Enantioselective Borylation of Aromatic C−H Bonds with Chiral Dinitrogen Ligands

The borylation of C−H bonds catalyzed by transition metals has been investigated extensively in the past two decades, but no iridium-catalyzed enantioselective borylation of C−H bonds has been reported. We report a set of iridium-catalyzed enantioselective borylations of aromatic C−H bonds. This reaction relies on a set of newly developed chiral quinolyl oxazoline ligands. This process proceeds under mild conditions with good to excellent enantioselectivity, and the borylated products can be converted to enantioenriched derivatives containing new C−O, C−C, C−Cl, or C−Br bonds.     

MIL-100(Fe) Supported Pt−Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3-Butadiene

Superior catalytic performance for selective 1,3-butadiene (1,3-BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt−Co nanoparticles and Pt nanoparticles supported on metal–organic framework MIL-100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL-100(Fe) and Pt/MIL-100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3-BD. Pt1Co1/MIL-100(Fe) presented better catalytic performance than Pt/MIL-100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL-100(Fe) catalyst displayed good stability in the 1,3-BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL-100(Fe) is the reason for its deactivation in 1,3-BD hydrogenation reaction. The spent Pt1Co1/MIL-100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3-BD conversion and butene selectivity with fresh catalysts. Moreover, the rate-determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL-100(Fe) catalyst illustrate that Pt−Co bimetallic catalysts are an ideal alternative for replacing mono-noble-metal-based catalysts in selective 1,3-BD hydrogenation reactions.     

Mechanism and Origin of MAD-Induced Ni/N-Heterocyclic Carbene-Catalyzed Regio- and Enantioselective C−H Cyclization of Pyridines with Alkenes

This work presents a DFT-based computational study on the regio- and enantioselective C−H functionalization of pyridines with alkenes at the relatively unreactive C4-position, which was successfully achieved by Shi et al. [J. Am. Chem. Soc. 2019 , 141, 5628–5634] using Ni⁰/N-heterocyclic carbene (NHC) catalysis under the assistance of an aluminum-based Lewis acid additive (2,6-tBu₂-4-Me-C₆H₂O)₂AlMe (MAD). The calculations indicate that the selective functionalization involves a three-step mechanism in which a unique H-migration assisted oxidation metalation (HMAOM) step is identified as the rate- and enantioselectivity-determining step. The newly proposed mechanism can well rationalize the experimental observation that the preferred product is the endo-type (vs. exo-type), R-configuration (vs. S-configuration) product at the C4 (vs. C2) position, and also unveil the reasons that the NHC ligand and the MAD additive can facilitate the reaction.     

Pt Complexes with High Molecular Weight Polyvinylmethyldimethylsiloxane Ligands Supported on Diatomite for Liquid-phase Hydrosilylation of 3, 3, 3-Trifluoropropene with Methyldichlorosilane

Hydrosilylation is one of the most important reactions for synthesis of modified siliane and polysiloxane. Since the discovery by Speier et al. in 1957 that hexachloroplatinic acid is a potent catalyst even under ambient conditions1, Pt complexes have bec…     

Characteristics of Pt Electrode Activated by Tb1 − xCexO2 − α Films in Contact with ZrO2 + 10 mol % Y2O3 Electrolyte

Porous platinum electrodes on ZrO₂ + 10 mol % Y₂O₃ solid electrolyte (YSZ) are activated by Tb_{1 ? x}Ce_xO_{2 ? α} (x = 0; 0.15; 0.33; 0.5; 1.0) mixed oxides by impregnation, and their polarization characteristics are studied. The activation is carried out under the conditions that an oxide activator nanofilm forms on the electrolyte surface as a result of heat treatment of the electrode. The activation is performed by impregnating the electrodes with low-concentrated alcohol solution of terbium and cerium nitrates (1.5% as recalculated to the oxides) and subsequent slow heating (≤50°C/h) to 850°C. An average thickness of the film on the electrolyte after a single activation (≈0.1 mg oxides/cm²) is estimated at 10–20 nm. The electrodes of Pt|YSZ|Pt cell activated by Tb_{1 ? x}Ce_xO_{2 ? α} films are studied by the impedance method in the oxidative and reductive atmospheres in the range of 700 to 500°C. The polarization conductivities of the activated electrodes increase by 2–3 orders of magnitude. The studied electrodes are discussed within the model of compact oxide electrodes, where platinum plays the role of collector. The advantage of these electrodes is that they can work both in the oxidative and reductive conditions. According to the aggregate of the properties, Tb_{1 ? x}Ce_xO_{2 ? α} compounds at x = 0.3–0.5 are recommended for activation.

     

Catalysis and deactivation of SO 4 2− /ZrO2 solid acid on the alkylation of benzene with 1-dodecene

Catalysis and deactivation of SO₄²⁻/ZrO₂ solid acid on the alkylation of benzene and 1-dodecene were studied by the characterization of XRD, BET, IR, TG/DTA, and NH₃-TPD techniques and the determination of the 1-dodecene conversion, the yield of dodecylbenzene and the selectivity of linear alkylbenzene respectively. In addition, some treatment methods, such as the extraction with benzene or THF as solvent, and the calcinations with or without the dipping of H₂SO₄ in air, were respectively used to recover the activity of deactivated catalyst. The results indicate that SO₄²⁻/ZrO₂ solid acid shows higher catalytic activity for the alkylation of benzene and 1-dodecene with nearly 100% of 1-dodecene conversion and more than 80% of dodecylbenzene yield, and higher selectivity of 2-LAB. The activity of catalyst for the alkylation of benzene is in proportion to the content and the strength of medium acid site. However, the distinct deactivation of catalyst was also obversed in the alkylation. According to the characterization of deactivated catalyst, the accumulation of hydrocarbon fragment and the removal of are mainly reasons of SO₄²⁻/ZrO₂ deactivation. The SO₄²⁻/ZrO₂ calcinated at higher temperature is apt to deactivate. The treatment by extraction with solvent or calcinations can recover the catalytic activity of spent catalyst at a certain extent, especially calcination with the dipping of H₂SO₄. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 455–463. The article is published in the original.     

Reductive Elimination or C−C Bond Activation with Model Ni,Pd, Pt Complexes? A High-Accuracy Comparative Computational Analysis of Reactivity

The development of Pd- and Ni-catalyzed reactions for C−C bond formation is one of the primary driving forces in modern organic synthesis and the fine chemical industry. However, understanding the role of conformational mobility in reaction mechanisms is a long-standing challenge. We highlight the effect of a multirotamer (multiconformer) system on the effective Gibbs free energy of activation in the key C−C coupling process and promote the use of a simplified version of multiconformer transition state theory that is straightforward to apply. Multivariate regression helped to quantitatively map the effect of coupled organic substituents (their structural and electronic parameters), as well as to determine the relative activity of metals. We provide computational evidence for solvent control of the equilibrium in RE/C−C-bond activation for some model complexes. We also demonstrate that Ni complexes, being unique in the catalysis of sp³-sp³ couplings, can be more challenging for machine learning and computational chemistry. The modeling was performed at an exceptionally high level, DLPNO-CCSD(T)/CBS//RIJCOSX-PBE0-D4/def2-TZVP. The Conclusions section contains an infographic summarizing the key findings related to the fields of cross-coupling catalysis, machine learning in catalysis, and computational chemistry.     

[α‐PW12O40]3− Immobilized on Ionic Liquid–Modified Polymer as a Heterogeneous Catalyst for Alcohol Oxidation with Hydrogen Peroxide

Ionic liquid–modified polystyrene resin beads were demonstrated to be an appropriate support for polyoxometalate. In this heterogeneous catalytic system, alcohols can be efficiently oxidized to corresponding carbonyl groups with H₂O₂ in CH₃CN. The catalyst can be easily recovered by filtration and recycled without apparent loss of catalytic performance.     

Selective Electrochemical Hydrogenation of Phenol with Earth-abundant Ni−MoO2 Heterostructured Catalysts: Effect of Oxygen Vacancy on Product Selectivity

Herein, we report highly efficient carbon supported Ni−MoO₂ heterostructured catalysts for the electrochemical hydrogenation (ECH) of phenol in 0.10 M aqueous sulfuric acid (pH 0.7) at 60 °C. Highest yields for cyclohexanol and cyclohexanone of 95 % and 86 % with faradaic efficiencies of ∼50 % are obtained with catalysts bearing high and low densities of oxygen vacancy (O_v) sites, respectively. In situ diffuse reflectance infrared spectroscopy and density functional theory calculations reveal that the enhanced phenol adsorption strength is responsible for the superior catalytic efficiency. Furthermore, 1-cyclohexene-1-ol is an important intermediate. Its hydrogenation route and hence the final product are affected by the O_v density. This work opens a promising avenue to the rational design of advanced electrocatalysts for the upgrading of phenolic compounds.     

Carbon-free D3d [E3ME3]2− (E=P, As; M=Ni, Pd, Pt): The smallest inorganic sandwich complexes with aromatic η3-P 3 − and η3-As 3 − ligands

A density functional theory and wave function theory investigation on the possibility of carbon-free phosphametallocenes [P₃MP₃]^2? and arsenametallocenes [As₃MAs₃]^2? (M=Ni, Pd, Pt) is presented in this work. Staggered singlet D_3d [E₃ME₃]^2? (E=P, As)-the smallest inorganic metallocenes possible to construct-proved to be the global minima of the heptaatomic systems and may be targeted in future experiments. Cyclo-P ₃ ^? and cyclo-As ₃ ^? turned out to possess similar aromaticity to cyclo-P ₅ ^? and cyclo-As ₅ ^? and may serve as effective ligands to sandwich a wide range of transition metals. The first vertical electron detachment energies of C_s [E₃ME₃]Li^? monoanions with a staggered [E₃ME₃]^2? sandwich core were predicted to be between 2.7 and 2.9 eV; the extent of stabilization by Li⁺ suggests that such materials be viable targets for experimental characterization.     

Hydroisomerization of <Emphasis Type="Italic">cis</Emphasis>-Stilbene into <Emphasis Type="Italic">trans</Emphasis>-Stilbene on Supported Heterogeneous Metal Catalysts (Rh,Pd, Pt,Ru, Ir/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)

The hydroisomerization of a cis-isomer to produce a trans-isomer on Rh, Pd, Pt, Ru, and Ir/α-Al₂O₃ catalysts is studied. It is shown that Rh and Ru catalysts on which the hydroisomerization reaction mostly takes place exhibit the most favorable characteristics, whereas on the other metals, the main route is the hydrogenation reaction. Rh/α-Al₂O₃ is the optimum catalyst, since it has much higher activity than Ru/α-Al₂O₃. It is found that the increased selectivity of the trans-isomer formation is facilitated by a decrease in the hydrogen pressure and by an increase in the substrate concentration. The maximum selectivity is achieved when the reaction is carried out in nonpolar n-hexane and toluene, whereas in the case of the more polar tetrahydrofuran (THF), dimethylformamide (DMFA), and methanol both the reaction rate and the selectivity of the trans-isomer formation decline.     

A Theoretical Study of the Water–Gas-Shift Reaction on Cu<Subscript>6</Subscript>TM (TM = Co,Ni, Cu,Rh, Pd,Ag, Ir,Pt, Au) Clusters

We perform density-functional theory calculations to investigate the water–gas-shift (WGS) reaction on Cu₆TM (TM = Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au) clusters through redox, carboxyl, and formate mechanisms, which correspond to CO* + O* → CO₂ (g), CO* + OH* → COOH* → CO₂ (g) + H*, CO* + H* + O* → CHO* + O* → HCOO** → CO₂(g) + H* respectively. An energetic span model is used to estimate the efficiency of the three mechanisms of different Cu₆TM. It finds that for groups 9 and 10, carboxyl mechanism is the predominant mechanism in the three. While for Cu₆TM (Cu, Ag, Au), it finds that the formate mechanism form the TDI and TDTS. Furthermore, the turnover frequency calculations are done for every Cu₆TM cluster. The results show that Cu₆Co is the best catalyst for WGS reaction. Finally, to understand the high catalytic activity of the Cu₆Co cluster, the nature of the interaction between adsorbate and substrate is also analyzed by the detailed electronic local density of states. These findings enrich the applications of Cu-based materials to the high activity catalytic field.     

Syntheses,weak interactions,and 3-D network structures of two salts based on [Ni(i-mnt)2]2− (i-mnt2−=iso-maleonitriled-ithiolate) anion with substituted pyridinium cation

Two new salts, [2-NaMePy]₂[Ni(i-mnt)₂] (1) and [2-NaMe-4-MePy]₂[Ni(i-mnt)₂] (2) ([2-NaMePy]⁺ = 1-(2′-naphthylmethyl)pyridinium, [2-NaMe-4-MePy]⁺ = 1-(2′-naphthylmethyl)-4-methylpyridinium and i-mnt^2? = iso-maleonitriledithiolate), have been prepared and characterized by elemental analyses, UV, IR, molar conductivity, and single crystal X-ray diffraction. The anions in 1 form a 1-D chain through short C ··· N interactions between the anions, while the cations in 2 stack a 1-D column via C–H ··· π and π ··· π stacking interactions between the cations. The effect of weak intramolecular interactions such as C–H ··· N, C–H ··· S, C–H ··· Ni hydrogen bonds, and π ··· π stacking interactions between the cations and the anions further generate a 3-D network structure. The change of the molecular topology of the countercation when the 4-substituted group in the pyridine ring is changed from H atom to CH₃ group results in different crystal system, space group, and the stacking mode of the cations and anions of 1 and 2.     

Comparative study on energetic distortions of SO42− ions matrix-isolated in compounds with kröhnkite-type chains,K2Me(CrO4)2·2H2O and Na2Me(SeO4)2·2H2O (Me = Mg,Co, Ni,Zn, Cd)

Infrared spectra of compounds with kröhnkite-type infinite octahedral–tetrahedral chains, K₂Me(CrO₄)₂·2H₂O and Na₂Me(SeO₄)₂·2H₂O (Me = Mg, Co, Ni, Zn, Cd), as well as infrared spectra of the title double salts containing matrix-isolated SO₄^2? guest ions are presented and discussed in the regions of the X–O stretching modes.The SO₄^2? guest ions matrix-isolated in selenate and chromate matrices exhibit four infrared bands corresponding to the four site-group components of the stretching modes in good agreement with the low site symmetry of the host ions (C₁ site symmetry). The values of Δν₃ (site-group splitting) and Δν_max (the difference between the highest and the lowest wavenumbered components of the stretching modes) are used as an adequate measure for the extent of energetic distortion of the matrix-isolated SO₄^2? guest ions.The influence of different crystal-chemical parameters (Me²⁺–OXO₃ bond strengths, sizes of the Me²⁺ and Me⁺ ions, electronic configurations of the Me²⁺ ions, hydrogen bond strengths, and unit-cell volumes of the host compounds) on the extent of energetic distortion of both the host SeO₄^2? and CrO₄^2? ions, and the SO₄^2? guest ions is analyzed. Correlations between the values of Δν₃ and Δν_max of the guest ions and both the degree of covalency of the respective Me²⁺–OXO₃ bonds and the electronic configurations of the Me²⁺ ions have been found and will be discussed. For example, the energetic distortion of SO₄^2? ions included in the chromate lattices decreases in the order Zn > Cd > Mg as a result of the decreasing covalency of the respective Me²⁺–O bonds in the same order (Δν₃ have values of 73, 58 and 36 cm^?1, respectively). Furthermore, the values of Δν₃ and Δν_max are larger when the metal ions have CFSE ≠ 0 (crystal field stabilization energy, Co²⁺, Ni²⁺). These cations are more resistant to angular deformations of the MeO₆ octahedra (i.e. changes in the O–Me–O bond angles), thus facilitating the extent of distortion of the matrix-isolated SO₄^2? ions as compared to those having CFSE = 0 (Mg²⁺, Zn²⁺ and Cd²⁺). For example, Δν₃ and Δν_max of SO₄^2? ions matrix-isolated in K₂Zn(CrO₄)₂·2H₂O have values of 73 and 163 cm^?1, and 116 and 207 cm^?1 in Na₂Zn(SeO₄)₂·2H₂O, whereas in the respective nickel lattices Δν₃ and Δν_max have values of 88 and 173 cm^?1 (K₂Ni(CrO₄)₂·2H₂O) and 127 and 212 cm^?1 (Na₂Ni(SeO₄)₂·2H₂O).The SO₄^2? guest ions included in selenate matrices, Na₂Me(SeO₄)₂·2H₂O, are remarkably much distorted than in chromate ones, K₂Me(CrO₄)₂·2H₂O, as deduced from the values of Δν₃ and Δν_max owing to a stronger static field caused by the smaller Na⁺ ions as compared to that caused by the larger K⁺ ions. The smaller unit-cell volumes of the selenate host compounds, i.e. the higher repulsion potential at the lattice sites at which the guest ions are situated additionally favor the extent of energetic distortion of the sulfate guest ions in the selenate matrices.