Tin (IV) Derivatives of the Tetradentate Ligand N, N Bis-(2-Pyridylmethylene)-Ethane-l, 2-Diamine
Jose Roberto da S. Maia a ' \ Rafael C. R. Chagas3, Vany P. Ferraz b and Maria I. Yoshida b
a
Departamento de QuDmica, CCET / UFV, A v. P. H. Rolfs s/n, Vinosa, MG, 36570-000,
b
Departemente de QuDmica, ICEx / UFMG, Belo Horizonte, MG, 31270-901,
Brasil.
Brasil.
ABSTRACT
A series of organotin(IV) (SnClJMu-x, χ = 1, 2, 3) and SnCL, derivatives of N, N'-bis-(2pyridylmethylene)-ethane-1, 2-diamine (pmed) have been prepared in 2:1 (M:L) molar ratio in
dichloromethane. The SnClPh3 derivative has afforded an equimolar product in contrast to the other metal
precursors. The materials were characterised by infrared, multinuclear ('H, "C,
n9
Sn) NMR spectroscopy,
thermal analysis (TG, DSC), gel permeation chromatography (GPC) and microanalysis. The spectroscopic
methods have given evidence for metal-ligand bond formation through pyridyl and azomethine nitrogen
atoms. For the SnClPh3 derivative a five-fold coordination metal centre has been revealed by 1,9Sn NMR in
CH2Cl2.in contrast to the SnClxPh4.x(x = 2, 3, 4) derivatives. In those both six- and seven-fold coordination
species have been revealed in DMF. The 119Sn NMR resulting data suggest that a dynamic process has taken
place in solution, leading to a structural rearrangement by auto-association. In addition, the GPC technique
has revealed in DMF higher values of weight-average molar mass in comparison to that established by the
elemental analysis. However, the molar mass obtained for those compounds does not correspond to
polymeric materials, as confirmed by DSC analysis.
INTRODUCTION
Schiff bases constitute an appealing class of organic compounds to work within the coordination
chemistry field /l, 2/. Those materials have been known for more than one hundred years and have an
enormous range of applications /3/. The interest of inorganic chemists in this class of compounds is in
connection to technological development concerning the usefulness of metal-Schiff base complexes. The
expectation of that is unquestionable. For instance, complexes have already been applied in asymmetric
catalysis /4/, non-linear optics /5/ as well as in the biological field /6, 7/ presenting a variety of biological
activity. This research field has been growing in recent decades. The presence of the metal seems to play an
* Author to whom correspondence should be addressed. E-mail: [email protected] 2
321
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Vol. 29, No. 6, 2006.
Tin(IV) Derivatives
ofArsenic(III):
important role in the activity of these compounds. To illustrate that, di- and trialkylorganotin(IV) derivatives
of Schiff bases /8/ has markedly increased the activity against Bacillus subtilis and Staphylococcus
aureus.
The biological activity of N, N'-bis-(2-pyridylmethylene)-ethane-l, 2-diamine (known as pade = pmed) has
been acknowledge against the green alga Chlorella 191. In this case, the pmed and its first-row transition
metal complexes have shown to be less toxic than the corresponding metal chlorides. Concerning the
coordination chemistry, pmed is an interesting ligand due to its polydentate character. A tetradentate
coordination mode for this ligand as well as an octahedral geometry for the metal centre has been
characterised in Ru(II) and lanthanide(III) derivatives /10, 11/. The literature also provides examples of
hexacoordinated Cr(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) 191. A tetradentate coordination is not
an unusual pattern, as it has been revealed by X-ray crystallography studies for first-row transition metals
and SnßuCl 3 Schiff base complexes /12, 13/. Particularly in the Ru(II) derivatives of pmed, the X-ray
diffraction shows the metal centre bound to the azomethine and pyridyl moiety resulting in three chelate rings
/ l l / . In this compound all 4-nitrogen atoms are in trans position to the Ru(II) ion. However, the coordination
chemistry involving pmed with tri-, di- and phenylorganotin(IV) chlorides as well as tin(IV) tetrachloride has
not been investigated so far. Consequently, several coordination modes of pmed are conceivable towards the
tin(IV) precursors as shown in Scheme 1.
\
Ν
\
•vjT)
•ir.
/
Naev
t •
II
w
to
\\
K
A
IV
M-
Ν
1
-ΛΙVI
Scheme 1:
Possible metal bonding coordination of pmed showing mono-, bi-, tri-, and tetradentate
coordination modes.
322
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Main Group Metal Chemistry
Jose Roberto da S. Maia et al.
Following our interest in organotin coordination chemistry, in the present work we report the synthesis
and characterisation of a series of tin(IV) derivatives of pmed. These compounds were prepared in a 2:1
(M:L) molar ratio and have been formulated as [SnPh3(pme</)]Cl.CH2Cl2 (1), [Sn2Cl4Ph4(pme<i)] (2),
[Sn2Cl6Ph2(pmei/)] (3) and [Sn2Cls(pmed)] (4). Their characterization was carried out by techniques such as
infrared, "H, ° C and
119
Sn NMR spectroscopy, thermoanalysis (TG), differential scanning calorimetry
(DSC), gel permeation chromatography (GPC) and microanalysis.
MATERIALS AND METHODS
2.1. Materials and methods
Experiments of 'H and n C{'H} NMR spectra were obtained using a Varian Mercury-300 and
ng
Sn{'H}
NMR using a Bruker DPX-400 spectrometer equipped with an 89 mm wide-bore magnet. The ° C NMR
shifts are reported relative to SiMe4 and
119
Sn NMR shifts to SnMe4 as internal standards (δ = 0). Infrared
spectra were recorded on a Perkin Elmer Spectrum 1000 grating spectrometer, using Nujol suspension
between Csl windows scanning from 4000 to 200 cm"'. Thermogravimetry analysis (TG) was carried out
using a TGA-50 Shimadzu at a heating rate of 10 °C min'1 in air with a rate flow of 30 ml min"1 from room
temperature to 750 °C. The differential scanning calorimetry (DSC) analysis was performed employing a
DSC-50 Shimadzu at a heating rate of 10 °C min"1 from room temperature to 400 °C. Gel permeation
chromatography (GPC) data were obtained by a GPC803D-GPC802D 2 χ 300 χ 8 mm column in
dimethylformamide (DMF) by means of a Shimadzu device. The microanalysis was carried out in a Perkin
Elmer 2400 CHN analyzer. Vacuum techniques, nitrogen atmosphere, and Schlenk glassware was used
throughout the experimental work for the preparation of the tin(IV) derivatives. The organotin reactants were
purchased from Aldrich.
2.2. Preparation of the Schiff base
The preparation of pmed was carried out in a 2:1 molar ratio between 2-pyridine-carboxaldehyde and
ethylenediamine in ethanol as described in the literature /10,11/.
N, N'-bis-(2-pyridylmethylene)-ethane-l,
2-diamine (pmed): Yield: 4.61 g (37%) of a pale yellow
material. Mp (°C) 63 - 64; Elemental analysis required for C14HI4N4: C, 70.56; H, 5.91; N, 23.51; found:
C, 70.10; H, 5.53; N, 24.21. IR (Nujol / Csl): 1644 (C=N)azo, 1583, 1563 (C=Npy + C=C), 'H NMR
(CDCI3, 300.0 MHz): δ 4.03 (s, CH2, 4H), 7.24 - 7.28 (m, py, 2H), 7.68 - 7.71 (td, py, 2H), 7.92 - 7.96
(dt, py, 2H), 8.38 (s, N=CH, 2H), 8.57 - 8.59 (m, py, 2H); ,3 C NMR (CDCI3, 75.4 MHz): δ 61.5 (CH2),
121.5 (py), 124.9 (py), 136.8 (py), 149.6 (py), 154.5 (py), 163.6 (N=CH).
323
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Vol. 29, No. 6, 2006.
Tin(fV) Derivatives of Arsenic(III):
2.3. Preparation of the tin(IV) derivatives
2.3.1. [SnPh3(pmed)]Cl.CH£l2
(1):
The metal precursor SnClPh 3 (0.81 g, 2.10 mmol) and pmed (0.25 g, 1.05 mmol) were dissolved in
dichloromethane (60 ml) and stirred for 2 h at room temperature. After that, the mixture was transferred to a
beaker and allowed to evaporate to dryness at room temperature. The brown solid obtained was washed
under vacuum with hexane, dichloromethane (2 χ 10 ml) and kept in desiccators. Yield: 1.03 g (97%). Mp
(°C): 72 - 73. Elemental analysis required for C33H31N4CI3S11: C, 55.93; H, 4.41; N, 7.90; found: C, 56.25; H,
4.31; N, 7.67; Mol Weight (g/mol): 1.4 χ 103; IR (Nujol / Csl): 1654 (C=N)a/„, 1588, 1568 (C=N py + C=C),
443, 412 (Sn-N), 274 (Sn-C). 'H NMR (CDC13, 300.0 MHz): δ 4.06 (s, CH2, 4H), 7.26 - 7.99 (m, Ph, py,
23H), 8.42 (s, N=CH, 2H), 8.61 - 8.63 (d, py, 2H), 10.09 (s, hydrogen bonding); UC NMR (CDC13, 75.4
MHz): δ 61.5 (CH 2 ), 121.6 (py), 125.0 (py), 129.3 (Ph), 130.7 (Ph), 136.3 (Ph), 136.8 (py), 149.6 (py), 154.5
(py), 164.0 (N=CH);
n9
Sn NMR {CH 2 C1 2 ,149.1 MHz, (R int %)}: δ -63.1 (broad).
2.3.2. [Sn&iPh/pmed)]
(2):
The procedure was similar to that described in 2.3.1, using 0.72 g (2.10 mmol) of SnCl 2 Ph 2 and 0.25 g of
pmed (1.05 mmol), leading to a white solid. The latter was filtered off under reduced pressure, washed with
dichloromethane (10 ml) and kept in desiccators. Yield: 0.53 g (55%). Mp (°C): 171 d. Elemental analysis
required for C ^ H J ^ C U S I U C, 49.31; H, 3.70; N, 6.05; found: C, 49.79; H, 3.73; N, 6.33; Mol Weight
(g/mol): 1.4 χ 103 and 7.4 χ 104; IR (Nujol / Csl): 1661 ( O N ) ^ , 1595, 1573 (C=Npy + C=C), 446, 419 (SnN), 329 (Sn-Cl), 279 (Sn-C). 'H NMR (DMSO-d*, 300.0 MHz): δ 5.74 (s, CH2, 4H), 7.26 - 7.99 (m, Ph, py,
26H), 8.42 (s, N=CH, 2H), 8.65 (d, py, 2H), 9.97 (s, hydrogen bonding); 13C NMR (DMSO-d 6 , 75.4 MHz): δ
57.4 (CH 2 ), 126.1 (py), 126.9 (py), 127.7 (Ph), 128.2 (Ph), 133.8 (Ph), 135.4 (py), 150.0 (py), 154.4, 156.6
(py);
I19
Sn NMR {DMF, 149.1 MHz, (R inl %)}: δ -330.7 (100), -429.4 (27), -437.4 (24), -443.2 (17), -444.5
(18), -447.2 (18), -467.0 (20), -468.4(43), -509.0 (78).
2.3.3. [Sn2Cl6Ph2(pmed)]
(3):
To a Schlenk tube, 0.25 g (1.05 mmol) of pmed was dissolved in dichloromethane (30 ml), and 0.63 g of
SnCl3Ph (0.35 ml, 2.10 mmol) was transferred onto the yellow solution by syringe. The mixture was stirred
for 2 h at room temperature. A pink solid separated which was filtered off under reduced pressure, washed
with dichloromethane (10 ml) and kept in desiccators. Yield: 0.87 g (99%). Mp (°C): 187 d. Elemental
analysis required for C 26 H 24 N 4 Cl 6 Sn 2 : C, 37.06; H, 2.87; N, 6.65; found: C, 36.95; H, 2.80; N, 6.85; Mol
Weight (g/mol): 1.6 χ 103; IR (Nujol / Csl): 1649 ( O N ) ™ , 1600, 1573 (C=Npy + C=C), 449, 421 (Sn-N),
340, 322, 296 (Sn-Cl), 279 (Sn-C). 'H NMR (DMSO-d*, 300.0 MHz): δ 5.74 (s, CH2, 4H), 7.22 - 7.97 (m,
Ph, py, 16H), 8.47 (s, N=CH, 2H), 8.61 - 8.64 (m, py, 2H), 9.98 (s, hydrogen bonding); ,3 C NMR (DMSOd*, 75.4 MHz): δ 55.6, 61.1 (CH 2 ), 122.3 (py), 125.8 (py), 128.2 (Ph), 129.2 (Ph), 130.6 (Ph), 137.6 (py),
150.1 (py), 154.4,156.1 (py), 163.7,165.2 (N=CH);
ll9
Sn NMR {DMF, 149.1 MHz, (R inl %)}: δ -430.1 (39),
-438.2 (37), -446.0 (100), -447.5 (95), -452.8 (28), -458.3 (24), -462.6 (24), -467.9 (48), -471.9 (32), -499.7
(46, broad), -510.1 (31), -519.5 (37).
324
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Main Group Metal Chemistry
Jose Roberto da S. Maia et al.
2.3.4. [SnfiUpmed)]
(4);
The procedure was identical as in 2.3.3 using 0.55 g (0.25 ml, 2.10 mmol) of SnCl4 and 0.25 g (1.05
mmol) of pmed affording 0.76g (96%) of a pink solid material. Mp (°C): 255 d. Elemental analysis required
for C14H14N4Cl8Sn2: C, 22.16; H, 1.86; N, 7.38; found: C, 21.09; H, 1.78; N, 7.03; Mol Weight (g/mol): 2.4 χ
103 and 5.1 χ 104; IR (Nujol / Csl): 1645 ( C = N U , 1600, 1570 (C=N py + C=C), 448, 422 (Sn-N), 321, 281
(Sn-Cl). 'H NMR (DMSO-c^, 300.0 MHz): δ 5.74 (s, CH 2 , 4H), 7.27 - 7.82 (m, py, 6H), 8.57 (s, N=CH, 2H),
8.61 - 8.64 (m, py, 2H), 9.98 (s, hydrogen bonding);
13
C NMR (DMSO-d*, 75.4 MHz): δ 57.5 (CH 2 ), 121.7
(py), 126.2 (py), 137.5 (py), 150.1 (py), 154.5, 158.0 (py), 165.2 (N=CH);
,19
Sn NMR {DMF, 149.1 MHz,
(Rim %)}: δ -542.7 (29), -544.3 (40), -559.6 (31), -562.3 (70), -562.8 (39), -571.0 (100), -571.5 (57), -580.7
(44), -591.6 (37), -629.7 (40), -667.1 (36).
?
RESULTS AND DISCUSSION
The pmed was soluble in methanol, dichloromethane as well as in several other organic solvents. The
tin(IV) derivatives were not as soluble as the free ligand in organic solvents. All derivatives were soluble in
dimethylsulfoxide (DMSO) and dimethylformamide (DMF). Complex 1 was an exception, which presented
satisfactory solubility in common organic solvents as well. First-row transiWon metals derivatives of pmed
have also shown an appreciable solubility in DMF /9/. Although the reactions were carried out in a 2:1 molar
ratio (M:L), complex 1 is an equimolar product according to the elemental analysis.
3.1. Infrared spectroscopy
The absorptions related to the C=N bond of azomethine and pyridine moiety of pmed upon coordination
were of strong to medium intensity. The infrared spectra of those tin(IV) derivatives have exhibited an
interesting pattern of bonding formation relative to the azomethine fragment. Complexes 1 and 2 have
revealed a shift towards high frequency up to 5 cm"1. For 3 and 4, the stretching frequency associated to this
moiety did not change significantly remaining in the region of 1647 cm"1, close to the free ligand at 1644
cm 1 . The vibrational stretching related to the azomethine moiety is frequently shifted to lower frequency
upon coordination, for instance, in copper(II) derivatives of bidentate aromatic Schiff bases /14/ as well as in
the trans-\Ru(papn)C\2\
(papn = pmed) / l l / . Similar results have been observed for organotin(IV) derivatives
of tetradentate Schiff bases /13/. However, shifts towards high frequency upon coordination associated to the
azomethine moiety have also been reported for Schiff base derivatives of organosilicon(IV), tin(IV)
tetrachloride and nickel(ll) salts /15-17/. On the other hand, a different coordination pattern of the pyridyl
moiety was observed for those organotin(IV)-p/nerf derivatives. The v(C=N py + C=C) was assigned in the free
ligand as two medium bands at 1583 and 1563 cm"1, which are in agreement with the literature / l l / . All
organotin-pmed derivatives have displayed for this moiety a shift towards higher frequency. In 1, however,
the shift was negligible. The up frequency was more pronounced in 2 (12 cm' 1 ), 3 (17 cm" ) and 4 (17 cm )
in comparison to the highest v(C=N py + C=C) of the free ligand. This is evidence of a strong interaction
325
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Vol. 29, No. 6, 2006.
Tin(IV) Derivatives of Arsenic(IIl):
between the metal and the pyridyl fragment in solid state. Nevertheless, it does not exclude a metal-ligand
bond formation through the azomethine moiety. The literature provides nickel(II)-Schiff base complexes in
which the shift correlated to both parts was insignificant. The molecular structural determination of the latter
has indeed revealed three chelate rings involving both azomethine and pyridyl parts /17/.
The v(Sn-N) stretching of the tin(IV) derivatives in this work has been assigned in the range of 400 to 450
cm"1, which is in agreement with the literature / l l , 13, 18, 19/. The spectral pattern for all complexes in that
range indicates cis configuration for the nitrogen atoms. Two new bands of medium intensity have been
exhibited in the region of 432 cm 1 . In this context, the metal centre plight be bound to either azomethine or
pyridyl and azomethine nitrogen atoms leading to chelate rings. This is in contrast to the vibrational spectrum
of the complex trans-[Ru(papn)C12] (papn = pmed) which has exhibited one single Sn-N infrared absorption.
Its structural determination has revealed all 4-nitrogen atom types in trans position to the metal centre / l l / .
Therefore, this coordination mode has been excluded as a possibility for the tin(I\)-pmed derivatives.
The v(Sn-Cl) stretching assignments are in agreement with the literature for tin(IV) compounds /13, 18/.
No vibrational stretching relative to the Sn-Cl bond has been observed in 1, which indicates chloride as
counter ion. This is compatible with the elemental analysis of the latter. Complex 2 exhibited a single band at
329 cm"1 due to chloride in trans position to the metal centre. Furthermore, this compound has shown an
interesting infrared datum several weeks after being isolated. Its spectrum has displayed two Sn-Cl bands at
322 and 296 cm"', suggesting cis / trans isomerism in solid state.
Complex 3 exhibited a weak and a medium band at 340 and 322 ein 1 respectively, plus a strong one at
296 cm '. Usually two and three bands are expected for fac and mer isomers respectively 1201. Thus, those
three bands in 3 are indicative of fac / mer stereoisomerism in solid state as in Ru(II) complexes /21/.
Complex 4 showed a strong band at 321 cm"' and a medium one at 281 cm"' suggesting cis / trans
stereochemistry for the chloride ions upon coordination. In this context, structural arrangements for 1, 2, 3
and 4 can be envisaged in Figure 1.
κ
2 R = R' = I'h
3 R = CT. R* = Πι
4 R ~ R = CI
Fig. 1: Proposed structural arrangements of the tin(IV) derivatives in which the pmed is displaying
bidentate and bridging bidentate coordination mode.
326
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Jose Roberto da S. Maia et al.
Main Group Metal Chemistry
The higher shift frequency observed for the azomethine moiety in 1 and 2 might be related to the
formation of chelate rings / l l , 15/. In 3 and 4, the negligible shift for the azomethine is most likely a result of
a strong interaction between the metal and the pyridyl moiety of the ligand. This fact suggests that the acid
character of the metal precursor plays a significant role on bonding formation to pmed in solid state.
3.2. NMR spectroscopy
The "H NMR spectra of those compounds have shown a typical range of hydrogen resonance for the
phenyl and pyridyl moiety. The methylene group displayed a singlet for all compounds, which is evidence of
being magnetically equivalent upon coordination, at least on an NMR time-scale. Although the chemical shift
relative to this group was insignificant in 1, it cannot be neglected in 2, 3, and 4. For those, a considerable
shift towards high values (δ 1.71) has been revealed. The chemical shift for the azomethine upon
coordination has been assigned to the range of δ 8.42 to 8.57, in conformity with the literature for tin(lV)
derivatives of chelated Schiff bases /13/. This is higher in comparison to the free ligand, but lower than that
found in the trans-[Ru{papn)C\i} (papn = pmed) (δ = 8.95) /11/. Nonetheless, in the first-row f r a c t i o n metal
derivatives of pmed the azomethine undergoes deshielding, exhibiting signals in the range of δ 8.3 to 7.8 191.
The chemical shift for the azomethine moiety appears to increase as the acid character of the metal precursor
increases in the series SnClxPh4.x, (x = 1, 2, 3, 4). Interestingly, in 2, 3, and 4 a strong metal-pyridyl bond is
symptomatic by infrared spectroscopy, especially in the latter two. This fact led us to assume that the
deshielding for the azomethine in those compounds is a result of an exchanging bond process in passing from
solid state into solution. In this context, the metal centre is switching bond strength between pyridyl and
azomethine in those compounds. A singlet in the region of δ 9.97 was exhibited in the spectrum of all
complexes in either CDC13 or DMSO. Similar chemical shift has also been observed for the trans[Ru(pap/i)Cl 2 ] complex as a doublet in the range of δ 9.20 to 9.43 in CDCI3 / l l / . This signal has been
assigned to the orto-hydrogen of the pyridyl group upon coordination. However, in 1, 2, 3 and 4 this singlet is
most likely a result of hydrogen bond formation. This is supported by the resonance signals of water at δ 1.51
and 3.33 exhibited in the spectra of CDCI3 and DMSO respectively. The hydrogen bond reinforces the
formation of 1 as shown in Figure 1, and raises a possible labile property of the pyridyl moiety in 2, 3, and 4
in solution. In the solid state there is no evidence of hydrogen bonding by infrared spectroscopy.
No significant chemical shift related to the pyridyl moiety was observed in the
l3
C NMR spectrum of
complex 1. This fact corroborates the metal-ligand bond formation through the azomethine moiety
preferably, as pointed out by the 'H NMR datum. In 2, 3, and 4, however, the carbon atoms related to the
pyridyl part has shifted in the range of δ 0.9 to 1.8. This is evidence that the metal at least is still bound to this
moiety in solution. For 1, 2, and 4 the methylene has exhibited a singlet, indicative of carbon atoms
magnetically equivalent. In the latter two, the methylene has shifted to lower values within the average of δ
4.9. This is in contrast to 1, in which the methylene resonating signal is comparable to the free ligand. In 3
two signals have been assigned to the methylene group, at δ 55.6 and 61.1. Those signals correspond to the
resonance of carbon atoms in different magnetic surroundings, suggesting either a different structural pattern
from that shown in Figure 1 or a mixture of compounds. The shielding of the methylene carbon atoms in 2, 3
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
327
Vol. 29, No. 6, 2006.
Tin(IV) Derivatives of Arsenic(III):
and 4 is presumably related to the acid character of the metal precursor, which increases upon replacing
phenyl by chloride. Complex 3 exceptionally exhibited two signals associated to the azomethine carbon at δ
163.7 and 165.2. This fact again suggests a structural rearrangement or a mixture of products in solution.
Nevertheless the chemical shift of the azomethine to higher values has occurred in the range of δ 0.4 to 1.6 to
all compounds. A missing azomethine peak has also been observed in the spectrum of 2, which is probably
due to the relaxation time of the carbon atom towards its fundamental state. On the other hand, two carbon
signals have been exhibited in the range of δ 154.4 to 158.0 in 2, 3 and 4. Those signals were assigned to C-5
(see Scheme 1) of pmed. They are magnetically different, suggesting a free pyridyl moiety as well as a
dissimilar coordination pattern for the pyridine group. In addition, the spectrum of 3 also displayed a signal
of very low intensity at δ 194.4 which was correlated to the C = 0 moiety of 2-pyridinecarboxaldehyde. This
indicates a little decomposition of 3, most probably due to reaction with water from the DMSO. Hydrolysis
of metal complexes derivatives of tetradentate Schiff bases has been acknowledged in the presence of DMSO
1221, although this phenomenon is documented since the 60 s decade /23/. The
1,9
Sn NMR spectra were
recorded in CH2C12 ( l ) and in DMF (2, 3, 4). Despite the heteronuclear decoupling technique, the spectra of
the tin(IV) derivatives of pmed were not simpler or easy to analyse. A number of resonating peaks have been
exhibited in 2, 3 and 4, but not in 1. The spectrum of the latter revealed a broad signal centred at δ -62.6,
indicating a dynamic process in solution. This chemical shift is within the range associated to five-fold
coordination species /24/. The broad signal is presumably due to subtle magnetic variation in the metal
environment, suggesting a bridging coordination mode of pmed. This is conceivable when accounting for
rotation along the C-C bond of the methylene moiety, leading to several twisted stereochemical
conformations. A proposed dynamic process of 1 can be envisaged in Figure 2.
A similar
dynamic process has been reported
for organotin
chlorides containing the (3-(2-
methoxy)ethoxy)propyl moiety /25/. It seems reasonable that 1 is a dimeric species in solution with the metal
at the centre of a trigonal-bipyramidal array. For a monomeric species (see Figure 2), the coplanar methylene
group does not allow rotation along the C-C bond. The
119
Sn chemical shift in 2 can be associated to either
six- or seven-fold coordination /24, 26/. The spectrum has revealed resonating signals of magnetically
different tin(IV) nuclei. An intense slightly broad signal at δ -330.7 put forward the formation of a 6coordinated species, although this signal is within the range associated to either octahedral or trigonalbipyramidal arrangement /24/. A set of three sharp signals at δ -429.4, -468.4 and -509.0 in 2 can also be
correlated to a 6- or 7-coordinated tin(IV) centre. The latter signal is concurrent with that at δ -510.0 of a
monomeric species having a seven-fold coordination at the tin(IV) nucleus /27/. The difference in the
chemical shift between the first peak and the second one is 39, raising a possible solvent effect. A similar
trend is observed between the second signal and the third one. Thus, it is questionable whether those peaks
are related to monomeric, dimeric or polymeric species. A possible correlation between the two intense
signals (δ -330.7 and -509.0) can be established, considering both as originally from a major species. The
difference in chemical shift between them (δ 179) is suggestive of an intramolecular coordination. The
literature expects the change from 6- to 7-coordination by intramolecular bonding to move the
nv
Sn chemical
shift values upfield by 90 to 300 1261. This effect is essentially dependent on the chelating properties of the
ligand. In this context, pmed is coordinated in 2 to at least two metal centres performing a six- as well as a
328
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Main Group Metal Chemistry
Jose Roberto da S. Maia et al.
seven-fold coordination as shown in Figure 3. Several signals of very low intense intensity were also
displayed within the
119
Sn NMR spectrum of 2. Those are most probably due to the presence of minor
species.
/
\
Fig. 2: Possible dynamic process of complex [SnPh3(pmei/)]Cl.CH2Cl2 (1) in CH2C12.
The spectrum of 3 displays an even more complicated pattern with the signals being exhibited in the
range associated with 6- and 7-coordinated species. Noticeable is the presence of a doublet centred at δ 446.7 which ascends from the top of a broad signal, exhibiting tin(IV) atoms in slightly different magnetic
environments. The intense doublet has been associated to major species in solution. A similar complicated
pattern has also been found in gem-distannyl compounds and triorganotin compounds of the type R3Sn-XSnR'3 (X = O, S) /28, 29/. The appearance of signals with variable intensity lines is probably due to
isotopomers (isomers of isotopes). Unfortunately the signal-to-noise was not high enough to allow the
determination of any possible J( U9 Sn-" 7 Sn) coupling constant. It seems reasonable that those intense lines
belong to the same species, which is in agreement with the proposed structure of 3 in Figure 1. Each peak of
the doublet could be due to the phenyl group in axial or equatorial position towards the appropriate metal
centre. In addition, rotation along the methylene C-C bond might cause a slight difference in the magnetic
environment of both tin atoms in Figure 1, justifying the doublet. Assuming that both tin atoms are coupled,
the magnitude of the coupling constant relative to the doublet itself agrees with a long-range coupling of
7('1<JSn-u<JSn) = 219.3 Hz /30/. Coupling constants across nitrogen within the same magnitude has been
reported for trimethylstannylhydrazines /31/. The latter corroborates the formation of 3 as shown in Figure 1.
329
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Vol. 29, No. 6, 2006.
Tin(IV) Derivatives of Arsenic(III):
In addition, a broad signal, similar to that exhibited in the spectrum of 1, was also revealed in 3 at δ -499.6.
By analogy to the former, this broad peak suggests a dynamic process which is presumably due to other
species. Hence, the spectrum of 3 is most likely a result of a mixture of compounds in solution.
4· R α
Fig. 3:
4" u
α
Proposed structural patterns for the major species of [Sn2Cl4Ph4(p/ne</)] (2) and [Sn2C\%(pmed)\ (4)
in DMF.
A difficult spectral pattern has also been exhibited in the spectrum of 4 and again, the number of peaks
and intensity are probably in connection to isotopomers in solution. The latter has displayed several sharp
peaks mostly within the chemical shift range associated to 6- and 7-coordinated species, as in 3. Along with
those, four peaks having proportional relative intensities resembling a doublet of doublets were revealed.
They were assigned to major species in solution. The chemical shift of those is indicative of dissimilar
magnetic surroundings at the metal centre. The relative intensity and the difference in chemical shift of the
signals suggest an isotopomeric correlation between them. Assuming that those signals correspond to tin
atoms spin-coupled, two coupling constants can be established. These coupling constants, l J M = 1288.2 Hz
and yJMi = 1289.7 Hz (see Figure 4), are consistent in magnitude to one-bond "''Sn- l l 7 Sn found in Zintlanions as well as in hexaorganoditins and distannene compounds /32-34/. The slight difference between those
is most likely a result of substituent effect as shown in the proposed arrangements 4' and 4" in Figure 3. In
view of this, both structural patterns might represent the major species of 4. Unfortunately, due to technical
reasons, it was not possible to use other NMR techniques such as refocused INEPT for further investigation.
330
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Main Group Metal Chemistry
Jose Roberto da S. Maia et al.
The formation of isomers as well as isomeric conformations of pmed may provide an explanation for the
number of
ll9
Sn NMR signals in solution. This is reasonable since those could be formed during the ligand
preparation, which would lead to a number of species upon coordination. In this case the metal centre would
have several coordination patterns in different chemical environments. However, neither 'H nor
l3
C NMR
has been conclusive about the formation of isomers or stereochemical conformations of pmed in solution. On
the other hand, the number of signals in the
119
Sn NMR is also suggestive of polymerisation. The variety of
chemical shift might also correspond to different magnetic surroundings at the metal centre within the
isotopolymer (polymer of isotopes) chain. In this context, further investigation has been carried out by
thermal and GPC analysis.
•»O -S»S -STO -97S -MO
540
560
Fig. 4: 149.1 MHz
580
,19
600
620
640
660
Sn NMR spectrum of tSn 2 Cl*(pmed)] (4) in DMF.
Thermal analysis (DSC, TG) and gel permeation chromatography (GPC)
Thermogravimetry analysis (TG) was employed herein in order to gain information on the amount of
hydrated water in those complexes. In all cases, the loss of weight is in agreement with the elemental
analysis. The thermal analysis (TG) carried out in 2, 3, and 4 has shown loss of weight in three steps mainly.
In 4 another step around 65 °C has shown a loss of 3.2 % in mass, which is associated to humidity. No
evidence for hydration water has been observed for those compounds. They started losing weight at around
180°C. The first and second step in 2 and 3 occurred in the region of 165 and 305 °C respectively. These
steps are correlated to loss of pmed and phenyl groups. However, the first two steps in 4 were not welldefined, accounting for the indistinguishable inflection point. The loss of 59.6 % in mass between 200 and
310 °C in the latter is consistent with ligand releasing and six chloro atoms at once. The remaining chloro
atoms have been released in the last step between 530 to 610 °C for all three complexes, leading to a white
solid of tin(IV) dioxide.
Gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) techniques were
employed herein to obtain information on the molar mass and phase ira«sitions in those materials. The
differential scanning calorimetry (DSC) is a very useful technique to search out information on polymeric
materials in solid state. No evidence has been achieved to support this in the range of temperature used by the
331
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Vol. 29, No. 6, 2006.
Tin(IV) Derivatives of Arsenic(III):
DSC technique. Endothermic and exothermic events have been simultaneously observed for all three
compounds above, which are in agreement with the decomposition point previously established. The GPC
analysis has revealed a weight-average molar mass for 1, 2, 3, and 4 in the range of 1451 to 2478 g/mol.
Although these values are far from those worked out by the elemental analysis, they corroborate autoassociation in solution but not polymer formation. In this context, these are certainly not polymeric materials,
either in solution or in solid state. Nevertheless, the molar mass distribution in 2 and 4 has shown a second
less intense peak (2.5% and 8.0%) with weight-average molar mass of 74791 and 51286 g/mol respectively.
The polydispersity (Mw/Mm) values of those were of 1.1 and 1.2 corroborating, a small amount of
polymerisation in DMF.
CONCLUSION
The resulting data points out a structural rearrangement of the tin(IV)-pmed compounds by autoassociation in solution leading most likely to an equilibrium mixture of compounds. As shown by " y Sn
NMR, the number of signals increases as the number of chloride ions are replaced by the phenyl groups in
the series SnCl„Ph4.x, (x = 1, 2, 3, 4). Presumably both the acid character of the metal precursor and steric
hindrance are particularly significant concerning the auto-association in those materials. However, the
participation of the solvent is still questionable.
ACKNOWLEDGEMENTS
The authors would like to thank the Brazilian Agency CNPq for granting a Scholarship to Rafael C. R.
Chagas as well as to FAPEMIG for financial support.
REFERENCES
1. M.S. Yadawe and S.A. Patil, Transition Met. Chem., 22, 220 (1997).
2. L.E. Khoo, P.G. Charland and E.J. Gabe, Inorg. Chim. Acta, 128,139 (1987).
3. A.G. Kolchinski, Coord. Chem. Rev., 174, 207 (1998).
4. L.S. Li and Y.L. Wu, Chin. J. Org. Chem., 20, 689 (2000).
5. P.G. Lacroix, Eur. J. Inorg. Chem., 2001 (2), 339.
6. M.R. Maurya, Coord. Chem. Rev., 237,163 (2003).
7. E. Tusuchida and K. Oyaizu, Coord. Chem. Rev., 237, 213 (2003).
8. A. Saxena, J.P. Tandon and AJ. Crowe, Polyhedron, 4,1085 (1985).
9. M. Kumar and T. Sharma, J. Indian Chem. Soc., 68,539 (1991).
10. M.G.B. Drew, M.R.S. Foreman, M.J. Hudson and K.F. Kennedy, Inorg. Chim. Acta, 357, 4102 (2004).
332
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Main Group Metal Chemistry
Jose Roberto da S. Maia et al.
l l . S . Pal and S. Pal, Polyhedron, 22, 867 (2003).
12. C. Ng, M. Sabat and C.L. Fraser, Inorg. Chem., 38, 5545 (1999).
13. B. Yearwood, S. Parkin and D.A. Atwood, Inorg. Chim. Acta, 333,124 (2002).
14. M. Tümer, Η. Köksal and S. Serin, Synth. React. Inorg. Met.-Org. Chem., 27, 775 (1997).
15. N.S. Biradar, V.L. Roddabasanagoudar and T.M. Aminabhavi, Indian J. Chem., 24A, 873 (1985).
16. T.R. Goudar, G.S. Nadagoud and S.M. Shindagi, J. Indian Chem. Soc., 65, 509 (1988).
17. M.I. Fernändez-Garcia, Β. Fernändez- Fernändez, Μ. Fondo, A.M. Garcia-Deibe, Ε. Gömez-Förneas, J.
Sanmartin and A.M. Gonzälez, Inorg. Chim. Acta, 304,144 (2000).
18. A.K. Mishra, N. Manav and N.K. Kaushik, Spectrohim. Acta, Part A, 61, 3097 (2005).
19. S.-G. Teoh, G.-Y. Yeap, C.-C. Loh, L.-W. Foong, S.-B. Teo and H.-K. Fun, Polyhedron, 13, 2213
(1997).
20. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B:
Applications in Coordination, Organometallic, and Bioinorganic Chemistry, 5th ed.; John Wiley &
Sons, Inc., New York; 1997.
21. G.V. Poelhsitz, M.P.d. Araujo, L.AAd. Oliveira, S.L. Queiroz, J. Ellena, E.E. Castellano, A.G. Ferreira
and A.A. Batista, Polyhedron, 21,2221 (2002).
22. N.J. Blundell, J. Burges and C.D. Hubbard, Trans. Met. Chem, 30,148 (2005).
23. H.A. Goodwin and F. Lions, J. Am. Chem. Soc., 82, 5013 (1960).
24. J. Otera, J. Organomet. Chem., 221,57 (1981).
25. J. Susperregui, M. Bayle, J.M. Lfiger, G. D616ris, M. Biesmans, R. Willem, Μ. Kemmer and M. Gielen,
J. Organomet. Chem., 545-546,559 (1997).
26. J. Otera, A. Kusaba and T. Hinoishi, J. Organomet. Chem., 228, 223 (1982).
27. G.F.d. Sousa, C.A.L. Filgueiras, A. Abras, S.S. Al-Juaid, P.B. Hitchcock and J.F. Nixon, Inorg. Chim.
Acta, 218,139 (1994).
28. J.C. Meurice, M. Vallier, M. Ratier, J.G. Duboudin and M. Pötraud, J. Chem. Soc., Perkin Trans., 1996
(2), 1311.
29. S.J. Blunden and R. Hill, J. Organomet. Chem.,333, 317 (1987).
30. B. Wrackmeyer, "Indirect nuclear
1,9
Sn-X spin-spin coupling", in: Advanced Applications of NMR to
Organometallic Chemistry, M. Gielen, R. Willem and B. Wrackmeyer (Eds.), John Wiley & Sons, New
York, 1996; pp. 87-117.
31. T. Gasparis-Ebeling, H. Noth and B. Wrackmeyer, J. Chem. Soc., Dalton Trans., 1983, 97.
32. R.W. Rudolph and W.L. Wilson, J. Am. Chem. Soc., 103, 2480 (1981).
33. S. Masamune and L.R. Sita, J. Am. Chem. Soc., 107,6390 (1985).
34. R.W. Rudolph, W.L. Wilson, F. Parker, R.C. Taylor and D.C. Young, J. Am. Chem. Soc., 100, 4629
(1978).
333
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30
Bereitgestellt von | De Gruyter / TCS
Angemeldet | 212.87.45.97
Heruntergeladen am | 31.10.12 15:30