COAP-Pd Catalyzed Asymmetric Allylic Alkylation of Azlactones with MBH Carbonates: Access to Unnatural α-Quaternary Stereogenic Glutamic Acid Derivatives.

A palladium-catalyzed regioselective and asymmetric allylic alkylation of azlactones with MBH carbonates has been developed with chiral oxalamide-phosphine ligands. The corresponding reaction afforded a range of optically active γ-arylidenyl glutamic acid derivatives bearing an α-chiral quaternary stereocenter in good yields with excellent linear regio- and high enantioselectivity. This protocol furnishes an alternative approach for the construction of enantio-enriched unnatural α-amino acid derivatives.

Intercalant-induced V t2g orbital occupation in vanadium oxide cathode toward fast-charging aqueous zinc-ion batteries.

Intercalation-type layered oxides have been widely explored as cathode materials for aqueous zinc-ion batteries (ZIBs). Although high-rate capability has been achieved based on the pillar effect of various intercalants for widening interlayer space, an in-depth understanding of atomic orbital variations induced by intercalants is still unknown. Herein, we design an NH4+-intercalated vanadium oxide (NH4+-V2O5) for high-rate ZIBs, together with deeply investigating the role of the intercalant in terms of atomic orbital. Besides extended layer spacing, our X-ray spectroscopies reveal that the insertion of NH4+ could promote electron transition to 3dxy state of V t2g orbital in V2O5, which significantly accelerates the electron transfer and Zn-ion migration, further verified by DFT calculations. As results, the NH4+-V2O5 electrode delivers a high capacity of 430.0 mA h g-1 at 0.1 A g-1, especially excellent rate capability (101.0 mA h g-1 at 200 C), enabling fast charging within 18 s. Moreover, the reversible V t2g orbital and lattice space variation during cycling are found via ex-situ soft X-ray absorption spectrum and in-situ synchrotron radiation X-ray diffraction, respectively. This work provides an insight at orbital level in advanced cathode materials.

Monolayer Thiol Engineered Covalent Interface toward Stable Zinc Metal Anode.

Interface engineering of zinc metal anodes is a promising remedy to relieve their inferior stability caused by dendrite growth and side reactions. Nevertheless, the low affinity and additional weight of the protective coating remain obstacles to their further implementation. Here, aroused by DFT simulation, self-assembled monolayers (SAMs) are selectively constructed to enhance the stability of zinc metal anodes in dilute aqueous electrolytes. It is found that the monolayer thiol molecules relatively prefer to selectively graft onto the unstable zinc crystal facets through strong Zn-S chemical interactions to engineer a covalent interface, enabling the uniform deposition of Zn2+ onto (002) crystal facets. Therefore, dendrite-free anodes with suppressed side reactions can be achieved, proven by in situ optical visualization and differential electrochemical mass spectrometry (DEMS). In particular, the thiol endows the symmetric cells with a 4000 h ultrastable plating/stripping at a specific current density of 1.0 mA cm-2, much superior to those of bare zinc anodes. Additionally, the full battery of modified anodes enables stable cycling of 87.2% capacity retention after 3300 cycles. By selectively capping unstable crystal facets with inert molecules, this work provides a promising design strategy at the molecular level for stable metal anodes.

Ligand Effects of BrettPhos and RuPhos on Rate-Limiting Steps in Buchwald-Hartwig Amination Reaction Due to the Modulation of Steric Hindrance and Electronic Structure.

The differences in catalytic activity between two catalyst ligands of Buchwald-Hartwig amination reaction, BrettPhos versus RuPhos, were investigated using density functional theory (DFT) calculations. The reaction process consists of three consecutive steps: (1) oxidative addition, (2) deprotonation, and (3) reductive elimination. Among them, the rate-limiting step of Pd-BrettPhos catalytic system is oxidative addition but that of Pd-RuPhos catalytic system is reductive elimination due to their differences in steric hindrance and electronic structure. It was also revealed that amines with large-size substituents or halides with electron-withdrawing groups would reduce the activation energy barriers of the reactions. The insights gained from the calculations of the Buchwald-Hartwig amination reaction would be helpful for the rational designing of new catalysts and reactions.

Selectivity control of Pd(PMe3)4-catalyzed hydrogenation of internal alkynes to E-alkenes by reaction time and water content in formic acid.

The modulation of selectivity of transfer hydrogenation of alkynes to E-alkenes using formic acid is a challenge due to the limited knowledge of the complex reaction network, including oxidative addition, decarboxylation, reductive elimination, Z→E isomerization, and ß-H elimination. Here, the search for the reaction pathway and experiment explorations revealed that the selectivity of Pd(PMe3)4-catalyzed hydrogenation of 1-phenyl-1-propyne to (E)-1-phenylpropene is controlled by the water content in the aqueous solution of formic acid and the reaction time. The combination of an automatic reaction pathway search and density functional theory (DFT) calculations found that the intermolecular hydrogen bonds with water molecules have an influence on lowering the free energy activation barrier of transition states in the oxidative addition steps. The reasonable reaction barriers of Z→E isomerization and hydrogenation result in the dependence of selectivity on reaction time, which has been supported by experiments. By using molecular sieves, the water in formic acid is removed, and the yield of the desired (Z)-1-phenylpropene product increases to the highest value (86%) in 5 hours but decreases to 54% when the reaction is run for 16 hours due to the further Z→E isomerization and hydrogenation. In the second stage which starts from (Z)-1-phenylpropene, the yield of (E)-1-phenylpropene decreased from 90% (with 4 Å MS) to 67% in the aqueous solution of formic acid.

Tuning the liquid-phase exfoliation of arsenic nanosheets by interaction with various solvents.

The interaction between monolayered arsenene and fourteen kinds of solvents is found to be correlated with the extent of charge transfer from arsenene to the solvents by density functional theory calculations. Among them, three kinds of aprotic solvents (cyclohexane, tetrahydrofuran and chloroform), representing different adsorbability with arsenene, were selected to exfoliate bulk arsenic crystals into nanosheets in experiments. The as-prepared concentrations of the three dispersions vary monotonically with the calculated adsorption energies and charge transfer per contact area. Transmission electron microscopy (TEM) characterization and size distribution analyses manifested that the lateral size distributions of the exfoliated arsenic nanosheets ranged from 100 nm to 1050 nm. This strategy shows the potential usage in liquid-phase exfoliation of multi-layered materials due to the interaction effects between the solvents and the surface of the materials.

Aggregation-induced visible light absorption makes reactant 1,2-diisocyanoarenes act as photosensitizers in double radical isocyanide insertions.

The joint computational and experimental efforts reveal that the organic molecule 1,2-diisocyano-4,5-dimethylbenzene (1) acts as both a reactant and a photosensitizer (PS) in a metal-free reaction with perfluoroalkylhalide (2) to produce 2-perfluoroalkyl quinoxalines (3) under visible light. Both the π-π stacking aggregation in crystals and the solvation in various solvents of PS 1 exhibited visible-light absorption at 466 nm in spite of its smaller coefficient than that of the ultraviolet-light absorption. Such an aggregation-assisted visible-light absorption phenomenon is rationalized by theoretical calculations of the condensed-phase properties with the consideration of the explicit polarization effect from the neighboring molecules. Upon irradiation with different wavelengths, the emission colors changed from navy to bright yellow. Fluorescence lifetime measurements show that the emission of 1 comes from its singlet excited state. The aggregation induced emission when excited at 420 nm has a shorter lifetime (0.45 ns) than that of the emission from isolated molecules (2.71 ns) when excited at 381 nm. It is conceived that the aggregation assisted visible light absorption properties may be general in other photo-reactive molecules, such as 1,4-diisocyano-2,5-dimethylbenzene (4), 1,4-dicyanobenzene (5), and 1,4-diisocyanobenzene (6), which are widely used in many photochemical reactions in the absence of any external photosensitizer.

Mechanism, reactivity, and regioselectivity in rhodium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes: a DFT Investigation.

The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT). DFT calculations predict a 98% ee for the enantioselectivity and only the 1,2-trans product as one regio- and diastereomer, in excellent agreement with experimental results. The solvent tetrahydrofuran(THF) plays a key role in assisting nucleophilic attack. Orbital composition analysis of the LUMO and the NPA atomic charge calculations were conducted to probe the origins of the regioselectivity. The orbital composition analysis reveals two potential electrophilic sites of the Rh-π-allyl intermediate M3 and the NPA atomic charges demonstrate that Cα carries more positive charges than Cγ, which suggests that Cα is the electrophilic site.

Enantioselective construction of functionalized thiopyrano-indole annulated heterocycles via a formal thio [3 + 3]-cyclization.

A formal thio [3 + 3]-cyclization catalyzed by a DPEN-derived chiral thiourea has been reported for the construction of optically active thiopyrano-indole annulated heterocyclic compounds in high yields with excellent enantioselectivities. The high reactivity between indoline-2-thione (keto-S) and 2-benzylidenemalononitrile has also been supported by density functional theory (DFT) calculations.

Organocatalytic enantioselective construction of multi-functionalized spiro oxindole dienes.

A diastereo- and enantio-selective domino Michael-cyclization-tautomerization reaction of isatylidene malononitriles with α,α-dicyanoalkenes catalyzed by a cinchona alkaloid-derived bifunctional thiourea catalyst has been developed. A series of multi-functionalized spiro oxindole diene derivatives have been obtained in good to excellent yields (up to 97%) with good to excellent enantioselectivities (up to 96%) as well as good diastereoselectivities (up to 7.9 : 1). In addition, an anomalous temperature effect on the enantioselectivity has also been studied for this transformation.