Defining Self-Assembling Linear Oligo(dioxaborole)s

A route to self-assembling linear oligo(dioxaborole)s and detailed characterization using Fourier transform infrared and 1 H NMR spectroscopies compared to small molecule analogues is described. The oligomer formed through the reaction between benzene-1,4-diboronic acid and 1,2,4,5-tetrahydroxybenzene is linked via covalent yet reversible cyclic boronate esters. Comparison of the spectral data for this oligomer compared to bis(dioxaborole) (diester) and anhydride containing model compounds forms a basis on which to derive information about bonding outcomes for larger polymeric systems from small molecule analogues. From this analysis, it is clear that caution must be exercised when evaluating the spectroscopic signatures related to certain boronate containing species because they are not always obvious and are highly dependent on molecular structure and environmental factors such as solvent. X-ray diffraction data along with 11 B NMR and molecular modeling confirmed the planarity of the bis(dioxaborole)s and provided adequate information to propose a supramolecular π-stacking orientation for the oligomeric compounds. Careful interpretation of information obtained about small molecule boronate esters in the structural analysis of macromolecular structures creates a foundation for developing and analyzing self-assembling polymers and covalent organic frameworks on the basis of this assembly motif.