Gem-Diboronic Acids: A Motif for Anion Recognition in Competitive Media

Gem-diboronic acid derivatives have previously been demonstrated to facilitate substrate binding within a metal's secondary coordination sphere, but their use as an anion recognition motif has not been explored. Here, we introduce the gem-diboronic acid motif as a highly effective group for recognition of oxoanions in aqueous solution. Anion receptors based on this motif demonstrate higher binding affinities than other common neutral motifs such as amides and (thio)ureas, and display a unique selectivity profile. Studies with a receptor bearing two gem-diboronic acid groups, receptor 2, indicate that the interaction with anions is highly directional. Despite its simplicity, receptor 2 represents one of the most selective receptors for malonate reported to date.