W. Wang et al.
throughout the catalyst networks could provide efficient
mass transport for the reactants and products.
and products during the catalytic reaction. As a result, the
catalytic performance of the acylation of alcohols indicates
that the DMAP-NCP catalyst possesses excellent catalytic
activity. A variety of aliphatic alcohols and phenols could be
effectively converted into the corresponding ester products
in excellent yields (92–99%). Moreover, the catalytic activi-
ty did not show an appreciable decrease after 14 cycles, or
after 536 h of continuous work, which illustrates the excel-
lent stability and recyclability of the DMAP-NCP catalyst.
Encouraged by these excellent catalytic results, which are
among the best reported so far,[33] we believe that DMAP-
NCP may act as a promising heterogeneous catalyst in a va-
riety of reactions catalyzed by DMAP (see the Supporting
Information). Also, the persistent catalytic ability of
DMAP-NCP under neat and continuous-flow conditions
demonstrates its potential as a robust heterogeneous catalyst
for industrial use. Furthermore, this study provides a new
avenue for the heterogenization of other organocatalysts, es-
pecially of chiral organocatalysts.[2] Research in this direc-
tion is underway in our laboratory.
In an effort to further demonstrate the persistent catalytic
ability of DMAP-NCP and explore its potential for industri-
al use, we installed the DMAP-NCP catalyst in a column to
conduct the catalytic acylation reaction under continuous-
flow conditions[36] (see the Supporting Information). The
catalytic activity of the DMAP-NCP catalyst (Figure 5) did
Experimental Section
Figure 5. Catalytic performance of DMAP-NCP in the acylation of 3
under continuous-flow conditions (reaction column: 5.5 mm inner diame-
ter and 15.1 cm length, 600 mg of DMAP-NCP catalyst; reaction condi-
tions: a mixture of acetic anhydride and 1-phenylethanol (3) as the flow
phase (2:1), flow rate=0.2 mLhÀ1, neat conditions, RT). The conversions
were determined by GC analysis.
General methods: All reagents purchased from commercial sources were
used as received. All solvents were purified and dried by standard meth-
ods prior to use. 1H and 13C NMR spectra were recorded on a Bruker
Avance 400 MHz spectrometer. Mass spectra were obtained on a Bruker
Daltonics APEX II 47e FT-ICR mass spectrometer. ESI-MS spectra
were recorded on a Bruker Daltonics esquire6000 mass spectrometer.
Column chromatography was performed on silica gel (200–300 mesh).
TLC was performed on silica gel GF254 plates.
not reduce after 536 h of continuous work, which further in-
dicates its superior persistent catalytic ability. Given its ex-
cellent stability and persistent catalytic ability as well as its
straightforward synthesis, this organocatalytic DMAP-NCP
porous polymer may, therefore, have potential practical ap-
plications in large-scale production.
We also demonstrated the catalytic utility of DMAP-NCP
in the silylation of alcohols (see the Supporting Informa-
tion). Primary alcohols were readily silylated in the presence
of 20 mol% DMAP-NCP, affording the desired products in
high yields. Moreover, DMAP-NCP promotes the selective
silylation of primary alcohols (see the Supporting Informa-
tion), which is very useful in organic synthesis.[32d] These re-
sults further illustrate the generality of DMAP-NCP in cata-
lyzing nucleophilic reactions.
Synthesis of DMAP-NCP: An oven-dried 25 mL Schlenk flask was
charged with 1,3,5-triethynylbenzene (2; 300 mg, 2.0 mmol), 3,5-dibromo-
N,N-dimethylpyridin-4-amine (1; 556 mg, 2.0 mmol), copper iodide
(30 mg, 0.15 mmol), and bis(triphenylphosphine)palladium dichloride
(70 mg, 0.1 mmol). Dry DMF (8.0 mL) and dry Et3N (1.2 mL) were
added to this flask under argon. The reaction mixture was heated at
808C for 72 h with stirring under argon. The mixture was then cooled to
room temperature, the resulting brown precipitate was filtered and
washed in turn (three times each) with water, ethanol, acetone, and
chloroform. Further purification of the precipitate was carried out by
Soxhlet extraction from methanol for 48 h to remove any unreacted mo-
nomer or catalyst residues. After drying in vacuum for 48 h at 608C,
DMAP-NCP was obtained as a brown powder (542 mg, 102%). Elemen-
tal analysis calcd (%) for C15H10N2: C 82.55, H 4.62, N 12.84; found: C
66.56, H 3.91, N 5.65. Found by energy-dispersive X-ray spectroscopy
(EDX) analysis (wt.%): C 68.50, Br 21.08, Pd 3.76, Cu 2.51, I 2.18, P
1.97. The slightly higher (than expected) yield and the deviations in the
elemental analysis can be attributed to the few unreacted bromopyridine
end groups and the catalyst residues,[24g] as identified by EDX (see Fig-
ure S7 in the Supporting Information).
Conclusion
General procedure for the DMAP-NCP-catalyzed acylation reactions:
The alcohol of choice was dissolved in dry CH2Cl2 (if necessary) and
then DMAP-NCP, triethylamine (if necessary), and acetic anhydride
were added to the solution. The mixture was stirred at ambient tempera-
ture (for the reaction times, see Tables 1 and 2). After the reaction, dieth-
yl ether (Et2O) was added to dilute the reaction mixture and the catalyst
was then isolated by centrifugation and thoroughly washed with Et2O.
The combined organic phase was evaporated under vacuum. The corre-
sponding acetates were obtained by column chromatography with ethyl
acetate/petroleum ether (16:1) as eluent. We conducted the following
control experiments to demonstrate that the metal traces (Pd and Cu) in
We have demonstrated for the first time the successful incor-
poration of an important organocatalyst, DMAP, into the
network of
a nanoporous conjugated polymer by the
“bottom-up” approach (Figure 1). The DMAP-NCP materi-
al we constructed possesses highly concentrated and homo-
geneously distributed catalytic sites, as well as enhanced sta-
bility. Moreover, the nanopores (mainly mesopores) of
DMAP-NCP could facilitate the mass transport of reactants
6332
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 6328 – 6334