Electrochemical Reduction of CO₂ to CO Catalyzed by a Bimetallic Palladium Complex

Abstract

The bis(triphosphine) ligand C6H4{P[CH2CH2P(C6H11)2]2}2, m-(triphos)2 (1), is synthesized by the reaction of m-bis(phosphino)benzene with 4 equiv of vinyldicyclohexylphosphine. Reaction of 1 with 2 equiv of [Pd(CH3CN)4](BF4)2 results in the formation of the bimetallic complex {m-(triphos)2[Pd(CH3CN)]2}(BF4)4 (2). A structural study of 2 confirms the presence of two [Pd(triphosphine)(CH3CN)]2+ substituents at the meta positions of a benzene ring. Complex 2 catalyzes the electrochemical reduction of CO2 to CO in acidic dimethylformamide solutions. The kinetics of this reaction have been studied, and the reaction is 0.5 order in catalyst and first order in CO2. This catalyst exhibits catalytic rates comparable to that of its monometallic analogues. Significantly higher turnover numbers are observed for 2 than observed previously for monometallic, bimetallic, and dendritic complexes of this class of catalysts.