Formation of borata-alkene/iminium zwitterions by ynamine hydroboration

Abstract

The ynamine TMP–CC–CH₃ adds HB(C₆F₅)₂ to give the unsaturated C₂-bridged N/B FLP 5. Compound 5 shows the structural data indicating a marked participation of the zwitterionic mesomeric borata-alkene/iminium form. It splits dihydrogen at r.t. with Z- to E-isomerization at the central CC double bond. Hydroboration of the ynamine Me₃Si–CC–NⁱPr₂ with HB(C₆F₅)₂ yields a N/B FLP that shows a strongly distorted central CC double bond with a rotation of the planes of the substituent pairs at its ends by ca. 57°.