Electron Paramagnetic Resonance Study of the Interaction of Surface Titanium Species with AlR3 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 (AlMe3), 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 (14CO) 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 g-values are consistent with the g-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.