Eighteenth paper from a Short-Term Scientific Mission (STSM) (December 10, 2017)
This paper represents the work published as a result of collaboration between the group of Christine McKenzie (University of Southern Denmark, DK) and Wesley Browne (University of Groningen, NL) in which Ph.D. student Christina Wegeberg (University of Southern Denmark) visited the University of Groningen as part of a Short Term Scientific Mission in order to perform time-resolved spectroscopic measurements. The STSM has formed the basis of a rich and fruitful collaboration between the two groups, where Christina regularly continues to visit Groningen to use the rRaman facilities as a part of her Ph.D. studies. Part of the work was presented by Christine McKenzie at the ECOSTBio meeting in Dublin (December 2017).
The work demonstrates that the reactivity of [FeIII(tpena)]2+ (tpena=N,N,N'-tris(2-pyridylmethyl)ethylenediamine-N'-acetate) as a catalyst for oxidation reactions depends on its ratio to the terminal oxidant H2O2 and presence or absence of sacrificial substrates. The outcome can be switched between: 1) catalyzed H2O2 disproportionation, 2) selective catalytic oxidation of methanol or benzyl alcohol to the corresponding aldehyde, or 3) oxidative decomposition of the tpena ligand. A common mechanism is proposed involving homolytic O-O cleavage in the detected transient [(tpenaH)FeIIIO-OH]2+. The resultant iron(IV) oxo and hydroxyl radical both participate in controllable hydrogen-atom transfer reactions. The work not only presents a germane mimic for non-heme iron chemistry, especially in terms of the carboxylato group and the second coordination sphere base, but it also adds to the knowledge of ligand design features important for activating H2O2, demonstrates controllable bifurcation in catalysed external substrate oxidation reactions, and indicates that destructive oxidation of the supporting ligand can be avoided through appropriate experimental design.
