Influences of the electronic and steric effects of the substituents in cyclopalladation of ferrocenylhydrazones

Article abstract of DOI:10.1016/S0022-328X(97)00701-8

The syntheses and characterization of seven novel ferrocenylhydrazones of general formulae: [(η⁵-C₅H₅)Fe{(η⁵-C ₅H₄)-CH=N-NH(R)}] {with R = C₆H₄-4-Cl (1a), C₆H₄-4-NO₂ (1b), C₆H₅ (1c), C₆H₃-2,4-(NO₂)₂ (1d), C₆H₃-2,5-(Cl)₂ (1e), C₆F₅ (1f) or C₆H₄-2-CH₃ (1g)} are reported. We also describe the reactions of compounds 1 with PdCl₂ in refluxing ethanol, by which different cyclopalladated complexes containing σ(C_{sp2, aryl}-Pd), σ(C_{sp2, ferrocene}-Pd) or σ(C_sp3-Pd) bonds were obtained. A comparative study of the ease by which a σ(C_{sp2, ferrocene}-H) or a σ(C_{sp2, aryl}-H) bond in compounds 1 and in the ferrocenylhydrazones: [(η⁵-C₅H₅)Fe{(η⁵-C ₅H₄)-C(CH₃)=N-NH(R)}] (1′) {derived from acetylferrocene} were to be activated is also reported.

Full text of DOI:10.1016/S0022-328X(97)00701-8

Journal of Organometallic Chemistry 555 (1998) 211–225
Influences of the electronic and steric effects of the substituents in
cyclopalladation of ferrocenylhydrazones
Concepcio´n Lo´pez *, Jaume Granell
Departament de Qu´ımica Inorga`nica. Uni6ersitat de Barcelona. Mart´ı Franque`s 1-11, 08028 Barcelona, Spain
Received 19 September 1997
Abstract
The syntheses and characterization of seven novel ferrocenylhydrazones of general formulae: [(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–
NH(R)}] {with R=C6H4-4-Cl (1a), C6H4-4-NO2 (1b), C6H5 (1c), C6H3-2,4-(NO2)2 (1d), C6H3-2,5-(Cl)2 (1e), C6F5 (1f) or
C6H4-2-CH3 (1g)} are reported. We also describe the reactions of compounds 1 with PdCl2 in refluxing ethanol, by which different
cyclopalladated complexes containing |(Csp , aryl–Pd), |(C
ferrocene–Pd) or |(C 3 –Pd) bonds were obtained. A comparative
2
2
sp ,
study of the ease by which a |(Csp , ferrocene–H) or a |(C
aryl–H) bond in cosmp pounds 1 and in the ferrocenylhydrazones:
2
2
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(R)}] (1%) {derivedspfr,om acetylferrocene} were to be activated is also reported. © 1998
Elsevier Science S.A. All rights reserved.
Keywords: Ferrocenylhydrazones; Palladium; Cyclopalladated
1. Introduction
tional group ꢁCꢀN– (endocyclic) [8], for the
analogous phenylhydrazones, the reaction also pro-
Cyclopalladated compounds derived from N-donor
ligands have been extensively studied during the last
decade [1], mainly due to their applications in a variety
of areas [2]. Although the most widely studied systems
described so far contain N-donor organic substrates, in
the last few years cyclopalladation of related ligands
containing ferrocenylunits {i.e. ferrocenyl amines,
imines, azines and oximes and azo-derivatives} has
allowed a novel type of palladacycles with a |(Pd–
duces metallacycles with a |(Pd–Csp , aryl) bond [9], but
2
in this case the ꢁCꢀN– moiety is exocyclic. On this
basis, it seemed interesting to study the cyclopallada-
tion of several ferrocenylhydrazones of general formula:
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(R)}]
(Fig. 1).
(1a–1g)
Ligands 1a–1g might produce different types of pal-
ladocyclic compounds depending on (a) the conforma-
tion of the ligand (E or Z) (Fig. 2) and (b) the nature
of the |(C–H) bond to be activated. For the E isomer
C
sp , ferrocene) bond to be isolated [3–5]. However, the
2
number of articles describing orthopalladation of ferro-
cenylhydrazones are scarce and to the best of our
knowledge only two examples of cyclopalladation of
ferrocenylhydrazones derived from 1-acetylferrocene or
its 1,1%-diacetyl derivative have been reported in the
literature [6,7]. On the other hand, it is well known that
although N-benzilideneanilines exhibit a strong ten-
dency to produce palladacycles containing the func-
of the ferrocenylhydrazones, the activation of a |(Csp ,
2
ferrocene–H) bond would produce in all cases five-mem-
bered metallacycles {containing the functional group
ꢁCꢀN–, endo-type} fused with the ferrocenyl moiety.
However, for substrates 1a–1d, the formation of identi-
cally sized metallacycles with a |(Pd–Csp , phenyl) bond
2
is also plausible, and in these cases the ꢁCꢀN– bond
would be exocyclic.
On the other hand, two different sorts of five-mem-
* Corresponding author.
bered rings with |(Pd–Csp , aryl) bonds could be ex-
2
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00701-8

212
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
Fig. 1. Schematic view of the new ferrocenylhydrazones under study. The asterisks denote the sites susceptible to activate in these ferrocenylhy-
drazones. For substrate (1g) the rotation around the N-aryl group may allow the activation of the |(Csp3 –H) bond.
pected a priori in the cyclopalladation of ligands 1e–1f.
One of them would arise from the activation of a
|(C–H) bond, while the other could be formed by an
oxidative addition of the ortho-C–Cl bond (in 1e) or
C–F bond (in 1f) of the phenyl ring to palladium(0)
species which may be generated in the course of the
reaction. In fact, reactions of this type have been
reported in the literature for ferrocenylimines of general
2. Results and discussion
2.1. The ligands
The ferrocenylhydrazones (1) were prepared by con-
densation of equimolar amounts of ferrocenecarbalde-
hyde and the corresponding hydrazines in ethanol at
room temperature. These compounds are orange/red
solids at room temperature and exhibit high solubility
in benzene, chloroform and dichloromethane, but they
are poorly soluble in hexane. The new ferrocenylhydra-
zones have been characterized by elemental analyses,
IR spectroscopy and proton-NMR. In all cases the
elemental analyses are consistent with the expected
formula:
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–(CH2)n–
(C6H3-2,6-Cl2)}] or N-benzylideneanilines [10]. How-
ever, if the ligand were to have the Z conformation, the
orientation of the lone pair on the imine nitrogen
would only allow the ferrocenyl moiety to metallate
giving exo- five-membered palladacycles.

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
213
Fig. 2. Schematic view of the two conformational isomers {anti-(E) or syn-(Z)} for the ferrocenylhydrazones. Cyclopalladated compounds
containing a |(Pd–Csp , ferrocene) bond and the funtional group ꢁCꢀN– {endocyclic} can exclusively be formed if the ligand retains the
2
anti-conformation; while the formation of exocyclic palladacycles {with a |(Pd–Csp , aryl) bond} can take place for the two conformations {syn-
2
or anti-} of the ferrocenylhydrazones (1a–1g).
values (see Section 3). The most outstanding feature
observed in their IR spectra was the existence of a
or
[(p5-C5H5)Fe{(p5-C5H4)–CH2–NꢀCH(2,6-Cl2–
C6H3)}] [12] which have demonstrated that the aryl
rings are nearly orthogonal to the functional group.
It is worth noting that the new ferrocenylhydrazones
decompose easier than the closely related ferro-
cenylimines of general formula: [(p5-C5H5)Fe{(p5-
C5H4)–CHꢀN–R}] (with R=aryl groups). For
instance, chloroform or benzene solutions of com-
pounds 1a–g and [(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–
N(CH3)2}] (1h) [13] turned brownish gradually, and a
similar behavior was also detected for the solid samples.
For instance, although ligands 1b, 1d and 1f could be
stored without detecting any modification in either their
color or their NMR spectra, the ferrocenylhydrazones
1c and 1h turned brown in ca. 1 day, and after this
period, their 1H-NMR spectra showed broad signals
which may be indicative of the presence of paramag-
netic species. According to these observations, the sta-
bility of substrates 1 in solid state decreases according
to the sequence: 1d ca. 1f\1b\1e\1a\1c ca. 1g\
1h.
sharp intense band in the range 1590–1620 cm−1
,
which is due to the asymmetric stretching of the
ꢁCꢀN– group. In addition, the infrared spectrum of 1
showed the typical stretching band of the N–H frag-
ment at ca. 3200–3400 cm−1
.
Proton-NMR spectra of 1 (Table 1) exhibited a
singlet due to the imine proton in the range: 7.00–8.00
ppm. The signals due to the protons of the ferrocenyl
unit appeared as a singlet and two triplets (with relative
intensities 5:2:2) in the range 3.00–5.00 ppm which can
be ascribed to the three types of protons of the ferro-
cenyl moiety: C5H5 and the pairs {H2, H5} and {H3,
H4}. Except for ligand 1d, the –NH– resonance ap-
peared as a singlet in the range 7.0–8.0 ppm. The low
field shift of the signal observed for substrate 1d, can be
understood as being derived from the existence of a
hydrogen bond between the amine proton and the
nitro-group in the ortho site. This result agrees with the
1
trends found in the H-NMR spectra of 2-nitro-substi-
tuted phenylhydrazones [9], for which structural studies
have confirmed the existence of such an interaction [11].
Fluorine-19 NMR spectra of compound 1f showed
three signals, which is in good agreement with the
presence of three different types of 19F nuclei in the aryl
ring. This result allows us to deduce that there is no
hydrogen interaction between one of the ortho-fluorines
of the aryl ring and the amine proton. Thus, indicating
that the bulky C6F5 substituent precludes the coplanar-
ity of the aryl ring and the N–NH fragment. The use of
molecular models revealed that a coplanar orientation
of these two groups would introduce strong steric re-
pulsions between the lone pair on the amine nitrogen
and the ortho-fluorine. This observation agrees with the
conclusions obtained from the X-ray crystal structures
of certain Schiff bases holding chloro or fluoro groups
in the ortho sites such as: [4-CH3–C6H4–NꢀCH(C6F5)]
In order to check whether the low stability of the
ligands 1 could be related to a redox process, cyclic
voltammetries of these substrates were performed. In all
cases, the cyclic voltammograms exhibited one anodic
peak with a directly associated cathodic peak in the
reverse scan. The half-wave potentials are summarized
in Table 2 together with the values reported for the
related
compounds:
[(p5-C5H5)Fe{(p5-C5H4)–
C(CH3)ꢀN–NH(R)}] (1%) [13].
Comparison of the values given in Table 2 reveals
that the proclivity of the Fe(II) to undergo oxidation in
the ferrocenylhydrazones: [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH(R)}] (1) is strongly dependent on the na-
ture of the substituents on the amine nitrogen, in
particular on the nature and position of the substituents
on the aryl R-group. This finding, which is similar to
that found for (1%) (Fig. 3), is in contrast with the

214
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
Table 1
Proton and 31P-NMR data (in ppm) for the ferrocenylhydrazones of general formula: [(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NHR}] (1) and their
cyclopalladated complexes
Complex
R
1H-NMR
31P-NMR
Ferrocenyl
–CHꢀN–
–NH–
Phenyl
a
1a
1b
4-Cl
3.99, s, Cp
7.62, s
7.25, d
7.06, d
—
—
4.36, t, H2, H5
4-NO2
4.20, s, Cp
7.67, s
7.33, s
7.90, s
7.43, s
7.71, s
8.17, d
7.03, d
4.63, t, H2, H5
4.41, t, H3, H4
1c
1d
1e
1f
H
4.17, s, Cp
7.58, s
7.04, d
7.24, d
6.82, d
—
4.58, t, H2, H5
4.31, t, H3, H4
2,4-(NO2)2
2,5-Cl2
2,3,4,5,6-C6F5
2-CH3
4.32, s, Cp
11.20, br. s
7.88, s
9.15, d
8.32, d
7.80, d
—
4.79, s, H2, H5
4.59, t, H3, H4
3.92, s, Cp
6.81, d
6.54, d
6.46, d
—
4.36, s, H2, H5
4.05, s, H3, H4
4.21, s, Cp
6.94, s
7.71, s
—
—
4.53, s, H2, H5
4.36, s, H3, H4
1gb
2a
4.20, t, Cp
7.67, s
7.48, d
7.09, d
6.79
—
a
4.62, t, H2, H5
4.33, t, H3, H4
4-Cl
4.33, s, Cp
8.42, d
8.49, s
6.21, dd
6.78, dd
7.80, dd
42.2
4.77, t, H2, H5
4.62, t, H3, H4
7.85, d
7.2–7.8, m (PPh3)
2b
4-NO2
4.33, s, Cp
8.57, d
8.78, s
8.57, d
8.87, s
6.70, d,
8.27, dd
7.3–8.8, m (PPh3)
42.0
44.0
44.7
4.74, t, H2, H5
4.64, t, H3, H4
2d
2,4-(NO2)2
2-CH3
4.30, s, Cp
11.65, br.s
8.78, d
7.3–7.8, m (PPh3)
4.95, t, H2, H5
4.77, t, H3, H4
2gc
4.31, s, Cp
6.10, dd
6.26, dd
6.72, dd
4.78, t, H2, H5
4.58, t, H3, H4
7.2–7.8, m (PPh3)
2g%d,e
2-CH3
4-Cl
4.24, s, Cp
7.90, d
8.77, s
7.1–7.8, m
41.9f
41.3f
4.51, t, H2, H5
4.60, t, H3, H4
3ag
4.28, s, Cp
8.60, s
8.32, s
6.12 dd
6.70, dd
6.85, d
7.3–7.8, m (PPh3)
28.9
24.9
28.9
4.75, t, H2, H5
4.63, t, H3, H4
3b
4-NO2
4.29, s, Cp
8.90, s
8.30, s
7.74, d
7.28, d
6.65, d
7.3–8.8, m (PPh3)
4.72, t, H2, H5
4.64, t, H3, H4
3cg
H
4.28, s, Cp
6.85, d
6.70, d
6.12, d
4.63, t, H2, H5
4.81, t, H3, H4
7.3–8.8, m (PPh3)

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
215
Table 1 (Continued)
Complex
R
1H-NMR
31P-NMR
Ferrocenyl
–CHꢀN–
–NH–
8.53
Phenyl
3eg
3fg
2,5-Cl2
4.26, s, Cp
8.30, s
6.78, dd
7.0–7.9, m (PPh3)
29.3
29.3
4.47, t, H2, H5
4.67, t, H3, H4
2,3,4,5,6-C6F5
4.22, s, Cp
4.59, t, H5
4.37, t, H4
4.31, t, H3
7.70, br.m
8.52, s
7.00, br
7.80, br
7.1–7.8, m (PPh3)
3gh
2-CH3
4.29, s, Cp
6.76, dd
6.11, dd
7.0–7.6, m (PPh3)
29.3
4.79, t, H2, H5
4.60, t, H3, H4
Labeling of the atoms refers to the schemes shown above.
a Masked by the resonances of the phenyl protons. b Additional signal at 2.23 ppm (CH3). c Exocyclic five-membered palladocycle with a
1
|(Pd–Csp , aryl) bond. d Data for this complex was obtained by comparison of the H-NMR spectrum of the (2g, 2g%) mixture and that of the pure
2
complex 2g. e The resonance of the –CH2– protons appears as two singlets centered at 2.64 and 2.84 ppm due to the diastereotopicity of these
two protons. f Two rotameric species are present in solution. g The 31P-NMR data for this complex obtained at 240 K, (see Section 3). h Additional
signal at 2.37 ppm (CH3).
results reported for the Schiff bases [(p5-C5H5)Fe{(p5-
C5H4)–C(R%)ꢀN–R}] {with R=aryl and R%=H, CH3
or C6H5} for which the degree of substitution of the
aryl group only produced tiny variations of the half-
wave potentials [14].
ity of the imine fragment. This finding is similar to
those reported in the electrochemical studies of the
ferrocenylimines derived from formyl or acetyl fer-
rocene [14].
It is well known that the proclivity of ferrocene to
undergo oxidation is strongly dependent on the nature
of the substituents, and in particular, more anodic
potentials are found for substrates holding electron
withdrawing groups, while the presence of electron
donor substituents involves more cathodic values [15].
On this basis, for the ferrocenylhydrazones 1 the elec-
tron withdrawing effect of the substituents upon the
ferrocenyl moiety, decreased according to the sequence:
1f\1d\1b\1a ca. 1e\1h. This trend is similar to
that observed for the stability, thus suggesting that the
low stability of these substrates may be related to a
redox process. In addition comparison of data shown in
Table 2 reveals that the ferrocenylhydrazones derived
from acetylferrocene (1%) are more prone to oxidize
than 1, thus suggesting that the methyl group at the
–C(R)ꢀN– fragment enhances the electron donor abil-
2.2. Cyclopalladation reactions
The general procedure described for the cyclopalla-
dation of most ferrocene derivatives {i.e. ferroceny-
lamines, imines, oximes and azines}, which consists in
the treatment of equimolar amounts of the free ligand,
Na2[PdCl4] and Na(CH3COO)·3H2O in methanol at
room temperature, was unsuccessful for the ferrocenyl-
hydrazones 1 under study, even when the reaction
periods were increased up to 72 h. All the experiments
revealed that for the shortest reaction times (3 h) the
ferrocenylhydrazones were recovered unaltered, while
for the longest periods (2–3 days) decomposition of the
ligands took place. These findings differ from the re-
sults reported previously which have shown that the
activation of the |(Csp , ferrocene–H) bond in the ferro-
2
cenylhydrazones: [(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–

216
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
Table 2
Half-wave potentials (in V) referred to ferrocene, E1/2(Fc), for the ferrocenylhydrazones 1 and 1% and for the ferrocenylimines of general formula:
[(p5-C5H5)Fe{(p5-C5H4)–C(R)ꢀN–R%}]
R=H
E1/2(Fc) R=CH3
E1/2(Fc)a
(A) Ferrocenylhydrazones of general formulae: [(p5-C5H5)Fe{(p5-C5H4)–C(R)ꢀN–NR%}]
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6H4-4-Cl)}]
0.01
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(C6H4-4-Cl)}]
−0.01
0.03
(1a)
(1%a)
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6H4-4-NO2)}]
0.05
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(C6H4-4-NO2)}]
(1b)
(1%b)
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6H3-2,4-(NO2)2}]
0.10
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(C6H4-2,4-(NO2)2)}]
0.07
(1d)
(1%d)
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6H3-2,5-Cl2)}]
(1e)
0.04
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(C6H3-2,5-Cl2)}]
0.02
(1%e)
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6H4-2-CH3)}]
(1g)
−0.02
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(C6H4-2-CH3)}]
(1%g)
−0.03
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6F5)] (1f)
0.13
−0.03
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–N(CH3)2}] (1h)
(B) Ferrocenylimines of general formula: [(p5-C5H5)Fe{(p5-C5H4)–C(R)ꢀN–R%}]b
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–C6H5}]
0.15
0.14
0.13
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–C6H5}]
0.15
0.14
0.09
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–(C6H4-2-CH3)]
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–(CH2–C6H4-2-CH3)]
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–(C6H4-2-CH3)]
[(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–(CH2–C6H4-2-CH3)]
a Data from ref. [13] and b ref. [14].
ethanol at room temperature for 3 h, the reaction
produced the coordination compound: trans-[Pd{(p5-
C5H5)Fe[(p5-C5H4)–CHꢀN–NH(C6H4-4-Cl)]}2Cl2], and
no evidence of the formation of a |(Pd–C) bond was
detected by 1H-NMR spectroscopy, while for longer
reaction periods {up to 2 days} decomposition of either
the coordination complex and/or the ligand took place.
This finding is in good agreement with previous studies
in this field which have shown that when the reaction
between the ferrocenylhydrazone: [(p5-C5H5)Fe{(p5-
C5H4)–CHꢀN–N(CH3)2}] (1h) and PdCl2 {in a 1:2 or
1:1 molar ratio} is carried out in ethanol or methanol at
room temperature the formation of the coordination
NH(R)}] (1%) and even in the 1,1%-ferrocenyldihydra-
zone: [Fe{(p5-C5H4)–C(CH3)ꢀN–NH(COCH3)}2] can
be easily achieved using the general procedure [6,7].
The varying reactivity of the ligands under study and
of 1% might be related to either the different basicity of
the iminic nitrogen, the stability of the starting ferro-
cenyl substrate, or both simultaneously. In fact, it is well
known that the methyl group is a better electron donor
substituent than the hydrogen and consequently, the
coordination of the palladium(II) to the iminic nitrogen
in [(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–NH(R)}] (1%)
or the 1,1%-derivative is expected to be more favorable
than in 1. A similar argument has also been used to
justify that the cyclopalladation of ferrocenylimines of
general formula: [(p5-C5H5)Fe{(p5-C5H4)–C(CH3)ꢀN–
R}] requires only 3 h, while for [(p5-C5H5)Fe{(p5-
C5H4)–CHꢀN–R}] at least 18 h were needed to detect
the formation of the metallacycle [4].
On the other hand, although the activation of |(C–
H) bonds for some organic N-donor ligands, has been
achieved using stronger reaction conditions {using
Pd(CH3COO)2 as a metallating agent in refluxing acetic
acid} this procedure also failed for the substrates under
study. This fact can be ascribed to the high instability of
ferrocene derivatives containing the functional group
ꢁCꢀN– in acidic media, which produces the protona-
tion of the ferrocenecarboxaldehyde formed through
hydrolyses of the ꢁCꢀN– bond [16].
complex:
N(CH3)2]}Cl2] takes place [13].
trans-[Pd{(p5-C5H5)Fe[(p5-C5H4)–CHꢀN–
In contrast, for ligand 1b (which according to the
electrochemical studies previously described, is more
reluctant to oxidize than 1a or 1h), the formation of the
metallacycle can be achieved in low yield (ca. 30%) when
equimolar amounts of the free ligand (1b) and PdCl2, in
ethanol are stirred at room temperature for 6 days.
However, when 1a, 1b and 1d were treated with PdCl2
in refluxing ethanol for 3 h, the reaction gave a brown
solid. Further treatment of this material with PPh3 in
benzene at room temperature for one hour produced a
brown suspension which was filtered out and the filtrate
was first reduced to dryness and then passed through a
SiO2-column chromatography. The red (for 2d) or
brown (for 2a, b) band eluted with chloroform was
concentrated to dryness and then treated with n-hexane
to induce the precipitation of the cyclopalladated com-
Based on these results we decided to study the reac-
tions of the ferrocenylhydrazones 1 with PdCl2 in
ethanol, which have been very useful in the cyclopalla-
dation of several organic hydrazones [9]. When ligand
[(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6H4-4-Cl)}] (1a)
was treated with PdCl2 {in a 1:1 or 1:2 molar ratio} in
‚
plexes: [Pd(C N)Cl(PPh3)] 2a, 2b and 2d, respectively
(Scheme 1), which contain an exocyclic five-membered
metallacycle with a |(Pd–Csp , aryl) bond fused with the
2
aryl ring.

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
217
Fig. 3. Plot of the half-wave potentials referred to ferrocene, E1/2(Fc), {in V}, for the two families of ferrocenylhidrazones of general formulae:
[(p5-C5H5)Fe{(p5-C5H4)–C(R%)ꢀN–NH(R)}] with R%=H (1) or CH3 (1%) and R=C6H4-4-Cl (a), C6H4-4-NO2 (b), C6H3-2,4-(NO2)2 (d),
C6H3-2,5-(Cl)2 (e) or C6H4-2-CH3 (g). The equation of the least-squares fit is: E1/2(Fc) for 1=1.7(3)×10−2+1.17(4) E1/2(Fc) for 1% (r2=0.996).
When the ferrocenylhydrazone 1e was used as start-
ing material, the formation of a palladium mirror in the
bottom of the flask was detected, in good agreement
with the stronger reductive nature of this ligand, and
the reaction yielded to [Pd{[(3,6-Cl2–C6H2)–NHꢀCH-
(p5-C5H4)]Fe(p5-C5H5)}Cl(PPh3)2] (3e), which also con-
complexes. The major component was the coordination
compound: [PdCl2(PPh3)2] and traces of the palladated
compound
[Pd{[(C6H4)–NHꢀCH–(p5-C5H4)]Fe(p5-
1
C5H5)}Cl(PPh3)2] (3c) were only detected by H- and
31P-NMR spectroscopies. No significant improvement
was detected when the reaction was carried out under
N2 and using different reaction periods (from 3 to 6 h).
For compound [(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–
NH(C6F5)}] (1f), the reaction also produces a mixture
of two compounds. The major component was the
coordination compound: [PdCl2(PPh3)2] but small
amounts (B10%) of the cyclopalladated complex:
[Pd{[(p5 -C5H3) – CHꢀN–NH(C6F5)]Fe(p5 -C5H5)}Cl-
tains a |(Pd–Csp , aryl) bond. The different structure of
2
the final products obtained in the cyclopalladation of
ligands 1a, b and d and in this case, 1e, may be related
to steric effects. It has been reported that for cyclopal-
ladated and cycloplatinated complexes derived from
organic imines and hydrazones, the presence of bulky
substituents in an adjacent position to the |(Pd–C)
bond enhances the reactivity of the Pd–N moiety. For
instance, it is well known that this sort of cyclometal-
lated compounds exhibit a higher proclivity to undergo
ring opening processes through the cleavage of the
Pd–N bond and the incorporation of the second phos-
phine in the coordination sphere of the palladium
([12]b)[17]. If a five-membered metallacycle similar to
compounds 2 was to be formed in the course of the
reaction with ligand 1e, the aryl rings of the phosphine
would be very close to the ortho-chloro group, thus
increasing the instability of the molecule. While if the
metallacycle opens up, the free rotation around the
Pd–C bond would significantly reduce the steric effects.
Although the nature of ligand 1c does not differ
substantially from those mentioned in the previous
paragraphs, the reaction produced a mixture of two
1
(PPh3)2] (3f) were also detected by H- and 31P-NMR
spectroscopies. This result can be attributed to several
effects, amongst which, the presence of electron-with-
drawing groups {which are expected to modify the
basicity of the nitrogen} and, the bulk of the C6F5
susbtituent {which may hinder the coordination of the
palladium} appear to play a crucial role in the process.
In addition, for ligand 1f, the formation of the exo-
cyclic five-membered palladacycle with
a |(Pd–
Csp , aryl) bond, would involve the activation of a |(C–
2
F) bond. These effects may be responsible for the
formation of compound: [Pd{[(p5-C5H3)–CHꢀN–
NH(C6F5)]Fe(p5-C5H5)}Cl(PPh3)2] (3f) in a low yield.
As a first attempt to improve the yield of the process,
the reaction was carried out using a longer reaction
period (3 h). However, no evidence of the formation of

218
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
Scheme 1. Reaction scheme indicating the conditions necessary to produce complexes 2a, 2b, 3c, 2d and 3e.

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
219
Scheme 2. Reaction scheme indicating the conditions necessary to produce complexes 3f and 2g%.
1
the cyclopalladated complex was detected by H-NMR,
for the longest periods, thus suggesting the low stability
of complex 3f.
spectroscopies. This finding is in sharp contrast with
the results obtained in the cyclopalladation of [(p5-
C5H5)Fe{(p5 - C5H3)–C(CH3)ꢀN–NH[C6H4 - 2 - CH3)]}]
(1%g), which produced exclusively a five-membered pal-
ladacycle fused with the ferrocenyl fragment, and no
evidence of the formation of any other type of pallada-
cycle was detected [7].
More interesting though are the results obtained
from the reaction with: [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH(C6H4-2-CH3)}] (1g) which contains
a
methyl group in the ortho-site of the aryl ring. In this
case the reaction produces a mixture of two cyclopalla-
dated compounds: 2g and 2g% (Scheme 2). The major
component (2g) which contains a five-membered pal-
ladacycle fused with aryl ring moiety could be isolated
as a pure material, while, the minor component of the
This is particularly remarkable since, although for
ligands 1g and 1%g, there are three different kinds of
|(C–H) bonds susceptible to activation {Csp ,
–
2
ferrocene
H; Csp , phenyl–H or Csp3 –H, Fig. 1}, for 1g the forma-
2
tion of an endocyclic palladacycle does not take place
although it is well known that ferrocene derivatives are
more prone to undergo electrophilic attacks than ben-
mixture which arises from the activation of a |(Csp
–
3
H) bond was only detected by 1H- and 31P-NMR

220
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
zene [16]. Thus suggesting that the proclivity of the
three types of |(C–H) bonds susceptible to activation
phenyl or C5H4 rings of R1 exhibit a stronger tendency
to be nearly co-planar with the functional group
{ꢁCꢀN–} {the dihedral angles vary from 0 to 15°}
[11], than the aromatic rings of the R2 substituent. On
this basis, the strong tendency of imines to form endo-
metallacycles has been explained in terms of the better
accessibility and orientation of the ortho C–H bond of
the R1 group to the coordination plane of the metal.
In contrast, the crystal structures of hydrazones:
R1C(R3)ꢀN–NHR2, show that the phenyl rings in R1
(or R3) and R2 and the functional group tend to be
coplanar [11]. In addition, for these substrates, the lone
pair on the nitrogen activates the hydrazine phenyl
ring. All these effects could explain the great tendency
of hydrazones: R1C(H)ꢀN–NHR2 to produce exocyclic
complexes, while for their analogues derived from ke-
tones: R1C(R3)ꢀN–NHR2 {R1, R3"H} the preferen-
tial formation of the endo-metallacycles can be related
to the steric hindrance introduced by the substituents:
R1 and/or R3, since in the exocyclic palladacycles the
environment of the palladium(II) is significantly more
crowded due to the proximity of one of the two groups
R1 or R3 {R1, R3"H} to the remaining ligands bound
to the palladium i.e. Cl or PPh3.
More recently, Garcia-Herbosa et al. [18] have postu-
lated that cyclopalladation of phenylhydrazones, takes
place along a different pathway than for their N-
methyl-N-phenyl analogues. This consists of the coordi-
nation of the ligand to the metal and the subsequent
deprotonation of the –NH– group, giving a highly
conjugated ‘azobenzene-like’ species, which is highly
prone to cyclometallation. The results reported in this
work, can also be explained by this mechanism, since
the presence of electron-withdrawing groups in the aryl
ring of 1, enhances the acidic character of the –NH–
proton, facilitating the activation of the |(C–H) bond
and the formation of the metallacycle. However, the
influence of other factors, such as the relative stability
of the free ligands {which plays an important role in
the first step of the cyclopalladation reactions} can not
be discarded in principle.
in 1g increases according to the sequence: Csp ,
–
2
ferrocene
HBCsp3 –HBCsp
, phenyl–H, while for 1%g the activa-
2
tion of the |(Csp , ferrocene–H) is strongly preferred.
2
Consequently, for ferrocenylhydrazones derived from
acetylferrocene the Csp3 –H and C phenyl–H bonds are
2
sp ,
more reductant to undergo metallation. On this basis,
the results summarized in this work reveal that the
replacement of the methyl by an hydrogen in the iminic
carbon of the ferrocenylhydrazones: [(p5-C5H5)Fe{(p5-
C5H4)–C(R%)ꢀN–NH(R)}] (R%=H, 1 or CH3, 1%) may
be important enough as to introduce a significant varia-
tion in the geometries of the ligands and/or in the
relative orientations of the C–H bonds susceptible to
activation. Any of these effects may be crucial in deter-
mining the nature of |(Pd–C) bond to be formed. In
fact, structural data for ferrocenylhydrazones: [(p5-
C5H5)Fe{(p5-C5H4)–C(R%)ꢀN–NH(R)}] with R%=H or
CH3 reveal that the larger bulk of the methyl sub-
stituent versus H involves the closing of the bond angle
Cipso, ferrocene–C(R%)ꢀN– {which fall in ranges: 118.5–
120.5° for R%=H and 115.5–116.7° for R%=Me} [11].
For the cyclopalladated complex: [Pd{(p5-C5H5)Fe[(p5-
C5H3)–C(CH3)ꢀN–NH(R)]}Cl(PPh3)] [7] {which con-
tains an endo-type five-membered metallacycle fused
with the ferrocenyl unit} the value of this angle is
112.4(14)°, thus indicating that the formation of the
palladacycles with a |(Pd–Csp , ferrocene) bond involves a
2
smaller variation of the angles around the iminic car-
bon for the ferrocenylhydrazones derived from acetyl-
ferrocene.
Although it has been previously reported that ferro-
cenylhydrazones derived from acetylferrocene (R=
CH3) exhibit a strong tendency to form five-membered
metallacycles with a |(Pd–Csp , ferrocene) bond, our re-
2
sults indicate that those with R=H produce preferen-
tially palladacycles with a |(Pd–Csp , phenyl) bond.
2
These findings agree with the results obtained in cyclo-
palladation of organic hydrazones derived from ketones
or aldehydes which produce endo and exo-five-mem-
bered metallacycles, respectively, thus indicating that a
change in the –C(R)ꢀN– fragment of free ligand (i.e.
the replacement of a –CH3 by a –H) is important
enough as to modify the nature of the final cyclopalla-
dated product [9].
On the other hand, it is well known that the mecha-
nism accepted for that cyclopalladation of N-donor
ligands involves the initial coordination of the ligand
and the subsequent electrophilic attack of the metal
atom. It has also been postulated, that the approach of
the C–H bond, which is to be activated to the coordi-
nation sphere of the metal favours the process. This is
in good agreement with an electrophilic attack of the
2.3. Reactions of compounds 2 with PPh3
In order to study the stability of the Pd–N bond in
‚
the cyclopalladated complexes: [Pd(C N)Cl(PPh3)], the
reaction of compounds 2 in CDCl3 {or in CH2Cl2} with
the stoichiometric amount of PPh3 were also studied. In
all cases the addition of the phosphine ligand produced
the cleavage of the Pd–N bond and the formation of
‚
the cyclopalladated compounds: [Pd(C N)Cl(PPh3)2]
(3). These results are in contrast with those reported
‚
previously for related compounds, where (C N) repre-
sents a cyclometallated ferrocenylimine, oxime or azine,
or in particular a ferrocenylhydrazone derived from
acetylferrocene, which do not react with excesses of
PPh3, thus indicating that the Pd–N bond in com-
palladium using its empty dx
2 orbital. The molecular
2−
y
structures of free imines: R1CHꢀN–R2 reveal that the

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
221
Scheme 3. Exchange of PPh3 through a fast equilibrium in 3, suggesting a great lability of one of the Pd–P bonds in solution.
pounds 2 is more labile. The different reactivity of the
two types of cyclopalladated complexes 2 and 2% versus
PPh3, can be related to the nature of the two sus-
btituents (R=H or CH3) which modify the basicity of
the imine nitrogen. These results are consistent with
previous studies on the reactivity of cyclopalladated
and cycloplatinated compounds which have shown
that, depending on the nature of the metallacycle and
the basicity of the nitrogen, the cleavage of the metal
nitrogen bond can be achieved [17].
paramagnetic anisotropy of the phenyl rings of the
PPh3 ligand in a cis-arrangement with the metallated
carbon atom. The signal due to the NH group in
compound 2d appears strongly shifted to low fields
(l=11.65 ppm), thus suggesting the existence of an
intramolecular hydrogen bond between the ortho-NO2
group and the amine hydrogen. This finding is in good
agreement with those reported for the cyclopalladated
derivatives derived from 2,4-dinitrophenylhydrazone,
for which the existence of this interaction has been
confirmed by X-ray difraction [11].
2.4. Characterization
Phosphorus-31 NMR spectral data of compounds 2
and 3 are presented in Table 1. For compounds 2 the
position of the signal {in the range of 37–45 ppm} is
consistent with a trans orientation of the phosphine
ligand and the nitrogen. 31P-NMR spectra of 3 revealed
the existence of dynamic processes in solution. The
singlet due to the coordinated phosphines {in the range
23–25 ppm} was only detected at low temperatures
{220 K}. In contrast when the spectra were recorded at
higher temperatures the signal became broad and at 240
K an additional signal centered at ca. 32 ppm appeared,
these findings indicate that compounds 3 exchange
PPh3 through a fast equilibrium shown in Scheme 3
{since the signal centered at ca. 32 ppm is placed
between those obtained for 2 and 3}, thus suggesting a
great lability of one of the Pd–P bonds in compounds
3 in solution. In addition, this finding also agrees with
the fact that when compound 3b is passed through an
SiO2 column using CHCl3 as eluant, only complex 2b
and the free phosphine could be recovered.
The new palladium(II) compounds are solids at room
temperature and exhibit higher stability than the corre-
sponding ferrocenyl hydrazones, since they can be
stored for several weeks without any appreciable
change in either their colour or their NMR spectra.
This finding reveals that the formation of the |(Pd–C)
bond increases the stability of the ferrocenylhydra-
zones. This fact is analogous to that reported for the
ferrocenylimines:
NꢀCH(C6H4R)}] (3c) and their cyclopalladated com-
plexes with a |(Pd–Csp , aryl) bond, for which the
increase of the stability was ascribed to more anodic
half-wave potentials of the palladium (II) compounds
when compared with the free ligands.
The palladated compounds 2 and 3 are soluble in
chloroform, dichloromethane, slightly soluble in
ethanol and practically insoluble in alkanes and ace-
tonitrile. Their IR spectra show the typical bands of
coordinated hydrazones and triphenylphosphine. Se-
lected NMR spectral data for compounds 2 and 3 are
summarized in Table 1. The assignment of the proton-
NMR data affords conclusive evidence of the pallada-
tion site (endo- or exo-structures). The aromatic proton
signals of the metallated ring in compounds 2 which
contain a Pd–N bond are shifted to high field. This
effect, which has also been observed for endocyclic
cyclopalladated complexes derived from organic imines
and hydrazones, has been interpreted in terms of the
[{(p5-C5H5)Fe[(p5-C5H4)–(CH2)n–
2
Dynamic processes similar to that shown in Scheme
3 have also been observed for a wide variety of
cyclopalladated
[M(C N)X(PR3)2] {with X=Cl, Br or I and R=
and
cycloplatinated
complexes:
‚
phenyl or alkyl} [19].
2.5. Conclusions
The results summarized in this work have allowed us
not only to establish general pathways for the prepara-

222
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
tion of ferrocenylhydrazones derived from ferrocenecar-
boxaldehyde, but also to elucidate the influences of the
substituents on the amine nitrogen on the liability of
the iron(II) to undergo oxidation.
Furthermore, cyclopalladation reactions of substrates
1, reveal that though ferrocene derivatives are more
likely to undergo electrophilic attacks than aromatic
ones, the formation of palladium(II) compounds with
the relative orientation of the C–H bond to be acti-
vated 6ersus the palladium linked to the nitrogen, the
E“Z isomerization of the ligand (the Z isomer does
not allow the formation of the endocyclic derivatives),
or the presence of electron-withdrawing groups which
may ease the deprotonation of the –NH– fragment, for
the mechanism postulated by Garcia-Herbosa et al. [18]
may also play a crucial role in these processes.
|(Pd–Csp , aryl) bonds is strongly preferred. Only for
2
ligand [(p5-C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6F5)] 1f,
for which the formation of a palladacycle with a |(Pd–
3. Experimental
Csp , aryl) bond, would require the activation of one of
2
the ortho C–F bonds, the formation of small amounts
Elemental analyses (C, H and N) were carried out at
the Serveis Cientifico-Te`cnics (Universitat de
Barcelona). Infrared spectra were obtained from KBr
of
a five-membered metallacycle with a |(Pd–
Csp , ferrocene) bond was detected by NMR spectroscopy.
2
1
It is also interesting to point out, that for substrate 1g,
for which three different types of |(C–H) bonds could
be activated (Fig. 1), the reaction produced: [Pd{[(2-
CH3–C6H3)–NHꢀCH–(p5 - C5H4)]Fe(p5 - C5H5)}Cl-
(PPh3)] (2g), and the formation of small amounts of the
cyclopalladated complex with a |(Pd–Csp3) bond was
also detected by NMR. However, no traces of the
formation of the endocyclic five-membered palladocycle
pellets using a NICOLET-520FTIR-spectrometer. H-
and 13C{1H}-NMR spectra were recorded at ca. 20°C
on
a GEMINI-200MHz spectrophotometer, using
CDCl3 (99.9%) {free of acid traces} as solvent and
Si(CH3)4 as internal reference. 31P-NMR spectra of
compounds 2 and 3 were obtained with a BRUKER-
DRX-250MHz spectrophotometer using CDCl3 as sol-
vent and trimethylphosphite as internal reference
1
{l(31P)=140.17 ppm}. H- and 31P-NMR data for the
with a |(Pd–Csp , ferrocene) bond were detected in the
2
compounds under study are presented in Table 1. 19F-
NMR for ligand 1f was recorded with a Varian 300
MHz instrument using CDCl3 as solvent and
F3CCOOH as reference.
course of the reaction, although it is well known that
ferrocene has a greater proclivity to electrophilic at-
tacks than benzene.
These findings are in sharp contrast with those ob-
tained for the ferrocenyl hydrazones: [(p5-C5H5)Fe{(p5-
C5H4)–C(CH3)ꢀN–NH(R)] (1%), the ferrocenylimines:
[(p5-C5H5)Fe{(p5-C5H4)–C(R%)ꢀN–R] {with R%=H,
CH3 or C6H5}, and the N-benzylideneamines, which
show a strong tendency to form endocyclic cyclopalla-
3.1. Materials and syntheses
Ferrocenecarboxaldehyde [(p5-C5H5)Fe{(p5-C5H4)–
C(O)H}] and the organic hydrazines were obtained
from commercial sources and used as received. All the
solvents were dried and distilled before use. Some of the
preparations described below require the use of benzene
which should be used with CAUTION. Compound 1h
was prepared as described previously [13].
dated compounds with a |(Pd–Csp , ferrocene) bond; but
2
agree with the conclusions reached from cyclopallada-
tion of the phenylhydrazones: [R–C6H4–CHꢀN–NH–
C6H4−xRx] which produce exocyclic cyclopalladated
compounds preferentially. Only when the aryl group
bound to the amine nitrogen contained chloro groups
at the ortho sites, was the isolation of the endocyclic
palladacycles achieved.
3.1.1. Preparation of the compounds
In conclusion, the results described in this work show
the strong tendency of hydrazones derived from fer-
rocenecarboxaldehyde to form exocyclic cyclopalla-
dated compounds. This tendency is so strong that the
metallation of an aliphatic C–H bond giving an exo
six-membered palladacycle has been observed for the
first time. These results are in sharp contrast with those
reported for imines, for which the formation of endo-
cyclic palladacycles is strongly preferred.
To sum up, while it is widely accepted that the
formation of cyclopalladated compounds containing
N-donor ligands involves the coordination of the ligand
and the subsequent electrophilic attack of the palladiu-
m(II) on the C–H bond to be activated, the results
reported in this study suggest that other factors, such as
3.1.1.1. Preparation of [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH(C6H4-4-Cl)}] (1a). Commercial ferrocene-
carbaldehyde (1.07 g, 4.98 mmol) was dissolved in the
minimum amount of ethanol (ca. 5 cm3) and the undis-
solved materials were filtered out and discarded. Then a
solution containing 4-chlorophenylhydrazine (1.69 g,
5.00 mmol) in 5 cm3 of ethanol was added to the
filtrate. The reaction mixture was stirred at room tem-
perature for 1.5 h and the orange/red solid formed was
filtered out, washed with three (5 cm3) portions of
ethanol and air-dried. (Yield: 66%). Characterization
data: Anal. (%) Calc. for C17H15N2ClFe (found): C,
60.32 (60.3); H, 4.47 (4.35) and N, 8.27 (8.1). IR: wmax
:
1596 (ꢁCꢀN–) and 3312 (N–H) cm−1
.

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
223
3.1.1.2. Preparation of [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH(C6H4-4-NO2)}] (1b). This complex was
prepared following the procedure previously described
for 1a, but using the stoichiometric amount of 4-nitro-
phenylhydrazine as reagent. (Yield: 74%). Characteriza-
tion data: Anal. (%) Calc. for C17H15N3O2Fe (found):
C, 58.48 (58.4); H, 4.33 (4.5) and N, 12.04 (12.1). IR:
brownish/red precipitate formed was filtered out and
air-dried. (Yield: 72%). Characterization data: Anal.
(%) Calc. for C34H30N4Cl4Fe2Pd (found): C, 47.77
(47.85); H, 3.51 (3.60) and N, 6.55 (6.6). IR: wmax: 1582
1
(ꢁCꢀN–) and 3264 (N–H) cm−1. H-NMR (in ppm),
selected data: 4.32 {s, 5H, (C5H5)}, 4.29 {s, 5H,
(C5H5)%}, 5.40 (t, 1H, H2), 5.27 (t, 1H, H2%), 4.58 (br.t
2H, H3 and H3%), 4.60 (t, 2H, H4 and H3%), 4.75 (t, 2H,
H5 an H5%), 8.01 (s, –CHꢀN–) and 2.20 (s, 2H, –NH–).
wmax: 1608 (ꢁCꢀN–) and 3295 (N–H) cm−1
.
3.1.1.3. Preparation of [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH(C6H5)}] (1c). Ferrocenecarbaldehyde (1.00
g, 4.67mmol) was added to ethanol (ca. 10 cm3) under
N2 and the mixture was stirred under nitrogen for an
additional 5 min. The undissolved materials were re-
moved by filtration under nitrogen. Phenylhydrazine
(4.67 mmol) was poured drop-wise to the filtrate and
the reaction mixture was vigorously stirred at room
temperature for 1.5 h. The orange solid formed during
this period was collected by filtration under nitrogen,
washed with three (5 cm3) portions of cold ethanol and
air-dried. (Yield: 52%). Characterization data for 1c:
Anal. (%) Calc. for C17H16N2Fe (found): C, 67.13
(67.0); H, 5.30 (5.3) and N, 9.21 (9.1). IR: wmax: 1597
3.1.1.6. Preparation of [Pd{[(4-Cl–C6H3)–NH–
NꢀCH–(p5-C5H4)]Fe(p5-C5H5)}Cl(PPh3)] (2a), [Pd{[(4-
NO2–C6H3)–NH–NꢀCH–(p5 -C5H4)]Fe(p5 -C5H5)}Cl-
(PPh3)] (2b), [Pd{[{2,4-(NO2)2C6H3)}–NH–NꢀCH–
(p5-C5H4)]Fe(p5-C5H5)}Cl(PPh3)] (2d) and [Pd{[(2-
CH3–C6H3)–NH–NꢀCH - (p5 - C5H4)]Fe(p5 - C5H5)}Cl-
(PPh3)] (2g). To a suspension containing 1.60 mmol of
the corresponding ferrocenylhydrazone {1a, 2a or 2g}
in 20 cm3 of ethanol, 0.284 g (1.60 mmol) of PdCl2 was
added. The resulting mixture was refluxed for 3 h.
During this period the formation of metallic palladium
was detected. The deep brown precipitate formed was
filtered out and washed with three portions of ethanol
(ca. 5 cm3) and air-dried. The solid was then suspended
in 20 cm3 of benzene and treated with 0.420 g of PPh3
(1.60 mmol) and the mixture was stirred at room
temperature for 1 h and then filtered out to remove the
undissolved materials. The brownish filtrate was con-
centrated to dryness in a rotary evaporator and the
residue was then passed through an SiO2-column (10×
250 mm), using CHCl3 as eluant. The first colored band
was collected and concentrated to dryness in a rotary
evaporator giving a red solid for 2d or a gummy
material for 2a, 2b or 2g. In the later cases the residual
was dissolved in the minimum amount of CH2Cl2 and
then treated with n-hexane to induce the precipitation.
The ochre solid formed was collected by filtration and
air-dried (Yields: 58 (2a), 63 (2b) 68 (2d) and 45% (2g)).
Characterization data for 2a: Anal. (%) Calc. for C35-
H29N2FeCl2PPd (found): C, 56.76 (56.6); H, 3.95 (3.9)
and N, 3.78 (3.7). IR: wmax: 1610 (ꢁCꢀN–) and 3204
(ꢁCꢀN–) and 3308 (N–H) cm−1
.
3.1.1.4. Preparation of [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH{C6H3-2,4-(NO2)2}] (1d), [(p5-C5H5)Fe{(p5-
C5H4)–CHꢀN–NH{C6H3-2,5-(Cl)2}]
(1e),
[(p5-
C5H5)Fe{(p5-C5H4)–CHꢀN–NH(C6F5)] (1f) and [(p5-
C5H5)Fe{(p5-C5H4)–CHꢀN–NH{C6H4-2-(CH3)}] (1g).
These complexes were prepared following the procedure
previosly described for 1a, but using the stoichiometric
amount of the corresponding hydrazine as reactant.
(Yields: 55 (1d), 57 (1e), 50 (1f) and 62% (1g)).
Characterization data for 1d: Anal. (%) Calc. for C17-
H14N4O4Fe (found): C, 51.80 (51.77); H, 3.58 (3.45)
and N, 14.21 (13.92). IR: wmax: 1616 (ꢁCꢀN–) and
3278 (N–H) cm−1
.
1e: Anal. (%) Calc. for
C17H14N2Cl2Fe (found): C, 54.73 (54.7); H, 3.78 (3.8)
and N, 7.51 (7.5). IR: wmax: 1591 (ꢁCꢀN–) and 3327
(N–H) cm−1. 1f: Anal. (%) Calc. for C17H11N2F5Fe
(found): C, 51.77 (51.81); H, 2.81 (2.9) and N, 7.11
(N–H)
cm−1
.
2b:
Anal.
(%)
Calc.
for
(7.1). IR: wmax: 1541 (ꢁCꢀN–) and 3261 (N–H) cm−1
.
C35H29N3FeClO2PdP (found): C, 55.92 (55.75); H, 3.89
(3.9) and N, 5.59 (5.5). IR (KBr pellets) wmax: 1610
(ꢁCꢀN–) and 3204 (N–H) cm−1. 2d Anal. (%) Calc.
for C35H28N4FeClO4PPd (found): C, 52.71 (52.7); H,
3.54 (3.8) and N, 7.0 (6.8). IR: wmax: 1592 (ꢁCꢀN–)
19F-NMR (ppm): −156.35 (d, F(2) and F(6)),
−164.31 (t, F(3), F(5) and −167.86 (t, F(4)). 1g: Anal.
(%) Calc. for C17H18N2Cl2Fe (found): C, 67.94 (67.85);
H, 5.70 (5.65) and N, 8.80 (8.7). IR: wmax: 1599
(ꢁCꢀN–) and 3344 (N–H) cm−1
.
and 3291 cm−1
.
2g. Anal. (%) Calc. for
C36H32N2FeClPPd (found): C, 59.94 (59.7); H, 4.47
(4.4) and N, 3.89 (3.7). IR: wmax: 1608 (ꢁCꢀN–) cm−1
3.1.1.5. Preparation of trans-[Pd{[(4-Cl-C6H4)–NH–
NꢀCH–(p5-C5H4)]Fe(p5-C5H5)}2Cl2]. A 0.50 g (1.48
mmol) sample of the ferrocenylhydrazone [(p5-
.
3.1.1.7. Preparation of [[Pd{[(4-Cl–C6H3)–NH–
NꢀCH–(p5-C5H4)]Fe(p5-C5H5)}Cl(PPh3)2] (3a). A 25
mg (3.4×10−5 mol) sample of 2a were dissolved in 2
cm3 of CH2Cl2, then 9 mg (3.4×10−5 mol) of PPh3
were added. The resulting solution was stirred at room
C5H5)Fe{(p5-C5H4)–CHꢀN–NH–(C6H4-4-Cl)}]
(1a)
(0.74 mmol) were dissolved in 50 cm3 of methanol and
then 0.74 mmol of PdCl2 were added. The reaction
mixture was stirred at room temperature for 2 h. The

224
C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
V.G. Gupta, E. Kiefer, Chem. Rev. 86 (1996) 451. (d) V.V.
Dunina, O.A. Zalewskaya, V.M. Potatov, Russ. Chem. Rev. 57
(1988) 250. (e) I. Omae, Coord. Chem. Rev. 32 (1980) 235.
[2] For reviews concerning the applications of cyclopalladated com-
plexes see: (a) A.D. Ryabov, Synthesis (1985) 233. (b) M. Pfeffer,
Recl. Trav. Chim. Pays-Bas 109 (1990) 567. (c) P. Espinet, M.A.
Esteruelas, L.A. Oro, J.L. Serrano, E. Sola, Coord. Chem. Rev.
117 (1992) 215. (d) M. Beley, S. Chodorowski-Kimmes, J.P.
Collin, P. Laine´, J.P. Launay, J.P. Sauvage, Angew. Chem. Int.
Ed. Engl. 33 (1994) 1775. (e) Y. Agnus, M. Gross, M. Labarelle,
R. Louis, B. Metz, J. Chem. Soc. Chem. Commun. (1994) 939.
(f) C. Navarro-Ranninger, I. Lo´pez-Solera, J.M. Pe´rez, J.R.
Masaguer, C. Alonso, Appl. Organomet. Chem. 7 (1993) 57. (g)
S.J. Loeb, G.K.H. Shimizu, J. Chem. Soc. Chem. Commun.
(1993) 1935.
[3] (a) C. Lo´pez, J. Sales, R. Zquiak, X. Solans, J. Chem. Soc.
Dalton Trans. (1992) 2322. (b) R. Bosque, C. Lo´pez, J. Sales, X.
Solans, M. Font-Bard´ıa, J. Chem. Soc. Dalton Trans. (1994)
735. (c) R. Bosque, C. Lo´pez, J. Sales, X. Solans, J. Organomet.
Chem. 483 (1994) 61. (d) C. Lo´pez, R. Bosque, M. Font-Bard´ıa,
X. Solans, D. Tramuns, G. Fern, J. Silver, J. Chem. Soc. Dalton
Trans. (1994) 3039. (e) R. Bosque, C. Lo´pez, J. Sales, J.
Organomet. Chem. 498 (1995) 147. (f) R. Bosque, C. Lo´pez, J.
Sales, D. Tramuns, J. Solans, J. Chem. Soc. Dalton Trans.
(1995) 2445.
temperature for 1 h. Slow evaporation of the solvent at
room temperature produced the precipitation of ochre
microcrystals. (Yield: 81.6%). Anal. (%) Calc. for
C53H44Cl2N2FePdP2 (found): C, 63.40 (63.2); H,
4.41(4.45) and N, 2.79 (2.8). IR (KBr pellets) wmax: 3205
(N–H) and 1608 (ꢁCꢀN–) cm−1
.
3.1.1.8. Preparation of [Pd{[(4-NO2–C6H3)–NH–
NꢀCH–(p5-C5H4)]Fe(p5-C5H5)}Cl(PPh3)2] (3b). This
complex was synthesized in a NMR tube by dissolving
10 mg of 2b in 0.7 cm3 of CDCl3 and then the stoichio-
metric amount of PPh3 was added. The resulting mix-
ture was shaken at room temperature for 1 min giving
a pale brown solution.
3.1.1.9. Preparation of [Pd{[(3,6-Cl2–C6H3)–NH–
NꢀCH–(p5-C5H4)]Fe(p5-C5H5)}Cl(PPh3)2] (3e). This
compound was prepared using the procedure previously
described for 2a, but using: [(p5-C5H5)Fe{(p5-C5H4)–
CHꢀN–NH–C6H3-2,5-(Cl)2] (1e), as starting material.
(Yield: 37%). Characterization data: Anal. (%) Calc. for
C53H43Cl3N2FePdP2 (found): C, 61.30 (61.15), H, 4.17
(4.20) and N, 2.69 (2.63). IR (KBr pellets) wmax: 1608
[4] (a) G.R. Knox, P.L. Pauson, D. Wilson, J. Organomet. Chem.
450 (1993) 177. (b) R. Bosque, C. Lo´pez, J. Sales, X. Solans, J.
Chem. Soc. Dalton Trans. (1996) 3195. (c) C. Lo´pez, R. Bosque,
X. Solans, M. Font-Bard´ıa, J. Organomet. Chem. 539 (1997) 99.
(d) Y.J. Wu, Y.H. Liu, L. Yang, Q.X. Zhi, Polyhedron 16 (1979)
1259.
(ꢁCꢀN–) cm−1
.
3.2. Electrochemical studies
[5] (a) J.C. Gaunt, B.L. Shaw, J. Organomet. Chem. 102 (1975) 511.
(b) V.I. Sokolov, L.L. Triotskaya, O.A. Reutov, J. Organomet.
Chem. 182 (1979) 537. (c)L.G. Kuz’mina, Yu. T. Struchkov,
L.L. Troitskaya, V.I. Sokolov, O.A. Reutov, Izv. Akad. Nauk B.
SSR Ser. Khim. Nauk (1979) 1472. (d) V.I. Sokolov, L.L.
Troitskaya, K.S. Kurcheava, Zh. Org. Khim. 18 (1982) 2606. (e)
V.I. Sokolov, L.L. Troitskaya, T.I. Ruzhave, Gazz. Chim. Ital.
117 (1987) 525. (f) L.C. Chang, L.Y. Show, L. Li, Jiegou
Huaxue, J. Struct. Chem. 9 (1990) 130. (g) S.Q. Huo, Y.J. Yu,
C.X. Du, Y. Zhu, H.Z. Yuan, X.A. Mao, J. Organomet. Chem.
438 (1992) 139. (g) Y.J. Wu, Y.H. Liu, K.L. Ding, H.Z. Zuan,
X.A. Mao, J. Organomet. Chem. 505 (1995) 37.
[6] M. Nonoyama, M. Sugimoto, Inorg. Chim. Acta 35 (1979) 131.
[7] C. Lo´pez, R. Bosque, X. Solans, M. Font-Bard´ıa, J. Organomet.
Chem. 547 (1997) 309.
[8] (a) J. Albert, J. Granell, J. Sales, M. Font-Bardia, X. Solans,
Organometallics 14 (1995) 1393. (b) J. Albert, M. Go´mez, J.
Granell, J. Sales,, X. Solans, Organometallics 9 (1990) 1405. (c)
J. Albert, R.M. Ceder, M. Go´mez, J. Granell, J. Sales,
Organometallics 11 (1992) 1536. (d) J. Albert, J. Granell, R.
Moragas, J. Sales, M. Font-Bardia, X. Solans, J. Organomet.
Chem. 494 (1995) 95.
Electrochemical data for the hydrazones under study
were obtained by cyclic voltammetry under argon at
20°C using acetonitrile (HPLC-grade) as solvent and
tetrabutylammonium hexafluorophosphate (0.1 mol×
dm−3) as supporting electrolyte. The redox half-wave
potentials were referred to an AgꢀAgNO3 (0.1 mol×
dm−3, in acetonitrile) electrode separated from the
solution by a medium porosity fritted disk. A platinum
wire auxiliary electrode was used in conjunction with a
platinum disk working electrode, TACUSSEL-EDI ro-
tatory electrode (3.14 mm2). Cyclic voltammograms of
10−3 mol×dm−3 solutions of the samples in acetoni-
trile were recorded with a VersaStat, EG&G Princenton
Applied Research potentiostat.
Acknowledgements
[9] (a) J. Granell, R. Moragas, J. Sales, M. Font-Bard´ıa, X. Solans,
J. Chem. Soc. Dalton Trans. (1993) 1237. (b) J. Granell, R.
Moragas, J. Sales, J. Organomet. Chem. 431 (1992) 359.
[10] (a) J. Albert, J. Barro, J. Granell, J. Organomet. Chem. 408
(1991) 115. (b) R. Bosque, C. Lo´pez, D. Tramuns, X. Solans, J.
Chem. Soc. Dalton Trans. (1995) 2445.
We are indebted to the Direccio´n General de Inves-
tigacio´n Cient´ıfica y Te´cnica (grant no. PB96-0164) and
to the Generalitat de Catalunya (grant no. 1995-SGR-
0044) for financial support.
[11] T.H. Allen, O. Kennard, Chem. Design Automation News 8
(1993) 146.
References
[12] (a) A.J. Adamson, Y. Archambeau, R.E. Banks, B.B. Beagley,
M. Helliwell, R.G. Prichard, A.E. Tipping, Acta Crystallogr.
Sect. C C50 (1994) 961. (b) C. Lo´pez, R. Bosque, X. Solans, M.
Font-Bard´ıa, J. Silver, G. Fern, J. Chem. Soc. Dalton Trans.
(1995) 4053.
[1] For reviews concerning the cyclopalladation reaction see: (a) I.
Omae, Coord. Chem. Rev. 83 (1988) 137. (b) A.D. Ryabov,
Chem. Rev. 90 (1990) 403. (c) R.G. Newkome, W.E. Puckett,

C. Lo´pez, J. Granell / Journal of Organometallic Chemistry 555 (1998) 211–225
[13] C. Lo´pez, R. Bosque, X. Solans, M. Font-Bard´ıa, J. Organomet. many, 1976.
225
Chem. 535 (1997) 99.
[17] (a) M. Crespo, X. Solans, M. Font-Bard´ıa, Organometallics 14
(1995) 355. (b) J. Albert, J. Granell, R. Moragas, J. Sales, M.
Font-Bard´ıa, X. Solans, J. Organomet. Chem. 494 (1995) 95.
[18] A. Garc´ıa-Herbosa, D. Mun˜oz, D. Miguel, S. Garc´ıa-Granda,
Organometallics 13 (1994) 1775.
[19] (a) J. Albert, J. Granell, A. Luque, J. Minguez, R. Moragas, M.
Font-Bard´ıa, X. Solans, J. Organomet. Chem. 522 (1996) 87. (b)
R.J. Cross, N.H. Tennent, J. Chem. Soc. Dalton Trans. (1974)
1444. (c) J. Granell, D. Sainz, J. Sales, X. Solans, M. Font-Bar-
d´ıa, J. Chem. Soc. Dalton Trans. (1986) 1785. (d) C.K. Ander-
son, R.J. Cross, S.A. Leame, F.J. Robertson, D.J. Rycroft, M.
Rocamora, J. Organomet. Chem. 388 (1990) 221.
[14] R. Bosque, C. Lo´pez, J. Sales, Inorg. Chim. Acta 244 (1996) 141.
[15] (a) P. Zanello, A. Cinquantini, S. Mangani, G. Opromolla, L.
Pardi, C. Janiak, M.D. Raush, J. Organomet. Chem. 471 (1994)
171. (b) P. Zanello, G. Opromolla, L. Pardi, K.H. Pannell, K.H.
Sharma, J. Organomet. Chem. 450 (1993) 193. (c) N.F. Blom,
E.W. Neuse, M.G. Thomas, Trans. Met. Chem. 12 (1987) 301.
(d) W.F. Little, C.N. Reilley, J.D. Johnson, A.P. Sanders, J. Am.
Chem. Soc. 86 (1964) 1382. (e) G.L. Hoh, W.E. Mc Ewen, J.
Kleinberg, J. Am. Chem. Soc. 83 (1961) 3949.
[16] Gmelin Handbuch der Anorganische Chemie, Eisen Organische
Verbindungen, Ferrocen, 1, Teil A, Springer, Heildelberg, Ger-
.