Direct Observation of Aryl Gold(I) Carbenes that Undergo Cyclopropanation, C−H Insertion, and Dimerization Reactions

Abstract

Mesityl gold(I) carbenes lacking heteroatom stabilization or shielding ancillary ligands have been generated and spectroscopically characterized from chloro(mesityl)methylgold(I) carbenoids bearing JohnPhos‐type ligands by chloride abstraction with GaCl 3 . The aryl carbenes react with PPh 3 and alkenes to give stable phosphonium ylides and cyclopropanes, respectively. Oxidation with pyridine N ‐oxide and intermolecular C−H insertion to cyclohexane have also been observed. In the absence of nucleophiles, a bimolecular reaction, similar to that observed for other metal carbenes, leads to a symmetrical alkene.

Gold Sulfonium Benzylide Complexes Undergo Efficient Benzylidene Transfer to Alkenes

“…Largely absent from the discussion of the mechanisms of gold to alkene carbene transfer are the potential insights gained from analysis of carbene transfer from well‐defined carbene complexes in the condensed phase . Recent efforts in this area have led to the identification of a small number of well‐defined gold carbene complexes that undergo carbene transfer to alkenes ( A – C ) . However, extracting detailed mechanistic information relevant to catalysis from these stoichiometric carbene transfer processes is complicated by the (1) excessive stabilization of the carbene complex, (2) in situ generation of the carbene complex with strong Lewis acids under cryogenic conditions, and/or (3) the extreme facility of carbene transfer …”

“…[4,[14][15][16][17][18][19] Largelya bsentf rom the discussion of the mechanisms of gold to alkene carbenet ransfer are the potentiali nsights gained from analysiso fc arbene transferf rom well-defined carbene complexes in the condensed phase. [20][21][22] However,e xtracting detailed mechanistic information relevant to catalysis from these stoichiometric carbene transfer processes is complicated by the (1) excessive stabilization of the carbene complex, (2) in situ generation of the carbene complex with strong Lewis acids underc ryogenic conditions, and/or( 3) the extreme facility of carbene transfer. [20][21][22] However,e xtracting detailed mechanistic information relevant to catalysis from these stoichiometric carbene transfer processes is complicated by the (1) excessive stabilization of the carbene complex, (2) in situ generation of the carbene complex with strong Lewis acids underc ryogenic conditions, and/or( 3) the extreme facility of carbene transfer.…”

“…[2,3] Recent efforts in this area have led to the identification of as mall number of well-defined gold carbene complexes that undergo carbene transfer to alkenes (A-C). [20][21][22] As an alternative to free gold carbene complexes, we sought to identify gold carbenoid complexest hat would spontaneously and reversibly generate reactive gold carbene complexes in solution under mild conditions, [23] thereby allowing kinetic and mechanistic analysiso fc arbene transfer processes from otherwise inaccessible gold carbene complexes.A lthoughasmall number of gold(I)c arbenoid complexes that undergo carbene transfer to alkenesh aveb een identified (e.g., D-F; Figure1), [17,19,24] only imidazolium sulfonyl complex F does so in solution withoutL ewis acid activation. [20][21][22] As an alternative to free gold carbene complexes, we sought to identify gold carbenoid complexest hat would spontaneously and reversibly generate reactive gold carbene complexes in solution under mild conditions, [23] thereby allowing kinetic and mechanistic analysiso fc arbene transfer processes from otherwise inaccessible gold carbene complexes.A lthoughasmall number of gold(I)c arbenoid complexes that undergo carbene transfer to alkenesh aveb een identified (e.g., D-F; Figure1), [17,19,24] only imidazolium sulfonyl complex F does so in solution withoutL ewis acid activation.…”

“…[20][21][22] However,e xtracting detailed mechanistic information relevant to catalysis from these stoichiometric carbene transfer processes is complicated by the (1) excessive stabilization of the carbene complex, (2) in situ generation of the carbene complex with strong Lewis acids underc ryogenic conditions, and/or( 3) the extreme facility of carbene transfer. [20][21][22] As an alternative to free gold carbene complexes, we sought to identify gold carbenoid complexest hat would spontaneously and reversibly generate reactive gold carbene complexes in solution under mild conditions, [23] thereby allowing kinetic and mechanistic analysiso fc arbene transfer processes from otherwise inaccessible gold carbene complexes.A lthoughasmall number of gold(I)c arbenoid complexes that undergo carbene transfer to alkenesh aveb een identified (e.g., D-F; Figure1), [17,19,24] only imidazolium sulfonyl complex F does so in solution withoutL ewis acid activation. [18,25,26] However carbene transferf rom F requiresf orcingc onditions and as tabilizing C1 anisyl group for spontaneous activation and undergoes irreversible carbene formation, all of whichw ould complicate kinetic andm echanistic analysiso fc arbene transfer.…”

Direct Observation of Aryl Gold(I) Carbenes that Undergo Cyclopropanation, C−H Insertion, and Dimerization Reactions

“…Gold(I) carbenoids (1a-e)w ere obtained by reaction of the complexes 6a-e with mesityl diazomethane,a nd their structures were confirmed by X-ray diffraction (Scheme 2). [14] Remarkably,u pon addition of GaCl 3 to 1a in CD 2 Cl 2 at À90 8 8C, the solution turned deep red, suggesting the formation of the mesityl gold(I) carbene 5a,w hich was characterized by NMR techniques (Table 1). Although gold(I) carbenoids bearing JohnPhos and different substitution patterns in the aryl group were tested under the same reaction conditions,the generation of gold(I) carbenes could not be detected by NMR spectroscopy in those cases.…”