Boron trihalide adducts of 1,1-bis(piperidinyl)ethylene. 13C and 11B nmr studies of a model system for β-carbon donation in enamine adducts

Abstract

1,1-Bis(piperidinyl)ethylene coordinates to the boron trihalides through the CH2 carbon, but the covalent adducts D.BX3 undergo rearrangement to give predominantly the ionic adducts D2BX2+.BX4−. Striking variations in 11B and 13C nmr peak widths support our proposed structures. The disappearance of peaks due to excessive broadening can be misleading in the interpretation of such systems.