Planar PtPd3 Complexes Stabilized by Three Bridging Silylene Ligands.

A heterobimetallic PtPd3 complex supported by three bridging diphenylsilylene ligands, [Pt{Pd(dmpe)}3 (µ3 -SiPh2 )3 ] (1, dmpe=1,2-bis(dimethylphosphino)ethane), has been synthesized from mononuclear Pd and Pt complexes. The hexagonal core composed of Pt, Pd, and Si atoms is slightly larger than that of the tetrapalladium complex, [Pd{Pd(dmpe)}3 (µ3 -SiPh2 )3 ] (2). Reaction of PhSiH3 with complex 1 in the presence and absence of Ph2 SiH2 results in the formation of a tetranuclear complex with silyl and hydride ligands at the Pt center, [PtH(SiPh2 H){Pd(dmpe)}3 (µ3 -SiHPh)3 ] (3), and an octanuclear complex, [{Pt{Pd(dmpe)}3 (µ3 -SiHPh)3 }2 (κ2 -dmpe)] (5), respectively. Both M-Si (M=Pt, Pd) bond lengths and the 29 Si NMR chemical shifts of 1 and 2 are located between those of mononuclear late transition-metal complexes with a silylene ligand and complexes with donor-stabilized silylene ligands. CuI and AgI adducts of 1 and 2, formulated as [M(µ-M'I){Pd(dmpe)}3 (µ3 -SiPh2 )3 ] (M=Pt, Pd; M'=Cu, Ag), undergo elimination of CuI (AgI) and regenerate the tetrametallic complexes upon heating or addition of a chelating diphosphine. Elimination of AgI from 2-AgI occurs more rapidly than elimination of CuI from 2-CuI, as determined from the results of kinetics experiments.