Zirconium and hafnium amide, alkoxide, and pyrrolyl complexes manifesting with pyrrolyl-linked N-donor ligands: Syntheses, characterization, and ring opening polymerization of ε-caprolactone

Abstract

A series of zirconium and hafnium alkoxide and amide complexes containing symmetrical tridentate pyrrolyl ligand, [C 4H 2NH(2,5-CH 2NMe 2) 2] have been synthesized conveniently by treatment of 2,6-di- tert-butylphenol, tert-butanol or pyrrole in pentane and their reactivity over ring opening polymerization of ε-caprolactone have been carried out. Reactions of [C 4H 2NH(2,5-CH 2NMe 2) 2] with M(NEt 2) 4 (M = Zr or Hf) originate [C 4H 2N(2,5-CH 2NMe 2) 2]M(NEt 2) 3 ( 1, M = Zr; 2, M = Hf). Furthermore, reactions of [C 4H 2N(2,5-CH 2NMe 2) 2]M(NEt 2) 3 with 2,6-di- tert-butylphenol, tert-butanol or pyrrole afford [C 4H 2N(2,5-CH 2NMe 2) 2]M(OC 6H 3-2,6- t Bu 2)(NEt 2) 2 ( 3, M = Zr; 4, M = Hf), [C 4H 2N(2,5-CH 2NMe 2) 2]M(O t Bu) 3 ( 5, M = Zr; 6, M = Hf) and [C 4H 2N(2,5-CH 2NMe 2) 2]M(C 4H 4N) 3 ( 7, M = Zr; 8, M = Hf), respectively, in satisfactory yield. All the complexes have been characterized by NMR spectra as well 3, 4 and 6 subjected to the X-ray diffraction analysis. Complexes 3– 8 have been used as initiators for the ring-opening polymerization of ε-caprolactone and observed broad PDI values (1.84–2.75) representing multiple reactivity centers of these complexes.