An iminoboronate construction set for subcomponent self-assembly

Recently we have demonstrated a series of systems in which complex structures were created from simple amine and aldehyde subcomponents by copper(I)-templated imine bond formation. We describe herein the extension of this subcomponent self-assembly concept to the generation of structures based upon the iminoboronate ester motif. Equimolar amounts of diol, amine, and 2-formylphenylboronic acid reacted by reversible B-O and C=N bond formation to generate iminoboronate esters, as has recently been reported by James et al. (Org. Lett. 2006, 8, 609-612). The extent of ester formation was shown to depend upon a number of factors. The exploration of these factors allowed rules and predictions to be formulated governing the self-assembly process. These rules allowed the construction of more complex structures containing multiple boron atoms, including a trigonal cage containing six boron centers, as well as pointing the way to the construction of yet more intricate architectures. The lability of the B-O and C=N bonds also allowed different diol and amine subcomponents to be substituted within these structures. Selection rules were also determined for these substitution reactions, allowing the products to be predicted based upon the electronic properties of the diols and diamines employed. These results thus demonstrate the generality of the subcomponent self-assembly methodology through its application to a new dynamic covalent system.