Oxidative Cycloaddition of 1,1,3,3-Tetramethyldisiloxane to Alkynes Catalyzed by Supported Gold Nanoparticles (original) (raw)
Canadian Journal of Chemistry, 2009
Azide-terminated alkyl thiolate monolayer-protected gold nanoparticles (1-C12MPN) with a core size of 1.8 ± 0.2 nm were prepared. 1-C12MPN was modified in high yields via an uncatalyzed 1,3-dipolar cycloaddition (click-type reaction) with a variety of terminal acyl–alkynes under hyperbaric conditions at 11 000 atm. The resulting 1,2,3-triazole modified MPNs (2-C12MPN) were characterized using 1H NMR spectroscopy and were verified by comparison of the spectra to those obtained for the products of the model reactions of 1-azidododecane with the same alkynes. TEM analysis showed that the high-pressure conditions did not affect the size of the gold core, suggesting that the only effect is to facilitate the chemical reaction on the particles.
Supported gold nanoparticles catalysts for organic transformations
2019
The research work described in this thesis concerns the synthesis, characterisation and study of the catalytic activity of supported gold nanoparticles (AuNPs) immobilised on various oxide supports, i.e. silica (SiO2), alumina (Al2O3), titania (TiO2) and magnetite (Fe3O4), previously functionalised with [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS). The alkynyl-carbamate moieties anchored on the support were capable of straightforwardly reducing the gold precursor chloroauric acid (HAuCl4) to afford Au/OS@Yne (OS = Oxide Support, Yne = organic functionalisation), without the need of additional reducing or stabilising agents. The resulting materials were characterised by means of several complementary techniques, such as thermogravimetric analysis (TGA), atomic absorption spectroscopy (AAS), transmission electron microscopy (TEM), solid state NMR spectroscopy (SS NMR) and x-rays photoelectron spectroscopy (XPS), in order to investigate their structural and chemical properties. Furthermore, the catalytic activity of the obtained Au/OS@Yne was evaluated first in the oxidation of alcohols and then in the hydroamination of alkynes. Finally, during a six months stay at the Karl-Franzens University of Graz, a second research work was carried out, concerning the study of metal organic frameworks biocomposites. The thesis organisation and the content of each chapter can be summarised as follows: Chapter 1. General introduction on the topic of nanocatalysis, followed by an overview on the synthesis and properties of gold nanoparticles, with a special focus on their application as catalysts. Moreover, a brief discussion on the main advantages of flow chemistry and the exploitation of this technology in heterogeneous catalysis is reported. Chapter 2. The Au/SiO2@Yne, Au/Al2O3@Yne and Au/TiO2@Yne systems were prepared by in situ reduction of a gold precursor in the presence of the alkynyl carbamate moieties grafted on the support surface. The physical and chemical characterisation of the obtained materials was then carried out, alongside an investigation on the mechanism of formation/stabilisation of AuNPs on the functionalised supports. Chapter 3. The catalytic activity of Au/SiO2@Yne, Au/Al2O3@Yne and Au/TiO2@Yne in the oxidation of benzyl alcohol was first evaluated in batch conditions, with the aim of tuning the reaction selectivity by employing different oxidising agents and solvent media. Furthermore, the oxidation of a variety of primary and secondary alcohols catalysed by Au/SiO2@Yne was performed, both in batch and in continuous-flow conditions. Finally, the effect of the oxide support on the catalytic properties of the system was studied in the oxidation of 1-phenylethanol. Chapter 4. A further functionalisation of the silica supported catalyst was carried out following two approaches: grafting with ethoxytrimethylsilane (Au/SiO2@Yne-TMS) and impregnation with thriethylamine (Au/SiO2@Yne-NEt3). The new synthesized materials were thoroughly characterised and employed as catalysts in the hydroamination of phenylacetylene with aniline. Chapter 5. The synthesis of nanomagnetite supports was performed by co-precipitation of iron salts in alkaline media (NH3 and NaOH), then the obtained magnetic nanoparticles were functionalised with PPTEOS and decorated with AuNPs. Furthermore the characterisation of these magnetic systems was carried out and compared with the analogues materials formed by immobilising AuNPs on bare magnetite. Chapter 6. Synthesis and characterisation of zeolitic imidazolate framework-8 biocomposites containing bovine serum albumin (BSA@ZIF-8). The possibility of tuning the ZIF-8 topology by varying the reaction conditions was first investigated in batch conditions, then the synthesis was carried out in a continuous-flow system with a special focus on the control of particle size.
Hydrosilylation of 1-hexyne promoted by acetone solvated gold atoms derived catalysts
Journal of Organometallic Chemistry, 2005
Supported gold nanoparticles, prepared by deposition of acetone solvated Au atoms on supports as carbon and c-Al 2 O 3 , behave as valuable catalysts for the regioselective hydrosilylation of 1-hexyne with different silanes. The catalytic behaviour of gold-based systems is compared with the activity of supported platinum catalysts and a different affinity between the metals and the silanes is observed.
Gold-Catalysed Oxidative Cycloisomerisation of 1,6-Diyne Acetates to 1-Naphthyl Ketones
A synthetic method to prepare 1-naphthyl ketones from gold(I)-catalysed oxidative cycloisomerisation of 1,6-diyne acetates is described. The proposed mechanism involves cyclopropenation-cycloreversion of the 1,6-diyne motif initiated by a 1,2-acyloxy migration. This is followed by nucleophilic attack of the ensuing gold carbenoid species by a molecule of water and autoxidation to give the aromatic product.
Gold-Catalyzed Oxidative Cyclizations ofcis-3-En-1-ynes To Form Cyclopentenone Derivatives
Angewandte Chemie International Edition, 2012
Cycloisomerizations of 1,n-enynes (n = 5, 6) catalyzed by transition metals are powerful tools for accessing complicated carbocycles. [1, 2] Such reactions have been intensively studied for many transition metals having diverse reaction mechanisms. Metal-catalyzed oxidative cyclizations of 1,n-enynes (n = 5, 6) are synthetically appealing because the product skeletons incorporate oxy or oxo functionalities, [3, 4] but there are fewer reported examples for enyne oxidative cyclizations than for their cycloisomerzation reactions. [1, 2] Our group and the groups of others have reported the catalytic cycloisomerizations of cis-3-en-1-ynes to form cyclopentadiene derivatives using ruthenium or platinum catalysts, respectively (Scheme 1 a); [5] the corresponding oxidative cyclization remains undocumented. Herein, we report new gold-catalyzed oxidative cyclizations of cis-3-en-1-ynes to give cyclopentenone skeletons using 8-methylquinoline oxide (Scheme 1 b). Notably, the mechanistic transformation of this C À H activation is proven to proceed through a noncarbene route, thus excluding the intermediacy of the a-carbonyl carbene A. [6, 7] The reaction of the cis-3-en-1-yne 3 a in the presence of various gold catalysts and 8-methylisoquinoline oxide [7] (3 equiv) as the oxidant were investigated (Table 1). The use of [PPh 3 AuCl]/AgNTf 2 (5 mol %) resulted in the complete consumption of 3 a in hot 1,2-dichloroethane (DCE, 80 8C, 10 h), thus giving 3-phenylindanone (4 a) in 42 % yield [**] We thank the National Science Council, Taiwan, for financial support of this work.
An efficient synthesis of 2-(N-aryl)aminobenzo[d]-1,3-thiazoles via intramolecular C–S bond formation/C–H bond functionalization utilizing an unusual cocatalytic Au-NPs/KMnO4 system under an oxygen atmosphere at 80 C is presented. Au-NPs can be easily prepared by using HAuCl4 with reductive potential of Kayea assamica (sia nahor) aqueous fruit extract. The catalyst can be easily separated and recycled eight times without any appreciable loss of activity.
Journal of the American Chemical Society, 2013
Gold-catalyzed intramolecular oxidation of terminal alkynes with an arenesulfinyl group as the tethered oxidant is a reaction in gold chemistry of high impact, as it introduced to the field the highly-valued concept of gold carbene generation via alkyne oxidation. The proposed intermediacy of α-oxo gold carbenes in these reactions, however, has never been substantiated. Detailed experimental studies suggest that the involvement of such reactive intermediates in the formation of dihydrobenzothiepinones is highly unlikely. Instead, a [3,3]-sigmatropic rearrangement of the initial cyclization intermediate offers a reaction path that can readily explain the high reaction efficiency and the lack of sulfonium formation. With internal alkyne substrates, however, the generation of a gold carbene species becomes competitive with the [3,3]-sigmatropic rearrangement. This reactive intermediate, nevertheless, does not proceed to afford the Friedel-Crafts type cyclization product. Extensive Density Functional Theory studies support the mechanistic conclusion that the cyclized product is formed via an intramolecular [3,3]-sigmatropic rearrangement instead of the previously proposed Friedel-Crafts type cyclization. With the new mechanistic insight, the product scope of this versatile formation of mid-sized sulfur-containing cycloalkenones has been expanded readily to various dihydrobenzothiocinones, a tetrahydrobenzocyclononenone, and even those without the entanglement of a fused benzene ring. Besides gold, Hg(OTf) 2 can be an effective catalyst, thereby offering a cheap alternative for this intramolecular redox reaction.
The effect of ring size on the selective oxidation of cycloalkenes using supported metal catalysts
Catalysis Science & Technology, 2013
In this work we expand on our previous studies on the oxidation of cyclic alkenes using supported gold nanoparticles together with catalytic amounts of peroxides. We demonstrate that various sized cyclic alkenes can be oxidised by this catalyst, under green conditions, without solvent and using air as the oxidant gas. The effect of support, preparation method and choice of metal have been investigated, we demonstrate that supported gold is superior to palladium or a gold palladium alloy, we show that oxides provide the best support for these gold catalysts and the preparation methods that afford the smallest particles are the most active. We show that the reactivity of the cyclic alkenes is related to the ring size with the smaller rings more reactive than the larger rings at the same temperature. The selectivity to the epoxide is dependent on the size of the cyclic alkene ring. In particular, the epoxide selectivity is very low for rings containing fewer than seven carbon atoms. We discuss the origins of this selectivity effect, using DFT calculations to investigate the effect of ring strain on the intermediates and reaction products.