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Spectroscopic Signature and Structure of Active Centers in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

preprint
revised on 24.08.2020 and posted on 25.08.2020 by Anton Ashuiev, Matthieu Humbert, David Gajan, Sebastien Norsic, Jan Blahut, Keith Searles, Daniel Klose, Anne Lesage, Guido Pintacuda, Jean Raynaud, Vincent Monteil, Christophe Copéret, Gunnar Jeschke
Despite decades of extensive studies, the atomic-scale structure of active sites in heterogeneous Ziegler-Natta (ZN) catalysts remains elusive and a matter of debate. Here, the structure of polymerization ZN catalysts is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl3 so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Notably, we show that EPR and NMR spectroscopy of the activated ZN catalysts enables to observe paramagnetic species whose amount increases in conjunction with the catalytic activity. The joint application of 2D HYSCORE experiments and DFT calculations reveals the presence of bimetallic alkyl-Ti(III),Al complexes that are assigned to the catalytic centers of MgCl2-supported Ziegler-Natta catalysts

Funding

SNF–ANR grant (Mr. CAT 2‐77275‐15)

ANR–SNF grant (MRCAT ANR-15-CE29-0025)

History

Email Address of Submitting Author

ccoperet@inorg.chem.ethz.ch

Institution

ETH Zürich

Country

Switzerland

ORCID For Submitting Author

0000-0001-9660-3890

Declaration of Conflict of Interest

no conflict of interest

Version Notes

This is the first version of this manuscript

Exports