Takani Masako, Takeda Takeshi, Yajima Tatsuo, Yamauchi Osamu
Faculty of Pharmaceutical Sciences, Kanazawa University, Kanazawa 920-1192, Japan.
Inorg Chem. 2006 Jul 24;45(15):5938-46. doi: 10.1021/ic060595k.
In view of the interesting metal-binding properties of lichen substances and the indole ring as a potential ligand, we studied the Pd(II) complexes of indole-containing ligands, N-(indole-3-ethyl)-Delta(2,11)-enaminousnic acid (IEU) and 4-[2-(indol-3-yl)-ethylamino]pent-3-en-2-one (IEP) obtained by condensation of tryptamine with usnic acid and its model acetylacetone, respectively. Reactions of Pd(II) with IEU and IEP gave isomeric complexes resulting from coordination of the C3 atom of the indole ring in the 3H-indole form, Pd2(IEUH(-2))(2) (1 and 2) and Pd2(IEPH(-2))(2) (3 and 4) (IEUH(-2) and IEPH(-2) denote doubly deprotonated forms of IEU and IEP, respectively). Complexes 1-4 were determined, from the NMR and MS spectra, to have dimeric structures doubly bridged by the indole rings, which were stacked in different orientations. X-ray crystal structure analysis of 3 and 4 established that they are indole-bridged dimers of the [C,N,O]-donor palladacycles with the Pd(II) centers in a square-planar geometry formed by a CN(2)O donor set and are anti and syn isomers with respect to the bridging indole rings, respectively. On the basis of the spectral similarity with 4, 1 and 2 were concluded to be stereoisomers assuming the syn form with the same donor set. The results demonstrate the metal binding and stacking abilities of the indole ring and the stereoisomerism from the sp3 C3 atom formed upon coordination.
鉴于地衣物质有趣的金属结合特性以及吲哚环作为潜在配体，我们研究了含吲哚配体N-(吲哚-3-乙基)-Δ(2,11)-烯胺缩苹果酸（IEU）和4-[2-(吲哚-3-基)-乙氨基]戊-3-烯-2-酮（IEP）的钯(II)配合物，它们分别是由色胺与松萝酸及其模型乙酰丙酮缩合得到的。钯(II)与IEU和IEP的反应生成了异构体配合物，这些配合物是由3H-吲哚形式的吲哚环的C3原子配位产生的，即Pd2(IEUH(-2))(2)（1和2）以及Pd2(IEPH(-2))(2)（3和4）（IEUH(-2)和IEPH(-2)分别表示IEU和IEP的双去质子化形式）。根据核磁共振和质谱光谱确定，配合物1 - 4具有由吲哚环双桥连的二聚体结构，这些吲哚环以不同取向堆积。对3和4的X射线晶体结构分析表明，它们是[C,N,O]供体钯环的吲哚桥连二聚体，钯(II)中心处于由CN(2)O供体集形成的平面正方形几何构型中，并且相对于桥连吲哚环分别为反式和顺式异构体。基于与4的光谱相似性，推断1和2为具有相同供体集的顺式形式的立体异构体。结果证明了吲哚环的金属结合和堆积能力以及配位时由sp3 C3原子形成的立体异构现象。
