Cyclo[6]pyridine[6]pyrrole: A Dynamic, Twisted Macrocycle with No Meso Bridges

A large porphyrin analogue, cyclo[6]­pyridine[6]­pyrrole,
containing
no meso bridging atoms, has been synthesized through Suzuki coupling.
In its neutral form, this macrocycle exists as a mixture of two figure-eight
conformers that undergo fast exchange in less polar solvents. Upon
protonation, the dynamic twist can be transformed into species that
adopt a ruffled planar structure or a figure-eight shape depending
on the extent of protonation and counteranions. Conversion to a bisboron
difluoride complex via deprotonation with NaH and treatment with BF3 acts to lock the macrocycle into a figure-eight conformation.
The various forms of cyclo[6]­pyridine[6]­pyrrole are characterized
by distinct NMR, X-ray crystallographic, and spectroscopic features.

一种不含中位桥接原子的较大环状卟啉衍生物，即环[6]吡啶[6]吡咯，通过 Suzuki 偶联反应成功合成。在它的中性形态下，该大环以两种八字形的构象混合存在，并在非极性溶剂中迅速交换。在质子化过程中，动态扭曲可转化为呈现皱褶平面结构或八字形结构的物种，其形态取决于质子化程度及反离子的种类。通过使用NaH脱质子化以及BF3处理，转化为双硼二氟化物复合物，这一过程将大环锁定在八字形构象中。环[6]吡啶[6]吡咯的多种形态均表现出独特的核磁共振、X射线晶体学和光谱学特征。