- Direct Arylation of Distal and Proximal C(sp3)-H Bonds of t-Amines with Aryl Diazonium Tetrafluoroborates via Photoredox Catalysis
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A visible light-mediated arylation protocol for t-amines has been reported through the coupling of γ- and α-amino alkyl radicals with different aryl diazonium salts using Ru(bpy)3Cl2·6H2O as a photocatalyst. Structurally different 9-aryl-9,10-dihydroacridine, 1-aryl tetrahydroisoquinoline, hexahydropyrrolo[2,1-a]isoquinoline, and hexahydro-2H-pyrido[2,1-a]isoquinoline frameworks with different substitution patterns have been synthesized in good yield using this methodology.
- Mondal, Pradip Kumar,Tiwari, Sandip Kumar,Singh, Pushpendra,Pandey, Ganesh
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p. 17184 - 17196
(2021/12/02)
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- The embedding of fluorescent: N -methyl-9-acridone into a topological new layered aluminophosphate SYSU-2 by one-pot synthesis
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A layered aluminophosphate |C14H11NO|2[Al4(HPO4)4F4(H2O)2] (denoted as SYSU-2) with a new topology has been hydrothermally synthesized with N-methyl-9-acridone (NMA) as the organic structure-directing agent. Single-crystal X-ray diffraction analysis reveals that SYSU-2 crystallizes in a triclinic space group P1, with the inorganic sheets stacked in an AA sequence. Hydrogen bonds are responsible for the neutral inorganic-organic layer connection. The layer structure of SYSU-2 is constructed by alternating AlO4F2 octahedra and PO4 tetrahedra. The topological analysis of SYSU-2 indicates an independent topology. The NMA layers are self-assembled with π-π interaction. SYSU-2 crystals show interesting dual-band emission fluorescence properties compared with NMA crystals. Under 406 nm UV irradiation, SYSU-2 crystals emit yellow light with two emission bands at 477 and 566 nm, while NMA crystals emit blue light with only one band at 473 nm. The differences may be derived from the difference of stacking orders and distance of NMA molecule layers between the two crystals
- Jiang, Jiuxing,Liang, Weichi,Wen, Jiali,Zhang, Meng,Zhao, Yukai
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p. 17033 - 17038
(2020/12/18)
-
- Oxo-Free Hydrocarbon Oxidation by an Iron(III)-Isoporphyrin Complex
-
Metal-halides that perform proton coupled electron-transfer (PCET) oxidation are an important new class of high-valent oxidant. In investigating metal-dihalides, we reacted [FeIII(Cl)(T(OMe)PP)] (1, T(OMe)PP = meso-tetra(4-methoxyphenyl)porphyrinyl) with (dichloroiodo)benzene. An FeIII-meso-chloro-isoporphyrin complex [FeIII(Cl)2(T(OMe)PP-Cl)] (2) was obtained. 2 was characterized by electronic absorption, 1H NMR, EPR, and X-ray absorption spectroscopies and mass spectrometry with support from computational analyses. 2 was reacted with a series of hydrocarbon substrates. The measured kinetic data exhibited a nonlinear behavior, whereby the oxidation followed a hydrogen-atom-transfer (HAT) PCET mechanism. The meso-chlorine atom was identified as the HAT agent. In one case, a halogenated product was identified by mass spectrometry. Our findings demonstrate that oxo-free hydrocarbon oxidation with heme systems is possible and show the potential for iron-dihalides in oxidative hydrocarbon halogenation.
- Doyle, Lorna M.,Farquhar, Erik R.,Gericke, Robert,Mcdonald, Aidan R.
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supporting information
p. 13952 - 13961
(2020/10/09)
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- Uncatalyzed Oxidative C?H Amination of 9,10-Dihydro-9-Heteroanthracenes: A Mechanistic Study
-
A new method for the one-step C?H amination of xanthene and thioxanthene with sulfonamides is reported, without the need for any metal catalyst. A benzoquinone was employed as a hydride (or two-electron and one-proton) acceptor. Moreover, a previously unknown and uncatalyzed reaction between iminoiodanes and xanthene, thioxanthene and dihydroacridines (9,10-dihydro-9-heteroanthracenes or dihydroheteroanthracenes) is disclosed. The reactions proceed through hydride transfer from the heteroarene substrate to the iminoiodane or benzoquinone, followed by conjugate addition of the sulfonamide to the oxidized heteroaromatic compounds. These findings may have important mechanistic implications for metal-catalyzed C?H amination processes involving nitrene transfer from iminoiodanes to dihydroheteroanthracenes. Due to the weak C?H bond, xanthene is an often-employed substrate in mechanistic studies of C?H amination reactions, which are generally proposed to proceed via metal-catalyzed nitrene insertion, especially for reactions involving nitrene or imido complexes that are less reactive (i.e., less strongly oxidizing). However, these substrates clearly undergo non-catalyzed (proton-coupled) redox coupling with amines, thus providing alternative pathways to the widely assumed metal-catalyzed pathways.
- van Leest, Nicolaas P.,Grooten, Lars,van der Vlugt, Jarl Ivar,de Bruin, Bas
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supporting information
p. 5987 - 5993
(2019/04/03)
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- Exogenous-oxidant-free electrochemical oxidative C-H phosphonylation with hydrogen evolution
-
We herein report a versatile and environmentally friendly electrochemical oxidative C-H phosphonylation protocol. This protocol features a broad substrate scope; not only C(sp2)-H phosphonylation, but also C(sp3)-H phosphonylation is tolerated well under exogenous-oxidant-free and metal catalyst-free electrochemical oxidation conditions.
- Yuan, Yong,Qiao, Jin,Cao, Yangmin,Tang, Jingmei,Wang, Mengqin,Ke, Guojuan,Lu, Yichen,Liu, Xue,Lei, Aiwen
-
supporting information
p. 4230 - 4233
(2019/04/30)
-
- Synthesis and Properties of Acridine and Acridinium Dye Functionalized Bis(terpyridine) Ruthenium(II) Complexes
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We present first principle studies on the rational design of an acridine/N-methylacridinium dye (Acr/MeAcr+) substituted terpyridine ligand to investigate if these chromophores can act as triplet-energy storage units in bis(terpyridine) ruthenium(II) complexes. We studied the influence of the dye form (Acr/MeAcr+) as well as the interconnecting linker unit (none, 4-phenyl, or 5-thien-2-yl) and investigated these aspects by steady-state/time-resolved spectroscopy, cyclic voltammetry, X-ray structure analysis, and DFT calculations.
- Eberhard, Jens,Peuntinger, Katrin,Fr?hlich, Roland,Guldi, Dirk M.,Mattay, Jochen
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supporting information
p. 2682 - 2700
(2018/06/04)
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- Frustrated Lewis Pair Mediated 1,2-Hydrocarbation of Alkynes
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Frustrated Lewis pair (FLP) chemistry enables a rare example of alkyne 1,2-hydrocarbation with N-methylacridinium salts as the carbon Lewis acid. This 1,2-hydrocarbation process does not proceed through a concerted mechanism as in alkyne syn-hydroboration, or through an intramolecular 1,3-hydride migration as operates in the only other reported alkyne 1,2-hydrocarbation reaction. Instead, in this study, alkyne 1,2-hydrocarbation proceeds by a novel mechanism involving alkyne dehydrocarbation with a carbon Lewis acid based FLP to form the new C?C bond. Subsequently, intermolecular hydride transfer occurs, with the Lewis acid component of the FLP acting as a hydride shuttle that enables alkyne 1,2-hydrocarbation.
- Fasano, Valerio,Curless, Liam D.,Radcliffe, James E.,Ingleson, Michael J.
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supporting information
p. 9202 - 9206
(2017/07/25)
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- Oxidative C-H bond functionalization and ring expansion with TMSCHN2: A copper(I)-catalyzed approach to dibenzoxepines and dibenzoazepines
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Tricyclic dibenzoxepines and dibenzazepines are important therapeutic agents for the pharmaceutical industry and academic research. However, their syntheses are generally rather tedious, requiring several steps that involve a Wagner-Meerwein-type rearrangement under harsh conditions. Herein, we present the first copper(I)-catalyzed oxidative C-H bond functionalization and ring expansion with TMSCHN2 to yield these important derivatives in a facile and straightforward way. Cut a long story short: Tricyclic dibenzoxepines and dibenzazepines are important therapeutic agents for pharmaceuticals, but their syntheses are generally rather tedious. A copper(I)-catalyzed oxidative C-H bond functionalization and ring expansion sequence with TMSCHN2 has been developed to yield these important derivatives in a facile and straightforward way.
- Stopka, Tobias,Marzo, Leyre,Zurro, Mercedes,Janich, Simon,Würthwein, Ernst-Ulrich,Daniliuc, Constantin G.,Alemán, José,Manche?o, Olga García
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supporting information
p. 5049 - 5053
(2015/04/27)
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- Steric Effects on the Primary Isotope Dependence of Secondary Kinetic Isotope Effects in Hydride Transfer Reactions in Solution: Caused by the Isotopically Different Tunneling Ready State Conformations?
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The observed 1° isotope effect on 2° KIEs in H-transfer reactions has recently been explained on the basis of a H-tunneling mechanism that uses the concept that the tunneling of a heavier isotope requires a shorter donor-acceptor distance (DAD) than that of a lighter isotope. The shorter DAD in D-tunneling, as compared to H-tunneling, could bring about significant spatial crowding effect that stiffens the 2° H/D vibrations, thus decreasing the 2° KIE. This leads to a new physical organic research direction that examines how structure affects the 1° isotope dependence of 2° KIEs and how this dependence provides information about the structure of the tunneling ready states (TRSs). The hypothesis is that H- and D-tunneling have TRS structures which have different DADs, and pronounced 1° isotope effect on 2° KIEs should be observed in tunneling systems that are sterically hindered. This paper investigates the hypothesis by determining the 1° isotope effect on α- and β-2° KIEs for hydride transfer reactions from various hydride donors to different carbocationic hydride acceptors in solution. The systems were designed to include the interactions of the steric groups and the targeted 2° H/D's in the TRSs. The results substantiate our hypothesis, and they are not consistent with the traditional model of H-tunneling and 1° /2° H coupled motions that has been widely used to explain the 1° isotope dependence of 2° KIEs in the enzyme-catalyzed H-transfer reactions. The behaviors of the 1° isotope dependence of 2° KIEs in solution are compared to those with alcohol dehydrogenases, and sources of the observed "puzzling" 2° KIE behaviors in these enzymes are discussed using the concept of the isotopically different TRS conformations. (Figure Presented).
- Maharjan, Binita,Raghibi Boroujeni, Mahdi,Lefton, Jonathan,White, Ormacinda R.,Razzaghi, Mortezaali,Hammann, Blake A.,Derakhshani-Molayousefi, Mortaza,Eilers, James E.,Lu, Yun
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p. 6653 - 6661
(2015/06/08)
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- N-Methylacridinium Salts: Carbon Lewis Acids in Frustrated Lewis Pairs for σ-Bond Activation and Catalytic Reductions
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N-methylacridinium salts are Lewis acids with high hydride ion affinity but low oxophilicity. The cation forms a Lewis adduct with 4-(N,N-dimethylamino)pyridine but a frustrated Lewis pair (FLP) with the weaker base 2,6-lutidine which activates H2, even in the presence of H2O. Anion effects dominate reactivity, with both solubility and rate of H2 cleavage showing marked anion dependency. With the optimal anion, a N-methylacridinium salt catalyzes the reductive transfer hydrogenation and hydrosilylation of aldimines through amine-boranes and silanes, respectively. Furthermore, the same salt is active for the catalytic dehydrosilylation of alcohols (primary, secondary, tertiary, and ArOH) by silanes with no observable over-reduction to the alkanes.
- Clark, Ewan R.,Ingleson, Michael J.
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supporting information
p. 11306 - 11309
(2016/02/19)
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- Oxygen-initiated chain mechanism for hydride transfer between NADH and NAD+ models. Reaction of 1-benzyl-3-cyanoquinolinium ion with N -methyl-9,10-dihydroacridine in acetonitrile
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A reinvestigation of the formal hydride transfer reaction of 1-benzyl-3-cyanoquinolinium ion (BQCN+) with N-methyl-9,10- dihydroacridine (MAH) in acetonitrile (AN) confirmed that the reaction takes place in more than one step and revealed a new mechanism that had not previously been considered. These facts are unequivocally established on the basis of conventional pseudo-first-order kinetics. It was observed that even residual oxygen under glovebox conditions initiates a chain process leading to the same products and under some conditions is accompanied by a large increase in the apparent rate constant for product formation with time. The efficiency of the latter process, when reactions are carried out in AN with rigorous attempts to remove air, is low but appears to be much more pronounced when MAH is the reactant in large excess. On the other hand, the intentional presence of air in AN ([air] = half-saturated) leads to a much greater proportion of the chain pathway, which is still favored by high concentrations of MAH. The latter observation suggests that a reaction intermediate reacts with oxygen to initiate the chain process in which MAH participates. Kinetic studies at short times show that there is no kinetic isotope effect on the initial step in the reaction, which is the same for the two competing processes. Our observation of the chain pathway of an NADH model compound under aerobic conditions is likely to be of importance in similar biological processes where air is always present.
- Hao, Weifang,Parker, Vernon D.
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p. 9286 - 9297
(2013/01/15)
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- Electron- and hydride-transfer reactivity of an isolable manganese(V)-Oxo complex
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The electron-transfer and hydride-transfer properties of an isolated manganese(V)-oxo complex, (TBP8Cz)MnV(O) (1) (TBP 8Cz = octa-tert-butylphenylcorrolazinato) were determined by spectroscopic and kinetic methods. The manganese(V)-oxo complex 1 reacts rapidly with a series of ferrocene derivatives ([Fe(C5H4Me) 2], [Fe(C5HMe4)2], and ([Fe(C 5Me5)2] = Fc*) to give the direct formation of [(TBP8Cz)MnIII(OH)]- ([2-OH] -), a two-electron-reduced product. The stoichiometry of these electron-transfer reactions was found to be (Fc derivative)/1 = 2:1 by spectral titration. The rate constants of electron transfer from ferrocene derivatives to 1 at room temperature in benzonitrile were obtained, and the successful application of Marcus theory allowed for the determination of the reorganization energies (λ) of electron transfer. The λ values of electron transfer from the ferrocene derivatives to 1 are lower than those reported for a manganese(IV)-oxo porphyrin. The presumed one-electron-reduced intermediate, a MnIV complex, was not observed during the reduction of 1. However, a MnIV complex was successfully generated via one-electron oxidation of the MnIII precursor complex 2 to give [(TBP8Cz)Mn IV]+ (3). Complex 3 exhibits a characteristic absorption band at λmax = 722 nm and an EPR spectrum at 15 K with gmax′ = 4.68, gmid′ = 3.28, and gmin ′ = 1.94, with well-resolved 55Mn hyperfine coupling, indicative of a d3 MnIVS = 3/ 2 ground state. Although electron transfer from [Fe(C 5H4Me)2] to 1 is endergonic (uphill), two-electron reduction of 1 is made possible in the presence of proton donors (e.g., CH3CO2H, CF3CH2OH, and CH3OH). In the case of CH3CO2H, saturation behavior for the rate constants of electron transfer (ket) versus acid concentration was observed, providing insight into the critical involvement of H+ in the mechanism of electron transfer. Complex 1 was also shown to be competent to oxidize a series of dihydronicotinamide adenine dinucleotide (NADH) analogues via formal hydride transfer to produce the corresponding NAD+ analogues and [2-OH]-. The logarithms of the observed second-order rate constants of hydride transfer (kH) from NADH analogues to 1 are linearly correlated with those of hydride transfer from the same series of NADH analogues to p-chloranil.
- Fukuzumi, Shunichi,Kotani, Hiroaki,Prokop, Katharine A.,Goldberg, David P.
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experimental part
p. 1859 - 1869
(2011/04/25)
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- Manganese(v)-oxo corroles in hydride-transfer reactions
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Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogues to manganese(v)-oxo corroles proceeds via proton-coupled electron transfer, followed by rapid electron transfer. The redox potentials (E red) of manganese(v)-oxo corroles exhibit a good correlation with their reactivity in hydride-transfer reactions.
- Han, Yejee,Lee, Yong-Min,Mariappan, Mariappan,Fukuzumi, Shunichi,Nam, Wonwoo
-
experimental part
p. 8160 - 8162
(2010/12/19)
-
- High-valent manganese(v)-oxo porphyrin complexes in hydride transfer reactions
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Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogues to trans-dioxomanganese(v) porphyrin complexes proceeds via proton-coupled electron transfer, followed by rapid electron transfer. The Royal Society of Chemistry 2009.
- Lee, Jung Yoon,Lee, Yong-Min,Kotani, Hiroaki,Nam, Wonwoo,Fukuzumi, Shunichi
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supporting information; experimental part
p. 704 - 706
(2009/06/05)
-
- Mechanistic insights into hydride-transfer and electron-transfer reactions by a manganese(IV)-oxo porphyrin complex
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Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogs to a manganese(IV)-oxo porphyrin complex, (TMP)MnIV(O) [TMP = 5,10,15,20-tetrakis(2,4,6-trimethylphenyl) porphyrin], occurs via disproportionation of (TMP)MnIV(O) to [(TMP)MnIII] + and [(TMP)MnV(O)]+ that acts as the actual hydride acceptor. In contrast, electron transfer from ferrocene derivatives to (TMP)MnIV(O) occurs directly to afford ferricenium ions and (TMP)MnIII(OH) products. The disproportionation rate constant of (TMP)MnIV(O) was determined by the dependence of the observed second-order rate constants on concentrations of NADH analogs to be (8.0 ± 0.6) × 106 M-1 s-1 in acetonitrile at 298 K. The disproportionation rate constant of (TMP)Mn IV(O) in hydride-transfer reactions increases linearly with increasing acid concentration, whereas the rate constant of electron transfer from ferrocene to (TMP)MnIV(O) remains constant irrespective of the acid concentration. The rate constants of electron transfer from a series of ferrocene derivatives to (TMP)MnIV(O) were evaluated in light of the Marcus theory of electron transfer to determine the reorganization energy of electron transfer by the (TMP)MnIV(O) complex.
- Fukuzumi, Shunichi,Fujioka, Naofumi,Kotani, Hiroaki,Ohkubo, Kei,Lee, Yong-Min,Nam, Wonwoo
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experimental part
p. 17127 - 17134
(2010/03/25)
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- Hydrogen-atom abstraction reactions by manganese(V)- and manganese(IV)-oxo porphyrin complexes in aqueous solution
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High-valent manganese(IV or V)-oxo porphyrins are considered as reactive intermediates in the oxidation of organic substrates by manganese porphyrin catalysts. We have generated MnV- and MnIV-oxo porphyrins in basic aqueous solution and investigated their reactivities in C-H bond activation of hydrocarbons. We now report that MnV- and Mn IV-oxo porphyrins are capable of activating C-H bonds of alkylaromatics, with the reactivity order of MnV-oxo>Mn IV-oxo; the reactivity of a MnV-oxo complex is 150 times greater than that of a MnIV-oxo complex in the oxidation of xanthene. The C-H bond activation of alkylaromatics by the MnV- and Mn IV-oxo porphyrins is proposed to occur through a hydrogen-atom abstraction, based on the observations of a good linear correlation between the reaction rates and the C-H bond dissociation energy (BDE) of substrates and high kinetic isotope effect (KIE) values in the oxidation of xanthene and dihydroanthracene (DHA). We have demonstrated that the disproportionation of MnIV-oxo porphyrins to MnV-oxo and MnIII porphyrins is not a feasible pathway in basic aqueous solution and that Mn IV-oxo porphyrins are able to abstract hydrogen atoms from alkylaromatics. The C-H bond activation of alkylaromatics by MnV- and MnIV-oxo species proceeds through a one-electron process, in which a MnIV-oxo porphyrin is formed as a product in the C-H bond activation by a MnV-oxo porphyrin, followed by a further reaction of the MnIV-oxo porphyrin with substrates that results in the formation of a MnIII porphyrin complex. This result is in contrast to the oxidation of sulfides by the MnV-oxo porphyrin, in which the oxidation of thioanisole by the MnV-oxo complex produces the starting Mn III porphyrin and thioanisole oxide. This result indicates that the oxidation of sulfides by the MnV-oxo species occurs by means of a two-electron oxidation process. In contrast, a MnIV-oxo porphyrin complex is not capable of oxidizing sulfides due to a low oxidizing power in basic aqueous solution.
- Arunkumar, Chellaiah,Lee, Yong-Min,Lee, Jung Yoon,Fukuzumi, Shunichi,Nam, Wonwoo
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experimental part
p. 11482 - 11489
(2010/04/29)
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- Intramolecular kinetic isotope effect in hydride transfer from dihydroacridine to a quinolinium ion. Rejection of a proposed two-step mechanism with a kinetically significant intermediate
-
The intramolecular kinetic isotope effect (KIE) for hydride transfer from 10-methyl-9,10-dihydroacridine to 1-benzyl-3-cyanoquinolinium ion has been found to be 5-6 by both 1H NMR and mass spectrometry. This KIE is consistent with other hydride transfers. It is inconsistent with the high intermolecular KIEs derived by fitting to a two-step mechanism with a kinetically significant intermediate complex, and it is inconsistent with the strong temperature dependence of those KIEs. We therefore reject the two-step mechanism for this reaction, and we suggest that other cases proposed to follow this mechanism are in error.
- Perrin, Charles L.,Zhao, Chen
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supporting information; experimental part
p. 3349 - 3353
(2009/02/05)
-
- The pH effect on the naphthoquinone-photosensitized oxidation of 5-methylcytosine
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The pH effect on the one-electron photooxidation of 5-methyl-2′- deoxycytidine (dmC) by sensitization with 2-methyl-1,4-naphthoquinone (NQ) was investigated. Photoirradiation of an aqueous solution containing dmC and NQ under slightly acidic conditions of pH 5.0 efficiently produced 5-formyl-2′-deoxycytidine, whereas similar NQ-photosensitized oxidation of dmC proceeded to a lesser extent under more acidic or basic conditions. Fluorescence-quenching experiments re vealed that the less-efficient photooxidation at pH values below 4.5 is attributed to the decreased rate of one-electron oxidation of dmC owing to protonation at the N(3)-position. The NQ-photosensitized oxidation of an N(4)-dimethyl-substituted dmC derivative under various pH conditions also sug gests that the pH change in the range of 5.0 to 8.0 may be responsible for a reversible deprotonation-protonation equilibrium at the N(4)-exocyclic amino group of the dmC radical cation. In accord with the photochemical reactivity of monomeric dmC, the 5-methylcytosine residue in oligodeoxynucleotides was oxidized efficiently by photoexcited NQ-tethered oligodeoxynucleotides under slightly acidic conditions to form an alkali-labile 5-formylcytosine residue.
- Yamada, Hisatsugu,Tanabe, Kazuhito,Ito, Takeo,Nishimoto, Sei-Ichi
-
experimental part
p. 10453 - 10461
(2009/12/07)
-
- Sequential electron-transfer and proton-transfer pathways in hydride-transfer reactions from dihydronicotinamide adenine dinucleotide analogues to non-heme oxoiron(IV) complexes and p-chloranil. Detection of radical cations of NADH analogues in acid-promoted hydride-transfer reactions
-
Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogues, such as 10-methyl-9,10-dihydroacridine (AcrH2) and its derivatives, 1-benzyl-1,4-dihydronicotinamide (BNAH), and their deuterated compounds, to non-heme oxoiron(IV) complexes such as [(L)FeIV(O)] 2+ (L = N4Py, Bn-TPEN, and TMC) occurs to yield the corresponding NAD+ analogues and non-heme iron(II) complexes in acetonitrile. Hydride transfer from the NADH analogues to p-chloranil (Cl4Q) also occurs to produce the corresponding NAD+ analogues and the hydroquinone anion (Cl4QH-). The logarithms of the observed second-order rate constants (log kH) of hydride transfer from NADH analogues to non-heme oxoiron(IV) complexes are linearly correlated with those of hydride transfer from the same series of NADH analogues to Cl 4Q, including similar kinetic deuterium isotope effects. The log kH values of hydride transfer from NADH analogues to non-heme oxoiron(IV) complexes are also linearly correlated with those of deprotonation of the radical cations of NADH analogues. Such linear correlations indicate that overall hydride-transfer reactions of NADH analogues to both non-heme oxoiron(IV) complexes and Cl4Q occur via electron transfer from NADH analogues to the oxoiron(IV) complexes, followed by rate-limiting deprotonation from the radical cations of NADH analogues and subsequent rapid electron transfer from the deprotonated radicals to the Fe(III) complexes to yield the corresponding NAD+ analogues and the Fe(II) complexes. The electron-transfer pathway was accelerated by the presence of perchloric acid, and the resulting radical cations of NADH analogues were detected by electron spin resonance spectroscopy and UV-vis spectrophotometry in the acid-promoted hydride-transfer reactions from NADH analogues to non-heme oxoiron(IV) complexes. This result provides the first direct evidence that a hydride transfer from NADH analogues to non-heme oxoiron(IV) complexes proceeds via an electron-transfer pathway.
- Fukuzumi, Shunichi,Kotani, Hiroaki,Lee, Yong-Min,Nam, Wonwoo
-
experimental part
p. 15134 - 15142
(2009/03/12)
-
- Effective thermal oxidation of isopropanol by an NAD+ model
-
The reaction of 10-methylacridinium cation (MA+) with isopropanol in the parent alcohol medium under dark, oxygen-free, and refluxing conditions gave hydride transfer product 10-methyl-9,10-dihydroacridine (MAH). The kinetics of the alcoholic oxidation reaction, including the kinetic isotope effect and the kinetic temperature effect, were determined. Hydride transfer is involved in the rate-determining step.
- Lu, Yun,Endicott, Donald,Kuester, William
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p. 6356 - 6359
(2008/02/12)
-
- Photocatalytic electron-transfer oxidation of triphenylphosphine and benzylamine with molecular oxygen via formation of radical cations and superoxide ion
-
Photooxygenation of triphenylphosphine (Ph3P) to triphenylphosphine oxide (Ph3P=O) with molecular oxygen (O 2) occurs under photoirradiation of 9-mesityl-10-methylacridinium perchlorate ([Acr+-Mes]ClO4-) which acts as an efficient electron-transfer photocatalyst. Photooxidation of benzylamine (PhCH2NH2) with O2 also occurs efficiently under photoirradiation of Acr+-Mes to yield PhCH2N=CHPh and hydrogen peroxide (H2O2). Each photocatalytic reaction is initiated by intramolecular photoinduced electron transfer from the Mes moiety to the singlet excited state of the Acr+ moiety to produce the electron-transfer state (Acr?-Mes?+). The Mes?+ moiety oxidizes Ph3P and PhCH 2NH2 to produce the radical cations (Ph3P ?+ and PhCH2NH2?+, respectively), whereas the Acr? moiety reduces O2 to O2?+. The produced Ph3P?+ binds with O2?+ as well as O2, leading to the oxygenated product (Ph3P=O). On the other hand, proton transfer from PhCH2NH2?+ to O2 ?+ occurs, followed by hydrogen transfer, leading to the dehydrogenated dimer product, PhCH2N=CHPh. In each case, the radical intermediates were detected by laser flash photolysis and ESR measurements to clarify the photocatalytic mechanism.
- Ohkubo, Kei,Nanjo, Takashi,Fukuzumi, Shunichi
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p. 1489 - 1500
(2007/10/03)
-
- A facile experimental method to determine the hydride affinity of polarized olefins in acetonitrile
-
(Chemical Equation Presented) Choosing a suitable hydride reducing agent and thermodynamic analysis of reduction mechanisms is facilitated by experimental hydride affinities ΔHH-A, which are reported herein for 28 polarized olefins 1 in acetonitrile (see scheme). The method should also be applicable to ketones, aldehydes, and imines.
- Zhu, Xiao-Qing,Zhang, Min,Liu, Qiao-Yun,Wang, Xiao-Xiao,Zhang, Jian-Yu,Cheng, Jin-Pei
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p. 3954 - 3957
(2007/10/03)
-
- Scandium ion-promoted photoinduced electron transfer from electron donors to acridine and pyrene. Essential role of scandium ion in photocatalytic oxygenation of hexamethylbenzene
-
Photoinduced electron transfer from a variety of electron donors including alkylbenzenes to the singlet excited state of acridine and pyrene is accelerated significantly by the presence of scandium trifiate [Sc(OTf)3] in acetonitrile, whereas no photoinduced electron transfer from alkylbenzenes to the singlet excited state of acridine or pyrene takes place in the absence of Sc(OTf)3. The rate constants of the Sc(OTf)3-promoted photoinduced electron-transfer reactions (ket) of acridine to afford the complex between acridine radical anion and Sc(OTf)3 remain constant under the conditions such that all the acridine molecules form the complex with Sc(OTf)3. In contrast to the case of acridine, the ket value of the Sc(OTf)3-promoted photoinduced electron transfer of pyrene increases with an increase in concentration of Sc(OTf)3 to exhibit first-order dependence on [Sc(OTf)3] at low concentrations, changing to second-order dependence at high concentrations. The first-order and second-order dependence of ket on [Sc(OTf)3] is ascribed to the 1:1 and 1:2 complexes formation between pyrene radical anion and Sc(OTf)3. The positive shifts of the one-electron redox potentials for the couple between the singlet excited state and the ground-state radical anion of acridine and pyrene in the presence of Sc(OTf)3 as compared to those in the absence of Sc(OTf)3 have been determined by adapting the free energy relationship for the photoinduced electron-transfer reactions. The Sc(OTf)3-promoted photoinduced electron transfer from hexamethylbenzene to the singlet excited state of acridine or pyrene leads to efficient oxygenation of hexamethylbenzene to produce pentamethylbenzyl alcohol which is further oxygenated under prolonged photoirradiation of an O 2-saturated acetonitrile solution of hexamethylbenzene in the presence of acridine or pyrene which acts as a photocatalyst together with Sc(OTf)3. The photocatalytic oxygenation mechanism has been proposed based on the studies on the quantum yields, the fluorescence quenching, and direct detection of the reaction intermediates by ESR and laser flash photolysis.
- Fukuzumi, Shunichi,Yuasa, Junpei,Satoh, Naoya,Suenobu, Tomoyoshi
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p. 7585 - 7594
(2007/10/03)
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- Selective Oxygenation of Ring-Substituted Toluenes with Electron-Donating and -Withdrawing Substituents by Molecular Oxygen via Photoinduced Electron Transfer
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A ring-substituted toluene with an electron-withdrawing substituent, p-tolunitrile, is oxygenated by molecular oxygen to yield the corresponding aldehyde with tetrafluoro-p-dicyanobenzene as a photocatalyst under photoirradiation with an Hg lamp (λ > 300 nm). The oxygenation of a ring-substituted toluene with an electron-donating substituent, p-xylene, by molecular oxygen is also achieved with 10-methyl-9-phenylacridinium ion as a photocatalyst under visible light irradiation, yielding p-tolualdehyde exclusively as the final oxygenated product. Both the oxygenation reactions are initiated by photoinduced electron transfer from the ring-substituted toluene to the singlet excited state of the photocatalyst. The reason for the high selectivity in the photocatalytic oxygenation of various toluene derivatives by molecular oxygen is discussed on the basis of the photoinduced electron transfer mechanism that does not involve the autoxidation process (radical chain reactions). The reactive intermediates in the photocatalytic cycle are successfully detected as the transient absorption spectra and the electron spin resonance spectra.
- Ohkubo, Kei,Suga, Kyou,Morikawa, Kohei,Fukuzumi, Shunichi
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p. 12850 - 12859
(2007/10/03)
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- Driving Force Dependence of Photoinduced Electron Transfer Dynamics of Intercalated Molecules in DNA
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A series of acridinium, quinolinium, and phenanthridinium ions (9-substituted-10-methylacridinium (AcrR+, R = H, PrI, and CH2Ph), 3-substituted-1-methylquinolinium (RQuH+, R = CN and Br), and 5-methylphenanthridinium (5-MePhen+) perchlorate salts) are shown to be intercalated into the DNA double helix from calf thymus. The one-electron reduction potentials (Ered0) of these intercalates have been determined in the absence and presence of DNA by both cyclic voltammetry and second harmonic ac voltammetry. The E0red values of intercalators are shifted in a positive direction by intercalation into the DNA double helix. The one-electron oxidation potential (E ox0) of ethidium bromide, which is known to be intercalated into DNA, is also shifted in a positive direction by the intercalation. The wide range of E0red values of intercalators thus determined in the presence of DNA allows us to examine the exact driving force dependence of the rates of photoinduced electron transfer from the singlet excited state of ethidium bromide to the intercalators in DNA for the first time. The resulting data were evaluated in light of the Marcus theory of electron transfer to determine the reorganization energy and the electron coupling matrix element in DNA.
- Fukuzumi, Shunichi,Nishimine, Mari,Ohkubo, Kei,Tkachenko, Nikolai V.,Lemmetyinen, Helge
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p. 12511 - 12518
(2007/10/03)
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- Model studies of the (6-4) photoproduct photoreactivation: Synthesis and photosensitized splitting of uracil oxetane adducts
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Uracil oxetane adducts, which are model compounds for the oxetane intermediates generated during the formation of (6-4) photoproducts or in their photoenzymatic repair, have been synthesized using 1,3-dimethyluracil with carbonyl compounds. On the basis of fluorescence measurements and photolysis experiments, it is demonstrated that the oxetane adducts can be split into the nucleotide base and carbonyl compounds via an electron transfer reaction from photosensitizer. The reaction is more efficient for a stronger electron donor.
- Song, Qinhua H.,Hei, Xiaoming,Xu, Zhixiu,Zhang, Xiang,Guo, Qingxiang
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p. 357 - 366
(2007/10/03)
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- Uphill photooxidation of NADH analogues by hexyl viologen catalyzed by zinc porphyrin-linked fullerenes
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In the absence of oxygen, the photolytically generated C60.- moiety in ZnP.+-C60.- and ZnP.+-H2P-C60.- radical ion pairs undergoes one-electron oxidation by hexyl viologen (HV2+), whereas the ZnP.+ moiety is reduced by NADH analogues (1-benzyl-1,4-dihydronicotinamide and 10-methyl-9,10-dihydroacridine). Thus, both ZnP-C60 and ZnP-H2P-C60 donor-acceptor ensembles act in benzonitrile as efficient photocatalysts for the uphill oxidation of NADH analogues by HV2+. In the case of ZnP-C60, the quantum yield of the photocatalytic reaction increases with increasing concentration of HV2+ or an NADH analogue to reach a limiting value of 0.99. The limiting quantum yields of ZnP-C60 and ZnP-H2P-C60 agree well with the quantum yields of radical ion pair formation, ZnP.+-C60.- and ZnP.+-H2P-C60.-, respectively. In the presence of oxygen, the lifetimes of the radical ion pairs are, however, markedly reduced because of an oxygen-catalyzed back electron transfer process between C60.- and ZnP.+. Such an impact on the radical ion pair lifetime consequences a significant decrease in the photocatalytic reactivity of the dyad (i.e., ZnP-C60) in the overall photooxidation of an NADH analogue by HV2+. By contrast, the reactivity of the triad (i.e., ZnP-H2P-C60) shows little effects upon admitting O2.
- Fukuzumi, Shunichi,Imahori, Hiroshi,Okamoto, Ken,Yamada, Hiroko,Fujitsuka, Mamoru,Ito, Osamu,Guldi, Dirk M.
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p. 1903 - 1908
(2007/10/03)
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- Strained heterocyclic systems. Part 21. The Menschutkin reaction
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Rate constants are determined for methyl iodide quaternisations of a series of 2-substituted quinolines and pyridines. Relative rates are interpreted in terms of steric effects, electronic effects and calculated geometries.
- Markgraf,Sangani,Manalansan,Snyder,Thummel
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p. 561 - 563
(2007/10/03)
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- Process for the preparation of optically active ortho-substituted 4-aryl-dihydropyridines
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The invention relates to a process for the preparation of optically active ortho-substituted 4-aryl- or heteroaryl-1,4-dihydropyridines by oxidation and subsequent reduction from their opposite enantiomers.
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- Marcus Theory of Hydride Transfer from an Anionic reduced Deazaflavin to NAD+ Analogues
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Eighteen rate constants, kij for hydride transfer from the conjugate base of 1,5-dihydro-3,10-dimethyl-5-diazaisoalloxazine to a variety of pyridinium, quinolinium, phenanthridinium, and acridinium ions have been determined. (All the oxidizing agents can be regarded as analogues of NAD+.) The kij values span 7 powers of 10 and the corresponding equilibrium constants, Kij, span more than 13 powers of 10.For reactions with ΔG0 near zero, the kij values are close to those given by modified Marcus theory (ref 10).However, with more negative ΔG0 values, the observed kij increase more strogly than the calculated values.Agreement can be produced by making the standard free energy of precursor complex formation, symbolized WT +- here, to indicate that it applies to reactants of opposite charge, a linear function of ΔG0, and treating the slope and interrcept of the linear relation as adjustable parameters.The best fit is obtained with WT+-(in kJ*mol-1)=-9.4+0.11ΔG0.An avarage discrepancy between calculated and observed ln kij values of 0.5 is achieved, which is a good as the overall fit achieved for hydride transfer from neutral NADH analogues to NAD+ analogues (ref 10).The form and the parameterization of Wf are shown to be a physically reasonable approximation for reactions with ΔG00.These results strengthen the conclusion (ref 10) that a wide range of hydride transfer rates can be quantitavely understood without introducing high-energy metastable intermediates (radicals and radical ions).
- Lee, In-Sook Han,Ostovic, Drazen,Kreevoy, Maurice
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p. 3989 - 3993
(2007/10/02)
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- KINETICS OF HYDRIDE TRANSFER BETWEEN NITROGEN HETEROAROMATIC CATIONS
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The kinetics of the reduction of the 3-cyano-1-methylquinolinium, 4-cyano-2-methylisoquinolinium, and 2-methyl-5-nitroisoquinolinium cations by 9,10-dihydro-10-methylacridine, and also the reduction of these same three cations as well as the 10-methylacridinium cation by 5,6-dihydro-5-methylphenanthridine, have been investigated in 20percent acetonitrile - 80percent water, ionic strength 1.0, 25 deg C.The reactions of the 2-methyl-5-nitroisoquinolinium cation with both reductants, and also of the 4-cyano-2-methylisoquinolinium cation with 9,10-dihydro-10-methylacridine, display kinetic saturation effects in the pseudo-first-order rate constants as a function of heterocyclic cation concentration.These effects are consistent with the formation of 1:1 association complexes between hydride donor and acceptor prior to the rate-determining step of the reduction.The second-order rate constants for these reactions, and also those for analogous heterocyclic cation reductions by 1,4-dihydronicotinamides, show systematic variations as a function of the hydride donor and acceptor species.
- Bunting, John W.,Luscher, Mark A.
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p. 2524 - 2531
(2007/10/02)
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- Zur diffusionskontrollierten Loeschung der Fluoreszenz von N-substituierten Acridiniumsalzen
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Es werden die Ergebnisse der dynamischen Fluoreszenzloeschung von 9 N-substituierten Acridiniumderivaten mit Naphthalen in Methanol vorgestellt.Die nach einem Weller-Mechanismus bestimmten thermodynamischen Groessen fuehren in allen Faellen zu einer diffusionskontrollierten Elektronentransferreaktion.Auf dieser Grundlage wird nur der Einfluss der durch den N-Substituenten veraenderten Molekuelgroesse auf die Loeschgeschwindigkeitskonstante beobachtet.Die erhaltene Abstufung in der Loeschgeschwindigkeitskonstanten wird quantitativ auf die fluorophorspezifischen Diffus ionseigenschaften zurueckgefuehrt.Des weiteren werden der Wechselwirkungsabstand und die Geschwindigkeitskonstante der Radikalpaardesaktivierung berechnet.
- Gebert, H.,Regenstein, W.,Bendig, J.,Kreysig, D.
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