Vanadium(V) oxo and imido calix[8]arene complexes: synthesis, structural studies, and ethylene homo/copolymerisation capability

Redshaw, Carl; Walton, Mark J.; Lee, Darren S.; Jiang, Chengying; Elsegood, Mark R. J.; Michiue, Kenji

Abstract

Interaction of p-tert-butylcalix[8]areneH₈ (L⁸H₈) with in-situ generated [NaVO(Ot-Bu)₄] (from VOCl₃ and four equivalents of NaOtBu) afforded the dark brown complex [Na(NCMe)₅][(VO)₂L⁸H]·4MeCN (1·4MeCN), in which the calix[8]arene adopts a saddle-shaped conformation. Increasing (to four equivalents per L⁸) the amount of [NaVO(Ot-Bu)₄] present in the reaction, led to the formation of the yellow octa-vanadyl complex {[(Na(VO)₄L⁸)(Na(NCMe))₃] [Na(NCMe)₆}₂·10MeCN (2·10MeCN), in which the calix[8]arene adopts a pleated loop conformation. In the presence of adventitious oxygen, reaction of four equivalents of [VO(Ot-Bu)₃] (generated from VOCl₃ and 3KOtBu) with L⁸H₈ afforded the alkali-metal free green complex [(VO)₄L⁸(μ³-O)₂] (3); the solvates 3·3MeCN and 3·3CH₂Cl₂ have been isolated. In both solvates, the L⁸ ligand adopts a shallow saddle-shaped conformation, supporting a core comprising of a (VO)₄O₄ ladder. In the case of lithium, in order to obtain crystalline material, it was found necessary to reverse the order of addition such that lithium tert-butoxide was added to L⁸H₈, and then subsequently treated (at –78 ⁰C) with two equivalents of VOCl₃; crystallization from tetrahydrofuran (THF) afforded {(VO₂)₂Li₆[L⁸](thf)₂(OtBu)₂(Et₂O)₂}·Et₂O (4·Et₂O). In the structure of 4·Et₂O, vanadium, lithium and oxygen form a central lattern-type cage, which is capped top and bottom by an Li₂O₂2 diamond; the calix[8]arene is in a ‘down, down, out, out, down, down’ conformation. When the ‘same reaction’ was extracted into acetonitrile (MeCN), the salt complex [Li(NCMe)₄][(VO)₂L⁸H]·8MeCN (5.8MeCN) was formed. In 5·8MeCN, the [Li(NCMe)₄] cations reside between the anions in the clefts of L⁸H, the latter adopting a saddle-shaped conformation. Use of the imido precursors [V(Nt-Bu)(Ot-Bu)₃] and [V(Np-tolyl)(Ot-Bu)₃] and L⁸H₈, afforded, via an imido exchange, the salt [t-BuNH₃]{[V(p-tolylN)]₂L⁸H}·3½MeCN (6·3½MeCN). The molecular structures of 1 to 6 are reported; data collections for complexes 2·10MeCN, 3·3MeCN and 3·3CH₂Cl₂ required the use of synchrotron radiation. Complexes 1, 3 and 4 have been screened as pre-catalysts for the polymerization of ethylene in the presence of a variety of co-catalysts (with and without a re-activator) at various temperatures and for the co-polymerization of ethylene with propylene; results are compared versus the benchmark catalyst VO(OEt)Cl₂. In some cases, activities as high as 136,000 g/mmol.v.h were achievable, whilst it also proved possible to obtain higher molecular weight polymers (in comparible yields) versus the use of VO(OEt)Cl₂. In the case of the co-polymerization, the incorporation of propylene was 7.1 – 10.9 mol% (cf 10 mol% for VO(OEt)Cl₂), though catalytic activities were lower versus VO(OEt)Cl₂.

Citation

Redshaw, C., Walton, M. J., Lee, D. S., Jiang, C., Elsegood, M. R. J., & Michiue, K. (2015). Vanadium(V) oxo and imido calix[8]arene complexes: synthesis, structural studies, and ethylene homo/copolymerisation capability. Chemistry: a European journal, 21(13), 5199-5210. https://doi.org/10.1002/chem.201406084

• Journal Article Type: Article
• Acceptance Date: Nov 13, 2014
• Online Publication Date: Feb 16, 2015
• Publication Date: Mar 23, 2015
• Deposit Date: Apr 22, 2015
• Publicly Available Date: Apr 22, 2015
• Journal: Chemistry : a European journal
• Print ISSN: 0947-6539
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 21
• Issue: 13
• Pages: 5199-5210
• DOI: https://doi.org/10.1002/chem.201406084
• Keywords: Vanadium; Calix[8]arene; Ethylene polymerization; Ethylene/propylene co-polymerization; Crystal structures
• Public URL: https://hull-repository.worktribe.com/output/372882
• Publisher URL: http://onlinelibrary.wiley.com/doi/10.1002/chem.201406084/abstract
• Additional Information: Author's accepted manuscript of an article which has been published in: Chemistry : a European journal, 2015, v.21, issue 13 at http://onlinelibrary.wiley.com/doi/10.1002/chem.201406084/abstract.
• Contract Date: Apr 22, 2015