Unsymmetrical dendrimers with tridentate pyridylthioether coordination sites as repeating units: Useful precursor for the synthesis of palladium-containing metallodendrimers

Article abstract of DOI:10.1016/S0040-4020(01)00871-7

Unsymmetrical pyridylthioether monomers derived from 2,6-bis(hydroxymethyl)-3-hydroxypyridine hydrochloride have been used to synthesize dendritic structures by a convergent route. The coupling of the monomers has been achieved by the Mitsunobu reaction. The presence of repeating SNS pincer units makes these molecules precursors of metallodendrimers. The complexation of each binding site with palladium has been achieved upon reaction either with Pd₂(DBA)₃CHCl₃ in the presence of fumaronitrile or PdCl₂(CH₃CN)₂.

Full text of DOI:10.1016/S0040-4020(01)00871-7

TETRAHEDRON
Pergamon
Tetrahedron 57 )2001) 8875±8882
Unsymmetrical dendrimers with tridentate pyridylthioether
coordination sites as repeating units: useful precursor for the
synthesis of palladium-containing metallodendrimers
Gavino Chessa,a,p Luciano Canovese,a Lucia Gemelli,a Fabiano Visentina and Roberta Seragliab
a
Á
Dipartimento di Chimica, Universita di Venezia, Calle Larga S. Marta 2137, I-31123, Venezia, Italy
Á Á
CNR, Centro di Studio sulla Stabilita e Reattivita dei Composti di Coordinazione, Via Marzolo 1, I-35100, Padova, Italy
b
Received 15 May 2001;accepted 30 August 2001
AbstractÐUnsymmetrical pyridylthioether monomers derived from 2,6-bis)hydroxymethyl)-3-hydroxypyridine hydrochloride have been
used to synthesize dendritic structures by a convergent route. The coupling of the monomers has been achieved by the Mitsunobu reaction.
The presence of repeating SNS pincer units makes these molecules precursors of metallodendrimers. The complexation of each binding site
with palladium has been achieved upon reaction either with Pd2)DBA)3CHCl3 in the presence of fumaronitrile or PdCl2)CH3CN)2. q 2001
Elsevier Science Ltd. All rights reserved.
1. Introduction
3 and 6 )Scheme 1). An additional feature of these mono-
mers is the unsymmetrical arrangement of the coupling
functionalities, which is rather unusual, because the
dendrimers described in the literature are generally prepared
using symmetrical building blocks. Since Denkewalter and
coworkers12 disclosed the synthesis of a chiral dendritic
polylysine in 1983, relatively few examples have been
reported of dendritic structures dealing with unsymmetrical
monomers. Most of these reports are concerned with
l-lisynyl13 or l-glutamyl14 dendrimers.15,16
The synthesis of metallodendrimers is one of the main areas
of interest in the chemistry of dendrimers because the result-
ing materials lead to investigations aimed at developing
applications in catalysis, electrochemistry and photo-
physics.1±4 The synthetic research on dendrimers has
allowed access to dendritic macromolecules incorporating
metal centres in speci®c zones as well as throughout all
layers.5,6 Usually, the synthesis of dendrimers with metals
in each repeat unit is based on the use of appropriate transi-
tion metal coordination complexes as building blocks. In
principle, metallodendrimers of this type could be
assembled by complexation of a preformed dendritic super-
structure with transition metals. For example by this
synthetic procedure small organophosphine dendrimers
containing up to ®ve palladium nuclei have been prepared.7
However, due to the complexity of the task, this approach
has few additional examples.8,9
In our research project aimed at the assembly of palladium-
containing dendrimers we became interested in the develop-
ment of dendritic structures containing binding sites with
high af®nity for palladium. To this end it is desirable to have
building blocks that, after incorporation in the dendritic
structure, can easily form stable complexes with palladium.
Previous studies10,11 in this area suggest that tridentate SNS
pyridylthioether ligands have the pre-requisite to achieve
this target. We have consequently chosen building blocks
Scheme 1. Reagents and conditions: i, 48% HBr, re¯ux, 6 h;ii, DMSO,
KOH, PhSH, 1 h, 258C;iii, CH Cl2, TsCl, Et3N, 24 h, 258C;iv, CH Cl2,
MsCl, Et3N, re¯ux;v, DMF, K 2CO3, 3-mercaptobenzyl alcohol, 18-crown-
Keywords: dendrimers;metallodendrimers;pyridylthioethers;palladium
complexes.
Corresponding author;e-mail: chessa@unive.it
2
2
p
6, 24 h, 458C.
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020)01)00871-7

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G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
With a view to enhance the knowledge of the applicability
of pyridine-based unsymmetrical building blocks like 3 and
6 in the synthesis of molecular scaffolds to encapsulate
transition metals and to achieve novel metal-containing
materials with interesting properties, this study explores
the synthesis of pyridylthioether-based dendrimers using a
convergent strategy and their complexation with palladium
derivatives.
Scheme 3. The crude product, a yellowish oil, proved
dif®cult to purify by silica gel column chromatography
due to the poor separation of the desired product from
contaminants. Nevertheless, use of dichloromethane with
increasing amounts )up to 3%) of diethyl ether allowed
separation of a product of acceptable purity in 66% yield.
The need to increase the yield of the coupling step prompted
us to examine an alternative approach for the assembly of
the G-2 dendron 9. Conversion to the corresponding
benzylic chloride of the two benzyl alcohol groups of
monomer 6 was thus undertaken by reaction with methane-
sulfonyl chloride and Et3N in re¯uxing dichloromethane.
Surprisingly, coupling of dichloride 7 with two equivalents
of monomer 3 under standard alkylation conditions )K2CO3/
DMF or NaH/THF) afforded a considerable amount )66%)
of a transesteri®cation product 8 )Scheme 1). This, presum-
ably, derived from reaction of the p-toluenesulfonate ester
function of the product 7 with the hydroxyl group of the
product 3. Compound 8 can be isolated by column chroma-
2. Results and discussion
The synthesis of the monomers 3 and 6 is depicted in
Scheme 1.
Both molecules were derived from 2,6-bis)hydroxymethyl)-
3-hydroxypyridine hydrochloride 1,17 which has been
smoothly prepared from commercially available 3-hydroxy-
pyridine. Treatment of 1 with 48% aqueous HBr, according
to the literature procedure,18 afforded the dibromide 2,
which, upon reaction with benzenethiol in dry DMSO in
the presence of powdered KOH, yielded the bis)phenylthio-
methyl)pyridinol 3 in 83% yield. To facilitate the experi-
mental conditions in the synthesis of the second building
block we employed the p-toluenesulfonate group to protect
the phenol-type functionality of 2,6-bis)hydroxymethyl)-3-
hydroxypyridine hydrochloride 1. Protection of 1 to obtain
the corresponding p-toluenesulfonate ester 4 was achieved
regioselectively in 85% yield using p-toluenesulfonyl
chloride and Et3N in dry dichloromethane.19 The two
hydroxymethyl functionalities were then converted to the
corresponding choromethyl groups by reaction with
methanesulfonyl chloride and Et3N in dry dichloro-
methane20 to afford the dichloride 5 in 88% yield. Finally,
regioselective S-alkylation of 3-mercaptobenzyl alcohol21
with the p-toluenesulfonate ester protected monomer 5
using K2CO3/18-crown-6 in dry DMF gave the hydroxy-
methyl-terminated building block 6 in 79% yield after
puri®cation by column chromatography.
1
tography, and its H NMR characterization is consistent
with the assigned structure. As a consequence, an unaccept-
ably low yield of the second generation dendron was
obtained.
Removal of the p-toluenesulfonate protecting group from 9
using Tesser's procedure25 gave the corresponding pyridinol
10 in 89% yield )Scheme 3). Hence, coupling of deprotected
dendron 10 to the trifunctional core 1,3,5-tris)bromo-
methyl)benzene, under conditions similar to those used for
11, gave the G-2 dendrimer 12 bearing 9 speci®c binding
sites in 69% isolated yield. The activated wedge 10 was also
reacted with monomer 6 under the same coupling conditions
used for the synthesis the second-generation dendron 9.
However, our attempt failed leading to the recovery of the
starting product 10. An alternative coupling procedure was
examined for the synthesis of the third-generation dendron.
Due to the availability of intermediate 7 containing two
benzyl chloride functionalities we reacted 7 with the
dendron 10 using DMF/K2CO3 coupling conditions.
Following a convergent strategy,22 monomer 3 was ®rst
attached to the core molecule 1,3,5-tris)bromomethyl)-
benzene,23 under typical conditions for ether synthesis
)K2CO3/DMF), to give the ®rst generation dendrimer 11
in 77% yield )Scheme 2).
In accordance with the results obtained for the previous
generation the reaction afforded the p-toluenesulfonate
protected dendron 9 as main product. Therefore, the
sulfonate protecting group, which was successfully
employed in the convergent synthesis of poly)aryl ether)
dendrimers,26 in our case proved to be only partly useful.
Consequently, an alternative protecting group or a new
synthetic route should be explored for the synthesis of
dendrons of higher generation. However, all our attempts
to protect the focal point of the building block 6 by
protecting groups compatible with the functionalities
on this monomer and the dendron have so far been
unsuccessful.
Then, pyridylthioether 3 was coupled to monomer 6 using
the Mitsunobu reaction )PPh3, DEAD, THF)24 to afford the
protected second-generation )G-2) dendron 9 as shown in
Consistent with our previous studies27 NMR proved very
useful for con®rming the structure and assessing the purity
of these products. In particular methylene signals can be
used to monitor the extent of coupling to either the
1
monomer 6 or the core moiety. As expected, the H NMR
spectrum of the second generation dendrimer 12 )Fig. 1)
shows six signals for the thiomethylene protons and three
signals for the benzylic protons. The ratio of these two
Scheme 2. Reagents and conditions: i, DMF, K2CO3, 24 h, 658C.

G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
8877
Scheme 3. Reagents and conditions: i, PPh3, DEAD, THF, 24 h, 258C;ii, dioxane, MeOH, 4 M NaOH, 3 h, 25 8C;iii, DMF, K 2CO3, 24 h, 658C.
groups of signals is in full agreement with the theoretical
ratio. The 13C NMR spectrum also is consistent with the
proposed structure for dendrimer 12. However, not all
resonances can be assigned because of the many over-
lapping signals. Finally, the MALDI-TOF spectrum of the
dendrimers 11 and 12 shows the expected molecular ion
peaks on the basis of the calculated molecular weights.
tiguous to chiral coordinate sulphur atom should generate
an AB system different to those belonging to the uncoordi-
nate wing.
Apparently some sort of ¯uxional rearrangement which
imparts an overall symmetry not compatible with a `frozen'
uncoordinated wing is operative. This behavior which is not
unprecedented,29 arises from the fast )on the NMR time
scale) alternating windscreen-wiper motion of the two
wing bearing the sulphur coordinating atoms. This
rearrangement and the consequent induced symmetry can
be used to explain all the observed spectral features. Under
these conditions no diasterotopic CH2S protons nor an AB
system ascribable to asymmetric fumaronitrile protons
could be observed.30 The down®eld shift )Ddˆca.
100 ppm) of fumaronitrile carbons in the 13C NMR
spectrum of 13 is also observed thereby con®rming the
ole®n coordination.
Reaction
of
11
with
three
equivalents
of
Pd2)DBA)3´CHCl328 in an anhydrous acetone±THF mixture
in the presence of fumaronitrile afforded the trinuclear
complex 13 in 78% yield, which was characterized by
NMR spectrometry.
1
The H NMR spectrum of this metallodendrimer deserves
some comments. In particular, upon coordination, the
signals ascribable to CH2S endocyclic and fumaronitrile
protons shift down®eld )Ddˆca. 0.2±0.3 and 3.2 ppm,
respectively) and a general simpli®cation of the spectrum
is observed. As a matter of fact, owing to the molecular
asymmetry and the planar tetracoordinate arrangement of
Pd)0) species, the original six signals of the CH2S protons
should be maintained. Moreover the CH2S protons con-
Such a reaction was then extended to dendrimer 12 with a
view to encapsulating nine palladium nuclei within the
dendritic structure. Addition of nine equivalents of
Pd2)DBA)3´CHCl3 to an acetone±THF solution of 12 in

8878
G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
Figure 1. 200 MHz 1H NMR spectrum )CDCl3) of the dendritic system 12 and its Pd)0) complex 14.
the presence of fumaronitrile gave the expected metallo-
dendrimer 14 in 81% yield )Scheme 4).
Spectroscopic con®rmation of the complexation is provided
by IR spectroscopy since the characteristic CN stretching
vibration of fumaronitrile shifts from 2250 to 2203 cm21
upon coordination.
Again, the coordination can be inferred from the chemical
1
shift changes in both H NMR )Fig. 1) and 13C NMR
spectra. Notably, in the NMR spectra there are no signals
that could arise from partially metallated dendrimer.
To further investigate their complexing ability we reacted
11 and 12 with PdCl2)CH3CN)2 in dry DMF. We obtained
Scheme 4. Synthesis of the nonanuclear palladium complex 14.

G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
8879
the complexes 13a and 14a in 83 and 85% yield, respec-
tively. Incorporation of Pd)II) in each available site leads
again to a signi®cant down®eld shift of the thiomethylene
protons )Ddˆca. 1.2 ppm) and carbon )Ddˆca. 11±
14 ppm) resonances in NMR spectra of 13a. Another indi-
cation for the coordination of the pyridylthioether units is
the broadening of the signals for methylene, pyridine and
aromatic protons. This effect is due to sulfur inversion,
which was found to be operative in related Pd)II) systems
even at low temperature.31
hydrofuran )THF) was distilled from Na benzophenone
immediately before use. Dimethylsulfoxide )DMSO) and
Ê
acetone were dried and stored over 3 and 4 A molecular
sieves, respectively. N,N-Dimethylformamide )DMF) was
puri®ed by distillation from CaH2 and stored over
Ê
4 A molecular sieves in a dark bottle. Dicloromethane was
freshly distilled from CaH2. p-Toluenesulfonyl chloride was
recrystallized from n-hexane. Other solvents and reagents
1
were generally used without further puri®cation. H- and
13C NMR spectra were obtained in CDCl3 solutions, unless
otherwise indicated, on Bruker AC 200 spectrometer using
the solvent signal as internal standard. IR spectra were
recorded on a Nicolet Magna-IRe 750 spectrometer. Melt-
ing points were taken in capillary tubes with a Buchi 535
apparatus and are uncorrected.
Similarly, the 1H NMR and analytical data for 14a
unambiguously indicate the formation of the nonanuclear
palladium complex. The metallodendrimer 14a, not sur-
prisingly, was found to be insoluble or poorly soluble in
1
organic solvents. However, the H NMR spectrum of 14a
could be recorded in DMF )d7). Several attempts have been
made to characterize metallodendrimers 13±14a using both
ESI and MALDI-TOF mass spectrometries. Unfortunately,
no signi®cative results have been obtained. In particular,
any molecular ion has not been detected using the two
ionization techniques. The data obtained by ESI-MS show
the presence of the dendritic skeleton, while peaks originat-
ing from fragmentation processes, already described for
pyridine-based dendrimers,32 are clearly detected by
MALDI-MS, even if different experimental conditions
)e.g. different matrices, different laser power, different
matrix/sample molar ratios) were tested.
Mass spectra of dendrimers were measured by Matrix
Assisted Laser Desorption Ionisation Mass Spectrometry
)MALDI-MS) and Electrospray Mass Spectrometry )ESI-
MS). The MALDI data were obtained using a REFLEXe
Time of Flight instrument )Bruker±Franzen Analytik)
equipped with a `Scout' ion source )nitrogen laser
lˆ337 nm;laser energy ˆ50 mJ;acceleration voltage ˆ
30 KV), operating in positive linear mode. 2,5-Dihydroxy-
benzoic acid )DHB) and 2-)4-hydroxyphenylazo)benzoic
acid )HABA) were used as matrices laid down in solution
with the sample. ESI measurements were performed on
LCQ ion trap instrument )Finnigan, Palo Alto, CA, USA)
operating in positive ion mode. The experimental conditions
used were sheathgas ¯ow )N2): 50 a.u.;source voltage:
4 KV;capillary voltage: 3 V;capillary temperature:
2008C. Sample solutions were directly injected into the
3. Conclusion
source by a syringe pump with a ¯ow rate of 8 mL min21
.
In this study we have successfully employed a two-step
synthetic strategy, based on the construction of a fully
organic dendritic structure followed by the complexation
with palladium derivatives, to assemble metallodendrimers
incorporating palladium.
4.1.1. 2,6-Bis.phenylthiomethyl)-3-hydroxypyridine .or
[G-1]-OH) .3). To a suspension of powdered KOH
)11.2 g, 0.2 mol) in anhydrous DMSO )30 mL) was added
benzenethiol )6.6 g, 60 mmol) and 2,6-bis)bromomethyl)-3-
hydroxypyridine 2 )5.43 g, 15 mmol). After stirring for 1 h
at room temperature the reaction mixture was ®ltered to
remove the excess KOH. The resulting solution, after addi-
tion of 10% aqueous acetic acid )50 mL), was extracted with
CH2Cl2 )2£75 mL). The combined extract was washed with
saturated NaCl solution )2£50 mL), dried )Na2SO4) and
concentrated to dryness on a rotary evaporator. The crude
product was repeatedly extracted with hot cyclohexane,
which afforded a white crystalline solid )4.21 g, 83%) on
cooling to room temperature;mp 116±117 8C;IR )KBr):
nmax )cm21) 3075, 3055, 2585, 1579, 1481, 1437, 1284,
The dendritic infrastructures were achieved by building
blocks having an unsymmetrical arrangement of the
coupling functionalities. A recent study15 indicates that the
structure of unsymmetrically branched dendritic wedges is
more compact than in the corresponding symmetrical
isomers as a result of a coiling effect, which originates
from the unsymmetrical substitution pattern in the branch-
ing unit.
For this reason future work will be devoted to the synthesis
of larger structures and the corresponding symmetrical
analogues although, as the size of dendrimers increase
they become more dif®cult to obtain. Further studies will
also undertake to explore the applicability of Pd)0) metallo-
dendrimers in cross-coupling catalysis and the ®eld of
materials chemistry.
1
1104, 847, 735; H NMR: d 4.14 )s, 2H, CH2S), 4.37 )s,
2H, CH2S), 6.79 )bs, 1H, OH), 7.03 )d, 1H, Jˆ8.4 Hz,
4-pyH), 7.10 )d, 1H, Jˆ8.4 Hz, 5-pyH), 7.15±7.42 )m,
10H, ArH); 13C NMR: d 37.0 )CH2S), 39.5 )CH2S), 123.3
)5-pyC), 124.9 )4-pyC), 126.3, 127.0, 128.8, 129.0, 129.6,
130.3, 133.9, 143.1 )ArC), 146.6 )2-pyC), 148.6 )6-pyC),
150.5 )3-pyC);[Found: C, 67.05;H, 5.06;N, 4.07;S, 18.77.
Anal. calcd for C19H17NOS2: C, 67.22;H, 5.05;N, 4.13;S,
18.89%].
4. Experimental
4.1. Materials and instrumentation
4.1.2. 2,6-Bis.hydroxymethyl)-3-hydroxypyridine p-
toluenesulfonate .4). To a suspension of 2,6-bis)hydroxy-
2,6-Bis)hydroxymethyl)-3-hydroxypyridine hydrochloride
117 and 2,6-bis)bromomethyl)-3-hydroxypyridine 218 were
prepared according to known synthetic procedures. Tetra-
methyl)-3-hydroxypyridine hydrochloride
1
40 mmol) in CH2Cl2 )80 mL) at 08C was added Et3N
)7.66 g,

8880
G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
)8.1 g, 80 mmol) and then p-toluenesulfonyl chloride
)7.63 g, 40 mmol). After 24 h at room temperature the reac-
tion mixture was washed with 5% aq. acetic acid )50 mL),
twice with equal volumes of water, dried )Na2SO4) and
evaporated under reduced pressure to give a solid material.
The crude product was recrystallized from CH2Cl2/diethyl
ether yielding a white crystalline solid )10.58 g, 85%), mp
114±1158C;IR )KBr): nmax )cm21) 3362, 2851, 1595, 1452,
1378, 1180, 1091, 1054, 852, 721, 665; 1H NMR: d 2.48 )s,
3H, CH3), 4.48 )s, 2H, CH2O), 4.77 )s, 2H, CH2O), 7.29 )d,
1H, Jˆ8.4 Hz, 4-pyH), 7.37 )d, 2H, Jˆ8.3 Hz, CH3ArH),
7.50 )d, 1H, Jˆ8.4 Hz, 5-pyH), 7.75 )d, 2H, Jˆ8.3 Hz,
SO2ArH); 13C NMR: d 21.8 )CH3), 59.5 )CH2O), 64.3
)CH2O), 120.1 )5-pyC), 128.3, 130.2, )TsC), 131.1
)4-pyC), 131.9, 142.1 )TsC), 146.3 )2-pyC), 151.6
)6-pyC), 157.5 )3-pyC);[Found: C, 54.25;H, 4.91;N,
4.50;S, 10.28. Anal. calcd for C 14H15NO5S: C, 54.36;H,
4.89;N, 4.53;S, 10.37%].
Jˆ8.3 Hz, SO2ArH); 13C NMR: d 21.7 )CH3), 35.2
)CH2S), 39.4 )CH2S), 64.6 )CH2O), 64.8 )CH2O), 122.7
)5-pyC), 125.1, 125.3, 128.0 )ArC), 128.3 )TsC), 128.7,
128.8, 129.0, 129.3 )ArC), 130.2 )TsC), 130.8 )4-pyC),
132.1 )TsC), 135.3, 135.6, 141.8, 141.9 )ArC),
143.1)TsC), 146.2 )2-pyC), 150.6 )6-pyC), 156.0 )3-pyC);
[Found: C, 60.58;H, 4.92;N, 2.56. Anal. calcd for
C28H27NO5S3: C, 60.74;H, 4.91;N, 2.53%].
4.1.5. 2,6-bis[..3-chloromethylphenyl)thio) methyl]-3-
hydroxypyridine p-toluene sulfonate .or .ClCH2)2-[G-
1]-OTs) .7). To a solution of 6 )1.075 g, 1.94 mmol) in
CH2Cl2 )50 mL) containing Et3N )587 mg, 5.82 mmol) at
08C was slowly added methanesulfonyl chloride )667 mg,
5.82 mmol). The reaction mixture was gently re¯uxed over-
night, after which water was added. The organic layer was
washed with water, dried )Na2SO4) and evaporated under
reduced pressure to give an oil. Puri®cation by ¯ash chro-
matography on silica gel eluting with CH2Cl2 afforded an oil
)780 mg, 68%);IR )KBr): nmax )cm21) 3059, 2960, 1598,
1460, 1387, 1196, 1183, 1084, 841, 665; 1H NMR: d 2.46 )s,
3H, CH3), 3.99 )s, 2H, CH2S), 4.21 )s, 2H, CH2S), 4.51 )s,
2H, CH2Cl), 4.52 )s, 2H, CH2Cl), 7.16±7.37 )m, 11H,
CH3ArH, ArH and 4-pyH), 7.41 )d, 1H, Jˆ8.5 Hz, 5-
pyH), 7.72 )d, 2H, Jˆ8.4 Hz, SO2ArH); 13C NMR: d 21.7
)CH3), 35.0 )CH2S), 39.4 )CH2S), 45.7 )CH2O), 45.8
)CH2O), 122.6 )5-pyC), 126.5 )ArC), 128.3 )TsC), 129.0,
129.2, 129.3, 129.4, 129.6, 129.7 )ArC), 130.1 )TsC), 130.9
)4-pyC), 132.2 )TsC), 136.1, 136.5, 138.0, 138.2 )ArC),
143.2 )TsC), 146.1 )2-pyC), 150.4 )6-pyC), 155.8 )3-
pyC);[Found: C, 56.76;H, 4.19;N, 2.39. Anal. calcd for
C28H25Cl2NO3S3: C, 56.94;H, 4.27;N, 2.37%].
4.1.3.
2,6-Bis.chloromethyl)-3-hydroxypyridine
p-
toluenesulfonate .5). To a solution of 4 )4.64 g, 15 mmol)
in CH2Cl2 )100 mL) containing Et3N )4.55 g, 45 mmol) at
08C was slowly added methanesulfonyl chloride )5.15 g,
45 mmol). The reaction mixture was gently re¯uxed over-
night, after which water was added. The organic layer was
washed with saturated aqueous NaHCO3 )50 mL), water
)2£50 mL), dried )Na2SO4) and evaporated under reduced
pressure. The crude product was recrystallized from
ethanol/water to give a pale brown crystalline solid
)4.55 g, 88%), mp 63±648C;IR )KBr): nmax )cm21) 3131,
1596, 1461, 1378, 1190, 1091, 862, 829, 806, 716, 683; 1H
NMR: d 2.49 )s, 3H, CH3), 4.46 )s, 2H, CH2Cl), 4.67 )s, 2H,
CH2Cl), 7.40 )d, 2H, Jˆ8.4 Hz, CH3ArH), 7.51 )d, 1H,
Jˆ8.5 Hz, 4-pyH), 7.64 )d, 1H, Jˆ8.5 Hz, 5-pyH), 7.81
)d, 2H, Jˆ8.4 Hz, SO2ArH); 13C NMR: d 21.7 )CH3),
41.0 )CH2Cl), 45.6 )CH2Cl), 123.8 )5-pyC), 128.4, 130.2
)TsC), 131.5 )4-pyC), 132.0, 143.8 )TsC), 146.4 )2-pyC),
149.2 )6-pyC), 155.0 )3-pyC);[Found: C, 48.21;H, 3.65;N,
3.95;S, 9.11. Anal. calcd for C 14H13Cl2NO3S: C, 48.57;H,
3.78;N, 4.05;S, 9.26%].
4.1.6. [G-2]-OTs .9). To a solution of 3 )1.29 g, 3.8 mmol),
6 )1 g, 1.81 mmol) and PPh3 )1.23 g, 4.71 mmol) in THF
)20 mL) was slowly added dropwise a THF solution
)20 mL) of DEAD )820 mg, 4.71 mmol). The mixture was
stirred at room temperature for 24 h and then evaporated
under reduced pressure. The residue was taken up in
CH2Cl2 )100 mL) washed with saturated aqueous NaHCO3
)2 x 50 mL), water )2£50 mL) and dried )Na2SO4). After
concentration of the ®ltered solution under reduced pressure
the crude product was puri®ed by ¯ash chromatography on
silica gel eluting with 1% diethyl ether in CH2Cl2 increasing
to 3% to yield a pale yellow oil )1.42 g, 66%);IR )KBr):
nmax )cm21) 3059, 2925, 1588, 1460, 1377, 1268, 1178,
4.1.4. 2,6-Bis[..3-hydroxymethylphenyl)thio) methyl]-3-
hydroxypyridine p-toluenesulfonate .or .HOCH2)2-[G-
1]-OTs) .6). A solution of 3-mercaptobenzyl alcohol
)925 mg, 6.6 mmol) in dry DMF )20 mL) containing
anhydrous K2CO3 )912 mg, 6.6 mmol) was stirred under
reduced pressure at room temperature for 30 min, then
2,6-bis)chloromethyl)-3-hydroxypyridine p-toluenesulfonate
5 )1.04 g, 3 mmol) and 18-crown-6 )159 mg, 0.6 mmol)
were added. The reaction mixture was allowed to react at
458C for 24 h under an atmosphere of argon, after which it
was evaporated under reduced pressure and the residue was
extracted with CH2Cl2 )100 mL) The organic extract was
washed with saturated NaCl solution )2£50 mL), dried
)Na2SO4) and concentrated under reduced pressure. The
residue was puri®ed by ¯ash chromatography on silica gel
eluting with CH2Cl2 gradually increasing to 1:1 CH2Cl2/
ethyl acetate to give a pale yellow oil )1.31 g, 79%);IR
)KBr): nmax )cm21) 3375, 3055, 2926, 2872, 1595, 1456,
1
1082, 833, 743, 698; H NMR: d 2.41 )s, 3H, CH3), 4.03
)s, 2H, CH2S), 4.19 )m, 6H, CH2S), 4.33 )s, 4H, CH2S), 4.94
)s, 4H, CH2O), 6.95±7.47 )m, 36H, CH3ArH, ArH and 4,5-
pyH), 7.7 )d, 2H, Jˆ8.4 Hz, SO2ArH); 13C NMR: d 21.5
)CH3), 34.9 )CH2S), 35.5 )CH2S), 39.1 )CH2S), 69.4
)CH2O), 69.6 )CH2O), 119.1 )50-pyC), 119.2 )50-pyC),
122.0 )40-pyC), 122.4 )5-pyC), 124.8, 125.7, 127.4, 127.9,
128.0, 128.4, 125.7, 127.4, 127.9, 128.0, 128.4, 128.6,
129.9, 129.5, 129.6, 129.9 )ArC and TsC), 130.5 )4-pyC),
132.0, 135.9, 136.0, 136.2, 136.4, 136.7, 136.9, 142.9 )ArC
and TsC), 145.9 )2-pyC), 146.9 )20-pyC), 148.2 )60-pyC),
150.3 )6-pyC), 151.1 )30-pyC), 155.5 )3-pyC);[Found: C,
65.98;H, 4.67;N, 3.46. Anal. calcd for C 66H57N3O5S7: C,
66.24;H, 4.80;N, 3.51%].
1
1377, 1195, 1180, 1080, 1045, 843, 784; H NMR: d 2.45
)s, 3H, CH3), 2.53 )bs, 2H, OH), 3.95 )s, 2H, CH2S), 4.16 )s,
2H, CH2S), 4.55 )s, 2H, CH2O), 4.58 )s, 2H, CH2O), 7.08±
7.39 )m, 12H, CH3ArH, ArH and 4,5-pyH), 7.69 )d, 2H,
4.1.7. [G-2]-OH .10). To a solution of [G-2]-OTs )1.41 g,
1.18 mmol) in dioxane/methanol )14:5, 15 mL) was added

G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
8881
15 mL of the same solvent mixture containing 1.5 mL of
4 M NaOH. The reaction mixture was allowed to stir at
room temperature until TLC showed no starting material
)3 h). Then the reaction mixture was neutralized by the
addition of acetic acid, concentrated to dryness and ®nally
dissolved in CH2Cl2 )100 mL). The resulting solution was
washed with water, dried )Na2SO4) and after ®ltration the
solvent was removed under reduced pressure. The crude
product was puri®ed by ¯ash chromatography on silica gel
eluting sequentially with CH2Cl2/diethyl ether )96:4) and
CH2Cl2/diethyl ether )96:8) affording a clear glassy solid
)1.09 g, 89%);IR )KBr): nmax )cm21) 3445, 3053, 2924,
)s, 6H, CH2S), 4.30 )s, 6H, CH2S), 4.32 )s, 6H, CH2S), 4.83
)s, 6H, CH2O), 4.90 )s, 6H, CH2O), 4.92 )s, 6H, CH2O),
6.86±7.48 )m, 105 H, ArH and 4,5-pyH); 13C NMR: d
35.1 )CH2S), 35.5 )CH2S), 38.9 )CH2S), 39.1 )CH2S), 69.5
)CH2O), 119.2, 122.0, 122.2, 124.3, 124.4, 125.3, 125.7,
126.9, 127.1, 128.0, 128.2, 128.4, 128.5, 128.7, 128.8,
129.4, 129.5, 136.1, 136.4, 136.6, 136.7, 136.8, 137.0,
137.3, 146.6, 146.7, 146.8, 148.0, 148.1, 151.1;MALDI-
MS )HABA matrix): [M1Na]1ˆ3263 m/z;calcd ˆ3264
m/z;[Found: C, 68.73;H, 4.86;N, 3.87. Anal. calcd for
C186H159N9O9S18: C, 68.92;H, 4.94;N, 3.89%].
1
1578, 1456, 1265, 1087, 737, 689; H NMR: d 4.13 )s,
4.2. General procedures for the synthesis of palladium
complexes
2H, CH2S), 4.18 )s, 2H, CH2S), 4.19 )s, 2H, CH2S), 4.31
)s, 2H, CH2S), 4.32 )s, 2H, CH2S), 4.34 )s, 2H, CH2S), 4.93
)s, 2H, CH2O), 4.94 )s, 2H, CH2O), 6.68 )bs, 1H, OH),
6.86±7.46 )m, 34 H, ArH, and 4,5-pyH); 13C NMR: d
35.4 )CH2S), 35.5 )CH2S), 36.0 )CH2S), 39.2 )CH2S), 69.5
)CH2O), 119.3, 122.0, 122.9, 124.2, 124.6, 124.9, 125.8,
125.9, 127.4, 127.7, 128.4, 128.5, 128.7, 128.8, 128.9,
129.6, 129.7, 135.0, 135.8, 135.9, 136.3, 136.4, 136.5,
136.7, 136.8, 143.0, 146.8 and 146.9 )2-pyC, 20-pyC),
4.2.1. .i) With Pd2.DBA)3´CHCl3. To a solution of
dendrimer 11 )100 mg, 0.088 mmol) or 12 )97.2 mg,
0.03 mmol) in anhydrous acetone±THF )2:1, v/v, 30 mL)
were added three )137 mg, 0.132 mmol) or nine )139.7 mg,
0.135 mmol) equivalents of Pd2)DBA)3´CHCl3 and a slight
excess of fumaronitrile )24.8 mg, 0.318 mmol) or )25.3 mg,
0.324 mmol), respectively. After 1 h of stirring at room
temperature under N2 activated charcoal was added. The
reaction mixture was stirred for 1 h and then ®ltered through
Celite. The resulting solution was evaporated under reduced
pressure, and the residue was dissolved in CH2Cl2 )5 mL)
which was then slowly added to diethyl ether )100 mL) with
stirring to give complexes 13 and 14 in 78±81% yield as
creamy or white powders.
148.1 and 148.2 )6-pyC, 60-pyC), 149.8 )3-pyC), 151.1
25
)30-pyC);ESI-MS )10
M
solution in CHCl3):
[M1H]1ˆ1042.3 m/z;calcd ˆ1042.2 m/z;[Found: C,
67.71;H, 4.86;N, 3.99. Anal. calcd for C 59H51N3O3S6: C,
67.98;H, 4.93;N, 4.03%].
4.1.8. [G-1]3-[C] .11). A mixture of 3 )1.12 g, 3.3 mmol)
and anhydrous K2CO3 )456 mg, 3.3 mmol) in dry DMF
)10 mL) was stirred under reduced pressure at room
temperature for 30 min, after which 1,3,5-tris)bromo-
methyl)benzene )375 mg, 1 mmol) was added and the reac-
tion mixture was heated at 658C for 24 h under an
atmosphere of argon. The mixture was evaporated under
reduced pressure and the residue was partitioned between
CH2Cl2 )100 mL) and water )100 mL). The organic extract
was washed with water )2£50 mL), dried )Na2SO4) and
evaporated under reduced pressure to give an oil, which
crystallized as a white solid from acetone. On drying
under reduced pressure, this solid turned into a clear glassy
solid )875 mg, 77%);IR )KBr): nmax )cm21) 3053, 2912,
1580, 1452, 1271, 741, 690; 1H NMR: d 4.22 )s, 6H,
CH2S), 4.35 )s, 6H, CH2S), 5.01 )s, 6H, CH2O), 7.02 )d,
3H, Jˆ8.4 Hz, 4-pyH), 7.05±7.52 )m, 36H, 5-pyH and
ArH); 13C NMR: d 35.7 )CH2S), 39.4 )CH2S), 69.7
)CH2O), 119.6 )5-pyC), 122.3 )4-pyC), 125.6 )ArC core),
126.0, 128.7, 128.8, 129.1, 129.5, 136.2, 136.8 )ArC), 137.3
)ArC core), 147.0 )2-pyC), 148.6 )6-pyC), 151.3 )3-pyC);
MALDI-MS )DHB matrix): [M1K]1ˆ1170 m/z;
calcdˆ1171 m/z;[Found: C, 69.81;H, 4.99;N, 3.68.
Anal. calcd for C66H57N3O3S6: C, 69.99;H, 5.07;N, 3.71%].
Complex 13: Mp 128±1298C )decomp.);IR )KBr): nmax
1
)cm21) 2203, 1578, 1464, 1273, 743, 690; H NMR: d
3.12 )6H, s, CHCN), 4.45 )s, 6H, CH2S), 4.61 )s, 6H,
CH2S), 5.03 )s, 6H, CH2O), 7.15±7.47 )m, 39H, 4,5-pyH
and ArH); 13C NMR: d 23.7 )CCN), 40.7 )CH2S), 45.1
)CH2S), 70.2 )CH2O), 120.5 )5-pyC), 122.0 )CN), 123.4
)4-pyC), 126.0 )ArC core), 128.1, 128.9, 129.2, 129.3,
131.2, 131.3 )ArC), 136.9 )ArC core), 148.7 )2-pyC),
149.4 )6-pyC), 152.2 )3-pyC);[Found: C, 55.48;H, 3.92;
N, 7.34. Anal. calcd for C78H63N9O3S6Pd3´0.25)C2H5)2O: C,
55.67;H, 3.87;N, 7.40%].
Complex 14: Mp 1458C )decomp.);IR )KBr): nmax )cm21
)
2203, 1575, 1458, 1272, 743, 689; 1H NMR: d 3.08 )s, 18H,
CHCN), 4.39 )s, 12H, CH2S), 4.45 )s, 12H, CH2S), 4.51 )s,
6H, CH2S), 4.61 )s, 6H, CH2S), 4.88 )s, 6H, CH2O), 4.92 )s,
6H, CH2O), 5.09 )s, 6H, CH2O), 7.11±7.56 )m, 105H, 4,5-
pyH and ArH); 13C NMR: d 23.3 )CCN), 40.7 )CH2S), 45.1
)CH2S), 69.8 )CH2O), 70.1 )CH2O), 120.5, 120.8, 121.9
)CN), 123.4, 123.6, 125.8, 126.4, 126.7, 128.1, 128.7,
129.0, 129.1, 129.5, 129.9, 130.3, 131.1, 131.5, 132.6,
134.0, 134.2, 136.5, 136.6, 147.8, 148.2, 148.6, 148.8,
148.9, 152.1, 152.2;[Found: C, 54.27;H, 3.74;N, 7.62.
Anal. calcd for C222H177N27O9S18Pd9´0.5)C2H5)2O: C,
54.48;H, 3.71;N, 7.66%].
4.1.9. [G-2]3-[C] .12). 1,3,5-Tris)bromomethyl)benzene
)48 mg, 0.135 mmol) was treated with the G-2 dendron 10
)447 mg, 0.429 mmol) in dry DMF )10 mL) with anhydrous
K2CO3 )62 mg, 0.45 mmol) by the procedure used for 11.
The crude product was puri®ed by ¯ash chromatography on
silica gel eluting sequentially with CH2Cl2/diethyl ether
)96:4) and CH2Cl2/diethyl ether )94:6) to give a white
glassy solid )303 mg, 69%);IR )KBr): nmax )cm21) 3053,
4.2.2. .ii) With PdCl2.CH3CN)2. A solution of dendrimer
11 )65.9 mg, 0.058 mmol) or 12 )50 mg, 0.015 mmol) in dry
DMF )5 mL) was added dropwise to a solution of three
)45.3 mg, 0.175 mmol) or nine )36 mg, 0.139 mmol)
equivalents of PdCl2)CH3CN)2 in DMF )5±25 mL). After
1 h at room temperature, diethyl ether was added to the
1
2924, 1578, 1454, 1265, 1105, 739, 689; H NMR: d 4.14
)s, 6H, CH2S), 4.16 )s, 6H, CH2S), 4.17 )s, 6H, CH2S), 4.27

8882
G. Chessa et al. / Tetrahedron 57 /2001) 8875±8882
G.;Canovese, L.;Visentin, F.;Uguagliati, P.
Commun. 1999, 2, 607±608.
Inorg. Chem.
reaction mixture giving the complexes 13a and 14a in
83±85% yield as orange powders.
12. Denkewalter, R. G.;Kole, J. F.;Lukasavage, W. J. US Patent
4410688, 1983; Chem. Abstr. 1984, 100, 103907p.
Complex 13a: Mp 208±2098C )decomp.);IR )KBr): nmax
1
)cm21) 1575, 1485, 1283, 749, 692; H NMR )DMF d7): d
13. )a) Roy, R.;Zanini, D.;Meunier, S. J.;Romanowska, A.
Chem. Commun. 1993, 1869±1872. )b) Maruo, N.;Uchiyama,
5.46 )bs, 6H, CH2S), 5.50 )bs, 6H, CH2S), 5.55 )bs, 6H,
CH2O), 7.25±8.40 )m, 39H, 4,5-pyH and ArH); 13C NMR
)DMF d7): d 49.9 )3C, CH2S), 50.2 )3C, CH2S), 71.8 )3C,
CH2O);[Found: C, 47.32;H, 3.39;N, 2.48. Anal. calcd for
C66H57Cl6N3O3S6Pd3: C, 47.63;H, 3.45;N, 2.52%].
M.;Kato, T.;Arai, T.;Akisada, H.;Nishino, N.
Chem.
Commun. 1999, 2057±2058. )c) Grandjeean, C.;Rommens,
C.;Gras-Mass, H.;Melnyk, O. Tetrahedron Lett. 1999, 40,
7235±7238.
14. )a) Twyman, L. J.;Beezer, A. E.;Mitchell, J. C. Tetrahedron
Lett. 1994, 35, 4423±4424. )b) Ranganathan, D.;Kurur, S.
Tetrahedron Lett. 1997, 38, 1265±1268.
Complex 14a: Mp 228±2308C )decomp.);IR )KBr): nmax
1
)cm21) 1574, 1474, 1283, 746, 684; H NMR )DMF d7): d
15. Weintraub, H. J. G.;Parquette, J. R. J. Org. Chem. 1999, 64,
3796±3797.
5.49 )bs, 54H, CH2S and CH2O), 7.10±8.30 )m, 105H, 4,5-
pyH and ArH);[Found: C, 45.83;H, 3.24;N, 2.54. Anal.
calcd for C186H159Cl18N9O9S18Pd9: C, 46.18;H, 3.31;N,
2.61%].
16. Peng, Z.;Pan, Y.;Xu, B.;Zhang, J. J. Am. Chem. Soc. 2000,
122, 6619±6623.
17. Baldo, M. A.;Chessa, G.;Marangoni, G.;Pitteri, B. Synthesis
1987, 720±723.
Acknowledgements
18. Chessa, G.;Marangoni, G.;Pitteri, B.;Visentin, F.
Polym. 1992, 18, 7±14.
19. Kurita, K. Chem. Ind. /London) 1974, 345.
React.
Á
This work was supported by Ministero dell'Universita e
della Ricerca Scienti®ca e Tecnologica )Construction of
Solid Supermolecules as Novel Functional Materials
Project).
20. van Oijen, A. H.;Huck, N. P. M.;Kruijtzer, J. A. W.;
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