An Efficient Homogeneous Intermolecular Rhenium-Based Photocatalytic System for the Production of H2

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Abstract
We present an artificial photocatalytic model for photosystem I (PSI) using [ReBr(CO)3bipy)] (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 (k1 = 2.5 ± 0.1 × 108 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 (kobs = 3.7 ± 0.1 M−1 s−1). Therefore, a second-order process in CoIII−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]solv2+, an efficient quencher of the excited state of 1.

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