Yuetao Zhang

Synthesis and crystal structures of unbridged bis(4-R-1,2-diphenylcyclopentadienyl)zirconium dichlorides (R=phenyl, cyclohexyl), and catalysis for olefin polymerization

Abstract Zirconocene complexes carrying sterically bulky tri-substituted cyclopentadienyl ligands, (η5-4-R-1,2-Ph2C5H2)2ZrCl2 [R=phenyl (3), cyclohexyl (4)], were synthesized by the reaction of ZrCl4 with lithio salt of 1,2,4-triphenylcyclopentadiene (1) or 4-cyclohexyl-1,2-diphenylcyclopentadiene (2), respectively. The single-crystal X-ray structure analysis reveals that both complexes crystallize in C2-symmetric conformation in solid state. When activated with methylaluminoxane (MAO), complexes 3 and 4 polymerize ethylene with moderate activities to produce ultra-high-molecular-weight polyethylenes with high melting transition temperatures at low Al/Zr ratios. Under ambient conditions, both systems of 3–MAO and 4–MAO show relatively high activities in propylene oligomerization. The molecular weight of the polypropylene produced from the 3–MAO system is lower than that from the 4–MAO system. In comparison with 4, complex 3 is more active in both ethylene and propylene polymerization.

Synthesis, crystal structure and catalysis for polyethylene of a paramagnetic chromium complex [(η5-CpSi)Cr(μ-Cl)Cl]2 [CpSi=(C5H4)Si(CH3)2(C6H5)]

Abstract The synthesis of the substituted silyl cyclopentadiene ligand (C5H5)Si(CH3)2(C6H5) (CpSiH) (1) is described. Deprotonation of (1) gives (CpSiLi) (2) which reacts with CrCl3 to produce the chloro-bridged complex [(η5-CpSi)Cr(μ-Cl)Cl]2 (3). Single-crystal X-ray structure analysis reveals that a centrosymmetric dimer exists in the solid state. When activated with methylaluminoxane (MAO), complex (3) exhibits several interesting features as a catalyst for ethylene polymerization. With the help of a semi-empirical MO calculation, a cationic sandwich intermediate structure in the catalytic process was proposed.

Synthesis, characterization and crystal structures of (Z)-1-[2-(tri-o-tolylstannyl)vinyl]-1-cyclohexanol and its o-tolylhalostannyl derivatives

(Z)-1-[2-(Tri-o-tolylstannyl)vinyl]-1-cyclopentanol (1) was synthesized by the additive reaction of 1-ethynylcyclopentanol with tri-o-tolyltin hydride. One or two of the o-tolyl groups of compound 1 was substituted by I, Br or Cl to yield derivatives of the type CH 2 (CH 2 ) 3 CH(OH)CH=CHSn(o-tol) 3 - n X n [n = 1, X = I (2), Br (3), Cl (4); n = 2, X = Br (5)]. The compounds 1-5 were characterized by elemental analysis, 1 H NMR and FT-IR spectroscopy. The crystal and molecular structures of 1 and 2 have been determined by single crystal X-ray diffraction analysis. The Sn atom in 1 exhibits a tetrahedral geometry distorted towards trigonal bipyramid, due to a weak intramolecular interaction between Sn and hydroxyl O atoms [2.813(4) A], while the Sn atom in 2 adopts a trigonal bipyramidal geometry with a significant Sn(1)←O(1) interaction [2.553(4) A].

Constrained geometry nitrogen-functionalised diphenylcyclopentadienyl chromium (III) complex : synthesis, structure and catalytic properties for ethylene polymerisation

A bidentate ligand 1-[2-(N,N-dimethylaminophenyl)]-3, 4-biphenylcyclopentadiene 1, as well as its corresponding constrained geometry chromium complex dichloro-η5-[1-(2-N,N-dimethylaminophenyl)-3,4-diphenylcyclopentadienyl] chromium (III) 2 have been synthesised and characterised. When activated with Al( i Bu)3 and Ph3C[B(C6F5)4], complex 2 exhibits reasonable catalytic activity for ethylene polymerisation, producing polyethylenes with moderate molecular weights and melting points. The effects of polymerisation temperature, ethylene pressure, B/Cr and Al/Cr ratios on catalytic activity were studied.

Synthesis, structures and luminescent properties of [ZnCl2(2,6-bis{1-(phenylimino)ethyl)pyridine)]

The complex 2, 6-Bis[1-(phenylimino)ethyl pyridine ZnCl2 (3) was synthesised via the reaction of ZnCl2 with the 2,6-bis[1-(phenylimino)ethyl]pyridine (L3) in CH2Cl2 and its structure determined by single-crystal X-ray diffraction. The geometry of 3 can be best described as distorted trigonal bipyramidal. 3 has blue luminescence at room temperature in solution and the solid state which is assumed to be from a π*→π transition centred on the ligand. The Zn(II) centre plays a key role in enhancing fluorescent emission of the ligand.