Current Organic Chemistry - Volume 19, Issue 8, 2015

Developments of mesoporous silica materials for use as supports to construct silica-supported chiral heterogeneous catalysts and explorations of their applications in asymmetric transfer hydrogenation represent an important branch of organic chemistry, in which understanding the supports role and controlling chiral environment are critical during the catalytic process. In this review, we briefly introduce the basic concepts with respect to general immobilization strategies and preparation methods. Main considerations focus on the preparation of heterogeneous catalysts according to the type of mesoporous silica supports and summarize their applications in asymmetric transfer hydrogenation. This paper also provides a perspective for further developing the design of silica-supported chiral heterogeneous catalysts.

As a major contributor to greenhouse effect, detrimental influence of CO2 has received more and more attention. Meanwhile, CO2 is also a valuable C1 building block, with several distinguished features such as low cost, nontoxicity, nonflammability, renewal, abundance. CO2 fixation is one of the most important priorities of the scientific community dedicated to reduce global warming. The last few decades have witnessed enormous attention utilizing CO2 to produce a variety of organic molecules, such as cyclic carbonates, which hold diverse applications as polar aprotic solvents, intermediates for organic and polymeric synthesis, and chemical ingredients for pharmaceutical/ fine chemicals in biomedical applications, electrolytic elements of lithium secondary batteries. Development of sustainable solid catalysts for the cycloaddition of epoxide with CO2 into cyclic carbonates is of paramount importance from a viewpoint of C1 chemistry and green chemistry. In this mini-review, we would like to update the recent advances in development of efficient heterogeneous catalysts including polymeric ionic liquids, metal organic frameworks, conjugated microporous polymer, polyamines, functionalized ion-exchange resins, polystyrene-supported ionic liquids, chitosan-based heterogeneous catalysts, silica-supported catalysts, magnetic nanoparticle supported catalysts, metal oxide and polyoxometalate, and others for the cycloaddition of epoxide with CO2, and we hope this presentation will stimulate further interest in chemical conversion of CO2 using sustainable catalysts.

This review gives a complete picture of the Heck-Matsuda reaction of arenediazonium salts with olefins catalyzed by heterogeneous palladium catalysts. The nature, preparation and characterization of the different forms of heterogeneous palladium catalysts are presented, while their activity on the Heck-Matsuda reaction is critically discussed.

Size and shape selective syntheses of nanoparticles and their catalytic applications are gaining considerable interest in the recent years. Homogeneous catalysis is important due to its inherent advantages like mild reaction conditions and high selectivity. However, it suffers with serious drawback of catalyst-product separation and recycles as compared to their heterogeneous counterparts restricting their applications. The use of catalyst in the form of nano-size is an alternative methodology for combination of advantages of heterogeneous and homogeneous catalysis. Silver nanoparticles are important as they find applications in catalysis, organic transformations, synthesis of fine chemicals and organic intermediates. This review covers an overview of the synthesis of Ag nanoparticles, supported Ag nanoparticles and bimetallic Ag-metal nanoparticles and their characterization by various techniques. The applications of Ag nanoparticles in several organic transformations including C-C, C-N, C-S, C-O bond formation reactions as well as reduction and oxidation reactions are also discussed. The use of Ag nanoparticles in catalysis is advantageous as it avoids the use of ligands; easy separation of catalyst for recyclability makes the protocol heterogeneous and economic. Ag nanoparticles gave good catalytic activity towards desired products due to high surface area. By considering these advantages, researchers have focused their attention towards applications of Ag nanoparticles in catalysis.

Ionic liquids are considered as one of the safe, green and environmentally benign solvents/catalysts for many organic reactions. Particularly, imidazolium based ionic liquids attracted much attention in basic as well as applied research. The major role of these ionic liquids is the replacement of the existing corrosive solvents, which are largely used in most of the organic processes and make these processes more eco-friendly. Recent report reveals the importance of imidazolium based ionic liquids, supported on silica gel or polystyrene in catalysis. The solid supports have well versed properties such as easy anchoring of ionic liquid, chemically and mechanically very stable and inert in nature. These ionic liquids can be tailored either by covalent attachment or simple deposition of the ionic liquid on the surface of the support. Both approaches showed enhanced reactivity and selectivity for various reactions. In this review, we made an attempt to review the recent reports related to synthesis and applications of tailor made ionic liquids and their use as catalyst in Aldol, Friedel-Crafts alkylation, hydroformylation, nucleophilic substitution and biomass transformation reactions.