- Oxidation of hindered aniline to iminocyclohexa-2,4-dienone by copper(II) complex of an N-substituted bis-benzimidazolyl ligand
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Copper(II) complex of an N-octylated bis-benzimidazolyl ligand is synthesized and characterized. X-ray diffraction study revealed that copper(II) is in a distorted square-planar environment of two benzimidazolyl imine nitrogens and two nitrato ligands. This complex carries out the oxidation of 2,4,6-tri-tert-butylaniline at room temperature utilizing low amounts of tert-butylhydroperoxide (TBHP) as an alternate source of oxygen. 3,5-Di-tert-butyl-6-iminocyclohexa-2,4-dienone is found to be the major product along with 3,5-di-tert-butylcyclohexa-3,5-diene-1,2-dione. The oxidation products have been isolated and characterized by 1H NMR, 13C NMR and COSY experiments. The catalytic oxidation proceeds via a copper(II)/copper(III) cycle.
- Yadav, Anjana,Mathur, Pavan
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- Quinone Complexes of Palladium: Synthesis and Characterisation of the Dimer 2> (dbsq=3,5-di-t-butyl-1,2-benzosemiquinone) formed by the Reaction between 3,5-Di-t-butyl-1,2-benzoquinone and Palladium(0)
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The dimer 2> has been prepared by treating a Pd0-alkene complex, (dba=dibenzylideneacetone), with 3,5-di-t-butyl-1,2-benzoquinone; it has been characterized spectroscopically and by X-ray crystallography.
- Fox, Glenn A.,Pierpont, Cortlandt G.
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- Extradiol oxidative cleavage of catechols by ferrous and ferric complexes of 1,4,7-triazacyclononane: Insight into the mechanism of the extradiol catechol dioxygenases
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The major oxygenation product of catechol by dioxygen in the presence of FeCl2 or FeCl3, 1,4,7-triazacyclononane (TACN), and pyridine in methanol is the extradiol cleavage product 2-hydroxymuconic semi-aldehyde methyl ester (Lin, G.; Reid, G.; Bugg, T. D. H. J. Chem. Soc. Chem. Commun. 2000, 1119-1120). Under these conditions, extradiol cleavage of a range of 3- and 4-substituted catechols with electron-donating substituents is observed. The reaction shows a preference in selectivity and rate for iron(II) rather than iron(III) for the extradiol cleavage, which parallels the selectivity of the extradiol dioxygenase family. The reaction also shows a high selectivity for the macrocyclic ligand, TACN, over a range of other nitrogen- and oxygen-containing macrocycles. Reaction of anaerobically prepared iron-TACN complexes with dioxygen gave the same product as monitored by UV/vis spectroscopy. KO2 is able to oxidize catechols with both electron-donating and electron-withdrawing substituents, implying a different mechanism for extradiol cleavage. Saturation kinetics were observed for catechols, which fit the Michaelis-Menten equation to give kcatapp = 4.8 × 10-3 s-1 for 3-(2′,3′-dihydroxyphenyl)propionic acid. The reaction was also found to proceed using monosodium catecholate in the absence of pyridine, but with different product ratios, giving insight into the acid/base chemistry of extradiol cleavage. In particular, extradiol cleavage in the presence of iron(II) shows a requirement for a proton donor, implying a role for an acidic group in the extradiol dioxygenase active site.
- Lin,Reid,Bugg
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- Palladium(II)-catalyzed synthesis of 2-alkoxytetrahydrofurans from allylic alcohols and vinyl ethers: Stereospecificity and catalysis
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The reaction of (E)- or (Z)-cinnamyl alcohol and ethyl vinyl ether with a catalyst consisting of Pd(OAc)2, Cu(OAc)2, and catechol (1:1:2) under O2 gives a good yield of (Z)- or (E)-4-benzylidene-2- ethoxytetrahydrofuran, respectively. Similarly, 2-butoxy-4- exomethylenetetrahydrofuran was obtained from allyl alcohol and butyl vinyl ether. In the case of allyl alcohol, however, the catalysis does not proceed well with forming palladium black, if a relatively large amount of Pd(OAc) 2, such as 0.25 mmol to 0.05 mmol, is used even in a lower palladium/substrate ratio, e.g. 1 mol% concentration of the catalyst. Georg Thieme Verlag Stuttgart.
- Kawamura, Yasufumi,Imai, Takuro,Hosokawa, Takahiro
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- A unique series of dinuclear transition metal-polyradical complexes with a m-phenylenediamine spacer and their catalytic reactivity
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A series of dinuclear transition metal complexes with either six or four iminosemiquinone radicals, in which the metal centres are separated by a distance of ～6.8 A, together with their catalytic reactivity is reported.
- Mukherjee, Soumen,Rentschler, Eva,Weyhermueller, Thomas,Wieghardt, Karl,Chaudhuri, Phalguni
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- Solution chemical properties and catecholase-like activity of the copper(II)-Ac-His-His-Gly-His-OH system, a relevant functional model for copper containing oxidases
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The solution chemical properties, Superoxide dismutase and catecholase activity of the copper(II)-Ac-His-HisGly-His-OH (hhgh) complexes were studied to identify functional and structural models of copper-containing oxidases. The solution speciation was de
- Jancso,Paksi,Jakab,Gyurcsik,Rockenbauer,Gajda
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- Design of a mononuclear copper(II)-phenanthroline complex: Catechol oxidation, DNA cleavage and antitumor properties
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A mononuclear copper(II) complex [Cu(phen)(OH2)2(NO3)](NO3) (1) [phen = 1,10-phenanthroline] has been synthesized and structurally characterized by different spectroscopic characterization methods including sing
- Dey, Dhananjay,Das, Subrata,Yadav, Hare Ram,Ranjani, Anandan,Gyathri, Loganathan,Roy, Sanjay,Guin, Partha Sarathi,Dhanasekaran, Dharumadurai,Choudhury, Angshuman Roy,Akbarsha, Mohammad Abdulkader,Biswas, Bhaskar
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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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- A family of vanadate esters of monoionized and diionized aromatic 1,2-diols: Synthesis, structure, and redox activity
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The concerned diols (general abbreviation, H2L) are catechol (H2L1) and its 3,5-Bu2t derivative (H2L2). Esters of the type VO(xsal)(HL), 2, are obtained by reacting H2L with VO(xsal)(H2O) or VO(xsal)(OMe)(HOMe), where xsal2- is the diionized salicylaldimine of glycine (x = g), L-alanine (x = a), or L-valine (x = v). The reaction of VO(acac)2 with H2L and the salicylaldimine (Hpsal) of 2-picolylamine has furnished VO(psal)(L), 3. In the structures of VO-(gsal)(HL1), 2a, and VO(vsal)(HL2), 2f, the HL- ligand is O,O-chelated, the phenolic oxygen lying trans to the oxo oxygen atom. The xsal2- coligand has a folded structure and the conformation of 2f is exclusively endo. In both 2a and 2f the phenolic oxygen atom is strongly hydrogen bonded (O···O, 2.60 A) to a carboxylic oxygen atom of a neighboring molecule. In VO(psal)(L2)·H2O, 3b, the diionized diol is O,O-chelated to the metal and the water molecule is hydrogen bonded to a phenoxidic oxygen atom (O···O, 2.84 A). The C-O and C-C distances in the V(diol) fragment reveal that 2 is a pure catecholate and 3 is a catecholate-semiquinonate hybrid. In solution each ester gives rise to a single 51V NMR signal (no diastereoisomers), which generally shifts downfield with a decrease in the ester LMCT band energy. The V(V)/V(IV) and catecholate-semiquinonate reduction potentials lie near -0.75 and 0.35, and 1.10 and 0.70 V vs SCE for 2 and 3, respectively. Molecular oxygen reacts smoothly with 2 quantitatively furnishing the corresponding o-quinone, and in the presence of H2L the reaction becomes catalytic. In contrast, type 3 esters are inert to oxygen. The initial binding of O2 to 2 is proposed to occur via hydrogen bonding with chelated HL-.
- Baruah, Bharat,Das, Samir,Chakravorty, Animesh
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- Employing Linear Tridentate Ligands with Pyrazole End Groups in Catalytic Tyrosinase Model Chemistry: Does Hemilability Matter?
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Several copper(I) and copper(II) complexes supported by hemilabile bis(pyrazolylmethyl)amine (pzma) ligands are synthesized and structurally characterized. The copper(I) complexes with hexafluoridophosphate or perchlorate anions are employed as catalysts for the tyrosinase-like oxygenation of 2,4-di-tert-butylphenol (DTBP-H). Their activities are comparable to that of [Cu(MeCN)2PMP]PF6 (PMP= pyrazolylmethylpyridine) investigated earlier. In contrast to the copper(I) pzma complexes, their congeners supported by non-hemilabile bis(pyrazolylethyl)amine (pzea) ligands are found to be catalytically inactive.
- Herzigkeit, Benjamin,Jurgeleit, Ramona,Fl?ser, Benedikt M.,Mei?ner, Nadja E.,Engesser, Tobias A.,N?ther, Christian,Tuczek, Felix
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- Oxygen binding and activation by the complexes of PY2- and TPA-appended diphenylglycoluril receptors with copper and other metals
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The copper(I) complexes of diphenylglycoluril basket receptors 1 and 2, appended with bis(2-ethylpyridine)amine (PY2) and tris(2-methylpyridine)amine (TPA), respectively, and their dioxygen adducts were studied with low-temperature UV-vis and X-ray absorption spectroscopy (XAS). The copper(I) complex of 1, [1-Cu(I)2] or 1a, forms a μ-η2:η2 dioxygen complex, whereas the copper(I) complex of 2, [2-Cu(I)2] or 2a, does not form a well defined dioxygen complex, but is oxidized to Cu(II). Dioxygen is bound irreversibly to la and the formed complex is stable over time. The coordination geometries of the above complexes were determined by XAS, which revealed that pyridyl groups and amine N-donors participate in the coordination to Cu(I) ions in the complexes of both receptors. The catalytic activities of various metal complexes of 1 and 2, that were designed as mimics of dinuclear copper enzymes that can activate dioxygen, were investigated. Phenolic substrates that were expected to undergo aromatic hydroxylation, showed oxidative polymerization without insertion of oxygen. The mechanism of this polymerization turns out to be a radical coupling reaction as was established by experiments with the model substrate 2,4-di-tert-butylphenol. In addition to Cu(II), the Mn(III) complex of 1 and the Fe(II) complex of 2 were tested as oxidation catalysts. Oxidation of catechol was observed for the Cu(II) complex of receptor 1 but the other metal complexes did not lead to oxidation. The Royal Society of Chemistry 2005.
- Sprakel, Vera S. I.,Feiters, Martin C.,Meyer-Klaucke, Wolfram,Klopstra, Marten,Brinksma, Jelle,Feringa, Ben L.,Karlin, Kenneth D.,Nolte, Roeland J. M.
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- Unprecedented hetero-geometric discrete copper(II) complexes: Crystal structure and bio-mimicking of Catecholase activity
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An unprecedented solid of coper(II) complexes, [Cu(dpa)2NCS]2[Cu(dpa)2(NCS)2](ClO4)2 (1) [dpa = 2,2′-dipyridylamine; SCN = thiocyanate], has been synthesized and crystallographically charac
- De, Abhranil,Dey, Dhananjay,Yadav, Hare Ram,Maji, Milan,Rane, Vinayak,Kadam,Choudhury, Angshuman Roy,Biswas, Bhaskar
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- Synthesis, crystallographic characterization and catecholase activity of a monocopper(II) and a dimanganese(III) complex with an anionic Schiff base ligand
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The mononuclear [CuII(HL)2] (1) and dinuclear [MnIII2(μ1,3-OAc)2L2] (2) [H2L = N-(2-hydroxypropyl)-3-methoxysalicylaldimine] compounds have been synthesized and charac
- Mitra, Merry,Maji, Ashis Kumar,Ghosh, Barindra Kumar,Kaur, Gurpreet,Choudhury, Anghsuman Roy,Lin, Chia-Her,Ribas, Joan,Ghosh, Rajarshi
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- Efficient oxidation of various phenols catalyzed by Di-μ-hydroxodicopper(II) complexes of a hexapyridine dinucleating ligand
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The di-μ-hydroxodicopper(II) complexes [Cu2(OH)2-(hexpy)](X)2 [X = ClO4 and CF3SO3, hexpy: 1,2-bis[2-di-(2-pyridyl)methyl-6-pyridyl]ethane] efficiently catalyze the oxidation of various phenols with H2O2.
- Kodera, Masahito,Shimakoshi, Hisashi,Tachi, Yoshimitsu,Katayama, Kou,Kano, Koji
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- Dopamine polymerization promoted by a catecholase biomimetic CuII(μ-OH)CuII complex containing a triazine-based ligand
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We describe herein the catecholase-like catalytic activity and dopamine polymerization by using a dinuclear [LCuII(μ-OH)2CuII](ClO4)2 (1) complex where L is the dinucleating triazine-based ligand 6-chloro-N2,N2,N4,N4-tetrakis(pyridin-2-ylmethyl)-1,3,5-triazine-2,4-diamine. The kinetic parameters (kcat = 0.318 s-1, KM = 1.6 × 10-3 mol L-1, and kcat/KM = 198.8 L s-1 mol-1), mechanistic insights into the oxidation of 3,5-di-tert-butyl catechol and early characterization of poly(dopamine) are presented.
- De Oliveira, José A. F.,Da Silva, Marcos P.,De Souza, Bernardo,Camargo, Tiago P.,Szpoganicz, Bruno,Neves, Ademir,Bortoluzzi, Adailton J.
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- Less symmetrical dicopper(II) complexes as catechol oxidase models - An adjacent thioether group increases catecholase activity
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Three new unsymmetrical compartmental dinucleating ligands, 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[{2-(1-piperidyl)ethyl}aminomethyl] phenol (HL1), 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[{2-(morpholin-4-yl) ethyl}aminomethyl]phenol (HL2), and 4-
- Merkel, Michael,Moeller, Niclas,Piacenza, Manuel,Grimme, Stefan,Rompel, Annette,Krebs, Bernt
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- Targeted water soluble copper-tetrazolate complexes: Interactions with biomolecules and catecholase like activities
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Two new mononuclear water soluble copper(ii) complexes, [Cu{(5-pyrazinyl)tetrazolate}2(1,10-phenanthroline)] 1 and [Cu{(5-pyrazinyl)tetrazolate}(1,10-phenanthroline)2](NO3)0.5(N3)0.52, have been synthesized using the metal mediated [2 + 3] cycloaddition reaction between copper bound azide and pyrazinecarbonitrile. The interactions of these copper tetrazolate complexes 1 and 2 with biomolecules like DNA and bovine serum albumin (BSA) are studied and the catecholase like catalytic activity of compound 2 is also explored. Structural determination reveals that both compounds 1 and 2 are octahedral in nature. Screening tests were conducted to quantify the binding ability of complexes (1 and 2) towards DNA and it was revealed that complex 2 has a stronger affinity to bind to CT-DNA. DFT studies indicated that a lower HOMO-LUMO energy gap between the DNA fragment and metal complexes might be the reason for this type of stronger interaction. DNA cleavage activity was explored by gel-electrophoresis and moderate to strong DNA cleavage properties were observed in the presence and absence of co-reagents. Inhibition of cleavage in the presence of sodium azide indicates the propagation of the activity through the production of singlet molecular oxygen. Furthermore enzyme kinetic studies reflect that complex 2 is also effective in mimicking catecholase like activities. An ESI-MS spectral study indicates the probable involvement of dimeric species [(phen)2Cu-(OH)2-Cu(phen)2]2+ in the catalytic cycle.
- Saha, Manideepa,Das, Mriganka,Nasani, Rajendar,Choudhuri, Indrani,Yousufuddin, Muhammed,Nayek, Hari Pada,Shaikh, Mobin M.,Pathak, Biswarup,Mukhopadhyay, Suman
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- Mononuclear copper(ll) aspirinate or salicylate complexes with methylimidazoles as biomimetic catalysts for oxidative dealkylation of a hindered phenol, oxidation of catechol and their superoxide scavenging activities
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Mononuclear complex bis(aspirinato) bis(2-methylimidazole) copper(II), Cu(asp)2 (2-MeIm)2 (1), has been synthesized and spectroscopically characterized. The biomimetic catalytic activities of this complex and our previously characterized complexes, Cu(asp)2 (1,2-MeIm)2 (2), Cu(Hsal)2 (1,2-MeIm)2 (3), and Cu(sal)(2-MeIm)3, (4) [H2sal = salicylic acid and MeIm = methylimidazole], for the oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone and the oxidative dealkylation of 2,4,6-tri-tert- butylphenol to 2,6-di-tert-butyl-1,4-benzoquinone and 4,6-di-tert-butyl-1,2- benzoquinone as the main products are reported. Complexes 1 and 2 are found to be potent SOD mimics and their SOD activities are compared with those obtained previously for complexes 3 and 4.
- Abuhijleh, A. Latif
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- Copper-(I) and -(II) complexes of a macrocycle derived from 2:2 condensation of pyridine-2,6-dicarbaldehyde and 4-azaheptane-1,7-diamine; oxygenation of the copper(I) complex
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A Schiff-base macrocycle was prepared by the 2:2 condensation of pyridine-2,6-dicarbaldehyde and 4-azaheptane-1, 7-diamine. It crystallized in the orthorhombic space group Fdd2 with a = 16.984(8), b = 31.322(12), c = 11.026(6) A and Z = 16. This 20-member
- Rockcliffe, David A.,Martell, Arthur E.,Reibenspies, Joseph H.
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- Catalytic and regiospecific extradiol cleavage of catechol by a biomimetic iron complex
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An iron(iii)-catecholate complex of a facial tridentate ligand reacts with dioxygen in the presence of ammonium acetate-acetic acid buffer to cleave the aromatic C-C bond of 3,5-di-tert-butylcatechol regiospecifically resulting in the formation of an extradiol product with multiple turnovers.
- Chatterjee, Sayanti,Sheet, Debobrata,Paine, Tapan Kanti
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- Catecholase activity of a copper(II) complex with a macrocyclic ligand: Unraveling catalytic mechanisms
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We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.14,7/su
- Koval, Iryna A.,Selmeczi, Katalin,Belle, Catherine,Philouze, Christian,Saint-Aman, Eric,Gautier-Luneau, Isabelle,Schuitema, Anna Maria,Van Vliet, Marcel,Gamez, Patrick,Roubeau, Olivier,Lueken, Matthias,Krebs, Bernt,Lutz, Martin,Spek, Anthony L.,Pierre, Jean-Louis,Reedijk, Jan
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- Biocatalysis, DNA–protein interactions, cytotoxicity and molecular docking of Cu(II), Ni(II), Zn(II) and V(IV) Schiff base complexes
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Four mononuclear metal complexes (Cu(II) (1), Ni(II) (2), Zn(II) (3) and V(IV) (4)) were synthesized using the Schiff base ligand 2,2′-{cyclohexane-1,2-diylbis[nitrilo(1E)eth-1-yl-1-ylidine]}bis[5-(prop-2-yn-1-yloxy)phenol] and structurally characterized
- Balakrishnan, Chithiraivel,Theetharappan,Kowsalya,Natarajan, Satheesh,Neelakantan,Mariappan
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- Studies in the oxidative ring-opening of catechols and o-benzoquinones. Lead tetraacetate versus the copper(I) chloride/pyridine/methanol system
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Lead tetraacetate oxidative ring-opening of a series of substituted catechols provides the corresponding substituted cis, cis-2,4-diene-1,6- dioates (1-10) in fair to good yields. A number of improvements on Wiessler's procedure for this reaction are repo
- Walsh, James G.,Furlong, Patrick J.,Byrne, Louise A.,Gilheany, Declan G.
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- EFFECTS OF SUPPORTS AND PREPARATION METHODS OF HETEROGENIZED FeCl3 CATALYSTS IN THE OXIDATION OF 3,5-DI-TERT-BUTYLCATECHOL IN APROTIC SOLVENTS
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FeCl3-catalyzed oxidation of 3,5-di-t butylcatechol (DTBC) to 3,5-di-t-butyl-o-benzoquinone (DTBQ) by molecular oxygen in tetrahydrofuran (THF) was significantly promoted by addition of SiO2, γ-Al2O3, and active carbon in situ.Activity of catalysts prepar
- Funabiki, Takuzo,Sugimoto, Tsunemi,Yoshida, Satihiro
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- Unique Copper-Organic Networks Self-Assembled from 1,3,5-Triaza-7-Phosphaadamantane and Its Oxide: Synthesis, Structural Features, and Magnetic and Catalytic Properties
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Three new coordination compounds, namely, a zero-dimensonal dicopper(II) complex [Cu2(μ-MeCOO)4(MeOH)2](PTA = O)2 (1), a three-dimensional (3D) copper(II)-organic framework [Cu3(μ-MeCOO)6(μ3-PTA=O)]n·3.5nMeCN (2), and a mixed-valence copper(I/II) one-dimensional (1D) coordination polymer [Cu3(μ-MeCOO)4(MeCOO)(μ-PTA)2(PTA)]n (3), were self-assembled from copper(II) acetate and cage-like aminophosphine 1,3,5-triaza-7-phosphaadamantane (PTA) or its P-oxide (PTA=O). The obtained products were isolated as air-stable crystalline solids and characterized by IR and electron paramagnetic resonance spectroscopy, thermogravimetric and elemental analysis, as well as single crystal X-ray diffraction. Although all compounds bear dicopper(II) paddle-wheel tetraacetate [Cu2(μ-MeCOO)4] blocks, they are arranged into very distinct metal-organic architectures. The structure of 2 reveals an intricate 3D metal-organic framework (MOF) driven by the μ3-PTA=O spacers acting in an unusual N,N,O-tridentate mode, whereas the compound 3 discloses an infinite 1D wave-like metal-organic chain with the dicopper(II) [Cu2(μ-MeCOO)4] and monocopper(I) [Cu(PTA)(MeCOO)] blocks being interlinked by the μ-PTA linkers acting in an N,P-bidentate mode. Topological analysis of underlying nets was performed, revealing a decorated uninodal 3-connected framework with the ths topology in 2 and a uninodal 2-connected chain with the 2C1 topology in 3. Compounds 2 and 3 broaden a still very limited family of MOFs or coordination polymers assembled from PTA or its P-oxide building blocks, also showing that PTA can be applied for the generation of unusual mixed-valence copper(I/II) derivatives. Besides, 2 represents the first example of a copper-containing 3D MOF that is driven by PTA=O or any other PTA-derived block. Magnetic properties of 1-3 were investigated, modeled, and discussed in detail, resulting in the exchange coupling parameters (J = -310, -320 cm-1) that indicate a strong antiferromagnetic interaction within the dicopper(II) paddle-wheel blocks. Moreover, compounds 1 and 2 show a notable catecholase activity in the aerobic oxidation of 3,5-di-tert-butyl-catechol to 3,5-di-tert-butyl-o-benzoquinone; turnover frequency values of up to 81 min-1 were attained.
- ?liwa, Ewelina I.,Nesterov, Dmytro S.,K?ak, Julia,Jakimowicz, Piotr,Kirillov, Alexander M.,Smoleński, Piotr
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- The "corey's" reagent, 3,5-di-tert-butyl-1,2-benzoquinone, as a modifying agent in the synthesis of fluorescent and double-headed nucleosides
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A new method for the synthesis of fluorescent nucleosides has been developed. It has been shown that a reaction of benzoquinone with aminopropenyl group at C-5-position of 2'-deoxyuridine or 2'-deoxycytidine and aminopropynyl group at the C-7-position of
- Timoshchuk, Victor A.,Hogrefe, Richard I.
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- Synthesis, crystal structure and catecholase activity of a vanadium(V) Schiff base complex
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An X-ray structurally characterized vanadium(V) complex, [VO2(L-H)] [L-H = H2L derived ligand (H2L = N,N′-(salicyaldimine)-1,3-diaminopropan-2-ol], was found to behave as an effective catalyst towards the oxidation of 3,5-
- Mal, Sunit Kumar,Mitra, Merry,Yadav, Hare Ram,Purohit, Chandra Shekhar,Choudhury, Angshuman Roy,Ghosh, Rajarshi
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- Synthesis, crystal structure and catecholase activity of a Ni(II) complex derived from a tetradentate Schiff base ligand
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A new nickel(II) complex [Ni(L)] (1) [H2L = 1,1′-(1E,1′E)-(propane-1,3-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol] was synthesized and X-ray crystallographically characterized. 1 crystallizes
- Basu, Pradipta Kumar,Mitra, Merry,Ghosh, Amrita,Thander, Latibuddin,Lin, Chia -Her,Ghosh, Rajarshi
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- Zeolite framework stabilized copper complex inspired by the 2-His-1-carboxylate facial triad motif yielding oxidation catalysts
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The stabilization of a mononuclear copper(II) complex with one MIm 2Pr ligand [MIm2Pr = 3,3-bis(1-methylimidazol-2-yl) propionate] in the supercages of zeolite Y was attempted, and the resulting materials were tested for their activi
- Kervinen, Kaisa,Bruijnincx, Pieter C. A.,Beale, Andrew M.,Mesu, J. Gerbrand,Van Koten, Gerard,Klein Gebbink, Robertus J. M.,Weckhuysen, Bert M.
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- Copper(II) complexes of aminocarbohydrate β-ketoenaminic ligands: Efficient catalysts in catechol oxidation
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Copper(II) complexes of tridentate dianionic β-ketoenaminic ligands derived from differently functionalized amino-deoxyglucoses were synthesized and characterized with respect to their structural, spectroscopic, and catalytic properties. The (probably dim
- Wegner, Rainer,Gottschaldt, Michael,Goerls, Helmar,Jaeger, Ernst-G.,Klemm, Dieter
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- Catecholase activity of a structurally characterized dinuclear iron(III) complex [FeIII2(L)2] [H3L = N,N′-bis(3-methoxysalicylaldimine)-1,3-diaminopropan-2-ol]
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A dinuclear Fe(III) complex, [FeIII2(L)2] (1) [H3L = N,N′-bis(3-methoxysalicylaldimine)-1,3- diaminopropan-2-ol], has been synthesized and characterized using microanalysis, spectroscopy and X-ray crystallography. Structural analysis reveals a pentadentate chelation behaviour of the trianionic ligand H3L, having a distorted octahedral coordination environment around each iron(III) center with an FeN2O4 chromophore. Variable-temperature magnetic susceptibility measurements of 1 indicate an antiferromagnetic interaction between the two iron(III) centers, coupled with J = -28.5. 1 behaves as an effective catalyst towards the oxidation of 3,5-di-tert-butylcatechol in different solvents, viz. methanol, dichloromethane and acetonitrile, to its corresponding quinone derivative in aerial oxygen. The reaction follows Michaelis-Menten enzymatic reaction kinetics with turnover numbers (K cat) 7.51 × 102, 1.69 × 103 and 1.23 × 103 h-1 in methanol, dichloromethane and acetonitrile, respectively.
- Mitra, Merry,Maji, Ashis Kumar,Ghosh, Barindra Kumar,Raghavaiah, Pallepogu,Ribas, Joan,Ghosh, Rajarshi
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- Reaction between Various Copper(II) Complexes and Ascorbic Acid or 3,5-Di-t-butylcatechol
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The electron transfer reactions between various copper(II) complexes and two-electron donors, such as ascorbic acid and 3,5-di-t-butylcatechol, were investigated.Mononuclear copper(II) complexes with a distorted tetrahedral and a trigonal bipyramidal stru
- Oishi, Naoyasu,Nishida, Yuzo,Ida, Kazuhiko,Kida, Sigeo
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- Antibacterial and catecholase activities of Co(III) and Ni(II) Schiff base complexes
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X-ray structural analyses of two newly synthesized Schiff base-complexes, [Co(L)3] (1) and [Ni(L)2] (2) [HL = 2-((E)-(2-pyridine-2-pyridin-2-ylthio)ethylimino)methyl)phenol], reveal the bidentate chelation behavior of the ligand HL w
- Ghosh, Ayon Kanti,Mitra, Merry,Fathima, Aafreen,Yadav, Hareram,Roy Choudhury, Angshuman,Nair, Balachandran Unni,Ghosh, Rajarshi
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- Catalytic activity of a benzoyl hydrazone based dimeric dicopper(II) complex in catechol and alcohol oxidation reactions
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The benzoyl hydrazone based dimeric dicopper(II) complex [Cu2(R)(CH3O)(NO3)]2(CH3O)2 (R-Cu2+), recently reported by us, catalyzes the aerobic oxidation of catechols (catechol (S1), 3,5-ditertiarybutylcatechol (S2) and 3-nitrocatechol (S3)) to the corresponding quinones (catecholase like activity), as shown by UV-Vis absorption spectroscopy in methanol/HEPES buffer (pH 8.2) medium at 25 °C. The highest activity is observed for the substituted catechol (S2) with the electron donor tertiary butyl group, resulting in a turnover frequency (TOF) value of 1.13 × 103 h-1. The complex R-Cu2+ also exhibits a good catalytic activity in the oxidation (without added solvent) of 1-phenylethanol to acetophenone by ButOOH under low power (10 W) microwave (MW) irradiation.
- Anbu, Sellamuthu,Alegria, Elisabete C.B.A.,Pombeiro, Armando J.L.
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- RUTHENIUM-CATALYZED OXIDATION OF ALCOHOLS AND CATECHOLS USING t-BUTYL HYDROPEROXIDE
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Ruthenium complexes catalyze the oxidation of alcohols to the corresponding ketones or aldehydes when t-BuOOH (70percent aq.) is used as an oxidant.The reactions proceed at room temparature to give the products in excellent to fairly good yields.Among the
- Tsuji, Yasushi,Ohta, Tetsuo,Ido, Toyoyuki,Minbu, Hideshi,Watanabe, Yoshihisa
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- A new family of multinuclear mixed-ligand copper(II) clusters: Crystal structures, magnetic properties and catecholase-like activity
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In this work we report a family of mixed-ligand copper(II) clusters obtained with different nuclearities: [Cu3(μ-OH)(μ-dppi)3(μ-hfac)3] (1), [Cu4(μ-dppi)4(Hdppi)2(hfac)4] (2), [Cu5(μ-O)2(μ-dppi)(μ-Hdppi)2(μ-hfac)3(hfac)2] (3) and [Cu6(μ-O)2(μ-dppi)2(μ-Hdppi)(μ-hfac)6] (4), where hfac?=?hexafluoroacetylacetonate, dppi?=?diphenylphosphinate and Hdppi?=?diphenylphosphinic acid. Complexes 3 and 4 are the first examples of copper(II) clusters containing a μ-oxo oxygen atom and hfac as bridging ligands. The magnetic properties of all compounds showed predominant antiferromagnetic interactions and the magnetic coupling constants were evaluated using an isotropic exchange model based on the spin topology. A spin frustration phenomena was observed for the equilateral cyclic trinuclear complex (1), thus an antisymmetric exchange term was also considered to fit the experimental magnetic data. The obtained J values are in the range from ?89?cm?1to 1.7?cm?1and were interpreted based on structural features. The electrochemical properties and catalytic activity of complexes 1 and 2 were investigated and compared with the [Cu(hfac)2] precursor. Catecholase-like activity of copper(II) complexes via oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) was performed.
- Calancea, Sergiu,Reis, Samira G.,Guedes, Guilherme P.,Cassaro, Rafael A. All?o,Semaan, Felipe,López-Ortiz, Fernando,Vaz, Maria G.F.
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- Mononuclear Iron(III) Complexes as Functional Models of Catechol Oxidases and Catalases
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Mononuclear amino triphenolate iron(III) complexes have been synthesized and characterized (UV/Vis spectroscopy, cyclic voltammetry, ESI-MS, 1H NMR spectroscopy, X-ray diffraction). These complexes act as biomimetic catalysts promoting the aero
- Badetti, Elena,Gjoka, Blerina,Nagy, Eszter Mrta,Bernardinelli, Grald,Kündig, Peter E.,Zonta, Cristiano,Licini, Giulia
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- Oxygenative aromatic ring cleavage of 2-aminophenol with dioxygen catalyzed by a nonheme iron complex: Catalytic functional model of 2-aminophenol dioxygenases
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2-Aminophenol dioxygenases catalyze the oxidative ring cleavage of 2-aminophenol to 2-picolinic acid using O2 as the oxidant. Inspired by the reaction catalyzed by these nonheme iron enzymes, a biomimetic iron(III)-2-amidophenolate complex, [(tBu-LMe)FeIII(4,6-di-tBu-AP)](ClO4) (1a) of a facial tridentate ligand (tBu-LMe = 1-[bis(6-methyl-pyridin-2-yl)-methyl]-3-tert-butyl-urea and 4,6-di-tBu-H2AP = 2-amino-4,6-di-tert-butylphenol) bearing a urea group have been isolated. The complex reacts with O2 to cleave the C-C bond of 4,6-di-tBu-AP regioselectively and catalytically to afford 4,6-di-tert-butyl-2-picolinic acid. An iron(II)-chloro complex [(tBu-LMe)FeIICl2(MeOH)] (1) of the same ligand also cleaves the aromatic ring of 4,6-di-tBu-AP catalytically in the reaction with O2. To assess the effect of urea group on the ring cleavage reaction of 2-aminophenol, two iron complexes, [(BA-LMe)2FeII2Cl4] (2) and [(BA-LMe)FeIII(4,6-di-tBu-AP)](ClO4) (2a), of a tridentate ligand devoid of urea group (BA-LMe = benzyl-[bis(6-methyl-pyridin-2-yl)-methyl]-amine) have been isolated and characterized. Although the iron complexes (1 and 1a) of the ligand with urea group display catalytic reaction, the iron complexes (2 and 2a) of the ligand without urea group do not exhibit catalytic aromatic ring fission reactivity. The results support the role of urea group in directing the catalytic reactivity exhibited by 1 and 1a.
- Chatterjee, Sayanti,Paine, Tapan Kanti
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- A chromophore-supported structural and functional model of dinuclear copper enzymes, for facilitating mechanism of action studies
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Type III dicopper centres are the heart of the reactive sites of enzymes that catalyze the oxidation of catechols. Numerous synthetic model complexes have been prepared to uncover the fundamental chemistry involved in these processes, but progress is still lagging much behind that for heme enzymes. One reason is that the latter gain very much from the informative spectroscopic features of their porphyrin-based metal-chelating ligand. We now introduce sapphyrin-chelated dicopper complexes and show that they may be isolated in different oxidation states and coordination geometries, with distinctive colors and electronic spectra due to the heme-like ligands. The dicopper(i) complex1-Cu2was characterized by1H and19F NMR spectroscopy of the metal-chelating sapphyrin, the oxygenated dicopper(ii) complex1-Cu2O2by EPR, and crystallographic data was obtained for the tetracopper(ii)-bis-sapphyrin complex[1-Cu2O2]2. This uncovered a non-heme [Cu4(OH)4]4?cluster, held together with the aid of two sapphyrin ligands, with structural features reminiscent of those of catechol oxidase. Biomimetic activity was demonstrated by the1-Cu2O2catalyzed aerobic oxidation of catechol to quinone; the sapphyrin ligand aided very much in gaining information about reactive intermediates and the rate-limiting step of the reaction.
- Chen, Qiu-Cheng,Fridman, Natalia,Gross, Zeev,Tumanskii, Boris
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p. 12445 - 12450
(2021/10/08)
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- Metal-Free Oxidative Condensation of Catechols, Aldehydes and NH4OAc towards Benzoxazoles
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Benzoxazoles extensively exist in biologically active compounds, natural products, pharmaceuticals and functional materials. Thus, facile and green synthesis of such valuable compounds from easily available substrates will make a contribution to drug, material, and fine chemistry. A method for the synthesis of benzoxazoles from catechols, aldehydes and ammonium acetate is developed using NaIO4 as oxidant under metal- and additive-free conditions. A broad range of benzoxazoles including some fluorescent whitening agents, JTP-426467 and tafamidis analogues are synthesized in 56–95% yields with outstanding functional group tolerance. Mechanistic investigations suggest that an interesting o-iminocyclohexa-diene alcohol intermediate is involved in the reaction. These salient features of the protocol make it an alternative for the synthesis of benzoxazoles. (Figure presented.).
- Dong, Jianyu,Geng, Furong,Su, Lebin,Wu, Shaofeng,Yin, Shuang-Feng,Zhou, Dan,Zhou, Yongbo
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p. 3607 - 3614
(2021/07/28)
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- Vanadium aminophenolates in catechol oxidation: Conformity with Finke's common catalyst hypothesis
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Six known aminophenolate vanadium complexes V1-V6 were examined in 3,5-di-tert-butylcatechol (1, 3,5-DTBC) oxidation. From the complexes V1-V5 have been previously shown to demonstrate catechol oxidase (catecholase) like behavior, catalytically oxidizing 1 to 3,5-di-tert-butyl-1,2-benzoquinone (2, 3,5-DTBQ). A critical re-evaluation of V1-V5, including V6 not assessed earlier, in the aerobic oxidation of 1 has revealed that several catechol dioxygenase products are obtained in addition to 2, which is produced partly by autoxidation. Mechanistic investigations into the V1-V6 catalyzed oxidation of 1 by EPR, negative mode ESI-MS and 51V NMR, in addition to semi-quantitative product distribution analyses with GC and column chromatography afford compelling evidence in support of the "common catalyst hypothesis"earlier proposed by Finke and co-workers. During the reaction, V1-V6 are partially converted in situ by H2O2 assisted leaching to vanadium catecholate complexes [V(3,5-DTBC)2(3,5-DTBSQ)] and [VO(3,5-DTBC)(3,5-DTBSQ)], where 3,5-DTBSQ = 3,5-di-tert-butyl-1,2-semiquinone, the latter of which has been implicated as the common true active catalyst in catechol dioxygenation as per the common catalyst hypothesis. The results herein suggest that vanadium aminophenolate complexes are sensitive to H2O2 mediated leaching in the presence of strong σ and π donating ligands such as 1 and 2. Furthermore, based on these results, the use of vanadium aminophenolate complexes as catechol oxidase mimics is not as warranted as previously understood.
- Salonen, Pasi,Savela, Risto,Peuronen, Anssi,Lehtonen, Ari
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supporting information
p. 6088 - 6099
(2021/05/19)
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- Solid-Phase ortho-Hydroxylation of 2,4-Di-tert-butylphenol and Its Derivatives
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Abstract: Direct phenol–catechol conversion has been realized as a result of the solid-phase reaction of 2,4-di-tert-butylphenol with cuprous oxide under high pressure and shear deformation on the Bridgman anvils. The yield of 3,5-di-tert-butylcatechol in this reaction was about 85%. When cupric oxide was used in the solid-phase process, oxidative coupling of the starting phenol took place, resulting in quantitative formation of tetra-tert-butyl-ortho-bisphenol. The reaction of 6-substituted derivatives of 2,4-di-tert-butylphenol with cuprous oxide was used as an example to demonstrate the possibility of substitutive ortho-hydroxylation yielding 7–20% of pyrocatechols.
- Kurkovskaya, L. N.,Ovsyannikova, M. N.,Vol’eva, V. B.,Zhorin, V. A.
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p. 350 - 352
(2020/04/21)
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- Study of the Oxidative Cleavage Proposed in the Biogenesis of Transtaganolides/Basiliolides: Pyran-2-one Aromaticity-Mediated Regioselective Control and Biogenetic Implications
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The synthetic feasibility of the oxidative cleavage: epoxidation of 7-O-geranylscopoletin followed by electrocyclic ring-opening, proposed in the biogenesis of transtaganolides/basiliolides is studied. Unlike the proposed pericyclic reactions, this pathway has not yet been addressed. Three synthetic strategies have been tested consisting of: i) Baeyer–Villiger oxidation of p-quinoids, ii) hydrolysis of quinone monoketals, or iii) direct fragmentation by using oxygen donors. Oxidation of the benzene ring of hydroxylated coumarins has been achieved using peroxyacids, but cleavage took place between undesired positions. The aromaticity conservation of the pyran-2-one cycle during oxidation is the controlling factor of these observed regioselectivities. The use of a 4,5-dihydroxy-2-methoxycinnamate model, in which the pyran-2-one ring does not exert influence on oxidation, has allowed the design of a synthetic sequence toward an analogue of the natural pyran-2-one isolated from Thapsia transtagana, key in the biogenesis. Mechanistic proposals for the obtained results as well as their biogenetic implications are raised.
- álvarez, José María,Jorge, Zacarías D.,Massanet, Guillermo M.
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- Thiosemicarbazone(s)-anchored water soluble mono- A nd bimetallic Cu(ii) complexes: Enzyme-like activities, biomolecular interactions, anticancer property and real-time live cytotoxicity
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The reactions of CuCl2·2H2O with chromone thiosemicarbazone ligands containing a-H or-CH3 substituent on terminal N yielded monometallic Cu(ii) complexes [Cu(HL1)Cl2] (1) and [Cu(HL2)Cl2] (2), whereas bimetallic Cu(ii) complexes [Cu(μ-Cl)(HL3)]2Cl2 (3), [Cu(μ-Cl)(HL4)]2Cl2 (4) and [Cu(μ-Cl)(L5)]2 (5) were obtained when a-C2H5,-C6H11 or-C6H5 substituent was present, respectively, in the ligands. The complexes were characterized using elemental analyses, UV-Vis, FT-IR, EPR, mass and TGA studies. The structures of neutral monometallic and dicationic bimetallic complexes were confirmed by single crystal X-ray diffraction, and they exhibited a distorted square pyramidal geometry around Cu(ii) ions. The catecholase-mimicking activity of complexes 1-5 was examined spectrophotometrically, and the results revealed that all the complexes except 5 had the ability to oxidize 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) under aerobic conditions with moderate turnover numbers. In order to find the possible complex-substrate intermediates, a mass spectrometry study was carried out for complexes 1-4 in the presence of 3,5-DTBC. The phosphatase-like activity of 1-5 was also investigated using 4-nitrophenylphosphate (4-NPP) as a model substrate. All the complexes exhibited excellent phosphatase activity in DMF-H2O medium. The complexes displayed significant biomolecular interactions and antioxidant potential. Complex 3 showed good interaction with apoptotic CASP3 protein, VEGFR2 and PIM-1 kinase receptors as revealed by a molecular docking study. Complexes (3-5) exhibited promising cytotoxicity against HeLa-cervical cancer cells with IC50 values of 2.24 (3), 2.25 (4) and 3.77 (5) μM, respectively, and showed a two-fold higher activity than cisplatin. The active complex 3 showed complete inhibition of colony formation at 10 μM concentration. In addition, the acridine orange (AO)/ethidium bromide (EB) staining and real-time live cell imaging results confirmed that complex 3 induced cell death in HeLa cells.
- Awale, Suresh,Balakrishnan, Nithya,Bhuvanesh, Nattamai,Dhanabalan, Ananda Krishnan,Dibwe, Dya Fita,Haribabu, Jebiti,Karvembu, Ramasamy,Sun, Sijia,Swaminathan, Srividya
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p. 9411 - 9424
(2020/09/09)
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- Oxidovanadium (V and IV) complexes incorporating coumarin based O^N^O ligand: Synthesis, structure and catalytic activities
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The tridentate ligand H2L1, [(E)-7-Hydroxy-8-[(2-hydroxy-phenylimino)-methyl]-4-methyl-chromen-2-one] has been used in the present work towards the synthesis of mononuclear oxidovanadium complexes. Three mononuclear complexes [VOL1(OMe)(MeOH)], 1; [VO(L1)(8-Hq)], 2 and [VO(L1)(1,10-phen)], 3 have been successfully synthesized with high yields by reacting [VO(acac)2] with H2L1 in 1:1 ratio in methanol under refluxing conditions where 8-hydroxyquinoline and 1,10-phenanthroline were used as co-ligands in the synthesis of complex 2 and 3. X-ray crystallographic studies reveal that in all the complexes synthesized in the present study, the ligand H2L1 binds as O^N^O coordinating ligand. The synthesized complexes were well characterized by using UV–Vis, IR, NMR and Mass spectral techniques. The physiochemical properties have been well interpreted by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The synthesized complexes were established to show some distinctive properties e.g. oxidative bromination of aromatic aldehyde with high conversion rate and enhanced selectivity as well as high TON and TOF. The above properties were all well matched and demonstrated by using UV–visible and fluorescence as well as quenching studies. Complex 1 reacts with 3,5-DTBC catalytically in presence of molecular oxygen to generate corresponding ortho-benzoquinone.
- Majumder, Mitali,Krishna Rajak, Kajal
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- Bioinspired Mo, W and V complexes bearing a highly hydroxyl-functionalized Schiff base ligand
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A series of bioinspired dioxidomolybdenum(VI), dioxidotungsten(VI) and oxidovanadium(V) complexes [MoO2(H2LSaltris)], [WO2(H2LSaltris)] and [VO(HLSaltris)]2 were prepared by the reaction of a hydroxyl-rich Schiff base proligand N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-3,5-di-tert-butylsalicylaldimine (H4LSaltris) with metal precursors in methanol solutions. Molybdenum and tungsten complexes crystallize as mononuclear molecules, whereas the vanadium complex forms dinuclear units. From the complexes, [VO(HLSaltris)]2 shows activity in the oxidation of 4-tert-butylcatechol and 3,5-di-tert-butylcatechol, mimicking the action of the dicopper enzyme catechol oxidase.
- Salonen, Pasi,Peuronen, Anssi,Lehtonen, Ari
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supporting information
(2020/01/21)
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- Facile synthesis of a new Cu(ii) complex with an unsymmetrical ligand and its use as an O3 donor metalloligand in the synthesis of Cu(ii)-Mn(ii) complexes: Structures, magnetic properties, and catalytic oxidase activities
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A new, facile Cu(ii) template method has been employed for the unsymmetrical dicondensation of 1,2-ethylenediamine with salicylaldehyde and o-vanillin. The mononuclear complex, [CuL] (1), thus obtained, has been used as an O3 donor metalloligand for the synthesis of four new Cu(ii)-Mn(ii) complexes, [(CuL)MnCl2] (2), [(CuL)Mn(NO3)2(CH3OH)]n (3), {[(CuL)Mn(benz)(H2O)]2·(CuL)2(ClO4)2} (4) and [(CuL)Mn(benz)Cl]2 (5) (where benz = benzoate). Single-crystal structural analyses reveal that 2 is a dinuclear complex while complex 3 is polymeric with a repeating dinuclear [(CuL)Mn(NO3)2(CH3OH)] unit, linked via the nitrate ion. Both 4 and 5 are discrete tetranuclear complexes, where the dinuclear units [(CuL)Mn(benz)(H2O)] and [(CuL)Mn(benz)Cl] are connected by double benzoate and double chloride bridges, respectively. In complex 4, two monomeric [CuL] units are cocrystallized with the tetranuclear complex. An important difference in the structure of 4 from the other three complexes is that one solvent water molecule is coordinated to each Mn(ii) ion, which makes complex 4 catalytically very active towards mimicking catecholase and phenoxazinone synthase-like oxidation reactions. The turnover numbers (kcat) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 399 h-1 and 230 h-1, respectively. The evidence of the intermediate species in the mass spectra indicates possible heterometallic cooperation where the Mn(ii) center helps in substrate binding and Cu(ii) participates in the oxidation reactions with molecular oxygen. Cyclic voltammetry measurements suggest the reduction of Cu(ii) to Cu(i) during the catalytic process. Temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 2-5 are antiferromagnetically coupled with the exchange coupling constants (J) of J = -13.5 cm-1 and J = -13.5 cm-1 for 2 and 3, respectively, J1 = -12.6 cm-1 and J2 = -1.20 cm-1 for complex 4 and J1 = -13.24 cm-1 and J2 = 0.36 cm-1 for complex 5 as is expected from the Cu-O-Mn bridging angles.
- Dutta, Sabarni,Mayans, Júlia,Ghosh, Ashutosh
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p. 1276 - 1291
(2020/02/13)
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- Probing the Proton-Coupled Electron-Transfer (PCET) Reactivity of a Cross-Conjugated Cruciform Chromophore by Redox-State-Dependent Fluorescence
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Proton-coupled electron transfer (PCET) reactions are of great importance in synthetic chemistry and in biology, but the acquisition of kinetic information for these reactions is often difficult. Herein, we report the synthesis of a new PCET reagent, showing redox-state dependent fluorescence, by merging the concept of cross-conjugated cruciform chromophores with the strategy of imposing redox activity and Br?nsted basicity to aromatic compounds by substitution with guanidino groups. The compound is isolated and characterized in all stable states—reduced, twofold and fourfold protonated and twofold oxidized—and then applied in PCET reactions by using its redox-state dependent fluorescence signal for kinetic measurements.
- Wagner, Conrad,Hübner, Olaf,Kaifer, Elisabeth,Himmel, Hans-J?rg
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supporting information
p. 3781 - 3785
(2019/02/20)
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- Activated Carbon-Promoted Dehydrogenation of Hydroquinones to Benzoquinones, Naphthoquinones, and Anthraquinones under Molecular Oxygen Atmosphere
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We found that the activated carbon-molecular oxygen system promotes the conversion of hydroquinones to benzoquinones, naphthoquinones, and anthraquinones, which are often found in natural products and pharmaceuticals. In particular, the one-pot synthesis of naphthoquinones and anthraquinones involving a Diels-Alder reaction is a useful protocol for this purpose.
- Kim, Sanghun,Matsubara, Ryosuke,Hayashi, Masahiko
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p. 2997 - 3003
(2019/03/08)
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- A Stereoselective Tyrosinase Model Compound Derived from an m-Xylyl- l -histidine Ligand
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The aim of mimicking enzyme activity represents an important motivation for the development of new catalysts. A challenging objective is the development of chiral complexes for bioinspired enantioselective oxidation reactions. Herein, we report a new chiral dinuclear copper(II) complex based on a m-xylyl-bis(histidine) ligand (mXHI) as a biomimetic catalyst for tyrosinase and catechol oxidase. The new ligand improves a previous system also containing two tridentate N3 units derived from l-histidine that were connected by a short, rigid ethanediamine bridge. In mXHI the bridge is provided by the more extended m-xylyl moiety. The dicopper(II) complex [Cu2(mXHI)]4+ was studied as a catalyst for stereoselective oxidations of enantiomeric couples of chiral catechols of biological interest (L/D-dopa, L/D-dopa methyl ester, and (R/S)-norepinephrine), showing excellent discrimination capability, particularly for the methyl esters of dopa enantiomers. The catechol oxidation was studied in acetate buffer as slightly acidic medium, and a role of acetate as bridging ligand between the two coppers, preorganizing the dinuclear center in a more catalytic efficient structure, could be established. The oxidation of β-naphthol and 3,5-ditertbutylphenol was studied as a model monophenolase reaction. The oxidation proceeds stoichiometrically, and the partial incorporation of 18O into β-naphthol when the reaction was performed using 18O2 suggests the existence of two competitive reaction pathways, a genuine monooxygenase mechanism and a radical pathway. However, the more challenging reaction on derivatives of l-/d-tyrosine did not lead to the desired monooxygenase product but only to products of radical oxidation. Complex [Cu2(mXHI)]4+ was also used for the catalytic sulfoxidation of thioanisole in the presence of hydroxylamine as cosubstrate, in a preliminary attempt to model the reaction of external monooxygenases. The reaction proceeds with 25 turnovers, but the enantiomeric excess of sulfoxide was modest.
- Presti, Eliana Lo,Perrone, Maria L.,Santagostini, Laura,Casella, Luigi,Monzani, Enrico
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supporting information
p. 7335 - 7344
(2019/06/04)
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- Thioether sulfur-bound [Cu2] complexes showing catechol oxidase activity and DNA cleaving behaviour
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Rational ligand design approaches allowed {Cu2(μ-OH/OMe)} cores to be accommodated within μ-phenoxido bis(tetradentate) and μ-phenoxido bis(tridentate) ligands having thioether donors. The complexes [Cu2(μ-H2L1)(μ-OH)](ClO4)2·2H2O (1), [Cu2(μ-L2)(μ-OH)(OH2)](ClO4)2 (2a) and [Cu2(μ-L2)(μ-OCH3)(OH2)](ClO4)2 (2b) were obtained from an N2O3S2 donor set bearing the H3L1 ligand (2,6-bis-[{2-(2-hydroxyethylthio)ethylimino}methyl]-4-methylphenol) and N2OS2 donor set containing the HL2 ligand (4-methyl-2,6-bis-[{2-(methylthio)phenylimino}methyl]phenol) without showing double phenoxido bridging or any type of preformed inter-fragment aggregation. Previously, we showed that H3L (2,6-bis[((2-(2-hydroxyethoxy)ethyl)imino)methyl]-4-methylphenol), the ether analogue of H3L1, in the presence of carboxylate anions, was responsible for the self-aggregation of preformed {Cu2} fragments and gave two types of [Cu4] complexes comprising [Cu4O] and [Cu4(OH)2] cores (T. S. Mahapatra, A. Bauzá, D. Dutta, S. Mishra, A. Frontera and D. Ray, ChemistrySelect, 2016, 1, 64-74). The molecular structures of 1, 2a and 2b were determined via single crystal X-ray diffraction and solution studies, which indicated the presence of [Cu2] species. This was further confirmed via UV-vis spectroscopy and HRMS analysis. The synthesized complexes were screened for their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2). A change in the mechanism of catalytic oxidation was observed with a change in the ligand backbone. All three complexes also showed DNA binding properties, which were further substantiated via molecular docking studies. Their DNA binding affinities were quantitatively ascertained using their intrinsic binding constant, Kb, values which were found to be 4.2 × 104, 5.6 × 104 and 4.8 × 104 M-1, respectively. Furthermore, the complexes displayed efficient DNA cleavage behaviour with pBR322 and the oxidative path was established in presence of ROS, singlet oxygen, 1O2, and the superoxide anion, O2·-.
- Das, Manisha,Afsan, Zeenat,Basak, Dipmalya,Arjmand, Farukh,Ray, Debashis
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supporting information
p. 1292 - 1313
(2019/01/29)
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- Tyrosinase Model Systems Supported by Pyrazolylmethylpyridine Ligands: Electronic and Steric Factors Influencing the Catalytic Activity and Impact of Complex Equilibria in Solution
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Two new copper(I) complexes supported by pyrazolylmethylpyridine (PMP) ligands are synthesized and investigated regarding their ability to catalyze the oxygenation of several monophenolic substrates. The PMP ligands containing a pyridine and a pyrazole donor group represent hybrids between dipyridylmethane (DPM) and bis(pyrazolyl)methane (BPM) ligands. The catalytic activity of the two new [Cu(MeCN)2PMP]PF6 complexes is found to be intermediate between that of catalytically inactive [Cu(MeCN)2DPM]PF6 and highly active [Cu(MeCN)2BPM]PF6, suggesting that the electronic properties of a multidentate ligand can be designed in a modular fashion. DFT calculations are used to explore the differences in reactivity between the two systems. Regarding the behavior of these complexes in solution, evidence for an equilibrium between homoleptic and heteroleptic forms is presented. The crystal structure of a dinuclear complex exhibiting two homoleptic CuII units bridged by a fluorido ligand is obtained, which might represent one of the decay products of PMP-type catalysts after prolonged reaction times.
- Herzigkeit, Benjamin,Fl?ser, Benedikt M.,Engesser, Tobias A.,N?ther, Christian,Tuczek, Felix
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supporting information
p. 3058 - 3069
(2018/07/29)
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- Click. Coordinate. Catalyze. Using CuAAC Click Ligands in Small-Molecule Model Chemistry of Tyrosinase
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Three triazolylmethylpyridine ligands are synthesized using the copper-catalyzed azide-alkyne cycloaddition (CuAAC). The corresponding copper(I) complexes are investigated as catalysts for the oxygenation of several monophenols, in analogy to the enzyme tyrosinase. Importantly, they show a higher catalytic activity than previously investigated systems. This is ascribed to the lower charge donation of the electron-poor triazole heterocycle, supporting the hydroxylation of phenolic substrates by an electrophilic substitution mechanism.
- Herzigkeit, Benjamin,Fl?ser, Benedikt M.,Mei?ner, Nadja E.,Engesser, Tobias A.,Tuczek, Felix
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p. 5402 - 5405
(2018/11/27)
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- Synthesis, structural and magnetic characterizations of a dinuclear copper(II) complex with an (N,S,O) donor ligand: Catecholase and phenoxazinone synthase activities
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A new dinuclear Cu(II) complex (1) was synthesized and crystallographically characterized. Each of the Cu(II) centres has penta coordination and been found to adopt square pyramidal geometry. Variable temperature magnetic measurements showed that there is weak ferromagnetic interaction between the Cu(II) centres in 1. 1 shows catecholase as well as phenoxazinone synthase activities in different solvents. The turn over numbers for the catecholase activity were 4.02 × 103 h?1 (MeOH) and 9.57 × 103 h?1 (MeCN), and that of phenoxazinone synthase activity were 1.065 × 103 h?1 (MeOH), 2.13 × 102 h?1 (MeCN) and 2.844 × 103 h?1 (DCM).
- Ghosh, Ayon Kanti,Ali, Anzar,Singh, Yogesh,Purohit, Chandra Shekhar,Ghosh, Rajarshi
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supporting information
p. 156 - 163
(2018/02/20)
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- Oxidative cross-coupling reaction of catechols with active methylene compounds in an aqueous medium using an AlPO4-supported Ru catalyst
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A green oxidative coupling reaction of catechols with active methylene compounds was achieved using an AlPO4-supported Ru catalyst, where O2 and H2O were used as the ideal oxidant and solvent, respectively. The catalyst is
- Maeno, Zen,Yamamoto, Masanobu,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro
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p. 5401 - 5405
(2018/11/20)
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- Copper(II) and Sodium(I) Complexes based on 3,7-Diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-5-oxide: Synthesis, Characterization, and Catalytic Activity
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The reaction of 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) with metal salts of CuII or NaI/NiII under mild conditions led to the oxidized phosphane derivative 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-5-oxide (DAPTA=O) and to the first examples of metal complexes based on the DAPTA=O ligand, that is, [CuII(μ-CH3COO)2(κO-DAPTA=O)]2 (1) and [Na(1κOO′;2κO-DAPTA=O)(MeOH)]2(BPh4)2 (2). The catalytic activity of 1 was tested in the Henry reaction and for the aerobic 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-mediated oxidation of benzyl alcohol. Compound 1 was also evaluated as a model system for the catechol oxidase enzyme by using 3,5-di-tert-butylcatechol as the substrate. The kinetic data fitted the Michaelis–Menten equation and enabled the obtainment of a rate constant for the catalytic reaction; this rate constant is among the highest obtained for this substrate with the use of dinuclear CuII complexes. DFT calculations discarded a bridging mode binding type of the substrate and suggested a mixed-valence CuII/CuI complex intermediate, in which the spin electron density is mostly concentrated at one of the Cu atoms and at the organic ligand.
- Mahmoud, Abdallah G.,Guedes da Silva, M. Fátima C.,?liwa, Ewelina I.,Smoleński, Piotr,Kuznetsov, Maxim L.,Pombeiro, Armando J. L.
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p. 2868 - 2880
(2018/09/20)
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- Tyrosinase and catecholase-like activities of a dinuclear Cu(II) complex
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A dinuclear Cu(II) complex was synthesized and crystallographically characterized. The compound was found to have antiferromagnetic interaction in between the Cu(II) centres in the molecule. It had weak intermolecular ferromagnetic interaction. The compound was found to be tyrosinase and catecholase active. In case of tyrosinase activity, the diphenol formed was isolated using thin layer chromatography (TLC) and characterized through 1H NMR as well as mass spectrometry. The o-quinone derivative formed in this reaction was characterized using GC–MS. The latter activity was monitored spectrophotometrically and the product o-quinone derivative was isolated (in MeOH and MeCN) column chromatographically and characterized using melting point determination. These were followed by Michealis–Menten kinetics with turnover numbers 4.95 × 103 and 1.58 × 103 h?1 in MeOH and MeCN, respectively.
- Chatterjee, Arnab,Yadav, Hare Ram,Choudhury, Angshuman Roy,Ali, Anzar,Singh, Yogesh,Ghosh, Rajarshi
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p. 140 - 146
(2017/12/26)
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- Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges
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The Schiff base ligand HL1 ({2,6-bis(allylimino)methyl}-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for a hierarchical family of CuII complexes. The ligand showed a unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO? ions in the absence and presence of externally added carboxylates (RCOO?; R = CF3, C6H5 and CH3) has been utilized to produce complexes {[Cu2(μ-L2)2(H2O)]2[Cu2(μ-L2)2(H2O)2](ClO4)6} (1) (HL2 = 3-{(allylimino)methyl}-2-hydroxy-5-methylbenzaldehyde), [Cu4(μ4-O)(μ-L1)2(μ1,3-O2CCF3)4] (2), [Cu4(μ4-O)(μ-L1)2(μ1,3-O2CC6H5)4]·H2O (3), and [Cu5(μ3-OH)2(μ-L1)2(μ1,3-OAc)2(OAc)2(H2O)4][Cu5(μ3-OH)2(μ-L1)2(μ1,3-OAc)2(OAc)3(H2O)](ClO4)3·2C2H5OH (4). The absence of carboxylate anions did not yield HO? ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinuclear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution has been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 from the air.
- Das, Manisha,Canaj, Angelos B.,Bertolasi, Valerio,Murrie, Mark,Ray, Debashis
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p. 17160 - 17176
(2018/12/13)
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- Development of 3,5-Di- tert -butylphenol as a Model Substrate for Biomimetic Aerobic Copper Catalysis
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We develop 3,5-di- tert butylphenol as a strategic substrate for the evaluation of biomimetic Cu 2 -O 2 complexes intended to mimic the activity of tyrosinase. We describe a practical and scalable synthesis and validate its use in an aerobic ortho -oxygenation catalyzed by N, N ′-di- tert -butylethylenediamine and [Cu(CH 3 CN) 4 ]PF 6.
- Kwon, Ohhyeon,Esguerra, Kenneth Virgel N.,Glazerman, Michael,Petitjean, Laurène,Xu, Yalun,Ottenwaelder, Xavier,Lumb, Jean-Philip
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supporting information
p. 1548 - 1553
(2017/08/11)
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- Synthesis of ortho-Azophenols by Formal Dehydrogenative Coupling of Phenols and Hydrazines or Hydrazides
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Azophenols are important chromophores and reagents in organic synthesis, with applications as pigments and molecular switches. Here, we describe a catalytic aerobic process that couples phenols and hydrazines or hydrazides for their synthesis. The key aromatic C?N bond is formed by condensation between the hydrazine or hydrazide and an ortho-quinone, which triggers a redox-isomerization to install the azo-functionality. Notable features include rapid access to highly functionalized azophenols with a range of electronic configurations, including “push–pull” systems, conditions that employ simple, unactivated substrates, occurrence at room temperature using an earth-abundant and commercially available copper catalyst, and production of water as the only stoichiometric byproduct.
- Esguerra, Kenneth Virgel N.,Lumb, Jean-Philip
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supporting information
p. 8596 - 8600
(2017/06/30)
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- Oxidation of Organic Molecules with a Redox-Active Guanidine Catalyst
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Herein, we report the first examples of the use of redox-active guanidines as catalysts in the green oxidation of organic molecules with dioxygen. In one half-reaction, the oxidized form of the redox-active guanidine is converted into the reduced, protonated state, thereby enabling dehydrogenative oxidation of the substrate (3,5-di-tert-butylcatechol→ortho-benzoquinone, benzoin→benzil, and 2,4-di-tert-butylphenol→biphenol). In the other half-reaction, efficient re-oxidation of the guanidine to the oxidized state is achieved with dioxygen in the presence of a copper catalyst. These results pave the way for the broader use of redox-active guanidines as oxidation catalysts.
- Wild, Ute,Sch?n, Florian,Himmel, Hans-J?rg
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p. 16410 - 16413
(2017/11/27)
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- OMS-2-Supported Cu Hydroxide-Catalyzed Benzoxazoles Synthesis from Catechols and Amines via Domino Oxidation Process at Room Temperature
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In the presence of manganese oxide octahedral molecular sieve (OMS-2) supported copper hydroxide Cu(OH)x/OMS-2, aerobic synthesis of benzoxazoles from catechols and amines via domino oxidation/cyclization at room temperature is achieved. This heterogeneous benzoxazoles synthesis initiated by the efficient oxidation of catechols over Cu(OH)x/OMS-2 tolerates a variety of substrates, especially amines containing sensitive groups (hydroxyl, cyano, amino, vinyl, ethynyl, ester, and even acetyl groups) and heterocycles, which affords functionalized benzoxazoles in good to excellent yields by employing low catalyst loading (2 mol % Cu). The characterization and plausible catalytic mechanism of Cu(OH)x/OMS-2 are described. The notable features of our catalytic protocol such as the use of air as the benign oxidant and EtOH as the solvent, mild conditions, ease of product separation, being scalable up to the gram level, and superior reusability of catalyst (up to 10 cycles) make it more practical and environmentally friendly for organic synthesis.
- Meng, Xu,Wang, Yanmin,Wang, Yuanguang,Chen, Baohua,Jing, Zhenqiang,Chen, Gexin,Zhao, Peiqing
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p. 6922 - 6931
(2017/07/15)
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- Synthesis, crystal structure and catecholase activity of [Co(SCN)2(L)] [L?=?N,N′-(bis(pyridine-2-yl)benzilidene)-1,2-ethanediamine]
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Synthesis and structural characterization of a mononuclear cobalt(II) complex [Co(SCN)2(L)] [L?=?N,N′-(bis(pyridine-2-yl)benzilidene)-1,2-ethanediamine] (1) is reported. Molecular geometry of the complex is found to be distorted octahedron with
- Maji, Ashis Kumar,Khan, Sumitava,Ghosh, Ayon Kanti,Lin, Chia -Her,Ghosh, Barindra Kumar,Ghosh, Rajarshi
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p. 489 - 494
(2017/05/10)
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- Synthesis, characterization, crystal structure, and reactivity of heterobimetallic dioxovanadium(V) complexes containing multidentate hydrazone ligands
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Two new heterobimetallic complexes of the composition [(VO2)2(μ3-slsch){Na2(μ-H2O)2(H2O)2}]n (1) and [(VO2)2(μ3-npsch){Na2(μ-H2O)2(H2O)2}(DMF)]n (2) were obtained by reaction of the ligand and vanadium pentoxide in a 1:1 molar ratio in methanol in the presence of Na2CO3 (2 equivalents). The complexes obtained were characterized using various spectroscopic studies. The structures of both the complexes were established by single crystal X-ray crystallographic study. We have also explored the catalytic behavior of the complexes in oxidative bromination of phenol red, which is the bio-inspired reaction catalyzed by an enzyme haloperoxidase.
- Kurbah, Sunshine D.,Kumar, Arvind,Sanentiba Ozukum,Syiemlieh, Ibanphylla,Lal, Ram A.
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p. 2969 - 2985
(2017/10/07)
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- Molecular Iodine-Mediated α-C-H Oxidation of Pyrrolidines to N,O-Acetals: Synthesis of (±)-Preussin by Late-Stage 2,5-Difunctionalizations of Pyrrolidine
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We previously reported an iterative synthesis of unsymmetrical 2,5-disubstituted pyrrolidines from pyrrolidine by two rounds of redox-triggered α-C-H functionalization. Although this approach can be used to introduce substituents at the 2- and 5-positions, it is lengthy because the redox auxiliary must be removed and then reinstalled. Therefore, we sought to develop a method to oxidize 2-functionalized pyrrolidine to cyclic N,O-acetal which could then react with a nucleophile for introduction of the 5-substituent. In this work, we found that molecular iodine can mediate the preferential oxidation of secondary over tertiary α-C-H bonds of α-substituted pyrrolidines to form cyclic N,O-acetals, improving the step economy of our previously reported method. With this strategy, (±)-preussin and its C(3) epimer were synthesized from (±)-pyrrolidin-3-ol.
- Rong, Hao-Jie,Yao, Jun-Jun,Li, Ji-Kun,Qu, Jin
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p. 5557 - 5565
(2017/06/07)
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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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- Synthesis and characterization of an iron(III) complex of an ethylenediamine derivative of an aminophenol ligand in relevance to catechol dioxygenase active site
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An ethylene diamine derivative of a bis(phenol)diamine ligand (H2L) was synthesized via the Mannich reaction and subsequent ring cleavage of the produced imidazoline ring (H2LIm), and then it was characterized by1H NMR and IR spectroscopies and CHN analysis. The iron(III) complex (FeLCl) of this ligand was synthesized and characterized by IR, UV–Vis, X-ray and magnetic susceptibility studies. X-ray analysis reveals that in FeLCl the iron(III) center has a distorted square pyramidal coordination sphere and is surrounded by a chlorine atom, two amine nitrogen and two phenolate oxygen atoms of the ligand. Variable-temperature magnetic susceptibility measurements indicate that FeLCl is a paramagnetic high spin iron(III) complex. It shows weak antiferromagnetic interactions through N[sbnd]H?Cl intermolecular interactions. The ligand-centered electrochemical oxidation of this complex, due to the oxidation of phenolate group to phenoxyl radicals, as well as the electrochemical metal-centered reduction of the ferric ion to the ferrous ion were investigated. In addition, the efficient cleavage by oxygenation of 3,5-di-tert-butyl-catechol with FeLCl in the presence of dioxygen was observed.
- Safaei, Elham,Naghdi, Narges,Jagli?i?, Zvonko,Pevec, Andrej,Lee, Yong-Ill
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p. 116 - 123
(2016/12/16)
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- Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations
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Four new imidazole-based ligands, 4-((1H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (LOL1), 4-((1H-imidazol-4-yl)methyl)-2-(tert-butyl)-4,5-dihydrooxyzole (LOL2), 4-((1H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (LOL3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1H-imidazol-4-yl-)ethyl amine (Limz1), have been synthesized. The corresponding copper(I) complexes [Cu(I)(LOL1)(CH3CN)]PF6 (CuLOL1), [Cu(I)(LOL2)(CH3CN)]PF6 (CuLOL2), [Cu(I)(LOL3)(CH3CN)]PF6 (CuLOL3), [Cu(I)(Limz1)(CH3CN)2]PF6 (CuLimz1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)(BIMZ)(CH3CN)]PF6 (CuBIMZ), are screened as catalysts for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC-H2) to 3,5-di-tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di-tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order CuLOL3?≈?CuLOL1?>?CuBIMZ?>?CuLOL2?>?CuLimz1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di-tert-butylphenol (2,4-DTBP-H), 3-tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl-l-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (CuLimz1 and CuBIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed.
- Wendt, Franziska,N?ther, Christian,Tuczek, Felix
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p. 777 - 792
(2016/08/26)
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- A cobalt compound, preparation method and its use
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The invention provides a cobalt complex, a preparation method and an application thereof, and belongs to the technical field of metal-organic complex materials. The cobalt complex has a molecular formula of [Co(qc)2(H2O)].2H2O, wherein qc represents 3-hydroxyl-2-quinoxaline carboxylate radicals. The invention also provides a method for preparing the cobalt complex. The cobalt complex is obtained by reacting 3-hydroxyl-2-quinoxaline carboxylic acid and a bivalent cobalt compound in a solution. The invention also provides an application of the cobalt complex in catalyzing an oxidative coupling reaction of 2,4-di-tert-butylphenol. The cobalt complex provided by the invention has a certain granularity and a unique structure, and has relatively high catalytic activity, selectivity and good stability. The preparation method of the cobalt complex is simple, has high yield and has no pollution to the environment. By using the cobalt complex to prepare biphenol, water can be used as a solvent; selectivity is good; yield is high; three wastes are little; and the product is free from pollution.
- -
-
Paragraph 0041; 0042
(2017/03/21)
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- Synthesis and Catalytic Reactivity of a Dicopper(II) μ-η2:η2-Peroxo Species Supported by 1,4,7-Tri-tert-butyl-1,4,7-triazacyclononane
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O2-derived CunO2 adducts are attractive targets for aerobic oxidation catalysis because of their remarkable reactivity, but oxidation of the supporting ligand limits catalytic turnover. We report that tBu3tacn (1,4,7-tri-tert-butyl-1,4,7-triazacyclononane) supports a dicopper(II) μ-η2:η2-peroxo species with the highest solution stability outside of an enzyme. Decomposition of this species proceeds without oxidation of the tBu3tacn ligand. Additive-free catalytic aerobic oxidation reactions at or above room temperature are described, highlighting the potential of oxidatively robust ligands in aerobic copper catalysis.
- Karahalis, Gregory J.,Thangavel, Arumugam,Chica, Bryant,Bacsa, John,Dyer, R. Brian,Scarborough, Christopher C.
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p. 1102 - 1107
(2016/02/09)
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- Competitive coordination aggregation for V-shaped [Co3] and disc-like [Co7] complexes: Synthesis, magnetic properties and catechol oxidase activity
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Unique dependence on the nature of metal salt and reaction conditions for coordination assembly reactions of varying architecture and nuclearity have been identified in V-shaped [Co3L4] and planar disc-like [Co7L6] compounds: [CoII3L2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [CoII7(μ-L)6(μ-OMe)6]Cl2 (2) (HL = 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol). At room temperature varying reaction conditions, cobalt-ligand ratios and use of different bases allowed unique types of coordination self-assembly. The synthetic marvel lies in the nature of aggregation with respect to the two unrelated cores in 1 and 2. Complex 1 assumes a V-shaped arrangement bound to L-, water and a trifluoroacetate anion, while 2 grows around a central CoII ion surrounded by a {CoII6} hexagon bound to methoxide and L-. Magnetic measurements revealed that the intermetallic interactions are antiferromagnetic in nature in the case of complex 1 and ferromagnetic in the case of 2 involving high spin cobalt(ii) ions with stabilization of the high-spin ground state in the latter case. In MeCN solutions complexes 1 and 2 showed catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in air. The kinetic study in MeCN revealed that with respect to the catalytic turnover number (kcat) 2 is more effective than 1 for oxidation of 3,5-DTBCH2.
- Singha Mahapatra, Tufan,Basak, Dipmalya,Chand, Santanu,Lengyel, Jeff,Shatruk, Michael,Bertolasi, Valerio,Ray, Debashis
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p. 13576 - 13589
(2016/09/04)
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- Bioinspired organocatalytic aerobic C-H oxidation of amines with an ortho -quinone catalyst
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A simple bioinspired ortho-quinone catalyst for the aerobic oxidative dehydrogenation of amines to imines is reported. Without any metal cocatalysts, the identified optimal ortho-quinone catalyst enables the oxidations of α-branched primary amines and cyclic secondary amines. Mechanistic studies have disclosed the origins of different performances of ortho-quinone vs para-quinone in biomimetic amine oxidations.
- Qin, Yan,Zhang, Long,Lv, Jian,Luo, Sanzhong,Cheng, Jin-Pei
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supporting information
p. 1469 - 1472
(2015/03/30)
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- Catalytic oxygenation of various monophenols by copper(I) complexes with bis(pyrazolyl)methane ligands: Differences in reactivity
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Three new mononuclear copper(I) complexes supported by the symmetric ligands 1,1′-methylenebis-1H-pyrazole (BPM), 1,1′-methylenebis(3-methyl-1H-pyrazole) (mBPM), and 1,1′-methylenebis(3,5-di-methyl-1H-pyrazole) (dmBPM) were synthesized as catalytic model systems of tyrosinase. The influence of various functional groups on the catalytic conversion of monophenols is investigated and the formation of the corresponding ortho-quinones is monitored using UV/vis and NMR spectroscopy. Comparison of various monophenols reveals the differences in reactivity which are analyzed and interpreted based on key intermediates of the mechanistic cycle.
- Hamann, Jessica Nadine,Schneider, Rebecca,Tuczek, Felix
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p. 3259 - 3271
(2015/09/22)
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- Catalytic Models of Tyrosinase: Reactivity Differences between Systems Based on Mono- and Binucleating Ligands
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A new tyrosinase model based on the binucleating ligand Lpy2 is synthesized and characterized. The ligand Lpy2 contains a combination of an imine and a pyridine function in the sidearms, which are bridged by a flexible alkyl spacer. As shown by UV/Vis and NMR spectroscopy, the Cu2Lpy2 complex catalyzed the conversion of the monophenol 2,4-di-tert-butylphenol (DTBP-H) into the o-quinone 3,5-di-tert-butylquinone (DTBQ) with a turnover number (TON) of 18. The dicopper complex of Lpy2 thus shows monophenolase activity that is comparable to that of the recently developed Lpy1 model of tyrosinase, which is based on a known mononucleating ligand (M. Rolff, J. Schottenheim, G. Peters, F. Tuczek, Angew. Chem. Int. Ed. 2010, 122, 6583). The electron-poor substrate 4-hydroxybenzoic acid methyl ester (MeBA-OH), in contrast, is converted by Cu2Lpy2 into the semiquinone. For both substrates, the oxygenation reactions were also conducted in a stoichiometric fashion to obtain information on the intermediates involved. For the substrate MeBA-OH, we detected a binuclear μ-catecholato copper(II) complex by high-resolution ESI mass spectrometry. These studies were complemented by investigations of deactivation mechanisms that could be invoked to explain the limitation of the TON. To this end, a bis-μ-hydroxido Lpy2 dicopper(II) complex as well as a semiquinone Lpy2 complex were prepared. Both complexes may represent decay products of the catalyst. A tyrosinase model based on the binucleating ligand Lpy2 was developed and characterized. The ligand Lpy2 contains a combination of an imine and a pyridine function in the sidearms that are bridged by a flexible alkyl spacer. The Cu2Lpy2 complex catalyzes the conversion of monophenol DTBP-H into the o-quinone DTBQ (TON = 18). An electron-poor substrate is converted into the semiquinone.
- Schottenheim, Julia,Gernert, Claus,Herzigkeit, Benjamin,Krahmer, Jan,Tuczek, Felix
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p. 3501 - 3511
(2015/08/06)
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- Monooxygenation of an appended phenol in a model system of tyrosinase: Implications on the enzymatic reaction mechanism
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A new tridentate N-donor ligand and its corresponding copper(i) complex have been synthesized to investigate the tyrosinase-like aromatic hydroxylation of an attached phenol. The results of the oxygenation reactions are compared to related systems having attached phenyl and catechol groups, respectively. The title complex is the first system mediating the monooxygenation of a phenol in the absence of an external base. This journal is
- Hamann, Jessica Nadine,Rolff, Malte,Tuczek, Felix
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p. 3251 - 3258
(2015/03/05)
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- New topological 3D copper(ii) coordination networks: Catechol oxidation catalysis and solvent adsorption via porous properties
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The reaction of CuX2 (X- = ClO4- and BF4-) with a new 1,3,5-tris(isonicotinoyloxymethyl)benzene (L) ligand gives rise to 3D coordination networks, [Cu3L4(CH3/sub
- Kim, Doeon,Kim, Byung Joo,Noh, Tae Hwan,Jung, Ok-Sang
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p. 2583 - 2590
(2015/03/18)
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- Practical oxidative dearomatization of phenols with sodium hypochlorite pentahydrate
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A highly efficient and practical oxidative dearomatization of phenols using sodium hypochlorite pentahydrate as an inexpensive, strong oxidant is reported for the first time. The oxidation reactions proceeded very rapidly in the presence of water to give the desired products in excellent yields, and sodium chloride and water were the only by-products derived from the oxidant.
- Uyanik, Muhammet,Sasakura, Niiha,Kuwahata, Mitsuyoshi,Ejima, Yasukazu,Ishihara, Kazuaki
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supporting information
p. 381 - 383
(2015/03/30)
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