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-Me 2 ] ( 20 ) and their corresponding Fe(II) complexes [{2-F-6-Me-PhN═C(Me)PyC(Me)═NPh-2-F-6-Me}FeCl 2 ] ( 4 ), [{2-F-6-MePhN═C(Me)PyC(Me)═NPh-2-Me}FeCl 2 ] ( 5 ), and {[2-F-6-MePhN═C(Me)PyC(Me)═NPh-2,4-Me 2 ]FeCl 2 } ( 6 ) and Co(II) complex [{2-F-6-MePhN═C(Me)PyC(Me)═NPh-2-Me}CoI 2 ] ( 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}FeCl 2 ] ( 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).