Ionic asymmetric oxidations

Horseradish peroxidase (HPO) has been reported to be threefold more stable at 80°C in 5-10% [bmim+][BF ] as compared to phosphate buffer [28], Okrasa et al. [29] reported the asymmetric oxidation of phenyl methyl- and 2-naphthyl methyl sulphides to sulphoxides catalysed by peroxidase from Coprinus cinereus in [bmim ] [PP6-] with 10% water [29], Although the enantioselectivity (63-92% ee) and yields (<32%) were similar to those in water, the reaction workup was easier because ionic liquids and the extraction solvent did not form emulsions. 

The radical or ionic character depends on the identity of the metal, the effective metal oxidation state, and the auxiliary ligands. These combined effects determine the reactivity, stereo- and regioselectivity toward acetylene insertion. For example, the reaction of CpCo(PPh3) (RC=CR ) with asymmetric acetylenes, RC=CR, gives a mixture of isomeric products ... 

Any electrons which reach the oxide—oxygen interface will be quickly utilized in the formation of 0" ions, and similarly, any positive holes which manage to reach the metal—oxide interface will be quickly annihilated by electrons from the parent metal. The asymmetrical surface reactions thus lead us to expect widely different electron concentrations in the oxide at the two interfaces of the oxide. This difference in electron concentration is equivalent to a difference in the chemical potential for the electronic species at the two interfaces. As in the case of the ionic defect species, such differences in concentration (and chemical potential) can be expected to produce particle currents of the defect species in question. If the primary electronic defects are excess electrons, then we can expect an electron particle current from metal to oxygen if the primary electron defects are the positive holes, then we can expect a positive-hole particle current from oxygen to metal. Of course, an intermediate situation is also possible in which electrons flow from the metal towards the oxygen while simultaneously a positive-hole current flows from the oxygen towards the metal, with recombination [8] (partial or total) occurring within the oxide film. 

The catalytic asymmetric epoxidation of alkenes offers a powerful strategy for the synthesis of enantiomerically enriched epoxides and enantioselective oxidation reactions in ionic liquids have been summarised previously.[39] Complexes based on chiral salen ligands - usually with manganese(III) as the coordinated metal - often afford excellent yields and enantioselectivities and the catalytic cycle for the reaction is depicted in Scheme 5.5 J40 ... 

Ionic solvents have been used to facilitate the Heck reaction (13-9), the oxidation of alcohols with hypervalent iodine reagents (19-3)," and the catalytic asymmetric dihydroxylation of olefins (15-48) using a recoverable and reusable osmium/... 

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