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 <b>1a-c</b>, 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 <b>1a</b>-<b>c</b> 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 <b>1a</b>-<b>c</b> resulted in the formation of the corresponding fluorescent cationic species <b>4a</b>-<b>c</b>, which exhibits a reversible oxidation process, as further supported by the CV measurements. Meanwhile, the reduction of <b>1a</b>-<b>c</b> led to the activation of carbene ligands to generate unprecedented anionic boraolympicenyl radicals <b>5a</b>-<b>c</b>. Furthermore, reactions of <b>1a</b>-<b>b</b> with half an equivalent of Ph₂Se₂ selectively afforded the boron-centered adducts <b>6a</b>-<b>b</b>, consistent with the relatively large spin density distribution on the boron center.