A new synthesis and electrochemistry of 1,1′-bis(β-hydroxyethyl)ferrocene

Article abstract of DOI:10.1016/j.ica.2008.09.017

The preparation of 1,1′-bis(β-hydroxyethyl)ferrocene (1) by oxidation of 1,1′-divinylferrocene is described. Compound 1 has been characterized by ¹H and ¹³C{¹H} NMR, and cyclic voltammetry. The electrochemical data are com

Full text of DOI:10.1016/j.ica.2008.09.017

Inorganica Chimica Acta 362 (2009) 2068–2070
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A new synthesis and electrochemistry of 1,10-bis(b-hydroxyethyl)ferrocene
1
*
Kevin P. Barry , Chip Nataro
Department of Chemistry, Lafayette College, Easton, PA 18042, United States
a r t i c l e i n f o
a b s t r a c t
The preparation of 1,10-bis(b-hydroxyethyl)ferrocene (1) by oxidation of 1,10-divinylferrocene is
described. Compound 1 has been characterized by 1H and 13C{1H} NMR, and cyclic voltammetry. The elec-
trochemical data are compared to ferrocene and the closely related 2-ferrocenylethanol, 2.
Ó 2008 Elsevier B.V. All rights reserved.
Article history:
Received 24 May 2007
Accepted 3 September 2008
Available online 16 September 2008
Keywords:
Cyclic voltammetry
Hammett parameter
NMR
1. Introduction
requires the use of potassium cyanide, and gives 1 in a 22% yield
from the initial ferrocene [11].
Ferrocene and its derivatives have been extensively studied
since ferrocene was first discovered [1,2]. One of the properties
of ferrocene derivatives that has been widely examined is the re-
dox potential of the iron center in ferrocene derivatives [3]. Of par-
ticular interest are the heteroannularly disubstituted derivatives of
ferrocene, for example, 1,10-bis(diphenylphosphino)ferrocene
(dppf) [4]. The redox potentials of these compounds are sensitive
to the electronic nature of the groups bound to the ferrocene back-
bone [5]. The synthesis and subsequent reactions of 1,10-dilithio-
ferrocene are among the primary reasons that a wide array of
groups can be bound to a ferrocene backbone [6].
In this report, the synthesis of 1 is carried out in three steps
from ferrocene. The potential at which oxidation of 1 was deter-
mined and used to estimate the Hammett parameter for the –
CH2CH2OH group. In addition, the synthesis, 1H NMR and electro-
chemistry of (C5H4CHO)Fe(C5H4CH@CH2) are presented.
2. Experimental
2.1. General procedures
Preparative reactions and purifications were carried out using
standard Schlenk techniques under an atmosphere of argon. Tetra-
hydrofuran (THF), hexanes, diethyl ether (Et2O), and methylene
chloride (CH2Cl2) were purified using a Solv-Tek solvent purifica-
tion system similar to one previously described [12]. Ph3PMeBr,
Ph3PMeI, dibenzo-18-crown-6, 1-formylpiperidene and BH3 ꢀ THF
(1.0 M in THF) were purchased from Aldrich. Tetramethylethylene-
diamine (TMEDA) was purchased from Aldrich and distilled prior
to use. Ferrocene and decamethylferrocene were purchased from
Strem. Electrochemical experiments were performed using HPLC
grade CH2Cl2 distilled from CaH2 under an argon atmosphere
prior to use. Tetrabutylammonium hexafluorophosphate
([NBu4]+[PF6]ꢁ]) was purchased from Aldrich and dried under
vacuum prior to use. The 1H and 13C{1H} NMR spectra were
obtained in CDCl3 and recorded using a JOEL Eclipse 400 FT-
NMR. The internal standard for 1H and 13C{1H} NMR data acquisi-
tion was TMS (d 0.00 ppm). Microanalysis was performed by QTI.
While the 1,10-bis(b-dihydroxyethyl) derivative of ferrocene (1)
had been reported previously, it was somewhat surprising to dis-
cover that there were no synthetic routes that employed 1,10-
dilithioferrocene. The first reported synthesis of 1 required the ini-
tial synthesis of C5H5CH2CH2OH from lithium cyclopentadienide
and ethylene oxide [7]. The C5H5CH2CH2OH was then purified by
fractional distillation, reacted with butyl lithium and iron(II) chlo-
ride to give 1 in 19% yield. The second reported preparation, albeit
with limited detail, involves the reduction of 1,10-ferrocenediacetic
acid [8]. A third synthetic method uses 1,10-bis(hydroxymethyl)fer-
rocene as the starting material, and after reaction with phosphorus
trichloride, potassium cyanide and lithium aluminum hydride,
yields 1 in 56% [9]. An additional report in which 1 is obtained from
an unpublished synthesis has also been made [10]. The final re-
ported synthesis requires seven steps from ferrocene, one of which
2.2. Synthesis of ferrocene-1,10-dicarbaldehyde (2)
* Corresponding author. Tel.: +1 610 330 5216; fax: +1 610 330 5714.
E-mail address: nataroc@lafayette.edu (C. Nataro).
Current address: Department of Chemistry, Wesleyan University, Middletown, CT
1
Ferrocene (10.0038 g, 53.8 mmol) was suspended in 120 mL of
hexanes and 67.2 mL of 1.6 M n-butyllithium in hexane
06459, United States.
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.09.017

K.P. Barry, C. Nataro / Inorganica Chimica Acta 362 (2009) 2068–2070
2069
(107.5 mmol) were added. TMEDA (8.4 mL, 55.7 mmol) was added
dropwise to the mixture; the reaction was stirred at room temper-
4.71 (s, 2H, C5H4–), 4.53 (s, 2H, C5H4–), 4.44 (s, 2H, C5H4–), 4.31
(s, 2H, C5H4–). Anal. Calc. for C13H12FeO: C, 65.04; H, 5.04. Found:
C, 64.80; H, 4.64%.
ature for 14 h.
A
solution of 1-formylpiperidine (12 mL,
104.1 mmol) in 20 mL of diethyl ether was added dropwise and
the reaction was allowed to stir for 30 min producing a deep red
solution. The solution was extracted with deionized water
(3 ꢂ 100 mL). The aqueous layer was then extracted with CH2Cl2
(4 ꢂ 100 mL). The CH2Cl2 layer was subsequently washed with
0.1 M aqueous HCl (2 ꢂ 100 mL) to remove unreacted 1-formylpi-
peridine, dried over MgSO4, and filtered. The volume of the solu-
tion was then reduced to approximately 10 mL. The product was
purified by column chromatography on silica gel using a mixture
of CH2Cl2 and hexanes (v:v, 1:1) as the eluent. The solvent was re-
moved in vacuo giving 2 as a dark red solid in an 80% yield. Spectral
data agreed with the literature values [13].
2.6. Electrochemistry
All cyclic voltammetric measurements were conducted using a
Princeton Applied Research 263-A potentiostat. Solutions used in
analysis were kept under an atmosphere of argon throughout the
experiments. A three-electrode configuration was used consisting
of a 1.5 mm glassy-carbon working electrode, a platinum wire coun-
ter electrode, and a non-aqueous Ag/AgCl electrode, separated from
the solution by a glass frit, as the reference electrode. Prior to use, the
working electrode was polished with 1
lm diamond paste followed
by 0.25 m diamond paste. The electrode was rinsed with acetone
l
after each polishing and rinsed with CH2Cl2 before experiments.
The oxidative electrochemistry of 1 and 4 was investigated in
CH2Cl2 using 0.10 M ([NBu4]+[PF6]ꢁ]) as the supporting electrolyte.
The analyte concentration was 1.0 mM, and experiments were con-
ducted at scan rates at 50 mV/s and from 100 to 1000 mV/s at
100 mV/s increments. The electrochemical potentials were col-
lected using Power Suite from Princeton Applied Research, and
all data were collected at ambient temperature (22 1 °C). Decam-
ethylferrocene was added toward the end of the experiment as an
internal standard, and the analyte potential was referenced to fer-
rocene by subtracting 0.548 V [14].
2.3. Synthesis of divinylferrocene (3)
A
mixture of Ph3PMeBr (12.1559 g, 34.0 mmol), KOtBu
(3.8178 g, 34.0 mmol), and a catalytic amount of dibenzo-18-
crown-6 (0.0315 g, 0.09 mmol) was dissolved in 45 mL of THF
and stirred for 30 min at room temperature. To this mixture, a
solution of 2 (4.1183 g, 17.0 mmol) in 80 mL of THF was added over
10 min. The resulting dark red-brown solution was stirred for 14 h.
Deionized water (80 mL) was added to the reaction mixture, and
the solution was stirred for 10 min. The reaction was extracted
with Et2O (2 ꢂ 100 mL), and the organic layer was dried over
Na2SO4. The solution was filtered, and the volume was reduced
to approximately 5 mL. The resulting oil was purified by column
chromatography on silica gel, and the product was eluted with
hexanes. The solution was dried in vacuo, yielding 3 as a bright or-
ange solid in a 63% yield. The 1H NMR spectra were identical to lit-
erature values [13].
3. Results and discussion
3.1. Synthesis
A new synthesis of 1 was carried out by hydroboration–oxida-
tion of 3 with BH3 ꢀ THF and H2O2 (Scheme 1). Compounds 2 and
3 were prepared using modifications of literature procedures
[13]. Previous syntheses of 1 have characteristically involved many
steps and low overall yields [7–11]. The new route presented here-
in gives 1 in three steps and an overall 22% yield from ferrocene.
While optimizing the conditions for the formation of 3, alter-
nate routes to generate 3 from 2 were examined. Based on the lit-
erature reaction of ferrocenecarbaldehyde with Ph3PMeI and 25%
NaOH in benzene to give vinylferrocene [15], a similar reaction
was attempted using 2 and appropriately scaled amounts of
Ph3PMeI and 25% NaOH. However, these reactions would only yield
the asymmetric compound 4. The reaction of 4 with excess
Ph3PMeI in refluxing benzene did not produce 3.
2.4. Synthesis of 1,10-bis(b-hydroxyethyl)ferrocene (1)
Compound 3 (0.1763 g, 0.74 mmol) was dissolved in 10 mL of
THF. BH3 ꢀ THF (2.25 mL, 2.25 mmol) was added dropwise, and
the solution stirred for 1 h. The reaction mixture was dried in va-
cuo, and 5 mL of THF were added. H2O2, 30% by wt. (0.2200 mL,
2.15 mmol) in 0.78 mL of 3 M NaOH was added and the reaction
mixture was stirred for 30 min. The reaction was extracted with
CH2Cl2 (2 ꢂ 50 mL) and dried over Na2SO4. The product was puri-
fied by column chromatography on silica gel, and 1 eluted with
acetone. Compound 1 was isolated as an orange oil after removing
solvent in vacuo and was obtained in a yield of 44%. Numerous at-
tempts at growing crystals suitable for single crystal X-ray analysis
were unsuccessful. 1H NMR (CDCl3): d 4.03 (s, 8H, C5H4–), 3.67 (t,
J = 6.6 Hz, 4H, –CH2OH), 2.54 (t, J = 6.6 Hz, 4H, C5H4–CH2–), 2.21
(br s, 2H, –OH). 13C{1H} NMR (CDCl3): d 85.0 (s, ipso), 69.2 (s,
C5H4), 68.4 (s, C5H4), 63.5 (s, –CH2OH), 32.7 (s, C5H4–CH2–).
3.2. Electrochemistry
Cyclic voltammetry was used to determine the potential at
which oxidation of 1 and 4 occur in CH2Cl2. The potentials at which
oxidation occurred were measured for each compound and are
listed in Table 1. A single reversible, one-electron wave was ob-
served in the oxidative electrochemistry of both 1 and 4 (Fig. 1).
The electrochemistry of 1 has been investigated previously in
aqueous solution [16] and in a polymer electrolyte [17].
In comparing the potential at which oxidation of 1 occurs to
that of the closely related 2-ferrocenylethanol [18], there is an
excellent correlation between the potential and the number of –
CH2CH2OH groups. For 1,10-disubstituted ferrocenes, the Hammett
2.5. Synthesis of 1-vinyl-10-carboxaldehydeferrocene (4)
Compound 2 (0.8114 g, 3.35 mmol) was dissolved in 5 mL of
benzene with Ph3PMeI (2.0215 g, 4.98 mmol). To this mixture,
25% NaOH (9 mL, 75.0 mmol) was added and the reaction was stir-
red vigorously for 2 h. The reaction was extracted with Et2O
(50 mL) and the organic layer was washed with 20% K2CO3
(2 ꢂ 40 mL) and deionized water (3 ꢂ 100 mL). The organic layer
was then dried over Na2SO4 and the product was purified by col-
umn chromatography on silica gel. The product was eluted with
a mixture of CH2Cl2 and hexanes (v:v, 4:1). The solvent was re-
moved in vacuo leaving a deep-red oil. 1H NMR (CDCl3): d 9.87 (s,
1H, –CHO), 6.33 (dd, J = 17.2 and 10.6 Hz, 1H, –CH@CH2), 5.38 (d,
J = 17.2 Hz, 1H, –CH=CH2), 5.13 (d, J = 10.6 Hz, 1H, –CH@CH2),
parameter (rp) for the substituent is correlated with the potential
at which oxidation occurs (EL where EL = 1/2E° versus NHE) [5].
Based on Eq. (1) and the potential at
EL ¼ 0:45rp þ 0:36
ð1Þ
which oxidation of 1 occurs, the
r
p for the –CH2CH2OH substituent
was calculated to be ꢁ0.17. The calculated
rp value for –CH2CH2OH

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K.P. Barry, C. Nataro / Inorganica Chimica Acta 362 (2009) 2068–2070
O
O
H
H
1-formylpiperidine, Et2O
BuLi, TMEDA
Fe
Fe
30 min
Hexanes,12 h
2
OH
OH
BH3.THF
THF, 1 h
Ph3PMeBr, KOtBu
H2O2
Fe
Fe
2
NaOH(aq)
diBz-18-crown-6
THF, 14 h
3
1
Scheme 1. Synthesis of 1 from ferrocene.
Table 1
for the individual substituents [5]. Based on the EL values for –
CHO and –CH@CH2, the calculated potential for the oxidation of
4 is 0.30 V versus FcH0/+, which is in good agreement with the
experimental value. However, using Eq. (1) and the average of
Electrochemical data for compounds 1–5 (in DCM)
Compound
E0 (V) vs. FcH0/+
Fe(C5H4CH2CH2OH)2 (1)
CpFeC5H4CH2CH2OH
Fe(C5H4CHO)2
Fe(C5H4CH@CH2)2
Fe(C5H4CHO)(C5H4CH@CH2) (4)
ꢁ0.09
ꢁ0.05a
0.56b
0.04b
0.30
the
r
p values for –CHO (0.42) and –CH@CH2 (ꢁ0.04) [19], the esti-
mated E0 for 4 is 0.23 V versus FcH0/+, which suggest that Eq. (1) is
not a valid means of estimating the potential at which oxidation of
asymmetric 1,10-disubstituted ferrocenes occurs.
a
Ref. [18].
Ref. [5].
b
4. Conclusions
A new synthesis of 1 has been developed in three steps from fer-
rocene. All three steps proceed in reasonable yield. The potentials
at which oxidation of 1 and 4 occur in CH2Cl2 were determined
by cyclic voltammetry. The effect on the potentials of the substit-
uents on ferrocene is as expected.
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