- Stable Boron Peroxides with a Subporphyrinato Ligand
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Subporphyrin B-peroxides have been synthesized in good yields by acid-catalyzed exchange reactions of subporphyrin B-methoxide with the corresponding hydroperoxides. Thermal dimerization of the subporphyrin B-hydroperoxide provided the peroxo-bridged bis(subporphyrin) quantitatively. These subporphyrin B-peroxides are fairly stable under ambient conditions, which allowed their isolation and full characterization as the first examples of structurally authenticated boron hydroperoxides, acyclic boron organylperoxides, and neutral peroxo-bridged diboron species. The subporphyrin B-peroxides thus prepared were investigated through their crystal structures, IR spectra, and cyclic voltammograms as well as by DFT calculations. The subporphyrin B-hydroperoxide oxidizes triphenylphosphine quantitatively to triphenylphosphine oxide. Acid-catalyzed exchange reactions of a subporphyrinatoboron methoxide with a range of hydroperoxides have resulted in the synthesis of a series of boron peroxides with a subporphyrinato ligand. The boron peroxides are prepared in good yields and are fairly stable under ambient conditions, thus allowing their isolation and full characterization as the first examples of structurally authenticated neutral and acyclic boron peroxides.
- Tsurumaki, Eiji,Sung, Jooyoung,Kim, Dongho,Osuka, Atsuhiro
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- Earth-Abundant Mixed-Metal Catalysts for Hydrocarbon Oxygenation
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The oxygenation of aliphatic and aromatic hydrocarbons using earth-abundant Fe and Cu catalysts and "green" oxidants such as hydrogen peroxide is becoming increasingly important to atom-economical chemical processing. In light of this, we describe that dinuclear CuII complexes of pyrrolic Schiff-base macrocycles, in combination with ferric chloride (FeCl3), catalyze the oxygenation of π-activated benzylic substrates with hydroperoxide oxidants at room temperature and low loadings, representing a novel design in oxidation catalysis. Mass spectrometry and extended X-ray absorption fine structure analysis indicate that a cooperative action between CuII and FeIII occurs, most likely because of the interaction of FeCl3 or FeCl4- with the dinuclear CuII macrocycle. Voltammetric measurements highlight a modulation of both CuII and FeIII redox potentials in this adduct, but electron paramagnetic resonance spectroscopy indicates that any Cu-Fe intermetallic interaction is weak. High ketone/alcohol product ratios, a small reaction constant (Hammett analysis), and small kinetic isotope effect for H-atom abstraction point toward a free-radical reaction. However, the lack of reactivity with cyclohexane, oxidation of 9,10-dihydroanthracene, oxygenation by the hydroperoxide MPPH (radical mechanistic probe), and oxygenation in dinitrogen-purge experiments indicate a metal-based reaction. Through detailed reaction monitoring and associated kinetic modeling, a network of oxidation pathways is proposed that includes "well-disguised" radical chemistry via the formation of metal-associated radical intermediates.
- Pankhurst, James R.,Curcio, Massimiliano,Sproules, Stephen,Lloyd-Jones, Guy C.,Love, Jason B.
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supporting information
p. 5915 - 5928
(2018/05/28)
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- Merging Photoredox with Br?nsted Acid Catalysis: The Cross-Dehydrogenative C?O Coupling for sp3 C?H Bond Peroxidation
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A photoredox and Br?nsted acid synergistically catalyzed cross-dehydrogenative C?O coupling reaction is developed in which isochroman peroxyacetals are formed through sp3 C?H bond peroxidation. The reported method is characterized by its extremely mild reaction conditions, excellent yields, and broad substrate scope. An oxocarbenium ion p-chlorobenzenesulfonate was speculated to be the reactive intermediate. The role of hemiacetals and oxygenated dimers on the effective stabilization of the oxocarbenium ion was investigated; the presence of acid appeared to establish equilibrium between hemiacetals and oxygenated dimers with the oxocarbenium ion pairs. The broad applicability of the method highlights the potential of the protocol for molecule synthesis.
- Xia, Qing,Wang, Qiang,Yan, Changcun,Dong, Jianyang,Song, Hongjian,Li, Ling,Liu, Yuxiu,Wang, Qingmin,Liu, Xiangming,Song, Haibin
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supporting information
p. 10871 - 10877
(2017/08/18)
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- A metal-free catalytic system for the oxidation of benzylic methylenes and primary amines under solvent-free conditions
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Iodine-pyridine-tert-butylhydroperoxide is developed as a green and efficient catalytic system for the oxidation of benzylic methylenes to ketones and primary amines to nitriles. The reaction conditions are quite mild and environmentally benign, no transition metals, organic solvents or hazard reagents being needed. The oxidation of benzylic methylenes gave the corresponding ketones in excellent yields with complete chemoselectivity, while the oxidation of primary amines was complete in several minutes, affording various nitriles in moderate to good yields.
- Zhang, Jintang,Wang, Zhentao,Wang, Ye,Wan, Changfeng,Zheng, Xiaoqi,Wang, Zhiyong
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scheme or table
p. 1973 - 1978
(2010/06/15)
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- Iron catalyst for oxidation in water: Surfactant-type iron complex-catalyzed mild and efficient oxidation of aryl alkanes using aqueous TBHP as oxidant in water
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Surfactant-type iron(III) complex, Fe2O(DS)4, was found to be effective for benzylic oxidation of simple aryl alkanes using aqueous t-butyl hydroperoxide (TBHP) as an oxidant. Copyright
- Nagano, Takashi,Kobayashi, Shu
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scheme or table
p. 1042 - 1043
(2009/12/02)
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- Iron-catalyzed benzylic oxidation with aqueous tert-butyl hydroperoxide
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A small amount of iron(III) chloride (2 mol%) catalyzes benzylic oxidations with tert-butyl hydroperoxide (TBHP) as oxidant in pyridine. The corresponding carbonyl compounds are obtained in high yields.
- Nakanishi, Masafumi,Bolm, Carsten
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p. 861 - 864
(2008/03/27)
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- The radical chemistry of t-butyl hydroperoxide (TBHP) - Part 3 - Further studies on hydrocarbon activation
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Further aspects of the chemistry of TBHP in the presence of Fe(II) and Fe(III) species have been investigated. Now all the results previously reported with TBHP can be understood in terms of radical chemistry. Oxidation states of iron higher than Fe(III) are not involved.
- Barton, Derek H. R.,Le Gloahec, Valerie N.
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p. 15457 - 15468
(2007/10/03)
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- Electroreduction of dialkyl peroxides. Activation-driving force relationships and bond dissociation free energies
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The electrochemical reduction of five dialkyl peroxides in DMF was studied by cyclic voltammetry. The electron transfer (ET) to the selected compounds is concerted with the oxygen-oxygen bond cleavage (dissociative ET) and is independent of the electrode material. Such an electrochemical behavior provided the opportunity to study dissociative ETs by using the mercury electrode and therefore to test the dissociative ET theory by using heterogeneous activation-driving force relationships. The convolution voltammetry analysis coupled to the double-layer correction led to reasonable estimates of the standard potential (E°) for the dissociative ET to dialkyl peroxides, as supported, whenever possible, by independent estimates. A thermochemical cycle based on the dissociative ET concept was employed to calculate the bond dissociation free energies (BDFEs) of the five peroxides, using the above E°s together with electrochemical or thermochemical data pertaining to the redox properties of the leaving alkoxide ion. The BDFEs were found to be in the 25-32 kcal/mol range, suggesting a small substituent effect. The dissociative ET E°s were also used together with the experimental quadratic free energy relationships to estimate the heterogeneous reorganization energies.
- Antonello, Sabrina,Musumeci, Martin,Wayner, Danial D. M.,Maran, Flavio
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p. 9541 - 9549
(2007/10/03)
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- THE SELECTIVE FUNCTIONALIZATION OF SATURATED HYDROCARBONS. PART 28. THE ACTIVATION OF BENZYLIC METHYLENE GROUPS UNDER GOAGGIV AND GOAGGV CONDITIONS
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Under GoAggIV and GoAggV conditions, cyclohexadienes were oxidized to give aromatic products instead of ketones and alcohols.At the same time, anthracene was oxidized to give anthraquinone.Under GoAggIV and GoAggV conditions, xanthene, fluorene and diphenylmethane were oxidized to give the corresponding xanthone, fluorenone and benzophenone following two possible pathways: a) alkane to alkyl t-butylperoxide to ketone, and b) alkane to ketone, in which alkyl hydroperoxide, derived from oxygen, may be the reaction intermediate.Xanthyl azide was formed when sodium azide was added to the reaction mixture of xanthene under GoAggIV and GoAggV conditions.The reaction of triphenylmethane under GoAggV conditions gave triphenylmethyl t-butyl peroxide as the major product and hydroperoxide as the minor product.When TEMPO was added, triphenylmethyl hydroperoxide was the only product.
- Barton, Derek H. R.,Wang, Tie-Lin
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p. 1011 - 1032
(2007/10/02)
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- Neophyl-like Rearrangement of Alkoxy Radicals: Direct Detection of a Bridged Intermediate by Time-Resolved Absorption Spectroscopy
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The neophyl-like rearrangment of alkoxy radicals was examinde by means of picosecond time scale absorption spectroscopy.The triphenylmethoxy radical (Ph3CO.) rearranges to form the α-phenoxydiphenylmethyl radical (Ph2COPh.) with a rate constant greater than 5 x 1010 s-.The rearrangment of 1,1-diphenylethoxy radical (PhCH3CO.) was also examined.In acetonitrile solution, an intermediate is formed in less than 17 ps and then decays with a lifetime of 312 ns.It is proposed that this intermediate is a brigded spirooctadiene-type radical.
- Falvey, Daniel E.,Khambatta, Binaifer S.,Schuster, Gary B.
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p. 1056 - 1059
(2007/10/02)
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