Generation of a Mn(IV)–Peroxo or Mn(III)–Oxo–Mn(III) Species upon Oxygenation of Mono- and Binuclear Thiolate-Ligated Mn(II) Complexes

Abstract

A thiolate-bridged binuclear complex [PPN][(Mn(PS3))] (1, PPN = bis(triphenylphosphine)iminium and PS3H = (2,2',2″-trimercapto-3,3',3″-tris(trimethylsilyl)triphenylphosphine)), prepared from the reaction of MnCl/[PPN]Cl and Li[PS3], converts into a mononuclear complex [PPN][Mn(PS3)(DABCO)] (2) in the presence of excess amounts of DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane). Variable temperature studies of solution containing 1 and DABCO by UV-vis spectroscopy indicate that 1 and 2 exist in significant amounts in equilibrium and mononuclear 2 is favored at low temperature. Treatment of 1 or 2 with the monomeric O-side-on-bound [PPN][Mn(O)(PS3)] (3) produces the mono-oxo-bridged dimer [PPN][(Mn(PS3))(μ-O)] (4). The electrochemistry of 1 and 2 reveals anodic peak(s) for a MnMn redox couple at shifted potentials against Fc/Fc, indicating that both complexes can be oxidized by dioxygen. The O activation mediated by 1 and 2 is investigated in both solution and the solid state. Microcrystals of 2 rapidly react with air or dry O to generate the Mn(IV)-peroxo 3 in high yield, revealing a solid-to-solid transformation and two-electron reduction of O. Oxygenation of 1 or 2 in solution, however, is affected by diffusion and transient concentration of dioxygen in the two different substrates, leading to generation of 3 and 4 in variable ratios.

Elucidating the Electronic Structure and Magnetic and Conducting Properties of μ-Oxo Mn-phthalocyanine [MnPc(CN)]2O Complex

“…These orbitals present large overlaps with the Mn d xz and d yz orbitals (Figure ), which are singly occupied in both ions and then control the magnetic interaction between them. Both the nature of the Mn–Mn interaction and its amplitude are in good agreement with those found for other quasi-linear Mn­(III)–O–Mn­(III) complexes. − …”

Synthesis and Characterization of Manganese Dithiocarbamate Complexes: New Evidence of Dioxygen Activation

“…When the complexes 1 and 4 came into contact with air, the yellow powder started to darken and progressively turned into a dark brown solid. Analyses of the products are consistent with the formation of the Mn(III) superoxide adduct ( 2 and 5 ) that can be generated from 1 and 4 by O 2 one-electron oxidation of the Mn(II) metallic center [ 7 , 16 , 17 , 18 , 19 , 20 ]. The effective magnetic moment results are in agreement with a d 4 high spin configuration characteristic of an octahedral Mn(III) environment.…”

“…After exposure of the product 4 to atmospheric dioxygen, the yellow powder started to darken and progressively turned into a dark brown solid, similar to what was observed with the product 1 . Analyses of the dark brown solid product are consistent with the formation of the Mn(III) superoxide adduct [MnL’ 2 (η 2 -O 2 )] ( 5 ) that can be generated from 4 by O 2 one-electron oxidation of the Mn(II) metallic center [ 17 , 18 , 19 , 20 , 21 , 22 ]. Elemental analyses of the dark brown product, collected 24 h after exposure to atmospheric oxygen, were in satisfactory agreement with theoretical values predicted for the formulation [MnL’ 2 (η 2 -O 2 )], where the O 2 ligand is supposedly coordinated in a side-on mode to preserve the octahedral arrangement.…”

“…A smaller peak is observed at m / z = 499.50. The peak at m / z = 383.06 is consistent with the formation of the Mn(III) superoxide adduct [MnL 2 (η 2 -O 2 )] (compound 2 ) that can be generated from 1 by O 2 one-electron oxidation of the Mn(II) metallic center [ 7 , 16 , 17 , 18 , 19 , 20 ]. Attempts at peak assignment suggest also that the peaks at m / z = 319.31 and 303.2 are consistent with the species [MnLH 2 O 2 (CH 3 CN) 2 ] + and [MnLH 2 O(CH 3 CN) 2 ] + , respectively, generated in CH 3 CN after the loss of the ligand L during mass analysis [ 17 ].…”

Improved Electrical Wiring of Glucose Oxidase Enzyme with an in-Situ Immobilized Mn(1,10-Phenanthroline)2Cl2-Complex/Multiwalled Carbon Nanotube-Modified Electrode Displaying Superior Performance to Os-Complex for High-Current Sensitivity Bioelectrocatalytic and Biofuel Cell Applications

“…The precursor Mn­(phen) 2 Cl 2 complex displayed characteristic peaks at 244, 290, and 350 analogous to the π–π* transition of the aromatic phen ligand (244, 290) and metal-to-ligand charge transistion (MLCT) of the manganese­(II)­bis­(1,10-phenanthroline) chloride complex . Whereas, the electronic spectra of ethanolic solution of GCE/f-MWCNT@Mn­(phen)Cl (Figure D, curve a) exhibits peaks at 239, 276, and 315 nm along with a low energy broad absorption peak at 478 nm due to transitions between molecular orbitals composed of orbital dπ of Mn and pπ of the oxo-bridge existing of a typical of oxo-ligand of a Mn­(phen) dimers, Mn III –μ-O oxo –Mn III . − In order to confirm the true Mn-complex species, ESI-MS analysis of ethanloic solution of the modified electrode was analyzed in comparison with the precursor complex [Mn II (phen) 2 Cl] + (ca. mol wt = 450.09) as in Supporting Information Figure S1A and B.…”