Nuclear magnetic resonance spectra of quinolinolato-complexes of aluminium, gallium, and indium dialkyls
1 H N.m.r. data are presented for a number of novel, organometallic compounds of the form R2MQ (R = Me, Et, or Bui; M = Al, Ga, or In; Q = the anion of quinolin-8-ol). Variations in the chemical shifts of the alkyl protons are rationalized in terms of the opposition of two effects, the first being inductive redistribution of electron density, and the second being the diamagnetic anisotropy of induced electronic circulation in the π-system of the ligand Q; the latter effect causes magnetic non-equivalence in the diastereotopic protons of the isobutyl groups of Bui2AlQ, but the increased inner electron density of the metal atom produces attenuation of this separation for M = Ga, and apparent annihilation of it for M = In. Anisotropic circulation of electrons in the N–M–O portion of the complexes is proposed to explain apparently anomalous chemical shifts of the protons adjacent to the heteroatoms in the aromatic ligand.