Catalytically\nRelevant Intermediates in the Ni-Catalyzed C(sp²)–H\nand C(sp³)–H Functionalization of Aminoquinoline\nSubstrates

Abstract

This Article describes\nthe synthesis and characterization of cyclometalated aminoquinoline\nNi^II σ-aryl and σ-alkyl complexes that have\nbeen proposed as key intermediates in Ni-catalyzed C–H functionalization\nreactions. These Ni^II complexes serve as competent catalysts\nfor the C–H functionalization of aminoquinoline derivatives\nwith I₂. They also react stoichiometrically with I₂ to form either aryl iodides or β-lactams within minutes\nat room temperature. Furthermore, they react with Ag^I salts\nat −30 °C to afford isolable five-coordinate Ni^III species. The Ni^III σ-aryl complexes proved inert\ntoward C­(sp²)–I bond-forming reductive elimination\nunder all conditions examined (up to 140 °C in DMF). In contrast,\na Ni^III σ-alkyl analogue underwent C­(sp³)–N bond-forming reductive elimination at 140 °C in DMF\nto afford a β-lactam product. However, despite the ability of\nthis latter Ni^III species to participate in stoichiometric\nproduct formation, the complex was not a competent catalyst for β-lactam\nformation. Overall, these results suggest against the intermediacy\nof Ni^III species in these C–H functionalization\nreactions.