Oxidation with Mono-Oxygen Donors

One class of polyoxometalate compounds is that in which transition or main group metals, often in a lower oxidation state, substitute for a tungsten- ormolybdenum-oxo group at the polyoxometalate surface. The substituting metal center is thus penta-coordinated by the parent polyoxometalate. The octahedral coordination sphere is 

It is important to note that the catalysts are orthogonal in their catalytic activity, that is, JMn 2ZnW(ZnW9034)2] is active only for alkene epoxidation but not for alcohol or alkylarene oxidation, while for [PV2M010O40] the opposite is true. The 

Further research into the reaction mechanism revealed that the reaction rate was correlated with the electron structure of the sulfoxide the more electropositive sulfoxides were the better oxygen donors. Excellent correlation of the reaction rates with the heterolytic benzylic carbon-hydrogen bond dissociation energies indicated a hydride abstraction mechanism in the rate-determining step to yield a carbocation intermediate. The formation of 9-phenylfluorene as by-product in the oxidation of triphenylmethane supports this suggestion. Further kinetic experiments and NMR showed the formation of a polyoxometalate-sulfoxide complex before the oxidation reaction, this complex being the active oxidant in these systems. Subsequently, in a similar reaction system, sulfoxides were used to facilitate the aerobic oxidation of alcohols [29]. In this manner, benzylic, allyUc, and aliphatic alcohols were all oxidized to aldehydes and ketones in a reaction catalyzed by Ke jn-type 

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Primary amines are oxidized to the corresponding oximes. The sequence of reactions closely parallels the sequence observed with other mono oxygen donors, i.e., oxidation to alkyl hydroxylamines (V) followed by oxidation to alkylnitroso compounds (VI) which, via a prototropic shift, rearrange to the oximes (VII) ... 

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