Synthesis and characterization of cobalt(iii) complexes containing 2-pyridinecarboxamide ligands and their application in catalytic oxidation of ethylbenzene with dioxygenElectronic supplementary information (ESI) available: full experimental and spectroscopic data for all compounds. See http://www.rsc.org/suppdata/cc/b3/b301963b/

Qi, Jianying; Ma, Hui; Li, Xianjun; Zhou, Zhóngyuan; Choi, Michael C. K.; Chan, Albert S. C.; Yang, Quanlu

doi:10.1039/b301963b

Cited by 69 publications

(7 citation statements)

References 13 publications

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“…Interestingly, no induction period (time lag before product formation) is observed, in contrast to other cobalt-catalyzed processes. The oxidizing ability of the cobalt(III) cubane complexe 1a thus appears superior compared with that of other reported systems that use Co-based catalysts for the oxidation of ethylbenzene to acetophenone. − Łukasiewicz et al obtained only 6% acetophenone in the presence of chlorobenzene as solvent after 18.5 h under atmospheric pressure using a mixed-valence Co II /Co III trimer . Similar homogeneous liquid-phase oxidation using a Co(II)−Schiff-base complex also led to a low yield of acetophenone .…”

Section: Resultsmentioning

confidence: 96%

Synthesis, Structure, Spectral and Electrochemical Properties, and Catalytic Use of Cobalt(III)−Oxo Cubane Clusters

2007

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Olive-green cobalt(III) complexes having the general formula Co4O4(O2CMe)4L4 (1) where L = py (1a), 4-Mepy (1b), 4-Etpy (1c), and 4-CNpy (1d) have been prepared by the H2O2 oxidation of a mixture of Co2+, MeCO2-, and pyridine or 4-substituted pyridines in a 1:2:1 molar ratio in methanol. Spectroscopic and X-ray crystallographic studies show that these complexes contain a tetrameric cubane-like core [Co4(mu3-O)4]4+ where the four cobalt atoms form an approximate tetrahedron with edge lengths of approximately 2.75 A. Each cobalt in the crystallographically determined structure of Co4(mu3-O)4(mu-O2CMe)4L4 in 1a.NaClO4.3.5H2O and 1b.3H2O is hexacoordinate. Infrared spectra of the complexes show characteristic bands near 700, 635, and 580 cm-1 due to the central cubane-like core. 1H NMR spectra of the complexes show that the dissolved species are essentially diamagnetic and also that the complexes maintain their integrity in solution. UV-vis spectra of the green solutions have been interpreted in terms of ligand-field and charge-transfer bands. The electrochemical behavior of the complexes studied by cyclic and differential pulse voltammetric techniques indicates that the [(CoIII)4(mu3-O)4]4+ core present in the complexes undergoes a reversible one-electron oxidation to the [(CoIII)3CoIV(mu3-O)4]5+ core with an E1/2 value below 1 V. This suggests that these complexes of cobalt may be suitable as catalysts for the oxidation of organic compounds. Preliminary investigations indicate that 1a has a role to play in the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene.

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Section: Resultsmentioning

confidence: 96%

Synthesis, Structure, Spectral and Electrochemical Properties, and Catalytic Use of Cobalt(III)−Oxo Cubane Clusters

2007

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“…However, because the triplet-state nature of molecular oxygen hampers its reaction with hydrocarbons in singlet states, , such processes depend largely on the development of catalysts. Therefore, over the past decades, many homogeneous transition metal compounds (Co, Mn, Cu, or Fe) have been developed as efficient catalysts for the liquid-phase oxidation of ethylbenzene to acetophenone with molecular oxygen as oxidant. , However, among such processes reported to date, the operation conditions are often harsh, , for example, under a pressure of 10 atm of air and at 140–190 °C, and furthermore, the chemistry is rarely selective due to the inertness of the alkyl group and low oxidation ability of oxygen. Various heterogeneous catalysts using transition metal compounds have been studied − to enhance the catalytic efficiency for oxidation.…”

Section: Introductionmentioning

confidence: 99%

Synchronously Synthesizing and Immobilizing N-Hydroxyphthalimide on Polymer Microspheres and Catalytic Performance of Solid Catalyst in Oxidation of Ethylbenzene by Molecular Oxygen

Gao

Meng

Yang

2015

Org. Process Res. Dev.

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Cross-linked copolymer microspheres of glycidyl methacrylate (GMA) and methyl methacrylate (MMA) were first prepared (GMA/MMA microspheres), and then N-hydroxyphthalimide (NHPI) was synchronously synthesized and immobilized on the GMA/MMA microspheres to form a recyclable heterogeneous catalyst, GMA/MMA-NHPI, via several steps of polymer reactions by molecular design. A compositional catalyst was made with GMA/MMA-NHPI microspheres as the main catalyst and a transition metal salt as co-catalyst, and this compositional catalyst was used in the oxidation of ethylbenzene by molecular oxygen. The mechanism of the catalytic oxidation reaction was investigated, and the effects of some main factors on the catalytic oxidation reaction were examined. The experimental results show that, among several transition metal salts, Co(OAc) 2 is the best co-catalyst, and the catalytic activity order is Co(OAc) 2 > CoCl 2 > Mn(OAc) 2 > CuCl 2 . The compositional catalyst composed of GMA/MMA-NHPI microspheres and Co(OAc) 2 can effectively catalyze the oxidation of ethylbenzene by molecular oxygen under mild conditions (at 100°C and ordinary molecular oxygen pressure), and transform ethylbenzene into acetophenone with a yield of 20.1% and a selectivity of 75.8% in 25 h. The catalytic oxidation follows a free radical chain reaction mechanism. The type of solvent used significantly affects the catalytic oxidation reaction, and acetic acid is a more suitable solvent compared with acetonitrile. For the compositional catalyst, there is an optimum amount of added co-catalyst Co(OAc) 2 ; correspondingly, the optimum ratio of immobilized NHPI on GMA/MMA-NHPI microspheres to Co(OAc) 2 is 14:1. The appropriate reaction temperature is 100°C. The solid catalyst, GMA/MMA-NHPI microspheres, exhibits good recycling and reusing properties.

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“…These ligands have been used in different transition metal-catalysed reactions. [29][30][31][32][33][34][35] Also, picolinamide-derived substrates are nowadays widely used as coordinating substrates in group-directed CÀH bond activation, due to their favourable coordination to the metal centre. [36][37][38] Reports recently appeared on the use of picolinamides as ligands in Cu-catalysed synthesis of biphenyls, [39] and as chiral ligands in asymmetric Mannich-type reactions.…”

Section: Introductionmentioning

confidence: 99%

Picolinamides as Effective Ligands for Copper‐Catalysed Aryl Ether Formation: Structure–Activity Relationships, Substrate Scope and Mechanistic Investigations

Sambiagio

Munday

Marsden

et al. 2014

Chemistry A European J

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The use of picolinic acid amide derivatives as an effective family of bidentate ligands for copper-catalysed aryl ether synthesis is reported. A fluorine-substituted ligand gave good results in the synthesis of a wide range of aryl ethers. Even bulky phenols, known to be very challenging substrates, were shown to react with aryl iodides with excellent yields using these ligands. At the end of the reaction, the first examples of end-of-life Cu species were isolated and identified as Cu(II) complexes with several of the anionic ligands tested. A preliminary mechanistic investigation is reported that suggests that the substituents on the ligands might have a crucial role in determining the redox properties of the metal centre and, consequently, its efficacy in the coupling process. An understanding of these effects is important for the development of new efficient and tunable ligands for copper-based chemistry.

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Abstract: Four novel cobalt(III) complexes were found to have high catalytic activities and excellent selectivities in the oxidation of ethylbenzene to acetophenone using O2 as oxidant without need of solvent.

Cited by 69 publications

References 13 publications

Synthesis, Structure, Spectral and Electrochemical Properties, and Catalytic Use of Cobalt(III)−Oxo Cubane Clusters

Synthesis, Structure, Spectral and Electrochemical Properties, and Catalytic Use of Cobalt(III)−Oxo Cubane Clusters

Synchronously Synthesizing and Immobilizing N-Hydroxyphthalimide on Polymer Microspheres and Catalytic Performance of Solid Catalyst in Oxidation of Ethylbenzene by Molecular Oxygen

Picolinamides as Effective Ligands for Copper‐Catalysed Aryl Ether Formation: Structure–Activity Relationships, Substrate Scope and Mechanistic Investigations

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