Dendritic host molecules with a polycationic core and an outer shell of dodecyl groups

Article abstract of DOI:10.1002/ejoc.200600727

The synthesis of a topologically new type of dendrimer is presented in which a permanently positively charged core is decorated with a shell that is apolar and aliphatic in nature. The novel polyionic dendrimers were successfully applied as hosts for a pr

Full text of DOI:10.1002/ejoc.200600727

FULL PAPER
DOI: 10.1002/ejoc.200600727
Dendritic Host Molecules with a Polycationic Core and an Outer Shell of
Dodecyl Groups
Rob van de Coevering,[a] Pieter C. A. Bruijnincx,[a] Cornelis A. van Walree,[a]
Robertus J. M. Klein Gebbink,*[a] and Gerard van Koten*[a]
Keywords: Dendrimers / Host–guest systems / Electrostatic interactions / Liquid crystals / Molecular modeling
The synthesis of a topologically new type of dendrimer is
presented in which a permanently positively charged core is
decorated with a shell that is apolar and aliphatic in nature.
The novel polyionic dendrimers were successfully applied as
hosts for a predefined number of anionic guests, as is shown
for the dye methyl orange. The aliphatic periphery of the
dendrimers efficiently shields the ion pairs and renders the
dendrimers fully soluble in organic solvents that are as apolar
as hexane and, furthermore, provides them with an interest-
ing phase behavior that appears not to be sensitive to the
type of anion associated with it.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
number of guest molecules that are bound by these dendri-
mers. This property allows the formation of well-defined
dendritic assemblies with a discrete number of reversibly
bound functional moieties as diverse as dyes,[8] homogen-
eous catalysts,[9] and fullerenes.[10] In these host–guest sys-
tems, the functional guest molecules are positioned with
their anionic (anchoring) group towards the ammonium
sites in the core of the dendrimer.[11] As a consequence of
Introduction
Applications of dendrimers can be found in many scien-
tific fields, for example, in photochemistry,[1] nanoscience,[2]
homogeneous catalysis,[3] and host–guest chemistry.[4] The
large diversity of functional dendrimers can be explained
by considering their unique branched structure consisting
of three distinctive segments; the core, the dendritic shell,
and the periphery with multiple end groups. The controlled
stepwise synthesis of dendrimers allows selective function-
alization of each of the segments of the dendritic structure.
Functionalities can either be introduced by means of cova-
lent incorporation of a functional moiety in one of the seg-
ments, or otherwise, by means of noncovalent interaction of
the dendrimer with functional “guests”. The internal voids
between the dendritic branches can accommodate guest
molecules,[5] which makes dendrimers good candidates as
container molecules for binding and delivery of multiple
substrate molecules.[6] A first example of a dendritic con-
tainer molecule is the “dendritic box” reported by Meijer
and coworkers, which involves a poly(propyleneimine) den-
drimer that physically entraps substrate molecules in its in-
ternal voids.[7] More recently, our group introduced ionic
core, shell dendrimers that consist of a rigid polyionic core
decorated with a soft condensed shell of Fréchet-type po-
lybenzyl aryl ether dendrons (Figure 1).[8] These polyionic
dendrimers were successfully applied as container molecules
for various anionic (in)organic substrate molecules. The
permanent charges in the dendrimer core predefine the
[a] Organic Chemistry & Catalysis, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Fax: +31-302523615
Figure 1. A core–shell dendrimer that bears an octacationic core
with bromide anions as counterions, a polybenzyl aryl ether shell,
and a periphery of benzyl end groups.
E-mail: r.j.m.kleingebbink@chem.uu.nl
g.vankoten@chem.uu.nl
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this binding mode, the rest of the guest molecule is either ing properties of these dendrimers were studied by means of
sticking outside the dendritic structure or is located in the their interaction with the anionic dye methyl orange (MO).
voids of the dendritic structure depending on the length of
Several examples exist of neutral dendritic compounds
the molecule and the thickness of the dendritic shell. Inter- that are covalently functionalized at the periphery with long
estingly, functional groups that are embedded by a dendritic aliphatic tails attached to gallic acid like building
shell can experience a (a)polar nanoenvironment created by blocks.[14–16] Studies on the thermotropic properties of these
the dendritic structure, which may influence the properties dendrimers revealed interesting phase behaviors for this
of the functional head group.[12]
type of dendrimer. We have, therefore, also studied the
In the present study, we changed the Fréchet-type[13] po- phase behavior of novel polyionic dendrimers [1]Br8 and
lybenzyl aryl ether shell of the dendrimers (Figure 1) to a [2]Br4, and their MO assemblies. Additionally, di- and
Percec-type[14] shell with apolar (dodecyl) end groups (Fig- monoionic wedges [3]Br2 and [4]Br were prepared, which
ure 2). By selectively varying the nature of the dendritic show structural resemblance to one quarter of the polyionic
shell around the polyionic core moiety, we aim to modify dendrimers (Figure 3). The properties of [3]Br2 and [4]Br
the physical properties of the dendrimer while leaving the were subsequently analyzed and compared with those of
host–guest binding properties unaffected. Through the long polyionic dendrimers [1]Br8 and [2]Br4.
aliphatic tails, the resulting polyionic dendrimers [1]Br8 and
[2]Br4 (Figure 2) can be expected to be soluble in apolar
solvents and to more effectively shield a bound functional
guest. To investigate whether the novel apolar shell influ-
ences the host–guest properties of the dendrimer, the bind-
Figure 3. Dendritic wedges [3]Br2 and [4]Br with a di- or monoionic
focal point.
Results and Discussion
Synthesis and Characterization of Ionic Core-Shell
Dendrimers [1]Br8 and [2]Br4
Dendrimers [1]Br8 and [2]Br4 were prepared by using a
convergent synthetic route starting from the core mole-
cules tetrakis(3,5-bis[(dimethylamino)methyl]phenyl)silane
[Si(NCN)4; 5], tetrakis(4-[(dimethylamino)methyl]phenyl)-
silane [Si(CN)4; 6], and 3,4,5-tridodecyloxybenzyl bromide
(8) (Scheme 1).[17] Core molecules Si(NCN)4 (5) and Si-
(CN)4 (6) were prepared according to literature pro-
cedures[8,18] and 8 was synthesized from 3,4,5-tridodecyl-
oxybenzyl alcohol (7)[14] (Scheme 1). A solution of 7 in ben-
zene was treated with PBr3, which afforded 8 as a white
solid in 94% isolated yield. The benzylic bromide group
of 8 was allowed to react with amino-functionalized core
molecules 5 and 6, which afforded the quaternized mole-
cules [1]Br8 and [2]Br4, respectively. A slight excess of 8 was
used to ensure full quaternization of the oligo(amino) cores.
Figure 2. Dendritic molecules [1]Br8 and [2]Br4 bearing a polyionic
core and an outer shell of dodecyl groups.
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Dendritic Host Molecules with a Polyionic Core and an Aliphatic Outer Shell
FULL PAPER
The excess amount of unreacted 8 was easily removed by Synthesis and Characterization of [3]Br2 and [4]Br
washing the crude products with acetone to afford [1]Br8
In addition to the synthesis of the two polyionic dendri-
(74% yield) and [2]Br4 (80% yield) as waxy white solids.
mers, diionic wedge [3]Br2 and monoionic wedge [4]Br were
synthesized (Figure 3). Quantitative quaternization of 1,3-
bis[(dimethylamino)methyl]benzene and N,N-dimethylben-
zylamine with a slight excess of dendron 8 afforded com-
pounds [3]Br2 (yield 45%) and [4]Br (71% yield), respec-
tively, as white solids. The NMR spectroscopic data of
[3]Br2 and [4]Br are in agreement with their proposed struc-
tures and confirm the quantitative quaternization of the
amino groups.
Synthesis and Characterization of Dendrimer/Methyl
Orange Host–Guest Assemblies
To investigate whether the apolar shell around the po-
lyionic core influences the host–guest properties of the
novel polyionic dendrimers, the binding properties of cat-
Scheme 1. Convergent synthesis for polyionic core, shell dendri-
ionic dendritic moieties [1]8+, [2]4+, [3]2+, and [4]+ were
mers [1]Br8 and [2]Br4.
studied by using methyl orange (MO) as a guest mole-
cule.[19] The binding studies were performed according to a
standard procedure that was developed earlier in our
group.[8] A biphasic system consisting of a slight excess of
MO (Na[MO]) in deionized water and a solution of ionic
dendritic molecules [1]Br8, [2]Br4, [3]Br2, or [4]Br in dichlo-
romethane was used to exchange the bromide anions of the
dendritic molecules for MO. Thorough mixing of the bi-
phasic system gave rise to an instantaneous colorization of
the organic phase. Because Na[MO] is insoluble in dichloro-
methane, the color change indicated that anion exchange
had occurred. The orange organic layer was separated and
repeatedly washed with deionized water to remove sodium
bromide. The orange-colored assemblies obtained by this
procedure were analyzed with 1H and 13C{1H} NMR spec-
The NMR spectroscopic, electrospray ionization mass
spectrometry (ESI-MS), and elemental analysis data of
[1]Br8 and [2]Br4 are in full agreement with their proposed
1
structures (see Figure 6 for H NMR spectrum of [1]Br8).
In the ESI-MS spectra of [1]Br8 and [2]Br4, characteristic
ion peaks were observed that correspond to the polyc-
ationic dendritic backbone with a variable number of bro-
mide counterions. The spectrum recorded for [1]Br8 (MW
= 6585.2) showed several characteristic fragment ion peaks
at m/z = 3213.8 (calcd. for [[1]Br6]2+ 3212.7), 2115.7 (calcd.
for [[1]Br5]3+ 2115.2), and 1566.8 (calcd. for [[1]Br4]4+
1566.4) (Figure 4). The spectrum recorded for [2]Br4 (MW
= 3460.8) showed typical fragment ions at m/z = 1650.7
(calcd. for [[2]Br2]2+ 1650.5) and 1073.9 (calcd. for [[2]Br]3+
1073.7). In the mass spectra of both [1]Br8 and [2]Br4, the
3,4,5-tridodecyloxybenzylic cation was observed at m/z =
643.8 (calcd. 644.1). Furthermore, peaks were observed that
can be attributed to dimeric clustered species derived from
[1]Br8 and [2]Br4, that is, m/z = 2554.9 (calcd. for [2ϫ[1]-
Br8 –5Br]5+ 2554.2) and 2228.0 (calcd. for [2ϫ[2]-
Br4 –3Br]3+ 2227.3), respectively. These characteristic ion
peaks in the mass spectra unequivocally point to the forma-
tion of dendritic molecules [1]Br8 and [2]Br4
1
troscopy, and ESI-MS. H NMR spectroscopic analysis of
the assemblies allowed the determination of the stoichiome-
try of the ion exchange procedure, that is, the ratio of MO
1
to dendritic host. Specific peak integration in the H NMR
spectra showed that in all four experiments stoichiometric
exchange of the bromide anions had been achieved
(Table 1); the assemblies are correctly formulated as
[1][MO]8, [2][MO]4, [3][MO]2, and [4][MO] (Figure 5).
Moreover, when an excess of MO was used in the exchange
procedure, the formation of the assemblies with higher MO
contents was not observed. The maximum amount of MO
that is accommodated by the novel core–shell dendrimers
is, therefore, predefined by the number of ammonium sites
comprised in the core of the dendritic compounds. A sim-
Table 1. The number of MO anions accommodated by polycationic
dendritic molecules [1]8+ and [2]4+ and cationic wedges [3]2+ and
1
[4]+ as determined by H NMR spectroscopy.
Host–guest assembly
MO/Host
[1][MO]8
[2][MO]4
[3][MO]2
[4][MO]
7.60
3.95
1.98
1.03
Figure 4. ESI-MS spectrum of octaionic dendrimer [1]Br8.
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Figure 5. MO assemblies [1][MO]8, [2][MO]4, [3][MO]2, and [4][MO].
ilar behavior was earlier observed for ionic core, shell den- spectra of octaionic dendrimer [1]Br8 and its corresponding
drimers with a shell of polybenzyl aryl ether dendrons.[8] MO assembly [1][MO]8 are shown in Figure 6.
The binding stoichiometry of the ionic core-shell dendri-
Upfield shifts (0.2–0.4 ppm) were found for protons in
mers is, therefore, not altered by the presence of long ali- the core of dendrimer [1]8+ upon introduction of MO,
phatic groups at the periphery.
[NMe2 grouping (g), benzylic protons (d, e), and aromatic
1H NMR spectroscopic analysis furthermore allowed the protons of the dendritic wedge (c)], whereas strong down-
determination of the positioning of the MO anions with field shifts of 0.5–0.7 ppm were observed for the Ar-H of
1
respect to the dendritic backbone (Table 2). The H NMR the tetraphenylsilane core unit (a, b). Similar changes in the
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Dendritic Host Molecules with a Polyionic Core and an Aliphatic Outer Shell
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Table 2. Selected 1H NMR spectroscopic data of the cationic host in [1]Br8, [2]Br4, [3]Br2, and [4]Br, and their corresponding MO
assemblies in CD2Cl2 (10–3 ) at room temperature.
Compound
ArHcore or ArHfocal
CH2NCH2Ar
NMe2
ArHshell
OCH2
[1]Br8
[1][MO]8
8.40, 8.10
8.85, 8.75
5.16, 4.85
4.78, 4.53
3.21
2.92
7.05
6.66
3.95
3.74, 3.64
[2]Br4
[2][MO]4
7.84, 7.24
7.81, 7.26
5.34, 4.88
5.15, 4.71
3.15
2.97
6.85
6.71
3.97
3.84, 3.74
[3]Br2
[3][MO]2
8.62, 7.83, 7.57
8.51, 7.52
5.14, 4.83
4.95, 4.71
3.15
3.07
6.86
6.73
3.98
3.91, 3.84
[4]Br
[4][MO]
7.64, 7.52
7.56, 7.48
5.01, 4.96
4.82, 4.81
3.09
3.01
6.84
6.81
3.99
3.92
1
Table 3. Selected H NMR spectroscopic data of the anionic guest
in MO assemblies [1][MO]8, [2][MO]4, [3][MO]2, and [4][MO] and
the tetrabutylammonium salt of MO in CD2Cl2 (10–3 ) at room
temperature.
Compound
H1
H2
H3
H4
NMe2
[Bu4N]][MO] 7.87
7.78
7.75
7.77
7.81
7.79
7.86
7.82
7.81
7.86
7.85
6.77
6.71
6.72
6.77
6.76
3.08
3.05
3.05
3.10
3.08
[1][MO]8
[2][MO]4
[3][MO]2
[4][MO]
7.83
7.81
7.95
7.97
1
Figure 6. The H NMR spectra of dendrimer [1]Br8 (bottom) and
the corresponding MO assembly [1][MO]8 (top). Spectra were re-
corded in [D2]dichloromethane, * denotes residual solvent peak.
[2][MO]4, MO is expected to fill up the internal voids of
chemical shift values were found for tetraionic dendrimer the dendritic hosts to afford a more congested molecular
[2]Br4 upon formation of dendritic MO assembly [2][MO]4. structure. The separation of the OCH2 peaks of [1][MO]8
The changes in the chemical shift values were, however, and [2][MO]4 may be due to a restricted mobility of the
smaller than those found for octaionic dendrimer [1][MO]8. dendritic shell. A congested dendritic structure would pre-
For the tetraphenylsilane core of [2]Br4, the chemical shift vent MO from penetrating as deeply into the dendritic
values are unaffected upon formation of the MO assembly. structure as the bromide anions, which explains the down-
Remarkably, the 1H NMR spectra of dendritic MO as- field shifts observed for the tetraphenylsilane core of den-
semblies [1][MO]8 and [2][MO]4 show two poorly resolved dritic MO assembly [1][MO]8. The idea of a more congested
triplets with a 2:1 ratio for the upfield shifted OCH2 pro- shell is supported by the results obtained with less-con-
tons (f) of the dodecyl tails, whereas original dendrimers gested assembly [2][MO]4, and wedges [3][MO]2 and
[1]Br8 and [2]Br4 show one broad signal.
[4][MO].[20] The introduction of MO guests gives smaller
In addition, small shifts were observed for the protons of shifts of the protons nearby the cationic site(s), and smaller
the MO guests, more specifically the protons ortho to the or, in the case of [4][MO], no separation of the OCH2 peaks.
sulfonato grouping (see H1 in Table 3). These aryl protons As a result of the “open” structure of [3][MO]2 and
shift upfield (0.04–0.08 ppm) in the presence of the poly- [4][MO], the signals of the protons of the aryl groups at the
cationic dendrimers and downfield (0.08–0.1 ppm) in the focal point (ArHfocal) shift upfield instead of downfield as
presence of the di- and monocationic wedge. The peaks of was observed for assembly [1][MO]8.
the other aryl protons (H2–H4) and the dimethylamino
group (NMe2) of the MO guest hardly shift in the presence MO assemblies [1][MO]8 and [2][MO]4, molecular mechan-
of the cationic host molecules.
ics calculations (MMFF94) were performed.[21] The calcu-
To gain more insight into the molecular structures of
The diagnostic shifts observed for the cationic host moie- lated structure of [1][MO]8 (5.1ϫ4.8ϫ4.5 nm) consists of a
ties and MO in the NMR spectra of [1][MO]8, [2][MO]4, spherical dendritic backbone that accommodates eight MO
[3][MO]2, and [4][MO] show that the MO guests are indeed guests. Assembly [2][MO]4 bears four MO guests and
bound to the (dendritic) host molecules. The strong shifts comprises
a
less congested disc-shaped structure
of the protons of the ammonium sites of the host molecules (5.0ϫ4.3ϫ1.9 nm) (Figure 7). The dodecyl groups of the
strongly indicate that the sulfonato group of the MO guest outer shell were set to an all-trans conformation prior to
is located nearby the cationic site(s) of the host molecules. the optimization of the molecular structure. Though the do-
In the case of dendritic MO assemblies [1][MO]8 and decyl groups retain their trans conformation, the aliphatic
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R. J. M. Klein Gebbink, G. van Koten et al.
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tails can easily adopt various alternative conformations at construction of macromolecules with specific physical prop-
room temperature. The calculated structures depicted in erties and has thus been actively studied.[15,16,22] Several sys-
Figure 7 should therefore be considered as “fully stretched” tems have been reported in which 3,4,5-tridodecyloxybenzyl
structures of [1][MO]8 and [2][MO]4. In assemblies [1]- groups are appended to the periphery as mesogenic units,
[MO]8 and [2][MO]4, the sulfonato groups of the MO guests similar to the compounds described here. This, together
are located nearby the ammonium sites in the core of the with the fact that some examples of ionic liquid–crystalline
dendritic backbone and the MO guests of assembly [1]- dendrimers have been reported,[16,23] prompted us to study
[MO]8 are embedded by the dendritic host. These observa- the phase behavior of our polyionic dendrimers, the model
tions are fully consistent with the results obtained by NMR compounds, and the MO assemblies. An initial study of the
spectroscopy.
phase behavior of dendrimers [1]Br8 and [2]Br4 and wedges
[3]Br2 and [4]Br was performed by using thermal optical
polarization microscopy (TOPM) and differential scanning
calorimetry (DSC). In addition, the thermal stability of
these compounds was studied by thermogravimetric analy-
sis (TGA).
Ionic core-shell dendrimers [1]Br8 and [2]Br4 are waxy
and malleable solids, which show birefringent domains un-
der the polarization microscope that become more fluid at
higher temperatures. An irreversible transition to an iso-
tropic liquid occurs at temperatures of 170 and 176 °C for
[1]Br8 and [2]Br4, respectively. Accordingly, the DSC traces
of dendrimers [1]Br8 and [2]Br4 do not show any reversible
transitions in the 20–190 °C range. TGA shows that the
irreversible transitions are caused by thermal decomposi-
tion of [1]Br8 and [2]Br4 (Tdec = 170 and 176 °C, respec-
tively). Similar irreversible isotropization was observed for
dendritic wedge [3]Br2 (Tdec = 175 °C). In the case of [4]Br,
however, the anisotropic phase does restore itself again
upon cooling of the isotropic liquid. Indeed, the DSC
shows one phase transition at 137 °C (∆H = 44.9 kJmol–1)
in good agreement with the observations made under the
microscope. According to TGA, thermal decomposition of
[4]Br occurs at 145 °C.
To study the influence of the MO guest molecules on the
phase behavior of the corresponding dendrimer assemblies,
[1][MO]8 and [2][MO]4 were also analyzed by TOPM and
DSC. Dendritic MO assemblies [1][MO]8 and [2][MO]4 both
show birefringence at room temperature. Upon heating, the
malleable specimens gradually become more fluid, while the
anisotropy remains. Isotropic liquids are irreversibly formed
at 120 and 160 °C, respectively. The phase behavior of den-
drimers [1]Br8 and [2]Br4 is, therefore, not substantially
changed upon the incorporation of MO. The only effect
that is observed is that the introduction of MO anions
causes a decrease in the thermal stability by 16 and 50 °C
for [1]Br8 and [2]Br4, respectively. In the case of host–guest
assemblies [1][MO]8 and [2][MO]4 based on dendrimers
[1]Br8 and [2]Br4, the properties are predominated by the
dendritic backbone, that is, the MO guest molecules are
subjected to the properties of the dendritic backbone. These
findings are supported by the solubility profiles earlier ob-
served for MO assemblies [1][MO]8 and [2][MO]4, which are
very similar to those of dendrimers [1]Br8 and [2]Br4.
Figure 7. Space filling models of the calculated molecular struc-
tures of dendritic MO assemblies [1][MO]8 and [2][MO]4 (side and
top view).
Solubility Properties
The earlier reported polyionic polybenzyl aryl ether den-
drimers are soluble in chlorinated hydrocarbons and tolu-
ene, but are insoluble in hexane.[8] The fact that dendrimers
[1]Br8 and [2]Br4, as well as their corresponding MO as-
semblies [1][MO]8 and [2][MO]4, are soluble in apolar sol-
vents like hexane implies an excellent shielding of the ion
pairs in the core by the aliphatic groups. Solubility studies
in hexane showed that the solubility of the MO assemblies
decreases going from [1][MO]8, [2][MO]4, [3][MO]2 to
[4][MO]. For comparison, the tetrabutylammonium salt of
MO is very poorly soluble in hexane, which is most proba-
bly due to the less efficient shielding of the ion pair. These
observations clearly demonstrate the influence of the shell
on the solubility profile of the core-shell dendrimers.
Phase Behavior
Conclusions
The incorporation of liquid crystalline fragments in a
We have presented the synthesis of a topologically new
dendritic structure offers interesting possibilities for the type of dendrimer in which a permanently positively
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Dendritic Host Molecules with a Polyionic Core and an Aliphatic Outer Shell
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30.3, 29.7, 29.6, 26.1, 22.7, 14.1 ppm. C43H79BrO3 (723.99): calcd
C 71.34, H 11.00; found C 71.45, H 11.12.
charged core is covered by a peripheral shell that is apolar
and fully aliphatic in nature. Owing to the presence of the
ammonium groups in the core, these dendrimers can be
used as hosts for a predefined number of anionic guests,
as was shown for MO. The aliphatic periphery renders the
dendrimers soluble in organic solvents that are as apolar as
hexane The binding properties of the core are not influ-
enced by this aliphatic shell in comparison to a more polar
shell like, for example, Fréchet-type polybenzyl aryl ether
wedges. Remarkably, the phase behavior of these dendri-
mers appear not to be sensitive to the type of anions that
[1]Br8: A mixture of Si(NCN)4 (5; 150 mg, 0.19 mmol) and 8
(1.20 g, 1.66 mmol) in CH2Cl2 (150 mL) was stirred for 24 h at
room temperature. The slightly yellow solution was concentrated
in vacuo and excess 8 was removed by washing with acetone
(5ϫ50 mL) to afford [1]Br8 as a yellow–white waxy solid (0.91 g,
0.14 mmol, 74%). 1H NMR (300 MHz, CD2Cl2, 25 °C): δ = 8.40
[s, 8 H, ArH(core)], 8.10 [s, 4 H, ArH(core)], 7.05 [s, 16 H, ArH(sh-
ell)], 5.16 [s, 16 H, NCH2(shell)], 4.85 [s, 16 H, CH2N(core)], 3.95
(br. signal, 48 H, OCH2), 3.21 [s, 48 H, N(CH3)2], 1.68 (m, 48
H, OCH2CH2), 1.40 (m, 48 H, OCH2CH2CH2), 1.26 (m, 384 H,
are associated with them, as was exemplified for MO whose 8ϫCH2), 0.88 (m, 72 H, CH3) ppm. 13C{1H} NMR (300 MHz,
CDCl3, 25 °C): δ = 153.5, 143.4, 140.2, 129.3, 122.0, 112.0, 73.6,
69.8, 67.5, 48.9, 32.1, 31.9, 30.6, 29.9, 29.8, 29.7, 29.6, 29.5, 26.4,
26.3, 22.8, 14.2 ppm. ESI-MS: m/z = 3213.8 (3212.7 calcd. for
[[1]Br6]2+), 2554.9 (2554.2 calcd. for [2ϫ[1]Br8 –5Br]5+), 2115.7
(2115.2 calcd. for [[1]Br5]3+), 1566.8 (1566.2 calcd. for [[1]Br4]4+),
643.8 (644.1 calcd. for [C43H79O3]+). C392H708Br8N8O24Si
(6585.17): calcd. C 71.50, H 10.84, N 1.70; found C 71.81, H 10.76,
N 1.64.
macroscopic properties, but not its functional properties,
are “overruled” by that of the dendritic host. In this respect,
this class of dendrimers can be regarded as versatile hosts
for anionic functional guests. As a result of their topology,
they may, furthermore, be of interest as highly charged nan-
ocontainers or reactors in apolar media.
[2]Br4: A mixture of Si(CN)4 (6) (400 mg, 0.71 mmol) and 8 (2.31 g,
3.19 mmol) in CH2Cl2 (150 mL) was stirred for 24 h at room tem-
perature. The slightly yellow solution was concentrated in vacuo
and excess 8 was removed by washing with acetone (5ϫ50 mL).
Product [2]Br4 was obtained as a white powder (1.95 g, 0.56 mmol,
Experimental Section
General Remarks: All solvents were carefully dried and distilled
prior to use. Compounds 5,[18] 6,[8] and 7[14] were prepared accord-
ing to reported procedures. 1H and 13C{1H} NMR spectroscopic
measurements were carried out with a Varian Mercury or Inova
spectrometer (200 and 300 MHz, respectively) at 25 °C and chemi-
cal shifts (δ) are given in ppm relative to the residual solvent peak.
Differential scanning calorimetry was performed by using a Mettler
DSC 12E with the samples in sealed aluminium pans (heating rate
10 °Cmin–1). Thermogravimetry was performed with a Perkin–El-
mer TGS-2 thermogravimetric system under a nitrogen atmosphere
(heating rate 10 °Cmin–1). Thermal optical polarization micro-
scopy was carried out with a Leitz Metallux 3 polarization micro-
scope provided with a Linkam THMS 600 hot stage and a Linkam
TMS 91 temperature controller. Elemental analyses were per-
formed by Dornis und Kolbe, Mühlheim a/d Ruhr, Germany. Time-
of-flight electrospray ionization mass spectra were recorded with a
Micromass LC-TOF mass spectrometer operating in the positive
ion mode by the department of Biomolecular Mass Spectrometry,
Utrecht University. In all experiments, dendrimer samples at a con-
centration of 10–20 µ were introduced into the electrospray need-
les. The nanospray needle potential was typically set to 1300 V and
the cone voltage to 60 V. The source block temperature was set to
80 °C.
1
3
80%). H NMR (300 MHz, CD2Cl2, 25 °C): δ = 7.84 [d, JH,H
=
3
7.2 Hz, 8 H, ArH(core)], 7.24 [d, JH,H = 7.5 Hz, 8 H, ArH(core)],
6.85 [s, 8 H, ArH(wedge)], 5.34 [s, 8 H, NCH2(shell)], 4.88 [s, 8 H,
CH2N(core)], 3.97 (br. signal, 24 H, OCH2), 3.15 [br. s, 24 H,
N(CH3)2], 1.72 (m, 24 H, OCH2CH2), 1.46 (m, 24 H,
OCH2CH2CH2), 1.27 (m, 192 H, 8ϫCH2), 0.87 (t, 3JH,H = 6.6 Hz,
36 H, CH3) ppm. 13C{1H} NMR (300 MHz, CDCl3, 25 °C): δ =
153.5, 140.4, 136.6, 133.3, 129.8, 121.6, 111.9, 73.5, 69.7, 69.1, 67.2,
48.4, 31.9, 30.4, 29.7, 29.6, 29.5, 29.4, 29.3, 26.2, 26.1, 22.6,
14.0 ppm. ESI-MS: m/z = 2228.0 (2227.3 calcd. for [2ϫ[2]-
Br4 –3Br]3+). 1650.7 (1650.5 calcd. for [[2]Br2]2+), 1073.9 (1073.7
calcd. for [[2]Br]3+), 643.8 (644.1 calcd. for [C43H79O3]+).
C208H364Br4N4O12Si (3460.84): calcd. C 72.19, H 10.60, N 1.62, Br
9.24; found C 72.11, H 10.64, N 1.57, Br 9.34.
[3]Br2:
A
mixture of 1,3-bis[(dimethylamino)methyl]benzene
(33 mg, 0.17 mmol) and 8 (260 mg, 0.36 mmol) in CH2Cl2 (40 mL)
was stirred at room temperature for 24 h. The colorless solution
was concentrated in vacuo ,and the crude product was purified by
two consecutive precipitations from CH2Cl2 by adding acetone.
Product [3]Br2 was obtained as
a white powder (130 mg,
0.08 mmol, 46%). 1H NMR (300 MHz, CD2Cl2, 25 °C): δ = 8.62
3,4,5-Tridodecyloxybenzyl Bromide (8): To a solution of 3,4,5-trido-
decyloxybenzyl alcohol (7) (40.26 g, 61 mmol) in benzene (250 mL)
at 0 °C was added dropwise a solution of PBr3 (1.99 mL, 21 mmol)
in benzene (50 mL) under a nitrogen atmosphere. The solution was
warmed to room temperature and stirred overnight. At the point
were NMR spectroscopic and TLC (hexanes/dichloromethane, 1:1)
analysis indicated full consumption of alcohol 7, the yellowish reac-
tion mixture was poured into iced water (250 mL), whereupon
CH2Cl2 (100 mL) was added. The organic layer was separated and
the aqueous layer was extracted with dichloromethane (3ϫ50 mL).
The combined organic layers were washed with H2O (200 mL),
dried with MgSO4, filtered, and concentrated in vacuo to give 8
3
[s, 1 H, ArH(core)], 7.83 [d, JH,H = 7.6 Hz, 2 H, ArH(core)], 7.57
[t, 3JH,H = 7.8 Hz, 1 H, ArH(core)], 6.86 [s, 4 H, ArH(wedge)], 5.14
[s, 4 H, NCH2(shell)], 4.83 (s, 4 H, CH2N), 3.98 (br. signal, 12 H,
OCH2), 3.15 [s, 12 H, N(CH3)2], 1.75 (m, 12 H, OCH2CH2), 1.27
3
(m, 108 H, 9ϫCH2), 0.88 (t, JH,H = 6.6 Hz, 18 H, CH3) ppm.
13C{1H} NMR (300 MHz, CDCl3, 25 °C): δ = 153.3, 139.8, 138.5,
135.2, 129.8, 128.7, 121.7, 111.6, 73.4, 69.6, 68.7, 66.9, 65.1, 48.7,
31.9, 30.4, 29.7, 29.6, 29.5, 29.3, 26.2, 26.1, 24.9, 22.6, 14.1 ppm.
ESI-MS: m/z = 1560.38 (1560.02 calcd. for [[3]Br]+), 1061.80
(1602.79 calcd. for [[3] + CH3C6H2(OC12H25)3]2+), 836.27 (836.39
calcd. for [[3] – CH2C6H2(OC12H25)3]+), 740.24 (740.80 for calcd.
[3]2+), 644.27 (644.09 calcd. for [CH2C6H2(OC12H25)3]+).
C98H178Br2N2O6·2H2O (1676.31): calcd. C 70.22, H 10.94, N 1.67;
found C 69.97, H 10.57, N 1.40.
1
as a white powder (41.39 g, 57 mmol, 94%). H NMR (200 MHz,
CDCl3, 25 °C): δ = 6.57 (s, 2 H, ArH), 4.43 (s, 2 H, CH2Br), 3.96
(m, 6 H, OCH2), 1.76 (m, 6 H, OCH2CH2), 1.27 (m, 54 H,
9ϫCH2), 0.88 (m, 9 H, CH3) ppm. 13C{1H} NMR (300 MHz,
CDCl3, 25 °C): δ = 153.2, 138.4, 132.5, 107.5, 73.5, 69.1, 34.6, 31.9,
[4]Br: A mixture of dimethylbenzylamine (56 mg, 0.41 mmol) and
8 (286 mg, 0.40 mmol) in CH2Cl2 (40 mL) was stirred for 24 h at
Eur. J. Org. Chem. 2007, 2931–2939
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2937

R. J. M. Klein Gebbink, G. van Koten et al.
FULL PAPER
room temperature. The colorless solution was concentrated in
vacuo, and the crude product was washed with hexanes (40 mL) to
1.69 (m, 12 H, OCH2CH2), 1.25 (m, 108 H, 9ϫCH2), 0.89 (m, 18
H, CH3) ppm. 13C{1H} NMR (300 MHz, CD2Cl2, 25 °C): δ =
154.0, 153.3, 148.2, 144.1, 140.4, 135.7, 129.5, 127.2, 125.7, 122.5,
1
give [4]Br as a white powder (250 mg, 0.29 mmol, 71%). H NMR
3
(200 MHz, CD2Cl2, 25 °C): δ = 7.64 [d, JH,H = 7.8 Hz, 2 H, 122.4, 111.9, 100.6, 73.9, 69.8, 49.3, 40.6, 32.5, 30.9, 30.4, 30.3,
ArH(core)], 7.46 [m, 3 H, ArH(core)], 6.84 [s, 2 H, ArH(wedge)],
30.2, 30.1, 30.0, 26.8, 26.7, 23.3, 14.5 ppm. ESI-MS: m/z = 2429.8
5.01 [s, 2 H, NCH2(shell)], 4.96 (s, 2 H, CH2N), 3.99 (br. signal, 6 (2429.9 calcd. for [[3][MO] + CH3C6H2(OC12H25)3]+), 1784.4
H, OCH2), 3.09 [s, 6 H, N(CH3)2], 1.75 (m, 6 H, OCH2CH2), 1.48 (1784.8 calcd. for [[3][MO]]+), 836.8 (836.4 calcd. for [[3] –
3
(m, 6 H, OCH2CH2CH2), 1.27 (m, 48 H, 8ϫCH2), 0.88 (t, JH,H
= 6.6 Hz, 9 H, CH3) ppm. 13C{1H} NMR (300 MHz, CDCl3,
25 °C): δ = 153.3, 140.0, 133.3, 130.5, 129.0, 127.4, 111.8, 73.4,
69.5, 68.2, 67.3, 48.2, 31.8, 30.3, 29.7, 29.6, 29.6, 29.4, 29.3, 26.1,
26.0, 22.6, 14.0 ppm. ESI-MS: m/z = 1637.77 (1638.49 calcd. for
[2ϫ[4]Br – Br]+), 779.29 (779.19 calcd. for [4]+). C52H92BrNO3
(859.20): calcd. C 72.69, H 10.79, Br 9.30, N 1.63; found C 72.78,
H 10.67, Br 9.42, N 1.54.
CH2C6H2(OC12H25)3]+), 740.1 (740.2 calcd. for [3]2+), 644.6 (644.1
calcd. for [CH2C6H2(OC12H25)3]+).
1
3
[4][MO]: H NMR (300 MHz, CD2Cl2, 25 °C): δ = 7.97 [d, JH,H
3
= 9.0 Hz, 2 H, ArH(MO)], 7.85 [d, JH,H = 9.3 Hz, 2 H,
ArH(MO)], 7.79 [d, 3JH,H = 8.7 Hz, 2 H, ArH(MO)], 7.56 [m, 2 H,
ArH(core)], 7.48 [m, 3 H, ArH(core)], 6.81 [s, 2 H, ArH(wedge)],
6.76 [d, 3JH,H = 9.3 Hz, 2 H, ArH(MO)], 4.82 [s, 2 H, NCH2(shell)],
4.81 (s, 2 H, CH2N), 3.92 (m, 6 H, OCH2), 3.08 [s, 6 H, N(CH3)2
(MO)], 3.01 [s, 6 H, N(CH3)2], 1.72 (m, 6 H, OCH2CH2), 1.43 (m,
6 H, OCH2CH2CH2), 1.25 (m, 48 H, 8ϫCH2), 0.86 (m, 9 H, CH3)
ppm. 13C{1H} NMR (300 MHz, CD2Cl2, 25 °C): δ = 154.0, 153.4,
148.5, 144.1, 140.3, 133.9, 131.1, 129.7, 128.2, 127.3, 125.6, 122.7,
122.4, 112.1, 112.0, 73.9, 69.9, 69.5, 68.5, 48.8, 40.6, 32.5, 30.9,
30.3, 30.2, 30.1, 30.0, 26.8, 26.7, 23.3, 14.5 ppm. ESI-MS: m/z =
1861.69 (1862.93 calcd. for [2ϫ[4][MO] – MO]+), 779.15 (779.29
calcd. for [4]+).
General Preparation and Characterization of Dendritic MO As-
semblies: A solution of methyl orange (Na[MO]; 43 mg, 151 µmol,
4.5 equiv.) in deionized water (25 mL) was added to a solution of
[2]Br4 (100 mg, 29 µmol) in dichloromethane (25 mL) and the mix-
ture was vigorously stirred overnight at room temperature. The
orange–colored dichloromethane layer was separated off and
washed with deionized water. The organic layer was then dried with
Na2SO4 and concentrated in vacuo. The red solid [2][MO]4 was
isolated in 87% yield (110 mg, 25.2 µmol). From the 1H NMR
spectrum, the amount of MO anions in the assemblies was calcu-
lated by using specific signal integration (see Table 1).
Acknowledgments
[1][MO]8: 1H NMR (300 MHz, CD2Cl2, 25 °C): δ = 8.85 [s, 8 H,
3
Financial support was obtained from the National Research School
Combination-Catalysis (R. J. M. K.).
ArH(core)], 8.75 [s, 4 H, ArH(core)], 7.83 [d, JH,H = 8.1 Hz, 16
3
H, ArH(MO)], 7.82 [d, JH,H = 9.3 Hz, 16 H, ArH(MO)], 7.75 [d,
3
3JH,H = 8.1 Hz, 16 H, ArH(MO)], 6.71 [d, JH,H = 9.3 Hz, 16 H,
ArH(MO)], 6.66 [s, 16 H, ArH(wedge)], 4.78 [s, 16 H, NCH2(shell)],
4.53 (s, 16 H, CH2N), 3.74 (t, 16 H, OCH2), 3.64 (t, 32 H, OCH2),
3.05 [s, 48 H, N(CH3)2 (MO)], 2.92 [s, 48 H, N(CH3)2], 1.54 (m, 48
H, OCH2CH2), 1.23 (m, 432 H, 9ϫCH2), 0.86 (m, 72 H, CH3)
[1] a) V. Balzani, F. Vögtle, C R. Chimie 2003, 6, 867–872; b) A.
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Chem. 1998, 197, 193–228.
ppm. 13C{1H} NMR (300 MHz, CD2Cl2, 25 °C): δ = 154.0, 153.9, [2] a) D. Astruc, F. Lu, J. R. Aranzaes, Angew. Chem. Int. Ed.
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153.3, 148.5, 144.1, 140.3, 129.7, 127.1, 125.7, 122.6, 111.9, 74.0,
69.9, 49.4, 40.6, 32.6, 32.5, 31.0, 30.1, 30.0, 26.9, 26.7, 23.3,
14.5 ppm. ESI-MS: m/z = 2487.6 (2489.22 calcd. for [[1][MO]5]3+),
1790.25 (1790.83 calcd. for [[1][MO]4]4+), 1950.77 (1952.11 calcd.
for [[1][MO]4 + CH3C6H2(OC12H25)3]4+), 606.87 (608.69 calcd. for
[[MO]2]+), 301.91 (304.35 calcd. for [MO]+).
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1
3
[2][MO]4: H NMR (300 MHz, CD2Cl2, 25 °C): δ = 7.99 [d, JH,H
= 8.4 Hz, 8 H, ArH(MO)], 7.81 [d, 3JH,H = 9.0 Hz, 16 H, ArH(MO)
and ArH(core)], 7.77 [d, 3JH,H = 8.7 Hz, 8 H, ArH(MO)], 7.26 [br.
3
signal, 8 H, ArH(core)], 6.72 [d, JH,H = 9.0 Hz, 8 H, ArH(MO)],
[4] M. W. P. L. Baars, E. W. Meijer, Top. Curr. Chem. 2000, 210,
6.68 [s, 8 H, ArH(wedge)], 5.15 (s, 8 H, NCH2), 4.71 (s, 8 H,
CH2N), 3.84 (t, 8 H, OCH2), 3.74 (t, 16 H, OCH2), 3.05 [s, 24 H,
N(CH3)2 (MO)], 2.97 [s, 24 H, N(CH3)2], 1.62 (m, 24 H,
OCH2CH2), 1.22 (m, 216 H, 9ϫCH2), 0.86 (m, 36 H, CH3) ppm.
13C{1H} NMR (300 MHz, CD2Cl2, 25 °C): δ = 153.9, 153.8, 153.2,
148.3, 143.9, 140.1, 137.3, 133.9, 130.5, 127.1, 125.6, 122.7, 122.5,
111.9, 73.9, 69.7, 48.4, 40.6, 32.5, 30.9, 30.4, 30.3, 30.2, 30.0, 26.9,
26.7, 23.3, 14.5 ppm. ESI-MS: m/z = 1874.9 (1875.0 calcd. for
[[2][MO]2]2+), 1148.6 (1148.5 calcd. for [[2][MO]]3+), 785.4 (785.3
calcd. for [2]4+).
131–182.
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[3][MO]2: 1H NMR (300 MHz, CD2Cl2, 25 °C): δ = 8.51 [s, 1 H,
ArH(core)], 7.95 [d, 3JH,H = 8.1 Hz, 4 H, ArH(MO)], 7.86 [d, 3JH,H
3
= 9.3 Hz, 4 H, ArH(MO)], 7.81 [d, JH,H = 8.4 Hz, 4 H,
ArH(MO)], 7.52 [t, 3JH,H = 7.6 Hz, 3 H, Ar-H(core)], 6.77 [d, 3JH,H
= 9.0 Hz, 4 H, ArH(MO)], 6.73 [s, 4 H, ArH(wedge)], 4.95 [s, 4 H,
NCH2(shell)], 4.71 (s, 4 H, CH2N), 3.91 (t, 4 H, OCH2), 3.84 (t, 8
H, OCH2), 3.10 [s, 12 H, N(CH3)2(MO)], 3.07 [s, 12 H, N(CH3)2],
[6] C. N. Moorefield, G. R. Newkome, C R. Chimie 2003, 6, 715–
724.
[7] J. F. G. A. Jansen, E. M. M. de Brabander-van den Berg, E. W.
Meijer, Science 1994, 266, 1226–1229.
2938
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2931–2939

Dendritic Host Molecules with a Polyionic Core and an Aliphatic Outer Shell
FULL PAPER
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[O3SC6H4N=NC6H4NMe2] anion. For clarity reasons, we use
the notation MO to designate the [O3SC6H4N=NC6H4NMe2]
anion throughout the paper.
van de Coevering, M. Kuil, R. J. M. Klein Gebbink, G. [20] Separation of peaks of the OCH2 (dodecyl) protons was also
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[21] Geometry optimization was performed by using the MMFF94
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Received: August 17, 2006
Published Online: April 30, 2007
[17] Although strictly spoken, compounds [1]8+ and [2]4+ are not
dendrimers, they can be regarded as the zeroth generation of a
class of dendrimers.
Eur. J. Org. Chem. 2007, 2931–2939
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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