Group 4 metal complexes bearing new tridentate (NNO) ligands: Benzyl migration and formation of unusual C-C coupled products

Group 4 metal complexes bearing new phenoxy(benzimidazolyl)-imine, -amine and-amide ligands have been synthesized. A series of metal chloride derivatives has been prepared via treatment of MCl4(THF)(2) (M = Ti, Zr, Hf) with the in situ generated sodium salt of the (benzimidazolyl) imine phenol 1. Reaction of the pro-ligand 2 with TiCl4(THF)(2) afforded the corresponding complex 8 in which the amine proton remains bound to the nitrogen donor. Benzyl complexes of zirconium and hafnium were synthesized via treatment of pro-ligands 1 and 2 with M(CH2Ph)(4) precursors. The complexes [NNO]M(CH2Ph)(3) (6 M = Zr, 7 M = Hf) were found to undergo benzyl migration from the metal centre to the imine carbon of the ligand backbone giving complexes 11 and 12; the migration follows first order kinetics. The reaction of 1 with Ti(NMe2)(4) led to the formation of an unusual C-C coupled product in which a new piperazine ring has formed. Complexes 11 and 12 undergo related transformations, leading to analogous C-C coupled products which were characterized by X-ray crystallography. Deuterium labelling experiments were carried out to determine the mechanistic pathway of the reactions. Chloride and benzyl complexes 3-12 were screened as pre-catalysts for olefin polymerization. (C) 2008 Elsevier B.V. All rights reserved.