Synthesis, structure and ethylene polymerisation behaviour of vanadium(IV and V) complexes bearing chelating aryloxides.

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.