Tautomerism and Self-Association in the Solution of New Pinene-Bipyridine and Pinene-Phenanthroline Derivatives.

Atena B Solea,Christophe Allemann,Aurelien Crochet,Vera Deneva,Katharina M Fromm,Liudmil Antonov,Olimpia Mamula,Ivan Cornu

doi:10.3390/molecules25020298

Abstract

Two novel pinene-type ligands have been synthesized and their tautomeric and self-associating behavior studied in solution and in the solid state. The first ligand, an acetylated derivative of 5,6-pinene-bipyridine, displays keto-enol tautomerism in solution. This tautomeric equilibrium was studied by NMR and UV-Vis spectroscopy in various solvents, and the results were compared with the ones obtained through DFT calculations. The second ligand was obtained by an unusual oxidation of the phenanthroline unit of a pinene-phenanthroline derivative. This compound exists as a single tautomer in solution and aggregates both in solution (as observed by NMR) and in the solid state through H-bonding as observed by X-ray structure determination and confirmed by DFT studies.

Highlights

Ligands with an annellated pinene backbone have been used extensively for chiral induction in coordination compounds of d and f metal ions, giving rise to well defined, enantiopure supramolecular structures [1,2,3,4,5]
The tautomerism and self-association of two novel ligands derived from pinene were characterized spectroscopically and corroborated with the theoretical calculations obtained by DFT
The keto-enol tautomerism of Compound 3 was studied by means of DFT calculations, 1 H-NMR, and UV-Vis spectroscopy

Summary

Introduction

Ligands with an annellated pinene backbone have been used extensively for chiral induction in coordination compounds of d and f metal ions, giving rise to well defined, enantiopure supramolecular structures [1,2,3,4,5]. Their ability to control the metal centers’ chirality makes them attractive in the field of supramolecular chemistry [2], and for various applications like enantioselective catalysis or single chiral molecular magnets [6,7,8,9]. Another important class of ligands derived from pinene are the so-called CHIRAGEN (chiral generators) ligands, which have two bridged 5,6- or Molecules 2020, 25, 298; doi:10.3390/molecules25020298 www.mdpi.com/journal/molecules

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Results

Conclusion