Photoinduced biphasic hydrogen evolution: decamethylosmocene as a light-driven electron donor

Excitation of the weak electron donor decamethylosmocene on illumination with white light produces an excited‐state species capable of reducing organically solubilized protons under biphasic conditions. Insight into the mechanism and kinetics of light‐driven biphasic hydrogen evolution are obtained by analysis with gas chromatography, cyclic voltammetry, and UV/Vis and 1H NMR spectroscopy. Formation of decamethylosmocenium hydride, which occurs prior to hydrogen evolution, is a rapid step relative to hydrogen release and takes place independently of light activation. Remarkably, hydride formation occurs with greater efficiency (ca. 90 % conversion) under biphasic conditions than when the reaction is carried out in an acidified single organic phase (ca. 20 % conversion). Cyclic voltammetry studies reveal that decamethylosmocene has a higher proton affinity than either decamethylferrocene or osmocene