title: Well-defined Ti4pre-catalysts for the ring-opening polymerisation of lactide.
abstract: The synthesis and full characterisation of four discrete tetrametallic titanium complexes is reported. These well-defined compounds are isostructural in the solid state and share the same general formula: Ti4(μ-O)2L4(L = 1, 2, 3 or 4). Using a combination of NMR techniques the complexes are found to be stable in solution, even at elevated temperatures. Further studies show that the carboxylate moieties of the supporting amine bis(phenolate) ligands can be displaced by a more strongly coordinating solvent. This reversible process causes the coordinatively saturated Ti4(μ-O)2L4complexes to separate into two Ti2(μ-O)L2subunits which we envisaged would be catalytically active. Proof-of-concept experiments establish that all four of these complexes display catalytic activity in the ring-opening polymerisation of rac-lactide. These aggregates can therefore be viewed as air and moisture stable pre-catalysts for a range of reactions.
authors.affiliation: Institute of Chemical Sciences Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, UK. R.McIntosh@hw.ac.uk.
authors.forename: Jean-Marie E P
authors.initials: JE
authors.lastname: Cols
authors.forename: Cameron E
authors.initials: CE
authors.lastname: Taylor
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Gagnon
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Teat
authors.forename: Ruaraidh D
authors.initials: RD
authors.lastname: McIntosh
mesh_terms: D000586:Amination; D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry; D058105:Polymerization; D014025:Titanium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D004146:Dioxanes; D008024:Ligands; D010636:Phenols; C091880:dilactide; D014025:Titanium