Oxidation-reduction Taube mechanism

Taube, H. (1968). Mechanisms of oxidation-reduction reactions. /. Chem. Educ. 45,453-461. 

The last two decades have seen a growing interest in the mechanism of inorganic reactions in solution. Nowhere is this activity more evident than in the topic covered by this review the oxidation-reduction processes of metal complexes. This subject has been reviewed a number of times previously, notably by Taube (1959), Halpern (1961), Sutin (1966), and Sykes (1967). Other articles and books concerned, wholly or partly, with the topic include those by Stranks, Fraser , Strehlow, Reynolds and Lumry , Basolo and Pearson, and Candlin et al ° Important recent articles on the theoretical aspects are those by Marcus and Ruff. Elementary accounts of redox reactions are included in the books by Edwards , Sykes and Benson . The object of the present review is to provide a more detailed survey of the experimental work than has hitherto been available. 

Henry Taube, the 1983 Nobel Prize winner in chemistry, has studied the mechanisms of oxidation-reduction reactions involving transition metal complexes. In one experiment he and his students studied the following reaction ... 

Oxidation-reduction processes involving the Fe -Fe couple have been intensively studied, and the elementary electron exchange, taking place either in solution or at an electrode interface, has served for a long time as a test case for theoretical interpretations of electron transfer kinetics. For reactions involving ground-state ions, the mechanisms of the reactions are now well understood for the homogeneous systems, for example, electron transfer can occur, as demonstrated by Taube, via either a simple outer-sphere electron... 

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. 

According to Taube, the inner sphere mechanism can takes place when both oxidizing and reducing agents are substitution inert and when ligand transfer from oxidant to reductant is accompanied by electron transfer. The inner sphere electron transfer mechanism may be represented by the scheme... 

The mechanisms of reductions of other ions by Cr2+ have been extensively studied especially by H. Taube and his co-workers, since the resulting Cr3 + complex ions are substitution-inert. Much information regarding ligand-bridged transition states (page 675) has been obtained in this way. The products of oxidation of Cr2 + depend on the nature of the oxidant. With one-electron oxidants, the ions [Cr(H20)6]3+ or [Cr(H20)5X]2+, where X is derived from the oxidant, are the usual products. With two-electron oxidants there is the possibility of oxidation by the route ... 

Metal-ion reduction of both mononuclear and dinuclear carboxylatocobalt(m) complexes have been reviewed. There continues to be substantial interest in this subject and in particular the adjacent-attack mechanism for complexes with simple monocarboxylate ligands now appears to be well understood. The importance of the iimer-sphere mechanism in reductions by Eu + has been amply demonstrated. Gould has also illustrated the usefulness of the comparison of rate data from the reactions of a common oxidant by several reductants. Many workers are currently involved in attempts to measure first-order rates of electron transfer within precursor complexes. In the search for likely systems, the one chosen by Taube ... 

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