Abstract
The reactivity, mechanism and chemoselectivity of the Mn-catalyzed intramolecular C–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 π backbonding of high-valent MnIII metal to N atom lead to high electrophilic reactivity of Mn-nitrene. The calculated energy barrier of C–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–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–H amination originates from the structural features of porphyrazine: a rigid ligand with the big π-conjugated bond. Electron-donating substituents can further increase Mn-catalyzed C–H amination reactivity. The controlling factors found in this work may be considered as design elements for an economical and environmentally friendly C–H amination system with high reactivity and high chemoselectivity.
Highlights
Direct nitrene transfer (NT) reaction is an emerging and powerful method to convert C–H intoC–N bonds from cheap and available starting materials [1,2,3,4,5,6]
As seen in Scheme 2, it is accepted that the whole process of Mn-catalyzed reaction can be divided into two parts: the formation accepted that the whole process of Mn-catalyzed reaction can be divided into two parts: the formation of Mn-nitrene intermediate (Part I) and the insertion of nitrene group into the C–H or C=C bond of Mn-nitrene intermediate (Part I) and the insertion of nitrene group into the C–H or C=C bond (Part (Part II)
This work presents a theoretical investigation on the reactivity, mechanism and chemoselectivity of Mn-catalyzed intramolecular nitrene transfer reaction: C–H bond amination vs. C=C bond aziridination
Summary
Direct nitrene transfer (NT) reaction is an emerging and powerful method to convert C–H into. Controlling the chemoselectivity of C–H bond amination vs C=C bond aziridination is imperative to harness the full potential of this emerging method [15,16,17,18,19] Noble metal such as rhodium [20,21,22], silver [23,24,25], ruthenium [26,27], palladium [28,29] and base metal such as iron [30,31,32], cobalt [33,34], copper [35,36] have been shown to accomplish C(sp3 )-H aminations.
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