Group 4 permethylindenyl complexes for the polymerisation of l-, d- and rac-lactide monomers

Abstract

A series of well-defined group 4 permethylindenyl complexes have been prepared and fully characterised by NMR spectroscopy and X-ray crystallography. ^Me₂SB(Cp,I*)ZrCl₂ ({(η⁵-C₉Me₆)Me₂Si(η⁵-C₅H₄)}ZrCl₂; 1), ^Me₂SB(Cp^Me,I*)ZrCl₂ ({(η⁵-C₉Me₆)Me₂Si(η⁵-C₅H₃Me)}ZrCl₂; 2), ^Me₂SB(Cp,I*)HfCl₂ (3) and Z-^Me₂SB(Cp,I*)ZrCl(O-2,6-Me-C₆H₃) (4) were investigated as initiators for the ring-opening polymerisation (ROP) of L-, D- and rac-lactide monomers in the presence of benzyl alcohol. 1–4 displayed second order dependence on monomer concentration and produced isotactic and heterotactic (P_r = 0.81) polylactides for the polymerisation of L-, D- and rac-lactide respectively. The effects of temperature, catalyst concentration, co-initiator concentration, solvent and scale were studied. At 80 °C, with two equivalents of benzyl alcohol, 4 was the most active initiator for the ROP of L-, D- and rac-lactide (k_obs = 6.39, 6.38 and 5.89 M⁻¹ h⁻¹ respectively). The polylactides were characterised by NMR spectroscopy, GPC and MALDI-TOF mass spectrometry.