C-H Bond Oxidation by Mn-Oxo Complexes: Hydrogen-Atom Tunneling and Multistate Reactivity.

The reactivity of six Mn-oxo complexes in C-H bond oxidation has been examined using a combination of kinetic experiments and computational methods. Variable-temperature studies of the oxidation of 9,10-dihydroanthracene (DHA) and ethylbenzene by these Mn-oxo complexes yielded activation parameters suitable for evaluating electronic structure computations. Complementary kinetic experiments of the oxidation of deuterated DHA provided evidence for hydrogen-atom tunneling in C-H bond oxidation for all Mn-oxo complexes.

Enhanced Understanding of Structure-Function Relationships for Oxomanganese(IV) Complexes.

A series of manganese(II) and oxomanganese(IV) complexes supported by neutral, pentadentate ligands with varied equatorial ligand-field strength (N3pyQ, N2py2I, and N4py) were synthesized and then characterized using structural and spectroscopic methods. On the basis of electronic absorption spectroscopy, the [Mn(O)(N4py)] complex has the weakest equatorial ligand field among a set of similar Mn-oxo species. In contrast, [Mn(O)(N2py2I)] shows the strongest equatorial ligand-field strength for this same series.

Differences in chemoselectivity in olefin oxidation by a series of non-porphyrin manganese(IV)-oxo complexes.

High valent metal-oxo intermediates are versatile oxidants known to facilitate both oxygen atom transfer (OAT) and hydrogen atom transfer (HAT) reactions in nature. In addition to performing essential yet challenging biological reactions, these intermediates are known for their selectivity in favoring the formation of one oxidation product. To understand the basis for this selectivity, we explore the role of equatorial ligand field perturbations in Mn-oxo complexes on chemoselectivity in cyclohexene oxidation.

Concerted proton-electron transfer reactions of manganese-hydroxo and manganese-oxo complexes.

The enzymes manganese superoxide dismutase and manganese lipoxygenase use Mn-hydroxo centres to mediate proton-coupled electron transfer (PCET) reactions with substrate. As manganese is earth-abundant and inexpensive, manganese catalysts are of interest for synthetic applications. Recent years have seen exciting reports of enantioselective C-H bond oxidation by Mn catalysts supported by aminopyridyl ligands.

Steric control of dioxygen activation pathways for Mn complexes supported by pentadentate, amide-containing ligands.

Dioxygen activation at manganese centers is well known in nature, but synthetic manganese systems capable of utilizing O as an oxidant are relatively uncommon. These present investigations probe the dioxygen activation pathways of two mononuclear Mn complexes supported by pentacoordinate amide-containing ligands, [Mn(dpaq)](OTf) and the sterically modified [Mn(dpaq)](OTf). Dioxygen titration experiments demonstrate that [Mn(dpaq)](OTf) reacts with O to form [Mn(OH)(dpaq)](OTf) according to a 4 : 1 Mn : O stoichiometry.