A Stable Trimethylenemethane Triplet Diradical Based on a Trimeric Porphyrin Fused π-System

Kenichi Kato; Ko Furukawa; Atsuhiro Osuka

doi:10.1002/anie.201804644

A Stable Trimethylenemethane Triplet Diradical Based on a Trimeric Porphyrin Fused π-System

Angew Chem Int Ed Engl. 2018 Jul 20;57(30):9491-9494. doi: 10.1002/anie.201804644. Epub 2018 Jun 21.

Authors

Kenichi Kato¹, Ko Furukawa², Atsuhiro Osuka¹

Affiliations

¹ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku Kyoto, 606-8502, Japan.
² Center for Instrumental Analysis, Niigata University, Nishi-ku, Niigata, 950-2181, Japan.

PMID: 29858542
DOI: 10.1002/anie.201804644

Abstract

Trimethylenemethane (TMM) diradical is the simplest non-Kekulé non-disjoint molecule with the triplet ground state (ΔE_ST =+16.1 kcal mol^-1 ) and is extremely reactive. It is a challenge to design and synthesize a stable TMM diradical with key properties, such as actual aliphatic TMM diradical centers and the triplet ground state with a large positive ΔE_ST value, since such species provide detailed information on the electronic structure of TMM diradical. Herein we report a TMM derivative, in which the TMM segment is fused with three Ni^II meso-triarylporphyrins, that satisfies the above criteria. The diradical shows delocalized spin density on the propeller-like porphyrin π-network and the triplet ground state owing to the strong ferromagnetic interaction. Despite the apparent TMM structure, the diradical can be handled under ambient conditions and can be stored for months in the solid state, thus allowing its X-ray diffraction structural analysis.

Keywords: diradicals; ferromagnetic interactions; fused-ring systems; porphyrinoids; trimethylenemethane.