AuCl catalyst

Figure 1. (a) XRD pattern of AuCls and HAuCl4/Ti02 A denotes anatase R indicates rutile. denotes the Instrument peak, (b) UV-Vis spectra of HAUCI4 and AuCls catalysts before and after CO oxidation. 

Intramolecular additions of alcohols or amines to olefins are recognized as useful methods to provide heterocyclic compounds. Kozmin and Zhang have achieved a gold-catalyzed synthesis of heterobicyclic alkenes by double cyclization of alcohols or sulfonamides which have a 1,5-enyne moiety [175]. As a typical example, unsaturated alcohol (95) is smoothly converted to 6-oxabicyclo[3.2.1]octane (96) in 90% yield using a 5 mol% of AuCls catalyst (Scheme 18.34). Cyclic ethers are also available from homopropargylic ethers with pendant alcohols through gold-catalyzed... 

In the hydroamination of unsaturated carbon-carbon bonds, gold catalysts play an important role. Intermolecular hydroamination of alkenes [177], 1,3-dienes [204], terminal and internal alkynes [205], and allenes [206] are known to proceed smoothly in the presence of PhsP AufI) or AuCls catalyst. In addition, amino olefins also efficiently undergo intramolecular hydroamination using similar gold catalysts. He and coworkers have developed the catalytic cycloaddition of tosylated amino olefins [207], A representative example is shown in Scheme 18.35. When N-tosylated y-amino olefin (97) is exposed to a mixture of PhsP AuCl and AgOTf (5 mol% each) in toluene at 85 °C, pyrrolidine (98) is obtained in 96% yield. The gold(I)-catalyzed intramolecular hydroamination is applicable to N-alkenyl carbamates [208], N-alkenyl carboxamides [209], and N-alkenyl ureas [210], The use of microwave irradiation results in completing the hydroamination in a much shorter time than that required under thermal reaction conditions [211], The... 

Genet and Michelet demonstrated a,a-disubstituted pentynoic acid 46 nicely cyclized in the presence of AuCl catalyst under mild conditions to give fxmctionalized Y-methylene-y-lactone 47 (Scheme 22) [36]. The reaction of substrates bearing terminal alkynes proceeded xmder 5-exo mode without touching alkene functionality. 

Asao, Sato, and co-workers reported that AuCl-catalyzed benzannulation of o-alkynylphenyl ketones 11 (R H) with benzenediazonium 2-carboxylate 51 gave a variety of anthracene derivatives 52. On the other hand, the reaction of o-alkynylbenzaldehyde 11 (R = H) afforded triptycyl ketones 53 (Scheme 15.21) [33]. The reaction proceeded most probably through [4 - - 2] cycloaddition between ben-zopyrylium intermediate and benzene. Zhu et al. investigated the mechanism of this reaction by theoretical calculation and reported that AuCl catalyst is more effective than AuCls, due to the lower activation free energy of the rate-determining step [34],... 

Allenedienes 106 were submitted to a [4+3] intramolecular cycloaddition in presence of a [AuCl(lPr)]/AgSbF catalytic system (Scheme 5.28) [28]. The cycloaddition adducts 107 and/or 108 were obtained in good yields at room temperature. In contrast, this cycloaddition reaction requires a much higher temperature (110°C) when PtCl is employed as the catalyst [29]. This fact shows that the use of [AuCl(IPr)]/AgSbF catalytic system is critical for the success of this cycloaddition. 

Gold catalysts containing NHC ligands can also promote cycloisomerisation reactions. Bicyclo[3.1.0]hexanes 137-139 can be prepared from the cycloisomerisation of 1,5-enynes bearing a propargyUc acetate (135) in the presence of catalytic amounts of [AuCl(lPr)]/AgBF (Scheme 5.36) [41]. The cycloisomerisation reaction of 135 occurs by a 1,3-OAc shift/aUene-ene cyclisation/l,2-OAc shift sequence. Experimental results with allenyl acetate 136 support this hypothesis as 139 is obtained in higher ratios than 137 and 138 [41b],... 

The hydration of C-C triple bonds represents one of the most atom economical and environmentally friendly oxidation reactions [37], Recently, Nolan and co-workers reported the cationic [Au(lPr)][SbF ] system, which was generated in situ from [AuCl(lPr)] and AgSbF. The catalyst system showed remarkable activity in the hydration of a large range of alkynes, at An loadings as low as 10 ppm (typically 50-100 ppm), under acid-free conditions (Table 10.6) [38],... 

This Au(I) complex was tested as co-catalyst in palladium-catalyzed alkynylation reactions but this derivative is much less active than the analogous chloride complex [AuCl(tht)] needing over twice as long to fully convert the starting material [42]. 

Tyrpical experimental procedures are as follows for DP method, which is used for the industrial production of gold catalysts. To an aqueous solution of H AuCU, the pH of which is 2-3, an aqueous solution of NaOH is added to adjust the pH at a fix point in the range of 6-10. In neutral or weakly basic solution AuClj" ion is transformed into AuCl (OH)4l ( = 4 0). To this solution support materials are immersed or dispersed. When the pH, concentration, and temperature are carefully adjusted, solid Au(OH)3 precipitate is deposited exclusively on the... 

Gold(I) complexes of the type [AuCl(PPh3)ra] (n= 1, 2) or [Au(N03)(PPh3)] show an excellent performance towards oxidative addition carbonylation or aromatic amines to form corresponding carbamates, and also towards the carbonilation of aliphatic amines to produce either alkylureas or formamides.2552,2553 Cationic gold(I) compounds of the type [AuL]+ where L = phosphine, phosphite, or arsine are excellent catalysts for the addition of alcohols to alkynes.2554... 

This reaction has lent itself to the development of its asymmetric version (Scheme 88). The trick here is to remove the choride ligands from the coordination sphere of the platinum-chiral ligand complex. This makes the metal center more electrophilic, thus reactive reactions can be run at lower temperature. Interestingly, the best ligand was found to be the atropisomeric monophosphine (fJ)-Ph-BINEPINE.312 Enantiomeric excess up to 85% was observed. Very recently, enantioselectivity up to 94% ee has been achieved using [(AuCl)2(Tol-BINAP)] as pre-catalyst for the reaction of another enyne.313... 

Species such as XXV, XXVI, or XXVII readily form coordination complexes when treated with AuCl, H20So(C0)j q, Idn(CO)3(r -C5Hj), Fe(C0)3(PhCH=CHC(0)CH3>, or [RhCl(CO)2]2 ( ) Tw results are of special interest. First, the skeletal nitrogen atoms in XXV-XXVII do not participate in the coordination process. Presumably, they are effectively shielded by the aryloxy units and are of low basicity. Second, coordinatlve crosslinking can occur when two phosphine residues bind to one metal atom. Ligand-exchange reactions were detected for the rhodium-bound species. The tri-osmium cluster adducts of XXV, XXVI, and XXVII are catalysts for the isomerization of 1-hexane to 2-hexene. 

Reactions between [ppn][Au(acac)2] and buta-l,3-diyne give [ppn][Au(C= CC=CH)2]. Similarly, (AuCl)2(/U-dppm) affords Au(C=CC=CH)2 (ju-dppm) while serendipitous use of a stoichiometric amount of Cul catalyst resulted in migration of dppm from gold to copper and formation of the curious bis(diynyl) species Cu3(/U3-I)(/.i3-C=CC=CAuC=CC=CH)(/r -dppm)3 (31). Direct reaction between [ppn][Au(C CC=CH)2] and [Cu2(/L-dppm)2(NCMe)2]" " afforded the dumbbell complex 32. 

In situ infrared study of catalytic CO oxidation over Au/Ti02 shows that the catalyst prepared from AuCls exhibits higher activity than those prepared from HAuC. The high activity of Au appears to be related to the presence of reduced and oxidized Au sites as well as carbonate/carboxylate intermediates during CO oxidation. Addition of H2O2 further promotes the oxidation reaction on Au/Ti02 catalysts. 

Two 1% Au/Ti02 catalysts, designated as HAuC and AuCls were prepared by deposition-precipitation of HAuC (Aldrich) and AuCls (Alfa Asar) onto Degussa-... 

Figure 2. (a) IR Spectra Temperature Programmed Reaction on AuCla and HAuCU-Catalyst, (b) Rate of formation of CO2 on AuCls and HAuCl4-Catalyst. 

Au/TiOz catalyst prepared from AuCls possesses reduced Au and oxidized Au sites which exhibit high CO oxidation activity. The catalyst produce carbonate and... 

Gold intramolecular processes are also possible. Using AuCl and K2C03 as catalysts, Harkat et al. achieved y- and 8-alkylidene lactonizations from co-acetylenic acids by efficient and stereoselective reactions [91]. 

Muller compared the activity of several metal catalysts for this reaction. He later reported that AuCl3 was not at all effective for the conversion [113]. However, later studies showed that the complex [AuCl(triphos)](N03)2 (1 mol%) could provide much better results TOF = 212 h-1 and quantitative conversions [114]. Lok et al. showed that gold can catalyze the rearrangements of alkynylamino heterocycles, albeit with concomitant gold mirror formation (Equation 8.50) [115]. 

As delineated above, hydroarylation of electron-poor alkynes such as acetylene carboxylic acid ethyl ester 4 is best catalyzed by Au(I) complexes. In addition to the previously mentioned Ph3PAuCl/BF3-OEt2, several other Au(I)-complexes have been shown to be active catalysts, if activation by silver salts or Lewis acids is ensured [2, 4]. Remarkably, the Au(I)-precursor LAuCl can be prepared in situ by reacting AuCl with a phosphorus ligand. 

Examples of gold-catalyzed carbonylation of amines and olefins exist related to the activation of carbonyl. The first case involves the formation of carbamates from anilines and CO in the presence of alcohols or the production of acetamides from aliphatic amines. In these examples, Au(I) (usually [AuCl(PPh3)]) catalysts are preferred. For the carbonylation of olefins, gold(I) carbonyls are prepared in situ in sulfiu ic acid media to afford carboxyhc acids. ... 

The last example included in this section is an oxidative cleavage of styrenes performed in water with tert-butyUiydroperoxide as the oxidant (equation 149). In this reaction, the first step is an olefin activation that should be followed by oxidation, although the mechanism is unknown. The catalyst employed is AuCl with neocuproine as the ligand. 

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