The oxomanganese­(IV) complex [(dpaq)­MnIV(O)]+-M n+ (1-M n+ , M n+ = redox-inactive metal ion, H-dpaq = 2-[bis­(pyridin-2-ylmethyl)]­amino-N-quinolin-8-ylacetamide), generated in the reaction of the precursor hydroxomanganese­(III) complex 1 with iodosylbenzene (PhIO) in the presence of redox-inactive metal triflates, has recently been reported. Herein the generation of the same oxomanganese­(IV) species from 1 using various combinations of protic acids and oxidants at 293 K is reported. The reaction of 1 with triflic acid and the one-electron-oxidizing agent [RuIII(bpy)3]3+ leads to the formation of the oxomanganese­(IV) complex. The putative species has been identified as a mononuclear high-spin (S = 3/2) nonheme oxomanganese­(IV) complex (1-O) on the basis of mass spectrometry, Raman spectroscopy, EPR spectroscopy, and DFT studies. The optical absorption spectrum is well reproduced by theoretical calculations on an S = 3/2 ground spin state of the complex. Isotope labeling studies confirm that the oxygen atom in the oxomanganese­(IV) complex originates from the MnIII–OH precursor and not from water. A mechanistic investigation reveals an initial protonation step forming the MnIII–OH2 complex, which then undergoes one-electron oxidation and subsequent deprotonations to form the oxomanganese­(IV) transient, avoiding the requirements of either oxo-transfer agents or redox-inactive metal ions. The MnIV–oxo complex cleaves the C–H bonds of xanthene (k 2 = 5.5 M–1 s–1), 9,10-DHA (k 2 = 3.9 M–1 s–1), 1,4-CHD (k 2 = 0.25 M–1 s–1), and fluorene (k 2 = 0.11 M–1 s–1) at 293 K. The electrophilic character of the nonheme MnIV–oxo complex is demonstrated by a large negative ρ value of 2.5 in the oxidation of para-substituted thioanisoles. The complex emerges as the “most reactive” among the existing MnIV/V–oxo complexes bearing anionic ligands.

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In biology, aromatic hydroxylation is carried out using a family of heme and nonheme oxygenases, such as cytochrome P450, toluene monooxygenases (TMOs), and methane monooxygenase (MMO). In contrast, a vast majority of synthetic iron based catalysts employed so far in aromatic hydroxylation are monomeric in nature. Herein, we have employed a diferric complex of an aminopyridine ligand ([(bpmen)2Fe2O(μ-O)(μ-OH)](ClO4)3 (2), bpmen = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) towards aromatic hydroxylation with H2O2 and acetic acid. The diiron(iii) complex shows promising reactivity in the hydroxylation of benzene and alkylbenzenes with a higher selectivity towards aromatic ring hydroxylation over alkyl chain oxidation. The μ-oxo diiron(iii) core has been shown to be regenerated at the end of catalytic turnover. However, mechanistic studies indicate that the diiron(iii) complex undergoes dissociation into its monomeric congener and the resulting iron(iii) complex mitigates aromatic hydroxylation.

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500 ns the difference spectrum evolves to a more resolved absorbance centered at 390 nm extending to 450 nm. This spectrum persists out to the maximum time delays obtainable (50-100 jus); notable is the fact that this spectrum is similar to that of TIH2 (see Figure 1). Time evolution of the absorbance at 390 and 460 nm is shown in Figure 2. At 460 nm a transient absorbance is noted; the transient decays to 20% of the initial value with a first-order rate constant k = 3.6 X 106 s"1 ( = 280 ns) and remains constant out to long times. At 390 nm an initial step is noted with the laser pulse followed by a grow in concurrent with the above decay. We attribute the 460-nm transient to the species TIH• as first a radical pair [TIH•, -D] and subsequently the free radical. The 390-nm absorbance appears due to both TIH• and TIH2, but primarily to the latter at long times.The laser flash experiments suggest that two pathways exist for formation of TIH2 from the radical pair formed via pho-( 19) Laser flash photolysis apparatus as described in ref 20, except a pulsed monitoring lamp was used.