Hydrolytic stability of nitrogenous-heteroaryltrifluoroborates under aqueous conditions at near neutral pH

The hydrolytic stability of heteroaryltrifluoroborates under physiological conditions has been analyzed by 19F NMR spectroscopy and is found to be greatly enhanced by the presence of endocyclic ring nitrogens. Stability is further enhanced by the presence of exocyclic electron withdrawing substituents. As with aryltrifluoroborates, NMR analysis suggests that the hydrolysis proceeds via single rate-determining step reflecting loss of the first fluoride atom. The stability of these complexes is significant both in terms of metal catalyzed cross-coupling reactions as well as the potential for generating boronic acid based 18F-PET imaging agents.