Electrochemical Reduction of CO2 by M(CO)4(diimine) Complexes (M=Mo, W): Catalytic Activity Improved by 2,2′-Dipyridylamine

Tetracarbonyl complexes of low-valent Group VI transition metals (Mo and W), containing diimine bidentate ligands, namely W(CO)(4)(4,6-diphenyl-2,2'-bipyridine) (1), W(CO)(4)(6-(2,6-dimethoxyphenyl)-4-phenyl-2,2'-bipyridine) (2), Mo(CO)(4)(2,2'-dipyridylamine) (3), and W(CO)(4)(2,2'-dipyridylamine) (4), were synthesized and tested as homogeneous catalysts for the electrochemical reduction of CO2 in nonaqueous media. Cyclic voltammetry performed under a CO2 atmosphere, revealed that these complexes have significant catalytic activity in acetonitrile, and gas chromatographic measurements together with exhaustive electrolysis showed that CO is the major reduction product. Mechanistic insights were obtained by IR-spectroelectrochemical measurements. The substantially different electrocatalytic performances obtained for the two classes of catalysts are compared and discussed.