Heterogenization of Some PNP Ligands for the Oligomerization of Ethylene
Bis(diphenylphosphino)amine ligands were supported on Merrifield’s resin and tested in catalytic ethylene oligomerization reactions with a chromium source. The supported ligands were characterized via IR, 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, IR and GC-MS. Oligomerization reactions were carried out in a Parr pressure reactor using Cr(acac)3 as the precursor and MMAO-3A as the activator. The system with the homogeneous ligands proved active in the tetramerization 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 latter showed a four-fold drop in activity compared to their homogeneous counterparts. The selectivity towards the main product, 1-octene, was less than 10 wt%. These supported ligands created a system that favoured the formation of C6 products more than any other product, with C6 cyclics (methylcyclopentane and methylenecyclopentane) being the most dominant, probably due to steric effects caused by the polymer chain.
Keywords: Oligomerization, bidentate phosphine, supported catalysts
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