Abdulhakim A Ahmed | University of Benghazi (original) (raw)
Papers by Abdulhakim A Ahmed
Structural Chemistry
Two pairs of complexes, [Mn(CO)3(benzene)]+/[Mn(CO)3(naphthalene)]+ and [Cr(CO)3(tropylium)]+/[Cr... more Two pairs of complexes, [Mn(CO)3(benzene)]+/[Mn(CO)3(naphthalene)]+ and [Cr(CO)3(tropylium)]+/[Cr(CO)3(benzotropylium)]+, have been used as a platform to establish the extent to which the well-known ‘indenyl effect’ translates into other bicyclic ligand systems. Density functional theory (DFT) suggests that the ‘naphthalene effect’ is minimal, the pathway for hydride reduction of [Mn(CO)3(naphthalene)]+ resembling closely that for the benzene analogue. In the benzotropylium system, in contrast, stabilisation of an η5 coordination mode through aromatisation of the six-membered ring plays a similar role to stabilisation of η3 in the indenyl effect. The greater influence of aromatisation in the five- and seven-membered ring systems stems from the presence of formal charge on the ligands in these cases: localisation of this charge on a subset of the available carbon atoms enhances the electrostatic component of the metal-ligand bond. This is particularly dramatic in the benzotropylium case, where the η7–η5 slippage corresponds to a formal 2-electron reduction of the ligand from [C7H7]+ to [C7H7]−.
The global isomeric structure in the gas phase and with water-assisted in solution is predicated ... more The global isomeric structure in the gas phase and with water-assisted in solution is predicated at B3LYP/6-31++G** // B3LYP/6-31G* levels of theory. The free energies, enthalpies of solvation and equilibrium constants are calculated at the same level of theory. Eight local minima structures (S1-S8) and nine hydrated structures (S1.H 2 O-S8.H 2 O) are extracted for silarhodanine molecule. The hydration processes are lowered the stabilization energy. S5 and S5.H 2 O are the global minimum in the gas phase and in water respectively. The calculations predict an important catalytic effect since the activation barrier has been decreased to 21.19 kcal/mol of hydration of S1 molecule.
The Z/E iminol forms of formohydroxamic acids (HX(OH)NHOH where X=C, Si, Ge, Sn and Pb) have been... more The Z/E iminol forms of formohydroxamic acids (HX(OH)NHOH where X=C, Si, Ge, Sn and Pb) have been investigated in the gas phase using B3LYP density functional theory at B3LYP/6-31++G(d,p) level of theory.The barrier to the rotation of Z to the more stable isomer E is significant in C, Si and Ge structures, whereas in Sn and Pb the Ztautomer is more stable than E. The highest energy point is TS1-2, which lies 46.35 kcal/mol above the E isomer 2.The rate constant for tautomeric interconversion lies between 5.6210-14 and 2.23109 s-1. The 34 interconversion exhibits the highest rate constant for the tautomeric interconversion. The equilibrium constant for interconversion of tautomer 1 to 2 is 4.45106. The solvent effect on formohydroxamic acid showed that the G1-2values are 0.37, 0.70, 0.58, 0.85, 1.97 and -9.07 kcal/mol, in DMSO, methanol, acetone, THF, cyclohexane and in gas phase respectively.
Journal of Molecular Structure, 2013
ABSTRACT The structure and reactivity of hydroxyaminosilanethione conformers were studied in the ... more ABSTRACT The structure and reactivity of hydroxyaminosilanethione conformers were studied in the gas phase using density functional theory. Eight local minima were located, including two featuring pentacoordinate silicon atoms (2Z, S2) and one with a nitrososilanethiol structure (4Z). The global minimum at the B3LYP/6-31++G(dp)//B3LYP/6-31G(d) levels of theory is S2. Natural bond orbital (NBO) analysis reveals that there is a strong nS2→σN3Si1∗ interaction in the majority of isomers. The 3d orbitals of silicon are of minor importance in bonding for the isomers with the exception of those where the silicon is penta-coordinate (2Z and S2), where the occupancy of the 3d orbitals is 2.93, 4.34 respectively. The charge density and its Laplacian at the bond critical point (BCP), (ρ(r) and ∇2ρ(r)), indicate that all SiS, SiN and SiH bonds were constructed by ionic or electrostatic interactions, whereas NH and OH bonds are predominantly covalent. In addition, seven transition states connecting the various minima were located. TS7 has the highest energy (75.75 kcal/mol) in the reaction coordinates and is therefore the rate-determining step in the conversion of 1Z–4Z. TS7, TS2 and TS3 have the highest energies (75.75, 66.50 and 57.92 kcal/mol, respectively). The computed harmonic frequencies results were in good agreement with available experimental values. The spectra of S1 and 2Z have the lowest NH frequencies (3117 and 2965 cm−1), this shift towards the lower frequency being attributable to the presence of intramolecular hydrogen bonding in S1 and 2Z.
Computational and Theoretical Chemistry, 2012
ABSTRACT The tautomerizm of (hydroxphosphino)silanethione molecule 1 were investigated by density... more ABSTRACT The tautomerizm of (hydroxphosphino)silanethione molecule 1 were investigated by density function theory calculations. The potential energy surface, the global isomeric structures and the transition states of intramolecular proton transfer were calculated at B3LYP/6-31G(d) level of theory. The energy was further studied by a single point calculation by means of B3LYP/6-311++G(d,p) level. The potential energy surface was built-in of ten tautomers 2-11 along with ten transition states TS1-TS10 located for molecule 1. The global minimum at the B3LYP/6-31++G(d,p)//B3LYP/6-31G(d) levels of theory is 1. Tautomer 3 possessed the highest energy (136.06 kJ/mol) above the global isomeric structure 1. The energies of the transition states reflect their different respective ring strains, TS2 with three-membered ring is possessed the highest energy (307.19 kJ/mol) whereas the TS10 with four-membered ring had the lowest energy (107.17 kJ/mol) among the transition states. The TS2 was clearly involved in the rate-determining step. The natural bond orbital (NBO) analysis reveals that the natural atomic charges are in conformity with bond lengths and electronic densities in the studied tautomers. The second order delocalization energies (E-(2)) showed that there is a strong n(s2) -> sigma(P3-Si1)* and n(s2) -> sigma(P3-Si1)* interactions in the tautomers excluding structures 3 and 10. A strong n(P3) -> sigma(P2-Si1)* interaction (240.10 kJ/mol) is located for 3. Finally, strong n(O4) -> sigma(P3-S2)* interaction (134.89 kJ/mol) was found for 10 as expected since 10 is the only structure possessed a P-S bond. The atoms in molecules (AIM) calculations of charge density at the bond critical point (BCP), (rho(r) and del(2)rho(r)) showed that for all Si-S, Si-P and Si-H bonds were constructed by ionic or electrostatic interactions, whereas O-H and S-H bonds are maintained the covalent bond nature. The computed harmonic frequencies at B3LYP/6-31G(d) level showed that the values of the stretching frequencies of the most structures under consideration were in good agreement with the experimental values which have been reported for similar stretches.
The syntheses of some Ni(II), Co(II) and Cu(II) Schiff base complexes have been reported. The Sch... more The syntheses of some Ni(II), Co(II) and Cu(II) Schiff base complexes have been reported. The Schiff base ligands H2L1 (C40H32N2O2), H2L2 (C32H28N2O2) and H2L3 (C22H26N2O2) under were prepared by the condensation of amines namely benzidine and 1,4-phenylenediamine with benzoin, benzoylacetone and acetylacetone. A fourth ligand H2L4 (C34H28N2O2) was obtained by the condensation of 1,4-phenylenediamine with benzoin. Schiff base ligands and their complexes have been subjected to elemental analysis, Infrared, electronic spectral studies, molar conductivity and magnetic moment measurements. The Ni(II) and Co(II) complexes showed an octahedral and square planar geometries. In addition, the analysis exhibited a different chelation mode towards metal and ligand substitution, since a mono- and dinuclear metal complexes have been identified.
The ligand and its complexes of Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) were investig... more The ligand and its complexes of Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II)
were investigated in terms of synthesis, elemental analysis, molar conductivity,
thermal analysis, infrared spectra and magnetic susceptibility measurements. The
ligand: 4-[4-(3-Hydroxy-1-ethyl-but-2-enylideneamino)-biphenyl-4-ylimino]-pent-2-
en-ol (C22H24N2O2) has been synthesized by the condensation of acetylacetone and
benzidine. The complexes have been synthesized by two different methods and their
geometries were investigated. A synthesis and characterization of novel complexes
of 4-[4-(3-Hydroxy-1-ethyl-but-2-enylideneamino)-biphenyl-4-ylimino]-pent-2-en-ol
has been achieved. The study also confirmed the formation of mono-, di- and novel
polynuclear metal complexes. The researcher recommended that the mentioned
complexes may have biological activity.
The Schiff base ligands and their complexes of divalent metals of Ni(II), Co(II) and Cu(II) were ... more The Schiff base ligands and their complexes of divalent metals of Ni(II), Co(II)
and Cu(II) were investigated in terms of synthesis, elemental analysis, molar
conductivity, thermal analysis, infrared spectra, ultraviolet-visible and magnetic
susceptibility measurements. The ligands have been synthesized by condensation
of benzoylacetone and ethylenediamine, o-phenylenediamine and 1,6-
hexanediamine to gives H2L1 = C22H24N2O, [N,N
-
bis(benzoylacetone)ethylenediamine]; H2L2
= C26H24N2O2 [N,N
-(benzoylacetone)-ophenylenediamine];
H2L3 = C26H32N2O2, [N,N
-bis (benzoylacetone)-1,6-
hexanediamine] respectively. The fourth ligand is formed by the condensation of
benzoin and o-phenylenediamine H2L4
=C34H28N2O2, [N,N
-
bis(Benzoin)-ophenylenediamine].
The ligands and their complexes have been synthesized by two
different methods and their geometries were investigated. A synthesis and
characterization of novel ligand and complexes of benzoin derivatives has been
achieved. The study also confirmed the formation of mon- and binuclear metal.
The binuclear metal complexes are synthesized by new methods. The researcher
recommended that the mentioned complexes may have biological activity.
The transformation of few isomeric tautomers of thioformohydroxamic (TFH), thioacetohydroxamic (T... more The transformation of few isomeric tautomers of thioformohydroxamic (TFH), thioacetohydroxamic (TAH) and thiobenzohydroxamic (TBH) acids via intramolecular hydrogen transfer were investigated by density functional calculations. The global isomeric structures, the transfer potential surfaces, the harmonic frequency and transition states geometries of intramolecular hydrogen transfer were calculated at the B3LYP/6-31++G** // B3LYP/6-31G* levels of theory. The order of stability of these tautomers was Z2>Z1>E2>E1>>>CS and Z1>Z2>E2>E1>>>CS. The Z1 and E1 are thione forms whereas Z2 and E2 are thiol forms and CS is the charge-separated structure. The reaction pathways for the interconversion between tautomers were through the transition structures TS1, TS2, TS3 and TS4. The TS3 was involved in the rate-determining step. The ring strain is clearly affecting the activation barrier. Some anionic structures are also examined to look whether the thiohydroxamic acids are O-acid, N-acid or S-acid.
First principle quantum chemical calculations at the HF level of theory, using the 3-21G and 3-21... more First principle quantum chemical calculations at the HF level of theory, using the 3-21G and 3-21G* split-valence basis sets have been used to investigate the molecular geometry and electronic properties of Bis(phosphino)methane (H2PCH2PH2) (BMP) conformers. Phosphine (PH3) (AP) and methyl phosphine (CH3PH2) (MP)are also investigated for a comparison grounds. Geometries, charges electronic density, total energies, HOMO-LUMO gap, LUMO energies, (1st, 2nd and 3rd) ionization energies and dipole momentum were calculated. The study investigated six Bis(phosphino)methane (BMP) conformers. The highest d-orbitals contribution to the HOMO and the LUMO is 00.0028% and 0.0125% respectively. The study demonstrated that it is not necessary to involve d-orbital participation in bonding in order to explain the geometries of the majority of these molecules. The relative stability of the conformers was calculated.
[(η5-Indenyl)Fe(CO)3]BF4 (I) undergoes facile monocarbonyl substitution at room temperature in ac... more [(η5-Indenyl)Fe(CO)3]BF4 (I) undergoes facile monocarbonyl substitution at room temperature in acetone by monophosphines, monophosphites and MPh3 (M =1cr; As, Sb, Bi) ligands (L) to form [(η5-Indenyl)Fe(CO)2L]BF4. Ditertiary phosphines, PPh2(CH2)n PPh2 (n = 1, 2, 4, 6, 8) and both the arsines, AsPh2(CH2)2AsPh2 and AsMe2 (CH2)5AsMe2 react similarly to form monosubstituted complexes e.g. [(η5-Indenyl)Fe(CO)2(η1- PPh2(CH2)nPPh2)]BF4 and dimeric complexes, e.g. [{(η5-Indenyl) Fe(CO)2}2-μ-PPh2(CH2)nPPh2)] [BF4]2 Prolonged refluxing of I with these ligands gives the chelates, e.g. [(η5-Indenyl)Fe(CO)(η2- PPh2(CH2)nPPh2)]BF4. The enhanced reactivity of the [(η5-Indenyl)Fe(CO)3]+ cation over that of [(η5,-C5H5)Fe(CO)3]+ in solvents such as acetone may be attributed to the “indenyl” effect, i.e. ring slippage from η5 to η3. However, no evidence was obtained for intermediates such as [(η3-C9 H7)Fe(CO)3(acetone)]+, and so the effect must operate solely in the transition state of the reaction.
Spectroscopic evidence is presented for the formation at low temperatures of the η3-indenyl inter... more Spectroscopic evidence is presented for the formation at low temperatures of the η3-indenyl intermediate [(η3-C9H7)Fe(CO3H], prior to formation of t by reduction of the tricarbonylironindenyl cation with sodium cyanoborohydride in acetone.
![Research paper thumbnail of Hydride reduction of [(η5-Indenyl)Fe(CO)3] BF4:evidence for (η5-Indenyl)(CO)2FeCHO and (η5-Indenyl)(CO)2FeH](https://attachments.academia-assets.com/40050962/thumbnails/1.jpg)
](Although the hydride ($-Cp(C0)2FeH is well documented (see ref. 1 and refs. therein) and the corr... more Although the hydride ($-Cp(C0)2FeH is well
documented (see ref. 1 and refs. therein) and the
corresponding formyl (r)5-Cp)(C0)2FeCH0 more re- cently identified by low temperature ‘H NMR spec- troscopy [2], there have been, to the best of our
knowledge, no previous reports of the analogous
indenyl compounds. We report now spectroscopic
(IR and ‘H NMR) evidence for these compounds
by reduction of the tricarbonylindenyliron cation
[(v5-In)Fe(C0)3]+ (1) by sodium borohydride in
acetone.
The Fourier transform infrared and Raman spectra of the cations [η5-C9H7Fe(CO)n dppa]+ (n = 1, 2;... more The Fourier transform infrared and Raman spectra of the cations [η5-C9H7Fe(CO)n dppa]+ (n = 1, 2; dppa=bisdiphenylphosphinoalkane, where alkane=methane, ethane, butane, hexane and octane) and [{η5-C9H7Fe(CO)2}2-μ-dppa]2+ indicate that the alkyl chain lengths have effects on the structures of the bidentate cations resulting in increased back-donation to carbonyl groups as the chain length increases. In contrast the alkyl chain lengths have no similar effects in the unidentate mononuclear and bridged cations.
The proton transfer processes have generated eight minimum structures of the silarhodanine molecu... more The proton transfer processes have generated eight minimum structures of the silarhodanine molecule. These
structures were studied in the gas phase by a high level theory complete basis set (CBS-Q). All the structure are
heterocyclic compounds except S2 structure. The global isomeric structure was S5 at the CBS-Q levels of theory.
The acyclic structure S2 is possessed the highest energy (60.17 kcal/mol) above the global minimum S5. Nine anions
and nine cations of various conformers have been investigated. The protonation and deprotonation reactions in the
gas phase are examined at the CBS-Q level. The S2OA showed the highest relative enthalpy (∆H= 24.65 kcal/mol)
and S3OA structure showed the highest Gibbs free energy (∆G=23.59 kcal/mol). The S2NC cation showed the
highest relative enthalpy and Gibbs free energy (∆H= 50.25 kcal/mol, ∆G=47.07 kcal/mol) in the cations section.
Energetically easiest process is the deprotonation of 2ZNA with the computed enthalpy and Gibbs free energy of
1274.52 kJ/mol and 1282.49 kJ/mol. The equilibrium constants at 298.15 K and 1 atmosphere pressure of the
deprotonation reactions are very small which means the reaction at this temperature favor the reactants. The
computed vibrational frequencies values for the structures are inconformity with the experimental ones.
Journal of Organometallic Chemistry, 2008
The fundamental processes involved in the hydride reduction of metal carbonyl compounds continue ... more The fundamental processes involved in the hydride reduction of metal carbonyl compounds continue to attract attention due to their importance in the FischerTropsch process [1], the water-gas shift reaction [2] and other industrially relevant processes [3]. The unsaturated nature of ...
Structural Chemistry
Two pairs of complexes, [Mn(CO)3(benzene)]+/[Mn(CO)3(naphthalene)]+ and [Cr(CO)3(tropylium)]+/[Cr... more Two pairs of complexes, [Mn(CO)3(benzene)]+/[Mn(CO)3(naphthalene)]+ and [Cr(CO)3(tropylium)]+/[Cr(CO)3(benzotropylium)]+, have been used as a platform to establish the extent to which the well-known ‘indenyl effect’ translates into other bicyclic ligand systems. Density functional theory (DFT) suggests that the ‘naphthalene effect’ is minimal, the pathway for hydride reduction of [Mn(CO)3(naphthalene)]+ resembling closely that for the benzene analogue. In the benzotropylium system, in contrast, stabilisation of an η5 coordination mode through aromatisation of the six-membered ring plays a similar role to stabilisation of η3 in the indenyl effect. The greater influence of aromatisation in the five- and seven-membered ring systems stems from the presence of formal charge on the ligands in these cases: localisation of this charge on a subset of the available carbon atoms enhances the electrostatic component of the metal-ligand bond. This is particularly dramatic in the benzotropylium case, where the η7–η5 slippage corresponds to a formal 2-electron reduction of the ligand from [C7H7]+ to [C7H7]−.
The global isomeric structure in the gas phase and with water-assisted in solution is predicated ... more The global isomeric structure in the gas phase and with water-assisted in solution is predicated at B3LYP/6-31++G** // B3LYP/6-31G* levels of theory. The free energies, enthalpies of solvation and equilibrium constants are calculated at the same level of theory. Eight local minima structures (S1-S8) and nine hydrated structures (S1.H 2 O-S8.H 2 O) are extracted for silarhodanine molecule. The hydration processes are lowered the stabilization energy. S5 and S5.H 2 O are the global minimum in the gas phase and in water respectively. The calculations predict an important catalytic effect since the activation barrier has been decreased to 21.19 kcal/mol of hydration of S1 molecule.
The Z/E iminol forms of formohydroxamic acids (HX(OH)NHOH where X=C, Si, Ge, Sn and Pb) have been... more The Z/E iminol forms of formohydroxamic acids (HX(OH)NHOH where X=C, Si, Ge, Sn and Pb) have been investigated in the gas phase using B3LYP density functional theory at B3LYP/6-31++G(d,p) level of theory.The barrier to the rotation of Z to the more stable isomer E is significant in C, Si and Ge structures, whereas in Sn and Pb the Ztautomer is more stable than E. The highest energy point is TS1-2, which lies 46.35 kcal/mol above the E isomer 2.The rate constant for tautomeric interconversion lies between 5.6210-14 and 2.23109 s-1. The 34 interconversion exhibits the highest rate constant for the tautomeric interconversion. The equilibrium constant for interconversion of tautomer 1 to 2 is 4.45106. The solvent effect on formohydroxamic acid showed that the G1-2values are 0.37, 0.70, 0.58, 0.85, 1.97 and -9.07 kcal/mol, in DMSO, methanol, acetone, THF, cyclohexane and in gas phase respectively.
Journal of Molecular Structure, 2013
ABSTRACT The structure and reactivity of hydroxyaminosilanethione conformers were studied in the ... more ABSTRACT The structure and reactivity of hydroxyaminosilanethione conformers were studied in the gas phase using density functional theory. Eight local minima were located, including two featuring pentacoordinate silicon atoms (2Z, S2) and one with a nitrososilanethiol structure (4Z). The global minimum at the B3LYP/6-31++G(dp)//B3LYP/6-31G(d) levels of theory is S2. Natural bond orbital (NBO) analysis reveals that there is a strong nS2→σN3Si1∗ interaction in the majority of isomers. The 3d orbitals of silicon are of minor importance in bonding for the isomers with the exception of those where the silicon is penta-coordinate (2Z and S2), where the occupancy of the 3d orbitals is 2.93, 4.34 respectively. The charge density and its Laplacian at the bond critical point (BCP), (ρ(r) and ∇2ρ(r)), indicate that all SiS, SiN and SiH bonds were constructed by ionic or electrostatic interactions, whereas NH and OH bonds are predominantly covalent. In addition, seven transition states connecting the various minima were located. TS7 has the highest energy (75.75 kcal/mol) in the reaction coordinates and is therefore the rate-determining step in the conversion of 1Z–4Z. TS7, TS2 and TS3 have the highest energies (75.75, 66.50 and 57.92 kcal/mol, respectively). The computed harmonic frequencies results were in good agreement with available experimental values. The spectra of S1 and 2Z have the lowest NH frequencies (3117 and 2965 cm−1), this shift towards the lower frequency being attributable to the presence of intramolecular hydrogen bonding in S1 and 2Z.
Computational and Theoretical Chemistry, 2012
ABSTRACT The tautomerizm of (hydroxphosphino)silanethione molecule 1 were investigated by density... more ABSTRACT The tautomerizm of (hydroxphosphino)silanethione molecule 1 were investigated by density function theory calculations. The potential energy surface, the global isomeric structures and the transition states of intramolecular proton transfer were calculated at B3LYP/6-31G(d) level of theory. The energy was further studied by a single point calculation by means of B3LYP/6-311++G(d,p) level. The potential energy surface was built-in of ten tautomers 2-11 along with ten transition states TS1-TS10 located for molecule 1. The global minimum at the B3LYP/6-31++G(d,p)//B3LYP/6-31G(d) levels of theory is 1. Tautomer 3 possessed the highest energy (136.06 kJ/mol) above the global isomeric structure 1. The energies of the transition states reflect their different respective ring strains, TS2 with three-membered ring is possessed the highest energy (307.19 kJ/mol) whereas the TS10 with four-membered ring had the lowest energy (107.17 kJ/mol) among the transition states. The TS2 was clearly involved in the rate-determining step. The natural bond orbital (NBO) analysis reveals that the natural atomic charges are in conformity with bond lengths and electronic densities in the studied tautomers. The second order delocalization energies (E-(2)) showed that there is a strong n(s2) -> sigma(P3-Si1)* and n(s2) -> sigma(P3-Si1)* interactions in the tautomers excluding structures 3 and 10. A strong n(P3) -> sigma(P2-Si1)* interaction (240.10 kJ/mol) is located for 3. Finally, strong n(O4) -> sigma(P3-S2)* interaction (134.89 kJ/mol) was found for 10 as expected since 10 is the only structure possessed a P-S bond. The atoms in molecules (AIM) calculations of charge density at the bond critical point (BCP), (rho(r) and del(2)rho(r)) showed that for all Si-S, Si-P and Si-H bonds were constructed by ionic or electrostatic interactions, whereas O-H and S-H bonds are maintained the covalent bond nature. The computed harmonic frequencies at B3LYP/6-31G(d) level showed that the values of the stretching frequencies of the most structures under consideration were in good agreement with the experimental values which have been reported for similar stretches.
The syntheses of some Ni(II), Co(II) and Cu(II) Schiff base complexes have been reported. The Sch... more The syntheses of some Ni(II), Co(II) and Cu(II) Schiff base complexes have been reported. The Schiff base ligands H2L1 (C40H32N2O2), H2L2 (C32H28N2O2) and H2L3 (C22H26N2O2) under were prepared by the condensation of amines namely benzidine and 1,4-phenylenediamine with benzoin, benzoylacetone and acetylacetone. A fourth ligand H2L4 (C34H28N2O2) was obtained by the condensation of 1,4-phenylenediamine with benzoin. Schiff base ligands and their complexes have been subjected to elemental analysis, Infrared, electronic spectral studies, molar conductivity and magnetic moment measurements. The Ni(II) and Co(II) complexes showed an octahedral and square planar geometries. In addition, the analysis exhibited a different chelation mode towards metal and ligand substitution, since a mono- and dinuclear metal complexes have been identified.
The ligand and its complexes of Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) were investig... more The ligand and its complexes of Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II)
were investigated in terms of synthesis, elemental analysis, molar conductivity,
thermal analysis, infrared spectra and magnetic susceptibility measurements. The
ligand: 4-[4-(3-Hydroxy-1-ethyl-but-2-enylideneamino)-biphenyl-4-ylimino]-pent-2-
en-ol (C22H24N2O2) has been synthesized by the condensation of acetylacetone and
benzidine. The complexes have been synthesized by two different methods and their
geometries were investigated. A synthesis and characterization of novel complexes
of 4-[4-(3-Hydroxy-1-ethyl-but-2-enylideneamino)-biphenyl-4-ylimino]-pent-2-en-ol
has been achieved. The study also confirmed the formation of mono-, di- and novel
polynuclear metal complexes. The researcher recommended that the mentioned
complexes may have biological activity.
The Schiff base ligands and their complexes of divalent metals of Ni(II), Co(II) and Cu(II) were ... more The Schiff base ligands and their complexes of divalent metals of Ni(II), Co(II)
and Cu(II) were investigated in terms of synthesis, elemental analysis, molar
conductivity, thermal analysis, infrared spectra, ultraviolet-visible and magnetic
susceptibility measurements. The ligands have been synthesized by condensation
of benzoylacetone and ethylenediamine, o-phenylenediamine and 1,6-
hexanediamine to gives H2L1 = C22H24N2O, [N,N
-
bis(benzoylacetone)ethylenediamine]; H2L2
= C26H24N2O2 [N,N
-(benzoylacetone)-ophenylenediamine];
H2L3 = C26H32N2O2, [N,N
-bis (benzoylacetone)-1,6-
hexanediamine] respectively. The fourth ligand is formed by the condensation of
benzoin and o-phenylenediamine H2L4
=C34H28N2O2, [N,N
-
bis(Benzoin)-ophenylenediamine].
The ligands and their complexes have been synthesized by two
different methods and their geometries were investigated. A synthesis and
characterization of novel ligand and complexes of benzoin derivatives has been
achieved. The study also confirmed the formation of mon- and binuclear metal.
The binuclear metal complexes are synthesized by new methods. The researcher
recommended that the mentioned complexes may have biological activity.
The transformation of few isomeric tautomers of thioformohydroxamic (TFH), thioacetohydroxamic (T... more The transformation of few isomeric tautomers of thioformohydroxamic (TFH), thioacetohydroxamic (TAH) and thiobenzohydroxamic (TBH) acids via intramolecular hydrogen transfer were investigated by density functional calculations. The global isomeric structures, the transfer potential surfaces, the harmonic frequency and transition states geometries of intramolecular hydrogen transfer were calculated at the B3LYP/6-31++G** // B3LYP/6-31G* levels of theory. The order of stability of these tautomers was Z2>Z1>E2>E1>>>CS and Z1>Z2>E2>E1>>>CS. The Z1 and E1 are thione forms whereas Z2 and E2 are thiol forms and CS is the charge-separated structure. The reaction pathways for the interconversion between tautomers were through the transition structures TS1, TS2, TS3 and TS4. The TS3 was involved in the rate-determining step. The ring strain is clearly affecting the activation barrier. Some anionic structures are also examined to look whether the thiohydroxamic acids are O-acid, N-acid or S-acid.
First principle quantum chemical calculations at the HF level of theory, using the 3-21G and 3-21... more First principle quantum chemical calculations at the HF level of theory, using the 3-21G and 3-21G* split-valence basis sets have been used to investigate the molecular geometry and electronic properties of Bis(phosphino)methane (H2PCH2PH2) (BMP) conformers. Phosphine (PH3) (AP) and methyl phosphine (CH3PH2) (MP)are also investigated for a comparison grounds. Geometries, charges electronic density, total energies, HOMO-LUMO gap, LUMO energies, (1st, 2nd and 3rd) ionization energies and dipole momentum were calculated. The study investigated six Bis(phosphino)methane (BMP) conformers. The highest d-orbitals contribution to the HOMO and the LUMO is 00.0028% and 0.0125% respectively. The study demonstrated that it is not necessary to involve d-orbital participation in bonding in order to explain the geometries of the majority of these molecules. The relative stability of the conformers was calculated.
[(η5-Indenyl)Fe(CO)3]BF4 (I) undergoes facile monocarbonyl substitution at room temperature in ac... more [(η5-Indenyl)Fe(CO)3]BF4 (I) undergoes facile monocarbonyl substitution at room temperature in acetone by monophosphines, monophosphites and MPh3 (M =1cr; As, Sb, Bi) ligands (L) to form [(η5-Indenyl)Fe(CO)2L]BF4. Ditertiary phosphines, PPh2(CH2)n PPh2 (n = 1, 2, 4, 6, 8) and both the arsines, AsPh2(CH2)2AsPh2 and AsMe2 (CH2)5AsMe2 react similarly to form monosubstituted complexes e.g. [(η5-Indenyl)Fe(CO)2(η1- PPh2(CH2)nPPh2)]BF4 and dimeric complexes, e.g. [{(η5-Indenyl) Fe(CO)2}2-μ-PPh2(CH2)nPPh2)] [BF4]2 Prolonged refluxing of I with these ligands gives the chelates, e.g. [(η5-Indenyl)Fe(CO)(η2- PPh2(CH2)nPPh2)]BF4. The enhanced reactivity of the [(η5-Indenyl)Fe(CO)3]+ cation over that of [(η5,-C5H5)Fe(CO)3]+ in solvents such as acetone may be attributed to the “indenyl” effect, i.e. ring slippage from η5 to η3. However, no evidence was obtained for intermediates such as [(η3-C9 H7)Fe(CO)3(acetone)]+, and so the effect must operate solely in the transition state of the reaction.
Spectroscopic evidence is presented for the formation at low temperatures of the η3-indenyl inter... more Spectroscopic evidence is presented for the formation at low temperatures of the η3-indenyl intermediate [(η3-C9H7)Fe(CO3H], prior to formation of t by reduction of the tricarbonylironindenyl cation with sodium cyanoborohydride in acetone.
Although the hydride ($-Cp(C0)2FeH is well documented (see ref. 1 and refs. therein) and the corr... more Although the hydride ($-Cp(C0)2FeH is well
documented (see ref. 1 and refs. therein) and the
corresponding formyl (r)5-Cp)(C0)2FeCH0 more re- cently identified by low temperature ‘H NMR spec- troscopy [2], there have been, to the best of our
knowledge, no previous reports of the analogous
indenyl compounds. We report now spectroscopic
(IR and ‘H NMR) evidence for these compounds
by reduction of the tricarbonylindenyliron cation
[(v5-In)Fe(C0)3]+ (1) by sodium borohydride in
acetone.
The Fourier transform infrared and Raman spectra of the cations [η5-C9H7Fe(CO)n dppa]+ (n = 1, 2;... more The Fourier transform infrared and Raman spectra of the cations [η5-C9H7Fe(CO)n dppa]+ (n = 1, 2; dppa=bisdiphenylphosphinoalkane, where alkane=methane, ethane, butane, hexane and octane) and [{η5-C9H7Fe(CO)2}2-μ-dppa]2+ indicate that the alkyl chain lengths have effects on the structures of the bidentate cations resulting in increased back-donation to carbonyl groups as the chain length increases. In contrast the alkyl chain lengths have no similar effects in the unidentate mononuclear and bridged cations.
The proton transfer processes have generated eight minimum structures of the silarhodanine molecu... more The proton transfer processes have generated eight minimum structures of the silarhodanine molecule. These
structures were studied in the gas phase by a high level theory complete basis set (CBS-Q). All the structure are
heterocyclic compounds except S2 structure. The global isomeric structure was S5 at the CBS-Q levels of theory.
The acyclic structure S2 is possessed the highest energy (60.17 kcal/mol) above the global minimum S5. Nine anions
and nine cations of various conformers have been investigated. The protonation and deprotonation reactions in the
gas phase are examined at the CBS-Q level. The S2OA showed the highest relative enthalpy (∆H= 24.65 kcal/mol)
and S3OA structure showed the highest Gibbs free energy (∆G=23.59 kcal/mol). The S2NC cation showed the
highest relative enthalpy and Gibbs free energy (∆H= 50.25 kcal/mol, ∆G=47.07 kcal/mol) in the cations section.
Energetically easiest process is the deprotonation of 2ZNA with the computed enthalpy and Gibbs free energy of
1274.52 kJ/mol and 1282.49 kJ/mol. The equilibrium constants at 298.15 K and 1 atmosphere pressure of the
deprotonation reactions are very small which means the reaction at this temperature favor the reactants. The
computed vibrational frequencies values for the structures are inconformity with the experimental ones.
Journal of Organometallic Chemistry, 2008
The fundamental processes involved in the hydride reduction of metal carbonyl compounds continue ... more The fundamental processes involved in the hydride reduction of metal carbonyl compounds continue to attract attention due to their importance in the FischerTropsch process [1], the water-gas shift reaction [2] and other industrially relevant processes [3]. The unsaturated nature of ...