Synthesis, structure and ethylenepolymerisation behaviour of vanadium(iv and v) complexes bearing chelating aryloxides

Abstract

The reaction of [V(Np-tolyl)Cl₃] with the sulfur-bridged diphenol ligand 2,2′-thiobis(4,6-di-tert-butylphenol), {2,2′-S[4,6-(t-Bu)₂C₆H₂OH]₂} (LSH₂) afforded the complexes [V(LS)₂] (1) and [VOCl₃(MeCN)₂][H₃Np-tolyl] (2). Complex 2 could also be prepared directly from [V(Np-tolyl)Cl₃] and ‘wet’ acetonitrile. Reaction of [V(Np-tolyl)(Ot-Bu)₃] with LSH₂ afforded [VO(μ₂-OH)(LS)]₂·6(MeCN) (3), whilst reaction of [VO(On-Pr)₃] with 2,2′-sulfinylbis(4,6-di-tert-butylphenol), {2,2′-SO₂[4,6-(t-Bu)₂C₆H₂OH]₂} (LSO₂H₂), afforded [V(LSO₂)₂]·MeCN (4). The reaction of [VO(Oi-Pr)₃] with the ethylidene-bridged diphenol 2,2′-ethylidenebis(4,6-di-tert-butylphenol), {2,2′-CH₃CH[4,6-(t-Bu)₂C₆H₂OH]₂} (LH₂) afforded the hydroxyl bridged complexes [(VOL)₂(μ₂-OH)(μ₂-Oi-Pr)] (5) (major product) and [VO(μ₂-OH)(L)]₂·4(MeCN) (6) (minor product). In general, we find that controlled hydrolysis of [V(NAr)(On-Pr)₃] (Ar = p-ClC₆H₄, p-OCNC₆H₄ or p-tolyl) in the presence of LH₂ reproducibly led to the vanadyl complex [VO(μ-On-Pr)L]₂·2(MeCN) (7), in which the n-propoxide bridges both unexpectedly lie above the V₂O₂ plane. Reaction of the linear triphenol 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-tert-butylphenol, [ArCH₂Ar¹CH₂Ar] (Ar = 4,6-di-tert-butylphenol; Ar¹ = 4-tert-butylphenol) (L¹H₃), and [VO(On-Pr)₃] afforded the complex [VOL¹]₂·3(MeCN) (8), whilst reaction of [V(Np-tolyl)(Oi-Pr)₃] with the related methylene-bridged linear triphenol 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-methylphenol, [ArCH₂Ar²CH₂Ar] (L²H₃) (Ar² = 4-methylphenol), gave {[V(μ₂-O)(Np-tolyl)][VO(Oi-Pr)]L²}₂·1.5(MeCN) (9). The crystal structures of 1 to 9 are reported. Complexes 1–4 and 7–9 were screened as pro-catalysts for the polymerisation of ethylene in the presence of the co-catalyst dimethylaluminium chloride (DMAC) and the re-activator ethyltrichloroacetate (ETA). All are highly active ethylene polymerisation catalysts with activities covering the range 2000 to 90 000 g mmol⁻¹ h⁻¹bar⁻¹, and these results are discussed in terms of the ligands present at vanadium in the pro-catalyst. Complex 3 has also been screened for ethylene/propylene copolymerisation.