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

Platinum complexes [Pt(NHC')(NHC)][BArF] (NHC' denotes the cyclometallated N-heterocyclic carbene ligand, NHC) react with primary silanes RSiH3 leading to the cyclometallated platinum(II) silyl complexes [Pt(NHC-SiHR')(NHC)][BArF] through a process that involves the formation of C−Si and Pt−Si bonds with concomitant extrusion of H2. Low temperature NMR studies indicate that the process proceeds with the initial formation of the σ-SiH complexes [Pt(NHC')(NHC)(HSiH2R][BArF] which are stable at temperatures below 0 °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'- SiH2R)(NHC)][BArF] that undergoes a second SiH bond activation producing the final products. Computational modelling of the reaction mechanism indicate 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 C−H, in contrast to previous results observed with tertiary silanes. Furthermore, the process involves a trans to cis isomerization of the NHC ligands before the second Si−H bond cleavage