Stable Radical Ion Pairs Induced by Single Electron Transfer: Frustrated Versus Nonfrustrated

Single electron transition reactions between amines (Lewis base) and B(C6F5)(3) (Lewis acid) in cooperation with benzoquinones gave rise to a frustrated radical pair 3 and a nonfrustrated radical pair 4. Both of them were isolated as stable crystals and studied by single-crystal X-ray diffraction, superconducting quantum interference device measurements, electron paramagnetic resonance, nuclear magnetic resonance, and UV-vis spectroscopy. Antiferromagnetic exchange coupling was observed among both 3 and 4. Radical anion and cation are basically separated in 3, while 4 featured a relatively strong anion-cation pi-pi stacking interaction. This work demonstrated that the Lewis acid coupled electron transfer is an efficient way to prepare stable radical ion pairs. [GRAPHICS] .