1,1-Organoboration, of alkynes

Quite a number of l-silacyclopent-2-ene derivatives have been obtained by Wrackmeyer and co-workers by the consecutive 1,2-hydroboration and intramolecular 1,1-organoboration of alkyn-l-yl(vinyl)silanes. For all compounds obtained the one- and two-bond C-Si couplings have been measured and for some of them DFT calculations have been performed reasonably good agreement has been observed between the computed and experimental data. 

One of the most versatile routes to siloles, germoles, stannoles, and eventually to plumboles of type 194, allowing for a great variety of substituents in all positions, is provided by 1,1-organoboration of the respective alkyn-l-ylmetal compounds <1995CCR125, 2006HAC188>. The sequence of reactions involved does not fit into the concept of bond formations (Sections 3.17.8.1-3.17.8.3) outlined so far and therefore it is dealt with separately. 

There is an alternative method for the preparation of organoborates which involves the reaction of triorganoborohydrides with alkenes or alkynes. The reaction with alkenes gives addition products (Eq. 5), whereas that with alkynes provides substitution products (Eq. 6). As 1-alkynyltrialkylborates are readily prepared by the reaction of trialkylboranes with lithium acetylides, the complexation reaction seems to be most convenient for producing tetracoordinate organoborates. 

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