Towards the Nature of Active Sites in Polymerization of Cyclic Esters Initiated by Aluminium Alkoxides: First Structurally Authenticated Aluminium-ε-Caprolactone Complex

The isolation and structural characterization of a methylaluminium(bisphenoxide)‐ε‐caprolactone complex is reported. While the three‐coordinate methylaluminium complex was found not to catalyze the polymerization of ε‐caprolactone, its oxygenation led to the formation of an aluminium methoxide compound, which appeared to be a very good initiator. The relative propensity of the AlX bonds for monomer insertion in the initial step of polymerization is also discussed. Structure of the methylaluminium(bisphenoxide)‐ε‐caprolactone complex reported here.