- Efficient Six-Electron Photoreduction of Nitrobenzene Derivatives by 10-Methyl-9,10-dihydroacridine in the Presence of Perchloric Acid
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Photoreduction of nitrobenzene derivatives by 10-methyl-9,10-dihydroacridine (AcrH2) occurs efficiently in the presence of perchloric acid in acetonitrile containing H2O (0.50 mol dm-3) to yield the corresponding six-electron reduced products (aniline derivatives) and 10-methylacridinium ion efficiently.The initial two-electron reduction of PhNO2 to PhNO by AcrH2 in the six-electron reduction of nitrobenzene (PhNO2) is started by electron transfer from AcrH2 to the n,?* triplet state (3PhNO2*), followed by acid-catalyzed thermal reduction of PhNO to PhNHOH by AcrH2 and the subsequent photoreduction of PhNHOH to PhNH2 by AcrH2.
- Fukuzumi, Shunichi,Tokuda, Yoshihiro
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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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- 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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- DEHYDROGENATION OF FORMATE BY 10-METHYLACRIDINIUM ION
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Formate is dehydrogenated to CO2 by 10-methylacridinium ion, mimicking formate dehydrogenase.The hydrogen and carbon kinetic isotope effects are 2.74 and 1.027 in a mixed solvent consisting of dimethylformamide and water in a 4 : 1 ratio, at 50 deg C.These values are similar to those observed in the enzymatic reaction (2.27 and 1.042, respectively) suggesting that the mechanisms of enzymatic and nonenzymatic reactions are the same, and transition state structures not too different.Marcus theory of atom and group transfer is used to locate the transition state for the nonenzymatic reaction 0.4 of the distance along the minimum energy path from precursor configuration to successor configuration.It is concluded, following Cleland and coworkers, that the protein of the enzyme dehydrates the formate and deforms the cofactor NAD+ so as to make the reaction more spontaneous.This produces an enzymatic transition state in which the covalency changes around hydrogen are less advanced than in the non-enzymatic transition state, but the environment of the carboxylate is much more suitable to the product, CO2.Yeast formate dehydrogenase brings about the oxidation of formate to CO2, in the process, transferring a hydride ion to the enzyme cofactor, Nicotinamide Adenine Dinucleotide (NAD+), reducing the latter to the corresponding 1,4-dihydropyridine, NADH (eq. 1) HCO2- + NAD+ ----> O2 + NADH Cleland and coworkers have made extensive studies of isotope effects on these reactions.They have shown that the reaction is essentially irreversible, and that the step involving the rearrangement of covalent bonds is fully rate-limiting.They have found that the NAD+ could be replaced with other pyridinium ions, and measured the changes in isotope effects which attended these replacements.They have found that N3- is a much more effective competitive inhibitor than NO3-.From these studies they have reached the following conclusions: 1.) Prior to the hydride transfer, the pyridinium ring is strongly distorted in the direction of dihydropyridine geometry, considerably increasing its hydride affinity (reduction potential). 2.) The transition state in the enzyme catalyzed reaction resembles the products much more closely than the reactants. 3.) Relatively small increases in the reduction potential of the cofactor significantly shift the transition state structure toward that of the reactants.Attempts to oxidize formate with simple NAD+ analogues have been unsuccessful but the reduction potential of 10-methylacridinium ion is -240 mv larger than that of NAD+ which should facilitate the reaction, according to Cleland's point 1.).Further, in refluxing formic acid solvent, formate has been shown to reduce 10-methylacridinium ion.We now report that formate is oxidized by 10-methylacridinium ion at measurable rates in both isopropanol (IPA) - water (4 : 1 by volume) and dimethylformamide (DMF) - water (4 :1 by volume) at 50 deg or 25 deg C. (2)HCOO- and H(13)COO- isotope effects have been measured and compared etc...............
- Hutchins, Jonathan E. C.,Binder, David A.,Kreevoy, Maurice M.
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- Scandium ion-promoted photoinduced electron transfer from electron donors to acridine and pyrene. Essential role of scandium ion in photocatalytic oxygenation of hexamethylbenzene
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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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- 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
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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
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- 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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- Structure and Reactivity of a Manganese(VI) Nitrido Complex Bearing a Tetraamido Macrocyclic Ligand
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Manganese complexes in +6 oxidation state are rare. Although a number of Mn(VI) nitrido complexes have been generated in solution via one-electron oxidation of the corresponding Mn(V) nitrido species, they are too unstable to isolate. Herein we report the isolation and the X-ray structure of a Mn(VI) nitrido complex, [MnVI(N)(TAML)]- (2), which was obtained by one-electron oxidation of [MnV(N)(TAML)]2- (1). 2 undergoes N atom transfer to PPh3 and styrenes to give Ph3P═NH and aziridines, respectively. A Hammett study for various p-substituted styrenes gives a V-shaped plot; this is rationalized by the ability of 2 to function as either an electrophile or a nucleophile. 2 also undergoes hydride transfer reactions with NADH analogues, such as 10-methyl-9,10-dihydroacridine (AcrH2) and 1-benzyl-1,4-dihydronicotinamide (BNAH). A kinetic isotope effect of 7.3 was obtained when kinetic studies were carried out with AcrH2 and AcrD2. The reaction of 2 with NADH analogues results in the formation of [MnV(N)(TAML-H+)]- (3), which was characterized by ESI/MS, IR spectroscopy, and X-ray crystallography. These results indicate that this reaction occurs via an initial "separated CPET"(separated concerted proton-electron transfer) mechanism; that is, there is a concerted transfer of 1 e- + 1 H+ from AcrH2 (or BNAH) to 2, in which the electron is transferred to the MnVI center, while the proton is transferred to a carbonyl oxygen of TAML rather than to the nitrido ligand.
- Shi, Huatian,Lee, Hung Kay,Pan, Yi,Lau, Kai-Chung,Yiu, Shek-Man,Lam, William W. Y.,Man, Wai-Lun,Lau, Tai-Chu
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supporting information
p. 15863 - 15872
(2021/09/30)
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- Radical and ionic mechanisms in rearrangements of o-tolyl aryl ethers and amines initiated by the Grubbs-stoltz reagent, et3SiH/KOtbu
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Rearrangements of o-tolyl aryl ethers, amines, and sulfides with the Grubbs-Stoltz reagent (Et3SiH + KOtBu) were recently announced, in which the ethers were converted to o-hydroxydiarylmethanes, while the (o-tol)(Ar)NH amines were transformed into dihydroacridines. Radical mechanisms were proposed, based on prior evidence for triethylsilyl radicals in this reagent system. A detailed computational investigation of the rearrangements of the aryl tolyl ethers now instead supports an anionic Truce-Smiles rearrangement, where the initial benzyl anion can be formed by either of two pathways: (i) direct deprotonation of the tolyl methyl group under basic conditions or (ii) electron transfer to an initially formed benzyl radical. By contrast, the rearrangements of o-tolyl aryl amines depend on the nature of the amine. Secondary amines undergo deprotonation of the N-H followed by a radical rearrangement, to form dihydroacridines, while tertiary amines form both dihydroacridines and diarylmethanes through radical and/or anionic pathways. Overall, this study highlights the competition between the reactive intermediates formed by the Et3SiH/KOtBu system.
- Kolodziejczak, Krystian,Murphy, John A.,Stewart, Alexander J.,Tuttle, Tell
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- Oxo-Free Hydrocarbon Oxidation by an Iron(III)-Isoporphyrin Complex
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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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- Diazaphosphinanes as hydride, hydrogen atom, proton or electron donors under transition-metal-free conditions: Thermodynamics, kinetics, and synthetic applications
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Exploration of new hydrogen donors is in large demand in hydrogenation chemistry. Herein, we developed a new 1,3,2-diazaphosphinane 1a, which can serve as a hydride, hydrogen atom or proton donor without transition-metal mediation. The thermodynamics and kinetics of these three pathways of 1a, together with those of its analog 1b, were investigated in acetonitrile. It is noteworthy that, the reduction potentials (Ered) of the phosphenium cations 1a-[P]+ and 1b-[P]+ are extremely low, being-1.94 and-2.39 V (vs. Fc+/0), respectively, enabling corresponding phosphinyl radicals to function as neutral super-electron-donors. Kinetic studies revealed an extraordinarily large kinetic isotope effect KIE(1a) of 31.3 for the hydrogen atom transfer from 1a to the 2,4,6-tri-(tert-butyl)-phenoxyl radical, implying a tunneling effect. Furthermore, successful applications of these diverse P-H bond energetic parameters in organic syntheses were exemplified, shedding light on more exploitations of these versatile and powerful diazaphosphinane reagents in organic chemistry.
- Cheng, Jin-Pei,Yang, Jin-Dong,Zhang, Jingjing
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p. 3672 - 3679
(2020/04/21)
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- Alkyl formates as reagents for reductive amination of carbonyl compounds
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Alkyl formates in the presence of basic additives can serve as a reagent in the direct reductive amination of carbonyl compounds. The developed procedure can be applied to various aldehydes and ketones with electron donating and electron withdrawing groups.
- Afanasyev, Oleg I.,Cherkashchenko, Ilia,Kuznetsov, Anton,Kliuev, Fedor,Semenov, Sergey,Chusova, Olga,Denisov, Gleb,Chusov, Denis
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p. 112 - 113
(2020/03/03)
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- Uncatalyzed Oxidative C?H Amination of 9,10-Dihydro-9-Heteroanthracenes: A Mechanistic Study
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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
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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
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supporting information
p. 4230 - 4233
(2019/04/30)
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- A Nucleophilicity Scale for the Reactivity of Diazaphospholenium Hydrides: Structural Insights and Synthetic Applications
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Nucleophilicity parameters (N, sN) of a group of representative diazaphospholenium hydrides were derived by kinetic investigations of their hydride transfer to a series of reference electrophiles with known electrophilicity (E) values, using the Mayr equation log k2=sN(N+E). The N scale covers over ten N units, ranging from the most reactive hydride donor (N=25.5) to the least of the scale (N=13.5). This discloses the highest N value ever quantified in terms of Mayr's nucleophilicity scales reported for neutral transition-metal-free hydride donors and implies an exceptional reactivity of this reagent. Even the least reactive hydride donor of this series is still a better hydride donor than those of many other nucleophiles such as the C?H, B?H, Si?H and transition-metal M?H hydride donors. Structure–reactivity analysis reveals that the outstanding hydricity of 2-H-1,3,2-diazaphospholene benefits from the unsaturated skeleton.
- Zhang, Jingjing,Yang, Jin-Dong,Cheng, Jin-Pei
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p. 5983 - 5987
(2019/04/03)
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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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- 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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- A classical but new kinetic equation for hydride transfer reactions
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A classical but new kinetic equation to estimate activation energies of various hydride transfer reactions was developed according to transition state theory using the Morse-type free energy curves of hydride donors to release a hydride anion and hydride acceptors to capture a hydride anion and by which the activation energies of 187 typical hydride self-exchange reactions and more than thirty thousand hydride cross transfer reactions in acetonitrile were safely estimated in this work. Since the development of the kinetic equation is only on the basis of the related chemical bond changes of the hydride transfer reactants, the kinetic equation should be also suitable for proton transfer reactions, hydrogen atom transfer reactions and all the other chemical reactions involved with breaking and formation of chemical bonds. One of the most important contributions of this work is to have achieved the perfect unity of the kinetic equation and thermodynamic equation for hydride transfer reactions. The Royal Society of Chemistry.
- Zhu, Xiao-Qing,Deng, Fei-Huang,Yang, Jin-Dong,Li, Xiu-Tao,Chen, Qiang,Lei, Nan-Ping,Meng, Fan-Kun,Zhao, Xiao-Peng,Han, Su-Hui,Hao, Er-Jun,Mu, Yuan-Yuan
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p. 6071 - 6089
(2013/09/12)
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- Nonconventional versus conventional application of pseudo-first-order kinetics to fundamental organic reactions
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Three new analysis procedures for pseudo-first-order kinetics are introduced and applied to eight different fundamental organic reactions. The reactions belong to the following classes: nitroalkane proton transfer, formal hydride ion transfers from NADH model compounds, and SN2 reactions of alkyl halides with ionic and neutral nucleophiles. The three methods consist of (1) half-life dependence of kapp, (2) sequential linear pseudo-first-order correlation, and (3) revised instantaneous rate constant analysis. Each of the three procedures is capable of distinguishing between one- and multistep mechanisms, and the combination of the three procedures provides a powerful strategy for differentiating between the two mechanistic possibilities. The data from the eight reactions chosen as examples clearly show how the procedures work in practice.
- Parker, Vernon D.,Hao, Weifang,Li, Zhao,Scow, Russell
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experimental part
p. 2 - 12
(2012/03/22)
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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
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supporting information; experimental part
p. 8160 - 8162
(2010/12/19)
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- Thermodynamic diagnosis of the properties and mechanism of dihydropyridine-type compounds as hydride source in acetonitrile with molecule id card
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A series of 45 dihydropyridine-type organic compounds as hydride source were designed and synthesized. The thermodynamic driving forces (defined as enthalpy changes or redox potentials in this work) of the dihydropyridines to release hydride anions, hydrogen atoms (hydrogen for short), and electrons in acetonitrile,the thermodynamic driving forces of the radical cations of the dihydropyridines to release protons and hydrogens in acetonitrile, and the thermodynamic driving forces of the neutral pyridine-type radicals of the dihydropyridines to release electron in acetonitrile were determined by using titration calorimetry and electrochemical methods. The rates and activation parameters of hydride transfer from the dihydropyridines to acridinium perclorate, a well-known hydride acceptor, were determined by using UV-vis absorption spectroscopy technique. The relationship between the thermodynamic driving forces and kinetic rate of the hydride transfer was examined. Thermodynamic characteristic graph (TCG) of the dihydropyridines as an efficient Molecule ID Card was introduced. The TCG can be used to quantitatively diagnose or predict the characteristic chemical properties of the dihydropyridines and their various reaction intermediates. The mechanism of hydride transfer from the dihydropyridines to acridinium perclorate was diagnosed and elucidated by using the determined thermodynamic parameters and the activation parameters..
- Zhu, Xiao-Qing,Tan, Yue,Cao, Chao-Tun
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experimental part
p. 2058 - 2075
(2010/07/16)
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- Hydride, hydrogen, proton, and electron affinities of imines and their reaction intermediates in acetonitrile and construction of thermodynamic characteristic graphs (TCGs) of imines as a molecule ID card
-
(Chemical Equation Presented) A series of 61 imines with various typical structures were synthesized, and the thermodynamic affinities (defined as enthalpy changes or redox potentials in this work) of the imines to abstract hydride anions, hydrogen atoms, and electrons, the thermodynamic affinities of the radical anions of the imines to abstract hydrogen atoms and protons, and the thermodynamic affinities of the hydrogen adducts of the imines to abstract electrons in acetonitrile were determined by using titration calorimetry and electrochemical methods. The pure heterolytic and homolytic dissociation energies of the C=N π-bond in the imines were estimated. The polarity of the C=N double bond in the imines was examined using a linear free-energy relationship. The idea of a thermodynamic characteristic graph (TCG) of imines as an efficient Molecule ID Card was introduced. The TCG can be used to quantitatively diagnose and predict the characteristic chemical properties of imines and their various reaction intermediates as well as the reduction mechanism of the imines. The information disclosed in this work could not only supply a gap of thermodynamics for the chemistry of imines but also strongly promote the fast development of the applications of imines. 2009 American Chemical Society.
- Zhu, Xiao-Qing,Liu, Qiao-Yun,Chen, Qiang,Mei, Lian-Rui
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scheme or table
p. 789 - 808
(2010/04/29)
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- 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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- 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)
-
- 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
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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)
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- Effective thermal oxidation of isopropanol by an NAD+ model
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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)
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- A mechanistic dichotomy in scandium ion-promoted hydride transfer of an NADH analogue: Delicate balance between one-step hydride-transfer and electron-transfer pathways
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The rate constant (kH) of hydride transfer from an NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2), to 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ) increases with increasing Sc 3+ concentration ([Sc3+]) to reach a constant value, when all TolSQ molecules form the TolSQ-Sc3+ complex. When AcrH 2 is replaced by the dideuterated compound (AcrD2), however, the rate constant (kD) increases linearly with an increase in [Sc3+] without exhibiting a saturation behavior. In such a case, the primary kinetic deuterium isotope effect (kH/kD) decreases with increasing [Sc3+]. On the other hand, the rate constant of Sc3+-promoted electron transfer from tris(2- phenylpyridine)iridium [Ir(ppy)3] to TolSQ also increases linearly with increasing [Sc3+] at high concentrations of Sc3+ due to formation of a 1:2 complex between TolSQ?- and Sc 3+, [TolSQ?- (Sc3+)2], which was detected by ESR. The significant difference with regard to dependence of the rate constant of hydride transfer on [Sc3+] between AcrH2 and AcrD2 in comparison with that of Sc3+-promoted electron transfer indicates that the reaction pathway is changed from one-step hydride transfer from AcrH2 to the TolSQ-Sc3+ complex to Sc3+-promoted electron transfer from AcrD2 to the TolSQ-Sc3+ complex, followed by proton and electron transfer. Such a change between two reaction pathways, which are employed simultaneously, is also observed by simple changes of temperature and concentration of Sc3+.
- Yuasa, Junpei,Yamada, Shunsuke,Fukuzumi, Shunichi
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p. 14938 - 14948
(2008/02/03)
-
- Chemiluminescent autoxidation of α-silyl carbanions derived from 9-silyl-10-methylacridanes
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The autoxidation of α-silyl carbanions derived from 9-trimethysilyl- and 9-triphenylsilyl-10-methylacridanes (1a and 1b) produced the fluorescent N-methylacridone (NMA) accompanied by weak chemiluminescence. Differences in the chemiluminescence quantum yields and the time course of the light emission were detected between the reactions of 1a and 1b, which was due to the substituent on the silicon atom. Additionally, the 9-trimethylsilyl-10-methylacridinium salt also underwent a chemiluminescent reaction when reacted with alkaline hydrogen peroxide. It is probable that these chemiluminescent reactions would proceed via the Peterson-type reaction and involve the dioxasiletanide-like species during the reaction pathway.
- Motoyoshiya, Jiro,Tokutake, Kunihiko,Kuroe, Motoki,Yoshioka, Sachiko,Nishii, Yoshinori,Aoyama, Hiromu
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p. 1667 - 1672
(2007/10/03)
-
- 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)
-
- Cleavage mode of benzyltributylstannane radical cations produced in photoinduced electron transfer
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Cleavage of metal-carbon bond of benzyltributylstannane radical cation produced in photoinduced electron transfer from benzyltributylstannane to 10-methylacridinium ion occurs to give benzyl radical rather than benzyl cation, resulting in formation of 9-benzyl-10-methyl-9,10-dihydroacridine selectively in dehydrated acetonitrile. In the presence of water, however, 10-methyl-9,10-dihydroacridine is also formed via electron transfer from benzyl radical to the dihydroacridine radical cation produced by protonation of acridinyl radical following the initial photoinduced electron transfer.
- Fukuzumi, Shunichi,Yasui, Kiyomi,Itoh, Shinobu
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p. 161 - 162
(2007/10/03)
-
- Addition versus oxygenation of alkylbenzenes with 10-methylacridinium ion via photoinduced electron transfer
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Addition of alkylbenzenes with 10-methylacridinium ion (AcrH+) occurs efficiently under visible light irradiation in deaerated acetonitrile containing H2O to yield 9-alkyl-10-methyl-9,10-dihydroacridine selectively. On the other hand, the photochemical reaction of AcrH+ with alkylbenzenes in the presence of perchloric acid in deaerated acetonitrile yields 10-methyl-9,10-dihydroacridine, accompanied by the oxygenation of alkylbenzenes to the corresponding benzyl alcohols. The photooxygenation of alkylbenzenes occurs also in the presence of oxygen, when AcrH+ acts as an efficient photocatalyst. The studies on the quantum yields and fluorescence quenching of AcrH+ by alkylbenzenes as well as the laser flash photolysis have revealed that the photochemical reactions of AcrH+ with alkylbenzenes in both the absence and presence of oxygen proceed via photoinduced electron transfer from alkylbenzenes to the singlet excited state of AcrH+ to produce alkylbenzene radical cations and 10-methylacridinyl radical (AcrH·). The competition between the deprotonation of alkylbenzene radical cations and the back electron transfer from AcrH· to the radical cations determines the limiting quantum yields. In the absence of oxygen, the coupling of the deprotonated radicals with AcrH· yields the adducts. The photoinduced hydride reduction of AcrH+ in the presence of perchloric acid proceeds via the protonation of acridinyl radical produced by the photoinduced electron transfer from alkylbenzenes. In the presence of oxygen, however, the deprotonated radicals are trapped efficiently by oxygen to give the corresponding peroxyl radicals which are reduced by the back electron transfer from AcrH· to regenerate AcrH+, followed by the protonation to yield the corresponding hydroperoxide. The ratios of the deprotonation reactivity from different alkyl groups of alkylbenzene radical cations were determined from both the intra- and intermolecular competitions of the deprotonation from two alkyl groups of alkylbenzene radical cations. The reactivity of the deprotonation from alkylbenzene radical cations increases generally in the order methyl ethyl isopropyl. The strong stereoelectronic effects on the deprotonation from isopropyl group of alkylbenzene radical cations appear in the case of the o-methyl isomer.
- Fujita, Morifumi,Ishida, Akito,Takamuku, Setsuo,Fukuzumi, Shunichi
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p. 8566 - 8574
(2007/10/03)
-
- Reacivity of Phosphorus-Centered Radicals Generated during the Photoreaction of Diphenylphosphinous Acid with 10-Methylacridinium Salt
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Diphenylphosphinous acid (1) reacts with 10-methylacridinium iodide (2a) in aqueous acetonitrile during irradiation by visible light under an argon atmosphere at 20 deg C to afford diphenylphosphinic acid (3) and 10-methylacridan (4).The effects of the solvent and atmosphere and the effect of added iodide ion (I(1-)) or iodine (I2) on the product distribution show that the mechanism involves initial single-electron transfer (SET) from 1 to 2a in the photoexcited state, by which cation radical 1(1+.) and dihydroacridinyl radical 2(.), are generated.Cation radical 1(1+.) undergoes electrophylic reaction with water in the solvent, and the resulting phosphoranyl radical decomposes through SET to iodine atom (I(.)) rather than unergoing β-scission, eventually giving 3.Protonation to 2(.) followed by reduction by I(1-) affords 4.These reaction sequences make up the catalytic I(.)/I(1-) couple.The results are interpreted on the basis of reported redox potentials.
- Yasui, Shinro,Shioji, Kosei,Ohno, Atsuyoshi,Yoshihara, Masakuni
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p. 2099 - 2105
(2007/10/02)
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- Photoinduced Hydride Reduction of 10-Methylacridinium Ion by Alkylbenzenes in the Presence of Perchloric Acid
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Photoinduced hydride reduction of 10-methylacridinium ion (AcrH+) by alkylbenzene occurs to yield 10-methyl-9,10-dihydroacridine in the presence of perchloric acid, while photoaddition occurs to yield 9-alkyl-10-methyl-9,10-dihydroacridine in the absence of perchloric acid.The hydride reduction of AcrH+ in the presence of perchloric acid proceeds via protonation of cridinyl radical produced by photoinduced electron transfer from alkylbenzene.
- Fujita, Morifumi,Ishida, Akito,Majima, Tetsuro,Fukuzumi, Shunichi,Takamuku, Setsuo
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p. 111 - 112
(2007/10/02)
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- THE THERMAL AND PHOTO-REACTIONS OF DIPHENYLPHOSPHINITE ESTER WITH N-METHYLACRIDINIUM ION
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The thermal reaction of diphenylphosphinite esters (1b-f) with N-methylacridinium iodide (2) resulted in the formation of a phosphonium ion through a polar process.On the other hand, when isopropyl derivative (1f) was reacted with 2 under the irradiation with visible light, N-methylacridan, along with isopropyl diphenylphosphinate, was formed through single electron transfer (SET) from 1f to 2.
- Yasui, Shinro
-
p. 197 - 200
(2007/10/02)
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- Electron-transfer oxidation of 9-substituted 10-methyl-9,10-dihydroacridines. Cleavage of the C-H vs C-C bond of the radical cations
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Electron-transfer oxidation of various 9-substituted 10-methyl-9,10-dihydroacridines (AcrHR) by Fe(ClO4)3 and [Fe(phen)3](PF6)3 (phen = 1,10-phenanthroline) results in cleavage of the C(9)-H or C(9)-C bond of AcrHR?+ depending on the substituent R. Transient electronic absorption spectra as well as electron spin resonance (ESR) spectra of AcrHR?+ have been detected by using a stopped-flow spectrophotometer and a rapid mixing flow ESR technique, respectively. The hyperfine splitting constants (hfs) are determined by comparing the observed ESR spectra with those from the computer simulation. Comparison of the hfs values with those expected from the molecular orbital calculations indicates the structural change of AcrHR?+ with the substituent R, which is reflected in the selectivity of the C-H vs C-C bond cleavage of AcrHR?+ depending on the substituent R. The decay rates of AcrHR?+ obey the mixture of first-order and second-order kinetics due to the deprotonation (or the C-C bond cleavage) and disproportionation reactions, respectively. Both the first-order and bimolecular second-order decay rate constants of AcrHR?+ are reported. The first-order decay rate constant for the deprotonation of AcrHR?+ by the C-H bond cleavage decreases with the substitution in order R = primary > secondary > tertiary alkyl groups, while the first-order decay due to the C-C bond cleavage becomes dominant with tertiary alkyl groups. The one-electron oxidation potentials of various AcrHR have been determined directly by applying fast cyclic voltammetry. The pKa values of AcrHR?+ (R = H and Me) have also been evaluated by analyzing the dependence of the first-order deprotonation rate constants on the concentrations of HClO4.
- Fukuzumi, Shonichi,Tokuda, Yoshihiro,Kitano, Toshiaki,Okamoto, Toshihiko,Otera, Junzo
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p. 8960 - 8968
(2007/10/02)
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- The Catalytic Role of Iodide Ion/Iodine Couple in the Photo-Reduction of 10-Methylacridinium Ion with Diphenylphosphine Oxide
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Photo-redox between diphenylphosphine oxide and 10-methylacridinium iodide with visible light in aqueous acetonitrile under argon atmosphere is initiated by single electron transfer from the phosphorus compound to the acridinium salt in the potoexcited state giving diphenylphosphinic acid and 10-methylacridan as the final products.Iodide ion/iodine couple plays a crucial role for transferring an electron in this reaction.
- Yasui, Shinro,Shioji, Kosei,Ohno, Atsuyoshi,Yoshihara, Masakuni
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p. 1393 - 1396
(2007/10/02)
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- The thermal- and photo-reactions of a diphenylphosphinite ester with 10-methylacridinium iodide. Discrimination between polar and single electron transfer processes
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The thermal-reaction of isopropyl diphenylphosphinite with 10-methylacridinuim iodide results in the formation of a phosphonium ion through a polar process, whereas the reaction under the irradation of light affords 10-methylacridan as well as isopropyl diphenylphosphinate through single electron transfer (SET) from the former to the latter.
- Yasui, Shinro,Shioji, Kosei,Yoshihara, Masakuni,Maeshima, Toshihisa,Ohno, Atsuyoshi
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p. 7189 - 7192
(2007/10/02)
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- The Reaction of a 10-Methylacridinium Salt with Tertiary Amines
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The reaction of 10-methylacridinium perchlorate with a variety of N,N-disubstituted alkylamines or aralkylamines was investigated in the presence or absence of air.In all cases studied, 10-methyl-9,10-dihydroacridine was produced in approximately 50percent yield or more.In addition, either 10-methyl-9(10H)-acridinone or 9-(dialkylamino)-10-methylacridinium perchlorate or both were isolated, each yield being greatly dependent on the bulkiness of alkyl groups on the amines.In the blanket of air, significant amounts of aldehyde was detected.The mechanism was discussed.
- Tamagaki, Seizo,Ueno, Masanori,Tagaki, Waichiro
-
-
- Electrochemistry of NADH/NAD+ analogues. A detailed mechanistic kinetic and thermodynamic analysis of the 10-methylacridan/10-methylacridinium couple in acetonitrile
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The electrochemical oxidation of 10-methylacridan (AH) at platinum and gold electrodes in acetonitrile containing various pyridine bases is investigated by means of cyclic voltammetric and potential step techniques. The conversion of AH to the 10-methylacridinium ion (A+) proceeds along an electron-proton-electron transfer mechanism, the second electron being abstracted by the initial cation radical, AH?+, rather than by the electrode itself in most cases. The use of ultramicroelectrodes (in the 10 μm diameter range) allows the determination of the standard potential of the AH?+/AH couple and of the rate constant of the deprotonation of AH?+; the latter was measured as a function of the pKa of a series of pyridine bases. Investigation of the reduction of A+ by the same techniques led to the determination of the standard potential of the A+/A? couple and of the dimerization rate constant of A?. The oxidation of AH as well as the reduction of A+ are kinetically controlled by follow-up homogeneous chemical steps rather than by the initial electron transfer, which appears as quite fast in both cases. The combination of an ultraslow spectrometric technique with the ultrafast electrochemical techniques allowed the determination of the pKa of the AH?+/A? couple from that of the standard potential of the overall reaction AH ? A+ + 2e- + H+ and hence the construction of a Br?nsted plot with a known driving force origin for the deprotonation of AH?+.
- Hapiot, Philippe,Moiroux, Jacques,Savéant, Jean-Michel
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p. 1337 - 1343
(2007/10/02)
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- Dynamics of hydride transfer between NAD+ analogues
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Primary kinetic isotope effects (KIE) for hydride transfer between 10-methylacridan and 1-benzyl-3-cyanoquinolinium perchlorate have been measured in 15 different solvents. There is a reduction of the KIE from 5.2 to about 2.9 in the more viscous, nonhydroxylic solvents. Hydroxylic solvents give the larger KIE regardless of their viscosity. These results suggest a three-step process. In the first step, the heavy atoms and solvent are reorganized to a configuration intermediate between reactants and products, while the hydride retains its original attachment. In the second stage, the hydride is transferred, probably by tunneling. In the final step the products are stabilized by further solvent and heavy-atom reorganization. For nonhydroxylic solvents, translational and rotational diffusion governs the heavy-atom reorganization steps and, therefore, determines which step is rate-limiting. Only when the heavy-atom reorganizations are fast is the second step rate-limiting and the KIE maximized. The rate constant for the tunneling process is assumed to be solvent-independent. It is of the right order of magnitude to compete with solvent relaxation. Changes in rate constant, k, and equilibrium constant, K, are modest, but there is a linear correlation between ln k and ln K, with a slope of 0.87. This slope suggests that it is the third step, rather than the first, which shares rate-limiting character with the second. There is no visible trend toward a maximum isotope effect at K = 1.
- Kreevoy, Maurice M.,Kotchevar, Ann T.
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p. 3579 - 3583
(2007/10/02)
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- Photoinduced Hydride Reduction of NAD+ Analogue with Permethylpolysilanes Acting as Electron Sources and Water as a Proton Source
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Photoinduced hydride reduction of an NAD+ analogue, 10-methylacridinium ion with permethylpolysilanes acting as electron sources and water as a proton source occurs efficiently in acetonitrile under irradiation of visible light (λ>360 nm) to yield 9,10-dihydro-10-methylacridine selectively.
- Fukuzumi, Shunichi,Kitano, Toshiaki,Mochida, Kunio
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p. 2177 - 2180
(2007/10/02)
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- Reversible Transformation between the Oxidized and Reduced Forms of Redox Coenzyme Analogues
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Reversible transformation between 10-methylacridinium ion (AcrH+) and 9,10-dihydro-10-methylacridine (AcrH2) has been achieved by combining the photo-reduction of AcrH+ by benzyl alcohol derivatives in MeCN at 298 K under irradiation of visible light of λ > 360 nm with the thermal oxidation of AcrH2 by the corresponding benzaldehyde derivatives at 333 K.The photo-reduction of AcrH+ by a benzyl alcohol derivative can also be combined with the photo-oxidation of ArcH2 by dibenzyl disulphide under irradiation of light of λ 285 nm which corresponds to the absorption maximum of ArcH2.Under continuous irradiation of light from Xenon lamp, the AcrH+ / AcrH2 redox pair acts as a photocatalyst for the oxidation of p-chlorobenzyl alcohol by dibenzyl disulphide to yield p-chlorobenzaldehyde and toluene-α-thiol.Reversible transformation between riboflavin-2',3',4',5'-tetra-acetate (Fl) and the corresponding 1,5-dihydroflavin (FlH2) has also been achieved by utilizing all possible combinations of thermal and photochemical reactions in controlling the direction of the redox reaction between Fl and benzenethiol derivatives, i.e., the forward thermal reduction of Fl by benzenethiol derivatives combined with the reverse photo-oxidation of FlH2 by the corresponding disulphides, the forward photo-reduction of Fl and the reverse photo-oxidation of FlH2 under irradiation with light of different wavelengths, and the forward photo-reduction of Fl combined with the reverse thermal oxidation of FlH2.
- Fukuzumi, Shunichi,Tanii, Kumiko,Ishikawa, Masashi,Tanaka, Toshio
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p. 1801 - 1806
(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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- Substrate-Specific Reduction Mechanisms for NADH Models. Reduction of N-Methylacridinium Iodide and α,α,α-Trifluoroacetophenone
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The reduction of α,α,α-trifluoroacetophenone by five N-substituted dihydronicotinamides (DHNAs) proceeds by a free radical chain process initiated by single electron transfer (SET).In dry acetonitrile the chain, whose propagation chain steps contain a SET-hydrogen atom transfer sequence, could be inhibited with m-dinitrobenzene or initiated by AIBN.Under the same reduction conditions methylacridinium iodide does not undergo homolytic chain reduction.The reduction of methylacridinium iodide by all five of the DHNAs followed clean second-order kinetics which wereconsistent with a bimolecular hydride transfer.Although a chain reaction involving solely cross termination can also follow second-order kinetics, no evidence could be obtained for either chain inhibition or initiation.The reduction mechanism followed by the NADH models appears to be substrate-specific and results reached from such model studies must be evaluated with some reservation.
- Tanner, Dennis D.,Kharrat, Abdelmajid
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p. 1646 - 1650
(2007/10/02)
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- Structure Sensitivity of the Marcus λ for Hydride Transfer between NAD+ Analogues
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Thirty-five rate constants, kij, for transfer of hydride between various pyridinium, quinilinium, acridinium, and phenantridinium ions spanning a range of over 10E11 in their equilibrium constants Kij and over 10E6 in kij
- Kreevoy, Maurice M.,Ostovic, Drazen,Lee, In-Sook Han,Binder, David A.,King, Gary W.
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p. 524 - 530
(2007/10/02)
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- The Photoreduction Mechanism of 10-Methylacridinium Chloride in Methanol. The Formation of 9,10-Dihydro-9-methoxy-10-methylacridine and Hydride Transfer
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The photolysis of 9,10-dihydro-9-methoxy-10-methylacridine (MeOA), which is a product of the nucleophilic addition of methanol to 10-methylacridinium chloride, yielded 9,10-dihydro-10-methylacridine (AH2) and 10,10'-dimethyl-9,9',10,10'-tetrahydro-9,9'-biacridinyl ((AH)2) in various solvents.The quenching experiment using 1,3-pentadiene indicates that AH2 and (AH)2 are produced from the photoexcited singlet and triplet states of MeOA respectively.The results on the solvent effects and the photolyses in solvent matrices at 77 K suggest that the photochemical reactionof MeOA yielding AH2 occurs via hydride transfer from the methoxide anion to the 10-methylacridinium cation, these ions being generated from the heterolysis of MeOA in the photoexcited singlet state.
- Kano, Koji,Zhou, Bin,Hashimoto, Shizunobu
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p. 1041 - 1048
(2007/10/02)
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- Hydride Transfer and Oxyanion Addition Equilibria of NAD+ Analogues
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Equilibrium constants, K, have been determined for the reduction of 10-methylacridinium ion by 15 N-heterocyclic hydride donors: acridine, quinoline, pyridine, and phenanthridine derivatives.The solvent was a mixture of 2-propanol and water in the ratio 4 : 1 by volume.Reduction potentials have been estimated for the corresponding cations in aqueous solution by assuming that the K's would be the same and accepting -361 mV as the reduction potential of the 3-(aminocarbonyl)-1-benzylpyridinium ion.These reduction potentials span 430 mV.Values of pKR have also been determined for six of the cations in the same solvent.For derivatives of the same ring system, -ΔlogK is approximately equal to ΔpKR, but a 4 log unit discrepancy appears when phenanthridine derivatives are compared with the 9-methylacridinium ion.
- Ostovic, Drazen,Lee, In-Sook Han,Roberts, Roger M. G.,Kreevoy, Maurice M.
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p. 4206 - 4211
(2007/10/02)
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