While one-electron homolytic radical chemistry is both rich in fundamental reactivities and attractive with practical advantages, the synthetic application of radical reactions has been long hampered by the formidable challenges associated with the control over reactivity and selectivity of high-energy radical intermediates. To fully harness the untapped potential of radical chemistry for organic synthesis, there is a pressing need to formulate radically different concepts and broadly applicable strategies to address these outstanding issues. In pursuit of this objective, we and others have been actively developing metalloradical catalysis (MRC) as a comprehensive framework to guide the design of general approaches for controlling over reactivity and stereoselectivity of homolytic radical reactions. Essentially, MRC exploits the potential of metal-centered radicals within open-shell metal complexes as on-electron catalysts for homolytic activation of substrates to generate metal-entangled organic radicals as the pivotal intermediates to govern the reaction pathway and stereochemical course of subsequent catalytic radical processes. Different from the conventional two-electron catalysis by transition metal complexes, MRC operates through one-electron chemistry utilizing stepwise radical mechanisms. For achieving enantioselective radical reactions via MRC, we have designed D₂-symmetric chiral amidoporphyrins with tunable electronic, steric, and chiral environments as a general ligand flatform to support the development of metalloradical catalysts. These structurally well-defined chiral metalloradical catalysts, such as Co(II) and Fe(III) complexes, can effectively catalyze a wide range of important organic transformations through distinctive radical mechanisms that involve fundamentally new α-metalloalkyl, α-metalloaminyl, α-metalloxyl, and other metal-entangled organic radicals as the catalytic intermediates.

Peter Zhang

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