Homogeneous green oxidation catalysts

VI. The Activity-Stability Parameterization of Homogeneous Green Oxidation Catalysts... 

To date, many soluble transition metal-based homogeneous catalysts including POMs have been developed for H202- and 02-based green oxidations. They are usually dissolved in reaction solutions, making all catalytic sites accessible to... 

The field of gold-catalysed oxidation reactions is clearly dominated by heterogeneous catalysts and many reports have been published on this topic. " Although much less predominant, some examples of efficient homogeneous gold-promoted oxidations using green oxidants have been reported. 

Abstract The catalytic oxidation is an area of the key technologies for converting petroleum-based feedstocks to useful chemicals such as diols, epoxides, alcohols, and carbonyl compounds. Many efficient homogeneous and heterogeneous oxidation systems based on polyoxometalates (POMs) with green oxidants such as H2O2 and O2 have been developed. This chapter summarizes the remarkable oxidation catalyses by POMs with multimetallic active sites. The multifunctionality of multimetallic active sites in POMs such as cooperative activation of oxidants, simultaneous activation of oxidants and substrates, stabilization of reaction intermediates, and multielectron transfer leads to their remarkable activities and selec-tivities in comparison with the conventional monometallic complexes. Finally, the future opportunities for the development of shape- and stereoselective oxidation by POM-based catalysts are described. 

Two major mechanisms have been proposed for alkene polymerization. These are the Cossee-Arlman mechanism and the Green-Rooney mechanism. A modified version of the latter has also been considered to explain the behavior of homogeneous, metallocene catalysts. The original Cossee-Arlman mechanism was proposed for the TiCl3 based heterogeneous catalyst. In the following sections we discuss these different mechanisms in some detail. In the following discussion in accordance with the results obtained from the metallocene systems, the oxidation states of the active surface sites are assumed to be 4+. 

---