Syntheses, characterisation and crystal structures of ferrocenyl β-diketones and their Schiff base N-N-O ligand derivatives with 2-picolylamine

Ferrocenyl beta-cliketones compounds beta 3-4 were synthesised by Claisen condensation reaction between acetylferrocene and ethyl benzoate or 4-bromoethyl benzoate. We also synthesised four new Schiff base ligands L1-4 by condensation reaction between beta 1-4 and 2-picolylamine. Identities of all these compounds were confirmed by satisfactory elemental analysis, H-1 nuclear magnetic resonance (NMR) correlation and infrared (IR) spectroscopy. In addition, all these compounds were authenticated by a single crystal X-ray diffraction analysis. In solution, H-1 NMR spectra of beta 3 and beta 4 exhibit a mixture of keto:enol tautomer ratios of 12:88 and 8:92, respectively, calculated by the integration of the free cyclopentadienyl ring. In contrast, the proton NMR spectra of L1-4 showed only the keto-enamine tautomer displacements. In addition, decoupled C-13 NMR spectrum clearly confirmed the existence of these tautomers. These results are in accordance with X-ray crystallographic studies, in which the enol and keto-enamine forms were elucidated for beta-diketones and Schiff base ligands, respectively. (C) 2016 Published by Elsevier B.V.