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

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.