Metalation Control of Open‐Shell Character in meso‐meso Linked Porphyrin meso‐Oxy Radical Dimers

E-ISSN： 1521-3765|24|7|1528-1532

ISSN： 0947-6539

Source： CHEMISTRY - A EUROPEAN JOURNAL, Vol.24, Iss.7, 2018-02, pp. : 1528-1532

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Abstract

AbstractControl of open‐shell character of meso‐meso linked porphyrin meso‐oxy radical dimers has been demonstrated by core metalation. Namely, Ni^II‐porphyrin dimer 6Ni exhibits a clear ¹H NMR spectrum and a distorted but rather coplanar quinonoidal structure consisting of two ruffled porphyrin rings, in accordance with the previous report. Freebase dimer 6H₂ shows a similar quinonoidal structure in the solid state but displays slightly broader and temperature‐dependent ¹H NMR spectra, indicating a partial diradical character in solution that increases at high temperature. In sharp contrast, bis‐imidazole‐coordinated Zn^II‐porphyrin dimer 6ZnIm₂ exhibits a perpendicular structure consisting of two planar Zn^II‐porphyrins and has been characterized as a distinct open‐shell diradical on the basis of its non‐observable ¹H NMR signals, a clear ESR signal, and a characteristic absorption spectrum reaching about 1700 nm. Despite the distinct diradical character, 6ZnIm₂ is an extremely stable molecule.