Metal complex photocatalyst

Keywords Electron transfer Metal complex photocatalyst Photocatalytic CO2 reduction Semiconductor photocatalyst Supramolecular chemistry... 

To this category belong, e.g., homogeneous photocatalytic systems based on soluble metal complexes or organic dyes as photocatalysts. Instructive examples are photoreactions assisted by heteropolyacids (HPAs), transition meal complexes with carbonyl, phosphine or some other ligands, and metal porphyrins. 

Scheme 7 illustrates the transformations of a bicycloheptadiene in the presence of transition metal complexes as photocatalysts or photogenerated catalysts [11] ... 

The selective oxidation and, more generally, the activation of the C-H bond in alkanes is a topic of continuous interest. Most methods are based on the use of strong electrophiles, but photocatalytic methods offer an interesting alternative in view of the mild conditions, which may increase selectivity. These include electron or hydrogen transfer to excited organic sensitizers, such as aryl nitriles or ketones, to metal complexes or POMs. The use of a solid photocatalyst, such as the suspension of a metal oxide, is an attractive possibility in view of the simplified work up. Oxidation of the... 

Although the experimental evidence suggests that the observed photogeneration of hydrogen may not involve homogeneous metal dithiolene photocatalysts, a theoretical study by Alvarez and Hoffmann addressed possible mechanisms for hydrogen elimination from ds square-planar bis(dithiolene) complexes (77). Concerted elimination of H2 from protonated sulfur atoms in the complex was proposed to be a thermally forbidden but photochemically allowed pathway, and protonation of a metal hydrido complex was also considered, as shown in Scheme 3. 

The photochemistry of Cp(arene)Fe + complexes has been extensively examined since the discovery of photochemical arene loss by Nesmeyanov, and this class of compounds has received considerable attention as a cationic photocatalyst for the polymerization of epoxides, dicyanate esters, and styrene among others. As in the case of the bis(arene)metal complexes described above, photolysis is believed to initiate an r] - transformation whereupon solvent enters the open site and thermally displaces the arene ligand. Consistent with this the quantum yields indicate a significant associative component in the ligand displacement. Time-resolved studies indicate that the initial photochemical event occurs on the fs or ps scale. There has been substantial confusion concerning the role of singlet and triplet excited states in the observed photochemistry. Sensitization studies established a... 

TRANSITION METAL COMPLEXES AS SOLAR PHOTOCATALYSTS IN THE ENVIRONMENT A SHORT REVIEW OF RECENT DEVELOPMENT... 

The role of photocatalysis by transition metal complexes in the environment is reviewed, and its influence on composition of the environmental compartments, transport between them, and activation of the environmental self-cleaning behavior is characterized. In description of atmospheric processes, the attention is paid to coordination compounds as photocatalysts of the transfer and redox reactions of nitrogen oxides. In the case of hydrosphere and soils, various mechanisms of organic pollutant photodegradations are presented in which the iron, copper, and chromium complexes play... 

The C—H bond can be activated by a metal complex, particularly when the complex plays the role of catalyst or photocatalyst. The reactions of hydrocarbons with metal complexes occur at low temperatures and can be selective. There are different pathways for C—H bond activation (i) by low-valence metal complexes, (ii) by high-valent metal-oxo compounds, (iii) by molecular oxygen and oxygen atom donors, (iv) by biological oxidation, or (v) by photocatalytic enhancement (21). 

Solar photocatalysts. See Transition metal complexes Spectral sensitization aspects, 248... 

The prototypical photochemical system for CO2 reduction contains a photosensitizer (or photocatalyst) to capture the photon energy, an electron relay catalyst (that might be the same species as the photosensitizer) to couple the photon energy to the chemical reduction, an oxidizable species to complete the redox cycle and CO2 as the substrate. Figure 1 shows a cartoon of the photochemical CO2 reduction system. An effective photocatalyst must absorb a significant part of the solar spectrum, have a long-lived excited state and promote the activation of small molecules. Both organic dyes and transition metal complexes have been used as photocatalysts for CO2 reduction. In this chapter, CO2 reduction systems mediated by cobalt and nickel macrocycles and rhenium complexes will be discussed. 

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