Decomposition of ethoxyethynyl(trimethyl)tin - Studied by 119Sn and 13C NMR spectroscopy

Article abstract of DOI:10.1515/znb-1999-0601

The thermally induced decomposition of ethoxyethynyl(trimethyl)tin (1) was studied by ¹¹⁹Sn NMR which revealed the formation of bis(trimethylstannyl) ketene (2) as the major product, bis(trimethylstannyl) acetic acid ethyl ester (3) as a minor product, and a small amount of tetramethyltin (4). Full NMR data sets, including coupling constants and isotope induced chemical shifts ¹ Δ^12/13C(¹¹⁹Sn) are provided for 1-3. The first example of ultra-high resolution ¹¹⁹Sn NMR is shown.

Full text of DOI:10.1515/znb-1999-0601

Decomposition of Ethoxyethynyl(trimethyl)tin - Studied by 119Sn
and 13C NMR Spectroscopy
Bemd Wrackmeyer1* and Sergei V. Ponomarevb
a Laboratorium für Anorganische Chemie, Universität Bayreuth, D-95440 Bayreuth, Germany
b Department of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119899 Moscow, Russia
* Reprint requests to Prof. Dr. B. Wrackmeyer. Fax: +49 921 552157.
E-mail: B.Wrack@uni-bayreuth.de
Z. Naturforsch. 54 b, 705-708 (1999); received February 23, 1999
Alkynes, Ketenes, Tin, NMR Data
The thermally induced decomposition of ethoxyethynyl(trimethyl)tin (1) was studied by
ll9Sn NMR which revealed the formation of bis(trimethylstannyl) ketene (2) as the major
product, bis(trimethylstannyl) acetic acid ethyl ester (3) as a minor product, and a small amount
of tetramethyltin (4). Full NMR data sets, including coupling constants and isotope induced
chemical shifts 1_ \ 12 13C( 1 l9Sn) are provided for 1 -3 . The first example of ultra-high resolution
"9Sn NMR is shown.
Heating of ethoxyethyne and its derivatives in-
duces thermal decomposition by elimination of
ethene to give ketenes [1 ], followed by vari-
ous further reactions. Organometallic substituted
alkoxyethynes are attractive starting materials for
numerous useful further transformations [2, 3]. Our
current interest in the 1 ,1 -organoboration of 1 -
alkynyltin compounds [4] prompted us to study
the decomposition of ethoxyethynyl(trimethyl)tin,
Me3Sn-C=C-OEt (1). 1 reacts readily with tri-
ethylborane by 1,1-organoboration [5]; however,
prolonged heating at > 80 °C of mixtures contain-
ing 1 -alkynyltin derivatives and sterically more hin-
dered triorganoboranes is frequently required in or-
der to start the 1,1-organoboration reaction. There-
fore, it is important to know how the tin compound
behaves under such conditions in the absence of
a borane reagent. It has been shown [6 a] that 1,1-
bis(trimethylstannyl) ketene, (Me3Sn)2C=C= 0 (2 ),
can be obtained by heating of 1 to > 80 °C, purified
by fractional distillation and characterised by IR,
'H and 13C [6 b] [NMR spectra. However, coupling
constants J(l19Sn,13C) and 119Sn NMR spectra have
not been reported. Indeed,119Sn NMR should be the
ideal tool to reveal the fate of the MeiSn group in the
course of thermal decomposition of 1 in solution.
After heating 1 in [Dgjtoluene solution at 100 °C
MeaSn
//-
.CH—C
Me3Sn—C=C—OEt
MeaSn'
OEt
[+ HOEt]
c = c = o
1
- C2H4 |
[+ MeaSnOEt]^,
Me3SnN
[Me3Sn—CH=C=0]
/
[- HC=COEt] Me3Sn
i
h2c = c = o + c 2H4
I
----- *- decomposition
Schem e
1
is no longer present. There are mainly three promi-
nent 119Sn NMR signals amounting to > 98% of the
integrated intensities. The major product (ca. 60%)
is the ketene 2 , followed by bis(trimethylstannyl)
acetic acid ethyl ester, (Me3Sn)2CHC(6 )OEt (3 )
(ca. 35%), and tetramethyltin, Me4Sn (4 ) (ca. 4%).
In more diluted samples the amount of 3 is notice-
ably reduced whereas the amount of 4 appears to
be slightly increased (Scheme 1). The ll9Sn NMR
data were confirmed by 'H and 13C NMR spectra
of the same mixtures. The formation of 3 and 4 has
not been reported previously. The small amount of
Me4Sn is the result of thermally induced redistribu-
tion reactions. However, the formation of the ester 3
is somewhat unexpected, since it requires either the
for several hours, the reaction mixture becomes reaction of the ketene 2 with ethanol or the interme-
dark-coloured, and 1l9Sn NMR spectra show that 1 diacy of trimethylstannyl ketene, Me3SnCH=C= 0
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B. W rackmeyer and S. V. Ponomarev • Decomposition of Ethoxyethynyl(trimethyl)tin
Table 1. I3C and ll9Sn NMR data3 of the 1-alkynyltin compound 1, bis(trimethylstannyl) ketene 2 and bis(trimethyl-
stannyl) acetic acid ethyl ester 3.
Compound
[.5mm] 6 ' ’C(Me^Sn) -7.8 [406.3]
Me3Sn-C =C -O E t(l)
(Me3 Sn)2C =C=0 (2)
(Me3Sn)2CHC(0)0Et (3)
-6.7 [373.9] [3.4 -J]
-15.4 [196. l]v
161.7 {10.5}
—
-8.0 [345.8]
15.8 [202.3]
176.2 [25.5]
59.5, 14.9
23.6 {232.7}
-11.2 (SnMe,);
-31.6 (Sn-CH)
<§13C(Sn-C)
<$,3C(CO)
<5n C(OEt)
<5,,9Sn
33.8 [545.7]
112.1 [130.3]
74.2 [6.9], 14.2
-61.5
32.7 {4.8}
-3.3 (SnMeO; -45.1 (Sn-C=);
-2 .4 (=CO)
_A12/ , 3C (ll9Sn)
+ 1.3 (SnMe,); -51.0 (Sn-C=);
-8.4 (=C O )
a In [Dsjtoluene at 22 ± 1 °C; coupling constants 7(119Sn,l3C) and 2/ ( ll9Sn,ll7 Sn) are given in brackets and curved
brackets (± 0.5 Hz), respectively, measured from the l3C satellites in the ll9Sn NMR spectra using high digital
resolution (see Fig. 1). Isotope induced chemical shifts _A are given in ppb with a negative sign if the 119Sn NMR
signals of the heavy isotopomer is shifted to lower frequencies;b 2/(= 13CSn13C) = 4.6 Hz (see Fig. 2 );c './(l3C =l3C)
= 83.45 Hz, ’z \12/ 13C (l3C) > -35.7 ppb (AB pattern of the l3C satellites was not taken into account).
Fig. 1. 186.5 MHz “ 9Sn
NMR spectrum of bis(trime-
thylstannyl) ketene
in [Dgjtoluene, 22
2
(5%
1 °C;
±
128 transients), recorded by
the refocused INEPT pulse
sequence [9b,c] (based on
2y r 9Sn,'HMe)
= 57.6 Hz)
with ’H decoupling, using a
digital resolution of 20 mHz.
The line width is ca. 80 mHz.
All satellites (as indicated) are
clearly resolved.
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B. W rackm eyer and S. V. Ponomarev • Decomposition of Ethoxyethynyl(trimethyl)tin
Fig. 2. 125.8 MHz 13C NMR
spectrum of bis(trimethyl-
stannyl) ketene
2
(5% in
[Dg]toluene, 22 ± 1 °C; 2048
transients), recorded by the
refocused INEPT pulse se-
quence [9b, c] (based on
V (13CSnC'H) = 2.5 Hz) with
'H decoupling, using a digi-
tal resolution of 10 mHz. The
line width of the central signal
is ca. 40 mHz. All satellites as
indicated are resolved.
,13C
(not detected in the reaction mixture), which then well (Fig. 2): 117/M19Sn satellites are visible already
could react with ethoxy(trimethyl)tin, Me3Sn-OEt after eight transients, and it proved possible (after
2048 transients) to detect even l3C satellites corre-
(also not detected), to give 3. In any case, this im-
plies that either EtOH or Me^Sn-OEt are formed sponding to '7(13C=13C) = 83.45 Hz for the ketene
system. The high resolution achieved in these ex-
periments also allows to observe 13C satellites due
to 2/(= 13CSn13CMe) = 4.6 Hz.
and trapped in the course of the decomposition of 1.
2 and 3 are attractive examples for applying con-
ditions set up for ultra-high resolution [7] 13C and
119Sn NMR spectroscopy. Examples are shown for
The sign of 2i ( 119S n,'l7Sn) is negative for cou-
2 in Figures 1 and 2. The complete 13C and 119Sn pling across an sp3 hybridised carbon as in 3 or
in stannyl-substituted methanes [10]. In 1,1-bis(tri-
methylstannyl) alkenes 2/ ( 119Sn,117Sn) is large and
positive [11]. For l,l-bis(trimethylstannyl) allenes
it was shown that 2J(l19Sn,' 17Sn) is still positive but
much smaller than in alkenes [12]. The small value
of 2i ( 119Sn,117Sn) = 4.8 Hz for 2 may be of either
sign and shows the strong influence of the nature of
the cumulene system on this parameter.
NMR data sets of 1, 2 and 3 is given in Table I.
For all three compounds, the coupling constants
/ ( 119Sn,13C) are more readily measured from 119Sn
(Fig. 1) than from l3C NMR spectra. Furthermore,
the 119Sn NMR spectra reveal the isotope induced
chemical shifts Z\12/ 13C(ll9Sn) [8] and confirm the
assignments in 13C NMR spectra. In addition, cou-
pling constants 2/ ( 119Sn,ll7Sn) are observed in the
cases of 2 and 3. The relaxation time of the ketene
The isotope induced chemical shifts 1ZXI2/ 13C
13C nucleus bearing the MejSn groups is rather long (119Sn) follow the pattern which has been estab-
lished for many organotin compounds [8, 13]. A
requires much spectrometer time. The application change in the sign of 1A is observed for Me^Sn
of polarisation transfer [9] from the MesSn hydro-
and therefore, the observation of 117/119Sn satellites
compounds if the magnitude of |'./(ll9Sn,13CMe)|
gen nuclei to this particular 13C nucleus works very exceeds 400 Hz. Although a change of the sign
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B. W rackmeyer and S. V. Ponomarev • Decomposition of Ethoxyethynyl(trimethyl)tin
of 1zA12//13C(119Sn) are found for different values
|’y(' 19Sn,13C)|, similar correlations can be expected
for any type of carbon atom. It appears that alkynyl
13C nuclei in l-alkynyl(trimethyl)tin compounds
exert the largest negative values o f 1_\l2/ 13C(* 19Sn).
up to 12 h. NMR spectra were run on Bruker ARX 250
and DRX 500 spectrometers. Chemical shifts are given
relative to Me4Si [<51?C (C6D5 CD3) = 20.4] and Me4 Sn
[<§119Sn = 0 for S ( 1 ,9Sn) = 37.290665 MHz], All pulse
angles for 'H, l?C and ll9Sn NMR measurements were
carefully calibrated, shim parameters were optimised, and
low power selective 1H decoupling was used in order to
keep temperature gradients in the sample at a minimum.
Experimental
The compounds were handled in an atmosphere of
Ar and oven-dried glassware was used. The synthesis
Acknowledgements
We are grateful to the Deutsche Forschungsgemein-
schaft, the Fonds der Chemischen Industrie and the Rus-
sian Foundation for Basic Research for support of this
work.
of ethoxyethynyl(trimethyl)tin
1 followed the literature
procedure [6 a ]. Concentrated (150 mg in 0.5 ml), samples
of 1 in [Ds]toluene and diluted (40 mg in 1 ml) samples
of 1 under the same conditions were heated to 100 °C
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