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-2[O-2-R-6-{(2,6-(Pr2C6H3)-Pr-i)N = CH)C6H3] [Ar = 2,6-Me2C6H3; R = H (1a), Me (1b), Bu-t (1c)] have been prepared in 64-78% yields from V(NAr)Cl-3 with LiO-2-R-6-[(2,6-(Pr2C6H3)-Pr-i)N = CH]C6H3. The structures for la-c 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 1c [90.49(2)degrees] is apparently smaller than those in 1a,b [91.97(7)degrees, 91.25(2)degrees, respectively], and the V-N(imine) bond distance in 1c [2.203(2) angstrom] is shorter than those in 1b,c [2.216(4), 2.2165(17) angstrom, respectively]. These complexes (especially lc) exhibited notable catalytic activities for ethylene polymerization in the presence of MAO, and the ortho substituent in the aryloxo ligand strongly affected the catalytic activity; the activity of the Bu-t analogue (1c) was higher than that of the reported V(NAr)Cl-2(O-2,6-Me2C6H3) under the same conditions. The reaction of 1.1 equiv of 2-Me-6-{(2,6-(Pr2C6H3)-Pr-i)N = CH}C6H3OH with V(NAr)Me(N =(CBu2)-Bu-t)(2) afforded another methyl complex without reaction with the methyl group occurring; unique reactivity of the methyl complex with phenol could thus be observed.