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

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).

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, 44(27), 12349-12356. https://doi.org/10.1039/c5dt00272a

• 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
• DOI: https://doi.org/10.1039/c5dt00272a
• Keywords: Ring opening polymerization ; Niobium; Tantalum; Tetraphenolate; Crystal structure; ε-caprolactone
• Public URL: https://hull-repository.worktribe.com/output/376442
• Publisher URL: http://pubs.rsc.org/en/Content/ArticleLanding/2015/DT/C5DT00272A#!divAbstract
• Additional Information: Author's accepted manuscript of an article which has been published in: Dalton transactions, 2015, v.44, issue 27.