Metal-ligand bifunctional based Mn-catalysts for CO2 hydrogenation reaction

Abstract

A series of monoligated bidentate aminophosphine (PN) based Noyori-type bifunctional Mn(I)-complexes has been studied for CO2 hydrogenation. The NH functionality of the PN ligand shows a metal–ligand cooperation (MLC) mechanism for CO2 hydrogenation. We show here that it is not essential for a NH functionality to show cooperation via cleavage/formation of NH bond as reported in the case of classical Noyori mechanism for ketone hydrogenation. Rather than this, the NH functionality can work as a chemically innocent ligand for stabilizing the formate anion via NH⋯O hydrogen bonding. More importantly, such stabilized formate anion favours the heterolytic H2 cleavage, which is otherwise a rate determining step. Furthermore, we show that the NH functionality plays a key role for such metal–ligand cooperation mechanism. Therefore, present study will provide an exclusive feature of chemically innocent cooperation in bifunctional catalysts for the development of more efficient catalysts design for CO2 hydrogenation reaction.