Reactions of ε-Caprolactone with (Alkyne)zirconocene Complexes: Investigation of Elemental Steps in Catalytic Ring-Opening Polymerization of Lactones

Abstract

The reactions of Cp2Zr(L)(η2-Me3SiC2SiMe3) (L = THF, pyridine) with ϵ-caprolactone, cyclohexanone and cycloheptanone result in an insertion of the carbonyl group into the zirconacyclopropene ring system of the alkyne complexes to yield the five-membered metallacyclic spiro-zirconadihydrofurane complexes 1, 3, 4. The product with ϵ-caprolactone is not stable at room temperature and was identified only by NMR spectra and chemical reactions. Starting from rac-(ebthi)Zr(η2-Me3SiC2SiMe3) with ϵ-caprolactone and ethylene carbonate under analogous conditions more stable complexes (2, 5) were obtained. Complexes 2 and 3 were characterized by X-ray crystal-structure analysis. Complexes 1 and 2 react with further ϵ-caprolactone in a catalytic ring-opening polymerization. The polymerization reactions were monitored by NMR spectroscopy.