Methyltrioxorhenium catalysis in nonconventional solvents: a great catalyst in a safe reaction medium

Reactivity of metal dioxo complexes

Metal dioxo chemistry and its diverse reactivity are presented with an emphasis on the mechanisms of reactivity. Work from approximately the last decade is surveyed and organized by metal. In particular, the chemistry of cis-dioxo metal complexes is discussed at length. Reactions are grouped by generic type, including addition across a metal oxo bond, oxygen atom transfer, and radical atom transfer reactions. Attention is given to advances in deoxygenation chemistry, oxidation chemistry, and reductive transformations.

A highly crosslinked, mesoporous poly(ionic liquid) containing salen–Pd for efficient, eco-friendly Suzuki–Miyaura coupling reactions

Mesoporous poly(ionic liquid) obtained by hyper-crosslinking of a salen-containing poly(ionic liquid) can efficiently catalyze Suzuki–Miyaura coupling reactions with excellent recyclability under an air atmosphere in 50% aqueous ethanol.

Methyltrioxorhenium (MTO) catalysis in the epoxidation of alkenes: a synthetic overview

Epoxides are biologically important moiety that is also used as synthetic intermediates. This review aims to present the up-to-date advancements in methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes using diverse oxidizing agents.

Dendrimer crown-ether tethered multi-wall carbon nanotubes support methyltrioxorhenium in the selective oxidation of olefins to epoxides

Benzo-15-crown-5 ether supported on multi-wall carbon nanotubes (MWCNTs) by tethered poly(amidoamine) (PAMAM) dendrimers efficiently coordinated methyltrioxorhenium in the selective oxidation of olefins to epoxides.

SBA-15 Anchored Metal Containing Catalysts in the Oxidative Desulfurization Process

Recalcitrant sulfur compounds are common impurities in crude oil. During combustion they produce SOx derivatives that are able to affect the atmospheric ozone layer, increasing the formation of acid rains, and reducing the life of the engine due to corrosion. In the last twenty years, many efforts have been devoted to develop conventional hydrodesulfurization (HDS) procedures, as well as alternative methods, such as selective adsorption, bio-desulfurization, oxidative desulfurization (ODS) under extractive conditions (ECODS), and others. Among them, the oxidative procedures have been usually accomplished by the use of toxic stoichiometric oxidants, namely potassium permanganate, sodium bromate and carboxylic and sulfonic peracids. As an alternative, increasing interest is devoted to selective and economical procedures based upon catalytic methods. Heterogeneous catalysis is of relevance in industrial ODS processes, since it reduces the leaching of active species and favors the recovery and reuse of the catalyst for successive transformations. The heterogenization of different types of high-valent metal transition-based organometallic complexes, able to promote the activation of stoichiometric benign oxidants like peroxides, can be achieved using various solid supports. Many successful cases have been frequently associated with the use of mesoporous silicas that have the advantage of easy surface modification by reaction with organosilanes, facilitating the immobilization of homogeneous catalysts. In this manuscript the application of SBA-15 as efficient support for different active metal species, able to promote the catalytic ODS of either model or real fuels is reviewed, highlighting its beneficial properties such as high surface area, narrow pore size distribution and tunable pore diameter dimensions. Related to this topic, the most relevant advances recently published, will be discussed and critically described.

Oxidative nucleophilic substitution selectively produces cambinol derivatives with antiproliferative activity on bladder cancer cell lines

Methyltrioxorhenium mediated oxidative addition/elimination nucleophilic substitution yielded alkylamino and arylamino cambinol derivatives characterized by anti-proliferative activity against wild-type and p53 mutated MGH-U1 and RT112 bladder cancer cell lines. Some of the novel compounds showed an activity higher than that of the lead compound. The reaction was highly regioselective, affording for the first time a panel of C-2 cambinol substitution products. Aliphatic primary and secondary amines, and primary aromatic amines, were used as nitrogen centered nucleophiles. Surprisingly, the antiproliferative activity of C-2 substituted cambinol derivatives was not correlated to the induction of p53 protein, as evaluated by the analysis of the cell viability on wild-type and p53 mutated cancer cell lines, and further confirmed by western blot analyses. These data suggest that they exert their antiproliferative activity by a mechanism completely different from cambinol.

Synthesis of coenzyme Q0 through divanadium-catalyzed oxidation of 3,4,5-trimethoxytoluene with hydrogen peroxide

The divanadium-substituted polyoxometalate (Bu₄N)_5−nH_n[γ-PW₁₀V₂O₄₀] (n = 1–2) is an efficient and recyclable catalyst used for the synthesis of coenzyme Q₀ using hydrogen peroxide as a green oxidant.

Olefin Epoxidation in Aqueous Phase Using Ionic-Liquid Catalysts

Hydrophobic imidazolium-based ionic liquids (IL) act as catalysts for the epoxidation of unfunctionalized olefins in water using hydrogen peroxide as oxidant. Although the catalysts are insoluble in both the substrate and in water, surprisingly, they are very well soluble in aqueous H2 O2 solution, owing to perrhenate-H2 O2 interactions. Even more remarkably, the presence of the catalyst also boosts the solubility of substrate in water. This effect is crucially dependent on the cation design. Hence, the imidazolium perrhenates enable both the transfer of hydrophobic substrate into the aqueous phase, and serve as actual catalysts, which is unprecedented. At the end of the reaction and in absence of H2 O2 the IL catalyst forms a third phase next to the lipophilic product and water and can easily be recycled.

Immobilization of Methyltrioxorhenium on Mesoporous Aluminosilicate Materials

The presented report focuses on an in-depth detailed characterization of immobilized methyltrioxorhenium (MTO), giving catalysts with a wide spectra of utilization. The range of mesoporous materials with different SiO₂/Al₂O₃ ratios, namely mesoporous alumina (MA), aluminosilicates type Siral (with Al content 60%–90%) and MCM-41, were used as supports for immobilization of MTO. The tested support materials (aluminous/siliceous) exhibited high surface area, well-defined regular structure and narrow pore size distribution of mesopores, and therefore represent excellent supports for the active components. Some of the supports were modified by zinc chloride in order to obtain catalysts with higher activities for instance in metathesis reactions. The immobilization of MTO was optimized using these supports and it was successful using all supports. The success of the immobilization of MTO and the properties of the prepared heterogeneous catalysts were characterized using X-ray Fluorescence (XRF), atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), physical adsorption of N₂, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (FTIR), Fourier Transform Infrared Spectroscopy (FTIR) using pyridine as a probe molecule and X-ray photoelectron spectroscopy (XPS). Furthermore, the catalytic activity of the immobilized MTO on the tested supports was demonstrated on metathesis reactions of various substrates.

New p-tolylimido rhenium(v) complexes with carboxylate-based ligands: synthesis, structures and their catalytic potential in oxidations with peroxides

Novel p-tolylimido rhenium(v) complexes were obtained and calculations at the DFT level were undertaken. The complexes exhibited high catalytic activity in oxidation of alkanes and alcohols with H₂O₂ or TBHP.

Deoxydehydration of glycerol to allyl alcohol catalyzed by rhenium derivatives

Both ReO₃ and methyltrioxorhenium combined with alcohol reductants are used for the efficient deoxydehydration of glycerol to allyl alcohol.

Selective oxidation reactions of natural compounds with hydrogen peroxide mediated by methyltrioxorhenium

We have investigated the oxidative behaviour of natural compounds such as methyl abietate (1), farnesyl acetate (2), α-ionone (3), β-ionone (4), methyl linolelaidate (5), methyl linolenate (6) and bergamottin (7) with the oxidant system methyltrioxo-rhenium/H₂O₂/pyridine. The reactions, performed in CH₂Cl₂/H₂O at 25 °C, have shown good regio- and stereoselectivity. The oxidation products were isolated by HPLC or silica gel chromatography and characterized by MS(EI), ¹H-, ¹³C-NMR, APT, gCOSY, HSQC, TOCSY and NOESY measurements. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects.

Ionic Liquids: Green Solvent for Pretreatment of Lingnocellulosic Biomass

Green technology has become the primary concern of nations around the world. In-line with this concern, lignocellulosic biomass is often advocated as significant starting material for a greener production. However, the current biomass conversion cannot be considered as green due to the use of acid or alkaline during its pretreatment. An introduction of ionic liquids (ILs) as replacement of acids or alkaline for the pretreatment of lingo-cellulosic materials is gaining interest due to their minimal waste, nonvolatility and low toxicity and therefore considered green. This paper discusses the benefits of ILs as a green solvent for pretreatment of lignocellulosic biomass.

Synthesis of 2'-deoxy-1'-homo-N-nucleosides with anti-influenza activity by catalytic methyltrioxorhenium (MTO)/H2O2 oxyfunctionalization

This paper describes a new route for the synthesis of 1'-homo-N-nucleoside derivatives by means of either methyltrioxorhenium (MTO) or supported MTO catalysts, with H(2)O(2) as the primary oxidant. Under these selective conditions, the oxyfunctionalization of the heterocyclic ring and the N heteroatom oxidation were operative processes, regardless of the type of substrate used, that is, purine or pyrimidine derivatives. In addition, the oxidation of 1'-homo-N-thionucleosides, showed the occurrence of site-specific oxidative nucleophilic substitutions of the heterocyclic ring. The MTO/H(2)O(2) system showed, in general, high reactivity under both homogeneous and heterogeneous conditions, affording the final products with high conversion values of substrates and from medium to high yields. Many of the novel 1'-homo-N-nucleoside analogues were active against the influenza A virus, without any cytotoxic effects, retaining their activity in both protected and unprotected forms.

Immobilised lipase on structured supports containing covalently attached ionic liquids for the continuous synthesis of biodiesel in scCO2

Different nanostructured supports, based on 1-decyl-2-methyimidazolium cations covalently attached to a polystyrene divinylbenzene porous matrix, were used as carriers to immobilise Candida antarctica lipase B. The suitability of these immobilised lipase derivatives for the synthesis of biodiesel (methyl oleate) by the methanolysis of triolein has been tested in both tert-butanol and supercritical (sc)CO(2) (18 MPa, 45 °C) as reaction media. The use of modified supports with low ionic-liquid loading covalently attached to the main polymeric backbone chains provide structured materials that led to the best biodiesel yields (up to 95 %) and operational stability (85 % biodiesel yield after 45 cycles of 8-4 h) in scCO(2) (45 °C, 18 MPa). The presence of tert-butanol as an inert cosolvent in the scCO(2) phase at the same concentration as triolein was key to avoid poisoning the biocatalyst through the blockage of its active sites by the polar byproduct (glycerol) produced in the biodiesel synthesis.