From CO2 to polysiloxanes: Di(carbamoyloxy)silanes Me 2Si[(OCO)NRR′]2 as precursors for PDMS

Article abstract of DOI:10.1021/om300313f

Double insertion of carbon dioxide into the Si-N bonds of diaminosilanes of the type Me₂Si(NRR′)₂ gives di(carbamoyloxy)silanes Me₂Si[(OCO)NRR′]₂. The reactions proceed exothermically and quantitatively in most cases. A comprehensive analysis of the CO₂-insertion products including single-crystal X-ray structure analyses was carried out. Quantum chemical calculations indicate an activation energy of about 124 kJ/mol for both the first and the second insertion and support the exothermal nature of the reaction. Investigation of the thermal decomposition of the di(carbamoyloxy)silanes Me₂Si[(OCO)NRR′] ₂ reveals the formation of oligo- and polysiloxanes. Depending on the thermolysis parameters, isocyanates, amines, and/or ureas are formed in addition to the siloxanes. Various methods were applied to study the decomposition process and to identify and quantify the products, including thermal analyses, mass spectrometry, and FTIR and NMR (solution and solid-state) spectroscopy. The overall reaction scheme provides a novel route to polysiloxanes which uses carbon dioxide as an oxygen source.

Full text of DOI:10.1021/om300313f

Article
pubs.acs.org/Organometallics
From CO2 to Polysiloxanes: Di(carbamoyloxy)silanes Me2Si[(OCO)
NRR′]2 as Precursors for PDMS
Konstantin Kraushaar, Conny Wiltzsch,† Jorg Wagler, Uwe Bohme, Anke Schwarzer, Gerhard Roewer,
̈
̈
and Edwin Kroke*
Institute for Inorganic Chemistry, TU Bergakademie Freiberg, Leipziger Straße 29, 09596 Freiberg, Germany
S
* Supporting Information
ABSTRACT: Double insertion of carbon dioxide into the Si−N bonds of diaminosilanes of
the type Me2Si(NRR′)2 gives di(carbamoyloxy)silanes Me2Si[(OCO)NRR′]2. The reactions
proceed exothermically and quantitatively in most cases. A comprehensive analysis of the CO2-
insertion products including single-crystal X-ray structure analyses was carried out. Quantum
chemical calculations indicate an activation energy of about 124 kJ/mol for both the first and
the second insertion and support the exothermal nature of the reaction. Investigation of the
thermal decomposition of the di(carbamoyloxy)silanes Me2Si[(OCO)NRR′]2 reveals the
formation of oligo- and polysiloxanes. Depending on the thermolysis parameters, isocyanates,
amines, and/or ureas are formed in addition to the siloxanes. Various methods were applied to study the decomposition process
and to identify and quantify the products, including thermal analyses, mass spectrometry, and FTIR and NMR (solution and
solid-state) spectroscopy. The overall reaction scheme provides a novel route to polysiloxanes which uses carbon dioxide as an
oxygen source.
Here, we present a novel route to polysiloxanes based on the
insertion of two CO2 molecules into the Si−N bonds of
diaminosilanes.13,14 The reactions take place at room temper-
ature and without any catalysts to give the di(carbamoyloxy)-
silanes Me2Si[(OCO)NRR′]2 in good yields or even
quantitatively. This double insertion of CO2 in diaminosilanes
followed by thermolysis to generate oligosilanes, together with
amines, isocyanates, and ureas, has not been studied so far.
INTRODUCTION
■
Oligo- and polysiloxanes are among the most important classes
of polymers with a wide range of applications, e.g., as heat-
resistant oils, electric insulators, or chemically resistant
elastomers.1 Currently, polysiloxanes are synthesized by
polycondensation of silanols obtained from chlorosilanes in
the presence of water or methanol (Scheme 1, route A). During
the polycondensation process hazardous hydrogen chloride or
chloromethane is evolved.1 For the synthesis of medical-grade
polysiloxanes, this problem can be circumvented by utilizing the
acetate group instead of chlorine in the starting silanes, thus
liberating acetic acid.2
The new alternative synthesis of polysiloxanes reported in
this study (Scheme 1, route B) is based on insertion of CO2 in
diaminosilanes to form di(carbamoyloxy)silanes3 followed by
thermolysis. The preparation of mono(carbamoyloxy)silanes
has been described, for example, by Sheludyakov et al. via
reactions of hexamethyldisilazane and amines or their salts in
the presence of carbon dioxide.4 Mironov et al. reported a
transamination with primary or secondary amines,5 while
Birkofer and Sommer used chlorosilanes in the presence of
silver carbamate or ammonium carbamate.6 Knausz et al.
prepared mono(carbamoyloxy)silanes by silylation of ammo-
nium carbamate with trimethylchlorosilane and investigated
their reactions with anhydrides.7 Breederveld,8 Mironov, and
other authors9−11 described the addition of carbon dioxide to
silylated alkylamines.
RESULTS AND DISCUSSION
■
Diaminosilane Synthesis. Diaminosilanes Me2Si(NRR′)2
are typically prepared from the corresponding chlorosilanes via
reactions with the corresponding amines, metal amides, or
silazanes.15 An alternative route that avoids the synthesis of
chlorosilanes via the Muller−Rochow process followed by
̈
substitution of the chlorine atoms with amines and the
separation of ammonium salts is a “direct synthesis” of
aminosilanes from silicon and amines (see Scheme 1).16
Similar direct routes are known for alkoxysilanes using silicon
and alcohols.17 The aminosilanes 2a−f were prepared using
methods described in the literature.18,19 Addition of the
respective amine to Me2SiCl2 in n-pentane at 20 °C affords
the aminosilanes in good yields as colorless liquids. The herein
reported dimethyldiaminosilanes reveal typical signals in the
29Si NMR spectra in the shift range of −5.6 to −9.5 ppm (see
Table 1).
CO2 Double Insertion. Most reports on carbamoylox-
ysilanes describe the insertion of one CO2 molecule into the
Si−N bond of a monoaminosilane. Few authors report on the
Recently Fuchter et al. used supercritical CO2 for the
synthesis of several di(carbamoyloxy)silanes and the decom-
position to different substituted ureas.12 Up to now, the
application of the di(carbamoyloxy)silanes is focused on the
organic synthesis of amides7 or ureas.12
Received: April 24, 2012
Published: June 26, 2012
© 2012 American Chemical Society
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Scheme 1. Route A and New CO2-Based Anhydrous Route B to Polysiloxanes
Table 1. 29Si NMR Chemical Shifts of Aminosilanes 2a−f
and Carbamoyloxysilanes 3a−f in Solution and in the Solid
State
di(carbamoyloxy)silanes 3a,c,d, the intermolecular interactions
obviously influence significantly the magnetic environment of
the silicon atoms (see Table 1).
c
aminosilane
δ/ppm
carbamoyloxysilane
δ/ppm
δ/ppm
a
a
2a
2b
2c
2d
2e
2f
−7.9
−7.9
−9.3
−9.4
−5.6
−9.5
b
3a
3b
3c
3d
3e
3.4
10.6
a
a
2.5
a
a
3.2
12.1
11.9
a
a
3.2
a
b
2.9
a
a
3f
2.0
a
c
Solvent: CDCl3. Solvent: C6D6/CDCl3. Solid-state 29Si CP/MAS.
insertion of two CO2 molecules per aminosilane.11,20 In many
cases the CO2 insertion into the Si−N bond is reversible,
resulting in equilibria. Contrarily, we found that the amino-
silanes Me2Si(NHR)2 with R = R′ = n-propyl, R = n-propyl, and
R′ = cyclohexyl and Me2Si(NEt2)2 insert two equivalents of
CO2 quantitatively. High yields in the range between 78% and
95% were obtained for R = R′ = ethyl, n-octyl, and n-dodecyl.
The resulting di(carbamoyloxy)silanes are transformed to
oligo-/polysiloxanes and urea derivatives at >130 °C.
Insertion of carbon dioxide to generate 3a−f is performed
using gaseous, dried CO2 bubbling into a solution of the
aminosilane in dry THF at room temperature. This exothermic
reaction requires cooling if a large batch of a di(carbamoyloxy)-
silane is intended to be prepared. Cleaning of the white
products 2a−f is not necessary.
Figure 1. Comparison of 29Si CP/MAS NMR (above) and solution
29Si NMR spectrum (in CDCl3) of 3a showing the difference in 29Si
chemical shift due to hydrogen bonds.
While the crystal structure of 3a shows half a molecule in the
asymmetric unit, 3b occurs with two half-molecules, which
show notable differences in the orientation of the n-propyl
moiety (Figure 2). All bond lengths and angles are within the
range of expected values. In both compounds the crystal
packing is dominated by the N−H···O interactions, giving rise
to N···O distances in the range of 2.8 and 2.9 Å (see Table 2).
These interactions enforce the formation of the molecular
strands as presented in Figure 3 for the ethyl derivative 3a and
influence the adjacent atoms (O−Si), resulting in weaker
shielding of the silicon atom in the solid-state NMR.
Table 1 shows the characteristic 29Si NMR shifts for the
di(carbamoyloxy)silanes 3a−f in the range of 2.0 to 3.4 ppm.
Surprisingly, low-field shifts of almost 9 ppm are observed for
the solid-state NMR spectra as compared to the solution
spectra. To rationalize these differences, we analyzed the
molecular structure of suitable single crystals of 3a and 3b via
X-ray crystallography.21 Strong hydrogen bonds of the N−
H···O type interconnect the molecules to molecular strands
(see below). These hydrogen bonds can influence the
molecular geometry significantly, resulting in the difference of
NMR chemical shifts. Probably the best known example in the
literature is acetyl acetone, where also large differences in the
solution and solid-state spectra are found.22 In the case of the
In addition, the hydrogen bonds can be detected in the solid-
state IR spectra. For instance, the shift of the N−H vibrations
from 3423 in 2c to 3360 cm−1 in 3c and an extra band at 3332
cm−1 for the O···H vibration indicate the N−H···O interaction.
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Figure 3. Crystal packing of 3a showing the role of the intermolecular
N−H···O hydrogen bonding N1−H1···O2 [d = 2.11(2) Å, D =
2.9144(18) Å, ϑ = 172(2)°] in forming molecular strands. Non-
relevant hydrogen atoms are omitted for clarity.
Figure 2. Molecular structure of (a) 3a and (b) 3b. 3a shows a
symmetry-related disorder of the methyl hydrogen atoms, which was
omitted for clarity. Thermal ellipsoids are drawn at the 50% probability
level including the used numbering scheme.
Table 2. Intermolecular Hydrogen Bonds in the Crystal
Structures of Compounds 3a and 3b and Urea Derivative 4b
Figure 4. TG (solid) and DTA (dashed) curves of 3a (2.41 mg)
recorded at a heating rate of 5 °C·min−1 under argon.
atoms involved
distance/Å
D···A
angle/deg
D−H···A
H···A
D−H···A
3a
for this second insertion is 123.1 kJ/mol (from II to TSII), and
it is also exothermic, albeit with only −16.7 kJ/mol. These
results correspond well with the experimental data, since (1) we
always isolated the double insertion products and (2)
exothermic reaction occurred for all the investigated amino-
silanes.
a
N1−H1···O2
2.11
2.9144
172
3b
b
N1−H1···O2
2.14
2.19
2.8844
2.9285
171
172
c
N2−H2···O4
4b
d
N1−H1N···O1
N2−H2N···O1
2.15
2.8961
155
154
Siloxane Formation. The thermal transformation of the
di(carbamoyloxy)silanes Me2Si[(OCO)NRR′]2 (3) was care-
fully analyzed. Figure 4 shows the results of a thermogravi-
metric/differential thermal analysis (TG/DTA) of 3a. The
diagram reveals three steps: an initial mass loss of 14.8% at ≤30
°C, a distinct second step at 145 °C with a mass loss of 17.6%
giving rise to a sharp endothermal DTA signal, followed by the
third step at 165 °C with a mass loss of 50.3%; afterward the
mass remains constant until 400 °C. Further thermal analyses
were performed using TG-MS and TG-FTIR. These studies
clearly indicate that the second step is due to the formation of
CO2. This corresponds very well with a calculated mass loss of
18.8% for one equivalent of CO2 per mole of di-
(carbamoyloxy)silanes 3a. The mass loss of the first step
varied from experiment to experiment. TG-MS and TG-FTIR
indicate the formation of CO2 and the corresponding amine
RNH2. These observations are interpreted in a way that partial
hydrolysis of the di(carbamoyloxy)silanes occurs according to
the reaction Me2Si[(OCO)NHR]2 + H2O → Me2Si[(OCO)-
NHR](OH) + RNH2 + CO2. A brief contact with air cannot be
avoided during sample preparation for TG analysis, which
2.05
b
2.8493
a
c
d
Symmetry codes: x, y, z+1. x, −1+y, z. x, 1+y, z. x, −1+y, z.
Similar shifts of the band are observed for the other compounds
3a, b, and 3d−f. Moreover, the IR spectroscopic study shows
the expected signals for the di(carbamoyloxy)silanes, e.g., for 3a
at about 1400 cm−1 representing the asymmetric SiCH3
deformation vibration and at 1038 cm−1 representing the
asymmetric Si−O−C stretch vibration.
To gain further insight into the reaction mechanism of the
carbon dioxide insertion (reaction 2 → 3 in Scheme 1), we
performed density functional calculations with a simple model
aminosilane (see Figure 5).23 Energy differences are given as
Gibbs free energies (at 298.15 K, 1 atm) in kJ/mol. Starting
from dimethyldi(methylamino)silane, Me2Si(NHMe)2 (I), the
insertion of one molecule of CO2 requires an activation energy
(from I to TSI) of 124.4 kJ/mol (see Figure 5). The first
insertion step is exothermic by −24.7 kJ/mol. The second
molecule of CO2 inserts into the remaining Si−N bond of II
under similar energetic conditions; that is, the activation energy
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Figure 5. Calculated potential energy profile for the carbon dioxide insertion (Gibbs free energy at 298.15 K, 1 atm).
causes this partial hydrolysis. The third mass loss step of 50.3%
(see Figure 4) is caused by formation of N,N′-diethylurea (4a),
as indicated by the MS and FTIR data. Signals for the
isocyanate and the amine are also detected. The mass loss
corresponds well with the calculated value of 49.6%.
To get a deeper insight in the decomposition reaction of the
carbamoyloxysilanes 3a−f, especially the resulting products, we
heated a sample of 3b to different temperatures for 15 min and
recorded 13C NMR spectra. Figure 6 shows the shift of the
silicones with hydroxyl functionalization on both ends with 10
to 30 D units.
Further attempts to understand the transformation process
of the di(carbamoyloxy)silanes 3a−f generating siloxanes and
N,N′-disubstituted ureas were performed in Schlenk flasks
followed by 1H, 13C, and 29Si NMR analysis of the volatiles and
the residues.
These thermal decomposition experiments were performed
as follows. A flask was equipped with a sublimation finger and a
cold trap (cooled with liquid nitrogen) and evacuated to a
pressure of 0.2 Torr to ensure the evaporation of the volatile
products. First, compounds 3 were heated to 70 °C, and this
temperature level was maintained for an hour. Then the
Schlenk flask was heated to 120 °C, then also kept for one
hour. Afterward, the temperature was increased stepwise over
several hours. In the first period (70 °C), the starting material
3d formed a white compound on the sublimation finger. This
compound was determined to be n-dodecylamine 1d, giving the
typical 13C and 1H NMR signals. Increasing the temperature to
120 °C afforded the urea derivative 4d and the corresponding
1-isocyanatododecane also on the sublimation finger. For the
decomposition of 3b and 3c, the formation of the isocyanates
and urea was observed, while the amines, probably due to the
low boiling points, could not be detected. As depicted in Figure
7, in the cooling trap the volatile cyclosiloxanes D3, D4, and D5
Figure 6. 13C NMR spectra of samples of the di(carbamoyloxy)silane
3b, heated to different temperatures for 15 min.
carbonyl moieties, indicating the formation of the urea 4b at
135 °C and decomposition of the carbamate 3b. The spectrum
of the sample heated to 135 °C shows an additional signal at
154.3 ppm, which may be assigned to the monoinsertion
product Me2Si[(OCO)NHR′]NHR′ or a related intermediate
(see below). Single crystals of 4b were obtained via sublimation
during the heating process. The urea 4b was found to crystallize
in the space group C2/c with one molecule in the asymmetric
unit showing bond lengths and angles within the expected
range.22 The crystal packing is dominated by molecular strands
formed along the b-axis and connected via a bifurcated
hydrogen bridge (see Table 2).
Mass spectral analysis of the residues formed after pyrolysis
at 200 °C was performed with MALDI-TOF (see Supporting
Information). The results clearly indicate the formation of
cyclic oligosiloxanes D13 to D18, as well as traces of linear
Figure 7. 29Si NMR spectra (in CDCl3) of the cyclosiloxanes D3, D4,
and D5 (5) evaporated upon heating di(carbamoyloxy)silane 3d.
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were detected. After several hours at a temperature greater than
120 °C nonvolatile polydimethylsiloxanes (PDMS) were
formed on the bottom of the Schlenk flask. The yield of
PDMS in relation to the starting materials 3a−f was
approximately 70%, and only small amounts of volatile
cyclosiloxanes were formed.
and the primary amine RNH2, followed by urea and
polysiloxane (PDMS) formation, is proposed.
The overall process represents a novel route to two useful
products (polysiloxanes and ureas) and a contribution to use
CO2 as a starting material for chemical syntheses. Our current
investigations are focused on the extension of the discussed
results on tri- and tetraaminosilanes to form the corresponding
(carbamoyloxy)silanes. Thermolysis of these precursors might
give silsequioxanes and silica materials, while mixtures of
(functionalized) mono-, di-, tri-, and/or tetra(carbamoyloxy)-
silanes should give functionalized PDMS derivatives and allow
adjusting the degree of cross-linking and the properties of the
respective products.
On the basis of the thermal analysis results a reaction path
described in Scheme 2 can be proposed. First, one equivalent of
Scheme 2. Suggested Reaction Path Based on the Presented
Results
EXPERIMENTAL SECTION
■
General Methods and Instrumentation. All syntheses and
manipulations were performed in Schlenk-type glassware or in a
glovebox (MBraun, Germany, O2 < 0.1 ppm, H2O < 0.1 ppm). All
solvents were purified and dried according to general procedures.
Commercially available chemicals were used in p.a. quality as obtained
from the suppliers. IR spectra were recorded in the range 400−4000
cm−1 at room temperature using a Nicolet 380 FT-IR spectrometer.
The samples (KBr pellets) were prepared under N2 atmosphere using
dry KBr powder. Standard 1H, 13C, and 29Si NMR spectra were
recorded on an AVANCE DPX 400 spectrometer at 293 K. Chemical
shifts are reported relative to tetramethylsilane (1H, 13C, 29Si NMR).
29Si CP/MAS NMR (79.51 MHz) spectra were recorded on a Bruker
Avance 400 MHz WB spectrometer using zirconia rotors with a 7 mm
probe head. The thermogravimetry measurements were performed
using TG/DTA (Seiko Instruments) with a heating rate of 5 K/min
under flowing argon (300 ml/min). Elemental analyses were
performed with a Heraeus CHN Rapid analyzer. Mass spectra were
obtained using a Hewlett-Packard GC-MS 5890 and a Shimadzu
Biotech Axima Performance.
General Procedure A (2a−f). The respective amine 1a−f was added
dropwise to a solution of 20 g (0.15 mol) of dichlorodimethylsilane in
300 mL of n-hexane, cooling with a water bath. Stirring at 20 °C for
one day gave the respective solid amine hydrochloride as a precipitate.
Separation of the hydrochloride, removing of the solvent under
reduced pressure, and distillation of the raw product yielded the
aminodimethylsilanes as colorless liquids.
General Procedure B (3a−f). To a solution of the respective
diaminodimethylsilane (2a−f) (2 g) in 50 mL of THF was added
gaseous CO2 (dried over sulfuric acid) via a gas inlet. The exothermic
reaction took place at room temperature. CAUTION: Larger amounts
require cooling of the solution! Removing the solvent at reduced pressure
yielded the (carbamoyloxy)silanes; further cleaning was not necessary.
Synthesis of Aminodimethylsilanes 2a−f. Preparation of
Bis(ethylamino)dimethylsilane, Me2Si(NHCH2CH3)2 (2a). General
procedure A using 5 g (38.74 mmol) of dichlorodimethylsilane and
ethylamine 1a (7 g, 0.15 mol) gave 2a (2.97 g, 74%) as a colorless
liquid: bp 139.7 °C (lit.24 139 °C). 29Si NMR (79 MHz, CDCl3): δ
−9.5 ppm. 13C NMR (100 MHz, CDCl3): δ 35.9 (NHCH2CH3), 20.6
(CH3), −1.3 (SiCH3) ppm. 1H NMR (400 MHz, CDCl3): δ 3.22 (4H,
CH2, quint, 3JH−H = 12.0, 8.0 Hz), 1.48 (6H, CH3, t, 3JH−H = 8.0 Hz),
0.92 (2H, NH, s), 0.42 (6H, SiCH3, s) ppm. IR (KBr): 3417 (vw, ν
NH); 2959, 2924, 2853 (m, ν CH); 1400 (m, δas SiCH3); 1250 (str,
δsym SiCH3) cm−1. Anal. Calcd for C6H18N2Si (146.31): C 49.26, H
12.40, N 19.15. Found: C 48.61, H 11.78, N 17.77.
CO2 is formed, yielding the monoinsertion product Me2Si-
[(OCO)NHR](NHR). An intra- or intermolecular H+-shift is
proposed to initiate the amine and isocyanate formation.
Concurrently, cyclic and linear dimethylpolysiloxanes are
generated. The N,N′-dialkylurea may be formed from the
amine and the isocyanate or directly from the intermediate.
CONCLUSION
■
Carbamoyloxysilanes are molecular precursors for the synthesis
of oligo- and polysiloxanes. The di(carbamoyloxy)silanes
Me2Si[(OCO)NRR′]2 are obtained via an exothermic double
insertion of CO2 into the Si−N bonds of diaminosilanes
Me2Si(NRR′)2. This is a quantitative reaction, and further
cleaning of the products is not necessary. Thermal decom-
position of the di(carbamoyloxy)silanes at >120 °C yields cyclic
and linear siloxanes. In addition, isocyanates and amines are
formed, which react with each other, giving the corresponding
N,N′-disubstituted ureas.
Di(carbamoyloxy)silanes are compounds with strong hydro-
gen bonds in solution and in the solid state. The crystal
structure of di(carbamoyloxy)silanes show these short N−
H···O contacts. The large high-field shift of ∼9 ppm of the 29Si
NMR resonance signals in solution compared to the 29Si-CP/
MAS NMR data is also attributed to loss of the strong
hydrogen-bonding interactions.
DFT calculations at B3LYP/6-31G(d) show a feasible
mechanism for the CO2 insertion process into the silicon
nitrogen bond of the aminosilanes under investigation. The
insertion steps proceed with moderate activation energies
around 124 kJ/mol (Gibbs free energy) and are slightly
exothermic (∼16−25 kJ/mol).
Preparation of Bis(n-propylamino)dimethylsilane, Me2Si-
(NHCH2CH2CH3)2 (2b). General procedure A using 20 g (0.15 mol)
of dichlorodimethylsilane and n-propylamine 1b (42 g, 0.7 mol) gave
2b (23.2 g, 89%) as a colorless liquid: bp 188 °C (lit.25 92−93 °C at
45 Torr). 29Si NMR (79 MHz, CDCl3): δ −7.9 ppm. 13C NMR (100
MHz, CDCl3): δ 43.4 (NHCH2CH2CH3), 27.9 (NHCH2CH2CH3),
The pathway of the thermally induced decomposition of the
di(carbamoyloxy)silanes appears to be relatively complex. A
mechanism based on CO2 formation, followed by a H+-shift,
and the elimination of the corresponding isocyanate RNCO
1
11.4 (CH3), −1.42 (SiCH3) ppm. H NMR (400 MHz, CDCl3): δ
3
2.53 (4H, NHCH2CH2CH3, t, JH−H = 8 Hz), 1.24 (4H,
3
NHCH2CH2CH3, m), 0.72 (6H, CH3, t, JH−H = 8 Hz), 0.44 (2H,
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NH, s), −0.15 (6H, SiCH3, s) ppm. IR (KBr): 3417 (m, ν NH); 2960,
2871, 2852 (str, ν CH); 1250 (str, δ SiCH3) cm−1. Anal. Calcd for
C8H22N2Si (174.36): C 55.1, H 12.7, N 16.1. Found: C 54.5, H 12.7,
N 17.1.
(CDCl3): δ 2.5 ppm. 13C NMR (CDCl3): δ 154.4 (CO), 43.3
(NCH2CH2CH3), 23.7 (NHCH2CH2CH3), 11.4 (CH3), −0.9
1
(SiCH3) ppm. H NMR (CDCl3): δ 5.47 (2H, NH, s), 3.10 (4H,
3
NCH2CH2CH3, t, JH−H = 8 Hz), 1.52 (4H, NHCH2CH2CH3, m),
0.92 (6H, CH3, t, 3JH−H = 8 Hz), 0.49 (6H, SiCH3, s) ppm. IR (KBr):
3344 (m, ν NH); 2964 (m, ν CH); 1670 (str, ν CO); 1259 (str, ν
SiCH3) cm−1. Anal. Calcd for C10H22N2O4Si (262.38): C 45.8, H 8.5,
N 10.7. Found: C 44.1, H 8.6, N 9.7.
Preparation of Bis(n-octylamino)dimethylsilane, Me2Si(NH-
(C2−8H2)7C1H3)2 (2c). General procedure A using 5.14 g (39.83
mmol) of dichlorodimethylsilane and n-octylamine 1c (20.83 g, 0.15
mol) gave 2c (12.45 g, quantitative) as a colorless, oily liquid: bp 270.3
°C. 29Si NMR (79 MHz, CDCl3): δ −9.3 ppm. 13C NMR (100 MHz,
CDCl3): δ 41.4 (C-8); 34.9 (C-3); 32.0 (C-7); 29.6 − 27.1 (C-4−C-
6); 22.8 (C-2); 14.1 (C-1); −0.9 (SiCH3) ppm. 1H NMR (400 MHz,
CDCl3): δ 2.85 (4H, H-8, q, 3JH−H = 16.0, 8.0 Hz); 1.52 (4H, H-7, m);
Preparation of Dimethylbis(n-octylcarbamoyloxy)silane, Me2Si-
[O(CO)NH(C2−8H2)7C1H3]2 (3c). General procedure B using 2c (6.19 g,
19.7 mmol) gave 7.45 g (95.1%) of 3c as a colorless solid: mp 84.1 °C.
29Si NMR (CDCl3): δ 3.2 ppm. 29Si NMR (CP/MAS): δiso 12.1 ppm.
13C NMR (CDCl3): δ 154.0 (CO), 41.9 (C-8), 31.8 (C-3), 29.8 (C-
3
1.42 (20H, H-2−H-6, m); 1.03 (6H, H-1, t, JH−H = 8.0 Hz); 0.69
(2H, N−H, m); 0.15 (6H, SiCH3,s) ppm. IR (KBr): 3423, 3317 (m, ν
NH); 2956, 2926, 2853 (str, ν CH); 1398 (m, δas SiCH3); 1259 (str,
δsym SiCH3) cm−1. Anal. Calcd for C18H42N2Si (314.62): C 68.71, H
13.46, N 8.90. Found: C 68.57, H 13.03, N 8.79.
7), 29.5 (C-4), 29.2 (C-5), 26.8 (C-6), 22.7 (C-2), 14.1 (C-1), −1.2
1
(C-9) ppm. H NMR (CDCl3): δ 5.15 (2H, NH, m), 3.29 (4H, H-8,
q, 3JH−H = 12.0, 8.0 Hz), 1.63 (4H, H-7, m), 1.43 (20H, H-2−H-6, m),
3
1.03 (6H, H-1, t, JH−H = 8 Hz), 0.15 (6H, H-9, s) ppm. IR (KBr):
Preparation of Bis(n-dodecylamino)dimethylsilane, Me2Si(NH-
(C2−12H2)11C1H3)2 (2d). General procedure A using 5 g (38.74 mmol)
of dichlorodimethylsilane and n-dodecylamine 1d (28.72 g, 0.15 mol)
gave 2d (16.46 g, quantitative) as a colorless, oily liquid: bp >300 °C.
29Si NMR (79 MHz, CDCl3): δ −9.4 ppm. 13C NMR (100 MHz,
3333 (m, ν NH); 2954, 2922, 2871 (str, ν CH); 1655 (str, ν CO);
1467 (m, δ CH); 1432 (str, δas SiCH3); 1260 (w, δs SiCH3); 1033 (m,
ν SiOC) cm−1. Anal. Calcd for C20H42N2O4Si (402.64): C 59.66, H
10.51, N 6.96. Found: C 60.66, H 11.19, N 7.72.
Preparation of Dimethylbis(n-dodecylcarbamoyloxy)silane,
Me2Si[O(CO)NH(C2−12H2)11C1H3)2 (3d). General procedure B using
2d (5.0 g, 12.0 mmol) gave 5.54 g (90.0%) 3d as a colorless solid: mp
89.9 °C. 29Si NMR (CDCl3): δ 3.2 ppm. 29Si NMR (CP/MAS): δiso
11.9 ppm. 13C NMR (CDCl3): δ 154.0 (CO), 42.3 (C-12), 33.9 (C-
3), 31.9 (C-11), 29.8−29.1 (C-4−C-9), 26.8 (C-10), 22.7 (C-2), 14.1
CDCl3): δ 41.4 (C-12); 35.3 (C-3); 32.3 (C-11); 30.1−29.8 (C-4−C-
9); 27.3 (C-10); 23.0 (C-2); 14.3 (C-1); −1.2 (SiCH3) ppm. 1H NMR
(400 MHz, CDCl3): δ 2.98 (4H, H-12, m); 1.60 (4H, H-11, m); 1.55
3
(36H, H-2−H-10, m); 1.16 (6H, H-1, t, JH−H = 8.0 Hz); 0.72 (2H,
N−H, m); 0.22 (6H, SiCH3, s) ppm. IR (KBr): cm−1 3330 (m, ν
NH); 2954, 2920, 2851 (str, ν CH); 1382 (m, δas SiCH3); 1258 (str,
δsym SiCH3). Anal. Calcd for C26H58N2Si (426.84): C 73.16, H 13.70,
N 6.56. Found: C 73.10, H 13.58, N 6.48%.
1
(C-1), −1.2 (C-13) ppm. H NMR (CDCl3): δ 4.96 (2H, NH, m),
3
3.14 (4H, H-12, q, JH−H = 12.0, 8.0 Hz), 1.48 (4H, H-11, m), 1.26
3
(36H, H-2−H-10, m), 0.88 (6H, H-1, t, JH−H = 8 Hz), 0.50 (6H, H-
13, s) ppm. IR (KBr): 3359, 3331 (m, ν NH); 2956, 2919, 2851 (str, ν
CH); 1667 (str, ν CO); 1470 (m, δ CH); 1389 (str, δas SiCH3); 1260
(w, δs SiCH3); 1048 (m, ν SiOC) cm−1. Anal. Calcd for C28H58N2O4Si
(514.86): C 65.32, H 11.35, N 5.44. Found: C 65.42, H 11.56, N 5.78.
Preparation of Dimethylbis(diethylcarbamoyloxy)silane, Me2Si-
[O(CO)N(CH2CH3)2]2 (3e). General procedure B using 2e (2 g, 9.9
mmol) gave 2.86 g (100%) of 3e as a yellowish liquid. 29Si NMR
(C6D6): δ 2.9 ppm. 13C NMR (C6D6): δ 153.3 (CO), 41.8
Preparation of Bis(diethylamino)dimethylsilane, Me2Si[N-
(CH2CH3)2]2 (2e). General procedure A using 20 g (0.15 mol) of
dichlorodimethylsilane and diethylamine 1e (47.5 g, 0.65 mol) gave 2e
(25.9 g, 85%) as a colorless liquid. 29Si NMR (79 MHz, CDCl3/
C6D6): δ −5.6 ppm. 13C NMR (100 MHz, CDCl3/C6D6): δ 39.2
1
(N(CH2CH3)2), 15.6 (N(CH2CH3)2), −1.2 (SiCH3) ppm. H NMR
(400 MHz, CDCl3/C6D6): δ 3.59 (8H, N(CH2CH3)2, m), 1.52 (12H,
N(CH2CH3)2, m), 0.01 (6H, SiCH3, s) ppm.
1
(N(CH2CH3)2), 13.4 (CH3), −0.01 (SiCH3) ppm. H NMR (C6D6):
Preparation of Cyclohexylamino-n-propylaminodimethylsilane,
Me2Si[NH(C1HC2H2C3H2C4H2C3H2C2H2)][NH(CH2CH2CH3)] (2f). A 9.5
g (0.16 mol) of n-propylamine 1b and 15.9 g (0.16 mol) of
cyclohexylamine 1f were added at once to a solution of 10 g (0.08
mol) of dichlorodimethylsilane in n-hexane (200 mL). Stirring for one
day at 20 °C led to the solid hydrochlorides, which were filtered off.
After removing the solvent in vacuum a mixture resulted of 2b,
bis(cyclohexylamino)dimethylsilane, and cyclohexylamino-n-propyla-
minodimethylsilane, 2f (5:1:4). Distillation of the raw product yielded
2f as a colorless liquid: bp 90 °C 4.7 Torr. 29Si NMR (79 MHz,
CDCl3): δ −9.5 ppm. 13C NMR (100 MHz, CDCl3): δ 49.9 (C-1),
43.3 (NHCH2CH2CH3), 38.8 (C-2), 27.7 (NHCH2CH2CH3), 25.8,
25.7 (C-3, C-4), 11.4 (CH3), −0.9 (SiCH3) ppm. 1H NMR (400
MHz, CDCl3): δ 2.6 (3H, NHCH2CH2CH3, H1, m), 1.7−0.7 (12H,
NHCH2CH2CH3, H2, H3, H4, m), 0.74 (3H, CH3, m), 0.4 (2H, NH,
br), −0.1 (6H, SiCH3, s) ppm. Anal. Calcd for C11H26N2Si (214.42):
C 61.62, H 12.22, N 13.06. Found: C 58.74, H 12.11, N 11.27.
Synthesis of Di(carbamoyloxy)silanes 3a−f. Preparation of
Dimethyl-di(ethylcarbamoyloxy)silane, Me2Si[O(CO)NHCH2CH3]2
(3a). General procedure B using 2a (2.82 g, 27.6 mmol) gave 4.15 g
(78.5%) of 3a as a colorless solid: mp 119.1 °C. 29Si NMR (CDCl3): δ
3.4 ppm. 29Si NMR (CP/MAS): δiso 10.6 ppm. 13C NMR (CDCl3): δ
153.8 (CO), 36.8 (NCH2CH3), 15.0 (CH3), −1.2 (SiCH3) ppm. 1H
NMR (CDCl3): δ 4.96 (2H, NH, s), 3.19 (4H, NCH2CH2CH3, quint,
δ 3.47 (4H, N(CH2CH3)2, t, 3JH−H = 7 Hz), 3.05 (4H, N(CH2CH3)2,
3
3
t, JH−H = 7 Hz), 1.98 (6H, CH3, t, JH−H = 7 Hz), 1.32 (6H, CH3, t,
3JH−H = 7 Hz), 0.01 (6H, SiCH3, s) ppm. Anal. Calcd for
C12H26N2O4Si (290.43): C 49.63, H 9.02, N 9.65. Found: C 49.8.,
H 9.3, N 9.5.
Preparation of Dimethyl(cyclohexylcarbamoyloxy)(n-
p r o p y l c a r b a m o y l o x y ) s i l a n e , M e 2 S i [ O ( C O ) N H -
(C1HC2H2C3H2C4H2C3H2C2H2)][O(CO)(CH2CH2CH3)] (3f). General pro-
cedure B using 2f (2 g, 9.3 mmol) gave 2.82 g (100%) of 3f as a
colorless solid. 29Si NMR (C6D6): δ 2.0 ppm. 13C NMR (C6D6): δ
154.4, 153.6 (CO), 50.4 (C1), 43.3 (NHCH2CH2CH3), 33.6 (C2),
26.2, 25.6, 23.6, (NHCH2CH2CH3, C3, C4), 11.3 (CH3), −1.2
(SiCH3) ppm. 1H NMR (400 MHz, C6D6): δ 6.6, 6.7 (2H, NH), 3.7−
3.3 (3H, NHCH2CH2CH3, H1, m), 1.9−1.4 (12H, NHCH2CH2CH3,
H2, H3, H4, m), 1.40 (3H, CH3, m), 0.68 (6H, SiCH3, s) ppm. Anal.
Calcd for C13H26N2O4Si (302.44): C 51.63, H 8.66, N 9.26. Found: C
50.87, H 8.61, N 9.08.
Thermal Decomposition of the Di(carbamoyloxy)silanes 3a−d.
The analysis data are included in the Supporting Information.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details and additional data (MALDI-TOF MS,
quantum chemical calculations) including cif files for 3a, 3b,
and 4b. This material is available free of charge via the Internet
at http://pubs.acs.org.
3
3JH−H = 12.0, 8.0 Hz), 1.14 (6H, CH3, t, JH−H = 8 Hz), 0.50 (6H,
SiCH3, s) ppm. IR (KBr): 3429 (m, ν NH); 2961, 2931, 2872 (str, ν
CH); 1736 (str, ν CO); 1466 (m, δ CH); 1400 (str, δas SiCH3); 1270
(w, δs SiCH3); 1083 (m, ν SiOC) cm−1. Anal. Calcd for C8H18N2O4Si
(234.33): C 41.01, H 7.74, N 11.95. Found: C 39.63, H 7.53, N 11.13.
Preparation of Dimethylbis(n-propylcarbamoyloxy)silane, Me2Si-
[O(CO)NHCH2CH2CH3]2 (3b). General procedure B using 2b (2 g, 11.5
mmol) gave 2.99 g (100%) of 3b as a colorless solid. 29Si NMR
AUTHOR INFORMATION
Corresponding Author
*E-mail: Edwin.Kroke@chemie.tu-freiberg.de.
■
4784
dx.doi.org/10.1021/om300313f | Organometallics 2012, 31, 4779−4785

Organometallics
Article
(19) Wiltzsch, C.; Wagler, J.; Roewer, G.; Kroke, E. Dalton Trans.
2009, 5474−5477.
Present Address
†GMBU e. V. Dresden, Bautzner Landstraße 45, 01454
Radeberg, Germany.
(20) (a) Sheludyakov, V. D.; Kotrikadze, E. L.; Khananashvili, L. M.;
Kuznetsova, M. G.; Kisin, A. V.; Kirilin, A. D. Zh. Obshch. Khim. 1981,
51, 2481−2485. (b) Mark, V.; Wilson, P. S. U.S. Patent 1980, US
4230611 A 19801028. (c) Mironov, V. F.; Kozyukov, V. P.; Kirilin, A.
D.; Sheludyakov, V. D.; Dergunov, Y. I.; Vostokov, I. A. Zh. Obshch.
Khim. 1975, 45 (9), 2007−2010.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(21) Crystal data for 3a [C8H18N2O4Si]: M = 234.33 g·mol−1,
orthorhombic, Pmmn, a = 16.3210(9) Å, b = 7.1980(4) Å, c =
5.0130(2) Å, Z = 2, V = 588.92(5) Å3, Dc = 1.321 Mg·m−3, T = 153(2)
K, μ = 0.198 mm−1, 7266 collected reflections, 612 unique reflections,
Rint = 0.0721, R1 = 0.0303 (all data), wR(F2) = 0.0784 (all data), R1 =
0.0277 (I > 2σ(I)), wR(F2) = 0.0759 (I > 2σ(I), S = 1.048, CCDC
868407. Crystal data for 3b [C10H22N2O4Si]: M = 262.39 g·mol−1,
monoclinic, P2/n, a = 16.8885(17) Å, b = 5.0436(3) Å, c =
17.8135(15) Å, β = 112.459(4)°, Z = 4, V = 1402.2(2) Å3, Dc = 1.243
Mg·m−3, T = 90(2) K, μ = 0.173 mm−1, 4216 collected reflections,
2750 unique reflections, Rint = 0.0333, R1(all data) = 0.1001, wR(F2)
0.0845 (all data), R1 = 0.0481 (I > 2σ(I)), wR(F2) = 0.0779 (I >
2σ(I)). S = 0.847, CCDC 812273. Crystal data for 4b [C7H16N2O]: M
= 144.22 g·mol−1, monoclinic C2/c, a = 19.935(6) Å, b = 4.5756(15)
Å, c = 18.573(6) Å, β = 94.004(7)°, Z = 8, V = 1690.0(10) Å3, Dc =
1.134 Mg·m−3, T = 90(2) K, μ = 0.077 mm−1, 7528 collected
reflections, 1443 unique reflections, Rint = 0.0807, R1 = 0.0751 (all
data), wR(F2) = 0.1382 (all data), R1 = 0.0545 (I > 2σ(I)), wR(F2) =
0.1305 (I > 2σ(I)), S = 1.066, CCDC 812272.
■
We thank Dipl. Chem. Erik Hennings (TU Bergakademie
Freiberg, Institute for Inorganic Chemistry) for performing
DTA/TG measurements and Dr. Erica Brendler (TU
Bergakademie Freiberg, Institute for Analytical Chemistry) for
the 29Si solid-state NMR studies. Also we acknowledge the TU
Bergakademie Freiberg for the financial support and for the
opportunity to use the HPC cluster for the quantum chemical
calculations.
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■
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