Next‐Generation D₂‐Symmetric Chiral Porphyrins for Cobalt(II)‐Based Metalloradical Catalysis: Catalyst Engineering by Distal Bridging

Abstract

Novel D 2 -symmetric chiral amidoporphyrins with alkylbridges across two chiral amide units on both sides of the porphyrin plane (designated "HuPhyrin") have been effectively constructed in am odular fashion to permit variation of the bridge length. The Co II complexes of HuPhyrin, [Co-(HuPhyrin)],r epresent new-generation metalloradical catalysts where the metal-centered d-radical is situated inside ac avity-like ligand with am ore rigid chiral environment and enhanced hydrogen-bonding capability.Asdemonstrated with cyclopropanation and aziridination as model reactions,t he bridged [Co(HuPhyrin)] functions notably different from the open catalysts,e xhibiting significant enhancement in both reactivity and stereoselectivity.F urthermore,t he length of the distal alkylb ridge can have ar emarkable influence on the catalytic properties.

Recent Developments in Enantioselective Transition Metal Catalysis Featuring Attractive Noncovalent Interactions between Ligand and Substrate

“…The hydrogen bond-donating ability of the amide groups in these new catalysts is improved, and the catalysts themselves show enhanced activity. 266 , 267 …”

A Chiral Macrocyclic Tetra‐N‐Heterocyclic Carbene Yields an “All Carbene” Iron Alkylidene Complex

“…[8,9] More recently,Z hang has employed chiral D 2 -symmetric porphyrin cobaltc omplexes (Figure 1C)f or enantioselective aziridination and cyclopropanation. [10][11][12] Nonetheless,t here are severald rawbacks for these catalystd esigns.F irst, they often require strong oxidants or have al imited substrate scope to form the required group (O, NR, or CR 2 )t hat is to be selectively transferred to the alkene. [13,14] Second, the synthesis of the ligands, particularly chiral porphyrins, is often cumbersome; many requirec hallenging multisteps yntheses as well as ac hiral resolution step.…”

“…Research by Che established that chiral aziridines could be synthesized catalytically from single enantiomer Mn or Ru porphyrin complexes (Figure B) . More recently, Zhang has employed chiral D 2 ‐symmetric porphyrin cobalt complexes (Figure C) for enantioselective aziridination and cyclopropanation . Nonetheless, there are several drawbacks for these catalyst designs.…”

Decarboxylative tandem C-N coupling with nitroarenes via SH2 mechanism

“…In the presence of iodide anion, the resulting (TPP)Fe(III) species and intermediate ( 90) may recombine to form the Fe-based complex ( 91 ). With the irradiation of blue LEDs, the homolytic S H 2 60 – 66 process can occur between 91 and alkyl radical, resulting in the formation of tertiary amines and the regeneration of (TPP)Fe(II). The by-products of the reaction might also confirm this mechanism (Supplementary Fig.…”