Formation of organopalladium complexes via C-Br and C-C bond activation. Application in C-C and C-N coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2013.03.006

Reaction of [Pd₂(dba)₃] (dba = dibenzylideneacetone) with two Schiff base ligands (L¹ and L²), derived from the condensation of 8-aminoquinoline with 2-bromobenzaldehyde or 2-bromoacetophenone, in refluxing tert-butanol afforded two organopalladium complexes 1 and 2. Crystal structure of complex 1 has been determined by X-ray diffraction studies. Structure of complex 2 has been optimized by DFT method. In both the complexes the imine ligands are coordinated, via C-Br bond activation, as tridentate CNN-donor and the fourth coordination position is occupied by an acetylide ion provided by an outgoing dba ligand via C-C bond cleavage. Both the complexes display intense absorptions in the visible and ultraviolet regions. Both the complexes catalyze C-C and C-N coupling reactions efficiently.

Full text of DOI:10.1016/j.jorganchem.2013.03.006

Journal of Organometallic Chemistry 736 (2013) 1e8
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Formation of organopalladium complexes via CeBr and CeC bond activation.
Application in CeC and CeN coupling reactions
*
Paramita Majumder, Piyali Paul, Poulami Sengupta, Samaresh Bhattacharya
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Reaction of [Pd2(dba)3] (dba ¼ dibenzylideneacetone) with two Schiff base ligands (L1 and L2), derived
from the condensation of 8-aminoquinoline with 2-bromobenzaldehyde or 2-bromoacetophenone, in
refluxing tert-butanol afforded two organopalladium complexes 1 and 2. Crystal structure of complex
1 has been determined by X-ray diffraction studies. Structure of complex 2 has been optimized by DFT
method. In both the complexes the imine ligands are coordinated, via CeBr bond activation, as
tridentate CNN-donor and the fourth coordination position is occupied by an acetylide ion provided by
an outgoing dba ligand via CeC bond cleavage. Both the complexes display intense absorptions in the
visible and ultraviolet regions. Both the complexes catalyze CeC and CeN coupling reactions
efficiently.
Article history:
Received 16 January 2013
Received in revised form
23 February 2013
Accepted 5 March 2013
Keywords:
CeBr bond activation
CeC bond cleavage
Organopalladium complex formation
CeC coupling reaction
CeN coupling reaction
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
by oxidative insertion of palladium(0) into the CeX (X ¼ halogen
atom) bond of an aryl halide, as a stable palladium(II) complex.
Palladium catalyzed carbonecarbon and carboneheteroatom
bond forming reactions have emerged as some of the most
powerful methods in synthetic organic chemistry [1e5], and we
have also started exploring this area recently [6e10]. According to
the proposed mechanisms of these cross-coupling reactions, all
such reactions are initiated by the oxidative insertion of palla-
dium(0) into a carbonehalogen bond of the aryl halide, used as
substrate, forming a palladium(II) intermediate. This key step is
followed by the coupling of reactants, reductive elimination of the
newly formed coupled product and regeneration of the palla-
dium(0) center. For these cross-coupling reactions to occur, ligands
with soft donor sites are often required in order to stabilize the
palladium(0) state, and also to satisfy the vacant coordination sites
of the palladium(II) intermediate. Bulky arylphosphines are
particularly popular as soft ligands for these reactions. Encouraged
by these very well-known reaction mechanisms, we thought of
designing a reaction whereby we could isolate the product, formed
Hence, we thought of a modified bromobenzene ligand with two
appropriately located soft donor atoms. In order to achieve our
target product, two Schiff base ligands, L1 and L2, were prepared by
the condensation of 8-aminoquinoline with 2-bromobenzaldehyde
or 2-bromoacetophenone. Both the ligands contain an aryl bromide
fragment along with two soft nitrogen donor centers, viz. the
imineenitrogen and the pyridineenitrogen. It was anticipated that
if a palladium(0) center activates the CeBr bond in these imine
ligands to form palladium(II) species (I), where the metal center
would be coordinated to an aryl-carbon, a bromide and also it
would simultaneously get coordinated by the two proximal
nitrogen donors, and thus the resulting organopalladium complex
should be stable and isolable. Herein, as the source of palladium(0),
we chose tris(dibenzylideneacetone)dipalladium(0), [Pd2(dba)3],
primarily because the
p-bonded dba ligands in it seemed to be
easily replaceable by the chelating ligands (such as L1 and L2).
Reactions of the selected Schiff base ligands (L1 and L2) with
[Pd2(dba)3] has indeed been found to afford two interesting orga-
nopalladium complexes, but of slightly different nature than I. The
chemistry of these two complexes is reported here, with special
reference to their formation, characterization and, catalytic appli-
cation in CeC and CeN coupling reactions.
* Corresponding author. Tel./fax: þ91 33 24146223.
E-mail address: samaresh_b@hotmail.com (S. Bhattacharya).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.006

2
P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
Table 1
ꢀ
ꢀ
Selected bond lengths (A) and bond angels ( ) for complex 1.
Br
ꢀ
Bond lengths (A)
Pd(1)eC(1)
Pd(1)eN(1)
Pd(1)eN(2)
Br
1.959(12)
1.988(9)
2.113(9)
2.017(13)
C(7)eN(1)
C(8)eN(1)
C(17)eC(18)
1.279(16)
1.390(15)
1.099(17)
Pd
N
R
N
R
N
Pd(1)eC(17)
N
Bond angles (ꢀ)
C(1)ePd(1)eN(1)
N(1)ePd(1)eN(2)
81.9(4)
79.8(4)
C(1)ePd(1)eN(2)
N(1)ePd(1)eC(17)
Pd(1)eC(17)eC(18)
161.6(4)
176.5(4)
178.7(11)
1
I
R = H for L
R = CH3 for L
2
been possible, as single crystals of this complex could not be
grown. However, its structure has been geometrically optimized
through DFT calculations [13], and the optimized structure
(Fig. S1 and Table S1, Supplementary material) is found to be very
similar to the crystal structure of complex 1. Mass spectral,
microanalytical, 1H NMR and IR data of complexes 1 and 2 are
also consistent with their compositions.
Formation of complexes 1 and 2 containing the acetylide
fragment, from rather simple reactions, has been quite intriguing.
However, it is apparent that this acetylide fragment has resulted
unexpectedly from CeC bond activation of the dibenzylidenea-
cetone attached to the palladium center in the metal precursor.
Such CeC bond activation providing an acetylide fragment is, to
our knowledge, unprecedented. Though the exact mechanism of
formation of complexes 1 and 2 is not clear to us, some specu-
lated sequences, that seem probable, and also adequately sup-
ported by mass spectrometry (vide infra) [14], are illustrated in
Scheme 1. Initially the two nitrogen donor sites of the imine
ligand seem to coordinate the palladium center forming an in-
termediate A, whereby a bonding interaction is set between the
palladium(0) center and the proximal CeBr bond. This is followed
by activation of the CeBr bond and coordination of the anionic
carbon center to the oxidized palladium generating another in-
termediate B. Owing to the increased oxidation state of palla-
2. Results and discussion
2.1. Synthesis and characterization
Reactions of L1 and L2 with [Pd2(dba)3] have been carried out
in refluxing tert-butanol, which have afforded complexes 1 and 2,
respectively, in decent yields. 1H NMR spectra of both the com-
plexes indicate that the imine ligands are probably coordinated to
the metal center in the expected CNN-mode as in I, however, the
ligand coordinated to the metal center in the fourth position
could not be confirmed. To authenticate composition of the
complexes, as well as binding mode of the imine ligand in them,
structure of complex 1 has been determined by X-ray crystal-
lography. The structure is shown in Fig. 1 and some relevant bond
parameters are listed in Table 1. The structure shows that the
imine ligand (L1) is indeed bound to palladium in the expected
CNN-fashion (as in I) forming two adjacent five membered rings
with CePdeN and NePdeN bite angles of 81.9(4)ꢀ and 79.8(4)ꢀ
respectively, and the remaining coordination site is interestingly
occupied by an acetylide fragment. Thus palladium is nested
in
a C2N2 coordination environment, which is significantly
distorted from ideal square planar geometry. The observed PdeC
and PdeN bond distances are all quite normal [11,12]. Structural
characterization of complex 2 by X-ray crystallography has not
dium in B the
p-cloud on the coordinated dibenzylideneacetone
gets attracted more strongly toward the metal center and, as a
consequence, the terminal benzene ring of dibenzylideneacetone,
that is closer to the metal center, becomes more electrophilic and
undergoes an intra-molecular attack by the bromide. This leads
to elimination of bromobenzene and formation of a
s bond be-
tween the palladium center and the sp2-hybridized terminal
carbon of the remaining fragment of dibenzylideneacetone,
generating a third intermediate C. This intermediate C is believed
to undergo a rearrangement, as a result of which an acetylide
fragment originates, which remains coordinated to the metal
center to yield the final product, and cinnamaldehyde is released
as a byproduct.
To have an insight into the formation of these interesting
organopalladium complexes via CeBr and unique CeC bond
cleavage reactions, attempts have been made to identify the
possible intermediates by mass spectrometry [14]. The mass
spectrum, recorded after the reaction has proceeded for 2 h, shows
a weaker peak at m/z ¼ 675 corresponding to intermediate A (for
[A þ Naþ]) and a much stronger peak at m/z ¼ 491 for C. The
observed peak for C actually depicts the mass of [(C-4H) þ Hþ]
species. This is because four protons attached with the two alkene
groups in C get lost under the mass spectral condition [15,16].
Detection of cinnamaldehyde (vide infra) confirms that this loss of
protons is not permanent. No peak corresponding to intermediate B
could be identified, indicating its transient existence. Also forma-
tion of complex 1 is observed by this time. But as the reaction
proceeds further the peak for C vanishes completely and only the
Fig. 1. Molecular structure of complex 1.

P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
3
H
O
Br
Br
H
[Pd (dba) ]
2
3
Pd
N
R
N
R
N
N
(A)
O
H
H
O
Br
H
H
Pd
N
Pd
N
C
R
Br
R
N
N
+
(C)
(B)
H
C
C
H
O
Pd
N
C
+
R
N
Scheme 1. Probable steps behind formation of complexes 1 and 2.
peak for complex 1 is observed. So it appears that lifetime of
intermediate is the longest among the three proposed
and ultraviolet regions. The absorptions in the ultraviolet region
are attributable to transitions within the ligand orbitals. To
understand the origin of the absorptions in the visible region,
electronic structure of both the complexes has been probed with
the help of DFT calculations [13]. Compositions of the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) are given in Table 3. Contour plots of
these molecular orbitals for complex 1 are shown in Fig. 2 and
the same for complex 2 are shown in Fig. S2 (Supplementary
material) respectively. In both the complexes the HOMO has
major (w75%) contribution from the CNN-coordinated imine
ligand, much less (w20%) contribution from the metal center, and
C
intermediates, and the kinetics of formation of complex 1 from C is
slower than formation of C from A. However, attempts to isolate
intermediate C by discontinuing the reaction after 2 h have failed,
and complex 1 could be isolated as the only characterizable species
in poor yield. Identification and quantification of the organic
byproducts, viz. bromobenzene and cinnamaldehyde, have been
done by GCeMS technique [17]. Hence the mass spectral studies
support the proposed reaction sequences behind formation of
complexes 1 and 2.
2.2. Electronic spectra
Complexes 1 and 2 are poorly soluble in dichloromethane,
chloroform, acetonitrile, etc., but are readily soluble in dimethyl
formamide and dimethyl sulfoxide producing bright yellow
solutions. Electronic spectra of these complexes have been
recorded in dimethyl sulfoxide solution, and the spectral data are
given in Table 2. Each complex shows absorptions in the visible
Table 2
Electronic spectral data in dimethyl sulfoxide solution.
Complex
lmax, nm ( 3 )
, Mꢁ1 cmꢁ1
1
2
476 (1500), 452(2300), 367(3300), 328(6900), 250(9700)
461(1400), 436(1800), 361(2700), 319(5300), 249(7900)

4
P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
Table 3
2.3. Catalysis
Composition of selected molecular orbitals of the complexes.
The reaction mechanisms for the CeC cross coupling reactions
propose the formation of palladium(II) intermediates with two
adjacent palladiumecarbon bonds, just prior to reductive elimina-
tion of the coupled product. Presence of two such palladiumecarbon
bonds, viz. the palladiumearyl bond and the palladiumeacetylide
bond, in complexes 1 and 2 have made them look as promising
catalysts for CeC cross-coupling reactions, particularly for Sonoga-
shira cross-coupling reaction. Hence, catalytic activity of these two
complexes has been examined first for Sonogashira coupling reac-
tion between aryl iodides and phenylacetylene. Both the palladium
complexes are found to catalyze the targeted coupling reactions
with comparable efficiency, with only 0.01 mol% catalyst loading at
room temperature (25 ꢀC), affording the expected coupled products
in good to excellent yields (Table 4, entries 1e6). The para-substit-
uent in the aryl iodide is observed to have notable influence on the
yield of the product (entries 1e6). For coupling of the corresponding
aryl bromides with phenylboronic acid higher (1 mol%) catalyst
loading was necessary to achieve similar yield as the corresponding
aryl iodides (entries 7e10). Here again complexes 1 and 2 show
comparable efficiency (entries 7 and 8). Encouraged by the suc-
cessful Sonogashira coupling reactions involving aryl iodides and
aryl bromides, we attempted similar reactions with aryl chlorides as
substrate. The reactions with aryl chlorides are found to be much
less facile, and afford the coupled products in poor yield (entries 11e
13). Attempts for similar coupling with aryl fluorides were unsuc-
cessful. It is relevant mentioning here that in all these reactions
homo-coupling of phenylacetylene has been observed along with
the usual Sonogashira cross-coupling. Such homo-coupling re-
actions of phenylacetylene, where palladium plays a very important
role as catalyst, are well known [18].
Complex
Contributing fragments
% contribution of fragments to
HOMO
LUMO
1
Pd
18.9
74.9
6.2
4.8
95.2
0.0
Imine ligand
Acetylide
Pd
Imine ligand
Acetylide
2
20.0
75.2
4.8
2.1
97.9
0.0
marginal (w5%) contribution from the coordinated acetylide. The
LUMO is found to be delocalized mostly (>95%) on the imine
ligand. The lowest energy absorption in both the complexes is
hence assignable to a transition from a filled orbital of the
coordinated imine ligand (HOMO) to a vacant orbital of the same
ligand (LUMO).
Encouraged by the facile Sonogashira reactions catalyzed by the
palladium imine complexes, Suzuki reactions of phenylboronic acid
and p-substituted iodobenzenes were tried to yield the biphenyl
products (Table 5). Both complexes 1 and 2 showed notable, as well
as comparable, catalytic efficiency under relatively mild experi-
mental condition (entries 1e6). Similar coupling between phenyl-
boronic acid and p-substituted bromobenzenes also took place
smoothly (entries 7e10), but ten times more catalyst and slightly
longer reaction time were needed to achieve similar yield.
Attempted coupling of phenylboronic acid with p-chloroaryls using
complex 1 as catalyst was also successful (entries 11e13), but with
significantly less catalytic efficiency. Finally we tried Suzuki
coupling with p-fluoroaryls, and as anticipated, the reactions were
found to be very difficult even with 1 mol% catalyst loading and
24 h reaction time, and the coupled products were obtained in poor
yields (entries 14e16).
The observed efficiency of the organopalladium complexes 1
and 2 in activating aryl CeX (X ¼ I, Br, Cl) bonds and thereby
inducing CeC coupling reactions, has prompted us to try these
complexes as catalyst in bringing about CeN coupling reactions
between aryl halides and amines. First we attempted the coupling
of iodobenzene and p-substituted anilines, and as envisaged, the
CeN coupling reactions proceeded smoothly affording the desired
products in good yields (entries 1e6 in Table 6), and both the
complexes showed comparable catalytic efficiency. Smooth CeN
coupling was also observed with bromobenzene, but ten times
more catalyst loading and twice more time were needed to get
similar yield (entries 7e9). CeN coupling reactions using chloro-
benzene were found to be rather difficult (entries 10e12), as re-
flected in much less yield of the products even with much higher
catalyst loading. We have also explored the scope for arylation of
secondary amines using piperidine and morpholine. With iodo-
benzene the targeted reactions could be achieved in good and
Fig. 2. Contour plots of the HOMO and LUMO of complex 1.

P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
5
Table 4
Sonogashira cross-coupling of aryl halides with phenylacetylene.a
catalyst, CuI
R
X
HC
C
R
C C
+
NaOH
ethanol-toluene(1:1)
o
25 C
Entry
R
X
Catalyst
Time (h)
mol% of catalyst
Yieldb (%)
1
2
3
4
5
6
7
8
COCH3
COCH3
CHO
CHO
CN
I
I
I
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
1
2
1
2
1
2
1
2
1
1
1
1
1
5
5
5
5
5
5
5
5
5
0.01
0.01
0.01
0.01
0.01
0.01
1
1
1
1
1
94
92
80
77
69
65
96
80
85
47
28
15
8
CN
COCH3
COCH3
CHO
CN
COCH3
CHO
CN
9
10
11
12
13
5
24
24
24
1
1
a
Reaction conditions: aryl halide (1.0 mmol), phenylacetylene (1.2 mmol), NaOH (2.0 mmol), Pd catalyst, CuI (10 mol%), solvent (4 mL).
Determined by GCeMS.
b
comparable yields using both complexes 1 and 2 as catalyst (entries
coupling reactions involving both primary and secondary amines.
While both the complexes show comparable efficiency, complex 1
has been found to be a slightly better catalyst than complex 2.
These complexes not only activated CeI and CeBr bonds, but also
could bring about much difficult CeCl bond activation successfully,
and it is relevant to mention here that cross-coupling reactions
involving chloro-substituted arenes have gained prominence in
recent years [19e21]. Another noticeable aspect of the observed
catalysis is that no additional ligand was necessary for any of the
cross-coupling reactions, and such ligand-free catalysis is relatively
less common [22e24].
13e16). However, compared to the primary aromatic amines (en-
tries 1e6), longer reaction time was needed for the secondary
amines. Similar CeN coupling reactions with bromobenzene and
chlorobenzene proceed with gradually increasing difficulty and
decreasing yields (entries 17e20). Attempts for CeN coupling re-
actions using fluorobenzene were unsuccessful with both primary
and secondary amine.
The organopalladium complexes (1 and 2), with two PdeC
bonds, are thus found capable of successfully catalyzing Sonoga-
shira and Suzuki type CeC coupling reactions, and also CeN
Table 5
Suzuki cross-coupling of aryl halides with phenylboronic acid.a
catalyst
R
X
(HO)2B
R
+
Cs2CO3
ethanol-toluene(1:1)
o
90 C
Entry
R
X
Catalyst
Time (h)
mol% of catalyst
Yieldb (%)
TONc
1
2
3
4
5
6
7
8
COCH3
COCH3
CHO
CHO
CN
I
I
I
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
F
1
2
1
2
1
2
1
2
1
1
1
1
1
1
1
1
3
3
3
3
3
3
5
5
5
5
8
8
8
24
24
24
0.001
0.001
0.001
0.001
0.001
0.001
0.01
0.01
0.01
0.01
0.01
100
97
100
95
92
90
100
96
97
76
51
43
36
13
9
100,000
97,000
100,000
95,000
92,000
90,000
10,000
9600
9700
7600
5100
4300
3600
13
CN
COCH3
COCH3
CHO
CN
COCH3
CHO
CN
COCH3
CHO
CN
9
10
11
12
13
14
15
16
0.01
0.01
1.00
1.00
F
F
9
7
1.00
7
a
Reaction conditions: aryl halide (1.0 mmol), phenylboronic acid (1.2 mmol), Cs2CO3 (2.0 mmol), Pd catalyst, solvent (4 mL).
Determined by GCeMS.
TON ¼ turnover number ((mol of product)/(mol of catalyst)).
b
c

6
P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
Table 6 (continued)
Table 6
CeN coupling of aryl halide with amines.a
Entry
X
Amine
Catalyst Time mol% Yieldb TONc
catalyst
(h)
of cat. (%)
N
N
X
R2
R2
+
H
t
R1
NaO Bu
R1
HN
HN
HN
HN
HN
14
I
2
1
2
1
1
24
0.01
0.01
0.01
0.1
87
8700
9400
9100
800
dioxane
90 oC
15
16
17
18
19
I
24
24
24
24
94
91
80
82
Entry
1
X
I
Amine
Catalyst Time mol% Yieldb TONc
O
O
(h)
of cat. (%)
H2N
I
1
2
1
2
1
2
1
1
1
1
1
12
0.01
0.01
0.01
0.01
0.01
0.01
0.1
100
93
100
97
98
91
93
95
97
46
55
10,000
H2N
H2N
Br
Br
2
I
12
12
12
12
12
24
24
24
24
24
9300
10,000
9700
9800
9100
930
0.1
820
O
O
3
I
OCH3
OCH3
Cl
HN
HN
Cl
Cl
1
1
24
24
1.0
1.0
67
62
67
62
H2N
H2N
H2N
4
I
20
5
I
Reaction conditions: aryl halide (1.0 mmol), aniline (1.2 mmol), NaOtBu
(1.3 mmol), Pd catalyst, solvent (4 mL).
a
b
Determined by GCeMS on the basis of residual aryl halide.
TON ¼ turnover number ((mol of product)/(mol of catalyst)).
c
6
I
Cl
3. Conclusions
H2N
H2N
7
Br
Br
Br
Cl
Cl
The present study demonstrates that the modified phenyl bro-
mides with the two soft N-donor centers, viz. L1 and L2, undergo
facile CeBr bond activation upon reaction with the palladium(0)
center in [Pd2(dba)3], and bind to the metal center as CNN-donors
(as in I). In addition, an unexpected CeC bond cleavage of an out-
going dibenzylideneacetone takes place providing an acetylide
ligand that takes up the fourth coordination site of the metal. This
study also shows that the organopalladium complexes with two
PdeC bonds are good catalysts for bringing about CeC and CeN
coupling reactions.
8
0.1
950
OCH3
Cl
H2N
9
0.1
970
H2N
H2N
4. Experimental
10
11
1
46
4.1. Materials
Palladium chloride was obtained from Arora Matthey, Kolkata,
India. 8-Aminoquinoline was procured from SigmaeAldrich.
1
55
OCH3
Cl
Benzaldehyde,
acetone,
2-bromobenzaldehyde
and
2-bromoacetophenone were obtained from Merck, India. Diben-
zylideneacetone (dba) was prepared by aldol condensation be-
tween benzaldehyde and acetone [25]. [Pd2(dba)3] were prepared
by following a reported methods [26]. The two imine ligands, viz. L1
and L2, were prepared by condensation of 8-aminoquinoline with
2-bromobenzaldehyde and 2-bromoacetophenone respectively in
1:1 ethanolewater mixture. All other chemicals and solvents were
reagent grade commercial materials and were used as received.
H2N
HN
12
13
Cl
I
1
1
24
24
1
59
91
59
0.01
9100

P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
7
Table 7
4.2. Physical measurements
Crystallographic data for complex 1.
Microanalyses (C, H, N) were performed using a Heraeus Carlo
Erba 1108 elemental analyzer. Mass spectra were recorded with a
Micromass LCT electrospray (Qtof Micro YA263) mass spectrom-
eter. 1H NMR spectra were recorded in CDCl3 solution on a Bruker
AV-300 spectrometer with TMS as the internal standard. Electronic
spectra were recorded on a JASCO V-570 UVeVISeNIR spectro-
photometer. IR spectra were obtained on a PerkineElmer (Paragon)
FT spectrometer with samples prepared as KBr pellets. Optimiza-
tion of ground-state structure and energy calculations of the
palladium complexes were carried out by density functional theory
(DFT) method using the Gaussian 03 (B3LYP/SDD-6-31G) package
[13]. For complex 1, the X-ray crystallographic coordinates were
utilized in the calculations. For complex 2 X-ray crystallographic
coordinates were not available, and hence the structure was opti-
mized prior to MO calculations. GCeMS study was done with a
Clarus 600 (PerkineElmer) machine.
Empirical formula
Formula weight
Crystal system
Space group
C18H12N2Pd,2(O)
394.72
Monoclinic
P21/c
10.0312(11)
7.1014(8)
22.225(2)
99.576(8)
1561.2(3)
4
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
b
(ꢀ)
3
ꢀ
V (A )
Z
F (000)
784
Crystal size (mm3)
T (K)
0.32 ꢂ 0.17 ꢂ 0.11
296
m
(mmꢁ1
)
1.199
0.0615
0.1796
0.98
R1a
wR2b
Gofc
P
P
a
R1 ¼ kFoj ꢁ jFck= jFoj:
P
P
wR2 ¼ ½ ½wðF2o ꢁ F2c Þ2ꢃ= ½wðFo2Þ2ꢃꢃ1=2
:
b
c
P
Gof ¼ ½ ½wðF2o ꢁ F2c Þ2ꢃ=ðM ꢁ NÞꢃ1=2
; where M is the number of
4.3. Syntheses of complexes
reflections and N is the number of parameters refined.
Both the palladium complexes were prepared by following a
general procedure. Specific details are given below for complex 1.
Complex 1: To a solution of L1 (68 mg, 0.22 mmol) in tert-
butanol (40 mL) was added [Pd2(dba)3] (100 mg, 0.11 mmol), and
the mixture was then refluxed for 4 h to yield a yellow solution. The
solvent was evaporated and the solid mass, thus obtained, was
subjected to purification by thin-layer chromatography on a silica
plate. With 1:3 acetonitrileebenzene solution as the eluant, a
yellow band separated, which was extracted with acetonitrile.
Evaporation of this extract gave complex 1 as a yellow crystalline
solid. Yield: 67%. Anal. Calcd. for C18H12N2Pd: C, 57.39; H, 3.19; N,
7.43. Found: C, 58.15; H, 3.59; N, 7.92%. 1H NMR [27]: 7.19e7.13 (2H)
*; 7.56e7.53 (3H)*; 7.87e7.82 (2H)*; 8.13 (d, 1H, J ¼ 8.1); 8.41 (d, 1H,
J ¼ 7.2); 8.73 (d, 1H, J ¼ 7.7); 8.87 (d, 1H, J ¼ 7.8); 9.3(s, 1H). MS (ESI),
positive mode: [complex 1 þ Na]þ, 386. IR: 435, 486, 675, 710, 785,
824, 1074, 1158, 1307, 1322, 1367, 1384, 1461, 1500, 1525, 1574, 1594,
1643, 2361, 3436.
Complex 2: Yield: (71%); Anal. Calcd. for C19H14N2Pd: C, 60.57;
H, 3.72; N, 7.44. Found: C, 60.77; H, 3.78; N, 7.78%. 1H NMR: 2.91
(s, 3H, CH3); 7.18e7.08 (2H)*; 7.50e7.47 (2H)*; 7.58(d, 1H, J ¼ 6.6);
7.83e7.78 (2H)*; 8.09 (d,1H, J ¼ 8.1); 8.30 (d,1H, J ¼ 7.8), 8.71 (d,1H,
J ¼ 8.4), 8.89 (s, 1H). MS (ESI), positive mode: [complex 2 þ Na]þ,
399. IR: 498, 521, 687, 762, 799, 918, 1020, 1151, 1276, 1310, 1446,
1493, 1626, 2361, 3452.
layers were washed with water (3 ꢂ 10 mL), dried over anhydrous
Na2SO4, and filtered. Solvent was removed under vacuum. The res-
idue was dissolved in hexane and analyzed by GCeMS.
4.6. General procedure for Suzuki coupling reactions
In a typical run, an oven-dried 10 mL round bottom flask was
charged with a known mole percent of catalyst, Cs2CO3 (1.7 mmol),
phenylboronic acid (1.2 mmol) and aryl halide (1 mmol) with 1:1
ethanoletoluene (4 mL). The flask was placed in a preheated oil
bath at 90 ꢀC. After the specified time the flask was removed from
the oil bath, water (20 mL) was added, and extraction with ether
(4 ꢂ 10 mL) was done. The combined organic layers were washed
with water (3 ꢂ 10 mL), dried over anhydrous Na2SO4, and filtered.
Solvent was removed under vacuum. The residue was dissolved in
hexane and analyzed by GCeMS.
4.7. General procedure for CeN coupling reactions
In a typical run, an oven-dried 10 mL round bottom flask was
charged with a known mole percent of catalyst, NaOtBu (1.3 mmol),
amine (1.2 mmol) and aryl halide (1 mmol) with dioxane (4 mL).
The flask was placed in a preheated oil bath at 90 ꢀC. After the
specified time the flask was removed from the oil bath, water
(20 mL) was added, and extraction with ether (4 ꢂ 10 mL) was
done. The combined organic layers were washed with water
(3 ꢂ 10 mL), dried over anhydrous Na2SO4, and filtered. Solvent was
removed under vacuum. The residue was dissolved in hexane and
analyzed by GCeMS.
4.4. X-ray crystallography
Single crystals of complex 1 were obtained by slow evaporation
of solvent from a solution of the complex in dimethyl sulfoxide.
Selected crystal data and data collection parameters are given
in Table 7. Data were collected on a Bruker SMART APEX CCD
diffractometer using graphite monochromated and Mo
Ka
ꢀ
radiation (
l
¼ 0.71073 A). X-ray data reduction and, structure so-
lution and refinement were done using SHELXS-97 and SHELXL-97
Acknowledgments
programs [28]. The structure was solved by the direct methods.
Financial assistance received from the Department of Science
and Technology, New Delhi, India [Grant No. SR/S1/IC-29/2009 and
SR/S1/RFIC-01/2009], is gratefully acknowledged. We thank Ipsita
Bhattacharya for her help with the DFT calculations. P.M. thanks
the University Grants Commission, New Delhi, India, for her
fellowship [Grant No. 10-2(5)2006(ii)-E.U.II]. Piyali Paul and Pou-
lami Sengupta thank the Council of Scientific and Industrial
Research, New Delhi, for their fellowship [Grant No. 09/096(0588)/
2009-EMR-I and 09/096(0583)/2007-EMR-I respectively].
4.5. General procedure for Sonogashira coupling reactions
To slurry of aryl halide (1 mmol), cuprous iodide (10 mol%) and
palladium catalyst (a known mol%) in 1:1 ethanoletoluene (4 mL),
phenylacetylene (1.2 mmol) and NaOH (1.7 mmol) were added and
heated at 25 ꢀC. After completion of the reaction (monitored by TLC),
the flask was removed from the oil bath and water (20 mL) added,
followed by extraction with ether (4 ꢂ10 mL). The combined organic

8
P. Majumder et al. / Journal of Organometallic Chemistry 736 (2013) 1e8
G. Scalamani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara,
Appendix A. Supplementary material
K. Toyota, R. Fukuda, I. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken,
C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth,
P. Salvador, J.J. Danneberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels,
M.C. Strain, O. Farkas, D.K. Malik, A.D. Rabuck, K. Raghavachari, J.B. Foresman,
J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu,
A. Liashenko, P. Piskroz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, L.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson,
W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03. Revision DO1,
Gaussian Inc., Pittsburgh, PA, 2003.
CCDC 894631 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Appendix B. Supplementary material
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.03.006.
[14] For the mass spectral study, aliquots of 0.5 mL were taken from the reaction
bed after certain time intervals and the aliquots were frozen immediately in
liquid nitrogen. These samples were brought to room temperature prior to
mass spectral analysis and the spectra were recorded as soon as possible.
[15] M. Distl, M. Wink, Potato Res. 52 (2009) 79e104.
[16] Z.-X. Zhao, H.-Y. Wang, Y.-L. Guo, Rapid Commun. Mass Spectrom. 25 (2011)
3401e3410.
[17] Cinnamaldehyde was detected in 98% and 96% yields with for complexes 1
and 2, respectively. Bromobenzene was detected in 95% and 93% yields for
complexes 1 and 2, respectively.
References
[1] C.J. Elsevier, Coord. Chem. Rev. 185 (1999) 809e822.
[2] R.B. Bedford, C.S.J. Cazin, D. Holder, Coord. Chem. Rev. 248 (2004) 2283e2321.
[3] K. Ferre-Filmon, L. Delaude, A. Demonceau, A.F. Noels, Coord. Chem. Rev. 248
(2004) 2323e2336.
[18] J.-H. Li, Y. Liang, Y.-X. Xie, J. Org. Chem. 70 (2005) 4393e4396.
[19] J.-X. Hu, H. Wu, C.-Y. Li, W.-J. Sheng, Y.-X. Jia, J.-R. Gao, Chem. Eur. J. 17 (2011)
5234e5237.
[20] N. Hadei, G.T. Achonduh, C. Valente, C.I. O’ Brien, M.G. Organ, Angew. Chem.
Int. Ed. Engl. 50 (2011) 3896e3899.
[21] X. Qian, C.M. Kozak, Synlett 6 (2011) 852e856.
[22] C. Pan, M. Liu, L. Zhang, H. Wu, J. Ding, J. Cheng, Catal. Commun. 9 (2007)
508e510.
[23] M. Guo, Z. Zhu, H. Huang, Q. Zhang, Catal. Commun. 10 (2009) 865e867.
[24] S.M. Islam, P. Mondal, K. Tuhina, A.S. Roy, S. Mondal, D. Hossain, J. Inorg.
Organomet. Polym. Mater. 20 (2010) 264e277.
[25] C.R. Conard, M.A. Dolliver, Org. Synth., Coll. vol. 2, John Wiley, 1943, p. 167.
[26] M.F. Rettig, P.M. Maitlis, Inorg. Synth. 17 (2007) 134.
[4] A. Fihri, P. Meunier, J.C. Hierso, Coord. Chem. Rev. 251 (2007) 2017e2321.
[5] V. Polshettiwar, C. Len, A. Fihri, Coord. Chem. Rev. 253 (2009) 2599e2626.
[6] P. Paul, S. Datta, S. Halder, R. Acharyya, F. Basuli, R.J. Butcher, S.M. Peng,
G.H. Lee, A. Castineiras, M.G.B. Drew, S. Bhattacharya, J. Mol. Catal. A 344
(2011) 62e74.
[7] D.K. Seth, M.G.B. Drew, S. Bhattacharya, J. Indian Chem. Soc. 88 (2011) 1233e
1240.
[8] S. Datta, D.K. Seth, S. Halder, W.S. Sheldrick, H. Mayer-Figge, M.G.B. Drew,
S. Bhattacharya, RSC Adv. 2 (2012) 5254e5264.
[9] J. Dutta, S. Datta, D.K. Seth, S. Bhattacharya, RSC Adv. 2 (2012) 11751e11763.
[10] P. Paul, P. Sengupta, S. Bhattacharya, J. Organomet. Chem. 724 (2013) 281e
288.
[11] A. Satake, H. Koshino, T. Nakata, J. Organomet. Chem. 595 (2000) 208e214.
[12] P. Chellan, S. Nasser, L. Vivas, K. Chibale, G.S. Smith, J. Organomet. Chem. 695
(2010) 2225e2232.
[13] M.J. Frisch, G.W. Tracks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman Jr., J.A. Monygomery, T. Vreven, K.N. Kudin, J.C. Burant,
J.M. Millam, S.S. Iyenger, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
[27] Chemical shifts are given in ppm and multiplicity of the signals along with the
associated coupling constants (J in Hz) are given in parentheses. Overlapping
signals are marked with an asterisk.
[28] G.M. Sheldrick, SHELXS-97 and SHELXL-97, Fortran Programs for Crystal
Structure Solution and Refinement, University of Gottingen, 1997.