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Homden D, Redshaw C, Warford L, Hughes DL, Wright JA, Dale SH, Elsegood MR: Synthesis, structure and ethylene polymerisation behaviour of vanadium (IV and V) complexes bearing chelating aryloxides. Dalton Trans. 2009 Nov 7;(41):8900-10. Epub 2009 Jul 7.
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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