σ-Silane Platinum(II) Complexes as Intermediates in C-Si Bond-Coupling Processes.

Platinum complexes [Pt(NHC')(NHC)][BAr ] (in which NHC' denotes a cyclometalated N-heterocyclic carbene ligand, NHC) react with primary silanes RSiH to afford the cyclometalated platinum(II) silyl complexes [Pt(NHC-SiHR')(NHC)][BAr ] through a process that involves the formation of C-Si and Pt-Si bonds with concomitant extrusion of H . Low-temperature NMR studies indicate that the process proceeds through initial formation of the σ-SiH complexes [Pt(NHC')(NHC)(HSiH R)][BAr ], which are stable at temperatures below -10 °C. At higher temperatures, activation of one Si-H bond followed by a C-Si coupling reaction generates an agostic SiH platinum hydride derivative [Pt(H)(NHC'-SiH R)(NHC)][BAr ], which undergoes a second Si-H bond activation to afford the final products. Computational modeling of the reaction mechanism indicates that the stereochemistry of the silyl/hydride ligands after the first Si-H bond cleavage dictates the nature of the products, favoring the formation of a C-Si bond over a C-H bond, in contrast to previous results obtained for tertiary silanes. Furthermore, the process involves a trans-to-cis isomerization of the NHC ligand before the second Si-H bond cleavage.