- A 1:1 copper-dioxygen adduct is an end-on bound superoxo copper(II) complex which undergoes oxygenation reactions with phenols
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Employing a strongly electron-donating tripodal tetradentate ligand along with a reaction strategy designed to suppress binuclear peroxo complex formation, an end-on bound superoxo-copper(II) complex [CuII(NMe2-TMPA)(O2-)]+ (1) has been generated in solution [UV-vis (THF, -85 °C): λmax = 418 nm (ε, 4300 M-1 cm-1), 615 nm (ε, 1100), 767 nm (ε, 840)]. Resonance Raman spectroscopy employing isotopically substituted dioxygen (including mixed isotope 16/18O2) proves the end-on superoxo CuII(O2-) structural formulation, ν(O-O) = 1121 cm-1; ν(Cu-O) = 472 cm-1. The first demonstration of CuII(O2-) oxidative reactivity with exogenous substrates, likely involving H-atom abstraction chemistry, comes with the finding that 1 effects the oxygenation and hydroperoxylation of substituted phenols. Copyright
- Maiti, Debabrata,Fry, H. Christopher,Woertink, Julia S.,Vance, Michael A.,Solomon, Edward I.,Karlin, Kenneth D.
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- An efficient preparation of 2,6-di-t-butyl-1,4-benzoquinone
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A convenient and high yielding preparation of 2,6-di-t-butyl-1,4-benzoquinone from the iron-catalyzed oxidation of 2,4,6-tri-t-butylphenol with t-butyl hydroperoxide (TBHP) under acidic conditions is reported.
- Barton, Derek H. R.,Le Gloahec, Valerie N.
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- The synthesis, characterization, DNA/protein interaction, molecular docking and catecholase activity of two Co(II) complexes constructed from the aroylhydrazone ligand
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Two Co(II) complexes, Co(BBH)phenMeCN (1) and Co(BSH)phenMeCN (2) (HBBH = benzophenone benzoyl hydrazone, HBSH = benzophenone salicylylhydrazone ligand and phen = 1,10-phenanthroline) were prepared and characterized by single X-ray crystallography. The investigation of the complexes binding with herring sperm DNA (HS-DNA) revealed that stronger binding interaction exists between the complexes and HS-DNA compared to the corresponding free ligands. And both complexes can bind to DNA through intercalation of the phenyl rings between adjacent base pairs in the double helix. Meanwhile, bovine serum albumin (BSA) binding studies reveal the complexes can effectively interact with BSA and change the secondary structure of BSA. Superoxide dismutase (SOD) mimic activity of the complexes was investigated and the results showed that complex 2 showed a stronger radical scavenging potency against O2 .- radical with an IC50 value of 16.10 μM. The catecholase-like activity of both complexes has been investigated with 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate in methanol solution under completely aerobic conditions. The catalytic reaction follows Michaelis-Menten enzymatic reaction kinetics with turnover numbers (kcat) of 34.14 h?1 and 30.36 h?1 for complex 1 and complex 2, respectively.
- Li, Yun,Li, Yueqin,Liu, Xiaohui,Yang, Yong,Lin, Dong,Gao, Qinwei
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- Effect of structural variation on enzymatic activity in tetranuclear (Cu4) clusters with defective cubane core
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The stimulus to the modeling of enzyme functioning sites comes from their potential to give insight into the natural enzyme’s mechanistic pathways, ascertain the role of that different metal ion in the active site and construct better catalysts motivated by nature. The presence of metal ion leads to the activation of molecular oxygen in the metalloenzymes. The metalloenzymes such as the catechol oxidase (CO) enzyme that oxidizes the catechol to corresponding quinones which eventually protect damage tissues from plant and pathogen. Thus, the design and characterization of catalysts used as selectively and efficiently oxidation reactions have grown to be unique challenges for modern inorganic chemists. In this work, two novel tetranuclear complexes (1 and 2) have been synthesized in excellent yield. The complexes were characterized using various spectroscopic techniques such as FTIR, UV–Visible and PXRD pattern. The structure of 1 and 2 was elucidated by SC-XRD (single crystal X-ray diffraction) analysis. The magnetic study reveals the presence of the antiferromagnetic nature of 1 and 2. Both 1 and 2 shows a very good catecholase-like activity by oxidizing the catechol to analogous quinone in methanolic solution. Thus, a structure-activity relationship can further help us design other substituted tetranuclear complexes with enhanced catecholase like activity. Communicated by Ramaswamy H. Sarma.
- Ahmad, M. Shahwaz,Ahmad, Musheer,Kamal, Samrah,Khalid, Mohd,Khan, M. Shahnawaz,Shahid, M.
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- Insight into the crystallization process: Relationships between crystal structures and properties of copper(ii) coordination polymers containing dimethylbis(4-pyridyl)silane
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A systematic investigation into the favorable reaction conditions for construction of copper(ii) coordination polymers was carried out. Various reactions of copper(ii) bromide with dimethylbis(4-pyridyl)silane (L) produce two kinds of skeletal structures: the 1D loop-chain and the square-tubular helix. The fast-formation condition affords the 1D loop-chain, whereas the slow-formation condition yields the helical structure. The formation of significant condition-dependent structures can be partially attributed to the nature of the bromide anion and angle strain around the copper(ii) cation. The relationships between structures and physicochemical properties such as anion exchangeability, catalytic oxidation of 3,5-di-tert-butylcatechol, and thermal properties are discussed in these pages.
- Moon, So Yun,Noh, Tae Hwan,Jung, Ok-Sang
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- Mononuclear Cu(II) complex of an oxime ligand derived from N-Heterocyclic hydrazide: Synthesis, spectroscopy, electrochemistry, DFT calculations and catecholase activity
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A new oxime derivative N-heterocyclic hydrazide ligand, N'-[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]-2-[(4-methyl-5-phenyl-4H-1,2,4-triazol-3-l)thio] acetohydrazide (1) and its mononuclear copper(II) complex (1a) have been synthesized and characterized by using IR, UV–Vis, NMR and MALDI-TOF mass spectrometry. DFT-based molecular orbital energy calculations and electrochemical behaviors of the compounds have been also studied to explain redox potential of the compounds. The catecholase-mimetic activity of the Cu(II) complex (1a) has been investigated by monitoring the formation of 3,5-di-tert-butyl-benzoquinone from 3,5-di-tert-butylcatechol. Irreversible electrochemical ring-closing of the ligand by oxidation is proposed. Electrochemical ring-closing reaction is shielded by the coordination of Cu(II) to the oxime moiety of the ligand and the title complex undergoes quasi-reversible oxidation and irreversible reduction. Under aerobic conditions, the title copper(II) complex behaves as an effective catalyst towards oxidation of 3,5-di-tert-butylcatechol to its corresponding quinone derivative in MeOH. The turnover number was found as 100.1 h?1.
- Zengin, Ali,Karao?lu, Kaan,Emirik, Mustafa,Mente?e, Emre,Serbest, Kerim
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- A N3S(thioether)-ligated CuII-superoxo with enhanced reactivity
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Previous efforts to synthesize a cupric superoxide complex possessing a thioether donor have resulted in the formation of an end-on trans-peroxo-dicopper(II) species, [{(Ligand)CuII}2(μ-1,2-O22-)]2+. Redesign/modification of previous N3S tetradentate ligands has now allowed for the stabilization of the monomeric, superoxide product possessing a S(thioether) ligation, [(DMAN3S)CuII(O2?-)]+ (2S), as characterized by UV-vis and resonance Raman spectroscopies. This complex mimics the putative CuII(O2?-) active species of the copper monooxygenase PHM and exhibits enhanced reactivity toward both O-H and C-H substrates in comparison to close analogues [(L)CuII(O2?-)]+, where L contains only nitrogen donor atoms. Also, comparisons of [(L)CuII/I]n+ compound reduction potentials (L = various N4 vs DMAN3S ligands) provide evidence that DMAN3S is a weaker donor to copper ion than is found for any N4 ligand-complex.
- Kim, Sunghee,Lee, Jung Yoon,Cowley, Ryan E.,Ginsbach, Jake W.,Siegler, Maxime A.,Solomon, Edward I.,Karlin, Kenneth D.
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- Liquid Phase Oxidation of 2,6-Di-t-butylphenol by Molecular Oxygen Using Magnesium Oxide Catalysts Modified with Metal Ion
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Mn(II), Co(II), Cu(II), or Fe(III) ion containing magnesium oxides catalyzed oxidation of 2,6-di-t-butylphenol to quinones by molecular oxygen. 98percent Yield to 1,1'-bis(4-oxo-3,5-di-t-butylcyclohexadienylidene) was obtained with 16.7 wtpercent Mn ion containing magnesium oxide catalyst.
- Kurokawa, Hideki,Ueda, Wataru,Morikawa, Yutaka,Moro-Oka, Yoshihiko,Ikawa, Tsuneo
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- Evaluation of catacholase mimicking activity and apoptosis in human colorectal carcinoma cell line by activating mitochondrial pathway of copper(II) complex coupled with 2-(quinolin-8-yloxy)(methyl)benzonitrile and 8-hydroxyquinoline
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To evaluate the cytotoxic potential of metal-based chemotherapeutic candidate towards the colorectal cancer, we have synthesized a new copper(II) complex [Cu(qmbn)(q)(Cl)] (1) (where, qmbn = 2-(quinolin-8-yloxy)(methyl)benzonitrile and q = 8-hydroxyquinoline) and structurally characterized by single crystal X-ray, Powder-XRD, FTIR and thermogravimetric analysis (TGA). The structural analysis reveals that copper(II) ions exist in a distorted square pyramidal (τ = ~0.1), with ligation of a chloride ion, oxygen atom and two nitrogen atoms at equatorial position and one oxygen atom at apical position. The cytotoxicity potential of complex 1 was executed against human colorectal cell lines (HCT116), which showed that 1 induces mitochondrion-mediated apoptotic cell death via activation of the Bax (pro-apoptotic protein) caspases-3 and 9 proteins. Interestingly, complex 1 was found to be a good candidate as electron-transfer catalyst which mimics catacholase with high turnover frequency (kcat = 1.03 × 102 h?1) for the conversion of the model substrate 3,5-di-tertbutylcatechol (3,5-DTBC) to 3,5-di-tertbutylquinone (3,5-DTBQ). Furthermore, molecular docking studies revealed that complex 1 was successfully localized inside the binding pocket of protein kinase (Akt), which validate the mechanism and mode of interaction of 1 that displayed cytotoxic activity experimentally. The obtained outcomes reveal that the complex 1 could be utilized as an encouraging perspective in the development of new therapeutic candidate for colon cancer.
- Ali, Arif,Mishra, Snehasis,Kamaal, Saima,Alarifi, Abdullah,Afzal, Mohd,Saha, Krishna Das,Ahmad, Musheer
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- Dioxygen Adducts of Cobalt(II) Complexes of 6,6'-Bis(p-substituted benzoylamino)-2,2'-bipyridines and Their Cytalytic Activities in Oxygenation of 2,6-Di-tert-butylphenol
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The oxygen affinities and properties of oxygen adducts of complexes has been studied by cyclic voltammetry and IR, electronic and ESR spectroscopy.The complexes exhibited oxygen-binding ability in the presence of an appropriate axial base ligand (B), and the oxygen adducts were of the end-on bonded CoIII(O2(1-)) type (CoL(B)(O2)>.More complete electron transfer from the metal centre to the oxygen was indicated compared to that with .Electron-donating substituents gave higher concentrations of the oxygen adducts.The superior catalytic activity of these complexes, especially the Me- and But-substitued derivatives, in the oxygenation of 2,6-di-tert-butylphenol to the corresponding quinone is interpreted in terms of the reactivity of the co-ordinated oxygen and the oxygen affinity of the complexes.
- Araki, Koji,Kuboki, Takashi,Otohata, Makihiro,Kishimoto, Nobuyuki,Yamada, Masaki,Shiraishi, Shinsaku
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- Catalytic activity of anion-exchange resins modified with metal-porphine in oxidative reactions of phenols
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Anion-exchange resins modified with metal-porphine (M-P(r)) have been investigated to develop a solid catalyst in the oxidative reaction of phenols by O2 in air. Co-P(r), which is easily prepared and separable from the reaction mixture, has been proved to accelerate the oxidative reaction of phenols such as 3,5-di-tert-butyl-4-hydroxyanisole. The resulting main oxidative products were identified to be quinones by using the GC-MS method.
- Iwado, Akimasa,Mifune, Masaki,Kato, Jiro,Oda, Junko,Chikuma, Masahiko,Motohashi, Noriko,Saito, Yutaka
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- Dinuclear mixed-valence CoIIICoII complexes derived from a macrocyclic ligand: Unique example of a CoIIICoII complex showing catecholase activity
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The work in this paper presents the syntheses, characterization, catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) study of three mixed-valence dinuclear CoIIICoII complexes of composition [CoIIICoIIL(N3) 3]·CH3CN (1), [CoIIICo IIL(OCN)3]·CH3CN (2), and [Co IIICoIIL(μ-CH3COO)2](ClO 4) (3), derived from a tetraimino diphenolate macrocyclic ligand H2L, obtained on [2 + 2] condensation of 4-ethyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane. While 1 and 2 are diphenoxo-bridged, 3 is a heterobridged bis(μ-phenoxo)bis(μ-acetate) system. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH2) as the substrate, the catecholase activity of all the three complexes has been checked in methanol/acetonitrile/N,N-dimethyl formamide. While 2 and 3 are inactive, complex 1 shows catecholase activity with turnover numbers of 482.16 h -1 and 45.38 h-1 in acetonitrile and methanol, respectively. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1-3 have been recorded in acetonitrile solutions and the positive ions have been well characterized. The ESI-MS positive spectrum of complex 1 in the presence of 3,5-DTBCH2 has also been recorded and, interestingly, two positive ions [CoIIICoIIL(N3) 2(3,5-DTBCH-)H]+ and [CoIICo IIL(μ-3,5-DTBCH2-)Na]+ have been identified. The Royal Society of Chemistry 2013.
- Majumder, Samit,Mondal, Suraj,Lemoine, Pascale,Mohanta, Sasankasekhar
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- A Cobalt(II) Complex of a New Salen Analogue as an Oxygenation Catalyst of Higher Activity
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A cobalt(II) complex of 6,6'-bis(benzoylamino)-2,2'-bipyridine > has been found to take up and activate oxygen and act as a catalyst of higher activity and selectivity than the structurally similar N,N'-di(salicylidene)ethylenediamine complexes in the oxygenation of 2,6-di-t-butyl phenol to 2,6-di-t-butyl-p-benzoquinone.
- Yamada, Masaki,Araki, Koji,Shiraishi, Shinsaku
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- A multifunctional heterogeneous catalyst: Titanium-containing mesoporous silica material encapsulating magnetic iron oxide nanoparticles
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Magnetic iron oxide nanoparticles coated with mesoporous silica involving single-site titanium oxide moiety have been first developed by adopting a two-step coating method. The catalytic performance and magnetically separable ability were demonstrated in the oxidation of 2,6-di-tert-butylphenol using hydrogen peroxide. Copyright
- Mori, Kohsuke,Kondo, Yuichi,Morimoto, Shotaro,Yamashita, Hiromi
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- DNA/protein binding, cytotoxicity and catecholase activity studies of a piperazinyl moiety ligand based nickel(II) complex
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The Ni(II) complex, {[Ni(HL)(SCN)2(H2O)]·2(DMF)} (1) [HL = 6-methoxy-2-{[2-(1-piperazinyl)ethylimino]methyl}phenol], was synthesized and characterized by X-ray crystal structure analysis and spectroscopic methods. The crystal structure of complex 1 reveals a distorted octahedral coordination geometry around the nickel centre which forms a supramolecular assembly through hydrogen bonds. The interaction of complex 1 with the calf thymus DNA (CT-DNA) was investigated using electronic absorption and fluorescence spectroscopic methods. The results show that complex 1 has binding affinity to CT-DNA in the order of 6.06 × 105 M-1. The interactions of complex 1 with bovine serum albumin (BSA) and human serum albumin (HSA) were also studied using electronic absorption and fluorescence spectroscopic techniques and the analysis show that interaction of complex 1 with BSA/HSA occur mainly with ground state association process. The number of binding sites and binding constant were calculated using double logarithm regression equation. Anticancer activity of 1 in human breast (MCF7) cancer cell lines reveals dose dependent suppression of cell viability with IC50 value 64 ± 3.7 μM. Catecholase activity of 1 has been investigated in methanol medium using 3,5-di-tert-butylcatechol (3,5-DTBC) as model substrate and the result shows that 1 is active for catalyzing aerobic oxidation of 3,5-DTBC to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ).
- Mistri, Soumen,Puschmann, Horst,Manna, Subal Chandra
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- Polyoxometalate-based supramolecular porous frameworks with dual-active centers towards highly efficient synthesis of functionalized: P -benzoquinones
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Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal-organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5- polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12- polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8-10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h-1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. This journal is
- An, Haiyan,Chang, Shenzhen,Chen, Yanhong,Huang, Yaohui,Luo, Huiyun,Zhu, Qingshan
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p. 8591 - 8603
(2021/11/17)
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- Organophotocatalytic Aerobic Oxygenation of Phenols in a Visible-Light Continuous-Flow Photoreactor
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A mild photocatalytic phenol oxygenation enabled by a continuous-flow photoreactor using visible light and pressurized air is described herein. Products for wide-ranging applications, including the synthesis of vitamins, were obtained in high yields by precisely controlling principal process parameters. The reactor design permits low organophotocatalyst loadings to generate singlet oxygen. It is anticipated that the efficient aerobic phenol oxygenation to benzoquinones and p-quinols contributes to sustainable synthesis.
- Wellauer, Jo?l,Miladinov, Dragan,Buchholz, Thomas,Schütz, Jan,Stemmler, René T.,Medlock, Jonathan A.,Bonrath, Werner,Sparr, Christof
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supporting information
p. 9748 - 9752
(2021/05/27)
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- Oxidative Dearomatization of Phenols and Polycyclic Aromatics with Hydrogen Peroxide Triggered by Heterogeneous Sulfonic Acids
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We report herein a method for the oxidative dearomatization of phenols and bare polycyclic arenes into the corresponding quinoid derivatives using hydrogen peroxide. The reaction is catalyzed by sulfonic acids and best results were achieved using heterogenized species. The best results using phenols were achieved using a hybrid material, namely a perfluorinated polymer functionalized with sulfonic acid groups supported on silica. The dearomatization of polycyclic aromatic hydrocarbons performed better using the polymeric acid catalyst. These methods operate under mild conditions, using mild and benign oxidants and thus minimizing the formation of waste.
- Pancrazzi, Francesco,Maestri, Giovanni,Maggi, Raimondo,Viscardi, Rosanna
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supporting information
p. 5407 - 5414
(2021/10/25)
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- Sterically Stabilized End-On Superoxocopper(II) Complexes and Mechanistic Insights into Their Reactivity with O-H, N-H, and C-H Substrates
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Instability of end-on superoxocopper(II) complexes, with respect to conversion to peroxo-bridged dicopper(II) complexes, has largely constrained their study to very low temperatures. This limits their kinetic capacity to oxidize substrates. In response, we have developed a series of bulky ligands, Ar3-TMPA (Ar = tpb, dpb, dtbpb), and used them to support copper(I) complexes that react with O2 to yield [CuII(?1-O2?-)(Ar3-TMPA)]+ species, which are stable against dimerization at all temperatures. Binding of O2 saturates at subambient temperatures and can be reversed by warming. The onset of oxygenation for the Ar = tpb and dpb systems is observed at 25 °C, and all three [CuII(?1-O2?-)(Ar3-TMPA)]+ complexes are stable against self-decay at temperatures of ≤-20 °C. This provides a wide temperature window for study of these complexes, which was exploited by performing extensive reaction kinetics measurements for [CuII(?1-O2?-)(tpb3-TMPA)]+ using a broad range of O-H, N-H, and C-H bond substrates. This includes correlation of second order rate constants (k2) versus oxidation potentials (Eox) for a range of phenols, construction of Eyring plots, and temperature-dependent kinetic isotope effect (KIE) measurements. The data obtained indicate that reaction with all substrates proceeds via H atom transfer (HAT), reaction with the phenols proceeds with significant charge transfer, and full tunneling of both H and D atoms occurs in the case of 1,2-diphenylhydrazine and 4-methoxy-2,6-di-tert-butylphenol. Oxidation of C-H bonds proved to be kinetically challenging, and whereas [CuII(?1-O2?-)(tpb3-TMPA)]+ can oxidize moderately strong O-H and N-H bonds, it is only able to oxidize very weak C-H bonds.
- Debnath, Suman,England, Jason,Kr?mer, Tobias,Laxmi, Shoba,Quek, Sebastian Y.,Van Gastel, Maurice
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supporting information
p. 19731 - 19747
(2021/11/30)
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- Ligand-Constraint-Induced Peroxide Activation for Electrophilic Reactivity
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μ-1,2-peroxo-bridged diiron(III) intermediates P are proposed as reactive intermediates in various biological oxidation reactions. In sMMO, P acts as an electrophile, and performs hydrogen atom and oxygen atom transfers to electron-rich substrates. In cyanobacterial ADO, however, P is postulated to react by nucleophilic attack on electrophilic carbon atoms. In biomimetic studies, the ability of μ-1,2-peroxo-bridged dimetal complexes of Fe, Co, Ni and Cu to act as nucleophiles that effect deformylation of aldehydes is documented. By performing reactivity and theoretical studies on an end-on μ-1,2-peroxodicobalt(III) complex 1 involving a non-heme ligand system, L1, supported on a Sn6O6 stannoxane core, we now show that a peroxo-bridged dimetal complex can also be a reactive electrophile. The observed electrophilic chemistry, which is induced by the constraints provided by the Sn6O6 core, represents a new domain for metal?peroxide reactivity.
- Ansari, Mursaleem,Chandra, Anirban,Kundu, Subrata,Monte-Pérez, Inés,Rajaraman, Gopalan,Ray, Kallol
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supporting information
p. 14954 - 14959
(2021/06/01)
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- Distribution of Spin Density on Phenoxyl Radicals Affects the Selectivity of Aerobic Oxygenation of Phenols
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Phenoxyl radical was generally suggested as the intermediate during copper-catalyzed aerobic oxygenation of phenols. However, the substrate-dependent selectivity has not been well interpreted, due to insufficient characterization of the radical intermediate under reaction conditions. When studying the CuCl-LiCl-catalyzed aerobic phenol oxidation, we obtained EPR spectra of phenoxyl radicals generated by oxidizing phenols with the preactivated catalyst. Upon correlation to the selectivity of benzoquinone, the hyperfine coupling constant of para-site proton (aH, para) was found to be better than the Hammett constant. The catalysis mechanism was studied based on EPR detection and the reaction results of phenoxyl radicals under N2 or O2 atmosphere. It appeared that the chemoselectivity depended on the attack of activated dioxygen on phenoxyl radicals, and the activation of dioxygen by [CunCln+1]- (n = 1, 2, 3) was suggested as the rate-determining step. Understanding of the substrate-dependent selectivity contributed to predicting the chemoselectivity in the aerobic oxidation of phenols.
- Chen, Kaizhou,Du, Renfeng,Fan, Mengtian,Guan, Jun,Jiang, Zheng,Li, Haoran,Lu, Rui,Mei, Bingbao,Wang, Yongtao,Yao, Jia
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- Hydrogen Atom Transfer Oxidation by a Gold-Hydroxide Complex
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AuIII-oxygen adducts have been implicated as intermediates in homogeneous and heterogeneous Au oxidation catalysis, but their reactivity is under-explored. Complex 1, ([AuIII(OH)(terpy)](ClO4)2, (terpy = 2,2′:6′,2-terpyridine), readily oxidized substrates bearing C-H and O-H bonds. Kinetic analysis revealed that the oxidation occurred through a hydrogen atom transfer (HAT) mechanism. Stable radicals were detected and quantified as products of almost quantitative HAT oxidation of alcohols by 1. Our findings highlight the possible role of AuIII-oxygen adducts in oxidation catalysis and the capability of late transition metal-oxygen adducts to perform proton coupled electron transfer.
- Lovisari, Marta,McDonald, Aidan R.
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supporting information
(2020/03/13)
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- Structure, Spectroscopy, and Reactivity of a Mononuclear Copper Hydroxide Complex in Three Molecular Oxidation States
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Structural, spectroscopic, and reactivity studies are presented for an electron transfer series of copper hydroxide complexes supported by a tridentate redox-active ligand. Single crystal X-ray crystallography shows that the mononuclear [CuOH]1+ core is stabilized via intramolecular H-bonds between the H-donors of the ligand and the hydroxide anion when the ligand is in its trianionic form. This complex undergoes two reversible oxidation processes that produce two metastable "high-valent"CuOH species, which can be generated by addition of stoichiometric amounts of 1e- oxidants. These CuOH species are characterized by an array of spectroscopic techniques including UV-vis absorption, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies (XAS), which together indicate that all redox couples are ligand-localized. The reactivity of the complexes in their higher oxidation states toward substrates with modest O-H bond dissociation energies (e.g., 4-substitued-2,6-di-tert-butylphenols) indicates that these complexes act as 2H+/2e- oxidants, differing from the 1H+/1e- reactivity of well-studied [CuOH]2+ systems.
- Garcia-Bosch, Isaac,Lancaster, Kyle M.,Macmillan, Samantha N.,Rajabimoghadam, Khashayar,Siegler, Maxime A.,Wu, Tong
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supporting information
p. 12265 - 12276
(2020/08/06)
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- Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O2 at an Iron(II)-Cyclam Center
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In soluble methane monooxygenase enzymes (sMMO), dioxygen (O2) is activated at a diiron(II) center to form an oxodiiron(IV) intermediate Q that performs the challenging oxidation of methane to methanol. An analogous mechanism of O2 activation at mono-or dinuclear iron centers is rare in the synthetic chemistry. Herein, we report a mononuclear non-heme iron(II)-cyclam complex, 1-trans, that activates O2 to form the corresponding iron(IV)-oxo complex, 2-trans, via a mechanism reminiscent of the O2 activation process in sMMO. The conversion of 1-trans to 2-trans proceeds via the intermediate formation of an iron(III)-superoxide species 3, which could be trapped and spectroscopically characterized at-50 °C. Surprisingly, 3 is a stronger oxygen atom transfer (OAT) agent than 2-trans; 3 performs OAT to 1-trans or PPh3 to yield 2-trans quantitatively. Furthermore, 2-trans oxidizes the aromatic C-H bonds of 2,6-di-tert-butylphenol, which, together with the strong OAT ability of 3, represents new domains of oxoiron(IV) and superoxoiron(III) reactivities.
- Kass, Dustin,Corona, Teresa,Warm, Katrin,Braun-Cula, Beatrice,Kuhlmann, Uwe,Bill, Eckhard,Mebs, Stefan,Swart, Marcel,Dau, Holger,Haumann, Michael,Hildebrandt, Peter,Ray, Kallol
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supporting information
p. 5924 - 5928
(2020/05/08)
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- A novel Cu(II) distorted cubane complex containing Cu4O4 core as the first tetranuclear catalyst for temperature dependent oxidation of 3,5-di-tert-butyl catechol and in interaction with DNA & protein (BSA)
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The tri-dentate Schiff base ligand 3-(2-hydroxyethylimino)-1-phenylbut-1-en-1-ol (L) produced the tetra-nuclear Cu(II) distorted cubane complex which contain Cu4O4 core, upon reaction with Cu(II)acetate.H2O. The complex was structurally characterized by X-ray crystallography and found that, in this tetrameric and tetra-nuclear distorted cubane structure, each two-fold deprotonated Schiff base ligand coordinated to a Cu(II) center with their alcoholic oxygens and imine nitrogens and formed six and five-membered chelate rings. At the same time, each ligand bridged to a neighboring Cu(II) atom by its alcoholic oxygen, thus the metal centers became penta-coordinated. The copper(II) complex with μ-?2-hydroxo bridges and Cu….Cu distance about 3 ? was structurally similar to the active site of natural catechol oxidase enzyme and exhibited excellent catecholase activity in aerobic oxidation of 3,5-di-tert-butyl catechol to its o-quinone. The kinetics and mechanism of the oxidation of 3, 5-DTBCH2 catalyzed by [CuL]4 complex, were studied at four different temperatures from 283 to 313K by UV-Vis spectroscopy. Interaction of [CuL]4 complex with FS-DNA was investigated by UV-Vis and fluorescence spectroscopy, viscosity measurements, cyclic voltammetry (CV), circular dichroism (CD) and agarose gel electrophoresis. The main mode of binding of the complexes with DNA was intercalation. The interaction between [CuL]4 complex and bovine serum albumin (BSA) was studied by UV-Vis, fluorescence and synchronous fluorescence spectroscopic techniques. The results indicated a high binding affinity of the complex to BSA. In vitro anticancer activity of the complex was evaluated against A549, Jurkat and Ragi cell lines by MTT assay. The complex was remarkably active against the cell lines and can be a good candidate for an anticancer drug. Theoretical docking studies were performed to further investigate the DNA and BSA binding interactions.
- Asadi, Zahra,Zarei, Leila,Golchin, Maryam,Skorepova, Eliska,Eigner, Vaclav,Amirghofran, Zahra
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- Manganese(ii) complex of an oxygen-nitrogen donor Schiff base ligand showing efficient catechol oxidase activity: Synthesis, spectroscopic and kinetic study
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Tridentate O,N,O-donor Schiff base ligand (E)-1-(2-hydroxybenzylidene)semicarbazide (H2L1) and its Mn(ii) complex have been synthesized. Both the ligand and the complex have been characterized by analytical and spectroscopic techniques. X-ray crystal structure determination of the Mn(ii) complex shows that the Mn(ii) atom is in a distorted octahedral environment and there are two crystallographically different manganese atoms in the unit cell. The Mn(ii) complex shows very high catalytic activity for catechol oxidation (kcat = 3.10 × 106 h-1, kcat/KM = 3.25 × 108 h-1 M-1), which is the highest catalytic efficiency for catechol oxidation by a manganese complex reported in the literature. The probable mechanism of the catalytic reaction is explored using ESI-MS and EPR spectroscopy.
- Adak, Piyali,Mondal, Antu,Chattopadhyay, Shyamal Kumar
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p. 3748 - 3754
(2020/03/17)
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- A three-dimensional manganese(II) coordination polymer: synthesis, structure and catecholase activity
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A manganese-based coordination polymer, [Mn2L2(μ-MeOH)2]n (H2L = 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone) was obtained by self-assembly of 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone and manganese(II) acetate. The coordination polymer was characterized by IR, EPR and UV–Vis spectroscopy. The single-crystal X-ray diffraction study reveals that the dibasic tridentate ligand (L2?) is bound via ONO donor sites to manganese(II). Two such [ML] fragments are connected by μ2-bridged methanol (MeOH) to form a di-manganese species. The sixth site of each of the manganese is occupied by the pyridyl N atom of the isonicotinoyl group. This arrangement gives a polynuclear complex of the formula [Mn2L2(μ-MeOH)2]n. The coordination geometry of manganese is distorted octahedral. The X-band electron paramagnetic resonance (EPR) measurement of the complex at 77 K shows a six-line spectrum and a signal at the half field, with g = 4.88. The half-field signal indicates the dimeric nature of the complex in the solution state. The cyclic voltammetric measurement of the complex shows a reversible MnIII/MnII redox couple. The complex catalyzes the conversion of 3,5-di-tert-butyl catechol to the corresponding o-quinone with a catalytic turnover rate of (kcat) 27.22 h?1.
- Bhattacherjee, Prama,John, Rohith P.,Mitra, Partha,Sarkar, Prasenjit
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- X-ray structurally characterized Mo (VI), Fe (III) and Cu (II) complexes of amide-imine conjugate: (bio)catalytic and histidine recognition studies
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An amide-imine conjugate, (E)-N′-((2-hydroxybenzen-1-yl) methylene)-4-methylbenzohydrazide (H2LPTASAL), derived from 4-methyl-benzoic acid hydrazide (PTA) and 2-hydroxybenzaldehyde is used to prepare Mo (VI), Cu (II) and Fe (III) complexes. The X-ray structurally characterized complexes have been explored as catalyst for amine assisted asymmetric ring opening (ARO) of epoxide, carbon-heteroatom cross-coupling and ethyl benzene oxidation. In addition, their catecholase like activities have thoroughly been investigated. Moreover, the Cu (II) complex selectively recognizes histidine by fluorescence spectroscopy.
- Ta, Sabyasachi,Ghosh, Milan,Salam, Noor,Das, Jayanta,Islam, Manirul,Brand?o, Paula,Félix, Vítor,Sanmartin, Jesus,Das, Debasis
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- High-Valent d7 NiIII versus d8 CuIII Oxidants in PCET
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Oxygenases have been postulated to utilize d4 FeIV and d8 CuIII oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal-oxygen adducts, [NiIII(OAc)(L)] (1b) and [CuIII(OAc)(L)] (2b), L = N,N′-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [NiII(OAc)(L)]- (1a) and [CuII(OAc)(L)]- (2a). The complexes 1a/b-2a/b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, X-ray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para-substituted 2,6-di-tert-butylphenols (p-X-2,6-DTBP; X = OCH3, C(CH3)3, CH3, H, Br, CN, NO2) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d8 CuIII oxidant displayed a small increase in the rate constant compared to that of the d7 NiIII oxidant. The d8 CuIII oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDEC-H) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b. It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.
- Unjaroen, Duenpen,Gericke, Robert,Lovisari, Marta,Nelis, Daniel,Mondal, Prasenjit,Pirovano, Paolo,Twamley, Brendan,Farquhar, Erik R.,Mcdonald, Aidan R.
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supporting information
p. 16838 - 16848
(2019/12/24)
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- Selective synthesis of benzoquinones over Cu(ii)-containing propylsalicylaldimine functionalized mesoporous solid catalysts
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The major product, 2,3,5-trimethyl-1,4-benzophenone (TMBO), was synthesised by an eco-friendly liquid-phase oxidation of 2,3,6-trimethylphenol (TMP-OH) over Cu(ii)-containing propylsalicylaldimine (CSA) functionalized mesoporous solid catalysts, namely, CSASBA-15(0.2), CSASBA-15(0.1) and CSAMCM-41(0.2), synthesized using various amounts of copper in a simple post-grafting method using different mesoporous silica materials, e.g., thick-silica walled SBA-15 and thin-silica walled MCM-41. The benzoquinones, i.e., 2,6-disubstituted p-benzoquinones (DSBQs), were also synthesised by the slurry-phase oxidation of di/tri-substituted phenols using the prepared catalysts. A promising chemical treatment was used for the removal of extra-framework copper species from the active surface of CSASBA-15(0.2), and the catalytic activity of the recovered catalyst, i.e. green mesoporous CSASBA-15(0.2) or W-CSASBA-15(0.2), was evaluated. Various reaction parameters, oxidants and solvents were used in this catalytic oxidation. To confirm the catalytic stability, recyclability and hot-catalytic filtration experiments were performed. On the basis of all catalytic results, it is worth noting that the mesoporous CSASBA-15(0.2) is an outstanding and a promising heterogeneous catalyst for the selective synthesis of TMBO and DSBQs, and produces 98% TMBO selectivity with 100% TMP-OH conversion at 353 K for 40 min and 97-99% DSBQ selectivity with 98-100% di/tri-substituted phenols conversion at 330 K for 1-3 h. The green mesoporous catalyst has unprecedented catalytic activity compared with that of other CSA functionalized mesoporous solid catalysts.
- Selvaraj, Manickam,Assiri, Mohammed A.
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supporting information
p. 3291 - 3299
(2019/03/13)
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- Selective activation of C–H bond into C[dbnd]O bond of phenols in para-position via aerobic oxidation
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An efficient method for the oxidation of phenols to 1,4-benzoquinones catalyzed by cuprous(I) chloride was achieved in a solution of acetonitrile and water using molecular dioxygen as an oxidant. Particularly, the inert phenols, such as phenol and mono-alkyl substituted phenols, were effectively oxidized to 1,4-benzoquinones via the selective activation of C–H bond in para-position into C[dbnd]O bond under mild conditions. The catalyst shows high activity for unsubstituted or alkyl substituted phenols, but no effect on substituted phenols with electron-withdrawing groups. This study offers an aerobic method for the selective oxidation of aromatic phenols to 1,4-benzoquinones.
- Yang, Shilei,Xu, Guoqiang,Shi, Song,Xin, Hongchuan,Gao, Jin,An, Zengjian
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p. 105 - 108
(2019/02/25)
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- Tetranuclear Schiff base copper(II) complexes: Syntheses, crystal structure, DNA/protein binding and catecholase-like activity
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Two tetranuclear Schiff base copper(II) complexes, namely [Cu4(L)2(LH)2(H2O)2](ClO4)2·3H2O (1) and [Cu4(L)2(LH)2(H2O)2](ClO4)·(tp)0.5·3H2O (2) (where H2L = 2-[(2-hydroxy-ethylimino)-methyl]-6-methoxy-phenol, tp = terephthalate), were synthesized and characterized by X-ray single crystal diffraction. Both complexes 1 and 2 are comprised of structurally similar tetranuclear cationic [Cu4(L)2(LH)2(H2O)2]2+ species with a double open cubane core, in which two metal centers possess a square pyramidal environment and the other two exhibit a slightly distorted octahedral coordination geometry. The interaction of complexes 1 and 2 with calf thymus DNA (CT-DNA) was investigated using electronic absorption and fluorescence studies, and the results showed that the complexes interact with CT-DNA with the related intrinsic binding constants (Kib) of 1.8 × 106 and 1.1 × 107 L mol?1 for 1 and 2, respectively. Their interactions with bovine serum albumin (BSA) and human serum albumin (HSA) were also investigated and spectroscopic techniques showed that both complexes interact with these proteins through a ground state association process. Using 3,5-di-tertbutylcatechol (3,5-DTBC) as a model substrate, both complexes show catecholase-like activity, being able to oxidase 3,5-DTBC to 3,5-di-tert-butylquinone (3,5-DTBQ) in the presence of oxygen.
- Manna, Soumen,Zangrando, Ennio,Puschmann, Horst,Manna, Subal Chandra
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p. 285 - 292
(2019/02/26)
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- Hexanuclear Zn(II) and Mononuclear Cu(II) Complexes containing imino phenol ligands: Exploitation of their Catalytic and Biological Perspectives
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A unique hexanuclear zinc(II) (1) and two mononuclear copper(II) (2 and 3) complexes anchored with imino phenol ligand HL1 and HL2 were synthesized with good yield and purity (where HL1?=?4-tert-butyl-2,6-bis((mesitylimino)methylphenol and HL2?=?5-tert-butyl-2-hydroxy-3-((mesitylimino)methyl)benzaldehyde). These complexes were characterized by utilizing various spectroscopic protocols like NMR, FTIR, UV as well as ESI-Mass spectrometry, elemental analysis and single crystal X-ray diffraction studies. Their potential to bind calf thymus DNA (CT-DNA) was tested utilizing different techniques such as UV–visible and fluorescence spectroscopy. The experiment implies that they interact with CT-DNA via non-intercalative mode with moderate capabilities (Kb ~ 104?M?1). On the other hand, these complexes have high capabilities to quench the fluorescence of bovine serum albumin (BSA) following the static pathway. In addition, they are active catalysts for the oxidation reaction of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) under aerobic condition. From the recorded EPR signals of all complexes, it has been concluded that the oxidation reaction proceeds via ligand oriented radical pathway instead of metal based redox participation. Kinetic studies using 1–3 indicate that it follows Michaelis–Menten type of equation with moderate to high turnover number (kcat). Apart from these aspects, complexes 1–3 were screened for their cytotoxic behavior towards HeLa cells (human cervical carcinoma) and found quite active with comparable IC50 values to cisplatin.
- Mondal, Shyam Sundar,Chatterjee, Manosree,Tiwari, Ranjay K.,Behera,Chanda, Nripen,Biswas, Sourav,Saha, Tanmoy Kumar
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- Catalyst-Enabled Chemodivergent Construction of Alkynyl- And Vinyl-Substituted Diarylmethanes from p-Quinone Methides and Alkynes
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Here, a catalyst-controlled chemodivergent 1,6-addition of p-quinone methides with alkynes was developed, affording diverse alkynyl- and vinyl-substituted diarymethanes. In this transformation, copper catalyzed the direct 1,6-addition of p-QMs with alkynes, while iron promoted the three components reaction of p-QMs, alkynes, and halogens from iron salts or added HX acid. The salient features of this transformation include completely controllable chemoselectivity, mild conditions, inexpensive catalysts, and good substrates scopes.
- Liu, Zhenli,Xu, Haofeng,Yao, Tengfei,Zhang, Junliang,Liu, Lu
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supporting information
p. 7539 - 7543
(2019/10/02)
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- Significant effect of 5,10,15,20-meso-tetraarylporphyrinatoiron(III) chloride/triflate and acidic/neutral/basic imidazolium ionic liquids in catalytic oxidation of phenols
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The influence of acidic, neutral and basic ionic liquids and their binary mixture with dichloromethane on the reactivity of iron(III)porphyrins was investigated during oxidation of phenols with hydrogen peroxide catalysed by 5,10,15,20-tetraarylporphyrinatoiron(III) chloride and 5,10,15,20-tetraarylporphyrinatoiron(III) triflate. The generation of different intermediates of iron(III) porphyrin in different ILs was studied through viscosity, density, UV–Vis and 1H NMR spectroscopy. The heterolytic cleavage efficiency of (TAP)FeIII-OOH and formation of quinone using iron(III)porphyrin (TAP)FeIIICl with Cl atom as an axial ligand, is influenced by the structure of imidazolium moiety and the counteranion following the order [(CH2)4SO3HMIm]CF3COO > [Hmim]CF3COO > [bmim]TFA ?? negligible amount in [bmim]CF3SO3, [Hmim]CF3SO3, [bmim]BF4, [bmim]PF6 and [bmim]Cl. On the other hand, the heterolytic cleavage efficiency of (TAP)FeIII-OOH with iron(III)porphyrin (TAP)FeIIICF3SO3 with triflate as an axial ligand, was found in the following order [(CH2)4SO3HMIm]CF3SO3 > [Hmim]CF3SO3 > [(CH2)4SO3HMIm]CF3COO > [Hmim]CF3COO > [bmim] CF3COO > [bmim]PF6 ≈ [bmim]BF4 ≈ [bmim]CF3SO3, while epoxidation and polymerization were mainly observed in basic and neutral ILs. The reactive intermediates formed by the reaction of monooxygen donors with (TAP)FeIIICl varied with ILs, as (TAP)+?FeIV = O intermediate was dominated in acidic ILs, while (TAP)FeIV = O was formed in neutral ILs and (TAP)FeIII-OO– was formed in basic ILs.
- Ahmad, Sohail,Gautam, Renu,Singhal, Anchal,Chauhan
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p. 292 - 303
(2018/04/10)
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- Synthesis tricyanovinyl derivatives via one-pot tandem reactions with heterogeneous catalyst Au@Cu(II)-MOF
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In this article, the heterogeneous catalyst of Au@Cu(II)-MOF was prepared with high performance catalytic activities. By adding 5% mol Au@Cu(II)-MOF, the substrate of 2,6-di-tert-butylphenol (1) was oxidized to 2,6-di-tert-butyl-p-benzoquinone (2) with the yield of 99% using H2O2 as an oxidizing reagent. Moreover, treating the catalytic reaction mixture with malononitrile, one new product of 2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane-1,1,2,-tricarbonitrile (3) was obtained with the isolated yield of 87%. However, in the absence of the catalyst of Au@Cu(II)-MOF, the intermedia of 2 and malononitrile react to form a product not 3 but its isomer 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarbonitrile (4). At the meanwhile, in the presence of Au@Cu(II)-MOF and H2O2, the product of 3 with comparable isolated yield of 86% was isolated when 1 and malononitrile directly reacted during one pot tandem reaction. Furthermore, the tautomerization of 3 and 4 was also observed in CH2Cl2 solution driven by trimethylamine and acetic acid.
- Jin, Fa-Zheng,Chen, Chao-Qun,Zhao, Qun,Kan, Jing-Lan,Zhou, Yang,Chen, Gong-Jun
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- Hydrogen atom transfer by a high-valent nickel-chloride complex
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Oxo-metal-halide moieties have often been implicated as C-H bond activating oxidants with the terminal oxo-metal entity identified as the electrophilic oxidant. The electrophilic reactivity of metal-halide species has not been investigated. We have prepared a high-valent nickel-halide complex [NiIII(Cl)(L)] (2, L = N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamide) by one-electron oxidation of a [NiII(Cl)(L)]? precursor. 2 was characterized using electronic absorption, electron paramagnetic resonance, and X-ray absorption spectroscopies and mass spectrometry. 2 reacted readily with substrates containing either phenolic O-H or hydrocarbon C-H bonds. Analysis of the Hammett, Evans-Polanyi, and Marcus relationships between the determined rate constants and substrate pKa, X-H bond dissociation energy, and oxidation potential, respectively, was performed. Through this analysis, we found that 2 reacted by a hydrogen atom transfer (HAT) mechanism. Our findings shine light on enzymatic high-valent oxo-metal-halide oxidants and open new avenues for oxidative halogenation catalyst design.
- Mondal, Prasenjit,Pirovano, Paolo,Das, Ankita,Farquhar, Erik R.,McDonald, Aidan R.
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supporting information
p. 1834 - 1841
(2018/02/17)
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- Synthesis and evaluation of catecholase activities of metal complexes of 1,4-substituted piperazine Mannich base of 4-acetamidophenol
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The synthesis and characterisation including 1H and 13C NMR spectroscopy of a Mannich base 1,4-di-(5- A cetamido-2-hydroxybenzyl)piperazine is herein reported. The Mannich reaction leading to the formation of the ligand took place at both ends of piperazine. Four metal complexes [Cu(II) and Fe(III)] including those bearing thiocyanate groups (SCN-) in N- A nd S-bonding modes have been studied for their abilities to mimic catecholase oxidase. All the metal complexes are catalytically active with the highest turnover rate (kcat) recorded for complex 3. The catalytic process as monitored by 1H NMR spectroscopy (isolation of 3, 5-DTBQ) and iodometric titration revealed the formation of H2O2 and thus implied that the mechanism of oxidation is through the formation of a semiquinolate species.
- Ayeni, Ayowole Olaolu,Watkins, Gareth Mostyn
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p. 1275 - 1284
(2018/10/23)
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- The mesoporous molecular sieve and its synthetic method and application and a 2, 6 - di-tert-butyl phenol oxidation method
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The invention provides a method for synthesizing a mesoporous titanium silicate molecular sieve. The method comprises: (1) hydrolyzing an organic silicon source, a titanium source, an acid source and a surfactant to obtain a mixture A, and carrying out primary crystallization on the mixture A; and (2) mixing the materials subjected to primary crystallization with an inorganic silicon source to obtain a mixture B, and carrying out secondary crystallization on the obtained mixture B. The invention provides the mesoporous titanium silicate molecular sieve and an application thereof. The invention provides a method for oxidizing 2,6-di-tert-butylphenol. According to the method disclosed by the invention, the inorganic silicon source which is relatively cheap can be used as a partial or even main silicon source, so that dosage of the organic silicon is reduced while hydrolysis time is shortened and synthesis benefits are greatly improved; and the mesoporous titanium silicate molecular sieve synthesized by the method disclosed by the invention is high in relative crystallinity, high in catalytic oxidation activity and high in selectivity. In a probe reaction of phenol, for example an oxidation reaction of the 2,6-di-tert-butylphenol, the mesoporous titanium silicate molecular sieve has the characteristic of high catalytic oxidation activity.
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Paragraph 0098; 0099; 0102
(2017/08/25)
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- Reactivity of a stable copper-dioxygen complex
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We report the isolation of a room temperature stable dipyrromethene Cu(O2) complex featuring a side-on O2 coordination. Reactivity studies highlight the unique ability of the dioxygen adduct for both hydrogen-atom abstraction and acid/base chemistry towards phenols, demonstrating that side-on superoxide species can be reactive entities.
- Iovan, Diana A.,Wrobel, Alexandra T.,McClelland, Arthur A.,Scharf, Austin B.,Edouard, Guy A.,Betley, Theodore A.
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supporting information
p. 10306 - 10309
(2017/09/23)
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- Spectroscopic, electrochemical and DNA binding studies of some monomeric copper(II) complexes containing N2S(thiolate)Cu core and N4S(disulfide)Cu core
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We report the synthesis, characterization and spectroscopic results of the Cu(II) complexes [Cu(pabt)(OH2)](ClO4) (1), [Cu(pabt)(Imz)](ClO4) (2), [Cu(pabt)(N-MeImz)](ClO4) (3), [Cu(pabt)Cl] (4), [Cu(pma)Cl] (5), [Cu(pdta)Cl]Cl (6) and [Cu(reduced-pdta)Cl]Cl (7), (Hpabt = N-(2-mercaptophenyl)-2′-pyridylmethylenimine, Hpma = N-(2-pyridylmethyl)-2-mercaptoaniline, pdta = 2,2′-di(pyridyl-2-methyleneimine)diphenyl disulfide, reduced-pdta = 2,2′-di(pyridyl-2-methylamine)diphenyl disulfide, Imz = imidazole, N-MeImz = N-methylimidazole). Electronic spectra of all these compounds display strong LMCT bands in the visible region mainly associated with S → Cu(II), and consistent with TDDFT results. A four-line EPR pattern originating from the interaction of the unpaired electron with the central63/65Cu nucleus (I = 3/2, natural abundances:63Cu, 69.17%;65Cu, 30.83%) with the isotropic coupling constant (Aiso) values of 80 ± 1.5 G at RT for all these complexes suggests monomeric nature in solution. The redox behavior of these compounds show either nearly reversible or quasi-reversible Cu(II)/Cu(I) couple with redox potentials within the range ?0.08 to ?0.20 V versus Ag/AgCl. Some of these compounds show strong intercalative DNA binding and its complete cleavage. 1–3 exhibit remarkable cytotoxicity against C6 glioma cell line and human cervical cancer HeLa cell line. IC50values of 2 and 3 for the cervical cancer HeLa cell line reveal that they exhibit higher cytotoxicity than many reported Cu(II) compounds.
- Koley, Manjuri K.,Chouhan, Om Prakash,Biswas, Sumit,Fernandes, Joseph,Banerjee, Arnab,Chattopadhyay, Anjan,Varghese, Babu,Manoharan, Periakaruppan T.,Koley, Aditya P.
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p. 179 - 198
(2016/12/23)
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- Organoruthenium(II) compounds with pyridyl benzoxazole/benzthiazole moiety: studies on DNA/protein binding and enzyme mimetic activities
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We report herein synthesis and characterization of four new organoruthenium(II) complexes of the type [RuH(CO)(PPh3)2(L1,2)]Cl (1, 3) and [Ru(CO)(Cl)2(AsPh3)(L1,2)] (2, 4) derived from the reaction of [RuHCl(CO)(EPh3)3] (E?=?P or As) with 2-(pyridine-2yl)benzoxazole (L1) and 2-(pyridine-2yl)benzthiazole (L2). Single-crystal X-ray diffraction data of 2 proved octahedral geometry of the complexes with a 1 : 1 ratio between the metal and the coordinated ligands. The binding affinities of 1–4 toward calf-thymus DNA (CT-DNA) and BSA were thoroughly studied by various spectroscopic techniques. Furthermore, the coordination compounds exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone and phosphatase-like activities in the hydrolysis of 4-nitrophenyl phosphate to 4-nitrophenolate ion. The kinetic parameters have been determined using Michaelis–Menten approach. The highest kcat values suggested that coordination compounds exhibit higher rates of catalytic efficacy.
- Gomathi, Asaithambi,Vijayan, Paranthaman,Viswanathamurthi, Periasamy,Suresh, Shanmugam,Nandhakumar, Raju,Hashimoto, Takeshi
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p. 1645 - 1666
(2017/05/15)
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- Catalytic promiscuity of an iron(II)–phenanthroline complex
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A mononuclear iron(II) complex, [Fe(phen)3]Cl2 (1) (phen =1,10-phenanthroline), has been synthesized in crystalline phase and characterized using various spectroscopic techniques including single crystal X-ray diffraction. Crystal structure analysis revealed that 1 crystallizes in a monoclinic system with C2/m space group. Complex 1 acts as a functional model for a biomimetic catalyst promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) through radical pathways with a significant turnover number (kcat =3.55?×?103?h?1) and exhibits catechol dioxygenase activity towards the same 3,5-DTBC substrate at room temperature in oxygen-saturated ethanol medium. The existence of an isobestic point at 610?nm from spectrophotometric data indicates the presence of Fe3+??3,5-DTBC adduct favouring an enzyme–substrate binding phenomenon. Upon stoichiometric addition of 3,5-DTBC pretreated with two equivalents of triethylamine to the iron complex, two catecholate-to-iron(III) ligand-to-metal charge transfer bands (575 and 721?nm) are observed and the in situ generated catecholate intermediate reacts with dioxygen (kobs =9.89?×?10?4?min?1) in ethanol medium to afford exclusively intradiol cleavage products along with a small amount of benzoquinone, and a small amount of extradiol cleavage products, which provide substantial evidence for a substrate activation mechanism. Copyright
- De, Abhranil,Garai, Mamoni,Yadav, Hare Ram,Choudhury, Angshuman Roy,Biswas, Bhaskar
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- Process for producing hydroquinone and derivates
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The present disclosure relates to an improved, environmentally friendly, process for producing compounds such as hydroquinone (benzene-1,4-diol) and its derivatives. The process can be carried out at ambient temperature and pressure using a recyclable copper catalyst and recyclable intermediate materials. The process generally entails reacting an aromatic compound such as benzene with hydrogen peroxide in the present of a pure elemental copper catalyst or a copper (I) salt catalyst to form oxidation product such as benzoquinone, and reducing the compound to hydroquinone or a hydroquinone derivative.
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Page/Page column 7-8
(2017/08/01)
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- Catalytic aspects of a copper(II) complex: biological oxidase to oxygenase activity
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Abstract: A coper(II) complex, [Cu(dpa) 2(OAc)](ClO 4) (1) [dpa =2 , 2 ′-dipyridylamine; OAc = acetate], has been synthesized and crystallographically characterized. X-ray structure analysis revealed that this mononuclear Cu(II) complex crystallizes as a rare class of hexa coordination geometry named bicapped square pyramidal geometry with P2 1/ c space group. This copper complex displays excellent catalytic efficiency, k cat/ K M(h - 1) = 6.17 × 10 5 towards the oxidative coupling of 2-aminophenol (2-AP) to aminophenoxazin-3-one. Further, upon stoichiometric addition of copper(II) complex to 3,5-DTBC in presence of molecular oxygen in ethanol medium, the copper complex affords predominantly extradiol cleavage products along with a small amount of benzoquinone and a trace amount of intradiol cleavage products at a rate, k obs= 1.09 × 10 - 3min - 1, which provide substantial evidence for the oxygen activation mechanism. This paper presents a novel addition of a copper(II) complex having the potential to mimic the active site of phenoxazinone synthase and catechol dioxygenase enzymes with significant catalytic efficiency. Graphical Abstract : SYNOPSIS The mononuclear copper complex having unusual hexa coordination geometry exhibits significant catalytic efficiency, k cat/ K M(h - 1) = 6.17 × 10 5 towards oxidation of 2-aminophenol which predominantly produced extradiol cleavage products at a rate, k obs= 1.09 × 10 - 3min - 1 upon addition of 3,5-DTBC in presence of molecular oxygen. [Figure not available: see fulltext.].
- Chowdhury, Biswajit,Maji, Milan,Biswas, Bhaskar
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p. 1627 - 1637
(2017/11/03)
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- A copper complex and its preparation method and application
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The invention discloses a copper complex, a preparation method and application thereof. The chemical formula of the copper complex is [Cu(dpca)(phen)(CH3OH)]NO3.H2O, Hdpca is 2,4-dihydroxy pyrimidine-5-carboxylic acid, and phen is phenanthroline. A monocrystal complex by self assembling of molecules has certain granularity, a unique structure, high catalytic activity, high selectivity and good stability, is mild in condition, high in yield, good in reproducibility and free of pollution in production, can be prepared at normal temperature and normal pressure, and has latent economic benefit, social benefit and environmental benefit.
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Paragraph 0036; 0037; 0038; 0039
(2016/10/09)
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- Catecholase and phenoxazinone synthase activities of a ferromagnetically coupled tetranuclear Cu(II) complex
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A crystallographically characterized tetranuclear Cu(ii) complex [CuII4(L)4] (1) [H2L = N-(2-hydroxyethyl)-3-methoxysalicylaldimine] is found to show overall ferromagnetic exchange coupling. Complex (1) mimics the catalytic activity of the plant enzyme catechol oxidase by oxidising 3,5-di-tert-butylcatechol to its corresponding quinone in methanol and dichloromethane medium in the presence of aerial oxygen. The reaction follows Michaelis-Menten enzymatic reaction kinetics with turnover numbers (Kcat) 6.99 × 103 and 1.85 × 103 h-1 in methanol and dichloromethane, respectively. 1 is also phenoxazinone synthase active in methanol medium with a turnover number of 1.21 × 105 h-1.
- Mitra, Merry,Kundu, Tanay,Kaur, Gurpreet,Sharma, Gyaneswar,Choudhury, Angshuman Roy,Singh, Yogesh,Ghosh, Rajarshi
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p. 58831 - 58838
(2016/07/07)
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- New metal complexes with diclofenac containing 2-pyridineethanol or 2-pyridinepropanol: synthesis, structural, spectroscopic, thermal properties, catechol oxidase and carbonic anhydrase activities
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Four new neutral diclofenac-based complexes, [Co(dicl)2(2-pyet)2] 1, [Ni(dicl)2(2-pyet)2] 2, [Cu2(dicl)2(2-pyet)2] 3, and [Cu2(dicl)2(2-pypr)2] 4 have been synthesized and characterized by elemental analysis, FT-IR, thermal analysis. Complexes 1, 3, and 4 have also been characterized by X-ray single-crystal structural analysis. The compounds of Co(II) and Ni(II) have octahedral geometry with two diclofenac and two 2-pyridineethanol ligands in the coordination sphere. The compounds of Cu(II) have square-pyramidal geometry and Cu(II) ions are linked via oxygens to the bridging 2-pyridineethanol or 2-pyridinepropanol ligands. The Δν values acquired by FT-IR are in agreement with the single XRD data. Studies on the thermal properties are reported and the complexes are stable to 196, 216, 215, and 201?°C in air, respectively. Two dinuclear Cu(II) complexes have demonstrated catalytic activity on oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone showing saturation kinetics at high substrate concentrations. The diclofenac complexes are investigated as inhibitors of the human cytosolic isoforms hCA I and II. The complexes are good as hCA I inhibitors (Kis of 1.52–55.06?μM) but only moderately efficient as hCA II inhibitors (Kis of 0.23–5.61?μM).
- Caglar, Sema,Dilek, Esra,Caglar, Bulent,Adiguzel, Ekrem,Temel, Ersin,Buyukgungor, Orhan,Tabak, Ahmet
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p. 3321 - 3335
(2016/10/18)
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- Efficient Metal-Free Catalytic Reaction Pathway for Selective Oxidation of Substituted Phenols
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Selective oxidation of substituted phenols to p-benzoquinones is known to be inefficient because of the competing C-O coupling reaction caused by phenoxy radicals. The poor stability of conventional metal-based catalysts represents another bottleneck for industrial application. Here, we describe a metal-free reaction pathway in which onion-like carbon (OLC) as a low-cost catalyst exhibits excellent catalytic activity and stability in the selective oxidation of mono-, di- and trisubstituted phenols to their corresponding p-benzoquinones, even better than the reported metal-based catalysts (e.g., yield, stability) and industrial catalysts for particular substrates. Together with XPS, Raman, DFT calculations, and a series of comparative experiments, we demonstrate that the zigzag configuration as a type of carbon defects may play a crucial role in these reactions by stabilizing the intermediate phenoxy radicals.
- Lin, Yangming,Li, Bo,Feng, Zhenbao,Kim, Yoong Ahm,Endo, Morinobu,Su, Dang Sheng
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p. 5921 - 5926
(2015/10/12)
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- Preparation of copper complexes coordinated by N21,N22-etheno bridged porphyrin and the application to photooxidation of phenol derivatives
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Copper(I) complexes coordinated with a N21,N22-etheno bridged porphyrin ligand were synthesized as a unique coordination structure. The copper porphyrin complexes promoted photooxidations of a phenol derivative in organic solution under aerobic condition with visible photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the reaction. The structural study found that the active species contributing to the photooxidation reaction was the di(μ-hydroxo)dicopper(II) complex of N21,N22-etheno bridged porphyrin generated by oxidation of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous condition.
- Takao, Yuko,Matsumoto, Fukashi,Moriwaki, Kazuyuki,Mizuno, Takumi,Ohno, Toshinobu,Setsune, Jun-Ichiro
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p. 786 - 793
(2015/10/29)
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- Preparation of copper complexes coordinated by N21,N22-etheno bridged porphyrin and the application to photooxidation of phenol derivatives
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Copper(I) complexes coordinated with a N21,N22-etheno bridged porphyrin ligand were synthesized as a unique coordination structure. The copper porphyrin complexes promoted photooxidations of a phenol derivative in organic solution under aerobic condition with visible photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the reaction. The structural study found that the active species contributing to the photooxidation reaction was the di(μ-hydroxo)dicopper(II) complex of N21,N22-etheno bridged porphyrin generated by oxidation of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous condition.
- Takao, Yuko,Matsumoto, Fukashi,Moriwaki, Kazuyuki,Mizuno, Takumi,Ohno, Toshinobu,Setsune, Jun-Ichiro
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p. 786 - 793
(2016/01/09)
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- Aerobic oxidation of 2,4,6-tri-tert-butylphenol to quinones catalyzed by copper(II) complexes of an N-octylated bis-benzimidazolyl ligand
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Abstract Copper(II) complexes of a N-octylated bisbenzimidazolyl ligand are synthesized and characterized. These complexes carry out the oxidative dealkylation of 2,4,6-tri-tertbutylphenol (TTBP) using molecular oxygen to 2,6-ditertbutylbenzoquinone and 4,6-di-tertbutylbenzoquinone. The oxidation proceeds via a phenoxyl radical species detected spectrophotometrically, and by EPR. A reactive copper(II)-dioxygen species is involved that carries out the oxidation reaction. A comparison of the rates of formation of the 4,6-di-tert-butylbenzoquinone versus 2,6-di-tert-butylbenzoquinone suggests that alternative pathway may exist for the formation of the para-quinone derivative. Isolation of an intermediate 4,4′-peroxybis(2,4,6-tri-tert-butylcyclohexa-2,5-dienone species and its structural characterization supports the above contention.
- Yadav, Anjana,Mathur, Pavan
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p. 206 - 214
(2015/08/03)
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- Azido bridge mediated catecholase activity, electrochemistry and magnetic behavior of a dinuclear copper(II) complex of a phenol based "end-off" compartmental ligand
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Abstract A dinuclear Cu(II) species [Cu2L2(H2O)2(N3)](NO3)2 (L = 2,6-bis(N-ethylpyrrolidine-iminomethyl)-4-methyl-phenolato) where two Cu centers are bridged by phenoxido and μ1,1-azido bridges with Cu-Cu separation of ～3 ? have been synthesized with the view to explore the role of azido bridge on catecholase activity and electrochemical property and the roles of both the bridging groups on magnetic coupling of two copper centers. The complex exhibits excellent catecholase activity in acetonitrile as well as in DMSO medium not only by oxidizing 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very thorny to oxidize, under aerobic conditions and becomes the first example of its own kind. CV study reveals three quasi-reversible reductive couples which are tentatively assigned as Cu2II to CuIICuI and CuICuI reduction followed by reduction of CuICuI complex to Cu0Cu0 species. Variable temperature magnetic study suggests the presence of an antiferromagnetic spin-exchange interaction between Cu(II) ions in the dimer via double bridge where the antiferromagnetic contribution of phenoxido bridge predominates over the ferromagnetic interaction of azido bridge.
- Chakraborty, Prateeti,Majumder, Ishani,Kara, Hulya,Chattopadhyay, Shyamal Kumar,Zangrando, Ennio,Das, Debasis
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supporting information
p. 139 - 145
(2015/08/24)
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- {Cu2+-Co3+-Cu2+} and {Cu2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co3+-Cu+} (3), {Cu+-Fe3+-Cu+} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu+} (3), {Cu+-Fe3+-Cu+} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes.
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2015/04/27)
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- A green mesostructured vanadosilicate catalyst and its unprecedented catalytic activity for the selective synthesis of 2,6-disubstituted p-benzoquinones
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We have developed a green method for the production of 2,6-disubstituted p-benzoquinones (DSBQs) by liquid-phase oxidations of di/tri-substituted phenols using two-dimensional hexagonally thick-walled mesoporous vanadosilicate catalysts. In particular, 2,6-di-tert-butyl-p-benzoquinone was synthesized by the oxidation of 2,6-di-tert-butylphenol, using various reaction parameters, over mesoporous VSBA-15 catalysts synthesized with various vanadium contents. A promising chemical treatment method for the preparation of green mesoporous VSBA-15(5) or W-VSBA-15(5) (W: washed) catalysts was successfully used in the presence of ammonium acetate solution to remove moderately toxic non-framework V2O5 crystallite species from the active surface, and the catalytic activity of the recovered green mesoporous VSBA-15(5) catalyst was determined. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. The combined results show that the green mesoporous VSBA-15(5) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of DSBQs (98-100%), and has unprecedented catalytic activity compared with other mesoporous vanadosilicate catalysts. The Royal Society of Chemistry 2014.
- Selvaraj,Park,Kim
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p. 958 - 966
(2014/01/06)
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- {Cu2+-Co3+-Cu2+} and {Cu 2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co 3+-Cu+} (3), {Cu+-Fe3+-Cu +} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu 2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu +} (3), {Cu+-Fe3+-Cu+} (4), {Cu 2+-Co3+-Cu2+} (5), and {Cu2+-Fe 3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes. Copyright
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2014/05/06)
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- User-friendly synthesis of highly selective and recyclable mesoporous titanium-silicate catalysts for the clean production of substituted p-benzoquinones
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Mesoporous titanium-silicates have been prepared following the evaporation-induced self-assembly (EISA) methodology and characterized by elemental analysis, XRD, N2 adsorption, SEM, DRS UV-Vis and Raman techniques. The use of acetylacetone during synthesis allowed the formation of highly dispersed dimeric and/or small oligomeric Ti species, within the mesostructured silica network, to be realized. The materials catalyse oxidation of alkylsubstituted phenols to corresponding p-benzoquinones with 100% selectivity using the green oxidant-30% aqueous hydrogen peroxide. The titanium-silicates prepared by the convenient and versatile EISA-based procedure reveal the true heterogeneous nature of the catalysis and do not suffer from titanium leaching. They show advantages over other types of mesoporous Ti,Si-catalysts, such as TiO2-SiO2 mixed oxides and grafted Ti/SiO2, in terms of the catalyst stability and reusability.
- Ivanchikova, Irina D.,Kovalev, Mikhail K.,Mel'Gunov, Maxim S.,Shmakov, Alexander N.,Kholdeeva, Oxana A.
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p. 200 - 207
(2014/01/06)
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- Highly selective H2O2-based oxidation of alkylphenols to p-benzoquinones over MIL-125 metal-organic frameworks
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The titanium-based metal-organic framework MIL-125 and its amine-functionalized analog, MIL-125-NH2, have been synthesized and characterized by elemental analysis, XRD, SEM, TEM, N2 adsorption measurements, and spectroscopic techniques, including FTIR, Raman, and DR UV/Vis spectroscopy. Catalytic properties of MIL-125 and MIL-125-NH2 were evaluated in the selective oxidation of two representative alkyl-substituted phenols, 2,3,6-trimethylphenol and 2,6-di-tert-butylphenol, with the clean oxidant H2O2. With both MIL-125 and MIL-125-NH 2, the selectivity toward the corresponding p-benzoquinones was 100 %. Samples of MIL-125 with different sizes of crystallites (0.5, 1.5, and 5 μm) demonstrated similar reaction rates, thus indicating the absence of diffusion limitations. The efficiency of the oxidant utilization and stability of the MIL-125 structure increased upon decreasing the amount of water in the reaction mixture. Even if the structural integrity of MIL-125 was destroyed by the reaction medium, the metal-organic framework acted as a precursor for the highly active, selective, and recyclable catalyst. The MIL-125-derived materials were stable toward titanium leaching, behaved as true heterogeneous catalysts, and could easily be recovered by filtration and reused several times without the loss of the catalytic properties. Copyright
- Ivanchikova, Irina D.,Lee, Ji Sun,Maksimchuk, Nataliya V.,Shmakov, Alexander N.,Chesalov, Yurii A.,Ayupov, Artem B.,Hwang, Young Kyu,Jun, Chul-Ho,Chang, Jong-San,Kholdeeva, Oxana A.
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p. 132 - 139
(2014/01/17)
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- Highly active and green mesostructured titanosilicate catalysts synthesized for selective synthesis of benzoquinones
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Two-dimensional hexagonal thick-walled mesoporous titanosilicate catalysts synthesized using various amounts of titanium were used for the synthesis of 2,3,5-trimethyl-1,4-benzoquinone (TMBO) by liquid-phase oxidation of 2,3,6-trimethylphenol (TMP-OH). These catalysts were also used for the oxidation of di-/tri-substituted phenols to produce 2,6-disubstituted p-benzoquinones (DSBQs). A promising chemical treatment method, for the preparation of green mesoporous TiSBA-15(6) or Washed TiSBA-15(6), was used for removal of non-framework TiO2 nanoparticle species from the active surface, and the catalytic activity of the recovered mesoporous TiSBA-15(6) catalyst has been evaluated. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. Based on the experimental results, it was found that the green mesoporous TiSBA-15(6) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of TMBO and DSBQs and produces >99% TMBO selectivity with 100% TMP-OH conversion at 353 K for 60 min and 90-100% DSBQs selectivity with 83-99% phenol conversion at 330 K for 1-5 h.
- Selvaraj
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p. 2674 - 2684
(2014/07/22)
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