Fac and mer isomers of Ru(II) tris(pyrazolyl-pyridine) complexes as models for the vertices of coordination cages: structural characterisation and hydrogen-bonding characteristics
Fac and mer isomers of Ru(II) tris(pyrazolyl-pyridine) complexes as models for the vertices of coordination cages: structural characterisation and hydrogen-bonding characteristics
复制标题
DOI：
10.1039/c3dt52479e
复制
发表时间：
2014-01-01
影响因子：
4
通讯作者：
Ward, Michael D.
中科院分区：
文献类型：
--
作者：
Metherell, Alexander J.;Cullen, William;Ward, Michael D.
我们已经制备了一系列单核的fac和mer异构体的Ru（II）配合物含有螯合吡唑基吡啶配体，检查他们的不同能力，作为氢键供体在MeCN。这是由我们早期的观察所提示的，即包含这些类型的金属顶点的八核立方体状配位笼可以结合异喹啉-N-氧化物等客体（K = 2100 M-1，在MeCN中），对键合的重要贡献是客体的富电子原子和氢原子之间的氢键相互作用，在笼的内表面上的键供体位点由靠近2+金属中心的CH 2质子的会聚集合形成。从[Ru（L-H）（3）]（2+）[L-H = 3-（2-吡啶基）-1H-吡唑]开始，由于fac异构体形成Cu（I）加合物，而mer异构体不形成Cu（I）加合物，因此分离几何异构体。吡唑基NH基团与甲基碘或苄基溴的烷基化分别得到[Ru（L-Me）（3）]（2+）和[Ru（L-bz）（3）]（2+），各自为它们的fac和mer异构体;所有都进行了结构表征。在fac异构体中，侧基-CH 2 R或-CH 3质子的会聚基团定义了氢键供体口袋;在mer异构体中，这些质子不会聚，并且预期涉及这些质子的任何氢键都较弱。对于[Ru（L-Me）（3）]（2+）和[Ru（L-bz）（3）]（2+），在MeCN中用异喹啉-N-氧化物进行的NMR滴定揭示了客体和络合物的fac异构体之间的弱1：1结合（K接近1 M-1），这在mer异构体中是不存在的，证实了这些络合物的氢键供体能力的差异与它们不同的几何形状相关。然而，与笼相比，由于来自阴离子的竞争而发生弱结合，阴离子以笼络合物中不发生的方式自由地与单核络合物阳离子形成离子对。我们的结论是，（i）的存在下的fac三螯合位点的笼作为氢键供体，和（ii）排除反离子从中央空腔离开这些氢键位点自由地与客人相互作用，都是重要的设计标准，为未来的协调笼主机。
We have prepared a series of mononuclear fac and mer isomers of Ru(II) complexes containing chelating pyrazolyl-pyridine ligands, to examine their differing ability to act as hydrogen-bond donors in MeCN. This was prompted by our earlier observation that octanuclear cube-like coordination cages that contain these types of metal vertex can bind guests such as isoquinoline-N-oxide (K = 2100 M-1 in MeCN), with a significant contribution to binding being a hydrogen-bonding interaction between the electron-rich atom of the guest and a hydrogen-bond donor site on the internal surface of the cage formed by a convergent set of CH2 protons close to a 2+ metal centre. Starting with [Ru(L-H)(3)](2+) [L-H = 3-(2-pyridyl)-1H-pyrazole] the geometric isomers were separated by virtue of the fact that the fac isomer forms a Cu(I) adduct which the mer isomer does not. Alkylation of the pyrazolyl NH group with methyl iodide or benzyl bromide afforded [Ru(L-Me)(3)](2+) and [Ru(L-bz)(3)](2+) respectively, each as their fac and mer isomers; all were structurally characterised. In the fac isomers the convergent group of pendant -CH2R or -CH3 protons defines a hydrogen-bond donor pocket; in the mer isomer these protons do not converge and any hydrogen-bonding involving these protons is expected to be weaker. For both [Ru(L-Me)(3)](2+) and [Ru(L-bz)(3)](2+), NMR titrations with isoquinoline-N-oxide in MeCN revealed weak 1 : 1 binding (K approximate to 1 M-1) between the guest and the fac isomer of the complex that was absent with the mer isomer, confirming a difference in the hydrogen-bond donor capabilities of these complexes associated with their differing geometries. The weak binding compared to the cage however occurs because of competition from the anions, which are free to form ion-pairs with the mononuclear complex cations in a way that does not happen in the cage complexes. We conclude that (i) the presence of fac tris-chelate sites in the cage to act as hydrogen-bond donors, and (ii) exclusion of counter-ions from the central cavity leaving these hydrogen-bonding sites free to interact with guests, are both important design criteria for future coordination cage hosts.