Reactions of the Octahedral Bis(α-diketone dioximato)iron(II) Complexes with Carbon Monoxide and Benzyl Isocyanide

Article abstract of DOI:10.1246/bcsj.56.881

The reactions of bis(α-diketone dioximato)iron(II) coordinated by two nitrogeneous base molecules (X) with carbon monoxide and benzyl isocyanide were studied kinetically in chloroform; here α-diketone dioxime = 2,2'-difurylglyoxime (H2fr) and dimethylglyoxime (H2dg).The reactions proceeded reversibly through a dissociative mechanism.For the reaction Fe(Hfr)2(X)2<*>Fe(Hfr)2(X) + X, plots of log k₁ vs. pK_a (K_a: dissociation constant of conjugate acid of base) for pyridines gave a negative correlation.The log k₁ of 4-cyanopyridine and 4-acetylpyridine systemswere smaller and that of 2,6-dimethylpyridine system larger than predicted by their pK_a values.Imidazole and 1-methylimidazole were more inert than pyridines.For the reaction Fe(Hfr)2(X) + CO<*>Fe(Hfr)2(X)(CO), log k_-2 vs. kP_a plots for sterically unhindered pyridines showed a linear relationship, but the basicity of pyridine bases did not affect the CO dissociation processes very much. 2-Methylpyridine, 2,4-dimethylpyridine, and 2,6-dimethylpyridine facilitated the dissociation of CO slightly as compared with pyridine.Imidazole and 1-methylimidazole allowed CO to be more inert and piperidine more labile than pyridines.The dissociation of the base was significantly affected by the change of substituents in α-diketone dioxime, and the dissociation of CO was slightly affected by the change of substituents.The reaction behavior was discussed on the basis of the activation parameters and infrared data.