Electronic Effects on the rate of Oxidation of Substituted Phenanthroline Complexes of Copper(I) by Molecular Oxygen

Reactions of molecular oxygen with copper(I) complexes are of interest partly as a result of the observation that certain marine life utilize a copper based oxygen transport system, hemocyanin, and that copper has been proposed as an active site for the disproportionation of superoxide by the enzyme superoxide dismutase.2,3 Additional interest arises from a general study of the mechanism of autoxidation of transition metal complexes. A limited number of studies have been made on the kinetics of autoxidation of various cuprous complexes.4–13 We wish to report here on the influence of electronic effects on the autoxidation kinetics of a series of substituted phenanthroline complexes of copper(I). The ligands investigated are 5,6-dimethyl-,5-chloro-, 5-nitro-, and unsubstituted 1,10-phenanthroline.14 Electron withdrawing or releasing substitutents were used at the 5 or the 5 and 6 positions to give maximum variation in electronic effects while keeping the ligand donor atom and stereochemistry constant. It is significant to note that the range of reactivity towards oxidation by molecular oxygen afforded by these substituted phenanthroline complexes is as wide as that reported in the literature for cuprous complexes with widely different ligand systems.