The effect of protonation on the spectroscopic and redox properties of a series of ferrocenoyl derivatives

Article abstract of DOI:10.1039/a807453d

Five ferrocenoyl derivatives, containing pyridine (1-4) and benzene (5) moieties, were synthesised and characterised. The effect on the spectroscopic and redox properties of these compounds upon addition of H⁺ was studied, with NMR studies indicating that protonation took place at the pyridine nitrogens of 1-4. A crystal structure determination of the bis(amide) derivative 4 revealed the presence of two intramolecular hydrogen bonds; these remained intact in solution but were cleaved upon protonation. Protonation induced anodic shifts in the ferrocene-centred redox potential of ferrocene receptors 1, 2 and 4 and also changes in the electronic and NMR spectra of 1-4. A bathochromic shift in the lowest energy spin-allowed d-d band upon protonation was only observed for those compounds which also displayed a pronounced redox response.

Full text of DOI:10.1039/a807453d

View Article Online / Journal Homepage / Table of Contents for this issue
The effect of protonation on the spectroscopic and redox
properties of a series of ferrocenoyl derivatives
Jonathan D. Carr,a Simon J. Coles,b William W. Hassan,a Michael B. Hursthouse,b
K. M. Abdul Malikb and James H. R. Tucker*a
a School of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD.
E-mail: j.h.r.tucker@exeter.ac.uk
b Department of Chemistry, University of Wales Cardiff, PO Box 912, Cardiff, UK CF1 3TB
Received 24th September 1998, Accepted 16th November 1998
Five ferrocenoyl derivatives, containing pyridine (1–4) and benzene (5) moieties, were synthesised and characterised.
The effect on the spectroscopic and redox properties of these compounds upon addition of Hϩ was studied, with
NMR studies indicating that protonation took place at the pyridine nitrogens of 1–4. A crystal structure
determination of the bis(amide) derivative 4 revealed the presence of two intramolecular hydrogen bonds; these
remained intact in solution but were cleaved upon protonation. Protonation induced anodic shifts in the ferrocene-
centred redox potential of ferrocene receptors 1, 2 and 4 and also changes in the electronic and NMR spectra of 1–4.
A bathochromic shift in the lowest energy spin-allowed d–d band upon protonation was only observed for those
compounds which also displayed a pronounced redox response.
O
O
Introduction
C
C
C
In the past few years, there have been numerous reports of
metallocene receptor compounds that bind cations,1 anions2
and more recently, neutral molecules.3,4 Owing to the potential
application of these derivatives as electrochemical sensors
and the current general interest in supramolecular electro-
chemistry,5 studies have largely concentrated on the effect of
complexation on the redox properties of the receptor. However,
cation complexation can also affect the chromogenic properties
of ferrocene ligands.6 This is perhaps not surprising, as it is well
known that the electronic spectrum of ferrocene is affected
by cyclopentadienyl (Cp) substituents.7 Accordingly, a few
attempts have been made to correlate electrochemical proper-
ties with spectroscopic properties of ferrocene derivatives,8
although no analogous systematic study has been carried out
on ferrocene ligands and their complexes. In this paper, the
synthesis, characterisation and proton binding properties of
five simple ferrocene derivatives 1–5 are reported, with a view to
rationalising the changes in both the redox and spectroscopic
properties of the ferrocene unit upon the addition of Hϩ. For a
comparative and systematic study with a range of receptors, Hϩ
has an advantage over metal cations in that Hϩ provides similar
steric and stoichiometric constraints for each receptor and the
complexation site is very specific. Furthermore, the high charge
density of Hϩ should bring about large spectroscopic and redox
effects. Recent work has indeed shown that Hϩ induces signifi-
cant changes in the redox properties of ferrocene derivatives
containing basic nitrogen atoms.6a,9
N
H
N
H
N
N
N
Fe
Fe
O
N
H
1
2
O
O
C
C
N
N
N
N
H
H
Fe
Fe
O
C
N
N
H
4
3
O
C
N
H
Fe
5
out using mass spectrometry, cyclic voltammetry, elemental
analysis, NMR, UV/VIS and IR spectroscopy.
Results and discussion
Crystal structure of compound 4
Synthesis
Suitable crystals of 4 for X-ray crystallography were grown by
slow diffusion of diethyl ether into a dichloromethane solution
of the ligand. A view of the molecule is presented in Fig. 1, with
selected bond distances and angles listed in Table 1. The main
point of interest is the presence of two intramolecular hydrogen
bonds; in each case, one amide proton on one arm is bonded to
one pyridine nitrogen on the other arm [N(3)–H(3) ؒ ؒ ؒ N(2)
distance 2.95 Å, N(3)–H(3) ؒ ؒ ؒ N(2) angle 158Њ; N(1)–
H(1) ؒ ؒ ؒ N(4) distance 3.06 Å, N(1)–H(1) ؒ ؒ ؒ N(4) angle 150Њ].
Compounds 1–5 were synthesised by addition of either chloro-
carbonylferrocene10 or 1,1Ј-bis(chlorocarbonyl)ferrocene10,11 to
the respective amine in dry dichloromethane, in the presence of
triethylamine as base. A modified synthesis of 1,1Ј-bis-
(chlorocarbonyl)ferrocene is given in the Experimental section.
Column chromatography on neutral alumina or recrystallis-
ation was used to purify the products, which were isolated in
good yield. Characterisation of these compounds was carried
J. Chem. Soc., Dalton Trans., 1999, 57–62
57

View Article Online
Table 1 Selected bond lengths (Å) and angles (Њ) for compound 4
Table 2 1H NMR spectroscopic data for compounds 1–4 displaying
the shifts in resonance values (ppm) upon the addition of stoichio-
metric amounts of Hϩ (298 K)
O(1)–C(11)
N(1)–C(11)
N(1)–C(12)
C(1)–C(11)
1.231(5)
1.347(5)
1.446(5)
1.484(5)
O(2)–C(18)
N(3)–C(18)
N(3)–C(19)
C(6)–C(18)
1.231(4)
1.338(5)
1.454(5)
1.486(6)
Ferrocene liganda
N–H
Cpc
Cpd
1
ϩ2.36
ϩ2.58
ϩ0.75
—
ϩ0.36
ϩ0.22
ϩ0.04
—
ϩ0.37
ϩ0.25
ϩ0.04
—
C(11)–N(1)–C(12)
O(1)–C(11)–N(1)
O(1)–C(11)–C(1)
N(1)–C(11)–C(1)
121.2(3)
122.1(4)
121.2(4)
116.7(4)
C(18)–N(3)–C(19)
O(2)–C(18)–N(3)
O(2)–C(18)–C(6)
N(3)–C(18)–C(6)
119.8(3)
122.3(4)
121.3(4)
116.4(3)
2
3
4e
Ferrocene ligandb
N–H
Cpc
Cpd
1
ϩ2.20
—
ϩ0.53
Ϫ1.99
ϩ0.21
—
ϩ0.07
ϩ0.12
ϩ0.22
—
ϩ0.10
ϩ0.23
2e
3
4
a Obtained at 300 MHz in CDCl3. b Obtained at 300 MHz in CDCl3–d6-
acetone (2:1 ratio). c Pair of protons adjacent to carbonyl group on
derivatised Cp ring. d Pair of protons furthest from carbonyl group on
derivatised Cp ring. e Precipitation occurred upon addition of two
equivalents of Hϩ.
0.04 M) induced small downfield shifts in these resonance
values (ϩ0.12 and ϩ0.27 ppm respectively), corresponding to
weak hydrogen bonding interactions with water. However, very
small changes <ϩ0.05 ppm were observed with 3 and 4, which
indicates that increasing the polarity of the solvent does not
disrupt the intramolecular hydrogen bonding in 4.
The addition of HBF4 to compounds 1 and 2 (ca. 0.001 M) in
CDCl3 induced downfield shifts in the resonances correspond-
ing to the pyridine, amide and Cp protons (Table 2). Titrations
of the most downfield Cp proton against Hϩ concentration
revealed the expected 1:1 stoichiometry for 1 and 2:1 (acid:
ligand) stoichiometry for 2.
In comparison with 1 and 2, addition of a slight excess of Hϩ
to 3 in CDCl3 induced smaller downfield shifts in the amide and
Cp proton resonances but similar changes were observed for
those corresponding to the pyridine protons. Treatment of 4
with Hϩ resulted in the immediate precipitation of an insoluble
orange solid, which was presumably protonated species. There-
fore, binding studies were repeated for all five compounds in
CDCl3–d6-acetone (2:1 ratio). In this new solvent system, the
amide proton resonance for 4 (δ 9.97) was still strongly
deshielded compared to 3 (δ 7.14), which indicated that
intramolecular hydrogen bonding was still intact. Once again,
addition of Hϩ produced changes in the NMR spectra, with
smaller shifts observed in the signals for the Cp protons and
amide protons of 3 compared with 1 and 4 (Table 2). Further-
more, whereas a small downfield shift in the amide proton
resonance of ϩ0.53 ppm was seen for 3, a large upfield shift of
Ϫ1.99 ppm was observed for 4. Therefore, as expected, proton-
ation of the two pyridine nitrogens necessitated cleavage of the
intramolecular hydrogen bonds in 4. The stoichiometry of 2:1
for the protonated complex of 4 was established by a titration
of the upfield shift of the amide proton resonance against
increasing Hϩ concentration (Fig. 2).
Fig. 1 Crystal structure of 4.
The cyclopentadienyl rings are virtually coplanar and eclipsed
with a rotation angle of only 2Њ.
1H NMR studies
The resonance values of amide protons give an indication as to
the extent of intra- or inter-molecular hydrogen bonding in
solution. The strongly deshielded value in CDCl3 for the
resonance corresponding to the two amide protons of 4 (δ 9.97)
indicates that hydrogen bonding is present in this compound in
solution, as well as in the solid state. Support for an intra-
molecular, inter-arm interaction, similar to that observed in the
crystal structure, is given by the fact that firstly, dilution from
0.04 M to 0.001 M produced no significant change in chemical
shift for the amide proton resonance and secondly, the corres-
ponding signal for the mono derivative 3 is considerably more
upfield at δ 6.99. Apart from compound 4, there is no evidence
for strong hydrogen bonding in CDCl3; the chemical shifts for
the amide proton resonances for 1 and 2 are similar, which
precludes strong inter-arm interactions as seen in 4. Further-
more, dilution from 0.04 M to 0.001 M produced no significant
changes in the resonance shift values for the amide protons of
1, 2, 3 and 5. These values are in fact similar to those observed
for related amidopyridine derivatives in CDCl3.12 The addition
of H2O (ca. 50-fold molar excess) to solutions of 1 and 2 (ca.
The addition of Hϩ produced no significant changes in the
NMR spectrum of 5 in either solvent system, which confirmed
that protonation was taking place at the pyridine nitrogens of
1–4. However, the addition of excess of Hϩ to 1–5 produced
broadened NMR spectra if solutions were left to stand for a
few hours, which indicated that any excess acid present was
oxidising the ferrocene unit.13
IR studies
IR studies in dichloromethane gave additional evidence for
intramolecular hydrogen bonding solution for the bis(amide) 4,
as evidenced by the lower stretching frequency for the amide
N–H group of 4 in CH2Cl2 (3255 cmϪ1), compared with 3 (3446
and 3402 cmϪ1). These differences in wavenumber reflect the
58
J. Chem. Soc., Dalton Trans., 1999, 57–62

View Article Online
Table 3 UV/VIS spectroscopic dataa for compounds 1–5 and the
chromogenic response to the addition of stoichiometric amounts of Hϩ
(CH2Cl2, 298 K)
Table 4 Electrochemical dataa for compounds 1–5 and the redox
response (∆EЊ) to the addition of stoichiometric amounts of Hϩ
(CH2Cl2, 298 K)
Ferrocene ligand
Ferrocene ligand with Hϩ
EЊ/V
∆EЊ/mV
λmax/nm
ε/dm3 molϪ1 cmϪ1
λmax/nm
ε/dm3 molϪ1 cmϪ1
1
2
3
4
5
ϩ0.24
ϩ0.44
ϩ0.09
ϩ0.16
ϩ0.35
ϩ70
ϩ180
<ϩ5
ϩ15
1
2
3
4
5
448
450
444
444
444
320
470
100
220
330
478
472
444
444
444
1280
1400
160
1880
360
<ϩ5
a Redox potentials (EЊ) were referenced to ferrocene as internal stand-
ard where EЊ = 0.5 (EЊpa Ϫ EЊpc). The confidence limit is 5 mV; for
conditions see Experimental section. For each voltammogram, the
reversibility of the redox wave matched that of the ferrocene internal
reference (∆EЊp = 70–100 mV).
a Data for the lowest energy spin-allowed d–d band of the ferrocene
unit.
Fig. 2 1H NMR titration of the upfield shift of the amide N–H reson-
ance of 4 as a function of molar equivalents of Hϩ in CDCl3–d6-
acetone (2:1 ratio).
fact that the amide N–H bonds in 4 are weaker as a result of
hydrogen bonding with the pyridine nitrogen.14 The addition of
Hϩ to CH2Cl2 solutions of the receptors produced very minor
changes in the N–H and carbonyl stretches of all pyridine
receptors apart from 4, for which the emergence of a new N–H
stretching band at higher energy (3388 cmϪ1) was observed, in
accordance with the hydrogen bonds in 4 being cleaved upon
protonation.
UV/VIS studies
Fig. 3 UV/VIS titration of the change in absorption intensity at
constant wavelength as function of molar equivalents of Hϩ for
compounds (a) 1 at 478 nm and (b) 2 at 472 nm in CH2Cl2.
All receptors gave a visible band in their electronic spectrum
between 400 and 500 nm of wavelength and intensity that was
characteristic of the lowest energy spin-allowed d–d band of
the ferrocene unit.15 Upon the addition of a slight excess of
HBF4 to receptors 1 and 2 in dichloromethane, respective
bathochromic shifts in this band of 30 nm and 22 nm occurred,
accompanied by an increase in the molar absorption coefficient
(Table 3). The stoichiometry of each complex was confirmed by
monitoring the change in absorbance of the d–d transition in
dichloromethane (ca. 1 mM) upon addition of aliquots of Hϩ
at a constant wavelength (Fig. 3).
The UV/VIS results for 1 and 2 contrast sharply with those
for compounds 3–5; in particular, no apparent bathochromic
shift in the lowest energy d–d transition was observed upon the
addition of Hϩ to either 3 or 4. In the case of 4, interpretation
was made more difficult because of strong bathochromic shifts
in higher energy bands which partially obscured the lowest
energy d–d band; these shifts were the main reason for the large
increase in intensity in this area of the spectrum. However, in
the case of 3, it is clear that the addition of one equivalent of
Hϩ induced only a small increase in intensity in this band,
whilst the wavelength of the transition remained constant. For
compound 5, as expected, virtually no change was observed in
any region of the visible spectrum between 300 and 500 nm
upon addition of approximately one equivalent of Hϩ. How-
ever, upon addition of excess Hϩ, bathochromic shifts were
observed, which in all probability were due to partial oxidation
of the ferrocene unit13 (see above).
Electrochemical studies
Cyclic voltammetry experiments were carried out in dichloro-
methane solution at 1 mM, containing tetrabutylammonium
perchlorate (0.1 M) as supporting electrolyte. The redox poten-
tials EЊ are displayed in Table 4, along with the change in the
redox potential, ∆EЊ, upon addition of Hϩ. It is clear from this
data that receptors 1 and 2 undergo the largest redox response
to protonation. Titrations with aliquots of Hϩ confirmed the
stoichiometry of the complexes with these receptors, with full
shifts in EЊ observed after adding exactly one equivalent of Hϩ
to 1 and two equivalents of Hϩ to 2. The direction of the
change in the redox potentials for 1 and 2 (i.e. anodic shifts) is
in agreement with results from other electrochemical studies on
ferrocene derivatives containing basic amines.6a,9 As expected,
the magnitude of ∆EЊ for 2 is approximately twice that of 1, in
accordance with two positive charges being introduced in close
proximity to the ferrocene unit.
J. Chem. Soc., Dalton Trans., 1999, 57–62
59

View Article Online
cations through amide coordination.16 However, upon reduc-
tion of both amide groups of 6 to form cryptand 7,17a the
chromogenic response to complexation of Ca2ϩ, which is now
bound within the macrocyclic cavity, is reduced,† whilst the
redox response is significantly enhanced (Fig. 4).‡ It follows
that a large redox response to complexation does not necessar-
ily imply a large bathochromic shift in this band. Therefore,
clearly other factors must be taken into account in order to
achieve a greater understanding of both redox and chromo-
genic effects. It has been suggested that Cp ring tilt,18 Cp ring
rotation6b and Fe–metal interactions17 affect the chromogenic
properties of the ferrocene centre. For example, in the case of
cryptand 7, an Fe–Agϩ interaction has been postulated to
explain the enhanced chromogenic and redox response to com-
plexation with this cation.17a
Fig. 4 The effect of 1:1 complexation with Ca2ϩ on the redox and
chromogenic properties of ferrocene cryptands 6 and 7 in CH3CN.
An analysis of the spectroscopic and electrochemical results
for these derivatives reveals interesting trends. Protonation of
1 and 2, at a nitrogen site four bond lengths away from the
ferrocene unit, affects the distribution of electron density at the
Cp ligands, as evidenced by the downfield shifts for the NMR
signals corresponding to the Cp ring proton resonances. How-
ever, the introduction of an additional methylene unit (3 and 4)
induces smaller downfield shifts, although the effect is slightly
larger for the bis(amide) 4, probably because of conformational
changes that are brought about by protonation. Furthermore,
only in the case of 1 and 2 is a pronounced redox response to
protonation observed, with both complexes harder to oxidise
than the corresponding ligands. Beer has suggested that the
origin of the redox response to complexation can either be a
through-spaceorthrough-bondinteraction.1a Clearly,athrough-
space interaction must dominate for those redox responsive sys-
tems in which there is little or no obvious conjugation between
the complexation site and the redox centre, as is the case for 1
and 2. Indeed, according to the work of Plenio,9a shifts of ϩ70
mV for 1 and <ϩ5 mV for 3 would be consistent with those
predicted for a simple electrostatic through-space interaction
for systems with a distance of four and five bond lengths
respectively between the Cp ring and the protonation site.
The origin of the small shift of ϩ15 mV found with receptor 4
upon protonation is unclear. However, a positive shift of this
magnitude would be consistent with a disruption of the intra-
molecular hydrogen bonding in this receptor upon protonation,
since previous work has shown that the formation of hydrogen
bonds via the amide N–H groups of 1 and 2, induces negative
redox shifts.3
There appears to be a general correlation between the redox
and spectroscopic properties of these ferrocene receptors in that
where protonation causes bathochromic shifts in the lowest
energy spin-allowed d–d band, a pronounced redox response is
also observed. In other words, protonation of either 1 or 2 must
not only lower the level of the Fe centred HOMO, as evidenced
by the increase in redox potential, but also decrease the energy
of this d–d band. Interestingly enough, an identical trend has
been observed when conjugated electron withdrawing substitu-
ents are introduced onto the Cp rings of the ferrocene unit.7,8
This trend has been explained by firstly, the substituent making
oxidation more difficult by withdrawing electron density away
from the Fe centre and secondly, the low-lying Cp π* orbitals
shifting to lower energy, which reduces the energy of the elec-
tronic transition. In addition, increased mixing of ligand
orbitals with metal d orbitals makes such a transition more
allowed by increasing the MLCT character, resulting in an
increase in absorption intensity. For receptors 1 and 2, proton-
ation certainly induces a similar effect, as shown by the increase
in the ε values in Table 3.
Conclusion
Studies on these simple redox-active proton receptors have
given further insight into the nature of the electrochemical and
spectroscopic properties of ferrocene derivatives. For those
compounds which give a pronounced redox response to proton-
ation, a larger spectroscopic response, in terms of changes in
the NMR spectra and bathochromic shifts in the visible spec-
tra, is also observed. Further spectroscopic and electrochemical
studies with these and other ferrocene receptors are now in
progress to establish the redox and chromogenic response to the
complexation of other charged species and neutral molecules.
Experimental
Unless specified otherwise, reagent grade reactants and solvents
were used as received from chemical suppliers. The synthesis of
all compounds was carried out under an inert gas atmosphere
of nitrogen. Chlorocarbonylferrocene was prepared according
to the literature procedure.10 Column chromatography was per-
1
formed on B.D.H. alumina (neutral, Brockman activity I). H
and 13C NMR spectra were recorded on either a Bruker AC
300 or a Bruker Advance DRX 400 spectrometer. IR spectra
were recorded on a Nicolet Magna 550 spectrometer. UV/VIS
spectra were recorded at 298 K on a Unicam UV4 spectrometer.
Mass spectra (LSIMS, liquid secondary ion mass spectrometry)
were obtained using a Kratos Profile HV3 instrument. The
crystal stucture of 4 was determined at Cardiff University. Cyc-
lic voltammograms were recorded at 298 K using an EG&G 273
potentiostat in dry, nitrogen-purged dichloromethane with
tetrabutylammonium perchlorate (0.1 M) as supporting electro-
lyte, Ag as a pseudo-reference electrode and Pt wire as both
counter and working electrode (scan rate 200 mV sϪ1). Fer-
rocene (ca. 1 mM) was used as an internal reference.
Synthesis
1,1Ј-Bis(chlorocarbonyl)ferrocene. Oxalyl chloride (5.5 g, 43
mmol) in CH2Cl2 (10 mL) was added dropwise to a suspension
of 1,1Ј-ferrocenedicarboxylic acid (2.0 g, 7.3 mmol) in dry
CH2Cl2 (25 mL) at 0 ЊC. The mixture was stirred overnight at
room temperature and then refluxed for approximately 2 hours
until a clear, dark red solution was obtained. This was then
evaporated under reduced pressure and the crude product sub-
jected to Soxhlet extraction with dry pentane (ca. 300 mL) for
24 hours. The pentane solution was then evaporated under
reduced pressure to give the title compound as a red solid (1.13
g, 50%); νmax/cmϪ1 (CO) 1765s (nujol); δH (300 MHz, CDCl3)
5.04 (m, 4H, CpH), 4.76 (m, 4H, CpH).
Bathochromic shifts in the d–d band centred at ca. 450 nm
and an accompanying increase in absorption upon complex-
ation have been observed with other ferrocene receptors upon
addition of protons and metal cations.6 An example of such a
ligand is the bis(amide) cryptand 6, which binds Group 2
† Chromogenic response. 6: ε (% increase) 39%; ∆λmax ϩ13 nm [data
taken from ref. 6(b)]; 7: ε (% increase) ca. 10%; ∆λmax ca. ϩ5 nm [data
taken from ref. 17(a)].
‡ Redox response. 6: ∆EЊ ϩ155 mV [data taken from ref. 16(b)]; 7: ∆EЊ
ϩ274 mV [data taken from ref. 17(a)].
60
J. Chem. Soc., Dalton Trans., 1999, 57–62

View Article Online
[{(6-Methyl-2-pyridyl)amino}carbonyl]ferrocene 1. A mixture
of triethylamine (0.20 g, 2.0 mmol) and 2-amino-6-methyl-
pyridine (0.220 g, 2.0 mmol) was added to anhydrous CH2Cl2
(10 mL). Chlorocarbonylferrocene (0.430 g, 1.8 mmol) in
anhydrous CH2Cl2 (60 mL) was added dropwise at 0 ЊC over a
period of 30 minutes. The reaction mixture was allowed to
return to room temperature and stirred for 24 hours. Saturated
NaHCO3 (30 mL) was then added and the mixture was
extracted with CH2Cl2 (3 × 50 mL). The combined extracts
were dried (MgSO4), filtered and the solvent removed under
reduced pressure to give an orange solid. The crude product
was purified by column chromatography on neutral alumina
(CH2Cl2 with 1% methanol) to give pure 1 as an orange solid
(0.437 g, 76%). The compound may be recrystallised from
CH2Cl2–diethyl ether to give thin orange needles, mp 150–
151 ЊC (Found: C, 61.99; H, 4.46; N, 8.36. C17H17FeN2O1.5 (0.5
1% methanol) to give pure 4 as an orange solid (0.30 g, 65%).
The compound may be recrystallised from CH2Cl2–diethyl
ether to give orange needles, mp 230 ЊC (decomp.) (Found: C,
63.50; H, 4.32; N, 12.29. C24H22FeN4O2 requires C, 63.47; H,
4.88; N, 12.33%); νmax/cmϪ1 (NH) 3255m, (CO) 1643s (CH2Cl2);
δH (300 MHz, CDCl3) 9.97 (2H, s, NH), 8.59 (2H, d, J 7.5,
C5H4N), 7.77 (2H, dd, J 7.5, 7.9, C5H4N), 7.46 (2H, d, J 7.9,
C5H4N), 7.30 (2H, t, J 5.1, C5H4N), 4.74 (4H, m, C5H4), 4.54
(4H, d, J 6.3 Hz, CH2), 4.34 (4H, t, C5H4); m/z (LSIMS) 454
(M)ϩ.
[{(3-Methylphenyl)amino}carbonyl]ferrocene 5. The same
method as for 1 was carried out, using a mixture of triethyl-
amine (0.19 g, 1.9 mmol) and m-toluidine (0.19 g, 1.9 mmol) in
anhydrous CH2Cl2 (10 mL), and chlorocarbonylferrocene (0.43
g, 1.8 mmol) in anhydrous CH2Cl2 (60 mL). A proportion of
the product precipitated out overnight after the addition and
this was filtered off. The remainder of the reaction mixture was
worked up as before and combined with the precipitate to give
an orange solid, which was then recrystallised from CH2Cl2–
diethyl ether to give pure 5 as orange crystals (0.49 g, 85%), mp
226 ЊC (decomp.) (Found: C, 67.28; H, 5.24; N, 4.34.
C24H22FeN4O2 requires C, 67.75; H, 5.37; N, 4.39); νmax/cmϪ1
(NH) 3435m, (CO) 1675s (CH2Cl2); δH (300 MHz, CDCl3) 7.48
(1H, s, NH), 7.36 (1H, d, J 6.1, C6H4), 7.36 (1H, s, C6H4) 7.23
(1H, dd, J 6.1, 7.5, C6H4), 6.94 (1H, d, J 7.5 Hz, C6H4), 4.78
(2H, m, C5H4), 4.42 (2H, m, C5H4), 4.26 (5H, s, C5H5), 2.37
(3H, s, CH); m/z (LSIMS) 319 (M)ϩ.
equivalent of H2O) requires C, 62.06; H, 4.86; N, 8.51%); νmax
/
cmϪ1 (NH) 3420m, (CO) 1677s (CH2Cl2); δH (300 MHz, CDCl3,
standard SiMe4) 8.12 (1H, d, J 8.3, C5H3N), 8.05 (1H, s, NH),
7.59 (1H, dd, J 8.3, 7.5 Hz, C5H3N), 6.88 (1H, d, J 7.5,
C5H3N), 4.82 (2H, t, J 1.9, C5H4), 4.42 (2H, t, J 1.9, C5H4),
4.24 (5H, s, C5H5), 2.48 (3H, s, CH3); m/z (LSIMS) 321
(M ϩ H)ϩ.
1,1Ј-Bis[{(6-methyl-2-pyridyl)amino}carbonyl]ferrocene
2.
The same method as for 1 was carried out, using a mixture
of triethylamine (0.31 g, 3.06 mmol) and 2-amino-6-methyl-
pyridine (0.305 g, 2.82 mmol) in anhydrous CH2Cl2 (10 mL)
and 1,1Ј-bis(chlorocarbonyl)ferrocene (0.44 g, 1.41 mmol) in
anhydrous CH2Cl2 (60 mL). After work-up, the crude product
was purified by column chromatography on neutral alumina
(CH2Cl2 with 1% methanol) to give pure 2 as an orange solid
(0.46 g, 73%). The compound may be recrystallised from
CH2Cl2–diethyl ether to give thin orange needles, mp 240 ЊC
(decomp.) (Found: C, 62.93; H, 4.61; N, 12.17. C24H22FeN4O2
requires C, 63.47; H, 4.88; N, 12.33%); νmax/cmϪ1 (NH) 3412m,
(CO) 1678s (CH2Cl2); δH (300 MHz, CDCl3) 8.31 (2H, s, NH),
8.04 (2 H, d, J 8.1, C5H3N), 7.53 (2H, dd, J 8.1, 7.6, C5H3N),
6.85 (2H, d, J 7.6 Hz, C5H3N), 4.93 (4H, m, C5H4), 4.52 (4H, m,
C5H4), 2.45 (6H, s, CH3); δC (100 MHz, CDCl3) 167.81 (CO),
156.50 (CR of C5H3N), 150.77 (CR of C5H3N), 138.58 (CH of
C5H3N), 118.90 (CH of C5H3N), 110.88 (CH of C5H3N), 77.63
(CR of C5H4), 72.88 (CH of C5H4), 70.19 (CH of C5H4), 24.00
(CH3); m/z (LSIMS) 455 [M ϩ H]ϩ.
Crystallography
Crystal data for 4. C24H22N4O2Fe, M = 454.31, triclinic, space
¯
group P1, a = 8.894(2), b = 9.855(2), c = 13.892(3) Å, α =
106.01(3), β = 98.80(3), γ = 113.58(3)Њ, U = 1023.6(4) Å3, T =
150(2) K, Z = 2, µ(Mo-Kα) = 0.767 mmϪ1, F(000) = 472, 4328
reflections were collected, θ range 2.36 to 25.02Њ (index ranges; h
Ϫ9 to 10, k Ϫ11 to 11, l Ϫ12 to 15), which merged to give 2804
unique reflections (Rint = 0.0800) to refine against 280 para-
meters. Final R indices were wR2 = 0.0955 and R1 = 0.0399
(I > 2σI) and 0.0993 and 0.0558 respectively for all data.
Residual electron densities were 0.399 and Ϫ0.348 e ÅϪ3
.
X-Ray crystal data were collected upon a crystal of size
0.2 × 0.16 × 0.12 mm on a Delft instruments FAST TV area
detector diffractometer at the window of a rotating anode
FR591 generator (50 kV, 50 mA), using a molybdenum target
[λ(Mo-Kα) = 0.71069 Å], controlled by a MicroVax 3200 and
driven by MADNES19 software.
[(2-Pyridylmethylamino)carbonyl]ferrocene 3. The same
method as for 1 was carried out, using a mixture of triethyl-
amine (0.04 g, 0.4 mmol) and 2-pyridylmethylamine (0.04 g, 0.4
mmol) in anhydrous CH2Cl2 (10 mL) and chlorocarbonyl-
ferrocene (0.91 g, 1.0 mmol) in anhydrous CH2Cl2 (30 mL). A
proportion of the product precipitated out overnight after the
addition and this was filtered off. The remainder of the reac-
tion mixture was worked up as before and combined with the
precipitate to give an orange solid, which was then recrystal-
lised from CH2Cl2–diethyl ether to give pure 3 as orange crys-
tals (0.26 g, 82%), mp 140–141 ЊC; νmax/cmϪ1 (NH) 3446m,
3402m, (CO) 1653s, (CH2Cl2); δH (300 MHz, CDCl3) 8.58
(1H, d, J 7.65, C5H4N), 7.68 (1H, dd, J 7.65, 7.8, C5H4N),
7.35 (1H, d, J 7.8, C5H4N), 7.22 (1H, t, J 6.8 Hz, C5H4N),
6.99 (1H, s, NH), 4.74 (2H, m, C5H4), 4.67 (2H, d, J 5.2,
CH2), 4.35 (2H, m, C5H4), 4.17 (5H, s, C5H5); m/z (LSIMS)
319 (M)ϩ.
The structure was solved by direct methods (SHELX-S20)
and then subjected to full-matrix least squares refinement based
on F2 (SHELX-9321). Non hydrogen atoms were refined aniso-
tropically with hydrogens included in idealised positions (C–H
distance = 0.97 Å) with isotropic parameters set at 1.2 times
the Ueq of the parent atoms. The weighting scheme used was
2
w = 1/[σ2(Fo ) ϩ (0.0433P)2], where P = (Fo2 ϩ 2Fc2)/3. An
absorption correction (DIFABS22) was applied once the struc-
ture had been fully elucidated giving correction factors of 0.725
and 1.121.
CCDC reference number 186/1253.
See http://www.rsc.org/suppdata/dt/1999/57/ for crystallo-
graphic files in .cif format.
UV/VIS, NMR and CV titrations
Titrations were carried out by adding aliquots of a stock solu-
tion of HBF4 [made up by diluting a 54% solution in diethyl
ether (Aldrich) with the appropriate solvent] to a solution of
the ferrocene ligand (ca. 10Ϫ3 M) in either CDCl3 or CDCl3–d6-
acetone (for NMR studies) or CH2Cl2 (for UV/VIS and CV
studies). The absorbance readings from the UV/VIS spectra
were adjusted to take into account the dilution of the solution
during the course of each experiment.
1,1Ј-Bis[(2-pyridylmethylamino)carbonyl]ferrocene 4. The
same method as for 1 was carried out, using a mixture of tri-
ethylamine (0.21 g, 2.1 mmol) and 2-pyridylmethylamine (0.21
g, 2.1 mmol) in anhydrous CH2Cl2 (10 mL) and 1,1Ј-
bis(chlorocarbonyl)ferrocene (0.30 g, 1.0 mmol) in anhydrous
CH2Cl2 (60 mL). After work-up, the crude product was purified
by column chromatography on neutral alumina (CH2Cl2 with
J. Chem. Soc., Dalton Trans., 1999, 57–62
61

View Article Online
8 M. E. N. P. R. A. Silva, A. J. L. Pombeiro, J. J. R. Frausto da Silva,
R. Herrmann, N. Deus and R. E. Bozak, J. Organomet. Chem.,
1994, 480, 81 and refs. therein.
9 (a) H. Plenio, J. Yang, R. Diodone and J. Heinze, Inorg. Chem.,
1994, 33, 4098; (b) M. J. L. Tendero, A. Benito, R. Martínez-
Máñez and J. Soto, J. Chem. Soc., Dalton. Trans., 1996, 4121;
(c) B. Delavaux-nicot, A. Bigeard, A. Bousseksou, B. Donnadieu
and G. Commenges, Inorg. Chem., 1997, 36, 4789.
Acknowledgements
We thank the University of Exeter for the award of a University
Research Studentship (to J. D. C.).
References
1 For general reviews and recent advances on the complexation of
metal cations by ferrocene derivatives, see (a) P. D. Beer, Chem. Soc.
Rev., 1989, 18, 409; (b) C. D. Hall, in Ferrocenes: Homogeneous
catalysis, organic synthesis, materials science, ed. A. Togni and
T. Hayashi, VCH, Weinheim, 1995, ch. 6; (c) P. Zanello, in
Ferrocenes: Homogeneous catalysis, organic synthesis, materials
science, ed. A. Togni and T. Hayashi, VCH, Weinheim, 1995, ch. 7;
(d) A. M. Allgeier, C. S. Slone, C. A. Mirkin, L. M. Liable-Sands,
G. P. A. Yap and A. L. Rheingold, J. Am. Chem. Soc., 1997, 119,
550.
10 H.-J. Lorkowski, R. Pannier and A. Wende, J. Prakt. Chem., 1967,
35, 149.
11 S. I. Goldberg, J. Org. Chem., 1960, 25, 482.
12 M. S. Goodman, A. D. Hamilton and J. Weiss, J. Am. Chem Soc.,
1995, 117, 8447; S. Goswami and K. Ghosh, Tetrahedron Lett., 1997,
38, 4503; P. D. Beer, A. R. Graydon. A. O. M. Johnson and D. K.
Smith, Inorg. Chem., 1997, 36, 2112; I. Prévot-Halter, T. J. Smith
and J. Weiss, J. Org. Chem., 1997, 62, 2186.
13 T, M, Miller, J. Ahmel and K. M. S. Wrighton, Inorg. Chem., 1989,
28, 2347.
2 P. D. Beer, Acc. Chem., Res., 1998, 31, 71 and refs. therein.
3 J. D. Carr, L. Lambert, D. E. Hibbs, M. B. Hursthouse, K. M. A.
Malik and J. H. R. Tucker, Chem. Commun., 1997, 1649.
4 G. C. Dol, P. C. J. Kamer, F. Hartl, P. W. N. M. van Leeuwen and
R. J. M. Nolte, J. Chem. Soc., Dalton Trans., 1998, 2083; C. Li,
J. C. Medina, G. E. M. Maguire, E. Abel, J. L. Atwood and G. W.
Gokel, J. Am. Chem. Soc., 1997, 119, 1609; P. D. Beer, Z. Chen,
M. G. B. Drew and P. A. Gale, Supramol. Chem., 1996, 7, 241; A.
Ori and S. Shinkai, J. Chem. Soc., Chem. Commun., 1995, 1771.
5 P. L. Boulas, M. Gómez-Kaifer and L. Echegoyen, Angew. Chem.,
Int. Ed., 1998, 37, 216.
6 (a) P. D. Beer and D. K. Smith, J. Chem. Soc., Dalton Trans., 1998,
417; (b) C. D. Hall, I. P. Danks and N. W. Sharpe, J. Organomet.
Chem., 1990, 390, 227; (c) A. Chesney, M. R. Bryce, A. S. Batsanov,
J. A. K. Howard and L. M. Goldenberg, Chem. Commun., 1998,
677; (d) R. J. Less, J. L. M. Wicks, N. P. Chatterton, M. J. Dewey,
N. L. Cromhout, M. A. Halcrow and J. E. Davies, J. Chem. Soc.,
Dalton Trans., 1996, 4055.
14 K. Kavallieratos, S. R. de Gala, D. J. Austin and R. H. Crabtree,
J. Am. Chem. Soc., 1997, 119, 2325.
15 Y. S. Sohn, D. N. Hendrickson and H. B. Gray, J. Am. Chem Soc.,
1971, 93, 3603.
16 (a) C. D. Hall, J. H. R. Tucker, S. Y. F. Chu and D. J. Williams,
J. Chem. Soc., Dalton Trans., 1992, 3133; (b) C. D. Hall, I. P. Danks
and N. W. Sharpe, J. Chem. Soc., Chem. Commun., 1989, 419.
17 (a) J. L. Medina, T. T. Goodnow, M. T. Rojas, J. L. Atwood, B. L.
Lynn, A. E. Kaifer and G. W. Gokel, J. Am. Chem Soc., 1992, 114,
10583; (b) M. Sato, K. Suzuki and S. Akabori, Bull. Chem. Soc. Jpn.,
1986, 59, 3611.
18 T. H. Barr and W. E. Watts, Tetrahedron, 1968, 24, 6111.
19 J. W. Pflugrath and A. Messerschmidt, MADNES, version 11
(September 1989), Delft instruments, Delft, 1989.
20 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
21 G. M. Sheldrick, University of Göttingen, 1993.
22 N. P. C. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39,
158; adapted for FAST geometry by A. Karaulov, University of
Wales, Cardiff, 1991.
7 J. C. Calabrese, L.-T. Cheng, J. C. Green, S. R. Marder and W. Tam,
J. Am. Chem. Soc., 1991, 113, 7227; M. M. Bhadhade, A. Das,
J. C. Jeffery, J. A. McCleverty, J. A. Navas Badiola and M. D. Ward
J. Chem. Soc., Dalton Trans., 1995, 2769.
Paper 8/07453D
62
J. Chem. Soc., Dalton Trans., 1999, 57–62