Synthesis of (Arylimido)vanadium(V) Complexes Containing (2-Anilidomethyl)pyridine Ligands and Their Use as the Catalyst Precursors for Olefin Polymerization

A series of (arylimido)vanadium(V) dichloride complexes containing (2-anilidomethyl)pyridine ligands of the type V(NAr)Cl-2[2-Ar'NCH2(C5H4N)] [Ar = 2,6-Me2C6H3; Ar' = 2,6-Me2C6H3 (1a), 2,6-(Pr2C6H3)-Pr-i (1b), 2,6-F2C6H3 (1c)] have been prepared from V(NAr)Cl-3 by treating with Li-[2-Ar'NCH2(C5H4N)], and the structures of 1b,c have been determined by X-ray crystallography. These complexes are effective catalyst precursors for ethylene polymerization in the presence of Al cocatalysts: 1b showed the highest catalytic activities in the presence of Et2AlCl (6000 kg PE/mol V.h), and the observed activities of 1a,b in the presence of Et2AlCl were much higher than those in the presence of MAO. V(NAr)(CH2SiMe3)(2)[2-Ar'NCH2(C5H4N)] (2a,b) have been prepared by treating 1a,b with 2.0 equiv of LiCH2SiMe3, and their structures have been determined by X-ray crystallography. The dialkyl complex 2b cleanly reacted with 2.0 equiv of (CF3)(2)CHOH in C6D6 at 25 degrees C to afford V(NAr)(CH2SiMe3)[OCH(CF3)(2)][2-Ar'NCH2(C5H4N)] (3), and the reaction with 3.0 equiv of (CF3)(2)CHOH eventually afforded V(NAr)[OCH(CF3)(2)](2)[2-Ar'NCH2(C5H4N)] (4) from 3 after 3 days. The dialkyl complexes 2a,b showed catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene in benzene at 80 degrees C in the presence of PMe3. The ROMP did not occur in the absence of PMe3 under the same conditions, suggesting that an additional coordination of PMe3 may be required to induce the alpha-hydrogen elimination.