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

• Published in: Dalton transactions : an international journal of inorganic chemistry 2011-01, Vol.40 (9), p.2033-2037
• Main Authors: Hancock, Stuart L, Mahon, Mary F, Jones, Matthew D
• Format: Article
• Language: English
• Subjects: Conversion; Coordination Complexes - chemical synthesis; Coordination Complexes - chemistry; Crystallography; Crystallography, X-Ray - methods; Dioxanes - chemistry; Ligands; Magnetic Resonance Spectroscopy - methods; Melts; Molecular Structure; NMR spectroscopy; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Piperazines - chemistry; Polyesters - chemical synthesis; Polyesters - chemistry; Polylactides; Polymers - chemical synthesis; Polymers - chemistry; Ring opening; Solutions - chemistry; Thermodynamic properties; Thermodynamics; Titanium - chemistry
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c0dt01542c

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)(O(i)Pr)(6) or Ti(2)(L)(2)(O(i)Pr)(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)(O(i)Pr)(6) ⇔ Ti(2)(L)(2)(O(i)Pr)(4) + 2 Ti(O(i)Pr)(4). The thermodynamic properties (ΔG, ΔH and ΔS) have been investigated via variable temperature NMR spectroscopy. With more sterically demanding ligands (3-8H(2)) the Ti(2)(L)(O(i)Pr)(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.