Synthesis, structural characterization and anion binding studies of palladium macrocycles with hydrogen-bonding ligands
作者:Pilar Diaz、Jorge A. Tovilla、Pablo Ballester、Jordi Benet-Buchholz、Ramón Vilar
DOI:10.1039/b703660d
日期:——
The reactions between [Pd(P–P)(OTf)2] (where P–P = dppp or dppf) and two different bipyridyl ligands (L1 = 1,3-bis(4-pyridylmethyl)urea and L2 = 1,3- bis(pyridinylmethyl)benzenedicarboxamide) containing hydrogen-bonding units have been studied. The X-ray crystal structures of three of these assemblies have been solved showing them to be the [2 + 2] metallo-macrocycles [Pd(P–P)(Ln)]2(OTf)4 [P–P = dppp, n = 1, (1); P–P = dppp, n = 2, (2); P–P = dppf, n = 1, (3)]. To confirm whether the dimeric assembly of one of these species (1) is retained in solution, several investigations have been carried out. 1H NMR studies in DMSO and high resolution ESI mass spectrometry have shown that 1 is in equilibrium with a larger [3 + 3] metallo-macrocycle. The equilibrium between these two species can be modified by changing the temperature, concentration or solvent. Also, addition of certain anions (e.g. [H2PO4]–) to the mixture shifts the equilibrium favoring the formation of the [2 + 2] metallo-macrocycle over the [3 + 3] (initially present in a larger proportion).
我们研究了[Pd(P-P)(OTf)2](其中 P-P = dppp 或 dppf)与含有氢键单元的两种不同双吡啶配体(L1 = 1,3-双(4-吡啶基甲基)脲和 L2 = 1,3-双(吡啶基甲基)苯二甲酰胺)之间的反应。其中三个组装体的 X 射线晶体结构已经解析,显示它们是 [2 + 2] 金属大环 [Pd(P-P)(Ln)]2(OTf)4 [P-P = dppp,n = 1,(1);P-P = dppp,n = 2,(2);P-P = dppf,n = 1,(3)]。为了确认这些物种之一(1)的二聚体是否保留在溶液中,我们进行了多项研究。DMSO 中的 1H NMR 研究和高分辨率 ESI 质谱分析表明,1 与一个较大的 [3 + 3] 金属大环处于平衡状态。这两种物质之间的平衡可以通过改变温度、浓度或溶剂来改变。此外,在混合物中加入某些阴离子(如 [H2PO4]-)也会改变平衡,使[2 + 2]金属大环的形成比[3 + 3](最初存在的比例较大)更有利。