A Robust Triplet Porphyrin-Stabilized Carbon Diradical

Synthesis of robust high-spin carbon radicals is an important topic in organic chemistry. Toward this end, we have systematically explored several porphyrin-stabilized radicals. Singly naphthalene-fused porphyrin radical was synthesized by a reaction sequence consisting of 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 has been also used to the synthesis of 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 mono radical, doubly naphthalene-fused porphyrins and anti -fused-anthracene-bridged porphyrin dimers have been shown to be closed shell molecules. Finally, the syn -dimer has been characterized as a surprisingly stable radical ( t 1/2 = 28 days under ambient air and at 80 oC conditions) that can be storable more than several months under ambient conditions, despite its high-spin triplet ground state carbon diradical.