Formation and Decomposition of Iron-Carbon ?-Bonds in the Reaction of Iron(II)-Poly(amino carboxylate) Complexes with CO2- Free Radicals. A Pulse Radiolysis Study

Article abstract of DOI:10.1021/ja00220a030

The reactions of ferrous poly(amino carboxylate) complexes with CO2^- were studied at neutral pH in aqueous solutions.The results indicate that complexes with metal-carbon ?-bonds are formed as unstable intermediates with maximum absorption bands at 405 nm (e = 620 +/- 50 M^-1 cm^-1) and at 420 nm (e = 950 +/- 100 M^-1 cm^-1) for the NTA and HEDTA complexes, respectively.The transient complexes are in equilibrium with the ferrous poly(amino carboxylate) complex and CO2^- free radical.The stability constants for the complexes of CO2^- with ferrous NTA and HEDTA complexes were determined to be larger than 1E5 M^-1.The kinetics of formation and decomposition and possibile reaction mechanisms for these intermediates are discussed.We determined the specific rate constants for the formation of the iron-carbon ?-bonds (1.5 x 1E7 and 6.2 x 1E6 M^-1 s^-1 for NTA and HEDTA, respectively) as well as for the homolytic cleavage of the metal-carbon bond (140 and 25 s^-1 for NTA and HEDTA, respectively).It is shown that the ferrous poly(amino carboxylate) complexes induce the disproportionation of the CO2^-1 free radicals to form CO and CO2 via CO2^- + L-Fe^IIICO2^2- with specific rate constants of 1.9 x 1E7 and 4.5 x 1E6 M^-1 s^-1 for L = NTA and HEDTA, respectively.