The Reaction of Cobalt(III) beta-Ketoenolates with Trifluoroacetic Acid

The reaction of cobalt(lll) beta-ketoenolates with trifluoroacetic acid (tfa) results in a ligand-to-metal electron-transfer process with the formation of radical species which have been detected and characterized by ESR spectroscopy. Depending upon the structure of the beta-ketoenolate ligand, the spin delocalization varies markedly, so that the radicals can be described as cationic derivatives of cobalt(lll) containing a cobalt-bonded beta-ketoenolyl radical or as cationic beta-ketoenolates of cobalt(IV). The formation of these radicals was accompanied by mononuclear high-spin cobalt(ll) derivatives whose ESR spectra became observable at temperatures below 50 K. Some aspects of the chemistry behind the reaction of tris(acetylacetonato)cobalt(lll) with tfa are understood through UV /VIS, I R, ESR and ion spray mass spectrometry studies. On the basis of these as well as of an ESR study of the reaction of tris(3-nitropentane-2.4-dionato)cobalt(111) with oxidants such as CoF3 , AgBF4 , TI(OCOCF3 ) 3 and tetracyanoethylene, a possible route to the radicals observed is discussed.