Synthesis of (Imido)vanadium(V) Complexes Containing 8‑(2,6-Dimethylanilide)-5,6,7-trihydroquinoline Ligands: Highly Active Catalyst Precursors for Ethylene Dimerization

A series
of (imido)­vanadium­(V) dichloride complexes containing
8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands of the type
V­(NR)­Cl2[8-(2,6-Me2C6H3)­N­(C9H10N)] (R = Ad (3), 2-MeC6H4 (4), 2,6-Me2C6H3 (Ar, 5)) have been prepared and identified,
and their structures have been determined by X-ray crystallographic
analysis. The ethylene dimerization catalyst generated from complex 3 upon treatment with an excess amount of MAO exhibited remarkable
catalytic activities (e.g. TOF = 9600000 h–1 (2670
s–1), Al/V = 4000 (molar ratio)), affording 1-butene
as the major product (95.0–99.4%). The activities of 3 and 4 were higher than those exhibited by the
corresponding 2-(anilide)­methylpyridine analogues; 3 showed
higher 1-butene selectivity than the others and the activity did not
decrease remarkably at 50 °C. Complex 5 afforded
a mixture of polymer and oligomers with low activities, suggesting
that a fine tuning of both the imido and the anionic donor ligands
plays an essential role in this catalysis.