Carbonyl multimetallic

These complexes exhibit in dichloromethane solution a first ferrocene-based oxidation with features of chemical reversibility, followed by a second irreversible oxidation, which is thought to be centered on the metal-carbonyl fragment. A poorly reproducible oxidation of the Au moiety is also observable [49]. The relevant redox potentials are summarized in Table 7-35. With respect to the oxidation of free l,T-bis(diphenylphosphino)ferrocene E° = - -0.66 V) [49], the multimetallic com-plexation makes oxidation of the ferrocene fragment significantly more difficult (by about 0.4 V). 

Pt group metals can activate alcohols and molecular oxygen under close to ambient conditions, producing the corresponding carbonyl or carboxylic acids in high yields. Enhanced selectivity and activity has been obtained by the use of bi- and multimetallic catalysts.35-37 However, as was the case with selective hydrogenation, the optimum catalysts developed to date have... 

Monomeric platinum carbonyls 52L 4.4.2 Multimetallic platinum carbonyls... 

Pt group metals can activate alcohols and molecular oxygen under close to ambient conditions, producing the corresponding carbonyl or carboxylic acids in high yields. Enhanced selectivity and activity has been obtained by the use of bi- and multimetallic catalysts. " However, as was the case with selective hydrogenation, the optimum catalysts developed to date have involved a combination of supported metals and selectivity promoters. The most commonly used catalysts consist of either Pt or Pd as the active metal combined with Bi or Pb as promoters, commonly on carbon or alumina supports. Other promoters reported include Cd, Co, Cu, Se, ° Ce, Te, Sn, Au and Ru. The catalysts can be prepared by simultaneous deposition and reduction of the metal precursors onto a suitable support. However, more commonly, preparation involves a... 

Multimetallic cluster carbonyls that obey the 48-, 60-, 72-, or 86-electron rule, depending on whether there are 3,4,5, or 6 metals, respectively, in the cluster skeleton. Examples of such compounds are Ru3(CO)i2, Ir4(CO)i2, Ni5(CO)i2,andRh6(CO)i6. 

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. 

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