Dicationic Boron Derivatives of Schlenk's and Thiele's Hydrocarbon

In recent years, neutral NHC-stabilized boryl radicals have been investigated as reactive species in various organic transformations. However, cationic boron radicals have been significantly less explored. In addition, boron-centered open-shell species with S > 1/2 have emerged as attractive synthetic targets. In this study, we provide a synthetic route to an NHC-stabilized boryl radical cation as a salt of the weakly coordinating [Al(OR^F)₄]^- (R^F = C(CF₃)₃) anion. The synthetic procedure was extended to dicationic diboron derivatives of Schlenk's and Thiele's hydrocarbons with meta- and para-phenylene coupling units between the spin centers. While most known isolable boron biradicals have a singlet ground-state with a thermally accessible triplet state, the boron version of Schlenk's hydrocarbon occupies a ground-state triplet spin-state, as shown by combined electron paramagnetic resonance spectroscopy and density functional theory studies. Furthermore, initial reactivity studies of the dications with elemental sulfur and diphenyldiselenide are presented.