Hyperbranched Ligands Research Articles

Selective ethylene oligomerization bearing hyperbranched bispyridylamine chromium catalyst

Two new hyperbranched bispyridylamine ligands and multinuclear chromium complexes were synthesized with 1.0 G hyperbranched macromolecules, 2-chloropyridine, 2-chloro-4-methylpyridine and CrCl3(THF)3 as raw materials. The structures of hyperbranched ligands and chromium complexes were characterized by UV, FT-IR, 1H NMR, ESI-MS, and elemental analysis. These hyperbranched chromium complexes were evaluated as catalyst precursors by using MAO as activator in the oligomerization of ethylene. Effects of reaction temperature, reaction pressure, Al/Cr molar ratio, concentration of catalyst, solvent, and the structure of catalysts on the catalytic activity and product selectivity were investigated. The oligomerization results showed that with increase of reaction temperature, reaction pressure, and Al/Cr molar ratio, the catalytic activity increased and then decreased; the catalytic activity continuously decreased as the amount of catalyst increased. The products were mainly based on C6 and C8. Under optimized conditions, the catalytic system of hyperbranched NNN/Cr(III)/MAO led to activity of 1.26 × 105 g/(mol·Cr·h) and 63.34% selectivity for C6 and C8.

Pore-Free Matrix with Cooperative Chelating of Hyperbranched Ligands for High-Performance Separation of Uranium.

A new strategy combining a pore-free matrix and cooperative chelating was proposed in the present paper in order to effectively avoid undesired nonselective physical adsorption and intraparticle diffusion caused by pores and voids in porous sorbents, and to greatly enhance uranium-chelating capability based on hyperbranched amidoxime ligands on the surface of nanodiamond particles. Thus, a pore-free, amidoxime-terminated hyperbranched nanodiamond (ND-AO) was designed and synthesized. The experimental results demonstrate that the strategy endows the as-synthesized ND-AO with the following expected features: (1) distinctively high uranium selectivity (SU = qe-U/qe-tol × 100%) from over 80% to nearly 100% over the whole weak acidity range (pH < 4.5); especially, the SU can reach up to unprecedented >91% at pH 4.5, more than 20% of selectivity increment over any analogous sorbent materials reported so far, with a uranium sorption capacity of 121 mg/g in simulated nuclear industry effluent samples containing 12 coexistent nuclide ions; (2) superfast equilibrium sorption time of <30 s; and (3) one of the highest distribution coefficients (Kd) of ∼3 × 106 mL/g for U(VI) as well as a fairly high sorption capacity of 212 mg/g at pH 4.5 in pure uranium solution. The strategy could also provide an optional approach for the design and fabrication of other new high-performance sorbing materials with prospective applications in selective separation of other interested metal ions.

Novel nickel complexes with hyperbranched structure: Synthesis, characterization and performance in ethylene oligomerization

Two novel nickel complexes with hyperbranched structure were synthesized with 1.0 generation hyperbranched polyamine molecules (1.0G), salicylaldehyde and anhydrous nickel chloride as materials via the Schiff’s base and the complexation reactions. The structures of the novel hyperbranched ligands and their nickel complexes were characterized by FT-IR, 1H NMR, UV, ESI-MS and elemental analysis. The hyperbranched nickel complexes were evaluated as catalyst precursors for ethylene oligomerization after being activated with methylaluminoxane (MAO), diethylaluminum chloride (Et2AlCl) and ethylaluminum sesquichloride (EASC). The influence of Al/Ni ratio, temperature and ethylene pressure on ethylene oligomerization was also investigated using the novel hyperbranched nickel complexes as pre-catalysts and MAO as co-catalyst. The catalytic activities of the two hyperbranched nickel complexes with dodecyl and octadecyl as cores (R12-complex and R18-complex) were 2.33×105g/(mol Ni·h) and 1.23×105g/(mol Ni·h), respectively, and the selectivities for C8+ oligomers of R12-complex and R18-complex were 56.16% and 88.64% respectively, when the Al/Ni molar ratio was 500:1, the temperature was 25°C, the pressure of ethylene was 0.5MPa and the co-catalyst was MAO. The catalytic activities and product distribution were largely dependent on the nature of the co-catalysts and the structures of nickel complexes. The catalytic activities decreased with increasing of the length of alkyl chain of the hyperbranched nickel complexes.

Functionalized polyglycidol-CuCl-complexes as catalysts in the oxidative coupling reaction of terminal acetylenes

Novel hyperbranched amino-terminated polyglycidoles have been synthesized and tested as macromolecular ligands in the oxidative coupling reaction of phenylacetylene. Amino-terminated polyglycidoles-CuCl complexes showed to be more effective catalysts than the reference monomeric tertiary amines-CuCl ones, but less effective than the most efficient N,N,N'N'-tetramethylethylenediamine-(TMDA) CuCl complex. The difference in performance of monomeric and hyperbranched ligands is probably due to two factors. The first one is better complexation abilities and the second is the local increase of reagent concentration.