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Polymerization of Ethylene by Silica‐Supported Dinuclear Cr III Sites through an Initiation Step Involving CH Bond Activation
Author(s) -
Conley Matthew P.,
Delley Murielle F.,
Siddiqi Georges,
Lapadula Giuseppe,
Norsic Sébastien,
Monteil Vincent,
Safonova Olga V.,
Copéret Christophe
Publication year - 2014
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201308983
Subject(s) - heterolysis , catalysis , ethylene , polymerization , chemistry , olefin fiber , polymer chemistry , metal , reaction mechanism , photochemistry , organic chemistry , polymer
The insertion of an olefin into a preformed metal–carbon bond is a common mechanism for transition‐metal‐catalyzed olefin polymerization. However, in one important industrial catalyst, the Phillips catalyst, a metal–carbon bond is not present in the precatalyst. The Phillips catalyst, CrO 3 dispersed on silica, polymerizes ethylene without an activator. Despite 60 years of intensive research, the active sites and the way the first CrC bond is formed remain unknown. We synthesized well‐defined dinuclear Cr II and Cr III sites on silica. Whereas the Cr II material was a poor polymerization catalyst, the Cr III material was active. Poisoning studies showed that about 65 % of the Cr III sites were active, a far higher proportion than typically observed for the Phillips catalyst. Examination of the spent catalyst and isotope labeling experiments showed the formation of a Si–(μ‐OH)–Cr III species, consistent with an initiation mechanism involving the heterolytic activation of ethylene at Cr III O bonds.