The influence of phenyl substituents on the redox potentials of sterically hindered tripodal ligand/copper complexes

Abstract

Abstract The structural characterization of Cu(I) and Cu(II) complexes of tris(6-phenyl-2-pyridylmethyl)amine (tppa), a derivative of the known tris(2-pyridylmethyl)amine (tpa), was recently reported. The phenyl substituents in [Cu(tppa)AN](ClO4)2 stabilize the Cu(I) state by 300–480 mV relative to [Cu(tpa)AN](ClO4)2. Reported here is the synthesis of the compounds bis(2-pyridylmethyl)-6-phenyl-2-pyridylmethylamine (Phtpa) and bis(6-phenyl-2-pyridylmethyl)-2-pyridylmethylamine (Ph2tpa) and the synthesis and cyclic voltammetry studies of their Cu(II) perchlorate complexes. The mechanism by which the phenyl groups increase the redox potential was found to be solvent-dependent: in AN, the increase in potential is primarily due to reduced local dielectric; in IBN, DMF, and DMA, the steric interaction between coordinated solvent and the phenyl substituents becomes important. The redox behavior of these complexes is consistent with anticipated modes of binding of solvent molecules in the inner sphere of the Cu(II) complexes.