Poly(trifluoromethanesulfonatosilyl)methanes - Precursors to Polysilylmethanes Sebastian Bommers, Hubert Schmidbaur* Anorganisch-Chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-80747 Garching Z. Naturforsch. 49b, 337-339 (1994); received December 14, 1993 Poly(silyl)methanes, Silanes, Trifluoromethanesulfonates A new and efficient synthetic route to di- and tri(silyl)methane is presented. Starting from bis- and tris(phenylsilyl)methane, bis- and tris(trifluoromethanesulfonatosilyl)methane can be obtained by Si-Ph cleavage with equivalent quantities of trifluoromethanesulfonic acid (tri­ flic acid). Their reduction with lithium aluminium hydride yields di- and tri(silyl)methane. Substitution of the previously employed liquid anhydrous hydrogen bromide by triflic acid thus offers an experimentally more simple alternative with shorter reaction times and high selectivity.

Introduction Results Due to the growing interest in highly silylated Bis- and tris(phenylsilyl)methane are readily methane derivatives (H 3Si)„H4_„C, n = 2,3,4, as available from standard chemicals [4-6]. Treat­ feedstock gases for chemical vapour deposition of ment of these two precursors with “triflic acid” silicon carbon alloys [1-3] there is presently con­ CF3S020H leads to selective cleavage of the siderable effort to improve the synthetical path­ S i-P h bonds. At 0 °C (see Experimental) the reac­ ways to these compounds. To date the most fa­ tion time for quantitative conversion is less than vourable route to di-, tri- and tetrasilylmethane is one hour (eq. (1, 2)). a three step synthesis via poly(arylsilyl)methanes (aryl = phenyl or /?-tolyl) and poly(bromosilyl)- CH2(SiH2Ph)2+2C F 3SO,OH —► (1) methanes [4-6], For the cleavage of the aryl 2C6H6+CH2(SiH20S 0 2CF3)2 groups from poly(arylsilyl)methanes treatment CH(SiH2Ph)3 + 3C F3SOX>H —► (2) with an excess of anhydrous liquid hydrogen bro­ 3 C6H6+CH(SiH20S 0 2CF3)3 mide at —78 °C in the absence of solvent is required in this process. To avoid Si-C cleavage in the re­ Bis(trifluoromethanesulfonatosilyl)methane, as sulting halosilanes, their reduction with lithium al­ well as tris(trifluoromethanesulfonatosilyl)methane, uminium hydride has to be carried out in a two are colourless liquids, which fume in air and can­ phase system employing a phase-transfer catalyst not be destilled without decomposition. However, and with long reaction times of up to 96 hours at spectroscopic data of the crude products are in ac­ ambient temperature. As an alternative the “pro- cordance with the proposed formulae (see Experi­ todesilylation” [7-10] of bis- and tris(phenylsilyl)- mental). methane using trifluoromethanesulfonic acid (triflic Upon storage at room temperature, both com­ acid) has now been introduced to replace the te­ pounds slowly undergo isomerisation and decom­ dious hydrogen bromide procedure for which the position. As derived from 'H NMR and 29Si NMR handling and disposal of large amounts of HBr gas spectroscopic results, inter- and intramolecular are indispensable. H/0S02CF3 exchange lead to compounds with -SiH (0S02CF3)2 and -SiH 3 fragments. Although * Reprint requests to Prof. Dr. H. Schmidbaur. the isomerisations do not necessarily affect the yield of the following reduction step, the rear­ Verlag der Zeitschrift für Naturforschung, D-72072 Tübingen ranged tris- and especially tetrakis(trifluoro- 0932-0776/94/0300-0337/$ 01.00/0 methanesulfonatosilyl)methane compounds un-

Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. 338 S. Bommers-H. Schmidbaur • Poly(trifluoromethanesulfonatosilyl)methanes dergo Si-C-cleavage reaction more readily, thus solvent was added. After 10 min the mixture was leading to silyltriflate SiH3(OSO,CF3), which gives allowed to warm to room temperature, and the rise to the formation of inflamable silane gas in the benzene formed in the reaction was removed under final step of the process. reduced pressure. The yield was almost quantita­ Only if the final conversion of bis- and tive. — 'H NM R (100 MHz, C6D6): S = 4.5 ppm (t, SiH,), '/(HSi) = 254 Hz, V(HSiCH) = 3.3 Hz; S = tris(trifluoromethanesulfonatosilyl)methane into 0.07 ppm (qui, CH,), V(HCSiH) = 3.3 Hz. - ,3C di- and trisilylmethane through the reduction with {’H} NM R (100.53 MHz, CDC13): S = 116.7 ppm lithium aluminium hydride is carried out imme­ (q, CF3), '/(C F) = 317 Hz; ö = 3.8 ppm CH,. - diately after the “protodesilylation”, the yields ob­ 29Si NM R (79.43 MHz, CDC13): Ö = -3.54 ppm tained are around 80%. Under standard reaction (t*t*t, SiH-,), '/(SiH ) = 254 Hz, 2/(SiCH ) - 9.9 conditions with common solvents the reaction Hz, V(SiCSiH) - 4.1 Hz. time will not exceed 4 hours for completion (eq. Tris(trifluoromethanesulfonatosilyl)methane: To (3, 4)). a solution of 2.6 g (8 mmol) tris(phenylsilyl)- CH2(SiH20S 0 2CF3)2 + LiAlH4 CH2(SiH3)2 (3) methane in 10 ml of toluene, 2.1 ml (24 mmol) of CH(SiH2OSO,CF3)3+LiAlH4 CH(SiH3)3 ~ (4) triflic acid was added at -20 °C. After 10 min the mixture was allowed to warm to room tempera­ In the reaction of tetrakis(/?-tolysilyl)methane ture and stirred for 1 h at room temperature. The with four equivalents of triflic acid the rearrange­ whole mixture was used in the following reduction ments preceding the decomposition mentioned step without any further purification. The yield above are even more rapid. Even at reaction tem­ was quantitative. - 'H NMR (100 MHz, C6D6): ö peratures as low as -78 °C only decomposition - 4.71 ppm (d, SiH,), '/(H Si) = 265 Hz, products are obtained. The reduction of the reac­ V(HSiCH) = 2.4 Hz; Ö = -0.5 ppm (sept, CH), V(HCSiH) = 2.4 Hz. - ,3C NMR (100.53 MHz, tion mixture with lithium aluminium hydride does C6D6): S = 118.8 ppm (q, CF3), ’/(C F ) = 318 Hz; not afford tetrasilylmethane. Large amounts of S = -4.47 ppm (d*sept, CH), '/(CH) = 107 Hz, gaseous self-inflamable silanes are generated. V(CSiH) = 9.7 Hz. - 29Si NMR (79.43 MHz, In summary, the synthetic route to C6D6): S = -7.44 ppm (t*d*qui, SiH2), '/(SiH) = poly(silyl)methanes via the corresponding silyltri- 265 Hz, 2./(SiCH) = 10.2 Hz, 3/(SiCSiH) = 4.3 Hz. flates offers significant advantages over the pre­ viously applied silylhalides. Experimental difficul­ Disilylmethane and trisilylmethane — general ties associated with working with large amounts of procedure: To a suspension of lithium aluminium hydride in 1.2-dimethoxyethane (glyme), the fresh­ liquid hydrogen bromide etc. can be avoided, and ly prepared silyltriflate dissolved in a small the reaction time required for the cleavage of the amount of glyme is added dropwise at 0 °C. The phenyl groups and for reduction can be reduced resulting mixture is stirred under reflux conditions from several days to only several hours. This ap­ for 4 h. Under reduced pressure the product is plies to both CH2(SiH3)2 and CH(SiH3)3. However passed through a condenser cooled to -25 °C or C(SiH3)4 is not obtained in appreciable yield owing 10 C, respectively, and received in a Schlenk tube to extensive C-Si cleavage by hydride in the last kept at liquid nitrogen temperature. step of the process. Disilylmethane: 4.56 g (20 mmol) of bis(phenylsilyl)methane, 3.51 ml (40 mmol) of triflic acid, and 0.46 g (12 mmol) of lithium alu­ Experimental minium hydride yield 1.21 g of the product (80%) All experiments were carried out under pure dry b.p. 15 °C. - 'H NM R (100 MHz, C6D6): Ö = 3.6 nitrogen. Glassware and solvents were purified, ppm (t, SiH,), '/(HSi) = 197.8 Hz, 3/(HSiCH) = dried and kept under nitrogen. C6D6 and CDC13 4.6 Hz; Ö = -0.60 ppm (sept, CH2). - 29Si-NMR was used as solvents for NMR spectroscopy, and (79.4 MHz, C6D6): = -60.0 ppm (q*t*q), SiH„ tetramethylsilane as the reference compound '/(SiH) = 200.4 Hz, 2/(SiCH) = 9.5 Hz, (JEOL GX 270, GX 400 and Bruker WT 100 SY V(SiCSiH) = 4.5 Hz. spectrometers). Trisilylmethane: 2.6 g (8 mmol) of Bis (trifluoromethanesulfonatosilyl) methane: To tris(phenylsilyl)methane, 2.1 ml of triflic acid, and 4.56 g (20 mmol) of bis(phenylsilyl)methane 3,51 0.27 g (7.2 mmol) of lithium aluminium hydride ml (40 mmol) trifiic acid was added at 0 °C. No gave 0.63 g of the product (74%). - 'H NMR (100 S. Bommers-H.Schmidbaur • Poly(trifluoromethanesulfonatosilyl)methanes ______339

MHz, C6D6): ö = -1.17 ppm (dez, CH); ö = 3.71 This work has been supported by Bundesmini- ppm (d, SiH3), !7(HSi) = 204 Hz, V(HSiCH) = 4.4 sterium für Forschung und Technologie, Bonn, Hz. - 29Si-NMR (79.4 MHz, C6C6): ö = -59.3 and by Fonds der Chemischen Industrie, Frank- ppm (q*d*sept), '/(SiH) = 202.2 Hz, 2/(SiCH) = furt. 9.2 Hz, 3/(SiCSiH) = 4.6 Hz.

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