Formation of mixed-ligand fluoroboron cations involving C=N donors. A F-19and B-11 NMR study

Mixed-donor difluoroboron and chlorofluoroboron cations DD'BF2+ and DD'BFCl + involving at least one C=N donor molecule can be formed by Cl- displaceme nt from the mixed boron trihalide adducts D . BF2Cl and D . BFCl2, provided that the steric hindrance of D' and especially D is not too great. The DD' BF2+ cations can also be formed by selective displacement of one donor mole cule in certain D2BF2+ cations, present in acetone as their PF6- salts, all owing isolation of the first salt of a mixed-donor difluoroboron cation, (q uinuclidine)(pyridine)BF2+. PF6-. In less favourable cases, however, either no reaction occurs or the reaction continues to give D-2'BF2+. Reactivitie s and F-19 and B-11 NMR parameters of mixed boron trihalide adducts and flu oroboron cations of a number of C=N donors are reported.