Easily Available Niobium(V) Mixed Chloro-Alkoxide Complexes as Catalytic Precursors for Ethylene Polymerization

The dinuclear [NbCl(n)(OR)((5-n))](2) (n = 4, R = Et, 1; n = 4, R - CH(2)Ph, 2; n - 3, R - Et, 3; n - 2, R - Et, 4; n - 2, R - CH(CH(2))(4)CH(Cl), 5), and [Nb(OEt)(5)](2), 6, and the mononuclear niobium compounds NbCl(4)[kappa(2)-OCH(2)CH(R')OR] (R = Me, R' = H, 7; R = Et, R' = H, 8; R = CH(2)Cl, R' = H, 9; R = CH(2)CH(2)OMe, R' = H, 10; R = R' = Me, 11), NbBr(4)[kappa(2)-OCH(2)CH(2)OMe], 12, and NbCl(3)(kappa(2)-OCH(2)CH(2)OMe)(kappa(1)-OCH(2)CH(2)OMe), 13, were tested in ethylene polymerization. Optimized reaction conditions included the use of D-MAO as co-catalyst and chlorobenzene as solvent at 50 degrees C. Complex 7, whose X-Ray structure is described here for the first time, exhibited the highest activity ever reported for a niobium catalyst in alkene polymerization [151 kg(polymer) x mol(Nb)(-1) x h(-1) x bar(-1)]. Compounds 1, 3-5, 8, 13 showed activities similar to that of 7. Linear polyethylenes (characterized by FT-IR, NMR, GPC, and DSC analyses) with a broad polydispersivity were obtained.