Formation of Elastomeric Polypropylene Promoted by a Dynamic Octahedral Titanium Complex

The complex Ti(Ph2PNpy)(NEt2)2 (2) was prepared by the reaction between 2 equiv of the
neutral ligand Ph2PNHpy (1) and 1 equiv of the homoleptic titanium tetrakis(diethylamine).
Complex 2 exhibits two dynamic processes as a function of the temperature. An equilibrium
among the diphenylphosphino moieties and a strong agostic interaction between the titanium
atom and one of the hydrogens of each of the methylene groups of the diethylamido ligand.
The strength of the chelating ligand was studied by its reaction with ethylamine, producing
the imido complex 3, showing that during the transformation 2 → 3 the pyridine rings of
the ligand are able to dissociate and recoordinate with different stereochemistries. In the
polymerization of propylene by complex 2 activated by MAO, elastomeric polymers are
obtained. The elastomeric polymers are a result of monomer insertions into two enantiomerically close configuration complexes, as is encountered in cationic nonbridged metallocenes.