Conjugated belts and nanorings with radially oriented p orbitals
Conjugated belts and nanorings with radially oriented p orbitals
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DOI：
10.1002/anie.200301671
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发表时间：
2003-01-01
影响因子：
16.6
通讯作者：
Scott, LT
中科院分区：
文献类型：
--
作者：
Scott, LT
自从量子力学诞生以来，p轨道的闭合环就吸引了化学家的想象力。[1]甚至在p轨道和离域π键作为概念出现之前，具有交替的单键和双键的原子环就已经引起了我们的科学前辈的兴趣和困惑。[1]我们中的许多人都知道凯库勒关于苯的结构的著名梦想的故事，[2]但迈向理论上感兴趣的新π系统的真实的第一步可以追溯到Willstätter在1911年具有里程碑意义的环辛四烯的合成，[3]苯的下一个高级同系物。半个世纪后，非苯型芳香族化合物的合成和研究在有机化学的发展中发挥了突出的作用。[1，4]最近，富勒烯的发现引发了一系列的活动，不仅涉及封闭的测地线聚芳烃和它们的内嵌复合物[5]，而且还涉及它们的开放测地线片段。[6]今天，一个迷人的新的共轭π系统正在形成;它包括共轭带和纳米环，p轨道径向取向，而不是垂直于大环的平面。首先出现的是[n]环碳，即交替的单键和三键的单环阵列（方案1a）。该家族的碳同素异形体的代表尚未被分离为稳定的实体;然而，这种大环被认为在从蒸发的碳形成富勒烯的机制中作为反应性中间体发挥关键作用。[7]由于Diederich及其同事的开创性合成，已经从定义明确的合成前体中产生了几种[n]环碳，并通过质谱法检测为瞬态物质。[7]由Herges及其同事[8a]报道的壮观的“picotube”（示意图1b）是第一个具有完全共轭径向取向p轨道的化合物，作为纯的，稳定的晶体物质被放入瓶中。这种紧张的烃可以正式地被视为仍然未知的母体[4]环对亚苯基的完全苯环化的衍生物，其是交替苯环和单环的单环阵列。
Closed loops of p orbitals have captured the imagination of chemists since the dawn of quantum mechanics.[1] Even before p orbitals and delocalized π bonding had emerged as concepts, rings of atoms with alternating single and double bonds already intrigued and confounded our scientific forefathers.[1] Many of us know the story of KekulØ's famous dream about the structure of benzene,[2] but the first real step toward new π systems of theoretical interest can be traced to Willstätter's landmark synthesis in 1911 of cyclooctatetraene,[3] the next higher homologue of benzene. Half a century later, the synthesis and study of nonbenzenoid aromatic compounds played a prominent role in the advancement of organic chemistry.[1, 4] More recently, the discovery of fullerenes sparked a flurry of activity, not only concerning the closed geodesic polyarenes and their endohedral complexes,[5] but also concerning their open geodesic fragments.[6] Today, a fascinating new class of conjugated π systems is taking shape; it comprises conjugated belts and nanorings with p orbitals oriented radially rather than perpendicular to the plane of the macrocycle. First on the scene were the [n] cyclocarbons, namely, monocyclic arrays of alternating single and triple bonds (Scheme 1a). No representative of this family of carbon allotropes has yet been isolated as a stable entity; however, such macrocycles are believed to play pivotal roles as reactive intermediates in the mechanism of formation of fullerenes from vaporized carbon.[7] Several [n] cyclocarbons have been generated from well-defined synthetic precursors and detected as transient species by mass spectrometry, thanks to the pioneering syntheses of Diederich and co-workers.[7]The spectacular “picotube” reported by Herges and co-workers [8a](Scheme1b) was the first compound with fully conjugated radially oriented p orbitals to be put in a bottle as a pure, stable crystalline substance. This strained hydrocarbon can be viewed formally as a fully benzannulated derivative of the still unknown parent [4] cycloparaphenylene, which is a monocyclic array of alternating benzene rings and single