The complex [Co(dmgH)(2)pyCl](2+) (1, dmgH = dimethylglyoximate, py = pridine) has been used as a molecular catalyst for visible light driven hydrogen production in the presence of [Pt(tolylterpyridine) (phenylacetylide)](+) (3) as a photosensitizer and triethanolamine (TEOA) as a sacrificial reducing agent. Complex 3 is quenched oxidatively by [Co(dmgH)pyCl](2+) (1) with a rate constant k(q) of 1.27 x 10(9) M-1 s(-1). Photogeneration of H-2 is only seen when 1 + 3 + TEOA are all present. H-2 production is maximized for this system at pH 8.5 and declines to very low levels at pH < 7 and pH > 12. Irradiation of the reaction solution initially containing 1.61 x 10(-2) M TEOA, 1.11 x 10(-5) M of 3, and 1.99 x 10(-4) M of Co catalyst 1 in MeCN/water (3:2 v/v) at pH = 8.5 for 10 h with lambda > 410 nm yields 400 turnovers of H-2. When TEOA is 0.27 M, similar to 1000 turnovers are obtained after 10 h of irradiation. Spectroscopic study of the photolyses solutions suggests that H-2 formation proceeds via Co(I) and protonation to form Co(III) hydride species.