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A density functional theory (DFT) mechanistic study of gold(I)-catalyzed alkynylation of the indole and pyrrole substrates, using a hypervalent iodine reagent

Citation

Ariafard, A, A density functional theory (DFT) mechanistic study of gold(I)-catalyzed alkynylation of the indole and pyrrole substrates, using a hypervalent iodine reagent, ACS Catalysis, 4, (9) pp. 2896-2907. ISSN 2155-5435 (2014) [Refereed Article]

Copyright Statement

Copyright 2014 American Chemical Society

DOI: doi:10.1021/cs500613t

Abstract

Density functional theory (DFT) was utilized to probe the mechanism of AuCl-catalyzed alkynylation of the indole and pyrrole substrates using a hypervalent iodine reagent ([(tri-iso-propysilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX)). An unprecedented reaction mechanism was shown to be operative. In this mechanism, the catalytic reaction starts with coordination of the alkyne moiety of the iodine(III) reagent to the AuCl catalyst, followed by transfer of the alkynyl group from IIII to AuI. The iodine(III) center was found to be capable of activating the alkyne triple bond more efficiently than the gold(I) center. The nucleophilic attack of the aromatic substrates on the IIII-activated alkyne gives a iodine(III) gold(I) vinyl complex. According to the calculations, this step was predicted to be the rate-determining step. Starting from the vinyl complex, the product is formed through the interaction of the occupied σAuC-orbital with the vacant σ*IC-orbital, followed by a very fast deprotonation reaction. This process that leads to the reduction of iodine(III) to iodine(I) occurs without protonation of the benzoate group of the iodine(III) moiety and with a small activation energy of 6.6 kcal/mol. It was concluded that the presence of the AuC σ-bond at the β-position converts the vinyl group to a potent reductant. The regioselectivity for the catalytic CH alkynylation of arenes is dictated by the stability of the vinyl complex. It was found that the cationic gold complexes such as PMe3Au+ are not effective catalysts for the alkynylation reaction, because they are strongly poisoned by coordination to the benzoate group of the iodine(III) reagent.

Item Details

Item Type:Refereed Article
Keywords:gold, alkynylation, indole, pyrrole, hypervalent iodine reagent, density functional theory (DFT)
Research Division:Chemical Sciences
Research Group:Inorganic Chemistry
Research Field:Transition Metal Chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Ariafard, A (Associate Professor Alireza Ariafard)
ID Code:98775
Year Published:2014
Web of Science® Times Cited:18
Deposited By:Chemistry
Deposited On:2015-03-02
Last Modified:2017-10-25
Downloads:0

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