Synthesis and structural characterization of highly chlorinated, brominated, iodinated, and methylated carborane anions, 1-H-CB₉X₉^-, 1-NH₂-CB₉X₉^- (X = Cl, Br, I), and 1-H-CB₉(CH₃)₉^-

The highly chlorinated, brominated, and iodinated carborane anions 1-R-CB₉X₉^- (R = H, NH₂; X = Cl, Br, I) were prepared in high yields by treatment of [Me₃NH][1-R-CB₉H₉] with excess ICl, Br₂/triflic acid, and I₂/triflic acid, respectively, in sealed tubes at 180-240 °C. With the aid of a Pd catalyst, B-I bonds could be converted into the B-Me bonds by treatment with excess MeMgBr, which led to the preparation of the permethylated species 1-H-CB₉Me₉^- in good yield. These new anions were fully characterized by ¹H, ¹³C, and ¹¹B NMR, IR, and negative-ion MALDI MS spectroscopy. Some were further characterized by single-crystal X-ray analyses. The weakly coordinating nature of these new anions was probed by ²⁹Si chemical shifts.