Stannylation of unsaturated carbon-carbon bonds by tin tetrachloride

Article abstract of DOI:10.1016/j.jorganchem.2011.06.002

The reactions of tin tetrachloride and four terminal alkynes (PhCCH, ^tBuCCH, ⁿBuCCH, HOCH₂CCH), norbornene, and norbornadiene in dichloromethane or chloroform solution lead to the formation of stannylation products, which

Full text of DOI:10.1016/j.jorganchem.2011.06.002

Journal of Organometallic Chemistry 696 (2011) 3023e3028
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Journal of Organometallic Chemistry
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Stannylation of unsaturated carbonecarbon bonds by tin tetrachloride
*
ꢀ
ꢀ
Izabela Czelusniak, Marta Jachimowska, Teresa Szymanska-Buzar
Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
The reactions of tin tetrachloride and four terminal alkynes (PhC^CH, tBuC^CH, nBuC^CH,
HOCH2C^CH), norbornene, and norbornadiene in dichloromethane or chloroform solution lead to the
formation of stannylation products, which were characterized by 1H, 13C and 119Sn NMR spectroscopy.
Article history:
Received 29 April 2011
Received in revised form
1 June 2011
Virtually complete a-regioselectivity was obtained in reaction of all four alkynes without any effect of the
Accepted 3 June 2011
relative steric bulk of the substituent R at the triple bond of alkyne RCb^CaH. The reaction of norbornene
and norbornadiene with SnCl4 is stereoselective, giving an exo stannylation product.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Stannylation
Alkynes
Norbornene
Norbornadiene
NMR
1. Introduction
2-cyclohexen-1-one and cinnamic aldehyde [15]. However, it is
not clear now what the role of the MeSn bond or the tri-
Oxidative addition of the CleSn
s
-bond of tin tetrachloride to
chlorostannyl ligand SnClꢀ3 is in the creation of catalytic activity of
those heterobimetallic complexes. Recently, it has been observed
that during the in situ generation of the catalyst, heterobimetallic
WeSn or MoeSn seven-coordinate complexes in dichloro-
methane solution, tin tetrachloride reacts with the transition
metal complex as well as with organic compounds to give stan-
nylation products. The reaction of tin tetrachloride with unsatu-
rated hydrocarbons also occurs in the absence of a transition
metal complex. It seems probable that this reaction can play an
important role in the activation of C]C and C^C bonds by SnCl4
as Lewis acid. Besides, this very easy stannylation reaction can be
applied for the synthesis of vinyl and alkyl stannanes. The stan-
nylation of alkynes and alkenes has attracted considerable
interest in organic chemistry because it provides a simple general
method for the synthesis of organostannanes, useful starting
materials for further transformation and building blocks in
organic synthesis [16e21]. As was described by Yamaguchi et al.,
the SnCl4eBu3N reagent promotes the vinylation of phenols with
ethyne and the alkylidenation of silyl enol ethers with terminal
alkynes [22,23]. Using aryl and alkenyltin trichlorides, the car-
bostannylation reaction of norbornene and norbornadiene has
been achieved in the presence of palladium catalyst [24,25].
In this study, we describe the formation and identification by
NMR spectroscopy of the stannylation products formed in the
molybdenum(0) and tungsten(0) carbonyl complexes has previ-
ously been shown to be a valuable route to Mo(II) and W(II)
seven-coordinate complexes [1e6]. In reaction of carbonyl
complexes such as [M(CO)6] or [M(CO)4L2] (L ¼ nitrogen or
phosphorous donor ligands) and SnCl4, binuclear and mono-
nuclear complexes of the type [(m-Cl)3{M2(SnCl3)(CO)7}] and
[MCl(SnCl3)(CO)3L2] (M ¼ Mo, W) are formed. These molybde-
num(II) and tungsten(II) complexes containing trichlorostannyl
ligand readily react with bicyclo[2.2.1]-hept-2-ene (norbornene,
(nbe)) and bicyclo[2.2.1]-hepta-2,5-diene (norbornadiene (nbd))
to initiate the ring-opening metathesis polymerization (ROMP) in
dichloromethane solution at room temperature [7,8], but in
reaction with terminal alkynes they initiate cyclotrimerization
and polymerization reactions [9]. In aromatic hydrocarbon solu-
tion, the heterobimetallic complex [(m-Cl)3{W2(SnCl3)(CO)7}] is,
however, a good catalyst for the hydroarylation of nbe [10]. Very
interesting catalytic activity has also been observed for other
complexes containing trichlorostannyl ligands; e.g. the iridium
complex [{(m-Cl)IrCl(SnCl3)(cod)}2], formed in reaction of [{(m-Cl)
Ir(cod)}2] and SnCl4, initiates the alkylation of arenes with benzyl
alcohols and ethers [11e14]. Other trichlorostannyl complexes of
iridium(III) are catalytically active in the hydrogenation of
t
reaction of SnCl4 with four terminal alkynes (PhC^CH, BuC^CH,
nBuC^CH, HOCH2C^CH), norbornene, and norbornadiene in
* Corresponding author. Tel.: þ48 71 3757221; fax: þ48 71 222 348.
ꢀ
E-mail address: tsz@wchuwr.pl (T. Szymanska-Buzar).
dichloromethane or CDCl3 solution at room temperature.
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.06.002

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I. Czelusniak et al. / Journal of Organometallic Chemistry 696 (2011) 3023e3028
3024
2. Experimental
1C, H2Ca), 29.4 (1C, H2Cb) 21.4 (1C, H2Cg), 13.65 (1C, Me). 119Sn{1H}
NMR (186.5 MHz, CDCl3, 298 K):
¼ ꢀ98.
1-trichlorostannyl-2-chloro-2-hydroxymethyl-ethene (4): 1H
d
All reactions were performed using standard Schlenk tech-
niques under an atmosphere of nitrogen and with substrates and
solvents freshly distilled from calcium hydride. 1H, 13C NMR, and
two-dimensional 1He1H COSY, 1He13C HMQC, and 1He13C HMBC
NMR spectra were recorded with a Bruker AMX 300 or 500 MHz
instrument. All proton and carbon chemical shifts were referenced
4
2
NMR (
d
, CDCl3, 500 MHz): 6.38 (t, JHeH ¼ 2.3 Hz, JHeSn(117/
¼
203/213 Hz, 1H, HSnC1), 4.54 (s, 1H, HO), 4.48 (d,
119)
4JHeH ¼ 2.3 Hz, 4JHeSn ¼ 18.7 Hz, 1JHeC ¼ 153 Hz, 2H, H2Ca). 13C{1H}
NMR (
d
, CDCl3, 125 MHz): 147.4 (2JCeSn(117/119) ¼ 135/140 Hz, 1C,
ClC2), 120.3 (1JCeSn(117/119) ¼ 1147/1200 Hz, 1C, HSnC1), 64.1
to the residual proton signal for 1H NMR (
natural abundant carbon signal of the solvent for 13C NMR (
CDCl3). 119Sn NMR chemical shifts were referenced relative to
Ph3SnCl (
d
7.24 CDCl3) or the
77.0
(3JCeSn ¼ 42 Hz, 1C, H2Ca). 119Sn{1H} NMR (112 MHz, CDCl3, 298 K):
d
d
¼ ꢀ190. ESI-MS method: found M ¼ 316.80, calculated for
C3H4Cl4OSn M ¼ 316.81.
d
ꢀ44.7 [26]) used as an external standard.
exo,exo-2-trichlorostannyl-3-chloro-bicyclo[2.2.1]-heptane (5):
Analyses of the reaction products were performed on a Hew-
lettePackard GCeMS system containing an HP590II gas chro-
matograph equipped with a HP-5MS column and an HP5971A mass
detector. Mass spectra were measured by electron impact with
ionizing energy of 70 eV and on apex-Ultra mass spectrometer
using the ESI method.
1H NMR (
d
, CDCl3, 300 MHz): 4.41 (d, 3JHeH ¼ 7.2 Hz, 3JHeSn ¼ 95 Hz,
1H, HClC3), 3.46 (dd, 3JHeH ¼ 7.2 Hz, 3JHeH ¼ 2.2 Hz, 2JHeSn ¼ 77 Hz,
1H, HSnC2), 2.92 (s, 1H, HC1), 2.68 (s, 1H, HC4), 2.27 (d,
2JHeH ¼ 11 Hz, 1H, H2C7), 1.77 (d, 2JHeH ¼ 8.3 Hz, 2H, 2H2C5,6), 1.55d
(2JHeH ¼ 11 Hz, 1H, H2C7), 1.24 (dd, 2JHeH ¼ 8.3 Hz, JHeH ¼ 2.1 Hz,
3
2H, 2H2C5,6). 13C{1H} NMR ( , CDCl3, 75 MHz): 70.2 (1JCeSn(117/
d
¼ 759/794 Hz, 1C, HSnC2), 64.5 (2JCeSn(117/119) ¼ 89/93 Hz, 1C,
119)
2.1. General procedure for stannylation of unsaturated
hydrocarbons by SnCl4
HClC3), 46.4 (3JCeSn ¼ 8.3 Hz, 1C, HC4), 40.2 (2JCeSn ¼ 33.3 Hz, 1C,
HC1), 35.5 (1C, H2C7), 30.1 (3JCeSn(117/119) ¼ 160/168 Hz, 1C, H2C6),
25.9 (4JCeSn ¼ 14 Hz, 1C, H2C5). 119Sn{1H} NMR (112 MHz, CDCl3,
A
dichloromethane solution (15 cm3) of SnCl4 (0.2 cm3,
298 K):
d
¼ ꢀ97.
1.7 mmol) and unsaturated hydrocarbon in a 1:1 molar ratio was
stirred at room temperature for 24 h. All volatile materials were
then evaporated under reduced pressure at room temperature, and
the residue was analyzed by NMR spectroscopy in CDCl3 solution,
which revealed the 100% conversion of the substrate and the
formation of one product.
exo,exo-5-trichlorostannyl-6-chloro-bicyclo[2.2.1]-hept-2-ene
(6a): 1H NMR (
d
, CDCl3, 500 MHz): 6.35 (dd, JHeH ¼ 5.6 Hz,
3
3JHeH ¼ 3.0 Hz, JHeSn ¼ 12 Hz, 1H, HC3), 6.18 (dd, JHeH ¼ 5.6 Hz,
4
3
3JHeH ¼ 3.2 Hz, JHeSn ¼ 14 Hz, 1H, HC2), 4.24 (dd, JHeH ¼ 7.0 Hz,
5
3
3JHeH ¼ 1.0 Hz, JHeSn ¼ 88 Hz, 1H, HClC6), 3.49 (d, JHeH ¼ 1 Hz,
3
3
3JHeSn ¼ 48 Hz, 1H, HC4), 3.31 (dd, JHeH ¼ 7.0 Hz, JHeH ¼ 2.0 Hz,
3
3
2JHeSn ¼ 45 Hz, 1H, HSnC5), 3.29 (s, 1H, HC1), 2.27 (d, 2JHeH ¼ 9.9 Hz,
2.2. General procedure for reactions in the NMR tube
1H, H2C7), 1.92 (d, 2JHeH ¼ 9.9 Hz, 1H, H2C7). 13C{1H} NMR (
d, CDCl3,
125 MHz): 140.3 (3JCeSn(117/119) ¼ 132/137 Hz, 1C, HC3), 135.6
(4JCeSn ¼ 17 Hz, 1C, HC2), 65.3 (1JCeSn(117/119) ¼ 716/751 Hz, 1C,
HSnC5), 58.6 (2JCeSn ¼ 47 Hz, 1C, HClC6), 51.6 (1C, HC1), 45.2 (1C,
H2C7), 45.1 (2JCeSn ¼ 24 Hz, 1C, HC4). 119Sn{1H} NMR (112 MHz,
The course of the stannylation reaction was also followed by 1H
NMR spectroscopy. As a general procedure for NMR experiments,
unsaturated hydrocarbon (ca. 0.85 mmol) was weighed into an
NMR tube. The tube was then capped with a septum. A portion of
CDCl3 (0.7 cm3) and SnCl4 (0.1 cm3, 0.85 mmol) was then added to
the NMR tube via a syringe. The tube was periodically monitored by
1H NMR spectroscopy over the desired length of time at 25 ꢁC.
CDCl3, 298 K):
d
¼ ꢀ88.
endo,endo-5-trichlorostannyl-6-chloro-bicyclo[2.2.1]-hept-2-
ene (6b): 1H NMR (
d
, CDCl3, 500 MHz): 6.65 (dd, JHeH ¼ 5.6 Hz,
3
3JHeH ¼ 2.8 Hz,1H, HC3), 6.40 (dd, 3JHeH ¼ 5.6 Hz, 3JHeH ¼ 2.8 Hz,1H,
HC2), 4.90 (dd, 3JHeH ¼ 7.7 Hz, 3JHeH ¼ 3.5 Hz, 3JHeSn(117/119) ¼ 131/
3
3
2.3. NMR characteristic of stannylation products
137 Hz, 1H, HClC6), 3.96 (dd, JHeH ¼ 7.7 Hz, JHeH ¼ 3.5 Hz,
2JHeSn ¼ 38 Hz, 1H, HC5), 3.49 (s, 1H, HC4), 3.45 (s, 1H, HC1), 1.90 (d,
2JHeH ¼ 9.7 Hz, 1H, H2C7), 1.43 (d, 2JHeH ¼ 9.7 Hz, 1H, H2C7). 13C{1H}
1-trichlorostannyl-2-chloro-2-phenyl-ethene (1): 1H NMR (
d,
3
4
CDCl3, 500 MHz): 7.67 (dd, JHeH ¼ 7.8 Hz, JHeH ¼ 2.0 Hz, 2H,
NMR (
d
, CDCl3, 125 MHz): 137.8 (3JCeSn ¼ 68 Hz, 1C, HC3), 135.5 (1C,
3
HCoePh), 7.49 (m, 1H, HCpePh), 7.43 (tt, JHeH
¼
7.8 Hz,
HC2), 68.3 (1JCeSn(117/119)
¼
876/917 Hz, 1C, HSnC5), 57.8
4JHeH ¼ 1.4 Hz, 2H, HCmePh), 6.56 (s, JHeSn(117/119) ¼ 174/182 Hz,
(2JCeSn ¼ 69 Hz, 1C, HClC6), 50.1 (3JCeSn ¼ 18 Hz, 1C, H2C7), 49.4
2
1H, HSnC1). 13C{1H} NMR (
d
, CDCl3, 125 MHz): 154.6 (2JCeSn ¼ 45 Hz,
(3JCeSn ¼ 20 Hz, 1C, HC1), 46.9 (2JCeSn ¼ 38 Hz, 1C, HC4). 119Sn{1H}
1C, ClC2), 134.7 (3JCeSn(117/119) ¼ 118/123 Hz, 1C, CiePh), 131.7 (1C,
NMR (112 MHz, CDCl3, 298 K):
d
¼ ꢀ93.
HCpePh), 128.3 (2C, HCmePh), 127.4 (2C, HCoePh), 122.7 (1JCeSn(117/
¼ 1097/1147 Hz, 1C, HSnC1). 119Sn{1H} NMR (186.5 MHz, CDCl3,
119)
298 K):
3. Results and discussion
d
¼ ꢀ98.
1-trichlorostannyl-2-chloro-2-t-butyl-ethene (2): 1H NMR (
d,
CDCl3, 500 MHz): 6.00 (s, 1JHeC ¼ 171 Hz, 2JHeC ¼ 40 Hz, 2JHeSn(117/
3.1. Stannylation of alkynes
¼ 190/199 Hz, 1H, HSnC1), 1.27 (s, 1JHeC ¼ 129 Hz, 2JHeC ¼ 40 Hz,
119)
5JHeSn ¼ 4.6 Hz, 9H, Me). 13C{1H} NMR (
d, CDCl3, 125 MHz): 169.0
The exothermic reaction of SnCl4 with various terminal alkynes
in dichloromethane solution gave stannylation products, which
were identified by NMR methods (1H, 13C{1H}, 1He1H COSY, and
1He13C HMQC) as a chlorovinyltin trichlorides 1e4 (Scheme 1). The
(2JCeSn ¼ 71 Hz, 1C, ClC2), 121.2 (1JCeSn(117/119) ¼ 1079/1129 Hz, 1C,
HSnC1), 42.2 (3JCeSn(117/119) ¼ 93/97 Hz, 1C, C3etBu), 28.8 (3C,
MeetBu). 119Sn{1H} NMR (186.5 MHz, CDCl3, 298 K):
d
¼ ꢀ102.
1-trichlorostannyl-2-chloro-2-n-butyl-ethene (3): 1H NMR (
d,
4
2
CDCl3, 500 MHz): 5.98 (t, JHeH ¼ 1.0 Hz, JHeSn(117/119) ¼ 191/
200 Hz, 1H, HSnC1), 2.57 (t, JHeH ¼ 7.7 Hz, JHeC ¼ 130 Hz, 2H,
3
1
R
Cl
H
SnCl3
R
H +
SnCl4
H2Ca), 1.61 (tt, 3JHeH ¼ 7.5 Hz, 2H, H2Cb), 1.36 (qt, 3JHeH ¼ 7.5 Hz, 2H,
CH Cl , r.t.
2
2
3
H2Cg), 0.93 (t, JHeH ¼ 7.4 Hz, 2H, H3Cd). 13C{1H} NMR (
d, CDCl3,
1 - 4
R = Ph,t Bu, nBu, HOCH2
125 MHz): 160.0 (2JCeSn ¼ 63 Hz, 1C, ClC2), 122.3 (1JCeSn(117/
¼ 1025/1073 Hz, 1C, HSnC1), 41.2 (3JCeSn(117/119) ¼ 108/113 Hz,
Scheme 1. Stannylation of alkynes.
119)

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3025
olefin proton signal of the vinyl moiety of these compounds was
observed in 1H NMR spectra in the range of
d
¼ 6.56e5.98 ppm. This
proton signal clearly shows 117/119Sn satellites due to coupling with
the tin atom (117Sn and 119Sn, I ¼ 1/2, natural abundance of 7.61%
and 8.58%) (Figs. 1a and 2a and Figs. 1S and 2S in Supplementary
Materials). The lowest value of the 1He117/119Sn coupling constant
was obtained for compound 1 derived from phenylacetylene
(2JHeSn ¼ 174/182 Hz), while the highest coupling constant was
obtained for compound
4 derived from propargyl alcohol
(2JHeSn ¼ 203/213 Hz) (Table 1). In the 2D 1He13C HMQC NMR
spectrum of 1, the proton signal at
d
¼ 6.56 correlates with the
carbon signal at 122.7 ppm, in which satellites due to coupling with
the tin atom are nicely observed (1JCeSn ¼ 1097/1147 Hz) (Fig. 1b).
Slightly lower values of carbonetin coupling constants were
obtained for compounds 2 and 3 (1079/1129 Hz and 1025/1073 Hz,
respectively), whereas the highest one was obtained for compound
4 (1JCeSn ¼ 1147/1200 Hz) (Fig. 2b, Table 1). These NMR data and,
first of all, the high value of carbonetin (1JCeSn) and protonetin
(2JHeSn) coupling constants obtained from the NMR spectra of 1e4
are in agreement with the regioselective a-stannylation of alkynes
(RCb^CaH) by SnCl4, regardless of their substitution patterns
(Table 1). In the applied reaction conditions, the vinylstannane
products were found to be stereochemically stable. No other
isomers were detected in any of the cases. Similarly high regio- and
stereoselectivity of stannylation had been observed before in
reactions of alkynols with Lewis acidic hydrostannane Bu2Sn(OTf)H
[27], while the hydrostannylation reaction of alkynols initiated by
Fig. 2. (a) Partial 1H NMR spectrum (500 MHz, CDCl3) showing signals of compound 4.
(b) Partial 13C{1H} NMR spectrum (125 MHz, CDCl3) showing signals of compound 4.
Asterisks denote 117/119Sn satellites (I ¼ ½, 7.61/8.58%). The proton and carbon signal
denoted by S is due to CDCl3.
radicals is not so selective [28]. However, in reaction of propargyl
alcohol and SnCl4 a small amount of another product was observed
by NMR spectroscopy, identified as HC^CCH2OSnCl3 due to three
Me
a
4
3
Me3C
H
1
2
carbon signals at
two proton signals at
product is much more unstable than 4 and decays in one day.
It can be proposed that the uniformly good -regioselectivity of
d
78.3 (C^), 77.3 (HC^), and 52.6 (CH2) ppm and
Cl
SnCl3
d
4.48 (CH2) and 2.66 (HC^) ppm. The latter
a
stannylation is due to polarization of the acetylenic bond
HCSn
d
(RCb^Ca ꢀeHdþ) and the addition of a trichlorostannyl group of the
polar CldꢀeSndþCl3 bond to the more electron-rich (^Cdꢀ
) a-
carbon of the triple bond. Thus, in contrast to the monosubstituted
alkyne PhC^CH, the disubstituted alkyne PhC^CMe did not react
with SnCl4.
Compounds 1e4 are fairly stable and under strictly anhydrous
conditions can be stored for some time. However, all attempts to
obtain their GCeMS spectra were unsuccessful. Only the proto-
nolysis product of 1, with Mr ¼ 138.594 (C8H7Cl), was detected. The
identification of the latter compound by NMR spectroscopy as
chlorostyrene (C6H5CCl]CH2) was possible due to two equally
s
* *
5.5
4.5
(ppm)
2.5
7.5
6.5
3.5
1.5
4
b
intense proton signals at d 5.76 and 5.51 ppm, observed as doublets
2
with JHeH ¼ 1.7 Hz, which in the 2D HMQC spectrum correlated
with the olefinic carbon signal at 112.65 ppm. The formation of the
protonolysis product was also detected by NMR in reaction of
compound 4, where a chloro(hydroxymethyl)vinyl moiety was
identified due to two equally intense olefinic proton signals at 5.56
1
Table 1
s
Selected chemical shifts (ppm) and coupling constants (Hz) for the four 1-
trichlorostannyl-2-chloro-ethenes (1e4) RClC]CH(SnCl3), R ¼ Ph (1) tBu (2), nBu
(3), HOCH2 (4).
3
2
* *
d
(1H)
HCSn
d
(
13C)
RClC HCSn
d
2J
119Sn) (1He117/119Sn)
1J
(
2J
(
170
90
110
(ppm)
70
150 130
50
30
(
13Ce117/119Sn)
13Ce117/119Sn)
1
2
3
4
6.56 154.6 122.7 ꢀ98 174/182
6.00 169.0 121.2 ꢀ102 190/199
5.98 160.0 122.3 ꢀ98 191/200
6.38 147.4 120.3 ꢀ190 203/213
1097/1147
1079/1129
1025/1073
1147/1200
45
71
63
135/140
Fig. 1. (a) Partial 1H NMR spectrum (500 MHz, CDCl3) showing signals of compound 2.
(b) Partial 13C{1H} NMR spectrum (125 MHz, CDCl3) showing signals of compound 2.
Asterisks denote 117/119Sn satellites (I ¼ ½, 7.61/8.58%). The proton and carbon signal
denoted by S is due to CDCl3.

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3026
and 5.46 ppm and two olefinic carbon signals at 116.4 ppm (CH2)
and 128.9 ppm (C). However, compound 4 was detected as the
anion C3H4Cl4OSn (M ¼ 316.8) by ESI-MS method.
formation of only one product (6a) were observed (Fig. 3a).
However, after a prolonged time (one day), another product (6b)
was detected and identified by NMR spectroscopy. After one week
reaction in an NMR tube, the 6a:6b ratio was calculated from the
integration of relevant signals as 83:17. The stereochemistry of both
products was assigned by NMR methods (1H, 13C{1H}, 1He1H COSY,
1He13C HMQC and 1He13C HMBC NMR).
3.2. Stannylation of norbornene
As was observed by 1H NMR monitoring, only ca. 35% of nor-
bornene decays in reaction with one equivalent of SnCl4 in CDCl3
solution (Fig. 3S in Supplementary Materials). The light yellow
stannylation product (chloronorbornyltin trichloride) (5) was
found to be stereochemically stable and characterized by NMR
methods (1H, 13C{1H}, 1He1H COSY, 1He13C HMQC and 1He13C
HMBC NMR) as exo,exo-2-trichlorostannyl-3-chloro-bicyclo[2.2.1]-
heptane (5) (Scheme 2). Its 13C{1H} NMR spectrum shows seven
carbon signals due to the norbornyl moiety. Six carbon signals
clearly show satellites due to coupling with the tin atom. The
highest value of the 13Ce117/119Sn coupling constant was obtained
The 13C{1H} NMR spectrum of 6a shows seven carbon signals
due to the norbornenyl moiety (Fig. 3b). Most of the carbon
signals clearly show satellites due to coupling with the tin atom.
The highest value of the 13Ce117/119Sn coupling constant was
obtained for the signal at
d
65.3 (1JCeSn ¼ 716/751 Hz). This
resonance can thus be assigned to the carbon atom adjacent to
the tin atom. In the 2D 1He13C HMQC NMR spectrum of 6a, the
latter carbon signal correlates with the proton signal at 3.31 ppm,
in which satellites due to coupling with the tin atom are nicely
observed (2JHeSn ¼ 45 Hz). The proton signal at 4.24 ppm corre-
lates with the carbon signal at 58.6 ppm but in the 2D 1He1H
COSY spectrum it correlates with the proton signal at 3.31 ppm.
The endo position of both protons indicates a rather low value of
the protoneproton coupling constant (3JHeH ¼ 7.0 Hz) and a high
value of the protonetin coupling constant (3JHeSn ¼ 88 Hz) for the
proton signal at 4.24 ppm, resulting from the trans position of this
proton and the SnCl3 unit. Additionally, the fairly high value of the
for the carbon signal at
the carbonetin coupling constant indicates the formation of a CeSn
d
70.2 (1JCeSn ¼ 759/794 Hz). The value of
s
bond. This resonance can thus be assigned to carbon adjacent to
the tin atom. In the 2D 1He13C HMQC NMR spectrum of 5, the latter
carbon signal correlates with the proton signal at 3.46 ppm, in
which satellites due to coupling with the tin atom are nicely
observed (2JHeSn ¼ 77 Hz). In the 2D 1He1H COSY spectrum, the
latter proton signal correlates with the proton signal at 4.41 ppm
and the value of the protoneproton coupling constant
3JHeH ¼ 7.2 Hz was calculated. The fairly high value of the proto-
netin coupling constant (3JHeSn ¼ 95 Hz) for the proton signal at
4.41 ppm suggests the trans position of this proton and the SnCl3
unit and the endo position of both protons and the exo position of
both substituents. In the 2D 1He13C HMQC NMR spectrum the
proton signal at 4.41 ppm correlates with the carbon signal at
64.5 ppm, in which satellites due to coupling with the tin atom
made it possible to calculate the 2JCeSn coupling constant (2JCeSn(117/
carbonetin coupling constant (3JCeSn(117/119)
detected on carbon signal at 140.3 ppm assigned to the carbon
atom in the trans position to the tin atom indicates the exo
position of the SnCl3 unit. The chemical shift of the proton signal
¼
132/137 Hz)
¼ 89/93 Hz). The chemical shift of the proton signal (4.41 ppm)
119)
and the carbon signal (64.5 ppm) assigned to the HClC unit
compare well with the chemical shift reported for exo-2-chloro-
bicyclo[2.2.1]-heptane (dH 3.87, dC 62.20) [29e31]. Additional
evidence for the exo position of the SnCl3 unit is provided by the
fairly high value of the carbonetin coupling constant (3JCeSn(117/
¼ 160/168 Hz) detected on carbon signal at 30.1 ppm assigned
119)
to the methylene carbon atom (H2C6) in the trans position to the tin
atom. The proper assignment of the methine carbons signals (HC1,4
)
was possible thanks to the 2D 1He13C HMQC and HMBC NMR
spectra. In the 1He13C HMQC NMR spectrum, the methine carbons
(signals at dC 46.4 and 40.2) correlate through one bond with the
proton signals at dH 2.68 and 2.92, respectively. In the 1He13C
HMBC NMR spectrum, these methine carbon signals correlate
through three bonds with the proton signals at dH 3.45 and 4.41,
respectively. Compound 5 can be isolated after evaporation of
chloroform and dissolved in toluene-d8 without noticeable
decomposition.
3.3. Stannylation of norbornadiene
The course of the stannylation reaction of nbd by SnCl4 was
followed by 1H NMR spectroscopy in CDCl3 solution. After mixing
the reagents, very fast exothermic conversion of nbd and the
SnCl3
Cl
+
SnCl4
CDCl3, r.t.
Fig. 3. (a) Partial 1H NMR spectrum (300 MHz, CDCl3) showing signals of compound
6a. (b) Partial 13C{1H} NMR spectrum (75 MHz, CDCl3) showing signals of compound
6a. Asterisks denote 117/119Sn satellites (I ¼ ½, 7.61/8.58%). The proton and carbon
signal denoted by S is due to CDCl3.
nbe
5
Scheme 2. Stannylation of norbornene.

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I. Czelusniak et al. / Journal of Organometallic Chemistry 696 (2011) 3023e3028
3027
(dH 4.24 ppm) and the carbon signal (dC 58.6 ppm) assigned to the
HClC unit compare well with the chemical shift reported for exo-
5-chloro-bicyclo[2.2.1]-hept-2-ene (dH 3.77, dC 59.0) [32]. The
proper assignment of the carbon signals to the norbornenyl
moiety was confirmed by the 2D 1He13C HMBC NMR spectra. In
the 1He13C HMBC NMR spectrum, the olefinic carbons (signals at
dC 135.6 and 140.3) correlate through three bonds with the proton
signals at dH 3.49 and 3.29, respectively. Based on these NMR
data, the isomer 6a was described as exo,exo-5-trichlorostannyl-6-
chloro-bicyclo[2.2.1]-hept-2-ene. As was observed by means of
NMR spectra, compound 6a undergoes rearrangement to give
a new norbornenyl compound (6b). The relatively low value of
the carbonetin coupling constant (3JCeSn ¼ 68 Hz) detected for
the carbon signal at 137.8 ppm assigned to the olefinic carbon
atom in the cis position to the tin atom and a very high value of
the 13Ce117/119Sn coupling constant (1JCeSn(117/119) ¼ 876/917 Hz)
SnCl3
Cl
+
SnCl4
CDCl3, r.t.
CDCl3, r.t.
nbd
6a
6b
SnCl3
Cl
SnCl3
Cl
6a
Scheme 3. Stannylation of norbornadiene.
SnCl4
CH2Cl2, r.t.
H
SnCl3
H
R
Cl
R
δ
H
R
R
H
+
SnCl4
δ
SnCl4
A
R = Ph, tBu, nBu, HOCH2
B
1 - 4
obtained for the signal at
d 68.3 assigned to the carbon atom
adjacent to the tin atom observed in the NMR spectra of 6b
suggest the endo position of the SnCl3 unit. A similar relationship
between the exo and the endo stereochemistry of stannyl deriv-
atives of norbornene and the value of the 13Ce117/119Sn coupling
constant have recently been observed for tributylstannyl and
triphenylstannylnorbornene [33] (Table 2). The endo position of
both substituents and the exo position of two protons observed in
the 1H NMR spectrum of 6b at 3.96 and 4.90 ppm are indicated by
the value of the protoneproton coupling constant (3JHeH ¼ 7.7 Hz)
and the value of the protonetin coupling constant (3JHeSn ¼ 131/
137 Hz) for the proton signal at 4.90 ppm, resulting from the trans
position of this proton and the SnCl3 unit. As has been reported
before for norbornene and norbornane derivatives, the resonance
of the exo proton adjacent to the endo substituent appears at
lower field than the resonance of the endo proton adjacent to the
exo substituent [30e36]. This agrees very well with the chemical
shifts detected here for 6a (3.31 and 4.24 ppm) and 6b (3.96 and
4.90 ppm). In reaction of nbd and SnCl4, the latter molecule
attacks the olefinic bond of nbd molecule from the less hindered
exo side to give the exo,exo substituted product. The formation of
6b can be explained by exoeendo isomerization of 6a in the
presence of SnCl4 in CDCl3 solution (Scheme 3). The thermal
interconversion of endo to exo isomer of norbornane derivatives
has been reported before by Tobler and Foster [36].
Scheme 4. A plausible reaction pathway for the stannylation reaction.
3.4. A plausible reaction pathway for the stannylation reaction
A speculative but plausible mechanism for the stannylation of
alkynes is illustrated in Scheme 4. It is most probable that the
interaction between SnCl4 (Lewis acid, electron acceptor) and
a triple C^C bond of alkyne (Lewis base,
p-electron donor) and the
formation of an
h
2-complex A is crucial for this addition reaction. In
fact, the color of the reaction mixture changed to orange when the
colorless reagents mixed in dichloromethane. The interaction of
phenylacetylene with SnCl4 in complex A can be stabilized by the
p
-system of the phenyl group and the formation of the zwitterionic
intermediate B. In this intermediate, tin tetrachloride as a Lewis
acid can accept electron density from an electron-rich alkyne
molecule to generate the corresponding vinyl cation and an SnCl4ꢀ
anion connected through an SneC bond. The transfer of a chlorine
anion from the SnClꢀ4 anion to the electron-deficient carbon from
the same side of the olefin bond can give the chlorostannylation
product stereoselectively (cis addition). The
a-regioselective
introduction of the stannyl group can be rationalized by the
avoidance of steric repulsion from the substituent and the appro-
priate polarization (RC^CdꢀeHdþ) of the acetylenic bond and the
addition of trichlorostannyl group of the polar CldꢀeSndþCl3 bond
to the more electron-rich (^Cdꢀ
) a-carbon of the triple bond. It is
Table 2
worth noting that the presence of water, even in trace quantities, is
generally detrimental to these reactions, due to the strong coordi-
nation of water with the Lewis acid e SnCl4.
Comparison of the selected chemical shifts (ppm) and coupling constants (Hz) for
6a and 6b and other exo and endo stannylation products of norbornadiene.a
d
(1H)
d
(
13C)
d
2J
1J
3J
HCSn HCSn
(
119Sn) (1He117/119Sn) (13Ce117/119Sn) (13Ce117/119Sn)
]CH
4. Conclusions
3.31 65.3 ꢀ88
3.96 68.8 ꢀ93
45
716/751
132/137
SnCl
Cl
In summary, we have described an efficient and stereoselective
method for the synthesis of norbornyl, norbornylidene, and vinyl-
stannanes by simple procedures, under mild reaction conditions,
and in very good yield. The stannylation products formed in reac-
tion of SnCl4 with four terminal alkynes (PhC^CH, tBuC^CH,
nBuC^CH, HOCH2C^CH), norbornene, and norbornadiene in
dichloromethane or chloroform solution have been characterized
38
876/917
313/327
68
50
SnCl
Cl
0.7
1.1
20.2 eb
21.1 eb
eb
Sn Bu
eb
362/378
393/412
22
61
Sn Bu
SnPh
by 1H, 13C and 119Sn NMR spectroscopy. Virtually complete
a-
regioselectivity was achieved in reaction of all four alkynes without
any effect of the relative steric bulk of substituent R at the triple
bond of the alkyne RCb^CaH. The cis (exoeexo) addition of the
SneCl bond of SnCl4 to the olefin bond of norbornadiene and nor-
bornene takes place with similarly high stereoselectivity.
1.61 23.0 ꢀ89.6 eb
2.30 24.8 ꢀ91.4 eb
458/478
28
SnPh
a
This very easy stannylation reaction can be applied for the
synthesis of vinyl and alkyl stannanes, which have great utility as
From reference [33].
Not determined.
b

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3028
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Acknowledgments
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We acknowledge Dr J. Skonieczny and S. Baczynski for
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Appendix. Supplementary material
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.06.002.
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