Sulphur vs NH Group: Effects on the CO 2 Electroreduction Capability of Phenylenediamine-Cp Cobalt Complexes.

The cobalt complex ( I ) with cyclopentadienyl and 2-aminothiophenolate ligands was investigated as a homogeneous catalyst for electrochemical CO 2 reduction. By comparing its behavior with an analogous complex with the phenylenediamine ( II ), the effect of sulfur atom as a substituent has been evaluated. As a result, a positive shift of the reduction potential and the reversibility of the corresponding redox process have been observed, also suggesting a higher stability of the compound with sulfur. Under anhydrous conditions, complex I showed a higher current enhancement in the presence of CO 2 (9.41) in comparison with II (4.12). Moreover, the presence of only one -NH group in I explained the difference in the observed increases on the catalytic activity toward CO 2 due to the presence of water, with current enhancements of 22.73 and 24.40 for I and II , respectively. DFT calculations confirmed the effect of sulfur on the lowering of the energy of the frontier orbitals of I , highlighted by electrochemical measurements. Furthermore, the condensed Fukui function f - values agreed very well with the current enhancement observed in the absence of water.