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Reaction of 1,3-diazidopropane with an electron-rich Mn(II) precursor results in oxidation of the metal center to a Mn complex with concomitant assembly of the macrocyclic ligand into the 1,2,3,4,8,9,10,11-octaazacyclotetradeca-2,9-diene-1,4,8,11-tetraido (OIM) ligand. Although describable as a Werner Mn(V) complex, analysis by X-ray diffraction, magnetic measurements, X-ray photoelectron spectroscopy, cyclic voltammetry, and density functional theory calculations suggest an electronic structure consisting of a Mn(III) metal center with a noninnocent OIM diradical ligand. The resulting complex, (OIM)Mn(NH t Bu), reacts via proton-coupled electron transfer (PCET) with phenols to form phenoxyl radicals, with dihydroanthracene to form anthracene, and with (2,4-di tert-butyltetrazolium-5-yl)amide to extrude a tetrazyl radical. PCET from the latter generates the isolable corresponding one-electron reduced compound with a neutral, zwitterionic axial 2,4-di tert-butyltetrazolium-5-yl)amido ligand. Electron paramagnetic resonance and density functional theoretical analyses suggest an electronic structure wherein the manganese atom remains Mn(III) and the OIM ligand has been reduced by one electron to a monoradical noninnocent ligand. The result indicates PCET processes whereby the proton is transferred to the axial ligand to extrude t BuNH 2 , the electron is transferred to the equatorial ligand, and the central metal remains relatively unperturbed.

A mechanistic pathway for the formation of the structurally characterized manganese-amide-hydrazide pinned butterfly complex, Mn4(μ3-PhN-NPh-κ(3)N,N')2(μ-PhN-NPh-κ(2)-N,N')(μ-NHPh)2L4 (L = THF, py), is proposed and supported by the use of labeling studies, kinetic measurements, kinetic competition experiments, kinetic isotope effects, and hydrogen atom transfer reagent substitution, and via the isolation and characterization of intermediates using X-ray diffraction and electron paramagnetic resonance spectroscopy. The data support a formation mechanism whereby bis[bis(trimethylsilyl)amido]manganese(II) (Mn(NR2)2, where R = SiMe3) reacts with N,N'-diphenylhydrazine (PhNHNHPh) via initial proton transfer, followed by reductive N-N bond cleavage to form a long-lived Mn(IV) imido multinuclear complex. Coordinating solvents activate this cluster for abstraction of hydrogen atoms from an additional equivalent of PhNHNHPh resulting in a Mn(II)phenylamido dimer, Mn2(μ-NHPh)2(NR2)2L2. This dimeric complex further assembles in fast steps with two additional equivalents of PhNHNHPh replacing the terminal silylamido ligands with η(1)-hydrazine ligands to give a dimeric Mn2(μ-NHPh)2(PhN-NHPh)2L4 intermediate, and finally, the addition of two additional equivalents of Mn(NR2)2 and PhNHNHPh gives the pinned butterfly cluster.

Mn4(μ-NHPh)4(μ-PhNNPh-κ(2)N,N')2(py)4 () is synthesized via self assembly from dimeric Mn2(μ-NHPh)2(NR2)2 and PhNHNHPh (R = SiMe3). This cluster represents the N-N cleaved version of the previously-reported Mn4(μ-NHPh)2(μ3-PhNNPh-κ(3)N,N')2(μ-PhNNPh-κ(2)N,N')(py)4 "pinned butterfly" cluster (), formally reduced by two hydrogen atoms. Cluster may be converted to by addition of N,N'-diphenylhydrazine as a two-electron reductant.

Mn4(IV)(μ3-N(t)Bu)4(N(t)Bu)4 is obtained from a previously reported asymmetric Mn(IV/V)-Li-(NR)(N) cluster by the removal of Li from the starting cluster by ion metathesis, which triggers reductive elimination of azo-tert-butane to give a tetranuclear heterocubane cluster.

The first structurally, spectroscopically, and electronically characterized metal-spiroligomer complexes are reported. The binuclear [M2L2](4+) ions (M = Mn, Zn) are macrocyclic "squares" and are characterized by X-ray diffraction, (1)H and (13)C NMR, electronic absorption, emission, and mass spectroscopies. The manganese complex contains two spin-independent Mn(II) ions and is additionally characterized using EPR and CD spectroscopies and CV.

High-valent, four-coordinate manganese imido- and nitrido-bridged heterodicubane clusters have been prepared and characterized by single-crystal X-ray diffraction and spectroscopic techniques. The title compound, a corner-nitride-fused dicubane with the chemical formula [Mn(5)Li(3)(μ(6)-N)(N)(μ(3)-N(t)Bu)(6)(μ-N(t)Bu)(3)(N(t)Bu)] (1), has been prepared as an adduct with a nearly isostructural tetramanganese cluster with one Mn atom replaced by Li. An important feature of the reported chemistry is the formation of nitride from tert-butylamide, indicative of N-C bond cleavage facilitated by manganese.

A metastable Mn(IV) tris(N,N')diphenylhydrazide complex, Li(2)Mn(κ(2)-N(2)Ph(2))(3) (1) has been prepared, and characterized by X-ray diffraction analysis and spectroscopic techniques. Mn precursors are reacted with LiNH(t)Bu to form an intermediate manganese-imido mixture, which reacts with N,N'-diphenylhydrazine, oxidizing the metal, and forming 1. Despite ease of formation, 1 is poised for reactivity, as loss of ether ligand triggers reductive elimination of azobenzene., (This journal is © The Royal Society of Chemistry 2011)

The preparation of four-coordinate tetramanganese-amide-hydrazide clusters is described. Reaction of Mn(NR(2))(2) (R = SiMe(3)) with N,N'-diphenylhydrazine resulted in the formation of a black intermediary mixture that converted to a four-coordinate tetranuclear "pinned butterfly" cluster, Mn(4)(μ(3)-N(2)Ph(2))(2)(μ-N(2)Ph(2))(μ-NHPh)(2)(THF)(4). This compound was isolated in ~90% yield and identified by single-crystal X-ray diffraction analysis. In pyridine, the THF ligands were replaced, giving the pyridyl complex Mn(4)(μ(3)-N(2)Ph(2))(2)(μ-N(2)Ph(2))(μ-NHPh)(2)(py)(4). Charge counting considerations indicate that the clusters had gained two protons and two electrons in addition to the formative fragments. Isolation of the black mixture was achieved by extraction techniques from a reaction with a decreased loading of hydrazine run at low temperatures with decreased solvent polarity. The black mixture was characterized by FT-IR, UV-vis, and (1)H NMR spectroscopy. In addition, an isolable, colorless dimer, Mn(2)(μ-NHPh)(2)(NR(2))(2)(THF)(2), was present in the mixture and identified by single-crystal X-ray diffraction. These intermediates are discussed in light of possible mechanisms for formation of the tetranuclear cluster.

Hydrogen atom transfer (HAT) reactions from dihydroanthracene to ArINTs (Ar = 2- tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) is catalyzed by Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole). Kinetics of HAT was monitored by gas chromatography. Conversion to the major products anthracene, TsNH 2, and ArI is too fast to be explained by direct HAT from the terminal imido complex TsN=Mn(tpfc), which forms from the reaction of Mn(tpfc) with ArINTs. Steady-state kinetics, isotope effects, and variation of the initial catalyst form (Mn (III)(tpfc) vs TsN=Mn (V)(tpfc)) support a mechanism in which the active catalytic species is an adduct of manganese(III) with the oxidant, (ArINTs)Mn (III)(tpfc). This species was detected by rapid-scan stopped-flow absorption spectroscopy. Kinetic simulations demonstrated the viability of this mechanism in contrast to other proposals.

Hydrogen atom transfer (HAT) reactions of (tpfc)MnNTs have been investigated (tpfc = 5,10,15-tris(pentafluorophenyl)corrole and Ts = p-toluenesulfonate). 9,10-Dihydroanthracene and 1,4-dihydrobenzene reduce (tpfc)MnNTs via HAT with second-order rate constants 0.16 +/- 0.03 and 0.17 +/- 0.01 M(-1) s(-1), respectively, at 22 degrees C. The products are the respective arenes, TsNH(2) and (tpfc)Mn(III). Conversion of (tpfc)MnNTs to (tpfc)Mn by reaction with dihydroanthracene exhibits isosbestic behavior, and formation of 9,9',10,10'-tetrahydrobianthracene is not observed, suggesting that the intermediate anthracene radical rebounds in a second fast step without accumulation of a Mn(IV) intermediate. The imido complex (tpfc)Mn(V)NTs abstracts a hydrogen atom from phenols as well. For example, 2,6-di-tert-butyl phenol is oxidized to the corresponding phenoxyl radical with a second-order rate constant of 0.32 +/- 0.02 M(-1) s(-1) at 22 degrees C. The other products from imido manganese(V) are TsNH(2) and the trivalent manganese corrole. Unlike reaction with dihydroarenes, when phenols are used isosbestic behavior is not observed, and formation of (tpfc)Mn(IV)(NHTs) is confirmed by EPR spectroscopy. A Hammett plot for various p-substituted 2,6-di-tert-butyl phenols yields a V-shaped dependence on sigma, with electron-donating substituents exhibiting the expected negative rho while electron-withdrawing substituents fall above the linear fit (i.e., positive rho). Similarly, a bond dissociation enthalpy (BDE) correlation places electron-withdrawing substituents above the well-defined negative slope found for the electron-donating substituents. Thus two mechanisms are established for HAT reactions in this system, namely, concerted proton-electron transfer and proton-gated electron transfer in which proton transfer is followed by electron transfer.

The reaction of Arl=NTs (Ar = 2-(tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) and (tpfc)Mn (tpfc=5,10,15-tris(pentafluorophenyl)corrole), 1, affords the high-valent (tpfc)MnV=NTs, 2, on stopped-flow time scale. The reaction proceeds via the adduct [(tpfc)MnIII(ArINTs)], 3, with formation constant K3 = (10 +/- 2) x 10(3) L mol-1. Subsequently, 3 undergoes unimolecular group transfer to give complex 2 with the rate constant k4 = 0.26 +/- 0.07 s-1 at 24.0 degrees C. The complex (tpfc)Mn catalyzes [NTs] group transfer from ArINTs to styrene substrates with low catalyst loading and without requirement of excess olefin. The catalytic aziridination reaction is most efficient in benzene because solvents such as toluene undergo a competing hydrogen atom transfer (HAT) reaction resulting in H2NTs and lowered aziridine yields. The high-valent manganese imido complex (tpfc)Mn=NTs does not transfer its [NTs] group to styrene. Double-labeling experiments with ArINTs and ArINTstBu (TstBu = (p-tert-butylphenyl)sulfonyl) establish the source of [NR] transfer as a "third oxidant", which is an adduct of Mn(V) imido, [(tpfc)Mn(NTstBu)(ArINTs)](4). Formation of this oxidant is rate limiting in catalysis.

The role of the manganese average oxidation state (AOS) in water oxidation catalysis by birnessite was investigated. Low AOS samples were most active, generating O2 immediately. Samples with a relatively high AOS showed an initial induction period and decreased turnover. Mn(ii- and iii)-enriched samples gave a 10–50 fold enhancement in turnover number. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of dark green, crystalline Li2[Mn(N t Bu)3 N]∙LiCl(THF)2 in two steps from commercially available starting materials is described. Reaction of MnF3 with LiNH t Bu and LiCl and subsequent workup represents an easy access to this historic complex. 1H NMR, absorption and FT-IR spectra, and single crystal X-ray diffraction data are reported and confirm the identity of the material. [Copyright &y& Elsevier]