Doubly cyclopalladated pyridazines: Chiral liquid crystals

Article abstract of DOI:10.1016/S0022-328X(01)01330-4

The mono and dicyclopalladation of new mesogenic pyridazines and subsequent reaction with β-diketones yields some novel metallomesogens. The monometallated derivatives have a flat central core. In contrast, the dimetallated derivatives have a sterically induced twist in the molecule that renders them chiral. Smectic A phases are typically exhinited by both the derivatives with transition temperatures in the region of 100-300 °C.

Full text of DOI:10.1016/S0022-328X(01)01330-4

Journal of Organometallic Chemistry 645 (2002) 246–255
www.elsevier.com/locate/jorganchem
Doubly cyclopalladated pyridazines: chiral liquid crystals
Jonathan W. Slater, Donocadh P. Lydon, Jonathan P. Rourke *
Department of Chemistry, Warwick Uni6ersity, Co6entry CV4 7AL, UK
Received 4 September 2001; accepted 25 September 2001
Abstract
The mono and dicyclopalladation of new mesogenic pyridazines and subsequent reaction with b-diketones yields some novel
metallomesogens. The monometallated derivatives have a flat central core. In contrast, the dimetallated derivatives have a
sterically induced twist in the molecule that renders them chiral. Smectic A phases are typically exhibited by both the derivatives
with transition temperatures in the region of 100–300 °C. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Cyclopalladated; Pyridazines; Mesogenic; Liquid crystal; Chiral
There is currently much interest in the synthesis of
metal-containing liquid crystals due to the perceived
advantages of combining the properties of liquid-crystal
systems with those of transition metals. The area has
been well reviewed recently [1–4], with excellent new
work appearing constantly [5–12]. Cyclopalladated
compounds have proved to be a particularly fertile area
of research with many different examples from many
different groups [13–29].
Previously, we have been studying a number of cyclo-
palladated Schiff’s base compounds, using two very
different co-ligands [30], variations on b-diketones [31],
amino acids [32] and two metals within the central core
[33]. Here we report our investigations into doubly
cyclopalladated mesogens which are inherently chiral.
Pyridazines (1) react cleanly with one equivalent of
palladium acetate at 60 °C in acetic acid to yield a
cyclopalladated species in high yield (Scheme 1). We
presume this species is the dimer 2, as an acetate-
bridged dimer is a very common feature of similar
palladium complexes [35]. We can then react this dimer
with sodium acetylacetonate (acac) to yield the
monomeric species 3. Whilst we lack a single-crystal
X-ray structure of 3, all the data that we have (NMR
spectroscopy, mass spectrometry and elemental analy-
sis) are consistent with this formulation. The proton
NMR spectrum of 3 is particularly useful, indicating
the inequivalence of the two protons in the pyridazine
ring, the presence of one metallated and one non-metal-
lated phenyl ring and one acetylacetonate per pyrida-
zine core. If we use two equivalents of palladium
acetate (or indeed, react our monometallated species 2
with a second equivalent) and an extended reaction
time, we can bring about a second cyclometallation to
give a new species 5. We have been unable to character-
ise the compound 5 in detail — solution NMR spectra
are too broad to interpret — but we believe the com-
pound to be doubly cyclopalladated. Whether 5 is
polymeric with bridging acetate groups or, by analogy
with other work [36,37], a simple dimer, is of little
relevance here. Subsequent reaction of 5 with sodium
acetylacetonate yields a well-characterised compound 6
with the formulation depicted in Scheme 1. In particu-
lar, the proton NMR spectrum of 6 is very informative:
the aromatic region shows only four resonances of
1. Synthesis
Four new series of mesogenic compounds were syn-
thesised from 3,6-diphenylpyridazines (1): the monocy-
clometallated compounds 3 and 4 and the doubly
cyclopalladated compounds 6 and 7 (Scheme 1). 3,6-
Diphenylpyridazines (1) are conveniently prepared by
the coupling of two equivalents of an aryl methyl
ketone as has been described elsewhere [34].
* Corresponding author. Tel.: +44-2476-523263; fax: +44-2476-
524112.
E-mail address: j.rourke@warwick.ac.uk (J.P. Rourke).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01330-4

J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
247
equal intensity (one singlet for the central pyridazine
ring and three multiplets for the metallated ring, one
doublet of 8.5 Hz, one doublet of 3 Hz and one double
doublet of 8.5 and 3 Hz), there is a singlet for the
central acetylacetonate proton of the same intensity as
the aromatic resonances and the resonances for the
methyl groups of the acetylacetonates are six times this
intensity. Whilst we were unable to grow a crystal of 5
suitable for X-ray diffraction, all other data fit with this
formulation.
Whilst we are confident that this is the correct formu-
lation for 6, it does raise the issue of the arrangement of
the acetylacetonate groups. Simple modelling demon-
strates the impossibility of achieving the preferred pla-
nar arrangement of the pyridazine core, both
cyclometallated rings and both acetylacetonate
groups — indeed this is one of the reasons we wanted
to make these compounds. Hence, the helical twist on
the structure of 6 suggested in Scheme 1. The practical
effect of this twist is to reduce the symmetry of the
compound, leaving a C2 axis as the only symmetry
element — hence the molecule must be chiral. It fol-
lows that, if these molecules are chiral, we must have a
racemic mixture as no attempt was made to control any
stereochemistry in the reaction. The solution state pro-
ton and carbon NMR spectra of 6 do not show any
unusual features: neither the chemical shifts of the
aromatic or acetylacetonate resonances are much differ-
ent to those in the monocyclopalladated 3. The only
potentially significant feature of the solution NMR
spectrum is the equivalence of the chemical shifts of the
methyl groups of the acetylacetonate — both ends of
the acetylacetonate resonate as singlets at 2.08 ppm in
the proton NMR spectrum and at 27.4 ppm in the
carbon NMR spectrum. This equivalence might at first
suggest that the correct structure is one in which the
palladiums are tetrahedral (with the acetylacetonate
groups perpendicular to the pyridazine core) but this
would require the palladiums to be paramagnetic, and
the sharp NMR spectrum precludes this possibility.
Scheme 1.

248
J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
Table 1
Mesogenic behaviour of 3,6-bis(4-alkoxyphenyl)pyridazines
n
Temperature/°C (DH/kJ mol−1
)
4
5
6
7
8
10
K
K
K
K
K
K
110 (0.11)
101 (24.7)
87 (8.83)
112 (40.3)
109 (32.9)
113 (10.3)
SG
SG
K%
K%
K%
K%
155 (6.97)
165 (12.1)
94 (15.4)
143 (10.3)
131 (10.1)
121 (10.0)
SF
SF
SG
SG
SG
K¦
166 (1.43)
241 (6.43)
139 (0.17)
145 (0.04)
142 (0.10)
129 (10.0)
SC
SC
SF
SF
SF
SG
170 (11.9)
248 a
165 (0.91)
165 (1.47)
166 (1.32)
163 (1.96)
SA 212 (0.11)
N
I
I
I
I
248 (1.3)
I
N
SI
SI
SI
SF
254 (3.64)
258 (11.2)
252 (13.1)
249 (13.3)
238 (15.7)
I
a Combined enthalpies.
Another interpretation of the solution NMR data is
that the molecule is fluxional and the ends of the
acetylacetonates are interchanging rapidly on the NMR
timescale, but cooling the sample to −80 °C did not
reveal any significant changes in the NMR spectrum.
Thus we conclude that there is an accidental equiva-
lence of the methyl groups in the NMR spectra and the
structure is indeed the helically twisted one depicted in
Scheme 1. Platinum derivatives of diphenyl pyridine
with a similar sterically imposed helical twist have been
isolated in good yields [38–42], indicating that our
proposed structure is not unprecedented. In addition,
our own work with doubly cycloplatinated pyridazines
provides support for our formulation [43]. It is not
obvious whether the enantiomers of our doubly cy-
clometallated acetylacetonate compound will be suffi-
ciently configurationally stable to ever allow their
separation.
In any event, the synthesis of the acetylacetonate
derivatives 3 and 6 proceeded in good yield, and these
complexes were purified by column chromatography
before their mesogenic behaviour was investigated. In
addition to the simple acetylacetonate derivatives, un-
decan-5,7-dione (‘butyl acetylacetonate’) derivatives of
both the mono and dipalladated pyridazines, 4 and 7,
respectively, were also isolated. In addition to the ex-
pected reductions in transition temperatures the un-
decadione derivatives have the added benefit of greater
chemical stability afforded by the butyl chains, ‘protect-
ing’ the palladium, which helps to eliminate the prob-
lem of decomposition seen in the some of the
acetylacetonate derivatives. The undecadione deriva-
tives of the dipalladated compounds proved to be tricky
to isolate in high yields. However, two analogues were
successfully synthesised from the reaction of two equiv-
alents of 5,7-undecadione and the dipalladated acetate-
bridged compound 5, in the presence of triethylamine,
in tetrahydrofuran. The difficulties encountered in the
syntheses are likely to be as a result of the steric
interactions between what would be two neighbouring
butyl chains in close proximity. Whilst it might be
expected that a total of four butyl chains would en-
hance the thermal stability of these molecules, it might
also be the case that the molecules would be desta-
bilised due to steric affects. In any event, all characteri-
sation was consistent with our proposed formulations.
Altogether six different pyridazines were used giving a
total of 20 new compounds.
2. Thermal properties
Whilst 3,6-bis-(4%-alkylphenyl)pyridazines have long
been known to be mesomorphic [44], with mesophases
in the 190–220 °C range, the 3,6-bis-(4%-alkyloxy
phenyl)pyridazines we use here do not appear to have
been studied before. All of the six homologues that we
synthesised exhibited mesogenic phases in the 110–
250 °C temperature range; their behaviour is detailed
in Table 1 and summarised in Fig. 1. Phases were
identified by their phase texture when viewed under the
crossed polars of a polarising microscope; these textures
are highly characteristic and can often be used to
definitively assign the phase. Thus the nematic and
smectic C phases exhibited schlieren textures, the ne-
matic showing both 4 and 2 point brushes, the smectic
C only 4 point brushes. The smectic F phase showed a
schlieren-mosaic type texture on cooling from the smec-
tic C. When both the smectic F and I phases were
observed, the order allowed us to distinguish them.
Transition temperatures were taken from the optical
microscope and confirmed by the onset of transitions in
the DSC.
Thus it can be seen that the longer terminal chain
length analogues of 1, C6–C10, show exclusively the
ordered hexagonal mesophases (smectic I, smectic F
and smectic G). This can be attributed to the rigid-pla-
nar structure of the mesogenic core (three directly
connected para substituted aromatic rings). This allows
highly efficient intermolecular hexagonal packing inter-
actions between the molecules in the mesophase. As the
chain length decreases (i.e. to five or four carbons) the
more disordered mesophases (smectic C, smectic A and
nematic phases) can be seen. This can be attributed to
the decreased length to breadth ratio of the molecule.
The thermal behaviour of the monocyclopalladated
acetylacetonate complexes 3 is listed in Table 2 and
summarised in Fig. 2. As can be seen, all compounds

J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
249
exhibited a smectic A phase. This smectic A phase was
identified by its phase texture, which appears as a
focal-conic fan texture; such a texture is highly charac-
teristic and can be used to definitively assign the phase.
Note that apart from the smectic B phase between the
crystal and smectic A phase exhibited by the shortest
chained homologue, no liquid crystal phase types other
than the smectic A were observed for these derivatives.
A general trend of decreasing clearing point tempera-
tures with an odd-even effect was seen as the chain
Fig. 1. Phase behaviour, compounds 1.
Table 2
Mesogenic behaviour of compounds 3, 4, 6 and 7
Compound
n
Transition temperature/°C (DH/kJ mol−1
)
3
4
5
6
7
8
10
K
K
K
K
K
K
156 (8.48)
182 (10.1)
196 (21.8)
196 (22.9)
162 (23.3)
184 (22.7)
SB
183 (15.9)
310 a
SA
I
I
I
I
276 a (0.58)
I
SA
SA
SA
SA
SA
280 a (0.57)
290 a(0.95)
264 a (1.51)
281 a (1.77)
I
4
6
7
4
5
6
7
8
10
K
K
K
K
K
K
154 (16.9)
154 (10.2)
112 (10.2)
119 (19.2)
104 (17.6)
90 (43.1)
SA
SA
SA
SA
SA
SA
184 b
I
I
I
I
I
I
180 (1.9)
190 (0.14)
185 (0.07)
186 (1.4)
180 (1.2)
4
5
6
7
8
10
Decomposition below 260
K
K
K
K
K
244 a
SA
SA
SA
SA
SA
236 a
244 a
147 (23.6)
169 (29.1)
250 a
210 a
I
I
5
6
K
K
128
123
I
I
a With decomposition.
b Combined enthalpies.

250
J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
Fig. 2. Phase behaviour, compounds 3.
length increased, but in all cases, there was a problem
of decomposition in the isotropic liquid due to the high
temperatures involved.
is expected because the butyl chains of the diketone will
disrupt the molecule’s ability to pack in orderly
mesophases [31]. Thermal behaviour was examined us-
ing hot-stage polarising microscopy and DSC. Full data
are listed in Table 3 and summarised in Fig. 3.
When one compares the pyridazines (1) with the
monopalladium acetylacetonate compounds 3 it is im-
mediately apparent that the melting points have been
increased by some 50 K with the presence of the
Pd(acac) moiety. Whilst one might expect that the
presence of the Pd(acac) moiety would increase the
width of the calamitic mesogen and consequently re-
duce its rod-like nature and ability to pack, resulting in
lower melting points, one might also expect the in-
creased mass to result in an increased melting tempera-
ture. In a previous case of Pd(acac) derivatives of some
Schiff’s base derived ligands we observed an effective
cancellation of these factors, resulting in an essentially
unchanged melting point [30]. In parallel to the increase
in the melting points observed for compounds 3, the
clearing points have increased by some 30–40 K, result-
ing in these monopalladated compounds exhibiting a
slightly smaller mesogenic range to their parent pyri-
dazines. The absence of the more ordered smectic I, F
and G phases that the pyridazines show is to be ex-
pected as the palladium acetylacetonate unit would be
expected to break up the lateral forces required for such
phases.
As expected the longer chain b-diketones caused a
lowering in the melting temperatures of the materials
causing them to decrease by nearly 100 K in some
cases, when compared to the acetylacetonate deriva-
tives. A slightly larger lowering of the smectic A to
isotropic phase transition can also be seen, resulting in
a reduced mesogenic range for compounds 4 compared
with compounds 3. This effect can be attributed to the
fact that the longer chains further disrupt the ability of
the molecules to pack in an orderly fashion. In addi-
tion, there is also the added benefit of greater chemical
stability afforded by the butyl chains, ‘protecting’ the
palladium, this helps to eliminate the problem of de-
composition seen in the acetylacetonate derivatives.
Thus, by comparison with their simple acetylacetonate
analogues, the monopalladated undecadione derivatives
are chemically more robust and exhibit their
mesophases at more accessible temperatures, albeit with
a slightly reduced mesogenic range.
A series of cis-dicyclopalladated acetylacetonate ana-
logues 6 were synthesised and their thermal behaviour
examined. Full data are summarised in Table 2. All
members of the series did show some mesogenic charac-
ter, exclusively exhibiting a smectic A phase. No clear-
ing point was observed for the C5, C6 and C7
analogues due to decomposition.
In an attempt to lower the transition temperatures,
and overcome the problem of decomposition, monopal-
ladated acetate-bridged dimers 2 were reacted with
5,7-undecadione, in place of acetylacetone, to give com-
pounds 4. The lowering of the transition temperatures

J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
251
Table 3
Elemental analysis data for compounds 1, 3, 4, 6 and 7
C (%)
Found
H (%)
Found
N (%)
Found
Compound
n
Expected
Expected
Expected
1
4
5
6
7
8
77.0
76.9
77.6
78.0
78.3
79.3
76.6
77.2
77.7
78.2
78.7
79.4
7.4
8.0
8.3
8.7
8.9
9.6
7.5
8.0
8.4
8.8
9.1
9.6
7.1
6.7
6.5
6.2
5.7
5.3
7.4
6.9
6.5
6.1
5.7
5.1
10
3
4
6
7
4
5
6
7
8
60.0
62.2
61.9
63.5
64.5
65.6
60.0
61.1
62.2
63.2
64.1
65.7
5.7
6.6
6.7
7.1
7.4
7.8
5.9
6.3
6.6
7.0
7.3
7.8
4.4
4.4
4.1
4.2
3.8
3.7
4.8
4.6
4.4
4.2
4.0
3.7
10
4
5
6
7
8
63.3
63.5
65.0
64.8
65.6
67.1
63.2
64.1
65.0
65.7
66.4
67.7
7.0
7.3
7.4
7.8
8.1
8.4
6.9
7.2
7.5
7.8
8.0
8.5
4.0
3.9
3.5
3.6
3.5
3.2
4.2
4.1
3.9
3.7
3.6
3.4
10
4
5
6
7
8
49.6
48.6
46.4
50.4
47.6
56.9
51.9
53.1
54.2
55.2
56.2
57.9
5.2
5.1
5.0
5.4
5.4
6.7
5.4
5.4
5.7
6.0
6.3
6.8
3.4
3.3
3.0
3.1
2.8
2.8
3.6
3.4
3.3
3.2
3.1
2.9
10
5
6
56.8
56.0
58.7
59.4
6.5
7.0
7.0
7.2
2.1
2.5
2.8
2.8
Fig. 3. Phase behaviour, compounds 4.

252
J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
On heating extensive decomposition, due to the low
being observed; we have the ability to tune transition
temperatures by varying ligands.
chemical stability of the molecules, was seen in all the
examples. The temperatures at which these dipalladated
molecules 6 exhibit their mesophases is always consider-
ably higher than that exhibited by their monopalla-
dated analogues 3. Presumably the extra mass of the
second palladium acetylacetonate unit within the
molecules results in a greater increase in the transition
temperatures than can be compensated for by the addi-
tional disruption that this group makes to the solid-
state packing (and hence reduction in the transition
temperatures) [45]. The lack of any long-lived meso-
genic behaviour in the shorter chain lengths can be
attributed to the reduction in length to breadth ratio
when the second acetylacetonate group is added. In
addition, the symmetrical nature of these molecules is
of relevance, as a symmetrical arrangement of this type
is often responsible for higher melting points [46,47].
The observation of only a smectic A phase is unfortu-
nate as there is no distinction between the chiral and
non-chiral variants.
4. Experimental
4.1. General
All chemicals were used as supplied, unless noted
otherwise. All NMR spectra were obtained in either a
Bruker Avance 300, 400 or 500 in CDCl3 and are
referenced to external TMS, assignments being made
with the use of decoupling, nOe and the DEPT and
COSY pulse sequences. Thermal analyses were per-
formed in an Olympus BH2 microscope equipped with
a Linkam HFS 91 heating stage and a TMS90 con-
troller, at a heating rate of 10 K min−1, and a Perkin–
Elmer Pyris 1 DSC. All elemental analyses were
performed by Warwick Analytical Service.
4.2. Preparation of
As with the monopalladated derivatives a different
b-diketone, 5,7-undecadione was used in place of the
acetylacetone in an attempt to induce more chemical
stability in the molecule so that mesophases could be
observed without decomposition. Attempts at synthesis-
ing this series of compounds have been somewhat unre-
liable. Two analogues have, however, been successfully
synthesised, from the reaction of two equivalents of
5,7-undecadione and the dipalladated acetate-bridged
ligand 5, in the presence of triethylamine, in tetrahydro-
furan, at room temperature, over 4 h. The difficulties
encountered in the syntheses are likely to be as a result
of the steric interactions between what would be two
neighbouring butyl chains in close proximity. As was
seen in the monopalladated examples, it might be ex-
pected that there would be enhanced thermal stability
of these molecules, as a result of the protecting butyl
chains. In this case, however, the molecules might be
destabilised due to steric affects.
3,6-bis(4%-n-alkyloxphenyl)pyridazines (1)
Six homologues (n=4, 5, 6, 7, 8, and 10) were
prepared in good yields (50–70%) using a literature
procedure [34]. The mesogenic behaviour of all homo-
logues is summarised in Fig. 1, and detailed in Table 1.
Elemental analyses are detailed in Table 3.
4.3. Preparation of dipalladium(v-acetato)-3,6-
bis(4%-butyloxyphenyl)pyridazine (2)
The butyloxy derivative is described in detail, all
other homologues were prepared similarly.
Palladium acetate (0.059 g, 2.63×10−4 mol) was
added to
a solution of 3,6-bis(4%butyloxyphenyl)-
pyridazine (0.1 g, 2.63×10−4 mol) in AcOH (25 cm3)
and heated (60 °C, 48 h). The solvent was removed to
yield a yellow solid (0.143 g, 1.31×10−4 mol, yield
assumed to be 100%).
The n=5 and 6 derivatives that have been synthe-
sised did not show any mesogenic behaviour with both
melting directly into the isotropic liquid below 130 °C,
presumably the extra four lateral alkyl chains increase
the width of the molecules by too great an extent for
any mesophases to exist.
4.3.1. NMR data for compound 2
3. Conclusions
Pyridazines have proved to be versatile compounds:
in there own right they exhibit rich mesogenic be-
haviour, and they can be readily derivatised. Thus we
have investigated both singly and doubly cyclopalla-
dated derivatives. These derivatives also exhibit meso-
genic behaviour with both smectic A and B phases
lH (CDCl3): 7.95 (2H, AA%XX%, J=7.5 Hz, Hj), 7.45
(1H, d, 3J=8.5 Hz, Hh/i), 7.05 (1H, d, 3J=8.5 Hz,
Hh/i), 7.00 (2H, AA%XX%, J=7.5 Hz, Hk), 6.75 (1H, d,
4
3J=8.5 Hz, Hf), 6.30 (1H, d, J=2.5 Hz, Hg), 6.25
(1H, dd, 3J=8.5 Hz, 4J=2.5 Hz, He), 4.00 (4H, t,

J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
253
Hd/d%), 2.35 (3H, s, Hl), 1.80 (4H, m, Hc/c%), 1.45 (4H, m,
4.5.1. NMR data for compound 4
Hb/b%), 0.95 (6H, m, Ha/a%).
4.4. Preparation of palladium(acac)-[3,6-bis(4-butyl-
oxyphenyl)pyridazine] (3)
The butyloxy derivative is described in detail, all
other homologues were prepared similarly.
Sodium acetylacetonate (0.036 g, 2.63×10−4 mol)
was added to a solution of dipalladium(m-acetato)-3,6-
bis(4%-butyloxyphenyl)pyridazine (1.31×10−4 mol) in
acetone (30 cm3). The solution was stirred at room
temperature (r.t.) for 18 h and the solvent removed to
yield a yellow solid that was purified on a silica column
using a 90:10, CHCl3–MeOH elutant. The solvent was
removed to yield a crystalline yellow solid (0.11 g,
1.92×10−4 mol, 73% yield).
lH (CDCl3): 8.00 (2H, AA%XX%, J=7.5 Hz, Hj), 7.85
(1H, d, 3J=8.5 Hz, Hh/i), 7.65 (1H, d, 3J=8.5 Hz,
Hh/i), 7.28 (1H, d, 3J=7.6 Hz, Hf), 7.25 (1H, d, 4J=2.5
Hz, Hg), 6.90 (2H, AA%XX%, J=7.5 Hz, Hk), 6.65 (1H,
dd, J=7.6 Hz, J=2.5 Hz, He), 5.35 (1H, s, Hl), 4.05
(2H, t, 3J=6.9 Hz, Hd/d%), 3.95 (2H, t, 3J=6.9 Hz,
Hd/d%), 2.30 (4H, m, Hc/c%), 1.70 (8H, m, Hm/m%), 1.40
(12H, m, Hn/n%/o/o%/b/b%), 0.90 (12H, m, Ha/a%,y/y%). FABMS
(NBA); m/z: 665 [M+], 482 (largest, [M+]−
undecandione).
3
4
4.4.1. NMR data for compound 3
The mesogenic behaviour of all homologues is sum-
marised in Fig. 2, and detailed in Table 2. Elemental
analyses are detailed in Table 3.
4.6. Preparation of bis-palladium-bis(v-acetato)-3,6-
bis(4%-butyloxyphenyl)pyridazine (5)
lH (CDCl3): 8.05 (2H, AA%XX%, J=7.5 Hz, Hj), 7.90
The butyloxy derivative is described in detail, all
other homologues were prepared similarly.
3
3
(1H, d, J=9 Hz, Hh/i), 7.65 (1H, d, J=9 Hz, Hh/i),
3
4
7.35 (1H, d, J=8.5 Hz, Hf), 7.25 (1H, d, J=2.5 Hz,
Hg), 6.95 (2H, AA%XX%, J=7.5 Hz, Hk), 6.65 (1H, dd,
3J=8.5 Hz, 4J=2.5 Hz, He), 5.45 (1H, s, Hl), 4.10 (2H,
Palladium acetate (0.24 g, 1.06×10−3) was added to
a solution of 3,6-bis(4-pentyloxyphenyl)pyridazine (0.20
g, 5.32×10−4 mol) in MeOH (100 ml). The reaction
mixture was heated to 60 °C and stirred for 2 days to
yield a dark red–orange solution. The solvent was
removed under reduced pressure and the solid dissolved
in CHCl3 and filtered through celite to remove traces of
palladium black. The CHCl3 was removed under re-
duced pressure to yield a dark red solid. NMR too
broad to interpret.
3
3
t, J=6 Hz, Hd/d%), 4.00 (2H, t, J=6 Hz, Hd/d%), 2.15
(3H, s, Hm/m%), 2.10 (3H, s, Hm/m%), 1.75 (4H, m, Hc/c%),
1.50 (8H, m, Hb/b%), 0.95 (6H, m, Ha/a%). FABMS
(NBA); m/z: 581 (largest, [M+]), 482 ([M+]−acac).
The mesogenic behaviour of all homologues is sum-
marised in Fig. 2, and detailed in Table 2. Elemental
analyses are detailed in Table 3.
4.5. Preparation of palladium(5,7-undecadione)-[3,6-
bis(4-hexyloxyphenyl)pyridazine] (4)
4.7. Preparation of [bis-palladium-bis(acetylacetonate)-
{3,6-bis(4-heptyloxyphenyl)pyridazine}] (6)
The hexyloxy derivative is described in detail, all
other homologues were prepared similarly.
The heptyloxy derivative is described in detail, all
other homologues were prepared similarly.
5,7-Undecadione (0.043 g, 2.31×10−4 mol) and
Et3N (0.023 g, 2.31×10−4 mol) were added to a
solution of dipalladium(m-acetato)-3,6-bis(4-hexyloxy-
phenyl)pyridazine (1,15×10−4 mol) in THF (60 ml).
The reaction mixture was stirred overnight at r.t. The
solvent was removed to yield a yellow solid which was
purified by chromatography on silica, eluting with
CHCl3–MeOH (90:10). The solvent was removed under
reduced pressure to yield a bright yellow solid (0.08 g,
1.15×10−4 mol, 49% yield).
Sodium acetylacetonate (0.052 g, 4.35×10−4 mol)
was added to a solution of bis-palladium-bis(m-acetato)-
3,6-bis(4%-heptyloxyphenyl)pyridazine (0.100 g, 1.18×
10−4 mol) in THF (125 ml). The solution was stirred at
r.t. for 4.5 h and the solvent removed. The resulting
yellow–orange product was washed with hexane (10
ml×2) and Et2O (10 ml×2) to yield a yellow solid
which was dried under vacuum (0.090 g, 1.04×10−4
mol, 87%).

254
J.W. Slater et al. / Journal of Organometallic Chemistry 645 (2002) 246–255
4.7.1. NMR data for compound 6
The mesogenic behaviour of all homologues is de-
tailed in Table 2. Elemental analyses are detailed in
Table 3.
Acknowledgements
We thank Johnson–Matthey for loan of chemicals.
3
lH (CDCl3): 7.80 (2H, s, Hh), 7.25 (2H, d, J=8.5
Hz, Hf), 7.10 (2H, d, 4J=3 Hz, Hg), 6.65 (2H, dd,
References
4
3J=8.5 Hz, J=3 Hz, He), 5.35 (2H, s, Hi), 4.00 (4H,
t, 3J=7.5 Hz, Hd), 2.08 (12H, s, Hj/k), 1.80 (4H, m, Hc),
1.30 (16H, m, Hb), 0.95 (6H, t, Ha). FABMS (NBA);
m/z: 771 (largest, [M+]−acac), 665 ([M+]−Pd acac).
The mesogenic behaviour of all homologues is sum-
marised in Fig. 3, and detailed in Table 2. Elemental
analyses are detailed in Table 3.
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3
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