Suzuki coupling reactions catalyzed with palladacycles and palladium(II) complexes of 2-thiophenemethylamine-based schiff bases: Examples of divergent pathways for the same ligand

Article abstract of DOI:10.1002/ejic.201403176

Activation of Suzuki coupling with a complex of palladium varies with the mode of coordination of its ligand. The moisture-/air-insensitive palladacycles and palladium complexes designed using the same ligand (Schiff base, coordinating as an N,C^- and N,O^- ligand, respectively) have been found to follow different pathways. Palladacycles are more efficient, as their 0.001 mol-% loading gives good conversion (yield > 90 %) in several cases. Higher loading than this is required for Pd complexes to obtain a similar yield. Activation with palladacycles involves the role of nanosized Pd-containing species generated in situ during catalysis, in which, as with Pd^II complexes, no such particle is formed and Pd⁰ probably remains protected by the sulfur of the thienyl group. The Schiff bases used here were designed by the reaction of 2-thiophenemethylamine with 2-hydroxybenzophenone/2-hydroxy-4-methoxybenzophenone/2-hydroxyacetophenone (L1/L2/L3). Upon treatment with [PdCl₂(CH₃CN)₂] and [Na₂PdCl₄] they gave palladacycles [PdL1/L2(CH₃CN)Cl] (1/3) and palladium(II) complexes [Pd(L1/L2/L3)₂] (2/4/5), respectively. Compounds L1-L3 and their complexes 1-5 were authenticated with ¹H and ¹³C{¹H} NMR spectroscopy, and HRMS. Single crystal structures of 1, 2, 4, and 5 reveal nearly square-planar geometry around Pd in each case. The PPh₃/Hg poisoning and two-phase tests indicate that the catalysis is homogeneous for both the palladacycle and palladium complexes, probably through leaching of Pd⁰ from NPs in the case of the former. Catalysis of Suzuki coupling reactions with palladacycles (≥ 0.001 mol-%) and palladium complexes (≥ 0.01 mol-%) proceeds with and without nanoparticles.

Full text of DOI:10.1002/ejic.201403176

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DOI:10.1002/ejic.201403176
Suzuki Coupling Reactions Catalyzed with Palladacycles
and Palladium(II) Complexes of 2-Thiophenemethylamine-
Based Schiff Bases: Examples of Divergent Pathways for
the Same Ligand
[
a]
[a]
[a]
Hemant Joshi, Om Prakash, Alpesh K. Sharma,
[a]
[a]
Kamal Nayan Sharma, and Ajai K. Singh*
Keywords: Homogeneous catalysis / Nanotechnology / Palladium / Palladacycles / C–C coupling
Activation of Suzuki coupling with a complex of palladium
varies with the mode of coordination of its ligand. The moist-
ure-/air-insensitive palladacycles and palladium complexes
designed using the same ligand (Schiff base, coordinating as
an N,C and N,O ligand, respectively) have been found to
follow different pathways. Palladacycles are more efficient,
as their 0.001 mol-% loading gives good conversion (yield Ͼ
thiophenemethylamine with 2-hydroxybenzophenone/2-
hydroxy-4-methoxybenzophenone/2-hydroxyacetophenone
(L1/L2/L3). Upon treatment with [PdCl
[Na PdCl ] they gave palladacycles [PdL1/L2(CH
(1/3) and palladium(II) complexes [Pd(L1/L2/L3) ] (2/4/5),
respectively. Compounds L1–L3 and their complexes 1–5
2
(CH
3
CN)
2
]
and
2
4
3
CN)Cl]
–
–
2
1
13
1
were authenticated with H and C{ H} NMR spectroscopy,
and HRMS. Single crystal structures of 1, 2, 4, and 5 reveal
nearly square-planar geometry around Pd in each case. The
9
0%) in several cases. Higher loading than this is required
for Pd complexes to obtain a similar yield. Activation with
palladacycles involves the role of nanosized Pd-containing
species generated in situ during catalysis, in which, as with
3
PPh /Hg poisoning and two-phase tests indicate that the ca-
talysis is homogeneous for both the palladacycle and palla-
II
0
0
Pd complexes, no such particle is formed and Pd probably
remains protected by the sulfur of the thienyl group. The
Schiff bases used here were designed by the reaction of 2-
dium complexes, probably through leaching of Pd from NPs
in the case of the former.
Introduction
fied. In a very large number of cases, such coupling reac-
Palladium species constitute a class of versatile and use- tions are performed under an inert atmosphere because
ful catalysts for C–C bond-forming reactions.[ The facile many of the known good catalytic species are sensitive to
1,2]
[
11]
interchange between oxidation states and the tolerance of oxygen or moisture. Therefore Suzuki coupling reactions
palladium compounds toward many functional groups (ow- that give high yield under aerobic conditions continue to be
ing to mild reaction conditions) are mainly responsible for an important challenge. Another challenge is to rationalize
[
2]
their versatility. Of the various C–C bond-forming reac- variation in catalytic efficiency of various palladium moie-
[
3]
[12]
tions, Suzuki–Miyaura coupling (SMC) is very important
ties. Palladium(II) complexes of Schiff bases
have
as the biaryl derivatives prepared by this coupling have emerged as a family of phosphine-free, air- and moisture-
promising roles in the production of pharmaceutical ingre- insensitive efficient catalysts. Palladacycles and Pd com-
[4]
dients, agrochemicals, and natural products for industrial plexes of pincer ligands in the family of Suzuki catalysts are
II
purposes. Complexes of Pd with bulky and electron-rich generally considered to be species that show high perform-
[
5,6]
[7]
[8,9]
phosphines,
carbenes, palladacycles,
and organo- ance. However, a straight comparison of palladacycles with
[
10]
10b]
II
chalcogens, as well as palladium chacogenide/phosphide Pd complexes, when both are formed with the same li-
[
nanoparticles
are among the high-efficiency moieties for gand, is not known. Such comparison can easily be envis-
Suzuki–Miyaura coupling. Many of these species are also aged as being important to offer an in-depth understanding
attractive owing to the ease with which they can be modi- of the higher efficiency of palladacycles relative to Pd com-
plexes and in turn in identifying a rationalization for the
[
a] Department of Chemistry, Indian Institute of Technology difference in their performances. Herein we report that acti-
Delhi,
vation of SMC with a palladium(II) complex varies with
New Delhi 110016, India
E-mail: aksingh@chemistry.iitd.ac.in
the mode of coordination of its ligand. Palladacycles and
palladium complexes designed using a Schiff base (coordi-
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.201403176.
–
–
nating as an N,C and N,O ligand, respectively) have been
found to follow different pathways. In view of this, this pa-
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per focuses on the design of Schiff base ligands that contain tion with thienyl sulfur in the case of Pd complexes. All
a thiophene ring (L1–L3), as their synthesis and use in pre- these results are part of this paper.
paring a catalyst for Suzuki–Miyaura coupling reaction is
not known, and it is shown that thienyl can protect the
catalytically active species if required. Palladacycles and Results and Discussion
II
Pd complexes (1–5) of these ligands have been prepared
and explored for Suzuki–Miyaura coupling reactions. The
in situ formation of Pd-containing NPs has been reported
The preparations of ligands (L1, L2, and L3) and their
palladium(II) complexes (1–5) are summarized in Scheme 1.
The syntheses of complexes 1–4 require a palladium precur-
in Suzuki–Miyaura coupling reactions catalyzed with palla-
[
9b]
sor and are solvent-dependent. Reaction of L1 and L2 with
[Pd(CH CN) Cl ] in acetonitrile at 70 °C resulted in pallad-
dacycles
of the organosulfur ligand as well as Pd com-
[12c]
3
2
2
plexes of sulfated Schiff bases.
acycles 1 and 3, respectively, whereas treating L1–L3 with
Na PdCl in an acetone/water (1:1) mixture at room tem-
2
4
II
perature isolated Pd complexes 2, 4, and 5. In an acetone/
water mixture the reactions of [Pd(CH CN) Cl ] with li-
3
2
2
gands did not result in palladacycles, even at 70 °C. Simi-
larly, Na PdCl did not give a palladacycle upon reaction
2
4
with the ligands in CH CN, even at 70 °C. It is probable
3
–
that the [Pd{L = (N,O ) }] complex is first formed in the
2
reaction of both Pd precursors and it remains stable in an
acetone/water mixture, therefore it cannot be isolated. In
coordinating CH CN it becomes labile, thereby finally re-
and in their sulting in a palladacycle. The yellow solids 1, 2, 4, and 5
3
[9g]
These NPs are stabilized with additives,
[
7d]
absence by ligands or their fragments.
There is enough were found to be stable enough to store under ambient con-
0
evidence to suggest that Pd species leached from the sur- ditions for three months (as evidenced by their proton
face of such NPs are the true catalysts for SMC. The size, NMR spectra). The solubility of L1–L3 in common organic
dispersion, and the chemical nature of these NPs can be solvents – namely, DMF, DMSO, CH CN, CH Cl , CHCl ,
3
2
2
3
affected by the bonding mode of the ligand. Thus NPs and THF – was found to be good. Complexes 1 to 5 show
might be considered for a rationalization of their catalytic good solubility in DMF, DMSO, CH CN, CH Cl , and
3
2
2
II
performances. In the case of Pd complexes, the formation CHCl . They are sparingly soluble in CH OH, diethyl ether,
3
3
of Pd-based NPs was not noticed, whereas in the case of and THF, and negligibly soluble in hexane.
palladacycles it occurs instantaneously at the start of the The air-insensitive ligands L1–L3 and their Pd complexes
coupling reaction. The in situ formation of NPs appears to 1–5 were characterized with H and C{ H} NMR spec-
1
13
1
1
13
1
be a possible reason for the higher performance of pallada- troscopy and HRMS. The H and C{ H} NMR spectra
cycles relative to Pd complexes. It is probable that aggrega- of L1–L3 and complexes 1–5 (see Figures S19–S33 in the
0
tion of Pd to give NPs is prevented by additional protec- Supporting Information) were found to be consistent with
Scheme 1. Synthesis of ligands and their PdII complexes.
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their molecular structures (Scheme 1). In the 1H NMR Palladium adopts a nearly square-planar geometry in all of
spectra of L1, L2, and L3, the signals of the OH proton the complexes. Ligands L1 and L2 are coordinated with Pd
–
were observed at δ = 15.15, 15.88, and 15.64 ppm, respec- in a bidentate N,C mode, thus forming a five-membered
[
13]
tively. Upon formation of palladacycles 1 and 3, the sig- chelate ring in the case of palladacycle 1. Ligands L1 to L3
1
–
nal of the OH proton in the H NMR spectra is shielded are coordinated with Pd in a bidentate N,O mode in the
and appears at a position of approximately δ = 12.0– case of 2, 4, and 5. Each of the two ligands forms a six-
1
1
3.0 ppm. In the H NMR spectra of complexes 2, 4, and membered chelate ring with Pd. The Pd–N1 bond lengths
5
, the signal of the OH proton was found to be absent as the in 1, 2, 4, and 5 [2.023(4)–2.044(3) Å] are consistent with
13
1
II
deprotonated OH group is coordinated to Pd. The C{ H} the reported values [2.002(2)–2.010(4) Å] for Pd complexes
[
14]
NMR spectrum of complex 1 has a new quaternary carbon of tridentate selenated Schiff bases
but somewhat
signal at δ = 163.3 ppm, which shows the palladation of L1, longer than the value of 1.986(6) Å reported[14] for
whereas in the case of 2, 4, and 5, no such signal was ob- [PdCl{(C H )(C H –2-O–)C=N(CH ) SePh}]. The Pd–C
6
5
6
4
2 3
served. In the mass spectra of Schiff base ligands L1, L2,
and L3, the peaks that appear at 294.0947, 324.1053, and
2
32.0791, respectively, have been ascribed to the [M + H]+
ion (see Figures S3–S8). The mass spectra of complexes 1
and 3 show peaks at 690.0633 and 751.0924, which might
+
be ascribed to the [(L) Pd] fragment of the corresponding
2
complex (see Figures S9, S10, S13, and S14). This surpris-
ing species is most likely formed as the loss of two CH CN
3
ligands is followed by the capture of L. The mass spectra
of complexes 2 and 5 show peaks at 713.0531 and 589.0215,
+
which have been ascribed to the [M + Na] fragment (Na
comes from sodium formate; see the Experimental Section)
of the corresponding complex (see Figures S11, S12, S17,
and S18), whereas in the mass spectrum of complex 4 [M
+
+
H] , the fragment peak was noticed at 751.0924 (see Fig-
ures S15 and S16).
Figure 2. Molecular structure of 2. Bond lengths [Å]: N1–Pd1
.023(4), O1–Pd1 1.972(4). Bond angles [°]: C6–N1–Pd1 125.2(4),
C5–N1–Pd1 114.9(3), C8–O1–Pd1 123.1(3), O1–Pd1–O1 180.0(2),
O1–Pd1–N1 90.52(18).
2
Crystal Structure
The crystal and refinement data of complexes 1, 2, 4, and
5
are given in Table S1 of the Supporting Information, and
their molecular structures (ellipsoids at 30% probability
level) are shown in Figures 1, 2, 3, and 4 with selected bond
lengths and angles (more values are given in Tables S2–S5).
Our attempts to crystallize complex 3 were unsuccessful.
Figure 1. Molecular structure of 1. Bond lengths [Å]: C14–Pd1
1
.979(4), N1–Pd1 2.034(4), Cl1–Pd1 2.3257(13), N2–Pd1 2.127(5).
Figure 3. Molecular structure of 4. Bond lengths [Å]: N1–Pd1
2.028(3), N2–Pd1 2.022(3), O1–Pd1 1.980(3), O2–Pd1 1.979(3).
Bond angles [°]: C6–N1–Pd1 116.0(3), C19–N2–Pd1 175.7(5), C14–
Pd1–N1 80.89(16), C14–Pd1–N2 175.12(17), N1–Pd1–N2 Bond angles [°]: O2–Pd1–O1 178.40(13), O2–Pd1–N2 90.20(12),
4.28(16). C5–N1–Pd1 114.7(2), C25–N2–Pd1 125.8(3).
9
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The intermolecular O1–H23···Cl1 [2.342 Å] interactions
in 1, C14–H14···π [2.664 Å] interactions in 2, and C2–
H2···O1 [2.611 Å] interactions in 5 result in chain struc-
tures.
Applications in Suzuki–Miyaura Coupling Reactions
The stability of organoboronic acids and the formation
of nontoxic byproducts have increased the appeal of Su-
zuki–Miyaura coupling protocols with several industrial ap-
[
15]
plications. The activation of this reaction is not restricted
to a homogeneous protocol, but in recent years hetero-
[
16,17]
geneous catalytic systems
have been developed for it.
Complexes 1 to 5 were investigated for the Suzuki–Miyaura
coupling reaction. The results given in Tables 1 and 2 sug-
gest that complexes 1–5 are efficient for this coupling, as
Figure 4. Molecular structure of 4. Bond lengths [Å]: N1–Pd1 good yields were obtained even with deactivated substrates
2
.044(3), O1–Pd1 1.974(2). Bond angles [°]: C5–N1–Pd1 114.4(2),
such as 4-bromoanisole with low palladium loading. For
the reaction between 4-bromobenzaldehyde and phenylbor-
onic acid under aerobic conditions at 90 °C for 10 h (cata-
C8–O1–Pd1 123.9(2), O1–Pd1–O1 180.0, O1–Pd1–N1 89.43(11).
distance [1.979(4) Å] of 1 is consistent with the value of lyzed with 1), different bases and solvents were explored
[
9d]
1.971(16) Å
reported earlier for this kind of a palladi- (see Table S8 in the Supporting Information). The yield of
um(II)–(S,C,S) pincer complex bond. The Pd–Cl bond coupled product was found to be approximately 81% when
length of 1 [2.326(13) Å] is also consistent with the value EtOH was used as the reaction medium and K CO was
2
3
II
[
2.3159(7) Å] reported for the Pd complex of a tridentate used as base. However, the best results were obtained at
[14]
sulfated Schiff base.
The Pd–O1 bond lengths of 2, 4, 90 °C (bath temperature) with K CO and DMF (3 mL)/
2 3
and 5 [1.972(4)–1.980(3) Å] are consistent with the values H O (2 mL). At room temperature, the yield of biaryl was
2
II
of 1.993(3)–1.986(16) Å reported for Pd complexes of tri- found to be 43% with 0.5 mol-% loading of catalyst 1
dentate sulfated Schiff bases.[ In the crystals of 1, 2, 4, (Table S8). The catalytic efficiency of palladacycles 1 and 3
14]
II
and 5 there are secondary interactions (see Figures 5, 6, as is higher than those of Pd complexes 2, 4, and 5. The
well as Figures S1–S2). Tables S6 and S7 show interatomic ligands in all complexes are the same or similar. Thus the
distances. The head-to-tail arrangement of chelating N,O present results give a direct comparison of palladacycles
ligands observed in the case of complexes 2, 4, and 5 is with palladium(II) complexes, with minimized ligand fac-
worth mentioning.
tors, which indicates the superiority of the former on the
Figure 5. Intermolecular interactions in complex 1.
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Figure 6. Intermolecular interactions in complex 2.
basis of experimental results with palladacycle or palladi- Table 2. Suzuki–Miyaura coupling reaction catalyzed by using 2, 4,
and 5.[
a]
um(II) complexes alone, irrespective of the difference in li-
gands. Among palladacycles 1 and 3 the activity of 3 (in
which OMe group is present) is a bit higher.
Yield[b] [%]
Entry Aryl halide
Pd [mol-%]
2
4
5
1
2
3
4
5
6
7
8
9
1
1
1
1
1
4-bromobenzaldehyde
0.01
0.01
0.01
0.01
0.01
0.01
0.1
94
91
86
91
85
84
82
88
81
79
90
88
90
85
96
93
90
95
90
91
88
93
86
85
94
92
95
90
87
86
81
86
78
79
81
83
74
73
78
76
78
71
Table 1. Suzuki–Miyaura coupling reaction catalyzed by using 1
4-bromobenzonitrile
1-bromo-4-nitrobenzene
4-bromoacetophenone
2-bromobenzaldehyde
2-bromoacetophenone
4-bromobenzoic acid
bromobenzene
4-bromotoluene
4-bromoanisole
2-bromopyridine
3-bromopyridine
[
a]
and 3.
Entry Aryl halide
Pd [mol-%]
Yield[b] [%]
0.1
1
3
0.01
0.01
0.01
0.01
0.01
0.1
0
1
2
3
4
1
2
3
4
5
6
7
8
9
1
1
1
1
1
4-bromobenzaldehyde
4-bromobenzonitrile
1-bromo-4-nitrobenzene 0.001
4-bromoacetophenone
2-bromobenzaldehyde
2-bromoacetophenone
4-bromobenzoic acid
bromobenzene
4-bromotoluene
4-bromoanisole
2-bromopyridine
3-bromopyridine
4-bromopyridine
3-bromoquinoline
0.001
0.001
92
90
87
89
88
87
90
89
84
82
91
87
90
86
95
94
91
93
91
92
94
92
93
91
94
93
95
91
4-bromopyridine
3-bromoquinoline
0.001
0.01
0.01
0.1
0.01
0.001
0.001
0.001
0.001
0.001
0.01
[a] Reaction conditions: 1.0 equiv. of aryl halide, 1.5 equiv. of phen-
ylboronic acid, 2 equiv. of K CO , DMF (3 mL)/H O (2 mL) as
solvent, reaction time 10 h, and temperature of bath 90 °C. [b] Iso-
lated yield.
2
3
2
0
1
2
3
4
thienyl-group sulfur after cleavage of the Pd–O bond. It is
possible that 1 and 3 behave like a precatalyst and black
a] Reaction conditions: 1.0 equiv. of aryl halide, 1.5 equiv. of phen- particles formed at the beginning of the reaction are Pd-
[
2 3 2
ylboronic acid, 2 equiv. of K CO , DMF (3 mL)/H O (2 mL) as
containing species, which have a role in the catalytic pro-
cess. Easy formation of NPs in the case of palladacycles is
corroborated by their thermogravimetric analysis (TGA; see
solvent, reaction time 10 h, and temperature of bath 90 °C. [b] Iso-
lated yield.
The scope of the present activation of Suzuki–Miyaura Figures S36 and S37 in the Supporting Information), which
coupling can be understood from Tables 1 and 2. When the shows their decomposition before 90 °C, the temperature of
reaction between 4-bromobenzaldehyde and phenylboronic the coupling reaction. However, chelates 2, 4, and 5 show
acid was carried out with 0.001 mol-% of complex 4, the signs of decomposition in TGA around 200 °C. In high-
yield of the coupled product was found to be 63%. Thus temperature Suzuki coupling, the combined effect of tem-
–
0
N,O chelates are roughly 30% slower. In the course of Su- perature, base, and solvent system results in Pd forma-
[
18]
zuki reactions catalyzed with 1 and 3, the solution turned tion.
In the present case, the S of the thienyl group is
0
black immediately upon mixing the reactants, whereas in nearby, which probably weakly coordinates with Pd to
the case of 2, 4, and 5 no such blackening was observed. make it stable. The palladacycles decompose and therefore
Thus in the case of activation with 2, 4, and 5, homogen- any stabilization from the thienyl group is ruled out. The
0
eous catalysis is most likely. The Pd required for initiating variation observed in catalytic efficiency with the presence
Suzuki coupling is probably stabilized as a complex by the of an –OMe group might be due to some difference between
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the black species generated in situ during the course of acti-
vation with 1 and 3, respectively.
The black particles formed from 1 and 3 during the
course of catalysis of the coupling reaction of 4-bromo-
benzaldehyde with PhB(OH) under optimum reaction con-
2
ditions were isolated (see the Experimental Section) and an-
alyzed in detail to establish the possibility of a correlation
between the catalytic activity and nature of the black par-
ticles (which were envisaged to be true catalysts or playing
a role in the catalysis). The SEM-EDX (see Figures S34
and S35 in the Supporting Information) and HRTEM (Fig-
ure 7) images of these black particles suggest that they are
nanosized and spherical in shape. They contain Pd and S.
On the basis of EDX analysis, the Pd/S ratio is nearly 7:1
and 6:1 in terms of NPs with 1 and 3, respectively. They
are stable in solution as well as in the solid state. The size
of 90–95% of these NPs is between approximately 2 and
4
nm (see Figure 8). The marginal difference in the effi-
ciency of 1 and 3 might be ascribed to a larger population
of small-sized NPs generated from 3 relative to 1 and some
difference in their dispersion (more in case of 3). In the case
of 2 and 4, the –OMe group makes a difference of 5–6% in
the yield. This small difference need not be accounted for
in view of order of error (ca. 2%) in determining the yield.
Figure 8. Size-distribution curve of NPs isolated from complexes
(
a) 1 and (b) 3.
Figure 7. HRTEM micrographs of NPs (left) 1 and (right) 3 iso- tion mixture ensures the presence of a catalytic process and
lated from complexes 1 and 3 during Suzuki–Miyaura coupling.
its real active species.
The two-phase test carried out with an immobilized aryl
Mercury poisoning and PPh3 tests were found to be bromide and complex 1 is shown in Scheme 2. 4-Bromo-
negative. Therefore, to identify whether the reactions cata- acetophenone and immobilized 4-bromobenzoic acid (as
lyzed with 1 and 3 were heterogeneous or homogeneous, a amide) were treated with phenylboronic acid under opti-
[
19]
two-phase test was carried out with complex 1, as in the mum reaction conditions. The soluble part was separated
1
absence of clear-cut poisoning tests there is the possibility by filtration and analyzed with H NMR spectroscopy after
of involvement of surface Pd atoms of nanoparticles in oxi- workup. The yield of the cross-coupled product (4-acetylbi-
II
dative addition to form a soluble Pd intermediate Ar–Pd– phenyl) was found to be approximately 96%. The solid
Br and driving the catalysis homogeneously thereafter also phase was hydrolyzed, and the resulting products after
[
20]
1
exists. This test (called a three-phase test when the cata- workup were analyzed with H NMR spectroscopy. Of the
lyst is a solid phase), developed by Rebek and co- immobilized 4-bromobenzoic acid (as amide), approxi-
[
19]
workers,
is considered to be more definitive when de- mately 90% was converted into the cross-coupled product
termining the presence of metal species that are homoge- (biphenyl-4-carboxylic acid). This observation suggests that
neously catalytically active. The test involves covalent im- the catalytically active Pd atoms leach out from the NPs
mobilization of one of the reaction partners. 4-Bromo- generated in situ and are probably responsible for carrying
benzoic acid was immobilized on silica in the present case. out catalysis homogeneously. The leaching might happen
If the catalyst behaves in a heterogeneous fashion, the first and is followed by the oxidative addition required for
immobilized substrate is not expected to be converted to coupling. The surface Pd atoms of nanoparticles undergo
II
a coupled product. When Pd is released (i.e., catalysis is oxidative addition to form soluble Pd intermediate Ar–
homogeneous), the anchored substrate can be converted to Pd–Br, and the catalysis is driven thereafter (homoge-
product. The addition of a soluble aryl halide to the reac- neously).
Eur. J. Inorg. Chem. 0000, 0–0
6
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
Scheme 2. Two-phase test for Suzuki–Miyaura coupling.
The catalysis in the present case is thus a largely homo- Pd complexes 1 and 3 are pre-catalysts that generate real
geneous process and is probably combined with oxidative catalytic species in situ, which are NPs approximately 2–
0
0
addition to Pd at the surface of NPs (followed by leaching 4 nm in size that contained Pd protected by the ligand or
into solution). This is shown independently by the catalytic its fragments. The two-phase test carried out by using 1
activity of nanoparticles for Suzuki coupling (Table 3). The indicated the homogeneous nature of the catalytic process,
0
isolated NPs appear to be somewhat deactivated relative to which probably occurs through leaching of Pd from these
those generated in situ, as their amount needed (1.0 mol-% NPs. Palladacycles 1 and 3 are catalytically more active
of Pd) for comparable conversion is greater than those of than the four-coordinated complexes 2, 4, and 5. Thus acti-
complexes. Some Pd might also be leached into the reaction vation of Suzuki coupling with palladium complex varies
mixture before isolation. This could result in lowering of with the mode of coordination of the ligand. Palladacycles
the reactivity, which might be further reduced owing to and palladium complexes designed using the same ligand
–
–
some aggregation in the course of isolation. The isolated [L1 and L2 coordinating as N,C and N,O ligands, respec-
NPs are not recyclable. Thus 1 and 3 are most probably tively] were found to follow different pathways. Thus a di-
dispensers of NPs, which probably further generate homo- rect comparison of palladacycle with palladium(II) com-
0
geneous real Pd catalysts. The level of catalytic activity of plexes with minimized ligand factors has been presented for
3
for the coupling of aryl bromides as substrates is generally the first time, which indicates the superiority of the former
good. Such an observation is important in the context of on the basis of experiments carried out on palladacycle or
designing efficient catalysts for Suzuki coupling.
palladium(II) complexes alone without accounting for dif-
ferences in ligands.
Table 3. Suzuki–Miyaura coupling reactions catalyzed by isolated
[
a]
NPs.
Entry
Aryl halide
NP1[b]
NP3[b]
Experimental Section
1
2
4-bromobenzaldehyde
4-bromotoluene
84
72
91
81
Physical Measurements: 1H and 13C{ H} NMR spectra were re-
corded with a Bruker Spectrospin DPX 300 NMR spectrometer at
300.13 and 75.47 MHz, respectively. The chemical shifts are re-
ported in ppm relative to the internal standard (tetramethylsilane)
1
[
a] Reaction conditions: 1.0 equiv. of aryl halide, 1.5 equiv. of phen-
ylboronic acid, 1.0 mol-% of Pd NPs, 2 equiv. of K CO , DMF
3 mL)/H O (2 mL) as solvent, reaction time 10 h, and temperature
2
3
(
2
1
13
1
of bath 90 °C. [b] Isolated yield.
in the case of both H and C{ H} NMR spectra. All reactions
were carried out in glassware dried in an oven. The diffraction data
on single crystals of 1, 2, 4, and 5 were collected using Mo-K
(
α
0.71073 Å) radiation at 298(2) K. The SADABS[ software was
21]
Conclusion
used for absorption correction (if needed) and SHELXTL for the
space group, structure determination, and refinements.[ Trans-
mission electron microscopic studies were carried out with a JEOL
JEM 200CX TEM instrument operated at 200 kV. The specimens
22]
Schiff base ligands (L1 to L3) were synthesized by reac-
tion of 2-hydroxybenzophenone, 2-hydroxy-4-methoxy-
benzophenone, and 2-hydroxyacetophenone with 2-thio- for these studies were prepared by dispersing the powdered sample
phenemethylamine, respectively. Their complexes 1 and 3 in ethanol by means of ultrasonic treatment. A few drops of the
are formed by treating L1 and L2 with [PdCl (CH CN) ] resulting homogenized slurry were put on a porous carbon film
2
3
2
supported on a copper grid and dried in air. The elemental compo-
sition of NPs was studied with a Carl ZEISS EVO5O scanning
electron microscope and an associated QuanTax 200 EDX system,
which is based on SDD technology and provides an energy resolu-
in CH CN at 70 °C, whereas complexes 2, 4, and 5 resulted
3
after treating L1–L3 with Na PdCl in acetone/water (1:1)
2
4
at room temperature. Compounds L1–L3 and 1–5 were au-
1
13
1
thenticated by H and C{ H} NMR spectroscopy and
HRMS. The single-crystal structures of 1, 2, 4, and 5 were
solved. Thermally stable, moisture- and air-insensitive com-
plexes 1–5 were found to be efficient catalysts for Suzuki–
α
tion of 127 eV at Mn-K . The sample was mounted on a circular
metallic sample holder with a sticky carbon tape. High-resolution
mass spectral (HRMS) measurements were performed with electro-
spray ionization (10 eV, 180 °C source temperature) and using so-
Miyaura coupling reactions. It appears that Pd complexes dium formate as calibrant with a Bruker MIcroTOF-Q II and by
2
, 4, and 5 catalyze the coupling homogeneously, whereas samples dissolved in CH CN.
3
Eur. J. Inorg. Chem. 0000, 0–0
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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/KAP1
Date: 16-02-15 12:10:58
Pages: 11
www.eurjic.org
FULL PAPER
CCDC-1015573 (for 1), -1015574 (for 2), -1015575 (for 4), and pound was filtered, washed with diethyl ether (10 mL), and dried
-
1015576 (for 5) contain the supplementary crystallographic data
under vacuum to give 1 and 3 as a yellow solid. Single crystals of
1 were grown by slow evaporation of its solution in acetonitrile and
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ methanol (3:1).
data_request/cif.
1
3
Compound 1: Yield: 0.078 g, 82%; m.p. 176 °C. H NMR (CDCl ,
5
3
Chemical and Reagents: 2-Hydroxybenzophenone, 2,4-dihydroxy- 25 °C, TMS): δ = 2.01 (s, 3 H, CH CN), 4.30 (s, 2 H, H ), 6.77–
1
1
2
3
9
benzophenone, 2-hydroxyacetophenone, 2-thiophenemethylamine,
palladium(II) chloride, sodium tetrachloropalladate, and methyl
iodide were procured from Sigma–Aldrich (USA) and used as re-
ceived. 2-Hydroxy-4-methoxybenzophenone was prepared by a pre-
6.91 (m, 1 H, H ), 7.42–7.44 (m, 3 H, H , H , H ), 7.49–7.55 (m,
4 H, H , H , H , H ), 7.61–7.68 (m, 3 H, H , H , H ), 12.05
1
10
12
17
15
16
18
1
3
1
(s, 1 H, OH) ppm. C{ H} NMR (CDCl
(CH of CH CN), 43.5, 116.8, 120.7, 125.4, 126.7, 127.5, 128.4,
129.9, 130.8, 131.1, 132.3, 132.5, 133.6, 136.4, 139.2, 147.8, 163.3,
3
, 25 °C, TMS): δ = 15.4
3
3
[13]
viously reported procedure. The solvents were dried and distilled
before use by means of standard procedures.[ The common rea-
gents and chemicals available commercially and domestically were
used.
23]
+
170.6 ppm. HRMS (CH
3
CN) [(L1)
690.0633; found 690.0628 (Δ = 5.1 ppm).
OPdS (475.28): calcd. C 50.54, H 3.61, N 5.89; found
C 50.48, H 3.56, N 6.03.
2
Pd] : m/z calcd. for
3
6
+
[C H28
2 2 2
N O PdS ]
C
20
H
17ClN
2
Synthesis of L1, L2, and L3: 2-Thiophenemethylamine (0.565 g,
1
5.0 mmol) was stirred in dry ethanol (20 mL) at room temperature
Compound 3: Yield: 0.081 g, 81%; m.p. 145 °C. H NMR (CDCl
3
,
for 0.5 h. 2-Hydroxybenzophenone (0.991 g, 5.0 mmol) or 2-
hydroxy-4-methoxybenzophenone (1.14 g, 5.0 mmol) or 2-hydroxy-
acetophenone (0.681 g, 5.0 mmol) dissolved in dry ethanol (20 mL)
was added dropwise with stirring. The mixture was stirred further
at room temperature for 5 h. The solvent was evaporated with a
rotary evaporator to result in L1 and L3 as yellow solid and L2 as
yellow oil, respectively.
25 °C, TMS): δ = 2.17 (s, 3 H, CH CN), 3.96 (s, 3 H, OMe), 4.95
(s, 2 H, H ), 6.56–6.68 (m, 2 H, H , H ), 6.88–6.98 (m, 3 H, H ,
3
2
5
11
1
3
9
12
17
15
H , H ), 7.14 (s, 2 H, H , H ), 7.56 (s, 1 H, H ), 7.76 (s, 2 H,
1
6
18
+
H , H ), 12.68 (s, 1 H, OH) ppm. HRMS (CH
3
CN) [(L2)
751.0924; found 751.0904 (Δ =
PdS (505.31): calcd. C 49.91, H 3.79, N
5.54; found C 49.83, H 3.21, N 5.46.
2
Pd] :
+
m/z calcd. for [C38
33 2 4 2
H N O PdS ]
4.2 ppm). C21 19ClN O
H
2 2
Ligand L1: Yield: 1.319 g, 90%; m.p. 97 °C. 1H NMR (CDCl
3
,
2
4
Synthesis of 2, 4, and 5: Na PdCl (0.029 g, 0.1 mmol) was dis-
5
3
2
5 °C, TMS): δ = 4.68 (s, 2 H, H ), 6.67 (t, JH,H = 7.5 Hz, 1 H,
solved in water (5.0 mL). A solution of ligand L1 (0.058 g,
0.2 mmol)/L2 (0.065 g, 0.2 mmol)/L3 (0.046 g, 0.2 mmol) in acet-
one (10 mL) was added with vigorous stirring. The mixture was
11
12
3
3
H ), 6.81–6.88 (m, 2 H, H , H ), 6.95 (t, JH,H = 4.8 Hz, 1 H,
H ), 7.05 (d, JH,H = 8.4 Hz, 1 H, H ), 7.20–7.32 (m, 4 H, H , H ,
2
3
9
1
10
15
14
16
H ), 7.52–7.55 (m, 3 H, H , H ), 15.15 (s, 1 H, OH) ppm. further stirred for 2 h. The orange-red reaction mixture was ex-
1
3
1
5
11
C{ H} NMR (CDCl
3
, 25 °C, TMS): δ = 50.7 (C ), 117.6 (C ),
tracted with chloroform (25 mL). The chloroform layer was washed
17.8 (C ), 119.8 (C ), 124.4 (C ), 124.5 (C ), 126.8 (C ), 127.2 with water (100 mL), dried with anhydrous Na SO , and the sol-
C ), 128.8 (C ), 129.2 (C ), 131.8 (C ), 132.6 (C ), 133.7 (C ), vents evaporated to dryness with rotary evaporator to obtain 2, 4,
9
7
2
3
1
1
(
2
4
15
14
16
12
10
13
4
8
6
1
41.9 (C ), 162.6 (C ), 174.8 (C ) ppm. HRMS (CH
3
CN) [M +
16NOS] 294.0947; found 294.0956 (Δ =
15NOS (293.38): calcd. C 73.69, H 5.15, N 4.77;
found C 73.59, H 5.06, N 4.84.
and 5 as an orange powder. Their single crystals were grown from
a mixture of CHCl /hexane (8:2).
+
+
H] : m/z calcd. for [C18
3.1 ppm). C18
H
3
–
H
1
3
Compound 2: Yield: 0.058 g, 85%; m.p. 211 °C. H NMR (CDCl ,
5 °C, TMS): δ = 5.08 (s, 4 H, H ), 6.35 (t, JH,H = 8.1 Hz, 2 H,
5
3
2
1
11
3
12
2
3
Ligand L2: Yield: 1.487 g, 92%. H NMR (CDCl , 25 °C, TMS): δ H ), 6.59 (d, JH,H = 8.4 Hz, 2 H, H ), 6.82–6.90 (m, 6 H, H ,
5
3
3
9
3
1
10
=
3.81 (s, 3 H, OMe), 4.65 (s, 2 H, H ), 6.71 (d, JH,H = 9.0 Hz, 1 H , H ), 7.10 (t, JH,H = 7.7 Hz, 2 H, H ), 7.18–7.22 (m, 6 H, H ,
11
9
3
12
3
15
14
16
13
1
3
H, H ), 6.89 (s, 1 H, H ), 6.94 (t, JH,H = 4.8 Hz, 2 H, H , H ), H ), 7.46–7.50 (m, 6 H, H , H ) ppm. C{ H} NMR (CDCl ,
.21–7.27 (m, 4 H, H , H , H ), 7.53–7.58 (m, 3 H, H , H ),
5.88 (s, 1 H, OH) ppm. C{ H} NMR (CDCl
1
2
15
14
16
5
11
12
1
7
1
=
(
25 °C, TMS): δ = 50.0 (C ), 114.8 (C ), 121.1 (C ), 125.0 (C ),
125.4 (C ), 125.9 (C ), 126.3 (C ), 128.0 (C ), 128.6 (C ), 129.1
(C ), 133.5 (C ), 134.5 (C ), 136.5 (C ), 141.5 (C ), 165.9 (C ),
13
1
7
3
2
15
16
3
, 25 °C, TMS): δ
5
11
9
7
14
10
9
13
4
8
49.4 (OMe), 55.2 (C ), 101.6 (C ), 105.8 (C ), 113.3 (C ), 124.5
2
3
1
15
14
16
6
+
C ), 124.6 (C ), 126.8 (C ), 127.4 (C ), 128.8 (C ), 129.3 (C ),
170.5 (C ) ppm. HRMS (CH
3
CN) [M + Na] : m/z calcd. for
713.0531; found 713.0521 (Δ = 3.7 ppm).
(691.15): calcd. C 62.56, H 4.08, N 4.05; found
C 62.57, H 3.95, N 4.07.
13
12
4
8
10
36
+
1
29.7 (C ), 133.0 (C ), 141.9 (C ), 163.7 (C ), 166.9 (C ), 174.0 [C H28
N
2
NaO
2 2
PdS ]
6
+
(C ) ppm. HRMS (CH
3
CN) [M
+
H] : m/z calcd. for
C
36
H
28
N
2
O
2
PdS
2
[C
19
H
18NO
2
S]+ 324.1053; found 324.1056 (Δ = –0.9 ppm).
1
1
Ligand L3: Yield: 1.041 g, 90%; m.p. 82 °C. H NMR (CDCl
3
,
3
Compound 4: Yield: 0.061 g, 81%; m.p. 206 °C. H NMR (CDCl ,
13
5
3
5
2
=
2
5 °C, TMS): δ = 2.42 (s, 3 H, H ), 4.95 (s, 2 H, H ), 6.81 (t, JH,H
7.8 Hz, 1 H, H ),6.94–6.99 (m, 3 H, H , H , H ), 7.23–7.33 (m,
H, H , H ), 7.55 (d, JH,H = 7.8 Hz, 1 H, H ), 15.64 (s, 1 H,
3 3
OH) ppm. C{ H} NMR (CDCl , 25 °C, TMS): δ = 14.8 (C ), H , H ) ppm. C{ H} NMR (CDCl , 25 °C, TMS): δ = 49.6
8.7 (C ), 117.5 (C ), 118.5 (C ), 119.6 (C ), 124.5 (C ), 124.7 (C ), (OMe), 55.1 (C ), 102.2 (C ), 105.1 (C ), 119.1 (C ), 124.6 (C ),
26.9 (C ), 128.1 (C ), 132.5 (C ), 141.7 (C ), 162.9 (C ), 172.1 125.5 (C ), 126.3 (C ), 127.9 (C ), 128.4 (C ), 128.8 (C ), 135.7
CN) [M + H] : m/z calcd. for [C13
NOS] 232.0791; found 232.0794 (Δ = –1.6 ppm). C13 13NOS
231.31): calcd. C 67.50, H 5.66, N 6.06; found C 67.44, H 5.61, N
.09.
25 °C, TMS): δ = 3.68 (s, 6 H, OMe), 4.97 (s, 4 H, H ), 5.94 (d,
JH,H = 9.3 Hz, 2 H, H ), 6.22 (s, 2 H, H ), 6.45 (d, 2 H, H ),
6.87 (s, 4 H, H , H ), 7.15–7.17 (m, 4 H, H , H ), 7.45 (s, 4 H,
3
2
9
11
3
11
12
2
1
10
3
12
3
9
1
15
13
1
13
14
16
13
1
5
11
9
7
2
3
5
11
9
7
2
4
1
(
1
12
10
4
8
3
1
15
14
16
6
+
13
12
4
8
10
6
C ) ppm. HRMS (CH
3
H
14
-
(C ), 136.7 (C ), 142.3 (C ), 164.0 (C ), 167.8 (C ), 169.7 (C )
+
+
H
ppm. HRMS (CH
3
CN) [M
751.0924; found 751.0930 (Δ = –2.4 ppm).
(751.20): calcd. C 60.76, H 4.29, N 3.73; found
C 60.80, H 4.27, N 3.64.
+
H] : m/z calcd. for
+
(
6
[C38
H
33
N
2
O
4
PdS
PdS
2
]
C
38
H
32
N
2
O
4
2
Synthesis of 1 and 3: [PdCl
added to a stirred solution of L1(0.058 g, 0.2 mmol)/L2(0.065 g,
.2 mmol) in CH CN (5 mL) at 70 °C. The reaction mixture was 25 °C, TMS): δ = 2.49 (s, 3 H, H ), 5.29 (s, 2 H, H ), 6.57 (t, JH,H
2 3 2
(CH CN) ] (0.516 g, 0.2 mmol) was
1
3
Compound 5: Yield: 0.047 g, 83%; m.p. 208 °C. H NMR (CDCl ,
1
3
5
3
0
3
3
3
2
3
stirred for 5 h, concentrated with a rotary evaporator up to 2 mL,
and mixed with diethyl ether (15 mL). The resulting orange com-
= 7.2 Hz, 1 H, H ), 6.73 (d, JH,H = 7.2 Hz, 1 H, H ), 6.95 (t, JH,H
9
1
11
3
= 4.8 Hz, 1 H, H ), 7.04–7.13 (m, 2 H, H , H ), 7.22 (d, JH,H
=
Eur. J. Inorg. Chem. 0000, 0–0
8 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I43176
/KAP1
Date: 16-02-15 12:10:58
Pages: 11
www.eurjic.org
FULL PAPER
1
0
3
12
13
1
5
.1 Hz, 1 H, H ), 7.36 (d, JH,H = 8.1 Hz, 1 H, H ) ppm. C{ H}
Procedure for Suzuki–Miyaura Coupling Catalyzed by NPs Ob-
tained from 1 and 3: The coupling reactions of 4-bromobenz-
13
5
9
NMR (CDCl
1
(
(
5
(
5
3
, 25 °C, TMS): δ = 19.4 (C ), 49.7 (C ), 115.3 (C ),
11
1
3
2
7
21.4 (C ), 124.8 (C ), 125.6 (C ), 126.6 (C ), 127.3 (C ), 130.2 aldehyde, 4-bromotoluene, and 4-bromoanisole in the presence of
12
10
4
8
6
C ), 132.9 (C ), 140.6 (C ), 165.5 (C ),169.3 (C ) ppm. HRMS
NPs obtained from 1/3 (Pd: 1.0 mol-%) were carried out under con-
ditions optimized for complexes 1/3. All products were authenti-
+
+
CH
89.0215; found 589.0202 (Δ
567.01): calcd. C 55.07, H 4.27, N 4.94; found C 54.94, H 4.13, N
.02.
3
CN) [M + Na] : m/z calcd. for [C26
H
24
N
2
NaO
2
PdS
PdS
2
]
1
13
1
=
3.0 ppm).
C
26
H
24
N
2
O
2
2
cated by means of H and C{ H} NMR spectra.
Acknowledgments
General Procedure for Suzuki–Miyaura Coupling Reaction of Aryl
Halides with Phenylboronic Acid: An oven-dried flask was charged
with aryl bromide (1.0 mmol), phenylboronic acid (1.5 mmol),
A. K. S. thanks the Council of Scientific and Industrial Research
(
CSIR) India [project number 01(2784)14/EMR-II] and the De-
K
2
CO
3 2
(2.0 mmol), DMF (3.0 mL), H O (2.0 mL), and a solution
–4
–5
partment of Science and Technology (DST), New Delhi [project
number SR/S1/IC-40/2010] for financial support. The authors
would like to thank SAIF, AIIMS New Delhi for providing its
HRTEM facility. H. J. and O. P. thank the University Grants Com-
mission (UGC), New Delhi for Senior Research Fellowships.
K. N. S. and A. S. thank the CSIR for Senior Research Fellowships.
of catalyst 1–5 in DMF (100 μL of 10 m ϵ 10 mmol or
–3
–3
–4
–2
1
0 mol-%; 100 μL of 10 m ϵ 10 mmol or 10 mol-%; 1000 μL
of 10 m ϵ 10 mmol or 10–1 mol-%) was then added with a sy-
–3
–3
ringe. The flask was fitted with a water condenser and placed on
an oil bath maintained at 90 °C. The reaction mixture was stirred
and the reaction monitored with TLC until the conversion of aryl
halide to product reached its maximum. Thereafter the mixture was
extracted with diethyl ether (2ϫ20 mL). The extract was washed
[
1] a) Metal-Catalyzed Cross-Coupling Reactions (Eds.: A. de Mei-
jere, F. Diederich), Wiley-VCH, Weinheim, Germany, 2004; b)
Metal-Catalyzed Cross-Coupling Reactions (Eds.: F. Diederich,
P. J. Stang), Wiley-VCH, Weinheim, Germany, 1998; c) Hand-
book of Organopalladium Chemistry for Organic Synthesis
(Eds.: E. Negishi, A. de Meijere), Wiley-Interscience, New
York, 2002, p. 1669.
with water (50 mL) and dried with anhydrous Na
of the extract was evaporated with a rotary evaporator, and the
residue was purified with a column of silica gel using CHCl (5%)/
hexane as an eluent. All coupling products were authenticated by
2 4
SO . The solvent
3
1
13
1
means of their H and C{ H} NMR spectra.
Hg Poisoning Test: An excess amount of Hg (Hg/Pd 400:1) was
added to a reaction flask before the addition of reactants. There-
after the coupling reaction of 4-bromobenzaldehyde (1.0 mmol)
with phenylboronic acid (1.2 mmol) using 1 or 2 (0.1 mol-%) as a
catalyst was carried out in the flask under optimum conditions. A
conversion of 94% was observed after 10 h of reaction.
[2] J. Dupont, C. S. Consorti, J. Spencer, Chem. Rev. 2005, 105,
2527.
[3] a) N. Miyaura, A. Suzuki, in: Advances in Metal-Organic
Chemistry (Ed.: L. S. Liebeskind), JAI, London, 1998, vol. 6,
p. 187; b) S. Kotha, K. Lahiri, D. Kashinath, Tetrahedron 2002,
5
8, 9633.
[
[
[
4] a) T. J. Colacot, Platinum Met. Rev. 2011, 55, 84; b) A. Suzuki,
Angew. Chem. Int. Ed. 2011, 50, 6722; Angew. Chem. 2011, 123,
6854; c) A. Suzuki, Y. Yamamoto, Chem. Lett. 2011, 40, 894;
d) A. Suzuki, J. Organomet. Chem. 1999, 576, 147; e) A. V.
Gaikwad, A. Holuigue, M. B. Thathagar, J. E. T. Elshof, G.
Rothenberg, Chem. Eur. J. 2007, 13, 6908.
3 3
PPh Poisoning Test: PPh (0.5 mol-%) was added under optimum
conditions to the coupling reaction of 4-bromobenzaldehyde with
phenylboronic acid before addition of catalyst 1 (0.1 mol-%). After
10 h of reaction cross-coupled products were obtained in 95%
yield.
5] a) J. P. Wolfe, S. L. Buchwald, Angew. Chem. Int. Ed. 1999, 38,
Two-Phase Test: 4-Bromobenzoic acid immobilized (as amide) sil-
ica (0.20 g) was prepared by following a standard procedure[ (de-
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2
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(
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Eur. J. Inorg. Chem. 0000, 0–0
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Received: December 10, 2014
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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/KAP1
Date: 16-02-15 12:10:58
Pages: 11
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FULL PAPER
Pd-Catalyzed Coupling Reactions
H. Joshi, O. Prakash, A. K. Sharma,
K. N. Sharma, A. K. Singh* ............ 1–11
Suzuki Coupling Reactions Catalyzed with
Palladacycles and Palladium(II) Com-
plexes of 2-Thiophenemethylamine-Based
Schiff Bases: Examples of Divergent Path-
ways for the Same Ligand
Keywords: Homogeneous catalysis / Nano-
technology / Palladium / Palladacycles / C–
C coupling
Catalysis of Suzuki coupling reactions
palladium complexes (Ն0.01 mol-%) pro-
with palladacycles (Ն0.001 mol-%) and
ceeds with and without nanoparticles.
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim