Tetramethylsilane: Substrate for C–H Functionalization

Tetramethylsilane, abbreviated as TMS, has the molecular formula Si(CH₃)₄. In its molecular structure, the silicon atom is covalently bonded to four methyl groups, forming a highly symmetrical tetrahedral structure. It is chemically stable and resistant to oxidation, substitution, and other chemical reactions. Tetramethylsilane is virtually insoluble in water but miscible with most organic solvents. Its primary use is as a standard reference substance in nuclear magnetic resonance (NMR) spectroscopy; its chemical shifts in hydrogen and carbon spectra are uniformly defined as 0 ppm, and it is used to calibrate the chemical shift values of various organic compounds.

Dissociation of tetramethylsilane for the growth of SiC nanocrystals

Atmospheric pressure microplasma has shown impressive capabilities of synthesizing important nanoparticles and nanocrystals (NCs) with unique features and properties. Microplasmas key features allow for the synthesis of ultrasmall nanoparticles and quantum dots with compositions that are most often complementary to low-pressure plasma processes. Scientists have applied this diagnostic method to an atmospheric pressure argon microplasma mixed with tetramethylsilane (TMS) that has been previously used to synthesize ultrasmall silicon carbide (SiC) NCs. The intent of this study is to produce relevant experimental results that could contribute to the understanding of the processes taking place within the microplasma and eventually support a description of the NC nucleation and growth mechanisms. Organosilicon compounds, which contain C–Si bonds, have great significance in the scientific community as they have been used for the synthesis of various materials like SiC, SiN and SiCxNy. Tetramethylsilane is a relatively simple organosilane, widely utilized as a precursor for the synthesis of many of these important materials and is the simplest precursor used in the synthesis of SiC nanoparticles and NCs. SiC/SiCxNy films can potentially be significant for applications demanding thermal and mechanical stability. These films can also be useful as low-cost wear/corrosion resistive coatings compared with diamond. Furthermore, SiC NCs have shown beneficial properties for biological/optoelectronic applications and catalytic applications, including water splitting and water purification. Indeed, the fragmentation of tetramethylsilane is also of wider interest to film deposition and other potential applications of these types of atmospheric pressure-operated microplasmas.[1]

Dissociation of tetramethylsilane in the plasma at atmospheric pressures was investigated by analysing the residual gases formed in the plasma with the help of QMS. This study revealed the dissociation and polymerization of the TMS in the plasma, which are dependent on the concentrations of TMS and applied power. It was found that the consumption of TMS is more effective at low TMS concentrations (280 ppm) compared with their consumptions at high concentrations (3,500 ppm) due to higher available power per TMS molecule. The highest measured tetramethylsilane depletion was only 73% (280 ppm) and therefore full atomization of TMS molecules was not achieved, excluding the possibility of NC nucleation initiated by aggregation of Si and C atoms. The lower relative tetramethylsilane depletion (<15%), but larger absolute TMS consumption and formation of larger polymerization products are observed under conditions with higher TMS concentrations. These observations and our assumptions suggest that the formation mechanism of SiC NCs in the Ar/TMS atmospheric plasma is the polymerization reactions of neutral TMS fragments where the resident time and tetramethylsilane concentration play the main role in determining the size and the size distribution of the NPs. The main difference from low-pressure plasma is the importance of neutral species and the limited contribution of ions.

C–H functionalization of tetramethylsilane employing a borylnitrene

The irradiation of 2-azido-4,4,5,5-tetramethyl-1,3,2-dioxaborol (pinBN3, pin = pinacolato) generates the corresponding borylnitrene that easily inserts into the CH bond of tetramethylsilane. This primary photoproduct, a monoborylated aminoborane, undergoes a subsequent reaction with pinBN3 forming a bisborylated aminoborane.  Established systems can transform alkanes into halides, alcohols and amines using superacids, radicals and radical cations, enzymatic systems, and most successful transition metals. Whereas a lot of work has been done with alkanes, there is not much known about the C–H activation of alkylsilanes. The bonds are also of low reactivity (D(C–H, methane) = 439 kJ mol−1 and D(C–H, neopentane)9 = 417 kJ mol−1 compared to D(C–H, tetramethylsilane) = 415 kJ mol−1) and difficulties arise in seeking to functionalize them. Among the best methods for the direct derivatisation of silanes are TMEDA (N,N,N′,N′-tetramethyldiamine) assisted lithiation and photochlorination. Solutions of pinBN31 (ca. 80 μmol ml−1) in neat tetramethylsilane (for UV spectrum, see ESI†) were irradiated with a low pressure mercury lamp.[2]

References

[1]Haq, A. U., Lucke, P., Benedikt, J., Maguire, P., & Mariotti, D. (2020). Dissociation of tetramethylsilane for the growth of SiC nanocrystals by atmospheric pressure microplasma. Plasma Processes and Polymers, 17(5), 1900243. https://doi.org/10.1002/ppap.201900243

[2]Matthias Müller , &nbsp;Holger F. B., &nbsp;Cäcilia Maichle-Mössmer. (2025). Correction: C–H functionalization of tetramethylsilane employing a borylnitrene. Chemical Communications, 61 12, Page 2588.