Photocatalytic CO2 reduction and surface immobilization of a tricarbonyl Re (I) compound modified with amide groups

Amide bonds have been utilized as covalent linkages between photosensitizers and molecular catalysts in some supramolecular photocatalysts. It is unclear how the presence of amide groups affects properties of the molecular catalysts. This study examines the effect of amide derivatization on photocatalytic CO2 reduction using Re(bpy)(CO)3Cl, where bpy is 2,2′-bipyridine. Our results indicate that derivatization with electron-withdrawing amide (−CONH) groups lowered the catalytic activity by a factor of 6 when the Re(I) compound was directly excited in the absence of additional photosensitizers but facilitated electron transfer between Ru(bpy)3•+ and the Re(I) catalyst when Ru(bpy)32+ was used as a photosensitizer for excited-state electron transfer. The electron-withdrawing amide bond was then utilized to graft the Re(I) complex onto the surface of silica nanoparticles. The surface Re(I) sites were found to be well separated in a diimine-tricarbonyl coordination environment. The surface-immobilized catalyst showed activity comparable to the homogeneous Re(I) compound in photocatalytic CO2 reduction. Photochemical properties of the surface Re(I) catalyst were further probed using in situ FTIR and EPR spectroscopies. In the presence of a sacrificial electron donor, bipyridine-based, one-electron reduction of the surface Re(I) catalyst occurred upon visible-light irradiation. The results are particularly relevant to the development of photoelectrochemical devices for sustainable fuel production via CO2 reduction.