Browsing by Author "Adeyemi, Olalere"

Now showing 1 - 13 of 13
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    Computational and Experimental Studies of 4-Aminoantipyrine as Corrosion Inhibitor for Mild Steel in Sulphuric Acid Solution
    (2012-01-01) Adeyemi, Olalere
    The inhibitive effect of 4-Aminoantipyrine (4-AAP) on the corrosion of mild steel in 0.5 M H2SO4 solution at 303 – 323 K was studied by weight loss measurement as well as computational techniques. Results obtained showed that 4-aminoantipyrine (4-AAP) is a good inhibitor for the corrosion of mild steel in sulphuric acid solution. The inhibition efficiency increased with 4-AAP concentration and also synergistically increased in the presence of KI and KSCN, but decreased with temperature, which is suggestive of physical adsorption mechanism. The adsorption of 4-AAP onto the mild steel surface was found to follow the Langmuir adsorption isotherm. Thermodynamics of adsorption such as enthalpy of adsorption, entropy of adsorption, equilibrium of adsorption and Gibbs free energy, were calculated and discussed. Quantum chemical calculations using DFT at the B3LYP/6-31G* level of theory was further used to calculate some electronic properties of the molecule in order to ascertain any correlation between the inhibitive effect and molecular structure of 4-aminoantipyrine.
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    Electron-transfer Chain Catalysis in Phosphine Replacement Reaction: Determination of Relative Donor Capability of Arylpyridylphosphines
    (2007-01-20) Adeyemi, Olalere
    The slight differences in the donor capabilities of PPhnPy3 n (n = 0–3) could be measured directly in the equilibrium of phosphine replacement reaction on (g5 -C5H5)Fe(CO)2-phosphine complexes, taking advantage of the radical pathway to establish equilibrium rap idly. The simultaneous determination of equilibrium constants is done in a single experiment. The donor capability increases in the order PPh3 < PPh2Py < PPhPy2 < PPy3 with quantified ðg5-C5H5ÞFeðCOÞ2 þ-affinity scales at 1, 4.90, 11.0, and 20.3, respectively. 2006 Elsevier B.V. All rights reserved
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    Facile Synthesis and Vapochromic Studies of Co(II) Complexes Bearing NO and OO Donor Ligands
    (2015-12-15) Adeyemi, Olalere
    Two Co(II) complexes containing malonic and isonicotinic acids have been prepared by manual grinding of stoichiometric amounts of the starting materials. Elemental analysis (CHN), IR, UV-vis spectroscopic techniques, TGA-DTG investigation and X-ray powder diffraction analy sis were used to characterize the two compounds. Isonicotinic acid coordinated to the metal via the pyridine ring nitrogen and one oxygen atom of the carboxylic group while malonic acid coordinated via both oxygen atoms of the carboxylate groups indicating bidentate co ordination mode in the two compounds. The compounds were exposed to some volatile organic compounds (VOCs) containing nitrogen or oxygen donor atoms in the solid state and their vapochromic behaviours studied using colour changes, FT-IR and solid state UV vis spectroscopies. Heating the samples exposed to the VOCs for a few minutes at 100 °C regenerates the original material without degradation, even after several heating cycles.
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    Hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands: Imidazole and oxazole ring Lewis basicity, Ni(II)/Pd(II) complex structures and spectra
    (2010-03-12) Adeyemi, Olalere
    Fourteen new organic molecules A1–A4, B1–B5, C1–C4 and D and a series of transition metal(II) com plexes (Ni1–Ni9 and Pd1–Pd2b) were synthesized and studied in order to characterize the hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands (A1–A4 = 2-R2 -6-(4,5-diphenyl-1R1 - imidazol-2-yl)pyridines, R1 = H or CH3, R2 = H or CH3; B1–B5 = 1-R2 -2-(pyridin-2-yl)-1R1 -phenan thro[9,10-d]imidazoles/oxazoles, R1 = H or CH3, R2 = H or CH3; C1–C4 = 2-(6-R2 -pyridin-2-yl)-1H-imi dazo/oxazo[4,5-f][1,10]phenanthrolines, R2 = H or CH3; D = 2-mesityl-1H-imidazo[4,5-f][1,10]phenan throline). They were also used to study the substituent effects on the donor strengths as well as the coor dination chemistries of the imidazole/oxazole fragments of the hemilabile ligands. All the observed protonation–deprotonation processes found within pH 1–14 media pertain to the imidazole or oxazole rings rather than the pyridyl Lewis bases. The donor characteristics of the imidaz ole/oxazole ring can be estimated by spectroscopic methods regardless of the presence of other strong N donor fragments. The oxazoles possessed notably lower donor strengths than the imidazoles. The elec tron-withdrawing influence and capacity to hinder the azole base donor strength of 4,5-azole substitu ents were found to be in the order phenanthrenyl (B series) > 4,5-diphenyl (A series) > phenanthrolinyl (C series). An X-ray structure of Ni5b gave evidence for solvent induced ligand reconstitution while the structure of Pd2b provided evidence for solvent induced metal–ligand bond disconnection. Interestingly, alkylation of 1H-imidazoles did not necessarily produce the anticipated push of electron density to the donor nitrogen. Furthermore, substituents on the 4,5-carbons of the azole ring were more important for tuning donor strength of the azole base. DFT calculations were employed to investigate the observed trends. It is believed that the information provided on substituent effects and trends in this fam ily of ligands will be useful in the rational design and synthesis of desired azole-containing chelate ligands, tuning of donor properties and application of this family of ligands in inorganic architectural designs, template-directed coordination polymer preparations, mixed-ligand inorganic self-assemblies, etc.
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    Multistage Optimization of the Adsorption of Methylene Blue Dye onto Defatted Carica papaya seeds
    (2009-07-01) Adeyemi, Olalere
    Carica papaya seeds were defatted and used for the adsorption of methylene blue dye (MB dye). The pHPZC and specific surface area (SSA) of the defatted and undefatted Carica papaya seeds were found to be 6.25 and 143.27 m2 g−1 respectively. The adsorption capacities of the defatted Carica papaya seeds were 1250 and 769.23 mg g−1. Fourier transformed infrared (FT-IR) spectra analysis of defatted seeds suggests the presence of , -unsaturated ketone, -keto (enolic) esters and lactones, quinones and carboxylic acids which were absent in the undefatted sample. The presence of carboxylic acid, phenolic and lactone functional groups were confirmed by surface chemistry studies. Adsorption of MB dye onto DPS adsorbent was found to be exothermic and spontaneous. FT-IR spectra of various particle sizes indicate the presence of functional groups on every particle size necessary for the adsorption of MB dye. Pseudo-second-order kinetic rate constant increased with increasing initial MB dye concentration. The adsorption reaction was observed to be very fast perhaps because of the presence of multiple functional groups with some of them having lone pair of electrons. Increasing pH was observed to have very little positive effect on the adsorption of MB dye on DPS adsorbent. Increasing particle size decreased the adsorption capacity of DPS adsorbent for MB dye. It is suggested that the mechanism for the adsorption of MB dye onto DPS adsorbent might not only be solely controlled by film diffusion but also by pore diffusion. Mathematical models for the optimization of adsorbent dose, number of adsorption stages and mini mum contact time were developed. The optimum conditions for the adsorption of 99% of 100 mg L−1 MB dye from 10 m3 of aqueous solution of the dye were five adsorption stages, ≈21 kg for each stage with a total minimum contact time of ≈71 min
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    Neighbouring Metal Induced Oxidative Addition at the Iron Centre amongst the Iron–arylpyridylphosphine Complexes
    (2008-05-06) Adeyemi, Olalere
    Complexes of the type (g4 -BuC5H5)Fe(CO)2(P) (P = PPh2Py 3, PPhPy2 4, PPy3 5; Py = 2-pyridyl) were sat isfactorily prepared. Upon treatment of 3 with M(CO)3(EtCN)3 (M = Mo, 6a; W, 6b), the pyridyl N-atom could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced an oxidative addition of the endo-C–H of (g4 -BuC5H5). This results in a bridged hydrido heterodimetallic complex [(g5 -BuC5H4)Fe(CO)(l-P,N-PPh2Py)(l-H)M(CO)4] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of 4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than one pyridyl N-atom. The reaction of 4 with M(CO)4(EtCN)2 (M = Mo, 9a; W, 9b) produced heterodimetal lic complexes [(g4 -BuC5H5)Fe(CO)2(l-P:N,N0 -PPhPy2)M(CO)4] (M = Mo, 10a, 81%; W, 10b, 83%). Treat ment of 5 with 6a,b gave [(g4 -BuC5H5)Fe(CO)2(l-P:N,N0 ,N00-PPy3)M(CO)3] (M = Mo, 12a, 96%; W, 12b, 78%)
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    Quantification of steric interactions in phosphine ligands from single crystal X-ray diffraction data. Crystal structures of (g5 -C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2, PhEt2, Et3)
    (2005-12-05) Adeyemi, Olalere
    Distorted square pyramidal complexes of molybdenum (g5 -C5H4Me)Mo(CO)2(PR3)I (R3 = PhMe2 (2a); PhEt2 (3a) and Et3 (4a)) have been synthesized and the structures of the lateral (cis) isomers have been determined by X-ray diffraction. The cone (H) and solid (X) angles as well as the angular profiles of the phosphine ligands in the complexes have been computed using the program STERIC. Values for the crystallographic cone and solid angles calculated for 2a, 3a and 4a are H (129 , 135 and 139 ) and X (2.73, 2.99 and 2.93 sr), respectively. A search of the Cambridge Structural Database (CSD) was made for piano stool, 5- and 6-coordinate complexes containing the title phosphine ligands. Results from this study show a wide range of sizes for each of the ligands and even the seemingly simple PPhMe2 ligand exhibited a wide range of values for the cone (113–137 ) and solid (2.49–3.07 sr) angles. These observations have been rationalized and related to the possible group conformations from the crystallographic data
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    Solid-state Isomerisation Reactions of (g5 -C5H4R)M(CO)2(PR3 0 )I (M ¼ W, Mo; R ¼ t Bu, Me; R0 ¼ Ph, Oi Pr3
    (2004-04-06) Adeyemi, Olalere
    The cis and trans monosubstituted cyclopentadienyl tungsten and molybdenum complexes (g5-C5H4R)M(CO)2(L)I (1) (M¼ W, R ¼ Me, t Bu, L ¼ P(Oi Pr)3, PPh3; M ¼ Mo, R ¼ Me, L ¼ PPh3) have been synthesised and fully characterised by elemental analysis and IR and NMR spectroscopy. It was found that 1 underwent a thermal solid-state ligand isomerisation reaction and that the favoured direction of the isomerisation reaction is related to the melting points of the cis and trans isomers, i.e., with intermolecular forces in the solid state. No obvious relationship between the melting point and the metal, the ring-substituent or the ligand was observed. Crystal structure determinations of the cis and trans isomers of (g5-C5H4Me)W(CO)2(PPh3)I reveal that a limited amount of isomer conversion can be accommodated in the unit cell of the trans isomer, prior to crystal fragmentation. The rearrangement of the molecules within the unit cell, during isomerisation, also leads to disorder in the crystal
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    The Solid-state Isomerization of cis and trans-(η5 -C5H4Me)Mo(CO)2(P(Oi Pr)3)I
    (2002-06-16) Adeyemi, Olalere
    The cis- and trans-(η5 -C5H4Me)Mo(CO)2(P(Oi Pr)3)I complexes undergo a bi-directional thermal ligand isomerization reaction to yield an equilibrium mixture of isomers (30/70 cis/trans ratio, 90 °C, < 80 min) in the solid state. The activation energy barrier for the cis-trans isomerization reaction (80–100 °C) was found to be 68 ± 10 kJ mol–1. In benzene (reflux, 2 h) this isomer ratio was found to be 70:30 cis/trans. DSC and powder XRD studies have revealed reactions that occur in the solid state entailing decomposition and isomerization. DSC experiments did not reveal the presence of the cis–trans isomerization reaction.
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    The solid-state isomerization of cis and trans-(η5 -C5H4Me)Mo(CO)2(P(Oi Pr)3)I
    (2004-04-06) Adeyemi, Olalere
    The cis and trans monosubstituted cyclopentadienyl tungsten and molybdenum complexes (g5-C5H4R)M(CO)2(L)I (1) (M¼ W, R ¼ Me, t Bu, L ¼ P(Oi Pr)3, PPh3; M ¼ Mo, R ¼ Me, L ¼ PPh3) have been synthesised and fully characterised by elemental analysis and IR and NMR spectroscopy. It was found that 1 underwent a thermal solid-state ligand isomerisation reaction and that the favoured direction of the isomerisation reaction is related to the melting points of the cis and trans isomers, i.e., with intermolecular forces in the solid state. No obvious relationship between the melting point and the metal, the ring-substituent or the ligand was observed. Crystal structure determinations of the cis and trans isomers of (g5-C5H4Me)W(CO)2(PPh3)I reveal that a limited amount of isomer conversion can be accommodated in the unit cell of the trans isomer, prior to crystal fragmentation. The rearrangement of the molecules within the unit cell, during isomerisation, also leads to disorder in the crystal.
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    Solvent-Free Organometallic Migratory Insertion Reactions
    (2003-03-10) Adeyemi, Olalere
    Migratory insertion reactions of organometallic complexes have been shown to occur in the absence of solvent and, more significantly, between solid reagents. Reaction between (η5-C5H5)M(CO)3Me (M ) Mo, W) or (η5-C5H5)Fe(CO)2Me and PPh3 (no solvent) took place at temperatures between 40 and 90 °C and gave the products (η5-C5H5)M(CO)2(PPh3)COMe and (η5-C5H5)Fe(CO)(PPh3)COMe in moderate to good yield (60-99%). The Mo and W complexes reacted in the solid state when T < 80 °C. The decarbonylation of (η5-C5H5)- Mo(CO)2(PPh3)COMe to yield (η5-C5H5)Mo(CO)2(PPh3)Me also occurred in the solid state (120 °C). Reaction of (η5-C5H5)Mo(CO)3Me with a range of ligands, L (L ) PPh3, P(p MeOC6H4)3, PCy3, PEt3, AsPh3, POPh3, P(OEt)3; 1:1 reagent ratio, 90 °C, 15 min), in the absence of solvent gave (η5-C5H5)Mo(CO)2(L)COMe (7-100% yield) and, on extended reaction, (η5-C5H5)Mo(CO)2(L)Me in varying yields. A kinetic study of the solid-state reaction between (η5-C5H5)Mo(CO)3Me and PPh3 yielded rate constants, e.g. k ) 5.18 × 10-5 s-1 (Mo:P ) 1:10; 50 °C), which compares with the literature solution data in toluene (k ) (0.8-2.5) × 10-5 s-1, 50 °C) using similar metal to ligand ratios. The data are consistent with a pseudo-first order reaction in the presence of PPh3. Diffusional effects on the reaction rate are detected at low temperature and low PPh3 ratios
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    Solventless Migratory-Insertion Reactions of Substituted Cyclopentadienyl Iron Complexes Induced by Electron Donor Ligands
    (2009-07-02) Adeyemi, Olalere
    Reaction between solid (C5H5)Fe(CO)2CH3 and a range of solid phosphine ligands, L (L = PPh3, P(m-CH3C6H4)3, P(p-CH3C6H4)3, P(p-FC6H4)3, P(p-ClC6H4)3, PCy3) occurred in the absence of solvent in the melt phase to give the migratory-insertion products, (C5H5)Fe(CO)(COCH3)(L). The reaction was more rapid with small electron withdrawing ligands. Insertion reaction between (RC5H4)Fe(CO)2R’ (R = H, CH3; R’ = CH3, CH2Ph) and gaseous ligands such as SO2 and CO were also studied. The insertion of SO2 occurred readily for all the substrates investigated, but CO insertion did not occur (< 1 %) using the solventless reaction condition.
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