Synthesis and ESR studies of redox reactivity of bis (3,5-di-tert-butyl-1,2-benzoquinone-2-monooximato)Cu(II)

Abstract

Complexing of 3,5-di-tert-butyl-1,2-benzoquinone-2-monooxime with Cu(II) in air and under N-2 gave Cu(qo)(2) and Cu(qo)(2). H2O (where go is 3,5-di-tert-butyl-1,2-benzoquinone-2-monooximato-anion) complexes, respectively. The ESR spectroscopy showed that the reduction of these complexes with P(PhX)(3) (X = H, m-Cl, m-CH3, p-Et2N-) and 1,4-bis(diphenyldiphosphino) butane (dppb) proceeds via the radical formation (phenoxazine, amino phenoxy and nitrene type radical intermediates) and pathways of reduction depend on the structure of these complexes. The reaction of Cu(qo)(2) with dppb and P(PhX)3 phosphines gave essentially identical ESR spectra. At the same time, reduction of Cu(qo)(2). H2O with PPh3 result in entirely different unstable radical spectrum (g = 2.0046) which is further converted to another relatively stable Cu-containing radical signal (g = 2.0052). The unstable radical species attributed to nitrene type radicals. The initial complexes and all radical products were characterized by their ESR and optical spectra. (C) 2000 Elsevier Science B.V. All rights reserved.