Synthesis and structural characterisation of redox-responsive N-ferrocenoyl amino acid esters; the X-ray crystal structure of N-ferrocenoyl alanine methyl ester; electrochemical anion recognition and 1H NMR complexation studies

Article abstract of DOI:10.1016/j.jorganchem.2004.02.001

The N-ferrocenoyl amino acid ester derivatives FcCOR {Fc=(η⁵-C₅H₅) Fe(η⁵-C₅H₄)} where R=Gly(OMe) 1, Gly(OEt) 2, Gly(OBn) 3, l-Ala(OMe) 4, l-Ala(OEt) 5, l-Leu(OMe) 6, l-Leu(OEt) 7, l-Leu(OBn) 8, l-Phe(OMe) 9 and l-Phe(OEt) 10, were prepared by coupling ferrocene carboxylic acid with the appropriate amino acid ester starting materials using the 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol and these have been characterised by spectroscopic techniques. The electrochemical anion sensing behaviour of compounds 1-10 with several anions using a platinum microdisk working electrode is described, together with ¹H NMR anion complexation studies. The X-ray single crystal structure of N-ferrocenoyl-l-alanine methyl ester 4 has been determined and contains two molecules which differ slightly in conformation in the asymmetric unit of space group P2₁ (No. 4); principal dimensions are amide N(H)C=O 1.224(6) and 1.231(6) A?, ester C=O 1.220(10) and 1.190(7) A?, with N-H?O=C(amide) as the primary intermolecular hydrogen bond, N?O 2.992(6) and 2.971(6) A? and with graph set C(4).

Full text of DOI:10.1016/j.jorganchem.2004.02.001

Journal of Organometallic Chemistry 689 (2004) 1511–1520
www.elsevier.com/locate/jorganchem
Synthesis and structural characterisation of redox-responsive
N-ferrocenoyl amino acid esters; the X-ray crystal structure of
N-ferrocenoyl alanine methyl ester; electrochemical anion
1
recognition and H NMR complexation studies
a
a,
b
c
Michael J. Sheehy , John F. Gallagher *, Mashita Yamashita , Yoshiteru Ida ,
d
d
d
Jennifer White-Colangelo , Jeremi Johnson , Ron Orlando , Peter T.M. Kenny
a,
*
a
School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
b
Kyushu Laboratories, Yoshitomi Pharmaceutical Industries Ltd., Yoshitomi-cho, Chikujo-gun, Fukuoka 871-8550, Japan
c
School of Pharmaceutical Science, Showa University, Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
d
Complex Carbohydrate Research Center, University of Georgia, 220 Riverbend Road, Athens, GA 30602-4712, USA
Abstract
The N-ferrocenoyl amino acid ester derivatives FcCOR {Fc ¼ (g5-C5H5)Fe(g5-C5H4)} where R ¼ Gly(OMe) 1, Gly(OEt) 2,
Gly(OBn) 3, L-Ala(OMe) 4, L-Ala(OEt) 5, L-Leu(OMe) 6, L-Leu(OEt) 7, L-Leu(OBn) 8, L-Phe(OMe) 9 and L-Phe(OEt) 10, were
prepared by coupling ferrocene carboxylic acid with the appropriate amino acid ester starting materials using the 1,3-dic-
yclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol and these have been characterised by spectroscopic
techniques. The electrochemical anion sensing behaviour of compounds 1–10 with several anions using a platinum microdisk
1
working electrode is described, together with H NMR anion complexation studies. The X-ray single crystal structure of N-ferr-
ocenoyl-L-alanine methyl ester 4 has been determined and contains two molecules which differ slightly in conformation in the
ꢀ
asymmetric unit of space group P21 (No. 4); principal dimensions are amide N(H)C@O 1.224(6) and 1.231(6) A, ester C@O
ꢀ
ꢀ
1.220(10) and 1.190(7) A, with N–Hꢀ ꢀ ꢀO@C(amide) as the primary intermolecular hydrogen bond, Nꢀ ꢀ ꢀO 2.992(6) and 2.971(6) A
and with graph set C(4).
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Ferrocene; Electrochemistry; Platinum microdisk electrode; 1H NMR coordination studies; X-ray crystal structure
1. Introduction
sensors, charge transfer chemistry and peptide mimetic
models [3–9]. The majority of organometallic derivatives
employed in anion receptor research contain a ferroce-
nyl (Fc) or a ferrocenoyl (FcCO) moiety with a pendant
macrocyclic group as integral components for recogni-
tion and binding studies. Research studies have also
focussed on 1,10-metallocenyl derivatives where exten-
sive hydrogen bonding can occur between the 1,10-sub-
stituents. Reports on the incorporation of a ferrocene
group onto proteins have shown the mediation of elec-
tron transfer between electrodes and the protein redox
sites [2,10]. Recently, the synthesis and characterisation
of several unusual N-ferrocenoyl and N-ferrocenyl
amino acid and peptide derivatives has been reported
[11–27].
The design and synthesis of novel molecular receptors
to complex and electrochemically recognise anionic
guest systems is of current scientific interest [1]. The
coordination of guest species is a major research area in
molecular recognition chemistry with the ultimate aim
of understanding fundamental biological processes [2,3].
Transition metal complexes, such as ferrocene deriva-
tives, have found a variety of applications in molecular
* Corresponding authors. Tel.: +353-1-7005-689 (P.T.M. Kenny),
+353-1-7005-114 (J.F. Gallagher); fax: +353-1-7005-503 (P.T.M.
Kenny).
E-mail addresses: John.Gallagher@dcu.ie (J.F. Gallagher),
peter.kenny@dcu.ie (P.T.M. Kenny).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.02.001

1512
M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
We now report the synthesis and spectroscopic
characterisation of a series of N-ferrocenoyl amino acid
esters, FcCOR {Fc ¼ (g5-C5H5)Fe(g5-C5H4)} where
that used by Degani and Heller to incorporate ferrocene
carboxylic acid onto proteins [2]. Condensation of fer-
rocene carboxylic acid with esters of the amino acids,
R ¼ Gly(OMe) 1, Gly(OEt) 2, Gly(OBn) 3,
L
-Ala(OMe)
-Ala(OEt) 5, -Leu(OEt) 7,
-Phe(OMe) 9 and L-Phe(OEt) 10. The
glycine,
L
-alanine,
L
-leucine and
L-phenylalanine
4,
L
L
-Leu(OMe) 6,
L
cleanly led to the formation of orange to yellow col-
oured ferrocenoyl amino acid ester derivatives in good
yield (Scheme 1). The compounds are reasonably stable
however they slowly decompose over a period of time.
Crystals suitable for X-ray crystallographic analysis
were obtained for compounds 1 [14], 3 [28] and 4. The
products were characterised by spectroscopic techniques
prior to the electrochemical studies to confirm their
structures.
L
-Leu(OBn) 8,
L
electrochemical properties of these unnatural amino
acid esters as anion receptors has been investigated us-
ing a platinum microdisk working microelectrode which
represents a relatively new departure from the wide-
spread use of conventional platinum macroelectrodes in
metal-organic analytical studies (electrochemical details
in experimental). The 1H NMR anion coordination
properties of compounds 1–10 are also reported, and the
X-ray crystal structure of N-ferrocenoyl alanine methyl
ester 4 has been determined for comparison with related
structures [7,12] and the reported N-ferrocenoyl glycine
ester derivatives [14,28]. The benefit of such crystal
structure analysis is that it can provide an understanding
of the possible interactions present in the structure of a
potential anion receptor as well as yield valuable infor-
mation for hydrogen binding modes and binding sites in
solution studies.
1
The H and 13C NMR spectra for compounds 1–10
showed peaks in the ferrocene region characteristic of a
mono-substituted ferrocene subunit [7]. For example, in
the case of the glycine derivatives 1, 2 and 3 the un-
1
substituted g5-C5H5 ring appears as a singlet in the H
NMR spectra at d 4.23, d 4.24 and d 4.22, respectively.
The NH proton is present as a triplet at d 8.25, d 8.22
and d 6.21 and the –NHCH2CO– protons appear as
doublets at d 3.90 (J ¼ 6 Hz) for 1, d 4.15 (J ¼ 5 Hz) for
1
2 and d 4.18 (J ¼ 5 Hz) for 3. Selected H NMR spec-
troscopic data for several of the ferrocenoyl amino acid
esters are presented in Table 1. The protons in the ortho
position on the substituted g5-C5H4 ring appear in the
region d 4.59–4.78 whereas the protons in the meta po-
sition occur in the chemical shift range d 4.32–4.41. The
unsubstituted g5-C5H5 ring system is observed as a
singlet for all of the compounds 1–10 in the chemical
shift range d 4.12–4.29. The 13C NMR spectra display
signals in the region d 67.2–75.6 indicative of a mono-
substituted ferrocene subunit with the ipso carbon of the
substituted Cp ring appearing in a narrow range of d
75.0–75.6.
2. Results and discussion
2.1. Synthesis
The synthesis of the ferrocenoyl amino acid ester
derivatives 1–10 was successfully carried out by reaction
of ferrocene carboxylic acid [29] and the appropriate
amino acid ester [30] under basic conditions in the
presence of dicyclohexylcarbodiimide (DCC) and 1-hy-
droxybenzotriazole (HOBt). The procedure is related to
O
O
Cl
Cl
AlCl3
+
Fe
Fe
CH2Cl2
Cl
KOC(CH3)3/DME/
H2O/reflux
O
O
R
Amino acid ester
OH
Fe
Fe
DCC/HOBt/
Et3N/CH2Cl2
Scheme 1. Synthesis of N-ferrocenoyl amino acid esters 1–10; R ¼ Gly(OMe) 1, Gly(OEt) 2, Gly(OBn) 3,
6, -Leu(OEt) 7, -Leu(OBn) 8, -Phe(OMe) 9 and -Phe(OEt) 10.
L-Ala(OMe) 4, L-Ala(OEt) 5, L-Leu(OMe)
L
L
L
L

M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
1513
Table 1
Selected 1H NMR spectroscopic data for a number of N-ferrocenoyl
amino acid derivatives (CDCl3, d in ppm, room temperature)
Chloride
Dihydrogen Phosphate
Bromide
Compound NH
CHa
Cportho
Cpmeta
Cp
3
4
6.21
6.25
4.18
4.69
4.34
4.32
4.22
4.2
2.5
2
4.69–75 4.64,
4.72
6
8
6.03
6.04
6.05
6.08
4.74–8
4.82–7
5.01–6
4.64,
4.71
4.65,
4.72
4.59,
4.63
4.59,
4.63
4.33
4.35
4.32
4.33
4.21
4.21
4.12
4.13
1.5
1
9
10
4.99–
5.04
a Hydrogen at a-carbon.
0.5
0
1
2.2. H NMR anion titration experiments
1H NMR spectroscopic studies were performed to
investigate the interaction between the neutral N-ferr-
ocenoyl amino acid derivatives and various anions. A
solution of the compound was prepared at concentra-
tions typically of the order of 0.01 mol dmꢁ3 in CDCl3.
0
1
2
3
4
5
Equivalents of Anion Added
Fig. 1. 1H NMR titration curve of N-ferrocenoyl glycine methyl ester 1
with various anions added as their [nBu4N]þ salts in CDCl3 at room
temperature.
1
After each addition of anion, the H NMR spectrum
was recorded and the changes in the chemical shift of the
amide protons were noted. The result of the experiments
was a plot of displacement in chemical shift of the amide
proton as a function of the quantity of anion added. The
N-ferrocenoyl glycine esters 1–3 exhibited some signifi-
cant solution interactions with the anions. Noteworthy
downfield shifts of the respective amide (–CONH–)
protons, ranging from ca. d 0.5–2.5 ppm, were exhibited
by the N-ferrocenoyl glycine esters 1–3 on addition of
various anions as their tetrabutylammonium salts,
[Bun4NþXꢁ, (Xꢁ ¼ HSO4ꢁ, Brꢁ, Clꢁ and H2POꢁ4 )] to
CDCl3 solutions. This observation agrees with previous
reports and strongly suggests the contribution of the
amide proton as a hydrogen donor in anion binding in
solution [31]. The N-ferrocenoyl glycine methyl ester 1 is
shown to sense halides and dihydrogen phosphate
(H2POꢁ4 1) guest anions, the trend being Clꢁ ꢂ
H2POꢁ4 > Brꢁ (Fig. 1) and a similar overall trend was
also observed for the ethyl 2 and benzyl esters 3. These
results suggest that a significant amide –CO–NHꢀ ꢀ ꢀ
(anion)ꢁ hydrogen bonding interaction is contributing
to the anion coordination process [1]. In contrast to this
derivatives contain the simplest and least sterically hin-
dered amino acid, glycine [6].
2.3. Electrochemical studies
The electrochemical behaviour of the ferrocene–ferr-
ocenium oxidation wave is relatively insensitive to the
amino acid R group, the E1=2 being in the range 590–610
mV. The behaviour of the N-ferrocenoyl amino acid
esters 1–10 as potential anion receptors was investigated
using microelectrochemical methods and a preliminary
account of this work has been published [14]. Estab-
lished methods of measuring electrochemical responses
in inorganic-based anion sensors have typically used
macroelectrodes for conventional measurements. Mi-
croelectrodes with dimensions in the micrometer range
(lm) possess some significant advantages over their
macroscopic counterparts (mm) in electrochemical
measurements, e.g. small currents, steady-state re-
sponses and short response times (for studying ultra-fast
processes). As the current measured at an electrode is a
function of the area, the current observed at micro-
electrodes lie in the pico- and nanoampere range, which
are several orders of magnitude smaller than those
measured using macroelectrodes. Some other advanta-
ges that microelectrodes have over macroelectrodes are
rapid mass transport, small double layer capacitance
and small ohmic drop, while an increased signal to noise
ratio, a steady-state time independent response and
higher sensitivity have also been noted. With a view to
recognising minute quantities of anions and the ultimate
the N-ferrocenoyl-L-alanine esters 4 and 5 were found to
elicit marginal downfield perturbations of the respective
amide proton ranging from ca. d 0.25–0.6 ppm. Negli-
gible shifts were observed under identical experimental
conditions with the other N-ferrocenoyl amino ester
derivatives 6–10. This strongly suggests that the amide
hydrogen bonding interaction with the anion is rela-
tively sterically hindered within the ferrocenoyl amide
niche and is optimally available for hydrogen bonding
interactions when the N-ferrocenoyl amino acid ester

1514
M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
aim of in vivo measurements, these microelectrodes offer
a relatively non-invasive means of monitoring, by being
small, hence less tissue damage, but also because of the
small concentrations of material electrolysed. For our
measurements, these microelectrodes have been em-
ployed as analytical probes to measure the electro-
chemical response of several anions interacting with
compounds 1–10. The electrochemical measurements
were recorded after progressively adding stoichiometric
equivalents of anion guests (10 equiv.) as their tetrabu-
tylammonium salts to solutions of the derivatives 1–10.
The electrochemical anion recognition properties for all
of the N-ferrocenoyl amino acid esters are outlined in
Table 2. The magnitude of the electrochemical shift on
the E1=2 potential of N-ferrocenoyl glycine methyl ester 1
upon addition of the various anions is shown in Fig. 2.
As depicted in this figure, the HSOꢁ4 , Clꢁ and H2PO4ꢁ
anions all produced negative shifts on the E1=2 potential
on addition to the various N-ferrocenoyl amino acid
solutions. The BFꢁ4 anion produced the only observed
positive perturbation. This is possibly due to the fact
that the Fe atom is sensing the positively charged boron
atom, hence the anodic shift. The dihydrogen phosphate
anion (H2POꢁ4 ) produced the largest magnitude of
negative perturbation of the ferrocene–ferrocenium re-
dox couple of up to 120 mV with the host N-ferrocenoyl
glycine methyl ester derivative 1. The electrochemical
1
findings complement the results obtained from the H
NMR titration experiments where N-ferrocenoyl glycine
methyl ester 1 exhibited the largest magnitude of amide
proton shift. Thus compound 1 may have potential for
the development of a novel electrochemical sensory de-
vice for the detection of the H2POꢁ4 anion. The results,
however, also highlight the interaction of the ferroce-
noyl unit with the anions as the order of perturbation
changes depending on which analytical technique is
utilised. This should not be surprising given that the two
different analytical techniques are being used to probe
different moieties within the electroactive sensor namely
1
the amide N–H for the H NMR titration experiments
and the ferrocene moiety for the electrochemical per-
turbation measurements. It was not possible to measure
the effect of the bromide anion as bromide oxidation
occurred at the E1=2 potential of the N-ferrocenoyl
amino acid derivatives and there was little or no elec-
trochemical shift of the ferrocene oxidation potential
observed on addition of the perchlorate anion (ClOꢁ4 ).
From analysis of the results obtained in this investi-
gation it is evident that replacing the amino acid has
little effect on the E1=2 potential. Likewise changing from
methyl to the ethyl and benzyl esters has little bearing on
the E1=2 potential. This should not be surprising given
that both the amino acid and ester functional groups are
not in close proximity to the electroactive ferrocenoyl
core. An important feature in the design of novel re-
ceptors is the incorporation of a redox center in close
proximity to the anion coordination site. This gives the
receptor the capability of electrochemically sensing an-
ionic guest species as coordination will perturb the
electrochemical response of the receptor. The pertur-
bation of the electrochemical properties (ferrocene oxi-
dation wave) of N-ferrocenoyl amino acid esters in the
presence of various anions suggests their application in
the construction of simple molecular sensors. The data
presented for several anions in Table 2 show that com-
pounds 1–10 recognise a variety of anions.
Table 2
Electrochemical dataa for 1–10 with electrochemical anion recognition
propertiesb
Compound E1=2
(mV)
DE
DE
DE
DE
(HSOꢁ4 ) (Clꢁ) (H2PO4ꢁ) (BF4ꢁ) (mV)
1
2
603
)25
)30
)15
)25
)25
)20
)15
)30
)20
)20
)20
)20
)15
)25
)25
)25
)25
)35
)30
)35
)120
)95
)110
)90
)85
)90
)90
)85
)95
)90
15
20
20
30
25
25
25
25
20
25
601
604
599
598
603
608
607
607
606
3
4
5
6
7
8
9
10
a See electrochemistry section in Section 4 for conditions.
b Shifts in the ferrocene–ferrocenium redox couple produced by the
presence of anion (10 equiv.) added as their [nBu4N]þ salts.
7
-
H2PO4
6
-
HSO4
5
Cl-
4
Anion free
-
3
BF4
Beer et al. [32] have reported comparable H2PO4ꢁ
shifts to our results in a series of neutral and cationic
macrocyclic heterobimetallic complexes. Further elec-
trochemical studies are in progress to investigate the
properties of some related N-ferrocenoyl dipeptide ester
derivatives as anion sensors.
2
1
0
-1
0
100
200
300
400
500
600
700
800
900
1000
Potential / mV
Microelectrodes are widely used as in vivo analytical
probes [33]. The imprinting of such a receptor onto a
polymeric support and subsequent bonding to the end of
a microelectrode would produce an electrochemical
Fig. 2. Linear sweep voltammograms of 1 at a microdisk electrode in
the presence of various anions added as their [nBu4N]þ salts. Sup-
porting electrolyte: 0.1 mol dmꢁ3 [NBu4]PF6, scan rate: 50
mV sꢁ1(error +/) 5 mV).

M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
1515
anion sensor [34,35]. Such a device would have huge
applications in determining the pH balance of the kid-
neys of which the H2PO4ꢁ anion is produced. In the
future it is hoped that subtle binding site modifications
of such receptors can lead to dramatic fundamental
changes in anion recognition properties and selectivity
series.
respectively; the g5-C5H5 ring of molecule B is disor-
dered over two positions with occupancies of 0.66(5)/
0.34(5), respectively. These were treated with appropri-
ate restraints and coordinates for the final refinement
cycles, were refined with anisotropic displacement pa-
rameters in the final least squares calculations. The final
R-factor is 0.030 for 1832 observed reflections
½I > 2rðIÞꢃ out of a total of 2448 measured reflections.
In compound 4 the principal dimensions are amide
2.4. X-ray crystallographic studies of 4
ꢀ
N(H)C@O 1.224(6) and 1.231(6) A, ester C@O
ꢀ
1.220(10) and 1.190(7) A for the two independent mol-
The crystal structure of 4 has been determined with
selected bond lengths and angles listed in Table 3 (per-
tinent crystallographic details are contained in Section
4.4), the two independent molecules of 4 in the asym-
metric unit are depicted in Fig. 3 and a packing diagram
is present in Fig. 4. The structure can be directly com-
pared with the glycine methyl and benzyl esters that
have been communicated previously by the authors
[14,28] and related structures that are available in the
literature [7,12].
ecules A and B (Table 3). The primary angle differences
are between the substituted cyclopentadienyl ring and
the amide C@ON–C plane, 14.8(4)° in molecule A and
2.7(5)° in B, as evidenced in Fig. 3. The primary inter-
molecular linkage is the N–Hꢀ ꢀ ꢀO@C(amide) hydrogen
bond which has Nꢀ ꢀ ꢀO distances of 2.992(6)
ꢀ
[N1Aꢀ ꢀ ꢀO1B] and 2.971(6)
A
[N1Bꢀ ꢀ ꢀO1A#,
#
¼ 1 þ x; y; z] and with graph set C(4). This involves the
molecules linked in
a one-dimensional chain as
Compound 4 crystallises in the monoclinic system.
The space group P21 (No. 4) was deduced from the
systematic absences and confirmed by the crystal struc-
ture analysis. The structure was solved using the Patt-
erson function and refined by full-matrix least squares
techniques. The hydrogen atoms were treated as riding
(Aꢀ ꢀ ꢀBꢀ ꢀ ꢀAꢀ ꢀ ꢀBꢀ ꢀ ꢀ) along the a-axis as depicted in Fig. 4.
These N–Hꢀ ꢀ ꢀO@C interactions are assisted by
(g5-C5H4)C–Hꢀ ꢀ ꢀO@C interactions and involving an
ortho-C–H unit to the same neighbouring carbonyl ox-
ygen atom with graph set R21(7). The C6Aꢀ ꢀ ꢀO1B and
ꢀ
C6Bꢀ ꢀ ꢀO1A distances are 3.341(7) and 3.425 A. The
ꢀ
atoms with C–H distances in the range 0.93–0.98 A; the
hydrogen atom bonded to nitrogen was refined to N–
reasons for two molecules being present in the asym-
metric unit presumably arise due to molecular confor-
mations being unable to sustain a growing linear chain
through hydrogen bonding without having to adjust to
accommodate it: this results in the observed
(Aꢀ ꢀ ꢀBꢀ ꢀ ꢀAꢀ ꢀ ꢀBꢀ ꢀ ꢀ) chain in the crystal structure of 4.
The molecular structure of 4 can be directly com-
pared with the related glycine ester analogues [14,28],
ꢀ
H ¼ 0.75(2) A. It was evident during the penultimate
stage of refinement (when R½F2 > 2rðF 2Þꢃ was 0.075)
that there were two types of disorder associated with the
two independent molecules of 4. The ester carbonyl
oxygen atom of molecule A is disordered over two sites
O2A/O2C with site occupancy factors of 0.76(2)/0.24(2),
Table 3
ꢀ
Selected molecular dimensions (A, °) for 4
O1A–C11A
O2A–C14A
O2C–C14A
O3A–C14A
O3A–C15A
N1A–C11A
N1A–C12A
1.224(6)
1.220(10)
1.43(4)
O1B–C11B
O2B–C14B
1.231(6)
1.190(7)
1.279(9)
1.451(10)
1.334(7)
1.437(7)
O3B–C14B
O3B–C15B
N1B–C11B
N1B–C12B
1.302(8)
1.448(8)
1.326(7)
1.447(7)
Cg(1)–Fe1A
Cg(2)–Fe1A
1.6468
1.6366
Cg(3)–Fe1B
Cg(4)–Fe1B
1.6295
1.6442
Cg(1)–Fe1A–Cg(2)
Cg(3)–Fe1B–Cg(4)
177.77
174.78
Intermolecular interactions
D–Hꢀ ꢀ ꢀA
D–H
0.86
0.86
0.93
0.93
0.93
0.93
Hꢀ ꢀ ꢀA
2.149
2.140
2.553
2.571
2.556
2.484
Dꢀ ꢀ ꢀA
angle
167
162
143
153
151
171
N1A–H1Aꢀ ꢀ ꢀO1B
N1B–H1Bꢀ ꢀ ꢀO1A
C6A–H6Aꢀ ꢀ ꢀO1B
C6B–H6Bꢀ ꢀ ꢀO1A
C8A–H8Aꢀ ꢀ ꢀO2B
C8B–H8Bꢀ ꢀ ꢀO1A
2.992(6)
2.970(6)
3.341(7)
3.425(7)
3.401(8)
3.406(7)

1516
M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
Fig. 3. An ORTEP diagram of the two independent molecules of 4 with the atomic displacement parameters depicted at the 50% probability level.
and related derivatives [7,12]. As can be evidenced by
analysis of the interplanar angles which are 16.7(2)° and
16.6(2)° in the glycine methyl and benzyl ester deriva-
tives, respectively, the overall molecular conformation is
broadly similar in the ferrocenyl amide moieties.
no acid esters 1, 2 and 3 give the optimum response
1
both in the H NMR titration and the electrochemical
L-Ala, L-Leu
studies in comparison to the bulkier
and -Phe derivatives. The crystal structure of the N-
L
ferrocenoyl-
described.
L-alanine methyl ester derivative 4 is also
3. Summary
4. Experimental
The N-ferrocenoyl ester derivatives 1–10, were pre-
pared by coupling ferrocene carboxylic acid with the
appropriate amino acid ester using the 1,3-dic-
yclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole
(HOBt) protocol and these have been characterised by
spectroscopic techniques. It has been shown that the
least sterically hindered ferrocenoyl glycine based ami-
4.1. General procedures
All chemicals were purchased from Sigma/Aldrich
and used as received. Ferrocene carboxylic acid was
prepared according to Reeves [29]. Amino acid ester
hydrochlorides were prepared by the method of Brenner

M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
1517
Fig. 4. A PLATON diagram depicting the intermolecular interactions in 4.
and Huber [30]. Where necessary solvents were purified
prior to use and stored under N2, with CH2Cl2 distilled
from calcium hydride: Et3N was distilled and stored
over KOH pellets. Commercial grade reagents were used
without further purification. Melting points were de-
termined using a Griffin melting point apparatus and are
uncorrected. Infrared spectra were recorded on a Nic-
olet 405 FT-IR spectrometer and UV–Vis spectra were
recorded on a Hewlett–Packard 8452A diode array UV–
Vis spectrophotometer. NMR spectra were obtained on
a Bruker AC 400 FT-NMR spectrometer operating at
400 MHz for H and 100 MHz for 13C NMR. The H
and 13C NMR chemical shifts (ppm) are reported
downfield from tetramethylsilane (TMS) as internal
standard and all coupling constants ðJÞ are in Hertz
(Hz). Electrochemical studies were performed on a Bas
100/W electrochemical analyser equipped with a PA-
100B/W low-current module for electrochemical mea-
surements. The electrochemical cell was an unsealed
one-compartment cell with a platinum microdisk (di-
ameter 28 lm) working electrode, Ag/AgCl reference
and platinum wire counter electrode and the experi-
ments were conducted at 21 °C. Elemental analyses were
performed in the Microanalytical Laboratory, Univer-
sity College Dublin. Positive ion fast atom bombard-
ment mass spectra were obtained on the first of two
sectors of a JEOL SX/SX 102 double focussing four
sector tandem mass spectrometer with thioglycerol or
nitrobenzyl alcohol as the matrix: MALDI-TOF mass
spectra were measured on a Kratos Kompact SEQ re-
flectron time of flight mass spectrometer using a-cyano-
4-hydroxycinnamic acid as the matrix.
4.2. General procedure for the synthesis of N-ferrocenoyl
amino acid esters: synthesis of N-ferrocenoyl glycine
methyl ester (1)
Glycine methyl ester hydrochloride (1.08 g, 8.7 mmol)
and triethylamine (1.22 ml, 8.7 mmol) (Et3N) were ad-
ded to a solution of ferrocene carboxylic acid (2.00 g, 8.7
mmol), 1-hydroxy-benzotriazole (HOBt) (1.15 g, 8.7
mmol) and 1,3-dicyclohexylcarbodiimide (DCC) (1.80 g,
8.7 mmol) in dichloromethane (50 ml) at 0 °C. The re-
action was allowed to reach room temperature after 30
min. and subsequently stirred for a further 48 h. The
precipitated N,N-dicyclohexylurea was removed by fil-
tration and the filtrate washed with water, 10% KHCO3,
5% citric acid and dried over magnesium sulfate. The
solvent was evaporated in vacuo and the resulting oil
was recrystallised from ethyl acetate/pet. ether 40–60 °C
to yield the title product as orange/brown rhomboids
(1.16 g, 44%). The crystals were of sufficient quality for
an X-ray diffraction study.
1
1
m.p. 127–128 °C. E1=2 ¼ 603 mV.
Mass spectrum:
C14H15N1O3Fe
found: [M]þ
requires:
301.02
301.04

1518
M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
IR tmax KBr: 3257, 3086, 2937, 1753, 1639, 1541 cmꢁ1
4.2.3. N-Ferrocenoyl-
L
-alanine methyl ester (4)
-Alanine methyl ester hydrochloride (1.21 g, 8.7
L
UV–Vis, kmax CH3CN: 262, 304, 442 (e 175) nm.
1H NMR (400 MHz) d (DMSO): 8.25 (1H, t, J ¼ 6
Hz, –NH–), 4.78 (2H, t, J ¼ 2 Hz, ortho-H on substi-
tuted Cp ring), 4.35 (2H, t, J ¼ 2 Hz, meta-H on
substituted Cp ring), 4.23 (5H, s, unsubstituted Cp ring),
3.90 (2H, d, J ¼ 6 Hz, –NHCH2CO–), 3.65 (3H, s,
–OCH3).
mmol) was used. Recrystallisation from ethyl acetate
yielded brown rhombic shaped crystals which were of
sufficient quality for an X-ray diffraction study (1.99 g,
72%).
25
m.p. 161–162 °C. E1=2 ¼ 599 mV. ½aꢃD ¼ ꢁ22° (10,
EtOH).
Mass spectrum:
C15H17N1O3Fe
found: [M]þ 315.0773
requires: 315.0558
13C NMR (100 MHz) d (DMSO): 170.6, 169.6, 75.5,
70.1, 69.4, 68.1, 51.6, 40.7.
IR tmax KBr: 3280, 3085, 2983, 1736, 1621, 1535
cmꢁ1
.
4.2.1. N-Ferrocenoyl glycine ethyl ester (2)
Glycine ethyl ester hydrochloride (1.20 g, 8.7 mmol)
was used as starting material. Recrystallisation from
ethyl acetate/pet. ether 40–60 °C yielded the title product
as a yellow crystalline solid (1.53 g, 48%).
UV–Vis kmax CH3CN: 276, 302, 334, 442 (e 132) nm.
1H NMR (400 MHz) d (CDCl3): 6.25 (1H, d, J ¼ 7
Hz, –NH–), 4.69–4.75 (2H, m, ortho-H on substituted
Cp and –NHCHCO–), 4.64 (1H, dd, JA ¼ 3 Hz, JB ¼ 2
Hz, ortho-H on substituted Cp ring), 4.32–4.33 (2H, m,
meta-H on substituted Cp ring), 4.20 (5H, s, unsubsti-
tuted Cp ring), 3.76 (3H, s, OCH3), 1.45 (3H, d, J ¼ 7
Hz, –NHC(H)CH3CO–).
m.p. 140–141 °C. E1=2 ¼ 601 mV.
Analysis:
found:
C, 57.66; H,
5.62; N, 4.93.
C, 57.17; H,
5.44; N, 4.45.
C15H17N1O3Fe
requires:
13C NMR (100 MHz) d (CDCl3): 173.8, 169.9, 75.1,
70.6, 69.8, 68.4, 67.9, 52.4, 47.8, 18.6.
IR tmax KBr: 3257, 3086, 1748, 1633, 1547 cmꢁ1
UV–Vis kmax CH3CN: 262, 304, 441 (e 210) nm.
1H NMR (400 MHz) d (DMSO): 8.22 (1H, s, –NH–),
4.71 (2H, t, J ¼ 2 Hz, ortho-H on substituted Cp ring),
4.36 (2H, t, J ¼ 2 Hz, meta-H on substituted Cp ring),
4.24–4.29 (7H, m, unsubstituted Cp ring and
–OCH2CH3), 4.15 (2H, d, J ¼ 5 Hz, –NHCH2CO–),
1.32 (3H, t, J ¼ 7 Hz, –OCH2CH3).
4.2.4. N-Ferrocenoyl-
The synthetic procedure employed for 5 was identical
to that for 4 except -alanine ethyl ester hydrochloride
(1.34 g, 8.7 mmol), was used. Recrystallisation from
ethyl acetate yielded 5 as a bright yellow crystalline solid
(1.85 g, 65%).
L
-alanine ethyl ester (5)
L
13C NMR (100 MHz) d (DMSO): 170.6, 170.3, 75.1,
70.6, 69.8, 68.2, 61.5, 41.3, 14.2.
25
m.p. 129–130 °C. E1=2 ¼ 598 mV. ½aꢃD ¼ ꢁ28° (15,
EtOH).
IR tmax KBr: 3269, 3086, 2983, 1742, 1621, 1535
cmꢁ1
.
4.2.2. N-Ferrocenoyl glycine benzyl ester (3)
Glycine benzyl ester tosylate (2.93 g, 8.7 mmol) was
used. Recrystallisation from ethyl acetate/pet. ether 40–
60 °C yielded a dark yellow crystalline solid (2.21 g,
68%). The crystals were suitable for an X-ray diffraction
study.
UV–Vis kmax CH3CN: 274, 303, 442 (e 176) nm.
1H NMR (400 MHz) d (DMSO): 8.04 (1H, d, J ¼ 7 Hz,
–NH–), 4.89 (1H, t, J ¼ 1 Hz, H ortho on Cp ring), 4.78
(1H, t, J ¼ 1 Hz, H ortho on Cp ring), 4.34–4.41 (3H, m, H
meta on Cp ring and –NHCHCO–), 4.21 (5H, s, unsub-
stituted Cp ring), 4.05–4.14 (2H, m, –OCH2CH3), 1.35
(3H, d, J ¼ 7 Hz, –NHC(H)CH3CO–), 1.20 (3H, t, J ¼ 7
Hz, –OCH2CH3).
m.p. 131–132 °C. E1=2 ¼ 604 mV.
Analysis:
found:
C, 63.49; H,
5.00; N, 3.64
C, 63.68; H,
5.08; N, 3.71
377.12
C20H19N1O3Fe
requires:
13C NMR (100 MHz) d (DMSO): 172.9, 169.1, 75.6,
70.2, 70.1, 69.4, 68.6, 68.1, 60.4, 47.8, 16.9, 14.1.
Mass spectrum:
C20H19N1O3Fe
found: [M]þ
requires:
377.07
IR tmax KBr: 3257, 3086, 1748, 1633, 1547 cmꢁ1
.
4.2.5. N-Ferrocenoyl-
Compound 6 was prepared according to the method
for 4 using -leucine methyl ester hydrochloride (0.47 g,
L
-leucine methyl ester (6)
UV–Vis kmax CH3CN: 263, 303, 443 (e 275 ) nm.
1H NMR (400 MHz) d (CDCl3): 7.32–7.37 (5H, m,
ArH), 6.21 (1H, t, J ¼ 5 Hz, –NH–), 5.21 (2H, s,
–OCH2Ph), 4.69 (2H, t, J ¼ 2 Hz, ortho-H on substi-
tuted Cp ring), 4.34 (2H, t, J ¼ 2 Hz, meta-H on
substituted Cp ring), 4.22 (5H, s, unsubstituted Cp ring),
4.18 (2H, d, J ¼ 5 Hz, –NHCH2CO–).
L
2.6 mmol). Recrystallisation from ethyl acetate/pet.
ether 40–60 °C furnished 6 as a yellow crystalline solid
(1.01 g, 79%).
25
m.p. 136–137 °C. E1=2 ¼ 603 mV. ½aꢃD ¼ ꢁ47° (20,
EtOH).
13C NMR (100 MHz) d (CDCl3): 170.7, 170.2, 135.1,
128.6, 128.5, 128.4, 75.0, 70.6, 69.8, 68.2, 67.2, 41.3.
IR tmax KBr: 3326, 3086, 2960, 1748, 1627, 1530
cmꢁ1
.

M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
1519
UV–Vis kmax CH3CN: 270, 301, 442 (e 121) nm.
1H NMR (400 MHz) d (CDCl3): 6.03 (1H, d, J ¼ 8:4
Hz, –NH–), 4.74–4.80 (1H, m, –NHCHCO–), 4.71–4.72
(1H, m, H ortho on Cp ring), 4.64–4.65 (1H, m, H ortho
on Cp ring), 4.33–4.34 (2H, m, H meta on Cp ring),
4.21 (5H, s, unsubstituted Cp ring), 3.75 (3H, s,
–OCH3), 1.66–1.71 (2H, m, –CH2CH(CH3)2), 1.58–1.62
(1H, m, –CH2CH(CH3)2), 0.96 (6H, d, J ¼ 6
Hz, –CH2CH(CH3)2).
13C NMR (100 MHz) d (CDCl3): 173.7, 170.7, 135.8,
129.0, 128.8, 128.7, 75.6, 71.0, 70.2, 68.8, 68.5, 67.5,
51.0, 42.1, 25.4, 23.4, 22.3.
4.2.8. N-Ferrocenoyl-
Compound 9 was prepared in a similar fashion to 4
using -phenylalanine methyl ester hydrochloride (1.77
L
-phenylalanine methyl ester (9)
L
g, 8.7 mmol). Recrystallisation from ethyl acetate gave 9
as a dark yellow solid (2.24 g, 68%).
13C NMR (100MHz) d (CDCl3): 174.3, 170.6, 75.6,
71.0, 70.1, 68.8, 68.4, 52.7, 50.8, 42.2, 25.4, 23.3, 22.3.
25
m.p. 120–122 °C. E1=2 ¼ 608 mV. ½aꢃD ¼ ꢁ12°
(6, EtOH).
IR tmax KBr: 3269, 3097, 1759, 1730, 1621, 1541
4.2.6. N-Ferrocenoyl-
Compound 7 was prepared in a similar fashion to 4,
using -leucine ethyl ester hydrochloride (1.70 g, 8.7
L
-leucine ethyl ester (7)
cmꢁ1
.
UV–Vis kmax CH3CN: 262, 300, 443 (e191) nm.
1H NMR (400 MHz) d (CDCl3): 7.19–7.36 (5H, m,
ArH), 6.05 (1H, d, J ¼ 8 Hz, –NH–), 5.01–5.06 (1H, m,
–NHCHCO–), 4.63 (1H, d, J ¼ 1 Hz, H ortho on Cp
ring), 4.59 (1H, d, J ¼ 1 Hz, H ortho on Cp ring), 4.32
(2H, d, J ¼ 1 Hz, H meta on Cp ring), 4.12 (5H, s,
unsubstituted Cp ring), 3.78 (3H, s, –OCH3), 3.13–3.26
(2H, m, PhCH2CH–).
L
mmol). Recrystallisation from ethyl acetate furnished 7
as a light yellow crystalline solid (2.15 g, 66%).
25
m.p. 127–128 °C. E1=2 ¼ 604 mV. ½aꢃD ¼ ꢁ27° (21,
EtOH).
IR tmax KBr: 3303, 3086, 2960, 1742, 1627, 1535
cmꢁ1
.
UV–Vis kmax CH3CN: 272, 302, 442 nm (e 124).
1H NMR (400 MHz) d (CDCl3): 6.03 (1H, d, J ¼ 8
Hz, –NH–), 4.74–4.79 (1H, m, –NHCHCO–), 4.71
(1H, s, H ortho on Cp ring), 4.64 (1H, s, H ortho on Cp
ring), 4.34 (2H, s, H meta on Cp ring), 4.18–4.23 (7H, m,
5H, unsubstituted Cp ring and –OCH2CH3), 1.66–1.74
(2H, m, –CH2CH(CH3)2), 1.57–1.64 (1H, m, –CH2CH
(CH3)2), 1.29 (3H, t, J ¼ 7 Hz, –OCH2CH3), 0.97 (6H,
d, J ¼ 6 Hz, –CH2CH(CH3)2).
13C NMR (100 MHz) d (CDCl3): 172.3, 170.1, 136.0,
129.2, 128.7, 127.2, 75.3, 70.9, 70.5, 69.7, 68.3, 68.0,
52.8, 52.4, 38.0.
4.2.9. N-Ferrocenoyl-
10 was prepared analogously to that described for 4
using -phenylalanine ethyl ester hydrochloride (0.87 g,
L
-phenylalanine ethyl ester (10)
L
4 mmol). Recrystallisation from ethyl acetate yielded the
10 as a yellow solid (1.04 g, 56%).
13C NMR (100 MHz) d (CDCl3): 173.5, 170.1, 75.3,
70.6, 70.5, 69.8, 68.4, 68.0, 61.4, 50.5, 42.0, 25.0, 22.9,
21.9, 14.2.
25
m.p. 149–151 °C. E1=2 ¼ 607 mV. ½aꢃD ¼ ꢁ5° (2,
EtOH).
Analysis:
found:
C, 65.34; H, 6.00;
N, 3.31
C22H23N1O3Fe requires: C, 65.20; H, 5.72;
4.2.7. N-Ferrocenoyl-
Compound 8 was prepared in a similar fashion to
that described for 3 using -leucine benzyl ester tosylate
L
-leucine benzyl ester (8)
N, 3.46
IR tmax KBr: 3291, 3097, 1753, 1627, 1535 cmꢁ1
UV–Vis kmax CH3CN: 256, 302, 442 (e 197) nm.
L
.
(0.79 g, 2.0 mmol). Recrystallisation from ethyl acetate/
ether yielded 8 as an orange crystalline solid (0.53 g,
61%).
1H NMR (400 MHz) d (CDCl3): 7.20–7.35 (5H, m,
ArH), 6.08 (1H, d, J ¼ 7 Hz, –NH–), 4.99–5.04 (1H, m,
–NHCHCO–), 4.63 (1H, s, H ortho on Cp ring), 4.59
(1H, s, H ortho on Cp ring), 4.33 (2H, s, H meta on cp
ring), 4.22 (2H, q, J ¼ 7 Hz, –OCH2CH3), 4.13 (5H, s,
unsubstituted Cp ring), 3.14–3.25 (2H, m, PhCH2CH–),
1.29 (3H, t, J ¼ 7 Hz, –OCH2CH3).
25
m.p. 112–113 °C. E1=2 ¼ 607 mV. ½aꢃD ¼ ꢁ17° (22,
EtOH).
Analysis:
found:
C, 66.69; H, 5.94;
N, 3.73
C24H27N1O3Fe requires:
C, 66.52; H, 6.28;
N, 3.23
13C NMR (100MHz) d (CDCl3): 171.9, 170.0, 136.1,
129.3, 128.6, 127.2, 75.4, 70.8, 70.5, 69.7, 68.3, 68.0,
61.5, 52.8, 38.1, 14.2.
IR tmax KBr: 3314, 2960, 1745, 1627, 1535 cmꢁ1
UV–Vis kmax CH3CN: 268, 304, 442 (e 135) nm.
.
1H NMR (400 MHz) d (CDCl3): 7.31–7.38 (5H, m,
ArH), 6.04 (1H, d, J ¼ 8 Hz –NH–), 5.21 (2H, s,
–OCH2C6H5), 4.82–4.87 (1H, m, –NHCHCO–), 4.72–
4.73 (1H, m, H ortho on Cp ring), 4.65–4.66 (1H, m, H
ortho on cp ring), 4.35–4.36 (2H, m, H meta on Cp
ring),), 4.21 (5H, s, unsubstituted Cp ring), 1.58–1.76
(3H, m, –CH2CH (CH3)2), 0.97 (6H, d, J ¼ 6 Hz,
4.3. Electrochemical studies
Electrochemical measurements were performed in
CH3CN with 0.1 M [nBu4N][PF6] as supporting elec-
trolyte. Cyclic voltammetry was performed in a three
electrode cell using a platinum microdisk working elec-
–CH2CH(CH ) ).
3 2

1520
M.J. Sheehy et al. / Journal of Organometallic Chemistry 689 (2004) 1511–1520
trode, Ag/AgCl reference electrode and a platinum wire
counter electrode. Compounds 1–10 exhibited a fully
reversible one-electron oxidation attributed to ferrocene
oxidation to the ferrocenium cation in the region +590
to +610 mV vs the Ag/AgCl electrode. Measurements
were recorded after addition of stoichiometric equiva-
lents of anion guests to the electrochemical solutions.
Solutions were ca. 1 ꢄ 10ꢁ3 mol dmꢁ3 in concentration
and potentials were determined at 21 °C, 50 mV sꢁ1 scan
rate. Anodic shifts in the ferrocene–ferrocenium redox
couple were produced by the presence of anion (10
equiv.) added as their [nBu4N]þ salts.
[3] A. Nomoto, T. Moriuchi, S. Yamazaki, A. Ogawa, T. Hirao, J.
Chem. Soc., Chem. Commun. (1998) 1963.
[4] A. Chesney, M.R. Bryce, A.S. Batsanov, J.A.K. Howard, L.M.
Goldenberg, J. Chem. Soc., Chem. Commun. (1998) 677.
[5] H. Plenio, C. Aberle, Organometallics 16 (1997) 5950.
[6] P.D. Beer, F. Szemes, V. Balzani, C.M. Sala, M.G.B. Drew, S.W.
Dent, M. Maestri, J. Am. Chem. Soc. 119 (1997) 11864.
[7] H.-B. Kraatz, J. Lusztyk, G.D. Enright, Inorg. Chem. 36 (1997)
2400.
[8] H. Fink, N.J. Long, A.J. Martin, G. Opromolla, A.J.P. White,
D.J. Williams, P. Zanello, Organometallics 16 (1997) 2646.
[9] T.J. Peckham, A.J. Lough, I. Manners, Organometallics 18 (1999)
1030.
[10] M. Kira, T. Matsubara, H. Shinohara, M. Sisido, Chem. Lett.
(1997) 89.
[11] P. Saweczko, H.-B. Kraatz, Coord. Chem. Rev. 192 (1999)
185.
4.4. Crystallographic footnote for (4)
[12] H.-B. Kraatz, D.M. Leek, A. Houmam, G.D. Enright, J. Lusztyk,
D.D.M. Wayner, J. Organomet. Chem. 589 (1999) 38.
[13] T. Moriuchi, A. Nomoto, K. Yoshida, T. Hirao, J. Organomet.
Chem. 589 (1999) 50.
Crystallographic
data:
Chemical
formula
,
C15H17FeNO3, molecular weight 315.15 g molꢁ1
monoclinic, space group P21 (No. 4), a ¼ 10:032ð2Þ,
[14] J.F. Gallagher, P.T.M. Kenny, M.J. Sheehy, Inorg. Chem.
Commun. 2 (1999) 200.
ꢀ
b ¼ 10:143ð2Þ, c ¼ 14:350ð1Þ A, b ¼ 95:98ð1Þ°,
[15] J.F. Gallagher, P.T.M. Kenny, M.J. Sheehy, Inorg. Chem.
Commun. 2 (1999) 327.
3
ꢀ
V ¼ 1452:1ð4Þ A , Z ¼ 4, T ¼ 296ð1Þ K, density ¼ 1.44
g cmꢁ3 (calc.), F ð000Þ ¼ 656, l ¼ 8:39 cmꢁ1, w-scans
absorption correction range 0.59–1.00, 2408 reflections
to 2h ¼ 120°, 2302 unique (with I > 2rI), 406 parame-
ters, R-factor is 0.030, wR2 ¼ 0:078 (based on F2 for with
I > 2rI using SHELXL97 as the refinement program [36],
[16] O. Brosch, T. Weyhermuller, N. Metzler-Nolte, Eur. J. Inorg.
Chem. 2 (2000) 323.
[17] A. Hess, J. Sehnert, T. Weyhermuller, N. Metzler-Nolte, Inorg.
Chem. 39 (2000) 5437.
[18] T. Moriuchi, K. Yoshida, T. Hirao, Organometallics 20 (2001)
3101.
GOF ¼ 1:04, density range in final D-map is )0.25 to
[19] Y.M. Xu, H.-B. Kraatz, Tetrahedron Lett. 42 (2001) 2601.
[20] T. Moriuchi, K. Yoshida, T. Hirao, J. Organomet. Chem. 637
(2001) 75.
ꢀꢁ3
+0.26 e A
.
[21] A. Wieckowska, R. Bilewicz, A. Misicka, M. Pietraszkiewicz, K.
Bajdor, L. Piela, Chem. Phys. Lett. 350 (2001) 447.
[22] H.-B. Kraatz, Y.M. Xu, P. Saweczko, J. Organomet. Chem. 637
(2001) 335.
5. Supplementary material
Crystallographic data (excluding structure factors)
for 4 have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication no.
192257. Copies of the data can be obtained free of
charge, on application to the CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44 (0) 1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
[23] T. Moriuchi, A. Nomoto, K. Yoshida, A. Ogawa, T. Hirao, J.
Am. Chem. Soc. 123 (2001) 68.
[24] S. Maricic, U. Berg, T. Frejd, Tetrahedron 58 (2002) 3085.
[25] S. Maricic, T. Frejd, J. Org. Chem. 67 (2002) 7600.
[26] D. Savage, J.F. Gallagher, Y. Ida, P.T.M. Kenny, Inorg. Chem.
Commun. 5 (2002) 1034.
[27] D.R. van Staveren, N. Metzler-Nolte, T. Weyhermuller, J. Chem.
Soc., Dalton Trans. (2003) 210.
[28] J.F. Gallagher, P.T.M. Kenny, M.J. Sheehy, Acta Crystallogr. C
55 (1999) 1257.
[29] P.C. Reeves, Org. Synth. 56 (1977) 28.
Acknowledgements
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[32] P.D. Beer, A.R. Graydon, A.O.M. Johnson, D.K. Smith, Inorg.
Chem. 36 (1997) 2112.
P.T.M.K. and M.J.S. thank Forbairt, Irish American
Partnership and Dublin City University for the funding
of a studentship award.
[33] M.G. Boutelle, H. Allen, O. Hill, M. Berners, R. John, P.D.
Dobson, P. Leigh, J. Mol. Recogn. 9 (1996) 664.
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