A significant number of isolable silylenes are currently known. They have quickly developed from laboratory curiosities to useful ligands in metal‐mediated homogeneous catalysis. This includes their ...utilization in various catalytic transformations, such as C−C cross‐coupling, cyclotrimerization, hydroformylation, borylation, deuteration, hydrosilylation, amination, hydrogenation, and transfer semi‐hydrogenation reactions. Recent studies suggest that the silylene ligands surpass the steering properties of their phosphine and N‐heterocyclic carbene (NHC) analogues and provide excellent chemo‐, regio‐, and stereoselectivites. Mechanistic studies suggest that their promoted performance of metal‐mediated catalytic transformations results from a strong σ‐donor character along with cooperative effects of their SiII centers. This Minireview covers the most recent advances in the field.
No longer laboratory curiosities: Stable silylenes are a versatile family of powerful steering ligands that increase catalytic activity and selectivity. This Minireview covers the recent progress of silylene ligands in homogeneous catalysis.
Heteroarenes are structural motifs found in many bioactive compounds and functional materials. Dehydrogenative cross‐coupling of heteroarenes with aliphatic C−H bonds provides straightforward access ...to functionalized heteroarenes from readily available materials. Established methods employ stoichiometric chemical oxidants under conditions of heating or light irradiation. By merging electrochemistry and photochemistry, we have achieved efficient photoelectrochemical dehydrogenative cross‐coupling of heteroarenes and C(sp3)−H donors through H2 evolution, without the addition of metal catalysts or chemical oxidants. Mechanistically, the C(sp3)−H donor is converted to a nucleophilic carbon radical through H‐atom transfer with chlorine atom, which is produced by light irradiation of anodically generated Cl2 from Cl−. The carbon radical then undergoes radical substitution to the heteroarene to afford alkylated heteroarene products.
An efficient photoelectrochemical dehydrogenative cross‐coupling of heteroarenes with C(sp3)−H species is described. Chlorine atoms, which are produced by light irradiation of anodically generated Cl2 from Cl−, a hydrogen atom from C(sp3)−H bonds to afford carbon radicals. The latter undergo Minisci alkylation to afford the final functionalized heteroarene products.
The direct acetoxylation of substituted benzylamines has been accomplished through methoxyiminoacyl (MIA)‐mediated Pd‐catalyzed C−H functionalization. A diverse array of phenylalanine substrates is ...amenable to this protocol, providing acetoxylation benzylamine derivatives with good to high efficiency. Computational results revealed that HOAc enhanced the stability of Pd−O bond, which obviously accelerate the reductive elimination step of the acetoxylation process.
A highly efficient MIA‐mediated acetoxylation of substituted benzylamines was reported, which tolerate various substituent groups with good to high yields. DFT‐Studies showed that a weaker electrostatic attraction of HOAc to OAc led to the preferential formation of a five‐membered cyclopalladium intermediate (OAc−Pd−C).
Lithium metal batteries are considered a promising candidate for high‐energy‐density energy storage. However, the strong reducibility and high reactivity of lithium lead to low Coulombic efficiency ...when contacting oxidants, such as lithium polysulfide caused by the serious “shuttle effect” in lithium–sulfur batteries. Herein we design selectively permeable lithium‐ion channels on lithium metal surface, which allow lithium ions to pass through by electrochemical overpotential, while the polysulfides are effectively blocked due to the much larger steric hindrance than lithium ions. The selective permeation of lithium ions through the channels is further elucidated by the molecular simulation and visualization experiment. Consequently, a prolonged cycle life of 75 cycles and high Coulombic efficiency of 99 % are achieved in a practical Li–S pouch cell with limited amounts of lithium and electrolyte, confirming the unique role the selective ion permeation plays in protecting highly reactive alkali metal anodes in working batteries.
Selectively permeable lithium‐ion channels, which were created by aminopropyl‐terminated polydimethylsiloxanes anchored on the lithium metal surface, allow lithium ions to get through, while the polysulfides are effectively blocked due to their much larger volume. The selective lithium ion channels enable a prolonged cycle life and a high Coulombic efficiency of 99 % in a practical Li–S pouch cell.
Iron is an essential trace metal for almost all organisms, including human; however, oxidative stress can easily be caused when iron is in excess, producing toxicity to the human body due to its ...capability to be both an electron donor and an electron acceptor. Although there is a strict regulation mechanism for iron homeostasis in the human body and brain, it is usually inevitably disturbed by genetic and environmental factors, or disordered with aging, which leads to iron metabolism diseases, including many neurodegenerative diseases such as Alzheimer's disease (AD). AD is one of the most common degenerative diseases of the central nervous system (CNS) threatening human health. However, the precise pathogenesis of AD is still unclear, which seriously restricts the design of interventions and treatment drugs based on the pathogenesis of AD. Many studies have observed abnormal iron accumulation in different regions of the AD brain, resulting in cognitive, memory, motor and other nerve damages. Understanding the metabolic balance mechanism of iron in the brain is crucial for the treatment of AD, which would provide new cures for the disease. This paper reviews the recent progress in the relationship between iron and AD from the aspects of iron absorption in intestinal cells, storage and regulation of iron in cells and organs, especially for the regulation of iron homeostasis in the human brain and prospects the future directions for AD treatments.
The synthesis and structure of the first 1,2‐bis(NHSi)‐substituted ortho‐carborane (LSi:)C2B10H10 (termed SiCCSi) is reported (NHSi=N‐heterocyclic silylene; L=PhC(NtBu)2). Its suitability to serve as ...a reliable bis(silylene) chelating ligand for transition metals is demonstrated by the formation of SiCCSiNiBr2 and SiCCSiNi(CO)2 complexes. The CO stretching vibration modes of the latter indicate that the SiII atoms in the SiCCSi ligand are even stronger σ donors than the PIII atoms in phosphines and CII atoms in N‐heterocyclic carbene (NHC) ligands. Moreover, the strong donor character of the SiCCSi ligand enables SiCCSiNiBr2 to act as an outstanding precatalyst (0.5 mol % loading) in the catalytic aminations of arenes, surpassing the activity of previously known molecular Ni‐based precatalysts (1–10 mol %).
The right bite: A chelating bis‐N‐heterocyclic silylene ligand bridged by an o‐carborane (SiCCSi) and its corresponding Ni complexes (see example) were synthesized, fully characterized, and successfully applied in Ni‐catalyzed Buchwald–Hartwig coupling reactions. SiCCSiNiBr2 is the most active precatalyst for this transformation that has been reported to date.
Early-season crop type mapping could provide important information for crop growth monitoring and yield prediction, but the lack of ground-surveyed training samples is the main challenge for crop ...type identification. Although reference time series based method (RBM) has been proposed to identify crop types without the use of ground-surveyed training samples, the methods are not suitable for study regions with small field size because the reference time series are mainly generated using data set with low spatial resolution. As the combination of Landsat data and Sentinel-2 data could increase the temporal resolution of 30-m image time series, we improved the RBM by generating reference normalized difference vegetation index (NDVI)/enhanced vegetation index (EVI) time series at 30-m resolution (30-m RBM) using both Landsat and Sentinel-2 data, then tried to estimate the potential of the reference NDVI/EVI time series for crop identification at early season. As a test case, we tried to use the 30-m RBM to identify major crop types in Hengshui, China at early season of 2018, the results showed that when the time series of the entire growing season were used for classification, overall classification accuracies of the 30-m RBM were higher than 95%, which were similar to the accuracies acquired using the ground-surveyed training samples. In addition, cotton, spring maize and summer maize distribution could be accurately generated 8, 6 and 8 weeks before their harvest using the 30-m RBM; but winter wheat can only be accurately identified around the harvest time phase. Finally, NDVI outperformed EVI for crop type classification as NDVI had better separability for distinguishing crops at the green-up time phases. Comparing with the previous RBM, advantage of 30-m RBM is that the method could use the samples of the small fields to generate reference time series and process image time series with missing value for early-season crop classification; while, samples collected from multiple years should be further used so that the reference time series could contain more crop growth conditions.
Cardiac surgery-associated acute kidney injury (CSA-AKI) is a major complication that results in increased morbidity and mortality after cardiac surgery. Most established prediction models are ...limited to the analysis of nonlinear relationships and fail to fully consider intraoperative variables, which represent the acute response to surgery. Therefore, this study utilized an artificial intelligence-based machine learning approach thorough perioperative data-driven learning to predict CSA-AKI.
A total of 671 patients undergoing cardiac surgery from August 2016 to August 2018 were enrolled. AKI following cardiac surgery was defined according to criteria from Kidney Disease: Improving Global Outcomes (KDIGO). The variables used for analysis included demographic characteristics, clinical condition, preoperative biochemistry data, preoperative medication, and intraoperative variables such as time-series hemodynamic changes. The machine learning methods used included logistic regression, support vector machine (SVM), random forest (RF), extreme gradient boosting (XGboost), and ensemble (RF + XGboost). The performance of these models was evaluated using the area under the receiver operating characteristic curve (AUC). We also utilized SHapley Additive exPlanation (SHAP) values to explain the prediction model.
Development of CSA-AKI was noted in 163 patients (24.3%) during the first postoperative week. Regarding the efficacy of the single model that most accurately predicted the outcome, RF exhibited the greatest AUC (0.839, 95% confidence interval CI 0.772-0.898), whereas the AUC (0.843, 95% CI 0.778-0.899) of ensemble model (RF + XGboost) was even greater than that of the RF model alone. The top 3 most influential features in the RF importance matrix plot were intraoperative urine output, units of packed red blood cells (pRBCs) transfused during surgery, and preoperative hemoglobin level. The SHAP summary plot was used to illustrate the positive or negative effects of the top 20 features attributed to the RF. We also used the SHAP dependence plot to explain how a single feature affects the output of the RF prediction model.
In this study, machine learning methods were successfully established to predict CSA-AKI, which determines risks following cardiac surgery, enabling the optimization of postoperative treatment strategies to minimize the postoperative complications following cardiac surgeries.
A sustainable and cost‐effective protocol for direct aminomethylation of imidazo‐fused heterocycles by decarboxylative coupling reaction of N‐phenylglycines with imidazo‐fused heterocycles in the ...presence of CsPbBr3 under the irradiation of visible light has been developed. This is the first example of CsPbBr3‐catalyzed aminomethylation of imidazo‐fused heterocycles. The eminent advantage of this work is in that, CsPbBr3 is easily prepared and can be used at least 5 times without obvious reduction in its activity, exhibiting high catalyst economic feature.
The synthesis and structures of the first SiII‐donor supported manganese(II) complexes L1MnCl2, L2MnCl2, and L32MnCl2 are reported, bearing a pincer‐type bis(NHSi)‐pyridine ligand L1, bidentate ...bis(NHSi)‐ferrocene ligand L2, and two monodentate NHSi ligands L3 (NHSi = N‐heterocyclic silylene), respectively. They act as unprecedented very active and stereoselective Mn‐based precatalysts (1 mol % loading) in transfer semi‐hydrogenations of alkynes to give the corresponding E‐olefins using ammonia–borane as a convenient hydrogen source under mild reaction conditions. Complex L1MnCl2 shows the best catalytic performance with quantitative conversion rates and excellent E‐stereoselectivities (up to 98 %) for different alkyne substrates. Different types of functional groups can be tolerated, except CN, NH2, NO2, and OH groups at the phenyl group of 1‐phenyl substituted alkynes.
Give me the E: The first N‐heterocyclic silylene (NHSi)–manganese(II) complexes have been synthesized and fully characterized. Among them, the L1MnCl2 complex, which bear bis‐NHSi pyridine pincer ligand L1, acts as a superior precatalysts in homogeneous transfer semi‐hydrogenation of alkynes, using ammonia‐borane as a convenient hydrogen source at mild reaction conditions (Mn=L1MnCl2).
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