New (η3-allyl)palladium complexes with pyridylpyrazole ligands: Synthesis, characterization, and study of the influence of N1 substituents on the apparent allyl rotation

Article abstract of DOI:10.1021/om070093u

The allylpalladium [Pd(η³-C₃H₅)(L)] (BF₄) (L = L¹ (1), L² (2), L³ (3), L⁴ (4)) complexes with pyridylpyrazole ligands 2-(5-phenyl-1H- pyrazol-3-yl)pyridine (L¹), 2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl) pyridine (L²), 2-(1-octyl-5-phenyl)-1H-pyrazol-3-yl)pyridine (L ³), and 2-(5-phenyl-3-(pyridin-2-yl)-pyrazol-1-yl)ethanol (L ⁴) were synthesized from the appropriate pyridylpyrazole ligand and [Pd(η³-C₃H₅)Cl]₂ in the presence of AgBF₄. The cationic complex 1 was converted into the neutral complex 5 under basic conditions. These complexes were characterized, and the crystal and molecular structure of [Pd(η³-C₃H ₅)(L²)](BF₄) (2) was resolved by X-ray diffraction. Also, we have studied the apparent allyl rotation, observed as H_syn-H_syn and H_anti-H_anti interconversions. The influences of the solvent, the traces of water, and the N1 substituent have also been studied.

Full text of DOI:10.1021/om070093u

Organometallics 2007, 26, 3183-3190
3183
New (η3-Allyl)palladium Complexes with Pyridylpyrazole Ligands:
Synthesis, Characterization, and Study of the Influence of N1
Substituents on the Apparent Allyl Rotation
Vanessa Montoya,† Josefina Pons,*,† Jordi Garc´ıa-Anto´n,† Xavier Solans,‡
Merce` Font-Bard´ıa,‡ and Josep Ros*,†
Departament de Qu´ımica, Unitat de Qu´ımica Inorga`nica, UniVersitat Auto`noma de Barcelona,
08193-Bellaterra, Barcelona, Spain, and Cristal.lografia, Mineralogia i Dipo`sits Minerals, UniVersitat de
Barcelona, Mart´ı i Franque`s s/n, 08028-Barcelona, Spain
ReceiVed January 31, 2007
The allylpalladium [Pd(η3-C3H5)(L)](BF4) (L ) L1 (1), L2 (2), L3 (3), L4 (4)) complexes with
pyridylpyrazole ligands 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L1), 2-(1-ethyl-5-phenyl-1H-pyrazol-3-
yl)pyridine (L2), 2-(1-octyl-5-phenyl)-1H-pyrazol-3-yl)pyridine (L3), and 2-(5-phenyl-3-(pyridin-2-yl)-
pyrazol-1-yl)ethanol (L4) were synthesized from the appropriate pyridylpyrazole ligand and [Pd(η3-
C3H5)Cl]2 in the presence of AgBF4. The cationic complex 1 was converted into the neutral complex 5
under basic conditions. These complexes were characterized, and the crystal and molecular structure of
[Pd(η3-C3H5)(L2)](BF4) (2) was resolved by X-ray diffraction. Also, we have studied the apparent allyl
rotation, observed as Hsyn-Hsyn and Hanti-Hanti interconversions. The influences of the solvent, the traces
of water, and the N1 substituent have also been studied.
that is frequently observed in complexes with N-donor ligands
is the apparent rotation of the allyl group. The apparent rotation
is observed as a syn-syn, anti-anti exchange and/or isomerization
process, depending on the molecular symmetry. Two main
mechanisms have been proposed for the apparent allyl rota-
tion: (a) an associative mechanism that involves five-
coordinated intermediates (coordination of the solvent, the anion,
or other molecules) that can undergo allyl pseudorotation9-11
and (b) dissociative mechanisms with formation of T-shaped
three-coordinated intermediates after dissociation of mono- or
bidentate (partial dissociation) ligands.12,13 Consequently, one
scope of this work is to determine whether the apparent allyl
rotation in derivatives with N-donor ligands involves Pd-N
bond breaking or not.
Pyrazoles are known as both monodentate and exo-bidentate
ligands, and their nitrogen atoms can coordinate to metal centers
as either anionic or neutral donor groups. Pyrazole ligands
having a 2-pyridyl group14 could be good candidates for the
production of both cationic and neutral (η3-allyl)palladium
complexes. They could also be helpful to study the apparent
allyl rotation in the complexes obtained.
Introduction
In recent years, nitrogen binding ligands have received a great
deal of attention, due to their promising properties in applied
sciences, mostly because of their high efficiency in homoge-
neous catalysis.1-3 To date, a number of N-ligand derivatives
have found practical applications and the search for new, more
effective and/or selective species is still in progress. Chelating
bi- or tridentate N-coordinating ligands such as diazabutanes,
bis(oxazolinyl)pyrroles, and dipyridylamides and their prospec-
tive applications have been recently reported.4 The relevance
of N-donors in organometallic chemistry has been exhaustively
discussed. In these complexes, ligands affect the metal center
electronically and sterically.
Allylpalladium chemistry is one of the most successful and
innovative areas of organometallic catalysis.5,6 The most general
coordination for allyl ligands is the η3 bonding mode. The
fluxional behavior of these systems directly related to the allyl
group or to the ancillary ligands has also attracted much
attention.7 One process frequently encountered in allylpalladium
complexes is the mutual exchange of syn and anti groups. This
process is believed to occur through an η3-η1-η3 isomerization
in (η3-allyl)palladium complexes.8 A second dynamic process
Results and Discussion
* To whom correspondence should be addressed. Fax: 34-93 581 31
01. E-mail: Josefina.Pons@uab.es (J.P.).
Synthesis and Spectroscopic Properties. Allylpalladium
complexes with four different pyridylpyrazole ligands have been
† Universitat Auto`noma de Barcelona.
‡ Universitat de Barcelona.
(1) Bolm, C.; Kaufmann, D.; Zehnder, M.; Neuburger, M. Tetrahedron
Lett. 1996, 37, 3985.
(2) Godleski, S. A. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: New York, 1991; Vol. 4.
(3) Trost, B. M.; Lee, C. In Catalytic Asymmetric Synthesis, 2nd ed.;
Ojima, I., Ed.; Wiley-VCH: New York, 2000.
(9) Crociani, B.; Di Bianca, F.; Giovenco, A.; Boschi, T. Inorg. Chim.
Acta 1987, 127, 169.
(10) Guerrero, A. M.; Jalon, F. A.; Manzano, B. R.; Rodriguez, A.;
Claramunt, R. M.; Cornago, P.; Milata, V.; Elguero, J. Eur. J. Inorg. Chem.
2004, 549.
(4) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994, 33.
(5) Tsuji, J. Palladium Reagents and Catalysts, InnoVation in Organic
Synthesis; Wiley: Chichester, U.K., 1996.
(6) Trost, B. M.; Van Vranken, D. L. Chem. ReV. 1996, 96, 395.
(7) Pregosin, P. S.; Salzman, R. Coord. Chem. ReV. 1996, 155, 35.
(8) Pregosin, P. S.; Salzmann, R.; Togni, A. Organometallics 1995, 14,
842.
(11) Jalon, F. A.; Manzano, B. R.; Moreno-Lara, B. Eur. J. Inorg. Chem.
2005, 100.
(12) Albinati, A.; Kunz, R. W.; Ammann, C. J.; Pregosin, P. S.
Organometallics 1991, 10, 1800.
(13) Gogoll, A.; O¨ rnebro, J.; Grennberg, H.; Ba¨ckvall, J.-E. J. Am. Chem.
Soc. 1994, 116, 3631.
(14) Satake, A.; Nakata, T. J. J. Am. Chem. Soc. 1998, 120, 10391.
10.1021/om070093u CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/25/2007

3184 Organometallics, Vol. 26, No. 13, 2007
Montoya et al.
Figure 1. Numbering scheme and reaction for the obtainment of complex 5.
Table 1. 1H NMR (250 MHz, 298 K) Spectroscopic Data for Complexes 1-5 in Acetonitrile-d3
chemical shift (ppm) coupling constant (Hz)
1
2
3
4
5
N-H
H1
13.21 (br)
8.75 (ddd, 5.4,
1.6, 0.9)
8.75 (d, 5.5)
8.74 (ddd, 5.7,
1.4, 0.6)
8.75 (dd, 5.4, 1.6)
8.59 (ddd, 5.4, 2.0, 0.9)
H3
H4
8.21 (td, 8.1, 1.6)
8.09 (ddd, 8.1,
1.4, 0.9)
8.20 (td, 7.7, 1.4)
8.06 (d, 7.7)
8.19 (td, 8.5,1.49)
8.04 (d, 8.5)
8.20 (td, 7.7, 1.6)
8.08 (d, 7.7)
7.96 (td, 7.5, 2.0)
7.78 (ddd, 7.2, 1.3, 0.9)
Hph
7.85-7.81 (m)
7.65-7.56 (m)
7.63-7.55 (m)
7.67-7.52 (m)
7.86 (d, 7.2), 7.40 (t, 7.2),
7.29-7.30 (m)
H
H5
ph, H2
7.63-7.54 (m)
7.41 (s)
7.15 (s)
7.17 (s)
7.17 (s)
7.04 (s)
H6
5.92 (m)
5.98 (m)
5.95 (m)
5.96 (m)
5.77 (m)
H7, H8 syn
H7, H8 anti
N-CH2
N-(CH2)xCH3
N-CH2CH2-
N-CH2CH2(CH2)5CH3
4.56 (d, 7.0)
3.51 (d, 12.4)
4.50 (d, 7.0)
3.58 (d, 12.5)
4.33 (q, 7.2)
1.41 (t, 7.2)
4.46 (d, 7.2)
3.54 (d, 12.2)
4.29 (t, 7.2)
0.84 (t, 6.6)
1.78-1.74 (m)
1.32-1.02 (m)
4.47 (d, 7.2)
3.55 (d, 12.4)
4.39 (t, 5.4)
4.17 (d, 7.0), 4.04 (d, 6.8)
3.31 (d, 12.2), 3.16 (d, 12.6)
3.87 (m)
prepared: 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L1),15 2-(1-
ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L2),15 2-(1-octyl-5-
phenyl)-1H-pyrazol-3-yl)pyridine (L3),16 and 2-(5-phenyl-3-
(pyridin-2-yl)pyrazol-1-yl)ethanol (L4). These ligands differ in
the substituent in the N1 position and were prepared by
following an efficient method published in the literature.15,16
The reaction of [Pd(η3-C3H5)Cl]2 with these ligands in the
presence of AgBF4 in dichloromethane and at room temperature
gave the new allylpalladium complexes [Pd(η3-C3H5)(L)](BF4)
(L ) L1 (1), L2 (2), L3 (3), L4 (4)) as pale yellow powders in
quantitative yield. Treatment of 1 in a mixture of CH2Cl2/CH3-
OH (1:1) with sodium methoxide produced the neutral (η3-allyl)-
palladium complex 5 (Figure 1).
(between 104 and 134 Ω-1 cm2 mol-1) are in agreement with
1:1 electrolytes, whereas for the complex 5 in acetonitrile the
value is 29 Ω-1 cm2 mol-1, in agreement with the nonelectro-
lytic nature of the complex.17,18
The 1H NMR spectroscopic data for complexes 1-5 in
acetonitrile-d3 are collected in Table 1. The assignment of each
proton was made on the basis of a previous publication of the
free ligands.16 In these complexes, the H1 chemical shift of the
pyridyl group and the signal of the pyrazolyl proton are
consistent with the coordination of both nitrogens to Pd(II). The
chemical shifts are observed toward higher frequencies for all
the complexes with respect to the free ligands.16 The same
behavior is observed in other Pd(II) complexes with the same
ligands ([PdCl2(L)]; L ) L1-L4).15,19,20 Concerning the allyl
group, a single doublet resonance is observed at room temper-
ature for the Hsyn protons and also for the Hanti protons for
complexes 1-4. This observation is not in accordance with a
static behavior of the complexes, where two nonequivalent Hsyn
protons and two nonequivalent Hanti protons would be expected,
due to the asymmetry of the nitrogen ligands. This constitutes
a clear indication of a dynamic situation that involves a syn-
syn, anti-anti interconversion, such as an apparent allyl rotation
process. This apparent allyl rotation is not observed in complex
5, which shows a doublet for each Hsyn proton and also for each
Hanti proton.
The complexes have been fully characterized by elemental
1
analysis, conductivity measurements, IR, H NMR, and 13C-
{1H} NMR spectroscopy, and mass spectrometry. For the
majority of these complexes, HMQC experiments were also
performed, and in some cases NOESY experiments were carried
out.
Elemental analysis and conductivity measurements confirm
the stoichiometries proposed for the compounds. To confirm
the existence of complexes 1-5, electrospray mass spectra were
recorded. The positive ionization spectra of 1-4 gave peaks
with m/z values of 368, 396, 480, and 412, respectively
(molecular peak of the cation). For complex 5, the m/z value is
368 and corresponds to [Pd(η3-C3H5)(L1) + H]+. Conductivity
measurements of 10-3 M samples in acetone for complexes 1-4
(17) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81.
(18) Thompson, L. K.; Lee, F. L.; Gabe, E. J. Inorg. Chem. 1988, 27,
39.
(15) Perez, J. A.; Pons, J.; Solans, X.; Font-Bardia, M.; Ros, J. Inorg.
Chim. Acta 2005, 358, 617.
(16) Montoya, V.; Pons, J.; Branchadell, V.; Ros, J. Tetrahedron 2005,
61, 12377.
(19) Montoya, V.; Pons, J.; Solans, X.; Font Bardia, M.; Ros, J. Inorg.
Chim. Acta 2005, 358, 2763.
(20) Montoya, V.; Pons, J.; Solans, X.; Font-Bardia, M.; Ros, J. Inorg.
Chim. Acta 2006, 359, 25.

(η3-Allyl)palladium Pyridylpyrazole Complexes
Table 2. 1H NMR (250 MHz, 298 K) Spectroscopic Data for Complexes 2-5 in Dichloromethane-d2
chemical shift (ppm) coupling constant (Hz)
Organometallics, Vol. 26, No. 13, 2007 3185
2
3
4
5
H1
H4
H3
8.72 (ddd, 5.4, 1.4, 0.9)
7.99 (ddd, 7.9, 1.2, 0.9)
8.18 (td, 7.9, 1.4)
8.73 (ddd, 5.4, 1.4, 0.7)
8.00 (ddd, 7.8, 1.2, 0.7)
8.18 (td, 7.9,1.6)
8.69 (dd, 5.4, 1.6)
7.98 (d, 7.7)
8.15 (td, 7.7, 1.6)
8.53 (dt, 5.4, 1.1, 1.1)
7.70 (dt, 8.0, 0.9)
7.92-7.85 (m), 7.40 (m),
7.25 (tt, 7.7, 1.1)
Hph
H2
7.65-7.60 (m), 7.57-7.52 (m)
7.63-7.60 (m), 7.55-7.51 (m)
7.65-7.52 (m)
7.16 (ddd, 7.4, 5.4, 1.4)
6.96 (s)
H5
7.00 (s)
7.00 (s)
7.00 (s)
H6
5.99 (m)
5.98(m)
5.99 (m)
4.57 (br)
4.10 (br)
4.44 (t, 5.4)
5.74 (m)
4.32 (d, 7.0), 3.93 (d, 6.9)
3.27 (d, 12.5), 3.24 (d, 12.4)
H7, H8 syn
H7, H8 anti
N-CH2
N-(CH2)xCH3
N-CH2CH2-
N-CH2CH2(CH2)5CH3
4.48 (d, 7.2)
3.81 (d, 11.7), 3.39 (d, 12.2)
4.34 (q, 7.3)
1.47 (t, 7.3)
4.50, 4.45 (d, 7.0)
3.76 (d, 12.5), 3.38 (d, 12.5)
4.29 (t, 7.9)
0.89 (t, 6.4)
1.81-1.71 (m)
1.32-1.16 (m)
3.98 (m)
Table 3. 1H NMR (250 MHz, 298 K) Spectroscopic Data for Complexes 1-4 in Acetone-d6
chemical shift (ppm) coupling constant (Hz)
1
2
3
4
N-H
H1
H3
13.30 (br)
8.83 (d, 5.5)
8.31 (td, 8.1, 1.6)
8.09 (d, 8.1)
7.85-7.5 (m)
7.52 (s)
8.84 (d, 5.3)
8.32 (td, 7.6, 1.5)
8.07 (d, 7.6)
7.73-7.62 (m)
7.45 (s)
8.85 (d, 5.6)
8.29 (td, 8.4, 1.4)
8.03 (d, 8.5)
7.73-7.65 (m)
7.51 (s)
8.85 (d, 5.5)
8.20 (td, 7.6, 1.5)
8.06 (d, 7.7)
7.77-7.62 (m)
7.40 (s)
H4
Hph, H2
H5
H6
6.05 (m)
6.04 (m)
6.19 (m)
5.96 (m)
H7, H8 syn
H7, H8 anti
N-CH2
N-(CH2)xCH3
N-CH2CH2-
N-CH2CH2(CH2)5CH3
4.65 (d, 6.8)
3.62 (br)
4.72 (d, 7.2)
3.76 (br)
4.48 (q, 7.1)
1.43 (t, 7.3)
4.69 (d, 7.2)
3.76 (br)
4.29 (t, 7.2)
0.87 (t, 6.7)
1.82-1.76 (m)
1.45-1.00 (m)
4.69 (d, 7.0)
3.72 (br)
4.35 (t, 5.4)
3.87 (m)
The 13C{1H} NMR spectra were recorded in acetonitrile-d3
for 1 and 4 and in dichloromethane-d2 for 2, 3, and 5, due to
the low solubility of the complexes. Spectroscopic data are
gathered in the Experimental Section. The assignment for each
carbon was made on the basis of the literature data and HMQC
However, when a noncoordinating solvent is used (dichlo-
romethane-d2), different spectra, depending on the complex,
were obtained. For complexes 2, 3, and 5, two Hanti signals are
observed, whereas for Hsyn, two signals are observed for 3 and
5 and only one signal is observed for 2. On the other hand,
1
complex 4 presents broad signals for both Hsyn and Hanti
.
experiments. Similar to the case for the H NMR spectra, a
1
single broad signal was observed for the terminal carbons of
the allyl moieties in complexes 1 and 4. This again reflects the
apparent allyl rotation. However, two different signals (one for
each terminal carbon) were observed for the spectra recorded
in dichloromethane-d2 (complexes 2, 3, and 5). This observation
indicates that the apparent allyl rotation is dependent on the
solvent and was further studied by NMR, in a number of
different solvents.
When the H NMR spectra were recorded in acetone-d6 for
1-4, only one doublet was observed for both Hsyn protons and
a broad band was observed for both Hanti protons.
These experiments indicate that the apparent allyl rotation is
dependent on the solvent. Consequently, this process would
involve an associative mechanism with the coordination of a
molecule of solvent (coordination 4 f 5 f 4 on Pd(II)).
In order to see if there was any kind of interaction with a
solvent such as acetone-d6, NOESY experiments were per-
formed, and they showed NOE interaction between the Hsyn and
H2O molecules in the solvent (commercial grade deuterated
solvents were used). This observation could indicate that, in
this case, the apparent allyl rotation involves the coordina-
tion of a water molecule. Scheme 1 shows the proposed
mechanism for this process: a five-coordinated Pd(II) interme-
diate is obtained by the coordination of X (X ) water,
coordinating solvent), followed by a pseudo-rotation of the allyl
group which interchanges the two allyl terminal hydrogens. The
decoordination of the X group leads to the final product, in
which the observed Hsyn-Hsyn Hanti-Hanti interchange has taken
place.
One special case is observed for complex 4 in dichlo-
romethane-d2. In this case, we observed the presence of broad
bands for both Hsyn and Hanti. Similar behavior is observed for
complexes 1-4 in coordinating solvents or solvents containing
H2O molecules. This would indicate that the hydroxyethyl group
of the pyridylpyrazole ligand interacts with the palladium atom,
NMR Studies in Different Solvents. In order to analyze the
dynamic behavior of the complexes, we performed H NMR
1
spectra of 1-5 in different solvents, acetonitrile-d3 (Table 1),
dichloromethane-d2 (Table 2), and acetone-d6 (Table 3), at room
1
temperature. It was not possible to obtain H NMR spectra of
complexes 1 and 5 in dichloromethane-d2 and acetone-d6,
respectively, due to their low solubility in these solvents.
1
As an example, Figure 2 shows the H NMR spectra in
different solvents for complex 2. In this study, the most
significant variations in the spectra are found for the allylic
signals (see Table 4). For complexes 1-4, in acetonitrile-d3 (a
coordinating solvent), only one signal for the anti hydrogens
and only one signal for the syn hydrogens are observed. This
does not occur for complex 5, where two signals for each kind
of proton are found. To confirm the data obtained for acetoni-
1
trile-d3, an additional H NMR experiment was performed for
1
4 in dimethyl-d6 sulfoxide. This H NMR spectrum is similar
to that found in acetonitrile-d3 (only one signal for Hsyn and
only one signal for Hanti).

3186 Organometallics, Vol. 26, No. 13, 2007
Montoya et al.
Figure 2. 1H NMR spectra (250 MHz, 298 K) of complex 2 in (a) acetone-d6, (b) acetonitrile-d3, and (c) dichloromethane-d2.
Table 4. 1H NMR (250 MHz, 298 K) Spectroscopic Data for
forming an intermediate similar to that found with H2O or a
molecule of coordinating solvent. Therefore, for complex 4 in
dichloromethane-d2, the process would take place through an
intramolecular associative mechanism (Scheme 2).
Variable-Temperature NMR Studies. Variable-temperature
1H NMR studies with different solvents (acetonitrile-d3, ace-
tone-d6, and dichloromethane-d2) were performed in order to
obtain more information about the dynamic behavior of
complexes 1-4 and the influence of the N1 substituent in the
apparent allyl rotation. The study of the apparent allyl rotation
was not performed at different temperatures with complex 5
because this complex presents a static situation in all of the
solvents.
Complexes 1-5
chemical shift (ppm) coupling constant (Hz)
complex
solvent
H7/H8 syn
H7/H8 anti
1
1
1
2
2
2
CD3CN
(CD3)2CO
CD2Cl2
CD3CN
(CD3)2CO
CD2Cl2
4.56 (d, 7.0)
4.65 (d, 6.8)
a
4.50 (d, 7.0)
4.72 (d, 7.2)
4.48 (d, 7.2)
3.51 (d, 12.4)
3.62 (br)
a
3.58 (d, 12.5)
3.76 (br)
3.81 (d, 11.7),
3.39 (d, 12.2)
3.54 (d, 12.2)
3.76 (br)
3.76 (d, 12.5),
3.38 (d, 12.5)
3.55 (d, 12.4)
3.72 (br)
3
3
3
CD3CN
(CD3)2CO
CD2Cl2
4.46 (d, 7.2)
4.69 (d, 6.8)
4.50 (d, 7.0),
4.45 (d, 7.0)
4.47 (d, 7.2)
4.69 (d, 7.0)
4.57 (br),
4.57 (d, 7.0)
4.18 (d, 7.0),
4.04 (d, 6.8)
a
As an example, Figure 3 shows the variable-temperature 1H
NMR spectra of 2 in acetone-d6.
4
4
4
4
5
CD3CN
(CD3)2CO
CD2Cl2
DMSO
For complexes 1-4, at low temperatures, two Hanti and two
syn signals were observed, as is expected for a static situation.
4.10 (br)
3.61 (d, 12.5)
3.31 (d, 12.2),
3.16 (d, 12.5)
a
3.27 (d, 12.5),
3.24 (d, 12.4)
H
CD3CN
A subsequent increase of the temperature allowed the determi-
nation of the corresponding coalescence temperatures. These
coalescence temperatures (Tc) and the separation of the two
doublet signals allowed us to calculate the ∆Gq values of the
processes21 (see Table 5). In some cases it was not possible to
determine the ∆Gq values, because either the signals were not
fully split at the minimum experimental temperature or the
5
5
(CD3)2CO
CD2Cl2
4.32 (d, 7.0),
3.93 (d, 7.0)
a 1H NMR spectra of complex 1 in CD2Cl2 and complex 5 in (CD3)2CO
could not be recorded, due to the insolubility of these complexes in these
solvents.

(η3-Allyl)palladium Pyridylpyrazole Complexes
Organometallics, Vol. 26, No. 13, 2007 3187
Scheme 1
Scheme 2
Figure 3. 1H NMR spectra (250 MHz) of complex 2 in acetone-
d6 at various temperatures (233-298 K).
Table 5. ν, Tc, and ∆Gq Data for Complexes 1-4
interchanging
groups
Tc
(K)
∆ν
(Hz) mol-1
)
∆Gq (kJ
complex
solvent
1
acetonitrile-d3
Hsyn-Hsyn
Hanti-Hanti
Hsyn-Hsyn
Hanti-Hanti
Hsyn-Hsyn
Hanti-Hanti
Hsyn-Hsyn
Hanti-Hanti
248
298
233
298
18.2
11.6
69.8
63.8
50.3
60.5
acetone-d6
Tc value was not reached at the maximum temperature
allowed by the solvent. For complexes 1-4, the values of
∆Gq in the solvents acetonitrile-d3 and acetone-d6 are similar
and are independent of the N1 substituent. In contrast, in
dichloromethane-d2, for complexes 2 and 3 the exact values
could not be obtained, as Tc was not reached at 305 K (the
maximum temperature allowed for this solvent). We have
calculated the ∆Gq values for this temperature, and we can only
suppose that the real values are higher than those obtained
at 305 K and also higher than the values obtained for aceto-
nitrile-d3 and acetone-d6. For complex 4 in dichloromethane-
d2, we could obtain exact ∆Gq values, because the Tc value is
298 K, due to the fact that the hydroxyethyl moiety favors an
intramolecular associative mechanism of the apparent allyl
rotation.
2
3
acetonitrile-d3
acetone-d6
298
64.5
60.7
dichloromethane-d2 Hsyn-Hsyn
Hanti-Hanti
acetonitrile-d3
>305 100
>61
Hsyn-Hsyn
Hanti-Hanti
Hsyn-Hsyn
Hanti-Hanti
acetone-d6
213
298
>305
>305
10.6
61.0
12.5 >66
95.0 >61
46.0
60.8
dichloromethane-d2 Hsyn-Hsyn
Hanti-Hanti
acetonitrile-d3
4
4
Hsyn-Hsyn
Hanti-Hanti
Hsyn-Hsyn
Hanti-Hanti
acetone-d6
233
15.6
49.7
dichloromethane-d2 Hsyn-Hsyn
Hanti-Hanti
298
298
18.2
70.5
63.8
60.5
Crystal and Molecular Structures of [Pd(η3-C3H5)(L2)]-
(BF4) (2). The crystal structure of complex 2 consists of [Pd-
The [Pd(η3-C3H5)(Npy)(Npz)] core (containing pyrazole and
pyridine nitrogen atoms and a η3-bonded allyl ligand) is found
in one complex described in the literature.22
(η3-C3H5)(L2)]+ cations and BF4 anions held together by
-
Coulombic forces. The cation [Pd(η3-C3H5)(L2)]+ is shown in
Figure 4.
The bond distance Pd-Npy is almost identical with the Pd-
pz distance (2.115(3) and 2.117(3) Å, respectively). The Pd-C
The metal atom is coordinated to a L2 ligand via one pyrazole
nitrogen, one pyridine nitrogen, and one allyl ligand in η3
coordination. The two terminal allyl carbons are 0.282(3) and
0.169(3) Å from the plane defined by the atoms PdNpyNpzC-
(17)C(18)C(19). The central carbon (C(18)) is -0.403(3) Å out
of this plane. L2 behaves as a bidentate ligand, forming a five-
membered metallacycle.
N
bond lengths of the allyl group are in the range expected for
these types of complexes.23 The distance measured for Pd-
C(terminal) in a disposition trans to Npy (2.114(3) Å) is of the
same order as the distance found for the other Pd-C(terminal)
and Pd-C(central) bonds (2.101(4) and 2.108(3) Å, respec-
tively).
(21) Friebolin, H. Basic One and Two Dimensional NMR Spectroscopy,
3rd ed.; Wiley-VCH: Weinheim, Germany, 1998.
(22) Dubs, C.; Inagaki, A.; Akita, M. Chem. Commun. 2004, 2760.
(23) Allen, F. A.; Kennard, O. Chem. Des. Autom. News 1993, 8, 31.

3188 Organometallics, Vol. 26, No. 13, 2007
Montoya et al.
Table 7. Crystallographic Data for
[Pd(η3-C3H5)(L2)](BF4) (2)
formula
Mr
temp (K)
cryst syst
space group
unit cell dimensions
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C19H20BF4N3Pd
483.59
293(2)
monoclinic
P21/c
8.028(5)
10.519(4)
23.157(10)
90
95.14(2)
90
1947.7(17)
4
1.649
Z
Dcalcd (g.cm-3
)
µ (mm-1
F(000)
)
0.999
968
Figure 4. ORTEP drawing of the cation [Pd(η3-C3H5)(L2)]+
cryst size (mm)
θ range (deg)
index ranges
no. of collected/unique rflns
no. of data/restraints/params
goodness of fit
0.2 × 0.1 × 0.1
(ellipsoids are shown at the 50% probability level).
2.55-29.99
-9 < h < 10, 0 < k < 14, 0 < l < 32
14 739/4418 (R(int) ) 0.0351)
4418/20/295
Table 6. Selected Bond Lengths (Å) and Bond Angles (deg)
for [Pd(η3-C3H5)(L2)](BF4) (2) with Estimated Standard
Deviations (Esd’s) in Parentheses
1.134
final R1, wR2
0.0384, 0.1104
0.0449, 0.1171
0.468 and - 0.647
Pd-N(1)
Pd-N(2)
Pd-C(17)
Pd-C(18)
2.115(3)
2.117(3)
2.101(4)
2.108(3)
Pd-C(19)
C(17)-C(18)
C(18)-C(19)
2.144(3)
1.373(8)
1.402(6)
R1 (all data), wR2
resid electron density (e Å-3
)
The n-alkyl group, which is bonded to the N(3) atom, moves
away from the chelating plane, giving a torsion angle N(2)-
N(3)-C(15)-C(16) of 89.5(3)°.
N(1)-Pd-N(2)
N(1)-Pd-C(17)
N(1)-Pd-C(18)
N(1)-Pd-C(19)
N(2)-Pd-C(17)
N(2)-Pd-C(18)
77.68(10)
102.78(18)
134.61(18)
170.71 (14)
171.11(17)
145.13(18)
N(2)-Pd-C(19)
C(17)-Pd-C(19)
C(17)-Pd-C(18)
C(18)-Pd-C(19)
C(17)-C(18)-C(19)
110.82(13)
68.23(19)
38.1(2)
38.48(18)
118.3(4)
Conclusions
Five new allylpalladium derivatives containing N-donor
ligands have been prepared and their fluxional behavior studied.
The apparent allyl rotation has been studied in detail. This
process presents low ∆Gq values and is favored by coordinating
solvents (or eventually traces of water present in the solvent),
meaning that the apparent allyl rotation takes place through an
isomerization of the square-planar geometry by an associative
mechanism. The process is also favored for complex 4, which
contains a hydroxyethyl moiety. This group takes the role of
the coordinating solvent when dichloromethane-d2 is used.
Therefore, in this case the process would take place through an
intramolecular associative mechanism. The low ∆Gq values
indicate that the process takes place without Pd-N bond rupture.
On the other hand, the process does not occur in the neutral
complex, probably due to the steric hindrance provoked in the
rotation by the free pair of electrons of the pyrazolyl group.
The Pd-Npy, Pd-Npz, and Pd-C bond lengths in 2 are in
the range of bond distances found in the literature for complexes
containing N,N′-ligands trans to an allylpalladium fragment.24-26
Selected bond distances and angles for this complex are
gathered in Table 6. The allyl group has deviated from the ideal
geometry (C-C distances of 1.36 Å and C-C-C angles of
120°): it presents two types of C-C distances at 1.373(8) and
1.402(6) Å and a C-C-C angle of 118.3(4)°. Similar distorted
allyl groups have also been described in other complexes
containing the [Pd(η3-C3H5)]+ fragment.27-29 The dihedral angle
between the allylic plane and the palladium coordination plane
is 66.90(9)°.
The N(1)-Pd-N(2) bite angle is 77.68(10)°. This angle is
smaller than those found in the literature: with 2-(5-phenyl-
1H-pyrazol-3-yl)pyridine (L1), [PdCl2(L1)],15 79.16 (14)°; 2-(1-
ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L2), [PdCl2(L2)],20
78.83(9)°; 2-(1-octyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L3),
[PdCl2(L3)],20 79.39(13)°.
Experimental Section
The L2 ligand is not planar. The pyridyl and phenyl groups
are twisted with respect to the pyrazole ring. The py-pz dihedral
angle is 7.05(17)°, and the ph-pz angle is 18.09(18)°. The py-
pz dihedral angle is greater than those found in the complexes
[PdCl2(Ll)] (py-pz 1.43(4)°),15 [PdCl2(L3)]19 (py-pz 1.5(2)°),
and [PtCl2(L2)]20 (py-pz 3.4(4)°), whereas the ph-pz angle is
smaller than those found in the complexes [PdCl2(L3)] (69.2-
(3)°) and [PtCl2(L2)]20 (54.0(4°)) but greater than that found
for [PdCl2(Ll)]15 (0.48(3)°).
General Methods. Standard Schlenk techniques were employed
throughout the synthesis using a double-manifold vacuum line with
high-purity dry nitrogen. All reagents were commercial grade
materials and were used without further purification. All solvents
were dried and distilled by standard methods. The elemental
analyses (C, H, N) were carried out by the staff of the Chemical
Analyses Service of the Universitat Auto`noma de Barcelona on a
Carlo Erba CHNS EA-1108 instrument. Conductivity measurements
were performed at room temperature in 10-3 M acetone and
acetonitrile samples employing a Crison Micro CM 2200 conduc-
timeter. Infrared spectra were performed on a Perkin-Elmer FT
(24) De Munno, G.; Bruno, G.; Rotondo, E.; Giordano, G.; Schiavo, S.
L.; Piraino, P.; Trisoldi, G. Inorg. Chim. Acta 1993, 208, 67.
(25) Canal, J. M.; Gomez, M.; Jimenez, F.; Rocamora, M.; Muller, G.;
Dunach, E.; Franco, D.; Jimenez, A.; Cano, F. H. Organometallics 2000,
19, 966.
(26) Guerrero, A. M.; Jalon, F. A.; Manzano, B. R.; Claramunt, R. M.;
Maria, M. D. S.; Escolastico, C.; Elguero, J.; Rodriguez, A. M.; Maestro,
M. A.; Mahia, J. Eur. J. Inorg. Chem. 2002, 3178.
(27) Tukada, N.; Sato, T.; Mori, H.; Sugawara, S.; Kabuto, C.; Miyano,
S.; Inoue, Y. J. Organomet. Chem. 2001, 627, 1212.
(28) Butts, C. P.; Crosby, J.; Lloyd-Jones, G. C.; Stephen, S. C. Chem.
Commun. 1999, 1707.
(29) Bhattacharyya, P.; Slawin, A. M. Z.; Smith, M. B. J. Chem. Soc.,
Dalton Trans. 1998, 2467.

(η3-Allyl)palladium Pyridylpyrazole Complexes
Organometallics, Vol. 26, No. 13, 2007 3189
Series 2000 spectrophotometer as KBr pellets in the range 4000-
ν(C-H)al, 1615 ν(CdC)ar, ν(CdN)ar, 1465 δ(CdC)ar, δ(CdN)ar,
1
400 cm-1 under a nitrogen atmosphere. The H NMR, 13C{1H}
1057 ν(B-F), 765 δ(C-H)oop.
13C{1H} NMR (dichloromethane-
NMR, HMQC, and NOESY spectra were run on a Bruker NMR-
d2 solution, 63 MHz, 298 K): δ 154.0 (C1), 151.8 (C15), 150.9
(C14), 148.7 (C16), 141.3 (C3), 130.8 (C11), 129.7 (C10, C12), 129.4
(C9, C13), 128.5 (C17), 126.6 (C2), 122.4 (C4), 118.4 (C6), 105.7
(C5), 65.9 (C7 or C8), 59.2 (C7 or C8), 51.7 (N-CH2(CH2)6CH3),
32.0-22.9 (N-CH2(CH2)6CH3), 14.2 (N-CH2(CH2)6CH3) ppm.
ES(+) MS (m/z (%)): 480 (100) [Pd(η3-C3H5)(L3)]+.
1
FT 250 MHz instrument. H NMR and 13C{1H} NMR chemical
shifts (δ) were determined relative to internal TMS and are given
in ppm. Liquid chromatography/electrospray mass spectrometry
experiments were performed by the Scientific Services of the
Universitat de Barcelona on a Shimadzu AD VP chromatography
instrument and API 150 (Applied Biosystems) mass spectrometer.
The carrier was CH3CN at a 0.2 mL min-1 flow rate. The samples
were dissolved in CH3CN at a concentration of 0.4 mg mL-1, and
5 µL of each solution was injected on line. In the case of the
electrospray interface, whole flow was introduced in the capillary
source and nebulized at a 12 (arbitrary units) nitrogen flow. The
auxiliary gas was nitrogen at a 7000 cm3 min-1 flow rate. The main
electrical conditions were as follows: positive electrospray capillary
at 4200 V; potentials DP ) 20 V, FP ) 200 V, EP ) -10 V;
mass range measured between 100 and 950 amu; full scan mode;
cycle time 2 s; source temperature 200 °C.
The compounds 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (L1),15
2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L2),15 2-(1-octyl-5-
phenyl)-1H-pyrazol-3-yl)pyridine (L3),16 and 2-(5-phenyl-3-(pyridin-
2-yl)pyrazol-1-yl)ethanol (L4) were prepared according to the
published methods (Figure 1). Samples of [Pd(η3-C3H5)Cl]2 were
prepared as described in the literature.30
Synthesis of the Complexes. Complexes [Pd(η3-C3H5)(L)]BF4
(L ) L1 (1), L2 (2), L3 (3), L4 (4)). A 0.37 mmol portion of the
corresponding ligand (L1, 0.083 g; L2, 0.092 g; L3, 0.123 g; L4,
0.098 g) was added to a mixture of AgBF4 (0.37 mmol, 0.070 g)
and [Pd(η3-C3H5)Cl]2 (0.18 mmol, 0.066 g) dissolved in dry
dichloromethane (40 mL) at 0 °C. After the light-protected mix-
ture was stirred at room temperature for 1.5 h, methanol (40 mL)
was added. The yellow solution was then filtered through a pad
of Celite. The solution was stirred for 1 h, most of the solvent
was removed under vacuum, and diethyl ether (5 mL) was then
added dropwise to induce precipitation. The yellow solid was
filtered off, rinsed twice with 5 mL of diethyl ether, and dried under
vacuum.
Data for 4 are as follows. Yield: 78% (0.144 g). Anal. Calcd
for C19H20BF4N3OPd (499.6): C, 45.68; H, 4.03; N, 8.41. Found:
C, 45.90; H, 3.96; N, 8.23. Conductivity (Ω-1 cm2 mol-1, 1.0 ×
10-3 M in acetone): 134. IR (KBr, cm-1): 3467 ν(O-H), 3050
ν(C-H)ar, 2924 ν(C-H)al, 1616 ν(CdC)ar, ν(CdN)ar, 1464 δ(Cd
C)ar, δ(CdN)ar, 1060 ν(B-F), 767 δ(C-H)oop.
13C{1H} NMR
(acetonitrile-d3 solution, 63 MHz, 298 K): δ 153.8 (C1), 151.7 (C15),
151.1 (C14), 149.5 (C16), 141.1 (C3), 130.7 (C11), 129.7 (C10, C12),
129.6 (C9, C13), 128.5 (C17), 126.3 (C2), 122.4 (C4), 118.5 (C6),
105.7 (C5), 61.4 (N-CH2CH2OH), 59.2 (C7, C8), 51.7 (N-
CH2(CH2)6CH3), 32.0-22.9 (N-CH2(CH2)6CH3). ES(+) MS (m/z
(%)): 412 (100%) [Pd(η3-C3H5)(L4)]+.
The values of 1H NMR spectra in acetonitrile-d3, dichlo-
romethane-d2, and acetone-d6 are presented in Tables 1-3, respec-
tively, except for complex 1 in dichloromethane-d2, due to its low
solubility in this solvent.
Complex [Pd(η3-C3H5)(L1)] (5). To a mixture of 1 (0.20 mmol,
0.091 g) and sodium methoxide (0.20 mmol, 0.011 g) were added
dichloromethane (0.25 mL) and methanol (0.25 mL) at room
temperature. The mixture was stirred with sonication for 5 min.
The solvent was evaporated. The yellow solid was rinsed with 5
mL of diethyl ether and dried under vacuum.
Data for 5 are as follows. Yield: 60% (0.044 g). Anal. Calcd
for C17H15N3Pd (367.7): C, 55.52; H, 4.11; N, 11.43. Found: C,
55.49; H, 3.89; N, 11.55. Conductivity (Ω-1 cm2 mol-1, 1.1 × 10-3
M in acetonitrile-d3): 29. IR (KBr, cm-1): 3025 ν(C-H)ar, 2962
ν(C-H)al, 1603 ν(CdC)ar, ν(CdN)ar, 1450 δ(CdC)ar, δ(CdN)ar,
761 δ(C-H)oop.
13C{1H} NMR (dichloromethane-d2 solution, 63
MHz, 298 K): δ 163.0 (C14), 157.6 (C15), 155.2 (C16), 153.1 (C1),
139.7 (C3), 135.9 (C17), 128.7 (C10, C12), 126.5 (C11), 125.4 (C9,
C13), 121.9 (C2), 119.2 (C4), 116.4 (C6), 99.3 (C5), 60.2 (C7 or C8),
56.2 (C7 or C8) ppm. ES(+) MS (m/z (%)): 390 (7) [Pd(η3-C3H5)-
(L1) + Na]+, 368 (100) [Pd(η3-C3H5)(L1) + H]+.
Data for 1 are as follows. Yield: 87% (0.147 g). Anal. Calcd
for C17H16BF4N3Pd (455.6): C, 44.82; H, 3.54; N, 9.22. Found:
C, 44.90; H, 3.62; N, 8.99%. Conductivity (Ω-1 cm2 mol-1, 9.1 ×
10-4 M in acetone): 132. IR (KBr, cm-1): 3416 ν(N-H), 3020
ν(C-H)ar, 2960 ν(C-H)al, 1616 ν(CdC)ar, ν(CdN)ar, 1454 δ(Cd
1
The values of the H NMR spectra in acetonitrile-d3, dichlo-
romethane-d2, and acetone-d6 are presented in Tables 1, 2, and 3,
respectively.
C)ar, δ(CdN)ar, 1084 ν(B-F), 768 δ(C-H)oop.
13C{1H} NMR
(acetonitrile-d3 solution, 63 MHz, 298 K): δ 154.4 (C1), 153.8 (C15),
150.6 (C14), 147.8 (C16), 141.4 (C3), 130.7 (C11), 130.0 (C10, C12),
127.4 (C17), 126.6 (C9, C13), 126.6 (C2), 122.7 (C4), 118.7 (C6),
102.01 (C5), 62.0 (C7, C8) ppm. ES(+) MS (m/z (%)): 368 (100)
[Pd(η3-C3H5)(L1)]+, 222 (3) [L1 + H]+.
X-ray Crystal Structure Analyses of the Complex [Pd(η3-
C3H5)(L2)](BF4). Suitable crystals for X-ray diffraction of the
compound [Pd(η3-C3H5)(L2)](BF4) were obtained through crystal-
lization from dichloromethane. Data were collected on a MAR345
diffractometer with an image plate detector. Intensities were
collected with graphite-monochromated Mo KR radiation. Unit-
cell parameters were determined from 3888 reflections (3 < θ <
31°) and refined by least-squares methods. A total of 14 739
reflections were assumed in the range 2.55 e θ e 29.99°, 4418 of
which were nonequivalent by symmetry (Rint(on I) ) 0.035). A
total of 3902 reflections were assumed as observed, applying the
condition I > 2σ(I). Lorentz-polarization, but not absorption,
corrections were made.
Data for 2 are as follows. Yield: 85% (0.152 g). Anal. Calcd.
for C19H20BF4N3Pd (483.6): C, 47.19; H, 4.17; N, 8.69. Found:
C, 46.90; H, 4.05; N, 8.38. Conductivity (Ω-1 cm2 mol-1, 9.2 ×
10-4 M in acetone): 113. IR (KBr, cm-1): 3066 ν(C-H)ar, 2924
ν(C-H)al, 1610 ν(CdC)ar, ν(CdN)ar, 1465 δ(CdC)ar, δ(CdN)ar,
1083 ν(B-F), 768 δ(C-H)oop.
13C{1H} NMR (dichloromethane-
d2 solution, 63 MHz, 298 K): δ 154.0 (C1), 151.8 (C15), 150.9
(C14), 148.2 (C16), 141.3 (C3), 130.8 (C11), 129.7 (C10, C12), 129.3
(C9, C13), 128.4 (C17), 126.6 (C2), 122.4 (C4), 118.4 (C6), 105.7
(C5), 65.8 (C7 or C8), 59.4 (C7 or C8), 46.9 (N-CH2CH3), 16.4
(N-CH2CH3) ppm. ES(+) MS (m/z (%)): 396 (100) [Pd(η3-C3H5)-
(L2)]+, 250 (13) [L2 + H]+.
Data for 3 are as follows. Yield: 80% (0.168 g). Anal. Calcd
for C25H32BF4N3Pd (567.8): C, 52.89; H, 5.68; N, 7.40. Found:
C, 52.92; H, 5.59; N, 7.36. Conductivity (Ω-1 cm2 mol-1, 1.0 ×
10-3 M in acetone): 104. IR (KBr, cm-1): 3099 ν(C-H)ar, 2952
The structure was solved by direct methods, using the SHELXS97
computer program,31 and refined by full-matrix least-squares
methods by the SHELXL97 computer program32 using 14 739
reflections (very negative intensities were not assumed). The
2
2 2
function minimized was ∑w||Fo| - |Fc| | , where w ) [σ2(I) +
(0.0623P)2 + 0.6986P]-1 and P ) (|Fo| + 2|Fc| )/3. Eighteen H
2
2
(31) Sheldrick, G. M. SHELXS97: Program for Crystal Structure
Determination; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(32) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(30) Ogoshi, S.; Yoshiva, W.; Ohe, K.; Murai, S. Organometallics 1993,
12, 578.

3190 Organometallics, Vol. 26, No. 13, 2007
Montoya et al.
atoms were located from a difference synthesis and refined with
overall isotropic temperature factors, and two H atoms were
computed and refined, using a riding model with an isotropic
temperature factor equal to 1.2 times the equivalent temperature
factor of the atom, which are linked. The final R(F) factor and
R(F2) values as well as the number of parameters and other details
concerning the refinement of the crystal structures are gathered in
Table 7.
CCDC-628754 contains supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Acknowledgment. Support by the Spanish Ministerio de
Educacio´n y Cultura (Project BQU2003-03582) is gratefully
acknowledged.
Supporting Information Available: Text and figures giving
details of the synthesis and characterization of the ligand 2-(5-
phenyl-3-(pyridin-2-yl)pyrazol-1-yl)ethanol (L4) and a CIF file
giving crystallographic data for [Pd(η3-C3H5)(L2)](BF4). This
material is available free of charge via the Internet at http://pubs.acs.
org.
OM070093U