Vanadium(III) and -(IV) Complexes withO,N-Chelating Aminophenolate Ligands: Synthesis, Characterization and Activity in Ethene/Propene Copolymerization

Monoanionic, potentially bi- or terdentate aminophenolates, ([OC6H3(CH2NMe2)-2-R-4)]−, R = H (a), Me (b), tBu (c), Cl (d), N=NPh (e), MeO (f) and [OC6H2(CH2NMe2)2-2,6-Me-4]− (g)), have been used in the synthesis of well-defined vanadium-based catalysts for the polymerization of α-olefins. The reaction of [Cp2V] with the parent phenol of g resulted in oxidation of the vanadium(II) nucleus to obtain the vanadium(III) (tris)phenolate [V(OC6H2(CH2NMe2)2-2,6-Me-4)3] (1). Vanadium(III) aminophenolates could not be obtained by reaction of [VCl3(THF)3] with the sodium phenolates because of incorporation of NaCl. However, use of the corresponding silyl ether Me3SiOC6H3(CH2NMe2)-2-Me-4 (2) resulted in the formation of the chlorovanadium (bis)phenolate [VCl(OC6H3(CH2NMe2)-2-Me-4)2] (3). Attempts to oxidize 3 to the corresponding dichlorovanadium(IV) (bis)phenolate were not successful. No reaction was observed with CuCl, AgCl and PbCl2. A dark blue compound 4 was obtained with CuCl2, which was tentatively assigned as a VIII/CuII dinuclear species. Treatment of the vanadium(IV) oxo (bis)phenolates 5a−5f with SOCl2 in benzene at room temperature or in toluene at reflux temperature resulted in the formation of dark blue compounds 6a−6f, whose stoichiometries indicated excess chloride. Only when 5a and 5d were reacted with SOCl2 at −70 °C could the desired dichlorovanadium (bis)phenolates [VCl2(OC6H4(CH2NMe2)-2)2] (7a) and [VCl2(OC6H3(CH2NMe2)-2-Cl-4)2] (7d) be obtained. X-ray crystal structure determination of 1 and 3 showed that both compounds have a trigonal bipyramidal geometry with two aminophenolate ligands bound in a bidentate η2-O,N fashion to the vanadium center in similar ways. The compounds 1, 3, 6 and 7 were tested for ethene/propene copolymerization.