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.