The coordination chemistry of (py)2BF2+ and related difluoroboron cations

The substitution and decomposition reactions of the difluorobis(pyridine)boron(III) cation, and of several substituted pyridine and other difluoroboron cations (D)2BF2+, are explored. Donor molecule displacement is greatly accelerated by the presence of electron-withdrawing meta and para pyridine substituents in (substituted pyridine)2BF2+ cations, and by electron-donating substituents on pyridine when the substituted pyridine is the attacking species. Increased steric hindrance of D in D2BF2+, and of the attacking base D′, slows or prevents displacement of D by D′. (py)2BF2+·PF6− undergoes slow decomposition in acetone, giving initially py·BF3 and finally py·H+·BF4− as the major fluoroboron species. A second decomposition pathway, giving rise to BF3OH− and several additional fluorine-containing products, is favoured by the presence of strong bases such as amidines and by the presence of NH and OH bonds. Increased susceptibility to ligand displacement facilitates the synthesis of new fluoroboron cations, but also increases the susceptibility to decomposition.