Chiral complexes of a new diazaallyl ligand: Group 4 aminooxazolinates

A new biaryl-bridged bis(iminooxazolidine) proligand H2L is prepared in good yield from 2,2-diamino-6,6'-dimethylbiphenyl. The direct reaction of H2L with [Ti(CH2Ph)(4)] leads via deprotonation of the ligand to the C-2-symmetric dibenzyl complex [LTi(CH2Ph)(2)] (85%) containing diazaallyl ligation. The analogous group 4 complexes [LZr(CH2Ph)(2)] (79%) and [LHf(CH2Ph)(2)] (91%) are similarly obtained. Molecular structures of these three compounds indicate C-2-symmetry in all cases and that the chirality of the backbone is well expressed in the coordination sphere. Reaction of H2L with Ti(NMe2)(4) gives the amide [LTi(NMe2)(2)] (90%), which on reaction with SiMe3Cl gives the chloride [LTiCl2] (78%). The dichloride [LZr(NMe2H)Cl-2] is prepared via treatment of H2L with Zr(NMe2)(2)Cl-2(THF)(2) (86%). The direct reaction of H2L with TiCl4(THF)(2) gives the adduct [(H2L)TiCl4] (83%), which is shown by X-ray crystallography to contain intramolecular (NHCl)-Cl-... hydrogen bond contacts. The complexes were tested as precatalysts for the polymerization of ethene and 1-hexene using a range of cocatalysts and were found to display low activity. Correspondingly, NMR studies on a presumed active species [LZr(CH2Ph)] [B(C6F5)(3)(CH2Ph)] were consistent with tight ion pairing on the NMR chemical shift time scale.