1-(Methylaminomethyl)silatrane: Synthesis, characterization and reactivity

Article abstract of DOI:10.1016/j.jorganchem.2014.10.005

1-(Methylaminomethyl)silatrane MeNHCH₂Si(OCH₂CH₂)₃N 2 was prepared and characterized by elemental analysis, IR, ¹H, ¹³C, and ²⁹Si NMR spectra. Solvate complex MeNHCH₂S

Full text of DOI:10.1016/j.jorganchem.2014.10.005

Journal of Organometallic Chemistry 775 (2015) 27e32
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
1-(Methylaminomethyl)silatrane: Synthesis, characterization
and reactivity
I.V. Sterkhova, I.M. Lazarev, V.I. Smirnov, N.F. Lazareva*
A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of The Russian Academy of Science, 1 Favorsky Street, 664033 Irkutsk, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
1-(Methylaminomethyl)silatrane MeNHCH2Si(OCH2CH2)3N
2 was prepared and characterized by
elemental analysis, IR, 1H, 13C, and 29Si NMR spectra. Solvate complex MeNHCH2Si(OCH2CH2)3N$C6H6
was isolated after recrystallization of silatrane 2 from benzene and its molecular structure has been
determined by X-ray diffraction study. It is the first example of X-ray study of acyclic N-(silatranylmethyl)
amine. The interaction silatrane 2 with HCl or CHCl3 led to the formation of its hydrochloride
[MeNHCH2Si(OCH2CH2)3N]$HCl 3. The composition and structure of compound 3 was confirmed by
elemental analysis, IR, 1H, 13C, 29Si NMR spectra and X-ray structure analysis.
Received 9 June 2014
Received in revised form
8 September 2014
Accepted 2 October 2014
Available online 12 October 2014
Keywords:
Silatrane
© 2014 Elsevier B.V. All rights reserved.
1-(Aminomethyl)silatrane
Reactivity
Hydrochloride 1-(aminomethyl)silatrane
NMR spectroscopy
X-ray
Introduction
properties and they widely apply as synthons in synthetic organic
chemistry [18,19]. Recently, we have found that the 1-(dia-
Silatranes
(or
2,8,9-trioxa-5-aza-1-silatricyclo-[3.3.3.01,5]
lkylaminomethyl)silatrane exhibit enhanced reactivity with
respect to polychloromethanes CHnCl4ꢀn [20e23]. They react with
alcohols and phenols in inert solvents at room temperature with
cleavage of the SieC bond [24], and reduce salts of some metals
[25].
There is little information on the synthesis, reactivity and
structure of 1-(aminomethyl)silatranes RNHCH2Si(OCH2CH2)3N
with secondary amino group. Despite the fact that the first repre-
sentatives of RR0NCH2Si(OCH2CH2)3N were obtained in the 70s of
the last century [26,27] their molecular and crystal structure re-
mains an unknown. In the last year the synthesis of 1-(methyl-
undecanes) XSi(OCH2CH2)3N are cyclic organosilicon ethers of
tris(2-oxyalkyl)amines. Silatranes are very important class of pen-
tacoordinate organosilicon compounds, they feature a hypervalent
silicon atom with a transannular dative bonding interaction be-
tween the silicon and the bridged nitrogen atom and their structure
and chemical properties have been the subject of intense study
[see, e.g., Refs. [1e4] and references cited therein] since their dis-
covery in 1961 [5]. Several hundreds of such compounds with
hydrogen, organyl, organoxy, aminoalkyl, thioorganyl, acyloxy,
halogen, pseudohalogen and other groups as substituent X have
been synthesized and studied. Among of 1-(aminoalkyl)silatranes
RR0N(CH2)nSi(OCH2CH2)3N (n ¼ 1e3) 1-(3-aminopropyl)silatrane
H2N(CH2)3Si(OCH2CH2)3N is one of the best investigated. This
compound is precursor for the synthesis of a number of N-de-
rivatives silatranes [see, for example Refs. [6e11]], which exhibit
biological activity [12e17]. Of specific interest are the 1-(amino-
methyl)silatranes RR0NCH2Si(OCH2CH2)3N as representatives of
aminomethyl)silatrane
MeNHCH2Si(OCH2CH2)3N
and
its
complexes with transition metal chlorides was described [28]. Data
of 1H NMR spectrum of this silatrane presented by the authors are
somewhat surprising. As compared to the spectra of 1-(dia-
lkylaminomethyl)silatrane RR0NCH2Si(OCH2CH2)3N [22,25,27] the
significant downfield shifts of the signals of NCH3 and NCH2Si
groups in the 1H NMR spectrum of this compound takes place.
What is the cause of this phenomenon? In the first place, this dif-
ference may be caused by structural features of the compound and
secondly, it may be due to the experimental error. As noted above
acyclic a-silylamines.
The amines RR0NCH2SiX3 containing the silicon atom in the
geminal position to nitrogen have unusual physical and chemical
a
-silatranylamines readily react with polychloromethanes
CHnCl4ꢀn (n ¼ 0e2) and with chloroform in particular [23]. Unfor-
tunately this important property of -silylamines was ignored by
* Corresponding author.
E-mail address: nataly_lazareva@irioch.irk.ru (N.F. Lazareva).
a
http://dx.doi.org/10.1016/j.jorganchem.2014.10.005
0022-328X/© 2014 Elsevier B.V. All rights reserved.

28
I.V. Sterkhova et al. / Journal of Organometallic Chemistry 775 (2015) 27e32
authors [28] and the mixture of chloroformehexane was used by
them for the recrystallization of this silatrane. It is not inconceiv-
able that this procedure gave rise to the formation of hydrochloride
1-(methylaminomethyl)silatrane.
Scheme 1. Synthesis of silane 1.
On the basis of present knowledge about chemical properties a-
silylamines we expect that 1-(methylaminomethyl)silatrane will
exhibit an unusual reactivity which will provide its use in organic
synthesis. Herein we report the results of synthesis of 1-(methyl-
aminomethyl)silatrane, the investigation of its structure by NMR
and X-ray methods and some evidence on its reactivity.
glass ampoule. During the 3-h ampoule was kept at temperature
15 ꢁC and then at room temperature for 2 days. After the ampoule
was cooled to ꢀ10 ꢁC and opened. The excess methylamine was
evaporated and freshly distilled Et2O (150 mL) was added to the
residue. The precipitate of MeNH2$HCl was filtered off, washed by
ether (35 mL ꢂ 2) and the solvent removed from the filtrate by
distillation on rotary evaporator. Compound 1 as colorless liquid
isolated by vacuum distillation of the resulting residue (yield 11.8 g,
Experimental section
General
72%). Bp 65e67 ꢁC/24 mm Hg. 1H NMR (C6D6,
d ppm): 2.27 (s, 2H,
SiCH2N), 2.40 (s, 3H, NCH3), 3.65 (s 9H, OCH3). 5.8 (broad s, 1H, NH).
All reactions were performed in the flame dried glassware under
an atmosphere of dry argon. The used solvents were purified ac-
cording to standard procedures [29]. As a further precaution,
diethyl ether was dried by filtration through column packed with
neutral alumina under a positive pressure of argon. The solvents
were stored under argon over molecular sieves. Chloroform was
purified just before use. The purification of chloroform involves
washing with water to remove the EtOH, drying with K2CO3,
refluxing with P2O5 and distilling. Triethanolamine was purified by
low-pressure distillation and stored on molecular sieves. Starting
silane ClCH2Si(OMe)3 was obtained according to Ref. [30].
Methylamine was obtained from water solution 40% (Merck), dried
by standing with sodium pellets at 0ꢁ during 18 h and was distilled.
IMPORTANT! Compounds 1 and 2 are extremely sensitive to
moisture.
13C NMR (C6D6,
29Si NMR (C6D6,
d
ppm): 36.9 (SiCH2N), 42.3 (NCH3), 51.3 (OCH3).
d
ppm): ꢀ48.25.
1-(Methylaminomethyl)silatrane (2)
Triethanolamine 1.49 g (10 mmol) was added drop wise to
cooled (þ15 ꢁC) solution 1.65 (10 mmol) of N-[(methylamino)
methyl]trimethoxysilane in 10 mL thoroughly dried ether at stir-
ring vigorously. Slight heating of the reaction mixture was observed
and the reaction temperature maintained between 15 and 20 ꢁC.
Solvent and the released methanol were removed in vacuum
immediately after homogenization of reaction mixture. The white
solid residue was dried in vacuum and yield is practically quanti-
tative (2.1 g), mp 96e97 ꢁC (in a sealed capillary). IR spectrum,
n,
cmꢀ1: 3391, 2939, 2881, 2790, 1622, 1456, 1275, 1087, 914, 794.
Anal. Calcd. for С8H18N2O3Si: C, 44.01; H, 8.31; N, 12.83, Si, 12.86.
Found: C, 44.32; H, 8.55; N, 12.95; Si, 12.24.
N-[(Methylamino)methyl]trimethoxysilane (1)
A mixture of 8.53 g (50 mmol) (chloromethyl)trimethoxysilane
and the excess of methylamine 16 g (~500 mmol) was sealed in
Colorless crystals suitable for structural analysis were obtained
by the recrystallization from benzene.
Table 1
Crystal data, details of intensity measurements, and structure refinement for compounds 2 and 3.
Parameter
Compound
2·C6H6
33
Empirical formula
Formula weight/g molꢀ1
Crystal system
Space group
Cell dimensions
a/Å
C14H24N2O3Si
296.44
Monoclinic
P21/c
C8H19ClN2O3Si
254.79
Monoclinic
P21/n
6.7586(5)
13.8374(11)
13.7508(12)
98.856(3)
1270.66(18)
296(2)
6.8882(12)
7.6958(15)
22.533(4)
96.742(6)
1186.2(4)
296(2)
b/Å
c/Å
ꢁ
b
/
Volume/Å3
Temperature/K
Z
4
4
Density (calculated)/g cmꢀ3
1.466
0.192
1.427
0.414
Absorptions coefficient/mmꢀ1
Radiation (
range/ꢁ
l/Å)
MoK
5.88e60.03
a
(0.71073)
MoKa (0.71073)
5.59e60.17
2
Q
Crystal size/mm
F(000)
0.12 ꢂ 0.13 ꢂ 0.50
0.18 ꢂ 0.25 ꢂ 0.28
600
544
Index ranges
ꢀ9 ꢃ h ꢃ 9, ꢀ19 ꢃ k ꢃ 19, ꢀ19 ꢃ l ꢃ 19
38,775
3747 (Rint ¼ 0.0652)
0.9100 and 0.9770
3747/0/163
0.0357/0.09733
0.0541/0.1035
1.066
0.896 and ꢀ0.830
ꢀ9 ꢃ h ꢃ 9, ꢀ10 ꢃ k ꢃ 10, ꢀ31 ꢃ l ꢃ 28
12,836
3186 (Rint ¼ 0.0522)
0.8930 and 0.9290
3186/0/137
0.0500/0.1364
0.0655/0.1433
1.131
0.498 and ꢀ0.504
Reflections collected
Independent reflections
Max. and min. transmission
Data/restraints/parameters
R1/wR2 [I > 2
s
(I)]a
R1/wR2 (all data)
S on F2
Largest diff. peak and hole/e Åꢀ3
w ¼ 1=½s2ðFo2Þ þ ð0:0482PÞ2 þ 16:3125Pꢄ; where P ¼ ðFo2 þ 2Fc2Þ=3:
a

I.V. Sterkhova et al. / Journal of Organometallic Chemistry 775 (2015) 27e32
29
Table 2
1H, 13C, 29Si NMR data for compounds 2 and 3.
Compound
d
, ppm
NeCH2Si MeeN NCH2 OCH2 NH
Solvent
29Si
Scheme 2. Synthesis of 1-(methylaminomethyl)silatrane 2.
2
1H 1.63 s
13C 40.36
1H 1.62 s
13C 40.11
1H 1.88 s
13C 40.54
1H 2.18
13C 35.83
1H 1.62
13C 40.50
1H 1.87
13C 35.74
1H 2.15
13C 35.87
1H 2.16
13C 35.84
1H 2.01
13C 44.19
2.25 s 2.81 t 3.65 t 2.1 br. s ꢀ75.28 CD3CN
43.45 50.20 56.67
a
2$C6H6
2.26 s 2.80 t 3.65 t 1.38 br. s ꢀ75.35 CD3CN
1-(Methylaminomethyl)silatrane hydrochloride (3)
43.32 50.14 56.63
2b
2.42 s 2.84 t 3.80 t 1.69 br. s ꢀ77.22 CDCl3
43.53 48.79 56.21
HCl (0.0365 g, 1 mmol) dissolved in carefully dried benzene was
slow added to benzene solution of compound 2 (0.218 g, 1 mmol) at
10 ꢁC. After 10 min, the reaction mixture was evaporated to remove
the solvent. The solid residue was purified by the recrystallization
from chloroform/benzene (1:2). Colorless crystals of the compound
3 were isolated (yield 0.13 g, 50%). Mp 195e197 ꢁC (in a sealed
2c
2.70
39.53 51.02 56.91
2.24
2.84 3.64 2.23 br. s ꢀ76.09 DMSO-d6
43.47 49.66 56.16
2.95 3.80
ꢀ81.61 CDCl3
2
3
2.45
2.99 3.74 1.92 br. s ꢀ83.56 DMSO-d6
39.55 49.01 56.22
3
2.71
2.97 3.84 1.85 br. s ꢀ81.92 CDCl3
capillary). IR spectrum, n
, cmꢀ1: 2930, 2879, 1461, 1272, 1120, 1090,
1020, 940, 916, 815, 793, 688. Anal. Calcd. for C8H19ClN2O3Si: C,
37.71; H, 7.52; N, 10.99, Si, 11.02. Found: C, 37.99; H, 7.94; N, 10.95;
Si, 11.62.
39.51 51.02 56.93
3d
2.73
2.98 3.86 2.34 br. s ꢀ81.92 CDCl3
39.53 51.04 56.91
2 [28]
2.64
3.25 4.05
ꢀ76.2 DMSO-d6
41.31 50.05 56.57
a
Signal of benzene in the 1H (7.35 ppm) and 13C (129.1 ppm).
Spectrum of compound 2 was recorded immediately after preparation of the
b
Reaction silatrane 2 with CHCl3
solution.
c
Spectrum of compound 2 was recorded 36 h after preparation of the solution.
Spectrum of compound 3, which was obtained by interaction of 2 with CHCl3.
Silatrane 2 (0.44 g, 2 mmol) was dissolved in chloroform
(10 mL). After 36 h, the excess of chloroform was removed, the
residue was purified by the recrystallization from chloroform/
benzene (1:2) mixture and 1-(methylaminomethyl)silatrane hy-
drochloride (3) was isolated, (yield 0.39 g, 75%).
d
Results and discussion
Synthesis
NMR study
Previously N-[(methylamino)methyl]trimethoxysilane
1 was
synthesized by interaction of (chloromethyl)trimethoxysilane with
methylamine on heating in an autoclave at 120 ꢁC/20 bar for 16 h
[32]. We have found that (chloromethyl)trimethoxysilane reacts
with methylamine at room temperature in a sealed glass ampoule
(Scheme 1). We used the cooling of ampoule by water during the
first few hours as a precautionary measure against explosion
because this reaction is exothermic. N,N-Bis[(trimethoxysilyl)
methyl]eN-methylamine is byproduct of this reaction and the
increasing of the ratio of amine/silane reduces its yield. Therefore
we used the molar ratio of amine/silane ¼ 10:1.
The 1H, 13C and 29Si NMR spectra of 10e20% solutions of com-
pounds 1e3 were registered on a Bruker DPX 400 spectrometer
(400.1, 100.6 and 79.5 MHz respectively) with tetramethylsilane as
an internal standard.
Crystal structure analyses
Suitable single crystals of 2$C6H6 were obtained by crystalliza-
tion of silatrane 2 from benzene (slow cooling of a boiling saturated
solution to room temperature), single crystals of 3 were obtained
by crystallization of silatrane from chloroform/benzene (1:1). This
operation consisted in slow evaporation of the solvent at room
temperature.
The typical procedure for the synthesis of silatranes
RSi(OCH2CH2)3N involves treatment of respective RSi(OAlk)3 with
triethanolamine N(CH2CH2OH)3 [1e5]. Interaction of N-[(methyl-
amino)methyl]trimethoxysilane 1 with triethanolamine led to
formation of 1-(methylaminomethyl)silatrane 2 with high yield
without the application of any catalyst (Scheme 2), this reaction is
exothermic.
Of special note is the ease cleavage of the SieC bond of formed
silatrane 2 by the methanol, as one would expect [24]. We dropped
the triethanolamine to the ether solution of compound 1 at the
stirring vigorously and cooling as a precautionary measures against
this side reaction.
Hydrochloride 1-(methylaminomethyl)silatrane 3 was synthe-
sized by the slowly mixing (drop by drop) of the solution HCl in dry
benzene with solution of silatrane 2 in dry benzene at 10 ꢁC
(Scheme 3). It is significant that an increasing of the temperature of
the reaction leads to the cleavage of the atrane skeleton and the
formation of byproducts.
Crystal data were collected on a Bruker D8 Venture diffrac-
tometer with MoK
a
radiation (
l
¼ 0.71073) using the 4 and
u scans.
The structures were solved and refined by direct methods using the
SHELX programs set [31]. Data were corrected for absorption effects
using the multi-scan method (SADABS). Non-hydrogen atoms were
refined anisotropically using SHELX [31].
The H-atoms (except for HeN of compound 2) were placed at
calculated positions using the instructions AFIX 43, AFIX 137. The
coordinates and the isotropic temperature factor for the H23 for
compound 2 atom (attached to N1) were refined from the residual
electron density map(AFIX 0).
Details of crystallographic data and experimental conditions are
presented in Table 1.
Scheme 3. Synthesis of hydrochloride 1-(methylaminomethyl)silatrane 3.
Scheme 4. Reaction silatrane 2 with CHCl3.

30
I.V. Sterkhova et al. / Journal of Organometallic Chemistry 775 (2015) 27e32
Scheme 5. Structural data were obtained for some silatranes with geminal NeCeSi group.
Table 3
recrystallization of compound 2 from benzene leads to the appear
of signal of benzene in the 1H and 13C NMR spectra. The value of
chemical shift of this signal is close to the value of chemical shift of
benzene in CD3CN. The precipitated crystals after the recrystalli-
zation were dried under vacuum at room temperature and the
increasing the drying time (10 h) at room temperature does not
lead to a change in the spectra. Drying the sample of compound 2
under vacuum at the more high temperature results to the removal
of benzene, but the crystals were destroyed. These results are
indicative of the formation of a complex between the compound 2
and benzene. The complexes the amines with the aromatic com-
pounds (including benzene) are described in the literature [33e39].
The significant downfield shift of the signals of NCH3 and
NCH2Si groups was observed in the 1H NMR spectrum of compound
3 with respect to the starting compound 2. Such changes in the
spectra are indicative of quaternization of the exocyclic nitrogen
atom and are typical for N-(silatranylmethyl)ammonium salts
[22,23,25,40].
Selected bond lengths for silatrane 2.
Parameter
l, Å
Parameter
l, Å
Si1eO1
Si1eO2
Si1eO3
Si1eC6
Si1eN2
O1eC10
O2eC12
O3eC13
C4eH10
1.667(2)
1.670(4)
1.675(4)
1.889(5)
2.159(2)
1.422(16)
1.419(16)
1.422(17)
0.960(9)
C4eN1
N1eC6
N1eH23
N2eC8
N2eC9
N2eC11
C8eC13
C9eC12
C10eC11
1.455(9)
1.473(8)
0.905(7)
1.479(9)
1.478(8)
1.477(9)
1.523(2)
1.522(2)
1.520(2)
The NMR monitoring of solution of compound 2 in CDCl3 shows
that the spectra recorded the immediately after preparation of the
solution essentially differ from the spectra obtained 36 h after
preparation of this solution (Table 2). This change is indicative of a
chemical reaction (Scheme 4).
The chemical shifts of signals of NeMe and NeCH2Si groups in
1H, 13C NMR spectra of previously synthesized compound 2 [28]
differ radically from our data not only for compound 2, but for
compound 3 as well.
At room temperature the reaction of silatrane 2 with excess
chloroform was completed after 36 h. The reaction time is
increased to 3e4 days at use of equimolar ratio of the reactants in
acetonitrile or benzene. The reaction time is reduced to
10e15 min by refluxing the reaction mixture. The dehydrochlori-
nation of chloroform gave rise to dichlorocarbene and this leads to
the production of terachloroethylene. The availability of a low in-
X-ray studies
tensity signal with
d
120.67 ppm in 13C NMR spectrum of the re-
To date, only crystal structures of N-(silatranylmethyl)amides
(A) [41,42], -imides (B) [43,44] and N-(silatranylmethyl) substituted
five-membered aromatic heterocycles (C) (derivatives of pyrrole,
indole, pyrazole, imidazole, triazole and carbazole) [45e55] with
geminal fragment NeCeSi have been described in the literature.
action mixture is indicated on its formation. Early we
demonstrated, that chloroform reacts with N,N-bis(sila-
tranylmethyl)methylamine MeN[CH2Si(OCH2CH2)3N]2 resulting in
its hydrochloride and dichlorocarbene [21]. So, it is not surprising
that the silatrane 2 reacts readily with CHCl3 with formation of the
hydrochloride 1-(methylaminomethyl)silatrane 3.
Amongst
the
N-(silatranylmethyl)amines
of
row
RR0NCH2Si(OCH2CH2)3N (D) (R, R0 ¼ H, Alk, Ar) only the single
crystal structure of trimethyl(1-silatranylmethyl)ammonium io-
dide has been studied [56] (Scheme 5).
NMR spectroscopic studies
The molecular structures of 1-(methylaminomethyl)silatrane 2
and its hydrochloride 3 were determined by single-crystal X-ray
diffraction. The selected bond lengths and angles are presented in
Tables 3e6. 1-(Methylaminomethyl)silatrane 2 exists as solvate
complex with benzene 2$C6H6, which was obtained after the
recrystallization of silatrane 2 from benzene. The geometry of the Si
The structure of compounds 1e3 was proved by multinuclear
NMR spectroscopy. Data of NMR spectra of compound 1 were given
in the experimental part, they agree closely with data [30]. Data of
NMR spectra of silatranes 2 and 3 are shown in Table 2. The
Table 4
Selected bond angles for silatrane 2.
Table 5
Selected bond lengths for silatrane 3.
ꢁ
Parameter
Angle,
Parameter
Angle, ꢁ
Parameter
l, Å
Parameter
l, Å
O1eSi1eO2
O1eSi1eO3
O2eSi1eO3
O1eSi1eC6
O2eSi1eC6
O3eSi1eC6
O1eSi1eN2
O2eSi1eN2
C4eN1eH23
118.41(5)
117.88(5)
119.87(5)
99.58(5)
94.79(5)
95.29(5)
83.82(4)
83.33(4)
107.3(11)
O3eSi1eN2
C6eSi1eN2
C10eO1eSi1
C12eO2eSi1
C13eO3eSi1
C3eC1eC2
C1eC3eC2
C4eN1eC6
C6eN1eH23
83.24(4)
176.59(5)
121.88(7)
122.63(8)
122.63(7)
119.72(11)
120.28(11)
112.37(10)
110.1(11)
Si1eO1
Si1eO2
Si1eO3
Si1eN2
Si1eC2
N1eC3
N1eC2
O1eC1
1.667(2)
1.675(2)
1.669(2)
2.078(2)
1.921(3)
1.482(3)
1.503(4)
1.441(3)
O2eC5
O3eC7
N2eC4
N2eC8
N2eC6
C1eC8
N1eH16
N1eH17
1.428(4)
1.429(3)
1.481(3)
1.484(3)
1.485(3)
1.512(4)
0.970(7)
0.970(7)

I.V. Sterkhova et al. / Journal of Organometallic Chemistry 775 (2015) 27e32
31
Table 6
Selected bond angles for silatrane 3.
ꢁ
ꢁ
Parameter
Angle,
Parameter
Angle,
O3eSi1eO1
O1eSi1eO2
O1eSi1eC2
O3eSi1eN2
O2eSi1eN2
C1eO1eSi1
C10eO3eSi1
C9eN2eC6
C6eN2eC7
C6eN2eSi1
118.39(6)
119.85(5)
94.83(6)
83.83(5)
83.26(5)
122.62(9)
121.83(9)
114.31(11)
113.23(11)
104.76(8)
O3eSi1eO2
O3eSi1eC2
O2eSi1eC2
O1eSi1eN2
C2eSi1eN2
C8eO2eSi1
O1eC1eC6
C9eN2eC7
C9eN2eSi1
C7eN2eSi1
117.92(5)
99.54(6)
95.27(6)
83.32(5)
176.62(6)
122.59(8)
108.70(11)
113.53(11)
104.43(8)
105.29(8)
coordination centers in compounds 2$C6H6 and 3 (Figs. 1 and 2,
respectively) is typical for the silatranes. The coordination poly-
hedron of the silicon atom in these compounds represents a dis-
torted trigonal bipyramid with N atom and C atom in the axial
positions and three oxygen atoms occupying the equatorial posi-
tions. The angles N / SieC axial fragment is almost linear in both
compounds (176.59ꢁ and 176.99ꢁ for silatrane 2$C6H6 and 3,
respectively). The displace of the silicon atom relative to the
equatorial plane defined by three oxygen atoms towards the apical
Fig. 2. Thermal ellipsoid plot for silatrane 3 (50% probability contours).
substituent (
2$C6H6 and 3, respectively. The deviation of the endocyclic nitrogen
atom from the plane of the neighboring carbon atoms ( N) com-
prises 0.38 Å and 0.41 Å for compound 2$C6H6 and 3, respectively.
According to the Cambridge Structural Database [31], these values
DSi) approximated 0.19 Å and 0.14 Å for compound
RSi(OCH2CH2)3N decreases on increasing the electron withdrawing
effect of the axial substituent R and silatranes 2$C6H6 and 3 follow
this rule. Correlations between geometrical parameters (including
D
the Si ) N bond distance) with the
s* inductive constants of
substituent R were found and discussed [58e60]. In particular it
was showed that with an increase in the order of the Si ) N bond,
the XeSi bond order reduces. The retention of the total order of the
axial bonds is one of the fundamental property of silatranes as well
as the other compounds with the pentacoordinate silicon atom
[61]. The obtained parameters of lengths of axial bonds of silatranes
2$C6H6 and 3 provide support for this view.
lie within the typical range for silatranes (
DSi z 0.09e0.24 Å and
DN z 0.34e0.40 Å). The values of Si ) N distance in compounds
2$C6H6 and 3 (2.159 Å and 2.078 Å, respectively) lie within the
typical range for silatranes (1.964e2.420 Å) and clearly show the
existence of Si ) N coordination bond. The lengths of SieC bond in
silatranes 2$C6H6 and 3 represent 1.889 Å and 1.921 Å, respectively.
The length of Si ) N coordination bond of molecule 2$C6H6 is
longer than in molecule 3 (
shorter on 0.032 Å. The protonation of the amino group (eNHMe)
D
l ¼ 0.081 Å), but length of SieC bond is
Conclusion
leads to significant increase of its electron withdrawing effect (s*
are 0.69 and 3.76 for eNHMe and eNþH2Me, respectively) [57]. As a
rule, the length of Si ) N coordination bond in silatranes
1-(Methylaminomethyl)silatrane 2 and its hydrochloride 3 were
synthesized and the solvate complex silatrane 2 with benzene was
Fig. 1. Thermal ellipsoid plot for silatrane 2 (50% probability contours).

32
I.V. Sterkhova et al. / Journal of Organometallic Chemistry 775 (2015) 27e32
€
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The structures of compounds in solutions and in the solid state
were confirmed by multinuclear NMR spectra and X-ray diffraction
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