Previous research has demonstrated that direct photoexcitation of Ni(II)−bipyridine complexes homolytically cleaves the Ni(II)−C(aryl) bond, generating aryl radicals and a formal Ni(I) species. The highly reactive Ni(I) intermediate is capable of essential bond-construction strategies, including coupling reactions forging sp2−sp3 and sp3−sp3 C–C and C–X bonds, and C–H activations. By evaluating an extensive array of photoredox catalysts, we have provided experimental evidence of the mechanism of the critical bond rupture step, implicating the involvement of high-energy, repulsive aryl-to-Ni LMCT states. The spectroscopic and computational insights have aided in a detailed description of the photophysical processes underlying the excited-state homolysis mechanism and identified the structural and electronic handles to promote (or discourage) radical formation. With the photochemically generated Ni(I) intermediates, we have screened their reactivity toward catalytically relevant oxidative addition reactions and provide a direct connection between reaction rates and complex electronic structure and photophysical properties. In brief, we demonstrate ground- and excited-state potential energy surfaces can be fine-tuned by various effects, including electronic and stereoelectronic modifications of the bipyridine ligand, which in turn leads to significant reactivity differences across a library of Ni(II)− and Ni(I)−bipyridine complexes.

Controlling the reactivity of nickel-bipyridine photoredox catalysts

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.