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

Tetracarbonyl complexes of low-valent GroupVI transition metals (Mo and W), containing diimine bidentate ligands, namely W(CO) sub(4)(4,6-diphenyl-2,2'-bipyridine) (1), W(CO) sub(4)(6-(2,6-dimethoxyphenyl)-4-phenyl-2,2'-bipyridine) (2), Mo(CO) sub(4)(2,2'-dipyridylamine) (3), and W(CO) sub(4)(2,2'-dipyridylamine) (4), were synthesized and tested as homogeneous catalysts for the electrochemical reduction of CO sub(2) in nonaqueous media. Cyclic voltammetry performed under a CO sub(2) 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. Great potential: Novel M(CO) sub(4)(dpa) (M=Mo, W; dpa=2,2'-dipyridylamine) complexes are synthesized and tested for the electrochemical reduction of CO sub(2). Improved catalytic activity towards CO sub(2) reduction is observed in acetonitrile homogeneous solutions of these complexes even in the absence of Broensted acids.