Theoretical, dynamic, and structural studies of the phenyl rotation in bispentafluorophenyl palladium complexes with scorpion-type ligands

Article abstract of DOI:10.1139/v05-232

A theoretical study at a DFT level has been carried out on the pentafluorophenyl rotation in the compounds [Pd(C₆F₅) ₂(bpzmPh)] (1) and [Pd(C₆F₅) ₂(bpz*mPh)] (2) (bpzm = bis(pyrazol-1-yl)phenylmethane and bpz*mPh = bis(3,5-dimethylpyrazol-1-yl)phenylmethane). The orientation of one C₆F₅ with respect to the coordination plane was forced to adopt specific values to simulate ring rotation and several parameters, such as the disposition of the other C₆F₅ group, the energy of the system, and the skeletal conformation of the bpz'm ligand, were analysed. The maximum energy value was found when the C₆F₅ ring was nearly coplanar with the coordination plane. In both complexes the minimum energy corresponds to a situation where the two rings are nearly parallel. A number of distortions that mainly affect the NPdN bite angle were predicted for the complex containing the bpz*mPh ligand (methylated pyrazoles). Four structures of complexes from this family were determined by X-ray diffraction and the same types of distortion were found. The differences in the free energies of activation for the pentafluorophenyl rotation in complexes containing methylated and non-methylated ligands were theoretically calculated. The calculated values were consistent with the data experimentally determined by NMR spectroscopy. The origin of the difference was attributed to the aforementioned distortions of the complexes containing the bpz*mPh ligand, which were more remarkable in the configuration of maximum energy.

Full text of DOI:10.1139/v05-232

2106
Theoretical, dynamic, and structural studies of the
phenyl rotation in bispentafluorophenyl palladium
complexes with scorpion-type ligands
M. Carmen Carrión, Félix A. Jalón, Isabel López-Solera, Blanca R. Manzano,
Francisco Sepúlveda, Lucía Santos, Ana María Rodríguez, Miquel Moreno, and
Martín Martínez-Ripoll
Abstract: A theoretical study at a DFT level has been carried out on the pentafluorophenyl rotation in the compounds
[Pd(C6F5)2(bpzmPh)] (1) and [Pd(C6F5)2(bpz*mPh)] (2) (bpzm = bis(pyrazol-1-yl)phenylmethane and bpz*mPh =
bis(3,5-dimethylpyrazol-1-yl)phenylmethane). The orientation of one C6F5 with respect to the coordination plane was
forced to adopt specific values to simulate ring rotation and several parameters, such as the disposition of the other
C6F5 group, the energy of the system, and the skeletal conformation of the bpz′m ligand, were analysed. The maximum
energy value was found when the C6F5 ring was nearly coplanar with the coordination plane. In both complexes the
minimum energy corresponds to a situation where the two rings are nearly parallel. A number of distortions that
mainly affect the NPdN bite angle were predicted for the complex containing the bpz*mPh ligand (methylated pyra-
zoles). Four structures of complexes from this family were determined by X-ray diffraction and the same types of dis-
tortion were found. The differences in the free energies of activation for the pentafluorophenyl rotation in complexes
containing methylated and non-methylated ligands were theoretically calculated. The calculated values were consistent
with the data experimentally determined by NMR spectroscopy. The origin of the difference was attributed to the afore-
mentioned distortions of the complexes containing the bpz*mPh ligand, which were more remarkable in the configura-
tion of maximum energy.
Key words: N ligands, palladium, theoretical studies, DFT calculations, dynamics.
Résumé : Nous présentons les résultats d’une étude théorique de calculs DFT sur la rotation des groupes pentafluoro-
phényles dans les composés [Pd(C6F5)2(bpzmPh)] (1) et [Pd(C6F5)2(bpz*mPh)] (2) (bpzm = bis(pyrazol-1-yl)phénylmé-
thane et bpz*mPh = bis(3,5-diméthylpyrazol-1-yl)phénylméthane). L’orientation d’un groupe C6F5 par rapport au plan
de coordination a été forcée à adopter des valeurs spécifiques pour simuler la rotation du cycle et nous avons analysé
plusieurs paramètres comme la disposition de l’autre groupe C6F5, l’énergie du système et la conformation du ligand
bpz′m. La valeur maximale d’énergie a été trouvée quand le cycle C6F5 est presque coplanaire avec le plan de coordi-
nation. Pour les deux composés l’énergie minimale correspond à une situation où les deux cycles sont presque parallè-
les. Nous avons prédit un nombre de distorsions qui affectent principalement l’angle de chélatation NPdN pour le
composé portant le ligand bpz*mPh (pyrazoles méthylés). Nous avons déterminé par diffraction de rayons X quatre
structures de composés de cette famille et nous avons trouvé les mêmes types de distorsion. Nous avons calculé théori-
quement les différences d’énergie libre d’activation pour la rotation des groupes C6F5 dans les composés portant des li-
gands méthylés et non-méthylés. Les valeurs calculées sont cohérentes avec les donnés expérimentales déterminées par
spectroscopie RMN. L’origine de la différence a été attribuée aux distorsions des composés contenant le ligand
bpz*mPh explicitées plus haut, lesquelles sont plus importantes dans la configuration d’énergie maximale.
Mots clés : ligands N, palladium, étude théorique, calculs DFT, dynamiques.
Carrión et al. 2119
Received 11 February 2005. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 11 February 2006.
M.C. Carrión, F.A. Jalón, I. López-Solera, B.R. Manzano,1 and F. Sepúlveda. Departamento de Química Inorgánica, Orgánica y
Bioquímica, Facultad de Químicas, IRICA Universidad de Castilla-La Mancha, Avda. C. J. Cela, 10, 13071 Ciudad Real, Spain.
L. Santos. Departamento de Química-Física, Facultad de Químicas, Universidad de Castilla-La Mancha, Avda. C. J. Cela, 10,
13071 Ciudad Real, Spain.
A.M. Rodríguez. Departamento de Química Inorgánica, Orgánica y Bioquímica, Escuela Técnica Superior de Ingeniería Industrial,
Universidad de Castilla-La Mancha, Avda. C. J. Cela, 3, 13071 Ciudad Real, Spain.
M. Moreno. Departament de Química, Facultat de Ciències, Universitat Autónoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
M. Martínez-Ripoll. Instituto Rocasolano del CSIC, Serrano, 119, 28006 Madrid, Spain.
1Corresponding author (e-mail: Blanca.Manzano@uclm.es).
Can. J. Chem. 83: 2106–2119 (2005)
doi: 10.1139/V05-232
© 2005 NRC Canada

Carrión et al.
2107
Scheme 1.
Introduction
R
C6F5
C6F5
The chemistry of polyfluorophenyl derivatives of Pd and
Pt has been extensively developed in organometallic chemis-
try (1). In contrast to other metal–aryl groups, the poly-
fluorophenyl ligands stabilize the metal–carbon bond
because of their special electronic properties (2). Far from
being simply spectator ligands, there are several examples in
which the polyfluorophenyl groups have been shown to be
reactive. For instance, it has been possible to study processes
of insertion into Pd—C6F5 bonds (3), the activation of C—F
bonds (4), aryl exchange (5), and other reactions (6, 7). An-
other aspect worth highlighting here related to polyfluoro-
aryl palladium and platinum complexes is the rotation of the
aryl group around the M—C bond. Examples of both free (8,
9) and restricted rotation of the polyfluorophenyl groups
have been described (9, 10–19). Kinetic activation parame-
ters have been calculated for some cases (11, 18–21). Of
particular interest is the use of the 3,5-dichlorotrifluoro-
phenyl ligand, whose presence simplifies the 19F NMR spec-
tra (22–24). When bulkier groups are present, such as 2,4,6-
tris(trifluoromethyl)phenyl (Fmes), the rotation is quenched
because of severe steric hindrance (25). The presence of a
larger atom, such as a bromo substituent, in the ortho posi-
tion also increases the energy barrier of the polyhalophenyl
rotation (26). It is important to note that a mirror plane coin-
cident with the coordination plane can exist either in a static
situation or because of fluxional processes (15, 18, 27, 28)
involving the ancillary ligands. In this case the rotational
process cannot be studied unless atropisomers are formed
because of the presence of two (or more) asymmetrically
substituted polyhalophenyl groups (haloaryls with Cs local
symmetry) (18, 26, 29, 30). It has been demonstrated that in
certain examples the rapid rotation takes place in a contact
ion pair formed by halide dissociation (21), where the de-
crease in the steric hindrance facilitates the rotation around
the metal–carbon bond. In other examples, it has been found
that the rotation takes place in square-planar derivatives
(11), and a case with a dual mechanism involving four- and
three-coordinate species (30) has even been reported. The
use of heteroscorpion-type ligands with the formula
bis(pyrazol-1-yl)Rmethane (bpz′mR) (see Scheme 1) as an-
cillary ligands in bispentafluorophenyl palladium complexes
gives rise to systems that are appropriate for studying the
pentafluorophenyl rotation process. Such complexes do not
have a symmetry plane coincident with the coordination
plane and the process of boat-to-boat inversion (see
Scheme 2) has never been observed when the spacer carbon
situated between the pyrazole rings is substituted with a rel-
atively bulky R group (31–34). The isomer in which the R
group is situated in an axial orientation in the metallacycle is
the only one that has been observed in these derivatives (31–
34). In any case, the presence of only one R group would
prevent the existence of a “dynamic plane” even if the boat-
to-boat process were operating because this process would
induce the change of the unique R group from an axial to an
equatorial disposition. The use of bis(pyrazol-1-yl)Rmethane
ligands offers the possibility of introducing different R sub-
stituents with distinct characteristics and sizes. Equally, the
pyrazole rings can be substituted differently. In a previous
study (34) we observed restricted rotation of the C6F5 groups
Pd
R3
N
N
H
N
N
R5
R5
R3
R3 = R5 = H
R3 = R5 = Me R = phenyl
R = phenyl
[Pd(C6F5)2(bpzmPh)]
1
2
3
4
5
6
7
8
[Pd(C6F5)2(bpzm*Ph)]
[Pd(C6F5)2(bpzmArOMe)]
[Pd(C6F5)2(bpzmArOH)]
[Pd(C6F5)2(bpzm*ArOMe)]
[Pd(C6F5)2(bpzm*Cy)]
[Pd(C6F5)2(bpzm*Fec)]
[Pd(C6F5)2(bpzm*py)]
R
3 = R5 = H
R3 = R5 = H
R = anisol-2-yl
R = phenol-2-yl
R3 = R5 = Me R = anisol-2-yl
3 = R5 = Me R = cyclohexyl
R3 = R5 = Me R = ferrocenyl
3 = R5 = Me R = pyrid-2-yl
R
R
in the complexes depicted in Scheme 1 (except 1, which is
described here for the first time), all of which contain this
type of ligand. The free energies of activation were calcu-
lated at the coalescence temperature. The absence of
dissociative processes and a negligible influence of the R
groups were demonstrated in this work. On studying this
family of complexes, we unexpectedly found that derivatives
where the bpz′mR ligands incorporate unsubstituted pyra-
zoles showed higher energy barriers than those with 3,5-
dimethylated pyrazoles. A similar case, concerning the
effect of the substituents on pyrazolate bridges cis to the
polyhaloaryl rings, has also been recently reported (24).
However, at first sight, a higher level of steric hindrance in
the region close to the aryl group would be expected to hin-
der aryl rotation. In an attempt to explain this apparent con-
tradiction we proposed the existence of a structural
deformation when substituents are present on the pyrazole
groups that would facilitate the fluoroaryl rotation (34). In-
deed, comparison of the X-ray structures of similar com-
plexes that differ in the presence of substituents in the 3-
position of the pyrazole ring show that such substituents
produce a significant distortion in the boat metallacycle,
thus reducing the N-Pd-N/N4 dihedral angle and also the bite
angle of the N-donor ligand (32, 35) (see Scheme 3). This
effect was more marked when a tert-butyl group was present
in the 3-position of the pyrazole ring (35). In our complexes,
this deformation would push away the Pd(C6F5)2 moiety
from the Me3 pyrazole substituents and decrease the steric
hindrance. The closure of the N-Pd-N angle would facilitate
the rotation of the C6F5 groups by opening the C-Pd-N and
(or) the C-Pd-C angles and decrease the steric crowding be-
tween the Fortho and the atoms in the cis disposition. In fact,
in previous works, higher energy barriers were found for the
aryl rotation when the size of the donor atoms flanking the
polyhaloaryl group in the coordination plane was increased
(11, 23, 26), more so when the rotation took place in square-
planar species. On the basis of these ideas, we decided to
perform a theoretical study at a DFT level of the whole pro-
cess of pentafluorophenyl rotation in two systems of this
type containing the ligands bis(pyrazol-1-yl)phenylmethane
(complex 1) and bis(3,5-dimethylpyrazol-1-yl)phenylmethane
(complex 2). Our goals in this study were: (i) to determine
© 2005 NRC Canada

2108
Can. J. Chem. Vol. 83, 2005
Scheme 2.
Scheme 3. (a) Distortion in the boat metallacycle owing to the
steric hindrance of the substituent in position 3 of the pyrazole
ring (R3). The N-Pd-N/N4 angle is reduced. (b) The distortion in-
dicated in (a) decreases the N-Pd-N angle and consequently, the
steric hindrance decreases between the pyrazole N-donor atom
and the C6F5 groups.
chiral pocket (39). The formation of chiral conformations
has also been reported for pentachlorophenyl derivatives that
exhibit restricted ring rotation (40).
We have also synthesized and studied the fluxional behav-
iour of complex 1 (Scheme 1) to complete this family of
complexes. The molecular structures of several derivatives of
this type were also determined by X-ray diffraction to ascer-
tain whether the stated deformations can be considered a
general trend.
Fo
(a)
Fo
R
R
Pd
Pd
N
N
Fo
H
N
N
H
Experimental
N
N
N
N
Fo
R3
R3
H
Methods
H
All manipulations were carried out under an atmosphere
of dry, oxygen-free nitrogen using standard Schlenk tech-
niques. Solvents were distilled from the appropriate drying
agents and degassed before use. Elemental analyses were
performed with a PerkinElmer 2400 CHN microanalyzer. IR
(b)
Fo
Fo
spectra were recorded on
spectrophotometer as KBr pellets. NMR spectra were re-
a
Nicolet Impact 410
Pd
Pd
Fo
Fo
N
N
N
N
corded at room temperature (≈25 °C) on a Varian UNITY-
(R3)
(R3)
1
1
300 (300 MHz for H, 75.4 MHz for 13C) spectrometer. H
and 13C NMR shifts were recorded using the residual proton
1
or carbon signal of the solvent as internal standard. A H–
whether the deformations observed in some X-ray structures
can be predicted by theoretical calculations; (ii) to analyse
the energy and the conformations of the systems in the
different steps of the pentafluorophenyl rotation. We were
particularly interested in determining whether the aforemen-
tioned deformations also occur in the situation of maximum
energy in the rotation process. Finally, (iii) to establish if a
higher energy barrier is theoretically predictable for the
complexes containing unsubstituted pyrazoles and to analyze
whether the origin of this difference is the aforementioned
deformation. To the best of our knowledge, this type of
study has never been performed and only a brief paragraph
concerning molecular mechanics calculations has previously
been published (36). This reference indicated that the most
stable conformation of a Pd(II) complex containing a substi-
tuted phenyl ligand is that in which the aryl ring is approxi-
mately perpendicular to the coordination plane. We believe
that these studies and the methodology used can be useful
when applied to other types of systems in connection with
the rotation of different types of aryl rings that may influ-
ence, for example, the enantioselectivity in catalytic pro-
cesses. In fact, several examples of enhancement of the
enantioselectivities (up to 40%–50%) (37, 38) in different
catalytic processes when substituents are introduced in an
aryl ring present in the asymmetric ligand have been de-
scribed. This fact has recently been attributed to the re-
stricted rotation of this ring, which gives rise to a more rigid
13C correlation experiment (gHMQC) was used to assign the
13C NMR resonances (Varian INOVA 500 MHz spectrome-
ter). Free energies of activation were calculated (20) from
the coalescence temperature (Tc) and the frequency differ-
ence between the coalescing signals (extrapolated at the co-
alescence temperature) with the formula ∆G ‡c = aTc[9.972 +
log(Tc/δν)] (a = 1.914 × 10–2). The estimated error in the
calculated free energies of activation is 0.2 kcal/mol (1 cal =
4.184 J). The probe temperature ( 1 K) was controlled by a
standard unit calibrated with a methanol reference.
Materials
[Pd(C6F5)2(cod)] was prepared according to the literature
procedure (41). Preparation and structural information of
complexes 2–8 have been previously reported (32, 34).
bpzmPh was prepared according to the literature method
(42).
Theoretical calculations
Calculations have been performed using the Gaussian 98
series of programs (43). Density functional theory (DFT)
was applied with the B3LYP functional (44, 45). Effective
core potentials (ECPs) were used to represent the innermost
electrons of the palladium atom. The basis set for the Pd
atom was that associated with the pseudopotential (46), with
a standard double-ξ LANL2DZ contraction (43). All calcula-
© 2005 NRC Canada

Carrión et al.
2109
Scheme 4.
tions were done with the split-valence 6-31G basis set for
the hydrogen, carbon, nitrogen, and fluoride atoms (47).
Within this basis set, the total number of basis functions was
already high for complex 1 where 397 basis functions were
needed, whereas complex 2 required 449 basis functions at
this level of calculation. The equilibrium geometries were
also localized with the higher 6-31G(d) basis set that in-
cludes polarization functions on heavy atoms.
N
N
φ
φ'
Pd
=
Cortho
Pd
N
R
N
Cipso
R
N
R
N
R
N
=
Ring 1
Ring 2
R
R = H, 1; Me, 2
Full geometry optimization and direct location of equilib-
rium geometries were carried out by means of the Schlegel
gradient optimization algorithm (48) by using redundant in-
ternal coordinates as implemented in the Gaussian 98 pack-
age (43). Diagonalization of the energy second-derivative
matrix was performed to provide the vibrational harmonic
frequencies that were used for evaluating the thermodynamic
corrections at 1 atm (1 atm = 101.325 kPa) and 298.15 K to
the initially obtained electronic energy. As per usual, we
made the approximations of the rigid rotor and the harmonic
model for the rotational and the harmonic degrees of free-
dom, respectively (49).
= C6F5
0.710 73 Å) at 23 °C. The data were collected with a frame
width of 0.3° in ω and a counting time of 25 s per frame at a
crystal-to-detector distance of 4 cm. The diffraction frames
were integrated using the SAINT (50) package and corrected
for absorption with SADABS (51). For 2 and 3 the intensity
data were collected on a NONIUS-MACH3 diffractometer
equipped with a graphite monochromator MoKα radiation
(λ = 0.710 73 Å) using an ω/2θ scan technique at room tem-
perature. For 8 the intensity data were collected on a Seifert
XRD3000-S diffractometer equipped with a graphite mono-
chromator CuKα radiation (λ = 1.541 78 Å) at room temper-
ature. The final unit cell parameters were determined from
25 well-centered reflections and refined by the least-squares
method. The space group was determined from the system-
atic absences and this was vindicated by the success of the
subsequent solutions and refinements. The structures were
solved by direct methods using SHELXS (52) (for 1, 2, and
3) and SIR92 (53) (for 8) computer programs and refined on
F2 by full-matrix least-squares (SHELXL-97) (54). All non-
hydrogen atoms were refined with anisotropic thermal pa-
rameters. The hydrogen atoms were included in calculated
positions and were refined with an overall isotropic tempera-
ture factor using a riding model. Weights were optimized in
the final cycles. Complex 3 crystallizes as a solvate with a
molecule of 1,2-dichloroethane.
Preparation of [Pd(C6F5)2(bpzmPh)] (1)
[Pd(C6F5)2(cod)] (100 mg, 0.18 mmol) was dissolved in
CH2Cl2 (20 mL) and bpzmPh (40.9 mg, 0.18 mmol) was
added. The solution was stirred at room temperature for
16 h. Complex 1 was obtained as a white powder after evap-
oration of the solvent to dryness and washing with pentane
(2 × 10 mL). Yield: 89% (106.1 mg). Complex 1, thus ob-
tained, is spectroscopically pure, but it can be crystallized
from dichloroethane–hexane. Monocrystals suitable for anal-
ysis by X-ray diffraction were obtained in this way. IR
1
(KBr, cm–1): 956, 1633, 1058 (C6F5). H NMR (300 MHz,
3
1,1′,2,2′-CDCl2CDCl2, 25 °C, ppm) δ: 6.42 (t, JH,H
=
2.4 Hz, 2H, H4pz), 6.60 (d, JH,H = 7.3 Hz, 2H, Hortho), 7.25
3
(d, JH,H = 2.0 Hz, 2H, H3pz), 7.44 (t, JH,H = 7.3 Hz, 2H,
3
3
3
H
meta), 7.50 (t, JH,H = 7.3 Hz, 1H, Hpara), 7.52 (s, 1H, Hα),
7.85 (d, JH,H = 2.4 Hz, 2H, H5pz). 13C NMR (75 MHz,
1,1′,2,2′-CDCl2CDCl2, 25 °C, ppm) δ: 76.1 (s, 1C, Cα),
107.3 (s, 2C, C4pz), 125.3 (s, 2C, Cortho Ph), 129.2 (s, 2C,
Cmeta Ph), 130.1 (s, 1C, Cpara Ph), 132.6 (s, 2C, C5pz), 135.2
3
Results and discussion
1
1
(dm, JC,F = 248 Hz, 4C, Cmeta, C6F5), 137.0 (dm, JC,F
=
The
complexes
[Pd(C6F5)2(bpzmPh)]
(1)
and
248 Hz, 2C, Cpara, C6F5), 144.0 (s, 2C, C3pz), 147.0 (dm,
1JCF = 248 Hz, 4C, Cortho, C6F5). Anal. calcd. for
C25H12F10N4Pd (664.8): C 45.17, H 1.82, N 8.43; found: C
44.90, H 1.96, N 8.18.
[Pd(C6F5)2(bpz*mPh)] (2) have been theoretically analyzed
by a DFT study. A number of different parameters that de-
pend on the dihedral angle φ have been analyzed for each
complex. The dihedral angle φ is defined by the torsion an-
gle N-Pd-Cipso-Cortho as shown in Scheme 4. This angle was
forced to adopt specific values (in the range from 0° to 180°)
and the energy of the structure was minimized until conver-
gence (see Tables 1 and 2). Only the data that correspond to
∆E = 0 in the tables have not been forced (φ = 63.5° for
complex 1 (Table 1) and φ = 83.4° for complex 2 (Table 2)).
In these cases, the system was allowed to adopt the structure
of lower energy without any restrictions. We have performed
some calculations with the SCF=TIGHT keyword. We have
seen that the energies are totally unaffected and the geome-
tries are almost equal (differences are less than 1° or
0.01 Å).
Preparation of monocrystals for X-ray diffraction
studies
Monocrystals of 1 were obtained by a slow evaporation of
hexane over a concentrated solution of 1,2-dichloroethane.
Monocrystals of 2 were obtained by a slow evaporation of
acetone-d6 in an NMR tube. Monocrystals of 3·C2H4Cl2
were obtained by slow vaporization of pentane over a 1,2-
dichloroethane solution of this complex. A sample of mono-
crystals of 8 was obtained by slow evaporation of pentane
over a solution of this complex in acetone.
X-ray structure determinations for compounds 1, 2,
3·C2H4Cl2, and 8
For 1 the intensity data were collected on a Bruker
SMART CCD diffractometer using MoKα radiation (λ =
The dependence on φ of different parameters that are di-
rectly or indirectly related with the rotation of the
perfluorophenyl groups of the complexes will be discussed
in the following sections.
© 2005 NRC Canada

2110
Can. J. Chem. Vol. 83, 2005
Table 1. Different parameters obtained after the theoretical cal-
culations for complex 1.
Table 2. Different parameters obtained after the theoretical cal-
culations for complex 2.
φa (°) φ′a (°) ∆E (kcal/mol) <N-Pd-N (°) <N-Pd-N/N4 (°)
φa (°) φ′a (°) ∆E (kcal/mol)
<N-Pd-N (°) <N-Pd-N/N4 (°)
10.0
20.0
30.0
40.0
50.0
63.5
80.0
85.0
88.0
90.0 113.8
100.0 117.0
110.0 117.1
120.0 118.4
130.0 117.6
140.0 117.1
150.0 118.2
71.2
70.2
68.3
67.8
67.2
66.9
67.9
68.8
69.7
9.4
8.1
5.4
3.5
2.4
0.0
0.6
2.8
3.1
1.8
0.7
0.04
0.3
1.3
3.3
6.4
10.0
20.0
30.0
50.0
70.0
80.0
83.4
90.0
100.0 100.5
120.0 120.4
140.0 129.4
160.0 127
95.2
88.3
84.9
84.8
86.3
90
9.7
7.4
4.8
1.6
0.4
0.06
0.0
0.08
0.4
3.7
7.2
9.9
81.6
82.7
83.5
84.2
84.8
85.1
85.1
85.0
84.9
85.6
85.4
85.2
84.9
84.6
84.0
82.8
80.7
81.0
145.2
146.9
148.9
150.8
152.0
153.4
152.4
151.9
151.6
154.9
154.9
153.6
152.2
151.3
149.5
146.6
144.6
147.3
79.6
80.7
81.6
83.5
84.1
84.1
84.1
84.0
83.9
81.8
79.3
78.7
78.9
79.4
138.4
139.8
141.3
145.1
146.8
146.4
146.1
145.8
145.4
138.8
133.5
134.1
136.4
138.1
91.5
97.8
170.0 117.1 10.8
180.0 104.6 10.3
aSee Scheme 4.
170.0 119.5 13.4
180.0 110.1 12.7
aSee Scheme 4.
understood in terms of the second C6F5 ring adapting to the
rotation of the first, with φ′ values within the allowed range.
␾ vs. energy
The dependence of the relative energy of the structures of
complexes 1 and 2 as a function of φ is indicated in Fig. 2
(see also Tables 1 and 2).
Mutual dependence of the rotation of the two C6F5
rings — ␾ vs. ␾′
As expected, in both cases the maximum energy value is
achieved when φ is near 180°. This value corresponds to a
situation where a C6F5 ring is nearly coplanar to the coordi-
nation plane and leads to the highest steric repulsion be-
tween the Fortho of the rotating ring and the vicinal
coordinated atoms (N and C). Comparison of the two dia-
grams in Fig. 2 shows that the conformations of the C6F5
rings are similar for the two complexes in the maximum en-
ergy configurations. However, in both complexes the mini-
mum of energy corresponds to conformations with different
values of φ and φ′. For complex 1, two states of minimum
energy (0 and 0.04 kcal/mol) are found. It is outstanding that
in these conformations the two C6F5 groups are not perpen-
dicular to the coordination plane, but they are nearly parallel
(φ = 63.5°, φ′ = 66.9° and φ = 110°, φ′ = 117.1°) leading to a
hypothetical minimum steric hindrance between the Fortho of
both rings. For complex 2, the minimum of energy is found
when both rings are nearly parallel and approximately per-
pendicular to the coordination plane (φ = 83.4°–90.0°, φ′ =
91.5°–97.8°). In this complex the conformation of the rings
found in 1 would probably involve considerable steric hin-
drance between the Fortho of one C6F5 ring and the Me
substituent of the pyrazole ring cis to it. For this reason such
an arrangement cannot correspond to an energy minimum.
In an effort to provide evidence for this proposal, the values
φ = 63.5° and φ′ = 66.9° were imposed on the structure of 2
and the energy was then minimized until convergence. A
value of 2.4 kcal/mol above the minimum was calculated for
this conformation of 2, thus showing its relative lack of sta-
bility with respect to the minimum energy situation.
For a better comparison with the data obtained from the
NMR studies, we also calculated the free energy of activa-
tion for the higher energy situation for both complexes in
the gas phase. The value obtained for complex 1 is
It is expected that the rotation of the two C6F5 rings will
be mutually dependent and, as a consequence, the depend-
ence of the dihedral angle φ′ with φ was first studied. The
angle φ′ was defined according to Scheme 4 and its depend-
ence on φ in 1 and 2 is indicated in Tables 1 and 2 and repre-
sented in Fig. 1. It is noteworthy that the two graphics of
Fig. 1 are not symmetrical, e.g., the φ′ values for small and
large φ values are different. This is due to the asymmetry of
the nitrogen donor ligand so that the coordination plane is
not a plane of symmetry (see Scheme 1). Consequently,
small or large φ values represent different situations of the
pentafluorophenyl ring in the complex (see Scheme 4).
Finally, note that φ = 0° and φ = 180° correspond to the same
structure.
For complex 1, two values of φ′ are clearly preferred. For
values of φ between 10° and 88°, the values of φ′ are from
67.2° to 71.2°, but for values of φ between 90° and 180°, φ′
is slightly below 120°. φ′ suddenly changes when φ changes
from 88° to 90°. In complex 2 the behaviour is different, al-
though some similarities are observed. In this case, a more
gradual variation in φ′ is observed as φ is changed. However,
two limiting values also exist. A minimum of 84.8° when φ
is 50° and a maximum of 129.4° when φ is 140°. It is notice-
able that the minimum value of φ′ is higher in 2 than in 1.
This can likely be attributed to the higher steric repulsion
expected between the Fortho of ring 2 and the methyl group
in the 3-position of the pyrazole ring when this angle is
small. It is also noticeable that φ′ does not adopt values that
are too low or too high in either of the two complexes, very
likely because of the repulsions of the second C6F5 ring
when it is nearly coplanar with the complex coordination
plane.
The mutual dependence found between φ and φ′ can be
© 2005 NRC Canada

Carrión et al.
2111
Fig. 1. Plot of the values (obtained from the theoretical calculations) of φ ′ (°) vs. φ (°) for the rotamers of complexes (a) 1 and (b) 2.
140
(a)
120
100
N
N
Pd
80
60
40
20
0
H
H
N
N
Pd
H
H
0
20
40
60
80
100
(°)
120
140
160
180
200
140
120
100
80
(b)
N
N
Pd
Me
Me
60
N
N
Pd
Me
Me
40
20
0
0
50
100
(°)
150
200
13.0 kcal/mol and that for complex 2 is 12.2 kcal/mol. These
values imply that the methylated complex has a lower free
energy activation barrier with a difference of 0.8 kcal/mol.
An overview of Fig. 3 shows that these two parameters
are linearly related in the sense that the dihedral angle in-
creases as the bite angle N-Pd-N opens. Given this mutual
relationship between these parameters, we chose the N-Pd-N
bite angle to report the conformation of the N-donor ligand
in the different steps of the C6F5 rotation. The effect on the
bite angle is due to both C6F5 groups and, to estimate how
much both rings deviate from normality (with respect to the
coordination plane), we defined the parameter α + α′ as α =
*φ – 90°* and α′ = *φ′ – 90°* (absolute values in both cases)
and studied its relation with the bite angle. One must also
take into account that the situation in which the two rings
are orthogonal (α and α′ = 0°) is the state of minimum
energy for complex 2, but in the case of complex 1 this dis-
position does not correspond to the minimum state but is not
far from it. The variation of the bite angle with α + α′ for 1
and 2 is represented in Fig. 4. The whole set of values fits
␾ vs. the skeletal conformation of the coordinated
bpz′m ligand — N-Pd-N bite angle and N-Pd-N/N4
dihedral angle
The skeletal conformation of the bpz′mR ligands must be
affected by the rotation of the C6F5 groups in the sense that
the ligand should adapt its conformation to facilitate this ro-
tation. Bearing in mind our previous proposal concerning the
distortions observed in complexes with substituted pyra-
zoles, we considered two skeletal parameters for the coordi-
nated N-donor ligand (see Scheme 3): (i) the bite angle N-
Pd-N and (ii) the dihedral angle between the coordination
plane (N-Pd-N) and the averaged plane of the four pyrazolic
nitrogens atoms (NNNN = N4).
© 2005 NRC Canada

2112
Can. J. Chem. Vol. 83, 2005
Fig. 2. Plot of the relative energy (kcal/mol) as a function of the φ angle for the rotamers of complexes (a) 1 and (b) 2.
(a)
(°)
(b)
(°)
well in a branch of a quadratic parabola. Then, it is clear
that an inverse relationship exists between these two param-
eters. In the case of 2, the variation in the value of the bite
angle is reasonably gradual, whereas for 1 it changes very
cess. This situation is consistent with our proposal concern-
ing the distortions induced in the complexes owing to the
presence of substituents in the 3-position of the pyrazolyl
rings (see Scheme 3).
slightly for small
α α′ values (e.g., when the
+
pentafluorophenyl rings are near the normal position), but de-
creases quite markedly when higher α + α′ values are
reached. Considering the relationship previously established,
one would expect that the dihedral angle N-Pd-N/N4 would
also be reduced when α + α′ is higher (this has been con-
firmed). In conclusion, when one C6F5 ring is near coplanar
with the coordination plane (high value of α + α′), the
bpz′mR facilitates, as far as possible, the rotation of the
C6F5 groups by reducing the N-Pd-N angle.
When comparing both complexes it can be seen that the
theoretical values found for the N-Pd-N angle are smaller for
the methylated complex for all values of α + α′. The same
applies to the N-Pd-N/N4 angle (see Tables 1 and 2 and
Fig. 4). In other words, the methylated complex 2 has more
favourable structures for ring rotation in all steps of the pro-
X-ray structures of [Pd(C6F5)2(bpzmPh)] (1),
[Pd(C6F5)2(bpz*mPh)] (2), [Pd(C6F5)2{bpzm(2-
C6H4OMe)}]·C2H4Cl2, 3·C2H4Cl2, and
[Pd(C6F5)2(bpz*mPy)] (8)
To complete the family of complexes we synthesized
complex 1 in a similar way to the complexes previously re-
ported (33). The corresponding analytical and spectroscopic
data are given in the Experimental section.
As previously stated, we were interested in evaluating
whether the distortions previously found in complexes of
this type with substituted pyrazoles were also present in the
solid state. With this aim in mind, we tried to obtain crystals
of several derivatives to determine their X-ray molecular
structures. Fortunately, suitable crystals could be obtained
for complexes 1 and 2 — on which the theoretical calcula-
© 2005 NRC Canada

Carrión et al.
2113
Fig. 3. Linear plot of the dihedral angle N-Pd-N/N4 vs. the bite angle N-Pd-N for 1 (᭜) and 2 (᭿) (see Scheme 3, data from the theo-
retical calculations).
160
155
150
145
140
135
130
125
120
115
78
79
80
81
82
83
84
85
86
Angle N-Pd-N (°)
Fig. 4. Plot of the bite angle N-Pd-N vs. the function (α + α′), as defined in the text, for complexes 1 (᭜) and 2 (᭿).
(°)
tions were performed for the isolated molecules — and two
other complexes previously reported (3 and 8). The ORTEP
plots of the molecules are shown in Figs. 5–8. The crystallo-
graphic data (Table 3) and a list of selected bond distances
and angles (Tables 4 and 5) are given. Two molecules are
present in the asymmetric unit of complex 1. These two
molecules are quite similar except for the orientation of the
phenyl ring of the CHR group (see the following). The data
corresponding to only one molecule are given in Table 4. A
comparison of experimental data (from X-ray studies) and
the calculated equilibrium geometries for 1 and 2 is also
given in Table 4. To see whether the 6-31G basis set is good
enough to study this system, we have also performed calcu-
lations with the larger 6-31G(d) basis set that includes polar-
ization functions on heavy atoms. Comparison of results
show that no major improvement emerges from the use of
the larger basis set. In fact, the bond length distances involv-
ing the palladium are better described by the 6-31G basis set
(probably because of cancellation of errors). In general we
see quite a good agreement between the X-ray and calcu-
lated geometries within both basis sets as the bond lengths
differ by less than 0.1 Å and angles agree within an error no
larger than 4° (less than 0.07 rad).
For all the complexes, the geometry around the palladium
atoms is approximately square-planar, with two coordinated
pyrazole nitrogens and the carbons of the pentafluorophenyl
rings. The distances of the Pd—N coordination bonds are
comparable to those of other bis(pyrazol-1-yl)methane com-
plexes (31–35, 55). Significant differences concerning the
Pd—N bond distances were not found on changing the
© 2005 NRC Canada

2114
Can. J. Chem. Vol. 83, 2005
Table 3. Crystallographic data for complexes 1, 2, 3·C2H4Cl2, and 8.
Complex
1
2
3·C2H4Cl2
8
Empirical formula
C25H12F10N4Pd
C29H20F10N4Pd
C28H18Cl2F10N4OPd
C28H19F10N5Pd
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
664.81
291(2)
720.89
290(2)
793.76
290(2)
721.9
292(2)
0.710 73
Monoclinic
P2(1)/n
17.169(6)
14.018(5)
21.491(8)
103.458(9)
5030(3)
8
0.710 73
Monoclinic
P2(1)/n
11.161(3)
15.714(3)
16.118(8)
103.35(4)
2750(2)
4
0.710 73
Monoclinic
P2(1)/c
14.321(1)
14.664(1)
15.415(1)
111.3(1)
3015.5(4)
4
1.541 78
Monoclinic
P2(1)/n
19.517(2)
15.976(1)
9.0688(6)
100.178(9)
2783.3(4)
4
b (Å)
c (Å)
β (ο)
Volume (Å3)
Z
Dcalcd (g cm–3)
1.756
1.741
1.748
1.723
Absorption coefficient (cm–1)
F(000)
8.35
2608
7.71
1432
8.85
1568
6.26
1432
Color, habit
Colorless, prismatic
0.15 × 0.15 × 0.14
1.37–25.00
–20 ≤ h ≤ 17
–16 ≤ k ≤ 12
–25 ≤ l ≤ 25
4243
Colorless, block
0.2 × 0.2 × 0.1
2.02–27.95
–14 ≤ h ≤ 14
0 ≤ k ≤ 20
0 ≤ l ≤ 21
3355
Colorless, prismatic
0.3 × 0.3 × 0.3
2.06–27.97
–18 ≤ h ≤ 17
0 ≤ k ≤ 19
0 ≤ l ≤ 20
4801
Colorless, block
0.3 × 0.2 × 0.2
3.6–66.74
–23 ≤ h ≤ 22
0 ≤ k ≤ 19
0 ≤ l ≤ 10
3797
Crystal size (mm)
θ range for data collection
Limiting indices
Observed reflections
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices (I > 2σ(I))
8780 (R(int) = 0.091 4) 6587 (R(int) = 0.065 2) 7247 (R(int) = 0.047 0) 4669 (R(int) = 0.028)
8780/0/722
0.964
6587/0/401
0.978
7247/0/458
1.016
3794/0/471
1.008
R1 = 0.074 9
wR2 = 0.159 2
R1 = 0.170 3
wR2 = 0.203 9
R1 = 0.057 2
wR2 = 0.108 5
R1 = 0.179 1
wR2 = 0.137 2
0.885 and –0.605
R1 = 0.046 3
wR2 = 0.139 7
R1 = 0.098 1
wR2 = 0.200 2
0.566 and –0.594
R1 = 0.029
wR2 = 0.032
R1 = 0.040
wR2 = 0.037
0.491 and –0.387
R indices (all data)
Largest diff. peak and hole (e Å–3) 0.927 and –0.824
Fig. 5. ORTEP plot with atom numbering of 1 (30% probability
Fig. 6. ORTEP plot with atom numbering of 2 (30% probability
ellipsoids).
ellipsoids).
C12
C10
C32
C34
C31
C35
C30
F44
C44
C9
F54
F45
C13
F9
F55
F10
C1
C15
F2
F1
C45
C8
C26
N11
C43
C55
F43
C24
C23
N21
C54
C53
C25
N12
C12
C13
C7
C4
Pd1
C22
N4
C16
8
C15
C14
C40
C42
N3
Pd1
N20
C14
C50
C51
C20
C23
C24
C25
C41 F53
F41
C17
N2
C22
C21
C16
C1
C5
C6
F42
N1
F3
C52
C19
C18
C3
C2
F51
F7
F6
F5
F4
pyridine rings in 1, 2, and 8 is not far from orthogonal
(dihedral angles of 92.0(5)° and 102.7(5)° for the two mole-
cules of the asymmetric unit of 1, 100.7(2)° for 2, and
102.8(1)° for 8). However, in complex 3 the plane of the
anisole ring is partially twisted (dihedral angle of 141.3(1)°).
substituent in the pyrazolyl ring. If a plane is defined con-
taining the palladium atom, the carbon of the CHR group
and the Cipso of the R ring, then the plane of the phenyl or
© 2005 NRC Canada

Carrión et al.
2115
Fig. 7. ORTEP plot with atom numbering of 3 (30% probability
Fig. 8. ORTEP plot with atom numbering of 8 (30% probability
ellipsoids).
ellipsoids).
C27
C33
C35
C25
C8
C32
C28
F23
F9
N5
F10
C13
C36
F22
C24
F16
C31
N3
O1
F1
F2
F15
C9
C23
C22
C15
C22
C21
C23
C1
C5
C20
C16
F8
N4
C4
N4
N1
C6
F24
C12
Pd1
N3
C14
Pd
C24
C14
C21
C26
C17
N2
F3
C7
C6
N2
C1
C7
C11
C4
C11
N1
C19
C15
C8
F14
C25
C18
C12
C16
F5
C10
C2
F25
C2
C3
C3
C13
F7
F26
F4
F6
F12
Table 4. Selected geometric parameters (in angstroms and degrees) of complexes 1 and 2 optimized at the B3LYP level in the gas
phase and experimental values from the X-ray structure determinations.
1
2
Geometrical feature
Exp. values
6-31G
6-31G*
Geometrical feature
Exp. values
6-31G
6-31G*
Bond lengths (Å)
Pd(1)—N(1)
Pd(1)—N(3)
Pd(1)—C(14)
Pd(1)—C(20)
N(2)—C(7)
N(4)—C(7)
C(7)—C(8)
N(1)—N(2)
N(3)—N(4)
2.066(9)
2.093(8)
2.01(1)
1.99(1)
1.45(1)
1.45(1)
1.55(1)
1.37(1)
1.36(1)
2.160
2.151
2.025
2.025
1.465
1.467
1.528
1.380
1.380
2.191
2.179
2.020
2.018
1.460
1.462
1.528
1.360
1.360
Pd(1)—N(12)
Pd(1)—N(20)
Pd(1)—C(40)
Pd(1)—C(50)
C(1)—N(11)
C(1)—N(21)
C(1)—C(30)
N(12)—N(11)
N(20)—N(21)
2.094(5)
2.127(5)
2.023(6)
2.016(6)
1.468(8)
1.450(8)
1.526(8)
1.363(6)
1.369(6)
2.164
2.181
2.030
2.032
1.464
1.463
1.528
1.389
1.392
2.206
2.218
2.023
2.023
1.458
1.459
1.528
1.366
1.367
Bond angles (°)
C(20)-Pd(1)-C(14)
C(20)-Pd(1)-N(1)
C(14)-Pd(1)-N(1)
C(20)-Pd(1)-N(3)
C(14)-Pd(1)-N(3)
N(1)-Pd(1)-N(3)
N(2)-C(7)-N(4)
N(2)-C(7)-C(8)
N(4)-C(7)-C(8)
86.2(4)
177.4(4)
91.6(4)
94.1(4)
179.4(4)
88.2(3)
109.5(8)
113.4(8)
112.7(8)
86.6
175.5
95.3
93.1
177.3
85.1
109.7
112.9
114.3
86.4
175.2
96.1
93.3
177.8
84.4
110.0
112.9
114.2
C(50)-Pd(1)-C(40)
C(50)-Pd(1)-N(12)
C(40)-Pd(1)-N(12)
C(50)-Pd(1)-N(20)
C(40)-Pd(1)-N(20)
N(12)-Pd(1)-N(20)
N(21)-C(1)-N(11)
N(21)-C(1)-C(30)
N(11)-C(1)-C(30)
86.2(2)
178.1(2)
93.3(2)
95.4(2)
175.8(2)
85.1(2)
110.7(5)
113.5(5)
114.4(5)
85.0
179.1
95.1
96.0
176.8
84.1
110.3
114.6
114.0
84.2
179.7
96.1
96.5
178.1
83.2
110.9
114.3
114.0
This difference probably arises because of the presence of
the OMe group, which lies almost in the anisole plane and
points away from the molecule. The disposition of the
anisole ring is similar to that found in an allylpalladium
complex containing the same N-donor ligand (33).
A selection of the structural parameters related to our pre-
vious discussion is compiled in Table 6. The data obtained
from the theoretical calculations for complexes 1 and 2 have
also been included in brackets (for 1 the values for the mini-
mum of ∆E = 0.04 kcal/mol are given). The parameters for
the structure of the previously reported ferrocenyl complex 7
are also included (33). A clear difference can be observed
between the data for complexes 1 and 3, where the pyrazole
rings are unsubstituted, and complexes 2, 7, and 8, which
contain 3,5-dimethylated rings. Both N-Pd-N and N-Pd-
N/N4 angles are higher in compounds 1 and 3 and lower and
quite similar for the other three compounds. The difference
in the stated angles that depends on the type of pyrazole
present in the ligand is in accordance with previous observa-
tions (33, 35) and with our theoretical predictions. The val-
ues of the two C-Pd-N angles are also reflected in Table 6. It
is possible to see that these angles are larger in the methyl-
ated complexes, a fact that should facilitate the C6F5 rota-
tion. As far as φ and φ′ are concerned, in complexes 1 and 3
these angles are comparable, far from the orthogonal posi-
tion and very similar to those calculated for the minimum
© 2005 NRC Canada

2116
Can. J. Chem. Vol. 83, 2005
Table 5. Selected bond lengths and angles for complexes
3·C2H4Cl2 and 8 from the X-ray structures.
A plot of the free energies of activation vs. the coales-
cence temperatures is given in Fig. 9. Two straight lines for
methylated and non-methylated derivatives can be plotted.
The fact that the points fit approximately to a straight line
independently of the solvent used (CDCl3 or 1,1′,2,2′-
CDCl2CDCl2) indicates that this is not an important factor
governing the C6F5 rotation. Furthermore, the nature of the
R groups in the ligands does not seem to have a clear influ-
ence either. It is evident from the data that higher values are
obtained in complexes with scorpion-type ligands that do not
contain substituents in the pyrazole groups than in those
with 3,5-dimethylated rings. If we compare the correspond-
ing two straight lines at room temperature, it can be esti-
mated that the free energy of activation is about 2.3 kcal/mol
higher for the non-methylated derivatives. The difference in
the free energies of activation between complexes 1 and 2
obtained in the theoretical calculations is 0.8 kcal/mol. Al-
though the two results are not quite close, in both cases
lower energy barriers are found for the methylated com-
plexes. At this point it is important to stress the fact that the-
oretical free energy calculations imply assuming that the
system behaves as an ideal gas and that the rotational and vi-
brational degrees of freedom are well-described through the
rigid rotor and harmonic approximations, respectively. Be-
sides, the theoretical calculations of free energy of activation
are referred to the gas phase and the experimental data cor-
respond to the complexes in solution. As stated, the values
of the bite and the N-Pd-N/N4 dihedral angles are higher for
1 than for 2. This is also true for the states of maximum and
minimum energy. It is remarkable that the differences be-
tween the two complexes are higher in the maximum than in
the minimum of energy. Consequently, one origin of the dif-
ferent experimental values obtained for the free energy of
activation in the two types of complex could lie in the fact
that the methylated complexes are more able to adapt the
nitrogenated ligand to the ring rotation steric requirements
that are more important in the maximum state of energy. In
the higher energy structure, the rotating C6F5 ring lies ap-
proximately in the coordination plane of the complex. In this
conformation it is reasonable to assume that the steric hin-
drance with the substituent in position 3 of the pyrazole
could be neglected and then the bite angle N-Pd-N is the
main factor to consider. Let us finally emphasize that our
calculations have allowed comparison of the structures in the
maximum energy situation and not only structures that
should correspond approximately to the minimum of energy,
such as those obtained from the X-ray determinations.
3·C2H4Cl2
8
Bond lengths (Å)
Pd(1)—C(11)
Pd(1)—C(21)
Pd(1)—N(1)
Pd(1)—N(4)
N(1)—N(2)
N(2)—C(1)
N(3)—N(4)
N(3)—C(1)
O(1)—C(8)
2.002(5)
2.010(5)
2.085(4)
2.094(4)
1.363(6)
1.463(6)
1.371(6)
1.457(7)
1.434(9)
1.349(9)
1.501(8)
Pd(1)—N(1)
Pd(1)—N(3)
Pd(1)—C(11)
Pd(1)—C(17)
N(1)—N(2)
N(3)—N(4)
N(2)—C(23)
N(4)—C(23)
C(23)—C(24)
2.092(3)
2.140(3)
2.012(4)
2.013(3)
1.363(4)
1.337(5)
1.448(4)
1.451(5)
1.518(5)
O(1)—C(32)
C(1)—C(31)
Bond angles (°)
C(11)-Pd(1)-C(21)
C(11)-Pd(1)-N(1)
C(21)-Pd(1)-N(1)
C(11)-Pd(1)-N(4)
C(21)-Pd(1)-N(4)
N(1)-Pd(1)-N(4)
C(32)-O(1)-C(8)
N(2)-C(1)-N(3)
N(2)-C(1)-C(31)
N(3)-C(1)-C(31)
87.7(2)
91.1(2)
176.7(2)
178.6(2)
93.7(2)
N(1)-Pd(1)-N(3)
C(11)-Pd(1)-C(17)
C(11)-Pd(1)-N(1)
N(1)-Pd-C(17)
N(3)-Pd-C(11)
N(3)-Pd-C(17)
N(2)-C(23)-N(4)
N(2)-C(23)-C(24)
N(4)-C(23)-C(24)
85.2(1)
85.5(1)
92.7(1)
177.8(1)
174.6(1)
96.4(1)
111.8(3)
114.2(3)
113.6(3)
87.5(2)
118.9(7)
109.6(4)
112.3(4)
115.2(4)
energy structure of 0.04 kcal/mol. In the methylated com-
plex 2, one of the C6F5 rings is not too far from the orthogo-
nal position (according to calculations), whereas the second
ring is tilted. For this φ′ value, less agreement with the theo-
retical results is observed. To analyze this point the values
of φ and φ′ were fixed according to the X-ray structure of 2
and the rest of the structure was minimized using the same
theoretical basis as in the preceding discussion. The energy
value for this hypothetical structure was 0.8 kcal/mol above
the minimum of this system. Perhaps the observed differ-
ences in the values of these angles with respect to the gas-
phase minimum can be ascribed to the effect of packing in
the solid state.2
Dynamics of the C6F5 rotation in [Pd(C6F5)2(bpz′mR)]
complexes in solution
The dynamics of the restricted rotation of C6F5 groups di-
rectly bonded to the square-planar Pd(II) centres for com-
plexes 2, 8 (32), and 3–7 (34) have been previously studied
in solution by 19F NMR spectroscopy. The corresponding
study for new complex 1 was also carried out in 1,1′,2,2′-
CDCl2CDCl2. At 253 K, one Fpara, one Fmeta, and two Fortho
signals were observed. The coalescence temperature was
reached at 338 K and the free energy of activation was cal-
culated. The data for all complexes are gathered in Table 7.
Conclusion
The rotation of a C6F5 group around the Pd—C axis in the
complexes [Pd(C6F5)2(bpz′mPh)] (bpz′mPh = bis(pyrazol-1-
yl)phenylmethane (1) and bpz′mPh = bis(3,5-dimethyl-
pyrazol-1-yl)phenylmethane (2)) has been theoretically stud-
2 Supplementary data for this article are available on the journal Web site (http://canjchem.nrc.ca) or may be purchased from the Depository
of Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 4071. For more
information on obtaining material refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 252030 ([Pd(C6F5)2(bpzmPh)]) and
244833–244835 ([Pd(C6F5)2(bpz*mPh)], [(Pd(C6F5)2(bpzmArOMe)·C2H4Cl2], and [Pd(C6F5)2(bpzmpy)], respectively) contain the crystallo-
graphic data for this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2005 NRC Canada

Carrión et al.
2117
Table 6. Selected structural parameters deduced from the X-ray structures of 1, 2, 3·C2H4Cl2, 7, and 8 (values in brackets correspond
to data from the theoretical calculations with the 6-31G basis set).
R (complex)
3,5 pz Substitutent
H
φ (°)
φ ′ (°)
<N-Pd-N (°)
<N-Pd-N/N4 (°)
<C-Pd-N (°)
Ph (1)
105.3
[110.0]
107.6
62.3
[83.4]
92.5
110.6
[117.1]
114.8
88.2
[91.5]
126.3
126.5
88.2(3)
[85.2]
87.5(2)
85.1(2)
[84.1]
159.6
[153.6]
158.9
144.9
[146.1]
144.0
91.6(4), 94.1(4)
[95.3], [93.1]
91.1(2), 93.7(2)
93.2(2), 95.4(2)
[95.1], [96.0]
2-Anis (3)
Ph (2)
H
Me
Fec (7)
Py (8)
Me
Me
84.22(13)
85.2(1)
92.26(15), 95.13(15)
92.7(1), 96.4(1)
96.7
145.5
Fig. 9. Linear plot of ∆G ‡c (kcal/mol) vs. Tc for the Fortho–Fortho ′ exchange (Pd–C6F5 rotation) in [Pd(C6F5)2(bpz′mR)] complexes. pz′ =
3,5-dimethylpyrazole (᭿) and pz′ = pyrazole (᭜). The numbers near the points refer to the specific complex.
T (K)
Table 7. Coalescence temperatures (Tc) and free energies of acti-
structure for both complexes involves the two pentafluoro-
vation at the coalescence temperature (∆G ‡c ) for the Fortho–Fortho ′
phenyl rings at a nearly parallel position. In the minimum
exchange (C6F5 rotation).
energy structure of complex 2, these rings are approximately
orthogonal to the coordination plane. This is not the case for
Complex
3,5 pz Substituent
Tc (K)
∆G ‡c (kcal/mol)
complex 1. Two skeletal parameters related with the coordi-
nation of the nitrogenated ligand, namely the bite angle and
the N-Pd-N/N4 dihedral angle, have also been analyzed.
Both angles are smaller when the pentafluorophenyl rings
deviate more from orthogonality with respect to the coordi-
nation plane. The values for these parameters are always
smaller in the case of the methylated complex 2, the effect
being more noticeable in the maximum energy geometry.
Lower free activation energies at the coalescence tempera-
ture (∆G ‡c) for the ring rotation process have been found
both theoretically and experimentally for the methylated de-
rivatives when compared with the complexes containing
unsubstituted pyrazolyl ligands. The origin of the energy dif-
ferences found in solution for the C6F5 rotation may be
found in the smaller values obtained from our theoretical
calculations for the N-Pd-N bite angle and for the skeletal
N-Pd-N/N4 dihedral angle in 2 as compared with 1 in the
state of maximum energy. This finding is consistent with
previous proposals that one important effect in the aryl rota-
tion was the “in-plane” hindrance of the donor atoms cis to
1a
3b
4a
2b
5b
6a
7a
8b
H
H
H
Me
Me
Me
Me
Me
338
301
327
283
298
349
273
311
16.0
15.6
16.1
12.9
12.9
15.5
12.5
13.6
a1,1′,2,2′-CDCl2CDCl2.
bCDCl3.
ied at a DFT level. Results have been compared with
experimental information obtained in solution (free energies
of activation determined by NMR) and in the solid state (X-
ray diffraction studies). Different structural parameters such
as the perfluorophenyl ring orientation, energy of the sys-
tem, and conformation of the nitrogenated ligand have been
analyzed. It has been found that when one ring is forced to
rotate, the other ring adapts its disposition. The most stable
© 2005 NRC Canada

2118
Can. J. Chem. Vol. 83, 2005
Forniés, C. Fortuño, A. Martín, and A.P. Martínez-Sariñena.
Organometallics, 16, 5849 (1997).
the polyhaloaryl group. According to our theoretical and ex-
perimental results, the direct steric repulsion of the Me3 of
the pyrazole groups with the pentafluorophenyl rings does
not have a clear effect over the C6F5 rotation.
Several X-ray structure determinations have been per-
formed for complexes 1, 2, and other derivatives of this fam-
ily. It has been found that the values of the bite angle and the
N-Pd-N/N4 dihedral angle are always smaller in the methyl-
ated derivatives, in accordance with theoretical predictions.
10. See, for example: J.M. Casas, J. Forniés, A. Martín, B.
Menjón, and M. Tomás. J. Chem. Soc. Dalton Trans. 2949
(1995); I. Ara, E. Delgado, J. Forniés, E. Hernández, E.
Lalinde, N. Mansilla, and M.T. Moreno. J. Chem. Soc. Dalton
Trans. 3201 (1996); J. Forniés, M.A. Gómez-Saso, A. Martín,
F. Martínez, B. Menjón, and J. Navarrete. Organometallics, 16,
6024 (1997); J. Forniés, F. Martínez, R. Navarro, E.P.
Urrialobeitia, and A.J. Welch. J. Chem. Soc. Dalton Trans.
2805 (1995); J. Forniés, R. Navarro, V. Sicilia, and M. Tomás.
Inorg. Chem. 32, 3675 (1993).
Acknowledgments
11. J.A. Casares, P. Espinet, J.M. Martínez-Illarduya, and Y.-S.
Lin. Organometallics, 16, 770 (1997).
12. G.B. Deacon, B.M. Gatehouse, and K.T. Nelson-Reek. J.
Organomet. Chem. 359, 267 (1989).
13. J. Ruiz, M.T. Martínez, C. Vicente, G. García, G. López, P.A.
Chaloner, and P.B. Hitchcock. Organometallics, 12, 4321 (1993).
14. A.C. Albéniz, J.C. Cuevas, P. Espinet, J. de Mendoza, and P.
Prados. J. Organomet. Chem. 410, 257 (1991).
We are grateful to the Spanish Ministerio de Educación y
Ciencia (Project Nos. CTQ2005-01430 and BQU-2002-
00301) and the Consejería de Ciencia y Tecnología of the
Junta de Comunidades de Castilla-La Mancha (PBI-05-003)
for financial support and the computational service of the
Universidad de Castilla-La Mancha.
15. E.W. Abel, K.G. Orrell, A.G. Osborne, H.M. Paint, V. Sik,
M.B. Hursthouse, and K.M. Abdul Malik. J. Chem. Soc. Dal-
ton Trans. 3441 (1994).
References
1. R. Usón and J. Forniés. Adv. Organomet. Chem. 28, 219
(1988).
16. A. Gelling, M.D. Olsen, K.G. Orrell, A.G. Osborn, and V. Sik.
Inorg. Chim. Acta, 264, 257 (1997); K.G. Orrell, A.G.
Osborne, V. Sik, and M.W. da Silva. J. Organomet. Chem. 530,
235 (1997).
17. F. Gómez-de la Torre, F.A. Jalón, A. López-Agenjo, B.R.
Manzano, A. Rodríguez, T. Sturm, W. Weissensteiner, and M.
Martínez-Ripoll. Organometallics, 17, 4634 (1998).
18. M.C. Carrión, A. Guerrero, F.A. Jalón, B.R. Manzano, A. de la
Hoz, R.M. Claramunt, V. Milata, and J. Elguero. Inorg. Chem.
42, 885 (2003).
2. A.J. Canty. Comprehensive organometallic chemistry. Vol. 9.
Edited by E.W. Abel, F.G.A. Stone, and G. Wilkinson.
Pergamon Press, Oxford. 1995. Chap. 5; P.M. Maitlis, P.
Espinet, and M.J.H. Russell. Comprehensive organometallic
chemistry. Vol. 6. Edited by E.W. Abel, F.G.A. Stone, and G.
Wilkinson. Pergamon Press, Oxford. 1982. Chap. 38.4.
3. R. Usón, J. Forniés, P. Espinet, E. Lalinde, P.G. Jones, and
G.M. Sheldrick. J. Chem. Soc. Dalton Trans. 2389 (1982); R.
Usón, J. Forniés, P. Espinet, and E. Lalinde. J. Organomet.
Chem. 254, 371 (1983); A.C. Albéniz, P. Espinet, Y. Jeanning,
M. Philoche-Levisalles, and B.E. Mann. J. Am. Chem. Soc.
112, 6594 (1990); A.C. Albeniz and P. Espinet. Organo-
metallics, 10, 2987 (1991); A.C. Albéniz, P. Espinet, and Y.-S.
Lin. Organometallics, 14, 2977 (1995); A.C. Albéniz, P. Espinet,
and Y.-S. Lin. J. Am. Chem. Soc. 118, 7145 (1996); I. Ara, J.
Forniés, A. García, J. Gómez, E. Lalinde, and M.T. Moreno.
Chem. Eur. J. 8, 3698 (2002).
19. K. Marshall, K. Rosmarion, O. Sklyut, N. Azar, R. Callahan,
and R. Rothchild. J. Fluorine Chem. 125, 1893 (2004).
20. J. Sandström. Dynamic NMR spectroscopy. Academic Press,
London. 1982.
21. J.A. Casares, S. Coco, P. Espinet, and Y.-S. Lin. Organo-
metallics, 14, 3058 (1995).
22. J.A. Casares and P. Espinet. Inorg. Chem. 36, 5428 (1997).
23. M.A. Alonso, J.A. Casares, P. Espinet, J.M. Mártinez-Ilarduya,
and C. Pérez-Briso. Eur. J. Inorg. Chem. 1745 (1998).
24. R. de la Cruz, P. Espinet, A.M. Gallego, J.M. Martín-Alvárez,
and J.M. Martínez-Ilarduya. J. Organomet. Chem. 663, 108
(2002).
25. C. Bartolomé, R. De Blas, P. Espinet, J.M. Martín-Alvárez,
and F. Villafañe. Angew. Chem. Int. Ed. 40, 2521 (2001).
26. A.C. Albeniz, A.L. Casado, and P. Espinet. Organometallics,
16, 5416 (1997).
4. S. Park, M. Pontier-Johnson, and D.M. Roundhill. J. Am.
Chem. Soc. 111, 3101 (1989).
5. A.L. Casado, J.A. Casares, and P. Espinet. Organometallics,
16, 5730 (1997).
6. A.L. Casado and P. Espinet. Organometallics, 17, 954 (1998).
7. A.L. Casado and P. Espinet. J. Am. Chem. Soc. 120, 8978
(1998).
8. See, for example: R. Usón, J. Forniés, M.A. Usón, M. Tomás,
and M.A. Ibañez. J. Chem. Soc. Dalton Trans. 401 (1994); I.
Ara, J. Forniés, E. Lalinde, M.T. Moreno, and M. Tomás. J.
Chem. Soc. Dalton Trans. 2735 (1994); L.R. Falvello, J.
Forniés, R. Navarro, V. Sicilia, and M. Tomás. J. Chem. Soc.
Dalton Trans. 3143 (1994); A.C. Albéniz, P. Espinet, Y.-S.
Lin, A.G. Orpen, and A. Martín. Organometallics, 15, 5003
(1996); J. Ruiz, V. Rodríguez, G. López, P.A. Chaloner, and
P.B. Hitchcock. Organometallics, 15, 1662 (1996).
9. L.R. Falvello, J. Forniés, R. Navarro, A. Rueda, and E.P.
Urriolabeitia. Organometallics, 15, 309 (1996); I. Ara, J.R.
Berenguer, J. Forniés, E. Lalinde, and M. Tomás.
Organometallics, 15, 1014 (1996); I. Ara, L.R. Falvello, S.
Fernández, J. Forniés, E. Lalinde, A. Martín, and M.T.
Moreno. Organometallics, 16, 5923 (1997); L.R. Falvello, J.
27. J. Forniés, F. Martínez, R. Navarro, and E.P. Urrialobeitia.
Organometallics, 15, 1813 (1996); J. Forniés, M.A. Gómez-
Saso, E. Lalinde, F. Martínez, and M.T. Moreno. Organo-
metallics, 11, 2873 (1992); J.R. Berenguer, J. Forniés, E.
Lalinde, F. Martínez, E. Urriolabeitia, and A.J. Welch. J.
Chem. Soc. Dalton Trans. 1291 (1994); J. Forniés, F.
Martínez, R. Navarro, E. Urriolabeitia, and A.J. Welch. J.
Chem. Soc. Dalton Trans. 2147 (1993); U. Amador, E.
Delgado, J. Forniés, E. Hernández, E. Lalinde, and M.T.
Moreno. Inorg. Chem. 34, 5279 (1995); S. Coco and P.
Espinet. J. Organomet. Chem. 484, 113 (1994).
28. J.A. Casares, P. Espinet, K. Soulantica, I. Pascual, and A.G.
Orpen. Inorg. Chem. 36, 5251 (1997).
29. F. Gómez-de la Torre, A. de la Hoz, F.A. Jalón, B.R. Manzano,
and A.M. Rodríguez. Inorg. Chem. 39, 1152 (2000).
© 2005 NRC Canada

Carrión et al.
2119
30. A.C. Albeniz, A.L. Casado, and P. Espinet. Inorg. Chem. 38,
2510 (1999).
31. P.K. Byers, A.J. Canty, and R.T. Honeyman. J. Organomet.
Chem. 385, 417 (1990); P.K. Byers and A.J. Canty.
Organometallics, 9, 210 (1990).
32. N. Arroyo, F. Gómez-de la Torre, F.A. Jalón, B.R. Manzano,
B. Moreno-Lara, and A.M. Rodríguez. J. Organomet. Chem.
603, 174 (2000).
33. M.C. Carrión, A. Díaz, A. Guerrero, F.A. Jalón, B.R.
Manzano, A. Rodríguez, R.L. Paul, and J.C. Jeffery. J.
Organomet. Chem. 650, 210 (2002).
V. Barone, M. Cossi, R. Cammi, B. Menucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala,
Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K.
Raghavachari, J.B. Foresman, J. Ciolowski, J.V. Ortiz, B.B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaroni, R.
Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham,
C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe,
P.M.W. Gill, B.G. Johnson, W. Chen, M.W. Wong, J.L.
Andrés, M. Head-Gordon, E.S. Replogle, and J.A. Pople.
Gaussian 98 [computer program]. Gaussian Inc., Pittsburgh,
Penn. 1998.
34. M.C. Carrión, A. Díaz, A. Guerrero, F.A. Jalón, B.R.
Manzano, and A. Rodríguez. New J. Chem. 26, 305 (2002).
35. S. Tsuji, D.C. Swenson, and R.F. Jordan. Organometallics, 18,
4758 (1999).
44. A.D. Becke. J. Chem. Phys. 98, 5648 (1993); A.D. Becke. J.
Chem. Phys. 96, 2155 (1992).
45. C. Lee, W. Yang, and R.G. Parr. Phys. Rev. B, B37, 785
(1988).
36. G.K. Anderson, R.J. Cross, L. Manojlovic-Muir, K.W. Muir,
and M. Rocamora. Organometallics, 7, 1520 (1988).
37. Y. Crameri, J. Foricher, U. Hengartner, C. Jenny, F. Kienzle,
H. Ramuz, M. Scalone, M. Schlageter, R. Schmid, and S.
Wang. Chimia, 51, 303 (1997); E.A. Broker, W. Burkhart, M.
Hennig, M. Scalone, and R. Schmid. Tetrahedron: Asymmetry,
9, 4043 (1998); T.V. Rajanbabu, T.A. Ayers, and A.L.
Caasalnuovo. J. Am. Chem. Soc. 116, 4101 (1994).
38. G. Trabesinger, A. Albinati, N. Feiken, R.W. Kunz, P.S.
Pregosin, and M. Tschoerner. J. Am. Chem. Soc. 119, 6315
(1997); M. Tschoerner, P.S. Pregosin, and A. Albinati. Organo-
metallics, 18, 670 (1999).
46. P.J. Hay and W.R. Wadt. J. Chem. Phys. 82, 299 (1985); W.R.
Wadt and P.J. Hay. J. Chem. Phys. 82, 284 (1985).
47. R. Ditchfield, W.J. Hehre, and J.A. Pople. J. Chem. Phys. 54,
724 (1971); R. Ditchfield, W.J. Hehre, and J.A. Pople. J.
Chem. Phys. 56, 2257 (1972); P.C. Hariharan and J.A. Pople.
Mol. Phys. 27, 209 (1974); M.S. Gordon. Chem. Phys. Lett.
76, 163 (1980); T. Clark, J. Chandrasekhar, G.W. Spitznagel,
and P.v.R. Schleyer. J. Comput. Chem. 4, 294 (1983).
48. C.Y. Peng, P.Y. Ayala, H.B. Schlegel, and M.J. Frisch. J.
Comput. Chem. 17, 49 (1996).
49. A.D. McQuarrie. Statistical thermodynamics. University Sci-
ence Books, Mill Valley, Calif. 1973.
39. P. Dotta, P.G. Anil Kumar, P.S. Pregosin, A. Albinati, and S.
50. Bruker AXS. SAINT. Version 6.26 [computer program].
Bruker Analytical X-ray Systems, Inc., Madison, Wis. 2000.
51. G.M. Sheldrick. SADABS empirical absorption program. Ver-
sion 2.03 [computer program]. Bruker Analytical X-ray Sys-
tems, Inc., Madison, Wis. 2000.
52. G.M. Sheldrick. Acta Crystallogr. Sect. A, 46, 467 (1990).
53. A. Altomare, G. Cascarano, C. Giacovazzo, and A. Guagliardi.
J. Appl. Crystallogr. 26, 343 (1993).
Rizzato. Organometallics, 23, 2295 (2004).
40. S. Alvarez, P. Alemany, and D. Avnir. Chem. Soc. Rev. 34,
293 (2005); P.J. Alonso, J. Forniés, M.A. García-Monforte, A.
Martín, B. Menjón, and C. Rillo. Chem. Eur. J. 8, 4056 (2002).
41. P. Espinet, J.M. Martínez-Ilarduya, C. Pérez-Briso, A.L.
Casado, and M.A. Alonso. J. Organomet. Chem. 551, 9 (1998).
42. L.K. Peterson, E. Kiehlmann, A.R. Sanger, and K.I. The. Can.
J. Chem. 52, 2367 (1974); K.I. The and L.K. Peterson. Can. J.
Chem. 51, 422 (1973).
54. G.M. Sheldrick. SHELXL-97 [computer program]. University
of Göttingen, Göttingen, Germany. 1997.
43. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A.
Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery,
Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam,
A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi,
55. G. Minghetti, M.A. Cinellu, A.B.G. Banditelli, F. Demartin,
and M. Manassero. J. Organomet. Chem. 315, 387 (1986); A.J.
Canty, N.J. Minchin, L.M. Engelhardt, B.W. Sketton, and A.H.
While. J. Chem. Soc. 645 (1986).
© 2005 NRC Canada