Harnessing Halide Ligands and External Electric Fields in Cobalt-Catalyzed Oxidative Cyclometalation: Mechanistic Insights and Reactivity Modulation.

This study explores the roles of halide ligands and external electric fields (EEFs) in tuning the reactivity of cobalt-catalyzed oxidative cyclometalation (OCM) of 1,6-enynes, focusing on the concerted mechanism. Using density functional theory (DFT), we investigate how these factors influence key processes in the OCM step, particularly the cleavage of π bonds, the formation of M-C bonds, and the creation of a new C-C bond. Our findings show that polar solvents lower activation barriers, while halide ligands increase them, inhibiting the reaction by weakening π back-donation and reducing orbital overlap. However, strategic application of EEFs counteracts this inhibition, enhancing electron back-donation, stabilizing the transition state, and facilitating bond formation. The Dewar-Chatt-Duncanson (DCD) model, distortion/interaction analysis, and quantum theory of atoms in molecules (QTAIM) delocalization index (DI) calculation reveal that halide ligands reduce electron density on the cobalt center, weakening π-back-donation and raising energy barriers. This work provides key insights into how electronic and geometric factors can be manipulated to optimize the catalytic performance in cobalt-catalyzed synthetic transformations.