Asymmetric Epoxidation of Olefins Catalyzed by Substituted Aminobenzimidazole Manganese Complexes Derived from L‐Proline

A family of manganese complexes [Mn(Rpeb)(OTf)2] (peb=1‐(1‐ethyl‐1H‐benzo[d]imidazol‐2‐yl)‐N‐((1‐((1‐ethyl‐1H‐benzo[d]imidazol‐2‐yl)methyl) pyrrolidin‐2‐yl)methyl)‐N‐methylmethanamine)) derived from L‐proline has been synthesized and characterized, where R refers to the group at the diamine backbone...

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Bibliographic Details
Published in:Advanced synthesis & catalysis 2022-02, Vol.364 (3), p.593-600
Main Authors: Tian, Jing, Lin, Jin, Zhang, Jisheng, Xia, Chungu, Sun, Wei
Format: Article
Language:English
Subjects:
Alkenes
Aminobenzimidazole
asymmetric epoxidation
Asymmetry
Backbone
Carboxylic acids
Catalytic activity
Crystallography
Diamines
Enantiomers
Epoxidation
Hydrogen peroxide
L-proline
Manganese
manganese complex
N4 ligand
Oxidizing agents
Proline
Substitution reactions
Topology
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Summary:A family of manganese complexes [Mn(Rpeb)(OTf)2] (peb=1‐(1‐ethyl‐1H‐benzo[d]imidazol‐2‐yl)‐N‐((1‐((1‐ethyl‐1H‐benzo[d]imidazol‐2‐yl)methyl) pyrrolidin‐2‐yl)methyl)‐N‐methylmethanamine)) derived from L‐proline has been synthesized and characterized, where R refers to the group at the diamine backbone. X‐ray crystallographic analyses indicate that all the manganese complexes [Mn(Rpeb)(OTf)2] exhibit cis‐α topology. These types of complexes are shown to catalyze the asymmetric epoxidation of olefins employing H2O2 as a terminal oxidant with up to 96% ee. Obviously, the R group of the diamine backbone can influence the catalytic activity and enantioselectivity in the asymmetric epoxidation of olefins. In particular, Mn(i‐Prpeb)(OTf)2 bearing an isopropyl arm, cannot catalyze the epoxidation reaction with H2O2 as the oxidant. However, when PhI(OAc)2 is used as the oxidant instead, all the manganese complexes including Mn(i‐Prpeb)(OTf)2 can promote the epoxidation reactions efficiently. Taken together, these results indicate that isopropyl substitution on the Rpeb ligand inhibits the formation of active Mn(V)‐oxo species in the H2O2/carboxylic acid system via an acid‐assisted pathway.
ISSN:1615-4150
1615-4169
DOI:10.1002/adsc.202101151