Chiral N-Heterocyclic Carbene Gold Complexes: Synthesis, Properties, and Application in Asymmetric Catalysis

Abstract

Nine new N-heterocyclic carbene gold chloride complexes (10–18) were synthesized starting from bulky chiral imidazolium salts (1–9) developed in this laboratory. Full characterization of all complexes, including the X-ray structures of gold(I)(1,3-bis((S)-1-(2-methoxyphenyl)-2,2-dimethylpropyl)-1H-imidazol-2(3H)-ylidene) chloride (13) and gold(I)(1,3-bis((S)-2,2-dimethyl-1-(naphthalen-1-yl)propyl)-1H-imidazol-2(3H)-ylidene) chloride (16), is reported. The complexes 10–18 were applied in the methoxycyclization of 1,6-enynes using AgNTf2 as an additive. Synthesis of the N-heterocyclic carbene gold triflimidate (19) was achieved by treating complex 12 with AgNTf2. The complex gold(I)(1,3-bis((R)-1-(2-methoxyphenyl)-2,2-dimethylpropyl)imidazolidin-2-ylidene)(1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methylsulfonamido) (19) was isolated and spectroscopically and structurally (X-ray) characterized

Broad Scope Aminocyclization of Enynes with Cationic JohnPhos–Gold(I) Complex as the Catalyst

“…8 Enantioselective hydroxy- and alkoxycyclizations of 1,6-enynes have been achieved with moderate to good enantioselectivities with a variety of chiral phosphines or NHC-gold catalysts. 9 The hydroxy- and alkoxycyclizations of 1,5- 4b,10,11 and 1,7-enynes take place similarly. 12 …”

When NHC Ligands Make a Difference in Gold Catalysis

“…By modification of the NHC structure, Kündig reported a new series of chiral NHC‐gold(I) complexes. These complexes appeared to improve the enantioselectivity of the alkoxycyclization up to 72% ee with L11 AuNTf 2 (Scheme ) 43. The yield was also increased up to 90%.…”

Some insights into the gold-catalysed A 3 -coupling reaction

“…12,13 Despite the ever burgeoning literature concerning gold-catalysed reactions, the majority of structurally defined chiral gold complexes are restricted to those bearing chiral phosphane ligands. [14][15][16][17][18][19] Given the fact the use of gold-NHC complexes [20][21][22][23][24][25][26] is now de rigour in synthesis, it is somewhat surprising that reports of structurally characterised, chiral, Au(I)-NHC [27][28][29][30][31][32][33][34][35][36] and Au(I)-ADC/NAC 37 complexes are still comparatively scarce. Likewise, the synthesis and characterisation and catalytic activity of cyclometallated gold(III) complexes is relatively unexplored, with only a handful of examples being cited in the literature.…”