3.0 Methodology
3.1
Material and apparatus
In this Suzuki reaction, the chemicals that was used for synthesis of ligand and complex
are Nickel (II) chloride (NiCI2), 1H-1,3-benzodiazole, 4-(bromomethyl)benzoic acid,
dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), dry methanol and nitrogen gas. 1bromo-4-nitrobenzene, bromobenzene, 1-(4-bromophenyl)ethan-1-one, 1-bromo-4methoxybenzene, 2-(4-bromophenyl)acetic acid,
4-bromobenzoic
acid,
phenylboronic acid, and potassium hexafluorophosphate (KPF6). (Akira Suzuki Facts, 2010)
The apparatus that was used are 3-neck round bottom flask, Liebig condenser, beakers,
vacuum filtration, vacuum dessicator, filter paper and hot plate with magnetic stirrer.
The synthesised product was characterised by four instruments which are Fourier
Transform Infrared (FTIR), Nuclear Magnetic Resonance (NMR), Electronicspray
Ionisation Mass Spectrometry (ESI-MS) and UV-Visible Spectroscopy (UV-Vis). First,
FT-IR is the preferred method of infrared spectroscopy and it is a technology that are
capable to identify chemicals by using an infrared light source to measure absorption.
it has high accuracy of wavenumber which the error is between the range ± 0.01cm-1.
It also has shorter scan time for all frequencies which approximately 1 seconds. While
the resolution is extremely high between 0.1 ~ 0.005 cm-1 and the scan range is wide
(1000 ~ 10 cm-1). By using a Bruker Advance 300, 1H and
13
C NMR was recorded at
300 and 75 MHz respectively. (Peramo et al., 2020) Next, ESI-MS will be used in
synthesizing the characterization of the product. First, ESI uses electrical energy to
support the transferring of ions from solution into the gaseous state before they were
introduced to mass spectrometric (MS) analysis. Then, MS which an analytical
technique will provide qualitative and quantitative result in term of structure and
molecular mass or concentration respectively.(Ho et al., 2003) Lastly, UV-Visible (UVVis) spectroscopy is used to gain the absorbance spectra of a compound in solution or
as a solid. Absorbance of light energy or electromagnetic radiation are
spectroscopically observed where electrons excites from ground state to the first singlet
excited state of the compound.
Catalytic activity of catalyst is determined as the increase in rate of chemical reaction
that influenced by the presence of a catalyst. The efficiency of a catalyst is measured
by the change in rate constant of the activation energy. There are other two term that
were used in this purpose which are turnover number (TON) and turnover frequency
(TOF). TON is an average number of cycles a catalyst can undergo before its
performance faded while TOF is number of times the overall catalyzed reaction take
place per catalyst per unit time. Formula for TON and TOF is shown below:
TON = kcat =Vmax/Et
TOF=TON/reaction time
Vmax = Maximum rate of reaction when all the enzyme catalytic sites are saturated
with substrate
Et = Total enzyme concentration or concentration of total enzyme catalytic sites
3.2
Synthesis of Nickel-benzimidazolium bromide catalyst
1-3-Bis(4-carboxybenzyl) benzimidazolium bromide is a ligand that was prepared by
dissolving 1H-1,3-Benzodiazole (1.1814 g) in 10 mL of THF in a beaker and
stirred. 4-(bromomethyl)benzoic acid (4.301 g) was then added into the beaker.
Then, the expected compound, 1,3-bis(4-carboxybenzyl) benzimidazolium
bromide was separated using vacuum filtration and washed with THF and
water. Then, it was dried in vacuum desiccator. Figure 1 show synthesis route
of 1-3-Bis(4-carboxybenzyl) benzimidazolium bromide, where R = COOH.
Figure 1: Synthesis route of 1-3-Bis(4-carboxybenzyl) benzimidazolium bromide,
where R = COOH.
The synthesis steps were continued with stirring of 1-3-Bis(4-carboxybenzyl)
benzimidazolium bromide in 15 mL dry methanol and then nickel chloride was added
slowly into the solution. The solution was refluxed for 2 hours. After refluxing, 37%
NaOH (3.5mL, 2.0 M) was added dropwise over 30 minutes. Then, it was further stirred
for 24 hours at room temperature. The suspension obtained was filtered, washed with
diethyl ether and dried in a desiccator. The product obtained was [bis(1,3-bis(4carboxybenzyl) benzimidazole)] dibromonickel (II) catalyst. The synthesis route is
shown in figure 2. This step was repeated by replace NiCI2 with KPF6 to produce 13-Bis(4-carboxybenzyl) benzimidazolium hexafluorophosphate.
Figure 2: Synthesis route of [bis(1,3-bis(4-carboxybenzyl) benzimidazole)]
dihexafluorophosphonickel(II) catalyst,
The Nickle(II) complex namely [bis(1,3-bis(4-carboxybenzyl) benzimidazole)]
dihexafluorophosphonickel(II) was prepared by reacting 1-3-Bis(4-carboxybenzyl)
benzimidazolium hexafluorophosphate with NiCI2. The synthesis route of [bis(1,3bis(4-carboxybenzyl) benzimidazole)] dihexafluorophosphonickel(II) was shown in
Figure 3.
Figure 3: Synthesis route of [bis(1,3-bis(4-carboxybenzyl) benzimidazole)]
dihexafluorophosphonickel(II)
3.3
Preliminary Complexation Study
Preliminary complexation study is to determine the stoichiometry between ligand and
metal. The study was conducted by using UV-Vis spectroscopy titration method.
Solution of ligand (2.5 × 10-5 M) and Ni2+ cation was individually prepared in
DMSO. The cuvette with 2.5 mL of ligand solution was titrated with Ni2+ cation
solution. After each titration, the UV-Vis spectra were recorded about 5 minutes in
the range of 270 nm – 300nm. (Nur Rahimah Said et al., 2020)
3.4
Catalytic Study
The catalytic activity of Suzuki reaction was investigated by testing on both
synthesized nickel catalyst and reacting phenylboronic acid with 1-bromo-4nitrobenzene, 1-bromobenzene, 1-(4-bromophenyl)ethan-1-one and 1-bromo-4methoxybenzene (4-bromoanisole) to produce p-phenyl-nitrobenzene, biphenyl, 4acetylbiphenyl and 4-methoxybiphenyl , respectively. 1-bromo-4-nitrobenzene (
0.202g; 1mmole), phenylboronic acid (0.024g; 0.20mmole), K2CO3 (0.202g; 1mmole
), nickel (II) complex (0.0013g) and N,N-dimethylacetamide, DMA (10ml) was
mixed together in three round bottom flask. After that, it will undergo reflux process
for 1 hour with the aid of nitrogen gas. Then, the product was left to cool down to
room temperature and continued with extraction process by using water (30 mL) and
three potion of dicholoromethane (10 mL). To obtain the final product, organic layer
that was formed was dried with MgSO4 and left to evaporate. Lastly, The
characterization of the product was determined by FTIR spectroscopy. (N. R. Said et
al., 2018)
Those steps were repeated by replacing 1-bromo-4-nitrobenzene with bromobenzene
(0.047g; 0.30 mmole), 1-(4-bromophenyl)ethan-1-one (0.060g; 0.30 mmole), and 1bromo-4-methoxybenzene ( 0.056g; 0.30 mmole).
Figure 4.1: Catalytic reaction of 1-bromo-4-nitrobenzne with phenylboronic acid
Figure 4.2: Catalytic reaction of bromobenzene with phenylboronic acid
Figure 4.3: Catalytic reaction of 1-(4-bromophenyl)ethan-1-one with phenylboronic
acid
Figure 4.4: Catalytic reaction of 1-bromo-4-methoxybenzene with phenylboronic
acid