Azacrown ethers containing oximic and Schiff base sidearms - Potential heteronuclear metal ion receptors

A simple synthetic pathway for the preparation of oxime-and Schiff base-containing aza-and diazacrown ethers is reported. N-Methoxymethyl-substituted aza-15-crown-5 and aza-18-crown-6 as well as N,N'-bis(methoxymethyl)-substituted substituted diaza-18-crown-6 were treated with 5-bromosalicylaldehyde to produce the N-(2'-hydroxy-3'-carbonyl-5'bromobenzyl)-substituted aza-15-crown-5 (8), aza-18-crown-6 (9) and N,N'-bis(2'-hydroxy-3'-carbonyl-5'-bromobenzyl)-substituted diaza-18-crown-6 (10) compounds. Compounds 8 and 10 were treated with hydroxylamine to give oxime-substituted ligands 12 and 13. A series of bis-Schiff base-containing diaza-18-crown-6 ligands were prepared by reacting 10 with 2-hydroxyaniline (to form 14), 5-nitro-2-hydroxyaniline (15), 2-aminopyridine (16), 2-hydrazinopyridine (17) and N-aminomorpholine (18). Compounds 12-18 are potential complexing agents for simultaneous binding of soft transition and hard alkali or alkaline earth metal ions in one molecule. These new oxime-and Schiff base-containing ligands interacted strongly with Na+ and K+ in methanol. The interaction of the aromatic portions of 9, 10, and 12-15 with transition metal ions was shown by the UV spectra of the metal ion complexes in 50% aqueous DMF. The X-ray structure of 10 is reported. (C) 1997 Elsevier Science Ltd.