Synthesis, characterization and structure of new diazoketiminato chelates of palladium(II): Potential catalyst for C-C coupling reactions

Article abstract of DOI:10.1016/j.poly.2011.11.026

The 1N-(N,N-diethylaminoethyl)-2-arylazoaniline, HL [where HL = ArN = NC₆H₄N(H){C₂H₄N(C₂H ₅)₂}; Ar = C₆H₅ (for HL ¹), p-MeC₆H₄ (for HL²) or p-ClC ₆H₄ (for HL³)], ligands were prepared by treating the appropriate 2-(arylazo)aniline with 2-bromo-N,N-diethylethanamine. Reactions of Na₂PdCl₄ with HL afforded the [(L)PdCl] complexes. HL binds palladium(II) in a tridentate fashion (N,N,N), forming a new diazoketiminato chelate. The X-ray structure of [(L³)PdCl] was determined to confirm the characterization. The newly synthesized complex [(L¹)PdCl] was utilized to carry out Suzuki and Heck reactions for a variety of substrates.

Full text of DOI:10.1016/j.poly.2011.11.026

Polyhedron 33 (2012) 67–73
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Polyhedron
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Synthesis, characterization and structure of new diazoketiminato chelates of
palladium(II): Potential catalyst for C–C coupling reactions
Jahar Lal Pratihar a,b, Poulami Pattanayak a, Debprasad Patra a, Chia-Her Lin c, Surajit Chattopadhyay a,
⇑
a Department of Chemistry, University of Kalyani, Kalyani 741235, India
b Department of Chemistry, Kandi Raj College, Murshidabad 742137, India
c Department of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2011
Accepted 7 November 2011
Available online 6 December 2011
The 1N-(N,N-diethylaminoethyl)-2-arylazoaniline, HL [where HL = ArN = NC6H4N(H){C2H4N(C2H5)2};
Ar = C6H5 (for HL1), p-MeC6H4 (for HL2) or p-ClC6H4 (for HL3)], ligands were prepared by treating the
appropriate 2-(arylazo)aniline with 2-bromo-N,N-diethylethanamine. Reactions of Na2PdCl4 with HL
afforded the [(L)PdCl] complexes. HL binds palladium(II) in a tridentate fashion (N,N,N), forming a new
diazoketiminato chelate. The X-ray structure of [(L3)PdCl] was determined to confirm the characteriza-
tion. The newly synthesized complex [(L1)PdCl] was utilized to carry out Suzuki and Heck reactions for
a variety of substrates.
Keywords:
1N-(N,N-diethylaminoethyl)-2-
arylazoaniline
Ó 2011 Elsevier Ltd. All rights reserved.
Palladium(II)
Diazoketiminato chelate
Suzuki and Heck reaction
1. Introduction
conditions is important in terms of their commercial application
[36–38].
This work stems from our interest on the coordination chemis-
try of palladium incorporating 2-(arylazo)aniline and related li-
gands [1–5]. The 2-(arylazo)aniline ligands and their derivatives,
1, have been employed recently in the development of the coordi-
nation chemistry of palladium(II). Formation of six membered dia-
zoketiminato chelates, 2, and orthopalladation, 3, are two
noteworthy binding modes of the ligand 1 [1–5]. Six membered
diazoketiminato chelates, 2, were obtained upon dissociation of
the amino proton when R0 = 2-benzyl pyridyl and H (Chart I),
whereas in the other cases orthopalladation occurred, as shown
in 3 [1–5].
Palladium(II) complexes incorporating nitrogen donor ligands
have been reported to exhibit catalytic activity in Suzuki and Heck
reactions (Eqs. (1) and (2), respectively) [14–25], which drew our
interest to study the catalytic activities of palladium(II) chelates
of nitrogen donor azo ligands in homogenous media. Palladium
chelates containing imines, oximes and diazobutadiene N-hetero-
cyclic carbene ligands were shown to be active catalysts for the
iodo and/or bromo aryl substrates (Eqs. (1) and (2)) [14–25]:
Ar-X þ PhBðOHÞ2 ! Ar-Ph
ð1Þ
X¼I or Br
The plausible mechanisms addressing the origin of such diver-
sity in the binding mode of 1 have been described earlier [2,3].
As a result, we were encouraged to design new ligands having a
specific binding mode. Over the past decade, several ligands, which
are sterically and electronically suitable, have been developed for
highly effective Suzuki and Heck reactions [6–41]. Efforts and ad-
vances have been made to design oxygen and/or moisture-stable
ligands due to the water- and/or air-sensitivity of most ligands.
Furthermore, our interest centered on Heck and Suzuki reac-
tions, catalyzed by coordination complexes of palladium, for both
practical and scientific reasons. Synthesis of new palladium che-
lates that are stable under the Heck and Suzuki coupling reaction
Ar-X þ Ph-CH@CH2 ! Ar-CH@CH-Ph
ð2Þ
X¼I or Br
Scientifically, the field is in the midst of a debate on the nature
of the active species and the mechanism of the Heck and Suzuki
coupling reactions. In particular, the mechanisms were unclear
when the catalysts used were palladacycle-based complexes or
other palladium(II) chelates [39–41].
Herein we describe the synthesis of some new azoamine li-
gands, 1N-(N,N-diethylaminoethyl)-2-arylazoaniline, HL (4) and
the reactions of these new ligands with Na2PdCl4. Formation of
the diazoketiminato chelate of the composition [(L)PdCl], 5, have
been authenticated on the basis of X-ray studies and 1H NMR spec-
troscopy. Suzuki and Heck coupling reactions were carried out, in
the presence of air and moisture, using [(L1)PdCl] as a catalyst.
⇑
Corresponding author. Tel.: +91 33 25828750; fax: +91 33 25828282.
E-mail address: scha8@rediffmail.com (S. Chattopadhyay).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.11.026

68
J.L. Pratihar et al. / Polyhedron 33 (2012) 67–73
R/ = -CH3
R
N
-C2H5
R
N
Ar
N
-C8H17
-CH2CHCH2
N
Pd
Pd
-CH2CO2C2H5
N
N
-2-MeOC6H4CH2
N
H
N
R/
-CH2Ph
N
H
-2-CH2C5H4N
-H
R/
2
3
R = H, CH3, Cl
1
Chart I. Coordination modes of 2-(arylazo)aniline and related ligands.
The stability of the [(L)PdCl] catalysts under the reaction condi-
tions has been verified.
form diazoketiminato chelates. Interestingly, the HL ligands affor-
ded only diazoketiminato chelates of Pd(II), [(L)PdCl], 5, upon
treatment with Na2PdCl4 in methanol at room temperature
(Scheme 1). The deprotonated HL ligand coordinated Pd(II) in a tri-
dentate (N,N,N) fashion, which is consistent with our proposition
reported earlier in the case of 6.
2. Results and discussion
2.1. Syntheses
2.2. Characterization
The new ligands 1N-(N,N-diethylaminoethyl)-2-arylazoaniline,
HL (4), have been prepared by substituting one of the amino pro-
tons of 2-(aryazo)aniline with 2-bromo-N,N-diethylethanamine in
the presence of potassium carbonate in refluxing acetonitrile
(Scheme 1). The ligands were isolated as orange liquids after col-
umn chromatographic purification. Earlier it was reported, with a
plausible mechanism, that tridentate (N,N,N) ligands of type 6 bind
Pd(II) through N(a), N(b) and N(c) to form diazoketiminato che-
lates, 7, dissociating the amino proton H(b).
All the ligands displayed characteristic UV–Vis spectra with an
absorption maxima near 325 nm, assigned to the n–p⁄ transition
of azo compounds [1,42,43]. The [(L)PdCl] complexes exhibited a
characteristic low energy absorption near 575 nm, which was as-
signed to a MLCT transition. Representative UV–Vis spectra of the
ligand HL1 and [(L1)PdCl] are shown in Fig. 1. Relevant data are col-
lected in Section 3. In the IR spectra, the mN@N band of the HL li-
gands (ꢀ1506 cmꢁ1) shifted to a lower frequency (1495 cmꢁ1
)
after formation of the Pd(II) chelates, [(L)PdCl], which was consis-
tent with coordination of the azo nitrogen [1,42,43].
R
R
The compositions of the ligands HL and the corresponding pal-
ladium complexes [(L)PdCl] matched well with the C, H, N analyt-
ical data and 1H NMR spectral data. The 1H NMR data are given in
Section 3. The 1H NMR spectra of the ligands and the complexes
have been described considering the atomic numbering scheme gi-
ven in 8. The HL ligands exhibited broad N–H signals with a triplet-
like structure due to coupling with two 13-H protons. This N–H
resonance is absent in the 1H NMR spectra of the [(L)PdCl] com-
plexes, signifying the dissociation of this proton upon complexa-
tion. As a result, the multiplet resonances (near d 3.26 ppm) for
the 13-H methylene protons of HL ligands turn into a triplet (near
d 3.71–3.44 ppm) in the spectra of the [(L)PdCl] complexes. The
methyl signal of HL2 was observed at d 2.34 ppm. The aromatic
proton resonances appeared in the region d 7.79–6.35 ppm and
are complicated due to overlapping of the signals, though the
Cl
N
N
(a)
N
N
Pd
N (b)
(c)
N
N
N
(b)
H
6
7
The coordinated N(c) is an sp2 ring nitrogen (specifically the
pyridyl nitrogen) in 6. As a sequel, it was interesting to examine
the coordination behavior of similar ligands where N(c) is an acy-
clic sp3 amino-N, with the expectation that the HL ligands would
R
R
R
Br
N
N
N
Na2PdCl4
N
Cl
N
N
N
N
N
Pd
K2CO3
NH2
NH
N
HL
[(L)PdCl]
5
4
R = H, CH3 , Cl
Scheme 1. Synthesis of HL and LPdCl.

J.L. Pratihar et al. / Polyhedron 33 (2012) 67–73
69
2.3. X-ray structure
Suitable crystals of [(L3)PdCl] were grown by slow diffusion of a
dichloromethane solution into petroleum ether. A perspective view
of the molecule is shown in Fig. 2 and selected bond distances and
angles are collected in Table 1. The geometry about palladium is dis-
torted square planar, where the mono anionic deprotonated ligand
(L) binds in a tridentate (N,N,N) fashion. A chloride ligand satisfies
the tetracoordination. The Pd(1)–N(azo), Pd(1)–N(aryl), Pd(1)–N(al-
Table 1
Selected bond distances (Å) and angles (°) for [(L3)PdCl], 3c.
Distances
Pd(1)–N(3)
Pd(1)–N(4)
N(1)–N(2)
N(2)–C(7)
N(4)–C(14)
N(4)–C(17)
C(13)–C(14)
C(7)–C(12)
C(9)–C(10)
C(10)–C(11)
1.9796(16)
2.1065(17)
1.285(2)
1.355(3)
1.486(3)
1.495(3)
1.495(3)
1.438(3)
1.402(4)
1.358(3)
Pd(1)–N(1)
Pd(1)–Cl(1)
N(1)–C(4)
N(3)–C(12)
N(3)–C(13)
N(4)–C(15)
C(7)–C(8)
2.0117(17)
2.3295(5)
1.443(3)
1.329(3)
1.463(3)
1.506(3)
1.425(3)
1.348(3)
1.432(3)
Fig. 1. UV–Vis spectra of HL1 (---) and [(L1)PdCl] (—) in dichloromethane.
C(8)–C(9)
C(11)–C(12)
Angles
N(3)–Pd(1)–N(1)
N(1)–Pd(1)–N(4)
N(1)–Pd(1)–Cl(1)
N(2)–N(1)–C(4)
N(1)–N(2)–C(7)
C(12)–N(3)–C(13)
C(13)–N(3)–Pd(1)
C(17)–N(4)–C(15)
C(15)–N(4)–Pd(1)
91.14(7)
174.38(7)
95.41(5)
110.18(16)
124.29(18)
119.20(17)
113.85(13)
109.71(17)
105.38(12)
N(3)–Pd(1)–N(4)
N(3)–Pd(1)–Cl(1)
N(4)–Pd(1)–Cl(1)
N(2)–N(1)–Pd(1)
C(4)–N(1)–Pd(1)
C(12)–N(3)–Pd(1)
C(14)–N(4)–C(17)
C(14)–N(4)–Pd(1)
C(17)–N(4)–Pd(1)
83.61(7)
166.74(5)
90.14(5)
126.45(14)
123.34(13)
125.42(14)
109.84(16)
103.04(12)
116.64(13)
Table 2
Suzuki cross coupling reaction with the catalyst [(L1)PdCl].x,y,z
Aryl halide
Product
Isolated yield
95
I
90
I
92
90
82
I
NO2
NO2
I
Fig. 2. Molecular structure of [(L3)PdCl] with the atomic numbering scheme.
Hydrogen atoms are omitted for clarity.
O2N
O2N
I
integrations match well with the number of protons. Therefore the
structure of the ligands and complexes in solution are very consis-
tent with the molecular structures obtained from the X-ray studies
(see below).
78
70
Br
R
Br
2
1
6
3
76
5
4
Br
NO2
N
N
Cl
N
15
17
16
18
7
Pd
8
NO2
N
9
12
x
y
z
Solvent = THF.
base = K2CO3.
time = 2 h.
11
13
14
10
8

70
J.L. Pratihar et al. / Polyhedron 33 (2012) 67–73
kyl) and Pd(1)–Cl(1) lengths (2.0117(17), 1.9796(16), 2.1065(17)
and 2.3295(5) Å, respectively) are within the normal range [1–
5,42]. The geometry about palladium is distorted square planar, jus-
tifying the oxidation state of Pd(II) and the uninegative ligand, since
the complex is a non-electrolyte. The bond lengths within the ligand
backbone are suitably altered due to delocalization of the negative
charge [1–3]. The C(12)–N(3) length (1.329(3) Å) is shorter than
the C–N single bond (N(1)–C(4), 1.443(3) Å) in the same molecule
and is close to the imine (C@N) distance [1–3]. The effect of imine
formation due to delocalization is reflected in the adjacent phenyl
ring, which is distorted with two short (ꢀ1.35 Å) and four long
(ꢀ1.42 Å) carbon–carbon bond distances. Thus the formation of an
azoimine chelate could be inferred from the X-ray studies [1–3]
and the structural formula of [(L3)PdCl] has been drawn accordingly
in 5 of Scheme 1 (vide supra).
At the end of each reaction the palladium catalyst was isolated
and it was found that coupling reactions did take place reusing
the isolated catalyst. This reusability of the catalyst was checked
up to three times for a reaction, keeping the other conditions intact.
The products were characterized by 1H NMR spectroscopy. The pal-
ladium catalyst [(L)PdCl] could be separated from the products eas-
ily by column chromatography since it appears as an intense violet
band with a lower Rf value than the products in the silica column.
The most important and probably most controversial issue in such
coupling reactions is the actual catalytic cycle. There have been dis-
cussions regarding two classes of palladium chelates that are used
as catalysts for C–C coupling reactions. For one class of such cata-
lysts, it was demonstrated that decomposition of the catalyst oc-
curred under the reaction conditions leaving ‘‘naked’’ palladium
as the active catalyst [43,44]. Another class of palladium complexes
exhibited complete stability under the reaction conditions, indicat-
ing a mechanism may operate by a Pd(II)–Pd(IV) cycle [45]. As a re-
sult we examined the stability of the [(L1)PdCl] catalyst under the
reaction conditions. Spectrophotometrically (kmax = 570 nm) we
have shown that the amount of [(L)PdCl] taken for a reaction dif-
fered negligibly from the amount after it was refluxed in THF for
2 h in the presence of K2CO3 (Fig. S19). This observation may keep
the issue of the Pd(0)–Pd(II) versus Pd(II)–Pd(IV) mechanism alive,
and this may inspire the proponents of the Pd(II)–Pd(IV) cycle [45].
Quite a large number of suitable experimental data are necessary to
come to a definite conclusion in this regard.
2.4. Catalytic reactions
2.4.1. Suzuki cross-coupling reaction
The Suzuki cross-coupling reaction is a powerful method for C–
C bond formation [6–25,36–41,43–45]. It is represented according
to Eq. (1), where phenylboronic acid and aryl halides are used as
substrates for C–C coupling. Synthesis of biaryl compounds
exploiting the Suzuki reaction has gained importance in organic
synthesis. Catalysts for Suzuki reactions are based on palladium
metal, and large numbers of palladium complexes have been
shown to be active catalysts for such reactions. Therefore, using
the new palladium complex [(L)PdCl] as a catalyst, we carried
out the Suzuki reaction (Eq. (3)) by coupling several arylhalides
and phenylboronic acid in THF solvent. Temperature sensitive cou-
pling reactions afforded the products only in low to moderate yield
at room temperature (30–35 °C), whereas higher yields were ob-
tained upon boiling whilst keeping the same reaction time. We car-
ried out the Suzuki coupling reactions in refluxing THF (ꢀ66 °C)
using K2CO3 as a base and keeping the reaction time constant, i.e.
for 2 h in all the cases. The isolated yields of the products varied
from 70% to 95% upon variation of aryl halide substrate. The results
of the transformations are given in Table 2. All the reactions were
carried out in contact with air:
2.4.2. Heck reaction
Heck coupling is another important palladium catalyzed C–C
coupling reaction, where the substrates are arylhalides (bromoar-
yls and iodoaryls) and styrene [26–35]. We have studied the cata-
lytic activity of [(L)PdCl] towards Heck coupling reactions.
Conversions of arylhalides to the corresponding stilbene deriva-
tives upon reaction with styrene using [(L)PdCl] as a catalyst in
refluxing methanol and in presence of K2CO3 (Eq. (4)) have been
examined. The results of the transformations are given in Table
3. All the reactions were carried out under ambient conditions.
Although the catalysis occurred smoothly, at the end of each reac-
tion the [(L)PdCl] catalyst could not be isolated, signifying the fact
that the catalyst may actually be a precatalyst in these reactions.
THF / DMF
Reflux
X
B(OH)2
+
K2CO3
R
R
ð3Þ
Catalyst3a
X = I or Br
R = H, Me, NO2
MeOH
Reflux
X
+
K2CO3
R
R
ð4Þ
Catalyst 3a
X = I or Br
R = H, Me, NO2

J.L. Pratihar et al. / Polyhedron 33 (2012) 67–73
71
Table 3
tridentate arylazo aniline derivatives are suitable for the formation
of diazoketiminato chelates of Pd(II). The new [(L)PdCl] complexes
have been used as catalysts for Suzuki and Heck coupling reactions.
The [(L)PdCl] complexes are stable under the conditions of Suzuki
coupling, indicating the catalytic activity of the molecular complex
itself.
Heck reaction with the catalyst [(L1)PdCl].x,y,z
Aryl halide
Product
Isolated yield
95
I
92
90
4. Experimental
I
4.1. Materials
I
The solvents used in the reactions were of reagent grade (E.
Marck, Kolkata, India) and were purified and dried by reported pro-
cedures [46]. The 2-(arylazo)anilines were prepared according to
the reported procedures [1,47,48]. Palladium chloride and potas-
sium carbonate were purchased from E. Merck, Kolkata, India. 2-
Bromo-N,N-diethylethanamine, phenylboronic acid, iodobenzene,
bromobenzene, 1-iodo-3,5-dimethylbenzene, 1-iodo-3,4-dimeth-
ylbenzene, 1-iodo-2-nitrobenzene, 1-iodo-3-nitrobenzene, 1-bro-
mo-3,5-dimethylbenzene, 1-bromo-2-nitrobenzene and styrene
were purchased from Aldrich. Disodium tetrachloropalladate was
prepared by a reported procedure [1].
NO2
NO2
88
92
I
I
O2N
O2N
76
80
Br
4.2. Physical measurements
Br
Microanalyses (C, H, N) was performed using a Perkin-Elmer
2400 C, H, N, S/O series II elemental analyzer. Infrared spectra were
recorded on a Parkin-Elmer L120-00A FT-IR spectrometer with the
samples prepared as KBr pellets. Electronic spectra were recorded
on a Shimadzu UV-1800 PC spectrophotometer. 1H NMR spectra
were obtained on Brucker 400 spectrometers in CDCl3.
80
Br
NO2
NO2
x Solvent = MeOH.
y base = K2CO3.
z time = 2 h.
4.3. Syntheses of the ligands
All the ligands, HL1, HL2 and HL3, were prepared following sim-
ilar procedures. A representative procedure for HL1 is given below.
Table 4
Crystallographic data for [(L3)PdCl], 3c.
4.3.1. HL1
A mixture of 2-(phenylazo)aniline (0.3 g, 1.52 mmol), 2-bromo-
N,N-diethylethanamine (0.27 g, 1.52 mmol) and 1 g of K2CO3 in
30 cm3 dry acetonitrile was refluxed for 5 h. The orange liquid
mass that was obtained after evaporation of the solvent, afforded
the ligand HL1, which was isolated by column chromatography
on silica gel (60–120 mesh) using the eluent petroleum ether:ben-
zene (1:1 v/v). Upon evaporation of the solvent after chromatogra-
phy, the orange-red liquid of pure HL1 was obtained. Yield: 60%.
Anal. Calc. for C18H24N3 (282): C, 76.59; H, 8.51; N, 14.89. Found:
Chemical formula
C18H22Cl2N4Pd
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
471.70
monoclinic
P21/c
7.6680(2)
10.5733(2)
23.1257(5)
90
90.6700(10)
90
0.71073
1874.81(7)
952
a
(°)
b (°)
(°)
c
k (Å)
C, 76.93; H, 8.36; N, 14.65%. UV–Vis kmax (CH2Cl2, nm) (e,
V (Å3)
F(000)
Z
Mꢁ1 cmꢁ1): 460 (8600), 320 (13400), 250 (15590), 230 (14740).
IR (KBr pellets, cmꢁ1): 1509 (N@N). 1H NMR (CDCl3, ppm) d: 8.81
(s, 1H), 7.79–7.75 (m, 3H), 7.40 (t, 2H), 7.31 (t, 1H), 7.19 (t, 1H),
6.72–6.67 (m, 2H), 3.30–3.25 (m, 2H), 2.70 (t, 2H), 2.58–2.52 (m,
4H), 0.99 (t, 6H).
4
T (K)
295(2)
1.671
1.283
0.0316
0.0590
1.050
D (mg mꢁ3
)
l
(mmꢁ1
)
R1 (all data)
wR2 [I > 2 (I)]
Goodness-of-fit (GOF)on F2
r
4.3.2. HL2 and HL3
The ligands HL2 and HL3 were prepared using 2-(p-tolylazo)ani-
line and 2-(p-chlorophenylazo) aniline in place of 2-(pheny-
lazo)aniline, respectively. Yield: HL2, 60% and HL3, 55%.
Anal. Calc. for C19H26N3 (296): C, 77.02; H, 8.78; N, 14.18. Found:
The yields of the products obtained from all the reactions were
determined after isolation, and the products were characterized
by 1H NMR spectra:
C, 76.73; H, 8.42; N, 14.45%. UV–Vis kmax (CH2Cl2, nm) (e,
Mꢁ1 cmꢁ1): 460 (6620), 325 (10290), 250 (10850), 230 (12010).
IR (KBr pellets, cmꢁ1): 1506 (N@N). 1H NMR (CDCl3, ppm) d: 8.68
(s, 1H), 7.74 (d, 1H), 7.69 (d, 2H), 7.20–7.17 (m, 3H), 6.71–6.65
(m, 2H), 3.28–3.24 (m, 2H), 2.69 (t, 2H), 2.57–2.51 (m, 4H), 2.34
(s, 3H), 0.98 (t, 6H).
3. Conclusion
The synthesis, characterization and structure of new diazoke-
timinato chelates of Pd(II) have been reported. Specifically N,N,N

72
J.L. Pratihar et al. / Polyhedron 33 (2012) 67–73
Anal. Calc. for C18H23N3Cl (316.5): C, 68.24; H, 7.26; N, 13.27.
4.6. General procedures for the Heck reaction
mixture containing styrene (3.5 mmol), aryl halide
Found: C, 68.45; H, 7.12; N, 13.52%. UV–Vis kmax (CH2Cl2, nm) (e,
Mꢁ1 cmꢁ1): 470 (6570), 325 (10230), 250 (10740), 210 (13010).
IR (KBr pellets, cmꢁ1): 1506 (N@N). 1H NMR (CDCl3, ppm) d: 8.86
(s, 1H), 7.75–7.71 (m, 3H), 7.35 (t, 2H), 7.23–7.18 (m, 1H), 6.72–
6.67 (m, 2H), 3.29–3.25 (m, 2H), 2.69 (t, 2H), 2.57–2.52 (m, 4H),
0.98 (t, 6H).
A
(3.5 mmol), the palladium complex [(L1)PdCl] (0.001 mmol) and
potassium carbonate (8.0 mmol) in methanol (10 ml) were heated
to reflux for 4 h, as mentioned in Table 3. After evaporation of the
solvent, the product was poured into water and extracted with
diethyl ether. The ether solution was dried over Na2SO4 and fil-
tered. The ether solution was passed through a 12 inch silica col-
umn (60–120 mesh) and the complex remain trapped. After
extraction of the desired compound, the complex was extracted
using dichloromethane. Upon evaporation of the ether, solid pure
products were obtained. The yields of the products obtained from
all the reactions were determined after isolation, and the products
were characterized by 1H NMR spectra.
4.4. Syntheses of the complexes
All the complexes, L1PdCl, L2PdCl and L3PdCl, were prepared fol-
lowing similar procedures. A representative procedure for L1PdCl is
given below.
4.4.1. L1PdCl
A solution of HL1 (0.146 g, 0.52 mmol) in 10 cm3 methanol was
added to a solution of Na2PdCl4 (0.153 g, 0.52 mmol) in 5 cm3
methanol. The mixture was stirred for 4 h. A dark solid precipitate
was separated by filtration and purified by column chromatogra-
phy using silica gel (60–120 mesh). The eluent was benzene:aceto-
nitrile (95:5 v/v) mixed solvent. Upon evaporation of the solvent, a
blue-violet solid of pure L1PdCl was obtained. Yield: 60%. Anal. Calc.
for C18H23N3PdCl (422.92): C, 51.07; H, 5.43; N, 9.93. Found: C,
5. Crystallography
A single crystal of [(L3)PdCl] was grown by slow diffusion of
petroleum ether into a dichloromethane solution at 298 K. Data
were collected by the
x
-scan technique on a Bruker Smart CCD dif-
radiation monochromated by graphite
fractometer with Mo K
a
crystal. The structure solution was done by direct methods with
the SHELXS-97 program [49,50]. Full matrix least square refinements
on F2 were performed using the SHELXL-97 program [49,50]. All non-
hydrogen atoms were refined anisotropically using reflections
I > 2r(I). All hydrogens were included at calculated positions. The
data, collection parameters and relevant crystal data are collected
51.18; H, 5.50; N, 10.00%. UV–Vis kmax (CH2Cl2, nm) (e
, Mꢁ1 cmꢁ1):
574 (4000), 321 (6300), 255 (31000). IR (KBr pellets, cmꢁ1): 1493
(N@N). 1H NMR (CDCl3, ppm) d: 7.64–7.62 (m, 1H), 7.43 (t, 2H),
7.30–7.16 (m, 4H), 6.76 (d, 1H), 6.51 (t, 1H), 3.59 (t, 1H), 3.24–
3.16 (m, 2H), 2.86–2.77 (m, 4H), 1.45 (t, 6H).
in Table 4.
4.4.2. L2PdCl and L3PdCl
Acknowledgments
The complexes L2PdCl and L3PdCl were prepared using HL2 and
HL3 in place of HL1, respectively. Yield: L2PdCl, 60% and L3PdCl,
55%.
We are thankful to the DST (New Delhi) for funding under DST-
SERC project (SR/S1/IC-0026/2007). The necessary laboratory and
infrastructural facility are provided by the Department of Chemis-
try, University of Kalyani. The support of DST under the FIST pro-
gram to the Department of Chemistry, University of Kalyani is
acknowledged.
Anal. Calc. for C19H25N3PdCl (436.92): C, 52.18; H, 5.72; N, 9.61.
Found: C, 52.35; H, 5.83; N, 9.50%. UV–Vis spectrum kmax (CH2Cl2,
nm) (e
, Mꢁ1 cmꢁ1): 574 (3700), 325 (5800), 254 (29000). IR (KBr
pellets, cmꢁ1): 1496 (N@N). 1H NMR (CDCl3, ppm) d: 7.50–7.48
(m, 1H), 7.19 (t, 2H), 7.10–7.05 (m, 3H), 6.94 (d, 1H), 6.61 (d,
1H), 6.31 (t, 1H), 3.44 (t, 2H), 3.09–3.03 (m, 2H), 2.70–2.63 (m,
4H), 2.15 (s, 3H), 1.30 (t, 6H).
Appendix A. Supplementary data
Anal. Calc. for C18H22N3PdCl2 (458.42): C, 47.61; H, 4.79; N, 9.16.
Found: C, 47.27; H, 4.75; N, 9.25%. UV–Vis spectrum kmax (CH2Cl2,
CCDC 803660 contains the supplementary crystallographic data
for [(L3)PdCl]. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2011.11.026.
nm) (e
, Mꢁ1 cmꢁ1) = 579 (4600), 324 (6900), 254 (31000). IR (KBr
pellets, cmꢁ1): 1496 (N@N). 1H NMR (CDCl3, ppm) d: 7.68 (dd,
1H), 7.46 (d, 2H), 7.34–7.28 (m, 4H), 6.85 (d, 1H), 6.59 (t, 1H),
3.69 (t, 2H), 3.51–3.24 (m, 2H), 2.94–2.86 (m, 4H), 1.54 (t, 6H).
4.5. General procedures for the Suzuki cross coupling reaction and
isolation of the catalyst
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