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Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl 3 ] Ethene Trimerization System: Mononuclear or Dinuclear?
Author(s) -
Venderbosch Bas,
Oudsen JeanPierre H.,
Martin David J.,
Bruin Bas,
Korstanje Ties J.,
Tromp Moniek
Publication year - 2020
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201901640
Subject(s) - cationic polymerization , chemistry , methylaluminoxane , catalysis , catalytic cycle , alkyne , octahedron , ethylene , stereochemistry , electron paramagnetic resonance , reactivity (psychology) , medicinal chemistry , reaction mechanism , photochemistry , crystallography , polymer chemistry , organic chemistry , crystal structure , metallocene , polymerization , medicine , alternative medicine , pathology , polymer , physics , nuclear magnetic resonance
Cr‐catalyzed ethene trimerization is an industrially important process to produce 1‐hexene. Despite its industrial relevance, the changing oxidation state and the structural rearrangements of the metal center during the catalytic cycle remain unclear. In this study, we have investigated the active species in a [(R‐SN(H)S−R)CrCl 3 ] (R=C 10 H 21 ) catalyzed ethene trimerization system using a combination of spectroscopic techniques (XAS, EPR and UV/VIS) and DFT calculations. Reaction of the octahedral Cr III complex with modified methylaluminoxane (MMAO) in absence of ethene gives rise to the formation of a square‐planar Cr II complex. In the presence of ethene (1 bar), no coordination was observed, which we attribute to the endergonic nature of the coordination of the first ethene molecule. Employing an alkyne as a model for ethene coordination leads to the formation of a dinuclear cationic Cr III alkyne complex. DFT calculations show that a structurally related dinuclear cationic Cr III ethene complex could form under catalytic conditions. Comparing a mechanism proceeding via mononuclear cationic Cr II /Cr IV intermediates to that proceeding via dinuclear cationic Cr II /Cr III intermediates demonstrates that only the mechanism involving mononuclear cationic Cr II /Cr IV intermediates can correctly explain the observed product selectivity.