Synthesis of metallasiloxanes of group 13-15 and their application in catalysis

Article abstract of DOI:10.1039/c3dt51408k

Herein we report on the synthesis, characterization and catalytic application of metallasiloxanes of group 13-15. Reactions of R(Me)Si(OH) ₂ (R = N(SiMe₃)-2,6-iPr₂C₆H ₃) (A) with Bi(NEt₂)₃, Sb(NEt₂) ₃, Ge[N(SiMe₃)₂]₂ and AlMe ₃ afforded [R(Me)SiO₂BiNEt₂]₂ (1), [R(Me)SiO₂SbOSi(OH)(Me)R]₂ (2), [R(Me)SiO ₂]₃(GeH)₂ (3), and [R(Me)SiO ₂AlMe(THF)]₂ (4), respectively. Reactions of RSi(OH) ₃ (B) with Bi(NEt₂)₃ and AlMe₃ produced complexes (RSiO₃Bi)₄ (5) and (RSiO ₃)₂[AlMe(THF)]₃ (6). Compounds 1-6 have been characterized by IR and NMR spectroscopy, single crystal X-ray structure and elemental analysis. Each of the compounds 1, 2 and 4 features an eight-membered ring of composition Si₂O₄Bi₂, Si ₂O₄Sb₂ and Si₂O₄Al ₂, while 3 and 6 exhibit a bicyclic structure with the respective skeletons of Si₃O₆Ge₂ and Si₂O ₆Al₃. Compound 5 has a cubic core of Si₄O ₁₂Bi₄. Compounds 1-6 exhibit very good catalytic activity in the addition reaction of trimethylsilyl cyanide (TMSCN) with benzaldehyde. Compound 5 was found to be the best catalyst and its activity was probed in the reactions of TMSCN with a number of aldehydes and ketones.

Full text of DOI:10.1039/c3dt51408k

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Synthesis of metallasiloxanes of group 13–15
and their application in catalysis†
Cite this: DOI: 10.1039/c3dt51408k
Yan Li,a Jinjin Wang,a Yile Wu,a Hongping Zhu,*a Prinson P. Samuelb
and Herbert W. Roesky*b
Herein we report on the synthesis, characterization and catalytic application of metallasiloxanes of group
13–15. Reactions of R(Me)Si(OH)2 (R = N(SiMe3)-2,6-iPr2C6H3) (A) with Bi(NEt2)3, Sb(NEt2)3, Ge[N-
(SiMe3)2]2 and AlMe3 afforded [R(Me)SiO2BiNEt2]2 (1), [R(Me)SiO2SbOSi(OH)(Me)R]2 (2), [R(Me)-
SiO2]3(GeH)2 (3), and [R(Me)SiO2AlMe(THF)]2 (4), respectively. Reactions of RSi(OH)3 (B) with Bi(NEt2)3
and AlMe3 produced complexes (RSiO3Bi)4 (5) and (RSiO3)2[AlMe(THF)]3 (6). Compounds 1–6 have been
characterized by IR and NMR spectroscopy, single crystal X-ray structure and elemental analysis. Each of
the compounds 1, 2 and 4 features an eight-membered ring of composition Si2O4Bi2, Si2O4Sb2 and
Si2O4Al2, while 3 and 6 exhibit a bicyclic structure with the respective skeletons of Si3O6Ge2 and Si2O6Al3.
Compound 5 has a cubic core of Si4O12Bi4. Compounds 1–6 exhibit very good catalytic activity in the
addition reaction of trimethylsilyl cyanide (TMSCN) with benzaldehyde. Compound 5 was found to be
the best catalyst and its activity was probed in the reactions of TMSCN with a number of aldehydes and
ketones.
Received 30th May 2013,
Accepted 4th July 2013
DOI: 10.1039/c3dt51408k
www.rsc.org/dalton
shown the use of silanetriol RSi(OH)3 (R = N(SiMe3)-2,6-
iPr2C6H3)11 as a precursor for the preparation of copper(I)
Introduction
In recent years, metallasiloxanes derived from organic silanols siloxane, [RSi(OCu)3]8, which features a 56-membered core
have attracted considerable interest because they act as struc- that resembles a metal-anchored silica-supported material.
tural models for the naturally occurring metallasilicates, syn- This compound exhibits good to excellent activity for catalyz-
thetic metal-containing zeolites,1 and for the heterogeneous ing the homogeneous Ullmann–Goldberg-type C–N cross-coup-
silica-supported transition metal catalysts.2 Interestingly, some ling reaction of aryl or 2-thienyl bromides with heterocyclic
of the transition metal-containing siloxanes have been proved nitrogen containing nucleophiles.12 However, so far only a few
to act as catalysts for reactions such as alkene polymerization,3 RSi(OH)3-derived main group metal compounds have been
metathesis,4 epoxidation,5 hydroformylation,6 and specified reported.14 The use of R(Me)Si(OH)2 for the synthesis of
Diels–Alder reactions7 with both homogeneous and hetero- related siloxanes is much less reported although other organo-
geneous applicability. So far, a considerable number of such silanediol-derived complexes have been documented.15 Herein
13
siloxane complexes including main group elements and tran- we report on the reactions of R(Me)Si(OH)2 and RSi(OH)3 to
sition metals have been synthesized and structurally produce main group metallasiloxanes. A series of bismuth,
characterized.8–10 However, investigations of the catalytic pro- antimony, germanium and aluminum siloxanes (1–6) exhibit-
perties of these complexes are still scarce. Recently, we have ing the ring and cage structures have been prepared and
characterized. Furthermore, compounds 1–6 show good cataly-
tic activity for the addition reaction of trimethylsilyl cyanide to
aldehydes and ketones.
aState Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering
Laboratory for Green Chemical Productions of Alcohols–Ethers–Esters, College of
Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian, China.
E-mail: hpzhu@xmu.edu.cn; Tel: +86 05922181912
bInstitut für Anorganische Chemie, Georg-August-Universität, Tammannstraβe 4,
Results and discussion
Synthesis and spectroscopic characterization
37077-Göttingen, Germany. E-mail: hroesky@gwdg.de; Tel: +49 5513933001
†Electronic supplementary information (ESI) available: Tables of crystal data
and structure refinement of compounds 1–6. Experimental procedures of the
catalysis and the NMR (1H, 13C, and 29Si) data of the catalytic reaction products.
Additional experimental details and discussions. CCDC 941559–941564. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3dt51408k
The reaction of R(Me)Si(OH)2 (A) with Bi(NEt2)3 in a molar
ratio of 2 : 2 proceeded smoothly in toluene in a temperature
range of −20 to 25 °C to afford [R(Me)SiO2BiNEt2]2 (1). Under
similar conditions, A reacted with Sb(NEt2)3 in a molar ratio of
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terminal RSiMe(OH)O group (for R(Me)SiO2: δ 0.08 (SiMe3),
−0.10 (SiMeO2), 4.84 (SiMe3), −40.51 (SiMeO2); for RSiMe(OH)
O: δ 0.09 (SiMe3), 0.23 (SiMe(OH)O), 7.02 (SiMe3), −33.33 ppm
(SiMe(OH)O)).16 The SiOH proton resonance (RSiMe(OH)O) is
1
not observed in the H NMR spectrum of 2. However, 2 exhi-
bits in the IR spectrum an absorption band found at ν
3647 cm−1 that clearly indicates the SiOH stretching
frequency.
The reaction of A with Ge[N(SiMe3)2]2 in toluene (−20 to
25 °C) gave
a germanium(IV) hydride siloxane [R(Me)-
SiO2]3(GeH)2 (3) in 78% yield, whereas the corresponding reac-
tion with AlMe3 in THF produced [R(Me)SiO2AlMe(THF)]2 (4)
(73% yield) (Scheme 1). The production of 3 involves the oxi-
dation of Ge(II) to Ge(IV) and simultaneously the reduction of a
proton of A to hydride. Similar compound (RSiO3GeH)4 has
been reported in 2005 from the reaction of RSi(OH)3 with Ge[N-
(SiMe3)2]2.17 Furthermore, the oxidative addition of an alcohol
to an alkylgermanium(II) compound is also known.18 The for-
mation of 4 resembles that of 1. However, CH4 is eliminated
instead of HNEt2. The coordination of the THF at the Al center
stabilizes 4 and the approach of a THF-free 4 in toluene or
n-hexane was not successful. Moreover, heating 4 under
vacuum to remove the coordinated THF resulted in the
decomposition of 4.
Scheme 1 Synthesis of compounds 1–4.
Compounds 3 and 4 are stable under an inert atmosphere
1
(N2 and Ar) but are moisture-sensitive. The H NMR spectrum
4 : 2 in n-hexane to afford [R(Me)SiO2SbOSi(OH)(Me)R]2 (2) of 3 exhibits a singlet resonance (δ 6.24 ppm) for the GeH
(Scheme 1). From these results, it can be shown that com- moiety and a characteristic stretching frequency (ν 2135 cm−1
)
pound 1 is formed under the elimination of four molecules of in the IR spectrum. These spectroscopic data are comparable
HNEt2 leaving one NEt2 group intact at each of the Bi atoms. to those found in (RSiO3GeH)4 (δ 5.83 ppm, νGeH 2211 and
Compound 2 may be generated by an intermediate [R(Me)- 2184 cm−1),17 N(CH2CH2O)3GeH (δ 5.77 ppm)19a,b and Ar2Ge
SiO2SbNEt2]2 in a similar way to that of 1. Our attempts to (H)R (Ar = C6H3-2,6-(C6H2-2,4,6-Me3)2, R = CN, F, N3, (OH2)
isolate [R(Me)SiO2BiOSi(OH)(Me)R]2 or [R(Me)SiO2SbNEt2]2 (SO3CF3): δ 5.42–6.79 ppm, νGeH 2117–2146 cm−1).19c In the 1H
were not successful, but the stoichiometries given in Scheme 1 NMR spectrum of 4, two multiplets (δ 3.58 and 1.76 ppm) are
are important to achieve high yields of 1 and 2.
assigned for the coordinated THF molecules. The AlMe methyl
Compounds 1 and 2 were isolated as light-yellow crystals protons resonate at a higher field (δ −1.06 ppm) when com-
with the respective yields of 81% and 65%, which are moist- pared with those of SiMe3 (δ −0.02 ppm) and SiMeO2 (δ
ure-sensitive but stable under inert atmosphere (Ar or N2). The 0.06 ppm). The 29Si NMR spectrum of 4 displays two reson-
1H NMR spectrum of 1 shows two quartet resonances (δ 4.21 ances (δ 0.75 and −52.26 ppm) for the SiMe3 and SiMeO2
and 4.07 ppm) for the methylene protons of the BiNEt2 group groups, respectively.
and one triplet resonance (δ 1.17 ppm) for the methyl protons.
For the synthesis of the metallasiloxanes with three-dimen-
This noticeable difference in the chemical shifts between the sional structures aminosiloxanetriols are used as building
methylene and methyl protons is mainly attributed to the pres- blocks.8a,b The aminosiloxanetriol RSi(OH)3 (B) was utilized
17
ence of a lone pair of electrons at the Bi center, which greatly for the preparation of germanium (RSiO3GeH)4 and anti-
20
affects the adjacent methylene proton resonances rather than mony (RSiO3Sb)4 complexes. A bismuth compound of com-
1
the remote methyl ones. H NMR measurement of 1 in C6D6 position (RSiO3)8Bi12(μ3-O)4Cl4(THF)8 was obtained by
between 20 and 80 °C clearly shows the coalescence of methyl- refluxing RSi(OH)3 with Bi(NMe2)3/Bi(NMe2)2Cl.20 Herein, we
ene proton resonances. This implies a faster rotation of the report on the reaction of RSi(OH)3 with Bi(NEt2)3 in toluene to
two ethyl groups about the Bi–N bond at elevated tempera- yield compound (RSiO3Bi)4 (5) under elimination of HNEt2
tures. The two singlet resonances found at higher field (δ 0.29 (Scheme 2). Although a series of alumosiloxane derivatives
and 0.42 ppm) are assigned for the SiMe3 and O2SiMe groups, have been reported, we tried the reaction of B with AlMe3 in a
respectively. The 29Si NMR spectrum shows the silicon reson- molar ratio of 2 : 3. As
a result, a bicyclic compound
ances for these two groups at δ 1.97 and −42.70 ppm. The (RSiO3)2[AlMe(THF)]3 was obtained (6, Scheme 2). 6 exhibits a
latter value is typical of the resonance for oxygen bound silyl unique structure among the known ring- [R(HO)SiO2AltBu
1
groups.9 Compound 2 exhibits two distinguishable sets of H (THF)]2,14a cube- (R′SiO3AlS) (R′ = N(SiMe3)-2,4,6-Me3C6H2,
NMR resonances for the bridged R(Me)SiO2 moiety and the N(SiMe3)-2,6-Me2C6H3, N(SiMe3)-2,6-Et2C6H3, N(SiMe3)-2,6-iPr2C6H3,
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Scheme 2 Synthesis of compounds 5 and 6.
CCo3(CO);9
S
=
1,4-dioxane, THF, N(CH2CH2)3N),6,11,16,21
and drum-like (R′′SiO3)2AltBu(AltBu2) (R′′ = N(SiMe3)-2,4,6-Me3C6H2,
N(SiMe3)-2,6-Me2C6H3, N(SiMe3)-2,6-iPr2C6H3)14a,16a compounds
so far isolated.
Fig. 1 Thermal ellipsoid (50%) drawing of 1. The H atoms are omitted for
clarity. Bi⋯arenecentroid: 3.321 Å.
Compounds 5 and 6 were isolated as colorless crystalline
solids in 90% and 89% yield, respectively. Compound 6 is
moisture-sensitive, while 5 is more stable in open air without
decomposition within one day. The 1H NMR spectrum of 5
exhibits one septet and two doublets typical of the isopropyl
methine and methyl protons at R (δ 3.90 (CHMe2), 1.36 and
1.28 ppm (CHMe2)) as well as one singlet (δ 0.35 ppm (SiMe3)).
The 29Si NMR spectrum shows two resonances (δ 2.42 and
−79.12 ppm) corresponding to the SiMe3 and SiO3 groups,
respectively. In compound 6, the resonance of methyl protons
of AlMe is observed at higher field (δ −1.03 ppm) when com-
pared with that of the SiMe3 (δ −0.09 ppm). The 29Si NMR
spectrum of
6 displays two resonances (δ 0.99 and
−79.96 ppm) for the SiMe3 and SiO3 groups.
Fig. 2 Thermal ellipsoid (30%) drawing of 3. The GeH hydrogen atom is not
able to be located by difference Fourier synthesis and other hydrogen atoms are
omitted for clarity.
Single crystal X-ray structures of 1–6
X-ray quality single-crystals of 1 and 4–6 were obtained by crys-
tallization at low temperature (−20 °C), where 5 co-crystallized
with one molecule of toluene and half a molecule of n-hexane
and 6 with one molecule of THF. The crystals of 2 and 3 were
obtained by slow evaporation under an inert atmosphere (Ar).
The structural analyses unambiguously confirm that com-
pounds 1, 2 and 4 each feature a cyclic structure with a metal-
anchored eight-membered ring core of Si2O4M2 (M = Bi, 1; Sb,
2; Al, 4). Compounds 3 and 6 adopt a bicyclic structure with
the respective skeleton cores of Si3O6Ge2 and Si2O6Al3,
whereas compound 5 has a cage structure with a cubic core of
Si4O12Bi4. The crystal structures of 1, 3, 5 and 6 are shown in
Fig. 1–4, respectively. The single crystal structure plots of 2
and 4 are added to the ESI.†
The cores of 1–6 show the silicon atom in a tetrahedral geo-
metry, while in 1, 2 and 5 the Bi and Sb atoms are three-coordi-
nate with the sum of the peripheral angles of 275.8(4)° in 1,
282.01(9)° in 2 and of 278.8(3)–305.3(3)° in 5. These angles are
close to 270°, which suggests that each Bi or Sb center adopts
a trigonal-pyramidal geometry with a lone pair of electrons in
the apex.22 It is interesting to note that the distances between
the metal center and the adjacent aryl ring from the R group
or the co-crystallized toluene molecule (M⋯arenecentroid) are
found of 3.321 Å (for aryl group at R) in 1, 3.312 Å (for aryl
group at R) in 2, and 3.225–3.273 Å (for aryl group at R and
toluene) in 5. These distances are comparable to those found
Fig. 3 Thermal ellipsoid (30%) drawing of 5. The iPr groups of the N-aryl sub-
stituents and H atoms are omitted for clarity. Bi⋯arenecentroid: 3.225, 3.252, and
3.273 Å (for aryl at R); 3.227 Å (for toluene).
in [(Ph2tBuSiO)3Bi]2 (3.340 Å)23a and [(2-Cl-C6H4CH2)3Bi]2
(3.659 Å),23b suggesting the presence of the bismuth(III) and
antimony(III)⋯arene π-interactions that have been extensively
documented in the literature.24 In the structures of 4 and 6,
each Al center is four-coordinate in a distorted tetrahedral geo-
metry. These structures fit well to the Loewenstein rule, one of
the fundamental principles applicable to the structures of
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Table 1 Addition reaction of TMSCN to benzaldehyde catalyzed by 5 with
different loadingsa
5b (mol%)
Reaction time
Yieldd (%)
1.00
0.75
0.40
0.10
0.05
0.01c
0.003c
0
5 min
5 min
5 min
5 min
15 min
24 h
≥99
≥99
≥99
≥99
≥99
10
Fig. 4 Thermal ellipsoid (50%) drawing of 6. The iPr groups of the N-aryl sub-
stituents and H atoms are omitted for clarity.
24–48 h
24–48 h
Trace
0
aluminosilicate solids, which states that the Si and Al geometric
tetrahedrons must be linked by one oxygen bridge.25,26 In the
structure of 3, the H atom at the Ge center could not be located
from difference Fourier synthesis. Nevertheless, the presence of
the GeH functionality has been unambiguously evidenced by IR
and NMR spectroscopy. In addition, the geometric features with
respect to the Ge–O bond lengths (1.717(6)–1.738(7) Å) and the
sum of the O–Ge–O angles (328.5(3)–331.5(4)°) are comparable
to those found in (RSiO3GeH)4 (Ge-O, 1.737(1)–1.742(1) Å; the
sum of the O–Ge–O angles ranges from 326.66(7) to 326.85(7)°).17
These data indicate that the Ge center in 3 exhibits actually a
tetrahedral geometry containing an H atom.
It is worth to mention that the eight-membered Si2O4M2
ring can be considered as a basic building block for constitut-
ing the cyclic cores of 1, 2, and 4, as well as the bicyclic cores
of 3 and 6, and the cubic core of 5. A lateral projecting view of
the ring system is given in the ESI.†
a Benzaldehyde, 2 mmol; TMSCN, 3 mmol; at ambient temperature.
b Based on benzaldehyde. c The amount was exacted by using diluted
toluene solution of 5. d Yield was obtained according to thin-layer
chromatographic (TLC) and 1H NMR spectral analysis.
the reaction is completed in 15 min. When 5 is reduced to
0.01 mol%, a significantly lower yield of the product (10%) is
given in 24 h. This reaction does not proceed with a loading of
0.003 mol% or less even by running for two days. Nonetheless,
when compared with other compounds mentioned above, 5
can be regarded as a superior catalyst. We continued to test its
catalytic property for the reactions of TMSCN with other alde-
hydes and ketones and such results are shown in Table 2.
It is generally considered that using a Lewis acidic catalyst
the reaction usually undergoes a preliminary coordinative
interaction between the catalytic metal center and the carbonyl
oxygen atom of the substrate followed by a nucleophilic attack
of the cyanide to the carbonyl carbon atom.28,32 The results in
Table 2 indicate that the reactions involving the ortho-substi-
tuted aryl aldehydes and double-substituted ketones show rela-
tively lower activities, meanwhile 2-thiophenecarboxaldehyde
appears to have a better reactivity than 2-furaldehyde. Accord-
ingly, it is reasoned that the steric and/or electronic properties
of the substitutes at the carbonyl functionality of the aldehyde
and ketone substrates may have a great influence on the inter-
action between the metal center and the carbonyl oxygen atom
and thereby on the catalytic activity (see Scheme S1 in ESI†).
Catalytic studies
The addition reactions of trimethylsilyl cyanide (TMSCN) to
aldehyde or ketone to form cyanohydrin trimethylsilyl ethers
(O-trimethylsilyl cyanohydrins) were first reported in 1973 by
Evans and Lidy.27 This type of reaction can be catalyzed by a
variety of Lewis acids and bases as well as nucleophiles. Group
13–15 metal halides and alkoxides have been used as the Lewis
acid catalysts for this reaction.28 Silanols are electron-withdraw-
ing ligands29 and in combination with group 13–15 metals an
increase in acidity is discovered.30,31 However, there is no report
on using metallasiloxanes as catalysts for the addition reaction
of TMSCN to aldehydes or ketones. Herein, we report on metalla-
siloxanes 1–6 as effective catalysts for this reaction.
Conclusion
The reaction of TMSCN with benzaldehyde was carried out In summary, we have prepared and structurally characterized a
in the presence of 1–6 (1 mol%, based on benzaldehyde) at series of 13–15 group metallasiloxanes 1–6 derived from amino-
ambient temperature under solvent-free condition. The com- siloxanediol and aminosiloxanetriol. Compounds 1, 2, and
plete results of compounds 1–6 as catalysts are given in the 4 are forming a cyclic structure with an eight-membered ring
ESI.† Herein, we selected the catalytic property of compound 5 core of Si2O4Bi2, Si2O4Sb2, and Si2O4Al2, respectively. Com-
for various aldehydes and ketones.
pound 3 and 6 exhibit a bicyclic structure with the skeletons of
The reactions of TMSCN with benzaldehyde catalyzed by 5 Si3O6Ge2 and of Si2O6Al3, whereas in 5 a cubic cage structure
with reduced loadings were carried out (Table 1). The results of Si4O12Bi4 is found. The Si2O4M2 (M = Bi, Sb, Ge, Al) rings in
indicate that the reaction can also be completed to give an 1–6 adopt different conformations. Metallasiloxanes 1–6 have
almost quantitative yield of product within 5 min even with been explored for the first time to show excellent activities for
0.10 mol% loading. When the loading is reduced to 0.05 mol%, the addition reaction of TMSCN to benzaldehyde, exhibiting
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Table 2 Addition reactions of TMSCN to aldehyde or ketone catalyzed by 5a
the advantages by the good solubility in the reaction system as
well as by the significantly low loadings over more conven-
tional catalytic systems (see ESI†). This is due to the increased
Lewis acidity of these compounds containing a highly elec-
tron-withdrawing environment at the metal centers.29–31 The
bismuth(III) siloxane 5 is still effective in this reaction with a
loading as low as 0.05 mol%. Moreover, this compound was
further tested to catalyze the reaction of TMSCN with a variety
of other aldehydes and ketones. The detailed investigations on
the use of the other metallasiloxanes for catalyzing this kind
of reactions as well as for other organic transformations will
be published in due course.
Aldehyde or
ketone
Reaction
time (min)
Yieldb
(%)
Product
5
5
5
≥99 (96)
92 (89)
≥99 (96)
5
5
≥88 (80)
≥99 (96)
Experimental section
Materials and methods
All syntheses and manipulations were carried out using a
Schlenk line or in an argon-filled MBraun glovebox (typically
oxygen and moisture were controlled at less than 1.2 ppm).
Toluene, n-hexane, and tetrahydrofuran were predried over
sodium wires and then refluxed with sodium/potassium ben-
zophenone under N2 prior to use. Benzene-d6 was degassed
and dried over sodium/potassium alloy, and CDCl3 and
5
5
≥99 (96)
≥99 (95)
CD2Cl2 were degassed and dried over CaH2. H, 13C, and 29Si
1
5
5
5
5
≥99 (95)
≥99 (96)
≥99 (95)
≥99 (94)
NMR spectra were recorded on Bruker Avance II 400 and
500 MHz spectrometers. Melting points of compounds were
measured in sealed glass tubes using Büchi-540 instrument.
Elemental analysis was performed on a Thermo Quest Italia
SPA EA 1110 instrument. Commercial reagents were purchased
from Aldrich, Acros, or Alfa-Aesar Chemical Companies and
used as received. R(Me)Si(OH)2,13 RSi(OH)3 (R = N(SiMe3)-
11
35
2,6-iPr2C6H3), Bi(NEt2)3,33 Sb(NEt2)3,34 and Ge[N(SiMe3)2]2
were prepared according to published procedures.
5
82 (77)
20 (13)
[R(Me)SiO2BiNEt2]2 (1)
A solution of Bi(NEt2)3 (0.14 g, 0.33 mmol) in toluene (10 mL)
was added to a solution of R(Me)Si(OH)2 (0.11 g, 0.33 mmol)
in toluene (20 mL) at −20 °C. The mixture was warmed to
room temperature and stirred for 12 h. After workup, all vola-
tiles were removed under reduced pressure and the residue
was extracted with n-hexane (10 mL). The extract was stored at
−20 °C for two days to obtain light-yellow crystals of 1. Yield:
120c
88d
≥99 (96)
0.16 g (80%). Mp 209 °C (dec). 1H NMR (C6D6, 400 MHz,
298 K, ppm): δ 7.06–6.90 (m, 6 H, C6H3), 4.21 (q, 4 H, JHH
120d
74 (68)
3
=
3
6.8 Hz), 4.07 (q, 4 H, JHH = 6.8 Hz) (NCH2CH3), 3.96 (sept,
2 H, 3JHH = 6.8 Hz), 3.72 (sept, 2 H, 3JHH = 6.8 Hz) (CHMe2), 1.46
120d
85 (80)
3
3
(d, 6 H, JHH = 6.8 Hz), 1.41 (d, 6 H, JHH = 6.8 Hz), 1.33 (d,
6 H, 3JHH = 6.8 Hz), 1.22 (d, 6 H, 3JHH = 6.8 Hz) (CHMe2), 1.17 (t,
3
12 H, JHH = 6.8 Hz, NCH2CH3), 0.42 (s, 6 H, SiMeO2), 0.29 (s,
18 H, SiMe3). 13C NMR (C6D6, 100 MHz, 298 K, ppm): δ 147.6,
144.6, 139.8, 125.5, 124.2, 123.3 (C6H3), 28.5, 28.0, 25.4, 24.8,
23.8 (CHMe2 and CH2CH3), 2.0 (SiMeO2), 0.8 (SiMe3). 29Si NMR
(C6D6, 99 MHz, 298 K, ppm): δ 1.97 (SiMe3), −42.70 (SiMeO2).
Anal. calcd for C40H78Bi2N4O4Si4 (Mr = 1209.37): C, 39.73; H,
6.50; N, 4.63. Found: C, 39.84; H, 6.62; N, 4.52.
a Aldehyde or ketone, 2 mmol; TMSCN, 3 mmol; 5, 0.002 mmol; at
ambient temperature. b Yield was obtained according to thin-layer
chromatographic (TLC) and 1H NMR spectral analysis. The value in
the bracket is the isolated yield. c This reaction must be run for a long
time to give the result. d The reaction of TMSCN with the ketone
required a long time to give optimal results.
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[R(Me)SiO2SbOSi(OH)(Me)R]2 (2)
0.16 g (73%). Mp: 257 °C (dec). 1H NMR (CDCl3, 500 MHz,
298 K, ppm): δ 7.00–6.90 (m, 6 H, C6H3), 3.77 (sept, 2 H, 3JHH
=
A solution of Sb(NEt2)3 (0.10 g, 0.33 mmol) in n-hexane
(10 mL) was added to a solution of R(Me)Si(OH)2 (0.21 g,
0.66 mmol) in n-hexane (20 mL) at −20 °C. The mixture was
warmed to room temperature and stirred for 12 h. After
workup, a small amount of precipitate was filtered off, and the
filtrate was kept under Ar atmosphere at ambient temperature,
allowing for slow evaporation. Light-yellow crystals of 2 were
3
7.0 Hz), 3.62 (sept, 2 H, JHH = 7.0 Hz) (CHMe2), 3.58 (m, 8 H,
OCH2CH2), 1.76 (m, 8 H, OCH2CH2), 1.19 (d, 3JHH = 7.0 Hz), 1.18
(d, 3JHH = 7.0 Hz), 1.14 (d, 3JHH = 7.0 Hz) (24 H, CHMe2), 0.06 (s,
6 H, SiMeO2), −0.02 (s, 18 H, SiMe3), −1.06 (s, 6 H, AlMe). 13C
NMR (CDCl3, 125 MHz, 298 K, ppm): δ 148.4, 147.6, 144.9, 122.6
(C6H3), 69.9 (OCH2CH2), 25.1 (OCH2CH2), 31.6, 27.5, 26.4, 25.3,
23.8, 22.6 (CHMe2), 2.0 (SiMe3), 1.0 (SiMeO2), −14.4 (AlMe). 29Si
NMR (CDCl3, 99 MHz, 298 K, ppm): δ 0.75 (SiMe3), −52.26
(SiMeO2). Anal. calcd for C42H80Al2N2O6Si4 (Mr = 875.40): C,
57.63; H, 9.21; N, 3.20. Found: C, 57.52; H, 9.12; N, 3.13.
1
formed after 5 days. Yield: 0.12 g (62%). Mp: 219 °C (dec). H
NMR (CD2Cl2, 400 MHz, 298 K, ppm): δ 7.09–7.03 (m, 12 H,
C6H3), 3.64–3.47 (m, 8 H, CHMe2), 1.27–1.13 (m, 48 H,
CHMe2), 0.23 (s, 3 H, SiMe(OH)O), 0.09 (s, 9 H, SiMe3 of R in
RSiMe(OH)O), 0.08 (s, 9 H, SiMe3 of R in RSiMeO2), −0.03 (s,
3 H, SiMeO2). The SiOH proton resonance was not observed.
13C NMR (CD2Cl2, 100 MHz, 298 K, ppm): δ 147.5, 147.4,
147.3, 141.1, 140.9, 124.7, 124.6, 124.1, 124.0, 123.9, 123.8,
123.9 (C6H3), 27.6, 27.4, 27.3, 26.1, 25.4, 25.2, 25.3, 24.7, 24.6,
24.5, 24.3 (CHMe2), 2.1 (SiMe3 of R in RSiMe(OH)O), 2.0 (SiMe3
of R in RSiMeO2), 0.74 (SiMe(OH)O), 0.16 (SiMeO2). 29Si NMR
(CD2Cl2, 99 MHz, 298 K, ppm): δ 7.02 (SiMe3 of R in RSiMe
(OH)O), 4.84 (SiMe3 of R in RSiMeO2), −33.33 (SiMe(OH)O),
−40.51 (SiMeO2). IR (Nujol mull, cm−1): ν 3647 (SiOH). Anal.
calcd for C64H118N4O8Sb2Si8 (Mr = 1539.85): C, 49.92; H, 7.72;
N, 3.64. Found: C, 50.12; H, 7.83; N, 3.49.
(RSiO3Bi)4 (5)
A solution of Bi(NEt2)3 (0.21 g, 0.50 mmol) in toluene (10 mL)
was added to a solution of RSi(OH)3 (0.16 g, 0.50 mmol) in
toluene (10 mL) at −20 °C. The mixture was warmed to room
temperature and stirred for 12 h. After workup, all volatiles
were removed under reduced pressure and the residue was
extracted with n-hexane (15 mL). The n-hexane filtrate was
evaporated to dryness to give 5 as colorless crystalline solid.
Yield: 0.24 g (90%). Mp: 310 °C (dec). 1H NMR (C6D6,
500 MHz, 298 K, ppm): δ 7.13–6.84 (m, 12 H, C6H3), 3.90 (sept,
3
3
8 H, JHH = 7.0 Hz, CHMe2), 1.36 (d, 24 H, JHH = 7.0 Hz), 1.28
(d, 24 H, JHH = 7.0 Hz) (CHMe2), 0.35 (s, 36 H, SiMe3). 13C
3
NMR (C6D6, 125 MHz, 298 K, ppm): δ 148.9, 145.3, 137.9,
129.3, 128.6, 125.7, 124.7, 124.3 (C6H3), 27.6, 26.8, 25.5
(CHMe2), 2.7 (SiMe3). 29Si NMR (C6D6, 99 MHz, 298 K, ppm): δ
2.42 (SiMe3), −79.12 (SiO3). Anal. calcd for C60H104Bi4N4O12Si8
(Mr = 2134.09): C, 33.77; H, 4.91; N, 2.63. Found: C, 33.54; H,
4.86; N, 2.52. X-ray quality single crystals of 5·toluene·0.5n-
hexane were obtained from recrystallization in a solvent
mixture (toluene–n-hexane = 1 mL/4 mL) at −20 °C.
[R(Me)SiO2]3(GeH)2 (3)
A solution of Ge[N(SiMe3)2]2 (0.12 g, 0.30 mmol) in toluene
(10 mL) was added to a solution of R(Me)Si(OH)2 (0.15 g,
0.45 mmol) in toluene (15 mL) at −20 °C. The mixture was
warmed to room temperature and stirred for 12 h. After
workup, all volatiles were removed under reduced pressure
and the residue was extracted with n-hexane (15 mL). The
n-hexane extract was kept under Ar atmosphere at ambient
temperature, allowing for slow evaporation. Colorless crystals (RSiO3)2[AlMe(THF)]3 (6)
of 3 were formed after 3 days. Yield: 0.13 g (78%). Mp: 226 °C
AlMe3 (1.5 mL, 1.5 mmol, 1 M solution in n-hexane) was added
(dec). 1H NMR (C6D6, 500 MHz, 298 K, ppm): δ 7.04–7.00 (m, 9
H, C6H3), 6.24 (s, 2 H, GeH), 3.73 (sept, 6 H, JHH = 7.0 Hz,
to a solution of RSi(OH)3 (0.33 g, 1.0 mmol) in THF (20 mL) at
−20 °C. During the addition, the CH4 gas evolution was
observed. The mixture was warmed to room temperature and
stirred for 12 h. After workup, all volatiles were removed under
reduced pressure and the residue was extracted with n-hexane.
The n-hexane extract was evaporated to dryness to give a color-
less crystalline solid of 6. Yield: 0.44 g (89%). Mp: 239 °C (dec).
1H NMR (CDCl3, 500 MHz, 298 K, ppm): δ 7.01–6.92 (m, 6 H,
C6H3), 4.00 (m, 12 H, OCH2CH2), 3.87 (sept, 4 H, 3JHH = 6.5 Hz,
CHMe2), 1.94 (m, 12 H, OCH2CH2), 1.22 (d, 12 H, 3JHH = 6.5 Hz),
3
CHMe2), 1.27 (d, 18 H, 3JHH = 7.0 Hz), 1.21 (d, 18 H, 3JHH = 7.0 Hz)
(CHMe2), 0.30 (s, 9 H) (SiMeO2), 0.2 (s, 27 H, SiMe3). 13C NMR
(C6D6, 125 MHz, 298 K, ppm): δ 147.7, 139.8, 125.7, 124.6
(C6H3), 30.2, 27.8, 25.5, 25.3 (CHMe2), 2.83 (SiMeO2), 1.35
(SiMe3). 29Si NMR (C6D6, 99 MHz, 298 K, ppm): δ 6.52 (SiMe3),
−30.92 (SiMeO2). IR (Nujol mull, cm−1): ν 2135 (GeH). Anal.
calcd for C48H89Ge2N3O6Si6 (Mr = 1118.03): C, 51.57; H, 8.02;
N, 3.76. Found: C, 51.36; H, 8.11; N, 3.52.
3
1.15 (d, 12 H, JHH = 6.5 Hz) (CHMe2), 0.09 (s, 18 H,
SiMe3), −1.03 (s, 9 H, AlMe). 13C NMR (CDCl3, 125 MHz, 298 K,
[R(Me)SiO2AlMe(THF)]2 (4)
AlMe3 (0.5 mL, 0.5 mmol, 1 M solution in n-hexane) was added ppm): δ 148.2, 143.2, 122.8, 122.6 (C6H3), 70.2 (OCH2CH2),
to a solution of R(Me)Si(OH)2 (0.16 g, 0.50 mmol) in THF 25.1 (OCH2CH2), 31.6, 27.4, 25.6, 24.8, 23.8, 22.6 (CHMe2), 2.2
(50 mL) at −20 °C. During the addition, the CH4 gas evolution (SiMe3), −13.6 (br, AlMe). 29Si NMR (CDCl3, 99 MHz, 298 K,
was observed. The mixture was warmed to room temperature ppm):
δ 0.99 (SiMe3), −79.96 (SiO3). Anal. calcd for
and stirred for 12 h. After workup, all volatiles were removed C45H85Al3N2O9Si4 (Mr = 991.45): C, 54.51; H, 8.64; N, 2.83.
under reduced pressure and the residue was extracted with Found: C, 54.35; H, 8.56; N, 2.75. X-ray quality single crystals
n-hexane–THF (5 mL, 4 : 1) solvent mixture. The extract was stored of 6·THF were formed by recrystallization from a solvent
at −20 °C within 3 days to give colorless crystals of 4. Yield: mixture (THF–n-hexane = 9 mL, 1 : 8) at −20 °C.
Dalton Trans.
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Paper
X-ray crystallographic analyses of complexes 1–6
1995, 95, 477–510; (d) G. G. Hlatky, Chem. Rev., 2000, 100,
1347–1376.
Crystallographic data for compounds 1–3, 5·toluene·0.5n-
hexane, and 6·0.75THF were collected on an Oxford Gemini S
Ultra system and the data for 4 was obtained on a Rigaku
R-Axis Spider IP. In all cases graphite-monochromatic Mo-Kα
radiation (λ = 0.71073 Å) was used. Absorption corrections
were applied using the spherical harmonics program (multi-
scan type). All the structures were solved by direct methods
(SHELXS-96)36 and refined against F2 using SHELXL-97
program.37 In general, the non-hydrogen atoms were located
from the difference Fourier synthesis and refined anisotropi-
cally, and hydrogen atoms were included using a riding model
with Uiso tied to the Uiso of the parent atoms unless otherwise
specified. In 1, the two ethyl groups of the BiNEt2 functionality
were both disordered and treated in a splitting mode. In 3,
three one-third target molecules were located. Due to the
quality of the crystals, the hydrogen atom at the Ge center
could not be located from different Fourier synthesis. Besides,
one of the iPr2C6H3 groups and one of the SiMe3 substituents
were disordered and treated in a splitting mode. The non-
hydrogen atoms of Ge(5), Ge(6), C(16), C(17A), and C(34) and
the atoms of the disordered iPr2C6H3 group were refined iso-
tropically due to instability upon anisotropic refinement. The
residual electron density of this structure thus appears high.
In 5·toluene·0.5n-hexane, the toluene solvent molecule was dis-
ordered and treated in a splitting mode. The carbon atoms
from the half molecule of n-hexane were refined isotropically
due to the significant vibration. In 6·0.75THF, the carbon
atoms of the non-coordinated THF molecules were refined iso-
tropically because of the significant vibration. Cell parameters,
data collection, and structure solution and refinement are
given in Tables S1 and S2 in the ESI.†
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This work was supported by the 973 Program (2012CB821704),
the National Nature Science Foundation of China (91027014
and 20972129), and the National Key Lab Foundation for
PCOSS (20923004) and the Innovative Research Team Program
(IRT1036).
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Dalton Trans.
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