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

• Published in: Journal of organometallic chemistry Vol. 694; no. 5; pp. 703 - 716
• Main Authors: Cariou, Renan, Gibson, Vernon C., Tomov, Atanas K., White, Andrew J.P.
• Format: Journal Article
• Language: English
• Published: LAUSANNE Elsevier B.V 01.03.2009; Elsevier
• Subjects: Carbon–carbon coupling; Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Ethylene polymerization; Group 4 metal complexes; Intramolecular benzyl migration; Physical Sciences; Science & Technology; Ethylene polymerization; Group 4 metal complexes; Intramolecular benzyl migration; Carbon–carbon coupling; Carbon-carbon coupling; OLEFIN POLYMERIZATION CATALYSTS; COENZYME-B12 MODEL COMPLEX; ETHYLENE OLIGOMERIZATION; MOLECULAR-STRUCTURE; ZIRCONIUM COMPLEXES; STRUCTURAL-CHARACTERIZATION; ALKYL BOND REARRANGEMENT; MONO(SALICYLALDIMINATO) TITANIUM; ETHENE POLYMERIZATION; SCHIFF-BASE COMPLEXES
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2008.11.064

A series of Group 4 metal complexes bearing new phenoxy(benzimidazolyl)-imine, -amine and -amide ligands has been synthesized. Derivatives containing benzyl ligands undergo benzyl migration and an unusual C–C coupling process to afford binuclear species in which the metals are linked by a central piperazine unit. Deuterium labelling experiments have been employed to determine the mechanistic pathways for these reactions. 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 MCl 4(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 TiCl 4(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(CH 2Ph) 4 precursors. The complexes [NNO]M(CH 2Ph) 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(NMe 2) 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.