Phosphanyl Methanimine (PCN) Ligands for the Selective Trimerization/Tetramerization of Ethylene with Chromium

1-Phosphanyl methanimine ligands, R2P–C­(Ph)NR′, may be prepared via a modular, convergent synthesis in good overall yield. Coordination chemistry studies with chromium confirm that they bind in a bidentate κ2-P,N mode. In combination with chromium and an activator, these ligands promote the selective oligomerization of ethylene to 1-hexene and 1-octene with high activity. Notably, an exceptionally high liquid fraction selectivity to saleable products (1-hexene + 1-octene) is observed (>95%), along with a potent ligand dependence, such that selectivity can be varied from pure trimerization through to mixed trimerisation/tetramerisation with a 1-octene:1-hexene (OTH) ratio of 1.7.