15N, 13C and 119Sn NMR and other spectroscopic studies of 8-quinolinol, its O- and N-methyl derivatives, and chelate di- and tri-organotin(IV) complexes

Abstract

The nature of the 8-quinolinato ligand in various forms has been examined by 15N, 13C and 119Sn NMR spectroscopy, with evidence also from electronic spectroscopy. These forms include 8-quinolinol (HQ), 8-quinolinate, the 8-hydroxyquinolinium ion, O- and N-methyl derivatives, 8-methoxyquinoline (MeQ), the zwitterionic N-methylquinolinium-8-olate and the N-methylquinolinium ion, and the chelating ligand in organotin(IV) complexes. The 15N shift from MeQ to HQ affords a measure of the intramolecular hydrogen bonding in HQ. The 15N shifts and 2 J( 15N 1H) couplings afford criteria of chelation, and the O- and N-methyl compounds provide useful reference points for its assessment. Evidence for chelation is demonstrated in three groups of compounds, [SnR 2Q 2] (R = Me, Et, Bu n , Oct n or Ph), [SnR 3Q] (R = Me, Et, Bu n or Ph) and [SnR 2ClQ] (R = Me, Et, Bu n or Oct n ), the 15N and 119Sn shielding increasing from the [SnR 3Q] to the [SnR 2Q 2] compounds.