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

Abstract

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)(HSiHR)][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′-SiHR)(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.