Formation and Characterization of Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph: (E)- and (Z)-[EtPhN+=CHCH2-B(C6F5)3

Abstract

The stoichiometric reaction of B(C6F5)3 and NEt2Ph I, at room temperature, in an aromatic solvent, has been investigated by 1D and 2D NMR spectroscopy (1H, 11B,13C, 15N and 19F). No Et2PhN·B(C6F5)3 adduct was observed. An equilibrium between free B(C6F5)3, NEt2Ph, [HB(C6F5)3]−(HNEt2Ph)+ and two zwitterionic stereoisomers (E)- and (Z)-[EtPhN+=CH-CH2-B−(C6F5)3] (30%) in an E/Z ratio of 3:2 was observed. Whatever the protic reagent Z-OH [Z = H, SiPh3, (c-C5H9)7O12Si8, or silanol group of silica], all the equilibria involved in solutions of I are quantitatively displaced towards the ionic form [Z-O-B(C6F5)3]−(HNEt2Ph)+. In the case of dimethylaniline, besides free B(C6F5)3 and Me2NPh, the 1:1 adduct (C6F5)3B·NMe2Ph and an iminium salt [PhCH3N=CH2]+[HB(C6F5)3]− have been identified. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)