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

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


Yahya Al-Khafaji

Xinsen Sun

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Dr Tim Prior
Senior Lecturer in Inorganic Chemistry

Mark R. J. Elsegood

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Professor Carl Redshaw
Professor of Inorganic Materials Chemistry and REF Lead for Chemistry


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).


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, 44(27), 12349-12356.

Journal Article Type Article
Acceptance Date Feb 17, 2015
Online Publication Date Feb 18, 2015
Publication Date Jul 21, 2015
Deposit Date Jul 14, 2015
Publicly Available Date Jul 14, 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
Keywords Ring opening polymerization ; Niobium; Tantalum; Tetraphenolate; Crystal structure; ε-caprolactone
Public URL
Publisher URL!divAbstract
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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