The California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569, USA.
Chemistry. 2010 Nov 8;16(42):12570-81. doi: 10.1002/chem.201001806.
The dynamic solution equilibria between molecular Borromean rings (BRs) and Solomon knots (SKs), assembled from transition metal-templated macrocycles, consisting of exo-bidentate bipyridyl and endo-tridentate diiminopyridyl ligands, have been examined with respect to the choice of the metal template and reaction conditions employed in the synthesis of the metalated BRs, otherwise known as Borromeates. Three new Borromeates, their syntheses templated by Cu(II), Co(II), and Mn(II), have been characterized extensively (two by X-ray crystallography) to the extent that the metal centers in the assemblies have been shown to be distanced sufficiently from each other not to communicate. The solid-state structure of the Co(II)-Borromeate reveals that six MeOH molecules, arranged in a [O--H...O] hydrogen bonded, chair-like conformation, are located within its oxophilic central cavity. When a mixture of Cu(II) and Zn(II) is used as the source of templation, there exists a dynamic equilibrium, in MeOH at room temperature, between a mixed-metal BR and a SK, from which the latter has been fractionally crystallized. By employing appropriate synthetic protocols with Zn(II) or Cd(II) as the template, significant amounts of SKs are formed alongside BRs. Modified crystallization conditions resulted in the isolation of both an all-zinc BR and an all-zinc SK, crystals of which can be separated manually, leading to the full characterization of the all-zinc SK by (1)H NMR spectroscopy and X-ray crystallography. This doubly interlocked [2]catenate has been identified retrospectively in recorded spectra, where it was attributed previously to a Borromeate with a Zn(II) cation coordinated to the oxophilic interior walls of the ensemble. Interestingly, these Zn(II)-templated assemblies do not interconvert in MeOH at room temperature, indicating the significant influence of both the metal template and solvent on the solution equilibria. It would also appear that d(10) metal ions favor SK formation-no evidence of Cu(II)-, Co(II)-, or Mn(II)-templated SKs has been found, yet a 1:0.9 ratio of BR:SK has been identified by (1)H NMR spectroscopy when Cd(II) is used as the template.
已研究了由过渡金属模板大环组装而成的分子 Borromean 环 (BR) 和 Solomon 结 (SK) 的动态溶液平衡，大环由外双齿联吡啶和内三齿二亚胺吡啶配体组成，其与 BR 金属化合成中所采用的金属模板和反应条件的选择有关，BR 金属化后通常被称为 Borromeates。我们已广泛表征了三种新的 Borromeates（它们的合成由 Cu(II)、Co(II)和 Mn(II)模板化），其程度足以证明组装体中的金属中心彼此之间的距离足够远，不会相互作用。Co(II)-Borromeate 的固态结构表明，有六个 MeOH 分子以[O--H…O]氢键椅式构象排列在其亲氧性的中心空腔内。当使用 Cu(II)和 Zn(II)混合物作为模板源时，在室温下的 MeOH 中存在一个混合金属 BR 和一个 SK 的动态平衡，后者已部分结晶。通过使用适当的合成方案，以 Zn(II)或 Cd(II)作为模板，可在 BR 旁边形成大量的 SK。经过改进的结晶条件得到了纯 Zn 的 BR 和纯 Zn 的 SK，它们的晶体可以手动分离，这使得对全 Zn 的 SK 进行了全面的表征，包括(1)H NMR 光谱和 X 射线晶体学。通过对记录的光谱进行回溯性识别，发现这种双互锁[2]套索已被鉴定为一种带有 Zn(II)阳离子与配合物亲氧内壁配位的 Borromeate。有趣的是，在室温下，这些 Zn(II)模板组装物在 MeOH 中不会相互转化，这表明金属模板和溶剂对溶液平衡有显著影响。这似乎表明 d(10)金属离子有利于 SK 的形成，目前还没有发现 Cu(II)、Co(II)或 Mn(II)模板化的 SK，但当使用 Cd(II)作为模板时，通过(1)H NMR 光谱鉴定出 BR:SK 的比例为 1:0.9。
