New photoreduction catalysis by [Cu(N–N)(PPh3)2]+(N–N = 2,9-dimethyl-1,10-phenanthroline or 4,4′,6,6′-tetramethyl-2,2′-bipyridine) and its application to cobalt(III) complexes

Abstract

The copper(I) complexes [Cu(N–N)(PPh₃)₂]⁺[N–N = 2,9-dimethyl-1,10-phenanthroline (dmphen) or 4,4′,6,6′-tetramethyl-2,2′-bipyridine (tmbipy)] photocatalytically reduce cobalt(III) complexes such as [CoCl(NH₃)₅]²⁺, [Co(edta)]^–(edta = ethylenediaminetetra-acetate), and [Co(acac)₃](acac = acetylacetonate), upon irradiation with near-u.v. light corresponding to the metal-to-ligand charge-transfer absorption band (about 360 nm) of the copper(I) complex. This is a new type of photocatalytic reduction by copper(I) complexes. The photosensitizing mechanism is discussed on the basis of the Stern–Volmer relationship. The dmphen complex has a higher activity than that of the tmbipy analogue, and the reactivity of the cobalt(III) complexes decreases in the order [CoCl(NH₃)₅]²⁺ > [Co(edta)]^– > [Co(acac)₃]. The results are discussed in terms of the lifetime of the excited copper(I) complex and the reduction potentials of the cobalt(III) complexes.