Easily accessible oxygen‐containing derivatives of niobium pentachloride as catalytic precursors for ethylene polymerization

The low catalytic activity of NbCl5 as an ethylene polymerization catalyst was significantly increased by the addition of a series of oxygen donors. The novel niobium derivatives NbCl5(OPh2) (1), NbCl5(OEt2) (3), NbCl5(OCPh2) (5), NbCl5(OCHPh) (6), NbCl5(OCHMe) (7) and [NbCl4(dppe)2](NbCl6) (18) (dppe is 1,2‐bis(diphenylphosphino)ethane) and the previously reported derivatives NbCl5(OMePh) (2), NbCl5(thf) (4) (thf is tetrahydrofuran), NbCl5(OCHOMe) (8), NbCl5(OCHNMe2) (9), NbCl5[OC(NMe2)2] (10), NbCl5(NCMe) (11), NbCl4(κ2‐1,2‐OC6H4OMe) (12), NbCl4[κ2‐OC(Me)CH2C(Me2)O] (13), (14), [NbCl4(O2CMe)]2 (15), NbCl3(dme)(µ‐O)NbCl5 (16) (dme is 1,2‐dimethoxyethane), [NbCl4(κ2‐dmm)2](NbCl6) (17) (dmm is dimethylmaleate), TaCl5(OCMe2) (19) and [TaCl4(O2CMe)]2 (20) were tested as catalytic precursors in the ethylene polymerization reaction using AlMe3‐depleted methylaluminoxane as co‐catalyst. Highly linear polyethylene was obtained. Compounds 1, 3, 5, 6 and 8–13 showed catalytic activities in the range 89–116 kgpolymer molNb−1 h−1 bar−1, i.e. comparable with the best performances reached with niobium pre‐catalysts up to now. However, the dinuclear compounds 14–16 and 18 were found to be less active, whereas17 and the tantalum derivatives 19 and 20 did not produce polymer. Relatively high molecular weights were achieved with the mononuclear compounds 1, 2, 8, 9, 10 and 12, the dinuclear 16 and the phosphine ionic 18.