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.