Synthesis of C2 and Cs symmetric zinc complexes supported by bis(phosphinimino)methyl ligands and their use in ring opening polymerisation catalysis
作者:Michael S. Hill、Peter B. Hitchcock
DOI:10.1039/b207358g
日期:2002.12.9
Synthetic routes to zinc complexes supported by sterically demanding bis(phosphinimino)methyl ligands are reported. Two aryl-substituted ligand precursors have been utilised, [CH2(Ph2PNC6H2Me3-2,4,6)2], 1, and [CH2(Ph2PNPh)(Ph2PNC6H2Me3-2,4,6)], 2. The second of these is the first example of an asymmetric bis(phosphinimino)methane. These ligands are converted to three-coordinate RZnX complexes (R = 1; X = Me, N(SiMe3)2; R = 2; X = Me) with either C2 or Cs symmetry in solution by reaction with either ZnMe2 or Zn[N(SiMe3)2]2 in toluene. All three derivatives have been shown to exist as three-coordinate monomers in the solid state by X-ray diffraction analysis. Protonolysis of these compounds with the bulky phenol 2,4-tBu2C6H3OH or triphenylmethanol resulted in the isolation of a series of three-coordinate aryloxy or alkoxyzinc derivatives. In contrast, reaction with less sterically demanding alcohols resulted in protonation of the bis(phosphinimino)methyl ligand. A similar result was obtained from reaction of RZnMe (R = 1) and triphenylsilanol and the product is the first example of a bis(triorganosiloxy)zinc compound to be structurally characterised. All the compounds have been examined for activity in ring opening polymerisation catalysis of rac-lactide. The aryloxy and triphenylmethoxy derivatives are active catalysts; however, no evidence of true ‘living’ behaviour or stereocontrol of diastereomer insertion has been observed.
本研究报告介绍了由立体要求较高的双(膦酰亚胺)甲基配体支持的锌配合物的合成路线。我们使用了两种芳基取代配体前体:[CH2(Ph2PNC6H2Me3-2,4,6)2],1 和 [CH2(Ph2PNPh)(Ph2PNC6H2Me3-2,4,6)],2。 其中第二种是不对称双(膦酰亚胺)甲烷的第一个实例。通过与 ZnMe2 或 Zn[N(SiMe3)2]2 在甲苯中反应,这些配体在溶液中被转化为具有 C2 或 Cs 对称性的三配位 RZnX 复合物(R = 1; X = Me, N(SiMe3)2; R = 2; X = Me)。X 射线衍射分析表明,所有这三种衍生物在固态下都是三配位单体。用笨重的苯酚 2,4-tBu2C6H3OH 或三苯基甲醇对这些化合物进行质子分解,可分离出一系列三配位芳氧基或烷氧锌衍生物。相反,与立体要求较低的醇反应则会导致双(膦酰亚胺)甲基配体质子化。RZnMe (R = 1)与三苯基硅醇的反应也得到了类似的结果,该产物是第一个在结构上得到表征的双(三有机硅氧基)锌化合物实例。我们对所有化合物在催化 rac-lactide 开环聚合过程中的活性进行了研究。芳氧基和三苯甲氧基衍生物是活性催化剂,但没有观察到真正的 "活 "行为或非对映异构体插入的立体控制。