Distinguishing Similar Benzyl Radicals via Metal-Mediated Noncovalent Interactions for Csp3–Csp3 Coupling

The mode that bonding metal catalyst and radical species to carbon-metal greatly enriches the diversities of radical cross coupling, while noncovalent interaction between carbon-centered radical and metal catalyst is seldom revealed, especially in the discrimination of highly similar/identical radical species. Here, we demonstrate an unprecedented cobalt-tuned π-π stacking paradigm with benzyl radical for selective C(sp3)-C(sp3) radical coupling by employing abundant methylarenes and redox-active alkyl esters as benzyl sp3 carbon radical source under noble metal-free photochemical conditions. This robust protocol enables the quickly selective bonding of structurally similar benzyl radicals for the production of secondary-quaternary, tertiary-quaternary, quaternary-quaternary, secondary-tertiary and tertiary-tertiary alkyl scaffolds for constructing high value pharmaceutical building blocks. Detailed mechanistic studies indicate that the easy-available tridentate N ligand terpyridine render the success of π-π stacking mechanism for overcoming the innate challenge of radical Csp3–Csp3 coupling.