Thio-Pybox and Thio-Phebox complexes of chromium, iron, cobalt and nickel and their application in ethylene and butadiene polymerisation catalysis.

A series of bis(thiazolinyl)- and bis(thiazolyl)pyridine Thio-Pybox ligands and their metal complexes of chromium(III), iron(II), cobalt(II) and nickel(II) has been prepared, as well as a nickel(II) complex containing a monoanionic bis(thiazolinyl)phenyl Thio-Phebox ligand. These new metal complexes have been characterised and used as catalysts, in combination with the co-catalyst MAO, for the polymerisation of ethylene and for the polymerisation of butadiene. In the case of ethylene polymerisation, the Thio-Pybox and Thio-Phebox metal complexes have shown relatively low polymerisation activities, much lower compared to the related bis(imino)pyridine complexes of the same metals. In the polymerisation of butadiene, several Thio-Pybox cobalt(II) complexes show very high activities, significantly higher than the other metal complexes with the same ligand. It is the metal, rather than the ligand, that appears to have the most profound effect on the catalytic activity in butadiene polymerisation, unlike in the polymerisation of ethylene, where bis(imino)pyridine ligands provide highly active catalysts for a range of 1st row transition metals.

The effect of the central donor in bis(benzimidazole)-based cobalt catalysts for the selective cis-1,4-polymerisation of butadiene.

A series of bis(benzimidazole)-based cobalt(II) dichloride complexes containing a range of different central donors has been synthesized and characterized. The nature of the central donor affects the binding of the ligand to the cobalt centre and determines the coordination geometry of the metal complexes. All complexes have been shown to catalyse the polymerization of butadiene, in combination with MAO as the co-catalyst, to give cis-1,4-polybutadiene with high selectivity. The nature of the central donor has a marked influence on the polymerization activity of the catalysts, but does not affect the polymer microstructure. The addition of PPh(3) generally increases the polymerization activity of these cobalt catalysts and results in predominantly (60-70%) 1,2-vinyl-polybutadiene.

Mono- versus bis-chelate formation in triazenide and amidinate complexes of magnesium and zinc.

Magnesium and zinc complexes of the monoanionic ligands N,N'-bis(2,6-di-isopropylphenyl)triazenide, L1, N,N'-bis(2,6-di-isopropylphenyl)acetamidinate, L2, and N,N'-bis(2,6-di-isopropylphenyl)tert-butylamidinate, L3, have been synthesized, but only L3 possesses sufficient steric bulk to prevent bis-chelation. Hence, the reaction of L1H with excess ZnEt2 leads to the isolation of (L1)2Zn, 1; L1H also reacts with Bu2Mg in Et2O to afford (L1)2Mg(Et2O), 2. Similar reactivity is observed for L2H, leading to the formation of (L2)2Zn, 3, and (L2)2Mg, 4. The reaction of L2H with ZnR2 may also afford the tetranuclear aggregates {(L2)Zn2R2}2O, 5 (R=Me) and 6 (R=Et). By contrast, the tert-butylamidinate ligand was found to exclusively promote mono-chelation, allowing (L3)ZnCl(THF), 7, [(L3)Zn(micro-Cl)]2, 8, (L3)ZnN(SiMe3)2, 9, (L3)MgiPr(Et2O), 10, and (L3)MgiPr(THF), 11, to be isolated. X-ray crystallographic analyses of 1, 2, 3, 4, 5, 6, 8, and 10 indicate that the capacity of L3 to resist bis-chelation is due to greater occupation of the metal coordination sphere by the N-aryl substituents.

An unprecedented alpha-olefin distribution arising from a homogeneous ethylene oligomerization catalyst.

Treatment of the bis(benzimidazolyl)amine chromium complex 2 with ethylene in the presence of MAO affords an exceptionally active oligomerization catalyst and an unprecedented distribution of 1-olefin products in which the C4n series is much more abundant than the C4n+2 series. Deuterium labeling studies are consistent with a metallacyclic chain growth mechanism in which the unusual product distribution arises from the interplay of two sites.

Experimental evidence for large ring metallacycle intermediates in polyethylene chain growth using homogeneous chromium catalysts.

Deuterio-ethylene labeling studies on two homogeneous chromium ethylene oligomerization catalysts show that chain propagation proceeds via metallacyclic intermediates; reactions performed in the presence of 1-nonene show no incorporation of the higher olefin, strongly implicating the involvement of large ring metallacycles.

Dramatic effect of heteroatom backbone substituents on the ethylene polymerization behavior of bis(imino)pyridine iron catalysts.

Bis(imino)pyridine iron complexes bearing ether and thioether backbone substituents have been synthesized and evaluated for the polymerization of ethylene. The methoxy derivative is inactive whereas bulky phenoxides or thioether derivatives afford activities as high as the most active systems reported to date.

Bis(benzimidazole)amine vanadium catalysts for olefin polymerisation and co-polymerisation: thermally robust, single-site catalysts activated by simple alkylaluminium reagents.

Vanadium complexes containing bis(benzimidazole)amine ligands, upon activation by simple alkylaluminium reagents, give unusually robust, single-site, catalysts for olefin polymerisation/co-polymerisation.