Achiral Dihydroxylation of Olefins by Osmate (OsO42−) Stabilised on Nanocrystalline Magnesium Oxide

A recoverable and reusable new heterogeneous AP‐Mg‐OsO₄ catalyst was designed and developed for the first time via a counterionic stabilisation of OsO₄²⁻ with Mg²⁺ present on the corner or edge of nanocrystalline MgO. AP‐Mg‐OsO₄ catalysed the dihydroxylation of olefins to afford diols with excellent yields in the presence of N‐methylmorpholine N‐oxide for the first time. The absence of osmium and no progress of the dihydroxylation reaction with the filtrate samples withdrawn periodically during the reaction rule out the leaching of osmium unambiguously and provide evidence for the heterogeneity of the reaction. Identification of surface intermediate species by XPS and TGA‐DTA‐mass thermography gives an insight into the mechanism of the dihydroxylation reaction.     

Heterogeneous Bifunctional Catalysts for the Synthesis of Chiral Vicinal Diols

Heterogeneous bifunctional catalysts consisting of palladate–osmate and osmate–tungstate developed by the ion exchange on quaternary ammonium salts covalently bound to resin, and their homogeneous bimetallic analogs are evaluated for the synthesis of chiral vicinal diols. The heterogeneous bifunctional catalyst (resin-PdOs) and its homogeneous analog are used in the tandem Heck-asymmetric dihydroxylation (AD) to afford diols with excellent yields and enantiomeric excesses (ee's) in the presence of various co-oxidants. The other bifunctional catalyst (resin-OsW) and its homogeneous analog are used in a simultaneous asymmetric dihydroxylation-N-oxidation of a wide range of olefins to obtain chiral vicinal diols with higher yields and ee's using H₂O₂ as terminal oxidant. The bifunctional resin catalysts are recovered quantitatively by a simple filtration and reused for a number of cycles with consistent activity.     

Catalytic Asymmetric Dihydroxylation of Aliphatic Olefins with Reusable Resin‐Osmium Tetroxide

Asymmetric dihydroxylation of aliphatic olefins to chiral diols with good yields and ees by a heterogeneous Resin‐OsO₄ catalyst using ferricyanide as cooxidant is disclosed for the first time. The catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.     

Osmium ligand deficient clusters as catalysts for liquid phase hydrocarbon transformations

Reduction of OsO₄ by molecular hydrogen in alkane (cycloalkane) or benzene media at 20–150 °C yields small osmium clusters of the Os₁C_0.34-0.48H_0-0.6 composition with a specific surface area of 34–46 m²/g. The systems obtained are shown to be ligand deficient osmium clusters (LDC) of 7–16 Å in diameter, stabilized by a small amount of carbonaceous ligands with Os-Os = 2.68-1.70 Å and Os-C = 2.11-2.19 Å. The characteristics of these chemically prepared Os-LDC are similar to those of Ni- and Co-LDC, prepared by a vapour phase synthesis. The novel Os-LDC effectively catalyze hydrogenolysis of alkanes and cycloalkanes at 100–150 ° C and initial H₂ pressure of 5 MPa, hydrogenation of cyclopentadiene and arenes at 20 ° C, multiple H/D exchange between CH₄ and D₂ at 100–120 ° C and methanation of CO₂ at 150–180 ° C.     

Voltammetric study of the cyanide complexes of osmium—I. The reduction of the cyanide complex of Os(VI) on a platinum rde

Two forms of cyanide complexes of hexavalent osmium were found in alkaline KCN solutions. The initially formed complex, OsO₂(OH)₂(CN)^2?₂, is stable only in solutions with at least a ten-fold excess of OH^? ions over CN^? ions. At higher cyanide concentrations it is converted into the OsO₂(CN)^2?₄ complex. Both these complexes are reduced to tervalent osmium. A more detailed study of complex OsO₂(OH)₂(CN)^2?₂ has shown that it is reduced electrochemically according to the scheme of a consecutive electrochemical reaction.OsO₂(OH)₂(CN)^2?₂ + 2e(k₁,α₁) → Os(IV) + e(k₂,α₂) → Os(OH)₄(CN)^3?₂The values α₁ = 0.65 and α₂ = 0.40 and the potential dependences of constants k₁ and k₂ were determined.     

Synthesis of cis Adducts of Cyclopenta[cd]Pyrene with Deoxyguanosine and Deoxyadenosine

Recent analysis of DNA adducts of cyclopenta[cd]pyrene (CPP) formed in vitro by reaction of CPP-3, 4-oxide, with calf thymus DNA, suggested ring opening of the enantiomeric 3,4-epoxide predominantly by cis addition. We describe herein the chemical synthesis of DNA adducts resulting from benzylic cis ring opening of CPP-3,4-oxide by the exocyclic amino group of 2′-deoxyguanosine (dG) and 2′-deoxyadenosine (dA). The methodology involves synthesis of cis-3,4-dihydro-3-amino-4-hydroxycyclopenta[cd]pyrene followed by its coupling with appropriately protected halo-purinedeoxyribose intermediates. The diastereomeric mixture of products resulted in the coupling reaction was separated by HPLC and characterized by ¹H NMR and MS analysis. Co-chromatography of the synthetic standards with in vitro adducts confirmed the identity and the stereochemical preference of the CPP-DNA adducts.     

The synthesis of lactic-acid-based telechelic prepolymers

We have studied how different catalysts and diols affect the properties of low-molecular-weight (M_w (GPC) < 49800 g/mol) lactic-acid-based telechelic prepolymers. The catalysts and diols were tested separately in our previous studies. In this study, we used the best previously tested diols and catalysts together in order to prepare different types of telechelic prepolymers (for example, crystalline or amorphous). All condensation polymerizations were carried out in the melt, using different diols and different catalysts. The prepolymers were characterized by differential scanning calorimetry, gel permeation chromatography, titrimetric methods, and ¹³C nuclear magnetic resonance (¹³C-NMR). According to NMR, the resulting polymers contained less than 1 mol % of lactic acid monomer and less than 5.1 mol % of lactide. Dibutyltindilaurate, like tin(II)octoate, produced quite good molecular weights, but the resulting prepolymers contained exceptionally high amounts of D-lactic acid structures, and, therefore, these prepolymers were totally amorphous. Antimony(III)oxide produced a high-molecular-weight prepolymer when the diol used was aliphatic. Like DBTL, Sb₂O₃ produced amorphous prepolymers, which contained a lower amount of D-lactic acid structures than DBTL prepolymers. 1,8-dihydroxyanthraquinone produced a different kind of chain structure with Ti(IV)bu and Ti(IV)iso because one prepolymer had high crystallinity, and the other showed only a slight crystallinity. Sulphuric acid produced a very high-molecular-weight prepolymer with aliphatic 2-ethyl-1,3-hexanediol; and with aromatic diols, it produced quite good molecular weights, except with 1,8-dihydroxyanthraquinone. High-molecular-weight prepolymers produced with H₂SO₄ also showed high crystallinity; and, according to ¹³C-NMR, they did not contain lactide and D-lactic acid structures. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1011–1016, 1998     

A Novel Chemoentrapment Approach for Supportless Recycling of a Catalyst: Catalytic Asymmetric Dihydroxylation

A simple method of recycling a metal catalyst through chemoentrapment in an aqueous layer using ethyl vinyl ether has been developed. Using this new methodology, a highly efficient, filtration‐free recycling of osmium for catalytic asymmetric dihydroxylation was accomplished. By means of the formation of a water‐soluble OsO₄²⁻ using EVE, AD reactions of mono‐ and disubstituted olefins with 1 mol % of OsO₄ proceeded for up to 9 cycles without any loss of yields and enantioselectivities.     

(Salen)chromium Complex Mediated Asymmetric Ring Opening of meso‐ and Racemic Epoxides with Different Fluoride Sources

The asymmetric ring opening of five meso‐ and three racemic epoxides with different fluorinating reagents in the presence of stoichiometric or slightly sub‐stoichiometric amounts of Jacobsen's enantiopure (salen)chromium chloride complex A gave the corresponding optically active vicinal fluorohydrins. Silver fluoride was used as one of the fluoride sources either in the presence of Bu₄N⁺H₂F₃⁻ in diethyl ether or in acetonitrile. The latter reactions starting from cyclohexene oxide ( 1 ) showed maximum 72% ee in the formed fluorohydrin 2 isolated in 90% yield. From other meso‐epoxides such as cyclopentene oxide and cycloheptene oxide the corresponding fluorohydrins were isolated in 80% and 82% yield with 65% and 62% ee, respectively. In case of ring opening under similar conditions of the racemic styrene oxide or phenyl glycidyl ether 83% and 75% of the fluorohydrins with fluorine in the primary position were isolated with 74% ee and 65% ee, respectively. Tetrahydronaphthalene oxide yielded a 2:1 mixture of trans‐ (23% ee) and cis‐2‐fluoro‐3,4‐benzocyclohexenol (2% ee) suggesting competing S_N2 and S_N1 type ring openings. Other epoxides such as cyclooctene oxide, cis‐stilbene oxide and α‐methylstyrene oxide did not react or gave the fluorohydrins with very small enantiomeric excess.     

Thermodynamics of chromate replacements by various homologous transition metal oxyanions

The free energy change is calculated for the interaction of 19 different oxyanions (metalates) with iron (steel) or aluminum surfaces. The oxyanions considered here are those of the transition metals in the fourth through sixth periods of the periodic table. The oxyanions which produce more negative values of ΔG ^o (per mole of oxyanion) than that of chromate (CrO₄ ⁻²) are permanganate (MnO₄ ⁻), nickelate (NiO₄ ⁻²), ruthenate (RuO₄ ⁻ or RuO₄ ⁻²), and rhodate (RhO₄ ⁻²). The oxyanions which produce values of ΔG ^o (per mole of oxyanion) similar to CrO₄ ⁻² are osmate (OsO₄ ⁻²), and iridate (IrO₄ ⁻²).     

Preparation and characterization of osmium hexacyanoferrate films and their electrocatalytic properties

Osmium hexacyanoferrate films have been prepared using repeated cyclic voltammetry, and the deposition process and the films’ electrocatalytic properties in electrolytes containing various cations have been investigated. The cyclic voltammograms recorded the deposition of osmium hexacyanoferrate films directly from the mixing of Os³⁺ and Fe(CN)₆³⁻ ions from solutions containing various cations. An electrochemical quartz crystal microbalance, cyclic voltammetry, and UV-visible spectroscopy were used to study the growth mechanism of the osmium hexacyanoferrate films. The osmium hexacyanoferrate films showed a single redox couple, and the redox reactions included “electron transfer” and “proton transfer” with a formal potential that demonstrates a proton effect in acidic solutions up to a 12 M aqueous HCl solution. The electrochemical and electrochemical quartz crystal microbalance results indicate that the redox process was confined to the immobilized osmium hexacyanoferrate film. The electrocatalytic reduction of dopamine, epinephrine, norepinephrine, S₂O₃²⁻, and SO₅²⁻ by the osmium hexacyanoferrate films was performed. The preparation and electrochemical properties of co-deposited osmium(III) hexacyanoferrate and copper(II) hexacyanoferrate films were determined, and their two redox couples showed formal potentials that demonstrated a proton effect and an alkaline cation effect, respectively. Electrocatalytic reactions on the hybrid films were also investigated.     

Cis and trans components of lipids: Analysis by 1H NMR and silver shift reagents

In this study, the methodology of shift reagents was exploited to distinguish cis and trans unsaturation in oils and fats. The differential binding of silver ions (in the form of AgFOD) to cis and trans double bonds allowed the separation of the allylic and olefinic proton signals in the ¹H NMR spectra of mixtures of cis and trans methyl esters of monoene aliphatic acids and unsaturated triacylglycerol mixtures at low frequency spectrometers (300 MHz). Careful integration of the appropriate proton resonances in the recorded quantitative ¹H NMR spectra afforded percentage concentrations in very good agreement with the actual values. This ¹H NMR methodology was validated by analyzing AOCS Laboratory Proficiency Program GC samples containing various percentages of saturated, cis‐mono unsaturated, and cis‐polyunsaturated fat as well as trans content. This fast and relatively low‐cost NMR methodology could be used on line for obtaining nutrition labeling compositional data (NLCD) required for fat‐containing food products. Attempts to differentiate lipid molecules with different degree of unsaturation and positional distribution of cis double bonds were unsuccessful.     

Exploring the Biocatalytic Scope of Alditol Oxidase from Streptomyces coelicolor

The substrate scope of the flavoprotein alditol oxidase (AldO) from Streptomyces coelicolor A3(2), recombinantly produced in Escherichia coli, was explored. While it has been established that AldO efficiently oxidizes alditols to D ‐aldoses, this study revealed that the enzyme is also active with a broad range of aliphatic and aromatic alcohols. Alcohols containing hydroxy groups at the C‐1 and C‐2 positions like 1,2,4‐butanetriol (K_m=170 mM, k_cat=4.4 s⁻¹), 1,2‐pentanediol (K_m=52 mM, k_cat=0.85 s⁻¹) and 1,2‐hexanediol (K_m=97 mM, k_cat=2.0 s⁻¹) were readily accepted by AldO. Furthermore, the enzyme was highly enantioselective for the oxidation of 1,2‐diols [e.g., for 1‐phenyl‐1,2‐ethanediol the (R)‐enantiomer was preferred with an E‐value of 74]. For several diols the oxidation products were determined by GC‐MS and NMR. Interestingly, for all tested 1,2‐diols the products were found to be the α‐hydroxy acids instead of the expected α‐hydroxy aldehydes. Incubation of (R)‐1‐phenyl‐1,2‐ethanediol with ¹⁸O‐labelled water (H₂¹⁸O) revealed that a second enzymatic oxidation step occurs via the hydrate product intermediate. The relaxed substrate specificity, excellent enantioselectivity, and independence of coenzymes make AldO an attractive enzyme for the preparation of optically pure 1,2‐diols and α‐hydroxy acids.     

In situ FTIR studies of the catalytic oxidation of ethanol on Pt(1 1 1) modified by bi-dimensional osmium nanoislands

This paper presents the study of ethanol electrooxidation on Pt(1 1 1) electrode modified by different coverage degrees of a submonolayer of osmium nanoislands, which were obtained by spontaneous deposition. The ethanol oxidation reaction was extensively studied by employing in situ FTIR. Collections of spectra of the ethanol adsorption and oxidation processes were acquired over a series of positive potential steps, in order to determine the intermediate species and the main products that are formed. It was shown that the increase in the catalytic activity of Pt(1 1 1) after osmium deposition for ethanol oxidation is greater than that observed on nonmodified Pt(1 1 1). It was also demonstrated that the mechanistic pathway for this reaction depends directly on the degree of osmium coverage. Thus, for low osmium coverage (θ_Os ≤ 0.28), the formation of CO as an intermediate is favored, and hence the full oxidation of adsorbed ethanol to CO₂ is increased, additionally, the formation of acetaldehyde is also observed in low degrees of osmium coverage. For intermediate osmium coverage (0.28 < θ_Os ≤ 0.40), the oxidation of ethanol to acetaldehyde and then to acetic acid is favored, although on Pt(1 1 1) the formation of acetaldehyde is promoted. For higher degrees of osmium coverage (θ_Os > 0.51), the catalytic activity of the electrode for ethanol oxidation decreases. For an almost complete osmium layer (θ_Os = 0.92), obtained by electrodeposition at 50 mV, catalytic activity for ethanol oxidation shows the lowest value. In addition, the direct oxidation of ethanol to acetic acid at lower potentials is observed.     

Aerobic Oxidation of Vicinal Diols Catalyzed by an Anderson‐Type Polyoxometalate, [IMo6O24]5–

An Anderson‐type polyoxometalate, [I^VIIMo₆O₂₄]^5–, has been used as a catalyst for the aerobic oxidation at 80 °C of vicinal diols (glycols). This is the first report on the use of such a polyoxometalate as an oxidation catalyst. Reactivity and selectivity were dependent on the substrate. Thus, aryl‐substituted diols yielded mostly the carbon‐carbon bond cleavage products, while 1,2‐cyclohexanediol yielded cyclohexanone‐2‐ol and 1,2‐cyclohexanedione. Aliphatic diols were less reactive but yielded carbon‐carbon bond cleavage products in the presence of additional acid. An abbreviated mechanistic study was carried out indicating that the polyoxometalate oxidizes the diol to the various products even under anaerobic conditions. The reduced polyoxometalates (heteropoly blues and heteropoly browns) formed in the oxidation of the diols are re‐oxidized by the molecular oxygen.     

Switching on the photochemical reactivity in heterodimetallic Os–Ru bipyridyl complexes containing a bis(bidentate) phosphine

For the first time the excited states of the RuP₂N₄ moiety belonging to a new heterodimetallic Os^II–Ru^II bipyridyl complex are successfully designed in order to introduce photochemical reactivity. This dramatic effect is achieved via the use of the sterically demanding bis(bidentate) phosphine cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb). Thus, the temperature dependence of the luminescence lifetimes ranging from 77 to 298 K for the novel homodimetallic species meso-(ΔΛ/ΛΔ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (1) and rac-(ΔΔ/ΛΛ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (2) clearly indicates that the d–d state responsible for photochemistry is not populated. By contrast, the analogous temperature dependence for the new heterodimetallic species ΔΛ/ΛΔ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (3) and ΔΔ/ΛΛ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (4) unequivocally shows that as a consequence of the population of the d–d state the photochemical reactivity is switched on. Since single crystal X-ray structure analyses are a major clue to the understanding of photophysical and photochemical properties, also the X-ray structures of 1–3 are given.     

Voltammetric study of the cyanide complexes of osmium—II. The behaviour of lower oxidation state cyanide complexes of osmium on a platinum rde

It was found that the product of the reduction of the cyanide complex of hexavalent osmium, OsO₂(OH)₂(CN)^2?₂ is the Os(OH)₄(CN)^3?₄ complex and the product of the reduction of the OsO₂(CN)^2?₄ complex is the Os(OH)₂(CN)^2?₂ complex. Further reduction of the Os(OH)₄(CN)^3?₄ complex of trivalent osmium is complicated by a follow-up chemical reaction and the stable reduction product is a complex of divalent osmium, Os(OH)₂(CN)^4?₄ which forms a reversible redox system with the Os(OH)₂(CN)^3?₂ complex with a formal redox protential (1 M KOH, 0.1 M KCN) of ?760 mV/sce. The Os(OH)₄(CN)^3?₂ and Os(OH)₂(CN)^4?₄ complexes are stable only in solutions with at least a ten-fold excess of OH^? ions over the concentration of CN^t- ions. At greater cyanide concentrations, the chemical reactioins, Os(OH)₄(CN)^3?₂ → Os(OH)₂(CN)^3?₄ and Os(OH)₂(CN)^4?₄ → Os(CN)^4?₆, occur. The reaction rate for the latter reaction was found to be ?₄ = 1.87 × 10^t-4 l mol^?1 s^?1 in solutions with pH = 11.8. The characteristics of the individual forms of the cyanide complexes of osmium are also discussed.     

Silica Gel‐Supported Cinchona Alkaloid‐OsO4 Complex for Catalytic Heterogeneous Asymmetric Dihydroxylation of Olefins by H2O2 using a Titanium Silicalite‐Based Coupled Catalytic System

A triple catalytic system designed for asymmetric dihydroxylation of olefins, composed of NMM and two divergent heterogeneous catalysts, titanium silicalite and silica gel‐supported 1,4‐bis(9‐O‐dihydroquinidinyl)phthalazine [SGS‐(DHQD)₂PHAL)]‐OsO₄ complex relays the transport of two electrons from olefin to H₂O₂ used as a terminal oxidant to provide chiral diols with good yields and high enantiomeric excesses in a single pot.     

Bifunctional Catalysts Stabilized on Nanocrystalline Magnesium Oxide for One‐Pot Synthesis of Chiral Diols

New bifunctional catalysts composed of PdCl₄²⁻, OsO₄²⁻ and OsO₄²⁻, WO₄²⁻ designed and prepared by a counterionic stabilization technique involving the reactions of Na₂PdCl₄‐K₂OsO₄ and K₂OsO₄‐Na₂WO₄ with nanocrystalline MgO are well characterized. These bifunctional catalysts, NAP‐Mg‐PdOs and NAP‐Mg‐OsW perform tandem Heck asymmetric dihydroxylation and asymmetric dihydroxylation‐N‐oxidation reactions, respectively, in the presence of the chiral ligand 1,4‐bis(9‐o‐dihydroquinidinyl)phthalazine [(DHQD)₂PHAL] in a single pot. It is quite impressive to note that H₂O₂ is used as a terminal oxidant to provide N‐methylmorpholine N‐oxide (NMO) in situ by the oxidation of N‐methylmorpholine (NMM) in the asymmetric dihydroxylation‐N‐oxidation catalyzed by NAP‐Mg‐OsW.     

Controlling Stereoselection in Aza-Cope-Mannich Reactions

The synthesis of 2-substituted cis-octahydroindolones from the reaction of cis-2-amino-1-alkenylcyclopentanols with aldehydes was studied to examine whether stereoselection in the aza-Cope–Mannich reaction could be controlled by the nature of the nitrogen substituent. 2-Alkylamino-1-(1-phenylethenyl)cyclopentanols 7 and 8 , which contain nitrogen substituents of widely differing size (Me and CHPh₂), were condensed with four aldehydes to give oxazolidines 9a–d and 10a-c. Rearrangement of these intermediates at 23–60 °C, in the presence of 0.9 equiv of (±)-10-camphorsulfonic acid in acetonitrile, gave cis-octahydroindolones 11a-d and 12a–c in yields of 77–95%. Using a combination of single-crystal X-ray crystallography, ¹H nOe measurements, and comparisons with known materials it was established that the N-methyl oxazolidines 9a–d provided exclusively cis-octahydroindolones having the 2-substituent trans to the angular substituents, while N-benzhydryl analogs 10a–c provided exclusively the all-cis products 12a–c. These results are interpreted to mean: (1) When the nitrogen substituent is small (Me), the stereochemistry-determining [3,3]-sigmatropic rearrangement occurs preferentially through a transition-state topography having the R² substituent oriented quasiequatorially ( 14 → 15 → 16 ); (2) When this substituent is large (CHPh₂), destabilizing steric interactions between the vicinal R¹ and R² substituents causes the rearrangement to occur preferentially through the alternate iminium ion stereoisomer ( 17 → 18 → 19 ).