Convergent and divergent noncovalent synthesis of metallodendrimers

Article abstract of DOI:10.1021/ja974031e

A new building block is constructed with one pyridine and two kinetically inert complexed Pd(II) ions, for the controlled assembly of metallodendrimers following either a convergent or a divergent route. The double pincer ligand 8 was cyclopalladated with

Full text of DOI:10.1021/ja974031e

6240
J. Am. Chem. Soc. 1998, 120, 6240-6246
Convergent and Divergent Noncovalent Synthesis of
Metallodendrimers
Wilhelm T. S. Huck,† Leonard J. Prins,† Roel H. Fokkens,‡ Nico M. M. Nibbering,‡
Frank C. J. M. van Veggel,*,† and David N. Reinhoudt*,†
Contribution from the Laboratory of Supramolecular Chemistry and Technology and MESA Research
Institute, UniVersity of Twente, P.O. Box 217, NL-7500 AE Enschede, The Netherlands, and
Institute of Mass Spectrometry, UniVersity of Amsterdam, Nieuwe Achtergracht 129,
NL-1018 WS Amsterdam, The Netherlands
ReceiVed NoVember 25, 1997. ReVised Manuscript ReceiVed March 29, 1998
Abstract: A new building block is constructed with one pyridine and two kinetically inert complexed Pd(II)
ions, for the controlled assembly of metallodendrimers following either a conVergent or a diVergent route.
The double pincer ligand 8 was cyclopalladated with Pd[CH3CN]4(BF4)2 and subsequently converted into the
neutral bis-palladium chloride complex 3. The pyridine moiety of 3, that is covalently attached to the spacer
bridging the two pincer complexes, coordinates to activated palladium centers. Via a combination of pyridine-
(3) and cyano-based (2) building blocks, dendrons up to generation three were assembled and characterized
with 1H NMR and FT-IR spectroscopy and MALDI-TOF mass spectrometry. These dendrons can coordinate
through a cyano ligand to an activated nucleus 1 forming conVergently assembled metallodendrimers.
Alternatively, building blocks 3 were used in the diVergent assembly of more stable metallodendrimers, because
of the stronger coordination of pyridine compared to cyano ligands. The formation of metallodendrimers is
1
evidenced by IR and H NMR spectroscopy and electro spray and MALDI-TOF mass spectrometry.
Introduction
rings.7 We have used coordination chemistry to synthesize
metallodendrimers.
Nanochemistry is a rapidly expanding field that is concerned
with the synthesis, characterization, and properties of structures
of nanosize dimensions.1 The use of conventional “covalent”
chemistry requires increasingly laborious multistep syntheses.
Therefore, supramolecular chemistry has exploited self-assembly
to synthesize large, finite structures using a range of noncovalent
interactions.2 There are two main approaches which are to a
certain extent inspired by nature. One exploits the formation
of hydrogen bonds between complementary units.3 The other
is the use of (reversible) coordination chemistry as the driving
force in the assembly process. Sauvage and co-workers were
the first to synthesize catenanes and knots using Cu+ ions as
the assemblers.4 The use of metal ions has also led to the
formation of double and triple helices, grids, and ladders.5
Another type of structures that can be constructed via coordina-
tion chemistry are metallocages and capsules.6 Last but not
least, the square planar coordination around Pd2+ and Pt2+ has
been extensively exploited by Fujita and Stang and their co-
workers in the formation of metallosquares and large metallo-
Dendrimers are attractive nanosize model compounds because
of their globular architecture and their highly functionalized
surface.8 These hyperbranched compounds are synthesized in
a repetitive reaction sequence of nearly quantitative reactions.
The synthetic route can either be diVergent,9 starting from the
nucleus toward the surface, or conVergent,10 where “dendrons”
or “wedges” are covalently linked to a polyfunctional nucleus.
Compared to dendrimers that are fully organic in nature, the
number of metallodendrimers is still limited.11 Metalloden-
drimers can have a metal in the core, in every generation, or
only at the outside.
Recently, we have developed a noncovalent, divergent
synthesis toward nanosize metallodendrimers.12 The “controlled
assembly” (Figure 1) is based on the activation of nucleus 1
(Chart 1), containing three Pd-Cl pincer complexes, by
removing the chloride ion with AgBF4. Subsequent addition
of 3 equiv of nitrile-containing building blocks 2 yields a first
(7) Fujita, M. In ComprehensiVe Supramolecular Chemistry; Lehn, J.-
M., Ed. in chief; Pergamon Press: Oxford, New York, Seoul, Tokyo, 1996;
Vol. 9, Chapter 7, pp 253-282. Stang, P. J. Chem. Eur. J. 1998, 4, 19-27.
Stang, P. J.; Olenyuk, B. Acc. Chem. Res. 1997, 30, 502-518.
(8) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic Mol-
ecules: Concepts, Design, PerspectiVes; VCH: Weinheim, 1996. Zeng,
F.; Zimmerman, S. C. Chem. ReV. 1997, 97, 1681-1712.
(9) Tomalia, D. A.; Naylor, A. M.; Goddard III, W. A. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 138-175.
(1) Ozin, G. A. AdV. Mater. 1992, 4, 612-649.
(2) Philp, D.; Stoddart, J. F. Angew. Chem., Int. Ed. Engl. 1996, 35,
1155-1196.
(3) Conn, M. M.; Rebek, Jr. J. Chem. ReV. 1997, 97, 1647-1668.
(4) Chambron, J.-C.; Dietrich-Buchecker, C.; Sauvage, J.-P. In Com-
prehensiVe Supramolecular Chemistry; Lehn, J.-M., Ed. in chief; Pergamon
Press: Oxford, New York, Seoul, Tokyo, 1996; Vol. 9, Chapter 2, pp 43-
83.
(5) Constable, E. C. In ComprehensiVe Supramolecular Chemistry; Lehn,
J.-M., Ed. in chief; Pergamon Press: Oxford, New York, Seoul, Tokyo,
1996; Vol. 9, Chapter 6, pp 213-252. Baxter, P. N. W. In ComprehensiVe
Supramolecular Chemistry; Lehn, J.-M., Ed. in chief; Pergamon Press:
Oxford, New York, Seoul, Tokyo, 1996; Vol. 9, Chapter 5, pp 165-211.
(6) Jacopozzi, P.; Dalcanale, E. Angew. Chem., Int. Ed. Engl. 1997, 36,
613-615.
(10) Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1990, 112, 7638-
7647.
(11) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic Mol-
ecules: Concepts, Design, PerspectiVes; VCH: Weinheim, 1996; Chapter
8, pp 201-222. Balzani, V.; Campagna, S.; Denti, G.; Juris, A.; Serroni,
S.; Venturi, M. Acc. Chem. Res. 1998, 31, 26-34. Frey, H.; Lach, C.;
Lorenz, K. AdV. Mater. 1998, 10, 279-293. Gorman, C. AdV. Mater. 1998,
10, 295-309.
S0002-7863(97)04031-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/12/1998

Synthesis of Metallodendrimers
J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6241
Scheme 1
ligands is described. Furthermore, because of the stronger
coordination of pyridine ligands to Pd centers,16 more stable
metallodendrimers are obtained.
Synthesis of Building Blocks
The synthesis of the pyridine-containing building blocks 3
(Scheme 1) is similar to the bis-Pd-Cl complexes 2 described
previously. The two pincer ligands 417 are coupled to a spacer
that introduces branching and allows introduction of a pyridine
group. Spacer 5 was synthesized by reacting R,R′,R′′-tribro-
momesitylene18 with potassium phthalimide. The coupling of
4 with 5 in acetonitrile with K2CO3 as base gave the benzylic
ether 6 in 70% yield. Subsequently, the phthalimido group of
Figure 1. Schematic representation of the controlled assembly of a
first generation metallodendrimer.
generation metallodendrimer by coordination of the nitrile
ligands to the palladium centers. Using controlled assembly
we were able to synthesize metallodendrimers up to generation
five.12,13
In this article we describe the combination of two different
ligands to construct metallodendrimers not only via a diVergent
but also via a conVergent route. To our knowledge only the
approach of Balzani and co-workers also allows a divergent
and convergent built up of the metallodendrimers.14 A number
of different metallodendrimers containing transition metals in
eVery generation have been reported in the literature.15 The
synthesis of building blocks 3 with pyridine instead of nitrile
(14) Serroni, S.; Denti, G.; Campagna, S.; Juris, A.; Ciamo, M.; Balzani,
V. Angew. Chem., Int. Ed. Engl. 1992, 31, 1493-1495. Campagna, S.; Denti,
G.; Serroni, S.; Juris, A.; Venturi, M.; Ricevuto, V.; Balzani, V. Chem.
Eur. J. 1995, 1, 211-221. Serroni, S.; Juris, A.; Venturi, M.; Campagna,
S.; Resino, I. R.; Denti, G.; Credi, A.; Balzani, V. L. Mater. Chem. 1997,
7, 1227-1236.
(15) Achar, S.; Puddephatt, R. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 847-849. Achar, S.; Puddephatt, R. J. J. Chem. Soc., Chem. Commun.
1994, 1895-1896. Constable, E. C. Chem. Commun. 1997, 1073-1080.
Constable, E. C.; Harverson, P.; Oberholzer, M. Chem. Commun. 1996,
1821-1822. Newkome, G. R.; He, E. J. Mater. Chem. 1997, 7, 1237-
1244. Newkome, G. R.; Gross, J.; Moorefield, C. N.; Woosley, B. D. Chem.
Commun. 1997, 515-516. Achar, S.; Immoos, C. E.; Hill, M. G.; Catalano,
V. J. Inorg. Chem. 1997, 36, 2314-2320. Achar, S.; Vittal, J. J.; Puddephatt,
R. J. Organometallics 1996, 15, 43-50. Miedaner, A.; Curtis, C. J.; Barkley,
R. M.; DuBois, D. L. Inorg. Chem. 1994, 33, 5482-5490. Ohshiro, N.;
Kiyotake, F.; Onitsuka, K.; Takahashi, S. Chem. Lett. 1996, 871-872.
(16) Davies, J. A.; Hartley, F. R. Chem. ReV. 1981, 81, 79-90.
(17) Huck, W. T. S.; van Veggel, F. C. J. M.; Reinhoudt, D. N. J. Mater.
Chem. 1997, 7, 1213-1219.
(12) Huck, W. T. S.; van Veggel, F. C. J. M.; Reinhoudt, D. N. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1213-1215. Huck, W. T. S.; Hulst, R.;
Timmerman, P.; van Veggel, F. C. J. M.; Reinhoudt, D. N. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1006-1008.
(13) Huck, W. T. S.; van Veggel, F. C. J. M.; Sheiko, S. S.; Mo¨ller, M.;
Reinhoudt, D. N. J. Phys. Org. Chem., in press.
(18) Vo¨gtle, F.; Zuber, M.; Lichtenhaler, R. Chem. Ber. 1973, 106, 717-
718.

6242 J. Am. Chem. Soc., Vol. 120, No. 25, 1998
Huck et al.
Chart 1
Scheme 2
6 was reduced quantitatively to the amine 7 using hydrazine
monohydrate.
Three different building blocks, 1,17 2,12 and 3 (Chart 1), are
available to assemble dendritic structures. Because of the large
size of these assemblies it is convenient to introduce schematic
representations for the building blocks. Dendrimers composed
entirely of 3 are all given the suffix “pyr” (e.g., G1,pyr). The
absence of this suffix indicates the exclusive use of cyano-
containing building blocks.
The pyridine moiety was introduced in high yields by reacting
amine 7 with isonicotinoyl chloride. The cyclopalladation of
8 was quantitative using Pd[CH3CN]4(BF4)2 in CH3CN. The
1H NMR spectrum of the complex shows a broad signal at δ
4.6 ppm for the CH2S protons in the five-membered palladium-
containing rings. No signal at δ 6.76 ppm corresponding to
the two aromatic protons ortho to both thiomethyl groups of
the starting material is observed, indicating complete cyclo-
metalation. The cyclopalladation reaction generates 2 equiv of
HBF4, and consequently the pyridine moiety is protonated. The
last step is the introduction of a strongly coordinating chloride
anion to obtain the overall neutral Pd-Cl complexes. The
reaction with brine failed to introduce the chloride ligand
because insoluble products were formed immediately upon
addition of water. The synthesis of 3 was achieved by adding
a few drops of pyridine to an acetonitrile-dichloromethane
solution of the cationic complex,19 before introducing the
chloride via Me4N+Cl-. After column chromatography and
trituration with MeOH, the pure building block 3 was obtained
in 60% yield.
Divergent Assembly
The three Pd-Cl centers of 1 were “activated” with 3 equiv
of AgBF4. Subsequently, 3 equiv of 3 were added, and a first
generation dendrimer G1,pyr was formed. Via a repetition of
the activation and assembly step, generations two (G2,pyr) and
three (G3,pyr) were assembled (Scheme 2).
1H NMR spectroscopy provides valuable information on the
1
formation of the metallodendrimers. The H NMR spectra of
3, G1,pyr, G2,pyr, and G3,pyr are shown in Figure 2. The
metallodendrimers are not soluble in most organic solvents. The
1H NMR spectra of G1,pyr and G2,pyr were recorded in a mixture
1
of CD2Cl2 and CD3NO2 at 35 °C. The H NMR spectrum of
G3,pyr was measured in CD3NO2 at 80 °C.
1
The H NMR data unequivocally show that the pyridine
groups are coordinated to the Pd center as the signal for the
R-pyridine protons shifts upfield from δ 8.69 to δ 8.30 ppm.
The shift of the â-pyridine protons is not significant. Another
indication for the coordination of pyridine to the Pd centers is
the broadening of the signals for the R-pyridine protons in the
dendrimers. This is probably due to hindered rotation of the
pyridine ligands with respect to the plane of coordination.
(19) The pyridine ligand is deprotonated in aqueous environments and
probably forms a (hyperbranched) polymer by coordinating to the activated
Pd centers. The addition of pyridine causes the polymers to break down.
See for similar hyperbranched polymers: Huck, W. T. S.; van Veggel, F.
C. J. M.; Kropman, B. L.; Blank, D. H. A.; Keim, E. G.; Smithers, M. M.
A.; Reinhoudt, D. N. J. Am. Chem. Soc. 1995, 117, 8293-8294. Huck, W.
T. S.; Snellink-Rue¨l, B. A.; van Veggel, F. C. J. M.; Lichtenbelt, J. W.
Th.; Reinhoudt, D. N. Chem. Commun. 1997, 9-10.

Synthesis of Metallodendrimers
J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6243
1
Figure 2. Part of the 400 MHz H NMR spectra of 3, G1,pyr, G2,pyr, and G3,pyr
.
Two different signals (∆δ 0.05 ppm) for the CH2O protons
are present in the spectrum of G1,pyr. In the 1H NMR spectrum
of G2,pyr, the second signal is present as a shoulder, and in the
case of G3,pyr, two sharp singlets can clearly be seen upon
magnification. One signal corresponds to the CH2O protons
of the chloride protected Pd complexes on the surface and the
other to the Pd-pyridine complexes. The ratio of the peaks is
roughly equal to the theoretically expected ratio. This difference
in shift is caused by the large electronic effect of the pyridine
ligand on the pincer ligand system especially on the para-
position. The ratios of the intensities of the signals around δ
6.7 ppm for the aromatic protons of the palladated ring (ArPdH)
and around δ 7.6 for the â-pyridine protons are in agreement
with the values expected for G1,pyr to G3,pyr. This shows that
the assembly of these metallodendrimers is a quantitative
process.
The ES-MS spectrum of G1,pyr shows the formation of the
metallodendrimer. In the spectrum a signal is present at m/z
1679.9 corresponding to [G1,pyr - 3BF4]3+. The loss of anions
has been observed for other metallodendrimers and is prece-
dented in the literature.12,20 Other signals that are present in
the ES-MS spectrum at m/z 1161.0 and 1516.4 correspond to
[3 - Cl]+ and [1 - Cl]+. The signal for the building blocks
originates most likely from disassembly of G1,pyr in the mass
spectrometer. ES-MS experiments with other generations did
not give signals at high m/z values. The low solubility of the
assemblies might render ionization of separate metallodendri-
mers difficult. The MALDI-TOF spectra of G1,pyr and G2,pyr
show peaks at 5205.7 and 12684, respectively, which are
assigned to [M - BF4]+.
As mentioned above, dendrimers G1,pyr-G3,pyr are poorly
soluble in nitromethane in contrast to the dendrimers G1-G3
described previously.12 To increase the solubility different
noncoordinating anions were introduced. By activating the Pd-
Cl complexes silver tosylate, analogous metallodendrimers with
more lipophilic anions were obtained. Unfortunately, initial
experiments did not seem to yield more soluble assemblies.
Subsequently, the coordination strength of the Pd-pyridine
bond was compared with the Pd-cyano bond. The Pd-Cl
centers of 1 were activated with AgBF4. To this activated core
3 equiv of 3 and 3 equiv of 2 were added simultaneously. The
1H NMR spectrum shows that only G1,pyr is formed. Hence, it
can be concluded that 2 does not coordinate in competition with
3. In principle this can still be a kinetic effect. Therefore,
titration experiments were carried out to study the stability of
the Pd-cyano and Pd-pyridine bond in the presence of the
competing ligands. Solutions of G1,pyr were prepared containing
0, 1, 3, 6, and 12 equiv of benzylcyanide, respectively. 1H NMR
measurements of these mixtures indicated that only coordinated
pyridine was present, since only one signal for the R-pyridine
protons at δ 8.30 ppm was visible. This means that the
-CH2CN ligand cannot displace coordinated pyridine. An
(20) Leize, E.; van Dorsselaer, A.; Kra¨mer, R.; Lehn, J.-M. J. Chem.
Soc., Chem. Commun. 1993, 990-993.

6244 J. Am. Chem. Soc., Vol. 120, No. 25, 1998
Huck et al.
Scheme 3
analogous experiment was carried out with a mixture of G1
containing 0, 1, 3, 6, and 12 equiv of isonicotinoyl benzylamide,
an analogue of 3. 1H NMR measurements showed a very fast
substitution of the -CH2CN ligand by the pyridine, since in all
cases only the signals of coordinated pyridine were present.
Convergent Assembly
The pyridine ligand in 3 coordinates much stronger to
activated palladium centers than the nitrile ligand in 2, which
makes a conVergent approach possible. The convergent route
starts with the synthesis of “dendrons” or “dendritic wedges”
which can be coupled to a polyfunctional nucleus to form the
dendrimer structure. A dendritic wedge (DG2) was constructed
via controlled assembly as shown in Scheme 3. Activation of
2 with AgBF4 and subsequent addition of 2 equiv of 3 gave
DG2 after coordination of the pyridine ligands. The IR spectrum
of this wedge only shows a signal at 2252 cm-1 for the
noncoordinated cyano groups.21 The 1H NMR spectrum of DG2
confirms the coordination of the pyridine moieties as only one
signal at δ 8.30 ppm is present for the R-pyridine protons. As
was observed for G1,pyr two signals for the CH2O protons are
present at δ 5.07 and δ 5.03 ppm; one for the Pd complex with
the pyridine ligand and one for the Pd-Cl complex. The
MALDI-TOF MS spectrum (Figure 3) shows a signal at m/z
3498.2, corresponding to [DG2 - BF4]+, (calcd 3502.8).
Figure 3. MALDI-TOF spectra of DG2 (top) and DG3 (bottom).
spectrum (Figure 3) clearly shows the formation of wedge DG3.
The signal at m/z 8490.3 corresponds to [DG3 - BF4]+, (calcd
8490.7).
Upon the addition of 3 equiv of DG2 to the activated nucleus
1, a second generation dendrimer was constructed via the
convergent assembly route (Scheme 3). The IR spectrum
confirms the connection to the nucleus via coordination of the
∼CH2CN ligands as the characteristic signal at 2290 cm-1 is
Conclusions
The combination of pyridine- with cyano-based building
blocks allowed the assembly of dendrons up to the third
generation. It has been possible to attach these dendrons to an
activated nucleus. This is an example of the assembly of
metallodendrimers via a conVergent route. This is a substantial
broadening of the scope of the controlled assembly process
which also allows the diVergent assembly of metallodendrimers.
The pyridine-based building blocks will be used to introduce
functionality in large, noncovalent assemblies.
1
visible.21 The H NMR spectrum of G2,conv shows the signals
for the pyridine, the ∼CH2CN ligands, and the CH2O protons
in the correct ratios.22
To show the possibility of constructing larger wedges, the
four Pd centers of the previously described dendron DG2 were
deprotected and 4 equiv of 3 were added. The 1H NMR
spectrum shows the coordination of the pyridine ligands. In
the IR spectrum a signal at 2252 cm-1 corresponding to
noncoordinated cyano ligands is present. The MALDI-TOF MS
Experimental Section
Melting points were determined with a Reichert melting point
apparatus and are uncorrected. 1H NMR and 13C NMR spectra were
recorded in CDCl3 (unless indicated otherwise) with Me4Si as internal
standard on a Bruker AC 250 spectrometer. FAB-MS spectra were
recorded with a Finnigan MAT 90 spectrometer using m-NBA as a
matrix. THF was freshly distilled from Na/benzophenone, hexane
(referring to petroleum ether with bp 60-80 °C), and CH2Cl2 from
(21) Storhoff, B. N.; Lewis, H. C. Coord. Chem. ReV. 1977, 23, 1-23.
(22) The MALDI-TOF spectrum of G2,conv, obtained from a mixture of
polypropylene glycol and the UV matrix indole-acrylic acid, shows a small,
but significant signal at an m/z value of 12 194, that can be assigned to [M
- BF4]+. However, also weak signals at higher m/z ratios are observed.
This might be an effect of the matrix and/or applied technique, which is
currently under investigation.

Synthesis of Metallodendrimers
J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6245
K2CO3. Nitromethane was washed with 1 N HCl and water and distilled
from CaCl2. NaH was a 50% dispersion in mineral oil and was used
after washing with hexane. Other chemicals were of reagent grade
and were used as received. Column chromatography was performed
with silica gel 60H (0.005-0.040 mm) from Merck. Pd[CH3CN]4-
(s, 4H), 4.80 (s, 4H), 3.90 (s, 8H), 3.76 (s, 2H); 13C NMR δ 158.9,
143.5, 139.2, 137.5, 136.2, 129.9, 128.9, 126.4, 126.0, 125.3, 122.1,
114.1, 69.8, 46.1, 39.0; EI-MS m/z: 807.231 (M+, calcd for
C49H45O2S4N: 807.233).
r,r′-Bis-(3,5-bis(phenylthiamethyl)phenyloxy)-r′′-(4-pyridinecar-
boxamido)mesitylene (8). Isonicotinoyl chloride hydrochloride (115
mg, 0.65 mmol) was added to a solution of 7 (260 mg, 0.32 mmol)
and Et3N (0.18 mL, 1.29 mmol) in CH2Cl2 (50 mL). The mixture was
stirred overnight at room temperature and subsequently washed with 1
N HCl (100 mL), NaHCO3 (100 mL), and brine (100 mL). After drying
over Na2SO4 the solvent was evaporated under reduced pressure.
Column chromatography (silica gel, eluent: CH2Cl2:MeOH 99:1) was
used to purify the product and after drying under vacuum compound 8
(BF4)2 and compound 417 were prepared according to literature
23
procedures.
Electrospray ionization mass spectrometry (ES-MS) was carried out
using a Micromass Platform quadrupole mass spectrometer, coupled
to a Micromass Masslynx data system. The samples were introduced
into the source by constant infusion or direct injection via a valve-
loop system. Constant infusions were made by loading the samples
(dissolved in nitromethane or chloroform) into a 10 mL gastight SGE
syringe. The sample was presented to the source at a rate of 10 µL/
min of nitromethane or chloroform solution via a Cole Palmer Model
74900 syringe pump. Loop injection was accomplished by using a
Rheodyne 7125 injector valve with a 10 µL loop.
Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-
TOF) mass spectrometry was carried out using a PerSeptive Biosystems
Voyager-DE-RP MALDI-TOF mass spectrometer. A 337 nm UV
Nitrogen laser producing 3 ns pulses was used in the linear and
reflectron mode. The samples were prepared by mixing 10 µL of a
50% nitromethane/chloroform solution of the sample with 20 µL of a
solution of 3 mg/L 2-(4-hydroxyphenylazo)benzoic acid (matrix 1) or
a mixture of 2,5-dihydroxybenzoic acid and 2-(4-hydroxyphenylazo)-
benzoic acid (ratio 2:1, matrix 2) in nitromethane. Of this solution 1
µL was loaded on the gold sample plate, giving approximately 100 µg
of sample.
1
was obtained as a white solid: (0.23 g, 79%). Mp 115-117 °C; H
NMR δ 8.65 (d, 2H, J ) 6.0 Hz), 7.49 (d, 2H, J ) 6.0 Hz), 7.30 (s,
1H), 7.26 (s, 2H), 7.20-7.07 (m, 20H), 6.76 (s, 2H), 6.73 (s, 4H),
4.88 (s, 4H), 4.59 (d, 2H, J ) 6.4 Hz), 3.94 (s, 8H); 13C NMR δ 165.4,
158.7, 150.6, 141.2, 139.3, 138.3, 138.0, 136.2, 129.8, 128.9, 126.7,
126.4, 126.1, 122.2, 120.9, 114.0, 69.5, 44.0, 38.9; FAB-MS 913.3
(M+, calcd 913.2). Anal. Calcd for C55H48O3N2S4‚H2O: C, 70.94; H,
5.41; N, 3.01. Found: C, 70.73; H, 5.26; N, 2.97.
Bis-Palladium Chloride Complex 3. Ligand 8 (70.0 mg, 0.077
mmol) was dissolved in a mixture of CH2Cl2 (25 mL) and CH3CN (75
mL), and Pd[CH3CN]4(BF4)2 (68.2 mg, 0.15 mmol) was added. After
stirring for 1 h at room temperature the solvents were evaporated, and
the cationic complex was used without further purification to prepare
3. The bis-palladium complex was dissolved in a mixture of CH2Cl2
(25 mL) and CH3CN (25 mL). After the addition of some droplets of
pyridine, tetramethylammonium chloride (4.0 g, 36 mmol) was added
whereupon the solution was stirred vigorously overnight at room
temperature. The mixture was filtered to remove excess tetramethyl-
ammonium chloride. The solution was evaporated to dryness and
subjected to column chromatography (silica gel, eluent CH2Cl2/MeOH
gradient 99:1 to 97:3) to give 3 as a yellow solid (56.0 mg, 61%). Mp
158-160 °C. 1H NMR 8,54 (d, 2H, J ) 6.0 Hz), 7.74-7.71 (m, 8H),
7.65 (d, 2H, J ) 6.0 Hz), 7.42-7.22 (m, 15H), 6.56 (s, 4H), 4.87 (s,
4H), 4.55 (d, 2H, J ) 6.4 Hz), 4.43 (s, 8H), 3.48 (s, 3H); 13C NMR δ
165.4, 156.6, 151.3, 150.4, 150.1, 140.9, 139.4, 137.5, 132.2, 131.3,
129.9, 129.7, 127.2, 121.3, 109.1, 69.8, 51.7, 43.8; FAB-MS 1194.2
(M+, calcd 1193.8). Anal. Calcd for C55H46O3S4N2Cl2Pd2‚CH3OH:
C, 54.82; H, 4.11; N, 2.28. Found: C, 54.25; H, 4.09; N, 2.20.
To make comparison with the dendritic structures possible, 3 was
also measured in a 1:1 solution of CD2Cl2 and CD3NO2. This resulted
in the following spectrum: 1H NMR (400 MHz, CD2Cl2:CD3NO2 )
1:1, 35 °C): δ 8.69 (d, 2H, J ) 6.0 Hz), 7.91-7.82 (m, 8H), 7.65 (d,
2H, J ) 6.0 Hz), 7.45-7.39 (m, 15H), 6.72 (s, 4H), 5.00 (s, 4H), 4.65
(bs, 10H).
r,r′-Dibromo-r′′-phthalimidomesitylene (5). A mixture of R,R′,R′′-
tribromomesitylene (8.0 g, 22.42 mmol) and potassium phthalimide
(4.63 g, 25.0 mmol) in DMF (100 mL) was stirred for 10 h at 40 °C.
DMF was evaporated and CH2Cl2 (100 mL) was added. Subsequently,
the organic layer was washed with a saturated aqueous solution of
NH4+Cl- (250 mL), 1 N HCl (100 mL), NaHCO3 (100 mL), and brine
(50 mL). The organic layer was dried over MgSO4 and evaporated to
dryness. Purification by column chromatography (silica, eluent:
CH2Cl2/hexane 90/10) gave 5 as a white solid (4.41 g, 47%). Mp 181-
1
183 °C; H NMR δ 7.88-7.83 (m, 2H), 7.75-7.70 (m, 2H), 7.38 (s,
2H), 7.35 (s, 1H), 5.2 (s, 1H), 4.82 (s, 2H), 4.43 (s, 4H); 13C NMR δ
168.1, 139.0, 137.8, 134.1, 131.8, 129.8, 129.3, 123.5, 40.1, 32.4; EI-
MS m/z: 420.932 (M+, calcd 420.931). Anal. Calcd for
C17H13O2NBr2‚0.5CH2Cl2: C, 46.05; H, 3.00; N, 2.98. Found: C,
45.81; H, 2.95; N, 2.78.
r,r′-Bis-(3,5-bis(phenylthiamethyl)phenyloxy)-r′′-phthalimidomes-
itylene (6). After a mixture of 4 (1.23 g, 3.64 mmol) and K2CO3 (0.60
g, 4.34 mmol) in CH3CN (75 mL) had been stirred for 1 h, compound
5 (0.78 g, 1.82 mmol) was added. The suspension was stirred overnight
at room temperature. After evaporation of DMF CH2Cl2 (100 mL)
was added to the remaining solid. Subsequently, the organic layer was
washed with a saturated solution of NH4+Cl- (250 mL) and water (50
mL). After drying over MgSO4, the solvent was evaporated, and
compound 6 was obtained as a white foam after column chromatography
(silica gel, eluent: CH2Cl2) (1.20 g, 70%). 1H NMR δ 7.73-7.68 (m,
2H), 7.58-7.53 (m, 2H), 7.33 (s, 2H), 7.27 (s, 1H), 7.19-7.01 (m,
20H), 6.75 (s, 2H), 6.68 (s, 4H), 4.79 (s, 4H), 4.76 (s, 2H), 3.91 (s,
8H); 13C NMR δ 167.9, 158.8, 139.2, 137.8, 137.0, 136.2, 134.1, 132.1,
130.0, 128.9, 127.4, 126.4, 126.2, 123.4, 122.0, 114.1, 69.6, 41.4, 39.0;
FAB-MS m/z 937.2 (M+, calcd 937.2). Anal. Calcd for
C57H47O4S4N‚2H2O: C, 70.27; H, 5.28; N, 1.44. Found: C, 70.1; H,
5.20; N, 1.51.
r,r′-Bis-(3,5-bis(phenylthiamethyl)phenyloxy)-r′′-aminomesit-
ylene (7). To a solution of 6 (1.13 g, 1.21 mmol) in THF (25 mL)
and ethanol (25 mL) was added hydrazine monohydrate (13 mL, 0.3
mol). The mixture was stirred overnight at 50 °C. The reaction was
quenched using 1 N HCl (50 mL) and subsequently extracted with
CH2Cl2 (100 mL). The organic layer was washed with NaHCO3 (100
mL) and brine (100 mL), followed by drying over MgSO4 and
evaporation to dryness. Compound 7 was obtained as a slightly yellow
oil (0.96 g, 99%). 1H NMR δ 7.19-7.00 (m, 23H), 6.74 (s, 2H), 6.71
G1,pyr. To a solution of 1 (10.0 mg, 6.44 µmol) in CH2Cl2 (5 mL)
was added 119.9 µL (19.32 µmol) of a freshly prepared stock solution
of AgBF4 in water (0.1611 µM). The mixture was stirred for 5 min,
and the color changed from bright to pale yellow. Subsequently, 3
(23.0 mg, 19.3 µmol) was added, and the mixture was stirred for 5
min after which all solvent was evaporated in vacuo. To remove all
water from the sample the residue was dissolved in dry nitromethane
(5 mL) and evaporated to dryness again under reduced pressure (three
times). Finally, dry nitromethane (5 mL) was added, and the suspension
was filtered through Hyflo/cotton to remove AgCl. After evaporation
of the solvent, G1 was obtained as a yellow solid (30.7 mg, 90%). Mp
1
168-172 °C; H NMR (400 MHz, CD2Cl2:CD3NO2 ) 1:1, 35 °C) δ
8.30 (bs, 6H), 7.75 (bs, 36H), 7.67 (bs, 6H), 7.50-7.32 (m, 66H), 6.73
(s, 18H), 5.08 (s, 12H), 5.02 (s, 6H), 4.75-4.55 (m, 42H); ES-MS m/z
1676.9 [(M-3BF4)3+, calcd 1677.9]; MALDI-TOF MS (matrix 2) m/z
5205.7 [(G1,pyr
-
BF4)+, calcd 5204.0].24 Anal. Calcd for
C234H195O12S18N6Pd9B3F12‚3CH3NO2: C, 54.10; H, 3.91; N, 2.40.
Found: C, 54.50; H, 3.83; N, 2.36.
G2,pyr. To a solution of 1 (5.0 mg, 3.22 µmol) in CH2Cl2 (5 mL)
was added 60.0 µL (9.66 µmol) of a freshly prepared stock solution of
AgBF4 (0.1611 µM). The mixture was stirred for 5 min, and
(24) Due to a too low resolution the isotope pattern was not observed.
However, the calculated isotope pattern with the experimental resolution
was in good agreement with the measured signals.
(23) Sen, A.; Ta-Wang, L. J. Am. Chem. Soc. 1981, 103, 4627-4629.

6246 J. Am. Chem. Soc., Vol. 120, No. 25, 1998
Huck et al.
subsequently 3 (11.5 mg, 9.65 µmol) was added. The mixture was
evaporated to dryness, and the residue dissolved in nitromethane (5
mL). After assembly of G1,pyr all solvent was evaporated; the residue
dissolved in dry nitromethane and evaporated to dryness again (three
times). Crude G1,pyr was dissolved in nitromethane (5 mL), and AgBF4
(119.9 µL, 19.32 µmol) was added again. After stirring for 5 min 3
(23.0 mg, 19.3 µmol) was added to assemble G2. The solvent was
evaporated after which the residue was dissolved in dry nitromethane
and evaporated to dryness again (three times). After filtration through
Hyflo/cotton G2,pyr was obtained as a yellow solid (40.8 mg, 95%).
Mp 165-167 °C; 1H NMR (400 MHz, CD2Cl2:CD3NO2 ) 1:1, 35 °C)
δ 8.26 (bs, 18H), 7.77 (bs, 84H), 7.67 (bs, 18H), 7.50-7.33 (m, 156H),
6.75 (s, 42H), 5.03 (bs, 42H), 4.71-4.53 (bs, 102H); MALDI-TOF
MS (matrix 2) m/z 12684 [(G2,pyr - BF4)+, calcd 12682].24 Anal. Calcd
for C564H471O30S42N18Cl12Pd21B9F36‚2CH3NO2: C, 52.74; H, 3.73; N,
2.17. Found: C, 52.54; H, 3.83; N, 2.50.
(bs, 4H), 7.50-7.32 (m, 45H), 6.78 (s, 4H), 6.75 (s, 8H), 5.07 (s, 8H)
5.03 (s, 4H), 4.75-4.53 (m, 28H), 3.86 (s, 2H); IR (KBr) 2252 cm-1
(CtN). MALDI-TOF MS (matrix 1) m/z 3498.2 [(DG2 - BF4)+, calcd
3502.8]. Anal. Calcd for C160H133O8S12N5Pd6Cl4B2F8‚2CH3NO2: C,
52.84; H, 3.80; N, 2.66. Found: C, 52.44; H, 3.80; N, 2.91.
G2,con. To a solution of 1 (3.58 mg, 2.31 µmol) in a 1:1 mixture of
CH2Cl2 and CH3NO2 (15 mL) was added AgBF4 (1.35 mg, 6.93 µmol).
After stirring for 15 min DG2 (24.85 mg, 6.93 µmol) was added. The
dendrimer G2,con was obtained after standard workup (solvation and
evaporation (3×), filtration over Hyflo) as a yellow solid.22 Mp 144-
148 °C. 1H NMR (400 MHz, CD2Cl2:CD3NO2)1:1, 35 °C) δ 8.30
(bs, 12H), 7.82 (bs, 84H), 7.64 (bs, 12H), 7.48-7.30 (m, 156H), 6.73
(s, 42H), 5.07 (s, 30H), 5.03 (s, 12H), 4.68-4.53 (m, 96H), 3.86 (s,
6H); IR (KBr) 2290 cm-1 (CtN).
549H456O27S42N15Cl12Pd21B9F36‚2CH3NO2: C, 52.37; H, 3.68; N, 1.88.
Found: C, 52.25; H, 3.77; N, 2.10.
Anal.
Calcd for
C
G
3,pyr. similar procedure as for G2,pyr; dark yellow solid; mp 164-
Dendron DG3. Wedge DG2 (9.32 mg, 2.59 µmol) was dissolved
in a 1:1:1 mixture of CH2Cl2, CH3NO2, and CH3CN (15 mL).
Deprotection with AgBF4 (2.02 mg, 10.38 µmol), after 15 min followed
by the addition of 3 (12.40 mg, 10.38 µmol). After standard workup
(solvation in CH2Cl2/CH3NO2 and evaporation (3×) subsequent filtra-
tion over Hyflo) DG3 was obtained as a yellow/brown solid. Mp 138-
140 °C: 1H NMR (400 MHz, CD2Cl2:CD3NO2 ) 1:1, 35 °C) δ 8.04
(bs, 12H), 7.86 (bs, 56H), 7.64 (d, 12H, J ) 6.0 Hz), 7.46-7.35 (m,
105H), 6.73 (s, 28H), 5.02 (s, 28H), 4.61 (bs, 68H), 3.82 (s, 2H); IR
(KBr) 2250 cm-1 (CtN). MALDI-TOF MS (matrix 1) m/z 8490.3
[(DG3 - BF4)+, calcd 8490.7]. Anal. Calcd for C380H317O20S28-
N13Cl8Pd14B6F24‚5CH3NO2: C, 52.06; H, 3.77; N, 2.84. Found: C,
51.84; H, 3.48; N, 2.73.
167 °C. 1H NMR (400 MHz, CD2Cl2:CD3NO2 ) 1:1, 35 °C) δ 8.56
(bs, 42H), δ 7.82 (bs, 180H), 7.66 (bs, 42H), 7.48-7.35 (m, 336H),
6.73 (s, 90H), 5.03 (bs, 90H), 4.71-4.58 (bs, 222H). Anal. Calcd for
C
1224H1023O66S90N42Cl24Pd45B21F84‚4CH3NO2: C, 52.73; H, 3.73; N,
2.30. Found: C, 52.84; H, 3.72; N, 2.69.
Dendron DG2. Cyano building block 2 (7.50 mg, 6.82 µmol) was
dissolved in a 1:1:1 mixture of CH2Cl2, CH3NO2, and CH3CN (10 mL).
AgBF4 (2.66 mg, 13.64 µmol) was added, and the mixture was stirred
for 15 min before pyridine building block 3 (16.3 mg, 13.63 µmol)
was added. After stirring for 5 min the solution was evaporated to
dryness under reduced pressure. The crude product was subsequently
dissolved in a 1:1 mixture of CH2Cl2 and CH3NO2 and evaporated.
This was repeated two times. After dissolving the wedge again in
CH2Cl2 and CH3NO2 the solution was filtered over Hyflo, followed by
evaporation of the solvents and drying under high vacuum. DG2 was
obtained as a yellow solid. Mp 142-146 °C. 1H NMR (400 MHz,
CD2Cl2:CD3NO2 ) 1:1, 35 °C) δ 8.32 (bs, 4H), 7.85 (bs, 24H), 7.67
Acknowledgment. We thank the Dutch Foundation for
Chemical Research (SON) for financial support.
JA974031E