Icosahedral Meta-Carboranes Containing Exopolyhedral B-Se and B-Te Bonds

Chalcogen-containing carboranes have been known for several decades and possess stable exopolyhedral B(9)-Se and B(9)-Te σ bonds despite the electron-donating ability of the B(9) vertex. While these molecules are known, little has been done to thoroughly evaluate their electrophilic and nucleophilic behavior. Herein, we report an assessment of the electrophilic reactivity of meta -carboranyl selenyl (II), tellurenyl (II), and tellurenyl (IV) chlorides and establish their reactivity pattern with Grignard reagents, alkenes, alkynes, enolates, and electron-rich arenes. These electrophilic reactions afford unique electron-rich B-Y-C (Y = Se, Te) bonding motifs not commonly found before. Furthermore, we show that meta -carboranyl selenolate, and even meta -carboranyl tellurolate, can be competent nucleophiles and participate in nucleophilic aromatic substitution reactions. Arene substitution chemistry is shown to be further extended to electron-rich species via palladium mediated cross-coupling chemistry. Electrophilic and nucleophilic reactivity of selenium- and tellurium-containing meta -carboranes is reported in this study. The newly synthesized compounds feature exopolyhedral B(9)-Se-C and B(9)-Te-C bonding motifs with electron-rich Se and Te sites present in the molecules. All compounds have been thoroughly characterized by heteronuclear NMR spectroscopy with key intermediates structurally characterized by single crystal X-ray diffraction.