Regioselective propylene dimerization by tetrahedral (imino)pyridine CoII dichloride complexes activated by MAO

On activation by MAO, tetrahedral CoII dichloride complexes supported by 6-organyl-2-(imino)pyridine ligands generate active catalysts for the dimerisation of propylene to hexenes. The nature of the substituent on the 6-position of the pyridine ring influences both the selectivity and activity of the catalysts. The 6-thienyl complexes CoCl2N2 2Th and CoCl2N2 2BT dimerise propylene prevalently to linear hexenes through a propagation pathway involving 1,2-insertion into Co-H, followed by 2,1-insertion and -hydride elimination. The 6-phenyl complex CoCl2N2 Ph is much less active and selective producing linear hexenes and methyl branched pentenes in comparable yields. The same activity trend and selectivity is observed for the dimerisation of 1-hexene, which however is one order of magnitude slower as compared to the dimerisation of propylene.