Recent Advances in Catalytic Hydrosilylations: Developments beyond Traditional Platinum Catalysts

Hydrosilylation reactions, which allow the addition of Si−H to C=C/C≡C bonds, are typically catalyzed by homogeneous noble metal catalysts (Pt, Rh, Ir, and Ru). Although excellent activity and selectivity can be obtained, the price, purification, and metal residues of these precious catalysts are problems in the silicone industry. Thus, a strong interest in more sustainable catalysts and for more economic processes exists. In this respect, recently disclosed hydrosilylations using catalysts based on earth-abundant transition metals, for example, Fe, Co, Ni, and Mn, and heterogeneous catalysts (supported nanoparticles and single-atom sites) are noteworthy. This minireview describes the recent advances in this field. © 2020 The Authors. Published by Wiley-VCH Gmb

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core-Shell Cobalt Nanoparticles

Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly-ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self-dehydrogenation and hetero-dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C-Si bonds. In general, the application of homogeneous platinum complexes prevails in industry and academia. Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105). A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles

Serum CA72-4 is specifically elevated in gout patients and predicts flares

Objectives Serum CA72-4 levels are elevated in some gout patients but this has not been comprehensively described. The present study profiled serum CA72-4 expression in gout patients and verified the hypothesis that CA72-4 is a predictor of future flares in a prospective gout cohort. Methods To profile CA72-4 expression, a cross-sectional study was conducted in subjects with gouty arthritis, asymptomatic hyperuricaemia, four major arthritis types (OA, RA, SpA, septic arthritis) and healthy controls. A prospective gout cohort study was initiated to test the value of CA72-4 for predicting gout flares. During a 6-month follow-up, gout flares, CA72-4 levels and other gout-related clinical variables were observed at 1, 3 and 6 months. Results CA72-4 was highly expressed in patients with gouty arthritis [median (interquartile range) 4.55 (1.56, 32.64) U/ml] compared with hyperuricaemia patients [1.47 (0.87, 3.29) U/ml], healthy subjects [1.59 (0.99, 3.39) U/ml] and other arthritis patients [septic arthritis, 1.38 (0.99, 2.66) U/ml; RA, 1.58 (0.95, 3.37) U/ml; SpA, 1.56 (0.98, 2.85) U/ml; OA, 1.54 (0.94, 3.34) U/ml; P 6.9 U/ml) was the strongest predictor of gout flares (hazard ratio = 3.889). Prophylactic colchicine was effective, especially for patients with high CA72-4 levels (P = 0.014). Conclusion CA72-4 levels were upregulated in gout patients who experienced frequent flares and CA72-4 was a useful biomarker to predict future flares

Neoproterozoic to Paleozoic long-lived accretionary orogeny in the northern Tarim Craton

The Tarim Craton, located in the center of Asia, was involved in the assembly and breakup of the Rodinia supercontinent during the Neoproterozoic and the subduction-accretion of the Central Asian Orogenic Belt (CAOB) during the Paleozoic. However, its tectonic evolution during these events is controversial, and a link between the Neoproterozoic and Paleozoic tectonic processes is missing. Here we present zircon U-Pb ages, Hf isotopes, and whole-rock geochemical data for the extensive granitoids in the western Kuruktag area, northeastern Tarim Craton. Three distinct periods of granitoid magmatism are evident: circa 830–820 Ma, 660–630 Ma, and 420–400 Ma. The magma sources, melting conditions (pressure, temperature, and water availability), and tectonic settings of various granitoids from each period are determined. Based on our results and the geological, geochronological, geochemical, and isotopic data from adjacent areas, a long-lived accretionary orogenic model is proposed. This model involves an early phase (circa 950–780 Ma) of southward advancing accretion from the Tianshan to northern Tarim and a late phase (circa 780–600 Ma) of northward retreating accretion, followed by back-arc opening and subsequent bidirectional subduction (circa 460–400 Ma) of a composite back-arc basin (i.e., the South Tianshan Ocean). Our model highlights a long-lived accretionary history of the southwestern CAOB, which may have initiated as part of the circum-Rodinia subduction zone and was comparable with events occurring at the southern margin of the Siberian Craton, thus challenging the traditional southward migrating accretionary models for the CAOB

Measurement and analysis of the radial motion error of aerostatic ultra-precision spindle

The measurement of the rotation error of an aerostatic ultra-precision spindle is critically important to evaluate and hence ensure the precision of machine tools. The Donaldson reversal method, which was taken as the efficient method for error separation theoretically, has been widely used to separate shape errors of standard artifact. However, the accuracy analysis of the Donaldson reversal method has not been fully studied and understood. In this study, a nanometer system for measuring the radial rotation error of aerostatic ultra-precision spindle was constructed based on the Donaldson reversal method. The comparative experiments were carried out to investigate the effects of the motor drive, and an angle correction algorithm was proposed to alleviate the effect of angle deviation. The method of harmonic analysis was applied to investigate the effect of artifact eccentricity, and the relationship between the axial motion and measuring error was also studied. The measuring accuracy can be improved by reducing the cogging torque of motor, the angle deviation, artifact eccentricity and spindle axial motion. Experimental results showed that the measurement uncertainty of both the spindle rotation error and artifact form error can be controlled in nanometer level. Besides, the separated value of the artifact form error was very close to the nominal roundness, which verifies the accuracy of the measurement system and the validity of the error separation method

Water as Co-Hydrogen Donor in Reductive Aminations

Reductive amination generates an important reaction in fine chemical synthesis. The employment of water as the hydrogen donor for reductive amination might solve the long-time hydrogen supply problem. Here, we present our new results on reductive <i>N-</i>methylation reactions of amine with paraformaldehyde with water as the co-hydrogen donor catalyzed by a simple supported nanogold catalyst, i.e., Au/Al₂O₃. <i>N-</i>Methyl amines or <i>N</i>,<i>N</i>-dimethyl amines can be selectively synthesized with excellent yields. Isotope tracing reactions confirmed the transformation of hydrogen from water in the final product. In addition, this method can be applied in the <i>N</i>-methylation reactions of bioactive molecules with excellent performance. This concept may supply a potential methodology for sustainable reductive amination

A Calculation Method to Investigate the Effects of Geometric Parameters and Operational Conditions on the Static Characteristics of Aerostatic Spherical Bearings

In this paper, a calculation method based on matlab partial differential equations (PDE) tool is proposed to investigate the static characteristics of aerostatic spherical bearings. The Reynolds equation of aerostatic spherical bearings is transformed into a standard elliptic equation. The effects of geometric parameters and operational conditions on the film pressure, bearing film force, and stiffness are studied. The axial and radial eccentricities result in different film pressure distributions; the bearing film force and stiffness are significantly influenced by geometric parameters and operational conditions. The relative optimal parameters are confirmed based on the calculation results. A comparison between the numerical and experimental results is also presented. The highest relative error between the numerical results and the experimental data is 11.3%; the calculation results show good agreements with the experimental data, thus verifying the accuracy of the calculation method used in this paper

Palladium-Catalyzed Synthesis of Alkylated Amines from Aryl Ethers or Phenols

Synthesis of alkylated amines is an important and attractive task in organic chemistry. Herein, we demonstrate a general protocol to produce alkylated amines via the catalytic coupling of amines with aromatic ethers or phenols. This transformation is performed in the presence of a heterogeneous palladium catalyst, and the key to its success is the use of a Lewis acid (LA) co-catalyst. This method shows broad substrate scope and a variety of phenols, including lignin-derived fragments, can be converted to the desired products smoothly. Preliminary mechanistic investigations reveal that this straightforward domino transformation occurs via a hydrogenolysis/reduction/condensation/reduction process

Reductive Amination of Aldehydes and Amines with an Efficient Pd/NiO Catalyst

<div><p></p><p>By applying a simple Pd/NiO catalyst, the reductive amination of amines and aldehydes can progress efficiently under mild reaction conditions, and 24 substituted amines with different structures were synthesized with up to 98% isolated yields.</p> </div