Ligand Exchange and Replacement

Ligand Exchange and Replacement. Three papers deal with ligand exchange at acetylacetonate complexes and the role of the solvent therein, for [Cr(acac)a] in... 

Several examples of ligand exchange and replacement were considered in the previous sections and most of these will not be described further in this section. Solvent Exchange.—Recent results for the exchange of DMSO with complexes of cobalt(in), chromium(iii), and iron(ii) are summarized in Table 24. Different mechanisms are proposed for all three metal ions, an la mechanism being favoured for cobalt(m), an h mechanism for chromium(in), and a D mechanism for the [Fe(CN)8-(DMSO)] ion. The contrasting values of AS for iron(n) and chromium(m)... 

Ligand Exchange and Replacement.—Reactivity patterns for neutral leaving groups from chromium(m) have been built up from a study of solvento-ligand replacements... 

This chapter deals with substitution reactions, including aquation, base hydrolysis, formation, and ligand exchange and replacement, and isomerization of inert metal complexes in which the metal has a co-ordination number of five or more. In fact the great majority of the references reported are concerned with octahedral complexes references to complexes of other coordination numbers have been collected together at the end of this chapter (Section 10). 

This unique iron site proves to be exceptionally labile, and supports a wide variety of ligand exchange and reactivity. Bridging to additional iron-sulfur clusters via a sulfide-containing bridge can also be supported at this site, allowing the construction of more complex clusters. Additionally, the unique iron atom can be removed altogether and replaced with other metals (as discussed in Section 4.3). 

Fig. 6. A schematic view of the [3Fe-4S] Emd [4Fe-4S] cores, as versatile structures. The absence of one site leads to the formation of a [3Fe-4S] core. The cubane structure can incorporate different metals (in proteins, M = Fe, Co, Zn, Cd, Ni, Tl, Cs), and S, N, O may be coordinating atoms from hgands (Li). The versatihty csm be extended to higher coordination number at the iron site and a water molecule can even be a ligand, exchangeable with substrate (as in the case of aconitase (,87)). The most characteristic binding motifs are schematically indicated, for different situations proteins accommodating [3Fe-4S], [4Fe-4S], [3Fe-4S] + [4Fe-4S], and [4Fe-4S] -I- [4Fe-4S] clusters. A disulfide bridge may replace a cluster site (see text).

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