Ethylene Trimerization with Cr−PNP and Cr−SNS Complexes:  Effect of Ligand Structure, Metal Oxidation State, and Role of Activator on Catalysis

Selected PNP and SNS ethylene trimerization ligands have been coordinated to CrII and CrIII, and further reactions of these complexes have been studied. The ligands are easily deprotonated to afford monoanionic tridentate ligands. All prepared complexes gave ethylene trimerization catalysis with varying degrees of activity upon activation with both MAO and AlR3/B(C6F5)3. The results of this study show that the role of MAO during activation is one of deprotonation, Cr reduction, and cation generation. A CrII → CrIV cationic mechanism is suggested.