Factors affecting the lability of the Pd-N bonds in palladacycles containing a σ(Pd-Csp2, ferrocene) bond. X-ray crystal structures of [Pd{[(η5-C5H3)-C(Me)=N-R]Fe (η5-C5H5)}C1(L)]

Article abstract of DOI:10.1016/S0277-5387(01)00739-2

The syntheses, characterization and molecular structures of the cyclopalladated complexes [Pd{[(η⁵-C₅H₃)-C(Me)=N-CH ₂-C₆H₅]Fe(η⁵- C₅H₅)}Cl(PEt₃)] (1) and [Pd{[(η⁵-C₅H₃)-C (Me)=N-C₆H₄-4-Me]Fe(η⁵-C ₅H₅)}Cl(PPh₂Et)] (2) are reported. A comparative study of the reactivity of 1 and 2 in front of PEt₃, reveals that the Pd-N bond is more prone to cleavage in 2 than in 1. These results have been interpreted on the basis of the differences detected in the structural characteristics of this sort of derivatives.

Full text of DOI:10.1016/S0277-5387(01)00739-2

Polyhedron 20 (2001) 987–994
www.elsevier.nl/locate/poly
Factors affecting the lability of the PdꢀN bonds in palladacycles
containing a s(PdꢀCsp , ferrocene) bond.
2
X-ray crystal structures of
[Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀR]Fe(h5-C5H5)}Cl(L)]
{with R=CH2ꢀC6H5 and L=PEt3
or R=C6H4-4-Me and L=PPh2Et}
Concepcio´n Lo´pez a,*, Ramo´n Bosque a, Xavier Solans b, Merce` Font-Bardia b
a Departament de Qu´ımica Inorga`nica, Facultat de Qu´ımica Uni6ersitat de Barcelona, Mart´ı i Franque`s 1-11, E-08028, Barcelona, Spain
b Departament de Cristallografia, Mineralogia i Dipo`sits Minerals, Facultat de Geologia, Uni6ersitat de Barcelona,
Mart´ı i Franque`s s/n. E-08028, Barcelona, Spain
Received 8 December 2000; accepted 31 January 2001
Abstract
The syntheses, characterization and molecular structures of the cyclopalladated complexes [Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀ
CH2ꢀC6H5]Fe(h5-C5H5)}Cl(PEt3)] (1) and [Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀC6H4-4-Me]Fe(h5-C5H5)}Cl(PPh2Et)] (2) are reported. A
comparative study of the reactivity of 1 and 2 in front of PEt3, reveals that the PdꢀN bond is more prone to cleavage in 2 than
in 1. These results have been interpreted on the basis of the differences detected in the structural characteristics of this sort of
derivatives. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Cyclopalladation; Ferrocenyl Schiff bases; Lability of PdꢀN bonds; Metallation
1. Introduction
C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-C5H5)}Cl(L)] in solution, i.e.
their proclivity to undergo an oxidation process, are
strongly dependent on the nature of the R and R%
substituents (on the imine group) and on the neutral L
ligand {L=PPh3, or an N-donor group} [6]. Besides
that, the X-ray crystal structures of a wide variety of
compounds of the type: [Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀR%]-
Cyclopalladated compounds containing a s(PdꢀCsp ,
2
ferrocene) bond have attracted great interest in the last
decade due to their potential applications [1]. Among
the variety of compounds of this kind reported so far,
the mononuclear derivatives of general formula:
[Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-C5H5)}Cl(L)] (Fig.
1), {where R is an hydrogen, a methyl or a phenyl
group; R% represents a phenyl, benzyl or naphthyl
group and L=neutral ligand} containing a five-mem-
bered palladacycle are probably the most widely stud-
ied [2–6]. In these compounds, L is in general
triphenylphosphine (PPh3) [2–4] or in a lesser extent an
N-donor group such as pyridine or imidazole [5]. It is
well known that the properties of compounds: [Pd{[(h5-
* Corresponding author. Tel.: +34-93-4021274; fax: +34-93-
4907725.
E-mail address: conchi.lopez@qi.ub.es (C. Lo´pez).
Fig. 1. Schematic view of some cyclopalladated complexes containing
five-membered palladacycles with a s(PdꢀCsp
) bond of general
2,
ferrocene
formula: [Pd{[h5-C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-C5H5)}Cl(L)].
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00739-2

988
C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
The new compounds were characterized by elemental
analyses, infrared and NMR spectroscopy. In the two
cases, the elemental analyses were consistent with the
proposed formulae (see Section 3). The infrared spectra
of 1 and 2 showed a sharp and intense band at approx-
imately 1590 (for 1) and 1575 cm−1 (for 2) which is
assigned to the stretching of the ꢂCꢁNꢀ group of the
ferrocenylimine. The typical bands of the coordinated
phosphines (PEt3 or PPh2Et) [10] were also detected in
the infrared spectra.
Compounds 1 and 2 have also been characterized by
{1H, 13C and 31P} NMR spectroscopy. The signals
1
observed in their H NMR spectra were assigned with
Scheme 1. i ) L in benzene.
the aid of two-dimensional heteronuclear {1H–13C}
NMR experiments. Proton NMR spectra of com-
pounds 1 and 2 (see Section 3) showed the typical
pattern of 1,2-disubstituted ferrocene derivatives [2–
6,11]: a group of four signals with relative intensities
5:1:1:1 in the range: 3.50–4.50 ppm. The chemical shift
of the proton (H3) in the adjacent position to the
metallated carbon (C2) in 2 appeared at higher fields
[l=3.58 ppm] than in 1 [l=4.28 ppm]. This fact may
be related to the proximity of the phenyl rings of the
PPh2Et ligand in 2. A similar argument was used to
explain the differences observed in the position of the
signal due to the (H3) proton in compounds [Pd{[(h5-
C5H3)ꢀC(H)ꢁNꢀCH2ꢀCH2ꢀC6H5]Fe(h5 - C5H5)}Cl(L)],
with L=PPh3 or PEt3 [2]. The signal due to the
diastereotopic protons of the ꢀNꢀCH2ꢀ moiety of 1
appeared as a doublet of doublets.
Fe(h5-C5H5)}Cl(PPh3)] have shown that in all cases the
phosphine and the imine nitrogen are in a trans
arrangement [2–6]. This arrangement is formally identi-
cal to that found in related cyclopalladated complexes
containing a s(PdꢀCsp , aryl) bond of general formula:
2
[Pd{C6H4ꢀC(R)ꢁNꢀR%}(X)(L)] {with X=Cl, Br or I
and L=P-donor group} [7,8] for which it has been
reported that depending on: (a) the nature and size of
the metallacycle; (b) the basicity of the imine; (c) the
nature of remaining ligands bound to the palladium(II)
and (d) the incoming ligand, the cleavage of the PdꢀN
bond, can be achieved [9]. On these basis and as a first
attempt to elucidate the relative importance of: (a) the
chelating ligand; and (b) the phosphine group bound to
the palladium on the lability of the PdꢀN bond in the
In the 13C{1H} NMR spectra of 1 and 2, the signals
due to the imine carbon and to the metallated carbon
atom (C2) exhibited low intensity, appeared as doublets
(due to phosphorus coupling) and they were shifted to
lower fields {at 182.44 in 1 and 182.95 ppm in 2} when
compared with the free imines [3]. A similar type of
variation has also been found for cyclopalladated com-
plexes derived from N-benzylideneanilines and N-ben-
zylidenebenzylamines [12].
cyclopalladated complexes with a s(PdꢀCsp ,
)
2
ferrocene
bond, we decided to prepare several derivatives of the
type: [Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀR%]Fe(h5-C5H5)}Cl(L)],
holding different phosphine ligands (Fig. 1) and to
compare their reactivity versus PEt3. In order to eluci-
date whether the lability of the PdꢀN bond in these
compounds could be related to structural differences
induced by the electronic or steric properties of the
phosphine ligand or by the basicity of the chelating
group, a comparative study of the crystal structures of
a wide variety of palladacycles of general formula:
[Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-C5H5)}Cl(L)] {with
R=Me, H or Ph, R%=phenyl or benzyl groups and
L=phosphine ligand} was also carried out.
31P NMR spectra of compounds under study showed
a singlet in the range 30–37 ppm, which suggested,
according to the literature [9,12], a cis arrangement of
the metallated carbon atom (C2) and the phosphine
ligand.
Compounds 1 and 2 have also been characterized by
X-ray diffraction. Their molecular structures together
with their atom labeling schemes are shown in Figs. 2
and 3. A selection of the most relevant structural
parameters of 1 and 2 is presented in Table 1.
The structures of 1 and 2 consist of discrete
molecules of [Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀCH2C6H5]Fe-
(h5-C5H5)}Cl(PEt3)] in (1) or [Pd{[(h5-C5H3)ꢀC(Me)ꢁ
NꢀC6H4-4-Me]Fe(h5-C5H5)}Cl(PPh2Et)] in 2 separated
by van der Waals contacts.
2. Results and discussion
The new compounds were prepared by treatment of
the corresponding di-m-chloro-bridged derivative:
[Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-C5H5)}(m-Cl)]2 {with
R=Me, R%=C6H4-4-Me and R=H, R%=CH2C6H5}
[3] with the stoichiometric amount of the corresponding
phosphine in benzene, followed by the subsequent
purification of the residue obtained after the concentra-
tion of the solvent on a rotary evaporator, by SiO2-
column chromatography (Scheme 1).
In each molecule the palladium atom is in a slightly
distorted square-planar environment bound to a chlo-
rine, the phosphorus (of the PEt3 group in 1 or of the

C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
989
PPh2Et ligand in 2), the nitrogen and the C(6) atom of
the ferrocenyl unit.1 The values of the PꢀPdꢀN bond
angles (Table 1): 172.36(12)° in 1 and 175.09(2)° in 2,
indicate a trans arrangement between the imine nitro-
gen and the phosphorus in good agreement with the
results obtained from 31P{1H} NMR spectroscopy.
The two compounds have a [5,5] bicyclic system in
which the C5H3 ring shares the C(6)ꢀC(10) bond with a
practically planar five-membered palladacycle.2
The ꢂCꢁNꢀ functional group is contained in the
metallacycle (endocyclic) and the ꢂCꢁNꢀ bond lengths
,
(1.292(5) in 1 and 1.288(5) A in 2) are similar to those
reported for the ketimines: [(h5-C5H5)Fe[(h5-
C5H4)ꢀC(R)ꢁNꢀR%] {with R=H, Me or C6H5 and
R%=phenyl or benzyl groups} [13,14].
In the two structures the ligands adopt the anti-
conformation as reflected in the values of the torsion
angle C(10)ꢀC(11)ꢀNꢀC(13): −174.61° (for 1) and
−175.52° (in 2).
Fig. 2. Molecular structure and atom labeling scheme for [Pd{[(h5-
C5H3)ꢀC(Me)ꢁNꢀCH2C6H5]Fe(h5-C5H5)}Cl(PEt3)] (1).
The phenyl rings of the R% group are planar3 and
their main planes form angles of 79.30° (in 1) and
110.78° (in 2) with the imine moiety.
The distances between the Fe and Pd atoms are:
,
3.6265 (in 1) and 3.5544 A (in 2), thus suggesting that
there is no direct interaction between the two metals.
The average CꢀC bonds of the pentagonal rings are
similar to those reported for most ferrocene derivatives
[14]. The FeꢀC ring bond lengths range from 2.015(5)
,
,
to 2.064(3) A (in 1) and from 2.018(5) to 2.081(4) A in
2. The pentagonal rings of the ferrocenyl unit are
planar4 and nearly parallel (tilt angles: 2.27° (in 1) and
0.76° (in 2)), and their relative arrangement deviate by
−0.90° (in 1) and by 5.84° (in 2) from the ideal eclipsed
conformation.
2 The least-squares equation of the planes defined by the sets of
atoms: Pd, N, C(6), C(10) and C(11) are: (0.4753)XO+
(−0.0634)YO+(0.8775)ZO=4.1670 in 1 (deviations from the main
plane are: Pd, 0.039; N, −0.023; C(6), −0.064; C(10), 0.058 and
,
C(11), −0.009 A) and (0.6941)XO+(0.1344)YO+(−0.7072)ZO=
0.9141 in 2 (deviations from the main plane are: Pd, −0.001; N,
,
−0.009; C(6), −0.060; C(10), 0.014 and C(11), −0.016 A).
3 The least-squares equation of the planes defined by the carbon
atoms of the C6H5 rings in the imine fragment in 1 and 2 are:
(0.1839)XO+(0.9829)YO+(0.0053)ZO=7.4275
(0.2908)XO+(−0.7448)YO+(0.6005)ZO= −0.4605 (for 2). Max-
ima deviations: in 1 C(13), −0.002 and C(15): 0.002 A and in 2:
(for
1)
and
Fig. 3. Molecular structure and atom labeling scheme for [Pd{[(h5-
C5H3)ꢀC(Me)ꢁNꢀC6H4-4-Me]Fe(h5-C5H5)}Cl(PPh2Et)] (2).
,
,
C(15), −0.006 and C(16), 0.005 A.
4 The least-squares equation of the planes defined by the sets of
atoms [C(1)ꢀC(5)] and [C(6)ꢀC(10)] in
(−0.6578)XO+(−0.0887)YO+(0.7480)ZO=2.6608
(−0.6480)XO+(−0.0926)YO+(0.7560)ZO= −0.6422,
1 and 2 are: for 1
1 The least-squares equation of the plane defined by the atoms
and
respec-
bound to the palladium in
1
and
2
are: (0.4917)XO+
(−0.0160)YO+(0.8706)ZO=3.3719 and (0.7488)XO+(0.1404)
YO+(−0.6477)ZO=1.2236, respectively. Deviations from these
tively. Maxima deviations were found for C(2): −0.008 and C(1):
,
0.008 A. For 2: (0.3423)XO+(0.0399)YO+(0.9384)ZO=0.7984 and
,
planes are: P, −0.025; Cl, 0.022; N, −0.029 and C(6), 0.031 A in 1
(0.3802)XO+(0.0388)YO+(0.9241)ZO=4.0889, respectively. Max-
,
,
and P, 0.064; Cl, −0.060, N, 0.075 and C(6), −0.079A in 2.
ima deviations were found for C(6): 0.007 and C(7): −0.007 A.

990
C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
Table 1
5
5
5
,
Selected bond lengths (A) and bond angles (°) for compounds [Pd{[(h -C5H3)ꢀC(Me)ꢁNꢀCH2C6H5]Fe(h -C5H5)}Cl(PEt3)] (1), [Pd[{(h -
C5H3)ꢀC(Me)ꢁNꢀC4H4-4-Me]Fe(h5-C5H5)}Cl(PPh2Et)] (2) and related derivatives of general formula: [Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-
C5H5)}Cl(L)], where L represents a phosphine ligand. For labeling of the atoms refer to Scheme 1
Compound
1
2
3
4
5
6
7
R=
R%=
L=
Me
CH2C6H5
PEt3
Me
C6H4-4-Me
PPh2Et
Me
C6H4-4-Me
PPh3
Me
C6H4-4-Cl
PPh3
Me
(CH2)2C6H5
PPh3
H
H
CH2C6H5
PPh3
(CH2)2C6H5
PEt3
Bond lengths
PdꢀP
PdꢀCl
2.2283(13)
2.3878(14)
2.131(4)
1.989(4)
1.437(7)
1.292(6)
2.2374(14)
2.3669(18)
2.142(3)
1.983(4)
1.443(6)
1.288(5)
2.2371(10)
2.3414(9)
2.136(3)
1.998(3)
1.446(6)
1.299(4)
2.2569(9)
2.3600(9)
2.135(3)
1.991(4)
1.450(6)
1.296(5)
2.247(2)
2.385(2)
2.130(6)
1.984(6)
1.418(11)
1.305(9)
2.247(2)
2.368(2)
2.146(6)
2.004(5)
1.475(9)
1.279(7)
2.243(2)
2.390(2)
2.148(5)
1.999(6)
1.467(9)
1.280(8)
PdꢀN
PdꢀC(6)
C(10)ꢀC(11)
C(11)ꢀN
Bond angles
ClꢀPdꢀP
PꢀPdꢀC(6)
C(6)ꢀPdꢀN
NꢀPdꢀCl
C(10)ꢀC(11)ꢀN
C(6)ꢀC(10)ꢀC(11)
Reference
94.36(5)
91.97(13)
80.40(17)
93.27(12)
114.9(4)
91.69(12)
94.68(12)
80.41(14)
93.18(12)
114.8(4)
95.08(3)
92.51(10)
80.25(12)
93.02(7)
113.5(3)
119.3(6)
[6c]
94.37(3)
94.8(1)
79.9(1)
91.93(9)
113.8(3)
117.8(3)
[1e]
94.55(2)
98.5(2)
80.8(3)
92.4(2)
114.7(7)
119.3(6)
[3]
95.4(1)
91.0(2)
80.8(2)
92.8(1)
115.2(3)
118.0(3)
[5]
95.5(1)
91.2(2)
81.1(2)
92.5(1)
117.0(7)
116.9(8)
[2]
118.0(4)
this work
118.1(4)
this work
In view of these findings, we decided to elucidate
whether the replacement of the PPh3 in the coordina-
tion sphere of the palladium and/or the use of a more
basic incoming group (such as PEt3) could be important
to modify the lability of the PdꢀN bond. As a first
approach to this problem, solutions of compounds 1 or
2 (in CDCl3) were treated separately on an NMR tube
with different amounts of PEt3 (molar ratios Pd:PEt3
varying from 1:1 to 1:20} and the resulting solutions
2.1. Reacti6ity with triethylphosphine
Previous studies on the reactivity of the PdꢀN bond
in cyclopalladated complexes of the type [Pd{C6H4−x
-
RxꢀCHꢁN−(CH2)n−C6H5−yR% }Cl(PPh3)], derived
y
from N-benzylideneanilines {n=0} or N-benzyli-
denebenzylamines {n=1}, have shown that the stabil-
ity of the PdꢀN bond is highly dependent on the
basicity of the nitrogen atom and on the properties of
the incoming ligand [9]. For instance, compounds
1
were characterized by H and 31P NMR spectroscopy.
When the reactions were performed using compound 1,
in all cases, the spectra showed only two signals, the
position of which were coincident with those expected
for the free PEt3 and complex 1, thus suggesting, that
even when larger excesses of the entering ligand (PEt3)
were used, the ring opening of the metallacycle did not
take place.
[Pd{C6H4−xRxꢀCHꢁNꢀR¦}Cl(PPh3)]
{with
R¦=
phenyl or ferrocenyl groups react with PPh3 to give:
[Pd{C6H4−xRxꢀCHꢁNꢀ(CH2)ꢀC6H5−xR% }Cl(PPh3)2]
x
through cleavage of the PdꢀN bond, while their ana-
logues derived from N-benzylidenebenzylamines {n=
1} do not undergo the opening of the metallacycle
under identical experimental conditions [8c,9]. The re-
placement of the PPh3 ligand by a more basic phos-
phine PEt3 produced [Pd{C6H4−xRxꢀCHꢁNꢀ(CH2)nꢀ
Similar results were obtained when 2 was treated
with PEt3 in molar ratios varying from 1:1 to 1:5.
However, the addition of larger excesses of PEt3 (15–20
times the stoichiometric amount) produced significant
variations in the 31P{1H} NMR spectra of the resulting
solution, i.e., the signal due to the phosphorus nuclei of
2 decreased its intensity and three new signals were
detected in the 31P NMR spectra. The chemical shifts of
two of them were coincident with those expected for the
free PEt3 and PPh2Et [15]. This finding suggested that a
chemical reaction involving the cleavage of the
PdꢀPPh2Et bond had taken place.
C6H5−yR% }Cl(PEt3)2] {with n=0 or 1}. This type of
y
reactions involves a change of the mode of coordina-
tion of the ligand {from (C,N)− bidentate to (C)−
monodentate} which is relevant in the view of their
potential applications in catalysis. In contrast with
these results, it has been reported that compounds:
[Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀ(CH2)n−C6H5]Fe(h5-C5H5)}-
Cl(PPh3)] {where R=H, CH3 or Ph and n=0 or 1} do
not react with large excesses of PPh3 to give [Pd{[(h5-
C5H3)ꢀC(R)ꢁNꢀ(CH2)nꢀC6H5]Fe(h5-C5H5)}Cl(PPh3)2],
thus suggesting the poor lability of the PdꢀN bond in
this sort of derivatives [2–4a].
The remaining signal observed in the 31P{1H} NMR
spectra, which appeared at higher fields than in 2,
suggested, according to the literature [16] the formation

C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
991
of a new complex containing two phosphine ligands
bound to the palladium in a trans arrangement.
containing one or two ꢀCH2ꢀ fragments between the
imine nitrogen and the phenyl ring. In the X-ray crystal
structure of 1 the distance between the chloro ligand
and one of the two hydrogen atoms {H(12A)} of the
In order to confirm this finding, the reaction was
scaled up and the residue obtained after the concentra-
tion to dryness of the solution on a rotary evaporator
was passed through a SiO2 column chromatography
(see Section 3). After working up of the column an
orange red solid was obtained and its characterization
data (see Section 3) were coincident with those expected
,
ꢀNꢀCH2ꢀ moiety of the ferrocenylketimine is (2.652 A)
clearly smaller than the sum of the van der Waals radii
,
of these atoms (Cl, 1.75 and H, 1.20 A [17]), thus
suggesting a weak C(12)ꢀH(12A)···Cl interaction. A
careful study of the structures of compounds 1, 5–7,
and of the cyclopalladated complexes containing
for
[Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀC6H4-4-Me]Fe(h5-
C5H5)}Cl(PEt3)2] in which the ligand behaves as a
s(PdꢀCsp ,
)
rings of general formulae:
2
phenyl
monoanionic (C)− group.
[Pd{(C6H4−xRx−C(R¦)ꢁNꢀ(CH2)nꢀR%}Cl(L)] {with
In view of these results obtained in the reactions of
compounds 1 or 2 with PEt3, and in order to clarify the
importance of the basicity of the chelating ligand in this
sort of reaction, the experiments were repeated using
[Pd{[(h5 - C5H3)ꢀC(H)ꢁNꢀCH2ꢀC6H5]Fe(h5 - C5H5)}Cl-
(PEt3)] (6) [2] and PEt3 under identical experimental
conditions and molar ratios varying from 1:1 to 1:20.
According to previous electrochemical and theoretical
studies, in complex 6 (which can be easily visualized as
derived from 1 by replacement of the ꢀCH3 group in
the imine carbon by an hydrogen) the donor ability of
the chelating ligand is smaller than in 1 [6a,c]. However,
there is no evidence for the formation of: [Pd{[(h5-
C5H3)ꢀC(H)ꢁNꢀCH2ꢀC6H5]Fe(h5-C5H5)}Cl(PEt3)2] (6)
through cleavage of the PdꢀN bond were detected by
NMR spectroscopy in any of the cases studied.
n=1 or 2, L=P-donor group, R%=phenyl or ferro-
cenyl groups and R¦=H, Me or Ph} previously re-
ported [7,8,14], reveals that in all cases the Cl− is also
very close to one of the hydrogens of the ꢀCH2ꢀ
fragment attached to the imine nitrogen. Thus, suggest-
ing also a weak CꢀH···Cl interaction. A similar type of
interaction between the halide X group and one of the
protons of the ꢀCH2ꢀ fragment has also been recently
reported in compounds [Pd{[(h5-C5H3)ꢀC(H)ꢁNꢀCH2ꢀ
C6H5]Fe(h5 - C5H5)}X(PPh3)] (X=Br or I) [18] which
do not undergo the cleavage of the PdꢀN bond in the
presence of large excesses of phosphines. Consequently,
for this sort of complex, the incorporation of the sec-
ond phosphine ligand in the coordination environment
of the palladium (which usually takes place in a cis
arrangement to the chlorine), would require not only
the approach of the entering ligand, but also the cleav-
ages of the CꢀH···Cl interaction and of the PdꢀN bond.
Thus, the comparison of the results presented here,
reveal that: (a) the higher lability of the PdꢀN bond in
complex 2 when compared with that of 1 and 6; (b)
despite the donor ability of the nitrogen atom and the
chelating ligand, in 1 and 6 is markedly different, the
PdꢀN bond does not cleave even in the presence of
large excesses of the more basic PEt3 ligand [15]. Thus
suggesting that for palladacycles containing s(Pdꢀ
3. Conclusions
The results presented here reveal not only the low
lability of the PdꢀN bond in cyclopalladated complexes
C
2,
sp
) in addition to the basicity of the ligand,
ferrocene
containing a s(PdꢀCsp , ferrocene) bond, but also the
2
other more subtle factors may also be important to
determine the proclivity of the PdꢀN bond to cleave. In
order to elucidate whether the differences detected in
reactivity of the PdꢀN bond in compounds 1, 2, 6 could
be related to structural features, a comparative study of
the most relevant bond lengths and angles in com-
pounds 1, 2 and in related cyclopalladated derivatives
of general formula: [Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀR%]Fe(h5-
C5H5)}Cl(L)] (with L=PPh3, R=Me and R%=C6H4-
4-Me (3) [6c], C6H4-4-Cl (4) [1e] or (CH2)2C6H5 (5) [3];
L=PPh3, R=H and R%=CH2ꢀC6H5 (6) [5] and L=
PEt3, R=H and R%=(CH2)2C6H5 (7) [2]) was carried
out. Data presented in Table 1 show that changes of the
neutral L ligand or the substituents on the imine group
do not introduce significant variations in the PdꢀN
bond, since the differences do not clearly exceed three
times the standard deviations.
importance of the substituent bound to the imine nitro-
gen (a phenyl or a benzyl group) in determining the
ease with which the cleavage of the PdꢀN bond takes
place.
4. Experimental
Elemental analyses (C, H and N) were carried out at
the Serveis Cientifico-Te`cnics de la Universitat de
Barcelona. Infrared spectra were obtained with a Nico-
let Impact 400 spectrophotometer using KBr pellets.
1
Routine H and 13C{1H} NMR spectra were recorded
at approximately 20°C on a Gemini-200 instrument
using CDCl3 (99.9%) as solvent and SiMe4 as internal
reference. High resolution 1H NMR spectra and the
two-dimensional NMR experiments were carried out
with a Varian 500 MHz instrument. 31P{1H} NMR
In compounds 2 and 3, holding NꢀC6H4-4-R groups,
the PdꢀCl bond length is shorter than in complexes

992
C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
spectra were obtained with a Bruker 250-DXR instru-
ment using CDCl3 as solvent and trimethylphosphite as
reference: l31P[P(OMe)3]=140.17 ppm.
l=3.81 (C5H5), 3.58 (H3), 4.13 (H4), 4.41 (H5), 2.04
(ꢀC(Me)=Nꢀ), 2.36 (Me), 2.15–2.40 (ꢀCH2ꢀ), 0.9–
1.40 (Me), 6.98 (Ha, Ha%), 7.19 (Hb, Hb%), 7.10–7.90 (m,
Hc, aromatic protons of the phenyl rings of the PPh2Et
group). 13C{1H} NMR (selected data)5: l=70.81
(C5H5), 101.61 (C1), 91.23 (C2), 69.64 (C3), 67.33 (C4),
69.42 (C5), 182.95 (ꢂCꢁNꢀ). 31P{1H} NMR (in ppm):
36.52.
4.1. Materials and synthesis
The di-m-chloro-bridged cyclopalladated complexes:
[Pd{[(h5-C5H3)ꢀC(R)ꢁNꢀCH2C6H5]Fe(h5-C5H5)}(m-Cl)]2
{with R=Me or H} and [Pd{[(h5-C5H3)ꢀC(Me)ꢁ
NꢀC6H4-4-Me]Fe(h5-C5H5)}(m-Cl)]2 were prepared as
described previously [2,3]. The phosphine PPh2Et was
kindly provided by Dr D. Panyella (U.B.). The solvents
used in the preparations, except benzene were dried and
distilled before use. The preparations described below
require the use of benzene which should be handled
with caution!
4.4. Preparation of (Pd{((p5-C5H3)ꢀC(Me)ꢁNꢀ
C6H4-4-Me)Fe(p5-C5H5)}Cl(PEt3)2)
Compound 2 (100 mg, 1.49×10−4 mol) was dis-
solved in 20 ml of benzene, then a large excess of
triethylphosphine (0.45 ml, 3.0×10−3 mol) was added
carefully. The resulting reaction mixture was then
refluxed for 1 h and filtered. The deep orange filtrate
was concentrated to dryness on a rotary evaporator.
The resulting deep brown residue was then dissolved in
the minimum amount of chloroform and purified by
SiO2 column chromatography6 (yield: 45%).
4.2. Preparation of [Pd{[(p5-C5H3)ꢀC(Me)ꢁNꢀ
CH2C6H5]Fe(p5-C5H5)}Cl(PEt3)] (1)
A 100 mg amount (1.1×10−3 mol) of the di-m-
chloro-bridged cyclopalladated complex: [Pd{[(h5-
C5H3)ꢀC(Me)ꢁNꢀCH2ꢀC6H5]Fe(h5-C5H5)}(m-Cl)]2 [3]
was suspended in 20 ml of benzene. Then, PEt3 (2.2×
10−3 mol) was carefully added. The resulting mixture
was stirred at room temperature (r.t.) for 1.5 h. The
undissolved materials were filtered off and discarded
and the filtrate was concentrated to dryness on a rotary
evaporator. The residue was then dissolved in the mini-
mum amount of CH2Cl2 and then allowed to evaporate
slowly at r.t. The reddish crystals formed were collected
and air-dried (yield: 72%).
Characterization data. Anal. Found: C, 53.5; H, 7.1;
N, 2.10. Calc. for C31H48ClFeNPdP2: C, 53.6; H, 6.97;
1
N, 2.02%. IR (cm−1): w(ꢂCꢁNꢀ)=1603. H NMR5:
l=4.24 (C5H5), 4.35 (H3), 4.47 (H4), 4.52 (H5), 2.10
(ꢀC(Me)ꢁNꢀ), 2.17 (Me), 1.08 and 1.97 (br. M, 30H,
ꢀCH2ꢀ and ꢀCH3), 6.82 (Ha, Ha%), 7.20 (Hb, Hb%).
31P{1H} NMR: l=19.17.
5. Crystallography
Characterization data. Anal. Found: C, 52.2; H, 5.8;
N, 2.4. Calc. for C25H33ClFeNPdP: C, 52.07; H, 5.73;
N, 2.43%. IR (cm−1): w(ꢂCꢁNꢀ) 1590. 1H NMR5:
l=4.03 (C5H5), 4.29 (H3), 4.36 (H4), 4.40 (H5), 4.64,
4.55 (ꢀNꢀCH2ꢀ), 2.11 (Me), 1.30, 2.05 (br. m, 15H,
ꢀCH2ꢀCH3), 7.22–7.60 (m, 5H, aromatic protons).
13C{1H} NMR (selected data)5: l=69.77 (C5H5), 97.01
(C1), 92.56 (C2), 68.86 (C3), 67.14 (C4), 69.77 (C5), 53.08
(ꢀNꢀCH2ꢀ), 182.44 (ꢂCꢁNꢀ). 31P{1H} NMR: l=
30.40.
A prismatic crystal of compound 1 or 2 (sizes in
Table 2) was selected and mounted on a Enraf–Nonius
CAD-4 four circle diffractometer. Unit cell parameters
were determined from automatic centring of 25 reflec-
tions in the range 12°BqB21° and refined by least-
squares method. Intensities were collected with graphite
monochromatized Mo Ka radiation, using ꢀ–2q scan-
technique. The number of reflections collected and of
those assumed as observed applying the condition I\
2|(I) are presented in Table 2. In the two cases three
reflections were collected for every 2 h as orientation
and intensity control and significant intensity decay was
not observed. Lorentz polarization corrections were
made but not for absorption.
4.3. Preparation of (Pd{((p5-C5H3)ꢀC(Me)ꢁNꢀC6H4-
4-Me)Fe(p5-C5H5)}Cl(PPh2Et)) (2)
This compound was prepared according to the proce-
dure described above for 1, but using (Pd{((h5-
C5H3)ꢀC(Me)ꢁNꢀC6H4-4-Me)Fe(h5-C5H5)}(m-Cl))2 [3]
as a starting material and PPh2Et as an entering ligand
(yield: 67%).
6 The preparation of the column was carried out as follows: 15 g of
silica gel (Merck, 60 mesh) were suspended in 60 cm3 of CHCl3 and
0.5 cm3 of NEt3 were added. In the absence of NEt3 the crude of the
reaction formed by: [Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀC6H4-4-Me]Fe(h5-
C5H5)}Cl(PEt3)2] and free phosphines [PPh2Et and PEt3], decom-
Characterization data. Anal. Found: C, 58.8; H, 4.95;
N, 2.1. Calc. for C33H33ClFeNPdP: C, 58.96; H, 4.95;
poses,
giving
a
mixture
of
[Pd{[(h5-C5H3)ꢀC(Me)ꢁNꢀ
1
N, 2.08%. IR (cm−1): w(ꢂCꢁNꢀ)=1575. H NMR5:
C6H4-4-Me]Fe(h5-C5H5)}Cl(L)] (L=PPh2Et and PEt3). This sort of
process has also been reported for related palladacycles with
5 Labeling of the atoms refers to those shown in Scheme 1.
s(PdꢀCsp , aryl) bonds. See for instance Ref. [16].
2

C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
993
The structures were solved by direct methods, using
SHELXS computer program [20] and refined by full-ma-
trix least-squares method [21]. The function minimized
2, respectively. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
www:http://www.ccdc.cam.ac.uk).
2
2 2
was SwꢀꢀFoꢀ −ꢀFcꢀ ꢀ , where w=[|2(Fo)+(0.007
2 2 −1
ꢀFoꢀ ) ]
for 1 and w=[|2(I)+(0.0386P)2]−1 for 2,
2 2
with P={(ꢀFoꢀ +2ꢀFcꢀ )/3}. ƒ, ƒ% and f ¦ were obtained
from the literature [22].
For 2, 29 hydrogen atoms were located from a
difference syntheses and refined with an overal isotropic
temperature factor; the remaining hydrogen atoms of 2
and all the hydrogen atoms of 1 were computed and
refined with an overal isotropic temperature factor us-
ing a riding model. The final R indices for the two
structures as well as further details concerning their
resolution and refinement are presented in Table 2.
Acknowledgements
This work was supported by the Ministerio de Edu-
cacio´n y Cultura of Spain and by the Generalitat de
Catalunya (grants: BQ4-2000-0652 and 199-SGR-
00045, respectively).
References
6. Supplementary data
[1] For recent publications on this field see: (a) G. Zhao, Q.C.
Wang, T.C.W. Mak, Organometallics 18 (1999) 3623. (b) A.D.
Ryabov, Y.N. Firsova, V.N. Goral, E.S. Ryabova, A.N.
Shelvelkova, L.L. Troitskaya, T.V. Demeschick, V.I. Sokolov,
Chem. Eur. J. 4 (1998) 806. (c) C. Lo´pez, R. Bosque, D. Sainz,
X. Solans, M. Font-Bard´ıa, Organometallics 16 (1997) 3261. (d)
M. Benito, C. Lo´pez, X. Solans, M. Font-Bard´ıa, Tetrahedron:
Asymmetry 9 (1999) 4219. (e) S.Q. Huo, Y.J. Wu, C.X. Du, Y.
Zhu, H.Z. Yuan, X.A. Mao, J. Organomet. Chem. 483 (1994)
139, and references therein.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 152931 and 152930 for 1 and
Table 2
Crystal data and details of the refinement of the crystal structures of
compounds: 1 and 2
[2] C.Lo´pez, J. Sales, X. Solans, R. Zquiak, J. Chem. Soc., Dalton
Trans. (1992) 2321.
[3] R. Bosque, C. Lo´pez, J. Sales, X. Solans, M. Font-Bard´ıa, J.
Chem. Soc., Dalton Trans. (1994) 735.
1
2
[4] (a) R. Bosque, C. Lo´pez, J. Sales, X. Solans, J. Organomet.
Chem. 483 (1994) 61. (b) M. Benito, C. Lo´pez, X. Morvan,
Polyhedron 18 (1999) 2583.
[5] C. Lo´pez, R. Bosque, X. Solans, M. Font-Bard´ıa, D. Tramuns,
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141. (b) A. Caubet, C. Lo´pez, R. Bosque, X. Solans, M. Font-
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977.
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A. Castin˜eiras, D. Lata, J.J. Ferna´ndez, A. Ferna´ndez, J.
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Minguez, G. Muller, D. Sainz, P. Valerga, Organometallics 16
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d´ıa, X. Solans, J. Organomet. Chem. 522 (1996) 59.
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Dalton Trans. (1996) 3195.
Empirical formula
Molecular weight
Temperature (K)
Wavelength (Mo Ka) (A)
Crystal system
C25H33ClFeNPPd
576.22
298(3)
0.71069
monoclinic
P21/n
C
672.27
298(3)
0.71069
monoclinic
P21/a
33H33ClFeNPPd
,
Space group
Unit cell dimensions
,
a (A)
11.398(2)
17.108(3)
13.684(2)
90.0
16.386(15)
11.170(5)
17.717(7)
90.0
,
b (A)
,
c (A)
h (°)
k (°)
i (°)
90.0
90.0
112.77(1)
2460.4(7)
1.556
117.48(4)
2877(3)
1.552
3
,
V (A )
Dcalc (Mg m−3
)
Z
4
4
Absorption coefficient
(mm−1
F(000)
1.506
1.301
)
1176
1368
Crystal size (mm)
Reflections collected
Unique reflections
0.1×0.1×0.2
7473
7135
[Rint=0.0179]
272
1.276
R1=0.0599,
wR2=0.1455
R1=0.0768,
wR2=0.1666
0.1×0.1×0.2
8705
8347
[Rint=0.0230]
459
0.988
R1=0.0482,
wR2=0.0859
R1=0.1318,
wR2=0.1045
0.457 and
−0.655
[9] (a) H. Onue, I. Moritani, J. Organomet. Chem. 43 (1972) 401.
(b) J. Albert, J. Granell, J. Sales, J. Organomet. Chem. 273
(1984) 393. (c) J. Albert, J. Granell, J. Sales, X. Solans,
Organometallics 14 (1995) 1393.
[10] K. Nakamoto, Infrared spectra of Inorganic and Coordination
Compounds, 3rd ed., Wiley, Washington, DC, 1978.
[11] Gmelin. Handbuch der Anorganische Chemie: Organoeisen
Verbinduge, A1-A11.
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Organometallics 12 (1992) 1536. (b) J. Albert, M. Go´mez, J.
Granell, J. Sales, X. Solans, Organometallics 9 (1990) 1405. (c) J.
Granell, R. Moragas, M. Font-Bardia, X. Solans, J. Organomet.
Chem. 522 (1996) 59.
Parameters
Goodness-of-fit on F2
R indices [I\2|(I)]
R indices (all data)
Largest difference peak and 0.467 and
−3
,
hole (e A
)
−0.474

994
C. Lo´pez et al. / Polyhedron 20 (2001) 987–994
[13] C. Lo´pez, R. Bosque, X. Solans, M. Font-Bardia, New. J. Chem.
20 (1996) 1285 (and references therein).
[18] S. Pe´rez, R. Bosque, C. Lo´pez, X. Solans, M. Font-Bard´ıa, J.
Organomet. Chem. (2000) (in press).
[14] T.H. Allen, O. Kennard, Chem. Design Automation News 8
(1993) 146.
[15] W.A. Henderson, C.A. Screuli, J. Am. Chem. Soc. 82 (1960)
5791.
[16] J. Granell, R. Moragas, J. Sales, M. Font-Bardia, X. Solans, J.
Organomet. Chem. 431 (1992) 359.
[17] (a) A. Bondi, J. Phys Chem. (1964) 441. (b) A.I. Kitaigorodsky,
Molecular Crystals and Molecules, Academic Press, London,
UK, 1973.
[20] G.M. Sheldrick, SHELXS, A Computer Program for Determina-
tion of Crystal Structures, University of Go¨ttingen, Germany,
1997.
[21] G.M. Sheldrick, SHELX-93S, A Computer Program for Determi-
nation of Crystal Structures, University of Go¨ttingen, Germany,
1997.
[22] International Tables of X-Ray Crystallography, in: Kynoch
Press (Ed.), vol. IV, 1974, pp. 99–100 and 149.
.