An Olefin Radical Based Thiele's Hydrocarbon Derivative and Macrocyclic Tetraradical

A persistent Thiele's hydrocarbon derivative, containing two five-membered dioxoborocyclic monoradical units bridged by a p-phenylene moiety, was generated. It exhibits an open-shell singlet ground state with a large singlet-triplet energy gap. A macrocyclic molecule composed of two units of the Thiele's hydrocarbon derivative was also prepared. The macrocyclic molecule possesses an open-shell singlet ground state but with considerable tetraradical character. The diradical and tetraradical compounds can be viewed as a zwitterionic species containing olefin radical cations. These newly formed compounds are stable in both the solid state and solution under an inert atmosphere for several days. They have been fully investigated by single-crystal X-ray diffraction, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and UV-vis spectroscopy, and SQUID measurements, as well as theoretical calculations.