Synthesis, structure and properties of nitronyl nitroxide diradicals with fused‐thiophene couplers

Abstract

AbstractFunctionalized diradicals are widely used in chemistry, physics, biology and material sciences because of their inherently high reactivity and magnetic activity, but the synthesis of planar diradical molecules is still a challenge. This paper describes the effective synthesis and properties of diradicals in which nitronyl nitroxide fragments and a fused‐thiophene bridge are almost coplanar. The diradicals DR1, DR2, DR4 were prepared in high yield by palladium‐catalyzed cross‐coupling of the (nitronyl nitroxide‐2‐ide)(triphenylphosphin)gold complex with 2,5‐diiodothieno[2,3‐b]thiophene, 2,5‐diiodothieno[3,2‐b]thiophene or 2,6‐diiododithieno[3,2‐b:2′,3′‐d]thiophene correspondingly. The torsion angles between planes of the nitronyl nitroxide fragments and fused‐thiophene systems lie in the range 2.6–8.5°. The planarity of DR2 and DR4 makes the Kekulé‐type coupler units effective bridges to transmit magnetic interactions by a spin polarization mechanism. According to the magnetic susceptibility measurements, supported by density functional theory calculations, the singlet–triplet energy splitting (2 J/kB) is −130 K for DR2 and close to −80 K for DR4. The singlet diradicals DR2 and DR4 are stable and demonstrate two one‐electron reversible electrochemical oxidation peaks and two‐electron quasi‐reversible reduction peaks resulting in the formation of the corresponding bis(oxoammonium) dication or bis(aminooxidanide) dianion. Copyright © 2016 John Wiley & Sons, Ltd.