Electron Paramagnetic Resonance Study of the Interaction
of Surface Titanium Species with AlR<sub>3</sub> Cocatalyst in Supported
Ziegler–Natta Catalysts with a Low Titanium Content
The
electron paramagnetic resonance (EPR) method was used to investigate
the formation of alkylated Ti(III) species in superactive titanium–magnesium
catalysts with a low titanium content during their interaction with
an organoaluminum activator (AlMe<sub>3</sub>), as well as the interaction
of alkylated Ti(III) surface species with carbon monoxide. EPR data
on the content of alkylated Ti(III) species in these catalysts agree
well with the number of Ti–R bonds that are determined after
the interaction of radioactive carbon monoxide (<sup>14</sup>CO) with
catalyst activated by triethylaluminum in the absence of monomer.
Parameters of EPR spectra of the Ti(III) species having different
structure and composition on the surface of titanium–magnesium
catalysts were calculated by quantum-chemical simulations. The calculated <i>g</i>-values are consistent with the <i>g</i>-values
observed in EPR spectra of the catalysts. Analysis of the literature
data and results of our study made it possible to propose the parameters
of EPR spectra characterizing the alkylated Ti(III) species that can
serve as precursors of the active sites in supported Ziegler–Natta
catalysts
