Silylenes rearrangement

Rearrangement of a silene to a silylene (40) via migration of a Me3Si group has been suggested as a step in the gas-phase silylene to silylene rearrangement. Labeling experiments, however, have indicated an alternative mechanism (Scheme 14.23). ... 

Tilley reported silene-silylene rearrangement in a cationic iridium complex (Eq. 13) [13b]. 

Summary The matrix-spectroscopic identification and photochemical interconversion of the isomeric silylenes 3-5, and silacyclopropyne (6) are of interest in many ways. For one, their isolation serves to illustrate the potential of matrix isolation spectroscopy. In addition, the structural assignments for these species are based on the comparison of the experimentally observed and calculated IR spectra and therefore emphasize the importance of simultaneously applying quantum chemical calculations and spectroscopic measurements. Moreover, practically no examples exist for this class of silylene rearrangements. Lastly, the C2H2Si isomers eventually play a decisive role in the chemistry of interstellar clouds. 

In contrast, carbene-to-carbene rearrangements are often reversible vinylcarbene-to-cyclopropene interconversions. High temperatures are required for silylene rearrangements because ring-closure via C-H insertion is mildly exothermic and has a significant barrier, higher than that... 

Summary Evaporation of silicon atoms and consecutive cocondensation with a suitable gas in an argon matrix was used to generate silylenes. Their isolation, matrix-spectroscopic investigation and photochemical isomerization demonstrates the potential of matrix isolation spectroscopy and leads further onto the relatively new field of silylene rearrangements. Structural assignments for the observed species are aided by calculated IR spectra and thus are a good example for the combination of quantum chemical calculations and experimental work. Apart from that, many of the described species as well as their carbon analogues are assumed to play an important role in interstellar chemistry. 

Several examples in which a C-H bond of a silylene shifts to yield a silene are mentioned in Section III.B.l.b, which discusses the reverse process of thermal silene-to-silylene rearrangement (see in particular References 75 and 229). 

Although the silene-to-silylene rearrangement would presumably be approximately thermoneutral in most cases, it has so far been only observed for substituents with particularly high migratory aptitudes, H and SiMe3. 

Another report of a silene-to-silylene rearrangement involves a 1,2-shift of a trimethylsilyl group, converting l-(trimethylsilyl)- 1-methylsilene into methyl[(tri-methylsilyl)methyl]silylene (equation 96)207. 

The pyrolysis of a precursor to cyclopropyl(trimethylsilyl)silylene is most easily interpreted by assuming that the silylene undergoes a rearrangement to l-(trimethylsilyl)-I-silacyclobutene which in turn undergoes a silene-to-silylene rearrangement (equation... 

Another case in which a silylene-silene-silylene sequence is believed to occur is shown in equation 98227. Other examples of possible silylene-to-silene-to-silylene rearrangements are known225,226,277. 

We have mentioned in Section III.A.2.b the reverse of the silene-to-silylene rearrangement. In particular, cyclopropylsilylenes are prone to rearrange to 1-silacyclo-butenes207,223,224. 

The Barton laboratory has found many other rearrangments of silylenes including strong evidence for the thermal isomerization of silylenes to silanones (equation 83) . Results were also found that were consistent with silanone-to-silylene " and silylene-to-silanone-to-silylene rearrangements, but alternative mechanisms could be written, e.g. 

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