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

A series of monoligated bidentate aminophosphine (PN) based Noyori-type bifunctional Mn(I)-complexes has been studied for CO2 hydrogenation. The N-H 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 N-H functionality to show cooperation via cleavage/formation of N-H bond as reported in the case of classical Noyori mechanism for ketone hydrogenation. Rather than this, the N-H functionality can work as a chemically innocent ligand for stabilizing the formate anion via N-H center dot center dot center dot O hydrogen bonding. More importantly, such stabilized formate anion favours the heterolytic H-2 cleavage, which is otherwise a rate determining step. Furthermore, we show that the N-H 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.