Metal trifluoroacetates elimination

Aryltrimethylsilanes undergo a facile metal etal exchanges with lead(IV) trifluoroacetate the intermediate aryllead species then eliminate lead(II) acetate to form the corresponding aryl trifluoroacetates in almost quantitative yield (Scheme 20). 

Trifluoroacetato complexes of transition metals have also been obtained from oxidative elimination reactions in which neutral tt-acceptor ligands have been displaced in reactions with trifluoroacetic acid. These reactions may lead to hydrido complexes [Eqs. (6) (253) and (7) (26)] or they may not [Eqs. (8) (39) and (9) (19)]. 

Direct C-H activation of hydrocarbon by means of transition metals has also been explored. Cyclohexane reacted with Pd(OAc)2 in the presence of potassium persulfate-trifluoroacetic acid under CO pressure and produced the desired cyclo-hexanecarboxylic acid in low yields and TON (eq. (13)). The electrophilic carbox-ylation is explained by the change of Pd(OAc)2 to Pd(OCOCp3)2 in trifluoroacetic acid as solvent. Electrophilic attack on a C-H bond should give an alkyl Pd complex. CO insertion followed by reductive elimination affords a reactive mixed anhydride which was detected before workup. 

The hydrolysis of methyl trifluoroacetate has two slow steps. increases the rate of the first slow step by providing metal-bound hydroxide ion, a better nucleophile than water. Zn " " increases the rate of the second slow step by decreasing the basicity of the group that is eliminated from the tetrahedral intermediate. 

According to the results from isotope labeling experiments, the isomerization involves the initial attack of the proton from the acid to the Cp atom of the alkynyl ligand of 197. The subsequent migratory insertion of the resulting vinylidene into the metal-benzyl bond gives an alkenyl intermediate containing a coordinated trifluoroacetate anion, which evolves into 198 by trifluoroacetic acid elimination (Scheme 53). 

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