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Issue 27, 2015
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Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone

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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).

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

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Publication details

The article was received on 20 Jan 2015, accepted on 17 Feb 2015 and first published on 18 Feb 2015


Article type: Paper
DOI: 10.1039/C5DT00272A
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Dalton Trans., 2015,44, 12349-12356

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

    Y. Al-Khafaji, X. Sun, T. J. Prior, M. R. J. Elsegood and C. Redshaw, Dalton Trans., 2015, 44, 12349
    DOI: 10.1039/C5DT00272A

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