Possible methods of formation of chelated fluoroboron cations (DD)BF 2 + and (DD)BFX +, where DD is 2,2′-bipyridine (bpy), 1,10-phenanthroline (1,10-phen), 2,2′,6′,2″-terpyridine (terpy) and 1,8-bis(dimethylamino)naphthalene (DMAN, ‘proton sponge’), have been investigated, primarily by 19F and 11B NMR and fast atom bombardment mass spectrometry. The most successful method involves displacement of weakly basic isoxazole (ISOX) and heavy halide ion from ISOX·BF 2X and ISOX·BFX 2 (X=Cl, Br). Displacement of pyridine from py·BF 2Cl and py·BFCl 2 is less effective because pyridine, more basic than isoxazole, competes with the chelating donor in forming fluoroboron cations when displaced from its adducts. 1,10-Phen, terpy and DMAN form (DD)BF 2 +·BF 4 − when reacted with Et 2O·BF 3 or with ISOX·BF 3 under our conditions, but bpy does not. None of these chelating ligands can displace pyridine from (py) 2BF 2 +·PF 6 − under conditions that are effective with tertiary-amine chelating donors. (1,10-Phen)BF 2 + but not the other (DD)BF 2 + species is attacked by dimethylsulfoxide (DMSO), to form first (DMSO) 2BF 2 + and finally DMSO·BF 3.