Improvement of the photochemical reactivity of [Cu(dmp)P2]+ (dmp = 2,9-dimethyl-1,10-phenanthroline; P = tertiary phosphine) by substituting triphenylphosphine with larger phosphines: application to photoreduction of methylviologen

Abstract

Cu(I) complexes containing heteroaromatic ligands such as 2,2'-bipyridine (bpy) or 1,10-phenanthroline exhibit a metal-to-ligand charge-transfer (MLCT) band in the visible to near-ultraviolet spectral region and have a triplet MLCT state as the lowest energy excited state like (Ru(bpy)3)S which has been applied extensively to the photochemical reduction of water to hydrogen gas. Nevertheless, application of those Cu(I) complexes to the photochemical reduction of water has not been carried out, excepting only one report of Sauvage et al. Recently, they reported that Cu(I) complexes containing a heteroaromatic ligand, (Cu(NN)(PPh3)2) (NN = 2,9-dimethyl-1,10-phenanthroline (dmp) or 4,4',6,6'-tetramethyl-2,2'-bipyridine), found application as a sensitizer in photocatalytic reduction of methylviologen (MVS ) upon near-UV-light irradiation. Unfortunately, however, the quantum yield for MVS reduction (phi/sub MV /) is lower than that of (Ru(bpy)3)S . In this work, they have succeeded in improving the photoreducing activity of (Cu(dmp)(PPh3)S) by using such bulky and/or donating tertiary phosphines as cyclohexyldiphenylphosphine, PCyPh2, and tris(p-methoxyphenyl)phosphine, P(p-C6H4OMe)3, instead of PPh3. Another emphasis presented here lies in investigating the phosphine ligand effect on the photoreactivity of Cu(I) complexes, because such investigation has not been carried out yet to their knowledge.