Carmela Aprile

New ionic liquid-modified silica gels as recyclable materials for L-proline- or H–Pro–Pro–Asp–NH2-catalyzed aldol reaction

L-proline and the tripeptide H–Pro–Pro–Asp–NH2 (1) have been supported, by adsorption, onto the surface of modified silica gels functionalized with a monolayer of covalently attached 1,2-dimethyl-imidazolium chloride, tetrafluoroborate or hexafluorophosphate ionic moieties, respectively. Three different linkers were used to attach the ionic liquid moiety to the surface of these supports. The resulting materials have been used as catalysts for the aldol reaction between acetone and several substituted benzaldehydes. Good yields and enantioselectivities, comparable to or better than those obtained under homogeneous conditions, were obtained. These materials are easily recovered by filtration, and studies regarding their re-use have been carried out. Studies performed using L-proline-supported materials have shown that the re-use of these materials is dependent on the nature of the linker. The supported tripeptide H–Pro–Pro–Asp–NH2 gave higher enantioselectivities than those obtained with supported-proline. Recycling investigations using tripeptide-supported materials showed continued good selectivities but diminishing conversions over consecutive runs. L-proline-supported materials however, can be used at least nine times without loss of either conversion or selectivity.

Multilayered supported ionic liquids as catalysts for chemical fixation of carbon dioxide: a high-throughput study in supercritical conditions

Multilayered, covalently supported ionic liquid phase (mlc-SILP) materials were synthesized by using a new approach based on the grafting of bis-vinylimidazolium salts on different types of silica or polymeric supports. The obtained materials were characterized and tested as catalysts in the reaction of supercritical carbon dioxide with various epoxides to produce cyclic carbonates. The material prepared by supporting a bromide bis-imidazolium salt on the ordered mesoporous silica SBA-15 was identified as the most active catalyst for the synthesis of cyclic carbonates and displayed improved productivity compared with known supported ionic liquid catalysts. The catalyst retained its high activity upon reuse in consecutive catalytic runs. This is the first report of the application of mlc-SILP materials as catalysts in a reaction for the fixation of carbon dioxide. Rapid, parallel screening and comparison of the catalysts was performed by means of high-throughput experimentation.

Synthesis and catalytic activity of periodic mesoporous materials incorporating gold nanoparticles

A mesoporous silica containing gold nanoparticles (mpAu–SiO2) has been obtained by one pot synthesis, starting from tetraethylorthosilicate (TEOS) and colloidal gold particles (2–5 nm) stabilized with N-[3-(triethoxysilyl)propyl] O-2(dicetylmethylammonium)ethyl urethane. This stabilizer ligand interacts with gold nanoparticles through the quaternary ammonium ions, whose long chains also show affinity for the cetyltrimethylammonium surfactant. On the other hand, the triethoxysilyl group is adequate to undergo co-condensation with TEOS during the formation of the silica. The periodic mesoporous structure of the mpAu–SiO2 materials was assessed by X-ray diffraction, TEM and isothermal gas adsorption of calcined mpAu–SiO2 (SBET 488 m2×g−1, pore size 3.5 nm). This material exhibits high activity and reusability for the solventless, aerobic oxidation of secondary alcohols to ketones.

Synthesis and high-throughput testing of multilayered supported ionic liquid catalysts for the conversion of CO2 and epoxides into cyclic carbonates

Multilayered covalently supported ionic liquid phase (mlc-SILP) materials were synthesised by grafting different bis-vinylimidazolium salts on thiol-functionalised silica. These materials, which contain a cross-linked oligomeric network of imidazolium units, were characterised and tested as catalysts for the reaction of carbon dioxide with various epoxides to produce cyclic carbonates. The materials prepared by supporting a bis-imidazolium iodide salt with xylene or octane as a linker between the imidazolium units were identified as the most active catalysts and displayed high turnover numbers and improved productivity compared to known supported ionic liquid catalysts. The most promising mlc-SILP catalysts were further studied to tune the reaction conditions towards optimum catalytic performance and to investigate their versatility with different substrates and their reusability. The rapid and parallel screening of the catalysts was efficiently carried out by means of high-throughput (HT) experimentation.

Studies on the stereoselective selenolactonization, hydroxy and methoxy selenenylation of α- and β-hydroxy acids and esters. Synthesis of δ- and γ-lactones

Abstract The diastereoselective synthesis of hydroxy substituted γ- and δ-lactones was accomplished following two approaches. A 5- or 6-endo cyclization promoted by electrophilic selenium reagents of α- or β-hydroxy acids and a 5- or 6-exo cyclization of hydroxy esters obtained through a diastereoselective hydroxy selenenylation reaction of α- or β-hydroxy esters. Moreover, the diastereoselective methoxy selenenylation of the above compounds was investigated showing a case in which the compound that was unreactive in the hydroxy selenenylation conditions gave, in the methoxy selenenylation conditions, the deprotected diol. The usefulness of the methoxy selenenylation procedure was proven by the preparation of a symmetric compound unsymmetrically functionalized. Yields and selectivities were found to depend on substituents (Ph or alkyl groups at the carbon atom that undergoes the nucleophilic attack), mode of cyclization, kinetic or thermodynamic control conditions. In the latter case, silica gel played an important role.

A polyhedral oligomeric silsesquioxane-based catalyst for the efficient synthesis of cyclic carbonates

Polyhedral oligomeric silsesquioxane functionalized with imidazolium chloride peripheries (POSS-Imi) was successfully synthesized through a novel synthesis protocol. The solid was extensively characterized via1H NMR, 13C NMR and IR spectroscopy as well as combustion chemical analysis, mass spectrometry and transmission electron microscopy. Moreover, an in-depth investigation through 29Si NMR was performed. POSS-Imi was used for the first time as a catalyst for the conversion of CO2 and epoxides into cyclic carbonates with excellent results in terms of both yield and selectivity. The catalyst displayed improved catalytic performance with respect to unsupported 1-butyl-3-methylimidazolium chloride. The enhanced activity was ascribed to the proximity effect generated by the increased local concentration of imidazolium species surrounding the inorganic silsesquioxane core.

Structured Mesoporous Tin Oxide with Electrical Conductivity. Application in Electroluminescence

Tin oxide nanoparticles (2-5 nm) have been structured using CTAB surfactant into mesoporous mpSnO(2) materials that exhibit lower electrical resistivity than the precursors SnO(2) nanoparticles and over nine orders the magnitude lower than that of mesoporous MCM-41 silica. The superior performance of these conductive mesoporous mpSnO(2) materials as hosts is clearly manifested by the fact that a conjugated polymer with 2,5-dimethoxyphenylenevinylene structure emits light at voltages below 10 V direct current when incorporated in mpSnO(2) materials, but not in analogous mesoporous MCM-41 silica or when adsorbed on the nonporous precursor SnO(2) nanoparticles.

Synthesis of 2,4,6-trisubstituted tetrahydropyrans via 6-exo selenoetherification of unsaturated alcohols

Abstract Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on the stereochemistry of the diols and on the presence of an oxygen atom close to the intermediate seleniranium ring. Silica gel was useful in order to obtain good yields. Reactions performed both under kinetic and thermodynamic control led to the same products.

Cross‐Linked Thiazolidine Network as Support for Palladium: A New Catalyst for Suzuki and Heck Reactions

A thiazolidine‐based material was used for the first time as support for palladium. The support was prepared by starting from a highly cross‐linked thiazolium‐based material, obtained by radical oligomerization of a bisvinylthiazolium dibromide salt in the presence of 3‐mercaptopropyl‐modified silica SBA‐15. Palladium was immobilized by treatment with tetrachloropalladate salt. Reduction with sodium borohydride afforded a thiazolidine‐based material that acted as ligands for the Pd species. The thiazolidine‐based palladium catalyst was fully characterized and, working in only 0.1 mol % amount, displayed good activity in the Suzuki–Miyaura and in the Heck reactions. Several biphenyl and alkene compounds could be prepared in high yields. The catalytic material proved to be fully recoverable and it was representatively used for three times in the Suzuki–Miyaura reaction without showing any decrease in its activity.

Imidazolium-based silica microreactors for the efficient conversion of carbon dioxide

Imidazolium-based silica microreactors were synthesized by a one-pot procedure. A straightforward synthesis approach was achieved through self-organization/polymerization of the amphipathic organic salts that behave as templates for the construction of silica architecture and as catalytic active sites. The porous silica shell allowed the diffusion of reactants and products to/from the active sites and conferred stability to the polymeric matrix. The solid was extensively characterised by transmission and scanning electron microscopy, N2 adsorption/desorption, X-ray diffraction, 29Si solid-state MAS-NMR and combustion chemical analysis. The material was tested as a catalyst for the reaction of carbon dioxide with various epoxides to produce cyclic carbonates. The organic–inorganic hybrid microreactors displayed excellent performance in terms of both yield and selectivity. Moreover, it can be used in multiple catalytic cycles.