Formation of stoichiometrically 18O-labelled oxygen from the oxidation of 18O-enriched water mediated by a dinuclear manganese complex—a mass spectrometry and EPR study

Abstract

Oxygen formation was detected for the oxidations of various multinuclear manganese complexes by oxone (HSO₅⁻) in aqueous solution. To determine to what extent water was the source of the evolved O₂, H₂¹⁸O isotope-labelling experiments coupled with membrane inlet mass spectrometry (MIMS) were carried out. We discovered that during the reaction of oxone with [Mn₂(OAc)₂(bpmp)]⁺ (1), stoichiometrically labelled oxygen (¹⁸O₂) was formed. This is the first example of a homogeneous reaction mediated by a synthetic manganese complex where the addition of a strong chemical oxidant yields ¹⁸O₂ with labelling percentages matching the theoretically expected values for the case of both O-atoms originating from water. Experiments using lead acetate as an alternative oxidant supported this finding. A detailed investigation of the reaction by EPR spectroscopy, MIMS and Clark-type oxygen detection enabled us to propose potential reaction pathways.