Synthetic techniques metal coordination

Coordination compounds have been produced by a variety of techniques for at least two centuries. Zeise s salt, K[Pt(C2H4)Cl3], dates from the early 1800s, and Werner s classic syntheses of cobalt complexes were described over a century ago. Synthetic techniques used to prepare coordination compounds range from simply mixing the reactants to employing nonaqueous solvent chemistry. In this section, a brief overview of some types of general synthetic procedures will be presented. In Chapter 21, a survey of the organometallic chemistry of transition metals will be presented, and additional preparative methods for complexes of that type will be described there. 

Additionally to the theoretical data and synthetic techniques for various metal complexes presented in Chaps. 2-A, we would like to pay special attention to three kinds of coordination compounds (complexes of phthalocyanines, quinones, and radioactive elements), whose syntheses, in our opinion, have been insufficiently generalized in monographs and textbooks on synthetic coordination chemistry. This choice is caused by the facts that phthalocyanines, as n-aromatic macrocyclic compounds, possess unusual thermal stability (nonstandard for organic and organometallic species) the quinone complexes have free-radical properties and coordination and organometallic compounds of radioactive elements are interesting at least for the reasons of necessity of special precautions in their syntheses and applications in the nuclear industry and nuclear medicine. So, this chapter is dedicated to the peculiarities of structure and properties and the main synthetic procedures for the complexes above. 

Direct evidence for the formation of radical o-quinone (and sometimes p-qui-none) complexes was established in the studies quoted above. Various synthetic techniques starting from elemental metals, nonmetals, metal salts, and complexes have been developed for obtaining these coordination compounds. The peculiarities of their thin structure and physical-chemical properties were investigated. The obtained products have practical applications, in particular for medical purposes. Quinone-based metal complexes have a potential applicability as cocatalysts in a wide range of reactions involving electron exchange between substrate and catalysts. Further studies in this field and on mechanisms of electron mobility between the metal center and the o-quinone ligands are still necessary to understand the vast and complex redox chemistry of these compounds. 

Among the natural and artificial radioactive elements (Tc, Pm, Po, Fr, Ra, Ac, and actinides), coordination and organometallic compounds of only technetium and the actinide series (An) are well represented at the present time. The interest in their metal complexes has been motivated by the extended use of Tc, available in kilogram amounts, for medical and technical purposes, meanwhile actinides are important on their own for the nuclear industry. A lot of original papers, reviews, and chapters of some books are dedicated to Tc and An complexes [263-281], In the present section, dedicated to the coordination and organometallic chemistry of the actinides and Tc, we intend to present the synthetic techniques for these compounds according to their ligand nature. 

A step-growth synthetic method for incorporating metal clusters into polymers was shown in Eq. 7.9. And, in the preceding section, metal clusters were incorporated into polymers and oligomers using bidentate ligands and the techniques of coordination polymerization. Yet a third synthetic route to these materials is to react selected metal clusters with acetylenes.13,38,39,40 In many such reactions, the two carbons of the acetylene unit are incorporated into the metal cluster. An example is shown in Eq. 7.32. 

One example of such a reaction sequence employs thallium(I) as the coordinating metal and allows clean alkylation of a P-diketone to be carried out (Scheme 69).274,275 This technique has become an established part of synthetic organic methodology. 

In relation to the synthetic direction of the present monograph, we would like especially to mention that the theoretical approach of Lewis is the basis of preparative techniques in the synthesis of coordination compounds described later (Chap. 3) interaction of the ligands with metal salts or carbonyls (Sec. 3.3.1) is described by Schemes (1.1) and (1.2), ligand exchange (Sec. 3.3.2.1) by Schemes (1.3) and (1.6), metal exchange (Sec. 3.2.2) by Schemes (1.4) and (1.7) ... 

The low affinity of sulfur for alkali metal ions, however, renders template effects of less consequence in the synthesis of polythia macrocycles. Thus, the competition between cycli-zation and linear polymerization is more statistically defined, with cyclization kinetically favored only at high dilution 64,65,66). Consequently, most of the synthetic methods for the synthesis of polythia rings involve high-dilution techniques coupled with relatively long reaction times. Historically, the study of the coordination chemistry of macrocyclic thioethers has been hindered by difficulties in the synthesis of the free ligands. The synthesis of [BJaneSa, first reported by Ochrymowycz and co-workers in 1977 101), illustrates this well. 

In spite of the many modern techniques available to the chemist, the known chemistry of polynuclear cobalt (III) complexes is essentially that deduced by Werner 60 years ago. Since his work, no new polynuclear cobalt complexes have been prepared and characterized and no new reactions uncovered. Modem work in this area is being aimed at attaining a better understanding of the electronic structures inherent in polynuclear ions, which would be of value in a variety of active fields. The chemistry of polynuclear complexes is important in such new areas as synthetic oxygen carriers, electron transfer reactions, and transition metal catalysis. The fact that these new investigations are solidly based on Werner s pioneer investigations testifies to the genius with which he opened up a new area of coordination chemistry, with only the simple chemical techniques available to him. His work in the area of polynuclear cobalt(III) ammine complexes should continue to serve as a model of solid research for some time to come. 

A synthetically useful technique for substituting (C-electrophilic) carbon monoxide ligands from metal carbonyls is a base reaction with the sufficiently nucleophilic trimethylamine oxide [8]. As represented by eq. (6), the same mechanistic scheme applies, with the zwitterionic intermediate breaking down into the (volatile, weakly coordinating) fragments CO2 and N(CH3)3 at the same time, a reactive fragment (e. g., the 16e-system Fe(CO)4 ) is being formed. 

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