Synthesis and characterisation of main-chain oligomeric cyclopalladated azobenzene complexes

Article abstract of DOI:10.1016/S0020-1693(99)00185-1

In this paper we report the synthesis of main-chain oligomeric cyclopalladated azobenzene complexes. The approach we followed was focused on the synthesis of difunctional azo-ligands substituted properly with terminal polymerisable OH groups, synthesis of

Full text of DOI:10.1016/S0020-1693(99)00185-1

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Inorganica Chimica Acta 292 (1999) 163–171
Synthesis and characterisation of main-chain oligomeric
cyclopalladated azobenzene complexes
Mauro Ghedini a,*, Stefania Morrone a, Ugo Caruso b, Antonio Roviello b
a Dipartimento di Chimica, Uni6ersita’ della Calabria, 87036 Arca6acata di Rende (Cs), Italy
b Dipartimento di Chimica, Uni6ersita’ di Napoli, 6ia Mezzocannone, 4-80134 Naples, Italy
Received 11 December 1998; accepted 8 April 1999
Abstract
In this paper we report the synthesis of main-chain oligomeric cyclopalladated azobenzene complexes. The approach we
followed was focused on the synthesis of difunctional azo-ligands substituted properly with terminal polymerisable OH groups,
synthesis of cyclopalladated monomers and polycondensation reaction with acid chlorides as comonomers. In this way, using the
interfacial method, two soluble cyclopalladated oligomers P1 and P2 were synthesised. © 1999 Elsevier Science S.A. All rights
reserved.
Keywords: Metallomesogens; Organometallic polymers; Azo polymers; Cyclopalladated complexes
materials is the synthesis of soluble species, which allow
for higher chemical purity and better characterisation.
Within this field, liquid-crystalline metal-containing
polymers, as recently reviewed by Oriol and Serrano [5],
represent a new-born area of research. Main-chain,
side-chain and cross-linked thermotropic liquid-crys-
talline polymers have been reported and most of them
are coordination polymers like copper salycilaldiminate
and more recently oxovanadium containing species [9],
copper b-diketonates or organometallic ferrocene-based
polymers and polymers with organo–tin flexible spac-
ers. As far as we know, only few examples of ther-
motropic polymeric cyclopalladated azo-containing
complexes are known and they are all cross-linked
polymers [10]. Only recently, the synthesis of a liquid-
1. Introduction
Transition metal based polymers combine the typical
flexibility and processability of organic polymers with
the high thermal stability associated with inorganic
species [1,2]. Furthermore, the incorporation of transi-
tion metals into a polymer chain offers considerable
potential for the preparation of processable materials
with properties that differ significantly from those of
conventional organic polymers. Properties like non-lin-
ear optics [3], ferroelectricity, ferromagnetism [4], liquid
crystallinity [5] and also catalytic activity have been
reported in these materials. Metal coordination poly-
mers are indeed more stable than the organometallic
counterpart in which a metal–carbon bond is formed.
Examples of stable organometallic polymers are the
ferrocene-based materials [6], the rigid-rod polymers as
for example polymetallaynes (M=Ni, Pd or Pt), which
were first isolated in 1977 by Hagihara and co-workers
[7], until the last developments in this field which
include gold and platinum-containing rigid-rod poly-
mers [8]. In general, an important issue about these
crystalline side-chain polyacrylate containing
a
mononuclear cyclopalladated azobenzene complex [11]
(Fig. 1) has been reported and studies on the photore-
fractivity of this material have been conducted [12].
Organic azo-containing polymers are a well-known
class of materials characterised by good mechanical and
thermal properties, bright colour and high stability.
More recently, their liquid-crystalline and non-linear
optical properties have been investigated as the azo-
group can be considered both a good mesogenic linking
group and NLO chromophore. Several examples of
* Corresponding author. Tel.: +39-0984-492 047; fax: +39-0984-
492 044.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00185-1

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M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
In this way a polymer film can be ‘written’ and then
‘erased’ several times [14,15,17]. The vast majority of
these studies are based on side-chain azoaromatic poly-
mers and only recently holographic images and surface
gratings in main-chain azopolymer films have been
studied [18].
The azobenzenes easily react with a palladium(II)
source and cyclopalladated complexes [19], structurally
¸¹¹¹¹¹¹¹¹¹¹¹º
featured by the five-membered –CꢀC(C)–NꢀN(C)–Pdꢀ
ring, forms. Cyclopalladation blocks the azo group in
the trans conformation, so preventing trans–cis iso-
merisation. However, optical storage, occurring with a
process which does not require –NꢀN– photoisomeri-
sation was observed also for the side-chain cyclopalla-
dated azobenzene polymer shown in Fig. 1 [12].
Within this frame, and in order to extend our knowl-
edge in the field, we planned the synthesis of mesogenic
main-chain oligomeric cyclopalladated azobenzene
complexes leading to stable and soluble materials that
could be tested for ordered thin film formation and for
optical properties.
Fig. 1. Molecular structure of the side-chain polyacrylate containing a
mononuclear cyclopalladated azobenzene.
side-chain azopolymers, where the polymer backbone
could be hydrocarbons, esters, amides, phosphazenes,
acrylates, siloxane, etc., and main-chain azopolymers,
mainly polyesters, polyureas, and polyamides, have
been synthesised and investigated as reviewed recently
by Natanshon and co-workers [13]. Furthermore, in
1987 since Wendorff and co-workers [14] demonstrated
reversible optical storage properties in some liquid-crys-
talline azo-polymer films there has been a tremendous
growth of interest for these materials as media for
optoelectronic applications. More recently, it has been
shown that liquid crystallinity is not a necessary condi-
tion for optical processes and reversible optical storage
effects have been detected also in amorphous side-chain
azopolymers with high glass transition temperatures
[15].
Reversible optical storage processes are based on the
photoinduced trans–cis–trans isomerisation of the
NꢀN group [16] (Fig. 2). Exposure of the polymer film
to linearly polarised light results in an anisotropy of
molecular orientation and, as a consequence, in the
induction of a stable photoinduced birefringence. This
process is commonly addressed as ‘writing’. ‘Erasing’,
i.e. the return to an isotropic molecular orientation, can
be achieved by circularly polarised light or by heating.
2. Results and discussion
Using our experience in the design and synthesis of
low molar mass metal-containing liquid crystals, i.e.
metallomesogens [20], we thought that the combination
of a rigid p-shaped cyclopalladated azo-containing
structural unit [21] with aromatic or aliphatic long
flexible spacers, which dilute the rigid units, could be a
good criterion to obtain soluble and, eventually, liquid-
crystalline oligomers. In general, two different ap-
proaches for the synthesis of metal-containing polymers
have been used. The first one consists of the synthesis
of a metallated monomer to be used in polymerisation
reactions; the second approach is to polymerise the
ligand first and then to graft the metal ion to the
polymeric backbone. The first method normally affords
purer products, which are also easier to characterise,
and it avoids cross-linking. For this reason the ap-
proach we followed is focused on the synthesis of
difunctional cyclopalladated monomers to be used in
polycondensation reaction with aromatic or aliphatic
dichlorides. The synthesis consisted of three main steps:
synthesis of bifunctional azo-ligands functionalised
properly with terminal polymerisable hydroxy groups,
synthesis of cyclopalladated monomers and polycon-
densation reactions with acid chlorides to give cyclopal-
ladated oligo-esters.
2.1. Synthesis of the azo-ligands
A family of substituted azobenzenes bearing two OH
terminated alkoxy chains in p,p% positions, p-(p%-
azobenzene)-oxyalkyl-n-ol, (n=8, 10, 12) and 4,4%-di-
hydroxy azobenzene, have been synthesised using
Fig. 2. The trans–cis photoisomerisation of azobenzene.

M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
165
Scheme 1. Synthesis of the 4,4%-disubstituted azo ligands. Key: (i) K2CO3, cyclohexanone, n-chloro-1-octanol, n=8, 10 or 12-bromo-1-dodecanol,
reflux 15 h. (ii) Pd/C, NH2NH2·H2O, absolute ethanol, 60°C, 7 h. (iii) HCl, NaNO2, PhOH, NaOH, r.t. 2 h. (iv) K2CO3, n-chloro-1-octanol, n=8,
10 or 12-bromo-1-dodecanol, cyclohexanone, reflux 15 h.
The 4,4%-dihydroxy azobenzene was synthesised with
a one-step synthesis starting from nitrophenol and us-
ing a method that is reported in the literature [22].
literature methods. The synthesis of the p-(p%-azoben-
zene)-oxyalkyl-n-ol, described in Scheme 1, started with
the alkylation of nitrophenol with chloro- or bromo-al-
cohol of different chain length to give 1-(p-nitrophen-
oxy)-alkyl-n-ols. Successive reduction of the nitro
derivatives using palladium on charcoal and hydrazine
monohydrate or SnCl2·5H2O affords the corresponding
1-(p-aminophenoxy)-alkyl-n-ols. The alkylation of ni-
trophenol works well with long-chain chloro and
bromo alcohols, while the attempt to use a short alco-
hol (3-chloro-1-propanol) resulted in a poor yield of the
reaction. Diazotization of the amine, coupling with
phenol and successive alkylation of the asymmetric azo
compounds gave the symmetric bifunctional ligands
p-(p%-azobenzenes)-oxyalkyl-n-ol in good yields.
2.2. Synthesis of the cyclopalladated monomers
The binuclear chloro-bridged complexes were ob-
tained by cyclopalladation of the ligands with
[Pd(PhCN)2Cl2] either in a mixture of methanol and
benzene at room temperature or in refluxing absolute
ethanol (see Experimental). The mononuclear cyclopal-
ladated complexes, 5–7, 8 were obtained by bridge-
splitting reaction using an excess of potassium
1
acetylacetonate (Scheme 2). The H NMR spectra of
the monomers clearly accounted for the formation of
expected products.
Scheme 2. Synthesis of the difunctional acetylacetonate monomers (n=8, 10, 12). Key: (i) [Pd(PhCN)2Cl2], EtOH reflux 6 h, (n=10, 12) or
MeOH/benzene, 2 days r.t. (n=8). (ii) Kacac (excess), absolute ethanol, under nitrogen, reflux, 3 h.

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M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
Table 1
signals expected for the acetylacetonate ligand. The
other synthetic pathway, i.e. grafting the metal frag-
ment to a preformed polymer, was not tried as it should
lead, in this case, to highly insoluble cross-linked
oligomers.
Mesomorphic behaviour of the mononuclear cyclopalladated difunc-
tional complexes a 5–7
Compound
Transition
T (°C)
DH (KJ mol−1
)
5
C–I
125
114
111
98
82.0
2.3
1.7
The interfacial method starting from phenol-termi-
nated bifunctional monomers is a well-known method
to obtain metallopolymers. In our case the 4,4%-dihy-
droxy-terminated cyclopalladated monomer is a good
starting point for polycondensation reaction leading to
oligo- or polyesters. Interfacial polycondensation was
achieved in water+chloroform using a blender, as the
monomer was soluble in water. As comonomer 4,4%-
dichloroformyl–a,v-diphenoxydodecane (I) or sebacoyl
chlorides (II) in slight excess were used alternatively
(Scheme 3). Tetrabutylammonium hydrogen sulphate
was used as phase transfer catalyst. The pH of the
reaction was kept around 9–10 in order to prevent the
formation of the binuclear complex, and the oligomers
(P1 and P2), arising from I and II, respectively, were
precipitated from hexane, filtered, washed with water
and a little ethanol and oven dried at 100°C.
(I–N) c
(N–SmA) c
SmA–C
32.9
6
7
C–SmA
SmA–I
I–SmA
SmA–C
102
111
6.6
0.8
7.6
105
b
C–SmA
SmA–I
I–SmA
SmA–C
96
107
24.8
12.9
11.7
111
b
a C, crystal; SmA, smectic A; N, nematic; I, isotropic.
b Not detected by DSC.
c Parentheses indicate monotropic transition.
The cyclopalladated acetylacetonate monomers 5–7,
which are amphiphilic molecules [23], were liquid-crys-
talline showing nematic and smectic mesophases. The
parent ligands, p-(p%-azobenzene)-oxyalkyl-n-ol, were
not mesomorphic, so this is one of the cases in which
coordination to a metal ion induces liquid-crystalline
behaviour. In particular, for n=8 monotropic nematic
and smectic mesophases were observed, while enan-
tiotropic smectic mesophases were observed when n=
10, 12. The smectic mesophases gave a homeotropic
texture with oily streaks near the air bubbles and near
the edges of the preparation, which is similar to the
P1 was not very soluble in CHCl3 and this prevented
molecular weight measurements. Nevertheless, the poly-
mer inherent viscosity was pinh=0.27 dl g−1. Ther-
mogravimetric analysis indicated an initial loss of
weight around 150°C and decomposition began to take
place around 220°C. Palladium determination by ther-
mogravimetry gave a value (10.0%) that was slightly
lower than the expected value (12.6%) and this result
could be a consequence of the fact that the reaction was
conducted in excess of the comonomer. The IR spec-
trum showed the typical band for the ester group at
1
Myelin figures observed for lyotropic smectic
A
w=1730 cm−1. The H NMR was not very helpful due
mesophases [24]. The same optical texture was observed
for the smectic mesophases of the oxydecyl-n-ol and
oxydodecyl-n-ol derivative. The optical behaviour was
confirmed by DSC analysis as reported in Table 1.
to the low solubility of P1 in the organic solvents
commonly used.
P2, on the other hand, is quite soluble in CHCl3 and
molecular weight measurements were performed by va-
(
pour pressure osmometry giving Mn=4500, corre-
(
2.3. Synthesis of the oligomers
sponding to a mean polymerisation degree P=8, and
an inherent viscosity pinh=0.15 dl g−1 was measured.
The H NMR spectrum consisted of broad resonances
1
One of the methods to obtain organometallic and
coordination polymers or oligomers is to use function-
alised metal-containing monomers in polycondensation
reactions [5]. Amongst polycondensation methods the
most used are the interfacial method and the solution
method using an organic base. The first one is used
mainly with water-soluble phenol-terminated mono-
mers, while the second one is used with diol-terminated
monomers. A first attempt of polycondensation using
the solution method was made starting from 5 and
using dodecaloyl chloride as comonomer in the pres-
ence of pyridine. In this case the IR spectrum of the
product obtained by precipitation with ethanol showed
the strong band characteristic for ester groups at 1730
which account for the expected polymer. In fact, broad
signals at values of l which are typical of the aromatic
protons for the cyclopalladated ring and for the acetyl-
acetonate moiety were observed. Palladium determina-
tion by thermogravimetry gave a value of 17.12%,
which is quite in accordance with the calculated value
of 17.21%. Thermogravimetric analyses in air indicated
decomposition at 344°C.
As far as polarising microscopy is concerned, P1
showed a birefringence around 250°C and decomposi-
tion was observed around 300°C (the colour of the
sample changes from orange to black). DSC, which
showed a very large and shallow peak around 200°C,
confirmed this behaviour and an exothermal peak due
1
cm−1, but the H NMR spectrum did not show the

M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
167
to decomposition of the sample, was observed when
3. Conclusions
the temperature was near to 300°C. X-rays investiga-
tion performed at room temperature is consistent with
a crystalline polymer. Then, after warming up the
sample to 257°C and quenching to room temperature
the spectrum was consistent with an amorphous solid
and a halo corresponding to a periodicity of 19.5
The synthesis of two main-chain oligo-esters con-
taining a cyclopalladated azobenzene mononuclear
complex has been achieved through polycondensation
of the metallorganic monomer. In this way we were
able to synthesise soluble oligomers using a design that
has already been proved useful for the synthesis of low
molar mass palladium-containing liquid crystals [21]. In
fact, monomeric p-shaped azo-palladated complexes
containing the acetylacetonate group show liquid-crys-
talline properties and low transition temperatures. In
principle, the acetylacetonate group can be assimilated
to a bulky organic pendent group and we know from
the literature that bulky organic groups even on flat
ligands such as porphyrins can enhance the solubility of
metal coordination polymers [1] and so a similar effect
is expected in our systems. In particular, P2 shows a
good solubility in the common organic solvents while
P1 is slightly less soluble. This difference can probably
be ascribed to the different structure of the two
oligomers. In fact, the oligomeric backbone of P1 con-
sists of a four-aromatic-ring repeating unit in the main-
chain, while only two aromatic rings are present in P2
structural unit. As a consequence P1 is a more rigid
system than P2 and this structural characteristic reflects
in the difference in solubility between P1 and P2. As far
,
A was observed. As the sample was not oriented it
is not possible to say if this distance is correlated to
a periodicity along the chain’s axis or to lateral pack-
ing.
P2 showed a birefringent phase which was not due
to mechanical stress and which persisted between 175
and 214°C. At this temperature the birefringence dis-
appeared but no melting was observed. DSC was con-
sistent with this observation. In fact, a glass transition
was detected at Tg=56°C and a broad DSC trace
with onset at 172°C was observed corresponding to
DH=3.81 J g−1. The room temperature X-ray spec-
trum was consistent with a total lack of crystallinity
,
and a periodicity of 10 A, which was compatible with
a lateral–lateral correlation of the acetylacetonate pen-
dent group in a pre-smectic organisation, was de-
tected. This periodicity disappeared when the sample
was cooled down to room temperature after heating at
210°C. The spectrum of the quenched sample did not
show any crystallinity.
Scheme 3. Synthesis of the oligomers P1 and P2. Reaction conditions: tetrabutylammonium hydrogen sulphate, KOH, water/chloroform.

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M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
as we know, these are the first examples of main-chain
cyclopalladated oligomers and in particular P2, due to
its solubility in organic solvents, is a promising material
that could be easily processed to form ordered thin
films, tested for NLO properties and also for optical
storage processes. Furthermore, as azobenzenes are
good substrates for cyclometallation, different combi-
nations of chromophores and ancillary ligands could be
introduced in the oligomeric backbone in order to
obtain oligomeric materials with novel properties. Fi-
nally, as oligomers fill the gap between monomeric and
polymeric systems, P1 and P2 can be considered exam-
ples of supermolecular materials [27].
reduced pressure. The resulting orange–yellow oil crys-
tallised after standing at room temperature and the
resulting solid was crystallised twice from absolute
ethanol. After crystallisation 10.5 g of a pale yellow
microcrystalline solid were obtained (yield 55%).
M.p. 88°C. Anal. Calc. for C14H21NO4: C, 63.86; H,
8.04; N, 5.32. Found: C, 63.37; H, 7.95; N, 5.11%.
1H NMR (CDCl3): l 1.3 (10H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (2H, q, HOCH2–
3.6 (2H, bt, HOCH2–
4.0 (2H, t, HOCH2–
(CH2)5CH2–CH2–O–); l 6.9 (2H, m, AA%XX% aro-
matic protons); l 8.2 (2H, m, AA%XX% aromatic
protons).
4. Experimental
4.2. 1-(p-Nitrophenoxy)-decyl-n-ol
All chemicals were used as received unless otherwise
specified. Microanalyses were performed at the Depart-
ment of Chemistry, Universita’ della Calabria.
Yield 63%. M.p. 93°C. Anal. Calc. for C16H25NO4: C,
65.96; H, 8.65; N, 4.81. Found: C, 65.37; H, 9.04; N,
4.67%.
Infrared spectra were recorded on a Perkin–Elmer
2000 FT-IR infrared spectrometer. Spectra were
1H NMR (CDCl3): l 1.3 (10H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (2H, q, HOCH2–
3.6 (2H, bt, HOCH2–
4.0 (2H, t, HOCH2–
1
recorded as KBr disks. H NMR spectra were recorded
on a Bruker AW 300 spectrometer; proton chemical
shifts are quoted to TMS as standard. Mesomorphism
was studied by heated stage polarising microscopy us-
ing a Zeiss axioscope microscope equipped with a
Linkam TH 600 hot stage and PR 600 temperature
controller. Calorimetric measurements were performed
on a Perkin–Elmer DSC7 equipped with an intracooler
at a rate of 5°C min−1 for the monomers and at 10°C
min−1 for the oligomers. At least two heating–cooling
cycles were performed. A Mettler TG50 apparatus was
employed for thermogravimetric analysis. X-ray diffrac-
tion patterns were recorded by the photographic
method utilising a flat-film camera and Ni-filtered Cu
Ka radiation. Inherent viscosities (pinh) of polymer
solutions were measured using N-methyl pyrrolidone
(P1) or CHCl3 (P2) solutions at 25°C and an Ubbelo-
hde viscosimeter. The molecular mass of P2 in CHCl3
solution at 37°C was obtained by means of a Knauer
vapour pressure osmometer.
(CH2)5CH2–CH2–O–); l 6.9 (2H, m, AA%XX% aro-
matic protons); l 8.2 (2H, m, AA%XX% aromatic
protons).
4.3. 1-(p-Nitrophenoxy)-dodecyl-n-ol
Yield 66%. M.p. 100°C. Anal. Calc. for C18H29NO4:
C, 67.97; H, 9.15; N, 4.38. Found: C, 67.47; H, 9.44; N,
4.35%.
1H NMR (CDCl3): l 1.3 (10H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (2H, q, HOCH2–
3.6 (2H, bt, HOCH2–
4.0 (2H, t, HOCH2–
(CH2)5CH2–CH2–O–); l 6.9 (2H, m, AA%XX% aro-
matic protons); l 8.2 (2H, m, AA%XX% aromatic
protons).
[Pd(PhCN)2Cl2] [25], 4,4%-dichloroformyl–a,v-diphe-
noxydodecane [26] and 4,4%-dihydroxyazobenzene [22]
were prepared as reported in the literature. For ho-
mologous series of compounds one detailed preparation
is given.
4.4. 1-(p-Aminophenoxy)-octyl-n-ol
In a typical preparation, 10 g (0.037 mol) of 1-(p-ni-
trophenoxy)-octyl-n-ol were dissolved in 70 ml of abso-
lute ethanol and palladium on charcoal (119 mg, 0.001
mol) was added to the solution. The suspension was
warmed up to 60°C and NH2NH2·H2O (44.9 ml, 0.925
mol) was added dropwise. After 7 h the suspension was
cooled down, filtered off and the solution refrigerated.
The colourless solid, which precipitates on cooling, was
filtered off and crystallised twice from absolute ethanol.
Yield 3.1 g, 35%.
4.1. 1-(p-Nitrophenoxy)-octyl-n-ol
In a typical preparation nitrophenol (10 g, 0.072 mol)
was dissolved in 60 ml of cyclohexanone and 4 equiv. of
potassium carbonate, (39.8 g, 0.288 mol) were added to
the solution. 8-Chloro-1-octanol (14.2 g, 0.086 mol) was
added and the resulting mixture was refluxed for 7 h,
filtered off while hot and the solution evaporated under
M.p. 75°C. Anal. Calc. for C14H23NO2: C, 70.85; H,
9.77; N, 5.90. Found: C, 70.57; H, 9.81; N, 5.80%.

M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
169
1H NMR (CDCl3): l 1.3 (10H, bm, HOCH2–
4.9. p-(Hydroxy)-p%-(oxydodecyl-n-ol)-azobenzene
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–); l 6.6 (2H, m, AA%XX% aro-
matic protons); l 6.8 (2H, m, AA%XX% aromatic
protons).
l
l
l
1.8 (2H, q, HOCH2–
3.6 (2H, t, HOCH2–
3.9 (2H, t, HOCH2–
Yield 40%. M.p. 138°C. Anal. Calc. for C24H34N2O3:
C, 72.33; H, 8.60; N, 7.03. Found: C, 72.23; H, 8.76; N,
7.60%.
4.10. p-(p%-Azobenzene)-oxyoctyl-n-ol
4.5. 1-(p-Aminophenoxy)-decyl-n-ol
In a typical preparation 4-hydroxy-4%-(octyloxy-n-ol)-
azobenzene (2 g, 0.0058 mol) was dissolved in 40 ml of
cyclohexanone and potassium carbonate (3.21 g, 0.0232
mol) was successively added to the solution. 8-Chloro-
1-octanol (1.03 g, 0.0070 mol) was added to the suspen-
sion which was refluxed overnight. The mixture was
filtered off while hot and the yellow solid, which pre-
cipitates in the solution, was filtered and crystallised
twice from absolute ethanol. 1.7 g were obtained; yield
63%.
Yield 57%. M.p. 84°C. Anal. Calc. for C16H27NO2: C,
72.41; H, 10.25; N, 5.28. Found: C, 73.76; H, 10.71; N,
4.46%.
1H NMR (CDCl3): l 1.3 (10H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (2H, q, HOCH2–
3.6 (2H, t, HOCH2–
3.9 (2H, t, HOCH2–
(CH2)5CH2–CH2–O–); l 6.6 (2H, m, AA%XX% aro-
matic protons); l 6.8 (2H, m, AA%XX% aromatic
protons).
M.p. 152°C. Anal. Calc. for C28H42N2O4: C, 71.91;
H, 9.11; N, 6.75. Found: C, 72.31; H, 9.12; N, 6.68%.
1H NMR (CDCl3): l 1.3 (20H, bm, HOCH2–
4.6. 1-(p-Aminophenoxy)-dodecyl-n-ol
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–); l 6.98 (2H, m, AA%XX% aro-
matic protons); l 7.85 (2H, m, AA%XX% aromatic
protons).
l
l
l
1.8 (4H, q, HOCH2–
3.65 (4H, t, HOCH2–
4.03 (4H, t, HOCH2–
Yield 62%. M.p. 93°C. Anal. Calc. for C18H31NO2: C,
73.67; H, 10.65; N, 4.77. Found: C, 73.11; H, 10.31; N,
4.75%.
1H NMR (CDCl3): l 1.3 (10H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (2H, q, HOCH2–
3.6 (2H, t, HOCH2–
3.9 (2H, t, HOCH2–
(CH2)5CH2–CH2–O–); l 6.6 (2H, m, AA%XX% aro-
matic protons); l 6.8 (2H, m, AA%XX% aromatic
protons).
4.11. p-(p%-Azobenzene)-oxydecyl-n-ol
Yield 67%. M.p. 149°C. Anal. Calc. for C32H50N2O4:
C, 72.96; H, 9.60; N, 5.32. Found: C, 72.04; H, 9.36; N,
5.09%.
4.7. p-(Hydroxy)-p%-(oxyoctyl-n-ol)-azobenzene
1H NMR (CDCl3): l 1.3 (28H, bm, HOCH2–
4.7.1. Under nitrogen
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (4H, q, HOCH2–
3.65 (4H, t, HOCH2–
4.03 (4H, t, HOCH2–
In a typical preparation 1-(p-aminophenoxy)-octyl-n-
ol (3 g, 0.0126 mol) was added to 3.2 ml of 12 M HCl
(0.0379 mol) and 10 ml of distilled water and stirred at
room temperature for 1/2 h. The mixture was cooled
down to 0°C and a solution of NaNO2 (0.869 g, 0.0126
mol) in 15 ml of distilled water was added dropwise. To
the resulting solution, phenol (1.98 g, 0.0211 mol) dis-
solved in 12.6 ml of 2 N NaOH was added dropwise.
The yellow mixture was stirred for 2 h and then filtered
off. The resulting light brown solid was dried in air and
crystallised twice from absolute ethanol giving 2.3 g of
the expected product. Yield 52%.
(CH2)5CH2–CH2–O–); l 6.98 (2H, m, AA%XX% aro-
matic protons); l 7.85 (2H, m, AA%XX% aromatic
protons).
4.12. p-(p%-Azobenzene)-oxydodecyl-n-ol
Yield 69%. M.p. 148°C. Anal. Calc. for C36H58N2O4:
C, 74.18; H, 10.03; N, 4.81. Found: C, 74.95; H, 10.43;
N, 4.30%.
M.p. 167°C. Anal. Calc. for C20H26N2O3: C, 70.15;
H, 7.65; N, 8.18. Found: C, 69.92; H, 6.75; N, 7.80%.
1H NMR (CDCl3): l 1.3 (36H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
(CH2)5CH2–CH2–O–);
l
l
l
1.8 (4H, q, HOCH2–
3.65 (4H, t, HOCH2–
4.03 (4H, t, HOCH2–
4.8. p-(Hydroxy)-p%-(oxydecyl-n-ol)-azobenzene
Yield 55%. M.p. 154°C. Anal. Calc. for C22H30N2O3:
C, 71.32; H, 8.16; N, 7.56. Found: C, 71.57; H, 8.12; N,
8.17%.
(CH2)5CH2–CH2–O–); l 6.98 (2H, m, AA%XX% aro-
matic protons); l 7.85 (2H, m, AA%XX% aromatic
protons).

170
M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
4.13. Synthesis of the binuclear complexes
Compound 6. Yield 44%. Anal. Calc. for
C37H56N2O6Pd: C, 60.77; H, 7.72; N, 3.83. Found: C,
60.57; H, 7.71; N, 3.90%.
The reaction was conducted under nitrogen. p-(p%-
Azobenzene)-oxyoctyl-n-ol (1 g, 0.0021 mol) was sus-
pended in MeOH (30 ml) and benzene (30 ml) was
added afterwards. An equimolar amount of
[Pd(PhCN)2Cl2] was added to the suspension and after
a few minutes a brown precipitate formed. The suspen-
sion was stirred for 2 days at room temperature, and
after this period of time the solid was filtered off,
washed several times with diethyl ether and vacuum
dried. 1.12 g of a yellow solid were obtained, yield 81%.
M.p. 229°C with decomposition. Anal. Calc. for
C56H82N4O8Cl2Pd2: C, 55.00; H, 6.76; N, 4.58. Found:
C, 55.81; H, 6.79; N, 4.55%.
1H NMR (CDCl3): l 1.3 (28H, bm, HOCH2–
(CH2)7CH2–CH2–O–);
l
1.8 (4H, q, HOCH2–
(CH2)5CH2–CH2–O–); l 2.12 (3H, s, CH3); l 2.03
(3H, s, CH3); l 3.6 (4H, t, HOCH2–(CH2)5CH2–CH2–
O–); l 4.1 (2H, t, HOCH2–(CH2)5CH2–CH2–O–); l
4.0 (2H, t, HOCH2–(CH2)5CH2–CH2–O–); l 5.4 (1H,
s, CH, acetylacetonate ring); l 6.7 (1H, dd, Jm=2.44
Hz, cyclopalladated ring); l 6.93 (2H, m, AA%XX%
aromatic protons); l 7.0 (1H, d, Jm=2.44 Hz, cyclo-
palladated ring); l 7.77 (1H, d, Jo=8.55 Hz, cyclopal-
ladated ring); l 7.98 (2H, m, AA%XX% aromatic
protons).
Cyclopalladation of the decyl and dodecyl homo-
logues was achieved in ethanol at reflux for 6 h while
for 4,4%-dihydroxyazobenzene a mixture of MeOH/ben-
zene was used as solvent. Yields and elemental analyses
are as follows:
Compound 7. Yield 54%. Anal. Calc. for
C41H65N2O6Pd: C, 62.46; H, 8.31; N, 3.55. Found: C,
63.04; H, 8.37; N, 3.50%.
1H NMR (CDCl3): l 1.3 (36H, bm, HOCH2–
(CH2)9CH2–CH2–O–);
l
1.8 (4H, q, HOCH2–
Compound 2. Yield 68%. M.p. 212°C with decompo-
sition. Anal. Calc. for C64H98N4O8Pd2Cl2: C, 57.58; H,
7.40; N, 4.20. Found: C, 57.12; H, 7.18; N, 4.18%.
Compound 3. Yield 75%. M.p. 207°C with decompo-
sition. Anal. Calc. for C72H114N4O8Pd2Cl2: C, 59.75; H,
7.94; N, 3.87. Found: C, 58.93; H, 7.83; N, 3.71%.
Compound 4. Yield: 47%. Anal. Calc. for
C24H18N4O4Pd2Cl2: C, 40.59; H, 2.55; N, 7.89. Found:
C, 39.30; H, 2.78; N, 7.47%.
(CH2)5CH2–CH2–O–); l 2.12 (3H, s, CH3); l 2.03
(3H, s, CH3); l 3.6 (4H, t, HOCH2–(CH2)5CH2–CH2–
O–); l 4.1 (2H, t, HOCH2–(CH2)5CH2–CH2–O–); l
4.0 (2H, t, HOCH2–(CH2)5CH2–CH2–O–); l 5.4 (1H,
s, CH, acetylacetonate ring); l 6.7 (1H, dd, Jm=2.44
Hz, cyclopalladated ring); l 6.93 (2H, m, AA%XX%
aromatic protons); l 7.0 (1H, d, Jm=2.44 Hz, cyclo-
palladated ring); l 7.77 (1H, d, Jo=8.55 Hz, cyclopal-
ladated ring); l 7.98 (2H, m, AA%XX% aromatic
protons).
Compound 8. Yield 96%. Purified by column chro-
matography on silica gel using a mixture of ethanol/
dichloromethane (90/10, v/v). Anal. Calc. for
C17H17N2O4Pd: C, 48.65; H, 4.08; N, 6.67. Found: C,
47.49; H, 4.62; N, 6.55%.
4.14. Synthesis of the acetylacetonate monomers
4.14.1. Under nitrogen
Compound 5. In a typical preparation the binuclear
complex 1 (1 g, 0.82 mmol) was suspended in absolute
ethanol and 3 equiv. of potassium acetylacetonate
(0.336 g, 2.4 mmol) were added. The suspension was
refluxed for 3 h, cooled to room temperature and
filtered off. The resulting dark red solid was crystallised
from absolute ethanol. Obtained 0.600 g of product,
yield 54%.
1H NMR (acetone): l 2.12 (3H, s, CH3); l 2.03 (3H,
s, CH3); l 5.5 (1H, s, CH acetylacetonate ring); l 6.7
(1H, dd, Jm=2.44 Hz, Jo=8.3 Hz, cyclopalladated
ring); l 6.94 (2H, m, AA%XX% aromatic protons); l 6.97
(1H, d, Jm=2.44 Hz, cyclopalladated ring); l 7.73
(1H, d, Jm=8.79 Hz, cyclopalladated ring); l 7.96
(2H, m, AA%XX% aromatic protons).
Anal. Calc. for C33H48N2O6Pd: C, 58.70; H, 7.16; N,
4.15. Found: C, 59.11; H, 7.54; N, 4.28%.
4.15. Synthesis of the oligomers
1H NMR (CDCl3): l 1.3 (20H, bm, HOCH2–
(CH2)5CH2–CH2–O–);
l
1.8 (4H, q, HOCH2–
Compound P1. Tetrabutylammoniumhydrogensul-
phate (0.203 g, 0.598 mmol) and KOH (0.170 g, 2.58
mmol) were dissolved in 50 ml of distilled water. The
bifunctional cyclopalladated monomer (0.400 g, 0.95
mmol) and an excess of 4,4%-dichloroformyl–a,v-diphe-
noxydodecane (0.761 g, 1.59 mmol) dissolved in 40 ml
of chloroform were added in succession. The mixture
was stirred in a blender for 5 min and then hexane was
added. The resulting orange–brown solid, which pre-
cipitates, was filtered off and washed with water and a
little absolute ethanol. Yield 0.540 g.
(CH2)5CH2–CH2–O–); l 2.12 (3H, s, CH3); l 2.03
(3H, s, CH3); l 3.6 (4H, t, HOCH2–(CH2)5CH2–CH2–
O–); l 4.1 (2H, t, HOCH2–(CH2)5CH2–CH2–O–); l
4.0 (2H, t, HOCH2–(CH2)5CH2–CH2–O–); l 5.4 (1H,
s, CH, acetylacetonate ring); l 6.7 (1H, dd, Jm=2.44
Hz, cyclopalladated ring); l 6.93 (2H, m, AA%XX%
aromatic protons); l 7.0 (1H, d, Jm=2.44 Hz, cyclo-
palladated ring); l 7.77 (1H, d, Jo=8.55 Hz, cyclopal-
ladated ring); l 7.98 (2H, m, AA%XX% aromatic
protons).

M. Ghedini et al. / Inorganica Chimica Acta 292 (1999) 163–171
171
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