THE INFLUENCE OF PHENYL SUBSTITUENTS ON THE REDOX POTENTIALS OF STERICALLY HINDERED TRIPODAL LIGAND COPPER COMPLEXES/

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 substit uents 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 t he compounds bis(2-pyridylmethyl)-6-phenyl-2-pyridylmethylamine (Phtpa ) and bis(6-phenyl-2-pyridylmethyl)-2-pyridylmethylamine (Ph(2)tpa) an d the synthesis and cyclic voltammetry studies of their Cu(II) perchlo rate 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, DM F, and DMA, the steric interaction between coordinated solvent and the phenyl substituents becomes important. The redox behavior of these co mplexes is consistent with anticipated modes of binding of solvent mol ecules in the inner sphere of the Cu(II) complexes.