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Ethylene Tetramerization Catalysis: Effects of Aluminum-Induced Isomerization of PNP to PPN Ligands

Lifschitz, Alejo M. and Hirscher, Nathanael A. and Lee, Heui Beom and Buss, Joshua A. and Agapie, Theodor (2017) Ethylene Tetramerization Catalysis: Effects of Aluminum-Induced Isomerization of PNP to PPN Ligands. Organometallics, 36 (8). pp. 1640-1648. ISSN 0276-7333. doi:10.1021/acs.organomet.7b00189.

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Diphosphinoamines (PNP) are commonly used to support Cr-catalyzed ethylene trimerization and tetramerization. Although isomerization of PNP to a PPN (iminobisphosphine) species has been established, such reactivity has not been studied in detail in the context of Cr-based selective ethylene oligomerization catalysis. Herein, we show that precursors that are stable as PNP frameworks can isomerize to PPN species in the presence of chlorinated aluminum activators relevant to ethylene oligomerization catalysis. Isomerization changes the pattern of reactivity of the ligands, making them more susceptible to nucleophilic attack by alkyl groups, resulting in a variety of degradation products. The isomerization-mediated degradation of PNP ligands leads to the formation of unwanted polymerization catalysts in ethylene tetramerization systems, thus providing insight into the formation of Cr species that affect the overall selectivity and activity values. For example, independently prepared [R_2PNR]^— leads to potent Cr polymerization catalysts. The susceptibility for isomerization is dependent on the nature of the N-substituent of the PNP precursor. Electron donating N-substituent i-Pr, which disfavors the PPN isomer compared to p-tolyl, and minimization of water contamination correlate with higher oligomerization activity and lower polymer byproducts. More broadly, the present study demonstrates the significant impact that Al-activators can have on the structure and behavior of the supporting ligand leading to detrimental reactivity.

Item Type:Article
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URLURL TypeDescription Information
Lee, Heui Beom0000-0002-9550-2649
Buss, Joshua A.0000-0002-3347-8583
Agapie, Theodor0000-0002-9692-7614
Additional Information:© 2017 American Chemical Society. Received 10 March 2017. Published online 13 April 2017. We are grateful to The Dow Chemical Company and Caltech for funding. T.A. .is grateful for Sloan, Dreyfus, and Cottrell fellowships. J.A.B. is grateful to the NSF for a Graduate Research Fellowship. We thank Michael K. Takase and Lawrence M. Henling for assistance with crystallography, and Sean Ewart, David Laitar, and Mari Rosen for insightful discussions.
Funding AgencyGrant Number
Dow Chemical CompanyUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Camille and Henry Dreyfus FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Issue or Number:8
Record Number:CaltechAUTHORS:20170414-070035593
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Official Citation:Ethylene Tetramerization Catalysis: Effects of Aluminum-Induced Isomerization of PNP to PPN Ligands Alejo M. Lifschitz, Nathanael A. Hirscher, Heui Beom Lee, Joshua A. Buss, and Theodor Agapie Organometallics 2017 36 (8), 1640-1648 DOI: 10.1021/acs.organomet.7b00189
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76562
Deposited By: Ruth Sustaita
Deposited On:14 Apr 2017 18:16
Last Modified:15 Nov 2021 17:00

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