Inductive, Steric, and Environmental Effects in the Nonaqueous Electrochemistry of Hexakis(aryl isocyanide)chromium Complexes

The electrochemical behavior of a series of hexakis(aryl isocyanide)chromium(I) complexes has been studied by cyclic voltammetry. The inductive effects of para substituents on E°′ for the (0 ↔ 1+), (1+ ↔ 2+), and (2+ ↔ 3+) couples have been found to give linear correlations with the Hammett σ_p parameter. Solvent and supporting-electrolyte effects have also been investigated and are discussed in terms of donor/acceptor theory and ion-pairing effects, respectively. The introduction of bulky ortho substituents on the aryl isocyanide ring was found to dramatically influence both the E°′_3+/2+ and the substitutional lability of the Cr(CNR)₆³⁺ complexes. These effects are attributed to significant weakening of the Cr^III-C bonds in the ortho-substituted complexes relative to the para-substituted complexes due to steric interactions among the ortho substituents.