High-Temperature Catalysts for the Production of α-Olefins Based on Iron(II) and Cobalt(II) Tridentate Bis(imino)pyridine Complexes with a Double Pattern of Substitution: <i>o</i>-Methyl plus <i>o</i>-Fluorine in the Same Imino Arm

Abstract

The new series of bis(imino)pyridine ligands [2-F-6-MePhN═C(Me)PyC(Me)═NPh-2-F-6-Me] (14), [2-F-6-MePhN═C(Me)PyC(Me)═NPh-2-Me] (19), and [2-F-6-MePhN═C(Me)PyC(Me)═N-Ph-2,4-Me2] (20) and their corresponding Fe(II) complexes [{2-F-6-Me-PhN═C(Me)PyC(Me)═NPh-2-F-6-Me}FeCl2] (4), [{2-F-6-MePhN═C(Me)PyC(Me)═NPh-2-Me}FeCl2] (5), and {[2-F-6-MePhN═C(Me)PyC(Me)═NPh-2,4-Me2]FeCl2} (6) and Co(II) complex [{2-F-6-MePhN═C(Me)PyC(Me)═NPh-2-Me}CoI2] (7) with a double pattern of substitution, o-methyl plus o-fluorine in the same imino arm, were synthesized and fully characterized. According to X-ray analysis 4, 5, and 7 exist mostly in the unexpected “up-up” conformers in the solid state. The Co−N bonds in 7 are shorter than the corresponding Fe−N bonds in the analogous complex 5 by 0.003−0.025 Å. This shortening of metal−N bonds going from iron(II) to cobalt(II) complexes can be explained by the smaller van der Waals radius of Co vs. that of Fe. The Fe complexes 4–6 afforded very productive catalysts for the production of α-olefins with a more linear Schultz−Flory distribution of α-olefins and with higher K values than the parent methyl-substituted Fe(II) complex [{2-MePhN═C(Me)PyC(Me)═NPh-2-Me}FeCl2] (1). The cobalt complex 7 was found to have very low activity in α-olefin oligomerization experiments within the tested range of temperatures (60–130 °C).