Polydentate, Macrocyclic, and Encapsulating Ligands

Aqua-polyaminocarboxylato complexes of iron(II) react with NO, MONO, and NO J in aqueous solution by concurrent substitution and redox pathways. The former include direct replacement of a water ligand by NO. The nature of the ligand—edta, dtpa, nta, etc.— has a marked effect on the balance between substitution and redox pathways as well as on overall reactivity. Although many of the reactions are fast, slow substitution is observed for several of these complexes at the higher end of the pH range (2.5 pH 5.8)studied.  

The N2S4 macrocycle (50) forms a deep blue low-spin iron(II) complex, characterized by X-ray diffraction. One hopes that kinetic studies will follow. Kinetic studies of N4 macrocycle complexes [Fe(N4)LL ] appear regularly, usually involving replacement of one or both of L, L. Reaction of phthalocyaninatoiron(II) with imidazole, in dimethyl sulfoxide solution, proceeds by consecutive first-order processes, the second some thousand times slower than the first. The N4 macrocycles (51) link this section with the previous section kinetics of reactions of [Fe(51)(MeCN)]2 with such ligands as 1-methylimidazole, pyridine, tributyl phosphite, tributyl phosphine, and carbon monoxide have been investigated. A series of complexes [Fe(51)L2], this time only for (51) with R = Me, has been studied with a 

8 Inert-Metal Complexes Other Inert Centers 

A few iron(III) complexes have already been mentioned, in connection with slow substitution at normally labile centers (Section and with 

The reaction of ferric protoporphyrin IX with cyanide, and its reaction with imidazole, are assigned associative mechanisms on the basis of their activation volumes. However, it is not entirely clear what assumptions are involved in relation to solvation and the partial molar volumes of the incoming groups.  

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