Fluorination fluoromethyl silanes

Similarly, a primary — CH2F fluorine adjacent to silicon is shielded by about 50 ppm compared to the respective hydrocarbon, with similar tin or germanium compounds being shielded slightly less. The value of -277 ppm observed for tetrakis(fluoromethyl)silane has the largest chemical shift known for a single carbon-bound fluorine (Scheme 3.40). 

The decrease of thermal stability of (fluoromethyl)silanes in comparison to the non-fluorinated methylsilanes is evident from their decomposition temperature under static conditions. This drops significantly in the series H3CSiH3 (> 340 °C), F3CSiH3, and F2HCSiH3 (> 180 °C) to FH2CSiH3... 

The CO2 laser-induced multiphoton decomposition of silanes, known to be a really homogeneous reaction, was utilized for the chemical vapour deposition of fluorine containing SiC films from the parent (fluoromethyl)silanes [25, 26]. In contrast to work with H3CS1H3, irradiation of (fluoromethyl)silanes with a single unfocused CO2 laser pulse at fluence of S 0.9 Jcm" tuned to absorption bands of either the SiH bending or the CF stretching vibrations results in an explosive reaction. This is accompanied by an intense chemoluminescence when the sample pressure exceeds a certain limit in the range of 0.1-6.7 kPa (Fig. 1). 

Multinuclear NMR data for homologous senes of fluoromethylated malo-nates [72] and trimethylsilanes [97] are compiled in Table 11. In both senes, fluoromethyl attachment is to a quaternary site These compounds are readily synthesized using fluorohalomethanes to incorporate the final fluoromethyl moiety All the malonates, except diethyl methyltnfluoromethylmalonate (4) [93], are isopropyl-substituted diethyl esters [72]. The silane data, with the exception of trimethyltrifluoromethylsilane (5) [95], are from reference 97 Chemical shift data are very comparable, with the malonates having higher proton and fluorine chemical shifts but slightly lower carbon values. The magnitudes of cf and 2J jp coupling are similar for both sets of compounds. 

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