REACTIVITY OF DIMETHYLSILYLENE STUDIED BY LASER FLASH-PHOTOLYSIS AT 295-K

The molar absorption coefficient of singlet dimethylsilylene (SiMe2), produced by laser flash photolysis of dodecamethylcyclohexasilane (c-( SiMe2)6) in cyclohexane (CH) at 295 K, was determined to be 3400 M-1 c m-1 at 470 nm. The SiMe2 produced at 295 K undergoes self-quenching di merization to form tetramethyldisilene (Me2Si=SiMe2) with absorption p eaks at 360 and 310 nm, according to second-order kinetics. The recomb ination reaction of SiMe2 occurs in a diffusion-controlled process. Ho wever, in the presence of substrates with lone-pair electrons (N-methy lpyrrolidine (N-Me), pyrrolidine (N-H), 1,4-diazabicyclo[2,2,2]octane (DABCO), tetrahydrofuran (THF), tetrahydrothiophene (THS) and tributyl phosphine (Bu-P)), SiMe2 forms the corresponding complexes which show absorption bands in the region 285-335 nm. The quenching rate constant s for the decay of SiMe2 by heteroatom substrates were found to be clo se to those of diffusion-controlled processes. The reactivity of SiMe, for complex formation was concluded to depend on the steric hindrance around the heteroatom substrates rather than on their ionization pote ntials. It was found that Me2Si=SiMe2 is produced not only by self-rec ombination but also via an SiMe2-THF complex.