Significant phosphine ligand effect on the photochemical reactivity of [Cu(N–N)L2]+(N–N = 1,10-phenanthroline or 2,9-dimethyl-1,10-phenanthroline; L = tertiary phosphine)

Abstract

Photo-induced electron-transfer reactions between [Co(edta)]^– and [Cu(N–N)L₂]⁺[N–N = 1,10-phenanthroline (phen) or 2,9-dimethyl-1,10-phenanthroline (dmphen), L = tertiary phosphine, edta = ethylenediaminetetra-acetate] have been investigated. Although [Cu(N–N)(PPh₃)₂]⁺ exhibits rather low photochemical reactivity, substituting PPh₃ by a bulky and/or donative phosphine significantly enhances the reactivity. In the case of N–N = dmphen, introducing a donative phosphine, P(C₆H₄OMe-p)₃, instead of PPh₃ remarkably increases the photochemical reactivity, but in the case of N–N = phen, substituting PPh₃ by a donative and bulky phosphine such as P(C₆H₁₁)₃ much improves the photochemical reactivity. A kinetic study has also been carried out and it is concluded that this reaction proceeds via a dynamic quenching mechanism. Phosphine ligand effects are discussed in terms of the lifetime of the excited copper(I) complexes and the facility of formation of the encounter complex.