Coordination complexes overview

This chapter, in previous volumes, concentrated on mechanistic studies of the stoichiometric reactions of coordinated a- and tt-hydrocarbons with nucleophiles and electrophiles. In order to provide a more comprehensive overview of the reactivity of coordinated ligands in general, related ligand reactions in classical coordination complexes are now also included. The stereospecificity of such processes and their potential for asymmetric synthesis has continued to attract increasing attention, and it is therefore appropriate to collect them all together in one chapter. There are three subsequent sections. The first is concerned with cobalt(III) complexes, and the second with complexes of other metals. The last section deals with the ligand reactivity of organometallic compounds. 

This section will selectively summarize concepts and principles governing electron transfer. The selectivity is an obvious necessity in view of the vast amount of material, some of it cited in the preceding section, and the author s experience and bias. The perspective of this chapter is phenomenological. Theoretical studies and concepts will be used as a framework for the consideration of experimental studies. The emphasis is on those theoretical issues and concepts that relate to experimental studies of coordination complexes. A good overview of the theory can be found in a recent chapter by Newton. 

Unlike most of the articles in Comprehensive Coordination Chemistry II this chapter is not a review. Exploration of charge transfer on the nanoscale is just beginning. We anticipate that, over the first few years of the twenty-first century and beyond, coordination complexes and coordination chemistry approaches will be exploited extensively to create new materials of both fundamental and applied importance. Here we try to provide tools to assist coordination chemists who engage in this exciting new research area. We provide a broad overview of types of systems that may be important in the future, with lead-in references, and analyses of the energetics and electron transfer barriers from a dielectric continuum model for a range of conditions. 

Coordination complexes of iron(II) and (III) are so numerous and usually easily oxidized and/or reduced, that it is impossible to give a comprehensive account of their electrochemistry in such a concise format. Again, the reader is urged to read the relevant chapters in books cited in Ref. 1 to contemplate the diversity of complexes of iron, ruthenium, and osmium in the II/III state, and find entries to their chemistry and electrochemistry. Here, we will first give an overview of some of the classic ligands used with metals of the iron group, especially when interesting electrochemistry has been described. Then... 

Detailed discussions on supramolecular structures of giant polyoxometalate clusters have been reported by Muller and co-workers." " The number of ionic lattices formed from anionic POM clusters and organic cations-coordination complex cations resulting in supramolecular structures is substantial and literally more than hundreds of new compounds in this class appear annuallyIn this overview, the supramolecular features of POM-based systems will be discussed mainly under three headings (a) supramolecular features of polyoxometalate supported transition metal complexes, (b) polyoxometalate-crown ether complexes with supramolecular cations, and (c) supramolecular water clusters associated with polyoxometalates. 

Abstract After an overview of chiral urea and thiourea synthetic methods, this review describes the main applications of urea and thiourea complexes in asymmetric catalysis. Some recent examples of thioureas as catalysts are also presented. Coordination chemistry of ureas and thioureas is briefly discussed. 

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. 

In order to give the usual overview of nickel complexes at increasing coordination numbers we begin with the usual square planar complexes of the Schiff bases salen and saloph.149,150 As an example, Figure 98 shows the molecular structure of [Nin(salen)]. 

To conclude this overview of nickel complexes we consider the NiN6 coordination. 

There have been two books devoted to the chemistry of iron, " and many reviews devoted to various aspects of its coordination chemistry, including structures and photochemistry (iron(III)). Iron complexes appear in a multi-author volume on the history of coordination chemistry, but there is disappointingly little about iron—just a brief mention of hexacyanoferrates in connection with pigments—in an otherwise excellent overview of the history of chemistry. ... 

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