Tao Jiang

Chromium‐Based Ethylene Tetramerization Catalysts Supported by Silicon‐Bridged Diphosphine Ligands: Further Combination of High Activity and Selectivity

A series of silicon‐bridged diphosphine (SBDP) ligands were synthesized and characterized. The Cr precatalyst supported by bis(diphenylphosphinomethyl)dimethylsilane achieved a high activity of 4.2×106 g (molCr h)−1 and a high selectivity of 78.44 % towards valuable 1‐octene by using methylcyclohexane as the solvent at an ethylene pressure of 4.0 MPa and 45 °C. An intramolecular β‐H transfer mechanism was proposed to explain the unequal molar proportions of cyclic C6 byproducts. The crystal structure data of two complexes proved that the SBDP system with a wide P−Cr−P bite angle could also exhibit superior performance in the tetramerization of ethylene.

Mixed aluminoxanes: efficient cocatalysts for bisphosphineamine/Cr(III) catalyzed ethylene tetramerization toward 1-octene

In this study, we examined catalyst systems comprising chromium(III) chloride tetrahydrofuran, diphenylphosphinoamine (PNP) ligand, and a mixed activator of methylaluminoxane (MAO) and alkylaluminum for the selective tetramerization of ethylene. By comparing the catalytic activities and the selectivities toward 1-hexene and 1-octene, we investigated the effects of various mixed aluminoxane systems on the ethylene tetramerization process. MAO/trimethylaluminum, MAO/triethylaluminum, and MAO/triisobutylaluminum were all effective cocatalysts for the PNP/Cr(III) ethylene tetramerization system, providing high catalytic activities and high selectivities. When using MAO/diethylaluminumchloride as the cocatalyst, PNP/Cr(III) exhibited an impressive switch in selectivity: from ethylene tetramerization to ethylene trimerization.

Efficient chromium-based catalysts for ethylene tri-/tetramerization switched by silicon-bridged/N,P-based ancillary ligands: a structural, catalytic and DFT study

High performance catalysts switched by a series of silicon-bridged/N,P-based ancillary ligands have been explored. The precatalyst supported by L1 possessed a large steric bulk and exhibited a high activity of 16.8 × 106 g (mol Cr)−1 h−1 as well as a total selectivity of 99% toward 1-hexene and 1-octene. The selectivity for 1-hexene was adjustable from 59% to 88%. The catalyst bearing an L2 ligand, facilitated by a smaller steric bulk, displayed an identical activity of 13.0 × 106 g (mol Cr)−1 h−1 and a superior selectivity of 75% towards 1-octene under the appropriate conditions. The DFT calculations elucidated the reason for these excellent and tunable activities and selectivities.

Hydrogen: efficient promoter for PNP/Cr(III)/MAO catalyzed ethylene tetramerization toward 1-octene

The effect of hydrogen addition on the catalytic activity and product selectivity of PNP/Cr(III)/MAO catalytic systems for ethylene tetramerization was investigated. The results showed that the catalytic activity could be increased twice and the polymer production could be reduced efficiently through hydrogen addition. It could be inferred from the analysis and characterization results of the products that there existed at least three sorts of catalytic active centers in the ethylene tetramerization reaction.

Constructing Biopolymer-Inorganic Nanocomposite through a Biomimetic Mineralization Process for Enzyme Immobilization

Inspired by biosilicification, biomimetic polymer-silica nanocomposite has aroused a lot of interest from the viewpoints of both scientific research and technological applications. In this study, a novel dual functional polymer, NH2-Alginate, is synthesized through an oxidation-amination-reduction process. The “catalysis function” ensures the as-prepared NH2-Alginate inducing biomimetic mineralization of silica from low concentration precursor (Na2SiO3), and the “template function” cause microscopic phase separation in aqueous solution. The diameter of resultant NH2-Alginate micelles in aqueous solution distributed from 100 nm to 1.5 μm, and is influenced by the synthetic process of NH2-Alginate. The size and morphology of obtained NH2-Alginate/silica nanocomposite are correlated with the micelles. NH2-Alginate/silica nanocomposite was subsequently utilized to immobilize β-Glucuronidase (GUS). The harsh condition tolerance and long-term storage stability of the immobilized GUS are notably improved due to the buffering effect of NH2-Alginate and cage effect of silica matrix.

Nickel-based ethylene oligomerization catalysts supported by PNSiP ligands

GRAPHICAL ABSTRACT ABSTRACT A series of nickel (II) complexes bearing silicon bridged diphosphines ligands (PNSiP) have been synthesized and characterized. All nickel precatalysts, activated with ethylaluminum dichloride (EtAlCl2), exhibited moderate to high activities for ethylene dimerization to butylene. The in situ nickel precatalysts formed by mixing N-cyclopentyl-N-((diphenylphosphanyl)dimethylsilyl)-1,1-diphenylphosphanamine (L2) with NiBr2(DME) showed high catalytic activity (2.40 × 108 g/(molNi·h)) and high product selectivity (88.6%) towards butene using methylcyclohexane as solvent at 1.0 MPa ethylene pressure and 45°C temperature, no polyethylene(PE) was observed. Ligand backbone tuning of PNSiP-based catalytic systems help in precise understanding of steric bulk variation effects on catalytic performance.

Diastereoselective Cyclization of 1,5-Dienes with Pyridine C−H Bond Catalyzed by a Cationic Mono(phosphinoamide) Alkyl Scandium Complex

The carbocyclization of non‐conjugated dienes mediated by organometallics is an important reaction for the synthesis of a variety of carbocyclic derivatives, but the direct annulation of dienes with an inert C−H bond of a substrate has remained unexplored to date. We herein report a series of novel rare‐earth dialkyl complexes bearing a phosphinoamide anion and demonstrate that the combination of a mono(phosphinoamido)‐ligated scandium dialkyl complex with B(C6F5)3 results in an excellent catalyst for the cis‐selective cyclization of 1,5‐dienes with the ortho‐C(sp2)−H bond of pyridines to afford a new family of pyridyl‐functionalized 1,3‐disubstituted cyclopentane derivatives containing monocyclic, bicyclic, spirocyclic, and heterocyclic skeletons in moderate to excellent yields with high diastereoselectivities (cis/trans up to 99:1).

Oligomerization of 1-Butylene to Lubricant Catalyzed by Bis(tetramethyl cyclopentadienyl) Zirconium Dichloride/MAO

Oligomerization of 1-butylene catalyzed by Bis(tetramethylcyclopentadienyl) Zirconium dichloride/MAO was investigated in detail under different conditions including reaction temperature, Al/Zr molar ratios, co-catalysts, concentration of catalyst to determine the optimal reaction conditions. The work shown that oligomer of 1-butylene in this catalyst system featured a kind of base oil of lubricant with pour point of -22 °C, kinematic viscosity of 2999 mm2/s at 40 °C and 2530 mm2/s at 100 °C, viscosity index of 258 and a moderate average molecular weight. In addition, the oligomer obtained was characterized by 1H-NMR and IR.

Study on Low Application Temperature Process of Three Layer Polyethylene Coating

The mechanical property of X80 longitudinally welded pipe, as part pipeline for second west-east natural gas transmission pipeline project, is disadvantageously affected by normal coating process of three layer polyethylene coating(3LPE). The low application temperature process of three layer polyethylene coating coated at 185~195°C was studied to meet the requirement of the coating temperature of X80 longitudinally welded pipe. The suitable epoxy powders and coating process were determined by evaluating coating properties of varied epoxy powders. The properties of 3LPE, which was coated by using suitable low temperature cured epoxy powder at temperature of 185~195°C, were nearly same to the ones of 3LPE at the normal coating temperature (200~230°C) and meet the requirement of external anti-corrosion properties of X80 longitudinally welded pipe. According to the results, a criteria was provided to CNPC and applied to project of second west-east natural gas transmission pipeline.

Synthesis of Asymmetric Tridentate Cobalt(II) Complex and Application in Ethylene Oligomerization

A kind of cobalt complex with asymmetric tridentate ligand was synthesized and used in ethylene oligomerization. The reaction temperature and Al/Co ratio had a great influence on the activities and distributions of the oligomer with methylaluminoxane as cocatalyst, and the main products were 1-butylene and hexene. A fast deactivation process was observed from the curve of the oligomerization kinetics.