Harnessing the β-boron effect for regioselective Ru-catalyzed hydrosilylation of internal alkynes

Metal-catalyzed hydrosilylation of alkynes is recognized as a straightforward and atom economic method for synthesizing alkenylsilanes. While substantial advancements have been made with terminal alkynes, achieving precise regio- and stereocontrol with unsymmetrical internal alkynes remains a significant challenge. In this study, we report the utilization of an intriguing β-boron effect in metal catalysis, enabling an exclusively regioselective Ru-catalyzed hydrosilylation of propargylic N-methyliminodiacetic acid boronates (B(MIDA)) to synthesize alkenylsilanes. Variations in the Ru catalyst can lead to stereo-divergency without compromising regioselectivity. Density functional theory (DFT) calculations indicate that the hyperconjugative effect of the σ(C–B) bond, which stabilizes the electrophilic metallacyclopropene intermediate with Fischer carbene character, is crucial for achieving high regioselectivity. The observed switch in stereoselectivity is attributed to the different steric effects of 1,2,3,4,5-pentamethylcyclopenta-1,3-diene (Cp*) and cyclopenta-1,3-diene (Cp) ligands in the catalyst. This method produces a diverse array of regio- and stereodefined products incorporating boryl, silyl, and alkene functionalities, each of which serves as a valuable handle for further functionalization.