Role of Gold(I) α‑Oxo Carbenes in the Oxidation Reactions of Alkynes Catalyzed by Gold(I) Complexes

The gas phase structures of gold­(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed β-gold­(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold­(I) α-oxo carbenenoids (a synthetic surrogate of the α-oxo carbenes) or pyridine adducts of gold­(I) enone complexes in the condensed phase and that the existence of naked α-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations