Facile synthesis and characterization of μ-chloro, azido, thiocyanato bridged cyclometallated Pd(II) containing Schiff-base ligands

Article abstract of DOI:10.1016/j.ica.2011.06.003

μ-Chloro bridged dinuclear cyclometallated Pd(II) complexes [Pd{(4-R)C₆H₃CHNC₆H₃-2,6-i-Pr ₂}(μ-Cl)]₂ (R = H, OMe) were prepared by reaction of Na₂PdCl₄ with benzyliden

Full text of DOI:10.1016/j.ica.2011.06.003

Inorganica Chimica Acta 376 (2011) 144–151
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Facile synthesis and characterization of
l-chloro, azido, thiocyanato bridged
cyclometallated Pd(II) containing Schiff-base ligands
Yuchun Jiang a, Yonglin Guo a, Xia Zhu a, Dandan Song a, Yu Wang a, Ximing Song a, Francis Verpoort b,c
,
Xiaohong Chang a,
⇑
a Liaoning Provincial Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036, PR China
b State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, PR China
c Department of Inorganic and Physical Chemistry, Laboratory of Organometallic Chemistry and Catalysis, Ghent University, Krijgslaan 281 (S-3), 9000 Ghent, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
l
-Chloro bridged dinuclear cyclometallated Pd(II) complexes [Pd{(4-R)C6H3CH@NC6H3-2,6-i-Pr2}(l-Cl)]2
Received 4 March 2011
Received in revised form 23 May 2011
Accepted 2 June 2011
(R = H, OMe) were prepared by reaction of Na2PdCl4 with benzylideneanilines. Unexpectedly, Na2PdCl4
reacted with Schiff-bases bearing a furyl or a thienyl ring to give N-coordinated non-cyclometallated
Pd(II) species [Pd(C4H3XCH@NC6H3-2,6-i-Pr2)2Cl2] (X = O, S). Treating [Pd{(4-R)C6H3CH@NC6H3-2,6-i-
Available online 12 June 2011
Pr2}(
l
-Cl)]2 (R = H, OMe) with an excess of NaN3 or NH4SCN generated
l
-N3 bridged or
l-SCN bridged
cyclometallated Pd(II) complexes [Pd{(4-R)C6H3CH@NC6H3-2,6-i-Pr2}(
The complexes were characterized by FTIR, NMR spectroscopy, elemental analysis and X-ray
crystallography.
l
-Y)]2 (R = H, OMe; Y = N3, NCS).
Keywords:
Cyclometallation
Schiff-base
Palladium
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Results and discussion
In the last few decades, cyclometallated Pd(II) complexes con-
taining C,N-chelating ligands have attracted more and more interest
because of their application as catalysts in organic reactions and as
key intermediates in organic and organometallic synthesis [1–8].
Moreover, cyclopalladation of C,N-chelating Schiff-base ligands is
one of the most extensively studied areas in Pd-chemistry [9–17].
It is worth noticing that in most cases cyclopalladation of
Schiff-bases is completed by the reaction of Pd(OAc)2 and Schiff-
2.1. Preparation of
complexes
l-chloro bridged dinuclear cyclometallated Pd(II)
One of the most common compounds used for cyclopalladation
of C,N-chelating Schiff-base ligands is Pd(OAc)2. Recently Albert et
al. reported that all attempts for cyclopalladation of imines by con-
densation of corresponding amino acid with 4-chlorobenzaldehyde
using mixtures of PdCl2/NaCl/Na2OAc, in different conditions, were
base ligands to produce
complexes. However, the examples of cyclopalladation obtained
by the combination of Na2PdCl4 and Schiff-base ligands are
l
-acetato bridged cyclometallated Pd(II)
unsuccessful [9]. Liu and co-workers prepared the
bridged binuclear cyclometallated Pd(II) complex [Pd(C6H4CH@
NC6H3-2,6-i-Pr2)( -Cl)]2 by stirring a mixture of (CH3CN)2PdCl2,
l-chloro
l
relatively rare. To the best of our knowledge, similar
l
-pseudoha-
sodium acetate and benzylidene(2,6-diisopropylphenyl)amine in
tetrahydrofuran at ambient temperature for 38 h [23]. In this
study, the reactions of Na2PdCl4 with Schiff-bases, as depicted in
Schemes 1 and 2, are studied.
The Schiff-base ligands 2,6-diisopropyl-N-(benzylidene)aniline
(L1), 2,6-diisopropyl-N-(4-methoxybenzylidene)aniline (L2), 2,6-
diisopropyl-N-(2-furylmethylidene)aniline (L3) and 2,6-diisopro-
pyl-N-(2-thienyl methylidene)aniline (L4) were prepared by
condensation of 2,6-diisopropylaniline with the corresponding
aldehyde in dried alcohol as solvent to which two drops formic
acid were added. Treating Schiff-base ligand L1 or L2 with Na2PdCl4
in the presence of NaOAc in methanol at room temperature,
lide (e.g. -N3 or -SCN) bridged cyclometallated Pd(II) complexes
l
l
characterized by molecular structure containing C,N-chelating
Schiff-base ligands have not been reported. Furthermore, it is also
known that coordinated azido and isothiocyanato (or thiocyanato)
groups show various coordination modes (Charts 1 and 2) [18–
22]. Herein, we report on the facile synthesis and the structures of
di-l-X (X = Cl, N3, SCN) bridged cyclometallated Pd(II) complexes
bearing Schiff-base ligands.
l
-chloro bridged dinuclear cyclometallated Pd(II) complex
[Pd(C6H4CH@NC6H3-2,6-i-Pr2)( -Cl)]2 (1) or [Pd{(4-OMe)C6H3CH@
NC6H3-2,6-i-Pr2}( -Cl)]2 (2) was generated, respectively. Both
l
⇑
Corresponding author. Tel.: +86 24 62207823; fax: +86 24 62202380.
E-mail addresses: cxh@lnu.edu.cn, c_x_hong@sina.com (X. Chang).
l
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.003

Y. Jiang et al. / Inorganica Chimica Acta 376 (2011) 144–151
145
the resonance for CH@NC proton at d 7.74 and d 7.61 ppm, respec-
tively, which was shifted to lower frequency due to N-coordination
of the imine [25]. And, two doublets at d 1.38 and 1.14 ppm for 1
and 2 were found for the methyl protons from the isopropyl group
compared to a doublet at d 1.17 ppm in the corresponding free li-
gands due to the lack of free rotation around the aryl-N bond
which renders the two methyls inequivalent. Moreover, the signal
of the 2-position H proton of the benzyl ring (Scheme 1) was not
observed, indicating the formation of Pd–C bond due to C–H
activation.
N
N
N
NNN
NNN
NNN
NNN
M
M
NNN
M
M NNN
M
M
M
N
N
N
(a)
(b)
(c)
(d)
Chart 1. Coordination modes of the azido ligand (N3).
Since
l-chloro bridged dinuclear cyclometallated Pd(II) com-
plexes 1 and 2 could be readily formed by the reaction of Na2PdCl4
with N-benzylideneaniline, we examined the reaction of Na2PdCl4
with Schiff-base ligands bearing a five-membered heterocycles
(Scheme 2). Initially the formation of novel cyclometallated Pd(II)
complexes was expected, however, when Schiff-base ligand, bear-
ing a five-membered heterocycle L3 or L4, was treated with
Na2PdCl4 in the presence of NaOAc in methanol at room tempera-
ture, no dinulear cyclometallated Pd(II) complexes were obtained.
This procedure generated only mononuclear non-cyclometallated
Pd(II) complexes [Pd(C4H3OCH@NC6H3-2,6-i-Pr2)2Cl2] (3) and [Pd
(C4H3SCH@NC6H3-2,6-i-Pr2)2Cl2] (4). The outcome of the reaction
is similar to the reaction reported by Lee and Lee [26]. On the other
hand, Kim and co-workers reported the reaction of Na2PdCl4 with
N C S
N C S
M
M
N C S
M
M
S C N
S
C
N
(I)
(II)
(III)
Chart 2. Coordination modes of the isothiocyanate ligand (NCS).
complexes were characterized by elemental analysis, spectroscopic
techniques (NMR, FTIR) and the molecular structure of 2 was
determined by single crystal X-ray analysis. The IR spectra of 1
and 2 show a strong stretch vibration at 1600 and 1601 cmꢀ1
,
2-(20-thienyl)pyridine resulting in
a
cyclometallated Pd(II)
respectively, due to the
m
(C@N), which was shifted to lower wave-
complex [27]. Most probably the cyclometallation depends on
the rigid structure of 2-(20-thienyl)pyridine. After the coordination
of N from pyridyl with Pd, rotation of the thienyl ring around C–C
axis to a suitable position can result in the activation of the b-H and
numbers compared to that of the free ligands (1636 and
1643 cmꢀ1) indicating that the N of the imine group coordinate
to the Palladium [24]. The 1H NMR spectra of 1 and 2 displayed
R
N
Cl
N
CH3OH
+
Na2PdCl4
HC
R
R = H, 1;
HC
R
Pd
Pd
CH
R = OMe, 2
NaOAC
Cl
2
3
N
R = H, L1;
R = OMe, L2
Scheme 1. Synthesis of
l-chloro bridged dinuclear cyclometallated Pd(II) complexes.
N
Cl
X
HC
Pd
Pd
CH
N
Cl
X
X
CH3OH
NaOAC
CH
N
+
Expected products
Na2PdCl4
X
Cl
HC
N
X = O, L3; X = S, L4
N
Pd
Cl
CH
X
X = O, 3; X= S, 4
Scheme 2. Synthesis of mononuclear non-cyclometallated Pd(II) complexes.

146
Y. Jiang et al. / Inorganica Chimica Acta 376 (2011) 144–151
tively, which were shifted to lower wavenumbers compared to that
of free ligands (1633 and 1627 cmꢀ1). Although, this observation in
IR is analogous to complexes 1 and 2, a different observation was
made in 1H NMR for 3 and 4, both displayed the resonance for
the CH@NC protons at d 9.13 and d 9.36 ppm, respectively, which
was shifted to higher frequency, indirectly proving that the
b-H from the furyl or the thienyl ring was not activated and hence
no cyclometallation occurred. Moreover, the signal of the b-H pro-
ton of the furyl or the thienyl ring did not disappear, demonstrat-
ing the formation of only a Pd–N coordinated complex.
Single crystals of 2–4 suitable for X-ray diffraction analysis
were obtained from
a
dichloromethane/hexane solution.
Figs. 1–3 show molecular structures of 2, 3, and 4, respectively. De-
tails on crystal data, intensity collection, and refinement details are
given in Table 1. As depicted in Fig. 1, the ligand L2 is bonded to the
di-l-chloro-bridge unit through the nitrogen of imine group and
an aromatic carbon atom providing a five-membered chelate ring.
Each palladium center adopt a square planar coordination geome-
try with two cyclometallated ligands in a trans arrangement with
respect to the Pdꢁ ꢁ ꢁPd axis, being similar to those reported by
Crispini et al. [28]. The five-membered chelate ring defined by
Pd1, C2, C1, C8 and N1 is essentially planar with the atomic
displacements not exceeding 0.0319 Å, to which the diisopropyl-
phenyl ring is nearly perpendicular with a dihedral angle 79.6(1)°.
The two molecules shown in Figs. 2 and 3 possess similar struc-
tural features. The Pd atom in complexes 3 and 4 reveals a square
planar coordination containing two trans-N-coordinated Schiff-
base ligands and two coordinated chloride atoms. The torsion an-
gle defined by Pd1, N1, C13 and C14 for 3 and by Pd1, N1, C1
and C2 for 4 is 171.8(2)° and 170.6(2)°, respectively. Confirming
that the b-C is drawn apart from the Pd center due to the hindered
rotation of bulky isopropyl group and thus no C–H activation
occurred. Moreover, the distance of Pd with a proton of a methyl
of isopropyl units is ca. 2.78 Å in compound 3 and ca. 3.07 Å in
compound 4, indicating that the non-bonding interaction results
in the location of a proton of a methyl in the 5th coordination site
of Pd. The furyl and the thienyl groups cannot interact with Pd
probably because one methyl group of the isopropyl units is taking
this position. Also, this interaction of non-bonding renders a
Fig. 1. Molecular structure of 2. Selected bond lengths (Å) and angles (°): Pd1–C2
1.971(4), Pd1–N1 2.036(3), Pd1–Cl1A 2.338(14), Pd1–Cl1 2.453(12), Pd1A–Cl1A
2.453(12), N1–C8 1.294(56); N1–Pd1–Cl1A 175.71(9), N1–Pd1–Cl1 97.817(86), C2–
Pd1–N1 80.949(137), C2–Pd1–Cl1 178.73(10), C2–Pd1–Cl1A 94.887(11).
thus to the formation of a cyclometallated Pd(II) complex. In con-
trast to the 2-(20-thienyl)pyridine, due to the flexible structure of
a Schiff-base ligand bearing a furyl or a thienyl ring lead to the
b-C is drawn apart from the Pd center after coordination of the N
atom of the imine group with Pd. Confirmation is obtained by
the molecular structures of complexes 3 and 4. Both complexes
were characterized by spectroscopic and elemental analysis and
their molecular structures were determined by single crystal
X-ray analysis. The IR spectra of 3 and 4 showed a strong stretch
vibration assignable to the m
(C@N) at 1616 and 1596 cmꢀ1, respec-
Fig. 2. Molecular structure of 3. Selected bond lengths (Å) and angles (°): Pd1–N1 2.0500(18), Pd1–Cl1 2.2928(7), Pd1–N1A 2.0500(17), Pd1–Cl1A 2.2928(7), C13–N1
1.289(3); N1–Pd1–N1A 180.000(1), N1–Pd1–Cl1A 88.93(6), N1A1–Pd1–Cl1A 191.07(6), N1–Pd1–Cl1 91.07(6), N1A–Pd1–Cl1 88.93(6), Cl1A–Pd1–Cl1 180.00(3), C13–N1–Pd1
117.98(16), C6–N1–Pd1 121.77(15).

Y. Jiang et al. / Inorganica Chimica Acta 376 (2011) 144–151
147
Fig. 3. Molecular structure of 4. Selected bond lengths (Å) and angles (°): Pd1–Cl1 2.2962(10), Pd1–N1 2.042(2), Pd1–N1A 2.042(2), Pd1–Cl1A 2.2962(10), C6–N1 1.451(3);
C1–N1–Pd1 118.33(19), C6–N1–Pd1 123.14(17), N1–Pd1–N1A 180.0, N1–Pd1–Cl1A 90.09(7), N1–Pd1–Cl1 89.91(7), N1A–Pd1–Cl1A 89.91(7), N1A–Pd1–Cl1 90.09(7), Cl1–
Pd1–Cl1A 180.0.
lowering of the chemical shift (downfield) of the CH unit interacting
with Pd. The 1H NMR of compounds 3 and 4 displayed the different
chemical shifts of both methyl protons (1.54 versus 0.81 ppm for 3
and 1.58 versus 0.83 ppm for 4). This non-bonding interaction of CH
with Pd(II) has been studied, which is different from the well-
known agostic CH...Pd interaction that usually leads to up-field
chemical shifts [29,30]. Both, the furyl ring and the thienyl ring
are nearly orthogonal with respect to the diisopropylphenyl ring
with a dihedral angle of 83.7(1)° and 75.7(1)°, respectively.
2.2. Preparation of
Pd(II) complexes
l-N3 and l-SCN bridged dinuclear cyclometallated
Since various coordination modes in pseudohalide ligands such
as N3 and SCN also belongs to our interest preparation of di- -N3
bridged and di- -SCN bridged cyclometallated Pd(II) complexes
[Pd(C6H4CH@NC6H3-2,6-i-Pr2)( -N3)]2 (5), [Pd{(4-MeO)C6H3CH@
NC6H3-2,6-i-Pr2}( -N3)]2 (6), [Pd(C6H4CH@NC6H3-2,6-i-Pr2)( -SC
N)]2 (7) and [Pd{(4-MeO)C6H3CH@NC6H3-2,6-i-Pr2}( -SCN)]2 (8)
l
l
l
l
l
l
Table 1
X-ray data collection and structure refinement.
2
3
4
5
7
Formula
Formula weight
T (K)
Crystal size (mm)
Crystal system
Space group
a (Å)
C
40H48Cl2N2O2Pd2
C34H42Cl2N2O2Pd
688.00
293(2)
0.37 ꢂ 0.32 ꢂ 0.27
monoclinic
C2/c
24.757(4)
9.0386(16)
15.166(4)
90
97.359(18)
90
3365.7(12)
4
1.358
0.741
C34H42Cl2N2PdS2
720.12
293(2)
0.30 ꢂ 0.26 ꢂ 0.21
ticlinic
P21/n
9.1304(18)
13.845(3)
14.119(3)
90.00
92.79(3)
90.00
1782.7(6)
2
1.342
0.812
C38H44N8Pd2
825.61
293(2)
0.31 ꢂ 0.25 ꢂ 0.21
monoclinic
P21/c
11.179(2)
10.436(2)
16.564(3)
90.00
104.35(3)
90.00
1872.1(6)
2
1.465
0.988
C40H44N4Pd2S2
857.71
293(2)
872.50
293(2)
0.30 ꢂ 0.26 ꢂ 0.22
0.30 ꢂ 0.26 ꢂ 0.21
triclinic
ticlinic
ꢀ
ꢀ
P1
P1
12.601(3)
13.411(3)
13.767(3)
92.47(3)
116.88(3)
105.20(3)
1966.9(8)
2
10.812(2)
11.100(2)
18.401(4)
84.33(3)
87.96(3)
61.56(3)
1932.2(7)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢀ3
)
1.470
1.085
1.474
1.071
l
(mmꢀ1
)
F(0 0 0)
884
1424
744
840
872
Tmin
Tmax
0.7367
0.7963
15 794
7052
443
0.644
0.7716
0.8261
4028
3313
188
0.7928
0.8480
13 961
3201
191
0.608
0.755
0.827
14 565
3373
221
0.7394
0.8261
15 443
6916
436
1.522
Number of reflections measured
Number of unique reflections
Number of parameters refined
Maximum in
Minimum in
D
q
(e Åꢀ3
(e Åꢀ3
)
)
0.240
0.912
D
q
ꢀ0.379
ꢀ0.329
ꢀ0.438
ꢀ1.004
ꢀ1.453
Goodness-of-fit (GOF) on F2
1.083
1.021
1.082
1.155
1.193
R (I > 2
r
(I))
wR2 (I > 2
R (all data)
0.0307
0.0737
0.0482
0.0843
0.0281
0.0688
0.0389
0.0743
0.0308
0.0795
0.0386
0.0867
0.0373
0.0867
0.0736
0.1405
0.0576
0.1491
0.1086
0.2366
a
r
(I))
a
wR2 (all data)
[w(F2o ꢀ F2c )2]/
R .
[w(F2o)2]1/2
a
wR2
=
R

148
Y. Jiang et al. / Inorganica Chimica Acta 376 (2011) 144–151
N
N
R
N
N
NaN3
R = H, 5;
HC
R
Pd
Pd
R
CH
R = OMe, 6
CH2Cl2/CH3OH
N
N
N
N
Cl
N
HC
R
Pd
Pd
CH
Cl
N
R
NH4SCN
N
SCN
NCS
R = H, 7;
R = H, 1;
R = OMe, 2
HC
R = OMe, 8
Pd
Pd
CH
CH2Cl2/CH3OH
N
R
Scheme 3. Synthesis of di-
l
-N3 bridged and di-
l
-SCN bridged cyclometallated Pd(II) complexes.
by means of metathesis using complex 1 or 2 was performed, see
Scheme 3.
Single crystals of 5 and 7 suitable for X-ray diffraction analysis
were obtained from a dichloromethane/hexane solution. Figs. 4
and 5 show the molecular structure of 5 and 7, respectively. Details
on crystal data, intensity collection, and refinement details are gi-
ven in Table 1. As shown in Fig. 4, in complex 5 each of two azido
groups bridges with two Pd atoms through the same nitrogen cre-
ating a four-membered ring. Each palladium center adopts square
planar coordination geometry with two cyclometallated ligands in
a trans arrangement with respect to the Pdꢁ ꢁ ꢁPd axis, which is sim-
ilar to those of complex 2. The Pdꢁ ꢁ ꢁPd distance (3.268 Å) excludes
the possibility of a metal–metal bond. The five-membered chelate
ring defined by Pd1, N1, C13, C14 and C15 is essentially planar with
atomic displacements not exceeding 0.0357 Å, to which the diiso-
propylphenyl ring is nearly perpendicular with a dihedral angle
84.4(1)°. The azido group is essentially linear with the bond angle
of 179.0(10)°. The Pd1–C15 bond (1.983(6) Å) is slightly longer
Recently, Kim and co-workers reported on l-N3 bridged cyclo-
metallated Pd(II) complexes containing C,N-chelating ligands, e.g.
2-(20-thienyl)pyridine, azobenzene, 3,30-dimethyl azobenzene,
N,N0-dimethylbenzylamine, 2-phenylpyridine [27]. However, it
was found difficult to purify and structurally characterize those
complexes due to their poor solubility in organic solvents. Com-
plexes 5, 6, 7 and 8 were characterized by spectroscopic and ele-
mental analysis and the molecular structure of 5 and 7 were
determined by single crystal X-ray analysis. The formation of com-
plexes 5 and 6 were readily confirmed by a characteristic stretch
vibration band at 2062 cmꢀ1 assigned to the bridged N3 group.
The formation of complexes 7 and 8 was readily confirmed by
two characteristic stretch vibrations, at 2142 and 2150 cmꢀ1 as-
signed to the bridged SCN group.
Fig. 4. Molecular structure of 5. Selected bond lengths (Å) and angles (°): Pd1–N1 2.037(5), Pd1–N2A 2.048(5), Pd1–N2 2.166(5), Pd1–C15 1.983(6), N2–N3 1.202(7), N3–N4
1.164(8); N3–N2–Pd1 127.3(5), Pd1–N2–Pd1A, 101.7(2), N4–N3–N2 179.0(10), C15–Pd1–N1 80.9(2), C15–Pd1–N2A 100.2(2), N1–Pd1–N2A 178.3(2), C15–Pd1–N2 177.3(2),
N1–Pd1–N2 100.5(2), N2–Pd1–N2A 78.3(2).

Y. Jiang et al. / Inorganica Chimica Acta 376 (2011) 144–151
149
Fig. 5. Molecular structure of 7. Selected bond lengths (Å) and angles (°): Pd1–N1 2.066(7), Pd1–N2A 2.081(9), Pd1–S1 2.320(3), Pd1–C1 1.982(10), N2A–C20A 1.159(13),
C20A–S1A 1.660(11); C1–Pd1–N1 82.2(3), N1–Pd1–N2A 93.5(3), C1–Pd1–S1 89.7(3), N1–Pd1–S1 171.8(2), C1–Pd1–N2 174.2(3), N2A–Pd1–S1 94.7(2), N2–C20–S1 178.7(10).
than in 2 (1.971(4) Å) and shorter than the calculated value of
2.05 Å based on the sum of the covalent radii of carbon and
palladium. The Pd1–N2 bond (2.166(5) Å) and Pd1–N2A bond
(2.048(5) Å) are longer than those found for the related complex
[Pd2(N3)6]2ꢀ ((2.016(11) Å) and (1.993(11) Å)) [31].
300 spectrophotometer in CDCl3 and TMS was applied as an inter-
nal standard. IR spectra were recorded on a Niclolet AVATAR 330
FT-IR spectrometer. Elemental analyses were performed on a Ther-
mo Flash EA1112 Analyzer.
Fig. 5 reveals that both SCN groups bridges two Pd atoms
through both S and N atoms forming an eight-membered ring in
7. The molecular of 7 shows a slightly distorted square-planar
coordination around the Pd center. The eight-membered hetero-
atom ring is non-planar. The distance from Pd to the plane defined
by S1, C20, N2, N2A, C20A, S1A measures 0.3064 Å. The thiocyanato
group is basically linear with the bond angle of 178.7(10)°. The
Pdꢁ ꢁ ꢁPd separation is 5.587(2) Å due to the bridging SCN group to
excluding any Pdꢁ ꢁ ꢁPd interaction. The length of Pd–C bond is sim-
ilar to the length found in 5 and Pd–N1 bond is longer than mea-
sured in 5.
3.2. Preparations
2,6-Diisopropyl-N-(benzylidene)aniline (L1). To a stirred solution
of benzaldehyde (1.1 mL, 10.6 mmol) in dried ethanol (15 mL),
2,6-diisopropylaniline (2.0 mL, 10.6 mmol) and formic acid (two
drops) were added. The reaction mixture was stirred for 24 h at
room temperature. Subsequently, the resulting solution was
concentrated to dryness resulting in an oily substance, which
was dissolved in hexane and cooled to ꢀ20 °C overnight to afford
pale green crystals of L1 (2.1 g, 78%). IR (KBr, cmꢀ1): 1636 (
mC@N);
m.p. : 58–60 °C; 1H NMR (300 MHz in CDCl3, d): 8.19 (s, 1H, –
CH@N), 7.93–7.89 (m, 2H, Ar), 7.52–7.49 (m, 3H, Ar), 7.17–7.10
(m, 3H, Ar), 2.98 (hepta, 2H, –CH), 1.17 (d, 12H, –CH3). Anal. Calc.
for C19 H23N: C, 85.99; H, 8.74; N, 5.28. Found: C, 86.01; H, 8.81;
N, 5.19%.
In summary, l-chloro bridged dinuclear cyclometallated Pd(II)
complexes were prepared by reaction of Na2PdCl4 with benzylide-
neaniline. However, the reaction of Na2PdCl4 with Schiff-base
ligands bearing a five-membered heteroatom ring only resulted
in mononuclear non-cyclometallated Pd(II) species.
2,6-Diisopropyl-N-(4-methoxybenzylidene)aniline (L2, 77%), 2,
6-diisopropyl-N-(2-furylmethylidene)aniline (L3, 76%) and 2,6-
diisopropyl-N-(2-thienyl methylidene)aniline (L4, 71%) were pre-
pared in a similar manner.
Di-
complexes were synthesized by means of metathesis of the corre-
sponding -chloro bridged cyclometallated Pd(II) complex with an
excess of NaN3 or NH4SCN. The molecular structures of -N3
bridged and -SCN bridged cyclometallated Pd(II) complexes con-
l-N3 bridged and di-l-SCN bridged cyclometallated Pd(II)
l
L2: White crystals: IR (KBr, cmꢀ1): 1643 (
mC@N); m.p.: 109–
l
110 °C; 1H NMR (300 MHz in CDCl3, d): 8.12 (s, 1H, –CH@N), 7.86
(d, 2H, Ar), 7.17–7.10 (m, 3H, Ar), 7.04–7.00 (m, 2H, Ar), 3.89 (s,
3H, –OCH3), 2.99 (hepta, 2H, –CH), 1.17 (d, 12H, –CH3). Anal. Calc.
for C20H25NO: C, 81.31; H, 8.53; N, 4.74. Found: C, 81.35; H, 8.53;
N, 4.64%.
l
firmed that the azido group bridged two palladium atoms through
the same nitrogen atom and the thiocyanato group bridged two
palladium atoms through both S and N atoms. Further studies
are in progress to explore applicability of these cyclometallated
Pd(II) complexes as building blocks toward supramolecular
construction.
L3: Pale yellow crystals: IR (KBr, cmꢀ1): 1633 (
mC@N); m.p.:
55–56 °C; 1H NMR (300 MHz in CDCl3, d): 7.98 (s, 1H, –CH@N),
7.64 (s, 1H, furyl), 7.17–7.10 (m, 3H, Ar), 6.95 (d, 1H, furyl), 6.59–
6.57 (m, 1H, furyl), 3.00 (hepta, 2H, –CH), 1.17 (d, 12H, –CH3). Anal.
Calc. for C17H21NO: C, 79.96; H, 8.29; N, 5.49. Found: C, 80.10; H,
8.23; N, 5.56%.
3. Experimental
3.1. General, materials and measurements
L4: Pale yellow crystals: IR (KBr, cmꢀ1): 1627 (
mC@N); m.p.:
48–49 °C; 1H NMR (300 MHz in CDCl3, d): 8.27 (s, 1H, –CH@N),
7.53 (d, 1H, thienyl), 7.43 (d, 1H, thienyl), 7.17–7.06 (m, 4H, Ar, thi-
enyl), 3.00 (hepta, 2H, –CH), 1.17 (d, 12H, –CH3). Anal. Calc. for
All manipulations of air-sensitive compounds were performed
under inert atmosphere using standard Schlenk techniques. All sol-
vents were purified and degassed before use. Other reagents were
used as supplied. 1H NMR spectra were obtained using a Mercury-
C17H21NS: C, 75.23; H, 7.80; N, 5.16. Found: C, 75.05; H, 8.07;
N, 5.02%.

150
Y. Jiang et al. / Inorganica Chimica Acta 376 (2011) 144–151
[Pd(C6H4CH@NC6H3-2,6-i-Pr2)(l-Cl)]2 (1), [Pd{(4-OMe)C6H3CH
[Pd(C6H4CH@NC6H3-2,6-i-Pr2)(l-SCN)]2 (7) and [Pd{(4-MeO)C6H4
@NC6H3-2,6-i-Pr2}(l-Cl)]2 (2), [Pd(C4H3OCH@NC6H3-2,6-i-Pr2)2Cl2]
CH@NC6H3-2,6-i-Pr2}( -SCN)]2 (8). To a 10 mL CH2Cl2 solution of
l
(3) and [Pd(C4H3SCH@NC6H3-2,6-i-Pr2)2Cl2] (4). To
a
20 mL
complex 1 (0.0980 g, 0.12 mmol) was added NH4SCN (0.0380 g,
0.50 mmol) solution dissolved in 2 mL methanol. The initial yellow
solution turned to a yellow suspension. After stirring for 18 h at
room temperature, the solvent was completely evaporated. The
resulting residue was dissolved in CH2Cl2 and insoluble material
was filtered out. The filtrate was evaporated to remove the solvent
completely and the obtained yellow solid was recrystallized from a
CH2Cl2/hexane solution to give yellow crystals of [Pd(C6H4CH@
methanol solution of Na2PdCl4 (0.500 g, 1.70 mmol) was added
2,6-diisopropyl-N-(benzylidene)aniline (0.901 g, 3.40 mmol) and
sodium acetate (0.279 g, 3.40 mmol). After stirring for 6 h at room
temperature, the dark green solids were filtered off and washed
with distilled water and ether. The crude product was dissolved
in CH2Cl2 and filtered, removing the insoluble materials. Evaporat-
ing the solvent a yellow solid was obtained that was recrystallized
from CH2Cl2/hexane to give yellow crystals of [Pd(C6H4CH@NC6H3-
NC6H3-2,6-i-Pr2)(
l
-SCN)]2 (7, 0.0875 g, 85%). IR (KBr, cmꢀ1): 1602
2,6-i-Pr2)(
l
-Cl)]2 (1, 0.573 g, 83%). IR (KBr, cmꢀ1): 1601 (
m
C@N); 1H
(m
C@N), 2142 (
m
SCN); 1H NMR (300 MHz in CDCl3, d): 7.83 (s, 2H,
NMR (300 MHz in CDCl3, d): 7.74 (s, 2H, –CH@N), 7.33–7.27 (m, 4H,
Ar), 7.23–7.14 (m, 6H, Ar), 7.08–7.03 (m, 4H, Ar), 3.51 (hepta, 4H, –
CH), 1.38 (d, J = 6.6 Hz, 12H, –CH3), 1.14 (d, J = 6.9 Hz, 12H, –CH3).
Anal. Calc. for C38H44Cl2N2Pd2: C, 56.17; H, 5.46; N, 3.45. Found:
C, 56.19; H, 5.48; N, 3.27%.
–CH@N), 7.35 (m, 2H, Ar), 7.29 (d, J = 8.1 Hz, 2H, Ar), 7.20 (d, J =
7.5 Hz, 4H, Ar), 7.10 (m, 4H, Ar), 6.91 (m, 2H, Ar), 3.40 (hepta,
4H, –CH), 1.36 (d, J = 6.6 Hz, 12H, –CH3), 1.15 (d, J = 6.9 Hz, 12H,
–CH3). Anal. Calc. for C40H44N4Pd2S2: C, 56.01; H, 5.17; N, 6.53; S,
7.48. Found: C, 55.92; H, 5.10; N, 6.51; S, 7.32%.
Complexes 2, 3 and 4 were prepared in a similar manner as
complex 1.
Complex 8 was prepared in similar manner.
[Pd{(4-MeO)C6H3CH@NC6H3-2,6-i-Pr2}(
l-SCN)]2 (8, 79%): IR (KBr,
[Pd{(4-OMe)C6H3CH@NC6H3-2,6-i-Pr2}(
l
-Cl)]2 (2, 55%): IR (KBr,
cmꢀ1): 1599 ( SCN); 1H NMR (300 MHz in CDCl3, d):
m
C@N), 2150 (
m
cmꢀ1): 1600 ( C@N); 1H NMR (300 MHz in CDCl3, d): 7.61 (s, 2H,
m
7.68 (s, 2H, –CH@N), 7.28 (m, 2H, Ar), 7.17 (d, J = 7.8 Hz, 4H, Ar),
7.08 (m, 2H, Ar), 6.58 (dd, J = 2.4 Hz, 2H, Ar), 6.41 (d, J = 2.4 Hz,
2H, Ar), 3.77 (s, 6H, –OCH3), 3.38 (hepta, 4H, –CH), 1.34 (d,
J = 6.9 Hz, 12H, –CH3), 1.12 (d, J = 6.9 Hz, 12H, –CH3). Anal. Calc.
for C42H48N4Pd2S2ꢁ0.5CH2Cl2: C, 54.99; H, 5.32; N, 6.04; S, 6.91.
Found: C, 55.06; H, 5.44; N, 6.05; S, 6.56%.
–CH@N), 7.26–7.14 (m, 8H, Ar), 6.71 (d, 2H, Ar), 6.58 (d,
J = 8.4 Hz, 2H, Ar), 3.73 (s, 6H, –OCH3), 3.52 (hepta, 4H, –CH),
1.38 (d, J = 6.9Hz, 12H, –CH3), 1.14 (d, J = 6.6 Hz, 12H, –CH3). Anal.
Calc. for C40H48Cl2N2O2Pd2: C, 55.06; H, 5.54; N, 3.21. Found: C,
54.61; H, 5.35; N, 3.13%.
[Pd(C4H3OCH@NC6H3-2,6-i-Pr2)2Cl2] (3, 79%): IR (KBr, cmꢀ1):
1616 (
m
C@N); 1H NMR (300 MHz in CDCl3, d): 9.13 (s, 2H, –HC@N),
3.3. X-ray structure determination
7.44 (s, 2H, furyl), 7.33 (m, 2H, Ar), 7.20 (d, J = 7.8 Hz, 4H, Ar), 6.25
(m, 2H, furyl), 5.26 (br, 2H, furyl), 3.44 (hepta, 4H, –CH), 1.54 (d,
J = 6.6 Hz, 12H, –CH3), 0.81 (d, J = 6.9Hz, 12H, –CH3). Anal. Calc.
for C34H42Cl2N2O2Pd: C, 59.35; H, 6.15; N, 4.07. Found: C, 59.60;
H, 6.14; N, 4.15%.
Suitable crystals for X-ray analysis of 2, 3, 4, 5 and 7 were ob-
tained by recrystallization from CH2Cl2/hexane. X-ray data of the
complexes were collected on a D-MAX 2200 VPC diffractometer.
All the determinations of unit cell and intensity data were per-
[Pd(C4H3SCH@NC6H3-2,6-i-Pr2)2Cl2] (4, 87%): IR (KBr, cmꢀ1):
formed with graphite-monochromated Mo
0.71073 Å). All data were collected at room temperature using
the -scan technique. Details of the data collection and refinement
Ka radiation (k =
1596 (m
C@N); 1H NMR (300 MHz in CDCl3, d): 9.36 (s, 2H, –HC@N),
7.44–7.36 (m, 6H, Ar), 7.25 (d, J = 3.9 Hz, 4H, thienyl), 6.96 (t,
J = 4.5 Hz, 2H, thienyl), 3.42 (hepta, 4H, –CH), 1.58 (d, J = 6.9 Hz,
12H, –CH3), 0.83 (d, J = 7.2 Hz, 12H, –CH3). Anal. Calc. for
x
are summarized in Table 1. All calculations were carried out with
the SHELXL-97 programs [32]. The structures were solved by direct
methods. The non-hydrogen atoms were refined with anisotropic
thermal parameters by using full-matrix least-squares methods.
C34H42Cl2N2PdS2: C, 56.70; H, 5.88; N, 3.89; S, 8.90. Found: C,
56.43; H, 6.01; N, 3.93; S, 8.76%.
[Pd(C6H4CH@NC6H3-2,6-i-Pr2)(l-N3)]2 (5 ) and [Pd{(4-MeO)C6
H3CH@NC6H3-2,6-i-Pr2}(l-N3)]2 (6). To a 10 mL CH2Cl2 solution of
Acknowledgments
complex (0.101 g, 0.12 mmol) was added NaN3 (0.033 g,
1
0.51 mmol) solution dissolved in 4 mL methanol. The initial yellow
solution turned to a yellow suspension. After stirring for 20 h at
room temperature, the solvent was completely evaporated. The
resulting residue was dissolved in CH2Cl2 and insoluble material
was filtered out. The filtrate was evaporated to remove solvents
completely to give yellow solids, which were recrystallized from
CH2Cl2/hexane to give yellow crystals of [Pd(C6H4CH@NC6H3-2,6-
This work was supported by the Project Sponsored by the Scien-
tific Research Foundation for the Returned Overseas Chinese Schol-
ars, State Education Ministry (2008), by the Scientific Research
Foundation funded by Liaoning Provincial Education Department
of China [No. 2008T073] and by the Scientific Research Foundation
funded by Liaoning University of China for young scholar [No.
2007LDQN04].
i-Pr2)(
l
-N3)]2 (5, 0.0710 g, 72%). IR (KBr, cmꢀ1): 1600 (
N@N@N); 1H NMR (300 MHz in CDCl3, d): 7.75 (s, 2H, –CH@
mC@N),
2062 (
m
Appendix A. Supplementary material
N), 7.34 (m, 4H, Ar), 7.26 (d, J = 6.9 Hz, 4H, Ar), 7.15 (m, 4H, Ar),
6.99 (d, J = 6.9 Hz, 2H, Ar), 3.51 (hepta, 4H, –CH), 1.46 (d, J = 6.6
Hz, 12H, –CH3), 1.18 (d, J = 6.6 Hz, 12H, –CH3). Anal. Calc. for C38
H44N8Pd2: C, 55.28; H, 5.37; N, 13.57. Found: C, 55.16; H, 5.31;
N, 13.13%.
CCDC 806544 contains the supplementary crystallographic data
for 2, 3, 4, 5 and 7. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/deposit. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.ica.2011.06.003.
Complex 6 was prepared in a similar manner.
[Pd{(4-MeO)C6H3CH@NC6H3-2,6-i-Pr2}(
l-N3)]2 (6, 71%): IR (KBr,
cmꢀ1): 1598 ( N@N@N); 1H NMR (300 MHz in CDCl3,
mC@N), 2062 (
m
d): 7.61 (s, 2H, –CH@N), 7.32–7.21 (m, 8H, Ar), 6.63 (dd, J = 2.4,
2.1 Hz, 4H, Ar), 6.53 (d, 2H, J = 2.1 Hz, Ar), 3.75 (s, 6H, –OCH3),
3.53 (hepta, 4H, –CH), 1.45 (d, J = 6.6 Hz, 12H, –CH3), 1.18 (d, J =
6.9 Hz, 12H, –CH3). Anal. Calc. for C40H48N8O2Pd2: C, 54.24; H,
5.46; N, 12.65. Found: C, 54.26; H, 5.53; N, 12.50%.
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