Vanadium(III) and -(IV) complexes with O,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 [O C6H(2)(CH2NMe2)(2)-2,6-Me-4](-) (g), have been used in the synthesis of wel l-defined vanadium-based catalysts for the polymerization of alpha -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 no t be obtained by reaction of [VCl3(THF)(3)] with the sodium phenolates beca use of incorporation of NaCl. However, use of the corresponding silyl ether Me3SiOC6H3(CH2NMe2)-2-Me-4 (2) resulted in the formation of the chlorovana dium (bis)phenolate [VCl(OC6H3(CH2NMe2)-2-Me-4)(2)] (3). Attempts to oxidiz e 3 to the corresponding dichlorovanadium(IV) (bis)phenolate were not succe ssful. No reaction was observed with CuCl, ASCl and PbCl2. A dark blue comp ound 4 was obtained with CuCl2, which was tentatively assigned as a V-III/C u-II dinuclear species. Treatment of the vanadium(IV) oxo (bis)phenolates 5 a-5f with SOCl2 in benzene at room temperature or in toluene at reflux temp erature resulted in the formation of dark blue compounds 6a-5f, whose stoic hiometries indicated excess chloride. Only when 5a and 5d were reacted with SOCl2 at -70 degreesC 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 bot h compounds have a trigonal bipyramidal geometry with two aminophenolate li gands bound in a bidentate eta (2)-O,N fashion to the vanadium center in si milar ways. The compounds 1, 3, 6 and 7 were tested for ethene/propene copo lymerization.