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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

Authors

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Professor Carl Redshaw C.Redshaw@hull.ac.uk
Professor of Inorganic Materials Chemistry and REF Lead for Chemistry

Mark J. Walton

Darren S. Lee

Chengying Jiang

Mark R. J. Elsegood

Kenji Michiue



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
Electronic ISSN 1521-3765
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
Copyright Statement ©2016 University of Hull
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.

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