Palladium nanoparticles on graphite oxide as catalyst for Suzuki-Miyaura, Mizoroki-Heck, and Sonogashira reactions

Article abstract of DOI:10.1002/hlca.201000412

Pd²⁺-Exchanged graphite oxide (GO) serves as a precatalyst for the formation of Pd-nanoparticles which are then deposited on the highly functionalized carbonaceous support. This versatile, air-stable, and ligand-free system was applied successfully to Suzuki-Miyaura couplings of some aryl chlorides and to the Mizoroki-Heck as well as the Sonogashira reaction showing relatively high activities and good selectivities. Like with other ligand-free supported systems, the reaction proceeded dominantly by a homogeneous mechanism, but attack of an aryl iodide to Pd-nanoparticles can be excluded as substantial contribution to the entire catalytic process. Beside its straightforward preparation and its stability in air, the system combines the advantages of both homogeneous and heterogeneous catalysis.

Full text of DOI:10.1002/hlca.201000412

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Helvetica Chimica Acta – Vol. 94 (2011)
Palladium Nanoparticles on Graphite Oxide as Catalyst for SuzukiꢀMiyaura,
MizorokiꢀHeck, and Sonogashira Reactions
by Luigi Rumia), Gil M. Scheuermannb), Rolf Mꢀlhauptc), and Willi Bannwarth*a)
a) Institut fꢀr Organische Chemie und Biochemie, Albert-Ludwigs-Universitꢁt Freiburg,
Albertstrasse 21, D-79104 Freiburg (phone: þ 49-761-2036073; fax: þ 49-761-2038705;
e-mail: willi.bannwarth@chemie.uni-freiburg.de)
b) Freiburger Materialforschungszentrum (FMF) & Institut fꢀr Makromolekulare Chemie,
Albert-Ludwigs-Universitꢁt Freiburg, Stefan-Meier Strasse 21 – 31, D-79104 Freiburg
c) Freiburg Institute for Advanced Studies (FRIAS), Soft Matter Research, Albertstrasse 19,
D-79104 Freiburg
Pd2þ-Exchanged graphite oxide (GO) serves as a precatalyst for the formation of Pd-nanoparticles
which are then deposited on the highly functionalized carbonaceous support. This versatile, air-stable,
and ligand-free system was applied successfully to SuzukiꢀMiyaura couplings of some aryl chlorides and
to the MizorokiꢀHeck as well as the Sonogashira reaction showing relatively high activities and good
selectivities. Like with other ligand-free supported systems, the reaction proceeded dominantly by a
homogeneous mechanism, but attack of an aryl iodide to Pd-nanoparticles can be excluded as substantial
contribution to the entire catalytic process. Beside its straightforward preparation and its stability in air,
the system combines the advantages of both homogeneous and heterogeneous catalysis.
Introduction. – Since the pioneering advances in graphene chemistry [1][2],
graphite oxide (GO) [3 – 9] and chemically derived graphenes (CDG) [10 – 12] have
been under thorough investigation as new materials, e.g., for nanoelectronic
applications [13 – 17] and polymer nanofillers [18 – 22]. However, in the past, only a
limited number of publications have dealt with the synthesis of transition metals and
their clusters supported by GO or CDG [23 – 26] and their applications [27 – 32]. The
preparation of GO can be accomplished either by controlled chemical or by
electrochemical oxidation of graphite via its nitrate or hydrogensulfate salts [33 –
37]. Different models have been published characterizing the structure of this
nonstoichiometric hygroscopic material [38 – 43]. The formation of functional groups
during oxidation enables sorption and intercalation of ions and molecules [40][44 – 46].
This behavior of GO and its high specific surface area of ca. 400 m2 gꢀ1 makes it a
versatile material for catalytic applications preventing for example the aggregation and
hence deactivation of the catalytic species [6][47] and thus, this system would be an
interesting alternative for unsupported nanoparticles and Pd/C, both of which have
been extensively investigated for its use in CꢀC coupling procedures [48 – 53]. In a
previous publication, we have reported on the formation of different Pd/GO and Pd/
CDG catalysts and their use in the SuzukiꢀMiyaura coupling of aryl bromides [54]. In
these studies, it was found that Pd2þ-exchanged GO was the most active catalyst among
the investigated new catalytic materials showing turnover frequencies (TOFs) of up to
39000 hꢀ1. In situ reduction of Pd2þ afforded highly dispersed and uniform Pd-
ꢂ 2011 Verlag Helvetica Chimica Acta AG, Zꢀrich

Helvetica Chimica Acta – Vol. 94 (2011)
967
nanoparticles of 4 ꢁ 1 nm in diameter. As a result, this allowed for good recyclability in
combination with a low leaching of < 1 ppm. Here, we have extended the scope of
application to a number of aryl chlorides in SuzukiꢀMiyaura couplings as well as to
MizorokiꢀHeck reactions and a number of Sonogashira couplings.
Results and Discussion. – The catalyst synthesis was carried out according to our
previously reported procedure [54]. The widened distance of 0.8 nm between the
highly functionalized graphitic layers is responsible for the high surface area of the GO
support. This morphology was confirmed by SEM (scanning electron microscope) and
WAXS (wide-angle X-ray scattering) measurements (Fig. 1).
Fig. 1. SEM Picture (left) and the X-ray diffraction pattern (right) display the layered nature of Pd/GO at
the microscale and at the nanoscale
When 1-chloro-4-nitrobenzene was coupled to phenylboronic acid in the presence
of 1 mol-% of Pd2þ/GO under the same conditions as for the reaction of aryl bromides
(1 mol-% of Pd2þ/GO, H2O/EtOH, 808) [54], only 8% of the desired 4-nitro-1,1’-
biphenyl was formed. However, switching to the solvent system N,N-dimethylacet-
amide (DMA)/H2O 20 :1 led to an increased conversion of 90%. As previously
reported, the solvent effect on the efficiency of the coupling may be related to the
reductive homocoupling pathway with the alcohol and/or boronic acid as reducing
agent [55]. The use of the nonreducing solvent DMA avoided this problem.
Application of the modified reaction conditions in combination with the use of Pd2þ/
GO enabled the SuzukiꢀMiyaura coupling of different aryl chlorides with moderate to
good conversions. The results are summarized in Table 1. As expected, the nature and
position of the substituents had an influence on the reactivity of the substrate. The high
conversion and good selectivity of the less reactive 2-chlorobenzaldehyde might be
caused via a directing effect of the aldehyde O-atom by complexation of palladium
(Table 1, Entry 8). Moreover, ester groups are stable under the applied conditions, and
ethyl 4-chlorobenzoate (Entry 10) was coupled in good yield and with high selectivity.
By doubling the amount of Pd to 2 mol-%, almost all conversions were enhanced
significantly but at the expense of selectivity. The TEM (transmission electron

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Helvetica Chimica Acta – Vol. 94 (2011)
Table 1. SuzukiꢀMiyaura Couplings of Phenylboronic Acid and Different Aryl Chlorides in the Presence
of Pd2þ/GO
Entry
R1
Conversiona)b) [%]
Selectivitya)b)c)
1
2
3
4
5
6
7
8
9
4-NO2
2-NO2
3-NO2
4-CF3
2-CF3
3-CF3
4-CHO
2-CHO
3-CHO
4-CO2Et
4-COMe
90 (95)
67 (87)
28 (45)
88 (100)
57 (58)
82 (96)
51 (60)
95
1 : 42 (1 : 1)
1 : 8 (1 : 10)
1 : 3 (1 : 1)
1 : 23 (1 : 31)
1 : 11 (1 : 18)
0 : 1 (0 : 1)
1 : 11 (1 : 4)
1 : 6
43
78 (99)
8 (34)
1 : 4
1 : 61 (1 : 16)
1 : 1 (1 : 4)
10
11
a) Conversion and selectivity determined by GC/MS. b) Results in parenthesis were obtained with 2 mol-
% of Pd. c) Molar ratio homocoupling product/SuzukiꢀMiyaura product.
Fig. 2. TEM Picture (left) and size distribution (right) of Pd-nanoparticles on GO generated in situ
during the SuzukiꢀMiyaura coupling
microscope) pictures of the catalyst after the reaction showed a narrow size distribution
of the Pd-nanoparticles of 6.6 ꢁ 1.3 nm (Fig. 2).
While the SuzukiꢀMiyaura reaction is the method of choice for the synthesis of
biarenes, the MizorokiꢀHeck coupling is the preferred procedure for coupling alkenes
to organic compounds bearing a suitable leaving group [56]. Pd/C has been applied to
this coupling reaction already back in 1973 and is since then regarded as the most
important heterogeneous catalyst [48][51][57][58]. To investigate the scope of
reactions catalyzed by the novel heterogeneous system Pd/GO, we applied 0.1 mol-

Helvetica Chimica Acta – Vol. 94 (2011)
969
% of Pd2þ/GO to MizorokiꢀHeck couplings of butyl acrylate (¼ butyl prop-2-enoate)
with a number of aryl bromides (Table 2). The transformations with activated aryl
bromides (Entries 1 – 9) as well as nonactivated aryl bromides (Entries 10 – 16) led,
after extractive workup and column chromatography, to the desired substituted olefin
derivatives in good yields. In addition, the selectivity of these reactions was high,
resulting in > 99% of the (E)-configured forms.
The Sonogashira reaction is the preferred method for the coupling of sp2-hybridized
C-atoms of aryl, heteroaryl, and vinyl halogenides with sp-hybridized C-atoms of
terminal alkynes [59][60]. Pd/C has often been used as heterogeneous catalyst for these
reactions under different reaction conditions [49][53][61 – 63], the most common being
Pd/C, CuI, and PPh3 in Et3N/DMF [64]. To demonstrate the versatility of the Pd/GO
system, amine-, copper-, and phosphine-free conditions were applied. Phenylacetylene
was coupled with different aryl iodides, and the results are shown in Table 3. Depending
on the electronic nature of the substituents, moderate to good conversions to the
desired products could be observed. In contrast, 4-methyl iodobenzoate could only be
converted by 25%, whilst a partial saponification of the starting material was observed.
TEM Pictures of the catalyst after the reaction showed an extremely narrow size
distribution of the Pd-nanoparticles of 2.9 ꢁ 0.5 nm on GO (Fig. 3).
Fig. 3. TEM Picture (left) and size distribution (right) of Pd-nanoparticles on GO generated in situ
during the Sonogashira coupling
During the last decade, the elucidation of the mechanism of heterogeneous CꢀC
couplings mediated by Pd has been an area of high activity. There is strong evidence for
a dissolution/redeposition process taking place during the reaction [65][66]. At the
beginning of the reaction, leaching of Pd ions and atoms is often very high but
diminishes while the reaction progresses, resulting in low values after complete
conversion. For Heck reactions, it was postulated that the reactions are not catalyzed by
nanoparticles but rather take place by an attack of the arylating agent on the Pd-atoms
at the outer rim of the nanoparticles [67][68]. These data were substantiated by
reactions employing a two-compartment membrane reactor [69][70].

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Table 2. MizorokiꢀHeck Couplings in the Presence of Pd2þ/GO
Entry
1
Product
Conversiona) [%]
Yield [%]
86
> 95
2
3
4
> 95
> 95
> 95
83
81
93
5
6
> 95
> 95
> 95
> 95
> 95
92
85
81
89
91
89
85
7
8
9
10

Helvetica Chimica Acta – Vol. 94 (2011)
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Table 2 (cont.)
Entry
11
Product
Conversiona) [%]
Yield [%]
79
88
92
80
86
89
79
12
13
14
15
16
87
74
80
81
73
a) Conversion determined via GC/MS.
Table 3. Sonogashira Couplings in the Presence of Pd2þ/GO
R
Hal
Conversiona) [%]
H
4-Br
I
I
95
73
3-Br
I
I
I
I
> 95
69
25
93
< 5
2-MeO
4-CO2Me
4-Ac
4-Ac
Br
a) Conversion determined via GC/MS.

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The reported data are in accordance with our observations for CꢀC coupling
reactions in the presence of GO-supported Pd-nanoparticles as catalytic system.
During the reactions, up to 49% of the applied Pd-concentration was leaching into
solution. However, after completion of the reaction, a maximum of 3 ppm was detected
in the reaction media. To establish that in our system, a soluble Pd-species is
responsible for the catalysis, we carried out filtration experiments where we observed a
continuation of the reaction, indicative of a soluble catalytic species. In addition, we
performed a so-called three-phase test [71][72] in which we subjected a solid-phase-
bound aryl iodide to [63][64] a MizorokiꢀHeck coupling as well as to a Sonogashira
coupling. The experiments were carried out under comparable conditions and in the
presence as well as in the absence of a soluble substrate. In all experiments, more than
90% conversion of the solid-phase-bound aryl iodide was observed. Since the solid-
phase-bound aryl iodide is unable to attack nanoparticles on GO, a proposed
substantial contribution of this catalytic pathway [68][69] to the entire catalytic process
can thus be ruled out.
Conclusions. – In summary, immobilization of Pd2þ on graphite oxide (GO)
followed by in situ reduction afforded an active catalyst of GO-supported Pd-
nanoparticle clusters for ligand-free SuzukiꢀMiyaura couplings of aryl chlorides and
for MizorokiꢀHeck as well as Sonogashira reactions. The catalyst could be readily
prepared and easily handled as it is stable in air. A low leaching of Pd was observed
after completion of the reaction, and the catalytic system could easily be recovered.
Filtration experiments and a three-phase test supported a homogeneous mechanism
but the latter approach established that an attack of the aryl iodide on the surface of the
nanoparticles can be ruled out as significant contribution to the entire catalytic process.
Experimental Part
General. All reagents were purchased from commercial sources (Aldrich, Fluka, Acros, ABCR, and
Alfa Aesar). HPLC Analysis: Agilent-1100 system with a Zorbax Eclipse XDB-C8 column (4.6 ꢂ 150 mm,
Agilent). M.p.: Electrothermal IA 9000; uncorrected. NMR Spectra: Bruker-AM-400 spectrometer; at
400 (1H) and 100.6 MHz (13C); CDCl3 soln.; d in ppm rel. to CHCl3 (d(H) 7.26, d(C) 77.23) as an internal
reference, J in Hz. CI-MS: Finnigan MAT312 with NH3 as gas (0.4 mbar, 2208, 250 eV, 1 mA, 2 kV); in m/
z (rel. %). EI-MS: Finnigan MAT8200 (2308, 70 eV, 1.0 mA, 3 kV); in m/z (rel. %). Elemental analyses:
Vario EL (Elementaranalysensysteme GmbH).
The characterization of the coupling products is given only for compounds 5 – 8 and 15 that are not
reported in the literature. However, all data can be requested from the corresponding author.
Catalyst Synthesis. Graphite oxide (GO) was synthesized according to the method of Hummers and
Offeman [35][48]. The ion exchange with Pd, i.e., the adsorption of Pd2þ ions by the functionalized GO
was achieved by dispersing GO (2.5 g) in H2O (200 ml). Subsequently, [Pd(AcO)2] (250 mg, 1.1 mmol)
was added, and the mixture was vigorously sonicated for 5 min and stirred overnight. After centrifugation
and several washings with H2O and acetone, the Pd2þ/GO was dried in vacuo at 408 and gently powdered
through a 150 mm mesh regaining a H2O content of 4.5%. The powder density was roughly estimated to
be 0.3 g cmꢀ3, and the Pd-content amounted to 3.4% as verified by atomic-absorption spectrometry
(AAS; digestion of the samples in hot aqua regia followed by analysis with an atomic-absorption
spectrometer Vario 6, Jena Analytics). Nanoparticles were characterized by transmission electron
microscopy (TEM) in suspension on a 200 m mesh Cu grid and as a microtome cut of the samples
embedded in epoxy resin with a LEO CEM 912 operating at 120 kV. The particle size was determined

Helvetica Chimica Acta – Vol. 94 (2011)
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counting at least 200 particles from different images by means of iTEM computer software from
Olympus-SIS. The morphology of the materials was observed via environmental scanning electron
microscopy (ESEM) in an Electroscan ESEM 2020. An acceleration voltage of 23 kV was applied, and
the samples were coated with gold/palladium prior to analyses. The wide-angle X-ray scattering (WAXS)
measurements were carried out on a Siemens-D-5000 diffractometer at 40 kV and 30 mA with CuKa
radiation in the 2q range from 18 to 1008 (step size 0.01568, step time 1 s, transmission rotation and
detection by a Braun PSD ASA S). Interplanar distances were calculated with the Bragg equation.
For a detailed characterization of the GO, see [54].
Suzuki Reactions of Aryl Chlorides in DMA/H2O: General Procedure. A pressure tube was charged
with phenylboronic acid (67 mg, 0.55 mmol, 1.1 equiv.), Na2CO3 (106 mg, 1 mmol, 2 equiv.), the chloro-
substituted benzene (0.5 mmol, 1 equiv.), and Pd2þ/GO (16.0 mg, 5 mmol, 1 mol-%). A DMA/H2O 20 :1
mixture (3 ml) was added. The vessel was closed, evacuated, and flushed with Ar, and the procedure was
repeated 4 ꢂ . Finally, the mixture was stirred in an oil bath at 1008 for the given time, followed by the
sampling (10 ml) for GC/MS analysis. After cooling to r.t., the mixture was filtered over a small column of
silica gel/kieselgur and the column washed with CH2Cl2 (10 ml). The product was extracted into the org.
phase (2 ꢂ 10 ml CH2Cl2) and the combined org. phase dried (MgSO4) and concentrated. In some cases,
purification of the crude product by column chromatography (SiO2, 2.5 ꢂ 13 cm, cyclohexane/AcOEt
4 :1) was necessary.
MizorokiꢀHeck Reaction (synthesis of 5 – 8 and 15): General Procedure. A Schlenk tube was
evacuated thoroughly and flushed with Ar prior to the addition of the aryl bromide (1 mmol, 1 equiv.),
AcONa (99 mg, 1.2 mmol, 1.2 equiv.), Pd2þ/GO (3.1 mg, 1.0 mmol, 0.1 mol-%), and NMP (¼1-
methylpyrrolidin-2-one; 2.4 ml). The mixture was stirred at 1208 during 2 min before the addition of
butyl prop-2-enoate (164 ml, 1.15 mmol, 1.15 equiv.). Thereafter, the mixture was stirred at 1408 during
15 h followed by withdrawal of an aliquot for GC/MS analysis (10 ml). After cooling to r.t., the mixture
was diluted with H2O (8 ml) and extracted with toluene (3 ꢂ 8 ml). The combined extract was washed
with H2O (3 ꢂ 8 ml) and brine (8 ml), dried (MgSO4), and concentrated, and the crude product purified
by flash chromatography (SiO2, 3 ꢂ 13 cm, cyclohexane/AcOEt 4 :1).
Ethyl 4-[(1E)-3-Butoxy-3-oxoprop-1-en-1-yl]benzoate (5): Rf (cyclohexane/AcOEt 4 :1) 0.24.
1H-NMR: 0.97 (t, J ¼ 7.4, Me); 1.40 (t, J ¼ 7.1, MeCH2O, overlapped with d(H) 1.44); 1.44 (sext., J ¼
7.5, 2 H); 1.66 – 1.73 (m, 2 H); 4.22 (t, J ¼ 6.7, OCH2CH2); 4.39 (t, J ¼ 7.1, MeCH2O); 6.52 (d, J ¼ 16.0,
HꢀC(2’)); 7.57 (Japp ¼ 8.1, 2 arom. H); 7.69 (d, J ¼ 16.1, HꢀC(1’)); 8.05 (Japp ¼ 8.3, 2 arom. H). 13C-NMR:
13.7; 14.3; 19.2; 30.8; 61.2; 64.6; 120.6; 127.9; 130.1; 131.7; 138.6; 143.2; 165.9; 166.6. EI-MS: 276 (26, Mþ),
231 (15, [M ꢀ OEt]þ), 219 (37, [M ꢀ Bu]þ), 203 (47, [M ꢀ OBu]þ, [M ꢀ CO2Et]þ), 192 (78), 175 (71,
[M ꢀ CO2Bu]þ), 102 (35), 44 (100). Anal. calc. for C16H20O4: C 69.54, H 7.30; found: C 69.28, H 7.39.
1
Butyl (2E)-3-(3,4-Difluorophenyl)prop-2-enoate (6): Rf (cyclohexane/AcOEt 4 :1) 0.42. H-NMR:
0.97 (t, J ¼ 7.4, Me); 1.44 (sext., J ¼ 7.5, 2 H); 1.65 – 1.75 (m, 2 H); 4.21 (t, J ¼ 6.7, CH2O); 6.35 (d, J ¼ 16.0,
HꢀC(2)); 7.17 (dd, J ¼ 8.5, 7.8, 1 arom. H); 7.23 – 7.27 (m, 1 arom. H); 7.34 (ddd, J ¼ 11.1, 7.5, 2.1, 1 arom.
H); 7.57 (d, J ¼ 16.0, HꢀC(3)). 13C-NMR: 13.7; 19.2; 30.8; 64.7; 116.2; 117.7; 119.5; 124.7; 131.7; 142.2;
149.3; 151.8; 152.7; 166.6. 19F-NMR (235 MHz): ꢀ 136.7; ꢀ 134.4. EI-MS: 240 (13, Mþ), 183 (97, [M ꢀ
Bu]þ), 167 (100, [M ꢀ OBu]þ), 139 (30, [M ꢀ CO2Bu]þ), 119 (33).
1
Butyl (2E)-3-(2,4-Difluorophenyl)prop-2-enoate (7): Rf (cyclohexane/AcOEt 4 :1) 0.31. H-NMR:
0.97 (t, J ¼ 7.4, Me); 1.44 (sext., J ¼ 7.5, 2 H); 1.65 – 1.73 (m, 2 H); 4.22 (t, J ¼ 6.7, CH2O); 6.48 (d, J ¼ 16.2,
HꢀC(2)); 6.85 (m (¼ꢃdddꢄ), Japp ¼ 10.8, 8.6, 2.4, 1 arom. H); 6.88 – 6.93 (m, 1 arom. H); 7.52 (ddd, J ¼ 8.6,
8.6, 6.3, 1 arom. H); 7.73 (d, J ¼ 16.2, HꢀC(3)). 13C-NMR: 13.7; 19.2; 30.8; 64.6; 104.6; 112.0; 120.5; 130.2;
136.1; 160.4; 162.7; 165.1; 166.8. 19F-NMR (235 MHz): ꢀ 106.2; ꢀ 109.9. EI-MS: 240 (14, Mþ), 183 (77,
[M ꢀ Bu]þ), 167 (100, [M ꢀ OBu]þ), 139 (30, [M ꢀ CO2Bu]þ), 119 (38).
Butyl (2E)-3-(4-Cyano-3-fluorophenyl)prop-2-enoate (8): Rf (cyclohexane/AcOEt 4 :1) 0.29.
1H-NMR: 0.96 (t, J ¼ 7.4, Me); 1.41 (sext., J ¼ 7.5, 2 H); 1.65 – 1.72 (m, 2 H); 4.21 (t, J ¼ 6.7, CH2O);
6.51 (d, J ¼ 16.0, HꢀC(2)); 7.34 (dd, J ¼ 9.5, 1.5, 1 arom. H); 7.39 (dd, J ¼ 8.0, 1.5, 1 arom. H); 7.59 (d, J ¼
16.1, HꢀC(3)); 7.63 (dd, J ¼ 8.2, 6.4, 1 arom. H). 13C-NMR: 13.7; 19.2; 30.7; 65.0; 113.5; 115.0; 123.3;
124.2; 133.9; 140.9; 141.6; 161.9; 164.6; 165.9. 19F-NMR (235 MHz): ꢀ 105.8. EI-MS: 247 (12, Mþ), 190
(43, [M ꢀ Bu]þ), 174 (100, [M ꢀ OBu]þ), 192 (78), 146 (34, [M ꢀ CO2Bu]þ), 126 (26), 44 (29).

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Helvetica Chimica Acta – Vol. 94 (2011)
Butyl (2E)-3-[4-(tert-Butyl)phenyl]prop-2-enoate (15): Rf (cyclohexane/AcOEt 4 :1) 0.69. 1H-NMR:
0.97 (t, J ¼ 7.3, Me); 1.33 (s, Me3C); 1.44 (m (¼ꢃsext.ꢄ), Japp ¼ 7.4, 2 H); 1.69 (m (¼ꢃquint.ꢄ), Japp ¼ 7.1,
2 H); 4.20 (t, J ¼ 6.7, CH2O); 6.40 (d, J ¼ 15.9, HꢀC(2)); 7.40 (mc, 2 arom. H); 7.47 (mc, 2 arom. H); 7.67
(d, J ¼ 16.0, HꢀC(3)). 13C-NMR: 13.8; 19.2; 30.8; 31.2; 34.9; 64.4; 117.4; 125.8; 127.9; 131.8; 144.4; 153.8;
167.3. EI-MS: 260 (29, Mþ), 245 (100, [M ꢀ Me]þ), 203 (11, [M ꢀ Bu]þ), 187 (13, [M ꢀ OBu]þ). Anal.
calc. for C17H24O2: C 78.42, H 9.29; found: C 78.24, H 9.48.
Sonogashira Reactions in iPrOH/H2O: General Procedure. Aryl iodide (0.51 mmol, 1 equiv.),
phenylacetylene (¼ethynylbenzene; 66 ml, 0.6 mmol, 1.2 equiv.), Na3PO4 · 12 H2O (357 mg, 1 mmol, 2
i
equiv.), Pd2þ/GO (4.0 mg, 0.125 mmol, 0.25 mol-%), and PrOH/H2O (1 ml) were placed in a Schlenk
tube under Ar and stirred at 808 during 24 h followed by withdrawal of an aliquot (10 ml) for GC/MS
analysis. After cooling to r.t., the mixture was diluted with H2O (8 ml) and extracted with Et2O (3 ꢂ
8 ml). The combined extract was washed with H2O (3 ꢂ 8 ml) and brine (8 ml), dried (MgSO4), and
concentrated, and the crude product purified by flash chromatography (SiO2, 3 ꢂ 12 cm, cyclohexane/
AcOEt 6 :1).
Solid-Supported Aryl Iodide on Novasyn TGR Resin. To an ice-cooled soln. of 4-iodobenzoic acid
(126 mg, 0.51 mmol) in THF (2.5 ml) and CH2Cl2 (2.5 ml), DMF (10 ml) and oxalyl chloride (0.1 ml,
1.2 mmol, 2.3 equiv.) were added and stirred overnight at r.t. The solvent was then evaporated and the
residue dissolved in THF (2.5 ml) and MeCN (2.5 ml). Separately, the Novasyn TGR resin (0.5 g) was
dried by co-concentration with MeCN (3 ꢂ 10 ml). The resin was then suspended in MeCN/pyridine 1:1
(20 ml) for 1 h. The previously synthesized soln. of 4-iodobenzoyl chloride was added, and the mixture
was shaken overnight at r.t. The resin was then filtered, washed with MeCN (3 ꢂ 15 ml) and dried under
reduced pressure: solid-supported aryl iodide.
Three-Phase Test: MizorokiꢀHeck Reaction (analogously for the SuzukiꢀMiyaura and Sonogashira
reactions). In a glass tube, NMP (1.3 ml) was added to the solid-supported aryl iodide (ca. 50 mg), butyl
prop-2-enoate (82 ml, 0.58 mmol, 1.15 equiv.), 4-iodoacetophenone (123.1 mg, 0.5 mmol, 1 equiv.), and
AcONa (50 mg, 0.6 mmol, 1.2 equiv.). After 1 h, Pd2þ/GO (1.6 mg, 0.5 mmol, 0.1 mol-%) was added. The
suspension was shaken at 1408. After 24 h, a small sample (25 ml) was taken and added to MeCN
(950 ml þ 25 ml of AcOH) for HPLC analysis. From this sample, the ratio of 4-iodoacetophenone to butyl
(2E)-3-(4-acetylphenyl)prop-2-enoate was determined and the conversion calculated. The mixture was
cooled to r.t. and filtered. The resin and graphite oxide were washed with H2O (2 ꢂ 2 ml) and AcOEt
(2 ꢂ 2 ml). MeCN/CF3COOH 1:1 (1 ml) was added to the mixture of resin and Pd and shaken at r.t. for
1 h. The mixture was then filtered. From the filtrate, the ratio of 4-iodobenzamide to 4-[(E)-3-butoxy-3-
oxoprop-1-en-1-yl]benzamide was determined by HPLC. Hence, the conversion of the solid-supported
aryl iodide was calculated.
Filtration Experiment: Heck Reaction (analogously for the SuzukiꢀMiyaura and Sonogashira
reactions). In a glass tube (˘ 2 cm), NMP (2.3 ml) was added to Pd2þ/GO (3.1 mg, 1.0 mmol, 0.1 mol-%),
AcONa (99 mg, 1.2 mmol, 1.2 equiv.), butyl prop-2-enoate (164 ml, 1.15 mmol, 1.15 equiv.), and ethyl 4-
bromobenzoate (163 ml, 1.0 mmol, 1 equiv.). Then the suspension was stirred at 1408. After 10 and
30 min, small probes (20 ml) were taken and given in HPLC vessels with MeCN (950 ml þ 30 ml of AcOH)
for analysis. Then, the hot mixture was filtered off. The soln. was further stirred at 1408. After 1, 5, and
24 h, small probes (20 ml) were taken and placed into HPLC vessels containing MeCN (950 ml þ 30 ml of
AcOH) for analysis. From these probes, the conversion was calculated by GC/MS.
The same reaction was carried out without filtration of the catalyst.
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Received November 9, 2010