Theoretical Design of Strong Neutral Radical-Boron Adducts: Trisubstituted Boranes as Potential Radical Scavengers

The conditions of formation of strong two-center one-electron bonds in neutral compounds are discussed. Both molecular orbital and valence bond analyses show that good candidates are adducts of radicals (.)AR(3) (A=C, Si, Ge) of low ionization energy (IE) with boranes BX3 of high electron affinity (EA). This is confirmed by ab initio calculations. The bond energy of adducts of B(CF3)(3) with various radicals ranges from 18 kcalmol(-1) for (CH3)-C-. to approximately 40 kcalmol(-1) for Me3Si., and a clear correlation with IE-EA difference is found. This allows one to expect B(CF3)(3), among other fluoroboranes, to be an efficient radical scavenger.