Octalenobisterphenylene and Its Diradical Dianionic Cyclodimer: Synthesis, Structural Analysis, and Properties

Octalenobisterphenylene 1 (also known as terphenylene dimer) was synthesized from 3,3',5,5'-tetraaryl-substituted biaryl by tert-butyllithium-mediated cyclization followed by oxidative coupling. This one-pot two-step protocol facilitated the successive formation of four four-membered and two eight-membered rings. Treatment of 1 with sodium metal, followed by crystallization from THF, yielded the remarkable diradical dianion [(1^•-)₂]^2-, where the two molecular halves are connected by four σ bonds. The cyclodimerization is driven by the pronounced reactivity and strain of the central six-membered ring within the [3]phenylene subunit. The structure and diradical nature of [(Na⁺)₂(1^•-)₂] were confirmed through X-ray crystallography, DFT computations, and ¹H NMR and ESR spectra. These investigations revealed that the two spins, one on each molecular half, exhibit minimal mutual interaction.