Electrochemical Behaviour of Cr and W Fischer Ethoxy Carbene Complexes: A Comparative Study

Abstract

A comparative electrochemical study of a series Fischer carbene complexes (FCCs) of Cr and W containing an ethoxy and an aryl group as carbene substituents, showed that the Cr-FCCs generally exhibit two one-electron oxidation processes, namely Cr (0) to Cr (I) to Cr (II) while W-FCCs are oxidized in two two-electron oxidation processes, namely W(0) to W(II) to W(IV). The first one-electron oxidation processes of Cr-FCCs is generally reversible, while the first two-electron oxidation processes of all W-FCCs are found to be irreversible. The first reduction process observed for both the W-FCCs and Cr-FCCs is a one-electron process located on the carbene ligand. Both the metal oxidation, as well as the carbene reduction of Cr-FCCs, occurs at lower potentials than for W-FCCs. Substitution of carbonyls coordinated to the metal, or the group attached to the carbene ligand, led to similar trends related to the ease of oxidation or reduction of Cr-FCC and W-FCCs. Density functional theory calculations support and led to a better understanding of experimental electrochemical behaviour.