Generation of manganese-(III) versus -(IV) complexes with a conjugated ONS donor set: controlling effect of ligand substituents †

Abstract

Manganese() complexes, [MnL 2 ] [H 2 L = MeC(OH)᎐ ᎐ CHCMe᎐ ᎐ NN᎐ ᎐ C(SH)SR (R = Me 1a or CH 2 Ph 1b)] and manganese() complexes, [Mn(O 2 CMe)L] 1c or [Mn(acac)L] 1d [acac = acetylacetonate; H 2 L = PhCH(OH)CPh᎐ ᎐ NN᎐ ᎐ C(SH)SCH 2 Ph] have been synthesized and characterized. The Schiff-base ligands which are derived from an aliphatic carbonyl function, favour the facile oxidation of manganese-() to -() under ambient conditions.The structure determination of 1a showed that the molecule is octahedral with the two equivalent tridentate ligands spanned meridionally. The EPR spectrum of 1a with a strong but structured signal at g ≈ 4.0 and a weak one at g ≈ 2.0 implies a large zero-field splitting, but the spectral profile differed from an ideal axial form. All the complexes exhibited reversible or quasi-reversible Mn IV -Mn III redox couples in their cyclic voltammograms at potentials commensurate with the nature of the substituents in the appropriate ligands. A reasonable basis is suggested by which one may predict whether a particular ligand will stabilize manganese-(), -() or -() in an aerobic medium.

X-Band Electron Paramagnetic Resonance Comparison of Mononuclear MnIV-oxo and MnIV-hydroxo Complexes and Quantum Chemical Investigation of MnIV Zero-Field Splitting

“…This results in overlapping transitions that complicate spectral simulations. Consequently, analysis of X-band EPR data collected for Mn IV centers is often limited to indicate whether | D | ≈ 0.3 cm –1 or | D | ≫ 0.3 cm –1 , based on the relative intensities of the resonances at g eff = 4 and g eff = 2. ,− When | D | ≫ 0.3 cm –1 , the rhombicity can be estimated from the g -value of the low-field transition, where this transition is observed at g eff = 4.1 and 5.5 at the axial ( E / D = 0) and rhombic ( E / D = 1/3) limits, respectively. ,, A more rigorous analysis of the spin Hamiltonian parameters requires extensive computer simulation of variable-temperature X-band EPR spectra and/or the use of larger microwave frequencies. − ,,, At much larger microwave frequencies (95–700 GHz) and magnetic fields, where | D | ≪ h ν, D and E can be accurately determined directly from the positions of the EPR resonances of Mn IV centers. , Alternatively, variable-temperature, variable-field magnetic circular dichroism (VTVH MCD) spectroscopy can be analyzed to determine ground-state zero-field splitting parameters for Mn IV centers. , However, this analysis has the complication that the VTVH MCD data are dependent on both ground-state spin Hamiltonian parameters ( g -values and ZFS parameters) and the transition moment products ( M xy , M xz , and M yz ) of the electronic transition under interrogation. , …”

A new heterogeneous catalyst for epoxidation of alkenes via one-step post-functionalization of IRMOF-3 with a manganese(ii) acetylacetonate complex

“…8c The spectrum of the functionalized MOF exhibited a new band at 1523 cm À1 , which may be attributed to vibration of the acetylacetonate anion. 10 The 1 H NMR spectrum of the digested IRMOF-3[Mn] (see Fig. S3, ESIw) shows three new peaks at 2.06, 1.94 and 1.85 ppm due to -CH 3 groups, 11 further confirming the presence of acac and imine-functionalized acac ligand species attached to IRMOF-3.…”

Electronic versus steric control in manganese-hydroxamate chemistry: synthesis and characterization of Mn(II) and Mn(III)-hydroxamate complexes and catalytic epoxidation of olefins using the Mn(III) complexes as catalyst and H2O2 as terminal oxidant

“…From the vapor pressure osmometric data (see Section 2) in acetonitrile the molecular weights of 2 and 3, were assessed, which are nicely comparable to the calculated value. The ease of oxidation of Mn(II) aerially to Mn(III) or even to Mn(IV) is well documented [6,19]. In this connection two reports from Refs.…”