Investigation of the Enantioselectivity Observed in Epoxidation Reactions Catalysed by Bis‐Strapped Chiral Porphyrins Derived from L ‐Proline

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

Novel D2 -symmetric chiral amidoporphyrins with alkyl bridges across two chiral amide units on both sides of the porphyrin plane (designated "HuPhyrin") have been effectively constructed in a modular fashion to permit variation of the bridge length. The CoII complexes of HuPhyrin, [Co(HuPhyrin)], represent new-generation metalloradical catalysts where the metal-centered d-radical is situated inside a cavity-like ligand with a more rigid chiral environment and enhanced hydrogen-bonding capability. As demonstrated with cyclopropanation and aziridination as model reactions, the bridged [Co(HuPhyrin)] functions 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 properties.

Chiral porphyrin imine manganese complex as catalyst for asymmetric epoxidation of styrene derivatives

New chiral porphyrin imine was synthesized from (S)-3-benzyl-2-methyl-4-phenylbutanal according to dipyrromethane method using trifluoroacetic acid, BF₃ etherate, and p-chloranil. Manganese complex of this chiral porphyrin imine ligand was used as catalyst in the asymmetric epoxidation of styrene derivatives possessing different substituents. Styrene derivatives possessing electron withdrawing groups gave the corresponding chiral epoxides in high yield up to 98% and ee up to 99%. The mechanism for the catalytic asymmetric epoxidation was also discussed based on transfer of oxygen.

Synthesis, characterisation and catalytic use of iron porphyrin amino ester conjugates

This study described the synthesis and characterisation of C₂-symmetrical chiral Fe(iii)(porphyrin)(OMe) complexes, whose activity as cyclopropanation catalysts was investigated from both experimental and theoretical viewpoints.

Langmuir-Schaefer films of a set of achiral amphiphilic porphyrins: aggregation and supramolecular chirality

A series of new achiral porphyrins with hydrophobic dodecyl chains and hydrophilic substituents were designed in order to clarify the relationship between molecular geometry and aggregation as well as the supramolecular chirality in Langmuir-Schaefer films. These achiral porphyrins have zero (TPPA0), one (TPPA1), two (TPPA2a, TPPA2b), three (TPPA3) and four (TPPA4) long hydrophobic chains, respectively. Most of the compounds showed good spreading behaviour on a water surface except TPPA4 and could be fabricated into LS films easily. Depending on the number of alkyl chains, the porphyrin derivatives showed different aggregation behaviour in the LS films. The transferred films were characterized by UV-vis, circular dichroism (CD) and FTIR spectroscopy, and atomic force microscopy (AFM). Interestingly, some of the porphyrin assemblies were found to be optically active in the LS films although the compounds themselves are achiral. TPPA3 showed a strong Cotton effect in the LS film and fiber-like morphology on mica surface. Weak supramolecular chirality was detected from the LS films of TPPA0, TPPA1 and TPPA4, but no Cotton effect was observed for the LS films of TPPA2a or TPPA2b. On the other hand, when the LS film of TPPA3 was dipped into hexane or exposed to HCl gas, which altered the hydrophobic effect among the dodecyl chains and destroyed the π-π interactions between the porphyrin macrocyclic rings, the CD signal decreased or disappeared. The different aggregation behaviour and supramolecular chirality in the films was suggested to be related to the molecular structure and subsequent packing in their organized molecular films.