Anion-triggered electrodeposition in ferrocene-functionalised ortho-phenylenediamine-based receptors

Article abstract of DOI:10.1039/b715125j

Ferrocene-functionalised anion receptors based on an ortho-phenylenediamine scaffold have been shown to undergo anion-triggered electrochemical deposition. This process may offer a new way of detecting anionic species in solution. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b715125j

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Anion-triggered electrodeposition in ferrocene-functionalised
ortho-phenylenediamine-based receptorswz
Marta Arroyo, Peter R. Birkin, Philip A. Gale,* Sergio E. Garcıa-Garrido
´
and Mark E. Light
Received (in Durham, UK) 2nd October 2007, Accepted 4th February 2008
First published as an Advance Article on the web 5th March 2008
DOI: 10.1039/b715125j
Ferrocene-functionalised anion receptors based on an ortho-phenylenediamine scaffold have been
shown to undergo anion-triggered electrochemical deposition. This process may offer a new way
of detecting anionic species in solution.
compounds were found to undergo an unusual anion-triggered
Introduction
electrochemical deposition process.
The selective recognition and sensing of anions by artificial
host molecules continues to attract the interest of the supra-
molecular chemistry community.1 Sensing is achieved by
coupling two components: (a) selective binding site and (b)
signalling subunits that are perturbed by the presence of the
guest and thus exhibit redox shifts, colour changes, or fluor-
escence quenching or enhancement.2 As part of the continued
interest in the development of novel molecular switches and
sensors, redox-active receptors for inorganic cations and
anions have been studied in great detail.3 Ferrocene deriva-
tives that bind and allow the electrochemical sensing of
cations4 and anions5 are a significant sub-group of this type
of sensor. The various interactions that allow these charged
species to be electrochemically recognized have been reviewed
in detail.3c
Results and discussion
Treatment of ferrocenecarbonyl chloride9 with 1 equiv. of
N-(2-aminophenyl)benzamide,10 1-(2-aminophenyl)-3-phenyl-
urea11 or N-(2-aminophenyl)-1H-pyrrole-2-carboxamide12 in
dichloromethane, and in the presence of 2.5 equiv. of NEt3,
generates compounds 1–3 as a yellow-orange solids in 55–77%
yield (Scheme 1).
Compounds that contain neutral hydrogen bond donor
groups, such as amides6 or ureas,7 have been shown to be
particularly effective anion receptors in organic solution.6,7
Hybrid receptors containing both amides and ureas have also
been synthesised, and in some cases shown to possess a
remarkably high anion affinity and selectivity.8
With these precedents in mind, we decided to study a series
of receptors formed by combining the redox activity of the
ferrocene moiety with the hydrogen bonding ability of amide
and urea groups. Here we report the synthesis, characteriza-
tion, anion coordination properties and electrochemistry of
new ferrocene-based anion receptors based on ortho-phenyle-
nediamine-functionalised hydrogen bonding arrays. These
School of Chemistry, University of Southampton, Southampton, UK
SO17 1BJ. E-mail: philip.gale@soton.ac.uk
w Electronic supplementary information (ESI) available: NMR spec-
tra, titration curves and cyclic voltammograms. See DOI: 10.1039/
b715125j
z Crystal data for 4. C24H21FeN3O2, Mr = 439.29, T = 120(2) K,
monoclinic, space group P21/c, a = 15.3994(6), b = 9.3582(4), c =
14.7688(6) A, b = 110.351(2)1, V = 1995.49(14) A3, rcalc = 1.462 g
cm ꢀ3, m = 0.782 mmꢀ1, Z = 4, reflections collected = 25 530,
independent reflections = 33 521 (Rint = 0.0927), final R indices
[I 4 2s(I)]: R1 = 0.0719, wR2 = 0.1321, R indices (all data): R1 =
0.0965, wR2 = 0.1431. CCDC 676118. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b715125j
Scheme 1
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Scheme 2
In a similar way, compounds 4–6 were synthesised as brown
solids in 55–87% yield by reaction of ferrocenoyl isocyanate,
prepared in situ from ferrocenoyl azide,9 with the appropriate
primary amine in freshly distilled toluene at 90 1C (Scheme 2).
Spectroscopic data (IR and 1H and 13C{1H} NMR) and
elemental analyses for compounds 1–6 are in agreement with
the proposed formulations (details are given in the Experi-
mental section). Moreover, the structure of complex 4 has
been unequivocally confirmed by a single-crystal X-ray dif-
fraction study. Crystals of 4 were grown by the slow evapora-
tion of a DMSO-d6–0.5% water solution of the receptor
(Fig. 1).z The structure shows an intramolecular hydrogen
bonding interaction between the oxygen of the amide moiety
and the urea-NH group close to the central benzene ring, with
a bond distance N2–H2Aꢂ ꢂ ꢂO2 of 2.729(5) A and a bond angle
of 134(1)1, in such a way that the amide NH group is
orientated in the opposite direction to the two urea NH groups
(see Fig. 1). Moreover, in the solid-state, compound 4 forms
hydrogen-bonded chains through urea–amide interactions
(Fig. 2). These involve intermolecular hydrogen bonds be-
tween the NH groups of the amide units and the oxygen of the
ureas, as well as between the urea NH groups close to the
ferrocene moiety and the oxygen of the amides (see Fig. 2).
Representative bond distances for both interactions are:
N1–H1Aꢂ ꢂ ꢂO2i 2.923(5) A and N3–H3Aꢂ ꢂ ꢂO1ii 2.865(5) A,
with N–Hꢂ ꢂ ꢂO angles being 164 and 1551, respectively
(symmetry codes: (i) ꢀx + 1, ꢀy + 1, ꢀz + 1; (ii) ꢀx + 1,
ꢀy, ꢀz + 1).
Fig. 2 Hydrogen-bonded chains in the solid-state structure of com-
pound 4.
butylammonium salts of the putative anionic guest
(0.1 mol dmꢀ3) were added to a solution of compounds 1–6
(0.01 mol dmꢀ3) in DMSO-d6–0.5% water. The resulting
stability constants are summarized in Table 1.
The addition of bromide and hydrogen sulfate did not cause
any significant spectral change, even when a high excess of
anion was employed. Thus, these anions form no (or very
weak) complexes with compounds 1–6 (Ka o 10 Mꢀ1; see
Table 1). On the other hand, analysis of the remaining titra-
tion data using the EQNMR13 computer program revealed
that these compounds form 1 : 1 receptor : anion complexes
with chloride, acetate, benzoate and dihydrogen phosphate
anions, showing a moderate to high affinity of receptors 1–6
for these anions in this compeꢀtitive solvent medium
(CH3CO2 4 C6H5CO2 E H2PO4 4 Clꢀ; Table 1). Sig-
nificant downfield shifts of the NH protons were observed
upon addition of these anions, consistent with the formation
of complex–anion hydrogen bonds.
ꢀ
ꢀ
As shown in Table 1, compounds containing urea moieties
(2 and 4–6) have a considerably higher affinity than com-
pounds with only amide or pyrrole units (1 and 3). As an
example, the 1H NMR spectral changes upon addition of
tetrabutylammoniun acetate to the DMSO-d6–0.5% water
Complexation studies
Initial complexation studies on complexes 1–6 were conducted
using 1H NMR titration techniques. Aliquots of the tetra-
Table 1 Stability constants Ka (Mꢀ1) of compounds 1–6 with a
variety of putative anionic guests (added as tetrabutylammonium
salts) at 298
K
in DMSO-d6–0.5% water,a as determined by
1H NMR titration techniques. In all cases, 1 : 1 receptor : anion
stoichiometry was observed
Anion
Compounds
1
2
3
4
5
6
Clꢀ
12
o10
20
13
11
49
10
Brꢀ
CH3CO2
o10
6030
514
877
o10
o10
123
65
151
o10
o10
1260
394
458
o10
o10
709b
430b
270b
o10
o10
1762
690
490
o10
ꢀ
ꢀ
53
25
C6H5CꢀO2
H2POꢀ4
HSO4
51
o10
Fig. 1 X-Ray crystal structure of compound 4. Thermal ellipsoids are
drawn at the 35% probability level. Non-acidic hydrogen atoms have
been removed for clarity.
a
b
Errors estimated to be no more than ꢃ10%. DMSO-d6–5.0%
water.
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tion studies of 5 were conducted using a more competitive
solvent medium (DMSO-d6–5.0% water), and a moderate-
to-high affinity for those anions were still obtained (i.e. Ka =
709 Mꢀ1 for acetate; see Table 1). Thus, except in the cases of
compounds 1 and 3, these compounds show a moderate
selectivity towards acetate over chloride, benzoate and phos-
phate (see Table 1).
Titration studies of complexes 1–6 with tetrabutylammo-
nium fluoride have been also performed. Unfortunately, the
1H NMR spectra obtained show a significant broadening of all
the NH and CH signals upon addition of the anion salt,
making a determination of the stability constant with this
anion not possible by this method.
Electrochemical investigations of the compounds have also
been undertaken. These take the form of cyclic voltammetry of
the ferrocene derivatives in the absence and presence of a
variety of anions. Fig. 4 shows a collection of results obtained
with compound 1 and a variety of different anions. In each
case, the voltammetry is shown at 0, 2 and 5 equivalents of the
anion with respect to the receptor. In the absence of an
appropriate anion, classic electrochemistry of the ferrocene
Fig. 3 Shifts of the NH protons in compound 2 (from 0.2 to excess
equivalents of anion) upon addition of tetrabutylammonium acetate
salt in DMSO-d6–0.5% water.
solution of compound 2 is shown in Fig. 3. The spectra show
that the urea NH groups shift downfield significantly upon
addition of acetate (Dd 4 2 ppm in both cases), but that the
amide group is hardly influenced by the presence of the oxo
anion (Dd o 0.3 ppm).
derivative can be seen (
). The electrochemistry of this
derivative (compound 1) shows both anodic and cathodic
processes, which, if assumed to be a one-electron transfer,
can be considered to be close to reversible in nature (peak-to-
peak potential B69 mV and ratio of the anodic to cathodic
peak 0.98). However, after the addition of an anion, the
electrochemical behaviour of this compound shows a distinct
change. This was found to be dependent on the particular
anion employed (see Fig. 4). In the case of the acetate anion
In the case of compound 5, the stability constants observed
after addition of acetate, benzoate and dihydrogen phosphate
tetrabutylammonium salts in DMSO-d6–0.5% water as sol-
vent are greater than 104 Mꢀ1, so are at the upper limits that
can be determined by this technique. Owing to this, complexa-
Fig. 4 Cyclic voltammetric data gathered for compound (1) at a 3 mm diameter glassy carbon disk as a functionꢀo3f the anion to ferrocene receptor
, respectively). The electrolyte consisted of 0.1 mol dm TBAPF6 in (95% CH3CN/5%
concentration ratio (0 : 1
, 2 : 1
and 5 : 1
DMSO). The initial ferrocene derivative concentration was 1 mM. All voltammetry was recorded at 20 mV sꢀ1 under anaerobic conditions at
20–24 1C.
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(CH3CO2ꢀ), the voltammetry transforms from a redox species
exhibiting a one-electron transfer process to a system where
only a large anodic signal can be seen. In addition, the
voltammetric data shows a shift in the redox potential of the
system, with the additional presence of two distinct redox
processes at intermediate ratios of anion to receptor (see
anion affinity, leading to more complex electrochemical pro-
cesses in the presence of anions, in addition to the electro-
chemical activity of the starting ferrocene derivative being
compound-dependant.
It would thus appear that anion binding by these molecules
has the added consequence of changing the electrode potential,
over which electrooxidation of the receptors can be driven,
and thus provides an interesting new method that may poten-
tially be applied to the detection of anionic species.
S. E. G.-G. would like to thank the Ministerio de Educacion
y Ciencia of Spain for the award of a Postdoctoral grant. We
would like to thank the EPSRC, together with Professor Mike
Hursthouse, for access to the crystallographic facilities at the
University of Southampton.
Fig. 4,
). This experimental data demonstrates that the
presence of the binding anion changes the electrochemistry
significantly. For example, if the voltammetry of the ferrocene
derivative is taken as a one-electron transfer reference peak,
then the addition of the anion (at a 5 : 1 anion to receptor
ratio) suggests that, on average, B2.7 electrons are transferred
to the compound when binding to the anion has occurred
(assuming no major changes in the diffusion coefficient of the
species involved). In addition, the anodic peak has shifted to
+0.176 V compared to the anodic wave of the ferrocene
derivative at +0.322 V. In addition to the voltammetric data,
it was found by experimental observation that the electrode
became passivated after the initial anodic response in the
presence of the anion. This passivation could be removed by
polishing the electrode surface. If we consider that the ferro-
cene is only able to accommodate one electron, then the
additional electrochemical oxidation must be associated with
the ortho-phenylenediamine section of the molecule. The
passivation of the electrode surface supports this hypothesis
as oxidation of ortho-phenylenediamine (oPD) can lead to
electrodeposits, indeed many examples involving the electro-
oxidation of oPD to form polymer-modified electrodes can be
found in the literature.14 Note also that the mechanistic details
for the deposition process are unclear at this stage. However,
the experimental evidence supports the hypothesis of addi-
tional electrooxidation of the ferrocene derivatives as a result
of anion binding. Whether this is as a result of activation of
the oPD backbone, oligomer formation or polymer formation
is unknown at this time. Nevertheless, the binding of the
anions clearly dramatically changes the electroactivity of these
novel derivatives.
Experimental
General procedures
All reactions were performed in oven-dried glassware under a
1
slight positive pressure of nitrogen. H NMR (300 MHz) and
13C{1H} NMR (75 MHz) spectra were determined on a Bruker
AV300. Chemical shifts for 1H NMR are reported in parts per
million, calibrated to the residual solvent peak set, with
coupling constants reported in Hertz (Hz). The following
abbreviations are used for spin multiplicity: s = singlet, d =
doublet, t = triplet, m = multiplet and br = broad. Chemical
shifts for 13C{1H} NMR are reported in ppm, relative to the
central line of a septet at 39.52 ppm for DMSO-d6. Deuterated
solvents were purchased from Apollo Ltd. ES MS were
measured on a Micromass Mattro II instrument. Infrared
(IR) spectra were recorded on a Mattson Satellite (ATR)
FTIR and are reported in wavenumbers (cmꢀ1). Melting
points were measured on a Gallenkamp melting point appa-
ratus. Elemental analyses were performed by Medac Ltd.
N-(2-(Ferrocenecarboxamido)phenyl)benzamide (1)
Clearly, this process is dependant on the nature of the anion
Ferrocenecarbonyl chloride (0.248 g, 1 mmol) was placed in a
dry round-bottomed flask under an N2 atmosphere and 20 cm3
of dichloromethane was added. To this was then added N-(2-
aminophenyl)benzamide (0.212 g, 1 mmol) and NEt3 (0.35
cm3, 2.5 mmol), and the mixture was left stirring at ambient
temperature for 5 h. The solvent was evaporated in vacuo and
the resulting residue recrystallized from dichloromethane/hex-
ane to obtain an orange solid, which was further purified from
acetonitrile to give 1 as an orange powder (0.327 g, 77% yield);
trigger. Fig. 4 shows that the anions with the strongeꢀst
ꢀ
polymeric triggering effect are CH3CO2 and C6H5CO2
,
ꢀ
while the H2PO4 and Clꢀ ions perturb the electrochemistry
of the ferrocene derivative to a lesser extent.
In addition to the electrochemistry of compound 1 and the
effects of the anion binding on this compound, the electro-
chemistry of compounds 3–6 were investigated in a similar
manner. In all cases, in the absence of a binding anion, the
electrochemistry of the ferrocene moiety was apparently simi-
lar (taking minor changes in diffusion coefficient and redox
potential into account) with additional redox chemistry ap-
parently depending on the molecule in question. However,
anion binding caused large changes to the electrochemistry
with multiple redox waves and electrode passivation observed
(see ESIw). This suggests that the anion-triggered multi-elec-
tron transfer is not a special pathway for compound 1 but a
general property of these ferrocene derivatives. The more
complex electrochemistry observed with compounds 3–6 vs.
compound 1 may be due to the more complex molecular
architecture of the anion receptor sections of the derivatives
(compounds 3–6). The derivatives 3–6 may also have a higher
1
mp = 225–228 1C; H NMR (300 MHz, DMSO, d): 10.26 (s,
1H, NH), 9.46 (s, 1H, NH), 8.04 (dd, J = 7.9 and 1.7 Hz, 2H,
Ar-H), 7.60 (m, 5H, Ar-H), 7.29 (m, 2H, Ar-H), 4.89 (t, J =
1.9 Hz, 2H, Cp), 4.46 (t, J = 1.9 Hz, 2H, Cp), 4.02 (s, 5H, Cp);
13C{1H} NMR (75 MHz, DMSO, d): 168.8 (C), 165.2 (C),
133.8 (C), 132.1 (CH), 131.4 (C), 130.8 (C), 128.7 (CH), 127.5
(CH), 125.8 (CH), 125.7 (CH), 125.4 (CH), 125.2 (CH), 75.5
(C), 70.8 (CH), 69.4 (CH), 68.4 (CH); LRMS (ES+): 424
[M]+, 447 [M + Na]+, 872 [2M + Na]+; IR (film, cmꢀ1):
3272, 3108, 1652, 1597, 1519, 1496, 1265, 1279, 1264, 1108,
1020, 821, 755, 711, 651, 500, 484, 473, Elemental analysis calc.
for C24H20N2O2Fe: C, 67.94; H, 4.75; N, 6.60. Found: C,
67.96; H, 4.65; N, 6.36%.
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1-(2-(Ferrocenecarboxamido)phenyl)-3-phenylurea (2)
for 18 h, after which the resulting brown precipitated product
was removed by filtration and washed with dichloromethane
(3 ꢄ 20 cm3), with 2 isolated as a brown solid (0.382 g, 87%);
Ferrocenecarbonyl chloride (0.248 g, 1 mmol) was placed in a
dry round-bottomed flask under an N2 atmosphere and 20 cm3
of dichloromethane was added. To this was then added 1-(2-
aminophenyl)-3-phenylurea (0.227 g, 1 mmol) and NEt3 (0.35
cm3, 2.5 mmol), and the mixture was left stirring at ambient
temperature for 3 h. The resulting orange precipitate was
removed via filtration, and washed with water (3 ꢄ 20 cm3)
and methanol (3 ꢄ 20 cm3) to afford the product as a pale
1
mp = 187–190 1C; H NMR (300 MHz, DMSO, d): 10.06 (s,
1H, amide-NH), 8.37 (s, 1H, urea-NH), 8.06 (d, J = 7.0 Hz,
2H, Ar-H), 7.91 (d, J = 7.7 Hz, 1H, Ar-H), 7.86 (s, 1H, urea-
NH), 7.58 (m, 3H, Ar-H), 7.36 (d, J = 7.7 Hz, 1H, Ar-H), 7.23
(t, J = 7.0 Hz, 1H, Ar-H), 7.07 (t, J = 7.0 Hz, 1H, Ar-H), 4.48
(t, J = 1.7 Hz, 2H, Cp), 4.11 (s, 5H, Cp), 3.93 (t, J = 1.7 Hz,
2H, Cp); 13C{1H} NMR (75 MHz, DMSO, d): 165.6 (C), 153.2
(C), 134.7 (C), 134.1 (C), 131.7 (CH), 128.4 (CH), 127.9 (C),
127.7 (CH), 127.2 (CH), 126.3 (CH), 122.5 (CH), 121.6 (CH),
96.6 (C), 68.6 (CH), 63.6 (CH), 60.4 (CH); LRMS (ES+): 439
[M]+, 462 [M + Na]+, 902 [2M + Na]+; IR (film, cmꢀ1):
3315, 3262, 3202, 3144, 3101, 3052, 1684, 1625, 1598, 1561,
1513, 1500, 1477, 1440, 1310, 1255, 1203, 1106, 1030, 821, 749,
691, 529, 498, 484. Elemental analysis calc. for
C24H21N3O2Fe: C, 65.62; H, 4.82; N, 9.56. Found: C, 65.52;
H, 4.76; N, 9.52%.
1
orange powder (0.290 g, 66%); mp = 201–204 1C; H NMR
(300 MHz, DMSO, d): 9.45 (s, 1H, amide-NH), 9.30 (s, 1H,
urea-NH), 8.07 (s, 1H, urea-NH), 7.69 (dd, J = 7.9 and 1.1
Hz, 1H, Ar-H), 7.47 (d, J = 7.5 Hz, 2H, Ar-H), 7.39 (dd, J =
7.5 and 1.5 Hz, 1H, Ar-H), 7.23 (m, 3H, Ar-H), 7.14 (td, J =
7.5 and 1.5 Hz, 1H, Ar-H), 6.95 (t, J = 7.1 Hz, 1H, Ar-H),
4.95 (t, J = 1.9 Hz, 2H, Cp), 4.47 (t, J = 1.9 Hz, 2H, Cp), 4.23
(s, 5H, Cp); 13C{1H} NMR (75 MHz, DMSO, d): 168.8 (C),
153.1 (C), 139.8 (C), 133.5 (C), 129.5 (C), 128.8 (CH), 128.7
(CH), 126.5 (CH), 125.7 (CH), 123.5 (CH), 121.8 (CH), 118.2
(CH), 75.8 (C), 70.6 (CH), 69.5 (CH), 68.7 (CH); LRMS
(ES+): 439 [M]+, 462 [M + Na]+, 902 [2M + Na]+; IR
(film, cmꢀ1): 3316, 3262, 3203, 3145, 3102, 3054, 1684, 1622,
1598, 1561, 1514, 1500, 1478, 1441, 1323, 1310, 1255, 1203,
1030, 821, 771, 749, 730, 498. Elemental analysis calc. for
C24H21N3O2Fe: C, 65.62; H, 4.82; N, 9.56. Found: C, 65.60;
H, 4.81; N, 9.40%.
1-(2-(Phenylureido)phenyl)-3-ferrocenylurea (5)
Ferrocenoyl azide (0.259 g, 1 mmol) and 1-(2-aminophenyl)-3-
phenylurea (0.227 g, 1 mmol) were placed in a dry round-
bottomed flask under an N2 atmosphere, 20 cm3 of freshly
distilled toluene was added and the solution was heated at 90
1C for 24 h. The precipitated product was removed via
filtration before suspending the product in dichloromethane
(50 cm3) and washing with aqueous HCl solution (3 ꢄ 20 cm3,
pH = 1). The organic phase was retained and the solvent
removed in vacuo. The residue was recrystallized from hot
acetone and dried under high vacuum. The product was
isolated as a brown solid (0.313 g, 69%); mp = 164–167 1C;
1H NMR (300 MHz, DMSO, d): 9.14 (s, 1H, urea-NH), 8.27
(s, 1H, urea-NH), 8.14 (s, 1H, urea-NH), 8.00 (s, 1H, urea-
NH), 7.70 (d, J = 7.9 Hz, 1H, Ar-H), 7.52 (m, 2H, Ar-H), 7.27
(t, J = 7.5 Hz, 2H, Ar-H), 7.06 (m, 2H, Ar-H), 6.95 (t, J = 7.5
Hz, 2H, Ar-H), 4.49 (br s, 2H, Cp), 4.14 (s, 5H, Cp), 3.93 (br s,
2H, Cp); 13C{1H} NMR (75 MHz, DMSO, d): 153.5 (C), 153.3
(C), 139.9 (C), 132.3 (C), 130.0 (C), 128.7 (CH), 124.5 (CH),
124.2 (CH), 123.1 (CH), 122.7 (CH), 121.7 (CH), 118.1 (CH),
96.6 (C), 68.7 (CH), 63.6 (CH), 60.7 (CH); LRMS (ES+): 454
[M]+, 477 [M + Na]+, 931 [2M + Na]+; IR (film, cmꢀ1):
3293, 3091, 1734, 1635, 1598, 1560, 1498, 1477, 1442, 1294,
1249, 1201, 1104, 1020, 1001, 803, 750, 692, 486. Elemental
analysis calc. for C24H22N4O2Fe: C, 63.45; H, 4.88; N, 12.33.
Found: C, 63.58; H, 4.80; N, 12.42%.
N-(2-(Ferrocenecarboxamido)phenyl)-1H-pyrrole-2-
carboxamide (3)
Ferrocenecarbonyl chloride (0.248 g, 1 mmol) was placed in a
dry round-bottomed flask under an N2 atmosphere and 20 cm3
of dichloromethane was added. To this was then added N-(2-
aminophenyl)-1H-pyrrole-2-carboxamide (0.201 g, 1 mmol)
and NEt3 (0.35 cm3, 2.5 mmol), and the reaction was then
heated to reflux and left stirring for 2 h. The crude product was
purified by column chromatography using ethyl acetate :
hexane 3 : 7 as the eluent, which yielded compound 5 as a
1
yellow powder (0.227 g, 55%); mp = 138–141 1C; H NMR
(300 MHz, DMSO, d): 11.86 (s, 1H, pyrrol-NH), 9.90 (s, 1H,
amide-NH), 9.48 (s, 1H, amide-NH), 7.57 (m, 2H, Ar-H), 7.25
(m, 2H, Ar-H), 7.01 (br s, 2H, Ar-H), 6.21 (t, J = 2.6 Hz, 1H,
Ar-H), 4.89 (t, J = 1.5 Hz, 2H, Cp), 4.46 (t, J = 1.5 Hz, 2H,
Cp), 4.07 (s, 5H, Cp); 13C{1H} NMR (75 MHz, DMSO, d):
168.4 (C), 159.3 (C), 131.1 (C), 130.6 (C), 125.3 (CH), 125.2
(CH), 125.1 (C), 125.0 (CH), 124.9 (CH), 122.9 (CH), 111.3
(CH), 109.1 (CH), 75.4 (C), 70.6 (CH), 69.3 (CH), 68.2 (CH);
LRMS (ES+): 413 [M]+, 436 [M + Na]+, 850 [2M + Na]+;
IR (film, cmꢀ1): 3401, 3245, 3115, 1633, 1595, 1549, 1510,
1481, 1434, 1404, 1377, 1312, 1274, 1127, 1106, 1042, 1027,
822, 744, 607, 526, 484. Elemental analysis calc. for
C22H19N3O2Fe: C, 63.94; H, 4.63; N, 10.16. Found: C,
63.95; H, 4.77; N, 10.10%.
1-(2-(1H-Pyrrole-2-carboxamido)phenyl)-3-ferrocenylurea (6)
Ferrocenoyl azide (0.259 g, 1 mmol) and N-(2-aminophenyl)-
1H-pyrrole-2-carboxamide (0.201 g, 1 mmol) were placed in a
dry round-bottomed flask under an N2 atmosphere and 20 cm3
of freshly distilled toluene was added. The solution was heated
at 90 1C for 8 h, after which the resulting brown precipitated
product was removed by filtration and washed with dichlor-
omethane (3 ꢄ 20 cm3), with being 6 isolated as a brown solid
(0.253 g, 59%); mp = 162–165 1C; 1H NMR (300 MHz,
DMSO, d): 11.63 (s, 1H, pyrrol-NH), 9.61 (s, 1H, amide-NH),
8.41 (s, 1H, urea-NH), 8.00 (s, 1H, urea-NH), 7.86 (d, J =
1-(2-(Benzamido)phenyl)-3-ferrocenylurea (4)
Ferrocenoyl azide (0.259 g, 1 mmol) and N-(2-aminophenyl)-
benzamide (0.212 g, 1 mmol) were placed in a dry round-
bottomed flask under an N2 atmosphere and 20 cm3 of freshly
distilled toluene was added. The solution was heated at 90 1C
ꢁc
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6.8 Hz, 1H, Ar-H), 7.36 (d, J = 6.8 Hz, 1H, Ar-H), 7.17 (br s,
1H, Ar-H), 6.99 (m, 3H, Ar-H), 6.18 (br s, 1H, Ar-H), 4.48 (br
s, 2H, Cp), 4.11 (s, 5H, Cp), 3.93 (br s, 2H, Cp); 13C{1H}
NMR (75 MHz, DMSO, d): 159.5 (C), 153.1 (C), 134.1 (C),
127.6 (C), 126.6 (CH), 125.8 (CH), 125.5 (C), 122.2 (CH),
122.1 (CH), 121.1 (CH), 111.0 (CH), 108.7 (CH), 96.4 (C), 68.4
(CH), 63.4 (CH), 60.2 (CH); LRMS (ES+): 428 [M]+, 451 [M
+ Na]+, 880 [2M + Na]+; IR (film, cmꢀ1): 3232, 3107, 3034,
1650, 1632, 1589, 1531, 1514, 1494, 1470, 1455, 1436, 1342,
1295, 1275, 1103, 812, 752, 737, 486, 471. Elemental analysis
calc. for C22H20N4O2Fe: C, 61.70; H, 4.71; N, 13.08. Found:
C, 61.55; H, 4.56; N, 12.92.
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Crystallography
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´
Data for 4 were collected on a Bruker Nonius KappaCCD
diffractometer mounted at the window of a Mo rotating
anode.z
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Electrochemical data was recorded on an in-house-constructed
electrochemical workstation and supporting software. Vol-
tammetry was recorded at a 3 mm diameter glassy working
carbon electrode in a three electrode arrangement, including a
Pt counter and a Ag/Ag+ reference electrode. The working
electrode was polished on 0.3 mm diameter alumina on a
Microcloth, followed by washing in dry DMSO prior to
recording each voltammogram. Data were gathered at room
temperature (22 ꢃ 2 1C) under aerobic conditions. The sweep
rate, unless stated otherwise, was 20 mV sꢀ1
.
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