An efficient homogeneous intermolecular rhenium-based photocatalytic system for the production of H2.

We present an artificial photocatalytic model for photosystem I (PSI) using [ReBr(CO)(3)bipy)] (1) as a photosensitizer, [Co(dmgH)(2)] (2) as a hydrogen evolution reaction catalyst, and triethanolamine as an irreversible reductive quencher. Complex 1 is more robust in the long run, and turnover numbers were more than doubled in the present study as compared to the commonly used photosensitizer [Ru(bipy)(3)](2+). The quantum yield for hydrogen production with 1 was found to be 26 +/- 2% (H produced per absorbed photon). Forward electron transfer between 1(-) and 2 was found to occur at a rate close to diffusion control (k(1) = 2.5 +/- 0.1 x 10(8) M(-1) s(-1)). The rate of hydrogen production exhibited a linear dependence on the photon flux and a quadratic dependence on the total concentration of Co (k(obs) = 3.7 +/- 0.1 M(-1) s(-1)). Therefore, a second-order process in Co(III)-H is proposed. The process showed a complex dependence on [AcOH]. An excess of dimethylglyoxime was systematically added to the system to ensure the complete formation of 2 and reduce the portion of free [Co](solv)(2+), an efficient quencher of the excited state of 1.