Reactions of tin(II) hydride species with unsaturated molecules

Article abstract of DOI:10.1002/anie.200805595

(Chemical Equation Presented) If anything can, tin can: The tin(II) hydride species [LSnH] (L=HC{CMeN(2,6-iPr₂C₆H₃)} ₂) reacts with various compounds containing unsaturated C - O, C - C, or C - N bonds, which re

Full text of DOI:10.1002/anie.200805595

Communications
DOI: 10.1002/anie.200805595
Hydrostannylation
Reactions of Tin(II) Hydride Species with Unsaturated Molecules**
Anukul Jana, Herbert W. Roesky,* Carola Schulzke, and Alexander Dꢀring
Dedicated to Professor Joachim Sauer on the occasion of his 60th birthday
SnH2 has been prepared and characterized in an argon
matrix.[1] At elevated temperature, SnH2 changed to an
insoluble solid of unknown structure. Terphenyl and b-
diketiminate ligands have been used for the preparation of
substituted tin(II) hydrides. The terphenyl derivatives exist in
the solid state as dimeric structures,[2] whereas the b-
diketiminate species incorporates a terminal tin(II) hydride
with very weak intermolecular interactions.[3] Until recently,
reactions of organotin hydrides were based on tin(IV)
precursors. Di- and triorganotin hydrides, of composition
R2SnH2 and R3SnH, with a formal oxidation state of SnIV
undergo a rich variety of chemical transformations.[4] The
most commonly used reagent of this class of compounds is
tributyltin hydride, which is widely used as a reducing agent in
organic and inorganic chemistry.[5] To our knowledge, there
are no hydrostannylation reactions described using tin(II)
hydride. Herein, we report the first hydrostannylation reac-
tions of carbon dioxide, ketones, aldehydes, alkynes, and
carbodiimides with [LSnH] (2, L = HC{CMeN(2,6-
iPr2C6H3)}2).
Carbon dioxide is a readily accessible atmospheric gas
that could be a useful feedstock for organic compounds.[7] The
kinetic and thermodynamic stability of carbon dioxide
present significant challenges in designing efficient chemical
transformations. Reactions of metal hydrides with carbon
dioxide to generate metal formate species are well known for
transition metal hydrides and alkali metal hydrides.[8] How-
ever, for group 14 metal hydrides there are only a few reports
on the hydrogenation of carbon dioxide using silicon(IV)
hydride[9] or tin(IV) hydride.[10] The reaction of carbon
dioxide and silicon(IV) hydride requires a transition metal
catalyst. Herein, we report on the synthesis of a stannylene
À À
formate [LSn O C(O)H] (3), by the reaction of 2 with
carbon dioxide at room temperature without any catalyst in
quantitative yield (Scheme 1).
We have previously reported the synthesis of 2 from the
reaction of the corresponding tin(II) chloride, [LSnCl] (1),[6]
with one equivalent of AlH3·NMe3 in toluene.[3] Preparation
of 2 from AlH3·NMe3 resulted in the formation of the
expected product contaminated with small amounts of the
starting material [LSnCl] (1), which , when it was used in
hydrostannylation reactions, led to products containing
chlorine. Furthermore, when contaminated with chlorine, 2
was unstable and decomposed in an inert atmosphere within
four days. Therefore, a different method of preparation was
required. Treatment of [LSnCl] (1) with potassium triisobu-
tylborohydride in toluene at À108C afforded the tin(II)
hydride 2 in high yield. The crude reaction product was
recrystallized from n-hexane and obtained as pure yellow
Scheme 1. Preparation of 3. Ar=2,6-iPr2C6H3
Stannylene formate 3 is a colorless solid, which is soluble
in benzene, THF, n-hexane, and n-pentane and shows no
decomposition on exposure to air. It was characterized by
multinuclear NMR and IR spectroscopy, EI mass spectrom-
etry, elemental analysis, and X-ray structural analysis. The
1H NMR spectrum of 3 exhibits an upfield shifted singlet (d =
8.97 ppm) which can be assigned to the CH proton and is
flanked by satellite peaks attributable to Sn (3J(119Sn,1H) =
52 Hz). The 119Sn NMR signal of 3 appears at d = À360 ppm,
which is very different from that for the starting compound 2.
The IR spectrum shows two bands at 2700 and 1641 cmÀ1,
1
crystals which were characterized by H (d = 13.96 ppm) and
119Sn (d = À4.45 ppm, 1J(119Sn,1H) = 64 Hz) NMR spectrosco-
py. The chemical shift for 119Sn of 2 given in ref. [3] is that of
[LSnCl].
which are assigned to the C H and C O stretching frequen-
cies.
À
=
Colorless compound 3 crystallizes in the triclinic space
¯
group P1, with two monomers in the asymmetric unit from
saturated n-hexane solution at À328C after two days.
Coordination around the tin center has a distorted tetrahedral
geometry with one lone pair (Figure 1).[11]
[*] A. Jana, Prof. Dr. H. W. Roesky, Prof. Dr. C. Schulzke, A. Dꢀring
Institut fꢁr Anorganische Chemie, Universitꢂt Gꢀttingen
Tammannstrasse 4, 37077 Gꢀttingen (Germany)
Fax: (+49)551-39-3373
The carbonyl group and its transformation to other
functional groups is very important in organic chemistry.[12]
There are numerous reports on hydrostannylation of com-
pounds with carbonyl groups using tin(IV) hydride.[13] Herein,
we demonstrate for the first time the hydrostannylation of a
variety of carbonyl compounds, such as 2-benzoylpyridine,
2,2,2-trifluoroacetophenone, and ferrocene carbaldehyde,
using tin(II) hydride 2.
E-mail: hroesky@gwdg.de
[**] Support of the Deutsche Forschungsgemeinschaft is highly
acknowledged.
Supporting Information for this article, containing experimental
synthetic details and physical data, is available on the WWW under
http://dx.doi.org/10.1002/anie.200805595.
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Figure 1. Molecular structure of 3. Thermal ellipsoids are set at 50%
probability. Hydrogen atoms are omitted for clarity reasons. Selected
bond lengths [ꢃ] and angles [8]: Sn2–O1 2.1353(15), O1–C1 1.299(2),
C1–O2 1.209(3), Sn2–N1 2.1655(17), Sn2–N2 2.1752(15); Sn2-O1-
C1 116.40(13), O1-C1-O2 126.78(18), N1-Sn2-N1 86.42(6).
Figure 2. Molecular structure of 4. Thermal ellipsoids are set at 50%
probability. Hydrogen atoms are omitted for clarity reasons. Selected
bond lengths [ꢃ] and angles [8]: Sn1–O1 2.0414(15), Sn1–
N2 2.2420(16), Sn1–N3 2.2632(18); N2-Sn1-O1 99.99(6), N2-Sn1-
N3 82.10(6).
Ketone insertion into the tin–hydrogen bond of various
complexes is well established.[14] Although 2 displayed no
reactivity toward acetone at room temperature, it reacted
cleanly with aromatic ketones. Treatment of 2 with 2-
benzoylpyridine and 2,2,2-trifluoroacetophenone led quanti-
tatively to the stannylene alkoxides 4 and 5, respectively
Compound 6 is an orange solid, which is soluble in
benzene, THF, n-hexane, and n-pentane and shows no
decomposition on exposure to air. It was characterized by
multinuclear NMR and IR spectroscopy, EI mass spectrom-
etry, elemental analysis, and X-ray structural analysis
1
(Scheme 2). The H NMR spectrum of 4 exhibits an upfield
1
(Figure 3).[11] The H NMR spectrum of 6 exhibits a singlet
(d = 4.81 ppm), which can be assigned to the CH2 protons and
is flanked by Sn satellite peaks (3J(119Sn,1H) = 13.5 Hz). The
119Sn NMR signal of 6 appears at d = À262 ppm.
Scheme 2. Preparation of 4, 5, and 6. Ar=2,6-iPr2C6H3
shifted singlet (d = 6.28 ppm) which can be assigned to the
quaternary CH proton. The 119Sn NMR resonance signal of 4
appears at d = À286 ppm. Compound 4 crystallized in the
¯
triclinic space group P1 with one molecule in the asymmetric
unit (Figure 2).[11]
Compound 5 has one CF3 group and gives rise to
interesting NMR spectra. The 1H NMR spectrum of 5 exhibits
a quartet (d = 5.15 ppm) which corresponds to the quaternary
Figure 3. Molecular structure of 6. Thermal ellipsoids are set at 50%
probability. Hydrogen atoms are omitted for clarity reasons. Selected
bond lengths [ꢃ] and angles [8]: Sn1–O1 2.0253(13), Sn1–
N1 2.1834(14), Sn1–N2 2.1894(14); Sn1-O1-C1 129.13(11), N1-Sn1-
O1 87.89(6), N1-Sn1-N2 85.10(5).
CH proton. The 19F NMR signal is
a doublet (d =
À76.29 ppm) with a coupling constant of 7.3 Hz and is flanked
by Sn satellite peaks (4J(119Sn,1H) = 42 Hz). The four isopro-
pyl groups of 4 and 5 give rise to four different resonances,
and the two methyl groups in the backbone exhibit two
different signals in the proton NMR spectra. Future study is
planned to generate enantiomerically pure secondary alco-
hols by using organocatalysts.
Ferrocene moieties are important in organometallic
chemistry, with respect to electrochemistry[15] and material
science, because bridging ferrocenophanes undergo polymer-
ization and generate organometallic polymers with high
molecular weight.[16] The reaction of 2 with ferrocene
The hydrostannylation of olefins and alkynes has been
established for nearly 50 years and follows either a polar or a
free-radical pathway, depending on substituents and condi-
tions.[17] In contrast to this result, the present hydrostannyla-
tion reaction of alkynes with 2 proceeds without any catalyst,
although alkyne insertion into transition metal–hydride bonds
is well established.[18]
ꢀ
ꢀ
carbaldehyde generated bimetallic tin(II) alkoxide
(Scheme 2).
6
Compound 2 reacts with MeC CCO2Et and MeO2CC
CCO2Me at room temperature to form stannylenes 7 and 8
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(Scheme 3), respectively. The 1H NMR spectrum of 7 shows a
broad resonance (d = 6.64 ppm), which can be tentatively
assigned to the vinyl proton. The IR spectrum of this
Scheme 4. Preparation of 9. Ar=2,6-iPr2C6H3
ring gives rise to a singlet (d = 8.30 ppm) and other reso-
nances as expected while the 119Sn NMR signal appears at d =
À175 ppm.
Scheme 3. Preparation of 7 and 8. Ar=2,6-iPr2C6H3
In summary, a number of reactions of [LSnH] (2) with
À
À
À
compounds containing unsaturated C O, C C, and C N
bonds resulted in simultaneous hydrogen and {LSn} transfer
to the organic substrates. Compounds 3–9 represent a unique
new class of stannylene compounds with an electron lone pair
on tin(II) that is suitable for complexation with transition
metal fragments. Moreover, most of these compounds are
stable to air and moisture.
compound exhibits a strong band at 1686 cmÀ1, which can
be tentatively assigned to the carbonyl group. The crystal
structure of 7 (Figure 4)[11] reveals a cis orientation of the tin
and hydrogen atom across the double bond and crystallizes in
Received: November 16, 2008
Published online: December 29, 2008
Keywords: alkynes · carbonyl compounds · hydrides ·
.
hydrostannylation · tin
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¯
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ꢀ
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À
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1
In the H NMR of 9, the CH proton of the four-membered
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Chemie
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