Gold catalysts reactions

This method is one of the dry methods in which no chemical reaction is involved. Preparation of ultrafine particles by physical vapor deposition (PVD) dose not require washing and calcination, which are indispensable for chemical preparation such as in CP and DP methods. As waste water and waste gases are not by-produced, the arc plasma (AP) method is expected to grow in popularity as one of the industrial production methods for gold catalysts and as a clean preparation method. 

Highly active gold catalysts can be prepared by an appropriate selection of preparation methods such as CP, DP, DR, and SG with dimethyl Au(III) acetylacetonate, depending on the kind of support materials and reactions... 

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 active sites or reaction sites proposed until now for CO oxidation over gold catalysts with different support metal oxides are as follows ... 

Figure 14. Reaction pathways for CO oxidation over supported gold catalysts [39].

Gold-based catalysis has attracted considerable attention in recent years. A gold-catalyzed aziridination reaction has recently been reported <06JOC5876>. A series of gold catalysts were examined for their ability to catalyze the aziridination of styrene with p-nitrophenylsulfonamide (NsNH2). Styrene and phenyl-substituted styrenes provided the N-nosyl aziridines in good to excellent yields. Cinnamate however provided the aziridine product in only 25% yield. The use of other sulfonamides (e.g. tosyl, trichloroethyl) gave much lower yields of the aziridine product. 

Burch, R. 2006. Gold catalysts for pure hydrogen production in the water-gas shift reaction Activity, structure and reaction mechanism. PCCP 8 5483-500. 

Studies in the 1950 s and 1960 s on gold electrocatalysts mainly focused on alkaline media. Hoare studied the gold electrodes of Au/Au-O and Au/Au203 in acidic media in 1966.206 The electrodes studied performed poorly for ORR because of the low activity of the catalyst due to the peroxide decomposition reaction (for Au/Au-O). The electrodes containing Au203 also were poor conductors. From this study, it was found that ORR in acid over gold catalysts proceeded via the two-electron path. 

The same reaction but with trimethylacetaldehyde results in the frans-adduct exclusively in 100% yield and in 97% ee. The use of the gold catalyst is essential for the high selectivity silver and copper catalysts are much less effective. The length of the side chain between the diethylamino group and the ferrocene nucleus is also an important factor in the selectivity. 

M. M. Schubert, S. Hackenberg, A. C. van Veen, M. Muhler, V. Plzak, and R. J. Behm, CO oxidation over supported gold catalysts— Inert and active support materials and their role for the oxygen supply during reaction, J. Catal. 197, 113-122 (2001). 

Figure 8. Activity of carbon-based gold catalysts in CO oxidation and their XRD results [75]. Panel A the conversions on Au/C, Au/MnOx/C, MnOx/C, and MnOx/Au/C pretreated in 02-Fle at 200°C. Reaction conditions 1% CO in air flow rate 37 mL/min 0.05 g catalyst. Panel B XRD patterns of as-synthesized catalysts. [Reproduced by permission of Elsevier from Ma, Z. Liang, C. D. Overbury, S. H. Dai, S. J. Catal. 2007, 252, 119-126.]...

Despite its apparent noble character, gold catalysts have been recently found to be active in many homogeneous and heterogeneous catalytic processes such as oxidation reactions, nucleophilic additions, cross-coupling reactions, and alkene and imine hydrogenations (69—71). Corma and co-workers showed that Au... 

The general mechanism proposed for these additions starts with the interaction of the gold catalyst with the -system of the substrate (Scheme 8.1). This forms an intermediate where the double or triple bond is activated for nucleophilic attack. In most examples, addition is anti to gold delivering vinyl gold species. The final step of the reaction involves the release of the gold catalyst by protodemetallation and the addition product. 

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