Demonstration of "Mobius" Aromaticity in Planar Metallacycles
Demonstration of "Mobius" Aromaticity in Planar Metallacycles
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DOI：
10.1002/chem.201000396
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Tsogoeva, Svetlana B.
中科院分区：
文献类型：
--
作者：
Mauksch, Michael;Tsogoeva, Svetlana B.
莫比乌斯芳香性是埃德加海尔布隆纳（Heilbronner）在1964年预测的一种具有奇数个轨道相位反转的4 n电子完全共轭环状分子（或过渡态）所表现出的稳定效应。虽然以前有人提出，这种效应也可能适用于平面金属杂环，其中过渡金属采用d轨道的δ型结合模式，只有很少的例子，稳定的扭曲分子组成的主族元素是已知的。我们在这里报告，第一个计算确认的4 n π芳香平面金属环的例子和他们的建设原则。83 π金属环庚三烯[Fe（CH）（6）H-2]的芳香稳定化能（ASE），具有四个双占据的It轨道和+0.80的HOMA值（参见图1）。苯=+1.0），NICS（0）值为-8.5（苯=-9.8，NICS =核独立化学位移），并且具有一个相转化，为+27.5 kcal mol（-1）（约为苯值的三分之二）。相反，未知的非莫比乌斯1，4-二金属苯[Fe-2（CH）（4）]H-4]]，也有8个π电子，没有相转化，ASE为-4.1 kcal mol（-1），NICS（0）=+15.6，表明反芳香性。利用磁性（NICS（0），NICS（1）（zz），Δ H-1）和几何（HOMA）芳香性标准，平面性，近等长的C C键长，成键分析（Wiberg键指数，NBO和NLMO分析），证实了所提出的Mobius芳香金属杂环的芳香性.波函数边界条件（周期与反周期）在化学中的作用进一步强调，相当于齐默尔曼的概念的节点宇称的Mobius/Huckel系统。
Mobius aromaticity, predicted by Edgar Heilbronner in 1964, is a stabilizing effect exhibited by 4n electron fully conjugated cyclic molecules (or transition states) with an odd number of orbital phase inversions. Although it has previously been suggested that this effect might also apply to planar metallacycles in which a transition metal employs a d orbital in delta-type binding mode, only very few examples of stable twisted molecules composed of main group elements are known. We report herein, the first computationally confirmed 4n pi aromatic planar metallacyclic examples and their building principles. Aromatic stabilization energy (ASE) of a 83 pi metalla-cycloheptatriene [Fe(CH)(6)H-2], with four doubly occupied It orbitals and a HOMA value of +0.80 (cf. benzene = +.1.0), an NICS(0) value of -8.5 (benzene = -9.8, NICS = nucleus independent chemical shift), and with one phase inversion, is +27.5 kcal mol(-1) (about two-thirds of the value for benzene). In contrast, an unknown non-Mobius 1,4-dimetallabenzene [Fe-2(CH)(4)]H-4]], also with 8 pi electrons, and without phase inversions, has an ASE of -4.1 kcal mol(-1) and a NICS(0) = +15.6, indicative of antiaromaticity. Aromaticity of the proposed Mobius aromatic metallacycles is confirmed by using magnetic (NICS(0), NICS(1)(zz), delta H-1) and geometric (HOMA) aromaticity criteria, planarity, and near equalized C C bond lengths, bonding analysis (Wiberg bond indices, NBO, and NLMO analysis). The role of wave function boundary conditions (periodic vs. antiperiodic) in chemistry is further stressed, being equivalent to Zimmerman's concept of nodal parity for Mobius/Huckel systems.