Catalytic synthesis of Bi- and teraryls in aqueous medium with palladium(II) complexes of 2-(pyridine-2-ylmethylsulfanyl)benzoic acid

Article abstract of DOI:10.1002/ejic.201403003

Suzuki-Miyaura coupling reactions of phenylboronic and 1,4-phenylenediboronic acid with ArBr to form bi- and teraryls have been efficiently catalyzed by the air- and moisture-insensitive complexes [PdCl₂L1] [1, L1 = 2-(pyridine-2-ylmethyl)sulfanylbenzoic acid; 0.05-0.5 mol-%] and [Pd(L2-H)₂] (2, L2-H = 2-pyridin-2-yl-benzo[b]thiophen-3-ol; 0.01-0.5 mol-%). The complexes were formed by the reaction of [Pd(CH₃CN)₂Cl₂] with L1, and the catalysis proceeds in water for 1. The loading of 0.1-0.5 mol-% of Pd is very promising for the coupling reactions to form teraryls. The COOH group imparts solubility to 1 in water. Ligand L2 is formed by the unprecedented cyclization of L1 in the course of the complexation reaction. The yield of 2 increases with the reaction time (5 h: 70%; 24 h: 85%). The two complexes and L1 have been characterized by NMR spectroscopy (¹H and ¹³C{¹H}). The single-crystal structures of 1 and 2 have been solved, and the Pd-S, Pd-N, and Pd-O bond lengths are 2.269(2), 1.999(6)-2.057(2), and 1.9787(17) A?, respectively. Nanoparticles (NPs) with a narrow size distribution (ca. 3.0-5.5 nm for 80-85% of the particles) formed at the start of these reactions and appear to be important for the catalytic coupling. Poisoning experiments and a two-phase test have shown that the catalysis is largely homogeneous and involves [Pd⁰-Pd^II] processes. The bond lengths and angles calculated by DFT are consistent with the experimental ones.

Full text of DOI:10.1002/ejic.201403003

FULL PAPER
DOI:10.1002/ejic.201403003
Catalytic Synthesis of Bi- and Teraryls in Aqueous
Medium with Palladium(II) Complexes of
2-(Pyridine-2-ylmethylsulfanyl)benzoic Acid
[
a]
[a]
[a]
Om Prakash, Hemant Joshi, Kamal Nayan Sharma,
[a]
[a]
Alpesh Kumar Sharma, and Ajai K. Singh*
Keywords: Nanoparticles / Palladium / S ligands / C–C coupling
Suzuki–Miyaura coupling reactions of phenylboronic and
tion time (5 h: 70%; 24 h: 85%). The two complexes and L1
1
1
,4-phenylenediboronic acid with ArBr to form bi- and
teraryls have been efficiently catalyzed by the air- and
moisture-insensitive complexes [PdCl L1] [1, L1 = 2-(pyr- solved, and the Pd–S, Pd–N, and Pd–O bond lengths are
idine-2-ylmethyl)sulfanylbenzoic acid; 0.05–0.5 mol-%] and
Pd(L2-H) ] (2, L2-H = 2-pyridin-2-yl-benzo[b]thiophen-3-ol;
.01–0.5 mol-%). The complexes were formed by the reaction
of [Pd(CH CN) Cl ] with L1, and the catalysis proceeds in
have been characterized by NMR spectroscopy ( H and
13
1
C{ H}). The single-crystal structures of 1 and 2 have been
2
2.269(2), 1.999(6)–2.057(2), and 1.9787(17) Å, respectively.
Nanoparticles (NPs) with a narrow size distribution (ca. 3.0–
5.5 nm for 80–85% of the particles) formed at the start of
these reactions and appear to be important for the catalytic
[
2
0
3
2
2
water for 1. The loading of 0.1–0.5 mol-% of Pd is very prom- coupling. Poisoning experiments and a two-phase test have
ising for the coupling reactions to form teraryls. The COOH
group imparts solubility to 1 in water. Ligand L2 is formed
by the unprecedented cyclization of L1 in the course of the
complexation reaction. The yield of 2 increases with the reac-
shown that the catalysis is largely homogeneous and involves
[Pd –Pd ] processes. The bond lengths and angles calculated
by DFT are consistent with the experimental ones.
0
II
Introduction
but also offers an additional advantage that most of the
substrates and products in Suzuki reactions are insoluble in
water; thus, the use of water-soluble catalytic systems con-
tributes to the easy separation, recovery, and recycling of
the catalyst. To design water-soluble palladium complexes,
the ligands surrounding the metal should be hydrophilic.
Thus, water-soluble complexes of palladium have been de-
signed by introducing various ionic groups such as sulf-
Biaryl compounds are important for pharmaceuticals,
agrochemicals, natural products, and functional materi-
als.[
1–4]
Teraryls have attracted attention owing to their
presence as structural units in natural products. In materials
science, chemical sensing, and some biological activity, the
potential role of teraryls has been recognized.[5–7] Palla-
dium-catalyzed C–C Suzuki–Miyaura coupling reactions
are very important synthetic tools for the synthesis of bi-
[
8]
[14c,15]
[16]
[17,18]
onate,
carboxylate,
and ammonium groups.
II
Pd complexes with a COOH group on the ligand scaffold
are of current interest, as this group readily provides some
II
[9]
and teraryls. Various Pd complexes of nitrogen, phos-
[
10]
[11]
phorus,
N-heterocyclic carbene (NHC),
and chalco-
miscibility with organic phases. Recently, water-soluble Pd
gen[ ligands have been employed for such couplings. To
develop the best catalytic system for Suzuki–Miyaura cou-
pling reactions, separation, air and moisture insensitivity,
recyclability, required loading, and the environmental
friendliness of the catalyst are some of the strategic aspects.
The use of environmentally friendly water as a solvent for
the Suzuki–Miyaura coupling[13] is of great interest because
12]
[11a,19]
complexes of a carboxylated carbene ligand
were syn-
–
thesized by introducing a COO group into a hydrophobic
NHC, and the prepared complexes have shown high cata-
lytic activity for Suzuki–Miyaura cross-coupling in water.
Palladium(II) complexes of a variety of organochalcogen
[12j,12k]
ligands, including 2-(RSCH )C H N (R = Me, Ph),
2
5
4
which is structurally close to the ligand used here [2-(pyr-
idine-2-ylmethyl)sulfanylbenzoic acid (L1)], show good
catalytic activity for the Suzuki coupling of aryl halides,
[
14]
it is not only safe, nontoxic, inexpensive, and plentiful
[
12]
[
a] Department of Chemistry, Indian Institute of Technology including aryl chlorides.
However, attempts to make
Delhi,
II
them water-soluble are few. Pd ENE pincer complexes (E
= S/Se/Te) have been explored recently for Suzuki–Miyaura
coupling reactions (required loading 2 mol-% of Pd) in
New Delhi 110016, India
E-mail: aksingh@chemistry.iitd.ac.in
ajai57@hotmail.com
http://chemistry.iitd.ac.in/faculty/singhak.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201403003.
[
12h]
aqueous medium.
Further, to the best of our knowledge,
palladium(II) complexes have not been applied in the cata-
Eur. J. Inorg. Chem. 2015, 520–526
520
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FULL PAPER
lytic formation of teraryls. Therefore, we thought it worth- ca. 70% for 2 when the reaction was performed for 5 h.
while to design water-soluble palladium complexes of or- When the reaction time was increased to 24 h, the yield of
ganochalcogen ligands with COOH groups and explore 1 decreased to only ca. 5%, whereas that of 2 increased to
them for Suzuki coupling reactions. Therefore, 2-(pyridine- 85%. This indicates that L2 is formed before complexation,
2-ylmethylsulfanyl)benzoic acid (L1) was thought to be a and 1 and 2i are probably in equilibrium (Scheme 2). The
good candidate for such a Pd catalyst. Thus, complex 1 was coordination of the Pd centre with the COOH group facili-
synthesized, but complex 2 also formed. The cyclization of tates the C–H activation of L1 in 2i. The ligand 2-phenyl-
L1 gives 2-pyridin-2-yl-benzo[b]thiophen-3-ol (L2), which sulfanylmethylpyridine, which is similar to L1 but does not
acts as a N,O ligand in 2. Both complexes are efficient for have a COOH group, reacts with an equimolar amount of
II
[20]
Suzuki coupling, but only 1 works in water.
[Pd(CH CN) Cl ] in CH CN to form a Pd complex
3 2 2 3
similar to complex 1. There is no activation of the benzylic
CH group.
2
Results and Discussion
The procedure used for synthesis of ligand L1 was re-
[
31]
ported previously.
The synthesis of the palladium(II)
complexes (1 and 2) is shown in Scheme 1. The reaction
of L1 with an equimolar amount of [Pd(CH CN) Cl ] in
3
2
2
CH CN resulted in 1 and 2 in two fractions, A and B,
3
respectively (Scheme 1). The fractions were separated by fil-
tration and, after workup, single crystals of 1 and 2 were
grown from CH CN (by diffusion of Et O) and N,N-di-
3
2
methylformamide (DMF), respectively. Both complexes are
air- and moisture-insensitive. Complex 1 shows good solu-
bility in CH CN, DMF, and dimethyl sulfoxide (DMSO)
3
and is sparingly soluble in CH Cl , CHCl , CH OH, diethyl
2
2
3
3
ether, tetrahydrofuran (THF), and water. It was also soluble
in alkaline water owing to the presence of the –COOH
group. On other hand, complex 2 was soluble only in DMF
and DMSO. The ligand 2-pyridin-2-yl-benzo[b]thiophen-3-
ol (L2) present in 2 is generated in situ by an unprecedented
palladium-promoted cyclization of L1, most probably by an
intramolecular Pd-promoted cyclization in 1 (Scheme 2). To
Scheme 1. Synthesis of 1 and 2.
6
Similarly, L1 reacts with [(η -C H )RuCl(μ-Cl)] and
6
6
2
6
the best of our knowledge, there are no other examples of NH PF at room temperature to form [(η -C H )-
4
II
6
6
6
[21]
such a cyclization. The resulting cyclized species L2 coordi- Ru ClL1][PF ],
and there is no activation of benzylic
6
II
nates with the Pd center to form 2. The yields of 1 and 2 group. These observations support indirectly the role of 2i
vary with reaction time. The yields were ca. 20% for 1 and and Pd in the cyclization.
Scheme 2. Mechanism for the formation of 2 from 1.
Eur. J. Inorg. Chem. 2015, 520–526
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Crystal Structure
The structures of 1 and 2 have been established by X-ray
diffraction studies of their single crystals. Further details of
the crystal data, structural refinements, and bond lengths
and angles are available in the Supporting Information
(Tables S1 and S2).
The molecular structures with ellipsoids of 30% prob-
ability are shown in Figures 1 and 2. In both cases, a dis-
torted square-planar coordination around the palladium
center was observed. The binding of the pyridyl nitrogen
II
atom and the sulfur atom to the Pd center in 1 results in
a five-membered chelate ring. In 2, the pyridyl nitrogen Figure 2. Molecular structure of 2. Bond lengths [Å] and angles
II
atom and the oxygen atom coordinate to the Pd center [°]: Pd(1)–N(1) 2.057(2), Pd(1)–O(1) 1.9787(17), S(1)–C(1) 1.762(3),
N(1)–Pd(1)–O(1) 92.13(8), N(1)–Pd(1)–N(1) 180.0, O(1)–Pd(1)–
and form two five-membered chelate rings.
O(1) 180.00(8), O(1)–Pd(1)–N(1) 87.88(8).
calculated by DFT (Table S4) is better for the Pd–Cl/O and
Pd–N bonds. The calculated and experimentally found
bond angles are also reasonably close (for details of DFT
results, see Supporting Information).
Complex 1 crystallizes with one molecule of water in its
crystal lattice. This water molecule and the carboxylic group
of 1 form hydrogen-bond interactions in the crystal lattice,
as shown in Figure S1. Additionally, the Cl atom of 1 is
involved in C–H···Cl and O–H···Cl secondary interactions,
which result in a two-dimensional sheet structure (Fig-
Figure 1. Molecular structure of 1. Bond lengths [Å] and angles
ure S1). In 2, the C–H···O and C–H…π secondary interac-
[
°]: Pd(1)–S(1) 2.269(2), Pd(1)–N(1) 1.999(6), Pd(1)–Cl(1) 2.301(2),
tions result in a three-dimensional packing framework (Fig-
ure S2). Selected secondary interaction distances are listed
in Table S3.
Pd(1)–Cl(2) 2.302(2), Cl(1)–Pd(1)–S(1) 174.00(9), Cl(2)–Pd(1)–S(1)
1.47(8), N(1)–Pd(1)–S(1) 85.41(19), N(1)–Pd(1)–Cl(1) 92.78(19),
9
N(9)–Pd(1)–Cl(2) 175.64(19), Cl(2)–Pd(1)–Cl(1) 90.63(9).
The Pd–S bond length in 1 [2.269(2) Å] is consistent with
previously reported values [2.254(4)–2.288(12) Å].[
The Pd–N bond lengths of 1 and 2 are within the range
12g,12h,12j]
Application of Pd Complexes 1 and 2 in Suzuki–Miyaura
Coupling Reaction
[
1.999(6)–2.057(2) Å] for such bonds in several previously
[
12a,12e]
reported species.
The Pd–O bond length in 2
As 1 is soluble and stable in water, its use for the catalysis
[
1.9787(18) Å] is consistent with the value [2.000(5) Å] re- of the Suzuki coupling of 4-bromoanisole with phenyl-
II
[12a]
ported for a Pd selenated Schiff base complex.
The boronic acid in water under ambient conditions was opti-
agreement between the observed bond lengths and those mized. The optimized reaction conditions are given in
Table 1. Suzuki–Miyaura coupling of phenylboronic acid and aryl bromide catalyzed with 1 and 2.
Entry Aryl halide
Catalyst 1[a]
T [h] Yield[b] [%] (TON)
Catalyst 2[c]
T [h]
Loading [mol-%]
Loading [mol-%]
Yield[b] [%] (TON)
1
2
3
4
5
6
7
8
1-bromo-4-nitrobenzene
0.05
0.05
0.05
0.1
0.1
0.1
5
8
5
98 (1960)
95 (1900)
95 (1900)
94 (940)
95 (950)
96 (960)
92 (1840)
95 (950)
0.01
0.01
0.01
0.05
0.1
0.1
0.01
0.01
5
8
5
10
15
24
10
10
99 (9900)
95 (9500)
98 (9800)
96 (1920)
95 (950)
95 (950)
90(9000)
99 (9900)
4-bromobenzonitrile
4-bromobenzaldehyde
4-bromobenzoic acid
4-bromotoluene
4-bromoanisole
4-bromobenzophenone
bromobenzene
8
20
24
8
0.05
0.1
8
[
(
(
a] Reaction conditions: aryl halide (1.0 mmol), phenylboronic acid (1.2 mmol), TBAB (1.0 mmol), and K
2
CO
5 mL), temperature 110 °C. [b] Isolated yield. [c] Reaction conditions: aryl halide (1.0 mmol), phenylboronic acid (1.2 mmol), and K
1.5 mmol), solvent: DMF/water (4:1, 5 mL), temperature 90 °C.
3
(1.5 mmol), solvent: water
2
CO
3
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Table 2. Suzuki–Miyaura coupling of 1,4-phenylenediboronic acid catalyzed with 1 and 2.
Entry Aryl halide
Catalyst 1[a]
T [h]
Catalyst 2[c]
T [h]
Loading [mol-%]
Yield[b] [%] (TON)
Loading [mol-%]
Yield[b] (TON)
1
2
3
4
5
6
1-bromo-4-nitrobenzene
0.1
0.1
0.1
0.5
0.5
0.5
8
8
10
12
20
24
98 (1960)
95 (1900)
95 (1900)
94 (940)
95 (950)
96 (960)
0.1
0.1
0.1
0.5
0.5
0.5
6
6
8
10
20
24
99 (9900)
95 (9500)
98 (9800)
96 (1920)
95 (950)
95 (950)
4-bromobenzonitrile
4-bromobenzaldehyde
4-bromobenzoic acid
4-bromotoluene
4-bromoanisole
[
a] Reaction conditions: aryl halide (1.0 mmol), 1,4-phenylenediboronic acid (0.6 mmol), TBAB (1.0 mmol), and K
solvent: water (5 mL), temperature 110 °C. [b] Isolated yield. [c] Reaction conditions: aryl halide (1.0 mmol), 1,4-phenylenediboronic acid
0.6 mmol), and K CO (2.0 mmol), solvent: DMF/water (4:1, 5 mL), temperature 90 °C.
2 3
CO (2.0 mmol),
(
2
3
Table S5. In the presence of tetrabutylammonium bromide
TBAB) as a phase-transfer catalyst[ and K CO as a
22]
(
2 3
base, maximum conversion was achieved. Complex 2 gives
a lower conversion owing to its poor solubility in aqueous
medium. However, 2 is efficient for the cross-coupling (con-
version up to 96%) at a loading of 0.1 mol-% in DMF with
water as a cosolvent (4:1; Table S4, Entry 12). The scope of
the catalytic system was explored with a range of aryl brom-
ides, and results are given in Table 1; several aryl bromides
can be coupled smoothly to give nearly quantitative yields
of biaryls.
The activities of 1 and 2 were studied for the coupling of
aryl bromides with 1,4-phenylenediboronic acid to afford
teraryls. Generally, aryl dihalides have been used to prepare
[23]
teraryls by the Suzuki coupling route. Examples that use
,4-phenylenediboronic acid are extremely rare.[
23]
Com-
1
plexes 1 and 2 both have good efficiency for the coupling
of aryl bromides at a catalyst loading of 0.1–0.5 mol-%
(
Table 2), which is lower than previously reported load-
[
23,24]
ings.
In the course of Suzuki reactions catalyzed by 1 and 2,
the solutions immediately became black. The black material
has been isolated and analyzed in detail to understand the
relationship between the catalytic activity and nature of the
black material. SEM with energy-dispersive spectroscopy
(SEM-EDX, Figures S4 and S5) and HRTEM (Figures S6
and S7) analysis of the black material suggest that it is Figure 3. Size distribution of NPs generated from 1 and 2 during
Suzuki–Miyaura coupling.
made of nanosized spherical particles, which contain Pd
and S. On the basis of the EDX results, the Pd/S ratios are
nearly 3:2 and 4:5 in the nanoparticles (NPs) formed from
1
and 2, respectively. However, nothing concrete can be geneously by NPs containing Pd and S. A two-phase test[25]
concluded about organic ligand fragments on the basis of was performed (Scheme 3) on catalysis with 1 and 2. A
SEM-EDX. The size of 80–85% of these NPs obtained homogeneous processes with leached Pd species coexists
from 1 and 2 is 3.0–5.5 nm (Figure 3). These NPs were ex- with heterogeneous catalysis. The surface Pd atoms of the
amined independently for the Suzuki coupling reaction and nanoparticles undergo oxidative addition to form soluble
II
were effective under optimum conditions (Table 3).
Pd intermediate Ar–Pd–Br, and thereafter catalysis is
[
12a]
[12a]
Hg
and triphenylphosphine
poisoning tests were driven homogeneously. Thus, the catalysis in the present
performed for coupling catalyzed with 1 and 2. Both tests case is a largely homogeneous process and is probably
0
suggest that catalysis does not proceed completely hetero- mixed with oxidative addition to Pd at the surface.
Eur. J. Inorg. Chem. 2015, 520–526
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Table 3. Suzuki–Miyaura coupling catalyzed with NP1 and NP2.
Entry Aryl halide
NP1[a]
T [h]
NP2[c]
T [h]
Pd [mg]
Yield[b] [%]
Pd [mg]
Yield[b] [%]
1
2
3
4
4-bromobenzonitrile
4-bromobenzaldehyde
4-bromotoluene
5
5
10
10
5
5
24
24
90
95
85
91
5
5
10
10
5
5
20
24
92
95
90
95
4-bromoanisole
[
(
a] Reaction conditions: aryl halide (1.0 mmol), phenylboronic acid (1.2 mmol), TBAB (1.0 mmol), and K
5 mL), temperature 110 °C. [b] Yield determined by NMR spectroscopy. [c] Reaction conditions: aryl halide (1.0 mmol), phenylboronic
acid (1.2 mmol), and K CO (1.5 mmol), solvent: DMF/water (4:1, 5 mL), temperature 90 °C.
2 3
CO (1.5 mmol), solvent: water
2
3
Scheme 3. Two-phase test for Suzuki–Miyaura coupling.
thermal parameters set at 1.2 times that of the carbon atom to
which they are attached. The least-square refinement cycles on F
Conclusions
2
The complexation of palladium(II) with 2-(pyridine-2-yl- were performed until the model converged. High-resolution TEM
methylsulfanyl)benzoic acid (L1) gives the normal complex characterization to reveal particle sizes and shapes was performed
1
in low yield and another complex 2, in which the ligand with a Philips Tecnai F20 TEM operated at 200 kV. The samples
for HRTEM were prepared by dispersing nanocrystals in cyclohex-
present L2 is formed by the unexpected cyclization of L1.
Complex 1 can catalyze Suzuki reactions in water. Com-
plexes 1 and 2 were used for Suzuki–Miyaura reactions of
ane or ethanol and drying a drop of the dispersion on a carbon-
coated copper grid. The elemental composition of the NPs was
studied with a Carl ZEISS EVO5O scanning electron microscope
1
,4-phenylenediboronic acid with aryl bromides to form
(
SEM) and associated EDX system (QuanTax 200), which is based
on a silicon drift detector (SDD) and provides an energy resolution
of 127 eV at Mn-K . The sample was mounted on a circular met-
allic sample holder with sticky carbon tape. The melting points
teraryls and are the first examples of organochalcogen
tailored Pd complexes suitable for the catalytic preparation
of teraryls. The loading of 0.01–0.5 mol-% of Pd is very
α
promising for the coupling leading to teraryls. The nano- were determined in open capillaries, yields refer to isolated yields
sized particles of palladium sulfide generated in situ from of compounds with purity Ն95%. DFT calculations were per-
II
[28]
[29]
[30]
the Pd complexes in the course of the catalysis of the Su- formed with the GAUSSIAN-09,
M06,
and LANL2DZ
programs, as detailed in the Supporting Information.
zuki–Miyaura C–C coupling reactions appear to play a role
in the catalysis. Poisoning experiments and two-phase tests
CCDC-1008530 (for 1) and -1008531 (for 2) contain the supple-
have shown that catalysis is largely homogeneous and in- mentary crystallographic data for this paper. These data can be
0
II
volves a [Pd –Pd ] process.
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Chemical and Reagents: Thiosalicylic acid, (2-chloromethyl)pyr-
idine hydrochloride and palladium(II) chloride were procured from
Sigma–Aldrich and used as received. 2-(Pyridine-2-ylmethylsulf-
anyl)benzoic acid was prepared by the method reported pre-
viously.[ All solvents were dried and distilled before use by stan-
dard procedures.[
Experimental Section
Physical Measurements: The C, H, and N analyses were performed
1
with a Perkin–Elmer 2400 Series II C, H, N analyzer. The H and
31]
13
1
C{ H} NMR spectra were recorded with a Bruker Spectrospin
32]
DPX-300 NMR spectrometer at 300.13 and 75.47 MHz, respec-
tively. IR spectra in the range 4000–400 cm–1 were recorded with a
Nicolet Protége 460 FTIR spectrometer with samples as KBr pel-
lets. The diffraction data of single crystals of 1 and 2 were collected
with a Bruker AXS SMART Apex CCD diffractometer with Mo-
[PdCl
benzoic acid (L1, 0.5 mmol) was suspended in dry CH
and added to a solution of [Pd(CH CN) Cl ] (0.129 g, 0.5 mmol)
in CH CN with continuous stirring at room temperature. The reac-
2
L1] (1) and [Pd(L2-H)
2
] (2): 2-(Pyridine-2-ylmethylsulfanyl)-
3
CN (50 mL)
3
2
2
3
K
α
(0.71073 Å) radiation at 298(2) K. The software SADABS[26]
tion mixture was stirred and heated to reflux for 5 h. After cooling
to room temperature, the reaction mixture was filtered. The precipi-
tate was dried in vacuo to afford 2 as yellow solid. The filtrate was
concentrated with a rotary evaporator to ca. 5 mL and mixed with
diethyl ether (15 mL) to afford 1 as an orange solid, which was
was used for absorption correction (if needed), and SHELXTL was
used for space group determination, structure solution, and refine-
[
27]
ments.
All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in idealized positions with isotropic
Eur. J. Inorg. Chem. 2015, 520–526
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collected by filtration and dried in vacuo. Single crystals of 1 and
were grown by slow evaporation of their solutions in CH CN
with diffusion of Et O) and DMF, respectively.
: Yield: 0.054 g, 20%. C13 NO PdS (422.60): calcd. C 36.95,
(5 mol-%) was added under optimal conditions before the addition
of catalyst 1 or 2 (1.0 mol-%). After 5 h of reaction, the yield of
cross-coupled products obtained was 5–10%.
2
(
3
2
1
H
11Cl
2
2
Two-Phase Test: The freshly prepared 4-bromobenzoic acid immo-
H 2.62, N 3.31; found C 36.92, H 2.66, N 3.32, m.p. 270 °C.
[33]
bilized
(as amide) silica (0.20 g), phenylboronic acid (0.36 g,
CO
0.56 g, 4 mmol) were added to a DMF/water (8:4 mL) mixture or
1
H NMR (CD
.40 (m, 2 H, 8-H), 7.25–7.69 (m, 4 H, 2-H, 10-H–12-H) 8.00–8.05
m, 2 H, 3-H, 4-H), 8.79–8.81 (m, 1 H, 13-H), 9.19–9.21 (m, 1 H,
3
CN, 25 °C): δ = 3.43 (br m, 1 H, COOH), 4.61–
3
(
mmol), 4-bromoacetophenone (0.20 g, 1 mmol), and K
2
3
5
(
deionized water (10 mL for 1), and the mixture was heated at 90
or 110 °C for 12 h. Thereafter, it was cooled to room temperature
and filtered through a G-4 crucible. The residue (A) was washed
1
5
1
1
1
ν
1
ν
-H) ppm. 13C{ H} NMR (CDCl
, 25 °C, Me Si): δ = 50.0 (C-8),
3 4
25.0 (C-10), 130.3 (C-12), 132.0 (C-2), 132.3 (C-2), 132.5 (C-3),
33.4 (C-5), 133.5 (C-4), 138.1 (C-11), 140.9 (C-1), 151.6 (C-13),
63.3 (C-9), 167.1 (C-7, COOH) ppm. IR (KBr): ν˜ = 3449 [m,
O–H(carboxylic acid)], 3115 [m, νC–H(aromatic)], 2920 [m, νC–H(aromatic)],
689 (m, νC=N), 1606 (m, νC=O), 1465 [m, νC=C(aromatic)], 1271 [m,
2
with H O (20 mL) followed by diethyl ether (50 mL). The filtrate
and washings were collected and mixed with water (50 mL). The
resulting mixture was extracted with diethyl ether (50 mL). The sol-
vent of the extract was evaporated with a rotary evaporator, and
–1
C–N(aromatic)], 753 [m, νC–H(aromatic)] cm .
1
the residue was subjected to H NMR spectroscopy. The residue A
2
: Yield: 0.190 g, 70%. C26
H
16
N
2
O
2
PdS
2
(558.94): calcd. C 55.87,
was hydrolyzed with KOH (1.68 g dissolved in 10 mL of EtOH and
1
H 2.89, N 5.01; found C 55.59, H 2.96, N 5.09, m.p. 255 °C. H
NMR (CDCl , 25 °C, Me
Si): δ = 7.19–7.66 (m, 8 H, 5-H, 6-H, ized with aqueous 20% (v/v) HCl and extracted with dichlorometh-
0-H, 12-H), 7.96–8.01 (m, 4 H, 4-H, 11-H), 8.59–8.78 (m, 2 H, 4- ane followed by ethyl acetate. The solvent of the combined extracts
2
5 mL of H O) at 90 °C for 3 d. The resulting solution was neutral-
3
4
1
13
1
1
H), 9.16–9.18 (m, 2 H, 13-H) ppm. C{ H} NMR (CDCl
3
, 25 °C,
was evaporated, and the resulting residue was analyzed by H
Me
4
Si): δ = 120.0 (C-1), 121.2 (C-12), 122.1 (C-10), 124.6 (C-10), NMR spectroscopy.
1
1
33.2 (C-6), 135.5 (C-3), 138.7 (C-11), 142.1 (C-8), 151.5 (C-2),
53.0 (C-13), 159.8 (C-9) ppm. IR (KBr): ν˜ = 3114 [m, νC–H(aromatic)
Isolation of NPs Generated from 1 and 2 in Suzuki–Miyaura Cou-
pling: A mixture of Pd complexes 1 and 2 (0.5 mmol), phenylbor-
onic acid (1.2 mmol), 4-bromobenzaldehyde (1.0 mmol), and
2 3
K CO (1.5 mmol) in a DMF/water (4.0:1.0 mL) mixture or deion-
II
], 1690 (m, νC=N), 1467 [m, νC=C(aromatic)], 1289 [m, νC–N(aromatic)],
–1
7
54 [m, νC–H(aromatic)] cm .
Procedure for Aqueous Suzuki–Miyaura Coupling Reactions in ized water (5 mL) was heated at 90 or 110 °C for 2 h and then
Water: Aryl bromide (1 mmol), phenylboronic acid (1.2 mmol) or
,4-phenylenediboronic acid (0.6 mmol), K CO (1.5 or 2.0 mmol),
cooled to room temperature. The black NPs were obtained by de-
canting or centrifuging the reaction mixture. The NPs were washed
with a water/acetone mixture (1:3) and dried in vacuo. The NPs
were characterized by SEM-EDX and HRTEM.
1
2
3
TBAB (1 mmol), and Pd complex 1 (0.05–0.1 mol-%) were mixed
with deionized water (5 mL) in a 25 mL round-bottomed flask
equipped with a magnetic stirring bar and a reflux condenser. The
reaction mixture was heated with an oil bath maintained at 110 °C,
and the reaction was monitored by TLC until the maximum con-
version of aryl bromide to the product occurred. Thereafter, the
reaction mixture was cooled to room temperature and extracted
with diethyl ether (2ϫ 20 mL). The extract was dried with anhy-
Procedure for Suzuki–Miyaura Coupling Catalyzed with NPs Ob-
tained from 1 and 2: The coupling reactions of 4-bromobenz-
aldehyde, 4-bromobenzonitrile, 4-bromotoluene, and 4-bromoanis-
ole in the presence of the NPs (5–10 mg) obtained from 1 and 2
were performed under the optimized conditions for 1 and 2. All
1
13
1
products were authenticated by H and C{ H} NMR spec-
troscopy.
drous Na
rotary evaporator, and the residue was purified through a column
of silica gel with CHCl /hexane as eluent. All coupling products
2 4
SO . The solvent of the extract was evaporated with a
3
1
13
1
were authenticated by their H and C{ H} NMR spectra.
Acknowledgments
Procedure for Suzuki–Miyaura Coupling Reaction in DMF: An
oven-dried flask was charged with aryl bromide (1.0 mmol), phen-
ylboronic acid (1.2 mmol) or 1,4-phenylenediboronic acid
The authors thank Professor B. Jayaram for computational facili-
ties. The authors also thank the Department of Science and Tech-
nology (DST), New Delhi for funding through research project no.
SR/S1/IC-40/2010 and partial financial assistance (under the FIST
programme) for a single-crystal X-ray diffractometer and mass
spectral facilities at IIT Delhi. O. P. and H. J. thank the University
Grants Commission (UGC), New Delhi, and K. N. S. and A. K. S.
thank the Council of Scientific and Industrial Research (CSIR),
New Delhi for the award of Junior/Senior Research Fellowships.
(0.6 mmol), K
2 3 2
CO (1.5 or 2.0 mmol), DMF (4.0 mL), H O
(1.0 mL), and 2 (0.01–0.1 mol-%). The flask was fitted with a water
condenser and heated with an oil bath at 90 °C. The reaction mix-
ture was stirred, and the reaction was monitored by TLC until
maximum conversion of the aryl bromide to the coupled product
occurred. Thereafter, the mixture was extracted with diethyl ether
(
2ϫ 20 mL). The extract was washed with water and dried with
anhydrous Na SO . The solvent of the extract was evaporated with
a rotary evaporator, and the residue was purified through a column
of silica gel with CHCl /hexane as eluent. All coupling products
were authenticated by their H and C{ H} NMR spectra.
2
4
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Received: October 18, 2014
Published Online: December 18, 2014
Eur. J. Inorg. Chem. 2015, 520–526
526
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim