NHC-gold complexe

In the same manner, dimethylsulfide substitution proved to be a practical procedure for the preparation of NHC-gold complexes. Good yields were obtained for the synthesis of monocarbene Au(I) complexes (104) from [(Me2S)AuCl] and one equivalent of free NHC (Scheme 17) iHios jjjg steric hindrance of NHCs was found to be of critical importance, since NHCs with smaller nitrogen substituents such as Mes, wo-propyl or n-butyl led to a lower yield and formation of a byproduct identified as the biscarbene complex [(NHC)2Au]+ Cl. Fortunately, the silver-mediated transmetallation was an efficient alternative route for these NHCs (see Section 2.6). When the same reaction was performed with two equivalents of in situ generated NHCs, the cationic biscarbene complex (105) [(NHC)2Au]X (X = Cl, Br, orPFe) was obtained as the only product. ... 

The combination of an (N-heterocyclic carbene) NHC-gold complex and Selectfluor was found to be a highly efficient catalyst system for car-bene-transfer reactions (140L4472). 

The syntheses and catalytic applications of NHC - gold complexes have been reviewed. Details are given for their applications in enyne chemistry and carboxylic rearrangements, 7r-activation, and hydration reactions. Carboxylation catalysed by highly basic NHC-AuOH and NHC-CuOBu-t complexes has been highlighted. ... 

Inspired by the work of Nolan, Thieuleux and coworkers designed and synthesised new NHC-gold complexes and tested them in the hydration of allq nes. Using a combination of [Au(NHC)Cl]/AgBF4 and methanesulfonic acid in methanol, they were able to convert 3-he)q ne to 3-hexanone and obtain TONs up to 800 000 and TOFs up to 294 000 (Scheme 16.7)." ... 

Recent work by Ott and co-workers has focused on the synthesis of NHC-gold complexes that are potent inhibitors of the TrxR enzyme. A large series of NHC-gold(i/iii) complexes was tested against the HT-29 cell line (human... 

The gold complex intermediates were also trapped by active methylene compounds or aldehydes (Scheme 1.158). The reaction pathway depended on the gold catalysts NHC-gold complex 326 gave cyclopropanes 327 in good yields in a chemoselective manner, while alkoxy-gold complex 328 formed exo-methylene compounds 329 [228]. 

The NHCs have been used as ligands of different metal catalysts (i.e. copper, nickel, gold, cobalt, palladium, rhodium) in a wide range of cycloaddition reactions such as [4-1-2] (see Section 5.6), [3h-2], [2h-2h-2] and others. These NHC-metal catalysts have allowed reactions to occur at lower temperature and pressure. Furthermore, some NHC-TM catalysts even promote previously unknown reactions. One of the most popular reactions to generate 1,2,3-triazoles is the 1,3-dipolar Huisgen cycloaddition (reaction between azides and alkynes) [8]. Lately, this [3h-2] cycloaddition reaction has been aided by different [Cu(NHC)JX complexes [9]. The reactions between electron-rich, electron-poor and/or hindered alkynes 16 and azides 17 in the presence of low NHC-copper 18-20 loadings (in some cases even ppm amounts were used) afforded the 1,2,3-triazoles 21 regioselectively (Scheme 5.5 Table 5.2). 

Similar to the abovementioned silver nhc coordination compounds, carbene chemistry has also been dominant in the field of gold organometallic chemistry. Noteworthy examples include a Au(PPh3)-compound derived from tetraaminoallene, that can be rationalised in terms of a dicarbene with ylide character and which, owing to the electron-rich character of the central carbon atom, offers the potential for dimetallation products.108 Non-activated allenes and alkynes have been found by Lavallo to be readily aminated by cationic carbene gold complexes.109 For this purpose, a 2,6-diisopropylphenyl functionalized cyclic alkylaminocarbene gold(I) complex... 

TADDOL-(a,a,a, a -tetraaryl-l, 3-dioxolan-4,5-dimethanol)-derived gold complex in the presence of AgBF4 (Scheme 4-46). By using electron-rich A-heterocyclic carbene (NHC)-gold catalysts, an alternative pathway toward [3+2]-cycloaddition products can be favored. ... 

Gold complexes containing iV-heterocyclic carbene (NHC) ligands, of which there are far fewer examples, are also part of recent advancement in this field. 

---