SEMINAR

Recently, the field of molecular photocatalysis and photochemistry using transition metal complexes has grown rapidly. In particular, one of the central research themes has been the development of efficient photocatalytic complexes based on earth-abundant metals as a potential eco-friendly, resource-efficient, and sustainable photochemical approach. The first part of the talk will discuss the photoreductive chlorine elimination from a Ni(III)Cl₂ complex supported by a tetradentate pyridinophane ligand, which is potentially related to the photocatalytic HX-splitting reactions for solar-to-fuel energy conversion. This work reports isolation and characterization of a stable Ni(III) complex using multi-dentate ligand structure, and developed complex exhibits efficient photochemical reaction both in solution and the solid-state. Subsequently, the Ni(III)Cl₂ species can be regenerated via a reaction with PhICl₂. The second part of the talk will discuss the chemistry of Ni complex with macrocyclic multi-dentate pyridinphane ligands. New types of tridentate pyridinophane ligands ^RN3 were developed for detailed mechanistic studies of the photocatalytic C–O cross-coupling reaction. The derived (^RN3)Ni complexes serve as active catalysts under mild conditions and without an additional photocatalyst. With the newly developed ^RN3 ligand, this work also provides direct evidence for key steps in the proposed catalytic cycle involving paramagnetic Ni species: the oxidative addition of an aryl halide to a Ni(I) species, the ligand exchange/transmetalation at a Ni(III) center, and the C–O reductive elimination from a Ni(III) species.