Dynamics of the Electrochemical Behavior of Diimine Tricarbonyl Rhenium(I) Complexes in Strictly Aprotic Media

The electrochemical behavior of the family of mononuclear Re(I) complexes, [Re^I(CO)<INF>3</INF>LX]ⁿ⁺, with L = 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen) and X = Cl, CN (n = 0); ACN (n = 1) and that of the metal−metal-bonded dimeric complexes [(L)(CO)<INF>3</INF>Re−Re(CO)<INF>3</INF>(L)] (L = bpy, phen) has been studied in various aprotic solvents using cyclic voltammetry (CV), chronoamperometry, and spectroelectrochemistry. The wide cathodic potential window investigated has permitted the observation of the largest number of redox processes so far obtained for these species. A detailed description of the kinetics of both oxidation and reduction processes of such species is given. The electrochemistry of the complexes [Re(CO)<INF>3</INF>(L)CN] (L = bpy, phen) is reported here for the first time. The electrochemical behavior of the monomeric species is greatly influenced by the nature of the monodentate ligand X. The concentration dependence of the cyclic voltammetric reductive behavior has evidenced the occurrence of bimolecular homogeneous processes. Such processes include homogeneous electron transfers and the competitive formation of metal−metal or μ-Cl bridged dimeric species. The influence of the solvent and that due to the presence or absence of Cl^- ions in solution is discussed. Digital simulation of the cyclic voltammetric curves is extensively used both for confirming the reaction mechanisms and for the evaluation of the relevant thermodynamic (E<INF>1/2</INF>) and kinetic parameters. Linear correlation between spectroscopic and electrochemical data for the whole family of monomeric and dimeric complexes has been found.