The Reactivity of Stable Donor Adducts

Investigations of the reactivity of stable silylene complexes are still at an early stage of development. The reactions known so far, however, are of interest, since most of them are model cases which have important mechanistic implications. 

An oxygen transfer from HMPA-O to silicon, which is known from the reduction of phosphine oxides with chlorosilanes, is not observed. On the contrary, the liberated HMPA can be recovered quantitatively (eq. 17, 18). 

Recently, a variety of silylenes were generated and characterized by matrix isolation techniques. The observed loose donor adducts between silylenes and the matrix molecules (THF, CO) are only stable at very low temperatures. Melting of the matrix induces polymerization of the silylenes which proceeds through disilenes. However, 0- Si transfer reactions do not occur only in the case of 1-methyl-THF has an insertion of the silylene into the C —O bond been observed [155-158], 

The photolysis of 4 in the presence of 2,3-dimethylbutadiene yields 3,4-dimethyl-l-silacyclobut(3)enes 47a,b as the reaction product of a formal [4 + 1] cyclo- 

At this stage of the discussion it is obvious that stable donor adducts of silylene complexes show a modified silylene reactivity and can thus be considered as model compounds for otherwise inaccessible reactive intermediates. 

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