Coordination complex reactivity electron transfer reactions

The rates of many electron transfer reactions have now been measured and, as new coordination complexes are prepared, characterized, and their solution properties studied, our understanding of fundamental structure (both geometric and electronic)-reactivity relationships continues to grow. Both inner- and outer-sphere reactions will be explored in Chapter 5. 

The reactivity of the Cu/3 complex was studied kinetically " in the two electron-transfer reactions shown below. Cu(II) ion was reduced with ascorbic acid through an inner-sphere process in which ascorbic acid coordinates to the Cu complex and then transfers an electron to the Cu(II) ion. Cu(II) ion was also reduced with Fe(II)(phenanthroline)3 via an outer-sphere mechanism in which electron-transfer occurs when a reductant and an oxidant move into sufficient proximity. 

In this context, the chemical reactivity of ATRP initiators such as bromo-terminated moieties has been illustrated from this chemical amplification scheme of defects by ATRP. The chemical reactivity under investigation corresponds to the reductive debromination of the C-Br bond in bromo-terminated initiators of ATRP immobilized on different surfaces. In organic solvents, the reductive debromination of bromo-derivatives (RBr) has been extensively investigated by homogeneous means (via an electron donor).i27U29 It is also of peculiar interest in the comprehension of ATRP processes as its reaction mechanism is based on an electron transfer reaction initiated and mediated by inner-sphere coordination complexes, like a Cu(I) complex. H... 

A key aspect of metal oxides is that they possess multiple functional properties acid-base, electron transfer and transport, chemisorption by a and 7i-bonding of hydrocarbons, O-insertion and H-abstraction, etc. This multi-functionality allows them to catalyze complex selective multistep transformations of hydrocarbons, as well as other catalytic reactions (NO,c conversion, for example). The control of the catalyst multi-functionality requires the ability to control not only the nanostructure, e.g. the nano-scale environment around the active site, " but also the nano-architecture, e.g. the 3D spatial organization of nano-entities. The active site is not the only relevant aspect for catalysis. The local area around the active site orients or assists the coordination of the reactants, and may induce sterical constrains on the transition state, and influences short-range transport (nano-scale level). Therefore, it plays a critical role in determining the reactivity and selectivity in multiple pathways of transformation. In addition, there are indications pointing out that the dynamics of adsorbed species, e.g. their mobility during the catalytic processes which is also an important factor determining the catalytic performances in complex surface reaction, " is influenced by the nanoarchitecture. 

In terms of the development of an understanding of the reactivity patterns of inorganic complexes, the two metals which have been pivotal are platinum and cobalt. This importance is to a large part a consequence of each metal having available one or more oxidation states which are kinetically inert. Platinum is a particularly useful element of this pair because it has two kinetically inert sets of complexes (divalent and tetravalent) in addition to the complexes of platinum(O), which is a kinetically labile center. The complexes of divalent and tetravalent platinum show significant differences. Divalent platinum forms four-coordinate planar complexes which have a coordinately unsaturated 16-electron d8 platinum center, whereas tetravalent platinum is an 18-electron d6 center which is coordinately saturated in its usual hexacoordination. In terms of mechanistic interpretation one must therefore consider both associative and dissociative substitution pathways, in addition to mechanisms involving electron transfer or inner-sphere atom transfer redox processes. A number of books and articles have been written about replacement reactions in platinum complexes, and a number of these are summarized in Table 13. 

Pyridylarenes undergo Cu(II)-catalysed diverse oxidative C-H functionalization reactions. The tolerance of alkene, alkoxy, and aldehyde functionality is a synthetically useful feature of this reaction. A radical-cation pathway (Scheme 4) has been postulated to explain the data from mechanistic studies. A single electron transfer (SET) from the aryl ring to the coordinated Cu(II) leading to the cation-radical intermediate is the rate-limiting step. The lack of reactivity of biphenyl led to the suggestion that the coordination of Cu(II) to the pyridine is necessary for the SET process. The observed ortho selectivity is explained by an intramolecular anion transfer from a nitrogen-bound Cu(I) complex.53... 

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