Protein Scaffold Activates Catalytic CO2 Hydrogenation by a Rhodium Bis(diphosphine) Complex

The utilization of CO2 to generate chemical fuels, such as formic acid, is a potentially beneficial route to balance carbon emissions and reduce dependence on fossil fuels. The development of efficient catalysts for CO2 hydrogenation is needed to implement this fuel generation. In the molecular catalyst design presented here, we covalently attached a rhodium complex, ([Rh-l((PNP)-P-gly)(2)](-), where (PNP)-P-gly is defined as P-Et2-CH2-N(CH2CO2-)-CH2-P-Et2) to a protein scaffold, (lactococcal multidrug resistant regulator from Lactococcus lactis) to use the protein environment around the metal center to control substrate delivery and therefore enable and improve catalytic activity. The reactivities of the rhodium complex and the synthetic metalloenzyme were characterized by high-pressure operando NMR techniques. In solution, the rhodium complex alone is not a catalyst for CO2 hydrogenation. Incorporation of the rhodium complex into the protein scaffold resulted in a gain of function, turning on CO2 hydrogenation activity. The metalloenzyme displayed a turnover frequency of 0.38 +/- 0.03h(-1) at 58 atm and 298 K and achieved an average turnover number of 14 +/- 3. Proposed catalytic intermediates generated and characterized suggest that the protein scaffold enables catalysis by facilitating the interaction between CO2 and the hydride donor intermediate.