Pentafluoroethylaluminates: A Combined Synthetic, Spectroscopic, and Structural Study

Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2 F5 )4 ]- were obtained from AlCl3 and LiC2 F5 . They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2 F5 )4 ]- ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3 ) under formation of [(C2 F5 )4-n AlFn ]- (n=1-4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2 F5 )AlF3 ]- ion was structurally characterized.

Innovative Syntheses of Cyano(fluoro)borates: Catalytic Cyanation, Electrochemical and Electrophilic Fluorination

Different types of high-yield, easily scalable syntheses for cyano(fluoro)borates Kt[BFn (CN)4-n ] (n=0-2) (Kt=cation), which are versatile building blocks for materials applications and chemical synthesis, have been developed. Tetrafluoroborates react with trimethylsilyl cyanide in the presence of metal-free Brønsted or Lewis acid catalysts under unprecedentedly mild conditions to give tricyanofluoroborates or tetracyanoborates. Analogously, pentafluoroethyltrifluoroborates are converted into pentafluoroethyltricyanoborates. Boron trifluoride etherate, alkali metal salts, and trimethylsilyl cyanide selectively yield dicyanodifluoroborates or tricyanofluoroborates. Fluorination of cyanohydridoborates is the third reaction type that includes direct fluorination with, for example, elemental fluorine, stepwise halogenation/fluorination reactions, and electrochemical fluorination (ECF) according to the Simons process. In addition, fluorination of [BH(CN)2 {OC(O)Et}]- to result in [BF(CN)2 {OC(O)Et}]- is described.

Protonation versus Oxonium Salt Formation: Basicity and Stability Tuning of Cyanoborate Anions

Anhydrous H[BH₂ (CN)₂ ] crystallizes from acidic aqueous solutions of the dicyanodihydridoborate anion. The formation of H[BH₂ (CN)₂ ] is surprising as the protonation of nitriles requires strongly acidic and anhydrous conditions but it can be rationalized based on theoretical data. In contrast, [BX(CN)₃ ]^- (X=H, F) gives the expected oxonium salts (H₃ O)[BX(CN)₃ ] while (H₃ O)[BF₂ (CN)₂ ]/H[BF₂ (CN)₂ ] is unstable. H[BH₂ (CN)₂ ] forms chains via N-H⋅⋅⋅N bonds in the solid state and melts at 54 °C. Solutions of H[BH₂ (CN)₂ ] in the room-temperature ionic liquid [EMIm][BH₂ (CN)₂ ] contain the [(NC)H₂ BCN-H⋅⋅⋅NCBH₂ (CN)]^- anion and are unusually stable, which enabled the study of selected spectroscopic and physical properties. [(NC)H₂ BCN-H⋅⋅⋅NCBH₂ (CN)]^- slowly gives H₂ and [(NC)H₂ BCN-BH(CN)₂ ]^- . The latter compound is a source of the free Lewis acid BH(CN)₂ , as shown by the generation of [BHF(CN)₂ ]^- and BH(CN)₂ ⋅py.