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Disclosure of some obscure mechanistic aspects of the copper-catalyzed click reactions involving N2 elimination promoted by the use of electron-deficient azides from a DFT perspective

Roohzadeh, R, Nasiri, B, Chipman, A, Yates, BF ORCID: 0000-0001-9663-3301 and Ariafard, A ORCID: 0000-0003-2383-6380 2019 , 'Disclosure of some obscure mechanistic aspects of the copper-catalyzed click reactions involving N2 elimination promoted by the use of electron-deficient azides from a DFT perspective' , Organometallics, vol. 38, no. 2 , pp. 256-267 , doi: 10.1021/acs.organomet.8b00691.

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Abstract

We have used density functional theory to explore the copper(I)-catalyzed reaction between a mesyl azide and a terminal alkyne that leads to a ketenimine whose interaction with nucleophilic water produces an amide. It is well reported in the literature that a cuprated triazole intermediate is formed during the course of such a catalytic cycle. In this contribution, we investigated the stability of this key intermediate by varying the R substituent on the azide and found that electron-withdrawing R substituents make this intermediate more reactive toward ring opening/N2 elimination; an electron-withdrawing R substituent facilitates this process by weakening the N–N bond being cleaved. We also rationalized why the cycloaddition step in this class of click reactions is required to proceed via a binuclear mechanism. The copper(I) acetylide intermediate formed during the catalysis gains extra stability upon scavenging a second Cu complex, resulting in the cycloaddition step occurring with a lower activation barrier. We also noticed that, similar to the ring closure step, inclusion of a second Cu complex may accelerate the ring opening/N2 elimination process. It was shown that the ketenimine needs to coordinate to a copper center via its nitrogen atom in order to be activated toward hydrolysis.

Item Type: Article
Authors/Creators:Roohzadeh, R and Nasiri, B and Chipman, A and Yates, BF and Ariafard, A
Keywords: density functional theory, activation energy, click reactions, electron-deficient azides
Journal or Publication Title: Organometallics
Publisher: Amer Chemical Soc
ISSN: 0276-7333
DOI / ID Number: 10.1021/acs.organomet.8b00691
Copyright Information:

© 2018 American Chemical Society

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