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

Abstract

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.

Elusive Reaction Intermediates in Solution Explored by ESI‐MS: Reverse Periscope for Mechanistic Investigations

“…[17] They analyzed ad ichloromethane reaction mixture containing an alkyne, pyridine N-oxide,a nd ag old(I) catalyst, and they detected several gold(I) intermediates.T he initial formation of b- Figure 12. Catalytic cycle for the CuAAC reaction carried out by using the imidazolium-based charged alkyne.…”

“…In our opinion, this comprehensive MS-based study by Roithovµ and co-workers, [17] together with the outstanding online monitoring exercises from the groups of McIndoe [16] and Cooks, [13a] can be considered the most impressive and reliable contribution to mechanistic investigations by using ESI-MS.…”

Expanding Roles for Lipid Droplets

“…Lipid droplets have been observed in culture in primary glia as well in glia-derived cell lines [99, 100]. When CPT2, a mitochondrial enzyme necessary for β oxidation of long-chain fatty acids, is abolished in flies, massive amounts of triglycerides accumulate specifically in the brain of adults; glial cells, but not neurons, accumulated abundant lipid droplets [101]. This seems to be a cell-autonomous effect because CPT2 is expressed predominantly in glia and CPT2 expression solely in glia is sufficient to reverse triglyceride accumulation in the brain.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Related gold-catalyzed reactions with nitriles and PNO's were also observed with diazoester-derived carbenoids. Efforts to observe gold α-oxocarbene complexes generated through oxygen transfer from pyridine-N-oxide to alkynes in the presence of gold complexes (via ESI-MS and infrared multiphoton dissociation spectroscopy) were conducted in gas and solution phases [1235]. The studies support the presence of gold α-oxocarbene complexes and the corresponding pyridine adducts, as well as enone complexes obtained from β C-H insertion in some of the cases examined.…”