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Synergizing Mn(IV)/Mn(III) Dual-Excitable Complexes and Chiral Cobalt Catalysis for Divergent Asymmetric
Xiuliang Cheng1, Tianci Xu1, Tao Huang1
1College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
None:
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 N-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.
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