Ethylene and 1-butene Oligomerization with Benzimidazole Complexes of Nickel and Iron: A Case of Tandem Reaction

The coordination chemistry of benzimidazole ligands combines σ donation and π backbonding. Owing to this electronic flexibility, benzimidazole ligands stabilize both electron deficient and electron-rich transition states in the catalytic cycle of Ziegler-Natta polymerizations. In this study, Fe(III) and Ni(II) complexes of 2-substituted-benzimidazoles were tested as catalysts for ethylene and 1-butene oligomerization. The tests realized in toluene yielded mainly butenes and minor amounts of hexenes. When dichloromethane was used as solvent, a tandem reaction took place and 1-butene produced by ethylene dimerization was further oligomerized, yielding octenes and dodecenes as main products. All tested catalysts exhibited moderate selectivity for 1-octene, indicating 1-ω enchainment in 1-butene dimerization. Beyond catalytic tests, a theoretical study of the ligand 2,2′-(furan-2,5-diyl)bis(1H-benzimidazole) confirmed the planar structure of this compound as evidenced by NMR spectroscopy.