Efficient Catalytic Systems for Electron Transfer from an NADH Model Compound to Dioxygen

Two-electron reduction of dioxygen with an NADH model compound, 10-methylacridan (AcrH₂), occurs efficiently in the presence of metalloporphyrins and perchloric acid in acetonitrile at 298 K. Overall four-electron reduction of dioxygen by AcrH₂ has also been made possible by adding iodide ion to the metalloporphyrin-catalyzed system. The catalytic mechanisms are discussed on the basis of detailed kinetics and the kinetic isotope effects for the overall CoTPP⁺-catalyzed reduction of dioxygen by AcrH₂ as well as for each half catalytic cycle, the oxidation of AcrH₂ by CoTPP⁺ and the reduction of dioxygen by CoTPP in the presence of HCIO₄.