Crystalline Neutral Boraolympicenyl Radicals with Electronic Regulation through Boron-Doping Sites

Incorporating heteroatoms into hydrocarbon PAH radicals offers a promising strategy to modulate their electronic structures, drawing significant experimental and theoretical research interest. In this work, three isolable neutral boraolympicenyl radicals 1a–c, each with single boron doping at the 3-, 5-, and 6-positions, respectively, have been synthesized and characterized by single-crystal X-ray diffraction, cyclic voltammetry (CV), and electron paramagnetic resonance (EPR) spectroscopy. The spin density of 1a–c is primarily localized on the central pentacyclic framework, exhibiting an uneven spin distribution with the largest spin located at the 6-position, revealing that the boron center notably influences the spin density. Moreover, their unique redox properties have been thoroughly investigated. The oxidation of 1a–c resulted in the formation of the corresponding fluorescent cationic species 4a–c, which exhibits a reversible oxidation process, as further supported by the CV measurements. Meanwhile, the reduction of 1a–c led to the activation of carbene ligands to generate unprecedented anionic boraolympicenyl radicals 5a–c. Furthermore, reactions of 1a–b with half an equivalent of Ph₂Se₂ selectively afforded the boron-centered adducts 6a–b, consistent with the relatively large spin density distribution on the boron center.