Ethylene Tetramerization with Cationic Chromium(I) Complexes

Various [Cr(CO)4(P∩P)]+ complexes have been synthesized and tested for the tetramerization of ethylene to give principally 1-octene. The effect of the anion has been investigated, and it has been found that for successful catalysis an extremely weakly coordinating anion is required. This study shows that when [Al(OC(CF3)3)4]- is employed as the anion, along with triethylaluminum and PNPiPr as the coordinated diphosphine, the system is active for the tetramerization of ethylene. This is the first example of CrI being used as a catalyst precursor for selective tetramerization and gives evidence toward the catalytic cycle acting through a CrI → CrIII cationic mechanism.