Free radical reactions with dimeric cobalt(II) sulphophthalocyanine. A pulse radiolytic study

Abstract

Reactions of cobalt(II) sulphophthalocyanine dimers with the free radicals e^–(aq), OH, ĊH₂OH, Me₂C(OH)ĊH₂, and Me₂ĊOH have been investigated by optical pulse-radiolysis methods. Rate constants have been determined to be ca. 3 × 10⁹ dm³ mol^–1 s^–1 for OH and e^–(aq), but an order of magnitude less for the alcohol radicals. Similarity has been observed in the spectra produced by OH and Me₂C(OH)ĊH₂ although the kinetics are markedly different. It is proposed that, following ligand-radical formation by OH, oxidation of the metal centre and subsequent dimer splitting occurs. In the case of Me₂C(OH)ĊH₂ the formation of a metal–alkyl bond appears likely, followed by splitting of the dimeric intermediate. The transient spectra produced by e^–(aq), ĊH₂OH, and Me₂ĊOH are also very similar to one another. In these cases spectral behaviour suggests reduction of the metal centre by a ligand radical, followed by dimer dissociation (t_½ca. 2 ms).