Non-planar co-ordination of C2-symmetric biaryl-bridged Schiff-base ligands: well expressed chiral ligand environments for zirconium †
作者:Paul R. Woodman、Ian J. Munslow、Peter B. Hitchcock、Peter Scott
DOI:10.1039/a906788d
日期:——
The C2-symmetric Schiff-base proligand (H2L1) synthesized by condensation of 2,2â²-diamino-6,6â²-dimethylbiphenyl and 3,5-di-tert-butylsalicylaldehyde reacted in its deprotonated form with [MCl4(THF)2] (MÂ =Â Zr or Hf) to give [ML1Cl2]. The molecular structures of these complexes show that they belong to the hitherto unknown cis-cis class of quadridentate Schiff-base complex. Most importantly, the two chloride ligands occupy mutually cis co-ordination sites in a well expressed chiral ligand environment that is structurally analogous to that of the ansa-metallocenes. Alkylations of the zirconium complex were unsuccessful, but an unstable complex [ZrL1(CH2Ph)2] was synthesized from H2L1 and Zr(CH2Ph)4. Amido complexes [ZrL1(NR2)2] (RÂ =Â Me or Et; R2Â =Â HBut) were synthesized by substitution reactions of [ZrL1Cl2] and by reaction of H2L1 with Zr(NR2)4. The reactions of [ZrL1(NR2)2] (RÂ =Â Me or Et) with SiH(OEt)3 and SiMe3Cl gave [ZrL1(OEt)2] and [ZrL1Cl2] respectively. The reaction of [ZrL1Cl2] with LiOPh gave [ZrL1(OPh)2]. The molecular structure of the latter confirms that it also has the cis-cis structure and also indicates the presence of edgeâface arene interactions between the phenoxide ligands and the salicylidene units. The reaction of [ZrL1Cl2] with LiAlH4 in pyridine (py) led to reduction in situ of the imine groups and elimination of both chloride ligands to give a complex containing the quadruply deprotonated reduced form of L1, i.e. [ZrL2(py)2]. This complex is also formed by reaction of H4L2 with Zr(NR2)4 in pyridine.
通过2,2'-二氨基-6,6'-二甲基联苯和3,5-二叔丁基水杨醛的缩合反应合成的C2对称席夫碱前体(H2L1),在其去质子化形式下与[MCl4(THF)2](M = Zr或Hf)反应,得到[ML1Cl2]。这些配合物的分子结构显示,它们属于迄今未知的cis-cis型四齿席夫碱配合物。最重要的是,两个氯配体在结构上类似于ansa-金属有机物的手性配体环境中占据相互cis配位位点。锆配合物的烷基化未能成功,但通过H2L1与Zr(CH2Ph)4合成了一种不稳定的配合物[ZrL1(CH2Ph)2]。通过[ZrL1Cl2]的取代反应和H2L1与Zr(NR2)4的反应,合成了氨基配合物[ZrL1(NR2)2](R = Me或Et;R2 = HBut)。[ZrL1(NR2)2](R = Me或Et)与SiH(OEt)3和SiMe3Cl的反应分别得到了[ZrL1(OEt)2]和[ZrL1Cl2]。[ZrL1Cl2]与LiOPh的反应得到了[ZrL1(OPh)2]。后者的分子结构确认其也具有cis-cis结构,并且表明苯氧基配体与水杨醛单元之间存在边缘-面芳烃相互作用。[ZrL1Cl2]在吡啶(py)中与LiAlH4反应,导致亚胺基团的还原和两个氯配体的消除,得到含有四重去质子化还原形式L1的配合物,即[ZrL2(py)2]。该配合物也可以通过H4L2与Zr(NR2)4在吡啶中的反应形成。