Synthesis, spectroscopy, and electrochemistry of copper(II) complexes with N,N′-bis(3,5-di-t-butylsalicylideneimine)polymethylenediamine ligands

Bulky salen CuLx derived from aliphatic polymethylene diamines, H2N(CH2)xNH2, where n=2-6, and 3,5-di-t-butylsalicylaldehyde (H2Lx) and some corresponding tetrahydrosalan complexes (CuLx′) have been synthesized and characterized by their IR, UV-vis absorption and EPR spectra, by magnetic moments and by cyclic voltammetry in acetonitrile (for H2Lx) and DMF (for CuLx). Complexes CuLx and CuLx′ are magnetically normal (μexp=1.83-1.91 μB). EPR spectra CuLx characterized by the axial g and ACu tensors with g||>g⊥ and without 14N-shf resolution in CHCl3/toluene at 300 and 150 K. The CV studies on acetonitrile solutions of H2Lx revealed a well-defined quasi-reversible redox wave at E1/2=0.95-1.15 V versus Ag/AgCl but CV of the CuLx complexes in DMF exhibit weak pronounced irreversible oxidation waves at Epa1=0.51−0.98 V and Epa2=1.16−1.33 V attributable to metal centered Cu(II/III) and ligand centered CuLx/CuLx+ couples, respectively. A poorly defined wave was observed for the quasi-reversible reduction Cu(II)/Cu(I) at potentials less than −1.0 V.