Synthesis, electrochemistry and IR spectroelectrochemistry of bisferrocenyl bridged benzene derivates

Article abstract of DOI:10.1016/j.jorganchem.2011.10.019

Two novel biferrocenylcarboxylate benzene derivatives, namely, 1,4-bis(2-Ferrocenecarboxylate) benzene (Fc₂B) and 1,4-bis(2-Ferrocenecarboxylate)-2′-methylbenzene (Fc₂M), have been synthesized. The as-prepared complexes have been con

Full text of DOI:10.1016/j.jorganchem.2011.10.019

Journal of Organometallic Chemistry 697 (2012) 57e64
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, electrochemistry and IR spectroelectrochemistry of bisferrocenyl
bridged benzene derivates
Peng Huang b, Baokang Jin a , Peng Liu , Longjiu Cheng , Wangxing Cheng b, Shengyi Zhang a
a
,
,
a
a
a,
*
a
Department of Chemistry, Anhui University, Hefei, Anhui 230039, People’s Republic of China
Anhui University of Traditional Chinese Medicine, Hefei, Anhui 230038, People’s Republic of China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2011
Received in revised form
Two novel biferrocenylcarboxylate benzene derivatives, namely, 1,4-bis(2-Ferrocenecarboxylate)
0
benzene (Fc
2
B) and 1,4-bis(2-Ferrocenecarboxylate)-2 -methylbenzene (Fc
2
M), have been synthesized.
1
The as-prepared complexes have been confirmed by IR, H NMR and MS. The electron transfer mecha-
3
October 2011
nisms of the two compounds and the other three bisferrocenyl bridged benzene complexes, 1,4-dis-
Accepted 11 October 2011
2 2
ferrocenyl benzene (Fc P), 1,4-bis(2-ferrocenylvinyl) benzene (Fc E), and 1,4-bis(2-ferrocenylacetyleneyl)
benzene (Fc Q), have been studied by cyclic voltammetry (CV), in situ difference FT-IR (SNFTIR), and
2
Keywords:
rapid-scan time-resolved FT-IR spectroelectrochemistry (RS-TRS FT-IR). The CV results suggest that the
redox formal potentials of the five bridged complexes are depended on their bridged groups and abilities
of withdrawing electron. IR absorption peaks arisen from intermediate appearance and disappearance in
the oxidation and reduction process of Fc B, Fc E, Fc P and Fc Q were clearly observed by the in situ
2 2 2 2
rapid-scan or SNFTIR spectroelectrochemistry. The results indicated the redox process of the four bis-
ferrocenyl bridged benzene complexes involved two consecutive one-electron steps. Although the
Bisferrocenyl bridged benzene derivates
Synthesis
IR spectroelectrochemistry
Cyclic voltabsorptometry
Electron transfer
intermediate peak of Fc
the redox process of Fc
2
M was not observed by in situ FT-IR spectroelectrochemistry, we still thought
M could involve two consecutive one-electron steps.
Ó 2011 Elsevier B.V. All rights reserved.
2
1
. Introduction
communications among covalently linked redox units. However,
the information obtained from voltammetric data are not enough to
elucidate the electron transfer mechanisms of molecules contain-
ing multiple noninteracting or interacting redox centers. Recently,
we introduce a method called IR Spectroelectrochemistry Cyclic
Voltabsorptometry [11,12] used to investigate the electrochemical
process, which can provide the direct evidences for the assignment
of each redox transition during CV scans. Thus, the approach can be
applicable to the study of a wide range of complex electrochemistry
process.
The concept of molecular wires has been investigated quite
intensively in recent years, because of their potential applications
in sensors, optoelectronics, photovoltaics, and emerging nanoscale
technologies [1e3]. Ferrocenes groups have been widely applied in
molecular wires because there are many advantages such as ideal
donor moieties, the good thermal stability, the ease of organic
functionalization and exceptional electrochemical properties
[4e6]. What is more, bridged biferrocenyl complexes have been
focused on which two ferrocenyl units are connected by different
covalent groups, so they can easily form mixed-valent (MV) Fe(Ⅱ)e
Fe(Ⅲ) species by electrochemical or chemical oxidation [4,7,8].
Multi-ferrocenyl compounds, including multi-metallic mixed-
valence, have received considerable attentions because of the ideal
redox properties of the ferrocenyl group due to their applicabilities
in molecular electronics, sensor applications and multi-redox
catalysis [9,10]. In particular, they have been used extensively
for electrochemical studies of the electronic intramolecular
In this work, two new biferrocenecarboxylate benzene
complexes (1,4-bis(2-Ferrocenecarbox ylate) benzene (Fc
2
B) and 1,4-
M)) have been
0
bis(2-Ferrocenecarboxylate)-2 -methylbenzene (Fc
2
prepared. The electrochemical behaviors of the two complexes and
the other three complexes (1,4-bis(2-ferrocenylvinyl)benzene(Fc E);
1,4-disferrocenylbenzene(Fc P); 1,4-bis(2-ferrocenylacetyleneyl) be-
nzene(Fc Q), see Scheme.1) were studied by CV and DPV. The redox
2
2
2
formal potentials of the five complexes depend on their abilities of
withdrawing electron with bridged groups. The in situ IR spec-
troelectrochemistry was used to study the redox properties of
biferrocenyl complexes. The intermediates of Fc
Fc E except Fc M, produced in the electrochemical process, were
facilely observed, which gave me a complete understanding for the
2 2 2
B, Fc P, Fc Q, and
*
Corresponding author. Fax: þ86 551 5107342.
E-mail address: bkjinhf@yahoo.com.cn (B. Jin).
2
2
0
022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.10.019

58
P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
C
H
C
H
C C
H H
C
C
C C
Fe
Fe
Fe
Fe
Fe
Fe
1
,4-bis(2-ferrocenylvinyl)benzene
1
,4-bis(2-ferrocenylacetyleneyl)benzene
1
,4-disferrocenylbenzene
(
Fc E)
2
(Fc Q)
(Fc P)
2
2
Scheme 1. The derivates of bisferrocenyl benzene.
electron transfer process. What is more, i-E curves of Fc
were reconstructed by Derivative Cyclic Voltabsorptometry (DCVA).
Two consecutive electron transfer process of Fc B and Fc E were
2
B and Fc
2
E
2.4. Preparation of 1,4-bis(2- ferrocenecarboxylate)benzene (3,
2
Fc B)
2
2
clearly observed during CV scan. The results suggest the electron-
transfer process of the five biferrocenyl bridged benzene complexes
are two consecutive one-electron steps.
The hydroquinone (0.5 g, 4.5 mmol) was dissolved in 20 mL of
THF, then NaH (0.26 g) was dissolved in 10 mL of THF and slowly
added into the previous solution under nitrogen. Chlorocarbonyl
ferrocene (3 g) was dissolved in 20 mL of THF and dropped into the
reaction solution under ice-bath. After that, the resulting solution
was stirred at room temperature for a period of 14 h. It was
quenched by addition of water and then extracted with ethyl
2
. Experimental
2.1. General procedures
4
acetate. The organic layer was separated and dried over MgSO , and
the solvents were removed under reduced pressure. The crude
product was purified by column chromatography (Silica, Petroleum
All chemicals were purchased as reagent grade and used
without further purification. The solvents were dried and distilled
according to standard procedures. IR spectra were recorded on
a Nicolet FT-IR instrument (Nexus 870) with KBr discs in the
ether/EtOAc, 95/5 (v/v)) to give 3(1.27 g, 76%) as an orange solid. IR
ꢀ1
(
1
d
KBr,cm ) :3112(m), 2921(m), 2859(m), 1762(s), 1701(s), 1562(s),
1
480(s), 1370(m), 1241(m), 1175(s). H NMR (400 MHz, CDCl
3
):
),
ꢀ
1
1
4
3
000e400 cm range. H NMR spectra in CDCl were recorded on
7.26 (s, 4H, ArH), 4.99e4.92 (d, 4H, C
.39e4.33 (d, 10H, C
5
H
4
), 4.58e4.53 (d, 4H, C
5
H
4
a Bruker-400 MHz spectrometer.
þ
4
5
H
5
); EI-MS (m/z) :534(M ).
0
2.2. Electrochemistry and FT-IR spectroelectrochemistry
2.5. Preparation of 1,4-bis(2- ferrocenecarboxylate)-2 -
methylbenzene (4, Fc M)
2
Electrochemical experiments were performed with an electro-
chemical analyzer CHI630C potentiostat. A homemade thin-layer in
situ FT-IR spectroelectrochemical cell was used with a 4 mm
diameter platinum disk working electrodes, a platinum wire
auxiliary, and Ag/AgCl reference electrode placed symmetrically
around the working electrode. All of the potentials reported in this
The 2-methylhydroquinone (0.6 g, 4.8 mmol) was dissolved in
20 mL of THF, then NaH (0.29 g) was dissolved in 10 mL of THF and
slowly added into the previous solution under nitrogen. Chlor-
ocarbonyl ferrocene (3.5 g) was dissolved in 20 mL of THF and
dropped into the reaction solution under ice-bath. After that, the
resulting solution was stirred at room temperature for a period of
18 h. It was quenched by addition of water and then extracted with
ethyl acetate. The organic layer was separated and dried over
þ
article are relative to Fc/Fc (Fc ¼ ferrocene). Tetrabutylammonium
perchlorate (TBAP) was recrystallized from ethanol and dried
overnight under reduced pressure before use.
In situ FT-IR spectroelectrochemistry experiments were carried
out simultaneously with the electrochemistry experiments. Rapids
scan time-resolved spectroscopic measurements were performed
on a Nicolet Nexus 870 spectrometer equipped with a specular
reflectance accessory (SMART iTR) and a HgCdTe/A(MCT/A)
detector cooled with liquid nitrogen. The experiments were carried
out in a homemade reflection-absorption spectroelectrochemical
cell, the sampling interval is 07e2.48 s, and the spectral resolution
MgSO , and the solvents were removed under reduced pressure.
The crude product was purified by column chromatography (Silica,
4
Petroleum ether/EtOAc, 90/5 (v/v)) to give 4 (1.3 g, 64%) as an
ꢀ
1
orange solid. IR (KBr,cm ): 3120(m), 2929(m), 1728(s), 1577(m),
1
1452(m), 1370(m), 1261(s), 1173(s), 1101(s). H NMR(400 MHz,
CDCl ):
3
d
7.08(q, J ¼ 2.4 Hz, 1H, ArH), 7.12(d, J ¼ 2.4 Hz, 1H, ArH),
7.18(d, J ¼ 8.4 Hz, 1H, ArH), 4.99(d, 4H, C H ), 4.53(t, 4H, C H ),
5
4
5 4
þ
4.38(d, 10H, C H ), 2.34(s, 3H, CH ); EI-MS (m/z): 550 (M ).
5
5
3
ꢀ1
is 16 cm . Experimental results were dealt with Grams/3D
software.
2
.6. Preparation of 1,4-bis(2-ferrocenylvinyl)benzene (Fc
disferrocenylbenzene (Fc P) and 1,4-bis(2-ferrocenylacetyleneyl)
benzene (Fc Q)
2
E), 1,4-
2
2.3. Preparation of chlorocarbonyl ferrocene (2)
2
Ferrocenecarboxylic acid (1) (3 g, 13 mmol) and triethylamine
1.5 mL) were dissolved in 20 mL of freshly distilled dichloro-
1,4-Bis(2-ferrocenylvinyl)benzene (Fc
2
P) and 1,4-Bis (2-ferrocenylacetyleneyl) benzene (Fc
2
E), 1,4-Disferrocenylbenzene
Q) were
(
(Fc
2
methane. Oxalyl chloride (2.4 mL, 27.62 mmol) was added via
syringe against a positive stream of nitrogen. After all gas
evolution had ceased, the deep red solution was stirred for
prepared following literature methods [14,15,16].All the compounds
were characterized with MS, H NMR and IR.
1
3
0 min at room temperature [13]. All volatile components were
2
2.6.1. Data for compound Fc E
Red crystals. IR (KBr, cm ) : 3011(m), 3095(m), 1629(s),
1511(m), 1459(m), 1409(m), 1105(s), 1001(s); H NMR(400 MHz,
ꢀ1
distilled off under reduced pressure to leave a reddish material
which was dried under reduced pressure at room temperature for
1
3
step.
0 min. The product was not purified to be used directly next
DMSO-d
5 4
and C H
6
):
5 5 5 4 5 5
d 4.32e4.56 (9H, C H and C H ), 4.09e4.24 (9H, C H
), 7.25e7.44 (dt, 4H, ArH), 6.34e6.40 (dd, J ¼ 12.5 Hz, 2H,

P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
59
1
0
5
0
5
A 10
B
Fc B
Fc M
Fc E
Fc P
Fc Q
5
0
-
-5
-10
-10
-15
-15
0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6
0.6 0.5 0.4 0.3 0.2 0.1 0.0
+
+
E/V vs.Fc/Fc
E/V vs.Fc/Fc
Fig. 1. (A) Cyclic votammogram (CV) of 1 Mm(Fc
2
E, Fc
2
P, Fc
2
Q) in CH
2
Cl
2
with 0.3 M TBAP at 289 K, the scan rate is 50 mV/s. (B) Cyclic votammogram (CV) of 1 Mm(Fc
2
B, Fc
2
M) in
CH Cl with 0.3 M TBAP at 289 K, the scan rate is 50 mV/s.
2
2
CH]CH), 6.72e6.99 (dd, 2H, J ¼ 12.8 Hz, CH]CH); ES-MS (m/z)
The CV result of Fc
2
P is shown in Fig.1. Two pairs of reversible
þ
1
1
2
:
498(M ).
redox peaks (E 1/2 (¼(Epa þ Epc)/2) ¼ ꢀ147.5 mV,
DE
p
¼ 65 mV; E 1/
E2
¼ 70 mV) are found. The reason may be that there
2
¼ ꢀ34 mV,
D
p
2
.6.2. Data for compound Fc
Orange pellets. IR (KBr, cm ): 3094 (m), 3026 (m), 1541 (s),
2
P
are strong electronic interactions between the two ferrocene units.
Furthermore, the interaction in benzene-bridged Fc P is stronger
than that in the other four compounds; whereas the FceFc distance
in Fc P (4.39 Å) is shorter than that of the other compounds (see
ꢀ
1
2
1
1440 (m), 1427 (m), 1409 (m), 1097 (s); H NMR(400 MHz, DMSO-
d
6
):
d
7.44 (s, 4H, ArH), 4.77 (s, 4H, C
5
H
4
), 4.33 (s, 4H, C
5
H
4
), 4.01 (s,
2
þ
10H, C
5
H
5
); ES-MS (m/z): 446 (M ).
Table 1). It causes electron delocalization by the strong coupling
effects between two ferrocene units. Therefore, two pairs of redox
peaks appear in the CV curves.
While the CV curves of the other four compounds exhibit only
one pair of redox peaks which is due to the FceFc distance enhance
giving rise to lower electron coupling effect in the ferrocene with
2
2
.6.3. Data for compound Fc Q
Orange pellets. IR(KBr,cm ): 3098 (m), 3080 (m), 2225 (s), 2203
ꢀ
1
þ
(
s), 1519 (s), 1411 (m), 1105 (s), 1006(m); ES-MS (m/z) : 494 (M ).
3
. Results and discussion
benzene. Besides, it is obvious that the formal potentials of Fc
2
B and
Fc M (Fc B ＞ Fc M ＞ Fc Q ＞ Fc P ＞ Fc E) shift more positively
2
2
2
2
2
2
3.1. Electrochemistry
than that of the other three complexes due to the stronger electron-
withdrawing effect of the carbonyl group.
Containing two ferrocenyl groups linked with different bridged
benzenes, the four complexes (Fc B, Fc M, Fc Q and Fc E) show one
2 2 2 2
In addition, the DPV results of the above five bisferrocenyl
bridged benzene derivates are consistent with the report of CV
excellently.
pairs of redox waves for their CV responses, the other one (Fc
2
P)
shows two pairs of redox waves.
3.2. FT-IR spectroelectrochemistry
Table 1
The electrochemical data of the bisferrocenyl derivatives studied in this thesis vs. Fc/
þ
Fc .
3.2.1. 1,4-Bis(2-ferrocenylvinyl)benzene
Eq/mV
On the basis of past work of our group, the intermediate IR peak
Sample
E
1/2/mV
ꢀ220
ꢀ103,e221
D
Ep/mV
D
FceFc(Å)
ꢀ
1
of Fc
by IR spectroelectrochemistry (see Table 2). The DCVA at 1589 cm
indicates the electron transfer of Fc E is two consecutive one-
electron steps. The reconstructed i-E curves make us further
understand the electron transfer process of Fc E, which shows
2
E at 1589 cm was observed during electrochemical process
Fc
Fc
Fc
Fc
Fc
2
2
2
2
2
E
P
Q
B
M
98
/
5.88
4.39
6.28
ꢀ1
65, 70
89
96
/
ꢀ21.5
2
a
296
274
103
102
/
/
9.99
a
9.98
2
a
The space of FceFc were calculated by Gaussian go9.
two consecutive one-electron steps (
DE ¼ 8 mV) [11]. The
Table 2
Infrared peak absorptions of bisferrocenyl bridged benzene derivatives and their oxidation products.
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
Compound
n
(CC, Fc),
n(CC, Ar), cm
n
(C]C), cm
n
(C^C), cm
n (C]O), cm
ꢀ
1
cm
þ
2þ
þ
þ
2þ
Fc
Fc
Fc
Fc
2
2
2
2
B(4, 4 , 4
)
1407
1407
1409
1409
1562, 1456
1577, 1452
1726(4), 1749(4 ), 1787(4 ,4 ),
þ
1
772(4), 1810(42
)
M(5 ,52
þ
)
1725(5)
1
756(52
þ
)
þ
2þ
þ
E(1,1 ,1 ) [11]
1511, 1459 1589(1 );
1629 (1);
1620 (1 ,1
þ
2þ
þ
2þ
)
1
470 (1 ,1
)
þ
2þ
)
P(2, 2 , 2
1541(2), 1443(2),
þ
1
1
427(2) 1604(2 ),
469(2 ), 1420 1454 (2
þ
2þ
)
þ
2þ
þ
Fc
2
Q(3, 3 , 3
)
1411
1519, 1411(3)
2225, 2203(3); 2202 (3 );
230, 2210(32
þ
)
2

60
P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
HO
OH
O
C
O
C
O
O
NaH,THF
Fe
Fe
O
O
3
2
(Fc B)
C
OH (COCl)
CH Cl
2
C Cl
3
H C
Fe
Fe
3
H C
2
2
O
C
O
C
HO
OH
O
O
1
2
Fe
Fe
NaH,THF
4
(Fc
2
M)
Scheme 2. Strategy of synthesis of the target complexes.
-
e
- e
Fc
C
H
C
H
C
H
C
H
Fc
Fc
C
H
C
H
C
H
C
H
Fc
Fc
C
H
C
H
C C Fc
H H
e-+
e-+
Scheme 3. The electron transfer mechanism of 1,4-bis(2-ferrocenylvinyl)benzene.
ꢀ
1
disproportionation equilibrium constant (Kdisp) can be expressed
and calculated as follows:
process. Obviously, the peak at 1787 cm should be assigned to the
intermediate IR peak. The appearance and disappearance of the
peak during both oxidation and reduction process could be inter-
ðRT=FÞlnKdisp
¼
D
E1=2 ¼ E1 ꢀ E2
1=2
1=2
(1)
preted as follows. When one Fc is be oxidized to Fc firstly and the
electron-withdrawing ability of Fc is stronger than that of Fc,
þ
þ
Fꢀ
ꢁ
which leads to form the D-
continues, the other Fc is oxidized to Fc , which results in
p
-A structure. As the oxidation process
D
E1=2
þ
Kdisp ¼ EXP
Kdisp ¼ 0:729
(2)
RT
reforming of the symmetry of the benzene ring A-
explanation can also be illuminated the phenomenon of reduction
process with the configuration type transfer from A- -A to D- -A
and finally to D- -D [17e20].
As a result, the peak at 1810 cm was employed to trace directly
p-A. The similar
The electron transfer mechanism of Fc
Schemes 2 and 3.
2
E can be expressed in
p
p
p
ꢀ
1
3
.2.2. 1,4-Bis(2-ferrocenecarboxylate)benzene
Fig. 2A shows the cyclic voltammogram of Fc
Only one redox couple is observed (Epc ¼ 317 mV, Epa ¼ 263 mV,
¼ 54 mV). The in situ rapid-scan IR spectra recorded during the
2þ
2
B in thin-layer cell.
2
the formation of the final product of p-(Fc-COO) Bz, the peak at
ꢀ1
1749 cm was employed to trace directly the formation of p-(Fc-
2
þ
þ
ꢀ1
DE
p
2
COO) Bz and Fc eCOOeBz-OOCFc, and the peak at 1787 cm
ꢀ1
CV scan in the 1800-1450 cm region are shown in Fig. 2B. Five
was employed to trace directly the formation of the intermediate of
ꢀ
1
þ
clear IR absorption peaks, 1726, 1749, 1772, 1787 and 1810 cm
which belong to the products of oxidation and reduction of Fc
can be observed. The absorbance at 1726 and 1772 cm gradually
decreased and disappeared in the oxidation process, then appeared
and reached to a maximum value in the reduction. The peak at
749 cm and 1810 cm gradually increased during the oxidation
process, and then gradually disappeared during the reduction
process. Two couples of dipolar peaks at 1726/1749 cm and 1772/
810 cm attributed to reactant and products, respectively (see
,
Fc eCOOeBzeOOCFc.
ꢀ
1
2
B,
The corresponding DCVA at 1749, 1787, and 1810 cm
are
ꢀ
1
ꢀ1
shown in Fig. 3A. The morphological DCVA at 1787 cm , in which
two couples of peaks are observed, is quite different from the cor-
responding CV. The first pair of oxidation(1) and reduction peaks(3)
shown in DCVA indicate the formation of the intermediate, and the
second pair of oxidation(2) and reduction(4) imply the consump-
tion of the intermediate. The results show that the dA/dt vs E wave
forms are distinguished with the CV responses for the electro-
chemical process. Two pairs of waves can be found in Fig.3A, but the
CV exhibits only one pair of waves [21].
ꢀ
1
ꢀ1
1
ꢀ
1
ꢀ
1
1
Table 2).
ꢀ
1
Interestingly, the absorbance at 1787 cm gradually increased
during the reduction process and reached a maximum value,
and then the absorbance began to diminish during the oxidation
In order to further study the electron transfer of Fc B, we
reconstruct i-E curves based on DCVA referring to our latest paper
2
2 2 2
Fig. 2. (A) Thin-layer CV of 5 mM Fc B in 0.2 M TBAP Acetonitrile/CH Cl and corresponding 3D spectra(B) of in situ FT-IR spectroelectrochemistry, potential scan rate 2 mV/s.

P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
61
A
80
B
40
20
0
1
1
1
787cm
749cm
810cm
i
i
i
3
4
40
0
-
40
80
1
-20
-40
2
-
0.6 0.5 0.4 0.3 0.2 0.1 0.0
0.6 0.5 0.4 0.3 0.2 0.1 0.0
+
+
E/V vs.Fc/Fc
E/V vs.Fc/Fc
Fig. 3. DCVAs(A) (smoothed with a fast Fourier transform smoothing algorithm) for the electrochemical reaction at 1749 cm 1, 1787 cmꢀ1 and 1810 cm and reconstructed i-E
ꢀ
ꢀ1
ꢀ1 ꢀ1
curves for i
, i
1 2
, and i(¼i
1
þ i
2
, total current). To make the DCVA data readily comparable to CV, the 1749 cm and 1787 cm (the second reduction and the first oxidation) in the
DCVA data were multiplied by ꢀ1. All experiments were measured at scan rates of 2 mV/s.
O
O
O
O
O
O
C
-
e
- e
e +
Fc
C
O
O
C
Fc
Fc
C
O
O C Fc
-
-
Fc
C
O
O
Fc
e +
Scheme 4. The electron transfer mechanism of 1,4-bis(2-ferrocenecarboxylate)-benzene.
0
[
1
11,12]. The reconstructed i-E curves (at IR absorption peaks of 1787,
749, and 1810 cm ) can help us understand the electrochemical
3.2.3. 1,4-Bis(2-ferrocenecarboxylate)-2 -methylbenzene
ꢀ
1
Fig.
4A
shows
the
thin-layer
CV
of
1,4-bis(2-
0
process of each step. From Fig. 3B, the ieE curves obviously indicate
ferrocenecarboxylate)-2 -methylbenzene. Only one redox couple
the two consecutive electron transfer processes during CV scan.
is observed in CV. The 3D spectra of the in situ rapid-scan IR spectra
1
2
ꢀ1
Two half-wave potentials, E 1/2 ¼ 297 mV and E 1/2 ¼ 345 mV
E ¼ 48 mV) for the first and the second electron transfer steps,
can be obtained respectively. Compared with Fc E, the E of Fc B is
greater than that of Fc E (
of Fc
2
M recorded during the CV scan in the 1800-1600 cm region
(D
are shown in Fig. 4B. The 3D spectra are gathered between ꢀ0.1 and
0.6 V using the spectrum recorded at ꢀ0.1 V as the reference
spectrum.
2
D
2
2
D
E ¼ 8 mV). This may be due to the
greater ability of electron-withdrawing of carbonyl group, which
leads to the enhancing electron couple effect between two Fc units.
In addition, the corresponding cyclic voltabsorptomograms
(CVAs) are shown in Fig. 5A. It is obvious that there is an increase
ꢀ
1
The apparent half potential (obtained from i
T
eE curve) is
and a decrease of the absorbance at 1756 and 1726 cm subjected
to the sweep potential (time), corresponding to the redox process.
3
20 mV and basically consistent with that obtained by CV. The
ꢀ
1
disproportionation equilibrium constant (Kdisp) can be calculated as
follows:
The absorbance at 1756 cm gradually increases in the oxidation
process and reaches its maximum at nearly 0.35 V (75 s), after
which, it starts to decrease in the reduction process and vanishes at
ꢀ
1
0
.05 V (225 s). The absorbance at 1726 cm gradually decreases
during oxidation process and reaches its minimum at nearly 0.35 V
75 s) and begins to increase gradually during the reduction
process.
As a result, two IR absorption peaks, 1726 and 1756 cmꢀ1, which
origin from vc¼o, can be employed to track the electrochemical
Fꢀ
ꢁ
D
E1=2
Kdisp ¼ EXP
Kdisp ¼ 0:1542
RT
(
The result strongly suggests that the redox process of Fc
2
B is two
consecutive one-electron steps. According to the electrochemical
reaction mechanism, the electron transfer mechanism of Fc
2
B can
ꢀ1
be expressed in Scheme 4.
reaction. The peak at 1726 cm is employed to track directly the
0
Fig. 4. (A) Thin-layer CV of 5 mM 1,4-Bis(2-Ferrocenecarboxylate)-2 -methylbenzene in 0.2 M TBAP Acetonitrile and (B) 3D spectra of in situ FT-IR spectroelectrochemistry, potential
scan rate 5mv/s.

62
P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
A 20
B
2
1756cm
1726cm
1756cm
10
1
0
1
2
0
-
-
-
-
10
20
30
40
1
726cm
-
-
-3
0
50 100 150 200 250
0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1
+
Time/s
E/V vs.Fc/Fc
Fig. 5. CVAs(A), calculated DCVAs(B) (smoothed with a fast Fourier transform smoothing algorithm) for the electrochemical reaction at 1726 (black line) and at 1756 cmꢀ1(red line).
For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
(
H
3
C
H C
3
3
H C
O
O
O
O
O
O
-
e
-
e
Fc
C
O
O
C
Fc
Fc
C
O
O
C
Fc
Fc
C
O
O C Fc
e-+
e-+
0
Scheme 5. Electron transfer mechanism of 1,4-bis(2-ferrocenecarboxylate)-2 -methylbenzene.
ꢀ
1
disappearance of FceCOOMeBzeOOCeFc, and 1756 cm is used to
weak. However, the IR intermediate peak at the process of thin-
layer electrochemistry can be observed by SNFTIR.
þ
þ
follow the formation of Fc eCOOMeBzeOOCeFc (see Table 2). It is
surprising that the intermediate IR peak of Fc M was not observed
compared with Fc B which was attributed to the affection of methyl
group, because, on the one hand, it directly affects the couple
vibration of carbonyl group and only one vibration peak of carbonyl
group can be observed in IR; on the other hand, it destroys the
symmetry structure [22,23].
2
The in situ difference FT-IR spectra of Fc
oxidation (E
¼ ꢀ0.6 V) and (B) reduction (E
Fig. 6. We can observe the tiny change of IR absorption, which is
2
P in the processes of (A)
2
R
R
¼ 0.5V) was shown in
ꢀ
1
assigned to
n(CeC) or n(CeH) of benzene ring, at 1800e1100 cm .
In the oxidation process, the absorbance peak at 1604 and
ꢀ
1
1469 cm appear at ꢀ0.2 V and then gradually vanished with the
The DCVAs are shown in Fig. 5B in which the shapes of DCVA at
potential shifting positive. In the reduction process, the absorbance
ꢀ
1
ꢀ1
1
726 and 1756 cm are similar to that of the Thin-layer CV shown
in Fig. 4A (Peakepeak separation,
¼ 61 mV (CV), whereas
¼ 36 mV (DCVAs)). However, we couldn’t track the change of its
intermediate by experiments. Therefore, on the basis of our
peak at 1604 and 1469 cm appeared at ꢀ0.2 V again and grad-
DE
p
ually vanished with the potential shifting negative. The results
ꢀ1
DE
p
strong suggest that the absorption peak at 1604 and 1469 cm
were assigned to the intermediate absorption peak of Fc P, which
was caused by the changes in configuration of the system during
2
supposition, the redox process of Fc
electron steps (see Scheme 5).
2
M is two consecutive one-
ꢀ1
the electrochemical reaction. The absorption peak at 1454 cm
began to appear at ꢀ0.1 V in the redox process, which was assigned
þ þ
to the formation of the final product (Fc eBzeFc ). The absorbance
3.2.4. 1,4-Disferrocenylbenzene
ꢀ
1
ꢀ1
For Fc P and Fc Q, the intermediate IR peak was not observed by
in situ IR spectroelectrochemistry, which due to the IR signals are
2
2
peak at 1604, 1469 cm and 1454 cm were assigned to
the benzene ring (see Table 2).
n(CeC) of
Fig. 6. (A) FT-IR spectroelectrochemistry difference spectra of the oxidation of 1,4-disferrocenylbenzene at 295 K on Pt disk electrode (
4
¼ 4 mm). ER ¼ ꢀ0.6 V. Test solution 3 mM
¼ 0.1 V. Spectral resolution is 8 cmꢀ . E/v vs. Fc/Fc .
1
þ
1,4-disferrocenylbenzene þ0.2 M TBAP in CH
2 2 R
Cl . (B) Reduction process, E
-
e
- e
Fc
Fc
Fc
Fc
Fc
Fc
e-+
e-+
Scheme 6. The electron transfer mechanism of 1,4-disferrocenylbenzene.

P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
63
Fig. 7. (A) FT-IR spectroelectrochemistry difference spectra of the oxidation of 1,4-bis(2-ferrocenylacetyleneyl) benzene at 295 K on Pt disk electrode (
4
¼ 4 mm). E
R
¼ ꢀ0.6 V. Test
¼ 0.5 V. Spectral resolution is 8 cmꢀ . E/v vs. Fc/Fc .
1
þ
solution 3 mM 1,4-bis(2-ferrocenylacetyleneyl) benzene þ 0.1 M TBAP in CH
2
Cl
2
. (B) Reduction process, E
R
-
e
- e
e-+
Fc
C
C
C
C
Fc
Fc
C
C
C C Fc
-
Fc
C
C
C C Fc
e +
Scheme 7. The electron transfer mechanism of 1,4-bis(2-ferrocenylacetyleneyl)benzene.
Based on IR spectroelectrochemistry results, it is obvious that
the redox process of Fc P is two consecutive one-electron steps. It
could be explained that Fc P was symmetrical in configuration D-
-D structure and then became D- -A when Fc lost one-electron in
p-D structure and then became D-p-A when Fc lost one-electron in
2
the process of oxidation. However, as the potential increased in the
þ
2
process of oxidation, the other Fc was oxidized to Fc too, which
p
p
resulted in reforming of the symmetry of the A-
p
-A structure, so
the peak at 2202 cm disappeared and simultaneously the model
of C) vibration returned to its intensity before electrochemical
reaction [24e26]. According to the electrochemical reaction
ꢀ1
the process of oxidation, which give rise to the benzene ring located
in the unsymmetry. Due to the effect of electron cloud density of Fc
(C
n ^
ꢀ
1
ꢀ1
group, the intermediate peaks appear at 1604 cm and 1469 cm
which the change of electron delocalization brought about the
enhance of the model of (CeC) benzene skeleton vibration.
,
mechanism, the electron transfer mechanism of Fc
expressed in Scheme 7
2
Q can be
n
However, as the potential increased in the process of oxidation, the
þ
other Fc was oxidized to Fc too, which resulted in reforming of the
ꢀ
1
symmetry of the A-
p
-A structure, so the peak at 1604 cm dis-
4. Conclusion
appeared. The similar explanation can also be illuminate the
phenomenon of reduction process with the configuration type
In this paper, two novel bisferrocenyl bridegd benzene
complexes (Fc B and Fc M) have been synthesized and character-
ized by IR, H NMR and MS. In the electrochemistry studies of the
bisferrocenyl derivates with bridged benzene ring, we can find that
their redox potential shifts are positive due to the effect of electron-
transfer from A-
p
-A to D-
p
-A and finally to D-
p-D. As a result, the
2
2
1
electron transfer mechanism of Fc
2
P is two consecutive one-
electron steps (see Scheme 6). Moreover, the result of CV further
confirms the process. The E1/2 for the first and second electron
transfer are ꢀ103 and ꢀ221 mV, respectively. The kdisp ¼ 0.0165 can
be obtained.
2
withdrawing group. For Fc P, two reversible redox waves were
observed by CV due to strong conjugative effect between the
ferrocene and benzene ring. In the studies of the other compounds,
the CV exhibited only a single redox wave. The spaces of FceFc in
3.2.5. 1,4-Bis(2-ferrocenylethynyl)benzene
The in situ difference FT-IR spectra of Fc
2
Q in the processes of (A)
¼ 0.5 V) was shown in
2 2
Fc B and Fc M are longer than those of the other complexes, but the
couple ability between two Fc units is still strong due to the
withdrawing electron ability of carbonyl group. Furthermore, in the
oxidation (E
Fig. 7. The peaks at 2202, 2210 and 2230 cm were assigned to
C) (see Table 2). In the oxidation process, the absorbance peaks
R
¼ ꢀ0.5 V) and (B) reduction (E
R
ꢀ
1
n
(C
^
2 2 2 2
IR Spectroelectrochemical studies of Fc E, Fc B, Fc P, and Fc Q, the
ꢀ
1
at 2210 and 2230 cm appeared at ꢀ0.1 V and then gradually
intermediate absorption peaks that appeared and disappeared both
in the oxidation and in the reduction process were clearly observed.
Therefore, the results of our studies suggest that the electron-
transfer mechanism of four bisferrocenyl bridged benzene
complexes is two consecutive one-electron steps. In addition, the
vanished with the potential shifting positive. In the reduction
ꢀ1
process, the absorbance peaks at 2210 and 2230 cm appeared at
.1 V again and gradually vanished with the potential shifting
0
ꢀ
1
negative. The absorption peak at 2202 cm appeared at ꢀ0.2 V,
then its intensity enhanced slowly, which disappeared at last with
the potential shift moving positive. As a result, the absorption peak
reconstructed i-E curves of Fc
the electron transfer process of two consecutive one-electron steps
further. However, the structure of Fc M was similar to that of Fc B,
it is surprising that the intermediate IR peak of Fc M was not
2 2
B and Fc E can help us to understand
ꢀ
1
at 2202 cm was assigned to the intermediate absorption peak of
Fc Q, which was assigned to the formation of the intermediate
2
2
2
2
þ
(
2
Fc eC^CeBZeC^CeFc) (see Table 2). The absorption peaks at
observed in the 3D spectra, which may attribute to the existence of
methyl group giving rise to directly effect the couple vibration of
carbonyl group and destroy the symmetry structure. Hence, based
ꢀ
1
210 and 2230 cm were assigned to the formation of the final
þ
þ
product (Fc eC^CeBZeC^CeFc ). Thus, it is obvious that the
oxidation process of Fc Q is two consecutive one-electron steps. It
could be explained that Fc Q was symmetrical in configuration D-
2
on our assumption, the electron-transfer mechanism of Fc
2
M is also
2
two consecutive one-electron steps.

64
P. Huang et al. / Journal of Organometallic Chemistry 697 (2012) 57e64
Acknowledgments
[11] B.K. Jin, L. Li, J.L. Huang, S.Y. Zhang, Y.P. Tian, J.X. Yang, Anal. Chem. 81 (2009)
476e4481.
12] B.K. Jin, J.L. Huang, A.K. Zhao, S.Y. Zhang, Y.P. Tian, J.X. Yang, J. Electroanal.
Chem. 650 (2010) 116e126.
[13] D. Plazuk, J. Zakrzewski, J. Organomet. Chem. 694 (2009) 1802e1806.
4
[
This work was supported by the National Nature Foundation of
China (Grants 21175001 and 20875001), the Program for New
Century Excellent Talents in University (China NECT-07-0002), the
Foundation of Scientific Innovation Team of Anhui Province
[
14] C. Zuo, Y. Zhou, J. Wu, Y. TianChin, J. Inorg.Chem. 20 (2004) 1018e1020.
15] I.P. Beletskaya, A.V. Tsvetkov, G.V. Latyshev, V.A. Tafeenko, N.V. Lukashev,
J. Organomet. Chem. 637-639 (2001) 653e663.
[
(
2006KJ007TD), and the 211 Project of Anhui University.
[16] T.M. Keller, S.B. Qadri, Chem. Mater. 16 (2004) 1091e1109.
[17] T.Y. Dong, S.F. Lin, C.P. Chen, S.W. Yeh, H.Y. Chen, Y.S. Wen, J. Organomet.
Chem. 694 (2009) 1529e1541.
References
[18] J.B. Flanagan, S. Margel, A.J. Bard, F.C. Anson, J. Am. Chem. Soc 100 (1978)
4248e4253.
[
[
1] S.H. Choi, B.S. Kim, C.D. Frisbie, Science 320 (2008) 1482e1486.
2] D.K. James, J.M. Tour, in , Molecular Wires: From Design to Properties, vol. 257,
[19] M. Lohan, F. Justand, T. Roisnel, P. Ecorchard, Heinrich Lang, Organometallics
29 (2010) 4804e4817.
2
005, pp. 33e62.
[20] N. Chawdhury, N.J. Long, M.F. Mahon, L.L. Ooi, D.J. Williams, M. Younus,
J. Organomet. Chem. 689 (2004) 840e847.
[21] J. Podlaha, P. Stepnicka, J. Ludvik, I. Cisarova, Organometallics 15 (1996)
543e550.
[22] L. Fernandez, H. Carrero, Electrochim. Acta 50 (2005) 1233e1240.
[23] J.X. Tao, W.J. Xiao, J. Organomet. Chem. 526 (1996) 21e24.
[24] X.Y. Wang, Z.X. Deng, B.K. Jin, Y.P. Tian, X.Q. Lin, Electrochim. Acta 47 (2002)
1537e1543.
[
[
[
3] S.M. Lindsay, M.A. Ratner, Adv. Mater. 19 (2007) 23e31.
4] Y. Li, M. Josowicz, L.M. Tolbert, J. Am. Chem. Soc. 132 (2010) 10374e10382.
5] R. Rulkens, A.J. Lough, I. Manners, S.R. Lovelace, C. Grant, W.E. Geiger, J. Am.
Chem. Soc. 118 (1996) 12683e12695.
6]. R.W. Heo, T.R. Lee, J. Organomet. Chem. 578 (1999) 31e42.
7] T. Moriuchi, T. Hirao, Tetrahedron Lett. 48 (2007) 5099e5101.
8] D.M. Guldi, M. Maggini, G. Scorrano, M. Prato, J. Am. Chem. Soc. 119 (1997)
[
[
[
9
74e980.
9] T. Sixt, M. Sieger, M.J. Krafft, D. Bubrin, J. Fiedler, W. Kaim, Organometallics 29
2010) 5511e5516.
10] P. Nguyen, P.G. Elipe, I. Manners, Chem. Rev. 99 (1999) 1515.
[25] B.K. Jin, P. Liu, Y. Wang, Z.P. Zhang, Y.P. Tian, J.X. Yang, S.Y. Zhang, F.L. Cheng,
J. Phys. Chem. B. 111 (2007) 1517e1522.
[26] X.Y. Wang, Z.X. Deng, B.K. Jin, Y.P. Tian, X.Q. Lin, Electrochim. Acta 47 (2002)
1537e1543.
[
(
[