Work

Lanthanum β‐Tetracyanoporphyrin Double‐Decker Complexes: Four‐Electron Reduction and Slow Ligand Rotation

Year: 2026

Type: article

Abstract: ABSTRACT Porphyrin double‐decker complexes undergo multiple redox processes, but accessing multiply reduced states remains challenging owing to the inherently high LUMO energies of the porphyrin ligands. Here, we report the synthesis and characterization of a lanthanum(III) β‐tetracyanoporphyrin double‐decker complex with an unprecedented four‐electron reduction capacity. Strategically incorporating electron‐withdrawing cyano groups at the β‐positions increases the reduction potentials by approximately 1.3 V compared to those of the tetraphenylporphyrin analog, enabling reduction at –0.78, –1.00, –1.42, and –1.66 V (vs. ferrocene/ferrocenium) in DMSO. Single‐crystal x‐ray diffraction reveals that the complex adopts the monoanion form with an azimuthal rotation angle of 33° and pronounced dome‐shaped distortion caused by steric interactions between the meso ‐phenyl groups and β‐cyano substituents. UV‐Vis/NIR spectroelectrochemistry and chemical reduction using cobaltocene confirm the formation of multiply reduced species, whereas density functional theory calculations reveal that the trianion exhibits a significant diradical character. Variable‐temperature NMR studies indicate unusually slow ligand rotation with a high activation barrier ( ΔG ‡ = 17.8 kcal mol – 1 at 298 K), which computational analysis primarily attributes to steric rather than electronic effects. This study establishes a rational design strategy for use in accessing multiply reduced porphyrin double‐decker complexes with potential for application in molecular electronics and redox‐switchable devices.

Source: Chemistry - A European Journal

DOI: 10.1002/chem.70894

Authors: Haruna Sugimura, Wataru Imanaka, Ken‐ichi Yamashita

Institution: The University of Osaka

Language: English

Topic: Porphyrin and Phthalocyanine Chemistry

Subfield: Materials Chemistry

Field: Materials Science

Domain: Physical Sciences

Open Access status: green

Funders: Iwatani Naoji Foundation, Japan Science Society, Iketani Science and Technology Foundation, Japan Society for the Promotion of Science

Awards: G1535933717, Systematic luminescence characterization of antiaromatic compounds aimed at the design of novel rare-earth-like luminescent dyes, Synthesis of face-to-face oligomers of antiaromatic compounds and elucidation of their aromaticity, 反芳香族性を設計指針とした可視・近赤外域で多重発光を示す有機発光色素の創出と新奇機能の探索, G891380399