C2- and Cs-symmetric diamidodichlorotitanium complexes: Syntheses, structures and 1-hexene polymerization catalysis |
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Authors: | Frank Heatley Robin G Pritchard Rebecca J Woods |
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Institution: | Organic Materials Innovation Centre, School of Chemistry, University of Manchester, Brunswick Street, Manchester M13 9PL, UK |
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Abstract: | The complexes l-CMe2{CHMeN(2-Pri-C6H4)}2TiCl2] (2) and (3), C2- and Cs-symmetric analogues, respectively, of McConville’s C2v hexene polymerization precatalyst (1), were prepared by high-dilution salt-elimination from the lithium amides and characterized spectroscopically and crystallographically. Complex 2, though less active than 1, was a highly active catalyst of polymerization of 1-hexene when activated by MAO. Complex 3 was inactive under similar conditions. NMR analysis confirmed that there were more mmmm pentads in polymer produced by 2 than in the statistically atactic material produced by 1, though the isotacticity index was not high. The results are interpreted in terms of an isotactic/atactic block structure, caused by syn/anti fluxion of the two 2-isopropylphenyl rings in 2. Kinetic profiles and polydispersities were consistent with a slow initiation step involving monomer, followed by rapid propagation, with some chain transfer to aluminium and only a small extent of β-hydride elimination. The rubber-like polymers were indistinguishable by thermal analysis from those prepared by Ziegler-Natta catalyst systems. |
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Keywords: | Polyhexen Titanium Diamido ligands |
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