Lewis Acids and Electron-Withdrawing Ligands Accelerate CO Coordination to Dinuclear Cu^I Compounds

A series of dinuclear molecular copper complexes werepreparedand used to model the binding and Lewis acid stabilization of CO inheterogeneous copper CO2 reduction electrocatalysts. Experimentalstudies (including measurement of rate and equilibrium constants)and electronic structure calculations suggest that the key kineticbarrier for CO binding may be a sigma-interaction between Cu-I and the incoming CO ligand. The rate of CO coordination canbe increased upon the addition of Lewis acids or electron-withdrawingsubstituents on the ligand backbone. Conversely, K (eq) for CO coordination can be increased by adding electrondensity to the metal centers of the compound, consistent with stronger pi-backbonding. Finally, the electrochemically measured kineticresults were mapped onto an electrochemical zone diagram to illustratehow these system changes enabled access to each zone. A family of dinuclear CuII compoundscoordinate two CO moleculesupon two successive reductions. The thermodynamics and kinetics forthe CO coordination reaction can be changed through modifying theligand backbone or adding Lewis acids to reaction conditions. Thereaction mechanism was mapped onto an EC Zone Diagram to show howmodest system changes can enable access to each zone.