Zinc(II) Homogeneous and Heterogeneous Species and Their Application for the Ring‐Opening Polymerisation of rac‐Lactide

Schiff base ligands (L1H–L8H) have been prepared and complexed to ZnII centres. All eight complexes have been characterised by single‐crystal X‐ray diffraction methods, multinuclear NMR spectroscopy and elemental analysis. It was shown that for L1H and L2H trimetallic complexes of the form Zn3(OAc)4(L1–2)2 were isolated. However, for L3H to L7H monometallic complexes were formed, Zn(L3–7)2. For L8H a trimetallic complex was also isolated with the same stoichiometry as Zn3(OAc)4(L1–2)2 but a different coordination motif was detected. The Schiff base ligand L1H was anchored to silica and treated with Zn(OAc)2·2H2O to form the heterogeneous ZnII system. This was characterised by 13C{1H} CP/MAS NMR spectroscopy. All homogeneous and heterogeneous catalysts were assessed for the ring‐opening polymerisation of rac‐lactide at 130 °C in the absence of solvent, using unsublimed monomer. All catalysts offered good conversions and a moderate degree of control.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)