Controlled N-Substitution of a B(8)-Ammonium Cobalt Bis-Dicarbollide

Mono-N-8-alkyl and mono-N-8-aryl amide derivatives of the cobalt bis-dicarbollide complex anion [1^-] were synthesized efficiently under mild conditions in acetonitrile using the B(8)ammonium cobalt bis-dicarbollide [3], N,N'-dicyclohexylcarbodiimide, triethylamine, and the corresponding organic acids. The resulting amide intermediates were subsequently converted into monoalkylated and monoarylated ammonium derivatives by reduction with a borane-tetrahydrofuran complex. In contrast, aluminum-based hydride reagents, including lithium aluminum hydride and diisobutylaluminum hydride, were found to be incompatible with this system. In parallel, selective synthetic procedures for the preparation of di- and trimethylated ammonium derivatives of [1^-] were optimized using dimethyl sulfate, a suitable solvent, and a base. All compounds were characterized by nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, mass spectrometry, ultraviolet-visible spectroscopy, thin-layer chromatography, melting point, and elemental analysis, and the structure of the trimethylated derivative was confirmed by single-crystal X-ray diffraction.