Copper-Catalyzed Borrowing Hydrogen Reaction for α-Alkylation of Amides with Alcohols.

We report the first example of copper-catalyzed α-alkylation of acetamides with alcohols via a borrowing hydrogen strategy. Catalyzed by the in situ-generated copper particles, acetamides and various substituted benzyl or alkyl alcohols were transformed into functionalized amides in good yields with excellent selectivity. Compared with previous work, this process is simple using commercially available Cu(OAc)2 as a precatalyst, without an additional ligand or a metal complex, and easier. Mechanistic studies revealed that aldehyde and α,ß-unsaturated amides were the intermediates of this reaction and also disclosed the role of copper in alcohol dehydrogenation and C═C bond hydrogenation.

Recent Advances in Reversible Liquid Organic Hydrogen Carrier Systems: From Hydrogen Carriers to Catalysts.

Liquid organic hydrogen carriers (LOHCs) have gained significant attention for large-scale hydrogen storage due to their remarkable gravimetric hydrogen storage capacity (HSC) and compatibility with existing oil and gas transportation networks for long-distance transport. However, the practical application of reversible LOHC systems has been constrained by the intrinsic thermodynamic properties of hydrogen carriers and the performances of associated catalysts in the (de)hydrogenation cycles. To overcome these challenges, thermodynamically favored carriers, high-performance catalysts, and catalytic procedures need to be developed. Here, significant advances in recent years have been summarized, primarily centered on regular LOHC systems catalyzed by homogeneous and heterogeneous catalysts, including dehydrogenative aromatization of cycloalkanes to arenes and N-heterocyclics to N-heteroarenes, as well as reverse hydrogenation processes. Furthermore, with the development of metal complexes for dehydrogenative coupling, a new family of reversible LOHC systems based on alcohols is described that can release H2 under relatively mild conditions. Finally, views on the next steps and challenges in the field of LOHC technology are provided, emphasizing new resources for low-cost hydrogen carriers, high-performance catalysts, catalytic technologies, and application scenarios.

Highly Efficient Depolymerization of Waste Polyesters Enabled by Transesterification/Hydrogenation Relay Under Mild Conditions.

The efficient depolymerization of polyesters under mild conditions remains a significant challenge. Herein, we demonstrate a highly efficient strategy for the degradation of a diverse array of waste polyesters as low to 80 °C, 1 bar H2 . The key to the success of this transformation relied on the initial transesterification of macromolecular polyester into more degradable oligomeric fragments in the presence of CH3 OH and the subsequent hydrogenation by the use of the rationally designed quinaldine-based Ru complex. Controlled experiments and preliminary mechanistic studies disclosed the quinaldine-based catalysts could be hydrogenated to the eventually active species, which has been confirmed by X-ray diffraction analysis and directly used as a catalyst in the hydrogenolysis of polyester. The strong viability and high activity of this new species in protic solvent were explained in detail. Besides, the crucial role of CH3 OH in promoting reaction efficiency during the whole process was also elucidated. The synthetic utility of this method was further illustrated by preparing 1,4-cyclohexanedimethanol (CHDM) from waste polyethylene terephthalate (PET).

Recyclable Silver-Catalyzed Selective Hydrogenation of Imides to Primary Amines via Dual C-N Bond Cleavage.

We report the first heterogeneous catalytic hydrogenation of N-substituted imides and polyimide to generate primary amines, diols, and lactones. Catalyzed by Ag/TiO2, this reaction proceeded smoothly in high yields and selectivities for N-alkyl and N-aryl phthalimides and N-aryl succinimides, which also had activity for the degradation of waste polyimide plastics. In contrast to the typical Gabriel process, this reaction does not need any toxic reagent, and the byproducts are also very useful. Recycling experiments showed that the catalyst Ag/TiO2 could be easily recovered without a decrease in catalytic activity.

Near-Ambient-Temperature Dehydrogenative Synthesis of the Amide Bond: Mechanistic Insight and Applications.

The current existing methods for the amide bond synthesis via acceptorless dehydrogenative coupling of amines and alcohols all require high reaction temperatures for effective catalysis, typically involving reflux in toluene, limiting their potential practical applications. Herein, we report a system for this reaction that proceeds under mild conditions (reflux in diethyl ether, boiling point 34.6 °C) using ruthenium PNNH complexes. The low-temperature activity stems from the ability of Ru-PNNH complexes to activate alcohol and hemiaminals at near-ambient temperatures through the assistance of the terminal N-H proton. Mechanistic studies reveal the presence of an unexpected aldehyde-bound ruthenium species during the reaction, which is also the catalytic resting state. We further utilize the low-temperature activity to synthesize several simple amide bond-containing commercially available pharmaceutical drugs from the corresponding amines and alcohols via the dehydrogenative coupling method.

Imminent rupture of abdominal aortic aneurysm complicated by arteriovenous fistulaization and hepatorenal failure: case report and literature review.

Arteriovenous fistula (AVF) is a rare complication of the abdominal aortic aneurysm (AAA) with complex clinical features. However, AVF and AAA usually cause no symptoms except when they rupture. This case study demonstrated that ultrasonography was a rapid and non-invasive method for the initial assessment of AAA and AVF. A 65-year-old man was admitted to the intensive care unit with hepatic and renal dysfunction. Physical examination revealed an abdominal vascular murmur and bilateral toe discoloration. Ultrasonic examination revealed an AAA and right common iliac artery aneurysm with an AVF located between the right common iliac artery and inferior vena cava. A computed tomography scan confirmed the sonographic findings. We propose that ultrasound should be used more commonly as part of the initial evaluation of the potential and established vascular diseases.

[Design and application of a patient's clothing for critical ultrasound examination].

OBJECTIVE: At present, most of the common medical clothes in clinic are uniform medical clothes, but there is no special clothes for patients in intensive care unit (ICU). In recent years, with the extensive application of critical ultrasound in the field of critical medicine, it is obviously difficult to meet the clinical needs on traditional patients' clothes. Guangdong Provincial People's Hospital designed a patient's clothing for critical ultrasound examination. The left/right chest, lateral chest, groin and abdomen of the patient's clothing body were covered with cloth and marked areas. When critically ill patients need to be examined by ultrasound and electrocardiogram, the site can be quickly located only by removing the cloth. At the same time, it can protect patients' privacy, avoid aggravating the condition due to cold, increase patients' comfort in clothing, and also facilitate medical care. It is worthy popularizing in clinic because of its practicability and novel design.

Ethylene Glycol as an Efficient and Reversible Liquid Organic Hydrogen Carrier.

Hydrogen has long been regarded as an ideal alternative clean energy vector to overcome the drawbacks of fossil technology. However, the direct utilization of hydrogen is challenging, due to low volumetric energy density of hydrogen gas and potential safety issues. Herein, we report an efficient and reversible liquid to liquid organic hydrogen carrier system based on inexpensive, readily available and renewable ethylene glycol. This hydrogen storage system enables the efficient and reversible loading and discharge of hydrogen using a ruthenium pincer complex, with a theoretical hydrogen storage capacity of 6.5 wt%.

A Reversible Liquid Organic Hydrogen Carrier System Based on Methanol-Ethylenediamine and Ethylene Urea.

A novel liquid organic hydrogen carrier (LOHC) system, with a high theoretical hydrogen capacity, based on the unpresented hydrogenation of ethylene urea to ethylenediamine and methanol, and its reverse dehydrogenative coupling, was established. For the dehydrogenation only a small amount of solvent is required. This system is rechargeable, as the H2 -rich compounds could be regenerated by hydrogenation of the resulting dehydrogenation mixture. Both directions for hydrogen loading and unloading were achieved using the same catalyst, under relatively mild conditions. Mechanistic studies reveal the likely pathway for H2 -lean compounds formation.

Palladium-Catalyzed Ring-Forming Aminoalkenylation of Alkenes with Aldehydes Initiated by Intramolecular Aminopalladation.

A palladium-catalyzed aminopalladation reaction followed by nucleophilic addition with aldehydes and dehydration is described. This direct and operationally simple procedure provides a rapid and reliable approach to a wide range of functionalized tetrahydroisoquinolines with high selectivity. Mechanistic studies disclosed that the nucleophilic addition, performed via a highly ordered transition-state, is the turnover-limiting step in which the inherent ß-hydride elimination of the key Csp3 -Pd species was controlled by the confined conformation and the nucleophilicity of the Csp3 -Pd bond was enhanced by the strong electron-donating effect of the nitrogen atom.

Highly Efficient Process for Production of Biofuel from Ethanol Catalyzed by Ruthenium Pincer Complexes.

A highly efficient ruthenium pincer-catalyzed Guerbet-type process for the production of biofuel from ethanol has been developed. It produces the highest conversion of ethanol (73.4%, 0.02 mol% catalyst) for a Guerbet-type reaction, including significant amounts of C4 (35.8% yield), C6 (28.2% yield), and C8 (9.4% yield) alcohols. Catalyst loadings as low as 0.001 mol% can be used, leading to a record turnover number of 18 209. Mechanistic studies reveal the likely active ruthenium species and the main deactivation process.

Enantioselective Aminomethylamination of Conjugated Dienes with Aminals Enabled by Chiral Palladium Complex-Catalyzed C-N Bond Activation.

A novel highly enantioselective aminomethylamination of conjugated dienes with aminals catalyzed by a chiral palladium complex ligated with BINOL-derived chiral diphosphinite has been successfully developed. This reaction proceeds via a Pd-catalyzed cascade C-N bond activation, aminomethylation, and asymmetric allylic amination reaction under mild reaction conditions, providing a unique and efficient strategy for the synthesis of enantiomerically pure allylic 1,3-diamines.

Copper-catalyzed decarboxylative cross-coupling of cinnamic acids and ACCN via single electron transfer.

A novel and convenient method for the synthesis of ß,γ-unsaturated nitriles using ACCN (1,1'-azobis(cyclohexane-1-carbonitrile)) as a cyano source was described. This reaction was amenable to a broad range of substrates and provided the desired ß,γ-unsaturated nitriles containing an all-carbon quaternary carbon center in moderate yields with high selectivity via single electron transfer and decarboxylation.

Decarboxylative Alkylcarboxylation of α,ß-Unsaturated Acids Enabled by Copper-Catalyzed Oxidative Coupling.

A facile and general method for copper-catalyzed decarboxylative alkylcarboxylation of cinnamic acids with dimethyl 2,2'-azobis(2-methylpropionate) has been developed. The scope and versatility of the reaction was demonstrated, and a broad range of substrates bearing electron-donating and -withdrawing groups on the aromatic rings were all compatible with this reaction to provide desired ß,γ-unsaturated esters in moderate to good yields. Moreover, α,ß-unsaturated acids with a carbonyl group on the γ-position of acrylic acids also smoothly proceeded to furnish the desired products in good yields.

Metal Bridging for Directing and Accelerating Electron Transfer as Exemplified by Harnessing the Reactivity of AIBN.

A new strategy for tuning the electron transfer between radicals and enolates has been developed. This method elicits the innate reactivity of AIBN with a copper catalyst and enables a cascade reaction with cinnamic acids. Electron paramagnetic resonance studies and control experiments indicate that the redox-active copper species not only activates the radical by coordination, but also serves as a bridge to bring the radical and nucleophile within close proximity to facilitate electron transfer. By exploiting possible combinations of redox-active metals and radical entities with suitable coordinating functional groups, this strategy should contribute to the development of a broad range of radical-based reactions.

Diboron as a reductant for nickel-catalyzed reductive coupling: rational design and mechanistic studies.

Diboron (B2pin2) has been identified as an efficient and environmentally benign reducing reagent for reductive coupling reactions for the first time, which enables the nickel-catalyzed reductive tetramerization of alkynes to be performed with high efficiency. Mechanistic and kinetic studies indicate that the facile reductive elimination to form the B-B bond from the dinuclear Ni-Ni complexes is responsible for the high efficiency. The activation enthalpy (ΔH(‡) = 56.5 kJ mol(-1)), entropy (ΔS(‡) = -128 J mol(-1) K(-1)) and the substituent effect (ρ = 1.43) on this reaction were obtained.

Palladium-catalyzed insertion of an allene into an aminal: aminomethylamination of allenes by C-N bond activation.

A new and atom-economic palladium-catalyzed aminomethylamination of allenes with aminals by CN bond activation is described. This direct and operationally simple method provides a fundamentally novel approach for the synthesis of 1,3-diamines. Mechanistic studies suggest that a unique cationic π-allylpalladium complex containing an aminomethyl moiety is generated as a key intermediate through the carbopalladation of the allene with a cyclometalated palladium-alkyl species.

Palladium-catalyzed difunctionalization of enol ethers to amino acetals with aminals and alcohols.

A new strategy was developed for intercepting the palladium-alkyl species generated in Heck reaction via nucleophilic addition prior to the step of migratory insertion, which leads to a new palladium-catalyzed difunctionalization of enol ethers with aminals and alcohols to afford amino acetals. Mechanistic studies suggested that the cationic cyclometalated Pd(II) complex generated by the oxidative addition of aminal to a Pd(0) species was crucial for this unusual transformation.

An efficient Rh/O2 catalytic system for oxidative C-H activation/annulation: evidence for Rh(I) to Rh(III) oxidation by molecular oxygen.

A novel and efficient Rh/O2 catalytic system has been developed and shown to catalyze highly efficient oxidative C-H activation/annulation reactions, producing a broad range of isoquinolinium salts with high turnover numbers (up to 740). Mechanistic studies provided strong evidence of facile oxidation of Rh(I) to Rh(III) by molecular oxygen facilitated by acid.

Palladium-catalyzed vinylation of aminals with simple alkenes: a new strategy to construct allylamines.

A novel, highly selective palladium-catalyzed vinylation reaction for the direct synthesis of allylic amines from styrenes and aminals has been established. The utility of this method was also demonstrated by the rapid synthesis of cinnarizine from aldehydes, amines, and simple alkenes in one-pot manner. Mechanistic studies suggested that the reaction proceeds through a valuable cyclometalated Pd(II) complex generated by the oxidative addition of aminal to a Pd(0) species.