Organosulfur oxidation by hydrogen peroxide using a dinuclear Mn-1,4,7-trimethyl-1,4,7-triazacyclononane complex

A mechanistic study of organosulfide oxidation by H₂O₂, using a dinuclear manganese complex as the catalyst, has revealed an unusual switch in the philicity of the oxidant for the first and the second oxygen transfer steps; this switch has been exploited to tune selectivity for each of the products.     

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex as an efficient catalyst for oxidation of alcohols with tert-butyl hydroperoxide

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex [PS–(QBIM)₂Cu(II)] was synthesized by functionalization of chloromethylated polystyrene cross-linked with 6.5 % divinyl benzene with 2-(2′-quinolyl)benzimidazole and subsequent treatment with Cu(OAc)₂ in methanol. The complex was characterized by physical, analytical and spectroscopic techniques. Electronic and ESR spectra, together with magnetic susceptibility measurements, indicated that the complex was paramagnetic with distorted octahedral geometry around the copper. The complex was found to be active toward oxidation of various alcohols including phenol, benzyl alcohol and cyclohexanol using 70 % aqueous tert-butyl hydroperoxide under mild conditions. Under the optimized reaction conditions, cyclohexanol gave 100 % conversion to cyclohexanone, benzyl alcohol gave 98 % yield of benzaldehyde and phenol gave 89 % yield of catechol and 4 % of hydroquinone. The complex was recycled five times without much loss in catalytic activity.     

Ruthenium complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane for atom and group transfer reactions

With support by macrocyclic tertiary amine ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me₃tacn), a number of mononuclear metal–ligand multiple bonded complexes have been isolated. Starting with a brief summary of these complexes, the present review focuses on ruthenium-oxo and -imido complexes of Me₃tacn. A family of monooxoruthenium(IV) complexes [Ru^IV(Me₃tacn)O(N–N)]²⁺ (N–N = 2,2′-bipyridines) and a cis-dioxoruthenium(VI) complex cis-[Ru^VI(Me₃tacn)O₂(CF₃CO₂)]⁺ have been isolated, and the structures of [Ru^IV(Me₃tacn)O(bpy)](ClO₄)₂ (bpy = 2,2′-bipyridine) and cis-[Ru^VI(Me₃tacn)O₂(CF₃CO₂)]ClO₄ have been determined by X-ray crystallography. Oxidation of [Ru^III(Me₃tacn)(NHTs)₂(OH)] (Ts = p-toluenesulfonyl) with Ag⁺ and electrochemical oxidation of [Ru^III(Me₃tacn)(H₂L)](ClO₄)₂ (H₃L = α-(1-amino-1-methylethyl)-2-pyridinemethanol) are likely to generate ruthenium-imido complexes supported by Me₃tacn. DFT calculations on cis-[Ru^VI(Me₃tacn)O₂(CF₃CO₂)]⁺ and proposed ruthenium-imido complexes have been performed. Complexes [Ru^IV(Me₃tacn)O(N–N)]²⁺ are reactive toward alkene epoxidation, and cis-[Ru^VI(Me₃tacn)O₂(CF₃CO₂)]⁺ efficiently oxidizes various organic substrates including concerted [3+2] cycloaddition reactions with alkynes and alkenes to selectively afford α,β-diketones, cis-diols, or CC bond cleavage products. Related oxidation reactions catalyzed by ruthenium Me₃tacn complexes include epoxidation of alkenes, cis-dihydroxylation of alkenes, oxidation of alkanes, alcohols, aldehydes, and arenes, and oxidative cleavage of CC, CC, and C–C bonds, all of which exhibit high selectivity. Ruthenium Me₃tacn complexes are also active catalysts for amination of saturated C–H bonds.     

Silylation of primary alcohols with recyclable ruthenium catalyst and hydrosilanes

The silylation of primary alcohols was achieved using hydrosilanes and a recyclable ruthenium catalyst without additives under mild conditions. Notably, this catalyst system is effective for the silylation of alcohols having haloaryl groups, which were intact during the silylation.     

A highly chemoselective Boc protection of amines using sulfonic-acid-functionalized silica as an efficient heterogeneous recyclable catalyst

A facile and versatile method for the chemoselective Boc protection of amines has been developed by a treatment with (Boc)₂O in the presence of sulfonic-acid-functionalized silica as a catalyst. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic), aromatic, and heteroaromatic amines; primary and secondary amines; aminols, amino-esters; and sulfonamides. The catalyst works under heterogeneous conditions and can be recycled.     

A new vanadium Schiff base complex as catalyst for oxidation of alcohols

The monoanionic bidentate Schiff base, N-(phenolyl)-benzaldimine (HL), has been employed to synthesize a new vanadium(IV) complex of general composition [VO(L)₂] (where L?=?O,?N donor of Schiff base). The ligand and complex have been fully characterized by elemental analyses, molar conductance data, FT-IR, ¹H- and ¹³C-NMR, and UV-Vis spectroscopies. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this complex catalyst using Oxone as oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.     

Efficient and green oxidation of alcohols with tert-butyl hydrogenperoxide catalyzed by a recyclable magnetic core-shell nanoparticle-supported oxo-vanadium ephedrine complex

A novel method for the oxidation of alcohols to the corresponding carbonyl compounds has been successfully developed using tert-butyl hydrogenperoxide (TBHP) in the presence of a catalytic amount of recyclable magnetic nanoparticle-supported oxo-vanadium ephedrine complex (VO(ephedrine)₂@MNPs) in PEG as a green solvent at 80 °C. The catalyst can be magnetically recycled and successfully reused in six subsequent reaction cycles with only slight decreases of its catalytic activity.     

氯铬酸甲铵/硅胶载体氧化剂的制备及其对醇的氧化研究

利用硅胶作载体，负载氯铬酸甲铵盐制备了一种新的载体铬(Ⅵ)氧化剂。该试剂制备方法简单、性质稳定。可在多种反应介质中对伯醇和仲醇氧化，高收率得到相应的醛和酮，反应操作简单，提纯方便。     

A unique rate-accelerating effect of certain amino acids in the H2O2 oxidation of alkanes catalyzed by a dinuclear manganese complex containing 1,4,7-trimethyl-1,4,7-triazacyclononane

Certain amino acids used in small amounts (10 catalyst equiv) strongly accelerate the H₂O₂ oxidation of cyclohexane catalyzed by a dinuclear manganese(IV) complex with 1,4,7-trimethyl-1,4,7-triazacyclononane. The efficiency of the co-catalyst dramatically depends on the nature and structure of the acid. Pyrazine-2,3-dicarboxylic acid (2,3-PDCA) has been found to be the most efficient co-catalyst whereas picolinic acid is almost inactive in this oxidation. The highest rate has been attained when 2,3-PDCA was used in combination with trifluoroacetic acid.     

Cobalt(II) schiff base functionalized mesoporous silica as an efficient and recyclable chemoselective acetalization catalyst

Cobalt(II) Schiff base functionalized mesoporous silica was synthesized from covalent attachment via the introduction of Co(OAc)₂ to salicylaldimine functionalized mesoporous silica. The catalyst proved to be chemoselective one for the acetalization of aldehydes to the corresponding acetals in alcohol. The immobilized catalyst can be easily recovered and reused for at least ten reaction cycles without significant loss of its catalytic activity.     

A high loading sulfonic acid-functionalized ordered nanoporous silica as an efficient and recyclable catalyst for chemoselective deprotection of tert-butyldimethylsilyl ethers

A high loading sulfonic acid-functionalized ordered nanoporous silica efficiently catalyzes the deprotection of a variety of alcoholic TBDMS (tert-butyldimethylsilyl)ethers in methanol. The catalyst shows high thermal stability (up to 240 °C) and can be recovered and reused for at least seven reaction cycles without loss of reactivity. This method can be used to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

A reasonable explanation for the mechanism of photo-promoted chemoselective aerobic oxidation of alcohols using (ON)Ru(salen) complex as catalyst

The mechanism of aerobic oxidation of alcohols using (ON)Ru(salen) complex as catalyst under photo-irradiation was examined through studies of kinetics of the oxidation, kinetic isotope effect in the oxidation, and effect of the ligand structure on the chemoselectivity of the oxidation of primary and secondary alcohols. It was demonstrated that the aerobic oxidation includes an intramolecular hydrogen atom transfer process that is attributed to realization of efficient differentiation of primary and secondary alcohols in the oxidation.     

Chromium(VI) supported and entrapped on silica and zirconia as recyclable materials for oxidation of alcohols

Oxidation of alcohols have been realized with Cr(VI) oxide supported or entrapped, via sol-gel methodology, on silica and zirconia. These materials were easily recovered from the reaction mixture without leaching of chromium in solution. Moreover, recycling studies have indicated that they can be regenerated by calcinations at 400-600°C or by treatment with ozone at room temperature. In the case of Cr(VI) entrapped into silica matrix up to 18 oxidation cycles have been realized without loss in activity.     

A recyclable fluorous thiourea organocatalyst for the chemoselective oxidation of sulfides

As a kind of organocatalyst, 1-[4-(perfluorooctyl)phenyl]-3-phenylthiourea was employed to the chemoselective oxidation of sulfides in the presence of 30% H₂O₂. A variety of diaryl, dialkyl, alkyl aryl sulfides could be oxidized to sulfoxide under the mild condition. The catalyst could be easily recovered by fluorous solid-phase extraction for reuse.     

Scandium trifluoromethanesulfonate as a recyclable catalyst for efficient methoxymethylation of alcohols

Scandium triflate [Sc(OTf)₃] has been found to be a recyclable catalyst for mild highly efficient methoxymethylation of a variety of alcohols using formaldehyde dimethyl acetal (FDMA).     

A water-soluble and "self-assembled" polyoxometalate as a recyclable catalyst for oxidation of alcohols in water with hydrogen peroxide

We have demonstrated that a simply prepared water-soluble polyoxometalate, Na12[WZnZn2(H2O)2(ZnW9O34)2], synthesized from readily available zinc and tungsten salts in the presence of nitric acid, is an effective catalyst for selective alcohol oxidation with hydrogen peroxide in biphasic (water-alcohol) reaction media. Experiments have shown that the "self-assembled" catalyst in its mother liquor was as active as the isolated catalyst. The aqueous catalyst solution is easily separated from the water-insoluble products and can be recycled without loss in activity or selectivity.     

Hydrocarbon oxygenation with Oxone catalyzed by complex [Mn2L2O3]2+ (L=1,4,7-trimethyl-1,4,7-triazacyclononane) and oxalic acid

Oxone (peroxysulphate) very efficiently oxidizes benzene to p-quinone (TON 1140) and alkanes to the corresponding alcohols and ketones (aldehydes) in aqueous acetonitrile 50 °C if catalytic amounts of complex [Mn₂L₂O₃]²⁺ (L=1,4,7-trimethyl-1,4,7-triazacyclononane) and oxalic acid are present in the solution. In contrast to the similar reaction with H₂O₂, the alkane oxidation with Oxone does not afford the corresponding alkyl hydroperoxides. Phenol was quantitatively oxidized to a mixture of p-quinone and pyrocatechol (9:1 ratio). Cyclohexanol gave cyclohexanone (TON 400). The proposed mechanism includes the formation of an oxidizing species containing the Mn(V)O fragment. A kinetic study demonstrated that an adduct of [Mn₂L₂O₃]²⁺ and oxalic acid is formed in the initial stage. This adduct reacts with Oxone to generate the oxidizing species.     

Solvent-free oxidation of alcohols by t-butyl hydroperoxide catalyzed by water-soluble copper complex

The catalytic system composed of CuCl₂ and 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC), was found to be highly efficient for the selective oxidation of secondary benzylic, allylic and propargylic alcohols to the corresponding ketones, with aqueous t-butyl hydroperoxide under phase-transfer catalysis conditions. The catalytic system is stable and can be recycled and reused several times without loss of activity.     

Hydrogen transfer type oxidation of alcohols by rhodium and ruthenium catalyst under microwave irradiation

Secondary alcohols were converted into the corresponding ketones by methyl acrylate and rhodium catalyst efficiently under microwave irradiation. Treatment of primary alcohols with the same condition resulted in the recovery of the starting materials. Primary alcohols were converted into aldehydes by hydrogen transfer reaction using methyl vinyl ketone and ruthenium catalyst under microwave irradiation.