Imidazolyl-substituted silatranes derived from triethanolamine and tris(isopropanol)amine: Syntheses and structural characterization

Article abstract of DOI:10.1080/00958972.2014.1003547

The syntheses of seven new silatranes, N-[3-(3,7,10-trimethylsilatranyl)propyl]imidazole (7), N-(3-silatranylpropyl)-4-methylimidazole (8), N-[3-(3,7,10-trimethylsilatranyl)propyl]-4-methylimidazole (9), N-(3-silatranylpropyl)-2-methylimidazole (10), N-[3-(3,7,10-trimethylsilatranyl)propyl]-2-methylimidazole (11), N-(3-silatranylpropyl)-2-imidazoline (12), and N-[3-(3,7,10-trimethylsilatranyl)propyl]-2-imidazoline (13), are reported. These silatranes were prepared by transesterification of triethoxysilanes, N-(3-triethoxysilylpropyl)imidazole (3), N-(3-triethoxysilylpropyl)-4-methylimidazole (4), N-(3-triethoxysilylpropyl)-2-methylimidazole (5) and N-(3-triethoxysilylpropyl)-2-imidazoline (6) with triethanolamine (1), and tris(isopropanol)amine (2). The structures of five silatranes (7, 8, 9, 10, and 12) were confirmed by X-ray crystallography. The compounds were investigated by elemental analysis, IR, ¹H, ¹³C NMR spectroscopy, thermogravimetric analysis, and mass spectrometry.

Full text of DOI:10.1080/00958972.2014.1003547

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Imidazolyl-substituted silatranes derived from
triethanolamine and tris(isopropanol)amine:
syntheses and structural characterization
Gurjaspreet Singh, Sheenam Girdhar, Sadhika Khullar & Sanjay K. Mandal
To cite this article: Gurjaspreet Singh, Sheenam Girdhar, Sadhika Khullar & Sanjay
K. Mandal (2015) Imidazolyl-substituted silatranes derived from triethanolamine and
tris(isopropanol)amine: syntheses and structural characterization, Journal of Coordination
Chemistry, 68:5, 875-894, DOI: 10.1080/00958972.2014.1003547
To link to this article: http://dx.doi.org/10.1080/00958972.2014.1003547
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Date: 14 September 2015, At: 01:36

Journal of Coordination Chemistry, 2015
Vol. 68, No. 5, 875–894, http://dx.doi.org/10.1080/00958972.2014.1003547
Imidazolyl-substituted silatranes derived from
triethanolamine and tris(isopropanol)amine: syntheses and
structural characterization
GURJASPREET SINGH*†, SHEENAM GIRDHAR†, SADHIKA KHULLAR‡ and
SANJAY K. MANDAL*‡
†Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University,
Chandigarh, India
‡Department of Chemical Sciences, Indian Institute of Science Education and Research, Mohali, India
(Received 29 May 2014; accepted 16 December 2014)
The syntheses of seven new silatranes, N-[3-(3,7,10-trimethylsilatranyl)propyl]imidazole (7), N-(3-sila-
tranylpropyl)-4-methylimidazole (8), N-[3-(3,7,10-trimethylsilatranyl)propyl]-4-methylimidazole (9),
N-(3-silatranylpropyl)-2-methylimidazole (10), N-[3-(3,7,10-trimethylsilatranyl)propyl]-2-methylimid-
azole (11), N-(3-silatranylpropyl)-2-imidazoline (12), and N-[3-(3,7,10-trimethylsilatranyl)propyl]-2-im-
idazoline (13), are reported. These silatranes were prepared by transesterification of triethoxysilanes,
N-(3-triethoxysilylpropyl)imidazole (3), N-(3-triethoxysilylpropyl)-4-methylimidazole (4), N-(3-trieth-
oxysilylpropyl)-2-methylimidazole (5) and N-(3-triethoxysilylpropyl)-2-imidazoline (6) with triethanol-
amine (1), and tris(isopropanol)amine (2). The structures of five silatranes (7, 8, 9, 10, and 12) were
1
confirmed by X-ray crystallography. The compounds were investigated by elemental analysis, IR, H,
13C NMR spectroscopy, thermogravimetric analysis, and mass spectrometry.
Keywords: Silatrane; Imidazole; Transesterification; Thermogravimetric analysis; Tris(isopropanol)
amine
1. Introduction
Since the concept of silatrane was first put forth by Frye and Vogel [1] and Turley and Boer
[2], a plethora of syntheses [3–6] and various applications of silatranes [7–11] have been
*Corresponding authors. Email: gjpsingh@pu.ac.in (G. Singh); sanjaymandal@iisermohali.ac.in (S.K. Mandal)
© 2015 Taylor & Francis

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G. Singh et al.
reported. The unique structural features of silatranes are caused by the intramolecular
N → Si donor-acceptor transannular bond [12, 13], forming a tricyclic cage with a trigonal
bipyramidal silicon [14, 15]. Among the various trialkoxysilanes, 3-chloropropyltriethoxysi-
lane is a precursor for synthesis of ionic liquids [16, 17], chloropropylsilatrane [18], hybrid
materials [19], and siloxanes immobilized ligand system [20]. Imidazole receives attention
for its tunable structure, thermal stability, and amphoteric behavior in solution. The imidaz-
ole ring is a versatile scaffold for ionic liquids bearing several applications [21]. Imidazole
is also important in biomolecules, including biotin, the essential amino acid histidine,
histamine, the pilocarpine alkaloids, and other alkaloids, which have interesting biological
activities [22]. The ability of substituted imidazoles to bind to cytochrome P-450 (type II)
and to inhibit microsomal drug-metabolizing enzyme activity is dependent on the position
of the substituent in the imidazole ring [23]. The concept of imidazoline receptors has been
developed and gained consensus [24]. Owing to their wide applications in academia and
industry, new methods and strategies for the generation of functionalized imidazole
derivatives are in demand. Imidazole-derived silatranes would be of interest for studying
the biological activities including antioxidant, bactericidal, insecticidal, fungicidal, sedative,
antitumor, etc.
In continuation of our previous studies [25, 26], we report herein the syntheses of
imidazolyl-substituted silatranes derived from triethanolamine and tris(isopropanol)amine.
The silatranes with methyl groups, that is, 3,7,10-trimethylsilatranes have the advantage
of being more stable toward hydrolysis, whereas unsubstituted silatranes have an advan-
tage in terms of inhibiting an enzyme because the active site should better accommodate
the less bulky ligands [27]. Therefore, we have synthesized and characterized both types
of silatranes to be used for the future biological studies. To the best of our knowledge,
we have reported the first example of 3,7,10-trimethyl-substituted carbofunctional
silatranes bearing imidazole functionality. The molecular structures of five silatranes
(7–10 and 12) were obtained from single crystal X-ray diffraction studies. Furthermore,
7–13 were analyzed by elemental analysis, IR and NMR spectroscopy, TGA-DSC, and
mass spectrometry.
2. Experimental
2.1. Materials
Imidazole (Aldrich), 2-methylimidazole (Aldrich), 4-methylimidazole (Aldrich), 3-chloro-
propyltriethoxysilane (Aldrich), triethanolamine (Merck), triethoxy-3-(2-imidazolin-1-yl)
propylsilane (Aldrich), and sodium hydride (SDFCL) were used as received. Tris(isopropa-
nol)amine (Merck) was distilled prior to use.
2.2. Experimental details
All the syntheses were carried out under a dry nitrogen atmosphere using a glass
vacuum line. The organic solvents used were dried and purified according to standard
procedures.

Imidazolyl substituted silatranes
877
2.3. Characterization methods
Infrared spectra were recorded in a Nicolet iS50 Fourier Transform Infra-Red (FTIR)
spectrometer. C, H, and N analysis were obtained on a FLASH-2000 Organic Elemental
Analyzer. Mass spectral measurements (TOF MS ES+ 1.38 eV) were carried out with a VG
1
Analytical (70-S) spectrometer. H and 13C NMR spectra were recorded on Jeol and Bruker
FT NMR (AL 300 MHz) spectrometers using CDCl3/DMSO-d6 as the solvent. The
chemical shifts were reported in ppm relative to tetramethylsilane.
2.4. Single crystal X-ray studies
Crystals of the compounds were transferred from the mother liquor to mineral oil for
manipulation, selection, and mounting, and they were then transferred to a thin glass fiber
on a goniometer head. Those studied at non-ambient temperature were placed under a cold
stream of nitrogen gas at 296 K (23 °C) followed by slow cooling or heating to the desired
temperature. Initial crystal evaluation and data collection were performed on a Kappa
APEX II diffractometer equipped with a CCD detector (with crystal-to-detector distance
fixed at 60 mm) and sealed-tube monochromated Mo Kα radiation. The diffractometer was
interfaced to a PC that controlled the crystal centering, unit cell determination, refinement
of the cell parameters, and data collection through the program APEX2 [28]. For each sam-
ple, three sets of frames of data were collected with 0.30° steps in ω and an exposure time
of 10 s within a randomly oriented region of reciprocal space surveyed to the extent of 1.3
hemispheres to a resolution of 0.85 Å. Using SAINT for the integration of the data, reflec-
tion profiles were fitted, and values of F2 and σ(F2) for each reflection were obtained. Data
were also corrected for Lorentz and polarization effects. The subroutine XPREP [28] was
used for processing of data that included determination of space group, application of an
absorption correction (SADABS) [28] merging of data, and generation of files necessary for
solution and refinement. The crystal structures were solved and refined using SHELX 97
[29]. In each case, the space group was chosen based on systematic absences and confirmed
by the successful refinement of the structure. Positions of most of the non-hydrogen atoms
were obtained from a direct methods solution. Several full-matrix least-squares/difference
Fourier cycles were performed, locating the remainder of the non-hydrogen atoms. All non-
hydrogen atoms, except where indicated otherwise, were refined with anisotropic displace-
ment parameters. In 8, the methyl group in the imidazole ring is rotationally disordered over
two positions C5 and C5A with site occupation factors of 0.5 each. All hydrogens were
placed in ideal positions and refined as riding with individual isotropic displacement param-
eters. Crystallographic parameters and basic information pertaining to data collection and
structure refinement for all compounds are summarized in table 1. All figures were drawn
using Mercury V 3.0 [30], and hydrogen bonding parameters were generated using
PLATON [31]. The final positional and thermal parameters of the non-hydrogen atoms for
all structures are listed in the CIF files (Supplementary material).
2.5. Thermogravimetric analysis
TGA-DSC analyses were run on a SDT Q 600 V20.9 Build 20 TGA Instrument. The
sample was loaded in alumina pans and ramped at 10 °C min−1 from 25 to 1000 °C in dry
air at 60 mL min−1.

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Imidazolyl substituted silatranes
879
2.6. Syntheses of silanes
2.6.1. General method of preparation of triethoxysilanes, N-(3-triethoxysilylpropyl)
imidazole (3), N-(3-triethoxysilylpropyl)-4-methylimidazole (4), and N-(3-triethoxysilyl-
propyl)-2-methylimidazole (5). To a suspension of NaH (22 mM) in anhydrous THF
(55 mL) at 0 °C, imidazole, 4-methylimidazole, and 2-methylimidazole (22 mM) were
added (for 3, 4 and 5, respectively) and the reaction mixture was allowed to stir for 30 min.
3-Chloropropyltriethoxysilane (22 mM) was then added at 0 °C. The reaction was allowed
to warm to room temperature and stirred under reflux for a further 24 h. The reaction was
cooled to room temperature, filtered, and washed with ether. The filtrate was concentrated
in vacuo, and oil was separated as the final product in each case which was used without
any further purification.
2.6.2. N-(3-triethoxysilylpropyl)imidazole (3). Colorless oil. Yield: 2.47 g, 82%. IR
1
(cm−1): 1070 (ν(as)Si-OC), 1442 (ν(as)C=C), 1507 (ν(as)C=N). H NMR (CDCl3): δ = 0.61
(t, 2H, SiCH2), 1.12 (t, 9H, CH3), 1.76 (m, 2H, CCH2C), 3.40 (t, 2H, CCH2 N), 3.70 (q,
6H, OCH2), 6.82 (s, 1H, imidazole-H), 7.39 (s, 1H, imidazole-H), 7.68 (s, 1H, imidazole-
H). 13C NMR (CDCl3): δ = 7.71 (SiCH2), 17.80 (CH3), 26.14 (CCH2C), 46.58 (CCH2 N),
57.74 (OCH2), 118.17, 120.88, 134.44 (imidazole-C).
2.6.3. N-(3-triethoxysilylpropyl)-4-methylimidazole (4). Yellow oil. Yield: 2.75 g, 88%.
IR (cm−1): 1068 (ν(as)Si-OC), 1424 (ν(as)C=C), 1563 (ν(as)C=N). 1H NMR (CDCl3):
δ = 0.63 (t, 2H, SiCH2), 1.12 (t, 9H, CH3), 1.75 (m, 2H, CCH2C), 2.28 (s, 3H, imidazole-
CH3), 3.37 (t, 2H, CCH2 N), 3.61 (q, 6H, OCH2), 6.75 (q, 1H, imidazole-H), 7.29 (s, 1H,
imidazole-H). 13C NMR (CDCl3): δ = 7.81 (SiCH2), 9.14 (imidazole-CH3), 17.95 (CH3),
26.24 (CCH2C), 46.67 (CCH2 N), 57.88 (OCH2), 118.53, 126.46, 143.51 (imidazole-C).
2.6.4. N-(3-triethoxysilylpropyl)-2-methylimidazole (5). Orange oil. Yield: 2.69 g, 86%.
IR (cm−1): 1069 (ν(as)Si-OC), 1444 (ν(as)C=C), 1563 (ν(as)C=N). 1H NMR (CDCl3):
δ = 0.62 (t, 2H, SiCH2), 1.18 (t, 9H, CH3), 1.75 (m, 2H, CCH2C), 2.28 (s, 3H, imidazole-
CH3), 3.34 (t, 2H, CCH2 N), 3.70 (q, 6H, OCH2), 6.75 (t, 1H, imidazole-H), 7.29 (d, 1H,
imidazole-H). 13C NMR (CDCl3): δ = 7.71 (SiCH2), 12.58 (imidazole-CH3), 17.86 (CH3),
26.16 (CCH2C), 46.58 (CCH2 N), 57.82 (OCH2), 118.17, 120.88, 134.44 (imidazole-C).
2.7. Syntheses of silatranes
2.7.1. N-[3-(3,7,10-trimethylsilatranyl)propyl]imidazole (7). N-(3-propyltriethoxysilane)
imidazole 3 (1.00 g, 3.67 mM) was added to tris(isopropanol)amine 2 (0.70 g, 3.67 mM) in
anhydrous benzene with a catalytic amount of KOH at room temperature in a two-necked
flask fitted with a Dean Stark trap. The resulting mixture was refluxed for 5 h to remove
azeotropically the ethanol formed during the reaction. The solvent was evaporated under
vacuum, and 10 mL of ether was added. The contents were stirred for 30 min, and product
was isolated as a white powder, filtered, and dried under vacuum. Crystals of 7 were
obtained as colorless blocks after 2 days from the extract in ether. M.p.: 135–137 °C, Yield:
0.95 g, 80%. Anal. Calcd for C15H27N3O3Si: C, 55.35; H, 8.36; N, 12.91; Si, 8.63. Found:

880
G. Singh et al.
C, 55.32; H, 8.34; N, 12.88; Si, 8.60. IR (cm−1): 1060 (ν(as)Si-OC), 663 (ν(as)N → Si),
1
1426 (ν(as)C=C), 1506 (ν(as)C=N). H NMR (CDCl3): δ = 0.33 (t, 2H, SiCH2), 1.08 (dt,
9H, CH3), 1.76 (m, 2H, CCH2C), 2.10 (m, 6H, NCH2), 3.80 (m, 3H, OCH), 3.54 (t, 2H,
CCH2 N), 6.87 (s, 1H, imidazole-H), 6.94 (s, 1H, imidazole-H), 7.42 (s, 1H, imidazole-H).
13C NMR (CDCl3): δ = 13.24 (SiCH2), 20.11 (CH3), 27.28 (CCH2C), 50.06 (CCH2 N),
61.62 (NCH2), 66.65 (OCH), 119.03, 128.61, 137.16 (imidazole-C). MS: m/z (relative
abundance: %, assignment): 326 (100, M + H)+, 348 (5.86, M + Na)+, 364 (8.50, M + K)+,
216 (46.71, N+(CH2CH(CH3)O)3Si).
2.7.2. N-(3-silatranylpropyl)-4-methylimidazole (8). The procedure was as described for
7, but 4-methyl-N-(3-propyltriethoxysilane)imidazole 4 (1.00 g, 3.49 mM) and triethanola-
mine 1 (0.46 g, 3.49 mM) were used as starting materials. Slow evaporation of the filtrate
gave 8 as colorless crystals. M.p.: 115–117 °C, Yield: 0.87 g, 85%. Anal. Calcd for
C13H23N3O3Si: C, 52.50; H, 7.79; N, 14.13; Si, 9.44. Found: C, 52.47; H, 7.75; N, 14.10;
Si, 9.41. IR (cm−1): 1095 (ν(as)Si-OC), 620 (ν(as)N → Si), 1450 (ν(as)C=C), 1599 (ν(as)
1
C=N). H NMR (CDCl3): δ = 0.26 (t, 2H, SiCH2), 1.65 (m, 2H, CCH2C), 2.10 (s, 3H,
CH3), 2.68 (t, 6H, NCH2), 3.63 (t, 2H, CCH2 N), 3.68 (t, 6H, OCH2), 6.51 (d, 1H, imidaz-
ole-H), 7.21 (d, 1H, imidazole-H). 13C NMR (CDCl3): δ = 9.38 (CH3), 13.04 (SiCH2),
26.77 (CCH2C), 47.81 (CCH2 N), 51.25 (NCH2), 57.67 (OCH2), 115.35, 126.47, 136.70
(imidazole-C). MS: m/z (relative abundance: %, assignment): 298 (100, M + H)+, 320
(10.02, M + Na)+, 617 (2.98, 2 M + Na)+, 216 (3.27, N+(CH2CH2O)3SiCH2CH2CH2), 174
(27.86, N+(CH2CH2O)3Si).
2.7.3. N-[3-(3,7,10-trimethylsilatranyl)propyl]-4-methylimidazole (9). The procedure
was as described for 7, but 4-methyl-N-(3-propyltriethoxysilane)imidazole 4 (1.00 g,
3.49 mM) and tris(isopropanol)amine 2 (0.46 g, 3.49 mM) were used as starting materials.
Slow cooling of the filtrate and standing for several days afforded yellow crystals. M.p.:
113–115 °C, Yield: 0.94 g, 80%. Anal. Calcd for C16H29N3O3Si: C, 56.60; H, 8.61; N,
12.38; Si, 8.27. Found: C, 56.57; H, 8.60; N, 12.34; Si, 8.24. IR (cm−1): 1052 (ν(as)Si-
1
OC), 663 (ν(as)N → Si), 1444 (ν(as)C=C), 1604 (ν(as)C=N). H NMR (CDCl3): δ = 0.26
(t, 2H, SiCH2), 1.03 (dt, 9H, CH3), 1.70 (m, 2H, CCH2C), 2.10 (s, 3H, CH3), 2.39 (m, 6H,
NCH2) 3.72 (m, 3H, OCH), 3.74 (t, 2H, CCH2 N), 6.52 (d, 1H, imidazole-H), 7.23 (d, 1H,
imidazole-H). 13C NMR (CDCl3): δ = 9.14 (imidazole-CH3), 13.17 (SiCH2), 20.12 (CH3),
27.17 (CCH2C), 49.93 (CCH2 N), 61.57 (NCH2), 65.01 (OCH), 115.50, 126.05, 136.10
(imidazole-C). MS: m/z (relative abundance: %, assignment): 340 (100, M + H)+, 362
(23.82, M + Na)+, 701 (9.45, 2 M + Na)+, 216 (20.44, N+(CH2CH(CH3)O)3Si).
2.7.4. N-(3-silatranylpropyl)-2-methylimidazole (10). The procedure was as described
for 7, but 2-methyl-N-(3-propyltriethoxysilane)imidazole 5 (1.00 g, 3.49 mM) and trietha-
nolamine 1 (0.46 g, 3.49 mM) were used as starting materials. Recrystallization from tolu-
ene gave 10 as colorless plates. M.p.: 150–152 °C, Yield: 0.89 g, 87%. Anal. Calcd for
C13H23N3O3Si: C, 52.50; H, 7.79; N, 14.13; Si, 9.44. Found: C, 52.44; H, 7.74; N, 14.11;
Si, 9.40. IR (cm−1): 1006 (ν(as)Si-OC), 678 (ν(as)N → Si), 1426 (ν(as)C=C), 1599 (ν(as)
1
C=N). H NMR (CDCl3): δ = 0.27 (t, 2H, SiCH2), 1.65 (m, 2H, CCH2C), 2.29 (s, 3H,
CH3), 2.70 (t, 6H, NCH2) 3.56 (t, 2H, CCH2 N), 3.64 (t, 6H, OCH2), 6.73 (d, 1H,

Imidazolyl substituted silatranes
881
imidazole-H), 7.18 (d, 1H, imidazole-H). 13C NMR (CDCl3): δ = 12.95 (CH3), 13.79
(SiCH2), 26.70 (CCH2C), 48.18 (CCH2 N), 51.21 (NCH2), 57.27 (OCH2), 119.09, 126.43
143.97 (imidazole-C). MS: m/z (relative abundance: %, assignment): 298 (100, M + H)+,
320 (4.11, M + Na)+, 216 (1.37, N+(CH2CH2O)3SiCH2CH2CH2), 174 (10.70,
N+(CH2CH2O)3Si).
2.7.5. N-[3-(3,7,10-trimethylsilatranyl)propyl]-2-methylimidazole (11). The procedure
was as described for 7, but 2-methyl-N-(3-propyltriethoxysilane)imidazole 5 (1.00 g,
3.49 mM) and tris(isopropanol)amine 2 (0.46 g, 3.49 mM) were used as starting materials.
After removing the volatiles under reduced pressure, 11 was obtained as white solid. M.p.:
162–164 °C, Yield: 0.99 g, 84%. Anal. Calcd for C16H29N3O3Si: C, 56.60; H, 8.61; N,
12.38; Si, 8.27. Found: C, 56.50; H, 8.58; N, 12.37; Si, 8.22. IR (cm−1): 1052 (ν(as)Si-
1
OC), 664 (ν(as)N → Si), 1444 (ν(as)C=C), 1604 (ν(as)C=N). H NMR (CDCl3): δ = 0.30
(t, 2H, SiCH2), 1.05 (dt, 9H, CH3), 1.67 (m, 2H, CCH2C), 2.23 (m, 6H, NCH2), 2.36 (s,
3H, CH3), 3.54 (t, 2H, CCH2 N), 3.80 (m, 3H, OCH), 6.72 (d, 1H, imidazole-H), 7.19 (d,
1H, imidazole-H). 13C NMR (CDCl3/DMSO-d6): 8.11 (imidazole-CH3), 12.60 (SiCH2),
19.02 (CH3), 23.82 (CCH2C), 47.75 (CCH2 N), 62.03 (NCH2), 65.24 (OCH), 114.24,
125.60, 135.13 (imidazole-C). MS: m/z (relative abundance: %, assignment): 340 (18.30,
M + H)+, 216 (3.94, N+(CH2CH(CH3)O)3Si), 192 (100, N+H(CH2CH(CH3)OH)3), 174
(55.10, N+(CH2CH2O)3Si).
2.7.6. N-(3-silatranylpropyl)-2-imidazoline (12). The procedure was as described for 7,
but triethoxy-3-(2-imidazolin-1-yl)propylsilane 6 (1.00 g, 3.49 mM) and triethanolamine 1
(0.46 g, 3.49 mM) were used as starting materials. After removing the solvent under vac-
uum, 12 was obtained as a white powder, filtered, and dried under vacuum. Crystals of this
compound were obtained from slow evaporation of the filtrate in ether. M.p.: 133–135 °C,
Yield: 0.90 g, 87%. Anal. Calcd for C12H23N3O3Si: C, 50.50; H, 8.12; N, 14.72; Si, 9.84.
Found: C, 50.47; H, 8.10; N, 14.69; Si, 9.80. IR (cm−1): 1084 (ν(as)Si-OC), 621 (ν(as)
N → Si), 1595 (ν(as)C=N). 1H NMR (CDCl3): δ = 0.23 (t, 2H, SiCH2), 1.46 (m, 2H,
CCH2C), 2.69 (t, 6H, NCH2) 3.64 (t, 6H, OCH2), 3.64 (t, 2H, CCH2 N), 2.95 (t, 2H, imi-
dazoline-CH2), 3.10 (t, 2H, imidazoline-CH2), 6.69 (s, 1H, imidazoline-H). 13C NMR
(CDCl3): δ = 12.88 (SiCH2), 24.06 (CCH2C), 50.67 (CCH2 N), 51.30 (NCH2), 57.80
(OCH2), 48.29, 53.98, 157.93 (imidazoline-C). MS: m/z (relative abundance: %, assign-
ment): 286 (100, M + H)+, 308 (8.06, M + Na)+, 216 (1.87, N+(CH2CH2O)3-
SiCH2CH2CH2), 174 (19.40, N+(CH2CH2O)3Si).
2.7.7. N-[3-(3,7,10-trimethylsilatranyl)propyl]-2-imidazoline (13). The procedure was as
described for 7, but triethoxy-3-(2-imidazolin-1-yl) propylsilane 6 (1.00 g, 3.49 mM) and
tris(isopropanol)amine 2 (0.46 g, 3.49 mM) were used as starting materials. Compound 13
was obtained as a colorless solid. M.p.: 119–121 °C, Yield: 0.94 g, 84%. Anal. Calcd for
C15H29N3O3Si: C, 55.01; H, 8.93; N, 12.83; Si, 8.58. Found C, 55.00; H, 8.89; N, 12.80;
1
Si, 8.54. IR (cm−1): 1084 (ν(as)Si-OC), 620 (ν(as)N → Si), 1596 (ν(as)C=N). H NMR
(CDCl3): δ = 0.29 (t, 2H, SiCH2), 1.03 (dt, 9H, CH3), 1.53 (m, 2H, CCH2C), 2.13 (t, 6H,
NCH2), 3.11 (t, 2H, CCH2 N), 3.74 (m, 3H, OCH), 2.50 (t, 2H, imidazoline-CH2), 3.02
(t, 2H, imidazoline-CH2), 7.12 (s, 1H, imidazoline-H). 13C NMR (CDCl3/DMSO-d6):

882
G. Singh et al.
δ = 13.36 (SiCH2), 19.83 (CH3), 26.57 (CCH2C), 44.67 (CCH2 N), 62.82 (NCH2), 66.05
(OCH), 53.38, 58.38, 163.36 (imidazoline-C). MS: m/z (relative abundance: %, assign-
ment): 328 (100, M + H)+, 230 (31.95, N+(CH2CH(CH3)O)3SiCH2), 192 (49.11, N+H
(CH2CH(CH3)OH)3), 174 (5.93, N+(CH2CH2O)3Si).
3. Results and discussion
3.1. Syntheses
Using literature method [32], N-(3-triethoxysilylpropyl)imidazole 3, as well as new silanes,
N-(3-triethoxysilylpropyl)-4-methylimidazole 4 and N-(3-triethoxysilylpropyl)-2-methylim-
idazole 5 were prepared in high yields without further purification (scheme 1). N-(3-trieth-
oxysilylpropyl)-2-imidazoline 6 was commercially available and used without purification.
Silatranes 7–13 were synthesized by transesterification reactions of triethanolamine and
tris(isopropanol)amine with the corresponding silanes 3–6 in the presence of KOH
(scheme 2). The products were stable in air and highly soluble in common organic
solvents.
3.2. FTIR spectroscopy
FTIR spectra of the compounds were recorded from 4000 to 400 cm−1. All bands observed
for silatranyl were consistent with previous literature reports [33, 34]. The absorption peaks
of interest were those of Si–O, N → Si, and imidazole ring stretching vibrations. In the IR
absorption spectra of all the compounds with Si–O–C groups, intense bands were present at
1052–1087 cm−1 which were assigned to asymmetric stretching vibration of the group Si–O
and frequencies of 877–884 cm−1 were attributed to the symmetric stretching vibration of
Si–O. Symmetric deformational vibration of the silatranyl skeleton with a predominant
contribution from the N → Si was observed from 619 to 678 cm−1. The C–H stretching
vibrations of methylene groups are at 2900–3000 cm−1. The bands were observed at
1055–1124 cm−1 and 972–980 cm−1 for symmetric and asymmetric stretching of the
NC3 fragment of the silatrane ring, respectively. The peaks at 1595–1604 cm−1 and
1426–1450 cm−1 were assigned to the C=N and C=C symmetric stretching of the imidazole.
O
O
O
O
NaH, THF
-NaCl
Si
Si
Cl
O
O
(3-5)
Me
N
N
N
N
;
N
3
4
;
=
N
5
Me
Scheme 1. Synthesis of triethoxysilanes 3–5.

Imidazolyl substituted silatranes
883
R
OH
R
O
C6H6, KOH
O
O
O
R
O
Reflux
Si
Si
N
R
N
O
- 3 EtOH
R
R
OH
OH
7-13
1-2
R = H
3-6
1
R = Me 2
Me
N
N
N
N
N
;
N
N
N
;
;
=
Me
12
13
R = H
R = H
R = Me
8
9
R = H
10
11
R = Me
7
R = Me
R = Me
Scheme 2. Synthesis of silatranes 7–13.
3.3. NMR spectroscopy
Multinuclear (1H and 13C) NMR spectra were consistent with the structures of 7–13. On
1
comparing H NMR spectra of silatranes with those of parent 1 and 2, a downfield shift for
the OCH2 and NCH2 protons of Si(OCH2CH2)3 N and OCH and NCH2 protons of Si(OCH
(Me)CH2)3 N moiety was observed. The presence of methyl in positions 3, 7, and 10 of the
silatranes (7, 9, 11, 13) containing three stereogenic carbons resulted in a complex NMR
splitting for each diastereomer. Each methyl of Si(OCH(Me)CH2)3 N showed its own dou-
blet due to steric factors. The triplet for SiCH2 protons appeared upfield at 0.23–0.33 ppm
due to direct Si–C bond. The multiplet due to protons of CCH2C at 1.46–1.76 ppm was
also observed. The triplet for CCH2 N was present at 3.10–3.68 ppm for all compounds.
The singlet at 2.10–2.36 ppm was assigned to protons of the CH3 of imidazole for 8–11.
Introduction of the electron-donating aliphatic methyl substituent into the imidazole ring
slightly enhanced the electron shielding of nuclei in the ring, and their signals were dis-
placed slightly upfield in the region 6.51–7.23 ppm as compared to unsubstituted imidazole
showing broad singlets at 6.87–7.42 ppm. The most downfield resonance was caused by
hydrogen adjacent to two electronegative ring nitrogens. The inductive effect of the imidaz-
ole ring was not extended to protons in the silatrane fragment. The presence of two distinct
triplets at 2.95, 2.50 ppm and 3.10, 3.02 ppm were attributed to CH2 of the imidazoline ring
for 12 and 13, respectively.
13C NMR spectra for all compounds were consistent with their structures. Triethoxysil-
anes 3–6 showed two peaks at 17.84–18.31 ppm and 57.54–57.88 ppm due to CH3 and
OCH2, respectively. For unsubstituted silatranes (8, 10, and 12), the peaks attributable to
silatranyl OCH2 and NCH2 were at 51.19–51.30 ppm and 57.27–59.63 ppm, respectively.
Due to more electronegative oxygen, the signals of the OCH2 were at lower field than those
of NCH2 in all the silatranes. The tris(isopropanol)amine-derived silatranes exhibited sepa-
rate signals for each NCH2, OCH, and CH3 carbon of the tris(isopropanol)amine cage. In
the 3,7,10-trimethylsilatranes (7, 9, 11, and 13), the signals ascribed to NCH2 and OCH are
slightly downfield at 59.14–62.03 ppm and 65.24–66.65 ppm, respectively. The signals for
Si-CH2 group were at considerably higher field, 12.60–13.79 ppm.

884
G. Singh et al.

Imidazolyl substituted silatranes
Table 3. Selected bond lengths and angles for 7.
885
Molecule 1
Molecule 2
Bond lengths (Å)
N(1)–Si(1)
C(10)–Si(1)
C(12)–N(2)
C(13)–N(2)
O(1)–Si(1)
O(2)–Si(1)
O(3)–Si(1)
C(14)–N(3)
C(10)–C(11)
C(11)–C(12)
2.179 (10)
1.904 (9)
1.472 (14)
1.322 (19)
1.669 (7)
1.663 (8)
1.652 (8)
1.349 (19)
1.517 (13)
1.524 (13)
N(4)–Si(2)
C(25)–Si(2)
C(27)–N(5)
C(28)–N(5)
O(4)–Si(2)
O(5)–Si(2)
O(6)–Si(2)
C(28)–N(6)
C(25)–C(26)
C(26)–C(27)
2.189 (11)
1.874 (10)
1.447 (14)
1.352 (15)
1.669 (9)
1.664 (6)
1.650 (8)
1.354 (14)
1.545 (13)
1.507 (13)
Bond angles (°)
O(1)–Si(1)–O(2)
O(1)–Si(1)–O(3)
O(2)–Si(1)–O(3)
C(11)–C(10)–Si(1)
C(12)–C(11)–C(10)
C(11)–C(12)–N(2)
N(3)–C(13)–N(2)
C(15)–N(2)–C(13)
C(14)–N(3)–C(13)
N(1)–Si(1)–C(10)
119.2 (4)
O(4)–Si(2)–O(5)
O(4)–Si(2)–O(6)
O(5)–Si(2)–O(6)
C(15)–C(25)–Si(2)
C(27)–C(26)–C(25)
C(26)–C(27)–N(5)
N(6)–C(28)–N(5)
C(30)–N(5)–C(28)
C(29)–N(6)–C(28)
N(4)–Si(2)–C(25)
121.1 (3)
117.7 (3)
118.1 (3)
116.7 (5)
112.0 (8)
114.1 (9)
111.3 (17)
107.8 (13)
103.8 (16)
177.9 (5)
116.8 (3)
117.1 (3)
115.8 (5)
110.8 (9)
114.1 (10)
111.5 (13)
104.1 (11)
103.5 (13)
178.0 (5)
Table 4. Selected bond lengths and
angles for 8.
Bond lengths (Å)
N(3)–Si(1)
C(3)–Si(1)
C(4)–N(2)
C(1)–N(2)
O(1)–Si(1)
O(2)–Si(1)
O(3)–Si(1)
C(7)–N(1)
C(2)–C(3)
C(4)–C(5)
2.174 (3)
1.886 (4)
1.373 (7)
1.451 (7)
1.660 (3)
1.658 (3)
1.657 (3)
1.296 (7)
1.514 (6)
1.491 (9)
Bond angles (°)
O(1)–Si(1)–O(2)
O(1)–Si(1)–O(3)
O(2)–Si(1)–O(3)
C(2)–C(3)–Si(1)
C(3)–C(2)–C(1)
C(2)–C(1)–N(2)
N(1)–C(7)–N(2)
C(1)–N(2)–C(7)
C(4)–N(2)–C(7)
N(3)–Si(1)–C(3)
119.0 (2)
118.85 (18)
117.57 (16)
113.9 (3)
115.0 (4)
112.7 (4)
112.4 (5)
126.2 (5)
106.6 (5)
178.11 (17)
3.4. Mass spectrometry
Mass spectra of 7–13 showed their respective molecular ion peaks, quasi molecular ion
peaks with addition of H, Na, and K, and their fragmentation showing the common features
of silatranes [35]. The silatranes reported herein have considerable stability, as indicated by

886
G. Singh et al.
Table 5. Selected bond lengths and angles for 9.
Molecule 1
Molecule 2
Bond lengths (Å)
N(1)–Si(1)
C(10)–Si(1)
C(12)–N(3)
C(16)–N(3)
O(1)–Si(1)
O(2)–Si(1)
O(3)–Si(1)
C(16)–N(4)
C(10)–C(11)
C(11)–C(12)
2.204 (4)
1.872 (4)
1.468 (5)
1.337 (5)
1.663 (3)
1.658 (3)
1.656 (3)
1.325 (6)
1.516 (5)
1.510 (5)
N(2)–Si(2)
C(26)–Si(2)
C(28)–N(5)
C(29)–N(5)
O(4)–Si(2)
O(5)–Si(2)
O(6)–Si(2)
C(32)–N(6)
C(26)–C(27)
C(27)–C(28)
2.188 (4)
1.883 (4)
1.446 (5)
1.364 (6)
1.654 (3)
1.649 (3)
1.657 (4)
1.318 (6)
1.506 (5)
1.503 (6)
Bond angles (°)
O(1)–Si(1)–O(2)
O(1)–Si(1)–O(3)
O(2)–Si(1)–O(3)
C(11)–C(10)–Si(1)
C(12)–C(11)–C(10)
C(11)–C(12)–N(3)
N(3)–C(16)–N(4)
C(16)–N(3)–C(9)
C(16)–N(4)–C(14)
N(1)–Si(1)–C(10)
117.06 (16)
117.51 (16)
119.91 (16)
116.9 (3)
113.5 (4)
114.1 (4)
111.5 (5)
128.6 (5)
106.2 (5)
178.4 (18)
O(4)–Si(2)–O(5)
O(4)–Si(2)–O(6)
O(5)–Si(2)–O(6)
C(27)–C(26)–Si(2)
C(28)–C(27)–C(26)
C(27)–C(28)–N(5)
N(5)–C(32)–N(6)
C(32)–N(5)–C(28)
C(32)–N(6)–C(30)
N(2)–Si(2)–C(26)
116.98 (16)
117.06 (18)
121.04 (17)
116.8 (3)
113.4 (4)
113.7 (4)
111.5 (5)
127.6 (4)
105.6 (4)
178.62 (17)
Table 6. Selected bond lengths and
angles for 10.
Bond lengths (Å)
N(3)–Si(1)
C(4)–Si(1)
C(2)–N(2)
C(1)–N(2)
O(1)–Si(1)
O(2)–Si(1)
O(3)–Si(1)
C(1)–N(1)
C(4)–C(3)
C(3)–C(2)
2.167 (4)
1.883 (4)
1.458 (5)
1.360 (6)
1.669 (3)
1.663 (3)
1.673 (3)
1.317 (6)
1.516 (6)
1.515 (6)
Bond angles (°)
O(1)–Si(1)–O(2)
O(1)–Si(1)–O(3)
O(2)–Si(1)–O(3)
C(3)–C(4)–Si(1)
C(2)–C(3)–C(4)
C(3)–C(2)–N(2)
N(2)–C(1)–N(1)
C(1)–N(2)–C(2)
C(1)–N(1)–C(12)
N(3)–Si(1)–C(4)
119.0 (15)
118.3 (16)
118.2 (17)
114.0 (3)
113.8 (3)
113.4 (3)
111.8 (4)
126.6 (4)
105.0 (4)
178.6 (16)
continued observation of a strong [M + H]+ as a base peak (except 11). The main peaks of
all the compounds are shown in table 2. In the unsubstituted silatranes, the presence of a
peak due to silatranyl cation formed by the homolytic cleavage of Si–CH2 bond at m/z 174
appeared to be a very common feature in the mass spectrum of silatranes; this fragment

Imidazolyl substituted silatranes
887
Table 7. Selected bond lengths and
angles for 12.
Bond lengths (Å)
N(1)–Si(1)
C(7)–Si(1)
C(12)–N(2)
C(9)–N(2)
O(1)–Si(1)
O(2)–Si(1)
O(3)–Si(1)
C(10)–N(2)
C(8)–C(7)
C(9)–C(8)
2.151 (6)
1.862 (7)
1.506 (11)
1.463 (10)
1.661 (5)
1.664 (4)
1.670 (3)
1.364 (9)
1.528 (9)
1.522 (9)
Bond angles (°)
O(1)–Si(1)–O(2)
O(1)–Si(1)–O(3)
O(2)–Si(1)–O(3)
C(8)–C(7)–Si(1)
C(9)–C(8)–C(7)
C(8)–C(9)–N(2)
N(2)-C(10)–N(3)
C(12)–N(2)–C(10)
C(12)–N(2)-C(10)
N(1)–Si(1)––C(7)
119.0 (2)
118.6 (2)
118.3 (2)
115.7 (5)
113.5 (6)
113.7 (7)
110.4 (7)
126.6 (4)
111.4 (7)
179.5 (3)
100
80
60
40
20
0
7
8
9
10
11
12
13
0
200
400
600
800
1000
Temperature (°C)
Figure 1. TGA curves for 7–13.
after losing one arm formed a bicyclic moiety at m/z 132. In addition, silatranyl moiety after
fragmentation showed peaks at m/z 150 corresponding to protonated molecular ion of trieth-
anolamine HN+(CH2CH2OH)3. The peak at m/z 192 was also observed due to formation of
+
silatranyl adduct with NH4 , which is also a general feature of silatrane fragmentation. The
cleavage from γ-carbon of propyl chain attached to imidazole moiety gave a fragment
having m/z 216, which further led to the loss of one –OCH2CH2 arm to form a bicyclic
fragment with alkyl chain at m/z 172. For methyl-substituted silatranes, besides the

888
G. Singh et al.
7.5
5.0
7
8
9
10
11
12
13
2.5
0.0
-2.5
-5.0
100
200
300
400
500
600
700
Temperature (°C)
Figure 2. DSC curves of 7–13.
molecular ion peaks, the peaks corresponding to silatranyl ion peak at m/z 216 were also
observed. An intense peak at m/z 192 was assigned to protonated tris(isopropanol)amine.
3.5. Thermogravimetric analysis
The thermal stabilities of 7–13 were studied by thermogravimetric analysis (figure 1) from
25 to 1000 °C under nitrogen. The TGA curve of 7 was a two step profile, the first step cor-
responding to loss of HCN at 110–180 °C during fragmentation of imidazole ring
(Calcd = 8.92%, expt = 8.30%) which was also confirmed from the mass spectrum (vide
supra) and the second step involved the decomposition of the rest of the molecule from
250 to 330 °C. In 8, the first step corresponded to loss of C2H3 N (Calcd = 13.61%,
expt = 13.80%) during the fragmentation of imidazole and the second step involved the
decomposition (Calcd = 75.60%, expt = 75.63%) to 340 °C. The TGA curve of 9 was a
two step profile, the first corresponding to loss of imidazole (Calcd = 22.42%,
Figure 3. A perspective view of two independent molecules of 7 showing atom numbering scheme.

Imidazolyl substituted silatranes
889
Figure 4. A perspective view of 8 showing atom numbering scheme.
Figure 5. A perspective view of two independent molecules of 9 showing atom numbering scheme.
expt = 23.89%) and the second with loss of the rest of the molecule (Calcd = 77.58%,
expt = 78.50%). The TGA curve of 10 depicted stability to 225 °C and a complete volatili-
zation at 320 °C. The TGA curve of 11 revealed the two main steps, the first corresponding
to loss of HCN during the fragmentation of imidazole (Calcd = 8.29%, expt = 7.96%). The
second showed decomposition of the rest of the molecule while the residue corresponded to
formation of SiO2 (Calcd = 17.09%, expt = 17.69%). Compound 12 was stable to 215 °C,
then entire volatilization at 310 °C. The TGA curve of 13 was a two step profile, the first
corresponded to loss of HCN during fragmentation of imidazole (Calcd = 7.79%,
expt = 8.25%) and the second decomposition of the rest of the molecule while the residue
corresponded to the formation of oxides of silicon. In DSC curves, small endothermic dips
were observed at the respective melting points for all the compounds (figure 2).
3.6. Single crystal X-ray structure analysis
Single crystals for 7–9 and 12 were grown from slow evaporation of ether solution whereas
those for 10 were grown via slow cooling of a hot toluene solution. Compounds 7, 8, 9, 10,

890
G. Singh et al.
Figure 6. A perspective view of 10 showing atom numbering scheme.
Figure 7. A perspective view of 12 showing atom numbering scheme.
and 12 crystallized in the monoclinic P21 chiral space group, monoclinic P21/n space
group, triclinic P-1 space group, monoclinic P21/n space group, and monoclinic C2/c,
respectively. There were two independent molecules in the asymmetric units of 7 and 9.
Structures of 7–10 and 12 with atom numbering scheme are shown in figures 3–7. The
crystallographic data and structure refinement parameters for 7–10 and 12 are listed in table
1 and selected bond lengths and angles for 7–10 and 12 are listed in tables 3–7. In each
case, the Si is five coordinate with slightly distorted trigonal bipyramidal geometry, sur-
rounded by three oxygens and one nitrogen of the triethanolamine and C of the propyl
chain bearing imidazole functionality and its methyl derivative at the apical position. The
N → Si transannular bonds in these compounds vary from 2.16 to 2.20 Å. In comparison
with the unsubstituted silatranes 8 and 10, methyl substitution on C at the 3, 7, and 10
positions of the skeleton in 7 and 9 caused a considerable lengthening of the N → Si dis-
tance, possibly due to a more strained atrane. The methyl substituents as electron-releasing
groups might reduce the electron-withdrawing effect of the oxygens attached to silicon.
Therefore, the less positive silicon formed a weaker interaction with the lone pair from

Imidazolyl substituted silatranes
891
Figure 8. Two independent molecules found in the asymmetric unit of 7 interacting with each other via C–H⋯O
interaction.
Figure 9. Intermolecular hydrogen bond in 10 showing molecules interacting with each other via C–H⋯N
interaction.
nitrogen. However, crystal packing effects might be the primary cause. In 9, N → Si is
further elongated in comparison to 7; the reason for it can be due to additional methyl
substitution on imidazole attached to the propyl chain.
The two independent molecules in 7 interact with each other via weak intermolecular
C–H⋯O interactions. The O(6) of the silatrane cage of one molecule interacts with one
γ-hydrogen H(3B) [symmetry: 1 + x, y, z] of the propyl chain attached to silatrane of
another molecule (see figure 8). In 10, weak C–H⋯N interactions were found between
nitrogen of the imidazole group and one of the hydrogens of methylene in the α-position to
nitrogen of the silatrane cage (the distance of N(1) and H(10B) [1/2 + x, 1/2 − y,−1/2 + z]
is 2.6 Å) as shown in figure 9. Similar to 7, C–H…O interactions were also found in 12.
The interaction was between O(2) of the silatrane cage and H(5B) at the α-position to the
nitrogen of the silatrane skeleton of another molecule [symmetry: x, −y, 1/2 + z], O(1) of
the silatrane cage and H(10) present adjacent to two imidazoline ring nitrogens of another
molecule [symmetry: x, −y, 1/2 + z], and between O(3) of the silatrane cage and H(5B) of
one of the CH2 groups of imidazoline ring [symmetry: −x, y, 1/2 − z] (see figure 10). All
hydrogen bonding parameters are summarized in table 8. The bond angles around Si can be

892
G. Singh et al.
Figure 10. Intermolecular hydrogen bond in 12 showing molecules interacting with each other via C–H⋯O
interaction.
discussed in terms of percentage trigonal bipyramid (% TBP). The Tamao parameters [36]
ηax and ηeq were calculated from three apical-to-equatorial bond angles θn which varied
from 109.5° in tetrahedral (TH) to 90° in trigonal bipyramidal (TBP) and three equatorial-
to-equatorial bond angles φn which varied from 109.5° in tetrahedral (TH) to 120° in trigo-
nal bipyramidal (TBP) according to Equations (1) and (2). The deviation of silicon from the
equatorial plane is the criteria for the deviation of the geometry from TBP to TH,
gax ¼ 100%½f109:5 ꢀ 1=3ðRhnÞg=ð109:5 ꢀ 90:0Þꢁ
geq ¼ 100%½f1=3ðRunÞ ꢀ 109:5g=ð120:0 ꢀ 109:5Þꢁ
(1)
(2)
where θn is average of angles Oeq–Si–Cax, and φn is average of angles Oeq–Si–Oeq.
The distance of silicon from the plane formed by the equatorial oxygens is given by ΔSi.
A strong N → Si interaction leads to formation of a more regular trigonal bipyramid around
silicon which lies closer to the equatorial plane. The extent of trigonal bipyramid formation
ηΩ [37] from tetrahedron (% TH → TBP) calculated on the basis of an integral character
ΔΩ (where Ω is a solid angle formed by three equatorial bonds of the central silicon) allows
Table 8. Hydrogen bonding parameters for 7, 10 and 12.
D–H⋯A
r(D–H) (Å) r(H⋯A) (Å) r(D⋯A) (Å) ∠D–H⋯A (°) Symmetry
7
C(24)–H(3B)⋯O(6)
0.94
0.97
0.99
0.95
0.99
2.49
2.60
2.51
2.43
2.53
3.327
3.394
3.376
3.372
3.453
149
139
146
172
154
1 + x, y, z
1/2 + x, 1/2 − y, 1/2 + z
x, −y, 1/2 + z
x, −y, −1/2 + z
−x, y, 1/2 − z
10 C(10)–H(10B)⋯N(1)
12 C(5)–H(5B)⋯O(2)
C(10)–H(10)⋯O(1)
C(12)–H(12B)⋯O(3)

Imidazolyl substituted silatranes
893
Table 9. Selected geometrical parameters and parameters describing the deviation of the silicon coordination
polyhedra from an ideal TBP in 7–10 and 12.
Compound
θn
φn
ηax (%)
ηeq (%)
ΔSi
ΔΩ
ηΩ (%)
7/1
7/2
8
9/1
9/2
10
12
97.43
97.85
97.10
97.43
97.85
96.95
96.66
118.33
118.46
118.46
118.35
118.16
118.58
118.63
61.89
59.74
63.58
61.89
59.57
64.35
65.84
84.04
85.33
85.33
84.28
82.47
86.47
86.95
0.216
0.207
0.206
0.213
0.227
0.202
0.195
4.97
4.53
4.56
4.93
5.52
4.35
4.04
97.23
97.46
97.46
97.26
96.93
97.58
97.75
one to clearly demonstrate the distortion of the coordination polyhedron of silicon as
depicted in Equations (3) and (4).
DX ¼ 2p ꢀ X ð0ꢂ for ideal TBP and 180ꢂ for ideal tetrahedronÞ
(3)
ꢀ
ꢁ
DX
gX ¼ 100% ꢃ 1 ꢀ
(4)
p
The bond angles θn and φn, five coordinate character (% TBPax) and (% TBPeq), ΔSi values,
and integral character ΔΩ agree with those predicted using structural correlations (listed in
table 9).
4. Conclusion
We have demonstrated the synthesis of unsubstituted and 3,7,10-trimethyl-substituted carbo-
functional silatranes 7–13 bearing imidazole and its derivatives. The compounds have been
fully characterized by X-ray crystallography (7–10 and 12), multinuclear NMR (1H and
13C), IR spectroscopy, thermogravimetric analysis, and mass spectrometry. The silatranes
are synthesized in good yields having high stability and sufficient solubility in organic sol-
vents. We have used different imidazole derivatives because it would be interesting to study
the structure-activity relationship of the inhibitory actions of the substituted imidazoles.
These imidazole-based organopropyl silatranes can find applications in material science,
sol-gel chemistry, agriculture, and biology including immune regulation, anti-inflammatory,
and anti-tumor activities.
Supplementary material
X-ray crystallographic data of the structures 7, 8, 9, 10, 12 H2O in CIF format (CCDC
numbers, 961661-961665, respectively) have been given.
Acknowledgements
The authors are thankful to UGC, New Delhi for providing financial support. S.K. would
like to thank CSIR, Govt. of India, for a research fellowship. The X-ray facility at IISER
Mohali is gratefully acknowledged.

894
G. Singh et al.
Supplemental data
Supplemental data for this article can be accessed here [http://dx.doi.org/10.1080/00958972.2014.1003547].
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