120-12-7Relevant articles and documents
In situelectrosynthesis of anthraquinone electrolytes in aqueous flow batteries
Aziz, Michael J.,Fell, Eric M.,Gordon, Roy G.,Jin, Shijian,Jing, Yan,Kerr, Emily F.,Pollack, Daniel A.,Wong, Andrew A.,Wu, Min
, p. 6084 - 6092 (2020)
We demonstrate the electrochemical oxidation of an anthracene derivative to a redox-active anthraquinone at room temperature in a flow cell without the use of hazardous oxidants or noble metal catalysts. The anthraquinone, generatedin situ, was used as the active species in a flow battery electrolyte without further modification or purification. This potentially scalable, safe, green, and economical electrosynthetic method is also applied to another anthracene-based derivative and may be extended to other redox-active aromatics.
Photochemistry of 9-Benzoylanthracene
Becker, Hans-Dieter,Langer, Vratislav,Becker, Hans-Christian
, p. 6394 - 6396 (1993)
Photoexcitation of 9-benzoylanthracene (1) in toluene solution under argon results in head-to-tail dimerization by 4? + 4? cycloaddition to give dibenzoyl-substituted dianthracene in about 60percent yield.The concomitant formation of both anthracene and 9,10-dibenzoylanthracene (ca. 4percent yield) suggests that intermolecular benzoyl group/hydrogen exchange may be an inefficient mode of deactivation the intermediate excimer.Irradiation of crystalline 1 gave the head-to-tail dimer, without byproducts, in a maximal yield of 50percent.It was established by X-ray diffraction that theasymmetric unit of 1 consists of two molecules, 1A and 1B, in which the carbonyl group is twisted out of the plane of the anthracene by 67.4 deg and 86.5 deg, respectively.Investigation of the packing pattern revealed that only parallel overlapping head-to-tail oriented molecules of 1A, characterized by an interplanar spacing of 3.35 Angstroem, can undergo photochemical dimerization by 4? + 4? cycloaddition.The spatial relation of adjacent molecules of 1B is such as to preclude their involvement in the photochemical dimerization.
Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O2 at an Iron(II)-Cyclam Center
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
, p. 5924 - 5928 (2020)
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.
Indium-catalyzed construction of polycyclic aromatic hydrocarbon skeletons via dehydration
Kuninobu, Yoichiro,Tatsuzaki, Tomohiro,Matsuki, Takashi,Takai, Kazuhiko
, p. 7005 - 7009 (2011)
Polycyclic aromatic compounds can be synthesized from 2-benzylic- or 2-allylbenzaldehydes using a catalytic amount of In(III) or Re(I) complexes. By using this method, polycyclic aza-aromatic compounds can also be prepared efficiently. In these reactions, only water is formed as a side product.
Synthesis and Pyrolysis of a Triafulvene Precursor
Muehlebach, Michel,Neuenschwander, Markus,Engel, Peter
, p. 2089 - 2110 (1993)
In view of retro-Diels-Alder reactions (RDA reactions), the triafulvene precursor 3 has been prepared in a simple three-step synthesis by dibromocarbene addition at dibenzo-barralene (11-->12; 44percent), halogen-Li exchange followed by methylation (12-->14, 100percent) and HBr elimination (14-->3, 62percent) Scheme 3).Reactivity of the so far unknown bridged 1,1-dibromocyclopropane 12 has been explored, including reductions, allylic rearrangements, and "carbene dimerizations" (Scheme 4).First experiments with respect to the thermal behaviour of 3 show that RDA reaction, although occuring in most cases, is not the predominant pathway.When 3 is heated in a sealed tube without solvent, two dimers 26 and 27 are isolated in a total yield of 55percent (Scheme 6).On the other hand, gas-phase pyrolysis of 3 at 400 deg mainly produces rearranged 28 (56percent; Scheme 7).It is assumed that bridged trimethylenemethane 29 is an essential intermediate in thermal rearrangements of 3 (Scheme 8).
Evaluation of the Transferability of the “Flexible Steric Bulk” Concept from N-Heterocyclic Carbenes to Planar-Chiral Phosphinoferrocenes and their Electronic Modification
Korb, Marcus,Schaarschmidt, Dieter,Grumbt, Martin,K?nig, Matthias,Lang, Heinrich
, p. 2968 - 2982 (2020)
The concept of “flexible steric bulk” is discussed at 2-phenylvinyl-1-phosphinoferrocenes. The introduction of freely rotatable 1'-silyl groups increases the catalytic productivity within the synthesis of tri-ortho-substituted biaryls by Suzuki–Miyaura C,C cross-coupling reactions, giving higher yields with 1/4 of catalyst concentration than for the non-silylated derivatives. Electronic modification of the P and the vinyl donor functionalities was investigated by introducing substituents in the para positions of both groups. Therein, electron-withdrawing phosphines increased the yield from 78 to 91 percent for a given biaryl, by changing from a diphenylphosphino to the P(p-CN-C6H4)2 unit. Opposite results, obtained from electron-donating and sterically demanding phosphines, were in accordance with the 1J(31P,77Se) values. However, the electron density of the ferrocenyl backbone, expressed by the redox potential of the first ferrocenyl-related redox process, cannot be correlated with the donor-properties at the P atom. Changing from a PPh2-substituted ferrocene to a (RA)-1,1'-binaphthyl-containing phosphonite, a complex interaction between the axial- and the planar-chiral motifs occurs, resulting a change of the absolute biaryl configuration.
The effect of oils on PAH, PCDD, PCDF, and PCB emissions from a spark engine fueled with leaded gasoline
Broz, Jan,Grabic, Roman,Kilian, Juraj,Lojkasek, Milan,Marklund, Stellan,Ocelka, Tomas,Pekarek, Vladimir,Pribyl, Josef,Tydlitat, Vratislav,Vyska, Jan
, p. 1905 - 1911 (2000)
The effect of synthetic and mineral oils on the formation of polyaromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) in emissions from a spark ignition engine was studied on a Skoda Favorit engine fueled with leaded gasoline. The test cycle simulated urban traffic conditions on a chassis dynamometer, in accordance with the ECC 83.00 test. The data for selected PAHs as well as PCDDs, PCDFs, and PCBs congener profiles are presented. PCDD/Fs emissions for an unused oil and the oil after 10 000-km operation varied from 300 to 2000 fmol/m3, PCBs emissions from 75 to 178 pmol/m3, and PAHs emissions from 150 to 420 μg/m3. The content of PCBs in oils varied from 2 to 920 mg/kg.
OXIDATION OF ARENES BY MOLTEN GALLIUM(III) CHLORIDE
Dworkin, A. S.,Brown, L. L.,Buchanan, A. C.,Smith, G. P.
, p. 2727 - 2730 (1985)
Molten, anhydrous Ga2Cl6 at 100-130 deg C readily oxidizes pyrene, anthracene and naphthacene with the concomitant reduction of Ga(III) to Ga(I).Dilute solutions of these arenes (ArH) are oxidized to their radical cations (ArH+.), wich decay very slowly in Ga2Cl6, while more concentrated solutions are oxidized to stable arenium ions (ArH2+) with hydrogen derived from aryl-aryl coupling reactions.
Metal organic frameworks as efficient heterogeneous catalysts for the oxidation of benzylic compounds with t-butylhydroperoxide
Dhakshinamoorthy, Amarajothi,Alvaro, Mercedes,Garcia, Hermenegildo
, p. 1 - 4 (2009)
Iron and copper metal organic frameworks of 1,3,5-benzenetricarboxylate [Fe(BTC) and Cu3(BTC)2] are efficient and reusable solid catalysts for the oxidation of benzylic compounds with t-butylhydroperoxide as oxidant in acetonitrile with moderate to good yields. The solids were stable under the reaction conditions as confirmed by comparison of the powder XRD of the fresh and reused catalysts. EPR spectroscopy using diphenyl-N-t-butyl nitrone as spin trap has allowed to detect C-centered radicals as reaction intermediates.
Agranat,Shih
, p. 865,866 (1974)
9,10-Dehydroanthracene: p-Benzyne-type biradicals abstract hydrogen unusually slowly
Schottelius, Marc J.,Chen, Peter
, p. 4896 - 4903 (1996)
The 9,10-dehydroanthracene biradical, a model for the p-benzyne-type biradicals implicated in DNA cleavage by the enediyne antitumor antibiotics, was prepared by photodissociation of a propellane in solution. Trapping products characteristic of biradicals, e.g. anthracene-d2, are found. The rates of hydrogen abstraction by the biradical from acetonitrile and isopropyl alcohol are measured directly by flash photolysis/transient absorption spectroscopy, giving second-order rate constants of k(MeCN,abstr) = (1.1 ± 0.2) x 103 M-1 s-1 and k(i-PrOH,abstr) = (6.5 ± 0.6) x 103 M-1 s-1 at room temperature, which are 100-200 times lower than the corresponding rate constants for phenyl or 9-anthryl radical. A second decay route for the biradical is found, and assigned, based on thermochemical, kinetic, and trapping arguments to a retro-Bergman reaction that converts the 9,10-dehydroanthracene biradical into the ring-opened 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne. Although the retro-Bergman reaction is relatively fast, k ~ 4 x 105 s-1 at room temperature, it is competitive with hydrogen abstraction by the biradical only because the hydrogen abstraction is slower than expected. Through-bond coupling in the 1,4-biradical is discussed as a rationalization for the 100- to 200-fold reduction in the abstraction rate.
Photochemical Debromination of Meso-Substituted Bromoanthracenes Studied by Steady-State Photolysis and Laser Photolysis
Hamanoue, Kumao,Tai, Shigeyoshi,Hidaka, Toshiharu,Nakayama, Toshihiro,Kimoto, Masaki,Teranishi, Hiroshi
, p. 4380 - 4384 (1984)
Debrominations of 9-bromoanthracene (BA) and 9,10-dibromoanthracene (DBA) in acetonitrile containing triethylamine (TEA) or N,N-dimethylaniline (DMA) have been studied by means of steady-state photolysis and laser photolysis.By the addition of TEA, the decay constants of the lowest excited singlet states of BA and DBA increase and the maximum yields of the triplet states decrease.The singlet quenching rate constants by TEA are calculated to be of the order of 1E10 M-1 s-1, showing that the reactions are diffusion controlled.Compared with the result of γ-radiolysis and pulse radiolysis, it is suggested that the photochemical debrominations of BA and DBA in the presence of amines take place via the anion radicals which are produced through exciplexes between amines and the lowest excited singlet states of bromoanthracenes.
Reactivity of bio-inspired Cu(II) (N2/Py2) complexes with peroxide at room temperature
Singh, Nirupama,Botcha, Niharika Krishna,Jones, Thomas M.,Ertem, Mehmed Z.,Niklas, Jens,Farquhar, Erik R.,Poluektov, Oleg G.,Mukherjee, Anusree
, (2019)
Developing coordination complexes of earth abundant metals that can perform substrate oxidations under benign conditions is an ongoing challenge. Herein, the reactivity of two mononuclear Cu-complexes toward the oxidant H2O2 is reported. Both complexes displayed ligand oxidation upon reaction with the oxidant. Analysis of spectroscopic data established that the respective product complexes contained mononuclear Cu(II) centers. Moreover, treatment of these Cu-complexes with oxidant in the presence of substrate resulted in the interception of ligand oxidation with preferential oxidation of the substrate. Computational studies identified plausible mechanistic pathways, suggesting a copper-oxyl intermediate as the likely reactive intermediate responsible for substrate and ligand oxidation. To our knowledge, this is the first Cu-mediated system that showed ligand oxidation, oxo-transfer capability, and external hydrocarbon oxidation under stoichiometric conditions.
Metal-Free Selective Borylation of Arenes by a Diazadiborinine via C-H/C-F Bond Activation and Dearomatization
Su, Yuanting,Huan Do, Dinh Cao,Li, Yongxin,Kinjo, Rei
, p. 13729 - 13733 (2019)
A newly developed annulated 5-chlorinated 1,3,2,5-diazadiborinine derivative (4) selectively activates a C-H bond of benzene (C6H6) and 1,3-di(trifluoromethyl)benzene, as well as a C-F bond in partially fluorinated arenes, to furnish borylation products under catalyst-, metal-, and irradiation-free conditions. Moreover, 4 readily undergoes a reversible dearomative coupling reaction with polycyclic aromatic hydrocarbons to afford diboration products. The latter represents the first reversible intermolecular dearomative diboration of arenes.
Dioxygen Activation by a Hexagonal SrMnO3 Perovskite Catalyst for Aerobic Liquid-Phase Oxidation
Kawasaki, Shuma,Kamata, Keigo,Hara, Michikazu
, p. 3247 - 3253 (2016)
Heterogeneous catalysts, which allow a reductive activation of dioxygen (O2) under mild reaction conditions, are promising candidates for highly efficient aerobic oxidation. An effective hexagonal SrMnO3 (SMO) perovskite catalyst for liquid-phase selective oxidation with O2 was successfully synthesized by the polymerized complex method. The activity of SMO for the aerobic oxidation of alcohols was higher than those of typical manganese oxide-based catalysts and was heterogeneous, so that the recovered catalyst could be reused without heat treatment under oxidative conditions while keeping its high catalytic performance. The reversible reaction on the surface Mn species on SMO with O2 leads to the formation of Mn–superoxo species, which catalyze the selective oxidative transformation of various types of organic substrates into the desired oxygenated or dehydrogenated products.
Stabilizing Terminal Ni(III)-Hydroxide Complex Using NNN-Pincer Ligands: Synthesis and Characterization
Shanmugam, Maheswaran,Rajpurohit, Jitendrasingh,Shukla, Pragya,Kumar, Pardeep,Das, Chinmoy,Vaidya, Shefali,Sundararajan, Mahesh,Shanmugam, Muralidharan
, p. 6257 - 6267 (2019)
The reaction of [Ni(COD)2] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis(imino)pyridyl (L1) reveals a susceptibility to oxidation in an inert atmosphere ([O2] level III(L1··)2-(OH)] (1). Various isotopically labeled experiments (16O/18O) assertively endorse the origin of terminal oxygen based ligand in 1 due to the activation of molecular dioxygen. The presence of proton bound to the terminal oxygen in 1 is well supported by NMR, IR spectroscopy, DFT calculations, and hydrogen atom transfer (HAT) reactions promoted by 1. The observation of shakeup satellite peaks for the primary photoelectron lines of Ni(2p) in the X-ray photoelectron spectroscopy (XPS) unambiguously confirms the paramagnetic signature associated with the distorted square planar nickel ion, which is consistent with the trivalent oxidation state assigned for the nickel ion in 1. The variable temperature magnetic susceptibility data of 1 shows dominant antiferromagnetic interactions exist among the paramagnetic centers, resulting in an overall S = 1/2 ground state. Variable temperature X-band EPR studies performed on 1 show evidence for the S = 1/2 ground state, which is consistent with magnetic data. The unusual g-tensor extracted for the ground state S = 1/2 is analyzed under a strong exchange limit of spin-coupled centers. The electronic structure predicted for 1 is in good agreement with theoretical calculations.
Pd(II) Coordination Sphere Engineering: Pyridine Cages, Quinoline Bowls, and Heteroleptic Pills Binding One or Two Fullerenes
Chen, Bin,Holstein, Julian J.,Horiuchi, Shinnosuke,Hiller, Wolf G.,Clever, Guido H.
, p. 8907 - 8913 (2019)
Fullerenes and their derivatives are of tremendous technological relevance. Synthetic access and application are still hampered by tedious purification protocols, peculiar solubility, and limited control over regioselective derivatization. We present a modular self-assembly system based on a new low-molecular-weight binding motif, appended by two palladium(II)-coordinating units of different steric demands, to either form a [Pd2L14]4+ cage or an unprecedented [Pd2L23(MeCN)2]4+ bowl (with L1 = pyridyl, L2 = quinolinyl donors). The former was used as a selective induced-fit receptor for C60. The latter, owing to its more open structure, also allows binding of C70 and fullerene derivatives. By exposing only a fraction of the bound guests' surface, the bowl acts as fullerene protecting group to control functionalization, as demonstrated by exclusive monoaddition of anthracene. In a hierarchical manner, sterically low-demanding dicarboxylates were found to bridge pairs of bowls into pill-shaped dimers, able to host two fullerenes. The hosts allow transferring bound fullerenes into a variety of organic solvents, extending the scope of possible derivatization and processing methodologies.
A Highly Reactive Seven-Coordinate Osmium(V) Oxo Complex: [OsV(O)(qpy)(pic)Cl]2+
Liu, Yingying,Ng, Siu-Mui,Lam, William W. Y.,Yiu, Shek-Man,Lau, Tai-Chu
, p. 288 - 291 (2016)
Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2″:6″,2-quaterpyridine, pic=4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of 1.7375 ?. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C-H bond dissociation energy as high as 90 kcal mol-1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species.
Bender,C.O.,Burgess,H.D.
, p. 3486 - 3493 (1973)
Strating et al.
, p. 125 (1969)
Base-Free Palladium-Catalyzed Borylation of Aryl Chlorides with Diborons
Yamamoto, Yutaro,Matsubara, Hiroshi,Yorimitsu, Hideki,Osuka, Atsuhiro
, p. 2317 - 2320 (2016)
The base-free palladium-catalyzed borylation of aryl chlorides with diborons was achieved. The base-free conditions offered acceptable functional group compatibility. Based on experimental and computational studies, it was shown that smooth boryl transfer from the diborons to the arylpalladium chloride was promoted by strong interaction between the Lewis acidic boron and the chlorine atom on palladium.
Alkaline Earth Metal-Ammonia-Anion Radical Complexes
Stevenson, Gerald R.,Schock, Laurel E.
, p. 3742 - 3743 (1983)
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C(sp3)-H Fluorination with a Copper(II)/(III) Redox Couple
Bower, Jamey K.,Cypcar, Andrew D.,Henriquez, Brenda,Stieber, S. Chantal E.,Zhang, Shiyu
, p. 8514 - 8521 (2020)
Despite the growing interest in the synthesis of fluorinated organic compounds, few reactions are able to incorporate fluoride ions directly into alkyl C-H bonds. Here, we report the C(sp3)-H fluorination reactivity of a formally copper(III) fluoride complex. The C-H fluorination intermediate, LCuF, along with its chloride and bromide analogues, LCuCl and LCuBr, were prepared directly from halide sources with a chemical oxidant and fully characterized with single-crystal X-ray diffraction, X-ray absorption spectroscopy, UV-vis spectroscopy, and 1H nuclear magnetic resonance spectroscopy. Quantum chemical calculations reveal significant halide radical character for all complexes, suggesting their ability to initiate and terminate a C(sp3)-H halogenation sequence by sequential hydrogen atom abstraction (HAA) and radical capture. The capability of HAA by the formally copper(III) halide complexes was explored with 9,10-dihydroanthracene, revealing that LCuF exhibits rates 2 orders of magnitude higher than LCuCl and LCuBr. In contrast, all three complexes efficiently capture carbon radicals to afford C(sp3)-halogen bonds. Mechanistic investigation of radical capture with a triphenylmethyl radical revealed that LCuF proceeds through a concerted mechanism, while LCuCl and LCuBr follow a stepwise electron transfer-halide transfer pathway. The capability of LCuF to perform both hydrogen atom abstraction and radical capture was leveraged to enable fluorination of allylic and benzylic C-H bonds and α-C-H bonds of ethers at room temperature.
Non-heme iron(ii/iii) complexes that model the reactivity of lipoxygenase with a redox switch
Mei, Fusheng,Ou, Chunping,Wu, Guiling,Cao, Li,Han, Fang,Meng, Xianggao,Li, Ji,Li, Dongfeng,Liao, Zhanru
, p. 4267 - 4269 (2010)
Three ferrous/ferric complexes of a N6 hexadentate ligand, N,N,N′,N′-tetrakis(2-benzimidazolyl-methyl)ortho-diamine-trans- cyclohexane (ctb), [FeII(ctb)](ClO4)2· EtOH (1), [FeIII(OEt)(Hctb)](ClO4)3·EtOH (2), and [FeIII(OMe)(Hctb)](ClO4)3· 3MeOH·4.5H2O (3), were synthesized and characterized as models of lipoxygenase. The lipoxygenase activities of the complexes were checked and the results indicate that ferrous complex 1 is inactive while ferric alkoxide complexes 2 and 3 show catalytic activity via the hydrogen atom abstraction reaction mechanism.
Spectroscopic capture and reactivity of a low-spin cobalt(IV)-oxo complex stabilized by binding redox-inactive metal ions
Hong, Seungwoo,Pfaff, Florian F.,Kwon, Eunji,Wang, Yong,Seo, Mi-Sook,Bill, Eckhard,Ray, Kallol,Nam, Wonwoo
, p. 10403 - 10407 (2014)
High-valent cobalt-oxo intermediates are proposed as reactive intermediates in a number of cobalt-complex-mediated oxidation reactions. Herein we report the spectroscopic capture of low-spin (S=1/2) CoIV-oxo species in the presence of redox-inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+, and the investigation of their reactivity in C-H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt-oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)CoIII(O.)]2- species to a more stable [(TAML)CoIV(O)(Mn+)] core. The present report supports the proposed role of the redox-inactive metal ions in facilitating the formation of high-valent metal-oxo cores as a necessary step for oxygen evolution in chemistry and biology. What is the metal's role? Cobalt(IV)-oxo complexes binding redox-inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+, are investigated in oxygenation reactions. Theory predicts that the binding of metal ions to the cobalt-oxo core increases the electrophilicity of the oxygen atom. This result supports the role of redox-inactive metal ions in facilitating the formation of high-valent metal-oxo cores as a necessary step for oxygen evolution in chemistry and biology. CAN=cerium ammonium nitrate.
A Bottleable Imidazole-Based Radical as a Single Electron Transfer Reagent
Das, Arpan,Ahmed, Jasimuddin,Rajendran,Adhikari, Debashis,Mandal, Swadhin K.
, p. 1246 - 1252 (2020/12/21)
Reduction of 1,3-bis(2,6-diisopropylphenyl)-2,4-diphenyl-1H-imidazol-3-ium chloride (1) resulted in the formation of the first structurally characterized imidazole-based radical 2. 2 was established as a single electron transfer reagent by treating it with an acceptor molecule tetracyanoethylene. Moreover, radical 2 was utilized as an organic electron donor in a number of organic transformations such as in activation of an aryl-halide bond, alkene hydrosilylation, and in catalytic reduction of CO2 to methoxyborane, all under ambient temperature and pressure.
Investigating reactivity and electronic structure of copper(II)-polypyridyl complexes and hydrogen peroxide
Khazanov, Thomas M.,Botcha, Niharika Krishna,Yergeshbayeva, Sandugash,Shatruk, Michael,Mukherjee, Anusree
, (2020/12/21)
This work presents a detailed study of the reactivity of three mononuclear CuII complexes supported by derivatives of the tetradentate ligand N,N'-bis(2-pyridylmethyl)-1,2-ethylenediamine (bispicen). The CuII complexes are capable of performing C[sbnd]H bond activation in the presence of NEt3 and H2O2 through what has been proposed computationally to be a [CuO]+ intermediate. A wavefunction-based quantum chemical investigation into the electronic structure of the proposed [CuO]+ intermediate reveals a triplet ground state predominantly consistent with an S = ? CuII center ferromagnetically coupled to an oxyl radical, though contributions from the corresponding biradicaloid CuI-oxene resonance structure may be nontrivial. Furthermore, correlation of the electronic structure of the proposed intermediate with analogous high-valent metal-oxo species capable of olefin epoxidation suggests that the CuII complexes might be also capable of olefin epoxidation in the presence of NEt3 and H2O2. To test this hypothesis experimentally, the CuII complexes are treated with NEt3 and H2O2 in the presence of alkene substrates, resulting in the formation of epoxides.
A Mononuclear Non-heme Iron(III)-Peroxo Complex with an Unprecedented High O-O Stretch and Electrophilic Reactivity
Ezhov, Roman,Guo, Yisong,Jang, Semin,Kim, Taeyeon,Lee, Yong-Min,Li, Xiao-Xi,Nam, Wonwoo,Pushkar, Yulia,Sarangi, Ritimukta,Seo, Mi Sook,Xiong, Jin,Zhu, Wenjuan
supporting information, p. 15556 - 15561 (2021/10/01)
A mononuclear non-heme iron(III)-peroxo complex, [Fe(III)(O2)(13-TMC)]+ (1), was synthesized and characterized spectroscopically; the characterization with electron paramagnetic resonance, M?ssbauer, X-ray absorption, and resonance Raman spectroscopies and mass spectrometry supported a high-spin S = 5/2 Fe(III) species binding an O2 unit. A notable observation was an unusually high νO-O at ～1000 cm-1 for the peroxo ligand. With regard to reactivity, 1 showed electrophilic reactivity in H atom abstraction (HAA) and O atom transfer (OAT) reactions. In the HAT reaction, a kinetic isotope effect (KIE) value of 5.8 was obtained in the oxidation of 9,10-dihydroanthracene. In the OAT reaction, a negative ρ value of -0.61 in the Hammett plot was determined in the oxidation of p-X-substituted thioanisoles. Another interesting observation was the electrophilic reactivity of 1 in the oxidation of benzaldehyde derivatives, such as a negative ρ value of -0.77 in the Hammett plot and a KIE value of 2.2. To the best of our knowledge, the present study reports the first example of a mononuclear non-heme iron(III)-peroxo complex with an unusually high νO-O value and unprecedented electrophilic reactivity in oxidation reactions.
