Bifunctional ferrocene derivatives for molecular recognition of DNA duplexes

Article abstract of DOI:10.1039/b004295l

Using l, l '-bis(chlorocarbonyl)ferrocene as the starting material the novel amide derivative 1, 1 '-bis(carbamoylmethylcarbamoyl)ferrocene has been isolated. Furthermore, the in situ reaction of l, l'-di(bromomethyl)ferrocene with several amines led to the formation of salt-like and tertiary amine ferrocene compounds. These compounds are all very stable in air and exhibit interesting hydrogen bonding patterns that can complement those of the DNA nucleobases. Differential pulse voltammetry was used to monitor the interactions of the water soluble ferrocene derivatives with DNA oligomers. The three compounds tested bind strongly to the DNA oligomers and the binding constants calculated are similar to those obtained for the [Fe(phen)3]3H2t ions. The interaction results from a combination of hydrogen bonding, electrostatic, hydrophobic and rc-stacking interactions. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b004295l

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Bifunctional ferrocene derivatives for molecular recognition of
DNA duplexes
Alexandra S. Georgopoulou,a D. Michael P. Mingos,*b Andrew J. P. White,a David J. Williams,a
Benjamin R. Horrocksc and Andrew Houltonc
a Department of Chemistry, Imperial College of Science, Technology and Medicine, London,
UK SW7 2AY
b The Principal’s Lodgings, St. Edmund Hall, Queen’s Lane, Oxford, UK OX1 4AR.
E-mail: michael.mingos@seh.ox.ac.uk
c Department of Chemistry, University of Newcastle upon Tyne, Newcastle-upon-Tyne,
UK NE1 7RU
Received 31st May 2000, Accepted 20th July 2000
Published on the Web 14th August 2000
Using 1,1Ј-bis(chlorocarbonyl)ferrocene as the starting material the novel amide derivative 1,1Ј-bis(carbamoyl-
methylcarbamoyl)ferrocene has been isolated. Furthermore, the in situ reaction of 1,1Ј-di(bromomethyl)ferrocene
with several amines led to the formation of salt-like and tertiary amine ferrocene compounds. These compounds
are all very stable in air and exhibit interesting hydrogen bonding patterns that can complement those of the DNA
nucleobases. Differential pulse voltammetry was used to monitor the interactions of the water soluble ferrocene
derivatives with DNA oligomers. The three compounds tested bind strongly to the DNA oligomers and the binding
constants calculated are similar to those obtained for the [Fe(phen)3]3ϩ/2ϩ ions. The interaction results from a
combination of hydrogen bonding, electrostatic, hydrophobic and π-stacking interactions.
derivatives functionalised with nucleobases such as thymine
Introduction
and adenine have also been prepared.6,7 These compounds are
During the past forty-five years a wide range of substituted
capable of interacting with nucleic acids via hydrogen bonding.
ferrocene compounds have been synthesized and studied. It
A series of ferrocene receptors that can bind and electro-
was, nevertheless, of some topical interest to incorporate sub-
chemically recognise anions has been reported8,9 and the recog-
stituents on the cyclopentadienyl rings, which would make such
nition of anions in solution has been investigated using 1H
substituted ferrocenes capable of recognising molecules of bio-
NMR titrations. Ferrocene is a unique functional handle
logical importance, such as DNA, through complementary
because it does not directly interact with the anion until it is
interactions. The well established reversible electrochemical
oxidised to the ferrocenium cation, at which stage electrostatic
properties of ferrocene derivatives provided a means of detec-
interactions with the guest are “switched on.”
ting and putting on a quantitative basis such interactions.
Metallocenes occur either as regular sandwich compounds,
e.g. ferrocene and cobaltocene, or bent sandwich compounds,
containing Ti, V, Nb, or Mo as the central metal atom.1,2 Strong
antitumour activities have been shown for some of the bent
metallocene complexes. Antitumour activities has also been
reported for ferrocenium compounds.3 These ionic, water sol-
uble complexes unlike the bent sandwich compounds do not
contain halide ligands bound in cis positions and are therefore
lacking the cis-dihalogenometal moiety characteristic of
cisplatin, [Pt(NH3)2Cl2]. Antitumour ferrocenium complexes
are represented by salt-like, water soluble compounds with a
range of anions XϪ, such as trichloroacetate (CCl3CO2Ϫ),
picrate (2,4,6-(O2N)3C6H2OϪ), µ-oxo-bis[trichloroferrate()]
(¹[Cl3FeOFeCl3]Ϫ), or tetrachloroferrate() ([FeCl4]Ϫ). These
Results and discussion
Amide derivatives
Ferrocene amide derivatives can be isolated from 1,1Ј-bis-
(chlorocarbonyl)ferrocene, by treatment with different amines.
This specific reaction has been utilised extensively by Beer and
his group10 for the formation of appropriately designed charged
or neutral redox- and photo-active transition metal organo-
metallic and co-ordination receptor systems that can selectively
recognise and sense anionic guest species either by electro-
chemical or optical measurements.
The new derivative 1,1Ј-bis(carbamoylmethylcarbamoyl)-
ferrocene 1 was isolated from the reactions of bis(chloro-
carbonyl)ferrocene with glycinamide hydrochloride and
characterised using IR and NMR spectroscopy, mass spec-
trometry and elemental analyses. This derivative was insoluble
in all common organic solvents and is only soluble in DMSO
and warm water.
¯
²
compounds have shown marked antitumour activity against
several animal and human tumours.4 Furthermore, iron com-
pounds are less toxic than platinum compounds. This observ-
ation opens the possibility of combination therapies with the
toxic side effects diminished.
The antitumour activities of bis(diphenylphosphines) and
their bis(gold()) complexes has also attracted some recent
interest.5 This, together with the finding that ferrocenium salts
are active against various tumours, suggested that the incorpor-
ation of the essential structural features of the bis(diphenyl-
phosphinogold) complexes with a ferrocene could provide
complexes with enhanced antitumour activities. Ferrocenyl
For the glycinamide derivative the following peaks were
observed in the infrared spectrum: ν(N–H) at 3409, 3319 and
3192 cmϪ1; ν(C–H) at 2940 cmϪ1; ν(C᎐O) at 1663 cmϪ1; amide I
᎐
at 1607 cmϪ1; amide II at 1561 cmϪ1; ν(C–N) at 1301 cmϪ1
and amide III at 1261 cmϪ1. Owing to the C2 symmetry of
the complex, the two terminal NH2 groups are equivalent.
However, within each group the two protons are magnetically
DOI: 10.1039/b004295l
J. Chem. Soc., Dalton Trans., 2000, 2969–2974
This journal is © The Royal Society of Chemistry 2000
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Fig. 2 One of the N–H ؒ ؒ ؒ O hydrogen bonded sheets of molecules
present in the structure of complex 1. The hydrogen bonding geometry
is N ؒ ؒ ؒ O 2.94, H ؒ ؒ ؒ O 2.04 Å and N–H ؒ ؒ ؒ O 177Њ.
Fig. 1 The molecular structure of complex 1. The hydrogen bonding
geometries are N ؒ ؒ ؒ O, H ؒ ؒ ؒ O (Å), N–H ؒ ؒ ؒ O (Њ): (a) 2.88, 2.08, 147
and (b) 2.95, 2.08, 165.
inequivalent due to the orientation of the adjacent carbonyl.
Consequently, only two peaks (at δ 7.74 and 7.30) are observed
for the NH2 units in the 1H NMR spectrum of the compound in
d6-DMSO. The remaining peaks observed are as follows: δ 8.64,
amide NH; 4.79 and 4.43, Cp H and 3.73, CH2. In the FAB(ϩ)
and FAB(Ϫ) mass spectra the molecular ion peaks for [M]ϩ and
[M Ϫ H]Ϫ are observed at m/z = 386 and 385 respectively.
Crystal structure of complex 1
Crystals of complex 1 were obtained from a water–DMSO
solution after refrigeration over a period of four days. In the
solid state (Fig. 1) the molecule has crystallographic C2 sym-
metry about an axis passing through the iron atom and bisect-
ing the vector between the two amide oxygen atoms O(6) and
O(6A). The two cyclopentadienyl rings are parallel to each
other (inclined by only 0.1Њ) with the C(6) amide group being
rotated by only ca. 6Њ out of the plane of its associated C5H4
ring. There is a ca. 85Њ torsional twist about the N(7)–C(8) bond
that facilitates the cross-linking of the two substituent side-
arms by a pair of intramolecular hydrogen bonds between the
N(7) amide hydrogen in one chain and the carbonyl oxygen
O(9A) of the other, and vice versa (a in Fig. 1). The dihedral
angle between the two substituent chains is 64Њ and the two Cp
rings are almost eclipsed, being rotated out of register by ca. 9Њ.
The centroid–centroid separation of the Cp rings is 3.29 Å,
which is the same as the mean interplanar separation of the two
rings, and the Cp–Fe–Cp angle is 178.5(2)Њ. Adjacent molecules
are linked via N–H ؒ ؒ ؒ O hydrogen bonds between one of the
terminal amide hydrogen atoms in one molecule and the O(6)
carbonyl atom of another (c in Fig. 2) to form a two-
dimensional sheet that extends within the 110 plane. These
sheets are then cross-linked by N–H ؒ ؒ ؒ O (b in Fig. 1) and
O–H ؒ ؒ ؒ O hydrogen bonds to the included water molecules
that are intercalated between the sheets (Fig. 3). The O–H ؒ ؒ ؒ O
hydrogen bonds from the water molecule are to the carbonyl
oxygens O(6) [O–H ؒ ؒ ؒ O, H ؒ ؒ ؒ O distances 2.80, 1.93 Å and
O–H ؒ ؒ ؒ O angle 162Њ] and O(9) [O–H ؒ ؒ ؒ O, H ؒ ؒ ؒ O distances
2.99, 2.15 Å and O–H ؒ ؒ ؒ O angle 154Њ].
Fig. 3 The intercalation between the hydrogen bonded sheets in the
structure of complex 1 by the solvent water molecules. The sheets are
cross-linked by O–H ؒ ؒ ؒ O hydrogen bonds from these included water
molecules (see text).
methyl)ferrocene dibromide 2 and [1,1Ј-bis(4-aminopyridinio-
methyl)ferrocene dibromide 3, shown in Scheme 1. A similar
reaction has been reported previously.11 Treatment of 1,1Ј-
ferrocenedimethanol with p-toluenesulfonyl chloride in the
presence of pyridine resulted in the isolation of the mixed salt
1,1Ј-bis(pyridiniomethyl)ferrocene p-toluenesulfonate chloride.
The pyridine in this mixed salt can be replaced and several
simple ferrocene amines, ferrocenophanes and ferrocene
cryptands have been synthesized from it.12
Both the complexes shown in Scheme 1 were characterised
using IR and NMR spectroscopy, mass spectrometry and
elemental analyses. In the IR spectrum of 2 the following
characteristic peaks were observed: ν(C–H) at 2981 and 2954
cmϪ1, ν(C᎐N) at 1629 and 1600 cmϪ1. For 3 the strongest bands
᎐
were exhibited for ν(N–H) at 3347, 3309, 3286 and 3112 cmϪ1
,
ν(C–H) at 2987 and 2967 cmϪ1 and ν(C᎐N) at 1650 cmϪ1. In the
᎐
1H NMR spectrum of 2 in d6-DMSO the peaks for the pyridine
protons can be observed at δ 8.16, 8.60 and 9.16, the peak for
the methylene protons occurs at δ 5.72 and the peaks for the Cp
protons occur at δ 4.68 and 4.40.
In the 1H NMR spectrum of complex 3 in D2O the peaks of
the pyridine protons can be observed at δ 7.96 and 6.76, the
peak for the methylene protons at δ 5.07 and the peaks for the
Cp protons at 4.44 and 4.39 ppm. The reactivity of 4-amino-
pyridine can be influenced by its resonance forms. As shown in
Scheme 2 two canonical forms are important: (a) and (b). In the
second form there is a partial positive charge on the 4-amino
Salt derivatives
Treatment of 1,1Ј-ferrocenedimethanol with PBr3 leads to the
formation of 1,1Ј-di(bromomethyl)ferrocene. The in situ reac-
tion of the dibromide with pyridine and 4-aminopyridine led to
the formation of the water soluble salts 1,1Ј-bis(pyridinio-
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Scheme 1
Fig. 4 The molecular structure of complex 2.
Scheme 2
group and this renders this nitrogen atom less nucleophilic.
Therefore in reactions involving nucleophilic attack the
4-aminopyridine is expected to react through the 1 position as
in the case of the formation of compound 3.
In the Fast Atom Bombardment FAB(ϩ) spectra of both the
salts the characteristic peak for [MؒBr]ϩ and [MؒBrؒH]ϩ were
respectively observed.
Crystal structure of complex 2
Crystals of the salt compound (2) suitable for crystallography
were obtained by recrystallisation from CH2Cl2. The X-ray
analysis shows the complex to have approximate, non-
crystallographic C2 symmetry (Fig. 4). The cyclopentadienyl
rings are nearly eclipsed (7Њ stagger) with their planes inclined
by ca. 4Њ to each other; the dihedral angle between the Cp
substituent bonds, C(7)–C(12) and C(19)–C(24), is 79Њ. The
torsional twists about these bonds are 81 and 83Њ respectively,
and those about the N(1)–C(7) and N(13)–C(19) bonds are 75
and 74Њ. The Cp ؒ ؒ ؒ Cp mean interplanar separation is 3.28 Å
with a centroid–centroid separation of 3.29 Å; the Cp–Fe–Cp
angle is 177.9(4)Њ.
Adjacent molecules are linked (in the crystallographic
a direction) to form chains via pairs of C–H π interactions
between one of the ortho Cp hydrogen atoms on each Cp ring of
one molecule and the pyridyl rings of the next (a and b in Fig. 5).
These interactions are supplemented by a π–π stacking inter-
action between adjacent Cp rings within the chain (c in Fig. 5).
There are no noteworthy interactions involving the BrϪ anions.
Fig. 5 One of the C–H ؒ ؒ ؒ π and π–π linked chains of molecules
present in the structure of complex 2. The H ؒ ؒ ؒ π distances (Å) and
C–H ؒ ؒ ؒ π angles (Њ) are (a) 2.88, 138 and (b) 2.82, 152. The centroid–
centroid and mean interplanar separations (c) are 3.87 and 3.57 Å
respectively.
the following characteristic peaks were observed: ν(C–H) at
2893, 2966 and 2927 cmϪ1, ν(C᎐N) at 1590 cmϪ1 and ν(NO2) at
᎐
1
1382 cmϪ1. In the H NMR spectrum in CDCl3 there are two
doublets at δ 8.14 and 6.88 corresponding to the protons of the
aniline, two triplets corresponding to the Cp protons at δ 4.18
and 4.10 and a singlet corresponding to the methylene protons
at δ 4.02. In the FAB(ϩ) mass spectra for this derivative the
molecular ion peak for [M]ϩ is observed at m/z = 348.
Crystal structure of complex 4
Tertiary amine derivatives
Crystals of complex 4 were obtained after slow evaporation of
a dichloromethane solution. The structure shows the nitro-
aniline to have bridged between the two methylene moieties of
the dimethylferrocene unit to form the complex illustrated in
When 4-nitroaniline reacts with 1,1Ј-di(bromomethyl)ferrocene
the tertiary amine derivative 1,1Ј-[2-(4-nitrophenyl)-2-aza-
propane-1,3-diyl]ferrocene 4 is synthesized. In the IR spectrum
J. Chem. Soc., Dalton Trans., 2000, 2969–2974
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[sites] = [NP]/2s
(1)
the binding site size in terms of base pairs.6 The binding con-
stant K can be written as in eqn. (2), where [free] and [bound]
are the concentrations of free and bound compound.
K = [bound]/[free][sites]
(2)
Although the Scatchard model is not strictly applicable to
DNA, it can be used when the overlap of binding sites is not an
important consideration. This is reasonable for small values of
s in base pairs. Values of current in the absence and presence of
nucleic acid were used to calculate the ratio of bound to free
compound. Experimental data for the ratio [bound]:[free] were
fitted by the model using a standard least-squares method with
K and s the only adjustable parameters.
Fig. 6 The molecular structure of complex 4.
The water soluble ferrocene derivatives synthesized all proved
to bind strongly to DNA. Scheme 3 presents the binding con-
Fig. 7 One of the the C–H ؒ ؒ ؒ π and π–π linked chains of molecules
present in the structure of complex 4. The H ؒ ؒ ؒ π distances (Å) and
C–H ؒ ؒ ؒ π angles (Њ) are (a) 2.92, 151 and (b) 3.05, 123.
Fig. 6. The ferrocenophane component has a geometry very
similar to that seen in both 2-N,N-dimethylammonio-(3)-1,1Ј-
ferrocenophane iodide and 2-N-ethylammonio-(3)-1,1Ј-ferro-
cenophane thiocyanate,12 though with the geometry at nitrogen
being significantly flattened in the neutral species; the nitrogen
atom lies 0.16 Å out of the plane of its substituents. The two Cp
rings are only 2Њ from an eclipsed conformation, but are
inclined by ca. 10Њ as a consequence of the CH2NCH2 bridge.
The Cp ؒ ؒ ؒ Cp centroid–centroid separation is 3.27 Å with a
Cp–Fe–Cp angle of 172.9(2)Њ. The mean torsional twist about
the N(13)–C(14) bond is ca. 3Њ.
As was seen in the structure of complex 2, adjacent molecules
are linked to form chains (in the 110 direction) by pairs of C–H
π interactions. Here Ci symmetric “dimer” pairs are formed by
an interaction between one of the meta Cp hydrogen atoms in
one molecule and the nitrophenyl ring of the next, and vice
versa (a in Fig. 7). These pairs are then linked across a neigh-
bouring inversion centre by weak C–H π interactions between
one of the methylene hydrogen atoms in one molecule and the
opposite face of the nitrophenyl ring in the next, and vice versa
(b in Fig. 7). The H ؒ ؒ ؒ π vectors a and b subtend an angle of
167Њ.
Scheme 3
stant and binding site size values obtained from DPV titrations
in the presence and absence of DNA for the metal complexes 1,
2 and 3.
Voltammetric methods have been used to probe the inter-
action of [Fe(phen)3]2ϩ/3ϩ with DNA. It has been shown that
both forms of the couple bind with approximately the same
affinity, K = 7.1( 0.2) × 103 and 1.47( 0.04) × 104 MϪ1 respec-
tively.13 Using DPV to determine binding constants it has been
shown that K = 6.4( 0.4) × 103 MϪ1 for the ferrocenylnucleo-
base derivative of thymine.6
In the case of the ferrocene compounds 1, 2 and 3 the binding
constants calculated are similar to that obtained for the
[Fe(phen)3]3ϩ complex. For the amide compound 1, which is not
very soluble in water and contains two hydrophobic amide
chains, this similarity could be due to hydrogen bonding as well
as hydrophobic interactions. For the two salt-like compounds 2
and 3 the binding constants are similar to that of [Fe(phen)3]3ϩ
although the pyridine and aminopyridine moieties are not
known to intercalate. Apart from possible π–π stacking inter-
actions, this binding could also be due to the fact that in these
compounds the two positive charges are better situated on the
nitrogen atoms in order to reach closer to the phosphate back-
bone of the DNA and therefore interact more strongly than in
the case of the [Fe(phen)3]3ϩ complex, where the positive charge
is concentrated on the Fe atom which cannot get very close to
the phosphate backbone.
Nucleic acid binding studies
Though studies of the binding of compound 4 were not pos-
sible due to its insolubility in water, we have investigated the
behaviour of the water soluble complexes 1, 2 and 3. If one
considers the binding of an electroactive metal centre to a given
length of duplex DNA,13 the simplest model of the binding
equilibrium (due to Scatchard7) can be obtained by assuming
each ferrocene complex binds independently and that the
number of binding sites is proportional to the concentration of
the nucleotide phosphate (NP) as shown in eqn. (1), where s is
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The binding site size is close to 2 for all three compounds,
meaning that there is one ferrocene molecule bound to every
two base pairs. This is exactly as expected since the distance
between the cyclopentadienyl rings in this type of ferrocene
derivatives is very similar to the distance between base pairs in
DNA.
In conclusion the experimental work described in this paper
has established that it is possible to make a series of ferrocenyl
derivatives which are capable of binding to DNA oligotides.
The derivatives may either be salt like and based on quaternated
pyridines or have a carbonyl glycinaimide attached to each
cyclopentadienyl ring of the ferrocene rings. Differential pulse
voltammetry was used to monitor the interactions of the water
soluble ferrocene derivatives with DNA oligomers. The three
ferrocene derivatives bind strongly to the DNA oligomers
and the bonding constants are comparable to those reported
previously for tris(phenanthroline) octahedral co-ordination
complexes.
20 ml of the Tris buffer solution were placed in the electro-
chemical cell, followed by an aliquot of the ferrocene complex
stock solution. A differential pulse voltammogram was run and
the peak current noted. Another aliquot of the ferrocene com-
plex stock solution was added to the cell, followed by another
differential pulse voltammogram. The second step involved
repeating the titration in exactly the same manner but with 20
ml DNA solution in place of buffer alone. As before, differen-
tial pulse voltammograms were recorded for each concentration
of metal complex. From these measurements, a graph of peak
current against concentration was plotted for both total metal
complex and free metal complex.
Preparations
1,1Ј-Bis(carbamoylmethylcarbamoyl)ferrocene 1. 1,1Ј-Bis-
(chlorocarbonyl)ferrocene (0.20 g, 0.6 mmol) and glycinamide
hydrochloride (0.17 g, 1.3 mmol) were refluxed in CH2Cl2 (250
ml) and an excess of NEt3 for 10 hours. A dark yellow solid was
obtained which was washed with water (2 × 20 ml) and then
treated with MeOH to afford a yellow solution. The solution
was filtered and the MeOH evaporated. Yellow crystals of the
product were obtained from a DMSO–water solution after
refrigerating for a period of four days. Yield: 0.16 g, 64.0%
(Found: C, 45.2; H, 5.0; N, 13.0%. Calc. for C16H18FeN4O4ؒ
2H2O: C, 45.5; H, 5.2; N, 13.3%). IR (cmϪ1): 3409s, 3319s,
3192s, 2940m, 1663s, 1607s, 1561s, 1301s and 1261m. 1H NMR
[d6-DMSO, 270 MHz]: δ 8.64 (1 H, t, 3JH-H 6.2, amide NH), 7.74
[2 H, s, amide NH2], 7.30 (2 H, s, amide NH2), 4.79 (2 H, t, 3JH-H
1.7, Cp H), 4.43 (2 H, t, 3JH-H 1.7, Cp H), 3.73 (2 H, d, 3JH-H 6.2
Hz, CH2), 3.38 (s, H2O) and 2.50 (s, DMSO). Mass spectrum:
FAB(ϩ), m/z 386 {60, [M]ϩ}; FAB(Ϫ): 385 {100%, [M Ϫ H]Ϫ}.
Crystal data. C16H18FeN4O4ؒ2H2O, M = 422.2, monoclinic,
space group C2/c (no. 15), a = 13.617(1), b = 9.886(1), c =
13.195(1) Å, β = 92.88(1)Њ, V = 1774.0(3) Å3, Z = 4 (the mole-
cule has crystallographic C2 symmetry), µ(Cu-Kα) = 7.21
mmϪ1, T = 293 K; orange-yellow needles, Siemens P4/PC
diffractometer, ω scans, 1324 independent reflections. The
structure was solved by the heavy atom method and the non-
hydrogen atoms were refined anisotropically using full matrix
least squares based on F2 to give R1 = 0.045, wR2 = 0.100 for
1082 independent observed absorption corrected reflections
[|Fo| > 4σ(|Fo|), 2θ < 120Њ] and 144 parameters.
Experimental
Instrumentation
Infrared spectra were recorded on a Perkin-Elmer FTIR1720
spectrometer as KBr discs, NMR spectra on either a JEOL GS
1
270 MHz or a GS 500 MHz spectrometer. H and 13C NMR
1
spectra were referenced internally to the residual H impurity
and 13C present in the deuteriated solvent. Chemical shifts are
reported in parts per million relative to TMS (δ 0). FAB(ϩ) and
FAB(Ϫ) mass spectra were recorded on a VG Autospec spec-
trometer using 3-nitrobenzyl alcohol for the sample matrix. The
ionising radiation was from a 35 keV Csϩ primary ion beam.
Differential Pulse Voltammetry (DPV) titrations of nucleic
acids with ferrocene complexes in solution were carried out in a
standard two compartment electrochemical cell of volume 20
ml. A three electrode system was used comprising of a gold
working electrode, a silver wire acting as a reference electrode
and a tungsten counter electrode. Prior to each measurement
the working electrode surface was polished with alumina paste,
then washed with distilled water to achieve a smooth clean sur-
face. Solutions of the complexes studied were prepared as
required using 0.1 M Tris buffer (tris(hydroxymethyl)methyl-
amine), pH 7 and 0.1 M potassium chloride as the supporting
electrolyte.
1,1Ј-Bis(pyridiniomethyl)ferrocene dibromide 2. A solution of
freshly distilled PBr3 (0.07 ml, 0.80 mmol) in THF (5 ml)
was added dropwise to a THF (20 ml) solution of 1,1Ј-
ferrocenedimethanol (0.20 g, 0.80 mmol) and pyridine (0.13 ml,
1.6 mmol) at 0 ЊC. The mixture was left stirring for 1 h at this
temperature, the ice bath was removed and the mixture left to
stir at room temperature for 3 h. The yellow precipitate formed
was filtered off and crystals suitable for X-ray analysis were
obtained by recrystallisation from CH2Cl2. Yield: 0.31 g, 70.5%
(Found: C, 48.0; H, 4.4; N, 4.9%. Calc. for C22H22Br2FeN2ؒH2O:
C, 48.2; H, 4.4; N, 5.1%). IR (cmϪ1): 3469(br), 3403m, 3033m,
2981m, 2954m, 1629s, 1600s, 1525s, 1481s, 1240m, 1052m,
Starting materials
1,1Ј-Ferrocenedicarboxylic acid, 1,1Ј-ferrocenedimethanol,
oxalyl chloride, phosphorus tribromide, glycinamide hydro-
chloride, 1-phenylbiguanide, 1-(3-chlorophenyl)biguanide
hydrochloride, 4-tert-butyl-2,6-diaminopyrimidine, 1-(o-tolyl)-
biguanide, 4-nitroaniline, 4-aminopyridine, 2-amino-4-
tert-butyl-6-hydroxy-1,3,5-triazine, tris(hydroxymethyl)methyl-
amine and triethylamine were purchased from Sigma-Aldrich
Chemicals Co. and used as received. 1,1Ј-Bis(chlorocarbonyl)-
ferrocene was prepared using reported procedures.14 The
solvents used in all preparations were dried and DMSO and
pyridine were distilled from BaO just prior to use.
DNA (type III, sodium salt from salmon testes) was pur-
chased from Sigma-Aldrich Chemicals Co. and used without
further purification. It was stored at 0 ЊC. DNA solutions were
prepared from stock solutions of 0.1 M Tris buffer, containing
0.1 M potassium chloride. Concentrations of DNA solutions
per nucleotide phosphate were determined spectrophoto-
metrically by UV absorbance at 260 nm with ε260 = 6600 dm3
molϪ1 cmϪ1. DNA solutions once prepared were discarded after
a period of two days.
1
1031m, 750s, 732s and 680s. H NMR [d6-DMSO, 270 MHz]:
3
3
δ 9.16 (2 H, d, JH-H 5.9, py), 8.60 (1 H, t, JH-H 8.0, py), 8.16
3
3
(2 H, t, JH-H 6.8, py), 5.72 (2 H, s, CH2), 4.68 (2 H, t, JH-H
1.73, Cp H), 4.40 (2 H, t, JH-H 1.73 Hz, Cp H), 3.32 (s, H2O)
3
and 2.50 (s, DMSO). FAB(ϩ) Mass spectrum: m/z 449 {50%,
[MؒBr]ϩ}.
Crystal data. [C22H22FeN2][Br]2ؒH2O, M = 548.1, monoclinic,
space group P21/n (no. 14), a = 7.002(1), b = 17.849(2),
c = 17.560(2) Å, β = 91.53(1)Њ, V = 2193.9(5) Å3, Z = 4, µ(Cu-
Kα) = 9.89 mmϪ1, T = 293 K, orange prismatic needles, 3258
independent reflections. The structure was solved by direct
methods, R1 = 0.058, wR2 = 0.110 for 2063 independent
observed absorption corrected reflections and 254 parameters.
Other details as for 1.
Titration procedure
The titration experiments were carried out in two steps. First,
J. Chem. Soc., Dalton Trans., 2000, 2969–2974
2973

View Article Online
1,1Ј-Bis(4-aminopyridiniomethyl)ferrocene dibromide 3.
A
Z = 2, µ(Cu-Kα) = 8.48 mmϪ1, T = 293 K, orange prisms, 2038
solution of freshly distilled PBr3 (0.04 ml, 0.42 mmol) in THF
(5 ml) was added dropwise to a THF (20 ml) solution of 1,1Ј-
ferrocenedimethanol (0.10 g, 0.4 mmol) at 0 ЊC. After the
addition was over stirring was continued for 1 h at 0 ЊC and 1 h
at room temperature. The resulting orange solution was added
dropwise to a solution of 4-aminopyridine (0.12 g, 1.2 mmol) in
THF (30 ml) and the mixture stirred for 4 h at room temper-
ature. The yellow precipitate obtained was filtered off, washed
with acetone and recrystallised three times from a DMSO–
CHCl3 mixture, in order to avoid formation of a gum. The final
product was dried in vacuo at 40 ЊC for 3 h. Yield: 0.15 g, 64.0%
(Found: C, 62.0; H, 4.7; N, 8.1%. Calc. for C18H16FeN2O2: C,
62.1; H, 4.7; N, 8.1%). IR (cmϪ1): 3347m, 3309m, 3286m,
3112m, 2987m, 2967m, 1650s, 1536s, 1238w, 1209m, 1162s,
1064m, 1037m and 838m. 1H NMR [D2O, 270 MHz]: δ 7.96 (H,
d, py), 6.76 (H, d, py), 5.07 (2 H, s, CH2), 4.80 (s, H2O), 4.44
(2 H, s, Cp H) and 4.39 (2 H, s, Cp H). FAB(ϩ) Mass spectrum:
m/z 480 {45%, [MؒBr ϩ H]ϩ}.
independent reflections. The structure was solved by direct
methods, R1 = 0.044, wR2 = 0.105 for 1772 independent
observed reflections and 209 parameters. Other details as for 1.
CCDC reference number 186/2102.
See http://www.rsc.org/suppdata/dt/b0/b004295l/ for crystal-
lographic files in .cif format.
Acknowledgements
We thank BP plc for generously funding D. M. P. M.’s Chair
whilst he worked at Imperial College.
References
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8901.
1,1Ј-[2-(4-Nitrophenyl)-2-azapropane-1,3-diyl]ferrocene 4. A
solution of freshly distilled PBr3 (0.04 ml, 0.42 mmol) in THF
(5 ml) was added dropwise to a THF (20 ml) solution of 1,1Ј-
ferrocenedimethanol (0.10 g, 0.4 mmol) at 0 ЊC. After the
addition was over stirring was continued for 1 h at 0 ЊC and 1 h
at room temperature. The resulting orange solution was added
dropwise to a solution of 4-nitroaniline (0.27 g, 2.0 mmol) in
THF (20 ml) and the mixture stirred for 3 h. When reducing the
THF volume an orange precipitate was formed which was
recrystallised from CH2Cl2. Orange crystals were obtained by
slow evaporation of a CH2Cl2 solution. Yield: 0.07 g, 50.3%
(Found: C, 62.0; H, 4.7; N, 8.1%. Calc. for C18H16FeN2O2: C,
62.1; H, 4.7; N, 8.1%). IR (cmϪ1): 3092w, 2966w, 2927w, 2893w,
2663w, 2419w, 1590s, 1509m, 1447m, 1382s, 1247m, 1203m,
8 P. D. Beer, A. R Graydon, A. O. M. Johnson and D. K. Smith, Inorg.
Chem., 1997, 36, 2112.
9 P. D. Beer, C. Hazlewood, D. Hesek, J. Hodacova and S. E. Stokes,
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1989, 111, 8901.
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1
1114s, 916s and 823m. H NMR [d-CDCl3, 270 MHz]: δ 8.14
3
3
(2 H, d, JH-H 9.6, Ph), 7.25 (s, CHCl3), 6.88 (2 H, d, JH-H 9.6
Hz, Ph), 4.18 (2 H, t, 3JH-H 1.72, Cp H), 4.10 (2 H, t, 3JH-H 1.72
Hz, Cp H) and 4.02 (2 H, s, CH2). FAB(ϩ) Mass spectrum: m/z
348 {40%, [M]ϩ}.
Crystal data. C18H16FeN2O2, M = 348.2, triclinic, space
¯
group P1 (no. 2), a = 8.147(1), b = 9.544(1), c = 10.771(1) Å,
α = 116.29(1), β = 93.36(1), γ = 102.47(1)Њ, V = 721.7(1) Å3,
2974
J. Chem. Soc., Dalton Trans., 2000, 2969–2974