REACTIONS OF EPSILON-CAPROLACTONE WITH (ALKYNE)ZIRCONOCENE COMPLEXES - INVESTIGATION OF ELEMENTAL STEPS IN CATALYTIC RING-OPENING POLYMERIZATION OF LACTONES

The reactions of Cp2Zr(L)(eta(2)-Me3SiC2SiMe3) (L = THF, pyridine) wit h epsilon-caprolactone, cyclohexanone and cycloheptanone result in an insertion of the carbonyl group into the zirconacyclopropene ring syst em of the alkyne complexes to yield the five-membered metallacyclic sp iro-zirconadihydrofurane complexes 1, 3, 4. The product with epsilon-c aprolactone is not stable at room temperature and was identified only by NMR spectra and chemical reactions. Starting from rac-(ebthi)Zr(eta (2)-Me3SiC2SiMe3) with epsilon-caprolactone and ethylene carbonate und er analogous conditions more stable complexes (2, 5) were obtained. Co mplexes 2 and 3 were characterized by X-ray crystal-structure analysis . Complexes 1 and 2 react with further epsilon-caprolactone in a catal ytic ring-opening polymerization. The polymerization reactions were mo nitored by NMR spectroscopy.