A highly chemoselective,diastereoselective, and regioselective epoxidation of chiral allylic alcohols with hydrogen peroxide,catalyzed by sandwich-type polyoxometalates: enhancement of reactivity and control of selectivity by the hydroxy group through metal-alcoholate bonding

Sandwich-type polyoxometalates (POMs), namely [WZnM2(ZnW9O34)2]q- [M = Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], are shown to catalyze selectively the epoxidation of chiral allylic alcohols with 30% hydrogen peroxide under mild conditions (ca. 20 degrees C) in an aqueous/organic biphasic system. The transition metals M in the central ring of polyoxometalate do not affect the reactivity, chemoselectivity, or stereoselectivity of the allylic alcohol epoxidation by hydrogen peroxide. Similar selectivities, albeit in significantly lower product yields, are observed for the lacunary Keggin POM [PW11O39]7-, in which a peroxotungstate complex has been shown to be the active oxidizing species. All these features support a tungsten peroxo complex rather than a high-valent transition-metal oxo species operates as the key intermediate in the sandwich-type POM-catalyzed epoxidations. On capping of the hydroxy functionality through acetylation or methylation, no reactivity of these hydroxy-protected substrates [1a(Ac) and 1a(Me)] is observed by these POMs. A template is proposed to account for the marked enhancement of reactivity and selectivity, in which the allylic alcohol is ligated through metal-alcoholate bonding, and the H2O2 oxygen source is activated in the form of a peroxotungsten complex. 1,3-Allylic strain promotes a high preference for the threo diastereomer and 1,2-allylic strain a high preference for the erythro diastereomer, whereas tungsten-alcoholate bonding furnishes high regioselectivity for the epoxidation of the allylic double bond. The estimated dihedral angle alpha of 50-70degrees for the metal-alcoholate-bonded template of the POM/H2O2 system provides the best compromise between 1,2A and 1,3A strain during the oxygen transfer. In contrast to acyclic allylic alcohols 1, the M-POM-catalyzed oxidation of the cyclic allylic alcohols 4 by H2O2 gives significant amounts of enone.     

A new Ru complex capable of catalytically oxidizing water to molecular dioxygen

We have prepared three new dinuclear ruthenium complexes having the formulas [Ru2II(bpp)(trpy)2(mu-L)]2+ (L = Cl, 1; L = AcO, 2) and [Ru2II(bpp)(trpy)2(H2O)2]3+ (3). The three complexes have been characterized through the usual spectroscopic and electrochemical techniques and, in the cases of 1 and 2, the X-ray crystal structures have been solved. In aqueous acidic solution, the acetato bridge of 2 is replaced by aqua ligands, generating the bis(aqua) complex 3 which, upon oxidation to its RuIVRuIV state, has been shown to catalytically oxidize water to molecular oxygen. The measured pseudo-first-order rate constant for the O2-evolving process is 1.4 x 10-2 s-1, more than 3 times larger than the higher one previously reported for Ru-O-Ru type catalysts. This new water-splitting catalyst also has improved stability with regard to any previously described, achieving a total of 18.6 metal cycles.     

Synthesis, structure, and redox and catalytic properties of a new family of ruthenium complexes containing the tridentate bpea ligand

We have prepared a new family of ruthenium complexes containing the bpea ligand (where bpea stands for N,N-bis(2-pyridyl)ethylamine), with general formula [Ru(bpea)(bpy)(X)](n+) (2, X = Cl(-); 3, X = H(2)O; 4, X = OH(-)), and the trisaqua complex [Ru(bpea)(H2O)(3)](2+), 6. The complexes have been characterized through elemental analyses, UV-vis and (1)H NMR spectroscopy, and electrochemical studies. For complex 3, the X-ray diffraction structure has also been solved. The compound belongs to the monoclinic P2(1)/m space group, with Z = 2, a = 7.9298(6) A, b = 18.0226(19) A, c = 10.6911(8) A, and beta = 107.549(8) degrees. The Ru metal center has a distorted octahedral geometry, with the O atom of the aquo ligand placed in a trans position with regard to the aliphatic N atom of the bpea ligand so that the molecule possesses a symmetry plane. NMR spectra show that the complex maintains its structure in aqueous solution, and that the corresponding chloro complex also has a similar structural arrangement. The pH dependence of the redox potential for the complex [Ru(bpea)(bpy)(H2O)](PF(6))(2) is reported, as well as the ability of the corresponding oxo complex to catalyze the oxidation of benzylic alcohol to benzaldehyde in both chemical and electrochemical manners.     

Fe2 and Fe4 clusters encapsulated in vacant polyoxotungstates: hydrothermal synthesis, magnetic and electrochemical properties, and DFT calculations

While the reaction of [PW(11)O(39)](7-) with first row transition-metal ions M(n+) under usual bench conditions only leads to monosubstituted {PW(11)O(39)M(H(2)O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe(II)(bpy)(3)][PW(11)O(39)Fe(2) (III)(OH)(bpy)(2)]12 H(2)O (bpy=bipyridine) complex (1) contains the dinuclear {Fe(micro-O(W))(micro-OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe(III) centers in complex 1 are weakly antiferromagnetically coupled (J=-11.2 cm(-1), H=-JS(1)S(2)) compared to other {Fe(micro-O)(micro-OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy](2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]14 H(2)O (2) (dmbpy=5,5'-dimethyl-2,2'-bipyridine) and H(2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]10 H(2)O (3) represent the first butterfly-like POM complexes. In these species, a tetranuclear Fe(III) complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe(III) cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the chi(M)T=f(T) curve leads to J(wb)=-59.6 cm(-1) and J(bb)=-10.2 cm(-1) (H=-J(wb)(S(1)S(2)+S(1)S(2*)+S(1*)S(2)+S(1*)S(2*))-J(bb)(S(2)S(2*))). While the J(bb) value is within the range of related exchange parameters previously reported for non-POM butterfly systems, the J(wb) constant is significantly lower. As for complex 1, this can be justified considering Fe(w)--O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH(3))(4)](10)[(PW(11)O(39)Fe(III))(2)O]12 H(2)O (4) has been isolated. In this complex, the two single oxo-bridged Fe(III) centers are very strongly antiferromagnetically coupled (J=-211.7 cm(-1), H=-JS(1)S(2)). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2, which is insoluble in common solvents, have been studied in the solid state.     

Lanthanide diruthenium(II,III) compounds showing layered and PtS-type open framework structures

Two types of lanthanide diruthenium phosphonate compounds, based on the mixed-valent metal-metal bonded paddlewheel core of Ru(2)(hedp)(2)(3-) [hedp = 1-hydroxyethylidenediphosphonate, CH(3)C(OH)(PO(3))(2)], have been prepared with the formulas Ln(H(2)O)4[Ru(2)(hedp)(2)(H(2)O)2].5.5H(2)O (1.Ln, Ln = La, Ce) and Ln(H(2)O)4[Ru(2)(hedp)(2)(H(2)O)(2)].8H(2)O (2.Ln, Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er). In both types, each Ru(2)(hedp)2(H2O)23- unit is linked by four Ln(3+)ions through four phosphonate oxygen (OP) atoms and vice versa. The geometries of the {LnO(P4)} group, however, are different in the two cases. In 1.Ln, the geometry of {LnO(P4)} is closer to a distorted plane, and thus a square-grid layer structure is found. In 2.Ln, the geometry of {LnO(P4)} is better described as a distorted tetrahedron; hence, a unique PtS-type open-framework structure is observed. The channels generated in structures 2.Ln are filled with water aggregates with extensive hydrogen-bond interactions. The magnetic and electrochemical properties are also investigated.     

Water oxidation by a mononuclear ruthenium catalyst: characterization of the intermediates

A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [Ru(II)-OH(2)](2+) (Ru = Ru complex with one 4-t-butyl-2,6-di-(1',8'-naphthyrid-2'-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H(2)(18)O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [Ru(IV)═O](2+) and [Ru(IV)-OO](2+). At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [Ru(III)-OH](2+)/[Ru(II)-OH(2)](2+) couple, which is equal to or higher than the potential of the [Ru(IV)═O](2+)/[Ru(III)-OH](2+) couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k(1) = 2 × 10(4) M(-1) s(-1). While pH-independent oxidation of [Ru(IV)═O](2+) takes place at 1420 mV vs NHE, bulk electrolysis of [Ru(II)-OH(2)](2+) at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [Ru(II)-OOH](+) over 2 weeks. While there remains some conflicting evidence, we have assigned this species as (1)[Ru(IV)-η(2)-OO](2+) based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer's group (J. Am. Chem. Soc. 2010, 132, 1545-1557).     

Water oxidation by mononuclear ruthenium complexes with TPA-based ligands

The synthesis, characterization, and water oxidation activity of mononuclear ruthenium complexes with tris(2-pyridylmethyl)amine (TPA), tris(6-methyl-2-pyridylmethyl)amine (Me(3)TPA), and a new pentadentate ligand N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy) have been described. The electrochemical properties of these mononuclear Ru complexes have been investigated by both experimental and computational methods. Using Ce(IV) as oxidant, stoichiometric oxidation of water by [Ru(TPA)(H(2)O)(2)](2+) was observed, while Ru(Me(3)TPA)(H(2)O)(2)](2+) has much less activity for water oxidation. Compared to [Ru(TPA)(H(2)O)(2)](2+) and [Ru(Me(3)TPA)(H(2)O)(2)](2+), [Ru(DPA-Bpy)(H(2)O)](2+) exhibited 20 times higher activity for water oxidation. This study demonstrates a new type of ligand scaffold to support water oxidation by mononuclear Ru complexes.     

The mechanism of formation of N-formylkynurenine by heme dioxygenases

Heme dioxygenases catalyze the oxidation of L-tryptophan to N-formylkynurenine (NFK), the first and rate-limiting step in tryptophan catabolism. Although recent progress has been made on early stages in the mechanism, there is currently no experimental data on the mechanism of product (NFK) formation. In this work, we have used mass spectrometry to examine product formation in a number of dioxygenases. In addition to NFK formation (m/z = 237), the data identify a species (m/z = 221) that is consistent with insertion of a single atom of oxygen into the substrate during O(2)-driven turnover. The fragmentation pattern for this m/z = 221 species is consistent with a cyclic amino acetal structure; independent chemical synthesis of the 3a-hydroxypyrroloindole-2-carboxylic acid compound is in agreement with this assignment. Labeling experiments with (18)O(2) confirm the origin of the oxygen atom as arising from O(2)-dependent turnover. These data suggest that the dioxygenases use a ring-opening mechanism during NFK formation, rather than Criegee or dioxetane mechanisms as previously proposed.     

cis,cis-[(bpy)2RuVO]2O4+ catalyzes water oxidation formally via in situ generation of radicaloid RuIV-O*

The mechanism of the catalytic oxidation of water by cis,cis-[(bpy)(2)Ru(OH(2))](2)O(4+) to give molecular dioxygen was investigated using Density Functional Theory (DFT). A series of four oxidation and four deprotonation events generate the catalytically competent species cis,cis-[(bpy)(2)Ru(V)O](2)O(4+), which breaks the H-OH bond homolytically at the rate determining transition state to give a hydroperoxo intermediate. Our calculations predict a rate determining activation barrier of 25.9 kcal/mol in solution phase, which is in reasonable agreement with the previously reported experimental estimate of 18.7-23.3 kcal/mol. A number of plausible coupling schemes of the two metal sites including strong coupling, weak ferromagnetic and weak antiferromagnetic coupling have been considered. In addition, both high-spin and low-spin states at each of the Ru(V)-d(3) centers were explored and we found that the high-spin states play an important mechanistic role. Our calculations suggest that cis,cis-[(bpy)(2)Ru(V)O](2)O(4+) performs formally an intramolecular ligand-to-metal charge transfer when reacting with water to formally give a cis,cis-[(bpy)(2)Ru(IV)O*](2)O(4+) complex. We propose that the key characteristic of the diruthenium catalyst that allows it to accomplish the most difficult first two oxidations of the overall four-electron redox reaction is directly associated with this in situ generation of two radicaloid oxo moieties that promote the water splitting reaction. A proton coupled metal-to-metal charge transfer follows to yield a Ru(V)/Ru(III) peroxo/aqua mixed valence complex, which performs the third redox reaction to give the superoxo/aqua complex. Finally, intersystem crossing to a ferromagnetically coupled Ru(IV)/Ru(III) superoxo/aqua species is predicted, which will then promote the last redox event to release triplet dioxygen as the final product. A number of key features of the computed mechanism are explored in detail to derive a conceptual understanding of the catalytic mechanism.     

Structure of Oxygen and CO Adsorption on Ru(0001) Electrode

It is important to understand the chemisorption of oxygen and CO on Ru(0001) surface. CO oxidation at oxygen precovered Ru(0001) surface at low oxygen coverages gave an extremely low CO oxidation rate, and it was also observed that, with a nominal oxygen coverage exceeding ca. 3 mL, rather high CO/CO2 conversion probabilities were achieved1. In the case of coadsorption of CO and oxygen on Ru(0001) surface under UHV conditions, a model comprising two CO molecules in an (22)-O unit cel…     

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

A mononuclear‐cobalt(II)‐substituted silicotungstate, K₁₀[Co(H₂O)₂(γ‐SiW₁₀O₃₅)₂] ? 23 H₂O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated [Ru(bpy)₃]³⁺ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s^?1), and quantum yield (Φ_QY; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely [Ni(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 2 ) and [Mn(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the [Ru(bpy)₃]²⁺/visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., [Co₄(H₂O)₂(α‐PW₉O₃₄)₂]^10? (Co₄‐POM) and [Co^IIICo^II(H₂O)W₁₁O₃₉]^7? (Co₂‐POM)) under optimum conditions.     

Tetranuclear polybipyridyl complexes of Ru(II) and Mn(II), their electro- and photo-induced transformation into di-mu-oxo Mn(III)Mn(IV) hexanuclear complexes

Three heterotetranuclear complexes, [{Ru(II)(bpy)(2)(L(n))}(3)Mn(II)](8+) (bpy = 2,2'-bipyridine, n = 2, 4, 6), in which a Mn(II)-tris-bipyridine-like centre is covalently linked to three Ru(II)-tris-bipyridine-like moieties using bridging bis-bipyridine L(n) ligands, have been synthesised and characterised. The electrochemical, photophysical and photochemical properties of these complexes have been investigated in CH(3)CN. The cyclic voltammograms of the three complexes exhibit two successive very close one-electron metal-centred oxidation processes in the positive potential region. The first, which is irreversible, corresponds to the Mn(II)/Mn(III) redox system (E(pa) approximately 0.82 V vs Ag/Ag(+) 0.01 M in CH(3)CN-0.1 M Bu(4)NClO(4)), whereas the second which is, reversible, is associated with the Ru(II)/Ru(III) redox couple (E(1/2) approximately 0.91 V). In the negative potential region, three successive reversible four electron systems are observed, corresponding to ligand-based reduction processes. The three stable dimeric oxidized forms of the complexes, [Mn(2)(III,IV)O(2){Ru(II)(bpy)(2)(L(n))}(4)](11+), [Mn(2)(IV,IV)O(2){Ru(II)(bpy)(2)(L(n))}(4)](12+) and [Mn(2)(IV,IV)O(2){Ru(III)(bpy)(2)(L(n))}(4)](16+) are obtained in fairly good yields by sequential electrolyses after consumption of respectively 1.5, 0.5 and 3 electrons per molecule of initial tetranuclear complexes. The formation of the di-micro-oxo binuclear complexes are the result of the instability of the {[Ru(II)(bpy)(2)(L(n))](3)Mn(III)}(9+) species, which react with residual water, via a disproportionation reaction and the release of one ligand, [Ru(II)(bpy)(2)(L(n))](2+). A quantitative yield can be obtained for these reactions if the electrochemical oxidations are performed in the presence of an added external base like 2,6-dimethylpyridine. Photophysical properties of these compounds have been investigated showing that the luminescence of the Ru(II)-tris-bipyridine-like moieties is little affected by the presence of manganese within the tetranuclear complexes. A slight quenching of the excited states of the ruthenium moieties, which occurs by an intramolecular process, has been observed. Measurements made at low concentration (<1 x 10(-5) M) indicate that some decoordination of Mn(2+) arises in 1a-c. These measurements allow the calculation of the association constants for these complexes. Finally, photoinduced oxidation of the tetranuclear complexes has been performed by continuous photolysis experiments in the presence of a large excess of a diazonium salt, acting as a sacrificial oxidant. The three successive oxidation processes, Mn(II)--> Mn(III)Mn(IV), Mn(III)Mn(IV)--> Mn(IV)Mn(IV) and Ru(II)--> Ru(III) are thus obtained, the addition of 2,6-dimethylpyridine in the medium giving an essentially quantitative yield for the two first photo-induced oxidation steps as found for electrochemical oxidation.     

Understanding LiOH Chemistry in a Ruthenium‐Catalyzed Li–O2 Battery

Non‐aqueous Li–O₂ batteries are promising for next‐generation energy storage. New battery chemistries based on LiOH, rather than Li₂O₂, have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru‐catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e⁻ oxygen reduction reaction, the H in LiOH coming solely from added H₂O and the O from both O₂ and H₂O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li₂O₂, LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long‐lived battery. An optimized metal‐catalyst–electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals.     

Effect of electron availability on selectivity of O2 reduction by synthetic monometallic Fe porphyrins

Herein we report that biomimetic analogues of cytochrome c oxidase (CcO) couple reduction of O(2) to oxidation of a single-electron carrier, Ru(NH(3))(6)(2+), under steady-state catalytic turnover. Higher Ru(II) concentrations favor the 4-electron vs 2-electron O(2) reduction pathway. Our data indicate that the capacity of electrode-adsorbed Fe-only porphyrins to catalyze reduction of O(2) to H(2)O is due to high availability of electrons and is eliminated under the biologically relevant slow electron delivery.     

Characterisation of tri-ruthenium dihydride complexes through the computation of NMR parameters

Density functional theory has been used to provide atomic-level detail on the structures of metal hydride intermediates that have previously been proposed in the hydrogenation of phenylacetylene using Ru(3)(CO)(10)(PPh(3))(2). Based on a comparison of energetic data along with computed chemical shifts and coupling constants, we suggest that the detected species share a Ru(3)(μ-H)(μ-H) motif, with two distinct bridging hydride sites, rather than the terminal hydride proposed previously. The work illustrates how theory can be used as a complement to spectroscopy to enhance the accuracy of deductions, and to provide a basis for future rational design of second generation catalysts.     

A new structural motif for photoinitiated electron collection: Ru,Rh bimetallics providing insight into H2 production via photocatalysis of water reduction by Ru,Rh,Ru supramolecules

Ru,Rh,Ru complexes are photocatalysts for the reduction of H(2)O to H(2)via a Rh(I) intermediate. The herein reported Ru,Rh bimetallics undergo PEC but do not catalyze the reduction of H(2)O, establishing intact supramolecules are photoactive in the Ru,Rh,Ru systems. The Ru,Rh(I) photoproduct dimerizes via Rh-Rh bond formation, deactivating the Rh(I) center sterically prohibited in the Ru,Rh,Ru trimetallic systems.     

Polyoxometalate-stabilized Pt nanoparticles and their electrocatalytic activities

The synthesis of long-term stable polyoxometalate (POM)-stabilized Pt nanoparticles (NPs) is described here. By means of controlled bulk electrolysis, the reduced POM anions, SiW(12)O(40)(4-) (or SiW(12)) and H(2)W(12)O(40)(6-) (or H(2)W(12)), respectively, served the dual role of reductant and protecting/stabilizing ligand for the Pt NPs. Transmission electron microscopy (TEM) images confirmed the formation of 3 to 4 nm sized Pt NPs, which coincidently was in the same size range of the commercial Pt black that was used as a reference. Elemental XPS analyses showed W/Pt ratios of 0.12 for the SiW(12)- and 0.18 for the H(2)W(12)-stabilized Pt NPs, but found no evidence of the presence of Cl(-) anion in the samples. Controlled electrochemical (EC), UV-Vis, and IR data provided unambiguous evidence for the structural integrity of the POM anions on the Pt NP surface. CO stripping, methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) were used to assess their electrocatalytic activities. It was found that both SiW(12)- and H(2)W(12)-stabilized Pt NPs showed enhanced activities in MOR and ORR as compared to that of Pt black, with the latter having higher enhancement. These observations clearly demonstrated that the stabilizing POM anions have a profound influence on the electrocatalytic activity of the underlying Pt NPs.     

Catalytic Activation of H(2) and C-H Bonds by Electron-Deficient Ruthenium(II) Porphyrins

The Ru(2) and RuNi derivatives of 1,8-bis(10,15,20-trimesityl-5-porphyrinato)anthracene-a recently reported cofacial diporphyrin ligand comprising two hindered porphyrins spanned by an anthracene bridge-have been synthesized. Both Ru(2)(DPAHM) and RuNi(DPAHM) are extremely reactive species that apparently contain 14-electron Ru(II) centers and, as is the case for their monoporphyrin analog, (5,10,15,20-tetramesitylporphyrinato)ruthenium [Ru(TMP)], must be rigorously protected from oxygen, nitrogen, and other ligating agents. In addition, these electron-deficient Ru(II) porphyrins all appear to bind aromatic solvents such as benzene and toluene, the weakest ligating solvents in which these Ru(II) porphyrins have been found soluble. Ru(TMP) and its metallodiporphyrin analogs, Ru(2)(DPAHM) and RuNi(DPAHM), catalyze H(2)/D(2) exchange in benzene solution and as solids. When adsorbed on a particularly nonpolar carbon support, these Ru(II) porphyrins all manifest significant activity with respect to catalytic H(2)/D(2) exchange [approximately 40 turnovers s(-)(1), when normalized for Ru(II) content]. In addition, these molecules slowly catalyze the exchange of H(2) into deuterated aromatic hydrocarbons and, in the absence of solvent, the exchange of D(2) into CH(4). Kinetic studies of H(2)/D(2) exchange catalyzed by these Ru(II) porphyrins on carbon supports indicate that exchange is likely to be effected by one face of a single Ru(TMP) moiety. The activity of each supported catalyst was suppressed by the presence of ligands, either exogenous (CO irreversibly and N(2) reversibly) or from polar functionalities on the surface of the supporting matrix.     

Development and Electrochemical Studies of Ruthenium Based Mixed Oxide Catalyst Electrodes for Chlorine Evolution

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Theoretical and experimental studies of diruthenium tetracarboxylates structure, spectroscopy, and electrochemistry

Quantum mechanical calculations at the density functional theory (DFT) level have been performed on diruthenium tetracarboxylates of different levels of molecular complexity: from unsolvated monomers to oligomers. The agreement between the calculated and experimental molecular structures and vibrational modes of the simple [Ru2(micro-O2CCH3)4]0/+ and [Ru2(micro-O2CCH3)4(H2O)2]0/+ systems made us confident in our calculation methodology. Therefore, it has been applied to the analysis of two different kinds of properties of these compounds: the trends in the UV/vis spectroscopy and electrochemistry along the [Ru2(micro-O2CCH3)4X2]- (X=Cl-, Br-, I-) series, and the crystalline polymorphism related to the polymeric strand conformation in extended Ru2(micro-O2CR)4Cl compounds. For the [Ru2(micro-O2CCH3)4X2]- series, we report new spectroscopic and electrochemical results and interpret the trends on the basis of time dependent DFT-polarized continuum model calculations, local charge and spin analysis, and X donor properties. As far as the polymeric conformation is concerned, it has been previously suggested that the Ru-Cl-Ru angle results from a compromise between packing, orbital overlap, and microsegregation. Our calculations on [Ru2(micro-O2CCH3)4Cl]2Cl- and [Ru2(micro-O2CCH3)4Cl]3Cl- oligomers provide insights on the influence of the first two factors on the strand conformation and allows a suggestion on what is the equatorial aliphatic chain's influence on this issue.