Crystallographic characterisation of Ti(iv) piperazine complexes and their exploitation for the ring opening polymerisation of rac-lactide

Abstract

In this paper a series of eight Ti(IV) piperazine based complexes have been prepared and fully characterised in the solid-state by X-ray crystallography and in solution viaNMR spectroscopy. In the solid-state either Ti₂(L)(OⁱPr)₆ or Ti₂(L)₂(OⁱPr)₄ were observed depending upon the nature of the starting ligand. For complexes with less sterically demanding ligands (1H₂ and 2H₂) an equilibrium was observed: 2 Ti₂(L)(OⁱPr)₆ ⇔ Ti₂(L)₂(OⁱPr)₄ + 2 Ti(OⁱPr)₄. The thermodynamic properties (ΔG, ΔH and ΔS) have been investigated viavariable temperature NMR spectroscopy. With more sterically demanding ligands (3–8H₂) the Ti₂(L)(OⁱPr)₆ form was the most prevalent in the solid-state and in solution. These complexes have been tested for the production of polylactide under melt and solution conditions with high conversions being obtained.