Accessing alkyl- and alkenyl-cyclopentanes from Cr-catalysed ethylene oligomerization using 2-phosphinophosphinine ligands

Robert Newland, Alana Smith, David M. Smith, Natalie Fey, Martin J. Hanton, Stephen M. Mansell

Research output: Contribution to journalArticle

Abstract

Desilylation of the 2-phosphinophosphinine 2-PPh2-3-Me-6-SiMe3-PC5H2 with HCl gave 2-PPh2-3-Me-PC5H2, demonstrating the late-stage modification of this class of heterocyclic ligand, complementing previous approaches where ligand substitution is fixed at an early stage. Group 6 metal carbonyl complexes of these ligands showed κ2-binding and very small bite angles of 65.1 – 68.3°, and also demonstrated that the donor properties of 2-phosphinophosphinines can be tuned readily by the presence of the SiMe3 group which gives a more π-accepting phosphinine ligand. The properties of 2-phosphinophosphinines were compared to bidentate diphosphorus ligands computationally, contextualizing them in the Ligand Knowledge Base for bidentate P,P donor ligands (LKB-PP) and were found to occupy an area of ligand space adjacent to Ar2PN(R)NAr2 ligands that have been successfully used in ethylene oligomerization reactions, but with well-separated properties in the second principal component. Testing 2-phosphinophosphinines in Cr-catalyzed ethylene oligomerization reactions showed key differences to standard PNP ligands in that a high proportion of alkyl- and alkenyl-cyclopentanes were formed. This demonstrates that the different donor properties of 2-phosphinophosphinines influence the reactivity of the key 7-membered metallacycle postulated in the metallacyclic reaction mechanism, generating products from isomerization and subsequent ethylene insertion. Alkyl- and alkenyl-cyclopentanes represent new products for the key industrial feedstock ethylene, with the alkenes having potential as new monomers, comonomers or additives for plastics. Computational evaluation of ligand properties and the resulting property maps can play a role in suggesting future ligand developments to change the selectivity of this industrially-relevant system in the pursuit of new products generated from ethylene.
LanguageEnglish
Pages1062−1073
Number of pages12
JournalOrganometallics
Volume37
Issue number6
Early online date14 Mar 2018
DOIs
StatePublished - 26 Mar 2018

Fingerprint

Cyclopentanes
Oligomerization
Ligands
ethylene
Alkenes
Isomerization
Feedstocks
Substitution reactions

Keywords

  • Ethylene
  • Chromium
  • phosphinine

Cite this

Newland, Robert ; Smith, Alana ; Smith, David M. ; Fey, Natalie ; Hanton, Martin J. ; Mansell, Stephen M./ Accessing alkyl- and alkenyl-cyclopentanes from Cr-catalysed ethylene oligomerization using 2-phosphinophosphinine ligands. In: Organometallics. 2018 ; Vol. 37, No. 6. pp. 1062−1073
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Accessing alkyl- and alkenyl-cyclopentanes from Cr-catalysed ethylene oligomerization using 2-phosphinophosphinine ligands. / Newland, Robert; Smith, Alana; Smith, David M.; Fey, Natalie; Hanton, Martin J.; Mansell, Stephen M.

In: Organometallics, Vol. 37, No. 6, 26.03.2018, p. 1062−1073.

Research output: Contribution to journalArticle

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T1 - Accessing alkyl- and alkenyl-cyclopentanes from Cr-catalysed ethylene oligomerization using 2-phosphinophosphinine ligands

AU - Newland,Robert

AU - Smith,Alana

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AB - Desilylation of the 2-phosphinophosphinine 2-PPh2-3-Me-6-SiMe3-PC5H2 with HCl gave 2-PPh2-3-Me-PC5H2, demonstrating the late-stage modification of this class of heterocyclic ligand, complementing previous approaches where ligand substitution is fixed at an early stage. Group 6 metal carbonyl complexes of these ligands showed κ2-binding and very small bite angles of 65.1 – 68.3°, and also demonstrated that the donor properties of 2-phosphinophosphinines can be tuned readily by the presence of the SiMe3 group which gives a more π-accepting phosphinine ligand. The properties of 2-phosphinophosphinines were compared to bidentate diphosphorus ligands computationally, contextualizing them in the Ligand Knowledge Base for bidentate P,P donor ligands (LKB-PP) and were found to occupy an area of ligand space adjacent to Ar2PN(R)NAr2 ligands that have been successfully used in ethylene oligomerization reactions, but with well-separated properties in the second principal component. Testing 2-phosphinophosphinines in Cr-catalyzed ethylene oligomerization reactions showed key differences to standard PNP ligands in that a high proportion of alkyl- and alkenyl-cyclopentanes were formed. This demonstrates that the different donor properties of 2-phosphinophosphinines influence the reactivity of the key 7-membered metallacycle postulated in the metallacyclic reaction mechanism, generating products from isomerization and subsequent ethylene insertion. Alkyl- and alkenyl-cyclopentanes represent new products for the key industrial feedstock ethylene, with the alkenes having potential as new monomers, comonomers or additives for plastics. Computational evaluation of ligand properties and the resulting property maps can play a role in suggesting future ligand developments to change the selectivity of this industrially-relevant system in the pursuit of new products generated from ethylene.

KW - Ethylene

KW - Chromium

KW - phosphinine

U2 - 10.1021/acs.organomet.8b00063

DO - 10.1021/acs.organomet.8b00063

M3 - Article

VL - 37

SP - 1062−1073

JO - Organometallics

T2 - Organometallics

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ER -