Wenguang Leng

Rapid and Efficient Functionalized Ionic Liquid-Catalyzed Aldol Condensation Reactions Associated with Microwave Irradiation

Five quaternary ammonium ionic liquid (IL) and two tetrabutylphosphonium ILs were prepared and characterized. An environmentally benign and convenient functionalized ionic liquid catalytic system was thus explored in the aldol condensation reactions of aromatic aldehydes with acetone. The aldol reactions proceeded more efficiently through microwave-assisted heating than through conventional thermal heating. The yield of products obtained under microwave heating for 30 min was approximately 90%, and the ILs can be recovered and reused at least five times without apparent loss of activity. In addition, this catalytic system can be successfully extended to the Henry reactions.

Bottom-up preparation of gold nanoparticle-mesoporous silica composite nanotubes as a catalyst for the reduction of 4-nitrophenol

Abstract Gold (Au) nanoparticle (NP)-mesoporous silica (SiO2) composite nanotubes were prepared by a bottom-up approach, in which Au NPs were anchored to the inner wall of mesoporous SiO2 tubular shells. In this composite, the agglomeration, exfoliation, and grain growth of Au NPs were restricted, and the loading and size of the catalyst NPs were easily tuned. The mesoporous shell, open ends, and one-dimensional passage of the SiO2 nanotubes all promote the diffusion of reactants, which enhanced the catalytic efficiency of this composite in the reduction of 4-nitrophenol. The Au NP-mesoporous SiO2 composite nanotubes also demonstrated good reusability, and no leaching or agglomeration of the Au NPs was observed during the catalytic reaction.

Gold nanoparticles supported on the periodic mesoporous organosilica SBA-15 as an efficient and reusable catalyst for selective oxidation of silanes to silanols

Gold nanoparticles are confined and stabilized within the channels of SBA-15 through the poly(ionic liquid) brushes that are anchored onto the pore walls of SBA-15. The supported gold catalyst exhibited remarkably high catalytic activities for selective oxidation of silanes into silanols using water as an oxidant without the use of organic solvents.

Ionic liquids as eco-friendly catalysts for converting glycerol and urea into high value-added glycerol carbonate

Abstract Acidic, basic and neutral ionic liquids (ILs) have been used as catalysts in the carbonylation of glycerol with urea. The results show that neutral ILs have high catalytic activity in the reaction. The excellent performance of the catalysts can be attributed to the synergistic effect of the cation and anion. We speculated that the cation with positive charge activates urea, and the anion with negative charge activates glycerol. In addition, the well balanced acid-basic properties of the catalysts are necessary for good catalytic performance. The ILs can be reused at least five times without loss of activity. Using ILs, instead of the traditional metal catalysts, reduces the use of non-renewable resources. It is eco-friendly that two inexpensive and bio-based raw materials were used and the catalytic reaction was carried out without solvent.

Thermo-Sensitive Polymer-Grafted Carbon Nanotubes with Temperature-Controlled Phase Transfer Behavior between Water and a Hydrophobic Ionic Liquid

Thermo-sensitive polymer-grafted carbon nanotubes were prepared by surface-initiated atom transfer radical polymerization and carefully characterized. A reversible, temperature-induced phase transfer behavior of these organic-inorganic hybrids between water (with a decrease in temperature to 20 °C) and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim]NTf2) (with an increase in temperature to 90 °C), was observed. Mechanism analysis suggests that this reversible phase transfer between water and [Emim]NTf2 is due to the relative affinity of the two solvents for the poly(ethylene oxide) units grafted on the carbon nanotubes. Our results pave the way for further design of carbon nanotube-based, recyclable phase transfer vehicles as well as heterogeneous catalysts suited for a water-hydrophobic ionic liquid biphasic system.

Nitrogen ligands in two-dimensional covalent organic frameworks for metal catalysis

Abstract We introduced bipyridine ligands into a series of two-dimensional (2D) covalent organic frameworks (COFs) using 2,2′-bipyridine-5,5′-dicarbaldehyde (2,2′-BPyDCA) as a component in the mixed building blocks. The framework of the COFs was formed by the linkage of imine groups. The ligand content in the COFs was synthetically tuned by the content of 2,2′-BPyDCA, and thus the amount of metal, palladium(II) acetate, bonded to the nitrogen ligands could be manipulated. Both the bipyridine ligands and imine groups can coordinate with Pd(II) ions, but the loading position can be varied, with one ligand favoring binding in the space between adjacent COFs′ layers and the other ligand favoring binding within the pores of the COFs. The Pd(II)-loaded COFs exhibited good catalytic activity for the Heck reaction.

Bimetallic docked covalent organic frameworks with high catalytic performance towards tandem reactions

Mn/Pd bimetallic docked covalent organic frameworks were fabricated via a programmed synthetic procedure. Within the framework, MnCl2 could only coordinate with the bipyridine ligands, while Pd(OAc)2 could occupy the rest of the nitrogen sites. Such bimetallic docked materials showed high catalytic activity in a Heck-epoxidation tandem reaction.