Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2-(2'-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization

Kotohiro Nomura; Mari Oshima; Takato Mitsudome; Hitoshi Harakawa; Peng Hao; Ken Tsutsumi; Go Nagai; Toshiaki Ina; Hikaru Takaya; Wen-Hua Sun; Seiji Yamazoe

doi:10.1021/acsomega.7b01225

Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2-(2'-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization

ACS Omega. 2017 Dec 6;2(12):8660-8673. doi: 10.1021/acsomega.7b01225. eCollection 2017 Dec 31.

Authors

Affiliations

¹ Department of Chemistry, Faculty of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan.
² Department of Materials Engineering Science, Osaka University, 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
³ Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190, China.
⁴ Japan Synchrotron Radiation Research Institute (JASRI, SPring-8), Sayo, Hyogo 679-5198, Japan.
⁵ International Research Center for Elements Science (IRCELS), Institute for Chemical Research (ICR), Kyoto University, Uji, Kyoto 611-0011, Japan.
⁶ Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

Abstract

(Imido)vanadium(V) dichloride complexes containing 2-(2'-benzimidazolyl)-6-methylpyridine ligand (L) of type V(NR)Cl₂(L) [R = 1-adamantyl (Ad, 1), C₆H₅ (2), and 2,6-Me₂C₆H₃ (3)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using 1-3 in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, 1-3 exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me₂AlCl; the phenylimido complex (2) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h^-1, 792 s^-1)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., M _n = 1.71-2.66 × 10⁶, M _w/M _n = 2.27-2.53]. On the basis of V nuclear magnetic resonance (⁵¹V NMR), electron spin resonance, and V K-edge X-ray absorption near-edge structure (XANES) spectra of the catalyst solution, the observed difference in the catalyst performance in the presence of (between) MAO and Me₂AlCl cocatalyst should be due to the formation of different catalytically active species with different oxidation states. Apparent changes in the oxidation state were observed in the (especially in the NMR and XANES) spectra upon addition of Me₂AlCl, whereas no significant changes in the spectra were observed in presence of MAO.