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Intramolecular Proton-Hydride Interactions in Iridium Complexes - a New Type of Hydrogen Bond
Sung Han Park
A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy in the Graduate Department of Chemistry University of Toronto
O Copyright by Sung Han Park 1998 National Library Bibliotheque nationale 191 of Canada du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada
The author has granted a non- L'auteur a accorde une licence non exclusive licence allowing the exclusive pennettant a la National Library of Canada to Bibliotheque nationale du Canada de reproduce, loan, distribute or sell reproduire, preter, distribuer ou copies of thls thesis in microfom, vendre des copies de cette these sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format electronique .
The author retains ownership of the L'auteur conserve la propriete du copyright in thls thesis. Neither the droit d'auteur qui protege cette these. thesis nor substantial extracts ~ornit Ni la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent &treimprimes reproduced without the author's ou autrement reproduits sans son permission. autorisation. Abstract Seven cationic hydrido pyridinethione (SpyH) complexes containing either PCy3 or PPh3 co-donor ligands have been prepared from iridium polyhydride complexes. These
include three PCy3 complexes [IrHi(q -SP~H)~(PC~~)~1 ( BFj) I. [IrH(q - SpyH)4(PCy3)1(BF4)24, [IrH(q i-SpyH)2(q2-Spy)(PCy3)l(BF4)5 and four PPh3 complexes [IrH(q l-~py~)(q~-spy)(~~h~)~](~~~)9. [IrHz(q l-spy~)(~~h~)~](BFj) 10. [IrHr(q 1-SpyH)2(PPh3)2](BF4)11 and [IrH(CO)(ql-S~yH)~(P~h3)21(BF?)2 12. All
contain NH--HIr proton-hydride bonding units in the solid state {d(HH): 1.8 to 2.1 A. X- ray analysis}. The proton-hydride bonds in these complexes are maintained in CH2Clz.
Stronger proton-hydride bonds are formed in complexes with PCy, co-donor ligands vs complexes with PPh3 co-donor ligands. The strength of proton-hydride bonds is decreased in complexes containing more PPh3 or CO ligands. The strength of the proton-hydride bonds in solution is probed for 1.1 and 5 by introducing a conventional H-bond acceptor (THF-dxor OPPh3). The H-H interactions in 1 are disrupted but remain intact in 4 and 5. Four chloro SpyH complexes cis-IrH2Cl(q l-~pyH)(~Cy~)~13. IrI-ICI?(q - SpyH)(PCy3)2 14a. IrClz(ql-SpyH)(q2-Spy)(pCy3)IS and [IrCl(qI-~py~)~(q2-~py)
(PCy3)](BF4)16 have been prepared from iridium polyhydride complexes. 13 and 14a contain NH--CIIr hydrogen bonds over NH- .HIr bonds d(H-421): 2.15(7) A. 15 ). 16 possesses an N-H-Cl(1r)---H-N hydrogen bonded network {d(N.-CI): 3.137, 3.045 A}. Ligmds other than HSpy used in the reaction with IrH5(PCy3):! include pyrazole. acetaldoxime and dirnethylglyoxime. The products of these reactions are iridium(l1I) dihydrides containing conventional Y-H-X hydrogen bonding units, Y. X = N. 0. An 18 electron Ir(II1) complex containing IrS.*FBF3and agostic Ir-H-C bonds is formed in the reaction of IrH5(PCy3)2 with HBF4 in benzene {d(Ir--HI: 2.04(5) A and d(Ir---F):2.172(3) A } . Mom and Dad, how wonde~$ulit is to be your son. Your never-ending love has made it all possible. For Hee Ymng & Swzg Ji Harmah Acknowledgments
The very first and foremost person I would like to express my sincere thanks to is my supervisor Robert H. Morris for his never-ending guidance and patience during the past years. He and his wife Colleen have always been there to encourage us whenever we encountered a light or heavy storm ! I thank Dr. Ravindranath Ramac handran for his initial introduction to the proton- hydride bonding complexes. Much of his effort was devoted to the very first paper on this topic we published in the Journal of the American Chemical Society. I am grateful to Drs. Wei Xu and Dmitri Goussev for their valuable thoughts and discussion regarding the proton- hydride bond and Marcel Schlaf and Cameron Forde for their advice and comments on dihydrogen chemistry. The former and present group members who have contributed in various ways include Dr. Kamaluddin Abdur-Rashid. Erin Baker. Tina Fong, Shaun Landau, Adrian Lee. Sandra Trentowsky, Tanya Bartucz, Edward Lueng. Bernhard Otto. Thomas Schleis and Patrick Amhein. I am indebted to Kamaluddin Abdur-Rashid, Erin Baker. Shaun Landau. Sandra Trentowsky and Avinash N. Thadani for their proofreading. I thank Nick Plavac for his valuable NMR experiments and Dr. Timothy S. Burrow for his diligent and cheerful assistance with the NMR spectrometers. Alan Lough's outstanding skill in X-ray spectrometry made it possible to understand many of proton- hydride bonding species. Other chemistry department colleagues Alex Young (FAB-MS studies). Ron Legge (Glass blowing) and Dan Mathers (instruments) are also thanked for their helpful assistance. Finally. I would like to thank my loving family. Hee Young Nah and Sung Ji Hannah Park for their love and patience until we are here. List of Abbreviations acdxd ace taldoxime bqH 7,8-benzoquinoline CP cyclophentadieny 1 dppe 1.2-bis(diphenylphosphino)ethane dppm bis(dipheny1phosphino)methane en e thy lenediamine ether diethyl ether glxmH2 dimethylglyoxime fCy3 tricyclohexylphosphine PPh3 triphenylphosphine
PYOH 2-hydroxypyridine P~H pyrazole QAMD quinolineacetamide SALEN N. N'-ethylenebis(sa1idene iminato)
SPYH Zpyridinethione or 2-mercaptopyridine
SPY Zpyridinethiolate THF te trahydro furan CSD Cambridge Structural Data COSY Correlation Spectroscopy FAB MS fast atom bombardment mass spectrometry IR Infrared NMR Nuclear Magnetic Resonance NOE NucIear Overhauser Effect RT room temperature
TI spin-lattice relaxation time Vr variable temperature Compound numbering Scheme Table of Contents
Abstract ...... il ... Dedication ...... 111 Acknowledgments ...... v List of Abbreviations ...... vi Compound numbering Scheme ...... vii Table of Contents ...... vii List of Figures ...... xi 1 List of Schemes ...... xviii
List of Tables ...... xix
Chapter 1 . The hydrogen bond in transition metal complexes ...... 1.1. Conventional or classical hydrogen bond ...... 1.1.1. History and definition ...... 1 .l.2. Geometry of conventional hydrogen bonds ...... 1.1.3. Classification of secondary bonds involving hydrogen in transition metal compounds ...... 1.2. Non-classical MH-MY hydrogen bond: the proton-hydride bond ...... 1.2.1. Speculation about M-Hm'.H-Ybonding before its discovery ...... 1.2.2. The discovery of short proton-hydride bonds ......
1.2.3. Bonding ...... , ...... 1.3. Preparation of species containing a proton-hydride bond ...... 1.3.1. Oxidative addition ...... 1.3.2. Substitution reaction ...... 1.3.3. Ring-opening reaction ...... 1.3.4. Substitution of polyhydride complexes ...... 1 .4. Characterization of proton-hydride bonding ...... 16 1.4.1. Infrared spectroscopy ...... 16
1.4.2. Spin lattice relaxation time (TI) measurement ...... i9 1 A.3. Nuclear Overhauser Effect ...... 23 1 .4.4. Correlation Spectroscopy ...... 21 1.4.5. Single crystal X-ray and neutron diffraction ...... 25 1.4.6. Theoretical studies ...... 28 1.5. Summary of the general features of the proton-hydride bond ...... 30 1.6. Background and the outline of the thesis ...... 37 1.7. References ...... 34
Chapter 2 . Intramolecular IrH-HN Bonds in Tricyclohexylphosphine Complexes of Ir(II1) ...... 38 2 . 1 . Introduction ...... 38 2.2. Results and Discussion ...... 42
2.2.1. Synthesis of [Ir{H(q l -SpyH) ) 2(PCy3)z](BF4) (I) ...... 42 2.2.2. General characterization of [Ir( H(q 1-SpyH) } 2(PCy3)2](BF4)(1) ...... 43 7.2.3. Studies on the proton-hydride interactions in solution of [Ir{H(q I-SpyH)) 2(PCy3)2](BF4)(1) ...... 46
2.2.4. H/D exchange studies of [Ir{H(q l-SpyH) J 2(~Cy3)2](~~4)(1) ...... 51 2.2.5. Synthesis of [IrH(q 1-SpyH)4(PCy3)](B~4)2(4) ...... 52 2.2.6. General characterization of [IrH(q -sp~H)~(PCy~)l(BF~)? (4) ...... 53 2.2.7. Studies on the proton-hydride interactions of [IrH(qI-SpyH)4(PCy3)](BF4)2(4) ...... 54 2.2.8. Synthesis of [IrH(q l-S~yH)~(q2-~py)(~Cy3)](~~~ (5) ...... 57 2.2.9. Characterization of [IrH(q ~-s~~H)~(~Z-S~~)(PC~~)](BF~)(5) ...... 58 2.2.10. Synthesis of I~H(T$s~~)~(Pc~~)(6) ...... 61 2.2.1 1 . Characterization of ~rH($-s~y)~(PCy~)(6) ...... 62
2.2.12. Formation of [{IrH(q -SpyH)(PCy3)}2(pSpy)2](BF4)2 (7) ...... 65 2.3. Conclusion ...... 66 2.4. Experimental ...... 68 2.5. References ...... 74
Chapter 3 . Iridium(II1) Complex Containing a Unique Bifurcated Hydrogen Bonding Interaction Intolving Ir-H-H (N )a-F-B atoms . Molecular Structure of [IrH(q l-SCSH4NH)(q2-~Cs~4~)(PPh3)2] (BFj)*0.5C6H ...... 80
3.1. Introduction ...... 80 3.2. Results and Discussion ...... 81 3.2.1. Starting materials ...... 81 3.2.2. Synthesis of cis-[~r~(q~-S~~H)(T$-S~~)(PP~~)~](BF~) (9) ...... 85 3.2.3. Studies on the proton-hydride interactions of cis- [IrH(q 1 -spyH)(q?-~py)(~~h~)~](~F~)(9) ...... 86 3.2.4. HID exchange studies ...... 88 3.2.5. X-ray structure analysis of cis-[~r~(q~-s~~H)($-sPY)(PP~~)~] (BF4) (9) ...... 90
3.3. Conclusion ...... 92 Experimental 3.5. References ...... 96
Chapter 4. Intramolecular IrH-HN Interactions in Triphenylphosphine Complexes of Iridium(II1) ...... 101 4.1. Introduction ...... 101 4.2. Results and Discussion ...... 103 4.2.1. Synthesis of [IrH2(q l -S~~H)(PP~~)~](BF~)(10) ...... 103 4.2.2. Characterization of [IrH2(q l-SpyH)(PPh3)3](BF4)(10) ...... 103 4.2.3. Formation of [IrH2(q 1-SpyH)2(~~h3)z~(~~4)(1I) ...... 106 4.2.4. Characterization of [IrH2(ql-Spy~)~(PPli~)~l(BF~) (11) ...... 108 4.2.5. Synthesis of [IrH(CO)(q l-~pyH)~(PPh~)~](B~4)2(12) ...... 110 4.2.6. X-ray structure analyses for 10 . 11 and 12 ...... 113 4.2.7. Comparison of the solid state structures containing SpyH-HIr bonds ..... 120 4.2.8. Comparison of spectroscopic features of proton-hydride bonds ...... 128 4.3. Conclusion ...... 130 4.3. Experimental ...... 131 4.3. References ...... 135
Chapter 5 . Intramolecular NH43Ir Hydrogen Bonding Interactions of the NH group of the Coordinated SpyH Ligand . Molecular Structures of IrC12(q 1-S~sH4NH)(q2-~~5~4~)(~~y3)*2~~2~12 and [IrCl(q 1- S C5~4~~)2(~12-S C5HJN)(~~y3)](~~q)*~~~~3-~7~8 ...... 136 5.1. Introduction ...... 136 5.2. Results and discussion ...... 137
5.2.1. Synthesis of IrH2Cl(q I-s~~H)(Pc~~)~(13) ...... 137
5.1.2. Characterization of IrHzCl(tll-SP~H)(PC~~)~ (13) ...... 138 5.2.3. Synthesis and characterization of IrHClr(q1-~py~)(~~y3)2(14) ...... 142
5.2.4. Formation of irClz(q -Spy~)($-~py)(~cy,) (15) ...... 144
5.2.5. Formation of [IrCl(tl -spy~)~(q*-~py)(~Cy~)](~~~)(16) ...... 145 5.2.6. X-ray structure analyses of 15 and 16 ...... 145 5.3. Conclusions ...... 153 5.4. Experimental ...... 154 5.5. References ...... 159 xii
Chapter 6 . Intra- and Inter-molecular Hydrogen Bonding in Dihydrido Pyrazole. Acetaldoxime or Glyoxime Complexes of Ir(II1). Molecular Structures of IrH2((q l-NC3H3N)2H)(~~y3)2C,HI). IrH2{(q1.N(0)CHMe)2H)(PCy3)2.Cc~c.slnd [IrHz{q2- N(OH)C(Me)C(Me)N(OH)J(PCy3)2](BF4)~1a5CH2C12*Oa5C6H6 .... 160 6.1. Introduction ...... 160 6.2. Results and discussion ...... 162 6.2.1. Pyrazole complex of iridiurn(Il1) ...... 162 6.2.2. Acetaldoxirne complex of iridiurn(lI1) ...... 164 6.2.3. Neutral dimethylglyoxime complex of iridium(II1) ...... 167 6.2.4. Cat ionic dirnethylglyoxime complex ...... 171 6.2.5. X-ray diffraction studies ...... 172 6.3. Conclusion ...... 180 6.4. Experimental ...... 180 6.5. Reference ...... 185
Chapter 7 . Molecular Structures of IrH2(BF4)(PCy3)2 that contains Ir-FBF3 and agostic Ir-mH-C bonds ...... 7.1. Introduction ...... 7.2. Results and discussion ...... 7.2.1. Formation of IrH2(B F4)(PCy3)2 (22) ...... 7.2.2. Discussion ...... 7.2.3. X-ray structure analysis of IrH2(B F4)(PCy3)2 (22) ...... 7.3. Conclusion ...... 7.4. Experimental ...... 7.5. References ...... Chapter 8 . Conclusions and Future work ...... 105 List of Figures
Figure 1.1. General modes of conventional hydrogen bond. -3
Figure 1.2. Heterolytic splitting of dihydrogen by an external (a) or internal (b) base. 5
Figure 1.3. Homolytic splitting of a dihydrogen ligand into hydrides.
Figure 1.4. Polarization between acidic dihydrogen and an internal or external base.
Figure 1.5. Four cases where the extent of proton transfer depends on the acidity of the dihydrogen ligand and the strength of the base B.
Figure 1.6. Simplified diagrams of a conventional hydrogen bond (I) vs a proton hydride interaction (11).
Figure 1.7. molecular orbitals of a B3-I-Y hydrogen bond.
Figure 1.8. Proposed molecular orbital diagram for a proton hydride bonding unit (MH-HY).
Figure 2.1. ORTEP diagram for the dimer analyzed at 293 K. The counterions BF4- are not shown for clarity.
Figure 2.2. Proposed structure of the cation of 1 with a labeling scheme for the NMR assignment (L = PCy3).
Figure 2.3. Molecular structure of the cation of [Ir(H(q1-SpyH) ) z(PCy3)2](BF4) 1 at 226 K as determined by X-ray analysis. 45 xiv
Figure 2.4. Plot of TIof the hydride and NH H nuclei of I in CD2C12 vs temperature. 48
Figure 2.5. Disruption of proton-hydride bonds in 1 by conventional H-bonding acceptors. 50
Figure 2.6. Proposed structures of two possible isomers of 4. 54
Figure 2.7. Possible isomers of 5 with hydride cis to the phosphine ligand. 59
Figure 2.8. ORTEP diagram for the cation of [IrH(q ~-S~~H)~(~~-S~~)(PC~~)J(BF~)
5. 60
Figure 2.9. ORTEP diagram for I~H(~~-s~~)~(Pc~~)6 at 293 K. 63
Figure 3.1. Triphenylphosphine complexes containing proton-hydride bonds (L= PPh3). 80
Figure 3.2. 'H NMR spectra at 500 MHz of the hydride resonance ofji~c-
Ir(H)3(PPh3)3 in toluene-d8 at (a) 90 OC. (b) 25 OC. (c) simulation of (b), (d) -40 OC, and (e)simulation of (d). 83
Figure 3.3. Proposed structures of three possible isomeric products of Reaction 3.3. 86
Figure 3.4. NMR spectra (25 OC): (a) lH (400 MHz, hydride region). and (b)
P{IH) (300 MHz). of 9 in CD2Cl2 (left) and 9-4 in CD~CIZwith MeOD (right). 89
Figure 3.5. Structure of the cation and anion of 9 which also shows the N-H--F-B interaction. 9 1 Figure 4.1. Iridiurn(I1I) complexes possessing one or two proton-hydride bonding units (L-YHm-Hlr).
Figure 4.2. Three possible isomers that might form in Reaction 4.2.
Figure 4.3. Comparison of the hydride and NH resonances and their TI(min) for 10.
Figure 4.4. Characteristic NH stretching frequencies for 12 (Nujol. KBr).
Figure 4.5. ORTEP diagram of the cation of [IrHt(q l-SpyH)(PPh3)3](~~4)10 at
173 K.
Figure 4.6. ORTEP diagram of the cation of [IrHz(q l-s~yH)~(Pph~)~](BF~)I1 (213 K).
Figure 4.7. Structure of 11 showing a hydrogen bonded polymeric chain with BF4- counterion.
Figure 4.8. ORTEP diagram of the cation of [IrH(CO)(q~-S~~H)~(PP~~)~](BF~)~
12 at 296 K.
Figure 4.9. Angles (degree) of coordinated SpyH ligands in 12.
Figure 4.10. Ir-S and S-Cdistances and sulfur angles vs tmns influence and SpyH ring character.
Figure 4.11. Three resonance structures of protonated pyridinethiolate and pyridine thione.
Figure 4.12. Comparison of the NH stretching frequencies of coordinated and free
SPYH. xvi
Figure 5.1. Competition between hydride and chloride ligands in the formation of an intramolecular hydrogen bond.
Figure 5.2. Unobserved isomers of 13 containing a proton-hydride bond.
Figure 5.3. Isotopomers of 13 formed in the reaction of 13 with D2 gas.
Figure 5.4. Unobserved isomer 14c.
Figure 5.5. ORTEP diagram for lrClz(ql-~pyH)(r(z-Spy)(PCy3)15 at 173 K.
Figure 5.6. ORTEP diagram for the cation of [IrCl(n 1-~py~)2(q2-~py)(~~y3)1(~~4)
16.
Figure 5.7. Side view of 15 and 16 through S(2) to Ir to CI(1) or S(3).
Figure 5.8. Comparison of the coordination angles (O) in the equatorial plane.
Figure 6.1. Examples of intramolecular proton-hydride hydrogen bonding interactions.
Figure 6.2. 'H NMR spectra (A, OH resonances; B. hydride resonances) of 18 (400
MHz. 6. toluene-dg): (a) 20 OC. (b) 0 OC. (c) -20 OC, (d) -40 OC. and (e)-60 *C .
Figure 6.3. Proposed structures of the product 19 from the reaction of IrHs(PCy3)z with dimethyl glyoxime.
Figure 6.4A. 1H NMR spectra (hydride resonances) of 19 (400 MHz. 6. toluene-ds):
(a) 20 OC, (b) 0 OC. (c) -20 OC. (d) -40 OC. (e) -60 OC. and (f) -80 OC.
Figure 6.4B. 1H NMR spectra (hydroxy proton region) of 19 (400 MHz. 6, toluene- ds): (a) 20 OC, (b) 0 OC, (c) -20 OC, (d) -40 OC, (e) -60 OC, and (0 -80 OC. xvii
Figure 6.5. Simplified structure of 20 to show C-H-e'H-Irand OH-'FBF3interacting units. 175
Figure 6.6. Structure of the pyrazole complex. 17 showing the N-He-N hydrogen bonding unit. The hydrogen bonding proton and the hydrides are in refined positions. 176
Figure 6.7. Structure of the acetaldoxime complex. 18. The proton on the hydrogen bonding hydroxy group and the hydrides are in refined positions. 177
Figure 6.8. Structure of the cation of 20 whose counteranion is not shown for clarity. Two cis hydrides and two hydroxy protons are in refined positions.
Figure 6.9. Structure of the cation and anion of 20 which also shows the 0-H-F-B hydrogen bonding interactions with fluorines of BF4 anions. For clarity two tram PCy3 groups are omitted.
Figure 7.1. Examples of octahedral geometry with a vacant site occupied by an agostic proton (a)or a non-coordinating counterion (b).
Figure 7.2. ORTEP diagram for IrH2(BF4)!PCy3)2 22.
Figure 7.3. Comparison of deviations from 90' L-M-P angles.
Figure 7.4. Comparison of the agostic triangular and linear structures. xviii
List of Schemes
Scheme 1.1. Coordination modes of mc nodentate pyridin ethione or pyridinethiolate.
Scheme 1.2. Simplified proposed mechanism for the hydrogenation by Pd(SALEN)
system.
Scheme 1.3. Structures of the first complexes to contain short intramolecular M- H.-H-N (a) or M-H"'H-0(b) proton-hydride bonds or intermolecular M-He-H-N (c) bonds.
Scheme 2.1. Mechanism of HID exchange in complex 1 in CDzClz under D2 (g).
Scheme 2.2. Proposed route to 6 in the reaction of 5 with triethylamine.
Scheme 2.3. Proposed route to 7 from the reaction of 6 with HBFj (P = PCyl).
Scheme 2.4. A reaction road map for the iridium complexes (L = PCy3).
Scheme 3.1. Various preparative approaches to iridium(V) pentahydrides.
Scheme 3.2. Two step synthesis offuc-iridium(II1) trihydride from iridium tric hloride.
Scheme 4.1. Transformation of 10 to 9 via 11 and 9'. the tram isomer of 9.
Scheme 5.1. Proposed mechanism for the deuteration process of 13 with dideuterium.
Scheme 7.1. Formation of 22 or 23 in the reaction of the pentahydride with tetrafluoroboric acid. xix
List of Tables
Table 1.1. Comparison of acidities and infrared absorption properties of the Y-H group of the proton donor in MH-HY bonds (M = Re. W). 17
Table 1.2. Comparison of acidities of phosphine co-ligands and v(0H) bands of donor. 18
Table 1.3. Examples of complexes characterized by TI measurement for proton- hydride bonds. 22
Table 1.4. Comparison of NOE enhancement percentages for proton-hydride bonding species. 24
Table 1.5. Proton-hydride bonding species showing JHH couplings in 'H NMR spectrum. 25
Table 1.6. Proton-hydride bonding complexes characterized by X-ray or neutron studies. 28
Table 1.7. Summary of the theoretical studies for proton-hydride bond. 30
Table 1.8. Summary of general features for proton-hydride bonding units. 3 1
Table 2.2. Characterization of the NH*-+I---HNproton-hydride bonding complexes. 55
Table 2.3. Summary of Crystal Data, Details of Intensity Collection, and Least- Squares Refinement Parameters for 1,s and 6. Table 2.4. Selected Bond Lengths (A) and Angles (deg) for 1.
Table 2.5. Selected Bond Lengths (A) and Angles (deg) for 5.
Table 2.6. Selected Bond Lengths (A) and Angles (deg) for 6.
Table 3.1. Summary of the selected spectroscopic results for 9.
Table 3.2. Summary of Crystal Data. Derails of Intensity Collection. and Least- Squares Refinement Parameters for 9. 98
Table 3.3. Selected Bond Lengths (A) and Angles (deg) for 9. 99
Table 4.1. Comparison of the selected NMR and TI(min) calculations for 1 and 11. 109
Table 4.2. Summary of Crystal Data. Details of Intensity Collection. and Least- Squares Refinement Parameters for Complexes 10. 11 and 12. 114
Table 4.3. Selected bond distances (A) and angles (0) for 10. 11, and 12. 115
Table 4.4. Selected angles and bond distances around the coordinated SpyH ligand. 12 1
Table 4.5. Bond distances for coordinated and free SpyH. 122
Table 4.6. Comparison of the selected angles and distances in Ir-H--+I-N units. 124
Table 4.7. Comparison of features for two PPh3 complexes 10 and 11. 125
Table 4.8. Comparison of features for two PPh3 complexes 11 and 12. 126
Table 4.9. Comparison of the N-9r distances versus co-donor ligands. 127
Table 4.10. Proton NMR, Tl(min) and IR bands for IrH and NH protons. 129 Table 5.1. Selected NMR and IR results for 13, 14 and 15,
Table 5.2. Summary of Crystal Data. Details of Intensity Coilection, and Least- Squares Refinement Parameters for complexes 15 and 16.
Table 5.3. Comparison of bonding distances and angles for 15 and 16.
Table 5.4. Comparison of M-S-Cbend angles and CI-N distances involving SpyH ligand.
Table 5.5. Comparison of angles and N-Cl distances involving H-bondings.
Table 6.1. Summary of selected 31~NMR, 1H data and TI values.
Table 6.2. Comparison of selected atomic distances and angles for 17. 18, and 20.
Table 6.3. Selected Bond Lengths (A) and Angles (deg) for complex 17.
Table 6.4. Selected Bond Lengths (A) and Angles (deg) for complex 18.
Table 6.5. Selected Bond Lengths (A)and Angles (deg) for complex 20.
Table 6.6. Summary of Crystal Data, Details of Intensity Collection. and Least- Squares Refinement Parameters for complexes 17, 18 and 20.
Table 7.1. Comparison of distances and angles involving M-H-C agostic bonds.
Table 7.2. Summary of Crystal Data, Details of Intensity Collection. and Least- Squares Refinement Parameters for 22.
Table 7.3. Selected bonding distances (A)and angles (0) for 22. Chapter 1. The hydrogen bond in transition metal complexes
1.1. Conventional or classical hydrogen bond
1.1.1. History and definition
The hydrogen bond continues to be of great interest due to its unique nature. and the significant role it plays in biology. Scientists have attempted to characterize this bond by use of experiment and theory for many decades. but definitive answers remain elusive. partly because the discovery of new types of hydrogen bonds continues. This thesis will describe such a discovery. Nevertheless through the years definitions of the hydrogen bond have been proposed by a number of scientists. including Latimcr and Rodebush ( 193_0).' Pnuling (1940).?
Pimentel and McClellan ( 1960)~' Atkins ( 1989),%and Zeeger-huyskens and Huyskens
( 199 1 )5 since the first proposal by Moore and winmilL6 The following general definition seems acceptable to most chemists. The hydrogen bond is an interaction between a covalently bound donor atom (Y-H) and a region of high electron density on an electronegative proton acceptor atom (x).' In other words. n proton is shared by two electron pairs occurring between Y-M and X where Y-H is a proton donor group and X is u proton acceptor group which can be a lone electron pair or a x-electron pair in il multiple bond. The total hydrogen bond length between X and Y is less than or equal to the sum of van der Waals radii of X and Y. The range typically falls within I .4 to 1.5 A for the H.-X distance. The strength of a hydrogen bond is normally less than 10 kcal/mol but can be as large as 37 kcal/mol in FHF-. For conventional and unconventional hydrogen bonds in transition metal compounds the bond enthalpy can be related to the difference in IR stretching frequency between v(YH) in YH-X and v(HY) of YH free from hydrogen bonding in a dilute solution. The typical range of v(HY). Y = 0. N in a hydrogen bonding unit is 3500 to
2500 crn-l. 1.1.2. Geometry of conventional hydrogen bonds
Although the hydrogen bonding geometry is usually linear (a) there are quite a number of other possibilities. For example, studies of simple organic molecules have identified four possible modes which include linear (a). cyclic (b), bifurcated (c). and trifurcated (d)(Figure 1.1 ). In addition hydrogen bonding can be intril- or inter-molecular.
-X--_ Y- _:H- Y bifurcated -x= perpendicular planar
(d) trifurcated
Figure 1.1. General modes of conventional hydrogen bond.
1.1.3. Classification of secondary bonds involving hydrogen in transition metal compounds
There are four general types in this category which include (a) MX-..HY. (b) MH."HY, (c)MH"'X, (d) M-HY, where R4 refers to a transition metal, X refers to a proton acceptor atom and HY refers to a proton donor group. Bonding type (a) involves a proton acceptor (X) directly attached to the metal. interacting with proton on Y of a molecule or a ligand group of the metal. This is a common form of conventional hydrogen bond occurring in transition metal complexes. In many cases the proton accepting unit X is a halide or pseudo halide ligand and Y is an electronegntive atom in a donor ligand such as a substituted pyridine (2-NC~HJZ.Z = OH. SH,NHR).'"' Representative examples are complexes containing one or two monodentate 2-pyridinethione ligand (SpyH). The SpyH ligand is present in most of the iridium complexes in this thesis.
A variety of hydrogen bonding modes are already known for this ligand (Scheme 1. I). Intramolecul~trhydrogen bonds are very common in six-membered metallocycle rings (i). Intermolecular hydrogen bonds can also occur with a counterion (ii). an anionic ligand of the neighboring molecule (iii), or the HN group of a free SpyH ligand (iv). Examples of hydrogen bonding SpyH complexes include Rh~C1~(p-Spy)z(~'-~py~)2(~~)z.~~py= 7-
SC5H4N). CUCI(S~YH)(PP~~)~?s~M~~cI~(s~~ H)~.'O { W(pI)I(C0)3(Spy H) } 2. '
Scheme 1.1. Coordination modes of monodentate pyridinethione or pyridinethiolate.
Bonding type (b) is substantially different from all of the others by having two hydrogens in the bonding unit. one of which is negatively, and the other. positively polarized to make the bond work. Like a conventional hydrogen bond. HY is a proton donor group and therefore the MH as a whole can be regarded as a proton acceptor base: this is exactly the opposite role to that in type (c)where MH group acts as proton donor acid. This type is unique in nature due to the opposite roles that two hydrogen atoms play in bonding and has left many questions behind since its discovery by the Morris group and Crabtree group in 1994 (see Section 1.2.1). It is the nature of the proton-hydride interaction that is the subject of this thesis. Type (c) is a recently discovered type of hydrogen bond which is characteristic only of transition metal complexes. A unique feature of this type is that the MH unit acts as a proton donor. Potential complexes with acidic hydrides are HCO(CO)~,[~[Cp%OsH] + . 13 and [~~~(d~~e)~]'.l5 Thus the cationic hydrides of 0s and W show the formation of the ionic-type ([MH]~-x') of hydrogen bonding between cationic hydrides and trifluoroacetate anion. Another example characterized iccently by IR is the cationic iridium(II1) dihydride
[I~H~(PP~~)~(co)~J+as a proton donor and triphenylphosphine oxide as an acceptor. l6 Final!y, in type (d) the transition metal itself accepts a proton provided by the donor group HY which is usually a part of the ligand attached to the same metal (i-e.. an agostic interaction). In this system an available metal d electron lone pair is at work to act as a proton acceptor. The dependence of the proton accepting ~bilitiesof basic metal centres and the proton donor properties of the carbinol HY groups have been studied and summarized in a review by Epstein. l7
1.2. Non-classical MH0*'HY hydrogen bond: the proton-hydride bond
The rest of this chapter will make use of the knowledge acquired by all the research groups in this new field as described in over 30 papers that have appeared since the discovery in 1994. Although Crabtree termed this new type of bond or interaction a dihyiro,qe~lhml. hereafter it will be called a proton-hydride bond for the following two reasons: i) two hydrogen atoms have specifically opposite electronic characters in the bond. one being proton-like and the other. hydride-like: ii) to avoid confusion in relation to a bond involving an $-dihydrogen ligand.
1.2.1. Speculation about M-H"'H-Ybonding before its discovery
In review. the first proposal of a proton-hydride interaction was made in 1972 by Schowen et a1 to describe the transition state of silicon hydride species in base-catalyzed alcoholysis reactions (Equation 1.1). In forming a dihydrogen molecule an OH proton of the
Referertcw page 34 alcohol is bonded simultaneously to the hydride while a nucleophile is attacking the silicon centre. In this system it is believed that in the absence of a nonbonding electron pair on the leaving group (the hydride), the reaction is assisted by a concerted donation of solvent proton (i-e.. OH of methanol) to the hydride in the course of its departure?
K % I MrO, P MeOH MeO- - - Si-10 H-- - - Si (1.1) Si- H * H - i \ $-' \ MeO' / j \ -Hz OMe d R I d R 1
In organometallic chemistry. the proton hydride interaction was discovered during the study of the heterolytic splitting of an acidic dihydrogen ligand (Figure 1.7). The other mode of H-H bond cleavage is the homolytic splitting in the oxidative addition of
dihydrogen (Figure 1.3). This will not be discussed further. s.. ..-. H + ".. I +/ I,,, I"' M I '"" M B 'I' 'I' 'I'
Figure 1.2. Heterolytic splitting of dihydrogen by an external (a) or internal (b) base.
.._ I homolytic \ / ....,,,, M.."'v, M-*-'-" "I' "I' Figure 1.3. Homolytic splitting of a dihydrogen Iigand into hydrides.
References page 34 Two possible pathways have been proposed for the base promoted heterolytic splitting mechanism: intermolecular splitting by an external base (a) and intramolecular splitting by an internal base (b). This is illustrated in Figure 1.2 where :B refers to a base with a lone pair to receive a proton. A proposal of such a heterolytic splitting of the dihydrogen bond goes back to the early 80's in hydrogenation reaction catalysis by Pd(SALEN). SALEN = N, N'- ethylenebis(sa1icylidene-iminato). l9 The reaction was proposed to involve two intermediate species prior to an intramolecular heterolytic splitting of a dihydrogen ligand. These are a dihydrogen species (11) and a 4 centered species (111) containing a dihydrogen interacting with a metal-oxygen bond intramolecularly. In this way a complete transfer of a proton from dihydrogen causes a vacant site for an incoming olefin to be created in IV by dissociation of the weak ROH ligand (Scheme 1.2). H-i- H
Scheme 1.2. Simplified proposed mechanism for the hydrogenation by Pd(SALEN) system.
Figure 1.4. Polarization between acidic dihydrogen and an internal or external base.
Figure 1.4 shows how the dihydrogen ligand can be polarized prior to proton transfer by the base to cause a splitting of the dihydrogen ligand. The extent of polarization
Referetices pcrge 34 Chapter I 7
of the dihydrogen ligand and proton transfer to the base depends on the acidity of the Ha ligand and the strength of the base.20 Figure 1.5 indicates four possible stages of proton transfer: case I. intermediate cases 11 and 111. and case IV, complete intramolecular heterolytic splitting. The interaction of the very acidic dihydrogen ligand in [Os(H2)(MeCN)(dppe)2](BF4)2with its counterion BF4- is an example of the case 11. The BF4 anion is a weak base. but is strong enough to have a shon contact (H-F of 2.5 A) with
the acidic dihydrogen.21 A possible example for case I11 is the iridiurn(II1) hydroxy complex ~~S-[I~H(OH)(PM~~)~]+reported in 1990 by Stevens et al.22*23The solid state structure OF this complex has a proton hydride distance of 2.4 A which is at the sum of van der Waals radii of two H atoms. The authors speculated that this is a favorable interaction. The hydrogen atom in a covalent bond has a van der Waals radius of 1.2 A. It is not known whether this geometry of the iridium complex is maintained in solution.
case I case I1 case I11 case IV
H2 ligand not acidic. acidic H2 ligand. H-.-Hbond resulting from no H-H bond. No interaction. H-H--B interaction. a very acidic H2ligand. proton transferred.
Figure 1.5. Four cases where the extent of proton transfer depends on the acidity of the dihydrogen ligand and the strength of the base B.
1.2.2. The discovery of short proton-hydride bonds
In early 1994 two iridium complex systems were reported independently to contain short Ir-H-H-Y contacts of 1.7 - 1.8 A~~*'~(case 111. Figure 1 S). These are hydrido
References puxe 34 complexes with proton donor ligands such as 2-pyridinethione24 (Morris group) or 8- quinolineirnino125 (Crabtree group). These are shown in Scheme 1.3. Complex (a) of Scheme 1.3 contains two proton-hydride honding Ir-Hu*H-N units while complex (b) has one Ir-He-'H-0unit. Both are fully characterized for the existence of the proton hydride bond in solution and in the solid state. The properties of complex (a) will be discussed in Chapter 2. The complex (c) is the first exemplified complex with an intermolecular interaction obtained by Crabtree in 1995. The presence of the intermolecular proton-hydride bond has been confirmed by neutron diffraction analysis.
(a) L = PCyl (b) L = PPh3
Scheme 1.3. Structures of the first complexes to contain short intramolecular M-He-H-N (a) or M-HS*-H-0(b) proton-hydride bonds or intermolecular M-H-H-N (c) bonds.
1.2.3. Bonding
Figure 1.6. Simplified diagrams of a conventional hydrogen bond (I) vs a proton-hydride interaction (11).
A hydrogen bond is a linkage that is formed by a proton between two electronegative atoms.' This concept for the conventional hydrogen bond (I) in Figure 1.6 may be extended
References page 34 to type (11) in which the proton acceptor is a hydride in the place of the electronegative atom
X in type (I). A hydride, carrying a negative charge. is basic. Thus an electrostatic interaction I1 similar to I is possible. However. a difference between these two types is the presence of a lone pair on X, versus a bonding pair in the M-H bond.' This means that the interaction of a hydrogen occurs between a Y lone pair and a HM bonding pair in the case of
the proton hydride bond. In order to understand this feature more clearly it is useful to
compare these two types of hydrogen bonds in terms of their molecular orbitals. A three centre-four electron interaction modez6 is a simple molecular orbital view of a conventional (Ba"HY)hydrogen bonding unit. This is shown in Figure 1.7.
B B*"H-Y H-Y Figure 1.7. Molecular orbitals of a B---HYhydrogen bond?
References page 34 All three orbitals are formed about the central hydrogen nucleus with appropriate symmetry:
the lowest bonding, the middle nonbonding, and the highest antibonding orbitals. It is noted that, in order to form a hydrogen bond between B and HY, both of the energies of the B-
HOMO and the HY-LUMO shou!d be similar and the energy level of the occupied orbitals are lower than those of the B and HY orbitals. Further discussion about the matching of orbital energies and the strength of hydrogen bonding can be found in reference 26.
H-Y
Figure 1.8. Proposed molecular orbital diagram for a proton-hydride bonding unit (MH-HY). A molecular orbital diagram (Figure 1.8) can be generated by applying the concepts of Figure 1.7 to a proton hydride bonding system (MHWY). It shows that the major bonding interaction occurs between the dX2.,,'(~)+s(~){or ~~(M)+s(H)} orbital of the MH unit and the s(H)+py(Y) orbital {s(H)+pZ(Y)}of the HY unit. The energy difference between the MH-HOMO and the HY-LUMO must be small to have a good match for an appropriate interaction. The occupied product orbitals are lower than both reactant components for a stable combination. Since the acidic proton (HY)remains on the donor side (Y) the HY-LUMO is slightly lower in energy than the MH-HOMO. The middle orbital is essentially nonbonding. Finally. the highest energy orbital involves an antibonding o* interactions of the MH and HY units. Since the major interactions occur at the proton between the hydride electron bonding pair and the pair of bonding electrons of Y. it is also regarded as another form of three centre-four electron bond. Another important factor to consider is the van der Wads radius of each of the two interacting hydrogen atoms in the MHS..HYunit. One often uses 1.3 A for the van der Waals radius of a bound hydrogen atom in a C-H bond for example. but this should not include a metal-hydride bond. An ionic hydride with two valence electrons is bigger than a hydrogen in a covalent bond. Some examples of the ionic radius of a hydride are found in saline hydrides: 1.37 A in LiH. 1.46 A in NaH and 1.52 A in KH.~' The van der Waal's radii of transition metal hydrides are not well known but might be expected to be larger than 1.2 A. One can derive the cova!ent radius of a hydride in a polar M(6+bH(6') bond by subtracting the radius of the metal ion of interest from the bond length of M-H. For example. the covalent radius of 0.80 A for a hydride in 6-coordinate iridium(II1) is calculated from the known radius of 0.82 A for a 6 coordinate I?+ ionz8 and a covalent bonding Ir(II1)-H distance of 1.62 A in a octahedral Ir(1II) To obtain the van der Waals radius. Bondi's correlation method 29 may apply (r, = r,,, + constant. r, = van der Waals radius. r,,, = covalent radius and constant = 0.76). The van der Wads radius of a hydride in iridium complexes of the type found in this study could be roughly 1.6 A if this approximation holds. Thus the distance limit of the IrH-HY proton-hydride bond is the sum of 1.6 A (hydride) plus 1.2 A (Hof YH), or almost about 2.8 A.
1.3. Preparation of species containing a proton-hydride bond 1.3.1. Oxidative addition
A simple preparative method is the oxidative addition of the X-H bond of an HX-YH reagent (X.Y denote donor atoms) by a coordinatively unsaturated complex to give the saturated product (Equation 1.2). H----H, ln+ Y
[ML4In+ HX-YH L ..*P.,,~~ ..... X L--I.L L--I.L
The four coordinate complex 1r(PMe~)~+has been used in such a reaction (Equation 1.3). In this reaction water undergoes oxidative addition to iridium(1) to give the hydrido hydroxy complex of iridium(II1) mentioned in Section 1.2.1 in which the OH group may interact weakly with the hydride at a distance of 2.4 A." The second part of Equation 1.3 is a metathesis reaction of hydroxide for methoxide which takes place in methanol as the solvent. An interesting feature of this methoxy complex is the involvement of one of the methoxy CH protons in a C-H--H-Ir interaction due probably to the weakly acidic nature of CH protons of the methoxy group. The H-H distance of 1.86 A (X-ray) in the CH-Hlr
References page 34 Chapter I
1 J.2. Substitution reaction
A key feature of this method is the replacement of a weakly coordinated solvent molecule in a hydrido complex by a ligand L-YH containing a hydrogen bond donor YH and a lone pair on L. One or two L-YH...HM proton hydride bonds can be expected from the cis-solvent0 complex of Equation 1.4. Tricyclohexylphosphine complexes (R = Cy. Z = BFJ. L-YH = 2-rnercaptothiazoline. 7-mer~a~tobenzothiazole)~~and the triphen y 1phosphine complex (R = Ph. Z = SbFa, L-L-YH = quinoline-8-acetamide)3' worked well with this approach. The former contains two proton-hydride bonding units while the latter has one.
L-L-YH
In some cases, chelation via L and Y donor atoms of L-YH can also occur. To avoid this cyclornetalation reaction. coordinating bases such as X-(X = halogen or pseudo halogen atoms) are added to induce species with a monodentate L-YH ligand for MH-HY-L bonding. A drawback of this method is the formation of a possible MX--HY-L conventional hydrogen bond. Studies using such an approach (Equation 1.5) reveal that both types of species are formed as a mixture in some instances (X= Cl, Br. I) while a single species is isolated in others (X = F). l2 An important observation is the large coupling (I = 5.5 Hz) in a IH COSY NMR spectrum due to the proton-hydride bond in the complex produced in the reaction of [Ir(H)2(sol)2(PR~)2]+,sol = acetone. R = Ph. with pyOH and BuJNC~(Equation 1 S).''
1.3.3. Ring-opening reaction
If a chelating ligand L-Yin a complex contains a basic Y site, it can be protonated by an external acid (HX. X = halogen. for instance) to open the chelate ring. This will produce species with a potential proton donor site HY on L (Equation 1.6). IrH?X(pyOH)(PPh3)2 (X = CI. Br, I: py = csH4~)12and IrHX2(C0)(2-Ph?PC6HJOH)(PPh3)(X = ~1)~'are examples prepared by this method using starting complexes IrH?(pyO)(PPh3)?and Ir(CO)(2-Ph2PC6H~O)(PPh3).respectively. Both exist as two rotomeric isomers in which the OH proton forms an IrH-.HO proton-hydride bond or an IrCl--HO conventional hydrogen bond.
References puge 33 In some cases it is also possible to produce a proton-hydride bond in a complex by the heterolytic splitting of a dihydrogen molecule (Equation 1-7) .33 The mechanism of this reaction might involve intermediates of type I and I1 of Figure 1.5.
1.3.4. Substitution of polyhydride complexes
In general. high oxidation state transition metal polyhydrides are reactive under suitable conditions (heating in donor solvent. addition of soft donor ligands and acids. for example) with respect to the reductive elimination of dihydrogen. Equation 1.8 illustrates the application of this concept to iridiurn(V) pentahydride complexes in the presence of appropriate donor ligands. The reaction thus gives an iridium(II1) trihydride possibly with a
n H eg. R = Ph, L YH = aminopyridine
2-Aminopyridine gives a uihydrido(aminopyridine) complex of this type in the reaction with bis(triphenylphosphine)pentahydridoiridium(~).33 The resulting species has a monodentate aminopyridine with a dangling NH2 unit which forms an NH-HIr proton-hydride bond (LYH = aminopyridine).
References page 34 Ctwpter I 16
For this method to work, the steric properties of the phosphine ligands attached to the polyhydride and the properties of the ligands (LYH)must be correct to avoid obtaining
undesired products containing L-Y chelation via the L and Y atoms. Such chelate complexes could form froo the elimination of two moles of dihydrogen. Examples are the reactions of IrHg(PR3)z with 2-NCsH4Y (Y= SH. OH and R = Ph. Cy) under elevated There is the possibility of opening the chelate ring by use of a strong acid (see Equation 1 A). Also protonation of one of the basic hydrides might produce a dihydrogen species (Equation 1.9). This is seen in the reaction of I~H~(~~-s~~)(Pc~~)~with HBF4 etherate?
L-YH R3p o,,, IILr,,,,.l.. IrH5(PR3l2 - -2H2 H~ 1 PR,
fi eg- L YH = hydroxy- or mercaptopyridine R = Ph, Cy
1.4. Characterization of proton-hydride bonding
1.4.1. Infrared spectroscopy
Hydrogen bonding is often detected by use of IR studies of the YH vibration of the hydrogen bond donor. Broad bands at lower frequencies with increased intensity are expected for the hydrogen bonding YH group.7 Similarly the stretching mode of the YH unit in most proton hydride bonded species in the solid and solution state is a broad band with a frequency lower than that of the free YH stretch. In Table 1.1 characteristic infrared features of proton-hydride bonded complexes are compared.36037 In all cases the spectral changes are analogous to those of conventional hydrogen bonds. exhibiting low-energy
Refererms page 33 shifts relative to v(YH) of the free donor molecules. The spectral parameters also indicate that the interactions are dependent on the acidity of the proton donors: in the examples given. the most acidic proton donor 2.4,6-Me3C6H20H in the Re system and the most acidic. (CF3)3COH, in the W system are the strongest donors. Steric properties of the donor must also play a role but appear to be less significant.
Table 1.1. Comparison of acidities and infrared absorption properties' of the Y-H group of the proton donor in MH-HY bonds (M = Re, W).
Donor compound p K,~ V( W)fk ~W-bndcdAV' -AHo ref.
Donor series lc - ---- PhNHMe 29 3433 3334 90 3 .O 36
PhNHnBu 27 3422 3320 102 3.1 36
PhNHPh 25 3400 3287 113 3.3 36
2,4,6-MenC+I20H 18 3600 3270 330 5.6 36
Donor series 2c . PhOH 10 3623 3328 295 5.2 37
"IR data in crn-1. brneasured in DMSO. 'Av values = v(YH)fiee - ~(YH)bonde&din kcal/mol. eReH5(PPh3)3 for donor series 1 and WH(C0)2(NO)(PMe3)2for donor series 2.
Another important factor affecting the shifts of v(YH) bands is the electron donating
abilities of the phosphine ligands on the hydride acceptor. A series of phosphine ligands in WH(C0)2(NO)L2 have been examined in reaction with a number of acidic proton donors
References puge 34 (Table 1.2). The results indicate that the strength of the proton-hydride bond increases roughly with an increase in the basicity of the phosphine ~i~ands.~' For hydrogen bonding in organic molecules, enthalpies (AH0) of hydrogen bonding are often correlated with the band shifts (Av) of YH and the integral intensities of the YH
bands. The correlation equation (Equation 1.10) which was originally proposed by 1oganscn3"or the calculation of hydrogen bonding strength in organic molecules has been used to characterize hydrogen bonding in organometallic complexes (Y= 0. N) .39.40
-AH0 = 18 AV (YH) / { AV (YH) + 720) (1.10)
Crabtree and co-~orkers~~and Berke and co-worker~~~have used this equation to calculate the strength of intermolecular proton-hydride bonds in Re and W hydride systems. respectively (Tables 1.1 and 1.2). Enthalpies of 3 to 6 kcal/rnol have been obtained for ReH5(PPh3)3 and ReH7(dppe) with weak acids such as indole (YH = NH) and Me3C6H20H (YH = OH). Similar enthalpies of 4.1 to 6.9 kcal/moI are obtained for WH(C0)2(NO)(PR3)2interacting with acidic alcohols such as PhOH. (CFJ)~CHOHand (CF3)3COH.
Table 1.2. Comparison of acidities of phosphine co-ligands and v(0H) bands of donor."b phosphine donors (L) PK~' ~(0H)bonded AV' -AHOC:
aIR data (in cm-1) for (CF3)2CHOH-.HW(C0)2(NO)L2.bData from ref. 37 unless stated. CpK, values from ref. 41. d~~ values = V(OH)&, - v(OH)bondej. em0in kcal/mol.
Refererrces page 34 1.4.2. Spin lattice relaxation time (TI)measurement
The proton-hydride bond results in a short hydrogen hydrogen distance of 1.75 to 2.0 A. This situation makes the measurement of TI a powerful tool to elucidate proton hydride bonds in solution. The measurement of TI.the spin-lattice or longitudinal relaxation time. is often used
in structural determinations when the relaxation is dominated by proton-proton dipole-dipole interactions. There are a number of factors that determine the relaxation time of each nucleus. These include the magnitude of the dipolar relaxation. the temperature and concentration of the sample. the viscosity of the solvent. the size of molecule as well as in certain cases other factors such as quadrupolar relaxation (I > 1/2). paramagnetic relaxation (with unpaired electrons) and chemical shift anisotropy relaxation? Of most significance is the dipole dipole relaxation phenomenon for very short H-H distances. This is readily seen
in the 'H NMR spectrum of dihydrogrn species where the a short TI time of the r12-~2
ligand is due to the shon H-dipole to H-dipole distance of 0.8 to 1.1 A. By contrast. hydride resonances in hydrido complexes have long TI times because there are no very shon
H.-H distances.43 A classic example is [Cp*Ru(dppe)(~~)]+which has a TI(rnin) of 18 ms versus [Cp*R~(dppe)(H)~]+which has a Tl(min) of 640 ms at 220 K at 400 MHz.44 The temperature of a sample also influences the TI time because of molecular motion. At high temperature the molecule has more energy and tumbles at higher frequencies. When the frequencies of motion of the molecule are different from the resonance frequencies of the nuclei in the molecule. for example. at temperatures above or below the minimum TI. one would expect a longer TI time. The temperature dependent TI time is given by Equation 1.1 1 below.
Referemes page 34 where h is Planck's constant. y is the gyromagnetic ratio of nuclei involved. Tc is the rotational correlation time (a measure of the time constant of molecular tumbling in solution). o is the Lamor frequency, I is the nuclear spin. and r is the distance between two dipolar
Homonuclear l H- H relaxation is described by Equation 1.12.
Rate = -1 - I 708x I o-)' ( + TI r"H6 +ZiTc2
where ~HHis in cm. r, in sec. in Hz. At the minimum TI.T, is equal to 0.6Yu =
0.62/2m where v is the spectrometer frequency. Rearrangement of Equation 1.12 gives il very useful simplified equation to calculate H-H distances between IH-IH units (Equation 1.13).
~HH= 5.816 6J T~(min) (rHHin A,T, in second. v in MHZ) ( 1.13) v
This equation is a reminder that the spectrometer frequency should always be reported when TI(min) values are reported. For example, Tl(min) will be twice as large on going from 200 MHz to 400 MHz for a given H---Hdistance. The contribution of neighboring nuclei to the relaxation rate of the nucleus of interest drops off rapidly as the distance increases since the relaxation rate is proportional to r6
(Equation 1.12). However the TI(min) values of a proton in a proton-hydride bond will be influenced by the presence of any protons within 2.5 A of the proton of interest. in order to account for the measured TI value of the nucleus of interest it is necessary to add up all of the contributing relaxation rates.13 This is shown in Equation 1.14 for
References page 34 Chapter I 2 1
MH,(L-YH)b(PR3),, for an example. where L-YH is a monodentate ligand via L and there is an MH-HY bond.
In Equation 1.14 Tl(obs)is at its minimum, R refers to the relaxation rates. H(m)H refers to cis-hydrides. H(1)H refers to protons on phosphines. and H(Y)H refers to protons on the ligand L-YH. It also includes RMH and RH~which are relaxation contributions from a dipolar metal (e.g. 55~n.5y~0, IS5~e, lg7~e) and a dipolar nucleus Y (e.g. 14~). respectively. The relaxation rates (R) are obtained from the following equation 1 .I 5:
where K, is a parameter (e.g., 77.5 1 for hydrogen at 500 MHz) calculated by Desrosiers et aP3 This parameter is related to the gyromagnetic ratio as seen in the following equation
( 1.16) of which Equation 1.15 is a simplified form.
Below in Table 1.3 we have examples of complexes containing intra- or inter- molecular proton-hydride bonding units for which a spin lattice relaxation time measurement was used to calculate the Hq-H distance in solution. The H--Hdistances in solution calculated from this method are in the range 1.7 to 2.1 A which are consistent with those in the solid states obtained by X-ray or neutron analyses which we will see later on. It is of interest that the T 1 (min) of the YH proton would be much longer (as high as 1 sec or more) if it were not for the existence of the MH-HY interaction.
Referewes page 34 Table 1.3. Examples of complexes characterized by TImeasurement for proton-hydride bonds. type" compound T 1 (min)/ms ct(HHjAb v/MHzC ref. inter C~RU(PC~$H~-.HOCH(CF~)~84 (RuH) 1.92 400 47 inter tr~ns-Ru(dpprn)~H~-HOPhd 100 (RuH, 293K) N/A 400 48 85 (RuH, 233K) 85 (PhOH, 233K) inter WH(C0)2(NO)(PMe3)2 330 (WH) 1.77 300 37 intra [IrH2(PPh3)2(QAMD)]+ 262 ( IrH) 1.8 300 3 1 QAMD = quinolineacetamide ------intra [IrH(2-thiazolidine)4(PCy3)]+ 180 (IrH) 1.9 400 30 230 (NH) ------intra OqH2(CO)1 o(NHEt2) 384 (OsH) 2.1 400 49 intra IrH2Cl(q '-pyOH)(PPh3)z 82 (IrH) 1.7 300 12 242 (IrH)fice intra IrH3(H2NC5bN)(PPh3)2 130 ( IrH) 1.8 300 33 25 1, 288 (IrH)frcc 127 (NH) intra RUHC~(CO)(NH~NH~)(P~P~~)~'170 ( IrH) 2.0 400 50 intra IrHClz(NH3)(PCy3)f 230 (IrH) 2.1 400 50 intra IrHC12(NH2NH2)(PCy3)rc 220 (IrH) 2.1 400 50 intra [IrHL4(PCy3)](BF4)2 190 (IrH) 2.0 400 30 L = 2-benzothiazolethione 240 (NH) intra [I~H~L~(PCY~)Z~(BFJ) L I : 220 (IrH) L1: 2.0 400 30 L = 2-rnercaptothiazoline (LI) 240 (NH) 2-rnercaptobenzothirtzole (L2) Lz: 230 ( IrH) "Interaction type (ha-or inter-molecular). bhe H-H distances calculated from Equation 1.13. 'Frequency of spectrometer used. d~l(rnin)are attributed to H-H interaction and/or exchanging intermediate of dihydrogen. The results are for 3.3 equiv. of PhOH used. e Complexes containing MH-HC interactions and d(HHj~are for d(MH--HC).M = Ru. Ir.
References page 34 Chapter I
1.4.3. Nuclear Overhauser Effect
The Nuclear Overhauser Effect (NOE) is a technique used for determining the
conformation of a molecule by detecting through-space dipole-dipole contacts. Since it involves the same dipolar relaxation mechanism as described for TI. for NOE to be effective. the two nuclei should be less than 3 A from each other. Simply by irradiating one or a group of nuclei one observes which other nuclei or groups show an alteration of intensities (i.e., increase in intensities)? ' In general the maximum NOE enhancement (q) is
given by the following equation ( 1.17) where A. B refer to observed and noise decoupled values, respectively.
The NOE is maximum when A and £3 are in the extreme narrowing region and
dipolar relaxation dominates? One can expect as much as a 50 % enhancement when yg is
equal to y~,but usually the increase is 5 to 10 %. The enhancement factor (q)is measured
by use of the intensity changes as shown in Equation 1.18 where I. is initial and if is NOE enhanced intensities? I, - I" tl= ( 1.18) I"
Species containing proton-hydride bonds are subject to NOE. Quite a number of complexes have been examined by this NOE method to verify the existence of the H--H interaction in solution. The results shown in Table 1.4 indicate that the dipolar interactions are fairly strong to give large enhancements of about 9 to 14 % .
References page 34 Table 1.4. Comparison of NOE enhancement percentages for proton-hydride bonding
Compound sites irradiated NOE % ref.
inter W(C0)2(NO)(PEt3)2H--HOR ROH 1 I(WH) 37
inter trmzs-~u(dppm)2H2.-HOPh PhOH e ffec tivea 48
intra [I~HL~(PCY~)~(BF~~ 30
L = 2-mercaptothiazoline IrH 14 (NH) 2-merca~tobenzothiazole IrH 13(NH) intra [I~H~L~(PC~~)Z~(BF~) 30 L = 2-mercaptothiazoline IrH 10 (NH) 2-mercaptobenzothiazole IrH 9 (NH) intra RuHCI(CO)(NH~NH~)(PC~~)~~PCy3 12.5 (IrH) 50 in tra IrHCiz(NH3)(PCy3)2b pcy3 13.5 (IrH) 50 intra IrHCl(NHzNHr)(~Cy3)2b Pcy3 1 1.5 ( IrH) 50
"NOE percentages are not assignable due to the involvement of dihydrogen intermediate species. b~omplexescontaining IrH-HC interactions: resonance groups for phosphorus ligand protons are irradiated.
1.4.4. Correlation Spectroscopy
Correlation spectroscopy (COSY)utilizes J coupling which is different from NOE that involves dipolar interaction through space? In a COSY experiment coherence of one spin is transferred into coherence of another spin when they have a scalar coupling. Thus a uue coupling is observed in a COSY experiment as off diagonal peaks. This method is often used to trace a coupling network. The application of this method to proton-hydride bonding systems has resulted in the observation of JHH couplings for several complexes (Table 1.5). Significant coupling constants in the range 3 to 6 Hz indicate that there is covalent bonding
References page 34 between the hydride and the HY proton. Thus a reasonable assumption is made that these
are l~~~ couplings and not SJHH coupling which are expected to be zero (see Table 1.5. for example).
Table 1.5. Proton-hydride bonding species showing JHH couplings in 'H NMR spectrum.
compound JHH couplingsNz" ref. [I~H~(~~-NN'cROH)(PP~~)~](S~F~)R = Me 3 (COSY) 33
NN'CROH=S-quinolinealkylirninol R=3.4-F2C6H3 3.9(COSY)
IrHzX(pyOH)(PPh3)2 X = Cl. Br. I 5.5 - 5.6 12
IrH3( H~NC~HJN)(PP~~)~ 2.6 (COSY) 33 il Coupling of NH or OH donor protons to hydride resonances.
1.4.5. Single crystal X-ray and neutron diffraction
One of the most definitive methods to determine solid state structures of organometallic transition metal complexes is the single crystal X-ray diffraction method. X- ray diffraction provides a measurement of electron density around each atom. Therefore an
atom with a great number of electrons such as a transition metal often dominates the diffraction pattern. The method is challenging when hydride locations are desired. Hydride ions have only two electrons and have large thermal motion. In some favorable cases the position of a hydride proton can be measured, but. only to M.05 P2with scintilation detectors and a.03 with CCD detectors. In most cases, however. hydrides are not located by X-ray analysis but their presence is indirectly evident by the presence of a vacant
References page 34 coordination site at the metal of the solved structure. It is also assignable by determinating an unusually long M-L distance of the ligand L trans to the unobserved hydride. The presence of a hydride in a crystal can be supported by other spectroscopic techniques such as infrared where there is a M-Hstretching band in the region 1900 to 2250 cnf ' : deuterium substitution leads to a M-D stretching band at v(MD) = v(MH)/1.4. Although X-ray diffraction is very useful since this technique only requires one tiny crystal it is also necessary to do NMR and IR studies to eliminate the possibility of the presence of other species formed in the crystallization process prior to X-ray analysis. Another method that is particularly useful for the solid state structural determination of hydride complexes is single crystal neutron diffraction. A beam of neutrons of uniform velocity behaves like a wave of definite wavelength and can be diffracted by crystals. In contrast to X-ray scattering amplitude which increases rapidly with atomic number. the scattering of neutrons by atoms is purely nuclear and most atoms scatter neutrons equally well within a factor of 2 or 3.53 This method therefore provides information on the location of the nuclei of light atoms such as hydrogen to nearly the same accuracy as it does other heavier atoms. However. the following shortcomings for a neutron structure determination are unavoidable and may prevent one from using this method more commonly: a nuclear reactor or a linear accelerator is required and large crystals (at least I rnrn3) are required to observe a sufficient number of diffraction events. Several species possessing one or two H-H units which have been examined by X- ray or neutron diffraction are shown in Table 1.6 (examples from the current thesis work are excluded). Although the estimated standard deviations in the Ha-H distances are high. the He-Hdistances are roughly in the range from 1.7 to 2.2 A which are less than the sum of the van der Wads radius of two hydrogen atoms (2.4 A). Another matter of concern is the short H-H distances observed between hydrides and CH hydrogens. Three examples with H---H distance of 1.7 to 2.2 a present in Table 1.6 are indicative of MHm--HCinteractions. These examples are only three out of 150 complexes containing such interactions which were
Refererrces page 34 ignored un ti1 the recent discovery of MH-HY proton-hydride bonds. General features of MH-HC interactions found in the CSD search by Crabtree et aP4 are: i) interactions are significant in aryl phosphine hydride complexes; ii) in most cases the interactions involve terminal hydrides which are more hydridic than bridging ones; iii) the MHv-HCinteractions
are favored in neutral complexes: iv) interactions are common in polyhydrides due to the low steric hindrance of the hydride group coordination sphere and the strong donor ability of hydrides; v) no examples are found for early transition metal hydrides which have the most negative hydrided4 Some examples of complexes containing the MH-HC interaction units are: [IrH(OMe)(PMe3)4](PFa).[I~~H?(NH~)~(NH~)z(PE~~)~ ](BPh& IrHClz(PMe2Ph)l (PiPr3). I~H?CI(PP~[BU~)~, R~(c~H~)( H)~(P'P~~P~)~. ReHs(PMePhz)3. ReHs(SiHPh2)z (piPr2Ph)2, CoH(CO)(PPh3)3. [OSCI(H~)(H~~~~)(P'P~~)~jCI. 0s2H4(PMe~Ph)5. Fe( H~)Hz(PP~~E~)~.Fe(p-H)3(PPh2Et)&u(PPh2Et), RhHCl(B {cat} )(P~P~~)~.Cp*RuH ($-CH~=S~P~~)(P'P~~).SJ
References page 33 Table 1.6. Proton-hydride bonding complexes characterized by X-ray or neutron studies.' compound d(M-H) interaction type method ref.
ReH5(PPh3)3indole 1.683(5) 1.734(8) inter. MH-HN neutron 55 2.2 1 ReH5(L)(PPh3)yL - 1.99(8) inter. MH-6,HN X-ray 56 L = imidazolc 1.68(2) cis-[IrH(OH)(PMe3)j](PFg) 1.6 17(9) 2.40( 1 ) intra. MH-.HO neutron 23 1.7 12(76) 2.44 intra. MH-HO X-ray 22
[I~HL~(PCY~)](BF~)~ 1.44(6) 2.1(1) intra. MH-.HN X-ray 30 L = 2-thiazolidinethione
IrHC12(CO)(PPh3)(L-YH) 1.7(2) 2.1(2) intra. MH-430 X-ray 32 L-YH= 2-Ph2PC6Hm
I~Hc~~(NH~)(PcY~)~~1.39(4) 2.2 intra. MH-.HC X-ray 50
[I~H(OM~)(PM~~)J~(PF~)~1.8 13 1 362 intra. MH-HC X-ray 22
Fe(Hr)Hz(PPhzEt)3bsc 1.5 14 1.77 intra. MH-.HC X-ray 54
"Distances are in A. bComplexes containing MH...HC interactions. For more examples see reference 54. 'The same hydride interacts with a cis-dihydrogen ligand at 1.86 A.
1.4.6- Theoretical studies
Decisive information on the existence of proton-hydride bonds and the strength of the bond for a number of related species in stable compounds or intermediates has been derived from ub irtitio and Hiickel calculation studies33957-59 and density functional rnethod~.~' Some examples are summarized in Table 1.7 with their characteristic features. The proton- hydride bonds are evident for a wide variety of metal ions involving iridium(II1). palladium(II), rhodium(I), and molybdenum(I1).
Refererlces page 34 Certain arnin~~~ridine~~and pyridinethione57 complexes of iridiurn(II1) contain one or two intramolecular NHs*.HIrinteraction units. The Mulliken atomic charges are -0.27 and +0.22 for the hydride and proton, respectively. The pyridinethione complex
[Ir { H(SpyH) ) 2L2 J(BF4) in Table 1.7, which is modeled with simplified phospbine ligands
(L = PH3) by Liu and ~offrnann~'is one of the first proton-hydride bonds discovered by Morris et al. The detailed preparation and characterization for the original species (L = PCy3) will be described in Chapter 2. The calculations reveal the presence of an attractive electrostatic interaction and a positive Mulliken overlap population of 0.016 for the (N)HS-.H(Ir)unit. The palladium(I1) model complex of Table 1.7 contains a tridentate pyrazolylborate group. The complex possessing a NHss.HPdinteraction unit is believed to be a transition state species where Hz elimination occurs from a proton-hydride bond? The rhodiurn(1) model complex is a postulated intermediate species having an intermolecular NH--'HRh interaction as a result of the base assisted heterolytic cleavage of the coordinated dihydrogen. The Mulliken atomic charge for one of the hydrogen atoms in the Hz ligand of +O. 16 indicates that this hydrogen is acidic and interacts with a base introduced prior to the heterolytic cleavage reaction? Finally the monohydrido rnolybdenum(1I) complexes are active proton acceptors from moderately donating HY groups. studiesbo of a series of molybdenum complexes and external proton donors have found the following dependence of proton-hydride bonding on the tram ligand and the proton donor ability of HY: i) the H--H interaction exists with a poor or moderate HY donor and with a stronger x-accepting rrms ligand Iike NO: ii) strongly acidic HY leads to an q2-~2structure: iii) strongly 0-donating cis-ligands (phosphine) strengthen the HUHinteraction.
References page 33 Chapter 1 30
Table 1.7. Summary of the theoretical studies for proton-hydride bond."
Model compound Bonding type Bond d(HH) Mulliken ref. energy (A) atomic charge (kcaVmol)
IrH3(2-pyNH2)L2 intra 6.02 1.96 IrH: -0.26 33 NH: +0.22
[I~(H(s~~H))~L~](BF~)~intra - 1.75 IrH: -0.27 57 NH: +0.22
PdH(OHIMe2 {(H2C=N- intra - 1.6 1 PdH: -0.08 58
NH)z(Hg=NH-NH)BH }
Rh(Hz)(HCO2)Lz inter with NH3 3 to 5 2.09 R~(H*H):-0.03' 59
~h(HH* ): +o.1 bd
MoH(CO)~(NO)L~' inter with HY > 5 1 .378f MoH: -0.034 60
MOH(CO)~L~L" Y = F, OH, 11 to 13 YH: +O.44 H~O+ L' = NO, C1, H "L = PH3. b~heauthor also studied (C0)5MnH4iF and found bond energy of 6.55 kcal/mol and d(HH) of 1 A83 A. 'Negatively charged hydrogen of the coordinated dihydrogen. d~ositivelycharged hydrogen of the coordinated dihydrogen (acidic hydrogen). 'Density function theory methods are useda6' fProbably an underestimate.
1.5. Summary of the general features of the proton-hydride bond
Table 1.8 summarizes the general features for those species relevant to the current study. The bond energies are in the range of 3 to 10 kcal/mol. as strong as a conventional hydrogen bond. The distances ( 1.6 to 2.1 A) between two hydrogen atoms are less than 2.4 A. twice the van der Waals radius of an H atom (1.2 A) and are in agreement in solution.
References puge 34 solid state and theoretical studies. A large NOE of over 10 5% and small TI minima for the YH donor hydrogens and the hydrides are indicative of close dipolar interactions. Formation of a partially covalent bond is indicated by the presence of H-H coupling constants of 3 to 6 Hz. Finally, attractive electrostatic interactions are of significance between a negatively polarized hydrogen (hydride) and a positively polarized hydrogen (proton) according to Mulliken atomic charge separations.
Table 1.8. Summary of general features for proton-hydride bonding units."
E(~~) d(~~) TI(HH,~ NOE(HH) ~HH) C~~F(HH) (kcaVmol) (4 (ms (%) (Hz)
3-7 (IR) 1.7-2.1(TI ) 63-262 (MH) > 10 3-6 -0.03 to -0.27 (hydridic H) 3-10 1.7-2.1 (d) 170- I80 (YH) ( theory) 1.6-2.1 +O. 16 to +0.U (theory (protonic H)
.. . . .-. . . - -- -- .. - it E refers to proton-hydride bond energy: HH refers to the proton hydride bond: Charge refers to Mulliken atomic charge; theory refers to theoretical calculation: d refers to X-ray or neutron diffraction studies. b~ ( min) calculated based on 300 MHz.
Although we still need more systematic information on the proton-hydride bond before making generalizations, with the above results in mind. we conclude that the interactions are certainly attractive and as strong as a conventional hydrogen bond. A question that comes to ones mind is: What makes this bond so strong ? It is interesting to point out that it is the amphoteric nature of this. the tiniest atom that makes the bond so special. Crabtree proposes the following answer: i) a close approach is possible due to the small size of two hydrogen atoms; ii) a hydride is polarized on approaching the donor HY group; iii) the proton acceptor hydride lacks a lone pair that causes the weakening of conventional hydrogen bonds due to repulsion between lone pairs.
References page 34 Choprer I
1.6. Background and the outline of the thesis
Dr. Ramachandran in this lab obtained an interesting dimeric species in the reaction of bis(tricyclohexylphosphine)pentahydridoiridium(V) with tetrafluoroboric acid etherate in the presence of 2-pyridinethione (see Chapter 2). The solid state structure of the product revealed by X-ray analysis possessed a unique proton hydride close contact involving the NH proton of coordinated pyridinethione ligand and the hydride. This interesting synthesis. however. was unable to be reproduced, leaving more works behind: i) preparation of the dimer and other analogous complexes: ii) the nature of a proton-hydride interaction versus a conventional hydrogen bond: iii) factors that govern the strength of such interactions. This study focuses mainly on the new chemical phenomenon of proton-hydride interactions. The major part of this thesis is devoted to the preparation and characterization of new hydrido species containing cis-ligands with potential proton donor HY groups to examine donor properties to hydride versus other conventional acceptors. The preparations. in most cases. involve bis(tricyclohexylphosphine)iridium(V) pentahydride as the starting material for substitution reactions. a method described in 1.3.4. In some cases. other polyhydrides are also used in reactions with HY-containing donor molecules. The complexes have the iridiurn(II1)-based general formula [IrX,(L- YH)b(L'),]Zd. where X is H, CI. L-YH is donor ligands. L' is trialkylphosphine ligands (PR3. R = Cy. Ph). Z is tetrafluoroborate. The study is divided into six chapters. Chapter 2 is devoted to attempts to remake Ramachandran's dimeric species by using IrH5(PCy3)2 and Zpyridinethione under acidic conditions. Chapter 3 deals with a synthetic approach to proton-hydride bonds in complexes with triphenylphosphine co-donor ligands. Chapter 4 is an extension of Chapter 3. The first part of this chapter describes the study of proton-hydride bonding in several triphenylphosphine complexes formed in efforts to prepare analogs of the
References page 34 C/JUP~~~1 33
tric yclohexy lphosphine complexes described in Chapter 2. The second part of this chapter focuses on deducing general features for the proton-hydride bond in IrH-HpyS systems studied through Chapter 2 to Chapter 4. Chapter 5 is an extension of work with the SpyH ligand. Its main feature focuses on the acceptor prcperties of a hydride versus a chloride with a SpyH donor. In Chapter 6 several other potential hydrogen bonding donor ligands are reacted with the pentahydride. They include pyrazole as an NH donor and acetaldoxime and dimethylglyoxime as an OH donor. Finally. Chapter 7 presents some preliminary
results on an @toluene complex and a complex containing Ir-FBF3 and agostic Ir-q H-C
bonds. formed during reaction of the known complex [I~H~(PC~~)~]',thought to be bis(dihydrogen)bis(dihydride) complex of iridium(II1). [Ir(H2)2(H)2(PCy3)?]+.
References page 34 Chapter I
1.7. References
Latimer, W. M.; Rodebush, W. H. J. Ant. Chem. Soc., 1920,42, 1419.
Pauling, L. Tlte Niiture of the Chemical Bond and the Structure of Molecules and Crystuls - An introduction to Modern Structural Clwnist~,2nd Ed. Oxford Univ. Press, 1940. Pimentel. G. C.: McClellan, A. L. The Hydrogen Bond. Freeman. 1960. Atkins. P. W. Generd Chemistry, Scientific American Books. 1989.
Huyskens, P. L.: Luck. W. A. P.: Zeegers-Huyskens, T. bitennolec~tlorFoi-crr-AII
Iittrod~tctionto mod en^ Metlzods and Results. Springer-Verlag. Berlin. 199 1. p I. Moore, T. S.; WinmiIl. T. F. J. Cher~z.Soc., 1912, 101. 1635. Vinogradov, S. N.; Linnell. R. H. Hydrogen Bond. Van Nostrand Reinhold Company, 197 1.
Deeming, A. J.; Meah, N. N.; Dawes. H. M.: Hursthouse. M. B. J. Orpmmer. Clzern.. 1986. 299, C25.
Lobana, T. S.; Bhatia. P. K.: Tiekink, E. R. T. J. Chenz. Soc., Ddtotz Trcrns, 1989. 749.
Valle. G.: Ettorre. R.: Vettori. U.: Peruzzo. V.: Plazzogna. G. J. Cllerrt. Soc.. Drrltoti Tratrs, 1987, 815.
Baker. P. K.; Hughes. S. J. Cr~ordClzem. 1995. 35. 1.
Lee. J. C.; Peris, E.; Rambo, J. R.; Eisenstein, 0.;Crabtree. R. K. J. Arm Clretn. Sac., 1995. 117, 3485.
Kristjansdottir, S. S.; Norton, J. R.: Moroz, A.: Sweany, R. L.: Whittenburg. S. L. Orgmornetallics, 1991,10. 2357. Shubina, E. S.: Krylov, A. N.: Kreindlin, A. 2.: Rybinskaya. M. I.: Epstein, L. M. J. Orgcinornet. Cltem.. 1994, 465, 259.
References page 34 Shubina. E. S.: Krylov. A. N.: Epstein. L. M.: Borisov. A. P.: Belkova. N. V.: Makaev, V. D. J. Orgnnomet. Chem.. 1995,493,275.
Peris, E.: Crabtree, R. H. J. Clzern. Sac.. Chent. Cornnwi., 1995, 2 179. Shubina, E. S.: Belkova, N. V.: Epstein. L. M. J. Organot~zet.Chrrn.. 1997.536. 17.
O'Donnell, K.: Bacon, R.; Chellappa, K. L.: Schowen. R. L.: Lee. J. K. J. Am.
Clrer~z. Soc., 1972, 94, 2500.
Brothers, P. J. Prog. fnorg. Chrrn., 1981. 28, 1, and references therein. Morris, R. H. Can. J. Chenr., 1996, 74, 1907.
Schlaf, M.; Lough, A. J.; Maltby. P. A.: Morris. R. H. Orgartometollics. 1996. 15. 2270.
Milstein, D.; Calabrese, J. C.; Williams. I. D. J. Am. Clzent. Soc.. 1986, 108 6387. MiIstein. D., Stevens, R. C.. Bau, R., Blum, 0.. Koetzle, T. F.. J. Clter~i.Soc., Daltorz Trurzs, 1990, 1429. Lough. A. J.: Park. S. H.: Rarnachandmn. R.: Morris, R. H. J. Atrl. Cliertt. Soc.. 1994.116. 8356. Lee. J. C.: Rheingold. A. L.: Muller. B.: Pregosin. P. S.: Crabtree. R. H. J. Clrertc.
Soc., Clzern. Cot~m~in.,1994, 102 1. Miessler, G. L.: Tan. D. A. Inorguizic Cliernistry. Prentice-Hall Inc., 199 1. p 2 10. Muller. U. Inorgarlic Stnict~trnlChemistry. John Wiley and Sons. 1993. p 34. Huheey, J. E.; Keiter. E. A.; Keiter, R. L. Itzorganic Clzrtnistry, Harper Collins
College Publishers, 1993, p 1 15.
Bondi, A. J. Phy. Chem.. 1964, 68, 44 1.
Xu. W.: Lough, A. J.; Morris. R. H. Inorg. Chrrn.. 1995. 35. 1549. Lee. J. C.: Rheingold, A. L.: Muller, B.: Pregosin. P. S.; Crabtree. R. H. J. Clzetn.
Soc-, Clzern. Cornmrin., 1994, 102 1.
References page 34 Chapter I 36
Dahlenburg, L.: Herbst, K.: Kuhnlein. M. 2. Anorg. Allg. Clletrl.. 1997. 623. 250. Lee. J. C.: Rheingold, A. L.: Peris, E.: Crabtree. R. H. J. Am. Clzrm. Soc.. 1994.
116. 11014. Alteparmakian. V.: Mura. P.: Olby. B. G.;Robinson. S. D. Itlnrg. I.Acrtr. 1985, 104, L5. The preparation of this dihydrogen complex is described in this thesis (Chapter 2).
Peris. E.; Wessel, J.; Patel, B. P; Crabtree, R. H. J. Clwm Soc., Clzern. Corrwzrrrz., 1995. 2 175. Shubina. E. S.: Belkova. N. V.; Krylov, A. N.: Vorontsov. E. V.: Epstein. L. M.:
Gusev, D. G.; Niedermann. M.; Berke, H. J. Atn. Cltein. Soc., 1996. 118, 1 105. logansen. A. V. Hydrogerl Bond: Nauka. Moscow, 1981. p 13.
Kazarian, S. G.: Hamley. P. A.: Poliakoff. M. J. Am. Chern. Soc.. 1993. 115. 9069. Epstein, L. M.: Krylov. A. N.: Shubina. E. S. T/rrucllern.. 1994.322. 345. Liu, H. Y.: Eriks. K.; Prock. A.; Giering. W. P. Orgcrnotncmllics. 1990. 9. 17%. Harris, R. K. Nuclear Magrletic Spectroscopy. Longman Group. Avon, 1986. Desrosiers. P. J.: Cai. L.; Lin. 2.: Richards. R.; Halpern. I. J. Atx Clleru. Soc.. 1991. 113. 4173. Jia. G.: Lough, A. J.; Morris. R. H. Orgm~ot~~etallics,1992. 11. 16 1. Crabtree. R. H. The Organonletallic Clzernisrry ofthe Trumition Metals. John Wiley and Sons. 1994. p 253. Bautista. M. T.: Earl. K. A.: Maltby, P. A.: Morris. R. H.; Schweitzer. C. T.: Sella.
A. J. Ant. Chem Soc., 1988, 110, 703 1.
Aime. S.: Gobetto. R.: Valls. E. Organornetallics. 1997. 16. 5140.
Ayllon. J. A.: Etienne. S. S.; Chaudret. B.: Ulrich. S.: Limbach. H. H. Ir2ot-g. Chim.
Acta, 1997. 259. 1.
References page 34 Ayllon. J. A.; Gervaux. C.;Etienne, S. S.; Chaudret, B. Organomrtcrllics. 1997. 16. 2000. Xu, W.: Lough, A. J.; Morris. R. H. Can. J . Chern., 1997, 75, 475.
Derome. A. E. Modern NMR Techniques far Chenzistry Research. Pergamon Press. 1987. Collman. J. P.; Hegedus, L. S. Principles and Applications of Orgu~lotrrmsitiorzMrrd Clirmisfry, University Science Books. 1980, p 6 1. Yoshihiko. S. bzorganic Molecltlnr Dissy~ninrtry.Springer-Verlag, 1979. p 24. Richardson, T. B.: Koetzle. T. F.: Crabtree. R. H. Irlorg. Chiin. Actcr. 1996. 250. 69. Wessel. I.: Lee. J. C.: Peris. E.: Yap. G. P. A.; Fortin. I. B.: Ricci. J. S.: Sini. G.:
Albinati, A.: Koetzle, T. F.; Eisenstein. 0.; Rheingold. A. L.: Crabtree. R. H. Arzgerv. Chenr. ht. Ed. Erzg I. 1995, 34. 2507. Patel. B. P.: Yao. W.: Yap. G. P. A.: Rheingold. A. L.: Crabtree, R. H. J. Clrr~n.
Soc., Clrrrn. Conzrnurr., 1996. 99 1. Liu, Q.: Hoffmann. R. J. Am. Clzera. Soc.. 1995. 11 7. 10 108.
Milet. A.: Dedieu. A.; Canty. A. J. Orgunometczllics. 1997. 16. 533 1.
Hutschka. F.; Dedieu, A. J. Chm. Soc.. Daltorz Trans. 1997. 1899.
Ovlora. G.; Scheiner, S. J. Phys. Chem.. A. 1998. 102. 260, and references therein.
References page 34 Chapter 2. Intramolecular IrH-HN Bonds in TricycIohexylphosphine Complexes of Ir(II1)
2.1. Introduction
Postdoctoral fellow R. Ramac handran discovered in 1993 that IrHs(PCy3)-7 reacts with tetrafluoroboric acid in the presence of 2.5 equivalents of pyridine-2-thione in CDCI3 to give a dicationic dinuclear iridium(II1) complex [{IrH(q -spy H)(Pc~~)) 2(q '+- Spy)r](BF~)2according to Equation 2.1. This complex was obtained as a yellow crystalline solid by slow evaporation of the solvent of the situ-reaction mixture.
The crystalline material obtained in this reaction was characterized by NMR spectroscopy for its solution structure and by an X-ray diffraction study for the solid state structure. The ~IP(IH} NMR spectrum of this material in CDC13 has a singlet at 15.34 pprn.
The hydridr resonance is at -20.6 ppm as a doublet with 2~pHof 17.4 Hz and the NH proton resonance is at 12.8 ppm. Unfortunately. VT-Tl measurements have not been done for this complex. The room temperature TI value for the hydride resonance is 0.289 s. An X-ray structural analysis at room temperature indicated the product was a dimer containing two proton hydride bonding units. The H-H distances of about 1.8 A were deduced. However the crystal degraded significantly in the X-ray beam. making the structure difficult to publish. This was the first complex to possess NH-HIr units characterized by X-ray analysis and is the only dimeric complex known to contain proton-hydride bonds. The synthesis of this dimer, however, could not be reproduced under the condition described in Equation 2.1
References puge 74 Chuprer 2 39
and could not be published. Thus. the starting point of current work was aimed at preparing and characterizing this dirneric compound.
Figure 2.1. ORTEP diagram for the dimer analyzed at 293 K. The counterions BF4 are not shown for clarity.
An important reaction that might be associated with such proton hydride interactions is the transfer of the proton to the hydride to produce a dihydrogen complex and the reverse reaction, the heterolytic splitting of dihydrogen. In hydrogen transfer processes a coordinated dihydrogen ligand splits heterolytically in two general pathways: intermolecularly in the
presence of an external base or intramolecularly with an internal base. This has been proven
for a number of complexes containing donor ligands with basic hydrogen acceptor sites such as carbon. oxygen, nitrogen or sulfur.
Refererrcrs page 74 Chapter 2 40
Equation 2.2 and the reverse show reactions at carbon acceptor sites which are believed to be involved in the mechanisms of hydr~~enol~sis.~-'and hydroformylation8reactions. In these cases the dihydrogen ligand protonates either an alkyl, aryl or alkenyl carbon bonded to the metal. but the dihydrogen intermediate species is not detected. Equations 2.3 and 2.4 indicate reactions at oxygen donor and nitrogen donor ligands observed in such complexes as [IrH(D20)(bq)(PCy~)d+ . where bqH = 7.8- benzoquinoline.Y"O and [I~H(NH~)~(PE~~)~](PF~).' I The key intranmlecular protonation steps occur via unobservable dihydrogen intermediate species in deuterium exchange reactions.
Systems more relevant to the current study are those containing sulfur acceptor sites. In such complexes. chelating sulfur ligands often play a role in the intramolecular protonation of a hydride to produce a dihydrogen intermediate species (to be called a HLMH-to-LM(H2) process). For example. the acidic thiol proton undergoes deuterium exchange processes very rapidly (Equation 2.5). l2 In some cases it is possible to control the equilibrium point of a reaction by electronic and steric means. For example. the dihydrogen pyridinethiolate complex in Equation 2.6 and dihydrogen quinolinethiolate complex in Equation 2.7 are in equilibrium with their nionahydrido tautomeric complexes. 13. I-l
PPh3 PPh3 - quinolinethiolate S- N-
A possible alternative to the HLMH-to-LM(H2) process of Equation 1.6 utilizes n pyridinethiol ligand which has a very acidic coordinated thiol sulfur and a basic pyridinr nitrogen. This can be realized when the nitrogen site is either free from coordination or pre- protonated as shown in Equation 2.8. It is the goal of this chapter to establish systems for the
HLMH-to-LM(H2) process (or the reverse) based on the idea in Equation 2.8. For this purpose. mercaptopyridine is protonated to give the thiopyridinium salt prior to introducing to iridium polyhydrides. Observations and the products of the reactions are detailed here.
References page 74 Chupter 2
2.2. Results and Discussion
2.2.1. Synthesis of [Ir{H(q I-Spy H)J2(PCy3)Z] (BF~) (I)
The starting material bis(tricyclohexylphosphine)pentahydridoiridium(V) (IrHs(PCy3)2) has been prepared in two steps from IrC13-3H20via IrHCl$PCyf)? according to the literature '5 and described in the experimental section in detail.
The reaction of IrHs(PCy3)z with cu. 2 equivalents of 7-thiopyridinium tetrafluoroborate (HSpy-HBF4, HSpy = HSCsH4N) prepared by treatment of pyridine-2- thione (SpyH) with tetrafluoroboric acid diethyl etherate (HBF4aEtzO) affords the monocationic iridium(II1) dihydride complex [Ir { H(q '-Spy H) } z(PCy+](BF4) 1 according to Equation 2.9.
HBF4-EtqO HSPY 2 [1r(~z)~(rl'-~py)(~~y3hl(~~,)3 RT,CH,CI, - RT. CHzClz- - -
Alternative synthetic routes to 1 start with the complex I~H~(~?-S~~)(PC~~)?2. 2 is a neutral iridium(II1) dihydride complex obtained in a similar manner to I~H?($-
S~~)(PP~~)~'~from the reaction of the pentahydride with SpyH (Equation 2.10) and characterized by NMR and microanalysis. Reaction of 2 with HSpy.HBF4 in CH?CIz produces 1 (Equation 2.1 1). Reaction of 2 with HBFJ-EtzO produces dihydrogen complex
References page 74 Chapter 2 43
[IrH(H2)(~2-Spy)(PCy3)2](~~4)3. Reaction of 3 with HSpy leads to 1 (Equation 2.12). The structure of complex 3 is proposed to contain a dihydrogen ligand on the basis of NMR measurements (see Experimental section).
2.2.2. General characterization of [Ir{H(q 1-Spy H) }z(PCy3)2J(BF4) (1)
1 is isolated in 74% yield as a yellow-orange powdery solid which is soluble in many organic solvents, such as chlorinated solvents. benzene. acetone. acetonitrile or tetrahydrofuran. 1 is moderately air stable in the solid state. and slowly decomposes in a solution exposed to air. In a coordinating solvent. such as tetrahydrofuran, acetonitrile. or acetone. it slowly decomposes at room temperature under argon to produce the dihydride 2.
Figure 2.2. Proposed structure of the cation of 1 with a labeling scheme for the NMR assignment (L = PCy3).
1 has been characterized by microanalysis, various NMR techniques (3lP and IH
NMR. 1H COSY, NOE difference experiment. variable temperature H TImeasurement ). infrared spectroscopy. and an X-ray diffraction study. Based on the following NMR observations. the structure of 1 has been proposed as in Figure 2.2. The labeling scheme for the NMR assignment is indicated. The 3 P{ H } NMR spectrum of 1 in CD2C12 consists of a singlet at 8.21 ppm due to two magnetically equivalent trans phosphorus nuclei. The proton
NMR spectrum of 1 in CDzCl2 contains peaks assigned to protons on the pyridine rings. cyclohexyl groups as well as the hydrides. Peaks for the cyclohexyl protons are in the region
References page 74 from 0.8 to 2.2 pprn. Two hydrides (H~)are magnetically equivalent. and appear at - 18.28 ppm as a triplet. due to coupling with the two phosphorus nuclei (3~pH= 15.3 Hz). Chemical shifts for the pyridine ring protons are in the region from 6.85 to 7.75 ppm as three broad triplets for ~b.HC and Hd and a doublet for Ha. NMR properties of the [rHS9-iN bonds will be detailed in Section 2.2.3. The solid state IR spectrum of 1 contains characteristic bands for v(1r-H) as well as v(NH). A broad band at 2 137 cm- (KBr)is due to v(lr-H). A v(1r-H) at 2 152 cm- has been reported for a proton-hydride bonding species, bis(hydrido)quinoline-8-iminolcomplex of iridium(lI1).l7 These values are a little lower in energy than the band at 2252 cm- of [I:H2(acetone)2(PPh3)2]+.a similar complex that does not have proton-hydride bonding. However. this difference may not reflect the influence of the LH-HM interactions because the atoms rnlrzs to hydride are different in this compound. The NH stretching frequency mode is often useful to characterize conventional hydrogen bonds as well as the proton-hydride bond (Chapter I). A useful comparison is with that of free pyridinethione. Pyridinethione exists as a dirner with two N-H--5hydrogen bonding units. The v(NH) of this dirner is 3900 cm-1. A dilute CCll solution of pyridinethione is free from hydrogen bonding and the stretching frequency is at much higher wavenumbers (3376 crn-1). Thus. the NH stretching frequency is conveniently used to judge the relative strength of hydrogen bonding. The NH stretching wavenumbers of 1 in
KBr are 3 184 and 3 1 1 1 cm-1. which are lower in energy (Av = 192 and 265 cm-I ) than that of free non-hydrogen bonding SpyH. but at higher energy than the dimeric SpyH. Further details about the energies of these hydrogen bonds are given in Chapter 4 along with other proton-hydride bonding species prepared in this study. The crystal and molecular structure of 1 has been determined by single crystal X-ray structure analysis at 226 K. Figure 2.3 shows the structure of the cation.
References page 74 Figure 2.3. Molecular structure of the cation of [Ir{H(q I-SpyH) J?(PCy3)2](BF4) 1 at 326
K as determined by X-ray analysis.
Referewes page 74 Chuprer 2 46
An iridium atom is found at the centre of a distorted octahedron. surrounded by two trans tricyclohexylphosphine ligands and two cis SpyH ligands coordinated via sulfur atoms. The hydr~genson the two nitrogens are well-defined in the electron difference map. and are piaced in calculated positions. The hydrides are not located. The Ir-S-C-N-H units appear to be planar and the hydride ligands can be placed at 1.61 A from the iridium atom rrms to sulfur and in the ir-S-C-N-H plane and about 1.75M.05 A from the hydrogen on nitrogen. The S(1)-C(2)and S(2)-C(6)distances ( 1.707(7) and 1.715(8) A} are comparable with that of free Lthiopyridinium cation { 1.73(2) A } .I9 These are similar to that of free pyridinethione (Spy H) ( 1.698(2) A} which is the predominant tautomer over pyridinethiol (HSpy). Further detail of the X-ray analysis will be described in Chapter 4 with reference to other complexes studied here.
2.2.3. Studies on the proton-hydride interactions in solution of rrr{H(rl1-SpyH)}2(PC~3)21(BF4)(1)
The NH protons (He in Figure 2.2) resonate at 12.18 ppm as a broad singlet. It is broad because of unresolved scalar coupling to the '%. 'J (1%. H". to the proton ~d. ~J(H'. H~)and possibly to the neighbouring hydride, 'J (He, H'). If we assume the existence of NH-HIr interactions. the widths of the hydride resonance (HI') and the NH resonance (He) are indicative of a 'J(H~.~f) coupling constant of 2 Hz or less. In order to prove the existence of the NH-HIr interaction in solution. several useful NMR experiments have been carried out: 1H COSY. NOE difference experiment. variable temperature I H TI (VT-TI ) measurement. These are summarized in Table 2.1. The H COSY NMR spectrum of 1 in CD2C12 at room temperature shows no significant coupling between the NH proton and hydride resonances. Study Method Results Elemental analysis (C) 5 1.86 / 5 1.43 (H)7.38 / 6.94 (N) 2.63 / 2.44 calc ,' found
12.18 (br. s, 2H, NHe), 7.73 (overlapping, dt. 4H. ffu. HJ).7.43 (br. t,4H,~"),6.88 (br. t.2H.W). 2.1-0.8 (m. 66H, ~(C~HII)~).-18.28 (br. t. 2H. IrH) 13.02 (br. s, 2H. NHe). 8.22 (br. t. 2H. ~d),7.65 (br. d. 2H. Ha). 7.53 (br. t, 2H. H~),6.92 (br. t. 2H. HC). 2.1-0.8 (m. 66H. P(C& I )3), -19.14 (t. 2~PH= 15.3, 2H. IrH)
NOE differencebq' 2137. v(1r-H)(br. w); 31 11, v(NH)(m): 3 184. v(NH)(sh. m): 285 1. v(CH of PCy)(s): 2950. v(CH of PC~)(S).'2110. v(Ir-H)(w): 2851. v(CH of PCy)(m): 2934, v(CH of PCy)(s).g 'NMR spectra measured at 400 MHz in CD2C12, unless otherwise stated: abbreviations: s. singlet; d, doublet; t, triplet: m. rnultiplet; br. broad: chemical shifts (6)in ppm, relative to 85% H3P04 for phosphorus and SiMe4 for protons; coupling constant in Hz: TI in ms. b~easuredin THF-dg. CLabeling of protons of pyridine ring see below. dcouplings among protons of cyclohexyl group are omitted. eEnhanced peaks after irradiation at hydride: numbers in the parentheses represent %. f~electedbands: measured at room temperature using KBr pellet: br. broad: s, strong; w. weak. g~easuredin CH2C12 at RT.
References page 74 Chapter 2 48
An NOE experiment for 1 has been done in CD2C12 at room temperature. When the hydride peak at -18.28 pprn is irradiated the intensity of the peak at 12.18 ppm due to NH protons is enhanced by about I 1%. A similar percentage of enhancement has been achieved for the hydride resonance when the NH proton resonance is irradiated. This result suggests that a short IrH-+HN distance is present. Furthermore. a VT-Ti minimum measurement has confirmed the presence of such a short contact (Figure 2.4). The hydride resonance centred at - 18.28 ppm exhibits a very short minimum TI value of 0.168 s at 233K at 400 MHz in CDzC12. The NH proton resonance at 12.18 ppm shows a similar short minimum TI value of 0.178 s at the same temperature.
Figure 2.4. Plot of TIof the hydride and NH IH nuclei of 1 in CDzC12 vs temperature.
References page 74 The hydride (IrH) - proton (HN) distance has been calculated based on the minimum TIvalues using Equations 1.13 and 1. M2' given in Chapter 1. The NH proton. with a Tl(min)of 0.178 s, has a total relaxation rate of 5.6/sec at 400 MHz. Each NH proton is near to two dipolar nuclei { 14N on pyridine ring and H of hydride ) . From the known H-N distance of about 1.0 A. we have ascertained the relaxation rate contribution of I4N to be about 1.4/sec. The neighboring hydride therefore has a relaxation rate contribution of 43sec (5.6 - 1.4 = 4.2). The distance from the NH proton to the hydride is calculated from this rate to be 1.68-10.05 A. Similarly the distance from hydride to the NH proton can be calculated from the Tl(min) for the hydride. The calculation gives 1.72M.05 A. In this case the total hydride relaxation rate (5.95/sec) is contributed by the cis hydride (0.5/s) at about 2.4 A,two cyclohexyl protons (0.85 x 21s) at about 1.2 A. and the proton on nitrogen (3.7Ys). Therefore the average H-H distance between the hydride and the NH proton is about 1.7M.05 A in CD?C12. The strength of the proton-hydride bond can be probed by introducing a conventional hydrogen bond acceptor. such as tetrahydrofumn or triphenylphosphine oxide. This has been done by a *HNOE difference experiment and VT-TI measurements either in THF-d~or in
CDZCI~containing 2 equivalents of triphenylphosphine oxide (Figure 2.5 ). In an NOE experiment. there is no significant enhancement of the NH resonance when the hydride resonance is irradiated in THF-d8 at room temperature. Instead. a resonance at 7.65 ppm due to the hydrogens (Ha in Figure 2.2) on the onho carbons (C2 and C7 in the X-ray structure) of the pyridinethiones is enhanced by 5%. suggesting that two pyridinethione rings have flipped approximately 1800 about the C-S bonds. Thus the NU-HIr proton-hydride interactions are broken by a conventional hydrogen bond acceptor. THF. This assignment has been supported by 1 H VT-TI measurement for 1 in THF-d8. The NH proton and the hydride have TI values of 0.29 s and 0.21 s. respectively. at 253 K. These TI values are longer than those TI values (0.19 s for NH and 0.18 s for IrH) of 1 in neat CDZCI~at the same temperature, as there is no proton-hydride bond in THF-ds solution. It has not been
References page 74 Chapter 2 50 possible to obtain the minimum TI values in THF-dg due to broadening of the peaks (below 250 K) and decoalescences (at 193 K) of the NH and IrH resonances into several peaks. This probably indicates the genziation of different hydrogen bonding conformers in the presence of conventional hydrogen bond acceptors. In addition. there is no evidence for the isomerization of 1 to a trans hydride structure in THF since there is little change in the IH and
31~{lH} NMR spectrum on going from CDzC12 to THF-d8. In general. trans dihydride complexes are less stable than cis ones. Very similar spectral changes have been observed in the CD2Cl2 solution of 1 in the presence of 2 equivalents of OPPh3. The minimum TI values for the above solution at crr. 250 K are observed to be 0.23 s for the NH protons and 0.19 s for the hydrides. Again. these values are longer than those minima (0.178 s and 0.168 s. respectively) in CD2C12 at 233 K.
(a) I in CDzClz (253 K)
I ' 177 rns 168 rns
(c) 1 in CD2C12 Tl(min) (233 K) (d) 1 in CD,Cl,- - + 2 equiv 0PPh3 Figure 2.5. Disruption of proton hydride bonds in 1 by conventional H-bonding acceptors.
References page 74 2.2.4. exchange study of [Ir{H(q ~-S~~H)}~(PC~~)~](BF~)(1)
An H/D exchange experiment has been carried out for 1 in CD2Clz at room temperature in order to test for !he presence of an intramolecular proton transfer similar to that of Equation 2.5. Exposure of CDzC12 solution of 1 to D2 gas at I atm for 5 minutes results in a significant decrease by cu. 75% in the intensities of the NH and IrH resonances in the proton NMR spectrum. This observation has been confirmed by the 'H NMR spectrum in CHzC12 that shows deuteration of the NH and IrH chemical shifts. and to a lesser degree. protons at the ortho carbons of the pyridine rings. and some carbons of the cyclohcxyl rings. Of interest is that under similar conditions. the THF-du solution of 1 does not show any reaction with D2 gas according to the 1H and *H NMR spectra over the same time period. These results are significant. They show that NH-HIr proton-hydride bonds are essential for the HID exchange process. The mechanism probably involves intramolecular proton transfer from NH to HIr (or ND to DIr) to generate the dihydrogen la and dideuterium lb tautomer (Scheme 2.1). However. in the presence of conventional hydrogen bond acceptors. such as THF. the NH protons of the pyridine rings are not appropriately positioned for such an intramolecular proton transfer step. The NOE experiments discussed in Section 1.2.3 have been used to suggest that the THF interaction moves the NH group far from the proton- hydride bonding position. Therefore H/D exchange could not occur under the same conditions. However. another mechanism that is difficult to rule out is that the H/Dexchange process is via dissociation of one of the SpyH ligands followed by the coordination of a D? molecule which may then undergo an exchange process with the hydrides.
References page 74 Chapter 2
Scheme 2.1. Mechanism of WD exchange in complex 1 in CD2C12 under D? (g).
Here important conclusianal remarks can be made for 1: the proton-hydride bonding
NH-.-HIrsystem of 1 is attractive at a distance of cu. 1.8 A and facilitates H/D exchange with D2 gas. The H-H interaction is weaker than conventional hydrogen bonds such as those in
SC5H4NH*@.SC5H4NH or Ir-SC5H4NH-a-OPPh3 as discussed above. If the H--H interaction were too strong, the proton of the donor group would be completely transferred to form a stable dihydrogen species.
2.2.5. Synthesis of [IrH(q l-SpyH)4(PCy3)](BF4)2 (4)
The pentahydride IrH5(PCy3)2 reacts with 4 equivalents of 2-thiopyridinium (HSpyHBF4) in dichloromethane at room temperature for 10 min to give dicationic species according to Equation 2.13. The product is identified by spectroscopic methods to be a tetrakis(pyridinethi0ne) complex of iridium(1II) with a formula of [IrH(q l-
SpyH)4(PCy3)j(BFj)?4. It is isolated as a microcrystalline yellow solid in over 75% yield after washing out the by-products using ether. 4 is moderately air stable in the solid state but in solution it slowly decomposes under argon at room temperature. 4 is also observed to form in the reaction of the dihydride 2 with an excess of HS~~-HBF,Iin CD2C12 after 3 h.
References puge 74 RT, CH2C12 IrH,(PCy,), - [Wq'-spy H),(PCY$I(BF.& 4 4HSp~.HBF4 + PCy3,HBF4 + HBFj - 3Hz
2.2.6. General characterization of [IrH(q l=Spy~)~(P~y~)](BF~)~(4)
4 has been characterized by microanalysis, NMR spectroscopy. and a preliminary X- ray crystallographic study. The 1H NMR spectrum in CDCI3 contains two characteristic broad singlets at 12.5 and 13.1 ppm. Each peak integrates to two hydrogen atoms relative to the hydride. indicating that there are two sets of NH protons of four SpyH ligands in only two different magnetic environments. In the hydride region. a doublet at - 18.5 pprn is
assigned to the hydride coupling to a cis tricyclohexylphosphine ligand (JPH = 16.8 Hz). The spectrum also possesses a number of multiplets in the region 6.8 to 8.7 ppm and 0.6 to 2.6 pprn due to protons of four monodentate SpyH ligands and protons of a cyclohexyiphosphine
ligand, respectively. The 3I P ( I H J NMR spectrum contains a singlet at 2.05 pprn for a PCy3
group in the complex. Removal of one PCy3 group is confirmed by the proton-coupled 3IP
NMR spectrum of the irl sini-solution of the reaction 2.13: it contains a doublet at eel. 30 ppm
{ I JpH = 68 Hz} for protonated tricyclohexylphosphine. Based on these spectroscopic observations as well as those concerning the proton-hydride bonds discussed below. the structure of 4 in CDC13 has been established as shown in Figure 2.6.
References page 74 4 Figure 2.6 Proposed structures of two possible isomers of 4.
The structure of 4 in Figure 2.6(a) is supported by a p reliminary X-ra crystallographic study from which only the location of non-hydrogen atoms has been possible.21 4 contains four pyridinethione ligands coordinated to the metal via sulfur atoms. The PCy3 and the undetected hydride are cis to each other and occupy the rest of the coordination sites for an octahedron around the metal. In this geometry two rings converge on the hydride position to form IrH-H'N interactions while the HbN of the other two rings are away from the contact.
2.2.7. Studies on the proton-hydride interactions of
[IrHOl 1-S~~H)4(PC~3)l(BF4)2(4)
Further NMR studies were conducted to probe the proton-hydride interactions in 4. The presence of the NHa--H(Ir)-HaN interactions of 4 in CDzCI? is supported by an NOE difference experiment at room temperature. The NHa resonance is enhanced by 4.3% when the hydride resonance is irradiated. while no enhancement is observed for the NH~ resonance.
References page 74 Table 2.2. Characterizationa of the NH"'H*.-HN proton-hydride bonding complexes.
Study Method Microanalysis
(calc / found)
12.5 (br s, NHU) 12.7 (br s, NH)
13.1 (br s, NH~) - 18.4 (d, IrH) 13.3, 13.2 (below 233 K. NH~) - 18.5 (d, IrH)
dtHH, from T 1 (rnin) cn. 1.8 8, cn. 1.7 a NOE difference': "NMR spectra measured at 400 MHz in CD2Ch: abbreviations: s. singlet: d. doublet: br. broad: chemical shifts (6)in pprn. relative to 85% HjPOj for phosphorus and SiMeJ for protons; TIin rns. b~ydrideand NH resonance regions only. 'see text for details.
VT-TI experiments have been carried out for the resonances of the NH protons at 12.5 and 13.1 pprn and the hydride at -18.5 ppm. The TI data are listed in Table 2.2. Below 233 K. these resonances broadened considerably. and the resonance at 13.1 pprn splits into two separate peaks centered at 13.3 and 13.2 ppm. The TIvalue of the NH peak at 12.5 pprn was 0.250 s and that at 13.3 and 13.2 pprn were 0.520 and 0.527 s. respectively. at 233 K and 400 MHz. The peak at 12.5 pprn with the shon TI is attributed to the NH3 set (Figure 2.6) of the pyridinethione ligands involving proton-hydride interactions of the
References puge 74 NHa-~H(Ir)+4-PNtype where one hydride interacts with two proton donors from opposite directions. The peaks at 13.3 and 13.2 ppm are due to the NH~set of the other two pyridinethiones, one of which is trans to the PCy3 group and the other trans to hydride. The behavior of the two NH~protons is dependent on the temperature. At temperatures above
233 K, rapid intramolecular NH+ proton exchange of the two pyridinethione ligands containing NH~is probably responsible for the singlet pattern of the NH~resonance. The longer TIof the two separate NH resonances suggests that the structure is 4 and not the one containing a hydride interacting with three NH proton units 4b (Figure 2.6). Based on the minimum TIvalues, the IrH--HaN distances have been calculated. The hydride with a minimum TI of 0.22 s is closest to two dipolar nuclei (NH" hydrogen atoms) which contribute to the total relaxation rate. The calculated distance from hydride to the NHa proton is 1.86H.05 A. For NHVrotons there are two dipolar nuclei nearby: and the hydride. The 14N nucleus at about 1.0 A contributes a relaxation rate of 1.4s to the TI minimum of 0.24 sec (4.1/s). The hydride therefore contributes a relaxation rate of 2.7/s. Thus. the hydride - NH" proton distance is 1.74k0.05 A. consistent with the distance obtained from the hydride. 4 undergoes H/Dexchange with deuterium oxide in CD2Clr. The resonances for the Ha and Hb protons on the pyridinethione rings immediately disappear when a small excess of deuterium oxide is added to the CD2C12 solution of 4. The hydride resonance, however. remains without significant change. It is slightly shifted downfield. A possible mechanism for the isotope exchange involves conventional hydrogen bonds (DzO-.HN= DHO-DN).
This process is not associated with the hydride ligand. When 4 is exposed to Dz gas for a few minutes. no changes are observable in NH proton and hydride resonances in the IH NMR spectrum. even after overnight. The lack of reaction of D2 with 4 is different from that in 1. Attempts have been made to disrupt the NH--.H(Ir)--HNunit in 4 by adding other hydrogen bond acceptors. The addition of THF to a CD2Cl2 solution of 4 leads to the
References page 74 liberation of one of the pyridinethione ligands to form the monocationic pyridinethiolate complex 5 (Equation 2.14). However. 5 remains in equilibrium with 4 as established overnight.
4 + THF . 3 + THF + HSpy*HBF,
2.2.8. Synthesis of [IrH(q 1-SpyH)2(q2-Spy)(PCy3)](~~J) (5)
The reaction of IrH5(PCyj)2 with 3.5 equivalents of 2-thiopyridinium tetrafluoroborate proceeds in chloroform under reflux for 24 h to give a clear yellow solution (Equation 2.15). The species formed in this reaction is identified as the monocationic iridiurn(II1) complex. [IrH(q 1-SpyH)z(~2-~py)(PCy3)](~)5. This complex can be also obtained in similar yield from the reaction of 4 with ca 1.5 equivalents of trierhylarnine in dichloromethane at 30 *C for 20 min according to Equation 2-16. The reaction temperature and the amount of Et3N must be carefully controlled to avoid the formation of fully deprotonated product 6.
5 has been isolated as a yellow microcrystalline solid in ca. 70% yield after recrystallization from dichloromethane and diethylether. 5 is soluble in chlorinated solvents. less soluble in diethylether. alcohols. and pentane and sparingly soluble in n-hexanes. Unlike
References page 74 Cltupte r 2 58
4, it is stable in coordinating solvents. such as THF. acetone, MeCN and as a solid in air at room temperature.
2.2.9. Characterization of [IrH(q 1-SpyH)z(q2-Spy)(PCy3)](B F4) (5)
The title complex has been characterized by microanalysis, NMR spectroscopy, infrared, and an X-ray diffraction study. The proton NMR spectrum in CD2C12 at room temperature contains two characteristic resonances for two NH protons and one hydride at
12.7 pprn and - 18.4 ppm, respectively. A doublet is assigned to the hydride located cis to phosphorus (JH~= 17.3 Hz). The spectrum also contains resonances at 6.6 to 8.7 pprn and 0.7 to 2.5 pprn for the SpyH and Spy ring protons. and the cyclohexyl protons. respectively.
The 31 P{ IH ] NMR spectrum shows a singlet at I. I pprn which is in the region of 2.05 pprn for 4. From the NMR observations. the structure of the title complex has been deduced to be either 5 or Sa. among the four possible isomers with the hydride cis to the phosphine ligand (Figure 2.7). The solid state NH stretching frequency of 5 has been examined at room temperature. The infrared spectrum contains a broad band at 3124 crn-l. assigned to an N-H unit in a hydrogen bond. This is much less than v(NH) of 3376 ern-' for the non hydrogen bonding SpyH (Section 2.2.2). The calculation for the relative strength (Av = 252 cm-') indicates the proton hydride bond in 5 is similar in strength to that in 1. The results of VT-TI measurements at 400 MHz for the hydride and NU proton resonances are shown in Table 2.2. The NH proton resonance has a minimum TIvalue of 0.215 s with a total relaxation rate of 4.651s. After subtraction of the relaxation rate contributions of 1.41s for the neighboring "N nucleus at about 1.0 A. the NH-HIr distance of 1.70k0.05 A is obtained. The minimum TI of the hydride of 0.165 s with a total relaxation rate 6.11s leads to the NH-HIr distance of 1.64M.05 A from a similar calculation (relaxation rate contribution of the neighboring cyclohexyl protons (0.91s) at about 2.2 A is
References puge 74 subtracted). The calculated H-H distance of about 1.7 in the proton-hydride bonding unit in 5 suggests a solution structure of the NH-.H(Ir)-HN type in a large ten-membered bicyclic ring of S-C-N-Ha--H(Ir)-.-H-N-C-S,as proposed for 4.
Figure 2.7. Possible isomers of 5 with the hydride cis to the phosphine ligand.
Additional evidence for the proton-hydride short contact has been obtained from an NOE difference experiment. A large enhancement of 12 B is achieved for the NH proton resonance upon irradiation at the hydride resonance in CD?C12.
The proton-hydride bond in 5 is surprisingly stable. Thus. it is unbroken by a conventional hydrogen bond acceptor. However. an NOE difference experiment for 5 in CDC13 solution containing an excess of OPPh3 shows similar enhancement of 10.4% to that (11.8%) in the absence of an external proton acceptor. Two explanations are possible. First. the proton-hydride bond in 5 may be stronger than a conventional NH-0 hydrogen bond. In other words. the hydride is a better proton acceptor than the oxygen lone pair of OPPh3. Another explanation might be a competition between OPPh3 and the BF;I counterion in interacting with NH proton groups.22 In a test for H/D exchange with D? gas. insignificant changes are observed even after 2 days.
References page 74 Figure 2.8. ORTEP diagram for the cation of [IrH(q ~-S~~H)~(T$S~~)(PC~~)](BF~)5.
References page 74 Chapter 2 6 1
The structure of 5 has been confirmed by single crystal X-ray structure analysis at
173 K (Figure 3.8). The iridium is in a distorted octahedral geometry defined by a PCy3 group, two monodentate pyridinethiones and a cis hydride, together with a chelating 2- pyridinethiolate ligand. The sulfur atom of the chelating pyridinethiolate ligand is tram to the hydride and shows a significantly longer S-M distance {2.486(2)A} than the other two (2.355(2). 2.35 l(2) A) of pyridinethiones due to the tram influence of the hydride. The proton-hydride bonding H-N-C-S-Ir-S-C-N-H unit is planar with a mean deviation of 0.04 A from the plane. The dihedral angle between this plane and the one with the iridium atom and the three sulfur atoms bound to it is 30°. The distances around the pyridine rings indicate that the monodentate ones act as neutral pyridinet hionc ligands. whereas the c helating one acts as an anionic pyridinethiolate ligand. Thus the iridium atom has a formal charge of +3 from two X ligands (i.e.. hydride and pyridinethiolate) and forms a monocationic species. The hydride electrons were located in a difference map and the Ir-H distance refined to 1.6 l(3) A. The proton-hydride distances in the NH-.H(Ir)-+IN unit are 1.9-2 A. which is close to the distance calculated from the TI relaxation time ( 1 JkO.05 A). Further X-ray data for 5 will be discussed in Chapter 4 where they are compared with related structures.
2.2.10. Synthesis of IrH(q Z-Spy)2(PCy3)(6)
The proton-hydride bonded NH units of the monodentate pyridinethione rings in [IrH(q ~-S~~H)~(PCY~)I(BF~)~4 and [IrH(q -S~~H)~(~~-S~~)(PC~~)~(BFJ) 5 have been deprotonated by triethylamine according to Equation 2.17. The reaction proceeds with an excess of triethylamine in refluxing dichloromethane for an hour to give a bright greenish yellow solution containing a bis(pyridinethio1ate) complex. I~H($-S~~)~(PC~~)6. This hydrido complex has been isolated as a yellow microcrystalline solid in ca. 70 8 yield from the solvent mixture of n-hexanes and diethylether. It is moderately stable both in solution and in air as a solid.
References page 74 Chapter 2 62
a) Excess Et3N. CH2C12,ldlux, 1 h
2.2.1 1. Characterization of IrH(q *-Spy)2(P~y3)(6)
The structure of 6 is proposed on the basis of NMR spectroscopy and confirmed by an X-ray diffraction study. In the proton NMR spectrum in CD?CI? at 20 OC at 200 MHz. there is a characteristic doublet centred at -23.68 ppm due to the hydride coupled to a cis
phosphorus nucleus (2~(Hp)= 22.5 Hz) in addition to the chemical shifts for the cyclohexyl
groups at 0.7 to 2.2 ppm and the chelate ring protons at 6.5 to 8.8 ppm. The P{ H } NMR spectrum exhibits a singlet at 7.8 ppm. An X-ray diffraction study reveals that the molecule has an octahedral core with an iridium(II1)centre surrounded by two chelating pyridinethiolates and a cyclohexylphosphine cis to a hydride (Figure 2.9). Two nitrogen atoms of the rings are trutts to the phosphine atom and the hydride. The bond distances are not unusual. but are useful for comparison with those for complexes 1 and 5. The two S-Ir distances {2.372(2).2.363(2) A} in 6 are not elongated by a trails influence ligand like hydride. With rrarls influences. sul fur-iridium distances are significantly longer as 2.45 1(2), 2.434(2) A in 1 and 2.486(2) A in 5. Unlike that in 5. the nitrogen atom of the chelating pyridinethiolate is trans to the hydride in 6. Thus, the longer N-Ir distance of 2.181(5) A is compared with that (2.105(5) A) for the other pyridinethiolate ring of 6. This difference refers indirectly to the presence of a hydride trans to the nitrogen atom in 6. The hydride in the crystal structure is located at 1.4 l(5) A from the iridium atom. It is interesting to note that, the hydride in 5 is trails to the sulfur atom of the chelate ring whle it is trans to the nitrogen atom in the product 6.
References page 74 Chapter 2
Figure 2.9. ORTEP diagram for II-H(~~-S~~)~(PC~~)6 at 293 K.
Refirertees page 74 Chapter 2 64
The mechanism for the formation of 6 may be simple. involving the action of triethylamine as a strong proton acceptor as proposed in Scheme 2.2. The hydrogen abstraction process by triethylamine is probably similar to that proposed it1 the reaction of I with a conventional proton acceptor such as THF or OPPh3 (Section 2.2.3). The strong base, triethylamine. can more easily disrupt the proton-hydride bonding system in 5, by hydrogen-bonding to one of the rings and, causing the ring to flip about 1800 before abstracting the proton. This process is followed by the chelation of the deprotonated ring via the nitrogen lone pair to stabilize the system.
Scheme 2.2. Proposed route to 6 in the reaction of 5 with triethylamine.
References page 74 Chapter 2
2.2.12. Formation of [{IrH(q 1-SpyH)(PCy3))2(p-Spy)2](BF4)2(7)
A chelate ring in 6 can be opened by treatment with acid. Upon addition of HBFj.Et20 under dihydrogen gas for 10 min, a new species showing both hydride and NH resonances is formed (Equation 2.18).
H2 [{~r~(q'-S~~H)?(PCY~) /?(l-Spy)21(BF-& 7 6 + HBF4.Et20 - (2.18) RT. CDCI, t other species
The lH NMR spectrum of the in sinc-solution of the reaction in CDC13 shows a doublet at
-20.5 ppm (2~Hp= 17.5 Hz) due to the hydride of the dirner prepared once by R. Ramachandran (see Section 2.1) and a broad singlet at 12.7 ppm due to the NU proton of a new species. The spectrum. however, also contains chemical shifts for several minor species. none of which are assigned to those described in this study. All these species show
doublets in the hydride region from - 17.2 to -2 1.5 pprn with coupling constants of 16.0 to
18.3 Hz as well as broad singlets in NH proton region from 1 1.7 to 13.1 ppm. The presence of a 3'~NMR resonance at 15.21 pprn (singlet) is supporting evidence that the hydride ligand is coupled to a cis-phosphorus ligand (JPH = 17.5 Hz). Based on this observation. the major species is assigned to the dimer [{IrH(q l -SpyH)(PCy3)} 2(p-Spy)2](BF4)2 7 aimed for in
this study. However. because of the difficulty in purifying and discriminating the major species, no further studies have been conducted here. Based on the solid state structures of 6 and 7. a two step process from 6 to 7 is proposed in Scheme 2.3. In terms of coordination geometry of the chelate rings, the structure of 7 is very similar to that of 6. In 6. two nitrogen atoms of the chelate rings are trms to the hydride and the phosphine ligand. In the presence of a strong acid the one trans to phosphine ligand is protonated while the one trans to the hydride is intact. What makes the nitrogen trans to the phosphine more basic and susceptible to an electrophilic attack is probably a steric
Rrferrnres page 74 Chapter 2 66
effect of the tricyclohexylphosphine group. A vacant site frans to the phosphine group. produced by the nitrogen in the protonation process provides a good chance for two identical molecules to couple to form a dirner 7.
Scheme 2.3. Proposed route to 7 from the reaction of 6 with HBF4 (P = PCy3).
2.3. Conclusion
The reaction of IrHs(PCy3)2 with [HSpyH]BF1 affords new iridium( 111) complexes
[Ir{Wrl l-SpyW 12(PCy3)2l(BF4) 1. [IrH(rl '-SpyH)4(PCy3)l(BF4)?4 or [IrH(rl I- SpyH)2(rlZ-Spy)(PCy3)](BF4) 5 possessing some of the first intramolecular proton-hydride bonds to be identified. The IrH--+INdistances are about 1.7 - 1.9 a in the solution (TI calculations) and solid state (X-ray). The Ir-H-H-N contact in 1 is disrupted by a conventional H-bond acceptor. such as THF-dg or OPPh3. but remains intact in 4 and 5. IrH(ql-~py)~(PCy~)6 prepared from the reaction of 4 or 5 with triethylamine is observed to react with a strong acid to give the dimeric complex [(IrH(q -S~~H)(PC~~))z(q-.p-7
Spy)2](BF4)2 7. Scheme 2.4 is a "road map" describing the relationships between all of these complexes. Chapter 2
(i) 2 equiv. [HSpyH]BF4 in MeOH-CHzC12, -80 OC. 20 rnin. (ii) Excess [HSpyH]BF4 in CH2Ch. RT, 30 min. (iii) Excess HSpy in benzene. reflux. 30 min. (iv) I equiv.
[HSpyH]BF4 in CH2C12, RT. 40 min. (v) Excess [HSpyHIBFd in CHZCIZ.RT. 3 h. (vi) THF. RT. 3 h l or Et3N in benzene. RT. 20 min. (vii) Excess [HSpyH]BF+ reflux in CHC13. 24 h. (viii) HBF4.Et2O in CHC13, RT. 5 rnin. (ix) HSpy in CHZCIZ.RT. 20 min.
(x) 1.5 equiv. Et3N in CH2C12, 30 OC. 20 min. (xi) Excess Et3N. reflux in CH?Clz. I h. (xii) HBF4-Et20 in CH2C12 under H2, RT, 10 min. Scheme 2.4. A reaction road map for the iridium complexes (L = PCy3).
Refererlces page 74 Chapter 2
2.4. Experirnen tal
General experiment. All preparations were carried out under an atmosphere of dry argon using convention& Schlenk techniques. All the solvents were distilled under argon over appropriate drying agents prior to use. Tetrahydrofuran (THF),diethyl ether (EtzO), and n-hexane were dried over and distilled from sodium benzophenone ketyl. Ethanol
( EtOH) and dichlorome thane were distilled from magnesium e thoxide and calcium hydride. respectively. Deuterated solvents were dried over Linde type 4 A molecular sieves and degassed prior to use. Tricyclohexylphosphine. sodium methoxide. Zmercaptopyridine. and an 85% solution of HBF4.Et20 complex were purchased from Aldrich Chemical Company Inc. Iridium trichloride hydrate was obtained from Johnson-Matthey Co. Sodium ethoxide was generated in the reaction of sodium metal with water-free ethanol under argon and dried to white powder before use. NMR spectra were obtained on a Unity-400. operating at 400.00 MHz for IH. 16 1.98 MHz for 3lP. or on a Gemini-300 operating at 300.00 MHz for H. 12 1.45 MHz for
3IP. All 3IP NMR spectra were obtained with proton decoupling unless otherwise stated.
31~NMR chemical shifts were measured relative to H~POJas internal reference. IH NMR chemical shifts were measured relative to deuterated solvent peaks or tetramethylsilane. Variable temperature TI measurements were made at 400 MHz using the inversion recovery method. Fast atom bombardment mass spectrometry (FAB MS) was carried out with a VG 70-250s instrument using a 3-nitrobenzylalcohol (NBA) matrix. All FAB MS samples were dissolved in acetone and placed in the matrix under a blanket of nitrogen. Microanalyses were performed by Guelph Chemical Laboratories Ltd.. Ontario. X-ray structure calculations were carried out using SHELXTL-PCand SHELXL-93. Summary of Crystal Data. Details of Intensity Collection. and Least-Squares Refinement Parameters for 1,s and 6 is in Table 2.3. Selected bond lengths and angles for 1. 5 and 6 are in Tables 2.4. 2.5 and 2.6. respectively.
References page 74 Preparation of IrHCI2(PCy3)2 IrC13.3H20 ( 1 .OO g, 2.84 mmol) was dissolved in 1.8 rnL of conc. HCI and 20 mL of ethanol in a 100 mL round bottom flask equipped with a magnetic stir-bar and a reflux condenser. to yield a dark brown solution. The solution was stirred and refluxed for 6 h. during which time it turncd greenish-brown in colour. The solution was then cooled to room temperature and PCy3 (1.6 g, 5.70 mmol) was added quickly. causing the solution to turn deep green instantly. After 1 h of reflux the solution turned red and a red solid started to precipitate out. Refluxing was then continued for a further period of 15 h. After cooling to room temperature, the red solid was filtered in air from a slightly yellow solution. washed with ice-cold ethanol ( 10 mL)twice. and dried under vacuum for 6 h to yield a pink solid ( 1.78 g. 76 %). IrHCI2(PCy3)? is a pink solid which is stable under nitrogen and can also be handled in the open air for short periods of time. It is moderately soluble in dichloromethane and chloroform. sparingly soluble in acetone. alcohols, or THF. 3lP { IH} NMR in CDC13. 25°C: 7 1.3 (s). H NMR in the hydride region (CDC13, 25'C) : -47.9 (t. ?J(PH) = 1 1.3 Hz). The chemical shift of the hydride is in agreement with the literature ~aiue.~~
Preparation of IrHj(PCy3)2 i) Using NuOEt. 1rHCl2(PCy3)2 ( 1980 mg. 2.4 mmol) and NaOEt (330 mg. 4.9 mmol) were suspended in THF (50 mL) in n 200 mL two- neck round bottom flask. The contents were stirred under an atmosphere of dihydrogen for 3 h. Then. a second batch of two more equivalents of NaOEt (330 mg, 4.9 mmol) was added to the mixture and stirring was continued. After 1 h the pink colour of the suspension faded. slowly turning yellow-white. Stirring under hydrogen was continued for another 6 h during which time the colour of the suspension turns pale cream. Solvent was removed in vacuum to yield a pale yellow-white solid. It was then stirred with 100 rnL of degassed water for 1 h under hydrogen gas. and then collected on a Schlenk frit. washed with a further 50 mL water. After drying the solid in vacuum for 4 h, it was then stirred with hexanes (50 mL) for I h. After filtration. the whlte solid was washed with ether (50 mLI until filtrate was clear and dried in vacuum. Yield : 1.44 g (79 %).
References page 75 ii) Using NuOMe. IrHC12(PCy3)2( 1980 rng. 2.4 mrnol) and excess NaOMe (330 mg, 4.9 mrnol) were suspended in THF (50 mL) in a 200 mL two-neck round bottom flask. The contents were stirred under an atmosphere of dihydrogen gas for 5 h after which time the pink colour of the suspension faded, slowly turning yellow-whi te. S timing under hydrogen was continued for another 24 h during which time the yellow-white colour of the suspension slowly turning to grey (reaction time can be adjusted according to the colour of the suspension). Solvent was removed in vacuum to yield a grey-white solid. It was then stirred with 100 mL of degassed water for 1 h under argon. and then collected on a Schlenk frit. washed with a further 50 mL water. After drying the solid in vacuum for 4 h. it was then stirred with hexanes (50 rnL) for I h. After filtration. the white solid was washed with ether
(50 rnL) until filtrate was clear and dried in vacuum. Yield : 1.44 g (79 8).IrHs(PCy3 )? is a white solid which is stable in the solid state in air at room temperature but slowly decomposes while in solution. It is insoluble in ether and hexanes. sparingly soluble in dichlorornerhane, chloroform, toluene and moderately soluble in benzene. 3IP{ 'H}NMR in C& / C&. 25OC: 3 1.6 (s). H NMR in the hydride region (CDC13, 25T) : - 1 1.3 (t.
'J(PH) = 12.0 Hz). (in C6D6,2S°C) -10.5 (t. ?J(PH) = 12.0 Hz). IR (Nujol) : v(1rH) 1945 cm-1 . Preparation of Ir(H)2(q2-Spy)(PCy3)2(2) IrHj( PCy3)z (300 mg. 0.396 mmol) was suspended in benzene (15 rnL) under argon. To this was added an excess of
HSpy (60 mg. 0.54 rnmol). The solution was then refluxed for 20 min. On cooling. a pale yellow powder precipitated out of the solution. The precipitate was filtered and washed with ether (3 x 2 mL) and then dried in vclcuo (285 mg. 83 %). Microanalysis. Calc. for CuH72IrNP2S: C, 56.85: H, 8.38; NT1.62. Found: C, 56.91: H. 8.09: N, 1.60. NMR (8,
300 MHz). lH (CDCI3): 8.2 - 6.5 (m,4H. SC5H4N). 2.3 - 0.7 {m. 66H. P(C& 1)3}.
-23.7 (unresolved td. lH, IrH), -23.85 (td, overlapping, 1H, IrH): P { H ) (C6D6):30.13 (s).
References page 74 Preparation of [1r(H2)(H)(q 2-Spy)(PCy3)2](B F4) (3) Ir(H)2(q2- Spy)(PCy3)2 (100 mg, 0.12 mmol) in CHCl3 (6 mL) was placed in a Schlenk flask fitted with a magnetic stirring bar under dihydrogen gas. This was stirred while HBF4-Et20 (90
pL of 85 % solution in Et2O. 0.52 mmoij was slowly being added at room temperature. In a few min the above suspension became clear yellow solution which was further stirred for 5 min. All the volatiles were then removed in vacuo. To the residue was added ether-hexanes
(1/5) solvent mixture ( 1.2 mL) to give a yellow powdery solid. This was filtered. dried bt vncuo to give a pale yellow powder (105 mg, 95%). Microanalysis. Calc. for C42H75BC12F41rNP2S: C. 48.6; H, 7.28: N. 1.35. Found: C. 48.31: H. 7.27: N. 1.47. NMR (6. CD2Clz. 300 MHz). 1H: 8.22 - 6.75 (m, 4H, SC5H4N). 2.4 - 0.8 {m.66H.
P(C~HII)~}.-1 1.86 (br s, 3H. average of IrH and Ir-HZ). 3IP(iH}:9.63 (s).
Preparation of [Ir(H(q 1-Spy H)J2(PCy3)2](BF4) (1) Method I. From pentahydride. IrHs(PCy3)2 (50 mg. 0.066 mmol) was suspended in MeOH (6 rnL) in a Schlenk flask. fitted with a stirring bar under argon. To this was slowly added CH?CI? solution of 2 equivalent of [HSpyH]BF4 (26 mg. 0.13 mrnol) while cooling down the flask in dry icdethanol bath. After completion of addition the solution was stirred for further 20
min at -30 OC. The solvent was then removed in vuaco. The resulting yellow powder was
washed with hexanes three times (3 x 1 rnL) and dried in vacito. Yield: 52 mg (74 % ).
Method 2. From dihydride. ~r(~)~(r$spy)(PCy~)~2 ( 100 mg, 0.12 mmol) and 1.5
equivalent of 2-mercaptopyridine (20 mg, 0.18 mmol) were suspended in dichloromethane (5 mL)in a Schlenk flask under argon. While the solution was being stirred. 85% HBF4.Et20 (ca. 80 yL) was slowly added through a septum using a syringe. After 10 min the solution
was filtered through Celite under Ar. Solvent was then evaporated 62 vcrcuo to dryness. To the residue was added ether (5 mL) and this mixture was swirled until the precipitation of a pale yellow powder. The powder was washed twice with ether (2 x 2 mL) before drying to give a pale yellow powder. Yield: 110 mg (89 %). See Table 2.1 for the spectroscopic results.
References puge 74 Preparation of [Ir(H)(ql-SpyH)4(PCy3)](BF4)2 (4) IrHs( PCy3)z (50 mg,
0.066 mmol) was suspended in CH2C12 (6 mL) in a Schlenk flask. fitted with a stirring bar under argon. To this was added CH2C12 solution of ca. 4 equivalent of [HSpyH]BF4 (53 mg, 0.26 rnrnol), and the suspension was stirred for 20 min to give yellow clean solution.
The volume was reduced to less than 1 rnL in vacuo. To the residue was added hexanes (2 mL) to result in a yellow powder. The product was washed with hexanes three times (3 x 1 mL)and dried in vcrcuo. Yield: 55 mg (76%). Analysis. Calc. for C~~HSJB~F~I~N#SJ:C. 41.75: H. 4.98; N. 5.13. Found: C, 11.59; H. 4.85: N. 4.83. NMR (CDC13. 6).31P{'H}:
2.1 (s); IH: -18.5 (d. 2~pH= 16.8 Hz. 1H. Ir-H). 0.6 - 2.6 {m, 33H. P(C6H,,)3}.6.8 - 8.7
{ m, 16H. (SC~HJNH)~},12.5 {br. s, 2H. (SC5H3NH"2}, 13.1 (br. s, 2H, (SC5H4NHb)2) . Preparation of [Ir(H)(q l-SpyH)z(q2-Spy)(PCy3)](BF4)(5) Merllod I:
Refluxing of IrH5(PCy3)2 with [HSpyH]BF4. IrH5(PCy3)? (100 rng. 0.13 mmol) was suspended in CHC13 (6 mL)in a Schlenk flask. fitted with a stirring bar under argon. To this was added ca. 3.5 equivalent of [HSpyH]BF4 (92 mg, 0.46 mmol). and the suspension was refluxed for 24 h to give yellow clean solution which. after partial removal of solvent. was filtered through celite in the air. The solvent was removed irz vncito. To the residue was added ether-hexanes (211) mixture (1.2 rnL) to result in a yellow powder. The product was washed with hexanes three times (3 x 1 mL)and dried in vacuo. Yield: 82 mg (70 6).
Method 2: Reaction of [Ir(H)(q l-SpyH)4(PCy3)](BF4)2with Et3N. [1r( ~)(qI - SpyH)4(PCy3)](BF4)2(100 mg, 0.09 mmol) was dissolved in CHzClr (6 mL) in a Schlenk flask. fitted with a stirring bar under argon. To this solution was slowly added cn. 2 equivalent of Et3N (26 p1.0.18 rnrnol) while warming up to ca. 36 OC for 20 min in a water bath. The volume was reduced to less than I mL irl vacuo. To the residue was added methanol ( 1 rnL) to result in a yellow powder. This was filtered. washed with hexanes three times (3 x 1 rnL) and dried in vacuo. Analysis. Calc. for C33H48BFJhN3PS3: C. 44.33: H.
5.42. Found: C. 44.57; H. 5.00. NMR (CDC13. 6). 31~(IH} : 1.1 (s): 1H: - 18.4 (d. ZJ~~=
References page 74 17.3 Hz, lH, Ir-H), 0.7 - 2.5 (m, 33H. P(C6Hrl)3},6.6 - 8.7 {m,12H. (SC~HJNH+)~ and SCSHJN}, 12.7 (br. s, 2H. (SCSHJNH+)Z).IR (KBr pellet. RT): 2193. v(Ir-H)(br. w); 3 124, v(NH)(m).
Preparation of Ir(H)(q -S~y)~(Pcy~)(6) [Ir(H)(q -SpyH)4( PCyl)] (BF4 12
4 (100 mg. 0.09 mmol) was dissolved in CH2C12 (6 mL) in a Schlenk flask. fitted with a stirring bar under argon. To the yellow solution was added cn. 4 equivalent of Et3N (5 1 p1.
0.36 mmol). This was refluxed for 20 min to result in a greenish yellow solution. After removal of the solvent in vacuo, methanol ( 1 mL)was added to the residue and swirled for 20 rnin to afford a yellow powder. This was filtered. washed with hexanes three times (3 x 1 mL) and dried in vncuo. Yield: 44 rng (70 5%). Analysis. Calc. for C29H.&l?IrN?PS?: C.
44.73: H. 5.7. Found: C. 43.95; H. 5.28. NMR (CD2C12, 6).31~{ H}: 7.8 (s): 'H:-13.68
(d, 2JpH = 22.5 Hz, 1H. Ir-H). 0.7 - 2.2 {m. 33H. P(C6H/,)3}.6.6 - 8.8 {m. 8H. overlapping SC5H4N).
References page 74 Chapter 2
2.5. References
Morris. R. H.; Jessop. P. G. Coord. Chetn.. 1992. 12I. 155.
Bianchini, C.; Meli, A,: Peruzzini. M.: Frediani. P.: Bohanna. C.; Esteruelas, M. A.; Oro, L. A. Organonzetallics. 1992. 11, 138.
Andriollo. A.; Esteruelas. M. A,; Meyer. U.; Oro. L. A.: Sanchez. D. R. A.: Sola. E.:
Valero. C.; Werner. ff. J. AIII. Chem. Soc.. 11989, 11 1. 743 1. Wochner. F.: Brintzinger. H. H. J. Orgmionlet. Clwrn. 1986. 309. 65.
Guo. Z. Y.: Bradley. P. K.: Jordan, R. F. Orgcttzonzetullics. 1992. 11. 1690.
Folga, E.: Ziegler, T.; Fan. L. New J. Clrern. 1991, 15, 74 1.
Albeniz, A. C.; Schulte. G.: Crabtree. R. H. Orgatzor?zcrctllics. 1992, 11. 742. Versluis. L.; Ziegler. T. Orgcmometcdlics, 1990. 9. 2985.
Crabtree, R. H.: Lavin, M. J. Chern. Soc., Clzem. Corwirrrz., 1985. 794.
Crabtree. R. H.: Lavin. M.; Bonneviot. L. J. Am. Clwrrt. Soc., 1986. 105. 4032.
Koelliker. R.: Milstein. D. J. Ant. CII~III.SOC.. 1991, 113. 8524. Morris. R. H.: Jessop. P. G. Inorg. Clrrrrr., 1993. 32, 2236. Schlaf, M. University of Toronto. Ph.D. Thesis. 1996.
Schlaf. M.: Morris. R. H. J. Clletn. Soc., Cl~ent.Cot?~nzurr.. 1995. 625.
Brinkmann. S.: Morris. R. H.; Rarnachandran, R.: Park. S. H. Inorg. Syrttl~..1998. 32. 303.
Alteparmakian, V.; Mura, P.; Olby, B. G.: Robinson, S. D. horg. Cltirzt. Acra. 1985. IOJ, L5.
Lee, J. C.: Rheingold. A. L.: Peris. E.; Crabtree. R. H. J. Anz. Cltrm. Soc.. 1994.
116, 11014.
Mura. P.: Olby. B.: Robinson. S. D. J. Chetn. Soc.. Dcilton Tralzs.. 1985. 2 10 1. Schlaf. M.: Lough. A. J.: Morris, R. H. Or.ganontetdlics. 1993. 12. 3808.
Referertces page 73 20 Desrosiers. P. J.: Cai, L.; Lin. Z.: Richards. R.; Halpern. J. J. Am. Clwrn. Soc.. 1991, 113, 4173. 21 Park, S. H.;Lough, A. J.: Morris. R. H. unpublished result. 22 Xu. W.; Lough. A. J.: Morris, R. H. Irzorg. Chenr.. 1995. 35. 1549.
23 Gusev, D. G.: Bakhmutov. V. I.: Grushin. V. V.: Volpin, M. E. Inorg. Cliinr. Acm.
1990, 177, 115. Chapter 2 76
Table 2.3. Summarya of Crystal Data, Details of Intensity Collection, and Least-Squares Refinement Parameters for 1.5 and 6. 1 6 empirical formula [C46H78irN2P2S23 CZ~H~~I~N~PS~ 0.72CHzC12 O.SCH2C12 crystal color, shape yellow, plate yellow, plate yellow 0.30 x 0.20 x 0.07 0.36 x 0.4 1 x 0.18 0.1 1 x 0.30 x 0.32 1294.34 954.05 736.39 Triclinic Monoclinic Triclinic P- 1 P2 ~/n P- 1 I3.593(2) 12.486(6) 9.86 l(3) 14.179(3) 16.552(4) 16.357(4) l7.O67(3) 19.535(4) 19.159(4) 111.60(I) 80.50( 1 ) lOl.S8(1) 85.75(2) 96.15( 1) 74.92(2) 2936.4(9) 294l.4( 13) 2 4 1.464 1.663 2.69 4.848 1323.6 1476 226(2) 293(2) 9277 18002 88 15 17093 0.0283 0.0265 0.0456 0.0500 Goodness-of-fit on F* 1.043 1.025 wR2 (all data) 3.1 179 0.1267 parameters refined 644 640 max/rnin density 1.853/- 1 .Ol5 1.360 and -2.240 in AF map, e/A3 'Weighting scheme:
References page 74 Table 2.4. Selected Bond Lengths (A) and Angles (deg) for 1.
I
I
I
(
(
I
-I
References page 74 Chupter 2
Table 2.5. Selected Bond Lengths (A)anc 4ndes (dee) for 5.
Ir-P( 1 ) Ir-S(2) Ir-H( 1 ir) S(2)-C(21)
P( 1 )-C(5 1 )
P( I )-C(4 1 ) N(22)-H(22A)
N( 12)-[r-P(1 ) N( 12)-Ir-S(3) P( 1 )-Ir-S(3) N( 12)-Ir-S(2) P( 1 )-Ir-S(2) S(3)-ir-S(2)
N( 12)-Ir-S(1 ) P( I )-Ir-S( I ) S(3)-Ir-S( I) S(2)-Ir-S(1) N( 12)-Ir-H(1 ir) P( 1 )-Ir-H( 1 ir)
S(3)-Ir-H( 1 ir) S(2)-Ir-H(1 ir)
S( 1 )-Ir-H( 1 ir) C( 1 1 )-S( 1 )-Ir C(2 1 )-S(2)-Ir C(3 1 )-S(3)-Ir
C(5 1 )-P( 1)-C(6 I ) C(51 )-F'( 1 )-C(4 1 )
C(6 1 )-P( 1 )-C(41 ) C(5 1 )-P(1 )-Ir C(6 1 )-P(1 )-Ir C(41 )-P(1 )-Ir
C( 16)-C( 1 1 )-S( 1 ) N(l2)-C(l1)-S(1)
C( l3)-N(lz)-b C( 13)-N( 12)-C(1 1 ) C(26)-C(2 1)-S(2) C( 1 1)-N( 12)-Ir C(36)-C(31)-S(3) N(22)-C(21)-S(2) N(32)-C(3 1 )-S(3)
Feferences puge 74 Chapter 2
Table 2.6. Selected Bond Lengths (A)an Angles (deg) for 6.
Ir( 1A)-N( 1 1A) Ir( 1A)-S(2A) Ir( 1A)-H( 1IR) S( 1 A)-C( 16A) Ir( 1B)-N(21B) Ir(1B)-P(1B) Ir( 1 B)-S( 1B) S(2B)-C(26B)
N(2 1 A)-Ir( 1 A)-N( 1 1 A) N(2 1A)-lr( 1 ALP( 1A)
N( 1 1A)-Ir( 1A)-P( 1A) N(2 1 A)-Ir( 1A)-S(2A)
N( 1 1 A)-Ir( l A)-S(2A) P( 1 A)-Ir( 1A)-S(2A)
N(2 1A)-Ir( 1 A)-S( 1A) N( 1 1 A)-Ir( 1 A)-S( 1 A) P( 1A)-If(1 A)-S( 1A) S(2A)-h(1 A)-S( 1A)
N(2 1A)-Ir( 1A)-H( 1 IR) N( 1 1A)-Ir( 1 A)-H( 1 IR) P( 1A)-h( 1A)-H( 1IR) S(2A)-Ir(I A)-H( 1IR) S( 1 A)-Ir( 1 A)-H( 1 IR) N(2 I B bIr( 1 B 1-N( 1 1 B)
N(2 I B)-IK(1 B)-P( I B) Y( 1 1 B)-Ir( 1 B)-P( 1B) N(2 1B)-Ir( 1B)-S(2B) Y( 1 1 B)-h(1 B)-S(2B) F( 1B)-Ir( 1 B)-S(2B) V(2 1B)-Ir( 1 B)-S( 1B)
N( 1 1B)-If( 1B)-S( 1B) ?(1 B)-Ir( 10)-S( 1B) S(2B)-Ir( 1B)-S( 1B) V(2 1B)-Ir( 1 WH(2IR)
N( 1 1B)-Ir( 1B)-H(2IR) '( 1B)-Ir( 1B )-H(2IR)
S(2B)-Ir( 1 B )-H(2IR) S( 1 B)-b( 1B)-H(2IR)
References page 74 Chapter 3. Iridium(II1) Complex Containing a Unique Bifurcated Hydrogen Bonding Interaction Involving Ir-H4-I( N)-F-B atoms. Molecular Structure of [I~H(~~-SCSH~NH)(~~-SC~H~N)(PP~~)~] (BF4)mO.SCsHs
3.1. Introduction
The main aim of the work described in this chapter was to prepare complexesi-? similar to 1 and 5 (Chapter 2) with PPh3 in the place of PCy3 to understand how the donor properties of the phosphine ligand influence proton-hydride bonding.
I :L Cl- h'- L' I H
I I1 111 IV Figure 3.1. Triphenylphosphine complexes containing proton-hydride bonds (L= PPh3).
Shown in Figure 3.1 are complexes containing two triphenylphosphine donor goups.3 Triphenylphosphine is less bulky (cone angle of 145O) than tricyclohexylphosphine (cone angle of 1700) and less effective in donating electrons to the metal.' The lower electron density at the metal might cause a decrease in the hydridic character of the hydride ligands. As a result. this may act to reduce the polarization of the proton hydride bond. However. the H-.Hdistances reported for I. I1 and III in Figure 3.1 (L= PPh3) are about 1.8 A which are similar to those of the tricyclohexylphosphine systems described in Chapter 2. Another factor
References page 96 Chapter 3 8 1 that might affect the strength of the proton hydride bonds is the electronic properties of the donor ligand LYH. For example, in the compounds I and I1 the proton-hydride bond strength is enhanced when R is an electron withdrawing group. This causes the Y-H bond (Y = 0, N) to become polarized in thc direction of the Y atom. In 111, hydroxypyridine (pyOH). with a good nitrogen donor site as well as a potential proton donor group (OH). has been introduced into a triphenylphosphine complex. With complexes I1 and I11 in mind, a good donor ligand like mercaptopyridine (SpyH) may be another good candidate to form a species containing a proton-hydride bond. That is, trihydrido SpyH complexes containing a strong proton-hydride bonding unit. similar to 11. In the course of our study. a route to a unique bifurcated hydrogen bonding species IV involving a hydride, an HN unit. and a fluorine atom of a tetrafluoroborate anion has been established. A new preparative method and the characterization of the known iridium(II1) trihydride f~~-IrH3(PPh3)jis also described here. The content of this chapter has been pu blished.5
3.2. Results and Discussion
3.2.1. Starting materials
Crude ,ner-Ir~Cl~(PPh~)~~-~~has been prepared by refluxing an ethanolic solution of iridium trichloride with concentrated hydrochloric acid and triphenylphosphine under arson.
This complex has three mer-phosphine ligands and two trans chlorides. based on the
3IP { [H} and proton NMR spectra. In fact, this type of reaction has been carried out pre~iously,ll-~3but the products depended on the kind of phosphine ligand used. For example, iridium(II1) complexes [IrC14(PiPr3)2][HPipr3] IrHcl~(Pcy~)~l2 and t1C13(PPh2Me)3~~have been obtained by similar reactions. All of these complexes have been used as precursors to iridium pentahydride complexes according to Scheme 3.1.
References page 96 i) HCl I EtOH I LI. LI = pipr3; ii) HCI 1 EtOH I L~.L~ = PCy3; iii) HCl I EtOH I ~3.
L~ = PPhzMe; iv) LiAIH* / THF: v) EtONa / THF Scheme 3.1. Various preparative approaches to iridium(V) pentahydrides.
However. the reaction of mer-IrHCl2(PPh3)3 under reducing conditions (NaOEt/THFlH?) produced the trihydride fnc-IrH3(PPh3)3 instead of the pentahydride complex irHs(PPh3)~ (Scheme 3.2). This product has been assigned as an iridium(II1) complex possessing three triphenylphosphine 1 igands and three hydrides based on the characteristic FAB mass spectrum. The singlet at 6 30.05 in the 31P( IH} NMR spectrum (25 'C) and the
AA'A"XX'X" pattern of the hydride resonances indicate that this complex has facially arranged hydrides and has the formulaJnc-IrH3(PPh~)3.Therefore in the process of hydride addition. a rearrangement of the phosphine groups occurs from ~~er-[Ir]tofilc-[Ir] under mild conditions. Even though this type of complex is kno~n.6-l0~~-1~NMR data have not been completely reported. The observed variable temperature H NMR spectra offi~-IrH~(PPh~)~ in the hydride region are shown in Figure 3.2. Approximate simulations of both the spectrum
(500 MHz) of fic-Ir(H)3(PPh3)3 in toluene-dx at 25 OC by use of parameters JPH(~~~~~,=
+ 120 HZ,JPH(~~~~ = - 18 Hz. JHH(~~~) = -3.5 HZ,Jpp(cisl = -3.2 Hz and the spectrum of -40
OC, JPH(~~~~~~= +I20 HZ, = -14 HZ, JHH(~~~)= O HZ. = -3.2 HZ are also shown in Figure 3.2. The same spectrum was obtained at 300 MHz. This fact along with the
lack of significant change of pattern when the sample is warmed to 90°C suggests that this is
not a fluxional process. Instead, it can be interpreted as a change in structure of the molecule with increasing temperature which results in an increase in JPH and JHH coupling constants. Large increases in JHH of hydride with temperature have been attributed to a quantum exchange coupling phenomenon. lW9
References page 96 Clrupter 3
Figure 3.2. *HNMR spectra at 500 MHz of the hydride resonance of fa~-Ir(H)3(PPh,)~in toluene-da at (a) 90 OC. (b) 25 OC, (c)simulation of (b), (d) -40 OC. and (e) simulation of (d).
References page 96 However the small change in JHH with temperature in the present system is not consistent with this. The TI at room temperature was reported previously. l7 The TI(min) value for the hydride was 0.144 s at -60 OC (300 MHz). This is consistent with a trihydride structure with H-H distances of about 1.83
i) HCI ii) 3PPh 3 E --- - C1- - under
Scheme 3.2. Two step synthesis of jizc-iridium(1II) tri hydride from iridium trichloride.
In general, the preparation of iridium polyhydrides (i.e.. trihydride. or pentahydride) involves one step.6-89 lM5 two steps,9*10*2*13q 16 or several steps22 with commercially available appropriate iridium precursors. It normally requires reaction with a large excess of NaBH4 or LiAIH4 as a hydride source and the yield is often low. In the case of iridium trihydrides there is the possibility of obtaining isomeric mixtures (i.e., ~nrr-[Ir]andfidc-[Ir])6-
8714-16 The method of Scheme 3.2 has several advantages: convenience of making and
handling sodium ethoxide. the relatively high yield. and the production of a single isomer under mild conditions. fuc-IrH3(PPh3)3 reacts readily with 2-mercaptopyridine (HSpy) in boiling benzene to give ir(~)~($-~py)(PPh~)~8, a dihydride complex possessing a chelating Spy ligand
(Equation 3.1). This structure was determined on the basis of the two characteristic hydride resonances of two doublets of triplets (-21 .O. -2 1.17 ppm (td. J~H= 17.5 Hz. JHH = 6.8
Hz)} in the IH NMR spectrum (CD2C12) and a singlet (2 1.3 ppm) in the 31~( IH } NMR (C6D6),along with microanalysis and FAB mass spectrum. This complex has been previously prepared from mer-Ir(H)3(PPh3)3 and characterized by X-ray analysis.23-24 An
Refererzces page 96 analogous complex of 8 containing bis-tricyclohexylphosphine ligands has been conveniently prepared from iridium(V) pentahydride.25 fac- or ~ner-IrH~(PPh;)~+ HSpy - I~(H)~($-S~~)(PP~~)~8 + PPh3 + Hz (3.1)
3.2.2. Synthesis of cis-[IrH(q l=SpyH)(q2-~~~)(~~hl)tl(~~~)(9)
Complex 8 reacts with one equiv. of 2-mercaptopyridine and a strong acid
(HBF4-Et20)in CH2C12 for 15 rnin at 20 OC to form after isolation a pale yellow. air stable microcrystalline solid (89%) (Equation 3.3). This is identified as an iridium(lI1) monocationic complex 9 containing two cis phosphine ligands. cis to the hydride according to spectroscopic studies. The hydride resonance at - 17.82 ppm appears as a doublet of a doublet and the phosphorus resonances at -1 1.4 and 10.6 ppm are two doublets with coupling constants of 16.3 Hz. The proton NMR spectrum of 9 in CDICI? also contains a broad singlet at 12.03 pprn due to the proton on the pyiidinium ring which is bound to iridium in a monodentate fashion via the sulfur atom.
HSpy in CH2C12
trans-Ir(~)~(q'-~~~)(~~h~)~ + I~H(~' -S~~H)(~'-S~~)(PP~,)? (3.3) HBF4 RT 8 ff 9
The proposed structure of 9 in solution is depicted in Figure 3.3 and is consistent with that obtained by X-ray analysis (Figure 3.5). Other possible isomers include tram-isomers, 9' and 9" which have not been observed in the final product. One of the trans isomers appears to be a kinetic product, only observed in a NMR tube scale reaction in CDzC12. This isomer has been also observed in another reaction and will be discussed in the following chapter.
References page 96 PPh, I S.. I,,,, .o-. 0;yLH,
Figure 3.3. Proposed structures of three possible isomeric products of Reaction 3.3.
3.2.3. Studies on the proton hydride interactions of
cis-UrH(q L-SpyH)(q2-Spy)(~~h3)2](~~j) (9)
The presence of the Ir-H---H-Ninteraction in 9 in solution was deduced by use of the powerful NMR tools of VT-TI and NOE measurements. Selected spectroscopic results including TI(min) and NOE results are summarized in Table 3.1. The proton on the
pyridinium ring has a minimum TI of 0.235 s and the hydride of 0.266 s at 233 K (400 MHz). The Ir-H...H-N distance is calculated from these Ti(min) values to be l.82fl.05 A which is close to the value (2.1(1) A) obtained from the X-ray derived structure (see later). In an NOE experiment a 12% enhancement for the resonance of the pyridinium proton in CD2Clz is achieved by selective irradiation at the hydride. An attempt to disrupt the Ir-He--H- N interaction by introducing the H-bond acceptor OPPh3 failed. In this attempt a CDrClz solution of 9 containing excess OPPh3 gave a similar enhancement (14%) for the NH resonance when the hydride is irradiated in a similar NOE experiment. Perhaps an He-F hydrogen bond between the NH group of the pyridinium ring and one of the fluorines of the BF4- group as seen in the solid state of the X-ray structure (Figure 3.5) prevents the OPPh3 from approaching the NH group. The N-H and Ir-H vibrational modes of 9 in Nujol appear as broad peaks at 3236 and 22 14 cm-l. respectively. The strength of the He--Hinteraction can
References page 96 be estimated on the basis of the v(NH) (see Chapter 4). This result indicates that a weak attraction exists between a proton and a hydride although it appears relatively weaker than that seen in tricyclohexylphosphine complexes 1 and 5. Two factors may explain the weaker H...H bond in 9: i) PPhs is not as basic as PCy3 and so reduces I~H~--H~+Npolarization
(Chapter 1); ii) the NH proton also forms a strong conventional hydrogen bond with a fluorine of BF4- counterion (see Section 3.2.5). The vibrations of the BFJ anion are those expected for a symmetrical tetrahedral geometry, apparently unperturbed by the F4-I i;lteraction.
Table 3.1. Summary of the selected spectroscopic results for 9.
Met hod ~esultsa *
1H NMR 8 12.03 (br. s, NH) 6 -17.82 (dd. JH~= 14.3 Hz. IrH)
1H TI(min) NH: 0.235 s (233 K) IrH: 0.266 s (233 K)
NOE experiment 14 % (NH) irradiated at IrH
31P{IH)NMRc S 10.6 (d. Jpp = 16.3 HZ) 6 -1 1.4 (d. Jpp = 16.3 Hz) IR v(NH): 3236 cm-' v(IrH): 22 14 cm- '
3Proton NMR. TI and NOE experiments run with 9 in CD?C12 at 400 MHz. ~IRmeasured in Nujol. CMeasured in CD2C12 at 300 MHz.
References page 96 3.2.4. H/D exchange studies
Complex 9 undergoes H/D exchange upon reaction with D2 gas (I atm), but only a very slow reaction has been observed (less than 50% deuteration of the NH group and IrH group in 24 hours). However. a much faster reaction of 9 with MeOD in CDzC12 solution at 20 OC is observed.
After I h. the lH NMR spectrum of the CD~CIZsolution of 9 containing a small excess of MeOD or CF3C02D shows a significant decrease (374)in the intensity of the resonance of the pyridinium proton. The hydride resonances (doublet of doublets in neat CD~CIZ)become broad and overlap with another set of doublet of doublets (0.009 ppm apart from the first set).
It is interesting to note that in the 31P{l~JNMR spectrum of this solution. the downfield doublet at 10.65 ppm is isotopically shifted by 0.0 18 ppm while the upfield doublet at - 1 1.40 ppm remains unchanged (Figure 3.4). Therefore when complex 9 is deuterated at the NH group, there is an isotopic perturbation in the chemical shifts of the hydride and of one the phosphorus groups. However. it is not clear why one phosphine group has an isotopic shift whle the other does not.
References page 96 Chapter 3
References puge 96 Chuprer 3
The structure of 9 (Figure 3.5) as determined at 173 K reveals that the iridium atom is surrounded by cis-PPh3 groups. a chelating 2-pyridinethiolate ligand. and a 2- pyridiniumthiolate ligand bound via the sulfur atom. Thus the requirement for an octahedral iridium(II1) centre is completed by a hydride ligand trans to S( I). The hydrogen on the nitrogen of the pyridiniurnthiolate is well defined in Fourier difference maps. and the hydride ligand could be located. The presence of the hydride is also indicated indirectly by the observed truns-influence on S(1): 2.535(2) A for the (truns)S-Ir bond length which is significantly longer than 2.394(2) A for the (cir)S-Ir distance. The P(2)-Ir-S(2)-C(10)-N(2) units are in a plane with a maximum deviation of 0.037 A for the iridium atom. In this plane the hydride ligand is located at 1.72(11) A from iridium, and at 82(4)O, 98(J)O to cis-P(2) and S(2). respectively. and at 11 1(4)0. 69(4)0 to cis-P( I) and the chelate nitrogen atom (NI). respectively. and 2.05(13) A from the proton of the pyridinium ligand. The structure also shows that the H on the nitrogen has a close contact of 1.96(8) A with one of the fluorines in the tetnfluoroborate anion. A similar type of hydrogen bonding interaction between an anion (CI-) and protons on the nitrogens of two pyridine-Zthiolate rings has been reported for a rhodium(II1)complex with a CI--N distance of 3.156 A.26
References page 96 Figure 3.5. Structure of the cation and anion of 9 which also shows the N-H---F-B interaction.
References page 96 3.3. Conclusion
The trihydride fac-IrH3(PPh3)3 has an unusual AA' A" XX'X" pattern which changes with temperature. A synthetic route to the novel iridium(II1) complex [IrH(q -spyH)($-
Spy)(PPh3)2](BF4) 9 has been established from ~r(~)~(q*-~py)(P~h~)~8. [IrH(q I- SpyH)(q2-~py)(PPh~)~](~~j)9 possesses a unique hydrogen bond interaction involving Ir- H--H(N)-SF-Batoms with the distances, of 2.05(13) A for the H-.Hunit and of 1.96(8) A for the F.-H unit. Isotopic shifts have been observed in the 31 P{ IH } and 1H NMR spectra of (IrH(q I -Spy~)(q~-Spy)(~~h~)~](~~j)941 produced by the reaction of 9 with MeOD or CF3COzD.
3.4. Experimental
General experiment All preparations were carried out under an atmosphere of dry argon using conventional Schlenk techniques. All the solvents were distilled under argon over appropriate drying agents prior to use. Tetrahydrofuran (THF),diethyl ether (Et20). and n-hexane were dried over and distilled from sodium benzophenone ketyl. Ethanol (EtOH) and dichlorornethane were distilled from magnesium ethoxide and calcium hydride. respectively. Deuterated solvents were dried over Linde type 4 A molecular sieves and degassed prior to use. Triphenylphosphine, 2-mercaptopyridine. and an 85% solution of HBFd.Et20 complex were purchased from Aldrich Chemical Company Inc. Iridium trichloride hydrate was obtained from Johnson-Matthey Co. Sodium ethoxide was generated by the reaction of sodium metal with water-free ethanol under argon and dried to white powder before use. NMR spectra were obtained on a Unity-400, operating at 400.00 MHz for H. 16 1.98
MHz for 3 l~.or on a Gemini-300 operating at 300.00 MHz for 1H. 12 1.45 MHz for 3 P.
All l~ NMR spectra were obtained with proton decoupling unless otherwise stated. lP
Referetlces page 96 Chapter 3 93
NMR chemical shifts were measured relative to H3PO4 as internal reference. IH NMR chemical shifts were measured relative to deuterated solvent peaks or tetramethylsilane. Variable temperature TImeasurements were made at 400 MHz using the inversion recovery method. Second order spectra were simulated using the program LAoCN-~.'~ IR spectra were recorded on a Niwlet 550 Magna-IR spectrometer. Fast atom bombardment mass
spectrometry (FAB MS) was carried out with a VG 70-250s instrument using a 3- nitrobenzylalcohol (NBA) matrix. All FAB MS samples were dissolved in acetone and placed in the matrix under a blanket of nitrogen. Microanalyses were performed by Guelph Chemical Laboratories Ltd., Ontario. X-ray Structure Determination Intensity data for 9 were collected on an Siemens P4 diffractometer, using graphite monochrornated Mo Ku radiation (h= 0.7 1073 A). The o scan technique was applied with variable scan speeds. Intensities of 3 standards measured every 97 reflections showed no decay. Data were corrected for Lorentz. and polarization effects and for absorption? The Ir atom position was solved by the Patterson method and other non-hydrogen atoms were located by successive difference Fourier syntheses. Non-h~ldrogenatoms were refined anisotropically by full-matrix least-squares on F'. Hydrogen atoms were positioned on geometric grounds (C-H0.96 A. Uiso = 0.033(4) A"). All calculations were done and diagrams created using SHELXL-93" and SHELXTL PC" on a 486-66 personal computer. A view of complex 9. including the crystallographic labeling scheme is shown in Figure 3.5. Crystal data. data collection. and least squares parameters are listed in Table 3.2. Selected bond lengths and angles for 9 are listed in Table 3 -3.
Synthesis of crude mer-IrHC12(PPh3)3 IrCl3.3 H20 ( 1.0 g. 2.84 mmol) was suspended in EtOH (I5 mL) in a Schlenk flask containing a stirring bar under argon. To this
was slowly added concentrated hydrochloric acid ( 1.8 mL) while the suspension was stirred. Heating at reflux for 5 h produced a dark greenish yellow solution. This was then cooled to room temperature and then 3 equiv. of triphenylphosphine (1.49 g. 5.68 mmol) were added.
Refererzces page 96 Chapter 3 94
The solution was refluxed for a further 12 h to produce a pale yellow precipitate. After cooling the solution to 0 OC. the product was filtered in air and washed with two portions of cold ethanol and dried irr vacuo. The product was a pale yellow powder containing a mixture of a major (mer-IrHC!:!PPhj)3) and minor species. Yield 2.3 g (77% based on met-- IrHC12(PPh3)3). This was used without further purifications as indicated below. Spectroscopic data for mer-IrHC12(PPh3)3: NMR (CD2C12. 6). P { H ) : -8.9 (d. Jpp = 13.3 HZ), -29.1 (t. Jpp = 13.3 HZ): ' H: - 13.88 (td. 1 H, 'JpHcCis,= 16.4 HZ, 2JpH(t,ns, = 162 HZ. Ir-H), 6.8 - 8.0 { m, 45H. P(CsHs)3} . NMR (CDC13, 6)for the minor species. P ( H } : 6.7 (d. J = 13.5 Hz. Int. = 0.02 relative to total intensity of 3 in mer-IrHC12(PPh3)3). - 1.8 (d. J =
16.4 Hz. Int. = 0.1). -6.8 (t. J = 16.4 Hz. Int. = 0.04); Iff: -19.16 (quartet. J = 14.1 Hz. Int. = 0.14 relative to intensity of one hydride in n~-IrHC12(PPh3)3).MS(FAB): calc. for c~~H~~~~CI~193~rP3,1050; observed. rnlz = 1049 (M+ - H). m/z = 1015 (M+ - CI). m/z = 979 (M+ - XI).
Synthesis of fa~-1r(H)~(PPh~)~Crude rner-IrHCl~(PPh3)3( 1.0 g. ca. 0.63 mmol) and a large excess of dried sodium ethoxide (0.8 g. 12 rnmol) were suspended in THF
( 15 mL) in a Schlenk flask containing a stirring bar under dihydrogen gas. After 30 min the stirred solution became orange-yellow and over a period of 24 h slowly turned pale yellow. The solvent was then evaporated to dryness. To the residue obtained was added a sufficient amount (ca. 20 rnL) of degassed distilled water to dissolve up sodium salts and this was stirred for 30 min before filtering under argon. The product was washed under argon twice with water (ca. 5 mL) then cold ethanol (cu. 1 mL) and dried in vacuo. Finally the pale yellow powder was washed with ether several times (3 x 5 rnL) until the filtrate was clear and the product was grey-white (0.95 g. 76 %). NMR (CDCl2. 6). 3 P{ H}: 30.05 (s): H: -12.25 (AA'A"XX'X". simulated see Figure 3.2. Ir-H). 6.8 - 7.8 (m.45H. P(ChH5)3). MS(FAB): calc. for C54H481931r~3,982; observed, 982 (M+), 979 (M+ - 3H). Synthesis of Ir(H)2(qf-sp~)(PPh~)~ (8) fac-Ir(H)3(PPh3)3 (1.0 g. 1.02 mmol) and excess 2-mercaptopyridine (0.2 18 g, 1.96 rnmol) in benzene ( 15 mL) were placed
References page 96 in a Schlenk flask containing a magnetic stirring bar under argon. This was stirred under reflux for 12 h and then the solvent was evaporated in vacua to dryness. The residue was redissolved in CHCl3 and filtered through Celite. Following removal of the solvent the resulting powder was washed with ether (ca. 5 mL)several times until the filtrate turned irom yellow to colourless and then dried to give a yellowish white powder. Yield 0.75 g. 89 % based on ,ner-Ir(H)3(PPh3)3. Analysis. Calc. for C~~HJ&NPZS+ CHCI3: C. 53.22: H, 3.94: N. 1.48. Found: C. 53.78: H, 4.1 1; N. 1.74. IR(Nujo1): v(lr-H) 1 l57(w). 2 1 1 1(m) cm-1. NMR. lP{ H } (C6D6, 8): 2 1.3 (s); lH (CD~CIZ.6): -2 1.0 (td. 1 H. J~H= 16.6 Hz.
JHH = 6.8 Hz. IrH). -21.17 (td. IH. J~H= 17.5 Hz. JHH= 6.8 Hz. IrH). 5.80 (br. t. IH. J = 6.4 Hz. SC5H4N). 5.98 (br. d. IH. J = 8.2 Hz. SCsH4N). 6.51 (br. d. IH. J = 5.5 Hz.
SCsH4N). 6.65 (br. t. 1H. J = 7.7 Hz. SC5H4N). 7.0 - 7.9 (m. 30H. PPh3J. MS(FAB): calc. for C4I H~~ 193~r~~2~, 829: observed, 829 (M+). 827 (M+ - 2H). Synthesis of cis-[IrH(q k3pyH)(q2-Spy)(PPh3)2J(BF4)(9) I~(H)~($-
Spy)(PPhj)~( I00 mg, 0.12 mmol) and 1.5 equiv. of 2-mercaptopyridine (20 mg, 0.18 mmol) were dissolved in dichloromethane (5 mL) in a Schlenk flask under argon. While the solution was being stirred, 85% HBF4bEt20 (cri. 80 yL)was slowly added through a septum using a syringe. After 10 min the solution was filtered through Celite under Ar. The solvent was then evaporated irz vacuo to dryness. To the residue was added 5 mL of ether and this mixture was swirled until the precipitation of a pale yellow powder occurred. The powder was then washed with ether (ccr. 3 mL) twice more before drying to give a pale yellow powder. Yield ( 1 10 mg. 89%). Analysis. Calc. for CJGHJOBFJI~NZP~S~+ CH?CIZ: C. 50.8: H, 3.81; N, 2.52. Found: C. 49.45: H. 3.96: N. 2.88. IR(Nujo1): v(N-H) 3236(m). v(1r-H) 22 M(m) cm-1. NMR (CD2Clz,6). -'l~(kf }: -1 1.4 (d, Jpp = 16.3 Hz). 10.6 (d. Jpp
= 16.3 Hz): H: - 17-82 (dd, lH, JH~= 14.3 Hz, IrH), 6.3 - 8.8 (m, overlapping, 9H, SCsH4N and SCSH~NH),7.0 - 7.6 (m, overlapping, 30H. PPh3). 12.03 (br. s. lH, NH). MS(FAl3): calc. for c~~H~~~~~I~N~P~s~,939: observed, 939 (M+), 828 (M+ - HSCSH~N).
References page 96
Heinekey. D. M. J. Am. Clwm Soc.. 1991. 113. 6074. To obtain this distance the Tl(min) value is corrected for the contributions by other
hydrogens on the PPh3 groups.21 Then it is assumed that two hydride nuclei on an equilater;?! triangle relax the third by the dipolar mechanisms.
Desrosiers. P. J.: Cai. L.: Lin. 2.: Richards, R.: Halpern. J. J. Am. Cltrm. Soc.. 1991, 113, 4173. Crabtree. R. H.: Felkin, H.: Morris. G. E. J. Orgurzotnet. Chern.. 1977. IJI. 205. Mura, P.; Robinson. S. D. Acta Cryst.. C40. 1984, 1798.
Alteparmakian, V.: Mura. P.: Olby. B. G.: Robinson, S. D. Inorg. Chitn. Acrcr, 1985. 104, L5. The preparition and the reaction of I~(H)~($-s~~)(Pc~~),with HSpyH+ have been described as an alternative to the reaction of IrHs(PCy3)z with HSpyH+ to give the hydrogen bonded species [Ir(H(q I- spy^) }~(PC~~)?J(BFJ)1 (Chapter 2).
Deeming, A. J.: Hardcastle. K. E.: Meah, M. N.: Bates. P. A.: Dawes, H. M.:
Hursthouse, M. B. J. Chent. Soc., Daltori Trcrns 1988, 227. Cassidei. L.: Sciacovelli, 0. Qrtar~trinl Cizer?~istryProgrorn Escizcrrrgr, No. 458. LAOCN-5. Sheldrick. G. M.. SHELXL-93. Program for Crystal Stnicture Refnemmt. University of Gottingen, Germany. 1994.
Sheldrick. G. M.. SHELXTL-PC.Siemens Analytical X-ray Instruments Inc.. Madison, Wisconsin, U.S.A.. 1990.
References page 96 Chupter 3 98
Table 3.2. Summary of Crystal Data. Details of Intensity Collection. and Least-Squares Refinement Parameters for 9. empirical formula C4gH43BF4IrN2P2S2~0.5C6~6
Mr 1064.92 crystal class Monoclinic
P2 l/c l7.723(3)
1 O.408( 1 ) 26.073(4)
1O8.O8( 1 )
4572.0( 1 1 ) 4 1.547 3.134 2124 8 range for data collection. deg 2.56 to 27.00 T, K l73(2) min., max. transmission" 0.5297, 0.7937 reflections coilected 10290 independent reflections 9964
Rint 0.0453 no obsd. data [I> 2@1)] 6153 RI [I > 20(I)lb 0.0468 wR2 (all data)c 0.1 156 parameters refined 556 "~bsorptioncorrection using SHELXA-90 in SHELXL-93.28 22 1/2 b~ = Z(Fo-Fc)EF,. 'wR2 = {Z[~(F~~-F~~)~/Z[W(F,) ] } . Ctlupter 3
Table 3.3. Selected Bond Lengths (A)and Angles (deg) for 9.
Ir-N( 1 ) Ir-P(2)
Ir-P( 1 ) Ir-S(2)
Ir-S( 1 ) lr-H( 1 Ir)
S(2)-C(10) S( 1 )-C(5)
P(1)-C(11) P( 1 )-a21 )
P( 1 )-C(31 ) P(2)-C(41 )
P(2)-C(61 ) P(2)-C(5I )
N( 1 )-C(5) N(l)-C(1) N(2)-C( 10) N(2)-C(6) N(2)****F(4) N(2)-H(2A)
C(2)-C(3) C( 1 )-C(2)
C(4)-C(5) C(3)-C(4 C(7)-C(8) C(6)-C(7) C(9)-C(10) C(8)-C(9)
B( 1 )-F(4) B( 1 )-F(3) B( 1)-F(1) B( 1 )-F(2) F(4)-H( 1 Ir) F(4)***H(2A) H( 1Ir)---H(2A)
N( 1)-Ir-P(2) N( 1 )-Ir-P( 1 )
P(2)- Ir-P( 1 ) N( 1 )-Ir-S(2) P(2)-Ir-S(2) P( 1)-Ir-S(2)
N( 1)-h-S(1 ) P(2)-IPS( 1)
P( 1 )-bS( 1) S(2)-Ir-S(1) N( 1 )-Ir-H( 1 Ir) P(2)-Ir-H( 1Ir)
References page 96 Chapter 3 100
P( 1)-Ir-H( 1Ir) S(2)-Ir-H( 1 Ir)
S( I )-Ir-H( 1 Ir) F(4)-.H( 1 Ir)-Ir C(5)-S( 1 )-Ir C( 10)-S(2)-Ir
C( 1 I )-P( 1)-C(2 i) C( 1 I )-P(1 )-C(3 I )
C(2 1 )-P(1 )-C(31 ) C(I 1 )-P(1 )-Ir
C(2 1 )-P( I )-Ir C( 3 1 )-P( 1 )-Ir C(5 1 )-P(2)-Ir C(4 1)-P(2)-Ir C( 1 )-N(1 )-C(5) C(6 1 )-P(2)-Ir
C(5)-N( 1 )- Ir C( 1 )-N( 1 )-[r C( 10)-N(2)-H(2A) C(6)-N(2)-C(10)
N( 1 )-C(1)-C(2) C(6)-N(2)-H(2A) C(4)-C(3)-C(2) C( 1 )-C(2)-C(3) N( 1)-C(5)-C(4) C(3)-C(4)-C(5)
C(4)-C(5)-S(1 ) N( 1 )-C(5)-S( 1 ) N(2)-C( 10)-S(2) C(9)-C(10)-S(2)
F(4)-B(1 )-F( 1 ) F(4)-B(1 )-F(3) F( 1)-B( 1)-F(3) F(3)-B(1 )-F(2) F( 1 )-B(1 )-F(2) F(3)-B( 1 )-F(2)
H( 1Ir).-F(4)-B( 1 ) F(4)...H(2A)-N(2)
References page 96 Chapter 4. Intramolecular IrH-*HN Interactions in Triphenylphosphine Complexes of Iridium(II1)
4.1. Introduction
Five types of structures of complexes of iridiurn(II1) containing intramolecular proton-hydride bonds have been described in Chapters 2 and 3 and elsewhere (Figure 4. I ). Types I. I1 and 111 are formed when the phosphine donor is bulky (P = PCy3). Species of the type I are obtained by two different routes: i) a substitution of weakly coordinated solvent molecules' in [~r~~(solvent)~(~~~)~]+,R = Cy; ii) a reaction of IrH5(PR3)2. with HY- LH'.' The latter method using an excess of hydrogen bond donor ligand and acid has afforded species of the type I1 and 111 (P = PC~~).~
H.,
,ti H-.. \ \ LY
Figure 4.1. Iridiurn(II1) complexes possessing one or two proton-hydride bonding units
References page 135 An objective of the current work is the synthesis of complexes of type I - I11 with PPh3 in order to compare their properties with those of PCy3 complexes. First the route to the known triphenylphosphine complexes of iridium containing proton-hydride bonds will be reviewed. An example of type IV is a neutral trihydrido aminopyridine (pyNH2) complex I~H~(~~NH~)(PP~~)~.'This was prepared from IrHs(PPh3)z with 2-aminopyridine under very mild conditions (room temperature for several hours) according to Equation 1.1. Due to the difficulty in obtaining IrH5(PPh3)2 in high yield. a trihydride IrH3(PPh3)3 was used in an attempt to make an analogous trihydrido species (IV. L-YH= SpyH) under similar condition (Chapter 3)? The result was the chelation of the pyridinethione ligand to give a complex of type VI in Equation 4.1. As noted in Chapter 3. the protonation of VI with an acid in the presence of proton donor ligand (SpyH) was attempted to obtain types I. I1 or 111 (P = PPh3). However. the reaction produced a monohydrido species of type V (Figure 4.1. P = PP~~)?Another possible synthetic approach is the use of IrH3(PPh3)3 in the direct reaction with HSpy and an acid. This will be described in the first part of this chapter.
'\ L-YH L ..,,,, I , PR3 IrH,(PR3 1, (1% -Hz R3P
IV (L-YH = pyNH?) VI (L-YH= SpyH) R=Phandx=3.y=3 R=Cyandx=5.y=2
In the second part of this chapter. a synthetic approach to hydrido carbonyl complexes containing the SpyH hydrogen bond donor group is described. A carbonyl ligand might be a weaker hydrogen bond acceptor than hydride and may not interfere with the formation of SpyH--HIr bonds. On the other hand. it is a strong x-acid and could influence the strength of the proton hydride bond. Some preliminary results are presented.
References page 135 Ctiupter 4 103
Finally. in the last part of this chapter. the features of the proton-hydride bonds in the seven pyridinethone complexes described in Chapters 2.3 and this chapter will be compared and discussed.
4.2. Results and Discussion
4.2.1. Synthesis of [IrHz(q I-S~~H)(PP~~)~](BF~)(10)
The reaction of fuc-lrHj(PPh3)~with tetrafluoroboric acid etherate in the presence of pyridine-Zthione in dichloromethane or chloroform gives a product identified as
[IrH2(SpyH)(PPh3)3](BF4)10 according to Equation 4.2. 10 is isolated in 91 % yield as a yellow microcrystalline solid which is slightly less soluble in CHCl3. toluene. benzene or acetone, but very soluble in CH2CI2. 10 has been also prepared from the mixture offitc- and mrr- isomers of the trihydride which is conveniently obtained in similar yield from iridium trichloride according to a method similar to that of Chatt et aL6
HSpy I excess HBF, IrH3(PPh3 13 - [I~H,(V'-s~~H)(PP~,),](BF,) 10 (4.2) RT. 10 min. CHCI,
4.2.2. Characterization of [IrH2(q 1-SpyH)(PPh3)3](BF4) (10)
10 has been characterized by microanalysis. NMR techniques (3 P and IH NMR. VT-T measurement), infrared spectroscopy. and an X-ray diffraction study. In CDC13 the
3lP( IH) NMR spectrum of 10 consists of two signals at 2.23 ppm as a doublet and -0.93 ppm as a triplet with an intensity ratio of 2: 1. The appearances of these resonances are monitored by 31~('H} NMR in comparison with the disappearance of the singlet at 10 ppm for the parent trihydride. The pattern of the new resonances indicates the formation of a
References page 135 single isomer with three phosphine ligands in two different magnetic environments. The proton NMR spectrum of 10 in CDC13 contains assignable peaks for the protons on the pyridine ring, the phenyl groups as well as the hydrides. Peaks for the pyridine ring protons are overlapping with those for phenyl ring protons in the region from 7.8 to 6.1 ppm. The chemical shifts for the two inequivalent hydrides are distinctive at - 12.7 pprn and - 15.8 ppm.
The former appears as a doublet of triplet of doublet due to couplings of trans J~H( 1 16 Hz). cis J~H(22 Hz). and cis JHH (3.6 Hz) while the latter appears as a pseudo quartet of doublets due to couplings with three cis-phosphorus nuclei and a cis-hydride nucleus. Finally the NH proton resonance appears at 10.9 pprn as a broad singlet. Other possible isomers such as fincis- l0a and nler-trczns-lob depicted in Figure 4.2 have not been observed in the product. Probably the former is less favored because of il steric reason involving three large phosphine !igands and the latter. for an energetic reason involving the instability of trans -hydrides. After co. 1 weeks. 10 undergoes a partial isomerization in the solid state under laboratory fluorescent light conditions. The isomerization yield is about 10 8 judged by the intensity ratio in the proton and phosphorus NMR spectra. The isomerization product is proposed to be the tram-hydride lob based on the following NMR characterization in CD2C12. The 31P{ IH} NMR spectrum of the isomerization product exhibits resonances characteristic for a typical mer-phosphine complex as a doublet (I = 15.67 Hz) and a triplet (J = 15.55 Hz) at -10.05 and - 17.32 ppm. respectively. 10a would also give this pattern. The proton NMR spectrum contains a hydride resonance at - 19.75 pprn as a doublet of triplets with coupling constants of 22.4 and 8.85 Hz due to coupling to the phosphorus nuclei in two different cis-environments. Two mutually rrans-hydrides are magnetically equivalent with respect to these three cis- phosphorus ligands and a cis-pyridinethione ligand. The NH resonance of the monodentate SpyH Iigand appears at 12.5 pprn as a broad singlet with half the intensity of the hydride resonances. The fact that the spectrum lacks a resonance with a large trans-PH coupling suggests that the possible jhc-isomer 10a is not formed. The intensity of the hydride and
References page I35 NH proton resonances of lob relative to those of 10 is about 10 % after a month and no further change is observed.
Figure 4.2. Three possible isomers that might form in Reaction 4.2.
The solid state IR spectrum of 10 contains characteristic bands corresponding to v(lr- H) and v(NH). Bands for v(1r-H) at 2063 and 2197 cm-I (KBr) are compared with those1-5
(2137. 2 120: 22 14 cm-I ) for the proton-hydride bonding complexes 1 and 9. respectively. The v(NH) of coordinated SpyH appears as a broad band at 3125 cd. This band is similar to that (3236 cm- l ) of 9. but at higher energy than that (3 1 1 1 cm- 1) of 1. This probably indicates that the Ir-HW-N interactions are weaker in 9 and 10 than those in 1 (see also Section 4.2.8). * ------Tl(rnin):0.23 s (6 - 15.8. psd q) I Ph3P . PPh3 41r--w 41r--w ----- Ph3P I ,* Tl(rnin):0.18 s (6 - 12.7. dtd)
Figure 4.3. Comparison of the hydride and NH resonances and their Tl(min)for 10.
The minimum TIvalues for the two hydrides and the NH proton of 10 have been obtained at 233 K at 400 MHz. These are shown in Figure 4.3 with a proposed structure of 10. The TI minima are 0.18 and 0.23 s for the hydrides and 0.22 s for the NH proton in
References pcige 135 Chapter 4 106
CD2C12. The shorter T l(min)of 0.18 s is assigned to the resonance for the hydride (Ha)cis to the SpyH ligand. The relaxation rate (5.6/s) for this TIvalue is attributed to two PPh3 protons ( 1.01s. 2.4 A). cis-hydride (~b)(0.7/s, 2.3 A) and the NH proton (3.9/s). The calculation7 gives the Ha..-H(N)distance of ca. 1.7 1 A from the TI(rnin) of the hydride (Ha). Using a Tl(min) of 0.12 s for the NH proton and the sole relaxation rate contribution (3.?/s) from the hydride. after subtraction of a contribution of 1.4/s for l4hi at 1.0 A, the H-..H distance of cu. 1.77 A is obtained. H/D exchange experiments have been carried out at room temperature with D2 gas or MeOD. Exposure of a CDzCIz solution of 10 to D? gas at 1 atm for 3 minutes resulted in no significant changes in the intensities of the NH and IrH resonances in the proton NMR spectrum. Isotopic shifts are observed when this solution is treated with an excess of MeOD, a result of the deuteration at the NH group. After 15 hrs in the presence of MeOD the pseudoquartet resonance at -15.7 pprn for the hydride tmm to SpyH ligand becomes a superimposed multiplet ( 15 lines evenly spaced) centered at - 15.48 pprn while the doublet of triplet of doublet resonance at -12.7 pprn for the other hydride is broadened by unresolved resonances due to isotopomers. Similarly. in the 3 P{lH ) NMR spectrum. the resonance at
-0.66 pprn (triplet) for the phosphine ligand rrcrrls to the hydride is unchanged while that of the other two equivalent phosphorus nuclei has shifted (A6 = 0.079) from 1.72 pprn (doublet) to 1.82 pprn (doublet). Similar isotopic perturbation with MeOD has been described for 9 (Chapter 3).
4.2.3. Formation of [IrHz(q i-SpyH)z(PPh3)2](BFj) (1 1)
One of the triphenylphosphine ligands in [IrH2(SpyH)(PPh3)3](BF4)10 is replaced by another 2-pyridinethione ligand at room temperature over a period of one week. Thus, the product is a bis(tripheny1phosphine) complex containing two SpyH proton donor groups. This is formulated as [IrH2(q1-SpyH)2(PPh3)2](BF4)11 which is a phosphine analog to 1.
References page 135 Chapter 4 107
However. 11 could not be isolated as it undergoes a further reaction to eliminate a
dihydrogen molecule (Scheme 4.1 ).
PPh, l+
Scheme 4.1. Transformation of 10 to 9 viu 11 and 9'. the trcrns isomer of 9.
Based on the following NMR observations. the structure of the species formed in this H? elimination reaction is proposed to be trrns-[IrH(r$SpyH)(q2-~py)(~~h~)~](~~~)9' which
is the trans-isomer of 9 that contains both chelate pyridinethiolate and monodentate
pyridinethione ligands. The hydride resonance of 9' at -16.68 ppm is a triplet (JPH = 12.2 1 Hz) and the NH proton resonance at 11.91 ppm is a broad singlet. These resonances are compared with those for 9 at -17.78 ppm as doublet of doublets for the hydride (JPH = 14.3 Hz) and 11.86 ppm as a broad singlet for the NH proton as described in Chapter 3. Although there are two possible trans isomers (i.e.. the hydride trans to S or N of the chelate ring) as proposed in Chapter 3. Scheme 4.1 shows the one with the sulfur atom trans to the hydride, which would result from the stereospecific elimination of Hz from 11.
References page 135 C/JUP~~?t- 4 108
9' is apparently an intermediate species observed by NMR spectroscopy in the transformation of 11 in CDC13 to the cis-product, 9 (Scheme 4.1). 9' has been also observed previously as an intermediate in the preparation of 9 from the reaction of the dihydride ~rH~(q~-~py)(~~h~)~8 with tetrafluoroboric acid in the precence of 2- pyridinethione (Chapter 3).
4.2.4. Characterization of [IrH2(qk3pyH)z(~~h3)2](~~4) (11)
Yellow crystals of 11 were obtained by fractional crystallization of the mixture of products from the reaction of 10 with one equivalent of 2-pyridinethione by layering in CHCl3 with ether. The NMR resonances for 11 are very similar to those for 1. a PCy3 analog (Table 4.1). In the proton NMR spectrum in CDzCh, the resonances for the NH protons and hydrides appear at 11.70 pprn as a broad singlet and -15.95 ppm as a triplet. respectively. The 3l P{I H ) NMR spectrum contains a singlet at 9.4 ppm. These results are consistent with the equivalence of ligand groups of two SpyH ligands. two hydrides and two phosphorus ligands. The short TIminima of 0.16 s for the NH protons and 0.20 s for the hydrides have been obtained for a solution of 11 in CD?CIz at 193 K, 400 IMHL These Tl(min) values and the relaxation rate contributions are compared with those for 1 in Table
4.1. The results suggest that the solution structure of 11 is very similar to that of 1.
References puge 135 Chuprer 4 I09
Table 4.1. Com~arisonof the selected NMR" and TI(min) calculations for 1 and f 1.
1 1 I
Ww 12.18 (br s) 1 1.70 (br s)
T 1 (min) (observed) 0.18 s (233 K) 0.X s (193 K)
Total relaxation rate 5.61s 6.21s
'4~contribution 1.41s (1.0 A) 1.41s I 1.0 A) other contributionb 1.41s (7.1 A: one H of PPhl) sole contribution of H(1r) 3.4/s TI(correct) 0.28 s d(HH) from T I (NU) 1.74k.05 A
6(IrH) - 18-28 (t. J = 15.3 HZ) -15.95 (t. J = 15.3 HZ)
TI(min) (observed) 0.17s(233 K) 0.20 s ( 193 K) Total relaxation rate 5.91s 5 .o/s cis-hydride contribution' 0% (2.4 a) 0.91s (2.2 a, PR3 proton contributionsd 1.7/s (2.2 and 2.2 A) 1.51s (2.2 and 2.3 a) sole contribution of H(N) 3.71s 2.6/s
TI (correct) 0.27 s 0.37 s d(HH) from T 1 (IrH) 1.72k.05 A 1.82k.05 A
Average d(HH) from Ti cn. 1.TO A cci. 1.78 A
31Pl. 'HI, 8.21 (s) 9.4 (s) "chemical shifts in ppm, NMR measured in CD2C12 at 400 MHz. Relaxation rate contributions and d(HH) calculations done using Equations 1.13 to 1.15 in Chapter 1. b~ontributionfrom PCyj protons in 1 is not added because the position of the hydrides is uncertain. 'The typical distance between two cis hydrides is assumed to be 2.4 A in I. d~wo trans PR3 groups each with two CH protons near to the hydrides.
Referert ces page 135 Chapter 4
4.2.5. Synthesis of [IrH(CO)(q '-spyH)~(PP~~)~](BF~)~ (12)
Triphenylphosphine complexes containing carbonyls are often prepared from the reaction of commercially available transition metal chlorides with reactive organic carbonyl- containing compounds such as aldehydes or alcohols in the presence of a strong base.' In our attempt. a tris(tripheny1phosphine)hydrido complex of ir(II1) was reacted with sodium hydroxide as a base and methanol as a carbonyl source, according to Equation 4.3. A mixture of hydrido species consisting of a major (cn. 90 %) and minor (ca. 10 %) species was obtained. The hydride resonances for the major species in CDClj appeared at - 10.10 and -10.55 ppm as a triplet of doublets (J~H= 16.6 Hz. JHH = 4.6) and a triplet of triplets
(J~H= 19.2 Hz. IHH= 4.2), respectively, with an intensity ratio of 2: 1. In the "P['H} NMR spectrum there is a singlet at 16.29 ppm for the major species. The presence of a carbonyl ligand is confirmed by a strong v(C0) band at 2077 cm-1. These NMR and IR observations are consistent with u trihydrido carbonyl complex irH3(CO)(~~h~)?."he minor species was not identified.
(i) (ii) IrHC12(PPh3), IrH3(CO)(PPh3), + minor species
(i) NaOH. 20 h, RT, THF under H, (ii) MeOH / H90
When crude IrH3(CO)(PPh3)2was treated with HBF4 in the presence of an excess of
HSpy in CDC13, the suspension became clear yellow in about 10 min and a 1 : 1 mixture of two species was formed according to the IH NMR spectrum. The products are proposed to be two dihydrido species [IrHz(CO)(q!-Spy H)(PP~I~)~](BF~)and IrHr(CO)( q I-
Spy)(PPh3)2 (Equation 4.4) based on the observation of one NH proton resonance ( 10.8 pprn) with two sets of hydride resonances of triplet of doublets: set 1: -7.28 (JPH= 17.5.
JHH= 4.56 Hz) and -18.5 ppm (JPH = 14.04, JHH= 4.68 Hz) and set 2: -8.78 (JPH= 17.6.
References page 135 JHH = 2.7 Hz) and -13.9ppm (J~H= 13.4, JHH = 2.6 Hz). The former is a cationic species containing a monodentate SpyH ligand cis to one of the hydrides while the latter is a neutral species with a monodentate pyridinethiolate. These complexes. however. could not be isolated as they undergo decomposition in less than 10 min to give several unidentifiable species.
One of these species has been crystallized in chloroform solution left for slow evaporation in the air over several weeks. The yellowish orange crystals were collected and analyzed by X-ray diffraction and infrared spectroscopy. The X-ray analysis of a single crystal at 396 K proves that the crystalline materials belong to a dicationic monohydridc complex formulated as [IrH(CO)(ql-SpyH)2(PPh3)2](BF4)2 12 containing two monodentate
SpyH ligands, one of which is cis to the hydride and the other. cis to the carbonyl.
One of the interesting features of this complex is the possession of two NH units of SpyH ligands as well as a carbonyl ligand for which IR is of use as a diagnostic tool. The infrared spectrum of 12 in Nujol shows a strong band at 2044 cm-1 for the carbonyl ligand. There are two NH stretching frequencies at 3287 cm-1 (sharp) and 3247 cm-1 (very broad) (Figure 4.4). The NHa-HIr unit is probably responsible for the broadening of the peak at
References page 135 lower frequency while NH~produces one at higher frequency. In comparison to the V( NH) of non hydrogen bonding HSpy (3376 cm-l),'O the NH" stretching frequency of 3247 cm-' in 12 is a little lower in energy. The Av value of 129 cm-I indicates that the NH"...HI~ interaction in 12 is relatively weak. Another band at 3187 crn-I is due to the NH~unit which is not involved in proton-hydride bonding. The Av value of this band in comparison with v(NH) of non hydrogen bonding HSpy is 89 cm". This difference can be attributed to the perturbation in v(NH) caused by the coordination of the ligand. However. it is difficult to confirm this since there is a very weak N-He-F hydrogen bond involving one of the BF4' counterions revealed by X-ray analysis (see later). For comparison purposes. however. both the vINH) of non hydrogen bonding free HSpy at 3376 cm-' and the NH~stretching frequency of 3287 cm-'in 12 are arbitrarily used as references to calculate the difference
(Av) and to estimate approximate bond energy using Iogansen's equation1 (see Section
1 4.2.8). i
Figure 4.4. Characteristic NH stretching frequencies for 12 (Nujol, KBr).
4.2.6. X-ray structure analyses for 10, 11 and 12
The summary of crystal data panmeters are shown in Table 4.2. Selected bond distances and angles for 10. 11 and 12 are shown in Table 4.3. The ORTEP diagrams of the cations for 10. 11 and 12 are shown in Figures 4.5. 4.6 and 4.8. respectively. 10 is a cationic octahedral complex with three triphenylphosphine ligands, a monodentate pyridinethione ligand and two hydrides trans to a phosphme and a sulfur atom
(Figure 4.5). It has a mirror plane in the equatorial plane through atoms of the
References puge 135 pyridinethione. the two hydrides and a phosphorus and its one phenyl ring atoms. Therefore half of the total atoms are assigned by symmetry relationship. The two hydrogens on the two nitrogens and the two cis-hydrides are well-defined in an electron difference map. One of the hydrides located at 1.81(!!! A from the iridium atom is in proximity to the NH proton at a distance of about 2.1 A. The two hydrides cause a lengthening of the tram M-L distances: Ir- S 1 {2.469(3) A } and Ir-P2 12.4 M(3) A}. Other structural features are compared with related structures Iater in this discussion. 11 is a structural analog to 1. It is a monocationic iridil~m(111) complex containing two trtins triphenylphosphine ligands and two monodentate pyridinethione ligands coordinated via sulfur atoms trans to two hydrides (Figure 4.6). Two hydrides are located in the difference map at about 1.52 A from the iridium atom. From the two elongated Ir-S distances (2.438(2) A. 2.447(2) A},the frws influence of the hydrides is evident. The
NH-.Hlr distances are found to be 2.0 to 2.2 A: a shorter distance (ctr. 2.0 A) in the
H(?B)4-I(2Ir)unit and a longer distance (cci. 3.2 A) in the H( 1 A)-H( l lr) unit. The fluorines of the counterion BF4- of 11 are also weakly associated by hydrogen bonding to the NH units at about 2.4 A. Both the NH units are involved in such intermolecular NH"'FBF3 hydrogen bonds to make a polymeric chain (Figure 4.7). Note that the counterion BF4' of the PCy3 analog 1 is observed to be farther away from the two
NH units of SpyH rings. As noted earlier. BF4' in 9 has been observed to form a hydrogen bond with an NH unit of a coordinated pyridinethione at about 2.0 A (Chapter 3).
References page 135 Chapter J 114
Table 4.2. Summary of Crystal Data. Details of Intensity Collection, and Least-Squares Refinement Parameters for Comdexes 10. 11 and 12. ------Complex 10 11 12 empirical formula C6 I H54BC16F4IrN C56.5~H54BF4Iriq2 C~8H4$32C12F~Ir p3s P2S2 NzOPzSz crystal size 0.42 x 0.38 x 0.44 0.63 x 4.5 x 3.1 0.10x 0.10 x 0.10 Formula weight 14 17.73 1 166.09 1226.63 Crystal class Monoclinic Monociinic Monoclinic Space group P2 i/m mc P2 11c 10.570(2) 37.528(4) l8.5325( 1 ) h, A 22.964(5) 1 S.BO(2) 15.344 1(2) c. A 12.75 l(2) 23.387(3) 18.44642) P, " 102.199( 12) IXO46(7) 94.22 1( 1) v, A3 3025.3( 10) 10979(2) 523 1.27(9) z 2 8 4 Dcalc. mg m3 t 36 1.41 1 1.557 p(M&). mm-l 2.638 2.617 2.86 1 F(000) 1416 4696 2432 T, K 173(2) 2 l3(2) 296(2) Reflections collected 7034 11983 40472 Indeperldent reflections 6686 1 1790 9 109 (Rint = 0.0696) (Rin, = 0.0465) (Ri,, = 0.043) Refinement method Full-matrix least- Full-matrix least- Full-matrix least- squares on FZ squares on F2 squares on F: Data I restraints 1 parameters Goodness-of-fit on FZ Rl [I > 20(0] wR2 (all data) Largest diff. peak and hole
References page 135 Chupter J
Table 4.3. Selected bond distances (A)and angles (0) for 10, 11, and 12. 10 Ir-S 1 Ir-P2 Ir-P 1 Ir-H 1 (If-H2) H 1 -H(N2)
11 Ir-P 1 Ir-P2 Ir-S 1 Ir-S2 Ir-H 1 (Ir-H2) IrH PH1 (N) IrH2-'H2(N)
12 Ir-P2 Ir-P 1 Ir-S 1 Ir-S2 Ir-C77 C77-078 [r-H 1 [rH 1.--N 1 [rH1 -H 1 (NI )
Rejererlces page 135 Chapter 4
Figure 4.5. ORTEP diagram of the cation of [IrH2(ql-SpyH)(PPh3)3](BF4)10 at 173 K.
References page I35 Figure 4.6. ORTEP diagram of the cation of [IrHz(q ~-SP~H)~(PP~~)~](BF~)11 (213 K).
References page 135 Chapter 4
Figure 4.7. Structure of 11 showing a hydrogen bonded polymeric chain with BFJ- counterion.
12 is a dicationic octahedral complex with an iridium(II1) centre surrounded by two triphenylphosphine ligands and two SpyH ligands cis to a hydride and a carbonyl ligand.
The ORTEP diagram for 12 is shown in Figure 4.8. Due to the presence of the frclns- hydride. the Ir-S2 distance is longer (2.478( 1) A} than that for Ir-S 1 {2.409(1 ) A}. The hydride was placed in an idealized position at about 1.62 A from the iridium atom. This places the hydride within about 2.1 A of the NH proton of the cis SpyH ligand (1rH.-N I distance is about 2.42 A). The SpyH ligand cis to the hydride is approximately in the equatorial coordination plane with dihedral angle of 16.9* about the C6-S I bond. The pyridine unit of the other SpyH ligand cis tn CO is much farther away from the coordination plane. The dihedral angle of this ring with respect to the plane consisting of Ir. H 1. S 1. S2. and C77 is about 3 1.80 (Figure 4.9). The cis S 1-Ir-S2 angle {79.98(5)0)in 12 is not much different from those {80.88(6). 79.13(4)0] for 1 and 11. respectively. Unusually wide angles of 128.3(5)O for S 1-C6-N 1 and 126.4(4) for S2-C 16-N 1 1 are found. These are shown in Figure 4.9. and compared with others in Table 4.4 (Section 4.2.7).
References puge 135 Chapter 4
Figure 4.8. ORTEP diagram of the cation of [I~H(CO)(~~-S~~H)~(PP~~)~](BF~)~12 at
296 K.
References page 135 Chapter 4
Figure 4.9. Angles (degree) of coordinated SpyH ligands in 12.
Similar to complex 11. 12 appears to have a weak F-'H-Nhydrogen bond between one of the BF4' counterions and one of the SpyH ligands. The NH0..F distance in (N I 1A)H.-FZ(B)unit is roughly 2.6 A which is less than the sum of the van der Waals radii of tne two atoms in contact (H. 1.2 A and F. 1.47A).
4.2.7. Comparison of the solid state structures containing SpyHW*HIrbonds
The angles and the bond distances around the coordinated SpyH ligands of six iridium(II1) complexes characterized by single crystal X-ray analyses are listed in Table 4.4. All are cationic species containing one or two SpyH ligands. These include two of the PCy3 complexes (1.5) and four of the PPh3 complexes (9 - 12). The angles. Ir-S-C and S-C-N are labeled as a and b, respectively, and the distances, Ir-S and S-Cas c and d, respectively. Also of possible importance are the pyridine ring dimensions. They are listed with related distances in the free pyridinethione dimer in Table 4.5.
The sulfur angles a of monodentate SpyH ligands are in the range of I 1 1 to 1 140 with an exception of 1 17.4(4)0 for 10. The carbon angles b in the range of 120 to 1230 are similar to that { 120.5( 1 )O) for free pyridinethione except for 12 { 126.4(4)0 and 128.3(5)0). Within a coordination plane, one can expect that the smaller the angles a and b are, the closer
References page 135 Cliupter 4 121 the NH unit can approach to the iridium hydride. The larger angles a or b in 10 and 12 might be responsible partially for the longer NHm-.HIrdistance.
Table 4.4. Selected itn fes and bond distances around the coordinated T-- T--
*Angles a, b in degree and distances c, d in A. The diagram of SpyH ring is either pyridinethiolate or pyridinethione form. AAtoms in brackets are tram atoms. #Data for chelate rings: sulfur trans to hydride.
References page I35
Chapter 4 123
The N-.'Ir distances e which are more reliable than the HV-Hdistances may be a useful indicator of the latter distances. The distances range from 3.49 to 3.61 A with the exceptions of complexes 10 (3.72 A) and 12 (3.67 and 3.91 A). The longer N--1r distance of 3.9 1 A is for the nitrogen on the non-interacting SpyH ring cis to the carbonyl ligand in 12. In comparison of N6.-Irdistances {3.49(l), 3.55(1) A J for 1 with those {3.61(1). 3.56(1) A} For 11, a slightly longer distance of ca. 0.13 A is found for one of the SpyH
rings in 1I.
In the structural series in Table 4.4. many of the sulfur atoms are ircrrzs to hydrides (X
= H) and the S-Ir distances are subject to their trms influence. The S-Ir distances in the influence are 2.44 to 2.54 A. comparably longer than the normal S-Ir distances of 2.35 A to 1.40 A. It might be interesting to see if the bonding Ir-S distances c and the S-C distances d also affect the N4r distance. There are four sulfur atoms that are not trclru to hydride: two in 5. one in 9 and one in 12. In order to have a shorter S-C distance d. the SpyH ring should have pyridinethione rather than protonated pyridinethiolate chmcter (Figure 4.10).
longer longer shoper longer s, / , I.---,
I j pyridine thione (A) I protonated pyridinethiolate (B) 1
Figure 4.10. Ir-S and S-C distances and sulfur angles vs trans influence and SpyH ring character.
References page 135 Chapter J 124
The S-C distances d are found in the range from 1.696 to 1.730 A which are comparable to that ( 1.698(2) A) for the free pyridinethione dimer. These are slightly shorter than those
{ 1.724(7) A and 1.74 l(7) A} for the chelate pyridinethiolate rings in 5 and 9, respectively. From the Tables 4.4 and 4.5 one finds, within experimental error. that the SCSN rings have mainly pyridinethione character with a partial protonated pyridinethiolate chuacter us shown
Figure 4.11. The influence of the distances c and d on the N-Ir distance may not be
Figure 4.11. Three resonance structures of protonated pyridinethiolate and pyridinethione.
Table 4.6. Comparison of the selected angles and distances in Ir-H-'H-Nunits.
Complex 4 IL .N ) dl~r-~) d~-H) ~HH A B Interacting unit (a) (A) [A) (A) (deg) (deg)
References page 135 Table 4.6 shows a comparison of the selected angles and distances in the Ir-Hs-H-N units. The range of Ir-Ha-H(N)angles is roughly 107 - 125' and the range of (Ir)H-W-N angles is 135 - 156'. The H...H distances are roughly in the range from 1.9 to 2.2 A. The shorter H...H distance 9f 1.9 A is due to complex 5 which has the shortest Ira-.Ndistances among the complexes given in Table 4.6.
Table 4.7. Comparison of features for two PPh3 complexes 10 and 11.
10: L = PPh3 11: L = SpyH
PPh3 ligand three PPh3 two PPh3
SpyH ligand one SpyH two SpyH a (degree) 1 17.4(4) 1 13.7(2) 1 13.1(2) b (degree) 122.7(9) 122.3(5) 12 1.8(5) d (A) 1.705( 12) 1.702(6) 1.696(7)
N-Ir (e) (A) 3.72( 1) 3.56( 1 ) 3.62( 1 ) h
In Table 4.7. the structural features of two PPh3 complexes 10 and 11 are compared. With two hydrides. these complexes may be a good comparison as one complex 10 contains three PPh3 with one SpyH while the other complex 11 has two PPh3 and two SpyH ligands. In both complexes, the SpyH ligands have pyridinethione character and the Ir-S distances show evidence of a trans hydride influence. The N-Ir distances in 11 are significantly shorter than that in 10. The (PPh3)3 donor set in 10 may make the hydride less hydridic
References page 135 than the (PPh3)2(SpyH) donor set in 11: thus the Hm-*Hinteraction is weaker and longer in 10 than 11. The larger Ir-S-C angle a of 1 17.4(4)0 in 10 is the main reason for the longer
N-Ir distance (ca. 3.72 A). The Ir-S-C bond angle a is flexible and can close down from 1 17' in 10 to 1 13' in 11 while all the other angles in the IrSCNHW..Hring remain constant. The flexibility of the Lr-S-Cangle is due in part to the ease of change of C-S bond character
from thione to thiolate (Figure 4.1 1 ).
Table 4.8. Comparison of features for two PPh3 complexes 11 and 12.
complex 11 12
L H CO
a (degree) 1 13.7(2) 1 13.1(2) 1 14.7(2) 1 12.5(2)*
1 N-Ir (e) (A) 3.62( 1) 3.56(1) 3.67( 1) 3.9 I( 1)*
*Data involving SpyH ligand cis to CO. A Data for monodentate sulfur trans to hydride.
Finally, in Table 4.8 the structural features for two PPh3 complexes 11 and 12 are compared. 11 and 12 are very similar in geometry. Both contain two cis SpyH ligands and two trans PPh3 ligands. 11 carries one positive charge and two X ligands (hydrides) while 12, with two positive charges. contains one X ligand (hydride) and one neutral donor
References page 135 (carbonyl). There are substantial differences at the angle b which makes significant differences in N--Ir distances between 11 and 12. The large angles b { 136.4(4), 128.3(5)) in 13 are very unusual for an sp2 carbon. It is not clear why the carbon angles b in 12 are out of the range of all others of the series in Table 4.4. Based on the N-Ir distances. the relative strezgth of the proton-hydride bonds may be roughly arranged as shown in the first row of Table 4.9. Table 4.9 also lists the donor ligands that may affect the strength of proton-hydride bonds. It is interesting to note that the proton hydride bond strength is related to the kind and the number of co-donor phosphine ligands. For example. stronger proton-hydride bonds occur when the co-donor ligands are
PCy3, while weaker proton-hydride bonds occur. when they are PPh3. Furthermore. in the series. the weakest bonds are observed when a complex has three PPh3 or two PPh3 with a CO. The number of sulfur donor ligands (SpyH and Spy) must be u factor.
Table 4.9. Comparison of the N-Ir distances versus co-donor ligands. complexesa 1 = 5 >fl> 9> 12 > 10
N ( 3.49(1) 3 SO( 1 ) 3.56( 1 ) 3.6 1( 1) 3.67( 1 ) 3.72( 1) 3.55( I) 3.52(1) 3.62( 1) trans to H S S S S S PPh3 cis to H PCy3 PCY~ PPh3 PPh3 PPh3 PPh3 cis to H PCy3 S PPh3 PPh3 PPh3 PPh3 cis to H H N H N CO H cis to H S S S S S S
'~...[rdistances are increasing in the order from complex 1to complex LO.
References page 13.5 Chapter 4
4.2.8. Comparison of spectroscopic features of proton-hydride bonds
Table 4.10 summarizes some important NMR and IR features for the proton-hydride bonds in the SpyH complexes prepared in this study. Three PCy3 complexes 1. 4 and 5 and three PPh3 complexes 9, 10 and 11 are examined by Tl(min) measurements. The Hm-.H distances calculated from Tl(min) are in the range from 1.7 to 1.8 A for the PCy3 and PPh3 complexes. Table 4.10 also includes the differences of the NH stretching frequencies in comparison with that of non-hydrogen bonding HSpy as well as with that of the SpyH unit (NH~)in 12. The differences (Av) vary from 265 cm-' to 129 cm- ' in comparison with the former and from 176 crn-' to 40 cm-' in comparison with the latter. If we apply logansen's equation to estimate approximate energy changes using the Av values the strength of the proton-hydride bond can be from 5 to 3 kcaUmol with respect to the v(NH) of free ligand and 4 to 1 kcal/mol with respect to the V(NH~)of complex 12. However. these values are not reliable because a proper reference compound is not yet available (i.e. an Ir(I1I) SpyH complex without a SpyH hydrogen bond is needed to obtain more reliable Av values). Nevertheless. this result indicates that proton-hydride bonds are stronger in complexes with PCy3 than with PPh3 donor ligands although the complexes under comparison are slightly different. Figure 4.12 shows the relative strength of proton-hydride bonds and N-H covalent bonds on an IR scale in comparison with those between the two extreme cases (pyridinethione dimer and dilute HSpy). It shows that the N-Hm.-H-Irproton-hydride bonds in PCy3 and PPh3 complexes are attractive. The proton-hydride bonds in PCy3 complexes are slightly stronger than those in PPh3 complexes. but weaker than the conventional N-H-.-S hydrogen bond in the pyridinethione dimer.
References page I35 Chapter 4
Table 4.10. Proton NMR, Tl(min) and IR bands for IrH and NH protons."qb NMR d(Ir+-N ) complex Tl(rnin)(IrH) Tl(min) (NH) d(~-H)IA' 1 0.17 0.!8 1.7k.05 3.49( 1 ) 3.5% 1 )
Infrared compound v(~r~)/cm-' v(~~)lcrn*' Av/(crn-' )' Av/(crn-' )f d( Ir-.N ) HSpyg - 3376h - - - 1 2137, 2120 31 11 265 176 3.49( 1 ) 3 184 192 103 3.53 1 ) 5 2 193 3 124 252 163 3.50( 1 ) 3.53 1 ) 9 22 14 3236 140 5 1 3.61i 1) 10 2063, 2197 3225 151 62 3.72( 1)
"Proton NMR and T,(rnin) (s) measured in CD2Clz at 400 MHz. b~~ spectra measured in Nujol using KBr unless otherwise stated. CH--Hdistances are the estimations discussed earlier in the thesis. d~aluesare for the hydride not associated with the proton-hydride bond. '~aluesfrom v(NH) of free HSpy. f~aluesfrom V(NH~)in 12. g~ilutesolution of HSpy in CC14, regarded as non-hydrogen bonding species.10 h~eferenceto obtain Av values in e. 1Reference to obtain AV values in f.
References page 135 pyridinethione dimer dilute HSpy
/ I I 1,s 9, 10, 12 I /' - * I i
2900 cm-' 3400 cm"
N-H bond weaker - stronger
hydrogen bond stronger weaker
Figure 4.12. Comparison of the NH stretching frequencies of coordinated and free spy~.''
4.3. Conclusion
The trihydride IrHj(PPh3)3 reacts with HBF4 in the presence of SpyH to afford [IrHz(q ~-S~~H)(PP~~)~](BF~)10. 10 undergoes a substitution reaction of a PPhj by SpyH to produce [IrH?(q 1-SpyH)2(PR3)2](BF4)11 (R = Ph) which is the triphenylphosphine analog to 1 (R = Cy). 11 slowly eliminates a dihydrogen molecule to form [IrH(q 1- SpyH)(q*-~py)(~~h~)~](~~~)9under mild conditions. [IrH(CO)(ql-
SpyH)~(PPh3)z](BFj)212 is obtained from IrH3(CO)(PPh3)2with HBF4 in the presence of SpyH. The PPh3 complexes 9 - 12 contain the proton-hydride bonding units in the solid state. The NHa..HIrdistances in these complexes are ca. 2.0 - 2.1 A by X-ray diffraction and 1.7 - 1.8 A by 'H NMR. Six SpyH complexes containing either PCy3 (1, 5) or PPh3 (9 - 12) are studied by single crystal X-ray analyses. Stronger proton-hydride bonds are formed in complexes with PCy3 co-donor ligands in comparison with complexes with PPh3 co-donor ligands. The strength of proton-hydride bonds is decreased in complexes containing more PPh3 or CO
References page 135 Chapter 4 131
ligands. The best indicators of HS.+Hbond strength are AV values from IR and the N"3r distance from the X-ray structures.
4.3. Experimental
General experiment All preparations were carried out under an atmosphere of dry argon using conventional Sc hlenk techniques. All the solvents were distilled under argon over appropriate drying agents prior to use. Tetrahydrofuran (THF)and diethyl ether (EtzO) were dried over and distilled from sodium benzophenone ketyl. Methanol was dried over sodium methoxide. Dichloromethane and chloroform were distilled from calcium hydride. Deuterated solvents were dried over Linde type 4 A molecular sieves and degassed prior to use. Distilled water was degassed prior to use. Triphenylphosphine. pyridine-z-thione. sodium hydroxide and an 85% solution of HBF4.EtzO complex were purchased from Aldrich Chemical Company Inc. Iridium trichloride hydrate was obtained from Johnson-Matthey Co. Sodium ethoxide was generated in the reaction of sodium metal with water-free ethanol under argon and dried to white powder before use. NMR spectra were obtained on a Unity-400, operating at 400.00 MHz for IH.
16 1-98 MHz for 31~,or on a Gemini-300 operating at 300.00 MHz for 1H. 12 1.45 MHz for
3lP. All 3lP NMR spectra were obtained with proton decoupling unless otherwise stated.
31~NMR chemical shifts were measured relative to H3P04 as internal reference. IH NMR chemical shifts were measured relative to deuterated solvent peaks or tetramethylsilane. Variable temperature TImeasurements were made at 400 MHz using the inversion recovery method. Microanalysis was performed by Guelph Chemical Laboratories Ltd.. Ontario. Crystallographic Structural Determination Complexes 10. 11 and 12 were crystallized by the slow evaporation of a chloroform solution at room temperature. A single crystal for 10. 11 and 12 suitable for X-ray analysis was mounted with epoxy glue and analyzed at 173 K (lo),213 K (11) and 296 K (12). The crystalline system for 10 was
Refererlces page 135 Chapter 4 132 found to be monoclinic with space group P2 ~lm.The unit cell dimensions of the crystal are a = 10.570(2) A, b = 22.964(5) A with P = 102.199(12)0. and c = 12.75 l(2) A. The crystal for 11 belongs to monoclinic space group C2lc with unit cell a = 37.528(4) A,b = l5.280(2) A with p = 1 25.046(7)0, and c = 23.387(3) 8.. Intensity data for 10 and 11 were collected on a Siemens P4 diffractometer, using graphite monochromated M,, K, radiation ()c = 0.7 1073 A). The o scan technique was applied with variable scan speeds. Intensities of 3 standards measured for each compound every 97 reflections showed no decay. Data were corrected for Lorentz, and polarization effects and for absorption. The [r atom position in the structure of 10 and 11 was solved by the Patterson method and other non-hydrogen atoms were located by successive difference Fourier syntheses. Non-hydrogen atoms were refined anisotropically by full-matrix least-squares on F'. Hydrogen atoms were positioned on geometric grounds (C-H 0.96 A). All calculations were done and diagrams created using SHELXTL PC on a Pentiurn-75 personal computer.
The crystal for 12 belongs to monoclinic space group P2 1lc with unit cell (1 = 18.5325(1) A. b = 15.3441(2) A with P = 94.221( 1)O, and c = 18.4464(2) A. The structure was solved by direct methods, completed by subsequent Fourier synthesis. and refined by full-matrix least-squares procedures. The two sounterions. and chloroform solvent molecule were located. All boron-fluorine interatomic separations were restrained to be equal. All other non-hydrogen atoms were refined with anisotropic displacement coefficients. Hydrogen atoms were treated as idealized contributions. Crystal data, data collection, and least squares parameters are listed in Table 4.2 and selected bond distances and angles are in Table 4.3. Views of cations of complexes 10. 11 and 12 including the crystallographic labeling scheme are shown in Figures 4.5.4.6 and 4.8. respectively. Preparation of [IrH2(q 1-SpyH)(PPh3)3](BFa) (10) Method 1: reaction of Jac-IrH3(PPh3)3 with HSpy and HBF4: fac-IrH3(PPh3)3 (1 g, 1.0 mmol) and HSpy (113 mg, 1.0 mrnol) were suspended in CHCl3 ( 15 mL) in a Schlenk flask under argon. To this
References page 135 was added excess HBF4 (500 yL in ether solution). The solution became clear yellow in a few min. After 10 min the clear solution was filtered through Celite. The solvent was then removed in vaciio. The resulting residue was washed with ether several times ( 10 rnL x 3) to give a bright ye!low powder. This was further dried in LVZCMO. Yield: I. 1 g, 9 1 %.
Method 2: reaction of IrH3(PPh3)3 @zc- and mer- mixture) with HSpy and HBF4:
A mixture of fac- and mer- IrHj(PPh3)3 ( 1 g. 1.0 mmol) and HSpy ( 1 13 mg, 1 .O mmol) were suspended in CH2C12 (15 mL) under argon. To this was added excess HBFj (500 pL in ether solution). The work up was similar to that of Method I with similar yield: Analysis.
Calc. for C5gH52BF41rNP3S-CHC13.: C. 55.5; H. 4.12; N. 1.08. Found: C. 55.72: H.
4.35; N, 1 .O6. NMR (CDC13.6). 31~(IH}: 2.23 (d, J = 15.2 Hz). -0.93 (t. J = 15.6 Hz);
1 H: - 12.7 (dtd. Jlp~= 1 16 HZ. Jcp~= 22 Hz. JHH = 3.6 Hz. 1 H. Ir-H). - 15.75 (qd. JHH = 3.6. IH. Ir-H). 6.4 - 7.8 {m. 49H. overlapping P(C&)3 with SC5H4NHf). 10.9 (br s. 1 H. (SC5H4NH+)}. IR (KBr pellet): v(Ir-H) 2063.2 197 cm-1: v(NH); 3225 cm-1.
Formation of [1rH2(q l-SpyH)2(~Ph3)2](BF4)(11) [IrHr(q 1-s py~) (PPh3)3](BFd)10 (100 mg, 0.085 mmol) and HSpy (53 mg. 0.477 mmol) dissolved in CHC13 (6 mL)were added to a Schlenk flask fitted with a magnetic stirring bar under argon. This was stirred for over a week at room temperature. The solution was monitored by
31~{1~}NMR. There was a major species with a resonance at 9.4 ppm (s) and a minor species at -9.97 ppm (s) in addition to unreacted 10. The solution was further stirred for a second week and checked by 31P(1~}NMR; no more unreacted 10 was observed. All the volatiles were then removed in vacuo. To the residue was added ether ( 10 rnL) to wash out excess HSpy and to give a light yellow powdery solid. Three species were observed by 31~{lH}NMR: the major species was [IrH2(~1-SpyH)2(PPh3)r](~~4)11 and the minor species are rruns-[IrH(q l -SpyH)($-~py)(PPh~)~J(BF4) 9' and cis-[IrH(q 1 -spy~)($-
Spy)(PPh3)2](BF4)9. The intensities of the minor resonances grow over time as the intensity of the resonances for the major species decreases. The final spectrum is consistent with that for cis-[IrH(q 1-SpyH)(q2-Spy)(~Ph3)2](BF4)9 (Chapter 3). Selected proton
References page 135 Chapter J 134
NMR resonances (6): NH: 1 1.74 (br s., 11): 1 I .9 1 (br s. 9'); 1 1.86 (br s. 9). IrH: - 16.10
(t, J~H= 15.3 HZ, 11); -16.68 (t, J~H= 12.21 HZ, 9'); -17.78 (dd, J~H= 14.3 HZ, 9). Preparation of crude I~H~(CO)(PP~J)~.I~HcI~(PP~~)~ ' (500 rng, 0.476 mmol) was suspended in THF (25 mL) in a Schlenk flask fitted with a stirring bar under dihydrogen gas. To this was added ground sodium hydroxide (1 g. 0.025 mol). The suspension was stirred for about 20 h at room temperature followed by evaporation of the solvent. To the residue was added degassed water (ca. 20 mL). This was stirred for 10 rnin before filtration. The wet residue was stirred in methanol (ca. 20 mL) for 10 min. This was followed by a vacuum filtration and drying to obtain a pale grey yellow powder. This was washed with ether (2x10 mL) and dried in vaciio. Yield: 280 mg. 78 % based on
I~H~(co)(PP~~)~.'NMR (CDCI3. 6) for the major species. 31P { H } : 16.29 (s): H: - 10.10
(td. J~H= 16.62 Hz. JHH = 4.6 Hz. 2H. Ir-H). -10.55 (tt, J~H= 19.2 Hz. JHH= 4.2 Hz.
IH, Ir-H), 6.4 - 7.9 (m, 30H. P(C&)2) IR (KBr. Nujol): v(C0). 2077 crn-1 (s). Selected NMR (CDCl3. 6) for the minor species. 31P{ IH}:8.25 (s): IH: - 15.4 (t). Crystallization of [IrH(CO)(q 1-S P~H)~(PP~~)~](BF~)~(12). In a
Schlenk flask crude IrH3(CO)(PPh3)2 (50 mg, 0.07 mmol) and HSpy ( 18 mg. 0.16 mol) were dissolved in CHC13 (2 mL). To this was added an excess of HBF4 etherate and allowed to react for 10 rnin during which time gas evolution occurred and the solution became clear yellow. This was left for slow evaporation at room temperature in air for about a week resulting in some orange-yellow crystals deposited among a yellow powdery solid. The crystals were collected and used for X-ray analysis and infrared studies. IR (KBr. Nujol): v(C0). 2044 cm-I (s): v(IrH), 2180,2216 cm-1 (m):v(NH). 3247 (w. br), 3287 cm-1 (w).
References page 135 Chuptr r 4
4.4. References
Xu. W.; Lough. A. J.; Morris. R. H. Inorg. Chcm., 1995. 35. 1549.
Lough. A. J.: Park, S. H.; Ramachandran, R.; Morris. R. H. J. Am. Clzrrn. Soc.. 1994, 116, 8356.
Park. S. H.: Ramachandran. R.; Lough, A. J.: Morris. R. H. J. Cllcm. Soc.. Clrem. Corrrtnrrn., 1994, 220 1.
Lee. I. C.; Rheingold. A. L.; Peris. E.: Crabtree. R. H. J. Am. Clzern. Soc.. 1994. 116, 11014. Park. S. H.: Lough. A. J.: Morris. R. H. Iizorg. Clzerlr.. 1996. 35. 3001.
Chatt, J.: Coffey. R. S.: Shaw, B. L. J. Clzern. Soc., 1965. 739 1. Desrosiers. P. J.: Cai, L.: Lin. Z.: Richards. R.: Halpern, J. J. Arn. Clrem. Soc.. 1991, 113. 4173.
Ahmad. N.: Levinson. J. J.: Robinson. S. D.; Uttley. M. F. Inorg. Sprth.. 1974. 15, 45.
Harrod. I. F.; Yorke. W. J. Inorg. Chern.. 1981.20, 1156. Mura. P.: Olby. B. G.: Robinson. S. D. I. Clieni. Soc.. Dalton Trcrrzs, 1985. 2101. Iogansen. A. V. Hydrogen Bond: Nauka. Moscow. 1981. p 13.
Ohms. U.: Guth. H.: Kutoglu. A.: Scheringer. C. Acrcl Cysr.. 1982. B38. 83 1. Brinkmann. S.: Morris, R. H.: Ramachandran. R.: Park. S. H. bzurg. Syrith..
References page 135 Chapter 5 136
Chapter 5. Intramolecular NH-CIIr Hydrogen Bonding Interactions of the SpyH Ligand. Molecular Structures of IrC12(~\1-S C5H4~EI)($- S CgIiqN)(PCy3)*2CH2C12 and [IrCliq 1-SCgHqNH)2(q2- SC5H4N)(PCy3)](BF4)*CHC13*C7Ha
5.1. Introduction
Pyridine derivatives. particularly 2-hydroxypyridine and 3-mercaptopyridine are very versatile ligands in coordination chemistry. ' In comparison to 2-hydroxy pyridine. the chemistry of hnercaptopyridine is more diverse probably due to its possession of both hard (N) and soft (S) donor sites which can coordinate to hard or soft metal centres. Various bonding modes for 2-mercaptopyridine have been found in the literat~re~-~(see Chaper I ). In the formation of hydrogen bonded species, these two pyridine derivatives play very irnportan t roles. but frequently in different ways. Unlike Zhydroxypyridine ( py OH). which often coordinates via nitrogen and acts as a hydrogen bond donor via the OH unit. 2- mercaptopyridine coordinates vhsulfur as in a pyridinethione tautomeric form (SpyH) and donates its polar NH unit for hydrogen bonding. The goal of the current research is the synthesis of trans-hydridochloro complexes containing the SpyH ligand in order to study the competition of the chloro and hydrido ligands for the hydrogen bond donor group of the SpyH ligand (Figure 5.1 ). Type (11) (L = PPh3, X = CI. Br. I) is an example that exists as two isomers involving an IrX--HOpy conventional hydrogen bond and an IrK-HOpy proton-hydride bond in competition with each other. lo
References page 159 Chupter 5
Figure 5.1. Competition between hydride and chloride ligands in the formation of an intramolecular hydrogen bond.
5.2. Results and discussion
5.2.1. Synthesis of Ir&Ci(q l-SpyH)(P~y~)~(13)
IrHg(PCy3)2 was reacted with an approximately 3 fold excess of HSC jH4N and an excess of concentrated HCl in dichloromethane. The reaction occurred within 2 rnin to give a yellow solution (Equation 5.1). Immediate removal of the solvent under vacuum precipitated a yellow powder containing one SpyH ligand per iridium. This has been assigned to be the cis-dihydrido species 13 as a single isomer on the basis of the spectroscopic results.
CH2C12,2 min -ZH2
References page 159 5.2.2. Characterization of IrHzCl(q I-Spy~)(~~y3)Z(13)
The structure of the product is proposed first on the basis of the distinctive chemical shifts for the NH proton and hydrides. The broad singlet for the NH proton in :he IH NMR spectrum in CDCI3 appears downfield at 15.0 ppm, indicating that this proton participates in a hydrogen bonding interaction with the coordinated chlorine atom. Similar observations have also been reported in some hydroxy- or amino-pyridine iridium comple~es.~~and in some mercaptopyridine tungsten complexes.6 It also contains two triplets of doublets at
- 18.38 ppm and -26.89 ppm which arise from two magnetically non-equivalent hydrides cis to two tricyclohexylphosphine ligands. The high-field chemical shift at -26.89 ppm is
probably due to the hydride trans to the chlorine ligand. These resonances for the NH proton and the hydrides remain unchanged in the temperature range of 353 K to 193 K in toluene- 4%
Figure 5.2. Unobserved isomers of 13 containing a proton hydride bond.
There is no evidence for the formation of complexes of the type 13a or 13b with an NH-HIr interaction (Figure 5.2). The Tl(min) of the NH proton at 253 K (400 MHz) is 0.326 s in CDC13. considerably longer than those for the hydride resonances at - 18.38 ppm (0.242 s) and -26.89 ppm (0.230 s), suggesting that the NH proton in 13 does not participate in a proton-hydride interaction. An NOE study of 13 in CDCI3 at 293 K also eliminates structures 13a and 13b. After selective irradiation at the hydride resonances at
Refererzces page 159 Chapter 5 139
-18.38 ppm or -26.89 ppm, no significant enhancement at the NH resonance is produced. although there is a 4.2 8 enhancement of the cis-hydride resonance. Elemental analysis supports the formulation of 13. The FAB mass spectrum indicates that 13 readily loses a C1- ligand under FAB coditions. 13 reacts readily with MeOD or D1 gas in CD2C12, CDCI3, or toluene-d8 at 293 K. When 13 is exposed to D2 gas for 2 minutes. the NH resonance decreases in intensity by cu.
90 % while the two hydride resonances of two triplets of doublets become two triplets at the
same shifts. These are only ca. 11 % of the intensity of the original hydride resonance and are probably due to two isotopomers (13-d2, 13'-d2) containing a hydride and a deuterium
cis to each other (Figure 5.3). The yield of the trideuterium isotopomer IrD?Cl(q I-
SpyD)(PCy3)? 13-d~is about 68 % after approximately 30 rnin in CDC13 ('H NMR. internal [SiMe20In reference).
Figure 5.3. Isotopomers of 13 formed in the reaction of 13 with D2 gas.
The isotope shift in the 31P{ H} NMR spectrum from 13 to 1343 is ccl. 0.16 ppm in CDCI3 (from 2 1.14 (s) ppm to 2 1.30 (s) ppm). No further changes in the above chemical
shifts in the 'H and 31~{IH} NMR spectra are observed over two days. A feasible mechanism for the deuteration of 13 involves the dihydrogen intermediate species which may be formed from the unobserved isomer 13a with a proton-hydride bond. The intermediate dihydrogen species should react with D2 gas to give a dideuterium species and finally complex 13-dl (Scheme 5.1). Attempts to inhibit the HID exchanging process in the reaction of 13 with D2 gas in CDCI3 at 293 K by addition of an H-bond acceptor have been
References puge 159 Chapter 5 140 made. However. the addition of an excess triphenylphosphineoxide has no significant effect on the rate of H/D exchange. The NH stretching frequency is informative. In the solid state IR spectrum. a broad band at 3 165 cm-I was observed. This gives Av of 21 1 crn-' in comparison with v(NH) of free HSpy (Table 5.1). This conventional hydrogen bond in 13 is very similar in strength to the proton-hydride bond in 1despite of the fact that the former is not disrupted by an external hydrogen bond acceptor while the latter is.
Scheme 5.1. Proposed mechanism for the deuteration process of 13 with dideuterium.
Since the N-H hydrogen bonds to the chlorine instead of the hydride in 13. a substitution of the chloride by another proton donor ligand would be worthwhile in order to observe species with an IrH..-HN interaction. Thus the reaction of 13 with HSpy/NaBF4 in
CHCl3/MeOH at room temperature leads to the liberation of the chlorine ligand and the formation of 1 with two IrH-HN units. There is also a minority (less than 10 %) of the
References page I59 Chapter 5 141 dihydride species 2 (Equation 5.2). Presumably the formation of 2 results from the hydrogen bonding type (b) in Scheme 5.1, involving the NH unit of the coordinated SpyH in 1 and the Cl- anion. Elimination of HCI would produce 2. A similar explanation accounts for the reaction of 5 with iriethyiarnine to form 6 (Chapter 2).
HSpy / NaBF, 13 1 + I~(H)~($-SPY)(PC~,),2 MeOH / CHC13 Major Minor
Table 5.1 Selected NMR and IR resultsa for 13, 14 and 15. Complex IH NMR ~IP{~H} IrH -18.38 (td, J~H= 21.13 (s) 3 165 (w) 16, JHH = 6.7) Tl(rnin): 242 ms -26.89 (td, J~H= 15.2, JHH = 6.4) TI(min): 230 rns 15.8 (br) -25.68 - 1 1.65 (s) Tl(min): 185 ms (t. JPH = 13.5) T 1 (rnin): 228 ms 13.6 (br) -20.9 - 10.26 (s) 3157 (w) TI(rnin): 289 ms (t, JPH = 11.8) Tl(min): 192 rns 15.1 (br) -25.0 (s) 3171 (w) aNMR in CDC13 (300 MHz) or otherwise stated; chemical shift in ppm. coupling constant in Hz, Tl(min) measured in CD2Clz at 253 K (400 Mz). b~~ in NujoVKBr. v in cm-', Av values obtained from subtraction of 3376 cm'l for v(NH) of free HSpy. CNMR in CDzClz (300 Mz). d14b obtained from trar1s-IrHC12(PCy3)2.
References page 159 5.2.3. Synthesis and characterization of IrHC12(ql-SpyH)(~~y~)~(14)
Reaction of the dihydride I~(H)~(I$S~~)(PC~~)~2 with concentrated HCI in
CH2CI2 for 2 h at 293 K gave a light orange solution containing a bright yellow precipitate.
The product was isolated in 83 % yield and identified to be ~r~Cl~(ql-~pyH)(PCy~)~14a. This complex could also be formed from the reaction of IrHs(PCy3)z with HSpy and concentrated HCl in CHrC12 for 20 minutes at 293 K. The product. in this case. appeared to be a mixture of 14a and 13 which could not be fully separated by fractional crystallization.
The 3l~{lH)NMR spectrum of 14a in CDC13 contains a singlet at -1 1.65 ppm due to two ircms PCy3 groups. The proton NMR spectrum of 14a in CDCI3 contains an NH resonance as a broad singlet at 15.8 pprn and a hydride resonance as a triplet at -25.68 ppm. 14a slowly but incompletely isomerizes in CDC13 at 293 K to the trans isomer 14b (Equation 5.4) which shows a broad singlet at 13.6 pprn (2.2 pprn upfield from the corresponding resonance for 14a) for the NH proton and a triplet at -20.9 ppm (4.78 pprn downfield from that of 14a) for the hydride. The 31P{ IH} NMR spectrum of 14b contains a singlet at - 10.26 pprn which is 1.39 pprn downfield from the corresponding resonance for 14a.
References puge 159 Chapter 5 143
PCY3
RT 1 . \ #,, 1 ,\'* ,a
The structure of 14a is proposed based on NMR observations and contains the N-
H-CI-Ir interaction. The Tl(min) values (400 MHz) of 0.185 s for the NH proton and 0.228 s for the hydride in 14a (253 K) are quite different. The same is true for the isomer 14b except for the fact that in 14b the Tl(min) (0.289 s) for the NH resonance is much larger than that for the IrH resonance (0.192 s). The possibility of the product being 14c with the H-H interaction as the other isomer of 14a has been ruled out for this reason. Neither of the two NH resonances in the isomeric mixture has shown a significant enhancement in an NOE experiment when either hydride is selectively irradiated in CDlCI? at room temperature.
Figure 5.4. Unobserved isomer 14c.
An alternative approach to 14b involves the reaction of tmns-IrHCIz(PCy3)? with HSpy (Equation 5.5) to produce a bright yellow solution containing 14b in less than a min in
CHC13 (IH and 3lP NMR). The same result from the reaction in THF probably indicates that an internal IrCl--HN hydrogen bond is preferred over an external O(~R".HNhydrogen bond. The NH stretching frequency of 3 157 cm-' with Av of 2 19 cm-I relative to v(NH) of free HSpy has been found in 14b (Table 5.1).
References page 159 The isomeric mixture 14a/14b reacts with HC1 in CHCl3/MeOH to produce Kl2(ql-~py~)(q2-Spy)(PCy~)15 and an unidentified species containing neither hydrides nor NH protons (1 H NMR) when left standing for approximately two weeks. Complex 15 is an air stable. orange solid crystallized from the above solution. It has been characterized by X-ray diffraction. microanalysis and FAB MS (m/z = 746 (MI, 728 [M-Cl]) as well as IR and NMR studies. The presence of an NH stretch at 3 17 1 cm-I in the IR spectrum (Nujol) of 15 is evidence for existence of an IrCIb%N hydrogen bond in comparison with the reference of the non-hydrogen bonded v(NH) of 3376 cm-I. The Av of 205 cm-' indicates all mono- or di-chloro complexes 13. 14 and 15 contain similar 1rClu.HN conventional hydrogen bonds (Table 5.1). A broad downfield peak at 15.1 ppm for the NH proton in the IH NMR spectrum of 15 in CDC13 is observed probably also due to this hydrogen bond. 5.2.5. Formation of [IrCl(q l-SpyH)2(q2-Spy)(PCy3)1(BF4)(16)
The monochloro complex 16 (X = CI) in the title is analogolis to 5. [IrX(q - s~~H)~(~~-S~~)(PC~~)](BF~),(X = H). In Chapter 2. the complexes 1 and 5 were prepared directly from the reaction of iridium pentahydride with thiopyridinium in a chlorinated solvent. 16 has been produced as a decomposition product of 5 in a chlorinated solvent after a long period of time. It was formed as crystalline materials from the following work-up. Iridium pentahydride was treated with rnercaptopyridine at elevated temperature in chloroform to allow the dihydride 2 to form. This was reacted in sin( with tetrafluoroboric acid. then the reaction mixture was layered with toluene. After over a month. some orange crystals formed. This material was a mixture of species including the monochloro pyridinium complex 16 which was characterized by single crystal X-ray analysis.
5.2.6. X-ray structure analyses of 15 and 16
15 is a neutral octahedral complex with an iridium centre surrounded by a PCy3 group cis to a sulfur-bonded thiopyridinium (SpyH), trms to nitrogen of a chelate pyridinethiolate ligand. and cis to two chloride ligilnds (Figure 5.5). The nitrogen atom of the monodentate SpyH ring in this geometry faces the cis chloride ligand (Cl(2)}. The H-
N(2) distance is 0.84(7) A and the He.-Cl(2)distance is 2.15(7) A. The SpyH ligand is oriented to maximize the H-bonding interaction of the N-He--CI-Irunit.
Referemes page 159 Figure 5.5. ORTEP diagram for lrClz(qI-SpyH)(qZ-spy)(~Cy~)15 at 173 K.
References page 159 Cationic complex 16 has an iridium(II1) centre in a distorted octahedral geometry occupied by a PCy3 ligand. a chloride ligand, two monodentate SpyH ligands, and an S-N chelate Spy ligand (Figure 5.6). Thc two monodentate SpyH ligands are effectively zwitterionic but also have a neutral thione resonance form. The atoms S(2), Ir and the atoms of the SpyH group containing S(3) are in a plane with a mean deviation of 0.013 1 A. The second SpyH ring attached to S(2) is out of this plane and bent down from the PCy3 group
(see below). The hydrogens bound to the nitrogens of the SpyH ligands are located in a difference electron density map at 0.86(4) A from the nitrogens. Both NH units of the dangling SpyH ligands are arranged to face the cis-chloride ligand in a N-H-Cl(1r)-H-N hydrogen bonding network. The hydrogen bonding distances for the two NH-CI units are 3. W(2) A for N(25)Cl and 3.045(2) A for N(35)-Cl. The former hydrogen bond may not be linear because the N-H group is not pointing directly at the C1 ligand. These are similar to the distance of 3.052(5) A for the bischloro complex 15 and to those of other
SpyH complexes. Sn(Me)lClz(SpyH)?{3.199(9) A } .J CuCI(SpyH)(PPh3 ). {3.079(7)~}5 and { RhCI(Spy)(SpyH)(CO)} 2 (3.003 A)3 (Table 5.4). The N-CI distances in 16 is also comparable to the N-CI distance of 3.105(4) A for the hydrogen bond between a chloride anion and the NH protons of the two traus-SpyH groups7 in [Rh(pyS)2(HpyS)2]CI,or 3.159. 3.177 A for an intermolecular case2 in C~(spyH)~Cl~.
References page 159 Chapter 5
Figure 5.6. ORTEP diagram for the cation of [IrCl(q -s~~H)~($-spy)(pcy3)] (BF~)16.
References page 159 Ciruprer 5 149
Table 5.2. Summary of Crystal Data. Details of Intensity Collection. and Least-Squares Refinement Parameters for com~lexes15 and 16. Complex 15 16 empirical formula C30H4&16IrN2PS2 CJ I H~~BCI~F&NJPS~ crystal size 0.32 x 0.25 x 0.19 0.20 x 0.10 x 0.10 Formula weight 934.68 1141.87 Crystal class Triclinic Monoclinic Space group P-1 P2 1 /c a. A 10.091(1) 14.4588( 1 ) h. A 11.447(1) 21.7141(2) c, 8, l6.76O( 1 ) l6.4989(2) y, degree 78 .O5( 1) 90 p, degree 80.80( 1 ), 108.175(1) a,degree 8 1 ,O7( 1) 90 v,A3 l854.6(3) 492 1.55(8) z 2 4 Dcalc,mg m-3 1.674 1.54 I p(M,,Kd. mm- 4.212 3.137 F(000) 932 2300 T, K l73(2) 298(2) Reflections colIected 7550 20074 Independent reflections 71 16 6427 Refinement method Full-matrix least- Full-matnx least- squares on F2 squares on F2 Data / restraints / parameters 6377 / 22 / 457 Goodness-of-fit on F2 1.053 R1 [I> 2a(O] 0.0398 ivR2 (all data) 3.0978 Largest diff. peak and hole ,722 & -.642 e~-3
Refererzccls page 159 Chapter 5 150
Table 5.3. Comparison of bonding distances and angles for 15 and 16.
Distance tih Comalex 15 Comalex 16
Ira"
Ir-S( L ) Ir-P Ir-N [r-S (2)
Ir-S (3) CI"*.-N CIa.--H N-H
Angles (deg)
N-Ir-P 172.5( 1 ) 169.4( 1 )
Cl%-S( 1 ) 160.22(4) 160.53(6)
"Cl(2) in complex 15 and C1( 1 ) in complex 16. b~ngleS(2)-Ir-Cl? .Angle S(2)-Ir-CI.
Similar interatomic distances around the hydrogen bonding units are found in 15 and 16. Selected bonding distances are compared in Table 5.3. No significant differences around coordinated atoms and Spy(H) rings are found with the exception that the iridium- ligand distances in 16 are slightly longer than those in 15. Figure 5.7 shows the IrPClSN planes of 15 and 16 and the angles that the SpyH rings make with the Cl to which they are hydrogen-bonded. Clearly ring (B) which is attached to S(2) has a wide angle of 50.60 compared to ring (A) in 15 and 16.
References page I59 15 16 Figure 5.7. Side view of 15 and 16 through S(2) to Ir to CI(1) or S(3).
In order to examine the arrangement of the hydrogen bonding rings. equatorial axes are viewed from the top (Figure 5.8). The S(1)-Ir-S(2) angle in 15 is 82.30(4)" which is identical to that in unit (A) of 16 {82.83(6)0}. These angles are much smaller than
10 1.39(4)O and 100.3 1 (6)O for Cl(2)-Ir-S(2) and Cl( 1 )-Ir-S(3) in 15 and 16. respectively. The large angles in 15 and 16 are a result of a distortion of the coordinated sulfur atom of the SpyH ligand from the idealized equatorial plane. presumably caused by the formation of NH-Cl hydrogen bonding.
Figure 5.8. Comparison of the coordination angles (O) in the equatorial plane.
As the two Ir-S-C angles in the SpyH ligands in 16 differ to some degree, the angles of the M-S-C units of other analogs that might be related in hydrogen bonding strength are compared in Table 5.4. No precise correlations between angles and the N-Cl bond lengths are found. although the distance appears to be related to other inner angles of the hydrogen- bonding heterocycle. If. for example. the sum of three reliable angles labeled as A, B. and
References page I59 Chapter 5 152
C (Table 5.5) is 340 to 3440 then the ring has a shorter N-meCl distance (stronger hydrogen bonding), while if below 3400 the N-CI distance is longer (weaker hydrogen bonding). The most appropriate value for the sum of the three angles for the shortest N-Cl distance appears to be 340° among given examples.
Table 5.4. Comparison of M-S-C bend angles and Cl-.-Ndistances involving SpyH lipand. Complexes Angles (deb) d(C1-N) (A) References Sn(Me)2C12(SpyH)2 105.1(3) 3.199(9) 4
CuCI(SpyH)(PPh3)2 1 12.8(3) 3.079(7) 5
Co(SpyH)2C1~" 106.5( 1 ), 107.0(1 ) 3.159, 3.177 2
[Rh(Spy)2(~py~)2]~lb 1 14.4(4), 1 14.0(4) 3.156, 3.105 7
t RhCKSpy)(SpyHNCO)12 3.003 3 15 117.8(2) 3.052(5) this work
16 114.7(2), 119.2(2) 3.137, 3.045 this work aIntermolecularCI-.-HN interactions. bhtermolecular C1--HN interaction with the counterion (Cl-1.
Table 5.5. Comparison of angles and N-•Cl distances involving H-bondines. complex A (deg) B (deg) C (deg) A+B+C (deg) d(N-CI) A
Cu" 109.2(1) 1 12.8(3) 122.2(6) 344.2 3.079 I
/ 16 (Unit A) 100.3 l(6) 1 19.2(2) 120.7(2) 340.2 1 3.045 1 (Unit B) 90.58(6) 1 14.7(2) 1 19.5(3) 324.78 3.137 I "Obtained from ref. 5 for CuCl(SpyH)(PPh3)?. bobtained from ref. 4 for
Referertces page 159 Another possible contribution to the distortion of unit B in 16 is an involvement of the BF4 anion in hydrogen bonding, as IrSpyH---FBF3units. seen in other SpyH complexes of I~(III).~The BF4 anion in 16 is indeed in close proximity to unit B. but away from the chloride ligand. This arrangement eliminates the possibility of an H-bonding network of the type NH-.F(BF3)-H'N', which is seen in the crystal structure of a 2-thiazolidinethione complex of Ir(II1).
5.3. Conclusions
Reaction of IrH~(Pcy3)zwith HSpy/HCl or I~(H)~(T$s~~)(Pc~~)~2 with HCl gives cis-IrH?Cl(q 1-SpyH)(PCy3).r13 or IrHClz(q l-SpyH)(~Cy~)~14 depending on the conditions. Both 13 and 14 possess an NH-ClIr hydrogen bonding unit in solution. IrClz(q I-SpyH)(q2-Spy)(PCy3)IS or [IrCl(q l-SpyH)z(q*-~py)(~Cy3)](~~4)16 obtained from the reactions of 2 with HSpylHCl or IrHs(PCy3). with HSpyaHBF4 in CHCl3. respectively, contain the NH-ClIr interaction unit or a novel N-Ha-Cl(1r)-43-N hydrogen bonded network in the solid state. The Ha-CI distances are 2.1 - 2.4 A. Ir-Cl-*H-N bonds are perferred over Ir-He--H-Nbonds.
References page 159 5.4. Experimental
General Experiment. All preparations were carried out under an atmosphere of dry argon using conventional Schlenk techniques. All !he solvents were distilled under argon over appropriate drying agents prior to use. Methanol (MeOH) was dried over magnesium methoxide. Benzene. diethyl ether (EtzO), and n-hexanes were dried over and distilled from sodium benzophenone ketyl. Dichloromethane and chloroform were distilled from calcium hydride. Toluene was distilled over sodium metal. Deuterated solvents were dried over Linde type 4 A molecular sieves and degassed prior to use. Tricyclohexylphosphine (PCy3) and an 85% solution of HBF46Et20 complex were purchased from Aldrich Chemical Company Inc. Iridium trichloride hydrate was obtained from Johnson-Matthey Co.
IrHg(PCy3)?was made from IrCI3.xH20 according to the literature procedure. '3 NMR spectra were obtained on a Unity-400. operating at 400.00 MHz for IH.
16 1.98 MHz for 3 P. or on a Gemini-300 operating at 300.00 MHz for H. 12 1.45 MHz for
31~.All 31~NMR spectra were obtained with proton decoupling. 31~NMR chemical shifts were measured relative to H3P04 as an internal reference. IH NMR chemical shifts were measured relative to deuterated solvent peaks or tetramethylsilane. Variable temperature TI measurements were made at 400 MHz using the inversion recovery method. Fast atom bombardment mass spectrometry (FAB MS) was carried out with a VG 70-250s instrument using a 3-nitrobenzylalcohol (NBA) matrix. All FAB MS samples were dissolved in acetone and placed in the matrix under a blanket of nitrogen. Microanalyses were performed by Guelph Chemical Laboratories Ltd.. Ontario. Crystallographic: Structural Determination. The chloro complexes 15 and 16 were crystallized by slow evaporation of MeOWCHCl3 and CHC13/toluene. respectively. The crystal structure of 15.2CH2C12 was deduced from an X-ray diffraction study at 173 K.
The neutral complex 15 crystallizes in the triclinic space group P- 1 with a = 10.09 1( 1 ) A,b
= 1 1.447( 1) A, c = l6.760( 1) A. a = 8 1 .O7(l)O, P = 8O.80( 1)o, y = 78.05( 1)O, V =
References page 159 1854.6(3) A,. and Z = 2. Intensity data for 15 was collected on a Siemens P4 diffractometer, using graphite monochromated Mo Ka radiation (h= 0.7 1073 A). The w scan technique was applied with variable scan speeds. Iniensities of 3 standards measured for each compound every 97 reflections showed no decay. Data were corrected for Lorentz. and polarization effects and for absorption.14 The ir atom position in each structure was solved by the Patterson method and other non-hydrogen atoms were located by successive difference Fourier syntheses. Non-hydrogen atoms were refined anisotropically by full- matrix least-squares on F? Hydrogen atoms were positioned on geometric grounds (C-H 0.96 A). All calculations were done and diagrams created using SHELXTL PC on a Pentium-75 personal computer. The crystal structure of 16CHClyC7Hs was deduced from an X-ray diffraction study at 298 K. The mono cationic complex 16 crystallizes in the monoclinic space group P21lc with rr = 14.4588(1) A. b = ?1.7141(2) A. c = 16.4989(2) A.P = 108.175(1)0.V=
4921.55(8) A3. and Z = 4. The structure was solved by direct methods. completed by subsequent Fourier synthesis. and refined by full-matrix least-squares procedures. The
counterion, and chloroform solvent molecule were located. A toluene solvent molecule was also located disordered at an inversion centre with a 50150 distribution. All boron-tluorine interatomic separations were restrained to be equal. All other non-hydrogen atoms were refined with anisotropic displacement coefficients. Hydrogen atoms were treated as idealized contributions. Crystal data, intensity collection, and least squares parameters are listed in Table 5.2. Views of complexes 15 and 16 . including the crystallographic labeling scheme are shown in Figures 5.5 and 5.6. Ir(H)2Cl(ql-SpyH)(PCy3)2(13). IrHs(PCy3);? (100 rng, 0.132 mmol) and
HSpy (15 mg, 0.27 mmol) were suspended in CH2C12 (2 mL) in a Schlenk flask fitted with a stirring bar under argon. To the stirring yellow suspension was quickly added 37% HCI (ca. 80 pL) by a microsyringe. Immediately after the appearance of a clear yellow solution
References page 159 (CCI. 1 min) the solvent was removed in vacrio to afford a yellow powder. If the solution is left stirring for more than 2 min it becomes again a suspension containing a mixture of two compounds: one the product 13 and the other being 14 which could not be separated. The residue was washed with a 1:3 etherh-hexane soiution (3 x 3 rnL) and dried in vclcuo to give a bright yellow powder (103 mg) in 87 % yield based on 1r(H)2CI(ql-SpyH)(PCy3)2.
Microanalysis. Calc. for C41H73ClIrNP2S:C. 54.58; H. 8.16: N. 1.55. Found: C. 53.77: H. 7.94: N. 1.66. NMR (6, CD2Cl2, 300 MHz). IH: 15.0 (br s. 1H. NH). 7.48 (br t. 1 =
6.1 Hz, 1H. ortho to N of SC5H4NH+). 7.36 (br d. J = 8.7 Hz. 1H. ortlro to S of
SC~HJNHC),7.02 (br t, J = 6.9 Hz. lH, para to N of SC~HJNH+).6.48 (br t. J = 6.5 Hz,
1 H. pcira to S of SCsH4NH+). 2.6 - 0.7 {m. 66H. P(C& 1 )3}. - 18.38 (td. J~H= 16.0. JHH= 6.7 Hz. IH. IrH). -26.89 (td. J~H= 15.2. JHH = 6.4 Hz. 1H. IrH): 31P(IH): 21.13
(s). MS(FAB): m/z = 866 [M-Cl] for C41~73C119%~~2~.IR (Nujol. cm-1 ): 2183 (m. br.). v(Ir-H); 3 165 (w), v(NH+).
Ir(H)2(q2-Spy)(PCy3)2(2). IrH5(PCy3)2 (300 mg. 0.396 mmol) was suspended in benzene (15 mL) under argon. To this was added an excess of HSpy (60 mg. 0.54 mmol). The solution was then refluxed for 20 min. On cooling. a pale yellow powder precipitated out of the solution. The precipitate was filtered and washed with ether (3 x 2 mL) and then dried in vclcuo (285 mg, 83%). Microanalysis. Calc. for CJIH72IrNPzS: C. 56.85: H. 8.38: N. 1.62. Found: C, 56.91: H. 8.09: N. 1.60. NMR (6. 300 MHz). IH (CDCl3): 8.2 - 6.5 (m, 4H. SC5H4N). 2.3 - 0.7 {m. 66H. ~(C~HII)~}.-23.7 tunresolved td. 1H Irm. -23.85 (td, overlapping, 1H. Irm: p{ IH}(C6D6):20.13 (s).
cis-IrHClt (q 1-SpyH)(PCy3)2 (14a). Ir(H12(q2-Spy)(PCy 3)2 ( 100 rng, 0.12 mrnol) and 2.5 equiv. of 2-mercaptopyridine (34 mg, 0.3 mmol) were suspended in 4 mL dichloromethane/2 rnL methanol (6 rnL) in a Schlenk flask under argon. While the suspension was stirred concentrated HCI (37%, ca. 100 pL) was slowly added through a septum using a syringe. After 2 h the volume was reduced to one-fifth in vclctro to give a yellow precipitate. To this was added 2 mL of methanol and the mixture was swirled for 10
References page 159 Chapter 5 157
min. After filtration, the product was washed with a mixture of methanol (3 mL) and
dichloromethane (0.5 mL) and then with ether (3 x 3 mL) before drying to give a pale yellow
powder 14a. Yield: 90 mg, 83 %. Microanalysis. Calc. for CjlH72C12IrNP2SCH2C12: C. 49.44: H, 7.32; N, 1.37. Found: C. 50.10: H, 7.65: N. 1.36. IR (Nu-jol. ~rn-~):2194 (w. br.), v(Ir-H); 3157 (w), v(NHf). NMR (6,CD2C12, 300 MHz). NMR for 14a. IH: 15.8
(br s. lH, NH), 7.8 - 6.6 (m, 4H, SC5H4NHf), 2.8 - 0.4 (m. 66H, P(C~HII)~].-25.68 (t, JPH = 13.5 Hz. lH, IrH): 3l~{l~):-11.65 (s). NMR for 14b. IH: 13.6 (br s. 1H.
NH), 7.5 - 6.4 (m, 4H, SCs&NH+), 2.8 - 0.4 {m.66H, P(C~HI~)~}, -20.9 (t. J~H= 1 1.8 Hz, lH, IrH): JIP{IH}: -10.26 (s). trans-IrHC12(q l-spyH)(PC~~)~(14b). 1rHC12(PCY~)~ (200 mg, 0.21
mmol) and mercaptopyridine (40 mg, 0.36 rnmol) were suspended in 8 rnL CH2C12/0.5 mL MeOH (8.5 mL) in a round bottom flask under argon. The solution became clear immediately and this was further stirred for 30 rnin. The solvent was evaporated to dryness and then diethylether (5 rnL) added to the residue. After stirring for approx 30 min the
product was filtered off and dried ill vcmo to give a yellow powdery solid (240 mg. 97 %).
Anal. Calc: for CJ IH~~CI~I~NP~S-CH~C~~:C, 49.4: H, 7.3: N. 1.37. Found: C. 49.8 1 ; H.
8.08: N, 1 S4. MS(FAB) for c~~H~~I~~~?c~~NP~s:m/z = 935 [MI. 900 [M-CI], 864 [M- Cl]. NMR (CDC13.ppm. 300 MHz): 1H: 13.6 (br s. IH. SC5H4NH). 7.37 (t.d.
overlapping, 2H. SC5H4NH), 7.08 (t, IH, SCSH~NH),6.50 (t, IH, SC5H4NH). 2.6 - 1.0
(m, 66H. P(C& 1)3), -20.85 (t, J~H= 14.1 HZ. 1 H. IrH). 31P{ 1HJ:-9.58 (s). IrClt(ql-SpyH)(q2-Spy)(PCy3)(IS). The procedure for the preparation of
14a was followed until the HCI was added. Then stirring for ca. 2 h afforded a yellow solution with a yellow suspension of 14a. This solution was left aside for 3 weeks to produce orange microcrystals and a yellow precipitate in an orange solution. The air-stable orange crystals were collected from the solution for X-ray and spectroscopic analysis and were identified as IrCI2(q ]-s~~H)($-spy)(pCy3) 15. Microanalysis. Calc. for
C28H42C121rN2PS2CH2C12: C, 41.03: H. 5.23; N, 3.3. Found: C. 41.72: H. 5.33; N,
Refererrces page 159 3.34. MS(FAB) for rn/z = 764 [MI. 728 [M-Cl]. 693 [M-Cl]. IR (Nujol. cm-I): 3171 (w, br.), v(NH+). NMR (6. CDCl3. 300 MHz). IH: 15.1 (br.s. 1 H.
NH). 8.6 - 6.2 (m. 8H. SC5H4N and SC5H4NH+). 2.5 - 0.6 {m. 33H. P(C6Hl 1)3}.
31P{lH): -25.0 (s). [IrCI(q ~-S~~H)~($-S~~)(PCY~)~(BF~)(16). IrHs(Pcy3)~ - (200 rng, 0.26
mmol) and 2.5 equiv. of HSpy (72 mg, 0.65 mmol) were suspended in CHC13 ( 10 mL) under argon. The suspension was refluxed for 20 min under argon to give a pale yellow
suspension of dihydride 2 which was cooled to room temperature before adding an excess of HBF4'EtzO (300 pL) while stirring. A few min after addition of the acid. a yellow solution resulted. The yellow solution was concentrated to a small volume and then layered with toluene. After over a month the layered solution deposited orange crystals of 16. suitable for an X-ray analysis.
References page I59 Chapter 5
5.5. References
Raper. E. S. Coord. Chern. Rev., 1996, 153, 199.
Binamira-Soriaga, E.: Lundeen. M.; Seff. K. Acta Cryst. 1979. B35. 2875.
Deeming, A. J.; Meah, M. N. N.: Dawes, H. M.; Hursthouse. M. B. J. Or~gurrorwt. Chem., 1986,299. C25. Valle. G.: Ettorre, R.; Vettori, U.; Peruzzo, V.; Plazzogna, G. J. Clzrm. Soc.. Daltott Trtrns, 1987, 8 15.
Lobana, T. S.; Bhatia. P.; Tiekink, E. R. J. Cltenz. Soc., Daltorr Trms. 1989, 749. Baker. P.: Hughes, S. J. Coord. Chent. 1995.35, 1.
Deeming. A. J.: Hardcastle. K. E.: Meah, M. N.; Bates. P. A.: Dawes. H. M.:
Hursthouse, M. B. J. Cller~r.Soc., Daitort Tram 1988, 227. Damude, L. C.; Dean. P. A. W.; Manivannan. V.: Srivastava, R. S.: Vittal, J. J. CCI~~. J. Cherzr., 1990, 68, 1323. Park, S. H.: Lough. A. I.: Morris. R. H. Inorg. Chmt., 1996,35. 3001.
Peris. E.: Lee. J. C.: Rambo, J. R.; Eisenstein, 0.; Crabtree, R. H. J. Airz. Clrerzz. Soc.,1995, 117, 3485. Joesten. M. D.; Schaad. L. J. Hydrogrrl Borrdir~g.Marcel Dekker. Inc. New York. 1974. Xu. W.; Lough. A. J.; Morris, R. H. Irzorg. Clrem., 1995, 35. 1549. Brinkmann, S.; Morris. R. H.; Ramachandran. R.; Park. S. H. horg. Synth.. 1998. 32, 303. Sheldrick. G. M., SHELXA, Program for absorption correction. University of G~ttingen.Germany, 1990.
Refereuces page I59 Chapter 6. Intra- and Inter-molecular Hydrogen Bonding in Dihydrido Pyrazole, Acetaldoxime or Glyoxime Complexes of Ir(II1). Molecuiar Structures of IrH2((r( l-NC3H3N)2H}(PCy3)2K7H8, IrH2((q '-N(O)CHMe)2H}(PCy3)2aC6H 6, and [IrH2(qz- N(OH)C(Me)C(Me)N(OH))(PCy3)2](BFq)*l.SCH2C12~0.5C~H~
6.1. Introduction
-A factor that may affect the strength of an intramolecular proton-hydride bondi*' MH-.HY is the geometry of the ring containing the proton-hydride bond. So far. stronger proton-hydride bonds are observed in six-membered rings. Proper ligands for such a geometry include pyridine derivatives such as pyYH (11) (Y= 0. NHR)', SpyH (111)~and quinoline-8-iminol (IV)~and thiazole derivatives (v)~as shown in Figure 6.1. One four- membered ring system (I) is known with a long H.-H distance.' The seven-membered ring systems (~1)~and (VII)~ have also been reported. It is not known yet if a five membered ring structure is favorable. The aim of this chapter is to study the preparation and characterization of proton- hydride bonding species involving proton donor ligands other than SpyH. which has been documented in Chapters 2 to 5. The ligands used in this study include pyrazole (pzH). acetaldoxime (acdxmH) and dimethylglyoxime (glxmH2) which might afford complexes of the types (VIII). (IX) and (X). respectively. forming pseudo-five-membered rings involving proton-hydride bonds. The reactions are carried out with IrH~(Pcy3)~that contains one of the most basic phosphine ligands. This allows for polarization of the hydride, a factor which is thought to increase the strength of Ir-H-H-Y bond.
Refererlces page 185 (VIII) (IX) Are 5-membered ring species possible ?
Figure 6.1. Examples of intramolecular proton-hydride hydrogen bonding interact ions.
A number of ligands (HX) including bi-imidazole. pyrazole. and alkylglyoxime can form intmmolecular or second sphere hydrogen bonds of the type X-H-X. lo-19 Such hydrogen bonds are encountered in the studies described in this chapter. The conjugated ligands 2.2'-bi-benzimidazole and 2,2'-bi-imidazole series form N-Ha--N hydrogen bonds within the ligand in some platinum metal complexes such as Ni(X-Heb.X)2(Hz0)2.10Rh(X-
~-~)(cod).l R~(X-HX)C~C~,l2 Ru(X-H--X)(H)(CO)(PP h3)2, 13 and Os(X-
H --X)(H?)(P~P~~)~, l4 or between ligands in Pd(X-H-X) (Me) 15. The ligand dialkylglyoxime, which has been used for Vitamin B 12 models, has long been known to have
References page 185 a pair of intramolecular 0-H-0 hydrogen bonds in oxime complexes (e-g.
Co(L)(R)(glyoxime)2).16- l9 An unusual intermolecular hydrogen bonding bridge between anions (BF4') and hydroxy groups iridium(II1) glyoxime cations as well as Ir-H--.H-Cinteractions between hydrides and protons of the PCy3 groups are discovered in this work.
6.2. Results and discussion
6.2.1. Pyrazole complex of iridium(II1)
A suspension of bis(tricyclohexylphosphine)pentahydridoiridium(V) reacts with 2 equivalents of pyrazole (pzH) in boiling benzene to give a moderately air-stable. light grey powder in over 90 % yield according to equation 6.1. This powder has been identified by
NMR experiments (31P. I H. VT-TI). FAB MS. and microanalysis as a neutral iridiurn(II1) pyrazole complex. Ir(H)?(pz)(pzH)(PCy3)217 in which the pz and pzH ligands are trans to the cis hydrides. and the two tricyclohexylphosphine ligands are in tram positions. The solid state structure has been confirmed by a single crystal X-ray analysis (Section 6.2.5).
1 A. .., I . H 2 pyrazole H- Lr""' /I'H /I'H C6H6 80°C. I h H r L = PCy,
The structure of 17 in solution is identified on the basis of the following NMR observations. First, a singlet at 17.3 ppm in the 31P{lH} NMR spectrum and a triplet at -22.40 ppm (J = 17.3 Hz) in the lH NMR spectrum are good indications for the existence of two trans phosphine groups cis to hydridecs). The two:two stoichiometry of hydride to
References page 185 Chapter 6 163 pyrazole or pyrazolate ligand is reinforced by the integration of their 1H resonances. The proton in the hydrogen bond N-H-.N in a (HPz2)- moiety has a resonance at 20.48 ppm for the complex in toluene-ds below 213 K. At this temperature the hydrides give a broad peak in the 1H NMR spectrum. When the temperature is raised this sharpens into the triplet observed at room temperature. This fluxional process probably involves proton transfer between the two nitrogen atoms in the N-H-.N unit. When the sample is cooled to 193 K in toluene-dg the hydride resonance becomes very broad. The TI(rnin) of 144(8) rns occurs at this temperature (400 MHz)(Table 6.1 ).
Table 6.1. Surnrnarya of selected 31P NMR, 'H data and TIvalues.
NMR method 17 18 19 20 -
~~P{IH} 17.3 13.35 16.4 (C&) 14.4 (ChDh)
lH (XH) 20.48 2 1.36 7.8 10.5
(br s. NH)~ (s, OH) (br s, OH)' (br s. OH)
H ( IrH) -22.40 (t) -22.50 (t) - 19.66 (dt), -20.1 (t) -21.25 (dt,
1 "NMR (ppm) measured in CDCI3, unless otherwise stated. IH TI (min)in ms measured in toluene-ds or stated otherwise. b~ppearedat 2 13 K and measured at 193 K in toluene-ds. '~ppearedat 253 K and measured at 253 K in toluene-dg. d~heIH TI at room temperature in CDC13.
Refererrces page 185 The TI of the NH proton. whose resonance first appears at 2 13 K. is 209(4) ms at 193 K.
This low TIvalue for the NH proton is caused by dipolar relaxation of two neighboring 14~ nuclei in the NHN unit. The unusually short TI(min) value for the hydride is probably due to close IrH-HC interactions with the protons of the PCy3 groups20 as observed in the solid state structure at 173 K (Section 6.2.5). No formation of a trihydrido complex containing a neutral pyrazole ligand i.e. Ir(H)g(pzH)(PCy3)2has been observed by use of proton NMR in the period before the formation of 17 (10 min to 1440 min) either at room temperature or under refluxing conditions in benzene-dg. The related trihydrido complex Ir(H)3(pyNHz)(PPh3)>py NH? = aminopyridine, has been reported previously.~
6.2.2. Acetaldoxime complex of iridiurn(II1)
The IrHg(PCy3)z complex in refluxing benzene reacts with 2 equiv. of an isomeric mixture (syn, anti) of acetaldoxime (acdxmH) to produce a light grey powder in over 70 B yield. This complex has been fully characterized by various NMR techniques (3' P{ I H }. I H. VT, and VT-TI). FAB MS. and microanalysis. This information is consistent with the formula Ir(H)2(acdxm)(acdxmH)(PCy3)~18. as confirmed by X-ray studies (Section
6-25). The complex contains two cis hydrides. two cis acetaldoxime ligands trans to the hydrides. and two trans phosphine ligands. No intermediate containing one acdxmH ligand was detected.
H L L --.I .H H.. I . H ~-'ya" 2 acetatdoxime - (6.2) /I'H /I'H C& 80 'C, 30 min L L = PCy3 -2H2 18
Refit-encespage 185 Chapter 6 165
The FAB mass spectrum of 18 shows an intense peak at rn/z = 753 corresponding to the loss of an [X2H]-moiety. The proton NMR spectrum provides useful information on its solution structure. There are well resolved peaks for a hydroxyl group (a singlet. 21.36 pprn), two CH protons (a quartel. 7.16 pprn). two methyl groups (a singlet. 2.1 pprn). two PCy3 groups (a multiplet. 3.0 - 0.9 ppm) and the hydrides (a triplet. -22.50 ppm). There is a singlet at 13.35 ppm in the ~IP(IH} NMR spectrum. Complex 18 possesses two acetaldoxime ligands rendered equivalent by fast IH exchange between oxygen sites in an O- H--0hydrogen bond. Unlike in the spectrum of complex 17. the resonance of the 0-H-0 proton of 18 appears at 21.36 pprn as a sharp singlet in the lH NMR spectrum at room temperature (Table 6.1). This proton resonance broadens greatly (vl~= 0.025 ppm) on cooling below 193 K or heating up to 353 K in toluene-da according to the H NMR spectrum. Interestingly, at low temperatures the hydride resonance (a triplet) splits (by 0.0 12 ppm) into two overlapping, but distinguishable triplets (Figure 6.2). This is probably a result of the freezing of two conformers due to two trcws-phosphine groups which become magnetically inequivalent at below 193 K. The fact that there are two sets of resonances indicates that this is not the result of freezing of the proton exchange between the two 0-H protons in the unsymmetrical OH*-0hydrogen bond. The variable temperature (353 K to 193 K) 1H TI measurements were done for complex 18 in toluene-dg at 400 MHz. At 193 K. the Tl(min) of the hydride is short at 149(1) ms. The dipole-dipole interactions between hydrides and protons of PCy3 groups as observed in 17 are responsible for the short TI rather than intramolecular IrH-H 0 interactions. TI values around 800 ms for the hydrogen of the hydroxy group have been observed throughout the range from 353 K to 193 K (Table 6.1). This confirms that the 0- H--.0unit is self-associated with a strong conventional hydrogen bond. No decomposition or distinctive isomerization of complex 18 has been observed under the given conditions (353 K to 193 K) in deutented benzene or toluene.
References page 185 Refererlces page I85 Chapter 6
6.2.3. Neutral dimethylglyoxime complex of iridiurn(II1)
A suspension of IrHs(PCy3)s in benzene reacts with 1 equivalent of dimethylglyoxime (glxrnH2) in acetone to give an air-stable ivory powder in over 65 % yield (Equation 6.3). This powder has been examined by FAB MS. and microanalysis and also by
NMR techniques (31~,IH, VT, VT-TI, NOE). to determine its structure and behaviour in solution. It is a neutral dihydrido iridium(II1) oxime complex, cis, truns-lr(~)~(q*- glxmH)(PCy3)2 19-
Figure 6.3. Proposed strucrures of' the product 19 from the reaction of IrH5(PCy3)2 with dimethylglyoxime.
The molecular weight calculated for 19 is consistent with the FAB MS result of rn/z =
87 1. The rrrms-PCy3 groups give a singlet in the 3 P ( I H } NMR spectrum at 16.4 ppm. In the IH NMR spectrum in C6D6 there is a singlet at 2.2 ppm for two methyl groups of the oxime ligand, a multiplet covering the range from 2.2 to 1.0 ppm for PCy3, and two sets of a doublet of triplets at - 19.64 and -2 1.3 ppm (JHH= 6. l. JPH = 17.5 Hz) for two inequivalent hydrides. No OH resonance is observed. The magnetic inequivalence of the hydridrs is due to a chelation of the oxime iigand in an unsymmetrical manner. There are two possible structures (A. B) that produce the unsymmetrical geometry with respect to two cis hydrides as shown in Figure 6.3. A in Figure 6.3. has an 0, N-chelating iigand. This however is unlikely because the hydrides have similar chemical shifts; when hydride is coordinated trans to oxygen. its chemical shift should appear to higher field compared to that when tram to
References page 185 Chapter 6 168
nitrogen? In structure B in Figure 6.3, the oxime ligand is chelated via two nitrogens. and contains a deprotonated hydroxy group. Resonance forms like Bl and B2 serve to stabilize the oximate group. This structural assignment as B is consistent with that deduced by a preliminary X-ray structure analysis of 19 for the crystal grown in CH2C12 I ~eOH.21The
chemical shift of the methyl groups must be coincidently similar. Selected resonances of a variable temperature IH NMR experiment (toluene-&) are
shown in Figure 6.4A (for hydride) and Figure 6.4B (for OH proton). Above 273 K there is
no significant change observed. Below 253 K a peak at 7.8 pprn appears as a broad singlet
which, with reduction of temperatures, becomes much broader (Figure 6.48). This peak
progressively moves ( 1.3 ppm) from 7.8 pprn (253 K) to 9.1 pprn (193 K). Under the same condition there is. a slight, but significant movement (0.21 ppm) and broadening of one (21.4 ppm) of the hydride resonances (~b,Figure 6.3, A) while the other at - 19.9 pprn remains unchanged as a doublet of triplets at - 19.9 ppm. A great down field movement of the chemical shift of the hydroxy proton may be due to a contact with the neighboring cis hydride. Proton-hydride bonds could be responsible for the broadening of the Hb peak but TImeasurements are not conclusive. The TI values of the hydrides (Fib and Ha) in toluene-& at 2 13 K are 283(4) and 299(4) ms (the minimum TI values of cn. 14 1 and 143 rns. respectively. at 193 K have too much error to be reliable). The minimum TIvalue of the hydroxyl proton is roughly 249 ms at 133 K. However a low temperature NOE experiment done at 233 K gives some evidence for an Ir-H-+H0 interaction. After selective irradiation at the hydride (Hb) resonance at -2 1.4 ppm, a small amount of NOE enhancement at the OH resonance is observed in toluene-d8 while there is no NOE on hydroxy proton when the hydride (Ha) resonance at -19.9 pprn is irradiated. In both cases. there is a large NOE enhancement of the tricyclohexylphosphine proton resonances at 1.5 pprn and this suggests that effects due to [r-Ha--HCcontacts are also imponant.
Referemes page 185 Chapter 6
Figure 6.44- lH NMR spectra (hydride resonances) of 19 (400 MHz, 6. toluene-dg): (a) 7-0 OC. (b) 0 OC,(c) -20 OC. (d) -40 QC.(e) -60OC. and (f) -80 OC.
References page 185 Chapter 6
References page 185 Chapter 6
6.2.4. Cationic dimethylglyoxime complex
- -N .. H glxmHl /(, xN-,acetone / C,H6 H acetone I C,H6 30 min. RT
glxrnH? = dimethylglyoxime
The neutral iridium(II1) glyoxime complex, 19 reacts in benzene-acetone solution with HBF4sether to give an air-stable orange-yellow solid in over 65 9% yield (Equation 6.3). This solid has been determined to be the monocationic iridium(iI1) oxime complex,
[IrH2(glxmH2)(PCy3)A(BF4)20 by use of NMR experiments (31~.'H. NOE). FAB MS. microanalysis. and X-ray analysis. 20 was also prepared directly from irH5(PCy3)2. In a FAB MS spectrum. the cation of 20 gives the expected peak at rnlz = 872. The
3lP{IH)NMR spectrum is a singlet at 16.85 ppm for the two trcms phosphorus nuclei. The proton NMR spectrum in CDC13 consists of a broad singlet at 8.68 ppm for hydrogen- bonded hydroxyl protons. a singlet at 2.25 ppm for 6 protons of two methyl groups of the oxime ligand. a multiplet for the PCy3 groups in the region from 2.1 to 1.1 ppm. and a triplet at -20.38 ppm for the hydrides. The complex has Czv symmetry in solution where the oximr ligand is chelated symmetrically via two nitrogens. An NOE experiment has been done at 293 K in CDC13. Selective irradiation at the hydride resonance results in no significant enhancement of the OH resonance. but instead an enhancement of the resonances of the PCy3 ligands. Therefore this complex exhibits C-
He-H-Ir interactions in solution. An exposure of this complex to D2 gas for 1 min in CDC13 at 293 K causes no significant decrease in intensity of either the hydride or hydroxy proton resonances in the 'H NMR spectrum. Thus HID exchange is slow or not possible.
References page 185 Chapter 6
6.2.5. X-ray diffraction studies
Views of the geometries of the pyrazolate complex Ir(H)z{(pz)2H}(PCy3)217, and the acetaldoxime complex Ir(H)2 ( (acdx m)2H } (PCy3)z 18 are shown in Figures 6.6 and 6.7. respectively. Two different views of the geometry of dimethy lglyoxime complex 20 with the crystallographic labeling scheme are shown in Figures 6.8 and 6.9. The lists of the selected bond distances and angles are shown in Table 6.3 for 17, Table 6.4 for 18, and Table 6.5 for 20. The crystal data and structure refinements for 17. 18 and 20 are compared in Table 6.6. Table 6.2 presents some important distances and angles for 17. 18 and 20 for comparison with one another. The iridium atom in complex 17 is in a distorted octahedral geometry with two tmns
PCy3 groups { P( 1 )-Ir-P( 1A) } = 16 1.67(5)O). Two cis hydride ligands were located from the electron density map and refined. The two cis pyrazole ligands are monodentate with ir-N distances of 2.14 l(4) A which is a little longer than the 0s-N distance (3.103(7) A) of another pyrazole 0s complex. lJ A nitrogen of each pyrazole ligand is facing the other and these are linked by an N-H-N hydrogen bond. The molecule has the C2v, 2/m symmetry of the crystal at the iridium. The two perpendicular mirror planes pass through the groups of atoms {H(2N) . Ir( 1), P( I)} and (C3N2 ring. Ir( 1). H( 1Ir)} , respectively. The proton of the hydrogen bonding unit has been found at 1.30(2) A from both nitrogen atoms with an NHN angle of 164( 10)O. The hydrogen bond could still be unsymmetrical and the single position of the hydrogen could be an artifact resulting from the imposed crystallographic symmetry. At a normal position of 1.50(5) A from the iridium centre are the hydrides. No N-H-H-Ir interaction is possible involving the pyrazole NH proton because of the presence of the strong N-He-N hydrogen bond. The C-H--H-Ir contacts involving protons of phosphine groups md hydrides, are at distances (2.307 A) making two C-H-H(Ir)---H-C interacting pairs: H( 1 1B)-H( 1IA)"-H(1 1C) and H( 1 1A)..-H( lIR)-+'H( 1 1). The He--Hdistances are near to the sum of the van der Wads radius of hydrogens ( 1.2 + 1.2 = 2.4 A).
References page 185 Table 6.2. Comparison of selected atomic distances and angles for 17. 18. and 20.
Bond and angle types 17 18 20 Ir-H (A) 1 .50(5) 1.44(6) 1.48(3) 1.50(5) 1.435) 1 .50(3) H..-B in AH-B (a) 1.30(2) 1.25(8) 1.99(4), 2.00(3)
(A=B=N) (A = B = 0) (A=O:B=F) i
A-H in AH-B (A) 1.30(2) 1.18(8) 0.76(4). 0.70(3)
(A = N) (A = 0) (A = 0)
Ir-N (A) 2. 141(4), 2. 141(4) 2.138(3), 2.158(4) 2.07 I(?). 2.088(2) A-H-B (deg.) 164( 10) 1648) 161(3) (H-bonding unit) 163(4) P( 1 )-Ir-P(2) (deg.) 16 1.67(5) 160.64(3) 156. 19(3)
Nccis)-Ir-H (deg.) 84(2), 84(2) 84(2), 86(2) 96.6( 14). 97.1 ( 14)
H( 1 )-Ir-H(2) (deg.) 98W 97(3) 93(2)
18 has a similar distorted octahedral geometry. The two methyl groups of the acetaldoxime ligands are positioned outside (i.e.. away from the bulky phosp hine groups) and both oxygens are in the anti conformation indicating that the coordination of a mixture of
anti and syn acetaldoxime leads to the isomerization of syn to artti cornformer. The oxygens are bridged by a proton to form a linear 0-H-0 hydrogen bond. The 0-0 distance of the hydrogen bonding unit is 2.406 A and is consistent with the distance of other oxime complexes (2.5 1-2.49 A for alkylcobaltoximel~).This makes an Ir-N( 1)-O( 1 )-H-O(2)-N(2)- Ir six-member ring. The molecule has crystallographic mirror symmetry with respect to the plane containing the iridium, the two hydrides. and the monoanion (acdxm2W) moiety. Interestingly the symmetry (Pnma) of the crystal of 18 is different from that (Cmcm) of 17.
References page 185 The hydrogen bonding proton is located in a slightly off-centre position which is at 1.25(8) and 1 .l8(8) A from the neighbouring oxygen atoms with an OH0 angle of 164(8)O(bending inward). Two cis hydrides have been placed from Fourier difference maps and refined with the isotropic parame!ers. They are located at reasonable ir-H distances of 1.44(6), 1.435) A in the plane of the 0(1)-N( 1)-Ir-N(2)-O(2) unit. The Ir-N distances are 2.138(3) and 2.158(4) A. which are longer than those (1.87-1.89 A) of other oxime complexes of
Co(111)~~because of the trans influence of the hydrides and the size of the metal. No close O- H-.H-Lror C-H-H-Ircontacts are observed. The iridium atom in 20 is also centred in a distorted octahedral geometry with two trans phosphorus atoms P 1 I-(2= l56.19(3)0}.two cis hydride ligands. and a chelating dimethylglyoxime ligand. The P-lr-P angle is more acute than that of the pyrazole
complex ( 16 1.67(5)0). the acetaldoxime complex { l60.64(3)0},or the ammine complex.
IrHCIl(NH3)(PCy3)2 ( 164.28(3)0}.20 The final positions of the protons on the hydroxyl groups of the neutral dimethylglyoxime are in refined positions in approximately linear O- H--F 10-H-F angles are 163(4). 161(4)O}hydrogen bonds to the BF4- anion. These hydrogen bonds are strong {~(H,..F)= 1.99(4). 2.00(3) A } . thus preventing the formation of the Ir-He-H-0 interactions. The 0-H-*F-BF2-F6..H'-0' hydrogen bonds link together the anions and cations. making chains in the lattice (Figure 6.9). Two cis hydrides are in refined positions at distances of 1.48(3) and 1.50(3) A from the iridium atom in the N( 1)-Ir-N(2)
plane. The N(,iS,-Ir-Hangles {96.6(14). 97.1(14)0} of this complex are greater than those of
the pyrazole complex { 84(2)0) and the acetaldoxime complex {84(2),86(2)O 1. The N-Ir distances {2.071(2) and 2.088(2) A} are shorter than those of the other complexes {pyrazole complex. 2. M(4)A. acetaldoxime complex. 2.135(3), 2.158(4) A). There are no 0-H--H- Ir close contacts as the hydrides are 2.66(5) and 2.8 l(5) A away from the hydroxyl protons. There are close contacts between IrH and the CH protons of two phosphine groups in the solid state: three CH protons {H(16), H(42). H(46)) are close to the hydrides with distances of 2.0 18, 2.22 1. and 2.164 A. respectively. These distances are significantly less than 2.4
References page 185 A. twice the van der Wads radii of two hydrogens. The bending of the P-Ir-P angle toward the hydrides may be related to the formation of these IrH-HC interactions. In the pyrarole and acetaldoxime complexes the P-Ir-P angle is less and no short IrH-HC contacts are observed. It has been sugggested that hydrogen bonds are possible involving a carbon atom in systems (C-H-X: d(H-X) = 2.1 to 2.7 AJ such as C-H-0 or C-H-N. Perhaps these C-H- H-Ir type interactions (d(H--H) = 2.0 to 2.4 A} are energetically favourable.
However P-M-P angles in dihydrides often bend toward the small hydride ligands for steric reasons. In such a case it is possible that there is some compression of MH-HC contacts.
Figure 6.5. Simplified structure of 20 to show C-H*.'H-Ir and OH-FBF3 interacting units.
References page 185 Figure 6.6. Structure of the pyrazole complex. 17 showing the N-H---N hydrogen bonding unit. The hydrogen bonding proton and the hydridrs are in refined positions.
References page I85 Chapter 6
Figure 6.7. Structure of the acetaldoxime complex, 18. The proton on the hydrogen bonding hydroxy group and the hydrides are in refined positions.
Referertces page 185 Chapter 6
Figure 6.8. Structure of the cation of 20 whose counteranion is not shown for clarity. Two cis hydrides and two hydroxy protons are in refined positions.
References page 185 References page 185 Chapter 6
6.3. Conchmion
IrHs(PCy3)2 reacts with pyrazole (pzH) or acetaldoxirne (acdxmH) to give neutral
iridium(II1) complexes. Ir(H)2(pz---Hpz)(PCyj)2 17 and Ir(H)2(acdxm--Hacdxrn)(PCy3)2 18, respectively, coiltaining a conventional X-H-•X hydrogen-bonded ligand system instead of an X-H-H-lr proton-hydride interaction. The Tl(min) of the hydrides are short due to weak C-H-H-Ir interactions involving hydrides and PCy3 hydrogens in toluene-dg. IrHs(PCy3)z reacts with dimethylglyoxime (glxmH2) to give a neutral iridium(II1) oxime complex. Ir(H)2(glxmH)(PCy3)219 which undergoes protonation with HBF4 to a monocationic iridium(II1) oxirne complex, [IrH~(glxmH2)(PCy3)~(BF~)20. There is rapid proton exchange between two hydroxyl sites in 19 in toluene-&. 20 at room temperature in CDC13 does not have 0-H-H-lr interactions. but does have C-H-.-H-Irinteractions with
PCy3 protons (2.0 to 2.2 A). The hydroxy protons are in 0-H-F hydrogen bonds { H-F =
1.99(4). 2.00(3) A} to the BF4 anions. The frms PCy3 groups tilt toward the hydrides
{ P( 1 )-Ir-P(3) = 156.19(3)O}.perhaps to maximize the C-H.-H-Ir interactions. On the other hand the short CH-HIr contacts might be a consequence of steric pressure around the complex.
6.4. Experimental
General experiment All preparations were carried out under an atmosphere of dry argon using conventional Schlenk techniques. All the solvents were distilled under argon over appropriate drying agents prior to use. Acetone was dried over potassium carbonate. Benzene. diethyl ether (Et20). and n-hexanes were dried over and distilled from sodium benzophenone ketyl. Dichloromethane was distilled from calcium hydride. Deuterated solvents were dried over Linde type 4 A molecular seives and degassed prior to use. Tricyclohexylphosphine (PCy3), pyrazole (pzH), acetaldoxime (acdxmH), dirnethylglyoxime
Refererlces puge 185 Chapter 6 181
(glxmH*). and an 85% solution of HBF4.Et20 complex were purchased from Aldrich Chemical Company Inc. Lridium vichloride hydrate was obtained from Johnson-Matthey Co. Iridium(V) pentahydride (IrHs(PCy3)2) has been made from IrHC12(PCy3)2 obtained from the reaction of IrClyxH~Owith PCy3 in boiling HCVEtOH solution.22 NMR spectra were obtained on a Unity-400. operating at 400.00 MHz for H. 16 1.98 MHz for 31P, or on a Gemini-300 operating at 300.00 MHz for H. 12 1.45 MHz for
31~.All 31~NMR spectra were obtained with proton decoupling. 3'~NMR chemical shifts were measured relative to H3P04 as internal reference. IH NMR chemical shifts were measured relative to deuterated solvent peaks or tetramethylsilane. Variable temperature TI measurements were made at 400 MHz using the inversion recovery method. Fast atom bombardment mass spectrometry (FAB MS) was carried out with a VG 70-250s instrument using a 3-nitrobenzylalcohol (MA)matrix. All FAB MS samples were dissolved in acetone and placed in the matrix under a blanket of nitrogen. Microanalyses were performed by Guelph Chemical Laboratories Ltd., Ontario. X-ray Structure Determination The pyrazolate complex 17. acetaldoxime complex 18 and dimethylglyoximr complex 20 are crystallised by slow evaporation of solution of toluene. benzene, and CH2C12henzene. respectively. in air. X-ray analysis of these crystals reveals the presence of an orthorhombic space group Cmcm, Z = 4 with unit cell a = 15.977(3), b = 10.3 15(2), and c = 27.843(5) A for 17 (173 Kf,an orthorhombic space group Pnma, Z = 4 with unit cell n = 17.3 l8(4). b = 27.589(4). and c = 9.552(3) A for
18 (293 K), and a monoclinic space group CYc, Z = 8 with unit cell n = 24.995(3). b =
2 l.544(2), and c = l9.370(2) A. and P = 100.662(9)0 for 20 ( 173 K). Intensity data for 17, 18. and 20 were collected on an Siemens P4 diffractometer. using graphite monochromated MoKa radiation (h= 0.7 1073 A). The o scan technique was applied with variable scan speeds. Intensities of 3 standards measured for each compound every 97 reflections showed no decay. Data were corrected for Lorentz. and polarization effects and for absorption.23 The Ir atom position in each structure was solved by the
References page 185 Chapter 6 182
Patterson method and other non-hydrogen atoms were located by successive difference Fourier syntheses. Non-hydrogen atoms were refined anisotropically by full-matrix least- squares on F~.Hydrogen atoms were positioned on geometric grounds (C-H 0.96 A). The hydrogen atoms of the hydride and the NH in 17, and the hydride and the hydroxyl in 18 and 20 were refined with isotropic thermal parameters. Crystal data. data collection. and least squares parameters are listed in Tables 6.3 to 6.6. All calculations were done and diagrams created using SHELXTL on a Pentiurn-75 personal computer. Views of complexes 17, 18, and 20. including the crystallographic labelling scheme are shown in Figures 6.6. 6.7 and 6.8. Preparation of the pyrazole complex IrH2{(N2C3H3)2H}(PCy3)2 (17). IrHs(PCy3)2 (400 mg, 0.53 mmol) and pyrazole (70 mg. 1.03 mmol) were suspended in benzene 12 mL in a round bottom flask. The solution was refluxed for 2 h under argon to give a clear solution. Solvent was evaporated in vucuo to dryness. The residue was then washed 3 times with 4 mL of n-
hexanes and dried in vucuo for 3 h to give a grey white powder (434 mg. 92. 5%). Anal. Calc:
for C~tH75IrN4P2:C, 56.6; H, 8.49; N, 6.29. Found: C. 56.39: H. 8.56: N. 6.06.
MS(FAB) for c~~H~~I~~~~N~P~:di = 892 [MI+. NMR (CDC13. ppm. 300 MHz. 20 OC):
lH: 7.54 (br. 2H. C3H3N2). 7.31 (br. 2H. C~H~NZ).6.09 (br. 2H. C~H~NZ).1.7 - 0.9 (m.
66H, P(C6H I 1)3), -22.40 (t, Jpu = 17.3 Hz. 2H, IrH). IP{ I H): 17.3 (s). I H NMR (toluene-dg, ppm, 400 MHz, -80 OC): 20.48 (br s, IH, (C3H3N2)H). 7.54 (br, 1H.
C3H3N2). 7.38 (br. 2H, C3H3N2), 6.16 (br, 2H. C~HJN,),2.2 - 0.5 (m. 66H.
P(CdI1 )3). -2 1.7 (br, 2H, IrH). Preparation of the acetaldoxime complex
I~H~~(N(O)CHM~)~H}(PC~J)~(18). IrH5(PCy3)2 (200 mg, 0.26 mmol) and ca. 3 equiv. acetaldoxime (47 mg, 0.79 mmol) were suspended in 8 rnL of benzene in a round bottom flask. The solution was refluxed for 30 rnin under argon to give a dark clear solution. This was filtered through Celite before drying in vacua The residue was then
References page 185 Chapter 6 183
washed 3 times with 2 mL of n-hexanes and dried in vacuo to give a white powder ( 165 mg.
72%). Anal. Calc: for C40H771rN202P2: C, 55.08; H, 8.9: N, 3.2 1. Found: C, 54.45; H, 8.85: N. 3.66. MS(FAB) for C40H771r192N202P2:rn/z = 753 [M-L2H-I. NMR (CDCl3,
ppm, 300 MHz): IH: 20.65 is, IH, OH of acdxmH), 6.65 (q, JHH= 5.5 Hz. 2H. CH of acdxrnH). 1.9 (s. overlapping PCy3, 6H.Me of acdxmH). 2.1 - 0.9 (m. 66H. P(C~HI~)~).
-22.90 (t. J~H= 17.7 Hz. 2H, LrH). 31P( 'H}: 13.35 (s). Preparation of dimethylglyoxirne complexes IrH2{N(OH)C(Me)C(Me)NO}(PCy3)2(19). IrHs(PCy3)z (100 mg. 0.13 mmol) was suspended in 5 mL of benzene in a round bottom flask. To this was added a
solution of dimethylglyoxime (23 mg, 0.2 mmol) in I mL of acetone. The solution was refluxed for 30 rnin under argon to give a greenish yellow solution. This was filtered through Celite before drying in vucuo. The residue was then washed 3 times with 2 rnL of n-hexanes
and dried in vacrco to give an ivory powder (74 mg, 65 %). Anal. Calc: for
C~OH~~I~N~O~P?:C. 55.14; H. 8.68: N, 3.22. Found: C. 56.40; H. 8.59: N. 4.64. MS(FAB) for C40H751r192Nz02P2:m/z = 871 [MI+. NMR (C6D6,ppm. 300 MHz): lH: 2.2 (s, 6H. Me of glxmH). 2.1 - 1 .O (m.66H. ~(C~HII)~),- 19.64 (dt, JHH = 6.1, J~H= 17.5 Hz, lH, IrH), -21.3 (dt, JHH = 6.1, JPH = 17.5 Hz, 1H. IrH). lH VT-NMR for OH of glxmH (toluene-d8, ppm, 400 MHz): 7.8 (br s., -20 OC), 8.5 (br s., -40 OC). 8.75 (br s.. -60 OC), 9.1 (br s.. -80 OC) : 31~(1H}:16.4 (s).
[IrHz{N(O H)C(Me)C(Me)N(OH)}(PCy3)2] (BFJ) (20). Method I. IrHs(PCy3)2 (100 mg, 0.13 mrnol) was suspended in 5 mL of benzene in a round bottom flask. This was heated under argon for a few min until the solution became clear. To this was added a solution of dimethylglyoxime (23 mg, 0.2 rnmol) in acetone I mL. followed by addition of HBF4-ether(ca. 80 pL) to give a pale yellow solurion. The solution was stirred further for 30 min under argon and then the solvent was removed in vuclco. To the residue was added CH2Cl2 and the resulting solution was filtered through Celite to give a clear orange solution. Again, the solvent was evaporated in vacuo. 0.5 rnL of ether was added to
References page 18.5 deposit an orange yellow powder. It was then washed 3 times with 2 rnL n-hexanes before drying to give the desired product (85 mg, 68%). Method 2. 19 (100 mg, 0.11 mmol) was dissolved in 5 rnL of benzene in a round bottom
flask. To this was added HBFp-ether (ca. 80 pL) to give a pale yellow solution. Worked up
similarly as Method 1. (80 mg, 72 %). And. Calc: for C~~H~~I~N~O~P~BFJ:C. 50.OS; H. 7.99; N. 2.92. Found: C, 50.14: H, 8.07; N, 2.80. MS(FAB) for c~~H~~I~~~~N~o~P~:m/z = 872 [M-BF4]+. NMR (CDCl3, ppm. 300 MHz): lH: 8.68 (br s, 2H. OH of glxmH2).
2.25 (s. 6H. Me of glxmHz), 2.1 - 1.1 (m, 66H. P(C6kfI 1)1). -70.78 (t. J~H= 17.6 Hz.
2H. IrH). IP ( IH }: 16.85 (s).
Referetzces page 185 Chapter 6
6.5. Reference
Milstein, D.: Stevens, R. C.;Bau, R.: Blum, 0.; Koetzie. T. F. J. Clzern. Soc., Dalton Tmns. 1990, 1429.
Peris. E.: Lee, J. C. Jr.: Rambo, J. R.; Eisenstein; 0.; Crabtree, R. H. J. Am. Clrern. Soc., 1995, 117, 3485.
Park. S. H.: Lough. A. J.; Morris. R. H. Inorg. Cllem.. 1996.35. 300 1.
Lee. J. C. Jr.: Peris. E.: Rheingold. A. L.; Crabtree. R. H. J. At~z.Clzertl. Soc.. 1994, 116, t 1014.
Xu, W.; Lough, A. J.: Morris, R. H. Irlorg. Clrem., 1995, 35, 1549. Yao, W.; Crabtree, R. H. Inorg. Chem.. 1996, 35, 3007. Dahlenburg, L.; Herbst. K.: Kuhnlein. M. Z. Arrorg. Allg C/zer?z..1997. 623. 250. Shubina, E. S.: Belkova. N. V.: Krylov, A. N.: Vorontsov. E. V.: Epstein. L. M.:
Gusev. D. G.; Niedermann, M.; Berke, H.J. Am. Clzern. Soc., 1996, I I& 1 105.
Peris. E.; Wessel, J.: Patel, B. P: Crabtree, R. H. J. Clrern. Soc., Chetn. Co/?trlrurz., 1995, 2 175.
Holmes, F.: Jones, K. M.; Terrible, E. G. J. Clzern. Soc., 1961, 4790. Kaiser. S. W.: Saillant. R. B.: Butler. W. M.: Rasmussen. P. G. Inorg. Chetn.. 1976, 15, 268 1.
Oro, L. A.: Cmona. D.; Lamata, M. P.; Tiripicchio, A.: Lahoz. F. J. J. CAenl.
Soc., Dalton Trans. 1986, 15. Garcia, M. P.; Lopez, A. M.; Esterueias. M. A.: Lahoz, F. J.; Oro. L. A. J. Chem. Soc., Dalton Trans. 1990, 3465.
Esteruelas, M. A.: Lahoz, F. J.; Oro, L. A.; Onate. E.: Ruiz, N. Dzorg. Clrenz.. 1994,33, 787. Uson. R.; Gimeno. J.: Oro, L. A.; Martinez. J. M.; Cabeza. I. A.: Tiripicchio. A.: Camellini, M. T. J. Chem. Soc.. Dalton Trans. 1983, 1729.
Refererrces page 1 85 Schrauzer, G. N. Acc. Chem. Res., 1967, I, 97. Brown, K. L. Organo(aquo)cobaloxi,nes in Organometallic Syntheses. Elsevier. 1986, vol 3, 186. Lenhert, P. G. J. Cltem. Soc., Chern. Comntun., 1967, 980. Ohgo, Y.; Ohashi, Y.; Klooster, W. T.:Koetzle, T. F. Chem Lett., 1996, 445. Xu. W.; Lough. A. J.; Morris. R. H. Can. J. Chem., 1997, 75. 475. Park, S. H.; Lough, A. J.; Morris, R. H. Unpublished results. A partial data was collected before the crystal decomposed. The crystal could not be remade.
Brinkmann. S.: Morris. R. H.: Ramachandran. R.: Park. S. H. Ir~org.Synth.. 1998 32. 303. Sheldrick. G. M.. SHELXA. Program for absorption correction. University of GOtingen. Germany, 1990. Sheldrick. G. M., SHELXTL-PC.Siemens Analytical X-ray Instruments Inc.. Madison, Wisconsin, U.S.A., 1990.
References page 185 Chapter 6 187
Table 6.3. Selected Bond Lengths (A)and Angles (deg) for complex 17.
Symmetry Transformations used to generate equivalent atoms:
# 1 -x+ 1, y . -~+3/2 #2 X, y , -~+3/2
Refererices page 185 Chapter 6 188
Table 6.4. Selected Bond Lengths (A)and Angles (deg) for complex 18.
Symmetry Transformations used to generate equivalent atoms: #I -x+ l . y. -z+3/2.
References page 185 Chapter 6 189
Table 6.5. Selected Bond Lengths (A)and Angles (deg) for complex 20. Ir( 1 )-H( 1Ir) Ir( 1)-N( 1) Ir( 1)-P(2) H( 1Ir)-H(2Ir) H(2Ir)-mH(20) 0(1)-N( 1 ) H( lo).--F(4)#1 O(2)-N(2) H(20)~--F(3) N(2)-C(2) F(4)---0( 1 )#2
H( 1 1r)-Ir(1 )-H(2Ir) H( 1 If)-Ir( 1 )-N( 1 ) H(2Ir)-Ir( 1 )-N( 1) H( 1Ir)-Ir( 1 )-N(2) H(2Ir)-Ir( 1 )-N(2) N( 1 )-Ir( 1 )-N(2) H( 1Ir)-Ir(1 )-P(2) H(2Ir)-Ir( 1 )-P(2) N( 1 )-Ir( 1 )-P(2) N(2)-Ir( 1 )-P(2) H( 1Ir)-Ir( 1 )-P(1) H(2Ir)-Ir( 1 )-P(1 ) N( 1 )-Ir( 1 )-P(1 ) N(2)-Ir( 1 )-P( 1 ) P( 1 )-Ir( 1)-P(2) Ir( 1 )-H(1Ir)-H( LO) Ir( 1 )-H(2Ir)-H(20) C(l1)-P(1)-k(1) C(3 1 )-P( 1 )-Ir( 1) C(5 1)-P(2)-Ir(1 ) C(2 1 )-P(1 )-Ir( 1) 0(1 )-H(10)--F(4)# 1 C(4 1 )-P(2)-Ir( 1) F(4)#I-H( 10)-H( 1 Ir) C(61 )-P(2)-Ir( 1 ) O(2)-H(20)*..F(3) O( 1)-H( 10)-N(1 ) F(3)-.H(20)-H(2Ir) O( 1 )-H(10)-H( 1 Ir) C( 1)-N(1)-H( 10) H(20)-O(2)-N(2) O( 1)-N( 1)-Ir( 1) O(2)-H(20)--H(21r) C(2)-N(2)-Ir(1) C( 1)-N( 1)-If( 1) C( 16)-C( 1 1)-P( 1) O(2)-N(2)-h( 1) C(42)-C(41 )-P(2) C( 12)-C( 1 1)-P( 1) C(46)-C(41 )-P(2)
B ( 1)-F(4)-..H( 10)#2 . , Symmetry Transformations used to generate equivalent atoms: #1 x* -y+2.z-1/2 #2 x, -y+2, z+1/2
Refererlces page 185 Chapter 6 190
Table 6.6. Summary of Crystal Data, Details of Intensity Collection, and Least-Squares
Refinement Parameters for complexes* 17, 18 and 20. Complex 17 20 empirical formula C49H82TrN4P2 C44.50H82BC13F4Ir N202P2 crystal size 0.43 x 0.32 x 0.2 1 0.72 x 0.40 x 0.40 0.62 x 0.48 x 0.38 Formula weight 98 1.33 950.28 1 124.42 Crystal class Orthorhombic Orthorhombic Monoclinic Space group Cmcm Pnrna ~IC 15.977(3) 17.318(4) 24.995(3) 10.3 15(2) 27.589(4) 2 1.543(2) 27.843(5) 9.552(3) 19.370(2) 90 90 100.622(9)" 4589(2) 4564(2) 1025 l(2) 4 4 8 1.42 1 1.383 1.457 3.017 3.033 2.875 2044 1984 4624 l73(2) 293(2) 173(2) Reflections collected 3537 6285 15116 Independent reflections 3537 6285 1481 1 Refinement method Full-matrix least- Full-matrix least- Full-matrix least- squares on F? squares on F2 squares on FZ Data Irestmints1 parameters 3537 I01 163 Goodness-of-fit on ~2 0.915 Rf [I > 2o(1)] 0.033 1 wR2 (all data) 0.0668 Largest diff. peak and hole ,733 & -.701 e~-3
References page 185 Chapter 7. Molecular Structure of IrH2(BF4)(PCy3)2 that contains Ir-FBF3 and Agostic Ira-H-C bonds
7.1. Introduction
The structural elucidation of transition metal polyhydrides has been of interest in order to better understand their bonding and reactions.' Many have already been examined or re- examined by X-ray or neutron diffraction analysis and some have been found to possess dihydrogen ligands. Due to the absence of structural evidence the solid state structure of the unstable polyhydrido iridium complex [I~H~(PCY~)~]+remains unclear. The preparation and charilcterization of [IrHa(~Cy3)2]+has been communicated by Crabtree et al? It is obtained by protonating IrH5(PCy3)2 with HBF4-Eta0at -80 OC. The proposed formula of this complex is [Ir(H2)2(H)2(PCy3)2](BFJ) 21 a bis(hydrid0)bis(dihydrogen) complex. This dihydrogen complex 21 is stable at -80 OC or at room temperature under an atmosphere of Hz. The evidence for the formulation of 21 is the low temperature proton NMR spectrum showing two resonances: one at -5.05 ppm for the Ir(H2)2 group and one at - 15.2 ppm for the IrH2 group. At room temperature these become a broad resonance at -8.3 ppm due to exchange between Ir-H and Ir-(H2) units2 In the course of studying this species. we obtained a number of different crystalline materials depending on the solvent system used. One interesting species investigated here is Ir(H)2(FBF3)(PCy3)2. The equatorial plane of the metal-centered octahedron of this complex is occupied by two hydrides, a CH proton of one of the PCy3 groups (an agostic M-H-C bond3) and a non-coordinating BF4- anion.
References page 203 Chapter 7
(b) X = BF4, PF6, AsF6, SbF6
Figure 7.1. Examples of octahedral geometry with a vacant site occupied by an agostic proton (a) or a non-coordinating counterion (b).
An agostic interaction as shown in Figure 7.l(a). is weak in general with an M4-I distance of 2.6 to 2.9 and is regarded as a two electron three centre bond. However. intramolecular interaction can lead to a strong $-binding of a Iigand's CH bond. Good
examples of very short Me-H distances are 1.87 A in [~e(P(oM~)~} (q3-Cx~ I 3)](~~4)4 and
[(CM~B(PY~~ZOIY~)21(~7~7) (CO)NO.~ The coordination of very weak bases such as fluorinated anions (Figure 7.l(b))to transition metals has been reviewed by Beck et aL6 There are quite a number of complexes with a type (b) interaction. Examples include [Ni(en)2(HzO) (B F4)] (B F4),7 W(PPhMe2)(CO)3(NO)(FSbF5)? and Cp W(N0)2(BF4).9 In most cases they are unstable and behave as strong Lewis acids since !he coordinated anion acts as a good leaving group in the presence of any donor molecule or solvent.
7.2. Results and discussion
7.2.1. Formation of IrH2(B FJ)(PCY~)~ (22)
In an attempt to grow crystals of 21, a sample of IrHs(PCy3)2 was suspended in C6H6 under N2. Immediately after the addition of HBF4Et20 to the suspension a clear.
References page 203 bright yellow solution formed. This solution was left in a Schlenk tube with n-hexanes for slow diffusion at 20 OC. Over a week the solution turned light green from which light green crystals were formed. These crystals were analyzed by X-ray studies and identified as an iridium(II1) dihydridc IrH2(BF4)(PCy3)222 (Section 7.2.3). The crystals are very air- sensitive and decomposed before other characterization could be done. An attempt to remake crystals of 22 lead to another product. After treatment of the suspension of the pentahydride with a slight excess of HBF4 in toluene under N, and stirring at room temperature for a week, the isolated ivory-yellow microcrystalline solid product was not 22. but a solvent-coordinated hydrido complex 23 (Equation 7.1) based on the following proton and phosphorus NMR spectra.
toluene -2H7
The 3l~{~H)NMR spectrum of the isolated product in CDzC12 contains two singlets at 38.1 and 28.1 ppm. In the proton-coupled 31~NMR spectrum these two singlets become a pseudo-triplet centered at 38.14 ppm (J = 66.4 Hz) and a doublet centered at 28.1 1 ppm (J~H= 409.6 Hz). The triplet is due to 23 while the doublet is assignable to HPCy3f. indicating the liberation of a PCy3 ligand from the complex. The characteristic resonance in the proton NMR spectrum of the product is a doublet at -17.3 ppm (JPH= 17 Hz) for the two equivalent hydrides. In addition, the appearance of multiplets in the region from 7 to 6 ppm confirms the presence of toluene as a ligand. A resonance with a large PH coupling constant appears as a doublet of quartets at 5.4 ppm (J = 476 Hz) for the hydrogen in the P-H of protonated phosphine.
Refeiwzces page 103 Chapter 7
7.2.2. Discussion
The complex 21 which is thought to form immediately in the reaction of pentahydride with HBF4 in CH~CIZreadily loses two dihydrogen ligands under N2. In such a situation. the iridium atom has to obtain two pairs of electrons to adopt a stable 18-electron configuration. As a result, a six-coordinate species is formed by making an agostic C-H-Ir bond and an F-Ir bond from BF3- (Scheme 7.1). The mechanism for the formation of 23 may involve the stepwise coordination of a toluene molecule from q2 to 114 to q6 as discussed elsewhere1*followed by the liberation of one of the PCy3 ligands.
Scheme 7.1. Formation of 22 or 23 in the reaction of the pentahydridc with tetrafluoroboric acid.
7.2.3. X-ray structure analysis of IrHz(BF4)(PCy3)2 (22)
The single crystal X-ray analysis of 22 at 173 K revealed that the complex has a pseudo-octahedral geometry about the iridium centre (Figure 7.2).
Referertces page 203 Chapter 7
Figure 7.2. ORTEP diagram for IrH2(BF4)(PCy3)2 22.
Referettccrs page 203 Chapter 7 196
There are two cis hydrides and two trans phosphorus Iigands, the F from the BF4- anion and a hydrogen atom H(63A) of one cyclohexyl group. The structure contains an equatorial square plane consisting of the H( 1Ir)-H(21r)-H(63A)-F(1 ) unit with mean deviation of 0.007 A from the H(1Ir)-H(2Ir)-Ir-H(63A)plane and 0.0025 A from the H( 1Ir)-H(2Ir)-Ir-F(1) plane. The hydrogen atom H(G3A) is tram to one hydride (H(2Ir)Jwith the angle of 178(2)O and is approximately cis to the coordinated fluorine atom of the BFj- anion
{87.2(13)O). but has a larger than octahedral angle to the cis hydride { 1O3(2)0). Despite the small angle of 76(3)' between the hydrides. the HS**Hdistance is 1.73(6) A and so this is a dihydride and not a dihydrogen complex. The bonding distances and angles of this complex differ significantly from those of other PCy3 complexes with agostic interactions.]1-13 The major difference is that 22 forms a 6 member ring with a y-H while the others form a 5 member ring with a P-H. This is illustrated in Table 7.1 and in Figure 7.3 where negative and positive signs indicate the increments of L-M-P angles from 900 to illustrate the distortion of axial P-M-P angle towards or away from the hydride in the P-M-P-H-L plane. The Ir-H(63A) distance in 22 is 2.045)
A which is much shorter than in the analogous tungsten (2.27 A) and chromium (3.340( i ) A} complexes. reflecting a strong interaction with the iridium center. The Me-C distance of 3.06 A in 22 is. however, longer than for the other complexes (2.88 - 2.95 A).
Figure 7.3. Comparison of deviations from 90' L-M-P angles.
The nature of its trans ligand is partially responsible for the change from to pH coordination. When L is the small hydride. the PR3 ligands bend toward it allowing the 6
References page 203 Chapter 7 197
member ring to be formed. When L is a carbonyl group, the P-M-P angle bends away and a 5 member ring is formed.
Table 7.1. Com~arisonof distances and angles involving: M-43-C a~osticbonds.
M-P-C 1 10.42(14) 97.6( 1 0) 99.0(2) 98.8( 1) P( 1 )-M-P(2) 169.85(4) 167.5(3) 160.94(4) 160.2( 1) Me.-H-C 147.4 127.6 123.7( 1 ) La-M-P(2) 92(2)b 95.4(10) 102.4(2) 10 1.8(2) La-M-P( 1 ) 82(2)b 94.6(9) 96.6(2) 97.9(2) distances. A M...H 2.04(5) - 2.27 2.240( 1 ) M .. .C 3.06 2.89(5) 2.9436) 2.884( 1 ) % = CO unless stated. bL = hydride.
With respect to the triangular Me-H-C unit involved in the two electron three center bond, a significantly shorter Ms.-H distance (2.04 A) and a much larger M-H-C angle (0)
(1470) is found for the iridium complex compared to W and Cr (Figure 7.4). The interaction
with the iridium center is closer to linear. A possible reason for such a result is that the
cationic iridium centre is more electrophilic than the neutral W or Cr systems.
References page 203 Chupter 7
I linear
Figure 7.4. Comparison of the agostic triangular and linear structures.
Another interesting structural feature of 22 is the coordination of the BFJ- anion. There are quite a number of complexes with BFJ- coordinated6q14 some of which have been characterized by X-ray analysis. There are several examples which include complexes copper( 11) 1% 16 si1ver.1~71 nickel. lYmanganese.?o palladium.2 rhenium? tungsten.--93-25 cobaltT26and iridium.27~28 Most relevant to this study are the iridium cornple~es~~+~~ IrHCl(BF4)(CO)(PPh3)2and 1rMe2(BF~)(PMe2Ph)3.In IrHCI(BF4)(CO(PPh)the BFJ- ligand is trans to the hydride and the coordinated fluorine atom is at a distance of 2.377-(3)A from the metal centre. This distance is consistent with that (2.282(3) A] found in 22. The
F-Is-H trans angle of 169(2)', in 22 is slightly less than that ( 174(3)O1 found in
IrHCl(BF4)(CO)(PPh3)2. The Ir-F(1)-B unit in 22 is bent { 133.3(4)0) as observed in
IrHCI(BF4)(CO)(PPh3)2( l25.7(3)O}. These angles are quite common for coordinated BF4
( 125 - 142O). with variation probably due to crystal packing forces or steric repulsion between BF4 and the cis ligands. There is a larger angle of 159.50 in I~M~Z(BF~)(PM~~P~)~
References page 203 Chapter 7 199 due to the steric repulsion of the three cis phosphine groups. The longer Ir-F distance (2.389(7))A in IrMe*(BF4)(PMezPh)3 could also be due to sterics?
7.3. Conclusion
An 18 electron Ir(II1) complex containing Irm.FBF3and agostic Ir6..H-Cbonds has been identified in the reaction of IrHs(PCy3)z with HBF4 in benzene. The IrH distance in the agostic unit is 2.04(5) A and the Ir-F distance in the Ir.-FBF, unit is 2.272(3) A. An 18 electron $-toluene complex is obtained under similar condition in toluene.
7.4. Experimental
The general experimental conditions can be found in Chapter 3. 22 crystallizes in the monoclinic space group P?I/~with a = 10.034(2). h = 21.894(3). c = I7.128(3) A. P =
96.7 16(12)0. V = 3736.9(11) A3. and Z = 4. The positions of the hydrides and the coordinated CH proton were refined with isotropic thermal parameters. Summary of the crystal data, details of intensity collection, and least-squares refinement parameters for 22 is shown in Table 7.2. Selected bonding distances (A)and angles (0)for 22 are shown in Table 7.3. [Ir(H2)2(H)2(PCy3)2](BFq) (21) To the suspension of IrHg(PCy3)Z (0.1 g. 0.14 mrnol) in dichloromethane (2 mL) under an atmosphere of dihydrogen gas was added tetrafluoroboric acid etherate (26 pL. 0.I5 mmol) via syringe at 25 OC. This instantly gave a clear light orange solution. This solution was stirred for 10 min and the solvent was removed in vncuo. The residue was washed with dry hexanes (5 rnL) twice and filtered using a glass frit to give an ivory white powder. The product was identified to be bis(hydrido)bis(dihydrogen) complex2 [Ir(H2)2(H)2(PCy3 )2](BF4) 21.
References page 203 Chr~pter7 200
Formation of IrH2(BF4)(PCy3)2 (22) IrH~(Pcy3)~(50 mg, 0.07 mmol) was suspended in CH2C12 (1 rnL) under dinitrogen. To this was added tetrafluoroboric acid
etherate (ca. 15 pL, 0.08 rnrnol) to give a bright yellow solution. This solution was left in a Schlenk tube containing ca. 2 rnL of n-hexanes in a testing tube for slow diffusion. Over a week the solution turned to light green and light green crystals suitable for X-ray analysis were obtained. [IrH2(q6-CaH5CH3)(PCy3)](BF4) (23) IrHs(PCy3)2 (0.1 g, 0.14 mrnol) was suspended in toluene (2 mL) under argon and treated with a slight excess of tetrafluoroboric acid etherate (ca. 30 pL). This was stirred at room temperature over a period of a week. Solvent was evaporated in vclcuo to give the ivory-yellow microcrystalline solid.
This was washed with ether several times (3 x 2 mL) to wash out protonated tricyclohexylphosphine. The product could not be separated from the by-product.
[HPCy3]BF+ NMR of @-toluene complex 23 (CDClj): ~IP( IH}. 38.85 (s). 28 ppm (s.
[HPCy3JBF4); 3lP. 38.85 (t, jp~= 66.4 Hz), 28 ppm (d, jp~= 409.6 Hz, [HPCy3]BF4): IH. 6.8 - 6.4 (m.5H. C~HSCH~),5.4 (doublet of quartet, J~H= 476. JHH = 4.1 I Hz. IH.
[HPCy3]BFj), 2.2 - 0.5 (m, 33H. (C& 1)3 and 3H. C6H5CH3 overlapping) and -16.82 ppm (d, JPH = 37.09 Hz. 2H. IrH).
References page 203 Chapter 7 20 1
Table 7.2. Summary of Crystal Data. Details of Intensity Collection. and Least-Squares Refinement Parameters for 22.
empirical formula C36H68BF41rP2 crystal size, rnrn 0.46 x 0.33 x 0.27
Mr 841.85 crystal class Monoclinic space group P211n
(I, A 10.034(2) 11. A 2 1.8W3) c. a 17.128(3) P. dcg 96.7 l6(l2) v,A3 3736.9( 1 1 ) z 4
1 A96 3.702 L 728 1 73(2) total no. refls. 8539 independent reflections. 8087
Ri n t 0.0406 RI [I > 2qf)] 0.0328 wR2 (dl data) 0.0765 refinement method full-matrix least-squares on F-'
data I restraints I parameters 8087 / 0 / 408
goodness of fit on F~ 1 -063 parameters refined 457 Largest diff. peak and hole, e/A3 0.988 and -0.697
References page 203 Table 7.3. Selected bonding distances (A) and angles (0)for 22.
References page 203 Chapter 7
7.5. References
Morris. R. H.; Jessop, P. G. Coord. Chern. Rev., 1992. 121, 155.
Crabtree, R. H.; Lavin, M. J. Chern. Soc., Chenz.. Conttnun., 1985. 166 1.
Braga, D.: Grepioni, F.; Biradha, K.: Desiraju, G. R. J. Clzern. Soc.. Daltorl Trurzs. 1996, 3925, and references therein. Brown, R. K.; Williams, J. M.; Schultz. A. J.: Stucky. G. D.: Ittel. S. D.: Harlow. R. L. J. ,4171. Chern. Soc., 1980, 102, 981.
Cotton, F. A.: Day, V. W. Cltern. Commwt., 1974. 415. Beck, W.; Siinkel, K. Cizern. Rev.. 1988. 88, 1405.
Tomiinson. A. A. G.: Bonamico, M.; Dessy. G.: Fares. V.: Scaramuzza. L. J. Clwr~i.
Soc.. Dirlrrm Tmts, 1972. 167 1.
Hersh, W. H. J. AI~.Clzent. Sac., 1985. 107, 4599. Legzdins. P.: bIartin. D. T. Or~qarzometctllics,1983.2. 1785.
Muetterties. E. L.: Bleeke. J. R.: Wucherer, E. J.: Albright. T. A. Clrer?~.Rev.. 1982.
82. 499. Hrinekey, D. M.: Schomber, B. M.: Radzewich. C. E. J. Am. Clzort. Soc.. 1994. 116, 4515.
Zhang. K.: Gonzalez. A. A.: Muke jee. S. L.; Chou, S-J.: Hoff. C. D.: Kubat-Martin.
K. A.: Barnhart, D.: Kubas, G. J. J. Am. Chon. Soc.. 1991. 113. 9 170.
Wasserman. H. I.: Kubas, G. J.; Ryan, R. R. I. Am. Chern. Soc.. 1986. 108. 2294.
Strauss. S. H. Chern. Rev.. 1993, 93, 927. Su. C-C.: Hwang, T-T.; Wang. 0. Y. P.: Wang, S-L.: Liao. F-L. Trcltu. Met. Chrm.. 1992, 17, 91. Su, C-C.; Wu, C-Y.J. Coord. Cltern., 1994.33, 1. Lmg, H.; Kohler, K.: Schiemenz, B. J. Organornet. Chem., 1995.495. 135.
References page 203 Sibert. J. W.; Lange, S. J.; Williams. D. J.; Barrett. A. G.; Hoffman, B. M. Inorg. Chenr., 1995, 33, 2300. Burch. R. R.; Calabrese. J. C.; Ittcl. S. D. Orgunornetallics, 1988. 7. 1642. Cockman. R. W.; Hoskins, B. F.: McCormick, M. J.; O'Donnell, T. A. Iuorg. Chem., 1988. 2 7, 2742. Rheingold. A. L.; Wu. G.; Heck. R. F. Inorg. Chiin. Actcl. 1987. 131. 147. Yang, C. S.: Horng, H. C.: Liao. F. L.: Cheng, C. P. J. Clrrrm Soc.. Clwrr.. Cornrnrin ., 1994, 1637.
Honeychuck. R. V.; Hersh. W. H. Iitorg. Cl~ert~..1989, 28. 2869. Van Der Sluys. L. S.; Kubat-Martin. K. A.: Kubas, G. J.: Caulton. K. G. I~rorg. Chenr., 199 1, 30. 306. Budzichowski, T. A,: Chisholm, M. H.: Huffman. J. C.; Kramer. K. S.: Fromhold.
M. G. Inorg. Chirn. Acm. 1993. 2 13. 14 1. Egan. J. W.: Theopold, K. H. Acra Cryst., See. C 46. 1990. 1013. Olgemoller, B.: Bauer. H.; Lobermann. H.: Nagel. U.: Beck. W. Clrem. Bcr.. 1982. 11.5. 2271. Lundquist. E. G.: Folting. K.: Huffman. J. C.: Caulton. K. G. Orgc~~lunrerc~flics 1990, 9, 2254.
References page 203 Chuprer 8
Chapter 8. Conclusions and Future work
Iridium(V) or (111) hydrido complexes are very good starting materials in the reaction with a proton donor LYH group to prepare intramolecular proton-hydride bonding species. Strong proton-hydride bonds with He-H distances of 1.7 to 2.0 A have been observed in the products [I~H,(LYH)~(PR~)~]"+ of these reactions where R = Cy or Ph and LYH = NCsH4YH (Y = 0,S, NH). The most appropriate arrangement for a good intramolecular proton-hydride bond is a pseudo six member ring containing an Y-Hm"H-Irunit. The proton-hydride bond can play an important role in H/D exchange reactions between D2 (g) and such iridium hydride complexes. Studies with SpyH as a proton donor ligand in Chapters 1 through 4 indicate that stronger proton-hydride bonds are formed in complexes with PCy3 co-donor ligilnds in comparison with complexes with PPh3 co-donor ligands. The strength of proton-hydride bonds is decreased in complexes containing more PPh3 or CO ligands. When SpyH complexes contain a chloride ligand. the NH-CIIr hydrogen bond is preferred over the
NHv-HIrbond. Further experiments should be designed: i) to find the hydrogen bond donors that form the shortest and strongest interactions and to deduce the major factors that favour short and strong H.-H interactions, ii) to understand the effect of the co-donor ligands on the He--Hinteractions. iii) to compare the properties of intramolecular proton-hydride bond and intermolecular proton-hydride bond, iv) finally to discover factors that favour a fast HLMH- to-LM(H2) proton transfer (or the reverse) which would influence catalytic hydrogenation. Chapter 8 206
There are three main steps in future studies on the intramolecular proton-hydride bonds based on the general formula [MH,(LYH)~(PR~),J~+:i) varying the transition metal M centre; ii) varying proton donor ligand LYH: and ~ii)varying the alhyl groups R in PR3 co-donor ligands. We are still at the stage of keeping M and LYH in the above formula unchanged (Ir, SpyH) and varying phosphine co-donor ligands. Another co-ligand to examine is triisopropylphosphine (p1Pr3)which is very similar to PCy3 in terms of its size and basicity but which causes complexes to crystallize easily. Thus products with P'P~ ligand. [I~H,(s~~H)~(P~P~~),~"+which could be obtainable from I~H~(P~P~~)?probably have proton-hydride bonds similar to those in 1.4 or 5 described in Chapter 2. The effect
of a very small phosphine ligand like PMe3 should also be examined using known IrHs(PMe3)2 as a starting material. The second stage may be to vary LYH in [I~H,(LYH)~(PR~),J"'.Attractive proton donors to be used include py-2-NH2 (NH donor). R2PCH2OH (OH donor). and cytosine (NH donor). All have the potential of forming proton-hydride bonding in six member rings which seem most appropriate as seen in
Chapters 4 and 6. A possible problem is the insolubility of biologically related hydrogen bonding compounds, such as cytosine and thiocytosine in organic solvents. We have preliminary results that show that soluble iridium complexes can be prepared. Further studies can be carried out by varying M in [MH,(SpyH)y(PR3),]n+. So far mainly iridium hydrides have been used as starting materials. Other metal hydrides to examine include
WH3L4, ReH5L3. OsHgL2 to see periodic trends in the formation and properties of [MH,(LYH),,(PR~),]"+. Strong intramolecular proton-hydride bonds involving W and Re hydrides might be expected on the basis of literature reports described in Chapter I.