Seventeen 3-substituted-2,4-pentanediones were synthesized. The effect of substituents in the position 3 on the tautomeric equilibria, i, e., keto-, cis-enol-and trans-enol-forms, has been investigated by nuclear magnetic resonance spectroscopy.It has been found that the percentage of each tautomer depends upon the electronic and steric effects of the substituents.The relative intensity of intramolecular hydrogen bonds in these compounds was evaluated from both the NMR and IR data.It has been found from the half-wave potential data of polarographic reduction and the Cu-O stretching frequencies of 16 copper chelates of 3-substituted-2,4-pentanediones that the relative stability of the chelate decreases with an increase in the electron-withdrawing effect of the substituents.

Various copper(II) chelates were found to be effective initiators in the polymerization reaction of the methyl methacrylate in the presence of triphenylphosphine. The conversion increases with an increase in the concentration of triphenylphosphine, reaching a constant level at the ratio of 1: 2 between copper chelates and triphenylphosphine. Di-μ-methoxo-bis(ethylacetoacetato)dicopper(II) was the most effective initiator. The dependence of the rate of the polymerization on the square root of the concentration of the complexes suggests that the polymerization by this initiation system proceeds via a radical mechanism. It can be assumed that the copper chelate coordinated the triphenylphosphine and that homolytic fission occurred to give a free ligand radical, accompanied by the reduction of the central copper atom. Stable copper (I) mixed chelates were obtained under conditions similar to those of the polymerization.

The electronic absorption spectra of [CoIII(dmgH)2B2]+ and [FeII(dmgH)2B2] (dmgH=dimethylglyoximate monoanion and B=pyridine derivatives) are inspected with respect to the effect of the axial pyridine ligands on the charge-transfer bands of the complexes. The characteristic bands observed in the 275–305 mμ region for the Co(III) complexes and in the 485–555 mμ region for the Fe(II) complexes, which have been assigned to a metal→oxime charge-transfer band, are shifted to shorter wavelengths with a decrease in the basicity of the pyridine derivatives. The results have been discussed by taking into account the π-interaction of the dπ(dxz, dyz) orbital of the central metal ion with the empty π-orbitals of both the dimethylglyoximate and the pyridine derivatives. It is suggested that the π-interaction is stronger in the Fe(II) complexes than in the Co(III) complexes, while the σ-bond is stronger in the latter. The infrared spectral evidence that the C=N stretching frequency is dependent on the axial pyridine derivatives, and that it is observed at a lower frequency in the Fe(II) than in the Co(III) complexes, is consistent with the above results.

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The preparation of diamagnetic CoII(dmgH)2NO (dmgH=dimethylglyoximato monoanion) is reported. The complex shows the IR absorption band of NO at 1641 cm−1, indicating a neutral NO ligand in the complex. The IR and electronic spectra are consistent with the structure of the penta-coordinate, the square-pyramidal configuration of the complex. In the presence of oxygen and water, the complex is oxidized rapidly (NO→NO2−, Co(II)→Co(III)) and converted into CoIII(dmgH)2NO2·OH2. During the reaction, a complex formulated as [CoII(dmgH)2NO·OH2] [CoIII(dmgH)2NO2]·2H2O is obtained. It is considered that, in the complex, the Co(II) is bound with the Co(III) through a NO bridge. The assignments of the IR spectra have been made using 15NO and 15NO2.