Hydrogen is a renewable source of reducing equivalents that could replace conventional organic sacrificial donors in artificial photosynthetic systems, fulfilling a prerequisite for the storage of solar energy. The development of transition-metal chromophore/catalyst complexes and pairings that drive hydrogen oxidation with light, and are suitable components for artificial photosynthetic systems, will be described. The chromophore/catalyst complexes are d2-configured tungsten–alkylidyne compounds of the type W(CR)L4X (R = aryl, L/X = neutral/anionic ligand). These luminophores are powerful photochemical reductants, with excited-state oxidation potentials of &lt; –3 V vs FeCp20/+ (near the one-electron reduction potential of CO2). Upon oxidation, they react sequentially with H2 and a Brønsted base to regenerate the d2 chromophore. The design parameters that allow control over redox potentials, excited-state energies, and emission lifetimes will be described. Separately, photocatalytic hydrogen oxidation has been accomplished through redox sensitization of DuBois-type Ni(PR2NR2)2n+ catalysts by chromophores including Ru(bpy)32+ and ZnTPP. These systems proceed via reductive quenching of the chromophore by Ni(PR2NR2)2+, with transient Ni(PR2NR2)22+ being trapped irreversibly by H2 prior to back electron transfer. A mechanism will be described in which turnover is achieved without an external sacrificial oxidant. The integration of these chromophore/catalyst pairs with CO2 reduction catalysts will be discussed.

Molecular systems for photocatalytic hydrogen oxidation

249th National Meeting (2015)

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