A close structural analogue of the cytochrome c oxidase active site has been synthesized. Oxygenation at -60 degrees C leads to a stable Fe(III)-superoxide-Cu(I) intermediate oxy-1 which reacts intramolecularly at -40 degrees C and faithfully reproduces the single turnover reaction that occurs in the enzyme leading to the formation of an oxoferryl-cupric-phenoxyl radical species 2.