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<sub>2</sub>[2-Ar′NCH<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>N)] [Ar = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>; Ar′ = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>1a</b>), 2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>1b</b>), 2,6-F<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>1c</b>)] have been prepared from V(NAr)Cl<sub>3</sub> by treating with Li[2-Ar′NCH<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>N)], and the structures of <b>1b</b>,<b>c</b> have been determined by X-ray crystallography. These complexes are effective catalyst precursors for ethylene polymerization in the presence of Al cocatalysts: <b>1b</b> showed the highest catalytic activities in the presence of Et<sub>2</sub>AlCl (6000 kg PE/mol V·h), and the observed activities of <b>1a</b>,<b>b</b> in the presence of Et<sub>2</sub>AlCl were much higher than those in the presence of MAO. V(NAr)(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>[2-Ar′NCH<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>N)] (<b>2a</b>,<b>b</b>) have been prepared by treating <b>1a</b>,<b>b</b> with 2.0 equiv of LiCH<sub>2</sub>SiMe<sub>3</sub>, and their structures have been determined by X-ray crystallography. The dialkyl complex <b>2b</b> cleanly reacted with 2.0 equiv of (CF<sub>3</sub>)<sub>2</sub>CHOH in C<sub>6</sub>D<sub>6</sub> at 25 °C to afford V(NAr)(CH<sub>2</sub>SiMe<sub>3</sub>)[OCH(CF<sub>3</sub>)<sub>2</sub>][2-Ar′NCH<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>N)] (<b>3</b>), and the reaction with 3.0 equiv of (CF<sub>3</sub>)<sub>2</sub>CHOH eventually afforded V(NAr)[OCH(CF<sub>3</sub>)<sub>2</sub>]<sub>2</sub>[2-Ar′NCH<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>N)] (<b>4</b>) from <b>3</b> after 3 days. The dialkyl complexes <b>2a</b>,<b>b</b> showed catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene in benzene at 80 °C in the presence of PMe<sub>3</sub>. The ROMP did not occur in the absence of PMe<sub>3</sub> under the same conditions, suggesting that an additional coordination of PMe<sub>3</sub> may be required to induce the α-hydrogen elimination.