Transition Metal Complexes of Ambiphilic Ligands
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TRANSITION METAL COMPLEXES OF AMBIPHILIC LIGANDS Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University LATE TRANSITION METAL COMPLEXES OF GROUP 13 LEWIS ACID- CONTAINING AMBIPHILIC LIGANDS By BRADLEY E. COWIE, H.B.Sc A Thesis Submitted to the School of Graduate Studies in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy McMaster University © Copyright by Bradley E. Cowie, October, 2015. Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University McMaster University DOCTOR OF PHILOSOPHY (2015) Hamilton, Ontario (CHEMISTRY) TITLE: Late transition Metal Complexes of Group 13 Lewis Acid-Containing Ambiphilic Ligands AUTHOR: Bradley E. Cowie SUPERVISOR: Prof. David J. H. Emslie NUMBER OF PAGES: lii, 380 ii Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University Lay Abstract Ambiphilic ligands are defined as ligands which contain both conventional Lewis basic donors and unconventional Lewis acidic moieties, and the focus of this thesis is to expand the transition metal chemistry of Group 13 Lewis acid-containing ambiphilic ligands. This work expands the knowledge base of fundamental coordination and organometallic chemistry by exploring the effects of ambiphilic ligands on the structures, stability and reactivity of the resulting late transition metal complexes. Three different ambiphilic ligand systems have been employed in this research (TXPB, FcPPB and FcPPAl), which vary either by the structural rigidity of the ligand backbone (TXPB = thioxanthene; FcPPB and FcPPAl = ferrocene), the donor groups available to bind to the metal centre (TXPB = phosphine/thioether; FcPPB and FcPPAl = phosphine/phosphine), or the identity of the appended Lewis acid (TXPB and FcPPB = aryldiphenylborane; FcPPAl = aryldimethylalane). These ligands have provided access to a wide variety of metal–Lewis acid and metal–co-ligand–Lewis acid bonding interactions and novel reaction pathways with small molecules, some of which are relevant to the future development of unique cooperative and catalytic reactivity. iii Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University Abstract The coordination chemistry of a structurally rigid phosphine–thioether–borane ligand, TXPB (TXPB = 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9- dimethylthioxanthene), as well as the Group 13 Lewis acid-appended analogues of 1,1'- 5 5 t bis(phosphino)ferrocene, FcPPB (FcPPB = [Fe(η -C5H4PPh2){η -C5H4P Bu(C6H4BPh2- 5 5 t o)}]) and FcPPAl (FcPPAl = [Fe(η -C5H4PPh2){η -C5H4P Bu(C6H4AlMe2-o)}]) has been explored with a range of transition metal pre-cursors. Previously reported [Rh(μ-Cl)(CO)(TXPB)] (1) reacted with Me3SiBr, Me3SiI, [NMe4]F, Tl[PF6] and NaBH4 to provide [Rh(μ-Br)(CO)(TXPB)] (2), [RhI(CO)(TXPB)] (3), [Rh(CO)(TXPB-F)] {(4); TXPB-F = {5-(2,7-di-tert-butyl-4-diphenylphosphino-9,9- dimethylthioxanthenyl)}diphenylfluoroborate]}, [Rh(CO)(TXPB)][PF6] (5) and [Rh(μ- H)(CO)(TXPB)] (6), respectively; the rhodium–borane and rhodium–co-ligand–borane coordination modes within these complexes are dependant on the co-ligand bound to rhodium (co-ligand = Cl, Br, I, F, H, or none in the case of cationic 5). Additionally, previously reported [(TXPB)Rh(μ-CO)2Fe(CO)Cp] (7) reacted with n various isonitriles (CNR; R = C6H4Cl-p, 2,6-Me2-C6H3, Bu) to yield the bridging borataaminocarbyne complexes [(TXPB)Rh(μ-CO)(μ-CNR)Fe(CO)Cp] (8–10). The borane-free analogue of (7), [(TXPH)Rh(μ-CO)2Fe(CO)Cp] (11; TXPH = 2,7-di-tert- butyl-4-diphenylphosphino-9,9-dimethylthioxanthene), was synthesized for comparison, and reacted with CNC6H4Cl-p to yield [(TXPH)Rh(CO)(μ-CNC6H4Cl-p)2Fe(CO)Cp] (12), featuring two bridging isonitrile ligands. The TXPB ligand reacted with [PtMe2(cod)] (cod = 1,5-cyclooctadiene), forming [PtMePh(TXPB')] (13; TXPB' = 2,7-di-tert-butyl-5-methylphenylboryl-4- diphenylphosphino-9,9-dimethylthioxanthene), which exists in equilibrium with zwitterionic [PtMe(TXPB-Me)] (13') in solution. When heated, [PtMePh(TXPB')] (13) was converted to [PtPh2(TXPB'')] (14; TXPB'' = 2,7-di-tert-butyl-5-dimethylboryl-4- diphenylphosphino-9,9-dimethylthioxanthene) as an 86:14 equilibrium mixture with 13. Moreover, [PtMePh(TXPB')] (13) reacted with PPh3 and P(OPh)3 to provide neutral iv Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University [PtMePh(PR3)(TXPB')] [R = Ph (15), OPh (16)], or with CNXyl to yield zwitterionic [PtMe(CNXyl)2(TXPB-Me)] (17; TXPB-Me = {5-(2,7-di-tert-butyl-4- diphenylphosphino-9,9-dimethylthioxanthenyl)}methyldiphenylborate). To address several limitations with the TXPB ligand, a new borane-containing ambiphilic ligand, FcPPB (26), was prepared in a seven step convergent synthesis from commercially available ferrocene and 1,2-dibromobenzene. The FcPPB ligand reacted with the Group 10 metal pre-cursors [Ni(cod)2], [Pd2(dba)3] (dba = trans,trans- dibenzylideneacetone) and [Pt(nb)3] (nb = norbornene), yielding co-ligand free [M(FcPPB)] complexes [M = Ni (28), Pd (29), Pt (30)] exhibiting κ2PP- and η3BCC- coordination of the FcPPB ligand. Alternatively, a trisphosphine-analogue of FcPPB, 5 5 t FcPPP (FcPPP = [Fe(η -C5H4PPh2){η -C5H4P Bu(C6H4PPh2-o)}]) (25), reacted with 2 [Ni(cod)2] and [Pd2(dba)3] to form [{Ni(FcPPP)}2(μ-N2)] (33) and [Pd(η -dba)(FcPPP)] (34), respectively. Platinum complex 30 reacted with CO, CNXyl and H2, providing [Pt(CO)(FcPPB)] (35), [Pt(CNXyl)(FcPPB)] (36) and [PtH(μ-H)(FcPPB)] (37), in which the borane is no longer η3BCC-coordinated; the arylborane in FcPPB is now engaged in η2BC-, η1B- and bridging Pt–H–B coordination, respectively. Moreover, [Pt(FcPPB)] (30) reacted with PhC2H to provide [Pt(C2Ph)(μ-H)(FcPPB)] (38), which rapidly isomerized to 5 5 the vinylborane complex, [Pt(FcPPB')] (39; FcPPB' = [Fe(η -C5H4PPh2)(η - t C5H4P Bu{C6H4BPh(CPh=CHPh-Z)-o})]). The FcPPB ligand also reacted with [Au(PPh3)][GaCl4] to yield [{Au(FcPPB)}2][GaCl4] (40) as a diastereomeric mixture, or with [W(CO)6] and [Ru3(CO)12] under photochemical and thermal conditions, respectively, to yield 5 5 t [W(CO)4(FcPPB*)] (41; FcPPB* = [Fe(η -C5H4PPh2){η -C5H3P( Bu)C6H4BPh-o}]) and 5 5 [Ru3(μ-H)(CO)10(FcPPB**)] (42; FcPPB** = [Fe(η -C5H4PPh2){η - t – C5H3P( Bu)C6H4BPh2-o}] ), respectively. Both [W(CO)4(FcPPB*)] (41) and [Ru3(μ- H)(CO)10(FcPPB**)] (42) are products of intramolecular attack of the borane on the adjacent cyclopentadienyl-ring. Free FcPPB did not undergo any reaction under similar conditions. However, FcPPB reacted with B(C6F5)3 and BF3·OEt2 to yield v Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University 5 5 t FcPPB{B(C6F5)3} (43; [Fe(η -C5H4PPh2{B(C6F5)3}){η -C5H4P Bu(C6H4BPh2-o)}]) and -Ph 5 5 t + [FcPPB ][BF4] (44; [Fe(η -C5H4PPh2){η -C5H4P Bu(C6H4BPh-o)}] ), respectively; the former is a phosphine–borane adduct, whereas the latter is a bisphosphine-stabilized boronium cation. The coordination chemistry of a dimethylalane-appended analogue of FcPPB, 2 FcPPAl (27), was also investigated; reaction with [Pt(nb)3] provided [Pt(η -nb)(FcPPAl)] 2 (45), which readily reacted with C2H4, C2Ph2, H2, and CO to provide [Pt(η - 2 C2H4)(FcPPAl)] (47), [Pt(η -C2Ph2)(FcPPAl)] (48), [PtH2(FcPPAl)] (49) and [Pt(CO)(FcPPAl)] (50), respectively. Alternatively, heating a benzene solution of [Pt(η2- nb)(FcPPAl)] (45) yielded co-ligand free [{Pt(FcPPAl)}2] (46). All of the isolated platinum-FcPPAl complexes feature κ3PPAl-coordination of the FcPPAl ligand to platinum, and are the first unambiguous examples of η1Al-coordinated alkylalane complexes. vi Ph.D. Thesis Bradley E. Cowie Department of Chemistry and Chemical Biology McMaster University Acknowledgments Firstly, I’d like to thank my supervisor, Dr. David J. H. Emslie, whom in my opinion is the greatest supervisor a graduate student can have the pleasure to work for. Your relentless enthusiasm towards chemistry, your ability to help any student at any time of the day regardless of your personal schedule and agenda, and your drive for innovation and success are an inspiration, and I hope to become half the supervisor you are some day. Additionally, I am extremely grateful for the countless reference letters sent on my behalf, and your willingness to proofread through any piece of work I have completed, whether it is for a publication or for a conference presentation. Furthermore, having a friend to enjoy a few beers with, along with the occasional wrestling match is something that I will always cherish, and this thesis would not be possible without you. I would like to thank all of the Emslie group members I have had the opportunity to work with over the years, which consists of Matt Ray, Jordan Thomson, Velislava Bacharova, Adam Pantaleo, Lilly Vo, Tara Dickie, Judy Tsao, Meera Mehta, Terry Chu, Katarina Paskaruk, Aathith Vasanthakumar, Kris Kolpin, Kelly Motolko, Jeffrey Price, Nick Andreychuk, Dr. Venkat Ramalingam, Dr. Preeti Chadha, Dr. Sougandi Ilango, Dr. Bala Vidjayacoumar, Dr. Carlos Cruz, Dr. Edwin Wong and Dr. Todd Whitehorne. More specifically, I would like to thank Dr. Bala Vidjayacoumar and Dr. Carlos Cruz for showing me what it meant to be an effective and productive graduate student, as well as an Emslie group member; I will always cherish the fb and “two pizzas” jokes. Additionally, I would like to extend a special thank you to Nick Andreychuk as a colleague and as a friend; having a lab mate to share a few beers with and discuss the challenges of life as a grad student is truly priceless, and I am very grateful for having the opportunity to work alongside a friend like you. I would also like to thank my Ph.D.