Optically active zwitterionic λ5Si, λ5Si′-disilicates: Syntheses, crystal structures, and behavior in aqueous solution

Article abstract of DOI:10.1002/chem.200701858

The zwitterionic λ⁵Si,λ⁵Si′- disilicates 1-8 were synthesized and characterized by solid-state and solution NMR spectroscopy. In addition, compounds 2·6H₂O, 3·2CH₃CN, 4·5/2CH₃CN, 6·CH ₃OH, 7, and 8·CH₃OH·CH₃CN were studied by single-crystal X-ray diffraction. The optically active (Δ,Δ,R,R,R,R)-configured compounds 1-8 contain two pentacoordinate (formally negatively charged) silicon atoms and two tetracoordinate (formally positively charged) nitrogen atoms. One (ammonio)alkyl group is bound to each of the two silicon centers, and two tetradentate (R,R)-tartrato(4-) ligands bridge the silicon atoms. Although these λ⁵Si, λ⁵Si′-disilicates contain SiO₄C skeletons, some of them display a remarkable stability in aqueous solution as shown by NMR spectroscopy and ESI mass spectrometry.

Full text of DOI:10.1002/chem.200701858

DOI: 10.1002/chem.200701858
5
5
Optically Active Zwitterionic l Si,l Si’-Disilicates: Syntheses, Crystal
Structures, and Behavior in Aqueous Solution
[
a]
Bastian Theis, Christian Burschka, and Reinhold Tacke*
5
5
Abstract: The zwitterionic l Si,l Si’-
disilicates 1–8 were synthesized and
characterized by solid-state and solu-
tion NMR spectroscopy. In addition,
dinate (formally negatively charged)
silicon atoms and two tetracoordinate
(formally positively charged)nitrogen
atoms. One (ammonio)alkyl group is
bound to each of the two silicon cen-
ters, and two tetradentate (R,R)-tartra-
to(4ꢀ)ligands bridge the silicon atoms.
5
5
Although these l Si,l Si’-disilicates
contain SiO C skeletons, some of them
4
compounds
2·6H O,
3·2CH CN,
7,
·CH OH·CH CN were studied by
single-crystal X-ray diffraction. The op-
tically active (D,D,R,R,R,R)-configured
compounds 1–8 contain two pentacoor-
display a remarkable stability in aque-
ous solution as shown by NMR spec-
troscopy and ESI mass spectrometry.
2
3
4
·5/2CH CN,
6·CH OH,
and
3
3
8
3
3
Keywords: coordination modes
·
silicates · silicon · stereochemistry ·
zwitterions
Introduction
differ in the ammonio groups, and 3–5 with N(CH ) H
groups differ in the alkylene spacers. Compound 8 also con-
A
C
H
T
R
E
U
N
G
3 2
The chemistry of higher-coordinate silicon compounds con-
tinues to be an area of lively interest (for reviews, see
ref. [1]; for recent reports, see ref. [2]). Several years ago, we
reported the synthesis and structural characterization of the
5
5
[3]
first zwitterionic l Si,l Si’-disilicate 1. Surprisingly, this
pentacoordinate dinuclear silicon(IV)complex with two
SiO C skeletons could be synthesized in water. In view of
4
the well-known sensitivity of the SiꢀO bond towards hydrol-
ysis, the existence of 1 in aqueous solution is quite remark-
able and not yet understood.
To obtain a better understanding of this phenomenon, we
performed systematic structure–reactivity studies with a
series of derivatives of 1, in which the influence of the am-
monio groups and the spacers between the silicon atom (ate
center)and the nitrogen atom (onium center)on the hydro-
lytic stability was investigated. All the compounds studied
(
1–8; Scheme 1)contain the same ( D,D,R,R,R,R)-configured
5
5
l Si,l Si’-disilicate skeleton, but 1–3 and 6 with CH spacers
2
[
a] Dipl.-Chem. B. Theis, Dr. C. Burschka, Prof. Dr. R. Tacke
Universität Würzburg
Institut für Anorganische Chemie
Am Hubland, 97074 Würzburg (Germany)
Fax : (+49)931-888-4609
E-mail: r.tacke@mail.uni-wuerzburg.de
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Scheme 1. Structural formulas of 1–8.
4618
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630

FULL PAPER
tains N
phenylene skeleton.
We report herein on the syntheses of the zwitterionic
A
C
H
T
R
E
U
N
G
(CH ) H groups, but the C spacers are part of a
Compounds 3–5 were prepared by the treatment of the
respective [(dimethylamino)alkyl]trimethoxysilanes 11–13
with (R,R)-tartaric acid (molar ratio 1:1) in acetonitrile/
methanol at 208C (yields: 3, 90%; 4, 79%; 5, 96%;
Scheme 3). Under the same conditions, 6 was synthesized
from trimethyl[(trimethoxysilyl)methyl]ammonium iodide
3
2
2
5
5
l Si,l Si’-disilicates 1–8 and their characterization by solid-
state and solution NMR spectroscopy. In addition, com-
pounds 2·6H O, 3·2CH CN, 4·5/2CH CN, 6·CH OH, 7, and
2
3
3
3
8
·CH OH·CH CN were structurally characterized by single-
(14)and was isolated as the solvate 6·CH OH (24% yield;
3
3
3
crystal X-ray diffraction. Furthermore, the behavior of 1–8
in aqueous solution (i.e., hydrolytic stability)was studied by
NMR spectroscopy and ESI mass spectrometry.
Scheme 3). Compounds 7 and 8 were synthesized from com-
pounds 15 and 16, respectively, according to Scheme 4.
The precursor 9 was synthesized by the treatment of
(
chloromethyl)trimethoxysilane with ammonia in an auto-
[4]
clave (32% yield; Scheme 5). The starting materials 10,
[5]
[6]
[7]
Results and Discussion
11, 12, and 16 were prepared according to previous re-
ports, and 13 was commercially available. The precursor 14
was synthesized by the reaction of 12 with iodomethane in
acetonitrile (92% yield; Scheme 3), and the treatment of
(iodomethyl)trimethoxysilane with 1-methylimidazole in
cyclohexane afforded 15 (70% yield; Scheme 5).
Syntheses: Compounds 1 and 2 were synthesized by the
treatment of (aminomethyl)trimethoxysilane (9)and trime-
thoxy[(methylamino)methyl]silane (10), respectively, with
[8]
(
2
R,R)-tartaric acid (molar ratio 1:1) in aqueous solution at
08C (yields: 1, 79%; 2, 72%; Scheme 2).
The binuclear (D,D,R,R,R,R)-configured silicon(IV) com-
plexes 1–8 are optically active. The formation of these com-
pounds occurred stereospecifically, and they were all ob-
tained as diastereomerically and enantiomerically pure
products. The absolute configuration of the two bridging
(
R,R)-tartrato(4ꢀ)ligands controls the absolute configura-
tion at the two silicon centers (both D configuration).
The title compounds 1–5, 6·CH OH, 7, and
3
8
·MeOH·CH CN were isolated as colorless solids with high
3
melting points in the temperature range 2508C
8·CH OH·CH CN, decomp)to >4008C (6·MeOH, 7). Due
(
3
3
to their zwitterionic nature, they are almost insoluble in
nonpolar organic solvents and exhibit a very poor solubility
in most polar organic solvents. The identities of 1–5,
6
·MeOH, 7, and 8·MeOH·CH CN were established by ele-
3
1
3
15
29
mental analyses (C, H, N)and solid-state ( C, N, Si)and
solution ( H, C, Si)NMR spectroscopic studies. In addi-
1
13
29
tion, compounds 2·6H O, 3·2CH CN, 4·5/2CH CN,
2
3
3
6
·MeOH, 7, and 8·MeOH·CH CN (and the intermediate 15)
3
Scheme 2. Syntheses of compounds 1 and 2.
Scheme 3. Syntheses of compounds 3–6 and 14.
Chem. Eur. J. 2008, 14, 4618 – 4630
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4619

R. Tacke et al.
Scheme 4. Syntheses of compounds 7 and 8.
For the solvates 2·6H O, 6·CH OH, and 8·CH OH·CH CN,
2
3
3
3
additional intermolecular OꢀH···O hydrogen bonds between
the solvent molecules and zwitterions were observed (for
details of the hydrogen-bonding systems, see the Supporting
[10]
Information).
In the case of the silicon-bound oxygen
atoms that are involved as acceptor atoms in NꢀH···O or
OꢀH···O hydrogen bonds, significantly elongated SiꢀO bond
lengths were observed relative to the analogous SiꢀO bonds,
in which the oxygen atoms are not involved in hydrogen-
bonding interactions.
There is no clear correlation between the structures of the
trigonal-bipyramidal silicon-coordination polyhedra and the
nature of the ammonio groups and the spacers between the
silicon and nitrogen atoms. It rather appears that the distor-
tion of the silicon-coordination polyhedra is mainly influ-
enced by the crystal packing, including hydrogen-bonding
interactions. This behavior is clearly illustrated by the quite
different Berry distortions observed for the four silicon-co-
ordination polyhedra of the two crystallographically inde-
pendent zwitterions in the crystal of 7 (molecule I: 23.4 and
14.3%; molecule II: 21.2 and 42.6%).
Scheme 5. Syntheses of compounds 9 and 15.
were structurally characterized by single-crystal X-ray dif-
fraction.
Crystal structure analyses: The crystal data and experimen-
tal parameters used for the single-crystal X-ray diffraction
studies of 2·6H O, 3·2CH CN, 4·5/2CH CN, 6·MeOH, 7,
2
3
3
8
·MeOH·CH CN, and 15 are given in Table 1. The molecu-
3
lar structures of the zwitterions 2–4 and 6–8 and of the
cation of 15 are shown in Figures 1–7; the selected bond
lengths and angles are given in the respective figure legends.
The silicon-coordination polyhedra of the zwitterionic
Solid-state and solution NMR studies: The zwitterionic
5
5
l Si,l Si’-disilicates 1–5, 6·CH OH, 7, and 8·CH OH·CH CN
3
3
3
were characterized by solid-state VACP/MAS NMR spec-
5
5
13
15
29
l Si,l Si’-disilicates 2–4 and 6–8 can be described as distort-
ed trigonal bipyramids, and each tetradentate (R,R)-tartra-
to(4ꢀ)ligand spans two axial (O1, O3; O7, O9)and two
equatorial sites (O2, O4; O8, O10). The Berry distortions of
troscopy ( C, N, Si). In addition, compounds 1–8 were
1
13
29
studied by solution NMR spectroscopy ( H, C, Si; sol-
vent: [D ]DMSO and D O (except for 4, 5, and 8)). The
6
2
NMR spectra obtained (see the Experimental Section)con-
[9]
29
the silicon-coordination polyhedra are given in Table 2. In
all the zwitterions, the axial sites are occupied by the car-
boxylato oxygen atoms. The axial SiꢀO bond lengths in the
firm the identities of the compounds studied. The Si NMR
chemical shifts determined in solution are very similar to
2
9
the isotropic Si NMR chemical shifts obtained in the solid
state (Table 3), thus indicating the presence of pentacoordi-
nate silicon atoms in solution as well (see the Experimental
Section for further details).
SiO C skeletons of 2–4 and 6–8 (1.786(2)–1.841(2) Š) are
4
significantly longer than the equatorial bond lengths
(
1
1.658(1)–1.678(2) Š). The SiꢀC bond lengths are 1.873(3)–
.921(2)Š.
Upon the dissolution of 1–5, 6·CH OH, and 7 in
3
ꢀ
1
As would be expected from the presence of potential NH
[D ]DMSO (concentration was approximately 5 mgmL )at
6
donor functions and oxygen acceptor atoms, intra- and/or in-
208C, the presence of only one zwitterionic species could be
detected, whereas in the case of 8·CH OH·CH CN an equi-
librium mixture of three zwitterionic species that were dis-
termolecular NꢀH···O hydrogen bonds exist in the crystals
3
3
of 2·6H O, 3·2CH CN, 4·5/2CH CN, and 8·CH OH·CH CN.
2
3
3
3
3
4620
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630

5
5
Zwitterionic l Si,l Si’-Disilicates
FULL PAPER
Table 1. Crystallographic data for compounds 2·6H
2
O, 3·2CH
3
CN, 4·5/2CH
3
CN, 6·CH
3
OH, 7, 8·CH
3
OH·CH
3
CN, and 15.
3 3
8·CH OH·CH CN 15
2·6H
2
O
3·2CH
3
CN 4·5/2CH
3
CN
6·CH
3
OH
7
empirical formula
formula mass [gmol
T [K]
C
546.56
12
H
30
N
2
O
18Si
2
C
548.62
18
H
28
N
4
O
12Si
2
C
597.20
21
H
33.5
N
4.5
O
12Si
2
C
526.61
17
H
30
N
2
O
13Si
2
C
540.56
18
H
20
N
4
O
12Si
2
C
663.74
27
H
33
N
3
O
13Si
2
8 2 3
C H17IN O Si
344.23
ꢀ
1
]
98(2) 100(2)100(2) 193(2)203(2) 173(2) 193(2)
l
A
C
H
T
R
E
U
N
G
(MoKa)[Š]
0.71073
orthorhombic
0.71073
monoclinic
0.71073
triclinic
P1 (1)
0.71073
orthorhombic
P2 (19)
0.71073
monoclinic
C2 (5)
0.71073
monoclinic
P2 (4)
0.71073
monoclinic
P2 /n (14)
1
crystal system
space group (no.)
a [Š]
P2
1
2
1
2
1
(19)
P2
1
(4)
1
2
1
2
1
1
8.6264(2)8.8002(2)9.1917(4) 10.9012(7 2) 5.0742(12 8) .4444(7) 11.6039(12)
b [Š]
c [Š]
14.6727(4)8.0619(2) 9.2041(3) 14.7074(9)8.7643(4) 15.9973(18) 7.5643(12)
17.9636(5)17.5122(4)18.6666(8) 14.7740(14 2) 0.0808(8) 11.3019(10) 16.2658(16)
a [8]
b [8]
g [8]
V [Š ]
90
90
90
90
100.9140(10)81.512(2)
90 66.333(2)90
76.693(2)90
90
90
90
90
91.699(3)
90
101.936(10)
90
1405.8(3)
100.064(11)
90
3
2273.70(10)1219.95(5) 1404.86(10) 2368.7(3) 4411.0(3) 1493.7(2)
Z
4
2
2
4
8
2
4
ꢀ
3
1
calcd [gcm
]
1.597
0.246
1152
1.494
0.215
576
1.412
0.194
630
1.477
0.219
1112
1.628
0.237
2240
1.476
0.192
696
1.626
2.356
680
ꢀ1
m [mm
]
F
000
crystal dimensions [mm] 0.4”0.2”0.2
0.1”0.04”0.03 0.3”0.17”0.07
0.4”0.2”0.2
4.66–56.02
ꢀ11ꢁhꢁ14
ꢀ19ꢁkꢁ18
ꢀ19ꢁlꢁ19
15895
0.37”0.12”0.07 0.4”0.4”0.3
0.5”0.5”0.5
5.96–56.08
ꢀ15ꢁhꢁ15
ꢀ9ꢁkꢁ9
ꢀ19ꢁlꢁ19
16004
2
q range [8]
3.58–57.06
4.72–56.80
ꢀ11ꢁhꢁ11
ꢀ10ꢁkꢁ10
ꢀ23ꢁlꢁ23
34200
4.50–56.96
ꢀ11ꢁhꢁ12
ꢀ12ꢁkꢁ12
ꢀ24ꢁlꢁ24
31706
3.24–56.70
ꢀ33ꢁhꢁ33
ꢀ11ꢁ kꢁ11
ꢀ26ꢁlꢁ26
96139
5.52–56.22
ꢀ11ꢁhꢁ11
ꢀ21ꢁkꢁ21
ꢀ14ꢁlꢁ14
19762
index ranges
ꢀ11ꢁhꢁ11
ꢀ
ꢀ
19ꢁkꢁ19
23ꢁlꢁ23
number of collected
reflections
65654
number of independent 5740
reflections
5844
12976
5646
10899
7082
3093
R
int
0.0516
0
0.0443
1
0.0447
3
0.0561
0
0.0602
1
0.0460
1
0.0340
0
restraints
number of parameters
357
1.033
0.0302/0.6256
0.0246
0.0678
337
1.038
0.0318/0.3365
0.0279
0.0870
737
1.019
0.0283/0.4551
0.0410
316
1.024
0.0658/0.0000
0.0398
0.0887
654
1.066
0.0429/2.7787
0.0347
0.1168
419
1.125
0.0403/1.5737
0.0517
0.0724
ꢀ0.01(12)–
140
1.047
0.0393/1.1760
0.0271
[
a]
S
[
b]
weight parameters a/b
R1 (I>2s(I))
[
c]
[
d]
wR2 (all data)0.0608
absolute structure
parameter
0.1006
0.00(7)0.02(7)0.00(7) 0.00(10 0) .00(9)
max./min. residual
electron density [eŠ
+0.295/ꢀ0.226 +0.366/ꢀ0.263 +0.603/ꢀ0.503
+0.519/ꢀ0.437 +0.399/ꢀ0.251
+0.524/ꢀ0.334
+0.555/ꢀ0.573
ꢀ
3
]
2
2
2
0.5
ꢀ1
2
2
2
2
2
[
[
a] S={ꢀ[w
c] R1=ꢀjjF
A
C
H
T
R
E
U
N
G
(F
o
ꢀF
jꢀjF
c
) ]/
A
C
H
T
R
E
U
N
G
(nꢀp)}
;
n=number of reflections; p=number of parameters. [b] w =s
A
H
R
N
(F
o
)+(aP) +bP, with P=
A
H
E
N
A
H
E
N
o c
[max(F ,0)+2F ]/3.
2
2
2
2
2
0.5
o
c
jj/ꢀjF
o
j. [d] wR2={ꢀ[w
A
H
R
U
(F
o
ꢀF
c
A
H
R
U
G
o
) ]/ꢀ[w(F ) ]} .
Figure 1. Molecular structure of 2 in the crystal of 2·6H
2
O (probability
3
Figure 2. Molecular structure of 3 in the crystal of 3·2CH CN (probability
level of displacement ellipsoids at 50%). Selected bond lengths [Š] and
angles [8]: Si1ꢀO1 1.8058(9), Si1ꢀO2 1.6739(10), Si1ꢀO3 1.7945(10), Si1ꢀ
O4 1.6724(10), Si1ꢀC1 1.8881(14), Si2ꢀO7 1.8086(10), Si2ꢀO8 1.6683(10),
Si2ꢀO9 1.8062(10), Si2ꢀO10 1.6659(9), Si2ꢀC6 1.8845(14); O1-Si1-O2
level of displacement ellipsoids at 50%). Selected bond lengths [Š] and
angles [8]: Si1ꢀO1 1.8367(11), Si1ꢀO2 1.6613(12), Si1ꢀO3 1.7876(11),
Si1ꢀO4 1.6737(11), Si1ꢀC1 1.8907(17), Si2ꢀO7 1.8092(11), Si2ꢀO8
1.6704(11), Si2ꢀO9 1.7982(11), Si2ꢀO10 1.6581(11), Si2ꢀC6 1.8963(16);
8
8.71(5), O1-Si1-O3 175.10(5), O1-Si1-O4 88.53(5), O1-Si1-C1 94.55(5),
O1-Si1-O2 88.26(5), O1-Si1-O3 177.25(5), O1-Si1-O4 88.11(5), O1-Si1-C1
92.91(7), O2-Si1-O3 91.36(6), O2-Si1-O4 122.70(6), O2-Si1-C1 120.79(7),
O3-Si1-O4 89.80(5), O3-Si1-C1 89.63(7), O4-Si1-C1 116.51(7), O7-Si2-O8
88.72(5), O7-Si2-O9 178.02(6), O7-Si2-O10 89.78(5), O7-Si2-C6 91.44(6),
O8-Si2-O9 89.88(5), O8-Si2-O10 122.16(6), O8-Si2-C6 121.64(6), O9-Si2-
O10 89.78(5), O9-Si2-C6 90.49(6), O10-Si2-C6 116.20(7).
O2-Si1-O3 88.89(5), O2-Si1-O4 123.59(5), O2-Si1-C1 119.60(6), O3-Si1-
O4 89.24(5), O3-Si1-C1 90.35(5), O4-Si1-C1 116.79(6), O7-Si2-O8
8
9.05(5), O7-Si2-O9 175.34(5), O7-Si2-O10 88.25(5), O7-Si2-C6 94.46(5),
O8-Si2-O9 88.83(5), O8-Si2-O10 123.09(5), O8-Si2-C6 120.13(6), O9-Si2-
O10 89.43(5), O9-Si2-C6 90.20(5), O10-Si2-C6 116.76(6).
Chem. Eur. J. 2008, 14, 4618 – 4630
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4621

R. Tacke et al.
3
Figure 4. Molecular structure of 6 in the crystal of 6·CH OH (probability
level of displacement ellipsoids at 50%). Selected bond lengths [Š] and
angles [8]: Si1ꢀO1 1.8392(16), Si1ꢀO2 1.6718(16), Si1ꢀO3 1.8105(16),
Si1ꢀO4 1.6646(16), Si1ꢀC1 1.915(2), Si2ꢀO7 1.8046(17), Si2ꢀO8
1
.6710(17), Si2ꢀO9 1.8082(17), Si2ꢀO10 1.6782(16), Si2ꢀC6 1.921(2); O1-
Si1-O2 88.50(8), O1-Si1-O3 175.41(7), O1-Si1-O4 87.96(8), O1-Si1-C1
1.06(9), O2-Si1-O3 89.86(8), O2-Si1-O4 123.14(8), O2-Si1-C1 120.65(9),
O3-Si1-O4 89.34(8), O3-Si1-C1 93.46(9), O4-Si1-C1 116.14(9), O7-Si2-O8
9.20(8), O7-Si2-O9 175.86(7), O7-Si2-O10 88.17(8), O7-Si2-C6 97.79(9),
9
8
O8-Si2-O9 89.80(8), O8-Si2-O10 123.53(8), O8-Si2-C6 116.91(10), O9-
Si2-O10 89.03(8), O9-Si2-C6 86.24(9), O10-Si2-C6 119.33(9).
2
9
Si NMR chemical shifts of 1–8 do not clearly correlate
Figure 3. Molecular structures of the two crystallographically independ-
ent zwitterions (top molecule I; bottom molecule II)of 4 in the crystal of
with the stability of these compounds in aqueous solution.
4
3
·5/2CH CN (probability level of displacement ellipsoids at 50%). Se-
lected bond lengths [Š] and angles [8] of molecule I: Si1ꢀO1 1.8090(16),
Stability studies in aqueous solution: Upon the dissolution
5
5
Si1ꢀO2 1.6630(18), Si1ꢀO3 1.8408(17), Si1ꢀO4 1.6669(17), Si1ꢀC1
of the zwitterionic l Si,l Si’-disilicates 1–8 in water (c=
.875(2), Si2
ꢀO7 1.8409(18), Si2ꢀO8 1.6639(17), Si2ꢀO9 1.8074(19), Si2ꢀ
ꢀ1
1
1
0 mmolL )at 20 8C, pH values of 5.5–6.4 were measured.
O10 1.6693(17), Si2ꢀC6 1.876(2); O1-Si1-O2 89.16(8), O1-Si1-O3
All the compounds underwent hydrolysis (cleavage of the
1
74.53(8), O1-Si1-O4 89.13(8) O1-Si1-C1 95.50(9), O2-Si1-O3 88.25(8),
SiꢀO bonds)to form ( R,R)-tartaric acid and the correspond-
O2-Si1-O4 121.78(9), O2-Si1-C1 117.58(10), O3-Si1-O4 88.14(8), O3-Si1-
C1 89.97(9), O4-Si1-C1 120.51(10), O7-Si2-O8 88.44(8), O7-Si2-O9
ing organylsilanetriol. This behavior is shown exemplarily
1
8
8
75.25(8), O7-Si2-O10 88.57(8), O7-Si2-C6 91.73(11), O8-Si2-O9
9.53(8), O8-Si2-O10 122.25(9), O8-Si2-C6 117.88(10), O9-Si2-O10
8.89(9), O9-Si2-C6 93.01(11), O10-Si2-C6 119.85(10). Selected bond
for the hydrolysis of 2 in Scheme 6. After six months at
ꢀ1
2
08C, the aqueous solutions of 1–8 (c=10 mmolL )had
pH values of 3.6–3.9.
lengths [Š] and angles [8] of molecule II: Si21ꢀO21 1.8040(17), Si21ꢀO22
.6670(18), Si21
ꢀO23 1.8393(16), Si21ꢀO24 1.6679(17), Si21ꢀC21
The kinetics of the hydrolytic cleavage of 1–8 were moni-
tored by NMR spectroscopy and were dependent on the
nature of the ammonio group and the spacer between the
silicon and nitrogen atoms (see below). The identities of the
respective organylsilanetriols 17–24 (Scheme 7)were estab-
lished by ESI mass spectrometry (see below). The aqueous
1
1
1
8
9
1
1
.874(3), Si22ꢀO27 1.8382(17), Si22ꢀO28 1.6627(17), Si22ꢀO29
.8092(18), Si22ꢀO30 1.6694(18), Si22ꢀC26 1.873(3); O21-Si21-O22
9.19(8), O21-Si21-O23 173.89(8), O21-Si21-O24 88.42(8), O21-Si21-C21
5.57(9), O22-Si21-O23 88.40(8), O22-Si21-O24 122.15(9), O22-Si21-C21
17.06(10), O23-Si21-O24 88.12(8), O23-Si21-C21 90.52(9), O24-Si21-C21
20.69(11), O27-Si22-O28 88.38(8), O27-Si22-O29 175.05(9), O27-Si22-
5
5
O30 88.58(8), O27-Si22-C26 91.95(11), O28-Si22-O29 89.23(8), O28-Si22-
O30 122.43(9), O28-Si22-C26 117.68(11), O29-Si22-O30 89.04(9), O29-
Si22-C26 93.00(11), O30-Si22-C26 119.88(11).
solutions of the l Si,l Si’-disilicates 1–8 did not undergo gel
formation at room temperature over six months.
NMR studies of aqueous solutions: Upon the dissolution of
2
in D O (10 mm solution)at 23 8C, hydrolytic cleavage of
2
tinguishable by NMR spectroscopy was observed (even at
temperatures up to 608C). This phenomenon is not yet un-
derstood, but might be explained by strong intramolecular
NꢀH···O hydrogen bonds that stabilize different conformers.
all the SiꢀOC bonds was observed. The kinetics of the hy-
1
drolysis reaction could be monitored by H NMR spectros-
copy (Figure 8). For this purpose, the resonance signals of
the CH moieties of the bound (R,R)-tartrato(4ꢀ)ligands
(d=4.60 ppm)and the free tartaric acid ( d=4.2–4.4 ppm;
concentration- and/or pH-dependent chemical shift)were
integrated as a function of time.
The influence of both the ammonio groups and the
2
9
(
CH ) spacers (n=1–3)on the Si NMR chemical shifts is
2 n
rather small but systematic. The elongation of the
Si
2
9
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
(CH ) N chain (3!4!5)leads to a downfield shift ( 3–5:
The Si NMR spectra measured 12 h and 31 days after
2
n
d=ꢀ94.2, ꢀ87.4, and ꢀ84.0 ppm, respectively), whereas the
the dissolution of 2 in water (D O; sample was kept at
2
successive exchange of NH functions by NCH groups (1!
238C)showed the existence of only one tetracoordinate sili-
3
2
ꢀ
!3!6)results in a highfield shift ( 1–3, and 6: d=ꢀ91.8,
con species formed by hydrolysis (Figure 9). The integration
2
9
93.0, ꢀ94.2, and ꢀ95.7 ppm, respectively). However, the
of the Si NMR resonance signals of the zwitterion 2 (d=
4622
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630

5
5
Zwitterionic l Si,l Si’-Disilicates
FULL PAPER
Figure 6. Molecular structure of 8 in the crystal of 8·CH
3 3
CN·CH OH
(
probability level of displacement ellipsoids at 50%). Selected bond
lengths [Š] and angles [8]: Si1ꢀO1 1.8141(19), Si1ꢀO2 1.6593(19), Si1ꢀ
O3 1.7925(19), Si1ꢀO4 1.663(2), Si1ꢀC1 1.886(3), Si2ꢀO7 1.786(2), Si2ꢀ
O8 1.670(2), Si2ꢀO9 1.806(2), Si2ꢀO10 1.658(2), Si2ꢀC6 1.877(3); O1-
Si1-O2 88.43(9), O1-Si1-O3 174.30(10), O1-Si1-O4 87.71(10), O1-Si1-C1
9
1
1
8
1
9
2.45(10), O2-Si1-O3 89.57(10), O2-Si1-O4 123.68(10), O2-Si1-C1
16.88(11), O3-Si1-O4 88.96(10), O3-Si1-C1 93.22(11), O4-Si1-C1
19.42(11), O7-Si2-O8 89.49(10), O7-Si2-O9 175.43(10), O7-Si2-O10
9.77(10), O7-Si2-C6 92.04(11), O8-Si2-O9 87.79(10), O8-Si2-O10
25.55(10), O8-Si2-C6 114.86(11), O9-Si2-O10 88.83(10), O9-Si2-C6
2.43(11), O10-Si2-C6 119.57(11).
Figure 5. Molecular structures of the two crystallographically independ-
ent zwitterions (top molecule I; bottom molecule II)of 7 (probability
level of displacement ellipsoids at 50%). Selected bond lengths [Š] and
angles [8] of molecule I: Si1ꢀO1 1.8194(19), Si1ꢀO2 1.667(2), Si1ꢀO3
Figure 7. Molecular structure of the cation in the crystal of 15 (probabil-
ity level of displacement ellipsoids at 50%). Selected bond lengths [Š]
and angles [8]: SiꢀO1 1.6123(19), SiꢀO2 1.612(2), SiꢀO3 1.6235(18), Siꢀ
1
1
.807(2), Si1ꢀO4 1.6662(19), Si1ꢀC1 1.905(3), Si2ꢀO7 1.8140(19), Si2ꢀO8
.668(2), Si2ꢀO9 1.8089(19), Si2ꢀO10 1.670(2), Si2ꢀC6 1.897(3); O1-Si1-
O2 89.26(9), O1-Si1-O3 176.74(10), O1-Si1-O4 88.15(9), O1-Si1-C1
C1 1.878(2); O1-Si-O2 107.90(10), O1-Si-O3 107.87(10), O1-Si-C1
9
1
1
9
1
9
0.68(11), O2-Si1-O3 90.83(9), O2-Si1-O4 124.27 (10), O2-Si1-C1
16.12(12), O3-Si1-O4 89.11(9), O3-Si1-C1 92.20(11), O4-Si1-C1
19.57(12), O7-Si2-O8 89.03(10), O7-Si2-O9 177.90(11), O7-Si2-O10
1.25(10), O7-Si2-C6 90.40(12), O8-Si2-O9 89.19(9), O8-Si2-O10
21.97(10), O8-Si2-C6 121.35(13), O9-Si2-O10 88.76(10), O9-Si2-C6
1.47(11), O10-Si2-C6 116.67(13). Selected bond lengths [Š] and angles
1
1
12.74(11), O2-Si-O3 115.08(12), O2-Si-C1 105.33(10), O3-Si-C1
08.04(10).
Table 2. Berry distortions of the silicon-coordination polyhedra of
2·6H O, 3·2CH CN, 4·5/2CH CN, 6·CH OH, 7, and 8·CH OH·CH CN.
[
8] of molecule II: Si21ꢀO21 1.809(2), Si21ꢀO2 2 1.664(2), Si21ꢀO23
.808(2), Si21ꢀO24 1.6691(19), Si21ꢀC21 1.894(3), Si22ꢀO27 1.7964(19),
Si22ꢀO28 1.6716(19), Si22ꢀO29 1.8061(19), Si22ꢀO30 1.672(2), Si22ꢀC26
.896(3); O21-Si21-O22 89.22(9), O21-Si21-O23 176.56(10), O21-Si21-
2
3
3
3
3
3
1
Compound
Si1 (C1 as the pivot
atom)[%]
Si2 (C6 as the pivot
atom)[%]
1
2
3
4
6
7
8
·6H
·2CH
·5/2CH
2
O
26.4
16.9
21.8, 24.7
23.8
24.1
15.1
20.8, 22.2
25.3
14.3, 42.6
O24 88.51(9), O21-Si21-C21 94.90(11), O22-Si21-O23 90.77(9), O22-Si21-
O24 122.39(10), O22-Si21-C21 115.52(11), O23-Si21-O24 88.59(9), O23-
Si21-C21 88.21(11), O24-Si21-C21 122.03(11), O27-Si22-O28 89.27(9),
O27-Si22-O29 174.69(11), O27-Si22-O30 88.62(9), O27-Si22-C26
3
CN
CN
[
a]
[b]
[b]
[a]
[c]
[c]
3
·CH
3
OH
[
a]
[a]
23.4, 21.2
CN 28.8
9
3.57(11), O28-Si22-O29 88.90(9), O28-Si22-O30 127.54(10), O28-Si22-
·CH
3
OH·CH
3
32.8
C26 115.03(11), O29-Si22-O30 88.55(9), O29-Si22-C26 91.72(11), O30-
Si22-C26 117.42(11).
[a] Molecule I (see the crystal structure). [b] Molecule II (see the crystal
structure), Si21 (C21 as the pivot atom). [c] Molecule II (see the crystal
structure), Si22 (C26 as the pivot atom).
ꢀ
91.4 ppm)and the hydrolysis product ( d=ꢀ51.3 ppm),
after baseline correction, led to the same intensity ratio as
1
observed for the CH resonance signals of 2 and (R,R)-tarta-
Additionally, an analogous H NMR experiment with an
1
ric acid in the corresponding H NMR spectra. The
aqueous solution of 2 and sodium 3-(trimethylsilyl)propane-
1-sulfonate (as the internal standard)in a molar ratio of 1:1
(10 mm each)was performed. The molar ratio was deter-
mined by integration of the respective resonance signals in
2
9
Si NMR resonance signal at d=ꢀ51.3 ppm can be assigned
to the cationic [(ammonio)methyl]silanetriol (18). Quite sur-
prisingly, neither T nor Q groups could be observed in the
29
1
Si NMR spectra, even after 31 days.
the H NMR spectrum measured 5 min after the dissolution
Chem. Eur. J. 2008, 14, 4618 – 4630
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4623

R. Tacke et al.
2
9
Table 3. Si NMR spectroscopic data for 1–5, 6·CH
3
OH, 7, and
[
a]
8
·CH
3
OH·CH
3
CN in the solid state and solution.
Compound
d [ppm]
Solution
[
b]
[c]
[d]
Solid state
Solution
1
2
3
4
5
ꢀ91.7, ꢀ90.1
ꢀ94.8, ꢀ91.8
ꢀ97.1, ꢀ93.7
ꢀ85.5 (4Si)
ꢀ83.2, ꢀ82.4
ꢀ94.5, ꢀ92.3
ꢀ91.5 (1Si),
ꢀ91.8
ꢀ93.0
ꢀ94.2
ꢀ87.3
ꢀ84.0
ꢀ95.7
ꢀ94.0
ꢀ89.9
ꢀ91.4
ꢀ92.6
[e]
[e]
6
·CH
3
OH
ꢀ94.0
7
ꢀ91.8
ꢀ
90.1 (3Si)
8
·CH
3
OH·CH
3
CN ꢀ97.9, ꢀ96.2
ꢀ97.1, ꢀ97.5, [e]
106.0
ꢀ
[
[
a] Spectra recorded at 228C in the solid state or at 238C in solution.
2
9
b] Isotropic chemical shifts obtained by Si VACP/MAS NMR spectro-
]DMSO.
O. [e] The Si NMR chemical shift
scopic experiments. [c] Chemical shifts obtained in [D
[
6
2
9
d] Chemical shifts obtained in D
2
2
could not be determined due to the fast hydrolysis in D O.
1
Figure 8. Partial H NMR spectra (238C, 500.1 MHz)of a 10 m m solution
of 2 in water (D
2
O; pH 5.8ꢂ0.2), showing the resonance signals of the
CH groups of 2 and (R,R)-tartaric acid (formed by hydrolysis of 2)as a
1
function of time (the H NMR chemical shift of the CH groups of (R,R)-
tartaric acid is concentration and/or pH dependent). The pH value given
was measured directly after sample preparation.
Scheme 6. Hydrolysis of compound 2.
2
9
Figure 9. Si NMR spectra (238C, 99.4 MHz; number of scans: 2048)of a
0 mm solution of 2 in water (D
1
2
O; pH 5.8ꢂ0.2)measured 12 h (bottom)
and 31 days (top), respectively, after sample preparation. The pH value
given was measured directly after sample preparation.
2
9
grals of the Si NMR resonance signals of the internal stan-
dard and the hydrolysis product showed a molar ratio of 1:2
after baseline correction and Lorentzian deconvolution.
Thus, the hydrolysis of 2 only results in the formation of 18,
and no subsequent formation of the condensation products
could be detected.
Evidently, within the detection limits of the NMR spectro-
scopic methods used in these studies, the cationic organylsi-
lanetriol 18 does not undergo condensation reactions (for-
mation of Si-O-Si moieties). This finding is strongly support-
ed by the results of ESI mass spectrometric studies (see sec-
tion on the ESI-MS studies). Analogous behavior was also
observed for the zwitterions 1 and 3–8. This is in sharp con-
Scheme 7. Structural formulas of the cationic organylsilanetriols 17–24.
1
of 2 in D O. The H NMR spectrum showed complete hy-
2
5
drolysis of 2 after nine days at 208C. A quantitative
trast to the behavior of the zwitterionic l Si-silicate 25,
29
Si NMR experiment, with 512 scans and a relaxation time
of 300 s, was performed with the same solution. The inte-
which upon dissolution in water forms an equilibrium mix-
[2g,k]
ture with the corresponding silsesquioxanes (Scheme 8).
4624
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630

5
5
Zwitterionic l Si,l Si’-Disilicates
FULL PAPER
5
Scheme 8. Equilibrium between the zwitterionic l Si-silicate 25 and sil-
sesquioxanes (formed by hydrolysis/condensation reactions)in aqueous
solution.
Figure 11. Kinetics of the hydrolysis of 3–5 and 7–8 upon dissolution in
D
2
O (10 mm; pH 6.4ꢂ0.2 (3), 5.6ꢂ0.2 (4), 5.5ꢂ0.2 (5), 6.2ꢂ0.2 (7),
To obtain more information about the influence of the
ammonium center and the length of the spacer between the
silicon and nitrogen atoms on the stability of the title com-
1
5
.9ꢂ0.2 (8)). The experimental data were extracted from H NMR spec-
tra (238C, 500.1 MHz)in which the CH resonance signals of the zwitter-
5
5
ionic l Si,l Si’-disilicates and free (R,R)-tartaric acid served as the probe.
The pH values given were measured directly after sample preparation.
1
pounds in water, time-dependent H NMR spectroscopic ex-
periments with solutions in D O (10 mm)were performed
2
(
Figures 10 and 11). To ensure that the slightly different
starting pH values of the samples did not significantly affect
the kinetics of the hydrolysis, an additional NMR experi-
ment on a solution of 3 and 6 (5 mm each; pH 6.0ꢂ0.2)in
one NMR tube was carried out. The kinetic values mea-
sured were almost identical with those obtained from solu-
tions containing 3 (pH 6.4ꢂ0.2)or 6 (pH 5.9ꢂ0.2)separate-
ly.
To obtain information about the influence of the concen-
5
5
tration of the l Si,l Si’-disilicate on the kinetics of the hy-
1
drolysis, an H NMR experiment with two different starting
concentrations of 2 (c=10 and 40 mm)was performed
(Figure 12). The degree of hydrolysis after about 300 h was
5
5
The NH-containing zwitterionic l Si,l Si’-disilicates 1–3
(CH ) H groups, n=0–2)undergo very slow hydrolysis
(
(
N
ACHTREUNG
3
n
3ꢀn
35–45% hydrolysis after 300 h), thus showing very similar
kinetic behavior (Figure 10). In contrast, derivative 6
2
Figure 12. Kinetics of the hydrolysis of 2 upon dissolution in D O at two
different concentrations (10 mm, pH 6.4ꢂ0.2; 40 mm, pH 6.3ꢂ0.2). The
1
experimental data were extracted from H NMR spectra (238C,
5
00.1 MHz)in which the CH resonance signals of the zwitterionic
5
5
l Si,l Si’-disilicates and free (R,R)-tartaric acid served as the probe. The
pH values given were measured directly after sample preparation.
Figure 10. Kinetics of the hydrolysis of 1–3 and 6 upon dissolution in
D
2
O (10 mm; pH 6.2ꢂ0.2 (1), 5.8ꢂ0.2 (2), 6.4ꢂ0.2 (3), 5.9ꢂ0.2 (6)).
1
38% (c=10 mm)and 17% ( c=40 mm), respectively, which
corresponds to a silanetriol concentration of 7.6 mm (10 mm
sample)and 14 m m (40 mm sample), respectively. Compared
to the saturation concentration of ortho-silicic acid at room
temperature (about 2 mm), the concentration of the silane-
triol 18 was significantly higher (by a factor of 3.8 and 7, re-
spectively).
The experimental data were extracted from H NMR spectra (238C,
5
00.1 MHz)in which the CH resonance signals of the zwitterionic
5
5
l Si,l Si’-disilicates and free (R,R)-tartaric acid served as the probe. The
pH values given were measured directly after sample preparation.
A
C
H
T
R
E
U
N
G
(N
hydrolysis after 150 h). The zwitterionic l Si,l Si’-disilicates
(Si(CH ) N groups), 5 (Si(CH ) N groups), and 8 (2-(dime-
thylammonio)phenyl groups) hydrolyze much faster than 1
SiCH N groups; Figure 11). Compound 7 (3-(1-methylimi-
A
C
H
T
R
E
U
N
G
(CH ) groups)hydrolyzes much faster (almost complete
3 3
5
5
From these studies, the following conclusions can be
drawn:
4
A
C
H
T
R
E
U
N
G
ACHTREUNG
2
2
2 3
(
1)The presence of SiCH 2N groups (1–3 and 6)favors the
2
5
5
dazolio)methyl groups) hydrolyzes faster than 1–3 but
slower than 6 (all these compounds contain SiCH N
groups).
hydrolytic stability of the zwitterionic l Si,l Si’-disili-
cates, whereas the elongation of the spacers between the
silicon and nitrogen atoms (4 and 5)leads to significant
2
Chem. Eur. J. 2008, 14, 4618 – 4630
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4625

R. Tacke et al.
destabilization. One might speculate that the positively
charged CH N(CH ) H group (n=0–3)next to the sil-
ACHTREUNG
2
3
n
3ꢀn
5
5
icon atom stabilizes the zwitterionic l Si,l Si’-disilicates.
)The presence of NH groups (SiCH 2NH moieties)favors
the hydrolytic stability as well, thus suggesting that intra-
molecular NꢀH···O hydrogen bonds may play an impor-
2
3
5
5
tant role in stabilizing the zwitterionic l Si,l Si’-disili-
cates.
5
5
)As all the zwitterionic l Si,l Si’-disilicates studied under-
go complete hydrolysis (with no indication of a thermo-
dynamic equilibrium), the above-mentioned stabilizing
effects have to be understood in terms of kinetic stabili-
zation.
5
5
ESI-MS studies: The stability of the zwitterionic l Si,l Si’-
disilicates 1–8 in aqueous solution was also investigated by
ESI mass spectrometric experiments (measuring range:
A
H
R
U
G
50–1000). For this purpose, aqueous solutions were analyzed
at 208C. Exemplarily, the results for 2 are depicted in
Figure 13.
The mass spectrum of a freshly prepared aqueous solution
+
of 2 shows signals for protonated 2 (m/z 439 [2+H ]), the
+
ammonium adduct of 2 (m/z 456 [2+NH ]), and the
4
+
sodium cation adduct of 2 (m/z 461 [2+Na ]; Figure 13A).
The mass spectrum recorded 24 h after sample preparation
at 208C shows a new signal, which can be assigned to the
hydrolysis product [(dimethylammonio)methyl]silanetriol
(
18; m/z 124), a signal for protonated 18 with decreased in-
tensity (m/z 439), and a signal for an adduct consisting of 2
and 18 (m/z 562; Figure 13B). The mass spectra of aqueous
5
5
solutions of the other l Si,l Si’-disilicates (1 and 3–8)also
showed signals of the respective protonated zwitterions,
their respective sodium cation adducts, and the respective
cationic organylsilanetriols. Additional HRMS–ESI-MS
studies of an aqueous solution of 2 and 6 confirmed the
identities of the respective hydrolysis products 18 (calcd:
Figure 13. Partial high-resolution (HR)MS–ESI-MS spectra of 2 in aque-
ous solution measured 5 min (A)and 24 h (B ), respectively, after sample
preparation at 208C (see the Experimental Section). A) The spectrum
shows signals of protonated 2 (m/z 439.04737), the ammonium adduct of
2 (m/z 456), and the sodium cation adduct of 2 (m/z 461). B) The spec-
trum shows the signals of 18 (m/z 124.04263), protonated 2 (m/z 439),
and the adduct of 2 and 18 (m/z 562).
m/z 124.04245; found: 124.04263)and
52.07375; found: 152.07367).
22 (calcd: m/z
A
H
R
U
G
1
Conclusion
were structurally characterized by single-crystal X-ray dif-
fraction. According to these studies, the silicon-coordination
polyhedra are best described as distorted trigonal bipyra-
mids, with Berry distortions ranging from 14.5 to 42.7%. As
shown by multinuclear NMR studies, 1–8 exist in solution as
well (solvent: dimethyl sulfoxide (DMSO)).
Upon dissolution in water, the zwitterionic l Si,l Si’-disili-
cates 1–8 undergo hydrolysis to give (R,R)-tartaric acid and
the respective [(ammonio)organyl]silanetriols (17–24). How-
ever, some of these pentacoordinate silicon compounds (1–
3)display remarkable stability in aqueous solution at 20 8C
and hydrolyze very slowly (35–45% hydrolysis after 300 h).
Structure–reactivity studies (kinetic NMR-spectroscopic in-
vestigations)demonstrated that the presence of both
With the syntheses of compounds 2–8, derivatives of (D,D)-
1
2
3
4
bis[(ammonio)methyl]bis[m-(R,R)-tartrato(4ꢀ)-O ,O :O
UG
RN
UG
AH
,O ]-
A
C
H
T
R
E
U
N
G
disilicate (1; herein resynthesized by using a modified proce-
A
C
H
T
R
E
U
N
G
[3]
5
5
dure), a series of new zwitterionic spirocyclic l Si,l Si’-disi-
licates with two SiO C skeletons have been prepared. These
optically active binuclear silicon(IV)complexes contain two
4
5
5
bridging tetradentate (R,R)-tartrato(4ꢀ)ligands and one
(
ammonio)alkyl group bound to each of the two silicon co-
ordination centers. The absolute configuration of the (R,R)-
tartrato(4ꢀ)ligands controls the absolute stereochemistry at
the two silicon atoms (each with a D configuration)of com-
pounds 1–8, which were all obtained as diastereomerically
and enantiomerically pure products. Compounds 2·6H O,
2
3
·2CH CN, 4·5/2CH CN, 6·MeOH, 7, and 8·CH OH·CH CN
SiCH N moieties and NH groups favors hydrolytic stability.
3
3
3
3
2
4626
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630

5
5
Zwitterionic l Si,l Si’-Disilicates
FULL PAPER
2
9
Most surprisingly, the [(ammonio)organyl]silanetriols re-
sulting from the hydrolysis of 1–8, the cationic species 17–
4, display remarkable stability in aqueous solution. The for-
mation of small amounts of silsesquioxanes (formed by the
condensation of 17–24)cannot be totally ruled out, but
under the experimental conditions used no condensation
products could be detected by NMR-spectroscopic and ESI
mass spectrometric studies. Aqueous solutions of 1–8 (c=
(SiCH
91.8 ppm; H NMR (D
6.6 Hz, 4H; SiCH N), 4.59 ppm (s, 4H; CH); C NMR (D
6.8 (SiCH N), 75.2 (CH), 175.7 ppm (C=O); Si NMR (D
2 6
N), 75.1 (CH), 173.0 ppm (C=O); Si NMR ([D ]DMSO): d=
1
2
ACHTREUNG
ꢀ
2
O): d=2.45 and 2.49 (AB system,
J
(H,H)=
O): d=
O): d=
2
N), 75.9 (3C) and
1
3
1
2
A
H
B
2
2
2
9
2
2
13
ꢀ
89.9 ppm; C VACP/MAS NMR: d=29.1 (SiCH
76.8 (1C)(CH ,) 172.5, 175.8, 177.2, and 178.1 ppm (C =O); N VACP/
1
5
2
9
MAS NMR: d=ꢀ347.0, ꢀ345.3 ppm; Si VACP/MAS NMR: d=ꢀ91.7,
90.1 ppm; elemental analysis calcd (%)for C 10 (410.40): C
9.27, H 3.44, N 6.83; found: C 29.0, H 3.6, N 6.7.
(D,D)-Bis[(methylammonio)methyl]bis[m-
(R,R)-tartrato(4ꢀ)-O ,O :
disilicate (2): Compound 10 (661 mg, 4.00 mmol)was added at 20 8C
to a stirred solution of (R,R)-tartaric acid (600 mg, 4.00 mmol) in water
(50 mL). The reaction mixture was stirred at 208C for 10 min and then
kept undisturbed at 208C for eight days (slow evaporation of the water).
The resulting precipitate was isolated by filtration, washed with cold
methanol (48C; 3”10 mL), and dried in vacuo (0.01 mbar, 808C, 5 h)to
give 2 (635 mg, 1.45 mmol; 72% yield)as a colorless solid. M.p. >3508C
ꢀ
14 2 2
H N O12Si
2
1
2
3
A
H
R
U
G
A
H
R
U
A
C
H
T
R
E
U
N
G
O ,-
1
0 mm)did not undergo gel formation at 20 8C over six
months.
The high hydrolytic stability of some of the zwitterionic
4
ACHTREUNG
A
H
R
U
G
5
5
l Si,l Si’-disilicates is one of the most remarkable results re-
ported herein, thus demonstrating the existence of optically
active, configurationally stable pentacoordinate silicon(IV)
complexes in aqueous solution, with a large window of time
for further experiments with these solutions. The second
most remarkable finding is the high stability of the [(ammo-
nio)organyl]silanetriols 17–24 in aqueous solution at 208C.
Future studies are needed to evaluate the potential of these
results for practical applications.
20
1
(
6
decomp); [a]D =+63.1 (c=0.5, DMSO); H NMR ([D ]DMSO): d=
2.21–2.36 (m, 4H; SiCH N), 2.41–2.46 (m, 6H; NCH ), 4.16 (s, 4H; CH),
2
3
1
3
7
.59–7.85 ppm (m, 4H; NH); C NMR ([D
9.4 (SiCH
6
3
]DMSO): d=36.0 (NCH ),
2
9
3
2
6
N), 75.1 (CH), 172.8 ppm (C=O); Si NMR ([D ]DMSO):
1
2
ACHTREUNG
d=ꢀ93.0 ppm; H NMR (D
6.2 Hz, 4H; SiCH N), 2.56 (s, 6H; NCH
O): d=35.8 (NCH ), 38.2 (SiCH
C=O); Si NMR (D
O): d=ꢀ91.4 ppm; C VACP/MAS NMR: d=
8.0, 39.9, 42.0, and 43.2 (NCH , SiCH N), 75.3 (2C), 76.3 (1C), and 77.1
1C)(CH ,) 173.9, 174.2, 174.7, and 176.8 ppm (C =O); N VACP/MAS
2
O): d=2.51 and 2.60 (AB system, J
), 4.60 ppm (s, 4H; CH);
N), 75.2 (CH), 175.5 ppm
(H,H)=
1
A
H
B
3
13
C NMR (D
2
3
2
2
9
13
(
2
3
(
3
2
1
5
Experimental Section
2
9
NMR: d=ꢀ345.7 ppm; Si VACP/MAS NMR: d=ꢀ94.8, ꢀ91.8 ppm; el-
emental analysis calcd (%)for C 12 (438.45): C 32.87, H 4.14,
N 6.39; found: C 32.8, H 4.2, N 6.3.
(D,D)-Bis[(dimethylammonio)methyl]bis[m-
18 2 2
H N O12Si
General procedures: All syntheses were carried out under dry argon. The
organic solvents were dried and purified according to standard proce-
dures and stored under nitrogen. The melting points were determined
with a Büchi Melting Point B-540 apparatus using samples in sealed ca-
pillaries. Compounds 10–12 and 16 were prepared according to proce-
dures given in refs. [4–7]. Compound 13 was purchased from ABCR. The
1
2
A
H
R
U
G
ACHTREUNG
3
4
ACHTREUNG
A
H
R
U
G
A
H
R
U
G
2
mixture of acetonitrile (15 mL)and methanol (30 mL ). The reaction mix-
ture was stirred at 208C for 10 min and kept undisturbed at 208C for six
days. The resulting precipitate was isolated by filtration, washed with
methanol (2”3 mL), and dried in vacuo (0.01 mbar, 408C, 8 h)to give
(209 mg, 448 mmol; 90% yield)as colorless solid. M.p. >3908C
1
13
29
solution H, C, and Si NMR spectra were recorded at 238C on a
1
13
29
Bruker DRX-300 ( H: 300.1 MHz; C: 75.5 MHz; Si: 59.6 MHz; 5, 9,
and 15), Bruker Avance 400 ( H: 400.1 MHz; C: 100.6 MHz; Si:
9.5 MHz; 14), or Bruker Avance 500 NMR spectrometer ( H:
00.1 MHz; C: 125.8 MHz; Si: 99.4 MHz; 1–4, 6·CH
1
13
29
3
1
a
7
5
8
2
0
1
1
3
2
9
(decomp); [a]
.46–2.54 (m, 2H; SiCH
2.80 (m, 6H; NCH ), 4.19 (s, 4H; CH), 8.2 ppm (brs, 2H; NH);
]DMSO): d=45.2 and 46.8 (NCH ), 49.8 (SiCH N), 75.0
D
=+42.1 (c=0.5, DMSO); H NMR ([D
6
]DMSO): d=
3
OH, 7, and
2
2
N), 2.60–2.67 (m, 8H; SiCH N, NCH
2
3
), 2.73–
·CH OH·CH CN)using C , [D ]DMSO, or D O as the solvent. Chem-
3
3
6
D
6
6
2
1
3
ical shifts (ppm)were determined relative to internal C
6
HD
5
( H: d=
1
3
1
1
C NMR ([D
(CH), 172.7 ppm (C=O);
6
3
2
7
.28 ppm, C
d=4.70 ppm, D
d=39.5 ppm, [D
6
D
6
) , [D
5
]DMSO ( H: d=2.49 ppm, [D
6
]DMSO), HDO ( H:
2
9
1
3
13
Si NMR ([D
O): d=2.71 and 2.86 (AB system,
SiCH H N), 2.75 (s, 6H; NCH ), 2.84 (s, 6H; NCH ), 4.63 ppm (s, 4H;
A B 3 3
2 3 3 2
CH); C NMR (D O): d=45.7 (NCH ), 47.2 (NCH ), 49.0 (SiCH N),
6
]DMSO): d=ꢀ94.2 ppm;
2
6 6 6 6 6
O), C D ( C: d=128.0 ppm, C D ) , [D]DMSO ( C:
1
2
1
3
H NMR (D
2
J(H,H)=16.1 Hz, 4H;
A
T
E
N
6
]DMSO), or external tetramethylsilane (TMS) ( C: d=
O; Si: d=0 ppm, C
C NMR data was supported by DEPT 135, C, H HMQC, and C, H
HMBC experiments. Solid-state C, N, and Si VACP/MAS NMR
2
9
0
ppm, D
2
6
D
6
, [D
6
]DMSO, D
2
1
O). Assignment of the
1
3
1
3
13
13
1
2
9
13
1
3
15
29
75.2 (CH), 175.4 ppm (C=O); Si NMR (D O): d=ꢀ92.6 ppm;
C
2
VACP/MAS NMR: d=47.4 (2C), 48.2 (1C), 50.0 (1C), 52.0 (1C), and
spectra were recorded at 228C on a Bruker DSX-400 NMR spectrometer
5
4.8 (1C)(NCH
172.8, and 173.4 ppm (C=O); N VACP/MAS NMR: d=ꢀ340.0 ppm;
Si VACP/MAS NMR: d=ꢀ97.1, ꢀ93.7 ppm; elemental analysis calcd
(%)for C H N O Si (466.51): C 36.05, H 4.75, N 6.00; found: C 35.8,
3 2
, SiCH N), 74.4, 75.6, 76.2, and 77.5 (CH), 171.3, 172.3,
2
with bottom-layer rotors of ZrO (diameter: 7 mm)containing approxi-
1
5
1
3
15
29
mately 50 mg of sample ( C: 100.6 MHz; N: 40.6 MHz; Si: 79.5 MHz;
2
9
1
3
29
15
external standard TMS ( C, Si: d=0 ppm)or glycine
342.0 ppm); contact time: 1 ms ( C), 3 ms ( N), or 5 ms ( Si); 908 H
(
N: d=
1
3
15
29
1
ꢀ
14 22
2
12
2
H 4.5, N 6.0.
transmitter pulse length: 3.6 ms; repetition time: 4 s). Optical rotations
were measured at 208C with a JASCO polarimeter P-1030; DMSO was
the solvent.
1
2
A
H
R
U
G
ACHTREUNG
3
4
ACHTREUNG
A
H
R
U
G
A
H
R
U
G
1
2
3
4
A
C
H
T
R
E
U
N
G
(D,D)-Bis
silicate (1): Compound 9 (151 mg, 998 mmol)was added in one single por-
tion at 208C to stirred solution of (R,R)-tartaric acid (150 mg,
99 mmol)in a mixture of acetonitrile (10 mL)and methanol (10 mL.)
A
C
H
T
R
E
U
N
G
[(ammonio)methyl]bis[m-
A
H
R
U
G
ACHTREUNG
di-
208C to a stirred solution of (R,R)-tartaric acid (150 mg, 999 mmol)in a
mixture of acetonitrile (40 mL)and methanol (40 mL ). The reaction mix-
ture was stirred at 208C for 10 min and kept undisturbed at 208C for
three days. The resulting precipitate was isolated by filtration, washed
with methanol (2”5 mL), and dried in vacuo (0.01 mbar, 208C, 6 h)to
give 4 (195 mg, 394 mmol; 79% yield)as a colorless solid. M.p. >3608C
ACHTREUNG
a
9
The reaction mixture was stirred at 208C for 10 min and kept undistur-
bed at 208C for 10 days. After the addition of water (20 mL), the reaction
mixture was stirred under reflux for 1 h and kept undisturbed at 208C for
two days. The resulting precipitate was isolated by filtration, washed with
cold methanol (48C; 3”5 mL), and dried in vacuo (0.01 mbar, 808C, 5 h)
to give 1 in (162 mg, 395 mmol; 79% yield)as a colorless solid. M.p.
2
D
0
1
(decomp); [a]
0.83–0.95 (m, 4H; SiCH
CCH N), 4.08 (s, 4H; CH), 8.7 ppm (brs, 2H; NH); C NMR
([D ]DMSO): d=14.1 (SiCH C), 41.2 (NCH ), 55.5 (CCH N), 75.0 (CH),
172.9 ppm (C=O); Si NMR ([D
]DMSO): d=ꢀ87.3 ppm; C VACP/
MAS NMR (data for two crystallographically independent zwitterions):
=+7.7 (c=0.5, DMSO); H NMR ([D
6
]DMSO): d=
2
C), 2.68 (s, 12H; NCH ), 2.89–2.98 (m, 4H;
3
1
3
2
6
2
3
2
2
D
0
1
29
13
>
3908C (decomp) ; a[ ] =+90.0 (c=0.5, DMSO); H NMR ([D
6
]DMSO):
N), 4.15
]DMSO): d=27.8
6
2
d=2.08 and 2.13 (AB system,
s, 4H; CH), 7.1 ppm (brs, 6H; NH); C NMR ([D
A
H
R
U
G
A B
J(H,H)=16.0 Hz, 4H; SiCH H
1
3
(
6
d=12.3–17.6 (SiCH
2
C), 39.4–48.7 (NCH
3
), 53.5–59.3 (CCH
2
N), 75.9 (4C)
Chem. Eur. J. 2008, 14, 4618 – 4630
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4627

R. Tacke et al.
1
5
and 76.3 (4C)(CH,) 171.7–179.8 ppm (C =O); N VACP/MAS NMR
SiCH
7.27 (m, 2H; NCHCHNCH
(D O): d=35.5 (NCHCHNCH
123.3 (NCHCHNCH , NCHCHNCH
3
A B 3
H N), 4.53 (s, 4H; CH), 7.18–7.20 (m, 2H; NCHCHNCH ), 7.25–
1
3
(
ꢀ
data for two crystallographically independent zwitterions): d=ꢀ333.3,
3
), 8.42–8.44 ppm (m, 2H; NCHN); C NMR
), 39.6 (SiCH N), 75.0 (CH), 123.2 and
), 135.9 (NCHN), 175.2 ppm (C=
2
9
332.6, ꢀ331.3, and ꢀ329.1 ppm; Si VACP/MAS NMR (data for two
2
3
2
crystallographically independent zwitterions): d=ꢀ85.5 ppm; elemental
3
2
9
13
analysis calcd (%)for C 16
found: C 38.8, H 5.4, N 5.7.
(D,D)-Bis[3-(dimethylammonio)propyl]bis[m-
H
26
N
2
O
12Si
2
(494.56): C 38.86, H 5.30, N 5.66;
O); Si NMR (D
two crystallographically independent zwitterions): d=35.1 (1C), 36.8
(3C), 38.9 (2C), and 40.4 (2C) (NCHCHNCH , SiCH N), 75.4 (1C) and
2
O): d=ꢀ91.8 ppm; C VACP/MAS NMR (data for
1
2
A
C
H
T
R
E
U
N
G
A
H
R
U
G
3
2
3
4
3
76.3 (7C)(CH,) 121.6–127.8 (N CHCHNCH3, NCHCHNCH ), 134.5
A
C
H
T
R
E
U
N
G
O ,
A
C
H
T
R
E
U
N
G
O ]
A
C
H
T
R
E
U
N
G
(
(
1C), 136.0 (2C), and 136.9 (1C) (NCHN), 172.1 (2C), 174.4 (2C), 176.0
1C), 176.5 (1C), 177.3 (1C), and 178.8 (1C) ppm (C=O); N VACP/
2
1
5
mixture of acetonitrile (40 mL)and methanol (40 mL ). The reaction mix-
ture was stirred at 208C for 10 min and kept undisturbed at 208C for
2 days. The resulting precipitate was isolated by filtration, washed with
methanol (5 mL), and dried in vacuo (0.01 mbar, 208C, 6 h)to give
MAS NMR (data for two crystallographically independent zwitterions):
d=ꢀ205.9 (3N), ꢀ204.8 (1N), ꢀ200.2 (1N), ꢀ197.4 (1N), ꢀ196.0 (1N),
1
2
9
and ꢀ192.7 (1N)ppm ( NCHCHNCH
3 3
, NCHCHNCH ); Si VACP/MAS
5
NMR (data for two crystallographically independent zwitterions): d=
ꢀ91.5 (1Si), ꢀ90.1 (3Si)ppm; elemental analysis calcd (%) for
(
(
751 mg, 1.44 mmol; 96% yield)as
a
colorless solid. M.p. >3308C
]DMSO): d=0.39–0.48 (m, 4H; SiCH C), 1.45–
C), 2.69 (s, 12H; NCH ), 2.84–2.99 (m, 4H; CCH N),
.05 (s, 4H; CH), 9.1 ppm (brs, 2H; NH); C NMR ([D ]DMSO): d=
4.7 (SiCH C), 19.8 (CCH C), 42.3 (NCH ), 59.6 (CCH N), 75.1 (CH),
73.4 ppm (C=O); Si NMR ([D
]DMSO): d=ꢀ84.0 ppm; C and
1
decomp); H NMR ([D
6
2
18 20 4 2
C H N O12Si (540.55): C 40.00, H 3.73, N 10.36; found: C 40.0, H 3.8,
1
4
1
1
.60 (m, 4H; CCH
2
3
2
1
3
N 10.4.
6
1
2
2
2
3
2
A
T
U
G
ACHTREUNG
2
9
13
15
3
4
ACHTREUNG
6
N
A
H
R
U
G
disilicate·acetonitrile·methanol (8·CH
3
3
VACP/MAS NMR: only poorly resolved spectra were obtained due to
(241 mg, 998 mmol)was added at 20 8C to a stirred solution of (R,R)-tar-
taric acid (150 mg, 999 mmol)in a mixture of acetonitrile (5 mL)and
methanol (15 mL). The reaction mixture was stirred at 208C for 5 min
and kept undisturbed at 208C for eight days. The resulting precipitate
was isolated by filtration, washed with methanol (2”5 mL), and dried in
2
9
the amorphous nature of the sample material; Si VACP/MAS NMR:
d=ꢀ83.2, ꢀ82.4 ppm; elemental analysis calcd (%)for C 18
522.61): C 41.37, H 5.79, N 5.36; found: C 40.1, H 5.8, N 5.3.
30 2 2
H N O12Si
(
1
2
3
4
A
C
H
T
R
E
U
N
G
(D,D)-Bis[m-
thyl]disilicate·methanol (6·CH
.25 mmol)in acetonitrile (20 mL)was added at 20 8C under the exclu-
sion of light to stirred solution of (R,R)-tartaric acid (188 mg,
.25 mmol)in a mixture of acetonitrile (5 mL)and methanol (15 mL.)
A
C
H
T
R
E
U
N
G
(R,R)-tartrato(4ꢀ)-O ,O :O ,O ]bis[(trimethyl
A
H
R
U
G
A
H
R
U
monio)
A
H
R
U
G
a stream of argon gas (208C, 1 h)to give 8·CH
3 3
OH·CH CN (290 mg,
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
3
OH): solution of 14 (402 mg,
A
4
37 mmol; 88% yield)as a colorless solid. M.p. >2508C (decomp);
1
2
0
13
[
a] =ꢀ11.4 (c=0.5, DMSO); C VACP/MAS NMR: d=1.4 (CH
3
CN),
a
D
4
3 3
4.3 (CH OH), 49.8 (NCH ), 75.6 (2C)and 76.5 (2C)(CH ), 120.8 (2C ),
1
1
30.9 (2C), 133.2 (2C), 137.8 (2C), 146.1 (2C), and 147.8 (2C) (C
6
H
4
),
The reaction mixture was stirred at 208C for 30 min and kept undistur-
bed at 208C for 10 days under the exclusion of light. The resulting precip-
itate was isolated by filtration, washed with cold methanol (48C; 1 mL),
and dried in a stream of argon gas (208C, 2 h)to give 6·CH OH
3
78.0 mg, 148 mmol; 24% yield)as a colorless solid. M.p. >4008C; [a] =
1
5
1
69.1, 170.0, 173.2, and 174.6 ppm (C=O); N VACP/MAS NMR: d=
2
9
ꢀ
324.6, ꢀ321.4 ppm (CH
3
CN not detected); Si VACP/MAS NMR: d=
OH·CH CN in [D ]DMSO
ꢀ
97.9, ꢀ96.2 ppm. Upon dissolution of 8·CH
3
3
6
ꢀ
1
2
D
0
(35 mgmL ), the existence of three species (8a–c)was observed, with a
(
+
1
1
molar
equilibrium
ratio
8a/8b/8c=0.84:0.08:0.08;
H NMR
76.3 (c=0.5, DMSO); H NMR ([D
6
]DMSO): d=2.94 (s, 4H;
(H,H)=5.3 Hz, 3H; CH OH),
OH), 4.25 ppm (s, 4H; CH); C NMR
OH), 55.3 (NCH ), 60.0 (SiCH N), 74.7
]DMSO): d=ꢀ95.7 ppm;
O): d=3.05 and 3.06 (AB system, (H,H)=15.4 Hz, 4H;
N), 3.07 (s, 18H; NCH ), 3.25 (s, 3H; CH OH), 4.65 ppm (s,
O): d=48.8 (CH OH), 56.4 (t,
(C,N)=2.3 Hz; SiCH N), 74.9 (CH), 174.9 ppm (C=O);
3
([D ]DMSO): 8a: d=2.06 (s, 3H; CH CN), 3.16 (s, 3H; CH OH), 3.34
SiCH
4
(
(
2
N), 3.04 (s, 18H; NCH
3
), 3.16 (d,
(H,H)=5.3 Hz, 1H; CH
]DMSO): d=48.6 (CH
J
A
H
R
U
G
3
6
3
3
3
13
3
(brs, 12H; NCH ), 4.39 (s, 4H; CH), 7.42–7.49, 7.53–7.58, 7.69–7.75, and
.08 (q, J
[D
CH), 172.2 ppm (C=O);
A
C
H
T
R
E
U
N
G
3
1
3
7
.77–7.84 (m, 8H; SiC
6 4
H N), 9.2 ppm (brs, 2H, NH); C NMR
6
3
3
2
2
9
([D ]DMSO): 8a: d=1.14 (CH CN), 46.3 and 47.7 (NCH ), 48.6
Si NMR ([D
6
6
3
3
1
2
(CH OH), 75.2 (CH), 119.6, 128.6, and 130.4 (C H ), 134.5 (C1, C H ),
H NMR (D
SiCH
H; CH); C NMR (D
2
J
A
H
R
U
G
3
6
4
6
4
2
9
1
36.0 (C
6
H
4
), 146.4 (C2,
C
6
H
4
), 171.3 ppm (C=O);
Si NMR
A
H
B
3
3
1
3
1
([D ]DMSO): 8a: d=ꢀ97.1 ppm; 8b: d=ꢀ97.5 ppm; 8c: d=
4
2
3
J
A
T
E
N
(C,N)=3.7 Hz;
6
1
ꢀ106.0 ppm; elemental analysis calcd (%)for C H N O Si (663.74): C
NCH
3
), 59.7 (t, J
Si NMR (D
O): d=ꢀ94.0 ppm;
CH OH), 57.0 (NCH ), 59.5 and 62.9 (SiCH
CH), 174.4 (2C) and 175.0 (2C) ppm (C=O); N VACP/MAS NMR:
A
C
H
T
R
E
U
N
G
2
27 33
3
13
2
2
9
13
48.86, H 5.01, N 6.33; found: C 48.6, H 4.8, N 6.4.
2
C
VACP/MAS NMR: d=50.1
N), 75.7 (2C) and 76.2 (2C)
(
(
3
3
2
(Aminomethyl)trimethoxysilane (9): A mixture of (chloromethyl)trime-
thoxysilane (17.4 g, 102 mmol)and ammonia (86.8 g, 5.10 mol)was
heated in an autoclave at 1008C/65 bar for 6 h. The reaction mixture was
allowed to cool to 208C and then stirred at this temperature for a further
13 h in the autoclave. The excess of ammonia was evaporated, and n-pen-
tane (300 mL)was added to the residue. The resulting precipitate was fil-
tered off, washed with n-pentane (3”100 mL), and then discarded. The
solvent was removed from the filtrate under reduced pressure, and the
1
5
2
9
d=ꢀ329.1, ꢀ328.4 ppm; Si VACP/MAS NMR: d=ꢀ94.5, ꢀ92.3 ppm;
elemental analysis calcd (%)for C 17
.74, N 5.32; found: C 38.6, H 5.7, N 5.4.
(D,D)-Bis[3-(1-methylimidazolio)methyl]bis[m-
H
30
N
2
O
13Si
2
(526.60): C 38.77, H
5
1
A
C
H
T
R
E
U
N
G
A
H
R
U
G
2
3
4
ACHTREUNG
A
C
H
T
R
E
U
N
G
O :
A
C
H
T
R
E
U
N
G
O ,O ]disilicate (7): A solution of 15 (344 mg, 999 mmol)in acetoni-
A
C
H
T
R
E
U
N
G
trile (10 mL)was added at 20 8C under the exclusion of light to a stirred
solution of (R,R)-tartaric acid (150 mg, 999 mmol)in a mixture of acetoni-
trile (10 mL)and methanol (10 mL ). The reaction mixture was stirred at
residue was distilled in vacuo (Vigreux column)to give 9 (4.88 g,
1
3
2.3 mmol; 32% yield)as a colorless liquid. B.p. 83 8C/19 mbar; H NMR
(
C
6
D
6
): d=0.7 (brs, 2H; NH
2
), 2.34 (s, 2H; SiCH
): d=25.2 (SiCH N), 50.5 ppm (OCH
): d=ꢀ46.9 ppm; elemental analysis calcd (%)for
4 3
C H13NO Si (151.24): C 31.77, H 8.66, N 9.26; found: C 31.6, H 8.6, N
2
N), 3.60 ppm (s, 9H;
2
08C for 5 min and kept undisturbed at 208C for four days under the ex-
1
3
29
OCH
NMR (C
3
); C NMR (C
6
D
6
2
3
); Si
clusion of light. The resulting precipitate was isolated by filtration and
dissolved in hot water (608C; 20 mL), and the solution was cooled slowly
to 48C and kept undisturbed at this temperature for four days. The re-
sulting precipitate was isolated by filtration, washed with cold water
6
D
6
8
.9.
(
4
48C; 5 mL), and dried in vacuo (0.01 mbar, 408C, 3 h)to give 7 (256 mg,
Trimethyl[(trimethoxysilyl)methyl]ammonium iodide (14): (Compound
2
0
[11]
74 mmol; 95% yield)as a colorless solid. M.p. >4008C; [a] =+13.4
14 has already been reported as an intermediate,
characterized.)Iodomethane (19.3 g, 136 mmol)was added at 20
but has not been
8C
D
1
(
c=0.5, DMSO); H NMR ([D
6
]DMSO): d=3.69 and 3.71 (AB system,
N), 3.77 (s, 6H; NCHCHNCH ), 4.17 (s,
H; CH), 7.41–7.43 (m, 2H; NCHCHNCH ), 7.53–7.54 (m, 2H;
NCHCHNCH ), 8.80–8.82 ppm (m, 2H;
]DMSO): d=35.3 (NCHCHNCH ), 40.7 (SiCH
NCHCHNCH ), 123.7 (NCHCHNCH ), 135.9 (NCHN), 172.5 ppm (C=
2
J
A
C
H
T
R
E
U
N
G
(H,H)=16.0 Hz, 4H; SiCH
A
H
B
3
within 30 min to a stirred solution of 11 (4.07 g, 22.7 mmol)in acetonitrile
(100 mL)under the exclusion of light, and the resulting mixture was
stirred under reflux for 2 h (exclusion of light). The reaction mixture was
allowed to cool to 208C and stirred at this temperature for a further 18 h.
The solvent and excess iodomethane were removed under reduced pres-
sure, and the residue was washed successively with cold acetonitrile
(48C; 5 mL)and diethyl ether (40 mL)and dried in vacuo (0.01 mbar,
4
3
1
3
3
NCHN);
C NMR
(
(
[D
6
3
2
N), 74.9 (CH), 122.6
3
3
2
9
1
O); Si NMR ([D
6
6
]DMSO): d=ꢀ94.0 ppm; H NMR (D
2
O): d=3.75 (s,
J(H,H)=16.4 Hz, 4H;
2
H; NCHCHNCH
3
), 3.83 and 3.90 (AB system,
A
H
R
U
G
4628
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630

5
5
Zwitterionic l Si,l Si’-Disilicates
FULL PAPER
4
08C, 4 h)to give 14 (6.69 g, 20.8 mmol; 92% yield)as a pale yellow
HRMS–ESI-MS studies carried out by Dr. M. Büchner (Institut für Or-
ganische Chemie, Universität Würzburg)is gratefully appreciated.
1
solid. M.p. 1258C; H NMR ([D
s, 2H; SiCH N), 3.59 ppm (s, 9H; OCH
0.9 (OCH ), 51.7 (SiCH N), 55.9 ppm (NCH
6
]DMSO): d=3.14 (s, 9H; NCH
3
), 3.23
]DMSO): d=
); Si NMR ([D ]DMSO):
Si (321.23): C
1
3
(
5
2
3 6
); C NMR ([D
2
9
3
2
3
6
d=ꢀ56.1 ppm; elemental analysis calcd (%)for C
7 3
H20INO
[
1] For selected reviews, see: a)R. R. Holmes, Chem. Rev. 1996, 96,
27–950; b)D. Kost, I. Kalikhman in The Chemistry of Organic Sili-
2
6.17, H 6.28, N 4.36; found: C 25.8, H 6.0, N 4.3.
9
1
-Methyl-3-[(trimethoxysilyl)methyl]imidazolium iodide (15): (Iodome-
con Compounds, Vol. 2, Part 2 (Eds: Z. Rappoport, Y. Apeloig),
Wiley, Chichester, 1998, pp. 1339–1445; c)V. Pestunovich, S. Kirpi-
chenko, M. Voronkov in The Chemistry of Organic Silicon Com-
pounds, Vol. 2, Part 2 (Eds: Z. Rappoport, Y. Apeloig), Wiley, Chi-
chester, 1998, pp. 1447–1537; d)C. Chuit, R. J. P. Corriu, C. Reye in
Chemistry of Hypervalent Compounds (Ed.: K.-y. Akiba), Wiley-
VCH, New York, 1999, pp. 81–146; e)R. Tacke, M. Pülm, B.
Wagner, Adv. Organomet. Chem. 1999, 44, 221–273; f)M. A. Brook,
Silicon in Organic, Organometallic, and Polymer Chemistry, Wiley,
New York, 2000, pp. 97–114; g)R. Tacke, O. Seiler in Silicon
Chemistry: From the Atom to Extended Systems (Eds: P. Jutzi, U.
Schubert), Wiley-VCH, Weinheim, 2003, pp. 324–337; h)D. Kost, I.
Kalikhman, Adv. Organomet. Chem. 2004, 50, 1–106.
[
6]
thyl)trimethoxysilane (7.86 g, 30.0 mmol)was added at 20 8C to a stirred
solution of 1-methylimidazole (2.46 g, 30.0 mmol)in cyclohexane
(
30 mL). The resulting mixture was stirred at 808C for 21 h under the ex-
clusion of light and then cooled to 208C. The lower layer of the resulting
two-phase system was separated with a syringe, washed with cyclohexane
(
5”20 mL)and dried in vacuo (0.01 mbar, 50 8C, 8 h)to give 15 (7.26 g,
1
2
(
(
8
3
1
1.1 mmol; 70% yield)as a pale yellow solid. M.p. 57 8C; H NMR
[D ]DMSO): d=3.53 (s, 9H; OCH ), 3.86 (s, 3H; NCHCHNCH ), 4.03
s, 2H; SiCH N), 7.53–7.58 and 7.68–7.72 (m, 2H; NCHCHNCH ), 8.93–
]DMSO): d=33.7 (SiCH N),
), 123.5 and 123.7 (NCHCHNCH ),
]DMSO): d=ꢀ54.8 ppm; elemental
6
3
3
2
3
1
3
.96 ppm (m, 1H; NCHN); C NMR ([D
6
2
5.8 (NCHCHNNCH
36.3 ppm (NCHN); Si NMR ([D
3
2
), 50.8 (OCH
3
3
9
6
analysis calcd (%)for C
8 2 3
H17IN O Si (344.22): C 27.91, H 4.98, N 8.14;
[
2] For selected recent reports, see: a)R. Tacke, R. Bertermann, C.
Burschka, S. Dragota, M. Penka, I. Richter, J. Am. Chem. Soc. 2004,
126, 14493–14505; b)N. Kano, M. Yamamura, T. Kawashima, J.
Am. Chem. Soc. 2004, 126, 6250–6251; c)E. P. A. Couzijn, M. Scha-
kel, F. J. J. de Kanter, A. W. Ehlers, M. Lutz, A. L. Spek, K. Lam-
mertsma, Angew. Chem. 2004, 116, 3522–3524; Angew. Chem. Int.
Ed. 2004, 43, 3440–3442; d)O. Seiler, C. Burschka, D. Schwahn, R.
Tacke, Inorg. Chem. 2005, 44, 2318–2325; e)C. Xu, T. H. Baum,
A. R. Rheingold, Inorg. Chem. 2004, 43, 1568–1573; f)O. Seiler, C.
Burschka, S. Metz, M. Penka, R. Tacke, Chem. Eur. J. 2005, 11,
7379–7386; g)R. Tacke, R. Bertermann, C. Burschka, S. Dragota,
Angew. Chem. 2005, 117, 5426–5429; Angew. Chem. Int. Ed. 2005,
44, 5292–5295; h)J. Wagler, U. Bçhme, E. Brendler, G. Roewer, Or-
ganometallics 2005, 24, 1348–1350; i)X. Kästele, P. Klüfers, F. Kopp,
J. Schuhmacher, M. Vogt, Chem. Eur. J. 2005, 11, 6326–6346; j)M.
Schley, J. Wagler, G. Roewer, Z. Anorg. Allg. Chem. 2005, 631,
2914–2918; k)X. Kästele, P. Klüfers, R. Tacke, Angew. Chem. 2006,
118, 3286–3288; Angew. Chem. Int. Ed. 2006, 45, 3212–3214; l)J.
Wagler, D. Gerlach, U. Bçhme, G. Roewer, Organometallics 2006,
25, 2929–2933; m)H. M. Anula, J. C. Berlin, H. Wu, Y.-S. Li, X.
Peng, M. E. Kenney, M. A. J. Rodgers, J. Phys. Chem. A 2006, 110,
found: C 27.5, H 4.7, N 8.4.
ESI-MS studies: Aqueous solutions of 1–8 were prepared by dissolving
the test compounds (2 mg)in water (2 mL; HPLC gradient grade
(
Acros)). The ESI-MS measurements were performed with a Finnigan
MAT triple-stage quadrupole TSQ 7000 mass spectrometer with an ESI
interface, using Finnigan Xcalibur 1.2 software. Nitrogen served as the
sheath gas. The electrospray ionization parameters were as follows: tem-
perature of the heated capillary: 2208C; electrospray capillary voltage:
4
.0 kV; sheath gas: 70 psi (1 psi=6894.74 Pa). For the measurements, the
sample solutions were continuously delivered at flow rate of
0 mLmin with a syringe-pump system (Harvard apparatus, No. 22,
South Natick, MA). Positive ions were detected by scanning from 100 to
a
ꢀ
1
2
7
1
00 u with a total scan duration of 1.0 s; 60 scans were collected within
min. The multiplier voltage was set to 1.6 kV.
HRMS–ESI-MS studies: Aqueous solutions of 2 and 6 were prepared by
dissolving the test compounds (2 mg)in water (2 mL; HPLC gradient
grade (Acros)). The samples were stored for 20 h at 208C and then dilut-
ed with water to a concentration of 2 mm. The ESI-MS measurements
were performed with a Bruker Daltonics micrOTOF focus spectrometer
equipped with an ESI ion source (Apollo).
5
215–5223; n)B. Gostevskii, N. Zamstein, A. A. Korlyukov, Y. I.
Crystal structure analyses: Suitable single crystals of 2·6H
2 3
O, 3·2CH CN,
Baukov, M. Botoshansky, M. Kaftory, N. Kocher, D. Stalke, I. Ka-
likhman, D. Kost, Organometallics 2006, 25, 5416–5423; o)J.
Wagler, Organometallics 2007, 26, 155–159; p)D. Gerlach, E.
4
·5/2CH CN, 6·MeOH, 7, and 8·CH OH·CH CN were isolated directly
3
3
3
from the respective reaction mixtures. Single crystals of 15 were obtained
from a solution of 15 (344 mg)in methanol/diethyl ether (1:2, v/v; 9 mL)
by crystallization at ꢀ208C over 10 days. The crystals were mounted in
an inert oil (perfluoroalkyl ether (ABCR)) on a glass fiber and then
transferred to the stream of cold nitrogen gas in the diffractometer
Brend
q)U. Bçhme, B. Günther, Inorg. Chem. Commun. 2007, 10, 482–
84; r)Y. Liu, S. A. Steiner III, C. W. Spahn, I. A. Guzei, I. S. Toulo-
A
H
R
U
G
4
khonova, R. West, Organometallics 2007, 26, 1306–1307; s)O.
Seiler, C. Burschka, T. Fenske, D. Troegel, R. Tacke, Inorg. Chem.
2
K. Lammertsma, J. Am. Chem. Soc. 2006, 128, 13634–13639; u)J.
Wagler, G. Roewer, Inorg. Chim. Acta 2007, 360, 1717–1724; v)I.
Kalikhman, B. Gostevskii, E. Kertsnus, M. Botoshansky, C. A. Tessi-
er, W. J. Youngs, S. Deuerlein, D. Stalke, D. Kost, Organometallics
(
Bruker Nonius KAPPA APEX II (2·6H
2 3 3
O, 3·2CH CN, 4·5/2CH CN, 7;
Goebel mirror, MoKa radiation, l=0.71073 Š); Stoe IPDS (6·MeOH,
007, 46, 5419–5424; t)E. P. A. Couzijn, A. W. Ehlers, M. Schakel,
8
0
9
3
·MeOH·CH CN, 15; graphite-monochromated MoKa radiation, l=
.71073 Š)). All the structures were solved by direct methods (SHELXS-
2
7)and refined by full-matrix least-squares methods on F for all unique
reflections (SHELXL-97). For the CH hydrogen atoms, a riding model
was employed. CCDC-675290 (2·6H O), CCDC-675291 (3·2CH CN),
CCDC-675292 (4·5/2CH CN), CCDC-675293 (6·MeOH), CCDC-675294
7), CCDC-675295 (8·CH OH·CH CN), and CCDC-675296 (15)contain
2
3
2
007, 26, 2652–2658; w)D. Troegel, C. Burschka, S. Riedel, M.
3
Kaupp, R. Tacke, Angew. Chem. 2007, 119, 7131–7135; Angew.
Chem. Int. Ed. 2007, 46, 7001–7005; x)S. Metz, C. Burschka, D.
Platte, R. Tacke, Angew. Chem. 2007, 119, 7136–7139; Angew.
Chem. Int. Ed. 2007, 46, 7006–7009; y)O. Seiler, C. Burschka, K.
Gçtz, M. Kaupp, S. Metz, R. Tacke, Z. Anorg. Allg. Chem. 2007,
(
3
3
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
[
12]
Centre via www.ccdc.cam.ac.uk/data_request/cif.
6
33, 2667–2670.
3] R. Tacke, M. Mühleisen, P. G. Jones, Angew. Chem. 1994, 106, 1250–
252; Angew. Chem. Int. Ed. Engl. 1994, 33, 1186–1188.
[
[
1
4] R. Tacke, R. Bertermann, A. Biller, O. Dannappel, M. Pülm, R. Wil-
leke, Eur. J. Inorg. Chem. 1999, 795–805.
Acknowledgements
[5] R. Tacke, A. Lopez-Mras, J. Sperlich, C. Strohmann, W. F. Kuhs, G.
Mattern, A. Sebald, Chem. Ber. 1993, 126, 851–861.
Experimental support for the ESI-MS studies carried out by W. Hümmer
[6] M. S. Sorokin, V. A. Lopyrev, N. N. Chipanina, L. V. Sherstyanniko-
va, M. G. Voronkov, Russ. J. Gen. Chem. 2004, 74, 551–558.
(
Lehrstuhl für Lebensmittelchemie, Universität Würzburg)and for the
Chem. Eur. J. 2008, 14, 4618 – 4630
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4629

R. Tacke et al.
[
[
[
7] R. Tacke, R. Bertermann, A. Biller, O. Dannappel, M. Penka, M.
Pülm, R. Willeke, Z. Anorg. Allg. Chem. 2000, 626, 1159–1173.
8] R. Tacke, F. Wiesenberger, A. Lopez-Mras, J. Sperlich, G. Mattern,
Z. Naturforsch. 1992, 47b, 1370–1376.
[10] a)The hydrogen-bonding systems were analyzed by using the
PLATON program system; A. L. Spek, PLATON, University of
Utrecht, Utrecht, The Netherlands, 2003.
[11] R. Tacke, J. Becht, O. Dannappel, R. Ahlrichs, U. Schneider, W. S.
Sheldrick, J. Hahn, F. Kiesgen, Organometallics 1996, 15, 2060–
2077.
[12] Tables of the atomic coordinates and equivalent isotropic displace-
ment parameters, anisotropic displacement parameters, experimen-
tal details of the X-ray diffraction studies, and bond lengths and
9] a)E. L. Muetterties, L. J. Guggenberger, J. Am. Chem. Soc. 1974,
9
1
6, 1748–1756; b)R. R. Holmes, J. A. Deiters, J. Am. Chem. Soc.
977, 99, 3318–3326. c)The degree of distortion was calculated by
using the dihedral angle method described in references [9a,b]; all
nine dihedral angles and the values for the reference geometry of
the ideal square pyramid given in reference [9a] were considered for
this calculation. d)The quantification of the distortion in this form
relates to the transition from the ideal trigonal bipyramid toward
the ideal square pyramid along the reaction coordinate of the Berry
pseudorotation.
2 3 3
angles for 2·6H O, 3·2CH CN, 4·5/2CH CN, 6·MeOH, 7, and
8·CH
3
OH·CH
3
CN, and 15 are available in the Supporting Informa-
tion.
Received: November 26, 2007
Published online: April 2, 2008
4630
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4618 – 4630