SPECTROELECTROCHEMICAL CHARACTERIZATION OF NITRIDOCHROMIUM(V) PORPHYRINS AND THEIR REACTIVITY WITH SUBSTITUTED ACETIC ANHYDRIDES

The redox reactivity of a variety of nitridochromium(V) porphyrins was investigated by cyclic and differential pulse voltammetry as well as electronic and EPR spectroelectrochemical techniques. Each complex investigated underwent two single-electron reversible oxidation and two single-electron reversible reduction reactions at a Pt electrode in several nonaqueous solvents on the cyclic voltammetric time scale. The site of each electron-transfer reaction was centered on the porphyrin ring. This compares with the previously documented redox behavior of nitridomanganese(V) porphyrins but contrasts with the general redox behavior of chromium porphyrins. The reaction of nitridochromium(V) porphyrins with substituted acetic anhydrides produced (acylimido) chromium porphyrins at rates at least 1 order of magnitude faster than the corresponding nitridomanganese porphyrins. However, the subsequent transfer of the acylimido group from the Cr center to olefins was not observed for the complexes and olefins investigated herein. A spectroelectrochemical investigation revealed that the (acylimido)chromium porphyrins are best described as Cr(IV) cation radicals. This is in contrast to the corresponding (acylimido)manganese porphyrin complexes, which possess Mn(V) centers, and may account for the unreactivity of the (acylimido)chromium porphyrins with olefins. © 1990, American Chemical Society. All rights reserved.