Octahedral Zirconium Salan Catalysts for Olefin Polymerization: Substituent and Solvent Effects on Structure and Dynamics

Dall'Anese, A.; Kulyabin, P.; Uborsky, D.; Vittoria, A.; Ehm, C.; Cipullo, R.; Budzelaar, P.; Voskoboynikov, A.; Busico, V.; Tensi, L.; Macchioni, A.; Zuccaccia, C.

Авторы: Dall'Anese Anna, Kulyabin Pavel, Uborsky Dmitry, Vittoria Antonio, Ehm Christian, Cipullo Roberta, Budzelaar Peter, Voskoboynikov Alexander, Busico Vincenzo, Tensi Leonardo, Macchioni Alceo, Zuccaccia Cristiano
Журнал: Inorganic Chemistry
Том: 62
Номер: 39
Год издания: 2023
Издательство: American Chemical Society
Местоположение издательства: United States
Первая страница: 16021
Последняя страница: 16037
DOI: 10.1021/acs.inorgchem.3c02153
Аннотация: Group 4 metal-Salan olefin polymerization catalysts typically have relatively low activity, being slowed down by apre-equilibrium favoring a non-polymerization active resting state identified as a mer-mer isomer (MM); formation of thepolymerization active fac-fac species (FF) requires isomerization. We now show that the chemistry is more subtle than previouslyrealized. Salan variations bearing large, flat substituents can achieve very high activity, and we ascribe this to the stabilization ofthe FF isomer, which becomes lower in energy than MM. Detailed in situ NMR studies of a fast (o-anthracenyl) and a slow (o-tBu)Salan precursor, suitably activated, indicate that preferred isomers in solution are different: the fast catalyst prefers FF while theslow catalyst prefers a highly distorted MM geometry. Crystal structures of the activated o-anthracenyl substituted complex with amoderately (chlorobenzene) and, more importantly, a weakly coordinating solvent (toluene) in the first coordination sphereemphasize that the active FF isomer is preferred, at least for the benzyl species. Site epimerization (SE) barriers for the fast catalyst(ΔS > 0, dissociative) and the slow catalyst (ΔS < 0, associative) in toluene corroborate the solvent role. Diagnostic NMe 13Cchemical shift differences allow unambiguous detection of FF or MM geometries for seven activated catalysts in different solvents,highlighting the role of solvent coordination strength and bulkiness of the ortho substituent on the isomer equilibrium. For the firsttime, active polymeryl species of Zr-Salan catalysts were speciated. The slow catalyst is effectively trapped in an inactive MM stateas previously suggested. Direct observation of fast catalysts is hampered by their high reactivity, but the product of the first 1-hexene insertion, maintains its FF geometry.
Добавил в систему: Уборский Дмитрий Вадимович

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Octahedral Zirconium Salan Catalysts for Olefin Polymerization: Substituent and Solvent Effects on Structure and Dynamicsстатья

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