Template-Directed Synthesis of Cyclocarbon Catenanes

该项目属于EPSRC物理科学研究领域，主题为合成超分子化学。除氢外，碳比其他任何元素形成的分子化合物都多。在过去的25年里，新的碳同素异形体的发现导致了化学和物理领域大量应用的新技术。然而，唯一完全由碳组成的分子是富勒烯（C60， C70等）。该项目旨在创造一类新的全碳环分子（环碳），这是一种完全基于sp杂化碳原子的难以捉摸的碳的同素异形体。一般来说，聚烯烃的稳定性随着相邻炔单元数目的增加而降低。有两种策略可用于增加线性多炔的稳定性：(i)使用大块的末端取代基和；（ii）将链穿过大环进行超分子包封。以前合成环碳化合物的尝试涉及使用精心设计的构建块，称为掩膜炔当量（MAEs），在合成过程中增加链的稳定性，并且可以在应用适当的刺激后“揭膜”以产生最终的聚烯烃。最近，Anderson小组报道了通过活性金属模板策略形成的聚环轮烷，其中基于菲罗啉的大环的Cu(I)配合物通过大环的空腔指导两个末端低聚炔的偶联。发现由于螺纹大环的保护作用，轮烷具有增强的热稳定性。该项目的主要目的是开发一种新的基于菲罗啉的MAE，并通过被动金属模板合成策略将其用于合成聚乙烯链烷。一个大环将基于邻菲罗啉部分，而另一个将包含一个基于邻菲罗啉的MAE。基于邻菲罗啉的MAE不仅可以掩盖炔烃骨架，而且可以同时用作可切割的超分子支架。这为涉及被动而非主动金属模板的联锁化合物提供了一种无迹合成途径。Williamson醚合成应该提供一种可靠的途径来耦合构建块，并且众所周知与类似的cu配合物兼容。或者，使用Cu(I)介导的氧化炔均偶联可能更优雅，化学反应应该是相容的。由于光化学的不同，与基于菲菲啉的MAEs相比，这些新的基于菲菲啉的MAEs可能具有优越的揭膜特性，从而产生比以前报道的更有效的长链多炔途径。目标环碳链烷将在溶液中使用不同的光谱技术进行研究，并在固体状态下通过x射线晶体学进行表征。物理研究将提供对环碳电子结构的详细了解。这些将包括紫外-可见-近红外吸收，荧光，红外和拉曼光谱和电化学。时间分辨红外和拉曼研究也将在卢瑟福-阿普尔顿实验室的中央激光设施进行，以获得有关电子激发态的振动行为和几何形状的信息。综上所述，本文提出了一种新的MAE，它可以作为机械连锁分子合成的支架。这种方法有许多潜在的应用：完全无迹合成联锁化合物（当使用活性金属模板合成与可切割结合位点结合时）；聚炔更紧密的包封；基于聚炔的互锁化合物以及具有可切割骨架的大环。

This project falls within the EPSRC Physical Sciences research area, in the theme of Synthetic Supramolecular Chemistry. Carbon forms more molecular compounds than any other element except hydrogen. During the last 25 years, the discovery of new carbon allotropes has led to new technologies with a multitude of applications in chemistry and physics. However, the only molecules consisting entirely of carbon that have been properly characterised are the fullerenes (C60, C70, etc.). This project aims to create a new class of all-carbon ring molecules (cyclocarbons), an elusive allotrope of carbon based entirely on sp-hybridised carbon atoms. In general, polyyne stability decreases with increasing number of adjacent alkyne units. Two strategies are available for increasing the stability of linear polyynes: (i) the use of bulky terminal substituents and; (ii) supramolecular encapsulation by threading the chain through macrocycles. Previous attempts towards the synthesis of cyclocarbons involved the use of carefully designed building blocks, known as masked alkyne equivalents (MAEs), that increase the stability of the chain during its synthesis, and can be 'unmasked' to yield the final polyyne upon application of a suitable stimulus. Recently, the Anderson group reported polyyne rotaxanes formed through an active metal template strategy, where a Cu(I) complex of a phenanthroline-based macrocycle directs the coupling of two terminal oligoynes through the cavity of the macrocycle. The rotaxanes were found to exhibit enhanced thermal stability due to the protective effect of the threaded macrocycle. The principal aims of this project are to develop a new phenanthroline-based MAE, and to use it to synthesise polyyne catenanes via a passive metal templated synthetic strategy. One macrocycle will be based on the phenanthroline moiety, while the other will contain a phenanthroline-based MAE. Using a MAE based on phenanthroline not only masks the alkyne backbone, but can also simultaneously be used as a cleavable supramolecular scaffold. This affords a traceless synthetic route to the interlocked compound involving a passive, rather than active, metal templates. Williamson ether synthesis should provide a reliable route to coupling the building blocks and is well known to be compatible with similar Cu-complexes. Alternatively, the use of Cu(I)-mediated oxidative alkyne homocoupling may be more elegant and the chemistry should be compatible. Owing to the different photochemistry, compared to phenanthrene-based MAEs, these novel phenanthroline-based MAEs may possess superior unmasking properties, thus yielding more efficient pathways to long chain polyynes than previously reported. The target cyclocarbon catenanes will be studied in solution using diverse spectroscopic techniques and characterised in the solid state by X-ray crystallography. Physical studies will provide detailed understanding of the electronic structures of cyclocarbons. These will include UV-vis-NIR absorption, fluorescence, IR and Raman spectroscopy and electrochemistry. Time-resolved IR and Raman studies will also be carried out at the Central Laser Facility, Rutherford-Appleton Laboratory, to gain information on the vibrational behaviour and geometry of electronic excited states. In summary, a new MAE is proposed that can be used as a scaffold for the synthesis of mechanically interlocked molecules. This methodology has many potential applications: completely traceless syntheses of interlocked compounds (when using active metal template synthesis in combination with cleavable binding sites); tighter encapsulation of polyynes; interlocked compounds based on polyynes as well as macrocycles with cleavable backbones.