Synthesis and characterization of Ni(II) complexes bearing of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives as highly active catalysts for ethylene oligomerization

Novel Ni(II) complexes of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives (HL_x: x  =  1–5; C1–C5 ) have been synthesized and characterized. In the mononuclear complexes, the ligands were coordinated as bidentate, via one imine nitrogen and the phenolate oxygen atoms. The structures of the compounds were confirmed on the basis of FT‐IR, UV–Vis, ¹H‐, ¹³C–NMR, inductively coupled plasma and elemental analyses (C, H and N). The purity of these compounds was ascertained by melting point (m.p.) and thin‐layer chromatography. The geometry optimization and vibrational frequency calculations of the compounds were performed using Gaussian 09 program with B3LYP/TZVP level of theory. All Ni(II) complexes were activated with diethylaluminum chloride (Et₂AlCl), so that C2 showed the highest activity [6600 kg mol^?1 (Ni) h^?1], where the ligand contains a chlorine substituent. Oligomers obtained from the complexes consist mainly of dimer and trimer, and also exhibit high selectivity for linear 1‐butene and 1‐hexene. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products.     

Rationalizing chain microstructure in the polyα-olefins synthesized by cationic AlCl3/H2O catalytic system

In this study, three middle range α-olefin monomers including 1-hexene, 1-octene, and 1-decene were oligomerized using conventional AlCl₃/H₂O catalytic system. Molecular weight and microstructure of the oligomers were analyzed by GPC and ¹HNMR, respectively. By ¹HNMR spectra, both internal (CHR=CHR′ and CHR=CR′R′′) and external (CH₂=CR′R′′) olefins containing di and tri-substituted C=C bonds were detected. After successful oligomerization, synthesized polyα-olefins underwent hydrogenation process using Pd(0)-Hal catalyst to yield synthetic oils of PHex, POct, and PDec, respectively and then completion of the hydrogenation was confirmed by ¹HNMR spectroscopy. The microstructure of the synthesized oligomers was rationalized using the ratio under the peak of CH?+?CH₂/CH₃ hydrogens (S1/S2) in ¹HNMR spectra and the degree of oligomerization obtained from M_n. According to the results, the best match between theoretical and real S1/S2 is obtained when considering double bond isomerization in the synthesized PAOs. By knowing PAO molecular weight, a relationship between monomer type and S1/S2 in the PAO homopolymers was detected. Our suggested methodology can be generalized to the unknown PAO homopolymers to unravel their monomer type by simple ¹HNMR and GPC analyses.     

Cobalt complexes based on 2-(1H-benzimidazol-2-yl)-phenol derivatives: preparation,spectral studies,DFT calculations and catalytic behavior toward ethylene oligomerization

In this study, five novel Co(II) complexes of 2-(1H-benzimidazol-2-yl)-phenol derivatives (HL_x: x = 1–5) have been synthesized and characterized. The general formula for complexes C1 and C2 is K₂[Co(HL_1,2)₂Cl₂]·H₂O, for complex C3 K₂[Co(HL₃)₂Cl₂], and for complexes C4 and C5 [Co(HL_4,5)₂]. In all complexes, the ligands are coordinated as bidentate, via one imine nitrogen and the phenolate oxygen atoms. The structures of the compounds were characterized by FT-IR, UV–vis, ¹H, ¹³C NMR spectroscopies, ICP and elemental analysis (C, H, and N). 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 spectra of the compounds. Based on the combined experimental and theoretical studies, six-coordinate octahedral structures have been proposed for complexes C1–C3, while complexes C4 and C5 had distorted tetrahedral geometry. All complexes were activated with diethylaluminum chloride (Et₂AlCl), cobalt(II) complexes containing bulky methyl groups in the aryl moiety show high catalytic activities (1774 kg?mol^?1(Co)?h^?1) for ethylene oligomerization. The oligomers obtained from the cobalt complexes exhibit good selectivity for linear 1-butene and 1-hexene. Results revealed that both the steric and electronic effects of ligands strongly affect the catalytic activities and the properties of the catalytic products.     

CuI@Sulfur-functionalized halloysite nanoclay: a novel recyclable catalyst for the ultrasonic-assisted synthesis of propargylamines: a combination of experimental and DFT simulation

Research on Chemical Intermediates - A novel heterogeneous catalyst, CuI supported on sulfur functionalized halloysite (CuI@HNTs-S), was designed and synthesized through functionalization of the...     

Rationalizing current strategies to protect N-heterocyclic carbene-based ruthenium catalysts active in olefin metathesis from C-H (de)activation

Defending second generation Ru-catalysts in olefin metathesis from C-H (de)activation reactions requires precise catalyst design strategies. Computer simulations are used here to rationalize precisely the role of the currently used catalyst structural modifications, and the way these modifications cooperate.     

Effect of metal type on the metallocene-catalyzed oligomerization of 1-hexene and 1-octene to produce polyα-olefin-based synthetic lubricants

1-Hexene and 1-octene oligomerization reactions were performed with Cp₂ZrCl₂ and Cp₂HfCl₂ in the presence of methylaluminoxane as cocatalyst at 25 and 80 °C to produce polyα-olefin-type oils. By examining the molecular weight results, obtained from gel permeation chromatography, the oligomeric structure of the products was confirmed. Hafnocene produced oligomers with higher molecular weights in comparison with zirconocene under the same reaction condition. In addition, with increasing temperature, the molecular weight decreased. Differential scanning calorimetry analysis of the poly1-hexene- and poly1-octene-type oligomers confirmed their amorphous nature. ¹H-nuclear magnetic resonance (NMR) analysis was performed to study the mechanism of termination reactions. The results obtained from the ¹H-NMR analysis confirmed the vinylidine form (vd) as the only unsaturated structure in all synthesized oligomers. Therefore, in the 1-hexene and 1-octene oligomerization reactions with these two catalytic systems, the chain termination is totally accomplished by β-hydride elimination at both reaction temperatures.     

Interaction of common cocatalysts in Ziegler–Natta-catalyzed olefin polymerization

In this study, density functional theory (DFT) molecular modeling studies were performed to explore mechanisms underlying the interactions of cocatalysts in Ziegler–Natta olefin polymerization using a range of commercially available cocatalysts, namely, trimethylaluminum (in monomeric and dimeric form, Al₂Me₆), dimethylaluminum chloride (in monomeric and dimeric form, Al₂Me₄Cl₂), and triisobutylaluminum. In this regard, after exploring structural and electronic features of cocatalysts, by steric maps and conceptual DFT, their interaction with possible impurities in hydrocarbon solvents and monomer feeds such as NH₃, CH₃OH, H₂O, H₂S, CO₂, and O₂ was considered. Then, activation of Ti species, adsorbed on the (110) and (104) surfaces, with the assistance of cocatalysts was studied as well. In this aspect, two possible reactions were investigated: (i) formation of first vacancy on Ti center and (ii) formation of first Ti–C bond by transalkylation reaction with cocatalysts. Finally, the effect of cocatalysts on the stereospecificity of Ti center adsorbed on the (110) surface was also taken into account by DFT calculations.     

Radar Absorption Properties of Ni0.5Zn0.5Fe2O4/PANI/epoxy Nanocomposites

A nitrate? citrate gel was prepared from metallic nitrates and citric acid by sol? gel process and was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄ nanocrystalline powder by auto‐combustion. Then, two novel 15 and 35% (w/w) magnetic Ni_0.5Zn_0.5Fe₂O₄ containing polyaniline nanocomposites, named as PANI‐Ni15 and PANI‐Ni35, respectively, were prepared via in‐situ polymerization of aniline in an aqueous solution containing proper amount of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder. The incorporation of the nanopowders to PANI matrix was confirmed by X‐ray diffraction (XRD), IR and SEM. Synthesized PANI‐NiZn ferrite composite particles were subsequently added to an epoxy resin matrix to produce related nanocomposites. The morphological properties of these nanocomposite materials were investigated by SEM and TEM. The electromagnetic‐absorbing properties were studied by measuring the reflection loss in the frequency range of 8.0 to 12.0 GHz. Results showed the reflection loss of the PANI‐Ni35 composite is higher than pure polyaniline and PANI‐Ni15. The good reflection loss of the nanocomposites suggests their potential applicability as radar absorber.