چكيده به لاتين
Abstract:
In this study, five novel metal complexes of 2-(1H-Benzimidazol-2-yl)-phenol derivatives (Lx: x= 1-5) [iron (II) [K2[Fe(L1)2Cl2]•4H2O, K2[Fe(L2)2Cl2]•H2O, K2[Fe(L3)2Cl2], [Fe(L4)2] and K2[Fe(L5)2Cl2]•(CH3OH)2], cobalt (II) [K2[Co(L1)2Cl2]•H2O, K2[Co(L2)2Cl2]•H2O, K2[Co(L3)2Cl2], [Co(L4)2] and [Co(L5)2], nickel (II) [K2[Ni (L1)2Cl2]•2H2O, K2[Ni(L2)2Cl2]•2H2O, K2[Ni(L3)2Cl2], K2[Ni(L4)2Cl2]•3H2O and [Ni(L5)2] have been synthesized and characterized. In all complexes, the ligands were coordinated as bidentate, via one imine nitrogen and the phenolate oxygen atoms. The structures of the compounds were characterized using FT-IR, UV-Vis, 1H-, 13C-NMR, ICP and elemental analysis (CHN). The purity of these compounds was ascertained by melting point (m.p.) and TLC. Geometry optimization of the studied complexes was done by Gaussian09 software at B3LYP/TZVP level of theory and satisfactory theoretical–experimental agreement was achieved for NMR and IR analyses of the compounds. Based on the combined experimental and theoretical studies, six-coordinated octahedral structures have been proposed for the K2 [Fe (L1)2Cl2]•4H2O, K2[Fe(L2)2Cl2]•H2O, K2[Fe(L3)2Cl2], K2[Fe(L5)2Cl2]•(CH3OH)2, K2[Co(L1)2Cl2]• H2O, K2[Co(L2)2Cl2]•H2O, K2[Co(L3)2Cl2], K2[Ni (L1)2Cl2]•2H2O, K2[Ni (L2)2Cl2]•2H2O, K2[Ni(L3)2Cl2] and K2[Ni (L4)2Cl2]•3H2O complexes, while the [Fe(L4)2], [Co(L4)2] and [Co(L5)2] complexes have distorted tetrahedral geometry and [Ni(L5)2] has square-planar geometry. All complexes were activated with diethylaluminum chloride (Et2AlCl), so that Ni (II) complex (C4) showed the highest activity (6600 kg. mol–1(Ni).h–1) when it contain a chlorine substituent. Oligomers obtained from the nickel complexes consist mainly of dimer and trimer, and also exhibit high selectivity for linear 1-butene and 1-hexene. The cobalt(II) complex containing bulky methyl groups in the aryl moiety (C14) shows high catalytic activity (1774 kg. mol–1(Co).h–1) for ethylene oligomerization. The oligomers obtained from the cobalt complexes exhibit good selectivity for linear 1-buten and 1-hexene. The iron (II) complex contain chlorine substituents (C12) showed the highest activity (1686 kg. mol–1(Fe).h–1) as well as, the iron complexes exhibit good selectivity for linear 1-buten. Results revealed that both the steric and electronic effects of ligands strongly affect the catalytic activities and the properties of the catalytic products. Comparison of the Fe, Co, Ni catalysts bearing similar ligands indicates the different trend in activity changes. The reason probably relates to the difference of the metal center. The different inherent electronic properties of the transition metals play a significant role in the catalyst activity, possibly leading to differences in the catalytic activity and product distribution.
Keywords: Benzimidazolyl-phenol, Iron, Cobalt, Nickel, DFT calculations, Ethylene oligomerization
