Interannular conjugation in new iron(II) 5-aryl tetrazolate complexes

Article abstract of DOI:10.1021/om020283z

The synthesis of new Fe(II) 5-aryl tetrazolate complexes [CpFe(CO)(L)(N₄C-C₆H₄-CN)] (4) [L = CO (4a); PPh₃ (4b); P(OCH₃)₃ (4c); CN-2,6-Me₂C₆H₃ (4d)] is described. The target compounds were obtained by addition of sodium azide to the parent 1,4-dicyanobenzene complexes [CpFe(CO)(L)(NC-C₆H₄-CN)][O₃SCF₃] (2a-d). X-ray molecular structure of 4c confirms the predictions based on NMR (¹H, ¹³C) studies concerning the coplanarity between the tetrazole and phenyl rings, with consequent interannular conjugation effect. The multidentate nature of the tetrazole ring involves the presence of different sites that can undergo electrophilic attack; reaction of complexes 4a-c with methyl triflate afforded the methylated cationic complexes [CpFe(CO)(L)(CH₃-N₄C-C₆H₄-CN)][O ₃SCF₃], 5a-c, whose ¹H and ¹³C NMR spectroscopy data suggested out-of-plane rotation of the phenyl ring and subsequent large reduction of interannular conjugation. Noteworthy, the same effect was obtained in a reversible way by addition of triflic acid to 4a, affording the protonated cationic complex [CpFe(CO)₂(H-N₄C-C₆H₄-CN)][O₃ SCF₃], 6a, which was easily converted into its neutral precursor by treatment with a base.

Full text of DOI:10.1021/om020283z

3774
Organometallics 2002, 21, 3774-3781
In ter a n n u la r Con ju ga tion in New Ir on (II) 5-Ar yl
Tetr a zola te Com p lexes
Antonio Palazzi,*,† Stefano Stagni,† Silvia Bordoni,† Magda Monari,‡ and
Simona Selva‡
Dipartimento di Chimica Fisica ed Inorganica, Universita´ Bologna, Viale Risorgimento 4,
I-40136 Bologna, Italy, and Dipartimento di Chimica “G. Ciamician”, Universita´ Bologna,
Via Selmi 2, I-40126, Bologna, Italy
Received April 10, 2002
The synthesis of new Fe(II) 5-aryl tetrazolate complexes [CpFe(CO)(L)(N4C-C6H4-CN)]
(4) [L ) CO (4a ); PPh3 (4b); P(OCH3)3 (4c); CN-2,6-Me2C6H3 (4d )] is described. The target
compounds were obtained by addition of sodium azide to the parent 1,4-dicyanobenzene
complexes [CpFe(CO)(L)(NC-C6H4-CN)][O3SCF3] (2a -d ). X-ray molecular structure of 4c
confirms the predictions based on NMR (1H, 13C) studies concerning the coplanarity between
the tetrazole and phenyl rings, with consequent interannular conjugation effect. The
multidentate nature of the tetrazole ring involves the presence of different sites that can
undergo electrophilic attack; reaction of complexes 4a -c with methyl triflate afforded the
methylated cationic complexes [CpFe(CO)(L)(CH3-N4C-C6H4-CN)][O3SCF3], 5a -c, whose
1H and 13C NMR spectroscopy data suggested out-of-plane rotation of the phenyl ring and
subsequent large reduction of interannular conjugation. Noteworthy, the same effect was
obtained in a reversible way by addition of triflic acid to 4a , affording the protonated cationic
complex [CpFe(CO)2(H-N4C-C6H4-CN)][O3SCF3], 6a , which was easily converted into its
neutral precursor by treatment with a base.
In tr od u ction
dicyanobenzene as a suitable bridging ligand and ob-
tained mononuclear LnM(NCC6H4CN) and, in lower
yields, dinuclear complexes LnM(NC-C6H4-CN)MLn.
Focusing our attention on the study of the behavior of
the coordinated nitrile, we have observed its transfor-
mation into a tetrazole ring by reaction with NaN3. In
this paper we report the synthesis of mononuclear iron-
(II) complexes bearing 1,4-dicyanobenzene and their
transformation into the corresponding 5-aryl tetrazolate
complexes LnM(N4CC6H4CN). Furthermore we discuss
the conjugative properties of the obtained 5-aryl tetra-
zolate ligand, the modifications of its geometry, and
electronic properties upon addition of electrophilic spe-
cies. The obtained results indicate this ambidentate
anionic species [N4C-C6H4-CN]- as a suitable ligand
for the synthesis of dinuclear bridged complexes, which
will be the topic of the next paper.
Dinuclear and polynuclear metal complexes bridged
by polydentate ligands have received great attention in
recent years in connection with the design of molecular
electronic devices. In particular, dinuclear complexes
bridged by conjugated ligands have been extensively
studied because they can have interesting NLO applica-
tions1 or behave as molecular wires2 or molecular
switches.3 Dinuclear complexes of the type [(η5-C5H5)-
Ru(PPh3)2(µ-CN)Ru(NH3)5]3+, in which the cyanide ion
exhibits its “end-on” coordination ability, have been
reported to exhibit a large second-order response.1c Since
the asymmetry of the bridging cyanide ligand seems to
play a key role in these processes,4 we have recently
synthesized5 numerous pairs of isomeric complexes such
as CpL(CO)Fe-CN-M(CO)5 and CpL(CO)Fe-NC-
M(CO)5 (M ) Cr, Mo, W) (L ) CO; PPh3) with the aim
to study the different spectroscopic properties of the two
metal fragments, C- or N-coordinated to the cyanide.
As an extension of these studies, we considered 1,4-
Discu ssion
Cationic complexes such as [CpFe(CO)(L)(THF)][O3-
SCF3] (1) [L ) CO (a ), PPh3 (b), P(OCH3)3 (c), CN-2,6-
Me2C6H3 (d )] react slowly, at room temperature, with
a slight excess of 1,4-dicyanobenzene to afford the
relative nitrile compounds (Scheme 1). In these pre-
parative conditions prevalent formation of mononuclear
complexes [CpFe(CO)(L)(NCC6H4CN)]+ (2) [L ) CO (a ),
PPh3 (b), P(OCH3)3 (c), CN-2,6-Me2C6H3 (d )] is ob-
served, even with different stoichiometric ratios of the
starting reagents. Small amounts of dinuclear com-
plexes [Cp(CO)(L)Fe(NCC6H4CN)Fe(L)(CO)Cp]2+ (3) [L
) CO (a ), PPh3 (b), P(OCH3)3 (c)] are also recovered by
chromatography on an alumina column. Compounds 2
* Corresponding author. Tel: 0039-051-6446496. Fax: 0039-051-
2093690. E-mail: palazzi@ms.fci.unibo.it.
† Dipartimento di Chimica Fisica ed Inorganica.
‡ Dipartimento di Chimica “G. Ciamician”.
(1) (a) Long, N. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 21. (b)
Laidlaw, W. M.; Denning, R. G.; Verbiest, T.; Chauchard, E.; Persoons,
A. Nature 1993, 59, 363. (c) Coe, B. J .; Harris, J . A.; Asselberghs, I.;
Persoons, A.; J effery, J . C.; Rees, L. H.; Gelbrich, T.; Hursthouse, M.
B. J . Chem. Soc., Dalton Trans. 1999, 3617.
(2) Ward, M. D. Chem. Ind. 1996, 568.
(3) Ward, M. D. Chem. Ind. 1997, 640.
(4) Bignozzi, C. A.; Argazzi, R.; Chiorboli, C.; Scandola, F.; Dyer, R.
B.; Schoonover, J . R.; Meyer, T. J . Inorg. Chem. 1994, 33, 1652.
(5) Bordoni, S.; Busetto, L.; Colucci, P.; Palazzi, A.; Zanotti, V. J .
Organomet. Chem. 1997, 117, 545.
10.1021/om020283z CCC: $22.00 © 2002 American Chemical Society
Publication on Web 08/07/2002

New Iron(II) 5-Aryltetrazolate Complexes
Organometallics, Vol. 21, No. 18, 2002 3775
Sch em e 1
can be distinguished from 3 because they exhibit two
well-separated infrared weak absorption of the CN
stretching at ca. 2255 cm-1 for the coordinated cyanide
group and ca. 2235 cm-1 for the end one in CH2Cl2.
Compounds 2a -d react in methanol with a slight
excess of NaN3 at room temperature in a few hours, to
give the corresponding neutral tetrazolate derivatives
[CpFe(CO)(L)(N4C-C6H4-CN)] [L ) CO (4a ), P(C6H5)3
(4b), P(OCH3)3 (4c), CN-2,6-Me2C6H3 (4d )]. These com-
plexes can be easily purified by chromatography and
have been well characterized by IR and 1H and 13C NMR
spectroscopy.
disubstituted tetrazoles.9,10 Many of these methods
generally require high-boiling solvents (toluene or ac-
etonitrile) and prolonged reaction times (even 72 h). Our
reaction proceeds quickly at room temperature without
the presence of any other activating agent and occurs
under approximately heterogeneous conditions, the
solubility of NaN3 in methanol being very low. In a
different approach, nitrile complexes 2a -c are dissolved
in CH2Cl2 and solid NaN3 is successively added at room
temperature. In both cases (using methanol or dichlo-
romethane) complexes 4a -d are obtained in good yields.
The cyclization mechanism probably involves nucleo-
philic attack of the azide anion to the carbon of the
coordinated nitrile, affording tetrazole derivatives even
in the presence of coordinated isocyanides and carbonyl
groups, as observed in the reaction (performed in the
same conditions as complexes 2a -c) of [CpFe(CO)(CN-
2,6-Me2C6H3)(NCC6H4CN)]+ (2d ) with sodium azide, in
which the N-coordinated tetrazole derivative [CpFe-
(CO)(CN-2,6-Me2C6H3)(N4CC6H4CN)] (4d) was obtained.
In these conditions high chemoselectivity is observed
and no traces of isocyanato complexes such as [CpFe-
(CO)2(NCO)], whose preparation under similar condi-
tions was reported,11a,b have been detected. It is also
worthy of note, relative to complexes 2a -e, the high
activation to nucleophilic attack exhibited by the carbon
atom of the coordinated nitrile. The reaction however
proceeds only in the presence of electron-withdrawing
groups in the para phenyl position of the nitrile ligand;
no reaction was observed between the benzonitrile
derivative [CpFe(CO)2(NCC6H5)]+ and NaN3, whereas
the 4-nitrobenzonitrile complex [CpFe(CO)(P(OCH3)3)-
(NCC6H4NO2)]+ (2e) easily afforded the corresponding
tetrazole derivative [CpFe(CO)(P(OCH3)3)(N4CC6H4-
NO2)] (4e). It is well known12a-c,13 that tetrazolate
complexes are prepared by reaction of azido d8 com-
plexes with nitriles or isonitriles in which the intramo-
lecular cycloaddition reaction involves the formation of
an intermediate species possessing azide and nitrile
Recently, synthetic methodologies for the preparation
of 5-substituted tetrazoles have received great attention,
since it has been demonstrated that the tetrazole
functionality, which is metabolically stable and with a
pKa similar to that of carboxylic acids, can replace the
-COOH group in drug preparations, causing better oral
bioavailability and cell penetration.6a-c Typically, tet-
razoles are prepared from the corresponding nitriles by
reaction with a hydrazoic source (e.g., sodium azide and
ammonium chloride) in high-boiling solvents such as
DMF,7a toluene,7b or water7c at high temperature (90-
120 °C) and, generally, in the presence of Lewis acids
as activating agents. These synthetic routes could
involve evolution of hydrazoic acid, which is known to
be highly toxic, extremely explosive, and volatile. Al-
ternative strategies, involving different azide anion
sources such as trimethylsilyl azide in the presence of
dialkyltin oxide,8 have been developed and promising
results obtained for the conversion of amides into 1,5-
(6) (a) Bookser, B. Tetrahedron Lett. 2000, 41, 2805. (b) Butler, R.
N. In Comprehensive Heterocyclic Chemistry; Potts, K. T., Ed., Tetra-
zoles; Pergamon Press: Oxford, 1984; Vol. 5, pp 791-838. (c) Butler,
R. N. In Comprehensive Heterocyclic Chemistry II; Storr, R. C., Ed.,
Tetrazoles; Pergamon Press: Oxford, 1996; Vol. 4, pp 621-678, and
references therein.
(7) (a) Finnegan, W. A., Henry, R. A., Lofquist, R. J . Am. Chem.
Soc. 1958, 80, 3908. (b) Koguro, K.; Oga, T.; Mitsui, S.; Orita, R.
Synthesis 1998, 910. (c) Demko, Z. P.; Sharpless, K. B. J . Org. Chem.
2001, 66, 7945.
(9) Duncia, J . V.; Pierce, M. E.; Santella, J . B., III. J . Org. Chem.
1991, 56, 2395.
(10) Thomas, E. W. Synthesis 1993, 676.
(11) (a) Angelici, R. J .; Busetto, L. J . Am. Chem. Soc. 1969, 91, 3197.
(b) Busetto, L.; Graziani, M.; Palazzi, A. J . Organomet. Chem. 1971,
26, 261.
(12) For a review see: Fruhauf, H. W. Chem. Rev. 1997, 5233. (a)
Beck, W.; Fehlhammer, W. P.; Bock, H.; Bauder, M. Chem. Ber. 1969,
102, 3637. (b) Beck, W.; Burger, K.; Fehlhammer, W. P. Chem. Ber.
1971, 104, 1816.
(8) Wittenberger, S. J .; Donner, B. G. J . Org. Chem. 1993, 58, 4139.
(13) Paul, P.; Nag, K. Inorg. Chem. 1987, 26, 2969.

3776 Organometallics, Vol. 21, No. 18, 2002
Palazzi et al.
Sch em e 2
groups simultaneously coordinated. The iron atom of
complexes 2a -e is coordinatively saturated; conse-
quently an intermolecular mechanism, with direct nu-
cleophilic attack of the azide anion on the carbon at the
carbon of the coordinated nitrile, is preferred. An ana-
logous behavior was reported by Purcell14 and J ackson,15
but in those cases the cyclization reaction of nitrile com-
plexes with sodium azide occurred in aqueous media,
affording N-1 or N-2 tetrazole-coordinated Co(III) com-
plexes. Tetrazolate complexes have also been prepared
by anionic metatheses of organometallic moieties with
tetrazolate salts in relative high yields.16 Some recent
examples of supramolecular structures having tetrazole
rings, in which each of the four ring nitrogens can act
as a coordination site, were reported.17a-c In our case
nucleophilic attack of azide anion at the carbon of the
coordinated nitrile and successive cycloaddition reaction
should afford 1-N tetrazolate complexes. 1H and 13C
NMR spectroscopic data however show formation of the
less hindered 2-N derivatives (Scheme 2).
The isomerization reaction of 1-N tetrazolate com-
plexes in 2-N derivatives has been studied in the case
of tetrazolate complexes of cobalt(III),14,15,18 whose rate
of transformation was slow enough to be monitored by
spectrophotometric techniques. In our case we had no
evidence of the presence of the kinetic intermediate,
probably very labile because of the relevant bulkiness
of the metallic fragment. Indeed, 13C chemical shift
values (δC5 ≈ 165 ppm) of the tetrazole carbon clearly
indicate that in the synthesized compounds the metal
atom is bound to the 2-N tetrazole. As reported by
Butler,19a the chemical shift of C5 tetrazole has been
assumed as a probe to distinguish 1-N (δC5 ) 152-157
ppm) from 2-N (δC5 ) 162-167 ppm) derivatives in an
isomeric series of organic 5-aryltetrazoles (Scheme 3).
Sch em e 3
The hindrance of the substituents in 1-N isomers
causes out-of-plane rotation of the tetrazole ring with
respect to the phenyl ring resulting in reduced inter-
annular conjugation, which is, on the contrary, present
in the 2-N isomers and is increased by the presence of
electron-withdrawing groups on the phenyl ring. Inter-
annular conjugation makes ortho (relative to tetrazole
group, see Scheme 4) phenyl protons deshielded and
meta and para protons shielded in the 2-N isomer
relative to the 1-N isomer, resulting in a larger separa-
tion between the chemical shifts of ortho and meta
protons. The same indications are given by 13C NMR
data; it has been assumed that large differences between
δC3′ and δC2′, in the range 2.9-3.7 ppm, involve
interannular conjugation.19a-c All these features were
observed in the complexes prepared by us, confirming
the formation of a conjugated 5-aryltetrazolate moiety
(see Table 1).
All spectra present a large difference between the
phenyl proton chemical shifts, for example, relative to
complex 4a , ∆δH(H0-Hm) ) 0.49 ppm and ∆δC(C3′-C2′)
) 5.7 ppm. Such a large separation of δC values, not
observed in organic tetrazole derivatives, could indicate
a strong interannular conjugation with the participation
in the delocalized system of the d-electrons of the metal
atom. The presence of a non-negligible back-bonding
interaction to the tetrazolate ligand is also inferred by
the analysis of the IR data (see Table 1), which show
carbonyl bands at high wavenumbers, 2065 and 2020
cm-1 in CH2Cl2, in 4a , with respect to parent compounds
such as [CpFe(CO)2X]. These values can be compared,
(14) Ellis, W. R.; Purcell, W. L. Inorg. Chem. 1982, 21, 834.
(15) J ackson, W. G.; Cortez, S. Inorg. Chem. 1994, 33, 1921.
(16) Alcock, N. W.; Henry, R. A.; Holt E. M.; Nelson, J . H.; Takach,
N. E. J . Am. Chem. Soc. 1980, 102, 2968.
(17) (a) Bhandari, S.; Mahon, M. F.; Molloy, K. C.; Palmer, J . S.;
Sayers, S. F. J . Chem. Soc., Dalton Trans. 2000, 1053. (b) Bhandari,
S.; Frost, G. C.; Hague, C. E.; Mahon, M. F.; Molloy, K. C. J . Chem.
Soc., Dalton Trans. 2000, 663. (c) Bhandari, S.; Mahon, M. F.;
McGinley, J . G.; Molloy, K. C.; Roper, C. E. E. J . Chem. Soc., Dalton
Trans. 1998, 3425.
(19) (a) Butler, R. N.; McEvoy, T. M. J . Chem. Soc., Perkin Trans.
2 1978, 1087. (b) Fraser, R. R.; Haque, K. E. Can. J . Chem. 1968, 46,
2855. (c) Begtrup, M. Acta Chem. Scand. 1973, 27, 301.
(18) Purcell, W. L. Inorg. Chem. 1983, 22, 1205.

New Iron(II) 5-Aryltetrazolate Complexes
Organometallics, Vol. 21, No. 18, 2002 3777
F igu r e 1. ORTEP plot of the molecular structure of 4c. Thermal ellipsoids are drawn at the 30% probability level.
Sch em e 4
Ta ble 1. Selected NMRa a n d IRb Da ta of
Com p lexes 4a -d a n d 5a -c (for n u m ber in g sch em e
see Sch em e 3)
Ta ble 2. Cr ysta l Da ta a n d Exp er im en ta l Deta ils
for [Cp F e(CO)(P (OCH3)3(N4CC6H4CN)] (4c)
formula
M
C17H18Fe1N5O4P1
443.18
δ(C5)
entry (ppm)
∆(δHo-δHm
)
∆(δC3′-δC2′) CO absorption
(cm-1
)
temperature, K
wavelength, Å
cryst symmetry
space group
a, Å
293(2)
(ppm)
(ppm)
0.71073
monoclinic
P21/c
7.6329(4)
18.0130(8)
14.7402(7)
90
98.927(2)
90
2002.1(2)
4
4a
5a
4b
5b
4c
5c
4d
165.1
157.2
164.4
156.1
164.2
156.4
164.4
0.48
0.07
0.30
0.16
0.49
0.13
0.49
5.67
2.69
5.71
3.09
5.79
2.68
2065; 2020
2074; 2029
1973
1987
1985
b, Å
c, Å
1999
2004
R, deg
â, deg
a
1H and 13C NMR experiments were performed using CDCl3
γ, deg
cell volume, Å3
Z
b
as solvent. CH2Cl2 as solvent.
in the same solvent, with the ones relative to cationic
species such as [CpFe(CO)2(THF)]+ (2067 and 2024
D
c, Mg m-3
1.470
0.866
912
µ(Mo KR), mm-1
F(000)
cm-1) or neutral [CpFe(CO)2(CN)] (2054 and 2014 cm-1
)
cryst size, mm
θ limits, deg
0.45 × 0.40 × 0.30
2.66-29.99
24 324 ((h, (k, (l)
5846
and [CpFe(CO)2(CNW(CO)5)] (2064 and 2024 cm-1).5
π-electron delocalization between the tetrazole and
phenyl rings, as evidenced by NMR data, requires
coplanarity, and evidence for this has been looked for
in an X-ray diffraction study on the complex [CpFe(CO)-
(P(OCH3)3(N4CC6H4CN)] (4c). The molecular stereoge-
ometry, Figure 1, shows the expected structure, with
the iron atom exhibiting a pseudotetrahedral asym-
metric coordination. The crystal is centric and therefore
contains the racemic mixture. The p-cyanophenyltetra-
zolate ligand is coordinated through N(2) and the Fe-N
bond, 1.950(2) Å long, and is indicative of a substantially
no. of reflns collected
no. of unique obsd reflns
[Fo > 4σ(Fo)]
goodness of fit on F2
R1(F),a wR2(F2)b
weighting scheme
largest diff peak and hole, e Å-3
0.795
0.0369, 0.0811
a ) 0.0457, b ) 0.0000b
0.347 and -0.226
a
b
2
R1 ) ∑||Fo| - |Fc|/∑|Fo|. wR2 ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2
where w ) 1/[ σ2(Fo2) + (aP)2 + bP] where P ) (Fo + 2Fc2)/3.
2
σ character, especially if compared to the Fe-C (carbo-
nyl) interaction, 1.758(3) Å.The presence of a π-bond

3778 Organometallics, Vol. 21, No. 18, 2002
Palazzi et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 4c
philic addition. In this case a significant rotation of the
tetrazole ring out of the plane of the phenyl ring should
be observed. Reaction of complexes [CpFe(CO)(L)(N4-
CC6H4CN)] (4a , 4b, 4c) with CH3O3SCF3 afforded the
methylated cationic complexes [CpFe(CO)(L)(CH3N4-
CC6H4CN)][O3SCF3] (5a , 5b, 5c), in which the addition
of the methyl group occurred at 4-N (see Scheme 4).22
This feature was evidenced by the upfield shift of δC5,
which falls at about 157-159 ppm, as expected in
tetrazoles having a substituent on the nitrogen adjacent
to the tetrazole carbon.23a
Fe(1)-P(1)
Fe(1)-N(2)
Fe(1)-C(9)
C(1)-C(3)
C(2)-C(6)
2.1499(7)
1.950(2)
1.758(3)
1.466(3)
1.446(3)
N(5)-C(2)
P(1)-O(2)
P(1)-O(3)
P(1)-O(4)
1.131(3)
1.627(2)
1.588(2)
1.573(2)
C(9)-Fe(1)-N(2)
C(9)-Fe(1)-P(1)
94.75(9)
93.19(8)
N(2)-Fe(1)-P(1)
93.63(5)
Ta ble 4. Som e C(tetr a zole)-C(p h en yl) Dista n ces
a n d Cor r esp on d in g In ter p la n a r An gles
Appreciable chemical shift variations are also ob-
served in 1H NMR spectra, in which the separation of
the phenyl proton signals becomes significantly smaller.
For example, the difference of 0.48 ppm between the
two phenyl signals in [CpFe(CO)2(N4CC6H4CN)] (4a )
becomes 0.07 ppm in the methylated compound [CpFe-
(CO)2(CH3N4CC6H4CN)][O3SCF3] (5a ); analogous be-
havior is observed in the phosphine derivatives (5b, 5c).
Furthermore, the difference between the chemical shift
of the phenyl C2′ and C3′ is reduced in the cationic
methylated complex (∆ ) 2.69 ppm in 5a ) with respect
to the starting neutral derivative (∆ ) 5.67 ppm in 4a ).
All these data strongly support removal of interannular
conjugation due to out-of-plane rotation of the tetrazole
ring in the methylated compounds 5a -c (see Table 1).
We have considered stimulating studying the effect of
proton addition to this kind of complexes. Addition to
tetrazolate complex 4a of stoichiometric quantities of
HO3SCF3 at low temperature has not resulted in de-
complexation and formation of free organic tetrazole
HN4CC6H4CN. On the contrary, we have observed
proton addition with formation of the cationic complex
[CpFe(CO)2(HN4CC6H4CN)][O3SCF3] (6a , see Scheme
4), as shown by the shift of carbonyl absorptions to
higher wavenumbers, 2078 and 2036 cm-1 versus 2065
and 2020 cm-1, of the correspondent carbonyl bands of
the starting neutral derivative (4a ). Organic 5-aryl
tetrazoles show a fast proton annular tautomerism;
comparison of tetrazole carbon chemical shifts between
1-N methyl and 2-N methyl isomers has been used to
monitor the relative percentage of the two isomers at
equilibrium.23b In the protonated complex (6a ) we have
observed general and significant changes of the 13C
chemical shifts, in particular, an upfield shift of the
tetrazole C5 chemical shift, 159.5 ppm versus 165.1 ppm,
of the neutral precursor (4a ), indicating a preferential
protonation of 4-N. We also note an upfield shift of C1′,
the ipso phenyl carbon bonded to the tetrazole ring, ∆δ
) 6.7 ppm, whereas the nitrile carbon is deshielded by
3.7 ppm. Moreover, we observe a significant decrease
of the value of ∆(δC3′-δC2′), even if smaller than that
observed in the analogous methylated complex (5a ). A
smaller separation between the phenyl proton chemical
shifts is also observed in the 1H NMR spectra, ∆δ )
0.152 ppm in 6a versus 0.478 ppm of the precursor 4a .
As evidenced before, these data indicate a preferential
protonation of 4-N, suggesting partial out-of-plane rota-
tion of the tetrazole ring with loss, or massive reduction,
dihedral
C-C (Å) angle (deg)
ref
[CpFe(CO)(P(OMe)3)(N4C-4-
CN-C6H4)]
1.467(2)
3.3(2)
this work
[Pd(N-N-S)(N4C-4-OMeC6H4] 1.467(6)
10.4(8)
4.4(8)
9.4(7)
24
[Sn(n-Bu)3(N4C-4-py)(H2O)]
[Sn(Et)3(N4C-3-py)(H2O)]
[Sn(Et)3(N4C-4-py)]
1.468(9)
1.463(8)
1.465(7)
17b
17b
17b
19.8(7)
component in the Fe-N interaction can be postulated
by comparison with other experimental values of Fe-
(II)-N(sp2) distances, for example, a series of octahedral
complexes containing borylated dioximate ligands in the
equatorial plane and pyridines in the axial positions.20
The Fe-N(dioxime) and Fe-N(pyridine) distances are
found in the ranges 1.88-1.90 and 2.00-2.06(1) Å,
respectively. The tetrazole ring is flat, with deviations
from the average plane in the range +0.004, -0.003,
and regular. In fact N-N and N-C distances are not
distinguishable [range 1.319-1.338(2), average 1.329-
(3) Å]. The C(tetrazole)-C(phenyl) inter-ring distance
is 1.467(2) Å, and the dihedral angle between the rings
is 3.3(2)°. Also the phenyl ring does not exhibit measur-
able deviations from a regular geometry, despite being
para-disubstituted [C-C distances in the range 1.373-
1.388(3), average 1.380(3) Å]. The flat conformation of
the ligand is indicative of inter-ring conjugation, but the
C(tetrazole)-C(phenyl) distance does not seem to be
significantly dependent on the inter-ring angle, as
illustrated by the examples in Table 4.
The delocalization showed by 5-aryl tetrazole moiety
in these mononuclear complexes led us to consider this
ligand an ideal system to allow electronic communica-
tion between two metal atoms in dinuclear complexes
having this ligand in a bridging bonding mode. Launay
et al. reported an example21 of a dinuclear complex
having 4-cyanophenylimidazole as bridging ligand, in
which the end-to-end Ru2+fRu3+ electron transfer
across this bridge can be transiently switched off by a
very short flash of light that makes the coplanar phenyl
and imidazolyl rings twisted. In our case the 4-cy-
anophenyltetrazolate anion, NC-C6H4-CN4-, being
capable of pluricentric interactions with all the ring
nitrogen atoms, could represent a more versatile ligand
with respect to 4-cyanophenylimidazole; thus we con-
sidered very interesting to investigate the possibility of
removing interannular conjugation by addition of elec-
trophilic species to the nitrogen atoms of the tetrazole
ring. We supposed the ring nitrogen in position 4 of the
ring, which suffers less from the steric encumbrance of
the metal fragment, as the most accessible to electro-
(22) In some cases, addition of methyl iodide to Ru(II) tetrazolate
complexes was reported to cause cleavage of an organometallic
fragment. See: Chang, K. H.; Lin, Y. C.; Liu, Y. H.; Wang Y. J . Chem.
Soc., Dalton Trans. 2001, 3154.
(20) Vernik, I.; Stynes, D. V. Inorg. Chem. 1996, 35, 6210.
(21) Hatzidimitriou, A.; Gourdon, A.; Devillers, J .; Launay, J . P.;
Mena, E.; Amouyal, E. Inorg. Chem. 1996, 35, 2212.
(23) (a) Butler, R. N.; Garvin, V. C. J . Chem. Soc., Perkin Trans. 1
1981, 390. (b) Butler, R. N.; Garvin, V. C. J . Chem. Soc., Perkin Trans.
2 1984, 721.

New Iron(II) 5-Aryltetrazolate Complexes
Organometallics, Vol. 21, No. 18, 2002 3779
[O3SCF 3] [L ) CO (2a ), P P h 3 (2b), P (OMe)3 (2c), CN-2,6-
Me2C6H3 (2d )]. A solution of the complexes 1a -d (0.500 g)
in CH2Cl2 was treated with a slight excess (1.1 equiv) of 1,4-
dicyanobenzene. The mixture was stirred at rt for 12 h.
Filtration over Celite and evaporation to dryness afforded a
residue, which was purified by column chromatography on
alumina using a dichloromethane-acetonitrile (5:1) mixture.
The complexes 2a -d were usually obtained as a second
fraction after discharging starting reagents or the compound
[Fe2Cp2(CO)4] in the case of 2a . Atom labeling for complexes
2a -d should be referred to Scheme 1. 2a : Yield: 0.420 g, 72%,
of interannular conjugation. Noteworthy, this feature
occurs by addition of electrophiles smaller than the
methyl group and in a perfectly reversible way; indeed,
addition of a base quantitatively re-forms the starting
complex [CpFe(CO)2(N4C-C6H4-CN)] (4a ), in which
tetrazole and phenyl rings are coplanar.
Con clu sion s
The synthesis of organometallic complexes having a
5-(4-cyanophenyl)tetrazolate ligand, by a simple and
selective addition of the azide anion to the relative
nitrile cationic complexes, represents an interesting
route to the formation of a tetrazolate ring in which the
transformation of the activated nitrile is carried out in
very mild conditions. The NMR data and X-ray diffrac-
tion studies have established that in these complexes
the metal is bonded to the 2-N atom of the tetrazole ring,
for steric reasons. This feature involves coplanarity
between the tetrazole and the phenyl ring and, conse-
quently, a strong interannular conjugation, which can
be removed by addition of electrophilic agents (CH3+ or
H+) to the nitrogen adjacent to the tetrazole carbon;
moreover, the proton addition is reversible by addition
of a base. The just described properties of this ligand
could permit an efficient electronic communication
between metal centers in dinuclear complexes. The
reversible removal of this communication, by proton
addition-elimination, should make these complexes
good models of pH-dependent molecular switches. The
synthesis of cyanophenyl tetrazole bridged dinuclear
complexes and the description of their spectroscopic and
electronic features will be reported in a successive paper.
3
yellow oil. NMR: δH(CDCl3) 8.14 (2H, d, J HH ) 15 Hz), 7.84
3
(2H, d, J HH ) 15 Hz), and 5.68 (5H, s, Cp) ppm. IR (CH2Cl2)
ν
max (cm-1): 2235w (CN), 2079s (CO), 2038s (CO). Anal. Calcd
for C16H9N2FeO5SF3: C, 42.2; H, 1.98; N, 6.16. Found: C, 42.5;
H, 2.01; N,6.2. 2b: Yield: 0.200 g, 37%, orange oil. NMR: δH
(CDCl3) 7.6-7.2 (19H, m, PPh3, C6H4), 5.05 (5H, s, Cp) ppm;
3
δC (CDCl3) 216.68 (CO, d, J CP ) 28 Hz), 133.86 (PPh3, d),
132.23 (PPh3, s), 132.7 (PPh3, s), 130.1 (PPh3, d), 134.6 (C3′),
133.0 (C2′), 134.5 (C1′), 117.8-117.7 (C5′-C6′), 115. 5 (C4′), 86.3
(Cp). IR (CH2Cl2) νmax (cm-1): 2254w (CN coord.), 2236w (CN),
1993s (CO). Anal. Calcd for C33H24N2FeO4PSF3: C, 57.5; H,
3.49; N, 4.06. Found: C, 57.3; H, 3.40; N, 3.9. 2c: Yield: 0.190
3
g, 40%, orange oil. NMR: δH (CDCl3) 7.95 (2H, d, J HH ) 8
3
Hz), 7.78 (2H, d, J HH ) 8 Hz), 5.13 (5H, s, Cp), 3.81 (9H,
3
3
(OCH3)3, d, J HP ) 11 Hz); δC (CDCl3) 214.0 (CO, d, J CP ) 45
Hz), 134.6 (C3′), 133.5 (C2′), 133.7 (C1′), 118.5-118.1 (C5′-C6′),
3
115.3 (C4′), 85.0 (Cp), 54.44-54.38 (OCH3, d, J CP ) 5 Hz). IR
(CH2Cl2) νmax (cm-1): 2254w (CN coord.), 2235w (CN), 2006s
(CO). Anal. Calcd for C18H18N2FePO7SF3: C, 39.3; H, 3.27; N,
5.1. Found: C, 39.2; H, 3.30; N, 5.4. 2d : Yield: 0.310 g, 82%,
3
yellow oil. NMR: δH (CDCl3) 7.92 (2H, d, J HH ) 9 Hz), 7.82
(2H, d, J HH ) 6 Hz), 7.35-7.19 (m, 3H, C6H3-2,6 (Me)2), 5.30
3
(5H, s, Cp), 2.48 (s, 6H, C6H3-2,6(CH3)2); δC (CDCl3) 212.9 (CO),
162.9 (CtN-), 136.1-129.0 (C6H4: C6H3-2,6-Me) 118.6 (C1′),
117.8 (C6′), 115.3 (C4′), 85.5 (Cp), 19.3 (Me). IR (CH2Cl2) νmax
(cm-1): 2258w (CN coord.), 2234w (CN), 2159s (CtN-), 2027s
(CO). Anal. Calcd for C24H18N3FeO4SF3: C, 51.7; H, 3.23; N,
7.5. Found: C, 51.65; H, 3.20; N, 7.3. In the case of complexes
2a -c, further elution with acetonitrile as eluent afforded small
amounts of dinuclear derivatives 3a -c, as shown by IR
spectroscopy with single CN absorptions at ca. 2255 cm-1 and
Exp er im en ta l Section
Ma ter ia ls a n d P r oced u r es. All reactions with organome-
tallic reagents or substrates were carried out under argon
using standard Schlenk techniques. Solvents were dried and
distilled under nitrogen prior to use. The prepared derivatives
were characterized by elemental analysis and spectroscopic
methods. IR spectra were recorded with a Perkin-Elmer
Spectrum 2000 FT-IR spectrometer. 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 characterization purposes. Elemental
analyses were performed on a ThermoQuest Flash 1112 Series
EA instrument. 1,4-Dicyanobenzene and 4-nitrobenzonitrile
were purchased from Aldrich and used as received. Cationic
precursors such as [CpFe(CO)(L)(THF)]+ [L ) CO (1a ), PPh3
(1b), P(OMe)3 (1c), CN-2,6-Me2C6H3 (1d )] were prepared from
the corresponding iodides25 by reaction with a stoichiometric
amount of Ag(CF3SO3) in a THF solution (15 mL) at room
temperature. Filtration over Celite and subsequent evapora-
tion to dryness afforded a mixture, which was used without
any further purification. All reactions were monitored by IR
spectroscopy. Petroleum ether (Etp) refers to a fraction of bp
60-80 °C. Typically, all chromatographies were performed on
an alumina column (diameter 1.5 cm; height 15 cm) under
argon atmosphere and using dichloromethane-acetonitrile
mixtures as eluent.
1
by H NMR spectra (CDCl3), in which a singlet in the region
7.40-8.10 ppm was observed.
P r ep a r a tion of [Cp F e(CO)(L)(NCC6H4NO2)][O3SCF 3]
(2e) [L ) P (OMe3)3]. This complex was prepared in the same
way as shown for compounds 2a -d , using 4-nitrobenzonitrile
in place of terephthalonitrile and yielding 0.164 g, 71%, of 2e
as a yellow oil. NMR: δH (CDCl3) 8.31 (br, 2H), 8.10 (br, 2H),
5.18 (s, 5H, Cp), 3.76 (br, 9H, Me). IR (CH2Cl2) νmax (cm-1):
2255w (CN coord.), 2003s (CO), 1521s (NO2). Anal. Calcd for
C
17H18N2FePO9SF3: C, 35.8; H, 3.15; N, 4.9. Found: C, 35.7;
H, 3.13; N, 5.1.
Cycliza tion Rea ction s: Syn th esis of [Cp F e(CO)(L)-
(N4CC6H4CN)] [L ) CO (4a ), P P h 3 (4b), P (OMe)3 (4c), CN-
2,6-Me2C6H3 (4d )]. Numbering of complexes 4a -d should be
referred to Scheme 3. 4a : To a solution of 2a (0.500 g, 1.10
mmol) in dichloromethane (20 mL) at room temperature was
added an excess of NaN3 (0.210 g, 3.20 mmol). The resulting
suspension was stirred at rt for 10 h. The mixture was filtered
on Celite and evaporated to dryness. Subsequent chromatog-
raphy of the residue on Al2O3 with CH2Cl2 as eluent gave, only
in this case, a first red fraction of [Fe2Cp2(CO)4], which was
discharged. Further elution with a mixture CH2Cl2-CH3CN
(2:1, v/v) afforded the complex 4a (0.291 g, 76%), obtained as
a
yellow microcrystalline powder. NMR: δH(CDCl3) 8.17
Typ ica l P r oced u r e for th e P r ep a r a tion of 1,4-Dicy-
a n oben zen e Ir on Com p lexes [Cp F e(CO)(L)(NCC6H4CN)]-
3
3
(2Hortho, d, J HH ) 8 Hz), 7.70 (2Hmeta, d, J HH ) 8 Hz), 5.29
(5H, s, Cp), δC(CDCl3) 211.2 (CO), 165.1 (C5), 134.4 (C1′), 133.0
(C3′), 127.3 (C2′), 119.5 (CN), 112.4 (C4′), 86.5 (Cp). IR (CH2-
Cl2) νmax (cm-1): 2230w (CN), 2065s (CO), 2020s (CO), 1615w
(CdN). Anal. Calcd for C15H9N5FeO2: C, 51.8; H, 2.59; N, 20.1.
(24) Das, R.; Paul, P.; Nag, K.; Venkatsubramanian, K. Inorg. Chim.
Acta 1991, 185, 221.
(25) Piper, T. S.; Wilkinson, G. J . Inorg. Nucl. Chem. 1956, 2, 38.

3780 Organometallics, Vol. 21, No. 18, 2002
Palazzi et al.
Found: C, 51.7; H, 2.60; N, 20.4. 4b: This complex was
prepared as 4a , using methanol as solvent. Complex 4b (0.223
g, 55%) was obtained as a red microcristalline powder by
chromatography on alumina eluting with a CH2Cl2-CH3CN
cases no trace of undesired species arising from dimerization
of cationic precursors was detected. 5b: Yield: 0.131 g, 98%,
dark red oil. NMR: δH (CDCl3) 7.84 (2Hortho, d, 3J HH ) 10 Hz),
3
7.67 (2Hmeta, d, J HH ) 10 Hz), 7.49-7.28 (PPh3, m), 4.89 (5H,
3
3
(5:1, v/v) mixture. NMR: δH (CDCl3) 7.91 (2Hortho, d, J HH ) 7
s, Cp), 3.91 (3H, s, CH3); δC (CDCl3) 217.7 (CO, d, J CP ) 28
3
Hz), 7.61 (2Hmeta, d, J HH ) 7 Hz), 7.49-7.28 (PPh3, m), 4.71
Hz), 156.1 (C5), 133.8 (PPh3, d), 132.4 (PPh3, d), 131.9 (PPh3,
s), 129.5 (PPh3, d), 133.6 (C3′), 130.5 (C2′), 126.3 (C1′), 118.3
(C4′), 116.3 (CN), 85.2 (Cp), 37.0 (N-CH3). IR (CH2Cl2) νmax
(cm-1): 2235w (CN), 1987s (CO). Anal. Calcd for C34H27N5-
FePO4SF3: C, 54.7; H, 3.62; N, 9.4. Found: C, 54.9; H, 3.67;
N, 9.6. 5c: Yield: 0.133 g, 97%, orange oil. NMR: δH (CDCl3)
(5H, s, Cp); δC (CDCl3) 219.6 (CO, d, 3J CP ) 28 Hz), 164.4 (C5),
133.7 (PPh3, d), 133.3 (PPh3, s), 130.9 (PPh3, s), 128.8 (PPh3,
d), 132.6 (C3′), 126.9 (C2′), 134.7 (C1′), 111.6 (C4′), 119.5 (CN),
84.5 (Cp). IR (CH2Cl2) νmax (cm-1): 2229w (CN), 1973s (CO),
1615w (CdN). Anal. Calcd for C32H24N5FeO: C, 69.8; H, 4.36;
N, 12.7. Found: C, 69.9; H, 4.40; N, 13.0. 4c: The same
procedure as 4a was adopted, using methanol (15 mL) as
solvent. The product was obtained (0.209 g, 52%) eluting with
a CH2Cl2-CH3CN (5:1, v/v) mixture and was successfully
recrystallized from a dichloromethane solution layered with
petroleum ether at rt, affording red crystals of 4c. NMR: δH
3
3
7.95 (2Hortho, d, J HH ) 7 Hz), 7.82 (2Hmeta, d, J HH ) 10 Hz),
3
4.98 (5H, s, Cp), 4.19 (3H, s, CH3), 3.70 (9H, (OCH3)3, d, J HP
) 11 Hz); δC (CDCl3) 215.8 (CO, d, J CP ) 44 Hz), 156.4 (C5),
3
133.5 (C3′), 130.845 (C2′), 126.4 (C1′), 118.3 (C4′), 116.2 (CN),
84.6 (Cp), 54.1 (OCH3), 37.3 (N-CH3). IR (CH2Cl2) νmax (cm-1):
2235w (CN), 1999s (CO). Anal. Calcd for C19H21N5FePO7SF3:
C, 37.5; H, 3.46; N, 11.5. Found: C, 37.6; H, 3.49; N, 11.8.
3
3
(CDCl3) 8.18 (2Hortho, d, J HH ) 8 Hz), 7.69 (2Hmeta, d, J HH
)
8 Hz), 4.91 (5H, s, Cp), 3.63 (9H, (OCH3)3, d, 3J HP ) 11 Hz); δC
P r ep a r a tion of P r oton a ted Com p lex [Cp F e(CO)(L)(4-
HN4C-C6H4-CN)] (6a ) [O3SCF 3] [L ) CO]. Numbering for
complex 6a is shown in Scheme 4. To a stirred solution of 4a
(0.500 g, 1.44 mmol) in CH2Cl2 (20 mL) was added dropwise
HOSO2CF3 (0.13 mL, 1.44 mmol, diluted in 5 mL of CH2Cl2)
at -60 °C. After 30 min the mixture was allowed to warm at
rt and the solvent removed in vacuo. The resulting mixture
was redissolved in dichloromethane and layered with diethyl
ether, causing the formation of yellow fine needles identified
as the protonated complex 6a (0.651 g, 91%). NMR: δH (CD3-
3
(CDCl3) 217.8 (CO, d, J CP ) 45 Hz), 164.2 (C5), 132.7 (C3′),
126.9 (C2′), 134.6 (C1′), 111.7 (C4′), 119.3 (CN), 83.9 (Cp), 53.1
(OCH3, d, J CP ) 5 Hz). IR (CH2Cl2) νmax (cm-1): 2229w (CN),
3
1985s (CO), 1616w (CdN). Anal. Calcd for C17H18N5FePO4: C,
46.0; H, 4.06; N, 15.8. Found: C, 46.1; H, 4.10; N, 15.5. 4d : A
workup analogous with that for complexes 4a -c afforded a
mixture, which was chromatographed on an alumina column.
Elution with a CH2Cl2-CH3CN (1:1, v/v) mixture gave the
product 4d as a yellow oil (0.260 g, 64%). NMR: δH (CDCl3)
3
3
3
3
8.16 (2Hortho, d, J HH ) 9 Hz), 7.67 (2Hmeta, d, J HH ) 6 Hz),
7.26-7.11 (m, 3H, C6H3-2,6 (CH3)2), 5.08 (s, 5H, Cp), 2.39 (s,
6H, C6H3-2,6(CH3)2); δC (CDCl3) 215.8 (CO), 170.5 (CtN-),
164.4 (C5), 135.2-126.9 (C6H4: C6H3-2,6-Me), 119.4 (-CtN),
111.8 (C4′), 84.26 (Cp), 18.9 (C6H3-2,6-Me). IR (CH2Cl2) νmax
(cm-1): 2229w (CN), 2148s (CtN-), 2004 s (CO), 1615w (Cd
N). Anal. Calcd for C23H18N6FeO: C, 61.3; H, 4.0; N, 18.7.
Found: C, 61.2; H, 3.95; N, 19.0.
CN) 8.14 (2Hortho, d, J HH ) 9 Hz), 7.99 (2Hmeta, d, J HH ) 9
Hz), 5.47 (5H, s, Cp); δC (CDCl3) 209.5 (CO), 159.4 (C5), 133.7
(C3′), 128.7 (C2′), 127.6 (C1′), 118.5 (C4′), 116.1 (CN), 86.9 (Cp).
IR (CH2Cl2) νmax (cm-1): 2235w (CN), 2078s (CO), 2036s (CO).
Anal. Calcd for C16H10N5FeO5SF3: C, 38.6; H, 2.01; N, 14.1.
Found: C, 38.7; H, 1.99; N, 13.9. Addition of a stoichiometric
amount of proton sponge to a solution of 6a in acetonitrile re-
forms quantitatively the neutral precursor 4a .
Syn t h esis of [Cp F e(CO)(L)(N4CC6H 4NO2)] (4e) [L )
P (OMe)3]. A 0.164 g (0.29 mmol) sample of 2e, dissolved in
CH3OH (15 mL), was treated with an excess of NaN3 (100 mg,
1.54 mmol) for 10 h at room temperature. Following the same
procedure as for complexes 2a -d , the product 4e was obtained
by chromatography on an alumina column eluting with a CH2-
Cl2-CH3CN (5:1, v/v) mixture and yielding 97 mg, 72%, of the
complex 4e as a dark yellow microcrystalline powder. NMR:
X-r a y Diffr a ction Exp er im en ts a n d Str u ctu r e Deter -
m in ation of [CpFe(CO)P (OCH3)3)(N4CC6H4CN)] (4c). Crys-
tal data and other experimental details for [CpFe(CO)-
(P(OCH3)3)(N4CC6H4CN)] are reported in Tables 2 and 3. The
X-ray diffraction data were measured on a Bruker AXS
SMART 2000 diffractometer, equipped with a CCD area
detector, using Mo KR radiation (λ ) 0.71073 Å) at room
temperature. Cell dimensions and orientation matrixes were
initially determined from least-square refinements on reflec-
tions measured in three sets of 20 exposures collected in three
different ω regions and eventually refined against all reflec-
tions. Full spheres of the diffraction space were measured by
0.3° ω steps, 20 s exposures with a sample-detector distance
kept at 5.0 cm. Intensity decay was monitored by re-collecting
the initial 50 frames at the end of each data collection and
analyzing the duplicate reflections. The collected frames were
processed for integration by using the program SAINT, and
an empirical absorption correction was applied using SAD-
ABS26 on the basis of the Laue symmetry of the reciprocal
space. The structure was solved by direct methods (SIR 97)27
and subsequent Fourier syntheses and refined by full-matrix
least-squares calculations on F2 (SHELXTL)28 using anisotro-
pic thermal parameters for all non hydrogen atoms. The three
oxygen atoms of the phosphite ligand were found disordered
over two sites, and an occupancy factor of 0.82 was refined for
their main images. All hydrogen atoms except for the methyl
H atoms were located experimentally, but their positions were
3
3
δH (CDCl3) 8.29 (2Hortho, d, J HH ) 9 Hz), 8.27 (2Hmeta, d, J HH
3
) 7 Hz), 4.94 (s, 5H, Cp) 3.67 (d, 9H, (OCH3)3, J HP ) 11 Hz);
δC (CDCl3) 218.0 (d, CO, 3J CP ) 45 Hz), 164.3 (C5), 148.1 (C4′),
136.7 (C1′), 127.4 (C3′), 124.6 (C2′), 84.2 (Cp), 53.5 (d, OCH3,
3J CP ) 5 Hz). IR (CH2Cl2) νmax (cm-1): 1985s (CO), 1606w (-Cd
N-), 1521s (NO2). Anal. Calcd for C16H18N5FePO6: C, 41.4;
H, 3.89; N, 15.1. Found: C, 41.5; H, 3.91; N, 15.3.
Meth yla tion Rea ction s: Syn th esis of [Cp F e(CO)(L)(4-
MeN4C-C6H4-CN)][O3SCF 3] [L ) CO (5a ), P P h 3 (5b),
P (OMe)3 (5c)]. Numbering for complexes 5a -c is shown in
Scheme 4. 5a : A solution of 4a (0.101 g, 0.29 mmol) in CH2Cl2
was treated with CH3O3SCF3 (0.033 mL, 0.29 mmol) with
stirring at -50 °C for 30 min. The mixture was then allowed
to warm at rt and stirred for an additional 3 h. Evaporation
of solvent and chromatography of the residue on an alumina
column with CH2Cl2 as solvent afforded a first red fraction of
[Fe2(Cp)2(CO)4], which was discharged. Elution with a CH2-
Cl2-CH3CN (5:1, v/v) mixture gave the complex 5a (98 mg,
67%), obtained as a pale brown oil. NMR: δH (CDCl3) 7.94
3
3
(2Hortho, d, J HH ) 7 Hz), 7.87 (2Hmeta, d, J HH ) 10 Hz), 5.45
(5H, s, Cp), 4.20 (3H, s, CH3); δC (CDCl3) 209.5 (CO), 157.2
(C5), 133.5 (C3′), 130.8 (C2′), 130.0 (C1′), 126.3 (C4′), 116.5 (CN),
87.5(Cp), 37.4 (CH3). IR (CH2Cl2) νmax (cm-1): 2235w (CN),
2075s (CO), 2031s (CO). Anal. Calcd for C17H12N5FeO5SF3: C,
39.9; H, 2.25; N, 13.7. Found: C, 40.0; H, 2.29; N, 14.0.
Compounds 5b [L ) PPh3] and 5c [L ) (P(OMe)3)] were
analogously prepared from 4b and 4c, respectively. In these
(26) Sheldrick, G. M. SADABS, Program for empirical absorption
correction; University of Go¨ttingen: Germany, 1996.
(27) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J . Appl. Crystallogr. 1999, 32, 115.
(28) Sheldrick, G. M. SHELXTLplus Version 5.1 (Windows NT
version), Structure Determination Package; Bruker Analytical X-ray
Instruments Inc.: Madison, WI, 1998.

New Iron(II) 5-Aryltetrazolate Complexes
Organometallics, Vol. 21, No. 18, 2002 3781
idealized [C(sp3)-H ) 0.98, C(sp2)-H ) 0.93 Å] and refined
riding the pertinent carbon atoms with isotropic thermal
parameters, U(H) ) 1.2Ueq(C) [U(H) ) 1.5Ueq(C-Me)]. The final
difference electron density map was featureless.
interactions of molecular fragments with metallic sites
in unconventional species”.
Su p p or tin g In for m a tion Ava ila ble: Further details of
the structure determination of 4c, including atomic coordi-
nates, bond distances and angles, and thermal parameters.
Crystallographic file in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. The authors wish to thank Dr.
Cristina Femoni for helpful discussions and the Minis-
tero dell’Universita´ e della Ricerca Scientifica e Tecno-
logica (MURST) for financial support to the National
Project “New strategies for the control of reactions:
OM020283Z