N-Salicylideneanilines:  Tautomers for Formation of Hydrogen-Bonded Capsules, Clefts, and Chains

The synthesis, characterization, and solid-state structures of new salicylaldimines are reported. Bis(N-salicylideneaniline)s (BSANs) and tris(N-salicylideneaniline)s (TSANs) are sterically encumbered compounds featuring a central six-membered ring in the keto-enamine tautomer. When extended with additional functional groups, these molecules may form hydrogen-bonded capsules, clefts, and extended structures. A TSAN with N-^tBOC-o-phenylenediamine groups has been structurally investigated. The complementary hydrogen-bonding motif in this molecule leads it to form dimers in solution and in the solid state. A BSAN with N-^tBOC-o-phenylenediamine substituents forms a hydrogen-bonded cleft in solution but forms an extended hydrogen-bonded ladder assembly of cofacial dimers in the solid state. When N-^tBOC-1,8-naphthalenediamine was utilized to extend the cleft, an unusual perimidine structure was obtained with the central core in the enol tautomer. In addition, ab initio calculations have been used to support the assignment of the keto-enamine or enol-imine tautomers of the BSANs and TSANs and to predict tautomerization in related BSANs and TSANs.