2,7-Di-tert-butyl-9,9′(10H,10′H)-spirobiacridine-10,10′-dioxyl as a ground triplet biradical: The role of tert-butylation

• Published in: Tetrahedron letters 2020-10, Vol.61 (43), p.152428, Article 152428
• Main Authors: Ichihashi, Kana, Kanetomo, Takuya, Enomoto, Masaya, Ishida, Takayuki
• Format: Article
• Language: English
• Subjects: Aminoxyl; Biradical; High-spin molecule; Intermolecular interaction; Spiro compound
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2020.152428

[Display omitted] •A new compound, doubly tert-butylated spirobiradical.•Intramolecular ferromagnetic interaction with 2 J/kB = +22.3(5) K.•Longer intermolecular O…O distances than those of non-tert-butylated compound.•tert-Butylation as a useful method to reduce the intermolecular interaction. The synthesis of a doubly tert-butylated spirobiradical, 2,7-di-tert-butyl-9,9′(10H,10′H)-spirobiacridine-10,10′-dioxyl is reported. The X-ray diffraction study clarified that the two dihydroacridine skeletons were fused at the sp3-carbon atom affording a cruciform structure. The frozen-solution electron spin resonance spectrum showed a typical zero-field-splitting pattern. The magnetic study revealed the presence of an intramolecular ferromagnetic interaction with 2J/kB = +22.3(5) K. The density-functional-theory calculation results are entirely consistent with the experimental results. After comparison with the known unsubstituted spirobiradical, we can conclude that tert-butylation is a useful method to reduce the intermolecular interaction without breaking the degeneracy of the singly occupied molecular orbitals.