Electrochemical reversibility of the CuI–Cu0couple in bis[2,9-di(o-substituted phenyl)-1,10-phenanthroline]-copper(I) complexes. Stability of the corresponding copper(0) species

Copper(I) complexes of 1,10-phenanthroline disubstituted at the 2,9 positions or monosubstituted at the 2 position by phenyl moieties having ortho substituents have been prepared and investigated by spectral and electrochemical methods. The bis[2,9-di(o-substituted phenyl)-1,10-phenanthroline]-copper(I) complexes, where Cul is surrounded by two disubstituted phenanthroline units, undergo reversible electrochemical reduction at about –1.72 V vs. saturated calomel electrode, whereas bis[2-(o-substituted phenyl)-1,10-phenanthroline]copper(I) complexes, where Cul is surrounded by two monosubstituted phenanthroline units, undergo quasireversible/irreversible electrochemical reduction at about –1.68 V. The electrochemical reversibility of the former complexes is related to the dual effect of stabilization of copper(0) species and the steric involvement of the ortho substituents on the phenyl ring.