title: A DFT Mechanistic Study on Ethylene Tri- and Tetramerization with Cr/PNP Catalysts: Single versus Double Insertion Pathways.
abstract: The mechanism of ethylene trimerization and tetramerization with a chromium-diphosphinoamine (Cr-PNP) catalyst system has been studied by theoretical (DFT) methods. Two representative ligands have been explored, namely Ph2PN(Me)PPh2and (o-MeC6H4)2PN(Me)P(o-MeC6H4)2. Calculations on the former ligand reveal how a combination of single and double ethylene insertion mechanisms may lead to 1-hexene, 1-octene and the major side products (cyclopentanes and n-alkanes). For the latter ligand, introduction of o-alkyl substitution leads to a more sterically congested active species, which suppresses the available pathways for tetramerization and side product formation. Hence, the high selectivity of o-aryl substituted PNP ligands for trimerization can be rationalized.
authors.affiliation: Department of Chemistry, Imperial College London, Exhibition Rd, South Kensington, London, SW7 2AZ, UK.
authors.forename: George J P
authors.identifier: http://orcid.org/0000-0001-9321-4814
authors.initials: GJ
authors.lastname: Britovsek
authors.affiliation: School of Physical Sciences, University of Tasmania, Private Bag 75, Hobart, 7001, Australia.
authors.forename: David S
authors.initials: DS
authors.lastname: McGuinness
keywords: chromium; homogeneous catalysis; oligomerization; tetramerization; trimerization