Synthesis, Spectroscopy, and Electrochemistry of Copper(II) Complexes with N,N '-bis(3,5-di-t-butylsalicylideneimine) Polymethylenediamine Ligands

Abstract

Bulky salen CuL<inf>x</inf> derived from aliphatic polymethylene diamines, H<inf>2</inf>N-(CH<inf>2</inf>)<inf>x</inf>-NH<inf>2</inf>, where n = 2-6, and 3,5-di-t-butylsalicylaldehyde (H<inf>2</inf>L<inf>x</inf>) and some corresponding tetrahydrosalan complexes (CuL′<inf>x</inf>) have been synthesized and characterized by their IR, UV - vis absorption and EPR spectra, by magnetic moments and by cyclic voltammetry in acetonitrile (for H <inf>2</inf>L<inf>x</inf>) and DMF (for CuL<inf>x</inf>). Complexes CuL <inf>x</inf> and CuL′<inf>x</inf> are magnetically normal (μ<inf>exp</inf> = 1.83-1.91 μ<inf>B</inf>). EPR spectra CuL<inf>x</inf> characterized by the axial g and A<inf>Cu</inf>, tensors with g∥ > g⊥ and without 14N-shf resolution in CHCl<inf>3</inf>/toluene at 300 and 150K. The CV studies on acetonitrile solutions of H<inf>2</inf>L <inf>x</inf> revealed a well-defined quasi-reversible redox wave at E <inf>1/2</inf> = 0.95-1.15 V versus Ag/AgCl but CV of the CuL<inf>x</inf> complexes in DMF exhibit weak pronounced irreversible oxidation waves at E <inf>pa</inf>1, = 0.51 - 0.98 V and Ep<inf>a</inf>1 = 1.16 - 1.33 V attributable to metal centered Cu(II/III) and ligand centered CuL <inf>x</inf>/CuL<inf>x</inf>̇+ couples, respectively. A poorly defined wave was observed for the quasi-reversible reduction Cu(II)/Cu(I) at potentials less than - 1.0 V. © 2004 Elsevier B.V. All rights reserved.