Angewandte
Chemie
Table 1: Particle sizes of polymer nanoparticles SCMP1–SCMP8.
boronic acid groups on the SCMP particles). Therefore, more
[
a]
[b]
iodo groups were left on the SCMP particles.
Pore size [nm]
Ax monomer By monomer DLS [nm]
To ascertain that the polycondensations are accessing the
internal palladium nanoparticles through the open channels,
we used the as-synthesized SCMPs of varying sizes as probes.
An orthogonal experiment was designed to check the relative
reactivity of these SCMPs with iodobenzene in these nano-
reactors. A heterogeneous catalyst with palladium nano-
particles on both the external and internal surface of SS-
SCMP1 3.4
1
1
1
1
4
5
5
6
2
2
2
3
2
2
3
2
2.4
3.8
5.4
4.0
4.1
3.9
4.0
3.8
SCMP2 5.4
SCMP3 7.2
SCMP4 5.4
SCMP5 5.4
SCMP6 5.4
SCMP7 5.4
SCMP8 5.4
[15]
CNM-3 (Pd/SS-CNM-3) was also used as a control. The
[
a] Pore sizes of nanoreactors were determined through nitrogen
consumption of iodobenzene was monitored with gas chro-
matography (GC). In all cases, the consumption of iodoben-
zene reaches a plateau in less than 10 hours with Pd/SS-CNM-
adsorption analysis. [b] Sizes of polymer nanoparticles were measured
using DLS.
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as the catalyst. In contrast, the same reaction takes place
sizes of the nanoreactors, thus implying that the sizes of
SCMPs are controlled by the pore sizes of the nanoreactors
because the polycondensations take place exclusively inside
the confined pores of SS-CNM nanoreactors. The SCMP
nanoparticles are also visualized with high-resolution TEM
much more slowly in all Pd@SS-CNMs, thus indicating that
the access of the SCMP nanoparticles to the internal
palladium catalysts is more difficult than to those on the
external surface. Table 2 shows the normalized consumption
(
HR-TEM) (Figure 3a–c). Uniformly distributed particles
Table 2: Normalized consumption of iodobenzene when reacted with
SCMPs in the presence of different catalysts.
with sizes from small to large (SCMP1 to SCMP3) were
clearly observed. The sizes measured with HR-TEM are
consistent with those obtained from dynamitic light scattering
SCMP1 [%]
SCMP2 [%]
SCMP3 [%]
[
a]
(
DLS) analysis. GPC analysis on the three SCMPs revealed
Pd/SS-CNM
100
54
38
3
71
33
4
35
6
1
Pd@SS-CNM-3
Pd@SS-CNM-2
Pd@SS-CNM-1
narrowly dispersed molecular weights from low to high (see
Figure S2). The molecular weights obtained from GPC might
be underestimated as these nanoparticles are structurally
0
0
[
11]
[a] Palladium nanoparticles were loaded on both external and internal
more compact than the polystyrene standards. To figure out
the most probable structures corresponding to SCMP1–
SCMP3, theoretical simulations are carried out based on
a model dendrimer structure from generation 2 to genera-
tion 4.5, where only H atoms are present at the termini. The
calculated sizes of generation 2, 3, and 4 dendrimers match
quite well with the experimental values of SCMP1, SCMP2,
and SCMP3, respectively (see Table S2).
surfaces of SS-CNM-3.
percentage of iodobenzene. The number drops gradually as
the size of SCMP particles used increases, thus implying the
lower contents of termini groups on the larger SCMP
particles. More interestingly, the smallest SCMPs (SCMP1)
can diffuse into the mesochannels of larger nanoreactors (SS-
CNM-2 and SS-CNM-3) to give considerable derivatization
degrees with iodobenzene. In contrast, the middle-sized
SCMP nanoparticles can only enter the largest nanoreactors,
while the largest SCMP nanoparticles can hardly enter either
nanoreactor, thus leading to negligible consumption of
iodobenzene. This set of experiments unambiguously dem-
onstrates that the polycondensation is a true confined growth
with the monomers accessing the palladium nanoparticles
through the open channels.
1
The H NMR spectra of the SCMPs are similar to that of
the model compound 1,3,5-triphenylbenzene (see Figure S3),
where the majority of the peaks appear between d = 7.0–
7
groups was confirmed by derivatization of these SCMPs.
Briefly, the as-prepared SCMPs were first treated with an
excess of 4-methoxyphenylboronic acid, and after that,
treated with 4-iodotoluene (large excess compare to 4-
methoxyphenylboronic acid) for 8 hours, in the presence of
a homogeneous catalyst [Pd(PPh ) Cl ]. After purification
.7 ppm. The presence of the iodine and boronic acid terminal
3
2
2
with column chromatography, the SCMP derivatives show
two peaks corresponding to the methoxy group (d =
The Suzuki-type polycondensation in the nanoreactors
were further explored by using different types of monomers,
like 4,4’-biphenydiboronic acid (3), tetrakis(4-bromophenyl)-
methane (4), 1,3,6,8-tetrabromopyrene (5), and 1,1,2,2-tetra-
kis(4-bromophenyl)ethane (6). All the SCMPs obtained are
fine powders. They are freely soluble in common organic
solvents. After solvent casting on a glass slide, all the SCMPs
form transparent films with smooth and uniform surfaces as
revealed by SEM (see Figures S1B and C). Interestingly, the
sizes of different kinds of SCMPs (SCMP2 and SCMP4–
SCMP8) are exactly the same when the polycondensations
are conducted in the nanoreactor of the same pore size
(Figure 3e), thus corroborating the size-controlled growth of
SCMP nanoparticles in the nanoreactors.
3
.74 ppm) and the methyl group (d = 2.28 ppm) in the
1
H NMR spectrum (see Figure S4). The ratio between the
iodine and the boronic acid termini on the original SCMP was
thus calculated based on the integration ratio of these two
peaks. The results show that more iodine atoms are present
than boronic acid groups on SCMPs, with the ratio around
4
.65:1. It is well acknowledged that the oxidative addition of
an aryl halide to a palladium(0) species is typically the rate-
[14]
determining step in a cross-coupling reaction.
Theoreti-
cally, it is more difficult for the iodo groups on a giant SCMP
particle to diffuse to the palladium nanoparticle than those
small molecular aryl iodides (which eventually react with the
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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