BIII subporphyrins are the legitimate ring-contracted porphyrins consisting of three pyrroles and three meso-carbons and their chemistry has been extensively developed since the first synthesis in 2006. However, subporphyrin free bases have never been synthesized, despite tremendous attempts to remove the BIII ion. Here we report that Suzuki–Miyaura coupling between α,α′-diborylated tripyrrane 1 and tetrabromide 5 gave subporphyrin free bases 6, 6 A, and free base dimer 7 in 6 %, 4 %, and 2 % yields as the first examples. Subporphyrin free bases exhibit curved bowl-like structures and distinct 14π-aromaticity. Steady-state and time-resolved spectroscopy revealed that the excited-state behaviors of the subporphyrin free bases are comparable with those of the corresponding BIII subporphyrins. Rotational relaxation processes in the excited states have been revealed, which enhance the electronic interactions with the meso-aryl substituents and between the two subporphyrins.
|Journal||Angewandte Chemie - International Edition|
|Publication status||Published - 2022 Dec 12|
Bibliographical noteFunding Information:
The work is supported by the National Natural Science Foundation of China (Grant Nos. 22071052, 21772036, 21702057, 21602058), Science and Technology Planning Project of Hunan Province (2018TP1017), Science and Technology Innovation Program of Hunan Province (2021RC4059). The work is also supported by a National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (Grant 2021R1A2C3006308, 2021R1C1C1013828 and 2021R1A6A1A03039503).
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