Octamethyl-1,2-disilacyclobutane

The thermolysis of hexamethylsilirane (315) under inert (argon) atmosphere leads to decomposition into 316 and tetramethylethene (328). 316 reacts with additional 315 and induces ring enlargement to afford octamethyl-l,2,-disilacyclobutane(-disiletane) (329) (equation 149)173. Besides the route as shown in equation 147, the formation of a 1,2-... 

Some of the products of UV irradiation of octamethyl-l,2-disilacyclobutane can be accounted for by postulating initial fragmentation into tetramethyldisilene and tetra-methylethylene, but the evidence is very weak54. 

Octamethyl-l,2-disilacyclobutane (56) reacts with terminal alkynes in refluxing benzene in the presence of (Ph3P)2PdCl2 as catalyst (equation 112) to give high yields of 1,4-disilacyclohexene products. Activated internal alkynes react analogously. 1,3-Butadiene... 

Several workers have studied the photochemistry of silacyclobutanes. In the gas phase, u.v. (185 nm < X < 210 nm) excitation of 1,1-dimethylsilacyclo-butane causes elimination of ethylene and the formation of Me2Si = CH2. This silaolefin, when formed, has an internal energy which is probably in excess of the Si—C 71-bond energy, and it may be that its reactivity is different from that of Me2Si=CH2 generated thermally or in solution. In particular it is possible that its isomerization to Me2HSiCH occurs and this might be an explanation for the substantial amounts of polymer that accompany the ethylene and 1,1,3,3-tetramethyl-l,3-disilacyclobutane as products. Mass spectrometric measurements show that the products from octamethyl-l,2-disilacyclobutane are mainly 2,3-dimethylbut-2-ene and hexamethylsilacyclopropane. The primary photoprocess is probably that shown in equation (8). 

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