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'-bis(phosphino)ferrocene, FcPPB (FcPPB = [Fe(η5-C5H4PPh2){η5-C5H4PtBu(C6H4BPh2-o)}]) and FcPPAl (FcPPAl = [Fe(η5-C5H4PPh2){η5-C5H4PtBu(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 various isonitriles (CNR; R = C6H4Cl-p, 2,6-Me2-C6H3, nBu) 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 [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, FcPPP (FcPPP = [Fe(η5-C5H4PPh2){η5-C5H4PtBu(C6H4PPh2-o)}]) (25), reacted with [Ni(cod)2] and [Pd2(dba)3] to form [{Ni(FcPPP)}2(μ-N2)] (33) and [Pd(η2-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 the vinylborane complex, [Pt(FcPPB')] (39; FcPPB' = [Fe(η5-C5H4PPh2)(η5-C5H4PtBu{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 [W(CO)4(FcPPB*)] (41; FcPPB* = [Fe(η5-C5H4PPh2){η5-C5H3P(tBu)C6H4BPh-o}]) and [Ru3(μ-H)(CO)10(FcPPB**)] (42; FcPPB** = [Fe(η5-C5H4PPh2){η5-C5H3P(tBu)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 FcPPB{B(C6F5)3} (43; [Fe(η5-C5H4PPh2{B(C6F5)3}){η5-C5H4PtBu(C6H4BPh2-o)}]) and [FcPPB-Ph][BF4] (44; [Fe(η5-C5H4PPh2){η5-C5H4PtBu(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, FcPPAl (27), was also investigated; reaction with [Pt(nb)3] provided [Pt(η2-nb)(FcPPAl)] (45), which readily reacted with C2H4, C2Ph2, H2, and CO to provide [Pt(η2-C2H4)(FcPPAl)] (47), [Pt(η2-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. / Thesis / Doctor of Philosophy (PhD) / 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.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18520 |
| Date | 04 November 2015 |
| Creators | Cowie, Bradley E. |
| Contributors | Emslie, David J. H., Chemistry and Chemical Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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