Competitive Gold-Activation Modes in Terminal Alkynes: An Experimental and Mechanistic Study

The competition between π‐ and dual σ,π‐gold‐activation modes is revealed in the gold(I)‐catalyzed heterocyclization of 1‐(o‐ethynylaryl)urea. A noticeable effect of various ligands in gold complexes on the choice of these activation modes is described. The cationic [Au(IPr)]+ (IPr=2,6‐bis(diisoprop...

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Published in:Chemistry : a European journal 2014-01, Vol.20 (3), p.683-688
Main Authors: Gimeno, Ana, Cuenca, Ana B., Suárez-Pantiga, Samuel, de Arellano, Carmen Ramírez, Medio-Simón, Mercedes, Asensio, Gregorio
Format: Article
Language:English
Subjects:
acetylides
Activation
Alkynes
Chemistry
Competition
dual activation
Gold
gold intermediates
ligand effects
Ligands
Spectrometry
Terminals
Ureas
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Summary:The competition between π‐ and dual σ,π‐gold‐activation modes is revealed in the gold(I)‐catalyzed heterocyclization of 1‐(o‐ethynylaryl)urea. A noticeable effect of various ligands in gold complexes on the choice of these activation modes is described. The cationic [Au(IPr)]+ (IPr=2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidene) complex cleanly promotes the π activation of terminal alkynes, whereas [Au(PtBu3)]+ favors intermediate σ,π species. In this experimental and mechanistic study, which includes kinetic and cross‐over experiments, several σ‐gold, σ,π‐gold, and other gold polynuclear reaction intermediates have been isolated and identified by NMR spectroscopy, X‐ray diffraction, or MALDI spectrometry. The ligand control in the simultaneous or alternative π‐ and σ,π‐activation modes is also supported by deuterium‐labeling experiments. Eclectic urea! A model to reveal the competition between π‐ and dual σ,π‐gold‐activation modes has been found in the ligand‐controlled heterocyclization of 1‐(o‐ethynylphenyl)urea (see scheme). The model contributes towards a better understanding of the key pathways in the activation of terminal alkynes in gold‐catalyzed reactions.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201304087