Redox reactions group 13 metals

This chapter reviews the literature published during the period July 1988 to December 1989. In keeping with previous practice, some selectivity has been exercised. Also, the chapter includes redox reactions between metallic and non-metallic species, regardless of whether or not the nonmetallic component is coordinated to the metal center during electron transfer. The format is such that reactions have been grouped according to their central or reactive nonmetallic element. Some topics have received scant coverage, particularly if they are dealt with elsewhere in this volume. Thus, oxidative addition/reductive elimination reactions are not within the scope of this section. 

Finally, the redox reactions of metal-carbene complexes lead to the transfer of H atom, alkyl group or carbene ligand. ... 

Friedrich et al. also used XPS to investigate the mechanisms responsible for adhesion between evaporated metal films and polymer substrates [28]. They suggested that the products formed at the metal/polymer interface were determined by redox reactions occurring between the metal and polymer. In particular, it was shown that carbonyl groups in polymers could react with chromium. Thus, a layer of chromium that was 0.4 nm in thickness decreased the carbonyl content on the surface of polyethylene terephthalate (PET) or polymethylmethacrylate (PMMA) by about 8% but decreased the carbonyl content on the surface of polycarbonate (PC) by 77%. The C(ls) and 0(ls) spectra of PC before and after evaporation of chromium onto the surface are shown in Fig. 22. Before evaporation of chromium, the C(ls) spectra consisted of two components near 284.6 eV that were assigned to carbon atoms in the benzene rings and in the methyl groups. Two additional... 

A very small quantity of the catalyst can produce an appreciable effect on the speed of reaction, e.g. an amount of 10 6-lCT8 mol dm 3 of platinum group metal ions is sufficient to catalyse various redox reactions. 

Although we have used for exemplification largely the surfaces of hydrous oxides, the concepts given apply to all surfaces. As has been pointed out, most hydrous surfaces are characterized by functional groups that acquire charge by chemical interaction with H+, OH, metal ions and by ligands. (For the moment we ignore redox reactions.)... 

Spectrophotometry has been a popular means of monitoring redox reactions, with increasing use being made of flow, pulse radiolytic and laser photolytic techniques. The majority of redox reactions, even those with involved stoichiometry, have seeond-order characteristics. There is also an important group of reactions in which first-order intramolecular electron transfer is involved. Less straightforward kinetics may arise with redox reactions that involve metal complex or radical intermediates, or multi-electron transfer, as in the reduction of Cr(VI) to Cr(III). Reactants with different equivalences as in the noncomplementary reaction... 

The Ag+ ion is labile. Even with cryptands, which react sluggishly with most labile metal ions, Ag reacts with a rate constant around 10 M s (in dmso). The higher stability of Ag(I) complexes compared with those of the main groups I and II resides in much reduced dissociation rate constants. Dissociation tends to control the stability of most metal cryp-tand complexes. Silver(I) is a useful electron mediator for redox reactions since Ag(I) and Ag(II) are relatively rapid reducers and oxidizers, respectively. Silver(I) thus promotes oxidation by sluggish, if strong, oxidants and catalyses a number of oxidations by S20 in which the rate-determining step is... 

Such pentacarbonyl species can be further decarbonylated when the sample is heated to 373 K under an inert gas stream and under reduced pressure. This slow decarbonylation process provides the surface Mo(CO)3 species depicted in Figure 9.4, which is stable up to 473 K [14]. In contrast with the relevant chemical behavior in solution (9.1 and 9.2), in the solid state, where the species are somewhat diluted and present low mobility, no dimeric species have been identified as resulting from penta- or tricarbonyl species. Heating to 673 K gives rise to the evolution of H2, CO, CO2 and CH4, due to redox reactions between the metal center and the OH surface groups. The resulting oxidation states, as determined by XPS measurements, are mainly II and IV, besides some Mo(0) species ]20]. It is worth underHn-... 

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