Trifluoromethylboranes and ‐Borates: New Synthetic Strategies and Applications

The synthesis of salts with the [B(CF 3 ) 4 ] − anion has been the starting point for new developments in the field of trifluoromethylboron chemistry. In contrast to the previous syntheses of (CF 3 ) n B derivatives (n=1–3), achieved exclusively by CF 3 transfer, the synthesis of the [B(CF 3 ) 4 ] − anion was accomplished by fluorination of the [B(CN) 4 ] − anion with ClF or ClF 3 in anhydrous HF. Owing to its thermal and chemical stability, [B(CF 3 ) 4 ] − is an attractive weakly coordinating anion. However, in concentrated sulfuric acid one of the four CF 3 groups is solvolyzed to a CO ligand to yield the neutral borane carbonyl (CF 3 ) 3 BCO. It has been shown that the borane carbonyl compound is a versatile synthetic building block, and numerous reactions have been investigated. The addition of nucleophiles to the C atom of the CO ligand is favored, and examples for new derivatives are the anions [(CF 3 ) 3 BCPnic] − (Pnic=N, P, As). Under certain conditions, ligand‐exchange reactions are also observed, for example, the formation of (CF 3 ) 3 BNCH. Finally, the borane carbonyl compound is a component of the conjugated Brønsted–Lewis superacid HF/(CF 3 ) 3 BCO.