Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes

The study presents (oligo)alkynes capped with main group elements except carbon atoms. The functionalization of many species with a terminal alkyne group proceeds via metalation of the terminal C(sp) carbon. The bis(dialkylboron) acetylenes are prepared by the reaction of dialkylboron iodide with acetylene dimagnesiumdibromide and the resulting alkynes are obtained in moderate yields. A more straightforward synthesis of diborylacetylenes is reported by reacting 2-chloro-1,2,3-benzodioxaborole or the congeners with bis(trimethylstannyl) acetylene. The substitution of the cobaltacarboranes at the 5- and 7-positions by halogen is used to prepare the carbon wired planar octagon. 1,2-dichlorodisilanes with carbon tethers are reacted with bis(bromomagnesium) acetylide to obtain a mixture of cyclic diynes, triynes, and tetraynes and also higher oligomers in low yield.