Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: Synthesis, characterization and ROP of ε-caprolactone

Li, Yuanzhuo; Zhao, Ke-Qing; Feng, Chun; Elsegood, Mark R.J.; Prior, Timothy J.; Sun, Xinsen; Redshaw, Carl

Abstract

By varying the reaction conditions, the reaction of [W(eg)₃] (eg = 1,2-ethanediolato) with p-tert-butylcalix[n]areneHn (n = 6 or 8) in refluxing toluene affords, following work-up, a number of products which have been fully characterized. From the reaction of p-tert-butylcalix[6]areneH₆ with one or two equivalents of [W(eg)₃], only the oxo-bridged complex {[W(eg)]₂(μ-O)p-tert-butylcalix[6]arene} (1) could be isolated, whereas the use of four equivalents of [W(eg)₃], in the presence of molecular sieves, afforded {[W(eg)₂]₂p-tert-butylcalix[6]areneH₂}·2MeCN (2); molecules of 2 pack in bi-layers. Under similar conditions, use of one or two equivalents of [W(eg)₃] and p-tert-butylcalix[8]areneH₈ afforded {[W(eg)]₂p-tert-butylcalix[8]arene}·MeCN (3) in which each tungsten centre was bound by four calixarene oxygens. By contrast, the small orange prisms resulting from the use of four equivalents of [W(eg)₃] and p-tert-butylcalix[8]areneH₈ were shown by synchrotron radiation to be a mixture of two isomers (4a/4b·3.5MeCN). In the major isomer {1,2-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4a), two tungsten centres bind to neighbouring sets of phenolate oxygens, whereas in the minor isomer {1,3-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4b), there is a protonated phenolic group between the two pairs of phenolate oxygens bound to tungsten; the major:minor ratio is about 83:17. Use of p-tert-butyltetrahomodioxacalix[6]areneH₆ with two equivalents of [W(eg)₃] resulted in the isolation of {[WO(eg)]₂p-tert-butyltetrahomodioxacalix[6]areneH₂} (5·0.83toluene·MeCN), in which each dimethyleneoxa bridge is bound to an oxotungsten(VI) centre. Complexes 1–5, together with the known complex [W(eg)p-tert-butylcalix[4]arene] (6), have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; for 1, 2 and 5, 6 conversion rates were good (>88%) at 110 °C over 12 or 24 h, whereas the calix[8]arene complexes 3 and 4 under the same conditions were inactive.

Citation

Li, Y., Zhao, K., Feng, C., Elsegood, M. R., Prior, T. J., Sun, X., & Redshaw, C. (2014). Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: Synthesis, characterization and ROP of ε-caprolactone. Dalton Transactions : an international journal of inorganic chemistry, 43(36), 13612-13619. https://doi.org/10.1039/c4dt01936a

• Journal Article Type: Article
• Acceptance Date: Jul 23, 2014
• Online Publication Date: Jul 28, 2014
• Publication Date: Sep 28, 2014
• Deposit Date: Jun 9, 2015
• Publicly Available Date: Jun 9, 2015
• Journal: Dalton transactions
• Print ISSN: 1477-9226
• Electronic ISSN: 1477-9234
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 43
• Issue: 36
• Pages: 13612-13619
• DOI: https://doi.org/10.1039/c4dt01936a
• Keywords: Ethyleneglycol tungsten complexes , Synthesis, ε-caprolactone
• Public URL: https://hull-repository.worktribe.com/output/374941
• Publisher URL: http://pubs.rsc.org/en/Content/ArticleLanding/2014/DT/C4DT01936A#!divAbstract
• Additional Information: Author's accepted manuscript of article published in: Dalton transactions, 2014, v.43, issue 36.