The role of Si in Ir(SiNN) catalyst and chemoselectivity of dehydrogenative borylation over hydroborylation: A theoretical study

An Ir(SiNN) complex has been reported that efficiently catalyzes dehydrogenative C-H borylation, rather than hydroborylation, of terminal alkynes. Here we performed density functional theory calculations to elucidate the reaction mechanism and attempt to explain the strict chemoselectivity for dehydrogenative borylation. The calculations suggest that the chemoselectivity arises mainly from (1) interaction between Si and the metal hydride, which stabilizes the metal center during the addition of HBpin or CH3CCH; and (2) migration of the Bpin onto the amide N of the SiNN pincer ligand, which twists the pincer ligand to provide space for oxidative addition of the terminal alkyne to the Ir center.