Stable hydrocarbon diradical, an analogue of trimethylenemethane

Hydrocarbon diradical 1, a new stable, 3-fold symmetric analogue of trimethylenemethane (TMM) with no heteroatom perturbation, is prepared and studied. Such diradicals should provide new building blocks for high-spin hydrocarbon polyradicals with very strong net ferromagnetic coupling. Magnetic studies (SQUID) and EPR spectroscopy indicate that 1 in tetrahydrofuran-d ₈ (THF-d₈) possesses a triplet (S = 1) ground state, with strong ferromagnetic coupling. After annealing at room temperature, the EPR spectra of 1 (∼0.02 M in frozen THF-d₈) consist of a single narrow resonance (ΔH_pp < 1 G), and intermolecular antiferromagnetic coupling is increased by 1 order of magnitude. This behavior is consistent with the presence of exchange narrowing, thus suggesting aggregation of 1 in THF-d₈. Blue solutions of 1 in THF-d₈ possess a strong UV-vis absorption band at λ_max ≈ 640 nm. Diradical 1 in THF-d₈ is stable (or persistent) at room temperature, with no detectable decomposition for at least 2 days.