Synthesis, Spectroscopy and Redox Chemistry of Bis(n-Aryl Butylsalicylaldiminato)-Copper(II) Complexes

Abstract

A series of new bis(N-aryl-3,5-di-tert-butylsalicylaldiminato)copper(II) complexes (I), prepared from 3,5-di-tert-butylsalicylaldehyde and mono-substituted anilines, X-C<inf>6</inf>H<inf>4</inf>NH<inf>2</inf> (X = H, o-F, Cl, Br, CH<inf>3</inf>, CH<inf>3</inf>O; p-F, Cl, Br, CH<inf>3</inf>, CH<inf>3</inf>O, t-Bu and 5,6-benzo), and their spectroscopic properties as well as electrochemistry and reactivity toward PPh<inf>3</inf> are described. Comparison of g<inf>∥</inf> (2.223-2.249), A<inf>∥</inf> (150-170G) tensors and the axial symmetry parameter, g<inf>∥</inf>/A<inf>∥</inf>, (140-155 cm) of I with those of model Cu(II) complexes reveals that the coordination site is distorted from square planar toward tetrahedral geometry. The di-tert-butyl groups on the salicylaldehyde moiety unlike those introduced on the aniline rings do not facilitate reactivity toward PPh<inf>3</inf>. Electrochemical studies of I in acetonitrile solutions reveal highly irreversible behavior, due to chemical or stereochemical changes subsequent to electron transfer. In the oxidation of some complexes with (NH<inf>4</inf>) <inf>2</inf>Ce(NO<inf>3</inf>)<inf>6</inf> in acetonitrile at 300 K, along with decreasing ESR signals of Cu(II), the appearance of coordinated phenoxyl radical signals centered at g = 2.004 were detected. The CV studies on acetonitrile solutions of I revealed well-resolved quasi-reversible redox waves at E <inf>1/2</inf>1 = 0.61-0.99 V and E<inf>1/2</inf>1 = 1.09-1.23 V (vs. Ag/AgCl) attributable to ligand-centered oxidation processes to yield corresponding coordinated phenoxyl radical species such as Cu(II)(phenoxyl)(phenolate) and Cu(II)(phenoxyl)<inf>2</inf>.