Linear alpha olefins, 1-alkenes in the range C4-C20, are important petrochemical products, used in many applications. 1-Hexene and 1-octene are particularly useful, and are produced commercially on a massive scale as co-monomers for the polyolefin industry. Most current technology relies on non-selective ethylene oligomerisation to make these products as a distribution of all possible even carbon numbers; butene, hexene, octene, decene, etc. This is a problem since the distribution of products must be separated and does not necessarily fit the market’s demand. What is needed is a catalyst system that selectively produce the desired 1-alkene on purpose.
In 2002, Duncan discovered chromium catalysts supported by N, N-bis(diarylphosphino)amine (“PNP”) ligands which are extremely selective and productive ethylene trimerisation catalysts to produce 1-hexene. Key to this high selectivity is the metallacyclic mechanism by which the catalysts operate. This result was extended independently by SASOL to make catalysts for selective tetramerisation to 1-octene – technology which SASOL is commercialising.