The reaction of cobalt(III)β-ketoenolates with trifluoroacetic acid

Abstract

The reaction of cobalt(III)β-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 β-ketoenolate ligand, the spin delocalization varies markedly, so that the radicals can be described as cationic derivatives of cobalt(III) containing a cobalt-bonded β-ketoenolyl radical, or as cationic β-ketoenolates of cobalt(IV). The formation of these radicals was accompanied by mononuclear high-spin cobalt(II) derivatives whose ESR spectra became observable at temperatures below 50 K. Some aspects of the chemistry behind the reaction of tris(acetylacetonato)cobalt(III) with tfa are 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 reaction of tris(3-nitropentane-2,4-dionato)cobalt(III) with oxidants such as CoF₃, AgBF₄, Tl(OCOCF₃)₃ and tetracyanoethylene, a possible route to the radicals observed is discussed.