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Ethylene Oligomerization with Cr-NHC Catalysts: Further Insights into the Extended Metallacycle Mechanism of Chain Growth
journal contribution
posted on 2023-05-16, 21:51 authored by McGuinness, DS, Suttil, JA, Michael GardinerMichael Gardiner, Noel DaviesNoel DaviesThe mechanism of ethylene oligomerization with chromium(III) complexes of bis(carbene)pyridine ligands in combination with MAO has been investigated. Oligomerization with mixtures of CH2CH2/ CD 2CD2 reveals that this system produces α-olefins via an extended metallacycle mechanism. Deviation form a Schulz-Flory distribution has been explained on the basis of less favorable product release at the early stages of metallacycle growth (Cr-C4 (±Cr-C6)). Significant amounts of branched olefins (methylidenes) and linear internal olefins are produced at the high catalyst loadings employed in this study, and these result from secondary incorporation of α-olefins into the metallacycle mechanism. Changing the ligand C∧N∧C coordination mode in any way resulted in a sharp loss of activity. In the case of bidentate carbene-pyridine and carbene-thiophene ligands, this is due to a change in the mechanism from metallacycle to linear chain growth. Thus, only those catalysts which support a metallacycle mechanism promote oligomerization with high activity. © 2008 American Chemical Society.
History
Publication title
OrganometallicsVolume
27Issue
16Pagination
4238-4247ISSN
0276-7333Department/School
School of Natural SciencesPublisher
American Chemical SocietyPlace of publication
WashingtonRepository Status
- Restricted