A Versatile NHC-Parent Silyliumylidene Cation for Catalytic Chemo- and Regioselective Hydroboration

This study describes the first use of a divalent silicon complex, NHC-parent silyliumylidene cation complex [(IMe)2SiH]I (1, IMe = :C{N(Me)C(Me)}2) as a versatile catalyst in organic synthesis. Com-plex 1 (loading: 10 mol%) was shown to act as an efficient catalyst (reaction time: 0.08 h, yield: 94 %, TOF = 113.2 h-1; reaction time: 0.17 h, yield: 98 %, TOF = 58.7 h-1) for the selective reduction of CO2 with pinacolborane HBpin to form the primarily reduced formoxyborane [pinBOC(=O)H]. The activity is better than the cur-rently available base-metal catalysts used for such reaction. It also catalysed the chemo- and regioselective hydroboration of carbonyl compounds and pyridine derivatives to form borate esters and N-boryl-1,4-dihydropyridine derivatives with quantitative conver-sions, respectively. Mechanistic studies show that the divalent sili-con centre in complex 1 activates the substrates and then mediates the catalytic hydroboration.