A new series of N,O-bidentate ligands, L1, L2, L3 and L4, and their Pd(II) complexes, PdL1, PdL2, PdL3
and PdL4 have been synthesised and characterised using various physico-chemical techniques, namely
elemental analyses, IR and 1
H and 13C NMR spectroscopies, and conductivity analysis. The molecular
geometries of PdL2 and PdL4 have been elucidated through single crystal X-ray crystallography revealing
2:1 molar equivalence of ligand: Pd with the Schiff bases that exhibited bidentate ligands behaviour,
in which they coordinated through the phenolic O donor atoms and imine N. Upon complexation, the
ν(C=N) around 1629-1639 cm-1 and ν(C-O) around 1251 to 1252 cm-1 shifted to lower frequencies by 4
to 23 cm-1. In this study, three parameters were chosen for the reaction conditions optimisation, which
were types of bases, loadings for the catalyst, and temperatures of the reaction. Pd(II) complexes exhibited
good catalytic activities for Heck coupling reaction with 100% conversion at 100°C within 12 hours of
reaction time. Reducing the reaction temperature to 80°C reduced the conversion to a maximum of 80%.
Six new Pd(II) and Ni(II) metal complexes of N, O-bidentate (L1, L2) and ONNO-tetradentate (L3) Schiff base ligands have been synthesized. The compounds were characterized via various physicochemical and spectroscopic techniques namely elemental analysis (CHN), FT-IR, 1H and 13C NMR as well as magnetic susceptibility measurement. All complexes showed diamagnetism indicating that they are square planar complexes. Catalytic performance of Pd(L1)2 and Pd(L2)2 were investigated for Heck cross-coupling reaction under optimum operating parameters, monitored using GC-FID for 6 h of reaction time in inert conditions. High catalytic activities of up to 90% were observed in the presence of triethylamine as base and DMA as solvent at 100oC with 1 mmol% catalyst loading. The mechanism of catalyzed Heck reaction is proposed to go through a series of conversion of Pd(0)/Pd(II).
Two Schiff bases, 3-(4-hydroxyphenylimino)-1,3-dihydroindol-2-one (OPI) and 3-(4-Chlorophenylimino)-1,3-dihydroindol-2-one
(CPI) were successfully synthesized through condensation
reactions giving yields of 82% and 63%, respectively. The compounds were characterized via
physical and spectroscopic techniques, namely elemental analysis (C, H, N), 1H and 13C Nuclear
Magnetic Resonance (NMR) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy and
melting point. The corrosion inhibiting property of the Schiff bases on mild steel in 1 M HCl solution
was investigated by the weight loss (WL) measurements, electrochemical impedance spectroscopy
(EIS) and linear polarization resistance (LPR). The concentrations of the Schiff bases were varied
from 1 x 10-3 M to 1 x 10-5 M. The inhibition efficiencies obtained from all the methods employed were
in good agreement where the percentage of inhibition efficiencies increased with concentration. OPI
showed better inhibition efficiency than CPI with 91 % highest inhibition efficiency at 1 x 10-3 M
additive concentration. This is likely to be caused by the resonance donating effect due to the
presence of the hydroxyl group. The adsorption behaviour obeyed Langmuir isotherm for monolayer
formation.
Two imines of different molecular sizes namely 3-(phenylimino) indolin-2-one (PII) and 3,3- (1,4-phenylenebis (azan-1-yl-1-ylidene) diindolin-2-one (PDI) were investigated for their corrosion inhibition on mild steel in 1 M HCl solution using electrochemical impedance spectroscopy (EIS). The bigger molecule PDI containing double the amount of isatin moiety exhibited higher inhibition efficiency of 87.3% while PII that contained monoisatin moiety showed a lower inhibition efficiency of 74.8%. Both compounds had an increase in inhibition efficiencies percentage as concentrations increased. Density functional theory (DFT) was used to determine the correlation between the corrosion inhibition efficiency and electronic parameters. The DFT calculations indicated that the corrosion inhibition efficiency was mainly dependant on the frontier orbital energy gap and the chemical softness/hardness of the imines.
A mononuclear and new tetranuclear metal complexes of Zn(II) with Schiff base ligands L1 and L2 respectively, were synthesised. L1 was obtained through the condensation of salicylaldehyde with ortho-phenylenediamine while L2 was the product of reaction between of ortho-vanillin with 2,4,6-trimethyl-m-phenylenediamine. The ligands and complexes were characterised via elemental analysis, melting point, IR and NMR spectroscopy. The shifting of v(C=N), v(C-OH) and v(O-CH3) infrared peaks upon coordination with Zn(II) indicated that these three moieties play a significant role in the complexation. It was found that L1 acted as tetradentate ligand, coordinating with Zn(II) centres through phenolic oxygen and imine nitrogen. The ligand L2 acted as a hexadentate ligand, bonded to metal via phenolic oxygen, imine nitrogen and methoxy oxygen, where four Zn(II) centres formed bridges to connect two ligands.
The syntheses of salicylideneaniline (L1a) and 4-hydroxybenzalaniline (L1b) was carried out via condensation reaction giving yields of 80.74% and 81.65% respectively. The compounds were characterised by physical and spectroscopic techniques, namely melting point, micro elemental analysis (C, H and N), 1H Nuclear Magnetic Resonance (NMR) and Infrared (IR) spectroscopy. The characteristic n(C=N) peaks were observed at 1615 cm-1 and 1575 cm-1 respectively. Chronoamperometry (CA) was employed to electrodeposit both compounds on mild steel at 0.1 M inhibitor concentration in 0.3 M NaOH at three different potentials, +0.8 V, +1.05 V and +1.7 V. Formation of yellow imine films was observed on the mild steel. The corrosion behaviour of coated and uncoated mild steel was studied using Linear Polarization Resistance (LPR) in 0.5 M NaCl. Coated mild steel showed better corrosion resistance and with the highest inhibition efficiency of 90.34%, L1a provides a better protection against corrosion for mild steel than L1b.
A symmetrical azomethine ligand L was synthesised from a reaction of m-phenylenediamine and o-vanillin in 1:2 molar ratio. Dinuclear complexes of Zn2L2 and Co2L2 have been successfully isolated and characterised through 1H NMR, IR and magnetic moment. The x-ray crystal structure of Zn2L2 showed that the two Zn(II) nuclei were coordinated to two L moieties through the phenolic oxygen and imine nitrogen atoms, forming a slightly distorted tetrahedral geometry around the Zn(II) centres. When coordinated to metal centres, the signature n(C=N) of Lat 1616 cm-1 experienced a shift towards lower wave numbers of 1573-1613 cm-1. The Zn(II) complex was diamagnetic whereas the Co2L2 complex was paramagnetic with 3 unpaired electrons having µeff = 4.07 B.M. An antibacterial screening against methicillin resistant Staphylococcus aureus (MRSA) revealed that the activity of the complexes was more pronounced than that of the uncoordinated L. The complex Zn2L2 revealed the lowest MIC value of 0.56 µg/µl MIC, indicating that it was a better bactericides than Co2L2 and L, in that order.
Chemical industries are greatly assisted by catalysts; and commonly used catalysts for C-C formation
reactions are mainly phosphine-based complexes which are air and moisture sensitive. New air stable
Schiff base Pd(II) complexes have been synthesised, characterised and screened for their catalytic potential.
This paper reports three ONNO Schiff bases, namely, L2C [2,2’-((1E,1’E)-((2,2-dimethylpropane-1,3-
diyl) bis (azanylylidene)) bis (methanylylidene)-) bis (4-chlorophenol)], L2M [2,2’-((1E,1’E)-((2,2-
dimethylpropane-1,3-diyl)bis(azanylyli-dene)) bis (methanylylidene)) bis (4-methylphenol)] and L2H
[2,2’-((1E,1’E) - ((2,2-dimethyl-propane-1,3-diyl) bis (azanylylidene)) bis (methanylylidene)) diphenol].
These were synthesised from 2,2-dimethyl-1,3-propanediamine and salicylaldehyde derivatives with Cl,
CH3 and H at the meta position, respectively. The compounds were reacted with palladium(II) acetate
yielding three palladium(II) complexes denoted as PdL2C, PdL2M and PdL2H. The structures of all
compounds were elucidated through elemental analysis, 1
H and 13C NMR, FTIR and melting point. The
complexes were screened for catalytic activities in Sonogashira coupling reaction between iodobenzene
and phenylacetylene in DMSO. PdL2H was found to be the most active catalyst with 87% iodobenzene
conversion after 12 hours of reaction.
This study investigates the effect of oxalic acid at different concentrations as doping agent on
the electrical properties of polyaniline (PANI). The polymerization of aniline to produce
PANI was carried out in media containing oxalic acid at 0.08 M, 0.09 M, 0.1 M, 0.2 M and
0.3 M in the presence of ammonium persulphate as oxidizing agent. The successful formation
of PANI doped with oxalic acid was confirmed by FTIR and the morphology studied using
XRD. An impedance investigation on the series of PANI formed revealed that doping in 0.1M
oxalic acid produced PANI of the highest conductivity of 2.52 x 10-6
Scm-1.