Gold complexes carbenes

Uson, R., Laguna, A. and Villacampa, M.D. (1984) Mono and binuclear gold complexes with diamine and carbene ligands. Inorganica Chimica Acta, 81(1), 25-31. 

Raubenheimer, H.G., Scott, F., Roos, M. and Otte, R. (1990) The synthesis of gold (1) carbene complexes using 4-methylthiazolyllithium. Journal of the Chemical Society, Chemical Communications, (23), 1722-1723. 

A series of dinuclear gold(I)-carbene complexes of imidazolium-linked cydo-phanes and related acyclic bis(imidazolium) salts have been synthesized and their spectroscopic properties were examined by Baker and coworkers [31]. X-ray stmctural analysis of the cation in 1 and 2 (Scheme 5.1) revealed intramolecular Au - Au contacts of 3.5425(6) and 3.0485(3) A respectively. The electronic absorption... 

Ishii, R., Kaharu, T., Pirio, N., Zhang, S.-W. and Takahashi, S. (1995) Liquid-crystalline gold(I)-carbene complexes. Journal of the Chemical Society, Chemical Communications, (12), 1215-1216. 

The majority of gold(I) carbene complexes are pure organometallic compounds and the are out of the scope of this work. Some halide or triphenylphosphine carbene complexes are known and they will be considered here. Nucleophilic addition of alcohols or amines to gold-coordinated isocyanides is one of the best-established methods to obtain gold carbene derivatives. The reaction of H[Au(CN)2] with propene oxide and estirene oxide yields (cyano)carbene complexes (380) avoiding the intermediate step.2257 A cyclic carbene compound is obtained by reaction of a dinuclear isocyanide with amine (Scheme 32).2258... 

Carbene complexes have also been prepared by transmetallation reactions. Lithiated azoles react with gold chloride compounds and after protonation or alkylation the corresponding dihydro-azol-ylidene compounds, e.g., (381) or (382), are obtained.22 9-2264 Silver salts of benz-imidazol have also been used to obtain carbene derivatives.2265 Mononuclear gold(I) carbene complexes also form when trimeric gold(I) imidazolyl reacts with ethyl chlorocarbonate or ethyl idodate.2266,2267 The treatment of gold halide complexes with 2-lithiated pyridine followed by protonation or alkylation also yields carbene complexes such as (383).2268 Some of these carbene complexes show luminescent properties.2269-2271... 

Early work focused on compounds with open-chain carbenes generally synthesized in the coordination sphere of the gold atom, for example, by addition of amines or alcohols to isocyanide ligands in the corresponding gold complexes. Subsequent synthetic approaches have relied on the in situ deprotonation of onium salt precursors by a... 

Similar observations were made with bis[alkoxy(alkylamino)carbene]gold complexes, which are prepared by ring opening of trinuclear precursors with trifluoromethanesulfonic (triflic) acid. Through anion metathesis, several crystalline forms were obtained, the structures of which were determined. The triflate salt has a chain of cations in the crystal, while the chloroform solvate of a />-benzoquinolate contains only monomeric cations. In the solvent-free crystals, dimers are present (Scheme 59).251... 

Figure 5.16 Heterogenization of the unsymmetrical N-heterocyclic carbene-gold complexes on silica or zeolite. (Redrawn form Corma et al. [70].)...

Carbenes are speties with a divalent carbon atom with various substituents and a lone pair of electrons. Classic carbene gold complexes were synthesized in the coordination sphere of the gold atom, addition of amines or alcohols to the coordinated isocyanide ligands. N-Heterocyclic carbenes (Arduengo s carbenes)... 

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. 

The biscarbene complexes were found (142) from their H-NMR spectra to be mixtures of geometrical isomers, due to hindered rotation about the C—N or C—O bonds, and the isomers have been separated by fractional crystallization in the case of [Au C(0Et)NHC6H4Me 2]+C10. Treatment of these species with triphenylphosphine gave mixed ligand complexes and formamidines [Eq. (39)]. They also underwent oxidative addition of iodine to yield the first gold(III) carbene complexes. 

For alcohol additions, mono- and dicarbene complexes have been synthesized, for palladium, platinum (487-489), and gold (475, 490- 493), from methanol, ethanol, or ethanethiol (494) additions to the isocyanide precursor. The stability of the gold(I) carbenes can be gauged from reactions with halogens which gave the oxidative addition product without loss of the carbene ligand (492). 

Bis(adamantylimido) compounds, with monomeric chromium(VI) complexes, 5, 348 Bis(alkene) complexes conjugated, Rh complexes, 7, 214 mononuclear Ru and Os compounds, 6, 401 -02 in Ru and Os half-sandwich rj6-arenes, 6, 538 with tungsten carbonyls and isocyanides, 5, 685 Bis(u-alkenylcyclopentadienyl) complexes, with Ti(II), 4, 254 Bis(alkoxide) nitrogen-donor complexes, with Zr(IV), 4, 805 Bis(alkoxide) titanium alkynes, in cross-coupling, 4, 276 Bis(alkoxo) complexes, with bis-Cp Ti(IV), 4, 588 Bis[alkoxy(alkylamino)carbene]gold complexes, preparation, 2, 288... 

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... 

Gold(I) carbene complexes are readily obtained from heterocyclic aryl ligands 57... 

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