hz, CH2CH2CH2). i 8.5.1.2 LiP Pr2 (3). Lithium phosphide was prepared following a modified method by P Fryzuk et al.16 n-Butyllithium (1.5 M in hexane, 50 mL, 0.097 mol) was Li added to diisopropylphosphine (8.3 g, 0.070 mol) in THF (40 mL) with 3 stirring. This procedure resulted in a bright yellow solution which was used directly in the next step. 3 iPr 8.5.1.3 P P3 (1). The lithium diisopropylphosphide solution from the previous step iPr P 2 (Section 8.5.1.2) was added to a stirring solution of tris(3- i P P Pr2 bromopropyl)phosphine (10 g, 0.023 mol) in THF (approx. 100 mL). i Pr2P The reaction mixture was left to stir at room temperature for 18 hours. 1 The solvent was removed under reduced pressure and benzene (20 mL) was added, followed by deaerated water (30 mL) which was added with care at 0°C until all excess lithium phosphide had been destroyed. Benzene (10 mL) was added and the mixture was 226 References begin on page 274. stirred for 2 hours. The organic layer was decanted, dried over anhydrous sodium sulfate and filtered to give a yellow solution. The solvent was removed under reduced pressure and the resulting yellow oil was heated under vacuum (0.4 mbar) at 100°C to remove volatile byproducts, leaving tris(3-diisopropylphosphinopropyl)phosphine (1) as a yellow oil (9.0 g, 18 mmol, 51% from tris(3-hydroxypropyl)phosphine). 31 1 i P{ H} NMR (162 MHz, benzene-d6): G 1.9 (3P, s, P Pr2); -34.7 (1P, s, P(CH2)3). 1 31 H{ P} NMR (400 MHz, benzene-d6): į 1.75 (6H, m, CH2CH2CH2); 1.58 (6H, m, 3 3 CH(CH3)2); 1.53 (6H, m, PCH2); 1.42 (6H, t, JH-H = 8 Hz, PCH2); 1.05 (18H, d, JH-H = 3 7 Hz, CH(CH3)2); 1.03 (18H, d, JH-H = 7 Hz, CH(CH3)2). 13 1 C{ H} NMR (101 MHz, benzene-d6): į 29.8 (dd, JC-P = 12 Hz, 15 Hz, PCH2); 25.4 (dd, JC-P = 20 Hz, 14 Hz, CH2CH2CH2); 24.1 (dd, JC-P = 20 Hz, 10 Hz, PCH2); 23.7 (d, 1 2 2 JC-P = 14 Hz, CH(CH3)2); 20.4 (d, JC-P = 16 Hz, CH(CH3)2); 19.0 (d, JC-P = 10 Hz, CH(CH3)2). HRMS (EI) m/z: [M+H]+ 509.3716 (calc. 509.3724) 3 iPr 8.5.2 Synthesis of [RuCl(P P3 )][BPh4] (4[BPh4]). i + 3 iPr PT Pr2 Tris(3-diisopropylphosphinopropyl)phosphine P P3 (1) i Pr2 PE Cl Ru (456 mg, 0.896 mmol) was added to a brown solution of i PC PE Pr2 dichlorotris(triphenylphosphine)ruthenium(II) (860 mg, 4 227 References begin on page 274. 0.896 mmol) in THF (approx. 30 mL) resulting in an immediate color change to green. A stoichiometric amount of sodium tetraphenylborate (306 mg, 0.894 mmol) was added and the solution slowly turned red with stirring. After 3 hours, the solvent was removed under reduced pressure to give a pink solid which was recrystallized twice from THF layered with pentane (300 mg, 53%). Anal Found: C 63.71, H 8.27 C51H80BClP4Ru (MW 964.41) requires C 63.52, H 8.36%. 31 1 2 P{ H} NMR (162 MHz, THF-d8): G 25.7 (3P, br, PE/T); 14.2 (1P, q, JP(C)-P(B/P) = 36.4 Hz, PC). 31 1 P{ H} NMR (243 MHz, 177.6 K, dichloromethane-d2): G 75.1 (Isomer-2,1P, m, PB); 72.0 2 2 (Isomer-1, 1P, m, PB); 15.4 (Isomer-2, 1P, ddd, JP(B)-P(D) = 45 Hz, JP(A)-P(D) = 32 Hz, 2 2 JP(C)-P(D) = 32 Hz, PD); 14.0 (Isomer-1, 1P, dt, m, PD); 4.1 (Isomer-1, 1P, dm, JP(A)-P(C) = 2 2 2 227 Hz, PA); 2.3 (Isomer-2, 1P, ddd, JP(A)-P(C) = 234 Hz, JP(A)-P(D) = 31 Hz, JP(A)-P(B) = 18 2 2 2 Hz, PA); -4.3 (Isomer-2, 1P, ddd, JP(A)-P(C) = 234 Hz, JP(A)-P(D) = 31 Hz, JP(A)-P(B) = 29 Hz, 2 PC); -8.1 (Isomer-1, 1 P, dm, JP(A)-P(C) = 227 Hz, PC) 1 H NMR (400 MHz, THF-d8): G 7.29 (8H, m, BPhortho); 6.86 (8H, m, BPhmeta); 6.72 (4H, 3 m, BPhpara); 2.64 (6H, sep, JH-H = 6.9 Hz, CH(CH3)2); 1.96 (6H, m, CH2CH2CH2); 1.83 (6H, m, PE/TCH2); 1.39 (18H, d, CH(CH3)); 1.12 (18H, d, CH(CH3)); 1.06 (6H, m, PCCH2). 13 1 C{ H} NMR (101 MHz, THF-d8): į 165.6 (m, BPhipso); 137.6 (s, BPhortho); 126.1 (m, BPhmeta); 122.2 (s, BPhpara); 30.8 (m, CH(CH3)2); 29.1 (m, PE/TCH2); 26.7 (m, CH2CH2CH2); 21.3 (s, CH(CH3)); 20.9 (s, CH(CH3)); 20.6 (m, PCCH2). 228 References begin on page 274. 3 iPr 8.5.3 Synthesis of Ru(P P3 )H2 (5). A suspension of potassium triethylborohydride (0.068 g, PiPr2 3 i iPr2 0.49 mmol) and [RuCl(P P 3)][BPh4] (4[BPh4]) (0.22 g, 0.23 P H Ru P H mmol) was stirred in toluene (10 mL) overnight. The color of PiPr2 the pink suspension changed to a faint yellow. The suspension was filtered through celite and the solvent was removed under 5 3 iPr reduced pressure to give Ru(P P3 )H2 (5) as a white crystalline powder (0.101 g, 0.165 mmol, 72 % yield). Crystals suitable for X-ray diffraction were grown by slow evaporation of a THF solution under an atmosphere of nitrogen. Anal Found: C 52.92, H 10.51 C27H62P4Ru (MW 611.75) requires C 53.01, H 10.22. 31 1 2 P{ H} NMR (121.49 MHz, benzene-d6): G 49.2 (2P, dd, JP(E)-P(C) = 28.5 Hz, 2 2 JP(E)-P(T) = 18.5 Hz, PE); 28.5 (1P, dt, JP(T)-P(C) = 28.5 Hz, PT); 0.4 (1P, dt, PC). 1 H NMR (400 MHz, toluene-d8): G 2.2-2.0 (2H, m, CH(CH3)2); 2.0-1.9 (4H, m, CH(CH3)2); 1.9-1.8 (6H, m, CH2); 1.8-1.7 (2H, m, CH2); 1.7-1.6 (4H, m, CH2); 1.5 (2H, m, CH2); 1.45-1.35 (4H, m, CH2); 1.3-1.15 (24H, m, CH(CH3)2); 1.15-1.05 (12H, m, 2 2 2 CH(CH3)2); -9.43 (1H, dtdd, JH-P = 59.6 Hz, JH-P = 24.2 Hz, JH-P = 18.8 Hz 2 2 2 2 JH-H = 6.2 Hz, RuH); -12.50 (1H, dtdd, JH-P = 63.2 Hz, JH-P = 34.0 Hz, JH-P = 15.0 Hz, RuH). 229 References begin on page 274. 13 1 C{ H} NMR (126 MHz, THF-d8): G 33.4 (s, CH(CH3)2) ; 33.3 (s, CH(CH3)2); 31.4 (dd, JC-P = 3.5 Hz, JC-P = 18 Hz, PCH2); 30.2 (t, JC-P = 16 Hz, PCH2); 30.0 (t, JC-P = 3.7 Hz, CH2CH2CH2); 29.8 (q, JC-P = 9 Hz, PCH2); 23.8 (t, JC-P = 4.7 Hz, CH2CH2CH2); 23.2 (d, JC-P = 5 Hz, CH(CH3)2); 22.9 (dd, JC-P = 11 Hz, JC-P = 7 Hz, PCH2); 21.2 (s, CH(CH3)2); 20.5 (s, CH(CH3)2); 20.1 (s, CH(CH3)2); 20.0 (s, CH(CH3)2); 18.8 (s, CH(CH3)2) 3 iPr 8.5.4 Synthesis of [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]). A concentrated solution of LiAlH4 in THF was added dropwise + PiPr2 iPr2 3 iPr P H to a solution of [RuCl(P P3 )][BPh4] (4[BPh4]) (0.16 g, Ru P H H 0.16 mmol) in THF (3 mL) until there was a color change from PiPr2 pink to colorless with a white suspension. Ethanol was added 6 carefully, dropwise, until effervescence had ceased (about four drops) and the color of the reaction mixture had turned to orange, then an additional four drops of ethanol was added. The reaction mixture was filtered through celite, and the solvent removed under reduced pressure. The orange powder was washed with pentane (10 mL) and dried under vacuum to 3 iPr give [Ru(H2)(H)(P P3 )][BPh4] (6[BPh4]) (0.050 g, 0.051 mmol, 33% yield). Anal Found: C 65.80, H 8.98 C51H83BP4Ru.C4H8O (MW 1004.10) requires C 65.79, H 31 1 2 9.13. P{ H} NMR (203 MHz, THF-d8): G 24.7 (3P, s br, PA/B/C); 5.4 (1P, q, JP-P = 37.5 Hz, PD). 230 References begin on page 274. 31 1 2 P{ H} NMR (203 MHz, THF-d8, 180K): G 31.3 (1P, d br, JP-P = 185 Hz, PA); 21.3 (1P, d 2 br, JP-P = 185 Hz, PB); 13.7 (1P, s br, PC); 4.3 (1P, s br, PD). 1 H NMR (400 MHz, THF-d8): G 7.20 (8H, m, BPhortho); 6.82 (8H, m, BPhmeta); 6.68 (4H, m, BPhpara); 2.1-1.9 (12H, m, CH(CH3)2/CH2); 1.9-1.8 (6H, m, CH2); 1.65-1.55 (6H, m, CH2); 1.25-1.05 (36H, m, CH(CH3)2); -8.57 (3H, s br, Ru(H2)(H)). 1 H NMR (600 MHz, THF-d8, 195K, high field only): G -7.44 (2H, s br, Ru(H2)); -10.29 2 2 (1H, dt br, JH-P = 57 Hz, JH-P = 32 Hz, Ru(H)). 13 C{1H} NMR (151 MHz, THF-d8): G 165.1 (m, BPhipso); 137.0 (s, BPhmeta); 125.4 (m, 1 BPhortho); 121.6 (s, BPhpara); 30.2 (s br, CH(CH3)2); 29.0 (d, JC-P = 32 Hz, PE/TCH2); 25.9 (m, PCCH2); 21.1 (s, CH2CH2CH2); 19.8 (s, CH(CH3)2); 19.2 (s, CH(CH3)2). 8.6 Chapter 3 Experimental t 8.6.1 Synthesis of Di(tert-butyl)phosphine, Bu2PH (7) Di(tert-butyl)phosphine was prepared by the reduction of P di(tert-butyl)chlorophosphine by lithium aluminium hydride17 following the H synthesis of di(tert-butyl)chlorophosphine by the treatment of phosphorus 7 trichloride by two equivalents of tert-butylmagnesium chloride. 8.6.1.1 Tert-butylmagnesium chloride, tBuMgCl (8) Tert-butylmagnesium chloride was prepared by the insertion of magnesium MgCl into the carbon-halogen bond of tert-butyl chloride following the method of Starowieyski et al.18 A portion (8.5 mL of freshly distilled tert-butyl chloride 8 231 References begin on page 274. (total 83.5 g, 0.768 mol) was added to a suspension of burnished magnesium turnings (24.01 g, 0.9879 mol) in diethyl ether (500 mL). Stirring the mixture activated the Grignard reaction and resulted in the solvent refluxing and a color change of the reaction mixture to black. The remaining tert-butyl chloride was added from a dropping funnel over two hours at a rate to maintain a gentle reflux. Once addition was completed, the solution was refluxed for thirty minutes, then allowed to cool to room temperature. The cooled solution was filtered and a small portion tested by acid/base titration to determine the concentration. A concentration of 0.949 M of tert-butylmagnesium chloride solution (500 mL), which was used directly in the next step. t 8.6.1.2 Di(tert-butyl)chlorophosphine, Bu2PCl (9) Di(tert-butyl)chlorophosphine was prepared by the nucleophilic substitution of phosphorus trichloride by the Grignard reagent P Cl tert-butylmagnesium chloride following the method of Hofmann et al.19 A 9 large flask was charged with phosphorus trichloride (30.5 g, 0.222 mol) and diethyl ether (500 mL) under a nitrogen atmosphere. The flask was fitted with a mechanical stirrer and cooled on an ice/salt bath. Tert-butylmagnesium chloride (500 mL, 0.949 M, 0.474 mol) was added to the stirred and cooled solution over a period of four hours, then stirred overnight. The solution was refluxed for thirty minutes while stirring. Dioxane (160 mL) was added and the solution was refluxed for another thirty minutes. The resulting solution was gravity filtered, and the filtrate was fractionally distilled with 232 References begin on page 274. collection of the fraction at 50 °C at 30 torr yielding di(tert-butyl)chlorophosphine (9) (8.68 g, 48.0 mmol, 22%). 31 1 P{ H} NMR (121.5 MHz, CDCl3): G 146.6 (1P, s). 1 3 H NMR (300 MHz, CDCl3): G 1.18 (18H, d, JH-P = 12 Hz) t 8.6.1.3 Di(tert-butyl)phosphine, Bu2PH. (7) Di(tert-butyl)phosphine was prepared by the reduction of di(tert-butyl)chlorophosphine by lithium aluminium hydride following the P H method of Timmer et al.17 A solution of di(tert-butyl)chlorophosphine 7 (15.0 g, 83.0 mmol) in a diethyl ether solution (30 mL) was added dropwise over a period of thirty minutes to a suspension of lithium aluminium hydride (3.45 g, 90.9 mmol) in diethyl ether (75 mL) chilled in an ice bath. The mixture was refluxed for one hour then allowed to cool to room temperature. Solid NaSO4·10H2O (5.0 g, 17 mmol) was added and the mixture was stirred for one hour. The solution was filtered and the filtrate was fractionally distilled under nitrogen. The fraction collected at 60-65 °C at 20 torr yielded di(tert-butyl)phosphine (9.70 g, 66.3 mmol, 80 %) 31 1 P{ H} NMR (121.5 MHz, diethyl ether/C6D6): G 20.3 (1P, s). 1 1 H NMR (300 MHz, diethyl ether/C6D6): G 3.14 (1H, d br, JH-P = 200 Hz), 1.16 (18 H, d, 3 JH-P = 11 Hz). 233 References begin on page 274. t 8.6.2 Synthesis of tris(2-di(tert-butyl)phosphinoethyl)phosphine, P(CH2CH2P Bu2)3, 2 t P P3 Bu. (10) Tris(2-di(tert-butyl)phosphinoethyl)phosphine was prepared by the t P Bu2 base catalysed addition of di(tert-butyl)phosphine to P tBu P PtBu trivinylphosphine in a method modified from that of Morris et al. 2 2 used in the synthesis of analogous tripodal tetradentate phosphine 10 ligands.20 8.6.2.1 Vinylmagnesium bromide, CH2CHMgBr. (11) Vinyl bromide (50.6 g, 473 mmol) was condensed into THF (100 mL) MgBr cooled at 0qC. An initial aliquot (10 mL) of the vinyl bromide solution was added to a stirred suspension of magnesium turnings (10.0 g, 411 mmol) in 11 THF (150 mL). The reaction was initiated by addition of a crystal of iodine and application of heat. After the reaction had commenced, the remainder of the solution was added dropwise at a rate which maintained a moderately vigorous reflux. On completion of the reaction the magnesium turnings were consumed leaving a brown solution of vinyl magnesium bromide in THF. This solution was refluxed for 30 mins with a needle vent above the condenser to remove any excess vinyl bromide. This solution of vinyl magnesium bromide was used directly in the future steps without further purification (§1.6 M, 250 mL). 8.6.2.2 Trivinylphosphine, P(CHCH2)3. (12) In a method modified from that of Maier et al.,4 trimethyl phosphite (6.60 mL, 6.94 g, 56.0 mmol) was added dropwise over a period of 15 min to P 234 References begin on page12 274. a THF solution of vinyl magnesium bromide (from Section 8.6.2.1) at 0qC. During the course of the reaction the color of the solution changed from brown to yellow. The solution was allowed to return to room temperature before the addition of diethyl ether (150 mL) and subsequently 1,4-dioxane (19.5 mL, 228 mmol) resulting in the formation of a white precipitate. The solution was filtered and then distilled yielding 2 fractions, the first fraction between 46-56qC at atmospheric pressure and a subsequent fraction at room temperature at 75 torr. The first fraction was solvent only and discarded. The second fraction was a solution of trivinylphosphine in THF/diethyl ether, the concentration of which was determined by 1H NMR spectroscopy by careful integration against a cyclooctadiene internal standard. This solution was used directly without further purification. 31 1 P{ H} NMR (162 MHz, THF/diethyl ether/benzene-d6): G -19.8 (1P, s). 8.6.2.3 Lithium Diisopropylamide, LiN(CH(CH3)2)2. (13) Diisopropylamine (7.0 mL, 50 mmol) was added to a flask containing THF N (50 mL) at 0qC. n-Butyllithium (2.32 M in hexane, 21.5 ml, 49.9 mmol) Li was added dropwise over a 10 min period with stirring to give a yellow 13 solution of lithium diisopropylamide. This solution was used directly in the future steps requiring lithium diisopropylamide without further purification. 235 References begin on page 274. t 2 tBu 8.6.2.4 Tris(2-di(tert-butyl)phosphinoethyl)phosphine, P(CH2CH2P Bu2)3, P P3 . (10) Di(tert-butyl)phosphine (11.5 mL, 9.08 g, 62.1 mmol) was added to t P Bu2 a solution of trivinylphosphine (ca. 15.7 mmol) in THF/diethyl P tBu P PtBu ether (100 mL). Lithium diisopropylamide in THF/hexane (as from 2 2 section 8.6.2.3) was added in stages with stirring over a period of 10 one hour. During the course of the reaction, the color of the solution turned bright orange. The reaction was monitored (31P{1H} NMR) and the addition of base halted when no trivinylphosphine or reaction intermediates remained (§ 70 mmol of lithium diisopropylamide used). All volatiles were removed under reduced pressure and the orange oil/solid residue was suspended in benzene (100 mL). Deaerated water (50 mL) was added with care to quench the excess base. The layers were separated and the aqueous layer was discarded. The organic layer was dried over anhydrous Na2SO4 and the volatiles removed 2 tBu under reduced pressure leaving P P3 (10) as an orange oil (6.77 g, 12.3 mmol, 78 % from trivinylphosphine). Anal. found: C 65.15, H 12.00. C30H66P4 (MW 550.74) requires C 65.42, H 12.08. 31 1 3 P{ H}se NMR (121.5 MHz, benzene-d6): G 34.1 (3P, d, JP-P = 24.9 Hz, PT); -15.3 (1P, q, PC). 13 1 1 C{ H} NMR (100.6 MHz, benzene-d6): G 31.6 (d, JC-P = 23.9 Hz, PC(CH3)3); 30.0 (d, 2 1 2 JC-P = 13.8 Hz, PC(CH3)3); 28.5 (dd, JC-P = 25.8 Hz, JC-P = 16.7 Hz, PCH2CH2P); 18.2 1 2 (dd, JC-P = 25.4 Hz, JC-P = 14.6. Hz, PCH2CH2P). 236 References begin on page 274. 1 H NMR (300 MHz, benzene-d6): G 1.89 (6H, m, CH2); 1.71 (6H, m, CH2); 1.12 (54H, d, 3 JH-P = 10.5 Hz, C(CH3)3). t 2 t 8.6.3 Synthesis of PhP(CH2CH2P Bu2)2 PhP P2 Bu (14) Bis(2-di(tert-butyl)phosphinoethyl)phenylphosphine was prepared tBu P PtBu by the base catalysed addition of di(tert-butyl)phosphine to 2 2 P divinylphenylphosphine in a method modified from that used to 2 tBu 14 synthesize P P3 (10). 8.6.3.1 Divinylphenylphosphine, PhP(CH=CH2)2. (15) A solution of vinylmagnesium bromide as prepared in section 8.6.2.1 was chilled to 0°C, resulting in the formation of a light brown P precipitate. Diethoxyphenylphosphine (31.4 g, 158 mmol) was then added dropwise over a period of 30 minutes to the chilled solution. The 15 solution was allowed to warm to room temperature at which point the precipitate disappeared, it was stirred for a further hour then heated under reflux for 30 min. The solution was cooled to room temperature and dioxane (35 mL, 410 mmol) was added, resulting in a large amount of precipitation. The solution was then briefly refluxed and THF (150 mL) was added before the solution was filtered. Volatiles were removed by distillation at 66-68qC leaving a red/orange solid which was extracted with diethyl ether (100 mL) to give a diethyl ether solution of divinylphenylphosphine (18.2 mmol by quantitative NMR against a cyclooctadiene internal standard). Divinylphenylphosphine 237 References begin on page 274. was not isolated from the diethyl ether solution (to prevent polymerization) and the solution was used directly in the preparation of bis(2-di(tert-butyl)phosphinoethyl)phenylphosphine without further purification. 31 1 P{ H} NMR (162 MHz, 25% benzene-d6/75% diethyl ether): G -16.1 (1P, s, PhP(CH=CH2)2) t 2 tBu 8.6.3.2 PhP(CH2CH2P Bu2)2 PhP P2 . (14) A solution of divinylphenylphosphine (2.95 g, 18.2 mmol) in t t diethyl ether (100 mL) from the previous step was added to a Bu2P P Bu2 P solution of di(tert-butyl)phosphine (9.0 mL, 49 mmol) in THF 14 (100 mL). Lithium diisopropylamide (ca. 150 mmol) in THF/hexane (200 ml) was added in stages with stirring over an hour. During the course of the reaction, the color of the solution turned dark red. The reaction was monitored (31P{1H} NMR) and the addition of base was halted when no divinylphenylphosphine or reaction intermediates remained. All solvent was removed under reduced pressure and the remaining red/brown oil/solid residue was suspended in benzene (150 mL). Deaerated water (50 mL) was added with care to quench any residual base. The aqueous layer was discarded and the organic layer dried over anhydrous Na2SO4. The benzene was removed 2 tBu under reduced pressure leaving PhP P2 (14) as an orange oil (6.17 g, 13.6 mmol, 75% yield from divinylphenylphosphine). 238 References begin on page 274. 31 1 3 P{ H} NMR (162 MHz, benzene-d6): G 34.0 (2P, d, JP-P = 27 Hz, PE/T); -16.9 (1P, t, PC). 1 H NMR (400 MHz, benzene-d6): G 7.58 (2H, m, Ar-H); 7.18 (3H, m, Ar-H); 2.06 (2H, m, CH2); 1.55 (2H, m, CH2); 1.43 (2H, m, CH2); 1.19 (2H, m, CH2); 1.03 (36H, m, CH3). 13 1 Ar C{ H} NMR (100.6 MHz, benzene-d6): G 139.0 (d, JC-P = 18 Hz, C ); 133.2 (d, JC-P = 19 Ar Ar Ar Hz, C ); 129.9 (d, JC-P = 44 Hz, C ); 128.6 (s, C ); 31.8 (d, JC-P = 24 Hz, C(CH3)3); 29.9 (d, JC-P = 14 Hz, C(CH3)3); 29.8 (d, JC-P = 14 Hz, C(CH3)3); 29.6 (dd, JC-P = 27 Hz, JC-P = 15 Hz, CH2); 17.7 (dd, JC-P = 25 Hz, JC-P = 14 Hz, CH2). HRMS (ES) m/z: [M + H]+ 455.3092 (calcd. 455.3125) t 3 tBu 8.6.4 Synthesis of P(CH2CH2CH2P Bu2)3, P P3 . (16) 3 tBu P P3 . (16) was prepared by the nucleophilic substitution of t P Bu2 bromide in tris(3-bromopropyl)phosphine with lithium di(tert- t P Bu2P butyl)phosphide following a modified version of the method P t Bu2 reported by Guest.15 16 8.6.4.1 LiP(C(CH3)3))2. (17) n-Butyllithium (2.5 M in hexane, 16 mL, 40 mmol) was added to a solution P of di(tert-butyl)phosphine (5.3 g, 36 mmol) in THF (50 mL) at 0°C with Li stirring. The solution remained colorless during the addition, until the 17 reaction was complete when a pale yellow color persisted. The reaction 239 References begin on page 274. mixture was allowed to warm to room temperature and THF (40 ml) was added, resulting in a bright yellow solution which was used directly in the next step. t 3 t 8.6.4.2 P(CH2CH2CH2P Bu2)3, P P3 Bu. (16) The lithium di(tert-butyl)phosphide solution from the previous step t P Bu2 was added to a stirring solution of tris(3-bromopropyl)phosphine t P Bu2P P (4.20 g, 10.6 mmol) in THF (approx. 40 ml) at 0°C. During the t Bu2 addition, a pink/orange color formed before the color returned to 16 yellow once addition was complete. The reaction mixture was left to stir at room temperature for 18 hours. The solvent was removed under reduced pressure and deaerated water (approx. 30 ml) added, with care, until all excess lithium phosphide had been destroyed. Benzene (approx. 40 ml) was added and the mixture was stirred for one hour. The organic layer was decanted, dried over anhydrous sodium sulfate and filtered to give a clear solution. The solvents were removed under reduced pressure and the resulting oil was heated under reduced pressure (0.4 mbar) to remove volatile impurities, leaving tris(3-di(tert-butyl)phosphinopropyl)phosphine as a clear wax (3.82 g, 6.44 mmol, 61% from tris(3-bromopropyl)phosphine). 31 1 P{ H} NMR (121.5 MHz, benzene-d6): G 26.2 (3P, s, PT); -35.5 (1P, s, PC). 1 31 3 H{ P} NMR (300 MHz, benzene-d6): G 1.87 (6H, m, CH2CH2CH2); 1.63 (6H, t, JH-H = 3 3 7.1 Hz, CH2P); 1.49 (6H, t, JH-H = 7.4, CH2P); 1.12 (54H, d, JH-P = 10.6 Hz, CH3). 240 References begin on page 274. 13 1 1 1 C{ H} NMR (100.6 MHz, benzene-d6): G 31.3 (d, JC-P = 30 Hz, C(CH3)3); 29.9 (d, JC-P = 14 Hz, C(CH3)3); 29.7 (dd, JC-P = 26 Hz, JC-P = 14 Hz, CH2); 27.3 (dd, JC-P = 28 Hz, JC-P = 14 Hz, CH2); 23.6 (dd, JC-P = 23 Hz, JC-P = 11 Hz, CH2). HRMS (ES) m/z [M + H]+ 593.4647 (calcd. 593.4663). 2 tBu 8.6.5 Synthesis of RuCl2(P P3 ), (18). A solution of dichlorotris(triphenylphosphine)ruthenium(II) t t P Bu2 Bu2 P Cl (1.18 g, 1.23 mmol) in THF (50 mL) was added to a solution Ru P Cl 2 tBu of tris(2-di(tert-butyl)phosphinoethyl)phosphine, P P3 (10), t Bu2P (5.00 mL, 245 mM, 1.23 mmol) in THF under nitrogen. The 18 brown solution was stirred overnight and a tan solid precipitated. The solid was collected by filtration and washed with THF (5 mL) to afford 2 tBu RuCl2(P P3 ) (18) (0.40 g, 0.55 mmol, 45%). Anal found: C 49.88, H 9.05 C30H66Cl2P4Ru (MW 722.72) requires C 49.86, H 9.20. 31 1 3 P{ H} NMR (162 MHz, dichloromethane-d2): G 106.2 (1P, dt, JP-P = 37 Hz, 3 3 JP-P = 17.5 Hz, PC); 91.4 (2P, br s, PE); 34.3 (1P, d, JP-P = 37 Hz, PF). 1 H NMR (400 MHz, dichloromethane-d2): G 2.45 (2H, m, CH2); 2.28-1.92 (6H, m, CH2); 3 3 1.83 (2H, m, CH2); 1.35 (18H, d, JH-P = 12.5 Hz, CH3); 1.24 (18H, d, JH-P = 12.5 Hz, 3 CH3); 1.14 (18H, d, JH-P = 10.8 Hz, CH3); 1.07 (2H, m, CH2). 241 References begin on page 274. 13 1 1 C{ H} NMR (100.6 MHz, dichloromethane-d2): G 39.9 (d, JC-P = 18 Hz, PC(CH3)3); 36.2 1 1 2 (d, JC-P = 10.5 Hz, PC(CH3)3); 32.1 (d, JC-P = 22.4 Hz, PC(CH3)3) 31.9 (d, JC-P = 2.9 Hz, 2 PC(CH3)3); 30.8 (dd, JC-P = 28.3 Hz, JC-P = 22.2 Hz, CH2 (pendant arm)) 30.0 (d, JC-P = 13.6 Hz, PC(CH3)3); 28.8 (s, PC(CH3)3); 27.2 (dd, JC-P = 28.0 Hz, JC-P = 6.5 Hz, CH2 (bound arm)); 24.9 (dd, JC-P = 21.1 Hz, JC-P = 12.6 Hz, CH2 (bound arm)); 16.3 (dd, JC-P = 25.6 Hz, JC-P = 5.7 Hz, CH2 (pendant arm)). 2 tBu 8.6.6 Synthesis of RuCl2(PhP P2 ) (19). t A solution of dichlorotris(triphenylphosphine)ruthenium(II) (1.06 g, t P Bu2 Bu2 P Cl 1.11 mmol) in THF (30 mL) was added to a solution of bis(2- Ru P Cl 2 tBu di(tert-butyl)phosphinoethyl)phenylphosphine, PhP P2 (0.520 g, Ph 1.14 mmol) in THF (10 mL) under nitrogen. The brown solution 19 was stirred overnight and a yellow solid precipitated out. Hexane (50 mL) was added to assist further precipitation of solid. The cloudy suspension was stirred for one hour, then 2 tBu the solid was isolated by filtration to give RuCl2(PhP P2 ) (19) (0.255 g, 0.407 mmol, 37%) as a yellow solid. Anal found C 49.52, H 7.60 C26H49Cl2P3Ru (MW 626.57) requires C 49.84, H 7.88. 31 1 2 P{ H} NMR (162 MHz, dichloromethane-d2): G 94.4 (1P, t, JP-P = 12.6 Hz, PhP(CH2)2); G 92.3 (2P, br s, PC(CH3)3). 242 References begin on page 274. 1 H NMR (300 MHz, dichloromethane-d2): G 8.16 (2H, m, ArH); 7.45 (3H, m, ArH); 2.4-2.1 3 3 (6H, m, CH2); 1.44 (18H, d, JH-P = 12.7 Hz, C(CH3)3); 1.19 (18H, d, JH-P = 12.7 Hz, C(CH3)3); 1.15-1.05 (2H, m, CH2). 13 1 1 Ar C{ H} NMR (100.6 MHz, dichloromethane-d2): G 137.7 (d, JC-P = 36.3 Hz, C ); 132.4 Ar Ar Ar (d, JC-P = 8.7 Hz, C ); 130.4 (d, JC-P = 2.4 Hz, C ); 128.8 (d, JC-P = 9.3 Hz, C ); 40.7 (d, 1 1 JC-P = 17.9 Hz, PC(CH3)3); 36.9 (d, JC-P = 11.4 Hz, PC(CH3)3); 31.9 (dd, JC-P = 31.0 Hz, 2 JC-P = 6.3 Hz, CH2); 31.8 (d, JC-P = 2.9 Hz, PC(CH3)3); 29.2 (s, PC(CH3)3); 25.3 (dd, JC-P = 22.7 Hz, JC-P = 13 Hz, CH2). 3 tBu 8.6.7 Synthesis of RuCl2(P P3 ) (20). Solid di-μ-chlorobis[(p-cymene)chlororuthenium] (100 mg, t Bu2P 3 tBu 0.163 mmol) was added to a solution of P P3 (16) (185 mg, P Cl PtBu Ru 2 0.312 mmol) in toluene (50 mL) under nitrogen. The solution was t Bu2P Cl stirred and refluxed overnight to afford an extremely dark green 20 solution with a suspended brown solid. The reaction mixture was filtered and the volatiles removed from the filtrate under vacuum. The resulting green solid residue was dried under 3 tBu 3 tBu vacuum for 3 hours to afford RuCl2(P P3 ) (20) (132 mg, 0.173 mmol, 55% by P P3 (16)). Anal found C 51.54, H 9.28 C33H72Cl2P4Ru (MW 764.81) requires C 51.83, H 9.49. 243 References begin on page 274. 31 1 2 2 P{ H} NMR (121 MHz, THF-d8): G 60.8 (1P, t, JP-P = 35 Hz, PC); 31.1 (2P, d, JP-P = 35 Hz, PE); 25.5 (1P, s, PF). 1 H NMR (300 MHz, acetone-d6): G 1.89 (2H, m, CH2); 1.79 (4H, m, CH2); 1.62 (8H, m, CH2); 1.48-1.62 (18H, m, CH3); 1.62 (4H, m, CH2); 1.12 (36H, m, CH3). 244 References begin on page 274. 8.7 Chapter 4 Experimental 2 tBu 8.7.1 Synthesis of RuHCl(P P3 ) (21). A suspension of potassium hydride (37 mg, 0.92 mmol) t Bu2P H 2 tBu and RuCl2(P P3 ) (57 mg, 0.079 mmol) in THF (20 mL) P PtBu Ru 2 P Cl was stirred at room temperature overnight. The brown t Bu2 suspension had turned orange and was filtered through 21 celite. The filtrate was evaporated to dryness under vacuum and the resultant residue extracted with benzene (5 mL) and filtered. The benzene filtrate was heated at 60 °C for 2 tBu six hours and volatiles were removed under vacuum to afford RuHCl(P P3 ) (21) (36 mg, 2 tBu 0.052 mmol, 66% from RuCl2(P P3 )) as an orange crystalline powder. Anal. Found: C 52.06, H 9.95. C30H67ClP4Ru (MW 688.28) requires C 52.35, H 9.81. Kinetic Isomer: 31 1 3 2 P{ H} NMR (162 MHz, benzene-d6): G 115.9 (1P, dt, JPC-PF = 21 Hz, JPC-PE = 17 Hz, 2 3 PC); 82.3 (2P, d, JPE-PC = 17 Hz, PE); 33.9 (1P, d, JPF-PC = 31 Hz, PF). 1 H NMR (400 MHz, benzene-d6): G 2.25 (2H, m, CH2); 2.00 (2H, m, CH2); 1.83 (2H, m, 3 CH2); 1.49 (2H, m, CH2); 1.44 (18H, t, JH-P = 6 Hz, CH3); 1.39 (2H, m, CH2); 1.32 (18H, 3 3 t, JH-P = 6 Hz, CH3); 1.10 (18H, d, JH-P = 11 Hz, CH3); 0.76 (2H, m, CH2); -30.61 (1H, dt, 2 2 JH-P = 42 Hz, JH-P = 18 Hz, RuH). Thermodynamic Isomer: 245 References begin on page 274. 31 1 3 2 P{ H} NMR (162 MHz, benzene-d6): G 120.8 (1P, dt, JPC-PF = 30 Hz, JPC-PE = 14 Hz, 2 3 PC); 86.4 (2P, d, JPE-PC = 14 Hz, PE); 33.7 (1P, d, JPF-PC = 30 Hz, PF). 1 H NMR (500 MHz, benzene-d6): G 2.25 (2H, m, CH2); 2.00 (2H, m, CH2); 1.83 (2H, m, 3 CH2); 1.49 (2H, m, CH2); 1.44 (18H, t, JH-P = 6 Hz, CH3); 1.39 (2H, m, CH2); 1.32 (18H, 3 3 t, JH-P = 6 Hz, CH3); 1.10 (18H, d, JH-P = 11 Hz, CH3); 0.76 (2H, m, CH2); -30.47 (1H, dt, 2 2 JH-P = 43 Hz, JH-P = 19 Hz, RuH). 13 1 1 1 C{ H} NMR (100.6 MHz, benzene-d6): G 37.3 (t, JC-P = 4 Hz, C(CH3)3); 36.3 (t, JC-P = 1 2 6 Hz, C(CH3)3); 31.6 (d, JC-P = 24 Hz, C(CH3)3); 30.1 (t, JC-P = 3 Hz, C(CH3)3); 30.0 (t, 2 2 1 JC-P = 3 Hz, C(CH3)3); 29.9 (m, CH2); 29.8 (d, JC-P = 14 Hz, C(CH3)3); 28.6 (dd, JC-P = 2 1 2 1 25 Hz, JC-P = 17 Hz, CH2); 22.1 (dt, JC-P = 11 Hz, JC-P = 9 Hz, CH2); 16.3 (dd, JC-P = 2 28 Hz, JC-P = 7 Hz, CH2). 2 tBu 8.7.2 Synthesis of RuH(BH4)(P P3 ) (22). 2 tBu t RuCl2(P P3 ) (50 mg, 0.069 mmol) and NaBH4 (50 mg, Bu2P H t P P Bu2 1.3 mmol) were stirred in methanol (15 mL) for 16 hours Ru P H t Bu2 H resulting in the formation of a light yellow precipitate. B H H The solid was collected by filtration to afford 22 2 tBu 2 tBu RuH(BH4)(P P3 ) (22) (30 mg, 0.045 mmol, 65% by RuCl2(P P3 )). Anal. Found C 53.63, H 10.43 C30H71BP4Ru (MW 667.67) requires C 53.97, H 10.72. 246 References begin on page 274. 31 1 3 3 P{ H} NMR (162 MHz, benzene-d6): G 118.5 (1P, dt, JPC-PF = 37 Hz, JPC-PE = 11 Hz, 3 3 PC); 97.7 (2P, d, JPE-PC = 11 Hz, PE); 35.5 (1P, d, JPF-PC = 37 Hz, PF). 1 H NMR (400 MHz, benzene-d6) G 5.49 (2H, s br, BH2); 2.05-1.85 (4H, m, CH2); 1.80 (2H, 3 m, CH2); 1.58-1.38 (2H, m, CH2); 1.45 (18H, t, JH-P = 6 Hz, CH3); 1.38-1.23 (2H, m, 3 3 CH2); 1.28 (18H, t, JH-P = 6 Hz, CH3); 1.2-1.15 (2H, m, CH2); 1.12 (18H, d, JH-P = 11 Hz, 2 2 CH3); -6.26 (2H, s br, RuHB); -19.18 (1H, dt, JH-P = 36 Hz, JH-P = 20 Hz, RuH). 2 tBu 8.7.3 Synthesis of RuH(AlH4)(P P3 ) (23). t A solution of LiAlH4 in THF (~1.5 M) was added Bu2P H t 2 tBu P P Bu2 dropwise to a stirred solution of RuCl2(P P3 ) (106 mg, Ru P H t Bu2 H 0.147 mmol) in THF (10 mL) until a color change from Al H H brown to colorless was observed. Volatiles were removed 23 under reduced pressure and the white residue extracted with benzene (10 mL). The benzene solution was filtered through celite and the volatiles removed to afford 2 tBu 2 tBu RuH(AlH4)(P P3 ) (23) (80.0 mg, 0.117 mmol, 80% by RuCl2(P P3 )). 2 tBu RuH(AlH4)(P P3 ) was unstable once isolated, in both the solution and solid state forms it would degrade from analytical purity after a few days. This instability prevented effective microanalysis. 31 1 2 3 P{ H} NMR (121.5 MHz, THF-d8): G 113.5 (2P, d, JP-P = 16 Hz, PE); 111.7 (1P, dt, JP-P 2 3 = 32 Hz, JP-P = 16 Hz, PC); 35.1 (1P, d, JP-P = 32 Hz, PF). 247 References begin on page 274. 1 H NMR (400 MHz, THF-d8): G 2.81 (2H, s br, Ru(μ2-H2AlH2)); 2.05-1.55 (6H, m, CH2); 1.46 (2H, m, CH2); 1.26 (36H, m, CH3); 1.17 (2H, m, CH2); 1.08 (2H, m, CH2); 1.05 (18H, 3 2 2 d, JH-P = 10.5 Hz, CH3); -10.13 (1H, dt, JH-P = 53 Hz, JH-P = 14.1 Hz, Ru(μ2-H2AlH2)); 2 2 2 -10.20 (1H, s br, Ru(μ2-H2AlH2)); -13.54 (1H, dtd, JH-P = 22 Hz, JH-P = 22 Hz, JH-H = 6.6 Hz, RuH). 13 1 1 1 C{ H} NMR (100.6 MHz, THF-d8): G 35.5 (t, JC-P = 9 Hz, C(CH3)3); 34.7 (t, JC-P = 1 2 1 3 Hz, C(CH3)3); 33.7 (dd, JC-P = 26 Hz, JC-P = 11 Hz, CH2); 31.6 (d, JC-P = 24 Hz, 2 2 C(CH3)3); 30.8 (t, JC-P = 3 Hz, C(CH3)3); 30.1 (t, JC-P = 2 Hz, C(CH3)3); 29.9-29.0 (m, 2 1 CH2), 29.5 (d, JC-P = 14 Hz, C(CH3)3); 26.1-25.5 (m, CH2); 17.0 (d, JC-P = 26 Hz, CH2). 2 tBu 8.7.4 Synthesis of K[RuH3(P P3 )] (24). A concentrated solution of LiAlH4 in THF was - K+ t Bu2P H 2 tBu added dropwise to a solution of RuCl2(P P3 ) P PtBu Ru 2 P H (106 mg, 0.147 mmol) in THF (10 mL) until a t Bu2 H color change from brown to colorless was observed. Volatiles were removed in vacuo and 24 the white residue extracted with benzene (10 mL). The benzene solution was filtered through celite and all volatiles removed under reduced pressure. Potassium tert-butoxide (34 mg, 0.30 mmol) in THF (10 mL) was added resulting in a light yellow solution. Volatiles were again removed under reduced pressure and the residue extracted with toluene (5 mL) which was filtered through celite. The filtrate was evaporated to dryness 2 tBu under reduced vacuum to afford K[Ru(H)3(P P3 )] (24) (53 mg, 0.076 mmol, 52 %) as a 248 References begin on page 274. 2 tBu very pale yellow solid. K[Ru(H)3(P P3 )] was unstable to the extended drying procedure for microanalysis, and decomposed under vacuum. 31 1 2 P{ H} NMR (162 MHz, benzene-d6): G 131.6 (2P, d, JP-P = 19 Hz, PE); 121.1 (1P, s br, 2 PC); (1P, d, JP-P = 31 Hz, PF). 1 H NMR (400 MHz, benzene-d6): G 2.23 (2H, m, CH2); 2.10 (2H, m, CH2); 1.84 (2H, m, CH2); 1.74 (2H, m, CH2); 1.60 (2H, m, CH2); 1.45 (36H, m, CH3); 1.17 (2H, m, CH2); 1.24 3 (18H, d, JH-P = 10.4 Hz, CH3); -9.10 (1H, m, RuH); -10.59 (1H, m, RuH); -13.70 (1H, m, RuH) 2 tBu 8.7.5 Synthesis of RuH2CO(P P3 ) (25). RuH (N )(P2P tBu) (26) (40 mg, 0.059 mmol) was 2 2 3 O tBu P C dissolved in toluene (3 mL) and degassed through a series 2 P PtBu Ru 2 of freeze pump thaw cycles and left under vacuum. P H t Bu2 H 1.2 atm of carbon monoxide was introduced to the flask and the solution stirred for 10 minutes. Volatiles were 25 removed to give an off white powder, which was recrystallized from pentane to give 2 tBu RuH2(CO)(P P3 ) (25) (26 mg, 0.038 mmol, 65% yield) as very pale yellow crystals. 249 References begin on page 274. Anal. Found C 54.47, H 10.16 C31H68OP4Ru (MW 681.85) requires C 54.61, H 10.05. 31 1 2 P{ H} NMR (121.5 MHz, toluene-d8): G 122.3 (2P, d, JP-P = 5 Hz, PE); 98.8 (1P, dt, 3 3 3 JP-P = 38 Hz, JP-P = 5 Hz, PC); 30.8 (1P, d, JP-P = 38 Hz, PF). 1 H NMR (300 MHz, toluene-d8): G 1.90-1.70 (4H, m, CH2); 1.63-1.53 (2H, m, CH2); 1.50- 1.32 (6H, m, CH2); 1.29 (18H, t, JH-P = 6 Hz, CH3); 1.25 (18H, t, JH-P = 6 Hz, CH3); 1.15 2 2 2 2 (18H, d, JH-P = 10 Hz, CH3); -7.68 (1H, dtd, JH-P = 83 Hz, JH-P = 19 Hz, JH-H = 2 Hz, 2 2 RuHA); -11.38 (1H, dt br, JH-P = 20 Hz, JH-P = 19 Hz, RuHB). IR (fluorolube): 1959 s Ȟ(CŁO) cm-1. 2 tBu 8.7.6 Synthesis of RuH2(N2)(P P3 ) (26). 2 tBu RuCl2(P P3 ) (263 mg, 0.364 mmol) and Na (242 mg, N tBu P N 10.5 mmol) were stirred in refluxing liquid ammonia 2 P PtBu Ru 2 (25 mL) for two hours. The liquid ammonia was allowed P H t Bu2 H to boil off and the remaining contents of the flask dried 26 in vacuo for 30 minutes. Pentane (50 mL) was added and the solution stirred for 15 minutes before filtration through celite. The filtrate volume was reduced in volume to approximately 4 mL under a stream of nitrogen resulting in the formation of a yellow precipitate. This solid was collected by filtration and dried on a 2 tBu small frit to afford RuH2(N2)(P P3 ) (26) (119 mg, 0.175 mmol, 48% yield from 2 tBu RuCl2(P P3 )). 250 References begin on page 274. Anal. Found: C 53.07; H 10.35, N 3.09. C30H68N2P4Ru (MW 681.85) requires C 52.85, H 10.05, N 4.11. Elemental analysis performed on crystalline product suggests some loss of weakly bound dinitrogen ligand upon application of vacuum during analytical procedure. 31 1 P{ H} NMR (162 MHz, THF-d8): G 121.7 (2P, s br, PE); 97.1 (1P, m, PC); 35.1 (1P, d, 3 JP-P = 34 Hz, PF). 1 31 H{ P} NMR (400 MHz, THF-d8): G 2.05-1.85 (4H, m, CH2); 1.77 (4H, m, CH2); 1.48 (4H, m, CH2); 1.33 (18H, s, CH3); 1.25 (18H, s, CH3); 1.09 (18H, s, CH3); -7.13 (1H, d, 2 2 1 JH-H = 4 Hz, RuHA); -17.03 (1H, d, JH-H = 4 Hz, RuHB). H NMR (400 MHz, THF-d8, 2 2 2 high field only): G -7.13 (1H, dtd, JH-P = 90 Hz, JH-P = 20 Hz, JH-H = 4 Hz, RuH); -17.03 2 2 2 (1H, tdd, JH-P = 24 Hz, JH-P = 21 Hz, JH-H = 4 Hz, RuH). IR (fluorolube): 2115 s Ȟ(NŁN), 1798 s br Ȟ(Ru-H) cm-1. NE 15 2 tBu 15 8.7.6.1 Synthesis of RuH ( N )(P P ) ( N -26). t 2 2 3 2 Bu2P ND t 2 tBu P P Bu2 RuH2(N2)(P P3 ) (26) (40 mg, 0.059 mmol) was Ru P H t Bu2 H dissolved in THF-d6 (0.5 mL) in an NMR tube fitted with 15 a concentric teflon valve under dinitrogen. The solution N2-26 was degassed with two freeze-pump-thaw cycles then frozen in liquid nitrogen and 15 evacuated for the third time before the introduction of N2 to the NMR tube headspace. The solution was thawed and allowed to warm to room temperature, affording a solution of 15 2 tBu 15 RuH2( N2)(P P3 ) ( N2-7) suitable for NMR analysis. 251 References begin on page 274. 15 1 1 N{ H} NMR (40.6 MHz, THF-d8): G -44.6 (1N, s br, Nȕ); -65.7 (1N, s br, NĮ). H NMR 2 2 2 (400 MHz, THF-d8, high field only): G -7.13 (1H, dtd, JH-P = 90 Hz, JH-P = 20 Hz, JH-H = 2 2 4 Hz, RuH); -17.03 (1H, td br, JH-P = 23 Hz, JH-P = 22 Hz) 2 tBu 8.7.7 Synthesis of RuH2(H2)(P P3 ) (27). 2 tBu RuH2(N2)(P P3 ) (26) (35 mg, 0.051 mmol) was t Bu2P H H P PtBu dissolved in THF-d6 (0.5 mL) in an NMR tube fitted with Ru 2 P H t a concentric teflon valve under dinitrogen. The solution Bu2 H was degassed with two freeze-pump-thaw cycles then 27 frozen in liquid nitrogen and evacuated for the third time before the introduction of 1.3 atm of H2 gas to the NMR tube headspace. The solution was thawed and the NMR tube shaken, resulting in a color change from yellow to colorless giving a pure solution of 2 tBu 2 tBu RuH2(H2)(P P3 ) (27). RuH2(H2)(P P3 ) (27) needed to be kept under a hydrogen atmosphere to retain complete purity and avoid dinitrogen substitution, which prevented elemental analysis. 31 1 3 P{ H} NMR (243 MHz, THF-d8): G 123.3 (2P, d, JP-P = 8 Hz, PE); 109.2 (1P, dt, 3 3 3 JP-P = 35 Hz, JP-P = 8 Hz, PC); 35.9 (1P, d, JP-P = 35 Hz, PF). 1 H NMR (300 MHz, THF-d8): G 2.1-1.7 (8H, m, CH2); 1.6-1.45 (4H, m, CH2); 1.45-1.25 1 (18H, m, CH3); 1.25-1.0 (36H, m, CH3); -8.45 (4H, s br, RuH2(H2)). H NMR (600 MHz, 200K, THF-d8, high field only): G -6.94 (3H, s br, Ru(H2)H); -12.83 (1H, s br, RuH). 252 References begin on page 274. 2 tBu 8.7.8 Synthesis of RuHCl(CO)(P P3 ) (28). 2 tBu A solution of RuHCl(P P3 ) (21) (48 mg, O tBu P C 0.070 mmol) in benzene (5 mL) was degassed by 2 P PtBu Ru 2 three freeze-pump-thaw cycles before addition of an P Cl t Bu2 H atmosphere of carbon monoxide, resulting in a color change from deep red to colorless. Volatiles were 28 2 tBu removed under reduced pressure to afford RuHCl(CO)(P P3 ) (28) (37 mg, 0.052 mmol, 2 tBu 74% from RuHCl(P P3 )) as a white solid. Anal. found: C 52.27, H 9.54. C31H67ClOP4Ru (MW 716.29) requires C 51.98, H 9.43. 31 1 3 3 P{ H} NMR (243 MHz, benzene-d6): G 113.8 (1P, dt, JP-P = 33 Hz, JP-P = 7 Hz, PC); 3 3 99.6 (2P, d, JP-P = 7 Hz, PE); 34.0 (1P, d, JP-P = 33 Hz, PF). 1 H NMR (600 MHz, benzene-d6): G 1.90 (2H, m, CH2); 1.62 (4H, m, CH2); 1.50 (18H, t, 3 3 JH-P = 6 Hz, CH3); 1.45 (2H, m, CH2); 1.38 (18H, t, JH-P = 6 Hz, CH3); 1.32 (4H, m, 3 2 2 CH2); 1.11 (18H, d, JH-P = 11 Hz, CH3); -7.39 (1H, dt, JH-P = 25 Hz, JH-P = 25 Hz, RuH). IR (fluorolube): 1968 s Ȟ(CŁO), 1875 s Ȟ(Ru-H) cm-1. 2 tBu 8.7.9 Synthesis of RuHCl(N2)(P P3 ) (29). 253 References begin on page 274. 2 tBu A solution of RuHCl(P P3 ) (21) (21 mg, 31 μmol) in t Bu2P Cl P PtBu a 1:2 mixture of THF:hexane was allowed to evaporate Ru 2 P N t N through a septum over a period of four weeks under an Bu2 H atmosphere of nitrogen to afford red crystals of 29 2 tBu 2 tBu RuHCl(N2)(P P3 ) (29) (6.5 mg, 9.1 μmol, 29% from RuHCl(P P3 )). 254 References begin on page 274. 8.8 Chapter 5 Experimental 8.8.1 Synthesis of Tris(2-di(cyclohexyl)phosphinoethyl)phosphine, P(CH2CH2PCy2)3, 2 Cy P P3 . (30) 2 Cy 21 P P3 (30) was synthesized using the method of Morris et al. PCy2 Dicyclohexylphosphine (10.2 g, 51.4 mmol) was added to P Cy2P PCy2 trivinylphosphine (1.575 g, 14.05 mmol) in THF (50 mL). Lithium diisopropylamide in THF/hexane (as from section 8.6.2.3) was added 30 in stages with stirring over a period of one hour. During the course of the reaction, the color of the solution turned bright orange. The reaction was monitored (31P{1H} NMR) and the addition of base halted when no trivinylphosphine or reaction intermediates remained (§ 35 mmol of lithium diisopropylamide). All volatiles were removed under reduced pressure and MeOH (30 mL) was added to the resultant orange oil. The solution became colorless and a white solid precipitated. The solution was stirred for 1.5 hours before the 2 Cy solid was collected by filtration and washed with MeOH to yield P P3 (30) as a white solid (8.37 g, 11.8 mmol, 84 % from trivinylphosphine). 31 1 3 P{ H} NMR (121.5 MHz, benzene-d6): G 0.0 (3P, d, JP-P = 22 Hz, PT); -16.7 (1P, q, PC). 2 Cy 8.8.2 Synthesis of [FeCl(P P3 )][BPh4] (31[BPh4]). + 2 Cy PCy2 [FeCl(P P3 )][BPh4] (31[BPh4]) was synthesized using the Cl method of Morris et al.21 FeCl (0.250 g, 1.97 mmol) and Fe 2 P PCy2 PCy2 255 References begin on page 274. 31 2 Cy P P3 (30) (1.39 g, 1.97 mmol) were combined in ethanol (40 mL) and stirred for 2 hours resulting in a deep purple solution. A solution of NaBPh4 (0.680 g, 1.99 mmol) in ethanol (10 mL) was added slowly to the stirred solution resulting in precipitation of a purple solid 2 Cy which was collected by filtration and washed with pentane to give [FeCl(P P3 )][BPh4] (31[BPh4]) (1.99 g, 1.78 mmol, 90% yield). 2 Cy 8.8.3 Synthesis of [RuCl(P P3 )][Cl] (32[Cl]). [RuCl(P2P Cy)][Cl] (32[Cl]) was synthesized using the method of 3 + PCy 21 2 Cy Cy2 2 Morris et al. P P3 (30) (960 mg, 1.36 mmol) and RuCl2(PPh3)3 P Cl Ru (1.26 g, 1.31 mmol) were dissolved in dichloromethane (30 mL). P PCy2 The solution was stirred for 1 hour then all volatiles were removed under reduced pressure. The resultant solid was stirred 32 in diethyl ether (20 ml) for 20 min and collected by filtration, and washed with pentane to 2 Cy yield [RuCl(P P3 )][Cl] (32[Cl]) (655 mg, 0.745 mmol, 57% yield) as a light brown powder. 31 1 3 P{ H} NMR (121.5 MHz, acetone-d6): 144.8 (1P, q, JP-P = 16 Hz, PC); 68.4 (3P, s br, PT/PE). 256 References begin on page 274. 2 Cy 8.8.3.1 [RuCl(P P3 )][BPh4] (32[BPh4]). 2 Cy A solution of [RuCl(P P3 )][Cl] (32[Cl]) (56 mg, 0.064 mmol) in + PCy Cy2 2 ethanol (10 mL) was added to a solution of NaBPh (22 mg, 0.064 P 4 Cl Ru mmol) in ethanol (5 mL) to give a light brown precipitate. This P PCy2 solid was collected by filtration and washed with pentane to give 2 Cy 32 [RuCl(P P3 )][BPh4] (32[BPh4]) (49 mg, 0.042 mmol, 66%) as a light brown solid. 2 Cy 8.8.4 Synthesis of Fe(N2)(P P3 ) (33). Potassium graphite (76 mg, 0.56 mmol) was added to a solution PCy2 N 2 Cy N of [FeCl(P P3 )][BPh4] (270 mg, 0.242 mmol) in THF Fe P PCy (approximately 15 mL). The reaction mixture was stirred under PCy2 2 nitrogen for 20 h. The resulting black suspension was filtered to 33 give an orange solution. The solvent was removed under reduced pressure, and the solid residue extracted into benzene (approximately 10 mL). The orange solution was filtered, 2 Cy and then reduced to around 1 mL under reduced pressure to precipitate Fe(N2)(P P3 ) (33) as a red/orange solid (63 mg, 0.080 mmol, 33%). Anal. Found. C 64.17, H 9.65, N 2.47, C42H78FeN2P4 (MW 790.837) requires C 63.79, H 9.94, N 3.54%. Elemental analysis performed on crystalline product suggests some loss of weakly bound dinitrogen ligand upon application of vacuum during analytical procedure, consistent for complexes of this type.22 257 References begin on page 274. 31 1 2 2 P{ H} NMR (121 MHz, benzene-d6): G 175.3 (1P, q, JP-P = 36 Hz, PC); 84.2 (3P, d, JP-P = 36 Hz, PE). 1 arm arm H NMR (400 MHz, benzene-d6): G 2.29 (4H, m, CH2 ); 2.13 (8H, m, CH2 ); 2.0-1.7 (26H, m, CyH); 1.48 (24H, m, CyH); 1.4-1.1 (16H, m, CyH). IR (fluorolube): 1996 s, Ȟ(NŁN) cm-1 2 Cy 8.8.5 Synthesis of Ru(N2)(P P3 ) (34) Potassium graphite (80 mg, 0.59 mmol) was added to a PCy2 N suspension of [RuCl(P2P Cy)]Cl (125 mg, 0.142 mmol) in THF N 3 Ru P (approx. 15 ml). The reaction mixture was stirred under PCy2 PCy2 nitrogen for 18 hours, after which it was filtered to afford a 34 dark yellow solution. The solvent was removed under reduced pressure and the resulting dark yellow solid was dissolved in pentane, filtered and the solvent removed under reduced 2 Cy pressure once more to afford Ru(N2)(P P3 ) (34) (41 mg, 0.049 mmol, 35%) as an orange solid. Anal. Found. C 60.13, H 9.57, N 2.92, C42H78N2P4Ru (MW 843.50) requires C 60.34, H 9.40, N 3.35%. 31 1 2 2 P{ H} NMR (121 MHz, benzene-d6): G 160.7 (1P, q, JP-P = 22 Hz, PC); 73.9 (3P, d, JP-P = 22 Hz, PE). 258 References begin on page 274. 1 arm H NMR (300 MHz, benzene-d6): G 2.1-1.6 (42H, m, CH2 /CyH); 1.6-1.1 (36H, m, CyH). IR (fluorolube): 2083 s, Ȟ(NŁN) cm-1. 15 2 Cy 15 8.8.5.1 Ru( N2)(P P3 ) ( N2-34). 2 Cy Ru(N2)(P P3 ) (34) (approximately 40mg, 50 μmol) was PCy2 dissolved in benzene-d6 (0.5 mL) in an NMR tube fitted with N N E Ru D a concentric Teflon valve under dinitrogen. The solution was P PCy2 PCy2 degassed with three freeze-pump thaw cycles before the 15 15 N2-34 introduction of N2 into the NMR tube headspace. NMR spectra indicated the successful exchange of the dinitrogen ligand following thawing of the solution and warming to room temperature. 31 1 2 2 3 P{ H} NMR (162 MHz, benzene-d6): G 160.8 (1P, dqd, JP-N = 31 Hz, JP-P = 22 Hz, JP-N 2 2 3 = 3 Hz, PC); 74.0 (3P, ddd, JP-P = 22 Hz, JP-N = 5 Hz, JP-N = 2 Hz, PE). 15 1 2 N{ H} NMR (40.56 MHz, benzene-d6): G -9.0 (1N, s br, Nȕ); -52.5 (1N, dqd, JN-P = 31 2 1 Hz, JN-P = 5 Hz, JN-N = 5 Hz, NĮ). 2 Cy 8.8.6 Synthesis of [Fe(N2)(P P3 )][BPh4] (35[BPh4]). Potassium graphite (17 mg, 0.13 mmol) was added to a + PCy2 N 2 Cy N solution of [FeCl(P P3 )][BPh4] (132 mg, 0.118 mmol) in Fe P PCy2 PCy2 259 References begin on page 274. 35 THF (approximately 15 mL). The reaction mixture was stirred under nitrogen for 20 h. The resulting black suspension was filtered to give a dark red solution. The solvent was removed under reduced pressure, and the solid residue washed with pentane (approximately 2 Cy 20 mL). The red solid was collected by filtration to afford [Fe(N2)(P P3 )][BPh4] (35[BPh4]) (58 mg, 0.052 mmol, 44%). Anal. Found. C 71.15, H 9.05, N 2.07, C66H98BFeN2P4 (MW 1110.05) requires C 71.41, H 8.90, N 2.52%. IR (fluorolube): 2059 s, Ȟ(NŁN) cm-1. 2 Cy 8.8.7 Synthesis of RuCl(P P3 ) (36). Potassium graphite (18 mg, 0.13 mmol) was added to a solution PCy2 2 Cy Cl of [RuCl(P P3 )][Cl] (102 mg, 0.116 mmol) in THF Ru P PCy (approximately 15 mL). The reaction mixture was stirred under PCy2 2 nitrogen for 20 h. The resulting black suspension was filtered to 36 give a very dark solution. The solvent was removed under reduced pressure, and the solid residue was extracted with pentane (approximately 30 mL). The solution was filtered to give a deep blue filtrate. The volume of the solution was reduced to 5 mL and allowed to stand overnight, resulting in the precipitation of a blue solid which was collected by 2 Cy filtration to afford RuCl(P P3 ) (36) (72 mg, 0.085 mmol, 74%). 260 References begin on page 274. Anal. Found. C 59.91, H 9.51, C42H78ClP4Ru (MW 843.50) requires C 59.81, H 9.32. 2 Cy 8.8.8 Synthesis of FeH2(P P3 ) (37). Potassium triethylborohydride (35 mg, 0.25 mmol) was added to a PCy Cy2 2 P 2 Cy H stirring suspension of [FeCl(P P3 )][BPh4] (120 mg, 0.107 mmol) in Fe P H toluene (10 mL) and the resulting mixture stirred under nitrogen for PCy2 3 hours. Volatiles were removed under reduced pressure. The 37 remaining orange residue was extracted with pentane (30 mL), filtered and volatiles 2 Cy removed from the filtrate to afford FeH2(P P3 ) (37) (57 mg, 0.075 mmol, 70 % yield) as an orange solid. Anal. Found. C 66.21, H 10.39, C42H80FeP4 (MW 764.84) requires C 65.96, H 10.54. 31 1 2 2 P{ H} NMR (162 MHz, benzene-d6): G 174.4 (1P, q, JP-P = 18 Hz, PC); 102.3 (3P, d, JP- P = 18 Hz, PE/PT). 1 arm arm H NMR (300 MHz, benzene-d6): G 2.39 (4H, m, CH2 ); 2.1-1.6 (32H, m, CH2 /CyH); 2 2 31 1 1.6-1.1 (42H, m, CyH); -12.84 (2H, qd, JH-P = 46 Hz, JH-P = 3 Hz, FeH). P{ H} NMR (243 MHz, toluene-d8, 190 K): G 175.0 (1P, s br, PC); 113.7 (1P, s br, PT); 96.8 (2P, s br, PE). 1 H NMR (600 MHz, toluene-d8, 190 K, high field only): G -7.98 (1H, s br, RuH); -17.67 (1H, s br, RuH). 261 References begin on page 274. 2 Cy 8.8.9 Synthesis of [FeH(N2)(P P3 )][BF4] (38[BF4]) A solution of lutidinium tetrafluoroborate (23 mg, 0.12 mmol) + PCy 2 Cy Cy2 2 in THF (5 mL) was added to a solution of FeH2(P P3 ) (37) P N N Fe (85.0 mg, 0.111 mmol) in THF (20 mL) and the reaction P H PCy2 mixture was stirred overnight under nitrogen, resulting in a 38 color change from pale orange to a darker pink/orange. The solution was filtered through celite and reduced in volume to 4 mL under reduced pressure. The addition of pentane (30 mL) resulted in the precipitation of a tan solid which was 2 Cy collected by filtration to afford [FeH(N2)(P P3 )][BF4] (38[BF4]) (58 mg, 0.066 mmol, 59%). Anal found C 57.35, H 9.19, N 2.57 C42H79BF4FeN2P4 (MW 878.649 ) requires C 57.41, H 9.06, N 3.19. Elemental analysis performed on crystalline product suggests some loss of weakly bound dinitrogen ligand upon application of vacuum during analytical procedure. 31 1 2 2 P{ H} NMR (162 MHz, THF-d8): G 160.7 (1P, dt, JPC-PT = 28 Hz, JPC-PE = 24 Hz, PC); 2 2 2 2 79.8 (2P, dd, JPE-PC = 24 Hz, JPE-PT = 11 Hz, PE); 70.3 (1P, dt, JPT-PC = 28 Hz, JPT-PE = 11 Hz, PT). 1 arm H NMR (400 MHz, THF-d8): G 2.7-2.2 (12H, m, CH2 ); 2.2-1.1 (66H, m, CyH); -14.62 2 2 2 (1H, tdd, JH-P = 69 Hz, JH-P = 53 Hz, JH-P = 25 Hz, FeH). IR (fluorolube): 2107 s, Ȟ(NŁN) cm-1. 262 References begin on page 274. 2 Cy 8.8.10 Synthesis of [RuH(N2)(P P3 )][BF4] (39[BF4]). Solid lutidinium tetrafluoroborate (11 mg, 0.056 mmol) was + PCy 2 Cy Cy2 2 added to a stirred solution of Ru(N2)(P P3 ) (34) (45 mg, P N N Ru 0.054 mmol) in THF (20 mL). The solution was initially pale P H PCy2 green in color then turned to a pale orange after one hour. The 39 volume of the solution was reduced to ~ 5 mL under reduced pressure before pentane (30 mL) was added resulting in the precipitation of a pale orange 2 Cy solid. The solid was collected by filtration to afford [RuH(N2)(P P3 )][BF4] (39[BF4]) (40 mg, 0.043 mmol, 80%). Anal. Found. C 54.39, H 8.46, N 2.02, C42H79BF4N2P4Ru (MW 923.87) requires C 54.60, H 8.62, N 3.03. Elemental analysis performed on crystalline product suggests some loss of weakly bound dinitrogen ligand upon application of vacuum during analytical procedure. 31 1 2 2 P{ H} NMR (243 MHz, THF-d8) G 140.7 (1P, dt, JP-P = 11 Hz, JP-P = 11 Hz, PC); 63.8 2 2 2 2 (2P, dd, JP-P = 11 Hz, JP-P = 11 Hz, PE); 51.4 (1P, dt, JP-P = 11 Hz, JP-P = 11 Hz, PT). 1 H NMR (600 MHz, THF-d8): G 2.55 (4H, m); 2.22 (2H, m); 2.12 (4H, m); 2.01 (4H, m); 2 1.92-1.65 (30H, m); 1.65-1.47 (14H, m); 1.47-1.20 (20H, m); -11.26 (1H, dtd, JH-P = 2 2 72 Hz, JH-P = 26 Hz, JH-P = 23 Hz, RuH). 263 References begin on page 274. IR (fluorolube): 2172 s, Ȟ(NŁN) cm-1. 264 References begin on page 274. 8.9 Chapter 6 Experimental 8.9.1 Synthesis of Tris[(2-dicyclohexylphosphino)ethyl]methane, HC(CH2CH2PCy2)3 H 2 Cy C P3 , (46) Tris[(2-dicyclohexylphosphino)ethyl]methane was prepared by PCy2 H nucleophilic substitution of chloride in CH(CH2CH2Cl)3 with lithium C Cy2P PCy2 dicyclohexylphosphide in a method modified from that of Field et al. used in the synthesis of analogous carbon centered podand 46 phosphine ligands.23 8.9.1.1 [(Methoxycarbonyl)methyl]triphenylphosphonium Bromide, [Ph3PCH2CO2Me]Br, (40) The title compound was synthesized according to a published Br- O + Ph3P procedure.24 A solution of methylbromoacetate (48.0 mL, 80.0 g, O 522 mmol) in ethyl acetate (60 mL) was added slowly to a solution of 40 triphenylphosphine (135 g, 515 mmol) in ethyl acetate (400 mL). The reaction mixture warmed up slightly and a white precipitate formed. The reaction mixture was then stirred at RT overnight. The white solid product was collected by filtration, air dried for 3 hours and was then dried in a vacuum desiccator to give [Ph3PCH2CO2Me]Br, (40) (211g, 98%). 1 H NMR (300 MHz, CDCl3): į 7.87-7.80 (m, 6H, ArH), 7.77-772 (m, 3H, ArH), 2 7.66-7.59 (m, 6H, ArH), 5.51 (d, JP-H = 13.6 Hz, 2H, CH2), 3.53 (s, 3H, CH3) ppm. 31 1 P{ H} NMR (121.5 MHz, CDCl3): į 21.03 ppm. 265 References begin on page 274. 13 1 2 4 C{ H} NMR (75 MHz, CDCl3): į 165.21 (d, JP-C = 2.9Hz, C=O), 135.30 (d, JP-C = 2.9 Hz, p-C of Ph), 134.05 (d, JP-C = 10.9 Hz, m-C or o-C of Ph), 129.40 (d, JP-C = 13.1 Hz, 1 1 o-C or m-C of Ph), 117.95 (d, JP-C = 88.6 Hz, ipso-C of Ph), 53.52 (s, CH3), 33.06 (d, JP-C = 57.4 Hz, CH2) ppm. 8.9.1.2 [(Methoxycarbonyl)methylene]triphenylphosphorane, Ph3P=CHCO2CH3, (41) Ph3P=CHCO2CH3 was synthesized according to a published O 24 Ph3P procedure. A solution of [Ph3PCH2CO2Me]Br (211 g, 507 mmol) in O dichloromethane (500 mL) was shaken vigorously with aqueous sodium 41 hydroxide (28.5g, 713 mmol in 300 mL water) in a separating funnel. The organic layer was separated and the aqueous layer was extracted twice with dichloromethane (2 x 150 mL). The combined organic layer was washed with saturated sodium chloride (100 mL), dried over magnesium sulfate filtered and the solvent removed in vacuo to afford Ph3P=CHCO2CH3 (41) as a white solid (164 g, 492 mmol, 97%). 1 H NMR (300 MHz, CDCl3): į 7.67-7.60 (m, 6H, ArH), 7.55-7.49 (m, 3H, ArH), 7.46-7.40 (m, 6H, ArH), 3.49 (s, CH3) (CH was not observed) ppm. 31 1 P{ H} NMR (121.5 MHz, CDCl3): į 19.89 ppm. 13 1 2 C{ H} NMR (75 MHz, CDCl3): į 171.76 (d, JP-C = 10.9 Hz, C=O), 133.09 (d, JP-C = 10.2 Hz, o or m-C of Ph), 132.11 (br, p-C of Ph), 128.87 (d, JP-C = 12.4 Hz, m or o-C of 1 1 Ph), 127.93 (d, JP-C = 90.1 Hz, ipso-C of Ph), 49.89 (s, CH3) 29.97 (d, JP-C = 127.2 Hz, CH) ppm. 266 References begin on page 274. 8.9.1.3 3-(Methoxycarbonyl)methylpent-2-enedioate, CH3O2CCHC(CH2CO2Me)2, (42) The compound was synthesized by modification of a literature O 25 O O procedure. A solution of Ph3P=CHCO2CH3 (48.8 g, 146 mmol) and O dimethyl 1,3-acetonedicarboxylate (22.8 mL, 25.4 g, 146 mmol) in dry O O toluene (150 mL) was refluxed under nitrogen overnight in which time 42 the reaction mixture changed to dark red. The solution was cooled to room temperature and the solvent was removed under reduced pressure on a rotary evaporator to afford a brown red solid and some oil. The residue was then extracted with hot hexane (5 x 50 mL) and the solvent removed under reduced pressure to afford CH3CO2CHC(CH2CO2Me)2 (42) as a very pale yellow oil (22.2 g, 96.6 mmol, 66%). 1 H NMR (300 MHz, CDCl3): į 5.94 (s, 1H, CH), 3.85 (s, 2H, CH2), 3.67 (s, 9H, CH3), 3.27 (s, 2H, CH2) ppm. 13 1 C{ H} NMR (75 MHz, CDCl3): į 170.28 (CO), 169.89 (CO), 165.81 (CO), 146.01 (C(CH2CO2Me)2), 122.20 (CHC(CH2CO2Me)2), 52.07, 51.92, 51.22, 43.50, 36.41 ppm. 8.9.1.4 3-(2-Hydroxyethyl)pentane-1,5-diol, CH(CH2CH2OH)3, (43) A solution of CH3O2CCH=C(CH2CO2Me)2 (22.2 g, 96.6 mmol) OH OH in THF (200 mL) was treated portion wise with solid LiBH4 (4.90 g, CH 225 mmol). The mixture was stirred at room temperature overnight. HO 43 267 References begin on page 274. The orange mixture was cooled in an ice bath, quenched with H2O (~20 mL) and filtered. The filtercake was washed with hot THF (3 u 50 mL). All volatiles were removed from the filtrate under reduced pressure. The resulting oil was taken up in DCM (125 mL) and methanol (10 mL) and the resultant solution was dried over Na2SO4, filtered and the volatiles removed under reduced pressure to afford CH(CH2CH2OH)3 (43) as a highly viscous oil (12.7 g, 85.6 mmol, 89%). 1 3 H NMR (300 MHz, CDCl3/CD3OD): į 4.27 (3H, s, OH), 3.33 (6H, t, JH-H = 6.78 Hz, 1 3 3 CH2OH), 1.43 ( H, septet, JH-H = 6.40 Hz, CH), 1.25 (6H, dt, JH-H = 6.78 Hz, CHCH2). 13 1 C{ H} NMR (75 MHz, CDCl3/CD3OD): į 59.46 (s, CH2OH), 36.23 (s, CHCH2), 27.63 (CH) ppm. 8.9.1.5 3-(2-Chloroethyl)-1,5-dichloropentane, CH(CH2CH2Cl)3, (44) CH(CH2CH2Cl)3 was prepared by modification of the literature Cl Cl procedure.26 Thionyl chloride (30 mL, 270 mmol) was added slowly to a CH solution of 3-(2-hydroxyethyl)pentane-1,5-diol (12.7 g, 85.6 mmol) and Cl pyridine (20 mL) in dichloromethane (120 mL). After the effervescence 44 ceased, the reaction mixture was heated at 50oC overnight. The reaction mixture was cooled to RT then on ice and hydrochloric acid (1M, 40 mL) was added very slowly to the reaction mixture followed by dichloromethane (130 mL). The organic layer was separated, washed with water (50 mL), saturated aqueous sodium hydrogen carbonate (50 mL) and 268 References begin on page 274. water (50 mL). The organic layer was dried over sodium sulfate, filtered and the solvent was removed under reduced pressure to afford a dark yellow oil. The crude product was dissolved in a mixture of acetone (70 mL), diethyl ether (70 mL) and hexane (200 mL). This solution was filtered through a silica plug. The silica plug was then washed with a 1:1 mixture of diethyl ether and hexane (3 X 100 mL) to give an orange solution. All volatiles were removed under reduced pressure to afford CH(CH2CH2Cl)3 (44) as an orange oil (4.48 g, 22.0 mmol, 26%). 1 3 3 H NMR (300 MHz, CDCl3): į 3.57 (t, JH-H = 7.16 Hz, 6H, CH2Cl), 2.02 (septet, JH-H = 3 6.40 Hz, 1H, CH), 1.81 (dt, JH-H = 7.16 Hz, 6H, CHCH2) ppm. 13 1 C{ H} NMR (75 MHz, CDCl3): į 42.36 (CH2Cl), 36.34 (CHCH2), 31.33 (CH) ppm. H 2 Cy 8.9.1.6 Tris[(2-dicyclohexylphosphino)ethyl]methane, C P3 (46) n-Butyllithium (2.40 M in hexanes, 24.3 mL, 58.3 mmol) was added slowly to a solution of dicyclohexylphosphine ((11.6 g, 58.3 mmol) in P Li THF (100 mL) at 0oC. The yellow solution of lithium 45 dicyclohexylphosphide (45) was stirred at 0oC for one hour and it PCy2 was then added slowly to a solution of CH(CH2CH2Cl)3 (44) (3.65 g, H C o 18.0 mmol) in THF (100 mL) at 0 C. The reaction mixture was Cy2P PCy2 stirred at 0oC for one hour and then at RT overnight. The solution 46 was then refluxed for one and a half hours and then all volatiles were completely removed 269 References begin on page 274. under reduced pressure to afford an off-white solid. Toluene (50 mL) was added to the solution followed by the careful addition of deoxygenated water (20 mL) to quench any remaining phosphide, followed by more toluene (50 mL). The mixture was stirred vigorously for one hour and was then transfer to a separating funnel under nitrogen. The organic layer was separated, washed with water (2 x 10 mL) and dried over sodium sulfate. After filtration to remove the drying reagent, the solvent was removed completely to afford a brown solid. The crude solid product was recrystallized with THF/methanol to afforded H 2 Cy C P3 (46) as white solid (4.21 g, 6.12 mmol, 34%). Anal. Found: C, 75.08; H, 11.37. Calculated for: C43H79P3: C, 74.96; H, 11.56. 1 H NMR (300 MHz, benzene-d6): į 2.10-1.55 (m, 50H), 1.48-1.22 (m, 29H). 31 1 P{ H} NMR (121.5 MHz, benzene-d6): į -8.04 ppm. 8.9.2 Synthesis of RuH2(N2)(PPh3)3, (47) RuH2(N2)(PPh3)3 was prepared by a modified version of the method PPh3 N Ph3P N used by Harris et al. to obtain RuH (PPh ) which could be worked Ru 4 3 3 H H 27 PPh3 up under nitrogen to afford RuH2(N2)(PPh3)3. RuCl2(PPh3)3 (1.10 47 g, 1.15 mmol) and NaBH4 (1.07 g, 28.3 mmol) were combined in a flask with benzene (30 mL) and methanol (50 mL). The solution was stirred for 30 min. and then the volume of the solution was halved by evaporation under reduced pressure. Methanol (80 mL) was added to the stirred solution, resulting in the formation of a white precipitate. The solid was collected by filtration and dried under a stream of nitrogen. The solid was then dissolved in THF (20 mL) and stirred under a stream of nitrogen until the 270 References begin on page 274. solvent had evaporated off. The beige solid was collected to give RuH2(N2)(PPh3)3 (47) (0.93 g, 1.01 mmol, 88%). 31 1 2 P{ H} NMR (121.5 MHz, benzene-d6/THF 1:1): G 52.9 (2P, d, JP-P = 16 Hz); 40.1 (1P, t, 2 JP-P = 16 Hz). 1 H NMR (300 MHz, toluene-d8): G 7.23 (9H, m, ArH); 7.10 (18H, m, ArH); 6.98 (18H, m, 2 2 2 ArH); -9.95 (1H, dtd, JH-P = 77 Hz, JH-P = 30 Hz, JH-H = 5 Hz, RuH); -13.1 (1H, m br, RuH). IR (fluorolube): 1143 s Ȟ(NŁN) cm-1. 2 Cy 8.9.3 Synthesis of RuH(CO)(C P3 ) (48). H 2 Cy RuH2CO(PPh3)3 (240 mg, 0.261 mmol) and C P3 (46) (200 mg, PCy Cy2 2 P O C 0.290 mmol) were dissolved in toluene (30 mL) under a nitrogen Ru C H atmosphere. The solution was refluxed for 16 hours resulting in the PCy2 color turning a very pale yellow. Volatiles were removed under 48 reduced pressure and the resulting residue was washed with pentane (30 mL). The resultant solid was then washed with methanol (20 mL) and collected and dried to yield 2 Cy RuH(CO)(C P3 ) (48) (135 mg, 0.165 mmol, 63% yield) as a white solid. Anal Found: C 64.29, H 9.53; C44H79OP3Ru (MW 818.10) requires C 64.60, H 9.73. 271 References begin on page 274. 31 1 2 2 P{ H} NMR (162 MHz, toluene-d8): G 69.4 (2P, d, JP-P = 17 Hz, PE); 56.1 (2P, d, JP-P = 17 Hz , PT). 1 H NMR (400 MHz, toluene-d8): G 2.50 (4H, m); 2.30-1.60 (44H, m); 1.60-1.35 (20H, m); 2 2 1.35-1.15 (10H); -10.31 (1H, dt, JH-PT = 77 Hz, JH-PE = 28 Hz, RuH). 13 1 31 C{ H, P} NMR (126 MHz, toluene-d8): G 203.4 (s, CŁO); 66.3 (s, C-Ru); 48.7 (s); 43.7; 43.5; 37.6, 33.5, 33.2; 32.3; 30.8; 30.6; 30.2; 28.9; 28.7; 28.6; 28.1, 28.0, 27.6, 27.4; 27.1. IR (fluorolube): 1894 s Ȟ(CŁO) cm-1. 2 Cy 8.9.4 Synthesis of RuH(N2)(C P3 ) (49). RuH2(N2)PPh3)3 (47) (606 mg, 0.660 mmol) was added to a PCy Cy2 2 P N H 2 Cy N solution of C P3 (46) (448mg, 0.650 mmol) in toluene (50 mL) Ru C H PCy under nitrogen. The solution immediately turn red and small 2 amounts of effervescence were observed. The solution was stirred 49 for 20 hours after which time a large amount of white precipitate had formed. The volume of the solution was reduced to § 10 mL under reduced pressure, resulting in more precipitation and a dark red supernatant. The precipitate was collected by filtration and 2 Cy washed thoroughly with pentane to yield RuH(N2)(C P3 ) (49) (474 mg, 0.579 mmol, 89 %) as a white solid. 31 1 2 2 P{ H} NMR (162 MHz, benzene-d6): G 61.0 (2P, d, JP-P = 16 Hz, PE); 47.4 (1P, t, JP-P = 16 Hz, PT) 272 References begin on page 274. 1 arm arm H NMR (400 MHz, toluene-d8): G 2.41 (2H, m, CH2 ); 2.27 (2H, m, CH2 ); 2.20-1.93 arm (10H, m, CH2 /CyH); 1.93-1.66 (24H, m, CyH); 1.66-1.34 (22H, m, CyH); 1.34-1.07 arm 2 2 (14H, m, CyH); 0.88 (4H, m, CH2 ); -9.89 (1H, dt, JH-PT = 82 Hz, JH-PE = 28 Hz, RuH). IR (fluorolube): 2098 s Ȟ(NŁN), 1894 s Ȟ(Ru-H) cm-1. 273 References begin on page 274. 8.10 References 1. Perrin, D. D. A., W. L. F., Purification of Laboratory Chemicals. 3rd ed.; Pergamon Press: Oxford, 1993. 2. Ohmori, H.; Takanami, T.; Shimada, H.; Masui, M., Chemical & Pharmaceutical Bulletin 1987, 35 2558-60. 3. Hallman, P. S.; Stephenson, T. A.; Wilkinson, G., Inorg. Synth. 1970, 12 237-40. 4. Maier, L.; Seyferth, D.; Stone, F. G. A.; Rochow, E. G., J. Am. Chem. Soc. 1957, 79 5884-9. 5. Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.; Goldman, A. S., J. Am. Chem. Soc. 2004, 126 13044-13053. 6. Weitz, I. S.; Rabinovitz, M., Journal of the Chemical Society, Perkin Transactions 1 1993. 7. Brown, C. A.; Krishnamurthy, S., J. Organomet. Chem. 1978, 156 111-21. 8. Ahmad, N.; Levison, J. J.; Robinson, S. D.; Uttlky, M. F.; Wonchoba, E. R.; Parshall, G. W., Complexes of Ruthenium, Osmium, Rhodium, and Iridium Containing Hydride Carbonyl, or Nitrosyl Ligands. In Inorganic Syntheses, John Wiley & Sons, Inc.: 2007; pp 45-64. 9. Reich, H. J. WinDNMR: Dynamic NMR Spectra for Windows, J. Chem. Educ. Software: 1998. 10. Originlab Origin 8.1 SR2, 8.1.88.89; Originlab Corporation: Northhampton, MA, USA, 2010. 274 References begin on page 274. 11. Kuprov, I.; Goez, M.; Abbott, P. A.; Hore, P. J., Rev. Sci. Instrum. 2005, 76 084103. 12. Aliaga-Alcalde, N.; DeBeer, G. S.; Mienert, B.; Bill, E.; Wieghardt, K.; Neese, F., Angew. Chem., Int. Ed. 2005, 44 2908-2912. 13. Betley, T. A.; Peters, J. C., J. Am. Chem. Soc. 2004, 126 6252-6254. 14. Brown, S. D.; Mehn, M. P.; Peters, J. C., J. Am. Chem. Soc. 2005, 127 13146- 13147. 15. Guest, R. Synthesis and Reactions of Iron and Ruthenium Dinitrogen Complexes. The University of Sydney, Sydney, 2008. 16. Fryzuk, M. D.; Carter, A.; Westerhaus, A., Inorg. Chem. 1985, 24 642-8. 17. Timmer, K.; Thewissen, D. H. M. W.; Marsman, J. W., Recl. Trav. Chim. Pays-Bas 1988, 107 248-55. 18. Starowieyski, K. B.; Lewinski, J.; Wozniak, R.; Lipkowski, J.; Chrost, A., Organometallics 2003, 22 2458-2463. 19. Eisentrager, F.; Gothlich, A.; Gruber, I.; Heiss, H.; Kiener, C. A.; Kruger, C.; Ulrich Notheis, J.; Rominger, F.; Scherhag, G.; Schultz, M.; Straub, B. F.; Volland, M. A. O.; Hofmann, P., New J. Chem. 2003, 27 540-550. 20. Jia, G.; Drouin, S. D.; Jessop, P. G.; Lough, A. J.; Morris, R. H., Organometallics 1993, 12 906-16. 21. Jia, G.; Drouin, S. D.; Jessop, P. G.; Lough, A. J.; Morris, R. H., Organometallics 1993, 12 906-916. 275 References begin on page 274. 22. Field, L. D.; Guest, R. W.; Vuong, K. Q.; Dalgarno, S. J.; Jensen, P., Inorganic Chemistry 2009, 48 2246-2253. 23. Allen, O. R.; Field, L. D.; Magill, A. M.; Vuong, K. Q.; Bhadbhade, M. M.; Dalgarno, S. J., Organometallics 2011, 30 6433-6440. 24. Boers, R. B.; Randulfe, Y. P.; van der Haas, H. N. S.; van Rossum-Baan, M.; Lugtenburg, J., Eur. J. Org. Chem. 2002, 2094-2108. 25. Yamagiwa, Y.; Koreishi, Y.; Kiyozumi, S.; Kobayashi, M.; Kamikawa, T.; Tsukino, M.; Goi, H.; Yamamoto, M.; Munakata, M., Bull. Chem. Soc. Jpn. 1996, 69 3317- 3323. 26. Baumeister, J. M.; Alberto, R.; Ortner, K.; Spingler, B.; Schubiger, P. A.; Kaden, T. A., Journal of the Chemical Society-Dalton Transactions 2002, 4143-4151. 27. Harris, R. O.; Hota, N. K.; Sadavoy, L.; Yuen, J. M. C., Journal of Organometallic Chemistry 1973, 54 259-264. 276 References begin on page 274. Appendix A1 Crystallography data Cif files for all structures are stored on the included CD 5 6 19 20 21 22 Chemical formula C27H62P4Ru C51.75H83BOP4Ru C26H49Cl2P3Ru C33H72Cl2P4Ru C30H67ClP4Ru C30H71BP4Ru Formula Mass 611.72 956.94 626.53 764.76 688.24 667.63 Crystal system Monoclinic Monoclinic Monoclinic Orthorhombic Monoclinic Monoclinic a/Å 17.099(2) 16.4283(7) 11.1544(11) 12.462(2) 8.0280(6) 8.2066(3) b/Å 17.3858(17) 17.7729(6) 16.0550(15) 14.307(3) 22.3513(18) 22.2411(10) c/Å 21.692(3) 18.1170(6) 16.0390(14) 21.914(4) 20.2652(13) 20.3594(11) Į/deg 90.00 90.00 90.00 90.00 90.00 90.00 ȕ/deg 100.723(4) 105.8920(10) 95.990(3) 90.00 95.535(2) 96.760(3) Ȗ/deg 90.00 90.00 90.00 90.00 90.00 90.00 V(Å3) 6335.9(13) 5087.6(3) 2856.6(5) 3907.1(12) 3619.4(5) 3690.2(3) Temperature/K 150(2) 150(2) 150(2) 150(2) 150(2) 150(2) Space group P2(1)/c P2(1)/n P2(1)/c P2(1)2(1)2(1) P2(1)/n P2(1)/n Z 8 4 4 4 4 4 ȝ(Mo KĮ) (mm-1) 0.711 0.469 0.918 0.723 0.701 0.615 N 43788 60017 17217 15684 20013 26284 Nind 11053 11057 5033 6760 6322 6485 Rint 0.0999 0.0563 0.0791 0.1778 0.1349 0.1140 Final R1 values 0.0426 0.0465 0.0393 0.0840 0.0464 0.0582 (I > 2ı(I)) Final wR(F2) values (I 0.1098 0.0955 0.0577 0.1695 0.1072 0.1085 > 2ı(I)) Final R1 values (all 0.0770 0.0668 0.0753 0.1939 0.0733 0.1188 data) Final wR(F2) values 0.1417 0.1029 0.0657 0.2326 0.1258 0.1306 (all data) Goodness of fit on F2 0.790 1.125 1.072 0.908 0.997 1.035 23 24 25 26 28 29 Chemical formula C30H71AlP4Ru C36H75KP4Ru C31H68OP4Ru C30H68N2P4Ru C31H67ClOP4Ru C30H67ClN2P4Ru Formula Mass 683.80 772.01 681.80 681.81 716.25 716.26 Crystal system Triclinic Triclinic Monoclinic Monoclinic Monoclinic Monoclinic a/Å 10.9783(3) 12.5716(8) 8.3997(3) 8.5017(6) 14.1083(9) 8.4338(4) b/Å 13.4176(5) 12.6716(9) 21.4472(7) 21.3304(16) 15.0181(9) 20.2875(7) c/Å 14.3526(5) 14.4181(10) 20.3982(6) 20.3462(13) 17.5206(11) 21.5007(8) Į/deg 69.2550(10) 71.966(3) 90.00 90.00 90.00 90.00 ȕ/deg 85.0090(10) 79.246(3) 99.013(2) 99.815(2) 95.491(3) 92.0640(10) Ȗ/deg 69.6890(10) 83.606(3) 90.00 90.00 90.00 90.00 V(Å3) 1852.61(11) 2142.1(3) 3629.4(2) 3635.7(4) 3695.2(4) 3676.4(3) Temperature/K 150(2) 150(2) 150(2) 150(2) 155(2) 150(2) Space group P1¯ P1¯ P2(1)/n P2(1)/n P2(1)/n P2(1)/n Z 2 2 4 4 4 4 ȝ(Mo KĮ) (mm-1) 0.637 0.634 0.629 0.628 0.692 0.695 N 22300 26692 25510 23007 31016 31508 Nind 6486 7368 6371 6394 8056 8012 Rint 0.0493 0.0737 0.0384 0.0302 0.0345 0.0545 Final R1 values 0.0253 0.0415 0.0323 0.0275 0.0232 0.0431 (I > 2ı(I)) Final wR(F2) values 0.0610 0.0812 0.0745 0.0837 0.0676 0.1001 (I > 2ı(I)) Final R1 values 0.0308 0.0678 0.0429 0.0426 0.0294 0.0548 (all data) Final wR(F2) values 0.0637 0.0931 0.0795 0.1098 0.0714 0.1070 (all data) Goodness of fit on F2 1.028 1.020 1.044 0.849 1.147 1.040 A-1 32[BPh4] 33 34 35[BPh4] 36 37 Chemical formula C70H106BClOP4Ru C45H81FeN2P4 C44.50H84N2P4Ru C66H96BFeN2P4 C44.50H83ClP4Ru C42H80FeP4 Formula Mass 1234.76 829.85 872.09 1107.99 878.51 764.79 Crystal system Monoclinic Triclinic Monoclinic Triclinic Monoclinic Triclinic a/Å 13.3779(5) 13.669(3) 13.6360(5) 12.7369(11) 13.905(2) 13.7011(9) b/Å 14.0391(6) 13.689(3) 14.2697(5) 14.0990(13) 26.160(5) 16.1969(11) c/Å 34.5248(14) 14.026(3) 23.6883(7) 17.5151(17) 14.691(3) 19.7521(13) Į/deg 90.00 96.14(3) 90.00 79.842(5) 90.00 80.320(3) ȕ/deg 96.731(2) 96.77(3) 90.5590(10) 75.048(5) 114.028(8) 83.021(3) Ȗ/deg 90.00 119.69(3) 90.00 83.820(5) 90.00 78.371(3) V(Å3) 6439.5(4) 2222.0(8) 4609.1(3) 2984.8(5) 4880.9(15) 4214.7(5) Temperature/K 155(2) 100(2) 152(2) 154(2) 160(2) 155(2) Space group P2(1)/c P1¯ P2(1)/n P1¯ P21/c P1¯ Z 4 2 4 2 4 4 ȝ(Mo KĮ) (mm-1) 0.427 0.516 0.511 0.402 0.534 0.537 N 46797 28651 40047 39524 35186 55487 Nind 11278 7306 10047 10247 8604 14758 Rint 0.0912 0.0250 0.0409 0.0880 0.1575 0.0572 Final R1 values 0.0485 0.0436 0.0268 0.0696 0.0715 0.0409 (I > 2ı(I)) Final wR(F2) values 0.1183 0.1087 0.0614 0.1760 0.1636 0.0825 (I > 2ı(I)) Final R1 values 0.0973 0.0460 0.0390 0.1491 0.1778 0.0789 (all data) Final wR(F2) values 0.1511 0.1105 0.0670 0.2126 0.2152 0.0970 (all data) Goodness of fit on F2 0.876 1.042 1.015 1.122 0.999 0.986 38[BF4] 39[BF4] 46 48 49 Chemical formula C88H166B2F8Fe2N4OP8 C44H82BF4N2OP4Ru C43H79P3 C44H79OP3Ru C43H79N2P3Ru Formula Mass 1829.33 966.88 688.97 818.05 818.06 Crystal system Triclinic Triclinic Triclinic Triclinic Triclinic a/Å 10.164(2) 10.3846(3) 11.0741(8) 10.511(3) 10.536(2) b/Å 13.584(3) 13.8215(4) 14.8454(9) 13.667(3) 13.668(2) c/Å 18.239(4) 18.2337(6) 15.0177(11) 15.024(3) 14.990(3) Į/deg 85.44(3) 84.1190(10) 65.260(2) 81.545(9) 81.717(11) ȕ/deg 78.68(3) 75.7350(10) 74.434(3) 86.104(9) 86.748(10) Ȗ/deg 83.89(3) 86.2970(10) 77.137(3) 83.236(8) 83.654(10) V(Å3) 2450.8(8) 2520.95(13) 2142.8(3) 2117.1(8) 2121.2(7) Temperature/K 100(2) 155(2) 166(2) 155(2) 155(2) Space group P1¯ P1¯ P1¯ P1¯ P1¯ Z 1 2 2 2 2 ȝ(Mo KĮ) (mm-1) 0.486 0.486 0.166 0.516 0.514 N 31485 41115 29174 25227 26451 Nind 8092 8846 7506 7385 7386 Rint 0.0515 0.0366 0.0370 0.2034 0.0686 Final R1 values 0.0717 0.0360 0.1537 0.0926 0.0612 (I > 2ı(I)) Final wR(F2) values 0.1985 0.1015 0.4457 0.1943 0.1690 (I > 2ı(I)) Final R1 values 0.0849 0.0403 0.2000 0.2370 0.0878 (all data) Final wR(F2) values 0.2077 0.1058 0.4917 0.2803 0.1830 (all data) Goodness of fit on F2 1.130 1.060 1.926 0.989 1.216 A-2 Appendix A2 Ruthenium dinitrogen complexes Species / Complex ƭNN NɁN Bond Ref. (cmí1) length (Å) a 1 NɁN 2331 1.0975 PhN=NPh 1442a 1.255 1 a 1 H2NíNH2 1111 1.460 Ru(0) Complexes iPr b 2 [Ru(PP 3)(N2)] 2083 1.109(4) iPr c 3 [K(THF)x][(SiP 3)Ru(N2)] 1960 1.130(3) Mes 4 [N3 ]Ru}2(ȝ-N2) - - Xyl 4 [N3 ]Ru}2(ȝ-N2) - - t Mes 4 [ Bu-N3 ]Ru}2(ȝ-N2) - 1.161(5) Ru(I) Complexes iPr c 3 [(SiP 3)Ru(N2)] 2088 1.097(5) Ru(II) Complexes t b,c 5 [RuCl(N2)(POP- Bu)](BPh4) * 2143 1.054(4) i c 5 [RuCl2(N2)(POP- Pr)] * 2115 1.101(5) b 6 [Ru(Tp)(dippae)(N2)](BArF24) 2157 0.999(8) b 6 [Ru(Tp)(N2)(R,R-dippach)](BArF24) 2160 1.054(4) 4 t c 7 [Ru(N2)(ƪ -PNPSi- Bu)](OTf) 2079 1.115(5) i h 8 cis-[^Ru(acac)2(P Pr3)`2(Ƭ-N2)] 2089 1.135(8) bu c 9 [Ru(py S4)(N2)] 2134 - c 10 [Ru(‘N2Me2S2’)(N2)(PCy3)] 2115 - c 10 [Ru(‘N2Me2S2’)(N2)(PPh3)] 2130 - i c 11 [Ru(‘N2Me2S2’)(N2)(P Pr3)] 2113 1.110(4) i d 11 [^Ru(‘N2Me2S2’)(P Pr3)`2(Ƭ-N2)] 2047 1.125(7) t c 12 [Ru(H)Cl(N2)(PNP- Bu)] 2111 1.107(4) t 12 [^RuCl2(PNP- Bu)`2(Ƭ-N2)] - 1.119(4) c 13 [RuCl((R,R)-CHIRAPHOS)2(N2)](OTf) 2155 1.02(1) t b 14 [Ru(SiPhHCl) 1,3-(P Bu2CH2)2C6H3 (N2)] 2042 1.099(3) d 15 [^Ru(C5H5)(dippe)`2(Ƭ-N2)](BArF24)2 2050 1.118(3) d 15 [^Ru(C5H5)(PEt3)2`2(Ƭ-N2)](BArF24)2 2064 1.114(5) b 15 [Ru(C5H5)(dippe)(N2)](BArF24) 2158 1.087(4) i b 15 [Ru(C5H5)(N2)(PMe Pr2)2](BArF24) * 2164 - i b 15 [Ru(C5H5)(N2)(PMe Pr2)(PPh3)](BArF24) * 2177 - + c 16 [RuCl(N2)(NNNN)] 2074 - + c 16 [Ru(OH)(N2)(NNNN)] 2055 - 2+ c 16 [Ru(N2)(NNNN)(OH2)] 2113 - 2+ d 17 [^RuCl(NNNN)`2(Ƭ-N2)] 2029 - b 18 [Ru(C5Me5)(N2)(PEt3)2](BPh4) * 2134 - t 19 [^Ru(H)(PCP- Bu)`2(μ-N2)] - 1.134(6) t e 19 [Ru(H)(PCP- Bu)(N2)] 2088 - d 20 [^RuCl2(NN’N)`2(Ƭ-N2)] 2099 1.110(3) i b 21 [^Ru(H)2(N2)(P Pr3)2`2(Ƭ-N2)] * 2165 1.105(2) 2131b 1.107(2) 2088b,i 1.113(2)d i 22 [Ru(H)Cl(N2)(P Pr3)2] * - 1.10(2) f 23 [^Ru(H)(SiMe3)(PMe3)3`2(Ƭ-N2)] * 2150 1.104(8) + b 24 trans-[Ru(H)(dppe)2(N2)] * 2194 - A-3 + b 25 trans-[Ru(H)(depe)2(N2)] * 2163 - b 26 [Ru(Tp)(N2)(dippe)](BPh4) 2165 - h 27 [Ru(Tp)(N2)(pn)](BPh4) 2182 1.097(5) b 28 [Ru(H)(R,R’-Me-DuPHOS)2(N2)](PF6) 2184 1.090(4) b 29 trans-[RuCl(16-TMC)(N2)](PF6) 2075 1.005(10) d,g 30 [Ru2(*Im)2(Ƭ-N2)(DPB)] 2112 - a 31 [Ru(NH3)5(N2)]Cl2 * 2105 1.12(8) a 31a [Ru(NH3)5(N2)]Br2 * 2114 - a 31a [Ru(NH3)5(N2)]I2 * 2129 - a 31a [Ru(NH3)5(N2)](BF4)2 * 2144 - a 31a [Ru(NH3)5(N2)](PF6)2 * 2167 - d 32 [^Ru(NH3)5`2(Ƭ-N2)](BF4)4 * 2100 1.124(15) c 33 [Ru(H)2(cyttp)(N2)] 2100 1.093(8) b 34 [(H)(PPh3)2Ru(Ƭ-H)3Ru(N2)(PPh3)2] * 2140 1.08(4) a 35 [Ru(OEP)(N2)(thf)] 2110 - a 36 [Ru(TMP)(N2)2] 2203 - a 36 [Ru(TMP)(N2)] 2137 - a 36 [Ru(TMP)(N2)(OEt2)] 2116 - a 36-37 [Ru(TMP)(N2)(thf)] 2116 1.074(16) a 37 [Ru(TMP)(dmf)(N2)] 2108 - a 37 [Ru(TMP)(Et3N)(N2)] * 2147 - i b 38 [Ru(Tp)(N2)(P Pr2Me)2](BPh4) 2159 - b 38 [Ru(Tp)(N2)(PEt3)2](BPh4) 2163 1.01(2) a 39 [Ru(Tp)(N2)(PPh3)2](BF4) 2177 - a 40 trans-[Ru(N3)(en)2(N2)](PF6) 2103 1.106(11) a 41 cis-[Ru(N3)(en)2(N2)](PF6) 2130 - a 41 cis-[Ru(N3)(N2)(trien)](PF6) 2120 - a 41 cis-[Ru(en)2(H2O)(N2)](BPh4)2 2130 - a 41 cis-[Ru(en)2(N2)2](BPh4)2 2220 - 2190a 5 b 42 [Ru(ƪ -edta)(N2)](NH4)2 2110 - 5 d 42 [^Ru(ƪ -edta)`2(N2)]Mg2 2060 - b 43 [(dcypb)(N2)Ru(Ƭ-Cl)3RuCl(dcypb)] 2124 - j 44 [(dppb)(N2)Ru(Ƭ-Cl)3RuCl(dppb)] 2175 - b 45 [Ru(H)(N2)(PP3)](BPh4) * 2182 - b 46 [Ru(H)2(N2)(PPh3)3] * 2147 - iPr b 2 [Ru(PP 3)H(N2)][BF4] 2171 1.092(4) iPr c 3 [(SiP 3)RuH(N2)] 2140 1.100(3) iPr F 3 [(SiP 3)Ru(N2)][BAr 4] - 1.071(3) (CF3)2 i 47 [(Bp )RuH( Pr2NH)]2(N2) - 1.138(8) i c 48 [RuCl(CH=CHPh)(N2)(P Pr3)2] 2067 1.088(8) f 49 [(CpRu(PPh3)2)2(ȝ-N2)][BAr 4]2 - 1.09(3) f k 49 [CpRu(dcype)(N2)][BAr 4] 1959 1.12(2) b 50 [RuHCl(IMes)2(N2)] 2041 x c 51 [Ru(2,2-bdmpzp)Cl(N2)(PPh3)] 2129 x j 52 [Ru(Me2bipy)(PPh3)2(– 2149 1.011(6) CŁCBut)(NŁN)][PF6] MsCl3 53 [(Ru )RuCl(PCy3)](N2) - 1.120(4) c 54 [Ru(F)(TMC)(N2)][PF6] 2064 1.144(8) * f b 55 [Cp Ru(N2)(dppm)][BAr 4] 2166 1.083(4) * f b 55 [Cp Ru(N2)(dppe)][BAr 4] 2159 - c,d 56 [(LOEtRu(bpy))2(μ-N2)][BF4]2 2000 1.130(6) [(Ș5:ı- - 1.099(10) 57 Me2Si(C5H4)(C2B10H10))Ru(PPh3)]2(μ-N2) A-4 1 f k 58 [(PCP)Ru(CO)(Ș -N2)][BAr 4] 2249 1.069(3) Xyl 59 [(N3 )Ru]2(ȝ-N2) - 1.161(5) Xyl 59 [(N3 )Ru(H)]2(ȝ-N2) - 1.132(6) Mes NN g 60 (N3 )Ru(Si )(N2) 2095 1.101(11) c 61 Ru(Ir3S4)(N2)(tmeda) 2019 1.06(1) 4 62 [((H(Na)C=C=)Ru(N Me8))2(μ-N2)-(μ-Na)4] - 1.284(15) 3 b 63 RuH(Ș -PCP)(PPh3)(N2) 2134 1.111(6) 64 [(PNN)Ru(Cl)2]2(μ-N2) - 1.121(6) t b 65 RuH(N2)[CH(C2H4PBu 2)2] 2061 1.117(5) * PO 66 [Cp Ru(I )]2(N2) - 1.131(8) * 2 i f b 67 Cp Ru(N2)(ț -P,N- Pr2PCH2(Quin))][BAr 4] 2169 1.096(3) * 2 i f b 67 Cp Ru(N2)(ț -P,N- Pr2PCH2Py)][BAr 4] 2152 - f b 68 [CpRu(N2)(R,R-dippach)][BAr 4] 2186 1.096(7) * f b 68 [Cp Ru(N2)(R,R-dippach)][BAr 4] 2142 - f b 68 [CpRu(N2)(dippae)][BAr 4] 2178 - * f b 68 [Cp Ru(N2)(dippae)][BAr 4] 2201 - 69 [(dcypb)(H)Ru(μ-Cl)3Ru(dcypb)(N2)] - 1.110(5) c 70 [Ru(OH)(TMC)(N2)](PF6) 2050 1.128(6) a – not reported; b – Nujol c – KBr; d – raman; e – toluene; f – pentane; g – benzene; h – ATR; i – weak / bridging; j – dichloromethane; k - flurobenzene, x - too disordered to determine accurate metric data, Ligand Abbreviations 16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane; f í BAr 4 = [B[3,5-(CF3)2C6H3]4] ; Bp(CF3)2 = dihydridobis(3,5-bis(trifluromethyl)pyrazolyl)borate; bpy = 2,2'-bipyridyl; 5 Cp = Ș -C5H5; * 5 Cp = Ș -C5Me5; dcypb = Cy2PCH2CH2CH2CH2PCy2; dcype = Cy2PCH2CH2PCy2 depe = Et2PCH2CH2PEt2; dippae = 1,2-bis((diisopropylphosphino)amino)ethane; i i dippe = Pr2PCH2CH2P Pr2; dmf = dimethylformamide; DPB = diporphyrinatobiphenylene tetraanion; dppb = Ph2PCH2CH2CH2CH2PPh2; dppe = Ph2PCH2CH2PPh2; dppm = Ph2PCH2PPh2; edta = eithylenediaminetetraacetate; en = ethylenediamine; *Im = 1-tert-butyl-5-phenylimidizole; IMes = N,N’-bis(mesityl)imidazol-2-ylidene; PO 2 i I = ț -P,O-1-P Pr2-2-indanone * 2- Ir3S4 = [(Cp Ir)3(μ3-S)(μ2-S)3] ; - LOEt [CpCo-(P(O)(OEt)2)3] ; Me2bipy = 4,4'-Me2-2,2'-bipyridine; Meso IX, DOE = mesoporphyrin IX dioctadecyl ester; A-5 Ligand Abbreviations cont. Me2bipy = 4,4'-Me2-2,2'-bipyridine; 4 N Me8 = meso-octamethylporphyrinogen tetraanion; Mes N3 = 2,6-(MesN=CMe)2C5H3N; 2- ‘N2Me2S2’ = [1,2-ethanediamine-N,N'-dimthyl-N,N'-bis(2-benzenethilate)] ; NN'N = 2,6-bis[(dimethylamino)methyl]pyridine; NNNN = 2,5,9,12-tetramethyl-2,5,9,12-tetraazatridecane; Xyl N3 = 2,6-(XylN=CMe)2C5H3N; OEP = octaethylporphyrin; t PCP = 2,6-(CH2P Bu2)2C6H3; t t - PCP- Bu = [2,6-(P Bu2CH2)2C6H3] ; pn = Ph2PCH2CH2NMe2; PNN = 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine PNP-tBu = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine; t t POP- Bu = O(CH2CH2P Bu2)2; i i POP- Pr = O(CH2CH2P Pr2)2; PP3 = P(CH2CH2PPh2)3; iPr i PP3 = P(CH2CH2P Pr2)3; Py = Pyridine bu 2- py S4 = [2,6-bis((3,5-di-tert-butyl-2sulfanylphenyl)thiomethyl)-pyridine] ; Quin = Quinoline (R,R)-CHIRAPHOS = 2,3-bis(diphenylphosphino)butane; R,R-dippach = (R,R)-1,2-bis(diisopropylphosphino)amino)cyclohexane; R,R'-Me-DuPHOS = 1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene; RuMsCl3 = Ruthenium(μ6-mesitylene)trichloride; NN t Si = Si[(NCH2Bu )2C6H4-1,2]; Pr - Pr - - (SiPi 3) ((SiPi 3) = (2-iPr2PC6H4)3Si ); Ph - Ph - - (SiP 3) ((SiP 3) = (2-Ph2PC6H4)3Si ); TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; tmeda = Me2NCH2CH2NMe2; TMP = tetramesitylporphyrin; Tp = hydro(tris(pyrazol-1-yl)borate)); References 1. 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A-9 Appendix A2 Ruthenium dinitrogen complexes Species / Complex ƭNN NɁN Bond Ref. (cmí1) length (Å) a 1 NɁN 2331 1.0975 PhN=NPh 1442a 1.255 1 a 1 H2NíNH2 1111 1.460 Ru(0) Complexes iPr b 2 [Ru(PP 3)(N2)] 2083 1.109(4) iPr c 3 [K(THF)x][(SiP 3)Ru(N2)] 1960 1.130(3) Mes 4 [N3 ]Ru}2(ȝ-N2) - - Xyl 4 [N3 ]Ru}2(ȝ-N2) - - t Mes 4 [ Bu-N3 ]Ru}2(ȝ-N2) - 1.161(5) Ru(I) Complexes iPr c 3 [(SiP 3)Ru(N2)] 2088 1.097(5) Ru(II) Complexes t b,c 5 [RuCl(N2)(POP- Bu)](BPh4) * 2143 1.054(4) i c 5 [RuCl2(N2)(POP- Pr)] * 2115 1.101(5) b 6 [Ru(Tp)(dippae)(N2)](BArF24) 2157 0.999(8) b 6 [Ru(Tp)(N2)(R,R-dippach)](BArF24) 2160 1.054(4) 4 t c 7 [Ru(N2)(ƪ -PNPSi- Bu)](OTf) 2079 1.115(5) i h 8 cis-[^Ru(acac)2(P Pr3)`2(Ƭ-N2)] 2089 1.135(8) bu c 9 [Ru(py S4)(N2)] 2134 - c 10 [Ru(‘N2Me2S2’)(N2)(PCy3)] 2115 - c 10 [Ru(‘N2Me2S2’)(N2)(PPh3)] 2130 - i c 11 [Ru(‘N2Me2S2’)(N2)(P Pr3)] 2113 1.110(4) i d 11 [^Ru(‘N2Me2S2’)(P Pr3)`2(Ƭ-N2)] 2047 1.125(7) t c 12 [Ru(H)Cl(N2)(PNP- Bu)] 2111 1.107(4) t 12 [^RuCl2(PNP- Bu)`2(Ƭ-N2)] - 1.119(4) c 13 [RuCl((R,R)-CHIRAPHOS)2(N2)](OTf) 2155 1.02(1) t b 14 [Ru(SiPhHCl) 1,3-(P Bu2CH2)2C6H3 (N2)] 2042 1.099(3) d 15 [^Ru(C5H5)(dippe)`2(Ƭ-N2)](BArF24)2 2050 1.118(3) d 15 [^Ru(C5H5)(PEt3)2`2(Ƭ-N2)](BArF24)2 2064 1.114(5) b 15 [Ru(C5H5)(dippe)(N2)](BArF24) 2158 1.087(4) i b 15 [Ru(C5H5)(N2)(PMe Pr2)2](BArF24) * 2164 - i b 15 [Ru(C5H5)(N2)(PMe Pr2)(PPh3)](BArF24) * 2177 - + c 16 [RuCl(N2)(NNNN)] 2074 - + c 16 [Ru(OH)(N2)(NNNN)] 2055 - 2+ c 16 [Ru(N2)(NNNN)(OH2)] 2113 - 2+ d 17 [^RuCl(NNNN)`2(Ƭ-N2)] 2029 - b 18 [Ru(C5Me5)(N2)(PEt3)2](BPh4) * 2134 - t 19 [^Ru(H)(PCP- Bu)`2(μ-N2)] - 1.134(6) t e 19 [Ru(H)(PCP- Bu)(N2)] 2088 - d 20 [^RuCl2(NN’N)`2(Ƭ-N2)] 2099 1.110(3) i b 21 [^Ru(H)2(N2)(P Pr3)2`2(Ƭ-N2)] * 2165 1.105(2) 2131b 1.107(2) 2088b,i 1.113(2)d i 22 [Ru(H)Cl(N2)(P Pr3)2] * - 1.10(2) f 23 [^Ru(H)(SiMe3)(PMe3)3`2(Ƭ-N2)] * 2150 1.104(8) + b 24 trans-[Ru(H)(dppe)2(N2)] * 2194 - A-3 + b 25 trans-[Ru(H)(depe)2(N2)] * 2163 - b 26 [Ru(Tp)(N2)(dippe)](BPh4) 2165 - h 27 [Ru(Tp)(N2)(pn)](BPh4) 2182 1.097(5) b 28 [Ru(H)(R,R’-Me-DuPHOS)2(N2)](PF6) 2184 1.090(4) b 29 trans-[RuCl(16-TMC)(N2)](PF6) 2075 1.005(10) d,g 30 [Ru2(*Im)2(Ƭ-N2)(DPB)] 2112 - a 31 [Ru(NH3)5(N2)]Cl2 * 2105 1.12(8) a 31a [Ru(NH3)5(N2)]Br2 * 2114 - a 31a [Ru(NH3)5(N2)]I2 * 2129 - a 31a [Ru(NH3)5(N2)](BF4)2 * 2144 - a 31a [Ru(NH3)5(N2)](PF6)2 * 2167 - d 32 [^Ru(NH3)5`2(Ƭ-N2)](BF4)4 * 2100 1.124(15) c 33 [Ru(H)2(cyttp)(N2)] 2100 1.093(8) b 34 [(H)(PPh3)2Ru(Ƭ-H)3Ru(N2)(PPh3)2] * 2140 1.08(4) a 35 [Ru(OEP)(N2)(thf)] 2110 - a 36 [Ru(TMP)(N2)2] 2203 - a 36 [Ru(TMP)(N2)] 2137 - a 36 [Ru(TMP)(N2)(OEt2)] 2116 - a 36-37 [Ru(TMP)(N2)(thf)] 2116 1.074(16) a 37 [Ru(TMP)(dmf)(N2)] 2108 - a 37 [Ru(TMP)(Et3N)(N2)] * 2147 - i b 38 [Ru(Tp)(N2)(P Pr2Me)2](BPh4) 2159 - b 38 [Ru(Tp)(N2)(PEt3)2](BPh4) 2163 1.01(2) a 39 [Ru(Tp)(N2)(PPh3)2](BF4) 2177 - a 40 trans-[Ru(N3)(en)2(N2)](PF6) 2103 1.106(11) a 41 cis-[Ru(N3)(en)2(N2)](PF6) 2130 - a 41 cis-[Ru(N3)(N2)(trien)](PF6) 2120 - a 41 cis-[Ru(en)2(H2O)(N2)](BPh4)2 2130 - a 41 cis-[Ru(en)2(N2)2](BPh4)2 2220 - 2190a 5 b 42 [Ru(ƪ -edta)(N2)](NH4)2 2110 - 5 d 42 [^Ru(ƪ -edta)`2(N2)]Mg2 2060 - b 43 [(dcypb)(N2)Ru(Ƭ-Cl)3RuCl(dcypb)] 2124 - j 44 [(dppb)(N2)Ru(Ƭ-Cl)3RuCl(dppb)] 2175 - b 45 [Ru(H)(N2)(PP3)](BPh4) * 2182 - b 46 [Ru(H)2(N2)(PPh3)3] * 2147 - iPr b 2 [Ru(PP 3)H(N2)][BF4] 2171 1.092(4) iPr c 3 [(SiP 3)RuH(N2)] 2140 1.100(3) iPr F 3 [(SiP 3)Ru(N2)][BAr 4] - 1.071(3) (CF3)2 i 47 [(Bp )RuH( Pr2NH)]2(N2) - 1.138(8) i c 48 [RuCl(CH=CHPh)(N2)(P Pr3)2] 2067 1.088(8) f 49 [(CpRu(PPh3)2)2(ȝ-N2)][BAr 4]2 - 1.09(3) f k 49 [CpRu(dcype)(N2)][BAr 4] 1959 1.12(2) b 50 [RuHCl(IMes)2(N2)] 2041 x c 51 [Ru(2,2-bdmpzp)Cl(N2)(PPh3)] 2129 x j 52 [Ru(Me2bipy)(PPh3)2(– 2149 1.011(6) CŁCBut)(NŁN)][PF6] MsCl3 53 [(Ru )RuCl(PCy3)](N2) - 1.120(4) c 54 [Ru(F)(TMC)(N2)][PF6] 2064 1.144(8) * f b 55 [Cp Ru(N2)(dppm)][BAr 4] 2166 1.083(4) * f b 55 [Cp Ru(N2)(dppe)][BAr 4] 2159 - c,d 56 [(LOEtRu(bpy))2(μ-N2)][BF4]2 2000 1.130(6) [(Ș5:ı- - 1.099(10) 57 Me2Si(C5H4)(C2B10H10))Ru(PPh3)]2(μ-N2) A-4 1 f k 58 [(PCP)Ru(CO)(Ș -N2)][BAr 4] 2249 1.069(3) Xyl 59 [(N3 )Ru]2(ȝ-N2) - 1.161(5) Xyl 59 [(N3 )Ru(H)]2(ȝ-N2) - 1.132(6) Mes NN g 60 (N3 )Ru(Si )(N2) 2095 1.101(11) c 61 Ru(Ir3S4)(N2)(tmeda) 2019 1.06(1) 4 62 [((H(Na)C=C=)Ru(N Me8))2(μ-N2)-(μ-Na)4] - 1.284(15) 3 b 63 RuH(Ș -PCP)(PPh3)(N2) 2134 1.111(6) 64 [(PNN)Ru(Cl)2]2(μ-N2) - 1.121(6) t b 65 RuH(N2)[CH(C2H4PBu 2)2] 2061 1.117(5) * PO 66 [Cp Ru(I )]2(N2) - 1.131(8) * 2 i f b 67 Cp Ru(N2)(ț -P,N- Pr2PCH2(Quin))][BAr 4] 2169 1.096(3) * 2 i f b 67 Cp Ru(N2)(ț -P,N- Pr2PCH2Py)][BAr 4] 2152 - f b 68 [CpRu(N2)(R,R-dippach)][BAr 4] 2186 1.096(7) * f b 68 [Cp Ru(N2)(R,R-dippach)][BAr 4] 2142 - f b 68 [CpRu(N2)(dippae)][BAr 4] 2178 - * f b 68 [Cp Ru(N2)(dippae)][BAr 4] 2201 - 69 [(dcypb)(H)Ru(μ-Cl)3Ru(dcypb)(N2)] - 1.110(5) c 70 [Ru(OH)(TMC)(N2)](PF6) 2050 1.128(6) a – not reported; b – Nujol c – KBr; d – raman; e – toluene; f – pentane; g – benzene; h – ATR; i – weak / bridging; j – dichloromethane; k - flurobenzene, x - too disordered to determine accurate metric data, Ligand Abbreviations 16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane; f í BAr 4 = [B[3,5-(CF3)2C6H3]4] ; Bp(CF3)2 = dihydridobis(3,5-bis(trifluromethyl)pyrazolyl)borate; bpy = 2,2'-bipyridyl; 5 Cp = Ș -C5H5; * 5 Cp = Ș -C5Me5; dcypb = Cy2PCH2CH2CH2CH2PCy2; dcype = Cy2PCH2CH2PCy2 depe = Et2PCH2CH2PEt2; dippae = 1,2-bis((diisopropylphosphino)amino)ethane; i i dippe = Pr2PCH2CH2P Pr2; dmf = dimethylformamide; DPB = diporphyrinatobiphenylene tetraanion; dppb = Ph2PCH2CH2CH2CH2PPh2; dppe = Ph2PCH2CH2PPh2; dppm = Ph2PCH2PPh2; edta = eithylenediaminetetraacetate; en = ethylenediamine; *Im = 1-tert-butyl-5-phenylimidizole; IMes = N,N’-bis(mesityl)imidazol-2-ylidene; PO 2 i I = ț -P,O-1-P Pr2-2-indanone * 2- Ir3S4 = [(Cp Ir)3(μ3-S)(μ2-S)3] ; - LOEt [CpCo-(P(O)(OEt)2)3] ; Me2bipy = 4,4'-Me2-2,2'-bipyridine; Meso IX, DOE = mesoporphyrin IX dioctadecyl ester; A-5 Ligand Abbreviations cont. Me2bipy = 4,4'-Me2-2,2'-bipyridine; 4 N Me8 = meso-octamethylporphyrinogen tetraanion; Mes N3 = 2,6-(MesN=CMe)2C5H3N; 2- ‘N2Me2S2’ = [1,2-ethanediamine-N,N'-dimthyl-N,N'-bis(2-benzenethilate)] ; NN'N = 2,6-bis[(dimethylamino)methyl]pyridine; NNNN = 2,5,9,12-tetramethyl-2,5,9,12-tetraazatridecane; Xyl N3 = 2,6-(XylN=CMe)2C5H3N; OEP = octaethylporphyrin; t PCP = 2,6-(CH2P Bu2)2C6H3; t t - PCP- Bu = [2,6-(P Bu2CH2)2C6H3] ; pn = Ph2PCH2CH2NMe2; PNN = 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine PNP-tBu = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine; t t POP- Bu = O(CH2CH2P Bu2)2; i i POP- Pr = O(CH2CH2P Pr2)2; PP3 = P(CH2CH2PPh2)3; iPr i PP3 = P(CH2CH2P Pr2)3; Py = Pyridine bu 2- py S4 = [2,6-bis((3,5-di-tert-butyl-2sulfanylphenyl)thiomethyl)-pyridine] ; Quin = Quinoline (R,R)-CHIRAPHOS = 2,3-bis(diphenylphosphino)butane; R,R-dippach = (R,R)-1,2-bis(diisopropylphosphino)amino)cyclohexane; R,R'-Me-DuPHOS = 1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene; RuMsCl3 = Ruthenium(μ6-mesitylene)trichloride; NN t Si = Si[(NCH2Bu )2C6H4-1,2]; Pr - Pr - - (SiPi 3) ((SiPi 3) = (2-iPr2PC6H4)3Si ); Ph - Ph - - (SiP 3) ((SiP 3) = (2-Ph2PC6H4)3Si ); TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; tmeda = Me2NCH2CH2NMe2; TMP = tetramesitylporphyrin; Tp = hydro(tris(pyrazol-1-yl)borate)); References 1. 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A-10 ARTICLE pubs.acs.org/IC Ruthenium Hydride Complexes of the Hindered Phosphine Ligand Tris(3-diisopropylphosphinopropyl)phosphine Mohan M. Bhadbhade,‡ Leslie D. Field,*,† Ryan Gilbert-Wilson,† Ruth W. Guest,§ and Paul Jensen§ † ‡ School of Chemistry and Mark Wainwright Analytical Centre, The University of New South Wales, NSW 2052, Australia §School of Chemistry, University of Sydney, NSW 2006, Australia bS Supporting Information ABSTRACT: The synthesis and characterization of the novel i hindered tripodal phosphine ligand P(CH2CH2CH2P Pr2)3 3 iPr (P P3 )(1) are reported, along with the synthesis and characterization of ruthenium chloro and hydrido complexes 3 i 3 i 3 iPr of 1. Complexes [RuCl(P P3 Pr)][BPh4](2[BPh4]), RuH2(P P3 Pr) (3), and [Ru(H2)(H)(P P3 )][BPh4](4[BPh4]) were characterized by crystallography. Complex 2 is fluxional in solution, and low-temperature NMR spectroscopy of the complex correlates well with two dynamic processes, an exchange between stereoisomers and a faster turnstile-type exchange within one of the stereoisomers. ’ INTRODUCTION This work reports a reasonable synthetic route to the hindered Polydentate phosphines have become important ligands for ligand as well as the formation and characterization of the iron controlling the stereochemistry of coordination complexes and and ruthenium chloro and hydrido complexes. Characterization have also been used to solubilize metal catalysts.1 PP ligands, such of these complexes allows analysis of the geometry around the 3 metal center as well as provides an initial assessment of the as P((CH2)nPR2)3 (n = 2, 3; R= Me, Ph), form metal complexes with a range of applications, especially for complexes of iron and chemistry of these metal complexes. ruthenium. Applications have ranged from the stabilization of complexes containing η2-dihydrogen to the formation of stable ’ RESULTS AND DISCUSSION dinitrogen complexes with iron and ruthenium in both the 0 Syntheses of other PP -type ligands with propylene bridges þ 2 3 and 2 oxidation states. The PP3-type ligand provides a strong between the apical and terminal phosphines have usually coordination environment and is able to coordinate to the metal at involved the radical-initiated addition of a dialkylphoshine up to four points through the four phosphine donors. Binding to (R2P H) across the double bond of triallylphosphine. Synth- form complexes with octahedral, trigonal bipyramidal, and also eses of both P(CH2CH2CH2PMe2)3 and P(CH2CH2CH2- 6e square-pyramidal geometry is possible with PP3-type ligands. In an PEt2)3 have been reported using this general approach. While i octahedral system, coordination of PP3-type ligands leaves two P(CH2CH2CH2P Pr2)3 (1) can be synthesized by this ap- free coordination sites for other ligands, and these are geometry proach, the long reaction time and the tendency to form i i constrained by the ligand to be in a cis arrangement. It is known P Pr2CH2CH2CH2P Pr2 as a reaction side product make it a that a cis arrangement of two ligands is a necessity for some parts of less than ideal synthesis. 3 3 i ffi common catalytic mechanisms, such as migratory insertion. Thus P P3 Pr (1) can be synthesized more e ciently using an PP3-type complexes often have higher catalytic activity, compared alternative approach via nucleophilic substitution of the halide to complexes with mono or bidentate ligands, which can form in tris(3-bromopropyl)phosphine with a dialkylphosphide inactive isomers where the two reactive ligands are in the unreac- 4 (Scheme 1). Tris(3-hydroxypropyl)phosphine was bromi- tive trans arrangement. nated using phosphorus tribromide to give the unstable tris- The encapsulating nature of PP3 ligands and the presence of (3-bromopropyl)phosphine. Tris(3-bromopropyl)phosphine sterically bulky groups on the terminal phosphines of PP3 ligands tends to form a mixture of oligomeric and polymeric products also has the propensity to restrict access to the metal center and on standing, probably by intramolecular or intermolecular enhance chemical reaction at any of the non-PP3 ligands. nucleophilic attack of the central phosphine on a brominated There is now an expanding range of sterically encumbered, γ 5 -carbon, to form an insoluble solid mass within a few hours. polydentate ligands available, and we report here the synthesis Tris(3-bromopropyl)phosphine was used immediately in the fi of the hindered tripodal tetradentate phosphine ligand next step of the sequence without further puri cation. P(CH2- i 3 iPr i 3 iPr P(CH2CH2CH2P Pr2)3 (P P3 ). This ligand is a more hindered CH2CH2P Pr2)3,PP3 (1) was prepared in moderate yield version of the PP3-type ligand skeleton, P(CH2CH2CH2PR2)3 which is known with either ethyl or methyl substituents on the Received: March 9, 2011 6 terminal phosphine donors. Published: June 01, 2011 r 2011 American Chemical Society 6220 dx.doi.org/10.1021/ic200492w | Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE (51% from tris(3-hydroxypropyl)phosphine) by the nucleo- grown from a THF/pentane solution of 2[BPh4] (Figure 1A), philic substitution of bromide in the reaction of lithium diiso- and selected bond angles and lengths are given in Table 1. i ffi propylphosphide, (LiP Pr2) with tris(3-bromopropyl)phosphine The two structures within the asymmetric unit are su ciently (Scheme 1). This method of synthesis is relatively direct and similar that the crystallographic data of only one of the config- clean and avoids the difficulty of the alternative radical route urations, namely Ru1, is detailed here. Each asymmetric unit which typically requires prolonged reaction times with volatile within the crystal structure contains one THF molecule, giving and reactive secondary phosphines and the known formation of half a THF solvate for each metal complex. 6e 3 iPr þ unwanted byproduct. The geometry of [RuCl(P P3 )] (2) is a distorted square- 31 {1 } i 3 iPr In the P H spectrum of P(CH2CH2CH2P Pr2)3,PP3 based pyramid with atoms Cl1, P1, P2, and P4 making up the (1), two resonances are observed at 1.9 and 34.7 ppm, and base and P3 at the apex (τ = 0.13).8 In this instance, the ° these are assigned to the terminal phosphines and the central PE Ru PE angle, P1 Ru1 P4, at 156.51(2) is appreciably phosphine respectively. Both resonances are singlets with no closer to that of a square-based pyramid (180°) than a trigonal ° discernible coupling between the two phosphine environments, bipyramid (120 ). In addition, the Ru PT bond length, 3 fi and this is consistent with data reported for other P P3-type Ru1 P3, at 2.2536(6) Å is signi cantly shorter than the Ru PE ligands incorporating propylene bridges between the apical and bond lengths Ru1 P1 and Ru1 P4 (2.4629(6) and 2.3892(7) terminal phosphines.6e Å, respectively), and this is characteristic of square-based pyr- fi Tripodal phosphorus ligands of the P((CH2)nPR2)3 (n =2,3) amid geometry. One of the isopropyl methyl groups lls and type are well established as good ligands at ruthenium centers,7 blocks the void under the base of the pyramid probably through 3 iPr and in this work, the P P3 ligand 1 was successfully employed an anagostic (pseudoagostic) interaction (d(Ru H) = 2.637 Å in the synthesis of the five-coordinate chloro complex of ruthe- (Ru1) and 2.369 Å (Ru2); Ru C H = 127.75°(Ru1) and 3 iPr þ ° 9 nium [RuCl(P P3 )] (2). 131.18 (Ru2)). 3 iPr þ [RuCl(P P3 )] . Addition of sodium tetraphenylborate to a There are three structures of ruthenium with the analogous 3 iPr 10 tetrahydrofuran (THF) solution of P P3 (1) and RuCl2- tripodal tetradentate ligand (P(CH2CH2CH2PMe2)3), how- 3 iPr (PPh3)3 afforded [RuCl(P P3 )][BPh4](2[BPh4]) as a pink ever, these are all six-coordinate complexes with approximate solid (Scheme 2). Crystals suitable for structural analysis were octahedral geometry around the metal center. The only comparative structure of a five-coordinate complex of ruthenium with a tripodal tetradentate phosphine ligand is that i 2a Scheme 1 of [RuCl(P(CH2CH2P Pr2)3)][BPh4], which can be approxi- mated to a distorted square-based pyramid in the same way as 2 (included in Figure 1B for comparison). In a similar fashion to 2, i [RuCl(P(CH2CH2P Pr2)3)][BPh4] also has one of the isopropyl Table 1. Selected Bond Lengths (Å) and Angles (°) for 2[Ru- 3 iPr Cl(P P3 )][BPh4] 3 THF (2[BPh4]) Ru1 Cl1 2.4351(7) Ru1 P2 2.2618(7) Scheme 2 Ru1 P1 2.4629(6) Ru1 P3 2.2536(6) Ru1 P4 2.3892(7) Cl1 Ru1 P2 165.53(2) Cl1 Ru1 P1 89.28(2) Cl1 Ru1 P3 103.06(2) Cl1 Ru1 P4 83.51(2) P2 Ru1 P1 89.20(2) P2 Ru1 P3 91.38(2) P2 Ru1 P4 92.25(3) P1 Ru1 P3 99.40(2) P1 Ru1 P4 156.51(2) P3 Ru1 P4 104.00(2) 3 iPr Figure 1. ORTEP plot (50% thermal ellipsoids) of: (A) 2[RuCl(P P3 )][BPh4] 3 THF (2[BPh4]) (see Supporting Information for more data) and for i 2a comparison (B) [RuCl(P(CH2CH2P Pr2)3)][BPh4]. Only one of the two complex cations in each asymmetric unit in shown. Selected hydrogen atoms, tetraphenylborate anions, and THF solvate have been omitted for clarity. 6221 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE Scheme 4 Figure 2. Variable-temperature 31P{1H} NMR spectra for [RuCl- 3 iPr (P P3 )][BPh4](2[BPh4]) (242.95 MHz, methylene chloride-d2). Scheme 3 Figure 3. ORTEP plot (50% thermal ellipsoids) of one of the two 3 iPr [RuH2(P P3 )] (3) units within the asymmetric unit. Selected hydro- gen atoms have been removed for clarity. phosphines, displayed as an exchange-broadened singlet at 72.1 ppm. The reversal in relative chemical shifts from 2 to i those of [RuCl(P(CH2CH2P Pr2)3)][BPh4] is rationalized by the five-membered ring effect in phosphorus metallocycles. methyl groups filling and blocking the sixth coordination site The 5-membered ring effect is reasonably well documented under the base of the pyramid. and describes how phosphorus nuclei involved in 5 member The metal-to-donor atom bond lengths of 2 are equivalent to, metallocycles are significantly shifted to downfield compared 11 or longer than, the analogous lengths in [RuCl(P(CH2CH2- to their 4, 6, and 7 member metallocycle anaologues. This i þ ff fi P Pr2)3)] .TheP Ru P bond angles are all greater in 2, e ect is magni ed for the central phosphorus PC in [RuCl- i ff and the Cl Ru P bond angles are all more acute than in (P(CH2CH2P Pr2)3)] since the central P is e ectively part of i þ [RuCl(P(CH2CH2P Pr2)3)] . Thus in [RuCl(P((CH2)n- three five-membered metallocycles, and this rationalizes why i þ P Pr2)3)] complexes with n = 2, 3, the complex with 3-carbon the two complexes, while chemically and structurally similar, straps is a less strained complex and shows relaxation of the have 31P chemical shifts for the central P atom which differ by ligand bite angles and a lengthening of the metal-to-donor almost 130 ppm. atom bond lengths. As the temperature of the 31P{1H} NMR spectrum of 31 {1 } In the P H NMR spectrum of 2[BPh4] at room tempera- 2[BPh4] is decreased, the spectra broaden and then sharpen ture, the signal for the three terminal phosphines appears as a (Figure 2). At 243 MHz, as the temperature decreases to 220 K, very broad resonance at 25.7 ppm, while the signal for the central thesinglebroadresonancefortheterminalphosphines phosphine appears as a sharp quartet at 14.2 ppm with a splitting separates into three distinct resonances representing the of 36.4 Hz. A modest increase (25 K) in the temperature of the terminal phosphines individually, giving four distinct reso- NMR experiment resulted in an appreciable sharpening of the nances representing the four different phosphine environ- resonances of the terminal phosphines. These spectra are ments. At still lower temperatures, each of the resonances i 2a analogous to those of [RuCl(P(CH2CH2P Pr2)3)][BPh4], eventually splits into two resonances of comparable intensity and the broadness can be rationalized by the facile exchange of (1:0.8) to give a total of 8 resonances, which we attribute to the terminal phosphine environments. two isomers of 2[BPh4]. The Cl resides either trans to the It is interesting to note that the central phosphine resonance in apical phosphorus or trans to a terminal phosphorus (Isomer- fi 2[BPh4] appears to high eld with respect to the terminal 1andIsomer-2)(Scheme3). phosphine signals. In the analogous compound with two-carbon In this system there are two exchange processes operating. i 31 {1 } straps [RuCl(P(CH2CH2P Pr2)3)][BPh4], the P H NMR One which exchanges the terminal phosphorus environments, spectrum shows the central phosphine as a quartet at 142.9 and one which interchanges Isomer-1 and Isomer-2. At 199 K, ppm (splitting 15.2 Hz) to low field of the three terminal the three resonances of the terminal phosphines of Isomer-2 6222 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE 2 12 31 {1 } (PA2,PB2,PC2) resolve with JP P coupling observed, while in Simulation of the exchange-broadened P H NMR spec- 3 iPr Isomer-1 the terminal phosphine resonances remain broad with trum of [RuCl(P P3 )][BPh4](2[BPh4]) was consistent with fi ≈ ≈ no de ned coupling. All of the resonances eventually sharpen at an exchange process where k1 3.5k2, and at 199 K, k1 385 ≈ 1 ≈ ≈ 1 178 K to display similar coupling patterns. and k2 110 s and at 210 K with k1 2135 and k2 610 s . 3 iPr The fact that the resonances of one isomer sharpen while the RuH2(P P3 ). Reaction of the ruthenium chloro complex 3 iPr resonances of the other remain broad suggests that the exchange [RuCl(P P3 )][BPh4](2[BPh4]) with two equivalents of 3 iPr of the terminal phosphines is faster in one isomer (Isomer-1) KBEt3H afforded the dihydride complex RuH2(P P3 )(3)as than in the other. The pattern and sequence of coalescences in a white crystalline solid (Scheme 4). Crystals suitable for the variable temperature NMR spectra can be rationalized by a structural analysis were grown by slow evaporation of a toluene model where exchange between the terminal phosphines in solution of 3 under nitrogen (Figure 3) and selected bond angles Isomer-1 (k1) is fast compared to the interchange between the and lengths are given in Table 2. 3 iPr isomers (k2, Scheme 3). We suggest that Isomer-1 is that in which The geometry of RuH2(P P3 )(3) is a distorted octahedron Cl is trans to the central phosphines since the exchange of the with the two hydrides in mutually cis coordination sites. terminal phosphines then involves simply a turnstile-type pro- There are eight previously reported structures of ruthenium(II) cess, with exchange of the terminal phosphines between adjacent tetraphosphine dihydrides of which four have defined and 13 coordination sites. refined hydrides.10c, The Ru H bond lengths of 1.62(5) and 1.69(5) Å sit comfortably within the ranges provided by the other 4 structures, with Ru H bond lengths of 1.51 to 1.77 Å. Similarly Table 2. Selected Bond Lengths (Å) and Angles (°) for ° 3 iPr the H Ru H bond angle of 91(2) sits within the range of [RuH2(P P3 )] (3) previously reported structures with bond angles between 77 to Ru1 -H1 1.62(5) Ru1 H2 1.69(5) 93°. Ru1 P1 2.2785(13) Ru1 P2 2.3162(12) The structure of 3 is analogous to that of [RuH2- 10c Ru1 P4 2.3502(12) Ru1 P3 2.3032(12) (P(CH2CH2CH2PMe2)3)], which contains the related tetra- H1 Ru1 P2 71.7(17) H1 Ru1 P1 85.1(19) dentate phosphine ligand with methyl substituents on the ter- H1 Ru1 P3 75.4(17) H1 Ru1 P4 176.7(18) minal phosphines instead of isopropyl substituents. The average of the Ru P bond lengths, 2.312 Å is slightly longer than for H2 Ru1 P2 88.4(15) H2 Ru1 P1 175.7(16) [RuH2(P(CH2CH2CH2PMe2)3)] for which the average Ru P H2 Ru1 P3 85.0(15) H2 Ru1 P4 90.7(16) bond length is 2.286 Å. This is probably due to the steric bulk of P2 Ru1 P1 89.45(4) P2 Ru1 P3 146.44(4) the isopropyl substituents when compared to the methyl sub- P2 Ru1 P4 105.33(4) P1 Ru1 P3 94.75(4) stituents, resulting in elongation of the core Ru P bonds. 31 {1 } 3 iPr P1 Ru1 P4 93.42(4) P3 Ru1 P4 107.62(4) In the P H NMR spectrum of RuH2(P P3 )(3), the H1 Ru1 H2 91(2) signal for the two terminal phosphines PE appears as a doublet of fi 1 3 iPr Figure 4. Selected high- eld region of H NMR (600 MHz, benzene-d6) RuH2(P P3 )(3) with coupling tree. 6223 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE Scheme 5 Table 3. Selected Bond Lengths (Å) and Angles (°) for 3 iPr [Ru(H2)(H)(P P3 )][BPh4].EtOH 4[BPh4] H2 H3 0.66(6) Ru1 H1 1.59(3) Ru1 H2 1.62(6) Ru1 H3 1.75(4) Ru1 P1 2.2890(9) Ru1 P2 2.3756(9) Ru1 P3 2.4270(8) Ru1 P4 2.3591(9) H1 Ru1 H2 75(2) H1 Ru1 H3 97.4(18) H2 Ru1 H3 23(2) H1 Ru1 P1 86.3(12) H1 Ru1 P2 75.1(12) H1 Ru1 P3 178.7(12) H1 Ru1 P4 74.1(12) H2 Ru1 P1 161(2) H2 Ru1 P2 89(2) H2 Ru1 P3 106(2) H2 Ru1 P4 79(2) H3 Ru1 P1 175.4(14) H3 Ru1 P2 89.2(13) H3 Ru1 P3 89.2(13) H3 Ru1 P4 90.1(13) P1 Ru1 P2 89.15(3) P1 Ru1 P3 92.36(3) P1 Ru1 P4 93.56(3) P2 Ru1 P3 104.61(3) P2 Ru1 P4 148.79(3) P3 Ru1 P4 106.33(3) Figure 5. ORTEP plot (50% thermal ellipsoids) of the complex cation 3 iPr of [Ru(H2)(H)(P P3 )][BPh4] 3 EtOH (4[BPh4]) (see Supporting Information for more data) within the asymmetric unit. Selected hydrogen atoms have been removed for clarity. doublets at 49.2 ppm, the signal for the terminal phosphine P is T 31 {1 } Figure 6. P H NMR spectrum (242.9 MHz, THF-d8)of a doublet of triplets at 28.5 ppm, and the central phosphine PC 3 iPr signal appears as a doublet of triplets at 0.4 ppm. [Ru(H2)(H)(P P3 )][BPh4](4[BPh4]) at 298, 244, and 215 K. The 1H NMR resonances for the two hydrido ligands of 3 both appear as doublets of triplets of doublets of doublets at 9.43 dihydrogen ligand was not refined. There have, however, been and 12.50 ppm due to coupling to the 4 phosphorus nuclei in 3 examples of ruthenium cis hydride dihydrogen complexes with different environments and to each other (Figure 4). The all ligands refined, including the dihydrogen ligand, and these 2 i 16 coupling constants JH P are 59.6 Hz, 24.2 and 18.8 Hz for the include [Ru(H)(H2)(X)(P Pr3)2] (X = benzoquinoline, 5) i 17 resonance at 9.43 ppm and 63.2 Hz, 34.0 and 15.0 Hz for the and [RuH(H2)(o-C6H5py)(P Pr3)2][BArf] 6[BArF]. The 2 resonance at 12.50 ppm, with the JH H coupling constant Ru1 H1 bond length for 4 (1.59(3) Å) is comparable to that between the two hydrides of 6.2 Hz. of 5 (1.54(4) Å) and 6[BArF] (1.528(20) Å). Likewise the 3 iPr ∼ [Ru(H2)(H)(P P3 )][BPh4]. A solution of LiAlH4 ( 1.5 M) in dihydrogen bond distances Ru1 H2 and Ru H3 for 4 of THF was added dropwise to a THF solution of 2[BPh4] to the 1.62(6) and 1.75(4) Å, respectively, are similar but slightly point where the color change from pink to colorless was elongatedcomparedtothosefor5 (1.57(5) and 1.68(4) Å) complete. Ethanol was added, and the resulting orange suspen- and 6[BArF] (1.564(20) and 1.547(21) Å). This elongation 3 iPr ff sion worked up to afford [Ru(H2)(H)(P P3 )][BPh4] 4[BPh4] is probably caused by the di erences in the donor atom as an orange crystalline solid (Scheme 5). Crystals suitable for in the coordination site trans to dihydrogen, with 5 being structural analysis were grown from a THF/pentane solution of carbon and 6[BArF] being nitrogen as opposed to phos- 4[BPh4] (Figure 5), and selected bond angles and bond lengths phorus in 4. 3 iPr fl are given in Table 3. [Ru(H2)(H)(P P3 )][BPh4](4[BPh4]) is clearly uxional 3 iPr þ The geometry of [Ru(H2)(H)(P P3 )] (4) is a distorted in solution. At low temperature (215 K) there are 4 resonances octahedral with the hydride and dihydrogen ligands in mutually for the coordinated phosphines (at 30.3, 21.3, 13.7, and 4.3 ppm, cis coordination sites. There are two other structures of dihydro- Figure 6). The appearance of four resonances is consistent with gen hydrido ruthenium complexes where the hydrido and the solid-state structure where the two mutually trans phos- dihydrogen ligands are in the cis arrangement with four other phines are not equivalent due to puckering of the six-mem- 14 phosphine donors, [Ru(H2)(H)(PPh2Me)4] and [Ru(H2)- bered metallocyclic rings. At low temperature, the two þ 15 (H)(P(CH2CH2PPh2)3)] . In both of these complexes, the mutually trans phosphines (PB and PC) exhibit a large resolved 6224 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE fi 1 {31 } 3 iPr Figure 7. Selected high- eld H P NMR spectrum (700 MHz, THF-d8) of partially deuterated [Ru(H2)(H)(P P3 )][BPh4](4[BPh4]) at 200 K with resolution enhancement. fi Table 4. Crystal Data Re nement Details for 2[BPh4], 3, and 4[BPh4] 2[BPh4] 34[BPh4] chemical formula C104H168OB2Cl2P8Ru2 C27H62P4Ru C52H86BOP4Ru formula mass 2000.82 611.72 956.94 crystal system triclinic monoclinic monoclinic a/Å 12.280(2) 17.099(2) 16.4283(7) b/Å 19.093(4) 17.3858(17) 17.7729(6) c/Å 23.928(4) 21.692(3) 18.1170(6) R/° 111.889(3) 90.00 90.00 β/° 98.687(3) 100.723(4) 105.8920(10) γ/° 90.272(3) 90.00 90.00 V (Å3) 5134.6(16) 6335.9(13) 5087.6(3) temperature/K 150(2) 150(2) 150(2) space group P1 P2(1)/c P2(1)/n Z 284 μ(Mo KR) (mm 1) 0.517 0.711 0.468 N 49295 43788 60050 Nind 23041 11053 11063 Rint 0.0245 0.0999 0.0561 σ Final R1 values (I >2 (I)) 0.0322 0.0426 0.0468 Final wR(F2) values (I >2σ(I)) 0.0754 0.1098 0.0975 Final R1 values (all data) 0.0496 0.0770 0.0670 Final wR(F2) values (all data) 0.0851 0.1417 0.1054 Goodness of fitonF2 1.034 0.790 1.095 coupling (about 180 Hz). As the temperature is raised to At 298 K, the 1H NMR resonances of the hydrido and 244 K, the resonances for PB and PC broaden and coalesce, and dihydrogen ligands of 4[BPh4] appear as a single broad reso- this is probably due to ring-flipping of the ligand backbone. At nance at 8.57 ppm, indicating fast exchange between the higher temperatures (above 298 K), there is mutual exchange hydrido and dihydrogen ligands. At 195 K the signal resolves to of all three of the terminal phosphines (a turnstile-type a broad 2-proton resonance at 7.44 ppm, assigned to the exchange), and the signals for the terminal phosphines are dihydrogen ligand and a phosphorus-coupled doublet of 2 averaged to a single broad resonance. Modeling of the triplets at 10.3 ppm ( JH P of 57 and 32 Hz) for the hydrido exchanges at 244 K indicates that the exchange of magnetism resonance. Further evidence for this assignment comes from fl fi between the mutually trans phosphines (ring ip) occurs at the T1 values for these two high eld resonances at 180 K with 1 ( a rate of about 3000 s and that the turnstile exchange of the dihydrogen resonance having a T1 of 68 3msandthe the terminal phosphines occurs at a significantly slower rate hydrido resonance a T of 594 ( 12 ms. It is characteristic 1 (about 300 s 1). of dihydrogen hydrido metal complexes that the dihydrogen 6225 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE fi ligand has a signi cantly faster relaxation time than the substituents may permit the chemistry of PP3 metal complexes hydrido ligand.6a to be tuned to access catalytic reactivity not possible with Under an atmosphere of deuterium gas, the dihydrogen ligand stronger ligand sets. exchanges for D2, partially incorporating deuterium into the 1 metal-bound hydrogens. In the H NMR spectrum at 200 K, ’ EXPERIMENTAL SECTION the dihydrogen (or hydrogen deuteride) resonance at about 10 ppm appears as a superimposition of signals (Figure 7) due General Information. All manipulations were carried out using to the different isotopomers. The two 3-line resonances corre- standard Schlenk and glovebox techniques under a dry atmosphere of sponding to the species with coordinated H D can be resolved nitrogen. Solvents were dried and distilled under nitrogen or argon using 21 and the JHD coupling of 31 Hz extracted. JHD greater than 15 Hz standard procedures and stored in glass ampules fitted with Youngs is considered to be characteristic of dihydrogen complexes,18 Teflon taps. Benzene was dried over sodium wire before distillation from clearly confirming the presence of η2-coordinated H D in this sodium/benzophenone, while ethanol was distilled from diethoxymag- species. Using the most recent interrelationship between H H nesium. THF (inhibitor free) and pentane were dried and deoxygenated bond distance (dHH) and H D coupling (JHD)ofdHH = using a Pure Solv 400-4-MD (Innovative Technology) solvent purifica- 19 tion system. Deuterated solvents THF-d , toluene-d , and benzene-d 1.47 0.0175 JHD Å determined by Gusev, dHH is determined 8 8 6 to be 0.927 Å. This is longer than the value determined from the were dried over and distilled from sodium/benzophenone and were 3 iPr vacuum distilled immediately prior to use. Dichlorotris(triphenyl- crystal structure of [Ru(H2)(H)(P P3 )][BPh4](4[BPh4]) of 22 23 0.66(6) Å but expected, as crystallographic techniques are phosphine)ruthenium(II), and diisopropylphosphine were prepared by literature methods. Tris(3-hydroxypropyl)phosphine was purchased notorious for giving foreshortened dHH because of rapid H2 rotation/vibration.18 from Strem and used without further purification. LiAlH4 was purchased [Ru(H )(H)(P3P iPr)][BPh ](4[BPh ]) is remarkably from Aldrich, and a concentrated solution in THF prepared by Soxhlet 2 3 4 4 extraction. Air-sensitive NMR samples were prepared in an argon- or stable and survives unchanged under a nitrogen atmosphere fi nitrogen-filled glovebox or on a high-vacuum line by vacuum transfer of inde nitely without substitution of the H2, even after several 1 solvent into an NMR tube fitted with a concentric Teflon valve. H, freeze pump thaw cycles. The lack of ready N2 substitution 13C{1H}, and 31P{1H} spectra were recorded on Bruker DPX300, probably reflects the fact that steric crowding from the bulky 3 iPr Avance III 400, Avance III 500, Avance III 600, or Avance III 700 P P3 ligand makes binding the smaller H2 more preferable than NMR spectrometers operating at 300, 400, 500, 600, and 700 MHz for the bulkier N2. 1 13 {1 } 3 iPr H, 100.61 or 150.92 MHz for C H , and 121.49, 161.98, 202.49, and Treatment of [Ru(H2)(H)(P P3 )][BPh4](4[BPh4]) with 242.95 MHz for 31P{1H} respectively. All NMR spectra were recorded potassium tert-butoxide in d8-THF results in clean deprotonation at 298 K, unless stated otherwise. 1H and 13C{1H} NMR spectra were 3 iPr 31 1 and formation of RuH2(P P3 )(3). Conversely, treatment of referenced to residual solvent resonances. P{ H} NMR spectra were fl 3 with tri ic acid in d8-THF in the presence of BPh4 results in referenced to external neat trimethyl phosphite at 140.85 ppm. Dynamic formation of 4[BPh4], and this acid/base behavior is consistent NMR simulations were performed using WinDNMR: Dynamic NMR 12 with that observed for other hydrido and dihydrido complexes of Spectra for Windows. T1 calculations were performed using the curve ruthenium and iron.20 fitting applications of Origin 8.1, by OriginLab.24 Microanalyses were carried out at the Campbell Microanalytical Laboratory, University of Otago, New Zealand. Details of the X-ray analyses are given in (Table 4). ’ CONCLUSIONS i 3 iPr Synthesis of P(CH2CH2CH2P Pr2)3,PP3 (1); P(CH2CH2- The new sterically hindered, tripodal tetradentate ligand CH2Br)3. Phosphorus tribromide (4.5 mL, 0.048 mol) was added 3 iPr P P3 (1) was synthesized and used in the synthesis of a series dropwise to a stirring suspension of tris(3-hydroxypropyl)phosphine of stable ruthenium compounds. The 5-coordinate chloro com- (7.2 g, 0.035 mol) in DCM (30 mL) under nitrogen. The reaction 3 iPr þ mixture was stirred at room temperature for 18 h. Saturated aqueous plex [RuCl(P P3 )] (2) was characterized crystallographically and by multinuclear NMR spectroscopy, with low-temperature sodium carbonate solution (approximately 30 mL) was added to the 31P{1H} NMR spectroscopy being used to explore the exchange reaction mixture until all effervescence ceased. The organic layer was mechanisms between its various isomers. Complex 2 was reacted separated and dried over anhydrous sodium sulfate. The solution was 3 iPr filtered, and the solvent was removed under reduced pressure to give with potassium triethylborohydride to produce RuH2(P P3 ) (3). Complex 2 was also reacted with lithium aluminum hydride, tris(3-bromopropyl)phosphine as a clear liquid (10.0 g, 73%). The crude P(CH2CH2CH2Br)3 was used immediately in the next step without followed by reaction with ethanol to produce the stable hydrido 31 δ 3 iPr þ further purification. P NMR (162 MHz, benzene-d6): 34.1 (1P, sept, dihydrogen species [Ru(H2)(H)(P P3 )] (4). Complexes 3 2 1 {31 } δ JP H =7Hz). H P NMR (400 MHz, benzene-d6): 2.99 (6H, m, and 4 were characterized both crystallographically and by multi- 13 {1 } CH2Br); 1.56 (6H, m, PCH2); 1.06 (6H, m, CH2CH2CH2). C H nuclear NMR spectroscopy. δ 3 3 iPr NMR (101 MHz, benzene-d6): 34.7 (d, JC P =14Hz,CH2Br); 29.4 (d, The bulky P P3 ligand is among the most sterically en- 1 2 JC P =16Hz,PCH2); 25.5 (d, JC P =15Hz,CH2CH2CH2). 3 iPr i cumbered PP3-type ligands so far synthesized. While the P P3 LiP Pr2. Lithium phosphide was prepared following a modified ligand, outlined in this paper, forms stable tetradentate 5- and method by Fryzuk et al.25 n-Butyllithium (1.5 M in hexane, 50 mL, 6-coordinate complexes with ruthenium, the complexes are 0.097 mol) was added to diisopropylphosphine (8.3 g, 0.070 mol) in fl hindered, and they are uxional and hemilabile in solution. This THF (40 mL) with stirring. This procedure resulted in a bright-yellow behavior is typical of many complexes where the metal P bonds solution which was used directly in the next step. 3 iPr are weakened because the bulky ligand substituents restrict the P P3 (1). The lithium diisopropylphosphide solution from the phosphorus donors from gaining optimal access to the metal previous step was added to a stirring solution of tris(3-bromopropyl)- center. phosphine (10 g, 0.023 mol) in THF (approximately 100 mL). The 3 iPr The synthetic approach to the P P3 ligand is generic, and it reaction mixture was left to stir at room temperature for 18 h. The is possible to introduce a range of substituents on the terminal solvent was removed under reduced pressure, and benzene (20 mL) was phosphorus using this method. Other bulkier and tailored added, followed by deaerated water (30 mL) which was added with care 6226 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Inorganic Chemistry ARTICLE ° δ at 0 C until all excess lithium phosphide had been destroyed. Benzene THF-d8): 33.4 (s, CH(CH3)2) ; 33.3 (s, CH(CH3)2); 31.4 (dd, JC P = (10 mL) was added, and the mixture was stirred for 2 h. The organic 3.5 Hz, JC P = 18 Hz, PCH2); 30.2 (t, JC P = 16 Hz, PCH2); 30.0 layer was decanted, dried over anhydrous sodium sulfate, and filtered to (t, JC P = 3.7 Hz, CH2CH2CH2); 29.8 (q, JC P = 9 Hz, PCH2); 23.8 give a yellow solution. The solvent was removed under reduced pressure, (t, JC P = 4.7 Hz, CH2CH2CH2); 23.2 (d, JC P = 5 Hz, CH(CH3)2); and the resulting yellow oil was heated under vacuum (0.4 mbar) at 22.9 (dd, JC P = 11 Hz, JC P = 7 Hz, PCH2); 21.2 (s, CH(CH3)2); 20.5 100 °C to remove volatile byproducts, leaving tris(3-diisopropylpho- (s, CH(CH3)2); 20.1 (s, CH(CH3)2); 20.0 (s, CH(CH3)2); 18.8 sphinopropyl)phosphine as a yellow oil (9.0 g, 18 mmol, 51% from (s, CH(CH3)2). 31 1 3 iPr tris(3-hydroxypropyl)phosphine). P{ H} NMR (162 MHz, benzene- Synthesis of [Ru(H2)(H)(P P3 )][BPh4] (4[BPh4]). A concen- δ i 1 {31 } d6): 1.9 (3P, s, P Pr2); 34.7 (1P, s, P(CH2)3). H P NMR (400 trated solution of LiAlH4 in THF was added dropwise to a solution of δ 3 iPr MHz, benzene-d6): 1.75 (6H, m, CH2CH2CH2); 1.58 (6H, m, [RuCl(P P3 )][BPh4](2[BPh4]) (0.16 g, 0.16 mmol) in THF (3 mL) 3 CH(CH3)2); 1.53 (6H, m, PCH2); 1.42 (6H, t, JH H = 8 Hz, PCH2); until there was a color change from pink to colorless with a white 3 3 1.05 (18H, d, JH H = 7 Hz, CH(CH3)2); 1.03 (18H, d, JH H = 7 Hz, suspension. Ethanol was added carefully, dropwise, until effervescence 13 {1 } δ CH(CH3)2). C H NMR (101 MHz, benzene-d6): 29.8 (dd, had ceased (about four drops) and the color of the reaction mixture had JC P = 12 Hz, 15 Hz, PCH2); 25.4 (dd, JC P = 20 Hz, 14 Hz, turned to orange, then an additional four drops of ethanol was added. 1 The reaction mixture was filtered through Celite, and the solvent CH2CH2CH2); 24.1 (dd, JC P =20Hz,10Hz,PCH2); 23.7 (d, JC P = 2 2 removed under reduced pressure. The orange powder was washed with 14 Hz, CH(CH3)2); 20.4 (d, JC P =16Hz,CH(CH3)2); 19.0 (d, JC P = þ þ pentane (10 mL) to give [Ru(H )(H)(P3P iPr)][BPh ] (0.050 g, 10 Hz, CH(CH3)2). HRMS (EI) m/z:[M H] 509.3716 (calcd 2 3 4 509.3724) 0.051 mmol, 33% yield). Anal. found: C, 65.80; H, 8.98; C51H83P4- 3 iPr 31 {1 } Synthesis of [RuCl(P P )][BPh ] (2[BPh ]). Tris(3-diisopro- RuB.C4H8O (MW 1004.10) requires: C, 65.79; H, 9.13. P H NMR 3 4 4 δ 2 pylphosphinopropyl)phosphine P3P iPr (1) (456 mg, 0.896 mmol) was (203 MHz, THF-d8): 24.7 (3P, s br, PA/B/C); 5.4 (1P, q, JP P = 37.5 3 31 {1 } δ Hz, PD). P H NMR (203 MHz, THF-d8, 180K): 31.3 (1P, d br, added to a brown solution of dichlorotris(triphenylphosphine)ruthenium- 2 2 (II) (860 mg, 0.896 mmol) in THF (approximately 30 mL) resulting in an JP P = 185 Hz, PA); 21.3 (1P, d br, JP P = 185 Hz, PA); 13.7 (1P, s br, 1 δ immediate color change to green. A stoichiometric amount of sodium PC); 4.3 (1P, s br, PD). H NMR (400 MHz, THF-d8): 7.20 (8H, m, tetraphenylborate (306 mg, 0.894 mmol) was added, and the solution BPhortho); 6.82 (8H, m, BPhmeta); 6.68 (4H, m, BPhpara); 2.1 slowly turned red with stirring. After 3 h, the solvent was removed under 1.9 (12H, m, CH(CH3)2/CH2); 1.9 1.8 (6H, m, CH2); 1.65 1.55 (6H, m, CH2); 1.25 1.05 (36H, m, CH(CH3)2); 8.57 (3H, s br, reduced pressure to give a pink solid which was recrystallized twice from 1 THF layered with pentane (300 mg, 53%). Crystals suitable for X-ray Ru(H2)(H)). H NMR (600 MHz, THF-d8, 195 K, high field only): δ δ 2 diffraction were collected. Anal. found: C, 63.71; H, 8.27; C H BClP Ru 7.44 (2H, s br, Ru(H2)); 10.29 (1H, dt br, JH P = 57 Hz, 51 80 4 2 13 { } δ (MW 964.41) requires: C, 63.52; H, 8.36%. 31P{1H} NMR (162 MHz, JH P = 32 Hz, Ru(H)). C 1H NMR (151 MHz, THF-d8): 165.1 2 δ (m, BPhipso) 137.0 (s, BPhmeta); 125.4 (m, BPhortho); 121.6 (s, THF-d8): 25.7 (3P, br, PE/T); 14.2 (1P, q, JP(C) P(B/P) = 36.4 Hz, PC). 1 31 {1 } δ BPhpara); 30.2 (s br, CH(CH3)2); 29.0 (d, JC P = 32 Hz, PE/TCH2); P H NMR (243 MHz, 177.6 K, methylene chloride-d2): 75.1 25.9 (m, PCCH2); 21.1 (s, CH2CH2CH2); 19.8 (s, CH(CH3)2); 19.2 (Isomer-2, 1P, m, PB); 72.0 (Isomer-1, 1P, m, PB); 15.4 (Isomer-2, 1P, 2 2 2 (s, CH(CH3)2). ddd, JP(B) P(D) =45Hz, JP(A) P(D) =32Hz, JP(C) P(D) =32Hz,PD); 2 14.0 (Isomer-1, 1P, dt, m, PD); 4.1 (Isomer-1, 1P, dm, JP(A) P(C) = 227 2 2 ’ Hz, PA); 2.3 (Isomer-2, 1P, ddd, JP(A) P(C) = 234 Hz, JP(A) P(D) =31Hz, ASSOCIATED CONTENT 2 2 JP(A) P(B) =18Hz,PA); 4.3 (Isomer-2, 1P, ddd, JP(A) P(C) = 234 Hz, 2 2 bS Supporting Information. A CIF file with crystallographic JP(A) P(D) =31Hz, JP(A) P(B) =29Hz,PC); 8.1 (Isomer-1, 1 P, dm, 2 1 3 iPr J = 227 Hz, P ); H NMR (400 MHz, THF-d ): δ 7.29 (8H, m, data for compounds [RuCl(P P3 )][BPh4] 3 THF (2[BPh4]), P(A) P(C) C 8 3 iPr 3 iPr BPhortho); 6.86 (8H, m, BPhmeta); 6.72 (4H, m, BPhpara); 2.64 (6H, sep, [RuH2(P P3 )] (3), and Ru(H2)(H)(P P3 )][BPh4] 3 EtOH 3 JH H =6.9Hz,CH(CH3)2); 1.96 (6H, m, CH2CH2CH2); 1.83 (6H, m, (4[BPh4]). This material is available free of charge via the PE/TCH2); 1.39 (9H, d, CH(CH3)); 1.12 (9H, d, CH(CH3)); 1.06 (6H, Internet at http://pubs.acs.org. 13 {1 } δ m, PCCH2). C H NMR (101 MHz, THF-d8): 165.6 (m, BPhipso); 137.6 (s, BPhortho); 126.1 (m, BPhmeta); 122.2 (s, BPhpara); 30.8 ’ AUTHOR INFORMATION (m, CH(CH ) ); 29.1 (m, P CH ); 26.7 (m, CH CH CH ); 21.3 3 2 E/T 2 2 2 2 Corresponding Author (s, CH(CH3)); 20.9 (s, CH(CH3)); 20.6 (m, PCCH2). 3 iPr *E-mail: [email protected]. Telephone: þ61 2 9385 2700. Synthesis of Ru(P P3 )H2 (3). A suspension of potassium 3 iPr triethylborohydride (0.068 g, 0.49 mmol) and [RuCl(P P3 )][BPh4] (2[BPh4]) (0.22 g, 0.23 mmol) was stirred in toluene (10 mL) over- ’ ACKNOWLEDGMENT night. The color of the pink suspension changed to a faint yellow. The suspension was filtered through Celite, and the solvent was removed The authors wish to thank Dr. Hsiu Lin Li and Dr. Alison 3 iPr under reduced pressure to give Ru(P P3 )H2 (3) as a white crystalline Magill for technical assistance and discussions. The authors also powder (0.101 g, 0.165 mmol, 72% yield). Crystals suitable for X-ray thank the Australian Research Council for financial support, and diffraction were grown by slow evaporation of a toluene solution R.G.-W. thanks the Australian Government and the University of under an atmosphere of nitrogen. Anal. found: C, 52.92; H, 10.51; New South Wales for postgraduate scholarships. 31 {1 } C27H62P4Ru (MW 611.75) requires: C, 53.01; H, 10.22. 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H.; Ricciuto, L.; Schleis, T. Inorg. Chim. Acta 1998, 270, 238–246. (15) Bianchini, C.; Masi, D.; Peruzzini, M.; Casarin, M.; Maccato, C.; Rizzi, G. A. Inorg. Chem. 1997, 36, 1061–1069. (16) Matthes, J.; Grundemann, S.; Toner, A.; Guari, Y.; Donnadieu, B.; Spandl, J.; Sabo-Etienne, S.; Clot, E.; Limbach, H.-H.; Chaudret, B. Organometallics 2004, 23, 1424–1433. (17) Toner, A. J.; Gr€undemann, S.; Clot, E.; Limbach, H.-H.; Donnadieu, B.; Sabo-Etienne, S.; Chaudret, B. J. Am. Chem. Soc. 2000, 122, 6777–6778. (18) Morris, R. H. Coord. Chem. Rev. 2008, 252, 2381–2394. (19) Gusev, D. G. J. Am. Chem. Soc. 2004, 126, 14249–14257. (20) (a) Baker, M. V.; Field, L. D.; Young, D. J. J. Chem. Soc., Chem. Commun. 1988, 546–8. (b) Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1987, 109, 5865–5867. (c) Cappellani, E. P.; Drouin, S. D.; Jia, G. C.; Maltby, P. A.; Morris, R. H.; Schweitzer, C. T. J. Am. Chem. Soc. 1994, 116, 3375–3388. (21) Perrin, D. D. A., W., L. F. Purification of Laboratory Chemicals; 3rd ed.; Pergamon Press: Oxford, U.K., 1993. (22) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970, 12, 237–40. (23) Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.; Goldman, A. S. J. Am. Chem. Soc. 2004, 126, 13044–13053. (24) Origin 8.1 SR2; Originlab Corporation: Northhampton, MA, 2010. (25) Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985, 24, 642–8. 6228 dx.doi.org/10.1021/ic200492w |Inorg. Chem. 2011, 50, 6220–6228 Article pubs.acs.org/IC New Superhindered Polydentate Polyphosphine Ligands t t t P(CH2CH2P Bu2)3, PhP(CH2CH2P Bu2)2, P(CH2CH2CH2P Bu2)3, and their Ruthenium(II) Chloride Complexes Ryan Gilbert-Wilson,† Leslie D. Field,*,† and Mohan M. Bhadbhade‡ † ‡ School of Chemistry and Mark Wainwright Analytical Centre, The University of New South Wales, NSW 2052, Australia *S Supporting Information ABSTRACT: The synthesis and characterization of the t extremely hindered phosphine ligands, P(CH2CH2P Bu2)3 2 tBu t 2 tBu (P P3 , 1), PhP(CH2CH2P Bu2)2 (PhP P2 , 2), and P- t 3 tBu (CH2CH2CH2P Bu2)3 (P P3 , 3) are reported, along with the synthesis and characterization of ruthenium chloro complexes 2 tBu 2 tBu 3 tBu RuCl2(P P3 )(4), RuCl2(PhP P2 )(5), and RuCl2(P P3 ) 2 tBu 3 tBu (6). The bulky P P3 (1) and P P3 (3) ligands are the most sterically encumbered PP3-type ligands so far synthesized, and in all cases, only three phosphorus donors are able to bind to 2 tBu 3 tBu the metal center. Complexes RuCl2(PhP P2 )(5) and RuCl2(P P3 )(6) were characterized by crystallography. Low 31 1 2 tBu temperature solution and solid state P{ H} NMR were used to demonstrate that the structure of RuCl2(P P3 )(4)is 2 tBu probably analogous to that of RuCl2(PhP P2 )(5) which had been structurally characterized. 7 ■ INTRODUCTION cyclohexyl groups (P(CH2CH2Cy2)3). The work described in The multihapticity, strong donor ability, and lipophilicity of this paper explores the effect of increasing steric bulk on alkyl-substituted polydentate phosphines make them good polydentate phosphines by investigating tetradentate PP3 ligands for controlling the stereochemistry of coordination ligands with tertiary-butyl groups as substituents on the complexes and solubilizing metal catalysts.1 Ruthenium and terminal phosphines. We report here the synthesis of the iron complexes of PP3-type ligands P((CH2)nPR2)3 (n =2,3; hindered tripodal tetradentate phosphine ligands P- i t 2 tBu t R = Me, Et, Pr, Ph) have been used in a wide variety of (CH2CH2P Bu2)3 (P P3 , 1)andP(CH2CH2CH2P Bu2)3 3 tBu applications including the formation of stable dinitrogen (P P3 , 3) as well as the hindered tridentate phosphine ligand − t 2 tBu complexes (in a range of oxidation states) and in the C H PhP(CH2CH2P Bu2)2 (PhP P2 , 2). activation and the stabilization of η2-dihydrogen complexes.2 This work reports the synthetic routes to the hindered The PP3-type ligands provide a strong coordination environ- ligands as well as the formation and characterization of their ment, and they generally coordinate up to four points through ruthenium chlorido complexes. Characterization of the the four strong phosphine donors. The geometry of complexes allows an analysis of the binding mode of this new coordination is constrained by the ligand, and when all four series of bulky ligands and the behavior of the complexes, both of the phosphines are bound, an octahedral complex must have in solution and the solid state. the remaining two coordination sites geometry constrained in a cis arrangement (in adjacent coordination sites). The cis ■ RESULTS AND DISCUSSION stereochemistry often results in higher catalytic activity for Preparation and Characterization of Phosphine processes like migratory insertion or reductive elimination Ligands. P(CH CH PtBu ) ,P2P tBu (1). This was prepared where a cis arrangement of the two nonphosphine ligands is 2 2 2 3 3 3 by the base-induced (lithium diisopropylamide, LDA) addition essential. of di(tert-butyl)phosphine to trivinylphosphine in a method Additionally, bulky phosphines have been particularly good modified from that of Morris et al. used in the synthesis of ligands to enhance the catalytic activity of transition metal analogous tripodal tetradentate phosphine ligands (Scheme 1).7 systems in a range of applications e.g. tri(cyclohexyl)phosphine 31 1 2 tBu ’ 4 In the P{ H} spectrum of P P3 (1), two resonances are enhances the activity of Grubbs catalyst, and the tertiary-butyl − groups on phosphine ligands such as tri(tert-butyl)phosphine observed at 34.1 and 15.3 ppm, in a ratio of 3:1 assigned to have also afforded particularly active catalysts.5 the three terminal phosphines and the central phosphine, There is now an expanding range of sterically encumbered, respectively. As is typical in PP3-type ligands with ethylene polydentate ligands available,6 but to this point, the bulkiest bridges, coupling between the terminal and central phosphines groups employed on the terminal phosphines of PP3-type polydentate phosphine ligands have been either isopropyl Received: December 19, 2011 i 2i i 2h groups (P(CH2CH2 Pr2)3 and P(CH2CH2CH2 Pr2)3 )or Published: February 17, 2012 © 2012 American Chemical Society 3239 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article Scheme 1 Scheme 4 In the 31P{1H} NMR spectrum of RuCl (P2P tBu)(4)at 3 2 3 − ( JP P = 24.9 Hz) is observed even before coordination to the room temperature, the two bound terminal phosphines PE/PT metal center. appear as a single very broad resonance (W1/2 = 55 Hz at 162 PhP(CH CH PtBu ) (PhP2P tBu, 2). 8 2 2 2 2 2 The literature methods MHz; CD2Cl2 solution) centered around 91.4 ppm. The central for the synthesis of divinylphenylphosphine from dichlorophe- phosphine PC appears as a doublet of triplets at 106.2 ppm with 3 2 nylphosphine by reaction with vinylmagnesium bromide are a JP−P coupling constant of 37 Hz to PF, and a JP−P coupling low yielding. Divinylphenylphosphine was synthesized by an constant of 17.5 Hz to PE/PT respectively. The resonance at alternative approach by reaction of 2 equiv of vinylmagnesium 34.3 ppm is assigned to the pendant phosphine (not bound to bromide with 1 equiv of diethoxyphenylphosphine in a method the metal center) because (i) PF displays no coupling to the analogous to that of King et al. using di(n-butoxy)- other terminal phosphines P and P ; and (ii) P has a chemical 9 2 tBu E T F phenylphosphine as the starting substrate. PhP P2 (2) was shift of 34.3 ppm, which is very close to the chemical shift subsequently prepared by the base-induced (lithium diisopro- observed for the terminal phosphines in the free ligand (34.1 pylamide) addition of di(tert-butyl)phosphine to divinylphe- ppm). nylphosphine in a method similar to that used above for the When the 31P{1H} NMR spectra of (4) were collected at 2 tBu 31 1 synthesis of P P3 (1) (Scheme 2). In the P{ H} spectrum lower temperatures (systematically down to about −100 °C, Figure 1), the PE/PT resonance broadened into the baseline Scheme 2 2 tBu of PhP P2 (2), two resonances are observed at 34.0 and −16.9 ppm, in a ratio of 2:1, and these are assigned to the two terminal phosphines and the central phosphine, respectively. 31 3 Coupling between the P nuclei ( JP−P = 27 Hz) is observed even before coordination to the metal center. t 3 tBu 3 P(CH2CH2CH2P Bu2)3,(PP3 , ). This was prepared by the nucleophilic substitution of bromide in the reaction of lithium t di(tert-butyl)phosphide, (LiP Bu2), with tris(3-bromopropyl)- phosphine (Scheme 3), in a method analogous that used for the Scheme 3 Figure 1. Variable temperature 31P{1H} NMR spectra (243 MHz, 2 tBu solvent: CD2Cl2) of RuCl2(P P3 )(4) with spectra at (from front) 174, 188, 204, 220, 236, 252, 268, and 284 K. before resolving and sharpening into two separate resonances at 132 and 50 ppm. This behavior can be ascribed to the two bound, terminal phosphines, PE and PT, being in fast exchange synthesis of a related tripodal tetradentate phosphine ligand at room temperature probably associated with the degenerate i 2h 31 1 isomerization of Cl in the coordination sphere (Scheme 5). P(CH2CH2CH2P Pr2)3. In the P{ H} NMR spectrum of 3 t − P P3 Bu (3), two resonances are observed at 26.2 and 35.5 ppm, in a ratio of 3:1 assigned to the terminal phosphines and Scheme 5 the central phosphine respectively. Both resonances are singlets with no discernible coupling between the two phosphine environments, and this is consistent with data reported for 3 other P P3-type ligands incorporating propylene bridges between the apical and terminal phosphines.2b,h Preparation and Characterization Ruthenium Chlor- 2 tBu 4 2 tBu 10 31 1 ido Complexes. RuCl2(P P3 )( ). Addition of P P3 (1) Simulation of the exchange-broadened P{ H} NMR 2 tBu to a tetrahydrofuran (THF) solution of RuCl2(PPh3)3 afforded spectrum of RuCl2(P P3 )(4) gives rates for the exchange 2 tBu ≈ −1 ≈ RuCl2(P P3 )(4) as a tan solid which was isolated by process where at 174 K, k 800 s and 220 K, k 100 000 filtration (Scheme 4). s−1. There is no evidence for the presence of a third steroisomer 3240 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article − ∠ − (4a) where the vacant coordination site is trans to PC (the (pseudoagostic) interaction (d(Ru H) 2.34(3) Å and (Ru central phosphine). H−C) 111(2)°).12 2 tBu 5 2 tBu RuCl2(PhP P2 )(). Addition of a THF solution of The structure of RuCl2(PhP P2 )(5) is comparable to that 2 tBu 13 RuCl2(PPh3)3 to a THF solution of PhP P2 (2), followed of RuCl2(PhP(CH2CH2CH2PCy2)2) and RuCl2(PhP- 14 by stirring overnight and addition of hexane, afforded (CH2CH2PPh2)2), both of which are 5-coordinate complexes 2 tBu n R RuCl2(PhP P2 )(5) as a yellow solid (Scheme 6). Crystals with similar PhP P2 ligands on ruthenium and two chloro ligands arranged in cis coordination sites. RuCl2(PhP- τ Scheme 6 (CH2CH2CH2PCy2)2)( =0.50)andRuCl2(PhP- τ (CH2CH2PPh2)2)( = 0.37) are both more significantly distorted toward a trigonal bipyramidal character than 5 but neither to the extent that they would be classified as trigonal bipyramidal geometry. There is also a difference in the way the tridentate ligand is bound geometrically. The central phosphorus of complexes RuCl2(PhP(CH2CH2CH2PCy2)2) and RuCl2(PhP(CH2CH2PPh2)2) is located at the apex of the suitable for structural analysis were grown by slow diffusion of square based pyramids while for complex 5 it is located within pentane into a dichloromethane solution of 5 (Figure 2) and the base of the pyramid with a terminal phosphine at the apex. selected bond angles and lengths are given in Table 1. There is a trend toward lengthening of the Ru−P bonds as the steric bulk on the terminal phosphines increases from phenyl (Ru−P = 2.198(2), 2.260(2), 2.280(2) Å) to cyclohexyl (Ru−P = 2.211(1), 2.276(1), 2.306(1) Å) to tert-butyl, (Ru−P= 2.265(1), 2.275(1), 2.385(1) Å). 31 1 2 tBu The P{ H} NMR spectrum of RuCl2(PhP P2 )(5) has the two bound terminal phosphines PE/PT as a very broad resonance at 92.3 ppm (W1/2 = 75 Hz at 162 MHz; CD2Cl2 solution, 298 K). The central phosphine PC appears as a triplet 2 at 94.4 ppm, with a JP−P coupling constant of 12.6 Hz to PE/ 31 1 PT. P{ H} NMR spectra were also collected at decreased temperatures down to about −90 °C (Figure 3). As the 2 tBu Figure 2. ORTEP plot (50% thermal ellipsoids) of RuCl2(PhP P2 ) (5), selected hydrogen atoms have been omitted for clarity. Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) 2 tBu for RuCl2(PhP P2 ) (5) 31 1 − − Figure 3. Variable temperature P{ H} NMR spectra (243 MHz, Ru1 Cl1 2.4257(10) Ru1 Cl2 2.4628(10) solvent: CD Cl ) of RuCl (PhP2P tBu)(5) with spectra at (from front) − − 2 2 2 2 Ru1 P1 2.2748(11) Ru1 P2 2.2652(11) 179, 184, 195, 211, 226, 226, 243, 259, 275, and 300 K. Ru1−P3 2.3849(11) Cl1−Ru1−Cl2 85.65(4) P1−Ru1−Cl1 96.06(4) temperature descended the P /P resonance broadened into − − − − E T P1 Ru1 Cl2 101.59(4) P1 Ru1 P2 82.00(4) the baseline before resolving into two separate resonances at P1−Ru1−P3 111.66(4) P2−Ru1−P3 81.96(4) 2 tBu 128 and 52 ppm. As observed for RuCl2(P P3 )(4), the P2−Ru1−Cl1 103.86(4) P2−Ru1−Cl2 169.52(4) − − − − resonances for PE and PT are in fast exchange at room P3 Ru1 Cl1 152.26(4) P3 Ru1 Cl2 87.56(4) temperature and the NMR data is consistent with a fluxional 5- coordinate complex with the exchange similar to that depicted The geometry of RuCl (PhP2P tBu)(5) is a distorted square- 2 2 in Scheme 5. This assignment is also consistent with the based pyramid with atoms Cl1, Cl2, P2, and P3 making up the structural data from the X-ray crystal structure. τ 3 tBu 6 3 tBu base and P1 at the apex. The structure has a value of 0.29, RuCl2(P P3 )(). While, RuCl2(P P3 )(6) could be 2 tBu where τ is a geometric parameter indicative of 5-coordinate prepared in a similar manner to the syntheses of RuCl2(P P3 ) 2 tBu τ (4) and RuCl2(PhP P2 )(5) (by the direct reaction of complex geometry where = 0 is perfect square pyramidal 3 tBu 11 RuCl2(PPh3)3 with P P3 ligand), the separation of geometry and τ = 1 is perfect trigonal-bipyramidal geometry. 3 tBu RuCl2(P P3 )(6) from the triphenylphosphine byproduct One of the tertiary-butyl methyl groups fills and blocks the void 3 tBu was difficult. A better route to RuCl2(P P3 )(6) was by 3 tBu μ under the base of the pyramid, through an anagostic reaction of a toluene solution of P P3 (3) with di- - 3241 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article 3 tBu chlorobis[(p-cymene)chlororuthenium]. RuCl2(P P3 )(6) X-ray diffraction, and this afforded only low quality diffraction was isolated cleanly as a green solid and crystals suitable for data due to the small crystal size. However, the solution was structural analysis were grown by slow evaporation of a toluene sufficient to determine that the structure was of a second solution (Figure 4). Selected bond angles and lengths are given isomer in which the ligand arm of the pendant phosphine PF is in Table 2. bent in the opposite direction to the original isomer. This difference can be clearly observed in an overlay of the two structures (Figure 5). 3 tBu Figure 4. ORTEP plot (50% thermal ellipsoids) of RuCl2(P P3 ) Figure 5. Overlay of structural data for the two isomers of (6). Hydrogen atoms have been removed for clarity. 3 tBu RuCl2(P P3 )(6) in the solid state. Hydrogen atoms have been removed for clarity. Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) t for RuCl (P3P Bu) (6) 31 1 3 tBu 2 3 In the P{ H} NMR spectrum of RuCl2(P P3 )(6), the Ru1−Cl1 2.416(3) Ru1−Cl2 2.467(3) central phosphine PC appears as a triplet at 60.8 ppm with a 2 Ru1−P1 2.411(4) Ru1−P2 2.195(4) JP−P coupling of 35 Hz to PE. The two bound terminal Ru1−P3 2.408(4) phosphines PE appear as a doublet at 31.1 ppm, and the Cl1−Ru1−Cl2 164.11(13) P1−Ru1−Cl1 88.96(13) pendant phosphine PF appears as a singlet at 25.5 ppm. The P1−Ru1−Cl2 89.57(14) P1−Ru1−P2 93.59(16) resonance at 25.5 ppm is assigned as a pendant phosphine not − − − − P1 Ru1 P3 172.88(17) P2 Ru1 P3 93.20(16) bound to the metal center for two reasons: first PF displays no − − − − P2 Ru1 Cl1 114.45(15) P2 Ru1 Cl2 81.43(14) coupling to the bound phosphines and second because PF has a P3−Ru1−Cl1 90.18(13) P3−Ru1−Cl2 89.32(14) chemical shift at high field in the spectrum, very close to the chemical shift observed for the terminal phosphines in the free 3 tBu The geometry of RuCl2(P P3 )(6) is a distorted square- ligand (26.2 ppm). In contrast to the fluxional behavior based pyramid with the central phosphorus P occupying the 2 tBu 2 tBu C observed in RuCl2(P P3 )(4), and RuCl2(PhP P2 )(5) apical position. Only two of the three terminal phosphines PE where there are ethylene bridges between central and terminal are bound to ruthenium and they are in mutually trans phosphorus atoms, the 31P{1H} NMR spectrum of positions. The two chloride ligands are also in mutually trans RuCl (P3P tBu)(6), where there are propylene bridges between positions, with the two terminal phosphines making up the base 2 3 τ the phosphine donors, is sharp at room temperature and of the pyramid ( = 0.15). There are six previously reported unchanged by variation in temperature. The presence of the structures of ruthenium(II) triphosphine dichloride complexes longer arms in the P3P tBu ligand probably results in a more with similar geometry with linked phosphines donors in a 3 stable framework with less backbone strain and a higher barrier meridional arrangement.15 The only other reported structure in which all three of the phosphine donors are part of the one to reorganization and isomerization of the coordination sphere ′ of the metal. ligand is [bis-1-(1 -diphenylphosphinoferrocenyl)- 31 1 phenylphosphine]dichlororuthenium(II),15a which has shorter Solid State NMR Analysis. Solid state P{ H} NMR − spectra can be used for characterization for metal phosphine Ru P bond distances to the terminal phosphines (2.332(1) 16 31 1 and 2.369(2) Å) than those observed in 6 (2.416(3) and complexes in the solid state, and comparison with P{ H} NMR spectra of complexes for which X-ray crystallographic 2.467(3) Å) probably due to the larger steric bulk of the 17,18 tertiary-butyl groups in 6, but otherwise the structure has very data is available provides additional structural information. 2 tBu similar bond lengths and angles. We have, so far, been unable to grow crystals of RuCl2(P P3 ) 3 tBu The structure of RuCl2(P P3 )(6) has a P222 space group (4) suitable for diffraction studies; however, solid state NMR indicating there are no mirror planes within the unit cell. There provides some level of structural characterization of complex 4, is only a single isomer of 6 within the crystal, that being the by comparison with the solid state NMR spectra of 3 tBu 2 tBu 3 tBu isomer pictured in Figure 4. A second crystal of RuCl2(P P3 ) RuCl2(PhP P2 )(5) and RuCl2(P P3 )(6) for which both (6) was also used for structural analysis through single crystal solid-state NMR and X-ray data are available. 3242 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article 31 1 2 tBu The solid state P{ H} NMR spectrum of RuCl2(PhP P2 ) metal-bound phosphines PE/T of only 4 and 7 ppm. Given that (5) shows the presence of a single species with three 31P the length of the straps and the substituents on the terminal resonances at 129, 88, and 47 ppm which we assign to PE/T,PC, phosphines are the same for complexes 4 and 5, the fact that and PE/T, respectively. These shifts correspond to those the observed shifts for 4 are closely aligned with 5 is indicative observed in solution state at low temperature (see Figure 3). that the geometric arrangement of the coordinated phosphines 31 1 3 tBu The solid state P{ H} NMR spectrum of RuCl2(P P3 ) in 4 are probably facially coordinated (as in 5). If 4 was to be (6) shows the presence of two species each with three meridionally coordinated the pattern of resonances would be resonances. Species A′ with resonances at 63, 32, and 31 ppm expected to be like that of 6 even though the strap length of the (masked by the PE signals for both species) corresponding to ligands would result in differences in the actual chemical ′ 19 PC,PE, and PF, respectively, and species B with resonances at shifts. 62, 31, and 13 ppm corresponding to PC,PE, and PF, respectively (Figure 6). The two species probably correspond ■ CONCLUSIONS to the 2 polymorphs of this compound identified by X-ray The new sterically hindered, tridentate ligands P- crystallography. t 2 tBu t (CH2CH2P Bu2)3 (P P3 , 1), PhP(CH2CH2P Bu2)2 2 tBu t 3 tBu (PhP P2 , 2), and P(CH2CH2CH2P Bu2)3 (P P3 , 3) were synthesized and used in the synthesis of the corresponding 2 tBu ruthenium dichloride compounds RuCl2(P P3 )(4), 2 tBu 3 tBu RuCl2(PhP P2 )(5), and RuCl2(P P3 )(6). Complexes 4, 5,and6 were all characterized by multinuclear NMR spectroscopy, with low temperature 31P{1H} NMR spectros- copy being used to explore the dynamic processes of exchange present in complex 4 and 5 in solution. Complexes 5 and 6 were both characterized crystallographically. 2 tBu 3 tBu The bulky P P3 (1) and P P3 (3) ligands are the most sterically encumbered PP3-type ligands so far synthesized. These ligands appear to be so sterically encumbered that they can only bind to ruthenium through three of the four phosphine donors leaving one of the terminal phosphines as a free pendant arm. All three ligands 1, 2, and 3 provide a highly sterically constrained ligand environment around the metal, and this restricts the nature of other groups that can bind to the metal center. 31 1 2 tBu Solid state P{ H} NMR of RuCl2(P P3 )(4), 2 tBu 3 tBu RuCl2(PhP P2 )(5), and RuCl2(P P3 )(6) was used to 2 tBu gain insights into the solid state structure of RuCl2(P P3 )(4) Figure 6. Solid state 31P{1H} NMR (121 MHz, 25 kHz MAS, 295 K) which could not be characterized crystallographically. Com- 2 tBu 2 tBu 3 tBu of RuCl2(P P3 )(4), RuCl2(PhP P2 )(5), and RuCl2(P P3 )(6). parative solid-state NMR analysis also indicate that the solid 2 tBu 31 1 2 tBu state structure of RuCl2(P P3 )(4) is analogous to that The solid state P{ H} NMR spectrum of RuCl2(P P3 ) 2 tBu determined by X-ray crystallography for RuCl2(PhP P2 )(5). (4) was initially obtained on material precipitated directly from a THF solution. These spectra displayed upward of five ■ EXPERIMENTAL SECTION differing species in varying proportions, all with very similar chemical shifts, and this probably indicates why it has been General Information. All manipulations were carried out using difficult to obtain diffraction-quality crystals for this compound. standard Schlenk, vacuum, and glovebox techniques under a dry 2 tBu atmosphere of nitrogen. Solvents were dried, distilled under nitrogen When RuCl2(P P3 )(4) was recrystallized from dichloro- 20 31 1 or argon using standard procedures, and stored in glass ampules methane, the solid state P{ H} NMR spectrum indicated the fitted with J. Youngs Teflon taps. Benzene was dried over sodium wire presence of only two species present in approximately equal before distillation from sodium/benzophenone. THF (inhibitor free), amounts. In the 31P{1H} NMR spectrum of (4), both species toluene, and pentane were dried and deoxygenated using a Pure Solv have four 31P resonances: species A with four resonances at 400-4-MD (Innovative Technology) solvent purification system. Deuterated solvents THF-d8, toluene-d8, and benzene-d6 were dried 136, 109, 51, and 35 ppm corresponding to PE/T,PC,PE/T, and P , respectively, and isomer B with four resonances at 136, 107, over, and distilled from, sodium/benzophenone and were vacuum F distilled immediately prior to use. Dichlorotris(triphenylphosphine)- 51, and 38 ppm corresponding to PE/T,PC,PE/T, and PF, ruthenium(II),21 trivinylphosphine,22 diethoxyphenylphosphine, and respectively (Figure 6). di(tert-butyl)phosphine23 were prepared by literature methods. Tris(3- The most significant difference in chemical shifts between hydroxypropyl)phosphine was purchased from Strem. Air sensitive the isomers appears to be in the two PF resonances, with a NMR samples were prepared in an argon- or nitrogen-filled glovebox or on a high vacuum line by vacuum transfer of solvent into an NMR smaller, but still significant, difference in the PC resonances. 1 13 1 The difference between the two isomers is likely to be the result tube fitted with a concentric Teflon valve. Solution H, C{ H}, and 31P{1H} NMR spectra were recorded on Bruker DPX300, Avance III of the pendant phosphine of the complex being able to adopt 400, Avance III 500, or Avance III 600 NMR spectrometers operating two different positions in the unit cell, as was observed in the 1 3 tBu at 300.3, 400.13, 500.13, and 600.13 MHz for H, 100.61 or 150.92 structure of RuCl2(P P3 )(6). MHz for 13C{1H}, and 121.49, 161.98, 202.49, and 242.95 MHz for 31 1 The chemical shifts for PC,PE, and PT of complex 4 and 5 are P{ H}, respectively. All NMR spectra were recorded at 298 K, unless very similar, with differences in chemical shift for the two stated otherwise. 1H and 13C{1H} NMR spectra were referenced to 3243 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article 31 1 2 1 δ solvent resonances. P{ H} NMR spectra were referenced to external JC−P = 14.6 Hz, PCH2CH2P). H NMR (300 MHz, benzene-d6): 3 neat trimethyl phosphite at 140.85 ppm. 1.89 (6H, m, CH2); 1.71 (6H, m, CH2); 1.12 (54H, d, JH−P = 10.5 31 1 Solid state NMR P{ H} were recorded on an Avance III 300 Hz, C(CH3)3). t 2 t Bruker NMR spectrometer equipped with an Oxford 300 Magnet and Synthesis of PhP(CH2CH2P Bu2)2 PhP P2 Bu (2); CH2CHMgBr. a 2-channel 2.5 mm probehead. Samples were spun at 25 kHz MAS at Vinyl bromide (50.6 g, 473 mmol) was condensed into THF (100 the temperatures described. Solid state 31P{1H} NMR spectra were mL) cooled to 0 °C. An initial aliquot (10 mL) of the vinyl bromide referenced to external ammonium dihydrogen phosphate (ADP) (δ = solution was added to a stirred suspension of magnesium turnings 1.0 ppm). Microanalyses were carried out at the Campbell (10.0 g, 411 mmol) in THF (150 mL). The reaction was initiated by Microanalytical Laboratory, University of Otago, New Zealand. High addition of a crystal of iodine and application of heat, and after the resolution mass spectrometry was carried out at the Bioanalytical Mass reaction had commenced, the remainder of the solution was added Spectrometry Facilities within the Analytical Centre of the University dropwise at a rate which maintained a moderately vigorous reflux. On of New South Wales on an Orbitrap LTQ XL (Thermo Fisher completion of the reaction, the magnesium turnings were consumed Scientific, San Jose, CA) ion trap mass spectrometer using a nanospray leaving a brown solution of vinylmagnesium bromide in THF. This ionization source. Details of the X-ray analyses are given in Table 3. solution was refluxed for 30 min with a needle vent above the condenser to remove any excess vinyl bromide. This solution was used Table 3. Crystal Data Refinement Details for 5 and 6 directly in the preparation of divinylphenylphosphine without further purification (≈1.6 M, 250 mL). 56PhP(CH CH2)2. The solution of vinylmagnesium bromide from the previous step was chilled to 0 °C, resulting in the formation of a chemical formula C26H49Cl2P3Ru C33H72Cl2P4Ru formula mass 626.53 764.76 light brown precipitate. Diethoxyphenylphosphine (31.4 g, 158 mmol) was then added dropwise over a period of 30 min to the chilled crystal system monoclinic orthorhombic solution. The solution was allowed to warm to room temperature at a/Å 11.1544(11) 12.462(2) which point the precipitate disappeared, it was stirred for a further b/Å 16.0550(15) 14.307(3) hour then heated under reflux for 30 min. The solution was cooled to c/Å 16.0390(14) 21.914(4) room temperature and dioxane (35 mL, 410 mmol) was added, α/deg 90.00 90.00 resulting in a large amount of precipitation. The solution was then β/deg 95.990(3) 90.00 briefly refluxed, and THF (150 mL) was added before the solution was γ/deg 90.00 90.00 filtered. THF was then distilled off at 66−68 °C leaving a red/orange V (Å3) 2856.6(5) 3907.1(12) solid which was extracted with ether (100 mL) to give an ether temperature/K 150(2) 150(2) solution of divinylphenylphosphine (18.2 mmol by quantitative space group P2(1)/c P2(1)2(1)2(1) NMR). Divinylphenylphosphine was not isolated from the ether solution (to prevent polymerization), and the solution was used Z 44 μ α −1 directly in the preparation of bis(3-di(tert-butyl)phosphinoethyl)- (Mo K ) (mm ) 0.918 0.723 phenylphosphine without further purification. 31P{1H} NMR (162 N 17217 15684 δ − MHz, 25% benzene-d6/75% ether): 16.1 (1P, s, PhP(CH CH2)2) N 5033 6760 2 t ind PhP P2 Bu (2). A solution of divinylphenylphosphine (2.95 g, 18.2 Rint 0.0791 0.1778 mmol) in ether (100 mL) from the previous step was added to a σ final R1 values (I >2 (I)) 0.0393 0.0840 solution of di(tert-butyl)phosphine (9.0 mL, 49 mmol) in THF (100 final wR(F2) values (I >2σ(I)) 0.0577 0.1695 mL). Lithium diisopropylamide (ca. 150 mmol) in THF/hexane (200 final R1 values (all data) 0.0753 0.1939 mL) was added in stages with stirring over an hour period. During the final wR(F2) values (all data) 0.0657 0.2326 course of the reaction, the color of the solution turned to dark red. 31 1 goodness of fit on F2 1.072 0.908 The reaction was monitored ( P{ H} NMR), and the addition of base was halted when no divinylphenylphosphine or reaction intermediates t 2 tBu remained. All solvent was removed under reduced pressure, and the Synthesis of P(CH2CH2P Bu2)3,PP3 (1); LiN(CH(CH3)2)2. Diisopropylamine (14.0 mL, 100 mmol) was added to a flask remaining red/brown oil/solid residue was suspended in benzene (150 mL). Deaerated water (50 mL) was added, with care, to quench any containing THF (100 mL) at 0 °C. n-Butyllithium (2.32 M in hexane, residual base. The aqueous layer was discarded and the organic layer 43.0 mL, 99.8 mmol) was added dropwise over a 10 min period with dried over anhydrous Na2SO4. The benzene was removed under stirring to give a yellow solution of lithium diisopropylamide. This 2 t reduced pressure leaving PhP P2 Bu (2) as an orange oil (6.17 g, 13.6 solution was used directly in the next step without further purification. 31 1 2 tBu mmol, 75% yield from divinylphenylphosphine). P{ H} NMR (162 P P3 (1). Di(tert-butyl)phosphine (11.5 mL, 9.08 g, 62.1 mmol) 3 MHz, benzene-d ): δ 34.0 (2P, d, J − = 27 Hz, P ); −16.9 (1P, t, was added to a solution of trivinylphosphine (ca. 15.7 mmol) in THF/ 6 P P E/T P ). 1H NMR (400 MHz, benzene-d ): δ 7.58 (2H, m, Ar-H); 7.18 ether (100 mL). Lithium diisopropylamide in THF/hexane (from the C 6 (3H, m, Ar-H); 2.06 (2H, m, CH2); 1.55 (2H, m, CH2); 1.43 (2H, m, previous step) was added in stages with stirring over a period of 1 h. 13 1 CH2); 1.19 (2H, m, CH2); 1.03 (36H, m, CH3). C{ H} NMR During the course of the reaction, the color of the solution turned δ Ar 31 1 (100.6 MHz, benzene-d6): 139.0 (d, JC−P = 18 Hz, C ); 133.2 (d, bright orange. The reaction was monitored ( P{ H} NMR) and the Ar Ar Ar J − = 19 Hz, C ); 129.9 (d, J − = 44 Hz, C ); 128.6 (s, C ); 31.8 addition of base halted when no trivinylphosphine or reaction C P C P (d, J − = 24 Hz, C(CH ) ); 29.9 (d, J − = 14 Hz, C(CH ) ); 29.8 intermediates remained (≈70 mmol of lithium diisopropylamide). C P 3 3 C P 3 3 (d, J − = 14 Hz, C(CH ) ); 29.6 (dd, J − = 27 Hz, J − = 15 Hz, All volatiles were removed under vacuum, and the orange oil/solid C P 3 3 C P C P CH2); 17.7 (dd, JC−P = 25 Hz, JC−P = 14 Hz, CH2). HRMS (ES) m/z: residue was suspended in benzene (100 mL). Deaerated water (50 [M + H]+ 455.3092 (calcd 455.3125) mL) was added with care to quench the excess base. The layers were t 3 t Synthesis of P(CH2CH2CH2P Bu2)3,PP3 Bu; Tris(3- separated, and the aqueous layer was discarded. The organic layer was bromopropyl)phosphine. Phosphorus tribromide (4.3 mL, 46 dried over anhydrous Na2SO4, and the volatiles removed under mmol) was added dropwise to a stirred suspension of tris(3- 2 tBu reduced pressure leaving P P3 as an orange oil (6.77 g, 12.3 mmol, hydroxypropyl)phosphine (7.7 g, 37 mmol) in dichloromethane (80 78% from trivinylphosphine). Anal. found: C 65.15, H 12.00. C30H66P4 mL). Initial portions of phosphorus tribromide caused the solution to (MW 550.74) requires C 65.42, H 12.08. 31P{1H} NMR (121.5 MHz, become viscous and made stirring difficult, but continued addition of δ 3 − benzene-d6): 34.1 (3P, d, JP−P = 24.9 Hz, PT); 15.3 (1P, q, PC). phosphorus tribromide dropwise resulted in the suspension returning 13 1 δ 1 C{ H} NMR (100.6 MHz, benzene-d6): 31.6 (d, JC−P = 23.9 Hz, to a less viscous solution which could be stirred. The reaction mixture 2 1 PC(CH3)3); 30.0 (d, JC−P = 13.8 Hz, PC(CH3)3); 28.5 (dd, JC−P = was stirred at room temperature for 18 h. Saturated aqueous sodium 2 1 25.8 Hz, JC−P = 16.7 Hz, PCH2CH2P); 18.2 (dd, JC−P = 25.4 Hz, carbonate solution (approximately 40 mL) was added to the reaction 3244 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article 31 1 mixture until all effervescence ceased. The organic layer was separated C26H49Cl2RuP3 (MW 626.57) requires C 49.84, H 7.88. P{ H} δ 2 and dried over anhydrous sodium sulfate. The solution was filtered and NMR (162 MHz, dichloromethane-d2): 94.4 (1P, t, JP−P = 12.6 Hz, δ 1 the solvent was removed under reduced pressure to give tris(3- PhP(CH2)2); 92.3 (2P, br s, PC(CH3)3). H NMR (300 MHz, δ − bromopropyl)phosphine as a clear liquid (4.2 g, 11 mmol, 29%). This dichloromethane-d2): 8.16 (2H, m, ArH); 7.45 (3H, m, ArH); 2.4 3 product was used immediately in the next step without further 2.1 (6H, m, CH2); 1.44 (18H, d, JH−P = 12.7 Hz, C(CH3)3); 1.19 3 − purification. (18H, d, JH−P = 12.7 Hz, C(CH3)3); 1.15 1.05 (2H, m, CH2). 31 1 δ 1 LiP(C(CH3)3))2. n-Butyllithium (2.5 M in hexane, 16 mL, 40 mmol) C{ H} NMR (100.6 MHz, dichloromethane-d2): 137.7 (d, JC−P = Ar Ar was added to a solution of di(tert-butyl)phosphine (5.3 g, 36 mmol) in 36.3 Hz, C ); 132.4 (d, JC−P = 8.7 Hz, C ); 130.4 (d, JC−P = 2.4 Hz, ° Ar Ar 1 THF (50 mL) at 0 C with stirring. The solution remained colorless C ); 128.8 (d, JC−P = 9.3 Hz, C ); 40.7 (d, JC−P = 17.9 Hz, 1 during the addition, until the reaction was complete when a pale PC(CH3)3); 36.9 (d, JC−P = 11.4 Hz, PC(CH3)3); 31.9 (dd, JC−P = 2 yellow color persisted. The reaction mixture was allowed to warm to 31.0 Hz, JC−P = 6.3 Hz, CH2); 31.8 (d, JC−P = 2.9 Hz, PC(CH3)3); room temperature and THF (40 mL) was added, resulting in a bright 29.2 (s, PC(CH3)3); 25.3 (dd, JC−P = 22.7 Hz, JC−P = 13 Hz, CH2). 3 tBu μ yellow solution which was used directly in the next step. Synthesis of RuCl2(P P3 ) (6). Solid di- -chlorobis[(p-cymene)- 3 tBu P P3 (3). The lithium di(tert-butyl)phosphide solution from the chlororuthenium] (100 mg, 0.163 mmol) was added to a solution of 3 tBu previous step was added to a stirring solution of tris(3-bromopropyl)- P P3 (6), (185 mg, 0.312 mmol) in toluene (50 mL) under phosphine (4.20 g, 10.6 mmol) in THF (approximately 40 mL) at 0 nitrogen. The solution was stirred and refluxed overnight to afford an °C. During the addition, a pink/orange color formed before the color extremely dark green solution with a suspended brown solid. The returned to yellow once addition was complete. The reaction mixture solution was filtered, the residue was discarded, and the volatiles of the was left to stir at room temperature for 18 h. The solvent was removed filtrate removed under vacuum. The resulting green solid residue was under reduced pressure and deaerated water (approximately 30 mL) dried under vacuum for 3 h to afford dichloro(tris(2-di(tert- added, with care, until all excess lithium phosphide had been butyl)phosphinopropyl)phosphine-κ3P)ruthenium(II) (132 mg, 3 tBu destroyed. Benzene (approximately 40 mL) was added and the 0.173 mmol, 55% by P P3 (6)). Anal. found C 51.54, H 9.28 31 1 mixture was stirred for 1 h. The organic layer was decanted, dried over C33H72Cl2RuP4 (MW 764.81) requires C 51.83, H 9.49. P{ H} δ 2 anhydrous sodium sulfate, and filtered to give a clear solution. The NMR (121 MHz, THF-d8): 60.8 (1P, t, JP−P = 35 Hz, PC); 31.1 2 1 solvents were removed under reduced pressure and the resulting oil (2P, d, JP−P = 35 Hz, PE); 25.5 (1P, s, PF). H NMR (300 MHz, δ was heated under reduced pressure (0.4 mbar) to remove volatile acetone-d6): 1.89 (2H, m, CH2); 1.79 (4H, m, CH2); 1.62 (8H, m, − impurities, leaving tris(3-di(tert-butyl)phosphinopropyl)phosphine as CH2); 1.48 1.62 (18H, m, CH3); 1.62 (4H, m, CH2); 1.12 (36H, m, a clear wax (3.82 g, 6.44 mmol, 61% from tris(3-bromopropyl)- CH3). 31 1 δ phosphine). P{ H} NMR (121.5 MHz, benzene-d6): 26.2 (3P, s, X-ray Structure Determinations. Single crystals of 5 and 6 were − 1 31 δ PT); 35.5 (1P, s, PC). H{ P} NMR (300 MHz, benzene-d6): 1.87 attached, with Exxon Paratone N, to a short length of fiber supported 3 (6H, m, CH2CH2CH2); 1.63 (6H, t, JH−H = 7.1 Hz, CH2P); 1.49 on a thin piece of copper wire inserted in a copper mounting pin. The 3 3 (6H, t, JH−H = 7.4, CH2P); 1.12 (54H, d, JH−P = 10.6 Hz, CH3). crystal was quenched in a cold nitrogen gas stream from an Oxford 13 1 δ 1 C{ H} NMR (100.6 MHz, benzene-d6): 31.3 (d, JC−P = 30 Hz, Cryosystems Cryostream. A Bruker kappa APEXII area detector 1 α C(CH3)3); 29.9 (d, JC−P = 14 Hz, C(CH3)3); 29.7 (dd, JC−P = 26 Hz, diffractometer employing graphite monochromated Mo K radiation JC−P = 14 Hz, CH2); 27.3 (dd, JC−P = 28 Hz, JC−P = 14 Hz, CH2); 23.6 generated from a fine focus sealed tube was used for the data + (dd, JC−P = 23 Hz, JC−P = 11 Hz, CH2). HRMS (ES) m/z [M + H] collection. The data integration and reduction were undertaken with 593.4647 (calcd 593.4663). APEX2, and subsequent computations were carried out with the X- 2 tBu Synthesis of RuCl2(P P3 ), (4). A solution of dichlorotris- Seed graphical user interface. The structures were solved by direct (triphenylphosphine)ruthenium(II) (1.18 g, 1.23 mmol) in THF (50 methods with SHELXS-97 and extended and refined with SHELXL- mL) was added to a solution of tris(2-di(tert-butyl)phosphinoethyl)- 97. The non-hydrogen atoms in the asymmetric unit were modeled 2 tBu phosphine, P P3 (1), (5.0 mL, 245 mM, 1.23 mmol) in THF under with anisotropic displacement parameters. A riding atom model with nitrogen. The brown solution was to stirred overnight and a tan solid group displacement parameters was used for the hydrogen atoms. precipitated. The solid was collected by filtration and washed with All calculations were performed using the crystallographic and THF (5 mL) to afford dichloro(tris(2-di(tert-butyl)phosphinoethyl)- structure refinement data summarized in Table 3. phosphine-κ3P)ruthenium(II) (0.40 g, 0.55 mmol 45%). Anal. found: C 49.88, H 9.05 C30H66Cl2RuP4 (MW 722.72) requires C 49.86, H ■ ASSOCIATED CONTENT 31 1 δ 9.20. P{ H} NMR (162 MHz, dichloromethane-d2): 106.2 (1P, dt, *S 3 3 Supporting Information JP−P = 37 Hz, JP−P = 17.5 Hz, PC); 91.4 (2P, br s, PE); 34.3 (1P, d, 2 tBu 3 1 δ CIF with crystallographic data for compounds [RuCl2(P P2 )] JP−P = 37 Hz, PF). H NMR (400 MHz, dichloromethane-d2): 2.45 3 tBu − (5) and [RuCl2(P P3 )] (6). This material is available free of (2H, m, CH2); 2.28 1.92 (6H, m, CH2); 1.83 (2H, m, CH2); 1.35 3 3 charge via the Internet at http://pubs.acs.org. (18H, d, JH−P = 12.5 Hz, CH3); 1.24 (18H, d, JH−P = 12.5 Hz, CH3); 3 13 1 1.14 (18H, d, JH−P = 10.8 Hz, CH3); 1.07 (2H, m, CH2). C{ H} δ 1 ■ AUTHOR INFORMATION NMR (100.6 MHz, dichloromethane-d2): 39.9 (d, JC−P = 18 Hz, 1 1 PC(CH3)3); 36.2 (d, JC−P = 10.5 Hz, PC(CH3)3); 32.1 (d, JC−P = Corresponding Author 2 22.4 Hz, PC(CH3)3) 31.9 (d, JC−P = 2.9 Hz, PC(CH3)3); 30.8 (dd, *E-mail: [email protected]. Telephone: +61 2 9385 2700. 2 JC−P = 28.3 Hz, JC−P = 22.2 Hz, CH2 (pendant arm)) 30.0 (d, JC−P = Notes 13.6 Hz, PC(CH ) ); 28.8 (s, PC(CH ) ); 27.2 (dd, J − = 28.0 Hz, 3 3 3 3 C P The authors declare no competing financial interest. JC−P = 6.5 Hz, CH2 (bound arm)); 24.9 (dd, JC−P = 21.1 Hz, JC−P = 12.6 Hz, CH (bound arm)); 16.3 (dd, J − = 25.6 Hz, J − = 5.7 Hz, 2 C P C P ■ ACKNOWLEDGMENTS CH2 (pendant arm)). 2 tBu Synthesis of RuCl2(PhP P2 ) (5). A solution of dichlorotris- The authors wish to thank Dr. Hsiu Lin Li and Dr. Alison (triphenylphosphine)ruthenium(II) (1.06 g, 1.11 mmol) in THF (30 Magill for technical assistance, proofreading, and discussions. mL) was added to a solution of bis(2-di(tert-butyl)phosphinoethyl)- 2 tBu The authors also thank the Australian Research Council for phenylphosphine, PhP P2 , (0.520 g, 1.14 mmol) in THF (10 mL) financial support, and R.G.-W. thanks the Australian Govern- under nitrogen. The brown solution was stirred overnight, and a yellow solid precipitated. Hexane (50 mL) was added to assist ment and the University of New South Wales for postgraduate precipitation of the solid. The cloudy suspension was stirred for 1 h, scholarships. NMR spectra and mass spectra were obtained then the solid was isolated by filtration to give dichloro(bis(2-di(tert- through the Mark Wainwright Analytical Centre at the butyl)phosphinoethyl)phenylphosphine-κ3P)ruthenium(II) (0.255 g, University of New South Wales. Subsidized access to these 0.407 mmol, 37%) as a yellow solid. Anal. found C 49.52, H 7.60 facilities are gratefully acknowledged. 3245 dx.doi.org/10.1021/ic2027169 | Inorg. Chem. 2012, 51, 3239−3246 Inorganic Chemistry Article ■ REFERENCES (19) Garrou, P. E. Chem. Rev. 1981, 81, 229−266. − (20) Perrin, D. D.; A., W. L. F. Purification of Laboratory Chemicals, (1) Mayer, H. A.; Kaska, W. C. Chem. Rev. 1994, 94, 1239 72. 3rd ed.; Pergamon Press: Oxford, 1993. (2) (a) Antberg, M.; Frosin, K. M.; Dahlenburg, L. J. Organomet. − (21) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. Chem. 1988, 338, 319 27. (b) Antberg, M.; Prengel, C.; Dahlenburg, 1970, 12, 237−40. L. Inorg. Chem. 1984, 23, 4170−4. 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Chem. 2012, 51, 3239−3246 Appendix A4 EPR simulations Code for compiling simulation in matlab with easy spin plugin 2 Cy Simulation for RuCl(P P3 ) (4) Sys = struct('S',1/2,'g',[2.0005 2.064 2.104]); A = [430, 385, 373]; Sys = nucspinadd(Sys,'31P',A); B = [40, 25, 45] Sys = nucspinadd(Sys,'Ru',B); C = [0, 34, 0]; Sys = nucspinadd(Sys,'31P',C); Sys = nucspinadd(Sys,'31P',C); Sys.lwpp = [.1 .3]; Sys.HStrain = [65 28 65]; Exp = struct('CenterSweep',[325 60],'mwFreq',9.4915); Opt = struct('Verbosity',1); pepper(Sys,Exp); [B spc] = pepper(Sys,Exp); xlswrite('RuClP2P3Cy',data); 2 Cy + Simulation for [Fe(N2)(P P3 )] (3) Sys = struct('S',1/2,'g',[2.225 2.04 1.999]); A = [45, 65, 65]; Sys = nucspinadd(Sys,'14N',A); B = [70, 130, 130]; Sys = nucspinadd(Sys,'31P',B); C = [45, 65, 65]; Sys = nucspinadd(Sys,'31P',C); Sys = nucspinadd(Sys,'31P',C); Sys.lwpp = [.1 .1]; Sys.HStrain = [50 80 55]; Exp = struct('CenterSweep',[325 80],'mwFreq',9.4915); Opt = struct('Verbosity',1); pepper(Sys,Exp); [B spc] = pepper(Sys,Exp); data = [B spc]; xlswrite('RuClP2P3Cy',data); A-28