Synthesis of P-Stereogenic Phosphine Oxides via Nickel-Catalyzed Asymmetric Cross-Coupling of Secondary Phosphine Oxides with Alkenyl and Aryl Bromides.

A general and mild nickel-catalyzed enantioselective C(sp2 )-P cross-coupling for synthesizing P-stereogenic phosphine oxides has been developed. The asymmetric alkenylation/arylation of racemic secondary phosphine oxides with alkenyl/aryl bromides generated P-stereogenic phosphine oxides with high yields and enantioselectivities. Various functional groups were tolerated, and the applications of this method were demonstrated through late-stage functionalization and product transformations.

Nickel-Catalyzed Asymmetric Synthesis of P-Stereogenic Phosphanyl Hydrazine Building Blocks.

Catalytic asymmetric methods for the synthesis of synthetically versatile P-stereogenic building blocks offer an efficient and practical approach for the diversity-oriented preparation of P-chiral phosphorus compounds. Herein, we report the first nickel-catalyzed synthesis of P-stereogenic secondary aminophosphine-boranes by the asymmetric addition of primary phosphines to azo compounds. We further demonstrate that the P-H and P-N bonds on these phosphanyl hydrazine building blocks can be reacted sequentially and stereospecifically to access various P-stereogenic compounds with structural diversity.

Asymmetric Synthesis of P-Stereogenic Secondary Phosphine-Boranes by an Unsymmetric Bisphosphine Pincer-Nickel Complex.

The first highly enantioselective catalytic synthesis of P-stereogenic secondary phosphine-boranes was realized by the asymmetric addition of primary phosphine to electron-deficient alkenes with a newly developed unsymmetric bisphosphine (PCP') pincer-nickel complex. Various P-stereogenic secondary phosphine-boranes were obtained in 57-92% yields with up to 99% ee and >20:1 dr. The follow-up alkylation upon P-C bond formation with alkyl halides provided a practical way to access P-chiral compounds with diverse functional groups.

Asymmetric photoredox transition-metal catalysis activated by visible light.

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules.

Catalytic Asymmetric Csp3 -H Functionalization under Photoredox Conditions by Radical Translocation and Stereocontrolled Alkene Addition.

This work demonstrates how photoredox-mediated C(sp3 )-H activation through radical translocation can be combined with asymmetric catalysis. Upon irradiation with visible light, α,ß-unsaturated N-acylpyrazoles react with N-alkoxyphthalimides in the presence of a rhodium-based chiral Lewis acid catalyst and the photosensitizer fac-[Ir(ppy)3 ] to provide a C-C bond-formation product with high enantioselectivity (up to 97 % ee) and, where applicable, with some diastereoselectivity (3.0:1 d.r.). Mechanistically, the synthetic strategy exploits a radical translocation (1,5-hydrogen transfer) from an oxygen-centered to a carbon-centered radical with a subsequent stereocontrolled radical alkene addition.

Asymmetric Radical-Radical Cross-Coupling through Visible-Light-Activated Iridium Catalysis.

Combining single electron transfer between a donor substrate and a catalyst-activated acceptor substrate with a stereocontrolled radical-radical recombination enables the visible-light-driven catalytic enantio- and diastereoselective synthesis of 1,2-amino alcohols from trifluoromethyl ketones and tertiary amines. With a chiral iridium complex acting as both a Lewis acid and a photoredox catalyst, enantioselectivities of up to 99% ee were achieved. A quantum yield of <1 supports the proposed catalytic cycle in which at least one photon is needed for each asymmetric C-C bond formation mediated by single electron transfer.

Enantioselective, Catalytic Trichloromethylation through Visible-Light-Activated Photoredox Catalysis with a Chiral Iridium Complex.

An enantioselective, catalytic trichloromethylation of 2-acyl imidazoles and 2-acylpyridines is reported. Several products are formed with enantiomeric excess of ≥99%. In this system, a chiral iridium complex serves a dual function, as a catalytically active chiral Lewis acid and simultaneously as a precursor for an in situ assembled visible-light-triggered photoredox catalyst.

Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions.

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,ß-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,ß-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.

Merger of visible light induced oxidation and enantioselective alkylation with a chiral iridium catalyst.

A single chiral octahedral iridium(III) complex is used for visible light activated asymmetric photoredox catalysis. In the presence of a conventional household lamp and under an atmosphere of air, the oxidative coupling of 2-acyl-1-phenylimidazoles with N,N-diaryl-N-(trimethylsilyl)methylamines provides aminoalkylated products in 61-93 % yields with high enantiomeric excess (90-98 % ee). Notably, the iridium center simultaneously serves three distinct functions: as the exclusive source of chirality, as the catalytically active Lewis acid, and as a central part of the photoredox sensitizer. This conceptionally simple reaction Scheme may provide new avenues for the green synthesis of non-racemic chiral molecules.

Photoinduced Copper-Catalyzed C(sp3)-P Bond Formation by Coupling of Secondary Phosphines with N-(Acyloxy)phthalimides and N-Fluorocarboxamides.

A photoinduced copper-catalyzed C(sp3)-P bond formation has been developed by using N-(acyloxy)phthalimides as radical precursors and secondary phosphine boranes as coupling partners. A variety of alkyl carboxylic acid derivatives can be readily transformed into the corresponding phosphines with high reaction efficiency and structural diversity. Besides, utilizing the 1,5-HAT of the N-centered radical process, the δ C(sp3)-H bond can be coupled with secondary phosphines, which provides a novel method for the regioselective formation of C(sp3)-P bonds.

Copper-catalyzed asymmetric C(sp2)-H arylation for the synthesis of P- and axially chiral phosphorus compounds.

Transition metal-catalyzed C-H bond functionalization is an important method in organic synthesis, but the development of methods that are lower cost and have a less environmental impact is desirable. Here, a Cu-catalyzed asymmetric C(sp2)-H arylation is reported. With diaryliodonium salts as arylating reagents, a range of ortho-arylated P-chiral phosphonic diamides were obtained in moderate to excellent yields with high enantioselectivities (up to 92% ee). Meanwhile, enantioselective C-3 arylation of diarylphosphine oxide indoles was also realized under similar conditions to construct axial chirality.

Burst Pressure Prediction of Subsea Supercritical CO2 Pipelines.

To improve transportation efficiency, a supercritical CO2 pipeline is the best choice for large-scale and long-distance transportation inshore and offshore. However, corrosion of the pipe wall will occur as a result of the presence of free water and other impurities present during CO2 capture. Defects caused by corrosion can reduce pipe strength and result in pipe failure. In this paper, the burst pressure of subsea supercritical CO2 pipelines under high pressure is investigated. First, a mechanical model of corroded CO2 pipelines is established. Then, using the unified strength theory (UST), a new burst pressure equation for subsea supercritical CO2 pipelines is derived. Next, analysis of the material's intermediate principal stress parameters is conducted. Lastly, the accuracy of the burst pressure equation of subsea supercritical CO2 pipelines is proven to meet the engineering requirement by experimental data. The results indicate that the parameter b of UST plays a significant role in determining burst pressure of pipelines. The study can provide a theoretical basis and reference for the design of subsea supercritical CO2 pipelines.

The complete chloroplast genome of Ilex 'Tall Boy', Ilex aquifolium × Ilex latifolia (Aquifoliaceae).

Thecomplete chloroplast (cp) genome of Ilex 'Tall Boy', an important economic plant with ornamental and ecological values, was sequenced to investigate its phylogenetic relationship. The entire cp genome of 'Tall Boy' was 157,527 bp in length with 37.65% overall GC content, including a large single-copy (LSC) region of 87,044 bp and a small single-copy (SSC) region of 18,429 bp, which were separated by a pair of inverted repeats (IRs) of 52,054 bp. The cp genome contained 135 genes, including 90 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis based on whole cp genome sequences showed that 'Tall Boy' is closest to I. latifolia Thunb. species.

All-optical laser-ultrasonic technology for width and depth gauging of rectangular surface-breaking defects.

In this paper, the width and depth of rectangular surface-breaking defects were successfully gauged using an all-optical laser-ultrasonic system. The finite element method was used to simulate propagating paths of defect-induced reflected and transmitted Rayleigh waves. It is observed that most Rayleigh waves with wavelengths less than the depth of the defect are reflected by the defect. A small part of the Rayleigh waves with wavelengths greater than the depth of the defect directly transmits through the bottom edge of the defect without acting on the left edge of the defect. Based on the simulation results, a three-step detection method of width and depth gauging of rectangular surface-breaking defects is proposed. In the first step, the pulsed laser and detection laser are irradiated on one side of the defect. In the second step, the sample is moved to a certain distance to ensure that both lasers reach the other side of the defect. In the third step, two lasers are irradiated on both sides of the defect. The width and depth of the defect are calculated according to the arrival time of the incident, reflected, and transmitted Rayleigh waves, as well as the movement distance of the sample. Experimental results are consistent with the reference-results measured by using a digital microscope. The proposed three-step detection method is proved to be feasible in simultaneous measurement of the width and depth of rectangular surface-breaking defects. Furthermore, it may be potentially useful for measuring other types of defect structures.

The complete chloroplast genome sequence and phylogenetic analysis of Ilex 'Beryl', a hybrid of Ilex cornuta × Ilex latifolia (Aquifoliaceae).

Ilex 'Beryl' is an ornamental and ecological tree widespread in southeastern China. In this study, the complete chloroplast (cp) genome of Ilex 'Beryl' was assembled and characterized to investigate its phylogenetic relationship. The entire cp genome of 'Beryl' was a typical quadripartite structure with 157,575 bp in length, including a large single-copy (LSC) region of 87,080 bp and a small single-copy (SSC) region of 18,427 bp, which were separated by a pair of inverted repeats (IRs) of 52,068 bp. There are 135 genes annotated, including 90 protein-coding genes, eight rRNA genes and 37 tRNA genes. Phylogenetic analysis based on whole cp genome sequences showed that 'Beryl' is closest to I. 'Emily Bruner' and I. 'tall boy'.

Characterization of the complete chloroplast genome of Ilex crenata Thunb. (Aquifoliaceae).

Ilex crenata Thunb. is a species of Aquifoliaceae with high ornamental and ecological values. In this study, the complete chloroplast (cp) genome of I. crenata was assembled and characterized through Illumina sequencing data. The entire cp genome of I. crenata was 157,988 bp in length with 37.64% overall GC content, containing a large single-copy (LSC) region of 87,414 bp and a small single-copy (SSC) region of 18,422 bp, which were separated by a pair of 26,076 bp inverted repeat (IR) regions. A total of 135 genes were annotated, including 88 protein-coding genes, 39 tRNA genes, and 8 rRNA genes. Phylogenetic analysis based on 78 conserved protein-coding genes demonstrated that I. crenata is closely related to I. viridis and I. szechwanensis.

Modeling and Compensation for Asymmetrical and Dynamic Hysteresis of Piezoelectric Actuators Using a Dynamic Delay Prandtl-Ishlinskii Model.

Piezoelectric actuators are widely used in micro- and nano-manufacturing and precision machining due to their superior performance. However, there are complex hysteresis nonlinear phenomena in piezoelectric actuators. In particular, the inherent hysteresis can be affected by the input frequency, and it sometimes exhibits asymmetrical characteristic. The existing dynamic hysteresis model is inaccurate in describing hysteresis of piezoelectric actuators at high frequency. In this paper, a Dynamic Delay Prandtl-Ishlinskii (DDPI) model is proposed to describe the asymmetrical and dynamic characteristics of piezoelectric actuators. First, the shape of the Delay Play operator is discussed under two delay coefficients. Then, the accuracy of the DDPI model is verified by experiments. Next, to compensate the asymmetrical and dynamic hysteresis, the compensator is designed based on the Inverse Dynamic Delay Prandtl-Ishlinskii (IDDPI) model. The effectiveness of the inverse compensator was verified by experiments. The results show that the DDPI model can accurately describe the asymmetrical and dynamic hysteresis, and the compensator can effectively suppress the hysteresis of the piezoelectric actuator. This research will be beneficial to extend the application of piezoelectric actuators.

Complete chloroplast genome sequence and phylogenetic analysis of Ilex × attenuata 'Fosteri' (Aquifoliaceae).

Ilex × attenuata 'Fosteri' is an important ornamental plant widely distributed in mid-southern China and south-eastern United States. In this study, we assembled the complete chloroplast (cp) genome of I. attenuata by high-throughput sequencing and bioinformatics. The full length of cp genome was 157,833 bp with 37.63% overall GC content, which contained two inverted repeats (IR) of 26,093 bp separated by a large single-copy (LSC) and a small single copy (SSC) of 87,188 bp and 18,459 bp, respectively. The cp genome contained 135 genes, including 88 protein-coding genes, 8 rRNA genes and 39 tRNA genes. Phylogenetic tree showed that the close relationship of three species of Ilex (I. attenuata, I. viridis and I. szechwanensis) in the Aquifoliaceae family.

Modeling and Compensation of Dynamic Hysteresis with Force-Voltage Coupling for Piezoelectric Actuators.

Piezoelectric actuators are widely used in the field of micro- and nanopositioning due to their high frequency response, high stiffness, and high resolution. However, piezoelectric actuators have hysteresis nonlinearity, which severely affects their positioning accuracy. As the driving frequency increases, the performance of piezoelectric actuators further degrades. In addition, the impact of force on piezoelectric actuators cannot be ignored in practical applications. Dynamic hysteresis with force-voltage coupling makes the hysteresis phenomenon more complicated when force and driving voltage are both applied to the piezoelectric actuator. Existing hysteresis models are complicated, or inaccurate in describing dynamic hysteresis with force-voltage coupling. To solve this problem, a force-voltage-coupled Prandtl-Ishlinskii (FVPI) model is proposed in this paper. First, the influence of driving frequency and dynamic force on the output displacement of the piezoelectric actuators are analyzed. Then, the accuracy of the FVPI model is verified through experiments. Finally, a force integrated direct inverse (F-DI) compensator based on the FVPI model is designed. The experimental results from this study show that the F-DI compensator can effectively suppress dynamic hysteresis with force-voltage coupling of piezoelectric actuators. This model can improve the positioning accuracy of piezoelectric actuators, thereby improving the working accuracy of the micro- or nano-operating system.

The complete chloroplast genome of Ilex 'Emily Bruner', Ilex cornuta 'Burfordii' × Ilex latifolia (Aquifoliaceae).

Ilex 'Emily Bruner' is an important economic plant with ornamental and ecological functions in southeastern China. In this study, we characterized the complete chloroplast (cp) genome sequence of 'Emily Bruner' to investigate its phylogenetic relationship. The entire cp genome of 'Emily Bruner' was 157,216 bp in length with 37.68% overall GC content, including a large single-copy (LSC) region of 86,721 bp and a small single-copy (SSC) region of 18,427 bp, which were separated by a pair of inverted repeats (IRs) of 52,068 bp. The cp genome contained 135 genes, including 90 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis based on whole cp genome sequences showed that 'Emily Bruner' is closest to I. cornuta species.