Synthesis, structure and α-olefin polymerization activity of group 4 metal complexes with [OSSO]-type bis(phenolate) ligands

The tetradentate [OSSO]-type bis(phenol) ligands, [{2,2'-(HOC6H2-4,6-R-2)(2)CH2SCH2CH2SCH2}] (R = Bu-t, 2; Br, 3) react with MBz(4) (M = Zr, Hf) to yield the corresponding dibenzyl complexes, [M{2,2'-(OC6H2-4,6R(2)) 2CH2SCH2CH2SCH2}Bz(2)] (R = Br, M = Zr, 4(Br); Hf, 5(Br); R = Bu-t, M = Hf, 5) in a good to very good yield. Zirconium diamido complexes, [Zr{2,2'-(OC6H2-4,6-R-2)(2)CH2SCH2CH2SCH2}(NMe2)(2)] (R = Bu-t, 6; Br, 6(Br)) were prepared in a reaction of the corresponding disodium salt of 2 or 3 generated in situ with ZrCl2(NMe2)(2)(THF)(2). Heating of 6 with TMSCl at 35 degrees C afforded zirconium dichloro complex, [Zr{2,2'- (OC6H2-4,6-Bu-t(2))(2)CH2SCH2CH2SCH2}Cl-2] (7), whereas the titanium analog 8 was prepared in a direct reaction with TiCl4. While for complexes 4(Br), 5, 5(Br), 6, 6(Br) and 7 single C-2-symmetric isomers were observed in solution at room temperature, as revealed by the NMR spectroscopic data, titanium complex 8 formed as a mixture of cis-alpha (8a) and cis-beta (8b) isomers in a ratio of approx. 20:80% (measured in CD2Cl2). The VT NMR studies revealed a reversible conversion of 8a into 8b above 60 degrees C. The X-ray crystal structure determination of complexes 4(Br), 5(Br) and 7 confirmed their C-2-symmetrical configuration in the solid state with cis-arranged benzyl/chloro groups and the trans-coordination of two bulky phenolato moieties. The zirconium dibenzyl complexes exhibit good catalytic activities in homopolymerization of 1-hexene (atactic poly(1-hexene), PDI = 1.5-1.7) and vinylcyclohexane (isotactic poly(vinylcyclohexane), PDI 1.2-1.8) upon activation with a co-catalyst. In both polymerizations no increase of activity was observed for the complex 4(Br) with electron-withdrawing substituents on phenolate rings. Moreover, polymerization of liquid propylene catalyzed by the titanium dichloro isomeric mixture 8 afforded at 5 degrees C ultrahigh molecular weight atactic/isotactic polypropylene mixtures. (C) 2011 Elsevier B.V. All rights reserved.