Synergizing Mn(IV)/Mn(III) Dual-Excitable Complexes and Chiral Cobalt Catalysis for Divergent Asymmetric Transformations

Despite growing interest in 3d transition metals for photoredox catalysis, manganese remains markedly underexplored in this domain. The advancement of Mn-based photochemical asymmetric transformations has been significantly hindered by the metal's extensive range of accessible oxidation states (from -3 to +7), intricate excited-state redox behavior, and the propensity to form highly reactive transient species─factors that collectively undermine precise stereochemical control. To overcome these limitations, we introduce a synergistic dual-catalytic system that integrates a unique Mn(IV)/Mn(III) dual-excitable complex featuring <i>N</i>-heterocyclic carbene (NHC) ligands with a chiral cobalt bisoxazoline complex. This well-defined manganese complex enables mechanistically distinct and controllable radical pathways through excitation at different oxidation states─Mn(IV)* and Mn(III)*─allowing each excited state to be selectively harnessed with cobalt-mediated stereocontrol. This adaptive strategy facilitates two challenging enantioselective transformations: asymmetric alkylation of acyclic α-imino esters to construct quaternary stereocenters, and enantioselective protonation to form tertiary stereocenters. A wide range of α-tertiary and α-secondary amino acid derivatives were obtained in up to 99% yield with excellent enantioselectivity (up to 99:1 er). Notably, the system exhibits pronounced nonlinear stereochemical amplification, delivering high-fidelity enantioselection (up to 99:1 er) even when using a partially enriched chiral ligand (65:35 er). By leveraging earth-abundant metals and visible-light activation, our approach provides a sustainable and versatile platform for synthesizing high-value chiral building blocks, with promising implications for pharmaceutical and materials science.