Dinuclear ruthenium sawhorse-type complexes containing carboxylato bridges and ferrocenyl substituents: Synthesis and electrochemistry

Article abstract of DOI:10.1016/j.ica.2006.10.020

The ferrocenyl-containing diruthenium complexes [Ru₂(CO)₄(μ₂-η²-OOCFc )₂L₂] (Fc = ferrocenyl, fc = ferrocen-1,1′-diyl; 1: L = NC₅H₄-COOC₆H₄- OC₁₀H₂₁, 2: L = NC₅H₄-COOC₆H₄- OC₁₆H₃₃, 3: L = NC₅H₄-OOC-fc-C₁₂H₂₅) and [Ru₂(CO)₄(μ₂-η²- OOC₆H₅)₂(NC₅H₄-OOC-fc- C₁₂H₂₅)₂] (4) have been synthesized from Ru₃(CO)₁₂, ferrocene carboxylic or benzoic acid and the corresponding pyridine derivative. The synthesis of the new pyridine derivative NC₅H₄-OOC-fc-C₁₂H₂₅ used for the preparation of 3 and 4 is also reported. Complexes 1-4 posses a so-called sawhorse structure consisting of the Ru₂(CO)₄ backbone and two bridging carboxylato ligands, while the coordination sphere around the ruthenium atoms is completed by the pyridine-derived ligands bonded in the axial positions. The electrochemical behavior of 1-4 and their known analogues [Ru₂(CO)₄(μ₂-η²-OOCFc )₂L₂] (5: L = NC₅H₅, 6: L = P(C₆H₅)₃, 7: L = NC₅H₄-OOCFc) has been studied by voltammetry on rotating disc electrode and by cyclic voltammetry.

Full text of DOI:10.1016/j.ica.2006.10.020

Inorganica Chimica Acta 360 (2007) 2023–2028
www.elsevier.com/locate/ica
Dinuclear ruthenium sawhorse-type complexes containing
carboxylato bridges and ferrocenyl substituents:
Synthesis and electrochemistry
a
a,
b
c
*
ˇ
´
´
Mathieu Auzias , Georg Suss-Fink , Petr Steˇpnicˇka , Jirˇı Ludvık
¨
a
ˆ ˆ
Institut de Chimie, Universite´ de Neuchatel, Chimie inorganique 2, Emile Argand 11, Case postale 158, CH-2009 Neuchatel, Switzerland
b
Charles University in Prague, Faculty of Science, Department of Inorganic Chemistry, Hlavova 2030, CZ-12840 Prague 2, Czech Republic
J. Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejsˇkova 3, CZ-18223 Prague, Czech Republic
c
Received 21 August 2006; received in revised form 16 October 2006; accepted 20 October 2006
Available online 27 October 2006
Abstract
The ferrocenyl-containing diruthenium complexes [Ru2(CO)4(l2-g2-OOCFc)2L2] (Fc = ferrocenyl, fc = ferrocen-1,10-diyl; 1:
L = NC5H4–COOC6H4–OC10H21, 2: L = NC5H4–COOC6H4–OC16H33, 3: L = NC5H4–OOC–fc–C12H25) and [Ru2(CO)4(l2-g2-
OOC6H5)2(NC5H4–OOC–fc–C12H25)2] (4) have been synthesized from Ru3(CO)12, ferrocene carboxylic or benzoic acid and the corre-
sponding pyridine derivative. The synthesis of the new pyridine derivative NC5H4–OOC–fc–C12H25 used for the preparation of 3 and
4 is also reported. Complexes 1–4 posses a so-called sawhorse structure consisting of the Ru2(CO)4 backbone and two bridging carboxy-
lato ligands, while the coordination sphere around the ruthenium atoms is completed by the pyridine-derived ligands bonded in the axial
positions. The electrochemical behavior of 1–4 and their known analogues [Ru2(CO)4(l2-g2-OOCFc)2L2] (5: L = NC5H5, 6:
L = P(C6H5)3, 7: L = NC5H4–OOCFc) has been studied by voltammetry on rotating disc electrode and by cyclic voltammetry.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Carboxylato bridges; Dinuclear complexes; Ruthenium; Ferrocene; Electrochemistry
1. Introduction
Ru2(CO)4 backbone in a sawhorse-type arrangement with
two symmetrical l2-g2-carboxylato bridges and two axial
(phosphine) ligands [2]. In the meantime, a considerable
number of such sawhorse-type diruthenium complexes with
carboxylato [3], carboxamido [4], phosphinato [5], sulfo-
nato [6], pyrazolato [7] or oximato [8] bridges have been
reported. We have found that complexes of the type
[Ru2(CO)4(l2-g2-OOC6H5)2L2], where L represents pyri-
dine ligands substituted with long aliphatic chains, exhibit
mesomorphic properties, forming nematic liquid crystals in
a temperature range of 150–225 ꢁC [9].
Sawhorse-type ruthenium complexes are well-known
since 1969, when Lewis and co-workers reported the for-
mation of [Ru2(CO)4(l2-g2-OOCR)2]n polymers by reflux-
ing Ru3(CO)12 in the corresponding carboxylic acid and
their depolymerisation in coordinating solvents to give
dinuclear complexes of the type [Ru2(CO)4(l2-g2-
OOCR)2L2], L being acetonitrile, pyridine or another
two-electron donor [1]. These dinuclear complexes have
been shown later, by a single-crystal X-ray structure anal-
ysis of [Ru2ðCOÞ ðl2-g2-OOCBunÞ PBut Þ ] to have a
Bearing this in mind, we synthesized the ferrocenecarb-
oxylato derivatives 1 and 2 as well as the analogous com-
4
2
3
2
plexes
3
and
4
containing additional ferrocenyl
substituents in the pyridine ligands. Unfortunately, light-
polarised microscopy shows 1–4 to have no mesomorphic
properties. On the other hand, the presence of chemically
*
Corresponding author. Tel.: +41 327182496; fax: +41 327182511.
E-mail addresses: georg.suess-fink@unine.ch (G. Suss-Fink), stepnic@
¨
ˇ
natur.cuni.cz (P. Steˇpnicˇka).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.10.020

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M. Auzias et al. / Inorganica Chimica Acta 360 (2007) 2023–2028
different ferrocenyl substituents makes 1–4 interesting sub-
strates for electrochemical studies. Herein, we report the
synthesis and characterization of 1–4 and that of the new
pyridine ligand NC5H4–OOC–fc–C12H25, as well as the
The new ferrocenyl-containing diruthenium complexes
1–4 as well as the known complexes [Ru2(CO)4(l2-g2-
OOCFc)2(NC5H5)2] (5), [Ru2(CO)4(l2-g2-OOCFc)2(P(C6-
H5)3)2] (6), [Ru2(CO)4(l2-g2-OOCFc)2(NC5H4–OOCFc)2]
(7) [10] have been electrochemically studied by cyclic vol-
tammetry at a rotating platinum disc electrode (RDE)
and by cyclic voltammetry at a stationary platinum disc
electrode in dichloromethane solutions.
electrochemistry
of
1–4
and
their
analogues
[Ru2(CO)4(l2-g2-OOCFc)2L2] (Fc = ferrocenyl, fc = ferro-
cen-1,10-diyl; 5: L = NC5H5, 6: L = P(C6H5)3, 7:
L = NC5H4–OOCFc) [10].
2. Results and discussion
2.2. Electrochemistry
2.1. Synthesis and characterization
The redox behavior of the ferrocenecarboxylato-
bridged complexes 5 and 6 (Table 1) is similar as far as
both compounds undergo two narrow-separated, revers-
ible one-electron oxidations, which can be assigned to
the oxidation of the ferrocene units, and a one-electron
irreversible oxidation of the diruthenium core. These
redox steps, however, are observed in different order: 6
becomes oxidized first at the Ru2 unit and then at the
ferrocene units, whereas 5 undergoes first ferrocene/
ferrocenium oxidations, followed by the irreversible,
Ru2-centered oxidation at a potential markedly higher
than that for 6 and associated with some chemical compli-
cations (probably adsorption) that are reflected by an
Dodecacarbonyltriruthenium reacts with ferrocene car-
boxylic acid or with benzoic acid in refluxing tetrahydrofuran
to give, in the presence of the corresponding pyridine deriva-
tive, the dinuclear complexes [Ru2(CO)4(l2-g2-OOCFc)2L2]
(1: L = NC5H4–COOC6H4–OC10H21, 2: L = NC5H4–
COOC6H4–OC16H33, 3: L = NC5H4–OOC–fc–C12H25) or
[Ru2(CO)4(l2-g2-OOC6H5)2(NC5H4–OOC–fc–C12H25)2]
(4), respectively. Complexes 1–4 are obtained as air-stable
orange or yellow powders, which have been unambiguously
characterized by their IR, NMR and MS data as well as by
correct micro-analytical data (see Section 3).
Fe
Fe
N
C
O
C
O
O
O
Fe
Fe
N
O
O
O
O
Ru
Ru
N
C
O
C
C10H21
O
OC10H21
C
C C
O O
C
O
O
O
O
O
O
O
O
Ru
Ru
N
1
C16H33
O
O
OC16H33
C
C C
O O
C
O
O
Fe
Fe
2
C
C
O
O
O
O
O
O
O
O
C
C
Ru
Ru
N
N
O
O
O
O
O
O
O
Fe
Fe
C
C C
O O
C
O
O
Ru
Ru
N
O
N
H25C12
C12H25
H25C12
Fe
Fe
C
C C
O O
C
3
O
O
C12H25
4
Fe
Fe
Fe
N
Fe
Fe
Fe
C
O
C
O
O
O
O
O
C
C
C
C
O
O
O
O
O
O
O
O
O
Ru
Ru
N
N
O
Fe
Fe
Ru
Ru
Ru
Ru
PPh3
N
Ph3P
C
C C
C
O O
O
O
C
C C
O O
C
C
C C
O O
C
O
O
O
O
7
5
6

M. Auzias et al. / Inorganica Chimica Acta 360 (2007) 2023–2028
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Table 1
Summary of cyclic voltammetric dataa
Compound
Epa
Epc
Assignmentb
1
+0.16
Ru
(+0.30)
+0.38
(+0.16)
+0.22
+0.23
(+0.30)
+0.09
Fc
Fc
Fc
Fc
2
3
4
(+0.15)
+0.66
+0.84
(+0.17)
(+0.23)
+0.35
Ru
follow-up process
Fc
Fc
Fcd
Ru or follow-up
Fc
Fc
Ru
(+0.09)
(+0.13)
+0.24
+0.65
(+0.18)
(+0.17)
+0.77
+0.11
+0.23
+0.86c
(+0.18)
(+0.17)
+0.86c
(+0.18)
+0.28
follow-up process
Fc
Fc
Ru + follow-up process
Fc
Fc
5
6
+0.11
+0.24
(+0.11)
+0.18
+0.78
+0.32
+0.59
Ru
Fce
Ru
7
+0.24
Fig. 1. Cyclic voltammograms of 6 (a) and 5 (b) as recorded at 100 mV sꢀ1
scan rate on platinum disc electrode for ca. 5 · 10ꢀ4 M analyte solutions in
dichloromethane containing 0.1 M Bu4NPF6 as the supporting electrolyte.
The potentials are given relative to ferrocene/ferrocenium.
a
Cyclic voltammograms were recorded at platinum disc electrode on ca.
5 · 10ꢀ4 M dichloromethane solutions containing 0.1 M Bu4NPF6 as the
supporting electrolyte at room temperature. The potentials are given rel-
ative to ferrocene/ferrocenium reference. Epa and Epc denote the anodic
and cathodic peak potentials, respectively. Only Epa values are given for
irreversible oxidations. The quoted values were obtained at the scan rate
of 100 mV/s. Brackets indicate where peaks are observed only as more or
less resolved shoulders.
The redox response of the pyridinecarboxylic esters 1
and 2 is very similar to that of 5. Upon raising the external
potential, the compounds first undergo two narrow spaced
oxidations at the ferrocene units, followed by an irrevers-
ible oxidation at the bimetallic core. In accordance with
very similar structures that differ only by the length of
the peripheral alkyl chain the corresponding waves are
found at nearly identical potentials.
b
Fc and Ru denote ferrocene- and Ru2-centered oxidations,
respectively.
c
Broad wave.
d
Probably bielectronic process. The counterwave is associated with
desorption.
e
Bielectronic process.
Moving the ferrocencarboxylic unit to the periphery as
in 4 has only a slight effect on the overall appearance of
the cyclic voltammogram, with the exception that the dis-
tant ferrocene units are oxidized independently, thus giving
rise to a reversible ferrocene/ferrocenium wave with DEp
characteristic for one-electron process and a height corre-
sponding to the two-electron exchanged. Similarly to 5,
the ferrocene oxidation is followed by an irreversible oxida-
tion at more positive potentials that shifts even further
anodically upon repeated scanning (Fig. 2).
The redox response of complexes that combine Ru-
bonded and pyridine ester ferrocenecarboxylic units is
rather complex. In the case of 7, a poorly resolved system
of three waves followed by a well-separated irreversible
wave with Epa + 0.65 V is observed. These redox processes
are further complicated by pronounced adsorption phe-
nomena. The analogous compound alkylated at the lateral
ferrocene units, 3, shows a similar voltammogram (Fig. 2).
The first wave is resolved only very poorly and followed by
an irreversible wave at a potential higher than for 7. In the
whole series, an increase of the molecular weight results in
lowering of the diffusion coefficients which is in turn
additional wave at ca. + 0.84 V versus ferrocene/ferroce-
nium (see Fig. 1).
The observed shift towards less positive potentials of the
core oxidation upon replacement of pyridine (complex 5)
with PPh3 (complex 6) is in accordance with the donor abil-
ity of these ligands: The phosphine as a stronger base
(donor) can be expected to increase the electron density
at the Ru2 core, thus facilitating the oxidation. However,
the variation of the redox potential of the Ru2-centered
oxidation as a function of the axial ligands is not that sim-
ple. As observed for 6, a lowering of the Ru2-centered oxi-
dation potential (or an increase in the donating ability of
the ligand) can shift the Ru2-wave negatively, so that it
even precedes the oxidation of the ferrocene unit. In such
case, however, the first oxidation has to influence the fol-
lowing one by making any subsequent electron removal
more difficult. This leads to a discontinuity in the changes
of the redox potentials. It is also noteworthy that the close
separation of the individual ferrocene/ferrocenium pro-
cesses (about 50 mV) points to a rather limited electronic
communication between the ferrocencarboxylato bridges.

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M. Auzias et al. / Inorganica Chimica Acta 360 (2007) 2023–2028
tube for 12 h. Then the solvent was evaporated to give a
yellow-brown residue, which was dissolved in tetrahydrofu-
ran, and the appropriate ligand (0.47 mmol) was added.
The solution was stirred at room temperature for 2–3 h,
the solution was evaporated and the product isolated from
the residue by crystallization from a tetrahydrofuran/hex-
ane mixture. In order to improve the purity, the raw prod-
uct was subjected to a thin-layer chromatography on silica
gel using dichloromethane as eluent and obtained as an
orange or yellow powder.
Data for [Ru2(CO)4(l2-g2-OOCFc)2(NC5H4–COO-
1
C6H4–OC10H21)2] (1): Yield 90% (209 mg, 0.14 mmol). H
NMR (400 MHz, CDCl3): 9.15 (d, 4H, Hpyr, J = 6 Hz),
8.26 (d, 4H, Hpyr, J = 6 Hz), 6.98–7.23 (m, 8H, Har), 4.60
(s, 4H, HCp), 4.23 (s, 4H, HCp), 4.10 (s, 10H, HCp),
4.01 (t, 4H, OCH2, J = 6,5 Hz), 1.84 (q, 4H, CH2,
J = 7 Hz), 1.32–1.50 (m, 28H, CH2), 0.92 (t, 6H, CH3,
J = 6 Hz). 13C NMR (100 MHz, CDCl3): 204.45 (4C,
CO), 184.32 (2C, COO), 163.86 (2C, COO), 157.81 (2C,
CO–C10H21), 153.21 (4C, NC), 144.07 (2C, COO–C),
138.50 (2C, C–COO), 124.89 (4C, NCH2CH2), 122.48
(4C, COOCHCH2), 115.70 (4C, COOCHCH2CH), 75.47
(2C, C–COO), 70.85–70.55–70.00 (12C, CCp), 68.91 (2C,
OCH2),
32.32–29.99–29.81–29.75–29.67–26.46
(14C,
Fig. 2. Cyclic voltammograms of 3 (a) and 4 (b) as obtained at scan rate
100 mV sꢀ1 on platinum disc electrode for ca. 5 · 10ꢀ4 M analyte
solutions in dichloromethane containing 0.1 M Bu4NPF6 as the support-
ing electrolyte. The potentials are given relative to ferrocene/ferrocenium.
CH2), 23.11 (2C, CH2–CH3), 14.55 (2C, CH3). ESI-MS:
1485.2 [M+2H]+. IR (CaF2, THF): m(CO) 2022.7 (vs),
1972.3 (m), 1942.2 (vs), m(OCO) 1559.7 (s) cmꢀ1. Anal. Calc.
for C70H76Fe2N2O14Ru2 (1483.19) C, 56.66, H, 5.27, N,
1.80. Found: C, 56.69, H, 5.16, N, 1.89%.
reflected by a significant lowering of the peak and limiting
currents.
Data for [Ru2(CO)4(l2-g2-OOCFc)2(NC5H4–COO-
C6H4–OC16H33)2] (2): Yield 90% (232 mg, 0.14 mmol). H
1
3. Experimental
NMR (400 MHz, CDCl3): 9.15 (d, 4H, Hpyr, J = 5 Hz),
8.27 (d, 4H, Hpyr, J = 5 Hz), 7.23 (d, 4H, Har, J = 9 Hz),
7.01 (d, 4H, Har, J = 9 Hz), 4.61 (t, 4H, HCp,
J = 1.8 Hz), 4.23 (t, 4H, HCp, J = 1.8 Hz), 4.11 (s, 10H,
HCp), 4.04 (t, 4H, OCH2, J = 6.5 Hz), 1.85 (q, 4H, CH2,
J = 7 Hz), 1.31–1.51 (m, 52H, CH2), 0.92 (t, 6H, CH3,
J = 6.6 Hz). 13C NMR (100 MHz, CDCl3): 204.45 (4C,
CO), 184.33 (2C, COO), 163.85 (2C, COO), 157.83 (2C,
CO–C16H33), 153.21 (4C, NC), 144.10 (2C, COO–C),
138.52 (2C, C–COO), 124.89 (4C, NCH2CH2), 122.47
(4C, COOCHCH2), 115.70 (4C, COOCHCH2CH), 75.47
(2C, C–COO), 70.86–70.57–70.00 (18C, CCp), 68.92 (2C,
3.1. General comments
All manipulations were carried out by routine under
nitrogen atmosphere. Organic solvents were degassed
and saturated with nitrogen prior to use. All reagents
were purchased either from Aldrich or Fluka and used
as received. NMR spectra were recorded on a Bruker
400 MHz spectrometer. IR spectra were recorded on a
Perkin–Elmer 1720X FT-IR spectrometer (4000–
400 cmꢀ1). Microanalyses were performed by the Labora-
tory of Pharmaceutical Chemistry, University of Geneva
(Switzerland). Electro-spray mass spectra were obtained
in positive-ion mode with an LCQ Finnigan mass spec-
trometer. Dodecacarbonyltriruthenium [11] was prepared
according to published method and 1-(pyridyloxy)car-
bonyl-10-dodecylferrocene was obtained by analogy using
the method reported by Donnio et al. [12] for 1-(pyridyl-
oxy)carbonyl-10-tetradecylferrocene.
OCH2),
32.35–32.00–30.13–30.03–29.83–29.80–29.68–
26.47–26.03 (24C, CH2), 23.12 (2C, CH2–CH3), 14.55
(2C, CH3). ESI-MS: 1652.6 [M+H]+. IR (CaF2, THF):
m(CO) 2022.9 (vs), 1973.0 (m), 1942.3 (vs), m(OCO) 1557.1
(s) cmꢀ1. Anal. Calc. for C82H100Fe2N2O14Ru2 (1651.51)
C, 59.64, H, 6.10. Found: C, 59.88, H, 6.43%.
Data for [Ru2(CO)4(l2-g2-OOCFc)2(NC5H4–OOC–fc–
1
C12H25)2] (3): Yield 83% (225 mg, 0.13 mmol). NMR H
400 MHz (CDCl3): 8.97 (d, 4H, Hpyr, J = 5.4 Hz), 7.50
(d, 4H, Hpyr, J = 5.4 Hz), 4.97 (t, 4H, HCp, J = 1.8 Hz),
4.64 (t, 4H, HCp, J = 1.6 Hz), 4.58 (t, 4H, HCp,
J = 1.8 Hz), 4.27–4.23 (m, 12H, HCp), 4.13 (s, 10H,
HCp), 2.38 (t, 4H, CH2CH2Cp, J = 8 Hz), 1.55–1.30 (m,
40H, CH2), 0.92 (t, 6H, CH3, J = 7 Hz). NMR 13C
3.2. Synthesis of complexes 1–4
A solution of Ru3(CO)12 (100 mg, 0.16 mmol) and the
appropriate carboxylic acid (0.47 mmol) in dry tetrahydro-
furan (40 ml) was heated at 120 ꢁC in a pressure Schlenk

M. Auzias et al. / Inorganica Chimica Acta 360 (2007) 2023–2028
2027
100 MHz (CDCl3): 204.96 (4C, CO), 184.11 (2C, COO),
169.43 (2C, COO), 159.21 (2C, Cpyr), 153.87 (4C, Cpyr),
118.11 (4C, Cpyr), 92.18 (2C, CCp), 75.8–73.71–71.71–
70.68–70.64–70.60–70.01–69.82–69.30 (18C, CCp), 34.4–
32.–31.6–30.1–30.07–29.9–29.8–29.3–26.1–25.4–23.1 (22C,
CCp), 14.56 (2C, CH3). ESI-MS: 1747.25 [M+Na]+. IR
(CaF2, CHCl3): m(CO) 2021 (vs), 1970 (m), 1939 (vs),
m(OCO) 1558 (s) cmꢀ1. Anal. Calc. for C82H92Fe4N2O12Ru2
(1723.13) C, 57.16; H, 5.38; N, 1.63. Found: C, 58.20; H,
5.81; N, 1.68% C82H92Fe4N2O12Ru2 Æ C6H14.
(460 mg, 2.23 mmol), 4-dimethylaminopyridine (136 mg,
1.12 mmol), 4-pyrrolidinopyridine (83 mg, 0.56 mmol)
and 4-hydroxypyridine (212 mg, 2.23 mmol) were intro-
duced together with anhydrous dichloromethane (30 mL).
The solution was stirred under nitrogen in the dark at
room temperature for 48 h. Then the red solution was
slowly filtered through Celite in order to eliminate the dic-
yclohexylurea. The product was obtained as an orange
powder from the filtrate after column chromatography
on silica gel using dichloromethane as eluent (442 mg,
0.93 mmol). Yield 64%. ESI-MS: 476 [M+H]+; 477
[M+2H]+. NMR 1H 400 MHz (CD3OD): 8.58 (d, 2H,
Data for [Ru2(CO)4(l2-g2-OOC6H5)2(NC5H4–OOC–fc–
1
C12H25)2] (4): Yield 73% (173 mg, 0.11 mmol). NMR H
400 MHz (CDCl3): 9.00 (dd, 4H, Hpyr, J = 5.3 Hz, J =
1.4 Hz), 7.94 (d, 4H, Hpyr, J = 7.4 Hz), 7.53–7.32 (m,
10H, HPh), 4.97 (t, 4H, HCp, J = 1.8 Hz), 4.58 (t, 4H,
HCp, J = 1.8 Hz), 4.26 (m, 8H, HCp), 2.37 (t, 4H, CH2Cp,
J = 7.4 Hz), 1.54 (m, 4H, CH2CH2Cp), 1.32–1.26 (m, 18H,
–(CH2)–), 0.91 (t, 6H, CH3, J = 7 Hz). NMR 13C 100 MHz
(CDCl3): 204.5 (4C, CO), 179.1 (2C, COO–), 169.4 (COO–-
pyr), 159.3 (OCpyr), 153.9 (Cpyr), 133.8 (Cpyr), 132.0 (4C,
Car), 130.1 (4C, Car), 128.3 (2C, Car), 118.3 (2C, Cpyr),
92.2 (2C, CCp), 69.8, 70.6, 71.7, 73.7 (8C, CCp), 23.1,
29.2, 29.8, 29.9, 30.06, 30.1, 31.6, 32.3 (22C, CH2), 14.6
(2C, CH3). ESI-MS: 1531.3 [M+Na+H]+. IR (CaF2,
CHCl3): m(CO) 2025 (vs), 1974 (m), 1941 (vs), m(OCO) 1559
(s) cmꢀ1. Anal. Calc. for C74H84Fe2 N2O12 Ru2(1507.3) C,
58.97; H, 5.62; N, 1.96. Found: C, 59.33; H, 5.89; N, 1.94%.
Hpyr, J = 5 Hz), 7.37 (d, 2H, Hpyr, J = 5 Hz), 4.85 (s, 2H,
HCp), 4.56 (s, 2H, HCp), 4.20 (s, 4H, HCp), 2.30 (t, 2H,
Cp–CH2, J = 7.6 Hz), 1.47 (m, 2H, –(CH2)–), 1.25 (m,
18H, –(CH2)9–), 0.88 (m, 3H, CH3). NMR 13C 100 MHz
(CD3OD): 170.6 (1C, COO), 160.0 (1C, COOꢀpyr), 151.9
(2C, Cpyr), 118.8 (2C, Cpyr), 92.8 (1C, CCp), 70.4, 71.3,
72.3, 74.3 (8C, CCp), 23.7, 29.7, 30.4, 30.5, 30.6, 30.7,
30.8, 32.1, 33.1, 49.3 (12C, CH2), 14.5 (1C, CH3). Anal.
Calc. for C28H37FeNO2 (475.44) C, 70.73, H, 7.84, N,
2.95. Found: C, 70.82, H, 7.83, N, 2.84%.
3.5. Electrochemistry
Electrochemical measurements were carried out with a
multipurpose polarograph PA3 interfaced to a Model
´
ˇ´
4103 XY recorded (both Laboratornı prıstroje, Prague) at
room temperature using a standard three-electrode cell:
rotating (RDE) or stationary platinum disc (1 mm diame-
ter) working electrode, platinum wire auxiliary electrode,
and saturated calomel electrode (SCE) reference electrode,
separated from the analyzed solution by a salt bridge filled
with 0.1 M Bu4NPF6 in dichloromethane. The samples were
dissolved in dichloromethane (Merck p.a.) to give ca.
5 · 10ꢀ4 M concentration of the analyte and 0.1 M
Bu4NPF6 (supporting electrolyte; Fluka, purissimum for
electrochemistry). The samples were deaerated with argon
prior to the measurement and then kept under an argon
blanket. Cyclic voltammograms were recorded at stationary
platinum disc electrode (scan rates 50–500 mV/s), whereas
the voltammograms were obtained at rotating disc electrode
(500 rpm, scan rates 10–100 mV/s). Redox potentials were
given relative to the ferrocene/ferrocenium reference
(Eꢁ0 = 0.41 V versus SCE under the experiment conditions).
3.3. Synthesis of 1-carboxy-10-dodecylferrocene
1-Carboxy-10-dodecylferrocene was synthesized simi-
larly to its known tetradecyl analogue [12]. A solution of
1-carbomethoxy-10-dodecylferrocene (450 mg, 1.1 mmol)
and KOH (367 mg, 6.6 mmol) in ethanol (25 mL) was stir-
red under reflux for 4 h. The solution was cooled to room
temperature and poured onto a stirred ice/water mixture.
Concentrated HCl was added slowly to acidified pH. The
solid which precipitated was recovered by filtration and
washed thoroughly with water. Purification of the residue
by column chromatography (CH2Cl2) gave pure 1-car-
boxy-10-dodecylferrocene as
a red powder (357 mg,
0.90 mmol). Yield 79%. ESI-MS: [MꢀH]ꢀ 397;
[2 · MꢀH]ꢀ 794.9; [2 · MꢀH+Na]ꢀ 817.3. NMR 1H
400 MHz (CDCl3): 4.80 (s, 2H, HCp), 4.43 (s, 2H, HCp),
4.15 (s, 4H, HCp), 2.30 (t, 2H, Cp–CH2, J = 7 Hz), 1.28
(m, 20H, –(CH2)10–), 0.90 (t, 3H, CH3, J = 6 Hz). NMR
13C 100 MHz (CDCl3): 179.0 (1C, COO), 91.7 (1C, CCp),
72.9 (1C, CCp), 69.7, 70.4, 70.6, 71.5 (8C, CCp), 23.1,
28.7, 29.8, 29.9, 30.08, 30.1, 30.12, 31.5, 32.4 (11C, CH2),
14.6 (1C, CH3). IR (CaF2, CHCl3): 1674 m(COO), 1478
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