Investigation of Ethylene Tetramerization Catalysis from Structurally-Defined Organochromium Compounds

Abstract

Chapter 1 is a general introduction to the topic of ethylene tetramerization catalysis. Chapter 2 presents the synthesis and catalytic utility of chromium multi-aryl complexes that were the first examples of ethylene tetramerization catalysts that could be produced without excess alkyl aluminum reagents. Chapter 3 describes the mechanistic analysis of the ethylene tetramerization reaction using isotopically labelled ethylene. Co-production of 1-hexene along with 1-octene was determined to be intrinsic to the reaction mechanism. This is due to the intermediacy of a chromacyclic species that can either eliminate 1-hexene or insert a fourth ethylene. Chapter 4 presents the synthesis of additional Cr tris(aryl) complexes, which are coordinatively saturated, and were used to generate a crystallographically-characterized Cr(III) cationic species. This was the first reported single-component precatalyst for ethylene tetramerization. Chapter 5 describes the isotopic labelling of a well-defined ethylene tetramerization precatalyst with a deuteriomethyl group. This label was tracked following protonation of the neutral Cr complex via pulse EPR. Successful detection of deuterium on Cr-alkyl ligands led to in situ analysis of the catalytic mixture. A low-spin species derived from deuterated ethylene was observed. Appendix 1 describes the synthesis of various Cr aryl amine complexes. Appendix 2 provides the results of additional catalytic experiments for ethylene tetramerization, including those with a more soluble precatalyst, and those at higher ethylene pressure. Appendix 3 details the synthesis of a molecular Re catalyst for CO2 electroreduction which was used to modify electrodes. Appendix 4 lists various X-ray crystal structures that were obtained, but not related elsewhere in the thesis.