- Harnessing redox-active ligands for low-barrier radical addition at oxorhenium complexes
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The addition of an [X]+ electrophile to the five-coordinate oxorhenium(V) anion [ReV(O)(apPh)2]- {[apPh]2- = 2,4-di-tert-butyl-6-(phenylamido)phenolate} gives new products containing Re-X bonds. The Re-X bond-forming reaction is analogous to oxo transfer to [ReV(O)(apPh) 2]- in that both are 2e- redox processes, but the electronic structures of the products are different. Whereas oxo addition to [ReV(O)(apPh)2]- yields a closed-shell [ReVII(O)2(apPh)2] - product of 2e- metal oxidation, [Cl]+ addition gives a diradical ReVI(O)(apPh)(isq Ph)Cl product ([isqPh]?- = 2,4-di-tert-butyl-6- (phenylimino)semiquinonate) with 1e- in a Re d orbital and 1e - on a redox-active ligand. The differences in electronic structure are ascribed to differences in the π basicity of [O]2- and Cl - ligands. The observation of ligand radicals in Re VI(O)(apPh)(isqPh)X provides experimental support for the capacity of redox-active ligands to deliver electrons in other bond-forming reactions at [ReV(O)(apPh)2] -, including radical additions of O2 or TEMPO? to make Re-O bonds. Attempts to prepare the electron-transfer series monomers between ReVI(O)(apPh)(isqPh)X and [Re V(O)(apPh)2]- yielded a symmetric bis(μ-oxo)dirhenium complex. Formation of this dimer suggested that Re VI(O)(apPh)(isqPh)Cl may be a source of an oxyl metal fragment. The ability of ReVI(O)(apPh)(isq Ph)Cl to undergo radical coupling at oxo was revealed in its reaction with Ph3C?, which affords Ph3COH and deoxygenated metal products. This reactivity is surprising because ReVI(O)(ap Ph)(isqPh)Cl is not a strong outer-sphere oxidant or oxo-transfer reagent. We postulate that the unique ability of Re VI(O)(apPh)(isqPh)Cl to effect oxo transfer to Ph3C? arises from symmetry-allowed mixing of a populated Re≡O π bond with a ligand-centered [isqPh]?- ligand radical, which gives oxyl radical character to the oxo ligand. This allows the closed-shell oxo ligand to undergo a net 2e- oxo-transfer reaction to Ph3C? via kinetically facile redox-active ligand-mediated radical steps. Harnessing intraligand charge transfer for radical reactions at closed-shell oxo ligands is a new strategy to exploit redox-active ligands for small-molecule activation and functionalization. The implications for the design of new oxidants that utilize low-barrier radical steps for selective multielectron transformations are discussed.
- Lippert, Cameron A.,Hardcastle, Kenneth I.,Soper, Jake D.
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Read Online
- N-Hydroxyphthalimide: A Hydrogen Atom Transfer Mediator in Hydrocarbon Oxidations Promoted by Nonheme Iron(IV)-Oxo Complexes
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The oxidation of a series of hydrocarbons by the nonheme iron(IV)-oxo complex [(N4Py)FeIV-O]2+ is efficiently mediated by N-hydroxyphthalimide. The increase of reactivity is associated to the oxidation of the mediator to the phthalimide N-oxyl radical, which efficiently abstracts a hydrogen atom from the substrates, regenerating the mediator in its reduced form.
- Barbieri, Alessia,Lanzalunga, Osvaldo,Lapi, Andrea,Di Stefano, Stefano
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Read Online
- Metal-Free Access to (Spirocyclic)Tetrahydro-β-carbolines in Water Using an Ion-Pair as a Superacidic Precatalyst
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The unprecedented triarylcarbonium ion-pair-catalyzed Pictet-Spengler reaction of tryptamines with aromatic aldehydes and cyclic ketones in water was disclosed. Under metal-free conditions, diverse tetrahydro-β-carbolines and spirocyclic tetrahydro-β-carb
- Ji, Liang,Jia, Zhenhua,Liu, Xiaoxiao,Loh, Teck-Peng,Zhang, Ting,Zhang, Zhenguo
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p. 2052 - 2057
(2022/02/10)
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- To Rebound or...Rebound? Evidence for the "alternative Rebound" mechanism in Ca'H Oxidations by the systems nonheme Mn Complex/H2O2/carboxylic acid
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In this work, it has been shown that aliphatic Ca'H oxidations by bioinspired catalyst systems Mn aminopyridine complex/H2O2/carboxylic acid in acetonitrile afford predominantly a mixture of the corresponding alcohol and the ester. The alcohol/ester ratio is higher for catalysts bearing electron-donating groups at the aminopyridine core. Isotopic labeling studies witness that the oxygen atom of the alcohol originates from the H2O2molecule, while the ester oxygen comes exclusively from the acid. Oxidation of ethylbenzene in the presence of acetic acid affords enantiomerically enriched 1-phenylethanol and 1-phenyl acetate, with close enantioselectivities and the same sign of absolute chirality. Experimental data and density functional theory calculations provide evidence in favor of the rate-limiting benzylic H atom abstraction by the high-spin (S = 1) [LMnV(O)OAc]2+active species followed by competitive OH/OC(O)R rebound. This mechanism has been unprecedented for Ca'H oxidations catalyzed by bioinspired Mn complexes. The trends governing the alcohol/ester ratios have been rationalized in terms of steric properties of the catalyst, acid, and substrate. copy; 2021 American Chemical Society.
- Ottenbacher, Roman V.,Bryliakova, Anna A.,Shashkov, Mikhail V.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
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p. 5517 - 5524
(2021/05/31)
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- Nonheme Diiron Oxygenase Mimic That Generates a Diferric-Peroxo Intermediate Capable of Catalytic Olefin Epoxidation and Alkane Hydroxylation including Cyclohexane
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Herein are described substrate oxidations with H2O2 catalyzed by [FeII(IndH)(CH3CN)3](ClO4)2 [IndH = 1,3-bis(2′-pyridylimino)isoindoline], involving a spectroscopically characterized (μ-oxo)(μ-1,2-peroxo)diiron(III) intermediate (2) that is capable of olefin epoxidation and alkane hydroxylation including cyclohexane. Species 2 also converts ketones to lactones with a decay rate dependent on [ketone], suggesting direct nucleophilic attack of the substrate carbonyl group by the peroxo species. In contrast, peroxo decay is unaffected by the addition of olefins or alkanes, but the label from H218O is incorporated into the the epoxide and alcohol products, implicating a high-valent iron-oxo oxidant that derives from O-O bond cleavage of the peroxo intermediate. These results demonstrate an ambiphilic diferric-peroxo intermediate that mimics the range of oxidative reactivities associated with O2-activating nonheme diiron enzymes.
- Kaizer, József,Oloo, Williamson N.,Que, Lawrence,Szávuly, Miklós
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- Rapid Iron(III)?Fluoride-Mediated Hydrogen Atom Transfer
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We anticipate high-valent metal–fluoride species will be highly effective hydrogen atom transfer (HAT) oxidants because of the magnitude of the H?F bond (in the product) that drives HAT oxidation. We prepared a dimeric FeIII(F)?F?FeIII(F) complex (1) by reacting [FeII(NCCH3)2(TPA)](ClO4)2 (TPA=tris(2-pyridylmethyl)amine) with difluoro(phenyl)-λ3-iodane (difluoroiodobenzene). 1 was a sluggish oxidant, however, it was readily activated by reaction with Lewis or Br?nsted acids to yield a monomeric [FeIII(TPA)(F)(X)]+ complex (2) where X=F/OTf. 1 and 2 were characterized using NMR, EPR, UV/Vis, and FT-IR spectroscopies and mass spectrometry. 2 was a remarkably reactive FeIII reagent for oxidative C?H activation, demonstrating reaction rates for hydrocarbon HAT comparable to the most reactive FeIII and FeIV oxidants.
- Doyle, Lorna M.,Gericke, Robert,McDonald, Aidan R.,Panda, Chakadola
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supporting information
p. 26281 - 26286
(2021/11/12)
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- Expeditious and practical synthesis of tertiary alcohols from esters enabled by highly polarized organometallic compounds under aerobic conditions in Deep Eutectic Solvents or bulk water
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An efficient protocol was developed for the synthesis of tertiary alcohols via nucleophilic addition of organometallic compounds of s-block elements (Grignard and organolithium reagents) to esters performed in the biodegradable choline chloride/urea eutectic mixture or in water. This approach displays a broad substrate scope, with the addition reaction proceeding quickly (20 s reaction time) and cleanly, at ambient temperature and under air, straightforwardly furnishing the expected tertiary alcohols in yields of up to 98%. The practicability of the method is exemplified by the sustainable synthesis of some representative S-trityl-L-cysteine derivatives, which are a potent class of Eg5 inhibitors, also via telescoped one-pot processes.
- Quivelli, Andrea F.,D'Addato, Giovanna,Vitale, Paola,García-álvarez, Joaquín,Perna, Filippo M.,Capriati, Vito
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- Fast Addition of s-Block Organometallic Reagents to CO2-Derived Cyclic Carbonates at Room Temperature, Under Air, and in 2-Methyltetrahydrofuran
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Fast addition of highly polar organometallic reagents (RMgX/RLi) to cyclic carbonates (derived from CO2 as a sustainable C1 synthon) has been studied in 2-methyltetrahydrofuran as a green reaction medium or in the absence of external volatile organic solvents, at room temperature, and in the presence of air/moisture. These reaction conditions are generally forbidden with these highly reactive main-group organometallic compounds. The correct stoichiometry and nature of the polar organometallic alkylating or arylating reagent allows straightforward synthesis of: highly substituted tertiary alcohols, β-hydroxy esters, or symmetric ketones, working always under air and at room temperature. Finally, an unprecedented one-pot/two-step hybrid protocol is developed through combination of an Al-catalyzed cycloaddition of CO2 and propylene oxide with the concomitant fast addition of RLi reagents to the in situ and transiently formed cyclic carbonate, thus allowing indirect conversion of CO2 into the desired highly substituted tertiary alcohols without need for isolation or purification of any reaction intermediates.
- Elorriaga, David,de la Cruz-Martínez, Felipe,Rodríguez-álvarez, María Jesús,Lara-Sánchez, Agustín,Castro-Osma, José Antonio,García-álvarez, Joaquín
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p. 2084 - 2092
(2021/04/02)
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- Samarium-based Grignard-type addition of organohalides to carbonyl compounds under catalysis of CuI
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Grignard-type additions were readily achieved under the mediation of CuI (10 mol%) and samarium (2 equiv.) by employing various organohalides,e.g.benzyl, aryl, heterocyclic and aliphatic halides (Cl, Br or I), and diverse carbonyl compounds (e.g.carbonic esters, carboxylic esters, acid anhydrides, acyl chlorides, ketones, aldehydes, propylene epoxides and formamides) to afford alcohols, ketones and aldehydes, respectively, with high efficiency and chemoselectivity, in which the organosamarium intermediate might be involved.
- Liu, Chen,Liu, Yongjun,Qi, Yan,Song, Bin,Wang, Liang,Xiao, Shuhuan
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supporting information
p. 6169 - 6172
(2021/06/30)
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- C-H Activation by RuCo3O4Oxo Cubanes: Effects of Oxyl Radical Character and Metal-Metal Cooperativity
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High-valent multimetallic-oxo/oxyl species have been implicated as intermediates in oxidative catalysis involving proton-coupled electron transfer (PCET) reactions, but the reactive nature of these oxo species has hindered the development of an in-depth understanding of their mechanisms and multimetallic character. The mechanism of C-H oxidation by previously reported RuCo3O4 cubane complexes bearing a terminal RuV-oxo ligand, with significant oxyl radical character, was investigated. The rate-determining step involves H atom abstraction (HAA) from an organic substrate to generate a Ru-OH species and a carbon-centered radical. Radical intermediates are subsequently trapped by another equivalent of the terminal oxo to afford isolable radical-trapped cubane complexes. Density functional theory (DFT) reveals a barrierless radical combination step that is more favorable than an oxygen-rebound mechanism by 12.3 kcal mol-1. This HAA reactivity to generate organic products is influenced by steric congestion and the C-H bond dissociation energy of the substrate. Tuning the electronic properties of the cubane (i.e., spin density localized on terminal oxo, basicity, and redox potential) by varying the donor ability of ligands at the Co sites modulates C-H activations by the RuV-oxo fragment and enables construction of structure-activity relationships. These results reveal a mechanistic pathway for C-H activation by high-valent metal-oxo species with oxyl radical character and provide insights into cooperative effects of multimetallic centers in tuning PCET reactivity.
- Amtawong, Jaruwan,Balcells, David,Handford, Rex C.,Skjelstad, Bastian Bjerkem,Suslick, Benjamin A.,Tilley, T. Don
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p. 12108 - 12119
(2021/08/20)
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- Formation of a hydride containing amido-zincate using pinacolborane
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Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin)viaZn-C/H-BPin exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)]?(Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzinc complex led to Zn-C/H-BPin metathesis being the major outcome. Independent synthesis and full characterisation of two LnLi[(dpa)ZnPh2] (L = THF,n= 3; L = PMDETA,n= 1) complexes,1and3, respectively, enabled reactivity studies that demonstrated that these species display zincate type reactivity (by comparison to the lower reactivity of the neutral complex (Me-dpa)ZnPh2,4, Me-dpa = 2,2′-dipyridyl-N-methylamine). This included1performing the rapid deprotonation of 4-ethynyltoluene and also phenyl transfer to α,α,α-trifluoroacetophenone in contrast to neutral complex4. Complex1reacted with one equivalent of HBPin to give predominantly PhBPin (ca.90%) and a lithium amidophenylzincate containing a hydride unit, complex7-A, as the major zinc containing product. Complex7-Atransfers hydride to an electrophile preferentially over phenyl, indicating it reacts as a hydridozincate. Attempts to react1with >1 equivalent of HBPin or with catecholborane led to more complex outcomes, which included significant borane and dpaZn substituent scrambling, two examples of which were crystallographically characterised. While this work provides proof of principle for Zn-C/H-BPin exchange as a route to form an amido-zincate containing a hydride, amido-organozincates that undergo more selective Zn-C/H-BPin exchange still are required.
- Ingleson, Michael J.,Nichol, Gary S.,Uzelac, Marina,Yuan, Kang
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supporting information
p. 14018 - 14026
(2021/10/19)
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- Fast Hydrocarbon Oxidation by a High-Valent Nickel–Fluoride Complex
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In the search for highly reactive oxidants we have identified high-valent metal–fluorides as a potential potent oxidant. The high-valent Ni–F complex [NiIII(F)(L)] (2, L=N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate) was prepared from [NiII(F)(L)]? (1) by oxidation with selectfluor. Complexes 1 and 2 were characterized by using 1H/19F NMR, UV-vis, and EPR spectroscopies, mass spectrometry, and X-ray crystallography. Complex 2 was found to be a highly reactive oxidant in the oxidation of hydrocarbons. Kinetic data and products analysis demonstrate a hydrogen atom transfer mechanism of oxidation. The rate constant determined for the oxidation of 9,10-dihydroanthracene (k2=29 m?1 s?1) compared favorably with the most reactive high-valent metallo-oxidants. Complex 2 displayed reaction rates 2000–4500-fold enhanced with respect to [NiIII(Cl)(L)] and also displayed high kinetic isotope effect values. Oxidative hydrocarbon and phosphine fluorination was achieved. Our results provide an interesting direction in designing catalysts for hydrocarbon oxidation and fluorination.
- Lovisari, Marta,McDonald, Aidan R.,Mondal, Prasenjit,Twamley, Brendan
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supporting information
p. 13044 - 13050
(2020/06/05)
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- Bulky N-Heterocyclic-Carbene-Coordinated Palladium Catalysts for 1,2-Addition of Arylboron Compounds to Carbonyl Compounds
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The synthesis of primary, secondary, and tertiary alcohols by the 1,2-addition of arylboronic acids or boronates to carbonyl compounds, including unactivated ketones, using novel bulky yet flexible N-heterocyclic carbene (NHC)-coordinated 2,6-di(pentan-3-yl)aniline (IPent)-based cyclometallated palladium complexes (CYPs) as catalysts is reported. The PhS-IPent-CYP-catalyzed reactions are efficient at low catalyst loadings (0.02–0.3 mol% Pd), and the exceptional catalytic activity for 1,2-addition is attributed to the steric bulk of the NHC ligand. These reactions can yield a wide range of functionalized benzylic alcohols that are difficult to synthesize by classical protocols using highly active organomagnesium or lithium reagents.
- Okuda, Yuta,Nagaoka, Masahiro,Yamamoto, Tetsuya
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p. 6291 - 6300
(2020/11/30)
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- Iron-catalysed 1,2-aryl migration of tertiary azides
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1,2-Aryl migration of α,α-diaryl tertiary azides was achieved by using the catalytic system of FeCl2/N-heterocyclic carbene (NHC) SIPr·HCl. The reaction generated aniline products in good yields after one-pot reduction of the migration-resultant imines.
- Wei, Kaijie,Yang, Tonghao,Chen, Qing,Liang, Siyu,Yu, Wei
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p. 11685 - 11688
(2020/10/19)
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- A Bifunctional Iron Nanocomposite Catalyst for Efficient Oxidation of Alkenes to Ketones and 1,2-Diketones
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We herein report the fabrication of a bifunctional iron nanocomposite catalyst, in which two catalytically active sites of Fe-Nx and Fe phosphate, as oxidation and Lewis acid sites, were simultaneously integrated into a hierarchical N,P-dual doped porous carbon. As a bifunctional catalyst, it exhibited high efficiency for direct oxidative cleavage of alkenes into ketones or their oxidation into 1,2-diketones with a broad substrate scope and high functional group tolerance using TBHP as the oxidant in water under mild reaction conditions. Furthermore, it could be easily recovered for successive recycling without appreciable loss of activity. Mechanistic studies disclose that the direct oxidation of alkenes proceeds via the formation of an epoxide as intermediate followed by either acid-catalyzed Meinwald rearrangement to give ketones with one carbon shorter or nucleophilic ring-opening to generate 1,2-diketones in a cascade manner. This study not only opens up a fancy pathway in the rational design of Fe-N-C catalysts but also offers a simple and efficient method for accessing industrially important ketones and 1,2-diketones from alkenes in a cost-effective and environmentally benign fashion.
- Ma, Zhiming,Ren, Peng,Song, Tao,Xiao, Jianliang,Yang, Yong,Yuan, Youzhu
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p. 4617 - 4629
(2020/05/19)
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- Determining the Inherent Selectivity for Carbon Radical Hydroxylation versus Halogenation with FeIII(OH)(X) Complexes: Relevance to the Rebound Step in Non-heme Iron Halogenases
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The first structural models of the proposed cis-FeIII(OH)(halide) intermediate in the non-heme iron halogenases were synthesized and examined for their inherent reactivity with tertiary carbon radicals. Selective hydroxylation occurs for these cis-FeIII(OH)(X) (X = Cl, Br) complexes in a radical rebound-like process. In contrast, a cis-FeIII(Cl)2 complex reacts with carbon radicals to give halogenation. These results are discussed in terms of the inherent reactivity of the analogous rebound intermediate in both enzymes and related catalysts.
- Yadav, Vishal,Rodriguez, Rodolfo J.,Siegler, Maxime A.,Goldberg, David P.
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supporting information
p. 7259 - 7264
(2020/04/22)
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- Highly Selective and Catalytic Oxygenations of C?H and C=C Bonds by a Mononuclear Nonheme High-Spin Iron(III)-Alkylperoxo Species
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The reactivity of a mononuclear high-spin iron(III)-alkylperoxo intermediate [FeIII(t-BuLUrea)(OOCm)(OH2)]2+(2), generated from [FeII(t-BuLUrea)(H2O)(OTf)](OTf) (1) [t-BuLUrea=1,1′-(((pyridin-2-ylmethyl)azanediyl)bis(ethane-2,1-diyl))bis(3-(tert-butyl)urea), OTf=trifluoromethanesulfonate] with cumyl hydroperoxide (CmOOH), toward the C?H and C=C bonds of hydrocarbons is reported. 2 oxygenates the strong C?H bonds of aliphatic substrates with high chemo- and stereoselectivity in the presence of 2,6-lutidine. While 2 itself is a sluggish oxidant, 2,6-lutidine assists the heterolytic O?O bond cleavage of the metal-bound alkylperoxo, giving rise to a reactive metal-based oxidant. The roles of the urea groups on the supporting ligand, and of the base, in directing the selective and catalytic oxygenation of hydrocarbon substrates by 2 are discussed.
- Ghosh, Ivy,Banerjee, Sridhar,Paul, Satadal,Corona, Teresa,Paine, Tapan Kanti
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p. 12534 - 12539
(2019/08/07)
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- Controlled Photocatalytic Hydrocarbon Oxidation by Uranyl Complexes
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Controlled, photocatalytic C?H bond activations are key reactions in the toolkits of the modern synthetic chemist. While it is known that the uranyl(VI) ion, [UVIO2]2+, the environmentally dominant form of uranium, is photoactive, most literature examines its luminescent properties, neglecting its potential synthetic utility for photocatalytic C?H bond cleavage. Here, we synthesise and fully characterise an air-stable and hydrocarbon-soluble uranyl phenanthroline complex, [UVIO2(NO3)2(Ph2phen)], UPh2phen, and demonstrate that it can catalytically abstract hydrogen atoms from a variety of organic substrates under visible light irradiation. We show that the commercially available parent complex, uranyl nitrate ([UVIO2(NO3)2(OH2)2]?4H2O; UNO3), is also competent, but from electronic spectroscopy we attribute the higher rates and selectivity of UPh2phen to ligand-mediated electronic effects. Ketones are selectively formed over other oxygenated products (alcohols, etc.), and the catalytic oxidation of substrates containing a benzylic C?H position is particularly improved for UPh2phen. We also show uranyl-mediated photocatalytic C?C bond cleavage in a model lignin compound for the first time.
- Arnold, Polly L.,Purkis, Jamie M.,Rutkauskaite, Ryte,Kovacs, Daniel,Love, Jason B.,Austin, Jonathan
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p. 3786 - 3790
(2019/03/07)
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- Directed: Ortho-metalation-nucleophilic acyl substitution strategies in deep eutectic solvents: The organolithium base dictates the chemoselectivity
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Directed ortho metalation (DoM) or nucleophilic acyl substitution (SNAc) can be efficiently programmed on the same aromatic carboxylic acid amide, in a choline chloride-based eutectic mixture, by simply switching the nature of the organolithium reagent. Telescoped, one-pot ortho-lithiation/Suzuki-Miyaura cross-couplings have also been demonstrated for the first time in Deep Eutectic Solvents.
- Ghinato, Simone,Dilauro, Giuseppe,Perna, Filippo Maria,Capriati, Vito,Blangetti, Marco,Prandi, Cristina
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p. 7741 - 7744
(2019/07/12)
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- NHC-coordinated palladacycle catalyzed 1,2-addition of arylboronates to unactivated ketones
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Palladium catalyzed intermolecular 1,2-addition of arylboronate to unactivated ketone was investigated. NHC-coordinated palladacycle 4c exhibited catalytic activity for the reactions and provided the corresponding tertiary alcohols and γ,γ-disubstituted γ-lactones in good to excellent yields.
- Akiyama, Ryo,Sugaya, Mariko,Shinozaki, Hiraku,Yamamoto, Tetsuya
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p. 1193 - 1201
(2019/05/06)
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- Radical Rebound Hydroxylation Versus H-Atom Transfer in Non-Heme Iron(III)-Hydroxo Complexes: Reactivity and Structural Differentiation
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The characterization of high-valent iron centers in enzymes has been aided by synthetic model systems that mimic their reactivity or structural and spectral features. For example, the cleavage of dioxygen often produces an iron(IV)-oxo that has been characterized in a number of enzymatic and synthetic systems. In non-heme 2-oxogluterate dependent (iron-2OG) enzymes, the ferryl species abstracts an H-atom from bound substrate to produce the proposed iron(III)-hydroxo and caged substrate radical. Most iron-2OG enzymes perform a radical rebound hydroxylation at the site of the H-atom abstraction (HAA); however, recent reports have shown that certain substrates can be desaturated through the loss of a second H atom at a site adjacent to a heteroatom (N or O) for most native desaturase substrates. One proposed mechanism for the removal of the second H-atom involves a polar-cleavage mechanism (electron transfer-proton transfer) by the iron(III)-hydroxo, as opposed to a second HAA. Herein we report the synthesis and characterization of a series of iron complexes with hydrogen bonding interactions between bound aquo or hydroxo ligands and the secondary coordination sphere in ferrous and ferric complexes. Interconversion among the iron species is accomplished by stepwise proton or electron addition or subtraction, as well as H-atom transfer (HAT). The calculated bond dissociation free energies (BDFEs) of two ferric hydroxo complexes, differentiated by their noncovalent interactions and reactivity, suggest that neither complex is capable of activating even weak C-H bonds, lending further support to the proposed mechanism for desaturation in iron-2OG desaturase enzymes. Additionally, the ferric hydroxo species are differentiated by their reactivity toward performing a radical rebound hydroxylation of triphenylmethylradical. Our findings should encourage further study of the desaturase systems that may contain unique H-bonding motifs proximal to the active site that help bias substrate desaturation over hydroxylation.
- Drummond, Michael J.,Ford, Courtney L.,Gray, Danielle L.,Popescu, Codrina V.,Fout, Alison R.
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supporting information
p. 6639 - 6650
(2019/05/06)
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- Carbonate encapsulation from dissolved atmospheric CO2 into a polyoxovanadate capsule
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An aqueous synthesis, involving the reduction of the VO3- anion in a mild alkaline pH in the presence of α-Bi2O3, led to the formation of a fully reduced polyoxovanadate (POV) capsule, with CO32- anion encapsulation in its internal cavity, in the compound [Na6(H2O)24][H8VIV15O36(CO3)]·3N2H4·10H2O (1). This CO32- anion encapsulation, the source of which is absorbed aerial CO2 in the pertinent aqueous alkaline reaction mixture, occurs only in the presence of α-Bi2O3. Compound 1 crystals, upon exposure to HCl acid vapor, exclude CO2 gas that can react with the Grignard reagent (PhMgBr) to form triphenylcarbinol and benzoic acid; during this solid-vapor interface reaction, compound 1 itself transforms into an amorphous material that includes the Cl- anion but could not be characterized unambiguously. Thus, we have synthesized a chloride ion (Cl-) encapsulated compound [Na10(H2O)24][H3VIV15O36(Cl)]·6H2O (2) in a direct synthesis protocol, which has been characterized by crystallography as well as by other spectroscopic methods. Compounds 1 and 2, each having fifteen vanadium(iv) centers, exhibit interesting magnetism in their solid states. The temperature-dependent magnetic susceptibilities for compounds 1 and 2 have been recordred at 0.1 T in the temperature range of 3-300 K. The temperature-dependent magnetic susceptibilities of compounds 1 and 2 are shown in the form of χMvs. T and their product χMT vs. T plots.
- Mulkapuri, Sateesh,Kurapati, Sathish Kumar,Das, Samar K.
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p. 8773 - 8781
(2019/06/24)
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- Dioxygen-Derived Nonheme Mononuclear FeIII(OH) Complex and Its Reactivity with Carbon Radicals
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A new tetradentate, monoanionic, mixed N/O donor ligand (BNPAPh2O-) with second coordination sphere H-bonding groups has been synthesized for stabilization of a terminal FeIII(OH) complex. The complex FeII(BNPAPh2O)(OTf) (1) reacts with O2 to give a mononuclear terminal FeIII(OH) complex, FeIII(OH)(BNPAPh2O)(OTf) (2), both of which were characterized by X-ray diffraction, electrospray ionization mass spectrometry, UV-vis, 1H and 19F nuclear magnetic resonance, 57Fe M?ssbauer, and electron paramagnetic resonance spectroscopies. Treatment of 2 with carbon radicals (Ar3C·) gives Ar3COH and the FeII complex 1, in direct analogy with the elusive radical "rebound" process proposed for nonheme iron enzymes.
- Yadav, Vishal,Gordon, Jesse B.,Siegler, Maxime A.,Goldberg, David P.
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supporting information
p. 10148 - 10153
(2019/07/05)
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- Deciphering the hydrogen-bonding scheme in the crystal structure of triphenylmethanol: A tribute to George Ferguson and co-workers
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The crystal structure of triphenylmethanol, C19H16O, has been redetermined using data collected at 295 and 153K, and is compared to the model published by Ferguson et al. over 25 years ago [Ferguson et al. (1992). Acta Cryst. C48, 1272-1275] and that published by Serrano-González et al., using neutron and X-ray diffraction data [Serrano-González et al. (1999). J. Phys. Chem. B, 103, 6215-6223]. As predicted by these authors, the hydroxy groups are involved in weak intermolecular hydrogen bonds in the crystal, forming tetrahedral tetramers based on the two independent molecules in the asymmetric unit, one of which is placed on the threefold symmetry axis of the R space group. However, the reliable determination of the hydroxy H-atom positions is difficult to achieve, for two reasons. Firstly, a positional disorder affects the full asymmetric unit, which is split over two sets of positions, with occupancy factors of ca 0.74 and 0.26. Secondly, all hydroxy H atoms are further disordered, either by symmetry, or through a positional disorder in the case of parts placed in general positions. We show that the correct description of the hydrogen-bonding scheme is possible only if diffraction data are collected at low temperature. The prochiral character of the hydrogen-bonded tetrameric supramolecular clusters leads to enantiomorphic three-dimensional graphs in each tetramer. The crystal is thus a racemic mixture of sup S and sup R motifs, consistent with the centrosymmetric nature of the R space group.
- Tzompantzi, Tomasa Rodriguez,Hernandez, Aldo Guillermo Amaro,Meza-Leon, Rosa Luisa,Bernes, Sylvain
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p. 1266 - 1273
(2019/09/18)
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- I-Pr2NMgCl·LiCl Enables the Synthesis of Ketones by Direct Addition of Grignard Reagents to Carboxylate Anions
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The direct preparation of ketones from carboxylate anions is greatly limited by the required use of organolithium reagents or activated acyl sources that need to be independently prepared. Herein, a specific magnesium amide additive is used to activate and control the addition of more tolerant Grignard reagents to carboxylate anions. This strategy enables the modular synthesis of ketones from CO2 and the preparation of isotopically labeled pharmaceutical building blocks in a single operation.
- Colas, Kilian,Dos Santos, A. Catarina V. D.,Mendoza, Abraham
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supporting information
(2019/10/08)
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- Introducing Glycerol as a Sustainable Solvent to Organolithium Chemistry: Ultrafast Chemoselective Addition of Aryllithium Reagents to Nitriles under Air and at Ambient Temperature
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Edging closer towards developing air and moisture compatible polar organometallic chemistry, the chemoselective and ultrafast addition of a range of aryllithium reagents to nitriles has been accomplished by using glycerol as a solvent, at ambient temperature in the presence of air, establishing a novel sustainable access to aromatic ketones. Addition reactions occur heterogeneously (“on glycerol conditions”), where the lack of solubility of the nitriles in glycerol and the ability of the latter to form strong intermolecular hydrogen bonds seem key to favouring nucleophilic addition over competitive hydrolysis. Remarkably, PhLi exhibits a greater resistance to hydrolysis working “on glycerol” conditions than “on water”. Introducing glycerol as a new solvent in organolithium chemistry unlocks a myriad of opportunities for developing more sustainable, air and moisture tolerant main-group-metal-mediated organic synthesis.
- Rodríguez-álvarez, María J.,García-álvarez, Joaquín,Uzelac, Marina,Fairley, Michael,O'Hara, Charles T.,Hevia, Eva
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p. 1720 - 1725
(2018/01/27)
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- Control of tandem isomerizations: Flow-assisted reactions of: O -lithiated aryl benzyl ethers
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Tandem chemical changes are often difficult to control at will, because they proceed rapidly through multiple unstable reactive intermediates. It is desirable to develop a novel method for controlling such tandem changes to obtain desired products with high selectivity. Herein, we report a flow microreactor platform for controlling tandem isomerizations of o-lithiated aryl benzyl ethers based on precise residence time control.
- Lee, Hyune-Jea,Kim, Heejin,Yoshida, Jun-Ichi,Kim, Dong-Pyo
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p. 547 - 550
(2018/01/19)
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- Reversible Twisting of Primary Amides via Ground State N-C(O) Destabilization: Highly Twisted Rotationally Inverted Acyclic Amides
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Since the seminal studies by Pauling in 1930s, planarity has become the defining characteristic of the amide bond. Planarity of amides has central implications for the reactivity and chemical properties of amides of relevance to a range of chemical disciplines. While the vast majority of amides are planar, nonplanarity has a profound effect on the properties of the amide bond, with the most common method to restrict the amide bond relying on the incorporation of the amide function into a rigid cyclic ring system. In a major departure from this concept, here, we report the first class of acyclic twisted amides that can be prepared, reversibly, from common primary amides in a single, operationally trivial step. Di-tert-butoxycarbonylation of the amide nitrogen atom yields twisted amides in which the amide bond exhibits nearly perpendicular twist. Full structural characterization of a range of electronically diverse compounds from this new class of twisted amides is reported. Through reactivity studies we demonstrate unusual properties of the amide bond, wherein selective cleavage of the amide bond can be achieved by a judicious choice of the reaction conditions. Through computational studies we evaluate structural and energetic details pertaining to the amide bond deformation. The ability to selectively twist common primary amides, in a reversible manner, has important implications for the design and application of the amide bond nonplanarity in structural chemistry, biochemistry and organic synthesis.
- Meng, Guangrong,Shi, Shicheng,Lalancette, Roger,Szostak, Roman,Szostak, Michal
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supporting information
p. 727 - 734
(2018/01/26)
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- Generation and Confinement of Long-Lived N-Oxyl Radical and Its Photocatalysis
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Generation of controllable carbon radical under the assistance of N-oxyl radical is an efficient method for the activation of C-H bonds in hydrocarbons. We herein report that irradiation of α-Fe2O3 and N-hydroxyphthalimide (NHPI) under 455 nm light generates phthalimide-N-oxyl radical (PINO), which after being formed by oxidation with holes, is confined on α-Fe2O3 surface. The half-life time of the confined radical reaches 22 s as measured by in situ electron paramagnetic resonance (EPR) after the light being turned off. This allows the long-lived N-oxyl radical to abstract the H from C-H bond to form a carbon radical that reacts with molecular oxygen to form R3C-OO· species, decomposition of which leads to oxygenated products.
- Zhang, Chaofeng,Huang, Zhipeng,Lu, Jianmin,Luo, Nengchao,Wang, Feng
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supporting information
p. 2032 - 2035
(2018/02/19)
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- A Catalyst-Free Amination of Functional Organolithium Reagents by Flow Chemistry
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Reported is the electrophilic amination of functional organolithium intermediates with well-designed aminating reagents under mild reaction conditions using flow microreactors. The aminating reagents were optimized to achieve efficient C?N bond formation without using any catalyst. The electrophilic amination reactions of functionalized aryllithiums were successfully conducted under mild reaction conditions, within 1 minute, by using flow microreactors. The aminating reagent was also prepared by the flow method. Based on stopped-flow NMR analysis, the reaction time for the preparation of the aminating reagent was quickly optimized without the necessity of work-up. Integrated one-flow synthesis consisting of the generation of an aryllithium, the preparation of an aminating reagent, and their combined reaction was successfully achieved to give the desired amine within 5 minutes of total reaction time.
- Kim, Heejin,Yonekura, Yuya,Yoshida, Jun-Ichi
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p. 4063 - 4066
(2018/03/21)
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- KOtBu as a single electron donor? Revisiting the halogenation of alkanes with CBr4 and CCl4
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The search for reactions where KOtBu and other tert-alkoxides might behave as single electron donors led us to explore their reactions with tetrahalomethanes, CX4, in the presence of adamantane. We recently reported the halogenation of adamantane under these conditions. These reactions appeared to mirror the analogous known reaction of NaOH with CBr4 under phase-transfer conditions, where initiation features single electron transfer from a hydroxide ion to CBr4. We now report evidence from experimental and computational studies that KOtBu and other alkoxide reagents do not go through an analogous electron transfer. Rather, the alkoxides form hypohalites upon reacting with CBr4 or CCl4, and homolytic decomposition of appropriate hypohalites initiates the halogenation of adamantane.
- Emery, Katie J.,Young, Allan,Arokianathar, J. Norman,Tuttle, Tell,Murphy, John A.
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- Method of preparing triphenylmethanol and biphenyl-4-formyl corey lactone
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The invention discloses a method of preparing triphenylmethanol and biphenyl-4-formyl corey lactone. The method comprises the steps of taking a commercial corey lactone dioldihydroxy derivative as a raw material, giving a hydrolysis reaction in a primary hydroxyl position under an acidic condition, neutralizing a reaction system, and performing crystallization and recrystallization to form triphenylmethanol and biphenyl-4-formyl corey lactone. The method has the benefits that the method has a few steps and is mild in condition and easy to control; neutralization reaction liquid is made full use for crystallization; both triphenylmethanol and biphenyl-4-formyl corey lactone are separated from the reaction system separately at a time; the method is time-saving and efficient and achieves an unexpected effect; double solvents are adopted for the recrystallization of triphenylmethanol and biphenyl-4-formyl corey lactone respectively; prepared triphenylmethanol or biphenyl-4-formyl corey lactone is low in impurity content and high in yield and purity; solid waste of triphenylmethanol is recycled; the treatment expense of the waste is saved; and the production cost is lowered.
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Paragraph 0045; 0093-0132
(2018/07/06)
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- Merging Photoredox with Br?nsted Acid Catalysis: The Cross-Dehydrogenative C?O Coupling for sp3 C?H Bond Peroxidation
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A photoredox and Br?nsted acid synergistically catalyzed cross-dehydrogenative C?O coupling reaction is developed in which isochroman peroxyacetals are formed through sp3 C?H bond peroxidation. The reported method is characterized by its extremely mild reaction conditions, excellent yields, and broad substrate scope. An oxocarbenium ion p-chlorobenzenesulfonate was speculated to be the reactive intermediate. The role of hemiacetals and oxygenated dimers on the effective stabilization of the oxocarbenium ion was investigated; the presence of acid appeared to establish equilibrium between hemiacetals and oxygenated dimers with the oxocarbenium ion pairs. The broad applicability of the method highlights the potential of the protocol for molecule synthesis.
- Xia, Qing,Wang, Qiang,Yan, Changcun,Dong, Jianyang,Song, Hongjian,Li, Ling,Liu, Yuxiu,Wang, Qingmin,Liu, Xiangming,Song, Haibin
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p. 10871 - 10877
(2017/08/18)
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- Synthesis of Tetraarylmethanes by the Triflic Acid-Promoted Formal Cross-Dehydrogenative Coupling of Triarylmethanes with Arenes
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The formal cross-dehydrogenative coupling of triarylmethanes with arenes promoted by triflic acid and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone is described. This method provides a variety of tetraarylmethane derivatives in good to excellent yields from triarylmethanes that can be readily prepared by our previous methods. Control experiments suggest a possible catalytic cycle involving the generation of a trityl cation intermediate followed by nucleophilic addition of the arene.
- Nambo, Masakazu,Yim, Jacky C.-H.,Fowler, Kevin G.,Crudden, Cathleen M.
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supporting information
p. 2936 - 2940
(2017/10/09)
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- The Barbier-Grignard-Type Arylation of Ketones and Unexpected Cross-Coupling of Phenolic Ketones using Unactivated Aryl Bromides
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A novel, highly versatile and efficient method has been developed for the Barbier-Grignard-type arylation of ketones and an unexpected cross-coupling of phenolic ketones was observed using unactivated bromides and magnesium in tetrahydrofuran/toluene at 96°C promoted by multicatalysts of cupric bromide (15 mol%), bismuth chloride (5 mol%) and silver bromide (10 mol%). The substituent and electronic effects on the reaction have been discussed. High yields of arylation and cross-coupling have been attained under mild conditions. A novel reasonable mechanism involving a quinone intermediate is proposed. The high chemical selectivity in the cross-coupling to the hydroxy group of phenolic ketones should help ketones find new applications.
- Wen, Yunming,Chen, Guifang,Huang, Shiqiang,Tang, Yu,Yang, Jun,Zhang, Yuanming
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p. 947 - 957
(2016/04/05)
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- Mononuclear Nonheme High-Spin Iron(III)-Acylperoxo Complexes in Olefin Epoxidation and Alkane Hydroxylation Reactions
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Mononuclear nonheme high-spin iron(III)-acylperoxo complexes bearing an N-methylated cyclam ligand were synthesized, spectroscopically characterized, and investigated in olefin epoxidation and alkane hydroxylation reactions. In the epoxidation of olefins, epoxides were yielded as the major products with high stereo-, chemo-, and enantioselectivities; cis- and trans-stilbenes were oxidized to cis- and trans-stilbene oxides, respectively. In the epoxidation of cyclohexene, cyclohexene oxide was formed as the major product with a kinetic isotope effect (KIE) value of 1.0, indicating that nonheme iron(III)-acylperoxo complexes prefer C? - ?C epoxidation to allylic C-H bond activation. Olefin epoxidation by chiral iron(III)-acylperoxo complexes afforded epoxides with high enantioselectivity, suggesting that iron(III)-acylperoxo species, not high-valent iron-oxo species, are the epoxidizing agent. In alkane hydroxylation reactions, iron(III)-acylperoxo complexes hydroxylated C-H bonds as strong as those in cyclohexane at -40 °C, wherein (a) alcohols were yielded as the major products with high regio- and stereoselectivities, (b) activation of C-H bonds by the iron(III)-acylperoxo species was the rate-determining step with a large KIE value and good correlation between reaction rates and bond dissociation energies of alkanes, and (c) the oxygen atom in the alcohol product was from the iron(III)-acylperoxo species, not from molecular oxygen. In isotopically labeled water (H218O) experiments, incorporation of 18O from H218O into oxygenated products was not observed in the epoxidation and hydroxylation reactions. On the basis of mechanistic studies, we conclude that mononuclear nonheme high-spin iron(III)-acylperoxo complexes are strong oxidants capable of oxygenating hydrocarbons prior to their conversion into iron-oxo species via O-O bond cleavage.
- Wang, Bin,Lee, Yong-Min,Clémancey, Martin,Seo, Mi Sook,Sarangi, Ritimukta,Latour, Jean-Marc,Nam, Wonwoo
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supporting information
p. 2426 - 2436
(2016/03/05)
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- Design and Performance Validation of a Conductively Heated Sealed-Vessel Reactor for Organic Synthesis
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A newly designed robust and safe laboratory scale reactor for syntheses under sealed-vessel conditions at 250 °C maximum temperature and 20 bar maximum pressure is presented. The reactor employs conductive heating of a sealed glass vessel via a stainless steel heating jacket and implements both online temperature and pressure monitoring in addition to magnetic stirring. Reactions are performed in 10 mL borosilicate vials that are sealed with a silicone cap and Teflon septum and allow syntheses to be performed on a 2-6 mL scale. This conductively heated reactor is compared to a standard single-mode sealed-vessel microwave instrument with respect to heating and cooling performance, stirring efficiency, and temperature and pressure control. Importantly, comparison of the reaction outcome for a number of different synthetic transformations performed side by side in the new device and a standard microwave reactor suggest that results obtained using microwave conditions can be readily mimicked in the operationally much simpler and smaller conventionally heated device.
- Obermayer, David,Znidar, Desiree,Glotz, Gabriel,Stadler, Alexander,Dallinger, Doris,Oliver Kappe
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p. 11788 - 11801
(2016/12/09)
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- Chemoselective Ketone Synthesis by the Addition of Organometallics to N-Acylazetidines
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A general and highly chemoselective method for the synthesis of ketones by the addition of organometallics to N-acylazetidines via stable tetrahedral intermediates is reported for the first time. The transformation is characterized by its wide substrate scope and exquisite selectivity for the ketone products even when a large excess of nucleophilic reagents is used. Even of broader interest is the use of N-acylazetidines as bench-stable, readily available amide acylating reagents, in which the reactivity is controlled by amide pyramidalization and strain of the four-membered ring to afford synthetically valuable building blocks.
- Liu, Chengwei,Achtenhagen, Marcel,Szostak, Michal
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supporting information
p. 2375 - 2378
(2016/06/09)
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- Strategic Utilization of Multifunctional Carbene for Direct Synthesis of Carboxylic–Phosphinic Mixed Anhydride from CO2
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Direct synthesis of carboxylic–phosphinic mixed anhydrides has been achieved by treating carbon dioxide with N-phosphine oxide-substituted imidazolylidenes (PoxIms) that contain both nucleophilic carbene and electrophilic phosphorus moieties. This novel mixed anhydride was efficiently derivatized into an ester, an amide, and an unsymmetrical ketone via transformation into its corresponding imidazolium salt followed by a dual substitution reaction. The presented work used well-designed multifunctional carbene reagents to establish a novel utility for carbon dioxide in organic synthesis.
- Hoshimoto, Yoichi,Asada, Takahiro,Hazra, Sunit,Kinoshita, Takuya,Sombut, Panukorn,Kumar, Ravindra,Ohashi, Masato,Ogoshi, Sensuke
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supporting information
p. 16075 - 16079
(2016/12/26)
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- A biomimetic oxidation catalyzed by manganese(III) porphyrins and iodobenzene diacetate: Synthetic and mechanistic investigations
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Abstract With iodobenzene diacetate [PhI(OAc)2] as the oxygen source, manganese(III) porphyrin complexes exhibit remarkable catalytic activity toward the selective oxidation of alkenes and activated hydrocarbons. Conspicuous is the fact that the readily soluble PhI(OAc)2 in the presence of a small amount of water is more efficient than the commonly used PhIO and other oxygen sources under same catalytic conditions. High selectivity for epoxides and excellent catalytic efficiency with up to 10,000 TON have been achieved in alkene epoxidations. It was found that the reactivity of manganese(III) porphyrin catalysts was greatly affected by axial ligand and the weakly binding perchlorate gave the highest catalytic activity in the epoxidation of alkenes. A manganese(IV)-oxo porphyrin was detected in the reaction of the manganese(III) porphyrin and PhI(OAc)2. However, our catalytic competition and Hammett studies have suggested that the more reactive manganese(V)-oxo intermediate was favored as the premier active oxidant, even it is too short-lived to be produced in detectable concentrations.
- Kwong, Ka Wai,Chen, Tse-Hong,Luo, Weilong,Jeddi, Haleh,Zhang, Rui
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p. 176 - 183
(2015/04/14)
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- Iron-catalyzed oxidation of unreactive C-H bonds: Utilizing bio-inspired axial ligand modification to increase catalyst stability
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Three different bio-inspired Fe(II) complexes are applied as powerful catalysts for the oxidation of unreactive C-H bonds under ambient conditions. Cyclohexane as the main model substrate is oxidized to cyclohexanol, cyclohexyl hydroperoxide, and cyclohexanone. Alcohol + cyclohexyl hydroperoxide to ketone ratios ((A + H)/K) of up to 26 are obtained with comparatively high turnovers of up to 43. Bio-inspired modification of the Fe(II) complexes in the axial positions is used to increase catalyst stability toward hydrogen peroxide, leading to an increase in turnovers of up to 34%. Several parameters for the catalytic oxidation are investigated, e.g., the amount and type of oxidant, reaction temperature, and the relative catalyst concentration. Among others, 9,10-dihydroantracene and 2,3-dimethylbutane are used as substrates for the catalytic C-H bond oxidation.
- Haslinger, Stefan,Raba, Andreas,Cokoja, Mirza,P?thig, Alexander,Kühn, Fritz E.
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p. 147 - 153
(2015/10/06)
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- Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions
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Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L1) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [FeII(CH3CN)(L)]2+ (L = L1 (1); L2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [FeIV(O)(L)]2+ (L = L1 (3); L2 (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and M?ssbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L1) and 2.5 h (L = L2). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([FeIV(O)(N4Py)]2+), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [FeIV(O)(L2)]2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.
- Mitra, Mainak,Nimir, Hassan,Demeshko, Serhiy,Bhat, Satish S.,Malinkin, Sergey O.,Haukka, Matti,Lloret-Fillol, Julio,Lisensky, George C.,Meyer, Franc,Shteinman, Albert A.,Browne, Wesley R.,Hrovat, David A.,Richmond, Michael G.,Costas, Miquel,Nordlander, Ebbe
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supporting information
p. 7152 - 7164
(2015/08/11)
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- ORGANIC METAL COMPLEX, METHOD OF PRODUCING THE SAME AND CATALYST FOR TERTIARY ALCOHOL PRODUCTION
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PROBLEM TO BE SOLVED: To provide a novel organic palladium complex and a novel organic platinum complex and methods of producing them, and a catalyst for tertiary alcohol production from diarylketone and aryl boron compounds. SOLUTION: This invention provides an organic palladium complex represented by general formula (1). COPYRIGHT: (C)2015,JPOandINPIT
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Paragraph 0328 - 0330
(2016/11/07)
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- Reactivity of mixed organozinc and mixed organocopper reagents: 12. Three component reaction of mixed (n-alkyl)(diaryl)zincates, chloroformates and phosphines for the synthesis of esters
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The reaction of mixed n-butyldiphenylzincate, n-BuPh2ZnMgBr with ethyl chloroformate, ClCOOEt in the presence n-Bu3P in THF takes place with quantitative yield and phenyl group transfer to give PhCOOEt. Ethoxycarbonylation of n-BuPh2ZnMgBr is preferable to the reaction of PhMgBr forming ester and triphenylcarbinol and also to the reaction of triphenylzincate, Ph3ZnMgBr for atom economy. Group selectivity in the phosphine catalyzed C-COOR coupling of n-BuPh2ZnMgBr and n-Bu2PhZnMgBr can be controlled by changing reaction parameters. n-Bu3P catalyzed reaction of n-BuPh2ZnMgBr with ClCOOEt takes place with phenyl selectivity whereas reaction of n-Bu2PhZnMgBr with ClCOOPh results in n-butyl transfer. Catalysis by Ph3P increases n-butyl group:phenyl group transfer ratio in the ethoxycarbonylation of both zincates. Selective transfer of aryl groups in n-Bu3P catalyzed reaction of n-butyl(aryl)2ZnMgBr reagents with ClCOOEt in THF provides a new procedure for the organometallic synthesis of arenecarboxylic acid ethyl esters at room temperature.
- ?zkan, Duygu,Erdik, Ender
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- Introducing deep eutectic solvents to polar organometallic chemistry: Chemoselective addition of organolithium and grignard reagents to ketones in air
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Despite their enormous synthetic relevance, the use of polar organolithium and Grignard reagents is greatly limited by their requirements of low temperatures in order to control their reactivity as well as the need of dry organic solvents and inert atmosphere protocols to avoid their fast decomposition. Breaking new ground on the applications of these commodity organometallics in synthesis under more environmentally friendly conditions, this work introduces deep eutetic solvents (DESs) as a green alternative media to carry out chemoselective additions of ketones in air at room temperature. Comparing their reactivities in DES with those observed in pure water suggest that a kinetic activation of the alkylating reagents is taking place, favoring nucleophilic addition over the competitive hydrolysis, which can be rationalized through formation of halide-rich magnesiate or lithiate species. Turning lithium green: A new protocol for the selective addition of Grignard and organolithium reagents to ketones in green, biorenewable, and deep eutectic solvents (DESs) is reported. The protocol establishes a bridge between main-group organometallic compounds and green solvents (ChCl=choline chloride; see picture). The DESs are superior reaction media for highly polar organometallic compounds.
- Vidal, Cristian,Garcia-Alvarez, Joaquin,Hernan-Gomez, Alberto,Kennedy, Alan R.,Hevia, Eva
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supporting information
p. 5969 - 5973
(2014/06/10)
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- Synthesis, stability and reactivity of the first mononuclear nonheme oxoiron(iv) species with monoamido ligation: A putative reactive species generated from iron-bleomycin
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The preparation and characterisation of an oxoiron(iv) species with monoamido ligation are described. Reactivity studies revealed the important role of the amido ligand in enhancing the ability of oxoiron(iv) complexes to promote hydrogen atom transfer from external alkanes. the Partner Organisations 2014.
- Hitomi, Yutaka,Arakawa, Kengo,Kodera, Masahito
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supporting information
p. 7485 - 7487
(2014/07/07)
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- Spectroscopic capture and reactivity of a low-spin cobalt(IV)-oxo complex stabilized by binding redox-inactive metal ions
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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.
- Hong, Seungwoo,Pfaff, Florian F.,Kwon, Eunji,Wang, Yong,Seo, Mi-Sook,Bill, Eckhard,Ray, Kallol,Nam, Wonwoo
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supporting information
p. 10403 - 10407
(2016/02/18)
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- Structural modeling of iron halogenases: Synthesis and reactivity of halide-iron(iv)-oxo compounds
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A structural synthetic model of the iron(iv)-oxo-halide active species of non-heme iron dependent halogenases is reported. Compounds with general formula [FeIV(O)(X)(Pytacn)]+ (1-X, X = Cl, Br) have been prepared and characterized spectroscopically and chemically with regard to their oxidizing ability. 1-X performs hydrogen-atom abstraction of C-H bonds at reaction rates 2-3 times faster than the corresponding solvato dicationic species, thus modelling the first step in C-H functionalization taking place in natural halogenation. the Partner Organisations 2014.
- Planas, Oriol,Clémancey, Martin,Latour, Jean-Marc,Company, Anna,Costas, Miquel
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supporting information
p. 10887 - 10890
(2014/11/08)
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- Highly efficient protection of alcohols as trityl ethers under solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H
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An efficient method was developed for the protection of alcohols as trityl ethers using triphenylmethanol in the presence of nanoporous MCM-41-SO3H as a heterogeneous catalyst under solvent-free ball-milling at room temperature. Low catalyst loading, high efficiency, reusability are among the advantages of this new solvent-free and environmentally friendly method. The deprotection of the produced trityl ethers was also efficiently achieved using the same catalyst in wet acetonitrile.
- Gholamzadeh, Zeynab,Naimi-Jamal, Mohammad Reza,Maleki, Ali
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p. 994 - 1001
(2015/01/09)
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- Solid-phase synthesis and biological evaluation of N-dipeptido L -homoserine lactones as quorum sensing activators
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Bacteria use small signaling molecules to communicate in a process termed quorum sensing (QS), which enables the coordination of survival strategies, such as production of virulence factors and biofilm formation. In Gram-negative bacteria, these signaling molecules are a series of N-acylated L-homoserine lactones. With the goal of identifying non-native compounds capable of modulating bacterial QS, a virtual library of N-dipeptido L-homoserine lactones was screened in silico with two different crystal structures of LasR. The 30 most promising hits were synthesized on HMBA-functionalized PEGA resin and released through an efficient acid-mediated cyclative release mechanism. Subsequent screening for modulation of QS in Pseudomonas aeruginosa and E. coli identified six moderately strong activators. A follow-up library designed from the preliminary derived structure-activity relationships was synthesized and evaluated for their ability to activate the QS system in this bacterium. This resulted in the identification of another six QS activators (two with low micromolar activity) thus illuminating structural features required for QS modulation. Behind the screen: A virtual screening approach identified a number of N-dipeptido L-homo-serine lactones as potential quorum sensing modulators. Selected compounds were synthesized and identified as activators of LasR, a protein regulating quorum sensing in Pseudomonas aeruginosa; EC50 values were in the low micromolar range. Copyright
- Hansen, Mette R.,Le Quement, Sebastian T.,Jakobsen, Tim H.,Skovstrup, Soren,Taboureau, Olivier,Tolker-Nielsen, Tim,Givskov, Michael,Nielsen, Thomas E.
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p. 460 - 465
(2014/03/21)
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- Extremely fast gas/liquid reactions in flow microreactors: Carboxylation of short-lived organolithiums
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Carboxylation of short-lived organolithiums bearing electrophilic functional groups such as nitro, cyano, and alkoxycarbonyl groups with CO 2 to give carboxylic acids and active esters was accomplished in a flow microreactor system. The successful reactions indicate that gas/liquid mass transfer and the subsequent chemical reaction with CO2 are extremely fast. Carboxylation of short-lived organolithiums bearing electrophilic functional groups such as nitro, cyano, and alkoxycarbonyl groups with CO 2 to give carboxylic acids and active esters was accomplished in a flow microreactor system. The successful reactions indicate that gas/liquid mass transfer and the subsequent chemical reaction with CO2 are extremely fast (see scheme).
- Nagaki, Aiichiro,Takahashi, Yusuke,Yoshida, Jun-Ichi
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p. 7931 - 7934
(2014/07/07)
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