Synthesis of poly(1‐oxodimethylene) via oxidation of poly(vinyl alcohol) with a hydrogen peroxide/hydrobromic acid system and metal complexation behavior of poly(1‐oxodimethylene)

Poly(1‐oxodimethylene) was synthesized via oxidation of poly(vinyl alcohol) with a hydrogen peroxide/hydrobromic acid system. The content of the carbonyl groups in poly(1‐oxodimethylene) depended on the amount of water added, and lower amounts of water were suitable for efficient oxidation due to higher acidity of the reaction system. The highest content of carbonyl groups was estimated to be above 88% by the titration with hydrazine that reacted with the carbonyl groups in poly(1‐oxodimethylene). The obtained poly(1‐oxodimethylene) complexed with Cu and Ni ions under basic conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2598–2605     

Crystal Structure and Characterization of Pd(II) Bis(diiso‐propyldithiocarbamate) Complex

The crystal and molecular structure of [Pd(iPr₂dtc)₂] (dtc = dithiocarbamate) have been determined by X‐ray crystallography. The unit cell of the crystal structure consists of two discrete monomelic molecules of [Pd(iPr₂dtc)₂]. The Pd(II) ion has an square‐planar geometry. The electronic and IR spectral data are in agreement with the X‐ray structure. The TG data indicate slight degradation of a few percent.     

Iron(II)‐Catalyzed Biomimetic Aerobic Oxidation of Alcohols

We report the first Fe^II‐catalyzed biomimetic aerobic oxidation of alcohols. The principle of this oxidation, which involves several electron‐transfer steps, is reminiscent of biological oxidation in the respiratory chain. The electron transfer from the alcohol to molecular oxygen occurs with the aid of three coupled catalytic redox systems, leading to a low‐energy pathway. An iron transfer‐hydrogenation complex was utilized as a substrate‐selective dehydrogenation catalyst, along with an electron‐rich quinone and an oxygen‐activating Co(salen)‐type complex as electron‐transfer mediators. Various primary and secondary alcohols were oxidized in air to the corresponding aldehydes or ketones with this method in good to excellent yields.     

Synthesis,characterization and catalytic activity of novel Co(II) and Pd(II)‐perfluoroalkylphthalocyanine in fluorous biphasic system; benzyl alcohol oxidation

Tetrakis[heptadecafluorononyl] substituted phthalocyanine complexes were prepared by template synthesis from 4‐(heptadecafluorononyloxy)phthalonitrile with Co(CH₃COO)^·₂H₂O or PdCl₂ in 2‐N, N‐dimethylaminoethanol. The corresponding phthalonitrile was obtained from heptadecafluorononan‐1‐ol and 4‐nitrophthalonitrile with K₂CO₃ in DMF at 50 °C. The structures of the compounds were characterized by elemental analysis, FTIR, UV–vis and MALDI‐TOF MS spectroscopic methods. Metallophthalocyanines are soluble in fluoroalkanes such as perfluoromethylcyclohexane (PFMCH). The complexes were tested as catalysts for benzyl alcohol oxidation with tert‐butylhydroperoxide (TBHP) in an organic–fluorous biphasic system (n‐hexane–PFMCH). The oxidation of benzyl alcohol was also tested with different oxidants, such as hydrogen peroxide, m‐chloroperoxybenzoic acid, molecular oxygen and oxone in n‐hexane–PFMCH. TBHP was found to be the best oxidant for benzyl alcohol oxidation since higher conversion and selectivity were observed when this oxidant was used. Copyright © 2008 John Wiley & Sons, Ltd.     

Trinuclear Pd3O2 Intermediate in Aerobic Oxidation Catalysis

The activation of O₂ is a key step in selective catalytic aerobic oxidation reactions mediated by transition metals. The bridging trinuclear palladium species, [(LPd^II)₃(μ³‐O)₂]²⁺ (L=2,9‐dimethylphenanthroline), was identified during the [LPd(OAc)]₂(OTf)₂‐catalyzed aerobic oxidation of 1,2‐propanediol. Independent synthesis, structural characterization, and catalytic studies of the trinuclear compound show that it is a product of oxygen activation by reduced palladium species and is a competent intermediate in the catalytic aerobic oxidation of alcohols. The formation and catalytic activity of the trinuclear Pd₃O₂ species illuminates a multinuclear pathway for aerobic oxidation reactions catalyzed by Pd complexes.     

Oxidation of sec‐alcohols with Ru(II)‐bearing microgel star polymer catalysts via hydrogen transfer reaction: Unique microgel‐core catalysis

Oxidation of sec‐alcohols was investigated with ruthenium‐bearing microgel core star polymer catalysts [Ru(II)‐Star]. The star polymer catalysts were directly prepared via RuCl₂(PPh₃)₃‐catalyzed living radical polymerization of methyl methacrylate (MMA), followed by the arm‐linking reaction with ethylene glycol dimethacrylate ( 1 ) in the presence of diphenylphosphinostyrene ( 2 ). The Ru(II)‐Star efficiently and homogeneously catalyzed the oxidation of 1‐phenylethanol ( S1 ) to give a corresponding ketone (acetophenone) in higher yield (92%) than the analogs of polymer‐supported ruthenium complexes. Importantly, the star catalyst afforded high recycling efficiency in the oxidation. They held catalytic activity against three times catalysis even though they were recovered under air‐exposure, whereas the conventional RuCl₂(PPh₃)₃ lost the activity for same recycling procedure due to the deactivation by oxygen. The stability of the star catalysts during the recycle experiment was confirmed by detailed spectroscopic characterization. The star polymers also catalyzed oxidation for a wide range of sec‐alcohols with aromatic and aliphatic groups. The substrate affinity was different from that with RuCl₂(PPh₃)₃, suggesting the unique selectivity caused by the specific structure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

A Highly Efficient and Selective Aerobic Cross‐Dehydrogenative‐Coupling Reaction Photocatalyzed by a Platinum(II) Terpyridyl Complex

Thanks to the superior redox potential of platinum(II) complex compared with that of Ru(bpy)₃²⁺ in the excited state, an efficient and selective visible‐light‐induced CDC reaction has been developed by using a catalytic amount (0.25 %) of 1 . With the aid of FeSO₄ (2 equiv), the corresponding amide could not be detected under visible‐light irradiation (λ=450 nm), but the desired cross‐coupling product was exclusively obtained under ambient air conditions. A spectroscopic study and product analysis revealed that the CDC reaction is initiated by photoinduced electron‐transfer from N‐phenyltetrahydroisoquinoline to the complex. An EPR (electron paramagnetic resonance) experiment provides direct evidence on the generation of superoxide radical anion (O₂^{? .} ) rather than singlet oxygen (¹O₂) under irradiation of the reaction system, in contrast to that reported in the literature. Combined, the photoinduced electron‐transfer and subsequent formation of superoxide radical anion (O₂^{? .} ) results in a clean and facile transformation.     

Cu(II) bromide catalyzed oxidation of aldehydes and alcohols

A variety of aromatic, aliphatic and conjugated aldehydes and alcohols were transformed to the corresponding carboxylic acids and ketones with a quantitative conversion in high yields with 70% t‐BuOOH solution in water in the presence of catalytic (5 mol%) amounts of CuBr₂ under room temperature conditions. The conversion of 4‐methoxybenzaldehyde to 4‐methoxybenzoic acid is extremely facile in MeCN at ambient temperature in the presence of 5 mol% CuBr₂ and 2 equiv. 70% t‐BuOOH (water) as the oxidant. Oxidation with t‐BuOOH (water) alone in MeCN was found to be negligible. The scope of our catalytic system is applicable for a wide range of aromatic, conjugated and aliphatic substrates. These aldehydes were converted to the corresponding carboxylic acids in good isolated yields in reasonable times. It is pertinent to mention here that mild halogenic oxidants like hypochlorites, chlorites and NBS are not suitable for substrates with electron‐rich aromatic rings, olefinic bonds and secondary hydroxyl groups. Substitutions at different positions on the phenyl ring do not hinder the reaction, although the reaction time is affected. Oxidation of α,β unsaturated derivatives resulted in the formation of the expected acid in good yield. In addition, the transformation of secondary alcohols to ketones is extremely facile. No recemization was observed for menthone. This method possesses a wide range of capabilities since it can be used with other functional groups which may not tolerate oxidative conditions, involves fairly simple method for work‐up, exhibits chemoselectivity and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time. Copyright © 2011 John Wiley & Sons, Ltd.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Iron(II)-Catalyzed Aerobic Biomimetic Oxidation of N-Heterocycles

Herein, an iron(II)-catalyzed biomimetic oxidation of N-heterocycles under aerobic conditions is described. The dehydrogenation process, involving several electron-transfer steps, is inspired by oxidations occurring in the respiratory chain. An environmentally friendly and inexpensive iron catalyst together with a hydroquinone/cobalt Schiff base hybrid catalyst as electron-transfer mediator were used for the substrate-selective dehydrogenation reaction of various N-heterocycles. The method shows a broad substrate scope and delivers important heterocycles in good-to-excellent yields.     

Oxidative homocoupling of arylboronic acids catalyzed by a 4‐aminoantipyrine–Pd(II)complex

A one‐step synthesis of symmetric biaryls is reported under very mild conditions via the homocoupling reaction of substituted arylboronic acids using an air‐ and moisture‐stable 4‐aminoantipyrine–Pd(II) complex as catalyst. The reaction is conducted at a low catalyst loading of 0.1 mol% at room temperature in methanol in the presence of K₂CO₃ as the base and KMnO₄ as the oxidant. The catalytic methodology is shown to be compatible with diverse functional groups and affords the desired biphenyls in good to excellent yields. Copyright © 2015 John Wiley & Sons, Ltd.     

Half‐sandwich Ir (III) and Rh (III) complexes as catalysts for water oxidation with double‐site

A series of neutral binuclear iridium and rhodium complexes were synthesized based on bis‐imine ligands under mild conditions. These half‐sandwich late transition metal complexes were isolated in good yields and characterized by elemental analysis, ¹H NMR, ¹³C NMR, HR‐MS, and FT‐IR spectroscopies, and the solid state structure of complexes 1 and 2 were further confirmed by single‐crystal X‐ray diffraction. Cyclic voltammetry (CV) characterization indicated that the complex 1 has the best catalyst for water oxidation process with TOF of 0.8 s^?1 at low overpotential of 0.325 V in methanol‐phosphate buffer. The proposed double‐site water oxidation mechanism had been also speculated .     

Preparation of a Yb(III)‐Incorporated porous polymer by post‐Coordination: Enhancement of gas adsorption and catalytic activity

We synthesized a Yb(III)‐incorporated microporous polymer (Yb‐ADA) and studied its gas adsorption property and catalytic activity. The adamantane‐based porous polymer (ADA) was obtained from an ethynyl‐functionalized adamantane derivative and 2,5‐dibromoterephthalic acid through Sonogashira–Hagihara cross‐coupling. ADA had two carboxyl groups which were used for Yb(III) coordination under basic conditions. The Brunauer‐Emmett‐Teller (BET) surface area of ADA was 970 m² g^?1. As Yb(III) ions were incorporated into ADA, the surface area of the polymer (Yb‐ADA) was reduced to 885 m² g^?1. However, Yb‐ADA exhibited a significantly enhanced CO₂ adsorption capacity despite the reduction of surface area. The CO₂ uptakes of ADA and Yb‐ADA were 1.56 and 2.36 mmol g^?1 at 298 K, respectively. The H₂ uptake of ADA also increased after coordination with Yb(III) from 1.15 to 1.40 wt % at 77 K. Yb‐ADA showed high catalytic activity in the acetalization of 4‐bromobenzaldehyde and furfural with trimethyl orthoformate and could be reused after recovery without severe loss of activity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5291–5297