Syntheses of C-substituted icosahedral dicarbaboranes bearing the 8-dioxane-cobalt bisdicarbollide moiety

The treatment of 1,2-, 1,7- and 1,12-carbaborane lithiated isomers with [3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-(1′,2′-C₂B₉H₁₁)] (1) at molar ratios 1:1 or 1:2 at room temperature in THF leads generally to the formation of a series of orange double-cluster mono and dianions. These were characterized by NMR and MS methods as [1′′-X-1′′,2′′-closo-C₂B₁₀H₁₁]⁻, [2]⁻; [1′′-X-1′′,7′′-closo-C₂B₁₀H₁₁]⁻, [3]⁻ and [1′′-X-1′′,12′′-closo-C₂B₁₀H₁₁], [4]⁻ for the monoanions, whereas [1′′,2′′-X₂-1′′,2′′-closo-C₂B₁₀H₁₀]²⁻, [2]²⁻; [1′′,7′′-X₂-1′′,7′′-closo-C₂B₁₀H₁₀]²⁻, [3]²⁻; and [1′′,12′′-X₂-1′′,12′′-closo-C₂B₁₀H₁₀]²⁻, [4]²⁻ for the dianions (where X = 3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-1′,2′-(C₂B₉H₁₁)). Moreover, these borane-cage subunits can be easily modified via attaching variable substituents onto cage carbon and boron vertices, which makes these compounds structurally flexible potential candidates for BNCT of cancer and HIV-PR inhibition.     

Emission of 2-phenylethanol from its β-d-glucopyranoside and the biogenesis of these compounds from [H8] l-phenylalanine in rose flowers

The hydrolysis of 2-phenylethyl β-d-glucopyranoside (3) was found to be partially inhibited by feeding with 2-phenyl-N-glucosyl-acetamidiumbromide (8), a β-glucosidase inhibitor, resulting in a decrease in the diurnal emission of 2-phenylethanol (2) from Rosa damascena Mill. flowers. Detection of [1,1,2,2′,3′,4′,5′,6′-²H₈]-2 and [1,2,2′,3′,4′,5′,6′-²H₇]-2 from R. ‘Hoh-Jun’ flowers fed with [1,1,2,2′,3′,4′,5′,6′-²H₈]-3 suggested that β-glucosidase, alcohol dehydrogenase, and reductase might be involved in scent emission. Comprehensive GC-SIM analyses revealed that [1,2,2,2′,3′,4′,5′,6′-²H₈]-2 and [1,2,2,2′,3′,4′,5′,6′-²H₈]-3 must be biosynthesized from [1,2,2,2′,3′,4′,5′6′-²H₈] l-phenylalanine ([²H₈]-1) with a retention of the deuterium atom at α-position of [²H₈]-1.     

The influence of sulfur substitution on the atomic displacement in Bi2Ti2O7

To clarify the role of A₂O′ and B₂O₆ networks on cation displacement observed in Bi₂Ti₂O′O₆, we used density functional theory calculations to examine the effect of sulfur substitution on the O′ and O sites on lone pair formation and resulting atomic displacement observed in Bi₂Ti₂O′O₆. Cation displacement in bismuth titanate is suppressed only when S is substituted on the O′ site. Analysis of the electronic structure shows that S substitution on the O′ site suppresses the formation of the asymmetric p-type lone pair by modifying the Bi-anion hybridization. Lone pair formation is favored in Bi₂Ti₂O′S₆ and the atomic displacement is larger than that observed in Bi₂Ti₂O′O_6. This enhanced displacement is due to weaker Bi-S versus Bi-O interactions leading to significantly stronger hybridization between the Bi and O′ states in Bi₂Ti₂O′S₆. We also induced lone pair formation in a metallic bismuth pyrochlore oxide (Bi₂Ru₂O′O₆) by modifying the Bi-O interactions through S substitution on the B₂O₆ network, indicating atomic displacement on the A₂O′ network may be achieved by modifying the B₂O₆ network.     

Synthesis of functional derivatives of the [3,3′-Co(1,2-C2B9H11)2] anion

A series of various functional derivatives of the cobalt bis(1,2-dicarbollide) anion [8-XCH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻ (X=OH, NH₂, and CH(NH₂)COOH) were prepared by the ring-opening reactions of [8-O(CH₂CH₂)₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] with different nucleophiles followed by functional group interconversion reactions. Acidic hydrolysis of [8-NCCH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻ resulted in the shorter-chain alcohol [8-HOCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻. Structures of (Bu₄N)[8-AcNHC(COOEt)₂CH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] and [8-(1-C₅H₅N)CH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] were determined by the single crystal X-ray diffraction method. Perspectives of application of functionalized cobalt bis(1,2-dicarbolide) derivatives in nuclear medicine are discussed.     

Two new supramolecular assemblies based on Keggin-type polyoxometalates through AgO and ππ stacking interactions

Two new supramolecular assemblies based on Keggin-type polyoxometalates, [Ag₃(4,4′-bipy)₂(2,2′-bipy)₂][Ag(2,2′-bipy)₂][{Ag(2,2′-bipy)}HSiW₁₁VO₄₀] (1) and [Ag₃(4,4′-bipy)₂(2,2′-bipy)₂][Ag(2,2′-bipy)₂][{Ag(2,2′-bipy)}PW₁₁VO₄₀] (2) (4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine), have been synthesized under the hydrothermal conditions and structurally characterized by IR, XPS, TG and single-crystal X-ray diffraction. Compound 1 has a 2D layer network structure via weak Ag^...O interactions. Compound 2 is isostructural with compound 1. In addition, the fluorescence of compound 1 is reported.     

The preparation and properties of some allyltin carboxylates:R3SnOOCR′ (R′ = CH3, CH2Cl), R2Sn(OOCR′)2 (R′ = CH2Cl,CHCl2) and [R2Sn(OOCR′)]2O (R′ = CH2Cl,CHCl2, CCl3)

Triallyl- and diallyltin carboxylates [(CH₂CHCH₂)₃SnOOCR′ with R′ = CH₃ and CH₂Cl, (CH₂CHCH₂)₂Sn(OOCR′)₂ with R′ = CH₂Cl and CHCl₂)] and tetraallyl-1,3-diacyloxydistannoxanes {[(CH₂CHCH₂)₂SnOOCR′]₂ with R′ = CH₂Cl,CHCl₂ and CCl₃}, have been prepared from the reaction of tetraallytin with carboxylic acids in methanol.     

Molecular conductors with 8,8′-diiodo cobalt bis(dicarbollide) anion

New molecular conductors on the base of 8,8′-diiodo cobalt bis(dicarbollide) anion (TTF)[8,8′-I₂-3,3′-Co(1,2-C₂B₉H₁₀)₂] (1), (BMDT-TTF)₄[8,8′-I₂-3,3′-Co(1,2-C₂B₉H₁₀)₂] (2) and (BEDT-TTF)₂[8,8′-I₂-3,3′-Co(1,2-C₂B₉H₁₀)₂] (3) were synthesized and their crystal structures and electrical conductivities were determined. All the radical cation salts prepared were found to be semiconductors. Some regularities in the crystal structures of the TTF-based radical cation salts with bis(dicarbollide) complexes of transition metals are discussed.     

Functionally substituted organotin compounds I. Addition of thiols to alkenyltin compounds

3-(Trialkylstannyl)propyl aryl sulphides (R₃SnCH₂CH₂CH₂SR′; R = Me, Et, Bu; R′ = Ph, p-tolyl) were prepared by the addition of arenethiols to allyltrialkyltin compounds. Preferential cleavage of the allyl group by the reaction R₃SnCH₂CHCH₂+R′SH→R₃SnSR′+CH₃CHCH₂ occurred when R = R′ = Bu and R = R′ = Ph. Diallyltin dibromide and benzenethiol gave stannous bromide. Mössbauer parameters of the products are recorded.     

A series of metal-organic frameworks constructed with arenesulfonates and 4,4′-bipy ligands

Five transition metal compounds containing arenesulfonates and 4,4′-bipy ligands, namely [Zn₂(N,N′-4,4′-bipy)(N-4,4′-bipy)₂(H₂O)₈](bpds)₂ · 5H₂O (1), [Ag₂(N,N′-4,4′-bipy)₂(bpds)] (2), [Cd(N,N′-4,4′-bipy)(H₂O)₄]₂(4-abs)₄ · 5H₂O (3), [Cu(N,N′-4,4′-bipy) (O-bs)₂(H₂O)₂] · 4H₂O (4), and [Zn(N,N′-4,4′-bipy)₂(H₂O)₂](4,4′-bipy)(bs)₂ · 4H₂O (5) (4,4′-bipy = 4,4′-bipyridine, bpds = 4,4′-biphenyldisulfonate, 4-abs = 4-aminobenzenesulfonate, bs = benzenesulfonate), have been synthesized and characterized by X-ray single crystal diffraction, elemental analyses and TG analyses, in order to investigate the coordination chemistry of arenesulfonates and 4,4-bipy, as well as to construct novel coordination frameworks via mixed-ligand strategy. Compounds 2, 4 and 5 could be obtained via hydrothermal or aqueous reactions. Compound 1 forms a binuclear octahedral metal complex. Compounds 2–4 form polymeric chains. Compound 5 consists of 2D square grids with one intercalated 4,4′-bipy molecule. Weak Ag–Ag interactions are observed in compound 2. These complexes show great structural varieties and there are three different coordination modes observed for both the 4,4′-bipy and the sulfonate ligands.     

Mononuclear and dinuclear iron thiocyanate and selenocyanate complexes of tris-pyrazolylmethane ligands

Treatment of Fe(NCE)₂ (E = S or Se) with 1 equiv. of tris-(3,5-dimethylpyrazol-1-yl)methane (tpm′) yields dimeric [{Fe(NCE)(μ-NCE)(tpm′)}₂]. These dimers are cleaved in MeCN solution, yielding isolable [Fe(NCE)₂(tpm′)(NCMe)], whose solvent ligands can be substituted by moderately basic heterocycle donors to give [Fe(NCE)₂(tpm′)(py)], [Fe(NCS)₂(tpm′)(im)] or [{Fe(NCE)₂(tpm′)}₂(μ-4,4′-bipy)]. The monodentate heterocycles in the latter compounds are readily lost in most solvents, regenerating the dimeric starting materials. [Fe(NCS)₂(tpm′)(py)] was also prepared by reacting [Fe(NCS)₂(py)₄] with tpm′. The mononuclear compounds are all high-spin between 5 and 300 K, despite mostly having regular coordination geometries and tpm′ ligand conformations that should in principal favour spin-crossover. Analogous products containing unsubstituted tris-(pyrazol-1-yl)methane (tpm) could not be isolated, but the crystal structure of the double salt [Fe(tpm)₂][Fe(NCS)₅(py)], containing a new iron(III) anion, is described.     

New fulvalenium salts of bis(dicarbollide) cobalt and iron: Synthesis, crystal structure and electrical conductivity

New radical cation salts (BEDT-TTF)₂[3,3′-Co(1,2-C₂B₉H₁₁)₂] (1), (BEDT-TTF)₂[8-I-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] (2), (BMDT-TTF)[3,3′-Co(1,2-C₂B₉H₁₁)₂] (3) and (TMTSF)₂[3,3′-Fe(1,2-C₂B₉H₁₁)₂] (4) were synthesized and their crystal structures and electrical conductivities were determined. Compound 4 is isostructural to the earlier reported Co analogue. All the radical cation salts synthesized are semiconductors.     

Synthesis and characterization of two novel organic–inorganic hybrid solids from Keggin ions and metal coordination complexes

Two new hybrid compounds, [Co(4,4′-bpy)₂(H₂O)₄][(4,4′-bpyH₂]₂[CoW₁₂O₄₀]·8H₂O (1) and [Fe(2,2′-bpy)₃]₃[H₂W₁₂O₄₀]·6H₂O (2), (4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine) have been hydrothermally synthesized. These solids were characterized by elemental analysis, thermogravimetric analysis, UV–Vis spectroscopy and X-ray diffraction. The hydrogen-bonding interactions in 1 lead to the formation of a three dimensional network consisting of [CoW₁₂O₄₀]⁶⁻ anionic clusters, [Co(4,4′-bpy)₂(H₂O)₄]²⁺ cations and lattice water molecules, while the discrete Keggin ion [H₂W₁₂O₄₀]⁶⁻ in compound 2 is surrounded by 14 [Fe(2,2′-bpy)₃]²⁺ complexes through CH?O interactions (2.24–2.56 Å).     

Synthesis and characterization of coordination polymers of a carboxylato cyclophane with metal [Zn(II) and Cd(II)]-2,2′-bipyridines

N,N′,N′′,N′′′-Tetrakis(3-carboxy-propionyl)-1,6,20,25-tetraaza-[6.1.6.1] paracyclophane, H₄cp has been complexed with metal (Zn(II) and Cd(II)) 2,2′-bipyridyls. The resulting complexes of the composition [{Zn(2,2′-bpy)}₂(cp)]_n·4H₂O 1 and [{Cd(2,2′-bpy)}₂(cp)]_n·5H₂O 2 (2,2′-bpy = 2,2′-bipyridine) have been characterized using spectroscopic (IR, solid state UV–Vis), elemental analysis and single-crystal X-ray diffraction measurements. In these complexes the cyclophane coordinates in different modes, and in complex 2, Cd(II) is hepta-coordinated. However, under harsh reaction conditions (using excess nitric acid and a longer reaction time) debranching of the cyclophane is observed in the reaction of Zn(2,2′-bpy)(NO₃)₂ with H₄cp, and a complex of the composition [Zn(2,2′-bpy)(Suc)]_n3 (suc = succinate) is isolated. Using non-covalent interactions, complexes 1 and 2 provide 3D supramolecular structures, whereas an infinite 1D chain structure is observed for complex 3. The thermal and photoluminescence properties of the complexes have also been studied.     

Production of mixed halogenated congeners of the natural product heptachloro-1′-methyl-1,2′-bipyrrole (Q1) by photolysis in the presence of bromine

Halogenated 1′-methyl-1,2′-bipyrroles (MBPs) are a class of marine halogenated natural products that have been detected in biota from all over the world. However, structures and standards of many mixed chlorinated/brominated MBPs are not available. For this reason, the known 2,3,3′,4,4′,5,5′-heptachloro-1′-methyl-1,2′-bipyrrole (Q1 or MBP-79) was UV-irradiated in the presence of bromine with the goal of inducing a chlorine → bromine exchange. A few drops of bromine were added to a solution of Q1 and 10 mL of either CH₂Br₂, CH₂Cl₂, or CHCl₃. The experiments were performed both at room temperature and elevated temperature for 30 min. At least four out of five possible bromohexachloro-1′methyl-1,2′-bipyrroles (BrCl₆-MBPs), at least seven out of 13 possible Br₂Cl₅-MBPs, as well as traces of Br₃Cl₄-MBPs and Br₄Cl₃-MBPs were obtained in this way. Selective fragment ions in the GC/ECNI-MS spectra as well as electrophilic bromination of hexachloro-MBP solutions were used to verify the structures of the BrCl₆-MBP isomers. The BrCl₆-MBPs eluted from DB-5-like columns in the order of 4′-bromo-2,3,3′,4,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-76), which co-eluted with 3′-bromo-2,3,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-78), followed by 2-bromo-3,3′,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-75), 3-bromo-2,3′,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-77), and 5′-bromo-2,3,3′,4,4′,5-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-74). These BrCl₆-MBPs were also detected in a sample of cetacean blubber from Australia, but the abundance pattern was different. While Br-MBP-76/Br-MBP-78 dominated in the cetacean, irradiation of Q1 (MBP-79) in the presence of bromine led to high proportions of Br-MBP-75. The suitability of the UV-induced Cl → Br exchange was confirmed by the Br-assisted UV-irradiation of pentachloroanisole (PCA). This experiment produced at least two bromotetrachloro- and three dibromotrichloroanisoles, the last eluting in each case being the most relevant. Thus, this method is most likely generally suited for the production of mixed-halogenated aromatic organohalogen compounds which are not readily obtainable by synthesis.     

Effect of 5-Me substituent(s) on the catalytic activity of palladium(II) 2,2-bipyridine complexes in CO/4-tert-butylstyrene copolymerization

The coordination of two 5-substituted-2,2^′-bipyridines L (L¹=5-methyl-2,2^′-bipyridine, L²=5,5^′-dimethyl-2,2^′-bipyridine) to palladium was studied. The neutral complexes [Pd(L)Cl₂] and [Pd(L)(Me)Cl], and the cationic complexes obtained after chlorine abstraction [Pd(L)₂][BAr^′₄]₂ and [Pd(L)(Me)(NCMe)][BAr^′₄] (Ar^′=3,5-(CF₃)₂-C₆H₃), respectively, were isolated and characterized by NMR and FAB mass spectroscopy. The complex [Pd(L²)(L³)][BAr^′₄]₂ (L³=2,2^′-bipyridine) bearing different ligands, was prepared for comparison purposes. The activity of the monocationic and dicationic complexes as catalytic precursors in the CO/4-tert-butylstyrene copolymerization was compared with that of related well-known catalysts containing the unsubstituted 2,2^′-bipyridine as nitrogen ligand, to evaluate the influence of the substituents in 5- and 5,5^′-position. The presence of one or two substituents on the nitrogen ligand has a positive effect on productivity using both types of precursors. No influence was observed on the polymer properties in terms of molecular weight and tacticity. Analysis of the reactivity of the methyl-palladium complexes towards carbon monoxide shows further differences depending on the nitrogen ligand.     

Complexes derived from the general copper(II)/maleamic acid/N,N′,N′′-chelate reaction systems: Synthetic,reactivity, structural and spectroscopic studies

The synthetic investigation of the Cu^II/maleamate(−1) ion (HL⁻)/N,N′,N′′-chelate general reaction system has allowed access to compounds [Cu₂(HL)₂(bppy)₂](ClO₄)₂·H₂O (1·H₂O), [Cu(HL)(bppy)(ClO₄)] (2) and [Cu(HL)(terpy)(H₂O)](ClO₄) (4) (bppy = 2,6-bis(pyrazol-1-yl)pyridine, terpy = 2,2′;6′,2′′-terpyridine). In the absence of externally added hydroxides, compound [Cu₂(L′)₂(bppy)₂](ClO₄)₂ (3) was obtained from MeOH solutions; L′⁻ is the monomethyl maleate(−1) ligand which is formed in situ via the Cu^II-assisted HL⁻ → L′⁻ transformation. In the case of tptz-containing (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) reaction systems, the Cu^II-assisted hydrolysis of tptz to pyridine-2-carboxamide (L1) afforded complex [Cu(L1)₂(NO₃)₂] (5). The crystal structures of 1–5 are stabilized by intermolecular hydrogen bonding and π–π stacking interactions. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands.     

Stereoselective synthesis of fluorine-containing analogues of anti-bacterial sanfetrinem and LK-157

The synthesis of (1′S,3R,4R)-4-acetoxy-3-(1′-trimethylsilyloxy-2′,2′,2′-trifluoroethyl)-2-azetidinone (10) precursor of modified carbapenems is described relying upon [Ru(C₆Me₆)(S,S)-(CH₂)₅NSO₂DPEN]-catalyzed asymmetric transfer hydrogenation under dynamic kinetic resolution using HCO₂H-Et₃N. This fluorine-containing precursor yielded the targeted trinems 1 and 2 via a stereoselective key step condensation with lithium (S)-6-methoxy-cyclohexenolate.     

Self-assembly of four new extended architectures based on reduced polyoxometalate clusters and cadmium complexes

Four new [P₄Mo₆] cluster-based extended structures containing cadmium complexes, [Cd₃(4,4′-Hbpy)₂(4,4′-bpy)₂(H₂O)₈][Cd(H₂PO₄)₂(HPO₄)₄(PO₄)₂(MoO₂)₁₂(OH)₆]·7H₂O 1, (4,4′-Hbpy)₂[Cd(4,4′-bpy)₃(H₂O)₃][Cd(4,4′-bpy)(H₂O)]₂[Cd(H₂PO₄)₂(HPO₄)₄ (PO₄)₂(MoO₂)₁₂(OH)₆]·H₂O 2, [Cd₄(phen)₂(H₂O)₄][Cd(phen)(H₂O)]₂[Cd(HPO₄)₄ (HPO₄)₄(MoO₂)₁₂(OH)₆]·5H₂O 3 and [Cd₄(2,2′-bpy)₂(H₂O)₄][Cd(2,2′-bpy)(H₂O)]₂ [Cd(HPO₄)₄(HPO₄)₄(MoO₂)₁₂(OH)₆]·3H₂O 4 (4,4′-bpy=4,4′-bpyridine, phen=1,10-phenanthroline, 2,2′-bpy=2,2′-bpyridine), have been synthesized and characterized by elemental analysis, IR, TG and single crystal X-ray diffraction. The structure of compound 1 is constructed from the Cd[P₄Mo₆]₂ dimers linked by [Cd₃(4,4′-Hbpy)₂(4,4′-bpy)₂(H₂O)₈] subunits to generate a plane layer. Compound 2 consists of the positive 2D sheets that constructed from Cd[P₄Mo₆]₂ dimers linked by [Cd(4,4′-bpy)(H₂O)] complexes, then the 2D sheets are further linked up together to form a 3D supramolecular framework via extensive hydrogen-bonding interactions among the [P₄Mo₆] clusters, free 4,4′-bpy molecules, dissociated [Cd(4,4′-bpy)₃(H₂O)₃]²⁺ complexes and water molecules. Compounds 3 and 4 show new 2D layered structure, with Cd[P₄Mo₆]₂ building blocks connected by tetra-nuclear [Cd₄{(phen)₂/(2,2′-bpy)₂}(H₂O)₄] clusters and [Cd(phen/2,2′-bpy)(H₂O)] complexes. The fluorescent activities of compounds 3 and 4 are reported.     

Role of hydrogen peroxide in the synthesis of nitrogen heterocycle containing cobalt complexes

The reactions of Co(O₂CCH₃)₂·4H₂O with the sodium salt of p-toluene sulfonic acid (NapTS) and pyridine (py) or 4-methylpyridine (4mepy) in the presence of hydrogen peroxide in methanol led to the formation of [Co(py)₃(H₂O)₃](pTS)₂ or [Co(4mepy)₂(H₂O)₄](pTS)₂·MeOH, respectively. The coordination polymer [{Co(44′bpy)(H₂O)₄}(pTS)₂]_n (4,4′-bipyridine = 44′bpy) was obtained from the reaction of Co(O₂CCH₃)₂·4H₂O with 44′bpy in the presence of NapTS. The reaction of Co(O₂CCH₃)₂·4H₂O, 2,2′-bipyridine (22′bpy) and NapTS with hydrogen peroxide resulted in the formation of the dinuclear complex [Co₂(μ-OH)₂(μ-O₂CCH₃)(O₂CCH₃)₂(22′bpy)₂](pTS). Characterization of these complexes and the role of hydrogen peroxide in these reactions are discussed. Similar reactions with sodium sulfamate gave the mononuclear [Co(22′bpy)₂(O₂CCH₃)]NH₂SO₃·2H₂O complex and [Co₂(μ-OH)₂(μ-O₂CCH₃)(O₂CCH₃)₂(22′bpy)₂](NH₂SO₃).     

Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2

Various Ru(L₁)(L₂) (1) complexes (L₁ = 2,2′-bipyridines, 2,2′:6′,2″-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl-2,2′-bipyridinyl or 2,2′-bipyridinyl-6-carboxylate; L₂ = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2′-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H₂O₂. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2′-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2′]bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed.