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Phenylene-Bridged OSSO-Type Titanium Complexes in the Polymerization of Ethylene and Propylene
journal contribution
posted on 2018-09-21, 18:05 authored by Rosita Lapenta, Antonio Buonerba, Ermanno Luciano, Francesco Della Monica, Assunta De Nisi, Magda Monari, Alfonso Grassi, Carmine Capacchione, Stefano MilioneThe dichloro titanium complexes (OSSOtBu)TiCl2 (1) and
(OSSOCum)TiCl2 (2) bearing o-phenylene-bridged
OSSO-type ligands [OSSOtBu-H = 6,6′-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-di-tert-butyphenol) and OSSOCum-H = 6,6′-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenol)]
were prepared and characterized. The X-ray structure of 1 revealed that Ti atom has an octahedral coordination geometry with
an fac–fac wrapping of the
[OSSO] ligand. In solution at 25 °C, 1 mainly retains
the C2 symmetric structure, whereas 2 shows an equilibrium between C2- and C1-symmetric stereoisomers. Activation
of 2 with (Ph3C)[B(C6F5)4] led to a highly active catalytic system with an activity
of 238 kgPE·molcat–1·bar–1·h–1; linear polyethylene with
a Tm of 122 °C and Mw of 107 kDa were obtained under these conditions. Catalyst 1 displayed the moderate activity of 59 kgPE·molcat–1·bar–1·h–1. Gel permeation chromatography analysis revealed
the formation of high-molecular-weight polyethylenes with very large
distributions of the molecular weights, indicating a low control of
the polymerization process, probably becaue of the presence of different
active species in solution. Density functional theory investigation
provides a rational for the relative high-molecular-weight polymers
obtained with these complexes. The precatalyst 2 was
also active in propylene polymerization producing atactic oligomers
terminated with unsaturated end groups.