Catalytically Relevant Intermediates in the Ni-Catalyzed C(sp2)–H and C(sp3)–H Functionalization of Aminoquinoline Substrates

This Article describes the synthesis and characterization of cyclometalated aminoquinoline NiII σ-aryl and σ-alkyl complexes that have been proposed as key intermediates in Ni-catalyzed C–H functionalization reactions. These NiII complexes serve as competent catalysts for the C–H functionalization of aminoquinoline derivatives with I2. They also react stoichiometrically with I2 to form either aryl iodides or β-lactams within minutes at room temperature. Furthermore, they react with AgI salts at −30 °C to afford isolable five-coordinate NiIII species. The NiIII σ-aryl complexes proved inert toward C­(sp2)–I bond-forming reductive elimination under all conditions examined (up to 140 °C in DMF). In contrast, a NiIII σ-alkyl analogue underwent C­(sp3)–N bond-forming reductive elimination at 140 °C in DMF to afford a β-lactam product. However, despite the ability of this latter NiIII species to participate in stoichiometric product formation, the complex was not a competent catalyst for β-lactam formation. Overall, these results suggest against the intermediacy of NiIII species in these C–H functionalization reactions.