COORDINATION COMPLEXES

WITH A TRIDENTATE NITROGEN

DONAR LIGAND

NAME : NELISWA MBATHA

STUDENT NUMBER : 216011130
DATE : 24/10/2018

1
TABLE OF CONTENTS

PAGE NUMBER

AIM…………………………………………………………………………….. 3
ABSTRACT……………………………………………………………………. 3
INTRODUCTION……………………………………………………………… 4-6
EXPERIMENTAL PROCEDURE……………………………………………… 7- 16
RESULTS……………………………………………………………………….. 17 - 20
DISCUSSION …………………………………………………………………... 21 - 23
CONCLUSION…………………………………………………………………. 23
REFERENCES…………………………………………………………………. 23-24
APPENDIX……………………………………………………………………… 25 -33

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AIM

The aim of this investigation was to synthesize the tridentate nitrogen donor ligand, propene
bis-(2-pyridylmethyl) amine (P-BPMA), to complex it with first row transition metals and to
determine the stability of these complexes. To perform a salt metathesis reaction to exchange
couterions on these complexes and to determine whether these complexes are paramagnetic.
Lastly to characterize the ligand (P-BPMA) and its transition metal complexes using H 1-
NMR, Infrared Spectroscopy and X-Ray crystallography.

ABSTRACT

The main objective of this investigation was to synthesise and characterize simple transition
metal complexes incorporating the propene bis-(2-pyridylmethyl) amine ligand. This was
done by first synthesizing the precursor ligand bis (2-pyridylmethyl) amine (BPMA) by
means of a Schiff base reaction involving pyridine carboxaldehyde and 2-pyridylmethyl
amine with methanol as the solvent. BPMA then undergoes an alkylation reaction with 3-
bromopropene to form P-BPMA which further undergoes complexation reactions with first
raw transition metals. A salt metathesis reaction to exchange counterions on the complexes is
to be performed as well the determination of their magnetic properties using the gouy
method. Very small quantities of BPMA were obtained and this resulted in a low percentage
yield of 0,0266 %. Various attempts were made to modify the original experiment procedure
in order to increase the BPMA yield but none of these were successful. Due to the low yield
of BPMA all other reagents were scaled down 47 times in order to synthesize P-BPMA. The
resulting P-BPMA formed was 0.048g and the resulting percentage yield was 15%. Further
experiments were not carried out due to insufficient yield of the P-BPMA ligand. One of the
factors that may have led to the poor yield of P-BPMA was pH control. Universal litmus
paper is not an accurate technique to monitor pH and thus in future it is recommended that a
pH meter be used in future. Another factor that may have affected the P-BPMA yield was
time as it was infeasible to keep the reaction mixture stirred for exactly 24 hours and the
stirring time was often exceeded greatly.

3
INTRODUCTION
A coordination complex is made up of a central atom or ion known as the coordinate centre
which is surrounded by oppositely charged ions or neutral molecules known as ligands. The
atom within the ligand that is attached to the central metal atom is called the donor atom.
Typically the metal ion is bonded to several donor atoms forming a ring structure known as
metal chelates [1].

Propene bis-(2-pyridylmethyl) amine (P-BPMA) is a tridentate nitrogen donor ligand

meaning that it has three nitrogen groups that can coordinate to the metal centre. The
presence of C=N group on this ligand results in larger splitting energies of the d-orbitals and
it is thus referred to as a strong field ligand. The nitrogen group on PBPMA has five valence
electrons two of which are non-bonding. The lone pair on the nitrogen bonds to the metal
centre upon complexation.

In order to synthesize P-BPMA it is necessary to first form its precursor ligand bis (2-
pyridylmethyl) amine (BPMA) and to do this a Schiff base reaction involving pyridine
carboxaldehyde and 2-pyridylmethyl amine in methanol is used. A Schiff base reaction is a
condensation reaction of an aldehyde with a primary amine. The resulting compound from
this reaction contains a C=N double bond which has replaced the original C=O double bond
on the aldehyde [2]. This compound is known as an imine or Schiff base. Schiff base
reactions containing aryl groups like the one illustrated in this investigation, are generally
more stable and more readily synthesized compared to those containing alkyl substituents.
The effective conjugation increases the stability of the reaction. Schiff base reactions are
reversible and usually takes place under acid base catalysis [2]. It is important to note that in
this investigation the reaction was not catalysed by an acid or base as the acid is only
introduced into the reaction mixture after the rate determining step which is the removal of
water.

Figure 1 illustrates a detailed reaction mechanism for the synthesis of P-BPMA. The reaction
starts with a nucleophilic attack from the amine on the aldehyde to give an unstable addition
compound known as the carbolamine [2]. This is followed by the protonation of the oxygen
and deprotonation of the nitrogen on the carbolamine to form water as the product. This is the
rate determining step and usually requires more than an hour to ensure complete protonation
and deprotonation. The intermediate then undergoes a reduction reaction to form a secondary

4
amine with sodium borohydride as the reducing agent. Hydrochloric acid is then added to the
reaction mixture to acidify the secondary amine to a pH of 4 and isolate the desired
intermediate known as the “iminium salt”. This iminium salt precipitates out of the methanol
solvent easily and it is polar which means it will dissolve in water. Sodium carbonate is then
added to the reaction mixture to change the medium to basic (pH 10) in order to remove any
unreacted sodium borohydride and to facilitate the isolation of BPMA during extraction [3].
BPMA then undergoes an alkylation reaction with 3-bromopropene to form the tridentate P-
BPMA ligand [2].

O
H3O H2O
O
N H2O H3O
OH
N
NH2 H2
N N
N
N H2O H3O H
N N

Figure 1: Reaction mechanism for the synthesis of P-BPMA [3]

5
In this investigation the synthesised P-BPMA ligand undergoes complexation reactions with
first row transition metals namely iron, nickel, copper and cobalt. It is important to study
metal complexes as most of them show catalytic activity in a variety of chemical processes.
They often have striking colours due to the electronic d-d transitions caused by the absorption
of light. For this reason they are often applied as pigments [1]

The BPMA precursor, P-BPMA ligand and the transition metal complexes are characterized
using Infrared Spectroscopy, NMR Spectroscopy and X-ray crystallography. Infrared
Spectroscopy is an analytical technique which can be used to determine functional groups
within a molecule. The advantage of IR spectroscopy is that it allows for the analysis of
samples in any state be it solid, liquid or gas. IR spectroscopy however does not give
information about the relative positions of the functional groups and thus it is best used
alongside NMR spectroscopy. NMR spectroscopy is a technique used to determine the
electronic structure of a molecule as well as its individual functional groups. X-ray
crystallography is a technique that utilises x-ray radiation to determine the structural form of
a molecule crystalized to solid state by measuring the angles and intensities of x-ray beams
diffracted by the crystalline structure. A three-dimensional picture of the electron density is
obtained and from this the position of the atoms in the crystal are obtained. The disadvantage
of this technique is that molecules in solution cannot be determined [4].

The transition metal complexes can be tested for paramagnetism using the gouy method. The
gouy balance which consists of a test tube suspended between magnetic two poles over it,
measures the observed change in the mass of the suspended sample as it is repelled or
attracted by the high magnetic field region between the poles. A positive change in mass
indicates that there is a net attraction to the field and this is observed in paramagnetism.
Paramagnetism arises due to presence of unpaired electrons within the material which spin
parallel to the induced magnetic field. Diamagnetism arises due to the presence of paired
electrons which spin in opposite directions to eachother thus no dipole moment is observed
and negative change or no change in mass is observed [5].

The last objective in this investigation is to perform a salt metathesis reaction to exchange

counterions in the transition metal complexes. The bonds between two chemical species are
exchanged and a product with similar bonding affiliations is obtained. This reaction will
proceed only if the resulting molecule is a more stable substance or natural molecule. In this

6
investigation anions such as halides will exchange with bulkier counter anions on the
transition metal complexes [6].

EXPERIMENTAL PROCEDURE

Experiment 1 Part A: Synthesis of Bis(2-pyridylmethyl)amine [BPMA]

Insufficient quantities of the starting reagents (aldehyde and amine) were provided and the
amounts/volumes had to be scaled down 10 times. It was then decided to make 3 three
different samples.
Three samples were prepared as follows:
Table 1: Quantities used to prepare the three samples
Reagent Sample
A B C
Methanol /mL 100 100 10
2-pyridylmethyl amine 0.97 0.97 0.97
/mL
2- 0.89 0.89 0.89
pyridinecarboxaldehyde /
mL

Methanol was not scaled down accordingly in sample A and B due to some confusion
regarding the volume on the graduated pipette. Sample B was allowed to stir for 1 hour on a
magnetic stirrer instead of the specified 12 hours. All the reagents in sample C were scaled
down by 10.

The reaction of all three sample mixtures was allowed to proceed for ~1 hour at room
temperature before 0.35 g of sodium borohydride was added to each and mixtures were
cooled down to 0°C in an ice bath. Sodium chloride was added to the ice bath to speed up the
cooling process and the mixtures reached 0°C within 5-10 minutes. The samples were then
left to mix on the magnetic stirrer and were sealed with parafilm while stirring took place.
Samples A and C were left to mix on magnetic stirrers from the Friday afternoon (~5pm)
until the following Tuesday (~10:30am) as it was infeasible to leave them mixing for exactly
12 hours. Sample B was allowed to stir for 1 hour on a magnetic stirrer.

7
A volume of 0.19 mL of the concentrated acid (32% HCl) was diluted with 20 mL of water to
form the 0.1 M HCl and 200 mL of this solution was then prepared by scaling up. This
solution was used to acidify the solutions to a pH of 4 which was verified using universal
litmus paper.

Table 2: Amount of HCl added to reach a pH of 4

Sample A Sample B Sample C

0.1 M HCl 70-80 mL 100 mL -

32% HCl - - 25 drops

pH Did not reached 4 Reached 4 Reached 4

The solvent was filtered off by suction for sample C and the resulting pale yellow residue was
collected. The residue was found to be very small in quantity and could not be weighed or
used efficiently for further extraction. The solvent for samples A and B was evaporated off
using the rotovap – No precipitate formation took place and these samples were discarded.
Based on the results we obtained, it was decided it would be best to start from scratch in
Week 2.

Repetition of Experiment 1 Part A: Synthesis of Bis(2-pyridylmethyl)amine

[BPMA]

WEEK 2 (07/09/2018)

 Two new samples were prepared following the procedure stated in the project brief
 Concentrated 32 % HCl was used instead of 0.1 M HCl to adjust the pH.

Sample 1

In an ice bath, a volume of 100 mL of methanol, 8.9 mL of 2-pyridinecarboxaldehyde and 9.7

mL of 2-pyridylmethylamine was measured out into a 250 mL conical flask. The mixture first

8
appeared to be orange-brown in color and turned lighter over time as the reaction proceeded
at room temperature for 1 hour. A mass of 3.506 g of fine granules of sodium borohydride
was added to the mixture slowly, in small increments, at room temperature. This lead to
bubbling in the reaction vessel as well as a temperature increase then decrease. The color of
solution turned to a much lighter orange.

The sample was then placed in an ice bath to cool to 0°C and NaCl was added to the ice to
increase the rate of cooling. Thereafter, the sample was covered with parafilm and left to mix
on a magnetic stirrer from the Friday afternoon (5:05pm) until the following Wednesday
(9:50am). The color of the solution changed to light yellow

After the sample was placed in an ice bath for several minutes, approximately 300 drops (~15
mL) of conc. 32% HCl was added to adjust the pH to 4 which was verified using universal
litmus paper. The mixture was placed back in the ice bath to cool for a further 10 minutes
before vacuum filtering off the solvent and collecting the off-white residue that resulted .This
was stored in a labelled glass vial for use in the next practical session. The filtrate was also
kept aside in the event of needing to recover more precipitate from the sample.

Sample 2

1) The same procedure carried out for sample 1 was done for sample 2. A mass of 3.514
g of sodium borohydride (fine granules for synthesis) was added to the mixture.

The sample was left to mix on a magnetic stirrer from the Friday afternoon (5:05pm) until the
following Wednesday (9:50am). Approximately 320 drops (~16 mL) of conc. 32% HCl to
adjust the pH to 4 and this was verified using universal litmus paper. The mixture was placed
back in the ice bath to cool for a further 10 minutes before vacuum filtering off the solvent
and collecting the off-white residue that resulted. This was stored in a labelled glass vial for
use in the next practical session. The filtrate was also kept aside in the event of needing to
recover more precipitate from the sample.

Continuation of Experiment 1 Part A:

Synthesis of Bis(2-pyridylmethyl)amine [BPMA]
WEEK 3 (14/09/2018)

9
Samples 1 and 2 from the previous week were extracted separately but at the same time.

A volume of 50 mL of water was added to the samples and this was transferred into a
separating funnel and 20 mL of dichloromethane (DCM) was then added. The upper aqueous
layers were collected and pH of each sample was adjusted to 10 by adding one medium-sized
spatula tip of solid sodium carbonate. This was verified using universal litmus paper.

For the second extraction the lower organic layers were collected and dried using magnesium
sulphate. Sample 1 required 4 spatula tips of magnesium sulphate whilst sample 2 required 2
spatula tips. The drying agent was then filtered off under gravity into pre-weighed round
bottom flasks.

The organic layers of samples 1 and 2 from the two extraction were kept in labelled beakers
and sealed with parafilm The solvent of the dried and filtered organic layer (from the second
extraction) of sample 2 was evaporated by rotary evaporation at 32°C. However, all the
solvent boiled off at ~29°C, and no brown oil (indicative of the BPMA precursor ligand) was
seen left behind. A few drops of DCM solvent was added to the flask and it was allow to
evaporate off at room temperature over the mid-semester break. (1 week)

Sample 1 was not placed in the rotavap it was sealed with parafilm and left to evaporate at
room temperature in the locker over the break (1 week)

A small volume from the aqueous layer of sample 2 (from the second extraction) was heated
on a hotplate. The sample was then cooled in an ice-bath. The filtrate of sample 2, which was
kept aside from the previous week, was cooled in an ice bath and re-acidified in order to
recover more precipitate, however no extraction was carried out on this resultant solid.

The filtrate of sample 1was re-acidified as well, however the pH was already at 4 and no
further precipitate had formed, therefore this was discarded.

Evaluation of Experiment 1 Part A:

Synthesis of Bis(2-pyridylmethyl)amine [BPMA]
WEEK 4 (26/09/2018)

10
The DCM solvent in the organic layers of sample 1 and 2 from the first extraction had
evaporated off at room temperature, leaving behind a hard yellow stain at the bottom of the
beakers The DCM added to sample 2 had evaporated off. Half the volume of the aqueous
layers (~25 mL) of both samples 1 and 2 (from the second extractions) were evaporated on a
hotplate. The white solids obtained were cooled in an ice-bath and kept in the beakers for
further investigation.

An IR analyses on the various intermediary samples prepared was conducted. The BPMA oil
synthesized from sample 2 and 2-pyridylmethylamine starting reagent were analyzed by
NMR.

IR instrument used: PerkinElmer Spectrum 100 FT-IR Spectrometer

NMR instrument used : 600 MHz, Ultra-shield NMR

From the IR and NMR analysis it was found that BPMA was synthesized however it was not
enough to proceed with the experimental procedure. Hence experiment 1 was repeated.

The starting reagent were scaled up by 2 for sample 3

Table 3: Preparation of sample 3

Volume of Methanol 200 mL

Volume of 2-pyridinecarboxaldehyde 17.8 mL

Volume of 2-pyridylmethylamine 19.4 mL

Mass of sodium borohydride 7.002 g

HCl = 32% concentrated acid was used

The following amendments were made to the procedure:

 Methanol was cooled to ~10°C.

 The aldehyde and amine were added slowly to the methanol in an ice bath on a
magnetic stirrer.

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  The solution was allowed to react for ~24 hours (without mixing) in the locker at
room temperature due to time constraints in the lab.

 A TLC analysis was carried before the addition of NaBH 4 using an ether: ethyl acetate
mobile phase (80:20) to verify whether the reaction went to completion.

 A small amount of the organic layer (top layer) was spotted onto a TLC plate
alongside the starting reagents (aldehyde and amine). The amine and aldehyde were
diluted with a small amount of the mobile phase.

 Sodium borohydride was then added to the flask in large increments whilst stirring
and keeping the solution in an ice bath (temperature remained at ~8°C). The mixture
was then left to mix in the ice bath on a magnetic stirrer for 3-4 hours and then at
room temperature for a further ~24 hours until the next practical session.

Continuation of Experiment 1 Part A:

Synthesis of Bis(2-pyridylmethyl)amine [BPMA]
WEEK 5 (28/09/2018)
Amount of HCl added to sample 3 = ~750 drops (~37.5 mL).

Two more TLC analyses was carried out before extraction

Re-precipitation:

IR analysis of filtrate was done to verify BPMA presence. The filtrate was then put into a
round bottom flask and evaporated at 55°C using the rotary evaporator.

Extraction 1:

Half of the solid sample was extracted first to prevent all the solids from being lost. The
resulting solid residue was dissolved in 50 mL of deionized water and the pH was adjusted to
10 using 60 drops of a saturated solution of sodium carbonate. The resulting solution was
then extracted with 20 mL of DCM and the lower organic layer was collected; dried with a
few spatula tips of magnesium sulphate and filtered under gravity into a pre-weighed round-
bottom flask.

12
The BPMA oil of sample 3 with the DCM solvent was left to evaporate off at room
temperature until the next practical session.

Continuation and Evaluation of Experiment 1 Part A:

Synthesis of Bis(2-pyridylmethyl)amine [BPMA]
WEEK 6 (03/10/2018)
The aqueous layers from sample 1 and sample 2 (second extractions) were left to evaporate
on a hotplate before extraction.

Extraction B:

The remaining batch of solid residue from sample 3 was extracted by dissolving the residue
in 50 mL of deionized water and the two extractions were carried out as mentioned
previously.

The aqueous layer was collected and 10 miniscule spatula tips of solid sodium carbonate was
added to adjust the pH to 10 and then it was extracted with 1 x 20 mL of DCM. The lower
organic layer was collected; dried with a few spatula tips of magnesium sulphate and filtered
under gravity into a round-bottom flask. The sample was put on the rotovap to evaporate off
the solvent and, as before, very little product was obtained (< 0.1 g).

Extraction C (of re-precipitated sample):

The following amendments were made to the procedure:

 Only one extraction was carried out

 The pH of the solution was adjusted to 10 first, before extraction with saturated
sodium carbonate solution.

13
  60 mL of DCM was used (3 × 20 mL) to extract.

 The organic layer was dried with MgSO4 and filtered under gravity. The solution was
evaporated using a rotary evaporator.

The BPMA oil synthesized from sample 3 Extraction A – which was left in the locker at
room temperature for the DCM to evaporate off in the previous session

Table 4: Mass of BPMA synthesized

Mass of empty round bottom flask before evaporation: 48.501 g

Mass of round bottom flask with product after evaporation: 48.673 g

Mass of BPMA oil synthesized from sample 3: 0.172 g

FTIR analysis:

The following samples were sent for IR analyses to compare the wavenumbers obtained to
that of pure BPMA.

 The white solid residue from the two aqueous layers of sample 1 and sample 2 which
evaporated on a hotplate at the start of the practical session. [Refer to Figures 9 and 8
in the Appendices for their respective IR spectra]
 The oily filtrate from sample 3 after re-precipitating and filtering. [Refer to Figure 7
in the Appendices for the IR spectrum of this sample]
 The BPMA oil synthesized from sample 3. [Refer to Figure 14 for the IR spectrum of
this sample]

Experiment 1 Part A: Sample 4

14
A new sample was prepared exactly as stated in the project brief. The solution was stirred for
16 hours. Conc. HCl (~300 drops) was added. Molecular sieves was added to remove any
water in the reaction mixture

DCM used in first extraction: 50 mL [2 x 20 mL + 1 x 10 mL]

Sodium carbonate added to aqueous layer: 5 miniscule spatula tips

DCM used in second extraction: 50 mL [1 x 20 mL + 1 x 30 mL]

The aqueous layer was extracted again with 40 mL of ethyl acetate to extract any product that
may have retained.

Rotary evaporator temperature: 55°C

An IR analysis was conducted on the sample obtained from this procedure. [Refer to Figure 6
in the Appendices for the IR spectrum of this sample ]

Continuation and Evaluation of Experiment 1 Part A:

Synthesis of Bis(2-pyridylmethyl)amine [BPMA]
WEEK 7 (05/10/2018)
FTIR analysis:

The BPMA oil obtained from the re-precipitate of sample 3 was sent for IR analysis to
validate the presence of BPMA. [Refer to Figure 7 in the Appendices for the IR spectrum of
this sample

Part B: Preparation of P-BPMA

Table 5: Quantities of reagents used to synthesize P-BPMA.

Mass of BPMA 0.172 g

Volume of acetonitrile 0.32 mL

Volume of triethylamine 0.12 mL

Volume of Allyl bromide 0.07 mL

15
The above three reagents had to be scaled down 47 times and were added to the round bottom
flask containing the BPMA oil

The resulting mixture was left to react in the locker for ~28 hours at room temperature. The
round bottom flask was scratched with a glass rod to induce crystal formation.

A volume of 0.32 mL of hexane and 0.32 mL of deionized water was added and this was
transferred into a separating funnel by means of a glass funnel with a fluted filter paper to get
rid of the triethylamine hydrogen bromide salts that appeared as white crystals in the desired
brown colored solution.

A further 15 mL of hexane and 15 mL of deionized water was added to the separating funnel
so that the layers could be easily distinguished.

The upper hexane layer was removed and put on the rotary evaporator at 40°C.

[Refer to Figure 5 for the IR spectrum of P-BPMA sample formed]

Melting point of iminium salt

Sample analyzed: Re-precipitate of sample 2

Range: 128-134°C

Experiment 2: Preparation of [Fe(P-BPMA)Cl3]

Mass of iminium salt used (instead of P-BPMA ligand): 0.200 g

Mass of iron (III) chloride hexahydrate: 0.244 g

The procedure was carried out as stated in the project brief.

16
RESULTS

Table 6: Quantities used for starting reagents

Quantities 2-Pyridinecarboxaldehyde 2-pyridylmethyl amine
Volume / mL 8.90 9.70
Density / g. mL-1 1.13 1.05
Molar mass / g.mol-1 107 108
Moles 0.0936 0.0941

C6H5NO + C6H8N2 → (C6H7N)2NH

Calculation using 2-Pyridinecarboxaldehyde
m
p=
v
m=pxv
= 1.13 g mL-1 x 8.90 mLa
= 10.02 g
m
n=
MM

17
 10.02 g
=
107.08 g /mol
= 0.0936
Same calculation was done for 2-pyridylmethyl amine
Since there is stoichiometric ratio is 1:1 it can be concluded that 2-Pyridinecarboxaldehyde is
the limiting reagent.
Table 7: Mass of BPMA synthesize from sample 1
Mass of empty round bottom flask before evaporation /g 64.259 g
Mass of round bottom flask with product after evaporation/ g 64.264 g
Mass of BPMA oil 0.005 g

Table 8: Mass of BPMA synthesized from sample 2

Mass of empty round bottom flask before evaporation /g 49.907
Mass of round bottom flask with product after evaporation / g 49.987
Mass of BPMA oil /g 0.08

Therefore bis (2-pryridyl methyl) amine: moles = 0.0936 moles

Molecular weight = 201,12 gmol-
∴ Theoretical yield of BPMA: mass = n x MM = ( 0,0936 mol) × (201,12 g/mol)
Theoretical Mass (BPMA) = 18.82 g
Actual mass (BPMA) = 0.005 g
% yield based of BPMA based on attempt 1:

% yield= ( theoretical mass )

actual mass
× 100

¿(
18.82 g )
0,005 g
×100

¿ 0,0266 %
Same calculation was done for sample 2 and the % yield was found
to be 4.25%

Key:
A- aldehyde K- amine P- product

18
Figure 2: TLC plate analysis showing reaction completion
Table 9: Part B Preparation of BPMA from Extraction 1 of sample 3.

Mass of empty round bottom flask before evaporation: 48.501 g

Mass of round bottom flask with product after evaporation: 48.673 g

Mass of BPMA oil synthesized from sample 3: 0.172 g

Table 10: Calculation of the yield P-BPMA ligand from extraction.

Quantities BPMA 3-bromopropene
Mass / g 0.172 0.098
Molar mass / g.mol-1 201.12 120.99
Moles 8.552×10-4 moles 8.1 x 10 -4 moles
Density/ g cm-3 1.107 1.40

0.172 g
n(BPMA) =
201.12 g /mol
= 8.552×10-4 moles
(C6 H7N)2NH + C3H5Br → (C6H7N)2N(C3H5) + HBr
Since the stoichiometric ratio is 1:1
Therefore BPMA is a limitting reagent and moles of P-BPMA = 8.552×10-4 moles
The theoritical mass = n × Mm
= 8.552 ×10-4 moles × 374.63 g.mol-1
= 0.320 g

actual mass
Percentage yeild P-BPMA = ×100
theoritical mass

19
 0.048
= x 100
0.320
= 15 %

Figure 3: NMR spectra for BPMA

107.7
105

2177.03 892.15
100 1971.03 1224.96 849.70
1297.33

95 1120.30
2849.40 1754.47 1094.60
1149.72 506.01
90
1049.06

85 996.16
2917.12 1668.52 402.94
3308.38
80 1362.94 627.58

75
3014.44
%T 3066.34
70
1474.34

65 1591.86

60
1570.01
1433.92
55

753.82
50

45
BPMA OIL 2
39.5
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1

Figure 4 : IR spectrum for BPMA

20
 107.8

105
2182.72 1726.82 460.81
3398.80 1977.30 1219.39
100 1642.02 841.20
878.39
3066.43 893.54
95 1089.09 564.37
3008.87 1297.17
518.72
1249.06 1047.17 615.20
90
1147.19
1119.76
2922.95
85 2849.22 1362.78 403.67

2818.38 1569.56
80 994.45 920.86
1472.76
%T
982.91
75
1588.89

70 1432.20

65

60
757.09

55

48.8
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1

Figure 5: IR spectrum for P-BPMA

DISCUSSION
The aim of this investigation was to synthesize the tridentate nitrogen donor ligand, propene
bis-(2-pyridylmethyl) amine (P-BPMA), to complex it with first row transition metals and to
determine the stability of these complexes. To perform a salt metathesis reaction to exchange
couterions on these complexes and to determine whether these complexes are paramagnetic.
Lastly to characterize the ligand (P-BPMA) and its transition metal complexes using H 1-
NMR, Infrared Spectroscopy and X-Ray crystallography.

After many unsuccessful attempts at synthesizing the P-BPMA ligand the investigation was
unable to proceed past experiment 1. Many modifications were done to the original
experimental procedure in attempts to increase the yield of BPMA and P-BPMA and some of
the key modifications include: In week one sample C was mixed for 1 hour instead of the
originally stated 12 hours and this was done to determine the effect of time on precipitate
formation but this could not be deduced fully, since the concentration of acid used to acidify
those samples did not yield positive results. The quantities of the starting reagents were
scaled down by a factor of 10 and scaled up by a factor of 2 but none of these adjustments
showed to have any effect on the yield of BPMA.

21
From the TLC plate in figure 2 it is evident that the reaction between the aldehyde and amine
does go to completion and this dismissed any assumption that the reaction may not be going
to completion. This is indicated by the absence of the amine on the product spot meaning that
all of it was used up during the reaction and it is thus the limiting reagent.

Since Schiff base reactions are reversible and are driven to completion by the removal of the
by product which is water, molecular sieve was added to absorb the water as the reaction
proceeded. Yet again no significant difference was observed in the product yield which
indicted that water is not the cause of the poor product yield.

Figure 3 represents an NMR spectrum for BPMA. The Hydrogens found in the BPMA
structure do not experience the same magnetic field due to local current generated by
electrons and thus they will produce different signals on the NMR spectrum. The peak at
1.5316 ppm represents a methyl group bonded to an aromatic ring. The peak at 3.7328 ppm
represents a proton attached to a nitrogen atom and thus the signal in slightly downfield due
to the deshielding observed from the N atom. The three peaks observed from 6 – 7 ppm
represent protons attached to an aromatic ring. Different peaks are observed as the protons
are not chemically equivalent. The peak at 8.312 ppm represents a proton on an aromatic ring
but it appears more downfield compared to the other protons as it is deshielded by the
nitrogen group of the aromatic ring

Figure 4 represents the IR spectrum for BPMA. The peak at 753.82 cm -1 represents the N-H
bending bond in an aliphatic secondary amine. The peak at 1049.01 cm -1 represents the C-N
bond in an aliphatic secondary amine. The peak at 1297.33 cm -1 represents the C-N stretch in
an aromatic ring and from this it is understood that an aromatic amine is present. The peak at
1591.86 cm-1 represents a C=C double bond in an aromatic ring. The peak at 3308.38 cm -1 is
very broad, this may be due to impurities present. It represents the N-H stretch in a secondary
amine. These peaks correspond to the characteristic peaks found in BPMA obtained from
literature. These include 3312, 3062, 3010, 2917, 2831, 1592, 1570, 1474, 1434 and 759 cm -1
[]

The IR spectra shown in figure 5 is for the P-BPMA ligand. The peak at 757.09 cm -1
represents the N-H bending bond in the aliphatic secondary amine. The peak at 1047.17 cm -1
represents the C-N bond in an aliphatic secondary amine and thus the presence of an aliphatic
secondary amine is confirmed. The peak at 1249.06 cm -1 represents the C-N bond in an
aromatic ring and from this it is understood that there is an aromatic amine present. Lastly the

22
peak at 1642.82 cm -1 represents the C=C double bond in propene as it is in the alkene region
of the IR spectrum. All of these individual groups obtained from the spectra are present in P-
BPMA however a major peak around 3300 cm-1 is missing which represent an N-H stretch in
a secondary amine. Some additional unidentified peaks which are not present in the P-BPMA
IR spectrum are present and indicate the presence of impurities.

The synthesis of an iron complex with the iminium salt instead of the P-BPMA ligand was
attempted. The salt did not dissolve well in ethanol despite attempts to heat and dissolve the
mixture. The color of the solution turned yellow from cloudy upon addition of the iron (III)
chloride hexahydrate and no yellow precipitate formed. Throughout the attempts made to
synthesize P-BPMA the most difficult step was converting the iminium salt back to BPMA
by the addition of sodium carbonate. This may be a result of the high stability of the iminium
salt and thus an alternative method could have been employed to isolate the BPMA.
Alternative methods which may have been used to synthesize P-BPMA include column
chromatography as a purification method to directly obtain the precursor and the reflux
method but these were not further investigated in our project.

The only variable that was kept constant throughout the synthesis of the P-BPMA ligand was
pH. During the synthesis of P-BPMA there are ionic intermediates which are formed and the
changes in charges with pH affect the activity and structural stability of these compounds.
Thus pH is an important factor that needs to be monitored and this may have not been
accurately determined by the use of litmus paper. Thus if this procedure is done in future it is
recommended that the pH be monitored with a more accurate device such as a pH meter.
Another factor that may have affected the P-BPMA yield was time as it was infeasible to
keep the reaction mixture stirred for exactly 24 hours and the stirring time was often
exceeded greatly which may have affected the formation of crystals.

CONCLUSION

The transition metal complexes were not synthesized due to insufficient quantities of P-
BPMA obtained thus the objectives of this investigations were not achieved. The pH of the
reaction mixtures were not accurately monitored using universal litmus paper and thus a pH
meter should be employed to increase accuracy. The time frames stated in the experimental
procedure was not properly adhered to which may have affected the formation of P-BPMA

23
ligand. Alternative methods that may be employed in future include column chromatography
and the reflux method.

REFERENCES

1. G.A. Lawrance, 2013, Introduction to Coordination Chemistry, pp 22

2. Roland G. Kallen, 1971, Mechanism of reactions involving Schiff base intermediates.
Thiazolidine formation from L-cysteine and formaldehyde, Journal of American
Chemical Society, pp 6236–6248
3. Bussey, K.A., Cavalier, A.R., Connell, J.R., Mraz, M.E., Holderread, A.S., 2015.
Synthesis and Characterization of Copper Complexes with a Tridentate Nitrogen-
Donor Ligand: An Integrated Research Experiment for Undergraduate Students.
Journal of Chemical Education. B-CD. Nicholls, Complexes of the First -Row
Transition Elements, pp. 100 – 111.
4. Carvalho N.M.F., Horn Jr. A., Bortoluzzi A.J., Drago V., Antunes O.A.C., 2006.
Synthesis and characterization of three mononuclear Fe(III) complexes containing
bipodal and tripodal ligands: X-ray molecular structure of the dichloro[N-
propanamide-N,N-bis-(2-pyridylmethyl)amine]iron(III) perchlorate. Inorganica
Chimica Acta 359, pp 90–98.
5. Soobramoney L, Bala M.D, Friedrich H. B, 2014, Coordination chemistry of Co
complexes containing tridentate SNS ligands and their applications as catalysts for the
oxidation of n-octane. Dalton Trans, pp. 15972
6. D.J. Liston, Y.Ja Lee, W. R Scheidt ,1989, Observations on silver salt metathesis
reactions with very weakly coordinating anions, Journal of American Chemical
Society, pp 6643–6648

24
 1216.47

APPENDIX
2168.59 1366.43
2007.62

1738.11

2918.08

2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1

25
Figure 6: IR spectrum of the BPMA oil synthesized from sample 4

26
Figure 7: IR spectrum of the oily filtrate from sample 3 after re-precipitating and filtering

27
 114.9
114
2898.54
112 2532.55
1400.10
110 2161.24
2034.51
108
106
104 1638.53
102
100
%T 98
3393.51
96
94
92
90
88
86
84
82.5
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000
cm-1

Figure 8: IR spectrum of the white solid residue from the aqueous layer of sample 2

28
 113.8
112
2541.88
110 1402.63

108 2033.38
2161.86
106
104
102
100
1638.93
98
96
%T 94
92
90
88 3405.68
86
84
82
80
78

75.4
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800
cm-1

Figure 9: IR spectrum of white solid residue from the aqueous layer of sample 1

29
Figure 10: NMR spectrum for BPMA

Figure 11: NMR spectrum for BPMA

30
 107.6
105
2177.99 1225.85 678.17
100 1979.29
858.85
95 1300.78
2833.68 1650.83
90 1362.28

1150.21
85 996.51
2927.22
80 3292.09
1120.99 1049.40
75
1093.68 627.28
%T
70
3067.09
65 1592.36
3011.04

60
1434.54

Figure 12: IR spectrum for BPMA in extract 1 sample 2

55 1570.26
755.92
1474.70
50

45
DCM extr. 1 (BPMA) sample 2
39.3
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
cm-1

31
 107.7
107
106
105 2577.44 1571.78
104
2176.37
103
102
1594.61
101 2029.68
1152.10
100
99
%T
98 3384.85 1051.30

97
96
95
94
93 998.27
1477.00
92
1437.11

Figure 13: IR spectrum for BPMA powder residue in sample 2

91 BPMA powder residue sample 2
90.0
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000
cm-1

32
 102.6
100
2167.26

95
1309.73
1366.28 1153.03 1052.32
1003.77
90
1093.00

85 1478.15
1639.56
1572.18
%T 80
1437.14
75
628.95
1595.89

Figure 14: IR spectrum for BPMA in sample 3

70 761.04

65
3289.16

60 bpma sample 3 - 2g
58.0
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 60
cm-1

33
 100.3

95 2386.84 1979.71
2162.51 1225.46

90 1298.59
1094.48
1361.66 1124.37
3304.95
85
3050.55 1048.15
3009.37 1148.92
80 2918.03 994.75
2830.97
75

%T 70

65 1473.69

60 1569.75
1590.78

55
1433.28
50

45 SAMPLE-3-BPMA ORG LAYER

42.9
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000
cm-1

Figure 15: IR spectrum for BPMA in the organic layer in sample 3

34