Robert T. Conlin

Chemical and photochemical approaches to amino(aryl)silylenes

Abstract Generation by two different methods of silylenes stabilized by o -amino(aryl) groups is reported. The halodemetallation of difluoro or dichloro-silanes with Li metal or lithium-naphthalene gave the same product, a stabilized sila-ylide (hypercoordinated silylene). Intramolecular Lewis base stabilization is not sufficient to isolate a monomeric species. The silylenes, however, have been trapped with 2,3-dimethylbutadiene. An unexpected intramolecular rearrangement to silaacenaphthene has been observed in the case of a six-membered ring amino(aryl) coordinated silylene. Photolysis of o -1-[( N , N -dimethylamino)inethyl]-2-[tris(trimethylsilyl)silyl]benzene produced, among other products, Me 3 SiSiMe 3 and the sila-ylide, which has been trapped with Et 3 SiH and dimethylbutadiene. Our mechanistic interpretation is supported by spectral observation of the photochemically generated reaction intermediates in a 3-methylpentane glass at low temperature.

The positions of λmax for some trimethylsilyl-substituted silylenes

Abstract Low-temperature photolysis of tris(trimethylsilyl)silane derivatives in a 3-methylpentane glass at 77 K yields hexamethyldisilane and trimethylsilyl-substituted silylenes. These silylenes exhibit broad n → p absorptions at wavelengths typically >600 nm in the UV and have been captured by 2,3-dimethylbutadiene in cyclohexane at room temperature. Exceptions to the usual position of λ max have been observed and are discussed.

Synthesis and thermal reactions of 3-trimethylsilyl-1-pyrazoline

Abstract The compound 3-trimethylsilyl-1-pyrazoline has been synthesized by addition of diazomethane to vinyltrimethylsilane at room temperature. In contrast, addition of trimethylsilyldiazomethane to ethylene at 55°C yields 1-trimethylsilyl-2-pyrazoline exclusively. The thermal isomerization of 3-trimethylsilyl-1-pyrazoline to 1-trimethylsilyl-2-pyrazoline has been followed kinetically by proton NMR spectroscopy and the reverse reaction has been detected by gas phase pyrolysis. Thermal elimination of nitrogen from either pyrazoline leads to cyclopropyltrimethylsilane, allyltrimethylsilane and E - and Z -1-propenyltrimethylsilane. The relative rates of methylene-H migration to radical centers α and γ to silicon are approximately equal.

Gas phase reactions of 1,1-dimethylsilabutadiene

Abstract Pyrolysis of 1,1-dimethyl-1-siletene at 363°C in a static reaction vessel produces three major products which are formal dimers of the starting material or the reactive isomer, the siladiene. Reactions with ethylene, propene, vinyltrimethylsilane and butadiene have been examined. Mechanisms leading to the Si2C10H20 products are discussed. The influence of temperature and concentration of coreactant on competing reaction pathways is interpreted.

A TRANSIENT SPECTROSCOPIC STUDY OF THE PHOTOCHEMISTRY OF VINYLDISILANES

Abstract The chemistry of the reactive intermediates produced by direct irradiation of pentamethylvinyldisilane ( 1 ), 1,1,2,2-tetramethyl-1,2-divinyldisilane ( 2 ), and 1,1,1,2-tetramethyl-2,2-divinyldisilane ( 3 ) in hydrocarbon solution have been studied by steady state and laser flash photolysis techniques. All three disilanes yield silenes derived from photochemical [1,3]-trimethylsilyl migration as the major product, as has been shown by the products of steady state trapping experiments. Direct irradiation of the three disilanes in 3-methylpentane matrices at 77 K leads to the formation of products with absorption maxima at 270, 270 and 325 nm, respectively, which disappear upon warming and are hence assigned to the silenes. Nanosecond laser flash photolysis of the disilanes in deoxygenated hexane solution at ambient temperatures gives rise to transient species with the same absorption maxima as found in the matrix experiments, and which decay over several tens of microseconds with mixed pseudo-first and second order kinetics. The assignment of these transients to the corresponding silenes is supported by their absolute rate constants for reaction with methanol, t -butanol, acetic acid, acetone, 2,3-dimethyl-1,3-butadiene (DMB), cyclohexene and oxygen, which vary over the range 10 5 –10 8 M −1 s −1 , depending on the reagent and the silene. The transient spectrum and reactivity of one of the silenes have also been examined in acetonitrile solution. The variation in spectroscopic properties and reactivity as a function of structure is discussed, and compared to previously reported data for closely related reactive silenes.

Alkali metal promoted transfer of dimethylsilylene from dodecamethylcyclohexasilane to silanes and dienes

Abstract Addition of sodium/potassium alloy to THF solutions containing dodecamethylcyclohexasilane and a diene or a silane, affords silacyclopentenes and disilanes, respectively.