A Structural and Functional Model for the 1-Aminocyclopropane-1-carboxylic Acid Oxidase

The hitherto most realistic low-molecular-weight analogue for the 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO) is reported. The ACCOs 2-His-1-carboxylate iron(II) active site was mimicked by a TpFe moiety, to which the natural substrate ACC could be bound. The resulting complex [Tp(Me,Ph)FeACC] (1), according to X-ray diffraction analysis performed for the nickel analogue, represents an excellent structural model, featuring ACC coordinated in a bidentate fashion-as proposed for the enzymatic substrate complex-as well as a vacant coordination site that forms the basis for the first successful replication also of the ACCO function: 1 is the first known ACC complex that reacts with O-2 to produce ethylene. As a FeOOH species had been suggested as intermediate in the catalytic cycle, H2O2 was tested as the oxidant, too, and indeed evolution of ethylene proceeded even more rapidly to give 65% yield.