Convenient synthesis of new water-soluble monosubstituted functional ferrocene derivatives

Article abstract of DOI:10.1016/j.inoche.2005.05.025

Two new water-soluble monosubstituted functional ferrocene derivatives, p-ferrocenyl benzene sulfonic acid (BSAFc) and 4-ferrocenyl-1,1′- azobenzene-3,4′-disulfonic acid (AYFc), bearing sulfonic groups and/or azo structure have been successfully synthesiz

Full text of DOI:10.1016/j.inoche.2005.05.025

Inorganic Chemistry Communications 8 (2005) 853–857
www.elsevier.com/locate/inoche
Convenient synthesis of new water-soluble
monosubstituted functional ferrocene derivatives
*
Hongyan Yang, Xing Chen, Wei Jiang, Yun Lu
Department of Polymer Science and Engineering, State Key Laboratory of Coordination Chemistry,
College of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
Received 20 April 2005; accepted 26 May 2005
Abstract
Two new water-soluble monosubstituted functional ferrocene derivatives, p-ferrocenyl benzene sulfonic acid (BSAFc) and 4-ferr-
ocenyl-1,10-azobenzene-3,40-disulfonic acid (AYFc), bearing sulfonic groups and/or azo structure have been successfully synthesized
in aqueous media according to the self-designed synthetic route. The preparation process is quite simple and convenient. 1H NMR,
FT-IR and element analysis data demonstrated the structures of the target products. UV–Vis spectra and cyclic voltammetry (CV)
measurements explained the electrophilic group that linked to BSAFc and AYFc was an influence on the orbital energy level of
ferrocene. The CVs in different concentration and type of anion existing in the solution demonstrated that the electrochemical activ-
ities of BSAFc and AYFc firmly rely on the anion.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Ferrocene derivatives; Azo structure; Sulfonic group; Electron-transfer ability
Ferrocene derivatives have long been the focus of re-
search due to their redox center, the p-conjugated sys-
tem and the resulting exclusive electron-transfer
ability. There is considerable interest in the synthesis
of new polymers via introducing functional ferrocene
derivative structure because of their potential applica-
tions in optical, electronic and magnetic materials [1].
However, the reports relating to conductive polymers
with ferrocene moiety are scarce.
As far as know, most of the known ferrocenyl com-
pounds are only soluble in hydrophobic media that
limited their application in aqueous systems [2,3]. Knox
et al. [4] had reported the preparation of water-soluble
Ferrocenyl sulfonic acid (SAFc) by sulphonation of
ferrocene at the presence of reagent of chlorosulphonic
acid in acetic anhydride. The synthetic method was
complex and not environment friendly. In this paper,
we designed and synthesized two new water-soluble fer-
rocene derivatives with sulfonic groups and/or azo
structure, which possess the excellent solubility in water
and could be worked into conductive polymer as a
dopant. These compounds were characterized by 1H
NMR, FT-IR, UV–Vis spectrum, elemental analyses,
atomic absorption spectrum, cyclic voltammetry and
melting point measurement. 1H NMR was recorded
on a Bruker DPX 300 instrument operating at a proton
frequency of 300 MHz; elemental analyses were per-
formed on a Heraeus CHN–O–Rapid instrument;
atomic absorption spectra were obtained on a Hitachi
180-80 instrument; UV–Vis spectra were carried
out on UV-3100 PC Shimadzu in the range of
200–800 nm; FT-IR spectra were recorded on a Bruker
IFS 66V instrument in the range of 400–4000 cmꢀ1
;
Melting points were determined on an X-4 digital dis-
play micro melting point apparatus. The CV curves
were performed in a one-compartment three-electrode
*
Corresponding author. Tel.: +86 25 83686423; fax: +86 25
83317761.
E-mail address: yunlu@nju.edu.cn (Y. Lu).
1387-7003/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.05.025

854
H. Yang et al. / Inorganic Chemistry Communications 8 (2005) 853–857
cell with the use of a PARC M273 potentiostat under
the nitrogen atmosphere monitored by a computer at
room temperature.
rise to 50 ꢁC. Sulfur dioxide was evolved and the dark
blue solution of [Fe(C5H5)2]+ resulted. This solution
was kept at room temperature overnight, and then
poured into ice and water. About 4.33 g of p-amino ben-
zene sulfonic acid was diazotized in 36.5% hydrochloric
acid (7 ml) at ꢀ5 to 0 ꢁC. The newly formed diazonium
salt was slowly added to the above solution of
[Fe(C5H5)2]+ at 0 ꢁC for 3 h under magnetic stirring.
Then, the stirred solution was kept overnight at room
temperature. A deep blue acid solution was obtained
upon filtration of the above solution. Subsequently, a
mixture precipitate containing unreacted ferrocene and
p-ferrocenyl benzene sulfonic acid resulted instantly
when the solution was adjusted to neutral by sodium
hydroxide. After removing the unreacted ferrocene by
washing the precipitate with acetone and filtrating, the
residue was recrystallized from water. Column chroma-
tography (trichloromethane/methanol = 5:1) on silica
gel gave p-ferrocenyl benzene sulfonic acid (0.8 g, 10%
yield) as an orange crystal melting at 246 ꢁC (decom-
The compounds, p-ferrocenyl benzene sulfonic acid
(BSAFc, I) and 4-ferrocenyl–1,10-azobenzene-3,40-disul-
fonic acid (AYFc, II), were prepared according to the
procedures we designed as shown in Schemes 1 and 2.
It is well known that the derivatives of ferrocene have
been made usually from ferrocene in its organic solvent
soluble form. Nevertheless, cationic form [Fe(C5H5)2]+
of ferrocene is also capable of reacting with aromatic
diazonium salts in dilute acid medium. [Fe(C5H5)2]+
can be produced by oxidation [5,6] of concentrated sul-
furic acid and ferrocene, and employed to react with dia-
zonium salts of aromatic amines in dilute sulfuric acid
medium at room temperature. Reactions occur with
nitrogen evolution and ferrocene derivatives substituted
with one or more aryl groups are obtained. The mono-
aryl ferrocene derivatives are usually formed at lower
yield and are always present in the cationic, dilute-acid
soluble form, which can be precipitated readily by add-
ing a reducing agent such as ascorbic acid. However, the
quantity of reducing agents is rather difficult to be deter-
mined. In this paper, we chose to add solid NaOH into
the dilute acid solution and adjusted the pH value of the
system. Precipitates containing the target products ap-
pear immediately as soon as the solution becomes neu-
tral. As indicated above, this dealing method is simple
and convenient.
1
posed) H NMR(DMSO): d 7.53–7.47(m, 4H), 4.02(s,
5H), 4.35(m, 2H), 4.80(m, 2H). Anal. Calcd. for
C16H14SO3Fe: C, 56.14%; H, 4.09%; Fe, 16.37%. Found:
C, 56.06%; H, 4.07%, Fe, 15.68%. IR (KBr, cmꢀ1): mOH
3440(s), mC–H 3103 (w), mC@C 1650, 1599(m), mS@O 1201
(s), 1133 (s).
Compound AYFc was prepared according to a simi-
lar procedure used for compound BSAFc via replacing
p-amino benzene sulfonic acid by Acid yellow 9#. Col-
umn chromatography of the concentrated filtrate (tri-
chloromethane/methanol = 3:1) on silica gel produced
AYFc (1.4 g, 20% yield) as a black-purple crystal not
The synthesis of BSAFc was detailed as follows. Fer-
rocene (4.6 g, 0.025 mol) was added to 98% sulfuric acid
(13 ml, 0.225 mol), while allowing the temperature to
HCl
NaNO2
H2N
SO3H
SO3H
ClN
N
-5
0
Fe
SO3H
(Derivative I)
Fe
-N2
Scheme 1.
SO3H
N
N
SO3H
H2N
HO3S
N
ClN
N
N
+
HCl
NaNO2
-5
0
HO3S
SO3H
N
(
Derivative
)
Fe
N
Fe
-N2
HO3S
Scheme 2.

H. Yang et al. / Inorganic Chemistry Communications 8 (2005) 853–857
855
melting below 320 ꢁC. 1H NMR(DMSO): d 7.88–
7.79(m, 7H), 8.07(d, 1H), 8.38(d, 1H), 5.21(m, 2H),
4.30(m, 2H), 4.08(s, 5H). Anal. Calcd. for C22H118N2
(SO3)2Fe: C, 50.19%; H, 3.42%; N, 5.32%; Fe, 10.65%.
Found: C, 51.20%; H, 3.80%; N, 5.31%; Fe, 10.66%.
IR (cmꢀ1): mOH 3426(s), mC–H 3094 (w), mC@C 1635(m),
1594(m,) 1395 (w), mS@O 1194 (s), 1123 (s).
Table 1
UV–Vis spectroscopic parameters for compounds I, II in aqueous
solution at 20 ꢁC
Compound
kmax (nm)
Absorbency A
I
247.0
285.0
341.0
449.0
1.443
1.357
0.195
0.066
The UV–Vis spectra of compounds I and II were dis-
played in Fig. 1, while the corresponding absorption
bands were recorded in Table 1, respectively. The
absorption band of compound I at 285 nm is attributed
to p–p* transition of substituted benzene ring which is
red-shifted more than 30 nm compared to that of unsub-
stituted benzene ring at 254 nm [7]. The shifting of the
absorption band to long wavelength is due to that the
electrophobic ferrocene group and the electrophilic sul-
fonic group connected to benzene can respectively in-
crease HOMO level and decrease of LOMO level,
which make the energy-level width of substituted ben-
zene narrower. The bands at 247, 341 and 449 nm of
compound I and 526 nm of compound II belong to
the d–d transition of monosubstituted ferrocene, which
are also red-shifted relative to that of unsubstituted fer-
rocene at 240 nm, 320 and 435 nm [7] because of the
existence of electrophilic sulfonic group. Owing to the
longer conjugated chain and better electro-transfer abil-
ity of compound II, the 91-nm displacement at 526 nm
of compound II is much greater than that 14-nm dis-
placement at 449 nm of compound I compared to the
band at 435 nm of unsubstituted ferrocene. The strong
band at 348 nm in Fig. 1(b) is belonging to azo group
[7] that shows an overlap with the absorption band of
substituted ferrocene in compound II.
II
348.0
526.0
1.983
0.253
ical method and permit the collection of excellent data at
low concentration of electro-active substance [8]. The
CV curves in Fig. 2 show that the redox characteristics
are similar for both compounds. The oxidation peaks
of BSAFc and AYFc are all 296 mV and the reduction
peaks are 202 and 196 mV, respectively. That is to
say, the separation of oxidation and reduction poten-
tials, DEP, are 94 and 100 mV at 100 mV/s, respectively,
for BSAFc and AYFc. These values are larger than that
expected for reversible one-electron transfer reaction,
which is given by 57/z mV, where z is the number of
electron transferred in the process [9], indicating that
the irreversibility of the electron-transfer process was
maintained under this condition. The half-wave poten-
tials of BSAFc and AYFc are 249 and 245 mV which
could be figured out easily. Generally, the half-wave po-
tential of monosubstituted ferrocene that linked with
electrophilic group would shift towards positive
potential compared to unsubtituted ferrocene. Antoni-
etta Baldo et al. [10] had found that the half-wave poten-
tial of ferrocene is 190 mV (vs. Ag/AgCl) in pure
aqueous solution. There were about 60 mV towards
more positive potential of BSAFc and AYFc, which is
consistent with the result of UV–Vis spectra.
The electrochemical behaviors of compounds I and II
were investigated in the potential range of 0.0–0.5 V by
cyclic voltammetry (CV) which is sensitive electrochem-
250
202
a
2.5
200
194
b
150
b
2.0
100
50
1.5
0
-50
-100
a
1.0
-150
296
0.5
0.0
-200
296
-250
0
100
200
300
400
500
E/mV vs Ag/AgCl
200
300
400
500
600
700
800
Fig. 2. Cyclic voltammogram of: (a) BSAFc (1 · 10ꢀ3 M); (b) AYFc
(1 · 10ꢀ3 M). Working electrode and auxiliary electrode: Pt disk.
Reference electrode: Ag/AgCl (1 M KCl). Scan rate: 100 mV/s.
Supporting electrode: NaCl aqueous solution (0.05 M).
wave length(nm)
Fig. 1. UV–Vis spectra: (a) BSAFc (I) (1 · 10ꢀ4M); (b) AYFc (II)
(1 · 10ꢀ4M).

856
H. Yang et al. / Inorganic Chemistry Communications 8 (2005) 853–857
potentials of BSAFc changed at different pH conditions.
450
400
350
300
250
200
150
The half-wave potential of BSAFc recorded at pH 1
shifts 20 mV to more negative than that at pH 4, and
the peak current is larger than that at pH 4, which can
be attributed to the formation of ion pair [11]. The fer-
rocene group of BSAFc becomes ferrocenium cation
(Fc+) upon oxidation and can easily form ion pair with
Clꢀ existing in the solution. The half-potential of
BSAFc becomes more negative and the electrochemical
activity of it enhances with the increase of concentration
of Clꢀ [11]. Meanwhile, the CVs of BSAFc at pH 7 and
9 reveal the same half-wave potentials as that at pH 4,
which is due to the same concentration of Clꢀ in these
three solutions and the difficulty of the interaction of
OHꢀ and Fc+ to form ion pair. In the other words, there
is almost no influence of concentration of OHꢀ on the
half-wave potential of BSAFc. When the concentration
of OHꢀ is increased to that at pH 13, the whole CV
curve moves downwards, which may be the result of
electrical catalytic activity of BSAFc. The pH value of
normal AYFc aqueous solution is 4 and also is adjusted
from 4.0 to 1.0 using hydrochloric acid and from 4.0 to
11.0 using NaOH solution. The CVs of AYFc showed in
Fig. 3 display similar behavior to that of BSAFc. The
half-wave potential of AYFc at pH 1 shifts 6 mV to
more negative than that at pH 4 and then holds the line
when the concentration of OHꢀ increases at the con-
stant concentration of Clꢀ. This experimental result
confirms the aforementioned discussion that concentra-
tion of OHꢀ has little impact on the half-wave potential.
In conclusion, two new water-soluble functional fer-
rocene derivatives with sulfonic groups and/or azo struc-
ture were synthesized conveniently in aqueous media.
The preparation process is quite simple and environ-
ment friendly. The electrochemical activities of BSAFc
and AYFc firmly rely on the anion existing in the solu-
tion, especially the type of anion. For the two new ferro-
cene derivatives, they should be of potential application
in development of new functional materials because of
their redox and optical properties and further studies
on their utilization in the preparation of conductive
polymers with ferromagnetic property are underway
and will be reported in due course.
a
b
196mV
206mV
c
d
e
100
50
0
-50
-100
-150
-200
-250
0
100
200
300
400
500
E/mV vs Ag/AgCl
Fig. 3. Cyclic voltammograms of AYFc in aqueous solution of
different pH value, pH 1 (a); pH 4 (b); pH 5 (c); pH 9 (d); pH 11 (e).
Working electrode and auxiliary electrode: Pt disk. Reference elec-
trode: Ag/AgCl (1 M KCl). Scan rate: 100 mV/s. Supporting electrode:
NaCl aqueous solution (0.05 M).
To study the electrochemical stability of BSAFc and
AYFc, their CVs were investigated in different pH media.
Fig. 3 shows CVs of AYFc in aqueous solution of pH
1(a), 4(b), 5(c), 9(d) and 11(e), respectively, and Fig. 4
shows CVs of BSAFc in aqueous solution of pH 1(a),
4(b), 7(c), 9(d) and 13(e), respectively. The normal pH
value of aqueous solution of BSAFc is 4. Herein, we ad-
just pH value of BSAFc solution from 4.0 to 1.0 using
hydrochloric acid and from 4.0 to 13.0 using NaOH
solution. Theoretically speaking, the half-wave potential
of BSAFc should be constant in different pH media be-
cause H+ or OHꢀ does not participate in the redox reac-
tion. However, it is found from Fig. 4 that the redox
600
a
192
215
400
200
0
b
e
c
d
-200
-400
-600
Acknowledgments
289
271
The authors are grateful for the supports from the
National Natural Science Foundation of China (No.
20174016) and Testing Foundation of Nanjing
University.
0
100
200
300
400
500
E/mV vs Ag/AgCl
Fig. 4. Cyclic voltammograms of BSAFc in aqueous solution of
different pH value, pH 1 (a); pH 4 (b); pH 7 (c); pH 9 (d); pH 13 (e).
Working electrode and auxiliary electrode: Pt disk. Reference elec-
trode: Ag/AgCl (1 M KCl). Scan rate: 100 mV/s. Supporting electrode:
NaCl aqueous solution (0.05 M).
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