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 (CuL'(x)) 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 CuL'(x) are magnetically normal (mu(exp) = 1.83-1.91 mu(B)). EPR spectra CuLx characterized by the axial g and A(Cu) tensors with g(parallel to) > g(perpendicular to) and without N-14-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 E-1/2 = 0.95-1.15 V versus Ag/AgCl but CV of the CuLx complexes in DMF exhibit weak pronounced irreversible oxidation waves at E-pa(1) = 0.51 - 0.98 V and E-pa(2) = 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. (C) 2004 Elsevier B.V. All rights reserved.