University of Bath PHD The Selective Trimerisation of alpha-Olefins with Chromium Triazacyclohexane Catalysts Coxon, Alex Award date: 2015 Awarding institution: University of Bath Link to publication Alternative formats If you require this document in an alternative format, please contact: [email protected] General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 23. Sep. 2021 The Selective Trimerisation of α-Olefins with Chromium Triazacyclohexane Catalysts Alexander Gregory Nicholas Coxon A thesis submitted for the degree of Doctor of Philosophy Department of Chemistry University of Bath November 2015 COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. A copy of this thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and they must not copy it or use material from it except as permitted by law or with the consent of the author. RESTRICTIONS This thesis may not be consulted, photocopied or lent to other libraries without the permission of the author and Lyondell Basell GmbH for three years from the date of acceptance of the thesis. Signed Contents Abbreviations ............................................................................................................... 4 Catalyst Notation ......................................................................................................... 5 Abstract ......................................................................................................................... 6 1. Olefin Oligomerisation ........................................................................................ 7 1.1 Non-Selective Oligomerisation ....................................................................... 8 1.2 Selective Dimerisation .................................................................................. 11 1.3 Ethylene Trimerisation and Tetramerisation ................................................. 25 1.4 Triazacyclohexanes as Ligands ..................................................................... 66 1.5 Chromium Triazacyclohexane Complexes in Catalysis ................................ 70 1.6 Summary ....................................................................................................... 72 2. Chromium Catalysed Linear α-Olefin Trimerisation .................................... 74 2.1 Catalyst Synthesis ......................................................................................... 76 2.2 Catalyst Optimisation .................................................................................... 84 2.3 Investigation of the Halogen Effect .............................................................. 95 2.4 Kinetic Analysis .......................................................................................... 102 2.5 Counter-Ion Variation Using Chromium Triflates ...................................... 107 2.6 Synthesis of Alternative Chromium Halides and Pseudo-Halides .............. 114 2.7 Single Crystal X-Ray Diffraction Analysis ................................................. 120 2.8 Summary ..................................................................................................... 128 3. Mechanistic Insights into α-Olefin Trimerisation ......................................... 129 13 3.1 Characterisation of the Trimer Products via C Labelling ......................... 132 3.2 Investigation of the Catalytic Intermediates................................................ 156 3.3 Investigation of the Elimination Pathways.................................................. 165 3.4 GCMS Analysis and the Discovery of Dimerisation .................................. 171 3.5 Identification of the Side Products of Activation ........................................ 175 3.6 Direct Observation of Catalytic Intermediates via Mass Spectrometry ...... 181 3.7 Summary ..................................................................................................... 200 4. Ethylene Trimerisation: Optimisation and Product Identification............. 202 4.1 Ambient Pressure Testing ........................................................................... 203 4.2 Pressurised Autoclave Testing .................................................................... 209 4.3 Mechanistic Investigation of Co-trimerisation ............................................ 227 4.4 Analysis of the Higher Oligomers ............................................................... 228 4.5 Summary ..................................................................................................... 240 2 5. Experimental Details ....................................................................................... 242 5.1 Catalyst Synthesis ....................................................................................... 243 5.2 Chromium Triflate Substitution Reactions ................................................. 256 5.3 Optimised Liquid LAO Trimerisation Method ........................................... 258 5.4 LAO Trimerisation Conditions ................................................................... 259 5.5 Defined Aluminate Synthesis and Doping .................................................. 273 13 5.6 C 1-Hexene Labelling ............................................................................... 275 2 5.7 H 1-Hexene Labelling ................................................................................ 276 5.8 Gaseous α-Olefin Trimerisation .................................................................. 279 5.9 Branched Alcohol Synthesis ....................................................................... 280 5.10 Air Sensitive Mass Spectrometry Procedure .............................................. 283 Conclusions ............................................................................................................... 284 Acknowledgements .................................................................................................. 286 References ................................................................................................................. 287 13 Appendix 1 - C NMR Data for the C18 Trimers ................................................. 295 Appendix 2 - Single Crystal X-Ray Diffraction Data ........................................... 301 3 Abbreviations 1-Cn A linear α-olefin containing n carbon atoms 1D / 2D One Dimensional / Two Dimensional 2H Deuterium BP Beyond Petroleum (formerly British Petroleum) Cn A hydrocarbon containing n carbon atoms COSY Correlation Spectroscopy (Two dimensional NMR spectroscopy) CrIV A chromium cation with the oxidation state given in superscript Cy Cyclohexyl DABCO 1,4-Diazabicyclo[2.2.2]octane DCM Dichloromethane DFT Density Functional Theory DMAB Dimethylanilinium tetrakis(pentafluorophenyl)borate Eq. Molar equivalents FID Flame Ionisation Detector GCMS Gas Chromatography – Mass Spectrometry HDPE High Density Polyethylene iBu iso-Butyl IR Infrared L Undefined neutral ligand LAO Linear α-Olefin LLDPE Linear Low Density Polyethylene M An undefined metal atom or ion. (m/z) Mass spectrometry peak representing mass over charge, in all cases the charge is equal to one and therefore the peak value equals the relative atomic mass. M Peak Peak corresponding to the monoisotopic mass of a molecule in a mass spectrometry fragmentation spectrum MAO/DMAO Methylaluminoxane / Dry (Depleted) Methylaluminoxane MMAO Modified Methylaluminoxane Na/K Sodium/Potassium liquid alloy NMR Nuclear Magnetic Resonance PET Petroleum Ether o-C6H4F2 ortho-difluorobenzene PNP Bis(diarylphosphino)amine based compounds PNPNH (Diarylphosphino)(aminoarylphosphino)amine based compounds RT Room Temperature R3TAC 1,3,5-Trisalkyl-1,3,5-triazacyclohexane (R3TAC)CrCl3 A generic chromium chloride triazacyclohexane complex TAC 1,3,5-Triazacyclohexane TACN 1,4,7-Triazacyclononane THF Tetrahydrofuran TM Transition Metal TOF Turnover Frequency TON Turnover Number TOF-MS Time Of Flight – Mass Spectrometry UV/Vis Ultraviolet/Visible light (spectroscopy) nC The isotope of carbon with a relative atomic mass of n amu 4 Catalyst Notation 5 Abstract Described herein is research into the production of hydrocarbons suitable for various industrial applications via α-olefin trimerisation.1 This work has been split into three principal chapters that each describe a different aspect of the research carried out. In addition, a comprehensive review is presented into the development of selective oligomerisation, with an emphasis on the role of metallacyclic intermediates. α-Olefin Trimerisation: Catalyst Synthesis and Optimisation The synthesis and characterisation of eight novel chromium triazacyclohexane catalysts is described, including a series