Cyclotrisilanes thermolysis

Insertion into Si H and Si Si Bonds. Silylenes, generated by thermolysis of cyclotrisilanes, inserted into the Si—Cl or Si—H bonds of monosilane to yield a variety of disilanes, which could be further functionalized. In contrast to carbenes, the insertion of silylenes into C—H bonds has not been observed. However, the insertion into Si—H bonds has been studied extensively. The occurrence of direct insertion has been indicated by formation of nongeminate homocoupling products. ... 

Belzner64 discovered a mild access to an intramolecularly coordinated silylene by the thermolysis of cyclotrisilanes 105 at moderate temperatures (40-60°C). It was furthermore shown73 that cyclotrisilane 105 and silylene... 

Siliranes are also formed by the reaction of the cyclotrisilane [2-(Me2NCH2)C6H4]6Si3 with terminal and strained internal olefins under mild thermal conditions. The products obtained from the thermolysis of the siliranes thus prepared suggest a thermal equilibrium of the silirane with the cyclotrisilane and the corresponding alkene. This observation provides evidence for an equilibrium between the silylene and the cyclotrisilane and, moreover, proves that free silylenes are involved in the silylene transfer reaction48. 

The 1,2,3-azadisiletidine 47 and 1,2,3-azadisiletine 48 are, in a formal sense, the products of a [2+2] cycloaddition reaction between nitriles and disilene (Scheme 20). It can be assumed that the latter is the crucial intermediate formed during the thermolysis of hexasubstituted cyclotrisilane <1995TL8187>. 

Summary New silacyclopropanes were synthesized quantitatively under mild thermal conditions by reaction of olefins with cyclotrisilane (cyclo-(Ar2Si)3, Ar = Me2NCH2QH4) 1, which transfers all of its three silylene subunits to terminal and strained internal olefins. Thermolysis of silacyclopropanes 3a und 3b indicated these compounds to be in a thermal equilibrium with cyclotrisilane 1 and die corresponding olefin. Silaindane 13 was synthesized by reaction of 1 with styrene via initially formed 2-phenyl-1-silacyclopropane 3d. Reaction of 1 with conjugated dienes such as 2,3-dimethyl-l,3-butadiene, 1,3-cyclohexadiene or anthracene resulted in the formation of the expected 1,4-cycloaddition products in high yield. 

Insertion of diarylsilylene (58) into three different silacyclopropenes gave the corresponding 1,2-disilacyclobutenes in quantitative yield (Scheme 21) <94CC1989>. Diarylsilylene (58) was generated in situ by thermolysis of a cyclotrisilane under mild conditions. 

Thermolysis of cyclotrisilane (112) generated an intermediate diarylsilylene, which added to alkynes to give silacyclopropenes in quantitative yield (five examples). This method allows for the preparation of rings with hydrogen at the vinylic carbon (Equation (45)) <93TL654l>. 

In addition, cyclotrisilane derivatives can be subjected to photolysis to generate organylsilylenes. For instance, the photolysis of hexakis-t-butylcyclotrisilane (369) in the presence of substituted acetylenes, e.g. (370) affords 1,1,4,4-tetrakis-t-butyl-2,3,5,6-tetraorganyl-l,4-disilacyclohexa-2,5-diene (371) (equation 167)190. Alternatively, thermolysis of disilanes in the presence of alkynes is a viable route to disilacyclohexane derivatives. Thus, thermolysis of l,2-dimethoxy-l,l,2,2-tetramethyldisilane (338) in the presence of diphenylacetylene (370) in a pressure vessel—via reactive intermediates and,... 

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