Computational and experimental evidence for Sb(v) metal mediated C-H activation and oxidative functionalization of arenes.

Inorganic Sb complexes are one of the most well-known Lewis acids that typically indirectly activate nonpolar hydrocarbon bonds by acting as Brønsted superacids. Here we have used a combination of quantum-chemical calculations and experiments to demonstrate that inorganic Sb complexes can directly activate aromatic sp C-H bonds and induce oxidative functionalization to form aryl esters. C-H activation was first demonstrated by reaction of Sb(TFA) (TFA = trifluoroacetate) with toluene at moderate temperatures that resulted in Sb-C bond intermediates (TFA)Sb(-tolyl) and (TFA)Sb(-tolyl).

Monomer Design Enables Mechanistic Mapping of Anionic Ring-Opening Polymerization of Aromatic Thionolactones.

Degradable chalcogenide polyesters, e.g., polythioesters (PTEs), typically exhibit improved thermal, mechanical, and optical properties.

Theoretical Exploration of the Synergistic Effect of Phosphate and Amidoxime for Uranium Recovery from Seawater.

Highly selective extraction of uranium from seawater is currently extremely challenging. Although the amidoxime group (HAO) is the commonly used ligand in seawater uranium extraction, it also has strong binding capacity for vanadium ion. It has been shown that the introduction of phosphate groups into amidoxime-based adsorbents can improve the adsorption performance of materials through a synergistic effect between functional groups.

Leveraging Electron Push-Pull Effect for Catalytic Polymerization and Degradation of a Cyclobutane Monomer System.

Ring-opening polymerization (ROP) offers a striking solution to solve problems encountered in step-growth condensation polymerization, including precise control over molecular weight, molecular weight distribution, and topology. This has inspired our interest in ROP of cycloalkanes with an ultimate goal to rethink polyolefins, which clearly poses a number of challenges. Practicality of ROP of cycloalkanes is actually limited by their low polymerizability and elusive mechanisms which arise from significantly varied ring size and non-polar C-C bonds in monomers.

ReaLigands: A Ligand Library Cultivated from Experiment and Intended for Molecular Computational Catalyst Design.

Computational catalyst design requires identification of a metal and ligand that together result in the desired reaction reactivity and/or selectivity. A major impediment to translating computational designs to experiments is evaluating ligands that are likely to be synthesized. Here, we provide a solution to this impediment with our ReaLigands library that contains >30,000 monodentate, bidentate (didentate), tridentate, and larger ligands cultivated by dismantling experimentally reported crystal structures.

C-H Insertion in Dirhodium Tetracarboxylate-Catalyzed Reactions despite Dynamical Tendencies toward Fragmentation: Implications for Reaction Efficiency and Catalyst Design.

Rh-catalyzed C-H insertion reactions to form β-lactones suffer from post-transition state bifurcations, with the same transition states leading to ketones and ketenes via fragmentation in addition to β-lactones. In such a circumstance, traditional transition state theory cannot predict product selectivity, so we employed molecular dynamics simulations to do so and provide a framework for rationalizing the origins of said selectivity. Weak interactions between the catalyst and substrate were studied using energy decomposition and noncovalent interaction analyses, which unmasked an important role of the 2-bromophenyl substituent that has been used in multiple β-lactone-forming C-H insertion reactions.

Theory and Experiment Demonstrate that Sb(V)-Promoted Methane C-H Activation and Functionalization Outcompete Superacid Protonolysis in Sulfuric Acid.

Sb(V) in strong Brønsted acid solvents is traditionally assumed to react with light alkanes through superacid protonolysis, which results in carbocation intermediates, H, and carbon oligomerization. In contrast to this general assumption, our density functional theory (DFT) calculations revealed an accessible barrier for C-H activation between methane and Sb(V) in sulfuric acid that could potentially outcompete superacid protonolysis. This prompted us to experimentally examine this reaction in sulfuric acid with oleum, which has never been reported because of presumed superacid reactivity.

Chiral-Anion-Mediated Asymmetric Heck-Matsuda Reaction of Acyclic Alkenyl Alcohols.

Acyclic internal alkenes are a class of challenging substrates in asymmetric Heck-type reactions due to difficulties related to both reactivity and selectivity control. Employing acyclic alkenyl alcohols, an asymmetric Heck-Matsuda reaction is developed through the strategy of chiral anion phase transfer. Various chiral ketones could be obtained in high levels of enantioselectivity.

Effects of electrostatic drag on the velocity of hydrogen migration - pre- and post-transition state enthalpy/entropy compensation.

Ab initio molecular dynamics calculations were used to explore the underlying factors that modulate the velocity of hydrogen migration for 1,2 hydrogen shifts in carbocations in which different groups interact noncovalently with the migrating hydrogen. Our results indicate that stronger electrostatic interactions between the migrating hydrogen and nearby π-systems lead to slower hydrogen migration, an effect tied to entropic contributions from the hydrogen + neighboring group substructures.

Potential for Ladderane (Bio)synthesis from Oligo-Cyclopropane Precursors.

Quantum chemical calculations were used to determine the energetic viability of several mechanisms for formation of ladderanes from oligocyclopropanes. Pathways involving radical cations, diradicals, and carbocations were considered, and a hybrid of carbocation and radical cation pathways was predicted to have the lowest overall barrier.

Effects of supplying silicon nutrient on utilization rate of nitrogen and phosphorus nutrients by rice and its soil ecological mechanism in a hybrid rice double-cropping system.

This study was conducted to reveal the effects of silicon (Si) application on nutrient utilization efficiency by rice and on soil nutrient availability and soil microorganisms in a hybrid rice double-cropping planting system. A series of field experiments were conducted during 2017 and 2018. The results showed that Si nutrient supply improved grain yield and the utilization rates of nitrogen (N) and phosphorus (P) to an appropriate level for both early and late plantings, reaching a maximum at 23.

[Impact of Newly Build Lead-Acid Battery Agglomeration Area on the Surrounding Soil Environment: A Study Based on the Spatial Characteristics of Heavy Metals].

To determine whether the newly built lead-acid battery agglomeration area in a town in northern Zhejiang had an impact on the surrounding soil environment after seven years of operation, 76 samples of surface soil around the lead-acid battery concentration area were collected, and the contents of Hg, As, Cu, Zn, Pb, Cd, Ni, and Cr in the soil were determined. Based on the spatial distance of the agglomeration area and 50, 450, and 850 m from the agglomeration area boundary, the soil environmental quality was evaluated using the single factor index, Nemerow comprehensive pollution index, and potential ecological risk index methods. The spatial distribution characteristics of the heavy metals were analyzed using the geostatistical method, and the sources of heavy metals affecting the soil environment were determined by correlation analysis.

Nucleophile Coordination Enabled Regioselectivity in Palladium-Catalyzed Asymmetric Allylic C-H Alkylation.

Branched selectivity in asymmetric allylic C-H alkylation is enabled by using 2-acylimidazoles as nucleophiles in the presence of a chiral phosphoramidite-palladium catalyst. A wide range of terminal alkenes, including 1,4-dienes and allylarenes, are nicely tolerated and provide chiral 2-acylimidazoles in moderate to high yields and with high levels of regio-, and enantio-, and E/Z-selectivities. Mechanistic studies using density-functional theory calculations suggest a nucleophile-coordination-enabled inner-sphere attack mode for the enantioselective carbon-carbon bond-forming event.

Palladium-catalyzed enantioselective carboannulation of 1,3-dienes with aryl iodides enables access to chiral indanes.

A palladium-catalyzed enantioselective carboannulation of 1,3-dienes and aryl iodides has been established by using a BINOL-based phosphoramidite ligand. This reaction proceeded via a tandem Heck-type insertion and asymmetric intramolecular Tsuji-Trost allylic alkylation, providing indane derivatives with high levels of enantioselectivity (up to >99% ee).

Pd(II)-Catalyzed Asymmetric Oxidative 1,2-Diamination of Conjugated Dienes with Ureas.

A palladium(II)-catalyzed asymmetric 1,2-diamination of 1,3-dienes with readily available dialkylureas was established by using a chiral pyridine-oxazoline ligand. The diamination reaction exclusively occurs at the terminal C-C double bond of the 1,3-dienes to give 4-vinylimidazolidin-2-ones in high yields and with excellent levels of enantioselectivity (up to 99% yield, 97% ee). The reaction could feasibly be applied for gram-scale synthesis with a 1:1 ratio of the diene and the urea.

Lewis Base/Copper Cooperatively Catalyzed Asymmetric α-Amination of Esters with Diaziridinone.

An enantioselective α-amination of esters by a Lewis base/copper(I) cooperative catalysis strategy has been developed. The transient chiral C1-ammonium enolate generated from pentafluorophenyl ester and nucleophilic Lewis base is nicely compatible with the copper intermediate formed from N, N-di- t-butyldiaziridinone and Cu(I) to allow for high levels of stereochemical control. The cooperative catalytic reaction leads to a diverse set of highly enantioenriched hydantoins in good yields with excellent enantioselectivities (90-99% ee).

An Asymmetric Dehydrogenative Diels-Alder Reaction for the Synthesis of Chiral Tetrahydrocarbazole Derivatives.

An asymmetric dehydrogenative Diels-Alder reaction of 2-methyl-3-phenylmethylindoles and α,β-unsaturated aldehydes has been established. The successful in situ generation of the indole ortho-quinodimethane intermediate and the iminium activation of enals are the keys to success, providing various tetrahydrocarbazole derivatives with up to >99% ee.

Palladium-Catalyzed Cascade sp C-H Functionalization/Intramolecular Asymmetric Allylation: From Aryl Ureas and 1,3-Dienes to Chiral Indolines.

A chiral Pd -catalyzed cascade sp C-H functionalization/intramolecular asymmetric allylation reaction is reported. A new chiral sulfoxide-oxazoline (SOX) ligand bearing single chiral center on the sulfur was identified as the optimal ligand for the reaction, being efficient both in the C-H cleavage step and the stereocontrol of the allylation step. The broad scope of this method with respect to aryl ureas and 1,3-dienes enables the rapid construction of valuable chiral indoline derivatives with high yields and enantioselectivities (up to 99 % yield, up to 95:5 e.

Palladium-Catalyzed Enantioselective Heteroannulation of 1,3-Dienes by Functionally Substituted Aryl Iodides.

The first enantioselective heteroannulation of 1,3-dienes by 2-iodoanilines and 2-iodobenzylic alcohols is described. The application of a BINOL-derived phosphoramidite ligand bearing electron-withdrawing substituents is the key to obtaining high enantioselectivity. This protocol provides an efficient way to access optically active chiral indolines and isochromans from readily available starting materials.

Theoretical insights into the structures and mechanical properties of HMX/NQ cocrystal explosives and their complexes, and the influence of molecular ratios on their bonding energies.

Molecular dynamics (MD) methods were employed to study the binding energies and mechanical properties of selected crystal planes of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)/nitroguanidine (NQ) cocrystals at different molecular molar ratios. The densities and detonation velocities of the cocrystals at different molar ratios were estimated. The intermolecular interaction and bond dissociation energy (BDE) of the N-NO2 bond in the HMX:NQ (1:1) complex were calculated using the B3LYP, MP2(full) and M06-2X methods with the 6-311++G(d,p) and 6-311++G(2df,2p) basis sets.

Gold-catalyzed [1,5]-hydride shift onto unactivated alkynes to trigger an intermolecular Diels-Alder reaction.

A [1,5]-hydride shift of sp(3) C-H onto an unactivated carbon-carbon triple bond catalyzed by a gold(I) complex enabled N-propargylisoindolines to be latent dienes and therefore triggered an intermolecular Diels-Alder reaction with dienophiles. This protocol provides an atom-economical and straightforward approach to access a wide range of polycyclic skeletons in high yields and with excellent diastereoselectivities from easily accessible molecules.

Enantioselective construction of [6,5,6]-carbocyclic systems by organo/metal-catalyzed sequential reactions.

An efficient strategy for the enantioselective construction of [6,5,6]-carbocyclic compounds has been established via one-pot reaction of (E)-4-(2-ethynylphenyl)but-3-en-2-ones with maleimide sequentially catalyzed by cinchona alkaloid-based primary amine and gold complex (Ph3PAuNTf2). This methodology provided a facile approach to access the [6,5,6]-tricyclic skeleton in fairly good yield and with perfect enantioselectivities (98% to >99% ee).

A UB3LYP and UMP2 theoretical investigation on unusual cation-pi interaction between the triplet state HB=BH (3 Sigma g-) and H+, Li +, Na +, Be 2+ or Mg 2+.

The nature of the unusual cation-pi interactions between cations (H(+), Li(+), Na(+), Be(2+) and Mg(2+)) and the electron-deficient B=B bond of the triplet state HB=BH (3 Sigma g-) was investigated using UMP2(full) and UB3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels, accompanied by a comparison with 1:1 and 2:1 sigma-binding complexes between BH and the cations. The binding energies follow the order HB=BH..