Microwave-assisted synthesis of 1,5-dioxo-3-substituted [5]ferrocenophanes

Article abstract of DOI:10.1016/j.jorganchem.2008.01.038

The Claisen-Schmidt reaction between 1,1′-diacetylferrocene and ferrocenecarboxaldehyde under microwave irradiation has been investigated in different conditions. The selective synthesis of 1,5-dioxo-3-ferrocenyl[5]ferrocenophane has been achieved and a simple protocol for its purification was established. The reaction was generally applicable to other non-enolizable aldehydes and the corresponding 1,5-dioxo-3-substituted [5]ferrocenophanes were obtained in high yield within 30 min.

Full text of DOI:10.1016/j.jorganchem.2008.01.038

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1375–1381
www.elsevier.com/locate/jorganchem
Microwave-assisted synthesis of
1,5-dioxo-3-substituted [5]ferrocenophanes
Sonia Pedotti, Angela Patti *
Istituto di Chimica Biomolecolare del CNR, Sez. di Catania,Via del Santuario 110, I-95028 Valverde CT, Italy
Received 26 November 2007; received in revised form 21 January 2008; accepted 21 January 2008
Available online 2 February 2008
Abstract
The Claisen–Schmidt reaction between 1,10-diacetylferrocene and ferrocenecarboxaldehyde under microwave irradiation has been
investigated in different conditions. The selective synthesis of 1,5-dioxo-3-ferrocenyl[5]ferrocenophane has been achieved and a simple
protocol for its purification was established. The reaction was generally applicable to other non-enolizable aldehydes and the correspond-
ing 1,5-dioxo-3-substituted [5]ferrocenophanes were obtained in high yield within 30 min.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: [5]Ferrocenophanes; Claisen–Schmidt condensation; Diacetylferrocene; Microwave-assisted synthesis
1. Introduction
from [5]ferrocenophane-1,5-dione, 1 (R = H) (see Fig. 1),
obtained by a sequence of Friedel–Crafts acylation of ace-
tylferrocene with 3-chloropropionyl chloride followed by
base-catalyzed cyclization [26]. The related 3-substituted
[5]ferrocenophane-1,5-diones 2 (R = Ar, alkyl) can be pre-
pared by means the reaction of 1,10-diacetylferrocene, 3
and aldehydes in NaOH ethanolic solution [27–31], result-
ing in a mixture of a,b-unsaturated ferrocenylketones and
ferrocenophanes, whose selective formation was obtained
in some cases [30,31]. Improved methods for the synthesis
of 2a (R = Ph) starting from 5a [26] or 6a [32] indepen-
dently prepared by Friedel–Craft acylations and treated
with NaOH ethanolic solution for long time (up to 65h),
have been proposed.
In the course of a study on the synthesis of 1,3-diferroce-
nylpropane systems, we investigated the Claisen–Schmidt
condensation of 3 with ferrocenecarboxaldehyde 4 and
evidenced that such reaction, when carried out under
microwave irradiation, can be easily driven toward the
exclusive formation of the [5]ferrocenophane system. This
one-pot procedure appeared highly effective also using
other non-enolizable aldehydes giving high yields of 1,5-
dioxo-3-substituted [5]ferrocenophanes and herein we
describe the obtained results.
Ferrocenophanes are cyclic organometallic compounds
bearing one or more bridges between two cyclopentadi-
enyl (Cp) rings on the same or different ferrocene unit
[1]. Metal-bridged [1]-ferrocenophanes and derivatives
with a short carbon chain in the bridge experience sub-
stantial strain between the Cp rings and easily undergo
a ring-opening polymerization reaction giving rise to poly-
mers with peculiar electronic properties [2–7]. Several
aza-ferrocenophanes have been designed as selective elec-
trochemical sensors for cations or anions [8–12] and more
recently the potential of ferrocene-based macrocycles as
molecular machines has been reported [13,14]. The syn-
thesis of homochiral ferrocenophanes and their applica-
tion as catalyst in asymmetric synthesis has been also
described [15–20].
Among the carbon-bridged ferrocenophanes, [3]- and
[4]-ferrocenophanes have been extensively investigated
[21–25] but a relatively small number of [5]-ferrocenophane
derivatives have been reported. Many of them are derived
*
Corresponding author. Tel.: +39 0957212136; fax: +39 0957212141.
E-mail address: angela.patti@icb.cnr.it (A. Patti).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.01.038

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S. Pedotti, A. Patti / Journal of Organometallic Chemistry 693 (2008) 1375–1381
Table 1
O
Claisen–Schmidt condensation of 3 and 4a
O
O
Fe
R
H
NaOH
O
+
2b
5b
6b
+
+
Fe
Fe
solvent
O
1
2
R = H
R = Ar, alkyl
3
4
Fig. 1. General structure of 1,5-dioxo-[5]ferrocenophanes.
Entry Solvent
3:4 mol. ratio Reaction mixture compositionb
3 (%) 2b (%) 5b (%) 6b (%)
2. Results and discussion
1
–
1:2
24
5c
4
2
8
51
15
6
64c
5f
24
44
84
88
78
15
79
88
30
95
76
16
38
25
ndd
5
7
30
3
nd
6
nd
7
14
26
12
5
7
4
3
6
nd
nd
4
Microwave technology has become a popular and useful
way to achieve consistent acceleration, in some instances
coupled with enhancements in selectivity, for a wide range
of organic reactions [33,34] and has been also applied to
the synthesis of ferrocenylchalcones [35]. On the contrary,
the effect of microwave activation in the Claisen–Schmidt
condensation of 1,10-diacetylferrocene with aldehydes has
not been systematically evaluated [36].
Since we were interested in the preparation of deriva-
tives containing more than one ferrocene unit we per-
formed different reactions under microwave irradiation
using 4 as aldehydic component. Each reaction was carried
out in a closed vessel using a microwave apparatus with a
single-mode cavity and equipped with temperature and
pressure control devices, which allowed us to achieve high
reproducibility. A 50 W microwave power was chosen as a
compromise between a sufficiently high speed of heating
and control of the temperature, set at 80 °C.
2
3
4
5
6
7
8
Dioxane
EtOH/water 1:2
EtOH/water 1:4
1:2
–
1:1
1:1
Dioxane
EtOH/water 1:1
EtOH/water 1:1e
9
10
a
EtOH/water 1:1g
EtOH/water 1:1h
13
68
14
2
Conditions: compound 3 (0.2 mmol), NaOH (2 mmol), solvent (2 mL),
80 °C, 50 W Mw power, 30 min reaction time.
b
Determined by 1H NMR analysis of the crude reaction mixture.
One hour of reaction time.
Not detected.
Conventional heating 80 °C.
Twenty four hours of reaction time.
Compound 3:NaOH 1:4 molar ratio.
K2CO3 was used as base.
c
d
e
f
g
h
Initial experiments were carried out under 30 min micro-
wave irradiation using 3 and 4 in a 1:2 molar ratio and 10
molar amount of NaOH, in order to evaluate the relative
ratios of all the possible products. In solvent-free condi-
tions the reaction was fast but not very selective affording
5b as main product; prolonging the reaction time increased
amounts of both 6b and 2b were observed (Table 1, entry
1).
In the presence of a polar solvent, ethanol/water 4:1
mixture or dioxane, compound 3 completely reacted giving
a 1:1 mixture of 2b and unreacted 4 (entries 2 and 3); the
use of an excess of aldehyde (entry 4), reported to enhance
the formation of the dienonylferrocene derivative [31,36],
resulted in a comparable composition of the final reaction
mixture.
According the mechanism previously proposed [26], the
first product of Claisen–Schmidt condensation between 3
and 4 is the 1-acetyl-10-(b-ferrocenylacryloyl)ferrocene 5b,
which can further react to afford the 1,10-diacryloylderiva-
tive 6b (path a) or undergo an intramolecular Michael
addition leading to the formation of the interannular
bridge of 2b (path b). Also compound 6b could contribute
to the formation of the ferrocenophane system via an
alkali-catalyzed retro-aldol reaction and subsequent intra-
molecular Michael addition [32] (Scheme 1).
Taking into account this mechanism, in the presence of
polar solvent and microwave irradiation the path a leading
to the formation of 6b appeared quite limited, indepen-
dently from the stoichiometry of the reacting aldehyde,
so that 5b selectively evolved to 2b. A fast conversion of
6b into 2b was ruled out, since parallel runs carried out
by treatment of separate 5b and 6b with ethanolic NaOH
without aldehyde for 30 min under Mw irradiation affor-
ded 2b in 60% and 25% yield, respectively.
The use of equimolar mixture of 3 and 4 resulted in
lower substrate conversion in the solvent-free reaction
(entry 5), while almost quantitative formation of 2b was
observed in polar solvents (entries 6–7). For the sake of
comparison, a parallel run was carried out using conven-
tional heating at 80 °C and a consistent reduction in the
reaction rate was observed (entry 8). Satisfactory values
of conversion and yield of 2b were also obtained using a
decreased amount of NaOH (entry 9), but not in the pres-
ence of K2CO3 as base (entry 10).
Ferrocenophane 2b was found highly insoluble in com-
mon organic solvents and sparingly soluble in CH2Cl2
(about 2 mg/mL) and attempts to purify it by chromato-
graphy led to severe decrease in the final yields. As a simple
protocol for the isolation of 2b, the reaction mixture was

S. Pedotti, A. Patti / Journal of Organometallic Chemistry 693 (2008) 1375–1381
1377
O
O
R
Fe
R
Fe
_
_
OH
CH2
path
b
O
O
O
O
2a R = Ph
2b R = Fc
O
NaOH
R
+
Fe
Fe
-
RCHO
R
H
path
a
O
O
O
O
RCHO
_
R
R
R
R
OH
3
4 R = Fc
5a R = Ph
5b R = Fc
Fe
Fe
O
O
_
O
6a R = Ph
6b R = Fc
Scheme 1. Mechanism of formation of [5]ferrocenophane system by Claisen–Schmidt condensation of 1,10-diacetylferrocene with aldehydes.
partitioned between water and a sufficient volume of
CH2Cl2, the organic phase taken to dryness and the residue
twice washed with hexane:AcOEt 1:1 (v/v) affording 2b as
gold-yellow solid. A preparative run on 2 mmol scale, per-
formed in open vessel applying conditions of entry 7 and
the above purification method, gave 2b in 75% isolated
yield (Table 2, entry 2) and 95% purity, the impurity
mainly due to 6b which showed similar solubility property.
This purification procedure gave a good compromise
between the isolated yield and chemical purity of 2b, which
could be used in this form as a substrate for further mod-
ification; pure 2b samples for its characterization were
obtained repeating the washing procedure more times or
by crystallization from CH2Cl2.
All compounds 2a and 2c–l could be purified exploiting
their low solubility in hexane:AcOEt as above described for
2b and fully characterized. As a common feature in their
Table 2
Microwave-assisted synthesis of 1,5-dioxo-3-substituted[5]ferroceno-
phanesa
O
NaOH
O
EtOH/H2O
Fe
3
R
+
R
H
Mw, 50W, 80 °C
30 min
O
The 1H NMR spectrum of 2b displayed four separate res-
onances, each accounting for two protons on the bridged
Cp rings, two partially overlapped double doublets for Ha
and Hb in the methylene groups and a broad triplet for
the methinic proton on the bridge so that an asymmetric
conformation of the molecule could be inferred [31]. The
ferrocenyl substituent at the 3-position appeared conform-
ationally unfixed giving rise to two singlets in a 4:5 ratio.
Our standard conditions were then applied to the
Claisen–Schmidt condensation between 3 and different non-
enolizable aldehydes as reported in Table 2. The reaction
works well with aromatic and heteroaromatic aldehydes
giving high yields of 1,5-dioxo-3-substituted [5]ferroceno-
phanes as sole products (the a,b-ferrocenylenone deriva-
tives not being detected in the reaction mixture) and no
obvious relationship between the electronic and/or steric
properties of aldehydes and their reactivity was evidenced.
Although p-NMe2-benzaldehyde resulted to be less reac-
tive, the obtained 40% isolated yield of 2d is comparable
with the results obtained in the synthesis of the N-diethyl
analogue using a fourfold excess of aldehyde and 18 h reac-
tion time [30].
2
Entry
R
Compound Conversion % Isolated yield of 2c
(%)b
(% purityd)
1
2
3
4
5
6
7
8
9
Ph
Fc
p-Cl–Ph
2a
2b
2c
74
93e
87
50f
94
92
77
64
73
94
63 (94)
75 (95)
78 (95)
40 (93)
80 (95)
78 (95)
69 (94)
52 (92)
61 (93)
82 (95)
p-NMe2–Ph 2d
p-Me–Ph
o-Me–Ph
b-Naphtyl
C(CH3)3
4-Pyr
2e
2f
2g
2h
2i
10
a
2-Quinoline 2l
Compound 3 (2 mmol), aldehyde (2 mmol), NaOH (10 mmol), EtOH/
H2O 4:1 (20 mL), 80 °C, 50 W Mw power, 30 min.
Determined by 1H NMR analysis of an aliquot of the crude reaction
b
mixture.
c
Referred to the starting diketone 3.
d
After two washing cycles with n-hexane:AcOEt (see Section 3).
The a,b-unsaturated ferrocenylketone 6b was present in the reaction
e
mixture (7%).
f
One hour of reaction time.

1378
S. Pedotti, A. Patti / Journal of Organometallic Chemistry 693 (2008) 1375–1381
O
O
a
b
Fe
Fe
Fe
Fc
Fc
Fc
O
2b
a) BH3 Me2S, CH2Cl2; b) MnO2, CH2Cl2
Fig. 2. Chemical modification of the keto-group of ferrocenophane.
7
8
1H NMR spectrum the methylenic protons were observed
as a well separated (about 0.4 ppm) triplet and broad dou-
blet, substantially unchanged upon heating up to 80 °C.
The keto-group modification of 1,5-dioxo-[5]ferroceno-
phanes and the peculiar chemistry of ferrocenes (e.g. the
nucleophilic substitution of an a-acetoxy group and the dia-
stereoselective ring metalation/electrophilic quenching
sequence, both occurring with stereochemical control [37])
could give access to a large number of derivatives with [5]fer-
rocenophane skeleton, many of them with defined chirality.
A simple deoxygenation–oxygenation sequence can be
applied to convert 1,5-dioxo-[5]ferrocenophanes into the
related derivatives possessing only one carbonyl group;
indeed, the treatment of 2b with BH3/Me2S in CH2Cl2
[38] gave the alkane derivative 7, which was in turn reacted
with MnO2 to afford monoketone 8 (Fig. 2).
3.1.1. Optimizazion of the reaction conditions for the
synthesis of 2b
To a solution of 3 (54 mg, 0.2 mmol) in EtOH/H2O (4:1
v/v 2 mL), aldehyde 4 in appropriate amount (see Table 1)
and NaOH (80 mg, 2 mmol) were added. The reaction was
carried out in a closed vessel using 50 W microwave power
and temperature set at 80°C. After 30 min the reaction mix-
ture was diluted with satd. NH4Cl (50 mL) and extracted
with CH2Cl2 (3 ꢀ 50 mL). The organic layer was washed
with brine, dried over Na2SO4 and an aliquot analyzed
1
by H NMR to determine the composition of the whole
crude reaction mixture.
3.2. General procedure for the synthesis of 1,5-dioxo-3-
substituted [5]ferrocenophanes
1
Due to the asymmetry of the molecule, the H NMR
To a solution of 3 (540 mg, 2.0 mmol) in EtOH/H2O
(4:1 v/v 20 mL), aldehyde (2.0 mmol) and NaOH
(800 mg, 20.0 mmol) were added. The reaction was carried
out in a 100 mL open vessel equipped with a reflux con-
denser using 50 W microwave power and temperature set
at 80 °C. After 30 min the reaction mixture was diluted
with satd. NH4Cl (50 mL) and extracted with CH2Cl2
(3 ꢀ 10 mL). The organic layer was washed with brine,
dried over Na2SO4 and, after have determined the compo-
sition of the reaction mixture as above, it was taken to dry-
ness. The residue was suspended in n-hexane:EtOAc 1:1
(15 mL) and the insoluble solid separated by filtration
and the solution discarded. The solid was dissolved in
CH2Cl2, the solution taken to dryness and the residue
washed again with n-hexane:EtOAc 1:1 (15 mL) leaving
ferrocenophanes as insoluble yellow solids with 92–95%
chemical purity, the main impurity being the starting 3,
and 80–90% recovery yield.
spectrum of 8 showed a separate resonance for each proton
on the bridge and the analysis of the coupling constants
evidenced a trans-diaxial relationship between the methinic
proton and two adjacent protons on C-2 and C-4 positions
of the bridge (JH3–H2a = 12.5 Hz and JH3–H4a = 9.8 Hz), so
that an equatorial disposition of the 3-substituent can be
deduced.
3. Experimental
3.1. General
All the aldehydes and 1,10-diacetylferrocene were com-
mercially available and used as received. Microprills
sodium hydroxide was purchased from Riedel–de-Hae¨n.
Microwave irradiation was performed in a CEM Discover
Benchmate equipped with a pressure control device. 1H
and 13C NMR spectra were recorded in CDCl3, unless
otherwise stated, at 400.13 and 100.62 MHz, respectively.
Chemical shifts (d) are given as ppm relative to the residual
solvent peak and coupling constants (J) are in Hz. In the
assignment of the NMR signals, CpH refers to cyclopenta-
dienyl protons or carbons whereas Cp refers to the quater-
nary carbon on the metallocene ring. ESI-MS spectra were
acquired on a Waters Micromass ZQ2000 instrument using
3.75 kV capillary voltage and 50 V cone voltage. Melting
points are uncorrected.
The above washing procedure was repeated on samples
of 2a–2l until satisfactory purity (>98%) for their NMR
characterization and elemental analyses was reached.
3.2.1. 1,5-Dioxo-3-phenyl[5]ferrocenophane (2a)
Obtained from the reaction of 3 and benzaldehyde, com-
pound 2a was known [26,32] but its NMR spectra were not
reported. 1H NMR d 2.51 (2H, br d, CH2a), 2.95 (2H, br t,
CH2b), 4.35 (1H, tt, J = 2.5 and 11.5, CH), 4.58 (2H, m,
CpH), 4.62 (2H, m, CpH), 4.89 (4H, m, CpH), 7.28 (2H,

S. Pedotti, A. Patti / Journal of Organometallic Chemistry 693 (2008) 1375–1381
1379
m, Ar-H), 7.37 (3H, m, Ar-H); 13C NMR d 45.6 (CH), 47.3
(CH2), 69.8 (CpH), 72.2 (CpH), 73.9 (CpH), 74.7 (CpH),
83.3 (Cp), 126.8 (Ar-CH), 127.0 (Ar-CH), 128.9 (Ar-CH),
145.1 (Ar-C), 202.4 (CO).
3.2.6. 1,5-Dioxo-3-(o-methylphenyl)[5]ferrocenophane
(2f)
From 3 and o-tolualdehyde, m.p. 275–276 (dec), 1H
NMR d 2.41 (2H, br d, CH2a), 2.56 (3H, s, CH3), 2.93
(2H, br t, CH2b), 4.56 (3H, m, CH and CpH), 4.62 (2H,
m, CpH), 4.90 (4H, br s, CpH), 7.22 (5H, m, Ar-H); 13C
NMR d 19.3 (CH3), 41.8 (CH), 45.8 (CH2), 69.2 (CpH),
71.8 (CpH), 73.5 (CpH), 74.3 (CpH), 82.1 (Cp), 125.2
(Ar-CH), 126.2 (Ar-CH), 126.6 (Ar-CH), 131.0 (Ar-CH),
135.3 (Ar-C), 143.2 (Ar-C), 198.5 (CO). ESI-MS: 394.8
(M ꢁ Na)+. Anal Calc. for C22H20FeO2: C, 70.99; H, 5.42.
Found: C, 70.91; H, 5.41%.
3.2.2. 1,5-Dioxo-3-ferrocenyl[5]ferrocenophane (2b)
From the reaction of 3 and ferrocenylcarboxaldehyde,
1
m.p. 302–303 (dec), H NMR d 2.72 (4H, two overlapped
AB systems, CH2), 4.08 (1H, m, CH), 4.15 (4H, br s,
CpH), 4.21 (5H, s, unsubstd. CpH), 4.55 (2H, br s,
CpH), 4.60 (2H, br s, CpH), 4.83 (2H, br s, CpH), 4.87
(2H, br s, CpH), 13C NMR d 41.0 (CH), 46.7 (CH2), 66.6
(CpH), 67.5 (CpH), 68.8 (unsubstd. CpH), 71.7 (CpH),
73.5 (CpH), 74.3 (CpH), 77.2 (CpH), 81.8 (Cp), 93.8
(Cp), 198.7 (CO); ESI-MS: 489 (M ꢁ Na)+. Anal Calc. for
C25H22Fe2O2: C, 64.42; H, 4.76. Found: C, 64.38; H,
4.73%.
3.2.7. 1,5-Dioxo-3-(b-naphthyl)[5]ferrocenophane (2g)
From 3 and b-naphthylaldehyde, m.p. 290–291 (dec), 1H
NMR d 2.61 (2H, br d, CH2a), 3.05 (2H, br t, CH2b), 4.51
(1H, br t, CH), 4.59 (2H, s, CpH), 4.63 (2H, s, CpH), 4.91
(2H, s, CpH), 4.94 (2H, s, CpH), 7.49 (3H, m, Ar-H), 7.79
(1H, s, Ar-H), 7.85 (3H, m, Ar-H); 13C NMR (CD2Cl2) d
46.3 (CH), 46.8 (CH2), 69.4 (CpH), 72.1 (CpH), 74.0
(CpH), 74.7 (CpH), 82.3 (Cp), 125.0 (Ar-CH), 126.0 (Ar-
CH), 126.5 (Ar-CH), 127.9 (Ar-CH), 128.7 (Ar-CH),
132.8 (Ar-C), 134.0 (Ar-C), 143.2 (Ar-C), 198.4 (CO).
ESI-MS: 430.8 (M ꢁ Na)+. Anal Calc. for C25H20FeNO2:
C, 73.55; H, 4.94. Found: C, 73.39; H, 4.91%.
3.2.3. 1,5-Dioxo-3-(p-chlorophenyl)[5]ferrocenophane (2c)
From 3 and p-chlorobenzaldehyde, m.p. 311–312 (dec)
1H NMR d 2.48 (2H, br d, CH2a), 2.90 (2H, br t, CH2b),
4.32 (1H, br t, CH), 4.59 (2H, s, CpH), 4.62 (2H, s,
CpH), 4.88 (4H, s, CpH), 7.33 (4H, m, Ar-H); 13C NMR
(CD2Cl2) d 45.6 (CH), 46.5 (CH2), 69.4 (CpH), 72.2
(CpH), 74.1 (CpH), 74.8 (CpH), 82.2 (Cp), 128.6 (Ar-
CH), 129.1 (Ar-CH), 132.6 (Ar-C), 144.2 (Ar-C), 198.1
(CO). ESI-MS: 414.8 (M ꢁ Na)+ and 416.8 (M ꢁ Na)+. Anal
Calc. for C21H17ClFeO2: C, 64.24; H, 4.36. Found: C,
64.18; H, 4.34%.
3.2.8. 1,5-Dioxo-3-(tert-butyl)[5]ferrocenophane (2h)
From 3 and pivalaldehyde, m.p. 309–310 (dec), 1H
NMR d 1.03 (9H, s, CH3), 2.44 (4H, br d, CH2), 2.85
(1H, br t, CH), 4.52 (2H, s, CpH), 4.56 (2H, s, CpH),
4.80 (4H, s, CpH); 13C NMR d 28.0 (CH3), 33.5 (C), 41.7
(CH2), 50.0 (CH), 69.9 (CpH), 71.9 (CpH), 73.6 (CpH),
74.4 (CpH), 82.5 (Cp), 200.0 (CO). ESI-MS: 360.6
(M ꢁ Na)+. Anal Calc. for C19H22FeO2: C, 67.47; H, 6.56.
Found: C, 67.38; H, 6.52%.
3.2.4. 1,5-Dioxo-3-(p-dimethylaminophenyl)[5]ferroceno-
phane (2d)
From 3 and p-dimethylaminobenzaldehyde, m.p. 254–
1
255 (dec) H NMR d 2.50 (2H, br d, CH2a), 2.91 (2H, br
t, CH2b), 2.95 (6H, s, N-CH3), 4.26 (1H, br t, CH), 4.56
(2H, br s, CpH), 4.60 (2H, br s, CpH), 4.87 (2H, br s,
CpH), 4.89 (2H, br s, CpH), 6.74 (2H, d, J = 8.6, Ar-H),
7.24 (2H, d, J = 8.6, Ar-H); 13C NMR d 40.7 (N-CH3),
45.0 (CH), 46.9 (CH2), 69.5 (CpH), 71.6 (CpH), 73.9
(CpH), 74.3 (CpH), 81.9 (Cp), 112.9 (Ar-CH), 127.3 (Ar-
CH), 133.1 (Ar-C), 149.5 (Ar-C), 198.6 (CO). ESI-MS:
423.9 (M ꢁ Na)+. Anal Calc. for C23H23FeNO2: C, 68.84;
H, 5.78; N, 3.49. Found: C, 68.80; H, 5.77; N, 3.47%.
3.2.9. 1,5-Dioxo-3-(4-pyridyl)[5]ferrocenophane (2i)
From 3 and 4-pyridinecarboxaldehyde, m.p. 265–266
1
(dec), H NMR d 2.51 (2H, br d, CH2a), 2.91 (2H, br t,
CH2b), 4.32 (1H, br t, CH), 4.60 (2H, s; CpH), 4.64 (2H,
s, CpH), 4.89 (4H, s, CpH), 7.31 (2H, d, J = 4.0, Ar-H),
8.60 (2H, d, J = 4.0, Ar-H); 13C NMR (CDCl3/CD3OD)
d 44.7 (CH), 45.1 (CH2), 69.1 (CpH), 72.0 (CpH), 74.1
(CpH), 74.9 (CpH), 81.3 (Cp), 122.5 (Ar-CH), 149.4 (Ar-
CH), 154.2 (Ar-C), 198.3 (CO). ESI-MS: 381.8 (M ꢁ Na)+.
Anal Calc. for C20H17FeNO2: C, 66.87; H, 4.77; N, 3.90.
Found: C, 66.80; H, 4.74; N, 3.88%.
3.2.5. 1,5-Dioxo-3-(p-methylphenyl)[5]ferrocenophane
(2e)
From 3 and p-tolualdehyde, m.p. 284–285 (dec), 1H
NMR d 2.35 (3H, s, CH3), 2.48 (2H, br d, CH2a), 2.93
(2H, t, J = 12.3, CH2b), 4.32 (1H, br t, CH), 4.57 (2H, m,
CpH), 4.62 (2H, m, CpH), 4.87 (2H, s, CpH), 4.89 (2H,
s, CpH), 7.17 (2H, d, J = 7.7, Ar-H), 7.26 (2H, d,
J = 7.7, Ar-H); 13C NMR d 21.0 (CH3), 45.5 (CH), 46.5
(CH2), 69.4 (CpH), 71.6 (CpH), 73.5 (CpH), 74.4 (CpH),
81.8 (Cp), 126.6 (Ar-CH), 129.4 (Ar-CH), 136.4 (Ar-C),
142.1 (Ar-C), 198.4 (CO). ESI-MS: 394.9 (M ꢁ Na)+. Anal
Calc. for C22H20FeO2: C, 70.99; H, 5.42. Found: C,
70.89; H, 5.39%.
3.2.10. 1,5-Dioxo-3-(2-quinolyl)[5]ferrocenophane (2l)
From 3 and 2-quinolylcarboxaldehyde, m.p. 282–283
(dec), 1H NMR d 2.65 (2H, br d, CH2a), 3.25 (2H, t,
J = 12.5, CH2b), 4.61 (5H, m, CH and CpH) 4.91 (2H, s,
CpH), 5.04 (2H, s, CpH), 7.53 (2H, m, Ar-H), 7.25 (1H, m,
Ar-H), 7.82 (1H, d, J = 8.2, Ar-H), 8.08 (1H, d, J = 8.4,
Ar-H), 8.15 (1H, d, J = 8.4, Ar-H); 13C NMR d 44.7 (CH),
48.3 (CH2), 69.1 (CpH), 72.2 (CpH), 73.5 (CpH), 74.3
(CpH), 82.1 (Cp), 120.8 (Ar-CH), 126.1 (Ar-CH), 127.1

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S. Pedotti, A. Patti / Journal of Organometallic Chemistry 693 (2008) 1375–1381
(Ar-C), 127.6 (Ar-CH), 129.0 (Ar-CH), 129.4 (Ar-CH), 136.8
(Ar-CH), 147.8 (Ar-C), 153.6 (Ar-C), 199.0 (CO). ESI-MS:
431.8 (M ꢁ Na)+. Anal Calc. for C24H19FeNO2: C, 70.43;
H, 4.68; N, 3.42. Found: C, 70.35; H, 4.65; N, 3.40%.
rocene and aldehydes is faster and more selective with
respect to other reported methods in producing 1,5-
dioxo-3-substituted[5]ferrocenophanes. The availability of
functionalized aldehydes and the subsequent modifications
of the keto-groups of the products can give access to a large
variety of [5]ferrocenophanes, some of which have been
here synthesized and characterized for the first time. Fur-
ther study on the related chiral ferrocenophanes and their
potential application in homogeneous catalysis field are
in progress.
3.3. Synthesis of 3-ferrocenyl[5]ferrocenophane (7)
To a solution of 2b (50 mg, 0.11 mmol) in CH2Cl2
(25 mL) was added BH3/Me2S (2 M in THF, 0.15 mL)
and the reaction was stirred at room temperature for 5 h.
As soon as the quantitative conversion of the substrate
was observed by TLC analysis (CH2Cl2/AcOEt 9:1), the
reaction was quenched by addition of MeOH, diluted with
satd. NH4Cl (30 mL) and extracted with CH2Cl2
(3 ꢀ 10 mL). The organic layer was washed with brine,
dried over Na2SO4 and taken to dryness under vacuum
to give a residue which was applied to Si gel column (n-hex-
ane:AcOEt). Pure 7 (42 mg, 89% yield) was obtained as a
yellow solid, m.p. 140–141, 1H NMR d 1.93 (2H, m),
2.17 (2H, dddd, J = 3.8, 3.8, 10.1 and 14.3), 2.29 (2H,
ddd, J = 3.8, 6.5 and 15.8) 2.49 (2H, ddd, J = 3.8, 10.1
and 15.8), 3.55 (1H, m), 4.02 (2H, m), 4.05 (2H, m), 4.07
(2H, m), 4.13 (2H, d, J = 1.6), 4.15 (2H, d, J = 1.6), 4.18
(2H, m), 4.20 (5H, s); 13C NMR d 24.2 (CH2), 31.9
(CH2), 34.55 (CH), 66.5 (CH), 66.6 (CH), 66.9 (CH), 67.2
(CH), 67.9 (CH), 68.4 (CH, Cp0), 68.8 (CH), 89.8 (C),
96.5 (C). ESI-MS: 474.7 (M ꢁ Na)+. Anal. Calc. for
C25H26Fe2: C, 68.53; H, 5.98. Found: C, 68.48; H, 5.96%.
Acknowledgement
Thanks are due to the project ‘‘Tecnologie sensoristiche
e sistemi automatici intelligenti per l’innalzamento compet-
`
itivo delle attivita produttive” POR Sicilia 2000–2006 –
misura 3.15 for financial support.
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