Inorganic-Chemical Practical Course
Spring Semester 2014
tris(ethylenediamine)cobalt(III) chloride
([Co(en)3]Cl3)
H2
H2
N H2 N
N
Cl3
Co
N N
H2 H2
N
H2
and
[Co(dinosar)]Br3
NO2
HN
NH
HN
Br 3
Co
HN
NH
NH
NO2
27/05/2014
Patrick Zwick
B2
Patrick Zwick
Exp 5
1 Aim of the experiment
The aim of the experiment was the synthesis of tris(ethylenediamine)cobalt(III) chloride
([Co(en)3]Cl3)
as
well
as
the
synthesis
of
1,8-dinitro-3,6,10,13,16-
hexaazabicyclo[6,6,6]eicosane cobalt(III) bromide ([Co(dinosar)]Br3). The cryptand ligand
dinosar was built around the metal centre of tris(ethylenediamine)cobalt(III) using template
methodology. The product [Co(en)3]Cl3 was analysed by 1H-NMR spectroscopy in two
different solvents (D2O and DMSO-d6). The product [Co(dinosar)]Br3 was analysed by 1HNMR spectroscopy in comparison with the spectra given by the instruction[2].
2 Introduction
The synthesized products are Co(III) complexes. Cobalt(III) complexes favour a d 6 low spin
octahedral configuration and are kinetically inert. This means that the ligands are not labile
and therefore it is common to prepare the analogue Co(II) species first and convert it into the
Co(III) complex by oxidation afterwards[4]. This was done for the first part of the experiment
were first [Co(en)3]2+ was synthesized and was secondly oxidised to [Co(en)3]Cl3 by H2O2.
The three bidentate ethylenediamine ligands form three 5 membered chelate rings in the metal
complex which leads to greater stability. The tris(ethylenediamine)cobalt(III) chloride
complex has (as all octahedral metal complexes with three bidentate ligands) two enantiomers
(Δ 'right-handed' and Λ 'left-handed'). This enantiomers can racemate if a rearrangement over
a trigonal bipyramidal- or a square-based pyramidal intermediate takes place while one of the
bidentate ligands donor atoms is uncoordinated (cf. Fig. 1)[5].
The dinosar ligand that is produced in a
M
template synthesis in the second part of the
trigonal bipyramidal
experiment is a cryptant ligand[2]. It also
forms
three
5-membered
rings
M
in
[Co(dinosar)]Br3. The stability of this
M
left-handed
right-handed
complex is even greater than the stability
M
of [Co(en3)][Cl]3 since all donor atoms sit
in one molecule. This cage-like cryptand
square-based pyramidal
Fig. 1: Enantiomers and possibility of
ligands like dinosar can be used to formrearrangement in an octahedral metal complex
complexes with unstable metal centres[6].
with three bidentate ligands
2
Patrick Zwick
Exp 5
3 Experimental part
3.1 Synthesis of tris(ethylenediamine)cobalt(III) chloride
CoCl2*6H2 O
H2O2
H2 N
NH2
HCl
EtOH, H2O, 0 °C, 1h
H2
H2
N H2 N
N
Cl3
Co
N N
H2 H2
N
H2
CoCl2·6H2O
C2H8N2
HCl
[Co(en)3]Cl3
1
2
3
4
6.00 g
4.51 mL
4.25 mL, 6M
2.09 g
25.0 mmol
67.5 mmol
25.5 mmol
7.61 mmol
1.0 eq.
2.7 eq.
1.0 eq.
30,44%
CoCl2·6H2O (1, 6.00 g, 25.0 mmol, 1.0 eq.) was dissolved in H2O (17.5 mL).
Ethylenediamine (2, 4.51 mL, 67.5 mmol, 2.7 eq.) and aqueous HCl (3, 6M, 4.35 mL, 25.5
mmol, 1.0 eq.) were added to H2O (12.5 mL) and cooled on ice. The aqueous CoCl2 solution
was added to the diethylenamin solution and H2O2 (5 mL, 30%) was added to this mixture
while it was constantly stirred. The mixture was placed on a heat plate and boiled gently until
there was only 30 mL left. Concentrated HCl (30 mL) and ethanol (60 mL) were added to the
mixture. The mixture was allowed to cool down to RT over 30 min. After the mixture was
cooled on ice, the precipitate was collected by filtration. The solid was washed with ethanol (2
x 10 mL) and diethyl ether (2 x 10 mL). The solid was air dried to obtain the product (4, 2.09
g, 7.61 mmol, 30%, Lit[3]: 65 %) as yellow crystals.
H-NMR (250 MHz, 298 K, DMSO-d6, δ/ppm): 5.90 – 5.59 (m, 6 H, 2), 5.48 – 5.17 (m, 6 H,
1
2), 2.82 – 2.55 (m, 6 H, 1), 2.54 – 2.44 (m, 6 H, 1).
1
H-NMR (250 MHz, 298 K, D2O, δ/ppm): 5.20 – 4.96 (m, 6 H, 2), 4.88 – 4.61 (m, 6 H, 2),
3.00 – 2.64 (m, 12 H, 1).
1a 1b
H2
2a H H
H N H2 N
N
H
2b
Co
Cl3
N N
N
H2 H2 H2
3
Patrick Zwick
Exp 5
3.2 Synthesis of [Co(dinosar)]Br3
NO2
H2
H2
N H2 N
N
Co
HN
1) H 2O, 40 °C, 1.5h
O
Cl3
CH 3NO2
Na 2CO3 *10H 2 O
H
N N
N
H 2 H 2 H2
HN
NH
Br 3
Co
H 2) Acetic acid, HBr
HN
NH
NH
NO2
[Co(en)3]Cl3
Na2CO3·10H2O
CH3NO2
CH2O
[Co(dinosar)]Br3
5
6
7
8
9
1.81 g
4.05 g
5 mL
40 mL, 37 %
0.56 g
5.22 mmol
14.2 mmol
92.3 mmol
537 mmol
1.10 mmol
1.0 eq.
2.7 eq.
18 eq.
103 eq.
21,07%
[Co(en)3]Cl3 (5, 1.81 g, 5.22 mmol, 1.0 eq.) and Na2CO3·10H2O (6, 4.05 g, 14.2 mmol, 2.7
eq.) were dissolved in water (90 mL). Acetonitrile (7, 5 mL, 92.3 mmol, 18 eq.) and
formaldehyde (8, 47 %, 40 mL, 537 mmol, 103 eq.) were added and the mixture was briefly
stirred. The mixture was heated to 40 °C for 1.5 h without stirring. The solution was stirred
with a glass rod to induce crystalisation. The solution was cooled on ice and the precipitate
was collected by filtration. The solid was dissolved with hot acetic acid (1M, 30 mL) and
concentrated HBr (15 mL) was added immediately to the yellow solution. The solution was
allowed to cool down to RT. The precipitate was collected by filtration, washed with MeOH /
H2O (1:1, 1 x 15 mL), MeOH (1 x 15 mL), diethyl ether (1 x 15 mL) and was air dried to
obtain the product (9, 0.56 g, 1.10 mmol, 21 %, Lit:[1]: 55 % ) as orange solid.
H-NMR (250 MHz, 298 K, D2O, δ/ppm): 3.88 (dd, 2JHH = 13.7, 1.7 Hz 6 H, 1), 3.57 (dd,
1
2
JBH = 11.7, 9.1 Hz, 6 H, 2), 3.36 (dd, 2JHH = 13.9, 2.0 Hz, 6 H, 1), 2.94 (dd, 2JBH = 11.7,
9.2 Hz, 6 H, 2).
1b
1a NO2
H
H
2a
H HN
NH
HN
H
2b
Co
HN
NH
Br3
NH
NO2
4
Patrick Zwick
Exp 5
4 Discussion
A
CoCl2*6H2 O
H2O2
H2 N
1
NH2
HCl
2
EtOH, H2O, 0 °C, 1h
3
H2
H2
N H2 N
N
Cl3
Co
N N
H2 H2
N
H2
4
NO2
H2
H2
N H2 N
N
B
Co
HN
O
Cl3
Na2CO3 *10H2 O
CH3NO2
6
7
N N
N
H2 H2 H2
5
1) H2O, 40 °C, 1.5h
8
NH
Br 3
Co
H 2) Acetic acid, HBr
H
HN
HN
NH
NH
NO2
9
The synthesis (A) of tris(ethylenediamine)cobalt(III) chloride (4) was done as described in the
reference[3]. Three ethylenediamine ligands were coordinated to a cobalt atom to form
[Co(en)3]Cl2 which was then oxidised by H2O2 to form the product [Co(en)3]Cl3 (4). For the
interpretation of the 1H-NMR spectra the protons had to be separated in two groups:
homotope and diastereotope. It was shown that the protons bonded to the nitrogen atoms (1)
and the protons bonded to cabon atoms (2) are diastereotope. So all protons are diastereotope.
This comes by the chirality since the ethylendiamine ligands can coordinate to the metal
centre forming Δ or Λ isomers. The DMSO-d6 spectrum shows four multiplets with integrals
of each 6 protons due to the diastereotope protons. The D2O shows only three multiplets
because the signals of 1a and 1b comes out as one signal with an integral of 12 protons. The
integrals of the reference peak overlapped signals could be worked out by a comparison of the
two spectra which actually was the reason for measuring the product in two solvents. The
multiplets at 2.82 – 2.55 ppm and 2.54 – 2.44 ppm in The DMSO-d6 spectrum respectively
3.00 – 2.64 ppm in the D2O spectrum belongs to the diastereotope protons bonded to the
nitrogen atoms (1a + 1b). The other two multiplets belong to the diastereotope protons (2a +
2b). The signals could not been differentiated to the protons (2a) and (2b) respectively (1a)
and (1b) because there is to less information with only these 1H-NMR spectra. The non
binomial triplet at 7.23 ppm belongs to some free protonated ethylenediamines which are not
coordinated to the metal.
The synthesis (B) of [Co(dinosar)]Br3 (9) also went well. This experimental part (B) was done
as described in the reference[1]. For the interpreatation of the 1H-NMR spectrum, the protons
5
Patrick Zwick
Exp 5
had to be separated in diastereotope an homotope again. It was shown that all protons bonded
to a carbon atom (1a, 1b, 2a, 2b) are diastereotope and the protons bonded to a nitrogen atom
do not even give a signal since they are exchanged by deuterium quickly. The 1H-NMR
spectrum shows four doublets of doublets. The literature[1,2] showed that the peak at -11 ppm
belongs to the former carbon atoms of ethylenedyamine and the peak at -15 ppm belongs to
the bridging carbon atoms. The peak at 22 ppm in the HMQC spectrum belongs to the carbon
carrying the nitro groups since it does not show any proton correlation. The proton signals at
3.88 ppm and 3.36 ppm (1a and 1b) correlate with the carbon signal at -11 ppm in the HMQC
spectrum. This correlation shows that this protons sit at the bridging carbon atoms. The proton
signals at 3.57 ppm and 2.94 ppm (2a and 2b) correlate with the carbon peak at -15 ppm in the
HMQC spectrum. Therefore this protons sit at the former carbon atoms of ethylendiamine.
The COSY spectrum shows that the proton signals at 3.88 ppm and 3.36 ppm (1a and 1b) are
correlating and that the proton signals at 3.57 ppm and 2.94 ppm (2a and 2b) are correlating.
This information shows that the diastereotope protons that sit on the same carbon atom are
coupling to each other. The measured coupling constants confirm that theory since the
coupling constants of the signals at 3.88 ppm and 3.36 ppm (1a and 1b) are the same and the
coupling constants of the signals at 3.57 ppm and 2.94 ppm (2a and 2b) are the same, too. The
signals of the diastereotope protons (1a, 1b and 2a, 2b) could not be differentiated with this
spectrum.
5 Conclusion
The aim of the experiment was reached. The synthesis of tris(ethylendiamine)cobalt(III)
chloride and the conversion of the ligand to dinosar to build the final product [Co(dinosar)]Br3
went well. The purity of the products were proved by 1H-NMR spectroscopy and the data was
discussed. All questions were answered and attached.
6 References
[1]
Harrowfield et al., J. Chem. Educ., 1985, 62, 804.
[2]
C. E. Housecroft, Task Sheet Experiment 5, 2014, 2 – 3.
[3]
Krause et al., J. Chem. Educ., 1976, 53, 667.
[4]
C. E. Housecroft, A. G. Sharpe, Inorganic Chemistry, Pearson, Harlow, 2012, 744 –
756.
6
Patrick Zwick
Exp 5
[5]
C. E. Housecroft, A. G. Sharpe, Inorganic Chemistry, Pearson, Harlow, 2012, 991
[6]
Geue et al., J. Am. Chem. Soc., 1984, 106, 5478.
7 Answers to the questions
7.1 The reaction to make [Co(dinosar)]3+ is an example of a template synhtesis. Explain
what this means.
When the reactants are hold together in a template, so that a combination of them is allowed
without many side reactions, it is called a template synthesis. In the specific case of this
synthesis it was the NH2 groups of ethylenediamine that are coordinated by the cobalt centre
close to each other in the tris(ethylenediamnie)cobalt(III) chloride template that react with
nitromethane and formaldehyde to give the dinosar ligand in the final product.
7.2 Explain why the stability of the following complexes decrease in the order:
[Co(dinosar)]3+ > [Co(en)3]3+ > [Co(NH3)6]3+
The dinosar and the ethylenediamine ligands form chelating rings in the metal complex.
Therefore this complexes are more stable than the ammonio complex since this ligand does
not chelate at all. The complex with the dinosar ligand is more stable than the
tris(ethylendiamine)cobalt complex because all six coordinated groups sit in the same
molecule instead of three molecules as in [Co(en)3]3+. The dinosar ligand is quite inflexible
and therefore more immutable in contrast to ethylenediamine. This effect also decreases from
[Co(en)3]3+ to [Co(NH3)]3+. This is an entropie effect since e.g. six molecules get free but only
three molecules get bonded to the complex in the ligand exchange from [Co(NH 3)]3+ to
[Co(en)3]3+.
7.3 What types of isomers could the following compounds show? Not all complexes
possess isomers. Draw the structures of all isomers and give names that tell the isomers
apart (e.g. cis and trans).
- octahedral [Rh(ox)3]3-
- square planar [PtBr2(NMe3)2]
- octahedral [TiCl3(THF)3]
- octahedral [Ir(acac)3]
- square planar [Rh(CO)(PPh3)2Cl]
- octahedral [Ru(bpy)3]2+
- octahedral [Ru(phen)2Cl2]
- tetrahedral [CoCl2Br2]27
Patrick Zwick
Exp 5
O
O
O
O
O
O
O
O
O
O
O
O
O
Rh
3
O
3
Rh
O
O
O
O
O
O
O
Br
O
Br
O
O
Δ
Λ
O
Cl
Cl
Ti
Ti
O
O
Me3 N
NMe3
Br
Cl
O
Cl
O
Pt
Br
NMe3
trans
O
O
Ir
O
O
NMe3
cis
O
Cl
Pt
O
O
O
O
O
Ir
O
O
O
Cl
fac
mer
Δ
Λ
2
2
N
N
N
N
N
N
N
N
OC
Cl
Rh
Ph3P
OC
PPh3
Ph3 P
cis
N
Ru
N
PPh 3
Δ
N
N
Cl
Cl
Cl
Ru
Λ
N
N
N
N
N
N
Ru
Cl
cis + Δ
N
cis + Λ
2
Cl
Cl
Co
Cl
trans
N
N
N
Cl
trans
N
Cl
Rh
N
Ru
Ru
Br
Br
no isomers
8. Spectra
The experimental spectra are attached to this protocol as followed:
8.1 250 MHz 1H-NMR spectrum of [Co(en)3]Cl3 in DMSO-d6 (p. 9).
8.2 250 MHz 1H-NMR spectrum of [Co(en)3]Cl3 in D2O (p. 10).
8.3 250 MHz 1H-NMR spectrum of [Co(dinosar)]Br3 in D2O (p. 11).
8
5500
5.32
5.74
6000
2.82
2.69
2.54
2.50
2.44
5.90
5.74
5.59
5.48
5.32
5.17
ac_praktI_.2900.1.fid
PZ Exp5 [Co(en)2][(Cl)]3 in dmso-d6
400
5000
5.4
6.00
5.6
5.5
f1 (ppm)
5.3
200
4500
100
4000
0
3500
5.2
2.50
5.7
2.54
5.8
2.69
5.9
6.00
300
3000
1000
2500
800
2000
600
400
1500
200
2.75
2.70
16.13
2.80
1000
0
2.65 2.60
f1 (ppm)
2.55
2.50
500
2.45
11.5 11.0 10.5 10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
16.13
6.00
6.00
0
5.5 5.0
f1 (ppm)
4.5
4.0
3.5
3.0
2.5
-500
2.0
1.5
1.0
0.5
0.0
-0.5
2.64
3.00
5.20
5.08
4.96
4.88
4.61
3000
2800
4.61
4.88
4.96
5.08
5.20
ac_praktI_.2892.1.fid
300
2600
2400
200
2200
100
4.9 4.8
f1 (ppm)
4.7
1800
4.6
2.64
5.0
15.22
5.1
0
3.00
5.2
6.00
2000
1600
400
1400
300
1200
200
1000
100
800
12.02
0
600
3.00 2.95 2.90 2.85 2.80 2.75 2.70 2.65
f1 (ppm)
400
200
11.5 11.0 10.5 10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5 5.0
f1 (ppm)
-200
12.02
15.22
6.00
0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
2.99
2.95
2.92
2.88
3.39
3.38
3.34
3.33
3.63
3.59
3.56
3.52
3.92
3.92
3.87
3.86
3.92
3.92
3.87
3.86
3.63
3.59
3.56
3.52
3.39
3.38
3.34
3.33
2.99
2.95
2.92
2.88
ac_praktI_.2916.1.fid
PZ exp5 [Co(dinosar)][Br]3 in D2O
1H NMR (250 MHz, Deuterium Oxide) δ 3.88 (dd, J = 13.7, 1.7 Hz, 7H), 3.57 (dd, J = 11.7, 9.1 Hz,
6H), 3.36 (dd, J = 13.9, 2.0 Hz, 6H), 2.94 (dd, J = 11.7, 9.2 Hz, 6H).
3600
3400
3200
1400
3000
1200
2800
2600
1000
2400
800
2200
600
2000
B (dd)
3.57
A (dd)
3.88
400
1800
D (dd)
2.94
1600
C (dd)
3.36
200
1400
1200
3.9
3.8
3.7
3.6
3.5
1000
6.00
6.03
6.01
6.00
0
3.4 3.3
f1 (ppm)
3.2
3.1
3.0
800
2.9
600
400
12.0 11.5 11.0 10.5 10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5 5.0
f1 (ppm)
4.5
4.0
3.5
0
6.00 6.00
6.00 6.99
6.01 5.83
6.03 6.41
200
3.0
-200
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0