Silylcarbenes formation

A diazosilene is probably also involved in the photochemical or copper-catalyzed decomposition of bis(diazoacetate) 156 in benzene (equation 36). In both cases, dia-zoketene 157 was the only identified product72. Its formation was explained by the silylcarbene-to-acylsilene-to-silylketene sequence outlined in Scheme 5. Efforts to achieve the N2 extrusion from the remaining diazo function by thermolysis in boiling toluene or by prolonged photolysis resulted only in unspecific decomposition. 

The photolysis of silyldiazoalkanes, species which are much stabler than their all-carbon analogs, leads to the formation of silylcarbenes. The subsequent behavior of the silyl-carbenes depends greatly on the nature of the groups attached to the diazo-carbon atom, as well as to the silicon atom. Early results have been reviewed2. In Scheme 43 several representative reactions are listed. 

The photochemical reactions that the silyldiazoalkanes undergo involve silylcarbene chemistry. In line with reactions described for the more conventional carbenes, a variety of processes are common to both types. Thus irradiation brings about 1,2-alkyl shifts, for example, when 515 is photolysed in alcohols to afford a carbene, which transforms into a silene. Four products 516-519 are obtained in good yield. The formation of 519... 

The complex reaction sequence shown in equation 34 might provide some rationalization. The formation of the silylcarbene 141 is suggested, based on experimental results from related reactions , but there is no evidence for the formation of 141 nor for a silylene intermediate. Thus, the transformation 137 142 might proceed via a dyotropic rearrangement as well. The facile 1,3-methyl shift in 2-trimethylsilylsilenes which interconverts 142 139 is well known from Wiberg -type silenes . 139 (R = i-Bu) is stable in solution at room temperature over days and isomerizes only slowly to 140 (R = t-Bu) which rapidly dimerizes giving a 1,3-disilacyclobutane . 

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