Visible-light-induced photocatalysis of poly(pyridine-2,5-diyl). Photoreduction of water, carbonyl compounds and alkenes with triethylamine

Abstract

Poly(pyridine-2,5-diyl)(PPy) exhibits heterogeneous and visible-light-induced photocatalysis toward the reduction of water, carbonyl compounds and alkenes in the presence of triethylamine (TEA) as a sacrifical electron donor. The water reductive H₂ evolution is ehnanced by colloidal noble metals concurrently photoformed from noble metal halides, and colloidal Ru gives the highest apparent quantum yield of H₂, 0.21 at 450 nm. With regard to the reduction of carbonyl compounds and electron-deficient alkenes, noble-metal-free PPy leads to the efficient and selective reduction to the corresponding alcohols and dihydro compounds, respectively. Carbonyl compounds whose reduction potentials are as negative as –1.83 V vs. SCE in acetonitrile are photoreducible. Deuterium incorporation experiments with dimethyl maleate and/or dimethyl fumarate in [O-²H]methanol have revealed that the photocatalysis of PPy should proceed through sequential two-electron transfer reduction, affording dideuteriated dimethyl succinate. Sequential electron transfer and hydride transfer mechanisms are proposed.