The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes

Abstract

The silyl ethers 3-Bu^t-2-(OSiMe₃)C₆H₃CHNR (2a–e) have been prepared by deprotonation of the known iminophenols (1a–e) and treatment with SiClMe₃ (a, R = C₆H₅; b, R = 2,6-Prⁱ₂C₆H₃; c, R = 2,4,6-Me₃C₆H₂; d, R = 2-C₆H₅C₆H₄; e, R = C₆F₅). 2a–c react with TiCl₄ in hydrocarbon solvents to give the binuclear complexes [Ti{3-Bu^t-2-(O)C₆H₃CHN(R)}Cl(µ-Cl₃)TiCl₃] (3a–c). The pentafluorophenyl species 2e reacts with TiCl₄ to give the known complex Ti{3-Bu^t-2-(O)C₆H₃CHN(R)}₂Cl₂. The mononuclear five-coordinate complex, Ti{3-Bu^t-2-(O)C₆H₃CHN(2,4,6-Me₃C₆H₂)}Cl₃ (4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti{3-Bu^t-2-(O)C₆H₃CHN(R)}Cl₃(THF) (5a–e). The reaction with ZrCl₄(THF)₂ proceeds similarly to give complexes Zr{3-Bu^t-2-(O)C₆H₃CHN(R)}Cl₃(THF) (6b–e). The crystal structures of 3b, 4c, 5a, 5c, 5e, 6b, 6d, 6e and the salicylaldehyde titanium complex Ti{3-Bu^t-2-(O)C₆H₃CHO}Cl₃(THF) (7) have been determined. Activation of complexes 5a–e and 6b–e with MAO in an ethene saturated toluene solution gives polyethylene with at best high activity depending on the imine substituent.