Enhanced Hydrogenation of Carbon Dioxide to Methanol by a Ruthenium Complex with a Charged Outer-Coordination Sphere

We report the hydrogenation of CO2 to MeOH by a Ru(triphos) catalyst containing a cationic tetraalkylammonium moiety in the outer coordination sphere. This catalyst affords higher TON and TOF values for MeOH than isostructural catalysts with neutral phosphine ligands. Kinetic data from operando NMR spectroscopy studies indicate the improvement in MeOH production arises from a 12-fold enhancement in the rate of hydrogenation of the transient formaldehyde intermediate. These results provide insight into the catalyst characteristics that promote MeOH formation.