Expanding the Scope of Palladium-Catalyzed B–N Cross-Coupling Chemistry in Carboranes
Xin Mu, Morgan Hopp, Rafal M. Dziedzic, Mary A. Waddington, Arnold L. Rheingold, Ellen M. Sletten, Jonathan C. Axtell, Alexander M. Spokoyny
Abstract
Over the past several years, a number of strategies for the functionalization of dicarba-closo-dodecaboranes (carboranes) have emerged. Despite these developments, B–N bond formation on the carborane scaffold remains a challenge due to the propensity of strong nucleophiles to partially deboronate the parent closo-carborane cluster into the corresponding nido form. Here we show that azide, sulfonamide, cyanate, and phosphoramidate nucleophiles can be straightforwardly cross-coupled onto the B(9) vertices of the o- and m-carborane core from readily accessible precursors without significant deboronation byproducts, laying the groundwork for further study into the utility and properties of these new B-aminated carborane species. We further showcase the select reactivity of the installed functional groups, highlighting some unique features stemming from the combination of the electron-donating B(9) position and the large steric profile of the B-connected carborane substituent.