Jameel Al Thagfi

Three generations of the first 1,3-bis(imino) N-heterocyclic carbene (NHC) ligand precursors were synthesized, isolated and characterized. The synthetic methodologies of the ligand precursors were controlled by the iminic carbon substituents. The corresponding complexes of Cr(III), Fe(II), Co(II), Pd(II), and Zn(II) were prepared from the in situ deprotonation of the NHC ligand precursors or from the related Cu(I) or Ag(I) adducts. The NHC ring fragment and iminic carbon substituents had a significant impact on the solid-state structure of these complexes in which mono-, bi- and tridentate coordination modes were observed. The catalytic activities of chromium, iron and cobalt complexes of 1,3-bis(imino) NHC ligands were evaluated in ethylene polymerization. The activities of chromium(III) complexes of imidazol-2-ylidene showed slightly enhanced activities with a relatively electron-poor phenyl group (compared to methyl) installed on the iminic carbons. These results suggest that a d...

Abstract The removal of sulfur compounds from petroleum is increasingly important because sulfur compounds poison catalysts (i.e. reduce the activity of the catalysts in oil refinery processes) and are a source of environmental pollution. On the other side, waste rubber tires contribute to environmental pollution. Here, the motive is the utilization of activated carbon (AC) from the waste tires as a support for bimetallic catalysts. Therefore, NiMo catalysts supported on waste tire-derived AC were prepared through an excessive wetness co-impregnation method and subjected to calcination at temperatures of 100, 200, 300 and 400 °C for hydrodesulfurization (HDS). A surface area analyzer, Fourier-transform infrared spectroscope, scanning electron microscope, and Raman spectroscope were used to characterize the prepared catalysts. The HDS reactions with the prepared catalysts were performed in a high-pressure reactor using a model fuel containing 1000 ppm dibenzothiophene at different reaction times. The results showed that the catalyst that is calcined at 300 °C (i.e. NiMo/AC300) is the most active for HDS as compared to the catalysts calcined at other temperatures (i.e. 100, 200 and 400 °C). This catalyst (i.e. NiMo/AC300) has a surface area of 352 m2/g, a 6 nm average pore diameter, a total acidity of 0.26 mmol ammonia/g and exhibits a moderate activation energy for NH3 desorption (i.e. Ea = 102 kJ/mol). The developed catalysts show promising results with the advantage of having a dual benefit – eliminating waste tire disposal problem and producing valuable supports for HDS catalysts to yield sulfur-free fuels.

New chromium(III), iron(II), and cobalt(II) complexes of acyclic 1,3-bis[(2,6-dimethylphenylimino)ethyl and benzyl]imidazol-2-ylidene were prepared from the corresponding silver or copper adduct as transmetalating agent or from in situ deprotonation of the parent imidazolium salt. The catalytic activities of all three complexes were evaluated for ethylene polymerization at atmospheric pressure and room temperature with activation by methylaluminoxane. The Cr(III) complexes were found to be the most active, with a rate of 35 kg PE mol–1 Cr h–1.

Abstract The removal of sulfur compounds from petroleum is increasingly important because sulfur compounds poison catalysts (i.e. reduce the activity of the catalysts in oil refinery processes) and are a source of environmental pollution. On the other side, waste rubber tires contribute to environmental pollution. Here, the motive is the utilization of activated carbon (AC) from the waste tires as a support for bimetallic catalysts. Therefore, NiMo catalysts supported on waste tire-derived AC were prepared through an excessive wetness co-impregnation method and subjected to calcination at temperatures of 100, 200, 300 and 400 °C for hydrodesulfurization (HDS). A surface area analyzer, Fourier-transform infrared spectroscope, scanning electron microscope, and Raman spectroscope were used to characterize the prepared catalysts. The HDS reactions with the prepared catalysts were performed in a high-pressure reactor using a model fuel containing 1000 ppm dibenzothiophene at different reaction times. The results showed that the catalyst that is calcined at 300 °C (i.e. NiMo/AC300) is the most active for HDS as compared to the catalysts calcined at other temperatures (i.e. 100, 200 and 400 °C). This catalyst (i.e. NiMo/AC300) has a surface area of 352 m2/g, a 6 nm average pore diameter, a total acidity of 0.26 mmol ammonia/g and exhibits a moderate activation energy for NH3 desorption (i.e. Ea = 102 kJ/mol). The developed catalysts show promising results with the advantage of having a dual benefit – eliminating waste tire disposal problem and producing valuable supports for HDS catalysts to yield sulfur-free fuels.

Abstract A comparative electronic and spectroscopic analysis of 2,4,6-trichloroaniline (TCA) and 2,4,6-tribromoaniline (TBA) was carried out by theoretical and experimental techniques. The NH2 inversion barrier in TCA and TBA molecules was predicted to be three times less than that in aniline and 2,4,6-trifluoroaniline. The size of the halogen substituents in the ortho positions is shown by density functional theory to play an important role in determining the electronic and structural properties of the amino group in the investigated haloaniline derivatives. A thorough interpretation of the infrared and Raman spectra has been performed on the basis of the observed and calculated infrared and Raman spectra as well as calculated potential energy distribution values. In addition, the SERS spectra for both trihaloanilines were successfully collected up to a concentration of 10−6 M using aged hydroxylamine-reduced silver colloid as an active substrate for TCA and TBA. SERS intensities of several peaks were found to linearly change with concentration allowing quantitative analyses of TCA and TBA. A relatively stronger interaction in the case of TBA–silver colloids is predicted compared to the TCA analogue.

Chromium(III), iron(II), and cobalt(II) complexes of bis(imino)benzimidazol-2-ylidene and bis(imino)pyrimidin-2-ylidene were successfully prepared by reaction of either the benzimidazolium or pyrimidinium salts or the corresponding copper complexes with the respective metal halide. X-ray diffraction analysis of the Cr(III) complex of the pyrimidin-2-ylidene ligand demonstrated, for the first time, the ability of bis(imino)carbene-type ligands to coordinate to metal centers in a tridentate fashion. The coordination mode of these ligands was surprisingly highly dependent on the nature of both the metal and the ligand itself. The activity of these complexes in ethylene polymerization was assessed under ambient conditions (room temperature and 1 atm of C2H4) using methylaluminoxane as cocatalyst. In contrast to the iron and cobalt complexes, both chromium complexes were active in ethylene polymerization.

Density functional theory calculations at the B3LYP/DGDZVP and UB3LYP/TZVP levels were performed on 1,3-bis[1-(2,6-dimethylphenylimino)ethyl]imidazolium and on the corresponding imidazol-2-ylidene iron(II) dichloride complex, respectively. The resulting geometrical parameters of the optimized structures were in good agreement with previously reported X-ray structures. The ground state for the high-spin (quintet multiplicity) iron complex is 82.4 kJ/mol lower in energy compared to the low-spin (triplet) configuration, in agreement with magnetic susceptibility measurements. Further calculations were carried out on related benzimidazol-2-ylidene and pyrimidin-2-ylidene ligands and on the corresponding iron complexes to gain insight into their electronic properties and reactivities. The energy of the highest occupied and lowest unoccupied molecular orbitals of all three carbenes suggests that the pyrimidin-2-ylidene and the benzimidazol-2-ylidene are the best σ-donor and best π-acceptor...