Improved syntheses of bis(ethynyl)-para-carboranes, 1,12-(RCC)2-1,12-C2B10H10 and 1,10-(RCC)2-1,10-C2B8H8 (R = H or Me3Si)

Copper-mediated cross-coupling reactions of the 12-vertex and 10-vertex para carboranes, 1,12-C₂B₁₀H₁₂ and 1,10-C₂B₈H₁₀, with trans-1-iodo-2-chloroethene gave the bis(trans-2-chloroethenyl) carboranes, 1,12-(ClCHCH)₂-1,12-C₂B₁₀H₁₀ and 1,10-(ClCHCH)₂-1,10-C₂B₈H₈, respectively, in good yield. The molecular structures of both compounds were determined by X-ray crystallography, verifying the trans disposition of the chloride and carboranyl substituents across the double bonds. These vinyl carboranes can be converted to bis(ethynyl) carboranes, 1,12-(RCC)₂-1,12-C₂B₁₀H₁₀ and 1,10-(RCC)₂-1,10-C₂B₈H₈ (R = H or Me₃Si), easily, and in high yields. These findings provide the most convenient routes to bis(ethynyl) carboranes from the commercially available carboranes, 1,12-C₂B₁₀H₁₂ and 1,10-C₂B₈H₁₀ reported to date.