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Switchover of the Mechanism between Electron Transfer and Hydrogen‐Atom Transfer for a Protonated Manganese(IV)–Oxo Complex by Changing Only the Reaction Temperature 下载免费PDF全文
Dr. Jieun Jung Surin Kim Dr. Yong‐Min Lee Prof. Dr. Wonwoo Nam Prof. Dr. Shunichi Fukuzumi 《Angewandte Chemie (International ed. in English)》2016,55(26):7450-7454
Hydroxylation of mesitylene by a nonheme manganese(IV)–oxo complex, [(N4Py)MnIV(O)]2+ ( 1 ), proceeds via one‐step hydrogen‐atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid‐bound manganese(IV)‐oxo complex, [(N4Py)MnIV(O)]2+‐(HOTf)2 ( 2 ), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2 , however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around ?0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT. 相似文献
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Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare‐Earth Complexes: Non‐Redox Oxygen Atom Transfer 下载免费PDF全文
Dr. Jianquan Hong Haiwen Tian Prof. Lixin Zhang Prof. Xigeng Zhou Dr. Iker del Rosal Prof. Linhong Weng Prof. Laurent Maron 《Angewandte Chemie (International ed. in English)》2018,57(4):1062-1067
The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes. 相似文献
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Oxygen‐Atom Transfer Chemistry and Thermolytic Properties of a Di‐tert‐Butylphosphate‐Ligated Mn4O4 Cubane 下载免费PDF全文
Kurt M. Van Allsburg Dr. Eitan Anzenberg Dr. Walter S. Drisdell Dr. Junko Yano Prof. T. Don Tilley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4646-4654
[Mn4O4{O2P(OtBu)2}6] ( 1 ), an Mn4O4 cubane complex combining the structural inspiration of the photosystem II oxygen‐evolving complex with thermolytic precursor ligands, was synthesized and fully characterized. Core oxygen atoms within complex 1 are transferred upon reaction with an oxygen‐atom acceptor (PEt3), to give the butterfly complex [Mn4O2{O2P(OtBu)2}6(OPEt3)2]. The cubane structure is restored by reaction of the latter complex with the O‐atom donor PhIO. Complex 1 was investigated as a precursor to inorganic Mn metaphosphate/pyrophosphate materials, which were studied by X‐ray absorption spectroscopy to determine the fate of the Mn4O4 unit. Under the conditions employed, thermolyses of 1 result in reduction of the manganese to MnII species. Finally, the related butterfly complex [Mn4O2{O2P(pin)}6(bpy)2] (pin=pinacolate) is described. 相似文献
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Chellaiah Arunkumar Dr. Yong‐Min Lee Dr. Jung Yoon Lee Shunichi Fukuzumi Prof. Dr. Wonwoo Nam Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11482-11489
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 MnIV–oxo porphyrins are capable of activating C? H bonds of alkylaromatics, with the reactivity order of MnV–oxo>MnIV–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 MnIV–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 MnIV–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 MnIII 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. 相似文献
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Mingqiang Ding Xiaowu Jiang Jinying Peng Lifen Zhang Zhenping Cheng Xiulin Zhu 《Macromolecular rapid communications》2015,36(6):538-546
A concept based on diffusion‐regulated phase‐transfer catalysis (DRPTC) in an aqueous‐organic biphasic system with copper‐mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC‐based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α‐bromophenylacetate (EBrPA) as an initiator, and tris(2‐pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well‐defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling.
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Giancarlo Masci Laura Giacomelli Vittorio Crescenzi 《Macromolecular rapid communications》2004,25(4):559-564
Summary: Controlled polymerization of N‐isopropylacrylamide (NIPAAM) was achieved by atom transfer radical polymerization (ATRP) using ethyl 2‐chloropropionate (ECP) as initiator and CuCl/tris(2‐dimethylaminoethyl)amine (Me6TREN) as a catalytic system. The polymerization was carried out in DMF:water 50:50 (v/v) mixed solvent at 20 °C. The first order kinetic plot was linear up to 92% conversion. Controlled molecular weights up to 2.2 × 104 and low polydispersities (1.19) were obtained. The living character of the polymerization was also demonstrated by self‐blocking experiments. Block copolymers with N,N‐dimethylacrylamide (DMAAM) and 3‐sulfopropyl methacrylate (SPMA) were successfully prepared.
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Yaeun Kang Hui Chen Dr. Yu Jin Jeong Wenzhen Lai Dr. Eun Hae Bae Sason Shaik Prof. Dr. Wonwoo Nam Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10039-10046
The proximal axial ligand in heme iron enzymes plays an important role in tuning the reactivities of iron(IV)‐oxo porphyrin π‐cation radicals in oxidation reactions. The present study reports the effects of axial ligands in olefin epoxidation, aromatic hydroxylation, alcohol oxidation, and alkane hydroxylation, by [(tmp)+. FeIV(O)(p‐Y‐PyO)]+ ( 1 ‐Y) (tmp=meso‐tetramesitylporphyrin, p‐Y‐PyO=para‐substituted pyridine N‐oxides, and Y=OCH3, CH3, H, Cl). In all of the oxidation reactions, the reactivities of 1 ‐Y are found to follow the order 1 ‐OCH3 > 1 ‐CH3 > 1 ‐H > 1 ‐Cl; negative Hammett ρ values of ?1.4 to ?2.7 were obtained by plotting the reaction rates against the σp values of the substituents of p‐Y‐PyO. These results, as well as previous ones on the effect of anionic nucleophiles, show that iron(IV)‐oxo porphyrin π‐cation radicals bearing electron‐donating axial ligands are more reactive in oxo‐transfer and hydrogen‐atom abstraction reactions. These results are counterintuitive since iron(IV)‐oxo porphyrin π‐cation radicals are electrophilic species. Theoretical calculations of anionic and neutral ligands reproduced the counterintuitive experimental findings and elucidated the root cause of the axial ligand effects. Thus, in the case of anionic ligands, as the ligand becomes a better electron donor, it strengthens the FeO? H bond and thereby enhances its H‐abstraction activity. In addition, it weakens the Fe?O bond and encourages oxo‐transfer reactivity. Both are Bell–Evans–Polanyi effects, however, in a series of neutral ligands like p‐Y‐PyO, there is a relatively weak trend that appears to originate in two‐state reactivity (TSR). This combination of experiment and theory enabled us to elucidate the factors that control the reactivity patterns of iron(IV)‐oxo porphyrin π‐cation radicals in oxidation reactions and to resolve an enigmatic and fundamental problem. 相似文献
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Photocatalytic Water Oxidation by a Mixed‐Valent MnIII3MnIVO3 Manganese Oxo Core that Mimics the Natural Oxygen‐Evolving Center 下载免费PDF全文
Dr. Rami Al‐Oweini Dr. Andrea Sartorel Dr. Bassem S. Bassil Dr. Mirco Natali Dr. Serena Berardi Prof. Franco Scandola Prof. Ulrich Kortz Prof. Marcella Bonchio 《Angewandte Chemie (International ed. in English)》2014,53(42):11182-11185
The functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi‐redox MnIII/MnIV manifold that evolves through five electronic states (Si , where i=0–4). The synthetic model system of this catalytic cycle and of its S0→S4 intermediates is the expected turning point for artificial photosynthesis. The tetramanganese‐substituted tungstosilicate [MnIII3MnIVO3(CH3COO)3(A‐α‐SiW9O34)]6? (Mn4POM) offers an unprecedented mimicry of the natural system in its reduced S0 state; it features a hybrid organic–inorganic coordination sphere and is anchored on a polyoxotungstate. Evidence for its photosynthetic properties when combined with [Ru(bpy)3]2+ and S2O82? is obtained by nanosecond laser flash photolysis; its S0→S1 transition within milliseconds and multiple‐hole‐accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7 %. 相似文献
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The Kinetic Isotope Effect as a Probe of Spin Crossover in the CH Activation of Methane by the FeO+ Cation 下载免费PDF全文
Binh Khanh Mai Prof. Dr. Yongho Kim 《Angewandte Chemie (International ed. in English)》2015,54(13):3946-3951
Two‐state reactivity (TSR) is often used to explain the reaction of transition‐metal–oxo reagents in the bare form or in the complex form. The evidence of the TSR model typically comes from quantum‐mechanical calculations for energy profiles with a spin crossover in the rate‐limiting step. To prove the TSR concept, kinetic profiles for C? H activation by the FeO+ cation were explored. A direct dynamics approach was used to generate potential energy surfaces of the sextet and quartet H‐transfers and rate constants and kinetic isotope effects (KIEs) were calculated using variational transition‐state theory including multidimensional tunneling. The minimum energy crossing point with very large spin–orbit coupling matrix element was very close to the intrinsic reaction paths of both sextet and quartet H‐transfers. Excellent agreement with experiments were obtained when the sextet reactant and quartet transition state were used with a spin crossover, which strongly support the TSR model. 相似文献
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Prof. Dr. Shunichi Fukuzumi Takuya Mizuno Tetsuya Ojiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15794-15804
Manganese(V)–oxo–porphyrins are produced by the electron‐transfer oxidation of manganese–porphyrins with tris(2,2′‐bipyridine)ruthenium(III) ([Ru(bpy)3]3+; 2 equiv) in acetonitrile (CH3CN) containing water. The rate constants of the electron‐transfer oxidation of manganese–porphyrins have been determined and evaluated in light of the Marcus theory of electron transfer. Addition of [Ru(bpy)3]3+ to a solution of olefins (styrene and cyclohexene) in CH3CN containing water in the presence of a catalytic amount of manganese–porphyrins afforded epoxides, diols, and aldehydes efficiently. Epoxides were converted to the corresponding diols by hydrolysis, and were further oxidized to the corresponding aldehydes. The turnover numbers vary significantly depending on the type of manganese–porphyrin used owing to the difference in their oxidation potentials and the steric bulkiness of the ligand. Ethylbenzene was also oxidized to 1‐phenylethanol using manganese–porphyrins as electron‐transfer catalysts. The oxygen source in the substrate oxygenation was confirmed to be water by using 18O‐labeled water. The rate constant of the reaction of the manganese(V)–oxo species with cyclohexene was determined directly under single‐turnover conditions by monitoring the increase in absorbance attributable to the manganese(III) species produced in the reaction with cyclohexene. It has been shown that the rate‐determining step in the catalytic electron‐transfer oxygenation of cyclohexene is electron transfer from [Ru(bpy)3]3+ to the manganese–porphyrins. 相似文献
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Dongyi Liu Ahmed M. El‐Zohry Maria Taddei Clemens Matt Laura Bussotti Zhijia Wang Jianzhang Zhao Omar F. Mohammed Mariangela Di Donato Stefan Weber 《Angewandte Chemie (International ed. in English)》2020,59(28):11591-11599
We prepared conceptually novel, fully rigid, spiro compact electron donor (Rhodamine B, lactam form, RB)/acceptor (naphthalimide; NI) orthogonal dyad to attain the long‐lived triplet charge‐transfer (3CT) state, based on the electron spin control using spin‐orbit charge transfer intersystem crossing (SOCT‐ISC). Transient absorption (TA) spectra indicate the first charge separation (CS) takes place within 2.5 ps, subsequent SOCT‐ISC takes 8 ns to produce the 3NI* state. Then the slow secondary CS (125 ns) gives the long‐lived 3CT state (0.94 μs in deaerated n‐hexane) with high energy level (ca. 2.12 eV). The cascade photophysical processes of the dyad upon photoexcitation are summarized as 1NI*→1CT→3NI*→3CT. With time‐resolved electron paramagnetic resonance (TREPR) spectra, an EEEAAA electron‐spin polarization pattern was observed for the naphthalimide‐localized triplet state. Our spiro compact dyad structure and the electron spin‐control approach is different to previous methods for which invoking transition‐metal coordination or chromophores with intrinsic ISC ability is mandatory. 相似文献
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Enhanced Electron Transfer Reactivity of a Nonheme Iron(IV)–Imido Complex as Compared to the Iron(IV)‐Oxo Analogue 下载免费PDF全文
Dr. Anil Kumar Vardhaman Dr. Yong‐Min Lee Dr. Jieun Jung Dr. Kei Ohkubo Prof. Dr. Wonwoo Nam Prof. Dr. Shunichi Fukuzumi 《Angewandte Chemie (International ed. in English)》2016,55(11):3709-3713
Reactions of N,N‐dimethylaniline (DMA) with nonheme iron(IV)‐oxo and iron(IV)‐tosylimido complexes occur via different mechanisms, such as an N‐demethylation of DMA by a nonheme iron(IV)‐oxo complex or an electron transfer dimerization of DMA by a nonheme iron(IV)‐tosylimido complex. The change in the reaction mechanism results from the greatly enhanced electron transfer reactivity of the iron(IV)‐tosylimido complex, such as the much more positive one‐electron reduction potential and the smaller reorganization energy during electron transfer, as compared to the electron transfer properties of the corresponding iron(IV)‐oxo complex. 相似文献
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Jakub Cedrowski Prof. Grzegorz Litwinienko Dr. Andrea Baschieri Dr. Riccardo Amorati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16441-16445
Hydroperoxyl (HOO.) and alkylperoxyl (ROO.) radicals show a different behavior in H‐atom‐transfer processes. Both radicals react with an analogue of α‐tocopherol (TOH), but HOO., unlike ROO., is able to regenerate TOH by a fast H‐atom transfer: TO.+HOO.→TOH+O2. The kinetic solvent effect on the H‐atom transfer from TOH to HOO. is much stronger than that observed for ROO. because noncovalent interactions with polar solvents (Solv???HOO.) destabilize the transition state. 相似文献
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Summary: The living polymerization of N,N‐dimethylacrylamide was achieved by atom transfer radical polymerization catalyzed by copper chloride complexed with a new ligand, N,N′‐bis(pyridin‐2‐ylmethyl 3‐hexoxo‐3‐oxopropyl)ethane‐1,2‐diamine (BPED). With methyl 2‐chloropropionate as the initiator, the polymerization reached high conversions (> 90%) at 80 °C and 100 °C, producing polymers with very close to theoretical values and low polydispersity. The ligand, temperature, and copper halide strongly affected the activity and control of the polymerization.
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Tzong‐Liu Wang Chien‐Hsin Yang Yeong‐Tarng Shieh An‐Chi Yeh 《Macromolecular rapid communications》2009,30(19):1679-1683
A hybrid inorganic–polymer nanocomposite using CdSe nanocrystals with high electron mobility has been successfully synthesized by atom transfer radical polymerization (ATRP). First the hydroxyl‐coated CdSe nanoparticles (i.e., CdSe–OH) were prepared via a wet chemical route. A polymerization initiator was then prepared for ATRP of N‐vinylcarbazole. FT‐IR, 1H NMR, and XRD analyses confirmed the successful synthesis of CdSe–poly(N‐vinylcarbazole) (PVK) nanohybrid. UV–Vis spectra and photoluminescence data revealed that grafting of PVK onto the surface of CdSe nanocrystals would reduce the band gap of PVK and cause the red shift of emission peak. TEM and SEM micrographs exhibited CdSe nanoparticles that were well‐coated with PVK polymer.