2SnBr2: Evidence for intramolecular Si-O bond activation

Article abstract of DOI:10.1021/om300200u

The synthesis of the intramolecularly coordinated diorganotin dibromide [Me₂(i-PrO)SiCH₂]₂SnBr₂ (2) is reported. It has been characterized by elemental analysis, electrospray mass spectrometry, ¹H, ¹³C, ²⁹Si, and ¹¹⁹Sn NMR spectroscopy, and single-crystal X-ray diffraction analysis. In compound 2 the tin atom is [4 + 2]-coordinate and shows a strongly distorted octahedral configuration. The intramolecular O→Sn coordination results in two four-membered chelate rings with Sn-O distances between 2.853(4) and 2.946(4) A. DFT and MP2 calculations reveal these intramolecular interactions to be electrostatic. Also reported are ¹¹⁹Sn and ²⁹Si NMR studies on the interaction between dimethyltin dihalides (R₂SnX₂; R = Me, Me₂N(CH₂) ₃, X = Br, Cl) with trimethylethoxysilane (Me₃SiOEt) and hexamethyldisiloxane (Me₃SiOSiMe₃), respectively.

Full text of DOI:10.1021/om300200u

Article
pubs.acs.org/Organometallics
[Me2(i-PrO)SiCH2]2SnBr2: Evidence for Intramolecular Si−O Bond
Activation
Samer Baba Haj,† Markus Schurmann,† Ljuba Iovkova-Berends,† Sonja Herres-Pawlis,*,‡,§
̈
and Klaus Jurkschat*,†
†Lehrstuhl fur Anorganische Chemie II, Fakultat Chemie der Technischen Universitat, D-44221 Dortmund, Germany
̈
̈
̈
‡Department Chemie, Ludwig-Maximilians-Universitat Munchen, Butenandtstraße 5-13, D-81377 Munchen, Germany
̈
̈
̈
S
* Supporting Information
ABSTRACT: The synthesis of the intramolecularly coordinated diorganotin dibromide
[Me2(i-PrO)SiCH2]2SnBr2 (2) is reported. It has been characterized by elemental analysis,
1
electrospray mass spectrometry, H, 13C, 29Si, and 119Sn NMR spectroscopy, and single-
crystal X-ray diffraction analysis. In compound 2 the tin atom is [4 + 2]-coordinate and
shows a strongly distorted octahedral configuration. The intramolecular O→Sn
coordination results in two four-membered chelate rings with Sn−O distances between
2.853(4) and 2.946(4) Å. DFT and MP2 calculations reveal these intramolecular
interactions to be electrostatic. Also reported are 119Sn and 29Si NMR studies on the
interaction between dimethyltin dihalides (R2SnX2; R = Me, Me2N(CH2)3, X = Br, Cl)
with trimethylethoxysilane (Me3SiOEt) and hexamethyldisiloxane (Me3SiOSiMe3),
respectively.
rganotin compounds have been used as catalysts for the
Ocuring of polysiloxanes for many years, but the
mechanism for the catalysis is not yet understood.1 In fact,
one task the catalyst has to fulfill is the activation of Si−O
bonds by O→Sn coordination. Model compounds for which
such activation is manifested by experimental data such as
single-crystal X-ray diffraction analyses are scarce. To the best
of our knowledge the 8- and 10-membered rings A2 and B3, the
trimethylsiloxy-substituted tin−oxo clusters C4 and D,5 and the
tin(IV) complex E6 (Chart 1) are the only such examples in
which intramolecular O→Sn interactions were shown from
oxygen atoms that are bound to silicon atoms.
RESULTS AND DISCUSSION
■
The reaction of [Me2(i-PrO)SiCH2]2SnPh2 (1) with elemental
bromine gave the corresponding intramolecularly coordinated
diorganotin dibromide [Me2(i-PrO)SiCH2]2SnBr2 (2) as a
crystalline material in very good yield (eq 1).
One question to be answered is whether the interactions in A
and B are attractive and are induced by pure Lewis acid−base
interaction or are forced by the proximity of the corresponding
atoms in the ring structure.
The solubility of compound 2 in common organic solvents
such as dichloromethane, chloroform, acetonitrile, tetrahydro-
furan, and toluene is very good.
Compound 2 crystallized in the monoclinic space group P21/
c as three independent molecules 2a−c that each appear four
times in the unit cell. As result of the spatial arrangement, each
molecule is chiral. The centrosymmetric space group implies
that the corresponding enantiomers are generated by mirroring
to give the racemate. The molecular structure of 2a is shown in
Figure 1, and selected bond lengths and bond angles of 2a are
In this work we report the synthesis and molecular structure
of the title compound [Me2(i-PrO)SiCH2]2SnBr2, which shows
intramolecular O→Sn interactions involving an oxygen atom
bound to silicon and carbon atoms that is not part of a ring. We
also look, by variable-temperature 119Sn NMR spectroscopy, at
the interaction between diorganotin dihalides (R2SnX2; R =
Me, Me2N(CH2)3, X = Br, Cl) and trimethylethoxysilane
(Me3SiOEt) and hexamethylsiloxane (Me3SiOSiMe3), respec-
tively. To the best of our knowledge, such simple investigations
have not been reported yet. The experimental work is
accompanied by DFT and MP2 calculations.
Received: March 12, 2012
Published: June 25, 2012
© 2012 American Chemical Society
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Chart 1
summarized in Table 1; those of 2b,c are given in the
Supporting Information (Figure S1 and Table S1).
distances seem to not be affected by the O→Sn interactions.
They are rather similar to the corresponding distances reported
for diethyltin dibromide (Et2SnBr2; 2.505(4) Å)9 and
dicyclohexyltin dibromide (cyclo-Hex2SnBr2; 2.492(3),
2.516(2) Å),10 which both contain tetrahedrally configured
tin atoms. These findings support the interpretation of the O→
Sn interaction in 2 being electrostatic rather than covalent.
The two four-membered rings that are formed as result of
the intramolecular O→Sn interactions are nearly planar.
A
119Sn NMR spectrum of compound 2 in CDCl3 solution
showed a single resonance at δ 17 that is shifted approximately
51 ppm to low frequency with respect to the parent
tetracoordinated diorganotin dibromide (Me3SiCH2)2SnBr2 (δ
68.3, CDCl3).11 At −40 °C the spectrum of 2 showed a
resonance at δ 2. The 13C NMR spectrum displayed a single
resonance for the SiCH2Sn carbon atom at δ 15.9 with
1J(13C−117/119Sn) couplings of 312/326 Hz. These couplings
are larger than the 1J(13C−119Sn) coupling of 296 Hz in
2
(Me3SiCH2)2SnBr2. Finally, the J(1H−117/119Sn) couplings of
Figure 1. ORTEP presentation at the 30% probability level of the
molecular structure of 2a.
107.6/112.3 Hz to the SiCH2Sn protons in 2 are larger than the
2
corresponding J(1H−119Sn) coupling of 89 Hz reported for
(Me3SiCH2)2SnBr2. These results suggest that the tin atom in
compound 2 exhibits a coordination number higher than 4 and
that the strength of the O→Sn interaction increases slightly at
low temperature.
The structures of 2a−c differ only slightly. Consequently,
only that of 2a is discussed in detail.
The Sn(1) atom can be seen as being [4 + 2]-coordinated,
with the Br(1), Br(2), C(1), and C(7) atoms forming a
distorted tetrahedron with angles ranging between 132.4(2)°
(C(1)−Sn(1)−C(7)) and 100.25(3)° (Br(1)−Sn(1)−Br(2))
(mean angle 108.7°) that is doubly face-attacked by O(1) and
O(2) at O−Sn distances of 2.946(4) and 2.912(4) Å
(2.853(4)−2.942(4)Å for 2b,c). These Sn−O distances are
shorter than the sum of the van der Waals radii of oxygen and
tin (3.70 Å).7 They are also shorter than the intramolecular O−
Sn distances observed for the 8- and 10-membered rings A
(3.074(2) Å)2 and B (3.312(2) Å),3 respectively. The distances
are of the same order of magnitude as the intramolecular O−Sn
separations of 2.90(1)/2.92(1) Å found for bis(o-methox-
yphenyl)tin dibromide ((2-MeOC6H4)2SnBr2).8 The O(1) and
O(2) atoms are trans to the Br(2) and Br(1) atoms, with
Br(1)−Sn(1)−O(2) and Br(2)−Sn(1)−O(1) angles of
166.97(8) and 165.81(8)°, respectively. Interestingly, the
Br(1)−Sn(1) (2.5240(8) Å) and Br(2)−Sn(1) (2.5164(8) Å)
An electrospray mass spectrum (ESI-MS, positive mode) of
compound 2 showed a major mass cluster centered at m/z
887.1 that fits with the protonated hydrolysis product F (Chart
2 and Figure 2).
A
119Sn NMR spectrum of compound 2 in CDCl3 solution to
which had been added 1 mol equiv of tetraphenylphosphonium
bromide (Ph4PBr) showed a major resonance at δ −21
(integral 94) and a minor intense resonance at δ −48 (integral
6). Addition of another 1 mol equiv of Ph4PBr caused low-
frequency shifts of these signals to δ −38 (integral 98) and δ
−65 (integral 2). At −40 °C, a further low-frequency shift of
the major signal to δ −69 was observed. The results are
interpreted in terms of the equilibrium shown in eq 2, involving
the tetraphenylphosphonium diorganotribromidostannate 3.
The equilibrium is fast on the 119Sn NMR time scale at both
room temperature and −40 °C, but the population of
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Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) in 2a and the Optimized Structures 2′, 2″, and 2″′
a
2a
2′ (B3LYP/def2-TZVP)
2″ (B97D/def2-TZVP)
2″′ (MP2/def2-TZVP)
Sn(1)−C(1)
Sn(1)−C(7)
Sn(1)−O(1)
Sn(1)−O(2)
Sn(1)−Br(1)
Sn(1)−Br(2)
Si(1)−O(1)
Si(2)−O(2)
Br(1)−Sn(1)−O(2)
Br(2)−Sn(1)−O(1)
Br(1)−Sn(1)−O(1)
Br(1)−Sn(1)−C(1)
Br(1)−Sn(1)−C(7)
Br(1)−Sn(1)−Br(2)
O(2)−Sn(1)−O(1)
O(2)−Sn(1)−C(1)
O(2)−Sn(1)−C(7)
O(2)−Sn(1)−Br(2)
C(1)−Sn(1)−C(7)
O(1)−Si(1)−C(1)
O(2)−Si(2)−C(7)
2.103(6)
2.077(6)
2.912(4)
2.946(4)
2.5240(8)
2.5164(8)
1.639(4)
1.640(4)
166.97(8)
165.81(8)
89.94(9)
105.02(18)
105.74(16)
100.25(3)
82.62(11)
81.05(19)
62.74(17)
89.05(8)
132.4(2)
100.1(2)
101.5(2)
2.151
2.176
2.113
2.833
2.492
1.677
164.1
3.317
2.540
1.663
162.7
3.175
2.550
1.671
159.8
87.6
92.9
90.1
106.5, 108.4
105.4, 106.4
103.0, 106.0
102.8
85.9
105.5
72.6
105.2
75.0
81.3
76.6
76.2
56.7
59.4
65.4
87.6
90.8
90.2
122.7
103.9
126.1
103.2
131.2
101.2
a
For this calculation the isopropyl substituents were replaced by methyl substituents and the symmetry was constrained to C2 in order to reduce the
calculation time.
Chart 2
compound 3 increases at low temperature. ESI-MS (negative
mode) showed major mass clusters centered at m/z 620.8
(100%) and 576.9 (10−15%) that are assigned to the
diorganotribromido and diorganodibromidohydroxido stannate
complexes [{Me2(i-PrO)SiCH2}2SnBr3]− and [{Me2(i-PrO)-
SiCH2}2SnBr2(OH)·H2O]−, respectively. Most remarkably, no
mass clusters corresponding to species in which the SiO-i-Pr
group is hydrolyzed were detected. Apparently, the coordina-
tion of the bromide ion at the tin atom prohibits Si−O bond
activation. Attempts at isolating compound 3 failed.
Considering the results reported above, we investigated the
interaction of Si-bound oxygen atoms that are not part of a ring
structure and that are not linked via a spacer with the Lewis
acidic tin moiety.
Thus, a 119Sn NMR spectrum of a solution of dimethyltin
dichloride (Me2SnCl2) in CDCl3 to which had been added 1
mol equiv of trimethylethoxysilane (Me3SiOEt) showed a
single resonance at δ 132, which is shifted 10 ppm to low
frequency with respect to Me2SnCl2 (δ 142).12a Interestingly,
the 29Si NMR spectrum of the same solution displayed one
resonance at δ 17.5 (integral ∼70) belonging to Me3SiOEt and
one resonance at δ 7.6 (integral ∼30) assigned to
hexamethyldisiloxane (Me3SiOSiMe3). A rather similar result
was observed for the 29Si NMR spectrum recorded from a
solution containing equimolar amounts of Me2SnBr2 and
Me3SiOEt. Apparently, activation of the Si−O bond in
Me3SiOEt took place. At −40 °C, a further low-frequency
shift of the 119Sn resonance to δ 60 was observed. Again, similar
results were observed for a mixture consisting of equimolar
amounts of Me2SnBr2 and Me3SiOEt (T = 22 °C, δ(119Sn) 66;
Figure 2. Experimental (from ESI-MS) and simulated mass cluster for
the hydrolysis product shown in Chart 2.
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T = −40 °C, δ(119Sn) 59). In contrast, a 119Sn NMR spectrum
of a solution of dimethyltin dichloride (Me2SnCl2) in CDCl3 to
which had been added 1 mol equiv of hexamethyldisiloxane
(Me3SiOSiMe3) showed a single resonance at δ 142 at both
room temperature and −40 °C. Apparently, there is an
equilibrium according to eq 3 that is completely on the left side
for R = Me3Si at both room and low temperature but that shifts
to the right for R = Et at low temperature.
Wiberg bond indices of 0.021 between tin and oxygen atoms do
not indicate any donor interaction as well. We relate the O→Sn
contact to electrostatic interactions with regard to the NBO
charges of +1.52 for tin (consistent with tin(IV))13c and −0.88
for the oxygen atoms.
In order to perform MP2 calculations with a def2-TZVP
basis set in a reasonable calculation time, in the model
compound 2″′ the isopropyl substituents were replaced by
methyl substituents and the symmetry was constrained to C2
(Table 1). The calculated model compound 2″′ fits well with
the experimentally determined structure of 2 (Table 1).
Especially, the O→Sn interaction is predicted correctly with a
distance of 2.833 Å as compared to the Sn−O distances of
between 2.853(4) and 2.946(4) Å found in the solid state for
compound 2. The corresponding NBO calculations do not
reveal a direct donor−acceptor interaction of the lone pairs of
the oxygen atoms to the tin atom but interactions of these lone
pairs with the antibonding orbitals of the surrounding
substituents. For instance, the oxygen lone pairs bind with 7
kcal/mol into the σ*(Sn−Br) orbitals and with 2 kcal/mol into
the σ*(Sn−C) orbitals. This finding can only be interpreted
within the localized scheme of NBO calculations and has to be
regarded as a further explanation for the hypercoordination at
the tin atom. Taking into account the NBO charges as a result
of the MP2 calculation, the picture of the DFT calculations
with the dispersion functional B97D can be extended: using
MP2 the tin atoms gain a positive charge of +1.83 whereas the
oxygen atoms possess a NBO charge of −0.96. Consequently,
the contribution of the electrostatic interaction between the tin
and oxygen atoms is the most dominant part of this
interaction.13d
The results clearly indicate that the Si−O bond in a
triorganoalkoxysilane such as Me3SiOEt can be activated by a
diorganotin dihalide such as Me2SnX2 (X = Br, Cl) but that
hexaorganodisiloxane apparently cannot. In line with this
statement is the observation that stirring a solution of
dimethyltin dichloride (Me2SnCl2) and trimethylethoxysilane
(Me3SiOEt) in CH2Cl2 for 20 h at room temperature in the
presence of air moisture affords, with formation of ethanol, full
conversion of Me3SiOEt to Me3SiOSiMe3.
From ESI-MS we learned that addition of bromide anion to
compound 2 caused enhanced stability against hydrolysis of the
Si−O bond (see above). This implies that addition of bromide
anion, as Ph4PBr, to Me2SnBr2 should decrease the catalytic
activity of the latter for Si−O hydrolysis. This is indeed the
1
case, as the H, 13C, and 29Si NMR spectra in CDCl3 of a
mixture containing equimolar quantities of Me2SnBr2 and
Me3SiOEt and a droplet of water that had been stirred for 4 h
indicated approximately 60% conversion to Me3SiOSiMe3.
Intramolecular N→Sn coordination in a functionalized
diorganotin dichloride completely prohibits Si−O bond
CONCLUSION
■
In conclusion, we have shown that Lewis acidic diorganotin
dihalides interact with triorganoalkoxysilanes and activate the
Si−O bond. The interaction is electrostatic, and this supports
the interpretation of the Si−O bond as having considerable
ionic character. Our work is a modest contribution to a further
understanding of the nature of the Si−O bond and its donor
capacity, a topic that is still the subject of some controversial
debate,14 and it might also contribute to catalyst design for
polysiloxane formation. Furthermore, we have demonstrated
that MP2 calculations handle O→Sn interactions more
accurately than DFT calculations do.
1
activation. Thus, the H, 13C, and 29Si NMR spectra of a
solution in CDCl3 containing equimolar amounts of the
intramolecularly coordinated diorganotin dichloride [Me2N-
(CH2)3]2SnCl2,12b Me3SiOEt, and a droplet of water that had
been stirred for 4 h indicated no Si−O hydrolysis at all.
DFT Calculations. In order to get more insight into the
nature of the O→Sn interaction, DFT calculations using
B3LYP and B97D density functional theory and the def2-TZVP
basis set have been performed.13a,b Remarkably, the gas-phase
optimization (2′ in Table 1) gave a O−Sn distance of 3.317 Å,
which is much longer than the values found in the solid state.
Even with the dispersion-corrected functional B97D (2″ in
Table 1), the O−Sn distances were predicted too long. On the
other hand, the calculated Br−Sn bond distances of 2.540 and
2.550 Å fit well with the experimentally determined values.
Moreover, the C−Sn and O−Si distances of (B3LYP) 2.151
and 1.663 Å, respectively, are in good agreement with the
molecular structure. The C−Sn−C angle is calculated to be
122.7° and Br−Sn−Br to be 102.8°. Here, it appears that
B3LYP theory cannot handle the O→Sn interaction correctly.
Hence, the C−Sn−C angle is predicted to be smaller than in
the crystal structure. Using the B97D functional, the C−Sn−C
angle widens to 126.1°, thus coming closer to the X-ray data,
but the Br−Sn−Br angle deviates from the experimental data at
105.5°. In the DFT-calculated structures, the configuration of
the tin atom resembles more a regular tetrahedron than an
octahedron.
EXPERIMENTAL SECTION
■
General Considerations. All solvents were dried and purified
according to standard procedures and freshly distilled prior to use. If
not otherwise stated, all reactions were carried out under an
atmosphere of dry argon. Me2(i-PrO)SiCH2Cl was synthesized
according to the literature method.15 A Bruker DPX-300 spectrometer
was used to obtain 1H, 13C, 29Si, and 119Sn NMR spectra. The 1H, 13C,
29Si, and 119Sn NMR chemical shifts (δ) are given in ppm and are
referenced to Me4Si (1H, 13C, 29Si), and Me4Sn (119Sn). Elemental
analyses were performed on a LECO-CHNS-932 analyzer. The
electrospray mass spectra were recorded with a Thermoquest-Finnigan
instrument, using CH3CN as the mobile phase. The samples were
introduced as solutions in CH3CN via a syringe pump operating at 5−
10 μL min−1.
DFT Calculations. The calculations were performed with the
program suite Gaussian09.16 The geometry was calculated using the
B3LYP or the B97D13b functional as implemented in Gaussian09.
Furthermore, second-order Møller−Plesset perturbation theory
(MP2) calculations were performed using Gaussian09 as well. As
NBO calculations revealed the absence of donor−acceptor
interactions between the oxygen lone pairs and the tin atom.
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−
the basis set for geometry optimizations and NBO calculations, def2-
TZVP was used, which includes an effective core potential on Sn.13a
The stationary point has been characterized with frequency analysis
and shows the correct number of negative eigenvalues (zero for a local
minimum). An NBO analysis was performed using NBO 3.017 as
implemented in Gaussian09 Rev. B.01.16
mode, 620.8 (100, [Me2(i-PrO)SiCH2]2SnBr3 ), 812.8 (25), 792.9
(25), 578.8 (10, [Me2(i-PrO)SiCH2]2SnBr2 + OH− + H2O); m/z (%),
positive mode, 339.1 (100, Ph4P+).
Reaction of [Me2(i-PrO)SiCH2]2SnBr2 (2) with 2 mol equiv of
Ph4PBr. A mixture of 2 (80 mg, 0.148 mmol) and tetraphenylphos-
phonium bromide (124 mg, 0.296 mmol) in CDCl3 (1 mL) was
stirred at room temperature for 5 min. Then an NMR sample was
taken.
Synthesis of [Me2(i-PrO)SiCH2]2SnPh2 (1). A solution of
diphenyltin dichloride (20.6 g, 60 mmol) in tetrahydrofuran (100
mL) was added dropwise to the Grignard reagent prepared from
Me2(i-PrO)SiCH2Cl (22.48 g, 135.0 mmol) and magnesium (3.94 g,
162.0 mmol) in tetrahydrofuran (150 mL). After the mixture had been
stirred overnight at room temperature, the thf was removed in vacuo
and the residue extracted three times under inert conditions with n-
hexane. The combined extracts were evaporated in vacuo to give 30.8
g of 1 (96.0%) as a colorless liquid.
1H NMR (300.13 MHz, CDCl3): δ 0.10 (s, 12H, (CH3)2Si), 0.96
(d, 12H, 3J(1H−1H) = 5.8 Hz, (CH3)2CH), 1.16 (s, 4H, 2J(1H−117Sn)
= 110.5 Hz, 2J(1H−119Sn) = 114.9 Hz, SiCH2Sn), 3.84 (m, 2H,
3J(1H−1H) = 6.1 Hz, (CH3)2CHO), 7.39−7.75 (m, 20 H, Ar H).
13C{1H} NMR (75.47 MHz, CDCl3): δ 0.58 (1J(13C−29Si) = 59 Hz,
3J(13C−117−119Sn) = 15 Hz, (CH3)2Si), 18.6 (1J(13C−117Sn) = 358 Hz,
1J(13C−119Sn) = 374 Hz, SiCH2Sn), 25.2 ((CH3)2CH), 65.1
((CH3)2CHO), 116.7 (1J(13C−31P) = 89 Hz, Ci), 130.3
(3J(13C−31P) = 13 Hz, Cm), 133.7 (2J(13C−31P) = 10 Hz, Co), 135.2
(4J(13C−31P) = 3 Hz, Cp). 29Si{1H} NMR (59.63 MHz, CDCl3): δ
15.1 (2J(29Si−117−119Sn) = 37 Hz). 119Sn{1H} NMR (111.92 MHz,
CDCl3): δ −38 (98.3%), −65 (1.7%). Electrospray MS: m/z (%),
1H NMR (300.13 MHz, CDCl3): δ 0.05 (s, 12H, (CH3)2Si), 0.42 (s,
4H, 2J(1H−117Sn) = 74.3 Hz, 2J(1H−119Sn) = 77.2 Hz, SiCH2Sn), 1.13
3
3
(d, 12H, J(1H−1H) = 6.2 Hz, (CH3)2CH), 3.99 (m, 2H, J(1H−1H)
= 6.0 Hz, (CH3)2CHO), 7.35−7.63 (m, 10H, Ar H). 13C{1H} NMR
(75.48 MHz, CDCl3): δ −3.2 (1J(13C−117Sn) = 249 Hz, 1J(13C−119Sn)
= 260 Hz, J(13C−29Si) = 58 Hz, SiCH2Sn), 1.2 (1J(13C−29Si) = 58.1
1
−
negative mode, 620.8 (100, [Me2(i-PrO)SiCH2]2SnBr3 ), 578.8 (15,
[Me2(i-PrO)SiCH2]2SnBr2 + OH− + H2O); m/z (%), positive mode,
Hz, (CH3)2Si), 25.8 ((CH3)2CH), 64.7 ((CH3)2CHO), 127.9
(3J(13C−117/119Sn) = 49, Cp), 128.3 (Cm), 136.7 (2J(13C−117/119Sn) =
38, Co), 141.5 (1J(13C−117Sn) = 468 Hz, 1J(13C−119Sn) = 490 Hz, Ci).
339.1 (100, Ph4P+).
NMR Studies on the Interaction of Dimethyltin Dihalides,
Me2SnX2 (X = Br, Cl) with Trimethylethoxysilane (Me3SiOEt)
and Hexamethyldisiloxane (Me3SiOSiMe3), Respectively. Di-
methyltin dihalide (80 mg) and an equimolar amount of the
corresponding silicon compound were dissolved in CDCl3 (0.7 mL)
and 119Sn and 29Si NMR spectra were recorded (Table 2).
2
29Si{1H} NMR (59.63 MHz, CDCl3): δ 15.1 (s, J(29Si−117/119Sn) =
18 Hz, 1J(29Si−13C) = 58 Hz). 119Sn{1H} NMR (111.92 MHz,
CDCl3): δ −54 (93%, 2J(119Sn−29Si) = 19 Hz, 1J(119Sn−13CH2) = 261
Hz, 1J(119Sn−13Ci) = 489 Hz, 2J(119Sn−13Co) = 39 Hz, 3J(119Sn−13Cm)
= 49 Hz), −52 (7%, not assigned).
Synthesis of [Me2(i-PrO)SiCH2]2SnBr2 (2). Over a period of 4 h,
a solution of bromine (9.60 g, 60.0 mmol) in dichloromethane (50
mL) was added dropwise at 0 °C to a solution of 1 (16.06 g, 30.0
mmol) in dichloromethane (50 mL). After it was stirred at 0 °C for 2
h, the mixture was warmed to room temperature and stirred overnight
at ambient temperature. The solvent and phenyl bromide were
removed in vacuo to give a solid residue. Recrystallization of this
residue from hot hexane gave 14.2 g (87%) of 2 as colorless single
crystals with mp 69−70 °C suitable for X-ray diffraction analysis.
Anal. Calcd for C12H30Br2O2Si2Sn (541.05 g/mol): C, 26.64; H,
Table 2
δ(119Sn)
22 °C −40 °C
δ(29Si)
22 °C
R2SnX2
Me3SiOR
X = Cl
X = Cl
X = Br
X = Br
R = Me3Si
R = Et
142
132
69
142
60
7.6
17.5 (70%), 7.6 (30%)
7.6
R = Me3Si
R = Et
66
59
17.5 (70%), 7.6 (30%)
1
5.59. Found: C, 26.4; H, 5.55. H NMR (300.13 MHz, C6D6): δ 0.13
(s, 12H, 4J(1H−117−119Sn) = 5.8 Hz, (CH3)2Si), 1.03 (d, 12H,
2
3J(1H−1H) = 6.2 Hz, (CH3)2CH), 1.13 (s, 4H, J(1H−117Sn) = 107.6
Reaction of Me2SnCl2 with Me3SiOEt. A mixture of dimethyltin
dichloride (150 mg, 0.68 mmol), trimethylethoxysilane (80 mg, 0.68
mmol), and dichloromethane that was not dried (5 mL) was stirred for
20 h at room temperature. Then an NMR sample was taken.
29Si{1H} NMR (59.63 MHz, C6D6): δ 7.5 ((Me3Si)2O).
Reaction of Me2SnBr2 with Me3SiOEt. A mixture of dimethyltin
dibromide (100 mg, 0.32 mmol), trimethylethoxysilane (38 mg, 0.32
mmol), 1 drop of water, and deuterated chloroform (1 mL) was stirred
for 4 h at room temperature. Then an NMR sample was taken.
1H NMR (300.13 MHz, CDCl3): δ 0.05 (s, 9H, (CH3)3Si), 1.22 (t,
3H, CH3CH2OH), 1.37 (s, 6H, 2J(1H− 117−119Sn) = 67.0 Hz,
(CH3)2SnBr2), 2.33 (s, H2O), 3.69 (q, 2H, CH3CH2OH). 13C{1H}
NMR (75.48 MHz, CDCl3): δ 1.9 (1J(13C−29Si) = 60 Hz, (CH3)3Si),
8.30 (1J(13C−117Sn) = 442 Hz, 1J(13C−119Sn) = 463 Hz,
(CH3)2SnBr2), 18.2 (CH3CH2OH), 58.4 (CH3CH2OH). 29Si{1H}
NMR (59.63 MHz, CDCl3): δ 7.6 ((Me3Si)2O).
2
3
Hz, J(1H−119Sn) = 112.3 Hz, SiCH2Sn), 3.72 (m, 2H, J(1H−1H) =
6.1 Hz, (CH3)2CHO). 13C{1H} NMR (75.48 MHz, C6D6): δ 1.4
(1J(13C−29Si) = 58 Hz, J(13C−117/119Sn) = 17 Hz, (CH3)2Si), 15.9
3
(1J(13C−117Sn) = 312 Hz, J(13C−119Sn) = 326 Hz, SiCH2Sn), 26.2
1
((CH3)2CH), 66.5 ((CH3)2CHO). 29Si{1H} NMR (59.63 MHz,
C6D6): δ 15.0 (2J(29Si−117/119Sn) = 46 Hz, J(29Si−13C) = 59 Hz).
1
119Sn{1H} NMR (111.92 MHz, C6D6): δ 18. 119Sn{1H} NMR (111.92
MHz, CDCl3): δ 17 (room temperature), δ 2 (T = −40 °C).
Electrospray MS: m/z (%) 887.1 (100, [{[O(Me2SiCH2)2Sn]O}3 +
H+], 959.1 (10, [{[O(Me2SiCH2)2Sn]O}3 + 4H2O + H+], 590.9 (6,
[{[O(Me2SiCH2)2Sn]O}2 + H+].
Reaction of [Me2(i-PrO)SiCH2]2SnBr2 (2) with 1 mol equiv of
Ph4PBr. A mixture of 2 (80 mg, 0.148 mmol) and tetraphenylphos-
phonium bromide (62 mg, 0.148 mmol) in CDCl3 (1 mL) was stirred
at room temperature for 5 min. Then an NMR sample was taken.
1H NMR (300.13 MHz, CDCl3): δ 0.16 (s, 12H, (CH3)2Si), 1.04
(d, 12H, 3J(1H−1H) = 6.2 Hz, (CH3)2CH), 1.20 (s, 4H, 2J(1H−117Sn)
= 110.5 Hz, 2J(1H−119Sn) = 114.9 Hz, SiCH2Sn), 3.91 (m, 2H,
3J(1H−1H) = 6.0 Hz, (CH3)2CHO), 7.46−7.82 (m, 20 H, Ar H).
Reaction of Me2SnBr2 with 2 Ph4PBr and Me3SiOEt. A mixture
of dimethyltin dibromide (100 mg, 0.32 mmol), tetraphenylphospho-
nium bromide (272 mg, 0.65 mmol), trimethylethoxysilane (38 mg,
0.32 mmol), and 1 drop of water in CDCl3 (1.5 mL) was stirred for 4
h at room temperature. Then an NMR sample was taken.
13C{1H} NMR (75.47 MHz, CDCl3): δ 0.75 (1J(13C−29Si) = 60 Hz,
3J(13C−117/119Sn) = 16 Hz, (CH3)2Si), 17.8 (1J(13C−117Sn) = 344 Hz,
1J(13C−119Sn) = 360 Hz, 1J(13C−29Si) = 57 Hz, SiCH2Sn), 25.4
((CH3)2CH), 65.4 ((CH3)2CHO), 116.9 (1J(13C−31P) = 89 Hz, Ci),
130.4 (3J(13C−31P) = 13 Hz, Cm), 133.9 (2J(13C−31P) = 10 Hz, Co),
135.4 (4J(13C−31P) = 3 Hz, Cp). 29Si{1H} NMR (59.63 MHz, CDCl3):
δ 15.3 (2J(29Si−117/119Sn) = 42 Hz). 119Sn{1H} NMR (111.92 MHz,
CDCl3): δ −21 (94%), −48 (6%). Electrospray MS: m/z (%), negative
1H NMR (300.13 MHz, CDCl3): δ −0.22 (s, [(CH3)3Si]2O), −0.19
(s, (CH3)3SiOEt), 0.87 (t, 3H, CH3CH2O), 1.35 (s, 6H,
2J(1H−117−119Sn) = 84.9 Hz, (CH3)2Sn), 2.68 (s (broad), H2O),
3.35 (q, 2H, CH3CH2O), 7.34−7.70 (m, 40H, Ar H). 13C{1H} NMR
(75.48 MHz, CDCl3): δ 0.7 ((CH3)3SiOEt), 1.2 ((CH3)3Si)2O), 17.5
(CH3CH2O), 21.8 ((CH3)2Sn), 56.6 (CH3CH2O), 116.5 (d,
1J(13C−31P) = 89 Hz, Ci), 130.0 (d, 3J(13C−31P) = 13 Hz, Cm),
4720
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Organometallics
Article
2
4
133.5 (d, J(13C−31P) = 11 Hz, Co), 135.0 (d, J(13C−31P) = 3 Hz,
Cp). 29Si{1H} NMR (59.63 MHz, CDCl3): δ 7.4 (60%, (Me3Si)2O),
15.0 (40%, Me3SiOEt).
S.H.-P. thanks the Bundesministerium fur Bildung und
̈
Forschung (MoSGrid, 01IG09006) for financial support.
Calculation time is gratefully acknowledged from the
ARMINIUS Cluster at the PC2 Paderborn.
Reaction of [Me2N(CH2)3]2SnCl2 with Me3SiOEt. A mixture
consisting of [Me2N(CH2)3]2SnCl2 (150 mg, 0.41 mmol), trimethy-
lethoxysilane (49 mg, 0.41 mmol), 1 drop of water, and CDCl3 (1.5
mL) was stirred for 4 h at room temperature. Then an NMR sample
was taken.
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CCDC-870583 contains supplementary crystallographic data for
this paper. These data can be obtained free of charge at www.ccdc.cam.
ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, U.K., fax
(internat.) +44-1223/336-033, e-mail deposit@ccdc.cam.ac.uk).
ASSOCIATED CONTENT
* Supporting Information
■
S
Figures, tables, and a CIF file giving NMR spectra and crystal
structure data. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Author Contributions
§DFT and MP2 calculations.
(17) Weinhold, F.; Landis, C. Valency and Bonding-A Natural Bond
Orbital Donor-Acceptor Perspective; Cambridge University Press: New
York, 2005.
Notes
The authors declare no competing financial interest.
(18) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(19) Sheldrick, G. M. SHELXL97; University of Gottingen,
̈
ACKNOWLEDGMENTS
■
Gottingen, Germany, 1997.
̈
We thank the anonymous reviewers for valuable comments.
S.B.H. is gratefully to Damaskus University for a scholarship.
(20) International Tables for Crystallography; Kluwer Academic:
Dordrecht, The Netherlands, 1992; Vol. C.
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(21) Sheldrick, G. M. SHELXTL Release 5.1 Software Reference
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