Redox and Substitution

Redox and Substitution. Redox processes can interfere with studies of substitution at gold(iii), for instance in the [AuCli]- plus iodide reaction mentioned above. Often, however, it can be shown that one or more substitution processes precede the oxidation of the substrate by the gold(iii). Recent examples of this pattern include the reactions of malonate, methylmalonate, and chloromalonate with [AuCl4]. Some other dicarboxylic acids, for example succinic and maleic, also react by this route, but mechanisms of reactions of other dicarboxylic acids, for example oxalic acid and ascorbic acid, seem to be more complicated. The reaction of [Au-(NH3)4] + with thiosulphate also involves rate-determining substitution at gold as the first step.  

All the reactions listed in the previous paragraph were carried out under thermal, rather than photochemical, conditions. Irradiation of some of the mixtures cited at appropriate wavelengths results in about a one hundred times increase in rate. It is believed that the mechanisms of the photochemical reactions are similar to those of the thermal reactions.  

Information more or less germane to associative substitution at square-planar nickel(ii) can be gleaned from recent reports on interaction between lanthanide shift 

Qualitative observations have been made on Ni exchange with mercaptoethyl-amine (LLH) complexes [Ni(LL)2] or (Pd(LL)-2], and with similar di- and tri-nuclear complexes containing nickel(n) and/or palladium(ii).  

The kinetics of planar tetrahedral isomerization at nickel have been the subject of a theoretical disquisition.  

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Schwarz HA, Creutz C, Sutin N. (1985) Homogeneous catalysis of the photoreduction of water by visible light. 4. Cobalt(I) polypyridine complexes. Redox and substitutional kinetics and thermodynamics in the aqueous 2,2 -bipyridine and 4,4 -dimethyl-2,2 -bipyridine series studied by the pulse-radiolysis technique. Inorg Chem 24 433H39. 

Functional groups are inter-related by a series of redox and substitutive transformations. The reactions of functional groups may be determined by the electronegativity differences between the component atoms. 

In these general reviews organic systems, and both redox and substitution reactions of inorganic species, are covered. 

There has been an increasing use of flow methods to investigate the redox and substitution reactions which certain complex ions undergo within the 10-10 second range. This paper describes two such studies. 

Some of the redox and substitution characteristics of [Rh(bipy)3] " and [Rh(bipy)2] and the mechanism of H2 production by [Rh(bipy)2] involving formation of a hydride species [Rh(bipy)2H] which is reduced by [Rh(bipy)3] to give the direct precursor to H2 formation have been reported. ... 

Rate-determining steps leading to I(IV) and I(III) are postulated, with subsequent rapid reduction of intermediate iodine species. An induction period followed by oxidation of the [Fe(phen)3] complex is a feature of the reaction of that complex with bromate ions. The rates of the corresponding reactions with CI2 and affected by Cl", Br", or hydrogen ion. The oxidations occur via the one-electron transfer steps and an analysis of the data and those for other metal ion reductants has been made using a Marcus theory approach. The kinetics of the peroxodisulfate oxidation of two [Fe(II)(a-diimine)3] complexes have been investigated in binary aqueous-solvent mixtures.The rate data have been dissected into initial and transition state energies. Comparisons between the relative contributions to these parameters for redox and substitution reactions remain a topic of interest. 

Kinetics and mechanisms of hydrazine-forming reactions, involving coupled redox and substitution processes, from dinitrogen-bridged dinuclear diethyldithiocarbamate complexes of niobium and tantalum have been reported and discussed. ... 

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