Sulfonamide- and hydrazine-based palladium catalysts: Stable and efficient catalysts for C-C coupling reactions in aqueous medium

Article abstract of DOI:10.1016/j.molcata.2006.12.023

Syntheses of a novel family of sulfonamide-based palladium complexes and phenylhydrazine-based palladacycles are described. These catalysts are thermally stable, and not sensitive to air and moisture and some are completely soluble in water. These catalysts have shown excellent activity (good yields and high turnover numbers) and product selectivity in several arylation reactions including Suzuki, Heck, and Sonogashira reactions carried out totally under aqueous conditions.

Full text of DOI:10.1016/j.molcata.2006.12.023

Journal of Molecular Catalysis A: Chemical 269 (2007) 218–224
Sulfonamide- and hydrazine-based palladium catalysts: Stable and
efficient catalysts for C–C coupling reactions in aqueous medium
N.S.C. Ramesh Kumar, I. Victor Paul Raj, A. Sudalai∗
Chemical Engineering and Process Development Division, National Chemical Laboratory,
Dr. Homi Bhabha Road, Pune 411008, India
Received 10 August 2006; received in revised form 12 December 2006; accepted 14 December 2006
Available online 20 December 2006
Abstract
Syntheses of a novel family of sulfonamide-based palladium complexes and phenylhydrazine-based palladacycles are described. These catalysts
are thermally stable, and not sensitive to air and moisture and some are completely soluble in water. These catalysts have shown excellent activity
(good yields and high turnover numbers) and product selectivity in several arylation reactions including Suzuki, Heck, and Sonogashira reactions
carried out totally under aqueous conditions.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Suzuki coupling reaction; Heck reaction; Sonogashira reaction; Arylation reaction; Palladium catalyst
1. Introduction
knowledge, no information is available on completely solu-
ble Pd-catalysts. We reported our earlier results on highly
active cyclopalladated sulfilimine-derived palladacycles for a
wide range of useful and well-known C–C coupling reactions
[11].
In the continuation of our interest in the development of new
ligands for Pd-catalyzed C–C bond forming reactions, we report
here the synthesis of several novel sulfonamide Pd complexes
(1–5) as well as phenylhydrazine-derived palladacycles (6–9)
(Fig. 1) and their catalytic performance in several C–C bond
forming cross-coupling reactions in water as the solvent.
Palladacycles have recently emerged as one of the most
promising classes of catalysts or catalyst precursors in the Pd-
catalyzed C–C bond forming reactions such as Heck–Mizoroki
[1], Suzuki–Miyaura [2], and Sonogashira reactions [3]. In the
last decade, a number of new types of ligands such as het-
erocyclic carbenes [4], thiourea [5], oxime palladaycles [6],
diazabutadienes [7] and 2-aryl-2-oxazolines [8] were employed
in these cross-coupling reactions. However, a high loading
of catalysts and an inert atmosphere in most reactions espe-
cially involving phosphapalladacycles [9] and phosphines-free
N-heterocyclic carbenes are generally required for achieving
better conversions. Thus, the search for new palladium cata-
lysts has received much attention particularly for the use of
less reactive aryl chlorides as substrates, under aerobic condi-
tions or even in aqueous solutions. Aqueous-phase palladium
catalyzed reactions are of much interest as environmentally
benign synthetic methods that would avoid the use of volatile
organic solvents and simplify the catalyst recovery. Although
there are a few reports available on Pd catalysts with water-
soluble sulfonated phosphine [10] ligands, to the best of our
2. Experimental
2.1. Materials and methods
Solvents were purified and dried by standard procedures
before use; petroleum ether of boiling range 60–80 ◦C was used.
Melting points are uncorrected. Infrared spectra were recorded
onaShimadzuFTIR-8400spectrometer. 1HNMRand13CNMR
were recorded on a Bruker AC-200 spectrometer. Mass spectra
were obtained with a Finnigan MAT-1020 B-70 eV mass spec-
trometer. Elemental analysis was carried out on a Carlo Erba
CHNS-O analyzer. The TEM analysis was carried out on a JEOL
2010 transmission electron microscope operating at 100 kV at
magnifications varying from 100 to 300 K.
∗
Corresponding author. Tel.: +91 20 25902174; fax: +91 20 25893359.
E-mail address: a.sudalai@ncl.res.in (A. Sudalai).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.12.023

N.S.C. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 218–224
219
Fig. 1. Sulfonamide-based palladium complexes (1–5) and phenylhydrazine-based palladacycles (6–9).
1683, 1733, 2671, 2854, 2923; 1H NMR (200 MHz, DMSO-d6):
δ 6.72–6.84 (m, 2H, ArH), 7.63–7.78 (m, 2H, ArH); 13C NMR
(50 MHz, DMSO-d6): δ 112.99, 127.86, 130.35, 152.31 (ArC);
elemental analysis calculated for C12H14Cl2N4O4Pd2S2: C,
23.02; H, 2.25; Cl, 11.32; N, 8.95; S, 10.25. Found: C, 23.25;
H, 2.17; Cl, 11.21; N, 8.74; S, 10.44%.
2.2. Preparation of palladium complexes 1–4 [12]
A two-necked 25 mL RB flask was charged with PdCl2
(177 mg, 1 mmol), LiCl (100 mg, 2.4 mmol) and MeOH (2 mL);
the resulting reaction mixture was stirred under argon atmo-
sphere at 25 ◦C for 2.5 h. Then to this reaction mixture
were added NaOAc (123 mg, 1.5 mmol), and a solution of 4-
methylsulfonamide (171 mg, 1 mmol) in MeOH (2 mL). The
resulting reaction mixture was stirred at 25 ◦C for 24 h. Then,
distilled water (6 mL) was added to it and the resulting solid
was filtered on a sintered funnel, washed with water and dried
under reduced pressure (5 mm of Hg) for 3 h to afford palladium
complexes 1 as yellow coloured solid (256 mg, 82%).
2.2.1.4. Palladium complex 4. Pale-yellow solid, yield:
(235 mg, 72%) mp: 220–223 ◦C (dec.); IR (KBr, cm−1) ν = 721,
1130, 1149, 1168, 1317, 1340, 1377, 1456, 1463, 1558, 1652,
1683, 2852, 2923, 2954; 1H NMR (200 MHz, acetone-d6):
δ 2.25 (s, 3H, CH3), 2.58 (s, 3H, CH3), 6.59–7.76 (m, 3H,
ArH); 13C NMR (50 MHz, acetone-d6): δ 20.03 (CH3), 20.95
(CH3), 127.04, 128.24, 133.45, 136.87, 139.71, 143.16 (ArC);
elemental analysis calculated for C16H20Cl2N2O4Pd2S2: C,
29.46; H, 3.09; Cl, 10.87; N, 4.30; S, 9.84. Found: C, 29.66; H,
2.98; Cl, 10.74; N, 4.45; S, 9.72%.
2.2.1. Characterization of palladium complex
2.2.1.1. Palladium complex 1. Pale-yellow solid, yield:
(256 mg, 82%) mp: 195–198 ◦C (dec.); IR (KBr) ν = 559, 721,
813, 1083, 1157, 1305, 1340, 1377, 1463, 1521, 2358, 2675,
2727, 2852, 2916 cm−1; H NMR (200 MHz, DMSO-d6): δ
1
2.3. Preparation of palladium complex 5
2.19 (s, 3H, CH3), 7.11–7.19 (m, 2H, ArH), 7.54–7.55 (m, 2H,
ArH); 13C NMR (50 MHz, DMSO-d6): δ 21.17 (CH3); 125.48,
129.57, 141.55, 142.19 (ArC); elemental analysis calculated
for C14H16Cl2N2O4Pd2S2: C, 26.94; H, 2.58; Cl, 11.36; N,
4.49; S, 10.28. Found: C, 26.88; H, 2.45; Cl, 11.54; N, 4.55; S,
10.19%.
A two-necked 25 mL RB flask was charged with PdCl2
(177 mg, 1 mmol), LiCl (100 mg, 2.4 mmol) and MeOH (2 mL);
the resulting reaction mixture was stirred under argon atmo-
sphere at 25 ◦C for 2.5 h. Then to this reaction mixture were
added NaOAc (123 mg, 1.5 mmol), and a solution of saccharin
(183 mg, 1 mmol) in MeOH (2 mL). The resulting reaction mix-
ture was stirred at 25 ◦C for 6 h. Then, the resulting solid was
filtered on a sintered funnel, dried under reduced pressure (5 mm
of Hg) for 3 h to afford palladium complex 5 as yellow coloured
solid (275 mg, 85%).
2.2.1.2. Palladium complex 2. Pale-yellow solid, yield:
(256 mg, 78%) mp: 198–201 ◦C (dec.); IR (KBr, cm−1) ν = 561,
680, 721, 804, 1022, 1085, 1153, 1261, 1301, 1375, 1456, 1538,
1652, 1683, 2673, 2852, 2923; 1H NMR (200 MHz, DMSO-d6):
δ 3.75 (s, 3H, OCH3), 7.01–7.12 (m, 2H, ArH), 7.79–7.82 (m,
2H, ArH); 13C NMR (50 MHz, DMSO-d6): δ 55.97 (OCH3),
114.40, 128.07, 136.27, 162.05 (ArC); elemental analysis
calculated for C14H16Cl2N2O6Pd2S2: C, 25.63; H, 2.46; Cl,
10.81; N, 4.27; S, 9.76. Found: C, 26.75; H, 2.35; Cl, 10.97; N,
4.23; S, 9.87%.
2.3.1. Characterization of palladium complex 5
Pale-yellow solid, yield: (275 mg, 85%) mp: 237–240 ◦C
(dec.); IR (KBr, cm−1) ν = 594, 756, 984, 1154, 1287, 1287,
1
1456, 1664, 1951, 3590; H NMR (200 MHz, DMSO-d6): δ
7.21–7.34 (m, 4H, ArH); 13C NMR (50 MHz, DMSO-d6): δ
119.74, 123.19, 131.95, 133.37, 134.65, 145.29, 169.02 (ArC);
elemental analysis calculated for C14H8Cl2N2O6Pd2S2: C,
25.95; H, 1.24; Cl, 10.94; N, 4.32; S, 9.9. Found: C, 25.87;
H, 1.40; Cl, 11.05; N, 4.15; S, 9.78%.
2.2.1.3. Palladium complex 3. Pale-yellow solid, yield:
(238 mg, 76%) mp: 305–308 ◦C (dec.); IR (KBr, cm−1) ν = 559,
678, 721, 891, 1087, 1151, 1313, 1375, 1456, 1506, 1558, 1652,

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2.4. Preparation of palladacycles (6–9)
K2CO3 (552 mg, 4.0 mmol), styrene (312 mg, 3.0 mmol), water
(6 mL) and tetrabutylammonium bromide (644 mg, 2 mmol). To
this mixture palladium complex 5 (0.00324 mg, 5 × 10−6 mmol)
was added. The reaction mixture was then heated in an oil bath
at specified temperature and time (Table 2). The progress of
the reaction was monitored by TLC. The reaction mixture was
then allowed to cool to 25 ◦C and extracted with ethyl acetate
(3 × 10 mL). The combined organic extracts were washed with
brine and dried over anhydrous sodium sulfate and concentrated
under reduced pressure to afford the crude product. The crude
product was then purified by column chromatography on silica
gel using petroleum ether and ethyl acetate as eluents to afford
the 1-(4-methoxyphenyl)-2-phenylethylene as a colourless solid
(391 mg, 93%).
A two-necked 25 mL RB flask was charged with PdCl2
(177 mg, 1 mmol), LiCl (100 mg, 2.4 mmol) and MeOH (2 mL);
the resulting reaction mixture was refluxed under argon atmo-
sphere for 2.5 h. Then to this reaction mixture was added a
solution of 2-ethylphenylhydrazine (136 mg, 1 mmol) in MeOH
(2 mL). The resulting reaction mixture was refluxed for 3 h.
Then, the resulting solid was filtered on a sintered funnel, dried
underreducedpressurefor3 htoaffordpalladacycles 6asyellow
coloured solid (186 mg, 67%).
2.4.1. Characterization of palladium complex
2.4.1.1. Palladacycle 6. Brown solid, yield: (186 mg, 67%)
mp: 310–312 ◦C (dec.); IR (KBr, cm−1) ν = 769, 1215, 1490,
1
2399, 3018, 3301; H NMR (200 MHz, CDCl3) δ 1.27–1.19
2.6. General procedure for the Suzuki coupling
(t, J = 8.0 Hz, 3H, CH3), 2.62–2.47 (q, J = 8.0 Hz, 2H, CH2),
7.13–6.96 (m, 3H, ArH); 13C NMR (50 MHz, CDCl3) δ 12.92
(CH3), 23.35 (CH2), 121.90, 125.99, 127.43, 127.79, 127.89,
136.21 (ArC); elemental analysis calculated for C8H11N2PdCl:
C, 34.68; H, 4.00; N, 10.11; Cl, 12.80. Found: C, 34.68; H, 4.06;
N, 10.15; Cl, 12.76%.
A two-necked 25 mL RB flask was charged with 4-
bromoanisole (935 mg, 5.0 mmol), phenylboronic acid (915 mg,
7.5 mmol), KOH (560 mg, 10 mmol), palladium complex
5 (0.032 mg, 5 × 10−5 mmol), tetrabutylammonium bromide
(1610 mg, 5 mmol) and water (15 mL). The reaction mixture
was stirred at 25 ◦C at specified time (Table 3) (the progress of
the reaction was monitored by TLC). After the specified time,
the product was isolated by extraction with dichloromethane
(3 × 25 mL). The combined organic extracts were washed with
brine and dried over anhydrous sodium sulfate and concentrated
under reduced pressure to afford the crude product. The crude
product was then purified by column chromatography on silica
gel using petroleum ether and ethyl acetate as eluent to afford
4-methoxybiphenyl as a colourless solid (746 mg, 81%).
2.4.1.2. Palladacycle7. Brownsolid, yield:(190 mg, 68%)mp:
291–294 ◦C (dec.); IR (KBr, cm−1); ν = 433, 769, 1217, 1238,
1504, 2352, 3232; 1H NMR (200 MHz, CDCl3) δ 4.03 (s, 1H,
OCH3), 5.85 (bs, 2H, NH2), 6.85 (d, J = 8.9 Hz, 1H, ArH),
7.70 (s, 1H, ArH), 7.82 (d, J = 8.9 Hz, 1H, ArH); 13C NMR
(50 MHz, CDCl3) δ 54.50 (OCH3), 122.50, 125.17, 127.23,
127.84, 135.84, 144.05 (ArC); elemental analysis calculated for
C7H9N2OPdCl: C, 30.13; H, 3.25; N, 10.04; Cl, 12.71. Found:
C, 30.08; H, 3.27; N, 10.07; Cl, 12.75%.
2.6.1. Reuse of catalysts for the Suzuki coupling of
2.4.1.3. Palladacycle 8. Brown solid, yield: (187 mg, 66%);
mp:308–311 ◦C(dec.);IR(KBr, cm−1);ν = 741, 836, 925, 1060,
1126, 1287, 1418, 1508, 1606, 1818, 2565, 2760, 2858, 3772;
1H NMR (200 MHz, CDCl3) δ 7.95 (d, J = 9.9 Hz, 1H, ArH),
8.35 (d, J = 9.9 Hz, 1H, ArH), 8.97 (s, 1H, ArH); 13C NMR
(50 MHz, CDCl3) δ 116.35, 117.95, 129.02, 129.17, 129.64,
141.73 (ArC); elemental analysis calculated for C6H6N2PdCl2:
C, 25.42; H, 2.13; N, 9.88; Cl, 25.02. Found: C, 25.45; H, 2.18;
N, 9.89; Cl, 25.08%.
4-bromotoluene with phenylboronic acid
A two-necked 25 mL RB flask was charged with 4-
bromotoluene (855 mg, 5.0 mmol), phenylboronic acid (915 mg,
7.5 mmol), KOH (560 mg, 10 mmol), palladium complex
5 (0.032 mg, 5 × 10−5 mmol), tetrabutylammonium bromide
(1610 mg, 5 mmol) and water (15 mL). The reaction mixture
was stirred at 25 ◦C for 3 h. The product was isolated by extrac-
tion with diethyl ether (3 × 25 mL) to yield 4-methylbiphenyl
as a colourless solid (798 mg, 95%). For the second cycle, 4-
bromotoluene (855 mg, 5.0 mmol), phenylboronic acid (915 mg,
7.5 mmol) were added to the aqueous layer from the first cycle
containing palladium catalyst and base. The resulting reaction
mixturewasstirredfor3 h. Thenthesameworkupprocedurewas
repeated to yield 4-methylbiphenyl (798 mg, 95%). Thus, the
catalyst was reused at least five times without any considerable
loss of the catalytic activity.
2.4.1.4. Palladacycle9. Brownsolid, yield:(168 mg, 64%)mp:
336–340 ◦C (dec.); IR (KBr, cm−1); ν = 653, 910, 1030, 1197,
1244, 1350, 1514, 1633, 1866, 2061, 2279, 2472, 3001, 3234; 1H
NMR (200 MHz, CDCl3) δ 2.22 (s, 1H, CH3), 6.92 (s, 1H, ArH),
7.12 (d, J = 8.1 Hz, 1H, ArH), 7.39 (d, J = 8.1 Hz, 1H, ArH); 13
C
NMR (50 MHz, CDCl3) δ 24.90 (CH3), 120.99, 124.21, 125.09,
126.35, 127.04, 136.49 (ArC); elemental analysis calculated for
C7H9N2PdCl: C, 31.96; H, 3.45; N, 10.65; Cl, 13.48. Found: C,
31.98; H, 3.47; N, 10.63; Cl, 13.45%.
2.7. General procedure for the Sonogashira coupling
A two-necked 25 mL RB flask was charged with iodobenzene
(1020 mg, 5 mmol), phenylacetylene (765 mg, 7.5 mmol), pal-
ladium complex 5 (0.324 mg, 5 × 10−4 mmol), KOH (560 mg,
10 mmol), tetrabutylammonium bromide (1610 mg, 5 mmol)
and water (15 mL). The resulting mixture was stirred at 100 ◦C
2.5. General experimental procedure for the Heck reaction
A two-necked 25 mL RB flask with double walled water con-
denser was charged with 4-bromoanisole (374 mg, 2.0 mmol),

N.S.C. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 218–224
221
for 6 h. Then the reaction mixture was extracted with ethyl
acetate (3 × 20 mL) and washed with brine, dried over anhy-
drous sodium sulfate and concentrated under reduced pressure.
This crude product was purified on column chromatography
using 10% ethyl acetate in petroleum ether as eluent to afford
1,2-diphenylethyne as a colourless solid (802 mg, 90%).
2.8. General procedure for arylation of allylic alcohol
A two-necked 25 mL RB flask was charged with iodobenzene
(1020 mg, 5 mmol), allyl alcohol (435 mg, 7.5 mmol), palla-
dium complex 6 (0.277 mg, 5 × 10−4 mmol), K2CO3 (1380 mg,
10 mmol), tetrabutylammonium bromide (1610 mg, 5 mmol)
and water (15 mL). The resulting mixture was stirred at 80 ◦C
for 6 h. Then the reaction mixture was extracted with ethyl
acetate (3 × 20 mL) and washed with brine, dried over anhy-
drous sodium sulfate and concentrated under reduced pressure.
This crude product was purified on column chromatography
using 5% ethyl acetate in petroleum ether as eluent to afford
3-phenylpropanal as a colourless liquid (597 mg, 89%).
Fig. 2. Representative examples of palladacycles for Heck reactions.
and other known palladacycles (Fig. 2), catalysts 5 and 6 gave
a high yield as well as high TON in the Heck reaction between
4-bromoanisole and styrene carried out in the aqueous medium.
(Table 1, entries 10–12).
3.1.1. Heck reaction of aryl bromides with olefins
We have then used a wide variety of aryl bromides and olefins
to Heck reaction using Pd catalysts 5 and 6 and the results are
shown in Table 2. For both activated and unactivated aryl bro-
mides excellent conversions were obtained within 6 h. However,
in the case of activated aryl chlorides (entries 12 and 13) catalyst
5 gave only a moderate yield.
3. Results and discussion
3.1. Catalytic Heck reaction
The catalytic activities of the synthesized Pd complexes
were evaluated for the Heck cross-coupling reaction between
4-bromoanisole and styrene at 100 ◦C in the presence of K2CO3
as base under aqueous, ligand-free conditions and the results are
presented in Table 1. It is noteworthy that among all the palla-
dium complexes screened catalysts 5 and 6 have exhibited high
activity for the Heck reaction with a turnover number (TON)
of 372,000 (yield: 93%) and 364,000 (yield: 91%) respectively
(entries 5 and 6). We observed that in comparison with Pd(OAc)2
3.2. Catalytic Suzuki cross-coupling reactions
The catalytic activity of Pd catalysts 5 and 6 for Suzuki reac-
tion was evaluated by taking aryl bromides and boronic acids as
coupling partners. Under the optimized conditions, various acti-
Table 2
Heck reaction between aryl halides and olefinic substrates catalyzed by 5 and 6a
Table 1
Heck reaction of 4-bromoanisole with styrene: screening of Pd catalystsa
Entry
ArX
Y
Yields of 13 (%)b
Catalyst 5
Catalyst 6
1
2
3
4
5
6
7
8
9
4-Bromotoluene
4-Bromotoluene
CO2Me
CO2nBu
Ph
CO2Me
CO2nBu
CO2nBu
CO2Et
CO2nBu
Ph
97
94
98
89
81
94
95
95
97
85
87
91
83
95
82
80
86
84
89
94
80
79
Entry
Palladium catalyst
Yield of 12 (%)b
TONc
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
89
85
82
88
93
91
86
85
86
71
78
51
356,000
340,000
328,000
352,000
372,000
364,000
344,000
340,000
344,000
1,420
1-Bromonaphthalene
1-Bromonaphthalene
1-Bromonaphthalene
3-Bromobenzotrifluoride
3-Bromobenzotrifluoride
Bromobenzene
Bromobenzene
4-Bromoanisole
2-Bromo-6-methoxy-
naphthalene
4-Chloronitrobenzene
4-Chloronitrobenzene
10
11
CO2Et
CO2nBu
1e
10
11
12
Pd(OAc)2
101f
111g
500
13,000
12
13
CO2Et
CO2nBu
45
56
NRc
NRc
a
a
Reaction conditions: 4-bromoanisole (2 mmol), styrene (3 mmol), K2CO3
(4 mmol), palladium complex (5 × 10−6 mmol), tetrabutylammonium bromide
(2 mmol), water (6 mL), 6 h.
Reaction conditions: aryl halide (2 mmol), olefin (3 mmol), K2CO3
(4 mmol), palladium complex (5 × 10−6 mmol), tetrabutylammonium bromide
(2 mmol), water (6 mL), 100 ◦C, 6 h.
b
b
Isolated yields after chromatographic purification.
TON = turnover number, defined as mmol of product/mmol of Pd.
Isolated yields after chromatographic purification.
No reaction occurred.
c
c

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N.S.C. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 218–224
Table 3
Table 4
Suzuki coupling of aryl halides with arylboronic acids catalyzed by 5 and 6a
Reusability study of the palladium complex 5 for the Suzuki coupling of 4-
bromotoluene with phenylboronic acida
Entry Arꢀ
ArX
Yields of 14(%)b
Entry
Reaction cycle
Yield (%)b
Catalyst 5 Catalyst 6
1
2
3
4
5
1
2
3
4
5
95
95
93
90
88
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-Bromoanisole
2-Bromoanisole
4-Bromotoluene
Bromobenzene
2-Bromonaphthalene
3-Bromobenzotrifluoride
4-Chloroacetophenonec
2-Nitrochlorobenzenec
81
78
95
96
89
90
78
75
78
72
83
98
82
85
NRd
NRd
67
63
70
90
78
77
73
71
76
78
78
a
Reaction conditions: aryl halide (5 mmol), phenylboronic acid (7.5 mmol),
KOH (10 mmol), palladium catalyst (5 × 10−5 mmol), tetrabutylammonium
bromide (5 mmol), water (15 mL), 25 ◦C, 3 h.
b
Isolated yields after chromatographic purification.
4-Toluenesulfonyl chloride 80
10
11
12
13
14
15
16
17
18
19
Benzenesulfonyl chloride
78
71
81
79
78
78
70
69
86
81
4-Acetyl Ph Bromobenzene
4-Acetyl Ph 4-Bromoanisole
4-Acetyl Ph 4-Bromotoluene
4-Acetyl Ph 1-Bromonaphthalene
3-Chloro Ph 4-Nitrobromobenzene
3-Chloro Ph 4-Bromotoluene
3-Chloro Ph 1-Bromonaphthalene
3-Chloro Ph Bromobenzene
of KOH (Table 5). Excellent yields of acetylenic compounds
(15) were obtained for the aryl iodides, although the Pd cata-
lysts have shown only the moderate activity for aryl bromides
as well as chlorides.
3.4. Catalytic arylation of allylic alcohols
1-Naphthyl
Bromobenzene
Arylation of allylic alcohols [14] constitutes a powerful
method in organic synthesis for the generation of a three-carbon
unit with an aldehydic group. We have carried out arylation of
allylic alcohols with aryl halides either with K2CO3 or diiso-
propylamineasbaseusingphenylhydrazine-based palladacycles
(6–9) as catalysts in water at 80 ◦C. The novel feature of our
system is the selective formation of either ␣,␤-unsaturated alco-
hols or saturated carbonyl compounds. Selective formation of
aromatic conjugated alcohols was observed in the case of aryl
halides with electron-withdrawing groups whereas saturated
aldehydeswereformedwhenarylhalideswithelectron-donating
groups were used. Good yields of ketones were obtained when
secondary allylic alcohol was subjected to arylation reaction
(entry 4; Table 6). This selectivity can be explained by the fact
that the ␤ hydride elimination from the carbopalladation inter-
mediate 16 can take place from both the available ␤-hydrogens.
Electron-withdrawing group on the aromatic ring makes the
a
Reaction conditions: aryl halide (5 mmol), phenylboronic acid (7.5 mmol),
KOH (10 mmol), palladium catalyst (5 × 10−5 mmol), tetrabutylammonium
bromide (5 mmol), water (15 mL), 25 ◦C, 3 h.
b
Isolated yields after chromatographic purification.
Reaction was carried out at 100 ◦C.
No reaction occurred.
c
d
vated and unactivated aryl bromides underwent coupling with
a wide range of phenylboronic acids in water as the solvent
(Table3). Amongthebases(K2CO3, KOtBu, KOHandCs2CO3)
screened, KOH gave the best yield.
It is remarkable that good yields of biaryls were obtained for
the aryl chlorides having electron-withdrawing groups like acyl,
nitro (entries 6 and 7). For the coupling of 4-chloroacetophenone
with phenylboronic acid, a good yield of 78% was achieved with
a TON of 78,000. Pd catalyst 5 is readily soluble in water under
ambient conditions, which makes its separation easier from the
biaryls formed.
The results of the reusability study of the palladium complex
5 for the Suzuki coupling of 4-bromotoluene with phenylboronic
acid for the five cycles is presented in Table 4. As can be seen,
there is only marginal decrease in the yield of the biphenyl (88%)
for the fifth cycle as compared to the yield obtained for the first
cycle (95%).
Table 5
Sonogashira coupling catalyzed water-soluble saccharin palladium complex 5a
Entry
Aryl halides (Ar-X)
Alkynes (R)
Yield of 15 (%)b
1
2
3
4
5
6
7
C6H5I
4-O2NC6H4I
C6H5Br
C6H5
C6H5
C6H5
4-MeC6H4
C6H5
90
93
70
66
72
57
20
3.3. Catalytic Sonogashira reactions
C6H5Br
Sonogashira reactions utilize palladium salts in catalytic
amounts along with other metal as a co-catalyst and a base.
Typically, copper is used as a co-catalyst but suffers from the
homocoupling of the expensive alkynes. Copper-free Sono-
gashira reactions have also been reported [13]. We evaluated the
effectiveness of Pd catalyst 5 for Sonogashira coupling reactions
under totally copper-free conditions using water in the presence
4-O2NC6H4Br
4-MeC6H4Br
C6H5Cl
C6H5
C6H5
a
Reaction conditions: aryl halide (5 mmol), alkyne (7.5 mmol), KOH
(10 mmol), tetrabutylammonium bromide (5 mmol), water (15 mL), palladium
complex 5 (5 × 10−4 mmol), 100 ◦C, 6 h.
b
Isolated yields after chromatographic purification.

N.S.C. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 218–224
223
Table 6
Arylation of aryl halides with (Ar-X) allylic alcohols catalyzed by palladacycle 6a
Entry
Ar-X
Alcohol
Base
Product
Yield (%)b
82
1
Ethyl 4-bromobenzoate
DIPAc
2
3
4
Methyl 4-bromobenzoate
4-Bromobenzoic acid
Iodobenzene
DIPA
88
71
63
K2CO3
K2CO3
5
6
7
Iodobenzene
Iodobenzene
4-Iodoanisole
K2CO3
K2CO3
K2CO3
89
73
73
8
9
4-Iodoanisole
DIPA
92
Methyl 2-iodobenzoate
Methyl 4-iodobenzoate
DIPA
DIPA
90
81
10
a
Reaction conditions: aryl halide (5 mmol), allyl alcohol (7.5 mmol), base (10 mmol), tetrabutylammonium bromide (5 mmol), water (15 mL), catalyst 6
(5 × 10−4 mmol), 80 ◦C, 12 h.
b
Isolated yields after chromatographic purification.
H1–␤ hydrogen more acidic, thus facilitating its removal as pal-
ladium hydride species resulting in the formation of aromatic
conjugated alcohols (route a) while formation of aldehydes takes
place by the elimination of H2–␤ hydrogen [15] (Scheme 1).
The formation of Pd(0) nanoparticles was investigated by
subjecting the reaction mixture consisting of iodobenzene, allyl
alcohol and palladacycle 6 in water after 12 h to “in situ”
Fig. 3. TEM image of Pd nanoparticles formed after 12 h for the reaction
between iodobenzene and allyl alcohol using palladacycle 6 in the aqueous
medium.
TEM analysis. The TEM measurement for the aqueous medium
(Fig. 3) confirms the presence of Pd(0) nanoparticles of spherical
morphology varying in diameter from 10 to 12 nm.
4. Conclusion
In summary, a novel family of sulfonamide-based palladium
complexes and phenylhydrazine-based palladacycles from
Scheme 1. Plausible mechanism for arylation with allylic alcohols.

224
N.S.C. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 269 (2007) 218–224
inexpensive and readily available ligands have been synthe-
sized. These novel Pd catalysts are air, moisture-stable and
some are completely soluble in water (Pd catalyst 5), which
were used for C–C bond forming reactions like Suzuki, Heck,
Sonogashira reactions and arylation of allyl alcohols. High
TON (often reaching up to 372,000), totally phosphine-free
conditions and reactions in aqueous media are some of the
salient features of the study. The TEM analysis confirms
the in situ formation of palladium(0) nanoparticles (size
10–12 nm) in the case of palladacycle. The palladium catalyst
was reused several times without significant loss of catalytic
activity.
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NSCR and VPRI thank CSIR, New Delhi for the award of
senior research fellowships. Financial Grants from DST, New
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edged. The authors also thank Dr. B.D. Kulkarni, Head, CE-PD
Division, for his constant encouragement and support.
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Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.molcata.2006.12.023.
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