Bis(Imido) Tungsten Complexes: Efficient Precatalysts for the Homogeneous Dimerization of Ethylene

The ethylene dimerization performance of a range of bis(imido)tungsten precatalysts, after activation with aluminum cocatalysts, has been assessed. The best-performing system achieved an activity of 409 410 (mol C2H4)(mol W)−1h–1 [79.6 wt % 1-butene] with a 1-butene selectivity of 82.4 wt % [290 770 (mol C2H4)(mol W)−1h–1 activity]. In addition to selected previously reported variants, the symmetrical bis(imido)tungsten(VI) complexes [WCl2(NPh)2(tmeda)] (3) and [WCl2(NR)2(dme)] [R = 2,4,6-trifluorophenyl, 7; 2,4,6-triphenylphenyl, 8; 2,4,6-tris(trifluoromethyl)phenyl, 9], were prepared. A series of unsymmetrical bis(imido)tungsten(VI) complexes [WCl2(NDipp)(NR)(dme)] (R = iPr, 11; tBu, 12; 2,4,6-trimethylphenyl, 13; 2,4,6-trichlorophenyl, 14; 2,4,6-trifluorophenyl, 15; 2,6-dinitrophenyl, 16; 2,4,6-triphenylphenyl, 17) were also synthesized using an improved version of a previous preparative route that eases purification. The molecular structures of complexes 5–13 and 15–17 were determined by X-ray crystal...