Kuhlman Matthew L, Rauchfuss Thomas B
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
J Am Chem Soc. 2003 Aug 20;125(33):10084-92. doi: 10.1021/ja035253h.
A series of heptametallic cyanide cages are described; they represent soluble analogues of defect-containing cyanometalate solid-state polymers. Reaction of 0.75 equiv of [CpRu(NCMe)3]PF6, Et(4)N[CpRh(CN)3], and 0.25 equiv of CsOTf in MeCN solution produced (Cs subset [CpCo(CN)3]4[CpRu]3)(Cs subset Rh4Ru3). 1H and 133Cs NMR measurements show that Cs subset Rh4Ru3 exists as a single Cs isomer. In contrast, (Cs subset [CpCo(CN)3]4[CpRu]3) (Cs subset Co4Ru3), previously lacking crystallographic characterization, adopts both Cs isomers in solution. In situ ESI-MS studies on the synthesis of Cs subset Rh4Ru3 revealed two Cs-containing intermediates, Cs subset Rh2Ru2+ (1239 m/z) and Cs subset Rh3Ru3+ (1791 m/z), which underscore the participation of Cs+ in the mechanism of cage formation. 133Cs NMR shifts for the cages correlated with the number of CN groups bound to Cs+: Cs subset Co4Ru4+ (delta 1 vs delta 34 for CsOTf), Cs subset Rh4Ru3 where Cs+ is surrounded by ten CN ligands (delta 91), Cs subset Co4Ru3, which consists of isomers with 11 and 10 pi-bonded CNs (delta 42 and delta 89, respectively). Although (K subset [CpRh(CN)3]4[CpRu]3) could not be prepared, (NH4 subset [CpRh(CN)3]4[CpRu]3) (NH4 subset Rh4Ru3) forms readily by NH4+-template cage assembly. IR and NMR measurements indicate that NH4+ binding is weak and that the site symmetry is low. CsOTf quantitatively and rapidly converts NH4 subset Rh4Ru3 into Cs subset Rh4Ru3, demonstrating the kinetic advantages of the M7 cages as ion receptors. Crystallographic characterization of CsCo4Ru3 revealed that it crystallizes in the Cs-(exo)1(endo)2 isomer. In addition to the nine mu-CN ligands, two CN(t) ligands are pi-bonded to Cs+. M subset Rh4Ru3 (M = NH4, Cs) crystallizes as the second Cs isomer, that is, (exo)2(endo)1, wherein only one CN(t) ligand interacts with the included cation. The distorted framework of NH4 subset Rh4Ru3 reflects the smaller ionic radius of NH4+. The protons of NH4+ were located crystallographically, allowing precise determination of the novel NH4...CN interaction. A competition experiment between calix[4]arene-bis(benzocrown-6) and NH4 subset Rh4Ru3 reveals NH4 subset Rh4Ru3 has a higher affinity for cesium.
本文描述了一系列七金属氰化物笼；它们代表了含缺陷氰基金属酸盐固态聚合物的可溶性类似物。在乙腈溶液中，0.75当量的[CpRu(NCMe)3]PF6、Et(4)N[CpRh(CN)3]与0.25当量的CsOTf反应生成了(Cs子集[CpCo(CN)3]4[CpRu]3)(Cs子集Rh4Ru3)。1H和133Cs NMR测量表明，Cs子集Rh4Ru3以单一的Cs异构体形式存在。相比之下，之前缺乏晶体学表征的(Cs子集[CpCo(CN)3]4[CpRu]3)(Cs子集Co4Ru3)在溶液中采用两种Cs异构体。对Cs子集Rh4Ru3合成的原位ESI-MS研究揭示了两种含Cs中间体，Cs子集Rh2Ru2+(1239 m/z)和Cs子集Rh3Ru3+(1791 m/z)，这突出了Cs+在笼形成机制中的参与。笼的133Cs NMR位移与与Cs+结合的CN基团数量相关：Cs子集Co4Ru4+(与CsOTf相比，δ为1对δ为34)，Cs子集Rh4Ru3中Cs+被十个CN配体包围(δ为91)，Cs子集Co4Ru3由具有11个和10个π键合CN的异构体组成(分别为δ为42和δ为89)。尽管无法制备(K子集[CpRh(CN)3]4[CpRu]3)，但(NH4子集[CpRh(CN)3]4[CpRu]3)(NH4子集Rh4Ru3)通过NH4+模板笼组装很容易形成。IR和NMR测量表明，NH4+的结合较弱且位点对称性较低。CsOTf能定量且快速地将NH4子集Rh4Ru3转化为Cs子集Rh4Ru3，证明了M7笼作为离子受体的动力学优势。CsCo4Ru3的晶体学表征表明它以Cs-(外)1(内)2异构体形式结晶。除了九个μ-CN配体外，两个CN(t)配体与Cs+形成π键。M子集Rh4Ru3(M = NH4、Cs)以第二种Cs异构体形式结晶，即(外)2(内)1，其中只有一个CN(t)配体与所含阳离子相互作用。NH4子集Rh4Ru3的扭曲框架反映了NH4+较小的离子半径。通过晶体学确定了NH4+的质子位置，从而能够精确测定新型的NH4...CN相互作用。杯[4]芳烃-双(苯并冠醚-6)与NH4子集Rh4Ru3之间的竞争实验表明，NH4子集Rh4Ru3对铯具有更高的亲和力。
