Electron-transfer kinetics of copper(II/I) complexes with the ligands 1,10-phenanthroline, 2,2'-bipyridine and their derivatives in acetonitrile

The electron-transfer kinetics of copper complexes formed with 2,2'-bipyridine, 1,10-phenanthroline, and the quinquedentate ligand, [15]aneS3-phen, have been studied using a series of cross-reactions with several different counter reagents primarily in acetonitrile solution to ensure ligand solubility. Copper(II/I) complexes with 2,2'-bipyridine and 1,10-phenanthroline are sensitive to ligand concentration in acetonitrile. Therefore, the electron-transfer process and the accompanying equilibria were best described by a stepladder scheme. Through electrochemical and kinetic studies, self-exchange rate constant values were determined for the copper(II/I) complexes of 2,2'-bipyridine and 1,10-phenanthroline. The CuII/I([15]aneS3-phen) system is the first quinquedentate macrocyclic ligand copper complex that incorporates both thiaether sulfur donor atoms and a phenanthroline ring fused to the macrocycle. This complex was fully characterized and the kinetics examined. It was determined that the CuII/I([15]aneS3-phen) system has a large self-exchange rate constant and, therefore, may be a reasonable model of the rapid electron-transfer processes found in blue copper proteins.