Mechanistic Investigations of the AuCl3-Catalyzed Nitrene Insertion into an Aromatic C-H Bond of Mesitylene

Abstract

The AuCl3-catalyzed nitrene insertion into an aromatic C-H bond of mesitylene demonstrates a unique activity and chemoselectivity in direct C-H aminations. Mechanisms for catalytic nitrene insertion are examined here using theory. The AuCl3 catalyst favors formation of a complex with the PhI═NNs (Ns = p-nitrobenzenesulfonyl) substrate, followed by the appearance of the key (N-chloro-4-nitrophenylsulfonamido)gold(III) chloride intermediate (INT5). However, the putative gold(III)-nitrene analogue (AuCl3-NNs complex) is thermodynamically unfavorable compared with INT5. Therefore, INT5 is suggested to play a critical role in the AuCl3-promoted aromatic C-H bond amination, a prediction in contrast to the previously reported crucial metal-nitrene intermediates. The activation of a C(sp(2))-H bond of mesitylene via σ-bond metathesis is proposed based on INT5, and the subsequent detailed pathways for the aromatic C-H bond amination are computationally explored. A chemoselective nitrene insertion into a mesitylene aromatic C-H bond, instead of a benzylic C-H bond, is rationalized for the AuCl3-catalyzed amination.