Liquid crystal behaviour of ionic allylpalladium complexes containing 2-pyrazolylpyridine as bidentate N,N′-ligand

Article abstract of DOI:10.1016/j.jorganchem.2005.09.053

Two types of Pd-complexes containing the new N,N′-ligands 2-[3-(4-alkyloxyphenyl)pyrazol-1-yl]pyridine (pz^Rpy; R = C ₆H₄OC_nH_2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1-6), na

Full text of DOI:10.1016/j.jorganchem.2005.09.053

Journal of Organometallic Chemistry 691 (2006) 765–778
www.elsevier.com/locate/jorganchem
Liquid crystal behaviour of ionic allylpalladium complexes containing
2-pyrazolylpyridine as bidentate N,N0-ligand
a
a,
a
a
b
M.C. Torralba , M. Cano *, J.A. Campo , J.V. Heras , E. Pinilla a,b, M.R. Torres
a
Departamento de Quı´mica Inorga´nica I, Facultad de Ciencias Quı´micas, Universidad Complutense, E-28040 Madrid, Spain
Laboratorio de Difraccio´n de Rayos-X, Facultad de Ciencias Quı´micas, Universidad Complutense, E-28040 Madrid, Spain
b
Received 18 July 2005; received in revised form 26 September 2005; accepted 26 September 2005
Available online 23 November 2005
Abstract
Two types of Pd-complexes containing the new N,N0-ligands 2-[3-(4-alkyloxyphenyl)pyrazol-1-yl]pyridine (pzRpy; R = C6H4OCn-
2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1–6), namely c-[Pd(Cl)2(pzRpy)] (7–10) and c-[Pd(g3-C3H5)(pzRpy)]BF4
H
(11–16), have been synthesised and characterised by different spectroscopic techniques. Those members of the second type containing the
largest chains (R = ddp 13, tdp 14, hdp 15, odp 16) have been found to have liquid crystal properties showing smectic A mesophases. By
contrast, neither the free ligands pzRpy nor their related c-[Pd(Cl)2(pzRpy)] complexes exhibited mesomorphism. The new synthesised
metallomesogens are mononuclear complexes with an unsymmetrical molecular shape as deduced from the X-ray structures of
c-[Pd(g3-C3H5)(pzRpy)]BF4 (R = hp, 11; dp, 12). Both compounds, which are isostructural, show a distorted square-planar environment
on the palladium centres defined by the allyl and the bidentate pzRpy ligands. The crystal structure reveals that both the counteranion
2
and the pzRpy ligand function as a source of hydrogen-bonding and intermolecular pꢀ ꢀ ꢀp contacts resulting in a D supramolecular
assembly.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Long-chained pyrazolylpyridine ligands; Palladium(II) complexes; Mesomorphism
1. Introduction
Related with these results we were also involved in inves-
tigating the liquid crystal behaviour of the compounds c-
[Pd(Cl)2(pzR2py)] (b), where pzR2py were the unsymmetrical
bidentate ligands 2-[3,5-bis(4-alkyloxyphenyl)pyrazol-1-
yl]pyridine [3]. These complexes exhibited mesomorphism,
which was not extensively different to that of t-[Pd(Cl)2-
(HpzR)2] [1]. In both types of compounds, a and b, the
mesophases presented an analogous accessibility, but the
latter exhibiting higher stability. The above results allowed
us to consider that the molecular shape and lowering the
symmetry of complexes by introducing pyrazolylpyridine-
type ligands were a successful strategy on metallomesogenic
compounds.
We are currently concerned with the design and synthe-
sis of metallomesogens based on pyrazole or related ligands
containing long-chained substituents.
In a previous work, we reported the liquid crystal beha-
viour of t-[Pd(Cl)2(HpzR)2] (a) complexes (HpzR = 3-alkyl-
oxysubstituted pyrazole; R = C6H4OCnH2n+1) which
exhibited a conventional rod-like molecular geometry con-
cerning with the trans orientation of the pyrazol groups [1].
By contrast, the free HpzR ligands resulted to have no
mesomorphic properties [1,2], this feature being associated
with their short molecular lengths which were about half
the complexes a [1].
On the other hand the relationship between chemical
structure and mesomorphism has been extensively inves-
tigated in the field of liquid crystals. In particular, devia-
tions from the rod-like molecular shape or a non-adequate
*
Corresponding author. Fax: +34 91 3944352.
E-mail address: mmcano@quim.ucm.es (M. Cano).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.09.053

766
M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
molecular length-to-width ratio have been proved to pre-
vent the mesomorphism of proposed molecules as calamitic
materials [1,3–5].
Following these precedents we are now interested in the
study of a new type of bidentate pyrazolylpyridine ligands
(pzRpy) containing only one alkyloxyphenyl (C6H4OCn-
containing the mesogenic 5-(1-hexyl)-2-{[40-(1-undecyl-
oxy)phenyl]}pyrimidine (HL) and 2,20-bipyridine as coli-
gand was proved to have mesomorphism when iꢁt was
isolated as BFꢁ4 salt, but larger anions as PF6ꢁ or SbF6 sup-
pressed the liquid crystal behaviour, this behaviour reflect-
ing the influence of uncoordinated counterion [15].
H
2n+1) substituent chain at the 3-position of the pyrazolyl
In the present work, we describe the preparation, charac-
terisation and study of a family of new 2-[3-(4-alkyloxyphe-
nyl)pyrazol-1-yl]pyridine ligands (pzRpy; R = C6H4OCn-
group, as well as their complexes with PdCl2 and [Pd(g3-
C3H5)]+ fragments. We propose that, by coordination of
the pzRpy ligands to the PdCl2 fragment, the molecular
length should be reduced about half the related liquid-
crystal compounds c-[Pd(Cl)2(pzR2py)] [3], this fact being
useful to evaluate their influence on the mesomorphic
properties. As extension we also try to consider the effectiv-
ity of [Pd(g3-C3H5)]+ as metallic fragment towards the
same pzRpy ligands in order to get new cationic complexes
of the type c-[Pd(g3-C3H5)(pzRpy)]+ as potential liquid
crystals.
H
2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16 (hdp), 18
(odp)) (1–6) and their complexes with PdCl2 and [Pd(g3-
C3H5)]+ groups (Scheme 1). Both free ligands and their
dichloropalladium derivatives have not shown liquid crystal
behaviour. By contrast, the related allylpalladium com-
plexes with BFꢁ4 as counteranion exhibit mesomorphic
properties.
As extension two new related derivatives containing the
same cationic metal complex and different counteranions
ðPFꢁ; CF3SOꢁÞ have also been studied and proved to have
Mesomorphism of palladium complexes containing
6
3
bidentate ligands has been specially developed on neutral
liquid crystal behaviour.
The palladium complexes of the type c-[Pd(g3-C3H5)-
(pzRpy)]+ constitute the second example of calamitic
materials based on cationic complexes containing N,N0-
bidentate ligands [3].
cyclopalladated N(sp2)-Pd-C(sp2) species. In this context,
azobenzene, benzylideneanilines, imines or substituted
bipyridine ligands, among others, gave rise to neutral
mono- or dinuclear cyclopalladated complexes, most of
them showing low transition temperatures and high ther-
mal stability [6–12]. Several N,N-coordinated bipyridine-
type ligands have been also proved to induce mesomor-
phism on PdCl2 complexes [13].
2. Experimental
2.1. Materials and physical measurements
In contrast, ionic metallomesogens are a more restricted
area inside the molecular and supramolecular species [14],
and from the best of our knowledge only two examples
containing palladium have been described [15,16]. In par-
ticular, an ionic ortho-metallated complex [Pd(L)(bpy)]+
All commercial reagents were used as supplied. The
starting Pd-complexes, [Pd(Cl)2(PhCN)2] and [Pd(l-Cl)-
(g3-C3H5)]2, were purchased from Sigma–Aldrich and used
as supplied.
LIGANDS
Pd(II) COMPLEXES
OCnH2n+1
OCnH2n+1
OCnH2n+1
4'
5'
3'
Hs'
Ha'
m
Cl
Pd
o
N
N
N
N
N
4
6
5
Hmeso
Pd
Cl
N
N
3
N
N
Ha
Hs
pzRpy
c-[Pd(Cl)2(pzRpy)] c-[Pd(η3-C3H5)(pzRpy)]BF4
pzhppy
pzdppy
pzddppy
pztdppy
pzhdppy
pzodppy
1
R= hp
11
12
13
14
15
n= 6
R= dp
2
3
4
5
6
n= 10
n= 12
n= 14
n= 16
n= 18
R= ddp
R= tdp
R= hdp
7
R= ddp
R= tdp
R= hdp
8
9
R= ohdp 10
R= ohdp 16
c-[Pd(η3-C3H5)(pzhdppy)]A
A= PF6
17
18
A= CF3SO3
Scheme 1.

M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
767
The 4-alkyloxyacetophenones were synthesised by alkyl-
2.2. Synthetic methods
ation of 4-hydroxyacetophenone with the corresponding
n-alkyliodide in acetone solution of potassium carbonate
as previously described [2,17]. All these compounds were
characterised satisfactorily by analytical and spectroscopic
techniques.
Elemental analyses for carbon, hydrogen, nitrogen and
sulphur were carried out by the Microanalytical Service
of the Complutense University. IR spectra were recorded
on a FTIR Nicolet Magna-550 spectrophotometer with
samples as KBr pellets in the 4000–400 cmꢁ1 region: vs
(very strong), s (strong), m (medium), w (weak).
2.2.1. Preparation of 2-[3-(4-alkyloxyphenyl)pyrazol-1-
yl]pyridine (pzRpy, R = C6H4OCnH2n+1, n = 6 (hp), 10
(dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1–6)
A solution of 4-alkyloxyacetophenone (9.42 mmol) and
ethyl formate (1.16 mL, 14.13 mmol) in toluene (15 mL)
was added to a slurry of an excess of 60% sodium hydride
(0.50 g, 12.5 mmol) in toluene (50 mL). A clear solution
was obtained, which became a slurry after 5 min. The mix-
ture was stirred overnight at room temperature and the
solid was filtered and washed with dichloromethane and
hexane. The solid obtained (1.48 mmol) was dissolved in
ethanol 96% (10 mL), and acidified by dropwise addition
of hydrochloric acid (ca. 2.5 mL, spec. grav. 1.18). 2-
Hydrazinopyridine (0.65 g, 5.92 mmol) dissolved in the
minimum amount of ethanol 96% was added to this solu-
tion. The mixture was refluxed for 3 h, and then the solvent
was evaporated to ca. half the original volume and the
resulting solution kept overnight at 4 ꢁC. The solid
obtained was filtered off, washed with hexane and dried
in air. Yields and analytical data are given in Table 1.
pzhppy (1): IR (KBr, cmꢁ1): m(CN) 1615 (vs), c(CH)py
1H NMR spectra were performed on a Bruker AC-200
or on a Bruker DPX-300 spectrophotometers (NMR Ser-
vice of the Complutense University) from solutions in
CDCl3. Chemical shifts d are listed in ppm relative to
TMS using the signal of the deuterated solvent as reference
(7.26 ppm), and coupling constants J are in hertz. Multi-
plicities are indicated as s (singlet), d (doublet), t (triplet),
m (multiplet), br s (broad signal). The atomic numbering
used in the assignment of the NMR signals is shown in
1
Scheme 1. The H chemical shifts and coupling constants
are accurate to 0.01 ppm and 0.3 Hz, respectively.
Phase studies were carried out by optical microscopy
using an Olympus BX50 microscope equipped with a Lin-
kam THMS 600 heating stage. The temperatures were
assigned on the basis of optic observations with polarised
light.
Measurements of the transition temperatures were made
using a Perkin–Elmer Pyris 1 differential scanning calorim-
eter with the sample (1–4 mg) hermetically sealed in alu-
minium pans and with a heating or cooling rate of 5–10ꢁ/
min.
1
777 (m). H NMR (CDCl3, d in ppm, J in Hz): 8.56 (d,
3J = 2.6, 1H, H50), 8.41 (d, 3J = 4.3, 1H, H6), 8.08 (d,
3
3J = 8.3, 1H, H3), 7.85 (d, J = 8.8, 2H, Ho), 7.80 (1H,
H4), 7.17 (dd, 3J = 7.4, 3J = 4.3, 1H, H5), 6.96 (d,
3
3J = 8.8, 2H, Hm), 6.72 (d, J = 2.6, 1H, H40), 4.01 (t,
3J = 6.6, 2H, OCH2), 1.81 (m, 2H, CH2), 1.5–1.2 (m, 6H,
3
CH2), 0.91 (t, J = 6.8, 3H, CH3).
pzdppy (2): IR (KBr, cmꢁ1): m(CN) 1612 (vs), c(CH)py
766 (s). 1H NMR (CDCl3, d in ppm, J in Hz): 8.56
3
(d, J = 2.7, 1H, H50), 8.41 (d, 3J = 4.3, 1H, H6), 8.08
Table 1
Yield and elemental analyses for the pzRpy ligands 1–6 and their Pd-complexes 7–18
Yield (%)
Molecular formula
Elemental analysis (%)
Found (calculated)
C
H
N
1
2
36
45
45
55
61
47
44
51
65
66
44
69
44
36
48
36
25
36
C
20H23N3O
74.4 (74.7)
76.7 (76.4)
76.9 (77.0)
77.2 (77.6)
77.9 (78.1)
78.3 (78.5)
50.0 (49.7)
50.9 (51.2)
56.6 (56.4)
55.9 (55.9)
49.4 (49.7)
52.7 (53.0)
54.1 (54.4)
53.3 (53.3)
57.3 (57.0)
55.8 (55.6)
51.2 (51.5)
53.9 (53.9)
7.5 (7.2)
8.6 (8.3)
8.8 (8.7)
9.0 (9.1)
9.3 (9.4)
9.6 (9.7)
5.5 (5.7)
6.0 (6.1)
6.6 (6.8)
6.9 (6.9)
5.0 (5.1)
5.8 (5.9)
6.2 (6.3)
6.2 (6.4)
6.9 (7.0)
6.8 (7.0)
6.2 (6.3)
6.4 (6.4)
13.1 (13.1)
10.9 (11.1)
10.5 (10.4)
9.6 (9.7)
9.0 (9.1)
8.5 (8.6)
6.7 (6.5)
6.4 (6.2)
6.7 (6.6)
6.3 (6.1)
7.6 (7.6)
6.8 (6.9)
6.5 (6.6)
6.3 (6.0)
6.1 (6.0)
5.7 (5.5)
5.6 (5.4)
5.5 (5.5)
C24H31N3O
C26H35N3O
3
4
C28H39N3O
5
C30H43N3O
6
C32H47N3O
7
C26H35PdCl2N3O Æ 3/4CH2Cl2
8
C28H39PdCl2N3O Æ 3/4CH2Cl2
30H43PdCl2N3O
C32H47PdCl2N3O Æ 1/3CH2Cl2
23H28PdBF4N3O
C27H36PdBF4N3O
29H40PdBF4N3O
C31H44PdBF4N3O Æ 1/2CH2Cl2
33H48PdBF4N3O
9
C
10
11
12
13
14
15
16
17
18
a
C
C
C
C35H52PdBF4N3O Æ 1/2CH2Cl2
C33H48PdF6N3OP Æ 1/4CH2Cl2
C34H48PdF3N3O4Sa
S: 4.4 (4.2).

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M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
3
3
3
(d, J = 7.7, 1H, H3), 7.84 (d, J = 8.4, 2H, Ho), 7.80 (1H,
H4), 7.17 (dd, 3J = 7.6, 3J = 4.3, 1H, H5), 6.96 (d, 3J = 8.7,
Hz): 9.01 (d, J = 5.4, 1H, H6), 8.45 (br s, 1H, H50), 8.10
3
3
(dd, J = 7.1, 1H, H4), 7.77 (d, J = 7.8, 1H, H3), 7.62
2H, Hm), 6.72 (d, J = 2.6, 1H, H40), 4.00 (t, 3J = 6.5, 2H,
(d, J = 8.6, 2H, Ho), 7.31 (dd, J = 6.3, 1H, H5), 6.91
3
3
3
3
OCH2), 1.88 (m, 2H, CH2), 1.5–1.2 (m, 14H, CH2), 0.89 (t,
3J = 6.8, 3H, CH3).
(d, J = 8.6, 2H, Hm), 6.66 (br s, 1H, H40), 3.98 (t,
3J = 6.1, 2H, OCH2), 1.79 (m, 2H, CH2), 1.5–1.2 (m,
pzddppy (3): IR (KBr, cmꢁ1): m(CN) 1612 (vs), c(CH)py
18H, CH2), 0.88 (t, J = 6.8, 3H, CH3).
3
1
766 (s). H NMR (CDCl3, d in ppm, J in Hz): 8.56 (d,
c-[Pd(Cl)2(pztdppy)] (8): IR (KBr, cmꢁ1): m(CN) 1612
3J = 2.8, 1H, H50), 8.40 (ddd, J = 4.6, J = 2.0, J = 0.8,
(vs), c(CH)py 772 (s). H NMR (CDCl3, d in ppm, J in
3
4
5
1
1H, H6), 8.08 (ddd, J = 8.2, J = 5J = 1.0, 1H, H3), 7.85
Hz): 9.06 (d, J = 5.5, 1H, H6), 8.38 (br s, 1H, H50), 8.09
3
4
3
(d, 3J = 8.8, 2H, Ho), 7.81 (ddd, 3J = 8.4, 3J = 7.4,
(dd, J = 7.8, 1H, H4), 7.69 (1H, H3), 7.63 (d, J = 8.3,
3
3
4J = 2.0, 1H, H4), 7.16 (ddd, J = 7.4, J = 4.8, J = 1.0,
1H, H5), 6.96 (d, 3J = 9.0, 2H, Hm), 6.71 (d, 3J = 2.6,
1H, H40), 4.00 (t, 3J = 6.6, 2H, OCH2), 1.81 (m, 2H,
2H, Ho), 7.33 (dd, J = 6.8, 1H, H5), 6.91 (d, J = 8.3,
2H, Hm), 6.68 (br s, 1H, H40), 3.99 (t, 3J = 6.4, 2H,
OCH2), 1.76 (m, 2H, CH2), 1.5–1.2 (m, 22H, CH2), 0.88
3
3
4
3
3
3
3
CH2), 1.5–1.2 (m, 18H, CH2), 0.88 (t, J = 6.8, 3H, CH3).
(t, J = 6.3, 3H, CH3).
pztdppy (4): IR (KBr, cmꢁ1): m(CN) 1613 (vs), c(CH)py
c-[Pd(Cl)2(pzhdppy)] (9): IR (KBr, cmꢁ1): m(CN) 1612
1
1
766 (s). H NMR (CDCl3, d in ppm, J in Hz): 8.58 (d,
(vs), c(CH)py 771 (s). H NMR (CDCl3, d in ppm, J in
3J = 2.8, 1H, H50), 8.41 (ddd, J = 4.8, J = 2.0, J = 1.0,
Hz): 9.07 (d, J = 5.6, 1H, H6), 8.35 (br s, 1H, H50), 8.09
3
4
5
3
1H, H6), 8.09 (ddd, J = 8.2, J = 5J = 1.0, 1H, H3), 7.86
(dd, J = 8.1, 1H, H4), 7.68 (1H, H3), 7.64 (d, J = 8.6,
3
4
3
3
(d, 3J = 9.0, 2H, Ho), 7.82 (ddd, 3J = 8.4, 3J = 7.4,
2H, Ho), 7.33 (dd, J = 7.1, 1H, H5), 6.93 (d, J = 8.6,
2H, Hm), 6.68 (br s, 1H, H40), 3.99 (t, 3J = 6.6, 2H,
OCH2), 1.80 (m, 2H, CH2), 1.5–1.2 (m, 26H, CH2), 0.88
3
3
4J = 2.0, 1H, H4), 7.17 (ddd, J = 7.4, J = 4.8, J = 1.2,
1H, H5), 6.96 (d, 3J = 8.8, 2H, Hm), 6.72 (d, 3J = 2.8,
1H, H40), 4.01 (t, 3J = 6.6, 2H, OCH2), 1.81 (m, 2H,
3
3
4
3
(t, J = 6.6, 3H, CH3).
3
CH2), 1.5–1.2 (m, 22H, CH2), 0.88 (t, J = 6.4, 3H, CH3).
c-[Pd(Cl)2(pzodppy)] (10): IR (KBr, cmꢁ1): m(CN) 1612
(vs), c(CH)py 771 (s). 1H NMR (CDCl3, d in ppm, J in Hz):
9.14 (d, 3J = 5.5, 1H, H6), 8.27 (d, 3J = 2.9, 1H, H50), 8.09
(ddd, 3J = 8.5, 3J = 7.4, 3J = 1.2, 1H, H4), 7.66 (d,
pzhdppy (5): IR (KBr, cmꢁ1): m(CN) 1613 (vs), c(CH)py
1
766 (s). H NMR (CDCl3, d in ppm, J in Hz): 8.56 (d,
3J = 2.8, 1H, H50), 8.41 (ddd, J = 4.8, J = 2.0, J = 1.0,
3
4
5
1H, H6), 8.08 (ddd, J = 8.4, J = 5J = 1.0, 1H, H3), 7.85
3J = 8.5, 2H, Ho), 7.60 (1H, H3), 7.36 (dd, J = 6.3, 1H,
3
4
3
(d, 3J = 8.8, 2H, Ho), 7.78 (ddd, 3J = 8.4, 3J = 7.4,
H5), 6.92 (d, 3J = 8.5, 2H, Hm), 6.70 (d, 3J = 2.9, 1H,
4J = 2.0, 1H, H4), 7.17 (ddd, J = 7.2, J = 4.8, J = 1.0,
1H, H5), 6.96 (d, 3J = 8.8, 2H, Hm), 6.72 (d, 3J = 2.8,
1H, H40), 4.00 (t, 3J = 6.6, 2H, OCH2), 1.81 (m, 2H,
H40), 3.99 (t, J = 6.3, 2H, OCH2), 1.80 (m, 2H, CH2),
3
3
4
3
3
1.5–1.2 (m, 30H, CH2), 0.88 (t, J = 6.8, 3H, CH3).
3
CH2), 1.5–1.2 (m, 26H, CH2), 0.88 (t, J = 6.6, 3H, CH3).
2.2.3. Preparation of c-[Pd(g3-C3H5)(pzRpy)]BF4
(R = C6H4OCnH2n+1, n = 6 (hp), 10 (dp), 12 (ddp),
14 (tdp), 16 (hdp), 18 (odp)) (11–16)
pzodppy (6): IR (KBr, cmꢁ1): m(CN) 1612 (vs), c(CH)py
1
766 (s). H NMR (CDCl3, d in ppm, J in Hz): 8.56 (d,
3J = 2.8, 1H, H50), 8.41 (ddd, 3J = 4.6, 4J = 2.0,
To a solution of [Pd(l-Cl)(g3-C3H5)]2 (100 mg, 0.273
mmol) in dry acetone (20 mL) was added AgBF4 (106.3
mg, 0.546 mmol) under nitrogen atmosphere. The mixture
was stirred overnight in the absence of light and then fil-
tered over Celite. The corresponding pzRpy (0.546 mmol)
in dichloromethane (15 mL) was added to the resulting
solution and let stirring overnight at room temperature.
Then the solvent was removed in vacuo and the solid
recrystallised in dichloromethane/hexane leading to the
precipitation of a colorless solid, which was filtered off,
washed with hexane and dried in vacuo. Yields and analyt-
ical data are given in Table 1.
5J = 1.0, 1H, H6), 8.08 (ddd, J = 8.4, J = 5J = 1.0, 1H,
3
4
H3), 7.84 (d, 3J = 8.8, 2H, Ho), 7.82 (ddd, 3J = 8.4,
3J = 7.4, J = 2.0, 1H, H4), 7.16 (ddd, J = 7.2, J = 4.8,
4J = 1.0, 1H, H5), 6.96 (d, 3J = 8.8, 2H, Hm), 6.71 (d,
3J = 2.8, 1H, H40), 4.01 (t, 3J = 6.6, 2H, OCH2), 1.81
4
3
3
3
(m, 2H, CH2), 1.5–1.2 (m, 30H, CH2), 0.88 (t, J = 6.8,
3H, CH3).
2.2.2. Preparation of c-[Pd(Cl)2(pzRpy)]
(R = C6H4OCnH2n+1, n = 12 (ddp), 14 (tdp), 16 (hdp),
18 (odp)) (7–10)
To a solution of the corresponding pzRpy ligand
(0.130 mmol) in chloroform (10 mL) was added
[Pd(Cl)2(PhCN)2] (50 mg, 0.130 mmol). The mixture of
reaction was refluxed for 3 h and then let stirring overnight
at room temperature. The solvent was removed and the
solid recrystallised in dichloromethane/hexane leading to
the precipitation of a yellow solid, which was filtered off,
washed with hexane and dried in vacuo. Yields and analyt-
ical data are given in Table 1.
c-[Pd(g3-C3H5)(pzhppy)]BF4 (11): IR (KBr, cmꢁ1):
m(CN) 1609 (vs), c(CH)py 777 (s), m(BF) 1052 (vs), d
1
(FBF) 522 (w). H NMR (CDCl3, d in ppm, J in Hz):
8.82 (d, J = 2.7, 1H, H50), 8.57 (d, 3J = 5.7, 1H, H6),
3
8.26 (d, 3J = 8.4, 1H, H3), 8.17 (dd, 3J = 8.4, 3J = 7.2,
3
3
1H, H4), 7.50 (d, J = 8.7, 2H, Ho), 7.43 (dd, J = 7.0,
3J = 5.4, 1H, H5), 7.02 (d, 3J = 8.7, 2H, Hm), 6.79 (d,
3J = 2.7, 1H, H40), 5.67 (m, 3Ja = 12.5, 3Js = 6.9, 1H,
Hmeso), 4.30 (br s, 1H, Hs), 4.04 (t, 3J = 6.6, 2H,
OCH2), 3.8-3.0 (br s, 3H, Hs + Ha), 1.84 (m, 2H, CH2),
c-[Pd(Cl)2(pzddppy)] (7): IR (KBr, cmꢁ1): m(CN) 1612
(vs), c(CH)py 772 (s). H NMR (CDCl3, d in ppm, J in
1
3
1.5–1.2 (m, 6H, CH2), 0.94 (t, J = 6.9, 3H, CH3).

M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
769
c-[Pd(g3-C3H5)(pzdppy)]BF4 (12): IR (KBr, cmꢁ1):
2.2.4. Preparation of c-[Pd(g3-C3H5)(pzhdppy)]A
(A = PF6 17, CF3 SO3 18)
m(CN) 1611 (vs), c(CH)py 783 (s), m(BF) 1052 (vs), d
1
(FBF) 522 (w). H NMR (CDCl3, d in ppm, J in Hz):
These compounds were prepared by the same way to
that of [Pd(g3-C3H5)(pzRpy)]BF4, starting from [Pd(l-
Cl)(g3-C3H5)]2 (50 mg, 0.137 mmol), AgPF6 (69.3 mg,
0.274 mmol) or AgCF3SO3 (70.4 mg, 0.274 mmol), and
pzhdppy (126.5 mg, 0.274 mmol). Yields and analytical data
are given in Table 1.
3
8.80 (d, J = 2.9, 1H, H50), 8.58 (d, 3J = 5.4, 1H, H6),
3
3
4
8.29 (ddd, J = 8.0, J = 7.3, J = 1.0, 1H, H4), 8.23 (d,
3J = 8.3, 1H, H3), 7.49 (d, J = 8.5, 2H, Ho), 7.42 (dd,
3
3J = 7.0, J = 5.4, 1H, H5), 7.02 (d, J = 8.5, 2H, Hm),
3
3
3
3
3
6.77 (d, J = 2.9, 1H, H40), 5.67 (m, Ja = 12.5, Js = 6.9,
1H, Hmeso), 4.38 (br s, 1H, Hs), 4.03 (t, 3J = 6.5, 2H,
OCH2), 3.59 (br s, 2H, Hs + Ha), 3.10 (br s, 1H, Ha),
1.83 (m, 2H, CH2), 1.6–1.2 (m, 14H, CH2), 0.88 (t,
3J = 6.8, 3H, CH3).
c-[Pd(g3-C3H5)(pzhdppy)]PF6 (17): IR (KBr, cmꢁ1):
m(CN) 1612 (vs), c(CH)py 780 (s), m(PF) 838 (vs), d (FPF)
1
557 (w). H NMR (CDCl3, d in ppm, J in Hz): 8.57 (d,
3
3
3J = 2.9, 2H, H50 + H6), 8.15 (dd, J = 8.0, J = 7.0, 1H,
c-[Pd(g3-C3H5)(pzddppy)]BF4 (13): IR (KBr, cmꢁ1):
m(CN) 1612 (vs), c(CH)py 783 (s), m(BF) 1056 (vs), d (FBF)
H4), 8.03 (d, 3J = 8.3, 1H, H3), 7.50 (d, 3J = 8.5, 2H,
3
3
Ho), 7.43 (dd, J = 6.3, 1H, H5), 7.02 (d, J = 8.5, 2H,
1
3
523 (w). H NMR (CDCl3, d in ppm, J in Hz): 8.82 (d,
Hm), 6.79 (d, J = 2.9, 1H, H40), 5.67 (m, 3Ja = 12.6,
3J = 2.7, 1H, H50), 8.57 (d, 3J = 5.4, 1H, H6), 8.28 (d,
3Js = 6.8, 1H, Hmeso), 4.33 (br s, 1H, Hs), 4.03 (t,
3J = 6.6, 2H, OCH2), 3.55 (br s, 2H, Hs + Ha), 3.16 (br
s, 1H, Ha), 1.83 (m, 2H, CH2), 1.5–1.1 (m, 26H, CH2),
3J = 8.3, 1H, H3), 8.19 (dd, J = 8.3, J = 7.8, 1H, H4),
3
3
3
3
7.50 (d, J = 8.5, 2H, Ho), 7.43 (dd, J = 5.8, 1H, H5),
7.02 (d, J = 8.5, 2H, Hm), 6.79 (d, J = 2.7, 1H, H40),
5.67 (m, Ja = 12.4, Js = 7.0, 1H, Hmeso), 4.32 (br s, 1H,
Hs), 4.02 (t, 3J = 6.1, 2H, OCH2), 3.55 (br s, 2H, Hs + Ha),
3.14 (br s, 1H, Ha), 1.83 (m, 2H, CH2), 1.5–1.2 (m, 18H,
3
3
3
0.88 (t, J = 6.6, 3H, CH3).
3
3
c-[Pd(g3-C3H5)(pzhdppy)]CF3SO3 (18): IR (KBr,
cmꢁ1): m(CN) 1611 (vs), c(CH)py 773 (s), m(SO3) + m(CF3)
1
1257 (vs). H NMR (CDCl3, d in ppm, J in Hz): 9.02 (d,
3
CH2), 0.88 (t, J = 6.8, 3H, CH3).
3J = 2.9, 1H, H50), 8.57 (d, 3J = 4.6, 1H, H6), 8.45 (d,
c-[Pd(g3-C3H5)(pztdppy)]BF4 (14): IR (KBr, cmꢁ1):
m(CN) 1612 (vs), c(CH)py 783 (s), m(BF) 1056 (vs), d
3J = 8.3, 1H, H3), 8.23 (ddd, J = 8.5, J = 7.3, J = 1.5,
3
3
4
3
3
1H, H4), 7.51 (d, J = 8.6, 2H, Ho), 7.45 (dd, J = 6.3,
1H, H5), 7.02 (d, 3J = 8.6, 2H, Hm), 6.81 (d, 3J = 2.9,
1H, H40), 5.68 (m, Ja = 12.7, Js = 6.8, 1H, Hmeso), 4.04
1
(FBF) 523 (w). H NMR (CDCl3, d in ppm, J in Hz):
8.83 (d, J = 2.9, 1H, H50), 8.57 (d, 3J = 5.1, 1H, H6),
3
3
3
3
3
3
8.28 (d, J = 8.3, 1H, H3), 8.19 (dd, J = 7.6, 1H, H4),
7.50 (d, J = 8.6, 2H, Ho), 7.43 (dd, J = 6.1, 1H, H5),
7.02 (d, J = 8.6, 2H, Hm), 6.80 (d, J = 2.9, 1H, H40),
5.67 (m, 3Ja = 12.4, 3Js = 6.9, 1H, Hmeso), 4.03 (t,
3J = 6.6, 3H, OCH2 + Hs), 3.31 (br s, 3H, Hs + Ha), 1.84
(t, J = 6.3, 3H, OCH2 + Hs), 3.33 (br s, 3H, Hs + Ha),
3
3
1.84 (m, 2H, CH2), 1.5–1.1 (m, 26H, CH2), 0.89 (t,
3
3
3J = 6.8, 3H, CH3).
2.3. X-ray structure determinations of c-[Pd(g3-C3H5)-
(pzRpy)]BF4 (R = hp 11, dp 12)
3
(m, 2H, CH2), 1.5-1.2 (m, 22H, CH2), 0.88 (t, J = 6.6,
3H, CH3).
c-[Pd(g3-C3H5)(pzhdppy)]BF4 (15): IR (KBr, cmꢁ1):
m(CN) 1612 (vs), c(CH)py 781 (s), m(BF) 1053 (vs), d
(FBF) 522 (w). 1H-NMR (CDCl3, d in ppm, J in Hz):
Suitable colorless crystals of c-[Pd(g3-C3H5)(pzhppy)]-
BF4 (11) and c-[Pd(g3-C3H5)(pzdppy)]BF4 (12) were grown
by layering dichloromethane solutions with hexane. The
crystals were mounted on a Smart CCD-Bruker diffractom-
eter with graphite monochromated Mo-Ka radiation
(k = 0.71073 A) operating at 50 kV and 20–25 mA. A sum-
mary of the fundamental crystal and refinement data for
these structures is given in Table 2.
In both cases, data were collected over an hemisphere of
the reciprocal space by combination of the three exposure
sets. Each exposure of 20 s covered 0.3ꢁ in x. The cell
parameters were determined and refined by a least-squares
fit of all reflections. The first 50 frames were recollected at
the end of the data collection to monitor crystal decay, and
no appreciable decay was observed. The structures were
solved by direct methods and conventional Fourier tech-
niques and refined by full-matrix least-squares on F2 [18].
Anisotropic parameters were used in the last cycles of
refinement for all non-hydrogen atoms with some excep-
tions. In both compounds, a non-resolvable disorder of
the fluorine atoms of the BF4 group and some carbon
atoms was found. The F-atoms were included in two iso-
tropical cycles for 12 and three anisotropical cycles for
3
8.81 (d, J = 2.9, 1H, H50), 8.58 (d, 3J = 4.9, 1H, H6),
8.25 (d, 3J = 8.3, 1H, H3), 8.14 (dd, 3J = 8.3, 3J = 7.3,
3
3
˚
1H, H4), 7.50 (d, J = 8.6, 2H, Ho), 7.42 (dd, J = 6.4,
1H, H5), 7.02 (d, 3J = 8.6, 2H, Hm), 6.78 (d, 3J =
3
3
2.9, 1H, H40), 5.67 (m, Ja = 12.5, Js = 6.8, 1H, Hmeso),
4.12 (br s, 1H, Hs), 4.03 (t, 3J = 6.6, 2H, OCH2), 3.32
(br s, 2H, Hs + Ha), 3.04 (br s, 1H, Ha), 1.83 (m, 2H,
CH2), 1.5–1.2 (m, 26H, CH2), 0.94 (t, 3J = 6.9, 3H,
CH3).
c-[Pd(g3-C3H5)(pzodppy)]BF4 (16): IR (KBr, cmꢁ1):
m(CN) 1612 (vs), c(CH)py 783 (s), m(BF) 1056 (vs), d
1
(FBF) 523 (w). H NMR (CDCl3, d in ppm, J in Hz):
3
8.82 (d, J = 2.9, 1H, H50), 8.57 (d, 3J = 5.1, 1H, H6),
8.27 (d, 3J = 8.3, 1H, H3), 8.17 (d, 3J = 7.8, 1H, H4),
3
3
7.50 (d, J = 8.8, 2H, Ho), 7.45 (dd, J = 6.1, 1H, H5),
3
3
7.02 (d, J = 8.8, 2H, Hm), 6.79 (d, J = 2.9, 1H, H40),
5.67 (m, 3Ja = 12.4, 3Js = 6.9, 1H, Hmeso), 4.03 (t,
3J = 6.3, 3H, OCH2 + Hs), 3.31 (br s, 3H, Hs + Ha), 1.83
3
(m, 2H, CH2), 1.5–1.2 (m, 30H, CH2), 0.88 (t, J = 6.6,
3H, CH3).

770
M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
Table 2
Crystal and refinement data for c-[Pd(g3-C3H5)(pzRpy)]BF4 (R = hp 11, dp 12)
11
12
Empirical formula
Formula weight
Crystal system
Space group
C23H28BF4N3OPd
555.69
Monoclinic
P21/c
C27H36BF4N3OPd
611.80
Monoclinic
P21/c
˚
a (A)
17.607(1)
9.8589(8)
14.763(1)
103.578(2)
2491.1(4)
4
21.034(2)
9.809(1)
14.928(2)
108.571(2)
2919.4(6)
4
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
T (K)
F(000)
293(2)
1128
1.482
0.794
296(2)
1256
1.392
0.685
qcalc. (g cmꢁ3
)
l (mmꢁ1
)
Crystal dimensions (mm)
Scan technique
0.36 · 0.12 · 0.08
x and /
0.40 · 0.10 · 0.07
x and /
Data collected
h range (ꢁ)
(ꢁ23,ꢁ12,ꢁ17) to (23,13,19)
1.19–28.94
15,554
5936 (Rint = 0.0707)
5936/5/221
2136
0.053
0.165
0.701
(ꢁ25,ꢁ11,ꢁ11) to (24,11,17)
2.04–25.00
14,845
5135 (Rint = 0.0809)
5135/12/227
1757
0.093
0.302
1.305
Reflections collected
Independent reflections
Data/restraints/parameters
Observed reflections [I P 2r(I)]
Ra
b
RwF
ꢁ3
˚
Largest residual peak (e A
)
P
P
a
[|Fo| ꢁ |Fc|]/ |Fo|.
P
P
2
2
1=2
b
f
½wðF 2o ꢁ F c2Þ ꢂ= ½wðF 2oÞ ꢂg
.
11, and in subsequent cycles their thermal parameters were
kept constant. Besides, analogous refinement was applied
for the carbon atoms of the decyl chain and the allyl group
in 12, and for the carbon atoms of the hexyl chain in 11.
These carbon atoms were also refined with geometrical
restraints and a variable common carbon–carbon distance.
Hydrogen atoms were included in calculated positions and
refined as riding on their respective carbon atoms. The
refinement converged to R values of 0.053 and 0.093 for
11 and 12, respectively.
The reaction of the ligands 1–6 and [Pd(Cl)2(PhCN)2] or
[Pd(g3-C3H5)(acetone)2]BF4 (prepared in situ by reaction
of the dimer [Pd(l-Cl)(g3-C3H5)]2 and AgBF4 in acetone
[21]) gave rise to the new compounds c-[Pd(Cl)2(pzRpy)]
(R = C6H4OCnH2n+1, n = 12, 14, 16, 18) (7–10) and c-
[Pd(g3-C3H5)(pzRpy)]BF4 (R = C6H4OCnH2n+1, n = 6, 10,
12, 14, 16, 18) (11–16) (Scheme 2). Both ligands and com-
pounds were characterised by analytical and spectroscopic
techniques (IR and 1H NMR), and all data agree with their
proposed molecular formulation. Some Pd-compounds
exhibit crystallisation solvent (dichloromethane) detected
The largest residual pꢁea3ks in the final difference map
1
˚
were 0.701 and 1.305 e A for 11 and 12, respectively, in
by elemental analysis and by H NMR through a signal
the vicinity of the fluorine atoms of the BF4 group. The
supplementary crystallographic data have been passed to
the Cambridge Crystallographic Data Centre (CCDC
deposition numbers 275433 and 275434 for 11 and 12,
respectively).
at 5.32 ppm, which was not removed even after large
periods in vacuo.
The 1H NMR spectra of the ligands 1–6 and com-
plexes 7–18, recorded in CDCl3 solution at room temper-
ature (see Section 2), show all the expected signals from
the pyrazole and pyridine groups as well as those from
the alkyloxyphenyl substituent. Some resonances appear
to be overlapped or masked by other signals. The main
difference in each series of compounds is the integration
of the (CH2)n signal.
3. Results and discussion
3.1. Synthetic and characterisation studies
The new ligands 2-[3-(4-alkyloxyphenyl)pyrazol-1-
yl]pyridine (pzRpy; R = C6H4OCnH2n+1, n = 6 (hp), 10
(dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1–6) were pre-
pared by reaction of the sodium salt of the corresponding
3-(4-alkyloxypropane)-1,3-dione and 2-hydrazinopyridine
in a HCl/EtOH media in a same way to related compounds
[3,19,20] (Scheme 2).
In relation to the pyrazole groups, the H40 and the
alkyl chain protons are scarcely modified in the complexes
compared with those from the free ligands. By contrast,
the pyridine and phenyl protons are markedly displaced
upon complexation. The most significant shift is produced
for the H6 proton of the pyridine moiety, which is down-
field moved by ca. 0.6 ppm from the free ligand (ca.

M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
771
OCnH2n+1
OCnH2n+1
N
NH2 HN
H
N
N
N
pzRpy
O
O
Na+
EtOH / HCl
R= hp, dp, ddp, tdp, hdp, odp (1-6)
OCnH2n+1
Cl
Pd
[Pd(Cl)2(PhCN)2]
CHCl3
N
Cl
c-[Pd(Cl)2(pzRpy)]
N
pzRpy
N
R= ddp, tdp, hdp, odp (7-10)
[Pd(η3-C3H5)(sol)2]A
OCnH2n+1
CH3COCH3
N
Pd
c-[Pd(η3-C3H5)(pzRpy)]A
N
A-= BF4 , PF6 , CF3SO3
-
-
-
N
(11-18)
R= hp, dp, ddp, tdp, hdp, odp
Scheme 2.
8.40 ppm) to the PdCl2 derivatives (ca. 9.00 ppm), while
for c-[Pd(g3-C3H5)(pzRpy)]BF4 the related shift is only
ca. 0.15 ppm. The above result could be explained by
considering the presence of interactions between the H6
proton and the neighbouring Pd-bonded chloride ligand.
On the other hand, the Ho protons from the phenyl
susbtituents at the pyrazole are upfield shifted by ca. 0.35
and 0.20 ppm on the c-[Pd(g3-C3H5)(pzRpy)]BF4 and
c-[Pd(Cl)2(pzRpy)] complexes, respectively.
NMR experiments at variable temperature (from ꢁ50 to
50 ꢁC) have been undertaken. However they proved to be
unsuccessful, the allyl signals being not resolved.
3.2. X-ray crystal structures of c-[Pd(g3-C3H5)-
(pzRpy)]BF4 (R = hp 11, dp 12)
Suitable crystals of compounds 11 and 12 were obtained
from dichloromethane/hexane solutions. Figs. 1 and 2
illustrate the molecular geometry of both compounds,
and Table 3 lists selected bond distances and angles. Both
compounds behave almost isostructural, showing only
slight differences. They crystallise in the monoclinic system,
P21/c space group, with one [Pd(g3-C3H5)(pzRpy)]BF4 per
asymmetric unit.
Due to the non-resolvable disorder found specially in 12
(see Section 2), we will only comment the crystal structure
of 11. However, as we have stated before, both compounds
are isostructural and therefore the conclusions deduced for
11 can also be applied to 12.
For c-[Pd(g3-C3H5)(pzRpy)]BF4, the asymmetry of the
compound accounts for a non-symmetrical allyl ligand,
which determines the presence of two signals each syn and
anti protons. These signals appear as three broad reso-
nances at ca. 4.3 (Hs), 3.6 (Hs + Ha) and 3.1 (Ha) ppm,
as a characteristic of a dynamic behaviour from the allyl
group. There are many examples in the literature describing
the dynamic behaviour of allylpalladium complexes [21–
24]. A multiplet at 5.67 ppm for the meso proton, from
which are determined the corresponding coupling con-
stants, is also observed.
Fig. 1. ORTEP plot of 11 with 30% probability. Hydrogen atoms have been omitted for clarity.

772
M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
Fig. 2. ORTEP plot of 12 with 30% probability. Hydrogen atoms have been omitted for clarity.
˚
from the ideal allyl geometry (ca. 1.36 A and 120ꢁ, respec-
tively). Similar distorted allyl groups have also been found
in other complexes containing [Pd(g3-allyl)]+ fragments
Table 3
3
R
˚
Selected bond distances (A) and angles (ꢁ) for c-[Pd(g -C3H5)(pz py)]BF4
(R = hp 11, dp 12)
˚
11
12
[25,27–30]. The Pd–C(allyl) distances (2.07–2.10 A) are in
the expected range for a [Pd(g3-allyl)]+ fragment with
Pd1–N1
Pd1–N3
Pd1–C11
Pd1–C12
Pd–C13
C11–C12
C12–C13
B1–F1
2.117(5)
2.095(5)
2.088(7)
2.073(7)
2.105(7)
1.244(11)
1.193(11)
1.354(9)
1.412(10)
1.291(8)
1.310(8)
2.11(1)
2.10(1)
2.15(2)
2.12(2)
2.21(2)
1.380(5)
1.375(5)
1.34(2)
1.36(2)
1.32(2)
1.22(2)
nitrogen ligands in trans position [21,22,26]. The Pd–C11
distance (2.088(8) A) is slightly shorter than the Pd–C13
one (2.105(7) A), this feature being related to a different
trans influence of the N-coordinated heterocycle.
˚
˚
The dihedral angle between the allyl plane (C11C12C13)
and the coordination plane defined by the Pd, N1 and N3
atoms is 3(1)ꢁ, with the allyl carbon atoms displaced a
B1–F2
B1–F3
B1–F4
˚
mean value of 0.16 A with respect to this PdN1N3 plane.
The pyrazole and pyridine planes are almost parallel
(dihedral angle of 4.4(2)ꢁ), defining an almost planar core
of the cationic entity. However, the benzene plane from
the substituent is twisted 33.5(3)ꢁ with respect to the own
pyrazole plane.
N1–Pd–N3
N1–Pd–C11
N1–Pd1–C12
N1–Pd1–C13
N3–Pd1–C11
N3–Pd1–C12
N3–Pd1–C13
C11–Pd1–C12
C11–Pd1–C13
C12–Pd1–C13
C11–C12–C13
F1–B1–F2
77.8(2)
176.8(3)
143.5(3)
110.3(2)
103.7(3)
138.3(3)
169.9(3)
34.8(3)
78.4(4)
178.5(5)
143.3(5)
106.6(5)
100.4(5)
137.1(5)
171.6(5)
37.8(2)
The distorted tetrahedral BFꢁ4 counterion (mean B–F dis-
˚
tance and F–B–F angle of 1.34(1) A and 109.1(7)ꢁ, respec-
tively) shows an interaction with the cationic unit through
67.9(3)
33.2(3)
74.5(3)
36.9(2)
˚
a weak coordinative Pdꢀ ꢀ ꢀ F1 contact of 3.543(6) A.
To a supramolecular level, each [Pd(g3-C3H5)(pzhppy)]-
BF4 entity interacts with the neighbour through a weak
non-conventional hydrogen bond C7ꢀ ꢀ ꢀF3 (ꢁx + 1,
148.1(9)
102.8(7)
115.6(7)
112.1(6)
102.7(7)
104.4(7)
117.0(8)
147(2)
102(2)
116(1)
118(1)
90(1)
F1–B1–F3
F1–B1–F4
F2–B1–F3
F2–B1–F4
˚
y ꢁ 1/2, ꢁz + 1/2) of 3.08(1) A, the molecules implicated
showing a head-to-tail orientation. In such a way these
interactions, which are propagated along the b-axis, give
rise to a zig-zag chain (Fig. 3).
103(2)
120(2)
F3–B1–F4
The interactions are further extended between the chains
which are held together through a non-conventional hydro-
The geometry about the palladium(II), in the cationic
entity, is distorted square-planar, the Pd atom deviating
0.081(1) A of the N1N3C11C13 plane. The square-planar
˚
gen bond C9ꢀ ꢀ ꢀF1 (ꢁx + 1, ꢁy + 2, ꢁz + 1) of 3.271(8) A.
˚
Additional non-covalent interactions that correspond to
face-to-face pꢀ ꢀ ꢀp contacts between aromatic pyridine and
benzene rings residing on the nearest neighbouring chains
are also observed. The groups associated with the pꢀ ꢀ ꢀp
geometry can also be established by the dihedral angle of
6.0(3)ꢁ defined by the Pd1N1N3 and Pd1C11C13 planes.
˚
The Pd–N distances (mean value of 2.101(5) A) are sim-
˚
ilar to those found in related compounds [21,22,25,26]. The
Pd–N1 and Pd–N3 bonds form the basis of the five-mem-
interactions show the shortest separation of ca. 3.5 A,
which is consistent with that between heterocyclic ligands
observed in several compounds [31–33]. The interchain
interactions so defined give rise to layers, which are located
almost parallel to the bc plane and generating a 2D network
(Fig. 4).
˚
bered chelate ring, the Pd–N3 distance (2.095(5) A) being
˚
slightly shorter than the Pd–N1 one (2.117(5) A) in accor-
dance with the expected difference in basicity of their
respective heterocycles.
The allyl group C11C12C13 shows C–C bond distances
of ca. 1.22 A and a C–C–C angle of 148(1)ꢁ, which deviate
In this layered model, we could also consider that each
molecule, which has a molecular geometry typical of
˚

M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
773
Fig. 3. View of the chain of 11 along the b-axis.
Fig. 4. 2D network of 11.
a rod-like shape, is associated by pꢀ ꢀ ꢀp interactions with
molecules of the own chain through the BFꢁ4 counterions,
dipole–dipole interaction (Fig. 4). The flexible chains of
contiguous layers are interdigitated, leading to a global
order which can be related to a lamellar interdigitated
supramolecular organisation.
˚
molecules of neighbouring chains at 3.5 A as well as with
giving rise such an ordering related with a favourable

774
M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
3.3. Thermal studies
were identified as smectic A mesophases. Figs. 6(a) and
(b) show textures of mesophases observed for some deriva-
tives as representative examples. The transition tempera-
tures as well as the corresponding enthalpies were
determined by DSC and are given in Table 4. As general
behaviour decomposition was observed after the meso-
phase was formed, and that decomposition was extensive
after clearing.
The thermal behaviour of the pzRpy ligands (1–6) and
their corresponding complexes c-[Pd(Cl)2(pzRpy)] (7–10)
and c-[Pd(g3-C3H5)(pzRpy)]BF4 (11–16) have been studied
by polarised optical microscopy (POM), differential scan-
ning calorimetry (DSC) and variable-temperature X-ray
diffraction (XRD).
Unlike their 3,5-disubstituted pyrazolylpyridine (pzR2py)
counterparts which showed monotropic smectic A meso-
phases [3], none of the new ligands pzRpy containing 3-
substituted pyrazole groups displayed mesomorphism.
These ligands were coordinated to the PdCl2 group to give
rise to the complexes c-[Pd(Cl)2(pzRpy)], which again did
not exhibit liquid crystal properties at difference to their
mesomorphic homologues c-[Pd(Cl)2(pzR2py)] [3]. The
above results appear to suggest that the vanishing of the
liquid crystal properties in both cases, in relation to
the 3,5-disubstituted counterparts, could be a reflect of
the shortening of the molecular length maintaining the same
width (Fig. 5).
However, the possibility of tuning the mesogenic prop-
erties, not only varying the length of the chains of the pyr-
azolylpyridine-type ligands but also the nature of metal
fragment to which it is coordinated, moved us to extend
the studies to those complexes containing [Pd(g3-C3H5)]+
as metal group. So, the thermal properties of the new com-
plexes of the type c-[Pd(g3-C3H5)(pzRpy)]+ (R = C6H4-
OCnH2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16
(hdp), 18 (odp)) containing BFꢁ4 as counterion (11–16)
were investigated.
In particular, complexes 13–16 show, on first heating, a
crystal–crystal transition in the range of 60–95 ꢁC, followed
by a unidentified phase at ca. 140 ꢁC. The observed viscos-
ity of this phase by POM agrees with either a highly
ordered phase or a soft crystal. After ca. 160 ꢁC, a smectic
A mesophase is identified which clears with decomposition
at temperatures higher than 200 ꢁC (Table 4). Typical DSC
thermogram is depicted in Fig. 7(a) showing these features.
To determine the solidification temperature avoiding the
decomposition, the samples were heated only at tempera-
tures close to the formation of the mesophase and then
they were cooled (Fig. 7(b)). Thus, the crystal–smectic A
transition (ca. 160 ꢁC) on heating was followed by the for-
mation of the solid (ca. 130 ꢁC) on cooling. Thermograms
from second and successive heatings were identical showing
only one transition from solid to mesophase (Fig. 7(b)).
As a general result, DSC analysis indicates that the
c-[Pd(g3-C3H5)(pzRpy)]BF4 complexes essentially exhibit
temperature-dependent polymorphism. These phase changes
take the form of crystal–crystal transitions that are only
observed on the first heating cycle. The second of these
transitions generally exhibits smaller enthalpies than the
third one (corresponding to the mesophase formation)
(Table 4), suggesting that the second intermediate phase
in these materials is crystalline rather than mesogenic
instead of its slight softness observed by POM.
The complexes with a chain from 12 to 18 carbon atoms
(13–16) display liquid crystal properties exhibiting meso-
phases with homeotropic and fan-shaped textures, which
N N
N
pzRpy
pzR2py
pzRpy
c-[Pd(Cl)2(pzR2py)] c-[Pd(Cl)2(pzRpy)]
Pd
Cl
Pd Cl
Cl
Cl
LC
(a)
No LC
(b)
No LC
LC
(c)
Fig. 5. Schematic molecular representation of the pzR2py (a) and pzRpy (b) ligands and their PdCl2 complexes, c-[Pd(Cl)2(pzR2py)] (c) and
c-[Pd(Cl)2(pzRpy)] (d), showing the relationship of the molecular length.

M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
775
Table 4
Phase properties of c-[Pd(g3-C3H5)(pzRpy)]BF4 (R = hp, dp, ddp, tdp,
hdp, odp) (11–16)
Transition
T (ꢁ)
175.0
169.2
93.6
134.3
150.4
253.7
61.5
148.4
162.6
209.8
79.3
134.9
169.2
244.0
90.8
132.4
156.2
ꢃ240b
DH (kJ molꢁ1
)
11 (hp)
12 (dp)
13 (ddp)
Crys ! I
15.7
18.2
11.0
9.9
4.7
1.6
12.5
8.1
11.8
0.5
16.2
11.5
15.0
1.7
20.6
13.2
15.7
Crys ! I
Crys ! Crys0
Crys0 ! Crys00
Crys00 ! SmA
SmA ! Ia
14 (tdp)
15 (hdp)
16 (odp)
a
Crys ! Crys0
Crys0 ! Crys00
Crys00 ! SmA
SmA ! Ia
Crys ! Crys0
Crys0 ! Crys00
Crys00 ! SmA
SmA ! Ia
Crys ! Crys0
Crys0 ! Crys00
Crys00 ! SmA
SmA ! Ia
Decomposition.
Observed by polarised optical microscopy (POM).
b
50
100
150
200
250
Temperature (ºC)
a
Fig. 6. Textures of the smectic A mesophase, observed on cooling, for: (a)
compound 13 at 178 ꢁC; (b) compound 15 at 180 ꢁC; (c) compound 17 at
156 ꢁC.
In order to get a better understanding of the nature of
these thermotropic transitions, we have examined the
phase behaviour of one representative complex c-[Pd(g3-
C3H5)(pzhdppy)]BF4 (15) by variable-temperature XRD.
The results confirm the crystalline nature of the two first
morphs on first heating cycle as well as the smectic meso-
phase produced after the third transition (Fig. 8(a)). In
agreement with its assignation as smectic mesophase, the
XRD pattern exhibits a low-angles sharp reflection
(Fig. 8(a)) and a broad peak at wide-angles (Fig. 8(b)),
which is consistent with a smectic-type layered structure
60
80
100
120
140
160
180
Temperature (ºC)
b
Fig. 7. DSC thermograms for c-[Pd(g3-C3H5)(pzhdppy)]BF4 (15) in (a) the
50–250 ꢁC range (first heating), and (b) the 50–180 ꢁC range: first heating
(straight line), first cooling (dashed line) and second heating (dotted line).
˚
that shows a d-spacing of 43.34 A. For this compound

776
M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
Crys
29.95º
Crys’
127.95º
Crys’’
SmA
147.95º
197.95º
SmA
197.95º
I
248.05º
30
I
248.05º
8
10
20
2
4
6
10
Position [˚2Theta]
Position [˚2Theta]
a
b
Fig. 8. (a) X-ray diffractograms of c-[Pd(g3-C3H5)(pzhdppy)]BF4 (15) at different temperatures in the low-angles region. (b) Full diffractograms for the
smectic A mesophase and isotropic liquid of 15.
˚
15, a molecular length L of ca. 34 A in a fully extended con-
figuration was estimated from the X-ray crystalline struc-
ture of 11. Because the d-spacing of the smectic layers
which consists of three aromatic coplanar rings (pyrazole,
pyridine and Pd five-membered ring) and a four cycle
Pd(g3-C3H5), determines the global geometry of the mole-
cule. Then, the compromise between the rigid planar
molecular core and the length of the chains should be
reflected in the liquid crystal properties of the complexes.
As it was previously reported, when the contribution of
chains prevails the transition temperatures decrease,
whereas if contribution of the rigid core prevails tempera-
tures increases [6,34], the latter feature being observed for
our complexes. Therefore, it is possible to suggest the pres-
ence of core–core interactions to explain the increase of the
melting temperatures. Again, from the crystal structures of
11 and 12, the presence of pꢀ ꢀ ꢀp interactions was observed,
and related interactions could be suggested in the meso-
phase molecular arrangement.
˚
˚
(43.34 A) is larger than L (ca. 34 A), but smaller than 2L
(ca. 68 A), we can deduce that the molecules are not
˚
arranged in single molecules layers but organised in inter-
digitated bilayers (Fig. 9). This supramolecular organisa-
tion of the mesophase can be related to that of the
crystal structure of 11 above described.
On the other hand, complexes 13–16 exhibit increased
melting temperatures when the length of the alkyl chain
is going from 12 to 16 carbon atoms. As deduced from
the crystal structures of 11 and 12, the Pd-containing
five-membered ring is essentially planar, in which a partial
electron delocalisation suggests certain aromaticity. In
addition, the fused pyrazole and pyridine groups are
almost coplanar to the Pd-ring as well as the Pd(g3-
C3H5) moiety. Therefore, in our complexes, the rigid core,
As conclusion, by comparing the mesogen c-[Pd(g3-
C3H5)(pzRpy)]BF4 with the non-mesomorphic c-[Pd(Cl)2-
34 Å
43.34 Å
N
Pd
N
N
c-[Pd(η3-C3H5)(pzRpy)]A
Fig. 9. Proposed molecular arrangement in the smectic A mesophase.

M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
777
Table 5
ecule. On this basis, we propose a molecular arrangement in
which the molecules in a head-to-tail disposition show inter-
digitation, giving rise to a semi-bilayered smectic phase.
In addition, the influence of the counteranion on the
mesomorphic properties has also been evidenced, the pres-
Phase properties of c-[Pd(g3-C3H5)(pzhdppy)]A (A = BF4 15, PF6 17,
CF3SO3 18)
Transition
T (ꢁ)
79.3
DH (kJ molꢁ1
)
15
Crys ! Crys0
Crys0 ! Crys00
Crys00 ! SmA
16.2
11.5
15.0
1.7
24.5
14.9
0.2
ence of CF3SOꢁ groups being responsible for the improve-
134.9
169.2
244.0
102.4
148.8
180.6
59.5
3
ment of the mesomorphism.
a
SmA ! I
17
18
a
Crys ! Crys0
Crys0 ! SmA
Acknowledgements
a
SmA ! I
ꢀ
Crys ! Crys0
Crys0 ! SmA
SmA ! I
37.3
´
We are grateful to the Direccion General de Investi-
ꢃ76.5
121.7
0.3
´
gacion/MEC of Spain (Project No. BQU2003-07343) for
financial support. We also thank to Comunidad de Madrid
for financial support (Project GR/MAT/0511/2004) and
Decomposition.
´
the contract to M.C.T. We thank Dr. J. Barbera (Facultad
(pzRpy)], it deserves to be noted that the [Pd(g3-C3H5)]+
fragment plays a key role in the improvement of the meso-
morphic behaviour. In addition, it is also possible to sug-
gest that the layer-like crystal structure observed for this
type of compounds could be related to the lamellar one
on the mesophases.
de Ciencias-ICMA, Universidad de Zaragoza-CSIC, Zara-
goza, Spain) for your helpful and assessment in the inter-
pretation of the XRD data.
References
The related compounds containing the same pyrazolyl-
pyridine ligand, pzhdppy, and PF6ꢁ (17) or CF3SOꢁ (18) as
[1] M.C. Torralba, M. Cano, J.A. Campo, J.V. Heras, E. Pinilla, M.R.
Torres, Inorg. Chem. Commun. 5 (2002) 887.
3
counteranions, have also been proved to have liquid crystal
behaviour (Fig. 6(c)), showing lower melting and clearing
temperatures than the BFꢁ4 derivative (15) (Table 5). Com-
plex 17, as it was already observed in 15, exhibits some
decomposition at the clearing point. By contrast, complex
18 behaves stable along all the temperature range. Addi-
tionally, the improvement of the mesomorphic properties
in 18 is evident, displaying the smectic A mesophase at
the lowest temperature. By analysing the thermal
properties of 15, 17 and 18, the influence of the counteran-
ion on the liquid crystal behaviour appears also to be clear.
A good molecular packing and strong intermolecular inter-
actions should give rise to high transition temperatures, this
feature being observed on the BFꢁ4 derivative. However the
lowest transition temperature observed for 18 agrees with a
less efficient packing of the molecules which could be related
[2] M.C. Torralba, M. Cano, J.A. Campo, J.V. Heras, E. Pinilla, M.R.
Torres, J. Organomet. Chem. 633 (2001) 91.
[3] M.J. Mayoral, M.C. Torralba, M. Cano, J.A. Campo, J.V. Heras,
Inorg. Chem. Commun. 6 (2003) 626.
[4] B. Donnio, D.W. Bruce, Struct. Bond. 95 (1999) 193.
[5] M.C. Torralba, M. Cano, J.A. Campo, J.V. Heras, E. Pinilla, M.R.
Torres, J. Organomet. Chem. 654 (2002) 150.
[6] M. Ghedini, A. Crispini, Comments Inorg. Chem. 21 (1999) 33.
[7] M. Ghedini, D. Pucci, A. Crispini, I. Aiello, F. Barigelletti, A. Gessi,
O. Francescangeli, Appl. Organomet. Chem. 13 (1999) 565.
´
´
´
[8] J. Buey, G.A. Dıez, P. Espinet, S. Garcıa-Granda, E. Perez-Carreno,
˜
Eur. J. Inorg. Chem. (1998) 1235.
´
[9] M.J. Baena, J. Buey, P. Espinet, C.E. Garcıa-Prieto, J. Organomet.
Chem. 690 (2005) 998.
´
´
[10] L. Dıez, P. Espinet, J.A. Miguel, M.P. Rodrıguez-Medina, J.
Organomet. Chem. 690 (2005) 261.
[11] F. Neve, M. Ghedini, A. Crispini, Chem. Commun. (1996) 2463.
[12] F. Neve, M. Ghedini, A. Francescangeli, S. Campagna, Liq. Cryst.
24 (1998) 673.
[13] D. Pucci, G. Barberio, A. Crispini, M. Ghedini, O. Francescangeli,
Mol. Cryst. Liq. Cryst. 395 (2003) 155.
with the bulkiest and non-symmetrical CF3-SOꢁanion.
3
4. Conclusions
[14] F. Neve, Adv. Mater. 8 (1996) 277.
[15] M. Ghedini, D. Pucci, J. Organomet. Chem. 395 (1990) 105.
[16] A. El-ghayoury, L. Douce, A. Skoulios, R. Ziessel, Angew. Chem.
Int. Ed. 37 (1998) 1255.
[17] K. Ohta, H. Muroki, K.I. Hatada, I. Yamamoto, K. Matsuzaki,
Mol. Cryst. Liq. Cryst. 130 (1985) 249.
[18] G.M. Sheldrick, SHELXL97, Program for Refinement of Crystal
Structure, University of Go¨ttingen, Germany, 1997.
[19] J.A. Campo, M. Cano, J.V. Heras, M.C. Lagunas, J. Perles, E.
Pinilla, M.R. Torres, Helv. Chim. Acta 85 (2002) 1079.
[20] M.L. Gallego, M. Cano, J.A. Campo, J.V. Heras, E. Pinilla, M.R.
Torres, P. Cornago, R.M. Claramunt, Eur. J. Inorg. Chem. (2005)
4370.
A new series of asymmetric N,N0-donor ligands of the
type 2-[3-(4-alkyloxyphenyl)pyrazol-1-yl]pyridine (pzRpy)
and their corresponding mononuclear neutral cis-dichlor-
opalladium(II) complexes c-[Pd(Cl)2(pzRpy)] and cationic
allylpalladium(II) complexes c-[Pd(g3-C3H5)(pzRpy)]+
have been prepared and characterised. Neither the ligands
nor the PdCl2 derivatives showed mesomorphism, while
coordination to the [Pd(g3-C3H5)]+ moiety yielded to met-
allomesogenic derivatives, confirming the role of the elec-
tron delocalisation in the mesomorphism.
´
´
[21] F. Gomez-de la Torre, A. de la Hoz, F.A. Jalon, B.R. Manzano, A.
The c-[Pd(g3-C3H5)(pzRpy)]BF4 complexes with large
chains (13–16) showed crystalline polymorphism and enan-
tiotropic smectic mesomorphism. The lamellar spacing was
larger than the estimated molecular length of a single mol-
´
´
´
Otero, A.M. Rodrıguez, M.C. Rodrıguez-Perez, Inorg. Chem. 37
(1998) 6606.
[22] F. Go´mez-de la Torre, A. de la Hoz, F.A. Jalo´n, B.R. Manzano,
´
´
A.M. Rodrıguez, J. Elguero, M. Martınez-Ripoll, Inorg. Chem. 39
(2000) 1152.

778
M.C. Torralba et al. / Journal of Organometallic Chemistry 691 (2006) 765–778
´
[23] J. Elguero, A. Fruchier, A. de la Hoz, F.A. Jalon, B.R. Manzano, A.
[29] P. Bhattacharyya, A.M.Z. Slawin, M.B. Smith, J. Chem. Soc.,
Dalton Trans. (1998) 2467.
´
Otero, F. Gomez-de la Torre, Chem. Ber. 129 (1996) 589.
´
[24] F.A. Jalon, B.R. Manzano, B. Moreno-Lara, Eur. J. Inorg. Chem.
[30] K. Tsutsumi, S. Ogoshi, S. Nishiguchi, H. Kurosawa, J. Am. Chem.
Soc. 120 (1998) 1938.
(2005) 100.
´
[25] M.C. Torralba, M. Cano, S. Gomez, J.A. Campo, J.V. Heras, J.
[31] Y. Go, X. Wang, E.V. Anokhina, A.J. Jacobson, Inorg. Chem. 43
(2004) 5360.
[32] H.-Y. Bie, J.-H. Yu, K. Zhao, J. Lu, L.-M. Duan, J.-Q. Xu, J. Mol.
Struct. 741 (2005) 77.
[33] P. Gamez, G.A. van Albada, I. Mutikainen, U. Turpeinen, J.
Reedijk, Inorg. Chim. Acta 358 (2005) 1975.
Perles, C. Ruiz-Valero, J. Organomet. Chem. 682 (2003) 26.
[26] M. Cano, J.V. Heras, M.L. Gallego, J. Perles, C. Ruiz-Valero, E.
Pinilla, M.R. Torres, Helv. Chim. Acta 86 (2003) 3194.
[27] N. Tsukada, T. Sato, H. Mori, S. Sugawara, C. Kabuto, S. Miyano,
Y. Inoue, J. Organomet. Chem. 627 (2001) 121.
[28] C.P. Butts, J. Crosby, G.C. Lloyd-Jones, S.C. Stephen, Chem.
Commun. (1999) 1707.
[34] G. Vertogen, W.H. de Jeu, Thermotropic Liquid Crystals. Funda-
mentals, Springer, Heidelberg, Germany, 1988.