Synthetic and Mechanistic Studies of Strained Heterocycle Opening Reactions Mediated by Zirconium(IV) Imido Complexes

The reactions of the bis(cyclopentadienyl)(tert-butylimido)zirconium complex (Cp2ZrN-t-Bu)(THF) (1) with epoxides, aziridines, and episulfides were investigated. Heterocycles without accessible β-hydrogens undergo insertion/protonation of the C−X bond to produce 1,2-amino alcohols (X = O) and 1,2-diamines (X = NR), whereas heterocycles with accessible β-hydrogens undergo elimination/protonation to produce allylic alcohols (X = O) and allylic sulfides (X = S). Mechanistic investigations support a stepwise pathway with zwitterionic intermediates for the first reaction class and a concerted pathway for the second reaction class. Additionally, the feasibility of chirality transfer from the planar-chiral ebthi (ebthi = ethylenebis(tetrahydroindenyl)) ligand was demonstrated with a chiral analogue, (ebthi)ZrNAr(THF) (Ar = 2,6-dimethylphenyl), 2, through the diastereoselective ring opening of meso epoxides.