Hexacoordinate organosilicon(IV) compounds with a tetradentate azomethine ligand

Article abstract of DOI:10.1081/SCC-120015390

Hexacoordinate silicon compounds with the tetradentate azomethine ligand N, N′-ethylenebis(2-hydroxyacetophenoneimine) have been prepared and characterized by elemental analyses, molecular weight determinations and spectral (IR, ¹H, ¹³

Full text of DOI:10.1081/SCC-120015390

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HEXACOORDINATE ORGANOSILICON(IV) COMPOUNDS
WITH A TETRADENTATE AZOMETHINE LIGAND
a
b
a
M. S. Singh , T. C. Sharma & P. K. Singh
a
Department of Chemistry , D.D.U. Gorakhpur University , Gorakhpur, 273 009, India
b
School of Studies in Chemistry , Vikram University , Ujjain, 456 010, India
Published online: 23 Aug 2006.
To cite this article: M. S. Singh , T. C. Sharma & P. K. Singh (2002) HEXACOORDINATE ORGANOSILICON(IV) COMPOUNDS WITH
A TETRADENTATE AZOMETHINE LIGAND, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 32:24, 3733-3741, DOI: 10.1081/SCC-120015390
To link to this article: http://dx.doi.org/10.1081/SCC-120015390
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 24, pp. 3733–3741, 2002
HEXACOORDINATE
ORGANOSILICON(IV) COMPOUNDS
WITH A TETRADENTATE
AZOMETHINE LIGAND
1
,
2
1
M. S. Singh, * T. C. Sharma, and P. K. Singh
1
Department of Chemistry, D.D.U. Gorakhpur
University, Gorakhpur-273 009, India
2
School of Studies in Chemistry,
Vikram University, Ujjain-456 010, India
ABSTRACT
Hexacoordinate silicon compounds with the tetradentate
0
azomethine ligand N,N -ethylenebis(2-hydroxyacetophenonei-
mine) have been preparedandcharacterizedby elemental
analyses, molecular weight determinations and spectral (IR,
1
13
H, C and Si NMR) studies. The data clearly demonstrate
29
the octahedral geometry around the silicon atom.
Hypervalent silicon compounds attract interest from both the struc-
[
1]
tural andreactivity point of view. The isolation of such compounds allows
detailed insight into mechanistic pathways of nucleophilic substitution at
[1e]
silicon.
On the other handcompoun ds basedon such synthons should
*
Corresponding author. E-mail: singhms1960@rediffmail.com
733
3
DOI: 10.1081/SCC-120015390
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3
734
SINGH, SHARMA, AND SINGH
exhibit interesting properties as electronic materials. Different types of
[
1–3]
hypercoordinated silicon compounds have so far been reported.
We
set out to synthesize hexacoordinate organosilicon complexes containing
the salen ligand. This ligand is able to chelate to silicon atom through
four O N N O donor atoms. There are some rare example of salen silicon
[
4,5]
compounds known from the literature.
[
Transition metal salen complexes
In continuation of our studies
we describe here the synthesis and
6–8]
have been investigatedextensively.
[
on organosilicon(IV) compounds,
9–11]
characterization of some new complexes of organosilicon(IV) with the titled
ligand.
Different types of salen ligands have been applied recently, mainly in
transition metal complex catalysts, for the transformations of organic sub-
[12]
0
strates.
We here useda slightly mo di fiedsalen ligand[
N,N -ethylene-
bis(2-hydroxyacetophenoneimine)] with methyl groups at the azomethine
carbon instead of hydrogen. This prevents unwanted side reactions caused
by the azomethien protons. Tri-, di- and monoorganosilicon(IV) derivatives
of the Schiff base ligandhave been synthesizedby the reaction of the corre-
sponding tri-, di- and monoorganosilicon(IV) chlorides with the sodium salt
of the ligand(preparedin situ) in de siredmolar ratios. These reactions are
found to be quite facile and the sodium chloride formed during the course of
the reaction is filteredoff.

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HEXACOORDINATE ORGANOSILICON(IV) COMPOUNDS
3735
This synthesis involves the initial formation of monoanion and
dianion from sequential deprotonations of the Schiff base ligand which
attacks organosilicon(IV) chlorides. Intermolecular nucleophilic attack
with elimination of chloride ion leads to the formation of products in
goodyiel ds .
All these synthesized compounds are colored solids, soluble
in common organic andcoo ri dn ating solvents. These were purified
by repeatedwashing with suitable solvent andtheir purity was checked
by T.L.C. on silica gel. Each of the complexes moves as a single spot
indicating the presence of only one component. The reported molecular
weights refer to the parent ion peak as recorded on a AEI MS 9 mass
spectrometer.
IR Spectra
The free Schiff base ligandexhibits a broadbandin the region
À1
3565–3315 cm due to ꢀ (O–H), which disappear completely in the com-
plexes 5 to 8 indicating deprotonation of both the –OH groups, whereas
only one –OH group deprotonates in complexes 1 to 4, providing an oxo-
[
13]
coordiantion. This is also evident from the appearance of ꢀ (Si–O) modes
À1
at 830–340 cm in the spectra of the complexes (Table 1). The ꢀ (C¼N)
À1
bandobservedat 1632 cm in the free liandis shiftedto lower frequencies
upon complexation in all the complexes indicating coordination by both the
[14]
C¼N groups.
bands in the region 564–552 cm
Table 1). In the literature a shift of this frequency to the higher as well
This fact is further supportedby the appearance of new
À1
[15]
ascribable to ꢀ (Si<ꢀ ꢀ ꢀ N) modes
[
16]
(
[17]
as lower wave number side has been reported and in some cases even no

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3
736
SINGH, SHARMA, AND SINGH

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HEXACOORDINATE ORGANOSILICON(IV) COMPOUNDS
3737
[18]
À1
change has been noted.
(Si–C) vibrations.
Strong bands around 760 cm may be due to
ꢀ
NMR Spectra
The protons of the –OH groups of the ligandgive signal at 12.35 ppm.
This signal disappears completely in the complexes 5–8 resulting from dia-
nion, suggesting deprotonation of both the –OH groups indicating the
bonding of silicon with both the oxygen atoms. It appears as a signlet
with an integration corresponding to one proton in the region
12.30–12.40 ppm in the spectra of the complexes 1–4, suggesting deprotona-
tion of only one –OH group andconsequently forming one silicon-oxygen
bond. The new proton signals in the region 0.22–0.26 ppm are due to the
[
19]
methyl protons attachedto the silicon
(Table 1).
1
3
The C NMR spectra of the compounds have been recorded in CDCl3
relative to TMS, which is a good diagnostic tool for determining the mode
of bonding. On coordination the resonances of the carbon atoms attached
to the C¼N and phenolic oxygen shift some 20–32 ppm downfield, suggest-
ing coordination of both the C¼N andphenolic oxygen groups to the metal
[5]
atom. The methyl groups attachedto silicon di splay single resonance at
7
7
.37 ppm for chemically equivalent carbons. Two resonances at 7.32 and
.36 ppm appear with a 1 : 2 intensity ratio for one equatorial andtwo axial
methyl groups in case of compound 1.
2
The Si NMR data (Table 1) support that silicon is hexa-coordi-
9
[
20]
nated
9
in all the complexes. Since the R group is bound di rectly to the
Si nucleus, it is not surprising that the value of ꢁ depends primarily on the
2
nature of this R group. When R ¼ Phenyl the complexes give much more
negative values of ꢁ than when R ¼ alkyl. Although the alkyl moiety has a
greater electron ‘pushing’ capacity (s donation) than the aryl, the deloca-
lized p system in the phenyl compoundallows for d p–pp interaction to
2
9
[3b]
dominate the overall shielding of the Si nucleus.
From the analytical andspectral da ta andthe monomeric nature of
the complexes, as evidenced from the molecular weights, it can be tentatively
proposedthe hexacoo ri dn atedenvironment aroundsilicon atom in
possibly octahedral geometry in the resulting complexes.
EXPERIMENTAL
Chemicals were obtainedfrom Al dr ich or Fluka andusedas such.
[
21]
Solvents were purified according to the standard procedures.
All

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738
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HEXACOORDINATE ORGANOSILICON(IV) COMPOUNDS
3739
operations were performed under nitrogen atmosphere using standard glass-
ware. IR spectra were recorded as KBr discs on a 983 G Perkin-Elmer
spectrophotometer. Melting points were determined using a calibrated ther-
mometer by Remi Digital Melting Point Apparatus andare uncorrected.
Elemental analyses were performedwith a Carlo-Erba 1100 apparatus from
1
13
29
the Central Drug Research Institute, Lucknow. H, C, and Si NMR
spectra were recorded at 270.13, 67.5 and 53.67 MHz, respectively on a
Bruker AM 270 spectrometer. All chemical shifts are reportedin parts per
million (ppm) relative to TMS as an internal standard in CDCl .
3
0
The Schiff base N,N -ethylenebis(2-hydroxyacetophenoneimine) was
prepared by the condensation of 2-hydroxyacetophenone and ethylene-
[
diamine in 2 : 1 molar ratio in dry ethanol by literature method. Yield,
5]
ꢁ
7
6%, m.p. 186 C, Found: C, 72.44; H, 6.38; N, 9.12 Calcd. for C H N O
1
8
20
2
2
(
296): C, 72.97; H, 6.76; N, 9.46%.
Reaction Between Trimethylsilicon(IV) Chloride and the
0
SodiumSalt of N,N -Ethylenebis(2-hydroxyacetophenoneimine)
in a 1 : 1 Molar Ratio
Zero point zero four eight gram (2 mmol) of sodium hydride and
0 mL of isopropanol were taken in a two-way roundbottom flask, fitted
2
with a cooledwater con de nser alongwith two way balloon system. It was
refluxed for about half an hour till a clear solution of sodium isopropoxide
0
was obtained. After cooling, 0.59 g (2 mmol) of N,N -ethylenebis(2-hydro-
xyacetophenoneimine) was added slowly at room temperature. The mixture
was stirredunder reflux for 6 h. The solution became light brown which was
allowedto attain room temperature. Trimethylsilicon(IV) chlori de (0.217 g,
2
mmol) was added dropwise with a static-pressure dropping funnel. The
solution became yellow, andthe reaction mixture was again refluxedfor 2 h
to ensure the completion of the reaction. The precipitated sodium chloride
was removed by filtration. Removal of the solvent under reduced pressure
gave the product, which was isolated and purified by column chromatogra-
phy to give the compound 1.
All other organosilicon(IV) derivatives of the Schiff base ligand were
synthesized analogously as described above in desired molar ratios. The
synthetic, physical and analytical data of the compounds are given in
Table 2.

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SINGH, SHARMA, AND SINGH
ACKNOWLEDGMENT
The authors are highly thankful to Council of Scientific andIndustrial
Research, New Delhi for providing financial assistance sanctioning scheme
No. 01(1561)/98/EMR-II.
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Receivedin the Netherlan ds November 26, 2001

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