A manganese(IV)-oxo complex derived from oxygen: Characterization and reactivity of [manganese(IV) hydrogen buea(oxygen)]-

Manganese-oxo complexes have long been investigated because of their proposed roles in biological and chemical catalysis. However, there are few examples of monomeric complexes with terminal oxo ligands, especially those with oxomanganese(IV) units. The research in this dissertation works toward expanding the knowledge of high-valent manganese oxo complexes and their properties using the ligand H6buea, described in the introductory chapter.;Chapter 2 will follow the one electron oxidation of a MnIII-oxo complex, (K2[MnIII(H3buea)(O)]), which has been previously prepared in the Borovik group. This reaction forms an unstable green species that is observed at -45°C in DMF and at room temperature in DMSO. The characterization of the oxidized product consists of UV-visible, quantitative EPR, and FTIR spectroscopies which all support the assignment of this green species as a monomeric MnIV-oxo complex. The chapter will examine the reactivity of the green species toward substrates promoting either hydrogen atom or oxygen atom transfer chemistry.;Chapter 3 explores the kinetics of hydrogen atom transfer (HAT) from various substrates to [MnIIIH3buea)(O)]- and [MnIVH3buea)(O)]-. This HAT event was predicted to proceed faster for the MnIV-oxo than the MnIII-oxo based on the bond dissociation energies previously calculated. The chapter takes a detailed look at the kinetics for the reaction of 9,10-DHA with both manganese complexes. The activation parameters for the reaction are derived and coupled with kinetic isotope effects to draw conclusions about the overall mechanism for each metal complex as well as the effects of basicity on hydrogen atom transfer reactions.;The topic of Chapter 4 is the mechanism of O2 activation by [MnIIH3buea(OAc)]2- and the intermediates observed along the way to forming [MnIIIH 3buea(OH)]2-. The mechanism for this reaction has been proposed in the past as a process in which two MnII complexes come together to activate one molecule of dioxygen creating two equivalents of what is proposed to be a MnIV-oxo complex. Using the knowledge learned from the study in Chapter 2, oxygen activation is revisited to probe for a MnIV-oxo intermediate. The chapter will also look at the ability of the MnII complex to catalytically transfer oxygen to phosphine substrates via this MnIV-oxo intermediate.