Easy synthesis of ‘half-units’: their use as ligands or as precursors of non-symmetrical Schiff base complexes

Abstract

This paper is devoted to a particular reaction able to give singly condesed Schiff base derivatives of ß-diketones (called ‘half-units’) in an easy way. Indeed, 1,2-diamino-2-methylpropane, which possesses an amine function sterically hindered by two methyl groups, reacts with a diketone such as 2,4-pentanedione or 2-hydroxyacetophenone only by its non-hindered amine function, yielding a ‘half-unit’. In a following step, this terdentate ligand can react with an aldehyde function to give a non-symmetrical tetradentate Schiff base. Such a reaction can be performed on the free ‘half-unit’ or on its ‘complexed form’. Some examples of nickel and copper complexes are given. A particular interest has been given to the use of imidazole-2-carboxaldehyde which yields non-symmetrical Schiff base complexes with a free nitrogen atom not included in the N 3O coordination site. According to the procedure of ‘complexes as ligands’, it is possible to isolate bimetallic complexes with imidazole bridges. Their genuine identity has been confirmed by NMR (nickel) and also by thermal variation of the magnetic susceptibility (copper).