Reaction of 2-(phenylazo)aniline with Na2PdCl4: Formation of a 2-(phenylazo)imino complex of bivalent palladium

Article abstract of DOI:10.1021/ic000369p

2-(Phenylazo)aniline, H₂L (H stands for amino protons), binds to bivalent palladium in a bidentate fashion (N,N) as HL^-. Structural studies show distortion in the phenyl ring adjacent to the chelate ring with two short and four long C-C distances.

Full text of DOI:10.1021/ic000369p

2204
Inorg. Chem. 2001, 40, 2204-2205
Avance DPX 300 NMR spectrometers in CDCl3. SiMe4 was used as
the internal standard.
Reaction of 2-(Phenylazo)aniline with Na2PdCl4:
Formation of a 2-(Phenylazo)imino Complex of
Bivalent Palladium
2-(Phenylazo)aniline (H2L). o-Phenylenediamine (2 g, 18.5 mmol),
nitrobenzene (2.28 g, 18.5 mmol), and sodium hydroxide (0.74 g, 18.5
mmol) were mixed and triturated followed by heating at 70 °C with
constant scratching for 20 min. The dark pasty mass thus obtained was
cooled to room temperature and extracted with benzene. The benzene-
soluble part was subjected to column chromatography on a silica gel
(60-120 mesh) column (2 cm × 45 cm). The first band that was eluted
by a benzene-petroleum ether mixture (5/95 v/v) was collected, and
upon evaporation of solvent, the pure 2-(phenylazo)aniline (H2L) was
obtained: yield 1.824 g (50%). 1H NMR (CDCl3): δ 5.9 (s, NH2); 6.7
(d, C6-H); 6.8 (t, C4-H); 7.2 (t, C5-H); 7.4 (t, C10-H); 7.5 (t, C9-H
and C11-H); 7.8 (d, C8-H, C12-H and C3-H). IR (KBr; cm-1):
Nilkamal Maiti, Satyanarayan Pal,† and
Surajit Chattopadhyay*
Department of Chemistry and Chemical Technology,
Vidyasagar University, Midnapore-721102,
West Bengal, India
ReceiVed April 5, 2000
3456, 3382 (νNH ); 1592 (νCdC); 1461 (νNdN); 1230 (νC-N). UV-vis
2
(CH2Cl2; λmax, nm (ꢀ, M-1cm-1)): 416 (8963), 313 (14 455), 243
(14 791). Anal. Calcd for C12H11N3: C, 73.09; H, 5.58; N, 21.32.
Found: C, 73.19; H, 5.52; N, 21.42.
Transition-metal chelates incorporating azo ligands have
drawn much attention in recent years. Among these, complexes
of arylazooximes,1 arylazophenols,2 arylazoimines,3 alkylthio-
azobenzenes,4 and sulfenylazobenzenes5 are some notable
examples. Interesting coordination modes and molecular struc-
tures, C-H bond activation, potential sites of facile electron
transfer, and interesting electronic structure due to the presence
of low-lying π* orbitals are some of the important properties
exhibited by these. Herein we scrutinize the synthesis and
structure of 2-(phenylazo)aniline (H2L) and bis chelate PdII-
(HL)2, wherein the ligand displays predominant azoimine
character due to delocalization.
[PdII(HL)2]. To an aqueous solution of Na2PdCl4 (0.374 g, 1.27
mmol) in a beaker was added a benzene solution of H2L (0.5 g, 2.54
mmol). The mixture was stirred for 3 h. The organic layer gradually
turned green. The green benzene solution was separated from the
aqueous layer and subjected to column chromatography on a silica gel
(60-120 mesh) column. A green band was eluted with benzene, and
upon evaporation of the solvent, pure PdII(HL)2 was obtained: yield
1
0.949 g (75%). H NMR (CDCl3): δ 4.9 (s, N-H); 6.0 (d, C6-H);
6.3 (t, C4-H); 6.9 (t, C5-H). IR (KBr; cm-1): 3332 (νNH); 1602 (νCd
N); 1342 (νNdN). UV-vis (CH2Cl2; λmax, nm; (ꢀ, M-1cm-1)): 628
(9327), 387 (9826), 333 (24 101), 262 (94 695). Anal. Calcd for
PdC24H20N6: C, 57.78; H, 4.01; N, 16.85. Found: C, 57.83; H, 4.08;
N, 16.88.
Experimental Section
The solvents used in the reactions were of reagent grade obtained
from E. Merck, Calcutta, India, and were dried by reported procedures.6
o-Phenylenediamine was recrystallized from ethanol-water (2/1 v/v)
before use. Palladium chloride was purchased from Arrora Matthey,
Calcutta, India. Disodium tetrachloropalladate was prepared by a
reported procedure.6 Microanalyses (C, H, N) were done on a Perkin-
Elmer 240C elemental analyzer. IR spectra were recorded on a Perkin-
Elmer 783 spectrometer with the sample prepared as KBr pellets.
Electronic spectra were recorded on a Hitachi U-2001 spectrophotom-
X-ray Crystallography. Crystals of PdII(HL)2 were grown by
diffusion of hexane into benzene solution at 25 °C. The size of the
crystal suitable for X-ray studies was 0.48 × 0.32 × 0.20 mm3. The
cell parameters were determined by least-squares fits of 25 machine-
centered reflections (2θ ) 15-25°). Data were collected by the ω-scan
technique on a Enraf-Nonius CAMX-3 diffractometer with Mo KR
radiation monochromated by a graphite crystal. No absorption correction
was performed. Crystal data were collected in Table 1. The structure
solution was carried out by direct methods with the SHELXS-90
program. Full-matrix least-squares refinements were performed using
the SHELX-97 program (PC version). All non-hydrogen atoms were
refined anisotropically using reflections with I > 2σ(I). Hydrogen atoms
were included at the calculated position.
1
eter. H NMR data were collected from Bruker AC-200 and Bruker
* To whom correspondence should be addressed. E-mail: scha8@
hotmail.com.
† Current address: School of Chemistry, University of Hyderabad,
Hyderabad-500046, India.
(1) (a) Pal, C. K.; Chattopadhyay, S.; Sinha, C.; Chakravorty, A. Inorg.
Chem. 1994, 33, 6140. (b) Pal, C. K.; Chattopadhyay, S.; Sinha, C.;
Chakravorty, A. Inorg. Chem. 1996, 35, 2442 and references therein.
(2) Basuli, F.; Peng, S.-M.; Bhattacharya, S. Polyhedron 1999, 18, 391
and references therein.
(3) (a) Bag, N.; Lahiri, G. K.; Chakravorty, A. Inorg. Chem. 1992, 31,
40. (b) Lahiri, G. K.; Bhattacharya, S.; Goswami, S.; Chakravorty, A.
J. Chem. Soc., Dalton Trans. 1990, 561. (c) Pal, C. K.; Chattopadhyay,
S.; Sinha, C.; Chakravorty, A. Polyhedron 1994, 13, 999. (d) Ghosh,
P.; Pramanik, A.; Bag, N.; Chakravorty, A. J. Chem. Soc., Dalton
Trans. 1992, 1883. (e) Mishra, T. K.; Das, D.; Sinha, C.; Ghosh, P.;
Pal, C. K. Inorg. Chem. 1998, 37, 1672. (f) Santra, P. K.; Das, D.;
Mishra, T. K.; Roy, R.; Sinha, C.; Peng, S.-M. Polyhedron 1999, 18,
1909 and references therein.
Results and Discussion
Synthesis and Characterization. An equimolar mixture of
o-phenylenediamine, nitrobenzene, and sodium hydroxide was
titurated and heated. Workup of the reaction mixture afforded
orange-red 2-(phenylazo)aniline (H2L; eq 1).
(4) (a) Chattopadhyay, S.; Sinha, C.; Basu, P.; Chakravorty, A. Organo-
metallics 1991, 10, 1135. (b) Pal, C. K.; Chattopadhyay, S.; Sinha,
C.; Chakravorty, A. J. Organomet. Chem. 1992, 439, 91 and references
therein.
(5) (a) Sinha, C.; Bandyapadhyay, D.; Chakravorty, A. Inorg. Chem. 1988,
27, 1173. (b) Mahapatra, A. K.; Bandyapadhyay, D.; Bandyapadhyay,
P.; Chakravorty, A. Inorg. Chem. 1986, 25, 2214. (c) Sinha, C.;
Bandyapadhyay, D.; Chakravorty, A. J. Chem. Soc., Chem. Commun.
1988, 468.
(6) (a) Chattopadhyay, P.; Nayak, M. K.; Bhattacharya, S. P.; Sinha, C.
Polyhedron 1997, 16, 1291. (b) Basuli, F.; Chattopadhyay, P.; Sinha,
C. Polyhedron 1996, 15, 2439.
The diamagnetic bis complex PdII(HL)2 was isolated by
reacting H2L and Na2PdCl4 in a 2/1 ratio in a benzene-water
mixture. The green complex shows an absorption at 630 nm
for the MLCT transition. On coordination the ligand undergoes
1
deprotonation to HL-, as is consistent with IR and H NMR
data.
10.1021/ic000369p CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/24/2001

Notes
Inorganic Chemistry, Vol. 40, No. 9, 2001 2205
Table 1. Crystallographic Data for PdII(HL)2
Table 2. Selected Bond Distances (Å) and Angles (deg) for
PdII(HL)2
chem formula
fw
space group
a, Å
C24H20N6Pd
498.86
P21/n
6.2220(11)
14.8034(19)
11.1229(15)
95.877(13)
1019.1(3)
Z
2
20
T, °C
λ, Å
Distances
0.710 73
1.626
0.935
2.43
6.50
1.095
Pd-N(1)
1.984(2)
2.0272(19)
1.322(3)
1.286(3)
1.358(3)
1.440(3)
C(1)-C(2)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.438(3)
1.435(3)
1.423(4)
1.360(4)
1.410(4)
1.350(4)
F
calcd, Mg/m3
Pd-N(3)
b, Å
µ, mm-1
R,a %
N(1)-C(1)
N(2)-N(3)
N(2)-C(2)
N(3)-C(7)
c, Å
â, deg
Rw,b %
GOFc
V, Å3
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑|Fo| ]; w-1
) σ2(|Fo| + g|Fo|)2. c The goodness of fit is defined as [w(|Fo| - |Fc|)2/
(no - nv)]1/2 where no and nv denote the numbers of data and variables,
respectively.
2
Angles
N(1)-Pd-N(3)#1
N(1)-Pd-N(3)
93.69(8)
86.31(8)
N(3)#1-Pd-N(3) 180.0
C(1)-N(1)-Pd
127.45(17)
128.96(16)
N(2)-N(3)-Pd
N(2)-C(2)-C(1) 126.10(2)
) 1.440(3) Å) in the same molecule and is similar to the typical
N-coordinated CdN (1.323(19) Å).7 The N-N distance of azo
nitrogens in the chelate ring (1.286(3) Å) is within the range of
coordinated azo lengths.1 Thus, it is reasonable to infer that PdII-
(HL)2 is an azoimine bis chelate obtained from an azoaniline
ligand precursor. Though the C2-N2 length (1.358(3) Å) is
not as short as the imine C-N length, it is considerably shorter
than the C-N single bond in the same molecule (vide supra),
suggesting a bond order between a single and a double bond.
The coordination mode of HL- is similar to one of the
coordination modes of arylazophenols,8 but unlike arylazophe-
nols the phenyl ring which is adjacent to the chelate ring is
distorted with two short (∼1.355 Å) and four long (∼1.427 Å)
C-C lengths. This type of distortion in the phenyl ring as a
consequence of delocalization due to formation of chelates has
been reported in the cases of o-arylenedimines9 and o-arylene-
dioxolenes,10 where the chelate rings are five-membered,9,10
unlike the present six-membered chelate.
Figure 1. ORTEP plot of PdII(HL)2 with atom-numbering scheme.
Hydrogen atoms, except that on N1, are omitted for clarity.
The free H2L ligand display symmetric and asymmetric νNH
2
bands at 3450 and 3370 cm-1. In contrast, PdII(HL)2 shows a
sharp single stretch at 3330 cm-1 characteristic of the NH
function.1a NdN of PdII(HL)2 is shifted to lower frequency (1340
ν
Acknowledgment. We are thankful to the Council of
Scientific and Industrial Research of India for financial support
and a fellowship to N.M. Vidyasagar University provided the
necessary laboratory facility. We are very much thankful to Prof.
A. Chakravorty of the IACS, Calcutta-700032, India, for his
inspiration and valuable suggestions. We acknowledge the help
of Dr. S. Pal of the University of Hyderabad for X-ray studies
and Dr. C. Sinha of Burdwan University for various physico-
chemical studies.
cm-1) compared to νNdN of H2L (1460 cm-1). In PdII(HL)2, a
strong band is observed at 1600 cm-1 which is absent in H2L.
This is assigned to νCdN, consistent with crystallographic results
(vide infra).
1
In the H NMR spectrum of H2L the relatively broad band
of the amino proton occurs at 5.9 ppm. On the other hand, in
PdII(HL)2 the signal is shifted to 4.9 ppm and its integration
corresponds to two protons of the equivalent NH groups.
X-ray Structure. The X-ray structure of PdII(HL)2 was
determined. A perspective view of the molecule and the atom-
numbering scheme are shown in Figure 1. Selected bond
parameters are collected in Table 2. The 2-(phenylazo)aniline
ligand binds in a bidentate (N,N) fashion. One ligand is
symmetry equivalent to the other, held in a trans position.
Palladium occupies a special position on a 2-fold axis of
symmetry, and the PdN4 coordination sphere is planar, consistent
with metal bivalency and monoionized nature of the ligands.
The chelate ring is, however, not planar. The fragment contain-
ing N2, C2, C3, C4, C5, C6, and C1 is satisfactorily planar
(mean deviation 0.05 Å), and its dihedral angle with the PdN4
plane is 24.5°. The dihedral angle between the pendant phenyl
ring and the PdN4 plane is 62.61°.
Supporting Information Available: 1H NMR and IR spectra of
H2L and PdII(HL)2 and X-ray crystallographic files in CIF format for
the structure determination of PdII(HL)2. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC000369P
(7) (a) Mitra, K. N.; Goswami, S. J. Chem. Soc., Chem. Commun. 1997,
49. (b) Mitra, K. N.; Majumdar, P.; Peng, S.-M.; Castneiras, A.;
Goswami, S. J. Chem. Soc., Chem. Commun. 1997, 1267.
(8) Sui, K.; Peng, S.-M.; Bhattacharya, S. Polyhedron 1999, 18, 631.
(9) (a) Hartl, F.; Snoeck, T. L.; Stufkens, D. J.; Lever, A. B. P. Inorg.
Chem. 1995, 34, 3887. (b) Masui, H.; Lever, A. B. P.; Dodsworth, E.
S. Inorg. Chem. 1993, 32, 258. (c) Vogler, A.; Kunkely, H. Angew.
Chem., Int. Ed. Engl. 1980, 19, 221.
(10) (a) Pierpont, C. G.; Lange, C. W. Inorg. Chem. 1993, 41, 381. (b)
Attia, A. S.; Bhattacharya, S.; Pierpont, C. G. Inorg. Chem. 1995, 34,
4427.
In the six-membered chelate ring, the N1-C1 length (1.322-
(3) Å) is considerably shorter than the C-N single bond (N3-C7