Transition metal substituted polyoxometalate 4 with

Goals and five limitations in conjunction with the development of selective catalytic homogeneous oxidation systems are evaluated. Systems are presented that address several of the problems or goals. One involves oxidation of alkenes by hypochlorite catalyzed by oxidatively resistant d-electron-transition-metal-substituted (TMSP) complexes. A second involves oxidation of alkenes by H2O2 catalyzed by specific TMSP complexes, and a third addresses functionalization of redox active polyoxometalate complexes with organic groups. 

Polyoxometalates (POMs), also known as heteropolyacids (HPA),3 are a class of compounds formed from negatively charged inorganic metal-oxygen building blocks. When charge-balanced with cationic species, POMs self-assemble into unusual 3D structures with specific topological and electronic properties.214 POMs are commonly formed from polyanions of early transition metals such as W, Mo or V. These anions can be substituted with other transition metals. The diversities in POMs composition and structure make them attractive for many applications, particularly as Bronsted acid and redox catalysts. For example,... 

Neumann and co-workers have used sandwich-type polyoxometalates as catalysts for such reactions.305 The sandwich consists of transition metal ions between two Keggin anions, as in Ki2WZnMn(II)2(ZnW9034)2. In some cases, quaternary ammonium salts were used as the cations to take the catalyst into organic solvents. Sulfides were oxidized to sulfoxides with 30% aqueous hydrogen peroxide in 85-90% yields, with some sulfone also being formed. The system was more than 99% selective in the conversion of cyclooctene to its epoxide. The system also shows good selectivity between double bonds (6.57), probably the result of the bulky anion and the increased electron density in alkyl-substituted double bonds. 

The pores of friendly nanomaterials could be used to store strong adds, even super acids, in some cases. Likewise, weak bases or strong bases could be stored for use as needed in killing or destroying advanced enemy toxins. In addition, the nanomaterial itself could be produced with acidic sites (metal ions and/or certain proton donors) built into the pore walls and crystal faces. For example, titanium or zirconium ions can serve as acid sites if adjacent to sulfate species. Likewise, the proton forms of some transition-metal oxygen-anion clusters (polyoxometalates or POMs ), like some metal oxides, are effective superacids in commercial processes. Polyoxometalates could be physically held within the pores or could be grafted onto the pore walls or onto the outer nanocrystal faces. Basic sites can also be built into the nanostructure, such as oxide anions near a metal cation vacancy. There are many other possibilities, such as sulfide substitution for oxide anions on the surface of the nanocrystals. 

Additional features of polyoxometalates impact some of the six limitations. First, polyoxometalates are oxidatively resistant as a great majority of them are composed of d° transition metal ions (most commonly W(VI), Mo(V), and/or V(V)) and oxide ions. Second, the unusually high stability of polyoxometalates coupled with the tunability of their catalytically relevant properties defines a considerable ability to avoid problems associated with intermediate oxidation states, p-oxo dimers, and product inhibition. Illustrations of two representative polyoxometalates, Wio0324 , an isopolyoxometalate (or isopolyanion) and (TM)XWii039 , a transition metal (TM) substituted heteropolyoxometalate (or heteropolyanion) in polyhedral notation are given in Figure 1. 

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