Formation and Reactivity of Gold Carbene Complexes in the Gas Phase
journal contributionposted on 22.12.2014 by Christopher A. Swift, Scott Gronert
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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 successfulprocesses 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.