Promoting Effect of Electrostatic Interaction between a Cobalt Catalyst and a Xanthene Dye on Visible-Light-Driven Electron Transfer and Hydrogen Production

TLDR: The readily obtained noble-metal-free molecular catalyst systems, with xanthene dyes (Rose Bengal, RB2−; Eosin Y, EY2-; and EOSin B, EB2−) as photosensitizers, [Co(bpy)3]Cl2 as catalyst, and triethylamine as sacrificial electron donor, are highly active for visible-light-driven (λ > 450 nm) hydrogen production from water.

Abstract: The readily obtained noble-metal-free molecular catalyst systems, with xanthene dyes (Rose Bengal, RB2–; Eosin Y, EY2–; and Eosin B, EB2–) as photosensitizers, [Co(bpy)3]Cl2 as catalyst, and triethylamine as sacrificial electron donor, are highly active for visible-light-driven (λ > 450 nm) hydrogen production from water. The turnover frequency is up to 54 TON/min versus RB2– with a RB2–/[Co(bpy)3]Cl2 molar ratio of 1:10 in CH3CN/H2O under optimal conditions in the first half hour of irradiation (λ > 450 nm), and the turnover number is up to 2076 versus RB2–. Comparative studies show the following: (1) The photocatalytic H2-evolving activity of the cationic cobalt complex [Co(bpy)3]Cl2 is apparently higher than the neutral cobaloxime complexes with xanthene dyes as potosensitizers, and also much higher than the analogous system of [Ru(bpy)3]Cl2/[Co(bpy)3]Cl2. (2) The UV–vis absorptions of xanthene dyes are red-shifted to different extents upon addition of [Co(bpy)3]Cl2 to the aqueous or CH3CN/H2O solution...