Synthesis and reactivity of a new Fe(II) 5-(4-pyridyl)-tetrazolate complex and X-ray structure of its doubly protonated derivative

Article abstract of DOI:10.1016/S0022-328X(03)00002-0

The synthesis of the new Fe(II) complex [CpFe(CO)₂(N₄C-C₅H₄N)] (2) is described. ¹H- and ¹³C-NMR spectroscopy data of (2) indicate the presence of interannular conjugation in the pyridyl-tetrazolate ligand, implying coplanarity between the two rings. Addition of electrophiles to 2 resulted in the formation of cationic complexes such as [CpFe(CO)₂(4-MeN₄-C₅H₄N)] [O₃SCF₃] (3), [CpFe(CO)₂ and of the doubly protonated complex [CpFe(CO)₂ (4-HN₄C-C₅H₄N-H)][O₃SCF ₃]₂ (5). In all cases, the out-of-plane rotation of the pyridyl ring occurred as a consequence of the quaternization of the N-4 of tetrazole ring. X-ray structure of complex 5 indicates a torsion angle of 20.9(2)° between the aromatic rings. Protonation reactions were found to be reversible and complexes 4-5 were easily converted into the starting complex 2 by addition of a base.

Full text of DOI:10.1016/S0022-328X(03)00002-0

Journal of Organometallic Chemistry 669 (2003) 135ꢀ140
/
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of a new Fe(II) 5-(4-pyridyl)-tetrazolate
complex and X-ray structure of its doubly protonated derivative.
Antonio Palazzi a,*, Stefano Stagni a, Simona Selva b, Magda Monari b
a Dipartimento di Chimica Fisica ed Inorganica, viale Risorgimento 4, I-40136 Bologna, Italy
b Dipartimento di Chimica ‘G. Ciamician’, via Selmi 2, I-40126 Bologna, Italy
Received 16 December 2002; received in revised form 23 December 2002; accepted 4 January 2003
Abstract
The synthesis of the new Fe(II) complex [CpFe(CO)2(N4Cꢀ
indicate the presence of interannular conjugation in the pyridyl-tetrazolate ligand, implying coplanarity between the two rings.
Addition of electrophiles to 2 resulted in the formation of cationic complexes such as [CpFe(CO)2(4-MeN4CꢀC5H4N)][O3SCF3] (3),
[CpFe(CO)2(4-HN4CꢀC5H4N)][O3SCF3] (4) and of the doubly protonated complex [CpFe(CO)2(4-HN4CꢀC5H4NꢀH)][O3SCF3]2
/
C5H4N)] (2) is described. 1H- and 13C-NMR spectroscopy data of (2)
/
/
/
/
(5). In all cases, the out-of-plane rotation of the pyridyl ring occurred as a consequence of the quaternization of the N-4 of tetrazole
ring. X-ray structure of complex 5 indicates a torsion angle of 20.9(2)8 between the aromatic rings. Protonation reactions were found
to be reversible and complexes 4ꢀ5 were easily converted into the starting complex 2 by addition of a base.
/
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Fe(II) organometallic complexes; Interannular conjugation; Tetrazolate ligands; X-ray diffractometry
1. Introduction
the cycloaddition to run in mild conditions and good
yields. In particular, the synthesis of a metal bound
tetrazole ring can be easily achieved either by addition
of organonitriles to azido complexes [6], or by reaction
of azide salts with an appropriate metal-coordinated
nitrile [7]. As a further example of the latter procedure,
we have recently prepared new organometallic Fe(II) 5-
In the last two decades tetrazole derivatives, owing to
their peculiar properties, have been extensively studied.
Indeed, the tetrazolic acid group ꢀCN4H shows similar
/
acidity and higher metabolic stability than the car-
boxylic acid group. These features have favoured the
aryl tetrazolate complexes such as [CpFe(CO)(L)(N4Cꢀ
/
replacement of ꢀ
/
CO2H group by the isosteric ꢀCN4H
/
C6H4ꢀCN)], [LꢂCO; PPh3; P(OCH3)3; CN-2,6-
/
/
moiety in several biologically active molecules, prompt-
ing the rapid development of tetrazole-based com-
pounds in several areas of research connected to
medicinal science [1]. A typical synthetic pathway
Me2C6H3] under mild conditions by addition of sodium
azide to the parent 1,4 dicyanobenzene complexes [8].
The characterisation of the produced complexes allowed
us to establish some interesting features such as the
regioselective formation of N-2 coordinated isomers and
a not significant interannular conjugation effect in the 5-
aryl tetrazolate ligand, involving the coplanarity be-
tween tetrazole and phenyl rings. Reactions of Fe(II) 5-
aryl tetrazolate complexes with electrophiles such as
CH3ꢁ or Hꢁ resulted in the regioselective quaternization
of the N-4 of the tetrazole ring causing, in all cases, the
out-of-plane rotation of the phenyl ring and the
consequent reduction of interannular conjugation. No-
teworthy in the reversibility of the protonation reaction
leading to tetrazole systems is given by the [2ꢁ3]
/
cycloaddition reaction between organonitriles and azido
salts or miscellaneous (silyl, stannyl, aliphatic or aro-
matic) azido derivatives [2,3]. Since the early work by
Beck and co-workers [4,5], it has been demonstrated
that the presence of metal ions in such reactions allows
* Corresponding author. Tel.: ꢁ
2093-690.
E-mail address: palazzi@ms.fci.unibo.it (A. Palazzi).
/
39-051-6446-496; fax: ꢁ39-051-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00002-0

136
A. Palazzi et al. / Journal of Organometallic Chemistry 669 (2003) 135ꢀ140
/
which introduces the possibility of modulating the
conjugative properties of the 5-aryl tetrazolate ligand
tion to dryness afforded a deep red solid which was used
without any further purification. The preparation of the
5-(4-pyridyl)-tetrazolate anion was easily achieved by
adding a stoichiometric amount of triethylamine to a
suspension in methanol (5 ml) of 4-(1H-tetrazol-5-yl)-
pyridine, which was prepared in 82% yield from 4-
cyanopyridine by following a literature procedure [10].
Therefore, starting reagents were mixed in methanol at
room temperature to afford the complex [CpFe(CO)2-
by an acidꢀbase mechanism. In order to further
/
substantiate our results, we now report the synthesis of
a new Fe(II) organometallic complex bearing 5-(4-
pyridyl)-tetrazolate ligand and the X-ray structure of
its doubly protonated derivative.
2. Results and discussion
(N4CꢀC5H4N)] (2) in 45% yield, this value being
/
affected by the presence of the undesired dimeric species
[Fe2Cp2(CO)4], to the formation of which could not be
avoided even though the metathesis reaction was
performed at low temperature. Methylated (3) (Eq.
2.1. General
The synthetic approach used in this study to prepare
(1)
pure and well defined target complexes is outlined in Eq.
(1).
The precursor complex [CpFe(CO)2(THF)][O3SCF3]
(2)) and protonated complexes (4 and 5) (Scheme 1)
were obtained by addition of appropriate amounts of
methyl triflate or triflic acid, respectively.
(2)
(1) was prepared from the corresponding iodide [9] by
reaction with a slight excess (1.1 equivalent) of silver
triflate in THF (15 ml) at room temperature for 4 h.
Filtration through a Celite pad and subsequent evapora-
The main FT-IR and NMR (1H, 13C) spectroscopic data
of all compounds are summarized in Table 1.
Scheme 1.

A. Palazzi et al. / Journal of Organometallic Chemistry 669 (2003) 135ꢀ
/140
137
Table 1
NMR (1H, 13C) and FT-IR data for complexes 2ꢀ
a
b
/5
Entry
dC5 (ppm)
dH2?,6? (ppm)
dH3?,5? (ppm)
dC2?,6? (ppm)
dC3?,5? (ppm)
CO absorption (cmꢃ1
)
2
3
4
5
164.2
154.1
156.7
153.9
8.69
8.90
8.87
8.98
7.94
8.34
8.51
8.56
150.4
147.5
143.7
143.9
120.1
128.5
125.2
125.1
2066; 2020
2074; 2029
2068; 2024
2075; 2030
a
CD3CN as solvent.
CH2Cl2 as solvent.
b
2.2. IR spectroscopy
tetrazole ring (Eq. (1)). It has been established that
coplanarity between the aromatic rings in organic N-2
substituted 5-aryl tetrazoles [13] as well as in the
corresponding N-2 coordinated metal complexes
[14,15] implies interannular conjugation, which is absent
in the parent N-1 derivatives. As we reported [8],
interannular conjugation in 5-aryl tetrazolate complexes
is removed, or strongly diminished, when a substituent
at N-4 of tetrazole ring induces rotation about the
tetrazole-aryl bond away from coplanarity. In particu-
lar, the out of plane rotation of the aryl ring resulted in
the downfield shift of the carbons ortho to the tetrazole
group. In light of those results, we performed electro-
philic additions to complex 2, which was at first
converted into the methylated cationic product 3 by
treatment with one equivalent of methyl triflate. The
methylation reaction occurs selectively at the position 4
of tetrazole ring (Eq. (2)), as evidenced by the 13C
chemical shift of C-5 at 154.1 ppm, which is typical of
tetrazoles having a substituent on the nitrogen adjacent
to the tetrazole carbon [16,17]. Interestingly, we did not
have any evidence of the presence of methyl group
bonded to the pyridine nitrogen, whereas such selectivity
was not reported for the electrophilic attack onto 4-(1H-
tetrazol-5-yl)-pyridine [18]. This behaviour could indi-
cate an increased electron density on the metal-coordi-
nated tetrazole ring with respect to the free ligand,
providing a further evidence of a metal-to-ligand
electron donating interaction, whose presence was pre-
viously detected by IR spectroscopy. Moreover, a
noticeable downfield shift of pyridine C-3? and C-5?
As expected, the formation of the neutral complex
[CpFe(CO)2(N4CꢀC5H4N)] (2) was witnessed by the
/
shift of the carbonyl bands of the cationic precursor 1
[IR(CH2Cl2) 2074; 2030 cmꢃ1] to lower wave numbers
[IR(CH2Cl2) 2066; 2020 cmꢃ1 for 2]. These values are
coincident with those reported for [CpFe(CO)2(N4Cꢀ
/
C6H4ꢀCN)] [8], but higher than those in
/
[CpFe(CO)2(CN)] [IR(CH2Cl2) 2054; 2014 cmꢃ1] and
comparable to the ones in [CpFe(CO)2(CNW(CO)5)]
[IR(CH2Cl2) 2064; 2024 cmꢃ1] [11]. This fact could
indicate the presence of a back-bonding interaction to
the tetrazolate ring in complex 2. Addition of electro-
philes resulted in the shift of the carbonyl absorptions to
higher frequency both for the methylated complex (3)
[IR(CH2Cl2) 2074; 2029 cmꢃ1] and for the protonated
derivatives 4 [IR(CH2Cl2) 2068; 2024 cmꢃ1] and 5
[IR(CH2Cl2) 2075; 2030 cmꢃ1].
2.3. NMR study
As mentioned in the Introduction section. We recently
prepared [8] some new 5-aryl tetrazolate Fe(II) organo-
metallic complexes. Due to the presence of two non-
equivalent nitrogen atoms in the tetrazole ring, the first
goal in the characterization of such compounds con-
sisted in the determination of the binding site of the
metal fragment to the tetrazolate ligand. To do this, we
took into account some NMR studies reported by
Butler [12], in which the chemical shift of C5 tetrazole
has been used as a probe to distinguish between N-1
(dC5ꢂ
167 ppm) derivatives of a series of 5-aryl tetrazoles. In
all the 5-aryl tetrazolate complexes we prepared, the 13
chemical shift values of the tetrazole carbon (dC5ꢂ
164ꢀ165 ppm) indicated the regiospecific coordination
at N-2 of tetrazole ring. The X-ray structure of the
complex [CpFe(CO)(P(OMe)3)(N4CꢀC6H4ꢀCN)] evi-
/
152ꢀ
/
157 ppm) and N-2 methylated (dC5ꢂ
/
162ꢀ
/
C
/
/
/
/
denced both the coordination at N-2 of the organome-
tallic fragment and the coplanarity between the tetrazole
and aryl rings. Likewise, in the present work complex
[CpFe(CO)2(N4CꢀC5H4N)] (2) exhibits the chemical
shift of C-5 at 164.2 ppm, suggesting the exclusive
coordination of the metal fragment at N-2 of the
/
Fig. 1. An ORTEP plot of the molecular structure of
C5H4Nꢀ
H)]2ꢁ (5). Thermal ellipsoids are drawn
at the 30% probability level.
[CpFe(CO)2(HN4Cꢀ
/
/

138
A. Palazzi et al. / Journal of Organometallic Chemistry 669 (2003) 135ꢀ140
/
Table 2
effect is indicated by the variation of chemical shift of C-
3? and C-5? (dC3?,5?ꢂ125.2 ppm versus 120.1 ppm in 2).
˚
Selected bond lengths (A) and bond angles (8) for 5
/
At the same time, it turns out that the reduced steric
hindrance of the hydrogen substituent with respect to
the methyl group results in a lower downfield shift of
dC3?,5?. Protonation of complex 2 was also carried out
with two equivalents of triflic acid in order to neutralize
the basic properties of the pyridine nitrogen. The NMR
values of the obtained diprotonated derivative 5 slightly
differed from the monocation 4 while a significant
difference between them was evidenced by their IR
spectra (see Table 1). The reversibility of such reactions
was evidenced by addition of the proper amount (one or
two equivalents) of triethylamine to complexes 4 and 5,
causing in both cases the quantitative reformation of the
neutral precursor 2.
Bond lengths
Fe(1)ꢀ
Fe(1)ꢀ
Fe(1)ꢀ
C(12)ꢀ
C(13)ꢀ
N(1)ꢀ
N(2)ꢀ
N(3)ꢀ
N(1)ꢀ
/
N(2)
1.956(2) N(4)ꢀ
1.793(4) C(1)ꢀ
1.791(4) C(2)ꢀ
1.139(5) C(3)ꢀ
1.124(5) C(5)ꢀ
1.340(4) C(6)ꢀ
1.303(4) N(5)ꢀ
/
C(1)
1.332(4)
1.469(4)
1.379(5)
1.375(5)
1.365(5)
1.378(5)
1.325(5)
1.328(5)
/C(12)
/
C(2)
C(3)
C(4)
C(6)
C(2)
/C(13)
/
/
O(1)
O(2)
/
/
/
/
N(2)
N(3)
N(4)
C(1)
/
/
/
C(4)
C(5)
/
1.327(4) N(5)ꢀ
/
/
1.316(4)
Bond angles
C(12)ꢀFe(1)ꢀ
C(13)ꢀFe(1)ꢀ
/
/
N(2)
92.4(1)
92.6(1)
C(12)ꢀ
/Fe(1)ꢀ
/C(13)
95.2(2)
/
/N(2)
Interplanar angle
C(tetrazole)ꢀC(pyridyl)
/
20.9(2)
2.4. X-ray discussion
was observed in going from complex 2 (dC3?,5?ꢂ
ppm) to the corresponding cationic compound 3
(dC3?,5?ꢂ128.5 ppm). The analysis of such NMR data
/
120.1
The molecular structure of the dication 5 is shown in
Fig. 1 and its stereogeometry is that expected on the
basis of the spectroscopic evidence.
Bond distances of interest are listed in Table 2. A
˚
comment is worth for FeꢀN(tetrazole) 1.956(2) A and
/
led us to assume the presence of some interannular
conjugation effect in complex 2, that is removed or
strongly reduced in complex 3, in which the presence of
a methyl group bonded at the nitrogen adjacent to the
tetrazole carbon results in the out-of-plane rotation of
the pyridyl ring. Reaction of complex 2 with one
equivalent of triflic acid (see Scheme 1) afforded the
protonated complex 4, in which the preferential proto-
nation at N-4 of tetrazole ring is shown by dC5 at 156.7
ppm and the diminution of interannular conjugation
/
˚
C(tetrazole)ꢀC(pyridine) 1.469(4) A. These values are
/
equal, within experimental errors, to those recently
reported in the similar molecule [CpFe(CO){P-
(OMe)3}(N4Cꢀ
/
C6H4ꢀCN)] [8], [1.950(2) and 1.463(3)
/
˚
A, respectively]; the only difference between the two
five-substituted tetrazole ligands being the inter-ring
angle 3.3(2)8 for N4Cꢀ
HN4CꢀC5H4NꢀH. The latter value confirms the pre-
viously discussed independence of the C(tetrazole)ꢀ
/
C6H4ꢀCN and 20.9(2)8 for
/
/
/
/
Table 3
Crystal data and experimental details for 5
C(phenyl) on the inter-ring angle, i.e. the inter-ring
conjugation of the p orbitals is small and not detectable
in terms of bond distances (Table 2).
Formula
M
Temperature (K)
C15H11F6FeN5O8S2
623.26
293(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21/n
3. Conclusions
Crystal system
Space group
Unit cell dimensions
The reaction of the cationic complex (1) with the
tetrazolate anion [N4Cꢀ
C5H4N]ꢃ led to the
˚
a (A)
15.3345(7)
8.3672(4)
18.725(1)
103.789(2)
2333.3(2)
4
pyridylꢀ
/
/
˚
b (A)
new organometallic complex [CpFe(CO)2(N4Cꢀ
/
˚
c (A)
C5H4N)] (2). The NMR spectroscopic characterization
of 2 indicated both the regioselective coordination of the
organometallic fragment at N-2 of tetrazole ring and the
presence of interannular conjugation effect in the
pyridyl tetrazolate ligand, involving coplanarity between
the two rings. These latter properties were modified by
addition of electrophilic species, which resulted in the
formation of N-4 alkylated derivative such as
b (8)
3
V (A )
˚
Z
Dcalc (Mg mꢃ3
Absorption coefficient (mmꢃ1
F(000)
Crystal size (mm3)
u limits (8)
Reflections collected
)
1.774
0.926
1248
)
0.40ꢄ
2.68ꢀ28.00
23411 (9h, 9
/0.35ꢄ0.30
/
/
/
/
k, 9l)
/
Unique observed reflections [Foꢀ
Goodness-of-fit on F2
Final R1(F) [I ꢀ2s(I)]
wR2(F2) (all data)
/
4s(Fo)]
5580
1.004
[CpFe(CO)2(4-MeN4Cꢀ
protonated complexes such as [CpFe(CO)2(4-HN4Cꢀ
C5H4N)][O3SCF3] (4) and [CpFe(CO)2(4-HN4CꢀC5H4-
NꢀH)][O3SCF3]2 (5). The X-ray structure of complex 5
confirmed the presence of a torsion angle of 20.9(2)8
/C5H4N)][O3SCF3] (3) or N-4
/
/
0.0565
0. 1613
/
ꢃ3
˚
Largest difference peak and hole (e A
/
)
0.818 and ꢃ0.713
/

A. Palazzi et al. / Journal of Organometallic Chemistry 669 (2003) 135ꢀ
/140
139
between the aromatic rings. At the same time, no
particular distortion of the pyridyl tetrazolate inter-
ring distance, consequent to diminution of conjugative
properties, was observed. However, since protonation
reactions were found to be reversible, it could be
possible to modify the structural and electronic features
of the target complex 2 by a proton addition-elimination
mechanism. Finally, it is worth noting that the com-
3JHH
ꢂ5 Hz), 5.41 (s, 5H, Cp), dC(CD3CN): 210.5
/
(CO), 164.2 (C-5), 150.4 (2?,6?-C5H4N), 136.8 (C-4?),
120.1 (3?,5?-C5H4N), 85.8 (Cp); IR (CH2Cl2) nmax
(cmꢃ1): 2066s (CO), 2020s (CO), 1610w (CÄ
/N); Anal.
Calc. for C13H9N5O2Fe: C, 48.3; H, 2.81; N, 21.7.
Found: C, 48.2; H, 2.79; N, 21.5%.
4.3. Methylation reaction: synthesis of [CpFe(CO)2(4-
plexes 2ꢀ/5 might represent good models for studying the
MeN4CꢀC5H4N)][O3SCF3] (3)
/
properties of differently substituted tetrazoles, whereas
the parent organic systems are normally obtained less
selectively or using more drastic conditions [19].
A solution of 2 (0.500 g, 0.92 mmol) in CH2Cl2 (20
ml) was treated with CH3OSO2CF3 (0.1 ml, 0.92 mmol)
with stirring, at ꢃ50 8C for 30 min. The mixture was
/
then allowed to warm to r.t. and stirred for additional 3
h. Evaporation of solvent and chromatography of the
brown residue on a short alumina filled column with
CH2Cl2 as solvent afforded a first red fraction of
[Fe2Cp2(CO)4] that was discharged. Elution with a
4. Experimental
4.1. General considerations
All reactions with organometallic reagents or sub-
strates were carried out under argon using standard
Schlenk techniques. Solvents were dried and distilled
under nitrogen prior to use. Unless otherwise stated,
chemicals were obtained commercially (e.g. Aldrich) and
used without any further purification. All the obtained
products were characterised by elemental analysis and
spectroscopic methods. IR spectra were recorded with a
FT-IR spectrometer Perkin Elmer spectrum 2000. The
routine NMR spectra (1H, 13C) were always recorded
using a Varian Gemini 300 instrument (1H, 300.1; 13C,
75.5 MHz). The spectra were referenced internally to
residual solvent resonance, and were recorded at 298 K
for characterisation purposes. Elemental analyses were
performed on a ThermoQuest Flash 1112 Series EA
Instrument. Petroleum ether (Etp) refers to a fraction of
mixture CH2Cl2ꢀ
(0.200 g, 70%), obtained as a pale brown oil. NMR:
3
dH(CD3CN): 8.90 (d, 2H, 2?,6?-C5H4N, JHH
/
CH3CN (2:1, v/v) gave the complex 3
ꢂ
/
7 Hz),
3
8.34 (d, 2H, 3?,5?-C5H4N, JHH
ꢂ
/
7 Hz), 5.45 (s, 5H,
Cp), 4.18 (3H, s, CH3); dC(CD3CN): 210.0 (CO), 154.1
(C-5), 147.5 (2?,6?-C5H4N), 138.0 (C-4?), 128.5 (3?,5?-
C5H4N), 87.8 (Cp), 37.6 (CH3); IR (CH2Cl2) nmax
(cmꢃ1): 2074s (CO), 2029s (CO), 1610w (CÄ
/N). Anal.
Calc. for C15H12N5O5FeF3S: C, 37.0; H, 2.48; N, 14.4.
Found: C, 36.9; H, 2.45; N, 14.5%.
4.4. Protonation reactions: synthesis of [CpFe(CO)2(4-
HN4Cꢀ
/
C5H4N)][O3SCF3] (4) and of [CpFe(CO)2(4-
HN4Cꢀ
/
C5H4NꢀH)][O3SCF3]2 (5)
/
To a stirred solution of 2 (0.300 g, 1.55 mmol) in
CH2Cl2 (20 ml), HOSO2CF3 (0.15 ml, 1.55 mmol,
diluted in 5 ml of CH2Cl2) was added dropwise at
b.p. 60ꢀ80 8C. Typically, all chromatographies were
/
performed on alumina filled column (diameter: 1.5 cm;
height 15 cm) under an Argon atmosphere and using
ꢃ60 8C. After 30 min the mixture was allowed to warm
/
dichloromethaneꢀ
/
acetonitrile mixtures as eluant.
to r.t. and the solvent removed in vacuo. The resulting
mixture was dissolved in 5 ml of acetonitrile and layered
with diethyl ether, causing the formation of a yellow
microcristalline powder which was identified as the
4.2. Synthesis of [CpFe(CO)2(N4CC5H4N)] (2)
Complex 1 (0.500 g; 1.26 mmol), dissolved in metha-
nol (5 ml), was added dropwise to a solution of 4-(1H-
tetrazol-5-yl)-pyridine (0.185 g, 1.26 mmol) and triethy-
lamine (0.18 ml; 1.30 mmol) in methanol (15 ml). The
complex 4 (0.65 g, 90%). NMR: dH(CD3CN): 8.87 (d,
3
2H, 2?,6?-C5H4N, JHH
ꢂ5 Hz), 8.51 (d, 2H, 3?,5?-
/
3
C5H4N, JHH
ꢂ5 Hz), 5.40 (s, 5H, Cp); dC(CD3CN):
/
210.5 (CO), 156.7 (C-5?), 143.7 (2?,6?-C5H4N), 141.2 (C-
4?), 125.2 (3?,5?-C5H4N), 87.5 (Cp); IR (CH2Cl2) nmax
resulting yellowꢀbrown suspension was stirred at room
/
temperature for 6 h., during which time the disappear-
ance of cationic species was monitored by IR spectro-
scopy. Filtration through a Celite pad and evaporation
to dryness afforded a reddish-brown crude product
which was purified by alumina filled column. After a
first red fraction of [Fe2Cp2(CO)4], the target complex 2
(0.183 g, 45%) was recovered as a yellow microcristalline
(cmꢃ1): 2068s (CO), 2024 s (CO), 1640w (CÄ
/N) Anal.
Calc. for C14H10N5O5FeF3S: C, 35.5; H, 2.11; N, 14.8.
Found: C, 35.4; H, 2.12; N, 14.9%. Complex 5 (0.77 g,
80%) was obtained in the same manner as 4 by using two
equivalents of triflic acid and it was re-crystallised, in the
presence of one of two more drops of acid, from an
acetonitrile solution layered with petroleum ether at r.t.,
powder by eluting with a dichloromethaneꢀ
/
acetonitrile
affording dark yellow plates. NMR: dH(CD3CN): 8.98
3
5:1 mixture. NMR: dH(CD3CN): 8.69 (d, 2H, 2?,6?-
(d, 2H, 2?,6?-C5H4N, JHH
ꢂ9 Hz), 8.56 (d, 2H, 3?,5?-
/
3
C5H4N, JHH
3
C5H4N, JHH
ꢂ
/
5 Hz), 7.94 (d, 2H, 3?,5?-C5H4N,
ꢂ9 Hz), 5.46 (s, 5H, Cp); dC(CD3CN):
/

140
A. Palazzi et al. / Journal of Organometallic Chemistry 669 (2003) 135ꢀ140
/
209.7 (CO), 153.9 (C-5?), 143.9 (2?,6?-C5H4N), 138.3 (C-
4?), 125.1 (3?,5?-C5H4N), 87.0 (Cp); IR (CH2Cl2) nmax
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
(cmꢃ1): 2075s (CO), 2030 s (CO), 1647w (CÄ
/N). Anal.
Calc. for C15H11N5O8FeF6S2: C, 28.9; H, 1.78; N, 11.2.
Found: C, 29.1; H, 1.80; N, 11.4%. Addition of one or
two equivalents of triethylamine to an acetonitrile
solution of complexes 4 or 5, respectively, reforms
quantitatively the neutral precursor 2.
Acknowledgements
The authors wish to thank the Ministero dell’Istru-
zione, dell’Universita` e Ricerca (MIUR) for financial
support to the National Project ‘New strategies for the
control of reactions: interactions of molecular fragments
with metallic sites in unconventional species’.
4.5. X-ray crystallography
A suitable crystal of compound 5 was mounted on a
glass fiber in air on a Bruker-AXS SMART CCD area
detector diffractometer, using Moꢀ
/
Ka radiation (lꢂ
/
References
˚
0.71073 A) at room temperature. Cell dimensions and
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full sphere of the diffraction space was measured by 0.38
v steps, 20 s exposures and sample-detector distance
kept at 5.0 cm. Intensity decay was monitored by
recollecting the initial 50 frames at the end of the data
collection and analysing the duplicate reflections. The
collected frames were processed for integration by using
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tion was applied using SADABS [20] on the basis of the
Laue symmetry of the reciprocal space. The structure
was solved by direct methods (SIR-97) [21] and sub-
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refined riding the pertinent carbon or nitrogen atoms
1.2Ueq (C or
/
Hꢂ
/
0.93 A, Nꢀ
/
Hꢂ0.86 A] and
/
˚
˚
Press, Oxford, 1984, pp. 791ꢀ838.
/
[14] D.S. Moore, S.D. Robinson, Adv. Inorg. Chem. 32 (1988) 171
(and references therein).
with isotropic thermal parameters, U(H)ꢂ
/
N). One of the two [O3SCF3]ꢃ anions was found
disordered (main image with occupancy factor 0.72(1)
for the fluorine atoms and occupancy factor 0.86(1) for
the oxygen atoms).
[15] N.W. Alcock, R.A. Henry, E.M. Holt, J.H. Nelson, N.E. Takach,
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1
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[17] R.N. Butler, V.C. Garvin, J. Chem. Soc. Perkin
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2
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[19] V.A. Ostrovskii, A.O. Koren, Heterocycles 53 (2000) 1421 (and
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[20] G.M. Sheldrick, SADABS, Program for Empirical Absorption
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 199639 for compound 5.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Correction, University of Gottingen, Germany, 1996.
¨
[21] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C.
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[22] G.M. Sheldrick, SHELXTL plus version 5.1 (Windows NT
version)-Structure Determination Package, Bruker Analytical X-
ray Instruments Inc., Madison, WI, 1998.
Cambridge CB2 1EZ, UK (Fax: ꢁ44-1223-336033; e-
/