Mechanistic insights into the visible-light-driven O -arylation of carboxylic acids catalyzed by xanthine-based nickel complexes

We present a photocatalytic protocol for the O -arylation of carboxylic acids using nickel complexes bearing C8-pyridyl xanthines. Our studies suggest that the underlying mechanism operates independently of external photosensitizers. Stoichiometric experiments and crystallographic studies characterize the catalytically relevant Ni complexes. Spectroscopic and computational investigations propose a thermally controlled Ni( i )/Ni( iii ) cycle followed by a photochemical regeneration of Ni( i ) species. Furthermore, the pathways leading to the hydrodehalogenation of aryl halides, the comproportionation of Ni( i ) and Ni( iii ) species, the dimerization of Ni( i ) intermediates and the influence of the counter ion on the cross-coupling reaction are unveiled. These investigations offer a comprehensive mechanistic understanding of the photocatalytic cross-coupling reaction catalyzed by a single Ni species and highlight key aspects of nickel-catalyzed metallaphotoredox reactions.