Improved syntheses of bis(ethynyl)-para-carboranes, 1,12-(RCtriple bond; length of mdashC)2-1,12-C2B10H10 and 1,10-(RCtriple bond; length of mdashC)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-(ClCHdouble bond; length as m-dashCH)2-1,12-C2B10H10 and 1,10-(ClCHdouble bond; length as m-dashCH)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-(RCtriple bond; length of mdashC)2-1,12-C2B10H10 and 1,10-(RCtriple bond; length of mdashC)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.