A Robust Porphyrin‐Stabilized Triplet Carbon Diradical
Kaisheng Wang, Pingting Liu, Fenni Zhang, Ling Xu, Mingbo Zhou, Akito Nakai, Kenichi Kato, Ko Furukawa, Takayuki Tanaka, Atsuhiro Osuka, Jianxin Song
Abstract
Abstract The synthesis of robust high‐spin carbon radicals is an important topic in organic chemistry. Toward this end, several porphyrin‐stabilized radicals have been systematically explored. A singly naphthalene‐fused porphyrin radical was synthesized by a reaction sequence consisting of a Suzuki–Miyaura coupling of β‐borylated porphyrin with 2‐bromobenzaldehyde, addition of mesityl Grignard reagent, intramolecular Friedel–Crafts alkylation, and final oxidation with DDQ or t BuOK/O 2 . This strategy was also used to synthesize doubly naphthalene‐fused porphyrins and syn ‐ and anti ‐fused‐anthracene‐bridged porphyrin dimers. While singly naphthalene‐fused porphyrin radical has been shown to be a stable monoradical, doubly naphthalene‐fused porphyrins and anti ‐fused‐anthracene‐bridged porphyrin dimers have been shown to be closed‐shell molecules. Finally, the syn ‐dimer was characterized as a surprisingly stable radical ( t 1/2 =28 days under ambient air and at 80 °C) that is storable for more than several months, despite its high‐spin triplet ground‐state carbon diradical.