Structural features of silatranes and germatranes

Article abstract of DOI:10.1023/B:RUGC.0000025170.06493.f9

In stabilization of the endo configuration of silatranes and germatranes, a major role is played not only by the Si (or Ge) and N atoms, but also by oxygen and other atoms of the atrane core, which is manifested in molecular orbital parameters. Calculation of the system of interacting methyltrimethoxysilane and trimethylamine shows that the energy of the system grows as the distance between the Si and N atoms is decreased from 5 to 2 A. The Si-N interaction in methylsilatrane, according to the calculations and precision X-ray diffraction studies, is the interaction of filled electronic shells and is electrostatic in nature. Analysis of the thermodynamic functions of formation of 1-methyl- and 1-hydroxysilatranes and -germatranes reveals an increase in the enthalpy and the decisive contribution of the entropy factors to stabilization of the reaction products. A ¹H NMR study of ethylgermatrane in aqueous solution revealed its equilibrium with the hydrolyzed form. The transition state in the first step of hydrolysis of methyl- and hydroxysilatranes and -germatranes was studied by methods of quantum chemistry (AM1, PM3; basis sets STO-3G, 6-31G, 6-31G*, 6-31G**; B3LYP method).

Full text of DOI:10.1023/B:RUGC.0000025170.06493.f9

Russian Journal of General Chemistry, Vol. 74, No. 1, 2004, pp. 58 65. Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 1, 2004,
pp. 65 73.
Original Russian Text Copyright
2004 by Chernyshev, Knyazev, Kirin, Vasilev, Alekseev.
Structural Features of Silatranes and Germatranes
E. A. Chernyshev, S. P. Knyazev, V. N. Kirin, I. M. Vasilev, and N. V. Alekseev
Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow, Russia
Received August 1, 2001
Abstract In stabilization of the endo configuration of silatranes and germatranes, a major role is played
not only by the Si (or Ge) and N atoms, but also by oxygen and other atoms of the atrane core, which is
manifested in molecular orbital parameters. Calculation of the system of interacting methyltrimethoxysilane
and trimethylamine shows that the energy of the system grows as the distance between the Si and N atoms is
decreased from 5 to 2 . The Si N interaction in methylsilatrane, according to the calculations and precision
X-ray diffraction studies, is the interaction of filled electronic shells and is electrostatic in nature. Analysis of
the thermodynamic functions of formation of 1-methyl- and 1-hydroxysilatranes and -germatranes reveals an
increase in the enthalpy and the decisive contribution of the entropy factors to stabilization of the reaction
1
products. A H NMR study of ethylgermatrane in aqueous solution revealed its equilibrium with the hydro-
lyzed form. The transition state in the first step of hydrolysis of methyl- and hydroxysilatranes and -ger-
matranes was studied by methods of quantum chemistry (AM1, PM3; basis sets STO-3G, 6-31G, 6-31G*,
6-31G**; B3LYP method).
Among organosilicon and organogermanium com-
pounds, atrane derivatives are of particular interest.
Silatranes and germatranes are ethers of triethanol-
amine and the corresponding organosilanetriols and
organogermanetriols [1 4]. Virtually all the silatranes
and germatranes studied show high biological activity;
plant growth regulators, cosmetics, and drugs (e.g.,
effective immunomodulators) have been developed on
their basis.
Scheme 1.
H
H
H
H
H
H
H
H
H
H
H
N
N
H
H
H
O
H
H
H
H
H
H
H
H
H
H
O
O
O
O
O
Si
R
Si
R
endo
exo
A common feature of atrane compounds is an in-
crease in the coordination number of Si or Ge to 5.
Silatranes and germatranes can exist in two main con-
formations: exo and endo (Scheme 1). The Si N inter-
atomic distance in the endo form of silatranes is 2
Thus, the existence of silatranes and germatranes in
the endo configuration and their relative stability are
the most important theoretical problems in the chem-
istry of atrane compounds. Various causes of these
effects were discussed in the literature: transfer of the
nitrogen lone electron pair to the silicon d orbitals [5],
conformational effects [6], dipole dipole (electrostat-
ic) interactions [7], etc. In 1970 1990, these concepts
gave way to the concept of hyperbonding due to for-
mation of a three-center bond [8], and in 1990s the
concept of dative interaction of nitrogen and silicon
was put forward [9].
2
.7 , being considerably shorter than the sum of the
van der Waals radii of these atoms. A characteristic
feature of silatranes and germatranes is stabilization
of their molecules in the endo configuration. It is this
fact that stimulated numerous studies on the nature of
bonding of nitrogen with the element (Si, Ge, etc.) in
atrane structures and generally in compounds with
extended coordination sphere of elements of Group IV
and other groups. It is commonly believed that the
transannular interaction makes a decisive contribu-
tion to the thermodynamic stability and high yields of
atrane structures under conditions of equilibrium syn-
thesis and that this interaction is largely responsible
for stabilization and decreased reactivity of silatranes
and germatranes as compared to common alkoxy de-
rivatives of Si and Ge, e.g., under conditions of hy-
drolysis.
Our studies of the molecular and electronic struc-
tures of silatrane and germatrane molecules revealed
new features of their structure and possible causes of
enhanced stability. We found that stabilization of the
endo form of silatranes and germatranes may be due
to the whole set of factors related to conformational,
dipole dipole (electrostatic), and covalent interactions.
For example, we found that the bonding molecular
1
070-3632/04/7401-0058 2004 MAIK Nauka/Interperiodica

STRUCTURAL FEATURES OF SILATRANES AND GERMATRANES
59
by the atomic orbitals of nitrogen. Figure 2c shows
the HOMO of methylsilatrane.
The stabilization of the endo configuration of
silatranes and germatranes is also revealed in the fea-
tures of their frontier molecular orbitals: the HOMOs
in the endo configuration lie lower, and the lowest
unoccupied molecular orbitals (LUMOs), higher than
the respective orbitals in the exo configuration. Cor-
respondingly, the energy gap between HOMO and
LUMO increases in going from the exo to endo struc-
tures, which is also indicative of the higher configu-
rational stability of the endo form compared to the
exo form (Table 1).
A precision X-ray diffraction study of methylsila-
trane molecule [10], performed by us in cooperation
with the Center for X-ray Structural Studies, Nesme-
yanov Institute of Organoelemental Compounds, Rus-
sian Academy of Sciences, gave important results. It
was found that the characteristic feature of this mole-
cule is the electron density localized on the nitrogen
atom and oriented toward the silicon atom. The elec-
tron density maximum is at a distance of 0.45 from
the nitrogen atom (Fig. 2b). Analysis of the topology
of the electron density distribution in methylsilatrane
suggests electrostatic interaction of filled electronic
shells of the nitrogen and silicon atoms, rather than
covalent bonding. Similar results were obtained in cal-
culations of the electron density distribution (Fig. 2a)
and HOMO (Fig. 2c) in the methylsilatrane molecule.
Thus, the results obtained indicate that a significant
contribution to stabilization of the endo configuration
is made by electrostatic interactions arising from the
electron density on the N atom and excess positive
Fig. 1. MO orbital in methylsilatrane, binding the N
3
2
and Si atoms. E 10.79 eV [ 0.32p N + 0.19p Si
x
x
3
(0.32p O)
0.22p C , AM1 calculation].
z
x Me
orbitals involving the atomic orbitals of nitrogen and
silicon or germanium necessarily involve also the
atomic orbitals of oxygen. One of such orbitals in
methylsilatrane is shown in Fig. 1. The structure of
this orbital suggests bonding interaction between the
nitrogen, silicon, and methyl carbon atoms, with the
oxygen atomic orbitals making a significant contribu-
tion to this orbital. The highest occupied molecular
orbital (HOMO) of silatranes and germatranes con-
taining no donor functional groups is mainly formed
(
a)
(b)
(c)
H2B
N1
Si1
H7C
Fig. 2. 1-Methylsilatrane: (a) electron density map (6-31G*/B3LYP calculation), (b) electron density map (X-ray diffraction
data) [10], and (c) HOMO of methylsilatrane (E 6.03 eV, 6-31G*/B3LYP calculation).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 1 2004

60
CHERNYSHEV et al.
Table 1. Parameters of the methylsilatrane molecule in the endo and exo configurations, calculated by various methods
6-31* B3LYP/6-31G*
AM1
STO-3G
Parameter
endo
exo
endo
exo
endo
exo
endo
exo
E , au
86.6634
86.6640
0.37
831.6082
5.58
7.99
12.26
20.25
831.5993
841.8930
3.83
9.47
6.10
841.8869
845.8120
3.01
6.03
2.18
8.21
845.8072
tot
1
E, kcalmol
EHOMO, eV
ELUMO, eV
EMO, eV
9.56
1.69
11.25
8.71
1.22
9.93
6.83
12.21
19.04
8.99
5.95
14.94
5.40
2.10
7.50
15.57
EMO, eV
l(E N),
Charge on Si, e
Charge on O, e
Charge on N, e
1.32
1.21
0.63
0.71
2.61
1.60
0.57
0.35
4.076
3.25
1.57
0.58
0.36
0.55
2.39
1.27
0.45
0.32
4.81
3.25a
1.25
0.45
0.31
0.63
2.74
1.57
0.76
0.69
3.86
3.25a
1.57
0.77
0.64
1.80
2.68
1.11
0.56
0.44
3.85
3.25a
1.12
0.57
0.39
1.63
,
D
a
The structure has no local minimum on the potential energy surface.
charge on the Si atom, estimated by various methods
at 1 1.6 units (Table 1).
matranol molecule, corresponding to the exo structure,
is located by 11 kcal mol 1 higher on the energy scale
as compared to the endo structure (Fig. 3).
The higher stability of germatrane structures com-
pared to silatrane structures is an interesting trend.
Figure 3 shows how the energies of the silatranol and
germatranol molecules depend on the element (Si,
Ge) nitrogen interatomic distance (AM1 calculation).
A striking feature is the higher stability of the endo
form of germatranes compared to silatranes, which is
manifested in the shorter interatomic distance Ge N
The ab initio calculations of the silatrane and
germatrane molecules (STO-3G, 6-31G*, 6-31G**,
B3LYP/6-31G*, B3LYP/6-31G**, etc.) give the re-
sults consistent with those of semiempirical calcula-
tions (AM1, PM3): In all the calculation versions, the
endo configuration is more advantageous than the exo
configuration, and the equilibrium interatomic dis-
tance Si N (or Ge N) is within 2.3 2.7 . The prin-
cipal result of the ab initio calculations of silatranes
and germatranes is the absence of the potential mini-
mum corresponding to the exo configuration on the
coordinate of the conformational transition between
the endo and exo forms. The energy of the system is
only weakly dependent on the Si N and Ge N inter-
atomic distance in the range 2 3 , which accounts
for major differences between the results of determin-
ing this parameter for, e.g., methylsilatrane by X-ray
(
2.33 ) compared to Si N (2.53 ) (Table 2) and in
the absence of the local minimum for the exo configu-
ration of germatranol. The inflection on the coordinate
of the endo exo conformational transition in the ger-
E , kcal mol 1
E , kcal mol 1
b
b
2
370
2
2
2
405
410
415
2375
2380
diffraction (crystal, Si N 2.1604 [10], 2.175 [11]),
2
electron diffraction (gas phase, Si N 2.453
and quantum-chemical calculations (AM1, 2.63
PM3, 2.54 ; STO-3G, 2.39 ; 6-31G*, 2.74
[12]),
;
;
1
B3LYP/6-31G*, 2.67 ; and MP2/6-31G*, 2.38 ).
In the range of N Si distances in methylsilatrane
3.31
2385
2390
2
2
420
425
2.332.53
2
.3 3.0 , the potential energy varies within a
1
1
.5 kcal mol range. Thus, the Si N coordinate is
soft and readily deformable, e.g., in a crystal field.
2
.0
2.5
3.0
3.5
To reveal the character of the covalent component
in interaction of the N and Si atoms in silatranes, we
studied a model system of trimethylamine and methyl-
trimethoxysilane molecules, simulating the methyl-
silatrane structure (Fig. 4). The energy of the system
l(E N),
Fig. 3. Binding energy E as a function of the distance
b
between the Ge (or Si) and N atoms in (1) silatranol and
2) germatranol (AM1 calculations).
(
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 1 2004

STRUCTURAL FEATURES OF SILATRANES AND GERMATRANES
61
considerably increased at the N Si distances corre-
sponding to the endo configuration in silatranes
2.4 ) as compared to the isolated molecules. The
energy growth (kcal mol ) determined by various
methods was as follows: PM3, 16.7; STO-3G, 6.63;
H
H
H
(
30
H
1
H
N
H
H
25
20
H
H
6
-31G, 7.56; and 6-31G*, 17.62.
H
H
H
15
10
5
H
O
The enhanced thermodynamic stability of silatranes
O
Si
O
H
and germatranes was repeatedly postulated in the liter-
ature on the basis of their virtually quantitative forma-
tion in equilibrium synthesis reactions, relative sta-
bility to hydrolysis, and some other properties. The
experimentally determined enthalpies of formation of
silatranes suggest, in the opinion of Voronkov et al.
H
H
H
|
|
|
H
H H
H
0
2
3
4
5
r(N Si),
Fig. 4. Coordinate of mutual approach of the trimethyl-
amine and methyltrimethoxysilane molecules (the sum
of the energies of isolated molecules is taken as zero).
[
13], the stabilizing effect of the N Si interaction
1
whose energy is estimated at 7 20 kcal mol . This
parameter was calculated as the difference between the
enthalpies of formation determined experimentally
and calculated by the additive scheme.
The calculated and experimental parameters coincide
within the experimental error (Table 4).
We calculated the thermodynamic parameters of
formation of methylsilatrane, methylgermatrane, sila-
tranol, and germatranol:
Our results disagree with the commonly accepted
views that the shift of the equilibrium of silatrane and
germatrane formation toward the reaction products is
due to stabilization of the atrane structures by hyper-
bonding of the N and Si (or Ge) atoms. According to
the calculation results, in all the systems under con-
sideration the internal energy of the system grows
upon formation of silatranes and germatranes (the
system gets destabilized). The negative free energies
of formation of methylsilatrane, methylgermatrane,
silatranol, and germatranol are determined by the
entropy factors. As a result, the reaction equilibrium
is fully shifted toward the reaction products (logK >
N(CH CH OH) + MeE(OMe)
3
2
2
3
=
N(CH CH O) EMe + 3MeOH,
2 2 3
N(CH CH OH) + E(OMe) + H O
2
2
3
4
2
=
N(CH CH O) EOH + 4MeOH,
2 2 3
E = Si, Ge.
The calculations were performed ab initio for iso-
lated molecules in the 6-31G* basis taking into ac-
count the electron correlation by the DFT method in
the B3LYP approximation. The calculation results for
the reactants and products are listed in Table 3.
Table 2. Calculated parameters of the silatranol and
germatranol molecules in the endo and exo configurations
(AM1 calculations)
Silatranol
Germatranol
The thermodynamic characteristics of the reactions
were determined as the differences between those of
the products and initial reactants (Table 4):
Parameter
endo
exo
endo
exo
E , kcalmol 1 2425.90
2422.86
2390.79 2379.8
11.0
H0r
0
0
H ,
in
b
=
=
H
1
E, kcalmol
EHOMO, eV
ELUMO, eV
EMO, eV
3.04
10.02
1.40
0
0
0
S
S
S ,
8.97
0.90
9.87
10.50
0.15
9.04
0.41
9.45
r
prod
in
0
0
0
0
0
T S0).
G = G
G
( G = H
r
prod
in
11.42
10.65
EMO, eV
l(E N),
1.55
1.20
The calculation results (Table 4) show that the
0
2.53
1.65
3.31
1.64
2.33
1.61
3.24
1.53
reaction enthalpy is positive ( H > 0), but its free
0
Charge on
Si(Ge) atom, e
Charge on
O atom, e
Charge on
N atom, e
energy is negative ( G < 0). Thus, formation of sila-
tranes and germatranes (shift of the equilibrium) is ex-
0
0.58
0.34
0.59
0.33
0.57
0.30
0.53
0.35
clusively due to the increase in the entropy ( S > 0).
We also calculated the enthalpy of formation of
methylsilatrane from the experimental enthalpies of
formation of the reactants and products (Table 3).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 1 2004

62
CHERNYSHEV et al.
Table 3. Thermodynamic parameters of reactants and products in the reactions of synthesis of methylsilatrane, methyl-
germatrane, silatranol, and germatranol
0
H(exp), kcalmol 1 S0, kcalmol 1 K 1
0
Compound
E , au
H , au
G , au
tot
N(CH CH OH)
3
518.0487
674.9314
2460.3734
750.1811
2535.5943
115.7144
76.4089
517.8116
674.7510
2460.1944
749.9934
2535.4088
115.6587
76.3840
133.44 [14]
225.62 [15]
96.29
113.95
111.72
119.647
119.207
56.73
517.8574
674.8052
2460.2476
750.0503
2535.4655
115.6856
76.4055
2
2
MeSi(OMe)3
MeGe(OMe)3
Si(OMe)4
Ge(OMe)4
MeOH
48.07 [16]
H O
45.14
2
N(CH CH O) SiMe
845.8119
2631.2671
881.7533
2667.1868
845.5677
2631.0239
881.5325
2666.9676
201.00 [13]
102.95
106.43
103.94
107.78
845.6166
2631.0745
881.5818
2667.0188
2
2
3
N(CH CH O) GeMe
2
2
3
N(CH CH O) SiOH
2
2
3
N(CH CH O) GeOH
2
2
3
Table 4. Thermodynamic characteristics of formation of
methylsilatrane, methylgermatrane, silatranol, and
germatranol (6-31G*/B3LYP)
Table 5. Energy of coordination of atranes with a water
molecule, kcal mol 1
Method
0
1
0
0
H , kcalmol
(
S ,
G ,
Compound
Compound
experiment) kcalmol K 1 kcalmol 1
1
PM3
STO-3G
6-31G**
Methyl-
silatrane
Silatranol
Methyl-
germatrane
Germatranol
11.82
(13.79 1.96)
13.68
62.90
6.94
Silatranol
Germatranol
Ethyl-
0.91
3.58
9.76
9.48
9.56
6.73
6.43
9.81
6.41
69.79
68.61
7.13
16.64
3.82
silatrane
Ethyl-
0.41
6.98
8.50
1.30
74.06
20.80
germatrane
a
Value calculated from the experimental data.
9
15). Stabilization of atranes toward hydrolysis is
Computer simulation of hydrolysis of silatranes
and germatranes gave interesting results. We found
that the potential barriers of these reactions are com-
apparently also due to this factor. Notably, the free
energy of formation of germatranes is much more
negative than that of silatranes.
1
parable and amount to 15 35 kcal mol depending on
the approximation level. A search for transition state
was performed for the first step of the model reaction
of silatranol and germatranol hydrolysis. Calculations
were performed in the HF/6-31G** approximation
using QST-2 and TS methods, with calculation of
normal vibrational modes. The calculated reaction
model involves the silatranol and water molecules
The reactivity of silatranes and germatranes may
also be determined by kinetic factors. The PM3 calcu-
lations suggest the possibility of formation of stable
hydrated germatrane (especially germatranol) mole-
cules (Table 5). At the same time, hydration of silatra-
nols, according to our calculations, increases the ener-
gy of the system compared to isolated molecules. In
all the calculated hydrates, the water oxygen atom
coordinates with the element (Si, Ge) atom. The ab
initio calculations in the 6-31G** basis, however,
suggest the absence of such coordination. Hydration
occurs as hydrogen bonding between the water mole-
cule and the oxygen atom of the atrane core. The
hydrated germatrane species are more stable than the
silatrane derivatives. This is consistent with the exper-
imental data on isolation of germatranol crystal hy-
drates [17].
brought to the distance of 2.6
between the Si and
water oxygen atoms as the reactants and structure III
as the product (addition of one water molecule with
H O
2
formation of a covalent bond Si O , with cleavage
of one of the Si O bonds in the silatrane and proton
transfer from the water molecule to the leaving oxy-
gen atom, Scheme 2).
The parameters of the transition states for silatranol
and germatranol are listed in Table 6. The structures
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STRUCTURAL FEATURES OF SILATRANES AND GERMATRANES
63
Scheme 2.
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
N
H
O
H
+
N
H
N
H
O
H
H
H
H
H
O
O
H
H
H
H
H
O
O
H
H
O
O
H
4
O
O
O
E
E 1
O
3H
E
O 2
O
H
H
H
O
H
H
I
II
III
found lie higher in the energy (enthalpy) relative
aqueous solutions within several hours or days, in
agreement with data of Voronkov et al.
to the isolated reactant molecules by 34.89 and
1
2
0.00 kcal mol , respectively; consideration of the
Thus, our results revealed new factors responsible
for stabilization of atrane structures and higher stabil-
ity of germatranes compared to silatranes. It was
shown that the models of hypervalent or dative in-
teractions of the N and Si (or Ge) atoms in these mol-
ecules do not exhaustively account for their structural
features. The stability of silatranes and germatranes in
the endo configuration is mainly due to the total con-
tribution of all the atoms of the atrane moiety and pri-
marily of the oxygen atomic orbitals, stabilizing this
configuration, rather than to the N Si or N Ge bond-
ing interaction [in many bonding molecular orbitals,
this interaction is andibonding, which is confirmed
by data for the model system Me N MeSi(OMe) ].
An appreciable role in stabilization of the endo form
of atrane structures is also played by electrostatic
interactions of the Si or Ge atom bearing a significant
positive charge with the electrons localized on the N
atom. Thus, stability of silatranes and germatranes in
formation and hydrolysis reactions is determined by
hydration energy increases the barrier height to 41.37
and 29.81 kcal mol , respectively. The difference
1
between the free energies of the transition state and
1
reactants is somewhat larger: 48 kcal mol for sila-
1
tranol and 33 kcal mol for germatranol.
The validity of the revealed transition state struc-
tures is confirmed by the analysis of their vibration
frequencies. In both cases (hydrolysis of silatranol and
germatranol), there is a single imaginary frequency,
which corresponds to a first-order saddle point on the
potential energy surface (transition state). The normal
mode analysis for the imaginary frequencies shows
that they correspond to the coordinate of the hydrogen
atom transfer from the water molecule to the leaving
oxygen atom (Scheme 2, Table 6). The calculated
potential barriers are apparently somewhat overesti-
mated, as the solvent effect is not taken into account
in the model.
3
3
On the whole, the results of computer simulation of
hydrolysis of silatranes and germatranes suggest that
these reactions are not kinetically forbidden. The lower
potential barrier of the model reaction for germatranes
suggests that their enhanced hydrolytic stability is
mainly due to the thermodynamic factors, especially
in the case of germatranol compared to silatranes. We
believe that the hydroxy group at the Ge atom mark-
edly stabilizes the molecule as regards formation and
hydrolysis in aqueous solution. The stabilization may
also be due to formation of hydrogen-bonded molecu-
lar associates.
Table 6. Parameters of the transition state (Scheme 2) of
the first step of hydrolysis of silatranol and germatranol
(
calculation, GAUSSIAN 98, 6-31G**/QST2/Freq)
Parameter
E, kcalmol 1
Silatranol Germatranol
34.89
34.53
44.94
13.40
47.93
1.902
1.175
1.194
1.925
2.163
1503
20.00
19.49
44.14
13.16
32.65
1.995
1.200
1.174
2.001
2.239
1492
0
1
H , kcalmol
0
1
1
S , cal mol
K
0
1
T S , kcalmol (T 298.15 K)
0
1
G , kcalmol
1
2
l(E O ),
2
3
Our results are consistent with the results of an
NMR study of hydrolysis of germatranes and sila-
tranes: Aqueous solutions of germatranol are hydro-
lytically stable; with ethylgermatrane, an equilibrium
is attained between germatrane and its hydrolysis
products (5 : 4 ratio in 20 30 min and 2 : 3 ratio in
l(O H ),
3
4
l(H O ),
1
4
l(E O ),
1
l(E N),
, cm 1 (imaginary frequency)
(O
H O) (O H O)
48 days); silatranes are completely hydrolyzed in
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 1 2004

64
CHERNYSHEV et al.
external (positive entropy and negative free energy of
formation) rather than internal factors (positive en-
thalpy of formation).
the atrane core give two triplets at 3.63 and 2.81 ppm,
respectively, and in the ethyl substituent the methyl
group gives a triplet (0.86 ppm), and the methylene
group, a quartet (0.22 ppm).
EXPERIMENTAL
1
The H NMR spectrum of 1-ethylsilatrane in D O
2
undergoes irreversible changes in time: Along with
two triplets of the CH O and CH N groups of the
Quantum-chemical calculations were performed
with HyperChem and GAUSSIAN 98 program com-
plexes [18].
2
2
atrane core at 3.81 and 3.02 ppm, two triplets of the
CH O and CH N groups of the forming triethanol-
2
2
The NMR spectra were recorded on a Bruker AM-
60 spectrometer from 6% solutions in acetone-d6,
amine appear at 3.74 and 2.81 ppm, respectively, and
grow with time. The concentration variation follows
a first-order equation, with the conversion half-time
of 10.7 h; after 11 h, gelation is observed.
3
CDCl , or D O relative to TMS.
3
2
The hydrolytic stability of silatranol, ethylsilatrane,
germatranol, and ethylgermatrane was studied by
NMR spectroscopy. Spectra of 6% solutions of sila-
1-Hydroxygermatrane was prepared according to
[17] by the reaction of germanium dioxide with tri-
ethanolamine and water; yield of 1-hydroxygerma-
trane monohydrate 97%, mp 154 156 C (154 156 C
[17]).
tranes and germatranes in D O were recorded at defi-
2
nite time intervals ar 300 K. The occurrence and de-
gree of hydrolysis were judged from the appearance
of the triethanolamine methylene proton signals at
.76 and 2.82 ppm and from the ratio of their inten-
sity to that of the methylene proton signals of the
starting atranes.
1
The H NMR spectrum of 1-hydroxygermatrane in
3
acetone-d consists of three signals with the relative
6
intensity of 6 : 6 : 1. The CH O and CH N groups of
2
2
the atrane core give two triplets at 3.69 and 2.91 ppm,
respectively, and the OH group gives a singlet at
2.76 ppm.
1-Hydroxysilatrane was prepared according to [19]
by the reaction of tetraethoxysilane with triethanol-
amine, followed by selective hydrolysis of the form-
ing tri(silatranyloxyethyl)amine. Yield 60%, mp 203
1
The H NMR spectrum of 1-hydroxygermatrane in
D O contains two triplets of equal intensity at 3.87
2
2
05 C (200 205 C [19]).
and 3.11 ppm, belonging, respectively, to the CH O
2
1
1
The H NMR spectrum of 1-hydroxysilatrane in
and CH N groups. The H NMR spectrum of 1-hy-
2
CDCl consists of three signals with the relative in-
droxygermatrane in D O, measured over a period of
60 days, remained unchanged.
3
2
tensity of 6 : 6 : 1. The CH O and CH N groups of
2
2
the atrane core give two triplets at 3.82 and 2.85 ppm,
respectively, and the OH group gives a singlet at
1
-Ethylgermatrane. An equimolar amount of tris-
(
trimethylsiloxyethyl)amine was added to a solution
1
.87 ppm.
of 15 g of ethyltrichlorogermane in 50 ml of heptane
at 60 70 C. The mixture was stirred at room temper-
ature until the distillation of trimethylchlorosilane
stopped; the mixture was vacuum-evaporated, and the
residue was recrystallized from toluene. Yield of
1-ethylgermatrane 12.3 g (70%), mp 146 147 C
(146 147 C [17]).
1
The H NMR spectrum of 1-hydroxysilatrane in
D O irreversibly changes in time: Along with two
2
triplets of the CH O and CH N groups of the atrane
2
2
core at 3.85 and 3.05 ppm, two triplets of the CH O
2
and CH N groups of the forming triethanolamine
2
appear at 3.73 and 2.81 ppm, respectively, and grow
with time. The conversion half-time is 0.5 h. Aqueous
solutions of 1-hydroxysilatrane and its hydrolysis
products remain transparent for 3 months; no signs of
gelation were observed.
1
The H NMR spectrum of 1-ethylgermatrane in
acetone-d consists of four signals with the relative
intensities of 6 : 6 : 3 : 2. The CH O and CH N
6
2
2
groups of the atrane ring give two triplets at 3.63 and
2.81 ppm, respectively; in the ethyl substituent, the
CH group gives a triplet at 1.02 ppm, and the CH
1
-Ethylsilatrane was prepared by the reaction of
triethanolamine with ethyltriethoxysilane in the pres-
ence of a catalyst (sodium ethylate) following the pro-
cedure described in [20]; yield 60%, mp 132 133 C
3
2
group, a quartet at 0.74 ppm.
1
The H NMR spectrum of 1-ethylgermatrane in
D O changes with time: Along with the two triplets
of the CH O and CH N groups of the atrane ring at
(132 133 C [20]).
2
1
The H NMR spectrum of 1-ethylsilatrane in ace-
2
2
tone-d consists of four signals with the relative inten-
3.81 and 3.04 ppm, two triplets of the CH O and
6
2
sities of 6 : 6 : 3 : 2. The CH O and CH N groups of
CH N groups of the forming triethanolamine appear
2
2
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 1 2004

STRUCTURAL FEATURES OF SILATRANES AND GERMATRANES
at 3.76 and 2.82 ppm, respectively. In 28 min, the Mendeleev Commun., 2000, vol. 10, no. 3, p. 88.
65
intensity ratio of the signals of the methylene protons
in the atrane core and triethanolamine (hydrolysis
product) reached 5 : 4, after which it varied insigni-
ficantly (in 48 h, the ratio of the starting compound
to the hydrolysis product approached 2 : 3). The
1
1
1
1. Parkanyi, L., Bihatsi, L., and Hencsei, P., Cryst.
Struct. Commun., 1978, vol. 7, no. 3, p. 435.
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1
-ethylgermatrane solution remained transparent
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were observed.
1
1
4. Minadakis, C. and Sabbah, R., Thermochim. Acta,
1
982, vol. 55, no. 2, p. 147.
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