Novel Chromium And Late Transition Metal Catalysts For Olefin Polymerization

The field of olefin polymerization catalysis has experienced Ziegler-Natta catalysts, metallocene catalysts and post-metallocene catalysts periods. Ziegler-Natta catalysts showed poor stereoselectivity forα-olefin polymerization. The high oxophilicity of early transition metal catalysts causes the active centre of metallocene catalyst to be poisoned by most functionalized olefins which contain O, S or N heteroatoms. A large amount of MAO or expensive fluorinated borate is generally required as cocatalyst for obtaining high activity. There is a great need to develop new catalyst systems which can provide high activity, high stereoselectivity, with no need of large amounts of expensive cocatalyst and good functional-group tolerance ability. In this dissertation, a series of novel half-sandwich chromium(â…¢) complexes bearingβ-ketoiminato andβ-diketiminate and hydroxylindanone-imine ligands; binuclear, divalent nickel and copper acetylacetonato complexes with 2,5-diamino-1,4-benzoquinonediimines; the nickel complexes with pyridyl-2-thione and pyridyl-2,6-dithione ligands and the cobalt complexes or coordination polymer supported by the bidentate thione or selone ligands were synthesized and characterized. The effects of catalyst structures, molar ration of catalyst/cocatalyst, reaction temperature on polymerization reaction have been discussed in detail. The full dissertation was summarized as follows:1. Six novel half-sandwich chromium(â…¢) complexes bearingβ-ketoiminato andβ-diketiminate ligands have been synthesized by the reaction of CpCrCl₂(THF) and the corresponding lithium salts of theβ-ketoiminato andβ-diketiminate ligands in THF at -78℃. The molecular structures of two complexes have been confirmed by single crystal X-ray analysis. Both of the complexes adopt three-legged piano stool geometry with a pseudo-octahedral coordination environment. Upon activation with a small amount of AlEt3(about 25 times), half-sandwich chromium(â…¢) complexes bearingβ-ketoiminato ligands can produce linear high molecular weight PE (93-112×10⁴ g/mol) with good activity (1.53×10⁵ gPE(mol Cr)^-1h^-1) under mild conditions. Theβ-ketoiminato catalysts showed higher activities than theβ-diketiminate complex. And also the catalytic activities of theβ-ketoiminato complexes decrease with the increasing of the steric hindrance on the nitrogen atom of theβ-ketoiminato ligand. The strong electron withdrawing trifluoro methyl group introduced in theβ-ketoiminato skeleton enhanced the activity for the ethylene polymerization.2. Reaction of the Cp^*CrCl₂(THF) and the sodium salts of the hydroxylindanone-imine ligands in THF at -78℃obtained six novel half-sandwich chromium(â…¢) complexes. The molecular structure of one complex has been confirmed by single crystal X-ray analysis. The complex also adopts three-legged piano stool geometry with a pseudo-octahedral coordination environment. After activated with a small amount of AIEt₃, these catalytic precursors exhibit high activities (1.68×10⁵ gPE(mol Cr)^-1h^-1) for ethylene polymerization to afford high molecular weight PE(5.45-9.12×10⁵gmol^-1). The results showed that the catalytic activities of the chromium complexes increase with the decreasing of the steric hindrance on the nitrogen atom of the hydroxyl-indanoneimine ligand. The introduction of the bulky ortho-butyl group and the para-chlorine atom on the phenol hydroxyl improved the activity for the polymerization.3. A series of binuclear, divalent nickel and copper acetylacetonato complexes of the type [M(acac){μ-C₆H₂((?)NAr)₄}M(acac)] (M = Ni, Cu) have been synthesized by the reaction of the corresponding M(acac)2 precursor with various bulky steric hindraceÏ€-acceptor N-substituted 2,5-diamino-l,4-benzoquinonediimines C₆H₂(NHAr)₂(=NAr)₂ (1a, Ar=4-C₆H₄Me; 1b, Ar = 2-C₆H₄Me; 1c, Ar= 2,6-C₆H₃Me₂), which are metalated and become bridging ligands. The ligands and complexes were determined by IR and UV-visible spectrum. Cyclic voltammetric behavior of complexes 2c and 3c has been tested. The molecular structures of the ligand 1c and the complexes [Ni(acac) {μ-C₆H₂((?)N(4-methyl-Ph))₄}Ni(acac)]) (2a), [Ni(acac){μ-C₆H₂((?)N(2,6-dimethyl-Ph))₄} Ni(acac)]) (2c) and [Cu(acac) {μ-₆H₂((?) N(2,6-dimethyl- Ph))₄}Cu(acac)]) (3c) have been determined by X-ray diffraction. The coordination geometry around the metal ions of the Ni and Cu complexes is square-planar, and a complete electronic delocalization of the quinonoidÏ€system occurs between the metal centers over the two N(?)C(?)C(?)C(?)N halves of the ligand. In the presence of MAO as co-catalyst, all the Ni complexes exhibited high activities both for insertion-polymerization of norbornene (4.25-6.64×10⁷g PNB/(mol·Ni·h) ) and methyl methacrylate (MMA) (3.9-4.5×l0⁴g PMMA/(mol·Ni·h) ) polymerization which produce syndiotactic-rich poly(methyl methacrylate) (PMMA) with broad molecular weight distribution(3.6-8.6); however, the Cu complexes show moderate activities for norbomene polymerization (0.7-6.5×10⁴g PNB/(mol·Cu·h) and inactive for MMA polymerization.4. The hard-soft nitrogen-sulfur donor ligands pyridyl-2-thione and pyridyl-2,6-dithione were readily prepared by deprotonation of corresponding imidazolium salt with potassium tert-butoxide in THF solution, followed by adding the sulfur under base mild conditions. Reaction of NiBr2(DME) with the corresponding [NS] and [SNS] ligands obtained five novel nickel complexes bearing pyridyl-2-thione and pyridyl-2,6-dithione ligands. X-ray diffraction showed that the nickel centre in pyridyl-2-thione nickel complexes and pyridyl-2,6-dithione nickel complexes was distorted tetrahedral and trigonal bipyramidal geometry, respectively. All the nickel complexes showed high catalytic activities for norbomene addition polymerization (up to 3.72×10⁷ gPNBmol^-1Nih^-1) in the presence of MAO.5. Reaction of CoCl₂ with different N-substituted, methylene- or ethylidine-bridged bidentate thione/selone ligands at room temperature, resulted in the formation of a series of Co(â…¡) complexes with two different coordination modes. X-ray diffraction showed that the N-methyl substituted compounds forms 1D coordination polymers which coexist left-handed and right-handed helical chains or zigzag chain. The N-isopropyl substituted compounds not only formed mononuclear complex, but also formed a Co(â…¡) coordination polymer which forms a zigzag chain in the same cocrystal. With further increase steric hindrance, the N-tertbutyl and 2,6-diisopropylphenyl substituted cobalt compounds completely formed mononuclear bidentate complexes. The cobalt centre can be described as a distorted tetrahedron. After activation with MAO, the mononuclear Co(â…¡) complexes showed low activity for norbornene addition polymerization.