Oxidative Cycloaddition of 1,1,3,3-Tetramethyldisiloxane to Alkynes Catalyzed by Supported Gold Nanoparticles (original) (raw)
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Tetrahedron, 2014
a b s t r a c t 1,1,3,3-Tetramethyldisiloxane (TMDS) is a highly reactive reducing reagent in the Au/TiO 2 -catalyzed hydrosilylation of carbonyl compounds relative to monohydrosilanes. The reduction of aldehydes or ketones with TMDS can be performed on many occasions at ambient conditions within short reaction times and at low loading levels of gold, whereas typical monohydrosilanes require excess heating and prolonged time for completion. The product yields are excellent, while almost stoichiometric amounts of carbonyl compounds and TMDS can be used. It is postulated that the enhanced reactivity of TMDS is attributed to the formation of a gold dihydride intermediate. This intermediate is also supported by the fact that double hydrosilylation of carbonyl compounds by TMDS is a negligible pathway.
ChemInform, 2015
We report the utilization of a novel catalyst for cycloisomerizations. The novel catalyst system contains gold nanoparticles supported on Al-SBA15, which was prepared by the ball-milling process. We developed a greener methodology for synthesizing spiroindolines under heterogeneous conditions, using this novel class of supported gold nanoparticles in combination with microwave irradiation. The catalyst is highly reusable and selective. Cycloisomerization reaction yields ranged from good to excellent leading to the formation of two novel classes of six-and seven-membered heterocycles, which have been unprecedented so far. The selectivity of the catalyst towards the desired products is high and the reaction can be performed in ethanol as the solvent. A one-pot cascade reaction could be established commencing with the Ugi-reaction to ensure diversity. Scheme 1 Obtained products for post-Ugi-cyclization reactions. † Electronic supplementary information (ESI) available: General experimental procedures; XRD, BET, TEM characterization and discussion of the catalyst; 1 H-NMR, 13 C-NMR spectra and HRMS results of the starting materials and products; the X-ray crystal structure of 4n. CCDC 1033069. For ESI and crystallographic data in CIF or other electronic format see
Functionalization of alkanes by gold nanoparticles stabilized by 1-dodecanethiol in organic media
Russian Journal of Physical Chemistry B, 2007
It was revealed that gold nanoparticles stabilized by a 1-dodecanethiol monolayer oxidize methane in a methylene chloride medium, presumably by the active oxygen species formed at the surface of the nanoparticles during their synthesis, to yield methanol (in stoichiometric amount), ethane, and an unidentified product. The same nanoparticles in a cyclohexene solution catalyze its oxidation by molecular oxygen to produce oxide (11%), alkylhydroperoxide (84%), and allyl ketone (5%). The only product of methane functionalization in toluene is ethylene. The results obtained on the oxidation of hydrocarbons suggest that, in the presence of gold nanoparticles, oxygen forms various active surface species, the structure of which is discussed. It is also demonstrated that gold nanoparticles catalyze multiple H-D exchange of methane with D 2 (but not D +), an observation indicative of the activation of C-H bonds by a gold compound in the low oxidation state (Au 0 or Au +).
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.