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首页> 外文期刊>Crystal growth & design >Influence of Fluorine Substitution on the Unusual Solid-State [2+2] Photo-Cycloaddition Reaction between an Olefin and an Aromatic Ring
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Influence of Fluorine Substitution on the Unusual Solid-State [2+2] Photo-Cycloaddition Reaction between an Olefin and an Aromatic Ring

机译：氟取代对烯烃与芳环之间异常固态[2 + 2]光环加成反应的影响

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Solid-state [2 + 2] photo-cycloaddition reactions observed so far were exclusively between a pair of olefin bonds. Usually when the phenylolefin bonds have been closely aligned, they were found to be either photoinert or sliding of molecules takes place for [2 + 2] cycloaddition reaction between olefins in the solid state, although intramolecular phenylolefin reactions are well-known in solution. In the crystal structure of [Zn-2(ptol)(4)(4spy)(2)] (ptol = para-toluate), the neighboring 4-styrylpyridine (4spy) ligands are organized in a head-to-tail manner. On one side of the complex in the crystal structure, the olefin bonds in the 4spy pairs are perfectly aligned to undergo cycloaddition reaction, but on the other side, the olefin bond pairs are slightly offset and found to be photoinert at 223 K forming only a dimer in single crystals. The sliding of 4spy groups has been restricted by the steric hindrance of the adjacent methyl group of the ptol ligands. A similar packing of 2-fluoro-4'-styrylpyridine (2F-4spy) pairs was found in [Zn-2(ptol)(4)(2F-4spy)(2)]. Again, normal cycloaddition reaction occurs on one side of the 2F-4spy ligand pairs, whereas the second offset 2F-4spy ligand pairs undergo a rare [2 + 2] cycloaddition reaction between the fluorophenyl group and olefin bond resulting in the formation of a one-dimensional coordination polymers containing a bicyclic product in a quantitative yield. The bicyclic ring in the photoproduct can be thermally cleaved back to olefin and phenyl groups. These observations have been confirmed by single-crystal X-ray crystallography, H-1 NMR, and F-19 NMR studies. Density functional theory calculations were performed to elucidate the nature of the interactions between the fluorophenyl and olefin groups. The greater reduction of aromaticity of 2F-4spy in the excited singlet state compared to the 4spy system may explain the observed reactivity difference between the two systems. The improved reactivity in 2F-4spy may also be attributed to the fact that the olefinphenyl distance is shorter in 2F-4spy than in 4spy (3.63 versus 3.69 angstrom). This solid state phenylolefin photodimerization helps to pave the way for making new bicyclic derivatives.
机译：迄今为止观察到的固态[2 + 2]光环加成反应仅在一对烯烃键之间。通常，当苯烯烃键紧密排列时，尽管在溶液中分子内苯烯烃反应是众所周知的，但发现它们对于固态烯烃之间的[2 + 2]环加成反应是分子发生光惰性或滑动。在[Zn-2（ptol）（4）（4spy）（2）]（ptol =对甲苯甲酸酯）的晶体结构中，相邻的4-苯乙烯基吡啶（4spy）配体以从头到尾的方式组织。在晶体结构的配合物的一侧，4spy对中的烯烃键完全对齐以进行环加成反应，但在另一侧，烯烃键对略有偏移，并发现在223 K下呈光惰性，仅形成一个单晶中的二聚体。 4spy基团的滑动受到ptol配体相邻甲基的空间位阻的限制。在[Zn-2（ptol）（4）（2F-4spy）（2）]中发现了类似的2-氟-4'-苯乙烯基吡啶（2F-4spy）对包装。同样，正常的环加成反应在2F-4spy配体对的一侧发生，而第二个偏移的2F-4spy配体对在氟苯基和烯烃键之间进行罕见的[2 + 2]环加成反应，从而形成一个定量收率的含双环产物的三维配位聚合物。可以将光产物中的双环热裂解成烯烃和苯基。这些观察已通过单晶X射线晶体学，H-1 NMR和F-19 NMR研究得到证实。进行密度泛函理论计算以阐明氟苯基和烯烃基团之间相互作用的性质。与4spy系统相比，在激发单重态下2F-4spy的芳香性降低程度更大，可以解释这两个系统之间观察到的反应性差异。在2F-4spy中提高的反应性还可能归因于以下事实：2F-4spy中的烯烃苯基距离比4spy中的烯烃苯基距离短（3.63对3.69埃）。固态苯烯烃光二聚化有助于为制备新的双环衍生物铺平道路。

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