THE REACTION OF COBALT(III) BETA-KETOENOLATES WITH TRIFLUOROACETIC-ACID

The reaction of cobalt(III) beta-ketoenolates with trifluoroacetic aci d (tfa) results in a ligand-to-metal electron-transfer process with th e formation of radical species which have been detected and characteri zed by ESR spectroscopy. Depending upon the structure of the beta-keto enolate ligand, the spin delocalization varies markedly, so that the r adicals can be described as cationic derivatives of cobalt(III) contai ning a cobalt-bonded beta-ketoenolyl radical, or as cationic beta-keto enolates of cobalt(IV). The formation of these radicals was accompanie d by mononuclear high-spin cobalt(II) derivatives whose ESR spectra be came observable at temperatures below 50 K. Some aspects of the chemis try behind the reaction of tris(acetylacetonato)cobalt(III) with tfa a re understood through UV/VIS, IR, ESR and ion spray mass spectrometry studies. On the basis of these as well as of an ESR study of the react ion of tris(3-nitropentane-2,4 dionato)cobalt(III) with oxidants such as CoF3, ASB F-4, Tl(OCOCF3)(3) and tetracyanoethylene, a possible rou te to the radicals observed is discussed.