Chelated fluoroboron cations II. Synthesis and NMR studies involving aromatic chelating ligands

Possible methods of formation of chelated fluoroboron cations (DD)BF2+ 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 (D MAN, 'proton sponge'), have been investigated, primarily by F-19 and B-11 N MR and fast atom bombardment mass spectrometry. The most successful method involves displacement of weakly basic isoxazole (ISOX) and heavy halide ion from ISOX . BF2X and ISOX . BFX2 (X = Cl, Br). Displacement of pyridine fr om py . BF2Cl and py . BFCl2 is less effective because pyridine, more basic than isoxazole, competes with the chelating donor in forming fluoroboron c ations when displaced from its adducts. 1,10-Phen, terpy and DMAN form (DD) BF2+ . BF4- when reacted with Et2O . BF3 or with ISOX . BF3 under our condi tions, but bpy does not. None of these chelating ligands can displace pyrid ine from (py)(2)BF2+ . PF6- under conditions that are effective with tertia ry-amine chelating donors. (1,10-Phen)BF2+ but not the other (DD)BF2+ speci es is attacked by dimethylsulfoxide (DMSO), to form first (DMSO)(2)BF2+ and finally DMSO . BF3. (C) 2000 Elsevier Science Ltd All rights reserved.