Metal complexes—continued substitution reactions

The catalytic activity of Hg in elimination and substitution reactions of transition-metal complexes continues to be the subject of study. Kinetic studies on the Hg" catalysed aquation of both cis-[Co(en)2(CN)Cl], cis-[(chloro)(aniline)CO(en)2], and [PdLX] (L = tetramethyldiethylenetriamine X = Cl, Br, or I) are consistent with intermediate adduct formation at the halide substituent. Mercury(ii) reacts reversibly with the [Co(NH3)5SCN] ion to yield [Co(NH3)5(SCN)Hg] which irreversibly undergoes either aquation to yield [Co(NH3)sH20] or isomerization to yield [Co(NH3)5(NCS)Hg] at approximately equal rates. The kinetics of the reaction... 

Continuing activity on platinum(II) antitumor drugs has resulted in several recent reviews/each of which cover mechanistic aspects. Other reviews include one on metal porphyrins, which features many reactions of 4- and 5-coordinate complexes, and substitution reactions at platinum(II) complexes with asymmetric olefin ligands have been discussed. ... 

The importance of 1,10-phenanthroline and substituted 1,10-phenanthrolines as metal complexing agents and their use in analytical applications has provided the impetus for an extensive study of procedures for their synthesis.182 The original synthesis of 1,10-phenanthroline by a double Skraup reaction on o-phenylenediamine using glycerol and sulfuric acid in the presence of an oxidizing agent continues to attract attention, and various improvements in reaction... 

The field of nickel complexes with macrocydic ligands is enormous and continuous interest in this area in recent years has resulted in innumerable publications. A number of books and review articles are also available covering the general argument of the bonding capability of the various macrocydic ligands towards transition and non-transition metals. 22 2627 Synthetic procedures for metal complexes with some tetraaza macrocycles have been reported.2628 Kinetics and mechanism of substitution reactions of six-coordinate macrocydic complexes have also been reviewed.2629... 

There is continued expansion in the use of metals as catalysts in substitution reactions. Copper iodide in the presence of /V./V -dimcthylcthylcncdiamine has been shown to be effective in the intramolecular substitution of aryl bromides carrying an o-l,3-dicarbonyl substituent reaction may involve either an oxygen centre or a carbon centre of the dicarbonyl moiety.26 The reaction of aryl halides with sodium trifluoroacetate in the presence of copper iodide may lead to the formation of the tri-fluoromethylated derivatives, possibly via CF3CuI as an intermediate.27 There have been theoretical calculations, PM3 and ab initio, on complexes formed from copper... 

Although quantitative studies of substitution reactions have only been launched quite recently, a considerable body of experimental data is available, so that theoretical principles of ligand substitution mechanisms in classical inorganic complexes have been developed. Unfortunately the same cannot be said for substitution reactions involving 7r-bonded hydrocarbon ligands, in spite of a continuously expanding number of publications in this field. In the majority of studies substitution reactions are used to obtain novel transition metal 7r-complexes, and a far lesser number of papers deal with the quantitative aspects of the exchange. 

Information on ligand substitution mechanisms should aid us to understand more profoundly homogeneous catalysis by transition metal complexes, where probably consecutive substitution and transfer reactions of ligands from metal to a substrate and back take place continuously. 

C tereochemistry has played a major role in the development of chemistry, and it continues to be most significant. Werner made extensive use of the information available to him on the stereochemistry of metal complexes in developing his coordination theory. He made the first meaningful attempt to understand the mechanisms of substitution reactions of these systems on the basis of the stereochemical changes accompanying such reactions. The paper 49) he wrote in 1912 is a real milestone and should be read by anyone interested in octahedral substitution reactions. It is valuable because of the large amount of experimental data it contains on reactions of cis and [Pg.408]

The chemistry of metal carbonyl radicals dates back to the discovery of "V (CO)6 in 1959.9 The electronic structure and reactions of this complex continue to be investigated.10 The rate of ligand substitution of V(CO)6 would be shown 15 years later to occur at a rate 1010 times faster than that in Cr(CO)6 and was ascribed to associative rather than dissociative pathways occurring for the radical complex ... 

The nature and properties of metal complexes have been the subject of important research for many years and continue to intrigue some of the world s best chemists. One of the early Nobel prizes was awarded to Alfred Werner in 1913 for developing the basic concepts of coordination chemistry. The 1983 Nobel prize in chemistry was awarded to Henry Taube of Stanford University for his pioneering research on the mechanisms of inorganic oxidation-reduction reactions. He related rates of both substitution and redox reactions of metal complexes to the electronic structures of the metals, and made extensive experimental studies to test and support these relationships. His contributions are the basis for several sections in Chapter 6 and his concept of inner- and outer-sphere electron transfer is used by scientists worldwide. 

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