Metal-complex catalysis free radical chain

Transition-metal ions such as Fe(III), Cu(II), Co(II), Co(III), and Mn(II) have been shown to be effective homogeneous catalysts for the autoxidation of sulfur dioxide in aqueous solution. Hoffmann and coworkers have shown that Fe(III) and Mn(II) are the most effective catalysts at ambient concentrations for the catalytic autoxidation of S(IV) to S(VI) in cloudwater and fogwatet (Jacob and Hoffmann, 1983 Hoffmann and Jacob, 1984 Hoffmann and Calvert, 1985). Mechanisms for the homogeneous catalysis by Fe(lII) and Mn(II) that have been proposed include a free-radical chain mechanism, a polar mechanism involving inner-sphere complexation followed by a two-electron transfer from S(IV) to bound dioxygen, and photoassisted electron transfer. 

One-electron oxidation or reduction of saturated molecules frequently results in the generation of free radicals . The catalysis of certain free-radical reactions by ions or complexes of transition metals, such as (Tu, Co, and Mn, which exhibit variable oxidation states, is a consequence of this. Among such reactions are the autoxidations of hydrocarbons and other organic molecules (initially to hydroperoxides), which proceed by free-radical chain mechanisms in which the important propogation steps are ... 

In recent years, the studies in the field of homogeneous catalytic oxidation of hydrocarbons with molecular oxygen were developed in two directions, namely, the free-radical chain oxidation catalyzed by transition metal complexes and the catalysis by metal complexes that mimic enzymes. Low yields of oxidation products in relation to the consumed hydrocarbon (RH) caused by the fast catalyst deactivation are the main obstacle to the use of the majority of biomimetic systems on the industrial scale. 

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