Hybrid Lewis acid/hydrogen-bond donor receptor for fluoride.

[reaction: see text] To verify if hydrogen-bond donor groups can assist fluoride binding at the boron center of triaryl boranes, o-(dimesitylboryl)trifluoroacetanilide has been synthesized. Reaction of this new borane with [n-Bu(4)N][F] in acetone affords the corresponding fluoroborate complex whose stability constant exceeds that of [Mes(3)BF](-) by at least 2 orders of magnitude. Presumably, the higher fluoride affinity of o-(dimesitylboryl)trifluoroacetanilide results from the cooperativity of the Lewis acidic boron center and the hydrogen-bond donor trifluoroacetamide group.