Synthesis, Characterization, and Reactivity of “NONO” Calix[4]arene Zirconium Complexes

Abstract A series of zirconium(IV) complexes with a bis(benzylamino)-p-tert-butylcalix[4]arene ligand, LZrX2, were synthesized and structurally characterized via single-crystal X-ray diffraction and NMR. The obtained complexes proved to be unexpectedly susceptible to protonation because of the low acidity of the ligand. A high flexibility of the calix[4]arene ligand allowed either distorted-octahedral coordination or coordination numbers greater than 6. Complexes with different ancillary ligands X showed modest activity and poor stereocontrol toward rac-lactide polymerization and proved to be unstable under polymerization conditions.