Role of the ligand and activator in selective Cr–PNP ethene tri- and tetramerization catalysts – a spectroscopic study

Venderbosch, Bas; Wolzak, Lukas A.; Oudsen, Jean‐Pierre H.; Bruin, Bas de; Korstanje, Ties J.; Tromp, Moniek

doi:10.1039/d0cy01168a

Cited by 12 publications

(11 citation statements)

References 31 publications

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“…41 In catalyst model A, all four benzene rings are free to rotate, while in catalyst model B, two oxygen atoms in the two methoxy groups coordinate to the chromium centre, limiting the spatial rotation of two benzene rings in which the methoxy groups are located. Compared with the Cr(II)/Cr(IV) cycle, 43,[66][67][68] the Cr(I)/Cr(III) cycle has been supported by many experimental and theoretical studies. 44,55,[69][70][71][72][73][74][75][76] According to these calculations, the Cr(I) complexes have a sextet ground spin state, while the Cr(III) complexes usually have a quartet ground spin state.…”

Section: Molecule Modelmentioning

confidence: 96%

Cr/PCCP-catalysed selective ethylene oligomerization: analysis of various conformations and the hemilabile methoxy group

Zhong

Liu

Xia

et al. 2022

Catal. Sci. Technol.

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Section: Molecule Modelmentioning

confidence: 96%

Cr/PCCP-catalysed selective ethylene oligomerization: analysis of various conformations and the hemilabile methoxy group

Zhong

Liu

Xia

et al. 2022

Catal. Sci. Technol.

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“…[72] Recently, Tromp used Cr K-Edge XAS and EPR experiments combined with DFT calculations to propose Cr II species as the active species in the trimerization of ethylene. [73,74] Square planar Cr II complexes were observed after activation with MMAO (400eq.) in two different cases (Scheme 30).…”

Section: Chromiummentioning

confidence: 99%

Alkene oligomerization via metallacycles: Recent advances and mechanistic insights

Petit

Magna

Mézailles

2022

Coordination Chemistry Reviews

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“…20,21 Although a significant body of experimental and theoretical findings support the importance of Cr III/I cycling, 22 limited spectroscopic evidence supporting such an assignment of the redox chemistry of Cr catalysts is available. 23 Obtaining evidence is challenging due to the presumed low concentration of the chromium-derived active species, measurements under catalytic conditions that involve multiple oxidation states, and the challenges inherent in measuring particular oxidation states of Cr, each of which presents unique spectroscopic challenges. 24−26 Here, we report the redox reactivity that is accessible to a family of Cr III complexes supported by bidentate P,N ligands in the absence of substrates, such as ethylene or related models like hexyne (Chart 2).…”

Section: ■ Introductionmentioning

confidence: 99%

Spectroscopic Interrogation of the Reduction of Model Chromium Precatalysts for Olefin Oligomerization

et al. 2022

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Chromium precatalysts typically undergo in situ or ex situ activation to enable olefin oligomerization. The activation processes significantly impact catalytic reactivity, but the conditions used often involve low concentrations of chromium, increasing the difficulty of obtaining mechanistic insights. Here, we describe investigations into the redox chemistry accessible to a family of Cr III precatalysts for ethylene oligomerization. Cyclic voltammetry (CV) studies of the Cr III complexes 1, 2, and 3 (Cr(P,N)-Cl 3 (THF), where (P,N) represents one of a series of bidentate phosphorus-and nitrogen-containing ligands and THF is innersphere tetrahydrofuran) reveal single quasi-reversible reductions for each of the complexes, all near −1.5 V versus ferrocenium/ ferrocene (Fc +/0 ). CV also indicates minor formation of heterogeneous material upon electrochemical reduction; these processes were quantified with electrochemical quartz crystal microbalance (EQCM) studies and X-ray photoelectron (XP) spectroscopy. Electron paramagnetic resonance (EPR; at X-band) studies of the paramagnetic Cr III complexes are reported as well as studies of the in situ reduction of the Cr III complexes. Treatment of the Cr III complexes with decamethylcobaltocene (Cp* 2 Co), triethylaluminum (AlEt 3 ), or modified methylaluminoxane (MAO) primarily results in production of S = 2 Cr II species. Minor quantities (ca. 1% conversion) of Cr I species are also produced. The structure of the Cr II form of 1 was obtained from single-crystal X-ray diffraction analysis and is consistent with the proposed reactivity pattern. Titration of 1 with Cp* 2 Co reveals isosbestic behavior in UV−vis spectra consistent with one-electron reduction of 1, confirming these findings. Notably, however, reduction of 1 with 2 equiv of Cp* 2 Co in the presence of AlEt 3 reveals that the system can cleanly undergo further reduction by at least two electrons. Taken together, these results provide insights into the redox chemistry accessible to Cr III precatalysts for ethylene oligomerization.

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Role of the ligand and activator in selective Cr–PNP ethene tri- and tetramerization catalysts – a spectroscopic study

Abstract: The reaction of the ethene tetramerization catalyst, ((C6H5)2P)2NiPrCrCl3(THF) (complex 1), and ethene trimerization catalyst, ((o-C6H4OMe)2P)2NMeCrCl3 (complex 2), with alkylaluminum reagents (AlMe3 and MMAO) was investigated using spectroscopic techniques (Cr K-edge...

Cited by 12 publications

References 31 publications

Cr/PCCP-catalysed selective ethylene oligomerization: analysis of various conformations and the hemilabile methoxy group

Cr/PCCP-catalysed selective ethylene oligomerization: analysis of various conformations and the hemilabile methoxy group

Alkene oligomerization via metallacycles: Recent advances and mechanistic insights

Spectroscopic Interrogation of the Reduction of Model Chromium Precatalysts for Olefin Oligomerization

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