C2- and Cs-symmetric diamidodichlorotitanium complexes: Syntheses, structures and 1-hexene polymerization catalysis

The complexes l-[CMe2{CHMeN(2-Pri-C6H4)}2TiCl2] (2) and u-[CMe2{CHMeN(2,6-Pr2iC6H3)}2TiCl2] (3), C2- and Cs-symmetric analogues, respectively, of McConville’s C2v hexene polymerization precatalyst [(CH2)3{N(2,6-Pr2i–C6H3)}2TiCl2] (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.

A new highly-active C2-symmetric diamidotitanium catalyst is described which polymerizes 1-hexene with moderate block tacticity control when activated with MAO. A bulkier Cs-symmetric analogue is inactive.Figure optionsDownload as PowerPoint slide