Chemistry of phosphine-borane adducts at platinum centers:: Synthesis and reactivity of PtII complexes with phosphinoborane ligands

Reaction of [Pt(PEt3)(3)] with the primary and secondary phosphineborane adducts PhRPH . BH3 (R = H, Ph) resulted in oxidative addition of a P-H bond at the Pt-0 center to afford the complexes trans-[PtH(PPhR . BH3)(PEt3)(2)] (1: R = H; 2: R = Ph). The products 1 and 2 were characterized by H-1, B-11, C-13, P-31, and Pt-195 NMR spectroscopy, and the molecular structures were verified by X-ray crystallography. In both cases, a trans arrangement of the hydride ligand with respect to the phosphidoborane ligand was observed. When 2 was treated with PhPH2 . BH3, a novel phosphidoborane ligand-exchange reaction occurred which yielded I and Ph2PH . BH3. Treatment of 2 with one equivalent of depe (depe = 1,2-bis-(diethylphosphino)ethane) resulted in the formation of the complex cis- [PtH(PPh2 . BH(3)depe)] (3), in which the hydride ligand and the phosphidoborane ligand are in a cis arrangement. Treatment of 3 with PhPH2 . BH3 was found to result in an exchange of the phosphidoborane ligands to give the complex cis-[PtH(PPhH . BH3)(depe)] (4) and Ph2PH . BH3- Complex 4 was found to undergo further reaction in the presence of PhPH2 . BH3 to give meso-cis-[Pt(PPhH . BH3)(2)(depe)] (5) and raccis-[Pt(PPhH - BH3)(2)(depe)] (6).