Intraligand charge transfer enables visible-light-mediated nickel-catalyzed cross-coupling reactions

We demonstrate that several visible-light mediated carbon–heteroatom cross-couplings can be carried out using a photoactive NiII precatalyst that forms in situ from a nickel salt and a bipyridine ligand decorated with two carbazole groups (Ni(Czbpy)Cl2). The activation of this precatalyst towards cross-couplings follows a hitherto undisclosed mechanism that is different from previously reported light-responsive nickel complexes that were reported to undergo metal-to-ligand charge transfer. Theoretic and spectroscopic investigations revealed that irradiation of Ni(Czbpy)Cl2 with visible-light causes an initial intraligand charge transfer event that triggers productive catalysis. Ligand polymerization affords a porous, recyclable organic polymer for heterogeneous nickel catalysis of cross-couplings. The heterogeneous catalyst shows stable performance in a packed-bed flow reactor during a week of continuous operation