Structures, host-guest chemistry and mechanism of stepwise self-assembly of M4L6 tetrahedral cage complexes
Structures, host-guest chemistry and mechanism of stepwise self-assembly of M4L6 tetrahedral cage complexes
复制标题
DOI：
10.1039/c1dt10781j
复制
发表时间：
2011-01-01
影响因子：
4
通讯作者：
Ward, Michael D.
中科院分区：
文献类型：
--
作者：
Hall, Benjamin R.;Manck, Lauren E.;Ward, Michael D.
配体L-bip含有两个双齿吡唑吡啶末端，由3,3'-联苯间隔物隔开，已用于制备形式为[M-4(L-bip)(6)]X-8的四面体笼形配合物，其中桥接配体跨越M-4四面体的六个边。为了研究阳离子笼与各种阴离子之间的相互作用，我们对几个新的例子进行了结构表征，包括各种金属阳离子和不同阴离子。像BF4-和NO3-这样的小阴离子可以占据中心空腔，在那里它们被一组CH中心点中心点中心点F或CH中心点中心点中心点与笼内表面的氢键相互作用所锚定。但更大的阴离子，如萘磺酸盐或四苯基硼酸盐位于腔外，并通过CH中心点中心点中心点pi相互作用或CH中心点中心点中心点O氢键与笼的外表面相互作用。用核磁共振光谱对M = Co和M = Cd笼进行了详细的研究。对于[Co-4(L-bip)(6)](BF4)(8)， H-1核磁共振波谱在-85到+110 ppm的范围内发生顺磁位移，但光谱已经完全通过测量每个峰的T-1弛豫时间与Co中心点中心点中心点H距离的相关性来分配。F-19 DOSY对阴离子的测量表明，在低温下，[BF4]（-）阴离子的扩散速度与其周围的笼形上层结构相似，表明它被困在中心笼腔内。此外，通过在不同温度下将L-bip乙腈溶液与Co（BF4）乙腈溶液进行光谱滴定的详细建模，阐明了笼状上层结构的平衡逐步自组装(2)。六种已确定:[Co2Lbip](4 +),(二氧化碳(L-bip) (2)] (4 +), [Co-4 (L-bip) (6)] (8 +), [Co-4 (L-bip)(8)](8 +),(二氧化碳(L-bip)(5))(4 +)和[有限公司(L-bip)(3)](2 +)。总的来说，笼的组装是由熵驱动的，而不是由焓驱动的。一旦组装起来，由于其机械纠缠的性质，笼表现出显著的动力学惰性：金属阳离子在纯Co-4和Cd-4笼的位置之间乱置，以得到Co-4， Co3Cd, Co2Cd2， CoCd3和Cd-4笼的统计混合物，在室温溶液中需要数月的时间。
The ligand L-bip, containing two bidentate pyrazolyl-pyridine termini separated by a 3,3'-biphenyl spacer, has been used to prepare tetrahedral cage complexes of the form [M-4(L-bip)(6)]X-8, in which a bridging ligand spans each of the six edges of the M-4 tetrahedron. Several new examples have been structurally characterized with a variety of metal cation and different anions in order to examine interactions between the cationic cage and various anions. Small anions such as BF4- and NO3- can occupy the central cavity where they are anchored by an array of CH center dot center dot center dot F or CH center dot center dot center dot O hydrogen-bonding interactions with the interior surface of the cage, but larger anions such as naphthyl-1-sulfonate or tetraphenylborate lie outside the cavity and interact with the external surface of the cage via CH center dot center dot center dot pi interactions or CH center dot center dot center dot O hydrogen bonds. The cages with M = Co and M = Cd have been examined in detail by NMR spectroscopy. For [Co-4(L-bip)(6)](BF4)(8) the H-1 NMR spectrum is paramagnetically shifted over the range -85 to +110 ppm, but the spectrum has been completely assigned by correlation of measured T-1 relaxation times of each peak with Co center dot center dot center dot H distances. F-19 DOSY measurements on the anions show that at low temperature a [BF4](-) anion diffuses at a similar rate to the cage superstructure surrounding it, indicating that it is trapped inside the central cage cavity. Furthermore, the equilibrium step-by-step self-assembly of the cage superstructure has been elucidated by detailed modeling of spectroscopic titrations at multiple temperatures of an acetonitrile solution of L-bip into an acetonitrile solution of Co(BF4)(2). Six species have been identified: [Co2Lbip](4+), [Co-2(L-bip)(2)](4+), [Co-4(L-bip)(6)](8+), [Co-4(L-bip)(8)](8+), [Co-2(L-bip)(5)](4+), and [Co(L-bip)(3)](2+). Overall the assembly of the cage is entropy, and not enthalpy, driven. Once assembled, the cages show remarkable kinetic inertness due to their mechanically entangled nature: scrambling of metal cations between the sites of pure Co-4 and Cd-4 cages to give a statistical mixture of Co-4, Co3Cd, Co2Cd2, CoCd3 and Cd-4 cages takes months in solution at room temperature.