Expanded Azaporphyrins Consisting of Multiple BODIPY Units: Global Aromaticity and High Affinities Towards Alkali Metal Ions
Yutao Rao, Ling Xu, Mingbo Zhou, Bangshao Yin, Atsuhiro Osuka, Jianxin Song
Abstract
Abstract The one‐pot self‐coupling reaction of 3‐amino‐5‐bromo‐BODIPY 9 under Buchwald–Hartwig amination conditions gave nitrogen‐bridged cyclic BODIPY tetramer 10 , pentamer 11 , and hexamer 12 . Oxidation of 10 , 11 , and 12 in the presence of alkali metal ions provided 13 , 15 , and 16 , respectively, as the first examples of expanded azaporphyrins possessing more than six pyrrole rings. Curiously, the oxidation even in the absence of alkali metal ions gave the same complexes as a result of spontaneous complexation. 10 – 12 showed large association constants (10 4 –10 6 M −1 ) with K + and Na + , but the spontaneous complexations were not observed, indicating the extremely high affinities of 13 – 16 toward alkali metal ions, which can be ascribed to the multiple and effective ion–dipole interaction of the alkali metal ion with the negatively polarized F atoms of the BF 2 walls surrounding the cavity. Importantly, 13 , 14 , and 15 show diatropic ring currents as a result of global aromaticity.