Synthesis, structure, and properties of a mononuclear ferrocenophane bearing two carbodiimide units as bridges

Article abstract of DOI:10.1016/j.tetlet.2016.01.084

A novel bis(carbodiimido)[11]ferrocenophane was synthesized using a methodology involving an aza, Wittig reaction of the 1,1′-bis(triphenylphosphoranylideneamino)ferrocene with the commercially available 1,3-bis(2-isocyanatopropan-2-yl)benzene. Moreover, its electrochemical and chemical properties were also examined. The ureido derivative formed when the bis(carbodiimido)ferrocenophane was hydrolyzed under acidic conditions, behaves as a chemodosimeter for sensing nitrite anions in aqueous solutions.

Full text of DOI:10.1016/j.tetlet.2016.01.084

Accepted Manuscript
Synthesis, structure, and properties of a mononuclear ferrocenophane bearing
two carbodiimide units as bridges
Antonia Sola, Raúl A. Orenes, A. Tárraga, Pedro Molina
PII:
S0040-4039(16)30083-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.01.084
TETL 47248
Reference:
Tetrahedron Letters
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Revised Date:
Accepted Date:
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20 January 2016
22 January 2016
Please cite this article as: Sola, A., Orenes, R.A., Tárraga, A., Molina, P., Synthesis, structure, and properties of a
mononuclear ferrocenophane bearing two carbodiimide units as bridges, Tetrahedron Letters (2016), doi: http://
dx.doi.org/10.1016/j.tetlet.2016.01.084
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Synthesis, structure, and properties of a
mononuclear ferrocenophane bearing two
carbodiimide units as bridges
Antonia Sola,a Raúl A. Orenes,b A. Tárraga*a and P. Molina*a
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1
Tetrahedron Letters
Synthesis, structure, and properties of a mononuclear ferrocenophane bearing two
carbodiimide units as bridges
Antonia Solaa, Raúl A. Orenesb, A. Tárragaa and Pedro Molinaa
aDepartamento de Química Orgánica, Facultad de Química, Universidad de Murcia. Campus de Espinardo, 30100 Murcia, Spain. E-mail: pmolina@um.es and
E-mail: atarraga@um.es.
bServicio de Apoyo a la Investigación (SAI), Campus de Espinardo. 30100 Murcia,Spain.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel bis(carbodiimido)[11]ferrocenophane was synthesized using a methodology involving
an aza, Wittig reaction of the 1,1’-bis(triphenylphosphoralydienamino)ferrocene with the
commercially available 1,3-bis(2-isocyanatopropan-2-yl)benzene. Moreover, its electrochemical
and chemical properties were also examined. The ureido derivative formed when the
Available online
bis(carbodiimido)ferrocenophane was hydrolyzed under acidic conditions, behaves as
chemodosimeter for sensing nitrite anions in aqueous solutions
a
Keywords:
Ferrocenophane
Aza-Wittig
2015 Elsevier Ltd. All rights reserved.
Carbodiimide
Crystal structure
Introduction
Although the ferrocenophane chemistry has already acquired a
high degree of maturity the synthesis of new types of these
fascinating class of molecules is still of high interest. For this
reason, and in a continuation of our ongoing studies involving the
synthesis and structural characterization of new families of
nitrogen-rich metallocenophanes with interesting structural,
electrochemical and optical properties7 we have now focused our
research on the synthesis, characterization and electrochemical
properties of the novel mononuclear [11]ferrocenophane 4 with
the characteristic feature of having two carbodiimide functions as
part of the ansa [11] bridge.
Since ferrocene was discovered in 19511 a remarkable
attention has been paid to this robust building block which can
easily be functionalized by using most of the procedures known
for organic synthesis. As a result, a wide variety of ferrocene-
based molecules have been directly synthesized starting from the
parent organometallic complex. On the other hand, the high
stability of such ferrocene-based derivatives together with their
easiness to reversibly undergo single electron oxidation to give
stable ferrocenium radical cations makes ferrocenyl systems
particularly attractive in many fields such as homogeneous
catalysis, especially in stereoselective and asymmetric
transformations, in electrochemistry, particularly in electron-
transfer processes, as new materials, as anticancer reagents, etc.2
The versatility of functionalization of ferrocene has opened the
way to the rapid expansion of its chemistry including the
preparation of bridged ferrocenes, called ferrocenophanes, which
are ring systems in which the two cyclopentadienyl groups of
ferrocene are linked by an atomic or a molecular bridge. Among
the different classes of ferrocenophanes reported in the last
decades particular attention have been paid to the families of
Despite the fact that the cyclic bis(carbodiimides) are
extremely unstable compounds that undergo intramolecular [2+2]
cycloadditions to give four-membered rings, such as 1,3-
diazetidine-2,4-diimines,8 it has also been reported that [3.3]
ferrocenophane derivatives, in which the ferrocenyl termini are
directly linked by two carbodiimide functions, can easily be
derivatized to give extremely nitrogen-rich ferrocenophanes with
unprecedented topologies.9
Results and discussion
mononuclear
[n]ferrocenophanes
and
multinuclear
A straightforward approach to 4 involves the use of the aza-
Wittig methodology,10 starting from the bis(iminophosphorane)
3, readily prepared by the Staudinger reaction between
triphenylphosphine and 1,1’-diazidoferrocene 2.9c An advantage
of this approach is that 1,1’-diazidoferrocene 2 is easily
[m.n]ferrocenophanes3 due to their applications in molecular
recognition and sensing,4 or in the preparation of conjugated
polymers via ring opening polymerization (ROP)5 or ring-
opening metathesis polymerization (ROMP).6
———
 Corresponding author. Tel.: +34-868-887-496; fax: +34-868-884-149; e-mail: pmolina@um.es
 Corresponding author. Tel.: +34-868-887-499; fax: +34-868-884-149; e-mail: atarraga@um.es

2
Tetrahedron
accessible
from
ferrocene
by
using
2,4,6-
Figure 1. Pattern of signals observed in the aliphatic and aromatic region
triisopropylbenzenesulfonyl azide (trisyl azide) as a strong azide-
transfer reagent.11 Thus, reaction of 1,1´-dilithioferrocene with
trisyl azide at 0º C afforded directly 2, which was used without
further purification for the next step in the Staudinger reaction
with triphenylphosphine. The aza-Wittig reaction of 3 with the
commercially available 1,3-bis(2-isocyanatopropan-2-yl)benzene
directly gave the bis(carbodiimido)[11]ferrocenophane 4, as the
only reaction product, in 26% yield (Scheme 1),12 which was
fully characterized by using the standard spectroscopic tecniques
(IR, 1H- and 13C-NMR,), mass spectrometry and elemental
analysis as well as by single crystal X-ray diffraction.13
of the 1H NMR of 4, in CDCl3.
The structure of compound 4 has been also resolved by single
crystal X-ray diffraction (Figure 2 up; see also ESI). Compound
4 crystallizes as an orange prism in the orthorhombic space group
P 212121 with one molecule in the asymmetric unit. The two
cyclopentadienyl (Cp) rings of the ferrocenyl moiety are
perfectly planar (the mean deviation from planes being 0.0027
and 0.0041 Å). The Cp rings are twisted from the eclipsed
conformation, the average torsion angle C1-centroid(Cp)1-
centroid(Cp)2-C10 being 27.55° and have an almost parallel
orientation with a tilt angle of 1.2°. The organic ligand is
attached to the C1 and C6 carbon atoms of the Cp rings through
the carbodiimide groups–N1=C11=N2- and –N3=C12=N4-,
respectively. The distances and angles of the carbodiimides are:
1.219(2) and 1.2215(19) Å and 170.73(15)° (N1-carbodiimide)
and 1.237(2) and 1.206(2) Å and 169.67(15)° (N3-carbodiimide).
The average torsion angle N1-centroid(Cp)1-centroid(Cp)2-N3 is
102.15° and the benzene ring of the ligand is rotated respect to
the Cp rings, the angle between mean planes being 118.2 (C1-
ring) and 118.5º (C6-ring).
Regarding the crystal structure of 4, molecules are interlinked
by intermolecular C-H··· interactions between the H23C
hydrogen atom and the benzene ring of the organic ligand of a
neighbouring molecule. The distance between the hydrogen and
the centroid of the ring is 2.807 Å. The result of these
interactions is the formation of infinite chains along the a-axis.
These chains are arranged in planes perpendicular to the b-axis in
a way that the chains of adjacent planes exhibit opposite
directions (Figure 2, down).
Scheme 1. Pathway followed for the preparation of ferrocenophane 4
Thus, the formation of the carbodiimide function is clearly
evidenced by the appearance in the IR spectrum of a strong
absorption band at ṽ = 2125 cm-1. Moreover, its 1H NMR
spectrum shows, in addition to the singlet associated to the
protons present in the four methyl groups, two different
pseudotriplets, corresponding to the H and H present in the Cp
units belonging to the ferrocene moiety. However,
a
characteristic feature of this 1H NMR spectrum is the appearance
of a different pattern for the aromatic signals, depending on the
deuterated solvent used. Thus, by using CD3CN two different
singlets at  = 7.43 ppm and  = 8.23 ppm, integrating three
protons and one proton respectively, were observed. However,
the 1H NMR spectrum carried out in CDCl3, showed a set of four
different signals for the magnetically different aromatic protons
(H2, H5, and H4/H6) present in 4. This pattern of signals (Figure
1), typical for an AMNN’ system, fully agrees with that of a
simulated model compound14 (see Electronic Supplementary
Information ESI, Figure SI 2) similar to 4, in which the ferrocene
and m-xylylene units are directly linked by cabodiimide groups.
On the other hand, the 13C NMR spectrum is also in agreement
with the structure proposed for 4.

3
Figure 2. Crystal structure of compound
4
(ORTEP molecular
characteristic of the tetrafluoroborate anion. To prove the above
representation and atom-labelling scheme)(up), and crystal packing diagram
mentioned hypothesis the hydrolysis reaction was carried out
under nitrogen atmosphere, but, interestingly, under such
conditions no green species were detected. However, when the
flask was opened and the solution was allowed to stand to the air,
it immediately acquired a greenish hue. These experimental and
spectroscopic results suggest that once the hydrolysis of the
carbodiimide has taken place, the resulting urea undergoes a
rapid oxidation of the ferrocene unit, by the action of the
atmospheric oxygen, to form the stable ferrocinium salt.17
of 4 (down).
The electrochemical behavior of ferrocenophane 4 was studied
by cyclic voltammetry (CV), and Osteryoung square-wave
voltammetry (OSWV) in solutions of CH3CN (c = 5 x 10-4 M)
containing 0.1 M of [(n-Bu)4N]PF6 (TBAHP) as supporting
electrolyte. As expected, the CV of 4 shows a reversible one-
electron oxidation wave at E1/2
=
450 mV versus
decamethylferrocene (DCMF) (Figure 3). The criteria applied for
reversibility was a separation of 60 mV between cathodic and
anodic peaks, a ratio for the intensities of the cathodic and anodic
currents Ic/Ia of 1.0, and no shift of the half wave potentials with
varying scan rates. Of course, the magnitude of this E1/2 is
identical as that obtained from the corresponding OSWV peak
(Figure SI 6).
To provide support to the observed phenomena and insight
into the proposed nature of the species 6, formed under
hydrolysis conditions, a set of electrochemical studies were
performed. Remarkably, linear sweep voltammetric (LSV)
studies carried out with 4 and 6 demonstrate a shift of the
sigmoidal voltammetric wave, from the region of anodic currents
to the region of cathodic currents, when passing from 4 to 6. This
particular behavior clearly indicates the different oxidation state
of the iron atom present in the bis-cabodiimidoferrocenophane 4
(Fe2+) and in the bis-ureidoferrocenophane 6 (Fe3+), and
constitutes an additional evidence for the structure of 5 (Figure 4)
Figure 3. CV of 4 (5 x 10-4 M) in CH3CN with TBAHP (0.1 M) as supporting
electrolyte, scanned at 0.1 V.s-1. Decamethylferrocene was used as an internal
standard
An interesting point in carbodiimide chemistry include their
hydrolysis to give the corresponding urea functions, which, in
turn, can be used as H-bond donors in a variety of anion
receptors.15 Therefore, we decided to explore the possibility of
converting the bis-carbodiimidophane 4 into a new kind of very
preorganized ferrocenophane receptor 5, bearing in its molecule a
ferrocene signaling unit directly attached to two urea binding
sites for anions.
Figure 4. LSV of 4 (solid line) and 6 (dashed line) (c = 5 x 10-4 M in
CH3CN, in each case) with TBAHP (0.1 M) as supporting electrolyte,
obtained using a rotating disk electrode at 100 mV s-1 and 1000 rpm
It is very well known that the hydrolysis of carbodiimides is a
relatively slow reaction. However, it can be catalyzed by under
acidic conditions.16 Thus, while treatment of 4 under neutral
conditions did not lead to any change in the molecule, when the
hydrolysis reaction was carried out in the presence of HCl a new
deep green species was formed, showing in its IR spectrum two
absorptions bands at ṽ = 3290 and ṽ = 1663 cm-1 which could be
attributable to the presence, in the new compound formed, of NH
To further evaluate the practical applicability of 6 as a
electrochemical probe for sensing reducing anions, titration
-
2-
experiments in the presence of anions such as NO2 , SO3 , I- or
ascorbate, by using electrochemical and optical techniques, were
carried out. Whereas negligible changes in the LSV
voltammogram of 6 were observed upon addition of SO32- and I-,
-
a significant modifications was observed upon addition of NO2
1
and C=O groups, respectively. However, the H- and 13C NMR
or ascorbate anions, although they were dependent on the anion
studied. Thus, rotating disk voltammetry studies carried out upon
addition of substoichiometric amounts of sodium ascorbate (c =
2.5 x 10-2 M in H2O) to a solution of 6 (c = 5 x 10-4 M in CH3CN)
show a significant shift of the sigmoidal voltammetric wave
toward anodic currents, indicating that this anion only promotes
the reduction of the ferrocinium salt 6. By contrast, the same
spectra of such species could not be obtained because it shown
paramagnetic character. Nevertheless, its high resolution mass
spectrum gave a molecular ion peak at m/z = 460.1564 which is
in agreement with the calculated for the urea derivative (m/z =
450.1562) (Figure SI 7). From these results, seems to be clear
that under such conditions the final urea product should be
formed but, immediately, it is oxidized to form a stable
ferrocinium salt. Similar results were also obtained when HBF4
was used instead of HCl, but, in this case, a new very broad band
at ṽ = 1060 cm-1 was also observed in the IR spectrum, which is
-
experiments carried out upon addition of NO2 anions to 6, in the
presence of 1L of HBF4, showed a significant shift of the
sigmoidal voltammetric wave toward more positive potentials,

4
Tetrahedron
indicating the development of a binding process between the
Figure 6. ESI MS spectrum of the species formed upon reaction of nitrite
ions with solution of 6, containing 1l of HBF4, indicating the
receptor 6 and this anion (Figure SI 8).
a
functionalization of the molecule with two NO groups.
The above mentioned sensing properties of 6 toward sodium
nitrite have also been studied by using absorption spectroscopy.
The UV-vis of 6 shows three absorption bands at  = 279, 434
and 600 nm, the lowest energy band being responsible for the
green color of the compound, when it is in solution. Interestingly,
the results obtained upon addition of aqueous solutions of the
anions under study confirm the electrochemical results
previously shown in the sense that the most characteristic
variations in the UV-vis spectrum of the receptor are promoted
upon addition of nitrite anions (c = 2.5 x 10-2 M in H2O) to a
solution of 6 (c = 1 x 10-4 M) in CH3CN. Such changes involved
the disappearance of the aforementioned three bands and the
simultaneous appearance of a new one at  = 357 nm (Figure 5).
These facts are responsible for the change of color from deep
green to yellow, which is perceptible to the naked-eye. From
these titration data, a detection limit18 of 1.2 x 10-5 M was
calculated (Figure SI 9).
Because the nitrite anion induces a chemical reaction giving
rise to a new product, different from the starting material, with
different optical properties, and allows the detection of the anion,
the compound 6 could be considered as a useful chemodosimeter
for the naked eye detection of nitrite anions, whose concentration
in drinking water is object of strict regulation and should not
exceed 65 M.20 Interestingly, although the research on the
development of different types of chemosensors for the selective
and sensitive determination of nitrite anions is very active,21 to
the best of our knowledge, methods based on the
chemodosimeter approach, using urea functions, have not been
described.
In summary, we report herein the synthesis, characterization
and redox properties of
a
novel and very stable
[11]ferrocenophane with the structural peculiarity of heaving an
ansa bridge linking the cyclopentadienyl rings of the ferrocene
unit, featuring carbodiimide functions as bridging groups.
Moreover, under acidic conditions, this compound is transformed
into the corresponding bis-ureido ferrocenophane which is easily
oxidized under such reaction conditions to give a ferrocinium salt
which can be used as chemodosimeter for sensing nitrite anions
in aqueous solutions.
Acknowledgments
We gratefully acknowledge the financial support from
MICINN-Spain, Project CTQ2011/27175, FEDER, and to Prof.
A. Arques for carrying out the simulated 1H NMR spectrum.
References and notes
1.
2.
Kealy, T.J.; Pauson, P. L. Nature 1951, 168, 1039-1040.
(a) Togni, A.; Hayashi, T. Ferrocenes: Homogeneous Catalysis,
Organic Synthesis, Materials Science, VCH: Weinheim, Germany,
1995; (b) Stepnicka, P. Ferrocenes: Ligands, Materials and
Biomolecules, Wiley: Chichester, U. K., 2008; (c) Dai, L.-X.; Hou,
X.-L- Chiral Ferrocenes in Asymmetric Catalysis: Synthesis and
Applications, Wiley-VCH: Weinheim, Germany, 2010; (d) Jaouen,
G.; Metzler-Nolte, N. Medicinal Organometallic Chemistry,
Springer: Berlin, 2010; Topics in Organometallic Chemistry 32; (e)
Braga, S. S.; Silva, A. M. S. Organometallics, 2013, 32, 5626-
5639.
Heo, R. W.; Lee, T. R. J. Organomet. Chem. 1999, 578, 31-42.
(a) Molina, P.; Tárraga, A.; Caballero, A. Eur. J. Inorg. Chem.
2008, 22, 3401-3417 and references cited therein; (b) Otón, F.;
Ratera, I.; Espinosa, A.; Wuerts, K.; Parella, T.; Tárraga, A.;
Veciana, J.; Molina, P. Chem. Eur. J. 2010, 16, 1532-1542.
(a) Manners, I.; Vogel, U. In Modern Cyclophane Chemistry;
Hening R. H. G., Ed.; Wiley-VCH: Weinheim, Germany, 2004; pp
415-433; (b) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew.
Chem. Int. Ed. 2007, 46, 5060-5081; (c) Bellas, V.; Rehahn, M.
Angew. Chem. Int. Ed. 2007, 46, 5082-5104; (d) Whittell, G. R.;
Hager, M. D.; Schubert, U. S.; Manners, I. Nature Mater. 2011, 10,
176-188; (e) Russell, A. D.; Gilroy, J. B.; Manners, I. Chem. Eur. J.
2014, 20, 4077-4085.
Figure 5. Changes in the absorption spectra of 6 (black) (c = 1 x 10-4 M in
CH3CN), upon addition of NaNO2 (c = 2.5 x 10-2 M in H2O), from 0 to 1
equiv (deep purple); arrows indicate the absorptions than increase or decrease
during the experiment. Inset: visual features observed upon addition of the
NO2- anion.
Unfortunately, all attempts to study, through 1H NMR
spectroscopy, the type of mechanism taking place in the
interaction between 6 and the nitrite anion were unsuccessful
because the resulting new species still remained paramagnetic.
However, the ESI MS spectrum showed a peak at m/z = 518
indicating that two nitroso groups have been incorporated to the
structure of 6, probably through a N-nitrosation reaction of the
urea functions19 (Figure 6).
3.
4.
5.
6.
7.
(a) Heo, R. W.; Park, J.-S.; Jason T. G; Claudio, G. C.; Takenaga,
M.; Albright, T. A; Lee, T. R. Tetrahedron 2004, 60, 7225-7235;
(b) (a) Heo, R. W.; Park, J.-S.; Lee, T. R. Macromolecules 2005,
38, 2564-2573.
(a) Tárraga, A.; Molina, P.; López, J. L.; Velasco, M. D.
Tetrahedron Lett. 2000, 41, 2479-2482; (b)Tárraga, A.; Molina, P.;
López, J. L.; Velasco, M. D.; Bautista, C.; Jones, P. G.
Organometallics 2002, 21, 2055-2065; (c) Tárraga, A.; Molina, P.;
López, J. L.; Velasco, M. D. Tetrahedron Lett. 2003, 44, 3371-
3375; (d) López, J. L.; Tárraga, A.; Espinosa, A.; Velasco, M. D.;

5
Molina, P.; Lloveras, V.; Vidal-Gancedo, J.; Rovira, C.; Veciana,
J.; Evans, D. J.; Wurst, K. Chem. Eur. J. 2004, 10, 1815-1826; (e)
Caballero, A.; Lloveras, V.; Tárraga, A.; Espinosa, A.; Velasco, M.
D.; Vidal-Gancedo, J.; Rovira, C.; Wurst, K.; Molina, P.; Veciana,
J. Angew. Chem. Int. Ed. 2005, 44, 1977-1981; (f) Otón, F.;
Tárraga, A.; Espinosa, A.; Velasco, M. D.; Molina, P. J. Org.
Chem. 2006, 71, 4590-4598; (g) Otón, F.; Espinosa, A.; Tárraga,
A.; Ratera, I.; Wurst, K.; Veciana, J.; Molina, P. Inorg. Chem.
2009, 48, 1566-1576; (h) Sola, A.; Orenes, R. A.; García, M. A.;
Claramunt, R.; Alkorta, I.; Elguero, J.; Tárraga, A.; Molina, P.
Inorg. Chem. 2011, 50, 4212-4220; (i) Sola, A.; Tárraga, A.;
Molina, P. Dalton Trans. 2012, 41, 8401-8409.
20. World Health Organization. In Guidelines for Drinking Water
Quality: Incorporating 1st and 2nd Addenda, Vol 1,
Recommendations, 3rd ed.; WHO Press, Geneva, Switzerland, 2008.
21. (a) Moorcroft, M. J.; Davis, J.; Compton, R. G. Talanta, 2001, 54,
785-803; (b) Afkhami, A.; Bahram, M.; Gholami, S.; Zand, Z.
Anal. Biochem. 2005, 336, 295-299; (c) Chadlaoui, M.; Abarca, B.;
Ballesteros, R.; Ramírez de Arellano, C.; Aguilar, J.; Aucejo, R.;
García-España, E. J. Org. Chem. 2006, 71, 9030-9034; (d)
Ballesteros-Garrido, R.; Abarca, B.; Ballesteros, R.; Ramírez de
Arellano, C.; Leroux, F. R.; Colobert, F.; García-España, E. New J.
Chem. 2009, 33, 2102-2106; (e) Feng, L.; Li, H.; Li, X.; Chen, L.;
Shen, Z.; Guan, Y. Anal. Chim. Acta. 2012, 743, 1-8; (f)
Mahapatra, A. K.; Hazra, G.; Mukhopadhyay, S. K.;
Mukhopadhyay, A. R. Tetrahedron Lett. 2013, 54, 1164-1168; (g)
Shi, G.; Gadhe, C. G.; Park, S-W.; Kim, K. S.; Kang, J.; Seema, H.;
Singh, N. J.; Cho, S. J. Org. Lett. 2014, 16, 334-337; (h) Kumar, V.
V.; Anthony, A. P. Anal. Chim. Acta. 2014, 842, 57-62; (i) Xu, H.;
Zhu, H.; Sun, M.; Yu, H.; Li, H.; Ma, F.; Wang, S. Analyst, 2015,
140, 1678-1685.
8.
9.
Alajarín, M.; Molina, P.; Sánchez-Andrada, P.; Foces-Foces, M. C.
J. Org. Chem. 1999, 64, 1121-1130.
(a) Tárraga, A.; Otón, F.; Espinosa, A.; Velasco, M. D.; Molina, P.;
Evans, D. J. Chem. Commun. 2004, 458-459; (b) Otón, F.; Tárraga,
A.; Molina, P. Org. Lett. 2006, 8, 2107-2110; (c) Otón, F.;
Espinosa, A.; Tárraga, A.; Ramírez de Arellano, C.; Molina, P.
Chem. Eur. J. 2007, 13, 5742-5752.
10. Molina, P.; Tárraga, A.; Alfonso, M. Eur. J. Org. Chem. 2011,
4505-4518, and references cited therein.
11. Molina, P.; Fresneda, P. M.; Sanz, M. A. J. Org. Chem. 1999, 64,
2540-2544.
12. To a solution of 1,3-bis(2-isocyanatopropan-2-yl)benzene (0.066g,
0.27 mmol) in dry THF (10 ml), at room temperature and under
nitrogen
atmosphere,
a
solution
of
1,1’-bis(N-
triphenylphosphoranylideneamino)ferrocene 3 (0.2 g, 0.27 mmol)
in the same solvent (30 ml) was added. The reaction mixture was
stirred at room temperature for 24 h and the solvent was removed
under reduced pressure. The residue was chromatographed on a
silica gel column using CH2Cl2/n-hexane (8:2) as eluent. Once the
solvent was evaporated under vacuum, the resulting product was
crystallized from CHCl3/diethyl ether (1:5) to give a yellow solid in
26% yield (0.030 g). Mp: 168-170 ºC. IR: ṽ cm-1 2125 (-N=C=N-).
1H NMR (300 MHz, CDCl3): /ppm 1.72 (s, 12H), 4.06 (m, 8H),
7.35 (m, 3H), 8.19 (m, 1H). 13C NMR (75 MHz, CDCl3): /ppm
31.4 (CH3), 61.9 (q), 62.5 (2xCH, Fc), 63.3 (2xCH, Fc), 97.4 (q,
Fc), 122.6 (CH), 123.1 (CH), 128.4 (CH), 147.4 (q, N=C=N). 1H
NMR (300 MHz, CD3CN): /ppm 1.74 (s, 12H), 4.02 (st, 4H), 4.07
(st, 4H), 7.43 (s, 3H), 8.23 (s, 1H). 13C NMR (75 MHz, CD3CN):
/ppm 31.6 (CH3), 62.4(q), 66.1 (2xCH, Fc), 67.3 (2xCH, Fc), 98.6
(q, Fc), 123.5 (CH), 124.4 CH), 129.7 (CH), 138.1 (q), 148.7 (q,
N=C=N). MS (ESI) m/z (%) 424 (M+, 100). Anal. Calc for
C24H24FeN4: C, 67.93; H, 5.70; N, 13.20. Found; C, 67.64; H, 5.35;
N, 12.93.
13. Crystallographic data (excluding structure factors) for the structure
4 reported in this Letter have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
numbers CCDC 1440651. Copies of the data can be obtained, free
of charge, on application to CCDC, 12 Union Road, Cambridge
CB2
1EZ,
UK
(fax:
+44-(0)1223-336033
or
e-
mail:deposit@ccdc.cam.ac.uk)
14. The simulated 1H NMR spectrum for the proposed
bis(carbodiimido)ferrocenophane model, was achieved by using the
software MestreNova 9.1.0, Mestrelab Research, chemistry
software solutions; 2014 Mestrelab Research S. L.
15. Bregovic, V. B.; Basaric, N.; Mlinaric-Majerski, K. Coord. Chem.
Rev. 2015, 295, 80-124 and references cited therein.
16. Williams, A.; Ibrahim, I. T. Chem. Rev. 1981, 81, 589-636.
17. To a solution of 1,1’-bis[N3,N3-(,’,’-tetramethylxylylen)-
N1,N1-carbodiiimido][11]ferrocenophane 4 (0.05 g, 0.12 mmol) in
THF (5 ml) a solution of diluted HCl (10%, 2 ml) was added
dropwise. As the acid addition progressed, a gradual change in the
color of the solution, from yellow to deep green, was observed. The
reaction was followed by TLC and, after completion, the resulting
compound was extracted with ethyl acetate (20 ml). The organic
phase was dried over anhydrous MgSO4 and the solvent was
removed under reduced pressure to give a green solid which was
crystallized from CH2Cl2/n-hexane (1:9) and identified as the
ferrocinium salt 6 (0.025 g, 47%). Mp: 221-225 ºC. IR: ṽ cm-1 3290
(NH), 1663 (C=O). HRMS (ESI, M+ + 1] calcd for C24H28FeN4O2
460.1562; found: 460.1564.
18. Shortreed, M.; Kopelman, R.; Kuhn, M.; Hoyland, B. Anal. Chem.
1996, 68, 1414-1418.
19. (a) Hervés, P.; Leis, J. R. J. Chem. Soc. Perkin Trans. 2 1995,
2035-2040; (b) Bravo, C.; Hervés, P.; Leis, J. R.; Peña, M. E. J.
Chem. Soc. Perkin Trans. 2 1991, 2091-2095.