title: Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone.
abstract: Reaction of the pro-ligand α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L(1)H4) with two equivalents of [NbCl5] in refluxing toluene afforded, after work-up, the complex {[NbCl3(NCMe)]2(μ-p-L(1))}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl2(OEt)(NCMe)]2(μ-p-L(1))}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl5] afforded the yellow complex {[TaCl2(OEt)(NCMe)]2(μ-p-L(1))}·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-L(2)H4) 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-L(2)H2)2]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L(2)H2)2]}·5MeCN (4·5MeCN). The molecular structures of 1-4 and the tetraphenols L(1)H4 and m-L(2)H4·2MeCN 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).
authors.affiliation: Department of Chemistry, University of Hull, Hull, HU6 7RX, UK. c.redshaw@hull.ac.uk.
authors.forename: Yahya
authors.initials: Y
authors.lastname: Al-Khafaji
authors.forename: Xinsen
authors.initials: X
authors.lastname: Sun
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Prior
authors.forename: Mark R J
authors.initials: MR
authors.lastname: Elsegood
authors.forename: Carl
authors.initials: C
authors.lastname: Redshaw
mesh_terms: D002208:Caproates / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D015394:Molecular Structure; D009556:Niobium / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D058105:Polymerization; D013635:Tantalum / Q000737:chemistry*
chemical_list: D002208:Caproates; D002712:Chlorides; D056831:Coordination Complexes; D007783:Lactones; D010636:Phenols; D009556:Niobium; C121056:caprolactone; D013635:Tantalum; C535111:niobium pentachloride