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 (PPh(3)) to the medium results in a significant improvement of the stability of the system, with up to ∼700 turnovers achieved within 10 h. UV-visible spectroscopic monitoring of the reaction allows identification of a PPh(3)-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 PPh(3) on the H(2)-evolution mechanism are discussed.