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Activation of [CrCl3{PPh2N(iPr)PPh2}] for the selective oligomerisation of ethene: a Cr K-edge XAFS study

Activation of [CrCl3{PPh2N(iPr)PPh2}] for the selective oligomerisation of ethene: a Cr K-edge XAFS study
Activation of [CrCl3{PPh2N(iPr)PPh2}] for the selective oligomerisation of ethene: a Cr K-edge XAFS study
The activation of the ethene tetramerisation catalyst system based upon [CrCl3(THF)3] and N(iPr)(PPh2)2 has been investigated in situ via the reaction of [CrCl3{PPh2N(R)PPh2}(THF)] 1a (R=iPr) with excess AlMe3 in toluene. The Cr K-edge XAFS spectrum of the solution freeze quenched after 1 min reaction time indicated monomethylation of the metal with the resultant product being [CrClMe(ClAlCl3){PPh2N(R)PPh2}(THF)] 4a (R=iPr). After 5 minutes reaction time the XAFS spectra indicate that ~50% of 4a had been converted to a Cr(II) species, with the central core being high spin [CrCl2{PPh2N(R)PPh2}] 7a (R=iPr); a similar species, [CrClMe{PPh2N(R)PPh2}] 9a (R=iPr) was observed as its adduct with AlMe3 (10a) (R=iPr) when spectra were recorded on samples maintained a room temperature. Detailed analysis (EXAFS and XANES) indicated that 7a and 9a are stabilised by adduct formation of a Cr-Cl bond to the Lewis acids B(C6F5)3 and AlMe3, respectiveley. Modelling with DFT methods indicated that five-coordination was achieved, respectively by Cr-F (11a) and Cr-C (10a) interactions. In the presence of [Ph3C][Al{OC(tBuF)3}4], the Cr XAFS of the room temperature solution was inconsistent with the maintenance of a phosphine complex, but could be modelled with a site like [Cr2Me8]4- {Cr-Cr 2.01(2), Cr-C 2.14(4)}, thus demonstrating considerable variation in the effects of differing Lewis acids.
2044-4753
6237-6246
Bartlett, Stuart A.
1adeb675-9e04-4635-bdb8-df3833333f34
Moulin, Jerome
568937e0-1a00-4347-9368-7ac2b13c1869
Tromp, Moniek
48c1ebbb-579c-42b6-83bb-7188c668b322
Reid, Gill
37d35b11-40ce-48c5-a68e-f6ce04cd4037
Dent, Andy J.
43d27d73-de43-4e9a-a21e-65c6095a7bf4
Cibin, Giannantonio
61a833d3-097f-4817-bcd3-6b26cf42dbe5
McGuinness, David S.
8b93fc01-6b9c-4d5b-b77b-6e992a783bde
Evans, John
05890433-0155-49fe-a65d-38c90ea25c69
Bartlett, Stuart A.
1adeb675-9e04-4635-bdb8-df3833333f34
Moulin, Jerome
568937e0-1a00-4347-9368-7ac2b13c1869
Tromp, Moniek
48c1ebbb-579c-42b6-83bb-7188c668b322
Reid, Gill
37d35b11-40ce-48c5-a68e-f6ce04cd4037
Dent, Andy J.
43d27d73-de43-4e9a-a21e-65c6095a7bf4
Cibin, Giannantonio
61a833d3-097f-4817-bcd3-6b26cf42dbe5
McGuinness, David S.
8b93fc01-6b9c-4d5b-b77b-6e992a783bde
Evans, John
05890433-0155-49fe-a65d-38c90ea25c69

Bartlett, Stuart A., Moulin, Jerome, Tromp, Moniek, Reid, Gill, Dent, Andy J., Cibin, Giannantonio, McGuinness, David S. and Evans, John (2016) Activation of [CrCl3{PPh2N(iPr)PPh2}] for the selective oligomerisation of ethene: a Cr K-edge XAFS study. Catalysis Science & Technology, 6, 6237-6246. (doi:10.1039/C6CY00902F).

Record type: Article

Abstract

The activation of the ethene tetramerisation catalyst system based upon [CrCl3(THF)3] and N(iPr)(PPh2)2 has been investigated in situ via the reaction of [CrCl3{PPh2N(R)PPh2}(THF)] 1a (R=iPr) with excess AlMe3 in toluene. The Cr K-edge XAFS spectrum of the solution freeze quenched after 1 min reaction time indicated monomethylation of the metal with the resultant product being [CrClMe(ClAlCl3){PPh2N(R)PPh2}(THF)] 4a (R=iPr). After 5 minutes reaction time the XAFS spectra indicate that ~50% of 4a had been converted to a Cr(II) species, with the central core being high spin [CrCl2{PPh2N(R)PPh2}] 7a (R=iPr); a similar species, [CrClMe{PPh2N(R)PPh2}] 9a (R=iPr) was observed as its adduct with AlMe3 (10a) (R=iPr) when spectra were recorded on samples maintained a room temperature. Detailed analysis (EXAFS and XANES) indicated that 7a and 9a are stabilised by adduct formation of a Cr-Cl bond to the Lewis acids B(C6F5)3 and AlMe3, respectiveley. Modelling with DFT methods indicated that five-coordination was achieved, respectively by Cr-F (11a) and Cr-C (10a) interactions. In the presence of [Ph3C][Al{OC(tBuF)3}4], the Cr XAFS of the room temperature solution was inconsistent with the maintenance of a phosphine complex, but could be modelled with a site like [Cr2Me8]4- {Cr-Cr 2.01(2), Cr-C 2.14(4)}, thus demonstrating considerable variation in the effects of differing Lewis acids.

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Accepted/In Press date: 17 May 2016
e-pub ahead of print date: 18 May 2016
Organisations: Organic Chemistry: SCF

Identifiers

Local EPrints ID: 395219
URI: https://eprints.soton.ac.uk/id/eprint/395219
ISSN: 2044-4753
PURE UUID: cfc76db9-8724-4753-b3c6-e9292f6c8569
ORCID for Gill Reid: ORCID iD orcid.org/0000-0001-5349-3468

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Date deposited: 26 May 2016 08:45
Last modified: 31 Jul 2019 05:27

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Contributors

Author: Stuart A. Bartlett
Author: Jerome Moulin
Author: Moniek Tromp
Author: Gill Reid ORCID iD
Author: Andy J. Dent
Author: Giannantonio Cibin
Author: David S. McGuinness
Author: John Evans

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