Microwave-assisted metal-catalyzed reactions of halogenated carboranes

Palladium-catalyzed Rosenmund-von Braun conditions were applied to iodinated carboranes to prepare the first examples of cyano substituted derivatives of 1-carba-closo-dodecaborate( -1). Optimized microwave-assisted conditions with Pd(PPh₃)₂Cl₂ and copper (I) cyanide formed [12-CB₁₁H₁₁CN]⁻, [7,12-CB₁₁H₁₀(CN)₂]⁻, and [7,8,9,10,11,12-CB₁₁H₆(CN)₆]⁻ with great selectivity; products were purified and isolated as [Et₄N]⁺ salts in up to 81% yield. The compounds were characterized by NMR (¹¹B, ¹H, and ¹³C), LCMS, and IR. Single crystal X-ray diffraction revealed the structure of the [Et₄N][CB₁₁H₁₁CN] cage. Nitriles are known to undergo many organic reactions, and a preliminary investigation of hydrolysis of the cyano substituent revealed that the [12- CB₁₁H₁₁COOH]⁻ cage can be formed. This work also reports improved microwave assisted synthesis of halogenated and alkynylated carboranes along with attempted reactions of these compounds.