Mechanism of H(2) Evolution from a Photogenerated Hydridocobaloxime

Proton transfer from the triplet excited state of brominated naphthol to a difluoroboryl bridged Co(I)-diglyoxime complex, forming Co(III)H, was monitored via transient absorption. The second-order rate constant for Co(III)H formation is in the range (3.5-4.7) × 10(9) M(-1) s(-1), with proton transfer coupled to excited-state deactivation of the photoacid. Co(III)H is subsequently reduced by excess Co(I)-diglyoxime in solution to produce Co(II)H (k(red) = 9.2 × 10(6) M(-1) s(-1)), which is then protonated to yield Co(II)-diglyoxime and H(2).