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The decomposition of 1,1-dimethyl-1-silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time-of-flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1-dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si-CH3 bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C-C bond and a ring Si-C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C-C bond is dominant over that of propene via an initial cleavage of a ring Si-C bond. When the collision-free condition is voided, secondary reactions in the gas-phase produce various methyl-substituted 1,3-disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3-tetramethyl-1,3-disilacyclobutane originated from the dimerization of 1,1-dimethylsilene. Copyright

Complexation of paramagnetic intermediates formed in the photolysis of 7,7-dimethyl-1,4,5,6-tetraphenyl-2,3-benzo-7-silanorbornadiene with n-donors (PPh3, O2) was studied by spin chemistry methods.

Silaethenes 1 and the isomeric methylsilylenes 2 are separately existing species, but can readily be interconverted in an argon matrix via a photochemically induced 1,2-H shift.In case of the thermal excitation in the gas phase examples for both directions have been dedected spectroscopically: the isomerisation of a silaolefin into the corresponding silylene (1d -> 2d) and the formation of a silene from a silylene (2f -> 1f).

Attempts to measure the kinetics of gas-phase insertion reactions of dimethylsilylene, generated by photolysis of dodecamethylcyclohexasilane, are described.Insertion of dimethylsilylene into silicon-hydrogen bonds was the main reaction with trimethylsilane, pentamethyldisilane, and sym-tetramethyldisilane; in all cases the activation energy for insertion was zero, and the rate constants were in the ratio of 1:3.1:4.3.Dimethylsilylene also inserted cleanly into hydrogen chloride with an activation energy of 28 kJ mol-1.Photochemical reactions with methylchlorosilanes were much more complex, involving little or no silylene chemistry; such reactions as did occur appeared to proceed almost entirely by radical mechanisms.