Catalytic activity of the Co(II)/Co(III) couple towards peptide bond cleavage and formation of molecular oxygen adducts in protic amide solutions

Formamide and N-methylformamide solutions containing variable amounts of Co(II) and Co(III) halide were employed as model systems to explain the catalytic potential of these ions towards amide bond cleavage reaction. The νCO downshifts in the IR spectra and the νCN upshifts in the Raman spectra are in agreement with the stabilization of a molecular structure near the dipolar amide form, which is considered the active species for catalysis. Quantitative analyses performed at the νCN and δOCN regions reveal the existence of four- and five-coordinate Co(II) complexes, but the addition of an oxidizing agent leads to the formation of five- and six-coordinate structures around Co(III) in 1:1 and 1:2 (O2/Co) type adducts. Attempt to correlate the electrostatic potential with the limiting canonical amide forms is also presented.