A tris(pyrazolyl)-based model for the aminocyclopropane carboxylic acid oxidase and its behavior towards oxidants

A low-molecular-weight analog of the 1-aminocyclopropane carboxylic acid oxidase (ACCO), [TpMesFeACC], 1, where the (His₂Asp)iron(II) moiety is mimicked by a hydrotris(3-mesitylpyrazol-1-yl)borato iron(II) unit, to which the natural substrate aminocyclopropane carboxylate is coordinated, has been accessed and structurally characterized. It was found to react slowly with O2 to yield the biological product ethylene. To create models of the intermediates proposed as part of the catalytic cycle of the ACCO 1 was treated with tBuOOH and mCPBA at low temperatures, which generated the respective FeIIIOOtBu and FeIV=O intermediates as shown by spectroscopic analysis. Studies on their behavior upon annealing reveal a non-biomimetic reactivity.Graphical Abstract