Synthesis and structure determination of a novel diastereomeric diaminodichlorodisilane

Inorganic Chemistry Communications 3 Ž2000. 428–432 www.elsevier.nlrlocaterinoche

Synthesis and structure determination of a novel diastereomeric diaminodichlorodisilane ) Uwe Bohme , Betty Gunther, Ben Rittmeister ¨ ¨ Technische UniÕersitat ¨ Bergakademie Freiberg, Institut f ur ¨ Anorganische Chemie, Leipziger Straße 29, D-09596 Freiberg, Germany Received 24 May 2000

Abstract Different aromatic diorganoamines were tested for their reactivity with 1,1,2,2-tetrachlorodimethyldisilane Ž1.. Indole reacts easily with 1, tetrakisŽindolyl.-1,2-dimethyldisilane Ž2. was isolated. The reaction of N-methylaniline with 1 yields ŽMePhN. 2 MeSi– SiMeŽ N MePh.Cl Ž3. and ClŽMePhN.MeSi–SiMeŽ N MePh.Cl Ž4. depending on the proportions of the starting materials. The crystal structure of 4 shows that the compound crystallizes as separated pure enantiomeric crystals. The value of optical rotation was estimated. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Amides; Silanes; Disilanes; Aminosilanes

1. Introduction The partial substitution of chloride ions in organosilanes by protecting groups has been used very recently for obtaining derivatives not accessible to straightforward synthesis. Different dialkylamides have been used as protecting groups w1–3x. A number of silyl diethylamido derivatives have been prepared, but it is often not possible to separate pure compounds from the mixture of liquid products w1,2x. Until now, there are no X-ray structures of aminochloroalkyloligosilanes available. Structural data are essential for obtaining information about the silicon–sili-

) Corresponding author. Tel.: q49 3731 39 2108; fax: q49 3731 39 4058. .. E-mail address: [email protected] ŽU. Bohme ¨

con bonds and stereochemical aspects and to generate starting geometries for molecular mechanics calculations. We intend to develop force field parameters for oligosilanes. These parameters should be applicable to a variety of organosilanes, thus we need X-ray structural data of oligosilanes with different substituents like chloride, alkyland amido-groups. Only one related structure of a dipyridyl adduct of 1,1,2,2-tetrachlorodimethyldisilane has been reported w4x. Seven aminoorganodisilanes with the structure unit CŽN.Si–SiŽN.C are registered in the Cambridge Crystallographic Database w5–10x. Since there are not enough suitable X-ray structures available we want to synthesise crystalline aminochloromethyldisilanes. Because of their chemical reactivity aminochloroalkyloligosilanes are synthetic building blocks, very useful for the preparation of a-olefin polymerization catalysts and stable silylenes, as potential precursors for the deposition

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U. Bohme et al.r Inorganic Chemistry Communications 3 (2000) 428–432 ¨

of silicon nitride by CVD processes, and as substrates for lithiation which allows a number of subsequent reactions w11–21x. Here, we report about the synthesis of crystalline aminochloromethyldisilanes.

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yldisilane Ž4.. Both products were characterized by 1 H, 13 C, 29 Si NMR, GCrMS analysis and melting point.

2. Results and discussion A number of different aromatic diorganoamines were tested for their reactivity with 1,1,2,2-tetrachlorodimethyldisilane Ž1.. The large flat aromatic groups should help to obtain crystalline products. Only indole and N-methylaniline are well reactive and the obtained products are well soluble in aprotic organic solvents. The results obtained with these two amines will be presented here. Cl 2 MeSi– SiMeCl 2 Ž1. reacts readily with two molar equivalents of indole. Triethylamine was used as the supporting base to bind the hydrogen chloride formed during the reaction. The voluminous precipitate of Et 3 NHCl was removed by filtration. An oily product was obtained after evaporation of the solvent. Characterization by NMR spectroscopy shows 9 signals for silicon bound methyl groups between 0.83 and 1.27 ppm in the 1 H and 9 signals for spectroscopically inequivalent silicon atoms in the 29 Si NMR. The 13 C NMR spectrum shows 9 signals for silicon bound methyl groups and for each signal of the indenyl carbon atoms. These data point to the fact that at least four different substitution products were formed, probably all products from monoindolyl-, bisindolyl-, trisindolyl- to tetrakisindolyldimethyldisilane including stereoisomers. We were not able to separate the different reaction products by recrystallization. Because of these problems we can conclude that indole is not suitable for the preparation of defined crystalline aminochloromethyldisilanes. The reaction of Cl 2 MeSi–SiMeCl 2 Ž1. with indole in molar ratio 1:5 leads to a single product, as shown by 29 Si NMR spectroscopy. The intensity ratio of the aromatic protons between 6.6 and 7.6 ppm and the methyl protons at 1.13 ppm reveals the formation of tetrakisŽindolyl.-1,2dimethyldisilane Ž2.. This fact is further supported by elemental analysis and the lack of chloride in the sample. The reaction of 1,1,2,2-tetrachlorodimethyldisilane with N-methylaniline proceeds more easily. It is possible to obtain at one’s discretion aminochloromethyldisilanes with one and two remaining chlorine atoms by changing the proportions of the starting materials. The reaction of 1 and N-methylaniline in molar ratio 1:4 in pentane afforded chlorotrisŽ N-methylanilino.-1,2-dimethyldisilane Ž3. in moderate yield. Attempts to synthesize the tetrakisŽ Nmethylanilino.-1,2-dimethyldisilane by using a large excess of N-methylaniline Ž1:5 or 1:6. were unsuccessful, 3 was isolated instead. The reaction of one mol equivalent Cl 2 MeSi–SiMeCl 2 Ž1. with two equivalents N-methylaniline gave 1,2-dichloro-1,2-bisŽ N-methylanilino.dimeth-

The 1 H and 13 C NMR spectra of 3 exhibit three signals for the N-methyl groups. The 1 H-NMR signal of the enantiomeric aminochloromethyl group is observed at 2.91 ppm. The two signals for the diastereotopic methyl groups of the SiMeŽ N MePh. 2 unit are found at 2.52 and 2.57 ppm. The 29 Si NMR resonance of the chlorine-substituted silicon atom appears at a characteristically lower field Ž6.27 ppm. than the signal of the diamino substituted silicon atom Žy7.94 ppm.. The NMR spectra of 4 indicate that a diastereomeric product was formed. There are two sets of signals, one for the meso- and the other one for the R, R- and S,S-isomer in intensity ratio 1:6. The 1 H and 13 C NMR resonances of the silicon bound methyl groups of the meso form are shifted a little bit to higher field compared to the signals of the enantiomers. The value of optical rotation was estimated from one crystal with w a x l s 3778. The melting point of 4 is at 388C. This low melting point means that handling the crystals is problematic. Nevertheless, we were able to obtain single crystals of the product suitable for X-ray structure analysis.

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Compound 4 crystallizes in two different enantiomorphs. The structure of one crystalline modification was determined. It crystallizes in the noncentrosymmetric space group C222 1. Only the half molecule, ClSiŽ N MePh.Me, is found in the asymmetric unit, so that the unit cell contains only four molecules. The second part of the molecule is generated by symmetry elements. Three times more reflections were collected than normally necessary for an orthorhombic space group in order to determine the absolute configuration through the anomalous scattering effect. Refinement of the Flack enantiopole parameter led to a value of ca. zero thus confirming the absolute structure of the crystal w22x. The molecular structure of 4 is shown in Fig. 1. The silicon atom has an R-configuration. The fact that both silicon atoms have the same configuration means that, in the crystal under examination, the molecules have an R, R-configuration. There are a number of chiral silicon compounds reported in the literature w23– 26x. Diastereomers have been mainly prepared with one chiral silicon atom and one chiral organic group such as the Ž-.menthoxy group. Only one diastereomeric dichlorodisilane with two chiral silicon atoms was found in the Cambridge Crystallographic Database w27x. The silicon atom in 4 is tetrahedral coordinated with bond angles between 103.1 and 111.98. The molecule has a staggered conformation with a torsion angle of y84.98 along ClŽ1a. –SiŽ1a. –SiŽ1. –ClŽ1.. The silicon–silicon bond ˚ which is normal for a tetracoordinated length is 2.341 A,

organodisilane. The phenyl groups in 4 are directed away from each other. No intramolecular p – p-interactions were found. 3. Conclusion Indole is not suitable to obtain defined crystalline aminochloromethyldisilanes. In contrast to that it is possible to synthesize well defined and crystalline aminochloromethyldisilanes by use of N-methylaniline. The Nmethylphenylamido substituents should be useful as protecting groups. It should be possible to perform reactions at the remaining Si–Cl bond and to cleave the Si–N bonds in a subsequent reaction. The chemistry of nucleophilic substitutions at 3 and 4 is under investigation. 4. Experimental All preparative work and handling of the samples was carried out under Ar using dry glassware and dry solvents. Pentane was freshly distilled from LiAlH 4 . Triethylamine was refluxed over sodiumrbenzophenone until the colour of the solution was violet, then freshly distilled prior to use. Commercially available N-methylaniline and indole were used as supplied. 1,1,2,2-tetrachlorodimethyldisilane Ž1. was prepared according to a well-known procedure w28x. Melting points were recorded in capillary tubes and are uncorrected. NMR spectra were recorded on a Bruker DPX 400. Elemental analyses were performed on a CHNO-RAPID ŽHeraeus.. Mass spectra were obtained on a Hewlett-Packard MS, Series 5971. 4.1. Reaction of indole with 1,1,2,2-tetrachlorodimethyldisilane

Fig. 1. Molecular Structure of 1,2-dichloro-1,2-bisŽ N-methylanilino.di˚x methyldisilane Ž4. with 50% thermal ellipsoids. Selected bond lengths wA and angles wdegx: SiŽ1. –NŽ1. 1.718Ž2., SiŽ1. –CŽ1. 1.845Ž3., SiŽ1. –ClŽ1. 2.097Ž1., SiŽ1. –SiŽ1a. 2.341Ž1., NŽ1. –SiŽ1. –CŽ1. 110.5Ž1., NŽ1. –SiŽ1. – ClŽ1. 111.88Ž8., CŽ1. –SiŽ1. –ClŽ1. 103.12Ž9., NŽ1. –SiŽ1. –SiŽ1a. 109.34Ž6., CŽ1. –SiŽ1. –SiŽ1a. 117.4Ž1., ClŽ1. –SiŽ1. –SiŽ1a. 104.41Ž4., CŽ1a. –SiŽ1a. –Si1–C1 141.9, ClŽ1a. –SiŽ1a. –SiŽ1. –ClŽ1. y84.9.

Indole Ž17.2 g, 147 mmol. was added as solid to a solution of 1,1,2,2-tetrachlorodimethyldisilane Ž16.3 g, 70 mmol. in 250 mL triethylamine. The reaction mixture was stirred at reflux temperature for 9 h. The precipitate formed during this time Žconsisting of Et 3 NHCl. was removed by filtration. The volume of the filtrate was reduced in a vacuum to ca. 80 mL. Ether Ž50 mL. was added and the solution was left overnight at 58C. A white precipitate formed. This consisted mainly of Et 3 NHCl. The precipitate was removed by filtration and the filtrate was further concentrated in vacuum to yield the reaction product as pale yellow oil Ž18.3 g, 67% yield calculated on basis of Žindolyl. 2 Si 2 Me 2 Cl 2 .. 1 H NMR Ž400 MHz, CDCl 3 . d s 0.83–1.27 Ž9 signals, MeSi., 6.71–7.66 Žm, indolyl.. 29 Si NMR Ž80 MHz, CDCl 3 . d s 21.0, 19.4 ŽCl 2 SiMe., 3.0, 2.2, 0.7, 0.1 ŽClSiŽMe.indolyl., y10.8, y11.8, y12.6 ŽMeSiŽindolyl. 2 .. The reaction of indole with 1 in molar ratio 2:1 in presence of stoichiometric amounts of triethylamine in pentane as solvent gave the same mixture of products.

U. Bohme et al.r Inorganic Chemistry Communications 3 (2000) 428–432 ¨

4.2. Synthesis of tetrakis(indolyl)-1,2-dimethyldisilane (2) For the synthesis of compound 2, the same method was used as described above using 6.2 g Ž27 mmol. of 1,1,2,2tetrachlorodimethyldisilane, 15.8 g Ž135 mmol. indole and 100 mL triethylamine. The crude product contains traces of indole and was recrystallized from a pentanerdichloromethane Ž3:1. mixture. White powder 8.7 g Ž58.5% yield., mp 1198C. C 34 H 30 N4 Si 2 Ž550.8.: calcd. C 74.1, H 5.49, N 10.17; found: C 73.9, 5.42, 10.19. 1 H NMR Ž400 MHz, CDCl 3 . d s 1.13 Žs, SiMe., 6.63, 6.81, 6.92, 7.10, 7.61, 7.63 Žm, indolyl.. 13 C NMR Ž100 MHz, CDCl 3 . d s 0.6 ŽSiMe., 108.1, 112.9, 121.1, 121.3, 122.8, 129.0, 131.8, 140.0 Žindolyl.. 29 Si NMR Ž80 MHz, CDCl 3 . d s y10.8. 4.3. Synthesis of (MePhN)2 MeSi–SiMe(NMePh)Cl (3) Triethylamine Ž16.7 mL, 12.1 g, 120 mmol. was added to a solution of 1,1,2,2-tetrachlorodimethyldisilane Ž5.47 g, 24 mmol. in 150 mL pentane. N-methylaniline Ž13 mL, 12.8 g, 120 mmol. was mixed with 60 mL pentane and added dropwise over a period of 1 h to the reaction mixture. The reaction mixture became warm and a voluminous white precipitate was formed. The solution was stirred at room temperature for 10 h and then the precipitate consisting of Et 3 NHCl was removed by filtration. The volume of the filtrate was reduced in a vacuum to ca. 100 mL and left overnight at 58C. A white precipitate formed. This consisted mainly of Et 3 NHCl. The precipitate was removed by filtration and the filtrate was concentrated to give 7.6 g Ž72% yield. 3 as a white crystalline product with mp 76.08C. 1 H NMR Ž400 MHz, CDCl 3 . d s 0.33 Žs, 3H, SiMe., 0.72 Žs, 3H, SiMe., 2.52 Žs, 3H, N Me., 2.57 Žs, 3H, N Me., 2.91 Žs, 3H, N Me., 6.72–7.27 Žm, 18H, Ph.. 13 C NMR Ž100 MHz, CDCl 3 . d s 1.47, 4.71 ŽSiMe.; 30.72, 34.50, 36.50 Ž N Me.; 112.41, 117.09, 117.25, 118.67, 119.51, 120.06, 120.87, 121.07, 121.54, 128.57, 128.64, 128.83, 149.57, 149.66, 149.79 ŽPh.. 29 Si NMR Ž80 MHz, CDCl 3 . d s y7.94 ŽSiMeŽ N MePh. 2 ., 6.27 ŽSiMeŽ N MePh.Cl., 1 JSiSi s 152 Hz. MS m r z 439 ŽMq. , 255 Ž100%, SiŽ N MePh. 2 Meq. , 226 ŽPhSiŽ N MePh.Meq. , 184 ŽClSiŽ N MePh.Meq. .

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d s 3.08 ŽSiMe, meso., 3.57 ŽSiMe, rac., 36.43 Ž N Me, rac., 37.86 Ž N Me, meso., 120.95, 122.19, 123.01, 123.10, 128.83, 129.0, 148.99, 149.18 ŽPh.. 29 Si NMR Ž80 MHz, CDCl 3 . d s 3.66 Žrac., 1.37 Žmeso.. MS m r z 368 ŽMq. , 262 ŽMq–N MePh., 184 Ž98%, Mq–N MePh–HCl., 149 Ž100%, SiŽ N MePh.Meq. . 4.5. X-ray crystal structure determination of 4 A suitable single crystal of 4 was mounted on glass fiber under paraffin oil and transferred to the diffractometer. Diffraction measurements were made on an Enraf– Nonius CAD-4 diffractometer at y1018C using graphite˚ . with monochromated Mo–K a radiation Ž l s 0.71073 A v –2 u scans. Empirical formula C 16 H 22 Cl 2 N2 Si 2 , M s ˚ bs 369.44, 0.7 = 0.3 = 0.3 mm, a s 9.273Ž2. A, ˚ c s 13.322Ž3. A, ˚ V s 1864.1Ž7. A˚ 3, rcalc s 15.090Ž3. A, 1.316 g cmy3 , m s 0.475 mmy1 , Z s 4, orthorhombic, space group C222 1 ŽNo. 20., theta range for data collection 2.58 to 27.98 deg., limiting indices y12 F h F 12, y19 F k F 19, y17 F l F 9, 6984 reflections collected, 2256 unique Ž RŽint. s 0.0535., 102 parameters, goodness-of-fit on F 2 s 1.006, final R indices w I ) 2 s Ž I .x R1 s 0.0376, wR2 s 0.0656, R indices Žall data. R1 s 0.0648, wR2 s 0.0723, absolute structure parameter y0.08Ž9., largest dif˚ y3 . The ference peak and hole 0.245 and y0.206 e A structure was solved by direct methods and refined by full-matrix least-squares on F 2 with anisotropic thermal parameters. Hydrogen atoms were calculated and allowed to ride on their corresponding carbon atoms. 5. Supplementary material X-ray structural data for 4, including a summary of crystallographic parameters, atomic coordinates, bond lengths and angles, and thermal parameters. The data have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-116146. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK ŽFax: q44-1223r336-033; e-mail: deposit@ ccdc.cam.ac.uk..

4.4. Synthesis of Cl(MePhN)MeSi–SiMe(NMePh)Cl (4) Acknowledgements For the synthesis of compound 4, the same approach was used as described for 3 using 6.0 g Ž26 mmol. of 1,1,2,2-tetrachlorodimethyldisilane, 14 mL Ž10.1g, 100 mmol. triethylamine and 5.7 mL Ž5.6 g, 52 mmol. Nmethylaniline. The crude product contains traces of 3 and was recrystallized from a pentanerether Ž5:1. mixture. Ivory coloured crystals 6.4 g Ž67% yield., mp 388C, w a x l s 3778 Ž0.165g r 100 mL n-pentane, 208C, 302 nm.. 1 H NMR Ž400 MHz, CDCl 3 . d s 0.51 Žs, SiMe, meso., 0.77 Žs, SiMe, rac., 2.67 Žs, N Me, rac., 3.0 Žs, N Me, meso., 6.83-7.23 Žm, Ph.. 13 C NMR Ž100 MHz, CDCl 3 .

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