Mono- and dinuclear palladium(II) compounds containing N,S donor ligands : Synthesis, characterization and thermal behavior

Article abstract of DOI:10.1007/s10973-006-7770-4

Synthesis, spectroscopic characterization and thermal analysis of the compounds [Pd₂(dmba)₂(μ-NCO)(μ-2-qnS)] (1), [Pd ₂(dmba)₂(μ-NCO)(μ-8-qnS)] (2), [Pd(2-qnS) ₂] (3) and [Pd(8-qn_S)2] (4) (

Full text of DOI:10.1007/s10973-006-7770-4

Journal of Thermal Analysis and Calorimetry, Vol. 87 (2007) 3, 721–724
MONO- AND DINUCLEAR PALLADIUM(II) COMPOUNDS CONTAINING
N,S DONOR LIGANDS
Synthesis, characterization and thermal behavior
A. C. Moro1, A. E. Mauro1*, S. R. Ananias2, A. Stevanato1 and A. O. Legendre1
1Instituto de Química de Araraquara, UNESP, C.P. 355, 14801-970 Araraquara, SP, Brazil
2Departamento de Análises Clínicas, Faculdade de CiÃncias FarmacÃuticas, UNESP, C.P. 502, 14801-902 Araraquara, SP, Brazil
Synthesis, spectroscopic characterization and thermal analysis of the compounds [Pd2(dmba)2(μ-NCO)(μ-2-qnS)] (1),
[Pd2(dmba)2(μ-NCO)(μ-8-qnS)] (2), [Pd(2-qnS)2] (3) and [Pd(8-qnS)2] (4) (dmba=N,N-dimethylbenzylamine; 2-qnS=2-quinoline-
thiolate; 8-qnS=8-quinolinethiolate) are described. The thermal decomposition of these compounds occurs in four consecutive steps
and the final decomposition products were identified as Pd(0) by X-ray powder diffraction. The thermal stability order of the com-
plexes is 4>3>1>2.
Keywords: chelates, cyclopalladated compounds, quinolinethiol, thermal analysis
Introduction
acterization and thermal behavior of the compounds
[Pd2(dmba)2(μ-NCO)(μ-2-qnS)] (1),
Benzylamines, such as N,N-dimethylbenzylamine
(dmba), are C,N donor ligands and good candidates to
the synthesis of cyclometallated species [1–5], which
constitute an important class of compounds within the
organometallic chemistry, whose preparation and
uses are currently under investigation in many labora-
tories [1, 2]. Cyclopalladated compounds, for exam-
ple, have been used as pathways to new products in
organic synthesis [6], as catalysts [7], anti-tumor
drugs [8], in photochemistry [7] and for the design of
metallomesogens [9].
[Pd2(dmba)2(μ-NCO)(μ-8-qnS)] (2), [Pd(2-qnS)2] (3)
and [Pd(8-qnS)2] (4).
Experimental
Preparation of the complexes
All the syntheses were carried out at room tempera-
ture. All reagents were obtained from commercial
suppliers and used without further purification. The
starting
[PdCl2(CH3CN)2] were prepared as previously
described [3, 16].
[Pd2(dmba)2(μ-NCO)(μ-2-qnS)]
materials
[Pd(dmba)(μ-NCO)]2
and
On the other hand, heterocyclic thiols attract con-
siderable attention because of their relevance in biologi-
cal systems [10]. Moreover, reactions between cyclo-
metallated compounds and 2-quinolinethiol (2-qnSH)
[1, 10] have been explored due to the ability of this
ligand to form stable compounds with several transition
metals [11, 12]. This thioligand exists predominantly in
the quinolinethione form and coordinates through the
sulfur atom in the most common S-monodentate coordi-
nation mode [13]. In addition, the versatility of the con-
jugate anion qnS– has been demonstrated in a large
number of complexes, yielding a variety of coordination
compounds with great structural diversity: S-mono-
dentate [13]; N,S-chelating [12] and μ-N,S-bridging
[10]. This behavior is analogous to the dominant coordi-
nation chemistry of pyridinethiolate [14, 15]. Previ-
ously, we had been interested in the spectroscopic and
thermogravimetric studies of cyclopalladated com-
pounds [1–5]. As a part of our research program in this
area, we report in the present study the synthesis, char-
(1)
and
[Pd2(dmba)2(μ-NCO)(μ-8-qnS)] (2) were prepared by
the addition of 0.030 g (0.18 mmol) of the thioligand
to a dichloromethane solution containing 0.10 g
(0.18 mmol) of [Pd(dmba)(μ-NCO)]2. The mixtures
were stirred for 1 h, the solvent was removed under
reduced pressure and the red (1) and yellow (2) solids
obtained were recrystallized from CHCl3/n-C5H12 and
dried in vacuum. The yield was 71% in each case.
[Pd(2-qnS)2] (3) and [Pd(8-qnS)2] (4) were syn-
thesized by the addition of 0.12 g (0.76 mmol) of the
thioligand and 0.031 g (0.76 mmol) of NaOH to an ac-
etone solution containing 0.10 g (0.38 mmol) of
[PdCl2(CH3CN)2]. The resulting suspensions were
stirred for 1 h and the orange (3) and red (4) solids
were filtered, washed with water, acetone, pentane
and then dried in vacuum. The yields were 55% for
(3) and 80% for (4).
*
Author for correspondence: mauro@iq.unesp.br
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2007 Akadémiai Kiadó, Budapest

MORO et al.
Instrumentation
Elemental analyses of carbon, nitrogen and hydrogen
were performed on an EAGER-200 CHNSO-CE
equipment. Infrared spectra (IR) were recorded on an
Nicolet Impact 400 spectrophotometer in the
4000–400 cm–1 spectral range as KBr pellets.
Simultaneous thermal analyses (TG-DTA) were
carried out using a SDT 2960 system (TA Instru-
ments Co.) under dynamic flow of dry synthetic air
(50 mL min–1) at a heating rate of 20°C min–1 using
α-alumina open crucibles for sample and reference.
The X-ray powder diffractograms were obtained in a
HGZ4/B horizontal diffractometer (G.D.R) equipped
with a proportional counter and pulse height
discriminator. The Bragg–Bentano arrangement was
adopted using CuKα radiation (λ=1.541 ) and set-
ting of 34 kV and 20 mA. The residues (Pd, PdO)
were identified using ICDD bases [17].
Fig. 1 Suggested structures for compounds 1–4
ing compound did not affect the integrity of the
orthometallatted ring. Concerning the NCO ligand, the
presence of the N-bridging cyanato group in (1) and (2)
was evidenced by the νCN band at 2172 and 2197 cm–1,
respectively [3, 18]. The bidentate coordination of
2-qnS and 8-qnS between [Pd(dmba)] moieties in (1)
and (2) was clearly evidenced by the appearance of ad-
Results and discussion
Elemental analyses for the synthesized compounds
are in agreement with the proposed formulae and are
given in Table 1 together with the melting points. In
dichloromethane solutions, the reactions between
[Pd(dmba)(μ-NCO)]2 and 2- and 8-quinolinethiol in
the 1:1 molar ratio occurred readily, leading to the
species [Pd2(dmba)2(μ-NCO)(μ-2-qnS)] (1) and
[Pd2(dmba)2(μ-NCO)(μ-8-qnS)] (2). These com-
plexes are more soluble than the starting compounds
in organic solvents. The mononuclear compounds
[Pd(2-qnS)2] (3) and [Pd(8-qnS)2] (4) were obtained
by reactions between [PdCl2(CH3CN)2] and 2- and
8-qnS in the 1:2 molar ratio. The infrared and
thermogravimetric data of the complexes 1–4 are
discussed as follows.
ditional IR bands at 1494–1495 cm–1 (νCN ),
ring
and 1071–1102 cm–1 (νCS). Regarding to the IR spectra
of (3) and (4), the coordination of the 2-qnS and 8-qnS
ligands was detected by the disappearance of the bands
at 2329 cm–1, attributed to the νCN of the acetonitrile
molecules, and of the ones at 3100 and 2500 cm–1 (νNH
and νSH, respectively), characteristics of the neutral
thioligands [1], as well as by the presence of bands
at 1543–1557 (νCC) and 1076–1088 cm–1 (νCS). The pro-
posed molecular structures for compounds 1–4 are
shown in Fig. 1.
Thermogravimetric analysis
At this point it is worthy to note that thermal analysis
has been scarcely employed for the study of
cyclometallated compounds, despite its large use for
other classes of metal complexes [1–4]. In the present
paper, the main objectives of the thermogravimetry
studies (TG) is to enlight the influence of the
thioligands on the initial decomposition temperature
of the complexes, as well as to propose decomposi-
Infrared spectra
The characteristic bands of the cyclometallated ring
at 3041–3047 cm–1 (νCH ), 2910–2972 cm–1 (νCH
and 2727–2854 cm–1 (νCH ) in the infrared spectra
)
3
ring
2
of (1) and (2) were found unchanged when compared to
those observed for the precursor [3]. Therefore, the in-
teraction between 2-qnS and 8-qnS ligands and the start-
Table 1 Elemental analyses and melting points for compounds 1–4
Carbon/%
Nitrogen/%
found
Hydrogen/%
found
Complex
Melting point/°C
found
49.0
49.6
50.1
50.3
calc.
49.2
49.2
50.6
50.6
calc.
8.20
8.20
6.56
6.56
calc.
4.42
4.42
2.84
2.84
1
2
3
4
119 (dec.)
108 (dec.)
215 (dec.)
242 (dec.)
8.24
7.98
6.40
6.70
4.41
4.35
2.60
2.94
722
J. Therm. Anal. Cal., 87, 2007

MONO- AND DINUCLEAR PALLADIUM(II) COMPOUNDS
tion steps. The TG/DTG and DTA curves for the
two consecutive steps, yielding a mixture of Pd
(ASTM 05-0681) and PdO (ASTM 06-0515) [17].
Afterwards, the TG curves also exhibit a progressive
mass gain up to 790°C due to the partial oxidation of
the Pd to PdO. The last mass loss is characterized by
the decomposition of the remaining PdO to Pd
(ASTM 05-0681) at 900°C. The ligands of the com-
pounds (3) and (4) are eliminated in the
dinuclear (1 and 2) and mononuclear compounds (3
and 4) are shown in Fig. 2. Table 2 presents the repre-
sentative thermal data of complexes 1–4, together
with the assignments for each decomposition step.
In the 100–480°C temperature range, com-
pounds (1) and (2) lose the organic (qnS and dmba)
and inorganic (NCO) ligands, with uptake of O2, in
Fig. 2 TG/DTG and DTA curves of 1–4 complexes
Table 2 Thermal analysis data for compounds 1–4
Δm/%
DTA peak/°C
Assignment
exo
Complex
Step
ΔT/°C
found
calc.
endo
1
111–295
295–480
480–790
790–900
–47.7
–19.4
+2.72
–3.98
31.6
–48.0
–19.6
+2.34
–3.51
31.1
189
–
218
416
–
–NCO–dmba–(2-qnS)+1/4O2
2
–dmba
+1/2O2
–3/4O2
1
3
–
4
812
–
–
residue
–
1
100–360
360–475
475–780
780–900
–43.7
–24.0
+2.76
–3.98
31.1
–44.2
–23.4
+2.34
–3.51
31.1
–
–
–
453
–
–NCO–2dmba+1/4O2
–(8-qnS)
2
2
3
4
3
–
+1/2O2
4
804
–
–
–3/4O2
residue
–
1
200–350
350–600
600–800
800–900
–23.9
–48.5
+0.6
–23.5
–50.6
+0.9
–
–
–
456
–
–2C4H2
2
–2C5H4NS+1/8O2
+1/8O2
3
–
4
–3.20
25.2
–1.93
24.9
822
–
–
–1/4O2
residue
–
1
230–430
430–560
560–795
795–900
–30.4
–43.5
+0.80
–1.62
25.3
–30.0
–43.2
+0.89
–1.88
24.9
–
–
–
513
–
–C10H8
2
–C8H4N2S2+1/8O2
+1/8O2
3
–
4
809
–
–
–1/4O2
residue
–
*minitial: (1) – 5.223 mg; (2) – 4.820 mg; (3) – 5.164 mg; (4) – 5.181 mg.
J. Therm. Anal. Cal., 87, 2007
723

MORO et al.
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DOI: 10.1007/s10973-006-7770-4
Acknowledgements
The authors wish to acknowledge FAPESP, CNPq and
CAPES for the financial support.
724
J. Therm. Anal. Cal., 87, 2007