Schiff Bases from TRIS and ortho-hydroxyarenecarbaldehydes: structures and tautomeric equilibria in the solid state and in solution

Martínez, R. Fernando, Ávalos, Martín, Babiano, Reyes, Cintas, Pedro, Jiménez, José L., Light, Mark E. and Palacios, Juan C. (2011) Schiff Bases from TRIS and ortho-hydroxyarenecarbaldehydes: structures and tautomeric equilibria in the solid state and in solution. European Journal of Organic Chemistry, 2011 (17), 3137-3145. (doi:10.1002/ejoc.201100275).

Abstract

Three Schiff bases generated by conventional condensation of a simple aminopolyol (TRIS) and 5-bromo- and 5-iodosalicylaldehyde, and 2-hydroxy-1-naphthaldehyde, have been fully characterized, both in solution and in the solid state. This study provides a complete analysis of imine–enamine equilibria, and sheds light onto the mechanism of hydrogen transfer, which has been controversial in the literature. Low-temperature X-ray diffraction accompanied by electron-density maps have further been complemented by theoretical studies at the B3LYP/6-31G* and M06-2X/6-311++G** levels. To ascertain the influence of crystal packing on tautomeric stability, the lattice has also been simulated by computation. This protocol involves the assessment of a supramolecular cluster around a core tautomer possessing either imine or enamine structures. Such an analysis, in full agreement with solid-state data, reveals the greater stability of zwitterionic structures for the salicyl derivatives. In contrast, these substances show preferential imine forms in solution, whereas the naphthyl-based compound exhibits a prevalent keto-enamine structure in all cases

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Contributors

Author: Mark E. Light

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