Comparative study of new chromium-based catalysts for the selective tri- and tetramerization of ethylene

Two new ligands, Ph 2 PN(iPr)P(Ph)N( c -Hex)(CH 3 ) ( 2 ) (Ph = phenyl, iPr = isopropyl, c -Hex = cyclohexyl) and Ph 2 PN( c -Hex)P(Ph)NEt(CH 3 ) (Et = ethyl) ( 3 ) were synthesized. 2 was characterized by X-ray analysis. To compare their applicability with the previously known Ph 2 PN(iPr)P(Ph)N(iPr)H ( 1 ) these ligands were investigated together with chromium( iii )acetylacetonate, different co-catalysts and solvents for the catalytic oligomerization of ethylene. The in situ prepared catalysts proved to be highly active, yielding highly pure 1-octene as the main product and 1-hexene as the main byproduct. It was possible to reach productivities of several hundred kg product per gram chromium and hour, up to almost 65 wt% 1-octene with about 99% purity and overall 1-hexene plus 1-octene yields of more than 85 wt%.