Photodriven HX-splitting (X = Cl, Br, OH) reactions underpin chemical strategies for solar energy conversion. Both HX and H<sub>2</sub>O splitting store approximately the same amount of energy per electron (E = 1.23 eV and 1.36 eV for H<sub>2</sub>O and HCl, respectively). Whereas the utility of water splitting is well-documented, the utility of HX splitting is less discussed, even though this conversion can be exploited for storing solar energy in the form of a redox flow battery or chemical fuel.  Halogen photoelimination reactions constitute the oxidative half-reaction that is needed to close a HX-splitting energy storage cycle; and it is this photoreaction that is the most kinetically and thermodynamically challenging. Usually chemical traps are required to promote halogen extrusion, which inevitably mitigates the utility of these reactions in energy storing catalysis. While trap-free halogen eliminations have begun to be developed for 4d and 5d metals, little progress has been made towards a halogen photoelimination chemistry involving non-critical 3d metal complexes. We report a family of mononuclear Ni(III) complexes that participate in trap-free halogen elimination photoreactions that are energy-storing, as determined from calorimetric measurements. Time-resolved spectroscopy and steady-state photocrystallography have revealed that a productive 3d photochemistry is realized by exploiting secondary coordination sphere effects to assist in the Ni-X bond activation process.

Energy storing photochemistry with first -row transition metal complexes

251st National Meeting (2016)

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