Integrating Hydrogen Production with Aqueous Selective Semi‐Dehydrogenation of Tetrahydroisoquinolines over a Ni2P Bifunctional Electrode

Exploring an alternative anodic reaction to produce value‐added chemicals with high selectivity, especially integrated with promoted hydrogen generation, is desirable. Herein, a selective semi‐dehydrogenation of tetrahydroisoquinolines (THIQs) is demonstrated to replace the oxygen evolution reaction (OER) for boosting H₂ evolution reaction (HER) in water over a Ni₂P nanosheet electrode. The value‐added semi‐dehydrogenation products, dihydroisoquinolines (DHIQs), can be selectively obtained with high yields at the anode. The controllable semi‐dehydrogenation is attributed to the in situ formed Ni^II/Ni^III redox active species. Such a strategy can deliver a variety of DHIQs bearing electron‐withdrawing/donating groups in good yields and excellent selectivities, and can be applied to gram‐scale synthesis. A two‐electrode Ni₂P bifunctional electrolyzer can produce both H₂ and DHIQs with robust stability and high Faradaic efficiencies at a much lower cell voltage than that of overall water splitting.     

In Situ Bismuth Nanosheet Assembly for Highly Selective Electrocatalytic CO2 Reduction to Formate

The reduction of carbon dioxide (CO₂) into value-added fuels using an electrochemical method has been regarded as a compelling sustainable energy conversion technology. However, high-performance electrocatalysts for CO₂ reduction reaction (CO₂RR) with high formate selectivity and good stability need to be improved. Earth-abundant Bi has been demonstrated to be active for CO₂RR to formate. Herein, we fabricated an extremely active and selective bismuth nanosheet (Bi-NSs) assembly via an in situ electrochemical transformation of (BiO)₂CO₃ nanostructures. The as-prepared material exhibits high activity and selectivity for CO₂RR to formate, with nearly 94% faradaic efficiency at −1.03 V (versus reversible hydrogen electrode (vs. RHE)) and stable selectivity (>90%) in a large potential window ranging from −0.83 to −1.18 V (vs. RHE) and excellent durability during 12 h continuous electrolysis. In addition, the Bi-NSs based CO₂RR/methanol oxidation reaction (CO₂RR/MOR) electrolytic system for overall CO₂ splitting was constructed, evidencing the feasibility of its practical implementation.     

Base-Promoted Electrochemical CoII-catalyzed Enantioselective C−H Oxygenation

Metalla-electrocatalyzed C−H oxygenation represents one of the most straightforward and sustainable approaches to access valuable oxygenated molecules. Despite the significant advances, the development of enantioselective electrochemical C−H oxygenation reaction is very challenging and remains elusive. Herein, we described the first electrochemical Co^II-catalyzed enantioselective C−H alkoxylation. A broad range of enantioenriched alkoxylated phosphinamides were obtained in good yields with excellent enantioselectivities (up to 98 % yield and >99 % ee). An unusual cobalt(III) alcohol complex was prepared and fully characterized, which was proven to be a key intermediate of this C−H alkoxylation reaction. Mechanistic studies revealed that the oxidation of Co^III to Co^IV was facilitated by a base and the whole process proceeded through a cobalt(III/IV/II) catalytic cycle.     

Mechanistic studies on the catalytic asymmetric Mannich-type reaction with dihydroisoquinolines and development of oxidative Mannich-type reactions starting from tetrahydroisoquinolines

Detailed mechanistic studies on our recently reported asymmetric addition reactions of malonates to dihydroisoquinolines (DHIQs) catalyzed by chiral Pd(II) complexes were carried out. It was found that an N,O-acetal was generated in situ by the reaction of DHIQ with (Boc)2O, and cooperative action of the Pd(II) complex as an acid-base catalyst allowed the formation of a chiral Pd enolate and a reactive iminium ion via alpha-fragmentation. The iminium ion was also accessible via oxidation with DDQ as an oxidant, and a catalytic asymmetric oxidative Mannich-type reaction was achieved with tetrahydroisoquinolines (THIQs) as starting materials. This oxidation protocol was applicable to N-acryloyl-protected THIQs, allowing the efficient synthesis of optically active tetrahydrobenzo[a]quinolizidine derivatives via intramolecular Michael reaction.     

Atroposelective Synthesis of Axially Chiral Biaryls by Palladium-Catalyzed Asymmetric C−H Olefination Enabled by a Transient Chiral Auxiliary

Atroposelective synthesis of axially chiral biaryls by palladium-catalyzed C−H olefination, using tert-leucine as an inexpensive, catalytic, and transient chiral auxiliary, has been realized. This strategy provides a highly efficient and straightforward access to a broad range of enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (95 to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (95 to >99 % ee, s-factor up to 600).     

Selective Activation of C−H Bonds in a Cascade Process Combining Photochemistry and Biocatalysis

Selective oxyfunctionalizations of inert C−H bonds can be achieved under mild conditions by using peroxygenases. This approach, however, suffers from the poor robustness of these enzymes in the presence of hydrogen peroxide as the stoichiometric oxidant. Herein, we demonstrate that inorganic photocatalysts such as gold–titanium dioxide efficiently provide H₂O₂ through the methanol‐driven reductive activation of ambient oxygen in amounts that ensure that the enzyme remains highly active and stable. Using this approach, the stereoselective hydroxylation of ethylbenzene to (R )‐1‐phenylethanol was achieved with high enantioselectivity (>98 % ee ) and excellent turnover numbers for the biocatalyst (>71 000).     

Selective Removal of Sulfate from Water by Precipitation with a Rigid Bis-amidinium Compound

A simple, readily prepared biphenyl bis-amidinium compound ( 1⋅Cl₂ ) is able to selectively precipitate sulfate from water. The precipitant is effective at concentrations as low as 1 mM and shows complete selectivity against monovalent anions, and high selectivity even against CO₃²⁻ and HPO₄²⁻. It is highly effective (>90 % sulfate removed) in both seawater and highly acidic conditions relevant to mining waste-streams. X-ray crystallography reveals that 1⋅SO₄ forms a tightly packed, anhydrous, structure where each sulfate anion receives eight hydrogen bonds from amidinium N−H hydrogen bond donors.     

Introducing the Chiral Transient Directing Group Strategy to Rhodium(III)-Catalyzed Asymmetric C−H Activation

The chiral transient directing group (TDG) strategy has been successfully introduced to the rhodium(III)-catalyzed asymmetric C−H activation. In the presence of a catalytic amount of a chiral amine and an achiral rhodium catalyst, various chiral phthalides were synthesized from simple aldehydes with high chemoselectivity, regioselectivity, and enantioselectivity (53 examples, up to 73 % yield and >99 % ee). It is noteworthy that the chiral induction model is different from the previously reported chiral TDG system using amino acid derivatives and palladium salts. The imino group generated in situ from chiral amine and aldehyde acts as the monodentate TDG to promote the C−H activation, stereoselectively generating the chiral rhodacycle bearing a chiral metal center. Moreover, the stereogenic center of the product is created and stereocontrolled during the Grignard-type addition of the C−Rh bond to aldehyde, rather than during the C−H activation step.     

钨过氧酸盐离子液体催化过氧化氢氧化苯甲醇制苯甲酸

用甲基三辛基氯化铵和钨酸钠一步法合成甲基三辛基季铵钨酸盐离子液体[(CH3)N(n-C8H17)3]2W2O11,以该离子液体为催化剂,在无反应溶剂条件下催化过氧化氢氧化苯甲醇生成苯甲酸。 考察了反应温度、催化剂用量以及氧化剂过氧化氢用量对苯甲酸产率的影响。 确定优化条件：反应温度70 ℃,苯甲醇用量5 mmol,催化剂用量是底物的0.4%(摩尔分数),30%过氧化氢用量2 mL,苯甲醇的转化率可达99%,苯甲酸选择性为98%。 该方法具有反应条件温和、产率高和选择性好的优点。     

IrIII-Catalyzed Selective ortho-Monoiodination of Benzoic Acids with Unbiased C−H Bonds

An iridium-catalyzed selective ortho-monoiodination of benzoic acids with two equivalent C−H bonds is presented. A wide range of electron-rich and electron-poor substrates undergo the reaction under mild conditions, with >20:1 mono/di selectivity. Importantly, the C−H iodination occurs selectively ortho to the carboxylic acid moiety in substrates bearing competing coordinating directing groups. The reaction is performed at room temperature and no inert atmosphere or exclusion of moisture is required. Mechanistic investigations revealed a substrate-dependent reversible C−H activation/protodemetalation step, a substrate-dependent turnover-limiting step, and the crucial role of the Ag^I additive in the deactivation of the iodination product towards further reaction.     

Merging N-Hydroxyphthalimide into Metal-Organic Frameworks for Highly Efficient and Environmentally Benign Aerobic Oxidation

Two highly efficient metal-organic framework catalysts TJU-68-NHPI and TJU-68-NDHPI have been successfully synthesized through solvothermal reactions of which the frameworks are merged with N-hydroxyphthalimide (NHPI) units, resulting in the decoration of pore surfaces with highly active nitroxyl catalytic sites. When t-butyl nitrite (TBN) is used as co-catalyst, the as-synthesized MOFs are demonstrated to be highly efficient and recyclable catalysts for a novel three-phase heterogeneous oxidation of activated C−H bond of primary and secondary alcohols, and benzyl compounds under mild conditions. Based on the high efficiency and selectivity, an environmentally benign system with good sustainability, mild conditions, simple work-up procedure has been established for practical oxidation of a wide range of substrates.     

Photo‐Electrochemical C−H Bond Activation of Cyclohexane Using a WO3 Photoanode and Visible Light

The photo‐electrochemical C?H bond activation of cyclohexane to produce cyclohexanol and cyclohexanone (KA oil) with high partial oxidation selectivity (99 %) and high current utilization ratio (76 %) was achieved in air at room temperature at atmospheric pressure. The production rate of KA oil was accelerated by applying a bias. The incident photon to current efficiencies at 365 and 420 nm were 57 % and 24 %, respectively.     

Palladium-Catalyzed Enantioselective C−H Olefination to Access Planar-Chiral Cyclophanes by Dynamic Kinetic Resolution

Planar-chiral cyclophanes have received increasing attention for drug discovery and catalyst design. However, the catalytically asymmetric synthesis of planar-chiral cyclophanes has been a longstanding challenge. We describe the first Pd(II)-catalyzed enantioselective C−H olefination of prochiral cyclophanes. The low rotational barrier of less hindered benzene ring in the substrates allows the reaction to proceed through a dynamic kinetic resolution. This approach exhibits broad substrate scope, providing the planar-chiral cyclophanes in high yields (up to 99 %) with excellent enantioselectivities (up to >99 % ee). The ansa chain length scope studies reveal that the chirality of the cyclophanes arises from the bond rotation constraint of the benzene ring around the macrocycle plane, rather than the C−N axis. The C−H activation approach is also applicable to the late-stage modification of bioactive molecules and pharmaceuticals.     

Wacker Oxidation of Methylenecyclobutanes: Scope and Selectivity in an Unusual Setting

Methylenecyclobutanes are found to undergo Wacker oxidation via a semi-pinacol-type rearrangement. Key to a successful process is the use of tert-butyl nitrite as oxidant, which not only enables efficient catalyst turn-over but also ensures high Markovnikov-selectivity under mild conditions. Thus, cyclopentanones (26 examples) can be accessed in an overall good yield and excellent selectivity (up to 97 % yield, generally >99 : 1 ketone:aldehyde ratio). Stereochemical analysis of the reaction sequence reveals migration aptitudes in line with related 1,2-shifts. By introducing a pyox ligand to palladium, prochiral methylenecyclobutanes can be desymmetrized, thus realizing the first enantioselective Wacker oxidation.     

Electrochemically Driven C−H Hydrogen Abstraction Processes with the Tetrachloro‐Phthalimido‐N‐Oxyl (Cl4PINO) Catalyst

The radical redox mediator tetrachloro‐phthalimido‐N‐oxyl (Cl₄PINO) is generated at a glassy carbon electrode and investigated for the model oxidation of primary and secondary alcohols with particular attention to reaction rates and mechanism. The two‐electron oxidation reactions of a range of primary, secondary, and cyclic alcohols are dissected into an initial step based on C−H hydrogen abstraction (rate constant k₁, confirmed by kinetic isotope effect) and a fast radical‐radical coupling of the resulting alcohol radical with Cl₄PINO to give a ketal that only slowly releases the aldehyde/ketone and redox mediator precursor back into solution (rate constant k₂). In situ electrochemical EPR reveals Cl₄PINO sensitivity towards moisture. DFT methods are applied to confirm and predict C−H hydrogen abstraction reactivity.     

Selective Enzymatic Oxidation of Silanes to Silanols

Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild-type cytochrome P450 monooxygenase (P450_BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non-native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C−H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C−H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire.     

Combined Dynamic Kinetic Resolution and C−H Functionalization for Facile Synthesis of Non-Biaryl-Atropisomer-Type Axially Chiral Organosilanes

Although asymmetric C−H functionalization has been available for the synthesis of structurally diverse molecules, catalytic dynamic kinetic resolution (DKR) approaches to change racemic stereogenic axes remain synthetic challenges in this field. Here, a concise palladium-catalyzed DKR was combined with C−H functionalization involving olefination and alkynylation for the highly efficient synthesis of non-biaryl-atropisomer-type (NBA) axially chiral oragnosilanes. The chemistry proceeded through two different and distinct DKR: first, an atroposelective C−H olefination or alkynylation produced axially chiral vinylsilanes or alkynylsilanes as a new family of non-biaryl atropisomers (NBA), and second, the extension of this DKR strategy to twofold o,o′-C−H functionalization led to the multifunctional axially chiral organosilicon compounds with up to >99 % ee.     

Enantioselective Twofold C−H Annulation of Formamides and Alkynes without Built-in Chelating Groups

Twofold C−H annulation of readily available formamides and alkynes without built-in chelating groups was achieved. Ni−Al bimetallic catalysis enabled by a bulky BINOL-derived chiral secondary phosphine oxide (SPO) ligand proved to be critical for high reactivity and high selectivity. This reaction uses readily available formamides as starting materials and provides a concise synthetic pathway to a broad range of chiral ferrocenes in 40–98 % yield and 93–99 % ee.     

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C−H Bond Functionalization

Gold coordinated to neutral phosphines (R₃P), N-heterocyclic carbenes (NHCs) or anionic ligands is catalytically active in functionalizing various C−H bonds with high selectivity. The sterics/electronic nature of the studied C−H bond, oxidation state of gold and stereoelectronic capacity of the coordinated auxiliary ligand are some of the associated selectivity factors in gold-catalyzed C−H bond functionalization reactions. Hence, in this review a comprehensive update about the action of different types of gold catalysts, from simple to sophisticated ones, on C−H bond reactions and their regiochemical outcome is disclosed. This review also highlights the catalytic applications of Au(I)- and Au(III)-species in creating new opportunities for the regio- and site-selective activation of challenging C−H bonds. Finally, it also intends to stress the potential applications in selective C−H bond activation associated with a variety of heterocycles recently described in the literature.     

Highly Stable Carbon-Shell Encapsulated Ni−Cu Bimetallic Catalysts for Efficient Conversion of Levulinic Acid to γ-Valerolactone

Non-noble Ni−Cu alloys serve as an alternative catalytic material for noble metal-based catalysts that could be applied in the efficient conversion of levulinic acid (LA) into the high value γ-valerolactone (GVL). However, maintaining the catalytic stability for Ni−Cu nanoparticles in the LA hydrogenation process remains a substantial challenge, Herein, this problem is solved by constructing carbon-protected catalytic sites within carbon layer-coated Ni−Cu nanoalloy composite via pyrolysis of NiCu_x(OH)/glucose precursor. The optimized NiCu_0.68@C catalyst exhibits excellent stability and selectivity to GVL (>99 %) in the hydrogenation of LA reaction. Various characterization indicates that the enhancement in stability originates from the protective effect of the carbon layer, which prevents the metal leaching, oxidation and aggregation of Ni−Cu nanoparticles during the reaction process. This work greatly advances non-noble metal-catalyzed conversion of LA to GVL and helps the rational design of bimetallic catalysts.