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 Zn-II 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 Zn-3(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 its Zn-3(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)center dot 2H(2)O to form the heterogeneous Zn-II system. This was characterised by C-13{H-1} CP/MAS NMR spectroscopy. All homogeneous and heterogeneous catalysts were assessed for the ring-opening polymerisation of rac-lactide at 130 degrees C in the absence of solvent, using unsublimed monomer. All catalysts offered good conversions and a moderate degree of control. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)