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.     

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.     

Microencapsulated Osmium Tetroxide‐Catalyzed Asymmetric Dihydroxylation of Olefins in Water without Using Organic Cosolvents

The asymmetric dihydroxylation of olefin using phenoxyethoxymethyl‐polystyrene (PEM)‐based microencapsulated osmium tetroxide (PEM‐MC OsO₄) proceeded smoothly in water as the sole solvent. The catalyst was recovered quantitatively by simple filtration and reused several times without loss of 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.     

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.     

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.     

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.     

Polymeric cinchona alkaloids for the catalytic asymmetric dihydroxylation of olefins

Three cinchona alkaloid copolymers (PMMA‐BQTP, PMA‐BQTP, PAN‐BQTP) have been synthesized by copolymerization. Their structure was characterized by FTIR, GPC, and element analysis. The catalytic activity of these copolymers in asymmetric dihydroxylation (AD) of olefins by OsO₄ was studied. The products enantiomeric excesses (ee) and the conversion of the substrate in the dihydroxylation reactions were determined using HPLC. The effect of time, temperature, and recycle times on the reaction was also discussed. The results showed that the copolymers catalyzed the dihydroxylation of the olefins to get diols in high optical yield. However, their catalytic efficiency was largely depended on the nature of olefins. The polymeric cinchona alkaloid can be simply recovered at the end of the reaction by centrifugation and then reused without radical change of activity or enantioselectivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Oxidative decolorisation of Eriochrome Black T with Chloramine‐T: kinetic,mechanistic, and spectrophotometric approaches

The kinetics and mechanism of oxidative decolorisation of Eriochrome Black T (EBT) with sodium N‐chloro‐p‐toluenesulfonamide or Chloramine‐T (CAT), catalysed by osmium tetroxide [Os(VIII)] in alkaline medium and uncatalysed in acid medium, have been spectrophotometrically investigated at 303 K. The reaction exhibited a first‐order dependence of rate on [CAT]₀ and [EBT]₀ in both media, and also with respect to [H⁺]. The order with respect to [OH^‐] and [Os(VIII)] was fractional. Activation parameters were deduced. It was observed that the uncatalysed decolorisation reaction was ca. eightfold faster in acid medium in comparison with alkaline medium, while the Os(VIII)‐catalysed reaction was ca. sevenfold faster than the uncatalysed reaction. Mechanisms and rate laws were determined. The chemical oxygen demand of Eriochrome Black T dye was also determined. Importantly, the developed oxidative decolorisation method is simple, efficient, inexpensive, requires less time, and is environmentally benign. Hence, it can be adapted for treating Eriochrome Black T present in industrial and laboratory wastewater.     

NBD‐Based Green Fluorescent Ligands for Typing of Thymine‐Related SNPs by Using an Abasic Site‐Containing Probe DNA

The binding behavior of green fluorescent ligands, derivatives of 7‐nitrobenzo‐2‐oxa‐1,3‐diazole (NBD), with DNA duplexes containing an abasic (AP) site is studied by thermal denaturation and fluorescence experiments. Among NBD derivatives, N¹‐(7‐nitrobenzo[c][1,2,5]oxadiazol‐4‐yl)propane‐1,3‐diamine (NBD‐NH₂) is found to bind selectively to the thymine base opposite an AP site in a DNA duplex with a binding affinity of 1.52×10⁶ M ^?1. From molecular modeling studies, it is suggested that the NBD moiety binds to thymine at the AP site and a protonated amino group tethered to the NBD moiety interacts with the guanine base flanking the AP site. Green fluorescent NBD‐NH₂ is successfully applied for simultaneous G>T genotyping of PCR amplification products in a single cuvette in combination with a blue fluorescent ligand, 2‐amino‐6,7‐dimethyl‐4‐hydroxypteridine (diMe‐pteridine).     

Vicinal Diol-Tethered Nucleobases as Targets for DNA Redox Labeling with Osmate Complexes

Six-valent osmium (osmate) complexes with nitrogenous ligands have previously been used for the modification and redox labeling of biomolecules involving vicinal diol moieties (typically, saccharides or RNA). In this work, aliphatic (3,4-dihydroxybutyl and 3,4-dihydroxybut-1-ynyl) or cyclic (6-oxo-6-(cis-3,4-dihydroxypyrrolidin-1-yl)hex-2-yn-1-yl, PDI) vicinal diols are attached to nucleobases to functionalize DNA for subsequent redox labeling with osmium(VI) complexes. The diol-linked 2′-deoxyribonucleoside triphosphates were used for the polymerase synthesis of diol-linked DNA, which, upon treatment with K₂OsO₃ and bidentate nitrogen ligands, gave the desired Os-labeled DNA, which were characterized by means of the gel-shift assay and ESI-MS. Through ex situ square-wave voltammetry at a basal plane pyrolytic graphite electrode, the efficiency of modification/labeling of individual diols was evaluated. The results show that the cyclic cis-diol (PDI) was a better target for osmylation than that of the flexible aliphatic ones (alkyl- or alkynyl-linked). The osmate adduct-specific voltammetric signal obtained for Os^VI-treated DNA decorated with PDI showed good proportionality to the number of PDI per DNA molecule. The Os^VI reagents (unlike OsO₄) do not attack nucleobases; thus offering specificity of modification on the introduced glycol targets.     

Fe(PyTACN)‐Catalyzed cis‐Dihydroxylation of Olefins with Hydrogen Peroxide

A family of iron complexes with general formula [Fe(II)(^R,Y,XPyTACN)(CF₃SO₃)₂], where ^R,Y,XPyTACN=1‐[2′‐(4‐Y‐6‐X‐pyridyl)methyl]‐4,7‐dialkyl‐1,4,7‐triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N‐4 and N‐7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis‐dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(^Me,Me,HPyTACN)(CF₃SO₃)₂] ( 7 ), was identified as the most efficient and selective cis‐dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7 , 2 equiv. of H₂O₂ as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis‐dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn‐diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe‐catalyzed cis‐dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron‐deficient and aromatic olefins.     

MCM-41 Anchored Cinchona Alkaloid for Catalytic Asymmetric Dihydroxylation of Olefins: A Clean Protocol for Chiral Diols Using Molecular Oxygen

MCM-41 anchored 1,4-bis(9-O-quininyl)phthalazine (MCM-(QN)₂PHAL)-OsO₄, is prepared for the first time and used in the heterogeneous asymmetric dihydroxylation of olefins to afford diols with good to excellent enantiomeric excesses in the presence of N-methylmorpholine N-oxide, K₃Fe(CN)₆ or molecular oxygen as cooxidants.     

Synthesis of Functionalized trans‐A2B2‐Porphyrins Using Donor–Acceptor Cyclopropane‐Derived Dipyrromethanes

meso‐Substituted trans‐A₂B₂‐porphyrins bearing specific patterns of substituents are crucial building blocks in porphyrin‐based biomimetic systems and molecular materials and can be used for the construction of well‐defined porphyrin‐based architectures. A new stepwise and rational synthesis of functionalized trans‐A₂B₂‐porphyrins is reported in which for the first time donor–acceptor‐substituted cyclopropane precursors (d–a cyclopropanes) are exploited. The three presented d–a cyclopropanes are readily accessible in a multi‐gram scale and serve as aldehyde equivalents in the reaction with an excess of pyrrole to afford the corresponding dipyrromethanes (DPMs). The three DPMs were synthesized in yields of 60–74%. They are stable in purified form in the absence of light and air and were subsequently condensed with a wide range of aliphatic and aromatic aldehydes bearing electron‐donating or electron‐withdrawing substituents followed by oxidation to form the corresponding trans‐A₂B₂‐porphyrins. Fourteen functionalized porphyrins were synthesized in yields of 14–31%, indicating the broad scope of the synthetic procedure. The possibility to introduce key functional groups is emphasized, which enables subsequent modification of these porphyrins with moieties inducing biological activity. Modification of the tetrapyrroles may occur by addition to one of the porphyrin peripheral double bonds, the use of substituents of the aryl groups or via the methoxycarbonyl group at two of the meso‐substituents. Three examples of porphyrins were converted into the corresponding 7,8‐dihydroxychlorins by osmium‐mediated dihydroxylation and one of the resulting chlorins was subjected to saponification to give a highly polar chlorin dicarboxylic acid. A 4‐bromophenyl‐substituted d–a cyclopropane was prepared by rhodium‐catalyzed cyclopropanation and then transformed into a DPM which was subsequently condensed to a porphyrin. Its Zn complex allowed a Heck reaction to afford the functionalized bis(alkenyl)‐substituted trans‐A₂B₂‐Zn‐porphyrin.     

New Mono‐Quarternized Bis‐Cinchona Alkaloid Ligands for Asymmetric Dihydroxylation of Olefins in Aqueous Medium: Unprecedented High Enantioselectivity and Recyclability

New mono‐quaternized allyl bromide salts of bis‐Cinchona alkaloid ligands, [(QD)₂PHAL‐Allyl]Br and [(QN)₂PHAL‐Allyl]Br, have been synthesized which can be converted into their highly water‐soluble multihydroxylated derivatives under asymmetric dihydroxylation (AD) conditions and, thus, easily recovered by a simple extraction method after reaction and reused. These mono‐quaternized ligands exhibited superior catalytic efficiency to their neutral counterparts such as (DHQD)₂PHAL and (DHQ)₂PHAL for the AD reactions of mono‐ and disubstituted styrenes under Upjohn conditions. Merely 0.1 mol % of osmium was enough to complete the reactions of mono‐ and disubstituted styrenes and, moreover, these ligands showed the highest enantioselectivities (e.g., for styrene, 97 % ee with [(QD)₂PHAL‐Allyl]Br) among those ever achieved under Upjohn conditions.     

Synthesis of PEG‐functionalized poly(diphenylacetylene)s and their gas permeation properties

The polymerizations of 1‐(3‐methylphenyl)‐2‐(4‐trimethylsilyl)phenylacetylene ( 1a ) and 1‐(4‐methylphenyl)‐2‐(4‐trimethylsilyl)phenylacetylene ( 1b ) were carried out with TaCl₅‐n‐Bu₄Sn to give relatively high‐molecular‐weight polymers ( 2a and 2b ) (M_n > 5 × 10⁵). The obtained polymers were brominated by using benzoyl peroxide and N‐bromosuccinimide first, followed by substitution reaction of three types of polyethylene glycol. When diethylene glycol was used as a reagent on substitution reaction of meta‐substituted polymer, PEG‐functionalized poly(diphenylacetylene) with the highest content of oxyethylene unit [ 4a(2) ] was obtained, and the degree of substitution was 0.60. The degrees of substitution decreased to 0.15 and 0.08 when the polyethylene glycols with higher molecular weights were used. PEG‐substitution reaction to the para‐substituted polymers was difficult to proceed, and hence the degree of substitution was 0.18 even when diethylene glycol was used. The CO₂/N₂ separation factor of PEG‐functionalized polymer [ 4a(2) ] was as large as 28.8, although that of 2a was 7.41. The other PEG‐functionalized polymers also exhibited high CO₂ permselectivity, and their CO₂/N₂ separation factors were over 20. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of cellulose derivatives containing carbazole chromophore

Cellulose derivatives containing long hydrocarbon side chains and the carbazole chromophore are prepared. N‐4′‐Bromobutylcarbazole is first synthesized from carbazole and 1,4‐dibromobutane. Alkylated carbazole is then reacted with cellulose acetate in dimethyl sulfoxide solution to produce cellulose ethers containing the desired chromophore. Polymers containing a mixture of alkyl side chains are also prepared by the subsequent addition of 1‐bromododecane to the reaction mixture. Characterization of the resulting cellulose derivatives by FTIR spectroscopy indicates that the deacetylation of cellulose acetate and the subsequent etherification are both complete. In addition, the incorporation of the carbazole chromophore is clearly shown by ¹H‐ and ¹³C‐NMR spectroscopy. Polymers of different carbazole content, ranging from 2.9 to 1.1 chromophores per anhydroglucose repeat unit, are obtained by varying the reaction conditions. Substitution is found to be controlled primarily by the quantity of alkylating agent introduced while variation of the reaction time has little effect. This method is used to prepare (dodecyl)_y(N‐4′‐carbazolylbutyl)_xcellulose, (decyl)_y(N‐4′‐carbazolylbutyl)_xcellulose, and (butyl)_y(N‐4′‐carbazolylbutyl)_xcellulose. Cellulose acetate can be replaced by (methyl)cellulose as the starting material to obtain analogous products. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2764–2772, 1999     

Osmium(VIII)/Ruthenium(III) Catalysed Oxidation of l-lysine by Diperiodatocuprate(III) in Aqueous Alkaline Medium: A Comparative Mechanistic Approach by Stopped Flow Technique

Abstract The kinetics of osmium(VIII) and ruthenium(III) catalysed oxidation of l-lysine (l-lys) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.15 mol dm⁻³ was studied spectrophotometrically. The reaction between l-lys and DPC in alkaline medium exhibits 1:2 stoichiometry in both catalysed reaction (l-lys: DPC). The reaction is first order in [DPC] and has less than unit order both in [l-lys] and [alkali]. Increase in periodate concentration decreases the rate. Intervention of free radicals was observed in the reaction. The main products were identified by spot test, IR and GC-MS studies. Probable mechanisms are proposed and discussed. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified. Graphical Abstract The kinetic and mechanistic investigations of the reaction between DPC and l-lysine has been studied in presence of microamounts of ruthenium(III) and osmium(VIII) in alkaline medium. The monoperiodatoargentate(III), [Ru(H₂O)₅OH]²⁺ and [OsO₄(OH)₂]²⁻ are considered as the active species of oxidant, DPC, ruthenium(III) and osmium(VIII) respectively.      

On the Sense of the Enantioselection in Hydrogen Transfer Reactions from 2‐Propanol to Ketones

An explanation for the reversal in the sense of the enantioselectivity observed in hydrogen transfer reactions from 2‐propanol to ketones catalyzed by the ruthenium or osmium amino acidates [(η⁶‐p‐MeC₆H₄‐i‐Pr)M(Aa)Cl] and [(η⁶‐p‐MeC₆H₄‐i‐Pr)M(Aa)]₃[BF₄]₃ [Aa=piperidine‐2‐carboxylate (pip), N‐methyl‐L ‐phenylalaninate (MePhe)] is given; the molecular structures of [(η⁶‐p‐MeC₆H₄‐i‐Pr)Os(Pip)Cl] ( 1 ), [(η⁶‐p‐MeC₆H₄‐i‐Pr)Os(Pip)]₃[BF₄]₃ ( 2 ), [(η⁶‐p‐MeC₆H₄‐i‐Pr)M(MePhe)Cl] [M=Ru ( 3 ), Os ( 4 )] are also reported.