The Multiple Roles of Bipyridine-Nickel(II) Complex in Versatile Photoredox C(sp2)-C(sp3) Cross-Coupling

The cross-coupling reaction of low-reactivity aryl halides has been proven challenging. Herein, an efficient photochemical C(sp(2))-C(sp(3)) cross-coupling reaction of (hetero)aryl halides and a range of C(sp(3)) radical precursors (organotrifluoroborates, 1,4-dihydropyridines (DHPs), redox-active esters (RA esters), Katritzky salts, hydrocarbons, and cyclic ethers) catalyzed by inexpensive and readily available Ni(II) complexes was reported, under UV light (365-370 nm) irradiation without any exogenous photosensitizer. The reaction demonstrated a broad substrate scope (>100 examples), good functional group tolerance, and the capability to scale up the reaction by 25 times, facilitating the modification and synthesis of drug molecules. Mechanistic studies and control experiments revealed that the nickel catalyst played irreplaceable multiple roles: activating the C(sp(3)) radical precursors and aryl halides and supporting the proposed reaction mechanism, where the bipyridine-nickel complex induces the formation of C(sp(3)) radicals, followed by single-electron transmetalation and subsequent reductive elimination to give the final products.