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Geometric isomers of mononuclear ruthenium(II) complexes

Capping TMβCD over AlTPyP has an excellent protective effect on seawater oxidation catalyzed by the supramolecular system AlTPyP@TMβCD against attack by Cl−.

The enantioselective reaction of 2H-azirines with oxazol-5-(4H)-ones (oxazolones) using a cinchona alkaloid sulfonamide catalyst has been developed. The reaction proceeded at the C-2 position of oxazolones to afford products with consecutive tetrasubstituted stereogenic centers in high yield with high diastereo- and enantioselectivity. The obtained aziridines were converted into various chiral compounds without loss of enantiopurity.

The crystal structure of an unprecedented silver complex of O-acetylsinigrin has shown chelating bonds of the sulfated thiohydroximate and an η2-bond of the ethylene moiety with Ag(i). Mechanistic studies on the formation and decomposition of the complex by the 1H NMR measurements and theoretical calculations with the DFT method indicated relevance to the glucosinolate degradation in biological systems.

An enantioselective aza-Friedel Crafts reaction of cyclic 4-aryl-3-oxo-1,2,5-thiadiazol-1,1-oxides as cyclic ketimines with indoles was developed. High enantioselectivities were observed for the reaction of various cyclic ketimines with indoles using chiral imidazoline-phosphoric acid catalysts. The obtained products can be converted to chiral α-amino amide and hydantoin.

We successfully developed an in situ UV–VIS absorption spectroscopic flow reactor system for investigation of solid-liquid two-phase reactions within the second time scale at high temperatures (solid-state-catalyst-mediated hydrothermal flow reactor system, SSCM-HF). The SSCM-HF consisted of a water reservoir, high-pressure pump, sample injector, high-temperature reactor involving solid-state catalysts, a cooling bath, a pressure regulator, and a temperature controller. The high-temperature reactor contains a reactor column having micrometer sized solid particles, and is connected to an optical window using transparent fused-silica capillary tubing. Liquid samples are exposed for the second time scale, which can be adjusted by changing the flow rate. In situ monitoring of reactions using SSCM-HF was performed at 200–1114 nm within 7.36–117.79 s at temperatures up to 300 °C and pressures up to 30 MPa. We demonstrated the usefulness of SSCM-HF by inspecting 5′-hydroxymethylfurfural (HMF) formation from glucose and cellulose. The influence of metal oxides, such as WO3 and Nb2O5, was investigated using both a conventional batch reactor and the SSCM-HF. The simple metal oxides showed catalytic activities for the dehydration of glucose to HMF. The SSCM-HF demonstrated in situ detection of a small amount of HMF in the presence of WO3 deposited solid particles within 29.4 s at 200 °C. This study demonstrates the application of the SSCM-HF as a new research tool for screening and investigating solid-state catalysts in detail in liquid-phase reactions at high temperatures.

We disclose herein an efficient enantioselective conjugate addition reaction between coumarin-3-carboxylic acids and malonic acid half thioesters (MAHTs). The reaction was catalyzed by N-heteroarenesulfonyl Cinchona alkaloid amides to afford double-decarboxylative conjugate addition products in good yield with high enantioselectivity. The reaction of various coumarin-3-carboxylic acids with MAHTs gave products in high yield with high enantioselectivity.

Oxidation combining three key technologies—reaction with H2O2, hydrothermal processing, and solid-state catalysis—is attractive for the development of environmentally friendly processes. However, the combination of these technologies has not been extensively investigated. We evaluated the potential for environmentally friendly oxidation of alcohols using H2O2 under hydrothermal conditions in the presence of several types of solid-state catalysts. The reactions were investigated using both a conventional batch reactor and a hydrothermal micro-flow reactor (HMFR), which was originally developed by our group for monitoring reactions with time scales within 0.002–200 s at temperatures of up to 400 °C. The oxidation of methanol, ethanol, propanol, and butanol to carboxylic acids using H2O2 did not readily proceed at 120 °C, unlike the oxidation of formaldehyde to formic acid. The catalytic effect of tungstate in the oxidation was observed, and the observation of near infrared (NIR) spectra at 2050–2040 nm indicated that zeolite possesses a catalytic property in the oxidation of formaldehyde to formic acid. Conversely, H2O2 was effective for oxidation of benzyl alcohol to benzaldehyde and benzoic acid at 120 °C and higher temperatures. The selective catalytic properties of tungstate and platinum group metal-deposited catalysts were observed in the oxidation of benzyl alcohol to benzaldehyde. The oxidation reaction was successfully detected using an HMFR with a reaction time of 0.64 s at 300 °C. This study demonstrates the potential and usefulness of the environmentally friendly combination of H2O2, hydrothermal conditions, and solid-state catalysis for the oxidation of aromatic and aliphatic alcohols.

The catalytic enantioselective reaction of diphenylmethylidene-protected α-aminoacetonitriles with imines has been developed. Good yields and diastereo- and enantioselectivities were observed for the reaction of various imines using chiral bis(imidazoline)/Pd catalysts. The reaction of α-aminonitriles with di-tert-butyl azodicarboxylate afforded chiral α,α-diaminonitriles in high yields with high enantioselectivities.

We report the synthesis and luminescent properties of halide-bridged tricopper(I) complexes with a polyaza cryptand having three 2,6-bis(aminomethyl)pyridyl spacers. The asymmetric {Cu3X3} structur...

The first catalytic enantioselective reaction of 2H-azirines with thiols has been developed. The obtained aziridines can be converted to optically active oxazolines, aziridylamides, or α-sulfonyl esters. Transformation of these optically active aziridines showed that 2H-azirines act as β,β-dicarbocationic amine synthons.

To understand the role of the unique equatorial coordination environment at the active center in nickel superoxide dismutase (NiSOD), we prepared a novel Ni(II) complex with an amino-carboxamido-dithiolato-type square-planar ligand (1, [Ni(2+)(L1)](-)) as a model of the NiSOD active site. Complex 1 has a low-spin square-planar structure in all solvents. Interestingly, the absorption wavelength and ν(C═O) stretching vibrations of 1 are affected by solvents. This provides an indication that the carbonyl oxygens participate in hydrogen-bonding interactions with solvents. These interactions are reflected in the redox potentials; the peak potential of an anodic wave (Epa) values of Ni(II)/Ni(III) waves for 1 are shifted to a positive region for solvents with higher acceptor numbers. This indicates that the disproportionation of superoxide anion by NiSOD may be regulated by hydrogen-bonding interactions between the carboxamido carbonyl and electrophilic molecules through fine-tuning of the redox potential for optimal SOD activity. Interestingly, the Epa value of the Ni(III)/Ni(II) couple in 1 in water (+0.303 V vs normal hydrogen electrode (NHE)) is similar to that of NiSOD (+0.290 V vs NHE). We also investigated the superoxide-reducing and -oxidizing reactions of 1. First, 1 reacts with superoxide to yield the superoxide-bound Ni(II) species (UV-vis: 425, 525, and ∼650 nm; electron paramagnetic resonance (EPR) (4 K): g// = 2.21, g⊥ = 2.01; resonance Raman: ν((16)O-(16)O)/ν((18)O-(18)O) = 1020/986 cm(-1)), which is then oxidized to Ni(III) state only in the presence of both a proton and 1-methylimidazole, as evidenced by EPR spectra. Second, EPR spectra indicate that the oxidized complex of 1 with 1-methylimidazole at the axial site can be reduced by reaction with superoxide. The Ni(III) complex with 1-methylimidazole at the axial site does not participate in any direct interaction with azide anion (pKa 4.65) added as mimic of superoxide (pKa 4.88). According to these data, we propose the superoxide disproportionation mechanism in superoxide-reducing and -oxidizing steps of NiSOD in both Ni(II) and Ni(III) states.

The synthesis, structures, and reactivity of dinuclear Fe0 complexes of N-heterocyclic carbenes (NHCs, denoted as L) are reported. The NHC adducts of ferric chloride (L)FeCl3 were prepared from the reactions of FeCl3 with L in toluene. The reduction of (L)FeCl3 with KC8 resulted in the formation of the dinuclear Fe0 complexes Fe2{μ-η1(C):η6(arene)-L}2 (2a, L = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes); 2b, L = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)), in which NHC ligands bridge two iron atoms using one of the arene rings as an η6 ligand. Their magnetic properties are different: 2a is paramagnetic and 2b is diamagnetic. The dinuclear complexes 2a,b serve as precursors for monomeric (NHC)Fe0 species, and treatment of 2a,b with 1 atm of CO led to the formation of (L)Fe(CO)4. Complex 2a was found to react with 1-azidoadamantane, giving rise to the dinuclear tetrazene complex (IMes)Fe(μ-NAd)2Fe(AdNNNNAd) (4).

We recently demonstrated the solid-state catalyst-mediated hydrothermal flow reactor system, SSCM-HF, for in situ ultraviolet–visible (UV–VIS) absorption spectrophotometric measurements of solid–liquid two-phase reactions within the second time-scale at high temperature. Successful results were obtained using SSCM-HF in the UV–VIS region, including the oxidation of alcohols to aldehyde with dissolved oxygen and the conversion of glucose into 5’-hydroxymethylfurfural. Here, the scope and detailed characteristics of the Hydrothermal Flow detection system for in situ absorption spectrophotometric measurements in the UV–VIS near-infrared (NIR) region (UVN region) (HF-UVN) as well as improvement of weak points of the previous system were investigated. The optical and mechanical performance of the HF-UVN, which consists of a high pressure pump, automatic sample injector, high-temperature reactor with a detection coupler, quenching bath, and automatic pressure controller, were evaluated at high temperature and pressure. Our previous study implied that the difficulty of detection was due to the drift at high temperature and pressure since the surfaces of optical fibers with 0.2 mm core size and capillary surfaces with outer and inner diameters of 0.375 mm and 0.1 mm, respectively, were placed at right angles inside the heating blocks without a tight coupler. The optical characteristic of the combination of fused-silica capillary and optical fibers in the HF-UVN was evaluated, and a coupler was designed to fix the fused-silica capillary and optical fibers. The distance between the axis of the light-receiving and that of the light-exit section, the influence of the angle between two optical fibers, the characteristics of the coupler were evaluated. The HF-UVN was applied to monitor the stability of chromogenic reagents at 300 °C and the oxidation of aldehyde to carboxylic acid. This study demonstrated that the HF-UVN can be applied for UV–VIS–NIR monitoring not only in the laboratory but also in practice for the optimization of chemical processes in the liquid phase at high temperature and pressure.

A half-sandwich, coordinatively unsaturated N-heterocyclic carbene complex of iron with a metallacycle was found to cleave the Si–H bonds of hydrosilanes to give 16-electron iron–silyl complexes. The reactions of silyl complexes with H2 led to the formation of dihydride complexes, in which hydride ligands weakly interact with the silicon atom. The molecular structures of these new complexes have been determined by means of X-ray crystallography.

The enantioselective oxidative ring-opening reaction of aziridines with α-nitroacetates has been developed. Good yields and enantioselectivity were observed for the reaction of various aziridines using a novel cinchona alkaloid amide/NiBr2 catalyst. Both enantiomers of products could be obtained by using pseudoenantiomeric chiral catalysts. This process offers an efficient route for the synthesis of α-aminoketones.

The highly enantioselective double-decarboxylative title reaction is applicable to 3-oxo-3-phenylpropanoic acid, but fails using α-cyanoacetic acid or α,α-dimethyl malonic acid half thioesters.

The synthesis and reaction of homoleptic iron(II) complexes with 2,6-di-adamantyl-substituted aryloxides [OC 6 H 2 –2,6-Ad-4-R] − ([OAr AdR ] − , Ad = adamantyl, R = Me, i Pr) are described. Monomeric two-coordinate iron aryloxides Fe(OAr AdR ) 2 (R = Me, 1 ; i Pr, 2 ) were synthesized by the reaction of Fe[N(SiMe 3 ) 2 ] 2 with 2 equiv of HOAr AdR . Treatment of 1 and 2 with 1-azidoadamantane resulted in intramolecular insertion of an adamantyl nitrene into a methylene C–H bond of the aryloxide adamantyl substituent, yielding the corresponding amine–aryloxide complexes Fe(OAr AdR )(OAr AdR –NHAd) (R = Me, 3 ; i Pr, 4 ). Molecular structures of all these complexes are reported.

α,β- and α,α- Diaminoacetonitriles are highly syn-selectively and enantioselectively obtained by reaction of N-protected α-aminoacetonitriles with various imines in the presence of a chiral Pd-catalyst.

The first highly enantioselective reaction of α-thioacetonitriles with imines in the presence of a bis(imidazoline)-palladium pincer complex as a chiral Lewis acid catalyst is presented.

The catalytic enantioselective reaction of α-phenylthioacetonitriles with imines has been developed. The reaction of various imines proceeds in good yields and diastereo- and enantioselectivities in the presence of chiral bis(imidazoline)–palladium catalysts. The obtained products can be converted into β-aminonitrile or β-aminoamide compounds without loss of enantiopurity.

A cyclometalated N-heterocyclic carbene ligand in a half-sandwich iron complex was found to couple with alkynes, leading to a unique type of ring opening of the carbene ligand and the formation of ferrocenyl-diimine complexes. An intermediary iron complex obtained from the reaction with phenylacetylene reveals that the ring opening follows the formation of a fused heterocycle consisting of an imidazole ring and two alkynes.

The coordinatively unsaturated iron(II) amido complex Cp*Fe{N(SiMe3)2} (1) serves as an efficient precursor for the cleavage of the N−N bond of diphenylhydrazine. The NN bond of azobenzene was also found to be activated by 1 in the presence of pinacolborane.

Reactions of the cyclometalated hydride complexes with diazo and azide substrates are reported. While diazoalkane undergoes four-electron N-N bond cleavage, azides undergo two-electron N(2) extrusion.

The reactions of the half-sandwich iron(II) complex [FeCl(Cp*)(tmeda)] (1; Cp*=η(5)-C(5)Me(5), TMEDA=N,N,N',N'-tetramethylethylenediamine) with potassium naphthalenide or potassium anthracenide gave the diamagnetic complexes [(Cp*)Fe(μ-polyarene)Fe(Cp*)] (polyarene=naphthalene (2), anthracene (3a)), which have two {(Cp*)Fe} units bound to opposite faces of the polyarene. One of two {(Cp*)Fe} units in 3a is located over the central ring of anthracene while the other is positioned over an outer ring. The {(Cp*)Fe} unit bound to the central ring of 3a migrates to the outer ring upon heating in the solid state to give the isomer 3b. The electrochemical potential separations between successive one-electron redox events for complexes 2 and 3b are large. The mixed valence complexes [2](+) and [3b](+) were synthesized by chemical oxidation. The mixed-valence complex [3b](+) is charge delocalized on the Mossbauer timescale at 78 K, and its absorption spectrum shows an intervalence charge-transfer band. Complex [2](+) exhibits two absorption bands in the near-IR region and a slightly broadened doublet in the Mossbauer spectrum. DFT calculations were carried out to examine the electronic structures of these dinuclear iron(I) complexes to elucidate the factors responsible for their diamagnetism and to determine the degree of charge delocalization in the mixed-valence complexes.

Organofluorine compounds are widely used in all aspects of the chemical industry. Although tetrafluoroethylene (TFE) is an example of an economical bulk organofluorine feedstock, the use of TFE is mostly limited to the production of poly(tetrafluoroethylene) and copolymers with other alkenes. Furthermore, no catalytic transformation of TFE that involves carbon-fluorine bond activation has been reported to date. We herein report the first example of a palladium-catalyzed coupling reaction of TFE with arylzinc reagents in the presence of lithium iodide, giving α,β,β-trifluorostyrene derivatives in excellent yields.

A coordinatively unsaturated iron-methyl complex having an N-heterocyclic carbene ligand, [Cp*Fe(L(Me))Me] (1; Cp*=eta(5)-C(5)Me(5), L(Me)=1,3,4,5-tetramethyl-imidazol-2-ylidene), is synthesized from the reaction of [Cp*Fe(TMEDA)Cl] (TMEDA=N,N,N',N'-tetramethylethylenediamine) with methyllithium and L(Me). Complex 1 is found to activate the C-H bonds of furan, thiophene, and benzene, giving rise to aryl complexes, [Cp*Fe(L(Me))(aryl)] (aryl=2-furyl (2), 2-thienyl (3), phenyl (4)). The C-H bond cleavage reactions are applied to the dehydrogenative coupling of furans or thiophenes with pinacolborane (HBpin) in the presence of tert-butylethylene and a catalytic amount of 1 (10 mol% to HBpin). The borylation of the furan/thiophene or 2-substituted furans/thiophenes occurs exclusively at the 2- or 5-positions, respectively, whereas that of 3-substituted furans/thiophenes takes place mainly at the 5-position and gives a mixture of regioisomers. Treatment of 2 with 2 equiv of HBpin results in the quantitative formation of 2-boryl-furan and the borohydride complex [Cp*Fe(L(Me))(H(2)Bpin)] (5). Heating a solution of 5 in the presence of tert-butylethylene led to the formation of an alkyl complex [Cp*Fe(L(Me))CH(2)CH(2)tBu] (6), which was found to cleave the C-H bond of furan to produce 2. On the basis of these results, a possible catalytic cycle is proposed.

International audience; {Tb3}[Sc2−xLux](Al3)O12 crystals have been grown and investigated for the first time for magneto-optical applications. Tb3Al5O12 exhibits the best magneto-optical features; however, its incongruent melting nature has led to the industrial use of Tb3Ga5O12. Tb3Sc2Al3O12 had been proposed as an alternative to Tb3Al5O12, but unfortunately its growth also presents several drawbacks. The present investigation shows that by the isovalent substitution of Sc3+ by Lu3+ in the octahedral site of the garnet structure, it is possible to improve the growth characteristics while preserving the superior magneto-optical properties. We demonstrate that {Tb3}[Sc2−xLux](Al3)O12 crystals show a higher visible transparency and a larger Faraday rotation than Tb3Ga5O12 crystals. {Tb3}[Sc2−xLux](Al3)O12 is therefore a very promising material in particular for new magneto-optical applications in the visible-near IR wavelength region.

Half-sandwich iron complexes of N-heterocyclic carbenes, Cp*Fe(L(R))Cl (2a; L(Mes) = 1,3-dimesityl-imidazol-2-ylidene, 2b; L(iPr) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, Cp* = eta(5)-C5Me5), have been synthesized by the reaction of Cp*Fe{N(SiMe3)2} (1) with the corresponding imidazolium salts. Treatment of 2a with either methyllithium or phenyllithium replaces the chloride with either a methyl or a phenyl group, generating Cp*Fe(L(Mes))R (3a; R = Me, 3b; R = Ph). These complexes, in turn, undergo cyclometalation at elevated temperatures, and Cp*Fe{kappa2-(C,C)-L'(Mes)} (4; L'(Mes) = CH2C6H2-3,5-Me2-2-(3-mesityl-imidazol-2-ylidene-1-yl)) was isolated. On the other hand, methylation of 2b at room temperature leads directly to the formation of a cyclometalated complex, Cp*Fe{kappa2-(C,C)-L'(iPr)} (6; L'(iPr) = CH2CH(CH3)(3-isopropyl-4,5-dimethylimidazol-2-ylidene-1-yl)). The Fe(II) center of 6 traps atmospheric dinitrogen reversibly to produce a dinuclear end-on N2 complex [Cp*Fe{kappa2-(C,C)-L'(iPr)}]2(mu-eta(1):eta(1)-N2) (7). Complex 6 also promotes C-H bond activation of thiophene, furan, benzothiophene, and benzofuran at room temperature. In these reactions, C-H bond cleavage occurred exclusively at the 2-position of the rings, generating Cp*Fe(L(iPr))(2-C4H3E) (8; E = S, 9; E = O) and Cp*Fe(L(iPr))(2-C8H5E) (10; E = S, 11; E = O), while C-H cleavage took place mainly at the 4-position in the case of pyridine. Coupling reactions between heteroarenes and catecholborane (HBcat) can be carried out by treatment of 6 with heteroarenes followed by the addition of excess HBcat, giving rise to 2-boryl-heteroarenes and the borohydride complex Cp*Fe(L(iPr))(H2Bcat) (14).

The use of a sterically demanding aryloxide ligand allows us to isolate a tetrakis(aryloxide)diniobium complex bridged by four hydride ligands. This hydride aryloxide undergoes reduction of CO via hydrogenation and deoxygenation, resulting in formation of a methylidene species. Further carbonylation gives a vinylidene complex.

A nitride complex [K(thf)2]2[{(O3)Nb}2(μ-N)2] (2), prepared from [K(DME)]2[{(O3)Nb}2(μ-H)4] (1) and N2, was protonated with 2,6-lutidinium chloride to yield ammonia and [(O3)NbCl3]– (3), where H3[O3] = tris(3,5-di-tert-butyl-2-hydroxy phenyl)methane. The reaction of 3 with KBHEt3 regenerated [K(DME)]2[{(O3)Nb}2(μ-H)4] (1), thereby completing a synthetic cycle for the conversion of N2 to NH3. Alkylation of 2 with methyl iodide led to formation of [K(thf)][{(O3)Nb}2(μ-N)(μ-NMe)] (4) and [{(O3)Nb}2(μ-NMe)2] (5). Treatment of 5 with pyridine afforded a terminal imide complex [(O3)Nb=NMe(py)2] (6). The imide monomer 6 reacted with CO2 to give [(O3)Nb{(MeN)2CO}(py)] (7) and [{(O3)Nb}2(μ-O)2] (8) in a 2:1 ratio, while the reaction of 6 with p-TolNCO gave an asymmetric ureate complex [(O3)Nb{p-TolNC(O)NMe}(py)] (9).

The optical and magneto-optical properties of the {Tb3}[Sc1.95Lu0.05](Al3)O12 garnet (TSLAG) crystal are analyzed in detailed and compared with those of the reference compound Tb3Ga5O12 (TGG). TSLAG presents a very high transmittance, particularly higher than that of TGG in the visible region, and its Verdet constant is 20% larger at any wavelength. The figure of merit and extinction features point out the superior characteristics of TSLAG respect to TGG. A prototype, polarization independent optical isolator based on a TSLAG rotator is demonstrated at 1080 nm. Its performance confirms the high optical quality of this crystal, indicating its mature development for Faraday rotator applications.

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