Selective Reduction of CO 2 to CO by a MolecularRe(ethynyl-bpy)(CO) 3 Cl Catalyst and Attachment to CarbonElectrode Surfaces

The catalytic properties of Re(ethynyl-bpy)(CO)(3)Cl and Re(vinyl-bpy)(CO)(3)Cl were studied and compared with those of the previously reported Re(tBu-bpy))CO)(3)Cl. As a molecular catalyst, Re(ethynyl-bpy)(CO)(3)Cl reduces CO2 to CO with lower overpotential (eta approximate to 0.525 V), higher selectivity for CO (FE 96%), and higher reaction rate (I-cat/I-p = 27) compared to similar catalysts reported to date. The catalyst undergoes electropolymerization at the surface of a glassy carbon electrode in dry acetonitrile solution, creating a polymer film that is electroactive under a CO2 atmosphere. In the presence of trifluoroethanol (TFE) (pK(a) 35.4, MeCN) these films exhibit high efficiencies for CO (FECO 97%). On the basis of preliminary studies, these electrodes show promise as heterogeneous electrocatalysts. Further optimization and understanding of deactivation pathways will be required to make these systems practical. The ethynyl functionalized Re(ethynyl-bpy)(CO)(3)Cl catalyst also can be attached to graphitic carbon electrodes through the "click" reaction. This represents the first example of attachment of a CO2 reduction catalyst to an electrode surface by "click" chemistry.