A Robust Porphyrin‐Stabilized Triplet Carbon Diradical

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 tBuOK/O2. 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 (t1/2=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.