From CO2 to Polysiloxanes: Di(carbamoyloxy)silanes Me

Jun 26, 2012 - Institute for Inorganic Chemistry, TU Bergakademie Freiberg, Leipziger Straße 29, 09596 Freiberg, Germany. •S Supporting Information...
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From CO2 to Polysiloxanes: Di(carbamoyloxy)silanes Me2Si[(OCO) NRR′]2 as Precursors for PDMS Konstantin Kraushaar, Conny Wiltzsch,† Jörg Wagler, Uwe Böhme, 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 CO2insertion 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.

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INTRODUCTION Oligo- and polysiloxanes are among the most important classes of polymers with a wide range of applications, e.g., as heatresistant 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 ammonium 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. Recently Fuchter et al. used supercritical CO2 for the synthesis of several di(carbamoyloxy)silanes and the decomposition 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 © 2012 American Chemical Society

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 temperature and without any catalysts to give the di(carbamoyloxy)silanes Me 2 Si[(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.

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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 Müller−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 29 Si NMR spectra in the shift range of −5.6 to −9.5 ppm (see Table 1). CO2 Double Insertion. Most reports on carbamoyloxysilanes describe the insertion of one CO2 molecule into the Si−N bond of a monoaminosilane. Few authors report on the Received: April 24, 2012 Published: June 26, 2012 4779

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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

a

aminosilane

δ/ppm

2a 2b 2c 2d 2e 2f

−7.9 −7.9a −9.3a −9.4a −5.6a −9.5a a

carbamoyloxysilane 3a 3b 3c 3d 3e 3f

δ/ppm a

3.4 2.5a 3.2a 3.2a 2.9b 2.0a

di(carbamoyloxy)silanes 3a,c,d, the intermolecular interactions obviously influence significantly the magnetic environment of the silicon atoms (see Table 1).

δ/ppmc 10.6 12.1 11.9

Solvent: CDCl3. bSolvent: C6D6/CDCl3. cSolid-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 aminosilanes 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. 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

Figure 1. Comparison of 29Si CP/MAS NMR (above) and solution 29 Si 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. In addition, the hydrogen bonds can be detected in the solidstate 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. 4780

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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. Nonrelevant 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 atoms involved D−H···A

distance/Å H···A

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.

angle/deg

D···A

D−H···A

2.9144

172

2.8844 2.9285

171 172

2.8961 2.8493

155 154

3a N1−H1···O2a

2.11

N1−H1···O2b N2−H2···O4c

2.14 2.19

N1−H1N···O1d N2−H2N···O1

2.15 2.05

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 aminosilanes. Siloxane Formation. The thermal transformation of the di(carbamoyloxy)silanes Me2Si[(OCO)NRR′]2 (3) was carefully analyzed. Figure 4 shows the results of a thermogravimetric/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 CO 2 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

3b

4b

a

Symmetry codes: x, y, z+1. bx, −1+y, z. cx, 1+y, z. dx, −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 4781

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Figure 5. Calculated potential energy profile for the carbon dioxide insertion (Gibbs free energy at 298.15 K, 1 atm).

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

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

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. 4782

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and the primary amine RNH 2, 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.

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. 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

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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). 29 Si 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. Preparation of Bis(n-propylamino)dimethylsilane, Me 2 Si(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), 11.4 (CH3), −1.42 (SiCH3) ppm. 1H NMR (400 MHz, CDCl3): δ 2.53 (4H, NHCH 2 CH 2 CH 3 , t, 3 J H−H = 8 Hz), 1.24 (4H, NHCH2CH2CH3, m), 0.72 (6H, CH3, t, 3JH−H = 8 Hz), 0.44 (2H,

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.

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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 decomposition 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 hydrogen 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). 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 4783

dx.doi.org/10.1021/om300313f | Organometallics 2012, 31, 4779−4785

Organometallics

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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. 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−C6); 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); 1.42 (20H, H-2−H-6, m); 1.03 (6H, H-1, t, 3JH−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. 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. 29 Si NMR (79 MHz, CDCl3): δ −9.4 ppm. 13C NMR (100 MHz, CDCl3): δ 41.4 (C-12); 35.3 (C-3); 32.3 (C-11); 30.1−29.8 (C-4−C9); 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 (36H, H-2−H-10, m); 1.16 (6H, H-1, t, 3JH−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%. Preparation of Bis(diethylamino)dimethylsilane, Me 2 Si[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 (N(CH2CH3)2), 15.6 (N(CH2CH3)2), −1.2 (SiCH3) ppm. 1H 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. 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-propylaminodimethylsilane, 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, 3 JH−H = 12.0, 8.0 Hz), 1.14 (6H, CH3, t, 3JH−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

(CDCl3): δ 2.5 ppm. 13C NMR (CDCl3): δ 154.4 (CO), 43.3 (NCH2CH2CH3), 23.7 (NHCH 2CH2CH3), 11.4 (CH3), −0.9 (SiCH3) ppm. 1H NMR (CDCl3): δ 5.47 (2H, NH, s), 3.10 (4H, NCH2CH2CH3, t, 3JH−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 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. 29 Si NMR (CDCl3): δ 3.2 ppm. 29Si NMR (CP/MAS): δiso 12.1 ppm. 13 C NMR (CDCl3): δ 154.0 (CO), 41.9 (C-8), 31.8 (C-3), 29.8 (C7), 29.5 (C-4), 29.2 (C-5), 26.8 (C-6), 22.7 (C-2), 14.1 (C-1), −1.2 (C-9) ppm. 1H 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), 1.03 (6H, H-1, t, 3JH−H = 8 Hz), 0.15 (6H, H-9, s) ppm. IR (KBr): 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 (C3), 31.9 (C-11), 29.8−29.1 (C-4−C-9), 26.8 (C-10), 22.7 (C-2), 14.1 (C-1), −1.2 (C-13) ppm. 1H NMR (CDCl3): δ 4.96 (2H, NH, m), 3.14 (4H, H-12, q, 3JH−H = 12.0, 8.0 Hz), 1.48 (4H, H-11, m), 1.26 (36H, H-2−H-10, m), 0.88 (6H, H-1, t, 3JH−H = 8 Hz), 0.50 (6H, H13, 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 (N(CH2CH3)2), 13.4 (CH3), −0.01 (SiCH3) ppm. 1H NMR (C6D6): δ 3.47 (4H, N(CH2CH3)2, t, 3JH−H = 7 Hz), 3.05 (4H, N(CH2CH3)2, t, 3JH−H = 7 Hz), 1.98 (6H, CH3, t, 3JH−H = 7 Hz), 1.32 (6H, CH3, t, 3 JH−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)(npropylcarbamoyloxy)silane, Me2Si[O(CO)NH(C1HC2H2C3H2C4H2C3H2C2H2)][O(CO)(CH2CH2CH3)] (3f). General procedure 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.

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ASSOCIATED CONTENT

S Supporting Information *

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.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 4784

dx.doi.org/10.1021/om300313f | Organometallics 2012, 31, 4779−4785

Organometallics

Article

Present Address

(19) Wiltzsch, C.; Wagler, J.; Roewer, G.; Kroke, E. Dalton Trans. 2009, 5474−5477. (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. (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. (22) Caminati, W.; Grabow, J.-U. J. Am. Chem. Soc. 2006, 128, 854− 857 , and references therein. (23) The computations were done with Gaussian 03: Frisch, M. J.; et al. Gaussian 03, revision D.02; Gaussian, Inc.: Pittsburgh, PA, 2003. For details, see the Supporting Information. (24) Larsson, E.; Smith, B.; Sillén, L. G. Acta Chem. Scand. 1949, 3, 487−492. (25) Klein, D. W.; Connally, J. W. J. Organomet. Chem. 1971, 33, 311−319.

†

GMBU e. V. Dresden, Bautzner Landstraße 45, 01454 Radeberg, Germany.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS 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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REFERENCES

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dx.doi.org/10.1021/om300313f | Organometallics 2012, 31, 4779−4785