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 PNP^iPr as the coordinated diphosphine, the system is active for the tetramerization of ethylene. This is the first example of Cr^I being used as a catalyst precursor for selective tetramerization and gives evidence toward the catalytic cycle acting through a Cr^I → Cr^III cationic mechanism.