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Synthesis, structure and ethylene polymerisation behaviour of vanadium(IV and V) complexes bearing chelating
Damien Homden1, Carl Redshaw, Lee Warford
1Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich, UK NR4 7TJ.
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(mu2-OH)(LS)]2 x 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] x 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(mu2-OH)(mu2-Oi-Pr)] (5) (major product) and [VO(mu2-OH)(L)]2 x 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(mu-On-Pr)L]2 x 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, [ArCH2Ar(1)CH2Ar] (Ar = 4,6-di-tert-butylphenol; Ar()1 = 4-tert-butylphenol) (L(1)H3), and [VO(On-Pr)3] afforded the complex [VOL(1)]2 x 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, [ArCH2Ar(2)CH2Ar] (L(2)H3) (Ar(2) = 4-methylphenol), gave {[V(mu2-O)(Np-tolyl)][VO(Oi-Pr)]L(2)}2 x 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(-1) bar(-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.
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