Synthesis of {CB11} Monocarborane Sulfonamides by B2-Selective Rhodium-Catalyzed B−H Activation

The synthesis of monocarborane sulfonamides is reported. The methodology relies on coupling of the anionic {CB₁₁} boron cluster to sulfonyl azides. Under rhodium catalysis and with the assistance of a pyridine or pyrimidine directing group at the C1 position, the cluster undergoes B−H activation. Conditions have been identified that lead to B2-selective mono-sulfonamidation with concomitant loss of N₂. The protocol requires no additional ligand, oxidant or base and enables B−N bond formation with various monocarborane and sulfonyl azide inputs. The new products possess the structure 1-(heteroaryl)-2-(NHSO₂Ar)−CB₁₁H₁₀]⁻ and have been fully characterized by NMR spectroscopy and mass spectrometry. In addition, three solid state structures confirm the particular B2 substitution pattern. Furthermore, the stoichiometric reaction of the pyridinyl monocarborane precursor with Rh(III) affords a cyclometalated complex with a direct B−Rh bond that has also been characterized by X-ray crystallography.