The photochemical water-gas shift reaction catalysed by bis(2,2′-bipyridyl)(carbonyl)chlororuthenium(II) chloride

Abstract

[RuCl(CO)(N–N)₂]Cl [N–N = 2,2′-bipyridyl (bipy) or 1,10-phenantholine] are shown to be active catalytic species for the water-gas shift reaction under mild conditions (1–3 atm CO, 100–160 °C) and under illumination with white light. Turnover numbers of up to 20 h^–1 are observed. Stoicheiometric reactions, including labelling studies, show that CO₂ is produced thermally, whilst H₂ is produced in a photochemical step. Mechanistic and kinetic data are presented for the catalytic reaction and they show that the reaction has a mechanism similar to those previously reported for the water-gas shift reaction and it does not involve formate decomposition. The rate-determining step at all pH is photochemical loss of H₂ from [RuClH₂(bipy)₂]⁺ and different activation energies at high and low pH are attributed to different contributions from pre-equilibria involving attack of OH^– on co-ordinated CO (dominant at low pH) or protonation of [RuClH(bipy)₂](dominant at high pH). Experiments at high conversion show that at 140 °C CO can be completely converted to products. Attempts to catalyse related reactions using unsaturated substrates are also described.