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We report the preparation, isolation, and reactivity of gas‐phase lanthanide nitrate and acetate complexes featuring the elusive trivalent LnIII=O bond. Complexes [LnIII(O)(X)2]− (X=NO3− or CH3CO2−; Ln=La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Tm, Lu) are prepared from [LnIII(CH3CO2)(X)3]− precursors through decarboxylation followed by nitromethane or acetone elimination. The oxo complexes hydrolyze at rates indicating LnIII=O bond stability. The rates for [LnIII(O)(NO3)2]− are essentially invariant, whereas those for [LnIII(O)(CH3CO2)2]− exhibit a moderate decrease across the lanthanide series. The kinetics of lanthanide‐oxo bond hydrolysis are assessed in the context of participation of 5d2 electrons in bonding, changes in covalency via variations in 5d orbital energies and radial extensions, and steric crowding around the lanthanide center. The observed fast hydrolysis rates and lack of correlation to electronic and qualitative covalent considerations confirm the expected strong polarization in LnIII=O bonding, with variations in covalency minimally impacting reactivity. The LnIII=O bond reactivity is compared with previous results for LnIII−O⋅ and LnIV=O, and actinide AnIII=O and AnIV=O; implications for lanthanide/actinide and lanthanide/lanthanide partitioning are discussed. Additionally, nitromethane and acetone elimination are demonstrated as useful for inducing a 2e− O‐atom transfer resulting in non‐oxidative formation of lanthanide‐oxos. [ABSTRACT FROM AUTHOR]

The conversion of an azacalixpyridine‐supported Mo(0) tricarbonyl into a Mo(VI) trioxo complex with dioxygen (O2) is investigated in homogeneous solution and in a molecular film adsorbed on Au(111) using a variety of spectroscopic and analytical methods. These studies in particular show that the dome‐shaped carbonyl complex adsorbed on the metal surface has the ability to bind and activate gaseous oxygen, overcoming the so‐called surface trans‐effect. Furthermore, the rate of the conversion dramatically increases by irradiation with light. This observation is explained with the help of complementary DFT calculations and attributed to two different pathways, a thermal and a photochemical one. Based on the experimental and theoretical findings, a molecular mechanism for the conversion of the carbonyl to the oxo complex is derived. [ABSTRACT FROM AUTHOR]

The new μ3‐methoxido bridged trinuclear vanadium(IV) complexes [VIV3O3(μ3‐OMe)(μ2‐OMe)3(L1,2)2] (1 and 2) have been synthesized using the azo ligands 1‐(2‐(thiazol‐2‐yl)diazenyl)naphthalene‐2‐ol (HL1) and 2‐(2‐(thiazol‐2‐yl)diazenyl)‐4‐methylphenol (HL2). X‐ray crystallography revealed a trinuclear structure with a lacunary heterocubane {(VO)3(μ3‐OMe)(μ2‐OMe)3}2+ core unit for complex 1, which contains a central μ3‐methoxido bridge. All three vanadium centers are in a slightly distorted octahedral coordination environment. Magnetic and theoretical studies reveal an antiferromagnetic coupling between the three vanadium(IV) centers within the triangular arrangement in 1. The complexes were also screened for in vitro cytotoxicity study against HeLa and HT‐29 cancer cell lines. The results indicated that both the complexes are cytotoxic but possess varying specificity towards different cell types. [ABSTRACT FROM AUTHOR]

A Zn,Al layered double hydroxide (LDH) with [Cp*MoO3]– (Cp* = η5‐C5Me5) anions in the interlayer has been prepared by a direct coprecipitation method. The intercalated LDH and the mixed metal oxide (MMO) obtained after its calcination were characterized by elemental and thermogravimetric analyses, powder X‐ray diffraction (PXRD), FT‐IR and FT‐Raman spectroscopy, 13C and 27Al MAS NMR, and scanning electron microscopy. The observed basal spacing of 17.1 Å for the LDH Zn,Al‐Cp*MoO3 (corresponding to a gallery height of 12.3 Å) suggests that the guest anions self‐assemble into dimers via offset face‐to‐face Cp*···Cp* interactions, which facilitates hydrogen‐bonding interactions between the oxido ligands of the complexes and the layer hydroxyl groups, while positioning the hydrophobic aromatic rings towards the center of the galleries. Calcination of Zn,Al‐Cp*MoO3 at 550 °C under air gave an MMO comprising well‐dispersed ZnO, α‐ZnMoO4 and ZnAl2O4 (spinel) oxides in a molar of ca. 1.4:1.6:1. The MMO exhibited catalytic activity for the epoxidation of cis‐cyclooctene with tert‐butylhydroperoxide (TBHP) as terminal oxidant, with quantitative yield of the epoxide being achieved within 24 h at 85 °C. [ABSTRACT FROM AUTHOR]

Analysis of extended X‐ray absorption fine structure (EXAFS) data for the MnIV‐oxo complexes [MnIV(O)(DMMN4py)]2+, [MnIV(O)(2pyN2B)]2+, and [MnIV(O)(2pyN2Q)]2+ (DMMN4py=N,N‐bis(4‐methoxy‐3,5‐dimethyl‐2‐pyridylmethyl)‐N‐bis(2‐pyridyl)methylamine; 2pyN2B=(N‐bis(1‐methyl‐2‐benzimidazolyl)methyl‐N‐(bis‐2‐pyridylmethyl)amine, and 2pyN2Q=N,N‐bis(2‐pyridyl)‐N,N‐bis(2‐quinolylmethyl)methanamine) afforded Mn=O and Mn−N bond lengths. The Mn=O distances for [MnIV(O)(DMMN4py)]2+ and [MnIV(O)(2pyN2B)]2+ are 1.72 and 1.70 Å, respectively. In contrast, the Mn=O distance for [MnIV(O)(2pyN2Q)]2+ was significantly longer (1.76 Å). We attribute this long distance to sample heterogeneity, which is reasonable given the reduced stability of [MnIV(O)(2pyN2Q)]2+. The Mn=O distances for [MnIV(O)(DMMN4py)]2+ and [MnIV(O)(2pyN2B)]2+ could only be well‐reproduced using DFT‐derived models that included strong hydrogen‐bonds between second‐sphere solvent 2,2,2‐trifluoroethanol molecules and the oxo ligand. These results suggest an important role for the 2,2,2‐trifluoroethanol solvent in stabilizing MnIV‐oxo adducts. The DFT methods were extended to investigate the structure of the putative [MnIV(O)(N4py)]2+⋅(HOTf)2 adduct. These computations suggest that a MnIV‐hydroxo species is most consistent with the available experimental data. [ABSTRACT FROM AUTHOR]

The tetraoxido ruthenium(VIII) radical cation, [RuO 4 ] + , should be a strong oxidizing agent, but has been difficult to produce and investigate so far. In our X-ray absorption spectroscopy study, in combination with quantum-chemical calculations, we show that [RuO 4 ] + , produced via oxidation of ruthenium cations by ozone in the gas phase, forms the oxygen-centered radical ground state. The oxygen-centered radical character of [RuO 4 ] + is identified by the chemical shift at the ruthenium M 3 edge, indicative of ruthenium(VIII), and by the presence of a characteristic low-energy transition at the oxygen K edge, involving an oxygen-centered singly-occupied molecular orbital, which is suppressed when the oxygen-centered radical is quenched by hydrogenation of [RuO 4 ] + to the closed-shell [RuO 4 H] + ion. Hydrogen-atom abstraction from methane is calculated to be only slightly less exothermic for [RuO 4 ] + than for [OsO 4 ] + ., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

High‐valent metal oxo oxidants are common catalytic‐cycle intermediates in enzymes and known to be highly reactive. To understand which features of these oxidants affect their reactivity, a series of biomimetic iron(V) oxo oxidants with peripherally substituted biuret‐modified tetraamido macrocyclic ligands were synthesized and characterized. Major shifts in the UV/Vis absorption as a result of replacing a group in the equatorial plane of the iron(V) oxo species were found. Further characterization by EPR spectroscopy, ESI‐MS, and resonance Raman spectroscopy revealed differences in structure and the electronic configuration of these complexes. A systematic reactivity study with a range of substrates was performed and showed that the reactions are affected by electron‐withdrawing substituents in the equatorial ligand, which enhance the reaction rate by almost 1016 orders of magnitude. Thus, the long‐range electrostatic perturbations have a major influence on the rate constant. Finally, computational studies identified the various electronic contributions to the rate‐determining reaction step and explained how the equatorial ligand periphery affects the properties of the oxidant. [ABSTRACT FROM AUTHOR]

Lewis acid–base pair chemistry has been placed on a new level with the discovery that adduct formation between an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introduction of steric demand, thus preserving the reactivity of both Lewis centers, resulting in highly unusual chemistry. Some of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting a variety of small molecules, such as dihydrogen, in a heterolytic and even catalytic manner. This is in sharp contrast to classical reactions where the inert substrate must be activated by a metal‐based catalyst. Very recently, research has emerged combining the two concepts, namely the formation of FLPs in which a metal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being a Lewis acid or base, also ancillary ligands can be used as part of the Lewis pair, still with the benefit of the redox‐active metal center nearby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition‐metal or rare‐earth‐metal compounds with the Lewis acid B(C6F5)3. It covers a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Future goals of this young and exciting area are briefly discussed. [ABSTRACT FROM AUTHOR]

Lewis acid–base pair chemistry has been placed on a new level with the discovery that adduct formation between an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introduction of steric demand, thus preserving the reactivity of both Lewis centers, resulting in highly unusual chemistry. Some of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting a variety of small molecules, such as dihydrogen, in a heterolytic and even catalytic manner. This is in sharp contrast to classical reactions where the inert substrate must be activated by a metal‐based catalyst. Very recently, research has emerged combining the two concepts, namely the formation of FLPs in which a metal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being a Lewis acid or base, also ancillary ligands can be used as part of the Lewis pair, still with the benefit of the redox‐active metal center nearby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition‐metal or rare‐earth‐metal compounds with the Lewis acid B(C6F5)3. It covers a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Future goals of this young and exciting area are briefly discussed. [ABSTRACT FROM AUTHOR]

Two enantiomerically pure chiral dioxidomolybdenum(VI) complexes (1 and 2) of the type [MoO2L] (L = dianionic, tetradentate ONNO‐ligand) were synthesized and investigated in enantioselective oxidation reactions. The solid‐state structures of complex 1 and 2, determined via single‐crystal X‐ray diffraction analysis revealed two fundamentally different coordination geometries: a C1‐symmetric cis‐β isomer (Λ‐1), and a C2‐symmetric cis‐α isomer (Δ‐2). In both cases, only one of the two possible helical enantiomers (Λ‐ or Δ‐helix) was formed. The complexes were examined as precatalysts in the epoxidation of the challenging prochiral substrate trans‐stilbene, using either tert‐butyl hydroperoxide (TBHP) or cumyl hydroperoxide (CHP) as oxidants. The asymmetric cis‐β complex 1 was found to be significantly more active in the epoxidation than its cis‐α counterpart 2, asymmetric induction was, however, negligible for both complexes. The complexes were also tested in catalytic enantioselective sulfoxidation reactions where chiral induction could be achieved, albeit small. The observed putative molybdenum oxido‐peroxido intermediate 1‐O2 could be identified as an important precomplex before formation of the active catalyst in sulfoxidation. [ABSTRACT FROM AUTHOR]

The 9‐fluorenone (fn) ketyl in [YbIII(DippForm)2(fn·‐O)] {DippForm = N,N′‐bis(2,6‐diisopropylphenyl)formamidinate}, underwent reduction to the dianion ({C13H8}‐O) upon single electron transfer from SmIII2(thf)2. The dianion was obtained as a decanuclear, deca‐9‐fluorenolato, tetraoxido mixed‐oxidation‐state samarium cage [Sm10O4{(C13H8)‐O}10(thf)10], obtained after ligand redistribution. The structure is relevant to the deoxygenation of ketones by lanthanoid metals. [ABSTRACT FROM AUTHOR]

Anionic Bismuth Oxido Clusters with Pendant Silver Cations: Synthesis and Structures of {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} and {Bi4(µ3-O)2(TFA)10(AgPPh3)2}n BiPh3 and trifluoroacetic acid (TFAH) react in toluene in the presence of Ag2O to form {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} (1; tol = PhMe). Similarly, BiPh3, TFAH, PPh3, and Ag2O react in hexane to form {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} and {Bi4(µ3-O)2(TFA)10(AgPPh3)2}n (2). Both contain {Bi4(µ3-O)2} units, which have been previously observed with a variety of carboxylate ligands in neutral compounds and anionic compounds. In contrast to other anionic [Bi4(µ3-O)2- (TFA)N](N-8)- with metal-based countercations, the Ag+ ions in 1 and 2 are directly attached to oxygen atoms of the TFA- ligands bonded to the bismuth core. A crystallographic evolution was observed for 1. Solvent-rich orthorhombic crystals grew initially on standing. However, by three weeks all crystals had converted to a triclinic unit cell that contained no free solvent. The molecular volume decreased from 3146.11 Å3 (orthorhombic) to 2954.06 Å3 (triclinic). The latter had an intermolecular π-π stacking system between silver- and bismuth-bound toluene molecules, which explains the reorganization to a nonsolvated morphology. Compound 2 crystallizes in the triclinic space group P11 as a coordination polymer through bridging carboxylate ligands. The presence of the PPh3 ligands on Ag+ results in a higher Ag/Bi ratio than in 1. The importance of Ag2O in generating the oxido ligands was confirmed by the isolation of {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2}(3) from the reaction of BiPh3 with TFAH in toluene in the absence of the metal oxide. [ABSTRACT FROM AUTHOR]

Anionic Bismuth Oxido Clusters with Pendant Silver Cations: Synthesis and Structures of {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} and {Bi4(µ3-O)2(TFA)10(AgPPh3)2}n BiPh3 and trifluoroacetic acid (TFAH) react in toluene in the presence of Ag2O to form {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} (1; tol = PhMe). Similarly, BiPh3, TFAH, PPh3, and Ag2O react in hexane to form {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} and {Bi4(µ3-O)2(TFA)10(AgPPh3)2}n (2). Both contain {Bi4(µ3-O)2} units, which have been previously observed with a variety of carboxylate ligands in neutral compounds and anionic compounds. In contrast to other anionic [Bi4(µ3-O)2- (TFA)N](N-8)- with metal-based countercations, the Ag+ ions in 1 and 2 are directly attached to oxygen atoms of the TFA- ligands bonded to the bismuth core. A crystallographic evolution was observed for 1. Solvent-rich orthorhombic crystals grew initially on standing. However, by three weeks all crystals had converted to a triclinic unit cell that contained no free solvent. The molecular volume decreased from 3146.11 Å3 (orthorhombic) to 2954.06 Å3 (triclinic). The latter had an intermolecular π-π stacking system between silver- and bismuth-bound toluene molecules, which explains the reorganization to a nonsolvated morphology. Compound 2 crystallizes in the triclinic space group P11 as a coordination polymer through bridging carboxylate ligands. The presence of the PPh3 ligands on Ag+ results in a higher Ag/Bi ratio than in 1. The importance of Ag2O in generating the oxido ligands was confirmed by the isolation of {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2}(3) from the reaction of BiPh3 with TFAH in toluene in the absence of the metal oxide. [ABSTRACT FROM AUTHOR]

A detailed electrochemical investigation of a series of iron complexes (biuret-modified tetraamido iron macrocycles FeIII-bTAML), including the first electrochemical generation of FeV(O), and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium are reported. Spectroelectrochemical and mass spectral studies indicated FeV(O) as the active oxidant, formed due to two redox transitions, which were assigned as FeIV(O)/FeIII(OH2) and FeV(O)/FeIV(O). The spectral properties of both of these high-valent iron oxo species perfectly match those of their chemically synthesised versions, which were thoroughly characterised by several spectroscopic techniques. The O−O bond-formation step occurs by nucleophilic attack of H2O on FeV(O). A kinetic isotope effect of 3.2 indicates an atom-proton transfer (APT) mechanism. The reaction of chemically synthesised FeV(O) in CH3CN and water was directly probed by electrochemistry and was found to be first-order in water. The p Ka value of the buffer base plays a critical role in the rate-determining step by increasing the reaction rate several-fold. The electronic effect on redox potential, WO rates, and onset overpotential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework. Changing the substituents from OMe to NO2 resulted in an eightfold increase in reaction rate, while the overpotential increased threefold. [ABSTRACT FROM AUTHOR]

This article reviews discrete complexes of platinum in its common oxidation states +II, +III, and +IV with aqua, hydroxido, oxido, and peroxido ligands, which at some point had been considered unstable and difficult to isolate because of an incompatibility between the “soft” nature of the metal and the “hard” nature of the O-ligands. The sheer number of structurally fully characterized examples contradicts this view, and numerous studies confirm their existence in solution and reveal at the same time distinct reactivity patterns. These make Pt complexes with O-donor atoms interesting candidates for medicinally important Pt antitumor drugs as well as catalytically relevant species. [ABSTRACT FROM AUTHOR]

The reactions of the tripodal tetradentate ONNO donor ligands 6,6′-{[(2-morpholinoethyl)azanediyl]bis(methylene)}bis(2,4-di- tert-butylphenol) (H2 L1), 6,6′-{[(2-morpholinoethyl)azanediyl]bis(methylene)}bis(2,4-dimethylphenol) (H2 L2) and 6,6′-{[(2-morpholinoethyl)azanediyl]bis(methylene)}bis[2-( tert-butyl)-4-methylphenol] (H2 L3) with [MoVIO2(acac)2] (acac = acetylacetonato) in a 1:1 molar ratio in MeOH gave the corresponding cis-dioxidomolybdenum(VI) complexes [MoO2( L1)], [MoO2( L2)] and [MoO2( L3)], respectively, in excellent yields. These complexes were characterized by various spectroscopic (IR, UV/Vis, 1H and 13C NMR), electrochemical, thermogravimetric, single-crystal XRD, and powder XRD (PXRD) studies. In these complexes, the geometry around the cis-[MoO2]2+ core is distorted octahedral, and the ligands are tetradentate and coordinate through two Ophenolate, one Ntripodal, and one Nmorpholine atoms. One of the oxido groups and the morpholine nitrogen atom occupy the axial sites. These complexes were used for catalytic oxygen atom transfer between benzoin and dimethyl sulfoxide (DMSO) in acetonitrile at 80 °C, and the formation of benzil was followed by HPLC. Detailed kinetic studies revealed a first-order rate in benzoin and catalyst, and the rate constant for the second-order oxygen atom transfer reaction was 0.0162 m-1 h-1. The formation of the dinuclear intermediates [LMoV-µ-O-MoVL] was established by MALDI-TOF MS and UV/Vis spectroscopy. Its reversible nature was further supplemented by UV/Vis spectroscopy. These complexes also catalyze the oxidation of pyrogallol in a fashion similar to that of transhydroxylases. Under aerobic conditions, the initially formed oxidation product phloroglucinol undergoes further oxidative coupling in the presence of H2O2 to give purpurogallin as the final product. This process follows Michaelis-Menten-type kinetics with respect to pyrogallol; the kcat values obtained were 394, 300 and 247 h-1 for [MoVIO2( L1)], [MoVIO2( L2)] and [MoVIO2( L3)], respectively. [ABSTRACT FROM AUTHOR]

The planar chiral Schiff base ligand 2, derived from ( Rp)-5-formyl-4-hydroxy-[2.2]paracyclophane (FHPC) ( 1), was utilised to form a Λ-CoIII cis-β-octahedral metal complex 3 with complete control of the metal-centred chirality. In addition, a di-µ-oxo Λ,Λ-MnIV complex 4 was synthesised with control of both metal-centred and ( P)-helical chirality. [ABSTRACT FROM AUTHOR]

Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O−O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is toluene

Cu-exchanged zeolites are promising heterogeneous catalysts, as they provide a confined environment to carry out highly selective reactions. However, the knowledge of how the zeolite framework and the location of Al atoms therein affect the adsorption of copper species is still not well understood. In this work, DFT was used to investigate the adsorption of potential Cu oxo active species suggested in the literature [Cu(η2-O2), Cu(µ-O)Cu, and Cu2O2] into zeolites with different pore sizes and shapes (AFI, CHA, TON, MOR, and MFI). The calculations revealed that both monomeric and dimeric Cu oxo species bind strongly to the O atoms of the lattice. For the monometallic species similar adsorption energies are obtained with the different zeolite frameworks, whereas an optimum Al-Al distance is required for the dimeric species. [ABSTRACT FROM AUTHOR]

The μ4-oxido motif is well known in copper clusters and often forms spontaneously and unexpectedly; however, little is known about the reaction conditions that generate μ4-oxido clusters. This is surprising because these μ4-oxido copper clusters seem to play an important role in catalysis. Herein, a systematic investigation of μ4-oxido cluster formation is reported. The influence of several factors on cluster formation was studied, namely, the ligand environment, the central chalcogenide atom, and the bridging halido ligands. In this context, the crystal structures of the copper clusters and complexes [Cu4OCl6 L24][Cu L22Cl2] ( L2 = phenethylamine), [Cu L32Cl2] ( L3 = N-methylbenzylamine), [Cu4OCl6 L44] ( L4 = N, N-dimethylbenzylamine), [Cu L54Cl2] ( L5 = cyclohexylamine), and [Cu4OCl6 L64] ·1.5[Cu L62Cl2] ( L6 = cyclohexanemethylamine) as well as that of H L4Cl are reported. Furthermore, the acetonitrile complexes [Cu(CH3CN)4][CuBr4], [Cu(CH3CN)Br], and [Cu(CH3CN)Br2] were obtained and characterized within attempts to prepare a μ4-sulfido unit. The reaction conditions that generate μ4-oxido cluster units are discussed in more detail. [ABSTRACT FROM AUTHOR]

By introducing steric constraints into molecular compounds, it is possible to achieve atypical coordination geometries for the elements. Herein, we demonstrate that a titanium-oxo cluster [{Ti4(μ4-O)(μ2-O)2}(OPri)6(fdc)2], which possesses a unique edge-sharing Ti4O17 octahedron tetramer core, is stabilized by the constraints produced by two orthogonal 1,1′-ferrocenedicarboxylato (fdc) ligands. As a result, a square-planar tetracoordinate oxygen (ptO) can be generated. The bonding pattern of this unusual anti-van't Hoff/Le Bel oxygen, which has been probed by theoretical calculations, can be described by two horizontally σ-bonded 2p x and 2p y orbitals along with one perpendicular nonbonded 2p z orbital. While the two ferrocene units are separated spatially by the ptO with an Fe⋅⋅⋅Fe separation of 10.4 Å, electronic communication between them still takes place as revealed by the cluster's two distinct one-electron electrochemical oxidation processes. [ABSTRACT FROM AUTHOR]

The dissolution of the indenyl (Ind) complex [{(η5-Ind)Mo(CO)2(μ-Cl)}2] ( 1) in N, N′-dimethylformamide (DMF) gives the ring-slipped complex [(η3-Ind)Mo(CO)2Cl(DMF)2] ( 2). The aerial oxidation of 2 leads to the formation of the dinuclear oxomolybdenum(V) chloride [Mo2O2(DMF)4(μ-O)2Cl2] ( 3). The structures of 2 and 3·DMF have been determined by single-crystal X-ray diffraction. Compounds 1 and 3 were examined as promoters of phosphoester bond hydrolysis in para-nitrophenylphosphate ( pNPP), which was used as a model substrate. The reactions were performed in aqueous solution at 55 °C and followed by 1H NMR spectroscopy. For assays performed with 30-100 mol-% of 1 or 3 relative to pNPP, both compounds promote the production of para-nitrophenol ( pNPh) from pNPP. Compound 3 is especially active in promoting the hydrolytic cleavage of the phosphoester bond ( t1/2 < 80 min). [ABSTRACT FROM AUTHOR]

Abstract: Compounds [Cp*2M2O5] (M = Mo, W) react with stoichiometric amounts of H2O2 (as a 30% w/w solution in water) and t BuOOH (TBHP, as a 70% w/w solution in decane) in MeCN solution to yield a variety of products as shown by the 1H NMR monitoring of the Cp* resonance. The reaction rate increases in the order W < Mo and TBHP < H2O2. While the total Cp* intensity remains constant when using stoichiometric amounts of oxidant, use of excess oxidant results in the ultimate total Cp* loss. From the decomposed solutions, crystals of [Cp*2Mo6O17] (1), (C5Me5O)[Cp*M6O18] (M = Mo, 2a; W, 2b), and (C5Me5O)2[Mo6O19] (3) were recovered and analyzed by X-ray diffraction. Catalytic cyclooctene epoxidation experiments with ( n Bu4N)2[M6O19] (M = Mo, W) in a 3:1 MeCN/toluene mixture at 55 °C using either aqueous H2O2 or TBHP/decane as oxidant revealed that these are not the active forms of the catalyst which is generated under the same conditions from [Cp*2M2O5], as reported in previous contributions from our group (Chem. Eur. J., 2010, 16, 9572–9584; Eur. J. Inorg. Chem., 2013, 2728–2735). Further catalytic studies using aged [Cp*2Mo2O5]/TBHP and [Cp*2W2O5]/H2O2 solutions show a small loss of activity (<50% in one week) attesting the robustness of the non-organometallic catalytically active species that is generated from the decomposition of [Cp*2M2O5]. These results cast doubts on the role of cyclopentadienyl as a supporting ligand for stable olefin epoxidation catalysts. [Copyright &y& Elsevier]

Trihalogenoruthenium(III) complexes bearing an ethylbis(2-pyridylmethyl)amine (ebpma) ligand, fac-[RuIIIX3(ebpma)] (X = Cl, Br), were reduced by zinc in acetone that contained halogeno acid to afford a reddish-orange solution. Two kinds of dinuclear complexes were synthesized from the solution. After removing the remaining zinc and adding counterions such as PF6- and BF4- with water, the solution was allowed to stand under air until the color of the solution changed. New oxido-bridged dinuclear complexes of mixed-valence RuIII-RuIV [{RuIII,IVX2(ebpma)}2(μ-O)]Y (X = Cl, Y = PF6, [ 1]PF6; Y = BF4, [ 1]BF4; X = Br, Y = PF6, [ 2]PF6; Y = BF4, [ 2]BF4), which showed a similar framework to the reported water oxidation catalysts, were obtained as deep-colored solids. In the reaction without addition of extra water, a different mixed-valence dinuclear complex of RuII-RuIII [{RuII,III(ebpma)}2(μ-Cl)3]2+, for which the metal centers were triply bridged by three chlorides, was formed. The synthetic procedures are useful for the development of multinuclear frameworks that function as molecular catalysts for redox reactions such as water oxidation. [ABSTRACT FROM AUTHOR]

The new carbodiimide compound La3Cl(CN2)O3 was obtained by a solid-state metathesis reaction from LaOCl and Li2(CN2) at 750 °C in a fused tube. Differential scanning calorimetry of the reaction mixture was performed. The crystal structure of La3Cl(CN2)O3 was determined by single-crystal X-ray diffraction studies (space group Cmcm, No. 63). The luminescent properties of the Eu3+- and Tb3+-doped compounds are reported. [ABSTRACT FROM AUTHOR]

Iron(IV)-oxo intermediates are involved in oxidations catalyzed by heme and nonheme iron enzymes, including the cytochromes P450. At the distal site of the heme in P450 Compound I (FeIV-oxo bound to porphyrin radical), the oxo group is involved in several hydrogen-bonding interactions with the protein, but their role in catalysis is currently unknown. In this work, we investigate the effects of hydrogen bonding on the reactivity of high-valent metal-oxo moiety in a nonheme iron biomimetic model complex with trigonal bipyramidal symmetry that has three hydrogen-bond donors directed toward a metal(IV)-oxo group. We show these interactions lower the oxidative power of the oxidant in reactions with dehydroanthracene and cyclohexadiene dramatically as they decrease the strength of the OH bond (BDEOH) in the resulting metal(III)-hydroxo complex. Furthermore, the distal hydrogen-bonding effects cause stereochemical repulsions with the approaching substrate and force a sideways attack rather than a more favorable attack from the top. The calculations, therefore, give important new insights into distal hydrogen bonding, and show that in biomimetic, and, by extension, enzymatic systems, the hydrogen bond may be important for proton-relay mechanisms involved in the formation of the metal-oxo intermediates, but the enzyme pays the price for this by reduced hydrogen atom abstraction ability of the intermediate. Indeed, in nonheme iron enzymes, where no proton relay takes place, there generally is no donating hydrogen bond to the iron(IV)-oxo moiety. [ABSTRACT FROM AUTHOR]

The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron-withdrawing and -donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1-octene, and ethylbenzene in various solvent systems, namely, toluene, CH2Cl2, CH3CN, and H2O/CH3CN (1:4). With an increase in the concentration of the easy-to-oxidize substrate cyclohexene in the presence of [(TMP)MnCl] ( 1 a) with electron-donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)MnOOC(O)R] species 2 a is the major active species. When the substrate was changed from the easy-to-oxidize one (cyclohexene) to difficult-to-oxidize ones (1-octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F20TPP)MnOOC(O)R] species 2 b generated from the reaction of [(F20TPP)MnCl] ( 1 b) with electron-withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)MnOOR] 2 a) depending on the concentration of the easy-to-oxidize substrate cyclohexene in all aprotic solvent systems except for CH3CN, whereas MnVO species is the major active oxidant in the protic solvent system. With difficult-to-oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1-octene in toluene, indicating that a MnVO intermediate generated from the heterolytic cleavage of 2 b becomes a major reactive species. We also studied the competitive epoxidations of cis-2-octene and trans-2-octene with two manganese(III) porphyrin complexes by meta-chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis- to trans-2-octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of Cp∗ 2W2O5 with HS(CH2)nCOOH (n = 1, 2) in MeOH or in CH2Cl2 solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp∗WO2(SCH2CH2CO2H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na2SO4 in CH2Cl2, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (<0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its 1H NMR spectrum suggests a different, asymmetric structure. [Copyright &y& Elsevier]

Abstract: The chemistry of organomolybdenum and -tungsten compounds in high oxidation states (mostly V and VI) is reviewed, with special attention on the behaviour in protic media and with respect to protic reagents. The high metal–carbon bond covalency imparts a great degree of inertness to these bonds relative to protonolysis. Hence, extensive chemistry in a wide variety of media and with protic reagents is possible without affecting the metal–(hydrocarbyl ligand) interactions. This article does not cover metallocene [i.e. bis(cyclopentadienyl)], alkylidene and alkylidyne derivatives, that have been extensively covered in other recent reviews. [Copyright &y& Elsevier]

Analysis of extended X-ray absorption fine structure (EXAFS) data for the Mn IV -oxo complexes [Mn IV (O)( DMM N4py)] 2+ , [Mn IV (O)(2pyN2B)] 2+ , and [Mn IV (O)(2pyN2Q)] 2+ ( DMM N4py=N,N-bis(4-methoxy-3,5-dimethyl-2-pyridylmethyl)-N-bis(2-pyridyl)methylamine; 2pyN2B=(N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine, and 2pyN2Q=N,N-bis(2-pyridyl)-N,N-bis(2-quinolylmethyl)methanamine) afforded Mn=O and Mn-N bond lengths. The Mn=O distances for [Mn IV (O)( DMM N4py)] 2+ and [Mn IV (O)(2pyN2B)] 2+ are 1.72 and 1.70 Å, respectively. In contrast, the Mn=O distance for [Mn IV (O)(2pyN2Q)] 2+ was significantly longer (1.76 Å). We attribute this long distance to sample heterogeneity, which is reasonable given the reduced stability of [Mn IV (O)(2pyN2Q)] 2+ . The Mn=O distances for [Mn IV (O)( DMM N4py)] 2+ and [Mn IV (O)(2pyN2B)] 2+ could only be well-reproduced using DFT-derived models that included strong hydrogen-bonds between second-sphere solvent 2,2,2-trifluoroethanol molecules and the oxo ligand. These results suggest an important role for the 2,2,2-trifluoroethanol solvent in stabilizing Mn IV -oxo adducts. The DFT methods were extended to investigate the structure of the putative [Mn IV (O)(N4py)] 2+ ⋅(HOTf) 2 adduct. These computations suggest that a Mn IV -hydroxo species is most consistent with the available experimental data., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lewis acid-base pair chemistry has been placed on a new level with the discovery that adduct formation between an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introduction of steric demand, thus preserving the reactivity of both Lewis centers, resulting in highly unusual chemistry. Some of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting a variety of small molecules, such as dihydrogen, in a heterolytic and even catalytic manner. This is in sharp contrast to classical reactions where the inert substrate must be activated by a metal-based catalyst. Very recently, research has emerged combining the two concepts, namely the formation of FLPs in which a metal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being a Lewis acid or base, also ancillary ligands can be used as part of the Lewis pair, still with the benefit of the redox-active metal center nearby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition-metal or rare-earth-metal compounds with the Lewis acid B(C 6 F 5 ) 3 . It covers a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Future goals of this young and exciting area are briefly discussed., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

C−H Activation The formation and high reactivity of the anti‐dioxo form of high‐spin μ‐oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic‐absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. These results provide insight into the high reactivity of the active species Q of soluble methane monooxygenases and the development of efficient alkane oxidation catalysts. For more details, see the Full Paper by M. Kodera et al. on page 5924 ff. [ABSTRACT FROM AUTHOR]

A detailed electrochemical investigation of a series of iron complexes (biuret-modified tetraamido iron macrocycles Fe III -bTAML), including the first electrochemical generation of Fe V (O), and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium are reported. Spectroelectrochemical and mass spectral studies indicated Fe V (O) as the active oxidant, formed due to two redox transitions, which were assigned as Fe IV (O)/Fe III (OH 2 ) and Fe V (O)/Fe IV (O). The spectral properties of both of these high-valent iron oxo species perfectly match those of their chemically synthesised versions, which were thoroughly characterised by several spectroscopic techniques. The O-O bond-formation step occurs by nucleophilic attack of H 2 O on Fe V (O). A kinetic isotope effect of 3.2 indicates an atom-proton transfer (APT) mechanism. The reaction of chemically synthesised Fe V (O) in CH 3 CN and water was directly probed by electrochemistry and was found to be first-order in water. The pK a value of the buffer base plays a critical role in the rate-determining step by increasing the reaction rate several-fold. The electronic effect on redox potential, WO rates, and onset overpotential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework. Changing the substituents from OMe to NO 2 resulted in an eightfold increase in reaction rate, while the overpotential increased threefold., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

By introducing steric constraints into molecular compounds, it is possible to achieve atypical coordination geometries for the elements. Herein, we demonstrate that a titanium-oxo cluster [{Ti4(μ4-O)(μ2-O)2}(OPr(i))6(fdc)2], which possesses a unique edge-sharing Ti4O17 octahedron tetramer core, is stabilized by the constraints produced by two orthogonal 1,1'-ferrocenedicarboxylato (fdc) ligands. As a result, a square-planar tetracoordinate oxygen (ptO) can be generated. The bonding pattern of this unusual anti-van't Hoff/Le Bel oxygen, which has been probed by theoretical calculations, can be described by two horizontally σ-bonded 2p(x) and 2p(y) orbitals along with one perpendicular nonbonded 2p(z) orbital. While the two ferrocene units are separated spatially by the ptO with an Fe⋅⋅⋅Fe separation of 10.4 Å, electronic communication between them still takes place as revealed by the cluster's two distinct one-electron electrochemical oxidation processes., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)