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)BC[triple bond]O. 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)BC[triple bond]Pnic](-) (Pnic=N, P, As). Under certain conditions, ligand-exchange reactions are also observed, for example, the formation of (CF(3))(3)BN[triple bond]CH. Finally, the borane carbonyl compound is a component of the conjugated Brønsted-Lewis superacid HF/(CF(3))(3)BCO.