Stable, but still reactive – investigations on the effects of Lewis acid binding on copper nitrene intermediates

Abstract

Copper nitrenes are proposed as reactive intermediates in a number of copper mediated aziridination and amination reactions. However, the isolation and characterization of such intermediates have proved challenging because of their transient nature. One successful approach for the stabilization of the copper‐nitrene cores is the employment of a redox innocent Lewis acid (LA) like Sc3+. We herein report the stabilization of two transient copper nitrene species 3 and 4 in the absence of LAs by employing electronegative −CF3 and −NO2 groups in the nitrene substituent. Detailed investigations of the spectroscopic properties of 3 and 4 by theoretical and experimental methods, and a comparison of their reactivities in presence and absence of LAs provide some vital insights into the effect of LAs on the geometric and electronic structures of the copper nitrenes.

Terminal Copper Nitrenoid Formation and Reactivity Induced by Absorption to an Antenna Ligand

“…They can either insert into a C−H bond or react stepwise by the initial hydrogen‐atom transfer (HAT) reaction followed by the radical rebound. The mechanism is affected by the electronic stabilization of the nitrene reactant [7,12] . Both pathways were considered for the C−H amination reaction of 3 2b to 1 4a (Figure 7).…”

“…The mechanism is affected by the electronic stabilization of the nitrene reactant. [7,12] Both pathways were considered for the CÀ H amination reaction of 3 2b to 1 4a (Figure 7).…”

Terminal Copper Nitrenoid Formation and Reactivity Induced by Absorption to an Antenna Ligand

“…Terminal copper nitrenoids can also be stabilized by dinuclear copper complexes [9][10][11] and Lewis acids. [6,12] In order to expand the CÀ N bond formation toolbox, it is important to explore new methods for generating terminal copper nitrenoids.…”

“…The intermediate was assigned as a copper(I) triplet nitrene based on experimental data and multireference calculations. Terminal copper nitrenoids can also be stabilized by dinuclear copper complexes [9–11] and Lewis acids [6,12] . In order to expand the C−N bond formation toolbox, it is important to explore new methods for generating terminal copper nitrenoids.…”

Nitrene transfer from a sterically confined copper nitrenoid dipyrrin complex

“…Cu nitrenoid (Cu–NR) species are commonly invoked as the reactive intermediate for C–H bond activation and alkene aziridination (Fig. 1); 5,10,14–36 however, the fleeting nature of these highly reactive intermediates has precluded their spectroscopic observation and direct analysis of their reactivity profiles. In the absence of structural authentication and rigorous characterization, the intermediacy of a copper nitrenoid can be inferred from computational support 37,38 and through kinetic analysis of enantioselective aziridination.…”