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.