Catalytic Four-Electron Reduction of Dioxygen by Ferrocene Derivatives with a Nonheme Iron(III) TAML Complex.

A mononuclear nonheme iron(III) complex with a tetraamido macrocyclic ligand (TAML), [(TAML)Fe] (), is a selective precatalyst for four-electron reduction of dioxygen by ferrocene derivatives in the presence of acetic acid (CHCOOH) in acetone. This is the first work to show that a nonheme iron(III) complex catalyzes the four-electron reduction of O by one-electron reductants. An iron(V)-oxo complex, [(TAML)Fe(O)] (), was produced by oxygenation of with O via the formation of triacetone triperoxide (TATP), acting as an autocatalyst that shortened the induction time for the generation of . Decamethylferrocene (MeFc) and octamethylferrocene (MeFc) reduced to by two electrons in the presence of CHCOOH to produce decamethylferrocenium cation (MeFc) and octamethylferrocenium cation (MeFc), respectively. Then, was oxygenated by O to regenerate via the formation of TATP. In the cases of ferrocene (Fc), bromoferrocene (BrFc) and 1,1'-dibromoferrocene (BrFc), initial electron transfer from ferrocene derivatives to occurred; however, neither a second proton-coupled electron transfer from ferrocene derivatives to nor a catalytic four-electron reduction of O occurred.