Electrochemical study of chromium(0) Fischer carbene complexes : trends in redox potential

Abstract

It is illustrated that the electrochemical redox potentials of chromium(0) Fischer carbene complexes containing a heteroaromatic substituent can be determined to a high degree of accuracy from the gas phase density functional theory (DFT) optimized frontier orbital energies, with a mean average error of the calculated redox potentials of 0.047 V for the chromium-based oxidation potential and 0.057 V for the carbene ligand based reduction potential. For the first time it was possible to distinguish between the Cr0/I oxidation peaks of the E and the Z-isomer of a cyclohexylamino pentacarbonyl chromium Fischer carbene complex, namely [(CO)5CrC(NHCy)(2-thienyl)]. The linear relationship obtained between the oxidation potential and the DFT calculated highest molecular orbital energies, made it possible to assign the oxidation peak at the lower less positive oxidation potential to the oxidation of the E isomer, and the peak at the slightly higher (more positive) oxidation potential to the oxidation of the Z isomer of [(CO)5CrC(NHCy)(2-thienyl)].