Formation and Reactivity of Gold Carbene Complexes in the Gas Phase

A series of ligated gold­(I) carbenes (where the ligand is Ph₃P, Me₂S, or an N-heterocyclic carbene, NHC) were formed in the gas phase by a variety of methods. Gold­(I) benzylidenes could be formed using Chen’s method of dissociating an appropriate phosphorus ylide precursor. The resulting carbene undergoes an addition reaction with olefins to give an adduct. The adduct undergoes a second gas-phase reaction with an olefin, where presumably a cyclopropanation product is displaced by the second olefin molecule. Both steps in the process were analyzed with linear free energy relationships (i.e., Hammett plots). Under collision-induced dissociation conditions, the adduct undergoes competing processes: (1) dissociation of the cyclopropanation product to give ligated gold­(I) species and (2) metathesis to give a more stable gold­(I) carbene. Attempts to form less stable gold­(I) carbenes in the gas phase by Chen’s approach or by reactions of diazo species with the ligated gold­(I) cations were not successfulprocesses other than carbene formation are preferred or the desired carbene, after formation, rearranges rapidly to a more stable species. In accord with other recent work, the data suggest that coordination to a ligated gold­(I) cation in the gas phase may not offer sufficient stabilization to carbenes to prevent competition from rearrangement processes.