Silanones transient species

Photolysis of 2,3-disiloxetanes 72 liberates the corresponding silene 73 and silanone 74 in a retro-[2 + 2] reaction52. The transient species are trapped by ethanol to give 75 and 76. In the absence of traps the silene undergoes a 1,3-hydrogen shift to give 77. Ene reaction of the initially formed intermediates, or cleavage of the 1,3-disiloxetane 78 yields the silyl ether 79 (equation 17). 

It is well known that thermal decomposition of allyl-substituted silanes proceeds by retro-ene reaction with formation of transient species having a Si=C bond, such as silaben-zene, silatoluene and dimethylsilaethylene4b e. The kinetic data on the gas-phase pyrolysis of a similar allyloxysilane derivative, (l,l-dimethylallyloxy)dimethylsilane (16), and the results on thermolysis of allyloxydimethylsilane (17) in a flow system both indicate the participation of an intermediate silanone, (CH3)2Si=0 (10), as shown in Scheme 523. 

In the previous reviews,1 la,d f syntheses of many examples of transient silicon-oxygen double bond compounds such as MeHSi=0, Me2Si=0, H2Si=0 (2), (H0)HSi=0 (silanoic acid), and (H0)2Si=0 (silicic acid) have been described, and they are reportedly isolated as stable species in the low temperature matrices. However, the stabilization of this extremely reactive double bond species is very difficult, and no stable example of silanone (RR/Si=0) has been isolated until now even by the methods of thermodynamic or kinetic stabilization. 

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