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.