Heteroscorpionate aluminium complexes as chiral building blocks to engineer helical architectures
作者:Jose A. Castro-Osma、Carlos Alonso-Moreno、M. Victoria Gómez、Isabel Márquez-Segovia、Antonio Otero、Agustín Lara-Sánchez、Juan Fernández-Baeza、Luis F. Sánchez-Barba、Ana M. Rodríguez
DOI:10.1039/c3dt51384j
日期:——
Treatment of heteroscorpionate ligand precursors pbptamH, pbpamH, sbpamH and (S)-mbpamH with 2 equivalents of AlR3 (R = Et, Me) yielded the corresponding binuclear organoaluminium complexes [Al2R4(μ-pbptam)] (R = Me 1, Et 2), [Al2R4(μ-pbpam)] (R = Me 3, Et 4), [Al2R4(μ-sbpam)] (R = Me 5, Et 6) and [Al2R4μ-(S)-mbpam}] (R = Me 7, Et 8). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers and mixtures of M- and P-handed diastereoisomers were obtained when achiral (1–4) and chiral (5–8) heteroscorpionate ligands were used as scaffolds, respectively. Re-crystallization from hexane allowed us to obtain M-homochiral architectures in the solid state for the helical complexes [Al2Et4(μ-sbpam)] (6) and [Al2Et4μ-(S)-mbpam}] (8). The reaction of heteroscorpionate ligands with 3 equivalents of AlR3 (R = Me, Et) led to the corresponding trinuclear organoaluminium complexes [Al3R7(μ3-pbptam)] (R = Me 9, Et 10), [Al3R7(μ3-pbpam)] (R = Me 11, Et 12), [Al3R7(μ3-sbpam)] (R = Me 13, Et 14) and [Al3R7μ3-(S)-mbpam}] (R = Me 15, Et 16). The extra AlR3 molecule contributes to the formation of a diastereomeric excess of the PS helicate for complexes 15 and 16. X-ray determination of some of the helical complexes allowed us to witness a versatile and efficient self-assembly process of the building blocks (heteroscorpionate aluminium complexes) directed by noncovalent intermolecular CH–π interactions. The structures of these complexes have been determined by spectroscopic methods and the X-ray crystal structures of 2, 6, 8, and 16 have also been established. Concentration-dependent 1H pulsed field-gradient spin echo (PFGSE) NMR experiments provided evidence for the self-assembly of the single molecular species of complex 2 in solution. The degree of aggregation was calculated for complex 2, with the average number of units constituting the aggregate (N) estimated to be a maximum of 4 molecules in solution before reaching the solid state.
用 2 个等量的 AlR3(R = Et、Me)生成相应的双核有机铝配合物 [Al2R4(μ-pbptam)] (R = Me 1, Et 2)、[Al2R4(μ-pbpam)] (R = Me 3, Et 4)、[Al2R4(μ-sbpam)] (R = Me 5, Et 6)和 [Al2R4μ-(S)-mbpam}] (R = Me 7, Et 8)。由于固定吡唑环的要求,这些配合物具有螺旋手性。通过核磁共振和 X 射线衍射,我们对这些螺旋体在溶液中的立体异构和自组装过程进行了较为详细的研究。当使用非手性(1-4)和手性(5-8)异蝎酸配体作为支架时,分别得到了 M 手和 P 手对映体的混合物以及 M 手和 P 手非对映异构体的混合物。通过从己烷中重结晶,我们得到了固态螺旋配合物 [Al2Et4(μ-sbpam)] (6) 和 [Al2Et4μ-(S)-mbpam}] (8)的 M-对映结构。杂蝎酸配体与 3 个等量的 AlR3(R = Me,Et)反应生成相应的三核有机铝配合物 [Al3R7(μ3-pbptam)] (R = Me 9、10)、[Al3R7(μ3-pbpam)](R = Me 11,Et 12)、[Al3R7(μ3-sbpam)](R = Me 13,Et 14)和[Al3R7μ3-(S)-mbpam}](R = Me 15,Et 16)。对于复合物 15 和 16 来说,额外的 AlR3 分子有助于形成非对映过量的 PS 赫合物。通过对一些螺旋状复合物的 X 射线测定,我们可以看到构件(异蝎酸铝复合物)在分子间 CH-π 非共价相互作用的引导下,进行了多用途、高效率的自组装过程。这些复合物的结构已通过光谱方法确定,2、6、8 和 16 的 X 射线晶体结构也已建立。浓度依赖性 1H 脉冲场梯度自旋回波(PFGSE)核磁共振实验为复合物 2 的单分子物种在溶液中的自组装提供了证据。计算了复合物 2 的聚集程度,估计在达到固态之前,溶液中构成聚集体的平均单元数(N)最多为 4 个分子。