Metal trifluoroacetates catalysis

The selective oxidation of C—H bonds in alkanes under mild conditions continues to attract interest from researchers. A new procedure based upon mild generation of perfluoroalkyl radicals from their corresponding anhydrides with either H2O2, m-CPBA, AIBN, or PbEt4 has been described. Oxidation of ethane under the reported conditions furnishes propionic acid and other fluorinated products.79 While some previously reported methods have involved metal-mediated functionalization of alkanes using trifluoroacetic acid/anhydride as solvent, these latter results indicate that the solvent itself without metal catalysis can react as an oxidant. As a consequence, results of these metal-mediated reactions should be treated with caution. The absolute rate constants for H-abstraction from BU3 SnH by perfluorinated w-alkyl radicals have been measured and the trends were found to be qualitatively similar to that of their addition reactions to alkenes.80 a,a-Difluorinated radicals were found to have enhanced reactivities and this was explained as being due to their pyramidal nature while multifluorinated radicals were more reactive still, owing to their electrophilic nature.80... 

In so far as metal trifiuoroacetates have been used as catalysts, the features of trifluoroacetate groups that would appear to be valuable in this respect include their ability to support a structure in which two or more metal centers are in close proximity, the ease with which they may be displaced from the coordination of an atom to generate sites for catalysis, together with their thermal stability and chemical inertness that minimize unwanted side reactions. 

Hydros lylation of a-amino ketones (66 and 68) exhibited extremely high levels of selectivity in either direction depending on the reaction conditions (equations 17 and 18). The iyn-alcohol (67) was the exclusive product of the fluoride-catalyzed reduction, while trifluoroacetic acid catalysis generated the anti isomer (69). Both these examples of highly diastereocontrolled reduction depended on the selection of either an open Felkin or a proton- or metal-bridged transition state. 

The O-phenylation reaction of enols by tetraphenylbismuthonium trifluoroacetate (6) was marginally improved by copper catalysis. Enolised diketones are 0-phenylated by triphenylbismuth diacylates in moderate to good yields. With the a-diketone (108), the best yields were obtained with triphenylbismuth bis(trifluoroacetate) in the presence of metallic copper. p-Diketones reacted only with triphenylbismuth bis(trifluoroacetate) in the presence of a copper catalyst.27... 

---