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

Abstract

Abstract 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\oversetk1\undersetk−1\ightleftharpoonsFe(Hfr)2(X)+X, plots of logk1 vs. pKa (Ka : dissociation constant of conjugate acid of base) for pyridines gave a negative correlation. The logk1 values of 4-cyanopyridine and 4-acetylpyridine systems were smaller and that of 2,6-dimethylpyridine system larger than predicted by their pKa values. Imidazole and 1-methylimidazole were more inert than pyridines. For the reaction Fe(Hfr)2(X)+(CO)\oversetk2\undersetk−2\ightleftharpoonsFe(Hfr)2(X)(CO), logk−2 vs. pKa 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.