Can weak interactions modify the binding properties of a strong nitrogen donor? Unusual N-coordination of a phosphoranylidene-substituted pyrazolone unit towards palladium(II) centres: An experimental and theoretical study

Article abstract of DOI:10.1039/b506352n

Selective N(2)-binding of 3-methyl-l-phenyl-4-(triphenylphosphoranylidene)- 2-pyrazolin-5-one (L) has been found in two palladium(II) complexes, [PdCl ₂L₂] (2) and [Pd(o-C₆H₄CH ₂NMe₂)ClL] (3). X-Ray diffraction studies show that the pyrazole rings lie almost perpendicular to the coordination plane. In both complexes the metal atom is located out of the plane defined by the pyrazole ring(s) (dihedral angle between the plane and the Pd - N vector ～30°). To investigate the origin of this distortion, a theoretical study was carried out on a simplified model of complex 2, where a single pyrazolone ligand was replaced by NH₃. From this study it could be inferred that the out-of-plane distortion mainly involves weak, electrostatic interactions between a chlorine atom and an ortho-aromatic H atom of the N(l)-linked phenyl group, as well as between the other chlorine atom and an ortho-aromatic H atom of the PPh₃ group. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b506352n

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F U L L P A P E R
Can weak interactions modify the binding properties of a strong
nitrogen donor? Unusual N-coordination of a phosphoranylidene-
substituted pyrazolone unit towards palladium(II) centres: an
experimental and theoretical study
Antonio J. Mota,a Alain Dedieu,*a Pierre Kuhn,b Dominique Matt,*b Richard Welterc and
Markus Neuburgerd
a Laboratoire de Chimie Quantique, UMR 7551 CNRS, Universite´ Louis Pasteur, 4 rue Blaise
Pascal, 67070, Strasbourg
b Laboratoire de Chimie Inorganique Mole´culaire, UMR 7513 CNRS, Universite´ Louis Pasteur,
1 rue Blaise Pascal, 67008, Strasbourg Cedex, France. E-mail: dmatt@chimie.u-strasbg.fr
c DECOMET, UMR 7513 CNRS, Universite´ Louis Pasteur, 4 rue Blaise Pascal, 67070,
Strasbourg Cedex, France
d Laboratory for Chemical Crystallography, Universita¨t Basel, Spitalstrasse 51, 4056, Basel,
Switzerland
Received 5th May 2005, Accepted 25th July 2005
First published as an Advance Article on the web 22nd August 2005
Selective N(2)-binding of 3-methyl-1-phenyl-4-(triphenylphosphoranylidene)-2-pyrazolin-5-one (L) has been found
in two palladium(II) complexes, [PdCl2L2] (2) and [Pd(o-C6H4CH2NMe2)ClL] (3). X-Ray diffraction studies show that
the pyrazole rings lie almost perpendicular to the coordination plane. In both complexes the metal atom is located
out of the plane defined by the pyrazole ring(s) (dihedral angle between the plane and the Pd–N vector ∼30◦). To
investigate the origin of this distortion, a theoretical study was carried out on a simplified model of complex 2, where
a single pyrazolone ligand was replaced by NH3. From this study it could be inferred that the out-of-plane distortion
mainly involves weak, electrostatic interactions between a chlorine atom and an ortho-aromatic H atom of the
N(1)-linked phenyl group, as well as between the other chlorine atom and an ortho-aromatic H atom of the PPh3 group.
Introduction
Pyrazolone units have been extensively employed in ligand
design, especially for the synthesis of highly efficient extract-
ing agents such as 4-acylpyrazole-5-ones.1–7 In most of these
ligands, the planar pyrazole ring serves as an effective electron-
Scheme 1 Two-step synthesis of L.
withdrawing function, while the carbonyl group behaves as a
coordinating group. Some recent studies have clearly established
that one of the two nitrogen atoms, namely the pyridine-like
donor, N(2), may also coordinate metal ions, but to date only two
pyrazolone derivatives have been reported where the sole metal-
binding atom is the N(2) atom.8,9 Other studies have shown that
this pyridinic nitrogen atom may sometimes be involved in weak,
supramolecular bonding interactions, thereby influencing the
whole structure of the metal derivatives.3,10 We now report on the
coordinative properties of the pyrazolone-derived phosphorus
ylide L, which, unlike other b-keto-stabilized phosphorus ylides,
does not behave as a C-11,12 or O-donor13,14 towards transition
metals. This study describes the first examples of N(2)-binding
of a pyrazolone unit to a palladium centre. Further, a theoretical
study provides a rationale for the observed out-of-plane binding
of the palladium atom with respect to the pyrazole ring.
of the resulting phosphonium salt with NaH/THF. The 31P
NMR spectrum of L displays a singlet at 10.6 ppm, while the IR
spectrum shows a strong and broad carbonyl band at 1603 cm−1.
Note that a more costly synthesis of L, which involves the
preparation of a nickel–phosphinoenolate, has been reported
recently, together with the X-ray structure of L.15
Keto-stabilized phosphorus ylides are ambidentate ligands
that usually behave either as C- or O-donor ligands. In the
present case, the b-keto ylide unit is fused to a pyrazole ring,
resulting in additional conjugation of the ylidic electron pair.
The strong electron withdrawing character of the pyrazole ring
has been demonstrated in a number of studies,16 and this feature
has also recently been exploited for the synthesis of electron poor
P,O-chelating phosphines for use in catalysis.15 We wondered
whether the presence of the pyrazole ring in L could totally
“neutralise” the binding/nucleophilic properties of the keto-
ylidic fragment and therefore investigated its reaction towards
palladium(II) centres. Palladium(II) was chosen because this
metal is known to bind carbonyl-stabilised ylides either through
the C- or the O-bonding mode.12,14
Reaction of [PdCl2(PhCN)2] with 2 equiv. of L afforded
complex 2 in 55% yield. The chemical shift of the phos-
1
phorus atom (10.9 ppm) as well as the J(PCpyrazole) coupling
Results and discussion
constant are almost unchanged with respect to that of L.
In contrast, the chemical shift of the pyrazole carbon atom
linked to the phosphorus atom has undergone a significant
downfield shift of ca. 5.2 ppm, indicating an important electronic
The phosphorus ylide L was obtained in two steps according to
Scheme 1: (i) reaction of the bromo-enol 1 with one equivalent
of triphenylphosphine in toluene at 90 ◦C; (ii) deprotonation
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 3 1 5 5 – 3 1 6 0
3 1 5 5
©

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perturbation of the pyrazole ring upon complexation. Bonding
of the pyridinic N(2) atoms was inferred from an X-ray
diffraction study (vide infra). Similarly, reaction of 2 equiv. of
L with [Pd(o-C6H4CH2NMe2)Cl]2 gave quantitatively the N-
coordinated complex 3. The NMR data of the ylidic ligand of
3 are very close to those found in complex 2 (see Experimental
section). The 1H NMR spectrum of 3 shows two NMe signals,
in keeping with a pyrazolone ligand that does not freely rotate
about the coordination bond. For both complexes, the IR
spectrum shows a strong carbonyl absorption at 1624 cm−1 (vs.
1603 cm−1 in L), a value which, a priori, justified exclusion of the
O-bonding mode.
Fig. 2 Molecular structure of [Pd(o-C6H4CH2NMe2)Cl]2 (3). Only one
conformation of the disordered metallomacrocycle is shown.
can be excluded in both structures. Important structural data for
the complexes compared to those of L are given in Scheme 2.
In the solid state, the complex 2 (Fig. 1) has a centrosymmetric
structure, the Pd atom having an almost ideal square planar
environment, with◦ N–Pd–Cl(1) and N–Pd–Cl(2) angles of
˚
88.6(2) and 91.4(2) , respectively. The Pd–Cl (2.315(2) A) and
˚
Pd–N distances (2.013(6) A) lie in the range expected for such
bonds. The most important structural modification observed on
going from free L to its coordinated form is that of the N–C(Me)
˚
bond, which undergoes a lengthening of 0.055 A. Each pyrazole
ring is strongly inclined with respect to the coordination plane,
the interplanar dihedral angle being 79◦. An intriguing feature
of this structure is the out-of-pyrazole-plane coordination of
the palladium atom. The distance of the metal atom to the plane
Scheme 2 Important structural data of complexes 2 and 3, compared
with those of L.
˚
defined by the pyrazolone rings is 0.83(1) A, which corresponds
to an angle between the N–Pd and N–G vectors of 164◦ (G being
the pyrazole barycentre). A similar bonding mode was found in
complex 3, the structure of which was also determined by an
X-ray diffraction study (Fig. 2). Here, the angle between the
N–Pd and N–G vectors is 159◦, while the distance of the metal
Theoretical study
That the Pd atom is significantly displaced out of the plane
defined by the pyrazolone ring is somewhat astonishing because
a closely related example of copper coordination shows a
perfectly planar metal–pyrazolone system,9 as is expected if
we consider an ideal aromatic system with a pure sp2 orbital
on the coordinating nitrogen atom (resonance forms A and B
in Scheme 3). A priori, several electronic effects may account
for the distortion encountered in the Pd complexes treated
here (2 and 3). In particular, a lack of delocalisation in the
pyrazolone ring, which would result in the pyramidalisation of
the coordinating nitrogen atom (resonance form C in Scheme 3)
could satisfactorily explain this occurrence. On the other hand,
it is well established that weak intramolecular interactions may
also significantly modify the metal’s first coordination sphere.17
˚
to the pyrazolone plane is 0.71 A. Clearly, there is a degree
of pyramidalisation of N(2). An explanation for this unexpected
behaviour is given below. We note that in complex 3, the pyrazole
plane also adopts an almost orthogonal orientation to the metal
plane (interplanar angle 89◦). Intermolecular interactions which
would explain the stereochemical distortion about the N(2) atom
Fig. 1 Molecular structure of [PdCl2L2] (2). The solvent molecules have
been omitted for clarity.
Scheme 3 Possible resonance forms with a significant contribution.
3 1 5 6
D a l t o n T r a n s . , 2 0 0 5 , 3 1 5 5 – 3 1 6 0

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Table 1 Experimental and calculated values for selected geometrical parameters.a,b,c
Entry
Parameter
X-Ray
DFT
MM
1
2
3
4
5
6
7
8
9
d(Pd–N2)
d(N1–N2)
d(N2–C3)
d(C3–C4)
d(C4–C5)
d(C5–N1)
d(C5–O)
2.013(6)
1.396(8)
1.372(10)
1.408(10)
1.442(11)
1.384(10)
1.259(9)
1.721(8)
2.949
2.067
1.407
1.344
1.426
1.452
1.399
1.268
1.750
2.796
3.246
1.963
1.366
1.417
1.466
1.463
1.415
1.389
1.756
3.039
3.075
d(C4–P)
d(HPh–Cl1)
d(Cl2–HPh
10
)
3.359
11
12
D(PdN2C3C4)
D(C5N1CipsoCo)
−150.4
+130.1
−147.3
+140.9
−147.0
+141.1
◦
a
d for distance in angstroms (A). D for dihedral in degrees ( ). b X-Ray and MM calculation refer to compound 2. DFT calculations refer to structure
˚
4. c D(PdN2C3C4) reflects the out-of-plane Pd distortion whereas D(C5N1CipsoCo) measures the torsion of the phenyl group with respect to the
pyrazolone ring.
The theoretical analysis was performed by quantum mechan-
ics calculations carried out at the DFT level, using a simplified
version of the X-ray structure of 2 as the starting geometry (see
computational details). One of the two pyrazolone ligands was
replaced by NH3 in order to obtain structure 4 (Table 1). This was
considered justifiable since the trans arrangement of the nitrogen
ligands in 2 should result in negligible steric interactions between
the two organic moieties. In fact, it proved to be an acceptable
approximation when comparing the geometries obtained by
both X-ray and DFT calculations (see Table 1). The rest of the
complex was unchanged. An additional molecular mechanics
calculation (see computational details), accounting for steric
and electrostatic interactions, was also carried out in order to
establish, by comparison with the DFT calculations, the origin
of the out-of-plane distortion of Pd in this complex.
From all these calculations, it can be concluded that the Pd
atom always prefers to be located out of the plane defined by
the pyrazolone ring, independently of the calculation method
chosen, in agreement with the crystal structure. Some significant
geometrical parameters derived from the X-ray crystallographic
data, from the DFT and the MM calculation are shown in
Table 1.
Although the MM geometry is not very accurate, the global
shape of complex 2 is well reproduced if compared to both
the X-ray structure and the calculated DFT geometry for 4
(Fig. 3). Most interestingly, the value for the D(PdN2C3C4)
dihedral angle (which is a measure of the out-of-plane Pd
distortion) given by MM coincides with the experimental and
DFT ones. This means that the deviation from planarity of the
Pd/pyrazolone system could have its origin in other factors than
the electronic properties of the pyrazolone ring, viz., steric and
electrostatic interactions.
Fig. 3 X-Ray crystal (thick line, blue) and molecular mechanics
(magenta) structures of compound 2. The DFT structure (thin line,
blue) is calculated for 4. Hydrogens have been omitted for clarity.
the d(N2–C3) distance in 2 has increased and the d(C3–C4)
distance has decreased when compared to the values found in
free L (Scheme 2). The same trend becomes apparent in the
DFT calculations on 4: thus, on going from L to 4 the d(N2–
˚
C3) distances vary from 1.329 to 1.344 A, and the d(C3–C4)
˚
distances from 1.445 to 1.426 A. However, for both structures
only slight differences can be found in the Mulliken charges.
Moreover, the NBO analysis gives approximately the same
charge distribution for L and 4 and almost the same bond
contribution and hybridization type for all atoms in the pyrazole
ring.
Due to the MM calculation, which account for the experi-
mental D(PdN2C3C4) dihedral angle, as well as the similarities
of L and 4 as established by NBO analysis, we considered
that the out-of-plane distortion of the Pd atom could have its
The bond distances within the pyrazolone ring shown by the
X-ray structures of L and 2 (see Scheme 2) are indicative of a
slight contribution of resonance form C in the complex. Thus,
D a l t o n T r a n s . , 2 0 0 5 , 3 1 5 5 – 3 1 6 0
3 1 5 7

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origin in steric and electronic factors instead of an electronic
distribution effect in the pyrazolone ring. In order to prove
this hypothesis, several DFT calculations, in which system 4
was structurally modified, were carried out. Thus, when the
phenyl group located at N(1) was replaced by a methyl group,
the Pd atom became completely coplanar with the pyrazolone
ring (the D(PdN2C3C4) dihedral angle changed to −177.5◦,
see entry 11, Table 1). However, when the same phenyl group
was replaced by the smaller pyrrolyl ring (attachment through
a Ca carbon atom),18 the distortion was approximately the
same (the D(PdN2C3C4) dihedral angle changing to −146.2◦),
but the torsion of the pyrrolyl ring drastically diminished
(D(C5N1CipsoCo) dihedral angle: +159.3◦) with respect to that of
the phenyl ring (entry 12, Table 1). In fact, the calculation points
to important Haromatic · · · Cl(1) attractive electrostatic interactions
(entry 9, Table 1) that favour the palladium displacement in both
4 and the pyrrolyl substituted system: indeed the d(HPh–Cl1)
there was no change in the steric component. However, the
out-of-plane distortion of the Pd atom became much smaller
due to the elimination of the two electrostatic Haromatic · · · Cl
interactions. Finally, the most clear evidence for the presence
of such electrostatic interactions consisted in the substitution of
the two chlorine atoms for the smaller but more electronegative
fluorine atoms. The consequences of this modification are quite
significant: the D(PdN2C3C4) dihedral angle became −132.9◦
(thus, the Pd out-of-plane shift drastically increased) and the
distances d(HPh–Cl1) and d(Cl2–HPh) decreased to 2.063 and
˚
2.144 A, respectively (the sum of the Van der Waals radii of H
˚
and F amounts 2.55 A) (Fig. 5).
˚
˚
distance is significantly smaller (2.796 A in 4 and 2.867 A in
the pyrrolyl substituted system) than the sum of the van der
˚
Waals radii (∼3.0 A). Obviously, the more planar orientation of
the pyrrolyl ring increases its conjugation with the pyrazolone
moiety. Overall, the inclination of an N-bonded aromatic ring
with respect to the pyrazolyl plane results from a balance
between three factors: (i) attractive electrostatic Haromatic · · · Cl
interactions; (ii) steric constraints (which become most apparent
in the case of the phenyl ring); (iii) stabilisation by conjugation.
In keeping with this assumption, we observe that when N(2) is
not coordinated (as in L) the phenyl ring becomes coplanar with
the pyrazolone ring, maximizing the p-delocalization.
Fig. 5 DFT structure of the complex obtained by replacement of the
chlorine atoms in 4 by fluorine atoms.
Careful analysis of the DFT calculations shows that there
exists an additional, but weaker attractive electrostatic inter-
action that amplifies the out-of plane shift of the metal. The
latter is established between the other chlorine atom and one of
In that case the N-linked phenyl ring becomes more conju-
gated to the pyrazolone system, the D(C5N1CipsoCo) dihedral
angle changing to +159.2◦. This is a direct consequence of an
increased electrostatic Haromatic · · · halide interaction as well as a
decrease of the steric hindrance between the phenyl ring and the
halide.
the phenyl rings of the phosphonium moiety (Cl(2) · · · Haromatic
,
entry 10, Table 1). This is best examplified by the substitution
in 4 of the PPh3 unit by PH3 (which suppresses this interaction).
In this case the D(PdN2C3C4) dihedral angle value changes
back to −165.3◦, which corresponds to a less important out-of-
plane displacement (distortion decrease: 18◦). Note that each of
these electrostatic Haromatic · · · Cl interactions occurs twice in the
experimental system because of the symmetry of the structure
(Fig. 4).
Taking into account the calculations presented above, it can
be concluded that the main contribution to the observed out-of-
plane Pd displacement arises from the attractive electrostatic in-
teractions established between the chlorine atoms and hydrogen
atoms of the closest phenyl groups: as shown by DFT-B3LYP
calculations, substitution of either the phenyl group at N(1) or of
the chloride ligands by methyl groups leads to an almost in-plane
coordination of the palladium atom. Conversely, substitution
of the chlorine atoms by fluorine atoms results in a more
distorted palladium complex with strong, attractive electrostatic
Haromatic · · · F interactions. Furthermore, replacement in 4 of the
Ph3P unit by H3P leads to a more planar system owing to the
suppression of the weaker Haromatic · · · Cl interaction. Finally,
when the N-bonded phenyl ring is replaced by the smaller
pyrrolyl group, the out-of-plane Pd distortion (which should
diminish if steric factors were predominant) does not change, but
is associated merely with a more conjugated pyrrolyl-pyrazolone
system.19 Overall, this study is a further confirmation that weak
intramolecular interactions can significantly modify the binding
properties of a strong donor.
Experimental
Fig. 4 The four main electrostatic interactions found in complex 2.
All syntheses were performed in Schlenk-type flasks under dry
nitrogen. Solvents were dried by conventional methods and
distilled immediately prior to use. CDCl3 was passed down a
5 cm-thick alumina column and stored under nitrogen over
molecular sieves (4 A). Routine H, C{ H} and P{ H} spectra
were recorded with an AC-200 Bruker FT instruments. 1H
NMR spectra were referenced to residual protonated solvents
(7.26 ppm for CDCl3 and 5.32 for CD2Cl2), 13C chemical
shifts are reported relative to deuterated solvents (77.0 ppm
for CDCl3 and 53.8 ppm for CD2Cl2), and the 31P NMR data
are given relative to external H3PO4. [PdCl2(PhCN)2],20
That electrostatic interactions are the main contributing
factors for the out-of-plane palladium shift can also be inferred
from substitutions made on the metallic moiety. For instance,
when the chlorine atoms were substituted by methyl groups
(which have a similar van der Waals radii but avoid possible
attractive electrostatic interactions), the D(C5N1CipsoCo) dihe-
dral angle varied only slightly, D = +137.7◦, whereas the
D(PdN2C3C4) dihedral angle became −166.3◦. Note that the
torsion of the N-linked phenyl group did not vary because
1
13
1
31
1
˚
3 1 5 8
D a l t o n T r a n s . , 2 0 0 5 , 3 1 5 5 – 3 1 6 0

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[Pd(o-C6H4CH2NMe2)Cl]2 and the bromo-enol 122 were pre-
152.92–122.90 (aryl-C and C-pyrazole), 73.75 (s, NCH2), 69.90
21
pared using a literature procedure.
(d, PCpyrazo, J(PC) = 132 Hz), 52.48 and 52.22 (2s, NCH3), 18.08
1
(s, CH3). 31P{ H} NMR (121 MHz, CDCl3): d 11.4 (s). Found:
C, 62.41; H, 4.77; N, 5.84. Calc. for C37H35ClN3OPPd (Mr =
3-Methyl-1-phenyl-4-triphenylphosphoranylidene-2-pyrazolin-5-
one L
710.54): C, 62.55; H, 4.97; N, 5.91%.
To a stirred solution of 3-methyl-1-phenyl-4-bromo-2-pyrazolin-
5-one 1 (10.000 g, 39.50 mmol) in toluene (150 cm3) was
added a solution of PPh3 (10.360 g, 39.50 mmol) in toluene
(200 cm3). After 0.5 h, a white precipitate appeared. The resulting
suspension was then warmed up to 90 ◦C and stirred for
15 h. After cooling, the supernatant solution was removed and
the residue was washed with cold toluene (2 × 20 mL). The
residue was then treated with NaH (60% in mineral oil, 1.600 g,
40.0 mmol) in THF (200 cm3). After stirring for 15 h, the solvent
was removed in vacuo, upon which the residue was redissolved
in toluene (200 cm−3). The solution was filtered through Celite,
then concentrated to 20% of its initial volume. Addition of Et2O
afforded a white microcrystalline powder. Yield: 7.720 g, 45%;
X-Ray crystallography
Crystal data for 2. Crystals suitable for X-ray diffraction
were obtained by slow evaporation of a chloroform solution.
C56H46Cl2N4O2P2Pd·4CHCl3, M = 1523.78, triclinic, space
¯
group P1, yellow prisms, a = 10.4860(4), b = 11.1350(5), c =
◦
˚
18.4870(8) A, a = 76.56(5), b = 87.92(5), c = 67.80(5) , V =
3
−1
˚
1940.57(14) A , Z = 1, l = 0.801 mm , F(000) = 768, Dc =
1.304 g cm−3. Crystals of the compound were glued to a glass
fibre and mounted on a Nonius Kappa CCD. X-Ray diffraction
measurements were made using graphite-monochromated Mo-
˚
Ka radiation (k = 0.71073 A) at 173 K. Data collection was
carried out using the Nonius collect suite. 8556 Reflections
collected (1.13 < h < 27.41◦), 5324 data with I > 2r(I). The
structure was solved by direct methods with SHELXS-97 and
refined with SHELXL-97.23 Hydrogen atoms were included and
refined using a riding model in SHELX-97. Final results: R1 =
0.0915, wR1 = 0.219, goodness of fit = 0.835, 376 parameters,
−1
1
=
IR (KBr, cm ): m(C O) 1603s. H NMR (300 MHz, CDCl3): d
8.12–8.09 (m, 2H, ArH), 7.80–7.51 (m, 15H, ArH), 7.33–7.28
(m, 2H, ArH), 7.05–6.99 (m, 1H, ArH), 1.43 (s, 3H, CH3).
1
13C{ H} NMR (75 MHz, CDCl3): d 167.50 (d, C(O), 2J(PC) =
18.5 Hz), 149.50–119.12 (aryl-C and quat.-C), 65.98 (d, PC,
1
−3
J(PC) = 130 Hz), 16.02 (s, CH3). 31P{ H} NMR (121 MHz,
largest difference peak = 0.996 e A . Important bond lengths
˚
CDCl3): d 10.6 (s). Found: C, 77.49; H, 5.38; N, 6.41. Calc. for
C28H23N2OP (Mr = 434.469): C, 77.40; H, 5.31; N, 6.45%.
and angles are given in Table 1.
Crystal data for 3. Crystals suitable for X-ray diffraction
were obtained by slow evaporation of a dichloromethane
solution: C37H35ClN3OPPd, M = 710.54, monoclinic, space
group P21, orange plates, a = 9.5561(1), b = 16.2957(2), c =
trans-Dichloro-bis(3-methyl-1-phenyl-4-triphenylphos-
phoranylidene-2-pyrazolin-5-one)palladium(II) 2
◦
3
˚
˚
To a stirred solution of 3-methyl-1-phenyl-4-triphenylphos-
phoranylidene-2-pyrazolin-5-one L (0.200 g, 0.50 mmol) in
chloroform (10 cm3) was added a solution of [PdCl2(PhCN)2]
(0.096 g, 0.25 mmol) in chloroform (10 cm3). The pale orange
solution was stirred for 1 h at room temperature, then heated
for a further 15 h under reflux. The solution was concentrated
to ca. 5 cm3. Upon cooling overnight at −20 ◦C, an orange
crystalline solid precipitated, which was collected by filtration,
washed successively with cold chloroform (5 cm3) and pentane
(10 cm3), and eventually dried in vacuo. Yield: 0.144 g, 55%; IR
11.0233(1) A, b = 110.4610(7) , V = 1608.29(3) A , Z = 2,
l = 0.744 mm−1, F(000) = 728. Crystals of the compound
were mounted on a Nonius Kappa CCD. Data collection with
˚
Mo-Ka radiation (k = 0.71073 A) was carried out at 173 K
using the Nonius collect suite.24 71068 reflections were collected
(3.2 < h < 27.5◦), 7233 being found to be unique (merging
R = 0.096). The structure was solved by direct methods with
the program SIR92.25 Least squares refinement was carried
out using the program CRYSTALS.26,27 Hydrogen atoms are
in calculated positions. Final results: R(F) = 0.0236 (I > 3r(I)),
wR(F) = 0.0281 (all data), goodness of fit = 1.0672, residual
−1
1
=
(KBr, cm ): m(C O) 1624s. H NMR (300 MHz, CD2Cl2): d
8.03–8.01 (m, 4H, ArH), 7.77–7.70 (m, 18H, ArH), 7.64–7.61
(m, 12H, ArH), 7.46–7.41 (m, 4H, ArH), 7.27–7.21 (m, 2H,
−3
˚
electron density minimum/maximum = −0.67/0.77 e A . A
disorder over two positions was found for the Me2NCH2 group.
Important bond lengths are given in Scheme 1.
ArH), 1.67 (s, 6H, CH3). 13C{ H} NMR (75 MHz, CD2Cl2): d
1
2
165.56 (d, C(O), J(PC) = 15 Hz), 155.17–121.48 (aryl-C and
Cquat), 71.20 (d, PCpyrazo, J(PC) = 133 Hz), 16.31 (s, CH3). 31P{ H}
CCDC reference numbers 271195 and 271196.
See http://dx.doi.org/10.1039/b506352n for crystallographic
data in CIF or other electronic format.
1
NMR (121 MHz, CD2Cl2): d 10.9 (s). Found: C, 64.08; H, 4.56;
N, 5.28. Calc. for C56H46Cl2N4O2P2Pd (Mr = 1046.27): C, 64.29;
H, 4.43; N, 5.35%. Monitoring the reaction by 31P NMR shows
the quantitative formation of an intermediate at an early stage of
the reaction which was not characterized (singlet at 10.6 ppm).
Presumably this compound corresponds to the cis isomer.
Computational details
The calculations were carried out at the DFT-B3LYP level28–30
with the Gaussian 03 program.31 We used as starting geometries
those provided by the X-ray structure. Owing to the symmetry
of the crystal structure, we have replaced one organic molecule
by the amino group. The geometries were fully optimized by
the gradient technique with the following basis: For Pd the
LANL2DZ basis set was modified following the prescription
of Couty and Hall.32 In this modified basis the innermost core
electrons (up to 3d) are described by the relativistic orbital-
adjusted effective core potential of Hay and Wadt33 and the
remaining outer core and valence electrons by a [341/541/31]
basis set where the two outermost 5p functions of the standard
LANL2DZ basis set have been replaced by a [41] split of the
5p function optimized by Couty and Hall. The carbon, oxygen,
nitrogen and hydrogen atoms34 were described by the standard 6-
31G basis set, whereas we used for the phosphorus and halogen
atoms the polarized 6-31G* basis set.35 The DFT d(Pd–N2)
distance values obtained with this basis set are in agreement
with those of experimental pyrazole–palladium complexes.36–38
Chloro(o-dimethylaminomethylphenyl)(3-methyl-1-phenyl-4-
triphenylphosphoranylidene-2-pyrazolin-5-one)palladium(II) 3
To a stirred solution of 3-methyl-1-phenyl-4-triphenylphos-
phoranylidene-2-pyrazolin-5-one L (0.200 g, 0.50 mmol) in
toluene (10 cm3) was added a solution of [Pd(o-C6H4CH2-
NMe2)Cl]2 (0.138 g, 0.25 mmol) in toluene (10 cm3). A pale
yellow precipitate formed immediately. After stirring for 0.5 h,
the precipitate was collected by filtration, washed first with
toluene (5 cm3), then pentane (10 cm3) before being dried in
−1
1
=
vacuo. Yield: 0.327 g, 92%; IR (KBr, cm ): m(C O) 1624s. H
NMR (300 MHz, CDCl3): d 8.10 (pseudo d, 2H, ArH), 7.80–
7.55 (m, 15H, ArH), 7.35–7.30 (m, 2H, ArH), 7.17–7.10 (m, 1H,
ArH), 6.91–6.75 (m, 3H, ArH), 6.26 (d, 1H, ArH, J = 7.1 Hz),
3.73 and 3.58 (AB spin system, 2H, NCH2, 2J = 14.0 Hz),
2.77 and 2.68 (2s, 2 × 3H, NCH3), 1.95 (s, 3H, CH3). 13C{ H}
1
NMR (75 MHz, CDCl3): d 165.97 (d, C(O), 2J(PC) = 15.6 Hz),
D a l t o n T r a n s . , 2 0 0 5 , 3 1 5 5 – 3 1 6 0
3 1 5 9

View Article Online
The molecular mechanics calculation was performed using
the MM+ force field (improved MM2) implemented on the
Hyperchem program.39
Cl(2) · · · Haromatic interaction is still present (the d(Cl2–HPh) distance
˚
˚
changed from 3.246 A to an even smaller value, 3.054 A, see entry 10,
Table 1). Moreover, there are some other attractive interactions that
result from the out-of-plane Pd distortion: these involve (i) the Pd
atom, which interacts with two hydrogen atoms, one originating from
the tert-butyl group and sitting apically above the metal (Pd · · · H
Acknowledgements
˚
2.539 A), the other one belonging to the C(3)-methyl group (Pd · · · H
This work was supported by the ministe`re de lꢀe´ducation
nationale, de lꢀenseignement supe´rieur et de la recherche (grant
to P. K.) and the Junta de Andaluc´ıa-Universidad de Granada
(grant to A. M.).
2.729 A); (ii) the Cl1 atom, which interacts with H atoms of the same
˚
˚
alkyl groups (Cl(1) · · · H distances: 3.043 and 2.905 A, respectively).
20 F. R. Hartley, The Chemistry of Platinum and Palladium, Wiley, New
York, 1973.
21 A. C. Cope and E. C. Friedrich, J. Am. Chem. Soc., 1968, 90, 909.
22 G. Westo¨o¨, Acta Chem. Scand., 1952, 6, 1499.
23 G. M. Sheldrick, SHELXL-97, Program for the refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
24 COLLECT Software, Nonius BV, 1997–2001.
25 A. Altomare, G. Cascarano, A. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27,
435.
26 D. J. Watkin, C. K. Prout, J. R. Carruthers, P. W. Betteridge and
R. I. Cooper, CRYSTALS, Issue 11, Chemical Crystallography
Laboratory, Oxford, UK, 2001.
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18 This group was chosen because it is the smallest uncharged aromatic
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3 1 6 0
D a l t o n T r a n s . , 2 0 0 5 , 3 1 5 5 – 3 1 6 0