Aqun Zheng

Immobilization of Chiral (salen)Manganese(III) Complexes Into Mesoporous Helical Silica for Asymmetric Epoxidation of Alkenes

Chiral (salen)Mn(III) complexes were immobilized into mesoporous helical silica for asymmetric epoxidation of unfunctionalized alkenes, and chiral synergistic effects between supporting material and (salen)Mn(III) were investigated. Characterization revealed both carriers and supported catalysts had a hierarchical structure composed of morphology and internal channels. Supporting materials had helical morphology and excessive left-handed channels, while most supported catalysts still had excessive left-handed channels although their morphology might degrade. Catalysis revealed the synergistic effects between mesoscopic and molecular chirality exist, and the combination of left-handed channels with (R,R)-(salen)Mn(III) appeared to be more enantioselective than that with (S,S)-salen counterpart in epoxidation of terminal and cyclic alkenes.Graphical Abstract

Macroporous Helical Silica Immobilizing Cobalt-Salen Complex Catalyzed Asymmetric Hydrolytic Kinetic Resolution of Epoxides

Based on an entropy-driven principle, new macroporous helical silica rods were synthesized by using mild templates in sol–gel, then functionalized for immobilizing Co-salen complexes to catalyze enantioselective hydrolytic kinetic resolution of epoxides. Characterization revealed both silica supports and heterogeneous Co-salen complexes were macroporous helical materials with affirmative chirality. Catalysis revealed enantioselective adsorption of substrate on silica supports dominated major configuration of resolution products rather than configuration of Co-salen. The (S)-amino alcohol-doped silica and Co-(R,R)salen comprised the most enantioselective combination, which proved chiral synergy between support and Co-salen did exist. This work would contribute to the design of new support materials for asymmetric catalysis.

Sol-gel synthesis of cerium dioxide nanoparticles coated with stimuli-responsive components and the application for conversion of d-(−)-fructose into platform molecules

AbstractA series of nanosized cerium dioxide particles coated with Pluronic P123, poly(vinyl alcohol) (PVA) or titanium oxide are prepared through a sol-gel process. Characterizations reveal sizes of cerium dioxide particles are maintained below 15 nm along with good crystallinity, and their crystal forms could be modulated by calcination. Furthermore, the organic components such as Pluronic P123 and PVA could be incorporated during sol-gel and affect sample porosity, while loading of titanium into cerium dioxide improves acid amount of sol-gel product. Catalysis reveals both PVA and titanium components show obvious and significant thermo- and pH-responsive properties for conversion of d-(−)-fructose into 5-(hydroxymethyl)-furfural, which mean a lot to the future large-scale production of biomass-derived fine chemicals. This work would not only contribute to the development of stimuli-responsive materials, but also show their promising application for conversion of biomass to platform molecules. The cerium dioxide-based materials having stimuli-responsive components that obtained through adjustable sol-gel process bring about highly efficient conversion of d-(-)-fructose into important platform molecules.HighlightsThe cerium dioxide nanoparticles that coated with Pluronic P123 and poly(vinyl alcohol), or titanium dioxide are prepared through sol-gel.The coated components such as poly(vinyl alcohol) and titanium dioxide show significant thermo- and pH-responsive properties during catalytic conversion of d-(-)-fructose into platform molecules.High yields of platform molecules could be obtained in water at 20 °C, and synthetic catalysts show satisfactory recycling behaviors.

Synthesis of mesoporous zirconium-containing silicates and their application for catalytic asymmetric addition of diethylzinc to aldehydes

A series of mesoporous zirconium-containing silicates were prepared in sol–gel, which were further functionalized by chiral sulfonyl chloride and proline for catalytic asymmetric addition of diethylzinc to aldehydes. These materials had good porosities, hexagonal symmetries and internal chiralities. Moreover, significant morphological variations were observed when preparative conditions were changed. These materials also showed good to excellent enantioselectivities in catalysis, and there was chiral induction synergy between silicate matrix and attached ligand. Recycling of catalyst was tested, and promising results were obtained. This study would contribute to the design of mesoporous chiral catalysts.

Chiral Mesoporous Silicates Immobilizing Titanium Dioxide for Catalytic Asymmetric Epoxidation of Alkenes

Two kinds of titanium-containing silicates were prepared by doping of titanium salt and chiral additive in a sol-gel process, which were further modified by chiral sulfonyl chloride in order for catalytic asymmetric epoxidation of alkenes. These titanium-containing materials had good porosities, ordered pore size distributions, high titanium incorporation yields, ordered morphologies, as well as internal chiral configurations. Particularly, they contained a lot of titanium dioxide particles according to TEM. In catalysis, the titanium silicates showed good conversion of alkenes, satisfactory yields and e.e. values of epoxides. The chiral inducing synergy appeared between silicate matrix and attached ligand, which was significant for transformations of styrene and α-methylstyrene. Moreover, iodosylbenzene, tert-butyl hydroperoxide and hydrogen peroxide were all promising oxidants. In addition, the present titanium catalysts showed satisfactory recycling behaviors and chemical stabilities. This work would contribute to the design of efficient chiral catalysts.

Synthesis and Catalytic Property of Fibrous Titanium-Containing Graphite Oxide

A new layered graphite oxide is synthesized by a two-step oxidation of commercial graphite powders, which is further covalently modified by a titanium complex in order for oxidation of alkenes. Characterizations reveal the present graphite oxide is thicker than classical graphene oxide, but shows fibrous morphology after modification of titanium complex. Furthermore, the composition and morphology of synthetic composite are highly relative to the heating condition in preparation. In catalysis, high conversions of alkenes as well as various oxidized products are obtained by using available and green terminal oxidants. Lastly, a composite catalyst is reused for nine rounds in oxidation of R-(+)-limonene, approving its satisfactory stability for recycling. This work provides a highly promising catalytic material, showing values for the design of solid catalysts.