Pyridine nitrosazones and their cobalt(III) chelates

Abstract

AHMAD SAMI SHAWALI and IKHLASS M. ABBASS. Can. J. Chem. 55,3707 (1977). Nitrosation of pyridine aldehyde p-tolylhydrazones 2 with amyl nitrite gives rise to p-tolueneazopyridine aldoximes 4 which form stable tris chelates with cobalt(II1). Spectral data (ir, uv, and 'Hmr) indicate that the ligands exist mainly in the assigned azooxime structure 4, and that their chelates have five-membered ring structure 7. Also, the 'Hmr spectra imply mer-configuration 9 for the chelates examined. No evidence for the tautomeric nitrosohydrazone structure 3 for the ligands and the fac-configuration 8 for Co(II1) chelates could be obtained. Using the HMO method, the azooxime form 4 for the ligand was shown to be more stable than the nitrosohydrazone structure 3. Also, good agreement was obtained between observed transition energies and those calculated by the HMO method. The acid dissociation constants of the ligands in 50 vol% ethanol-water at 25'C and ionic strength of 0.1 were determined spectrophotometrically.AHMAD SAMI SHAWALI et IKHLASS M. ABBASS. Can. J. Chem. 55,3707 (1977). La nitrosation dep-tolylhydrazones aldehydiques de pyridine 2 par le nitrite d'amyle conduit a des aldoximesp-tolueneazopyridine 4 lesquels forment des chelates stables avec le cobalt(II1).Les donnees spectrales (ir, uv et rmn) indiquent que les ligands existent principalement sous la forme azooxime 4 et leurs chelates possedent une structure comportant un cycle a cinq membres 7. De plus, les spectres rmn suggerent une configuration mer 9 pour les chelates CtudiCs. On ne peut obtenir de preuves evidentes pour une structure tautomere nitrosohydrazone 3 pour les ligands et d'une configuration fac 8 pour les chelates Co(II1). En utilisant la mCthode HMO, on peut demontrer que la forme azooxime 4 pour le ligand est plus stable que la structure nitrosohydrazone 3. Un bon accord est aussi obtenu entre les energies de transition observees et celles calculees par la methode HMO. Les constantes de dissociation acide des ligands dans une solution a 50% par volume ethanol-eau a 25°C a une force ionique de 0.1 sont determinees spectrophotometriquement.[Traduit par le journal]Various nitrosazones of type 1 (X = H, alkyl, or aryl and Ar = substituted phenyl) have been described (1-4). However, nitrosazones in which X (in 1) is a heterocyclic group have so far not been reported. In this paper we describe the synthesis of three heterocyclic nitrosazones, namely 4a to 4c, and report on their spectroscopic and acid dissociation properties. We have also probed the synthesis, structure, and stereochemistry of cobalt(II1) chelates with these X--C( : N0H)N : NAr 1 heterocylic nitrosazones, and the results are described in this report. The present investigation was undertaken to see the effect of the presence of a heteronitrogen atom in the X group on the tautomeric structure of 1, and to establish the relative stability of the possible tautomeric forms of 1 within the framework of the Huckel molecular orbital method (HMO). Also, it wasIAuthor to whom all correspondence s...