Five- and six-membered palladacycles derived from [(η5-C5H5)Fe{(η5-C 5H4)-CH=N-(C6H4-2-C 6H5)}]

Article abstract of DOI:10.1016/S0277-5387(99)00163-1

The reaction of the novel ferrocenyl Schiff base: [(η⁵-C₅H₅)Fe{(η⁵-C ₅H₄)-CH=N-(C₆H₄-2-C ₆H₅)}] (1) with Na₂[PdCl₄] and Na(CH₃COO)·3H₂O in a 1:1:1 molar ratio in methanol is reported. In this reaction two different di-μ-chloro-bridged cyclopalladated complexes: [Pd{[(η⁵-C₅H₃)-CH=N-(C₆H ₄-2-C₆H₅)]Fe(η⁵-C ₅H₅)}(μ-Cl)]₂ (2a) and [Pd{[(C₆H₄-2-C₆H₄)-N=CH-(η ⁵-C₅H₄)]Fe(η⁵-C ₅H₅)}(μ-Cl)]₂ (2b) can be formed depending on the experimental conditions. Compounds 2a and 2b, which differ in the nature of the metallated carbon atom (C_sp²,ferrocene or C_sp²,biphenyl, respectively), undergo cleavage of the 'Pd(μ-Cl)₂Pd' bridges in the presence of thallium (I) acetylacetonate, deuterated pyridine or triphenylphosphine giving the monomeric derivatives: [Pd(C^∧N)(acac)] (3a, 3b) and [Pd(C^∧N)Cl(L)] {with L=py- d₅(4a, 4b), PPh₃(5a, 5b)}. The reactions of 2 with 1,2-bis(diphenylphosphino)ethane (dppe) reveal that the two isomers (2a and 2b) exhibit different reactivity versus dppe. These results have been interpreted on the basis of steric effects. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00163-1

Polyhedron 18 (1999) 2583–2595
Five- and six-membered palladacycles derived from
[(h5-C5H5)Feh(h5-C5H4)-CH5N-(C6H4-2-C6H5)j]
*
´
´
´
Monica Benito, Concepcion Lopez , Xavier Morvan
´
`
´
´
`
Departament de Quımica Inorganica, Facultat de Quımica, Universitat de Barcelona, Martı Franques 1-11, 08028 Barcelona, Spain
Received 9 March 1999; accepted 17 May 1999
Abstract
The reaction of the novel ferrocenyl Schiff base: [(h5-C5H5)Feh(h5-C5H4)-CH5N-(C6H4-2-C6H5)j] (1) with Na2[PdCl4] and
Na(CH3COO)?3H2O in a 1:1:1 molar ratio in methanol is reported. In this reaction two different di-m-chloro-bridged cyclopalladated
complexes: [Pdh[(h5-C5H3)-CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j(m-Cl)]2 (2a) and [Pdh[(C6H4-2-C6H4)-N5CH-(h5-C5H4)]Fe(h5-
C5H5)j(m-Cl)]2 (2b) can be formed depending on the experimental conditions. Compounds 2a and 2b, which differ in the nature of the
metallated carbon atom (Csp
or Csp ,biphenyl, respectively), undergo cleavage of the ‘Pd(m-Cl)2Pd’ bridges in the presence of
2
2
,ferrocene
thallium (I) acetylacetonate, deuterated pyridine or triphenylphosphine giving the monomeric derivatives: [Pd(C N)(acac)] (3a, 3b) and
[Pd(C N)Cl(L)] hwith L5py- d5 (4a, 4b), PPh3(5a, 5b)j. The reactions of 2 with 1,2-bis(diphenylphosphino)ethane (dppe) reveal that the
two isomers (2a and 2b) exhibit different reactivity versus dppe. These results have been interpreted on the basis of steric effects.
1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
length of the -(CH2)n-chain, or (b) the R group bound to
the imine carbon atom are enough to modify the structure
of the metallacycle [28,29] (Fig. 1).
In order to elucidate whether the incorporation of a
bulky substituent on the imine nitrogen in: [(h5-
C5H5)Feh(h5-C5H4)-C(H)5N-R9j] could also be important
in determining the type of s(C-H) bond to be activated, we
studied the cyclopalladation of the ferrocenylimine: [(h5-
C5H5)Feh(h5-C5H4)-C(R)5N-(C6H4-2-C6H5)j] (1) (Fig.
1C). This substrate could produce two types of palladacy-
During the last decade the interest in cyclopalladated
compounds derived from N-donor ligands has increased
exponentially [1–3] mainly due to their novel and out-
standing applications [4–13]. To date most of these
systems contain organic amines, imines, oximes and, to a
lesser extent, hydrazones or azo-derivatives, bound to the
palladium atoms through a Csp
or a Csp3, carbon
2
,phenyl
atom. More recently, the study of cyclopalladation of
N-donor ferrocenyl ligands (such as: ferrocenylamines,
imines, oximes, hydrazones, azines and azoderivatives) has
allowed the isolation and characterization of a novel type
cle: (a) a six-membered ring with a s(Pd-Csp ,biphenyl) bond
2
or (b) a five-membered palladacycle containing the .C5
N- bond, which would require the activation of the ortho-
of palladacycle with a s(Pd-Csp ,ferrocene) bond [14–43].
2
s(Csp
-H) bond.
2
,
ferrocene
Furthermore, these studies have shown that although the
cyclopalladation of the ferrocenyl Schiff bases: [(h5-
C5H5)Feh(h5-C5H4)-C(R)5N-R9j] hR5H, CH3 or C6H5
and R95susbtituted phenyl, benzyl ringsj (Fig. 1A) pro-
In this paper we describe the synthesis of compound 1
and the activation of two different ortho s(C-H) bonds:
s(Csp ,ferrocene-H) or s(Csp ,biphenyl-H). This study has
2
2
allowed us to isolate and characterize two types of
duced five-membered rings with a s(Pd-Csp ,ferrocene) bond
2
metallacycle, containing a s(Pd-Csp ,biphenyl) or a s(Pd-
2
[28,29], the results obtained for: [(h5-C5H5)Feh(h5-C5H4)-
(CH2)n-N5CH(R)j] hn51 or 2 and R5substituted phenyl
groupsj (Fig. 1B) revealed that minor changes in (a) the
Csp ,ferrocene) bond.
2
2. Experimental
*Corresponding author. Tel.: 134-93-402-1274; fax: 134-93-490-
7725.
´
E-mail address: clopez@kripto.qui.ub.es (C. Lopez)
Elemental analyses (C, H and N) were carried out at the
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00163-1
1999 Elsevier Science Ltd. All rights reserved.

2584
M. Benito et al. / Polyhedron 18 (1999) 2583–2595
Fig. 1. Schematic view of some of the ferrocenylimines used in the cyclopalladation reactions (A–B) and of the novel ferrocenyl Schiff base under study
(C). All these ligands could produce two different types of palladacycles depending on the relative position of the functional group .C5N- versus the
metallacycle (endo- and exo-derivatives).
`
Serveis Cientifico-Tecnics de la Universitat de Barcelona.
was dissolved in benzene (ca. 20 ml) and 0.615 g (3.63
1023 mol) of the amine was added. The flask was again
connected to the Dean–Stark apparatus and the procedure
was repeated. Finally, the solution obtained after the reflux
was filtered out. The undissolved materials were discarded
and the filtrate was concentrated to dryness on a rotary
evaporator, producing a red–brownish oily residue, which
contained ligand 1. The addition of n-hexane to the residue
followed by vigorous stirring for ca. 10 min at room
temperature, produced 1 (yield: 72%). Characterization
Infrared spectra were obtained with a Nicolet-500-FTIR
instrument using KBr pellets for the solid samples or NaCl
discs for the imine 1. Routine 1H-NMR spectra were
recorded at 208C on a Gemini-200 MHz instrument using
benzene -d6 or CDCl3 (99.9%) as solvents. Si(CH3)4 was
used as internal standard in the later cases. 13Ch1Hj and
31P-NMR spectra were recorded with a Bruker-250DXR
instrument using CDCl3 (99.9%) as solvent. Tri-
methylphosphite was used as internal reference for 31P-
NMR spectra [d31P for P(OCH3)3: 141.17 ppm].
data for 1: IR: n(.C5N-)51625 cm21
.
2.1.2. Preparation of compounds 2
2.1. Materials and synthesis
The imine 1 (1.81 g, 4.9631023 mol), Na2[PdCl4] (1.46
g, 5.0731023 mol) and Na(CH3COO)?3H2O (0.68 g,
5.0031023 mol) were suspended in 25 ml of methanol.
The reaction flask was protected from the light with
aluminium foil and the reaction mixture was stirred at
room temperature for 3 h (for 2b) or 7 days (for 2a). The
isolation of complex 2a was achieved as follows: the red
precipitate formed was dissolved in the minimum amount
of CHCl3 and purified by SiO2-columm chromatography
using CHCl3 as eluant. The red band eluted was collected
and concentrated in vacuum on a rotary evaporator. The
resulting residue was then treated with n-hexane (ca. 20
ml) and stirred at room temperature for 20 min. The solid
formed was filtered out and dried in vacuum (yield: 65%).
When the reaction was carried out for 3 h the solid formed
consisted of a 1.3:1.0 mixture of 2a and 2b, which were
separated by SiO2-column chromatography using a CHCl3:
n- hexane (100:10) mixture as eluant. During the elution,
two red bands were collected. The former contained
complex 2b. The solution of 2b was concentrated to
dryness on a rotary evaporator, and the residue was
dissolved in the minimum amount of CH2Cl2 and the
addition of n-hexane followed by vigorous stirring at room
temperature for 5 min produced the precipitation of 2b
(yield: 32%). When this treatment was repeated with the
Ferrocenecarboxaldehyde,
2-phenylaniline,
tri-
phenylphosphine, thallium acetylacetonate and 1,2-bis-
(diphenylphosphino)ethane were obtained from commer-
cial sources and used as received. The solvents, except
benzene, were dried and distilled before use. Some of the
procedures described below require the use of hazardous
materials, such as thallium(I) salts or benzene, which
should be handled with caution.
2.1.1. Preparation of the ferrocenylimine (1)
Ferrocenecarboxaldehyde (2.00 g, 9.3431023 mol) and
2-phenylaniline (1.58 g, 9.3431023 mol) were dissolved
in 25 ml of benzene. The reaction flask was connected to a
Dean–Stark apparatus and to a condenser. The reaction
mixture was then refluxed on an ethyleneglycol bath until
ca. 20 ml of the azeotrope benzene–water had condensed
in the Dean–Stark. The resulting solution was concentrated
1
to dryness on a rotary evaporator. The H-NMR spectrum
of the residue (in CDCl3) was recorded to check the
progress of the reaction, and revealed that the residue
contained a 1:2 mixture of unreacted ferrocenecarbox-
aldehyde and the ferrocenyl Schiff base (1). In order to
achieve the total conversion of the aldehyde, the residue

M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2585
second eluted band it yielded complex 2a (yield: 20%)
which was collected by filtration and air-dried. Compound
2a can also be obtained using the following procedure:
palladium(II) acetate (0.500 g, 2.23 31023 mol) and the
imine 1 (0.815 g, 2.2331023 mol) were refluxed in glacial
acetic acid (30 ml) for 2 h. Then the resulting suspension
was concentrated to dryness on a rotary evaporator and the
residue was treated with LiCl (106 mg, 2.531023 mol) in
ethanol (40 ml). The resulting reaction mixture was
refluxed for 30 min. The orange–red solid formed was
filtered out, washed with three portions (5 ml) of ethanol
and air-dried. Finally the solid was purified by SiO2
column chromatography using CHCl3 as eluant (yield:
49%). Characterization data for 2a: Anal. (%) Calcd. for
C46H36N2Cl2Fe2Pd2 (found): C, 54.5 (54.6); H, 3.6 (3.59)
and N, 3.1 (2.77). IR: n(.C5N-)51586 cm21. For 2b:
Anal. (%) Calcd. for C46H36N2Cl2Fe2Pd2 (found): C, 54.4
(54.6); H, 3.6 (3.59) and N, 2.9 (2.77). IR: n(.C5N-)5
undissolved materials were removed by filtration and
discarded. The filtrate was then concentrated to dryness on
a rotary evaporator, giving an orange–red solid which was
collected and air-dried. (yield: 87 and 72% for 5a and 5b
respectively). Characterization data for 5a: Anal. (%)
Calcd. for C41H33NClFePPd (found): C, 63.9 (64.0); H,
4.3 (4.29) and N, 1.8 (1.87). IR: n(.C5N-)51590 cm21
.
For 5b: Anal. (%) Calcd. for C41H33NClFePPd (found): C,
64.1 (64.1); H, 4.3 (4.5) and N, 1.8 (2.0). IR: n(.C5N-)
51617 cm21
.
2.1.6. Preparation of compound 6b
A 100 mg (9.931025 mol) amount of the di-m-chloro-
bridged cyclopalladated derivative 2b was suspended in 20
ml of CH2Cl2, and the stoichiometric amount of dppe (40
mg, 4.931025 mol) was then added. The resulting mixture
was stirred at room temperature for 20 min and filtered out.
The orange–red filtrate was concentrated to dryness on a
rotary evaporator. Addition of n-hexane produced the
precipitation of the compound, which was filtered out and
air-dried. (yield: 65%). Characterization data for 6b: Anal.
(%) Calcd. for C49H42NClFeP2Pd (found): C, 65.1
(65.15); H, 4.7 (4.6) and N, 1.6 (1.45). IR: n(.C5N-)5
1603 cm21
.
2.1.3. Preparation of compounds 3
A 0.100-g (9.931025 mol) amount of the corresponding
di-m-chloro-bridged cyclopalladated derivative (2a or 2b)
was suspended in 20 ml of acetone, then the stoichiometric
amount of thallium(I) acetylacetonate was added. The
resulting mixture was stirred at room temperature for 1.5 h
and then filtered out with Whatman paper, to remove the
thallium(I) chloride formed during the process. The re-
sulting solution was concentrated to dryness on a rotary
evaporator. The red solid formed was washed with n-
hexane and air-dried (yield: 74 and 68% for 3a and 3b,
respectively). Characterization data for 3a: Anal. (%)
Calcd. for C27H35NClFeO2Pd (found): C, 58.9 (59.00); H,
1611 cm21
.
2.2. Computational details
The calculations were performed with the SPARTAN 4.1
suite of programs [58] using silicon graphics (model:
INDIGO-2 power ZX). The pm3 method was used with
the default parameters provided by the program. Geometri-
cal restrictions were not imposed in any case. The calcula-
tions were undertaken with the option SCF5converge and
the number of cycles required for the optimization of the
geometry of the ligand and of the model complex: [Pdh(h5-
C5H5)Fe[(h5-C5H4)-CH5N-(C6H4-2-C6H5)]jCl3]2 was
greater than the default value (200 cycles). A minimum of
103 cycles was necessary in both cases.
4.6 (4.40) and N, 2.5 (2.52). IR: n(.C5N-)51590 cm21
.
For 3b: Anal.(%) Calcd. for C27H35NClFeO2Pd (found):
C, 58.9 (59.00); H, 4.69 (4.40) and N, 2.5 (2.52). IR:
n(.C5N-)51598 cm21
.
2.1.4. Preparation of compounds 4
These compounds were prepared in situ and character-
ized by NMR spectroscopy. The method used for these
preparations was the following: the corresponding complex
2 (30 mg, 2.9731025 mol) was suspended in 0.7 ml of
CDCl3. An excess of deuterated pyridine (5 ml, 6.231025
mol) was then added and the reaction mixture was shaken
vigorously for 2 min to aid the dissolution of the di-m-
chloro-bridged cyclopalladated complex, which produced a
dark orange solution.
3. Results and discussion
3.1. The ligand
The new ferrocenylimine [(h5-C5H5)Feh(h5-C5H4)-
CH5N-(C6H4-2-C6H5)j] (1) was prepared following the
general procedure described for the synthesis of related
ferrocenyl Schiff bases of general formula: [(h5-
C5H5)Feh(h5-C5H4)-CH5N-Rj] hwith R5phenyl or
benzyl groupsj [26–28], which consists of the reaction of
stoichiometric amounts of ferrocenecarboxaldehyde and
the corresponding amine under reflux using a Dean–Stark
apparatus (to remove the benzene–water azeotrope formed
in the course of the reaction). When this reaction was
performed in identical experimental conditions, but using
2.1.5. Preparation of compounds 5
Triphenylphosphine (178 mg, 6.9 31024 mol) was
added to a suspension containing 340 mg (3.4 31024 mol)
of the corresponding di-m-chloro-bridged cyclopalladated
complex (2a or 2b) and 10 ml of benzene. The reaction
mixture was then stirred at room temperature for 1 h. The

2586
M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2-phenylaniline as reagent, a mixture of the imine: [(h5-
C5H5)Feh(h5-C5H4)-CH5N-(C6H4-2-C6H5)j] (1) and fer-
rocenecarboxaldehyde (in a 5:1 molar ratio) was obtained.
However, the complete conversion of the aldehyde was
easily achieved using a large excess of the amine. The use
of excesses of amines were also required in the preparation
of ferrocenyl Schiff bases derived from acetyl or benzoyl
ferrocene and it has been postulated that an increase in the
bulk of the reagents hinders the condensation process
[26–28].
introduces planar chirality (Rp or Sp), and the formation of
several diastereomers of [Pdh[(h5-C5H3)-CH5N-(C6H4-2-
C6H5)]Fe(h5-C5H5)j(m-Cl)]2 cannot be ruled out. Conse-
quently, the cyclopalladation of 1 may produce a wide
variety of isomeric species.
In order to try and elucidate the nature of the com-
ponents of the mixture, SiO2 column chromatography was
used. Elution with a CHCl3: n-hexane (100:10) mixture
allowed us to isolate two different compounds 2a and 2b
(in a ratio: 2b/2a51.3). Elemental analyses of these solids
were consistent with those expected for a di-m-chloro-
bridged cyclopalladated complex: [Pd(C N)(m-Cl)]2, thus
suggesting that two different isomers formed during the
reaction. The proton NMR spectrum of the minor com-
ponent, 2a, was coincident with one of the sets of signals
observed in the NMR spectrum of the crude material,
showing one singlet at 8.06 ppm (Table 1). The signals
due to the ferrocenyl fragment appeared as four singlets of
relative intensities 1:1:1:5 in the range: 3.50–5.20 ppm
(Fig. 2A), thus suggesting the formation of [Pdh[(h5-
C5H3)-CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j(m-Cl)]2 (2a)
which contains a five-membered palladacycle with a s(Pd-
3.2. Activation of s(C–H) bonds in [(h5-C5H5 )Feh(h5-
C5H4 )-CH5N-(C6H4-2-C6H5 )j] (1)
When compound 1 was reacted with Na2[PdCl4] and
Na(CH3COO)?3H2O (in a 1:1:1 molar ratio) in methanol
at room temperature for 3 h a reddish precipitate formed
(Scheme 1). Elemental analyses of this solid were con-
sistent with those expected for a di-m-chloro-bridged
cyclopalladated complex: [Pd(C N)(m-Cl)]2. However, its
1H-NMR spectra showed two superimposed sets of signals.
For instance, two singlets due to the imine proton appeared
at 8.64 and 8.06 ppm. The relative intensities of these
signals was 1.3:1.0. In addition, thin layer chromatography
revealed that the solid consisted of a mixture of at least
two compounds.
Csp , ferrocene) bond.
2
In contrast with these results, the 1H-NMR spectra of
the major component (2b) showed a group of five singlets
(with a relative intensity of 1:1:1:1:5) which suggested that
the ferrocenyl fragment contained a non-metallated C5H4
ring (Fig. 2B). In addition, the resonance of the H11
proton1 appeared at higher fields than in the free ligand (1)
Ligand 1 has two different s(C-H) bonds susceptible to
metallation hs(Csp ,ferrocene-H) and s(Csp ,biphenyl-H)j.
2
2
Thus, the reaction could produce different types of isomer
depending on (i) the relative arrangement of the two imine
nitrogens (syn- or anti-) in the dimers and (ii) the nature of
1
and in complex 2a. Previous H-NMR studies on cyclopal-
1For the identification of this atom see scheme shown at the bottom of
Scheme 1.
the metallated carbon atom (Csp
addition, the activation of the s(Csp ,ferrocene-H) bond
or Csp ,biphenyl). In
2
2
2
,ferrocene
Scheme 1. (i) Na2[PdCl4], Na((CH3COO)?3H2O, room temperature (see Section 3.2). (ii) SiO2-column chromatography using a mixture: CHCl3:
n-hexane (100:10), as eluant. (iii) Pd(CH3COO)2, glacial CH3COOH, reflux, 2 h. (iv) LiCl in ethanol, 30 min. (v) SiO2-column chromatography using
CHCl3 as eluant.

M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2587
Table 1
Selected 1H-NMR data (in ppm) for compounds under study and chemical shifts of 31P (in ppm) for compounds 4a,b and 6a,b. Numbering of the atoms
refers to the schemes shown below
Compound
Proton-NMR data
C5H5
31P-NMR data
H2
H3
H4
H5
-CH5N
d(31P)
1a
4.10
3.75
3.81
3.91
3.81
3.83
3.75
3.81
3.70
4.16
3.68
4.70
–
4.32
–
3.55
–
3.45
–
4.42
3.40
4.26
4.42
4.57
4.31
4.59
4.34
4.58
4.20
4.59
4.42
4.29
4.38
4.34
4.45
4.25
4.54
4.72
4.77
4.40
4.49
4.70
4.45
4.60
4.75
4.72
4.70
4.84
4.76
4.80
4.65
5.52
8.26
8.05
8.64
8.12
8.51
8.07
8.61
8.20c
–
–
–
–
–
–
–
34.8
2ab
2bb
3a
3b
4a
4b
5a
5b
6ad
6b
3.55
–
4.59
8.56c
34.3
e
43.41f,g and 56.89f,h
39.81f,g and 55.36f,h
8.19c
a In the free ligand the protons H2 and H5 are equivalent and the same happens with H3 and H4.
b Low solubility.
c Doublet due to phosphorus coupling.
d In this case the spectrum was recorded at 240 K (see Section 3.5).
e Masked by the multiplet due to the aromatic protons of the 1,2-bis(diphenylphosphino)ethane.
f Doublet.
g Phosphorus trans- to the nitrogen.
h Phosphorus cis- to the nitrogen.
ladated compounds of general formulae: [Pdh(C6H4)-CH5
N-R9j(m-Cl)]2, (with R5phenyl or benzyl groups) which
contain an ortopalladated imine ligand, have shown that
C5H3)]Fe(h5-C5H5)j(m-Cl)]2 which arises from the bis(in-
sertion) of hex-3-yne into the s(Pd-C) bond of complex 2b
confirm that in 2b metallation occurred on the biphenyl
group [48,49].
the formation of the s(Pd-Csp , aryl) bond produces a high
2
field shift of the proton on the adjacent position to the
metallated carbon [44–47]. These results suggested that
complex 2b contained a six-membered palladacycle fused
with the biphenyl ring, which would arise from the
In order to elucidate whether the preferential formation
of 2a and 2b could be controlled experimentally, several
strategies were used. First, the cyclopalladation process
was studied at room temperature using different reaction
periods (from 3 h to 7 days). In all cases, the elemental
analyses of the solids obtained in each one of the experi-
ments were consistent with those expected for di-m-chloro-
bridged cyclopalladated compounds: [Pd(C N)(m-Cl)]2.
activation of a s(Pd-Csp , biphenyl) bond. The formulae
2
proposed for the two isomeric complexes: [Pdh[(h5-C5H3)-
CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j(m-Cl)]2 (2a) and
[Pdh[(C6H4 -2-C6H4)N5CH-(h5 -C5H3)]Fe(h5 -C 5H5)j-
(m-Cl)]2 (2b), which differ in the nature of the metallated
carbon atom is also supported by the results obtained in the
study of the reactions of these complexes with neutral
ligands such as deuterated pyridine, PPh3 (see below) and
with alkynes [48,49]. The X-ray crystal structure of the
complex: [Pdh[hEt-C5C-Et)2(C6H4-2-C6H4)jN5CH-(h5-
1
The compositions of these materials were studied by H-
NMR spectroscopy immediately after the addition of the
solvent. When the reaction was carried out for short times
(3 h), the 1H-NMR spectrum (in CDCl3) showed two
singlets (at ca. 8.06 and 8.64 ppm in a relative ratio
1.0:1.3) due to the imine protons were detected and their

2588
M. Benito et al. / Polyhedron 18 (1999) 2583–2595
described so far, the number of published articles involv-
ing the formation of isomeric palladacycles with different
s(Pd-C) bond is scarce [52–54]. As far as we know only
three examples of this sort of reaction have been described
so far. In one of them, the cyclopalladated complex at the
peri-position of the di(naphthalene-1-yl)diazene (com-
pound Ia in Scheme 2) [52] evolves under heating in
toluene to the five-membered metallacycle Ib, in which the
palladium is bound to the ortho site. A few years ago,
Ryabov [53] reported that when the cyclopalladated com-
plex derived from 1-(3,4-dimethyloxyphenyl)-2-(4-nitro-
phenyl)-2-azopropene (compound IIa in Scheme 2), was
refluxed in a benzene: acetic acid (1:1) mixture for 4 h, the
reaction produced the palladated complex (IIb) (Scheme
2) in which the palladium is bound to the nitrosubstituted
phenyl ring. In these two cases the isomerization involves
the cleavage of a s(Pd-Csp , aryl ring) bond in the starting
2
material and the formation of
a
different s(Pd-
Csp , aryl ring) bond. Albert et al. [54] have also reported
2
that exocyclic five-membered palladacycles of general
fomula
[Pdh2-[CH2-N5CH-29,49,69-(CH3)3-C6H2]-3-
(C6H3-R)j(m-CH3COO)]2 hwith R5H or CH3j h(IIIa) in
Scheme 2j isomerized in acetic acid to give the six-
membered cyclopalladated complexes (IIIb) with a s(Pd-
Csp3 ) bond. Besides that, recent mechanistic studies have
Fig. 2. Partial views of the proton spectrum of (A) [Pdh[(h5-C5H3)-CH5
N-(C6H4-2-C6H5)]Fe(h5-C5H5)(m-Cl)]2(2a) and (B) [Pdh[(C6H4-2-
C6H4)-N5CH-(h5-C5H4)]Fe(h5-C5H5)(m-Cl)]2 (2b).
positions and multiplicities were identical to those of 2a
and 2b. For intermediate reaction periods (from 1 day to 6
days) the intensities of the signals due to the ‘endocyclic’
palladacycle (2a) increased progressively in respect to
those of (2b).
In contrast, when the reaction was performed for 7 days,
the 1H-NMR spectrum showed one signal and the 1H-
NMR spectrum was identical to that of complex: [Pdh[(h5-
C5H3)-CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j(m-Cl)]2 (2-
a), in which the palladium is bound to the ferrocenyl unit.
The comparison of the results obtained in these experi-
ments suggests that when the reaction time of the cyclopal-
ladation process increases, a greater proportion of the
‘endocyclic’ complex 2a is formed. This suggests that 2a
might be formed under thermodynamic control.
Furthermore, for shorter reaction times (i.e. 1.5 h), the
isolated solid consisted of a mixture of the two di-m-
chloro-bridged cyclopalladated compounds 2 and the
coordination complex: [Pdh(h5-C5H5)Fe[(h5-C5H4)-CH5
N-(C6H4-2-C6H5)]j2Cl2] (29). According to the general
mechanism accepted for the cyclopalladation of N-donor
ligands, the reaction takes place in two steps: (a) the
coordination of the ligand and (b) the subsequent elec-
trophilic attack of the coordinated palladium to the carbon
[50,51]. On this basis, the formation of 29 could be
expected to take place before the activation of the s(C-H)
bond.
Scheme 2. (i) In boiling toluene at 1368C. (ii) In benzene: CH3COOH
(1:1), 4 h at 708C. (iii) In refluxing CH3COOH during 45 min. (For
further information about these reactions see Refs. [52–54].)
Despite the large variety of cyclopalladated complexes

M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2589
shown that the five-membered exocyclic cyclopalladated
3.3. Approaches to rationalize the activation of s(C-H)
bonds in 1
complexes: [Pdh(3-R-C6H3)-2-CH2-N5CH-C6H4-R9j(m-
CH3COO)]2 hwith R5H and R953-NO2 or 2,4,6-Me3 and
R5Me, R952,4,6-Me3j h(IIIa) in Scheme 2j in acetic acid
produce a deep red solution which rapidly evolves to give
the corresponding endocyclic metallacycles (IIIb) in quan-
titative yield [55,56].
In an attempt to explain how it is possible to activate the
two types of s(C-H) bonds in [(h5-C5H5)Feh(h5-C5H4)-
CH5N-(C6H4-2-C6H5)j] (1), molecular models were
used. Their manipulation showed that in 1 the bulk of the
biphenyl group precludes the free rotation around the
N-Cipso bond in the free ligand. In order to confirm this
finding, semiempirical calculations were performed using
the SPARTAN 4.0 program [58] and the pm3(tm) method. For
this substrate, the formation enthalpy of the molecule,
DHform . was calculated for a wide variety of orientations of
the three unsaturated rings: C5H4 and the two aryl rings of
the biphenyl group. Such arrangements were generated by
modifying the torsion angles: [C(2)-C(1)-C(6)-N], [C(6)-
N-C(19)-C(29)] and [C(19)-C(69)-C(79)-C(129)], (here-
inafter referred to as F1, F2 and F3, Fig. 3).
Though the calculations were carried out for different
F1 values (from 08 to 908), the results showed that a
co-planar orientation of the C5H4 ring and the imine
fragment (F1|08) is strongly preferred. This is consistent
with earlier results on the ferrocenyl Schiff bases: [(h5-
C5H5)Feh(h5-C5H4)-C(R)5N-R9j], [59] (with R5H, Me
or Ph and R95phenyl or benzyl groups). The minimum
values of the formation enthalphy (DHform) correspond to
F2 and F3 larger than zero. Consequently, the arrangement
of these groups precludes the p-conjugation between (a)
the two phenyl rings of the (C6H4-2-C6H5) group or (b)
the imine group and the phenyl ring (of the bipenyl group)
bound to the nitrogen.
In view of these facts, we decided to perform the
cyclopalladation reaction in acidic media. When equimolar
amounts of 1 and palladium(II) acetate were refluxed in
acetic acid for 2 h a dark red suspension was obtained. The
removal of the solvent, followed by the subsequent treat-
ment with LiCl in ethanol at room temperature produced a
red solid (Scheme 1). The proton-NMR spectrum of the
crude material showed one singlet at ca. 8.05 ppm and a
group of four signals of relative intensities 1:5:1:1 in the
range 3.5–4.5 ppm. The position and multiplicities of these
signals were identical to those observed for [Pdh[(h5-
C5H3)-CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j(m-Cl)]2 (2a)
and no evidence of the formation of any other cyclopalla-
dated complex was detected by 1H-NMR spectroscopy.
These findings suggests that the formation of the metal-
lacycle with a s(Pd–Csp ,ferrocene) bond is strongly pre-
2
ferred in acidic media.
On the other hand, it should also be mentioned that the
‘exocyclic’ complex 2b degradates slowly in CDCl3 at
room temperature. For instance, after 3 days of storage at
1
room temperature (ca. 208C) the H-NMR spectrum also
revealed the presence of small amounts (ca. 8%) of the
‘endocyclic’ 2a. For longer periods an increase of the
relative proportion of 2a:2b was observed. The coexist-
ence of a nearly equimolar ratio of the two isomers (2a
and 2b) was detected after 10 days. However, when these
experiments were repeated using benzene-d6 instead of
CDCl3, no evidence of any isomerization change was
detected after 15 days. These findings suggest that the
2b→2a interconversion takes place in protic solvents, and
that it could be promoted by the traces of acids, in good
agreement with the results obtained when the cyclopallada-
tion reaction was carried out in acetic acid, which yielded
the ‘endocyclic’ derivative 2a, exclusively.
To sum up, the results described in this section are in
sharp contrast with our previous results on cyclopallada-
tion of ferrocenylimines of general formula: [(h5-
C5H5)Feh(h5-C5H4)-C(R)5N-R9j] (with R5H, Me or Ph
and R95phenyl or benzyl groups) [26–38] for which the
formation of five membered metallacycles with s(Pd-
The F2 and F3 angles obtained for the optimized
geometry (Fig. 3A) of this molecule were 121.68 and 74.68,
respectively. For this arrangement of substituents the two
C-H bonds susceptible to activation hC(2)-Hj and hC(129)-
Hj are on the same side as the lone pair of the imine
nitrogen, thus suggesting that when the palladium(II) binds
to the nitrogen, the two carbon atoms are expected to be
very close to the palladium.
Further, it is widely accepted that cyclopalladation of
N-donor ligands proceeds in two steps, which consist of
the coordination of the nitrogen to the palladium and
subsequent electrophilic attack [50,51]. On this basis, we
attempted to assess whether, once the Pd-N bond is
formed, the orientation of the two s(C-H) bonds suscep-
tible to metallation (Csp ,ferrocene-H or Csp ,biphenyl-H) could
2
2
be suitable for the electrophilic attack. The optimization of
the geometry of the model complex: [Pdh(h5-C5H5)Fe[(h5-
C5H4)-CH5N-(C6H4-2-C6H5)]jCl3]2, (where the pal-
ladium is bound to the imine through the nitrogen exclu-
sively), was undertaken using the pm3(tm) model [58].
The results revealed that the ‘PdCl3’ fragment is nearly
orthogonal to the imine group (Fig. 3B). This arrangement
is similar to that found for: trans-[Pdh(h5-C5H5)Fe[(h5-
C5H4)-CH5N-N(CH3)2]j2Cl2] [60] whose crystal struc-
ture shows that the two ferrocenyl ligands are practically
orthogonal to the ‘PdCl3’ unit. In addition, for the opti-
Csp ,ferrocene) bonds was detected exclusively. It should be
2
noted that despite for ligands with R95benzyl groups the
formation of five- or six-membered palladacycles with a
s(Pd-Csp ,aryl) could also take place no evidences of the
2
formation of the metallacycles was detected by NMR
[26–38]. These differences suggest that the activation of
the s(Csp ,biphenyl-H) bond in 1 could be attributable to the
2
higher bulk of the R9 substituent (biphenyl versus benzyl
[57]) in the substrate under study, which could induce
steric effects.

2590
M. Benito et al. / Polyhedron 18 (1999) 2583–2595
Fig. 3. Optimized geometries of: (A) the ferrocenylimine [(h5-C5H5)Feh(h5-C5H4)-CH5N-(C6H4-2-C6H5)] and (B) the coordination complex: [Pdh(h5-
C5H5)Feh(h5-C5H4)-CH5N-(C6H4-2-C6H5jjCl3]2. The values of the F2 and F3 torsion angles for the optimized geometries are: 121.68 and 74.68 (for the
ligand, 1) and 124.48 and 56.78 for the coordination complex.
mized geometry, the distances between the palladium and
the carbon atoms potentially involved in the metallation
process are C(2) and C(129), 2.77 A and 2.83 A, respec-
tively. These values are quite similar and consequently,
according to this approach, the orientation of the two C-H
bonds appears to be suitable for activation. Besides that,
Addition of the stoichiometric amount of thallium(I)
acetylacetonate to a suspension of 2a in acetone at room
temperature produced the precipitation of TlCl, which was
removed by filtration. The subsequent concentration of the
bright-red filtrate to dryness produced [Pdh[(h5-C5H3)-
˚
˚
CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j(acac)] (3a) in
a
fairly good yield (74%).
since the activation of the s(Csp ,ferrocene-H) or
2
The reaction of 2a with deuterated pyridine or tri-
s(Csp ,biphenyl-H) requires the electrophilic attack of the
2
phenylphosphine
produced:
[Pdh[(h5-C5H3)-CH5N-
coordinated palladium(II) to the carbon atom [50,51], the
viability of the formation of compounds 2a or 2b from
[Pdh(h5 -C5H5)Fe[(h5 -C5H4)-CH5N-(C6H4 -2-C6H5)]j-
Cl3]2 is expected to depend also on the net charges on the
two carbon atoms susceptible to palladation C(2) and
C(129). For the complex under study the differences in the
values of the net charges on C(2) (-0.27) and C(129)
(-0.33) are very small. Consequently, the results obtained
from this approach suggest that the arrangement of ligands
around the palladium(II) atom and the tiny differences of
the net charges on the carbons C(2) and C(129) in the
model complex [Pdh(h5-C5H5)Fe[(h5-C5H4)-CH5N-
(C6H4-2-C6H5)]jCl3]2 may be responsible for the forma-
tion of the two types of palladacycle 2a and 2b, which
(C6H4-2-C6H5)]Fe(h5-C5H5)jCl(L)] hL5py-d5 (4a) or
PPh3 (5a)j, (Scheme 3), which contain a five-membered
metallacycle with a s(Pd-Csp ,ferrocene) bond.
2
Similarly, when these reactions were carried out using
complex 2b as starting material, compounds: [Pdh[(C6H4-
2-C6H4)-N5CH-(h5-C5H4)]Fe(h5-C5H5)j(acac)] (3b) and
[Pdh[(C6H4 -2-C6H4)-N5CH-(h5 -C5H4)]Fe(h5-C5H5)j-
Cl(L)] hL5py-d5 (4b) or PPh3 (5b)j (Scheme 4) were
obtained. According to the NMR spectra (vide infra) these
compounds contain a six-membered palladacycle with a
s(Pd-Csp ,biphenyl) bond. It should be noted that previous
2
studies on cyclopalladation of N-donor ferrocenyl sub-
strates have shown that except when (a) the N-donor ligand
has a stereogenic centre or (b) chiral aminoacids were
present in the cyclopalladation process [21–25,48,49], in
the remaining cases, the monomeric derivatives:
[Pd(C N)Cl(L)] hwith L5py or PR3j, containing s(Pd-
arise respectively from the activation of a s(Csp
-
2
,ferrocene
H) or a s(Csp ,biphenyl-H) bond.
2
3.4. Reactivity of the ‘Pd(m-Cl)2Pd’ units in compounds
2
Csp ,ferrocene) bonds are racemates [14–20,26–38]. On this
2
basis, we assume that compounds 3a–5a consist on a 1:1
mixture of the two enantiomers hRp and Spj.
The reactions of the di-m-chlorobridged cyclopalladated
complexes with PPh3 have also been very useful in
The action of thallium(I) acetylacetonate, deuterated
pyridine and triphenylphosphine on the di-m-chloro-
bridged cyclopalladated compounds 2, was also studied.

M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2591
Scheme 3. (i) Tl(acac), acetone. (ii) py-d5 in CDCl3 for (4a), or PPh3 in benzene (5a). (iii) dppe in CH2Cl2 (see Section 3.4).
confirming the nature of the complexes formed in the
cyclopalladation reaction using different reaction times
(see above). A small amount of the crude materials
obtained in each case (reaction periods equal to 12 h, 2
days and 6 days) was suspended in CDCl3 and treated with
the stoichiometric amount of PPh3 to produce the bridge
splitting reaction and the coordination of the phosphine
performed with the material obtained after longer reaction
periods. This finding also indicates that an increase of the
reaction period favours the formation of the ‘endocyclic’
derivative.
More interesting are the reactions of compound 2 with
1,2-bis(diphenylphosphino)ethane (dppe). The addition of
the stoichiometric amount of the diphosphine to a CH2Cl2
suspension of 2b produced a dark red solution, which
yielded (after concentration to dryness) [Pdh[(C6H4-2-
C6H4)-N5CH-(h5-C5H4)]Fe(h5-C5H5)j(dppe)]Cl (6b). In
this complex the dppe acts as a neutral (P, P9) bidentate
1
ligand, giving compound 5. The comparison of the H and
31P NMR of the solutions obtained immediately after the
mixing (Fig. 4A–C), revealed that the amount of the
‘exocyclic’ complex 2b decreased for the experiments
Scheme 4. (i) Tl(acac), acetone. (ii) py-d5 in 4b, or PPh3 in benzene 5b. (iii) dppe in CH2Cl2.

2592
M. Benito et al. / Polyhedron 18 (1999) 2583–2595
Fig. 4. Partial views of the proton and 31P-NMR spectra of the solutions obtained by treatment of the solids obtained in the cyclopalladation reaction using
reaction periods equal to 12 h (A), 2 days (B) and 6 days (C), with triphenylphosphine in CDCl3.
1
ligand. No evidence of the formation of any other complex
containing dppe as ligand was detected by 31P-NMR
spectrocopy. In contrast, the reaction of complex 2a with
dppe is more complex. For instance, when the reaction was
carried out at room temperature, only one singlet at ca.
64.10 ppm was detected in the 31P-NMR spectrum. The
position of this signal was similar to that reported for the
coordination complex [PdCl2(dppe)] (7) hd31P564.20 ppm
[59]j. However, when the 31P-NMR spectrum was re-
corded at low temperature (240 K, immediately after
mixingj two doublets centered at: 43.41 and 56.89 ppm
(Fig. 5) were detected. In addition, the proton NMR
spectrum showed the typical pattern of 1,2-disubstituted
ferrocenes (Table 1). These results suggested the formation
of [Pdh[(h5-C5H3)-CH5N-(C6H4-2-C6H5)]Fe(h5-C5H5)j-
(dppe)]Cl (6a).
also detected in the H-NMR spectra of these samples, i.e.
two singlets (at ca. 9.95 ppm and 4.28 ppm) and two
triplets (at ca. 4.82 ppm and 4.26 ppm) appeared and their
intensity increased with time. The position and multip-
licities of these signals were coincident with those of
ferrocenecarboxaldehyde [60]. These observations sug-
gested that complex 6a deteriorated in solution.
The results obtained in this reaction are in sharp contrast
with those reported previously for the cyclopalladated
complexes
[Pdh[(h5-C5H3)-CH5N-(CH2)n-C6H5)]-
Fe(h5-C5H5)j(m-Cl)]2 hwith n51 (2c) or 2 (2d)j, which
react with dppe to give: [Pdh[(h5-C5H3)-CH5N-(CH2)n-
C6H5)]Fe(h5-C5H5)j(dppe)]Cl and no evidence of the
decomposition of these materials was detected either in
solution or in the solid state [14]. The comparison of the
results obtained in the reaction of complexes 2a, 2c and 2d
with dppe suggested that the different reactivity could be
ascribed to the presence of the bulky biphenyl group [57].
The use of molecular models for compound 6a indicated a
strong steric hindrance between one of the phenyl groups
bound to the phosphorus in a trans- arrangement to the
metallated carbon and the biphenyl ring, which could be
responsible for the low stability of complex 6a. Quite
recently, it has been postulated that the decomposition
However, 1H and 31P-NMR changed with time (Fig. 5).
For instance, after 2 h of storage, an additional singlet at
ca. 64.10 ppm appeared in the 31P-NMR spectrum (Fig.
5B). For longer times, the singlet was more intense than
the two initial doublets (Fig. 5C). These observations
suggested that a reaction involving complex 6a was taking
place. The position of the singlet was identical to that
reported for [PdCl2(dppe)] (7) [59]. Several changes were

M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2593
1650–1500 cm21, which is ascribed to the stretching of the
.C5N bond.
NMR spectra [1H, 13C and 31P- (for 5a,b and 6a,b)] of
compounds under study were also recorded. The proton-
NMR spectrum of 1 (Table 1) showed a group of three
signals in the range: 3.0–5.0 ppm due to the three types of
proton of the ferrocenyl moiety (the pairs: (H3, H4) and
(H2, H5) and those of the C5H5 ring). The signal due to
the methinic proton appears as a singlet at ca. 8.17 ppm.
Only one isomer of 1 was detected in solution, and the
position of the signals due to the ferrocenyl fragment and
the methinic proton were consistent with those of related
ferrocenylimines: [(h5-C5H5)Feh(h5-C5H4)-C(H)5N-R9j]
hwith R95phenyl or benzyl groupsj for which an anti-
conformation has been reported [61,62].
Comparison of the chemical shifts of the ligand and
those of compounds 2a–6a in the range 3.00–6.00 ppm
(Table 1) shows that the two doublets due to the pairs hH2,
H5j and hH3, H4j of the imine split into three signals (of
relative intensities 1:1:1) upon metallation, thus confirming
the formation of the s(Pd-Csp ,ferrocene) bond. In contrast,
2
for 2b–6b a group of five signals (of relative intensities:
1:1:1:1:5) was detected in the same region, and in these
cases the resonance due to the proton (H119) on the
adjacent position to the metallated carbon (C129) was
strongly shifted to high fields. These findings are con-
sistent with the formation of the six-membered palladacy-
cles with a s(Pd-Csp ,biphenyl) bond. Furthermore, in 2b–
2
6b, the signal due to the imine proton is clearly low-field
shifted in respect to that of 1, thus suggesting that the
ligand adopts the Z-conformation in these compounds. In
contrast, for 2a–6a, the signal appeared at higher fields,
indicating an E-conformation of the imine. It should be
mentioned that since only the anti-isomer of the imine 1
was detected in solution, the formation of the ‘exocyclic’
derivatives 2b–6b requires the anti-→syn-isomerization of
the free ligand and/or the coordination complex [Pdh(h5-
C5H5)Fe[(h5-C5H4)-CH5N-(C6H4-2-C6H5)]j2Cl2] (29)
which forms before the activation of the s(C-H) bond.
However, recent studies have demonstrated that the en-
thalpy required for the anti-→syn-isomerization of the
related coordination complex [Pdh(h5-C5H5)Fe[(h5-C5H4)-
CH5N-CH2-CH2-N(CH3)2]j2Cl2] is very small (4.32
kcal/mol) [63,64].
Fig. 5. Variation of the 31P- NMR spectrum of the solution obtained by
treatment of complex 2a with the stoichiometric amount of dppe: (A)
immediately after the mixing (at 240 K); (B) after 2 h and (C) after 1
day. The signal at ca. 64.10 ppm corresponds to compound
[PdCl2(dppe)] [59], (see Section 3.4).
7
of complex: [Pdh[(h5-C5H3)-CH(CH3)-N(CH3)2]Fe(h5-
C5H5)j[(2)-binap]]Cl h(2) binaph5bis(diphenylphos-
phino)-1,19-naphthylj, which also contains a five-mem-
bered metallacycle with a s(Pd-Csp ,ferrocene) bond, was
2
induced by steric effects [43].
3.5. Characterization of the compounds
Except for 2a,b (which have low solubility) and 6a
(which decomposes in solution), the remaining compounds
were also characterized by 13C-NMR. A summary of the
most relevant data is presented in Table 2. In all cases the
number and position of the signals observed are compat-
ible with the proposed formulae.
Phosphorous-31 NMR spectra for 5a and 5b, which
contain a five- and a six-membered palladacycle, respec-
tively, showed a singlet [at 34.3 (for 5a) and at 33.9 (for
5b) ppm]. The position and multiplicity of this signal are
consistent with the values obtained for related cyclopalla-
All the compounds used in this study are orange or
dark-red solids at room temperature, except ligand 1 which
is an oil. The mononuclear complexes show high solubility
in the most common solvents: CHCl3, CH2Cl2, benzene,
toluene, but they are practically insoluble in alkanes and
methanol. However, the di-m-chloro-bridged compounds
2a and 2b are less soluble in most common solvents.
Elemental analyses of the complexes are consistent with
the proposed formulae (see Section 2). Infrared spectra of
all the compounds show a sharp intense band in the range

2594
M. Benito et al. / Polyhedron 18 (1999) 2583–2595
Table 2
Selected 13C-NMR data (in ppm) for compounds under study. Labelling of the atoms corresponds to the schemes shown in the lower part of Table 1
Compound
C5H5
C1
C2
C3
C4
C5
-CH5N-
1a
69.13
69.68
70.22
70.29
69.93
69.92
70.16
70.07
84.41
101.10
80.55
68.93
97.77
71.49
72.65
73.74
69.39
74.75
72.69
73.95
74.03
71.49
74.68
74.40
73.93
74.84
73.90
74.95
73.96
68.93
73.63
72.65
73.52
73.09
73.40
72.49
74.34
161.06
166.91
169.46
167.61
168.61
165.75
166.47
167.91
3a
3b
4a
4b
5a
5b
6b
75.62
b
b
b
b
b
72.75
b
69.22
75.36
81.05
a In the free ligand the carbons C2 and C5 are equivalent and the same happens with C3 and C4.
b Not observed.
dated complexes containing ferrocenyl units [26–31], for
which structural studies have revealed a trans-arrangement
between the phosphine ligand and the imine nitrogen
[26–31]. The phosphorus-31 NMR spectra of 6a and 6b
showed two doublets centered at: 43.41 and 56.89 ppm for
6a (in this case the spectrum was recorded at 240 K), and
at 44.30 and 60.10 ppm for 6b. The position and multip-
licities of these signals are in good agreement with the
results obtained for related cyclopalladated derivatives
containing five- or six-membered palladacycles and dppe
as a bidentate group.
Besides that, the different reactivity of 2 with dppe
indicates that the presence of the bulky biphenyl group
bound to the imine nitrogen in 2a introduces strong steric
hindrance, which reduces the stability of compound:
[Pdh[(h5-C5H3)-CH5N-(C6H4-2-C6H5)]Fe(h5-
C5H5)j(dppe)]Cl (6a), which degradates to the coordina-
tion compound [PdCl2(dppe)] (7).
Finally, it is well known that one of the interests of
cyclopalladated complexes is their usefulness as precursors
for the organic and organometallic syntheses by insertion
of small molecules into the s(Pd-C) bond [4,5,65–70]. In
these reactions the nature of the final product is strongly
dependent on several factors of which the nature of (a) the
inserted molecule, (b) the metallated ligand and (c) the
remaining ligands bound to the palladium are specially
important [4,5]. Compounds 2a and 2b differ exclusively
in the nature of the metallated ligand, thus they appear to
be candidates to undertake a comparative study of the
3.6. Conclusions
Cyclopalladation of ferrocenyl Schiff bases of general
formula: [(h5-C5H5)Feh(h5-C5H4)-C(R9)5N-Rj] (with R5
phenyl or benzyl groups and with R95H, Me or Ph)
produces the corresponding five-membered palladacycles
fused with the ferrocenyl fragment. However, for ligand 1
which contains a biphenyl ring bound to the nitrogen, two
types of palladacycle can be formed. One of which (2a)
reactivity of the s(Pd-Csp ,ferrocene) and s(Pd-Csp
)
2
2
,biphenyl
bonds. Further work on this field is now in progress.
arises from the activation of the s(Csp ,ferrocene-H) bond,
2
while the other (2b), which contains a six-membered cycle
fused with the biphenyl ring, forms through the activation
Acknowledgements
of the s(Csp ,biphenyl-H) bond. Complex 2a is formed
2
´
We are grateful to the Ministerio de Educacion
(DGICYT) and to the Generalitat de Catalunya for finan-
cial support (Grants N.: PB96-0164 and 1997-SGR-0174).
preferentially for longer reaction periods or when the
reaction is carried out in acidic media (glacial acetic acid),
thus suggesting that it might be formed under thermo-
dynamic control. The semiempirical calculations, based on
the pm3(tm) method [58], reported in this work, have
allowed us to explain the formation of the two types of
metallacycle, since once the palladium binds to the imine
nitrogen the distances between the palladium and the two
References
[1] R.G. Newkome, W.E. Puckett,V.G. Gupta, E. Kiefer, Chem. Rev. 86
(1986) 451.
[2] I. Omae, Coord. Chem. Rev. 83 (1988) 137.
[3] V.V. Dunina, O.A. Zalevskaya, V.M. Potatow, Russ. Chem. Rev. 57
(1988) 250.
[4] A.D. Ryabov, Chem. Rev. 90 (1990) 403.
[5] M. Pfeffer, Recl. Trav. Chim. Pays-Bas 109 (1990) 567.
[6] A.J. Klaus, A.E. Peters, H.S. Freeman, in: Modern Colorants:
Synthesis and Structure, Vol. 3, Blakie Academic and Professional,
London, UK, 1995, p. 1.
carbon atoms susceptible to metallation (Csp
,
2
,ferrocene
Csp ,biphenyl) as well as the net charges on these carbons are
2
similar. The reactions of compounds 2a and 2b with
Tl(acac), py-d5 or PPh3 have allowed us to isolate and
characterize two isomers of the monomeric cyclopalladated
complexes 3–5a,b. Compounds 3a–5a contain a five
membered palladacycle with a s(Pd-Csp ,ferrocene) bond,
2
while in 3b–5b, the palladium is linked to the biphenyl
group forming a six-membered ring that does not contain
the functional .C5N- group (‘exocyclic’).
[7] P. Espinet, M.A. Esteruelas, L.A. Oro, J.L. Serrano, E. Sola, Coord.
Chem. Rev. 117 (1992) 215.

M. Benito et al. / Polyhedron 18 (1999) 2583–2595
2595
´
[8] F. Zamora, J.M. Gonzalez, J.M. Perez, J.R. Masaguer, C. Alonso, C.
[42] Y.J. Wu, Y.H. Huo, K.L. Ding, H.Z. Yuan, X.A. Mao, J. Organomet.
Chem. 483 (1994) 139.
Navarro-Ranninger, Appl. Organomet. Chem. 11 (1997) 659.
´
[9] C. Navarro-Ranninger, I. Lopez-Solera, J.R. Masaguer, C. Alonso,
´
´
[43] C. Lopez, R. Bosque, D. Sainz, X. Solans, M. Font-Bardıa,
Appl. Organomet. Chem. 7 (1993) 57.
Organometallics 16 (1997) 3261.
´
´
´
[10] C. Navarro-Ranninger, I. Lopez-Solera, V.M. Gonzalez, J.M. Perez,
[44] H. Onue, I. Moritani, J. Organomet. Chem. 43 (1972) 431.
[45] J. Granell, D. Sainz, J. Sales, X. Solans, M. Font., J. Chem. Soc.,
Dalton Trans. (1986) 1785.
´
´
A. Alvarez-Valdes, A. Martın, P.R. Raithby, J.R. Masaguer, C.
Alonso, Inorg. Chem. 35 (1996) 5181.
[11] S.B. Wild, Coord. Chem. Rev., and references therein 166 (1997)
291.
´
[46] J. Albert, M. Gomez, J. Granell, X. Sales, X. Solans, Organometal-
lics 9 (1990) 1405.
[12] P.K. Santra, C.R. Saha, J. Mol. Catal. 39 (1987) 279.
[13] A. Bose, C.R. Saha, J. Mol. Catal. 49 (1989) 271.
[14] J.C. Gaunt, B.L. Shaw, J. Organomet. Chem. 102 (1975) 511.
[15] V.I. Sokolov, L.L. Troitskaya, N. Khurcheava, Zh. Org. Khim. 18
(1982) 2606.
[47] J. Albert, J. Barro, J. Granell, J. Organomet. Chem. 408 (1991) 115.
[48] M. Benito, Estudio de la reactividad de compuestos ciclopaladados
con enlaces s(Pd-Csp ,ferroceno) o s(Pd-Csp ,bifenilo) frente a alquinos.
2
2
Universitat de Barcelona, 1997.
´
´
[49] M. Benito, C. Lopez, X. Morvan, X. Solans, X. Font-Bardıa, in
[16] A. Kasahara, T. Izumi, M. Maemura, Bull. Chem. Soc. Jpn. 50
(1977) 1878.
preparation.
[50] A.D. Ryabov, I.K. Kakodinskaya, A.K. Yatimirsky, J. Chem. Soc.,
Dalton Trans. (1985) 2629.
[51] A.D. Ryabov, A.K. Yatimirski, Inorg. Chem. 23 (1984) 789.
[52] L. Kind, A.J. Klaus, P. Rys, V. Gramlich, Helv. Chim. Acta 81
(1998) 307.
[17] M. Nonoyama, M. Sugimoto, Inorg. Chim. Acta 35 (1979) 131.
[18] M. Nonoyama, Inorg. & Nucl. Chem. Lett. 14 (1978) 337.
[19] I.R. Butler, Organometallics 11 (1992) 74.
[20] G.R. Knox, P.L. Pauson, D. Willison, J. Organomet. Chem. 450
(1993) 177.
[21] G. Zhao, Q.G. Wang, T.C.W. Mak, Organometallics 17 (1998) 3437.
[22] G. Zhao, F. Xue, Z.Y. Zhang, T.C.W. Mak, Organometallics 16
(1997) 4023.
[23] V.I. Sokolov, L.L. Troitskaya, O.A. Reutov, J. Organomet. Chem.
182 (1979) 537.
[24] V.I. Sokolov, L.L. Trotiskaya, T.I. Rozhkova, Gazz. Chim. Ital. 117
(1987) 525.
[53] A.D. Ryabov, Inorg. Chem. 26 (1987) 1252.
[54] J. Albert, R.M. Ceder, M. Gomez, J. Granell, J. Sales, Organometal-
´
lics 11 (1992) 1536.
´
´
[55] M. Gomez, J. Granell, M. Martınez, Organometallics 16 (1997)
2539.
´
´
[56] M. Gomez, J. Granell, M. Martınez, J. Chem. Soc., Dalton Trans.
(1998) 37.
[57] C. Hansch, A. Leo, D. Hoekman, Exploring QSAR, Hydrophobic,
Electronic and Steric Constants, ACS Professional Reference Books,
ACS, Washinghton, USA, 1995.
[58] SPARTAN 4.0, Wavefunction Inc., 1995, 18401-Von Karman, Av.
3370-Irvine, CA-92715, USA.
[59] C.H. Lindsay, L.S. Benner, A.L. Balch, Inorg. Chem. 19 (1980)
3503.
[60] Gmelin, Handbuch der Anorganische Chemie, Organische Verbin-
dunge, Ferrocen, A1, Springer, 1976, Heidelberg, Germany.
´
´
[25] M. Benito, C. Lopez, X. Solans, M. Font-Bardıa, Tetrahedron:
Asymm. 9 (1998) 4219.
´
[26] C. Lopez, J. Sales, R. Zquiak, X. Solans, J. Chem. Soc., Dalton
Trans. (1992) 2321.
´
[27] R. Bosque, C. Lopez, J. Sales, X. Solans, J. Organomet. Chem. 483
(1995) 61.
´
´
[28] R., Bosque, C. Lopez, J. Sales, X. Solans, M. Font-Bardıa, J. Chem.
Soc., Dalton Trans. (1994) 735.
´
[29] R., Bosque, C. Lopez, J. Sales, D. Tramuns, X. Solans, J. Chem.
´
[61] C. Lopez, R. Bosque, X. Solans, M. Font-Bardia, New. J. Chem. 20
Soc., Dalton Trans. (1995) 2445.
(1996) 1285.
´
[30] R. Bosque, C. Lopez, J. Sales, J. Organomet. Chem 498 (1995) 147.
´
´
[62] R. Bosque, M. Font-Bardıa, C. Lopez, J. Sales, J. Silver, X. Solans,
J. Chem. Soc., Dalton Trans. (1994) 747.
[63] A. Caubet, C. Lopez, R. Bosque, X. Solans, M.J. Font-Bardıa,
Organomet. Chem. 577 (1999) 292.
[64] R. Bosque, A. Caubet, C. Lopez, E. Espinosa, E. Molins, J.
Organomet. Chem. 544 (1997) 233.
[65] G. Dyker, Chem. Ber. 130 (1997) 1565.
[66] I. Omae, in: Applications of Organometallic Compounds, John
Wiley & Sons, Chichester, UK, 1998, p. 435, Chapter 20.
[67] A. Albinati, P.S. Pregosin, R. Ruedi, Helv. Chim. Acta 68 (1985)
´
´
[31] C. Lopez, R. Bosque, X. Solans, M. Font-Bardıa, New J. Chem. 22
(1998) 977.
´
´
´
´
[32] C. Lopez, R. Bosque, X. Solans, M. Font-Bardıa, J. Organomet.
Chem. 535 (1997) 99.
´
´
[33] C. Lopez, J. Granell, J. Organomet. Chem. 555 (1998) 211.
´
[34] R. Bosque, C. Lopez, J. Sales, X. Solans, J. Silver, J. Chem. Soc.,
Dalton Trans. (1996) 3195.
´
´
[35] C. Lopez, R. Bosque, X. Solans, M. Font-Bardıa, J. Organomet.
Chem. 547 (1997) 309.
¨
´
´
[36] C. Lopez, R. Bosque, X. Solans, M. Font-Bardıa, J. Organomet.
2046.
Chem. 535 (1997) 99.
[37] J.C. Kotz, E.E. Getty, L. Lin, Organometallics 4 (1985) 610.
[68] J. Vicente, J.A. Abad, J. Gil-Rubio, Organometallics 15 (1996)
3509.
[69] J. Vicente, J.A. Abad, R. Bergs, J.P. Jones, M.C. Martınez de
Arellano, Organometallics 15 (1996) 1422.
[70] J. Vicente, J.A. Abad, K.F. Show, J. Gil-Rubio, M.C. Martınez de
´
[38] R. Bosque, C. Lopez, Polyhedron 18 (1998) 135.
´
[39] S.Q. Huo, Y.J. Wu, C.X. Du, H.Z. Yuan, X.A. Mao, J. Organomet.
Chem. 483 (1994) 139.
[40] Y.J. Wu, Y.H. Liu, K.L. Ding, H.Z. Yuan, X.A. Mao, J. Organomet.
Chem. 505 (1995) 37.
´
Arellano, Organometallics 16 (1996) 4557.
[41] Y.J. Wu, S.Q. Huo, Y. Zhu, L. Yang, J. Organomet. Chem. 481
(1994) 235.