Structural influences on the electrochemistry of 1,10-di(hydroxyalkyl) ferrocenes. Structure of [Fe{h5-C5H4eCH(OH)e(CH2)3OH}2]

Article abstract of DOI:10.1016/j.jorganchem.2013.05.006

Abstract A series of 1,1'-di(hydroxyalkyl)ferrocenes, [Fc'{(CH ₂)_nOH}₂], with n = 1 (1), 2 (2), 3 (3) and 4 (4) and Fc' = Fe(η⁵-C₅H₄)₂, was synthesized. The electrochemistry of the di(hydroxyalkyl)ferrocenes was studied by cyclic voltammetry in CH₂Cl₂/0.1 M [N ⁿBu₄][PF₆] utilizing a glassy carbon working electrode. The ferrocenyl group showed reversible electrochemistry with the formal reduction potential, E^o' , inversely proportional to alkyl chain length and approximately 59 mV smaller than those of the corresponding mono(hydroxyalkyl)ferrocenes derivatives [Fc(CH₂)mOH] with m = 1 (1m), 2 (2m), 3 (3m), and 4 (4m) and Fc = Fe(η⁵-C ₅H₅)(η⁵-C₅H₄ ^-). The tetraalcohol [Fc'{CH(OH)(CH₂)₃OH} ₂], 5, possessing four OH functionalities, two in the terminal positions and two more, one on each of the two α-C relative to the ferrocenyl (Fc' for dialcohols or Fc for monosubstituted derivatives) group, was isolated as a side product during the synthesis of 4. The formal reduction potential of 5 was E^o' = -24 mV vs. FcH/FcH⁺ and closely approached E^o' of [FcCH(OH)CH₃] (E^o' = -11 mV), [Fc'{CH(OH)CH₃}₂] (-21 mV) and 1 (0.00 mV vs. FcH/ FcH⁺). The single crystal X-ray structure of the tetraalcohol 5 (Z = 8, orthorhombic, space group Pbca) was also solved.

Full text of DOI:10.1016/j.jorganchem.2013.05.006

Journal of Organometallic Chemistry 740 (2013) 61e69
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structural influences on the electrochemistry of 1,10-di(hydroxyalkyl)
ferrocenes. Structure of [Fe{
h
5-C5H4eCH(OH)e(CH2)3OH}2]
*
Ron Claus, Jan P. Lewtak, Theunis J. Muller, Jannie C. Swarts
Department of Chemistry, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa
a r t i c l e i n f o
a b s t r a c t
A series of 1,10-di(hydroxyalkyl)ferrocenes, [Fc0{(CH2)nOH}2], with n ¼ 1 (1), 2 (2), 3 (3) and 4 (4) and
Article history:
Fc0 ¼ Fe(
h
5-C5H4)2, was synthesized. The electrochemistry of the di(hydroxyalkyl)ferrocenes was studied
Received 28 March 2013
Received in revised form
27 April 2013
by cyclic voltammetry in CH2Cl2/0.1 M [NnBu4][PF6] utilizing a glassy carbon working electrode. The
0
ferrocenyl group showed reversible electrochemistry with the formal reduction potential, Eo , inversely
Accepted 3 May 2013
proportional to alkyl chain length and approximately 59 mV smaller than those of the corresponding
mono(hydroxyalkyl)ferrocenes derivatives [Fc(CH2)mOH] with m ¼ 1 (1m), 2 (2m), 3 (3m), and 4 (4m)
Keywords:
Ferrocene
Alcohol
Dialcohol
and Fc ¼ Fe(
h
5-C5H5)(h5-C5H4ꢀ). The tetraalcohol [Fc0{CH(OH)(CH2)3OH}2], 5, possessing four OH func-
tionalities, two in the terminal positions and two more, one on each of the two a-C relative to the fer-
rocenyl (Fc0 for dialcohols or Fc for monosubstituted derivatives) group, was isolated as a side product
0
during the synthesis of 4. The formal reduction potential of 5 was Eo ¼ ꢀ24 mV vs. FcH/FcHþ and closely
Cyclic voltammetry
0
0
approached Eo of [FcCH(OH)CH3] ðEo ¼ ꢀ11 mVÞ, [Fc0{CH(OH)CH3}2] (ꢀ21 mV) and 1 (0.00 mV vs. FcH/
FcHþ). The single crystal X-ray structure of the tetraalcohol 5 (Z ¼ 8, orthorhombic, space group Pbca)
was also solved.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
ferrocenyl moiety by introducing electron-donating or electron-
withdrawing substituents onto the cyclopentadienyl (C5Hꢀ5 ) rings.
Ferrocene (FcH) and its derivatives are susceptible to a large
number of organic reactions [1] such as alkylation [2], lithiation
[3,4], FriedeleCrafts acylation [5] or metal promoted CeC cross-
coupling reactions [6]. The ferrocenyl group (Fc) has strong elec-
tron donating properties [7] and exhibits reversible one electron
transfer electrochemical behaviour [8]. These characteristics allow
ferrocene and its derivatives to be useful in a wide range of different
applications. Based on its electrochemical signature, ferrocene de-
rivatives are extensively used as molecular sensors [9]. Addition-
ally, the electron-donating characteristics of the ferrocenyl group,
the electron-withdrawing properties of the oxidized ferrocenium
species (Fcþ possessing a FeIII cation) [10] and the stability of both
the oxidized and reduced states allow ferrocene derivatives to be
used in electron transfer [11] and energy transfer studies [12]. They
are also used as high burning rate catalysts in rocket propellants
[13] and as catalyst in various chemical reactions [14,15]. As a part
of a ligand system it will enhance oxidative addition reactions [16]
but retard substitution processes [17]. These applications are
mostly driven by manipulating the oxidation potential of the
A particularly interesting application of ferrocene derivatives,
which are strongly dependent on fine tuning of the ferrocenyl
oxidation potential with suitable substituents, lies in the field of
cancer therapy. It has been shown that the cytotoxicity of a series of
mono(hydroxyalkyl)ferrocenes Fc(CH2)mOH (m ¼ 1e4) [18] are
0
directly proportional to Eo of the ferrocenyl group. Other ferrocene
derivatives show similar trends [18be18d]. However, many
potentially good cytotoxic agents are clinically not usable due to
their poor compatibility with an aqueous biological system [19]. To
overcome this, a water-insoluble cytotoxic agent may be bound to a
water-soluble polymeric drug carrier [20].
To incorporate ferrocene derivatives with different oxidation
potentials into macromolecules or polymers, it is necessary to
synthesize ferrocene species with side chains having reactive
functional groups [21e23]. One of these functional groups which
are often used to covalently bind the ferrocenyl moiety to larger
target molecules is the alcohol functionality [24]. There are two
main ways to include the ferrocenyl group into polymeric species.
For the first approach, one may use a monofunctionalized ferro-
cenyl derivative to covalently bind the metallocenyl moiety via a
short side chain to the polymer main chain [22]. Secondly, one may
use difunctionalized cyclopentadienyl derivatives and condense
* Corresponding author. Tel.: þ27 (0)51 4012781; fax: þ27 (0)51 4446384.
E-mail address: swartsjc@ufs.ac.za (J.C. Swarts).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.05.006

62
R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
them with other difunctionalized monomers into polymers bearing
the ferrocenyl group as part of the main chain [23].
the synthesis of 1m, [FcCH(OH)CH3] and [Fc0{CH(OH)CH3}2]
[13c,22b,27], we and other researchers used LiAlH4- or NaBH4-
induced reduction of 9, FcCOCH3 and Fc(COCH3)2 and the reaction
mixture was worked-up by quenching the reaction with water. For
1, in our hands, this approach led to substantial decomposition and,
hence, low yields of 1. The observed decomposition if 1 is related to
the elimination of H2O from Fc-(CH2OH)2, a reaction which is
driven by the stability of Fc-CHþ2 cations [13c,22b,28]. We found it
best not to quench the reaction with acid or H2O initially, but to first
filter the reaction medium through Celite. The remaining residue
on the Celite was then extracted with THF and quenched with
water. In this way we could increase yields of 1 to well above 80%.
1,10-Di(2-hydroxyethyl)ferrocene, 2, was obtained by a six-step
synthesis [29] in an overall yield of 32% based on ferrocene
(Scheme 1). A key precursor to obtain 2 is the dinitrile 13. All at-
tempts to obtain 13 from 1,10-di(N,N,N-trimethylamoniummethyl)
ferrocene diiodide, Fc0{CH2N(CH3)3}.22I [30], as is possible for the
corresponding mononitrile, FcCH2CN [31], failed. Consequently, we
synthesized 13 starting from 1 via the dichloride 12. 1,10-Di(chlor-
omethyl)ferrocene, 12, was obtained by treating 1 with PCl3.
Complex 12 is only moderately stable due to the relatively good
leaving properties of chloride as an anion and especially the sta-
bilisation effect the electron-donating ferrocenyl group has on Fc-
(CHþ2 )2 cations [28]. Hence 12 was not isolated but reacted in situ by
addition of the crude reaction mixture containing 12 to an aqueous
KCN solution. Chloride substitution from 12 by the cyanide anion
resulted in the formation of the dinitrile 13 in 50% yield after col-
umn chromatography. Basic hydrolysis of the dinitrile afforded
In this publication we describe efficient methods to synthesize
and characterize a series of 1,10-di(hydroxyalkyl)ferrocenes with
general formula [Fc0{(CH2)nOH}2] (compounds 1e4 with n ¼ 1, 2, 3
and 4, Scheme 1) and we show how the formal oxidation potential
of the ferrocenyl group changes with increase in alkyl chain
length (i.e. larger values of n). Electrochemical results are compared
with the ferrocenyl oxidation potentials of the related series of
mono(hydroxyalkyl)ferrocenes [Fc(CH2)mOH] where m ¼ 1e4,
compounds 1me4m. In addition, we could isolate and characterise
by single crystal X-ray analysis the tetraalcohol [Fc0-{CH(OH)-
(CH2)3OH}2], 5, which was obtained as a side product during the
synthesis of 4.
2. Results and discussion
2.1. Synthesis
The diol 1,10-di(hydroxymethyl)ferrocene, 1, was synthesized
[25] by reduction of dialdehyde, 9, with 1.5 equiv of NaBH4 per
aldehyde functionality (Scheme 1). The dialdehyde 9 was obtained
in high yield utilizing Mueller and Westerhoff’s general method
[4,26] via dilithiation of ferrocene (6) in the presence of TMEDA
(N,N,N0,N0-tetramethylethylenediamine) and subsequent reaction
with DMF (dimethylformamide). With this two-step protocol, 1
could be obtained in overall yield of 84%. Yields of the reduction of 9
to liberate 1 are highly dependent on the work-up method. For
Scheme 1. Synthesis of 1,10-di(hydroxyalkyl)ferrocenes 1e4. The tetrahydroxy derivative 5 can be made purposefully, but it was also isolated as a side product during the synthesis
of 4. Compound numbers 1me4m in the text refer to the analogous monosubstituted ferrocenyl alcohols [Fc(CH2)mOH] where m ¼ 1e4.

R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
63
ferrocenyl-1,10-diacetic acid, 14. LiAlH4 reduction of 14 gave diol 2
as a yellow oil in near quantitative yield.
For the synthesis of 1,10-di(3-hydroxypropyl)ferrocene, 3 [32],
dicarboxaldehyde 9 was converted quantitatively to the unsatu-
rated ester 10 with the WittigeHorner reaction by treating 9 with
the phosphonate anion obtained in situ from triethyl phospho-
noacetate and sodium metal (Scheme 1). Quantitative hydrogena-
tion of the double bonds of 10 with hydrogen in presence of 10%
palladium-on-charcoal followed by the reduction of the ester
groups with LiAlH4 gave the target dialcohol 3 in 75% overall yield.
An alternative route towards 3 that was also explored involves the
reaction of 9 with malonic acid in the presence of piperidine to
obtain ferrocene-1,10-diacrylic acid followed by the hydrogenation
of the double bonds with hydrogen in presence of 10% palladium-
on-charcoal and reduction of the carboxylic acid groups. This
route resulted in the formation of 3 in poor yields (5%) in our hands.
The weakest step is low conversion of 9 to ferrocene-1,10-diacrylic
acid.
Fig. 1. The relationship between the number of CH2 spacers, n, separating the ferro-
cenyl group and an electron-withdrawing substituent functionality X in disubstituted
ferrocene derivatives [Fc0{(CH2)nX}2] (Y-axis) and the 1H NMR position (
d values/ppm)
of each of the two C5H4 pseudo-triplets for the indicated compounds of this study
highlights the pseudo-triplets are only resolved into two separate signal sets for n ¼ 0
and 1. For n ꢁ 2 the pseudo-triplets moved so close to each other that they overlapped.
For 7, the substituent is COCH2CH2COOMe, i.e. no CH2 spacer between Fc0 and CO while
for 5 the substituent is CH(OH)e(CH2)3eOH implying n ¼ 1.
1,10-Di(4-hydroxybutyl)ferrocene, 4, was obtained in two steps
(Scheme 1) first by performing a FriedeleCrafts diacylation on
ferrocene with 3-(carbomethoxy)propionyl chloride [33] to obtain
7 in 35% yield. The subsequent one-pot reduction of all four
carbonyl groups with one equivalent of LiAlH4 and two equivalents
of fresh AlCl3 per each carbonyl group resulted in almost quanti-
tative formation of 4. Alternatively, 4 can be obtained in two steps
via Clemmensen reduction of the keto groups of 7 followed by
reduction of ester functionalities to give 4 in 25% overall yield
[24b,23a]. To our surprise, we frequently also isolated the previ-
ously unknown tetraalcohol 5, [Fc0-{CH(OH)e(CH2)3OH}2], as a
yellow oil that solidifies within three days from the reaction
mixture during the synthesis of 4. The use of fresh AlCl3 in the
indicated quantities proved to be essential to prevent formation of
this previously unknown tetraalcohol.
in the crystallographic section below. Especially the observed
intramolecular bonds (see Table 2 crystallographic section) may
contribute to this effect, but the use of different deuterated sol-
vents did not induce a different integration pattern [34]. However,
these CH2 protons are enantiotopic, and enantiotopic protons
have the same chemical shift in the vast majority of situations.
However, if they are placed in a chiral environment, which is the
case here, they will have slightly different and more complex
chemical shifts, making them non-equivalent. This could also
contribute to the observed integral ratio of 1:3 rather than the
expected ratio of 2:2.
The coupling constants for the two observed pseudo-triplets of
the aromatic C5H4 group were 3J ¼ 1.73e1.95 Hz, depending on the
compound. Coupling constants for the olefinic CH]CH group
(3J ¼ 15.7 Hz for 10) and aliphatic CH2eCH2 (3J ¼ 6.6 Hz for 2 or 7)
or CH2CH3 groups (3J ¼ 7.1 Hz for 10, 11) are much larger. The
15.7 Hz coupling constant of 10 is consistent with the E-isomer.
Also, from 4, it is evident that R1eCH2eCH2eR2 coupling is influ-
enced by the substituent R1 and R2. For 4, [Fc0(CH2eCH2eCH2e
CH2eOH)2], the coupling constant of the triplet of the CH2 group
next to the electron-donating ferrocenyl group is 6.6 Hz, while 3J
for the triplet of the CH2 group next to the inductive electron-
withdrawing OH functionality is 5.20 Hz. For 3, [Fc0(CH2eCH2e
CH2eOH)2], the same tendency was observed: the coupling con-
stant of the triplet of the CH2 group next to the electron-donating
ferrocenyl group was 3J ¼ 8.20 Hz. This is 1.84 Hz larger than the
coupling constant for the CH2 group adjacent to the electron-
withdrawing OH functionality.
Upon further investigating methods to obtain the tetraalcohol 5
during a purposeful synthesis (Scheme 1), we found 5 could be
obtained in near quantitative yields by treating 7 with 4 equiv of
LiAlH4 in the absence of AlCl3. Crystallographic quality crystals may
be obtained by crystallization from ethyl acetate and the crystal
structure of 5 was solved, see next section.
2.2. 1H NMR and IR spectroscopy
1H NMR analysis of the aliphatic disubstituted compounds [Fc0
{(CH2)nX}2] with n ¼ 0e4 and X ¼ OH, CN, COOEt, CHO or COe
CH2CH2COOMe showed only those complexes without any or with
just one CH2 spacer between the ferrocenyl group and an
electron-withdrawing functional group, X, exhibited the charac-
teristic two pseudo-triplets of the ferrocenyl moiety as two
separate resonances in an 1H NMR spectrum. These two pseudo-
triplets were overlapping (i.e. they were unresolved) in com-
plexes with two or more CH2 spacers (n ¼ 2, 3, 4). Fig. 1 sum-
marises the influence of alkyl chain length on the coalescence of
these two pseudo-triplets for compounds of this study. Addi-
tionally, the downfield shift of the pseudo-triplets with increasing
value of n reached an asymptotic minimum at n ¼ 4. This result
was echoed in the electrochemical study described below. The 1H
NMR of 5, [Fc0-{CH(OH)-(CH2)3OH}2], bearing two chiral centers in
Being disubstituted ferrocenyl derivatives, the IR of 1e5 did not
show the unsubstituted C5H5 bands at 1000 and 1100 cmꢀ1, but the
OH functionalities showed the typical broad, strong alcohol bands
at 3200e3500 cmꢀ1 (OeH stretching) and 1050e1211 cmꢀ1 (CeO
stretching). The strong C]O stretching bands of
7
(1650,
11
the
particular, the signals of the two CH2eOH molecular fragments
were found at
¼ 3.96e3.88 and 3.84e3.77 ppm, while those of
the two CH(OH)eCH2eCH2 fragments were observed in an inte-
gral ratio of 1:3 rather than the expected ratio of 2:2 at
a
position next to the ferrocenyl group was more complex. In
1730 cmꢀ1), (1664 and 1684 cmꢀ1), 10 (1706 cmꢀ1
9
)
(1737 cmꢀ1) and 14 (1675 cmꢀ1) were also observed. The nitrile
groups of 13 exhibited an IR stretching frequency of 2260 cmꢀ1. Ce
H stretching frequencies were between 2900 and 3150 cmꢀ1 with
the aromatic ferrocenyl CeH stretching bands at slightly
longer wavenumbers than the aliphatic CeH bands. Complex 10,
[Fc0(CH]CHCOOEt)2], showed a C]C stretching vibrational band at
d
d
¼ 2.26e
2.17 and 2.02e1.89 ppm. This unexpected resonance pattern is at
least in part attributed to hydrogen bonding patterns which may
enforce inequivalence of the respective CH2 species as discussed
1626 cmꢀ1
.

64
R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
2.3. Single crystal X-ray structure of 5
experiments were performed on 0.25 mM solutions of 1e5 in dry
CH2Cl2/0.1 M [NnBu4][PF6], utilising a standard three-electrode
cell. Electrochemical data are summarized in Table and
Crystallographic quality crystals were obtained by recrystalli-
zation of chromatographed 5, after the oil that was obtained from
the column solidified, from ethyl acetate. The molecular structure
of 5 with atom numbering is shown in Fig. 2; selected bond dis-
3
presented in Figs. 3 and 4. Quasi reversible electrochemical behav-
iour was observed for the ferrocenyl moiety in 1e5 with
D
Ep ¼ Epa ꢀ Epc ꢃ 80 mV at a scan rate of 100 mV sꢀ1 (Table 3, Fig. 4).
ꢂ
ꢀ
tances (A) and angles ( ) are summarized in the caption. Refine-
ment parameters and crystal data are summarised in Table 1.
Compound 5 crystallizes in the orthorhombic space group Pbca. The
cyclopentadienyl rings deviate 8.27ꢂ from an eclipsed conformation
while the dihedral angle between the two alkyl chains is 63.87ꢂ.
The distance between cyclopentadienyl rings from the centroid of
Electrochemical reversibility is ideally characterized by a theoretical
DEp value of 59 mV for a one-electron transfer process [37]. Peak
cathodic/peak anodic current ratios for 1e5 were in the range
0
0.98 < ipc/ipa < 1. Formal reduction potentials, Eo ¼ 1=2ðEpa þ Epc
Þ
were scan rate independent between 100 and 500 mV sꢀ1 (Fig. 3).
0
A peculiarity is the Eo of 1 being exactly 0.00 V, i.e. at the same
potential as the free FcH/FcHþ couple. This is interpreted to imply
that the combined electronic effect of two CH2OH groups on the FeII
centre of 1 via through-bond and through-space pathways, and
promoted by a hydrogen bonding network similar to that described
ꢀ
C(1)eC(5) to the centroid of C(6)eC(10) is 3.300 A and the dihedral
angle between the two cyclopentadienyl planes is 1.97ꢂ.
The CeC bonds in the cyclopentadienyl rings show an average
ꢀ
bond length of 1.421 A for the two substituted rings. This is about
0.02 A shorter than bond lengths in unsubstituted cyclopentadienyl
for 5 above and for Fc0{CH(OH)CH3}2 [38], accidently led to the
ꢀ
0
observed oxidation potential. The observed negative shift of the Eo
ꢀ
rings [35]. The largest deviation (þ0.015 A) from this average was
for C(6)eC(7). sp3esp3 CeC single-bond distances and sp3 CeO
value with increasing alkyl chain length (Table 3) is a consequence
of the larger alkyl spacer size between Fc and OH groups. It isolates
the electron-withdrawing OH moiety from the ferrocenyl group
more effectively with increasing alkyl chain length and ultimately
the ferrocenyl group only experiences the electron-donating effect
bond distances for the aliphatic portions of the alkyl chains aver-
ꢀ
aged 1.510 and 1.432 A respectively, and are in good agreement
with published values [36]. Bond angles for the cyclopentadienyl
rings approached 108ꢂ with the largest deviation of 1.9ꢂ for C(1)e
C(5)eC(4), while CeCeC angles around atoms C(11)eC(18)
were between C(12)eC(13)eC(14) ¼ 110.1ꢂ and C(16)eC(17)e
C(18) ¼ 117.7ꢂ. The six OeCeC angles averaged 108.1ꢂ.
of the alkyl spacer.
0
The relationship between the alkyl chain length and Eo of dia-
lcohols 1e5 and monoalcohols 1me4m [39] is shown in Fig. 5. The
0
An extensive hydrogen bonding network was observed in 5. The
dihedral angle C(1)eC(11)eC(6)eC(15) ¼ 63.9ꢂ, Fig. 2, is attributed
to the intramolecular hydrogen bond O(1)eH/O(3) with an O(1)e
increase of the alkyl chain length from n ¼ 1 to n ¼ 4 causes Eo of
compound series 1e4 to approach an asymptotic minimum at
n ¼ 4. An asymptotic minimum was also approached at m ¼ 4 in the
ꢀ
O(3) distance of 2.738(5) A, Table 2. The intermolecular hydrogen
monofunctionalized ferrocene complexes (Fig. 5). The difference
0
bonds via OeH/O interaction connects a central molecule of 5
with six adjacent molecules. Hydrogen bond lengths and angles are
summarized in Table 2. Fig. S1 in Supplementary Information
shows a second view of this hydrogen bonding network.
between the Eo of mono- and difunctionalized hydrox-
yalkylferrocenes 1e4 was for each n ¼ m value almost the same
(Fig. 5, Table 3) and averaged 59 mV.
0
In addition, Eo values of 1 (0 mV), 5, (ꢀ24 mV) and [Fc0{CH(OH)
CH3}2] (ꢀ21 mV) [39] are very close to each other (Table 3, Fig. 5),
0
which indicates that Eo for these compounds are mainly influenced
2.4. Electrochemical studies
0
by the alcohol functionality in the
a
-position. That Eo of the
monoalcohol [FcCH(OH)CH3] (ꢀ11 mV) [39] is so close to that of
The redox properties of the di(hydroxyalkyl)ferrocene com-
pound series 1e5 were studied by cyclic voltammetry (CV). CV
the other three -hydroxylated compounds is consistent with an
a
Fig. 2. Left: Molecular structure of [Fe{h5-C5H4eCH(OH)e(CH2)3eOH}2], 5; thermal ellipsoids are drawn at 50% probability level. Selected bond length (A) and angles ( ) are: Fe(1)e
C(1) 2.056(5), Fe(1)eC(2) 2.045(5), Fe(1)eC(3) 2.037(5), Fe(1)eC(6) 2.051(4), Fe(1)eC(7) 2.049(5), Fe(1)eC(9) 2.039(5), C(1)eC(2) 1.421(8), C(2)eC(3) 1.424(8), C(3)eC(4) 1.409(8),
C(6)eC(7) 1.436(6), C(7)eC(8) 1.422(7), C(8)eC(9) 1.417(7), C(1)eC(11) 1.479(8), C(11)eC(12) 1.558(7), C(12)eC(13) 1.443(10), C(13)eC(14) 1.559(8), C(6)eC(15) 1.507(6), C(15)e
C(16) 1.508(7), O(1)eC(11) 1.424(7), O(2)eC(14) 1.427(8), O(3)eC(15) 1.445(5), O(4)eC(18) 1.431(6), C(1)eC(11)eC(12) 115.7(5), C(6)eC(15)eC(16) 111.3(4), C(11)eC(12)eC(13)
114.0(6), C(15)eC(16)eC(17) 114.4(4), O(1)eC(11)eC(1) 110.4(4), O(2)eC(14)eC(13) 110.3(5), O(3)eC(15)eC(6) 107.0(4), O(4)eC(18)eC(17) 109.0(4). Right: Hydrogen bonding in 5.
Each molecule is hydrogen-bonded to six neighbouring molecules; these are labelled next to the Fe atom as 1 through 6. Symmetry transformations used to generate equivalent
atoms may be found in Table 2, footnote “a”.
ꢂ
ꢀ

R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
65
Table 1
Crystal data and structure refinement for 5.
Empirical formula
C18H26FeO4
362.24
Absorption coefficient/mmꢀ1
range for data collection/ꢂ
Index ranges
0.922 mmꢀ1
Molecular weight
Crystal size/mm3
Temperature/K
q
2.18e28.00ꢂ
0.42 ꢄ 0.09 ꢄ 0.08
ꢀ17 ꢃ h ꢃ 17, ꢀ12 ꢃ k ꢃ 8, ꢀ35 ꢃ l ꢃ 33
100(2)
Reflections collected
Independent reflections
44,013
ꢀ
Wavelength/A
0.71073
Orthorhombic
Pbca
4025 [R(int) ¼ 0.0481]
99.9%
0.9299 and 0.6981
Full-matrix least-squares on F2
3330/0/172
Crystal system
Space group
Unit cell dimensions/A
Completeness to
Max. and min. transmission
Refinement method
q
¼ 28.42ꢂ
ꢀ
a ¼ 12.9558(9)
b ¼ 9.5202(6)
c ¼ 27.0387(19)
Data/restraints/parameters
Goodness-of-fit on F2
1.046
3
ꢀ
ꢀ
Volume/A
3335.0(4) A
8
Final R indices [I > 2
s
(I)]
R1 ¼ 0.0789, wR2 ¼ 0.1886
Z
R indices (all data)
Largest diff. peak and hole/e A
R1 ¼ 0.0981, wR2 ¼ 0.2024
Density (calc.)/Mg mꢀ3
1.443
1536
1.605 and ꢀ1.044 e A
ꢀꢀ3
ꢀꢀ3
F(000)
intermolecular hydrogen bond network in [FcCH(OH)CH3]
imposing almost the same electron density on the FeII center of this
compound as in the combined inter- and intramolecular networks
of 5 and [Fc0{CH(OH)CH3}2].
hexane were purified by distillation from sodium/benzophenone
ketyl. Dichloromethane was dried over molecular sieves (4 A). All
ꢀ
reactants (SigmaeAldrich or Merck) were used as received unless
otherwise stated. Chromatography was performed on silica gel 60
(220e240 mesh, Fluka). Melting points were determined with an
Olympus BX 51 microscope with a Linkham THMS 600 heating
apparatus and are uncorrected. 1H NMR spectra were recorded on a
Bruker Advance DPX 300 NMR spectrometer at 300.13 MHz and
3. Conclusions
The di(hydroxyalkyl)ferrocenes compound series [Fc0{(CH2)n
OH}2] with n ¼ 1 (1), 2 (2), 3 (3), 4 (4) and [Fc0{CH(OH)(CH2)3OH}2]
(5) was synthesized. Compound 5 was separated as the main side
product during the reduction of [Fc0{CO(CH2)2COOMe}2], 7 to 4
with LiAlH4/AlCl3 and crystallizes in the orthorhombic space group
Pbca. An extensive hydrogen bonding network exists in the crystal
structure of 5. The ferrocenyl groups of 1e5 all showed electro-
chemical reversible behaviour. Hydroxyalkyl chain length and
oxidation potential potentials of 1e4 were inversely proportional to
each other. Oxidation potentials of the dihydroxyalkyl ferrocenes
were consistently approximately 59 mV smaller for each hydrox-
yalkyl substituent compared to the corresponding mono-
20 ꢂC with chemical shifts presented as
d values referenced to
SiMe4 as internal standard at 0.00 ppm utilizing CDCl3 or DMSO-d6
as solvents. The following abbreviations are used to describe peak
patterns: s ¼ singlet, br s ¼ broad singlet, d ¼ doublet, pt ¼ pseudo-
triplet, t ¼ triplet, q ¼ quartet, m ¼ multiplet. IR spectra (cmꢀ1
)
were recorded on a Bruker Tensor 27 spectrometer with a PIKE
MIRacle ATR-attachment. Elemental analysis was conducted by the
Analytical Chemistry of Chemistry Department of the UFS on a Leco
TruSpec Micro instrument.
4.2. Synthesis
hydroxyalkyl ferrocenes 1me4m. Hydroxylation in the
a position
4.2.1. 1,10-Di(hydroxymethy1)ferrocene (1) via 1,10-ferrocenedicar-
boxaldehyde (9)
relative to the ferrocenyl group in mono and dihydroxyalkyl de-
rivatives 1, 5, [Fc(CHOH)CH3] and [Fc0{(CHOH)CH3}2] resulted in
4.2.1.1. 1,10-Ferrocenedicarboxaldehyde (9). The literature proce-
dure [26b] for the preparation of 9 was modified as follows: To a
room temperature solution of ferrocene (10 g, 0.054 mol) in dry
hexane (200 mL) was added n-butyl lithium solution (67 mL, 1.6 M
in hexanes, 0.10 mol) dropwise followed by addition of tetra-
methylene ethylenediamine (TMEDA) (14.7 g, 0.25 mol). No dif-
ference in yields was detected if the additions were made at ꢀ50 ꢂC.
After stirring the reaction mixture for 18 h at room temperature,
dilithiated ferrocene has precipitated as an orange solid. The sus-
pension was cooled to 0 ꢂC, DMF (7.85 g, 0.11 mol, 8.3 mL) was
oxidation potentials being grouped fairly close together in the
0
range 0 < Eo < 24 mV vs. FcH/FcHþ and is interpreted to be at least
in part
a consequence of the crystallographically observed
hydrogen bonding networks.
4. Experimental
4.1. General procedures and instruments
All reactions were carried out under an argon atmosphere using
standard Schlenk techniques. Tetrahydrofuran, diethyl ether and n-
Table 3
Cyclic voltammetric data at 100 mV sꢀ1 scan rate (potentials vs. FcH/FcHþ) of
0.25 mM solutions of 1e5 as well as the monoalkylalcohol complexes 1me4m in dry
dichloromethane containing 0.1 M of [NnBu4][PF6] as a supporting electrolyte at
25 ꢂC.a
Table 2
a
ꢂ
ꢀ
Hydrogen bonds (A) and angles ( ) in 5.
OeH/O0 interaction
O(1)eH(1A)/O(3)b
d(H/O0)
d(O/O0)
<(OHO0)
0
0 a
0 c
Eo
(mV)
D
(mV)
Ep
ipa
A)
ipc/ipa
Comp.
Eo
D
Eo
1.98
1.85
2.06
2.11
2.54
2.738(5)
2.678(6)
2.674(5)
2.850(5)
2.919(7)d
149.2(3)
170.5(3)
129.3(2)
147.1(3)
102.6(3)d
Comp.
Epa
(mV)
c
O(2)eH(2A)/O(1)#1
O(3)eH(3A)/O(2)#2
O(4)eH(4A)/O(3)#3
(
m
(mV)
(mV)
c
c
1
2
3
40
ꢀ68
ꢀ68
ꢀ77
12
0
80
76
78
74
72
2.35
2.36
2.36
2.39
2.39
0.98
1.00
0.98
1.00
1.00
1m
2m
3m
4m
5mb
60
ꢀ46
ꢀ52
ꢀ54
ꢀ11
60
62
50
60
13
ꢀ106
ꢀ107
ꢀ114
ꢀ24
C(12)eH(12B)/O(2)b
a
Symmetry transformations used to generate equivalent atoms: #1: ꢀx þ 1/2,
4
ꢀ
5b
y þ 1/2, z; #2: x ꢀ 1/2, ꢀy þ 1/2, ꢀz; #3: ꢀx ꢀ 1/2, y þ 1/2, z; d(OeH) ¼ 0.84 A;
ꢀ
D(CeH) ¼ 0.99 A.
a
Data for the monoalcohols 1me4m and complex 5m are from Ref. [39].
Complex 5 ¼ [Fc {CH(OH)e(CH2)3eOH}2], complex 5m ¼ [FcCH(OH)CH3]; Eo of
b
Intramolecular bond.
Intermolecular bond from the parent molecule to adjacent molecule number 1,
0
0
b
c
[Fc0{CH(OH)CH3}2] is ꢀ24 mV [39].
2 or 3.
o0
o0
0
c
D
Eo ¼ E
ꢀ E
.
d
Fc monofunctionalized
Fc difunctionalized
d(C/O) and angle(CHO).

66
R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
1m
40
1
0
5
2m
-40
-80
3m
4m
3
3
2
4
-120
0
1
2
4
Fig. 3. CV’s of 4 (n ¼ 4) in CH2Cl2/0.100 M [NnBu4][PF6] at 25 ꢂC and scan rates of 100
(the smallest current), 200, 300, 400, 500 (the largest current) mV sꢀ1 at a glassy
carbon working electrode.
m or n (alkyl chain length)
0
Fig. 5. Relation between Eo and the number of carbon atoms (m or n) in the alkyl
chain of the mono-functionalized alcohols 1me4m (-), [Fc(CH2)mOH], and [FcCH(OH)
CH3] (þ) [38], as well as difunctionalized alcohols 1e4 [Fc0{(CH2)nOH}2] (A), 5 [Fc0
{CH(OH)(CH2)3OH}2], (:) and [Fc0{CH(OH)CH3}2] (C) [38].
added, and the stirring continued for further 2 h at room temper-
ature. After quenching the reaction mixture with 200 mL ice-cooled
5 M aqueous HCl, it was extracted with diethyl ether (3 ꢄ 100 mL).
The combined organic fractions were dried over MgSO4 and the
solvent was removed to give crude 9 as a dark red solid. The crude
product was purified by column chromatography (hexane:di-
chloromethane v/v 1:1, Rf ¼ 0.65) to afford pure 9 as red crystals
(3 ꢄ 20 mL). Caution: Quenching with water or dilute acid before
filtering severely lowers yields. The Celite with remainder of the
reaction residue still on it was suspended in THF (100 mL) and
water (10 mL) was added. This suspension was stirred for 5 min,
filtered, and the organic layer was separated and dried over MgSO4.
The combined THF fractions were evaporated to dryness to obtain
the product, 1, as yellow crystals. Yield 1.0 g (99%), m.p. 105e107 ꢂC,
(11.06 g, 85%), m.p. 181 ꢂC. 1H NMR (CDCl3)
d/ppm: 4.65 (pt,
J ¼ 1.9 Hz, 4H, 2ꢄ C5H4), 4.87 (pt, J ¼ 1.9 Hz, 4H, 2ꢄ C5H4), 9.93 (s,
2H, CHO). 13C{1H} NMR (CDCl3)
d/ppm: 192.8 (CHO), 80.43 (Cipso),
Rf (DCM) ¼ 0.5. 1H NMR (CDCl3)
d/ppm: 3.79 (s, 2H, OH) 4.19 (pt,
74.18 (Cp), 70.83 (Cp). IR, neat, nmax/cmꢀ1: 1684, 1664, 1456, 1372,
J ¼ 1.9 Hz, 4H, 2ꢄ C5H4), 4.22 (pt, J ¼ 1.9 Hz, 4H, 2ꢄ C5H4), 4.39 (s,
1246, 1040, 745.
4H, 2ꢄ CH2). 13C{1H} NMR (CDCl3)
d/ppm: 89.3 (Cipso), 67.9 (Cp),
66.9 (Cp), 60.2 (CH2). IR, neat, nmax/cmꢀ1: 3276, 3081, 2935, 2858,
4.2.1.2. 1,10-Di(hydroxymethy1)ferrocene (1). To a stirred mixture of
NaBH4 (350 mg, 8.8 mmol) in dry THF (15 mL), 1 g (4.12 mmol) of
solid 1,10-ferrocenedicarboxaldehyde, 9, was added in small por-
tions. The mixture was stirred at room temperature for 15 min and
two more portions of NaBH4 (each 200 mg, 5.3 mmol) was added
within 10 min of each other. Thereafter the reaction is filtered
through a pad of Celite and the Celite-residue washed with THF
1197, 982.
4.2.2. 1,10-Di(2-hydroxyethy1)ferrocene (2) via 1,10-di(hydroxy-
methy1)ferrocene (1)
Conversion of 1 to 2 takes place in four steps via the synthesis of
1,10-di(chloromethyl)ferrocene, 12, 1,10-di(cyanomethyl)ferrocene,
13, and ferrocenyl-1,10-diacetic acid, 14. Although the method was
used before [29], neither full experimental details nor compound
characterisation was provided. We adopted this procedure as
follows:
4.2.2.1. 1,10-Di(chloromethyl)ferrocene (12). A solution of 1 (5 g,
19.00 mmol) in dry (100 mL) THF containing pyridine (1 mL) was
added to a solution of PCl3 (2.5 g, 18 mmol) in THF (10 mL). After
stirring for 3 h at room temperature the reaction mixture contained
sufficient amounts of 1,10-di(chloromethyl)ferrocene, 12, to proceed
with the synthesis of 13, but 12 was not isolated due to its moderate
stability. The reaction mixture containing 12 was thus transferred
to a dropping funnel under an argon counter stream for use in the
synthesis of 1,10-di(cyanomethyl)ferrocene, 13.
4.2.2.2. 1,10-Di(cyanomethyl)ferrocene (13). In a 500 mL three-neck
flask, KCN (15 g, 230 mmol) dissolved in water (30 mL; caution,
HCN, b.p. 25.6 ꢂC, may be evolved) was flushed with argon. Under
rapid stirring the THF reaction mixture containing 12 was added
dropwise at room temperature. The addition results in exothermic
processes (e.g. water interacting with PCl3) and may require occa-
sional cooling in an ice bath to prevent thermal runaway that de-
stroys 12. The resulting mixture was stirred for a further hour
before the THF layer was separated, washed with brine (3 ꢄ 50 mL),
dried over MgSO4 and after solvent removal, crude 13 is obtained as
brownish crystals. Further purification by column chromatography
utilizing hexane:dichloromethane ¼ 1:1 v/v as eluent gives 13
(Rf ¼ 0.65) as yellow crystals in 49% yield (2.6 g, 9.8 mmol), m.p.
Fig. 4. CV’s of complexes 1e5 at a scan rate of 100 mV sꢀ1 utilising a glassy carbon
working electrode in dichloromethane solutions (0.25 mmol Lꢀ1) at 25 ꢂC and a
supporting electrolyte of 0.1 mol Lꢀ1 [NnBu4][PF6].

R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
67
68 ꢂC. 1H NMR (CDCl3)
d
/ppm: 4.31 (pt, J ¼ 1.8 Hz, 4H, 2ꢄ C5H4), 4.28
C5H4), 2.59e2.72 (m, 4H, CpeCH2), 2.44e2.57 (m, 4H, CH2eCO),
(pt, J ¼ 1.8 Hz, 4H, 2ꢄ C5H4), 3.47 (s, 4H, CH2). 13C{1H} NMR (CDCl3)
1.26 (t, J ¼ 7.11 Hz, 6H, CH2eCH3). 13C{1H} NMR (CDCl3)
d/ppm:
d/ppm: 118.1 (CN), 78.7 (Cipso), 69.6 (Cp), 69.3 (Cp), 18.6 (CH2). IR,
172.7 (C]O), 87.4 (Cipso), 68.4 (Cp), 68.1 (Cp), 60.1 (CH2eCH3), 35.7
(Cp-CH2), 24.6 (CH2eCO), 14.2(CH2eCH3). IR, neat, nmax/cmꢀ1: 3160,
2978, 2902, 1684, 1178, 1086.
neat, nmax/cmꢀ1: 3140, 2260, 1408, 1300, 1237, 1041, 1029, 910.
4.2.2.3. Ferrocene-1,10-diacetic acid (14) 1,10-Di(cyanomethyl)ferro-
cene (2 g, 7.6 mmol) was dissolved in ethanol (10 mL) and NaOH
(2 g, 50 mmol) dissolved in water (20 mL) was added in one portion.
The reaction mixture was refluxed until the evolution of NH3 had
ceased (4 h). The mixture was allowed to cool to room temperature
and then acidified with 20 mL ice cold 30% H2SO4. The fine yellow
precipitate was collected by filtration, washed with water and dried
under reduced pressure overnight to give 14 as a yellow crystalline
solid in 97% (2.22 g, 7.35 mmol) yield, m.p. 169 (d) ꢂC. Further
4.2.3.3. 1,10-Di(3-hydroxypropyl)ferrocene (3). A solution of 11
(1.2 g, 3.12 mmol) in dry diethyl ether (10 mL) was added dropwise
to a solution of LiAlH4 (0.14 g, 3.70 mmol) in dry diethyl ether
(10 mL). After 1 h of reflux, the mixture was allowed to cool to room
temperature and hydrolysed by adding water (20 mL) drop by drop.
The reaction mixture was acidified with concentrated HCl (3 mL)
and extracted with diethyl ether (2 ꢄ 30 mL). The combined organic
phases were washed with water and dried over MgSO4. Removal of
all volatiles at reduced pressure afforded 11 as a yellow oil in 78%
recrystallization was not required. 1H NMR (DMSO-d6)
(br s, 2H, COOH), 4.12 (s, 4H, 2ꢄ C5H4), 4.06 (s, 4H, 2ꢄ C5H4), 3.25 (s,
d/ppm: 12.19
yield (0.74 g). 1H NMR (CDCl3)
d
/ppm: 4.00 (m, 8H, 2ꢄ C5H4), 3.66 (t,
4H, CH2). 13C{1H} NMR (DMSO-d6)
d
/ppm: 172.8 (C]O), 81.8 (Cipso),
J ¼ 6.36 Hz, 4H, 2ꢄ CH2eOH), 2.41 (t, J ¼ 8.20 Hz, 4H, 2ꢄ FceCH2),
70.0 (Cp), 68.6 (Cp), 35.3 (CH2). IR, neat, nmax/cmꢀ1: 2906, 2256,
1.76 (m, 4H, 2ꢄ CH2eCH2eCH2), 1.59 (bs, 2H, 2OH). 13C{1H} NMR
1705, 1685, 1401, 1327, 1294, 1239, 1211, 1158, 1401, 1022.
(CDCl3) d/ppm: 89.0 (Cipso), 69.1 (Cp), 68.3 (Cp), 62.9 (CH2eOH),
34.5 (CpeCH2), 26.0 (CH2eCH2). IR, neat, nmax/cmꢀ1: 3311, 3084,
2936e2866, 1444, 1033, 1018, 930, 909, 823, 804.
4.2.2.4. 1,10-Di(2-hydroxyethyl)ferrocene (2). To a solution of 14
(1.75 g, 6.1 mmol) in THF (50 mL), LiAlH4 (2.8 g, 7.3 mmol) was
added in one portion and the mixture was refluxed overnight,
allowed to cool to room temperature and quenched with water
(10 mL). The water phase was extracted three times with
dichloromethane, dried over MgSO4 and after solvent removal the
crude product was obtained as deep orange oil. Analytically pure 2
could be obtained in 99% yield (1.6 g; 5.84 mmol) by purification
with column chromatography using dichloromethane/methanol in
4.2.4. 1,10-Di(4-hydroxybutyl)ferrocene (4)
Compound 4 was obtained in two steps from ferrocene and 1,10-
di(methyl-4-oxybutyrate)ferrocene, 7, utilizing an adaptation of
Navarro’s procedure [32]:
4.2.4.1. 1,10-Di(methyl-4-oxybutyrate)ferrocene (7). A solution of
ferrocene (9.3 g, 50 mmol) in dry dichloromethane (75 mL) was
added dropwise to an ice-cooled mixture of 3-(carbomethoxy)
propionyl chloride (15 g,100 mmol) [33] and AlCl3 (26 g, 200 mmol)
in dry dichloromethane (100 mL). The reaction mixture was heated
for 2 h under reflux before being allowed to cool to room temper-
ature. Stirring continued for an additional hour. The reaction
mixture was poured onto ice (200 g), acidified with concentrated
HCl (5 mL) and extracted with dichloromethane (3 ꢄ 100 mL). The
combined organic phases were washed with water (3 ꢄ 50 mL),
dried over anhydrous MgSO4, filtered, and the solvent removed
under reduced pressure. Crude 7 was purified by column chroma-
tography utilizing hexane:diethyl ether ¼ 1:3 v/v as eluent to afford
pure 7 (Rf ¼ 0.5) as a red crystalline solid, m.p. 103e104 ꢂC, in 43%
a ratio 98:2 as eluent (Rf ¼ 0.35). 1H NMR (CDCl3)
d/ppm: 4.03 (br s,
8H, 2ꢄ C5H4), 3.67 (t, J ¼ 6.6 Hz, 4H, CH2eOH), 2.54 (t, J ¼ 6.6 Hz, 4H,
CpeCH2), 2.21 (br s, 2H, 2ꢄ OH). 13C{1H} NMR (CDCl3)
d/ppm: 85.0
(Cipso), 69.2 (Cp), 68.4 (Cp), 63.5 (CH2OH), 32.7 (Cp-CH2). IR, neat,
nmax/cmꢀ1: 3273, 3089, 2928, 2880, 1469, 1225, 1036, 805.
4.2.3. 1,10-Di(3-hydroxypropyl)ferrocene (3)
1,10-Di(3-hydroxypropyl)ferrocene, 3, may be obtained from 9 in
three steps via 1,10-di[2-(ethyloxycarbonyl)ethenyl]ferrocene, 10,
and 1,10-di[2-(ethyloxycarbonyl)ethyl]ferrocene, 11.
4.2.3.1. 1,10-Di[2-(ethyloxycarbonyl)ethenyl]ferrocene
(10). After
dissolving sodium (0.18 g, 8.16 mmol) in absolute ethanol (50 mL;
caution, hydrogen is evolved), one equivalent of triethyl phospho-
noacetate (1.62 mL, 8.16 mmol) followed by a solution of 9 (0.94 g,
3.88 mmol) in absolute ethanol (25 mL) was added dropwise at
yield (8.9 g, 21.5 mmol) relative to ferrocene. 1H NMR (CDCl3)
d/
ppm: 4.88 (pt, J ¼ 1.95 Hz, 4H, 2ꢄ C5H4) 4.58 (pt, J ¼ 1.95 Hz, 4H, 2ꢄ
C5H4) 3.72 (s, 6H, eCH3), 3.02 (t, J ¼ 6.05 Hz, 4H, COeCH2eCH2), 2.7
(t, J ¼ 6.05 Hz, 4H, COeCH2eCH2). 13C{1H} NMR (CDCl3)
d/ppm: 201
0
ꢂC. The mixture was allowed to warm up to room temperature
(C]O), 173 (COO), 79.5 (Cipso), 73.4 (Cp), 70.4 (Cp), 51.4 (CH2eCOO),
34.1 (COeCH2), 27.9 (CH3). IR, neat, nmax/cmꢀ1: 3080, 3020, 2850,
1730, 1650, 1437, 1246, 1203, 905.
and stirred for 1 h. Removal of the solvent followed by column
chromatography (hexane:ether v/v 1:1) gave analytically pure 10
(Rf ¼ 0.35) as a dark red crystalline solid in 80% (1.27 g, 3.1 mmol)
yield w.r.t. 9, m.p. 92e93 ꢂC. 1H NMR (CDCl3)
d/ppm: 7.39 (d,
4.2.4.2. 1,10-Di(4-hydroxybutyl)ferrocene (4). To an ice cold sus-
pension of LiAlH4 (623.2 mg, 16.4 mmol) in dry diethyl ether
(10 mL), a suspension of AlCl3 (2.39 g, 18 mmol) in dry diethyl ether
(100 mL) was added slowly under an argon atmosphere. Compound
7 (1.7 g, 4.1 mmol) and AlCl3 (2.04 g, 15.3 mmol) dissolved in dry
diethyl ether (20 mL) was added and the mixture was stirred for
30 min at room temperature before being refluxed for 3 h. To the
cooled solution, water (75 mL) followed by concentrated H2SO4
(3 mL) was added. The mixture was extracted with ether
(3 ꢄ 200 mL), dried over MgSO4 and the solvent was removed
under reduced pressure to afford 4 as a yellow oil in 96% (1.30 g,
J ¼ 15.8 Hz, 2H, CpeCH]CH), 5.96 (d, J ¼ 15.8 Hz, 2H, CpeCH]CH),
4.44 (pt, J ¼ 1.8 Hz, 4H, 2ꢄ C5H4), 4.36 (pt, J ¼ 1.8 Hz, 4H, 2ꢄ C5H4),
4.21 (q, J ¼ 7.1 Hz, 4H, eCH2eCH3), 1.32 (t, J ¼ 7.1 Hz, 6H, CH2eCH3).
13C{1H} NMR (CDCl3)
d/ppm: 166.9 (C]O), 143.7 (CpeCH]CH),
116.2 (CpeCH]CH) 79.9 (Cipso),72.2 (Cp), 69.7 (Cp), 60.1 (CH2), 14.2
(CH3). IR, neat, nmax/cmꢀ1: 3180, 2978, 2902, 1706, 1626, 1120, 1066.
4.2.3.2. 1,10 Di[2-(ethyloxycarbonyl)ethyl]ferrocene (11). It was pre-
pared according to a literature procedure [32] as follows: A solution
of 10 (1.3 g, 3.15 mmol) and 10% palladium-on-charcoal (0.3 g,
2.82 mmol) in ethyl acetate (100 mL) was degassed under argon for
30 min. The mixture was then saturated with hydrogen, stirred
vigorously for 72 h, filtered and the solvent removed under reduced
pressure to give 1.2 g (99%) of 11 as a yellow oil. 1H NMR (CDCl3)
3.94 mmol) yield. 1H NMR
d
(CDCl3)
d
3.98 (bs, 8H, 2ꢄ C5H4), 3.57 (t,
J ¼ 5.2 Hz, 4H, CH2eOH), 2.35 (t, J ¼ 6.6 Hz, 4H, FceCH2), 1.58 (m,
8H, FceCH2eCH2eCH2eOH), 1.37 (bs, 2H, OH). 13C{1H} NMR
(CDCl3)
d/ppm: 91.4 (Cipso), 70.1 (Cp), 69.1 (Cp), 62.3 (CH2eOH), 32.3
d/ppm: 4.06 (q, J ¼ 7.16 Hz, 4H, 2OeCH2eCH3), 4.01 (br s, 8H, 2ꢄ
(CpeCH2), 28.6 and 27.1 (CH2eCH2). IR, neat, nmax/cmꢀ1: 3334,

68
R. Claus et al. / Journal of Organometallic Chemistry 740 (2013) 61e69
3084, 2931, 2858. If the AlCl3 was not fresh (i.e. not optimally
reactive) a chromatographic separation of 4 and 5 utilising first
hexane:ether ¼ 1:3 afforded 4 (Rf ¼ 0.15), followed by elution with
ethyl acetate allowed the isolation of 5 (Rf ¼ 0.66; 5 does not elute
in hexane:ether 1:3). Further characterisation of 5 is as per para-
graph 4.2.5.
internal standard and then repeated in the presence of <0.5 mmol
dmꢀ3 decamethylferrocene (Fc*) [49]. In a separate experiment
only ferrocene and decamethylferrocene were measured under the
identical conditions. Potentials were then manipulated in a spread
sheet to allow potential reporting. Under the conditions of this
study the Fc*/Fc*þ couple was observed at ꢀ550 mV vs. FcH/FcHþ or
0
Eo ¼ 670 mV vs. Ag wire, ipc/ipa ¼ 0.99,
DEp ¼ 73 mV.
4.2.5. 1,10-Bis(1,4-dihydroxybutyl)ferrocene (5)
LiAlH4 (1.22 g, 32.1 mmol) in dry THF (40 mL) was stirred for
10 min and a solution of 7 (2.2 g, 5.3 mmol) in dry THF (15 mL) was
added dropwise at such a rate as to maintain gentle THF reflux. The
reaction mixture was stirred for 3e4 h at room temperature fol-
lowed by cooling to 0 ꢂC, quenching by slow addition of ice (5 g),
and stirring for an additional 1 h. The reaction mixture was filtered
and extracted with ether. After solvent removal, the residue was
purified by column chromatography utilizing ethyl acetate as
eluent to give the product as yellow oil in 95% yield. After three
days the oil solidified. The crystals can be recrystallized from ethyl
acetate, m.p. 158e159 ꢂC. Elemental analysis (%): calc. for
C18H26O4Fe (362.1): C, 59.7; H 7.2; found: C, 59.4; H 7.0. 1H NMR
Acknowledgements
The authors acknowledge the Central Research Fund of the UFS
and the NRF under grant 81829 for financial support.
Appendix A. Supplementary material
CCDC 927232 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(CDCl3)
d
/ppm: 4.72 (m, 2H, FceCH(OH)), 4.19e4.12 (m, 8H, 2ꢄ
Appendix B. Supplementary data
C5H4), 3.96e3.88 (m, 2H, CH2eOH), 3.84e3.77 (m, 2H, CH2eOH),
2.26e2.17 (m, 2H, eCH2e), 2.02e1.89 (m, 6H, eCH2e). 13C{1H} NMR
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.05.006.
(CDCl3) d/ppm: 93.9 (Cipso), 93.6 (Cipso), 69.9 (Cp), 69.2 (Cp), 67.6
(Cp), 67.5 (Cp), 67.4 (Cp), 66.7 (Cp), 66.1 (Cp), 65.7 (Cp), 62.5 (CH2e
OH), 37.3 (CpeCH), 36.7 (CpeCH), 29.1 and 28.9 (eCH2eCH2e). IR,
neat, nmax/cmꢀ1: 3284, 2941, 2859.
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