Dehalogenation triple bond

In recent years, several attempts have been made to prepare the first disilynes, compounds having Si-Si triple bonds,791 792 until Sekiguchi et al. in 2004 succeeded in the isolation and full characterization of the first member of this compound class.793 West et al. have studied the dehalogenation of 2,6-Mes2C6H3SiF3 761 with sodium, which has afforded the bis(silafluorene) derivative 762, whose formation may be rationalized in terms of two intramolecular insertion reactions of a bis(silylenoid) 763 into two C(.r/>z)-C(.r/>3) bonds (Scheme 99). 794... 

Fluorinated alkynes are usually prepared from the corresponding alkenes, but a twofold didechlorination of the corresponding alkane has also been applied. Alkynes bearing a fluorine atom on the triple bond are extremely reactive and hence special precautions have to be taken in their preparation under ordinary conditions, this fluorine atom is lost to afford a non-halogenated triple bond. Perfluoroalkynes with an internal triple bond can even be prepared using zinc. Examples of dehalogenations of fluorinated compounds to provide fluoroalkynes are listed in Table 3. 

The inversion in selectivity between the insertion into an H—Si bond favored by the intermediate in the dehalogenation and the addition to a triple bond favored by the intermediate formed upon silirane pyrolysis suggests that different reactive intermediates are formed. Since free silylene is implicated in the silirane pyrolysis, the lithium-induced deiodination probably involves a silylenoid such as a complex of the silylene with Lil or with THF. For a further discussion of this possibility, see Section II.E. 

The main reaction paths for the electroreductive cleavage of the carbon-halogen bond lead to total or partial dehalogenated products with the formation of C-H and/or single, double and triple C-C bonds according to the prevailing coupling or elimination reactions. 

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