Derivatization of Undecahalogenated closo-Dodecaborates [B₁₂X₁₁NH₃]^- (X = F-I): Attaching Isocyanate, Amidinium, and...

Halogenated closo-dodecaborates are very robust and versatile weakly coordinating anions for numerous applications. The introduction of additional substituents, e.g., pseudohalides, allows the tuning of their chemical and physical properties. In this report, the synthesis of the isocyanate-substituted closo-dodecaborates [B₁₂X₁₁(NCO)]^2- (X = H, F-I) was investigated. In an attempt to synthesize the undecahalogenated derivatives, a selective and halogen-dependent reaction yielding boron clusters carrying the functional groups amidinium (-NHCHNMe₂) and formamide (-NHC(O)H) was discovered. The halogenated anions were fully characterized by vibrational and NMR spectroscopy, mass spectrometry, and X-ray diffraction. Salts of the formamide-substituted anion [B₁₂X₁₁(NHC(O)H)]^2- are surprisingly thermally stable in the condensed phase. In contrast, collision-induced dissociation in the gas phase reveals that the isolated dianion [B₁₂X₁₁(NHC(O)H)]^2- in the gas phase preferentially loses water, while the protonated form, which was generated from decomposition of the tetraalkylammonium counterion [B₁₂X₁₁(NHC(O)H)H]^-, tends to lose carbon monoxide. Possible reaction mechanisms are discussed.