Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712-1224 , United States.
Department of Chemistry , Yonsei University , Seoul 03722 , Korea.
J Am Chem Soc. 2018 Dec 5;140(48):16455-16459. doi: 10.1021/jacs.8b11158. Epub 2018 Nov 26.
A fully conjugated three-dimensional (3D) expanded carbaporphyrin (2) was prepared in a one-pot procedure that involves a [2+4] condensation reaction between a dibenzo[ g, p]chrysene-bearing tetrapyrrole precursor (1) and pentafluorobenzaldehyde, followed by oxidation. Single crystal X-ray diffraction analysis revealed that 2 possesses a cage-like structure consisting of four dipyrromethenes and two bridging dibenzo[ g, p]chrysene units. As prepared, 2 is nonaromatic as inferred from UV-vis-NIR and H NMR spectroscopy and a near-zero (-1.75) nucleus-independent chemical shift (NICS) value. In contrast, after protonation with trifluoroacetic acid (TFA), the cage gains global aromatic character as inferred from the large negative NICS value (-11.63) and diatropic ring current observed in the anisotropy of the induced current density (ACID) plot, as well as the ca. 8-fold increase in the excited state lifetime. In addition, the size of the cavity increases to ca. 143 Å upon protonation as deduced from a single crystal X-ray diffraction analysis. To our knowledge, this is the largest carbaporphyrin prepared to date and the first with a fully conjugated 3D cage structure whose size and electronic features may be tuned through protonation.
一种完全共轭的三维（3D）扩展碳卟啉（2）是通过一锅法制备的，该方法涉及含有二苯并[g，p]色烯的四吡咯前体（1）与五氟苯甲醛之间的[2+4]缩合反应，然后进行氧化。单晶 X 射线衍射分析表明，2 具有笼状结构，由四个二吡咯甲烷和两个桥连的二苯并[g，p]色烯单元组成。如制备的那样，2 是非芳香的，这可以从紫外可见近红外和 H NMR 光谱以及接近零（-1.75）核独立化学位移（NICS）值推断得出。相比之下，在用三氟乙酸（TFA）质子化后，笼状结构获得了全局芳香性，这可以从大的负 NICS 值（-11.63）和在各向异性诱导电流密度（ACID）图中观察到的反磁环电流推断得出，以及在激发态寿命增加约 8 倍。此外，从单晶 X 射线衍射分析推断，质子化后空腔的尺寸增加到约 143Å。据我们所知，这是迄今为止制备的最大的碳卟啉，也是第一个具有完全共轭的 3D 笼状结构的碳卟啉，其大小和电子特性可以通过质子化来调节。
