Ji-Hu Su

Accelerated crystallization of zeolites via hydroxyl free radicals

Radically faster synthesis Zeolite synthesis normally proceeds under basic conditions that allow the oxide bridges between aluminum and silicon atoms to break and reform. Feng et al. show that the formation of hydroxyl radicals, either by irradiation with ultraviolet light or with the Fenton reagent, can speed up the formation of the crystallized zeolite by about a factor of 2. Science, this issue p. 1188 Hydroxyl radicals generated with ultraviolet light or Fenton reagents can approximately double the rate of zeolite synthesis. In the hydrothermal crystallization of zeolites from basic media, hydroxide ions (OH–) catalyze the depolymerization of the aluminosilicate gel by breaking the Si,Al–O–Si,Al bonds and catalyze the polymerization of the aluminosilicate anions around the hydrated cation species by remaking the Si,Al–O–Si,Al bonds. We report that hydroxyl free radicals (•OH) are involved in the zeolite crystallization under hydrothermal conditions. The crystallization processes of zeolites—such as Na–A, Na–X, NaZ–21, and silicalite-1—can be accelerated with hydroxyl free radicals generated by ultraviolet irradiation or Fenton’s reagent.

A novel approach for the one-pot preparation of α-ketoamides by anodic oxidation

The direct oxidative synthesis of α-ketoamides via anodic oxidation was developed by using dioxygen as a reactant under mild conditions. This methodology has a broad substrate scope (aromatic amines, aliphatic amines and ammonium acetate) and opens up an interesting and attractive avenue for the synthesis of α-ketoamide derivatives.

The Basic Properties of the Electronic Structure of the Oxygen-evolving Complex of Photosystem II Are Not Perturbed by Ca2+ Removal

Background: EPR/55Mn ENDOR spectroscopy of the oxygen-evolving complex (OEC) and Mn2+ in Ca2+-depleted photosystem II. Results: Electronic model of the Ca2+-depleted OEC; characterization of Mn2+ binding. Conclusion: Ca2+ is not critical for maintaining the electronic and spatial structure of the OEC. Its removal exposes a Mn2+ binding site supposedly in an extrinsic subunit. Significance: Mechanistic implications for water oxidation; Mn2+ in photoassembly/D1 protein repair. Ca2+ is an integral component of the Mn4O5Ca cluster of the oxygen-evolving complex in photosystem II (PS II). Its removal leads to the loss of the water oxidizing functionality. The S2′ state of the Ca2+-depleted cluster from spinach is examined by X- and Q-band EPR and 55Mn electron nuclear double resonance (ENDOR) spectroscopy. Spectral simulations demonstrate that upon Ca2+ removal, its electronic structure remains essentially unaltered, i.e. that of a manganese tetramer. No redistribution of the manganese valence states and only minor perturbation of the exchange interactions between the manganese ions were found. Interestingly, the S2′ state in spinach PS II is very similar to the native S2 state of Thermosynechococcus elongatus in terms of spin state energies and insensitivity to methanol addition. These results assign the Ca2+ a functional as opposed to a structural role in water splitting catalysis, such as (i) being essential for efficient proton-coupled electron transfer between YZ and the manganese cluster and/or (ii) providing an initial binding site for substrate water. Additionally, a novel 55Mn2+ signal, detected by Q-band pulse EPR and ENDOR, was observed in Ca2+-depleted PS II. Mn2+ titration, monitored by 55Mn ENDOR, revealed a specific Mn2+ binding site with a submicromolar KD. Ca2+ titration of Mn2+-loaded, Ca2+-depleted PS II demonstrated that the site is reversibly made accessible to Mn2+ by Ca2+ depletion and reconstitution. Mn2+ is proposed to bind at one of the extrinsic subunits. This process is possibly relevant for the formation of the Mn4O5Ca cluster during photoassembly and/or D1 repair.

Electrochemical synthesis of the aryl α-ketoesters from acetophenones mediated by KI.

a-Ketoesters play an essential role in biological processes. They serve as the backbones in some natural products, such as the 3-deoxy-2-ulosonic acids and their derivatives. In addition, a-ketoesters are also used as key intermediates for the synthesis of highly valued substrates. Over the past several decades, chemists have paid great attention to the synthesis of a-ketoesters. Classical methods include oxidation of a-hydroxy esters with various kinds of oxidant, oxidation of methyl 2-phenylacetate, Friedel– Crafts acylation, hydrolysis and esterification of acyl cyanides, hydrolysis of 2-aryl-2-nitroacetates, and other methods. However, these protocols usually require stoichiometric amounts of metal oxidants, and thus a large amount of waste is formed in the reaction. It has been known that electrochemistry is a green method for fine chemical synthesis. Recently the synthesis of esters from aldehydes and the corresponding alcohols was realized by virtue of an anode oxidation in the presence of N-heterocyclic carbine (NHC)/1,8-diazabicyclo ACHTUNGTRENNUNG[5.4.0]undec-7-ene (DBU). In our laboratory, we have been attempting to prepare a-ketoesters from aryl ketones and the corresponding alcohols by an anode oxidation. We conceive that this oxidation of methyl ketones in the presence of potassium iodide could avoid the waste pollution under electrochemical conditions. Previously, the reaction of methyl ketones with iodine was a typical haloform reaction, affording carboxylic acids or esters with a loss of one carbon atom. It is a challenge to functionalize the methelene of methyl ketones without losing the methyl carbon atom. Herein, we describe a novel method to synthesize a-ketoesters via an anode oxidation from acetophenones under mild conditions inhibiting the occurrence of the haloform reaction without any chemical waste. Initially the reaction was carried out in an undivided cell, while MeOH was employed as the solvent, acetophenone as the model substrate, and amine as the additive under an oxygen atmosphere. It was found that the acetophenone can be oxidized into 2-oxo-2-phenylacetaldehyde (see Table S1 in the Supporting Information). Then we screened various amines and tert-butylamine was found to be the most effective additive to afford the desired product with a yield of 64 % (see Table S1 in the Supporting Information). To our knowledge, the 2-oxo-2-phenylacetaldehyde could be an intermediate and further transformed into a hemiacetal in the presence of alcohol. Then this hemiacetal can be converted into the a-ketoester under electrochemical oxidation. To enhance the anode oxidation, we increased the electric current from 20 to 40 mA. As expected, the a-ketoester was obtained in 30 % yield (Table 1, entry 1), which encouraged us to further optimize the reaction conditions. Under the electric current of 40 mA, the reaction base amine was examined again. After examination of various amines, 2,2,6,6-tetramethylpiperidine (TMP) was the best choice for this reaction (see Table S2 in the Supporting Information). From the result of Table S2, it was found that only the amines with a large steric hindrance could catalyze the reaction well. Perhaps the amines without steric hindrance could be converted into a-ketoamides. Subsequently, we attempted to improve the hemiacetal yield by the addition of some additive. At first, we assumed that this additive could catalyze the formation of hemiacetal. This meant that the additive should be an acidic compound. At the same time, this additive could not protonize the amine in the reaction mixture. Therefore ammonium acetate, nitroalkanes, and phenols were examined in the reaction. To our delight, when two equivalents of nitromethane were added to the reaction, a significant increase in yield was observed (Table 1, entry 3). When more than two equivalents of nitromethane was added, the yield decreased a little. Inspired by this result, other nitro compounds were examined and it was found that the p-nitrophenol was the best additive for this transformation, giving the a-ketoester with a high yield of 81 % (entry 10). The dosage of p-nitrophenol in this reaction was also very important. When the amount of p-nitrophenol was increased from 0.5 to 1.0 equivalents, the reaction yield was decreased to 78 % although the reaction time was prolonged to 3 h (entry 11). When the p-nitrophenol was de[a] Z. Zhang, Z. Zha, Prof. Dr. Z. Wang Hefei National Laboratory for Physical Sciences at Microscale CAS Key Laboratory of Soft Matter Chemistry and Department of Chemistry, Univ Sci & Technol China Hefei, Anhui, 230026 (P.R. China) Fax: (+86) 551-3603185 E-mail : zgzha@ustc.edu.cn zwang3@ustc.edu.cn [b] Prof. Dr. J. Su Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, Univ Sci & Technol China Hefei, Anhui, 230026 (P.R. China) [] These two authors have the equal contribution to this manuscript. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201302307.

Copper-Catalyzed Radical Methylation/C-H Amination/Oxidation Cascade for the Synthesis of Quinazolinones

A copper-catalyzed radical methylation/sp(3) C-H amination/oxidation reaction for the facile synthesis of quinazolinone was developed. In this cascade reaction, dicumyl peroxide acts not only as a useful oxidant but also as an efficient methyl source. Notably, a methyl radical, generated from peroxide, was confirmed by electron paramagnetic resonance for the first time.

Synthesis and Reactivity of Nickel Hydride Complexes of an α‑Diimine Ligand

Reaction of L(0)NiBr(2) with 2 equiv of NaH yielded the Ni(II) hydride complex [(L(•-))Ni(μ-H)(2)Ni(L(•-))] (1) (L = [(2,6-iPr(2)C(6)H(3))NC(Me)](2); L(0) represents the neutral ligand, L(•-) is its radical-anionic form, and L(2-) denotes the dianion) in good yield. Stepwise reduction of complex 1 led to a series of nickel hydrides. Reduction of 1 with 1 equiv of sodium metal afforded a singly reduced species [Na(DME)(3)][(L(•-))Ni(μ-H)(2)Ni(L(•-))] (2a) (DME = 1,2-dimethoxyethane), which contains a mixed-valent core [Ni(μ-H)(2)Ni](+). With 2 equiv of Na a doubly reduced species [Na(DME)](2)[L(2-)Ni(μ-H)(2)NiL(2-)] (3a) was obtained, in which each monoanion (L(•-)) in the precursor 1 has been reduced to L(2-). By using potassium as the reducing agent, two analogous species [K(DME)(4)][(L(•-))Ni(μ-H)(2)Ni(L(•-))] (2b) and [K(DME)](2)[L(2-)Ni(μ-H)(2)NiL(2-)] (3b) were obtained. Further treatment of 3b with 2 equiv of K led to a trinuclear complex [K(DME)(THF)](2)K(2)[L(2-)Ni(μ-H)(2)Ni(μ-H)(2)NiL(2-)] (4), which contains one Ni(II) and two Ni(I) centers with a triplet ground state. When 1 and 3a were warmed in toluene or benzene, respectively, three reverse-sandwich dinickel complexes, [(L(•-))Ni(μ-η(3):η(3)-C(7)H(8))Ni(L(•-))] (5) and [Na(DME)](2)[L(2-)Ni(μ-η(3):η(3)-C(6)H(5)R)NiL(2-)] (6: R = CH(3); 7: R = H), were isolated. Reaction of 1 with Me(3)SiN(3) gave the N(3)-bridged complex [(L(•-))Ni(μ-η(1)-N(3))(2)Ni(L(•-))] (8). The crystal structures of complexes 1-8 have been determined by X-ray diffraction, and their electronic structures have been fully studied by EPR/NMR spectroscopy.

Low-Temperature Reactivity of Zn+ Ions Confined in ZSM-5 Zeolite toward Carbon Monoxide Oxidation: Insight from in Situ DRIFT and ESR Spectroscopy

We report the low-temperature catalytic reactivity of Zn(+) ions confined in ZSM-5 zeolite toward CO oxidation. In situ DRIFT and ESR spectroscopy demonstrated that molecular O2 is readily activated by Zn(+) ion to produce O2(-) species at room temperature (298 K) via facile electron transfer between Zn(+) ion and O2 and that the formation of the active O2(-) species is responsible for the high activity of the ZnZSM-5 catalyst toward CO oxidation.

Direct Electrosynthesis of Ketones from Benzylic Methylenes by Electrooxidative CH Activation

Electrify your chemistry! Direct electrosynthesis of ketones from benzylic methylenes in an undivided cell was realized in moderate to good yields. In this electrosynthesis, electrons instead of conventional oxidants and catalysts are employed to make the reaction environmentally benign. Moreover, the reaction intermediate radical was detected by ESR spectroscopy and the reaction mechanism was clarified.

Electrosynthesis of (E)-Vinyl Sulfones Directly from Cinnamic Acids and Sodium Sulfinates via Decarboxylative Sulfono Functionalization

A variety of (E)-vinyl sulfones were constructed directly from cinnamic acids and sodium sulfinates with high regioselectivity at room temperature by virtue of an electrocatalytic oxidation. A radical intermediate was detected, and the corresponding mechanism was investigated.

β-Ketophosphonates formation via deesterification or deamidation of cinnamyl/alkynyl carboxylates or amides with H-phosphonates

We report here an unprecedented Fe/Cu synergistically catalyzed deesterificative or deamidative oxyphosphorylation of unsaturated carboxylates or amides with H-phosphonates. The valuable β-ketophosphonates were obtained along with chemoselective cleavage of Csp2–C(CO) or Csp–C(CO) bonds in good yields under oxygen atmosphere with a wide substrate scope.