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 Ph2SiH2 results in the formation of a tetranuclear complex with silyl and hydride ligands at the Pt center, [PtH(SiPh2H){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 29Si 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. The family three: Planar hexagonal PtPd3Si3 complexes (see figure), stabilized by electron‐releasing silylene ligands, were prepared and fully characterized. Reaction with excess PhSiH3 resulted in exchange of the bridging Si ligands of the PtPd3 core. The CuI and AgI‐coordinated PtPd3Si3 complexes are more stable than the analogous adducts of the Pd4Si3 core.