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Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone

Al-Khafaji, Y.; Sun, X.; Elsegood, Mark R. J.; Al-Khafaji, Yahya; Sun, Xinsen; Prior, Timothy J.; Elsegood, Mark R. J.; Redshaw, Carl

Authors

Y. Al-Khafaji

X. Sun

Mark R. J. Elsegood

Yahya Al-Khafaji

Xinsen Sun

Mark R. J. Elsegood

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

Abstract

Reaction of the pro-ligand α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L¹H₄) with two equivalents of [NbCl₅] in refluxing toluene afforded, after work-up, the complex {[NbCl₃(NCMe)]₂(μ-p-L¹)}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl₅] afforded the yellow complex {[TaCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α′,α′tetra(3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L²H₄) only the use of [Nb(O)Cl₃(NCMe)₂] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb(NCMe)Cl(m-L²H₂)₂]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L²H₂)₂]}·5MeCN (4·5MeCN). The molecular structures of 1–4 and the tetraphenols L¹H₄ and m-L²H₄·2MeCN have been determined. Complexes 1–4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat).

Journal Article Type Article
Publication Date Jul 21, 2015
Journal Dalton transactions
Print ISSN 1477-9226
Electronic ISSN 1477-9234
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 44
Issue 27
Pages 12349-12356
Institution Citation Al-Khafaji, Y., Sun, X., Prior, T. J., Elsegood, M. R. J., & Redshaw, C. (2015). Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone. Dalton transactions : an international journal of inorganic chemistry / RSoC, 44(27), 12349-12356. https://doi.org/10.1039/c5dt00272a
DOI https://doi.org/10.1039/c5dt00272a
Keywords Ring opening polymerization ; Niobium; Tantalum; Tetraphenolate; Crystal structure; ε-caprolactone
Publisher URL http://pubs.rsc.org/en/Content/ArticleLanding/2015/DT/C5DT00272A#!divAbstract
Copyright Statement ©2016 University of Hull
Additional Information Author's accepted manuscript of an article which has been published in: Dalton transactions, 2015, v.44, issue 27.

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