Synthesis and Catalytic Activity of Gold Chiral Nitrogen Acyclic Carbenes and Gold Hydrogen Bonded Heterocyclic Carbenes in Cyclopropanation of Vinyl Arenes and in Intramolecular Hydroalkoxylation of Allenes

Abstract

Mononuclear and dinuclear chiral gold(I) carbene complexes with carbene ligands of the type HBHC (hydrogen bonded heterocyclic carbenes) and NAC (nitrogen acyclic carbenes) have been prepared by reaction of isocyanide gold(I) complexes and chiral amines or diamines. The reaction of [AuCl(CNPy-2)] (1) (Py = pyridyl) with the corresponding chiral primary amines afforded the chiral HBHC complexes (R)-[AuCl{C(NH(CHMePh))(NHPy-2)}] ((R)-2), and (S)-[AuCl{C(NH{CHMe(1-naphthyl)})(NHPy-2)}] ((S)-3), while the reaction of 2 equiv of 1 with diamines produced (S)-2,2'-bis[NH{C(AuCl)(NHPy-2)}](2)-binaphthyl ((S)-4), (1R,2R)-1,2-bis[NH{C(AuCl)(NHPy-2)}]-diphenylethane ((1R,2R)-5), and (1R,2R)-1,2-bis[NH{C(AuCl)(NHPy-2)}]-cyclohexane ((1R,2R)-6). On the other hand the addition of alkyl amines to (S)-2,2'-[NCAuCl](2)-binaphthyl ((S)-8) gave the chiral NAC complexes (S)-2,2'-bis[NH{C(AuCl)(NMe(2))}](2)-binaphthyl ((S)-9) and (S)-2,2'-bis[NH{C(AuCl)(N(i)Pr(2))}](2)-binaphthyl ((S)-10), while the addition to (S)-2,2'-[NCAuCl](2)-3,3'-Ph(2)-binaphthyl ((S)-12) yielded (S)-2,2'-bis[NH{C(AuCl)(NMe(2))}](2)-3,3'-Ph(2)-binaphthyl ((S)-13) and (S)-2,2'-bis[NH{C(AuCl)(NEt(2))}](2)-3,3'-Ph(2)-binaphthyl ((S)-14). All the complexes are active catalysts in the cyclopropanation of vinyl arenes and in the intramolecular hydroalkoxylation of allenes, providing good yields and modest or poor enantioselectivity. The results show that all these ligands are compatible with different functions and reaction conditions and are worth considering as alternative systems to NHCs or phosphines in gold catalyzed reactions.

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

“…[92]. Regarding the synthetic route to gold(I) complexes 119, the disclosed approach offers straightforward access directly from readily accessible isocyanide 117, as reported earlier by Espinet [93] and Toste [94,95]. As a result, the formation of diastereomeric "in" and "out" rotamers was observed in the case of acyclic carbene gold(I) complexes bearing a binaphthyl skeleton (Scheme 19) [92].…”

Carbene Complexes Derived from Metal‐Bound Isocyanides: Recent Advances

“…Third, despite the fact that ADC ligands have been explored much less as catalysts compared to NHC derivatives, the previously reported results in this fi eld [24,31,32,34,37,38,40,43,65] clearly indicate a high potential for ADC complexes in catalysis. Taking into account that the generation of M -ADCs via other routes, as distinct from the use of metal -ligated isocyanides, is often associated with experimental diffi culties, it is to be expected that the development of a metalmediated approach to complexes with ADC ligands from isocyanide precursors will play a major role in the further involvement of these compounds in catalysis.…”

“…Both, mononuclear and dinuclear chiral gold ( I ) complexes containing acyclic diaminocarbene ligands were prepared by the reactions of isocyanide gold(I) complexes with chiral amines or diamines ( Figure 15.1 , c -e ), as demonstrated by Espinet et al [34] . The reactions proceeded without racemization, and the absolute confi guration of the chiral centers was maintained intact.…”

Enantioselective Gold-Catalyzed Synthesis of Heterocyclic Compounds

“…In a later study, Mikami et al showed formation of the monocationic complex through reduction of silver phosphate loading allowed for slightly improved ees for selected hydroxyallene substrates [66]. Espinet et al also showed hydrogen-bonded heterocyclic carbene (HBHC) dinuclear gold(I) catalysts are also competent at facilitating this transformation [67]. This methodology was applied to the synthesis of pyrazolidines, isoxazolidines, and tetrahydrooxazines by Toste et al in 2010 [68].…”