Novel route to silanetriols and silanediols based on acetoxysilylalkoxides

Article abstract of DOI:10.1016/j.poly.2016.10.051

An easy and versatile method for the preparation of molecular alkoxysilanols as molecular organosilicates based on acetoxysilylalkoxides (ASA, (RO)(tBuO)_nSi(OAc)_3?nor (AcO)_3?n(tBuO)_nSi-O-R-

Full text of DOI:10.1016/j.poly.2016.10.051

Accepted Manuscript
Novel Route to Silanetriols and Silanediols based on Acetoxysilylalkoxides
Miriam de J. Velásquez-Hernández, Aarón Torres-Huerta, Uvaldo Hernández-
Balderas, Diego Martínez-Otero, Alejandra Nú ñez-Pineda, Vojtech Jancik
PII:
S0277-5387(16)30548-4
DOI:
http://dx.doi.org/10.1016/j.poly.2016.10.051
POLY 12304
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
30 August 2016
30 October 2016
31 October 2016
Please cite this article as: M.d.J. Velásquez-Hernández, A. Torres-Huerta, U. Hernández-Balderas, D. Martínez-
Otero, A. Nú ñez-Pineda, V. Jancik, Novel Route to Silanetriols and Silanediols based on Acetoxysilylalkoxides,
Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.10.051
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Novel Route to Silanetriols and Silanediols based on
Acetoxysilylalkoxides
Miriam de J. Velásquez-Hernández,a Aarón Torres-Huerta,a Uvaldo Hernández-Balderas,a Diego
Martínez-Otero,a Alejandra Núñez-Pinedaa and Vojtech Jancik*a
aCentro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Carr. Toluca-Atlacomulco
km 14.5, 50200 Toluca, Estado de México, México.
* Corresponding Author. Tel.: +52 722 2766610; fax: +52 55 56162217.
E-mail address: vjancik@unam.mx (V. Jancik)
Silanols • Hydrolysis • Acetoxysilylalkoxides • Structural study • CO2 Conversion.
Abstract
An easy and versatile method for the preparation of molecular alkoxysilanols as molecular
organosilicates based on acetoxysilylalkoxides (ASA, (RO)(tBuO)nSi(OAc)3–n or (AcO)3–n(tBuO)nSi-
O-R-O-Si(OtBu)n(OAc)3–n, R = organic group; n = 0 or 1) is presented. These ASA precursors are
prepared from silicon tetraacetate and suitable alcohols and are cleanly hydrolyzed in water to the
corresponding alkoxysilanols in the absence of a base or organic solvents. The compounds were
characterized by common spectroscopic methods including X-Ray structural analysis. Alkoxysilanols
were tested in the catalytic conversion of CO2 to styrene carbonate and show quantitative conversion
within 15 hours at 60 oC and 1 atm of CO2.

1. Introduction
Organosilanols combine in their molecule Si(OH)n (n = 1–3) moiety, which provides remarkable
hydrogen-bonding capabilities and tunable acidity, with an organic residue providing structural
modularity and solubility [1–3]. Thus their final properties can be easily adjusted according to the
desired application. Therefore, it is not surprising that they have found many applications in both
academia and industry. The most significant are cross-coupling reactions, synthesis of hybrid organic-
inorganic materials with long-range order [4–9], molecular recognition [10–12], environmentally
friendly surfactants based on organosilanetriols [13]; as well as unique bioisosteres, that do not have
stable carbon analogues, and are used in improving the advance of new therapeutic agents [14–19].
Furthermore, discrete alkoxysilanols (RO)nSi(OH)4–n (n = 2, 3) with a silicon atom immediately
coordinated to four oxygen atoms as in silica materials, have been used in the preparation of molecular
models to understand the local active sites on the surface of heterogeneous catalysts [20–12]. More
recently organosilanediols have been applied in enantioselective hydrogen-bond donor catalysis (HBD)
[23–26] and the binary catalytic system silanediol/TBAI has been described by Cokoja et al. [27] as a
“potential metal-free system that bridges the gap between metal containing and organic catalysts”.
Despite the above-mentioned promising applications, wider use of organosilanols is hampered by the
available synthetic methods [1–3,28,29]. The most important are based on the hydrolysis of
organochlorosilanes [2,3,28] or organoalkoxysilanes [29,30] (RnSiCl(4–n) and RnSiOR’(4–n); R’= Me, Et,
n = 1–3 respectively), synthesized from SiCl4 or tetramethoxy- or tetraethoxysilanes and
organometallic reagents. Eventually, they can also be prepared using catalytic hydrosilylation of
dienes, starting from HSiCl3 or HSi(OR)3 (R = Me, Et) [31]. These precursors are converted to the
corresponding silanols by hydrolysis. However, each precursor type has its disadvantages. The
hydrolysis of the chlorosilanes produces HCl, which causes condensation of the silanols and thus it has
to be trapped using stoichiometric amounts of a base such as aniline or pyridine. However, an excess of
2

the base can also cause decomposition of the products [2,3,28]. The hydrolysis of alkoxysilanes
produces alcohols that by themselves do not accelerate the condensation of the silanols, but this
hydrolysis requires acidic catalysis and long reaction times (up to 34 days!), which always results in a
partial condensation and thus product loss [29,30]. Finally, both methods require, especially in the case
of silanols with two or three OH groups, large quantities of organic solvent to dilute the reagents and
thus protect the silanols from condensation. In addition, the synthesis of alkoxysilanols (RO)nSi(OH)4–n
starts from the respective chloro derivatives (RO)nSiCl4–n and is even more problematic than the
synthesis of silanols with Si–C bonds, due to the low stability of the Si–OR bond under the synthetic
conditions [32]. However, they feature higher potential as a catalyst for HBD due to the higher acidic
character of their OH groups [33].
These facts prompted us to pursue a new sustainable synthetic pathway, which would afford stable
alkoxysilanols (RO)nSi(OH)4–n (n = 1, 2) under mild conditions. Therefore, we envisioned that the use
of acetoxysilylalkoxides (ASA) prepared from Si(OAc)4 and suitable tertiary alcohols as organic
moiety would represent a facile and efficient strategy for the preparation of alkoxysilanols. Although
the hydrolysis of some acetoxysilyl derivatives to the corresponding silanols have been in a limited
extent explored earlier, they used additional reagents such as carbonates or emulsifiers and in general
had low yields and thus did not became more widespread. [3] Unlike their chlorosilanes analogues the
ASA compounds are more stable and easier to handle but at the same time still more reactive than
alkoxysilanes, as the AcO– is a better leaving group. Furthermore, Pohl and Osterholtz [34] determined
that the condensation rate of alkylsilanetriols has a minimum at the pH of 4.5. This is just slightly lower
than the pKa of the acetic acid (4.76 at 25 °C). Therefore, we hypothesized that the acetic acid formed
during the hydrolysis would, in fact, stabilize the proposed alkoxysilanols from forming undesired
condensation by-products. A further advantage of this procedure would be that the released acetic acid
is biodegradable and much less corrosive than HCl and thus the use of a base during the hydrolysis
could be avoided.
3

Herein, we report a base- and organic solvent-free synthesis of molecular air-stable alkoxysilanols,
with tailored HB capabilities from acetoxylsilylalkoxides in an aqueous medium. Furthermore,
preliminary results of their catalytic activity in the conversion of CO2 into cyclic carbonate as a
function of the steric protection and the number of silanol groups are also reported.
2. Results and Discussion
2.1. Synthetic aspects and spectral characterization
To prepare the ASA precursors, tertiary diols 1,4-bis(diethylhydroxymethyl)benzene and 3,6-diethyl-4-
octyne-3,6-diol were reacted with Si(OAc)4 as the silicon source, in toluene to yield the corresponding
bis(triacetoxylsilyl)alkoxides 1 and 2. In the case of the bulkier alcohols Ph3COH and (4R,5R)-
TADDOL (TADDOL = (4R,5R)-2,2-dimethyl-α,α,α’,α’-tetraphenyldioxolane-4,5-dimethanol), reflux
2
in toluene was necessary to obtain full conversion either to the cyclic chiral κ -O,O’-(diacetoxylsilyl)-
(4R,5R)-TADDOLate 3 or triacetoxylsilyltriphenylmethanolate 4 (Schemes 1 and 2). Furthermore, the
compounds 1 and 4 can be directly reacted with tBuOH to yield the corresponding
diacetoxylsilylalkoxides 5 and 6. This allows an efficient control of the number of remaining acetate
groups attached to each silicon center. With the exception of 5, which it is colorless oil, all acetoxysilyl
derivatives are off-white crystalline powders that are soluble in polar organic solvents and toluene.
These ASA derivatives were suspended directly in ice-cold water, stirred for 2–15 min and the
corresponding alkoxysilanols 7–12 (Scheme 3), with one or two OSi(OH)n (n = 2, 3) groups, were
filtered off as white precipitates in good yields (71–96 %). A mixture of water and few drops of
ethylacetate were used to prevent the oily 5 from sticking to the glass walls during its hydrolysis to 7.
In the case of 6, ammonia was used to accelerate its hydrolysis to 11. All compounds were fully
characterized by 1H, 13C, 29Si NMR and IR spectroscopy, elemental analysis, and mass spectrometry. In
addition, the molecular structures of most of the compounds were determined by single crystal X-ray
diffraction (see Supporting Information). The formation of the ASA compounds 1–6 was confirmed by
4

OAc
Si OAc
OAc
OtBu
Si OAc
OAc
Si(OAc)4
– AcOH
tBuOH
Et
HO
Et
Et
OH
Et
R
O
R O
R
OH
– AcOH
H2O / 4 ºC
– 3 AcOH
H2O / 4 ºC
– 2 AcOH
Et
HO
Et
Et
OH
Et
R–OH =
O
AcO– =
OH
Si OH
OH
OtBu
Si OH
OH
O
Ph
Ph
Ph
OH
R
O
R O
Scheme 1 General synthetic route towards molecular alkoxysilanols
Ph
Ph
Ph
Ph
O
Ph
O
Ph
O
O
O
O
OH
OH
O
O
OAc
OAc
OH
Si(OAc)4
– 2 AcOH
H2O / 4 ºC
– 2 AcOH
Si
Si
OH
Ph
O
O
Ph
Ph
Ph
Ph
Ph
O
AcO– =
(4R,5R)-TADDOL
3
12
O
Scheme 2 Synthesis of chiral compounds 3 and 12 from (4R,5R)-TADDOL
Ph
Ph
O
AcO
AcO Si
AcO
Et
OAc
Si OAc
OAc
AcO
AcO Si
AcO
Et
OAc
Si OAc
OAc
OAc
Si OAc
OAc
Et
Et
Ph
Ph
Ph
O
O
OAc
O
O
O
O
O
Si
O
OAc
Et
Et
Et
Et
Ph
3
1
5
2
Ph
4
Ph
Ph
O
Ph
OtBu
Ph
OH
Ph
Ph
Ph
OtBu
tBuO
AcO Si
AcO
Et
Et
OtBu
Si OAc
OAc
O
OH
Ph
Ph
O
Si OAc
OAc
Ph
Ph
O
Si OH
OH
O
Si OH
OH
O
O
Si
O
OH
O
Et
Et
6
10
11
12
Ph
Ph
Et
tBuO
HO Si
HO
Et
OtBu
Si OH
OH
HO
HO Si
HO
Et
O
OH
Et
HO
Et
O
OH
Si OH
OH
Et
O
Si OH
OH
O
O
HO Si
HO
O
Et
Et
Et
Et
Et
Et
9
8
7
Scheme 3 Acetoxysilyl derivatives and the corresponding hydrolyzed alkoxysilanols
13
13
1H and C NMR spectroscopy (1H: δ 1.52–2.10 ppm, C: δ 21.8–23.0 for CH3COO–, δ 167.7–168.6
ppm for C=O). Additionally, in comparison with Si(OAc)4 ( 1760 cm–1), these compounds shifted to
lower wavenumbers ( 1739–1752 cm–1) in the bands associated with C=O stretching vibration. All
silanediols are soluble in polar organic solvents and toluene; however, their silanetriols analogues are
soluble only in highly polar solvents such as DMSO and only sparingly in THF. This can be explained
by the higher polarity of the OH moieties in the silanetriol group and, thus, higher strength of the
5

present hydrogen bonds (vide infra). These inductive effects, associated with substituents such as OH
1
and OR in organosilanol compounds, are supported by H NMR spectroscopy where the signals
corresponding to the OH groups are in the range of δ 5.90–6.89 ppm. Furthermore, the corresponding
normalized integrals match with the number of the OH groups expected for each silanol. Also, in 29Si
NMR spectra, the sharp signals of the silanols shifted up-field with each consecutive substitution of the
OH moiety by OR groups Si(OH)4 (29Si: δ –72 ppm) [35], ROSi(OH)3 (29Si: δ –78.3 to –80.9 ppm),
(RO)(tBuO)Si(OH)2 (29Si: δ –83.8 to –87.0 ppm). The retention of organic moieties in the molecular
alkoxysilanols after the hydrolysis process was confirmed by elemental analysis and NMR
13
spectroscopy (1H and C) where the signals corresponding to the organic moieties remained present;
while those for the acetate groups, were essentially absent (see Supporting Information). Also, the
absence of any condensation by-products in the alkoxysilanols was corroborated by the lack of the
band corresponding to the siloxane bridge Si-O-Si ( 1060–1220 cm–1) in their FT-IR spectra [28].
Moreover, the shift to upper wavenumber of the broad band attributed to OH groups in 7 and 11 (
3373 and 3381 cm–1) compared to their respective alkoxysilanetriol analogues 8 and 10 ( 3128 and
3312 cm–1), clearly evidences the influence of the number of OH groups attached to the same silicon
center and on the strength of the hydrogen bond interactions in solid state. This behavior was also
supported by X-ray structural analysis. Additionally, these findings seem to have important
implications in the relative catalytic activity of the silanols in HBD (vide infra).
The relative thermal stability of alkoxy(bis-silanetriol) 8 and its analogous alkoxy(bis-silanediol) 7 was
studied by thermogravimetry (TG) and differential scanning calorimetry (DSC). 8 and 7 were thermally
stable up to 161.6 and 72.4 °C respectively. The TG-DSC curves exhibited single stage decomposition
for 8; while 7 decomposes in a multistage process. For both compounds, the final product at 450 °C is a
slightly impure silica (for more details see the Supporting Information).
6

2.2. Description of molecular and crystal structures of compounds 1 – 4, 6 – 8, 10 – 12
The molecular structures of the (acetoxylsilyl)alkoxides 1 – 4, 6, alkoxysilanediols 7, 11 and 12, and
the alkoxysilanetriols 8 and 10, were determined by single crystal X-ray diffraction. Crystals suitable
for X-ray diffraction studies were obtained either from saturated toluene (1, 2) and THF (3, 4, 6, 7, 8,
10) solutions at –24 ºC; while single crystals of 11 and 12 were grown either from DMSO (11·DMSO)
or wet dichloromethane solutions (11·H2O and 12·CH2Cl2) by slow solvent evaporation. In a neat form,
8 always precipitates as a microcrystalline powder and all attempts to grow bigger crystals failed.
Nonetheless, it has been shown that silanetriols can be co-crystallized with organic diamines due to
strong hydrogen-bonding interaction [36,37]. Hence, 8 was co-crystallized with two equivalents of
DABCO (DABCO = diazabicyclo[2.2.2]octane). Compounds 2, 4, 6 – 8 and 11·H2O crystallized in the
1
triclinic P space group, compounds 3 and 12 in the orthorhombic P21212 and P212121 space groups,
respectively, while the rest of the compounds crystallized in monoclinic space groups: C2 (1), P21/n
(10) or C2/c (11·DMSO). The asymmetric unit contains half a molecule (2, 3, 6, 8), one molecule (4,
7, 10 – 12) or one complete and two halves of a molecule, together with one molecule of DABCO
(8·2DABCO), THF (10·THF), DMSO (11·DMSO), H2O (11·H2O) or CH2Cl2 (12·CH2Cl2). The
molecular structures of all compounds are shown in Figure 1, while selected crystallographic details are
listed in Tables 1 and 2. In all compounds, the SiO4 unit has a distorted tetrahedral geometry with
angles ranging from 99.3(1)° to 116.1(1)°. The Si–O bond distances are only slightly influenced by the
different substituents, as the values for the Si–O(C) (1.578(2)–1.641(1) Å), Si–OAc (1.640(1)–1.654(1)
Å) and Si–OH bonds (1.607(1)–1.624(1) Å) fall in a very narrow range. However, the Si–OAc bond
lengths are always slightly longer (0.03 Å) than the corresponding Si–OH distances due to both the
electronic effect of the acetate groups and their larger steric bulk, but show no variation compared to
the parent silicon tetraacetate (Si–OAc = 1.624 Å) [38]. These values are comparable to those in related
silicate based silanols [Ph2Si(µ-O)Si(OH)2(µ-O)]2, Me2Si[(µ-O)SiMe2(µ-O)]2Si(OH)2 and
7

[(tBuO)3Si(µ-O)Si(OH)2](µ-O) (Si-O(C) 1.608 – 1.612 Å, Si–OH (1.592 – 1.625 Å, O-Si-O 104.7 –
112.4 º),[39a–c] but one of the Si–OH (1.625 Å) bond lengths in [(Mes*O)2Si(OH)2]·2THF is
significantly longer.[39d] Selected bond lengths and angles for compounds 1 – 4, 6 – 8 and 10 – 12 are
listed in Table 3, while Table 4 contains details of the above-described hydrogen bonds. While the
acetates are isolated molecules in the crystal, the silanols are always aggregated by strong Hydrogen-
bonding interaction. Overall, five different hydrogen-bonding patterns (I–V) were observed, as a
function of the steric bulk of the organic groups and the number of OH groups per silicon atom that
regulates the degree of self-association and were described using the graph set analysis (Figure 2) [40].
Table 1. Crystal data and structure refinement details for compounds 1 – 4, 6
3d
C35H34O8Si
610.71
1c
C28H42O14Si2
658.79
2
C24H38O14Si2
606.72
4
C25H24O7Si
464.53
6
C27H30O6Si
478.60
Empirical formula
Formula mass (g/mol)
Space group
T (K)
C2
P21212
P
P
P
1
1
1
100(2)
100(2)
100(2)
100(2)
100(2)
1.54178
20.3982(4)
13.8584(4)
24.3524(6)
90
1.54178
1.54178
13.4373(3)
9.5065(2)
11.8659(3)
90
0.71073
0.71073
λ (Å)
9.0912(2)
9.1134(2)
9.3268(2)
87.784(1)
83.045(1)
76.746(2)
746.58(3)
9.9282(4)
10.7649(4)
13.0781(5)
110.8963(7)
97.5728(8)
110.4489(7)
1169.85(8)
8.6997(2)
9.0317(2)
17.0129(4)
99.2568(5)
90.5947(5)
109.8012(5)
1238.31(5)
a (Å)
b (Å)
c (Å)
α (º)
β (º)
γ (º)
94.712(2)
90
90
90
V (Å3)
6860.8(3)
1515.77(6)
0.207
0.178
8
x
0.200
x
0.165
0.124
1
x
0.141
x
0.123
0.097
2
x
0.118
x
0.373
0.251
2
x
0.350
x
0.300
0.219
2
x 0.280 x
Crystal size (mm)
Z
ρcalc. (g·cm−3)
1.276
1.486
2800
1.349
1.658
322
1.338
1.131
644
1.319
0.144
488
1.284
0.135
508
µ (mm−1
)
F(000)
θ range for data collection 1.820 to 67.747
4.777 to 67.711
3.725 to 69.967
1.743 to 26.369
2.432 to 26.371
(º)
48551
8081
18442
19964
37746
No. of reflections
No. of
independent 12124 (0.0195)
2608 (0.0198)
2885 (0.0228)
4801 (0.0243)
5062 (0.0191)
reflections (Rint)
No.
of 12124 / 1 / 813
2608 / 0 / 186
1.066
2885 / 0 / 202
1.059
4801 / 130 / 330
1.029
5062 / 0 /312
1.028
data/restraints/parameters
Goodnes-on-fit (GOF) on 1.055
F2
R1,a wR2b (I > 2σ(I))
R1,a wR2b (all data)
0.0402, 0.1081
0.0407, 0.1088
0.0412, 0.1231
0.0468, 0.1286
0.407 / –0.309
0.0270
0.0309, 0.0784
0.0341, 0.0807
0.306 / –0.355
0.0296, 0.0766
0.0311, 0.0778
0.356 / –0.342
0.0709
Largest diff. peak/hole 0.541 / –0.269
0.201 / –0.250
(e·Å–3)
CCDC
1453225
1453226
1453230
1453228
1453229
2
2 2 ½
a R1 = Σ||Fo| − |Fc||/Σ|Fo|. b wR2 = [Σw(Fo − Fc2)2/Σw(Fo ) ] . c Flack parameter 0.487(4). d Flack parameter: –0.008(5).
8

Figure 1. Molecular structures of 1 – 4, 6 – 8·DABCO, 10·THF, 11·DMSO and 12·CH2Cl2 with
thermal ellipsoids set at 50 % probability level. Carbon bound hydrogen atoms and solvating solvent
molecules were eliminated for the sake of clarity.
9

Table 2. Selected crystallographic data for compounds 7, 8, 10 – 12.
c
8·2DABCO
C28H54N4O8Si2
630.93
10·THF
C23H26O5Si
410.53
11·DMSO
C25H32O5SSi
472.65
11·H2O
C23H27O4.5Si
403.53
12·CH2Cl2
7
C24H46O8Si2
518.79
C32H32Cl2O6Si
611.56
Empirical formula
Formula mass (g/mol)
Space group
P21/c
C2/c
P212121
100(2)
P
P
P
1
1
1
100(2)
100(2)
100(2)
100(2)
100(2)
T
(K)
(Å)
0.71073
0.71073
0.71073
12.3488(3)
8.9576(2)
19.5820(4)
90
0.71073
30.6391(6)
8.7736(2)
20.1977(4)
90
0.71073
0.71073
9.2264(2)
13.6523(3)
23.0659(6)
90
λ
7.1203(2)
10.0366(3)
10.5331(3)
102.7633(5)
95.1489(5)
103.8582(5)
704.63(4)
8.5208(4)
9.8696(5)
11.7679(6)
103.7594(11)
97.5810(11)
113.1915(11)
854.90(7)
8.8728(3)
10.2369(3)
12.7680(4)
113.0905(6)
95.8921(6)
91.7488(6)
1057.99(6)
a
b
c
(Å)
(Å)
(Å)
(º)
α
β
(º)
107.9408(5)
90
113.6567(4)
90
90
γ
(º)
(Å3)
90
2060.75(8)
4973.19(18)
2905.42(12)
V
0.417 x 0.301 x 0.189 x 0.052 x 0.286 x 0.218 x 0.296 x 0.261 x 0.289 x 0.207 x 0.251 x 0.248 x
Crystal size (mm)
0.206
0.040
0.184
0.239
0.163
0.226
1
1
4
8
2
4
Z
ρcalc. (g·cm−3)
1.223
1.226
1.323
1.263
1.267
1.398
µ
(mm−1
(000)
0.168
0.154
0.146
0.211
0.139
0.310
)
282
342
872
2016
430
1280
F
2.005 to 26.368
13531
1.841 to 26.371
16864
1.733 to 26.370
20204
2.095 to 26.369
22388
1.747 to 26.372
17675
1.733 to 27.483
64011
θ
range for data collection (º)
No. of reflections
No. of independent reflections 2872 (0.0159)
Rint
No.
3500 (0.0390)
4200 (0.0250)
5078 (0.0240)
4316 (0.0210)
6660 (0.0192)
(
)
of 2872 / 0 / 165
3500 / 3 / 201
4200 / 251 / 317 5078 / 107 / 330 4316 / 73 / 311
6660 / 93 / 406
data/restraints/parameters
Goodnes-on-fit (GOF) on F2
1.025
1.018
1.025
1.033
1.033
1.049
R1
,
a wR2b
(
I
> 2
σ(I))
0.0292, 0.0748
0.0303, 0.0756
0.371, –0.310
0.0335, 0.0786
0.0436, 0.0844
0.341, –0.252
1453231
0.0346, 0.0892
0.0378, 0.0916
0.379, –0.372
1453232
0.0310, 0.0800
0.0346, 0.0828
0.383 / –0.321
1453234
0.0414, 0.1083
0.0446, 0.1109
0.488 / –0.522
1453235
0.0210, 0.0561
0.0213, 0.0563
0.295 / –0.197
1453236
R1
,
a wR2b (all data)
Largest diff. peak/hole (e·Å–3)
CCDC
1453233
½
a R1
=
Σ
||Fo
|
−
|
Fc||/
Σ
|
Fo|. b wR2 = [Σw
(
Fo2 − Fc2)2/Σw
(
Fo2)2] . c Flack parameter: 0.008(6)
Figure 2. Hydrogen-bonding patterns found in compounds 12·CH2Cl2 (I), 11·DMSO (II), 11·H2O
(III), 10·THF (IV) and 7 (V).
10

In this study, the TADDOL derivative 12 contains the bulkiest organic group, which resulted in the
formation of only a single hydrogen-bond. Thus the proton from one Si–OH group coordinates to the
oxygen atom from the second Si–OH group belonging to a neighboring molecule of 12 to form an
extended chain C(4) a (Figure 2, motif I). The proton of this accepting OH group is involved in an
ꢁꢂ ꢃ
H···π interaction. In the case of 11·H2O, the characteristic Si–OH···H homodimer ring pattern ꢀꢁ 8
usually found in organosilanediols structures is present, and the water molecule serves as O–H donor to
ꢁꢂ ꢃ
interconnect these ꢀꢁ 8 synthons (Figure 2, motif III). On the contrary, when 11 was crystalized from
DMSO, two molecules of this solvent were included in the structure and break the strong Si–OH···H
ꢁꢂ ꢃ
ꢁꢂ
ꢃ
homodimer ꢀꢁ 8 to give heterosynthon formed by discrete solvated rings ꢀꢄ 12 abab (Figure 2,
motif II). The oxygen atom in DMSO acts as hydrogen-bond acceptor supressing the formation of the
extended network. In 10, the tBuO group present in 11 is replaced by a third OH group leading to a
higher acidity and lower steric protection. Thus, 10 presents a modulated equilibrium between solvent
interaction and self-association through (Si–OH···O–Si) hydrogen-bonding; hence, the THF breaks one
ꢁꢂ ꢃ
of the two hydrogen bonds involved in the ꢀꢁ 8 synthon to give an interconnected ring
ꢁꢂ
ꢃ
patternꢅꢀꢆ 10 abc; which is classified as third level graph-set. Also, this could be described on a
ꢈꢂ ꢃ
binary-level through hydrogen bonding chains C(4) b and ꢇꢁ 6 ac (Figure 2, Motif IV). In the case of
alkoxy(bis-silanols) 7 and 8, the organic group acts as bridging moiety between two silicate centers,
resulting in higher order structures than in the monosilicate analogs. For the compound 7, the self-
ꢁꢂ
ꢃ
ꢁꢂ ꢃ
association produces a zig-zag interconnected ꢇꢁ 26 [ꢀꢁ 8 ] chain formed of alternated ring
ꢁꢂ ꢃ
ꢁꢂ ꢃ
homodimers (ꢀꢁ 8 aa, ꢀꢁ 8 bb) between silicate centers; where the organic “spacer” allows the
multiple macrocyclic rings, without the inclusion of solvent molecules (Figure 2, Motif V). In the case
of alkoxy(bis-silanetriol) co-crystal 8·2DABCO the interaction of diamine with 8 creates a macrocyclic
ꢄꢂ
ꢃ
2D system ꢀꢄ 36 bcbc (dSi···Si = Si(1)–Si(1a) 10.51 Å and Si(1)–Si(1c) 9.86 Å). We observed three
different OH···A (A = O, N) hydrogen-bonds per Si(OH)3 unit with O···A distances of 2.780(1) Å,
11

[O(2)–H(2)···(O4)]; 2.742(2) Å, [O(3)–H(3)···(N2)]; 2.658(2) Å, [O(4)–H(4)···(N1)], respectively. In
the crystal lattice, the self-association between adjacent alkoxy(bis-silanetriol) molecules creates a
ꢁꢂ
ꢃ
ꢁꢂ ꢃ
ꢄꢂ
ꢃ
chain ꢇꢁ 26 [ꢀꢁ 8 ] along the c axis. These chains are linked by DABCO pillars ꢇꢄ 36 bccb to give
two-dimensional ABABAB stacking type formed by diamin···silanol alternating layers (Figure 3).
Table 3. Selected bond distances (Å) and angles (°) for compounds 1 – 4, 6 – 8 and 10 – 12.
Si–OAc Si–Ospacer Si–OtBu
Si–OH
<O-Si-O
<O-Si-O
mono- and bis(triacetoxysilyl)alkoxides
1.642(1) 1.590(1)
1.648(2) 1.578(2)
1.640(1) 1.588(1)
–
–
–
–
–
–
114.09(5)
100.84(4)
4
1
2
114.14(13) 104.06(13)
114.72(7)
102.35(7)
(diacetoxysilyl)alkoxides
1.654(1) 1.608(1) 1.597(1)
–
–
114.83(4)
116.06(6)
103.24(4)
99.34(6)
6
3
1.642(1) 1.611(1)
–
alkoxymono- and bis(silanediols)
–
–
–
–
1.616(1)
–
1.608(1) 112.01(6)
105.35(6)
103.47(5)
106.59(6)
106.90(4)
12·CH2Cl2
11·DMSO
11·H2O
7
1.628(1) 1.676(1) 1.617(1) 113.05(5)
1.618(1) 1.637(1) 1.620(1) 113.68(6)
1.613(1) 1.641(1) 1.607(1) 112.83(4)
alkoxymono- and bis(silanetriols)
–
–
1.618(1)
1.632(1)
–
–
1.624(1) 113.82(5)
1.622(1) 113.22(6)
104.17(6)
105.04(5)
10·THF
8·2DABCO
Figure 3. Detail of the hydrogen bonded layer formed by 8 and DABCO in 8·2DABCO.
12

Table 4. Geometric parameters for the hydrogen-bonds in the crystal structures of compounds [Å
and º]
Compound
H-bond
D–H (Å)
0.81(1)
0.82(1)
0.82(1)
0.81(1)
0.86(2)
0.86(2)
0.82(2)
0.81(2)
0.83(1)
0.83(1)
0.83(1)
0.83(1)
0.83(1)
0.84(1)
H···A (Å) D···A (Å) <DHA (º)
Symmetry code
–x+1,–y+1,–z
O(2)–H(2)···O(4)
O(3)–H(3)···O(2)
O(3)–H(3)···O(5)
O(4)–H(4)···O(5)
O(3)–H(3)···O(5)
O(4)–H(4)···O(2)
O(5)–H(5)···O(4)
O(5)–H(5)···O(6)
O(2)–H(2)···O(5)
O(3)–H(3)···O(2)
O(4)–H(4)···O(5)
O(2)–H(2)···O(4)
O(3)–H(3)···N(2)
O(4)–H(4)···N(1)
1.91(1)
1.92(1)
1.96(2)
1.89(2)
1.77(2)
1.88(2)
2.06(2)
1.94(2)
1.85(2)
2.08(1)
1.99(3)
1.95(1)
1.91(1)
1.84(1)
2.715(1)
2.721(1)
2.773(1)
2.678(1)
2.600(3)
2.731(2)
2.870(3)
2.744(2)
2.670(2)
2.908(2)
2.780(3)
2.780(2)
2.742(2)
2.658(2)
171.6(2)
169.0(2)
170.7(2)
167.2(2)
161.0(5)
172.0(2)
168.0(4)
171.0(2)
170.0(2)
173.0(2)
158.0(2)
173.2(2)
171.7(2)
162.6(2)
7
–x+2,–y+1,–z
11·DMSO
11·H2O
–x+1/2,–y+3/2,–z+1
–x+1/2,–y+3/2,–z+1
–x+1,–y+1,–z+1
–x+1,–y+1,–z+1
–x+2,–y+1,–z+1
x+1/2,–y+3/2,–z+1
–x+1,y+1/2,–z+3/2
–x+1,y+1/2,–z+3/2
–x+1,y–1/2,–z+3/2
–x+1,–y+1,–z+1
–x+1,–y+1,–z
12
10
8·2DABCO
x,y+1,z
2.3. Catalytic studies
These results clearly demonstrate the advantage of this synthetic method, since it is possible to
easily modulate the steric and/or electronic effects around the silicon atom. Therefore, the acidity of
the OH groups and, consequently, the number and strength of hydrogen bonds are tunable. This
should have a direct effect on the activity of Si–OH groups in HBD organocatalysis. To evaluate
this hypothesis, the organocatalytic cycloaddition of CO2 with styrene oxide (SO) to yield styrene
carbonate (SC) was tested using selected alkoxysilanols in the presence of tetrabutylammonium
iodide (TBAI) as a nucleophile source (Scheme 4).
The synergic effect between onium salts such as phosphonium and ammonium halides and Si–OH
groups in the catalytic cycloaddition of CO2 to epoxides has been reported previously [41–44].
However, most of them operate as a heterogeneous catalyst where silica is used as silanol source
13

acting as a support to immobilize the onium salts. Although, this approach facilitates the separation
and recycling of the catalyst; traditionally, most of them require harsh reaction conditions, such as
high pressure and temperature. As an alternative, the use of molecular bis(1-naphtyl)silanediol in
the presence of tetrabutylammonium halides as co-catalysts has been reported [45]. This is a
homogeneous system that under mild conditions affords excellent yield in the CO2 coupling with
SO. Unfortunately, the major drawback of this is the catalyst synthesis and recovery. Thus the
binary systems (10 mol% organosilanol/TBAI) were used under solvent free and mild reaction
conditions (60 °C, 15 h, using a balloon of CO2). Quantitative conversions (93% – >99%, Table 5)
were observed, even though SO is a rather difficult substrate due to the lack of electron-withdrawing
substituents, which would facilitate the nucleophilic attack on the epoxide ring. In addition, SO’s
high viscosity reduces the diffusion of CO2 in the reaction media. In the absence of alkoxysilanol,
only 31% of SO was converted to SC (entry 1), while, a conversion of 93% was observed for 8
(entry 2); in the case of 7 and 10–12), conversions above 98% were obtained (entries 3 to 6).
Nonetheless, the results seem to be counterintuitive since it is generally assumed that the most
acidic silanols are the best catalysts. Nevertheless, 8 presented the lowest conversion, even when it
is one of the most acidic alkoxysilanol in this study and contains six hydroxyl groups per molecule.
This behavior can be rationalized in terms of the strong self-association present in 8, which reduces
the availability of catalytically active hydroxyl groups as well as the solubility of such compound in
Scheme 4. Catalytic cycloadition of CO2 to styrene oxide
14

Table 5. Conversion of styrene oxide (SO) and CO2 into styrene carbonate (SC) using the binary
catalytical alkoxysilanol /TBAI system.
Catalyst Yield (%)a,b Entry Catalyst Yield (%)a,b
Entry
1
2
3
–
8
7
31
93
99
4
5
6
10
11
12
>99(96)c, 85d
>99
98
b
1
a Each experiment was repeated 3 times and the average yield is reported; reported yields are based on H NMR spectroscopic
c
analysis using toluene as internal standard (selectivity > 99% for SC), yield obtained after 12 h, d yield obtained with only 5 mol %
10 /TBAI.
the reaction media. In comparison, 7 showed better catalytic performance, even though the
substitution of two OH groups by two tBuO moieties lowers its acidity. Nonetheless, this
substitution significantly increases the solubility of 7 and the steric protection around the silicon
atom. Consequently, this reduces its self-association and increases the availability of the OH groups
in the catalytic process. Therefore, a balance between solubility and acidity is essential for an
optimum catalytic performance. Finally, 10 showed practically quantitative conversion after 12 h.
However, with regards to a sustainable and economical process for potential applications, the
recycling of the catalysts plays an important role. Therefore, the mixture of 10 and TBAI was
recycled by filtration through the addition of diethyl ether/hexane (1:2) mixture, which dissolves the
SC preferentially. Moreover, 10 can be used in three consecutive runs with only 13% activity loss in
the third cycle. However, slight catalyst leaching effects were observed. Although 8 shows only
93% of conversion, it is insoluble in diethyl ether and thus easily recyclable. Nonetheless, after the
second run, we observed significant loss of activity. This fact could be explained due to its higher
tendency to undergo self-condensation under reaction conditions (Figure 4). Furthermore, the binary
catalytic system 10/TBAI can be easily recycled through filtration as heterogeneous catalysts and its
15

catalytic performance in the cycloaddition of CO2 with SO to SC is comparable with that reported
for bis(1-naphtyl)silanediol and others homogeneous HB organocatalysts reported in the
literature.[27,46]
Figure 4. Comparative yields of SC obtained after three consecutive runs using recycled catalysts 8
and 10.
3. Conclusion
To summarize, acetoxylsilylalkoxides (ASA) offer a straightforward, scalable and cost-efficient
synthetic pathway towards alkoxysilanols. Such pathway eliminates the main disadvantages of the
current synthetic methods, such as large quantities of organic solvent, the use of a base, and long
reaction times. Additionally, it allows a stepwise tuning of the steric and electronic environment of
the silicon atom; the precise control of the number of OH groups attached to each silicon atom, as
well as their Bronsted acidity and consequently their hydrogen bonding capabilities. Therefore, their
organocatalytic properties can be easily tailored, as observed in the cycloaddition of CO2 with
styrene oxide, to form styrene carbonate in the presence of TBAI. We also demonstrated that the
hydrogen-bonding interactions between alkoxy(bis-silanetriol) and DABCO allow the formation of
16

higher order structures with great potential in the synthesis of hybrid ordered materials. Such studies
are currently underway in our research group. Finally, compound 8 is to the best of our knowledge
the first structurally characterized silicate- alkoxy(bis-silanetriol).
4. Experimental Section
4.1. General methods
The syntheses of the ASA compounds (1–6) were performed under a dried dinitrogen atmosphere
using Schlenk and glove-box techniques. The solvents were purchased from Sigma-Aldrich and
dried prior use with an MBraun SPS solvent purification system using Grubs’ columns. tert-Butyl
alcohol was dried with Na and distilled before use; tetrabutylammonium iodide (TBAI) was
purchased from Sigma-Aldrich and recrystallized from a CH2Cl2/hexane mixture. The Ph3COH,
DABCO and styrene oxide, were purchased from Sigma-Aldrich and used without further
purification, whereas Si(OAc)4, 1,4-bis(diethylhydroxymethyl)benzene and 3,6-diethyl-4-octyne-
3,6-diol were prepared according to the literature procedures [47–50]. C6D6 was distilled from a
Na/K alloy and degassed before use, whereas CDCl3 was dried with P4O10 and degassed before use.
DMSO-d6 was purchased from ABCR and used as received. Industrial grade extra dry CO2 was
purchased from INFRA S.A. de C.V. and used as received. NMR spectroscopic data were recorded
on a Bruker Avance III 300 MHz spectrometer and referenced to residual signals of the deuterated
1
13
29
solvent for H and C nuclei, or TMS as an external standard for the Si spectra. Electron impact
mass spectrometry (EI-MS) and chemical ionization mass spectrometry were carried on a Shimadzu
GCMS-QP2010 Plus using direct injection in the detection range of m/z 20 – 1090. Elemental
analyses (C, H, N) were determined on an Elementar MicroVario Cube analyzer. FT-IR spectra
17

were recorded on a Bruker ALPHA FTIR spectrometer placed inside a glove-box using the ATR
technique with a diamond window in the range of 500 – 4000 cm−1. Melting points were measured
in sealed capillaries on a Büchi B-540 melting point apparatus. DSC/TG measurements were carried
on a Netzsch STA 449 F3 Jupiter with the heating rate of 10 °C/min from room temperature to 450
°C. The measurements were performed with a constant flow of dinitrogen gas (50 mL/min), using 5
mm aluminum crucible. Savitzky-Golay smoothing algorithm was employed for TG and DSC
curves.
4.2. Preparationof compounds 1 – 12.
1,4-[(AcO3Si)OCEt2]C6H4 (1). A solution of 1,4-bis(diethylhydroxymethyl)benzene (0.50 g, 2.00
mmol) in toluene (5 mL) was added dropwise to a suspension of silicon tetraacetate (1.06 g, 4.01
mmol) in toluene (10 mL). The reaction mixture was stirred for 4 h. Afterwards, all volatiles were
removed under reduced pressure to afford the product as a white solid. Yield: 1.19 g, 1.81 mmol,
90%. M.p. 115 – 117 °C. Single crystals of compound 1 were grown from a saturated toluene
solution at –25 °C. Elemental analysis (%) Calcd for C28H42O14Si2 (658.80 g·mol–1): C 51.05, H
6.43; Found: C 50.67, H 6.26. FT-IR (ATR) (cm–1)
C=O), 951 (s, Si–O). 1H NMR (300.53 MHz, C6D6): δ (ppm) 0.85 (t, 6H, 3JH–H = 7.3 Hz, CH2CH3),
2980, 2941 (w, C–H, CH3, CH2), 1739 (s,
2
3
1.73 (s, 9H, OCCH3), 1.93 (dq, 2H, JH–H = 14.5 Hz, JH–H = 7.3 Hz, CH2), 2.13 (dq, 2H, 2JH–H
=
3
13
14.5 Hz, JH–H = 7.3 Hz, CH2), 7.47 (s, 2H, ArH). C{1H} NMR (75.57 MHz, C6D6): δ (ppm) 8.3
(CH2CH3), 22.0 (OCCH3), 35.7 (CH2CH3), 87.2 (CEt2), 125.9, 141.9 (o, i, C of Ar), 168.0 (C=O).
29Si NMR (59.63 MHz, C6D6): δ (ppm) –101.4. EI-MS: m/z (%) 629 (9) [M – Et]+, 407 (100) [M –
Et – Si(OAc)3 – OH]+.
1,2-[(AcO3Si)OCEt2]C2 (2). A solution of 3,6-diethyl-4-octyne-3,6-diol (0.50 g, 2.50 mmol) in
toluene (5 mL) was added dropwise to a suspension of silicon tetraacetate (1.33 g, 5.05 mmol) in
18

toluene (10 mL). The reaction was stirred for 4 h. Afterwards, all volatiles were removed under
reduced pressure to afford the product as a white solid. Yield: 1.36 g, 2.24 mmol, 90%. M.p. 49 – 51
°C. Single crystals of compound 2 were grown from a saturated toluene solution at –25 °C.
Elemental analysis (%) Calcd for C24H38O14Si2 (606.72 g·mol–1): C 47.51, H 6.31; Found: C 47.31,
1
H 6.31. FT-IR (ATR) (cm–1) 2983, 2946 (w, C–H, CH3, CH2), 1744 (s, C=O), 947 (s, Si–O). H
3
NMR (300.53 MHz, C6D6): δ (ppm) 1.12 (t, 6H, JH–H = 7.4 Hz, CH2CH3), 1.78 (s, 9H, OCCH3),
13
1.97 – 1.82 (m, 4H, CH2CH3). C{1H} NMR (75.57 MHz, C6D6): δ (ppm) 8.8 (CH2CH3), 22.1
(OCCH3), 35.0 (CH2CH3), 78.4 (C≡C), 86.6 (CEt2), 167.9 (C=O). 29Si NMR (59.63 MHz, CDCl3): δ
(ppm) –99.2. EI-MS: m/z (%) 577 (1) [M – Et]+, 547 (2) [M – AcO]+, 517 (3) [M – AcO – C2H6]+,
355 (12) [M – Si(AcO)3 – Et – H2O]+.
O,O’-TADDOL-Si(OAc)2 (3). A solution of (4R,5R)-2,2-dimethyl-α,α,α’,α’-tetraphenyldioxolane-
4,5-dimethanol (TADDOL) (0.40 g, 0.86 mmol) in toluene (10 mL) was added to a suspension of
silicon tetraacetate Si(OAc)4 (0.23 g, 0.86 mmol) in toluene (5 mL) and the reaction mixture was
heated under reflux over a period of 3 h. Afterwards, all volatiles were removed under reduced
pressure and the product was isolated as a white solid. Yield: 0.41 g, 0.67 mmol, 78%. M.p. 263 °C.
Elemental Analysis (%) Calcd for C35H34O8Si (610.73 g·mol–1): C 68.83, H 5.61; Found: C 68.36,
1
H 5.90. FT-IR (ATR) (cm–1)
1752 (m, C=O), 937 (m, Si–O). H NMR (300 MHz, CDCl3): δ
(ppm) 0.52 (s, 6H, C(CH3)2), 1.78 (s, 6H, CH3CO), 5.24 (s, 2H, Ph2CCHO), 7.13 – 7.38 (m, 16H,
3
CH of Ph), 7.58 (d, 4H, JH–H = 7.9 Hz, CH of Ph). 13C{1H} NMR (75.57 MHz, CDCl3): δ (ppm)
22.1 (CH3CO), 27.0 (C(CH3)2), 80.9 (Ph2CCHO), 84.3 (CPh2), 114.3 (C(CH3)2), 127.1, 127.1,
127.3, 127.7, 128.1, 129.1, 141.3, 146.0 (C of Ph), 168.2 (C=O). 29Si NMR (59.63 MHz, CDCl3): δ
(ppm) –94.3. EI-MS: m/z (%) 610 (16) [M]+, 510 (21.5) [M – C5H8O2]+.
Ph3COSi(OAc)3 (4). To a mixture of triphenylmethanol (1.00 g, 3.84 mmol) and silicon tetraacetate
19

(1.01 g, 3.84 mmol) was added toluene (20 mL). The reaction mixture was heated under reflux over
a period of 3 h. Afterwards, all volatiles were removed under reduced pressure, to afford the product
as a white solid. Yield: 1.52 g, 3.27 mmol, 85%. M.p. ˃ 350 °C. Single crystals of compound 4 were
grown from a saturated THF solution at –35 ºC. Elemental analysis (%) Calcd for C25H24O7Si
(464.55 g·mol–1): C 64.64, H 5.21; Found: C 64.30, H 5.26. FT-IR (ATR) (cm–1) 3059, 3023 (w,
1
C–H, Ph), 1749 (s, C=O), 955 (s, Si–O). H NMR (300.53 MHz, CDCl3): δ (ppm) 1.52 (s, 9H,
3
OCCH3), 7.11 – 6.99 (m, 3H, CH of Ph), 7.26 – 7.12 (m, 6H, CH of Ph), 7.70 (d, 6H, JH–H = 8.0
13
Hz, CH of Ph). C{1H} NMR (75.57 MHz, C6D6): δ (ppm) 21.8 (OCCH3), 88.7 (CPh3), 127.8,
29
128.2, 129.0, 145.5 (p, m, o, i, C of Ph) 167.7 (C=O). Si NMR (59.63 MHz, CDCl3): δ (ppm) –
101.8. EI-MS: m/z (%): 464 (21) [M]+, 421 (100) [M – Ac]+, 387 (17) [M – Ph]+.
1,4-[{(AcO)2(tBuO)Si}OCEt2]C6H4 (5). tBuOH (3 mL) was added to 1 (1.00 g, 1.52 mmol) and the
reaction mixture was stirred over a period of 12 h. All volatiles were removed under reduced
pressure and the product was isolated as a colorless oil. Yield: 0.87 g, 2.64 mmol, 87%. Elemental
analysis (%) Calcd for C32H54O12Si2 (686.93 g·mol–1): C 55.95, H 7.92; Found: C 55.65, H 7.88.
1
FT-IR (ATR) (cm–1)
2975, 2937 (w, C–H, CH3, CH2), 1743 (s, C=O), 984 (s, Si–O). H NMR
(300.53 MHz, CDCl3): δ (ppm) 0.69 (t, 6H, 3JH–H = 7.2 Hz, CH2CH3), 1.37 (s, 9H, C(CH3)3), 1.84 –
2.05 (m, 4H, CH2CH3), 2.10 (s, 6H, OCCH3), 7.28 (s, 2H, ArH). 13C{1H} NMR (75.57 MHz,
CDCl3): δ (ppm) 8.2 (CH2CH3), 23.0 (OCCH3), 31.3 (C(CH3)3), 35.0 (CH2CH3), 76.2 (C(CH3)3),
29
85.3 (CEt2), 125.4, 142.0 (o, i, C of Ar), 168.6 (C=O). Si NMR (59.63 MHz, CDCl3): δ (ppm) –
104.8. EI-MS: m/z (%) 657 (55) [M – Et]+, 627 (10) [M – AcO]+, 613 (30) [M – tBuO]+.
Ph3COSi(OtBu)(OAc)3 (6) tBuOH (3 mL) was added to 4 (1.00 g, 2.15 mmol) and the reaction
mixture was stirred over a period of 12 h. Afterwards, all volatiles were removed under reduced
pressure and the product was isolated as a white solid. Yield: 0.70 g, 1.46 mmol, 68%. M.p. 87 – 89
20

°C. Elemental analysis (%) Calcd for C27H30O6Si (478.61 g·mol–1): C 67.76, H 6.32; Found: C
67.58, H 6.50. FT-IR (ATR) (cm–1)
3057 (w, C–H, Ph), 2982, 2937, (w, C–H, CH3), 1740 (s,
1
C=O), 951 (s, Si–O). H NMR (300.53 MHz, CDCl3): δ (ppm) 1.17 (s, 9H, C(CH3)3), 1.88 (s, 6H,
OCCH3), 7.22 – 7.32 (m, 9H, CH of Ph), 7.38 – 7.42 (m, 6H, CH of Ph). 13C{1H} NMR (75.57
MHz, CDCl3): δ (ppm) 22.7 (OCCH3), 31.0 (C(CH3)3), 76.2 (C(CH3)3), 87.2 (CPh3), 127.3, 127.7,
128.8, 145.5 (p, m, o, i, C of Ph) 168.3 (C=O). 29Si NMR (59.63 MHz, CDCl3): δ (ppm) –105.1. EI-
MS: m/z (%) 478 (5) [M]+, 421 (44) [M – tBu]+, 401 (18) [M – Ph]+, 243 (96) [Ph3C]+.
1,4-[{(HO)2(tBuO)Si}OCEt2]C6H4 (7). 5 (0.20 g, 0.29 mmol) was added to a mixture of water (5
mL) and ethyl acetate (10 drops, 0 °C) and stirred for 15 min. The solvents were decanted and the
product was isolated as white solid. Single crystals were obtained by slow evaporation of THF
solution at ambient temperature. Yield: 0.09 g, 0.17 mmol, 87%. M.p. 160 – 161 °C. Elemental
analysis (%) Calcd for C24H46O8Si2 (518.79 g·mol–1): C 55.51, H 8.86; Found: C 55.09, H 8.72. FT-
IR (ATR) (cm–1) 3373 (s, SiO–H), 2975, 2935 (w, –CH3, –CH2), 961 (s, Si–O). 1H NMR (300.53
MHz, DMSO-d6): δ (ppm) 0.59 (t, 6H, 3JH–H = 7.2 Hz, CH2CH3), 1.29 (s, 9H, C(CH3)3) 1.70 – 2.08
(m, 4H, CH2CH3), 6.19 (s, 2H, Si(OH)2), 7.26 (s, 2H, ArH). 13C{1H} NMR (75.57 MHz, DMSO-
d6): δ (ppm) 8.3 (CH2CH3), 31.3 (C(CH3)3), 34.5 (CH2CH3), 71.2 (C(CH3)3), 81.0 (CEt2), 124.8,
142.9 (o, i, C of Ar). 29Si NMR (59.63 MHz, DMSO-d6): δ (ppm) –85.5. EI-MS: m/z (%) 489 (100)
[M – Et]+.
1,4-[(HO)3SiOCEt2]C6H4 (8). 1 (0.35 g, 0.53 mmol) was suspended in cold distilled water (5 mL).
The reaction mixture was vigorously stirred at 0 °C for 10 min. Afterwards, the white powder was
collected via filtration and washed with cold water (2 x 2 mL) in order to remove the remanent
acetic acid. Yield: 0.20 g, 0.50 mmol, 93%. M.p. ˃ 350 °C (dec). Elemental analysis (%) Calcd for
C16H30O8Si2 (406.58 g·mol–1): C 47.27, H 7.44; Found: C 46.90, H 7.30. FT-IR (ATR) (cm–1)
21

1
3128 (s, SiO–H), 2972, 2937 (w, C–H, CH3, CH2), 918 (s, Si–O). H NMR (300.53 MHz, DMSO-
d6): δ (ppm) 0.59 (t, 6H, 3JH–H = 7.3 Hz, CH2CH3), 1.76 – 2.04 (m, 4H, CH2), 6.04 (s, 3H, Si(OH)3),
7.26 (s, 2H, ArH). 13C{1H} NMR (75.57 MHz, DMSO-d6): δ (ppm) 8.4 (CH2CH3), 34.7 (CH2CH3),
80.6 (CEt2), 124.9, 143.0 (o, i, C of Ar). 29Si NMR (59.63 MHz, DMSO-d6): δ (ppm) –79.4. EI-MS:
m/z (%) 377 (6) [M – Et]+.
1,4-[(HO)3SiOCEt2]C2 (9). 2 (0.33 g, 0.54 mmol) was suspended in cold distilled water (1.5 mL).
The reaction mixture was vigorously stirred at 0 °C for 2 min. Afterwards, the white powder was
collected via filtration and washed with cold water (2 x 1 mL) in order to remove the remanent
acetic acid. Yield: 0.14 g, 0.40 mmol, 75%. M.p. ˃ 350 °C (dec). Elemental analysis (%) Calcd for
C12H26O8Si2 (354.50 g·mol–1): C 40.66, H 7.39; Found: C 39.42, H 7.23. FT-IR (ATR) (cm–1)
1
3145 (s, SiO–H), 2972, 2940 (w, C–H, CH3, CH2), 928 (s, Si–O). H NMR (300.53 MHz, DMSO-
d6): δ (ppm) 0.94 (t, 6H, 3JH–H = 7.3 Hz, CH2CH3), 1.59 – 1.74 (m, 4H, CH2), 6.18 (s, 3H, Si(OH)3).
13C{1H} NMR (75.57 MHz, DMSO-d6): δ (ppm) 8.9 (CH2CH3), 34.3 (CH2CH3), 73.3 (C≡C), 85.9
(CEt2). 29Si NMR (59.63 MHz, DMSO-d6): δ (ppm) –78.3. EI-MS: m/z (%) 325 (5) [M – Et]+.
Ph3COSi(OH)3 (10). 4 (0.32 g, 0.69 mmol) was suspended in cold distilled water (10 mL). The
reaction mixture was vigorously stirred at 0 °C for 10 min. Afterwards, the white powder was
collected via filtration and washed with cold water (2 x 2 mL) in order to remove the remanent
acetic acid. Yield: 0.20 g, 0.59 mmol, 85%. M.p. 95 – 97 °C. Elemental analysis (%) Calcd for
C19H18O4Si (338.43 g·mol–1): C 67.43, H 5.36; Found: C 66.39, H 5.12. FT-IR (ATR) (cm–1)
1
3312 (s, SiO–H), 3057 (w, C–H, Ph), 928, 898 (s, Si–O). H NMR (300.53 MHz, DMSO-d6): δ
(ppm) 5.90 (s, 3H, Si(OH)3), 7.18 – 7.32 (m, 15H, CH of Ph). 13C{1H} NMR (75.57 MHz, DMSO-
29
d6): δ (ppm) 84.1 (CPh3), 126.6, 127.3, 128.2, 147.1 (p, m, o, i, C of Ph). Si NMR (59.63 MHz,
DMSO-d6): δ (ppm) –80.9. EI-MS: m/z (%) 338 (1) [M]+.
22

Ph3COSi(OtBu)(OH)3 (11). Hydrolysis route 1: 7 (1.00 g, 2.08 mmol) was suspended in a mixture
of cold distilled water (20 mL) and concentrated ammonia solution (1 mL) and stirred at room
temperature for 15 min. Subsequently, the product was extracted with ethylacetate and isolated after
removing all volatiles. Yield: 0.53 g, 0.13 mmol, 65%. Hydrolysis route 2: 7 (1.00 g, 2.08 mmol)
was suspended in cold distilled water (20 mL) and stirred at room temperature for 15 hours.
Subsequently, the product was isolated as a white powder via filtration. Yield: 0.58 g, 0.14 mmol,
71%. Single crystals of compound 11 were grown: a) from a DMSO solution by slow solvent
evaporation at ambient temperature b) by slow evaporation of wet dichloromethane solution. M.p.
73 – 75 °C. Elemental analysis (%) Calcd for C23H26O4Si (394.54 g·mol–1): C 63.53, H 6.80; Found:
C 61.91, H 6.67. FT-IR (ATR) (cm–1) 3381 (m, SiO–H), 2973 (w, C–H, CH3), 928 (s, Si–O). 1H
NMR (300.53 MHz, DMSO-d6): δ (ppm) 1.03 (s, 9H, C(CH3)3), 6.12 (s, 2H, Si(OH)2), 7.18 – 7.32
(m, 15H, CH of Ph). 13C{1H} NMR (75.57 MHz, DMSO-d6): δ (ppm) 31.1 (C(CH3)3), 71.2
29
(C(CH3)3), 84.4 (OCPh3), 126.6, 127.2, 128.4, 147.0 (p, m, o, i, C of Ph). Si NMR (59.63 MHz,
DMSO-d6): δ (ppm) –87.0. EI-MS: m/z (%) 394 (5) [M]+, 379 (8) [M – Me]+, 337 (100) [M – tBu]+,
317 (80) [M – Ph]+.
O,O’-TADDOL-Si(OH)2 12. 3 (0.31 g, 0.51 mmol) was suspended in cold distilled water (10 mL)
and stirred for 10 min. Then the white solid was filtered off and washed once with 5 mL of water.
Yield: 0.26 g, 0.49 mmol, 96%). M.p. 204 °C (dec). Elemental Analysis (%) Calcd for
C31H30O6Si·0.66(CH2Cl2) (583.25 g·mol–1) C 65.21, H 5.41. Found: C 65.13, H 5.49. FT-IR (ATR)
(cm–1) 3577 (s, SiO–H), 939 (m, Si–O). 1H NMR (300.53 MHz, DMSO-d6): δ (ppm) 0.51 (s, 6H,
13
C(CH3)2), 4.89 (s, 2H, Ph2CCHO), 6.89 (s, 2H, SiOH), 7.22 – 7.51 (m, 20H, CH of Ph). C{1H}
NMR (75.57 MHz, DMSO-d6): δ (ppm) 26.8 (C(CH3)2), 80.9 (Ph2CCHO, CPh2), 112.5 (C(CH3)2),
29
126.6, 126.8, 126.9, 127.1, 127.9, 128.9, 142.5, 147.0 (C of Ph). Si NMR (59.63 MHz, DMSO-
23

d6): δ (ppm) –83.8. EI-MS: m/z (%) 526 (8) [M]+, 468 (3.5) [M – (CH3)2C=O]+.
8·2DABCO. A solution of diazabicyclo[2.2.2]octane (DABCO, 0.11 g, 0.98 mmol) in THF (2 mL)
was added to a solution of 8 (0.20 g, 0.49 mmol) in THF (5 mL) and the mixture was stirred for 15
min. The white precipitate was filtered off. Crystals of 8·2DABCO were grown from a saturated
THF solution at –25 °C. Yield: 0.24 g 0.37 mmol, 76%. M.p. ˃350 °C (dec). Elemental analysis (%)
Calcd for Si2N4O8C28H54 (630.52 g·mol–1) C 53.34, N 8.88, H 8.56; Found: C 52.65, N 8.52, H
8.47. FT-IR (ATR) (cm–1) 2958, 2881 (w, C–H, CH3, CH2), 927 (s, Si–O).
4.3. General procedure for the catalytic cycloaddition of CO2 to styrene oxide.
A 10 mL reaction vial was charged with the racemic mixture of styrene oxide (1 equiv SO, 0.11 g,
0.88 mmol), tetrabutylammonium iodide (0.1 equiv, 0.033 g, 0.088 mmol), and silanol catalyst
which were used as obtained from the synthesis (0.1 equiv, 0.088 mmol). The vial was purged once
with CO2. Afterwards, it was put under a positive pressure with a balloon of CO2, and the reaction
1
mixture was stirred for 15 h at 60 °C. The conversion degree was determined using H NMR
spectroscopy using toluene as internal standard (1 equiv, 0.081 g, 0.88 mmol), and DMSO-d6 as the
deuterated solvent. Silanol catalyst and TBAI were precipitated in diethyl ether; the mixture was
filtered and the volatiles were removed from the filtrate to yield the product. The NMR
1
spectroscopic data for the product SC match those reported in the literature [45]. H NMR (300.53
MHz, DMSO-d6): δ (ppm) 4.42 (apparent t, 1H, JH–H = 8.3 Hz), 4.89 (apparent t, 1H, JH–H = 8.3
13
Hz), 5.86 (apparent t, 1H, JH–H = 8.0 Hz), 7.30 – 7.57 (m, 5H, CH of Ph). C{1H} NMR (75.57
MHz, DMSO-d6): δ (ppm) 70.9, 77.8, 126.7, 128.9, 129.4, 136.3, 154.8.
4.4. X-Ray Crystallography
Single crystals were mounted on a Bruker APEX DUO diffractometer equipped with an Apex II
24

CCD detector at 100 K. Frames were collected using omega scans and integrated with SAINT [51].
Multi-scan absorption correction (SADABS) [51] was applied. The structures were solved by direct
methods (SHELXS) [52] or using intrinsic phasing (SHELXT) [53] and refined using full-matrix
least-squares on F2 with SHELXL [54] using the ShelXle GUI [55]. Weighted R factors, Rw and all
goodness-of-fit indicators, are based on F2. All non-hydrogen atoms were refined anisotropically.
The hydrogen atoms of the C–H bonds were placed in idealized positions, whereas the hydrogen
atoms from the OH moieties in 7, 8·2DABCO, 11·DMSO, 11·H2O and 12 were localized from the
difference electron density map and their position was refined with Uiso tied to the parent atom with
distance restraints (DFIX or SADI). The disordered groups and solvent molecules (4 1 x CH3C(O);
10·THF 1 x THF; 11·DMSO 1 x DMSO; 11·H2O 1 x tBu, 1 x OH; 12 1 x CH2Cl2) were refined
using geometry (SADI, SAME) and Uij restraints (SIMU, RIGU) implemented in SHELXL [54].
The Flack parameter for compound 1 0.487(4) suggests that an inversion center could be present,
but the structure cannot be refined neither in the C2/c or C2/m space group. Thus this unusual value
is caused by the presence of racemic twinning.
The molecular graphics were prepared using GRETEP, POV-RAY and GIMP [56]. CCDC-
1453225, 1453226, 1453228 – 1453236 contain the supplementary crystallographic data for this
paper.
Copies
of
the
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Author contributions
The manuscript was written through contributions of all authors. All authors have given approval to
25

the final version of the manuscript.
Acknowledgement
N. Zavala-Segovia and L. Triana-Cruz are acknowledged for their technical assistance. We thank
also to Dr. Marcos Hernández Rodríguez for a sample of (4R,5R)-TADDOL. This work was
supported by the Dirección General de Asuntos del Personal Académico from the UNAM (PAPIIT
Grant IN205115) and CONACyT (Grants No. 179348 and 252496). M.J.V.-H. and U.H.-B. are
gratefull to CONACyT for their Ph.D. and postdoctoral fellowships, (Grants No. 262860 and 14045,
respectively). A.T.-H. acknowledges DGAPA-UNAM for postdoctoral fellowship.
Supplementary data
CCDC-1453225, 1453226, 1453228 – 1453236 contain the supplementary crystallographic data for
this paper. Copies of the data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
References
[1] V. Chandrasekhar, R. Boomishankar, S. Nagendran, Chem. Rev. 104 (2004) 5847–5910.
[2] R. Pietschnig, S. Spirk, Coord. Chem. Rev. 323 (2016) 87–106.
[3] P. D. Lickiss, In Advances in Inorganic Chemistry; The synthesis and structure of
Organosilanols, Vol. 42, Academic Press inc. (1995), 147–262.
[4] J. Alauzun, A. Mehdi, C. Reyé, R.J.P. Corriu, J. Mater. Chem. 15 (2005) 841–843.
[5] G. Cerveau, S. Chappellet, R.J.P. Corriu, J. Mater. Chem. 13 (2003) 2885–2889.
[6] S. Inagaki, S. Guan, T. Ohsuna, O. Terasaki, Nature 416 (2002) 304–307.
[7] M.P. Kapoor, Q. Yang, S. Inagaki, J. Am. Chem. Soc. 124 (2002) 15176–15177.
26

[8] K. Kuroda, A. Shimojima, K. Kawahara, R. Wakabayashi, Y. Tamura, Y. Asakura, M.
Kitahara, Chem. Mater. 26 (2014) 211–220.
[9] L.D. Carlos, V. de Z. Bermudez, V.S. Amaral, S.C. Nunes, N.J.O. Silva, R.A. Sa Ferreira,
J.C.V. Santilli, D. Ostrovskii, Adv. Mater. 19 (2007) 341–348.
[10] S. Kondo, Y. Bie, M. Yamamura, Org. Lett. 15 (2013) 520–523.
[11] M. Yamamura, S. Kondo, M. Unno, Tetrahedron Lett. 55 (2014) 646–649.
[12] S. Kondo, T. Harada, R. Tanaka, M. Unno, Org. Lett. 8 (2006) 4621–4624.
[13] N. Hurkes, H.M.A. Ehmann, M. List, S. Spirk, M. Bussiek, F. Belaj, R. Pietschnig, Chem.
Eur. J. 20 (2014) 1–7.
[14] M. Blunder, N. Hurkes, S. Spirk, M. List, R. Pietschnig, Bioorg. Med. Chem. Lett. 21 (2011)
363–365.
[15] K. Franz, S.O. Wilson, J. Med. Chem. 56 (2013) 388–405.
[16] J.L.H. Madsen, T.L. Andersen, S. Santamaria, H. Nagase, J.J. Enghild, T. Skrydstrup, J. Med.
Chem. 55 (2012) 7900–7908.
[17] S.M. Sieburth, C.A. Chen, Eur. J. Org. Chem. (2006) 311–322.
[18] S. Singh, S.M. Sieburth, Org. Lett. 14 (2012) 4422–4425.
[19] M. wa Mutahi, T. Nittoli, L. Guo, S.McN. Sieburth, J. Am. Chem. Soc. 124 (2002) 7363–
7375.
[20] D.A. Ruddy, J. Jarupatrakorn, R.M. Rioux, J.T. Miller, M.J. Mcmurdo, J.L. Mcbee, K.A.
Tupper, T.D. Tilley, Chem. Mater. 20 (2008) 6517–6527.
[21] C. Copéret, A. Comas-Vives, M.P. Conley, D.P. Estes, A. Fedorov, V. Mougel, H. Nagae, F.
Núñez-Zarur, P.A. Zhizhko, Chem. Rev. 116 (2016) 323–421.
[22] D. Pinkert, C. Limberg, Chem. Eur. J. 20 (2014) 9166–9175.
27

[23] G. Schafer, J.M. Wieting, T.J. Fisher, A.E. Mattson, Angew. Chem. Int. Ed. 52 (2013) 11321–
11324.
[24] N.T. Tran, S.O. Wilson, A.K. Franz, Org. Lett. 14 (2012) 186–189.
[25] J.M. Wieting, T.J. Fisher, A.G. Schafer, M.D. Visco, J.C. Gallucci, A.E. Mattson, Eur. J. Org.
Chem. (2015) 525–533.
[26] S.O. Wilson, N.T. Tran, A.K. Franz, Organometallics 31 (2012) 6715–6718.
[27] M. Cokoja, M.E. Wilhelm, M.H. Anthofer, W.A. Herrmann, F.E. Kühn, ChemSusChem 8
(2015) 2436–2454.
[28] J. Suzuki, A. Shimojima, Y. Fujimoto, K. Kuroda, Chem. Eur. J. 14 (2008) 973–980.
[29] G. Cerveau, S. Chappellet, R.J.P. Corriu, B. Dabiens, J.L. Bideau, Organometallics 21 (2002)
1560–1564.
[30] G. Cerveau, R.J.P. Corriu, B. Dabiens, J.L. Bideau, Angew. Chem. Int. Ed. 39 (2000) 4533–
4537.
[31] Y. Nakajima, S. Shimada, RSC Adv. 5 (2015) 20603–20616.
[32] B. Arkles, Y. Pan, G.L. Larson, M. Singh, Chem. Eur. J. 20 (2014) 9442–9450.
[33] M. Liu, N.T. Tran, A.K. Franz, J.K. Lee, J. Org. Chem. 76 (2011) 7186–7194.
[34] F.D. Osterholtz, E.R. Pohl, Kinetics and Mechanism of Aqueous Hydrolysis and
Condensation of alkyltrialkoxysilanes. In Molecular characterization of composite interfaces,
Proceedings of the (ACS) Symposium on Polymer Composites: Interfaces, Washington,
March 1983, H. Ishida, G. Kumar, Eds., Plenum Press: New York (1985) 157–170.
[35] C.J. Brinker, G.W. Scherer, Sol-Gel Science The Physics and Chemistry of Sol-Gel
Processing, Academic Press: San Diego (1990).
[36] G. Prabusankar, R. Murugavel, R.J. Butcher, Organometallics 23 (2004) 2305–2314.
28

[37] K. Krekić, N.F. Hurkes, C. Bruhn, F. Belaj, R. Pietschnig, Z. Anorg. Allg. Chem. 642 (2016)
302–305.
[38] L. Wicke, E. Alig, L. Hans-Wolfram, M. Bolte, Acta Crystallogr. E58 (2002) o927–o928.
[39] a) V.E. Shklover, I.L. Dubchak, Yu.T. Struchkov, E.S. Khinku, A.A. Zhdanov, J. Struc.
Chem. 22 (1981) 225–229; b) C. Wendler, H. Reinke, H. Kelling, J. Organomet. Chem. 626
(2001) 53–58; c) R. Rulkens, M.P. Coles, T.D. Tilley, J. Chem. Soc., Dalton Trans. (2000)
627–628; d) S. Spirik, M. Nieger, G. N. Rechberger, R. Pietschnig, Appl. Organomet. Chem.
20 (2006) 683–686.
[40] J. Bernstein, R. E. Davis, L. Shimoni, N. L. Chang, Angew. Chem. Int. Ed. 34 (1995) 1555–
1573.
[41] J. Wang, J. Leong, Y. Zhang, Green Chem. 16 (2014) 4515–4519.
[42] J. Q. Wang, D. L. Kong, J. Y. Chen, F. Cai, L. N. He, J. Mol. Catal. A: Chem. 249 (2006)
143–148.
[43] M. M. Dharman, H. J. Choi. D. W. Kim, D. W. Kim, D. W. Park, Catal. Today 164 (2011)
544–547.
[44] T. Takahashi, T. Watahik, S. Kitazume, H. Yasuda, T. Sakakura, Chem. Commun. (2006)
1664–1666.
[45] M. Hardman-Baldwin, A.E. Mattson,. ChemSusChem 7 (2014) 3275–3278.
[46] a) M.E. Wilhelm, M.H. Anthofer, M. Cokoja, L.I.E.Markovits, W.A. Herrmann, F.E. Kühn,
Chemsuschem 7 (2014) 1357–1360. b) C.J. Whiteoak, A. Nova, F. Maseras, A.W. Kleij,
Chemsuschem 5 (2012) 2032–2038.
[47] J.H. Balthis, E.G. Rochow, D.G. White, In Inorganic Syntheses; J.C. Bailar, Ed.; Silicon
Tetraacetate, Vol. 4, Part. IV; Wiley & Sons: Hoboken, NJ (2007) pp 45–47.
29