Silicon—selenium bonds reactions with

Since genuine [4-1-2] cycloaddition products had previously not been prepared, it was surprising to find that the action of sulfur on 24 resulted in a formal [4-I-1] cycloaddition to furnish the first ftve-membered ring with an endocyclic silicon-silicon double bond 25. The heavier chalcogens selenium and tellurium did not react with 24. However, in the presence of small amounts of triethylphosphane smooth reactions with these elements did occur to furnish two further ftve-membered ring compounds 26, 27, each with an endocyclic silicon-silicon double bond (Eq. 8) [14]. 

Corriu and coworkers found that the reaction of the pentacoordinated functionalized silane 6 (see also Sections II.B.l and II.C.l) with elemental selenium leads to a stable silaneselone 140, which is stabilized by intramolecular coordination of the nitrogen-containing substituent to the doubly-bonded silicon (Scheme 42) . Although the structure of 140 was supported by Si and NMR and MS spectra, including a downfield Si chemical shift (S = -1-29.4) and a high coupling constant with Se (JseSi = 257 Hz), neither the crystallographical structure analysis nor the reactivity of this isolable Si=Se compound has been reported. 

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