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 

Bradic, D. Pavlovic, M. Pribanic, and S. Asperger,/. Inorg. Nuclear Chem., 91S, 37, 600. 

Kinetic results for the replacement of X (F, Cl, or Br) in [RuX2(bipy)2] by pyridine in a variety of aprotic solvents indicate a dissociative mechanism with a transient [RuX(bipy)a]+ intermediate. The range of rate constants for nucleophilic substitution in [PdX(dien)]+ cations by a given series of incoming groups shows that there is a marked decrease in nucleophilic discrimination in going from, e.g., water or methanol to the dipolar aprotic solvents DMF or DMSO.  

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

Samus and Nguen Than Hong, Russ. J. Inorg. Chem., 1976, 21, 687. 

The Ni + cation shows little discrimination between ligands in propylene carbon-ate. 2 Kinetic parameters have been communicated for reactions of Ni-+ and Co + with ammonia in aqueous methanol and for Ni + with ethylenediamine or 2,2 -bipyridyl in aqueous dimethylformamide, and with 2,2 -bipyridyl derivatives in aqueous ethanol. The kinetics of reaction of Fe + with benzoylacetanilides have also been studied in aqueous ethanol the kinetic pattern for reaction of Fe + with thiocyanate in aqueous carboxylic acids is complicated by parallel complex formation with solvent-derived carboxylate. Copper(ii)-formazan (2) chelate complex formation has been shown to take place in discrete steps in aqueous ethanol. Carboxy-late anion effects on the copper(ii)-tetraphenylporphine reaction have been studied in dimethylformamide.  

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Plate-and-Frame Systems. The membrane cast on support paper is exchanged and replaced by membranes cut out in the proper size. 

Octahedral Complexes Exchange and Replacement Processes Involving Solvated and Ligated Metal Ions... 

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)... 

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). 

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