Thiosemicarbazonates of palladium(II): The presence of methyl/phenyl substituents (R2) at C2 carbon atom induces C-H activation of R1 rings of thiosemicarbazones {R1R2C 2N3-N<sup

Article abstract of DOI:10.1016/j.jorganchem.2011.11.028

A series of palladium(II) complexes involving C-H and N-H bond activations of the R¹ rings of thiosemicarbazones {R¹(R ²)C²-N³-N²(H)-C¹(S)- N¹HR³; R¹

Full text of DOI:10.1016/j.jorganchem.2011.11.028

Journal of Organometallic Chemistry 701 (2012) 17e26
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Thiosemicarbazonates of palladium(II): The presence of methyl/phenyl
substituents (R2) at C2 carbon atom induces CeH activation of R1 rings
of thiosemicarbazones {R1R2C2]N3eN2HeC1(]S)eN1HR3}
,
a
b
c
c
Tarlok S. Lobana a , Poonam Kumari , Ray J. Butcher , Takashiro Akitsu , Yoshikazu Aritake ,
*
Josefina Perles d, Francisco J. Fernandez e, M. Cristina Vega e
a Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India
b Department of Chemistry, Howard University, Washington DC 20059, USA
c Department of Chemistry, Tokyo University of Science, Tokyo 1628601, Japan
d Facultad de Ciencias Químicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
e Department of Structural and Quantitative Biology, Center for Biological Research (CIBeCSIC), Ramiro de Maeztu 9, E-28040 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
A series of palladium(II) complexes involving CeH and NeH bond activations of the R1 rings of thio-
semicarbazones {R1(R2)C2eN3eN2(H)eC1(]S)eN1HR3; R1, R2: thiopheneyl, Me, H2L1 (R3 ¼ Me), H2L2
(R3 ¼ Ph); R1, R2: Ph, Me, H2L3 (R3 ¼ Me), H2L4 (R3 ¼ Ph); R1, R2: Ph, Ph, H2L5 (R3 ¼ Me), H2L6 (R3 ¼ Ph)
and R1, R2: pyrrole, Me, H2L7 (R3 ¼ Me), H2L8 (R3 ¼ Ph)} are described. Methyl group (R2) at C2 carbon in
H2L1 and H2L2 induced CeH bond activation of the thiopheneyl ring and formed cyclometallated
complexes, [Pd(k3eC4,N3,SeL)(PPh3)] (L ¼ L1, 1; L2, 2). Similarly, phenyl rings (R1) in H2L3, H2L4, H2L5, H2L6
at C2 carbon have shown CeH activations forming cyclometallated complexes, [Pd(k3eC4,N3,SeL)(PPh3)]
(L ¼ L3, 3; L4, 4; L5, 5; L6, 6). However, pyrrole ring did not exhibit similar CeH activation behavior, rather
involved NeH activation and formed complexes, [Pd(k3eN4,N3,SeL)(PPh3)] {L ¼ L7, 7; L8, 8}. All these
complexes have been characterized with the help of analytical data, spectroscopic techniques (IR, 1H and
31P NMR), and single crystal X-ray crystallography (1, 2, 4, 5, 7 and 8). The thiosemicarbazone ligands
behave as dinegative C4, N3, S-chelating in 1e6 and N4, N3, S-chelating in complexes 7 and 8. Interest-
ingly, complexes 2, 4 and 8, with phenyl substituent at N1 atom, have two independent molecules in their
respective crystal lattices.
Article history:
Received 8 July 2011
Received in revised form
14 November 2011
Accepted 22 November 2011
Keywords:
Palladium(II)
2-AcetylthiopheneyleN1emethyl
thiosemicarbazone
2-AcetylpyrroleeN1ephenyl
thiosemicarbazone
Triphenyl phosphine
Cyclometallation
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
agents, Pd(II) thiosemicarbazones have been shown to act upon
viral DNA without causing cell apoptosis (Kovala-Demertzi et al.,
The intramolecular activation of aromatic CeH bonds of
coordinated ligands by transition metals represents an active area
of research due to their applications in organic and organome-
tallic synthesis, as active catalysts, as liquid crystals, as analytical
tools and for the design of metal complexes with promising
anticancer or photochemical properties [1e11]. The coordination
chemistry of thiosemicarbazones (I, Chart 1) has invited consid-
erable interest in view of their variable donor ability, structural
diversity, analytical and biological applications [12]. Palladium(II)
complexes with thiosemicarbazones have been particularly
interesting because of their antitumor, antibacterial, antifungal
and catalytic activities [13e27]. As alternative antiherpes simplex
2007), whereas as a tumor antiproliferative drug, a Pd phenan-
threnequinone thiosemicarbazone appears to elicit apoptotic
effects upon breast and other cancer cells (Padhye et al., 2005;
Ferraz et al., 2007). Chart 1 depicts complexes in which R1
substituent at C2 carbon of thiosemicarbazones involves CeH
bond activation forming cyclopalladated complexes [28e36]. It
may be noted that the methyl/ethyl groups (R2) at C2 carbon or
the presence of Cl substituent in the phenyl group (R1) appears to
be necessary for the activation of CeH bonds of the aromatic
rings.
In view of our interest in coordination chemistry of thio-
semicarbazones, we have observed that the substituents at C2 and
N1 influence the type of the product [12,37,38]. For example, the
furan-2-carbaldehyde thiosemicarbazones, namely, C4H3O(R2)
C2eN3eN2(H)eC1(]S)eN1HR3 with NiII formed trans square planar
complexes when R3 substituents at N1 were Me and Et and a cis
* Corresponding author. Fax: þ91 183 2 258820.
E-mail address: tarlokslobana@yahoo.co.in (T.S. Lobana).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.11.028

18
T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
2. Experimental
S
N3
1
N2H
I
R1
S
C
C2
3
N
PdCl2, 2-acetylthiopheneyl, 2-acetylpyrrole, acetophenone,
2
N1HR3
benzophenone, PPh3, N-methyl-, and N-phenyl- thio-
semicarbazides were procured from Aldrich Sigma Ltd. The thio-
semicarbazone ligands were prepared by the reported methods
[42]. Trans-PdCl2(PPh3)2 was prepared by reacting a solution of
PdCl2 in CH3CN with 2 mol of PPh3 [43]. Elemental analysis for C, H
and N were carried out using a thermoelectron FLASHEA1112
analyzer. The melting points were determined with a Gallenkamp
electrically heated apparatus. The IR spectra were recorded using
KBr pellets on a Varian 666-IR FTeIR spectrometer. Nuclear
Magnetic Resonance (NMR) spectra were recorded on a JEOL AL300
FT (1H NMR at 300 MHz in CDCl3 with TMS as the internal refer-
ence, 31P NMR spectra were recorded at 121.5 MHz with 85% H3PO4
as the external reference taken as zero position) and BRUKER
AVANCE II 400 NMR (13C NMR at 100.61 MHz in CDCl3 with TMS as
the internal reference) spectrometers.
Pd
R
4
C
L
C4
Me
C4
C4
C4
C4
R1
Cl
Cl
H
R2
R3
L
Et
Me
Me
Me
Et
H
H
Me
Me
dppm
dppm
MePh2P
PPh3
PPh3
Chart 1.
square planar complex for R3 ¼ Ph, keeping R2 at C2]H substituent
[37]. On changing H by Me (R2), furan ring showed unprecedented
furan ring coordination to NiII and formed octahedral complexes for
all the three R3 substituents (Me, Et, Ph) at N1 atom [38]. The anal-
ogous thiophene-2-carbaldehyde thiosemicarbazones only formed
trans square planar complexes. Further, it was found that for R2 ¼ H,
thiophene-2-carbaldehyde-, pyrrole-2-carbaldehyde- and benzal-
dehyde- thiosemicarbazones (R2 ¼ H, R3 ¼ H) have formed square
planar PdII complexes, [Pd(k2eN3,SeL)(PPh3)Cl], [Pd(k2eN3,SeL)2]
and [Pd(k3eN4,N3,SeL)(PPh3)], with no activation of CeH bond
of the thiopheneyl, pyrrole and phenyl rings [39e41].
It was believed that the presence of methyl or phenyl substit-
uents (R2) at C2 carbon might induce cyclopalladation by changing
electronic and steric properties. The presence of methyl or phenyl
substituents (R3) at N1 nitrogen was expected to alter the donor
properties of thiosemicarbazones by their positive (methyl) or
negative (phenyl) inductive effects. Specifically it was felt that these
substituents might alter chelation through S, N3 or S, N2 donor
atoms along with metalation by R1 ring. Both types of modes of
coordination are well documented in literature [12]. Chart 2 gives
details of various thiosemicarbazones used for their interaction
with palladium(II). The resulting complexes have been character-
ized using analytical data, spectroscopic techniques and X-ray
crystallography.
2.1. Synthesis of [Pd(k3eC4,N3,SeL1)(PPh3)] 1
To trans-PdCl2(PPh3)2 precursor (0.050 g, 0.071 mmol) sus-
pended in toluene (15 mL) was added solid H2L1 (0.014 g,
0.071 mmol), followed by the addition of Et3N base (1 mL). The
mixture was stirred for 3 h during which a clear light orange solution
was formed along with insoluble Et3NHþClꢀ which was filtered and
solution was allowed to evaporate at room temperature. The orange
mass was crystallized in a mixture of dichloromethane and meth-
anol (3:1:v/v) (Yield 68%). M.p. 265e267 ꢁC. Found: C 53.54, H 4.27,
N 7.31; C26H24N3PPdS2 requires: C 53.80, H 4.14, N 7.24 (%). IR bands
(KBr pellets, cmꢀ1):
n
(N1eH) 3414br;
n(CeH) 3040m, 2942m,
2878w; (C]C) 1567m, 1508s;
n
(C]N) þ
n
n
(PeC) 1099s; (CeN)
n
1021s, 996sh, 867s; n d 7.58 (m, o-H(Ph),
(CeS) 759s. 1H NMR (CDCl3):
6H), 7.40 (m, p- and m-H(Ph), 9H), 6.78 (d, C5H,1H), 5.79 (d, C6H,1H),
4.65 (s, br, N1H, 1H), 2.92 (d, CH3(C2), 3H), 2.36 (s, CH3(N1), 3H) ppm.
31P NMR(CDCl3):
d
40.41 ppm, Δ
d
(dcomplex
ꢀ
dPPh3) 45.10 ppm.
Complexes 2, 7 and 8 were prepared similarly.
2.2. Synthesis of [Pd(k3eC4,N3,SeL2)(PPh3)] 2
Yield 70%. M.p. 215e217 ꢁC. Found: C 57.89, H 4.11, N 6.52;
C31H26N3PPdS2 requires: C 57.94, H 4.05, N 6.54 (%). IR bands (KBr
pellets, cmꢀ1):
n
(N1eH) 3385br;
n(CeH) 3053m, 2920m;
n(C]
N) þ
n
(C]C) 1593m, 1493s;
n
(PeC) 1108s; (CeN) 1027s, 990sh,
n
861s; n d 7.64 (m, o-H(Ph), 8H), 7.55 (m,
(CeS) 768s. 1H NMR (CDCl3):
p-H(Ph), 4H), 7.43 (m, m-H(Ph), 8H), 6.92 (q, C5H, 1H), 5.83 (d, C6H,
1H), 6.64 (s, br, N1H,1H), 2.45 (d, CH3(C2), 3H) ppm. 31P NMR(CDCl3):
S
R1
1
C
N2H
d
40.28, 33.34 ppm, Δ
d
(dcomplex
ꢀ
dPPh3) 44.98, 38.04 ppm.
C2
3
N
R2
N1HR3
2.3. Synthesis of [Pd(k3eC4,N3,SeL3)(PPh3)] 3
R1
S
R2
R3
To trans-PdCl2(PPh3)2 precursor (0.050 g, 0.071 mmol) sus-
pended in acetonitrile (15 mL) was added solid H2L3 (0.015 g,
0.071 mmol), followed by the addition of Et3N base (1 mL). The
mixture was stirred for 3 h during which a clear yellow solution was
formed which was filtered and solution was allowed to evaporate at
room temperature. Yellow colored crystals were formed along with
Et3NHþClꢀ (Yield 67%). M.p. 240e242 ꢁC. Found: C 58.50, H 4.57, N
7.29; C28H26N3PPdS requires: C 58.54, H 4.53, N 7.32 (%). IR bands
2-acetylthiophene-N-methylthiosemicarbazone (H2L1)
2-acetylthiophene-N-phenylthiosemicarbazone (H2L2)
Me
Ph
Me
Me
Me Acetophenone-N-methylthiosemicarbazone (H2L3)
Acetophenone-N-phenylthiosemicarbazone (H2L4)
Ph
Ph
Benzophenone-N-methylthiosemicarbazone (H2L5)
Benzophenone-N-methylthiosemicarbazone (H2L6)
Me
Ph
(KBr pellets, cmꢀ1):
n
(N1eH) 3412s;
n
(CeH) 3047m, 2908m,
(PeC) 1097s; (CeN)
(CeS) 751s. 1H NMR (CDCl3):
1062s, 1013m, 825m; n d 7.68 (m, o-
2-acetylpyrrole-N-methylthiosemicarbazone (H2L7)
2-acetylpyrrole-N-phenylthiosemicarbazone (H2L8)
Me
Me
Ph
2878m; (C]C) 1572m, 1504s;
n
(C]N) þ
n
n
n
N
H
H(Ph), 6H), 7.40 (m, p þ m-H(Ph) þ C5H, 10H), 7.07 (dd, C8H, 1H),
Chart 2.
6.85 (tb, C6H, 1H), 6.30 (qd, C7H, 1H), 4.64 (s, br, N1H, 1H), 2.91 (d,

T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
19
CH3(C2), 3H), 2.39 (s, CH3(N1), 3H) ppm. 31P NMR(CDCl3):
39.13 ppm, Δ dcomplex dPPh3) 43.83 ppm.
Complexes 4e6 were prepared similarly.
pellets, cmꢀ1):
n
(N1eH) 3422br;
n
(CeH) 3077m, 2945m, 2897w;
d
d
(
ꢀ
n
(C]N) þ
n
(C]C) 1532s, 1497s; n(PeC) 1099s; n(CeN) 1030s, 813;
n
(CeS) 751s. 1H NMR (CDCl3):
d 7.65 (m, o-H(Ph), 6H), 7.42
(m, p-H(Ph) þ m-H(Ph), 9H), 6.47 (dd, C6H,1H), 5.78 (q, C4H, 1H), 5.63
(q, C5H, 1H), 4.53 (s, br, N1H, 1H), 2.89 (d, CH3(C2), 3H), 2.35
2.4. Synthesis of [Pd(k3eC4,N3,SeL4)(PPh3)] 4
(s, CH3(N1), 3H) ppm. 31P NMR (CDCl3):
d 34.84 ppm, Δd
Yield 67%. M.p. 260e262 ꢁC. Found: C 62.31, H 4.37, N 6.56;
(dcomplex
ꢀ
dPPh3) ¼ 39.54 ppm.
C33H28N3PPdS requires: C 62.26, H 4.40, N 6.60 (%). IR bands
(KBr pellets, cmꢀ1):
n
(N1eH) 3420br;
n
(CeH) 3112m, 3020m;
n(C]
2.8. Synthesis of [Pd(k3eN4,N3,SeL8)(PPh3)] 8
N) þ
n
(C]C) 1599s, 1543s;
n
n
(PeC) 1098sh; (CeN) 1044s, 927sh,
n
(CeS) 758s. 1H NMR (CDCl3):
d 7.75 (m, o-H(Ph), 8H), 7.40
Yield 71%. M.p. 270e272 ꢁC. Found: C 59.48, H 4.37, N 9.01;
800m;
(m, p þ m-H(Ph) þ C5H, 15H), 7.07 (dd, C8H, 1H), 6.85 (tb, C6H, 1H),
C31H27N4PPdS requires: C 59.52, H 4.32, N 8.96 (%). IR bands
6.30 (qd, C7H, 1H), 4.64 (s, br, N1H, 1H), 2.91 (d, CH3(C2), 3H) ppm.
(KBr pellets, cmꢀ1):
n
(N1eH) 3396br;
n(CeH) 3051s, 2997sh;
31P NMR(CDCl3):
d
38.32 ppm, Δ
d
(dcomplex
ꢀ
dPPh3) 43.79 ppm.
n
(C]N) þ
n
(C]C) 1619s, 1480s;
n
(PeC) 1096s; (CeN) 999s, 825s;
n
n
(CeS) 767s. 1H NMR (CDCl3):
d 7.68 (m, o-H(Ph), 8H), 7.53 (m,
2.5. Synthesis of [Pd(k3eC4,N3,SeL5)(PPh3)] 5
p-H(Ph)þm-H(Ph), 12H), 6.90 (t, C6H, 1H), 6.54 (d, C4H, 1H), 6.64
(s, br, N1H, 1H), 5.70 (dd, C5H, 1H), 2.47 (d, CH3(C2), 3H) ppm. 31P
Yield 70%. M.p. 252e254 ꢁC. Found: C 58.45, H 4.49, N 6.63;
C31H29N3PPdS requires: C 58.40, H 4.55, N 6.59 (%). IR bands (KBr
NMR (CDCl3):
d
28.73 ppm, Δ
d
(dcomplex
ꢀ dPPh3) ¼ 34.20 ppm.
pellets, cmꢀ1):
n
(N1eH) 3409br;
n
(CeH) 3013m, 2965m, 2889m;
(PeC) 1097sh; (CeN) 1034s,
2.9. X-ray crystallography
n
(C]N) þ
n
(C]C) 1525s, 1497s;
n
n
916sh;
n
(CeS) 770s. 1H NMR0(CDCl3):
d 7.72 (m, o-H(Ph), 6H), 7.40
Crystals suitable for X-ray diffraction were obtained in dichlor-
omethaneemethanol mixture (1, 2, 7 and 8) or acetonitrile (3e5).
The single crystals of compounds were mounted on Bruker APEX-II
CCD (1e3 and 5) and Xcalibur, Ruby, Gemini (4, 7 and 8) diffrac-
0
0
0
(m, p þ m-H(Ph) þ C5,8H, C4 ,5 ,8 H 15H), 6.73 (d, C7H þ C7 H, 2H),
0
6.45 (q, C6H, 1H), 6.34 (q, C6 H, 1H), 4.70 (s, br, N1H, 1H), 2.70
(d, CH3(N1), 3H) ppm. 31P NMR(CDCl3):
d 39.26 ppm, Δd
(
dcomplex
ꢀ
dPPh3) 43.96 ppm.
tometer, equipped with a graphite monochromator and MoeK
a
radiation ( ¼ 1.54178 Å; 5).
l
¼ 0.71073 Å; 1e4, 7, 8) and CueK
a (l
2.6. Synthesis of [Pd(k3eC4,N3,SeL6)(PPh3)] 6
The unit cell dimensions and intensity data were measured at 296 K
for 1, at 120 K for 2, 100 K for 3 and 5, and 123(2) K for 4, 7 and 8
respectively. The structures were solved by the direct methods, and
refined by the full matrix least square based on F2 with anisotropic
thermal parameters for the non-hydrogen atoms using Bruker
APEX2 (data collection) [44] and Bruker SAINT (cell refinement,
data reduction) [45] (for 1e3 and 5), with experimental absorption
correction by SADABS [Bruker (1998)]. SMART and SADABS Soft-
ware Reference Manuals. Bruker AXS Inc] (for 3 and 5); CrysAlisPro
(cell refinement, data reduction) (for complexes 4, 7 and 8) and
SHELXS-97 (computing structure solution) [46], SHELXL-97
(computing structure refinement) [47] and Bruker SHELXTL
(computing molecular graphics) (for 1e5, 7 and 8) [46]. Table 1
contains crystal data while Table 2 gives some important bond
distances for complexes 1e5, 7 and 8 (For more details see
supplementary material).
Yield 71%. M.p. 270e272 ꢁC. Found: C 61.11, H 4.39, N 5.98;
C36H31N3PPdS requires: C 61.08, H 4.43, N 6.01 (%). IR bands
(KBr pellets, cmꢀ1):
n
(N1eH) 3405br;
n
(CeH) 3015m, 2983m;
n
(C]N)
þ
n
(C]C) 1530s, 1508s;
n
n
(PeC) 1098sh; (CeN)
n
1035s, 897m;
(CeS) 761s. 1H NMR (CDCl3):0 d0 7.82 (m, o-H(Ph),
0
8H), 7.65 (m, p þ m-H(Ph) þ C5,8H, C4 ,5 ,80 H 18H), 6.83 (d,
0
C7H þ C7 H, 2H), 6.50 (q, C6H, 1H), 6.48 (q, C6 H, 1H), 4.78 (s, br,
N1H, 1H) ppm. 31P NMR(CDCl3):
d
¼
39.12 ppm,
Δd
(
dcomplex
ꢀ
dPPh3) ¼ 44.59 ppm.
2.7. Synthesis of [Pd(k3eN4,N3,SeL7)(PPh3)] 7
Yield 69%. M.p. 248e250 ꢁC. Found: C 55.39, H 4.49, N 9.98;
C26H25N4PPdS requires: C 55.42, H 4.44, N 9.95 (%). IR bands (KBr
Table 1
Crystal data for complexes 1e5, 7 and 8.
1
2
3
4
5
7
8
Empirical formula
M
C
26H24N3PPdS2
C31H26N3PPdS2
642.04
C28H26N3PPdS
573.95
C33H28N3PPdS
636.01
C33H28N3PPdS
636.01
C26H25N4PPdS
562.93
C31H27N4PPdS
625
579.97
T(K)
296
120
100(2)
123(2)
100(2)
123(2)
123(2)
Crystal system
Space group
a(Å)
b(Å)
c(Å)
Triclinic
Pꢀ1
Triclinic
Pꢀ1
Triclinic
Pꢀ1
Triclinic
Pꢀ1
Monoclinic
P21/n
15.539(3)
11.998(2)
16.061(3)
90.00
107.57(3)
90.00
2854.8(10)
4
Triclinic
Pꢀ1
Triclinic
Pꢀ1
9.6725(15)
9.9409(15)
14.254(2)
75.895(2)
77.727(2)
71.428(2)
1246.4(3)
2
9.8863(11)
11.5707(13)
13.2194(15)
89.3930(10)
68.5090(10)
77.3960(10)
1369.1(3)
2
9.6256(8)
9.9786(8)
14.2636(12)
76.129(2)
76.904(2)
72.251(2)
1249.18
2
11.6179(3)
14.6215(4)
17.5722(4)
106.289(2)
100.600(2)
92.455(2)
2802.16(12)
4
9.5814(3)
9.9057(3)
14.0255(4)
75.948(2)
77.968(3)
71.729(3)
1213.51(6)
2
11.5352(2)
14.4837(3)
17.6115(4)
107.409(2)
100.579(2)
94.373(2)
2732.77(10)
4
a
(ꢁ)
(ꢁ)
b
g
(ꢁ)
V(Å3)
Z
Dcalcd (g cmꢀ3
)
1.545
0.996
1.557
0.915
1.529
7.54
1.508
0.822
1.482
6.663
1.541
0.939
1.519
0.842
m
(mmꢀ1
)
Reflections collected
7465
8156
24 915
38 804
19 607
15 090
42 377
Independent reflections
5349 [R(int)
¼ 0.0202]
R1 ¼ 0.0419,
wR2 ¼ 0.1284
6824 [R(int)
¼ 0.0164]
R1 ¼ 0.0318,
wR2 ¼ 0.1015
4488 [R(int)
¼ 0.0217]
R1 ¼ 0.0192,
wR2 ¼ 0.0509
18 522 [R(int)
¼ 0.0397]
R1 ¼ 0.0623,
wR2 ¼ 0.1420
4578 [R(int)
¼ 0.0213]
R1 ¼ 0.0208,
wR2 ¼ 0.0539
7982 [R(int)
¼ 0.0262]
R1 ¼ 0.0196,
wR2 ¼ 0.0496
18 260 [R(int)
¼ 0.0375]
R1 ¼ 0.0333,
wR2 ¼ 0.0687
final R indices[I > 2s(I)]

20
T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
Table 2
Comparison of bond lengths (Å) and angles (ꢁ) of complexes 1e5, 7 and 8.
Complex no.
PdeC4/N4
PdeN
PdeS
PdeP
1
2
3
4
5
7
8
2.026(5)
2.050(14), 2.036(12)
2.0390(19)
2.036(4), 2.103(2)
2.3335(7)
2.0468(15)
2.034(4)
2.045(13), 2.029(14)
2.0283(16)
2.038(3), 2.058(3)
2.0285(17)
2.0179(14)
2.3237(15)
2.333(4), 2.320(4)
2.3347(5)
2.3225(9), 2.3014(10)
2.3335(7)
2.2668(5)
2.2417(14)
2.239(4), 2.241(4)
2.2489(5)
2.2592(9), 2.2554(10)
2.2466(6)
2.2607(4)
2.0444(16), 2.0626(17)
2.0200(15), 2.0209(16)
2.2511(5), 2.2537(5)
2.2646(5), 2.2641(5)
SePdeN
C4/N4ePdeN
C4/N4ePdeS
NePdeP
1
2
3
4
5
7
8
82.34(14)
83.4(4), 81.3(4)
83.18(5)
82.80(9)
83.41(5)
81.5(2)
82.1(5), 80.4(5)
81.15(7)
81.41(13)
81.39(8)
163.78(16)
165.4(4), 161.5(4)
164.27(5)
164.02(11)
164.35(6)
173.85(13)
173.7(3), 176.1(4)
173.54(5)
176.69(9)
178.44(5)
83.72(4)
83.63(5), 83.19(5)
80.50(6)
80.46(7), 80.90(7)
164.21(4)
163.81(5), 164.06(5)
174.98(4)
176.17(5), 175.26(5)
3. Result and discussion
3.2. Molecular structures
The crystal structure of complex [Pd(k3eC19,N1,S2eL1)(PPh3)] 1
3.1. Synthesis and IR spectroscopy
has shown that PdII is bonded to one thio- ligand through its C19, N1
and S2- donor atoms and one PPh3 ligand (Fig. 1). Thus the H2L1
ligand is dinegative tridentate after metalation through C4 carbon
of thiopheneyl ring and deprotonation of eN2H group (C4, N3, S-
donor atoms). The Pd(1)eC(19) bond distance {2.026(5) Å} is
similar to 2.033(5) Å found in cyclometallated [Pd{C6H4C(Et)]
NeN]C(S)eNH2}(PMePh2)] complex [33]. This PdeC bond
distance is slightly shorter than the sum of their covalent radii
{2.07 Å} [48]. Other bond distances, Pd(1)eN(1) {2.034(4) Å},
Pd(1)eS(2) {2.3237(15) Å} are quite close to those found in the
literature {PdeN, 2.029(4); PdeS, 2.327(14) Å} [33]. The trans angle,
C(19)ePd(1)eS(2) {163.78(16)ꢁ} deviates significantly from line-
arity vis-à-vis the second trans angle, N(1)ePd(1)eP(1)
{173.85(13)ꢁ}, probably due to strain in the five membered chelate
rings. The bond parameters suggest a distorted square planar
Scheme 1 shows a schematic representation of formation of
palladium(II) complexes with various thiosemicarbazones,
[PdL(PPh3)] {L ¼ L1, 1; L2, 2; L3, 3; L4, 4; L5, 5; L6, 6; L7, 7; L8, 8}. The
analytical data has revealed that complexes have stoichiometry,
[PdL(PPh3)]. It suggested that ligands are probably acting as
dinegative anions which removed both the chlorides as solid
Et3NHþClꢀ salt. The IR spectroscopy revealed deprotonation of
eN2He group in complexes 1e8 [35]. In addition, eC4He (1e6) and
eN4He (7, 8) groups are also deprotonated during complex
formation which is further confirmed by single crystal X-ray crys-
tallography (vide infra). The diagnostic n(CeS) bands show low
energy shift vis-à-vis the free ligands and suggested that thio-
ligands are coordinating to palladium through thiolato sulfur
atom. The presence of phosphine is supported by its characteristic
n
(PeCPh
)
bands in the range, 1096e1108 cmꢀ1 [35] (see
geometry
around
palladium
center.
Other
complexes
supplementary material).
[Pd(k3eC4,N3,S1eL2)(PPh3)] 2, [Pd(k3eC1,N1,S1eL3)(PPh3)] 3,
Me
Me
PdCl2(PPh3)2
N
NHR3
3
N
C
C
S
N
+
NHR3
i
3
C
C
S
N
S
N4
H
S
i
1
C
R1
R2
N2
C4
3
N
C2
Pd
N1HR3
Pd
PPh3
7, 8
PPh3
1, 2
ii
ii
R3
R2
R1
4
Me
Ph
H
H
C
Me
1
Me
N
N
C
NHR3
NHR3
3
3
C
C
2
C
S
Ph
N
N
4
C4
C4
3
4
C
Me
Ph
S
S
Me
Ph
Pd
Pd
4
H
C
Me
Ph
5
6
PPh3
3, 4
PPh3
5, 6
7
8
Me
Ph
Me
4
N
i) Et3N, toluene; ii) Et3N, acetonitrile
H
Scheme 1. Synthesis of complexes.

T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
21
Fig. 3. Molecular structure of complex [Pd(k3eC28,N24,S21eL3)(PPh3)] 3 (note: C28,
N24 and S21 are designated as C4, N3 and S in Scheme 1).
square planar geometry around metal center. Complex
[Pd(k3eN1,N2,SeL8)(PPh3)] 8 has molecular structure and bond
parameters similar to those in 7 (Fig. 7). However, complex 8 has
two independent molecules in the crystal lattice with slightly
different bond parameters.
Fig. 1. Molecular structure of complex [Pd(k3eC19, N1, S2eL1)(PPh3)] 1 (note: C19, N1
and S2 are designated as C4, N3 and S in Scheme 1).
Table 2 shows various core bond lengths and angles. The PdeC
bond lengths fall in the range, 2.026(5)e2.334(7) Å in complexes
1e5. When C2 carbon has two phenyl groups (R1, R2 ¼ Ph, Ph) as in
complex 5, the PdeC bond length {2.334(7) Å} is the longest. The
change of substituents at C2 (R1 ¼ thiopheneyl, phenyl, pyrrole;
R2 ¼ methyl, phenyl) and N1 (R3 ¼ methyl, phenyl) atoms did not
alter the other bond lengths, PdeN, PdeS and PdeP. In complexes
1e8, trans angles C4/N4ePdeS and NePdeP lie in the range
161.5e165.4 and 173.54e178.44ꢁ respectively and are not signifi-
cantly affected by the groups at C2 and N1 atoms.
[Pd(k3eC1,N1,S1eL4)(PPh3)] 4 and [Pd(k3eC29,N26,S21eL5)(PPh3)]
5 have molecular structures and bond parameters similar to those
of complex 1 (Figs. 2e5). Complexes 2 and 4 have two independent
molecules in their respective crystal lattices with slightly different
bond parameters. The crystal
structure of complex
[Pd(k3eN1,N2,SeL7)(PPh3)]
7
suggested that dinegative thio-
ligand (L7) coordinates to PdII metal center via N1, N2 and S donor
atoms. The fourth site is occupied by PPh3 ligand (Fig. 6). The bond
distances, PdeN(2)azomethine {2.018(14) Å}, PdeN(1)pyrrole
{2.047(15) Å}, PdeS {2.267(5) Å} and PdeP {2.261(4) Å} are close to
those observed in complex, [Pd(k3eN,N,SeL)(PPh3)] L ¼ pyrrole-2-
3.3. Packing interactions
carbaldehydethiosemicarbazonate,
reported
in
literature
An analysis of the packing diagrams of complexes 1e5, 7 and 8
reveals interesting trends of intermolecular interactions that are
influenced by the presence of the substituents at C2 and N1 atoms of
{PdeNazomethine, 2.005(4), PdeNpyrrole, 2.029(4), PdeP, 2.2364(13)
and PdeS, 2.257(13) Å} [40]. The trans angle, N(1)ePdeS
{164.21(4)ꢁ} deviates significantly from linearity vis-à-vis the other
trans angle N(2)ePdeP {174.98(4)ꢁ} and suggested a distorted
thiosemicarbazones. Complex [Pd(k3eC19,N1,S2eL1)(PPh3)]
1
exists as a H- bonded dimer, formed through intermolecular inter-
actions between hydrogen atom of phenyl ring of PPh3 coligand
and
(Fig.
p
electrons of C2]N moiety, (C2]N)
p
/HeC(ph) 2.853 Å
molecules of complex
(ph) (2.85, 2.66,
(ph) (3.31, 3.36 Å) interactions
and formed a dimer (Fig. 9). This dimer further interacts with
similar dimeric units {(ph)CeH/ (ph), 2.79, 2.87, 2.66, 2.71, 2.83 Å}
and formed a zig-zag 1D chain. These 1D chains are linked to one
another through (ph)CeH/
(ph) 2.79 and N1H/S(thiopheneyl)
8).
Two
independent
[Pd(k3eC4,N3,S1eL2)(PPh3)] 2 involve (ph)CeH/
p
2.79, 2.77 Å) and (thiopheneyl)p/p
p
p
2.85 Å interactions and formed 2D sheet (Fig. 10).
In complex [Pd(k3eC28,N24,S21eacptscNeMe)(PPh3)] 3, one
molecule is linked with the adjacent molecule via NeH/SeC, 2.90 Å
interaction and formed a dimer. This dimeric unit further interacts
with similar unit {(ph)CeH/
formation of zig-zag 1D chain. Interactions between adjacent 1D
chains {(ph)CeH/SeC, 2.97 and (ph)CeH/ (N]C), 2.67 Å}
p(C]N), 2.87 Å} and led to the
p
formed 2D sheet (Fig. 11). Two independent molecules of complex
[Pd(k3eC1,N1,S1eL4)(PPh3)] 4 involve N1eH/SeC, 2.59, 2.65 Å
interaction and formed a dimer (Fig. 12). This dimeric unit interacts
with the similar unit through methyl and phenyl groups at C2 carbon
Fig. 2. Molecular structure of complex [Pd(k3eC4, N3, S1eL2)(PPh3)] 2.
{H2CeH/p(ph) 2.86, 2.79, 2.88 Å} and formed 1D chain. This 1D

22
T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
Fig. 4. Molecular structure of complex [Pd(k3eC1, N1, S1eL4)(PPh3)] 4 (note: C1, N1 and S1 are designated as C4, N3 and S in Scheme 1).
chain interacts with similar chain through phenyl rings {(ph)
CeH/ (ph) 2.82, 2.68, 2.73 Å} and formed a 2D sheet (Fig. 13).
molecules of complex [Pd(k3eN,N,SeL8)(PPh3)]
8
involve
p
N1H/SeC 2.67 Å interaction and formed a dimer (Fig. 16). This
Phenyl ring of one independent molecule in complex
dimeric unit is linked with the similar unit through phenyl rings of
PPh3 {(ph)CeH/p(ph) 2.89, 2.81 Å} and formed a 1D zig-zag chain.
2D sheet is formed via (ph)CeH/p(ph) 2.78, 2.89 Å interactions
between 1D chains (Fig. 17).
[Pd(k3eC29,N26,S21eL5)(PPh3)] 5 is linked with amino hydrogen of
adjacent molecule through (ph)
and formed a dimer. This dimeric unit is connected with similar
unit through methyl and phenyl groups {(ph) /HeCH2 2.74 Å,
(ph)CeH/ (ph) 2.87 Å}. These interactions led to the formation of
p
/HeN1 2.65, 2.75 Å interaction
p
p
3.4. NMR spectroscopy
zig-zag 1D chain. The 2D sheet is formed via (ph)CeH/p(ph) 2.83,
The disappearance of N2H proton signal (free ligand, H2L1:
8.59 ppm) showed the deprotonation of the N2H hydrogen in
2.90 Å interactions between 1D chains (Fig. 14).
In complex [Pd(k3eN1,N2,SeL7)(PPh3)] 7, one molecule is linked
with second adjacent molecule via CeS/HeC(ph) 2.96,
d
complex 1. The diagnostic C4H signal at
d 7.29 ppm in the free ligand
N1H/
p
(ph) 2.83 Å interactions and second molecule is linked with
third molecule via CH2eH/ (C]N) 2.90 Å interaction. Further
first molecule is connected with third and second molecule is
connected with fourth molecule through H2CeH/ (ph) 2.85 Å
interaction and resulted in the formation of 1D chain. This 1D chain
is linked with the similar chain through (ph)CeH/ (C]N) 2.74 Å
disappeared in complex 1 which supported the formation of PdeC
p
bond. The phenyl ring protons of PPh3 are present as multiplets in
the range,
complex showed upfield shift relative to the free ligand (
7.52 ppm). The methyl group at C2 carbon {
2.92 ppm} moved
d d 4.65 ppm in
7.40e7.58 ppm. The N1H proton signal at
p
d
d
p
interaction and formed 2D sheet (Fig. 15). Two independent
Fig. 5. Molecular structure of [Pd(k3eC29, N26, S21eL5)(PPh3)] 5 (note: C29, N26 and
Fig. 6. Molecular structure of [Pd(k3eN1, N2, SeL7)(PPh3)] 7 (note: N1 and N2 are
S21 are designated as C4, N3 and S in Scheme 1).
designated as N4 and N3 in Scheme 1).

T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
23
Fig. 7. Molecular structure of [Pd(k3eN1, N2, SeL8)(PPh3)] 8 (note: N1 and N2 are designated as N4 and N3 in Scheme 1).
Fig. 8. Interactions between two molecules of complex 1.
Fig. 10. Packing diagram of complex 2 showing 2D network.
signal (H2L3:
signal at
d
129.78 ppm) [36]. The complex 2 also showed C4
upfield relative to the free ligand {
d
3.27 ppm}. Complexes 2e6 also
d
164.45 ppm (free ligand, H2L2: 128.50 ppm). 1H NMR
d
showed the disappearance of N2H proton during complex forma-
tion. The characteristic signals due to groups at N1 and C2 atoms of
these complexes are listed in the experimental section. The met-
alation by phenyl ring at C2 could not be ascertained. However the
13C NMR of complex 3 has shown the C4 signal of phenyl group at C2
supported the deprotonation of both N2H and N4H proton signals in
complexes 7 and 8.
The 31P NMR spectra of complexes 1, 3e8 showed one signal
with the coordination shift in the range
d 45.11e34.20 ppm, sup-
porting coordination of P atom to Pd in each case. Thus the solution
phase behavior of these complexes is in line with the solid state
structures discussed earlier and supported the equivalence of PPh3
ligands. These shifts are similar to those shown by other complexes
with N, S- donor ligands reported in the literature [35,37,38].
carbon at d 164.39 ppm which is markedly different from the ligand
However, complex 2 showed two signals with Δ
38.04 ppm, due to restricted CeNH(Ph) bond as given below.
d
¼ 44.98,
Ph
H
N
N
H
Ph
N
C
N
C
3
3
N
Me
S
N
Me
S
C
C
Pd
Pd
C
C
PPh3
PPh3
S
S
B
A
Fig. 9. Interactions between two independent molecules in complex 2.

24
T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
Fig. 11. Packing diagram of complex (3) showing 2D network.
Fig. 12. Interactions between two independent molecules in complex 4.
Fig. 15. Packing diagram of complex 7 showing 2D sheet.
Fig. 13. Packing diagram of complex 4 showing 2D network.
Fig. 16. Interactions between two independent molecules in complex 8.
Fig. 14. Packing diagram of complex 5 showing 2D sheet.
Fig. 17. Packing diagram of complex 8 showing 2D sheet.

T.S. Lobana et al. / Journal of Organometallic Chemistry 701 (2012) 17e26
25
3.5. Factors controlling cyclometalation
appear to influence cyclometallation or coordination behavior of
thio-ligands under investigation in complexes 1e6.
As described earlier, for R2 ¼ H, there was no activation of CeH
bond of thiopheneyl ring (R1) (structures C and D, Chart 3) [39].
Thus as shown in the current studies, for R2 ¼ Me at C2 carbon in
place of H, CeH bond activation of the thiopheneyl ring has been
observed in 1 and 2 and their formation is shown in Chart 3 (see E
and F). It is noted that for R2 ¼ H, sulfur atom of thiopheneyl ring
formed short intramolecular contacts with the deprotonated
hydrazinic nitrogen atom (S/N2, 2.729e2.831 Å) and inhibited its
lability for the possible cyclopalladation. However, for R2 ¼ Me,
there is no such interaction (S/N2) and thiopheneyl ring is free for
cyclopalladation as in the present case. It is added here that in case
of ruthenium, the CeH bond activation of thiopheneyl ring (R2 ¼ H)
was observed for the first time in the presence of a diphosphine
ligand, Ph2PeCH2ePPh2 [49].
Acknowledgments
Financial assistance from CSIR, (letter no. 09/254(0188)/2009-
EMR-I), New Delhi to one of us (Poonam Kumari) is gratefully
acknowledged. MCV acknowledges support for this work from the
grant BFU2010-22260-C02-02 from the Spanish Ministry of Science
and Innovation (MICINN). We thank reviewers for their healthy
comments.
Appendix A. Supplementary material
CCDC 821241, 821242, 831551, 821243e821246 contains the
supplementary crystallographic data for Compounds 1e5, 7 and 8
respectively. This data can be obtained free of charge via https://
www.ccdc.cam.ac.uk/services/structure_deposit/ or from the
Cambridge Crystallographic Data Centre,12 Union Road, Cambridge
CB2 1EZ, UK (fax: þ44(0)1223 762911; e-mail: kamila@ccdc.cam.ac.
uk). See supplementary for more spectroscopic details.
Further, for R2 ¼ Me, the CeH bond activation of the phenyl ring
was reported for R3 ¼ H (N1) [35]. For R2 ¼ Me, with methyl or
phenyl substituents at N1 (R3 ¼ Me, Ph), again cyclopalladation
occurred as in 3 and 4. It is observed that the presence of phenyl
group (R2) at C2 carbon also induced CeH bond activation of phenyl
ring (R1) in complexes 5 and 6. It is pointed out here that the
introduction of methyl or phenyl substituents at N1 (R3 ¼ Me, Ph),
neither altered the CeH bond activation of phenyl rings(R1) nor
mode of coordination, viz, S, N3, C in complexes 1e6. For R2 ¼ Me,
introduction of methyl and phenyl groups (R3) at N1 did not alter
the bonding behavior of pyrrole ring and formed complexes 7 and
8. The lack of cyclopalladation in this case is attributed to the higher
bond polarity of NeH versus that of CeH bond.
Appendix. Supplementary material
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.2011.11.
028.
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3 N
N
C
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3 N
N
C
C
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C
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Pd
H
H
Pd
H
S
N
C
PPh3
Cl
C
N
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H2N
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D
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H
N1HR3
S
H
N1HR3
C
N
C
H
3
N
C
2
C
N
3
N
Me
S
S
C
Et3N
Pd
C4
Pd
C
H
-Et3NHCl
PPh3
S
Cl
E (1, 2)
PPh3
F (1, 2)
Chart 3.
4. Conclusion
The interaction of a series of N1-substituted thiosemicarbazone
ligands, {R1C2(R2)]N3eN2HeC1(]S)N1HR3, R2, R3 ¼ Me, Ph}with
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both methyl (positive inductive effect) and phenyl (negative
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metallation by thiopheneyl and phenyl rings (1e6), but not of
pyrrole ring (7, 8). Further, cyclometallation is attributed to the
steric effect of R2 substituents at C2. The substituents at N1 do not
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