C–H Amination Mediated by Cobalt Organoazide Adducts and the Corresponding Cobalt Nitrenoid Intermediates

Year: 2020

Type: article

Abstract: Treatment of ( Ar L)CoBr ( Ar L = 5-mesityl-1,9-(2,4,6-Ph 3 C 6 H 2 )dipyrrin) with a stoichiometric amount of 1-azido-4-( tert -butyl)benzene N 3 (C 6 H 4 - p - t Bu) furnished the corresponding four-coordinate organoazide-bound complex ( Ar L)CoBr(N 3 (C 6 H 4 - p - t Bu)). Spectroscopic and structural characterization of the complex indicated redox innocent ligation of the organoazide. Slow expulsion of dinitrogen (N 2 ) was observed at room temperature to afford a ligand functionalized product via a [3 + 2] annulation, which can be mediated by a high-valent nitrene intermediate such as a Co III iminyl ( Ar L)CoBr( • N(C 6 H 4 - p - t Bu)) or Co IV imido ( Ar L)CoBr(N(C 6 H 4 - p - t Bu)) complex. The presence of the proposed intermediate and its viability as a nitrene group transfer reagent are supported by intermolecular C–H amination and aziridination reactivities. Unlike ( Ar L)CoBr(N 3 (C 6 H 4 - p - t Bu)), a series of alkyl azide-bound Co II analogues expel N 2 only above 60 °C, affording paramagnetic intermediates that convert to the corresponding Co-imine complexes via α-H-atom abstraction. The corresponding N 2 -released structures were observed via single-crystal-to-crystal transformation, suggesting formation of a Co-nitrenoid intermediate in solid-state. Alternatively, the alkyl azide-bound congeners supported by a more sterically accessible dipyrrinato scaffold t Bu L ( t Bu L = 5-mesityl-(1,9-di- tert -butyl)dipyrrin) facilitate intramolecular 1,3-dipolar cycloaddition as well as C–H amination to furnish 1,2,3-dihydrotriazole and substituted pyrrolidine products, respectively. For the C–H amination, we observe that the temperature required for azide activation varies depending on the presence of weak C–H bonds, suggesting that the alkyl azide adducts serve as viable species for C–H amination when the C–H bonds are (1) proximal to the azide moiety and (2) sufficiently weak to be activated.

Source: Journal of the American Chemical Society

DOI: 10.1021/jacs.0c04252

Authors: Yunjung Baek, Anuvab Das, Shao-Liang Zheng, Joseph H. Reibenspies, David C. Powers, Theodore A. Betley

Institutions: Harvard University, Texas A&M University

Language: English

Topic: Synthesis and Catalytic Reactions

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: green

Funders: National Science Foundation, U.S. Department of Energy, Welch Foundation, Camille and Henry Dreyfus Foundation, Harvard University, Kwanjeong Educational Foundation, National Institutes of Health, National Institute of General Medical Sciences, Division of Materials Research, Division of Chemistry, Basic Energy Sciences

OpenAlex ID: W3032669994