Coordination compounds chelate effect

Of particular interest as catalysts are the incompletely coordinated metal chelate compounds, which are sufficiently stabilized by the ligand to be stable in solution at pH values much higher than that at which the aquo metal ion would precipitate as the hydroxide and thus to become unavailable for homogeneous catalysis. Such a metal chelate would be particularly effective as a catalyst for the activation of a substrate which can coordinate to the metal ion in the chelate compound. The interaction of the substrate with the metal ion would increase its reactivity toward nucleophilic reagents such as solvent molecules or hydroxyl ions, in accordance with the following scheme ... 

No discussion of the Jahn-Teller effect in coordination compounds would be complete without including the special features of chelated compounds (see Chapter 12 for a more thorough discussion of chelated complexes). The very nature of the chelated ring tends to restrict the distortion of a complex from a perfect octahedron because the ligand will have a preferred bite or distance between the coordinating atoms ... 

All the standard texts listed in Section A.3 of the Appendix have lengthy sections on coordination and organometallic compounds of the transition elements. See also the books listed in Sections A.10 and A.ll. Bell (1977) gives the fullest account of the chelate effect. Cotton and Wilkinson (1988) (Section A.3) is best for the catalytic applications of complexes. Jolly (1984) (Section A.3) discusses electron-counting in polynuclear carbonyls in some depth. 

Other theoretical considerations for synthetic coordination chemistry (isolobal and isoelectronic analogies, chelate, cis and trans effects, factors affecting the acid/ base properties of coordination compounds, bond theories, etc.) are covered in detail in excellent recent monographs [3,34b,104,106] and, for this reason, are not presented in this book. 

The peculiarities of classical localized coordination bonds (two-electron and two-center [1,4,5]) are displayed most clearly in MCC. Mostly, the elements of the first period of the Periodic Table (C, N, O) participate as electron donors in the formation of such bonds. In complexes of this type, the role of Ji-dative interactions is significant. These interactions are revealed in coordination compounds of ligands containing the elements of the next periods as donor centers (P, As, Sb S, Se, Te Cl, Br, I). We note that the examined complexes are the most successful objects to study the influence of ligand and metal nature on the character of the coordination bond, since, in this case, the factors which could distort this influence (chelate, macrocyclic, and other effects [117,135]) are absent. 

A general feature of MC is the presence of metallocycles in their molecules, whose main role is to produce stabilization effects (chelate, macrocyclic, and other effects) on the complexes [117,135-139]. An outstanding role in the study of this type of coordination compound belongs to the Russian scientist L.A. Chugaev (to whom the... 

A large class of coordination compounds, metal chelates, is represented in relation to microwave treatment by a relatively small number of reported data, mainly p-diketonates. Thus, volatile copper) II) acetylacetonate was used for the preparation of copper thin films in Ar — H2 atmosphere at ambient temperature by microwave plasma-enhanced chemical vapor deposition (CVD) [735a]. The formed pure copper films with a resistance of 2 3 pS2 cm were deposited on Si substrates. It is noted that oxygen atoms were never detected in the deposited material since Cu — O intramolecular bonds are totally broken by microwave plasma-assisted decomposition of the copper complex. Another acetylacetonate, Zr(acac)4, was prepared from its hydrate Zr(acac)4 10H2O by microwave dehydration of the latter [726]. It is shown [704] that microwave treatment is an effective dehydration technique for various compounds and materials. Use of microwave irradiation in the synthesis of some transition metal phthalocyanines is reported in Sec. 5.1.1. Their relatives - porphyrins - were also obtained in this way [735b]. 

---