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Instruments / Technical Area	Publication Details	Published	Actions
B18-Core EXAFS	Role of the ligand and activator in selective Cr–PNP ethene tri- and tetramerization catalysts – a spectroscopic study Bas Venderbosch , Lukas A. Wolzak , Jean-Pierre H. Oudsen , Bas De Bruin , Ties J. Korstanje , Moniek Tromp Catalysis Science & Technology 91 DOI: 10.1039/D0CY01168A Diamond Proposal Number(s): [22331] Open Access Show Abstract ▼ 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 XAS, X-band EPR and UV-vis) and catalytic studies. In all cases the majority of chromium was reduced to the divalent oxidation state and only a minor fraction of chromium was reduced further to the monovalent oxidation state. It is demonstrated that MMAO and the ligand (through a pendant ether donor) can facilitate ion pair formation for these divalent Cr complexes, providing insights into the role of the ligand and activator in the activation process. Via the use of dienes, we succeeded in characterizing a monocationic CrII alkene complex, providing evidence that catalysis could proceed via cationic CrII/CrIV intermediates. This is supported by DFT calculations, where it is shown that a mechanism proceeding via dicationic CrII/CrIV intermediates explains the observed product selectivity.	Aug 2020
B18-Core EXAFS	Spectroscopic investigation of the activation of a chromium-pyrrolyl ethene trimerization catalyst Bas Venderbosch , Jean-Pierre H. Oudsen , Lukas A. Wolzak , David J. Martin , Ties Johannis Korstanje , Moniek Tromp Acs Catalysis DOI: 10.1021/acscatal.8b03414 Diamond Proposal Number(s): [17599] Open Access Show Abstract ▼ Abstract: 1-Hexene is an important α-olefin for polyethylene production, and is produced from ethene. Recent developments in the α-olefin industry have led to the successful commercialization of ethene trimerization catalysts. An important industrially applied ethene trimerization system uses a mixture of chromium 2-ethylhexanoate, AlEt3, AlEt2Cl and 2,5-dimethylpyrrole (DMP). Here, we have studied the activation of this system using catalytic and spectroscopic experiments (XAS, EPR and UV-Vis) under conditions employed in industry. Firstly, chromium 2-ethylhexanoate was prepared and characterized to be [Cr3O(RCO2)6(H2O)3]Cl. Next, the activation of chromium 2-ethylhexanoate with AlEt3, AlEt2Cl and DMP was studied, showing immediate reduction (<5 ms) of the trinuclear Cr(III) carboxylate and formation of a neutral polynuclear Cr(II) carboxylate complex. Over time this Cr(II) carboxylate complex is partially converted into a chloro-bridged dinuclear Cr(II) pyrrolyl complex. In cyclohexane, small quantities of an unknown Cr(I) complex (~1% after 1 hour) are observed, while in toluene the quantity of Cr(I) is much higher (~23% after an hour). This is due to the formation of cationic bis(tolyl)Cr(I) complexes, which likely leads to the observed inferior performance using toluene as the reaction solvent. Catalytic studies allow us to exclude some of the observed Cr(I) and Cr(II) complexes as the active species in this catalytic system. Using this combination of techniques, we have been able to structurally characterize complexes of this selective Cr-catalyzed trimerization system under conditions which are employed in industry.	Dec 2018

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