Current Catalysis - Volume 1, Issue 3, 2012

The catalytic system Ni(COD)2/ BF3·OEt2 was studied in the ethylene oligomerization. It was shown that in the absence of tertiary phosphines the system converted ethylene into dimers with a high selectivity to butene-1 (55%). It opens a way toward atom-economical ligand-free catalytic systems for oligomerization of low molecular weight olefins. The addition of tertiary phosphines made the system active even under the atmospheric pressure of ethylene increasing the selectivity to butene-1 up to 74%. On the basis of the ethylene product distribution and ESR data on the nickel species formed in the system a complete mechanism has been first proposed for the oligomerization of low molecular weight olefins in the catalytic nickel complex systems containing paramagnetic cationic nickel species. The proposed mechanism is based on the conventional key stages of catalytic reactions: metallocyclic ethylene oligomerization and cationic isomerisation of activated olefins which occur with the participation of Ni (I) and Ni (III) species.

Organic synthesis is a creative science involving the construction and cleavage of bond(s), which attracts particular attention because of its immense importance to life and society. The strategies regarding construction and cleavage of bonds represent the central theme in organic synthesis. Development of practical catalysts for efficient synthesis is of key importance to both academia and the chemical industry. A meticulous literature survey at this stage revealed that P2O5 has recently emerged as a powerful catalyst and has been widely utilized in various transformations. Considering the lack of review in the area of P2O5 catalyzed organic reactions and in continuation of our efforts on more sustainable syntheses catalyzed by P2O5 and/or P2O5 embedded on solid support, here an updated overview of the developments in P2O5 catalyzed reactions in solvent and/or under solvent-free conditions is provided. The present report would encompass the developments up to the end of 2011 with special emphasis on the most recent developments. In the last section of this review, some prospects about the future developments in the field covered by this review, giving special emphasis to those aspects that still require further research to be solved satisfactorily have been discussed.

A green and robust solid base MgO has been synthesized by a rapid microwave-assisted solution combustion synthesis method and evaluated for multicomponent Mannich reaction under solvent-free conditions at ambient temperature in the liquid phase. The synthesized catalyst was characterized by various techniques to ascertain its phase composition and thermal stability. Catalyst characterization studies revealed that magnesium oxide synthesized by microwaveassisted solution combustion synthesis method offers stable nanosized MgO crystallites. Good to excellent yields of β-amino carbonyl compounds were achieved with aromatic aldehydes bearing an electron withdrawing group.

Sodium carbonate sesquiperhydrate catalyzed efficient one-pot synthesis of novel spiro[indoline-3,2'- oxirane]dicarboxamides was achieved via Knoevenagel adduct of isatin with malononitrile as the key step followed by a sequential tandem reaction. The Knoevenagel adduct transpires into oxirane with the geminal dicyano functionality being hydrolysed in to corresponding dicarboxamide. Further extension of the scope of reaction with various other cyclic ketone such as 9H-fluoren-9-one, 1H-indene-1,2,3-trione and cycloheptanone was found to be equally feasible as well as efficient, rendering the final spiro compounds in good yields. This method has the advantages of short synthetic route, operational simplicity, shorter reaction times, for small scale high-speed synthesis and is environmentally benign. The structure elucidation and attribution of relative stereochemistry were unequivocally determined by X-ray structural analysis.

Silica functionalized with both ammonium and vinyl groups had been synthesized. By using the functionalized silica as a support, an immobilized platinum catalyst had been prepared and its catalytic properties in the hydrosilylation of alkenes had been investigated. Excellent catalytic performance was observed in the hydrosilylation of alkenes with triethoxysilane. The supported catalyst could be reused several times without any obvious loss of catalytic activity.

A green chemistry approach is used for the synthesis of copper phthalocyanine (CuPc) and its application for the conversion of 2-naphthol to 2-hydroxy-1,4-naphthoquinone (HNQ, Lawsone) in alkaline aqueous solution using H2O2 as an oxidizing agent. The product obtained was compared with that of authentic sample and was found to be identical. Further the effect of amount of catalyst, amount of NaOH, amount of starting material and amount of H2O2, on the rate of reaction was investigated. The efficiency of The reaction was checked using different solvents, temperature, use of substituted CuPc and other metals phthalocyanines.

A simple and efficient method for the synthesis of polysubstituted cyclohexene derivatives has been developed. One-pot multicomponent reactions (MCRs) between aromatic aldehydes, malononitrile and nitromethane by using Rhizopus oryzae lipase as a biocatalyst in a biodegradable deep eutectic solvent (DES) were carried out. The simple quaternary ammonium DES, easily synthesized from choline chloride and urea was used in the reaction, which is easily available, cheap and environment friendly. This method provides access to pharmaceutically relevant products using environmentally friendly reaction conditions in excellent yields. The remarkable catalytic activity and reusability of lipase and DES widen their applicability in MCRs for the synthesis of polysubstituted alkenes with better yields.

A Keggin heteropolyanions-based Bronsted acidic ionic liquid that combined an imidazolium cation with heteropolyanions was synthesized and used as a catalyst for regioselective mononitration of aromatic compounds in HNO3 (67%). The reactions were carried out at 60°C to 80°C with reasonable to good yields and improved para-selectivities for halogenobenzenes compared to those without the catalysts. In addition, this heteropolyanions-based ionic liquid could be recovered and reused at least five times without noticeable decrease in the catalytic activity.

A simple and efficient synthesis of N-substituted imides has been developed by reaction of anhydrides with aromatic amines using tetra butyl ammonium bromide (TBAB) melt as neutral, cost-effective and recyclable ionic liquid under solvent-free i. e green conditions at 105°C for 20-45 minutes.

A series of proline-based heterogeneous polymeric organocatalysts was synthesized as monoliths via the chemo-enzymatic route. These were characterized by various techniques and the one that was synthesized with 1% crosslinker was used as the candidate catalyst in the three-component one pot reaction, i.e., Mannich-type reaction to synthesize 3-substituted 2,6-diarylpiperidin-4-ones and 4-aryldihydropyrimidinones. The merits of the monolith catalyst, the mild reaction conditions, simple protocol, and clean reaction makes the synthetic protocol practical and economically attractive. The catalyst exhibited high efficiency, easy recyclability, reusability and selectivity, especially, with the aromatic substrates having electron withdrawing substituents which resulted in high conversion.

LaNi1-xFexO3 perovskites (x= 0, 0.2 and 0.4) were synthesized by the combustion method with urea and used as catalyst precursors in the partial oxidation of methane (POM). LaNiO3 was obtained as a single phase, while NiO and La(OH)3 were also detected in Fe-doped samples. The substitution of Ni by Fe in LaNiO3 perovskite resulted in a decrease in the specific surface area and an increase in the reduction temperature. The perovskite structure was completely decomposed by reduction, with formation of Ni°-Fe° and La2O3 phases. Activity cycles between 400 and 800°C revealed that the introduction of Fe decreased the catalytic activity for POM reaction at high temperatures. The catalysts showed great stability during 24 h on stream at 750°C without carbon deposition.

5-Hydroxymethylfurfural (HMF) has been considered as a green platform chemical with a wide range of applications due to its rich chemistry and potential availability from renewable biomass resources. In recent years, considerable efforts have been made to transform carbohydrates into HMF using homogeneous and heterogeneous acid catalysis. In this critical review, the direct conversion of cellulose into HMF catalyzed by transition metals is described because of the present important utility of such metals. Since solid acids are deemed less noxious than traditional liquid acids, significant attention is given to hydrolysis, isomerization, and dehydration reactions successively carried out in a one-pot mode from the polysaccharide using heterogeneous catalysts.