CHEMCATCHEM
FULL PAPERS
and the spectra were acquired in the constant-pass-energy mode
at Epas =44 eV. The overall energy resolution was 1.2 eV as a full-
width at half maximum (FWHM) for the Ag 3d5/2 line of a pure Ag
reference. The recorded spectra were fitted by using XPS Peak 4.1
software that employed Gauss–Lorentz curves after subtraction of
a Shirley-type background. The powder sample was introduced in
the UHV system through a loadlock under inert gas (N ) flux, to
2
minimize the exposure to air contaminants, and kept in the intro-
duction chamber for at least 12 h before the measurements. UV/
Vis spectra were recorded by a Perkin–Elmer UV/VIS/NIR Spectrom-
eter Lambda 19 by using a 1 cm quartz cuvette. The solvent used
was water, and the concentration of the solution was approximate-
Figure 8. Bright-field TEM image of 1 after nine catalytic cycles. Scale
bar=200 nm.
À4
ly 5.6ꢁ10 m. PXRD data were collected by using an X’Pert PRO
Catalyst 2 was also recycled in proof-of-concept tests in the
hydrogenation of 1-dodecene, cinnamyl alcohol, and cis-4-
hepten-1-ol under the conditions described in Table 2 (see en-
tries 2, 6, and 7 for the first runs) to obtain the hydrogenated
products in 87.5, 100, and 94.4% yields, respectively, in the
second runs. The overall TONs considering the first and second
runs are 5307, 220, and 299, respectively.
diffractometer with CuK radiation (l=1.5418). Inductively coupled
a
plasma atomic emission spectroscopy (ICP-AES) was performed by
using an ICP-OES dual vision Perkin–Elmer instrument at the De-
partment of Chemistry of the University of Florence. The samples
were measured in the axial mode to increase sensitivity. GC analy-
ses were performed by using a Shimadzu 2010 gas chromatograph
(
(
with polar column) equipped with a flame ionization detector
FID) and a VF-WAXms capillary column (30 m, 0.25 mm internal di-
ameter, 0.25 mm film thickness) and a Shimadzu GC-14A gas chro-
matograph (with apolar column) equipped with an FID and a SPB-
Conclusions
1
Supelco fused silica capillary column (30 m, 0.25 mm internal di-
An efficient and reproducible method for the preparation of
water-soluble Pd nanoparticles (NPs) from widely available
starting materials is described. The new materials have been
characterized in solution and in the solid state by TEM, induc-
tively coupled plasma atomic emission spectroscopy (ICP-AES),
X-ray photoelectron spectroscopy (XPS), and UV/Vis and NMR
spectroscopy. The distribution of NPs was found to be general-
ly in a narrow range, with mean diameters of 2.8, 3.2, and
ameter, 0.25 mm film thickness).
Preparation of TOAB-capped Pd NPs, Pd@TOAB (1:4)
À2
To a solution of K PdCl4 (80.0 mg, 2.45ꢁ10 mmol, 1 equiv.) in
2
À2
water (8.16 mL, 3.0ꢁ10 m) was added a solution of TOAB
À2
(587.0 mg, 1.07 mmol, 4.4 equiv.) in toluene (21.4 mL, 5.0ꢁ10 m).
Under an inert atmosphere and after stirring at high speed for
2À
3.5 nm, respectively, for Pd@PTA (1:4) (1), Pd@PTA (1:1) (2), and
30 min, the transfer of [PdCl4] from the aqueous phase to the or-
ganic layer was completed as revealed by the decoloration of the
water phase and the red–brown color of the organic phase. The
water phase was removed by syringe, and a freshly prepared
NaBH4 aqueous solution (6.1 mL, 0.1m, 23.2 mg, 0.613 mmol,
Pd@(mPTA)I (3). The aqueous colloidal suspensions of PTA-sta-
bilized Pd NPs 1 and 2 were tested as catalysts in the biphasic
hydrogenation of selected unsaturated substrates in water at
room temperature under 10 bar of H , which showed moder-
2
2
.5 equiv.) was added dropwise over 1 h with vigorous stirring. The
À1
ate to good conversions and TOFs of 257 and 360 h in the
reaction mixture gradually darkened and, after stirring for 2 h at RT,
the colorless water phase was discarded and the organic phase
was recovered, washed with HCl solution (20 mL, 0.1m), NaOH so-
lution (20 mL, 0.1m), and deionized water (3ꢁ20 mL). The organo-
hydrogenation of 1-dodecene and diphenylacetylene, respec-
tively. The catalytic system 1 shows excellent recyclability, up
to nine times, to afford an overall TON of 1728. Work is in
progress to expand the scope of the catalytic system to other
substrates.
sol was dried over anhydrous Na SO and stored at 48C. The for-
2 4
mation of Pd@TOAB NPs was confirmed by TEM analysis, which
gave an average diameter of 3.2Æ0.4 nm. The molar concentration
of Pd in the colloidal toluene solution was measured by ICP-AES.
Experimental Section
All chemicals used were of analytical grade. Potassium tetrachloro-
palladate (K PdCl ) and TOAB were purchased from Aldrich and
Preparation of PTA-capped Pd NPs Pd@PTA (1:4) (1)
2
4
[18]
[48]
[49]
À2
used as received. PTA, (mPTA)I, and Pd(dba)2 (dba=dibenzy-
lideneacetone) were prepared according to known procedures. Pd
NPs capped by TOAB were prepared following a variation of the
Method A: Firstly, a solution of PTA (19.3 mg, 1.23ꢁ10 mmol,
À3
3.78ꢁ10 m, 4 equiv.) in degassed water (32.5 mL) was prepared
and divided into two aliquots of approximately 16.2 mL each. The
first aliquot was added to a dark brown sol of Pd@TOAB (1:4)
[15]
method previously developed by Brust
and Gittins and
[10]
À3
Caruso. TEM studies were performed by using a Philips instru-
ment operating at an acceleration voltage of 100 kV. A few drops
of the Pd colloidal suspension, obtained by using either toluene or
water, were placed on the TEM lacy copper/carbon grid or copper/
Formvar grid, respectively, air dried, and measured. The XPS meas-
(10 mL, 3.08ꢁ10 m, 1 equiv.) in toluene, prepared as described
above. After stirring at RT for 10 min, the two phases were allowed
to separate, the aqueous phase was removed by using a syringe
under N and placed in a separate Schlenk flask, and the second
2
aliquot of the PTA solution was added to the organic layer left
after the phase separation. After stirring at RT for an additional
10 min, the color of the organic phase faded completely. The
brown–yellow water phase so-obtained was removed by syringe
urements were performed by using an ultrahigh vacuum (UHV,
À9
1
0
mbar) system equipped with a VSW HAC 5000 hemispherical
electron-energy analyzer and a non-monochromatized MgK X-ray
a
[
50]
source (1253.6 eV). The source power was 100 W (10 kVꢁ10 mA)
under N and combined with the previous water phase. The re-
2
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