Sodium tetrachloroaurate

Also in the activation of alkynes for nucleophilic attack, gold salts prove to be soft, exceptionally carbophilic Lewis acids, as confirmed by the examples shown in Scheme 3 [10]. According to Utimoto and Fukuda both the addition of water as well as of amines to alkynes are catalyzed by gold(III) salts, in particular by sodium tetrachloroaurate ketones such as 8 and imines such as the ant toxin 10 are obtained as products in excellent yields [10a-e]. In the cyclization reaction giving the 1,4-dioxane 12 developed by Teles et al.,... 

Yet the first examples of cyclization of 1,5-enynes with gold were disclosed by the group of Arcadi in the context of a new synthesis of pyridines (equation 48). The cyclization of propargyl enamines catalyzed by sodium tetrachloroaurate gives substituted pyridines in a general way. The enamines were formed in situ from propargylamine and the corresponding ketone. 

Sodium tetrachloroaurate(HI) dihydrate (0.397 g, 1.0 mmole) is dissolved in water (10 mL), and the solution is cooled in ice. To this solution is added the thiodiglycol (0.366 g, 3.0 mmoles), undiluted, with stirring. This addition must be made very slowly (45 minutes) and may be stopped when the yellow color of the solution is discharged. A solution of the ligand, 4-ethylbenzenethiol (0.140 g, 1.0 mmole), in chloroform (20 mL) is added dropwise with stirring over 20 minutes. The chloroform layer is separated and added dropwise to methanol (40 mL), and the pale yellow complex, 4-ethylbenzenethiolatogold(I) (0.33 g, 98%), precipitates. The product is filtered, washed with methanol, and dried... 

Gold(m) complexes have been obtained by using a chelating diarsine ligand from the reaction with sodium tetrachloroaurate(m) in presence of sodium iodide. The iodide [Au(diars)2I2]I and other cations, [Au(diars)2l]2+ and [Au(diars)2]3 +, can be obtained. It is held that these are species with six, five and four coordination for Au111 with octahedral,33 trigonal bipyramidal and planar structures, respectively. Chelating phosphine complexes also exist. 

Sodium tetrachloroaurate(lll) dihydrate NaAuCl4-2H30 13874-02-7 397.800 oran-yel rhom cry 100 dec 160 s FtOH, eth... 

Gold(III) chloride (0.33m for gold). Dissolve 13.3 g sodium tetrachloroaurate(III) dihydrate, NaAuC -2H20, in water and dilute to 100ml. Alternatively, dissolve 6.57 g gold metal in 50 ml aqua regia, evaporate the solution to dryness, and dissolve the residue in 100 ml water. 

Sodium tetrachloroaurate cat yzes the photo-oxidation of hydrocarbons in solution. Typical of this is the irradiation with wavelengths >310 nm of aerated solutions of cyclohexane in acetonitrile or methylene chloride. The principal isolable products formed from this treatment are cyclohexanol and cyclohexanone . A mechanism that might involve the formation of a metal peroxo or metal oxo complex has been suggested. Such complexes are known to react with alkanes to yield hydroxy derivatives . The principal organic intermediate is the unstable cyclohexylhydroperoxide that readily decomposes to afford cyclohexanone and cyclohexanol. Further study has shown that the hydroperoxide accumulates during the oxidation . The influence of wavelength (A. 300, 365 or 436 nm) on the reaction has also been studied . Hexane and ethylbenzene can be similarly oxidized to yield analogous products . 

Utimoto has also shown that simple gold(III) salts catalyze the intramolecular hydroamination of alkynes with arylamines [4]. For example, treatment of 2-(3,3-dimethyl-l.butynyl)aniline with a catalytic amount of sodium tetrachloroaurate in refluxing TH F for 30 min led to isolation of 2-f-butylindole in 90% yield (Eq. (11.3)). Marinelli has modified and expanded the scope of Utimoto s procedure through employment of ethanol, ethanol/water [5], or ionic liquids 6] solvents. As an example of this modified protocol, treatment of 2-alkynylaniline 2 with a catalytic amount of NaAuCU dihydrate in ethanol at room temperature for 6h led to isolation of 2-(4-chlorophenyl)indole 3 in 92% yield (Eq. (11.4)). A similar hydroamination protocol employing AUCI3 as a catalyst has been recently reported by Majumdar [7]. 

Che has reported the tandem hydroamination/hydroarylation of aromatic amines wirh terminal alkynes to form dihydroquinolines in which 1 equiv of aniline combines with 2 equiv of alkyne [23]. For example, reaction of 3-methoxyanilme with pheny-lacetylene (5 equiv) and a catalytic 1 1 mixture of the gold(I) N-heterocydic carbene complex (IPr)AuCl (IPr= l,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgOTf at 150 °C under microwave irradiation led to isolation of dihydroquinoline 21 in 82 % yield (Eq. (11.15)). Alternatively, reaction of o-acetylaniline with pheny-lacetylene catalyzed by a mixture of (IPr)AuCl and AgOTf at 150 °C led to isolation of the quinoline derivative 22 in 93% yield via incorporation of a single equivalent of alkyne (Eq. (11.16)). Arcadi has reported the gold(IlI)-catalyzed hydroamination/ hydroarylation of 2-alkynylanilines with a,p-enones to form C3-alkyl indoles [24]. As an example of this transformation, treatment of 2-(phenylethynyl)aniline with 4-phenyl-3-buten-2-one and a catalytic amount of sodium tetrachloroaurate dihydrate in ethanol at 30°C formed 1,2,3-trisubstituted indole 23 in 88% yield (Eq. (11.17)). 

The reaction of 5,10,15,20-tetraphenyl-p-benziporphyrin, sodium tetrachloroaurate(iii) dihydrate, and potassium carbonate in dichloro-methane, carried out by Szyszko et yielded gold(in) 5,10,15,20-tet-raphenyl-21-carbaporphyrin owing to the contraction of p-phenylene to cyclopentadiene. This molecule is the very first representative of a true 5,10,15,20-tetraphenyl-21-carbaporphyrin complex where four trigonal donor atoms are involved in equatorial coordination. The NMR spectrum of this Au complex resembles the basic pattern of aromatic carbaporphyrinoids with an AB spin system at d = 8.78, H(7,18), and 8.67 ppm, H(8,17) with a coupling, /hh of 4.9 Hz, which is typical of the pyrrole ring in porphyrinoids. 

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