Geometry Change in a Series of Zirconium Compounds during Lactide Ring-Opening Polymerization

A new series of zirconium compounds, (salfen)­Zr­(OtBu)2 (salfen = N,N′-bis­(2,4-di-tert-butylphenoxy)-1,1′-ferrocenediimine), (salfen)­Zr­(OiPr)2, and (salfen)­Zr­(OnPr)2, was synthesized and characterized, featuring a cis-β coordination geometry for the major isomer found in solution. An isomerization between the trans and cis-β coordination geometry was observed at ca. 100 °C in solution. This isomerization was also observed in the presence of l-lactide (LA) before its ring-opening polymerization could occur. The isolation of a (salfen)­Zr­(OnPr)2 lactide intermediate supports the change to the trans coordination geometry necessary before polymerization.