Formation and Reactivity of Gold Carbene Complexes in the Gas Phase

Abstract

A series of ligated gold(I) carbenes (where the ligand is Ph 3 P, Me 2 S, 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.

Are Copper(I) Carbenes Capable Intermediates for Cyclopropanations? The Case for Ylide Intermediates

“…The rigid phenanthroline ligand is capable of suppressing the insertion process, but the copper did not provide enough stabilization to prevent a spontaneous Wolff rearrangement. As we have now observed in cobalt, iron, gold,14 and copper gas‐phase systems,13 the back‐bonding in metal carbenes may not effectively inhibit characteristic unimolecular carbene chemistry.…”

“…Gas-phase studies have provent ob ee xtremely useful in identifying intermediatesi no rganometallic reaction processes and probing their characteristics. [7][8][9][10][11][12] In the past, we have examined the gas-phase formationof metal carbenes involving cobalt(III) and iron(III)porphyrins [13] as well as triphenylphosphine-ligated gold(I)c omplexes [14] and concluded that the carbene intermediatesa re unstable and spontaneously undergo insertionsi nto am etal-ligand bond to produceametal ylide producto ru ndergo other rearrangements. There is literature precedencef or the insertions and it is also supported by computational modelling.…”

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

“…1436) through collision-induced dissociation of carbene complex triphenylphosphine adducts (e.g. 1435) and their reactions with various alkenes were also reported [1267].…”

Gold(I) Carbenoids: On‐Demand Access to Gold(I) Carbenes in Solution

“…[5] Ther educed steric shielding provided by commonly used ligands and the intrinsically high electrophilicity [6] exhibited by simple gold(I) carbenes preclude their isolation in condensed phase.Such species are however of high interest as demonstrated by gas-phase studies by Chen, [7] Schwarz, [8] and others. [9] Theisolation of this type of compounds,ortheir functional equivalents,i st herefore of great importance for the fundamental understanding of the reactivity of electrophilic gold carbenes.T ransition-metal complexes of the type [M(CHXR)],formally defined as carbenoids, [10] show similar reactivity to their carbene counterparts [11] and offer an attractive alternative to otherwise non-isolable species.T o date,h owever, very little is known about gold(I) carbenoids and their reactivity. [12] Herein we report the synthesis of easily accessible gold carbenoids bearing bulky ligands as gold carbene equivalents in solution.…”

“…[9] Theisolation of this type of compounds,ortheir functional equivalents,i st herefore of great importance for the fundamental understanding of the reactivity of electrophilic gold carbenes.T ransition-metal complexes of the type [M(CHXR)],formally defined as carbenoids, [10] show similar reactivity to their carbene counterparts [11] and offer an attractive alternative to otherwise non-isolable species.T o date,h owever, very little is known about gold(I) carbenoids and their reactivity.…”