Mild and Selective Carbon Dioxide Hydroboration to Methoxyboranes Catalyzed by Mn(I) PNP Pincer Complexes

Abstract

Well-defined Mn(I)-PNP pincer-type complexes were tested as non-precious transition metal catalysts for the selective reduction of CO2 to boryl-protected MeOH in the presence of hydroboranes (HBpin, 9-BBN) and borates as Lewis acids (LA) additives. The best performance was obtained under mild reaction conditions (1 bar CO2, 60 °C) in the presence of the hydridocarbonyl complex [MnH(PNPNH–iPr)(CO)2] and B(OPh)3 as co-catalyst. Preliminary mechanistic studies suggest that the initial activation step may occur by cationization of the metal center by the strong LA, and that both metal-catalyzed and metal-free steps are present in the overall catalytic system.