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A General Mechanism for the Copper- and Silver- Catalyzed Olefin Aziridination Reactions: Concomitant Involvement of the Singlet and Triplet Pathways.
MedLine Citation:
PMID:  23276287     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The olefin aziridination reaction catalyzed by copper and silver complexes bearing hydrotrispyrazolylborate (Tpx) ligands has been investigated from a mechanistic point of view. Several mechanistic probe reactions were carried out, specifically competition experiments with p-substituted styrenes, stereospecificity of olefins, and the effects of the radical inhibitors. Data from these experi-ments seem to be contradictory, as they do not fully support for the reported concerted or stepwise mechanisms. Theoretical calcula-tions have provided the reaction profiles for the both silver and copper systems with different olefins to satisfy all experimental data. A mechanistic proposal has been made on the basis of the information that we collected from experimental and theoretical studies. In all cases, the reaction starts with the formation of a triplet metallonitrene species that interacts with the olefin, and aziridination reac-tion proceeds on the triplet surface. The silver-based systems hold a minimum energy crossing point (MECP) between the triplet and closed-shell singlet surfaces, which induces the direct formation of the aziridines, and therefore stereochemistry of the olefin is re-tained. In the case of copper, a radical intermediate is formed, and this intermediate constitutes the starting point for competition steps involving ring-closure (through a MECP with the open-shell singlet surface) or carbon-carbon rotation, that would explain the loss of stereochemistry with a given substrate. Overall, all the initially contradictory experimental data fit in the mechanistic proposal.
Authors:
Lourdes Maestre; W M C Sameera; M Mar Diaz-Requejo; Feliu Maseras; Pedro J Pérez
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-12-31
Journal Detail:
Title:  Journal of the American Chemical Society     Volume:  -     ISSN:  1520-5126     ISO Abbreviation:  J. Am. Chem. Soc.     Publication Date:  2012 Dec 
Date Detail:
Created Date:  2013-1-1     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7503056     Medline TA:  J Am Chem Soc     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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