Synthesis and structural characterization of 1-(3-aminopropyl)silatrane and some new derivatives

Article abstract of DOI:10.1016/j.poly.2011.11.014

The research goal was to synthesize and structurally characterize a silatrane intended to be subsequently incorporated into metal complex structures. 3-Aminopropyltrialkoxysilane was reacted with triethanolamine in 1:1 molar ratio, either in bulk, in the presence of metallic sodium, or in a solvent mixture. 1-(3-Aminopropyl)silatrane in carbamate form or having free amine groups was obtained. The latter was reacted with 2-hydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde and CoCl₂ or with CoCl₂ only. The crystalline reaction products were characterized by elemental and spectral (FTIR and ¹H NMR) analyses and single crystal X-ray diffractometry, which revealed the formation of new, either sought (1-(3-aminopropyl)silatrane, 1-(3-salicyliminopropyl)silatrane) or unexpected (N-carboxylated 1-(3-aminopropyl)silatrane and 1-chlorocobaltrane) structures.

Full text of DOI:10.1016/j.poly.2011.11.014

Polyhedron 33 (2012) 119–126
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Polyhedron
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Synthesis and structural characterization of 1-(3-aminopropyl)silatrane
and some new derivatives
Ana–Maria-Corina Dumitriu a, Maria Cazacu a, , Sergiu Shova a,b, Constantin Turta a,c
,
⇑
Bogdan C. Simionescu a,d
a ‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania
b Institute of Applied Physics of ASM, Academiei Str. 5, 2028 Chisinau, Republic of Moldova
c Institute of Chemistry of ASM, Academiei Str. 3, 2028 Chisinau, Republic of Moldova
d ‘‘Gh. Asachi’’ Technical University of Iasi, Department of Natural and Synthetic Polymers, Bd. D. Mangeron 71A, 700050 Iasi, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
The research goal was to synthesize and structurally characterize a silatrane intended to be subsequently
incorporated into metal complex structures. 3-Aminopropyltrialkoxysilane was reacted with triethanola-
mine in 1:1 molar ratio, either in bulk, in the presence of metallic sodium, or in a solvent mixture.
1-(3-Aminopropyl)silatrane in carbamate form or having free amine groups was obtained. The latter was
reacted with 2-hydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde and CoCl2 or with CoCl2 only. The crystal-
line reaction products were characterized by elemental and spectral (FTIR and 1H NMR) analyses and single
crystal X-ray diffractometry, which revealed the formation of new, either sought (1-(3-aminopropyl)
silatrane, 1-(3-salicyliminopropyl)silatrane) or unexpected (N-carboxylated 1-(3-aminopropyl)silatrane
and 1-chlorocobaltrane) structures.
Received 2 October 2011
Accepted 10 November 2011
Available online 25 November 2011
Keywords:
Silatrane
Aminopropylsilatrane
Carbamate
Cobaltrane
Ó 2011 Elsevier Ltd. All rights reserved.
Single crystal X-ray
Azomethine
1. Introduction
[8] was reported, silatranes typically consist of five members (Si,
O, C, C, N) in their tricyclic system. Such compounds are synthesized
Silatranes, heterotricyclic compounds having an intramolecular
transannular dative Si N bond, are of high interest both from
their structural and applications point of view [1]. The existence
of this hypervalent bond in silatranes was clearly established, these
compounds being considered as examples of systems where silicon
is pentacoordinated [1]. The analysis of the electron density distri-
bution in silatrane led to the conclusion that the interaction be-
tween nitrogen and silicon is rather electrostatic and less
covalent, involving a negative charge at nitrogen and a positive
one at silicon [2].
The decisive influence of the hypervalent Si N bond, quite dif-
ferent from a covalent bond, on the physicochemical and spectro-
scopic characteristics of silatranes has been demonstrated [1,3].
The strength of the dative bond depends not only on the substituent
on the silicon, but also on the skeletal structure of the parent ring
[1]. On the other hand, the silatranyl group has an important stereo-
electronic influence in shaping the reactivity of the exocyclic func-
tional group apical to the transannular bond [4–7]. Although in
2001 a new class of silatranes having six members (Si, O, C, C, C,
N) in their tricyclic system and named as six-membered silatranes
directly from inexpensive and widely available starting materials,
trialkoxysilane and triethanolamine or substituted triethanolamine
in 1:1 molar ratio in the presence or absence of a third reagent. The
reaction proceeds smoothly in common solvents such as benzene,
toluene or alcohol using a basic catalyst at room temperature or un-
der reflux [1]. A more simple procedure uses the hydrolysis product
of organyltrichlorosilanes (polyorganosilsesquioxanes) or poly-
organylsiloxanols in the presence of an alkaline metal hydroxide
catalyst [9]. The most interesting feature of silatranes consists in
the variation of Si–N bond length depending on the axial substituent
of Si. Therefore, the optimization of the substituted groups on the
silicon atom is important, the properties of the silatranes being cor-
related with these groups [1]. Therefore, trialkoxy- or trichlorosil-
anes having different substituents at silicon were used to prepare
silatranes: H, CH3, C2H5, (CH3)2CH, CH2@CH, C6H5, C2H5O,
p-CH3C6H4O [9], F, Cl, OH, NH2, SH, PH2, SiH3 [10], aminopropyl
[11], chloroalkyl [12], allyl, etc. Aminopropylsilatranes are of high
interest due to their potential for the preparation of new silatranes
by the derivatization of the amino group. Therefore, they act as po-
tential precursor materials for the synthesis of a number of N-deriv-
atives of silatranes [1].
Silatranes are relatively stable to moisture being more difficult
to hydrolyze as compared to their analogs (trialkoxysilanes) and
⇑
Corresponding author.
E-mail address: mcazacu@icmpp.ro (M. Cazacu).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.11.014

120
A.-M.-C. Dumitriu et al. / Polyhedron 33 (2012) 119–126
can be used in various reactions, e.g. addition, nucleophilic substi-
tution, exchange, complexation, or photochemical reactions [1].
Due to their particularities, silatranes proved useful in many prac-
tical areas. In sol–gel processes, they are used as a silica source for
the preparation of ultra-fine silica fibers [13] or as ceramic precur-
sor [14], being more stable and controllable hydrolytically. In
atomic force microscopy, aminopropylsilatrane is preferred to the
easily hydrolysable 3-aminopropyltriethoxysilane to modify the
surface of mica in order to obtain reliable imaging of DNA [15].
Silatranes are also used as coupling agents or adhesion promoters
for curable silicone compositions or to obtain silatrane-containing
polymers, which are useful as molding materials, catalyst supports,
adhesion promoters and in non-linear optics (transparent com-
pounds whose hyperpolarizability relies on the existence of do-
nor–acceptor weak bonds) [2]. Due to their demonstrated
pilotropic, antiviral, anti-inflammatory, antienzymatic, anticancer
and antitumour, antibacterial and antifungal activities, as well as
to their antistress and immunostimulant action [1,16], wound
cicatrizing and burns healing effects, animal production and seed
germination effects, etc., silatranes are widely used in biological
systems [1]. Nontoxic or low toxicity silatranes stimulate the bio-
synthesis of nucleic acids and proteins and the growth of some
cells, especially regenerating cells of connective tissue and liver
[16]. Silatranes properly derivatized can lead to redox or biological
active complexes with transition metals [4].
This paper reports the preparation of 1-(3-aminopropyl)silatrane,
2, named according to IUPAC rules 1-(3-aminopropyl)-2,8,9-trioxa-
5-aza-1-silabicyclo[3.3.3.01.5]undecane, by using two routes, one of
them leading to the carbamate complex of the silatrane, 1, that was
characterized as such, the other resulting in the silatrane with a free
amine group. The latter was derivatized by reacting with 2-hydroxy-
benzaldehyde, yielding a new imino-silatrane, 3. The attempt to pre-
pare in one step the cobalt complex of 2,4-dihydroxybenzimine-
silatrane led to the unexpected formation of the new, unreported 1-
chlorocobaltrane, 4. Reaction of the aminopropylsilatrane with CoCl2
caused the decomposition of the silatrane with formation of trietha-
nolamine chlorohydrate, 5. All crystalline reaction products were
investigated by elemental and spectral (FTIR and 1H NMR) analyses
and the structures were established by single-crystal X-ray diffrac-
tion. It is expected that, among other properties, the resulted com-
pounds to be biologically active.
The samples were incorporated in dry KBr and processed as pellets
in order to be analyzed.
The proton magnetic resonance (1H NMR) spectra were ac-
quired in CDCl3 or D2O at 25 °C with a Bruker Avance DRX
400 MHz spectrometer operating at 400.13 MHz for 1H. The spec-
trometer was equipped with a 5 mm four nuclei, direct detection
z-gradient probehead.
The carbon, hydrogen, nitrogen, and silicon contents were
determined by standard methods. The molar ratio Co/Cl was esti-
mated by using an Energy-Dispersive X-ray Fluorescence (EDXRF)
system EX-2600 X-Calibur SDD.
2.3. X-ray crystallography
Crystallographic measurements for 1, 2, 3 and 4 compounds were
carried out with an Oxford-Diffraction XCALIBUR E CCD diffractom-
eter using graphite-monochromated MoKa radiation. The crystals
were placed 40 mm from the CCD detector. The unit cell determina-
tion and data integration were carried out using the CrysAlis pack-
age of Oxford Diffraction [17]. All structures were solved by direct
methods using SHELXS-97 [18] and refined by full-matrix least-
2
squares on Fo with SHELXL-97 [18] with anisotropic displacement
parameters for non-hydrogen atoms. All H atoms attached to carbon
were introduced in idealized positions (dCH = 0.96 Å) using the rid-
ing model with their isotropic displacement parameters fixed at
120% of their riding atom. Positional parameters of the H attached
to N and O atoms were obtained from difference Fourier syntheses
and verified by the geometric parameters of the corresponding
hydrogen bonds. In the structures 3 and 4 the atoms from the silatra-
ne moieties presented large thermal ellipsoids, so that disordered
models, in combination with the available tools (PART, DFIX, and
SADI) of SHELXL-97 were applied in order to better fit the electron
density. In both 3 and 4 structures, the silatrane part was found to
be disordered over two resolvable positions with the equal probabil-
ities of 50%. The main crystallographic data together with refine-
ment details are summarized in Table 1.
2.4. Procedures
2.4.1. Synthesis of 1-(3-aminopropyl)silatrane
2.4.1.1. Procedure I (leading to compound 1). A catalytic amount of
sodium metal (5 mg) was added to triethanolamine (15.0 mL,
16.8 g, 0.11 mol) in a 250 mL round-bottom flask to form a solu-
tion. A glass tube was attached to the flask through a septum to al-
low the capture of the resulted hydrogen into a rubber balloon. The
mixture was heated up to 130 °C for 1 h and then cooled at room
temperature. An equivalent amount of (3-aminopropyl)trimethox-
ysilane (25.0 g, 0.11 mol) was added and the mixture was heated at
60 °C for 1 h. The methanol formed as a result of the reaction
occurrence was removed by distillation in rotavap when a white
solid remained. White needles crystals, 1, suitable for single crystal
X-ray analysis were separated after 2 days from the extract in THF.
Yield: 8 g (83.9%); Anal. Calc. for C19H40O8N4Si2 (M = 508 g/mol):
C, 44.9; H, 7.9; N, 11.0; Si, 11.0. Found: C, 45.2; H, 7.9; N, 10.54; Si,
10.62%.
2. Experimental
2.1. Materials
3-Aminopropyltrimethoxysilane, H2N(CH2)3Si(OCH3)3, (APTMS),
(Fluka, M = 179.19, bp = 91–92 °C/15 mm Hg, d240 ¼ 1:016 g=mL).
3-Aminopropyltriethoxysilane, (C2H5O)3Si(CH2)3NH2, (APTES),
(Fluka, M = 221.37, bp = 213–216, d240 ¼ 0:949).
Triethanolamine, (HOCH2CH2)3N, (Sigma–Aldrich), M = 149.19, pur-
iss. p.a. (>99%), 190–193 °C/5 mm Hg, n2D0 ¼ 1:485, d25 = 1.124 g/mL.
2-Hydroxybenzaldehyde (Aldrich), M = 122.12, reagent grade
(8%, b.p. 197 °C, m.p. 1–2 °C, density: 1.146 g/mL).
2,4-Dihydroxybenzaldehyde (Aldrich), (HO)2C6H3CHO, 98%,
M = 138.12, m.p. 135–137.
FTIR (KBr pellet, cmꢁ1): 3379s, 2936m, 2879s, 2642vw, 2584vw,
2517vw, 2170vw, 1630m, 1562m, 1534m, 1486s, 1476s, 1417vw,
1430vw, 1372m, 1324m, 1279m, 1192w, 1172w, 1124vs, 1098vs,
1088vs, 1053m, 1017m, 940m, 911m, 880w, 862vw, 822w,
806m, 763vs, 719s, 665m, 618m, 584m, 576m, 499vw, 461w.
The poor solubility of the compounds in usual organic solvents
did not allow the registration of a qualitative 1H NMR spectrum.
Cobalt(II) chloride hexahydrate, CoCl2ꢀ6H2O, 98% (Sigma–
Aldrich).
2.2. Measurements
Fourier transform infrared (FT-IR) spectra were recorded using a
Bruker Vertex 70 FT-IR spectrometer. Analyses were performed in
the transmission mode in the 400–4000 cmꢁ1 range, at room tem-
perature, with a resolution of 2 cmꢁ1 and accumulation of 32 scans.
2.4.1.2. Procedure II (leading to compound 2). In one-necked, flat-bot-
tom flask, equipped with reflux condenser were introduced (3-ami-
nopropyl)triethoxysilane (0.24 mol, 4.3 g, 4.4 mL), triethanolamine

A.-M.-C. Dumitriu et al. / Polyhedron 33 (2012) 119–126
121
Table 1
Crystallographic data, details of data collection and structure refinement parameters for 1–4.
Compound
1
2
3
4
Empirical formula
Molecular weight (g/mol)
T (K)
C
19H40N4O8Si2
C9H20N2O3Si
232.36
200(2)
C16H24N2O4Si
336.45
200(2)
C6H14CoClNO3
242.56
200(2)
508.73
200(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Orthorhombic
P212121
6.6445(8)
13.7806(16)
27.248(5)
90
0.71073
Monoclinic
P21
6.638(4)
12.9757(11)
7.1106(17)
90
0.71073
Monoclinic
P21/n
12.211(5)
14.100(2)
19.274(4)
90
0.71073
Orthorhombic
Pnma
16.9041(3)
7.8788(2)
6.78770(10)
90
a
(°)
b (°)
90
90
2495.0(6)
4
1.354
106.97(4)
90
585.8(4)
2
1.317
0.192
92.84(3)
90
3314.3(15)
8
1.349
0.164
90
90
904.01(3)
4
1.782
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
l
(mmꢁ1
)
0.193
2.161
hmin, hmax (°)
Crystal size (mm)
2.96–25.99
0.25 ꢂ 0.15 ꢂ 0.15
8559/4508 [Rint = 0.0610]
0.45(18)
0.0676
0.0811
1.005
0.307 and ꢁ0.269
3.00–26.00
0.20 ꢂ 0.10 ꢂ 0.10
2468/1886 [Rint = 0.0151]
ꢁ0.03(14)
0.0361
0.0911
1.080
0.205 and ꢁ0.310
3.00–26.00
0.35 ꢂ 0.15 ꢂ 0.15
17532/6501 [Rint = 0.0264]
3.25–25.97
0.20 ꢂ 0.15 ꢂ 0.15
Reflections collected/unique
Absolute structure parameter
3778/950 [Rint = 0.0224]
a
R1
0.0482
0.1202
1.081
0.231and ꢁ0.286
0.0338
0.0819
1.007
0.445 and ꢁ0.629
b
wR2
Goodness-of-fit (GOF)c
D
qmax and
D
qmin (e/Å3)
P
P
a
b
c
R1
=
||Fo| ꢁ |Fc||/ |Fo|.
P
P
P
wR2 = { [w(Fo ꢁ Fc2)2]/ [w(Fo2)2]}1/2
.
2
GOF = { [w(Fo ꢁ Fc2)2]/(n ꢁ p)}1/2, where n is the number of reflections and p is the total number of parameters refined.
2
(6.7 mol, 1.49 g, 1.57 mL), MeOH 14.2 mL, BuOH 1 mL and toluene
50 mL. The mixture was stirred 3 h at 60 °C and then concentrated
by rotavap. White crystals, labeled as 2, were obtained after 24 h.
Yield: 0.60 g (77.7%); Anal. Calc. for C9H20O3N2Si (M = 232
g/mol): C, 46.5; H, 8.6; N, 12.1; Si, 12.1. Found: C, 46.2; H, 8.7; N,
11.9; Si, 12.3%.
N–CH2–CH2–O–); 6.82–6.87 (1H, aromatic), 6.95–6.97 (1H, aro-
matic), 7.22–7.25 (1H, aromatic), 7.27–7.32 (1H, aromatic), 8.32,
(1H,
–CH@N–),
14.03
(1H,
–OH)
intensity
ratio:
2:2:2:6:6:1:1:1:1:1:1.
2.4.3. Procedure leading to 1-chlorocobaltrane, 4
FTIR (KBr pellet, cmꢁ1): 3359s, 3294m, 3192m, 2931s, 2878s,
1631sh, 1580s, 1483s, 1386m, 1329m, 1310m, 1279m, 1192m,
1125vs, 1097vs, 1050s, 1037s, 1020s, 941m, 912m, 880w, 862w,
763s, 718m, 670m, 697m, 620m, 582m, 484w, 455w.
1H NMR (400.13 MHz, CDCl3), d, ppm: 0.21–0.25 (2H,
–(CH3)2Si–CH2–), 1.32–1.40 (2H, –(CH3)2Si–CH2–CH2–CH2–NH2);
2.46–2.49 (2H, –(CH3)2Si–CH2–CH2–CH2–NH2); 2.83–2.92 (6H,
N–CH2–CH2–O–); 3.65–3.68 (6H, N–CH2–CH2–O–); intensity ratio:
1:1:1:3:3.
In one-necked flat-bottom flask equipped with reflux condenser
were introduced MeOH (15 mL) and 2 (4.64 g, 0.02 mol). 2,4-Dihy-
droxybenzaldehyde (2.76 g, 0.02 mol) was added, and the mixture
was stirred 3 h at 65 °C when an orange precipitate was formed.
The reaction mixture was cooled to room temperature, filtered to
give a clear filtrate, to which was further added CoCl2ꢀ6H2O
(4.75 g, 0.02 mol) dissolved in 3 mL MeOH. The mixture was left
for slow evaporation of the solvent and red crystals, 4, were ob-
tained after 2 months. These were further investigated.
Anal. Calc. for C6H12NO3SCoCl (M = 240.5 g/mol): C, 29.93; H,
4.98; N, 5.82. Found: C, 30.01; H, 4.95; N, 5.79%.
2.4.2. Procedure for the synthesis of 1-(3-salicyliminopropyl)
silatrane, 3
The Co/Cl molar ratio determined by XRF was 1:1 corresponding
to %: Co, 24.32; Cl, 14.69 (Anal. Calc.: Co, 24.54; Cl, 14.77).
FTIR (KBr pellet, cmꢁ1): 3552s, 3348s3313vs, 3212s, 3158s,
3041s, 2937s, 2724m, 2628w, 1606m, 1549w, 1488s, 1461m,
1442m, 1404s, 1327m, 1227m, 1135vs, 1098vs, 1032s, 1005s,
917m, 900m, 845w, 790w, 748w, 699m, 606m, 545w, 528m, 477w.
1H NMR (400.13 MHz, D2O), d, ppm: broad peaks centered at
3.03 (6H, N–CH2–CH2–O–Co–); 3.81 (6H, N–CH2–CH2–O–Co–).
In one-necked, flat-bottom flask, equipped with a reflux con-
denser, were introduced MeOH (15 mL) and 2 (4.64 g, 0.02 mol).
2-Hydroxybenzaldehyde (2.44 g, 0.02 mol) was added, and the
reaction mixture was stirred for 3 h at 65 °C and then left for slow
evaporation of the solvent. Yellow crystals, 3, were obtained after
48 h.
Yield: 5 g (74.4%); Anal. Calc. for C16H24N2O4Si (M = 336 g/mol):
C, 57.14; H, 7.14; N, 8.33; Si, 8.33. Found: C, 57.0; H, 7.2; N, 8.28; Si,
8.4%.
2.4.4. Procedure leading to triethanolamine hydrochloride, 5
In one-necked, flat-bottom flask were introduced MeOH
(15 mL) and 2 (2.32 g, 0.01 mol). CoCl2ꢀ6H2O (4.75 g, 0.02 mol) dis-
solved in MeOH (3 mL) was added with stirring at room tempera-
ture. The mixture was left for slow evaporation and crystals labeled
as 5 were obtained after 1 week.
FTIR (KBr pellet, cmꢁ1): 3435m, 3260w, 2965m, 2936s, 2919s,
2873s, 2838m, 2807w, 1634vs, 1610s, 1583m, 1505m, 1483m,
1459m, 1441m, 1415m, 1383w, 1371w, 1351w, 1340w, 1278s,
1245w, 1213w, 1197m, 1189m, 1175m, 1127vs, 1101vs, 1053m,
1031m, 1015s, 983w, 960w, 936m, 908s, 876m, 864m, 852m,
810m, 776vs, 718s, 677w, 650m, 614m, 586m, 567w, 484vw,
460w.
3. Results and discussions
1H NMR (400.13 MHz, CDCl3), d, ppm: 0.49–0.51 (2H, –Si–CH2–),
1.80–1.87 (2H, Si–CH2–CH2–CH2–NH2); 3.58–3.61 (2H, Si–CH2–
CH2–CH2–NH2); 2.83–2.86 (6H, N–CH2–CH2–O–); 3.79–3.82 (6H,
We have approached two procedures to prepare 1-(3-aminopropyl)
silatrane, both involving the treatment of a 3-aminopropyltrialkox-

122
A.-M.-C. Dumitriu et al. / Polyhedron 33 (2012) 119–126
ysilane with triethanolamine in 1:1 molar ratio, in the presence
(procedure I, Scheme 1a) [15] or absence (procedure II, Scheme
1b) of a third reagent, metallic sodium. Procedure I used 3-
aminopropyltrimethoxysilane and procedure II used 3-aminopro-
pyltriethoxysilane. While procedure I occurred in bulk, without
solvent, a mixture of solvents was used as reaction medium in the
second approach.
can be found in the spectrum of the compound 2 prepared by pro-
cedure II: split band at 1097, 1125, 1020 and 941 cmꢁ1 is assigned
to Si–O–C–C– structural fragment; the doublet at 718, 763 cmꢁ1 is
due to a band split in the second frequency
670 cmꢁ1 bands are assigned to
(Si–C) and s(Si–O), respectively;
the band at 582 cmꢁ1 is associated to
(Si N); the silatrane cyclic
skeleton structure presents specific bands at 1386 and 1483 cmꢁ1
mas(Si–O); 620 and
m
m
m
,
Product formation was verified by FTIR spectroscopy. The most
characteristic absorption bands associated with silatrane structure
assigned to deformation modes of the CH2 group [11,19,20], but
also at about 1050 cmꢁ1, identified with stretching vibrations of
Scheme 1. Reaction pathway leading to: a – [1-(3-ammoniumpropyl)silatrane]1-(3-carbamatepropyl)silatrane, 1; b – 1-(3-aminopropyl)silatrane, 2.
Scheme 2. Reaction pathway leading to: c – 1-(3-salicyliminopropyl)silatrane, 3; d – 1-chlorocobaltrane, 4; e – triethanolamine chlorohydrate, 5.

A.-M.-C. Dumitriu et al. / Polyhedron 33 (2012) 119–126
123
the C–C bond in the silatrane skeleton, according to literature [9].
The bands at 3294 and 3192 cmꢁ1 are assigned to N–H stretching
while the medium strong band at 1580 cmꢁ1 is assigned to N–H
bending [21]. All peaks expected according to literature data are
present in 1H NMR, the intensities ratio corresponding to the pre-
sumed structure.
It is assumed [22] that silatrane formation involves a change of
hybridization of silicon from sp3 to sp2 leading to the formation of
the dative Si N bond. These neutral pentacoordinated silicon
compounds are charge-transfer complexes. The dative bond is
weaker than a covalent bond and is very sensitive to the inductive
effects of the substituents, and is shortened as the number of elec-
tron-withdrawing groups linked to silicon increases. The length of
this bond is also influenced by the position, axial or equatorial,
occupied by the substituent at the silicon as well as by cage effects
[22].
product would be based on well-known tendency of the amines
to undergo carbonation in air to form sec-ammonium N-carboxyl-
ates (carbamates) [24] that is stimulated at high pH values [25] as
in the present case when the synthesis occurred in the presence of
sodium. Carbamates themselves represent another important class
of organic compounds, used in a variety of applications including
polyurethanes, pesticides, fungicides, medicinal drugs, and syn-
thetic intermediates [26]. When subjected to heating under vac-
uum [26] or in presence of moisture [27], the carbamates can
decompose to the initial amine.
1-(3-Aminopropyl)silatrane was reacted with 2-hydroxybenz-
aldehyde to obtain azomethine 3 (Scheme 2c). The reaction prod-
uct was separated as high quality crystals able to be investigated
by single-crystal X-ray diffraction. The structure was first verified
by spectral (FTIR and 1H NMR) analyses. The disappearance of
the free amine groups (3294 and 3192 cmꢁ1) and the presence of
the band at 1634 cmꢁ1 prove the azomethine formation. The other
silatrane characteristic bands can also be found in the spectrum at
about the same wavelength as in 1-(3-aminopropyl)silatrane.
In the 1H NMR spectrum one can notice the presence of the peak
at 8.32, assigned to the imine proton, besides those belonging to
aromatic protons and the displacement of the protons of the propyl
group: from 0.21–0.25 (2H, –Si–CH2–), 1.32–1.40 (2H, Si–CH2–
CH2–CH2–NH2); 2.46–2.49 (2H, Si–CH2–CH2–CH2–NH2); 2.83–
2.92 (6H, N–CH2–CH2–O–); 3.65–3.68 (6H, N–CH2–CH2–O–) in 2
to 0.49–0.51 (2H, –Si–CH2–), 1.80–1.87 (2H, Si–CH2–CH2–CH2–
NH2); 3.58–3.61 (2H, Si–CH2–CH2–CH2–NH2) in 3.
Although the synthesis of 1-(3-aminopropyl)silatrane is re-
ported in literature [1,11], its structure is not known. In the first at-
tempt we chose to work in bulk, without any solvent, in the
presence of metallic sodium, according to the procedure described
in Ref. [15] when an unexpected structure was obtained, namely
silatrane carbamate, 1. Its IR spectral pattern differs from that of
the compound 2 mainly by the absence of the bands corresponding
to free NH2 group. At the same time, a new well-defined band as-
signed to C@O symmetric stretching of carbamate appears at
1534 cmꢁ1 [23], while the N–H bending is shifted to 1562 cmꢁ1
.
A shifting to higher wavenumbers and splitting of the bands as-
signed to CH2 group (1486, 1476 cmꢁ1) also occurred. The other
specific bands (C–O–Si and Si N) can be found at about the same
frequencies as in the uncarbonated silatrane (1017–1124 and
584 cmꢁ1, respectively). The explanation for the formation of this
In a different approach, 1-(3-aminopropyl)silatrane, 2, was re-
acted with 2,4-dihydroxybenzaldehyde and subsequently with
CoCl2. The aim was to prepare the corresponding azomethine suit-
able to form a cobalt complex in a one-pot procedure by involving
Fig. 1. X-ray structure of compound 1. Thermal ellipsoids are drawn at 40%
probability level. Two intermolecular H-bonds N2–Hꢀ ꢀ ꢀO7 [N2–H 0.890 Å, Hꢀ ꢀ ꢀO7
1.950 Å, N2ꢀ ꢀ ꢀO7 2.810(4) Å, N2–Hꢀ ꢀ ꢀO7 162.2°] and N4–Hꢀ ꢀ ꢀO3 [N4–H 0.860 Å,
Hꢀ ꢀ ꢀO3 2.425 Å, N4ꢀ ꢀ ꢀO3 3.127(4) Å, N4–Hꢀ ꢀ ꢀO3 139.2°] are also shown. Selected
bonds (Å) and angles (°): Si2–O6 1.667(3), Si2–O5 1.670(3), Si2–O4 1.674(3), Si2–
C16 1.878(4), Si2–N3 2.203(4), Si1–O2 1.657(3), Si1–O1 1.671(3), Si1–O3 1.676(3),
Si1–C7 1.878(4), Si1–N1 2.189(4); O6–Si2–O5 118.9(2), O6–Si2–O4 116.57(2), O5–
Si2–O4 119.60(2), O6–Si2–C16 97.50(2), O5–Si2–C16 97.04(2), O4–Si2–C16
97.84(2), O6–Si2–N3 82.72(2), O5–Si2–N3 82.29(2), O4–Si2–N3 82.62(2), C16–
Si2–N3 179.32(2), O2–Si1–O1 118.39(2), O2–Si1–O3 118.64(2), O1–Si1–O3
118.24(2), O2–Si1–C7 97.40(2), O1–Si1–C7 97.84(2), O3–Si1–C7 96.56(2), O2–
Si1–N1 82.24(2), O1–Si1–N1 83.43(2), O3–Si1–N1 82.53(2), C7–Si1–N1 178.69(2).
Fig. 2. X-ray structure of compound 2. Thermal ellipsoids are drawn at 40%
probability level. Selected bonds (Å) and angles (°): Si1–O3 1.660(2), Si1–O1
1.664(2), Si1–O2 1.667(2), Si1–C7 1.874(3), Si1–N1 2.171(2); O3–Si1–O1 118.61(1),
O3–Si1–O2 117.28(1), O1–Si1–O2 119.38(1), O3–Si1–C7 97.71(1), O1–Si1–C7
97.61(1), O2–Si1–C7 96.47(1), O3–Si1–N1 83.04(9), O1–Si1–N1 82.45(9)°, O2–
Si1–N1 82.73(9), C7–Si1–N1 179.10(1).

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A.-M.-C. Dumitriu et al. / Polyhedron 33 (2012) 119–126
Fig. 5. The association of the RNH3+ cations and RNHCO2ꢁ anions into the bands in
the crystal structure 1. H-bonds parameters: N2–Hꢀ ꢀ ꢀO7 [N2–H 0.890 Å, Hꢀ ꢀ ꢀO7
1.842 Å, N2ꢀ ꢀ ꢀO7(x ꢁ ½, ꢁy + 3/2, ꢁz + 1) 2.713(4) Å, N2–Hꢀ ꢀ ꢀO7 165.9°]; N2–Hꢀ ꢀ ꢀO8
[N2–H 0.890 Å, Hꢀ ꢀ ꢀO8 1.978 Å, N2ꢀ ꢀ ꢀO8(x ꢁ 1, y, z) 2.837(4) Å, N2–Hꢀ ꢀ ꢀO8 161.8°].
azomethine group and OH group from 2 position, that from 4 posi-
tion remaining available for further derivatization. However, the
high quality red crystals separated after 2 months proved to be a
new, unexpected compound, 1-chlorocobaltrane, 4, formed by
replacement of the aminopropyl substituted silicon in 1-(3-amino-
propyl)silatrane with Co having a chlorine atom attached.
The FTIR spectrum of compound 4 presents the main bands
characteristic for triethanolamine-derived atrane but slightly
shifted from those of silatrane: 1135, 1098, 1032 and 1005 cmꢁ1
assigned to sequence Co–O–C–C– and 528 for
m
(Co N).
The 1H NMR peaks in compound 4 (3.81 for –O–CH2– and
3.03 ppm for –CH2–N<) are downfield shifted as compared with
corresponding ones from free triethanolamine (3.68–3.71 and
2.73–2.76 ppm, respectively), both spectra being registered in
D2O solution. The largest shift (0.27 ppm) was recorded for the
peak corresponding to the protons from –CH2–N< group, which re-
flects the presence of the partial positive charge on the tertiary
nitrogen in this compound [9,28]. The peak broadening is due to
the presence of paramagnetic cobalt ion.
Fig. 3. X-ray structure of compound 3. Thermal ellipsoids are drawn at 40%
probability level. Only one of two disordered positions for silatrane fragment is
shown for clarity. H-bond parameters: O4A–Hꢀ ꢀ ꢀN2A [O4A–H 0.820 Å, Hꢀ ꢀ ꢀN2A
1.795 Å, O4Aꢀ ꢀ ꢀN2A 2.528(5) Å, O4A–Hꢀ ꢀ ꢀN2A 148.1°]. Selected bonds (Å) and
angles (°) (for component A): Si1–O1 1.682(4), Si1–O2 1.638(8), Si1–O3 1.634(8),
Si1–C7 1.849(2), Si1–N1 2.185(2); O3–Si1–O2 120.5(6), O3–Si1–O1 120.0(5), O2–
Si1–O1 116.5(4), O3–Si1–C7 94.9(4)°, O2–Si1–C7 95.7(4), O1–Si1–C7 96.85(2), O3–
Si1–N1 84.3(4), O2–Si1–N1 84.4(4), O1–Si1–N1 83.94(2), C7–Si1–N1 179.07(1).
When mixed only with CoCl2, 1-(3-aminopropyl)silatrane
decomposed forming triethanolamine chlorohydrate, 5, as proved
by the X-ray structural analysis of the formed crystals (Scheme 2e).
The X-ray single-crystal investigation revealed that in all syn-
thesized compounds, the silicon, as well as the cobalt atom,
exhibits a pentacoordinated environment with slightly distorted
trigonal-bipyramidal geometry. The perspective view of 1–4
structures, along with atom-labeling schemes is given in Figs. 1–
4, respectively.
+
Crystal 1 has an ionic structure build of RNH3 cations and
RNHCO2ꢁ anions in 1:1 ratio, where R is the propylsilatrane moiety
(Fig. 1). The ionic components of the structure are linked into the
bands along [011] (Fig. 5), due to the multiple N–Hꢀ ꢀ ꢀO H-bonds,
the formation of which being completely realized in the crystal.
The father extension of the crystal structure occurs via the weak
C–Hꢀ ꢀ ꢀO intermolecular contacts with distances: C6–H 0.97 Å, C6–
Hꢀ ꢀ ꢀO20 (1 + x, y, z) 3.544(5) Å, Hꢀ ꢀ ꢀO2 2.62 Å, C6–Hꢀ ꢀ ꢀO2 160.1°;
C11–H 0.97 Å, C11–Hꢀ ꢀ ꢀO80 (1 ꢁ x, y ꢁ ½, ½ ꢁ z) 3.280(5) Å, Hꢀ ꢀ ꢀO8
2.45 Å, C11–Hꢀ ꢀ ꢀO8 143.9°; C15–H 0.97 Å, C15–Hꢀ ꢀ ꢀO40(x ꢁ 1, y, z)
3.273(5) Å, Hꢀ ꢀ ꢀO4 2.61 Å, C15–Hꢀ ꢀ ꢀO4 125.9°. The others intermo-
lecular contacts are equal or exceed the sum of van-der-Waals radii.
The crystal structure 2 is built from the parallel packing along
[001] of the infinite ribbons, the view of which is depicted in
Fig. 6. Within the ribbon the molecules are consolidated through
N–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀN and C–Hꢀ ꢀ ꢀO intermolecular contacts (Fig. 6).
The asymmetric part of the unit cell in crystal structure 3 con-
tains two discrete molecules (denoted as A and B) as crystallo-
graphically independent units, which exhibit quite similar
Fig. 4. Molecular structure of compound 4. Only one of two disordered positions
are shown. Thermal ellipsoids are drawn at 40% probability level. Symmetry code:
(i) x, 0.5 ꢁ y, z. Selected bonds (Å) and angles (°): Co1–O1 1.986(3) Å, Co1–O2
2.043(2) Å, Co1–N1 2.168(4) Å, Co1–Cl1 2.307(1) Å; O1–Co1–O2 117.36(7)°, O2–
Co1–O2i 117.16(1)°, O1–Co1–N1 82.09(1)°, O2–Co1–N1 79.60(8)°, O1–Co1–Cl1
99.62(1)°, O2–Co1–Cl1 99.54(6)°, N1–Co1–Cl1 178.29(1)°.

A.-M.-C. Dumitriu et al. / Polyhedron 33 (2012) 119–126
125
Fig. 6. View of crystal structure 2. Three intermolecular H-bonds: N2–Hꢀ ꢀ ꢀO1 [N2–H 0.898 Å, Hꢀ ꢀ ꢀO1 2.472 Å, N2ꢀ ꢀ ꢀO1(x ꢁ 1, y, z) 3.327(4) Å, N2–Hꢀ ꢀ ꢀO1 159.1°]; C3–Hꢀ ꢀ ꢀN2
[C3–H 0.99 Å, Hꢀ ꢀ ꢀN2 2.50 Å, C3ꢀ ꢀ ꢀN2(-x, y ꢁ ½, 2 ꢁ z) 3.454(4) Å, C3–Hꢀ ꢀ ꢀN2 161.4°] and C1–Hꢀ ꢀ ꢀO2 [C1–H 0.99 Å, Hꢀ ꢀ ꢀO2 2.65 Å, C1ꢀ ꢀ ꢀO2(1 + x, y, z) 3.566(3) Å, C1–Hꢀ ꢀ ꢀO2
154.4°] are also shown.
Fig. 7. 2D supramolecular layer in crystal structure 4. H-bond: O2–Hꢀ ꢀ ꢀO1 [O2–H 0.965 Å, Hꢀ ꢀ ꢀO1 1.616 Å, O2ꢀ ꢀ ꢀO1(ꢁx + 3/2, 1 ꢁ y, ½ + z) 2.580(3) Å, O2–Hꢀ ꢀ ꢀO1 179.3°].
geometric parameters. In both molecules all the carbon and oxygen
atoms of silatrane fragments are disordered over two resolvable
positions with the equal probabilities of s.o.f. As an example, the
structure of molecule A is presented in Fig. 3.
H-bond: O2–Hꢀ ꢀ ꢀO1 [O2–H 0.965 Å, Hꢀ ꢀ ꢀO1 1.616 Å,
O2ꢀ ꢀ ꢀO1(ꢁx + 3/2, 1 ꢁ y, ½ + z) 2.580(3) Å, O2–Hꢀ ꢀ ꢀO1 179.3°.
4. Conclusion
To the best of our knowledge, compound 4 is the first re-
ported example of cobalt containing metallatranes (Fig. 4). The
Co2+ ion has a slightly distorted trigonal-bipyramidal coordina-
tion provided by tridentate thriethanolamine ligand and chloride
anion in apical position at 2.307(1) Å. The central atom is dis-
placed from the average equatorial 3O plane at 0.335(2) Å to-
wards chlorine atom. The X-ray study demonstrated that
triethanolamine ligand in compound 4 is coordinated to Co atom
in monodeprotonated form, so that the charge balance is in
agreement with the formation of species 4. Two negative charges
provided by Co2+ ion are balanced by the one negative charge of
monodeprotonated tridentate ligand and one negative charge of
chloride anion. The view of crystal packing for compound 4 is
depicted in Fig. 7. It consists of alternate two-dimensional layers
oriented along a bc crystallographic plane. The layers are built
from neutral molecules 4 connected via a system of intermolec-
ular O–Hꢀ ꢀ ꢀO hydrogen bonds. Each molecule acts ones as proton
acceptor and twice as proton donor, thus fulfilling all H-bonds
opportunities in the crystal.
3-Aminopropyltrialkoxysilane was reacted with triethanola-
mine to obtain 1-(3-aminopropyl)silatrane. Either silatrane having
a free amine group or an ammonium carbamate pair were obtained
depending on the reaction conditions. A new azomethine structure
was obtained by reacting 1-(3-aminopropyl)silatrane with 2-
hydroxybenzaldehyde. The attempt to prepare the azomethine de-
rived from aminopropylsilatrane with 2,4-dihydroxybenzaldehyde
and its cobalt complex resulted in formation of a new, unexpected
crystalline atrane. The treatment of 1-(3-aminopropyl)silatrane
with CoCl2 led to the complete decomposition of the silatrane with
separation of triethanolamine chlorohydrate. The biological activ-
ity of the obtained compounds will be further studied.
Acknowledgements
This research was financially supported by European Regional
Development Fund, Sectoral Operational Program ‘‘Increase of

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