The study and synthesis of Group 4 transition metal complexes in Ziegler-Natta catalysis

Abstract

In this thesis a study of Group 4 transition metal complexes and their possible use as Ziegler-Natta catalysts for alkene polymerisation is described. Several tetradentate Schiff base ligands have been synthesised and characterised, including some previously unreported examples. The products obtained from the reactions of Group 4 transition metal halides with the disodium salts of these ligands have been isolated and identified. The stereochemistry of these complexes is important for their use as Ziegler-Natta catalysts, and several complexes have been characterised by X-ray crystallography. [Ti(DMSALEN)Cl2], [Ti(PhSALEN)Cl2], [Ti(SLPNDM)Cl2] and [Zr(SLPNDM)Cl2(THF)] have a trans- geometry at the metal, and the complex [Ti(EtCycH)Cl2] has a cis- geometry. The remaining complexes have been studied by molecular modelling to establish a likely stereochemistry. The reactions of these dichloro complexes with trimethyl aluminium have been studied to gain insight into the chemistry involved in the polymerisation reactions. These reactions proceed with retention of the two chlorine atoms yielding complexes of the type [M(L)Cl2(AlMe3)2] (M = Ti, Zr; L =Schiff base). Side reactions also occur and the by-products [AlMe(EtSALEN)Al(Me)2][AlMeCl3] and [(AlMe2)2(AlMe3)2(EtSALEN)] have been isolated, and characterised by X-ray crystallography. Work was also carried out on the synthesis of complexes of the type (MCl2L) (M = Ti, Zr; L = tetra-azamacrocycle) by the reactions of MCl4 with the dilithium salt of the ligand. These complexes have been fully characterised and the molecular structure of the complex [Zr(omtaa)Cl2] determined by X-ray crystallography. Finally all these complexes have been tested as Ziegler-Natta catalysts for ethene polymerisation. A few selected complexes were also tested for their use in styrene polymerisation and found to be inactive