Mesogenic palladium complexes with pincer ligands derived from dipicolinic acid

Article abstract of DOI:10.1021/ic0001457

4-Substituted pyridine-2,6-dicarboxylic acids, (E)-dipicH₂, and 4-substituted pyridine-2,6-bis(thiocarboxylic) acids, (E)-pdtcH₂, (E = OC(n)H(2n+1), SC(n)H(2n+1)) have been synthesized and used as O,N,O- and S,N,S-pincer ligands with palladium. In the fourth coordination site the complexes bear 4-decyloxy-4'-stilbazole (L¹), 4-decyloxy-N-(4-pyridylmethylene)anilines (L²), decyl 4-pyridinecarboxylate (L³), 4-(4'-decyloxyphenyl)pyridinecarboxylate (L⁴), 4-(3',4',5'-tridecyloxybenzyl)pyridinecarboxylate (L⁵), 4-isocyano-l-decyloxybenzene (L⁶), or 4-isocyano-4'-decyloxybiphenyl (L⁷). Thermotropic mesomorphism is observed for the (E)-dipic complexes with L⁵ and n = 12, which display columnar phases. The complexes with S,N,S-pincers show an important depression in the melting point compared to their O,N,O homologues and this change gives rise to mesomorphic materials (Sc). However, in the case of L⁵ the mesomorphic behavior observed for the O,N,O derivative is lost in its S,N,S analogue. The alkylsulfanyl compounds exhibit lower transition temperatures and wider mesophase ranges than their alkoxy analogues.

Full text of DOI:10.1021/ic0001457

Inorg. Chem. 2000, 39, 3645-3651
3645
Mesogenic Palladium Complexes with Pincer Ligands Derived from Dipicolinic Acid†
Pablo Espinet,* Esther Garc´ıa-Orodea, and Jesu´s A. Miguel
Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad de Valladolid,
47005 Valladolid, Spain
ReceiVed February 11, 2000
4-Substituted pyridine-2,6-dicarboxylic acids, (E)-dipicH2, and 4-substituted pyridine-2,6-bis(thiocarboxylic) acids,
(E)-pdtcH2, (E ) OCnH2n+1, SCnH2n+1) have been synthesized and used as O,N,O- and S,N,S-pincer ligands with
palladium. In the fourth coordination site the complexes bear 4-decyloxy-4′-stilbazole (L1), 4-decyloxy-N-(4-
pyridylmethylene)anilines (L2), decyl 4-pyridinecarboxylate (L3), 4-(4′-decyloxyphenyl)pyridinecarboxylate (L4),
4-(3′,4′,5′-tridecyloxybenzyl)pyridinecarboxylate (L5), 4-isocyano-1-decyloxybenzene (L6), or 4-isocyano-4′-
decyloxybiphenyl (L7). Thermotropic mesomorphism is observed for the (E)-dipic complexes with L5 and n )
12, which display columnar phases. The complexes with S,N,S-pincers show an important depression in the
melting point compared to their O,N,O homologues and this change gives rise to mesomorphic materials (SC).
However, in the case of L5 the mesomorphic behavior observed for the O,N,O derivative is lost in its S,N,S
analogue. The alkylsulfanyl compounds exhibit lower transition temperatures and wider mesophase ranges than
their alkoxy analogues.
Introduction
alkyl or alkyloxy tails.3 On the other hand, attempts to produce
complexes with a net dipolar moment of the type trans-[PdX2-
The field of metallomesogens (liquid crystals based on metal-
containing molecules) is growing quite fast because of interest
in exploring the new structural possibilities that metals offer,
and the consequences of their presence on the properties of the
material.1 Some types of ligands, salicylaldimines2 or imines1e
for example, have been systematically explored but there are
still many other interesting systems and metals that have not
been used for liquid crystal systems and that can give new
physical properties or permit a better control of the desired
properties. Therefore, it is of interest to design and prepare novel
structures to add to the still-limited types of metallomesogenic
materials.
The use of ligands making strong bonds to the metal helps
to produce reasonably inert and thermally robust materials, and
chelating ligands are particularly suited for this purpose.
Moreover, for calamitic materials it is convenient to look for
molecules which are anisotropic in shape but which will pack
easily to fill the space efficiently, which possess a high
anisotropy of polarizability, and, in most cases, which possess
a permanent dipole.
LL′] usually lead to symmetrization to a mixture of trans-
[PdX2L2] and trans-[PdX2L′2] and this is difficult to avoid when
using monodentate ligands. With these ideas in mind we have
designed a new structural type of metal-containing liquid crystals
based on the dipicolinic acid and its derivatives.
Although many different bidentate chelating moieties have
been successfully used for the design of metallomesogens, there
are only a few examples of tridentate binding units, namely:
(a) an example of lyotropic mesophase with Ru(II) coordinated
to terminal 4′-substituted terpyridine derivatives;4 (b) the C,N,N
chelating ligand 6′-phenyl-2,2′-bipyridine cyclometalated to
Pd(II), which displays a monotropic nematic phase;5 and (c)
some examples exhibiting discotic mesomorphism (dinuclear
copper(II) complexes derived from tridentate 1,3,5-triketonate
ligands;6 mononuclear Ni(II), Cr(0), Mo(0), and W(0) with the
tridentate ligand 1,4,7-triazacyclononane;7 and (pyridinediyl-
2,6-dimethanolato)dioxomolybdenum complexes).8
We have previously reported on palladium complexes con-
taining the dipicolinate anion9 and its sulfur analogue, 2,6-bis-
(thiocarboxylate),10 on which we explored the coordination
A way to prevent intermolecular interactions that are too
strong, which are responsible for the undesired high melting
points often found in metal-based molecules, is to incorporate
some asymmetry in the molecular shape, together with long
(3) Baena, M. J.; Espinet, P.; Ros, M. B.; Serrano, J. L. Angew. Chem.,
Int. Ed. Engl. 1991, 30, 711.
(4) Holbrey, J. D.; Tiddy, G. J. T.; Bruce, D. W. J. Chem. Soc., Dalton
Trans. 1995, 1769.
(5) Neve, F.; Ghedini, M.; Crispini, A. J. Chem. Soc., Chem. Commun.
1996, 2463.
† Dedicated to Professor J. Barluenga on the occasion of his 60th birthday.
* E-mail: espinet@qi.uva.es.
(1) (a) Giroud-Godquin, A.-M.; Maitlis, P. M. Angew. Chem., Int. Ed.
Engl. 1991, 30, 375. (b) Espinet, P.; Esteruelas, M. A.; Oro, L. A.;
Serrano, J. L.; Sola, E. Coord. Chem. ReV. 1992, 117, 215. (c)
Inorganic Materials; Bruce, D., O’Hare, D., Eds.; John Wiley and
Sons: Chichester, U.K., 1992; Chapter 8. (d) Hudson, S. A.; Maitlis,
P. M. Chem. ReV. 1993, 93, 861. (e) Metallomesogens; Serrano, J. L.,
Ed.; VCH: Weinheim, Germany, 1996. (f) Collinson, S. R.; Bruce,
D. W. In Transition Metal in Supramolecular Chemistry; Sauvage, J.
P., Ed.; John Wiley and Sons: Chichester, U.K., 1999; Chapter 7, p
285. (g) Donnio, B.; Bruce, D. W. Struct. Bonding (Berlin) 1999, 95,
193.
(6) (a) Lai, C. K.; Serrette, A. G.; Swager, T. M. J. Am. Chem. Soc. 1992,
114, 7949. (b) Serrette, A. G.; Lai, C. K.; Swager, T. M. Chem. Mater.
1994, 6, 2252.
(7) (a) Lattermann, G.; Schmidt, S.; Kleppinger, R.; Wendorff, J. H. AdV.
Mater. (Weinheim, Ger.) 1992, 4, 30. (b) Schmidt, S.; Lattermann,
G.; Kleppinger, R.; Wendorff, J. H. Liq. Cryst. 1994, 16, 693.
(8) Serrette, A. G.; Swager, T. M. Angew. Chem., Int. Ed. Engl. 1994,
33, 2342.
(9) Espinet, P.; Miguel, J. A.; Garc´ıa-Granda, S.; Miguel, D. Inorg. Chem.
1996, 35, 2287.
(10) Espinet, P.; Lorenzo, C.; Miguel, J. A.; Bois, C.; Jeannin, Y. Inorg.
Chem. 1994, 33, 2052.
(2) Hoshino, N. Coord. Chem. ReV. 1998, 174, 77.
10.1021/ic0001457 CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/11/2000

3646 Inorganic Chemistry, Vol. 39, No. 16, 2000
Espinet et al.
Chart 1
Scheme 1a
behavior on Pd with regard to their possible functionalization
to produce metallomesogens. These compounds showed high
thermal stability and usually displayed a rigid tridentate
coordination (“pincer” ligands). The coordination of a long-
tail ligand in the fourth coordination site was not sufficient to
induce mesogenic properties in the material. To obtain liquid
crystals based on this chemical system it seemed to us a
reasonable strategy to further elaborate the pyridinic ring of the
dipic or pdtc ligands, or to incorporate additional benzene rings
in the ligands coordinated in the fourth position. In this paper
we report the preparation and thermal behavior of uncommon
mesogens containing these modified pincer ligands with pal-
ladium and 4-decyloxy-4′-stilbazole (L1), 4-decyloxy-N-(4-
pyridylmethylene)anilines (L2), decyl 4-pyridinecarboxylate (L3),
4-(4′-decyloxyphenyl)pyridinecarboxylate (L4), 4-(3′,4′,5′-tri-
decyloxybenzyl)pyridinecarboxylate (L5), 4-isocyano-1-decyl-
oxybenzene (L6), or 4-isocyano-4′-decyloxybiphenyl (L7) oc-
cupying the fourth coordination position (see Chart 1).
a Reagents and conditions: i, BuOH, sulfuric acid, toluene, reflux;
ii, CnH2n+1Br, K2CO3, DMF, 65 °C; iii, for derivatives a, b, d, e, KOH,
EtOH; HCl; for c, f, HBr, (Bu4N)Br; iv, PCl5, CCl4, reflux; EtOH; v,
NH4SCN, acetic acid, H2O, reflux; vi, (H4N)2S, EtOH, reflux; vii,
CnH2n+1Br, DMF; viii, SOCl2, reflux; H2S, Py, THF; HCl.
Scheme 2
Results and Discussion
Synthesis, Characterization, and Mesogenic Behavior of
4-Alkoxypyridine-2,6-dicarboxylic Acids, 4-Alkylsulfanyl-
pyridine-2,6-dicarboxylic Acids, and Their Metal Complexes.
The synthetic steps used to prepare the 4-substituted dipicolinic
acids are summarized in Scheme 1. Chelidamic acid (I) was
esterified with butanol to yield dibutyl 4-hydroxypyridine-2,6-
dicarboxylate (II). Treatment with CnH2n+1Br in the presence
of K2CO3, in anhydrous dimethylformamide (DMF), generated
the dibutyl 4-alkoxypyridine-2,6-dicarboxylate (III). The sulfur
analogues, diethyl 4-alkylsulfanylpyridine-2,6-dicarboxylates
(VII), were obtained following a procedure described by
Markees.11 Upon hydrolyses of these esters, the corresponding
4-substituted pyridine-2,6-dicarboxylic acids (VIII), ((E)-
dipicH2, where E ) OCnH2n+1, SCnH2n+1), were obtained.
The acids were coordinated to palladium by reaction with
[Pd(AcO)2]3 in acetonitrile to give 1 (Scheme 2), as reported
previously by us for [Pd(dipic)(NCCH3)].9 The compounds gave
satisfactory C, H, and N analyses and their IR spectra were
consistent with the proposed structure. The 1H NMR spectra of
the acetonitrile complexes 1 in CDCl3 solution reveal the
coexistence in solution of the dimeric and monomeric isomers
shown in Scheme 2, in a ratio ca. 45:55, respectively, at 293
K.
isolated. The reason for the instability of the isocyanide
complexes is discussed later.
The mesogenic behavior of 2-6 is summarized in Table 1
and in Figure 1. The free acids and their related Pd(II) complexes
with acetonitrile (1), decyloxystilbazole (2c), (pyridylmethyl-
ene)aniline (3c), decyl pyridinecarboxylate (4c), and phenyl
pyridinecarboxylate (5c) are high-melting solids which, with
the exception of 4c, decompose before melting.
The use of L5, containing three alkoxy chains, noticeably
lowered the melting points of the complexes, but complexes
6b and 6e still were not mesomorphic. However, when the
length of the alkyl chain in the pyridine ring of the (E)-dipic
ligand was increased from n ) 8 to n ) 12, the complexes (6c
and 6f) displayed mesomorphism. Their fluidity and optical
textures determined by polarized optical microscopy, on cooling
from the isotropic phase, show birefringent areas in the form
4-Substituted pyridine ligands L (L1-L5) easily displace the
weakly coordinated acetonitrile (Scheme 2) to give the corre-
1
sponding monomeric complexes 2-6. Their H NMR spectra
in CDCl3 show only the resonances expected for the monomo-
lecular structure. However, the reaction with isocyanides (L6
and L7) produced mixtures of complexes which could not be
(11) Markees, D. G. J. Org. Chem. 1963, 28, 2530.

Mesogenic Palladium Complexes with Pincer Ligands
Inorganic Chemistry, Vol. 39, No. 16, 2000 3647
Table 1. Optical, Thermal, and Thermodynamic Data for
Compounds 2-14
compound
transitiona
temp. (°C)
∆H (kJ mol-1
)
2c
3c
4c
5c
6b
6c
C - Ib
256c
C - Ib
254c
C - I
181.5
192.6
117.5
89.2
110.1
119.2
73.2
113.0
251.7
268.2
169.7
241.5
261.4d
118.9
230.7
259.5
147.7
191.4
261.2
88.2
38.4
C - Ib
C - I
45.6
8.9
4.9
36.1
8.2
5.1
44.6
6.5
9.8
33.7
4.5
34.5
33.0
5.6
C - Colh
Colh - I
C - I
6e
6f
C - Colh
Colh - I
C - SC
SC - Ib
C - C′
C′ - SC
SC - Ib
C - C′
C′ - SC
SC - Ib
C - C′
C′ - SC
SC - I
8a
8b
8c
8e
9a
10.0
26.8
10.1
15.6
2.6
C - C′
C′ - C′′
C′′ - I
183.5
219.2
208.3
207.6
87.8
33.3
20.4f
e
I - SC
SC - C
C - C′
C′ - I
9b
9c
20.8
25.5
21.9f
213.9d
210.7
207c
e
I - SC
SC - C
C - C′
C′ - C′′
C′′ - I
71.6
21.9
2.4
26.3
1.1
14.4
18.6
4.9
17.2
2.7
43.5
53.7
13.9
35.3
31.5
2.3
2.6
0.9
29.7
7.8
21.8
2.4
125.9
217.5d
216.1d
212.4
88.0
111.1
192.2
209.5d
166.0
215.9
55.8
181.4
202.2
233.6d
232.9
202.2
198.6
126.7
179.6
183.8
226.4
63.5
181.9
229.3
84.2
157.2
173.6
211.3
150.2
201.8
139.2
208.7
e
I - SC
SC - C
C - C′
C′ - C"
C" - SC
SC - I
C - I
9e
10c
11c
12c
13c
14a
Figure 1. Thermotropic behavior of Pd complexes with O,N,O- and
S,N,S-pincers and the ligands L in the fourth coordination site. C,
crystal; SC, smectic C; N, nematic; Colh, columnar hexagonal; m,
monotropic transition.
C - I
C - I
C - I
C - N
N - I
because complexes 6, bearing four long chains, can no longer
be considered rodlike.
I - N
e
N - SC
It is interesting to note that the substitution of E ) OCnH2n+1
for E ) SCnH2n+1 does not produce a noticeable effect for C8
(complexes 6b and 6e), but induces a clear decrease in the
melting temperature and range of mesophase for the longer C12
chain (compounds 6c and 6f). This is in agreement with the
effect noticed for some organic alkoxy- and alkylsulfany-
substituted biphenyls with terminal isocyanato substituents.13
Synthesis, Characterization, and Mesogenic Behavior of
the 4-Substituted pyridine-2,6-bis(thiocarboxylic) Acids
andTheir Metal Complexes. The new 4-substituted pyridine-
SC - C
C - C′
C′ - C′′
C′′ - SC
SC - I
14b
9.6
14c
14d
C - C′
C′ - SC
SC - I
C - C′
C′ - SC
SC - N
N - I
C - SC
SC - I
C - SC
SC - I
13.2
21.3
10.6
4.7
32.1
0.4
1.6
30.5
7.8
2,6-bis(thiocarboxylic) acids, (E)-pdtcH2 (IX) (E ) OCnH2n+1
,
14e
14f
SCnH2n+1), were synthesized as shown in Scheme 1. The
corresponding acid chlorides, obtained by treatment with thionyl
chloride of the (E)-dipicH2 acids (VIII), were reacted with SH2
in THF, and the resulting precipitate was treated with diluted
hydrochloric acid.
24.3
10.6
a C, crystal; SC, smectic C; I, isotropic liquid; N, nematic; Colh,
columnar hexagonal. b Transition with decomposition. c Observed by
means of polarized-light microscopy. d Peak temperature. e Monotropic
transition. f Combined enthalpies.
These acids were reacted with [Pd(acac)2], giving the bi-
nuclear complexes 7 (Scheme 3). The analytical results, the two
(12) Sua´rez, M.; Lehn, J. M.; Zimmerman, S. C.; Skoulios, A.; Heinrich,
B. J. Am. Chem. Soc. 1998, 120, 9526.
(13) Hird, M.; Seed, A. J.; Toyne, K. J.; Goodby, J. W.; Gray, G. W.;
McDonnell, D. G. J. Mater. Chem. 1993, 3, 851.
of “petals” coalescing to produce broken-shaped units and dark
areas of uniform extinction, characteristic of a columnar phase
(apparently hexagonal, Figure 2).12 This is not unexpected

3648 Inorganic Chemistry, Vol. 39, No. 16, 2000
Espinet et al.
cm-1, at wavenumbers ca. 90 cm-1 higher than those for the
free isonitriles, as reported for other palladium isocyanide
1
compounds.10,14 The H NMR spectra of 8-14 show a singlet
corresponding to two equivalent pyridinic hydrogens in a
monomeric species, as proposed in Scheme 3.
The dinuclear derivatives 7 are not mesogenic. This is not
surprising considering their unfavorable length-to-width ratio.
However, they are useful precursors for the synthesis of the
mononuclear calamitic molecules 8-14. The mesogenic be-
havior of the latter is summarized in Table 1 and in Figure 1.
Comparing compounds with the same chain length for L1-
L5 it can be seen that, with the unexpected exception of L4,15
each S,N,S derivative shows an important depression in the
melting point relative to its O,N,O homologue. In most cases
this change gives rise to mesomorphic behavior (SC), but in the
case of L5 the mesomorphic behavior observed for the O,N,O
compound (Colh) is lost in the S,N,S homologue. Comparing
the Pd(O,N,O) and Pd(S,N,S) fragments it seems reasonable to
assume that substitution of O for the less electronegative S can
produce a reduction in the polarity of each bond to Pd, and in
the polarity of the fragment as a whole. Moreover, the acceptor
character of this moiety toward the fourth ligand Ln can be
substantially reduced. Both effects can cooperate to reduce the
intramolecular interactions and depress the melting points. In
the case of the columnar mesophases (L5), where intense core-
to-core interactions seem substantial for LC behavior after
melting of the chains, the weakening of these core interactions
suppresses the LC behavior, even at lower temperatures.14 Thus,
this is another example of columnar mesophases being sup-
pressed when polar groups are replaced by less polar ones in
the center of disklike molecules: the core polarity is decreased
and the tendency to give columnar association of the cores
diminishes.16
Figure 2. Microphotograph showing the texture of the columnar
mesophase of 6f formed at 105 °C on cooling the isotropic liquid.
The complexes with stilbazole (L1) undergo some decom-
position in the transition to the isotropic liquid, possibly because
of the high temperatures (ca. 260 °C) at which the clearing
happens. The comparison between the alkylsulfanyl compound
8e and its oxygen-containing analogue (compound 8b) shows
that, again, substitution of E ) OCnH2n+1 for E ) SCnH2n+1
causes an important decrease in the melting point while the
clearing temperature is maintained, thus producing a broadening
of the mesogenic range.
Scheme 3
The complexes 9 containing the pyridine-imines L2 have
lower melting points than those of the corresponding derivatives
with stilbazole (complexes 8), but are only monotropic liquid
crystals. The alkylsulfanyl derivative 9e also shows a melting
point lower than that of the alkoxy analogue 9b and displays
enantiotropic, instead of monotropic, liquid crystal behavior.
Neither the pyridinecarboxylate derivative 10c, with just one
phenyl ring, nor 11c is mesogenic. A comparison can be made
among 11c, 8c, and 9c (phenyl pyridinecarboxylate, stilbazole,
and (pyridylmethylene)aniline derivatives, respectively). The
decreased planarity of the pyridinecarboxylate ligand (L4)
compared to the imine (L2) or stilbazole (L1) ligands, in
concordance with X-ray structures of trans-stilbene,17 ben-
zylideneanilines18 and phenyl benzoates,19 might be a further
difficulty for 11c to form mesophases.
well-separated ν(CdO) bands in their IR spectra in the solid
state, and the nonequivalence of the two pyridinic hydrogens
observed in their 1H NMR spectra, are consistent with the
dimeric structure proposed. Reactions of 7 with 4-substituted
pyridines (L1-L5) yielded the mononuclear compounds 8-12
with acceptable yields. Moreover, in contrast to the (E)-dipic
complexes, the reactions with isocyanides (L6, L7) gave the
stable isocyanide compounds 13 and 14. It seems that the
remarkable difference in stability between the O,N,O- and the
S,N,S-pincers, when isocyanide is to be coordinated in the fourth
position, is related to the harder nature of the Pd core in the
O,N,O-complexes (π-back-donation is important in stabilizing
the Pd-isocyanide bond) and to the high trans influence of the
isocyanide ligand which induces a long Pd-N bond. This
elongation very highly destabilizes the strained situation existing
in the O,N,O-complexes involving short C-O distances,
whereas it is compatible with the less strained S,N,S-complexes
involving longer Pd-S distances.9,10 The IR spectra of the
isocyanide complexes show a ν(CtN) absorption around 2215
(14) Coco, S.; D´ıez-Expo´xito, F.; Espinet, P.; Ferna´ndez-Mayordomo, C.;
Mart´ın-Alvarez, J. M.; Levelut, A. M. Chem. Mater. 1998, 10, 3666.
(15) In fact, the temperature given for 5c is a decomposition temperature
whereas the temperature given for 11c is a real melting point.
(16) Pegenau, A.; Go¨ring, P.; Tschierske, C. J. Chem. Soc., Chem. Commun.
1996, 2563.
(17) Young, W. R.; Aviram, A.; Cox, R. J. J. Am. Chem. Soc. 1972, 94,
3976.

Mesogenic Palladium Complexes with Pincer Ligands
Inorganic Chemistry, Vol. 39, No. 16, 2000 3649
Complex 13c, with 4-isocyano-1-decyloxybenzene (L6), is not
a mesogen, but all of the biphenyl isocyanide compounds 14a-
14f (L7) display liquid crystal behavior, indicating the necessity
of an extended conjugated system. The biphenyl isocyanide
complexes form more stable phases and exhibit better liquid
crystal properties than the stilbazole or imine compounds. This
may be related to the planarity and linearity of the biphenyl
isocyanides which exhibit mesomorphism by themselves.20 The
biphenyl isocyanide compounds show both SC and N phases
when the pyridine rings have a short tail (n ) 4), and only SC
phases when the terminal chain contains 8 or 12 carbon atoms.
The SC mesophases display two microscopic textures, schlieren
and focal-conic. Both textures are formed directly on cooling
from the isotropic liquid, but the schlieren texture is more
abundant. The nematic phases were identified by the appearance
of droplets and the formation of a typical nematic schlieren
texture.
used without further purification. C, H, and N analyses were carried
out on a Perkin-Elmer 2400 microanalyzer. All of the new compounds
gave satisfactory elemental analyses (Table S1, Supporting Information).
IR spectra were recorded on a Perkin-Elmer FT-1720X spectrometer
using Nujol mulls between polyethylene plates. 1H NMR spectra were
recorded on Bruker AC-300 or ARX-300 MHz spectrophotometers.
The textures of the mesophases were studied with a Leitz microscope
equipped with a Mettler FP82HT hot stage and a Mettler FP90 central
processor and polarizers at a heating rate of approximately 10 °C min-1
.
Transition temperatures and enthalpies were measured by differential
scanning calorimetry, with a Perkin-Elmer DSC-7 operated at a scanning
rate of 10 °C min-1 on heating. The apparatus was calibrated with
indium (156.6 °C, 28.5 J g-1) as standard, the samples were sealed in
aluminum capsules in air, and the holder atmosphere was dry nitrogen.
Only representative syntheses are described because they are very
similar for the rest of the compounds in each series.
Dibutyl 4-Hydroxypyridine-2,6-dicarboxylate (II). Compound II
was synthesized as reported for dibutyl pyridine-2,5-dicarboxylate using
chelidamic acid (5.00 g, 24.8 mmol) as starting material,28 except that
the final product was chromatographed over SiO2 using CHCl3/EtOAc
(5:1) as eluent. Yield 82%.1H NMR (CDCl3, δ, ppm): 7.33 (s broad,
2H, H3,5), 4.37 (t, J ) 6.5 Hz, 4H, O-CH2), 1.74 (m, 4H, O-CH2-
CH2), 1.42 (m, 4H, O-CH2-CH2-CH2-), 0.94 (t, 6H, O-CH2-CH2-
CH2-CH3). IR (Nujol, cm-1) ν(CdO): 1735.
Again, the alkylsulfanyl derivatives 14d-f exhibit lower
transition temperatures and significantly wider mesophase ranges
than their alkoxy analogue derivatives 14a-c. Thus, this
interesting and favorable influence seems to be quite constant
in different types of derivatives.
Dibutyl 4-Octyloxypyridine-2,6-dicarboxylate (III). Compound II
(5.00 g, 16.9 mmol) and K2CO3 (7.00 g, 50.6 mmol) were combined
in DMF (30 mL) under a N2 atmosphere. Octylbromide (3.26 g, 16.9
mmol) was added, and the mixture was heated to 65 °C. After 20 h,
the reaction was cooled to room temperature and the DMF was distilled
off. The residue was diluted with water and extracted into CH2Cl2.
The combined organic extracts were washed with water, dried (MgSO4),
and evaporated. The product was purified on a silica gel column using
Conclusions
The use of a series of new ligands, 4-substituted pyridine-
2,6-dicarboxylic acids and 4-substituted pyridine-2,6-bis(thio-
carboxylic) acids, allows the synthesis of O,N,O- and S,N,S-
palladium complexes, respectively, that display liquid crystal
properties. These ligands are remarkable as they permit building
of a promesogenic core taking three coordination positions on
the metal.
The O,N,O-pincers usually give rise to materials with very
high melting points and decomposition is often observed. The
substitution of O for the less electronegative S produces a
reduction of the intramolecular interactions, and lower melting
points (often producing the appearance of mesophases) are
observed for the S,N,S-pincer complexes. The same effect
(lowering of the melting points, often producing a broadening
of the mesogenic range) is observed when alkyloxy chains are
substituted by alkylsulfanyl.
1
CHCl3/EtOAc (5:2) as eluent. Yield 87%. H NMR (CDCl3, δ, ppm):
7.72 (s, 2H, H3,5), 4.37 (t, J ) 6.7 Hz, 4H, O-CH2), 4.10 (t, J ) 6.4
Hz, 2H, O-CH2), 1.80 (m, 4H, O-CH2-CH2-), 1.46 (m, 4H,
O-CH2-CH2-CH2-), 1.29 (overlapped peaks, 12H, -CH2-), 0.95
(t, 6H, CH3-), 0.85 (t, 3H, -CH3). IR (Nujol, cm-1): ν(CdO) 1751,
1723.
4-Octyloxypyridine-2,6-dicarboxylic Acid (VIIIb). Hydrolysis of
dibutyl 4-octyloxypyridine-2,6-dicarboxylate (IIIb) (3.44 mmol) was
achieved by boiling in aqueous ethanolic KOH for 2 h. After
acidification with 5% HCl solution, the precipitate was washed with
water and dried under vacuum; mp 156 °C. Yield 87%. Other (E)-
dipicH2 melted in the range 140-170 °C. 1H NMR ((CD3)2CO, δ,
ppm): 7.86 (s, 2H, H3,5), 4.35 (t, J ) 6.5 Hz, 2H, O-CH2), 1.86 (m,
2H, O-CH2-CH2-), 1.52 (m, 2H, -O-CH2-CH2-CH2), 1.35
(overlapped peaks, 8H, -CH2-), 0.87 (t, 3H, CH3-). IR (Nujol, cm-1):
ν(CdO) 1730.
Experimental Section
Literature methods were used to prepare [Pd(µ-OAc)2]3,21 [Pd-
(acac)2],22 and the ligands L1,23 L2-L4,24 L6,25 and L7.26 L5 was
synthesized as described for L4 using 3,4,5-tridecyloxybenzylic alco-
hol.27 Chelidamic acid was obtained from commercial sources and was
Diethyl 4-Octylsulfanylpyridine-2,6-dicarboxylate (VIIe). Com-
pound VIIe was synthesized as reported for diethyl 4-butylsulfanyl-
pyridine-2,6-dicarboxylate,11 from ammonium 2,6-dicarbethoxypyridine-
4-thiolate (0.50 g, 1.8 mmol) and octylbromide (0.39 g, 2.0 mmol) in
DMF (5 mL). The product was purified on a silica gel column using
(18) (a) Burgi, H. B.; Dunitz, J. D. HelV. Chim. Acta 1970, 53, 1747. (b)
Bernstein, I.; Izak, I. J. Chem. Soc., Perkin Trans. 2 1976, 429. (c)
Van, G. V.; Vijayan, K. Mol. Cryst. Liq. Cryst. 1977, 42, 249. (d)
Bryan, R. F.; Forcier, P. G. Mol. Cryst. Liq. Cryst. 1980, 60, 133.
(19) (a) Arora, S. L.; Fergason, J. L.; Taylor, T. R. J. Org Chem. 1970,
35, 4055. (b) Adams, J. M.; Morsi, S. E. Acta Crystallogr., Sect. B
1976, 32, 1345. (c) Bumeister, V.; Harting, H.; Gdaniec, M.; Jaskolki,
M. Mol. Cryst. Liq. Cryst. 1981, 69, 119. (d) Haase, W.; Paulus, H.;
Pendzialek, R. Mol. Cryst. Liq. Cryst. 1983, 101, 429.
(20) Kaharu, T.; Tanaka, T.; Sawada, M.; Takahashi, S. J. Mater. Chem.
1994, 4, 859.
(21) Stephenson, T. A.; Morehouse, S. M.; Powell, A. R.; Heffer, J. P.;
Wilkinson, G. J. Chem. Soc. 1965, 3632.
(22) Grinberg, A. A.; Simonova, L. K. Zh. Prikl. Khim. 1953, 26, 880;
Chem. Abstr. 1953, 47, 11060g.
(23) Bruce, D. W.; Dunmur, D. A.; Lalinde, E.; Maitlis, P. M.; Styring, P.
Liq. Cryst. 1988, 3, 385.
1
CHCl3/EtOAc (1:1) as eluent. Yield 82%. H NMR (CDCl3, δ, ppm):
8.02 (s, 2H, H3,5), 4.45 (q, J ) 7.2 Hz, 4H, O-CH2), 3.05 (t, J ) 7.3
Hz, 2H, S-CH2), 1.72 (m, 2H, S-CH2-CH2-), 1.43 (t, 6H, -CH3),
1.27 (overlapped peaks, 10H, -CH2-), 0.84 (t, 3H, CH3-). IR (Nujol,
cm-1): ν(CdO) 1714.
4-Octylsulfanylpyridine-2,6-dicarboxylic Acid (VIIIe). Compound
VIIIe was synthesized by hydrolysis of VIIe as described for III; mp
143 °C. Yield 84%. Other (E)-dipicH2 melted in the range 120-165
°C. 1H NMR ((CD3)2CO, δ, ppm): 8.16 (s, 2H, H3,5), 3.28 (t, J ) 7.3
Hz, 2H, S-CH2), 1.87 (m, 2H, S-CH2-CH2-), 1.53 (m, 2H, S-CH2-
CH2-CH2-), 1.31 (overlapped peaks, 8H, -CH2-), 0.86 (t, 3H,
CH3-). IR (Nujol, cm-1): ν(CdO) 1749, 1725, 1703.
(24) Marcos, M.; Ros, M. B.; Serrano, J. L.; Esteruelas, M. A.; Sola, E.;
Oro, L.; Barbera´, J. Chem. Mater. 1990, 2, 748.
(25) Alejos, P.; Coco, S.; Espinet, P. New J. Chem. 1995, 19, 799.
(26) Benouazzane, M.; Coco, S.; Espinet, P.; Mart´ın-Alvarez, J. M. J. Mater.
Chem. 1995, 5, 441.
(27) Balagurusamy, V. S. K.; Ungar, G.; Percec, V.; Johansson G. J. Am.
Chem. Soc. 1997, 119, 1539.
(28) Utley, J. H. P.; Gao, Y.; Gruber, J.; Lines, R. J. Mater. Chem. 1995,
5, 1297.

3650 Inorganic Chemistry, Vol. 39, No. 16, 2000
Espinet et al.
4-Octyloxypyridine-2,6-bis(thiocarboxylic) Acid (IXb). The fol-
lowing is a modification of the procedure reported for pyridine-2,6-
bis(thiocarboxilic) acid.29 A mixture of VIIIb (1.00 g, 3.19 mmol) and
SOCl2 (30 mL) was refluxed under N2 atmosphere, until the evolution
of HCl gas ceased (ca. 2 h). After the mixture was cooled to room
temperature, the excess of thionyl chloride was distilled off and the
residue was dissolved in dry THF (30 mL). Pyridine (1.18 g, 14.9 mmol)
was added, and SH2 was bubbled for 4 h. The resulting yellow
suspension was filtered, and the precipitate was washed with cold THF
(2 × 5 mL), stirred with dilute HCl (20 mL), washed with water, and
then vacuum-dried; mp 65 °C. Yield 60%. Other (E)-dptcH2 melted in
6b: Yield 60%. 1H NMR (CDCl3, δ, ppm): 8.61, 8.00 (AA′XX′, J
) 6.6 Hz, 4H, NC5H4), 7.36 (s, 2H, H3,5), 6.62 (s, 2H, H2,6 L5), 5.31
(s, 2H, OCH2), 4.15 (t, J ) 6.5 Hz, 2H, OCH2), 3.96 (m, 6H, OCH2),
1.83 (m, 8H, -CH2), 1.57 (m, 8H, -CH2), 1.27 (overlapped peaks,
44H, -CH2), 0.88 (m, 12H, -CH3). IR (Nujol, cm-1): ν(CdO) 1723,
1669.
1
6e: Yield 78%. H NMR (CDCl3, δ, ppm): 8.58, 7.99 (AA′XX′, J
) 6.6 Hz, 4H, NC5H4), 7.59 (s, 2H, H3,5), 6.60 (s, 2H, H2,6 L5), 5.29
(s, 2H, OCH2), 3.94 (m, 6H, OCH2), 3.06 (t, J ) 7.3 Hz, 2H, SCH2),
1.72 (m, 8H, -CH2), 1.45 (m, 8H, -CH2), 1.25 (overlapped peaks,
44H, -CH2), 0.86 (m, 12H, -CH3). IR (Nujol, cm-1): ν(CdO) 1733,
1678, 1662.
1
the range 70-80 °C. H NMR (CDCl3, δ, ppm): 7.64 (s, 2H, H3,5),
4.12 (t, J ) 6.5 Hz, 2H, O-CH2), 1.82 (m, 2H, O-CH2-CH2-), 1.42
(m, 2H, O-CH2-CH2-CH2-), 1.30 (m, 8H, -CH2-), 0.88 (t, 3H,
CH3-). IR (Nujol, cm-1): ν(CdO) 1669; ν(S-H) 2539, 2511.
Synthesis of 7b. [Pd(acac)2] (0.47 g, 1.53 mmol) and the acid IXb
(0.5 g, 1.53 mmol) were stirred in CHCl3 (30 mL) for 24 h. The orange
solution was filtered through Celite and the solvent was removed under
reduced pressure. The resulting orange solid was washed with acetone
(3 × 5 mL), collected on a frit, and dried in vacuum; mp 219 °C (dec).
Yield 66%. Other complexes 7 decomposed above 200 °C except 7a
and 7c (both with n ) 4) which seem thermally stable below 300 °C.
1H NMR (CDCl3, δ, ppm): 7.47, 7.24 (d, J ) 2.9 Hz, 4H, H3, H5),
4.24 (t, J ) 6.5 Hz, 4H, OCH2), 1.90 (m, 4H, -CH2), 1.57 (m, 4H,
-CH2), 1.30 (overlapped peaks, 16H, -CH2), 0.88 (m, 6H, -CH3).
IR (Nujol, cm-1): ν(CdO) 1689, 1636.
4-Octylsulfanylpyridine-2,6-bis(thiocarboxylic) acid (IXe). A
mixture of VIIIe (0.70 g, 2.13 mmol) and SOCl2 (6 mL) in toluene
(30 mL) was refluxed until the evolution of HCl gas ceased (ca. 2 h).
The solvent and the excess of thionyl chloride were distilled off, and
the resulting diacid chloride was treated with SH2 as described for IXb.
Yield 61%. 1H NMR (CDCl3, δ, ppm): 7.92 (s, 2H, H3,5), 3.06 (t, J )
7.3 Hz, 2H, S-CH2), 1.80 (m, 2H, S-CH2-CH2-), 1.46 (m, 2H,
O-CH2-CH2-CH2-), 1.28 (overlapped peaks, 8H, -CH2-), 0.89 (t,
3H, -CH3). IR (Nujol, cm-1): ν(CdO) 1681; ν(S-H) 2564, 2530.
Synthesis of 1b and 1e. [Pd(OAc)2]3 (0.72 g, 3.19 mmol) and VIIIb
(1 g, 3.19 mmol) were stirred in acetonitrile (10 mL) for 24 h. The
precipitate 1b was collected on a frit, washed with acetonitrile (3 × 5
mL), and air-dried; mp 225 °C (dec). Yield 81%. 1H NMR (CDCl3, δ,
ppm): dimer (43%), 7.30, 7.22 (s, 4H, H3, H5), 4.15 (m, 4H, OCH2),
2.01 (s, 6H, NCCH3); monomer (57%), 7.30 (s, 2H, H3,5), 4.15 (m,
2H, OCH2), 2.42 (s, 3H, NCCH3). IR (Nujol, cm-1): ν(CdO) 1696,
1674; ν(CtN), δ(CH3) + ν(C-C) 2325, 2297. 1e was prepared
similarly; mp 201 °C (dec). Yield 76%. Other complexes 1 melted in
the range 190-230 °C with decomposition. 1H NMR (CDCl3, δ,
ppm): dimer (38%), 7.55, 7.40 (s, 4H, H3, H5), 3.04 (m, 4H, SCH2),
2.00 (s, 6H, NCCH3); monomer (62%), 7.55 (s, 2H, H3,5), 3.04 (m,
2H, SCH2), 2.42 (s, 3H, NCCH3). IR (Nujol, cm-1): ν(CdO) 1682;
ν(CtN), δ(CH3) + ν(C-C) 2323, 2295.
Synthesis of 2c. To a suspension of 1c (0.05 g, 0.10 mmol) in
dichoromethane, 4-decyloxy-4′-stilbazole (0.04 g, 0.12 mmol) was
added and the mixture was stirred for 1 h. The pale yellow precipitate
was collected on a frit, washed with acetonitrile (3 × 3 mL), and dried
in a vacuum. Yield 44%. 1H NMR (CDCl3, δ, ppm): 8.27, 7.41
(AA′XX′, J ) 6.7 Hz, 4H, NC5H4), 7.37, 6.88 (d, J ) 16.3 Hz, 2H,
-HCdCH-), 7.50, 6.92 (AA′XX′, J ) 8.8 Hz, 4H, C6H4), 7.35 (s,
2H, H3,5), 4.13 (t, J ) 6.5 Hz, 2H, OCH2), 3.99 (t, J ) 6.5 Hz, 2H,
OCH2), 1.82 (m, 4H, -CH2), 1.57 (m, 4H, -CH2), 1.27 (overlapped
peaks, 28H, -CH2), 0.88 (m, 6H, -CH3). IR (Nujol, cm-1): ν(CdO)
1663.
1
7e was prepared similarly. Yield 53%. H NMR (CDCl3, δ, ppm):
7.72, 7.48 (d, J ) 2.3 Hz, 4H, H3, H5), 3.14 (t, J ) 7.3 Hz, 4H, SCH2),
1.80 (m, 4H, -CH2), 1.52 (m, 4H, -CH2), 1.30 (overlapped peaks,
16H, -CH2), 0.87 (m, 6H, -CH3). IR (Nujol, cm-1) ν(CdO): 1689,
1634.
Synthesis of 8b. To a solution of 7b (0.05 g, 0.06 mmol) in
dichloromethane (20 mL) was added 4-decyloxy-4′-stilbazole (0.05 g,
0.16 mmol) and the mixture was stirred for 17 h. The solvent was
evaporated off, and the yellow residue was washed with diethyl ether
(3 × 5 mL), filtered to collect the product, and dried in a vacuum.
1
Yield 63%. H NMR (CDCl3, δ, ppm): 8.47, 7.41 (AA′XX′, J ) 6.5
Hz, 4H, NC5H4), 7.35, 6.84 (d, J ) 16.4 Hz, 2H, -HCdCH-), 7.49,
6.92 (AA′XX′, J ) 8.7 Hz, 4H, C6H4), 7.27 (s, 2H, H3,5), 4.17 (t, J )
6.5 Hz, 2H, OCH2), 4.00 (t, J ) 6.5 Hz, 2H, OCH2), 1.80 (m, 4H,
-CH2), 1.60 (m, 4H, -CH2), 1.28 (overlapped peaks, 20H, -CH2),
0.87 (m, 6H, -CH3). IR (Nujol, cm-1): ν(CdO) 1627.
The following compounds were prepared similarly:
8e: Yield 88%. 1H NMR (CDCl3, δ, ppm): 8.46, 7.41 (AA′XX′, J
) 6.6 Hz, 4H, NC5H4), 7.35, 6.84 (d, J ) 16.3 Hz, 2H, -HCdCH-),
7.49, 6.92 (AA′XX′, J ) 8.8 Hz, 4H, C6H4), 7.54 (s, 2H, H3,5), 3.99 (t,
J ) 6.5 Hz, 2H, OCH2), 3.07 (t, J ) 7.2 Hz, 2H, SCH2), 1.76 (m, 4H,
-CH2), 1.45 (m, 4H, -CH2), 1.26 (overlapped peaks, 20H, -CH2),
0.87 (m, 6H, -CH3). IR (Nujol, cm-1): ν(CdO) 1620.
9b: Yield 67%. 1H NMR (CDCl3, δ, ppm): 8.71, 7.87 (AA′XX′, J
) 6.6 Hz, 4H, NC5H4), 8.49 (s, 1H, -HCdN-), 7.33, 6.95 (AA′XX′,
J ) 8.8 Hz, 4H, C6H4), 7.26 (s, 2H, H3,5), 4.16 (t, J ) 6.4 Hz, 2H,
OCH2), 3.99 (t, J ) 6.5 Hz, 2H, OCH2), 1.81 (m, 4H, -CH2), 1.58
(m, 4H, -CH2), 1.27 (overlapped peaks, 20H, -CH2), 0.87 (m, 6H,
-CH3). IR (Nujol, cm-1): ν(CdO) 1627.
The following compounds were prepared similarly:
1
3c: Yield 88%. H NMR (CDCl3, δ, ppm): 8.47, 7.86 (AA′XX′, J
) 6.6 Hz, 4H, NC5H4), 8.52 (s, 1H, -HCdN), 7.35, 6.93 (AA′XX′, J
) 8.9 Hz, 4H, C6H4), 7.34 (s, 2H, H3,5), 4.13 (t, J ) 6.4 Hz, 2H, OCH2),
3.98 (t, J ) 6.5 Hz, 2H, OCH2), 1.82 (m, 4H, -CH2), 1.55 (m, 4H,
-CH2), 1.27 (overlapped peaks, 28H, -CH2), 0.88 (m, 6H, -CH3).
IR (Nujol, cm-1): ν(CdO) 1673.
9e: Yield 81%. 1H NMR (CDCl3, δ, ppm): 8.70, 7.87 (AA′XX′, J
) 6.5 Hz, 4H, NC5H4), 8.49 (s, 1H, -HCdN-), 7.33, 6.94 (AA′XX′,
J ) 8.7 Hz, 4H, C6H4), 7.53 (s, 2H, H3,5), 3.98 (t, J ) 6.5 Hz, 2H,
OCH2), 3.07 (t, J ) 7.3 Hz, 2H, OCH2), 1.75 (m, 4H, -CH2), 1.59
(m, 4H, -CH2), 1.27 (overlapped peaks, 20H, -CH2), 0.87 (m, 6H,
-CH3). IR (Nujol, cm-1): ν(CdO) 1630, 1622.
1
4c: Yield 49%. H NMR (CDCl3, δ, ppm): 8.61, 7.99 (AA′XX′, J
) 6.6 Hz, 4H, NC5H4), 7.37 (s, 2H, H3,5), 4.40 (t, J ) 6.8 Hz, 2H,
OCH2), 4.16 (t, J ) 6.6 Hz, 2H, OCH2), 1.83 (m, 4H, -CH2), 1.56
(m, 4H, -CH2), 1.27 (overlapped peaks, 28H, -CH2), 0.88 (m, 6H,
-CH3). IR (Nujol, cm-1): ν(CdO) 1726, 1666.
1
10c: Yield 82%. H NMR (CDCl3, δ, ppm): 8.83, 7.99 (AA′XX′,
J ) 6.7 Hz, 4H, NC5H4), 7.26 (s, 2H, H3,5), 4.38 (t, J ) 6.7 Hz, 2H,
OCH2), 4.16 (t, J ) 6.5 Hz, 2H, OCH2), 1.80 (m, 4H, -CH2), 1.58
(m, 4H, -CH2), 1.26 (overlapped peaks, 28H, -CH2), 0.88 (m, 6H,
-CH3). IR (Nujol, cm-1): ν(CdO) 1719, 1632.
1
5c: Yield 91%. H NMR (CDCl3, δ, ppm): 8.69, 8.15 (AA′XX′, J
1
) 6.6 Hz, 4H, NC5H4), 7.13, 6.95 (AA′XX′, J ) 9.0 Hz, 4H, C6H4),
7.38 (s, 2H, H3,5), 4.16 (t, J ) 6.4 Hz, 2H, OCH2), 3.96 (t, J ) 6.5 Hz,
2H, OCH2), 1.83 (m, 4H, -CH2), 1.55 (m, 4H, -CH2), 1.27 (overlapped
peaks, 28H, -CH2), 0.88 (m, 6H, -CH3). IR (Nujol, cm-1): ν(CdO)
1738, 1687.
11c: Yield 89%. H NMR (CDCl3, δ, ppm): 8.90, 8.15 (AA′XX′,
J ) 6.6 Hz, 4H, NC5H4), 7.29 (s, 2H, H3,5), 7.10, 6.94 (AA′XX′, J )
9.2 Hz, 4H, C6H4), 4.15 (t, J ) 6.4 Hz, 2H, OCH2), 3.96 (t, J ) 6.5
Hz, 2H, OCH2), 1.80 (m, 4H, -CH2), 1.57 (m, 4H, -CH2), 1.27
(overlapped peaks, 28H, -CH2), 0.88 (m, 6H, -CH3). IR (Nujol, cm-1):
ν(CdO) 1739, 1631, 1615.
1
12c: Yield 86%. H NMR (CDCl3, δ, ppm): 8.82, 8.00 (AA′XX′,
(29) Hildebrand, U.; Ockels, W.; Lex, J.; Budzikiewicz, H. Phosphorus
Sulfur Relat. Elem. 1983, 16, 361.
J ) 6.7 Hz, 4H, NC5H4), 7.25 (s, 2H, H3,5), 6.59 (s, 2H, H2,6 L5), 5.28

Mesogenic Palladium Complexes with Pincer Ligands
Inorganic Chemistry, Vol. 39, No. 16, 2000 3651
(s, 2H, OCH2), 4.15 (t, J ) 6.5 Hz, 2H, OCH2), 3.96 (m, 6H, OCH2),
1.80 (m, 8H, -CH2), 1.45 (m, 8H, -CH2), 1.26 (overlapped peaks,
52H, -CH2), 0.87 (m, 12H, -CH3). IR (Nujol, cm-1): ν(CdO) 1733,
1620.
7.59 (s, 2H, H3,5), 4.00 (t, J ) 6.4 Hz, 2H, OCH2), 3.10 (t, J ) 7.3 Hz,
2H, SCH2), 1.77 (m, 4H, -CH2), 1.57 (m, 4H, -CH2), 1.28 (overlapped
peaks, 20H, -CH2), 0.88 (m, 6H, -CH3). IR (Nujol, cm-1): ν(CtN)
2218; ν(CdO) 1630.
1
13c: Yield 44%. H NMR (CDCl3, δ, ppm): 7.42, 6.92 (AA′XX′,
J ) 9.0 Hz, 4H, C6H4), 7.31 (s, 2H, H3,5), 4.18 (t, J ) 6.5 Hz, 2H,
OCH2), 3.99 (t, J ) 6.5 Hz, 2H, OCH2), 1.82 (m, 4H, -CH2), 1.57
(m, 4H, -CH2), 1.27 (overlapped peaks, 28H, -CH2), 0.88 (m, 6H,
-CH3). IR (Nujol, cm-1): ν(CtN) 2212; ν(CdO) 1632.
14b: Yield 83%. 1H NMR (CDCl3, δ, ppm): 7.64, 7.53 (AA′XX′,
J ) 8.4 Hz, 4H, C6H4), 7.50, 6.98 (AA′XX′, J ) 8.6 Hz, 4H, C6H4),
7.31 (s, 2H, H3,5), 4.18 (t, J ) 6.4 Hz, 2H, OCH2), 4.00 (t, J ) 6.3 Hz,
2H, OCH2), 1.82 (m, 4H, -CH2), 1.56 (m, 4H, -CH2), 1.27 (overlapped
peaks, 20H, -CH2), 0.88 (m, 6H, -CH3). IR (Nujol, cm-1): ν(CtN)
2213; ν(CdO) 1626.
Acknowledgment. We gratefully acknowledge financial
support by the Spanish Comisio´n Interministerial de Ciencia y
Tecnolog´ıa (Project MAT99-0971), and the Junta de Castilla y
Leo´n (Project VA16/99). E.G-O. thanks the Spanish Ministerio
de Educacio´n y Ciencia for a studentship.
Supporting Information Available: Table S1 including the micro-
analysis and yield of the (E)-dipic and (E)-pdtc complexes. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
14e: Yield 41%. H NMR (CDCl3, δ, ppm): 7.65, 7.54 (AA′XX′,
J ) 8.5 Hz, 4H, C6H4), 7.51, 6.99 (AA′XX′, J ) 8.7 Hz, 4H, C6H4),
IC0001457