[(η5-C5H5)Fe(CO)2](Fp)- complexes of the parabanic acid mono- and dianion: Synthesis, X-ray structures and reactivity of the heterocyclic ligand

Article abstract of DOI:10.1016/j.poly.2004.02.015

[(η⁵-C₅H₅)Fe(CO)₂](Fp)- complexes of the parabanic acid mono- and dianion have been synthesised in a photochemical reaction of FpI with parabanic acid and diisopropylamine in benzene. The former contains a reactive N(3)-H bond and can be readily thallated with TlOEt. Reaction of the thallated complex with Ph₃PAuCl, benzyl chloride and ethyl bromoacetate in DMF gave N(3)-aurated, N(3)-benzyl and N(3)-carboethoxymethyl complex, respectively. The structures of these complexes were confirmed by X-ray diffraction. The ester function in the N(3)-carboethoxymethyl complex was hydrolysed to afford air-stable, water-soluble acid, a potential metallocarbonyl labelling reagents for proteins.

Full text of DOI:10.1016/j.poly.2004.02.015

Polyhedron 23 (2004) 1441–1446
www.elsevier.com/locate/poly
[(g5-C5H5)Fe(CO)2](Fp)-complexes of the parabanic acid mono- and
dianion: synthesis, X-ray structures and reactivity of the
heterocyclic ligand
a
a,
b
Konrad Kowalski , Janusz Zakrzewski *, Agnieszka Rybarczyk-Pirek
a
Department of Organic Chemistry, University of Łꢀodꢀz, 90-136- Łꢀodꢀz, Narutowicza 68, Poland
Department of Crystallography, University of Łꢀodꢀz, 90-236 Łꢀodꢀz, Pomorska 149/153, Poland
b
Received 6 December 2003; accepted 26 February 2004
Available online 12 April 2004
Abstract
[(g5-C5H5)Fe(CO)2](Fp)-complexes of the parabanic acid mono- and dianion have been synthesised in a photochemical reaction
of FpI with parabanic acid and diisopropylamine in benzene. The former contains a reactive N(3)–H bond and can be readily
thallated with TlOEt. Reaction of the thallated complex with Ph3PAuCl, benzyl chloride and ethyl bromoacetate in DMF gave
N(3)-aurated, N(3)-benzyl and N(3)-carboethoxymethyl complex, respectively. The structures of these complexes were confirmed
by X-ray diffraction. The ester function in the N(3)-carboethoxymethyl complex was hydrolysed to afford air-stable, water-soluble
acid, a potential metallocarbonyl labelling reagents for proteins.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Parabanic acid; Iron; Cyclopentadienyl; Carbonyl; Thallium; Gold (I) complex; Alkylation
1. Introduction
In this paper, we report on synthesis of the Fp-com-
plexes derived from parabanic acid 1 (Scheme 1). It is a
dibasic acid forming mono- and bis-anion. Therefore,
one can expect formation of its mono- and bis-Fp com-
plexes. The former will contain a reactive imide N(3)–H
bond, providing a possibility of further fuctionalisation.
We thought that it would be of interest to check if it is
possible to alkylate or metallate N(3) without affecting
rather labile Fp group because this would open a way to
substituted or binuclear complexes.
The [(g5-C5H5)Fe(CO)2](Fp)-moiety forms neutral
and cationic complexes with a variety of nitrogen li-
gands [1–5]. In this laboratory, we have elaborated a
way to Fp-complexes of anions of N–H acids by the
photochemical substitution of iodide in FpI (Eq. (1)),
where X and/or Y are electron-withdrawing groups and
dipa stands for diisopropylamine [6–14]:
hm
FpI þ HNðXÞðYÞ þ dipa!FpNðXÞðYÞ þ dipaHþIꢀ
ð1Þ
2. Results and discussion
We have synthesised using this approach Fp-complexes
of anions of a variety of NH acids, e.g., pyrroles, in-
doles, cyclic imides, sulfonamides, sulfamates, hydan-
toins and barbiturates. Some of these compounds
proved useful metallocarbonyl labelling reagents of
biomolecules [12–15].
All reactions described in this work are presented in
Schemes 1 and 2.
Photolysis of FpI with 1 in benzene containing di-
isopropylamine yielded a mixture of mono-Fp and bis-
Fp complexes (2 and 3, respectively).
Previous experiments have shown that the best sol-
vent for photochemical reactions of FpI with NH-acids
and diisopropylamine is benzene. Unfortunately, 1 is
* Corresponding author. Tel.: 4842-678-4731; fax: 4842-678-6583.
E-mail address: janzak@uni.lodz.pl (J. Zakrzewski).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.02.015

1442
K. Kowalski et al. / Polyhedron 23 (2004) 1441–1446
O
ratio FpI to 1, both mono-Fp (2) and bis-Fp (3) prod-
O
ucts were formed. They were separated by column
chromatography and their structure confirmed by
spectral and analytical data as well as by X-ray dif-
fraction (vide infra). At the molar ratio of FpI to 1
equals 0.25, the isolated yields of 2 and 3 were 40% and
17%, respectively, whereas at the FpI to 1 ratio equals
2.3, these yields were 5% and 27%, respectively. The bis-
Fp product 3 was therefore formed even when an excess
of 1 was used. This may be explained by the fact that 2 is
much better soluble in benzene than 1 and therefore
efficiently competes with this compound in the photo-
reaction with FpI. Another interesting fact is also worth
noting. It has been found that irradiation with visible
light of 3 in the presence of 1 and diisopropylamine
leads to the formation of 2 (via Fpþ dissociation?).
Compound 2 contains an imide N–H bond, offering a
possibility of N-alkylation or N-metallation of the het-
erocyclic ligand. However, since it has been found that
Fp-complexes with N-imidato ligands decompose in al-
kaline media [15] we wanted to avoid generation of al-
kaline metal N-anions. We have decided to try to
transform 2 into thallium(I) salt 4 (Scheme 2), which
was expected to react under mild conditions with reac-
tive organic halides or compounds having metal–halo-
gen bonds with formation of nitrogen–carbon or
nitrogen–metal bonds, respectively.
Fe
+
HN
OC
I
NH
OC
O
1
dipa /hν
(-HI)
O
O
O
Fe
OC
Fe
OC
Fe
OC
+
OC
N
N
OC
N
CO
NH
O
O
O
2
3
Scheme 1.
2 + TlOEt
O
O
Fe
OC
OC
N
PPh3AuCl
PhCH2Cl
N
AuPPh3
In fact, it is known that pyrrylthallium(I) reacts with
alkyl halides to afford 1-alkylpyrroles [16], and reaction
of succinimidylthallium(I) with Mn(CO)5Br leads to
Mn(CO)5 (g1-N-succinimidato) [17].
O
O
Fe
OC
OC
N
5
N-Tl+
O
The treatment of 2 with thallium(I) ethoxide in eth-
anol at 0–5 °C brings about precipitation of a rather
unstable pale-yellow solid, for which we suggest the
structure 4 (Scheme 2). This material has been filtered
off, dried and used without additional purification or
analyses in further syntheses. It has been found that
reaction of 4 Ph3PAuCl in DMF at r.t. leads to the
heterobinuclear complex 5 isolated in 50% yield. The
coordinated triphenylphosphane ligand in this com-
pound gives the 31P NMR signal at 31.7 ppm, which is
close to the value reported for the PPh3-Au bound to the
N-anion of hydantoin, 32.7 ppm [18].
Reaction of 4 with benzyl chloride and ethyl bro-
moacetate proceeded smoothly in DMF at r.t. to afford
the N-alkylated complexes 6 and 7 in 53% and 88%
yield, respectively. The structures of these compounds
have been confirmed by spectral and analytical data and
for 5 and 6 also by X-ray diffraction (vide infra). A
careful acid hydrolysis of 7 in 0.1 M aqueous HCl at 50
°C gave acid 8 in 55% yield. This complex is air-stable,
water-soluble, yellow crystalline solid. It can be re-
garded as a metallocarbonyl derivative of the simplest
aminoacid, glycine. Its stability and solubility in water
make it interesting for bioorganometallic applications
(e.g., as an IR-detectable marker for biomolecules).
O
4
O
BrCH2COOEt
Fe
OC
OC
N
N
CH2Ph
O
O
O
Fe
OC
COOEt
6
OC
N
N
O
H2O /H+
O
7
O
O
Fe
OC
COOH
OC
N
N
O
8
Scheme 2.
only scarcely soluble in this solvent and we had to
photolyse solutions of FpI in benzene containing diiso-
propylamine and suspended 1. However, hopefully, it
has been found that a small solubility of 1 in benzene is
sufficient for a substitution of iodide in FpI by the anion
of 1 to take place quite efficiently. Regardless of the

K. Kowalski et al. / Polyhedron 23 (2004) 1441–1446
1443
The aforementioned reactions demonstrate that
chemical modification of the parabanic acid ligand in 2
using its Tl(I) salt 4 is feasible and can proceed with
formation of either N–C or N–metal bond. This opens a
new entry to complexes of N-substituted parabanic acids
and to bimetallic complexes.
The infrared data for synthesised compounds provide
an evidence that the electronic properties of the Fp-
moiety bound to N(1) are influenced by the substitution
at N(3) (Table 1).
Table 1
The m
It is seen that replacement of the N–H nitrogen in 2
by a metal centre results in diminution of the m
frequencies of the Fp moieties. This means that there is
stronger backbonding from nitrogen to iron caused by
the second electron-donating metal centre. On the other
hand benzylation of N(3) practically does not influence
these frequencies.
frequencies measured in CHCl3 solutions
ðCBOÞ
ðCBOÞ
Compound
m
(cmꢀ1
)
ðCBOÞ
2
3
5
6
2062, 2015
2056, 2011
2056, 2009
2061, 2014
Table 2
Crystallographic data and structure refinement details
2
3
5
6
Crystal data
Formula
C
10H6FeN2O5
C17H10Fe2N2O7
465.97
C28H22AuFeN2O6P
766.26
C17H12FeN2O5
380.14
Formula weight
Crystal description
Crystal size (mm)
Space group
290.02
yellow plate
0.6 ꢁ 0.25 ꢁ 0.05
Pca21
7.434(2)
11.041(3)
26.402(3)
90
yellow plate
0.2 ꢁ 0.1 ꢁ 0.05
Pbcn
6.692(2)
22.778(1)
11.404(1)
90
yellow prism
0.3 ꢁ 0.1 ꢁ 0.1
yellow needle
0.5 ꢁ 0.05 ꢁ 0.05
P21=c
12.913(5)
6.278(3)
20.151(2)
90
ꢁ
P1
ꢂ
a (A)
9.714(1)
12.463(1)
12.926(2)
72.96(1)
93.58(1)
104.55(1)
1449(1)
2
ꢂ
b (A)
ꢂ
c (A)
a (°)
b (°)
c (°)
90
90
90
90
100.69(2)
90
3
ꢂ
V (A )
2167(1)
8
1.778
1739(1)
4
1.781
1605(1)
4
1.573
Z
dx (g/cm3)
1.757
Data collection
Diffractometer
Rigaku AFC5S
Cu Ka/1.54178
11.358
ꢂ
Radiation type/k (A)
l (mmꢀ1
)
13.809
14.293
7.825
Temperature
Index ranges
293(2)
0 6 h 6 8, 0 6 k 6 13,
0 6 l 6 31
1953
ꢀ7 6 h 6 7, ꢀ13 6 k 6 27,
ꢀ11 6 h 6 11, 0 6 k 6 14, 0 6 h 6 14, 0 6 k 6 7,
ꢀ7 6 l 6 13
2900
1546
ꢀ14 6 l 6 15
5303
5054
ꢀ24 6 l 6 23
2867
2736
Number of reflections collected
Number of independent reflections
1953
Number of reflections with I > 2rðIÞ 1143
Solution and refinement
680
3805
1794
Solution
direct methods
full-matrix least-squares on F 2
constrained
Refinement method
H atoms treatment
Number of parameters
328
0.0416
128
0.0591
356
0.0578
226
0.0497
a
RðF Þ for I > 2rðIÞ
a
RðF Þ
0.0960
0.1474ꢂꢂ
0:1763ꢂꢂ
0.002
0.0765ꢂꢂꢂꢂ
0.2162ꢂꢂꢂ
wRðF 2Þ for I > 2rðIÞ
0:0972ꢂ
0:1068ꢂ
0.000
0:1539
0:1572
0:1130
b
wRðF 2Þ
0:1578ꢂꢂꢂꢂ
0.000
0:1466ꢂꢂꢂ
0.000
b
ðD=rÞ
max
ꢀ3
ꢂ
Largest difference peak/hole (e A
)
0.406/)0.429
0.094
0.491/)0.592
2.237/)2.346
0.269/)0.356
Flack parameter
P
P
a RðF Þ ¼ ðjFo ꢀ FcjÞ= jFoj.
P
P
2
2 1=2
b wRðF 2Þ ¼ ½ wðjFo ꢀ FcjÞ = jFoj ꢃ
.
2
* w ¼ exp½ðsin h=kÞ ꢃ=½r2ðFo2Þ þ ð0:0590P2Þꢃ, where P ¼ ½ðFo2Þ þ 2ðFc2Þꢃ=3.
2
2
** w ¼ exp 0:9½ðsin h=kÞ ꢃ=½r2ðFo2Þ þ ð0:1010PÞ ꢃ.
2
2
*** w ¼ exp 4:7½ðsin h=kÞ ꢃ=½r2ðFo2Þ þ ð0:0542PÞ ꢃ.
2
**** w ¼ 1=½r2ðFo2Þ þ ð0:1090PÞ ꢃ.

1444
K. Kowalski et al. / Polyhedron 23 (2004) 1441–1446
O25
3. X-ray crystal structures of 2, 3, 5, 6
O24
O51
The structures of compounds 2, 3, 5, 6 were deter-
mined by single-crystal X-ray diffraction (Table 2 and
Figs. 1–4).
C25
C24
C50
N21
C11
C12
N23
Fe1
C31
C33
C34
C22
C60
C15
C14
O24a
O25a
C32
C13
O51a
O22
C3
C25a
N21a
O61
C37
C24a
N23a
C50a
C36
Fe1a
C11a
Fig. 4. Molecular drawing of compound 6. Displacement ellipsoids are
ꢂ
shown at 30% probability level. The Fe–N distance 1.958 (6) A.
C22a
C12a
C60a
C15a
O61a
O22a
C13a
C14a
N23b
H23b
Fig. 1. Molecular drawing of compound 2 (molecule a). Displacement
ellipsoids are shown at 30% probability level. The Fe–N distances:
O22a
ꢂ
ꢂ
1.955 (6) A (2a) and 1.976 (6) A (2b).
O22b
H23a
N23a
O25
O25a
C25
O51
C25a
C50
Fig. 5. Scheme of hydrogen bonding in crystal structure of 2.
C15
C14
N21a
N21
Fe1
C11
C22
Table 3
Geometry of hydrogen bonding in dimers of 2
C13
C12
C60
O61
D–H
ꢂ
(A)
Hꢄ ꢄ ꢄA
Dꢄ ꢄ ꢄA
D–Hꢄ ꢄ ꢄA
(°)
O22
ꢂ
(A)
ꢂ
(A)
N23a–H23aꢄ ꢄ ꢄO22ba
N23b–H23bꢄ ꢄ ꢄO22ab
0.86
0.86
1.984
1.987
2.833(4)
2.840(4)
169
171
Fig. 2. Molecular drawing of compound 3. Displacement ellipsoids are
ꢂ
shown at 30% probability level. The Fe–N distance 1.959 (6) A.
a symmetry codes: x ꢀ 1, y, z.
b symmetry codes: x þ 1, y, z.
They confirm in all the cases the g1-N-coordination.
In the solid state compound, 2 forms dimers through
intermolecular N–Hꢄ ꢄ ꢄO bonds (Fig. 5 and Table 3).
The Fe–N bonding distances in the investigated
complexes are the same within experimental error
O24
O25
C42
C41
O51
C25
C24
C43
C40
C15
C50
C11
C38
P1
Au1
C39
C32
N23
ꢂ
N21
(ꢅ1.962(8) A) and similar to that found in 1-Fp-5,5-di-
Fe1
C12
C22
C33
ꢂ
phenylhydantoin, 1.949(3) A [12]. Therefore, the length
C14
of this bond does not seem to be sensitive to electronic
or steric factors in the heterocyclic ligand.
C34
C26
O22
C13
C60
C37
C31
C35
O61
C36
C27
C30
4. Conclusion
C29
C28
We have synthesised Fp-complexes of parabanic acid
mono- and dianion. The mono-Fp complex has proven
Fig. 3. Molecular drawing of compound 5. Displacement ellipsoids are
ꢂ
shown at 30% probability level. The Fe–N distance 1.961 (6) A.

K. Kowalski et al. / Polyhedron 23 (2004) 1441–1446
1445
useful staring material in syntheses of N(3)-substituted
and metallated complexes.
1H NMR (d, ppm): 7.5 (m, 15H, Ph), 5.11 (s, 5H, Cp).
31P NMR (d, ppm): 31.7. IR (cmꢀ1): 2056, 2009, 1657,
1635. Elemental Anal. Calc. for C28H22AuFeN2PO6
(monohydrate): C, 43.89; H, 2.89; N, 3.66. Found: C,
43.60; H, 2.66; N, 3.59%.
5. Experimental
All reactions were carried our under argon. Benzene
was distilled over sodium-benzophenone. Other solvents
and reagents were reagent grade and were used without
prior purification. Chromatographic separations were
carried out using silica gel 60 (Merck, 230–400 mesh
ASTM). NMR spectra were recorded in CDCl3 on a
Varian Gemini 200BB (200 MHz for H) spectrometer.
IR spectra were recorded in CHCl3 on a Biorad 175C
apparatus.
5.4. Synthesis of 6
Benzyl chloride (43 ll, 0.37 mmol) was added to the
solution of 4 (77 mg, 0.15 mmol) in DMF (10 ml) at r.t.
After 30 min stirring the colourless precipitate of TlCl
was filtered off and the solvent evaporated under vac-
uum. Column chromatography (eluent-chloroform) af-
forded 6 as a yellow crystalline solid. Analytical sample
was recrystallized from chloroform–hexane. Yield: 30
mg (53%).
1
5.1. Synthesis of 2 and 3
1H NMR (d, ppm): 7.26–7.36 (m, 5H, Ph), 5.11 (s,
5H, Cp), 4.69 (s, 2H, CH2). IR (CHCl3, cmꢀ1): 2061,
2014, 1658, 1637. Elemental Anal. Calc. for
C17H12FeN2O5: C, 53.71; H, 3.18; N, 7.37. Found: C,
53.40; H, 3.00; N, 7.34%.
A magnetically stirred solution of FpI (151 mg, 0.5
mmol) in benzene (15 ml) and diisopropylamine (1 ml),
containing suspended parabanic acid (112 mg, 2 mmol)
was photolysed (4 ꢁ 150 W tungsten lamp and external
cooling with ice-water) for 2 h. The solid residue was
filtered off and washed with benzene. The solvent was
evaporated from the filtrate and the residue dissolved in
chloroform–methanol (25:1) and chromatographed us-
ing the same solvent mixture as eluent. Two yellow
fractions were collected: the first one containing 3 and
the second containing 2. Analytical samples were pre-
pared by crystallisation from chloroform–hexane.
Yields: 3: 20 mg (17%); 2: 56 mg (40%).
5.5. Synthesis of 7
Ethyl bromoacetate (113 ll, 1 mmol) was added to
the solution of 4 (254 mg, 0.5 mmol) in DMF (15 ml) at
r.t. After 30 min stirring the colourless precipitate of
TlBr was filtered off and the solvent evaporated under
vacuum. Column chromatography (eluent-chloroform)
afforded 7 as an yellow oil. Yield: 165 mg (88%).
1H NMR (d, ppm): 5.21 (s, 5H, Cp), 4.26 (s, 2H,
CH2), 4.18 (t, J ¼ 8 Hz, 2H, CH2 in Et), 1.25 (t, J ¼ 8
Hz, 3H, CH3 in Et). IR (cmꢀ1): 2062, 2015, 1749, 1657,
1637. Elemental Anal. Calc. for C14H12FeN2O7: C,
44.71; H, 3.22; N, 7.45. Found: C, 44.77; H, 3.31; N,
7.40%.
1
3. H NMR (d, ppm): 5.08 (s, Cp) IR (cmꢀ1): 2056,
2011, 1651, 1633. Elemental Anal. Calc. for
C17H10O7FeN2: C, 43.82; H, 2.16; N, 6.01. Found: C,
43.94; H, 2.30; N, 6.07%.
1
2. H NMR (d, ppm): 7.97 (bs, 1H, NH), 5.15 (s,
5H,Cp). IR (cmꢀ1): 2062, 2015, 1701, 1682. Elemental
Anal. Calc. for C10H6O5FeN2: C, 41.42; H, 2.09; N,
9.66. Found: C, 41.80; H, 2.14; N, 9.60%.
5.6. Synthesis of 8
Compound 7 (169 mg, 0.44 mmol) was dissolved in 50
ml of 0.1 M aq. HCl and heated to 50 °C for 5 h. Ex-
traction with CH2Cl2 and chromatography (SiO2,
CHCl3–methanol 10:3 v/v) afforded 8 as an yellow solid.
Yield: 93 mg (55%).
1H NMR (d, ppm): 5.21 (s, 5H, Cp), 4.01 (s, 2H,
CH2). IR (cmꢀ1): 3424, 2051, 2001, 1742, 1683, 1617.
Elemental Anal. Calc. for C12H8FeN2O7 ꢄ 2H2O: C,
37.50; H, 3.15; N, 7.29. Found: C, 37.25; H, 3.19; N,
7.01%.
5.2. Synthesis of 4
Thallium(I) ethoxide (45 ll, 0.63 mmol) was added to
a stirred solution of 2 (98 mg, 0.33 mmol) in ethanol (12
ml) at 0–5 °C. After 30 min strirring at this temperature
the pale yellow solid was filtered off, washed with eth-
anol and dried under vacuum. Yield: 170 mg (100%).
5.3. Synthesis of 5
(PPh3)AuCl (198 mg, 0.40 mmol) was added to the
solution of 4 (190 mg, 0.38 mmol) in DMF (15 ml) at r.t.
After 1.5 stirring the colorless precipitate of TlCl was
filtered off and the solvent evaporated under vacuum.
Column chromatography (eluent-chloroform) afforded
5 as a yellow crystalline solid. Yield: 130 mg (48%).
6. X-ray structure determinations
X-ray data were collected on Rigaku AFC5S difrac-
tometer [19] using Cu Ka X-ray source and graphite
monochromator. For all the crystals procedure of

1446
K. Kowalski et al. / Polyhedron 23 (2004) 1441–1446
measurement, structure solution and refinemnt was the
same. The unit cell dimensions were obtained from least-
squares fit to setting angles of 25 reflections. Monitoring
of three standard reflections during data collections
show no significant change of intensities under X-ray
radiation. Reflection intensities were corrected for Lo-
rentz and polarization effects and analytical absorption
corrections were applied [20]. A summary of X-ray de-
tails is given in Table 2. The crystal structures were
solved using SHELXS86 [21] program and refined using
full-matrix least squares calculation using SHELXL97
[22]. In the final step of refinement procedure, all non-
hydrogen atoms were refined with anisotropic themal
displacement parametrs. Hydrogen atoms were included
in calculated positions with ideal geometry using rigid
body model. They were given isotropic displacement
parametrs equal to 1.2 (for aromatic C parent atoms) or
1.5 (in the other cases) of the equivalent displacement
parameters of the atoms to which they are attached. The
molecular geometry was calculated by SHELXL and the
plots were made by PLATON [23].
Acknowledgements
Support of this work by the Polish State Committee
for Scientific Research (KBN, Grant PBZ-KBN 15/09/
T09/99/01) is thankfully acknowledged.
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molecular drawing of this compound the water molecule
is omitted for clarity.
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CCDC No. 207093 for compound 5 and CCDC No.
207094 for compound 6) have been deposited at the
Cambridge Crystallographic Data Centre and are
available on request from the Director, CCDC, 12 Un-
ion Road, Cambridge CB2 1EZ, UK (fax: +44-1223-
336-033; Email:deposit@ccdc.cam.ac.uk or http://
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