Synthesis and Structural Analysis of (Arylimido)vanadium(V) Complexes Containing Phenoxyimine Ligands: New, Efficient Catalyst Precursors for Ethylene Polymerization

A series of (arylimido)vanadium(V) complexes containing phenoxyimine ligands of the type V(NAr)Cl<sub>2</sub>[O-2-R-6-{(2,6-<i><sup>i</sup></i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)NCH}C<sub>6</sub>H<sub>3</sub>] [Ar = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>; R = H (<b>1a</b>), Me (<b>1b</b>), <i><sup>t</sup></i>Bu (<b>1c</b>)] have been prepared in 64−78% yields from V(NAr)Cl<sub>3</sub> with LiO-2-R-6-[(2,6-<i><sup>i</sup></i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)NCH]C<sub>6</sub>H<sub>3</sub>. The structures for <b>1a</b>−<b>c</b> determined by X-ray crystallography indicate that these complexes have distorted square-pyramidal structures around vanadium, consisting of the arylimido ligands in the apical site of a distorted square-pyramid and the N,O-chelate ligand, which forms a plane including both the aryloxo ring and the imino nitrogen. The Cl−V−Cl bond angle for <b>1c</b> [90.49(2)°] is apparently smaller than those in <b>1a</b>,<b>b</b> [91.97(7)°, 91.25(2)°, respectively], and the V−N(imine) bond distance in <b>1c</b> [2.203(2) Å] is shorter than those in <b>1b</b>,<b>c</b> [2.216(4), 2.2165(17) Å, respectively]. These complexes (especially <b>1c</b>) exhibited notable catalytic activities for ethylene polymerization in the presence of MAO, and the <i>ortho</i> substituent in the aryloxo ligand strongly affected the catalytic activity; the activity of the <i><sup>t</sup></i>Bu analogue (<b>1c</b>) was higher than that of the reported V(NAr)Cl<sub>2</sub>(O-2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) under the same conditions. The reaction of 1.1 equiv of 2-Me-6-{(2,6-<i><sup>i</sup></i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)NCH}C<sub>6</sub>H<sub>3</sub>OH with V(NAr)Me(NC<i><sup>t</sup></i>Bu<sub>2</sub>)<sub>2</sub> afforded another methyl complex without reaction with the methyl group occurring; unique reactivity of the methyl complex with phenol could thus be observed.