Catalytic Alkene Hydrosilylation and Dinitrogen Silylation by Bis(silylene) and Bis(diphenylphosphino) Cobalt Chlorides

Three [SiC(sp³)Si]-pincer ligands (<b>L1</b>–<b>L3</b>) and three [PC(sp³)P]-pincer ligands (<b>L4</b>–<b>L6</b>) were reacted with CoCl(PMe₃)₃ to evaluate how silylene and phosphine coordination groups influence both stoichiometric C(sp³)–H activation behavior and catalytic performance in olefin hydrosilylation and dinitrogen silylation. Notably, the [SiCH₂Si]-pincer ligand <b>L1</b> underwent oxidative addition into a bridging methylene C(sp³)–H bond upon reaction with CoCl(PMe₃)₃, yielding a cobalt(III) hydride complex (<b>1</b>); in contrast, the [PC(sp³)P]-pincer ligand <b>L4</b>bearing the identical dipyrromethene scaffoldunderwent only ligand exchange to afford a cobalt(I) chloride complex (<b>4</b>).

In catalysis, complex <b>1</b> proved most effective for alkene hydrosilylation, operating under mild conditions and delivering excellent reactivity and regioselectivity. Mechanistic studies confirmed that initial C(sp³)–H activation at the bridging methylene group is crucial for generating the active cobalt species and thereby enabling high catalytic efficiency. Conversely, complex <b>4</b> exhibited superior activity in dinitrogen silylation relative to bis(silylene)-supported cobalt complexes.