Al-Khafaji Yahya, Sun Xinsen, Prior Timothy J, Elsegood Mark R J, Redshaw Carl
Department of Chemistry, University of Hull, Hull, HU6 7RX, UK.
Dalton Trans. 2015 Jul 21;44(27):12349-56. doi: 10.1039/c5dt00272a.
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).
前体配体α,α,α',α'-四(3,5-二叔丁基-2-羟基苯基-对-)二甲苯-对-四苯酚(p-L(1)H4)与两当量的[NbCl5]在回流甲苯中反应，后处理后得到配合物{[NbCl3(NCMe)]2(μ-p-L(1))}·6MeCN (1·6MeCN)。当反应在过量乙醇存在下进行时，形成橙色配合物{[NbCl2(OEt)(NCMe)]2(μ-p-L(1))}·3½MeCN·0.614甲苯(2·3½MeCN·0.614甲苯)。使用[TaCl5]进行类似反应得到黄色配合物{[TaCl2(OEt)(NCMe)]2(μ-p-L(1))}·5MeCN (3·5MeCN)。对于间位前体配体，即α,α,α',α'-四(3,5-二叔丁基-2-羟基苯基-间-)二甲苯-间-四苯酚(m-L(2)H4)，仅使用[Nb(O)Cl3(NCMe)2]可分离得到晶体物质，即橙色双螯合物配合物{[Nb(NCMe)Cl(m-L(2)H2)2]}·3½MeCN (4·3½MeCN)或{[Nb(NCMe)Cl(m-L(2)H2)2]}·5MeCN (4·5MeCN)。已确定了1-4以及四苯酚L(1)H4和m-L(2)H4·2MeCN的分子结构。已对配合物1-4作为ε-己内酯开环聚合的预催化剂进行了筛选，反应中有无苄醇或溶剂存在，以及在不同温度下进行；转化率大多优异(>96%)，在>100 °C下20小时(在甲苯中)或1小时(纯物质)时具有良好的可控性。
