Mechanism and Chemoselectivity of Mn-Catalyzed Intramolecular Nitrene Transfer Reaction: C–H Amination vs. C=C Aziridination

Autor: Ting Li, Xiaojing Zhan, Juping Wang, Kangcheng Zheng
Jazyk: angličtina
Rok vydání: 2020
Předmět:
Zdroj: Catalysts
Volume 10
Issue 3
Catalysts, Vol 10, Iss 3, p 292 (2020)
ISSN: 2073-4344
DOI: 10.3390/catal10030292
Popis: The reactivity, mechanism and chemoselectivity of the Mn-catalyzed intramolecular C&ndash
H amination versus C=C aziridination of allylic substrate cis-4-hexenylsulfamate are investigated by BP86 density functional theory computations. Emphasis is placed on the origins of high reactivity and high chemoselectivity of Mn catalysis. The N p orbital character of frontier orbitals, a strong electron-withdrawing porphyrazine ligand and a poor &pi
backbonding of high-valent MnIII metal to N atom lead to high electrophilic reactivity of Mn-nitrene. The calculated energy barrier of C&ndash
H amination is 9.9 kcal/mol lower than that of C=C aziridination, which indicates that Mn-based catalysis has an excellent level of chemoselectivity towards C&ndash
H amination, well consistent with the experimental the product ratio of amintion-to-aziridination I:A (i.e., (Insertion):(Aziridination)) >
20:1. This extraordinary chemoselectivity towards C&ndash
H amination originates from the structural features of porphyrazine: a rigid ligand with the big &pi
conjugated bond. Electron-donating substituents can further increase Mn-catalyzed C&ndash
H amination reactivity. The controlling factors found in this work may be considered as design elements for an economical and environmentally friendly C&ndash
H amination system with high reactivity and high chemoselectivity.
Databáze: OpenAIRE
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