Synthesis of Ethylene/1-Octene Copolymers with Ultrahigh Molecular Weights by Zr and Hf Complexes Bearing Bidentate NN Ligands with the Camphyl Linker

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series of zirconium and hafnium complexes, [2,6-(R1)2-4-R2-C6H2-N-C(camphyl)=C(camphyl)-N-2,6-(R1)2-4-R2-C6H2]MMe2(THF) (1-Zr: R1 = Me, R2 = H, M = Zr; 2-Zr: R1 = Me, R2 = Me, M = Zr; 1-Hf: R1 = Me, R2 = H, M = Hf; 2-Hf: R1 = Me, R2 = Me, M = Hf), bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of α-diimine ligands with MMe4 (M = Hf or Zr). All Zr and Hf metal complexes were analyzed using 1H and 13C NMR spectroscopy, and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction, revealing that the original α-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes. Zr complexes 1-Zr and 2-Zr showed moderate activity (up to 388 kg(PE)·mol−1(M)·h−1), poor copolymerization ability, but unprecedented molecular weight capability toward ethylene/1-octene copolymerization. Therefore, copolymers with ultrahigh molecular weights (> 600 or 337 × 104 g∙mol−1) were successfully synthesized by 1-Zr or 2-Zr, respectively, with the borate cocatalyst [Ph3C][B(C6F5)4]. Surprisingly, Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions, revealing the great influence of metal centers on catalytic performances.

Controlling Polyethylene Molecular Weights and Distributions Using Chromium Complexes Supported by SNN-Tridentate Ligands

“…Although imines are generally prepared by acid-catalyzed condensation, ,− attempts to synthesize imines 1 – 4 by reaction between 8-bromo-2-quinoline­carboxaldehyde and substituted anilines under such conditions led to incomplete conversions, complicated purifications, and low yields. Therefore, the primary aniline was first treated with trimethyl­aluminum (TMA) to afford aminoalanes that could readily convert aldehydes to imines because the Al–O bond is much stronger than the Al–N bond. , In this way, imines 1 – 4 were isolated in good yields (65–72%). Next, ligands L1 – L4 were synthesized by palladium-catalyzed coupling reactions between compounds 1 – 4 and 1 equiv of 2-propanethiol, while ligands L5 and L6 were formed by reaction of 1 with 1 equiv of tert -butylthiol or 2,6-dimethyl­benzenethiol, respectively.…”

“…Therefore, the primary aniline was first treated with trimethylaluminum (TMA) to afford aminoalanes that could readily convert aldehydes to imines because the Al−O bond is much stronger than the Al−N bond. 60,61 In this way, imines 1−4 were isolated in good yields (65−72%). Next, ligands L1−L4 were synthesized by palladium-catalyzed coupling reactions between compounds 1−4 and 1 equiv of 2-propanethiol, while ligands L5 and L6 were formed by reaction of 1 with 1 equiv of tertbutylthiol or 2,6-dimethylbenzenethiol, respectively.…”

Chromium complexes supported by NNO-tridentate ligands: an unprecedented activity with the requirement of a small amount of MAO

“…2,3 However, the mounting demand for high-value-added polyolefins in recent years has spurred extensive interest in both industry and academia to develop homogeneous metal catalysts for olefin polymerization, [4][5][6][7][8][9][10] which are also beneficial for better understanding the polymerization mechanism and, in turn, are greatly helpful in developing new-generation catalysts with high-performances. [11][12][13] In the past few decades, a series of homogeneous metal catalysts, including metallocene 14 and non-metallocene catalysts, [15][16][17][18][19][20][21] have been developed and applied to synthesize a variety of high-value-added polyolefins, such as polar functionalized polyethylene, [22][23][24][25] ultrahigh molecular weight polyethylene (UHMWPE), 26,27 syndiotactic polypropylene (sPP), 28 syndiotactic polystyrene (sPS), 29 polyolefin elastomers (POE), 30 and cyclic olefin copolymers (COC). 31,32 Although the great successes as mentioned above have been achieved, homogeneous metal catalysts still have many unexpected defects.…”

Effect of Activator and Outgoing Ligand Nature on the Catalytic Behavior of Bis(phenoxy-imine) Ti(IV) Complexes in the Polymerization of Ethylene and Its Copolymerization with Higher Olefins

“…However, the high molecular weight and the presence of a large number of entanglements between chains cause a very high melt viscosity, which greatly complicates the processing of this polymer by conventional methods). For the synthesis of such E/O copolymers, various catalytic systems are used, for example, (F-salalen)TiCl 2 /MAO [ 53 ], hydrocarbyl Zr and Hf complexes supported by α-diimine ligands with the camphyl linker/[Ph 3 C][B(C 6 F 5 ) 4 ] [ 54 ].…”