Cyclopalladated complexes with 9-anthraldehyde aroylhydrazones: Synthesis, properties and structures

Article abstract of DOI:10.1016/j.jorganchem.2011.12.018

Reactions of equimolar amounts of Li₂PdCl₄, 9-anthraldehyde 4-R-benzoylhydrazones (H₂Lⁿ; n = 1 and 2 for R = H and NMe₂, respectively) and CH₃COONa· 3H₂O in methanol produce the

Full text of DOI:10.1016/j.jorganchem.2011.12.018

Journal of Organometallic Chemistry 701 (2012) 62e67
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cyclopalladated complexes with 9-anthraldehyde aroylhydrazones: Synthesis,
properties and structures
*
A.R. Balavardhana Rao, Samudranil Pal
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
Reactions of equimolar amounts of Li2PdCl4, 9-anthraldehyde 4-R-benzoylhydrazones (H2Ln; n ¼ 1 and 2
for R ¼ H and NMe2, respectively) and CH3COONa$3H2O in methanol produce the cyclopalladated
complexes with the formula [Pd(HLn)Cl] (1 (R ¼ H) and 2 (R ¼ NMe2)). Reactions of [Pd(HLn)Cl] (1 and 2)
with 2 mol equivalents of PPh3 in acetone provide the complexes of formula [Pd(Ln)(PPh3)] (3 (R ¼ H)
and 4 (R ¼ NMe2)). Complexes 1e4 have been characterized by elemental analysis and spectroscopic (IR,
UVevis, fluorescence and NMR) measurements. Molecular structures of 1e4 have been confirmed by X-
ray crystallography. In [Pd(HLn)Cl] (1 and 2), the C,N,O-donor (HLn)ꢀ and the chloride form a CNOCl
square-plane around the metal centre, while (Ln)2ꢀ and the PPh3 assemble a CNOP square-plane around
the metal centre in [Pd(Ln)(PPh3)] (3 and 4).
Article history:
Received 5 November 2011
Received in revised form
17 December 2011
Accepted 20 December 2011
Keywords:
Palladium(II)
Aroylhydrazone
Cyclometallation
Crystal structure
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
explored the palladium(II) chemistry with Schiff bases (H2Ln)
prepared from 4-R-benzoylhydrazines (R ¼ H and NMe2) and
The long-standing and continuing interest in cyclometallated
complexes is due to their applications in a wide variety of research
areas ranging from organic synthesis to catalysis, photochemistry,
biological and pharmaceutical chemistry and materials science
[1e18]. A common strategy to generate metallacycles is the met-
allation of a pendant aromatic ring of the coordinated ligand. In
literature ortho-metallation of pendant phenyl ring is more prev-
alent than the metallation of hetero cyclic rings and fused aromatic
rings. We have been working for quite some time now on ortho-
metallated species with C,N,O-donor Schiff bases derived from acid
hydrazides and benzaldehyde or its substituted derivatives
[19e22]. Recently we have reported a series of cylcometallated
palladium(II) complexes with indole-3-carboxaldehyde aroylhy-
drazones [23]. These complexes provide examples of regioslective
peri-palladation of the indole fragment of the ligand. In all these
complexes, endocyclic cyclometallation [24] of the Schiff bases and
the coordination of the amide- or amidate-O lead to the formation
of fused chelate rings. Ortho-metallation of the benzaldimine
moiety provides 5,5-membered [19e22], while peri-metallation of
the indole fragment produces 6,5-membered fused chelate rings
[23]. In view of the very few reports on cyclopalladated complexes
involving anthracene [25e29], in the present work we have
9-anthraldehyde. In this effort, we have isolated two types of
complexes [Pd(HLn)Cl] and [Pd(Ln)(PPh3)] (Scheme 1). In the
following account, we have described the synthesis, properties and
X-ray structures of these complexes.
2. Experimental
2.1. Materials
All the chemicals used in this work were of analytical grade
available commercially and were used as received. The solvents
used were purified by standard methods [30].
2.2. Physical measurements
Microanalytical (C, H, N) data were obtained with a Thermo
Finnigan Flash EA1112 series elemental analyser. IR spectra in KBr
pellets were recorded on a Jasco-5300 FT-IR spectrophotometer. A
Shimadzu LCMS 2010 liquid chromatograph mass spectrometer
was used for the purity verification of H2L1 and H2L2. Solution
electrical conductivities were measured with a Digisun DI-909
conductivity metre. A PerkineElmer Lambda 35 UV/vis spectro-
photometer was used to collect the electronic spectra. The fluo-
rescence spectra were recorded using
a Horiba Jobin Yvon
Fluoromax-4 spectrofluorometer. The NMR spectra were recorded
with the help of Bruker 400 and 500 MHz NMR spectrometers.
* Corresponding author. Tel.: þ91 40 2313 4829; fax: þ91 40 2301 2460.
E-mail address: spsc@uohyd.ernet.in (S. Pal).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.12.018

A.R.B. Rao, S. Pal / Journal of Organometallic Chemistry 701 (2012) 62e67
63
10
4
5
8
11
12
14
6
7
3
2
13
N
9
1
15
N
Pd Cl
O
N
Pd PPh3
O
(ii)
(i)
HN
N
HN
O
16
17
18
19
22
21
20
R
R
R
H2Ln
1
3 (R = H)
(R = H)
2 (R = NMe2)
4
(R = NMe2)
R = H (n = 1) and NMe2 (n = 2)
Scheme 1. (i) Li2PdCl4 and CH3COONa$3H2O (equimolar amounts in methanol) and (ii) PPh3 (2 mol equivalents in acetone).
2.3. Synthesis of H2L1
(s, 1H, NH), 10.11 (s, 1H, H15), 8.98 (s, 1H, H10), 8.76 (8) (d, 1H, H8),
8.63 (br, s, 1H, H4), 8.27 (8) (d, 1H, H5), 8.14 (7) (d, 2H, H18, H22),
9-Anthraldehyde (206 mg, 1 mmol) and a few drops of acetic
acid were added to an ethanol solution of benzoylhydrazine
(136 mg, 1 mmol). The mixture was boiled under reflux for 3 h.
The pale yellow solid separated was collected by filtration, washed
with ethanol and then dried in air. Yield: 265 mg (82%). Anal. calcd
for C22H16N2O: C, 81.45; H, 4.97; N, 8.65. Found: C, 81.23; H, 4.78;
N, 8.47. Mass in Me2NCHO: m/z ¼ 325. UVevis in Me2NCHO:
8.02 (8) (d, 1H, H2), 7.86 (8) (t, 1H, H20), 7.70 (m, 4H, H6, H7, H19
,
H
21), 7.41 (8) (t, 1H, H3).
The red [Pd(HL2)Cl] (2) was synthesized in 65% yield by
following a procedure very similar to that described for 1 using
H2L2 instead of H2L1. Anal. calcd for PdC24H20N3OCl: C, 56.71; H,
3.97; N, 8.27. Found: C, 56.58; H, 3.91; N, 8.36. UVevis in Me2NCHO:
lmax (nm) (10ꢀ3
ꢁ
3
(Mꢀ1 cmꢀ1)) ¼ 524 (15.2), 490 (16.0), 461 (9.8),
lmax (nm) (10ꢀ3
ꢁ
3
(Mꢀ1 cmꢀ1)) ¼ 438sh (10.3), 390 (52.4), 374
381sh (11.2), 314sh (23.4), 287 (29.2). Emission in Me2NCHO: lmax
(47.5), 350sh (27.4), 334sh (15.5), 300sh (33.9). Emission in
(nm) (excitation at
l
(nm)) ¼ 645 (460). 1H NMR in (CD3)2SO:
Me2NCHO: lmax (nm) (excitation at
l
(nm)) ¼ 480 (390). 1H NMR
d
(ppm) (J (Hz)) ¼ 13.70 (s, 1H, NH), 10.10 (s, 1H, H15), 8.96 (s, 1H,
in (CD3)2SO:
d
(ppm) (J (Hz)) ¼ 12.12 (s, 1H, NH), 9.69 (s, 1H, H15),
H
10), 8.78 (9) (d, 1H, H8), 8.61 (br, s, 1H, H4), 8.26 (8) (d, 1H, H5), 8.02
8.79 (s, 1H, H10), 8.77 (5) (d, 2H, H1, H8), 8.19 (8) (d, 2H, H4, H5),
8.05 (7) (d, 2H, H18, H22), 7.66 (m, 3H, H19, H20, H21), 7.61 (m, 4H,
H2, H3, H6, H7).
(8) (d, 1H, H2), 7.98 (9) (d, 2H, H18, H22), 7.85 (8) (t, 1H, H7), 7.68 (8)
(t, 1H, H6), 7.40 (8) (t, 1H, H3), 6.90 (6) (d, 2H, H19, H20), 3.09 (s, 6H,
NMe2).
H2L2 was prepared in 83% yield from equimolar amounts of 9-
anthraldehyde and 4-dimethylaminobenzoylhydrazine in pres-
ence of acetic acid using the same procedure as described for H2L1.
Anal. calcd for C24H21N3O: C, 78.44; H, 5.76; N, 11.44. Found: C,
78.26; H, 5.69; N, 11.32. Mass in Me2NCHO: m/z ¼ 368. UVevis in
2.5. Synthesis of [Pd(L1)(PPh3)] (3)
Solid PPh3 (131 mg, 0.5 mmol) was added to a suspension of
[Pd(HL1)Cl] (1) (116 mg, 0.25 mmol) in acetone (10 ml) and the
mixture was stirred at room temperature for 24 h. The complex
[Pd(L1)(PPh3)] (3) separated as an orange solid was collected by
filtration, washed with acetone and finally dried in air. Yield:
104 mg (60%). Anal. calcd for PdC40H29N2OP: C, 69.52; H, 4.23; N,
4.05. Found: C, 69.31; H, 4.32; N, 3.91. UVevis in Me2NCHO: lmax
Me2NCHO: lmax (nm) (10ꢀ3
ꢁ
3
(Mꢀ1 cmꢀ1)) ¼ 440sh (22.3), 417sh
(49.2), 398 (54.9), 370sh (39.3), 314 (71.1). Emission in Me2NCHO:
lmax (nm) (excitation at
l
(nm)) ¼ 700 and 490 (415). 1H NMR in
(CD3)2SO:
d
(ppm) (J (Hz)) ¼ 11.81 (s, 1H, NH), 9.61 (s, 1H, H15), 8.78
(s, 1H, H10), 8.73 (14) (d, 2H, H1, H8), 8.16 (8) (d, 2H, H4, H5), 7.91 (8)
(d, 2H, H18, H22), 7.61 (m, 4H, H2, H3, H6, H7), 6.81 (9) (d, 2H, H19
21), 3.02 (s, 6H, NMe2).
,
(nm) (10ꢀ3
ꢁ
3
(Mꢀ1 cmꢀ1)) ¼ 515 (17.7), 485 (21.2), 460 (15.1),
H
425sh (6.8), 388 (5.2), 368sh (4.5), 292 (25.2). Emission in Me2N-
CHO: lmax (nm) (excitation at
l
(nm)) ¼ 585 (510). 1H NMR in
2.4. Synthesis of [Pd(HL1)Cl] (1)
(CD3)2SO:
d
(ppm) (J (Hz)) ¼ 10.06 (s, 1H, H15), 8.92 (s, 1H, H10), 8.87
(br, s, 1H, H8), 8.24 (8) (d, 1H, H5), 7.65 (m, 24H, H2, H4, H6, H7,
A mixture of PdCl2 (178 mg, 1.0 mmol) and LiCl (86 mg,
2.0 mmol) was taken in methanol (20 ml) and boiled with stirring
under reflux for 1 h. It was then cooled to room temperature and
filtered. The filtrate was added drop-wise with stirring to a meth-
anol solution (20 ml) of H2L1 (324 mg, 1.0 mmol) and CH3COO-
Na$3H2O (136 mg, 1.0 mmol). The mixture was stirred at room
temperature for 48 h. The complex precipitated as orange solid
was collected by filtration, washed with methanol and finally dried
in air. Yield: 290 mg (62%). Anal. calcd for PdC22H15N2OCl: C, 56.80;
H, 3.25; N, 6.02. Found: C, 56.95; H, 3.33; N, 6.12. UVevis in
H
d
18e22, Hs of PPh3), 6.78 (br, s, 1H, H3). 31P NMR in (CD3)2SO:
(ppm) ¼ 25.51.
[Pd(L2)(PPh3)] (4) was synthesized as an orange-red solid in 65%
yield from 1 mol equivalent of [Pd(HL2)Cl] (2) and 2 mol equiva-
lents of PPh3 using a very similar procedure described above. Anal.
calcd for PdC42H34N3OP: C, 68.71; H, 4.67; N, 5.72. Found: C, 68.49;
H, 4.74; N, 5.57. UVevis in Me2NCHO: lmax (nm) (10ꢀ3
ꢁ
3
(Mꢀ1 cmꢀ1)) ¼ 523 (20.0), 491 (21.4), 460sh (12.6), 431sh (6.3),
370sh (13.2), 284(44.9). Emission in Me2NCHO: lmax (nm) (excita-
tion at
l
(nm)) ¼ 660 (460). 1H NMR in (CD3)2SO:
d (ppm) (J
Me2NCHO: lmax(nm) (10ꢀ3
453 (11.2), 424sh (9.1), 390 (9.8), 368sh (8.5), 323sh (12.8), 288
ꢁ
3
(Mꢀ1 cmꢀ1)) ¼ 512 (13.9), 482 (15.9),
(Hz)) ¼ 10.28 (s, 1H, H15), 8.98 (s, 1H, H10), 8.75 (br, s, 1H, H8), 8.27
(8) (d, 1H, H5), 7.95 (7) (d, 1H, H4), 7.87 (8) (t, 1H, H7), 7.65 (m, 19H,
H2, H6, H18, H22, and Hs of PPh3), 6.81 (br, s, 1H, H3), 6.76 (br, s, 2H,
(26.6). Emission in Me2NCHO: lmax (nm) (excitation at
l
(nm)) ¼ 570 (510). 1H NMR in (CD3)2SO:
d
(ppm) (J (Hz)) ¼ 12.11
H
19, H21), 3.04 (s, 6H, NMe2). 31P NMR in (CD3)2SO:
d
(ppm) ¼ 25.53.

64
A.R.B. Rao, S. Pal / Journal of Organometallic Chemistry 701 (2012) 62e67
2.6. X-ray crystallography
and 4-R-benzoylhyrazines (R ¼ H and NMe2) in presence of a few
drops of acetic acid in ethanol. Elemental analysis and spectro-
scopic (IR, 1H NMR and mass) measurements were used to char-
acterize these Schiff bases. Reactions of equimolar amounts H2Ln,
CH3COONa$3H2O and Li2PdCl4 (generated in situ using PdCl2 and
LiCl in 1:2 mol ratio) in methanol produce [Pd(HLn)Cl] (1 (R ¼ H)
and 2 (R ¼ NMe2)) in 62 and 65% yields. Reactions of [Pd(HLn)Cl] (1
and 2) with PPh3 in 1:2 mol ratio in acetone provide the complexes
[Pd(Ln)(PPh3)] (3 (R ¼ H) and 4 (R ¼ NMe2)) in 60 and 65% yields.
Presumably the excess PPh3 provides a mild basic environment for
the deprotonation of the amide functionality of (HLn)ꢀ in 1 and 2. It
is very likely that this deprotonation increases the PdeO bond
strength (vide infra) and facilitates the dissociation of PdeCl bond
resulting in the formation of 3 and 4 (Scheme 1). All the four
complexes are orange to red in colour and they are diamagnetic.
The elemental analysis data of 1e4 are in good agreement with
their corresponding molecular formula. Complexes 1 and 2 are
highly soluble in dimethylformamide and dimethylsulfoxide and
sparingly soluble in acetone and acetontrile. The solubility behav-
iours of 3 and 4 are very similar to that of 1 and 2, except for their
high solubility in halogenated solvents such as chloroform and
dichloromethane. In solution, they behave as nonelectrolyte.
Single crystals of [Pd(HLn)Cl] (1 and 2) were grown by diethyl
ether vapour diffusion into their corresponding dimethylforma-
mide solutions, while those of [Pd(Ln)(PPh3)] (3 and 4) were ob-
tained by slow evaporation of their corresponding acetonitrile
solutions. Both
1 and 2
crystallize as [Pd(HLn)Cl]$Me2NCHO
(1$Me2NCHO and 2$Me2NCHO). Complex 3 crystallizes as 3$CH3CN,
while complex 4 crystallizes as it is. A Bruker-Nonius SMART APEX
CCD single crystal diffractometer, equipped with
monochromator and a Mo K fine-focus sealed tube (
a
graphite
a
l
¼ 0.71073 Å)
was used to determine the unit cell parameters and intensity data
collection at 298 K for 1$Me2NCHO and 4. The SMART and the
SAINT-Plus packages [31] were used for data acquisition and data
extraction, respectively. The SADABS program [32] was used for
absorption corrections. Determination of the unit cell parameters
and the intensity data collection at 298 K for each of 2$Me2NCHO
and 3$CH3CN were performed on an Oxford Diffraction Xcalibur
Gemini single crystal X-ray diffractometer using graphite mono-
chromated Mo K
a
radiation (
l
¼ 0.71073 Å). The CrysAlisPro soft-
ware [33] was used for data collection, reduction and absorption
correction. The structures of all four complexes were solved by
direct method and refined on F2 by full-matrix least-squares
procedures. All non-hydrogen atoms were refined anisotropically.
The hydrogen atom of the amide functionality of the tridentate
ligand in each of 1$Me2NCHO and 3$CH3CN was located in
a difference map and refined with Uiso(H) ¼ 1.2Uiso(N). The
remaining hydrogen atoms of 1$Me2NCHO and 3$CH3CN and all the
hydrogen atoms of 2$Me2NCHO and 4 were included in the struc-
ture factor calculation at idealized positions by using a riding
model. The SHELX-97 programs [34] available in the WinGX
package [35] were used for structure solution and refinement. The
ORTEX6a [36] and Platon [37] packages were used for molecular
graphics. Selected crystallographic data are summarized in Table 1.
3.2. Spectroscopic properties
IR spectra of all the compounds display a large number of bands
in the frequency range 400e1650 cmꢀ1 and a few bands within
3000e3220 cmꢀ1 of various intensities. We have only attempted to
assign a few characteristic bands by comparing with the spectra of
similar compounds reported earlier [19e23,38e40]. The free Schiff
bases (H2Ln) show the medium intensity NeH stretching band at
w3210 cmꢀ1. The strong band at w1645 cmꢀ1 and the following
overlapping medium intensity band at w1615 cmꢀ1 are assigned to
the C]O and C]N stretches, respectively. In the spectra of 1 and 2,
a weak band observed at w3200 cmꢀ1 is possibly due to the NeH
stretch of the ligand (HLn)ꢀ. Two strong bands observed at w1610
and w1570 cmꢀ1 are attributed to the coordinated C]O and C]N
groups of (HLn)ꢀ, respectively. The spectra of 3 and 4 do not display
any band assignable to the NeH and C]O stretches. Thus the amide
functionality of the tridentate (Ln)2ꢀ in 3 and 4 is in deprotonated
form (Scheme 1). The strong and sharp band observed at
3. Results and discussion
3.1. Synthesis and characterization
The Schiff bases H2Ln (n ¼ 1 and 2) [38] were synthesized in
slightly more than 80% yields by condensation of 9-anthraldehyde
Table 1
Selected crystallographic data.
Complex
1$Me2NCHO
2$Me2NCHO
3$MeCN
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
PdC25H22N3O2Cl
538.34
Triclinic
P1
9.1279(7)
11.3041(8)
11.9347(9)
65.176(1)
77.392(1)
75.122(1)
1071.60(14)
2
PdC27H27N4O2Cl
581.41
Monoclinic
P21/c
10.7700(4)
30.1455(11)
8.0191(4)
90
105.383(4)
90
PdC42H32N3OP
732.13
Monoclinic
P21/n
12.300(4)
13.354(3)
21.260(8)
90
104.35(4)
90
PdC42H34N3OP
734.15
Monoclinic
P21/c
10.3624(6)
14.4229(8)
22.6557(13)
90
96.096(1)
90
b (Å)
c (Å)
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
V (Å3)
2510.26(18)
4
1.538
3383.1(2)
4
1.437
3366.9(3)
4
1.448
Z
r
(g cmꢀ3
(mmꢀ1
)
)
1.668
1.020
m
0.878
0.634
0.637
Reflections collected
Reflections unique
10,272
3762
10,588
4412
12,407
5947
31,774
5926
Reflections (I ꢃ 2
s(I))
3622
294
3413
323
3489
434
5491
435
Parameters
R1, wR2 (I ꢃ 2
s
(I))
0.0239, 0.0619
0.0249, 0.0626
1.080
0.647 and ꢀ0.336
0.0529, 0.1094
0.0745, 0.1144
1.151
0.736 and ꢀ0.675
0.0405, 0.0820
0.0796, 0.0892
0.871
0.552 and ꢀ0.867
0.0297, 0.0742
0.0323, 0.0759
1.068
0.353 and ꢀ0.333
R1, wR2 (all data)
GOF (F2)
Largest peak and hole (e Åꢀ3
)

A.R.B. Rao, S. Pal / Journal of Organometallic Chemistry 701 (2012) 62e67
65
w1600 cmꢀ1 for these two complexes is very likely to be due to the
conjugated C]NeC]N fragment of (Ln)2ꢀ
.
Dimethylformamide solutions of the Schiff bases (H2L1 and H2L2)
and the corresponding complexes 1e4 with them were used to
record the electronic spectra. Representative spectra are shown in
Fig. 1. The spectral profiles of all the four complexes and the free
Schiff bases (H2Ln) are very similar. Interestingly except for the
highest energy band all the spectra resemble that of pure anthra-
cene [38,41,42]. Thus the absorptions in 1e4 are by and large due to
ligand centred transitions only. However, there is a gradual red-shift
of the band positions from anthracene to the Schiff bases to the
complexes. This type of red-shift of
pep* absorption bands due to
alteration of the -energy levels and thus the decrease of the pep*
p
gap caused by substituent on the arene and also by metal coordi-
nation to aromatic heterocycle is documented before [42e44].
Fluorescence spectra of both Schiff bases (H2L1 and H2L2) and
complexes 1e4 were collected using their corresponding dime-
thylformamide solutions. All the compounds are emissive in nature.
On excitation at 390 nm H2L1 shows a broad emission band centred
at 480 nm. On excitation at 510 nm complexes 1 and 3 with H2L1
also display a similar broad emission band centred at 570 and
585 nm, respectively. In contrast to H2L1, H2L2 displays dual fluo-
rescence property. On excitation at 410 nm, it shows two emission
bands at 490 and 700 nm (Fig. 2). Presumably after excitation the
strong donor group NMe2 on the aroyl moiety of H2L2 induces
a conformational change and hence it exhibits two emission bands
from two conformational isomers of the excited state [45,46].
However, dual fluorescence has not been observed for the
complexes with H2L2. On excitation at 460 nm 2 and 4 display
a broad emission band at 645 and 660 nm, respectively (Fig. 2).
Perhaps in these cases metal ion coordination causes stabilization
of only one conformation of the excited state.
Fig. 2. Fluorescence spectra of H2L2 (0.54 ꢁ 10ꢀ3 M) (——) and [Pd(HL2)Cl] (2)
(0.59 ꢁ 10ꢀ3 M) (d) in dimethylformamide.
1H NMR spectra of H2L1, H2L2 and complexes 1e4 with them
were recorded in dimethylsulfoxide-d6. The spectra of 1 and 2
show all the protons of (HLn)ꢀ, whereas for 3 and 4 except for a few
the remaining aromatic protons of (Ln)2ꢀ could not be clearly
assigned due to the PPh3 phenyl ring protons. The Schiff bases and
the complexes 1 and 2 display the resonance corresponding to the
NeH proton as a singlet in the range
d 11.81e13.70. As expected, 3
and 4 do not display any such signal due to the deprotonated form
of the amide functionality in (Ln)2ꢀ (Scheme 1). The methyl protons
of NMe2 in H2L2, 2 and 4 appear as singlet within
d
3.02e3.09. The
8.77 and 8.73
in H2L1 and H2L2, respectively. In contrast, 1e4 display a doublet or
a broad singlet in the same range ( 8.75e8.87) corresponding to
H1 and H8 protons resonate together as a doublet at
d
d
a single proton (H8) due to the metallation at C1 position. By and
large, there is a downfield shift of the H2 and H4 protons and an
upfield shift of the H3 proton in the complexes compared to the free
Schiff bases. These shifts further substantiate the metallation at C1
position in 1e4. Generally the resonances corresponding to H2e4
and H18e22 are upfield shifted in 3 and 4 compared to that in free
Schiff bases and the chloro complexes (1 and 2) due to the shielding
effects of the PPh3 phenyl rings. The 31P NMR spectra of 3 and 4
have been also examined. A signal around
d 25.5 confirms the
phosphine coordination in 3 and 4.
3.3. X-ray structures
The molecular structures of [Pd(HLn)Cl] (1 and 2) and
[Pd(Ln)(PPh3)] (3 and 4) determined by X-ray crystallography are
illustrated in Figs. 3 and 4, respectively. Selected bond parameters
associated with the metal ion for 1e4 are listed in Table 2. The metal
centres are in distorted square-planar environment in all the
complexes. The anthracenyl peri-C, the azomethine-N and the
amide-O atom donor planar (HLn)ꢀ and the chloride form a CNOCl
Fig. 1. Electronic spectra of H2L1 (0.62
ꢁ
10ꢀ5 M) (——) and [Pd(L1)(PPh3)] (3)
(0.58 ꢁ 10ꢀ4 M) (d) in dimethylformamide.

66
A.R.B. Rao, S. Pal / Journal of Organometallic Chemistry 701 (2012) 62e67
Fig. 3. Molecular structures of (a) [Pd(HL1)Cl] (1) and (b) [Pd(HL2)Cl] (2) with the atom
labelling schemes. All non-hydrogen atoms are represented by their 50% probability
thermal ellipsoids.
square-plane around the metal centres in 1 and 2. On the other
hand, the anthracenyl peri-C, the azomethine-N and the amidate-O
atom donor (Ln)2ꢀ and the PPh3 assemble a CNOP square-plane
around the metal centres in 3 and 4. In both type of complexes
the tridentate ligands form 6,5-membered fused chelate rings. Each
chelate ring is satisfactorily planar (rms deviations 0.01e0.13 Å). The
values of the dihedral angle between the two fused chelate rings in 1
and 2 are 1.0(1) and 3.1(2)ꢂ, respectively, while that in 3 and 4 are
12.3(2) and 6.00(3)ꢂ, respectively. This relatively more non-
coplanarity of the two chelate rings in 3 and 4 is most likely due
to the bulky PPh3. In 1 and 2, the C(16)eO(1) bond length is shorter
and the C(16)eN(2) bond length is longer compared to the corre-
sponding bond lengths in 3 and 4 (Table 2). This difference is in
agreement with the protonated form of the amide functionality in 1
and 2 and the deprotonated form of the amide functionality in 3 and
Fig. 4. Molecular structures of (a) [Pd(L1)(PPh3)] (3) and (b) [Pd(L2)(PPh3)] (4) with the
atom labelling schemes. All non-hydrogen atoms are represented by their 50% prob-
ability thermal ellipsoids.
Table 2
4 [19e23,39]. The amidate-O is expected to have better s-bonding
Selected bond lengths (Å) and angles (ꢂ) for 1$Me2NCHO, 2$Me2NCHO, 3$MeCN
and 4.
ability and hence better trans directing ability than the amide-O
atom. As a consequence the PdeO(1) bond length is shorter and the
PdeC(1) bond length is longer in 3 and 4 compared to the corre-
sponding bond lengths in 1 and 2 (Table 2). Significantly longer
PdeN(1) bond length in 3 and 4 than that in 1 and 2 is due to the
superior trans effect of PPh3 compared to that of chloride. Within
[Pd(HLn)Cl] (1 and 2), the PdeO(1) bond length in 1 is longer than
that in 2. Similarly in [Pd(Ln)(PPh3)] (3 and 4), the PdeO(1) bond
length in 3 is longer than that in 4. The strong electron donating
ability of the substituent NMe2 at para to the aroyl group makes the
amide-O of (HL2)ꢀ and the amidate-O atom of (L2)2ꢀ a better donor
Complex
1$Me2NCHO
2$Me2NCHO
3$MeCN
4
PdeC(1)
PdeN(1)
PdeO(1)
PdeCl/P
C(16)eO(1)
C(16)eN(2)
C(1)ePdeN(1)
C(1)ePdeO(1)
C(1)ePdeCl/P
N(1)ePdeO(1)
N(1)ePdeCl/P
O(1)ePdeCl/P
1.980(2)
1.959(2)
2.141(2)
2.3256(6)
1.243(3)
1.354(3)
91.57(8)
171.26(8)
99.00(7)
79.69(6)
169.38(5)
89.74(4)
1.994(5)
1.961(4)
2.123(3)
2.3146(16)
1.252(5)
1.348(6)
91.76(18)
171.60(17)
98.26(15)
79.90(14)
169.91(12)
90.10(10)
2.005(4)
1.990(3)
2.108(2)
2.2876(11)
1.292(4)
1.329(5)
91.10(14)
167.63(12)
97.36(11)
78.76(11)
167.67(10)
93.81(8)
2.001(2)
1.989(2)
2.070(2)
2.2927(6)
1.280(3)
1.321(3)
92.28(9)
169.86(8)
98.93(7)
78.43(7)
165.94(5)
90.87(4)
compared to the corresponding O-atoms in (HL1)ꢀ and (L1)2ꢀ
respectively and hence the PdeO(1) bond lengths turn out to be
,

A.R.B. Rao, S. Pal / Journal of Organometallic Chemistry 701 (2012) 62e67
67
different in 1 and 2 and in 3 and 4. Overall the PdeC, PdeN, PdeO,
PdeCl and PdeP bond lengths and the bond angles observed in 1e4
are comparable with the values reported for cyclopalladated
complexes with similar ligands [19,20,23e25,27,39,47,48].
charge from the Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Among 1e4 only [Pd(L2)(PPh3)] (4) crystallizes without any
solvent molecule. [Pd(HLn)Cl] (1 and 2) crystallize as [Pd(HLn)Cl]$
Me2NCHO (1$Me2NCHO and 2$Me2NCHO) from dimethyl-
formamideediethylether. In each case, the solvent molecule is
hydrogen bonded to the complex molecule. The O-atom of the
Me2NCHO is connected to the adjacent amide NeH and metal
coordinated polarized azomethine CeH groups of the ligand (HLn)ꢀ.
The N(2)/O(2) distances and the N(2)eH/O(2) angles are
2.762(2) Å and 168(3)ꢂ and 2.765(5) Å and 162(5)ꢂ for 1$Me2NCHO
and 2$Me2NCHO, respectively. The C(15)/O(2) distances and the
C(15)eH/O(2) angles are 3.120(3) Å and 145ꢂ and 3.115(6) Å and
144ꢂ for 1$Me2NCHO and 2$Me2NCHO, respectively. [Pd(L1)(PPh3)]
(3) crystallizes from acetonitrile as 3$CH3CN. However, no signifi-
cant interaction between the acetonitrile and the complex mole-
cule could be detected here.
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Financial support (Grant No. SR/S1/IC-10/2007) received from
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Appendix A. Supplementary material
CCDC 847010e847013 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of