Theoretical Unraveling of Selective 1-Butene Oligomerization Catalyzed by Iron-Bis(arylimino)pyridine

We report a theoretical study, based oil density functional theory, devoted to the comprehension of the oligomerization reaction of 1-butene catalyzed by the Fe(II) bis(arylimino)pyridine complex ({2,6-(2-(CH3)C6H4N=C(CH3))(2)-C5H3N}Fe(II)Cl-2). Starting from the activated species ([{2,6-(2-(CH3)C6H4N=C(CH3))(2)-C5H3N)Fe(III)H](2+)), the obtained results are compared with available experimental data in order to determine the reaction mechanisms and to explain the unexpected predominant formation of linear octenes. All reaction steps (insertions, terminations) take place on the quartet potential energy surface, which appears to be the most stable all along the reaction path. The unique reaction path toward linear octenes (i.e., (1,2) and (2,1) successive insertions of 1-butene) is found as the most kinetically favorable to the detriment of all other possible paths. The first insertion into the Fe-hydride catalyst is found to be strongly exergonic and thermodynamically directed. Dimers can be formed by either beta-hydrogen-elimination termination or beta-hydrogcn-transfer termination. However, termination reactions become competitive and favorable only for the third monomer insertion reactions, which is consistent with experimental data. The beta-hydrogen-transfer termination reactions are largely dominant with respect to terminations by beta-hydrogen elimination. A kinetic model is proposed to compare quantitatively the ratios of different generated species, and the obtained results are in good agreement with the experimental data.