Gold complexes acetylene

Hydroarylations of alkynes are catalyzed by gold complexes and these bear some resemblance to the Fujiwara Pd-catalyzed reaction. In general, when using gold chemistry, better Z/E selectivities are observed compared with palladium, lower catalyst loadings and milder conditions (neutral not TFA) are used. The mechanism involves the attack of ArH on the Au-coordinated alkyne. Flowever, electron-poor acetylenes only appear to work with palladium chemistry (Equations (75) and (76)).72... 

As already mentioned, CAAC ligands can stabilize electron-deficient metal centers such as in cationic gold complexes. Complex 29 catalyzes a very unique reaction of enamines with acetylene, which produces a cumulene and an imine... 

The only other report (88) of a gold(I) acetylene complex concerns [AuBr(cyclooctyne)2], which was prepared from aurous bromide and cy-clooctyne. 

Bardaji M, De la Cruz MT et al (2005) Luminescent dinuclear gold complexes of bis(diphenylphosphano)acetylene. Inorg Chim Acta 358 1365-1372... 

Olefin and acetylene complexes of Au(I) can be prepared by direct iateraction of the unsaturated compounds with a Au(I) hahde (190,191). The resulting products, however, are not very stable and decompose at low temperatures. Reaction with Au(III) hahdes leads to halogenation of the unsaturated compound and formation of Au(I) complexes or polynuclear complexes with gold ia mixed oxidatioa states. 

Figure 1.6 Representative TEM image (a) and particle size distribution (b) obtained for a Au/Ti02 catalyst prepared by grafting of a [Au6(PPh3)6](BF4)2 complex onto Ti02 particles followed by appropriate reduction and oxidation treatments [42], The gold particles exhibit approximately spherical shapes and an average particle size of 4.7 nm.The measured Au particle sizes could be well correlated with the activity of the catalyst for carbon monoxide oxidation and acetylene hydrogenation. (Reproduced with permission from Springer.)...

Even a rod-like backbone derived from acetylene is conceivable and has been realised by Liu et al. [367] starting from l,4-dichlorobutin-2. The usual reaction with methyl imidazole and subsequent reaction with silver(l) oxide and carbene transfer to gold(I) [Au(SEtj)Cl] makes the dimeric silver(I) and gold(l) complexes accessible featuring argentophilic and aurophilic interactions, respectively. 

Note The acetylene backbone is not flexible enough to allow the formation of a chelate complex with silver or gold, both preferring a linear arrangement of ligands. 

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