Mechanistic Investigations of the Ethylene Tetramerisation Reaction

Overett, Matthew J.; Blann, Kevin; Bollmann, Annette; Dixon, J; Haasbroek, Daleen; Killian, Esna; Maumela, Hulisani; McGuinness, David S.; Morgan, D. H.

doi:10.1021/ja052327b

Cited by 234 publications

(236 citation statements)

References 29 publications

(28 reference statements)

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“…The selectivity to 1-hexene decreased and the selectivity to 1-octene increased with increasing ethylene pressure. Changes in product distribution were in good agreement with the metallacycle mechanism proposed by Overett et al [24]. This is indicative of a strong ethylene concentration influence on the product distribution in general and the formation of 1-octene in particular.…”

Section: The Effect Of Reaction Pressure On Catalytic Propertiessupporting

confidence: 88%

Ethylene tetramerization with a highly active and long-lifetime trinuclear diphenylphosphinoamine/Cr(III)/MAO catalyst

et al. 2012

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The synthesis and characterization of a novel trinuclear diphosphinoamine ligand 2 are reported. The ligand combined with Cr(III), activated with methylaluminoxane, lead to highly active and long-lifetime catalytic systems for the tetramerization of ethylene to form 1-octene. The effects of reaction temperature, reaction pressure, molar ratio of Al/Cr and bis(diphenylphosphino)amine/Cr on the catalytic activity and product selectivity were studied. Compared with its mononuclear analogue 1, ligand 2 showed a higher catalytic activity and longer lifetime for ethylene tetramerization in the presence of methylaluminoxane as cocatalyst. High molecular weight polyethylene was generated as a by-product with extremely broad molecular weight distributions. In recent years there has been a substantial acceleration in research activity concerned with homogeneous transition metal catalysts for ethylene oligomerization and polymerization. Chromium catalysts play an important role in both of these processes [1][2][3][4][5][6][7][8]. Since the first report of ethylene tetramerization to form 1-octene using Cr-bis(diphenylphosphino)amine (PNP) catalysts [9], numerous studies have investigated the relationship between ligand structure and catalytic properties. We were attracted by the potential for using chromium as an ethylene tetramerization active center because of its high catalytic activity and high selectivity to 1-octene. Here, we describe a new trinuclear PNP ligand that displays higher activity and a long lifetime for ethylene tetramerization to 1-octene.

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Section: The Effect Of Reaction Pressure On Catalytic Propertiessupporting

confidence: 88%

Ethylene tetramerization with a highly active and long-lifetime trinuclear diphenylphosphinoamine/Cr(III)/MAO catalyst

et al. 2012

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“…A previous investigation into the formation of methylcyclopentane and methylenecyclopentane by PNP based ethylene tetramerisation systems has proposed two possible mechanisms by which the species can form. 76 In that report the authors suggest that the readily formed chromacycloheptane can rearrange either via a concerted mechanism (Scheme 3, pathway a) or a formal β-hydride transfer to chromium and subsequent cyclisation of the 5-hexenyl moiety by reinsertion (Scheme 3, pathway b) to generate the cyclopentylmethylchromium intermediate 20. View Article Online disproportionation process (either mono-or bimetallic) or via cyclopentylmethyl radicals (although 5-hexen-1-yl radicals cannot be discounted); however experimental evidence disfavoured the latter mechanism.…”

Section: Methodsmentioning

confidence: 99%

A survey of pendant donor-functionalised (N,O) phosphine ligands for Cr-catalysed ethylene tri- and tetramerisation

Suttil

Wasserscheid

McGuinness

et al. 2014

Catal. Sci. Technol.

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In this study three classes of ligands are explored for ethylene tri-/tetramerisation in conjunction with chromium and both triethylaluminium (AlEt 3 ) and methylaluminoxane (MAO) co-catalysts. Hydrazine based ligands containing an N-H functionality [PN(NH)P], analogous to Rosenthal's previously reported PNPNH system, show selectivity towards 1-hexene and 1-octene formation in conjunction with AlEt 3 , and act as PNP tetramerisation analogues when MAO is employed. PNP ligands containing non-protic pendant donor moieties generally show poor activity and selectivity when AlEt 3 is employed as an activator, however when MAO is used good activities and selectivities are achieved. n-Propylcyclopentane and 2-propenylcyclopentane, and higher homologues, are produced during catalysis when oxygen is the donor atom. The formation of such products is discussed with respect to the generation of methylenecyclopentane and methylcyclopentane by PNP based tetramerisation catalysts. Simple phosphine ligands containing O-H functionalisation are also explored and it was shown that the catalyst selectivity is highly dependent on both the activator and structural features of the ligand employed.

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“…The results of this study gave a reasonably realistic picture of the complex nature of this catalytic system, but the mechanism is unlikely to be general for all Cr systems. In addition to studies on trimerization of ethylene, the chromium catalyzed tetramerization mechanism was also proven to be an extended metallacyclic mechanism [72]. These studies were so far based on pre-catalysts which require activation by alkyl aluminium compounds before Scheme 9 Synthesis of the isolated single-component oligomerization and polymerization catalyst they can actually take part in catalysis.…”

Section: Ethylene Oligomerizationmentioning

confidence: 99%

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

et al. 2015

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In the context of homogeneous catalysis, openshell systems are often quite challenging to characterize. Nuclear magnetic resonance (NMR) spectroscopy is the most frequently applied tool to characterize organometallic compounds, but NMR spectra are usually broad, difficult to interpret and often futile for the study of paramagnetic compounds. As such, electron paramagnetic resonance (EPR) has proven itself as a useful spectroscopic technique to characterize paramagnetic complexes and reactive intermediates. EPR spectroscopy is a particularly useful tool to investigate their electronic structures, which is fundamental to understand their reactivity. This paper describes some selected examples of studies where EPR spectroscopy has been useful for the characterization of open-shell organometallic complexes. The paper concentrates in particular on systems where EPR spectroscopy has proven useful to understand catalytic reaction mechanisms involving paramagnetic organometallic catalysts. The expediency of EPR spectroscopy in the study of organometallic chemistry and homogenous catalysis is contextualized in the introductory Sect. 1. Section 2 of the review focusses on examples of C-C and C-N bond formation reactions, with an emphasis on catalytic reactions where ligand/substrate non-innocence plays an important role. Both carbon and nitrogen centered radicals have been shown to play an important role in these reactions. A few selected examples of catalytic alcohol oxidation proceeding via related N-centered ligand radicals are included in this section as well. Section 3 covers examples of the use of EPR spectroscopy to study important commercial ethylene oligomerization and polymerization processes. In Sect. 4 the use of EPR spectroscopy to understand the mechanisms of Atom Transfer Radical Polymerization is discussed. While this review focusses predominantly on the application of EPR spectroscopy in mechanistic studies of C-C and C-N bond formation reactions mediated by organometallic catalysts, a few selected examples describing the application of EPR spectroscopy in other catalytic reactions such as water splitting, photo-catalysis, photo-redox-catalysis and related reactions in which metal initiated (free) radical formation plays a role are included as well. EPR spectroscopic investigation in this area of research are dominated by EPR spectroscopic studies in isotropic solution, including spin trapping experiments. These reactions are highlighted in Sect. 5. EPR spectroscopic studies have proven useful to discern the correct oxidation states of the active catalysts and also to determine the effective concentrations of the active species. EPR is definitely a spectroscopic technique that is indispensable in understanding the reactivity of paramagnetic complexes and in conjunction with other advanced techniques such as X-ray absorption spectroscopy and pulsed laser polymerization it will continue to be a very practical tool.

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Mechanistic Investigations of the Ethylene Tetramerisation Reaction

Cited by 234 publications

References 29 publications

Ethylene tetramerization with a highly active and long-lifetime trinuclear diphenylphosphinoamine/Cr(III)/MAO catalyst

Ethylene tetramerization with a highly active and long-lifetime trinuclear diphenylphosphinoamine/Cr(III)/MAO catalyst

A survey of pendant donor-functionalised (N,O) phosphine ligands for Cr-catalysed ethylene tri- and tetramerisation

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

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