Diazoketiminato complexes of Au(III): Syntheses, characterisation and structure

Article abstract of DOI:10.1016/S0277-5387(03)00466-2

A series of 2-(arylazo)aniline ligands were synthesised. The reaction of these ligands with HAuCl₄ afforded diazoketiminato complexes of Au(III). The ligands and complexes were characterised by ¹H NMR, IR and UV-Vis spectroscopic data. The X-ray structure of one of the complexes has been determined and the formation of a diazoketiminato species has been established.

Full text of DOI:10.1016/S0277-5387(03)00466-2

Polyhedron 22 (2003) 3109–3113
www.elsevier.com/locate/poly
Diazoketiminato complexes of Au(III): syntheses,
characterisation and structure
a
Nilkamal Maiti , Bimal Kumar Dirghangi , Surajit Chattopadhyay
b
a,
*
a
Department of Chemistry, University of Kalyani, Kalyani 741235, India
b
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
Received 22 April 2003; accepted 27 June 2003
Abstract
A series of 2-(arylazo)aniline ligands were synthesised. The reaction of these ligands with HAuCl4 afforded diazoketiminato
1
complexes of Au(III). The ligands and complexes were characterised by H NMR, IR and UV–Vis spectroscopic data. The X-ray
structure of one of the complexes has been determined and the formation of a diazoketiminato species has been established.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: 2-(Arylazo)anilines; Gold(III) complex; Diazoketiminato species
1. Introduction
tributed to the delocalisation in the ligand backbone.
Analogous delocalisation has been stated as the origin
of several unusual properties in the complexes of 2-
((arylamido)phenylazo)pyridines [4]. Among the delo-
calised azo ligands, arylazopyridine, arylazoimidazole
and arylazooximates have been demonstrated to afford
transition metal complexes with interesting structures
and properties [5]. Identical number of valance elec-
trons of palladium(II) and gold(III) encouraged us to
examine the formation of a diazoketiminato chelate of
Au(III).
The transition metal chelates of ligands with deloca-
lised p conjugation within the chelate ring have drawn
much attention in recent years [1]. Among these ligand
systems b-diketonates (1), b-enaminoketonates (2) and
b-diketiminates (3) are noteworthy [2].
Herein we describe the syntheses, characterisation
and structure of the first diazoketiminato complexes of
Au(III). The ligand precursors, 2-(arylazo)anilines, LH2
(Chart 1), bind the metal as an uninegative anion (LHꢀ),
dissociating an amino proton. In LH2, H represents
amino protons.
Such anionic bidentate ligands bind the transition
metals forming a six membered chelate ring with 6p
electrons (4n + 2 rule). Recently we have reported the
palladium(II) chelate incorporating the diazoketimi-
nato ligand (4) [3]. The ligand systems 1, 2, 3, and 4
are isoelectronic with respect to the chelate ring p
electrons. The structural characteristics in the dia-
zoketiminato complex of palladium(II) has been at-
Syntheses and characterisation of L2H2 and L3H2
have also been described here for the first time.
2. Experimental
2.1. Materials
* Corresponding author.
E-mail address: scha8@rediffmail.com (S. Chattopadhyay).
All starting materials were used as received from
commercial sources; the solvents were purchased from
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00466-2

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N. Maiti et al. / Polyhedron 22 (2003) 3109–3113
2.3.1. (L1H)AuCl2
An ethanolic solution (20 cm3) of L1H2 (0.13 g, 0.677
mmol) was added to an aqueous solution (20 cm3) of
HAuCl4 (0.23 g, 0.677 mmol). The colour of the solution
turned pink. The resulting pink solution was stirred for
3 h, filtered off and washed with distilled water several
times. A pure compound was obtained by recrystallisa-
tion from dichloromethane. Yield 80%. Anal. Found: C
31.05, H 2.25, N 9.03. Calc. for C12H10N3AuCl2: C
Chart 1.
1
31.03, H 2.20, N 9.00 %. H NMR (CDCl3): ¼ 7.61 (s,
NH); 6.84 (t, 5H); 6.96 (d, 6H); 7.43–7.55 (m, 9H 11H
12H 8H and 4H); 7.72 (d, 3H).
E. Marck, Kolkata, India, and purified and dried by
reported procedures [6]. o-Phenylenediamine, nitroben-
zene, p-methyl and p-chloro nitrobenzene from Loba,
Kolkata, India. Tetrachloroauric acid (HAuCl4, XH2O)
from SRL, Kolkata, India. Ethyl alcohol from Bengal
Chemical, Kolkata, India. The ligand 2-(phenylazo)an-
iline (L1H2) was prepared following the reported pro-
cedure [3].
2.3.2. (L2H)AuCl2
This complex was prepared following a similar pro-
cedure as described for (L1H)AuCl2 using ligand L2H2
in place of L1H2. Yield 75%, Anal. Found: C 32.70, H
2.59, N 8.80. Calc. for C13H12N3AuCl2: C 32.64, H 2.51,
1
N 8.79 %. H NMR (CDCl3): ¼ 6.85 (t, 5H); 6.96 (d,
6H); 7.25 (d, 9H and 11H); 7.46–7.50 (m, 8H 12H and
4H); 7.71 (d, 3H); 2.43 (s, p-CH3).
2.2. Synthesis of ligands
2.3.3. (L3H)AuCl2
2.2.1. L2H2
This complex was prepared following a similar pro-
cedure as described for (L1H)AuCl2 using ligand L3H2
in place of L1H2. Yield 72%, Anal. Found: C 28.90, H
1.90, N 8.50. Calc. for C12H9N3AuCl3: C 28.89, H 1.81,
o-Phenylenediamine (2 g, 18.5 mmol), p-methylni-
trobenzene (2.5 g, 18.5 mmol) and sodium hydroxide
(0.74 g, 18.5 mmol) were mixed and heated at 70 °C
with constant scratching for 30 min. The dark pasty
mass thus obtained was cooled to room temperature
and extracted with benzene. The pure 2-(p-toly-
lazo)aniline, L2H2 was obtained by column chroma-
tography on a silica gel (60–120 mesh) column using
benzene-petroleum ethere mixed solvent (10/90 v/v) as
an eluant. Yield 51%. Anal. Found: C 73.95, H 6.20,
N 19.92. Calc. for C13H13N3: C 73.93, H 6.16, N
19.90%. 1H NMR (CDCl3): d ¼ 5:81 (s, NH2); 6.75
(d, 6H); 6.81 (t, 5H); 7.19 (t, 4H); 7.28 (d, 9H and
11H); 7.74 (d, 8H and 12H); 7.80 (d, 3H); 2.41 (s, p-
CH3).
1
N 8.43 %. H NMR (CDCl3): ¼ 7.56 (s, NH); 6.77 (t,
5H); 6.88 (d, 6H); 7.34–7.42 (m; 8H, 12H, 9H, and 11H);
7.47 (t, 4H); 7.63 (d, 3H).
2.4. Physical measurements
Microanalysis (C,H,N) were performed using a Per-
kin–Elmer 240C elemental analyzer. Infrared spectra
were recorded on a Perkin–Elmer 783 spectrometer with
the samples prepared as KBr pellets. Electronic spectra
were recorded on a Simadzu UV 1601 spectrophotom-
eter. 1H NMR spectra were obtained on Brucker
Avance DPX 300 and Brucker Avance DPX 400 NMR
spectrometers in CDCl3 using TMS as the internal
standard.
2.2.2. L3H2
2-(p-Chlorophenylazo)aniline (L3H2) was prepared
following a similar procedure as described for 2-(p-tol-
ylazo)aniline using p-chloronitrobenzene in place of p-
methylnitrobenzene. Yield 7 1%. Anal. Found: C 62.25,
H 4.39, N 18.19. Calc. for C12H10N3Cl: C 62.20, H 4.32,
2.5. Crystallography
Single crystals of (L1H)AuCl2 were grown by slow
evaporation of dichloromethane solution at 298K.
The size of the crystal suitable for X-ray studies was
0.32 ꢁ 0.26 ꢁ 0.20 mm3. Cell parameters were deter-
mined by least square fits of 25 machine centered re-
flections (2h ¼ 15–28°). Data were collected by the
x- scan technique on a Nicolet R 3m/v diffractometer
with Mo Ka radiation monochromated by graphite
crystal. Absorption correction was not done. Crystal
data were collected in Table 1. The structure solution
was done by direct methods with the SHELXS 90 pro-
1
N 18.14%. H NMR (CDCl3): d ¼ 5:73 (s, NH2); 6.60
(d, 6H); 6.66 (t, 5H); 7.06 (t, 4H); 7.28 (d, 9H and 11H);
7.62 (d, 8H and 12H); 7.67 (d, 3H).
2.3. Synthesis of complexes
The complexes (L1H)AuCl2, (L2H)AuCl2 and
(L3H)AuCl2 were prepared by the reaction of HAuCl4
with L1H2, L2H2 and L3H2, respectively, in ethanol. The
details are given below.

N. Maiti et al. / Polyhedron 22 (2003) 3109–3113
3111
Table 1
Crystallographic data for (L1H)AuCl2
The ligands and complexes display characteristic
UV–Vis spectra. The transitions in the visible region
(ꢂ420 nm) for the ligands are assigned for n ! pꢃ and
the higher energy transitions (UV-region) for p ! pꢃ.
The spectra of the metal complexes are distinctly dif-
ferent to that of the ligands. The absorption ꢂ500 nm
has been assigned as a metal to ligand charge transfer
(MLCT) transition. Representative spectra of the ligand
(L1H2) and the corresponding complex ((L1H)AuCl2)
have been shown in Fig. 1. The UV–Vis spectral data are
collected in Table 2.
Chemical formula
Formula weight
Crystal System
Space group
C12H10N3AuCl2
464.10
monoclinic
P21/n
ꢀ
a (A)
9.553(4)
8.386(4)
16.978(7)
102.05(3)
1330.2(10)
4
ꢀ
b (A)
ꢀ
c (A)
b (°)
V (A )
3
ꢀ
Z
Temperature (K)
293
ꢀ
The IR spectra of LH2 exhibit a couple of closely
spaced absorptions in the range 3360–3458 cmꢀ1char-
acteristic of mNH2 [7], on the contrary, for (LH)AuCl2 a
single band appeared in the range 3257–3320 cmꢀ1
characteristic for mNH. This supports the dissociation of
an amino proton from LH2 upon complex formation
k (A)
0.71073
2.317
11.445
qcalcd (M g/m3)
l (mmꢀ1
Reflections collected
Independent reflections
Rint
)
2445
2265
0.0518
0.0482
R1(I > 2r)
wR2(I > 2r)
GOFa
1
0.1066
1.075
and is consistent with H NMR and X-ray data (vide
infra). The red shift of mN¼N (in the range 1337–1353
cmꢀ1) in (LH)AuCl2 compared to LH2 (1458–1474
cmꢀ1) indicates the coordination of the azo nitrogen
[5a,5h–5k]. The absorption near 1610 cmꢀ1 in
(LH)AuCl2 has been assigned for mC¼N which are absent
in LH2. The selected IR data are listed in Table 2.
2
1=2
a The goodness-of-fit is defined as fW ðjFoj ꢀ jFcjÞ =ðno ꢀ nvÞg
where no and nv denote the numbers of data and variables, respec-
tively.
gram. Full matrix least square refinements were per-
formed using the SHELX 97 program (PC version). All
non hydrogen atoms were refined anisotopically using
reflections I > 2rðIÞ. All hydrogens were included at
calculated positions.
1
The ligands and complexes display well resolved H
NMR spectra. The broad amino proton resonances for
(L1H)AuCl2 and (L3H)AuCl2 appear in the aromatic
region (7.61 and 7.56 ppm, respectively) for the one
equivalent proton. In contrast for the L1H2 and L3H2,
the amino protons resonate at 5.90 and 5.73 ppm, re-
spectively, for the two equivalent protons. This is con-
sistent with the dissociation of an amino proton from
the ligands (L1H2 and L3H2) upon coordination. For
(L2H)AuCl2 the same signal is probably obscured by
other aromatic proton resonances in the range 7.46–7.50
ppm, however, the amino protons of L2H2 have been
observed at 5.81 ppm for two the equivalent protons. In
3. Results and discussion
The ligands L2H2 and L3H2 have been synthesised in
one pot by the reaction of o-phenylenediamine with p-
methylnitrobenzene and p-chloronitrobenzene, respec-
tively, in presence of the sodium hydroxide at elevated
temperature (Eq. (1)). Synthesis of L1H2 has been de-
scribed earlier [3].
1
the H NMR spectra of the ligands (LH2), 6H and 4H
appear in the range 6.60–6.75 ppm and 7.06–7.20 ppm,
respectively, whereas for the complexes ((LH)AuCl2) the
ð1Þ
The reaction of equimolar LH2 ligand and tetra-
chloroauric acid in ethanol affords a dark coloured solid
of composition (LH)AuCl2. The complexes are non-
conducting, diamagnetic and soluble in common or-
ganic solvents giving a pink solution. The analytical
data (C,H,N) match well with the composition.
Fig. 1. UV–Vis spectra of L1H2 ( – – ) and (L1H)AuCl2 (- - - - - -). The
arrows indicate scales of the corresponding spectrum.

3112
N. Maiti et al. / Polyhedron 22 (2003) 3109–3113
Table 2
UV–Visa and IRb spectral data
m/cmꢀ1
Compound
k )
max/nm (e/Mꢀ1 cmꢀ1
m
NH2
mNH
mC@N
mN@N
mAu–Cl
L1H2
416 (8963), 313 (14,455), 243 (14,791)
421 (2668), 321 (5260), 271 (8787)
421 (11,768), 320 (36,693), 233 (28,770)
499 (2656), 380c (2755), 304 (8787)
501 (10,436), 400c (11,155), 305 (30,432)
501 (3496), 385c (3561), 304 (10860)
3456, 3382
3458, 3378
3432, 3360
1461
1458
1474
1337
1353
1342
L2H2
L3H2
(L1H)AuCl2
(L2H)AuCl2
(L3H)AuCl2
3257
3320
3311
1601
1616
1617
334, 273
302, 291
300, 287
a In dichloromethane.
b In KBr disc.
c Shoulder.
Table 3
same resonances are downfield shifted and observed
within 6.88–6.96 ppm and 7.43–7.50 ppm, respectively.
The numbering scheme for the H NMR analysis has
1
ꢀ
Selected bond distances (A) and angles (°) for (L H)AuCl2
1
Distances
Au–N(1)
Au–Cl(1)
N(1)–C(1)
N(2)–C(2)
C(1)–C(2)
C(2)–C(3)
C(4)–C(5)
1.973(12)
2.308(4)
1.35(2)
1.37(2)
1.42(2)
1.43(2)
1.38(3)
Au–N(3)
2.044(11)
2.289(4)
1.27(2)
1.44(2)
1.40(2)
1.32(2)
1.33(2)
been followed as shown in Fig. 2.
Au–Cl(2)
N(2)–N(3)
N(3)–C(7)
C(1)–C(6)
C(3)–C(4)
C(5)–C(6)
The crystal structure of (L1H)AuCl2 has been deter-
mined by X-ray crystallography at 293K. A perspective
view of the molecule with the atom numbering scheme is
shown in Fig. 2. Selected bond distances and angles have
been summarised in Table 3.
The gross geometry about Au(III) is square planar,
coordinated by the bidentate (N,N) ligand and two
chlorides satisfying the tetracoordination. The planar
geometry about gold is consistent with its trivalency
and the binding of anionic (LH)ꢀ can be inferred
since the complex is nonconducting. This is also in
accordance with the IR and 1H NMR results (vide
supra).
Angles
N(1)–Au–N(3)
Cl(1)–Au–Cl(2)
C(1)–N(1)–Au
C(1)–C(2)–N(2)
N(2)–N(3)–Au
86.4(5)
90.6(2)
N(3)–Au–Cl(1)
Cl(2)–Au–N(1)
N(1)–C(1)–C(2)
C(2)–N(2)–N(3)
N(1)–Au–Cl(1)
93.5(4)
89.5(4)
120.5(10)
123.8(14)
123.5(10)
121.5(14)
124.8(12)
178.0(4)
considerably shorter than the C–N single bond length
which is expected to occur as a result of delocalisation
and formation of diazoketiminato chelate, 7.
In the six membered chelate ring, the N(1)–C(1)
ꢀ
length (1.35(2) A) is considerably shorter than the C–N
ꢀ
single bond length (N(3)–C(7); 1.44(2) A) in the same
molecule. The phenyl ring (C(1), C(2)ꢄ ꢄ ꢄC(6)) is dis-
ꢀ
torted with four long (ꢂ1.41 A) and two short bonds
ꢀ
ꢀ
(ꢂ1.32 A). The C(2)–N(2) length (1.37(2) A) is also
In the square planar complex Cl(1) and Cl(2) are
trans to N(1) and N(3), respectively, where the Au–Cl(1)
ꢀ
distance (2.308(4) A) is longer than Au–Cl(2) (2.289(4)
ꢀ
A) due to the stronger trans influence of the imino ni-
trogen (N(1)) than the azo nitrogen (N(3)).
The fragment containing N(1), N(3), Au, Cl(1) and
ꢀ
Cl(2) is planar with a mean deviation 0.01 A. On the
other hand the fragment containing N(1), C(1), C(2),
N(2), and N(3) is also satisfactorily planar (mean devi-
ꢀ
ation 0.03 A). The dihedral angle between these two
Fig. 2. ORTEP plot of (L1H)AuCl2 with atom-numbering scheme.
Hydrogen atoms, except that on N(1), are omitted for clarity.
planes, 38.6°, is in accordance with the boat structure of
the chelate ring, 8.

N. Maiti et al. / Polyhedron 22 (2003) 3109–3113
3113
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4. Supplementary data
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC reference number 198808. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK. E-mail: deposit@ccdc.cam.ac.uk.
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Acknowledgements
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We are thankful to the Council of Scientific and In-
dustrial Research, India for financial support and fel-
lowship to NM. Vidyasagar University, Midnapur and
University of Kalyani, Nadia provided the necessary
laboratory facility. We acknowledge the National Dif-
fractometer facility at the Department of Inorganic
Chemistry, IACS, Kolkata-32 for X-ray structure de-
termination.
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