Iron catalysis transfer hydrogenation

Recently, iron catalysis gained general importance. Its catalytic chemistry has been summarized ([2] recent reviews [3, 4]). Iron(II) and iron(III) salts have a long history in radical chemistry. The former are moderately active in atom-transfer reactions as well as initiators for the Fenton reaction with hydrogen peroxide or hydroperoxides (reviews [5-12]). Important applications of this principle are the Kharasch-Sosnovsky reaction (the allylic oxidation of olefins) [13], which often... 

Low-Valent Iron Catalysis 1,5-Hydrogen Transfer/Kumada Coupling... 

The identity of active catalytic species for the TH of ketones with our iron carbonyl [6.5.6]-P-N-N-P complexes was still unclear. Did the imine or imines on the ligand get reduced in situ, allowing catalysis to occur through a bifunctional outer sphere mechanism, as seen with the analogous ruthenium systems This question drove us to further investigate the mechanism of transfer hydrogenation with our first generation [6.5.6]-P-N-N-P systems. 

Recent developments on iron catalysis have shown the enormous potential of this metal in the reduction of carbonyl groups with hydrogen or using transfer hydrogen and silanes as reducing agents [69]. However, the use of well-defined iron-NHC complexes as catalysts for these reduction processes is rather undeveloped [72]. 

The mechanism of catalysis by HRP [Eqs. (5)—(7)] is generally well understood (8). The enzyme in its iron(III) resting state reacts initially with hydrogen peroxide to afford the so-called Compound I of HRP, which is two oxidation equivalents above the resting state. Compound I is involved in two one-electron oxidations. Transfer of the first electron at Compound I generates Compound II, which is one... 

The nse of polysnlfide complexes in catalysis has been discnssed. Two major classes of reactions are apparent (1) hydrogen activation and (2) electron transfers. For example, [CpMo(S)(SH)]2 catalyzes the conversion of nitrobenzene to aniline at room temperature, while (CpMo(S))2S2CH2 catalyzes a number of reactions snch as the conversion of bromoethylbenzene to ethylbenzene and the rednction of acetyl chloride, as well as the rednction of alkynes to the corresponding cw-alkenes. Electron transfer reactions see Electron Transfer in Coordination Compounds) have been studied because of their relevance to biological processes (in, for example, ferrodoxins), and these cluster compounds are dealt with in Iron-Sulfur Proteins. Other studies include the use of metal polysulfide complexes as catalysts for the photolytic reduction of water by THF and copper compounds for the hydration of acetylene to acetaldehyde. ... 

As was mentioned in the introduction and is discussed more fully under catalysis by iron salts, it is possible for hydrogen peroxide to react by single electron transfers thus giving rise to the free radicals HO- and HO2. Mechanisms for the reactions of the halides and halogens based on these ideas have been proposed by Weiss (26) and by Abel (27). The oxidation of iodide may be formulated ... 

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