Trifluoromethylboranes and -Borates: New Synthetic Strategies and Applications

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Abstract

The synthesis of salts with the [B(CF3)4] anion has been the starting point for new developments in the field of trifluoromethylboron chemistry. In contrast to the previous syntheses of (CF3)nB derivatives (n=1–3), achieved exclusively by CF3 transfer, the synthesis of the [B(CF3)4] anion was accomplished by fluorination of the [B(CN)4] anion with ClF or ClF3 in anhydrous HF. Owing to its thermal and chemical stability, [B(CF3)4] is an attractive weakly coordinating anion. However, in concentrated sulfuric acid one of the four CF3 groups is solvolyzed to a CO ligand to yield the neutral borane carbonyl (CF3)3BC[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 [(CF3)3BC[TRIPLE BOND]Pnic] (Pnic=N, P, As). Under certain conditions, ligand-exchange reactions are also observed, for example, the formation of (CF3)3BN[TRIPLE BOND]CH. Finally, the borane carbonyl compound is a component of the conjugated Brønsted–Lewis superacid HF/(CF3)3BCO.

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