Photobromination of Si-Methylated Carbosilanes

An increasing degree of bromination decreases the reaction rate increasing the reaction temperature favors the formation of unknown polymers which deposit on the walls of the reaction flask, preventing any further reaction [77]. 

SiMe3 Me2Si SiM 2 Br /SiMe3 Me2Si SIMe2 /SiMe3 MezSi SiMe  

In the photochlorination of l,3,5,7-tetramethyl-l,3,5,7-tetrasilaadamantane both the methyl and methylene groups are chlorinated. However, selective halogenation is possible by means of photobromination [80]. The possibility to form partially brominated Si-adamantanes arises from the results presented in Table 27. Here 0.25 molar solutions of Me Ad in CCl were treated with varying amounts of bromine in mole ratios of Me AdrBr = 1 1, 1 2, 1 4 and 1 8 and irradiated with a high pressure Hg UV source. 

Compounds formed and their % content have been determined by H-NMR spectroscopy 

Reaction II can be very easily controlled by observing the characteristic color of solutions containing low concentrations of bromine. If irradiation is ceased after 50 % of Me Ad has converted, then after distilling off the solvent and removal of unreacted Me Ad by sublimation at 30 °C/10 mm Hg, Me4AdBr2 is separated at 60 °C/10 mm Hg as a white crystalline substance of mp. 114 °C. 

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