Deuteration of boranes: catalysed versus non-catalysed processes

A dichotomy in the reactivity of B-H bonds is reported. A bis(N-heterocyclic carbene)-ligated iridium(iii) complex can effect rapid deuteration of boronate esters at room temperature with low catalyst loadings; however, borane and 9-BBN both undergo deuteration in the absence of catalyst, and do not react with the iridium complexes. This is proposed to result from the inductive electron-withdrawing properties of the boronic ester substituents. Deuterated boronic esters can be accessed rapidly at room temperature with only very low loadings of iridium catalyst.