Metal oxide-based compounds electron transfer reaction

First of all, note that the term "oxidation" is based on a historical premise that is not relevant from a more modem perspective namely, the combining of another element with oxygen to form a simple binary compounds i.e., an "oxide" similarly, the removal of oxygen atoms from an oxide molecule leaving the "reduced" element was the concept intended for the term "reduction". Although this idea works fairly well for many of the more simple interactions of oxygen with both metal and non-metal elements, a better, more comprehensive, definition that includes similar reactions with other elements, such as fluorine and chlorine, evolved that was based on the transfer of electrons from one atom (or ion) to another. 

The aim of this chapter is to examine the application of well-defined N-heterocyclic carbene (NHC) complexes, as well as the systems prepared in situ which involve free NHCs or the precursor salt, for the reduction of unsaturated organic molecules such as alkynes, alkenes and carbonyl compounds. The most active complexes for such reactions are based on electron-rich, late transition metals in low oxidation states. Herein, reductions useful for organic synthesis will be classified into four types according to the hydride source used (i) hydrogenations, (ii) transfer hydrogenation, (iii) hydrosilylation and (iv) hydroboration. For examples of reduction reactions with systems containing non-classical NHC ligands, the reader is referred to Chapter 5. 

The development of an electrode reaction is highly dependent on the nature of the electrode-solution interface. Most electrochemical processes are still performed using classical metallic or carbon electrodes. However, modifications brought to the surface of the working electrode may result in the enhancement of particular properties which can be exploited in electroanalytical chemistry. In such a way, many electrode materials, such as metals, metal oxides but also carbon based electrodes have been submitted to chemical or non-chemical modifications. Most of the immobilized compounds are electroactive, the electron transfer having to be reversible. They are mainly used as catalysts for electrochemical reactions which cannot be performed at conventional electrodes. In addition, a judicious choice of a catalyst exhibiting a particular structure may also provide more or less specificity towards certain molecules or ions. Electro-inactive substances may also be immobilized and act as intermediates for... 

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