Boronic ester functionalised 1,8-diboryl-naphthalene scaffolds: fluoride versus oxide chelation.

1,8-Bis(boronic ester) derivatives of naphthalene, 1,8-C 10 H 6 {B(OR) 2 } 2 , present an attractive target as receptors for the fluoride ion via B-F-B chelation, but are synthetically challenging to access due to the competing formation of a very stable anhydride containing a B-O-B motif. By contrast, unsymmetrical systems of the type 1,8-C 10 H 6 {B(OR) 2 }(BR' 2 ) can be synthesized for (OR) 2 = 1,2-O 2 C 6 H 4 ( i.e. Cat) and R' = Mes. This system is shown to be competent for the uptake of F - , making use of a chelating mode of action and the formation of a bridging B-F-B motif between the two boron centres. However, both experimental and quantum chemical studies indicate that the μ 2 -F adduct is the kinetic product of fluoride uptake, with an alternative structural motif featuring a terminal B-F bond and a B-O-B bridge using one of the catechol oxygens being (marginally) more favourable thermodynamically.