Novel homogeneous selective electrocatalysts for CO2 reduction: an electrochemical and computational study of cyclopentadienyl-phenylendiamino-cobalt complexes

Four cyclopentadienyl-phenylendiamino-cobalt complexes [CoCp(bqdi)] with different substituents (R) at the phenylene moiety (bqdi, I; o-perfluoro-bqdi, II; p-NO2-bqdi, III; p-COOH-bqdi, IV) have been studied with the aim to investigate their capability as catalysts for CO2 reduction. These compounds were characterized by cyclic voltammetry measurements both under nitrogen and CO2 atmospheres, showing a increase of the cathodic current ranging from 3.36 (III) to 5.59 times (II) respect to the measurement under nitrogen. Moreover, by addition of water the current enhancement in the presence of CO2 arrives till 31.07 times in the case of complex II. Interestingly, these complexes present a very good selectivity toward CO2 reduction respect hydrogen even in the presence of water. Relative turnover frequencies have been also estimated given values ranging from 3.23 (III) to 187.21 s-1 (II) in the presence of water. In addition, these results have been analysed by means of density functional theory (DFT) calculations and Fukui functions analysis. In particular, DFT results clearly show the effects of the different substituents on the electrochemical properties of these compounds. Whereas the Fukui functions analysis indicates that the most favourable positions for electrophilic attack on the reduced complex are the nitrogen and the cobalt atoms.