Triketiminate bis(borohydride) complexes of rare-earth metals [(2,6-Me2C6H3N=CMe)2C(2,6-Me2C6H3N=CBut)]Ln(BH4)2(THF)2 (Ln = Y, Nd): synthesis, structure, and catalytic activity in polymerization of rac-lactide, ε-caprolactone, and isoprene

Resumo

A new triketimine (2,6-Me₂C₆H₃N=CMe)₂CH(2,6-Me₂C₆H₃N=CBu^t) (1) was synthesized by the reaction of imidoyl chloride 2,6-Me₂C₆H₃N=CClBu^t with lithium diketiminate (2,6-Me₂C₆H₃N=CMe)₂CHLi. In the crystalline state, compound 1 exists in the diimineenamine form; in solution, in the triimine form. The metalation of triketimine 1 with n-butyllithium in THF at 0 °C produced lithium triketiminate [(2,6-Me₂C₆H₃N=CMe)₂C(2,6-Me₂C₆H₃N=CBu^t)]Li(THF)₂ (2). The metathesis reactions of Ln(BH₄)₃(THF)₃ (Ln = Y, Nd) with compound 2 (1: 1 molar ratio, THF) gave the neutral triketiminate bis(borohydride) complexes [(2,6-Me₂C₆H₃N=CMe)₂C(2,6-Me₂C₆H₃N=CBu^t)]Ln(BH₄)₂(THF)₂ (Ln = Y (3), Nd (4)). As opposed to the complexes with neutral triketimine, the monoanionic triketiminate ligand is coordinated to Li and Y or Nd cations in a bidentate fashion. Complexes 3 and 4 catalyze the polymerization of rac-lactide and ε-caprolactone; in combination with [Ph₃C][B(C₆F₅)₄] and AlBu₃ⁱ (1 : 1 : 10 molar ratio), these compounds exhibit catalytic activity in the polymerization of isoprene.