Electrocatalytic CO2 reduction by M( bpy-R)( CO)4 (M = Mo, W; R = H, tBu) complexes. Electrochemical, spectroscopic, and computational studies and comparison with group 7 catalysts

The tetracarbonyl molybdenum and tungsten complexes of 2,2'-bipyridine and 4,4'-di-tert-butyl-2,2'-bipyridine (M(bpy-R)(CO)(4); R = H, M = Mo (1), W (2); R = tBu, M = Mo (3), W (4)) are found to be active electrocatalysts for the reduction of CO2. The crystal structures of M(bpy-tBu)(CO)(4) (M = Mo (3), W (4)), the singly reduced complex [W(bpy)(CO)(4)][K(18-crown-6] (5) and the doubly reduced complex [W(bpytBu)( CO) 3][K(18-crown-6)](2) (6) are reported. DFT calculations have been used to characterize the reduced species from the reduction of W(bpy-tBu)(CO)(4) (4). These compounds represent rare examples of group 6 electrocatalysts for CO2 reduction, and comparisons are made with the related group 7 complexes that have been studied extensively for CO2 reduction.