Ziwei Gao

Salicylato Titanocene Complexes as Cooperative Organometallic Lewis Acid and Brønsted Acid Catalysts for Three-Component Mannich Reactions

A binary acid system has been developed that features an air-stable organometallic precursor, titanocene dichloride, and simple organic cooperative Brønsted acids, which allowed for mild and highly efficient Mannich reactions of both aryl and alkyl ketones with excellent yields and satisfactory diastereoselectivity. Mechanistic studies, including (1) Hu2005NMR titration, X-ray structure analyses as well as isolation of catalytically active species, elucidated the dramatic synergistic effects of this new binary acid system.

Star-PDMAEMA-β-CD-Stabilized Colloidal Gold Nanoparticles: Synthesis, Characterization and pH-Controlled Assembly

Colloidal gold nanoparticles were prepared through in situ reduction in the presence of water-soluble star homopolymer with β-cyclodextrin core and poly[2-(dimethylamino) ethyl methacrylate] arms (star PDMAEMA-β-CD) at ambient temperature. In this process, star PDMAEMA-β-CD acted as both reducing agent and stabilizing agent for gold nanoparticles. More importantly, the optical properties and the morphology of star-PDMAEMA-β-CD-stabilized colloidal gold nanoparticles were sensitive to the solution pH due to structural changes of the polymer. Different assemblies can be formed by tuning the pH of the medium. Fourier transform infrared (FT-IR), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), dynamic laser light scattering (DLS) and X-ray diffraction (XRD) were used to characterize the synthetic gold nanoparticles and the pH-controlled assembly of gold nanoparticles.

Preparation of the substituted salicylato of titanocene derivatives by the liquid–liquid interfacial reaction

Abstract The reaction of Cp 2 TiCl 2 with several substituted salicylic acids in H 2 O+CHCl 3 medium was discussed in detail. By interfacial reaction (methods 1–3), ten titanocene derivatives were prepared, respectively. The compounds were characterized by elemental analysis, UV–vis, IR and 1 H-NMR. Based on the UV–vis spectrum, the following mechanism of reaction was proposed: first, Cp 2 TiCl 2 in the organic phase interfacially with water in the aqueous phase to form its hydrolysate (such as [Cp 2 Ti(OH)(OH 2 )] + ). When 5-sulfosalicylic acid (H 2 Ssal) is present in the reaction system, the hydrolysate transforms itself into [Cp 2 Ti(Ssal)] + and the reaction is prompted. The resulting species undergoes an interfacial interaction with substituted salicylic acid to form the final complexes, which stay in the organic phase. Then the ‘Cp 2 Ti’ species return to the organic phase.

Electro-response characteristic of starch hydrogel crosslinked with Glutaraldehyde

The facile synthesis of the starch hydrogel with anisotropic microstructure and dynamic behaviors was developed in the presence (A-gel) and absence of DC electric field (B-gel). The microstructures of hydrogels were characterized by environmental scanning electron microscope. Their electro-responsive property of hydrogels was investigated with their storage modulus (G′). The result demonstrates that the G′ of A-gel is greater than that of B-gel, and the modulus of A-gel increases along with the external field, which signifies positive electroresponse. In addition, the G′ of A-gel and B-gel ( and ) also continuously increases with increasing starch concentration, whereas both the maximum of modulus increment (ΔG′ = − ) and that of modulus increment sensitivity (ΔG′/) occur with the starch weight fraction at around 36.5%. To enhance the electro-responsive effects of the hydrogels, dielectric particles were dispersed in the hydrogel. It is found that BaTiO3/chitosan core-shell composite particles significantly enhance the electroresponse of the hydrogel. The mechanism of the electro-response mode is proposed.

Synthesis and characterization of two bis (η5-methylcyclopentadienyl)hydroxynaphthoatotitanium complexes

Based on the reaction of bis(η5-methylcyclopentadienyl) dichlorotitanium ( , Cp′ = η5-C5H4Me) with 3-hydroxy-2-naphthoic acid (HNA-1) and 1-hydroxy-2-naphthoic acid (HNA-2), in the presence of β-cyclodextrin polymer (βCDP) as a catalyst, two titanocene complexes: bis(η5-methylcyclopentadienyl) 3-hydroxy-2-naphthoatotitanium (1) and bis(η5-methylcyclopentadienyl)1-hydroxy-2-naphthoatotitanium (2), were synthesized and characterized by elemental analysis, IR and 1H NMR spectra. X-ray diffraction analysis of 1 and 2 show mononuclear TiIV and indicate that the geometries at titanium are distorted tetrahedra with coordination number four. Both complexes exhibit 3-D frameworks constructed through H-bonding and C–H ··· π interactions. There are no π–π stacking interactions between the naphthyl rings and cyclopentadienyl rings of 1, while there are three types of π–π interactions in the structure of 2, owing to their different hydroxyl position in naphthalene rings.

Bifunctional Furfuryl Cations Strategy: Three-Component Synthesis of Enamidyl Triazoles.

A new multicomponent synthesis of functionalized enamidyl triazoles starting from simple and readily available starting materials is described. A simple treatment of a dichloromethane solution of an azide, amine, and 5-bromo-2-furylcarbinol with a Lewis acid provides the enamidyl triazole in good to high yield. A triple domino sequence, formal [3+2] cycloaddition/ring-opening/amidation, is involved in this new skeleton-generating reaction.

PH-tuned synthesis of gold nanoplates using star CD-PDMAEMA

We here report a one-step, wet-chemical approach to synthesizing gold nanoplates from a chloroauric acid precursor at ambient temperature in the absence of additional reductant or energy input by aqueous star homopolymer with β-cyclodextrin core and poly (2-(diethylamino) ethylmethacrylate) arms (star CD-PDMAEMA), without introducing additional capping agent or surfactant. In this reaction, star CD-PDMAEMA acted as both reducing and derecting agents for gold nanoplates. More importantly, star CD-PDMAEMA is a tertiary-amine-containing pH-responsive and water-soluble star homepolymer, which plays important role in the formation of final products. This facile approach may be extended to the synthesis of other metal nanomaterials of different size and shape.