Mn-Peroxo adduct supported by a new tetradentate ligand shows acid-sensitive aldehyde deformylation reactivity.

The new tetradentate L7BQ ligand (L7BQ = 1,4-di(quinoline-8-yl)-1,4-diazepane) has been synthesized and shown to support MnII and MnIII-peroxo complexes. X-ray crystallography of the [MnII(L7BQ)(OTf)2] complex shows a monomeric MnII center with the L7BQ ligand providing four donor nitrogen atoms in the equatorial field, with two triflate ions bound in the axial positions. When this species is treated with H2O2 and Et3N at -40 °C, a MnIII-peroxo adduct, [MnIII(O2)(L7BQ)]+ is formed.

Spectroscopic and Computational Investigation of Low-Spin Mn(III) Bis(scorpionate) Complexes.

Six-coordinate Mn complexes are typically high-spin ( = 2), however, the scorpionate ligand, both in its traditional, hydridotris(pyrazolyl)borate form, Tp and Tp* (the latter with 3,5-dimethylpyrazole substituents) and in an aryltris(carbene)borate (, -heterocyclic carbene, NHC) form, [Ph(MeIm)B], (MeIm = 3-methylimidazole) lead to formation of bis(scorpionate) complexes of Mn with spin triplet ground states; three of which were investigated herein: [TpMn]SbF (SBF), [Tp*Mn]SbF (SBF), and [{Ph(MeIm)B}Mn]CFSO (CFSO). These trigonally symmetric complexes were studied experimentally by magnetic circular dichroism (MCD) spectroscopy (the propensity of to oxidize to Mn precluded collection of useful MCD data) including variable temperatures and fields (VTVH-MCD) and computationally by ab initio CASSCF/NEVPT2 methods. These combined experimental and theoretical techniques establish the A electronic ground state for the three complexes, and provide information on the energy of the "conventional" high-spin excited state (E) and other, triplet excited states.

X-ray Emission Spectroscopy of Biomimetic Mn Coordination Complexes.

Understanding the function of Mn ions in biological and chemical redox catalysis requires precise knowledge of their electronic structure. X-ray emission spectroscopy (XES) is an emerging technique with a growing application to biological and biomimetic systems. Here, we report an improved, cost-effective spectrometer used to analyze two biomimetic coordination compounds, [Mn(OH)(MeEBC)] and [Mn(O)(OH)(MeEBC)], the second of which contains a key Mn═O structural fragment.

X-Band Electron Paramagnetic Resonance Comparison of Mononuclear Mn(IV)-oxo and Mn(IV)-hydroxo Complexes and Quantum Chemical Investigation of Mn(IV) Zero-Field Splitting.

X-band electron paramagnetic resonance (EPR) spectroscopy was used to probe the ground-state electronic structures of mononuclear Mn(IV) complexes [Mn(IV)(OH)2(Me2EBC)](2+) and [Mn(IV)(O)(OH)(Me2EBC)](+). These compounds are known to effect C-H bond oxidation reactions by a hydrogen-atom transfer mechanism. They provide an ideal system for comparing Mn(IV)-hydroxo versus Mn(IV)-oxo motifs, as they differ by only a proton.

Formation, Characterization, and O-O Bond Activation of a Peroxomanganese(III) Complex Supported by a Cross-Clamped Cyclam Ligand.

Although there have been reports describing the nucleophilic reactivity of peroxomanganese(III) intermediates, as well as their conversion to high-valent oxo-bridged dimers, it remains a challenge to activate peroxomanganese(III) species for conversion to high-valent, mononuclear manganese complexes. Herein, we report the generation, characterization, and activation of a peroxomanganese(III) adduct supported by the cross-clamped, macrocyclic Me2EBC ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.

Geometric and electronic structure of a peroxomanganese(III) complex supported by a scorpionate ligand.

A monomeric Mn(II) complex has been prepared with the facially-coordinating Tp(Ph2) ligand, (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin Mn(II) ion. Treatment of this Mn(II) complex with excess KO2 at room temperature resulted in the formation of a Mn(III)-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate.