Cerium(IV)‐Driven Water Oxidation Catalyzed by a Manganese(V)–Nitrido Complex

The study of manganese complexes as water‐oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen‐evolving complex of photosystem II. In most of the reported Mn‐based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one‐electron oxidants such as Ce^IV. Now, a different class of Mn‐based catalysts, namely manganese(V)–nitrido complexes, were explored. The complex [Mn^V(N)(CN)₄]²⁻ turned out to be an active homogeneous WOC using (NH₄)₂[Ce(NO₃)₆] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min⁻¹. The study suggests that active WOCs may be constructed based on the Mn^V(N) platform.     

Bi‐Microporous Metal–Organic Frameworks with Cubane [M4(OH)4] (M=Ni,Co) Clusters and Pore‐Space Partition for Electrocatalytic Methanol Oxidation Reaction

Embedding cubane [M₄(OH)₄] (M=Ni, Co) clusters within the matrix of metal–organic frameworks (MOFs) is a strategy to develop materials with unprecedented synergistic properties. Herein, a new material type based on the pore‐space partition of the cubic primitive minimal‐surface net (MOF‐14‐type) has been realized. CTGU‐15 made from the [Ni₄(OH)₄] cluster not only has very high BET surface area (3537 m² g^?1), but also exhibits bi‐microporous features with well‐defined micropores at 0.86 nm and 1.51 nm. Furthermore, CTGU‐15 is stable even under high pH (0.1 m KOH), making it well suited for methanol oxidation in basic medium. The optimal hybrid catalyst KB&CTGU‐15 (1:2) made from ketjen black (KB) and CTGU‐15 exhibits an outstanding performance with a high mass specific peak current of 527 mA mg^?1 and excellent peak current density (29.8 mA cm^?2) at low potential (0.6 V). The isostructural cobalt structure (CTGU‐16) has also been synthesized, further expanding the application potential of this material type.     

乙二醛缩双(邻氨基苯酚)合锰(II)配合物的合成及其催化行为研究

合成了乙二醛缩双(邻氨基苯酚)合锰(II)配合物, 讨论了其在DMF中的载氧行为、氧合动力学; 设计正交试验考察了以分子氧为氧源, 该配合物催化氧化醋酸去氢表雄酮生成7-酮基醋酸去氢表雄酮的性能, 最高收率达78.4%.     

Aziridination Reactivity of a Manganese(II) Complex with a Bulky Chelating Bis(Alkoxide) Ligand

Treatment of Mn(N(SiMe₃)₂)₂(THF)₂ with bulky chelating bis(alkoxide) ligand [1,1′:4′,1′′-terphenyl]-2,2′′-diylbis(diphenylmethanol) (H₂[O-terphenyl-O]^Ph) formed a seesaw manganese(II) complex Mn[O-terphenyl-O]^Ph(THF)₂, characterized by structural, spectroscopic, magnetic, and analytical methods. The reactivity of Mn[O-terphenyl-O]^Ph(THF)₂ with various nitrene precursors was investigated. No reaction was observed between Mn[O-terphenyl-O]^Ph(THF)₂ and aryl azides. In contrast, the treatment of Mn[O-terphenyl-O]^Ph(THF)₂ with iminoiodinane PhINTs (Ts = p-toluenesulfonyl) was consistent with the formation of a metal-nitrene complex. In the presence of styrene, the reaction led to the formation of aziridine. Combining varying ratios of styrene and PhINTs in different solvents with 10 mol% of Mn[O-terphenyl-O]^Ph(THF)₂ at room temperature produced 2-phenylaziridine in up to a 79% yield. Exploration of the reactivity of Mn[O-terphenyl-O]^Ph(THF)₂ with various olefins revealed (1) moderate aziridination yields for p-substituted styrenes, irrespective of the electronic nature of the substituent; (2) moderate yield for 1,1′-disubstituted α-methylstyrene; (3) no aziridination for aliphatic α-olefins; (4) complex product mixtures for the β-substituted styrenes. DFT calculations suggest that iminoiodinane is oxidatively added upon binding to Mn, and the resulting formal imido intermediate has a high-spin Mn(III) center antiferromagnetically coupled to an imidyl radical. This imidyl radical reacts with styrene to form a sextet intermediate that readily reductively eliminates the formation of a sextet Mn(II) aziridine complex.     

Manganese(I)‐Catalyzed C–H Aminocarbonylation of Heteroarenes

A versatile manganese(I) catalyst was employed in C? H aminocarbonylation reactions of heteroarenes with aryl as well as with alkyl isocyanates using a removable directing group approach. Detailed experimental mechanistic studies were suggestive of an organometallic C? H manganesation step, followed by a rate‐determining migratory insertion.     

Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Iron(III)–Superoxo and Manganese(IV)–Peroxo Complexes

Reactions of nonheme Fe^III–superoxo and Mn^IV–peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)Fe^III(O₂)]^2? and [(TAML)Mn^IV(O₂)]^2?, with nitric oxide (NO) afford the Fe^III–NO₃ complex [(TAML)Fe^III(NO₃)]^2? and the Mn^V–oxo complex [(TAML)Mn^V(O)]^? plus NO₂^?, respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that M^III–peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)Fe^III(O₂)]^2? and [(TAML)Mn^IV(O₂)]^2? with NO, are converted into M^IV(O) and ^.NO₂ species through O?O bond homolysis of the peroxynitrite ligand. Then, a rebound of Fe^IV(O) with ^.NO₂ affords [(TAML)Fe^III(NO₃)]^2?, whereas electron transfer from Mn^IV(O) to ^.NO₂ yields [(TAML)Mn^V(O)]^? plus NO₂^?.     

Anodic Oxidation of Hypophosphite on a Nickel–Phosphorus Electrode in the Presence of Some Organic Compounds

The effects some sulfur-, nitrogen-, or oxygen-containing organic compounds exert on the hypophosphite oxidation are compared. Catalytic and inhibiting effects of additives, which depend on their nature and occur in different concentration intervals, are discovered and examined. The inhibiting effect, exerted by all substances studied, is accompanied by a shift of steady-state potential in the positive direction and is determined by the adsorbability of substances, which is a function of the nature and number of heteroatoms and substituents. The best inhibiting properties are intrinsic to an additive with an –S–S– fragment and NH₂ groups. Catalytic influence, which is typical only for sulfur-containing compounds at low concentrations, is accompanied by a shift of steady-state potential in the negative direction and may be related to a surface modification and a change in the metal–hydrogen bond energy.     

Oxidation Reactivity of Bis(μ‐oxo) Dinickel(III) Complexes: Arene Hydroxylation of the Supporting Ligand

In the nick(el) of time : Bis(μ‐oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H₂O₂, are capable of hydroxylating the xylyl linker of the supporting ligand to give 3 . Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding μ‐η²:η²‐peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.

     

Manganese(III) acetate promoted acetoxylation of various α,β-unsaturated cyclopentanones

We describe the results of manganese(III) acetate based regioselective oxidation of various α,β-unsaturated cyclopentanones leading to α′-acetoxy α,β-unsaturated cyclopentanones in good yields. Products due to monophenyl and diphenyl substituted dimerization have been identified as byproducts of the reaction.     

Oxidation by oxygen and sulfur of Tin(IV) derivatives containing a redox-active o-amidophenolate ligand

Oxidation of tin(IV) o-amidophenolate complexes [Sn(ap)Ph(2)] (1) and [Sn(ap)Et(2)(thf)] (2) (ap=dianion of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (ImQ)) with molecular oxygen and sulfur in toluene solutions was investigated. The reaction of oxygen with 1 at room temperature forms a paramagnetic derivative [Sn(isq)(2)Ph(2)] (3) (isq=radical anion of ImQ) and diphenyltin(IV) oxide [{Ph(2)SnO}(n)]. Interaction of 1 with sulfur gives another monophenyl-substituted paramagnetic tin(IV) complex, [Sn(ap)(isq)Ph] (4), and the sulfide, [Ph(3)Sn](2)S. The oxidation of 2 with oxygen and with sulfur proceeds through the derivative [Sn(isq)(2)Et(2)] (7), which undergoes alkyl elimination to give two new tin(IV) compounds, [Sn(ap)(isq)Et] (5) and [Sn(ap)(EtImQ)Et] (6) (EtImQ=2,4-di-tert-butyl-6-(2,6-diisopropylphenylimino)-3-ethylcyclohexa-1,4-dienolate ligand), respectively, along with the corresponding alkyltin(IV) oxide and sulfide. Complexes 3-5 and 7 were studied by EPR spectroscopy. The structures of 3, 4 and 6 were investigated by X-ray analysis.     

Effect of Manganese(II) Ions on Regular Self-Oscillations in the Belousov–Zhabotinskii Reaction in a Tank Reactor with Constant Stirring

The effect of manganese(II) ions on the asymptotically regular self-oscillation regime of the Belousov–Zhabotinskii reaction, catalysed by ferroin, in a tank reactor with constant stirring has been studied. An increase in the manganese(II) ion concentration in the system leads to an increase in the period of the self-oscillations. The sensitivity of the self-oscillation of the chemical reaction on the addition of Mn²⁺ ions is decreased with an increase in acidity. To explain the results obtained we have used a reversible Oregonator model, which is supplemented with reactions between manganese(II) and manganese(III) ions and bromoxyl radicals, malonic acid, and ferroin.     

Manganese(III)-based oxidation of 1,2-disubstituted pyrazolidine-3,5-diones in the presence of alkenes

The manganese(III)-catalyzed aerobic oxidation of 1,2-disubstituted pyrazolidine-3,5-diones 1 in the presence of alkenes 2 gave the corresponding pyrazolidinediones 3 which were doubly hydroperoxyalkylated at the 4-position in high yields. On the other hand, pyrazolidinediones 1 were oxidized with manganese(III) acetate in the presence of alkenes 2 at elevated temperature to produce the 4,4-bis(alkenyl)pyrazolidinediones 4 in good yields instead of the pyrazolidine-fused dihydrofuran analogue IV. A similar cerium(IV)-mediated oxidation of pyrazolidinedione 1a with an alkene 2a afforded the doubly 4-methoxyethylated derivative 5. The stability of the free hydroperoxyl group and the reaction pathway for the aerobic and the metal-mediated oxidation reactions were also discussed.     

Generation and Reactivity of a One-Electron-Oxidized Manganese(V) Imido Complex with a Tetraamido Macrocyclic Ligand

The synthesis and X-ray structure of a new manganese(V) mesitylimido complex with a tetraamido macrocyclic ligand (TAML), [Mn^V(TAML)(N-Mes)]⁻ ( 1 ), are reported. Compound 1 is oxidized by [(p-BrC₆H₄)₃N ]^+.[SbCl₆]⁻ and the resulting Mn^VI species readily undergoes H-atom transfer and nitrene transfer reactions.     

O2 Activation and Double CH Oxidation by a Mononuclear Manganese(II) Complex

A Mn^II complex, [Mn(dpeo)₂]²⁺ (dpeo=1,2‐di(pyridin‐2‐yl)ethanone oxime), activates O₂, with ensuing stepwise oxidation of the methylene group in the ligands providing an alkoxide and ultimately a ketone group. X‐ray crystal‐structure analysis of an intermediate homoleptic alkoxide Mn^III complex shows tridentate binding of the ligand via the two pyridyl groups and the newly installed alkoxide moiety, with the oxime group no longer coordinated. The structure of a Mn^II complex of the final ketone ligand, cis‐[MnBr₂(hidpe)₂] (hidpe=2‐(hydroxyimino)‐1,2‐di(pyridine‐2‐yl)ethanone) shows that bidentate oxime/pyridine coordination has been resumed. H₂¹⁸O and ¹⁸O₂ labeling experiments suggest that the inserted O atoms originate from two different O₂ molecules. The progress of the oxygenation was monitored through changes in the resonance‐enhanced Raman bands of the oxime unit.     

Synthesis and Crystal Structure of a Novel Tetranuclear Manganese(II) Complex with a Tripodal Peptide Ligand

1 INTRODUCTION Amides play an important role in the evolution ofnature. The amidate participates in the coordinationof iron with the ligands containing biomolecules, suchas antitumor drug bleomycin[1] and nitrile hydra-tase[2]. Bleomycin is a clinically useful antitumoragent which catalyzes the cleavage of oxidative DNAand oxidizes a number of organic substrates with di-oxygen or H2O2 . This has raised more interest in [3]the coordination of amide complexes[4, . …     

Manganese(III) acetate based oxidation of substituted α′-position on cyclic α,β-unsaturated ketones

Selective oxidation of the tertiary α′-position on various 2-cyclopentenone, 2-cyclohexenone and aromatic ketone derivatives with manganese(III) acetate is described.     

Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Catalytically active MnO_x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO_x catalysts form without supports in situ under photocatalytic conditions. Our most active ⁴MnO_x catalyst (～0.84 mmol O₂ mol Mn^?1 s^?1) forms from a Mn₄O₄ bearing a metal–organic framework. ⁴MnO_x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m²g^?1) and small regions of crystallinity and layer flexibility. In contrast, the ^SMnO_x formed from Mn²⁺ salt gives an amorphous species of lower surface area (80 m²g^?1) and lower activity (～0.15 mmol O₂ mol Mn^?1 s^?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p_3/2 core levels detects enriched Mn³⁺ and Mn²⁺ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.