Synthetic, Crystallographic, and Computational Studies of Extensively Hydrogen Bonded Bilayers in Thermally Stable Adamantane Hydroperoxides

The use of molecular iodine as a heterogeneous catalyst for the peroxidation of adamantan-2-one with 30% H2O2 resulted in an unexpected hydroperoxydiadamantyl peroxide and oxahomoadamantan-5-one, in addition to the expected adamantanyl bishydroperoxide. The crystal structures of both the hydroperoxides are reported for the first time. Crystallographic studies revealed that these peroxides are stabilized by extensive intra- and intermolecular hydrogen bonds, which are combined in hydrogen-bonded double layers. These bilayers envelop the hydrophilic interiors consisting of sensitive peroxy groups with the outer surface covered by hydrophobic adamantane groups. The bilayers are held together by weak van der Waals interactions at the layer boundary, which further enhances the thermal stability. Thermal studies demonstrate the remarkable stability of crystalline hydroperoxides at room temperature. A computational study rationalizes the stability of these peroxides. NCI (non-covalent interactions) plots help to decipher the nature of the interaction between the adamantane units as stabilizing dispersion contacts. QTAIM (quantum theory of atoms in molecules) topological analysis also indicates the presence of strong intermolecular hydrogen bonds along with a number of weak dihydrogen contacts.