Highly Active Yttrium Catalysts for the Ring-Opening Polymerization of ε-Caprolactone and δ-Valerolactone

The activity of several yttrium alkoxide and aryloxide complexes supported by a ferrocene-based ligand incorporating two thiol phenolates, thiolfan (1,1'-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene), was studied. The tert-butoxide complex could only be isolated in the ate form, while a monophenoxide complex could be obtained for OAr = 2,6-di-tert-butylphenolate. The synthetic utility of these yttrium complexes has been demonstrated by the ring-opening polymerization of cyclic esters, with a high activity toward epsilon-caprolactone and delta-valerolactone being found for the yttrium phenoxide complex.