Organotin(IV) complexes with imidazo[1,2-a]pyridines

Article abstract of DOI:10.1016/j.poly.2013.12.030

The three-components reaction of dimethyltin dibromide with imidazo[1,2-a]pyridine and allyl bromide in ethanol affords an ionic complex, bis(1-allylimidazo[1,2-a]pyridinium) dimethyltetrabromostannate(II). X-ray crystal structure analysis of the complex reveals the tin atom to be hexacoordinated, forming a dianion. Organotin(IV) halides on reacting with imidazo[1,2-a]pyridines yield 1:2 complexes. The X-ray crystal structure analysis of such a complex shows the tin atom to be hexacoordinated, with two imidazo[1,2-a]pyridine molecules coordinated through the N1 atom. Bis(imidazo[1,2-a]pyridine)dimethyltin dibromide does not show any reactivity towards allyl bromide or 1-(1-pyrrodinyl)cyclohexene, even on refluxing in ethanol.

Full text of DOI:10.1016/j.poly.2013.12.030

Polyhedron 70 (2014) 138–143
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Organotin(IV) complexes with imidazo[1,2-a]pyridines
Rati Agrawal a, Varsha Goyal a, Raakhi Gupta a, Raghavaiah Pallepogu b,
Ramesh Kotikalapudi b, Peter G. Jones c, Raj K. Bansal a,
⇑
a Department of Chemistry, The IIS University, Jaipur 302020, India
b Department of Chemistry, University of Hyderabad, Hyderabad 500046, India
c Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, D-38023 Braunschweig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The three-components reaction of dimethyltin dibromide with imidazo[1,2-a]pyridine and allyl bromide
in ethanol affords an ionic complex, bis(1-allylimidazo[1,2-a]pyridinium) dimethyltetrabromostan-
nate(II). X-ray crystal structure analysis of the complex reveals the tin atom to be hexacoordinated, form-
ing a dianion. Organotin(IV) halides on reacting with imidazo[1,2-a]pyridines yield 1:2 complexes. The
X-ray crystal structure analysis of such a complex shows the tin atom to be hexacoordinated, with two
imidazo[1,2-a]pyridine molecules coordinated through the N1 atom. Bis(imidazo[1,2-a]pyridine)dimeth-
yltin dibromide does not show any reactivity towards allyl bromide or 1-(1-pyrrodinyl)cyclohexene, even
on refluxing in ethanol.
Received 1 November 2013
Accepted 13 December 2013
Available online 8 January 2014
Keywords:
Organotin(IV) complexes
Imidazo[1,2-a]pyridine
Dimethyltetrabromostannate(II)
X-ray structure
Ó 2014 Elsevier Ltd. All rights reserved.
1H–119Sn coupling
119Sn NMR
1. Introduction
an octahedral geometry [18–23]. Heptacoordinated organotin(IV)
complexes with 2,6-diacetylpyridine derivatives have also been
The chemistry of organotin(IV) complexes continues to be pur-
sued actively due to its multifaceted picture comprising a broad
spectrum of biocidal properties, catalytic activity, use as stabilizers
and fascinating structural diversity. Diorganotin complexes with
nitrogen donor ligands have attracted much attention due to their
potential activity against P388 leukemia [1,2]. Likewise, many di-
and triorganotin complexes on being screened against MCF-7, a
mammary tumour, and WiDr, a colon carcinoma, exhibited prom-
ising antitumour activities [3–7]. A number of biocidal formula-
tions containing organotin compounds have found applications
as fungicides, miticides, molluscicides, marine antifouling paints,
surface disinfectants and wood preservatives [8]. Non-biocidal
uses of mono- and diorganotin(IV) compounds include stabiliza-
tion of PVC, homogeneous catalysis and water repellent properties
[8]. With regards to the structural perspective, diorganotin and tri-
organotin complexes present a rich and diverse structural chemis-
try. The tin atom in the complexes can be pentacoordinated [9–11]
or hexa-coordinated [12–15] and the complexes often show
fluxional stereochemical behavior [8,13]. Several hypervalent
organotin complexes with ligands having nitrogen and chalcogen
atoms, such as Schiff bases [16,17] and pyridines [18–22], have
been prepared. o-Substituted pyridines often act as bidentate che-
lating ligands and give hexacoordinated tin(IV) complexes having
obtained and characterized [22]. In this context, we found an inter-
esting report [23] on a three-components reaction of diphenyltin
dibromide (1), allyl bromide (2a) or 3-bromocyclohexene (2b)
and pyridine (3) to give a hexacoordinated tin(IV) pyridine com-
plex (4) with concomitant Sn-C bond formation resulting from
1,2-addition of a Sn-Br moiety across the carbon–carbon double
bond of the allyl bromide or 3-bromocyclohexene (Scheme 1).
A similar reaction was given by triphenyltin bromide when
addition of the Sn-Br moiety to the carbon–carbon double bond
of allyl bromide or 3-bromocyclohexene occurred besides coordi-
nation with pyridine [23].
Although organotin(IV) complexes have been prepared with
imidazole- and benzimidazole derivatives [24,25], we could not
find any report pertaining to the reaction of organotin(IV) halides
with imidazo[1,2-a]pyridine in the presence or absence of allyl
bromide/3-bromocyclohexene. In view of the known bioactivity
of imidazo[1,2-a]pyridines [26], it was expected that the resulting
organotin(IV) complexes with this heterocyclic system might show
interesting biocidal activity [27] . Besides, the expected reaction of
the Sn-X moiety of the resulting imidazo[1,2-a]pyridine complex
with the carbon–carbon double bond of allyl bromide or 3-bromo-
cyclohexene, as reported in the case of the organotin(IV) pyridine
complex, was another point of interest. However, our results about
the reaction of dimethyltin dibromide with imidazo[1,2-a]pyri-
dines in the presence of allyl bromide turned out to be quite differ-
ent from those reported for the analogous reaction of diphenyltin
⇑
Corresponding author. Tel.: +91 141 2651030; fax: +91 141 2395494.
E-mail address: rk.bansal@iisuniv.ac.in (R.K. Bansal).
0277-5387/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.12.030

R. Agrawal et al. / Polyhedron 70 (2014) 138–143
139
Ph
Br
Ethanol
R1HC=CHCHR2Br
n
+
. n(Py)
CHR1CHBrCHR2Br
Ph2SnBr2
Sn
+
N
reflux
Ph
1
2
3
4
a. R1 = R2 = H
b. R1 R2 = -(CH2)3-
n = 1,2
Scheme 1. Reaction of diphenyltin dibromide with allylbromide/3-bromocyclohexene and pyridine.
dibromide with pyridine. The reaction leads to the formation of a
2.3. Reaction of organotin(IV) halides with imidazo[1,2-a]pyridines
new type of ionic hexacoordinated tin(IV) complex resulting from
the coordination of the liberated bromide ions, instead of the
N-heterocycle, with dimethyltin dibromide.
(8a–j)
2.3.1. General procedure
The organotin(IV) halide (3.2 mmol) and imidazo[1,2-a]pyri-
dine (6.4 mmol) were added to absolute ethanol (15 mL) taken in
a 100 mL round bottom flask. The mixture was stirred and refluxed
for 3 h under anhydrous conditions. A clear solution resulted,
which was concentrated to about half the volume and left in a
refrigerator (ꢀ ꢁ20 °C) overnight. Pale yellow fine crystals depos-
2. Materials and methods
2.1. Physical measurements
Melting points were determined on a Paramount apparatus and
were uncorrected. Elemental analyses were done on a CHNS Ana-
lyzer Perkin Elmer Ser.Second 2400. The 1H and 13C NMR spectra
were recorded on a Bruker DPX-300 NMR spectrometer at 300.00
and 75.47 MHz frequency in DMSO-d6 using TMS as an internal
reference. The 119Sn NMR spectra were recorded on a Bruker
Avance II 400 NMR spectrometer at 149.12 MHz in DMSO using
SnMe4 as an external reference. The IR spectra were scanned on
an AGILENT Tech, CARY660 spectrometer using KBr pellets. Imi-
dazo[1,2-a]pyridine, organotin(IV) halides and allyl bromide were
purchased from Sigma Aldrich and were used as such. The substi-
tuted imidazo[1,2-a]pyridines were prepared according to the pub-
lished method [28]. The solvents were dried by standard methods
and all the reactions were carried out under anhydrous conditions.
ited, which were separated, washed with
a small volume
(ꢀ2 mL) of cold ethanol and dried. The mother liquor, on concen-
tration and cooling, afforded a second crop of the product.
8
1'
2'
7
N
2
X
N
6
1" 2"
3
5
X=H, OCH3, NO2
2.3.2. Bis(imidazo[1,2-a]pyridine-1-yl)dimethyltin dibromide (8a)
Yield: 74%, m.p. 188–189 °C. IR (KBr)
max (cmꢁ1): 3112 (Ar–H)s,
1560 (Ar–C@C)s, 575 (Sn-Me). 1H NMR (DMSO-d6, d ppm, J Hz):
m
3
3
8.56 (d, JHH = 7.0, 2H, H5), 7.96 (d, JHH = 6.6, 2H, H2), 7.95 (d,
3JHH = 6.6, 2H, H3), 7.66 (d, JHH = 7.0, 2H, H8), 7.37 (t, JHH = 7.0,
3
3
2.2. Bis(1-allylimidazo[1,2-a]pyridinium)
dimethyltetrabromostannate(II) (7)
2H, H7), 6.98 (t, JHH = 7.0, 2H, H6), 1.23 (2J
Sn = 116.6, 6H,
3
1
119
H,
2CH3). 13C NMR (DMSO-d6, d ppm): C9 (148.34), C2 (135.29), C3
(132.24), C5 (131.87), C6 (120.84), C7 (118.50), C8 (118.50), CH3
(29.48). 119Sn NMR (DMSO, d ppm): ꢁ284.59. Anal. Calc. for C16H18-
Br2N4Sn: C, 35.27; H, 3.32; N, 10.28. Found: C, 35.10; H, 3.07; N,
10.22%.
He
Hd
Hb
Ha
8
Hc
N
7
6
2.3.3. Bis((2-phenyl)-imidazo[1,2-a]pyridin-1-yl)dimethyltin
2
N
dibromide (8b)
3
m
max (cmꢁ1): 3492 (Ar–H)s,
5
Yield 60%; m.p. 179–180 °C. IR (KBr)
1624 (Ar–C@C)s, 569 (Sn–Me). 1H NMR (DMSO-d6, d ppm, J Hz):
Dimethyltin dibromide (1.0 g, 3.2 mmol), imidazo[1,2-a]pyri-
dine (765 mg, 0.65 mL, 6.4 mmol) and allyl bromide (783 mg,
0.56 mL, 6.4 mmol) were added to absolute ethanol (15 mL) taken
in a 100 mL round bottom flask. The mixture was stirred and re-
fluxed for 3 h under anhydrous conditions. A clear solution re-
sulted, which was concentrated to about half the volume and left
in a refrigerator (ꢀ ꢁ20 °C) overnight. Colorless fine crystals depos-
ited, which were separated, washed with a small volume (ꢀ2 mL)
of cold ethanol and dried. The mother liquor, on concentration and
cooling, afforded a second crop of the product. [Me2SnBr4]2ꢁ
3
3
8.70 (d, JHH = 6.6, 2H, H5), 8.37 (s, 2H, H3), 7.94 (d, JHH = 7.2,
4H, H10,100), 7.55 (d, JHH = 8.4, 2H, H8), 7.43 (t, JHH = 7.2, 4H,
3
3
H20,200), 7.23 (t, JHH = 6.6, 2H, H7), 7.21 (t, JHH = 7.2, 2H, H3’),
3
3
6.80 (t, 3JHH = 6.6, 2H, H6), 1.06 (2J1
Sn = 136.3, 6H, 2CH3). Anal.
119
H,
Calc. for C28H26Br2N4Sn: C, 48.24; H, 3.76; N, 8.03. Found: C, 48.14;
H, 3.64; N, 7.96%.
2.3.4. Bis(2-(4-methoxyphenyl)-imidazo[1,2-a]pyridin-1-
yl)dimethyltin dibromide (8c)
Yield: 70%; m.p. 169–170 °C. IR (KBr) m
max (cmꢁ1): 3112 (Ar–H)s,
+
[1-allylimidzopyridinium]2 (7) (76%), m.p. 197–199 °C. IR (KBr)
mmax (cmꢁ1): 3160 (Ar–H)s, 1590 (Ar–C@C)s, 445 (Sn–Me). 1H
1613 (Ar–C@C)s, 1186 (–C–O–C–), 561 (Sn–Me). 1H NMR (DMSO-
3
3
NMR (DMSO-d6, d ppm, J Hz): 8.70 (d, JHH = 2.1, 2H, H5), 8.55 (d,
d6, d ppm, J Hz): 8.50 (d, JHH = 6.6, 2H, H5), 8.29 (s, 2H, H3), 7.89
3JHH = 6.9, 2H, H2), 8.20 (d, JHH = 2.4, 2H, H3), 8.00 (d, JHH = 1.2,
(d, JHH = 8.5, 4H, H10,100), 7.54 (d, JHH = 7.0, 1H, H8), 7.50 (d,
3
3
3
3
3JHH = 8.5, 4H, H20,200), 7.23 (t, JHH = 7.0, 2H, H7), 6.97 (t,
3
3
3
2H, H8), 7.49 (t, JHH = 7.8, 2H, H7), 7.08 (t, JHH = 6.6, 2H, H6),
119
6.09 (m, 2H, HC), 5.45 (unresolved dd, 2H, Ha), 5.40 (unresolved
3JHH = 7.0, 2H, H6), 3.80 (s, 6H, –OCH3), 1.08 (2J1
Sn = 110.5,
H,
3
13
dd, 2H, Hb), 5.22 (d, JHH = 5.7, 4H, Hd, He), 1.25 (2J1
6H, 2CH3). C NMR (DMSO-d6, d ppm): C20,200 (144.59), C10,100
(144.24), C9 (126.80), C2 (126.58), C3 (126.58), C5 (124.60), C6
(116.19), C7 (113.96), C8 (111.97), CH3 (21.90). 119Sn NMR (DMSO,
H,
119
117
Sn = 113.7, 2J1
Sn = 109.2, 6H, 2CH3). Anal. Calc. for C22H28Br4-
N4Sn: C, 33.58; H, 3.58; N, 7.12. Found: C, 33.69; H, 3.62; N, 7.06%.
H,

140
R. Agrawal et al. / Polyhedron 70 (2014) 138–143
d ppm): ꢁ202.56. Anal. Calc. for C30H30Br2N4O2Sn: C, 47.59; H,
d ppm): ꢁ395.70. Anal. Calc. for C20H17Cl3N4Sn: C, 44.61; H, 3.18;
3.99; N, 7.40. Found: C, 47.50; H, 3.88; N, 7.30%.
N, 10.40; Found: C, 44.11; H, 3.08; N, 9.94%.
2.3.5. Bis(2-(4-nitrophenyl)-imidazo[1,2-a]pyridin-1-yl)dimethyltin
dibromide (8d)
2.3.11. Bis(2-(4-nitrophenyl)-imidazo[1,2-a]pyridin-1-yl)phenyltin
trichloride (8j)
Yield: 80%; m.p. 208–209 °C. IR (KBr) m
max (cmꢁ1): 3112 (Ar–H)s,
Yield: 70%; m.p. 250–251 °C. IR (KBr)
1656 (Ar–C@C)s, 1428 (O–N–Ar). 1H NMR (DMSO-d6, d ppm, J Hz):
m
max (cmꢁ1): 3115 (Ar–H)s,
1613 (Ar–C@C)s, 1493 (O–N–Ar), 456 (Sn–Me). 1H NMR (DMSO-d6,
d ppm, J Hz): 8.90 (s, 2H, H3), 8.34 (d, 3JHH = 8.7, 4H, H10,100), 8.32 (d,
3JHH = 8.7, 4H, H20,200), 8.22 (d, 3JHH = 8.1, 2H, H8), 7.86 (d, 3JHH = 7.5,
2H, H5), 7.69 (t, 3JHH = 8.1, 2H, H7), 7.28 (t, 3JHH = 7.9, 2H, H6), 1.29
3
3
8.90 (s, 2H, H3), 8.80 (d, JHH = 7.5, 2H, H5), 8.41 (d, JHH = 7.2, 4H,
H10,100), 8.23 (d, JHH = 7.2, 4H, H20,200), 7.91 (t, JHH = 7.3, 2H, H7),
3
3
3
3
7.73(d, JHH = 7.3, 2H, H8), 7.31 (t, JHH = 7.5, 2H, H6), 7.22 (m, 5H,
Ph). Anal. Calc. for C32H23Cl3N6SnO4: C, 49.23; H, 2.96; N, 10.76.
Found: C, 49.10; H, 2.23; N, 10.46%.
119
13
(2J1
,
Sn = 126.3, 6H, 2CH3). C NMR (DMSO-d6, d ppm): C20,200
H
(147.42), C10,100 (142.43), C9 (136.65), C2 (135.72), C3 (131.01),
C6 (126.32), C7 (124.45), C5 (123.34), C8 (115.79) CH3 (29.42).
119Sn NMR (DMSO, d ppm): ꢁ375.20. Anal. Calc. for C28H24Br2N6-
SnO4: C, 42.72; H, 3.07; N, 10.67. Found: C, 42.68; H, 3.04; N,
10.50%.
2.4. X-ray diffraction studies
Single crystals of C22H28Br4N4Sn (7) and C16H18N4Br2Sn (8a) in
the form of elongated prisms were grown from methanol solutions.
Intensity data for 7 were registered on an Oxford Diffraction Xcal-
ibur E diffractometer at low temperature and for 8a on a Bruker
Smart Apex diffractometer at 296 K, using monochromated Mo
2.3.6. Bis(imidazo[1,2-a]pyridine-1-yl)diphenyltin dichloride (8e)
Yield: 73%, m.p. 140–141 °C. IR (KBr)
1652 (Ar–C@C)s. 1H NMR (DMSO-d6, d ppm, J Hz): 8.62 (d,
m
max (cmꢁ1): 3087 (Ar–H)s,
3
3
3JHH = 7.9, 2H, H5), 8.61 (d, JHH = 6.9, 2H, H2), 7.96 (d, JHH = 6.9,
3
3
Ka radiation (k = 0.71073 Å) in both cases. The structures were
2H, H3), 7.68 (d, JHH = 8.0, 2H, H8), 7.34 (t, JHH = 7.9, 2H, H7),
7.26–6.90 (m,10 H, Ph), 7.07 (t, JHH = 7.9, 2H, H6). 119Sn NMR
3
solved by direct methods and the refinements were carried out
against F2 using SHELXL-97 (G. M. Sheldrick, University of Göttingen,
Germany). All non-hydrogen atoms were refined anisotropically;
hydrogens were included using a riding model or rigid methyl
groups. Relevant crystallographic data and structure refinement
details of 7 and 8a are listed in Table 1.
(DMSO, d ppm) ꢁ402.65. Anal. Calc. for C26H22Cl2N4Sn: C, 53.83;
H, 3.81; N, 9.65; Found: C, 53.52; H, 3.71; N, 9.56%.
2.3.7. Bis(2-phenyl)-imidazo[1,2-a]pyridin-1-yl)diphenyltin dichloride
(8f)
Yield: 60%; m.p. 118–119 °C. IR (KBr) m
max (cmꢁ1): 3087 (Ar–H)s,
1655 (Ar–C@C)s. 1H NMR (DMSO-d6, d ppm, J Hz): 8.72 (d,
3. Results and discussion
3JHH = 6.9, 2H, H5), 8.63 (s, 2H, H3), 7.96 (d, JHH = 7.2, 2H, H8)
3
7.93 (d, JHH = 6.6, 4H, H10,100), 7.64 (t, JHH = 6.6, 4H, H20,200), 7.52
3
3
0
3.1. Reaction of dimethyltin dibromide with imidazo[1,2-a]pyridine
and allyl bromide
3
3
3
(t, JHH = 7.2, 2H, H7), 7.43(t, JHH = 7.5, 2H, H3 ), 7.32 (t, JHH = 6.9,
2H, H6), 7.18–6.90 (m, 10H, Ph). Anal. Calc. for C38H30Cl2N4Sn: C,
62.32; H, 4.12; N, 7.65. Found: C, 62.42; H, 4.07; N, 7.5%.
The reaction of dimethyltin dibromide with imidazo[1,2-a]pyr-
idine and allyl bromide in refluxing ethanol afforded a white crys-
talline high melting compound, which was found to be insoluble in
chloroform and other common organic solvents. The 1H NMR spec-
trum of the compound in DMSO-d6 indicated the presence of an al-
lyl moiety, thus ruling out the occurrence of 1,2-addition of the Sn-
Br moiety across the carbon–carbon double bond of allyl bromide.
2.3.8. Bis(2-(4-methoxyphenyl)-imidazo[1,2-a]pyridin-1-
yl)diphenyltin dichloride (8g)
Yield: 72%; m.p. 100–102 °C. IR (KBr)
1655 (Ar–C@C)s, 1186 (–C–O–C–). 1H NMR (DMSO-d6, d ppm, J Hz):
m
max (cmꢁ1): 3119 (Ar–H)s,
3
3
8.85 (d, JHH = 7.4, 2H, H5), 8.70 (s, 2H, H3), 7.91 (d, JHH = 7.8, 4H,
H10,100), 7.71 (d, JHH = 7.8, 4H, H20,200), 7.48 (d, JHH = 7.4, 2H, H8),
3
3
3
3
7.34 (t, JHH = 7.4, 2H, H7), 7.27 (t, JHH = 7.4, 2H, H6), 7.26–6.90
(m, 10H, Ph). 13C NMR (DMSO-d6,
d
ppm): 161.23, 153.50,
3.2. Crystal structure of complex 7
140.67, 135.17, 129.28, 128.26, 128.15, 127.67, 117.42, 115.39,
112.62, 110.41. 119Sn NMR (DMSO, d ppm): ꢁ399.41. Anal. Calc.
for C40H34O2N4Cl2Sn: C, 60.63; H, 4.33; N, 7.07. Found: C, 60.26;
H, 4.40; N, 7.30%.
Selected bond distances and angles for complex 7 are given in
Table 2.
The crystal structure of compound 7 is shown in Fig. 1.
The X-ray crystal structure of the complex reveals that allyl bro-
mide, instead of undergoing 1,2-addition with the Sn-Br moiety,
has reacted with imidazo[1,2-a]pyridine forming the 1-allylimi-
dazo[1,2-a]pyridinium ion, accompanied by liberation of the bro-
mide ion. Two bromide ions so generated coordinate with the tin
atom of dimethyltin dibromide to produce the dimethyltetrab-
romostannate (Me2Br4Sn2ꢁ) ion (Scheme 2).
The dimethyltetrabromostannate(II) ion has an octahedral
geometry. Two bromine atoms occupy apical positions, whereas
the other two bromine atoms are present in equatorial positions,
disposed in a trans orientation. The apical Sn-Br bond distances
(2.792 Å) are slightly longer than the corresponding equatorial
bond distances (2.774 Å). The Br–Sn–Br and C–Sn–C angles are
each 180°, showing an almost a perfect octahedral geometry. How-
ever, the H3C–Sn–Br1 and H3C–Sn–Br2 angles deviate slightly from
90°. We then decided to carry out the reaction of dimethyltin
dibromide with imidazo[1,2-a]pyridine and allyl bromide in suc-
cessive steps.
2.3.9. Bis(2-(4-nitrophenyl)-imidazo[1,2-a]pyridin-1-yl)diphenyltin
dichloride (8h)
Yield: 76%; m.p. 220–221 °C. IR (KBr)
1654 (Ar–C@C)s, 1428 (O–N–Ar). 1H NMR (DMSO-d6, d ppm, J Hz):
m
max (cmꢁ1): 3082 (Ar–H)s,
3
3
8.90 (s, 1H, H3), 8.80 (d, JHH = 7.6, 2H, H5), 8.41 (d, JHH = 6.9, 4H,
H10,100), 8.25 (d, JHH = 6.9, 4H, H20,200), 7.93 (d, JHH = 7.2, 2H, H8),
3
3
3
3
7.39 (t, JHH = 7.2, 2H, H7), 7.28 (t, JHH = 7.6, 1H, H6), 7.24–6.92
(m, 10H, Ph). 119Sn NMR (DMSO, d ppm): ꢁ401.28. Anal. Calc. for
C38H28Cl2N6SnO4: C, 55.50; H, 3.43; N, 10.22. Found: C, 55.34; H,
3.40; N, 9.82%.
2.3.10. Bis(imidazo[1,2-a]pyridine-1-yl)phenyltin trichloride (8i)
Yield: 76%; m.p. 89–90 °C. IR (KBr) mmax (cmꢁ1): 3118 (Ar–H)s,
1640 (Ar–C@C)s. 1H NMR (DMSO-d6, d ppm, J Hz): 8.62 (d,
3
3
3JHH = 6.9, 2H, H5), 8.60 (d, JHH = 6.9, 2H, H2), 7.91 (d, JHH = 6.9,
3
2H, H3), 7.63 (d, JHH = 7.2, 2H, H8), 7.50 (m, 5H, Ph), 7.34 (t,
3
3JHH = 7.2, 2H, H7), 7.01 (t, JHH = 6.9, 1H, H6). 119Sn NMR (DMSO,

R. Agrawal et al. / Polyhedron 70 (2014) 138–143
141
Table 1
Crystallographic data and structure refinement for complexes 7 and 8a.
Identification code
7
8a
Empirical formula
Formula weight
T (K)
C
22H28Br4N4Sn
C16H18N4Br2Sn
218.64
296(2)
786.81
100(2)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
P21/n
0.71073
orthorhombic
Pbca
8.64052(15),
14.1150(2), b (°) = 92.838(2)
11.14311(17),
1357.36(4)
2
1.925
6.845
756
a
(°) = 90
7.745(2)
14.440(4)
16.052(4)
1795.3(9)
4
2.016
5.878
1048.0
b (Å)
c (Å)
c (°) = 90
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F (000)
)
Crystal size (mm)
h (°)
0.4 ꢂ 0.3 ꢂ 0.2
0.4 ꢂ 0.22 ꢂ 0.18
2.33–30.91
2.54–25.78
Index ranges
Reflection collected
ꢁ12 6 h 6 12, ꢁ20 6 k 6 20, ꢁ16 6 l 6 15
70753
ꢁ9 6 h 6 9, ꢁ17 6 k 6 7, ꢁ19 6 l 6 1
7104
Independent reflections (Rint
)
4135 (0.0307)
1716 (0.0287)
Completeness
99.9% to h 30
99.2% to h 25
Absorption correction
Maximum and minimum transmission
Refinement method
semi-empirical from equivalents
1.000 and 0.557
semi-empirical using Sadabs
0.418 and 0.202
full-matrix least-squares on F2
4135/0/143
full-matrix least-squares on F2
1717/0/118
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.09
1.09
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0164, wR2 = 0.0337
R1 = 0.0202, wR2 = 0.0345
0.45 and ꢁ0.42
R1 = 0.0251, wR2 = 0.0640
R1 = 0.0300, wR2 = 0.0665
0.38 and ꢁ0.57
Largest difference in peak and hole (e Åꢁ3
)
Table 2
Bond lengths (Å) and angles (°) for complex 7.
Sn(1)–C(11)
Sn(1)–Br(1)
Sn(1)–Br(2)
N(1)–C(7A)
N(1)–C(2)
N(1)–C(8)
C(2)–C(3)
C(3)–N(3A)
2.123(15)
2.774(14)
2.792(14)
1.351(18)
1.384(18)
1.473(18)
1.349(2)
N(3A)–C(7A)
N(3A)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(7A)
C(8)–C(9)
C(9)–C(10)
1.371(17)
1.377(18)
1.357(2)
1.414(2)
1.369(2)
1.403(2)
1.495(2)
1.318(2)
1.396(19)
C(11)#1–Sn(1)–C(11)
C(11)#1–Sn(1)–Br(1)
C(11)–Sn(1)–Br(1)
Br(1)–Sn(1)–Br(1)# 1
C(11)#1–Sn(1)–Br(2)
C(11)–Sn(1)–Br(2)
Br(1)–Sn(1)–Br(2)
Br(1)#1–Sn(1)–Br(2)
Br(2)–Sn(1)–Br(2)#1
C(7A)–N(1)–C(2)
180.0
C(2)–C(3)–N(3A)
C(7A)–N(3A)–C(4)
C(7A)–N(3A)–C(3)
C(4)–N(3A)–C(3)
C(5)–C(4)–N(3A)
C(4)–C(5)–C(6)
106.8(12)
121.7(13)
108.8(12)
129.5(13)
118.3(14)
120.8(14)
120.9(14)
117.5(14)
107.1(12)
132.2(13)
120.7(13)
112.2(12)
122.2(15)
89.3(4)
90.7(4)
180.0
89.1(5)
90.9(5)
90.8(4)
89.2(4)
180.0
109.0(12)
125.8(12)
125.1(12)
108.4(13)
C(7)–C(6)–C(5)
C(6)–C(7)–C(7A)
N(1)–C(7A)–N(3A)
N(1)–C(7A)–C(7)
N(3A)–C(7A)–C(7)
N(1)–C(8)–C(9)
C(10)–C(9)–C(8)
C(7A)–N(1)–C(8)
C(2)–N(1)–C(8)
C(3)–C(2)–N(1)
Fig. 1. The X-ray crystal structure of complex 7. The asymmetric unit is numbered.
Symmetry transformation: #1 ꢁx + 1, ꢁy + 1, ꢁz + 1.
3.3. Reaction of organotin(IV) halides with imidazo[1,2-a]pyridines
two methyl groups in the complexes 8a–d [20,30]. The 2J1H,117Sn
coupling, however, could only be resolved in 8a. The 119Sn NMR
signal at d ꢁ202.56 toꢁ402.65 ppm confirms the hexacoordinated
state of the tin atom in the complexes [20].
Organotin(IV) halides (5) on reacting with imidazo[1,2-a]pyri-
dine (2 equivalents) in refluxing ethanol afforded high melting
crystalline complexes (8) in good yields (Scheme 3).
The complexes are colorless or light colored sharp melting sol-
ids, which are insoluble in chloroform and other common organic
solvents. In the IR spectra, an absorption band at 457–575 cmꢁ1 is
observed due to the mSn–C stretching vibration [29]. In the 1H NMR
spectra, a singlet at d 1.06–1.29 ppm with side bands due to cou-
pling with 119Sn (2J1H,119Sn = 110–136.3 Hz) is observed due to
3.4. Crystal structure of complex 8a
It has been possible to grow a single crystal of appropriate
dimensions for complex 8a and to determine its X-ray crystal
structure, which is shown in Fig. 2. Selected bond distances and an-
gles for the complex are given in Table 3.

142
R. Agrawal et al. / Polyhedron 70 (2014) 138–143
Ethanol
+ CH2CH=CH2
N
Me2Br4Sn2-
Me2SnBr2
2HC =CHCH Br +
+
N
2
2
2
reflux
N
N
2
5
6a
7
Scheme 2. Reaction of dimethyltin dibromide with imidazo[1,2-a]pyridine and allyl bromide.
EtOH
Reflux
R1R2SnX2
N
+
R1R2SnX2
2
N
N
N
R3
R3
2
5
6 a-d
8 a-j
8
X
R1
R2 R3
a
b
c
d
e
f
H
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
Cl
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Cl
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Ph
Ph
Ph
p-C6H4-OCH3
p-C6H4-NO2
H
Ph
g
h
i
p-C6H4-OCH3
p-C6H4-NO2
H
j
Cl
p-C6H4-NO2
Scheme 3. Complexation of organotin(IV) halides with imidazo[1,2-a]pyridines.
Table 3
The X-ray crystal structure of complex 8a is shown in Fig. 2.
Bond lengths (Å) and angles (°) for complex 8a.
The tin atom is hexacoordinated and the molecule of the com-
plex possesses octahedral geometry. However, in contrast to com-
plex 7, the two methyl groups in 8a occupy apical positions. Two
imidazo[1,2-a]pyridine molecules are present in equatorial posi-
tions and are disposed trans to each other. The two Sn–C bond dis-
tances are equal and have a value of 2.119 Å each. Likewise, the
two Sn–N bond distances and also the two Sn–Br bond distances
are equal and have values of 2.356 and 2.743 Å respectively. The
C–Sn–C and N–Sn–N bond angles are 180° each, showing almost
a perfect octahedral geometry of the complex. However, the C–
Sn–Br and C–Sn–N angles deviate slightly from 90°.
C(1)–C(2)
C(1)–N(1)
C(1)–N(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–N(2)
C(6)–C(7)
1.405(4)
1.333(4)
1.378(4)
1.355(4)
1.404(5)
1.344(5)
1.366(4)
1.332(5)
C(6)–N(2)
C(7)–N(1)
1.369(4)
1.380(4)
2.119(3)
2.356(3)
2.743(7)
2.119(3)
2.356(3)
2.743(7)
C(8)–Sn(1)
N(1)–Sn(1)
Br(1)–Sn(1)
Sn(1)–C(81)
Sn(1)–N(11)
Sn(1)–Br(11)
N(1)–C(1)–C(2)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
C(5)–C(4)–C(3)
C(4)–C(5)–N(2)
C(7)–C(6)–N(2)
C(6)–C(7)–N(1)
C(1)–N(1)–C(7)
131.8(3)
109.6(2)
118.6(3)
118.3(3)
121.6(3)
120.1(3)
118.9(3)
106.0(3)
111.5(3)
105.2(3)
C(8)–Sn(1)–C(81)
C(8)–Sn(1)–N(1)
C(81)–Sn(1)–N(1)
C(8)–Sn(1)–N(11)
C(81)–Sn(1)–N(11)
C(81)–Sn(1)–Br(11)
C(8)–Sn(1)–Br(11)
C(81)–Sn(1)–Br(1)
C(8)–Sn(1)–Br(1)
N(1)–Sn(1)–N(11)
180.00(9)
88.31(11)
91.69(11)
91.69(11)
88.31(11)
90.43(11)
89.57(11)
89.57(11)
90.43(11)
180.00(11)
3.5. Attempted reaction of bis(imidazo[1,2-a]pyridin-1-yl)dimethyltin
dibromide (8a) with allyl bromide
Symmetry transformation: 12 ꢁ x, 1 ꢁ y, 1 ꢁ z.
Complex 8a was reacted with allyl bromide (1 equivalent) in
ethanol, but no reaction occurred, even on refluxing for 3 h. It is
obvious that the tin atom of 8a after coordination with imi-
dazo[1,2-a]pyridine molecules is no longer sufficiently electro-
philic to react with the C@C functionality of allyl bromide. A
stronger nucleophile, such as the enamine 1-(1-pyrrodinyl)cyclo-
hexene, also did not show any reactivity towards 8a.
Fig. 2. The X-ray crystal structure of bis(imidazo[1,2-a]pyridine)dimethyltin dibromide (8a).

R. Agrawal et al. / Polyhedron 70 (2014) 138–143
143
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The Sn–Br bond of dimethyltin dibromide is not sufficiently
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Acknowledgements
We acknowledge the help from the DST for the crystallographic
analysis of one sample at the University of Hyderabad, Hyderabad,
India.
Appendix A. Supplementary data
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CCDC 954809 and 965676 contain the supplementary data of
compounds 7 and 8a, respectively. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223-336-033; or email:
deposit@ccdc.cam.ac.uk.
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