Heterogenisation of selective ethylene tetramerisation catalysts.
The aim of the study was to heterogenise existing tetramerisation catalysts by supporting the bis(diphenylphosphino)amine ligands on polymer. The polymer of choice was Merrifield’s resin which was functionalized to enable attachment of the ligands. These supported ligands were characterized via ATR, solid-state NMR, SEM and TGA-DSC. In order to compare activity of the supported and unsupported ligands, homogeneous bis(diphenylphosphino)amine ligands were synthesized and characterized via NMR, elemental Analysis, ATR and GC-MS. Tetramerisation reactions were carried out in a Parr pressure reactor using Cr(acac)₃as the precursor and MMAO-3A as the activator. The homogeneous ligands proved active in the tetramerisation of ethylene, with the selectivity of 1-octene in the C8 fraction being comparable with that mentioned in literature (> 98 wt%). When comparing the homogeneous ligands with their heterogeneous counterparts, the heterogeneous ligands performed poorly due to steric effects caused by the polymer chain. The activity dropped by more than four times that of their homogeneous counterparts and the selectivity towards the main product, 1-octene, was very low (< 10 wt%). These ligands seemed to create a system that favoured the formation of the C6 products more than any other product, with the C6 cyclics being the most dominant.