New‐Generation D2‐Symmetric Chiral Porphyrins for Co(II)‐Based Metalloradical Catalysis: Catalyst Engineering via Distal Bridging

Novel D2‐symmetric chiral amidoporphyrins with alkyl bridges across two chiral amide units on both sides of the porphyrin plane (designated as "HuPhyrin") have been effectively constructed in a modular fashion to permit variation of bridge length. The Co(II) complexes of HuPhyrin, [Co(HuPhyrin)], represent new‐generation metalloradical catalysts where the metal‐centered d‐radical is situated inside a cavity‐like ligand with more rigid chiral environment and enhanced hydrogen‐bonding capability. As demonstrated with cyclopropanation and aziridination as model reactions, the bridged [Co(HuPhyrin)] function notably different from the open catalysts, exhibiting significant enhancement in both reactivity and stereoselectivity. Furthermore, the length of the distal alkyl bridge can have a remarkable influence on the catalytic property.

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