Tetrameric cyclic double helicates as a scaffold for a molecular Solomon link.
Tetrameric cyclic double helicates as a scaffold for a molecular Solomon link.
复制标题
DOI：
10.1002/anie.201302634
复制
发表时间：
2013-06-17
影响因子：
16.6
通讯作者：
Pritchard, Robin G.
中科院分区：
文献类型：
--
作者：
Beves, Jonathon E.;Campbell, Christopher J.;Leigh, David A.;Pritchard, Robin G.
1链接在亚历山大-布里格斯符号[1])，是两个相互交织的环的拓扑结构，在最简单的表示（图1）中相互交叉四次这种双缠绕的[2]链烷仍然很少见，[3-5]，迄今为止仅报道了两个具有完全有机骨架的小分子例子[4,5]。所罗门链是迄今为止使用Sauvage首创的方法制造的最复杂的拓扑结构，该方法通过连接线性双链金属螺旋的末端产生高阶互锁结构。原则上，[2b， d]环状双螺旋[7]可以提供一系列拓扑结构所需的交叉，同时将连接位点定位在靠近的位置，以帮助在使用长线性螺旋[8]时可能出现问题的大环化反应（图1）。最近用一种五聚体螺旋状支架制备了一种小分子五边形结（五个交叉点）在这里，我们报告了使用四聚体圆螺旋作为所罗门链的基础，说明了这种方法在复杂分子拓扑结构组装中的一般效用。我们之前合成五叉结[9]时使用的配体是基于Lehn使用的三（联吡啶）基序[7a， b， d]来组装五聚和六聚环螺旋，但两个外部联吡啶单元都被2-甲酰基吡啶取代，可以与胺缩合形成亚胺并生成三（双齿）配体链。除了提供一种方便的连接金属结合部件的方法外，亚胺键的形成是可逆的，在装配过程中提供了一种错误检查机制在Lehn ' s三（联吡啶）配体的每个联吡啶基团之间的乙烯间隔剂中加入一个额外的氧原子，形成环状四聚螺旋。[7b]因此，为了生成所罗门链所需的四个交叉点，我们引入了与五氟结合成中使用的配体类似的结构变化，其形式为1（关于1的合成，请参阅支持信息），并研究了其与伯胺和FeII盐的配位化学（方案1）。1与正己胺和FeCl2 (DMSO, 608C, 24 h，方案1)[8]反应产生深紫色溶液，典型的低自旋铁（II）三（二亚胺）配合物。24小时后，用KPF6水溶液沉淀，以47%的收率分离出六氟磷酸盐2。电喷雾电离质谱分析（ESI-MS，见图S1的辅助信息）表明，2是一种金属配体四聚体，其分子式为[Fe4L4]-(PF6) 8][11]（L=二亚胺配体，由1与两分子正己胺缩合而成）。1H NMR波谱（图2a）表明，2具有高度对称性，非对映位CH2-O-CH2质子的分裂符合方案1所示的手性（外消旋）螺旋拓扑结构。当使用4.4等量的铁（II）盐时，2的产率提高到71%（分离产物的产率）（见支持信息，图S9）。四聚环螺旋酸的形成并不局限于使用FeCl2作为铁（II）盐（方案1），Fe (BF4) 2和Fe (ClO4) 2也会产生2，尽管产率明显较低（见支持信息，图S13），并且受到其他聚合物和低聚物副产物的污染。当以二氧化二铁为铁源时，得到不同的主要产物（方案1）；
1 link in Alexander–Briggs notation [1]), is a topology of two interwoven rings that cross each other four times in the simplest representation (Figure 1).[2] Such doubly-entwined [2] catenanes are still rare,[3–5] with only two small-molecule examples with wholly organic backbones reported [4, 5] to date. The Solomon link is the most complex topology to have been produced [4] using Sauvage s pioneering route [6] of generating higher order interlocked structures through the connection of the termini of linear double-stranded metal helicates. In principle,[2b, d] cyclic double helicates [7] can provide the crossings required for a range of topologies, while simultaneously positioning connecting sites in close proximity to aid the macrocyclization reactions that can be problematic when employing long linear helicates [8](Figure 1). A small-molecule pentafoil knot (five crossings) was recently prepared using a pentameric circular helicate scaffold.[9] Here we report on the use of a tetrameric circular helicate as the basis for a Solomon link, illustrating the general utility of this approach for the assembly of complex molecular topologies. The ligand used in our earlier synthesis of a pentafoil knot [9] was based on a tris (bipyridine) motif employed [7a, b, d] by Lehn to assemble penta-and hexameric cyclic helicates, but with both outer bipyridine units replaced by 2-formylpyridine groups that could condense with amines to form imines and generate tris (bidentate) ligand strands. As well as providing a convenient way of connecting metal binding components, imine bond formation is reversible, imparting an error checking mechanism during the assembly process.[10] Incorporating an additional oxygen atom in the ethylene spacer between each bipyridine group of Lehn s tris (bipyridine) ligand led to cyclic tetrameric helicates.[7b] Accordingly, in an attempt to generate the four crossings required for a Solomon link, we introduced a similar structural change to the ligand used in the pentafoil knot synthesis in the form of 1 (for the synthesis of 1 see the Supporting Information) and investigated its coordination chemistry with primary amines and FeII salts (Scheme 1).The reaction of 1 with n-hexylamine and FeCl2 (DMSO, 608C, 24 h, Scheme 1)[8] produced an intensely colored purple solution typical of low-spin iron (II) tris (diimine) complexes. After 24 hours, the product was isolated in 47% yield as the hexafluorophosphate salt 2 by precipitation with aqueous KPF6. Electrospray ionization mass spectrometry (ESI-MS; see the Supporting Information, Figure S1) revealed that 2 was a metal–ligand tetramer with the formula [Fe4L4]-(PF6) 8][11](L= bis (imine) ligand resulting from the condensation of 1 with two molecules of n-hexylamine). 1H NMR spectroscopy (Figure 2a) indicated that 2 was highly symmetrical, with the splitting of the diastereotopic CH2-O-CH2 protons consistent with the chiral (racemic) helicate topology shown in Scheme 1. The yield of 2 was increased to 71%(yield of isolated product) when employing 4.4 equivalents of the iron (II) salt (see the Supporting Information, Figure S9). The formation of the tetrameric cyclic helicate was not limited to the use of FeCl2 as the iron (II) salt (Scheme 1), both Fe (BF4) 2 and Fe (ClO4) 2 also produced 2, although in significantly lower yields (see the Supporting Information, Figure S13) and contaminated with other polymeric and oligomeric by-products. When FeBr2 was employed as the iron source, a different main product was obtained (Scheme 1),
登录
查看更多内容
影响因子：
4.6
作者：
Argent, Stephen P.;Adams, Harry;Ward, Michael D.
通讯作者：
Ward, Michael D.
影响因子：
4
作者：
Beves, JE;Chapman, BE;Wei, G
通讯作者：
Wei, G
影响因子：
15
作者：
Campos-Fernández, CS;Clérac, R;Dunbar, KR
通讯作者：
Dunbar, KR
影响因子：
15
作者：
Ayme, Jean-Francois;Beves, Jonathon E.;Schultz, David
通讯作者：
Schultz, David
影响因子：
4.3
作者：
Childs, LJ;Pascu, M;Hannon, ML
通讯作者：
Hannon, ML