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Photochemical Nickel-Catalyzed C–H Arylation: Synthetic Scope and Mechanistic Investigations

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journal contribution
posted on 21.09.2016, 15:20 by Drew R. Heitz, John C. Tellis, Gary A. Molander
An iridium photocatalyst and visible light facilitate a room temperature, nickel-catalyzed coupling of (hetero)­aryl bromides with activated α-heterosubstituted or benzylic C­(sp3)–H bonds. Mechanistic investigations on this unprecedented transformation have uncovered the possibility of an unexpected mechanism hypothesized to involve a Ni–Br homolysis event from an excited-state nickel complex. The resultant bromine radical is thought to abstract weak C­(sp3)–H bonds to generate reactive alkyl radicals that can be engaged in Ni-catalyzed arylation. Evidence suggests that the iridium photocatalyst facilitates nickel excitation and bromine radical generation via triplet–triplet energy transfer.