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Jan 12, 2010 - In the presence of traces of NH4Cl, working as an acid catalyst, 5−8 slowly ... Eric M. Press , Eric A. Marro , Sravan K. Surampudi ,...
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Organometallics 2010, 29, 618–623 DOI: 10.1021/om9010017

Synthesis and Reactivity of NH2 Derivatives of Dodecamethylcyclohexasilane Harald Stueger,* Gottfried Fuerpass, Thomas Mitterfellner, and Judith Baumgartner Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 16, A-8010 Graz, Austria Received November 16, 2009

The reactions of the chloropermethylcyclohexasilanes Si6Me12-nCln (1; n = 1), 1,3-Cl2Si6Me10 and 1,4-Cl2Si6Me10 (2 and 3, respectively; n = 2), and 1,3,5-Cl3Si6Me9 (4; n = 3) with NH3 or NaNH2, respectively, afforded the corresponding amino derivatives Si6Me12-n(NH2)n (5-8), which are surprisingly stable toward self-condensation in the pure state. In the presence of traces of NH4Cl, working as an acid catalyst, 5-8 slowly decompose by loss of NH3 to give polysilazanes still containing intact cyclohexasilanyl moieties. In the case of 1,4-diaminodecamethylcyclohexasilane (7) the intramolecular condensation product 9 is formed along with some polymeric material. The X-ray structure analysis of 9, which is the first structurally characterized 7-azahexasilanorbornane, exhibits a norbornane-like structure with the cyclohexasilane ring in a boat conformation. Aminoundecamethylcyclohexasilane (5) is easily deprotonated by n-BuLi to give the expected lithium amide LiHNSi6Me11. With NaNH2, however, the open-chain ring scission product 1,5-dihydrodecamethylpentasilane (12) was formed nearly exclusively.

Introduction In cyclic polysilanes delocalization of σ(Si-Si) electrons over the ring silicon atoms gives these molecules a variety of properties resembling those of aromatic hydrocarbons,1 such as unusually long wavelength UV absorption maxima, low ionization energies, nonlinear optical behavior,2 fluorescence,3 and photochemical activity.4 Certain cyclic polysilanes can also be converted to anion or cation radicals which show complete delocalization of the odd electron over the cyclosilane ring.5 In addition, pronounced substituent effects on cyclopolysilane properties such as bathochromically shifted UV/visible absorption maxima are observed, when unsaturated organic side groups or atoms with π symmetric lone pairs as in the halogens are linked directly *To whom correspondence should be addressed. Tel: þ43/316/8738708. Fax: þ43/316-8701. E-mail: [email protected]. (1) The chemistry and the properties of cyclopolysilanes have been summarized in various reviews: (a) Hengge, E.; Stueger, H. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1998; Vol. 2, p 2177. (b) Hengge, E.; Janoschek, R. Chem. Rev. 1995, 95, 1495. (c) West, R. In Comprehensive Organometallic Chemistry II; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1995; Vol. 2, p 77. (d) West, R. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; p 1207. (e) West, R. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982; Vol. 2, p 365. (2) Grogger, C.; Rautz, H.; Stueger, H. Monatsh. Chem. 2001, 132, 453. (3) Stueger, H.; Fuerpass, G.; Renger, K. Organometallics 2005, 24, 6374. (4) Ishikawa, M; Kumada, M. J. Chem. Soc. D: Chem. Commun. 1970, 612. (5) (a) Wadsworth, C. L.; West, R.; Nagai, Y.; Watanabe, H.; Muraoka, T. Organometallics 1985, 4, 1659. (b) Bock, H.; Kaim, W.; Kira, M.; West, R. J. Am. Chem. Soc. 1979, 101, 7667. pubs.acs.org/Organometallics

Published on Web 01/12/2010

to the polysilane backbone.6 Extraordinarily low energy first UV absorption bands, for instance, are shown by perhalocyclopolysilanes so that some of these compounds are even colored.7 Cyclopolysilanes have been known since the fundamental work of Kipping in 1921,8 who synthesized the four-, five-, and six-membered perphenylcyclopolysilanes from diphenyldichlorosilane and sodium. Since then numerous cyclopolysilanes bearing mainly simple alkyl or aryl side groups have been prepared. Selected functionalized derivatives such as the perhalocyclopolysilanes (SiX2)n (X = Cl, Br, I; n = 4-6)9 or cyclohexasilanes of the general type Si6Me12-nXn (X=H, halogen, NR2, SR, OR, OH, main group or transition metal; n = 1-3)1a,b,3,10 have also been described in the literature. Nevertheless, there still exists a strong demand for additional cyclopolysilane derivatives in order to provide a better understanding of the substituent effects described above and to further develop the chemistry of this interesting class of compounds. Herein, we report the synthesis and the properties of previously unknown aminopermethylcyclohexasilanes containing unsubstituted primary amino (NH2) groups.

Results and Discussion Aminopermethylcyclohexasilanes (NH2)nSi6Me12-n are readily available, starting from the chlorinated cyclosilane (6) (a) Sakurai, H. J. Organomet. Chem. 1980, 200, 261. (b) Sakurai, H. Pure Appl. Chem. 1987, 59, 1637. (c) Pitt, C. G. J. Am. Chem. Soc. 1969, 91, 6613. (7) Stueger, H.; Hengge, E. Monatsh. Chem. 1988, 119, 873. (8) Kipping, F. S.; Sands, J. E. J. Chem. Soc. 1921, 119, 830. (9) (a) Hengge, E.; Kovar, D. Angew. Chem., Int. Ed. 1981, 20, 678. (b) Hengge, E.; Kovar, D. Z. Anorg. Allg. Chem. 1979, 458, 163. (c) Hengge, E.; Kovar, D. J. Organomet. Chem. 1977, 125, C29. (10) Spielberger, A.; Gspaltl, P.; Siegl, H.; Hengge, E. J. Organomet. Chem. 1995, 499, 241. r 2010 American Chemical Society

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precursors ClSi6Me11 (1), 1,3-Cl2Si6Me10 (2), 1,4-Cl2Si6Me10 (3), and 1,3,5-Cl3Si6Me9 (4), which can be synthesized from Si6Me12 and SbCl5 using published procedures.3,10,11 Aminoundecamethylcyclohexasilane (5) can be easily obtained according to Scheme 1 by the reaction of 1 with NH3 (method a), with a solution of Na in liquid NH3 (method b), or with NaNH2 (method c). In a recent study Roesky et al. investigated the reaction of MeSiCl3 with Na/NH3 to the cagelike polysilazane (MeSi)6(NH)9 and postulated a reaction mechanism via the primary formation of NaNH2 by loss of H2, which subsequently reacts with the chlorosilane to give the Si-N product and NaCl.12 An analogous mechanism is most likely to operate also in the course of method b, last but not least due to the fact that NaCl is produced instead of NH4Cl, which rules out any direct displacement of Cl by NH3. Methods a and b turned out to be equally suitable for the preparation of the 1,3-diamino and 1,3,5-triamino derivatives 6 and 8 (compare Scheme 2). When 6 and 8 prepared according to method a, however, are stored at room temperature, they slowly condense to give polysilazane oligomers, while both compounds made via method b are completely stable upon storage. The attempted synthesis of the 1,4-analogue 7 by method a completely failed because of competing inter- and intramolecular condensation reactions during the synthesis, yielding a mixture of cis- and trans-7, the intramolecular condensation product 9, and open-chain polysilazane oligomers, from which 9 can be isolated by sublimation. Pure 7, however, is easily accessible by method b (Scheme 2). Quite interestingly, only the trans isomer of 7 is obtained according to 13C NMR, showing just three resonance lines as would be expected for pure trans-7, while isomeric mixtures of cisand trans-6 (seven resonance lines from cis-6 and five resonance lines from trans-6 in 13C NMR) and cis,cisand cis,trans-8 (three resonance lines from cis,cis-8 and six resonance lines from cis,trans-8 in 13C NMR), respectively, are formed under the same reaction conditions.

Attempts to separate the stereoisomers of 6 and 8 by crystallization were not successful. The limited stability of 6-8 prepared by method a can be explained by the presence of residual traces of NH4Cl capable of catalyzing condensation of the primarily formed aminosilane. In order to prove this assumption, we investigated the condensation behavior of the less reactive monoamino derivative 5 (compare Scheme 3) in more detail. Heating a hydrocarbon solution of 5 prepared by method a in a sealed tube to 150 C for 24 h resulted in the quantitative formation of condensation product 10, which can be synthesized independently from 1 and lithiated 5 (compare Scheme 5). When the same procedure, however, is applied to 5 prepared by method b, which affords NaCl instead of NH4Cl in the course of the salt elimination reaction, the starting material remains unaffected even up to 250 C. Heating of 5 prepared by method b in the presence of catalytic amounts of NH4Cl again leads to clean formation of 10, proving the presence of traces of weakly acidic NH4Cl to be necessary to bring about condensation. When an excess of NH4Cl is used in boiling heptane, 5 is rechlorinated to 1. Under more severe reaction conditions, the cyclohexasilane skeleton is destroyed. The sensitivity of 5-8 toward self-condensation under slightly acidic conditions parallels the behavior of other bulky silylamines, which give the corresponding silazanes in the presence of an acid catalyst such as ammonium sulfate or even precipitated amine hydrochloride.13 If crystalline samples of 8 containing traces of NH4Cl are allowed to stand at room temperature for several weeks under an inert atmosphere, condensation polymerization occurs and an opaque mass is formed, which is still soluble in THF (Scheme 4). The 29Si NMR spectrum of the product shows poorly resolved signal groups typical for polymers containing SiN(H)Si (-10 to -12 ppm), uncondensed SiNH2 (-15 to -18 ppm), and endocyclic SiMe2 (-45 to -47 ppm) moieties with an intensity ratio of approximately 1:1:2, which shows that about 50% of the amino groups originally present in 8 condensed to give silazane units. The fact that 4 is regained in quantitative yields after the resulting polymer is treated with acetyl chloride clearly demonstrates the presence of intact cyclohexasilanyl rings in the condensation product. 5 is easily deprotonated by bases such as n-BuLi to give LiHNSi6Me11, which is a valuable synthon for further derivatization (Scheme 5). Thus, for instance, it can be reacted with 1 or Me3SiCl, respectively, to give the N-silylated products 10 and 11. Stirring a toluene solution of 5 for 12 h at room temperature with an equimolar amount of NaNH2, however, exclusively affords the open chain ring scission product 1,5-dihydrodecamethylpentasilane (12) instead of the expected sodium amide NaHNSi6Me11. Gaseous NH3 and a small amount of insoluble precipitate of unknown structure and composition are obtained as byproducts. In addition there is some evidence from 1H and 29Si NMR for the formation of further soluble polymeric products possibly arising from the MeSiN fragment “lost” during the course of the

(11) (a) Hengge, E.; Eibl, M. J. Organomet. Chem. 1992, 428, 335. (b) Eibl, M.; Katzenbeisser, U.; Hengge, E. J. Organomet. Chem. 1993, 444, 29. (12) R€ ake, B.; Roesky, H. W.; Us on, I.; M€ uller, P. Angew. Chem., Int. Ed. 1998, 37, 1432.

(13) (a) Brendler, E.; Fr€ uhauf, S.; Roewer, G.; M€ uller, E. Chem. Mater. 2004, 16, 1368. (b) Armitage, D. A. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982; Vol. 2, p 120.

a Here and elsewhere throughout the paper dots will be used to represent silicon atoms bearing sufficient methyl groups to bring the valence of Si to 4.

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Stueger et al. Scheme 2

reaction. Further studies in order to elucidate the mechanism of this unprecedented reaction pattern, including structure elucidation of the byproduct, are currently underway. 12 easily can be isolated in preparative amounts and further derivatized. Chlorination of the Si-H bonds using N-chlorosuccinimide, for instance, provides a convenient access to 1,5-dichlorodecamethylpentasilane (13), which is an important precursor for the preparation of heterocyclohexasilanes.14 All previously unknown compounds were fully characterized by spectroscopic means and elemental analyses. Pronounced electronic effects of the amino substituents on the ring silicon atoms are apparent in the 29Si NMR spectra, causing a marked downfield shift of the R-Si resonances relative to Si6Me12.15 Analytical data (14) (a) Newman, T. H.; West, R.; Oakley, R. T. J. Organomet. Chem. 1980, 197, 159. (b) Stueger, H.; Eibl, M.; Hengge, E. J. Organomet. Chem. 1992, 431, 1. (15) Kovar, D.; Utvary, K.; Hengge, E. Monatsh. Chem. 1979, 110, 1295.

(compare the Experimental Section) are consistent with the proposed structures in all cases. For compounds 6-9 and 11 elemental analyses could not be performed properly due to incomplete combustion. In these cases HRMS data are given instead. In contrast to decamethyl-7-oxahexasilanorbornane, which cocrystallizes with 1,4-dihydroxydecamethylcyclohexasilane with three molecules in the unit cell in a 1:2 ratio,10 pure 9 can be crystallized from mixtures with 7. The molecular structure of 9 as determined by singlecrystal X-ray crystallography is shown in Figure 1, and selected data are summarized in Table 1. To the best of our knowledge, 9 is the first structurally characterized 7-azahexasilanorbornane. Compound 9 crystallizes in the monoclinic space group C2/c. Due to the bicyclic norbornane-like structure the cyclosilanyl ring is forced into an atypical conformation, giving rise to considerable variations in the Si-Si;Si angles with — Si(2)-Si(1)-Si(3A) = 113.8, — Si(2)-Si(3)Si(1A) = 97.8, and — Si(1)-Si(2)-Si(3) = 96.1. The average

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Scheme 3

Figure 1. Ortep drawing of the molecular structure of 9 (hydrogens are omitted for clarity). Ellipsoids are drawn at the 30% probability level. Table 1. Selected Bond Lengths (A˚), Bond Angles (deg), and Torsion Angles (deg) of 9 Bond Lengths

Scheme 4

Si1-Si2 Si(1)-Si(3A) Si(2)-Si(3) Si(3)-Si(1A)

2.3486(8) 2.3657(9) 2.3571(9) 2.3656(9)

N(1)-Si(1) N(1)-Si(1A) Si-Cmethyl (mean)

1.7550(15) 1.7550(15) 1.882

Bond Angles Si(2)-Si(1)-Si(3A) Si(1)-Si(2)-Si(3)

113.80(3) 96.11(4)

Si(2)-Si(3)-Si(1A) Si(1A)-N(1)-Si(1)

97.78(4) 113.88(15)

Torsion Angles -177.17(9) 7.16(2) 72.35(3)

Si(1A)-N(1)-Si(1)-C(1) Si(1)-Si(2)-Si(3)-Si(1A) Si(3A)-Si(1)-Si(2)-Si(3)

Scheme 5

cyclohexasilane derivatives.3,10,16 The Si-N bond length of 1.755 A˚ is also significantly longer than the usual Si-N distances around 1.74 A˚ previously observed in cyclodi- and cyclotrisilazanes.17 The Si(1)-N(1)-Si(1A) bond angle of 113.9 is somewhat smaller than the Si-O-Si angle of 116.2 in decamethyl-7-oxahexasilanorbornane10,16a but significantly larger than the Si-S-Si angle of 94.9 in the corresponding sulfur-bridged compound.16b

Conclusions A general synthetic approach to several previously unknown NH2-substituted permethylcyclohexasilanes has been developed. The stability of the aminocyclohexasilanes described above toward self-condensation varies with the number and position of NH2 groups attached to the cyclohexasilanyl ring and is drastically reduced by the presence of traces of NH4Cl working as an acid catalyst.

Si-Si distances of 2.359 A˚ are slightly elongated as compared to that in elemental silicon, 2.35 A˚, and those in related

(16) (a) Larkin, D. Y.; Korlyukov, A. A.; Matukhina, E. V.; Buzin, M. I.; Chernyavskaya, N. A.; Antipin, M. Y.; Chernyavskii, A. I. Russ. Chem. Bull. Int. Ed. 2005, 54, 1612. (b) Wojnowski, W.; Dreczewski, A. H.; Pweters, K.; Peters, E. M.; von Schnering, H. G. Angew. Chem., Int. Ed. 1985, 24, 992. (c) Carrell, H. L.; Donohue, J. Acta Crystallogr. 1972, B28, 1566. (d) Straumanis, M. E.; Aka, E. Z. J. Appl. Phys. 1952, 23, 330. (17) (a) Szollosy, A.; Parkanyi, L.; Bihatsi, L.; Hencsei, P. J. Organomet. Chem. 1983, 251, 159. (b) Parkanyi, L.; Argay, G.; Hencsei, P.; Nagy, J. J. Organomet. Chem. 1976, 116, 299. (c) Blake, A. J.; Ebsworth, E. A. V.; Kulpinski, J.; Lasocki, Z. Acta Crystallogr. 1991, C47, 1440. (d) Glowka, M. L.; Olczak, A.; Martynowski, D.; Kozlowska, K.; Kulpinski, J. J. Mol. Struct. 2002, 613, 145.

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Aminoundecamethylcyclohexasilane (5), furthermore, turned out to be a valuable precursor for the preparation of R,ω-difunctionalized permethylpentasilanes, which otherwise are rather complicated to obtain.

Experimental Section All experiments were performed under a nitrogen atmosphere using standard Schlenk techniques. Solvents were dried using a column solvent purification system.18 NH3 was dried by passing through KOH and subsequent condensation onto Na. Commercially available NaNH2 (95%, Sigma Aldrich) was used without further purification. The cyclohexasilane derivatives Si6Me12,19 ClSi6Me11,3 1,3- and 1,4-Cl2Si6Me10,10,11a and 1,3,5Cl3Si6Me911b were synthesized as previously reported. 1H (300.13 MHz), 29Si (59.62 MHz), and 13C (75.4 MHz) NMR spectra were recorded on a Varian Inova 300 spectrometer in C6D6 solution versus external TMS. Mass spectra were run either on a HP 5971/A/5890-II GC/MS coupling (HP 1 capillary column, length 25 m, diameter 0.2 mm, 0.33 μm poly(dimethylsiloxane)) or on a Kratos Profile mass spectrometer equipped with a solid probe inlet. Infrared spectra were obtained in Nujol mulls on a Perkin-Elmer 883 spectrometer. Melting points were determined using a Buechi apparatus by Dr. Tottoli and are uncorrected. Elemental analyses were carried out on a Hanau Vario Elementar EL apparatus. Aminoundecamethylcyclohexasilane (5). Method a. Thoroughly dried NH3 gas was slowly passed through a solution of 4.0 g (10.8 mmol) of 1 in 150 mL of pentane at room temperature for approximately 1 h, and the mixture was subsequently stirred for an additional 1 h until complete conversion was achieved (reaction monitored by GC/MS). Filtration of the salts and removal of the solvent under vacuum gave 3.8 g of white crystals, from which 3.5 g (92%) of pure 5 could be obtained by recrystallization from pentane at -70 C. Method b. To a solution of 0.46 g of Na in 20 mL of dry NH3 was slowly added 7.38 g (20.0 mmol) of 1 dissolved in 100 mL of pentane at -60 C. The obtained two-phase mixture was stirred for another 30 min at -60 C. After the mixture was warmed to room temperature and excess NH3 was evaporated, the salts were filtered and the solvent was stripped off under vacuum. From the resulting solid residue 6.0 g (86%) of pure 5 could be recovered after recrystallization from pentane at -70 C. Method c. A 0.30 g portion (7.7 mmol) of solid NaNH2 was suspended in a solution of 2.60 g (7.0 mmol) of 1 in 20 mL of toluene. After the mixture was stirred for 48 h at room temperature, complete conversion was usually achieved (reaction monitored by 29Si NMR). Filtration of the salts and removal of the solvent under vacuum gave 2.4 g of white crystals, from which 2.2 g (89%) of pure 5 could be obtained after recrystallization from pentane at -70 C. Mp: 150 C dec. Anal. Found: C, 37.53; H, 9.56; N, 3.91. Calcd for C11H35NSi6: C, 37.76; H, 9.73; N, 4.00. IR (Nujol mull): ν(N-H) 3453 (w), 3376 cm-1 (m). 29Si NMR (C6D6, external TMS; ppm): -15.26 (SiRingMeNH2); -42.27, -42.57, -44.11 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.361 (s, 3H), 0.248 (s, 6H), 0.245 (s, 3H), 0.241 (s, 6H), 0.221 (s, 3H), 0.217 (s, 6H), 0.210 (s, 6H) (SiRingCH3); -0.13 (b, 2H) (NH2). 13C NMR (C6D6, ext.ernal TMS; ppm): -0.49 (H2NSiRingCH3); -5.88, -5.92, -5.94, -6.02, -6.18, -6.40 (SiRing(CH3)2). HRMS: m/e calcd for [C11H34NSi6]•þ (Mþ - H) 348.129 97, found 348.130 70. 1,3-Diaminodecamethylcyclohexasilane (6). Method a. The procedure followed was that used for 5 with 1.9 g (4.9 mmol) of 2 in 200 mL of pentane. Yield: 1.7 g (99%) of a colorless solid (isomeric mixture of cis- and trans-6). Due to the presence of (18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518. (19) Carberry, E.; West, R. J. Am. Chem. Soc. 1969, 91, 5440.

Stueger et al. NH4Cl traces the obtained product was unstable upon storage even at -30 C in hydrocarbon solution and decomposed within weeks to give complex polysilazane mixtures. Method b. The procedure followed was that used for 5 with 0.37 g (16.26 mmol) of Na, 20 mL of NH3, and 3.15 g (8.1 mmol) of 2 in 80 mL of pentane. Recrystallization of the crude product from pentane at -70 C afforded 2.1 g (74%) of a white and waxy solid (isomeric mixture of cis- and trans-6), which could be stored without any noticeable decomposition. cis- and trans-6 cannot be separated by crystallization. Mp: 140 C dec. IR (Nujol mull): ν(N-H) 3450 (w), 3380 cm-1 (m). 29Si NMR (C6D6, external TMS; ppm): -14.70, -15.57 (SiRingMeNH2); -43.06, -43.21, -44.13, -44.27, -45.82, -46.30 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.358, (s), 0.380 (s); 0.275 (s), 0.271 (s), 0.257 (s), 0.238 (s), 0.229 (s), 0.227 (s), 0.218 (s), 0.199 (s), 0.184 (s) (33H, SiRingCH3); -0.1 (b, 4H) (NH2). 13C NMR (C6D6, external TMS, ppm): -0.46/-1.02 (H2NSiRingCH3); -5.68, -6.02, -6.05, -6.23, -6.32, -6.41, -6.46, -6.68, -6.70, -7.24 (SiRing(CH3)2). HRMS: m/e calcd for [C10H34N2Si6]•þ (Mþ) 350.133 77, found 350.133 20. 1,4-Diaminodecamethylcyclohexasilane (7). The procedure followed was that used for 5 (method b) with 0.38 g (16.6 mmol) of Na, 25 mL of NH3, and 3.22 g (8.3 mmol) of 3 in 80 mL of pentane. Recrystallization of the crude product from pentane at -70 C afforded 2.2 g (77%) of white crystalline trans-7. Mp: 140 C dec. IR (Nujol mull): ν(N-H) 3454 (w), 3378 cm-1 (m). 29Si NMR (C6D6, external TMS; ppm): -15.17 (SiRingMeNH2); -44.61 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.387 (s, 6H), 0.240 (s, 12H); 0.236 (s, 12H) (SiRingCH3); -0.12 (b, 4H) (NH2). 13C NMR (C6D6, external TMS; ppm): -0.53 (H2NSiRingCH3); -6.18, -6.51 (SiRing(CH3)2). HRMS: m/e calcd for [C10H34N2Si6]•þ (Mþ) 350.133 77, found 350.130 86. 1,3,5-Triaminononamethylcyclohexasilane (8). Method a. A solution of 2.22 g (5.4 mmol) of 4 in 50 mL of pentane was quickly added to 50 mL of thoroughly dried liquid NH3 at -60 C. The mixture was subsequently warmed to room temperature with stirring. Filtration of the salts, removal of the solvent under vacuum, and recrystallization of the crude product from pentane at -70 C gave 1.7 g (91%) of a white and waxy solid (isomeric mixture of cis- and trans-8). Due to the presence of NH4Cl traces the obtained product was unstable upon storage even at -30 C in hydrocarbon solution and decomposed within weeks to give complex polysilazane mixtures. Method b. The procedure followed was that used for 5 with 0.22 g (9.6 mmol) of Na, 40 mL of NH3, and 1.34 g (3.3 mmol) of 4 in 120 mL of pentane. Recrystallization of the crude product from pentane at -70 C afforded 0.9 g (78%) of a white and waxy solid (isomeric mixture of cis- and trans-8), which could be stored at room temperature without any noticeable decomposition. Mp: 120 C dec. IR (Nujol mull): ν(N-H) 3442 (w), 3382 cm-1 (m). 29Si NMR (C6D6, external TMS; ppm): -14.33, -15.31, -16.10 (SiRingMeNH2); -45.87, -46.38, -46.69 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.409 (s), 0.380 (s), 0.374 (s), 0.292 (s), 0.275 (s), 0.254 (s), 0.225 (s), 0.212 (s), 0.171 (s) (27H, SiRingCH3); -0.01 (b, 6H, NH2). 13C NMR (C6D6, external TMS; ppm): -0.26, -0.97, -1.47 (H2NSiRingCH3); -6.12, -6.39, -6.48, -6.90, -7.24, -7.52 (SiRing(CH3)2). 1,2,2,3,3,4,5,5,6,6-Decamethyl-7-azahexasilanorbornane (9). The procedure followed was that used for 5 (method a) with 2.04 g (5.2 mmol) of 3 in 80 mL of pentane. After removal of the solvent under vacuum 1.8 g of a colorless oil was obtained, from which 0.6 g (34%) of pure 9 could be isolated by sublimation at 50 C (0.03 mbar) and subsequent recrystallization of the resulting crystalline solid from pentane at -70 C. Mp: 171-173 C. IR (Nujol mull): ν(N-H) 3372 (w) cm-1 (m). 29 Si NMR (C6D6, external TMS; ppm): -9.48 (SiRingMeNH);

Article -44.46 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.476 (s, 6H), 0.317 (s, 12H); 0.263 (s, 12H) (SiRingCH3); -0.82 (b, 1H) (NH). 13C NMR (C6D6, external TMS; ppm): -4.87 (HNSiRingCH3); -5.69, -6.79 (SiRing(CH3)2). HRMS: m/e calcd for [C10H31NSi6]•þ (Mþ) 333.107 22, found 333.108 63. Bis(undecamethylcyclohexasilanyl)amine (10). To a solution of 2.10 g of 5 in 30 mL of diethyl ether was slowly added 4.0 mL (6.0 mmol) of a 1.5 M cyclohexane solution of n-BuLi at 0 C. After the mixture was warmed to room temperature and stirred for 1 h, 2.22 g (6.0 mmol) of 1 dissolved in 50 mL of THF was added to the resulting colorless solution of lithium (undecamethylcyclohexasilanyl)amide. Subsequently the mixture was heated at reflux for 36 h. After aqueous workup with saturated NH4Cl and extraction with pentane the combined organic layers were dried over Na2SO4. Removal of the solvent under vacuum gave 4.04 g of a pale yellow solid, from which 2.67 g (65%) of pure crystalline 10 could be isolated by repeated crystallization from boiling acetone. Mp: 161-162 C. Anal. Found: C, 38.59; H, 9.77; N, 1.95. Calcd for C22H67NSi12: C, 38.70; H, 9.89; N, 2.05. IR (Nujol mull): ν(N-H) 3357 (w). 29Si NMR (C6D6, external TMS; ppm): -10.63 (SiRingMeNH); -42.47, -42.52, -43.34 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.549 (s, 6H), 0.337 (s, 12H), 0.293 (s, 12H), 0.271 (s, 12H), 0.236 (s, 6H), 0.229 (s, 6H), 0.215 (s, 12H) (SiRingCH3); -0.54 (b, 1H) (NH). 13C NMR (C6D6, external TMS; ppm): -0.36 (HNSiRingCH3); -5.50, -5.74, -5.78, -6.10, -6.37 (SiRing(CH3)2). HRMS: m/e calcd for [C22H67NSi12]•þ (Mþ) 681.250 50, found 681.252 91. N-Trimethylsilylaminoundecamethylcyclohexasilane (11). To a solution of 1.22 g (3.5 mmol) of 5 in 20 mL of diethyl ether was slowly added 2.3 mL (3.5 mmol) of a 1.5 M cyclohexane solution of n-BuLi at 0 C. After the mixture was warmed to room temperature and stirred for 1 h, the resulting colorless solution of lithium (undecamethylcyclohexasilanyl)amide was transferred to an addition funnel and slowly added to 0.38 g (3.5 mmol) of Me3SiCl dissolved in 50 mL of diethyl ether. After the mixture was stirred overnight at room temperature, the solvents were removed under vacuum and replaced by 50 mL of pentane. Filtration of the salts and evaporation of the solvent afforded 1.4 g of a yellow oil, from which 0.64 g (44%) of pure 11 could be isolated by Kugelrohr distillation as a colorless oil. Bp: 140 C (0.03 mbar) (Kugelrohr). IR (Nujol mull): ν(N-H) 3370 (m). 29Si NMR (C6D6, external TMS; ppm): 3.86 (SiMe3); -14.33 (SiRingMeNH); -42.48, -42.54, -43.63 (SiRingMe2). 1H NMR (C6D6, external TMS; ppm, relative intensity): 0.459 (s, 3H), 0.263 (s, 6H), 0.230 (s, 12H), 0.216 (s, 3H), 0.209 (s, 3H), 0.196 (s, 6H), 0.122 (s, 9H) (SiRingCH3); -0.28 (b, 1H) (NH). 13C NMR (C6D6, external TMS; ppm): 3.00 (Si(CH3)3); -0.88 (HNSiRingCH3); -5.72, -5.73, -5.78, -6.12, -6.30 (SiRing(CH3)2). HRMS: m/e calcd for [C14H34NSi7]•þ (Mþ) 421.178 05, found 421.176 54. 1,5-Dihydrodecamethylpentasilane (12). To a solution of 3.40 g (9.7 mmol) of 5 in 20 mL of toluene was added 0.40 g (10.3 mmol) of solid NaNH2. After it was stirred overnight at room temperature, the mixture was filtered and worked up by addition to aqueous saturated NH4Cl solution. After extraction with pentane the combined organic layers were dried over Na2SO4. Removal of the solvent under vacuum gave 3.0 g of a pale yellow liquid, from which 1.6 g (57%) of pure 12 could be isolated after distillation at 0.04 mbar over a 10 cm Vigreux column. Bp: 49 - 50 C (0.04 mbar). 29Si NMR (C6D6, external TMS; ppm): -36.59 (SiMe2H); -41.26, -43.66 (SiMe2). 1H NMR

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(C6D6, external TMS; ppm, relative intensity): 4.084 (hep, J(H-H) = 4.6 Hz, 2H); 0.258 (s, 12H), 0.230 (s, 6H) (Si(CH3)2); 0.191 (d, 2J(H-H) = 4.6 Hz, 12H) (HSi(CH3)2). MS (m/e (relative intensity)): 292 (5.5%, Mþ). 1,5-Dichlorodecamethylpentasilane (13). A 1.00 g (7.5 mmol) portion of N-chlorosuccinimide was added to a solution of 1.0 g of 12 in 20 mL of THF. After the mixture was stirred overnight at room temperature, the solvent was removed under vacuum and replaced by 10 mL of CCl4. Filtration of precipitated succinimide and evaporation of the solvent afforded 1.2 g (93%) of spectroscopically pure 13. 29 Si NMR (C6D6, external TMS; ppm): 25.79; -41.46; -41.88 consistent with literature.20 Rechlorination of (Si6Me9N1.5H1.5)n. A 0.3 g portion of crystalline 8 was stored at room temperature under inert gas for 8 weeks. To the opaque mass thus obtained were added 5 mL of acetyl chloride and 0.5 mL of water at 0 C. After the mixture was stirred overnight at room temperature, the volatile components were stripped off carefully under vacuum. Addition of 5 mL of ether, filtration of insoluble acetyl amide, and evaporation of the solvent afforded a white solid residue, which was identified as spectroscopically pure 4 by 1H and 29Si NMR.11b X-ray Crystallography. Suitable crystals of 9 were grown by cooling a pentane solution to -70 C. For X-ray structure analysis the crystal was mounted onto the tip of a glass fiber at -50 C, and data collection was performed with a BRUKER-AXS SMART APEX CCD diffractometer using graphite-monochromated Mo KR radiation (0.710 73 A˚). Details of the crystal data and structure refinement are provided as Supporting Information. The data were reduced to Fo2 and corrected for absorption effects with SAINT and SADABS.21 The structures were solved by direct methods and refined by full-matrix least-squares methods (SHELXL97).22 All nonhydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were calculated to correspond to standard bond lengths and angles. Crystallographic data (excluding structure factors) for the structure of compound 9 reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication no. CCDC-752563. Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax (internat.) þ44-1223/336-033; e-mail deposit@ccdc. cam.ac.uk). 2

Acknowledgment. We thank the FWF (Wien, Austria) for financial support within the Forschungsschwerpunkt “Novel Approaches to the Formation and Reactivity of Compounds containing Silicon-Silicon Bonds” and Wacker Chemie GmbH (Burghausen, Germany) for the donation of silane precursors. Supporting Information Available: CIF file giving crystallographic data for compound 9. This material is available free of charge via the Internet at http://pubs.acs.org. (20) Stansilawski, D. A.; West, R. J. Organomet. Chem. 1981, 204, 307. (21) (a) SAINTPLUS: Software Reference Manual, Version 6.45; Bruker-AXS: Madison, WI, 1997-2003. (b) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. SADABS: Version 2.1; Bruker AXS, Madison, WI, 1998 (22) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.