Chemistry

V. M. VDOVIN, R. SULTANOV, E. L. LUBUZH
and Corresponding Member of the Academy of Sciences of the USSR A. D. PETROV

ORGANOSILICON COMPOUNDS WITH HYDROCARBON BRIDGES BETWEEN SILICON ATOMS

ALKYLATION OF $\omega$-CYANOALKYLTRIMETHYLSILANES WITH HALOMETHYLTRIMETHYLSILANES

Disilanes with a hydrocarbon bridge between silicon atoms, $(\mathrm{CH}_3)_3\mathrm{Si}—\mathrm{R}—\mathrm{Si}(\mathrm{CH}_3)_3$, are of interest as monomers for obtaining polymeric materials with alternating hydrocarbon siloxane fragments ($^1$), and also silicon-hydrocarbon polymers ($^2$). Whereas methods exist for bridged disilanes of the type $(\mathrm{CH}_3)_3\mathrm{Si}—\mathrm{R}—\mathrm{Si}(\mathrm{CH}_3)_3$ (where —R— is a hydrocarbon radical) ($^3$), such compounds with a functional group in the radical —R— are difficult to obtain. In the present work we investigated the possibility of obtaining bridged disilanes containing a cyano group in the radical —R—. It should be noted that a cyano group bound to the $\beta$-carbon atom (relative to Si) can be converted into a variety of functional groups without cleavage of the cyanoalkyl radical from silicon ($^{4-6,8}$). The reaction for obtaining bridged cyano-containing compounds was carried out according to scheme (1), under the conditions for alkylation of acetonitrile ($^3$).

\[ (\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_n\mathrm{CH}_2\mathrm{CN} \ \xrightarrow[\text{ether}]{\mathrm{Na}}\ [(\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_n\mathrm{CH}(\mathrm{Na})\mathrm{CN}] \ \xrightarrow{\mathrm{XCH}_2\mathrm{Si}(\mathrm{CH}_3)_3}\ (\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_n \overset{\beta}{\mathrm{CH}} \overset{\alpha}{\mathrm{CH}}_2\mathrm{Si}(\mathrm{CH}_3)_3 + \mathrm{NaX}, \tag{1} \]

\[ \hspace{3.5cm} \begin{matrix} |\\[-2pt] \mathrm{CN} \end{matrix} \]

where $n = 1$ and 2; $\mathrm{X} = \mathrm{Cl}, \mathrm{Br}, \mathrm{J}$.

The structure of the compounds obtained was proved by IR spectra. The frequency 2238 cm$^{-1}$ for the disilane nitriles obtained lies in the region characteristic of the cyano group, but is somewhat lowered compared with its value in $\omega$-nitriles—$(\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_n\mathrm{CN}$ (for $n = 2$ and 3, 2249 cm$^{-1}$). This fact is in good agreement with the known phenomenon of a decrease in the frequency of an electronegative group with increasing branching of the radical bound to this group. For example, on going from $\mathrm{H}—\mathrm{C}_4\mathrm{H}_9—\mathrm{CN}$ to tert.-$\mathrm{C}_4\mathrm{H}_9—\mathrm{CN}$, the frequency of the —$\mathrm{C}\equiv\mathrm{N}$ group falls from 2250 cm$^{-1}$ to 2218 cm$^{-1}$ ($^7$). In addition, the structure of the compounds obtained was proved by converting them into ketones (2):

\[ (\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_n \overset{\beta}{\mathrm{CH}}(\mathrm{CN}) \overset{\alpha}{\mathrm{CH}}_2\mathrm{Si}(\mathrm{CH}_3)_3 \xrightarrow{\mathrm{CH}_3\mathrm{MgJ}\ \mathrm{H}_2\mathrm{O}} (\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_n\mathrm{CH}(\mathrm{COCH}_3)\mathrm{CH}_2\mathrm{Si}(\mathrm{CH}_3)_3 \tag{2} \]

(where $n = 1$ and 2).

It is known that isonitriles or $\alpha$-nitriles

\[ \left[\equiv \mathrm{Si}—\overset{\alpha}{\mathrm{C}}—\mathrm{CN}\right] \]

do not form ketones in this reaction ($^8$).

The best yield of nitrile by reaction (1) was achieved for $(\mathrm{CH}_3)_3\mathrm{SiCH}_2\mathrm{J}$ ($\sim 40\%$). In the case of $(\mathrm{CH}_3)_3\mathrm{SiCH}_2\mathrm{Cl}$, the yield of disilane nitrile was

smallest (\(\sim 20\%\)). Here reaction (1) was accompanied by the formation of a considerable amount of a by-product. By molecular weight and elemental analysis this substance corresponded to the dimer of the starting \(\beta\)-cyanoethyltrimethylsilane. The ability of nitriles not containing silicon to dimerize under the action of sodium is known \((^9)\). In our case this was confirmed by an additional experiment (in the absence of \(\mathrm{XCH_2Si(CH_3)_3}\)) according to reaction (3):

\[ 2(\mathrm{CH_3})_3\mathrm{SiCH_2CH_2CN} \xrightarrow[\text{ether}]{\mathrm{Na,\ H_2O}} ((\mathrm{CH_3})_3\mathrm{Si})_2\mathrm{C_6H_8N_2}. \tag{3} \]

Of the two possible structures usually assigned to dimers of nitriles not containing silicon, (A) and (B),

\[ \begin{array}{cc} \mathrm{RCH_2-C-CH-R}^{(9)} & \mathrm{RCH_2-C=C-R}^{(10,11)}\\ \text{(A)}\quad \| \ \ \ | & \text{(B)}\quad | \ \ \ |\\ \mathrm{NH}\ \ \mathrm{CN} & \mathrm{NH_2}\ \mathrm{CN} \end{array} \]

on the basis of spectral data we choose structure (B) (where \(\mathrm{R=-CH_2Si(CH_3)_3}\)). In the IR spectrum of this compound a frequency of \(2201\ \mathrm{cm^{-1}}\) was observed, which may be assigned to the stretching vibration of the group \(\mathrm{-C\equiv N}\). This frequency is lowered*, apparently owing to the presence of a chain of conjugated groups:

\[ \mathrm{NH_2-C=C-C\equiv N}. \]

The frequencies 3400 and \(3448\ \mathrm{cm^{-1}}\) are assigned to the symmetric and asymmetric stretching vibrations of the \(\mathrm{NH_2}\) group \((^{13})\). In the IR spectrum of a solution (in \(\mathrm{CCl_4}\)) of this substance***, the frequency \(1630\ \mathrm{cm^{-1}}\) is characteristic of the bond \(\mathrm{-C=C-}\). In the UV spectrum of this substance an intense frequency at \(248\ \mathrm{m\mu}\) was observed (\(E=46500\)).

When an \(\omega\)-nitrile of the type \(\mathrm{NC-CH_2-CH_2-O-(CH_2)_3Si-(CH_3)_3}\) was alkylated, a different reaction occurred: \(\gamma\)-oxypropyltrimethylsilane and polyacrylonitrile were formed. In a control experiment (in the absence of \(\mathrm{XCH_2Si(CH_3)_3}\)) the \(\gamma\)-alcohol was also formed according to scheme (4):

\[ \begin{aligned} &(\mathrm{CH_3})_3\mathrm{Si}(\mathrm{CH_2})_3-\overset{1}{\mathrm{O}}-\overset{2}{\mathrm{CH_2}}-\overset{3}{\mathrm{CH}}-\overset{4}{\mathrm{H}} \ \xrightarrow[\text{ether}]{\mathrm{Na}}\\ &\hspace{85pt} \bigg|\\[-6pt] &\hspace{85pt} \mathrm{CN}\\[4pt] &\to ((\mathrm{CH_3})_3\mathrm{Si}(\mathrm{CH_2})_3-\overset{1\delta-}{\mathrm{O}}-\overset{2}{\mathrm{CH_2}}-\overset{3}{\mathrm{CH}}-\overset{4\delta+}{\mathrm{Na}})\to \tag{4}\\ &\hspace{160pt} \bigg|\\[-6pt] &\hspace{160pt} \mathrm{CN}\\[4pt] &\to (\mathrm{CH_3})_3\mathrm{Si}(\mathrm{CH_2})_3-\overset{1}{\mathrm{O}}-\overset{4}{\mathrm{Na}} +\overset{2}{\mathrm{CH_2}}=\overset{3}{\mathrm{CH}}(\mathrm{CN})\\ &\hspace{120pt}\downarrow\mathrm{H_2O}\hspace{75pt}\downarrow\\ &\hspace{68pt}(\mathrm{CH_3})_3\mathrm{Si}(\mathrm{CH_2})_3\mathrm{OH}+\mathrm{NaOH} \hspace{62pt}\text{Polymer} \end{aligned} \]

The cleavage of systems \(\mathrm{-Y=C-C-M}\) (where \(Y\) is an electronegative atom and \(M\) an electropositive atom), studied in detail by A. N. Nesmeyanov and co-workers \((^{14})\), is their characteristic feature in cases where \(M\) is a metal.

In a special experiment we established that the alkoxide \((\mathrm{CH_3})_3\mathrm{Si(CH_2)_3ONa}\) formed in the reaction does not react, under the experimental conditions, with \(\mathrm{XCH_2Si(CH_3)_3}\).

Experimental Part

Starting substances. Halomethyltrimethylsilanes were obtained by chlorination \((^{15})\) and bromination \((^{16})\) of trimethylchlorosilane and subsequent methylation of the halomethyl derivatives obtained; in the synthesis of \((\mathrm{CH_3})_3\mathrm{SiCH_2J}\) from \(\mathrm{Cl(CH_3)_2SiCH_2Cl}\), methylation was carried out by the action of \(\mathrm{CH_3MgJ}\) at \(100^\circ\) \((^{17})\). \(\beta\)-Cyanoethyltrimethylsilane was obtained by a known method \((^6)\),

* Recorded on an IKS-12 instrument; NaCl prism—region \(2000\text{–}700\ \mathrm{cm^{-1}}\), LiF prism—region \(1900\text{–}4000\ \mathrm{cm^{-1}}\). The substance was recorded pressed in KBr.
* The lowering of the frequency of the \(\mathrm{-C\equiv N}\) group conjugated with a double bond is known—see the frequency factor \((^{12})\).
** Recorded on a double-beam UR-10 instrument.

γ-Cyanopropyltrimethylsilane was obtained from $\mathrm{Cl_2(CH_3)SiCH_2CH_2CH_2CN}$ and $\mathrm{BrMgCH_3}$ by an analogous procedure \((^6)\) in 72% yield, $n_D^{20}$ 1.4271, b.p. 80° at 12 mm. For the $\omega$-nitriles: $(\mathrm{CH_3})_3\mathrm{Si}(\mathrm{CH_2})_n\mathrm{CN}$, in the IR spectra (IKS-12 instrument, LiF prism), frequency values characteristic of the $\mathrm{-C \equiv N}$ group were obtained: for $n = 2$, 2248 cm$^{-1}$; for $n = 3$, 2249 cm$^{-1}$. γ-(β-Cyanoethyl)oxypropyltrimethylsilane was obtained from $\mathrm{Cl_2(CH_3)Si(CH_2)_3OCH_2CH_2CN}$ and $\mathrm{CH_3MgBr}$ in 62% yield, b.p. 110.5° at 5 mm, $n_D^{20}$ 1.4369, $d_4^{20}$ 0.8800.

Synthesis of 1,3-di-(trimethylsilyl)-2-cyanopropane (I). 62 g (0.29 mole) of $(\mathrm{CH_3})_3\mathrm{SiCH_2J}$, 89 g (0.70 mole) of $(\mathrm{CH_3})_3\mathrm{SiCH_2CH_2CN}$, and 2 g of metallic sodium, from a weighed amount of 9.2 g (0.38 mole), were heated in a solution of 150 ml of abs. ethyl ether until the reaction began (spontaneous warming and gas evolution). The remaining sodium was added in several portions with vigorous stirring of the reaction mixture. After the warming ceased, the mixture was refluxed for another 6 h; it was then carefully poured into water, and the ether layer was washed several times with water. The ether extracts were dried over calcium chloride and distilled. 25 g of crude (I) was obtained, b.p. 103–106° at 12 mm. The properties of the analytically pure substance are given in Table 1*.

Table 1

Properties of hexamethyldisilylalkanes with functional groups in the bridge

* Under the line—the pressure in millimeters of mercury.
** By the cryoscopic method in benzene.

Found, %: Si 26.00; 25.30; C 56.83; 56.90; H 10.86; 11.03; N 6.49; 6.53
$\mathrm{C_{10}H_{23}NSi_2}$. Calculated, %: Si 26.31; C 56.26; H 10.85; N 6.56

Yield of (I) 40.5% (based on iodide taken) and about 70% (based on iodide consumed).

In the case of the other nitriles and halomethyltrimethylsilanes, the reaction was carried out under analogous conditions and with analogous ratios of reagents. From $(\mathrm{CH_3})_3\mathrm{SiCH_2Br}$, (I) was obtained in 31.5% yield; from $(\mathrm{CH_3})_3\mathrm{SiCH_2Cl}$—in 20.8% yield. In the latter case, crystalline (V) was isolated in approximately the same weight amount as (I); purified by three recrystallizations from n-hexane (m.p. 91.0°), (V) had the following composition:

Found, %: Si 22.10; 22.25; N 10.61; 10.90
$\mathrm{C_{12}H_{26}N_2Si_2}$. Calculated, %: Si 22.07; N 11.00

(II) was obtained from $(\mathrm{CH_3})_3\mathrm{Si(CH_2)_3CN}$ and $\mathrm{JCH_2Si(CH_3)_3}$ in 32.5% yield.

Found, %: Si 24.40; 24.04; C 58.19; 58.42; H 11.19; 11.39
$\mathrm{C_{11}H_{25}NSi_2}$. Calculated, %: Si 24.69; C 58.07; H 11.07

* The properties of other newly obtained compounds are also given in Table 1.

Dimerization of $(\mathrm{CH}_3)_3\mathrm{SiCH}_2\mathrm{CH}_2\mathrm{CN}$ with sodium.
23.7 g of the indicated nitrile and 1.97 g of sodium were refluxed in 100 ml of abs. ether for 3 h with stirring. After the usual work-up, 11.2 g of the starting nitrile was recovered and 5.0 g of crude (V) was obtained (yield 19%), b.p. 164–167° at 3 mm. After two recrystallizations from n-hexane the substance melted at 91.3°. A mixed melting point of the substance obtained in this experiment and, as a by-product, in reaction (1) showed no depression.

Alkylation of $(\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_3{-}\mathrm{OCH}_2\mathrm{CH}_2\mathrm{CN}$ with $\mathrm{XCH}_2\mathrm{Si}(\mathrm{CH}_3)_3$ and sodium.
The reaction was carried out by the analogous alkylation procedure, with the difference that the ether extracts were dried over anhydrous $\mathrm{CuSO}_4$. In the case of both $(\mathrm{CH}_3)_3\mathrm{SiCH}_2\mathrm{Cl}$ and $(\mathrm{CH}_3)_3\mathrm{SiCH}_2\mathrm{Br}$, together with unchanged nitrile, $(\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_3\mathrm{OH}$ was isolated in 80–86% yield based on the sodium taken. The γ-alcohol obtained had the following properties: b.p. 75–76° at 15 mm, $n_D^{20}$ 1.4297, $d_4^{20}$ 0.8307. Literature data $(^{18})$: b.p. 83° at 27 mm, $n_D^{20}$ 1.4290, $d_4^{20}$ 0.8316.

Interaction of $(\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_3{-}\mathrm{OCH}_2\mathrm{CH}_2\mathrm{CN}$ and sodium.
13.6 g of nitrile and 1.7 g of sodium were stirred in boiling ether until the sodium had completely dissolved, and then the brown paste formed was stirred for another 6 h. After the usual work-up, $(\mathrm{CH}_3)_3\mathrm{Si}(\mathrm{CH}_2)_3\mathrm{OH}$ was obtained in 81.5% yield. The properties were analogous $(^{18})$.

Interaction of nitriles (I) and (II) with $\mathrm{CH}_3\mathrm{MgJ}$.
$\mathrm{CH}_3\mathrm{MgJ}$ was added to an ethereal solution of the nitrile (3 moles of $\mathrm{CH}_3\mathrm{MgJ}$ per 1 mole of nitrile). In the case of (II) there was slight warming of the mixture. The reaction mixture was then heated on a water bath; after the ether had been distilled off, the thick mass was heated for 10 h at 80–95°. (III) was obtained in 60.5% yield, and (IV) in 70% yield. In the IR spectrum of (III) and (IV) a frequency of 1710 cm$^{-1}$ was found, characteristic of the keto group; in the IR spectrum of $(\mathrm{CH}_3)_3\mathrm{SiCH}_2\mathrm{CH}_2\mathrm{COCH}_3$ $(^{6})$ the frequency of the group $=\mathrm{C}=\mathrm{O}$ is 1710 cm$^{-1}$ (NaCl prism, region 1600–3000 cm$^{-1}$).

Found, %: C 58.75; 58.79; H 11.46; 11.58; Si 22.53; 22.41;
$\mathrm{C}_{12}\mathrm{H}_{28}\mathrm{Si}_2\mathrm{O}$ (IV). Calculated, %: C 58.94; H 11.54; Si 22.97

N. D. Zelinsky Institute of Organic Chemistry
Academy of Sciences of the USSR

Received
14 II 1961

CITED LITERATURE

1. L. H. Sommer, G. R. Ansul, J. Am. Chem. Soc., 77, 2482 (1955).
2. V. M. Vdovin, K. S. Pushchevaya, A. D. Petrov, Izv. AN SSSR, OKhN, 1961, No. 2; V. M. Vdovin, K. S. Pushchevaya, N. A. Belikova, R. Sultanov, A. F. Plate, A. D. Petrov, DAN, 136, No. 1 (1961).
3. V. M. Vdovin, A. D. Petrov, ZhOKh, 30, 838 (1960).
4. V. M. Vdovin, Candidate’s dissertation, Institute of Organic Chemistry, Academy of Sciences of the USSR, 1958.
5. A. D. Petrov, V. M. Vdovin, ZhOKh, 29, 2910 (1959); A. D. Petrov, L. Kh. Freidlin, T. A. Sladkova, V. M. Vdovin, Izv. AN SSSR, OKhN, 1960, 1878.
6. A. D. Petrov, S. I. Sadykh-zade, V. M. Vdovin, DAN, 100, 711 (1955).
7. J. McBride Jr., H. C. Beachel, J. Am. Chem. Soc., 74, 5247 (1952).
8. S. Nozakura, S. Konotsune, Bull. Chem. Soc. Japan, 29, No. 3, 322 (1956); ibid., 29, No. 3, 326 (1956).
9. I. Guben, Methods of Organic Chemistry, 4, Book 1, Moscow, 1949, p. 63.
10. R. A. Show, J. Chem. Soc., 1956, 2779.
11. H. Adkins, J. Whitman, J. Am. Chem. Soc., 64, 150 (1942).
12. R. E. Kitsoa, N. E. Griffith, Anal. Chem., 24, 334 (1952).
13. N. B. Colthup, J. Opt. Soc. Am., 40, 397 (1950).
14. A. N. Nesmeyanov, Selected Works, 3, Publishing House of the Academy of Sciences of the USSR, 1959, pp. 549, 678, 684.
15. A. D. Petrov et al., DAN, 97, 687 (1954).
16. J. Speir, J. Am. Chem. Soc., 73, 826 (1956).
17. V. A. Ponomarenko, V. F. Mironov, DAN, 94, 485 (1954).
18. L. H. Sommer et al., J. Am. Chem. Soc., 71, 3056 (1949).