One Carbon Ring Expansion of Bipyrrole to Bipyridine Enables Access to a π‐Extended, Non‐innocent, Corrole‐like Ligand

Diazatriphenylene was synthesized by a double, one-carbon-insertion reaction. Following elaboration, this key precursor allowed access to an unprecedented Ni^II-bipyricorrole radical and a cationic square planar complex upon one-electron oxidation.

Abstract

A π-extended, diaza-triphenylene embedded, mono-anionic corrole analogue and its Ni^II complex were synthesized from a diaza-triphenylene precursor, which was obtained from a double one-carbon insertion into a naphthobipyrrole diester. Following conversion to the corresponding activated diol and acid-catalyzed condensation with pyrrole, subsequent reaction with pentafluorobenzaldehyde afforded mono-anionic, π-extended bipyricorrole-like macrocycle. Attempted Ni^II insertion with Ni(OAc)₂ ⋅ 4H₂O resulted an ESR active, Ni^II bipyricorrole radical complex, which was converted to a stable cationic Ni^II complex upon treatment with [(Et₃O)⁺(SbCl₆)⁻]. Both complexes were characterized by ¹H and ¹³C NMR, UV/Vis spectroscopy and single crystal X-ray diffraction analysis. The Ni^II bipyricorrole radical complex is converted to a cationic Ni^II complex by single-electron reduction using cobaltocene. Both the cationic Ni^II complex and the radical Ni^II complex exhibited ligand-centered redox behavior, whereas the Ni^II remains in the +2 oxidation state.

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