Gold catalysis carbenes

Rearrangements of 1,3-diynes (43) to dienynes (45a) and (45b) have been carried out catalytically a metal-carbene intermediate (44) is likely to be involved.41 Interestingly, gold catalysis provides mainly (45a) whereas platinum catalysis under a CO atmosphere yields predominantly (45b). 

Like in other areas of homogeneous catalysis, soon after the isolation of the first free Al-heterocyclic carbene (NHC) by Arduengo et al. [2], NHCs were employed as ancillary ligands in gold catalysis [3]. From this point on, due to their unique electronic and steric properties, their high tolerance against moisture and air, as well as their thermal stability, which exceeds that of the phosphine complexes, NHC-gold(I) complexes became a serious alternative to the commonly used catalysts [4,5]. 

The first discussed example was reported by Bertrand and coworkers. By using different iminium salts they reported the coordination of an array of different abnormal NHC ligands, so-called CAAC ligands, to an AuQ fragment. Here, depending on the bulkiness of the free carbene used, the formation of mono- or biscarbene gold complexes is observed [12]. The synthesis of the most known representative of this class of Au(I) complexes in gold catalysis is shown in Scheme 9.3. The unique thermal stabiUty of this NHC-Au(I) complex is discussed in more detail in Section 9.3. 

Carbenes form stable complexes with many metals in the periodic table of the elements, and gold is no exception. In fact, the chemistry of this class of organogold compounds for some time has been one of the fastest growing subdisciplines. While the corresponding chapters were still short in previous accounts,1 2 the inventory for this review is now particularly rich and diverse.230 As for other classes of carbene complexes, this upsurge is based on expectations for potential applications in various fields such as NLO materials, liquid crystalline phases, and catalysis. Where applicable, this is indicated for each of the entries in this chapter. 

Until 1998, only gold(III) was believed to be effective for catalyzing these processes because, as mentioned previously, only the gold(I) compound K[Au (CN)2] was tested and it was inert to catalysis. Fortunately, Teles et al. reported very strong activity in the addition of alcohols to alkynes when they used cationic gold( I) -phosphane complexes [14]. In this study, the aforementioned authors tested for the first time the suitability of nucleophilic carbenes that displayed even greater activity than other gold complexes, but they were unable to synthesize the subsequent cationic derivatives. 

Cyclic amino-carbenes, in molybdenum carbonyls, 5, 457 Cyclic bis(phosphine) dichlorides, with iron carbonyls, 6, 48 Cyclic carbenes, as gold atom ligands, 2, 289 Cyclic carbometallation, zirconium complexes, 10, 276 Cyclic carbozirconation characteristics, 10, 276 intermolecular reactions, 10, 278 intramolecular reactions, 10, 278 Cyclic dinuclear ylides, and gold , 2, 276 Cyclic 1,2-diols, intramolecular coupling to, 11, 51 Cyclic enones, diastereoselective cuprate additions, 9, 515 Cyclic esters, ring-opening polymerization, via lanthanide catalysis, 4, 145 Cyclic ethers... 

The interest in functionalised carbene complexes of gold(I) derives not only from the longer known biological applications [21-23], but also from a recent interest in their performance in catalysis [14,15,24,25]. Ray et al. tested a series of nonfunctionalised, hydroxy functionalised and hydroxy/keto difunctionalised NHC ligands in the ROP of L-lactide [14]. There is no significant difference in the activities of the two functionalised NHC... 

Constructing molecular complexity firom alkynol derivatives A journey firom Fischer carbene complexes to tandem catalysis with gold and other carbophilic Lewis acids 13SL1757. 

In this review, the applications in homogeneous catalysis of N-heterocyclic carbene-containing copper, silver and gold complexes will be presented. N-Heterocyclic carbenes (NHCs) are two-electron a-donor ligands that share a... 

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