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

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 via NMR spectroscopy. In the solid-state either Ti-2(L)((OPr)-Pr-i)(6) or Ti-2(L)(2)(OiPr)(4) were observed depending upon the nature of the starting ligand. For complexes with less sterically demanding ligands (1H(2) and 2H(2)) an equilibrium was observed: 2 Ti-2(L)((OPr)-Pr-i)(6) double left right arrow Ti-2(L)(2)((OPr)-Pr-i)(4) + 2 Ti((OPr)-Pr-i)(4). The thermodynamic properties (Delta G, Delta H and Delta S) have been investigated via variable temperature NMR spectroscopy. With more sterically demanding ligands (3-8H(2)) the Ti-2(L)((OPr)-Pr-i)(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.