Competitive gold-activation modes in terminal alkynes: an experimental and mechanistic study
Ana Gimeno1, Ana B Cuenca, Samuel Suárez-Pantiga
1Departamento de Química Orgánica, Universidad de Valencia, Avda. Vicent Andrés Estellés s/n 46100-Burjassot, Valencia (Spain), Fax: (+34) 963544939.
Abstract:
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.
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