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Ethylene Trimerization Catalysts Based on Chromium Complexes with a Nitrogen-Bridged Diphosphine Ligand Having ortho-Methoxyaryl or ortho-Thiomethoxy Substituents: Well-Defined Catalyst Precursors and Investigations of the Mechanism

Schofer, Susan J. and Day, Michael W. and Henling, Lawrence M. and Labinger, Jay A. and Bercaw, John E. (2006) Ethylene Trimerization Catalysts Based on Chromium Complexes with a Nitrogen-Bridged Diphosphine Ligand Having ortho-Methoxyaryl or ortho-Thiomethoxy Substituents: Well-Defined Catalyst Precursors and Investigations of the Mechanism. Organometallics, 25 (11). pp. 2743-2749. ISSN 0276-7333. http://resolver.caltech.edu/CaltechAUTHORS:20170308-143404019

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Abstract

Chromium-based ethylene trimerization catalyst precursors ((PNP^(OMe)_(-d)_(12))CrPh_3 (4) and (PNP^(OMe)_(-d)_(12))CrPh_2Cl (7)) having a bis(diphenylphosphino)amine ligand (o-CD_3OC_6H_4)_2PN(CH_3)P(o-CD_3OC_6H_4)_2 ((PNP^(OMe)_(-d)_(12)) = 1) have been prepared and characterized. A thioether analogue (o-CD_3SC_6H_4)_2PN(CH_3)P(o-CD_3SC_6H_4)_2 ((PNP^(SMe)_(-d)_(12)) = 2) and its triphenylchromium complex (PNP^(SMe))CrPh_3 (5) have also been synthesized. The solid-state structures of 4 and 7 display octahedral geometries with a κ^3-(P,P,O) coordination of PNP^(OMe) ligands having chromium−oxygen bond lengths of 2.29−2.44 Å. Compound 5 differs, exhibiting (S,P,S)-κ^3 coordination of the PNP^(SMe) ligand. The deuteromethyl groups allow for ^2H NMR characterization of these paramagnetic complexes in solution. Dynamic exchange processes occur in solution at room temperature to render all four of the methoxy or thioether groups equivalent on the ^2H NMR time scale; two distinct coalescence processes are observed by variable-temperature ^2H NMR spectroscopy for all compounds. The neutral species 4 and 7 react with ethylene (1 atm) by insertion into chromium−phenyl bonds with the release of styrene and ethylbenzene, but 1-hexene is not observed under these conditions. Activation of 4 by protonation and activation of 7 by halide abstraction in the presence of ethylene provide active trimerization catalysts that give turnover numbers for 1-hexene as high as 3000 mol 1-hexene·mol^(-1) Cr. These catalysts display comparable activity and selectivity for 1-hexene compared to the original BP system, where the catalyst is generated in situ from CrCl_3(THF)_3, 1, and MAO. Both the well-defined systems and the CrCl_3(THF)_3/PNP^(OMe)/MAO system provide catalysts that undergo an initiation period followed by an apparent first-order decomposition process. Activated complexes 4 and 7 initiate trimerization primarily through ethylene insertion into the chromium−phenyl bond, followed by β-hydrogen elimination and reductive elimination to give the active species, rather than via reductive elimination of biphenyl.


Item Type:Article
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URLURL TypeDescription
http://dx.doi.org/10.1021/om0506062DOIArticle
http://pubs.acs.org/doi/full/10.1021/om0506062PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/om0506062PublisherSupporting Information
ORCID:
AuthorORCID
Labinger, Jay A.0000-0002-1942-9232
Additional Information:© 2006 American Chemical Society. Received 19 July 2005. Published online 28 April 2006. Published in print 1 May 2006. We thank Dr. Steven A. Cohen for helpful discussions. We are grateful to BP Chemicals (now Innovene) for financial support.
Funders:
Funding AgencyGrant Number
BP ChemicalUNSPECIFIED
Record Number:CaltechAUTHORS:20170308-143404019
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170308-143404019
Official Citation:Ethylene Trimerization Catalysts Based on Chromium Complexes with a Nitrogen-Bridged Diphosphine Ligand Having ortho-Methoxyaryl or ortho-Thiomethoxy Substituents:  Well-Defined Catalyst Precursors and Investigations of the Mechanism Susan J. Schofer,Michael W. Day,Lawrence M. Henling,Jay A. Labinger, and John E. Bercaw Organometallics 2006 25 (11), 2743-2749 DOI: 10.1021/om0506062
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74923
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:08 Mar 2017 23:07
Last Modified:08 Mar 2017 23:07

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