Spectroscopic Signature and Structure of the Active Sites in Ziegler–Natta Polymerization Catalysts Revealed by Electron Paramagnetic Resonance

Despite decades of extensive studies, the atomic-scale structure active sites in heterogeneous Ziegler–Natta (ZN) catalysts, one most important processes chemical industry, remains elusive and a matter debate. In present work, ZN catalysts absence ethylene, referred to as dormant sites, is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts BCl3 so enhance concentration observe clear spectroscopic signatures. Using electron paramagnetic (EPR) NMR spectroscopies, particular 2D HYSCORE complemented by density functional theory (DFT) calculations, we show that activated contain bimetallic alkyl-Ti(III),Al species whose amount directly linked polymerization activity MgCl2-supported catalysts. This connects those signatures formed presence ethylene enables us propose an mechanism observed based DFT computations.