High Yielding Preparation of Dicarba-<i>closo</i>-dodecaboranes Using a Silver(I) Mediated Dehydrogenative Alkyne-Insertion Reaction

The synthesis of 1,2-dicarba-<i>closo</i>-dodecaboranes (<i>ortho</i>-carboranes) is often low yielding which is a critical issue given the increasing use of boron clusters in material science and medicinal chemistry. To address this barrier, a series of Cu, Ag, and Au salts were screened to identify compounds that would enhance the yields of <i>ortho</i>-caboranes produced when treating alkynes with B₁₀H₁₂(CH₃CN)₂. Using a variety of functionalized ligands including mono- and polyfunctional internal and terminal alkynes, significant increases in yield were observed when AgNO₃ was used in catalytic amounts. AgNO₃ appears to prevent unwanted reduction/hydroboration of the alkyne prior to carborane formation, and the process is compatible with aryl, halo, hydroxy, nitrile, carbamate, and carbonyl functionalized alkynes