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

A new series of zirconium compounds, (salfen)Zr(O t Bu) 2 (salfen = N, N ′-bis(2,4-di- tert -butylphenoxy)-1,1′-ferrocenediimine), (salfen)Zr(O i Pr) 2, and (salfen)Zr(O n Pr) 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(O n Pr) 2 lactide intermediate supports the change to the trans coordination geometry necessary before polymerization.