An effective method for the synthesis of monoferrocenylbenzene derivatives

Article abstract of DOI:10.1080/00958972.2012.732696

Three new ferrocenylbenzene derivatives, 1-ferrocenyl-2,3,4,5- tetramethylbenzene (1), 1-ferrocenyl-2,4-diphenylbenzene (2), and 1-ferrocenyl-2,4-ditrimethylsilylbenzene (3), were synthesized by cycloaddition of ferrocenylacetylene cobalt cluster with dif

Full text of DOI:10.1080/00958972.2012.732696

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An effective method for the synthesis
of monoferrocenylbenzene derivatives
Rui-Jun Xie a , Li-Min Han a , Yuan-Yuan Gao b , Ning Zhu a , Hai-
Long Hong a & Quan-Ling Suo a
a Chemical Engineering College, Inner Mongolia University of
Technology , Hohhot 010051 , P.R. China
b Department of Chemistry , Nankai University , Tianjin 300071 ,
P.R. China
Accepted author version posted online: 21 Sep 2012.Published
online: 11 Oct 2012.
To cite this article: Rui-Jun Xie , Li-Min Han , Yuan-Yuan Gao , Ning Zhu , Hai-Long Hong & Quan-
Ling Suo (2012) An effective method for the synthesis of monoferrocenylbenzene derivatives,
Journal of Coordination Chemistry, 65:23, 4086-4095, DOI: 10.1080/00958972.2012.732696
To link to this article: http://dx.doi.org/10.1080/00958972.2012.732696
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Journal of Coordination Chemistry
Vol. 65, No. 23, 10 December 2012, 4086–4095
An effective method for the synthesis of
monoferrocenylbenzene derivatives
RUI-JUN XIEy, LI-MIN HAN*y, YUAN-YUAN GAOz, NING ZHUy,
HAI-LONG HONGy and QUAN-LING SUOy
yChemical Engineering College, Inner Mongolia University of Technology,
Hohhot 010051, P.R. China
zDepartment of Chemistry, Nankai University, Tianjin 300071, P.R. China
(Received 11 May 2012; in final form 27 August 2012)
Three new ferrocenylbenzene derivatives, 1-ferrocenyl-2,3,4,5-tetramethylbenzene (1),
1-ferrocenyl-2,4-diphenylbenzene (2), and 1-ferrocenyl-2,4-ditrimethylsilylbenzene (3), were
synthesized by cycloaddition of ferrocenylacetylene cobalt cluster with different alkynes and
characterized by elemental analysis, FT-IR, NMR, and MS. The molecular structures of 2 and
3 were identified by single-crystal X-ray diffraction. The oxidation potentials of ferrocenyl unit
in these compounds were investigated by cyclic voltammetry and theoretical calculations.
The results indicated that the electron-donating or electron-withdrawing effect of substituents
on the central phenyl was the key factor that influenced the oxidation potential of the
ferrocenyl unit.
Keywords: Ferrocenylbenzene derivatives; Ferrocenylacetylene cobalt cluster; Oxidation
potential
1. Introduction
Since aryl-ferrocene derivatives can be used in nonlinear optical materials [1], magnetic
materials [2], biology, pharmacy [3], and asymmetric catalysis [4], attention has grown
for synthesis of aryl-ferrocene derivatives. Several methods have been reported for
synthesis of aryl-ferrocenes. The typical method is cross-coupling, such as arylation of
ferrocene with aryldiazonium salts [5–8], the Negishi reaction of halobenzenes and
ferrocenylzinc chloride with Pd(PPh3)4 as catalyst [9], the Suzuki reaction of
ferrocenylboronic acid and halobenzenes with PdCl2 derivatives as catalyst [10], the
Stille reaction of ferrocenyltin and halobenzenes [11], and the Pd-catalyzed cross-
coupling of diferrocenyl mercury with halobenzenes [12]. The classical method is
cycloaddition, such as the transition metal catalyzed [2 þ 2 þ 2] cycloaddition with
ferrocenylacetylene [13–15], the [2 þ 4] cycloaddition Diels–Alder reaction between
tetraphenylcyclopentadienone and ferrocenylacetylene derivatives [16, 17] and the
*Corresponding author. Email: hanlimin_442@hotmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.732696

Ferrocenylbenzene derivatives
4087
[3 þ 3] cyclization reaction by using 1-ꢀ5-ferrocenyl-3,3-bis(methylthio)prop-2-en-1-
ones as the 1,3-electrophile [18]. Another method is reaction of tetraalkylcyclobuta-
diene–AlCl3 complexes with 3-ferrocenylpropynoates [19].
Cobalt complex-catalyzed cycloaddition of acetylenes were reported by Kruerke, and
¨
a rational catalytic reaction mechanism was proposed (scheme 1) simultaneously [20].
Although Co2(CO)8 and acetylene react in one pot, the four-step reactions were carried
out. However, several cycloaddition products were produced when two alkynes were
used in Kruerke’s reaction. Based on this mechanism and our previous work on the
¨
synthesis of cobalt clusters [21–23], we decomposed Kruerke’s reaction processes. In
¨
this article, the intermediate product with monoferrocenyl group, Co2(CO)6(ꢁ2-
ferrocenylacetylene), was synthesized in advance. Then, it was used as a precursor to
react with 2-butyne, phenylacetylene, and trimethylsilylacetylene, respectively. Three
new monoferrocenylbenzene derivatives were synthesized (scheme 2). The redox
potentials of the ferrocenyl unit were investigated by cyclic voltammetry and theoretical
calculations, showing the effect of substituents on the central phenyl ring.
2. Experimental
2.1. General procedures
All operations were carried out under an atmosphere of purified argon using
standard Schlenk techniques. Octacarbonyl dicobalt, 2-butyne, phenylacetylene,
Scheme 1. Mechanism of Co2(CO)8-catalyzed cycloaddition of alkynes.
Scheme 2. Syntheses of 1–3.

4088
R.-J. Xie et al.
and trimethylsilylacetylene were obtained from Alfa-Asia Chem. Ferrocenylacetylene
and Co2(CO)6(ꢁ2-ferrocenylacetylene) were prepared according to the previously
reported method [24]. Dioxane was distilled under nitrogen over sodium. Reactions
were monitored by thin layer chromatography.
IR spectra were measured on a Nicolet FT-IR spectrometer using KBr pellets.
1
Elemental analysis was carried out on an Elementar var III-type analyzer. H- and
13C-NMR spectra were recorded on a Jeol-Jnm-Al 500FT-MHz spectrometer in
CDCl3. Mass spectra were determined using a Micromass LCT instrument. The crystal
structures of 2 and 3 were measured on a Bruker SMART APEX CCD diffractometer
˚
with graphite monochromated Mo-Ka (ꢂ ¼ 0.71073 A) radiation. Data were collected
using the ꢃ and ! scan techniques. The structures were solved using direct methods and
expanded using Fourier techniques. An absorption correction based on SADABS was
applied. Structure solution and refinement were performed using SHELXSL 97 [25].
Cyclic voltammetry experiments were performed on a CHI 760C electrochemical
analyzer using a platinum disc of radius 0.8 mm as a working electrode. The electrode
surface was polished with 0.05 mm alumina before each run. The reference electrode was
Ag|AgCl and the auxiliary electrode was a coiled platinum wire. The supporting
electrolyte used in all electrochemical experiments was tetra-n-butylammonium
hexafluorophosphate (TBAHFP) with concentration 0.1 in acetonitrile and dichlor-
omethane (1 : 1, v : v). Oxygen was purged from the one-compartment cell before the
electrochemical run. Calculations were carried out on a personal computer with
Gaussian 03 program package.
2.2. Synthesis of 1-ferrocenyl-2,3,4,5-tetramethylbenzene (1)
Co2(CO)6(ꢁ2-ferrocenylacetylene) (112.6 mg, 0.227 mmol) and 2-butyne (0.036 mL,
0.46 mmol) were dissolved in dioxane (10 mL) at 0ꢀC. The reaction solution was stirred
for 1 h at 0ꢀC and 3 h at 70ꢀC, then cooled to room temperature. The solvent was removed
in vacuum. The residues were dissolved in a minimum of dichloromethane and subjected
to chromatographic separation on a neutral alumina column (È ¼ 2.0 ꢁ 30.0 cm. Elution
with a mixture of hexane and dichloromethane (3 : 1, v/v) afforded a yellow band (1).
Crystals of 1 were obtained by recrystallizing from a mixture of hexane and
dichloromethane. Yield: 73.0%; m.p. 90–91ꢀC. Anal. Calcd for C20H22Fe: C, 75.48; H,
6.97. Found: C, 75.19; H, 6.38. IR (KBr, disc): 3093.19 [Cp, ꢄC–H]; 3007.57 [Ph, ꢄC–H];
2918.05, 2859.68 [CH3, ꢄC–H]; 1603.29, 1497.51 [Ph, ꢄC¼C]; 1104.43, 1053.84, 995.35 [Cp,
ꢅ
C–H]; 820.32 [Cp, ꢆC–H]. 1H-NMR (500 MHz, CDCl3, ꢅ): 2.21 [s, 3H, CH3–H], 2.22 [s,
3H, CH3–H], 2.27 [s, 3H, CH3–H], 2.33 [s, 3H, CH3–H]; 4.16 [s, 5H, Cp–H], 4.26 [s, 2H,
Cp–H], 4.38 [s, 2H, Cp–H]; 7.43 [s, 1H, Ph–H]. 13C-NMR (125 MHz, CDCl3, ꢅ): 16.20,
16.69, 17.77, 21.00 [CH3]; 67.56, 69.64, 70.61 [Cp]; 130.57, 132.48, 133.04, 133.50, 134.52,
135.45 [Ph]. MS (ESI, relative abundance): 318.3 (Mþ, 100%).
2.3. Synthesis of 1-ferrocenyl-2,4-diphenylbenzene (2)
Co2(CO)6(ꢁ2-ferrocenylacetylene) (101.2 mg, 0.204 mmol) and phenylacetylene
(0.045 mL, 0.41 mmol) were dissolved in dioxane (10 mL) at room temperature. The
solution was stirred for 1 h at room temperature and 3 h at 70ꢀC. The solvent was
removed in vacuum. The residues were dissolved in a minimum of dichloromethane and

Ferrocenylbenzene derivatives
subjected to chromatographic separation on
4089
a
neutral alumina column
(È ¼ 2.0 ꢁ 30.0 cm. Elution with a mixture of hexane and dichloromethane (5 : 1, v/v)
afforded a yellow band (2). Crystals of 2 were obtained by recrystallizing from a mixture
of hexane and dichloromethane. Yield: 72.6%; m.p. 185–186ꢀC. Anal. Calcd for
C28H22Fe: C, 81.17; H, 5.35. Found: C, 81.30; H, 5.48. IR (KBr, disc): 3085 [Cp, ꢄC–H];
3050 [Ph, ꢄC–H]; 1602, 1485 [Ph, ꢄC¼C]; 1108, 999 [Cp, ꢅC–H]; 820 [Cp, ꢆC–H]; 761, 695 [Ph,
ꢆ
C–H]. 1H-NMR (500 MHz, CDCl3, ꢅ): 4.06 [s, 5H, Cp–H], 4.08 [s, 2H, Cp–H], 4.11 [s, 2H,
Cp–H]; 7.20–7.35 [m, 6H, Ph–H], 7.42–7.46 [m, 3H, Ph–H], 7.58 [d, 1H, J ¼ 8.0 Hz,
central Ph–H], 7.58 [d, 2H, J ¼ 7.5 Hz, Ph–H], 7.91 [d, 1H, J ¼ 8.0 Hz, central Ph–H]. 13C-
NMR (125 MHz, CDCl3, ꢅ): 68, 69, 70, 86 [Cp], 125, 126, 127, 127, 128, 128, 129, 129, 131,
136, 138, 140, 141, 142 [Ph]. MS (ESI, relative abundance): 414.2 (Mþ, 100%).
2.4. Synthesis of 1-ferrocenyl-2,4-ditrimethylsilylbenzene (3)
Co2(CO)6(ꢁ2-ferrocenylacetylene) (96.3 mg, 0.194 mmol) and trimethylsilylacetylene
(0.056 mL, 0.4 mmol) were dissolved in dioxane (10 mL) at room temperature. The
solution was stirred for 1 h at room temperature and 3 h at 70ꢀC and then cooled to
room temperature. The solvent was removed in vacuum. The residues were dissolved in
a minimum of dichloromethane and subjected to chromatographic separation on a
neutral alumina column (È ¼ 2.0 ꢁ 30.0 cm. Elution with a mixture of hexane and
dichloromethane (5 : 1, v/v) afforded a yellow band (3). Crystals of 3 were obtained
by recrystallizing from a mixture of hexane and dichloromethane. Yield: 68.4%; m.p.
105–106ꢀC. Anal. Calcd for C22H30FeSi2: C, 65.00; H, 7.44. Found: C, 65.25; H, 7.18.
IR (KBr, disc): 3093 [Cp, ꢄC–H]; 3046 [Ph, ꢄC–H]; 2953, 2890 [CH3, ꢄC–H]; 1579, 1497
[Ph, ꢄC¼C]; 1248 [Si(CH3)3, ꢅC–H]; 1123, 1061, 1003 [Cp, ꢅC–H]; 855 [Si(CH3)3, ꢄSi–C]; 828
1
[Cp, ꢆC–H]. H-NMR (500 MHz, CDCl3, ꢅ): 0.07 [s, 9H, Si(CH3)3–H], 0.30 [s, 9H,
Si(CH3)3–H]; 4.20 [s, 5H, Cp–H], 4.26 [s, 2H, Cp–H], 4.41 [s, 2H, Cp–H]; 7.94 [d, 1H,
J ¼ 7.5 Hz, Ph–H], 7.64 [s, 1H, Ph–H], 7. 55 [dd, 1H, J1 ¼ 7.5 Hz, J2 ¼ 1.0 Hz, Ph–H].
13C-NMR (125 MHz, CDCl3, ꢅ): ꢂ1 [Si(CH3)3], 0.96 [Si(CH3)3]; 67, 69, 71, 93 [Cp];
131, 133, 137, 138, 139, 145 [Ph]. MS (ESI, relative abundance): 406.3 (Mþ, 100%).
3. Results and discussion
3.1. Syntheses of 1–3
If Co2(CO)8-catalyzed cycloaddition reactions of ferrocenylacetylene and other alkynes
(2-butyne, phenylacetylene or trimethylsilylacetylene) were carried out in one pot, self-
cycloaddition or co-cycloaddition occurs; the molar ratio of alkynes may be different
(1 : 2 or 2 : 1) in co-cycloaddition reactions. These reactions are seldom specific;
products are varied and difficult to separate (scheme 3).
In this article, to obtain monoferrocenyl-substituted benzene, the monoferrocenyl
cobalt carbonyl cluster Co2(CO)6(ꢁ2-ferrocenylacetylene) was synthesized first, then
used as a reaction precursor to perform cycloaddition with other alkynes, and the molar
ratio of Co2(CO)6(ꢁ2-ferrocenylacetylene) and alkynes was controlled strictly in 1 : 2.
Only the 1,2,4-substituted benzenes were obtained and 1,3,5-substituted benzenes were

4090
R.-J. Xie et al.
Scheme 3. The Co2(CO)8-catalyzed cycloaddition of different alkynes in one pot.
not found in reactions of 2 and 3. This may be ascribed to steric hindrance. The
reactions carried out in this work are illustrated in scheme 2.
3.2. Characterizations of 1–3
The three compounds were confirmed by FT-IR, 1H-NMR, 13C-NMR, elemental
analysis, and MS (data listed in section 2). The molecular structures of 2 and 3 were
determined by single-crystal X-ray diffraction (figures 1 and 2). Crystal data and
relevant structural parameters are enumerated in table 1. Selected bond lengths and
torsion angles are listed in table 2.
Both 2 and 3 crystallize in the monoclinic space group C2/c. The average C–C bond
˚
lengths in Fc units are 1.41 A, while the average Fe–C bond lengths are 2.04 A. The
˚
˚
length from Fe to Cp ring plane is 1.643 to 1.650 A. There is no significant difference
from other ferrocenyl groups. The dihedral angle of two Cp ring planes in each
ferrocene of 2 and 3 is 0.82ꢀ and 2.46ꢀ, indicating the Cp rings are nearly parallel. The
dihedral angles of Cp ring plane to central phenyl ring plane in 2 are 41.54ꢀ and 51.90ꢀ.
The maximum torsion angle of central benzene rings in 2 and 3 is 2.69ꢀ (table 2),
showing that six carbons of phenyl are approximately co-planar. Ferrocenes are
˚
attached to the central phenyl ring with bonds lengths of C9–C11 1.484 A (2) and C3–C4
˚
1.481 A (3).
As expected, chemical shifts of protons on the central phenyl are sensitive to the
electron-withdrawing or electron-donating effect of substituent groups. For example, 1
with four electron-donating substituents (methyl) on the central phenyl has proton
NMR of central benzene ring at 7.43 ppm, upfield from ferrocenylbenezene. The central
phenyls of 2 and 3 are substituted by strong electron-withdrawing groups (phenyl
and trimethylsilyl), so the proton NMR of central benzene shows downfield shift at
7.58–7.91 ppm and 7.55–7.94 ppm, respectively.
3.3. Electrochemistry
Oxidation potential and reversibility of 1–3 and ferrocenylbenzene (FcB) were
determined by cyclic voltammetry (synthesis and characterization of FcB are seen in

Ferrocenylbenzene derivatives
4091
Figure 1. Molecular structure of 2.
Figure 2. Molecular structure of 3.

4092
R.-J. Xie et al.
Table 1. Crystal data and structural parameters of 2 and 3.
Compounds
2
3
Empirical formula
Formula weight
Temperature (K)
C28H22Fe
414.31
296(2)
0.71073
Monoclinic
C2/c
C22H30FeSi2
406.49
296(2)
0.71073
Monoclinic
C2/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions (A, )
ꢀ
˚
a
b
c
ꢇ
ꢈ
ꢆ
34.0052(12)
6.0997(2)
20.8358(6)
90.00
112.690(2)
90.00
3987.3(2), 8
1.380
0.768
37.105(5)
6.1225(8)
22.062(3)
90.00
119.234(2)
90.00
4373.6(10), 8
1.235
0.801
3
˚
Volume (A ), Z
Calculated density (Mg mꢂ3
)
Absorption coefficient (mmꢂ1
F(000)
)
1728
1728
Crystal size (mm3)
ꢉ range for data collection (ꢀ)
Limiting indices
0.15 ꢁ 0.03 ꢁ 0.03
1.30–28.31
ꢂ41 ꢃ h ꢃ 45;
ꢂ7 ꢃ k ꢃ 8;
ꢂ26 ꢃ l ꢃ 27
18,964
0.15 ꢁ 0.05 ꢁ 0.05
1.86–28.24
ꢂ48 ꢃ h ꢃ 40;
ꢂ7 ꢃ k ꢃ 8;
ꢂ18 ꢃ l ꢃ 28
13,450
Reflections collected
Independent reflections
Completeness to ꢉ (%)
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I 4 2ꢊ(I)]
R indices (all data)
4920
99.4
0.8936/0.9773
4920/0/262
0.963
R1 ¼ 0.0513, wR2 ¼ 0.0859
R1 ¼ 0.1525, wR2 ¼ 0.1129
0.327 and ꢂ0.511
5266
97.5
0.8936/0.9773
5266/0/232
1.022
R1 ¼ 0.0418, wR2 ¼ 0.1057
R1 ¼ 0.0723, wR2 ¼ 0.1190
0.313 and ꢂ0.232
ꢂ3
˚
Largest difference peak and hole (e A
)
ꢀ
˚
Table 2. Selected bond lengths (A) and torsion angles ( ) of 2 and 3.
Compound 2
C11–C12
C14–C15
C9–C11
C11–C12–C13–C14
C14–C15–C16–C11
1.391(4)
1.391(4)
1.484(4)
0.28
C12–C13
C15–C16
C14–C23
C12–C13–C14–C15
C15–C16–C11–C12
1.374(4)
1.395(4)
1.480(4)
C13–C14
C16–C11
C11–C16
C13–C14–C15–C16
C16–C11–C12–C13
1.387(4)
1.406(4)
1.406(4)
0.43
ꢂ0.87
0.61
ꢂ1.19
0.78
Compound 3
C1–C2
C8–C3
C3–C4
C1–C2–C5–C8
C8–C3–C6–C1
1.387(3)
1.388(3)
1.481(3)
C2–C5
C3–C6
C6–Si2
C2–C5–C8–C3
C3–C6–C1–C2
1.389(3)
C5–C8
C6–C1
C2–Si3
C5–C8–C3–C6
C6–C1–C2–C5
1.378(3)
1.401(3)
1.870(2)
1.27
1.405(3)
1.882(2)
0.89
ꢂ1.41
ꢂ2.69
2.24
ꢂ0.19
‘‘Supplementary material’’). The cyclic voltammograms (CVs) of 1–3 and FcB, depicted
in figure 3, display one electrochemically reversible redox wave, assigned to the
Fe(II)/Fe(III) redox couples. The oxidation potentials of 1, 2, 3, and FcB are 499 mV,
536 mV, 541 mV, and 526 mV, respectively (table 3). The oxidation potential of 1 shifts
negatively and the oxidation potentials of 2 and 3 shift positively compared to FcB,
indicating the substituent of central phenyl influences oxidation potential of ferrocenyl.

Ferrocenylbenzene derivatives
4093
ferrocenylbenzene
1
0
1
2
3
0
0.5
1
E / V vs Ag|AgCl
Figure 3. The CVs of 1, 2, 3, and ferrocenylbenzene.
Table 3. CV data and Mulliken charge density of 1–3 and FcB.
Oxidation
potential
(mV)
Mulliken
charge density
of ‘‘Fe’’ atom
Compounds
1
2
3
FcB
499
536
541
526
0.624
0.575
0.561
0.600
The difference in oxidation potential can be ascribed to the electron-donating and
electron-withdrawing effects of groups on the central phenyl. The electron-donating
1
effect of methyl has been identified by H-NMR of 1 and the protons of the central
phenyl shift upfield, so the oxidation potential of 1 is negative to that of FcB. The
electron-withdrawing effect of phenyl and trimethylsilyl in 2 and 3 can also be identified
1
by H-NMR, and the oxidation potentials of 2 and 3 are positive to that of FcB.
Configuration of central phenyls were not obviously changed, maintaining planar
character. Thus the electron-donating and electron-withdrawing effects of substituents
partially transfer to ferrocenyl unit through central phenyl. This result is consistent with
that obtained in our previous work [26].
Based upon a starting geometry from the X-ray structure analysis of 2, 3, and FcB,
Mulliken population analyses were carried out using the B3LYP density function and the
6–31G basis set [27]. We also obtained optimized geometry and Mulliken atomic charge
of 1 using the B3LYP density function and the 6–31G basis set. The Mulliken atomic
charge density of ‘‘Fe’’ in 1, 2, 3, and FcB are 0.624, 0.575, 0.561, and 0.600, respectively
(table 3), indicating the charge density of iron increased by the electron-donating of
methyl in 1. The charge density of iron was decreased by the electron-withdrawing of

4094
R.-J. Xie et al.
phenyl and trimethylsilyl in 2 and 3, consistent with oxidation potentials positive to that
of FcB.
4. Conclusion
Three monoferrocenylbenzene derivatives, 1-ferrocenyl-2,3,4,5-tetramethylbenzene (1),
1-ferrocenyl-2,4-diphenylbenzene (2), and 1-ferrocenyl-2,4-ditrimethylsilylbenzene (3),
were obtained by cycloaddition with Co2(CO)6(ꢁ2-ferrocenylacetylene) as precursor.
The oxidation potentials of 1–3 and FcB were investigated by cyclic voltammetry and
theoretical calculations; the electron-donating or electron-withdrawing of substituent
on the central phenyl affected oxidation potential of the ferrocenyl unit.
Supplementary material
Crystallographic data for structures reported in this article in the form of CIF files have
been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication CCDC Nos 816932 and 816930 for 2 and 3, respectively. Copy of the data
can be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: þ44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk).
Acknowledgments
We are grateful to the Program for New Century Excellent Talents in University
(NCET-08-858) and the Natural Science Foundation of China (NSFC-21062011).
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