Synthesis and characterization of imidazole-triphenylsilane complexes

Article abstract of DOI:10.1016/j.jorganchem.2010.03.005

Three imidazole-based triphenylsilane complexes were synthesized as preliminary model complexes to those that have been proposed as intermediates during the enzymatic biomineralization of silica by certain sponges. The active site of the enzyme includes histidine-serine moieties that appear to be vital to functionality. The model compounds include ligands that are bound to the silicon via a Si-O-C linkage and have a potentially chelating imidazole ring. Synthesis of these compounds was achieved by reaction of triphenylchlorosilane with two equivalents of ligand, one equivalent acting as a base for the HCl generated during the reaction. The compounds are highly reactive toward hydrolysis and were characterized by NMR, MS, elemental analysis, and X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2010.03.005

Journal of Organometallic Chemistry 695 (2010) 1507–1512
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of imidazole–triphenylsilane complexes
*
Tatiana Eliseeva, Matthew J. Panzner, Willey J. Youngs, Claire A. Tessier
Department of Chemistry, University of Akron, 190 East Buchtel Commons, Akron, OH 44325-3601, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Three imidazole-based triphenylsilane complexes were synthesized as preliminary model complexes to
those that have been proposed as intermediates during the enzymatic biomineralization of silica by cer-
tain sponges. The active site of the enzyme includes histidine-serine moieties that appear to be vital to
functionality. The model compounds include ligands that are bound to the silicon via a Si–O–C linkage
and have a potentially chelating imidazole ring. Synthesis of these compounds was achieved by reaction
of triphenylchlorosilane with two equivalents of ligand, one equivalent acting as a base for the HCl gen-
erated during the reaction. The compounds are highly reactive toward hydrolysis and were characterized
by NMR, MS, elemental analysis, and X-ray crystallography.
Received 4 January 2010
Received in revised form 2 March 2010
Accepted 3 March 2010
Available online 7 March 2010
Keywords:
Silica biomineralization
Silicatein model complexes
Triphenylsilane complexes
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
a high vacuum line by pumping overnight. Pyridine and triethyl-
amine were dried by stirring over BaO overnight, distilled and
The high level of interest in the mechanisms of silica biominer-
alization is associated with use of silicon compounds as reagents
for new materials [1–3]. During biomineralization, amorphous sil-
ica forms from Si(OH)4 under ambient condition and in the pres-
ence of biomolecules, especially proteins. In sponges the process
is enzymatic and the enzymes are termed silicateins [4]. Studies
by Cha and Morse using the non-biological reagent Si(OEt)4 sug-
gested that histidine and serine sites of silicateins play a crucial
role in silica formation, and proposed that a five-coordinate silicon
intermediate was involved (Fig. 1) [5]. Compounds with similar
features to those of Fig. 1 could serve as models for this chemistry.
Described herein are compounds that model some of the fea-
tures of Fig. 1. The synthesized compounds are of general form Si-
Ph3OL, where L contains imidazole and have been characterized by
NMR, mass spectrometry, elemental analyses and X-ray
crystallography.
stored under argon. Compound HOL3 (6-imidazole-1-ylmethyl-
pyridine-2-ylmethanol) was previously synthesized by the litera-
ture procedure and purified by sublimation under vacuum [7].
All deuterated solvents (THF, acetonitrile, methylene chloride, di-
methyl sulfoxide) were purchased from Cambridge Isotope Inc.
and were dried by literature procedures [8,9]. Unless otherwise
specified, all reactions were assembled in a glove box under argon
or assembled while the glassware was still hot and immediately
pumped down using a Schlenk line [10]. The volatile components
were removed from the final products on a high vacuum line,
which had an ultimate capability of 2 ꢀ 10ꢁ4 torr, or using a
Schlenk line (ꢂ1 ꢀ 10ꢁ3 torr).
1H, 13C, and 29Si NMR spectra were obtained on 400 MHz Inova
instrument. 1H spectra were referenced internally to the residual
protons of the deuterated solvents. The 13C NMR spectra were ref-
erenced internally to the solvent peaks. 29Si NMR spectra refer-
enced externally to SiMe4. In all 29Si NMR samples, chromium
acetylacetonate (Cr(acac)3) was added to decrease the relaxation
time [11]. Mass spectrometry data were obtained on a Bruker Es-
quire-LC mass spectrometer. Elemental analyses were performed
by Microanalysis Laboratory (University of Illinois, Urbana).
2. Experimental
2.1. General comments
All solvents (THF, ether, acetonitrile, benzene, and methylene
chloride) were purchased from Fisher, and were dried and purified
by a Pure Solv system by Innovative Technology Inc. [6]. Triphenyl-
chlorosilane (SiPh3Cl) was purchased from Gelest and any trace
amounts of HCl were removed under vacuum. 4-Hydroxymethyl-
5-methyl imidazole was purchased from VWR and was dried on
2.2. Synthesis
2.2.1. Synthesis of 1-hydroxydecyl-imidazole (HOL1)
A solution of 1.4 g (21 mmol) imidazole in 50 mL of dry THF was
added to a solution of 0.81 g (21 mmol) potassium hydride in
50 mL of dry THF by canula at 0 °C. The mixture was stirred for
2 h and a solution of 5.0 g (21 mmol) of bromodecanol in 20 mL
of THF was added by canula. The mixture was refluxed at 60 °C
* Corresponding author. Tel.: +1 330 972 5304; fax: +1 330 972 6085.
E-mail address: tessier@uakron.edu (C.A. Tessier).
0022-328X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.03.005

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T. Eliseeva et al. / Journal of Organometallic Chemistry 695 (2010) 1507–1512
134.6, 135.5, 135.7, 135.9, 136.3 (CH Ph and imidazole rings). 29Si
His
(79 MHz, CD2Cl2, ppm): d ꢁ13. Anal. Calc. for C23H22SiON2: C,
74.76; H, 5.73; N, 7.58. Found: C, 74.01; H, 5.77; N, 5.18%.
Route B. By this route, formation of two products is observed. A
solution of 1.32 g (4.5 mmol) SiPh3Cl in 20 mL acetonitrile was
added to a suspension of 0.5 g (4.5 mmol) 4-hydroxymethyl-5-
methyl imidazole (HOL2) and 0.5 g (4.5 mmol) of triethylamine in
acetonitrile. The mixture was refluxed at 80 °C for 24 h, cooled to
RT and stirred for 24 h. No precipitate was observed. A quarter of
the solvent was removed on Schlenk line and a white precipitate
appeared. The mixture was filtered via a frit. The volatile compo-
nents were removed under vacuum. Acetonitrile (30 mL) was
added to the product and the mixture was filtered via a frit. The
volatile components were removed from the solution slowly on
the vacuum line. The acetonitrile extraction was repeated three
times. Crystals formed over 12 h. M.p. = 97 °C. SiPh3OL2 was ob-
tained in very low yield (under 10%). 1H NMR (400 MHz, THF-d8,
ppm): d 1.97 (s, CH3), 3.62 (s, CH2), 7.32, 7.60 (m, Ph and imidazole
rings overlap). 13C NMR (100 MHz, THF-d8, ppm): d 11.0 (CH3), 58.8
(CH2), 128.5, 128.7, 130.3, 130.8, 135.6, 136.0, 136.5, 138.2 (CH Ph
and imidazole rings). 29Si (79 MHz, THF-d8, ppm): d ꢁ14, ꢁ10. ESI-
MS, m/z: 371 [M+H]+.
Ser CH2
N
NH
O
Si
EtO
OEt
OEt
Fig. 1. The five-coordinated silicon intermediate proposed for the reaction of
Si(OEt)4 and a silicatein.
for 5 days. The color changed from white to light cream. The pre-
cipitate was removed via a frit. The volatile components were re-
moved from the solution under vacuum. From this point, the
reaction was conducted in air. Water (10 mL) and 40 mL of ether
were added to the product. The ether portion was separated by
the separatory funnel and dried with magnesium sulfate, filtered,
and the volatile components were removed with a rotary evapora-
tor. The solid product was washed with 20 mL of 4:1 hexane/ethyl
acetate and the volatile components were removed on the vacuum
line for 48 h. An air stable, colorless, crystalline, solid was obtained
in 25% yield, 1.18 g. M.p. = 65 °C. 1H NMR (400 MHz, DMSO-d6,
ppm): d 1.23 (b, 12H, CH2), 1.39 (b, 2H, CH2), 1.67 (m, 2H, CH2),
3.34 (b, OH), 3.92 (t, J = 7 Hz, 2H, CH2), 4.33 (t, J = 7 Hz, 2H, CH2),
6.86, 7.14, 7.59 (s, 3H, imidazole ring). 13C NMR (75 MHz, DMSO-
d6, ppm): d 25.5 (CH2), 25.9 (CH2), 28.5 (CH2), 28.9 (CH2), 29.01
(CH2), 30.6 (CH2), 32.6 (CH2), 46.6 (CH2), 61.4 (CH2), 119.6 (CH),
128.9 (CH), 134.8 (CH). ESI-MS, m/z: 225 [M+H+].
Impurities: (CH3CH2)3N H+Clꢁ: 1H NMR (400 MHz, THF-d8,
ppm): d 1.77 (s), 3.60 (s). 13C NMR (100 MHz, THF-d8, ppm): d
11.0, 58.8.
2.2.4. Preparation of 6-imidazole-1-ylmethyl-pyridine-2-yl-methoxy-
triphenylsilane (SiPh3(OL3))
A solution of 0.16 g (0.5 mmol) SiPh3Cl in 15 mL acetonitrile
was added to a solution of 0.2 g (1.1 mmol) 6-imidazole-1-yl-
methyl-pyridine-2-yl-methanol (HOL3) in 15 mL of acetonitrile.
The mixture was stirred overnight at RT and no precipitation was
observed. The volatile components were removed slowly on a
Schlenk line and a white precipitate formed. Methylene chloride
(30 mL) was added to dissolve the product. The mixture was stir-
red and filtered via a frit. The volatile components from the solu-
tion were slowly removed on the vacuum line. Colorless crystals
formed overnight. The yield was 89%, 0.20 g. M.p. = 89 °C. 1H
NMR (400 M Hz, CD2Cl2, ppm): d 4.95 (s, CH2), 5.13 (s, CH2), 6.86
(b, CH), 6.96 (s, CH), 7.02 (s, CH), 7.27 (m, CH), 7.40 (m, CH), 7.47
(b, CH), 7.53 (b, CH, phenyl and imidazole rings overlap), 7.65,
7.67 (pyridine ring). 13C NMR (100 MHz, CD2Cl2, ppm): d 53.4
(CH2), 67.7 (CH2), 120.8 (CH aromatic), 128.9 (CH aromatic), 129.2
(CH aromatic), 130.6 (CH aromatic), 131.1 (CH aromatic), 131.5
(CH aromatic), 134.9 (CH aromatic), 136.3 (CH aromatic), 136.6
(CH aromatic), 138.8 (CH aromatic), 139.0 (CH aromatic). 29Si
(79 MHz, CD2Cl2, ppm): dꢁ11. ESI-MS, m/z: 448 [M+H+]. Anal. Calc.
for C28H25SiON3: C, 75.15; H, 5.63; N, 9.39. Found: C, 68.76; H,
5.61; N, 11.33%.
2.2.2. Preparation of 1-oxy-10-imidazole-decyl-triphenylsilane
(SiPh3(OL1))
A solution of 0.26 g (0.9 mmol) SiPh3Cl in 15 mL acetonitrile
was added to a mixture of 0.2 g (0.9 mmol) hydroxydecyl-imidaz-
ole (HOL1) and 0.06 g of pyridine (0.9 mmol) in 30 mL of acetoni-
trile. The mixture was stirred overnight at RT and was heated
24 h at 50 °C. No precipitation was observed. The volatile compo-
nents were removed slowly on a Schlenk line, which produced a
white solid. Ether (30 mL) was added and the mixture was filtered
to separate the product from the pyridine salt. Benzene (30 mL)
was added and solution was filtered. A white solid was obtained
in 45% yield, 0.20 g. M.p. = 105 °C. 1H NMR (400 MHz, CD2Cl2,
ppm): d 1.31 (b, 12H), 1.54 (b, 2H), 1.89 (b, 2H), 3.60 (t, J = 6 Hz,
2H, CH2), 4.17 (b, 2H, CH2), 7.29 (m), 7.36 (m), 7.49 (m, Ph and
imidazole rings overlap), 8.71 (b). 13C NMR (100 MHz, CD2Cl2,
ppm): d 26.2 (CH2), 26.5 (CH2), 29.1 (CH2), 29.5 (CH2), 29.7 (CH2),
30.6 (CH2), 33.3 (CH2), 50.3 (CH2), 63.2 (CH2), 100.6 (CH2), 121.0
(CH aromatic), 128.3 (CH aromatic), 128.9 (CH aromatic), 130.4
(CH aromatic), 135.7 (CH aromatic), 136.0 (CH aromatic), 136.0
(CH aromatic). 29Si (79 MHz, CD2Cl2, ppm): d ꢁ19. ESI-MS, m/z:
484 [M+H]+. Anal. Calc. for C31H38OSiN2: C, 77.13; H, 7.93; N,
5.80. Found: C, 70.98; H, 6.10; N, 3.87%.
2.3. Single-crystal X-ray diffraction studies
2.2.3. Preparation of 4-methoxy-5-methyl-imidazole-triphenylsilane
(SiPh3(OL2))
Crystal structures of HOL1, SiPh3(OL2) and SiPh3(OL3) were ob-
tained. In the glovebox, the crystals were put into paratone oil on
a glass slide and were placed in a desiccator. In air and as quickly
as possible, the oil-covered crystals were examined under a micro-
scope and mounted in the cold stream of the diffractometer.
Crystal data were collected on Bruker APEX CCD diffractometer
Route A. 4-Hydroxymethyl-5-methyl imidazole (HOL2) (0.5 g,
4.5 mmol) was added to a solution of 0.66 g (2.3 mmol) SiPh3Cl
in 40 mL acetonitrile and stirred under N2 at RT. After 15 min, for-
mation of a white precipitate was observed. The mixture was stir-
red for 24 h and filtered via a frit. The volatile components were
removed under vacuum. Methylene chloride (30 mL) was added
to dissolve the product. The suspension was filtered via a frit.
The volatile components were removed under vacuum. A colorless,
crystalline solid was obtained in 81% yield, 0.69 g. M.p. = 98 °C. 1H
NMR (400 MHz, CD2Cl2, ppm): d 1.99 (s, CH3), 4.78 (s, CH2), 7.39,
7.61 (m, phenyl and imidazole rings). 13C NMR (100 MHz, CD2Cl2,
ppm): d 11.0 (CH3), 58.1 (CH2), 128.5, 129.3, 130.4, 130.7, 133.9,
with graphite-monochromated Mo K
a radiation (k = 0.71073 Å).
The unit cells were determined as a result of reflection of three dif-
ferent orientations. Integrations of the data were done by SAINT and
for an empirical absorption corrections (as well as and other cor-
rections) multi-scan SADABS were applied [12]. Structure solution,
refinement and modeling were completed using the Bruker SHELXTL
package [13]. The structure was determined by full-matrix least-
squares refinement of F2 and the selection of the appropriate atoms

T. Eliseeva et al. / Journal of Organometallic Chemistry 695 (2010) 1507–1512
1509
Table 1
Crystallographic and data collection parameters.
C13H24N2O (HOL1)
C23H22N2OSi (SiPh3OL2)
C28H25N3OSi (SiPh3OL3)
Formula weight
T (K)
224.34
100(2)
370.52
100(2)
447.60
100(2)
Crystal dimension (mm)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.34 ꢀ 0.32 ꢀ 0.08
monoclinic
P21
7.3483(14)
5.0942(10)
17.320(3)
90
94.455(3)
90
646.42(2)
2
0.70 ꢀ 0.13 ꢀ 0.07
0.46 ꢀ 0.18 ꢀ 0.09
monoclinic
P21/c
9.9518(11)
23.709(3)
10.7519(12)
90
113.432(2)
90
2327.7(4)
4
triclinic
ꢀ
P1
9.7024(15)
14.885(2)
16.040(3)
111.814(3)
106.339(3)
95.631(3)
2009.6(5)
4
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (mg mꢁ3
)
1.153
0.073
1.225
0.131
1.277
0.127
l
(mmꢁ1
)
2h limit (°)
52.6
56.6
52.6
ꢁ9 6 h 6 9
ꢁ6 6 k 6 6
ꢁ21 6 l 6 21
5156
ꢁ12 6 h 6 12
ꢁ19 6 k 6 19
ꢁ21 6 l 6 21
17 597
ꢁ12 6 h 6 12
ꢁ29 6 k 6 29
ꢁ13 6 l 6 13
18 458
Total data collected
Number of independent reflections
Rint
2585
0.0302
9093
0.0448
4730
0.0424
Absorption correction
Transmission: tmin/tmax
Number of data/restraints/parameters
multi-scan (SADABS
0.9773/0.9942
2585/1/146
0.0514
)
multi-scan (SADABS
0.9137/0.9909
9093/0/489
0.0619
)
multi-scan (SADABS
0.9439/0.9887
4730/0/298
0.0455
)
R1 ½F2o P 2ðF2oÞꢄ
wR2 ½F2o P ꢁ3ðF2oÞꢄ
0.1229
1.182
0.1225
1.069
0.0996
1.077
Goodness-of-fit
from the generated difference map. Hydrogen atom positions were
calculated with the exception of the imidazole N-hydrogen atoms
in the structure of SiPh3(OL2). Crystallographic and data collection
parameters are listed in Table 1.
o
2
2
2 10
o
3. Results and discussion
2
Three compounds of general formula SiPh3OL where L contains
an imidazole were prepared. The three HOL precursor ligands are
defined in Eq. (1). HOL2 was available commercially and HOL3 by
following a literature synthesis [7]. The synthesis of HOL1 is re-
ported below.
2 10
Scheme 1. Synthesis of HOL1.
HOL1 was synthesized by
a two-step reaction sequence
(Scheme 1). Imidazole was deprotonated with KH in THF at 0 °C
to the potassium imidazole salt. The potassium imidazole was re-
acted with bromodecanol in refluxing THF to give HOL1 and a
precipitate, presumably KBr. The low yield of the compound
HOL1 was due to its partial solubility in water during the ether
extraction in the work-up. The 1H NMR spectrum of HOL1 showed
a broad signal at d 1.23, 1.39 and multiplet at d 1.67 ppm, consis-
tent with the long organic chain. A broad signal at d 3.34 ppm
was assigned to the hydroxyl group and triplets at d 3.92 and
4.33 ppm indicated methylene groups next to a hydroxyl group
and an imidazole ring. The three singlets at 6.87, 7.14 and
7.59 ppm were assigned to imidazole ring. 13C NMR data sup-
ported structure of HOL1. ES mass spectroscopy showed m/z
225 for H(HOL1)+. HOL1 was soluble in DMSO, acetonitrile, meth-
ylene chloride, and THF.
The three SiPh3(OL) compounds were obtained from the reac-
tions of SiPh3Cl with the three HOL in the presence of a base to ab-
sorb the HCl under very strict anaerobic conditions (Eq. (1))
ð1Þ
The thermal ellipsoid plot of HOL1 is depicted in Fig. 2. The
asymmetric unit contains one HOL1 molecule. The solid state struc-
ture consists of an imidazole ring substituted at the N1 nitrogen
atom by a linear decanol chain. All bond lengths and angles are
at the expected values. Extended linear chains of HOL1 molecules
are generated in the solid by means of O–Hꢃ ꢃ ꢃN hydrogen-bonds
(N(2)ꢃ ꢃ ꢃO(1) = 2.834 Å) at both ends of the molecules.

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T. Eliseeva et al. / Journal of Organometallic Chemistry 695 (2010) 1507–1512
Fig. 2. Molecular structure of HOL1 with thermal ellipsoids depicted at 50% probability.
The best syntheses of SiPh3(OL2) and SiPh3(OL3), which were
on Scheme 1 and ES mass spectroscopy showed m/z for a proton-
ated SiPh3(OL-H)+ ion.
obtained in over 80% yields, involved the reactions of 1 M equiva-
lent of SiPh3Cl with 2 M equivalents of the respective HOL at room
temperature. Under these conditions, the imidazole of one equiva-
lent of HOL removes HCl from reaction by formation of HOL(HCl)
and second equivalent of the ligand reacts with SiPh3Cl to form Si-
Ph3OL. The use of cheaper base pyridine was acceptable in the syn-
thesis of SiPh3OL1, which was obtained in 45% yield. The use of the
cheaper and less basic (than the imidazole of HOL) NEt3 was not
the best choice for the synthesis of SiPh3OL2 and SiPh3OL3 because
low yields were obtained. The SiPh3OL2 and SiPh3OL3 products
from such reactions were difficult to separate from HNEt3Cl and
formation of both SiPh3OL and Ph3SiOSiPh3 was observed. The for-
mation of the by-product SiPh3OSiPh3 is probably due to the reac-
tion of HOL with HCl to first give Cl–L and H2O. The H2O then reacts
with SiPh3Cl to give Ph3SiOSiPh3 and more HCl, which can reini-
tiate the process that leads to the Ph3SiOSiPh3 [14]. Apparently,
with the weaker bases, HCl is less tightly bound and more able ini-
tiate the two-step synthesis of SiPh3OSiPh3. The crystal structure
and other characterizational data for SiPh3OSiPh3 were as those
in the literature [15,16].
Crystals of SiPh3(OL2) and SiPh3(OL3) suitable for single crystal
X-ray diffraction studies were grown from concentrated acetoni-
trile and methylene chloride solutions, respectively, but suitable
crystals of SiPh3(OL1) could not be obtained. Selected distances
and angles of SiPh3(OL2) and SiPh3(OL3)are listed in Table 2 and
thermal ellipsoid plots are shown in Figs. 3 and 4, respectively.
The asymmetric unit of SiPh3(OL2) consists of two slightly different
molecules whereas that of SiPh3(OL3) consists of one molecule. In
both SiPh3(OL2) and SiPh3(OL3), the distorted, tetrahedral silicon
atom is coordinated to three phenyl groups and one OL ligand.
Table 2
Selected distances and angles in the crystal structures of SiPh3(OL2) and SiPh3(OL3).
Bond length (Å)
SiPh3(OL2)
Molecule 1
SiPh3(OL3)
Molecule 2
Si–O
Si–C
1.6443(16)
1.867(2)
1.868(2)
1.871(2)
1.6430(16)
1.864(2)
1.875(2)
1.880(2)
1.6394(13)
1.8628(17)
1.8697(18)
1.8711(17)
The three SiPh3OL compounds had limited solubility in organic
solvents. The compounds were reactive towards water, especially
in solution. Satisfactory elemental analyses were difficult to attain.
Though there was no evidence of a persistent bond between the
imidazole nitrogen atom and the silicon center of the three SiPh3OL
(see below), the presence of an imidazole-containing L substituent
appears to increase their water reactivity relative to SiPh3OR that
contain hydrocarbon R groups [17].
Bond angle (ꢁ)
O–Si–C
103.15(9)
110.66(9)
111.83(9)
109.49(10)
110.41(10)
111.08(10)
124.87(15)
104.11(9)
109.55(10)
112.61(9)
107.52(10)
109.66(10)
113.33(10)
126.16(14)
104.07(7)
109.76(7)
112.15(7)
109.10(8)
109.38(8)
112.35(8)
125.58(11)
C–Si–C
Si–O–C
The three SiPh3OL were characterized by 29Si NMR spectros-
copy. The 29Si chemical shifts for SiPh3(OL1), SiPh3(OL2), and Si-
Ph3(OL3) were observed at ꢁ19, ꢁ13, and ꢁ11 ppm, respectively,
which is consistent with four-coordinated silicon compounds of
the general form SiPh3OR [18]. For example, the chemical shift
for SiPh3OEt is ꢁ14 ppm (DMSO-d6).
The SiPh3OL compounds were characterized by other spectral
means. The 1H NMR spectrum of SiPh3(OL1) showed broad signals
at d 1.31, 1.54, and 1.89 ppm that are assigned to the long organic
chain, and broad signals at d 3.60 ppm and d 4.17 ppm indicated
methylene groups next to the oxygen and an imidazole ring of
the complex. Some broadening of the signals and discrepancies
in the elemental analysis may be attributed to partial protonation
of the imidazole ring by HCl generated in the reaction. A multiplet
at d7.29–7.49 ppm is attributed to the overlap the resonances from
the imidazole and phenyl rings of SiPh3(OL1). The 1H NMR spec-
trum of the compound SiPh3(OL2) showed a singlet at d 1.97 ppm
corresponding to the methyl group, a singlet at d 4.77 ppm for
methylene group, and two multiplets at d 7.32 and 7.60 ppm for
the imidazole and phenyl rings protons. The 1H NMR spectrum of
SiPh3(OL3) showed broad signals at d 4.95 and 5.13 ppm for the
methylene groups near to oxygen and imidazole and pyridine.
The signals at d 6.86, 7.02, 7.27, 7.40, 7.47, and 7.53 ppm assigned
to the phenyl and imidazole rings. The signals at d 6.96, 7.65, and
7.67 ppm are attributed to the pyridine ring of SiPh3(OL3). 13C
NMR data of the three SiPh3(OL) supported the structures shown
Fig. 3. Molecular structure of one of the two molecules of SiPh3(OL2) with thermal
ellipsoids depicted at 50% probability.

T. Eliseeva et al. / Journal of Organometallic Chemistry 695 (2010) 1507–1512
1511
Fig. 4. Molecular structure of complex SiPh3(OL3) with thermal ellipsoids depicted at 50% probability. Hydrogen atoms were removed for clarity.
Fig. 5. (Top) One of the two chains of N–Hꢃ ꢃ ꢃN hydrogen bonds in a column of SiPh3OL2 molecules viewed roughly along the a axis with thermal ellipsoids depicted at 50%
probability. Four molecules of SiPh3OL2 are shown completely. The nitrogen atoms of four next nearest molecules (additional N1 and N4 atoms) are also shown to indicate the
direction of the next N–Hꢃ ꢃ ꢃN hydrogen bonds. (Bottom) A column of stacked SiPh3OL2 molecules viewed roughly perpendicular to the a axis and shown with thermal
ellipsoids depicted at 50% probability. There are two chains of N–Hꢃ ꢃ ꢃN hydrogen-bonded imidazoles per column of SiPh3OL2 molecules.

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T. Eliseeva et al. / Journal of Organometallic Chemistry 695 (2010) 1507–1512
The Si–O distances of the two molecules of SiPh3OL2 are slightly
longer than those in SiPh3OL3 and both are shorter than those in
O(SiPh3)2 (1.616(1) Å). As expected [16], the Si–O–C angles in both
structures are about 15–16° higher than that expected of a tetrahe-
dral structure.
Several intermolecular distances shorter than the sum of van
der Waal’s radii were observed in both the structures SiPh3(OL2)
and SiPh3(OL3) and these may account for the low solubility of
the compounds. Most importantly, N–Hꢃ ꢃ ꢃN hydrogen bonding
interactions were observed between molecules of SiPh3(OL2) with
a donor-acceptor distance of 2 .83 Å between N(2) and N(3) and
2.80 Å between N(1) and N(4). As in unsubstituted imidazole
[19], the N–Hꢃ ꢃ ꢃN hydrogen bonds connect the imidazole rings of
SiPh3(OL2) into a chain. The long range structure of SiPh3(OL2) con-
sists of columns along the a axis, with two such imidazole chains
running along the center of the column and the triphenylsilyl
groups at the periphery of the column (Fig. 5). Other short contacts
in the crystal structure of SiPh3(OL2) were observed, specifically
Acknowledgments
This material is based upon work supported in part by the Na-
tional Science Foundation under Grants Nos. 0316944 and
0616601. We would like to thank the University of Akron and
the Ohio Board of Regents for additional support.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2010.03.005.
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