A. Scott Hinman

Oxidative voltammetry of some tetraphenylporphyrins in the presence of nucleophiles leading to isoporphyrins

Abstract The oxidation of tetraphenylporphinatozinc has been examined in dichloroethane or dichloromethane solutions in the presence of nitrate, trifluoroacetate, or methanol by dc, ac, and thin layer voltammetry, and by thin layer visible and FTIR spectroelectrochemistry. Data is also presented for oxidation of tetraphenylporphine in dichloroethane saturated with water, and of chloro(tetraphenylporphinato)manganese(III) in dry dichloroethane. In all of these cases, isoporphyrin formation is indicated after the removal of two electrons from the porphyrin ring. The isoporphyrin undergoes one-electron oxidation at more positive potentials, and can be reduced with two electrons back to starting material. Two competing mechanisms are indicated for the isoporphyrin reduction.

Spectroscopic determination of the ac voltammetric response

Abstract It is shown that the spectroscopic response of a redox system to a sinusoidally modulated potential ramp mirrors the ac voltammetric response. This response, however, contains no contribution from the charging current and is specifically sensitive to individual species in the overall redox process. Thus homogeneous and heterogeneous kinetic behaviour of the individual species may be studied. Results are presented for the ferro-ferricyanide system.

Redox chemistry of trinuclear complexes possessing a hexathiolatomolybdate(IV) core : in situ syntheses, characterization and geometry optimization

The trinuclear heterobimetallic clusters [(Ph3P)Cu(µ-SR)3Mo(µ-SR)3Cu(PPh3)](R = C6H4Me-4 2, C6H4F-4 3, C6H4Cl-4 4 or C6H4Br-4 5) have been found to undergo reversible one-electron reductions. The reduction potential is sensitive to the para substituent on the thiolate and has been correlated with the electron-donating properties of the substituent. In addition, 2 undergoes a reversible one-electron oxidation. According to EPR measurements, the oxidation of 2 is molybdenum-based. Geometry optimizations based on density functional theory of the oxidized and reduced model cluster [(H3P)Cu(µ-SH)3Mo(µ-SH)3Cu(PH3)], assuming retention of the D3 point-group symmetry, have shown that both redox processes will lead to an elongation of the Mo–Cu vector. Reduction of the central molybdenum fragment will decrease the strength of the Cu to Mo donor bond. Oxidation of the central molybdenum fragment will result in a decrease of electrostatic interaction with the [(H3P)CuCu(PH3)]2+ fragment. The reaction of 2 with NOBF4 results in oxidation of the cluster. The IR spectrum of the diamagnetic reaction product shows a band at 1657 cm–1 suggesting the presence of co-ordinated NO–. Further evidence is provided by 14N NMR spectroscopy. The reactions of 2 and 5 with arenediazonium salts result in degradation of the clusters, with the liberation of organic sulfides and disulfides, suggesting the involvement of free thiyl radicals.