Chemistry of phosphine borane adducts at platinum centers: dehydrocoupling reactivity of Pt(II) dihydrides with P-H bonds

The reaction of the Pt(II) dihydride complex cis-[PtH2(dcype)] (dcype = 1,2-bis(dicyclohexylphosphino)ethane) with the primary or secondary phosphine borane adducts PhRPH.BH3 (R = H, Ph) was found to exclusively afford the mono-substituted complexes cis-[PtH(PPhR.BH3)(dcype)] (1: R = H; 2: R = Ph) via a dehydrocoupling reaction between Pt-H and P-H bonds. Similar reactivity was observed between the uncoordinated phosphines PhRPH (R = H, Ph) and cis-[PtH2(dcype)], which gave cis-[PtH(PPhR)(dcype)] (4: R = H; 5: R = Ph). The complexes were characterized by H-1, B-11, C-13 and P-31 NMR spectroscopy, IR, MS and, in the case of 2, X-ray crystallography that confirmed the cis geometries. The di-substituted complex cis-[Pt(PhPH.BH3)(2)(dcype)] (3) was prepared from the reaction of cis-[PtCl2(dcype)] with two equivalents of Li[PPhH.BH3]. This suggested that steric reasons alone cannot be used to explain the lack of reactivity with respect to a second dehydrocoupling reaction involving the remaining Pt-H bond in complexes 1, 2, 4 and 5.