Substitution reactions four-coordinate complexes

Cquare planar complexes are generally of the low-spin d8 type. This includes the four-coordinated complexes of Ni (II), Pd(II), Pt(II), Au(III), Rh(I) and Ir(I). The best known and most extensively studied are the compounds of Pt(II). The kinetics and mechanisms of substitution reactions of these systems have been investigated in considerable detail. Studies on complexes of the other metal ions are rather limited, but the results obtained suggest that their reaction mechanism is similar to that of the Pt(II) systems. This paper briefly surveys some of the available information, and presents the current view on the mechanism of substitution reactions of square planar complexes. 

Platinum(II) complexes containing the tridentate ligands diethylenetriamine (dien) and 2,2 6, 2"-terpyridine (terpy) have provided useful substrates for mechanistic studies in substitution reactions at planar four-coordinated complexes. Moreover, there has been considerable interest in terpy complexes... 

The fact that the five-coordinate complex [Ni(CN)s] can be detected does indeed explain why substitution reactions of the four-coordinate complex [Ni(CN)4l are fast. The reason is that, for a detectable amount of [Ni(CN)5] to build up in solution, the forward rate constant kf must be numerically dose to or greater than the reverse rate constant... 

Strontium, aquatetrakis(diacetamide)-structure, 98 Strontium, heptaaqua-dodecaiodide structure, 72 Strontium, octaaqua-stnicture, 84 Structure nomenclature, 124 Substitution reactions, 281-329 base catalyzed, 300 four-coordinate complexes planar d , 311... 

Ideally, chemists hope to understand a number of reaction mechanisms well enough that predictions about a diverse assortment of complexes involving different metals, ligands, and reaction conditions can be made. A good example of a type of reaction for which this level of understanding has been achieved is substitution in four-coordinate square planar complexes. 

In terms of the development of an understanding of the reactivity patterns of inorganic complexes, the two metals which have been pivotal are platinum and cobalt. This importance is to a large part a consequence of each metal having available one or more oxidation states which are kinetically inert. Platinum is a particularly useful element of this pair because it has two kinetically inert sets of complexes (divalent and tetravalent) in addition to the complexes of platinum(O), which is a kinetically labile center. The complexes of divalent and tetravalent platinum show significant differences. Divalent platinum forms four-coordinate planar complexes which have a coordinately unsaturated 16-electron d8 platinum center, whereas tetravalent platinum is an 18-electron d6 center which is coordinately saturated in its usual hexacoordination. In terms of mechanistic interpretation one must therefore consider both associative and dissociative substitution pathways, in addition to mechanisms involving electron transfer or inner-sphere atom transfer redox processes. A number of books and articles have been written about replacement reactions in platinum complexes, and a number of these are summarized in Table 13. 

Dissociative Activation in the Substitution Reactions of Four-coordinate, Planar d Metal Complexes 320... 

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