Mechanistic Links in the in-situ Formation of Dinuclear Manganese Catalysts, H2O2 Disproportionation, and Alkene Oxidation

The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [Mn-2(IV)(mu-O)(3)(tmtacn)(2)](2+) (1; tmtacn = 1,4,7-tri-methyl-1,4,7-triazacyclononane) is promoted by the addition of carboxylic acids through the in situ formation of bis-(carboxylato) complexes of the type [Mn-2(III)(mu-O)(mu-RCO2)(2)-(tmtacn)(2)](2+). The conversion of 1 to these complexes requires a complex series of redox reactions coupled with the overall exchange of mu-oxido ligands for mu-carboxylato ligands. Here, we show that the mechanism by which this conversion occurs holds implications with regard to the species that is directly engaged in the catalytic oxidation of alkenes. Through a combination of UV/Vis absorption, Raman, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy, it is shown that the conversion proceeds by an autocatalytic mechanism and that the species that engages in the oxidation of organic substrates also catalyses H2O2 decomposition, and the former process is faster.