FORMATION OF CATIONIC MPT HETEROBIMETALLIC MU-PHOSPHIDO MU-HYDRIDO COMPLEXES

The cationic secondary phosphine complexes [CpM(CO)(L)(PR2H)]+X- (M = Ru, PR2H = PPh2H, PPhH2) L = CO; M = Fe, PR2H = PPh2H, L = CO, MeC≡CMe, C2H4; M = Mn PR2H = PCy2H, PPr2H, L = NO; X- = BF4-, PF6-) and [(η7-C7H7)(CO)2Mo(PCy2H)]PF6, prepared by following literature procedures for the synthesis of their PPh3 analogues, react with Pt(C2H4)(PPh3)2 to give [Cp(L)M(µ-PR2)(µ-H)Pt(PPh3)2]X and [(η7-C7H7)(CO)Mo(µ-PCy2)(µ-H)Pt(PPh3)2]X as the final products. The reactions proceed by one or both, of two possible reaction pathways. One pathway involves the initial oxidative addition of a P‒H bond to the Pt(0) complex to give [Cp(CO)LM(µ-PR2)PtH(PPh3)2]X followed by PPh3 loss from Pt and CO transfer from M to Pt (via a bridging CO). The rate of this CO-transfer step is sterically driven, in a manner similar to that observed for ortho-metalation reactions, with observed relative rates being as follows: µ-PPh2 ≫ μ-PPhH; µ-PCy2 > μ-PPr2; µ-PPh2 ≫ µ-AsPh2; Cr > Mo > W; Fe > Ru; Mn ≫ Re; η5-C5H4Me > η5-C5H5. The more acidic (P‒H) secondary phosphine complexes react with Pt(0) complexes by a route that involves deprotonation of the coordinated secondary phosphine to give a phosphidometal complex, which then substitutes a ligand from Pt(0) followed by CO transfer to Pt. Reprotonation of the resultant complex gives [Cp(L)M(H)(µ-PR2)Pt(CO)(PR3)]+ (PR3 = PPh3). Several complexes of this type (PR3 = PCy3) were prepared and studied from the reaction of [CpM(CO)(L)(PR2H)]+ with Pt(C2H4)2(PCy3). The deprotonation pathway provides for faster Pt-assisted CO labilization/loss than the P‒H oxida-tive-addition route. The1J195Pt-31Pµ coupling constants for a series of bimetallic μ-phosphido μ-hydrido complexes of the type [M](μ-PPh2)(μ-H)Pt(PPh3)2+ are shown to be much more sensitive to structural changes than the1J195Pt-31P values of the PPh3 trans to PM. While a plot of individual1J195Pt-31P vs1J195Pt-1H values gives relatively poor correlations, a plot of ∑1J195Pt-31P (all three31P nuclei) vs1J195Pt-1H is considerably improved suggesting an overall self-compensating effect for distortions/structural changes in individual Pt‒P bonds as [M] is varied. For these structurally very similar complexes2J31Pµ-31P(trans) varies almost linearly with1J195Pt-31Pµ +1J195Pt-31P(trans to Pµ). © 1990, American Chemical Society. All rights reserved.