Synthesis of ortho-diferrocenylbenzene with cobalt clusters as reaction precursors: Crystal structure and electrochemical properties

Article abstract of DOI:10.1016/j.poly.2012.02.018

Five new ortho-diferrocenylbenzene derivatives, 1,2-diferrocenyl-4,5- dimethylbenzene (2), 1,2-diferrocenyl-4,5-diphenylbenzene (3), 1,2-diferrocenyl-4,5-ditrimethylsilylbenzene (4), 1,2-diferrocenyl-3,4,5,6- tetramethylbenzene(5), and 1,2-diferrocenyl-3,4,5,6-tetraphenyl -benzene (6), were synthesized through the cycloaddition reactions of alkynes with the cobalt cluster Co₂(CO)₆(μ²-alkyne) as reaction precursors, and characterized by elemental analysis, FT-IR, NMR, and MS. The molecular structures of compounds (2-6) were identified using single-crystal X-ray diffraction, and the electron interactions between two ferrocenyl units of each of the five compounds were investigated using cyclic voltammetric techniques. The results of electrochemical experiment indicated that the charge density of the aryl bridge is the key factor that influences electron communications between two ferrocenyl units.

Full text of DOI:10.1016/j.poly.2012.02.018

Polyhedron 38 (2012) 7–14
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis of ortho-diferrocenylbenzene with cobalt clusters as reaction
precursors: Crystal structure and electrochemical properties
⇑
Rui-Jun Xie, Li-Min Han , Ning Zhu, Hai-Long Hong, Quan-Ling Suo, Peng Fu
Chemical Engineering College, Inner Mongolia University of Technology, Hohhot 010051, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Five new ortho-diferrocenylbenzene derivatives, 1,2-diferrocenyl-4,5-dimethylbenzene (2), 1,2-diferr-
ocenyl-4,5-diphenylbenzene (3), 1,2-diferrocenyl-4,5-ditrimethylsilylbenzene (4), 1,2-diferrocenyl-
3,4,5,6-tetramethylbenzene(5), and 1,2-diferrocenyl-3,4,5,6-tetraphenyl -benzene (6), were synthesized
Received 29 November 2011
Accepted 2 February 2012
Available online 3 March 2012
through the cycloaddition reactions of alkynes with the cobalt cluster Co2(CO)6(l
2-alkyne) as reaction
precursors, and characterized by elemental analysis, FT-IR, NMR, and MS. The molecular structures of
compounds (2–6) were identified using single-crystal X-ray diffraction, and the electron interactions
between two ferrocenyl units of each of the five compounds were investigated using cyclic voltammetric
techniques. The results of electrochemical experiment indicated that the charge density of the aryl bridge
is the key factor that influences electron communications between two ferrocenyl units.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Ortho-diferrocenylbenzene derivatives
Carbonyl cobalt
Electronic interaction
1. Introduction
Krüerke and Hübel utilized the cobalt carbonyl cluster
[Co2(CO)8]-catalyzed cycloaddition reactions of alkynes to prepare
The intramolecular electron transfer processes of multi-ferroce-
nyl derivatives are highly interesting in the field of organometallic
electrochemistry [1–6]. In the frame of a general study of such pro-
cesses, we had examined the factors that affect the charge transfer
processes of aliphatic carbon-bridged biferrocenyl derivatives, and
found that the charge density of the carbon bridge was a key factor
for intramolecular electron transfers [7]. Determining the phenom-
ena that should be present in aromatic-bridged diferrocenyl deriva-
tives is the backbone of this research on the synthesis and
electrochemistry of aromatic-bridged ortho-diferrocenylbenzene
derivatives.
Diferrocenylbenzene derivatives are prepared via the Nigishi or
Suzuki reactions. A typical synthesis, for instance, involves the
Nigishi reaction of dihalobenzenes and ferrocenylzinc chloride
with the catalyst of Pd(PPh3)4 form para-diferrocenylbenzene [8];
para-diferrocenylbenzene and meta-diferrocenylbenzene are syn-
thesized through the Suzuki reaction of ferrocenylboronic acid
and dihalobenzenes in a dimethoxyethane/aqueous NaOH mixture
solution, using PdCl2(dppf) as a catalyst [9,10]. Unfortunately,
these cross-coupling reactions are not suitable for the synthesis
of ortho-diferrocenylbenzene, and the highest yield of ortho-
diferrocenylbenzene reported for these methods is only 8% [11].
Thus, it is necessary to devise a simple and efficient method of
preparing ortho-diferrocenylbenzene derivatives.
substituted benzene derivatives, and described a logical and
rational catalytic reaction mechanism (see Scheme 1) [12]. Based
on this mechanism, as well our previous work on the synthesis
of cobalt clusters [13–15], we modified Krüerke’s one-step synthe-
sis method and turned it into a two-step method: The cobalt clus-
ter [Co2(CO)6(l
2-alkyne)] was synthesized in the first step, and
then used as a reaction precursor in the cycloaddition reaction
with other alkynes in the second step. This synthetic method could
conveniently control the position, type and number of substituted
ferrocenyl groups in the benzene ring in the resulting products.
In this paper, the position-controlled synthesis of several
ortho-diferrocenylbenzenes was realized for the first time using
Co2(CO)6(l l
2-diferrocenyl acetylene) and Co2(CO)6( 2-2-butyne)
as precursors. Five new ortho-diferrocenylbenzene derivatives
were prepared via our two-step synthesis method, and the effect
of the aromatic bridge on the electron communication processes
between two ferrocenyl units is investigated using cyclic
voltammetry.
2. Experimental
2.1. General procedures
All operations were carried out under an atmosphere of purified
argon using standard Schlenck techniques. Solvents were dried and
distilled according to standard procedures. Reactions were moni-
tored by thin layer chromatography (TLC). Co2(CO)8, HC„CC6H5,
HC„CSi(CH3)3, H3CC„CCH3 and H5C6C„CC6H5 were obtained
⇑
Corresponding author. Tel.: +86 471 6576137; fax: +86 471 6575722.
E-mail address: hanlimin_442@hotmail.com (L.-M. Han).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.02.018

8
R.-J. Xie et al. / Polyhedron 38 (2012) 7–14
R1
R1
R3
R1
R1
OC
O
C
O
C
CO
OC
OC Co
CO
OC
R2
R3
+ R1
R1
OC Co
OC
Co CO
CO
OC
OC Co
Co CO
CO
OC
R2
Co
OC CO
R1
R1
R3
R1
R1
R3
R2
R1
OC
R3
R1
R2
R3
R2
R3
CO
OC Co
Co
R3
OC
OC
Co
CO
OC
R2
R2 R2
Co
OC
CO
Scheme 1. The mechanism of Co2(CO)8-catalyzed cycloaddition of alkynes.
from Alfa-Asia Chem. Ferrocenylacetylene and 1,2-diferrocenyl-
acetylene were prepared using methods found in the literature
[16,17]. Infrared (IR) spectra were measured on a Nicolet FT-IR
spectrometer using KBr pellets. Elemental analyses were carried
out on an Elementar var III-type analyzer. 1H and 13C NMR spectra
in CDCl3 were recorded on a Jeol-Jnm-Al 500 FT-MHz spectrome-
ter. The mass spectra were determined using a Micromass LCT
2.3. Synthesis of 1,2-diferrocenyl-4,5-dimethylbenzene (2)
2-2-butyne) (109 mg, 0.32 mmol) and ferrocenyl-
Co2(CO)6(
l
acetylene (134 mg, 0.64 mmol) were dissolved in 10 mL dioxane
at room temperature. The solution was stirred for 3 h at 70 °C
and then cooled to room temperature. The solvent was removed
under vacuum. The residues were dissolved in a minimal amount
of CH2Cl2 and subjected to chromatographic separation on a neu-
tral alumina column (2.0 cm ꢀ 30 cm). Elution with a mixture of
hexane and CH2Cl2 (3:1, v/v) afforded an orange band 2. Crystals
of 2 were obtained by recrystallizing solid 2 from a mixture of hex-
ane and CH2Cl2 at ꢁ20 °C. Yield: 94 mg (63%). M.p. 155 °C. Anal.
Calc. for C28H26Fe2: C, 70.92; H, 5.53. Found: C, 70.68; H, 5.16%.
instrument. The crystal structures of Co2(CO)6(l
2-diferrocenylacet-
ylene) (1), 1,2-diferrocenyl-4,5-dimethylbenzene (2), 1,2-diferr
ocenyl-4,5-diphenylbenzene (3), 1,2-diferrocenyl-4,5-ditrimethyl-
silylbenzene (4), 1,2-diferrocenyl-3,4,5,6-tetramethylbenzene (5),
and 1,2-diferrocenyl-3,4,5,6-tetraphenyl-benzene (6) were deter-
mined on a Bruker SMART APEX CCD diffractometer with graphite
monochromated Mo
collected using the
K
and
a
(k = 0.71073 Å) radiation. Data were
scan techniques. The structures were
IR (KBr cmꢁ1): 3089
CH3), 1599, 1501 (CC, Ph). 1108, 1002 d(CH, Cp, monosubstituted
ferrocene) [18,19], 816 k(CH, Cp). 1H NMR (500 MHz CDCl3): d 2.33
(s, 6H, CH3), 3.99–4.19 (m, 18H, Cp–H), 7.53 (s, 2H, Ph–H) ppm. 13
m(CH, Cp), 3058 m(CH, Ph), 2958, 2861 m(CH,
u
x
m
solved using direct methods and expanded using Fourier tech-
niques. An absorption correction based on the SADABS was applied.
C
Structure solution and refinement were performed using SHELXSL
97 software.
Cyclic voltammetry was performed on a CHI 760C electrochem-
ical analyzer, using a platinum disk as the working electrode; the
-
NMR (125 MHz CDCl3): d 19.7 (CH3), 66.8, 67.2, 69.3, 69.5, 69.6,
70.7, 71.2, 72.9, 88.0 (Cp), 132.7, 134.1, 134.7 (benzene) ppm. MS
(ESI) m/z: 474.2 [M+].
electrode surface was polished with 0.05 lm alumina prior to each
2.4. Synthesis of compounds 3–6
run. The reference electrode was an Ag/AgCl electrode, and the
auxiliary electrode was a coiled platinum wire. The solvent was
composed of dichloromethane and acetonitrile (1:1, v/v) contain-
ing 0.1 M tetra-n-butylammonium hexafluorophosphate as a sup-
porting electrolyte. The scan rate was 0.1 V/s. The different
concentration (3.8 mmol/L for 2, 6.0 mmol/L for 3, 3.2 mmol/L for
4, 6.1 mmol/L for 5 and 2.3 mmol/L for 6) were used for the cyclic
voltammetries. Oxygen was purged from the one-compartment
cell before each electrochemical run.
The synthetic method for the preparation of 3–6 is very similar.
Co2(CO)6(l
2-diferrocenylacetylene) and corresponding alkynes
were dissolved in 10 mL dioxane at room temperature. The mix-
ture solution was stirred for 3 h at 70 °C and then cooled to room
temperature (the mixture solution was stirred for 1 h at 0 °C and
for 3 h at 70 °C and then cooled to room temperature for the syn-
thesis of compound 5), after which the solvent was removed under
vacuum. The residues were dissolved in a minimal amount of
CH2Cl2 and subjected to chromatographic separation on a neutral
alumina column (2.0 cm ꢀ 30 cm). Elution with a mixture of hex-
ane and CH2Cl2 afforded an orange band. Crystals were obtained
by recrystallizing solid from a mixture of hexane and CH2Cl2 at
ꢁ20 °C.
2.2. Synthesis of Co2(CO)6(l
2-diferrocenylacetylene) (1)
A dioxane solution of Co2(CO)8 (123 mg, 0.36 mmol) and diferr-
ocenylacetylene (142 mg, 0.36 mmol) was stirred for 2 h at room
temperature, after which the solvent was removed under reduced
pressure. The residue was dissolved in a minimal amount of hex-
ane and subjected to chromatographic separation on a silica gel
column (2.0 cm ꢀ 30 cm). Elution with hexane afforded a dark
green band 1. Crystals of 1 were obtained by recrystallizing solid
1 from hexane at ꢁ20 °C. Yield: 229 mg (94%). M.p. 141 °C. Anal.
Calc. for C28H18Fe2Co2O6: C, 49.46; H, 2.67. Found: C, 49.32; H,
2.4.1. Compound 3
Co2(CO)6(l
2-diferrocenylacetylene) (96 mg, 0.14 mmol) and
HC„CC6H5 (0.03 mL, 0.28 mmol) were used as starting material.
After finished the reaction, a mixture of hexane and CH2Cl2 (3:1,
v/v) was used for eluent in the purification process. Yield: 54 mg
(64%). M.p. 290 °C. Anal. Calc. for C38H30Fe2: C, 76.28; H, 5.05.
2.86%. IR (KBr, cmꢁ1): 3089
m
(CH, Cp), 2058, 1986
m(CO), 1103,
Found: C, 76.06; H, 4.89%. IR (KBr cmꢁ1): 3081
m(CH, Cp), 3023
1002 d(CH, Cp), 816 k(CH, Cp). 1H NMR (500 MHz, CDCl3): d
4.063–4.616 (m, 18H, Cp–H) ppm. 13C NMR (125 MHz, CDCl3): d
69.3, 69.9, 70.2, 86.2, 92.9 (Cp), 199.9 (CO) ppm. MS (ESI) m/z:
680.0 [M]+.
m(CH, Ph); 1602, 1484 m(CC, Ph), 1104, 1069 d(CH, Cp), 812 k(CH,
Cp), 762, 699 k(CH, Ph). 1H NMR (500 MHz CDCl3): d 3.57–4.32
(m, 18H, Cp–H), 7.09–7.62 (br, 10H, substituted benzene), 7.85 (s,
2H, central phenyl ring) ppm. 13C NMR (500 MHz CDCl3): d 67.4,

R.-J. Xie et al. / Polyhedron 38 (2012) 7–14
9
69.5, 70.7, 87.2 (Cp), 126.5, 126.8, 128.1, 129.7, 133.6, 136.6, 137.8,
Table 1
141.4 (benzene) ppm. MS (ESI) m/z: 598.3 [M+].
Synthesis of ortho-diferrocenylbenzene with cobalt clusters as reaction precursors.
R2
R1
R1
R3
R1
R2
R3
2.4.2. Compound 4
dioxane
CO
CO
CO
OC
OC
OC
Co2(CO)6(l
2-diferrocenylacetylene) (95 mg, 0.14 mmol) and
2 R2
R3
+
Co
Co
70 °C/ 3h
HC„CSi(CH3)3 (0.04 mL, 0.30 mmol) were used as starting mate-
rial. After finished the reaction, a mixture of hexane and CH2Cl2
(3:1, v/v) was used for eluent in the purification process. Yield:
53 mg (65%). M.p. 220 °C. Anal. Calc. for C32H38Fe2Si2: C, 65.09; H,
R1
Compounds
R1
R2
R3
6.49. Found: C, 65.14; H, 6.38%. IR (KBr cmꢁ1): 3089
m
(CH, Cp),
(CH, CH3), 1633, 1528 (CC,
(SiC, TMS), 812
2
3
4
5
6
CH3
Fc
Fc
Fc
Fc
Fc
Ph
Si(CH3)3
CH3
Ph
H
H
H
CH3
Ph
3054
m
(CH, Ph), 2953, 2898, 2848
m
m
Ph), 1248 d(CH, TMS), 1108, 1003 d(CH, Cp), 839
m
k(CH, Cp), 754 k(CH, Ph). 1H NMR (500 MHz, CDCl3): d 0.47 (s,
18H, TMS–H), 4.04–4.14 (m, 18H, Cp–H), 8.08 (s, 2H, Ph–H) ppm.
13C NMR (125 MHz, CDCl3): d 2.3 (CH3), 67.5, 69.6, 70.9, 87.9
(Cp), 136.6, 138.8, 142.4 (benzene) ppm. MS (ESI) m/z: 590.1 [M+].
2.4.3. Compound 5
Co2(CO)6(l
2-diferrocenylacetylene) (106 mg, 0.16 mmol) and
H3CC„CCH3 (0.03 mL, 0.35 mmol) were used as starting material.
After finished the reaction, a mixture of hexane and CH2Cl2 (2:1,
v/v) was used for eluent in the purification process. Yield: 55 mg
(68%). M.p. 275 °C. Anal. Calc. for C30H30Fe2: C, 71.74; H, 6.02.
Found: C, 71.61; H, 6.28%. IR (KBr cmꢁ1): 3089
m(CH, Cp), 2958,
2878 m(CH, CH3), 1602, 1498 m(CC, Ph), 1104, 1053 d(CH, Cp), 816
k(CH, Cp). 1H NMR (500 MHz, CDCl3): d 2.317 (s, 6H, CH3), 2.934
(s, 6H, CH3), 3.766–4.049 (m, 18H, Cp–H) ppm. 13C NMR
(125 MHz CDCl3): d 17.04, 18.87 (CH3), 66.4, 69.1, 73.3, 89.9 (Cp),
133.0, 134.2, 134.7 (benzene) ppm. MS(ESI) m/z: 502.2 [M+].
2.4.4. Compound 6
Co2(CO)6(l
2-diferrocenylacetylene) (103 mg, 0.15 mmol) and
H5C6C„CC6H5 (54 mg, 0.30 mmol) were used as starting material.
After finished the reaction, a mixture of hexane and CH2Cl2 (2:1,
v/v) was used for eluent in the purification process. Yield: 65 mg
(58%). M.p. 302 °C. Anal. Calc. for C50H38Fe2: C, 80.02; H, 5.10.
Found: C, 79.87; H, 5.35%. IR (KBr cmꢁ1): 3089
m(CH, Cp), 3046,
3015 m(CH, Ph), 1633, 1524 m(CC, Ph), 1108, 1003 d(CH, Cp), 812
k(CH, Cp), 762, 699 k(CH, Ph). 1H NMR (500 MHz, CDCl3):
d 3.681–3.922 (m, 18H, Cp–H), 6.645–7.256 (m, 20H, Ph–H) ppm.
13C NMR (125 MHz, CDCl3): d 67.3, 69.5, 73.4 (Cp), 124.9, 126.5,
126.6, 126.7, 131.6, 133.2, 138.0, 138.7, 140.7, 141.0, 141.1
(benzene) ppm. MS (ESI) m/z: 750.0 [M+].
Fig. 1. The molecular structure of compound 1. The H atoms have been omitted for
clarity.
of ferrocenyl. These results indicate that the synthesis method we
selected was suitable for constructing ortho-diferrocenylbenzene
derivatives, and the stereoselectivity of the 4 and 5 positions
appeared to be a common law for this synthetic strategy. Guided
3. Results and discussion
3.1. Synthetic methods of compounds (2–6)
by the experiments above, we synthesized Co2(CO)6(l
2-2-butyne)
Transitional-metal-catalyzed cycloaddition reactions are widely
used to synthesize various substituted benzene derivatives. For
example, Fe, Co, Ni, Pd, Ru, Rh, and Zr have been used to catalyze
the cycloaddition reactions of alkynes. In this work, we prepared
ortho-diferrocenylbenzenes using the following procedure. First,
we performed a Co2(CO)8-catalyzed cycloaddition reaction using
diferrocenylacetylene and diphenylacetylene as reactants to pre-
pare substituted benzene. Unfortunately, hexaphenylbenzene was
produced at a yield of 76%, and no ferrocenylbenzene was obtained
(see Supplementary Materials). This result could be attributed to the
steric hindrance effect of ferrocenyl units [20]. After changing our
and used it as a precursor to react with ferrocenylacetylene. The
ortho-diferrocenyl 2 was obtained (see Table 1). The experimental
results showed that this synthetic strategy we selected was highly
efficient for the synthesis of ortho-diferrocenylbenzene derivatives.
Moreover, compounds 5 and 6, which have large steric hindrance,
could be prepared successfully by our synthetic method. This fur-
ther proved the effectiveness of our synthetic strategy for the
ortho-diferrocenylbenzene derivatives.
3.2. Characterization and molecular structure of complex (1)
synthetic strategy, we produced Co2(CO)6(l
2-diferrocenylacety-
lene), which then be used as a precursor to react with HC„CC6H5
or HC„CSi(CH3)3. Ortho-diferrocenyl compounds 3 and 4 were ob-
tained with high yields (64% and 65%, respectively), and the
trimethylsilyl and phenyl groups were located at the 4 and 5 posi-
tions of the central phenyl ring due to the steric hindrance effect
The molecular structure and IR spectra of Co2(CO)6(l
2-diferr-
ocenylacetylene) were similar to those of our previously reported
structures [Co2(CO)6(l2-R0–C„C–R)] [14]. An approximately
tetrahedral (
l
2-alkyne) dicobalt moiety was bound to the cyclo-
pentadiene rings of two ferrocenyls (see Fig. 1). The CO ligands

10
R.-J. Xie et al. / Polyhedron 38 (2012) 7–14
Table 2
Crystal data and relevant structural parameters for compounds (1–6).
Compounds
1
2
3
4
5
6
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
28H18Co2Fe2O6
C28H26Fe2
474.19
296(2)
0.71073
monoclinic
C2/c
12.606(11)
19.884(17)
9.859(15)
90.00
C38H30Fe2
598.32
296(2)
0.71073
monoclinic
P2(1)/c
10.0480(16)
22.584(4)
12.425(2)
90.00
C32H38Fe2Si2
590.50
296(2)
C30H30Fe2
502.24
296(2)
C50H38Fe2
750.17
296(2)
0.71073
monoclinic
C2/c
18.3617(19)
15.8469(16)
14.0760(15)
90.00
679.98
173(2)
0.71073
monoclinic
P2(1)/n
15.598(3)
9.9595(17)
17.267(3)
90.00
108.868(3)
90.00
2538.2(8), 4
1.779
0.71073
triclinic
0.71073
triclinic
ꢀ
ꢀ
P1
P1
6.1995(2)
12.7645(5)
18.8821(7)
89.231(2)
85.928(2)
78.566(2)
1460.86(9), 2
1.342
10.672(5)
11.382(5)
11.809(6)
63.639(8)
82.366(9)
63.099(8)
1142.0(9), 2
1.461
b (Å)
c (Å)
a
(°)
b (°)
115.031(10)
90.00
2239(4), 4
1.407
94.016(3)
90.00
2812.6(8), 4
1.413
98.250(7)
90.00
4053.4(7), 4
1.369
c
(°)
Volume (Å3), Z
Density (Mg/m3)
l
(mmꢁ1
)
2.447
1.307
1.058
1.094
1.286
0.883
F(000)
1360
984
1240
620
524
1728
Crystal size (mm)
h range (°)
Limiting indices
0.50 ꢀ 0.48 ꢀ 0.42 0.20 ꢀ 0.05 ꢀ 0.05 0.20 ꢀ 0.05 ꢀ 0.05 0.30 ꢀ 0.20 ꢀ 0.10 0.20 ꢀ 0.05 ꢀ 0.05 0.15 ꢀ 0.10 ꢀ 0.10
1.53–30.01
ꢁ21 6 h 6 20
ꢁ14 6 k 6 14
ꢁ18 6 l 6 24
25723
2.06–27.94
ꢁ15 6 h 6 15
ꢁ26 6 k 6 25
ꢁ7 6 l 6 12
6784
1.80–28.40
ꢁ13 6 h 6 13
ꢁ25 6 k 6 30
ꢁ15 6 l 6 14
18100
1.63–27.68
ꢁ8 6 h 6 8
ꢁ16 6 k 6 15
ꢁ24 6 l 6 24
24702
1.93–25.00
ꢁ12 6 h 6 12
ꢁ11 6 k 6 13
0 6 l 6 14
3930
1.71–27.94
ꢁ21 6 h 6 24
ꢁ20 6 k 6 16
ꢁ18 6 l 6 18
18095
Reflections collected
Independent reflections
Completeness to h
7206
97.4%
2592
96.0%
6874
97.2%
6665
97.6%
3930
97.6%
4754
97.7%
Maximum and minimum
Data/restraints/parameters
Goodness-of-fit on F2
0.358/0.306
7206/0/344
1.209
0.937/0.925
2592/0/137
1.069
0.948/0.938
6874/0/361
0.948
0.8985/0.7349
6665/15/331
0.995
0.938/0.926
3930/0/294
1.018
0.915/0.899
4754/0/249
1.036
Final R indices [I > 2
r
(I)]
R1 = 0.0567
wR2 = 0.1142
R1 = 0.0622
wR2 = 0.1171
0.452/ꢁ0.613
R1 = 0.0312
wR2 = 0.0819
R1 = 0.0392
wR2 = 0.0859
0.397/ꢁ0.208
R1 = 0.0540
wR2 = 0.1017
R1 = 0.1332
wR2 = 0.1268
0.471/ꢁ0.378
R1 = 0.0558
wR2 = 0.1263
R1 = 0.1267
wR2 = 0.1529
0.448/ꢁ0.653
R1 = 0.0928
wR2 = 0.2429
R1 = 0.1424
wR2 = 0.2685
1.014/ꢁ1.045
R1 = 0.0539
wR2 = 0.1590
R1 = 0.0990
wR2 = 0.1863
0.873/ꢁ0.667
R indices (all data)
Largest differences in peak and hole
(eÅꢁ3
)
Table 3
Selected bond lengths (Å) of compounds (1–6).
1
2
3
4
5
6
C7–C8
C7–C9
1.351(5)
1.448(5)
1.447(4)
1.992(3)
1.959(3)
1.974(3)
1.978(3)
2.4567(7)
C1–C12
C12–C22
C22–C32
C32–C3
C3–C2
1.426(4)
1.409(3)
1.396(3)
1.412(4)
1.396(3)
1.409(3)
1.495(3)
1.495(3)
1.517(3)
1.517(3)
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C1–C6
C1–C7
C2–C17
C4–C27
C5–C33
1.389(5)
1.400(4)
1.391(5)
1.407(5)
1.386(4)
1.389(4)
1.485(4)
1.482(5)
1.486(4)
1.491(5)
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
C1–C13
C2–C23
C4–Si1
C5–Si2
1.392(5)
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
C1–C7
C2–C17
C3–C27
C4–C28
C5–C29
C6–C30
1.447(15)
1.380(16)
1.379(18)
1.457(19)
1.365(18)
1.414(16)
1.497(16)
1.501(16)
1.523(17)
1.526(19)
1.459(19)
1.518(18)
C1–C12
C12–C22
C22–C32
C32–C3
C3–C2
1.401(7)
1.423(4)
1.400(5)
1.400(7)
1.400(5)
1.423(4)
1.496(4)
1.496(4)
1.472(5)
1.472(5)
1.496(5)
1.496(5)
1.392(5)
1.402(5)
1.444(5)
1.388(5)
1.397(5)
1.482(5)
1.479(5)
1.882(4)
1.891(4)
C8–C19
C7–Co1
C7–Co2
C8–Co1
C8–Co2
Co1–Co2
C1–C2
C2–C1
C1–C4
C1–C4
C12–C42
C3–C14
C32–C142
C12–C42
C2–C14
C22–C142
C3–C20
C32–C202
coordinated with Co atoms are terminal (vide infra). Each of the
cobalt atoms carries an ‘axial’ CO and two ‘pseudoequatorial’ CO
ligands, as indicated by the corresponding bond angles. The Co–
Co bond distance is 2.4567(7) Å and the C–C bond length of the
C2Co2 fragment is 1.351(5) Å, which are typical for alkyne dicobalt
complexes [21]. The well-defined molecular structure of 1 is a good
precondition for the synthesis of compounds (3–6).
For instance, the proton NMR peaks of the central benzene ring of
4 locate at 8.084 ppm, which shows a downfield shift compared to
2 (7.526 ppm). The carbon NMR peaks of the central benzene ring
of 4 locate at the region of 136.61–142.44 ppm, which also show a
downfield shift compared to 2 (132.70–134.69 ppm).
The molecular structures of compounds (2–6) were determined
using single crystal X-ray diffraction. Crystal data and relevant
structural parameters are listed in Table 2. Selected bond lengths
are listed in Table 3, and selected angles are listed in Table 4. The
selected torsion angles see Supplementary Materials.
3.3. Characterization and molecular structure of compounds (2–6)
The successful synthesis of compounds (2–6) was determined by
elemental analysis, FT-IR, NMR, and MS (corresponding data are
listed in the Section 2). As expected, the chemical shifts of the pro-
tons and carbons of the central benzene ring are sensitive to the
electron-withdrawing or electron-donating effects of substituents.
The molecular structure of 2 is shown in Fig. 2. The bond lengths
and bond angles of central phenyl ring are ranging from 1.396(3) to
1.426(4) Å and from 117.90(11) to 123.50(19)°, respectively. And
2
its maximum torsion angle is 4.4(2)° (C2ꢁC1ꢁC1 ꢁC22), which
shows that the six carbon atoms of the central phenyl ring are

R.-J. Xie et al. / Polyhedron 38 (2012) 7–14
11
Table 4
Selected bond angles (°) of compounds (2–6).
2
3
4
5
6
C1–C12–C22
C12–C22–C32
C22–C32–C3
C32–C3–C2
C3–C2–C1
117.90(11)
123.50(19)
118.50(12)
118.50(12)
123.50(19)
117.90(11)
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C1
C6–C1–C2
117.7(3)
123.8(3)
118.0(3)
117.8(3)
124.1(3)
118.6(3)
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C1
C6–C1–C2
118.0(3)
124.8(4)
117.2(3)
116.4(3)
125.5(4)
118.1(3)
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C1
C6–C1–C2
119.2(12)
121.9(12)
119.5(11)
118.4(12)
122.4(13)
118.0(11)
C1–C12–C22
C12–C22–C32
C22–C32–C3
C32–C3–C2
C3–C2–C1
118.33(19)
119.2(3)
119.9(2)
119.9(2)
119.2(3)
118.33(19)
C2–C1–C12
C2–C1–C12
Fig. 2. The molecular structure of compound 2. The H atoms have been omitted for clarity.
approximately co-planar. Two ferrocenyl groups are attached to
the central phenyl ring at the 1 and 2 positions with bond lengths
of 1.495(3) Å (C1–C4 and C12–C42). Two cyclopentadienyls (Cps)
present an eclipse configuration and adopt an approximate
up-down fashion. Both of dihedral angles of the central phenyl ring
and Cp planes are 37.7°, which are smaller than the reported value
(42.3°) for ortho-diferrocenyl benzene derivatives [22].
Fig. 3 shows the molecular structure of 3. The bond lengths and
bond angles of central phenyl ring are 1.386(4)–1.407(5) Å and
117.7(3)–124.1(3)°, respectively. The maximum torsion angle of
central phenyl ring is 2.9(9)° (C6ꢁC1ꢁC2ꢁC3). So the central phenyl
ring maintains a planar character. Two ferrocenyl groups are at-
tached to the central phenyl ring at the 1 and 2 positions with bond
lengths of 1.485(4) Å (C1ꢁC7) and 1.482(5) Å (C2ꢁC17). Two phenyl
groups are attached to the central phenyl ring at the 4 and 5 posi-
tions, and the bonds lengths of C4ꢁC27 and C5ꢁC33 are 1.486(4) and
1.491(5) Å, respectively. In contrast to 2, the two Cp planes at-
tached to the central phenyl ring of 3 are arranged in an approxi-
mately face-to-face fashion, the dihedral angles of which are
40.7° and 44.7°, respectively.
Fig. 4 shows the molecular structure of 4. The bond lengths and
bond angles of central phenyl ring are ranging from 1.388(5) to
1.444(5) Å and 116.4(3) to 124.8(4)°, respectively. And its maxi-
mum torsion angle is 2.9(9)° (C3ꢁC4ꢁC5ꢁC6). This shows the six
carbon atoms of the central phenyl ring are also approximately
co-planar. The two ferrocenyl groups are attached to the central
phenyl ring at the 1 and 2 positions with bond lengths of
1.482(5) Å (C1ꢁC13) and 1.479(5) Å (C2ꢁC23). Two trimethylsilyl
Fig. 3. The molecular structure of compound 3. The H atoms have been omitted for
clarity.
groups are attached to the central phenyl ring at the 4 and 5 posi-
tions, and the bond lengths of Si1ꢁC4 and Si2ꢁC5 are 1.882(4) and

12
R.-J. Xie et al. / Polyhedron 38 (2012) 7–14
Fig. 4. The molecular structure of compound 4. The H atoms have been omitted for
clarity.
Fig. 6. The molecular structure of compound 6. The H atoms have been omitted for
clarity.
1.891(4) Å, respectively, which close to the average bond length of
the SiꢁC bond (1.922 Å) reported for hexamethylsilyl-substituted
benzene [20]. Two Cp planes attached to the central phenyl ring
are arranged in an approximate face-face fashion, and the dihedral
angles of which are 48.9° and 59.8°, respectively.
The molecular structure of 5 is described in Fig. 5. The bond
lengths and bond angles of central phenyl ring are 1.365(18)–
1.457(19) Å and 118.0(11)–121.9(12)°, respectively. The maximum
torsion angle of central phenyl ring is 7.7(5)° (C3ꢁC4ꢁC5ꢁC6).
Although there are six substituents on the central phenyl ring,
the six carbon atoms are approximately co-planar. Two ferrocenyl
groups are attached to the central phenyl ring at the 1 and 2 posi-
tions with bond lengths of 1.497(16) Å (C1ꢁC7) and 1.501(16) Å
(C2ꢁC17). The Cps of the two ferrocenyl groups present an eclipse
configuration and adopt an approximate up-down form relative
to the central phenyl ring. The dihedral angles of the Cps and the
central phenyl ring are 37.6° and 44.4°.
A comparison of the four molecular structures discussed above
shows that the central phenyl rings of compounds (2–5) easily
maintain their planar character. Hence, the central phenyl ring
can serve as a conjugated aromatic bridge between two ferrocenyl
groups to realize their charge transfer functions.
Although the bond lengths (1.400(5)–1.423(4) Å) and bond an-
gles (118.33(19)–119.9(2)°) have no significant deviation contrast
to normal phenyl ring, the configuration of the central phenyl ring
of compound 6 (Fig. 6) is obviously different from that of 2–5. The
six carbon atoms of 6 are not co-planar due to the large steric
Fig. 5. The molecular structure of compound 5. The H atoms have been omitted for clarity.

R.-J. Xie et al. / Polyhedron 38 (2012) 7–14
13
the most negative, which indicates that the electron-withdrawing
effects have no influence on the ferrocenyls. This phenomenon can
be ascribed to the central phenyl ring is not planar and the conju-
gated bridge effect disappears.
(3)
(2)
(5)
The order of oxidation potential difference (DE1/2) of com-
5
0
pounds (2–5) (Table 5) is 5 > 2 > 4 > 3. This order is also a represen-
tation of the electron transfer abilities of the four compounds [24].
The electron transfer between two ferrocenyls of an ortho-diferr-
ocenylbenzen derivative is controlled by the style and number of
substituents and the characteristic of central phenyl ring. The elec-
tron transfers between two ferrocenyls can be increased with
increasing electron-donating groups.
(4)
(6)
The special
DE1/2 of compound 6 is attributed to the deformed
structure of the central phenyl ring. The two ferrocenyls of 6 ap-
pear like diferrocenylethylene. Therefore, the oxidation potential
difference of 6 is also similar to that of diferrocenylethylene [25].
-5
0
0.5
E / V vs Ag|AgCl
1
4. Conclusion
Five new ortho-diferrocenylbenzene derivatives: 1,2-diferroce-
nyl-4,5-dimethylbenzene (2), 1,2-diferrocenyl-4,5-diphenylben-
Fig. 7. The cyclic voltammograms of compounds (2, black line), (3, red line), (4,
green line), (5, blue line), (6, brown line). (Color online.)
zene
(3),
1,2-diferrocenyl-4,5-ditrimethylsilylbenzene
(4),
1,2-diferrocenyl-3,4,5,6-tetramethylbenzene (5), and 1,2-diferroce-
nyl-3,4,5,6-tetraphenyl-benzene (6) were obtained through the
cycloaddition reaction. This work is the first time to report the
position-controlled synthesis of ortho-diferrocenylbenzenes using
hindrance among them. The compound adopts a twist-boat config-
2
uration with torsion angles of 26.0(1)° (C2ꢁC1ꢁC1 ꢁC22) and
2
13.1(3)° (C2ꢁC3ꢁC3 ꢁC22). The central phenyl ring is partially de-
Co2(CO)6(l l
2-diferrocenylacetylene) and Co2(CO)6( 2-2-butyne) as
formed and the aromatic characters of the normal phenyl ring
are lost.
precursors. The electron transfer abilities of five ortho-diferrocenyl-
benzene derivatives were investigated using cyclic voltammetry.
The electron-donating or electron-withdrawing effect of substitu-
ents on the central phenyl ring and the planar characteristics of
the central phenyl ring were the key factors for the electron commu-
nication between two ferrocenyls.
3.4. Electrochemistry of compounds (2–6)
The redox potential and reversibility of compounds (2–6) were
determined using cyclic voltammetry. All of compounds display
two redox waves in the range of 0–1.2 V (Fig. 7), which are as-
signed to the two FeII/FeIII redox couples. The electrochemical data
was reported in Table 5. From the Ipa/Ipc (ꢂ1) values of each cou-
ple, it can be seen that the redox processes were chemically revers-
ible processes [23].
The difference in first oxidation potentials can be ascribed to
the electron-donating or electron-withdrawing effects of substitu-
ents and the characteristics of central phenyl rings. The electron-
donating effect of methyl was identified by the upfield 1H NMR
chemical shift of the central phenyl in compound 2. The elec-
tron-withdrawing effects of phenyl and trimethylsilyl in 3 and 4
could also be identified by the downfield shift in their 1H NMR.
From the molecular structures of compounds (2–5), we can see
that the configurations and the original planar characteristics of
the central phenyl rings have no change. The electron-donating
and electron-withdrawing effects of substituents can be partially
transferred to ferrocenyls through the central phenyl rings. Thus,
the first oxidation potentials of 2 and 5 are more negative, and
the first oxidation potentials of 3 and 4 are more positive.
Compound 6 has four electron-withdrawing phenyl groups on
the central phenyl ring, and the first oxidation potential should
be more positive. However, the first oxidation potential of 6 is
Acknowledgements
We are grateful to the Program for New Century Excellent
Talents in University (NCET-08-858), the Natural Science Founda-
tion of China(NSFC 21062011) and the Natural Science Foundation
of the Inner Mongolia (20080404MS020).
Appendix A. Supplementary data
CCDC 817283, 816928, 816927, 816935, 816926 and 816936
contains the supplementary crystallographic data for 1, 2, 3, 4, 5
and 6, respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2012.02.018.
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