NMR spectra of some alkyl(oxinato)tin(IV) complexes

Proton magnetic resonance spectra of a series of alkyl(oxinato)tin(IV) complexes, alkyl(oxinato)thallium(III), dimethylbis(oxinato)lead(IV), 8-methoxyquinoline, 2-methyl-8-hydroxyquinoline and 8-hydroxyquinoline were studied. The indirect spin-spin coupling constants J₂₃, J₃₄ and J₂₄ of the oxinato ligand in the alkyl(oxinato)tin(IV) complexes and of 8-methoxyquinoline were found to be 4.4 ± 0.2, 8.3 ± 0.2 and 1.7 ± 0.2 Hz, respectively. When the interaction between tin and nitrogen in the oxinato ligand is not strong as in trialkyl(oxinato)tin(IV), the resonance of the 2-proton of the ligand shifts to high magnetic field relative to that of 8-methoxyquinoline, but in the case of the strong interaction, as in dimethyl(oxinato)halogenotin(IV), the resonance is shifted to low magnetic field. The 4-proton signals, however, shift monotonously to low magnetic field with increasing interaction. The behaviour of the 2-proton signals was explained by a paramagnetic anisotropic effect of a nitrogen lone pair of the oxinato ligand and an intramolecular electric field effect and that of the 4-proton by the latter effect. By comparing the change of the δ-values of the 2-, 3- and 4-protons of the alkyl(oxinato)tin(IV) complexes and those of 8-hydroxyquinoline by altering the solvents, from methylene chloride to benzene, it was found that the electron density around the 2-carbon is reduced in the complexes compared with that of 8-hydroxyquinoline.