Phosphine Coordination to a Cobalt Diimine-Dioxime Catalyst Increases Stability during Light-Driven H2 Production

The combination of cobalt diimine-dioxime complexes with a cyclometalated iridium photosensitizer gives efficient systems for hydrogen generation under visible-light irradiation using triethylamine as a sacrificial electron donor. Interestingly, the addition of triphenylphosphine (PPh3) to the medium results in a significant improvement of the stability of the system, with up to similar to 700 turnovers achieved within 10 h. UV-visible spectroscopic monitoring of the reaction allows identification of a PPh3-coordinated Co-I intermediate as the active species. Mechanistic issues regarding (i) the photogeneration of the Co-I species, (ii) the nature of the active species, and (iii) the influence of PPh3 on the H-2-evolution mechanism are discussed.