Synthesis, characterization, and antibacterial activity of diorganotin(IV) complexes of 4-methylphenol

Article abstract of DOI:10.1080/10426507.2011.557415

Diorganotin(IV) complexes R₂Sn(OC₆H ₄Me-4)₂ (R = Ph, Me, and n-Bu) have been synthesized in good yields by the reaction of Ph₂SnCl₂, n-Bu ₂SnCl₂, and Me₂SnCl₂ with NaOC ₆H₄Me-4, while complex n-Bu₂SnCl(OC ₆H₄Me-4) has been obtained from the reaction of n-Bu ₂SnCl₂ with 4-methylphenol in the presence of triethylamine in carbon tetrachloride. The complexes have been characterized by elemental analyses, molar conductance measurements, molecular weight determination, IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy as well as by mass spectrometry. The reactions of the complexes with 2- and 3-cyanoanilines yielded 1:2 coordination compounds authenticated by physicochemical as well as by IR, ¹H, and ¹³C NMR spectroscopic data. The bases behaved as monodentate ligands wherein 2-cyanoaniline is bonded through nitrile nitrogen atom, while 3-cyanoaniline is coordinated through amino nitrogen atom. The diorganotin(IV) complexes have also been screened for their antibacterial activity against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, Shigella flexneri, Proteus mirabilis, and Pseudomonas aeruginosa. The minimum inhibitory concentration values of these complexes show enhanced activity. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2011.557415

Phosphorus, Sulfur, and Silicon, 186:2071–2085, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.557415
SYNTHESIS, CHARACTERIZATION, AND ANTIBACTERIAL
ACTIVITY OF DIORGANOTIN(IV) COMPLEXES OF
4-METHYLPHENOL
Neeraj Sharma and Vijay Kumar
Department of Chemistry, Himachal Pradesh University, Shimla, India
GRAPHICAL ABSTRACT
Abstract Diorganotin(IV) complexes R2Sn(OC6H4Me-4)2 (R = Ph, Me, and n-Bu) have
been synthesized in good yields by the reaction of Ph2SnCl2, n-Bu2SnCl2, and Me2SnCl2
with NaOC6H4Me-4, while complex n-Bu2SnCl(OC6H4Me-4) has been obtained from the
reaction of n-Bu2SnCl2 with 4-methylphenol in the presence of triethylamine in carbon
tetrachloride. The complexes have been characterized by elemental analyses, molar conduc-
tance measurements, molecular weight determination, IR, 1H, 13C, and 119Sn NMR spec-
troscopy as well as by mass spectrometry. The reactions of the complexes with 2- and
3-cyanoanilines yielded 1:2 coordination compounds authenticated by physicochemical as
well as by IR, 1H, and 13C NMR spectroscopic data. The bases behaved as monodentate
Received 6 October 2010; accepted 20 January 2011.
Vijay Kumar is grateful to CSIR New Delhi, India, for awarding JRF. The authors thank the Department of
Biotechnology, Himachal Pradesh University, Shimla, for providing laboratory facilities (for antibacterial activity),
the Department of Science and Technology (DST), Government of India, New Delhi, for providing financial
assistance for FT-IR, Sophisticated Analytical Instrument Facility (SAIF), CDRI, Lucknow, for recording mass
spectra and elemental analysis, and the Punjab University Chandigarh for recording NMR spectra.
Address correspondence to Neeraj Sharma, Department of Chemistry, Himachal Pradesh University, Summer
Hill, Shimla 171005, India. E-mail: neerajsharma univ@yahoo.co.in
2071

2072
N. SHARMA AND V. KUMAR
ligands wherein 2-cyanoaniline is bonded through nitrile nitrogen atom, while 3-cyanoaniline
is coordinated through amino nitrogen atom. The diorganotin(IV) complexes have also been
screened for their antibacterial activity against Escherichia coli, Staphylococcus aureus,
Staphylococcus epidermidis, Shigella flexneri, Proteus mirabilis, and Pseudomonas aerug-
inosa. The minimum inhibitory concentration values of these complexes show enhanced
activity.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Dialkyltin/diaryltinchlorides; 4-methylphenol; spectral studies; antibacterial activ-
ity
INTRODUCTION
Literature on organotin chemistry abounds with numerous organotin compounds de-
rived from a variety of ligands, predominantly carboxylates,1,2 peptides,3–5 Schiff bases,6,7
dithiocarbamic acids,8 and hydroxamic acids,9–12 because of their diverse structural and
biological importance. Diorganotin(IV) compounds, in particular, are known as potential
antitumor and anticancer agents.13–17 The potential applications of organotin compounds
such as polyvinyl chloride (PVC) stabilizers, catalyst for transesterification reactions,18,19
polyurethane polymerization, and room temperature vulcanization (RTV) silicone curing
agents are also well documented.20,21 Organotin compounds find use as industrial and
agricultural biocides22–24 owing to their antifungal properties. Of organotin complexes con-
taining tin–oxygen bond, derived from hydroxides, oxides, alkoxides and phenoxides, per-
oxides, and alkyl peroxides, there are numerous studies concerning organotin alkoxides. The
reactions of organotin chlorides with the sodium salt of the appropriate alcohol/phenol25,26
and organotin oxide with phenols27 are quite common and are frequently used. However,
they do not always provide a successful synthetic route to organotin alkoxides and phenox-
ides because of the formation of tetraalkyl dialkoxydistannoxanes in the latter reaction.28,29
A ladder-type structure of tetrabutyl diphenoxydistannoxane [Sn4(C4H9)8(C6H5O)4O2] has
been reported.30
The other synthetic methods employed include the reactions of organotin amines
with alcohols and the nucleophilic displacement of alkoxides, hydroxides, or stannyl
oxide.31 The studies on the catalysis of the reaction of organotin phenoxides with
diethyl acetylene dicarboxylate have been described.32 Despite the fact that organ-
otin phenoxides are known to possess antibacterial effects and constitute a potential
component of Ziegler-Natta system, only a few reports are encountered on organotin ary-
loxides.33 Of the large variety of substituted phenols containing both electron-withdrawing
and electron-donating substituents, among methyl-substituted phenols, only 2,6-dimethyl
phenol34 seems to be well studied. Simple o-, m-, and p-cresols, perhaps due to their
unique physical properties, have obviously remained rather unexplored. In view of the
above observations and in continuation of our previous work on organotin(IV) arylox-
ide chemistry,35 we report herein the synthesis of diorganotin(IV) complexes derived
from 4-methylphenol, their structural characterization, and Lewis acid behavior in the
presence of nitrogen bases. The antibacterial activity of the complexes has also been
assayed.

DIORGANOTIN(IV) COMPLEXES OF 4-METHYLPHENOL
2073
RESULTS AND DISCUSSION
The formation of diorganotin(IV) 4-methyl phenoxides in quantitative yields can be
proceeded according to the Equations (A) and (B):
MeOH
CH3 + 2NaCl
2NaO
HO
CH3
R2Sn O
(A) R2SnCl2
+
2
Reflux
(where R = Ph, n-Bu, and Me)
THF
(B) n-Bu2SnCl2
CH3
+ Et3N
n-Bu2SnCl O
+
Et3NHCl
CH3
+
Reflux
The elemental analyses (Table 1) confirmed the stoichiometric compositions. The
diphenyl, dimethyltin, and dibutyltin(IV) 4-methyl phenoxides are brown, cream colored,
light yellow, and white solids, respectively. The complexes exhibit sharp melting points
except Ph2Sn(OC6H4Me-4)2. The complexes are stable under dry conditions and are sol-
uble in most of the common organic solvents. The molar conductance values of 10−3
M
solutions of the compounds in nitrobenzene suggest that they are nonelectrolytes.36 The
molecular weight determination by Rast’s camphor method suggested that they exist as
dimers.
FTIR Spectra
The formation of diorganotin(IV) 4-methyl phenoxide complexes was ascertained
from a comparison of the IR spectra of the new complexes with that of free 4-methylphenol.
The broad absorption band in the region of 3600–3200 cm−1 due to υ(OH) mode in free
4-methylphenol was found to be absent in the spectra of the complexes. The absorption
bands in the region of 1240–1160 cm−1 in free 4-methylphenol ascribed to υ(C O) mode
appeared in the complexes in the region of 1258–1171 cm−1, suggesting the involvement of
the phenolic oxygen atom in bonding. The bonding of the phenolic oxygen atom to tin metal
was further supported by the appearance of bands at 535–490 cm−1 attributed to υ(Sn–O)
mode.1,2 The sharp bands observed at 765–680 cm−1 may be assigned to υ(Sn–O–Sn)37–39
mode, which is indicative of their dimeric nature. The absorption bands observed at 280
and 250 cm−1, 602 cm−1, 601 cm−1, and 545 and 525 cm−1 in diphenyl, n-butyl, and
methyltin(IV) 4-methyl phenoxides may be assigned to υ(Sn–C) mode.40
1H NMR Spectra
A comparison of the 1H NMR spectrum of the free ligand with those of the complexes
1
provides further evidences for their formation (Table 2). The H NMR spectrum of 4-
methylphenol exhibits signals at 5.18, 6.45, 6.79, and 2.20 ppm, which are attributed to
the phenolic –OH group, the protons of the aromatic ring (o-H and m-H), and the protons
of the methyl substituent, respectively.41 The absence of the signal at 5.18 ppm in the
complexes confirms the deprotonation of phenolic function. The phenolic ring protons
were found to undergo significant downfield shifts in the case of n-Bu2Sn(OC6H4Me-4)2
and n-Bu2SnCl(OC6H4Me-4), while moderate downfield shifts have been observed for
Ph2Sn(OC6H4Me-4)2 and Me2Sn(OC6H4Me-4)2. This may be ascribed to deshielding of

2074

DIORGANOTIN(IV) COMPLEXES OF 4-METHYLPHENOL
2075
Table 2 1H NMR data of diorganotin(IV) complexes
1H NMR δ (ppm)
Aromatic protons
Complex
-OH
ortho
meta
Substituent -Me
R-Sn
—
7.83–7.98 (m,10H)
0.87–0.97 (t, 6H)
CH3
4-methylphenol
Ph2Sn(OC6H4Me-4)2
n-Bu2SnCl(OC6H4Me-4)
5.18
—
—
6.45
6.52 (d, 4H)
6.50 (d, 2H)
6.79
6.96 (d, 4H)
6.98 (d, 2H)
2.20 (s, 3H)
2.23 (s, 3H)
2.26 (s, 3H)
1.39–1.50 (m, 4H)
CH2(α)
1.53–1.85 (m, 4H)
CH2(β)
1.39–1.50 (m, 4H)
CH2(γ )
n-Bu2Sn(OC6H4Me-4)2
—
—
6.48 (d, 4H)
6.97 (d, 4H)
2.25 (s, 3H)
0.89–0.95 (t, 6H)
CH3
1.36–1.48 (m, 4H)
CH2(α)
1.50–1.79 (m, 4H)
CH2(β)
1.36–1.48 (m, 4H)
CH2(γ )
Me2Sn(OC6H4Me-4)2
6.70 (d, 4H)
6.99 (d, 4H)
2.26 (s, 3H)
1.18 (s, 6H)
1
the protons due to a shift of electron density from the ring to the tin metal. The H NMR
signal of the methyl substituent at the aromatic ring of free 4-methylphenol does not undergo
any change on complexation. The resonances of the n-butyl, methyl, and phenyl groups
attached to tin metal in the respective complexes remain unchanged with respect to the
corresponding diorganotin dichlorides.
13C NMR Spectra
A comparison of the 13C NMR spectra (Table 3) of the complexes with that of the free
ligand shows that the resonances of the carbon atoms of the phenol ring occurring in the
range of 115.3–152.6 ppm for 4-methylphenol are shifted downfield upon complexation,
resulting from an electron density transfer from the ligand to tin metal. The carbon reso-
nance of the methyl substituent at 21.1 ppm in free 4-methylphenol does not change upon
complexation. The carbon resonances of the organic groups attached to tin also remained
unaltered relative to those of the chloride precursors.
The values of nJ(119Sn–13C) coupling constants are known to depend on the properties
of the ligands in organotin compounds and to increase with an increase of coordination
1
3
2
number around tin. The order J(119Sn–13C) >> J(119Sn–13C) > J(119Sn–13C) is more
probable for phenyltin than for alkyltin complexes. The magnitudes of the coupling con-
1
13
stants J(119Sn− C) for diorganotin(IV) complexes are consistent with four-coordinate
n
13
geometry around tin. As the coupling constants J(119Sn− C) are known to yield im-
portant structural information, the C–Sn–C angle in complexes was determined using the

2076

DIORGANOTIN(IV) COMPLEXES OF 4-METHYLPHENOL
2077
equations given by Howard’s (1) and Lockhart (2):
θ(C − Sn − C) = 0.178 J1[Sn119 − C12] + 14.7
(1)
(2)
J1[Sn119 − C12] + 875
θ(C − Sn − C) =
11.4
◦
◦
◦
◦
The C–Sn–C angles of 109.93 , 114.03 , 113.42 , and 111.92 found by em-
ploying Equations (1) and (2) for diphenyl-, di-n-butyl-, and dimethyltin(IV) complexes,
respectively, confirm the tetrahedral arrangement around tin.
119Sn NMR Spectra
119Sn NMR spectra of diphenyl-, n-butyl-, and methyltin(IV) 4-methyl phenoxides
exhibit a single resonance at −118.6, −38.0, −35.9, and 116.5 ppm, respectively, charac-
teristic of tetrahedral Sn(IV) center. The tetrahedral geometry around tin in organotin(IV)
4-methyl phenoxides resulting from 1H, 13C, and 119Sn NMR data is in accord with previous
reports42 that dimeric/polymeric structures are lost in solution.
Mass Spectra
The most important fast atom bombardment (FAB) mass data for n-
Bu2SnCl(OC6H4Me-4) and n-Bu2Sn(OC6H4Me-4)2 are given in Table 4 (Schemes
Table 4 Mass spectral data of diorganotin(IV) complexes
n-Bu2Sn(OC6H4Me-4)2 (M)
m/z(%)
n-Bu2SnCl(OC6H4Me-4) (M)
m/z(%)
[{n-Bu2Sn(OC6H4Me-4)2}2
–Me +H]+
882 (100%)
825 (51.0%)
[{n-Bu2SnCl(OC6H4Me-4)}2
+ Me]+
767 (100.0%)
654 (91.66%)
[n-Bu2Sn(OC6H4Me-
4)2SnBu(OC6H4Me-
4)(OPh)]+
[n-Bu2Sn(OPh)2SnBu2]+
[n-Bu2Sn(OC6H4Me-
4(OPh)SnBu2(OPh)]+
[n-Bu2Sn(OPh)2Sn +H]+
[n-BuSn(OPh)2 +Na -H]+
[n-Bu2Sn(OC6H4Me-4)
+Na]+
761 (40.0%)
[n-Bu2SnCl(OPh)2Bu -H]+
631 (30.55%)
541 (48.57%)
385 (77.14%)
364 (80.0%)
[n-Bu2SnCl(OPh)2Sn]+
[n-Bu2Sn (OPh)2Sn -H]+
[n-Bu2SnCl(OC6H4Me-4)Sn
+H]+
575 (11.11%)
539 (41.66%)
497 (22.22%)
[n-BuSn(OC6H4Me-4) +Na]+
[n-Bu2Sn-H]+
307 (37.14%)
233 (25.71%)
[n-Bu2Sn(OC6H4Me-4)Sn]+
[n-Bu2SnCl(OC6H4Me-4)
+2Me]+
461 (11.11%)
406 (100%)
[n-BuSn]+
[Sn]+
177 (74.28%)
121 (11.42%)
[n-Bu2SnCl(OPhPh) +Na]+
[Sn(OC6H4Me-4)SnCl]+
[Sn(OPh)SnCl -H]+
[n-Bu2SnCl +Na
-H]+/[ClSnOSn]+
[n-Bu2SnCl]+
385 (41.66%)
382 (19.44%)
367 (16.66%)
291 (25.0%)
269 (33.33%)
256 (11.11%)
235 (11.0%)
177 (19.44%)
121 (8.3%)
[SnOSn]+
[n-Bu2SnH]+
[n-BuSn]+
[Sn]+

2078
N. SHARMA AND V. KUMAR
Figure 1 Proposed structure of n-Bu2ClSn(OC6H4Me-4).
S1 and S2, Supplemental Materials). The complexes do not display a molecular ion peak.
The most intense peak at m/z 767 and 882 corresponds to [{n-Bu2SnCl(OC6H4Me-4}2
+ Me]+ and [{n-Bu2Sn(OC6H4Me-4)2}2 – Me + H]+ in the respective complexes and
indicates a marked tendency of the complexes toward association, suggesting thereby their
dimeric nature. The presence of [n-Bu2Sn]+ units bridged by 4-methylphenoxo groups is
also indicated by the mass spectra. A number of fragment ions observed for the complexes
are in accord with the structures deduced from the IR spectra.
Based upon analytical data, IR and mass spectral data dimeric structures (Figures 1
and 2) for the complexes may tentatively be proposed.
Figure 2 Proposed structure of R2Sn(OC6H4Me-4)2 (R = Ph, n-Bu, and Me).

DIORGANOTIN(IV) COMPLEXES OF 4-METHYLPHENOL
2079
Reactions of Diorganotin(IV) 4-Methylphenoxides with 2-
and 3-Cyanoanilines
The reaction of diorganotin(IV) 4-methyl phenoxides with two equivalents of 2- and
3-cyanoanilines in absolute alcohol yields 1:2 coordination compounds of composition
R2Sn(OC6H4Me-4)2 · 2 L and n-Bu2SnCl(OC6H4Me-4) · 2 L (R = Ph, n-Bu, and Me, and
L = 2- and 3-cyanoaniline), as is indicated by the analytical data (Table 1). The compounds
are white to dark brown solids. The molar conductance values of a millimolar solution of
the coordination compounds in nitrobenzene showed them to be nonelectrolytes.
The IR spectra of the adducts of 2-cyanoaniline show that the υ(CN) mode occurring
at 2212 cm−1 in uncoordinated 2-cyanoaniline has moved significantly to higher wave
number in the region of 2300–2320 cm−1. The absorption bands due to υasymNH and
υsymNH modes, which appear at 3457 and 3363 cm−1 in free 2-cyanoaniline, remain
unchanged. These observations suggest bonding of 2-cyanoaniline through the nitrile group
only. It is important to mention here that 2-cyanoaniline is known to coordinate through
nitrile as well as the amino group.43,44
In the case of the coordination compounds of diorganotin(IV) 4-methyl phenoxides
with 3-cyanoaniline, the absorption band due to υCN mode, occurring at 2229 cm−1 in
free base, shifts insignificantly to lower wave number by approximately 5–8 cm−1, thus
excluding the possibility of bonding through nitrile nitrogen atom. On the contrary, the
absorption bands due to υasymNH and υsymNH mode observed at 3400 and 3323 cm−1
in uncoordinated 3-cyanoaniline shift significantly to higher wave numbers and appear at
approximately 3470–3460 and 3376–3370 cm−1, respectively, suggesting coordination of
3-cyanoaniline through –NH2 group. It is worth pointing out that the observed trend of
shift of the υNH mode in case of 3-cyanoaniline adducts is different from earlier reports,43
where the bonding through –NH2 group suffers a negative shift. Bonding through nitrogen
is further supported by the appearance of bands at 340–280 cm−1 assigned to υ(Sn–N)
mode45 and a six-coordinate distorted octahedral environment around the tin atom may be
proposed.
1H NMR Spectra
1
A comparison of the room temperature H NMR spectra of the coordination com-
pounds with those of free 2- and 3-cyanoanilines further indicates their formation (Table 5).
1
The H NMR spectra of 2- and 3-cyanoanilines exhibit signals at 6.99–7.30 ppm and
7.00–7.32 ppm, respectively, due to the aromatic ring protons. The coordination com-
pounds show the resonances of the aniline ring protons to shift downfield. The resonances
due to the protons of the phenol ring in the parent complexes also suffer a slight downfield
shift on complexation with bases. The resonances due to the methyl substituent and the
phenyl and butyl groups attached to tin remain almost unchanged.
13C NMR Spectra
The 13C NMR spectra of 2- and 3-cyanoaniline display the resonances of the ring
carbon atoms at 98.2–148.3 ppm and 115.2–145.8 ppm, respectively. The carbon resonance
of the cyano group is observed at 116.0 and 116.5 ppm in the respective bases. The
coordination compounds of diorganotin(IV) 4-methyl phenoxides with these nitrogen bases

2080
N. SHARMA AND V. KUMAR
Table 5 1H NMR data of coordination compounds
1H NMR δ(ppm)
Aromatic protons
Complex
Aniline ring
Phenolic ring
Substituent -Me
R-Sn
n-Bu2Sn(OC6H4Me-4)2·2(2-
7.06–7.35
6.54–6.99
2.23
0.89–0.93 (t, 6H)
CH3
CNAn)
1.38–1.46 (m, 4H)
CH2(α)
1.54–1.79 (m, 4H)
CH2(β)
1.38–1.46 (m, 4H)
CH2(γ )
Me2Sn(OC6H4Me-4)2·2(2-
CNAn)
7.05–7.35
7.07–7.40
7.03–7.37
6.75–6.99
6.73–7.01
6.54–7.01
2.26
2.25
2.26
1.17 (s, 6H)
Ph2Sn(OC6H4Me-4)2·2(3-
7.80–7.95 (m, 10H)
CNAn)
n-Bu2SnCl(OC6H4Me-4)·2(3-
CNAn)
0.86–0.97 (t, 6H)
CH3
1.38–1.53 (m, 4H)
CH2(α)
1.53–1.85 (m, 4H)
CH2(β)
1.38–1.53 (m, 4H)
CH2(γ )
show moderate to appreciable downfield shifts of the signals of the aniline ring carbon atoms
(Table 6). A slight downfield shift in carbon resonances of the phenol ring compared with
those of the parent complexes was also observed for the coordination compounds.
Antibacterial Activity
The antibacterial activity of 4-methyphenol and diorganotin(IV) 4-methyl phe-
noxides was tested in vitro against Escherichia coli, Staphylococcus aureus, Staphylo-
coccus epidermidis, Shigella flexneri, Proteus mirabilis, and Pseudomonas aeruginosa
(Table 7). The results show that the ligand inhibits the bacterial growth at a con-
centration of 125–250 µg/mL, while n-Bu2SnCl(OC6H4Me-4), n-Bu2Sn(OC6H4Me-4)2,
Me2(SnOC6H4Me-4)2, and Ph2(SnOC6H4Me-4)2 were found to inhibit at a concentration
of 7.81–62.5 µg/mL. Of the four complexes studied, the complexes n-Bu2SnCl(OC6H4Me-
4) and n-Bu2Sn(OC6H4Me-4)2 were found to exhibit a significantly enhanced activity at
minimum inhibitory concentration (MIC) 7.81–15.62 µg/mL toward all bacteria under
study. This enhancement in activity may be due to the coordination of the phenol moiety
to the tin atom and an efficient diffusion of the complexes into the bacterial cell.46,47 The
antibacterial activity of these compounds was also compared with the commercial antibiotic
streptomycin (See Table S1, Supplemental Materials)

2081

2082
N. SHARMA AND V. KUMAR
Table 7 Antibacterial activity of ligand and diorganotin (IV) Complexes by MIC method in µg/mL
Compound
E. coli
S. aureus
S. epidermidis
S. flexneri
P. mirabilis
P. aeruginosa
4-methylphenol
125
62.5
7.81
15.62
7.81
31.25
250
62.5
15.62
7.81
7.81
62.5
125
15.62
7.81
15.62
31.25
62.5
125
125
250
62.5
7.81
15.62
7.81
31.25
Ph2Sn(OPhMe-4)
n-Bu2SnCl(OPhMe-4)
n-Bu2Sn(OPhMe-4)2
Me2Sn(OPhMe-4)2
Streptomycin
31.25
15.62
15.62
15.62
62.5
31.25
15.62
15.62
15.62
31.25
CONCLUSION
The dimeric structures for diorganotin(IV) 4-methyl phenoxides are derived from
physicochemical, IR, and mass spectral data. The 13C and 119Sn NMR spectra, the C–Sn–C
n
angle, and the coupling constants J(119Sn–13C) suggest a tetrahedral geometry around
the tin atom, indicating that the dimeric structures are lost in solution. The coordination
compounds of diorganotin(IV) 4-methyl phenoxides with 2- and 3-cyanoaniline indicate
coordination of the bases through the nitrile nitrogen atom in the case of 2-cyanoaniline
and through the amino nitrogen atom in the case of 3-cyanoaniline. The new complexes
show promising antibacterial activity.
EXPERIMENTAL
Materials
All the solvents used were of analytical reagent (AR) grade and were dried by standard
methods. The 4-methylphenol (Merck) was recrystallized from benzene and the purity was
checked by its melting point (34 ◦C–35 ◦C). Ph2SnCl2, n-Bu2SnCl2, Me2SnCl2, and 2- and
3-cyanoaniline were of Merck grade.
Tin in the complexes was determined gravimetrically as SnO2, while chlorine was
determined by Volhard’s method. Elemental analyses were performed on Carlo-Erba 1108
Elemental Analyzer. The conductivity measurements in nitrobenzene were made on an
Elico Conductivity Bridge type CM-82T. Molecular weights were determined by Rast’s
camphor method. IR spectra of the complexes were recorded as KBr pellets with a Nicolet-
5700 FTIR spectrophotometer. The pellets were prepared in a dry box to avoid the action
of moisture. 1H, 13C, and 119Sn NMR spectra were recorded with a Bruker Avance II 400
NMR spectrometer. The FAB mass spectra were recorded with a Jeol SX 102/Da-6000
Mass Spectrometer Data system using argon/xenon (6 kV, 10 mA) as the FAB gas. The
accelerating voltage was 10 kV and m-nitrobenzylalcohol (NBA) was used as the matrix.
Syntheses
NaOC6H4Me-4. To a solution of 4-methylphenol (5 g, 46 mmol) in CCl4 was added
an equimolar amount of sodium metal (1.06 g, 46 mmol). The reactants were stirred at room
temperature for 10 h during which a dirty white solid separated out. It was collected by
filtration, washed with CCl4, and dried under vacuum. Yield: 4.8 g, 79%.
R2Sn(OC6H4Me-4)2. To a solution of n-Bu2SnCl2 (1.14 g, 3.7 mmol), Ph2SnCl2
(1.29 g, 3.7 mmol), or Me2SnCl2 (0.82 g, 3.7 mmol) in methanol was added a methanolic

DIORGANOTIN(IV) COMPLEXES OF 4-METHYLPHENOL
2083
solution of NaOC6H4Me-4 (0.98 g, 7.5 mmol). The reactants were then refluxed for 8–10 h,
whereupon the separation of a white solid was observed. It was filtered and the filtrate was
concentrated by distilling off the solvent. The concentrate was dried under vacuum, where-
upon fine cream to pale yellow solids separated out. These were washed with petroleum
ether and dried under vacuum.
n-Bu2SnCl(OC6H4Me-4). In a typical reaction to a solution of n-Bu2SnCl2 (0.5 g,
1.6 mmol) in dry tetrahydrofuran (THF) were added equimolar amounts of 4-methylphenol
(0.17 g, 1.6 mmol) and triethylamine (0.16 g, 1.6 mmol), dissolved in the same solvent. The
mixing of the reactants resulted in the immediate formation of a white solid. The reactants
were refluxed for 6 h, to ensure the completion of the reaction. The solid was removed by
filtration and the filtrate was concentrated by distilling off the solvent. It was dried under
vacuum, whereupon a fine crystalline white solid separated out.
Reactions with 2- and 3-Cyanoanilines
A solution of Ph2(SnOC6H4Me-4)2, n-Bu2(SnOC6H4Me-4)2, n-Bu2Cl(SnOC6H4Me-
4), or Me2(SnOC6H4Me-4)2 in absolute ethanol (15 mL) was treated with two equiva-
lents of 2- or 3-cyanoaniline in separate experiments. The reaction mixture was stirred
at room temperature for 7–8 h. The addition of acetonitrile to the addition compound of
Me2(SnOC6H4Me-4)2 with 2-cyanoaniline resulted in the formation of a white solid, while
the other compounds were obtained by the addition of petroleum ether. These were then
dried under vacuum.
Antibacterial Activity Test
The ligand 4-methylphenol and its diorganotin(IV) complexes were screened in vitro
for their antibacterial activity on selected bacteria E. coli, S. aureus, S. epidermidis, S.
flexneri, P. mirabilis, and P. aeruginosa using the MIC method as recommended by National
Committee for Clinical Laboratory Standard (NCCLS).48 All the samples were tested in
triplicate. Experimental details are presented in the Supplemental Materials.
MIC Determination by Two-Fold Serial Dilution
The MIC assay49 was performed in a 96-well microtitre plate. For MIC assay of each
tested drug, a row of 12 wells was used out of which last two wells were taken as control (no
drug added). Each of the 10 wells received 100 µL of the Muller-Hinton broth, except the
first well, which received 200 µL of broth containing 500 µg/mL concentration of the test
drug. From the first well (containing test drug), 100 µL broth was withdrawn with a sterile
tip and the same was added to the 100 µL of the broth in the second well; contents were
mixed four times. Then, 100 µL was withdrawn from second well and was added to the
third well. This way, a range of two-fold serial dilution was prepared (500–0.98 µg/mL).
The broth in each of the wells was inoculated with 2 µL of the bacterial culture (E. coli, S.
aureus, S. epidermidis, S. flexneri, P. mirabilis, and P. aeruginosa) and the contents were
mixed by 10 clockwise and 10 anticlockwise rotations on a flat surface. The plate was
incubated at 35 ◦C. The observations for growth of bacteria were recorded after 24 h.

2084
N. SHARMA AND V. KUMAR
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