Henk Hagen

Homogeneous vanadium-based catalysts for the Ziegler–Natta polymerization of α-olefins

Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homogeneous Ziegler–Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/α-olefin copolymers with high α-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vanadium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.

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 [OC6H2(CH2NMe2)2-2,6-Me-4]- (g)), have been used in the synthesis of well-defined vanadium-based catalysts for the polymerization of -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 2-O,N fashion to the vanadium center in similar ways. The compounds 1, 3, 6 and 7 were tested for ethene/propene copolymerization.

O,N-Chelated boron aminophenolate complexes. Crystal structure of BPh2(OC6H4(CH2NMe2)-2)

Abstract Two diphenylboron ortho-aminophenolate complexes, [BPh2(OC6H4(CH2NMe2)-2)] (2) and [BPh2(OC6H2(CH2NMe2)2-2,6-Me-4)] (6), have been prepared in a one-pot procedure approach starting from B(OMe)3. The starting material was reacted with two equivalents of phenylmagnesium bromide, followed by hydrolysis with HCl. The resulting borinic acid, BPh2(OH), was reacted with either HOC6H4(CH2NMe2)-2 or HOC6H2(CH2NMe2)2-2,6-Me-4 to give 2 or 6, respectively. An X-ray structure determination of 2 showed it to be a four-coordinate boron compound with a tetrahedral coordination geometry. The six-membered chelate ring in 2 is puckered. Variable temperature 1H-NMR analysis of 6 showed the existence of two dynamic processes in solution, i.e. one process involving flipping of the puckered chelate ring conformation (ΔG‡=41 kJ mol−1) and a second, higher energy, process (ΔG‡=65 kJ mol−1) in which exchange of coordinated and non-coordinated amine functions occurs. The exchange is (at least partly) assisted intermolecularly.

The twinned structure of the μ-isopropoxidodiisopropoxido(p-tolylimido)vanadium(V) dimer, twin refinement against CCD area-detector data

The title compound, [V 2 (C 7 H 7 N) 2 (C 3 H 7 O) 6 ], crystallizes as a non-merohedrical twin in the triclinic space group P1. The twin operation is a twofold rotation around the reciprocal [110] direction, leading to split reflections. The intensities of both twin domains were evaluated separately and the structure refinement resulted in a population ratio of 72.6(1):27.4(1). The molecular geometry of this dimeric compound is in line with similar vanadium compounds found in the literature. The vanadium is in a distorted trigonal-bipyramidal environment. The dimer is formed by the asymmetric bridging of two isopropoxido groups with bond lengths of 1.8560(13) and 2.2151 (13)A.