Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2-(2′-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization

(Imido)vanadium(V) dichloride complexes containing 2-(2′-benzimidazolyl)-6-methylpyridine ligand (L) of type V(NR)Cl2(L) [R = 1-adamantyl (Ad, 1), C6H5 (2), and 2,6-Me2C6H3 (3)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using 1–3 in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, 1–3 exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me2AlCl; the phenylimido complex (2) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h–1, 792 s–1)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., Mn = 1.71–2.66 × 106, Mw/Mn = 2.27–2.53]. On the basis of V nuclear magnetic resonance (51V NMR), ele...