Asymmetric Photoredox Catalysis with Chiral-at-Rhodium Complexes

Chiral transition metal catalysts in which the chirality exclusively originates from a stereogenic metal center witness a more recent advance and their excellent catalytic performance has been demonstrated through applications into diverse enantioselective transformations, especially visible-light-activated photoredox reactions. This thesis deals with the synthesis of new chiral-at-metal rhodium Lewis acid catalysts and their applications in enantioselective photoredox chemistry. 1) Synthesis of a new member of the rhodium-based chiral Lewis acids family, named RhS, with exclusive octahedral centrochirality which features the Λ-configuration (left-handed propeller) and Δ-configuration (right-handed propeller) has been accomplished. Both enantiomers Λ-and Δ-RhS contain two cyclometalating 5-tert-butyl-2-phenylbenzothiazoles in addition to two exchange-labile acetonitriles with a hexafluorophosphate counterion, were synthesized conveniently through a chiral-auxiliary-mediated strategy. Compared with the previously developed Λ/Δ-RhO complexes bearing corresponding benzoxazoles, the Λ/Δ-RhS have been recognized as better chiral Lewis acid catalysts due to the higher steric congestion directed by the benzothiazole ligands, in which the longer C-S bonds over C-O bonds position the steric bulky tertiary butyl groups closer to the substrate coordination site (chapter 3.1). Subsequently, the newly developed chiral-at-rhodium Lewis acids were applied to visible-light-activated asymmetric photoredox catalysis as discussed in chapters 3.2-3.5. 2) The chiral Lewis acid Λ-RhS combined with the photoredox catalyst [Ru(bpy)3](PF 6) 2 enabled the visible-light-activated redox coupling of alpha-silyl alkyl amines with 2-acyl imidazoles to afford, after desilylation, 1,2-amino-alcohols in yields of 69–88% and with high enantioselectivities (54–99% ee). The reaction is proposed to proceed via single electron transfer (SET) between the alpha-silylamine (electron donor) and the rhodium-chelated 2-acyl imidazole (electron acceptor), followed by a stereocontrolled radical–radical recombination (chapter 3.2). 3) A new and simple commercially available photoredox mediator 4,4-difluorobenzil was developed to cooperate with the chiral-at-rhodium Lewis acids Λ/Δ-RhS. This synergistic catalytic system permits an enantioselective three-component photoreaction to provide the fluoroalky l-containing products under dual C bond formation with high enantioselectivities (up to 98% ee) and modest diastereoselectivities (up to 6:1 dr). Excellent diastereoselectivities (up to >38:1:1 dr) for natural chiral compound derivatives were observed. The photoexcited 4,4-difluorobenzil is VI proposed to enable the single electron oxidation of sodium perfluoroalkyl sulfonates under the generation of corresponding perfluoroalkyl radicals which are trapped by electron-rich vinyl ethers to deliver alpha-oxy carbon-centered radicals. These nucleophilic radical species are involved in a subsequent Rh-catalyzed radical conjugate addition with acceptor-substituted alkenes (chapter 3.3). 4) The single chiral-at-rhodium Lewis acids catalyzed radical conjugate addition of alpha-amino alkyl radicals with acceptor-substituted alkenes provided the C formation products in good yields (up to 89%) and with excellent enantioselectivities (up to 97% ee) under visible-light-activated photocatalyst-free conditions. The -amino alkyl radicals are generated from simple glycine derivatives upon single electron reduction triggered by the photoreductant Hantzsch ester. This methodology is recognizedas a practical and versatile avenue to access diverse pharmaceutically demanding chiral beta-substituted gamma-aminobutyric acid analogs, including previously unaccessible derivatives containing fluorinated quaternary stereocenters. Synthetically valuable applications are demonstrated by providing straightforward access to the pharmaceuticals or related bioactive compounds (S)-pregabalin, (R)-baclofen, (R)-rolipram and (S)-nebracetam (chapter 3.4). 5) Visible-light-activated enantioselective β-C(sp3)H functionalization of 2-acyl imidazoles and 2-acylpyridines with 1,2-dicarbonyl compounds catalyzed by a single chiral-at-rhodium Lewis acid Δ-RhS derivative was developed. The C bond formation products are obtained in high yields (up to 99%) and with excellent stereoselectivities (up to >20:1 drand up to >99% ee). Experimental and computational studies support a mechanism in which a photoactivated Rh-enolate intermediate, produced through the coordination of an acceptor-substituted ketone to the central rhodium in the presence of base, transfers a single electron to the 1,2-dicarbonyl compound followed by deprotonation at β position of initial ketone and a subsequent stereocontrolled radical-radical recombination. The chiral-at-rhodium Lewis acid is capable of serving a dual function as a chiral catalyst and a photoredox (pre)catalyst (chapter 3.5)

National Culture and Bank Liquidity risk of MSc Banking & Finance

Liquidity is always a very important influencing factor for banks. It is crucial to maintain a high level of liquidity and a low level of liquidity risk. This article uses the Horsfield individualist cultural indicators and the collectivist indicators of the global project to analyse the cultural tendency to represent individualism. The essay uses a sample of the 50 largest commercial banks in each of 17 countries over a 15-year period from 2005 to 2020. The essay runs GLS random effects regressions on this panel data. The paper concludes that individualism in a country's national culture is significantly and positively associated with the liquidity risk of banks in that country. We finally suggest that countries should regulate bank liquidity risk to different degrees depending on their culture. Countries with a higher degree of individualism should be more aware of the potential for greater liquidity risk in banks and take the necessary measures to control it. In this way, the risks of banks can be reduced and the stability of banks and of the national economy can be ensured

Demo: Reconfigurable Distributed Antennas and Reflecting Surface (RDARS)-aided Integrated Sensing and Communication System

Integrated sensing and communication (ISAC) system has been envisioned as a promising technology to be applied in future applications requiring both communication and high-accuracy sensing. Different from most research focusing on theoretical analysis and optimization in the area of ISAC, we implement a reconfigurable distributed antennas and reflecting surfaces (RDARS)-aided ISAC system prototype to achieve the dual-functionalities with the communication signal. A RDARS, composed of programmable elements capable of switching between reflection mode and connected mode, is introduced to assist in uplink signal transmission and sensing. The developed RDARS-aided ISAC prototype achieves reliable user localization without compromising the communication rate, showcasing its potential for future 6G systems.Comment: 2 pages, 3 figures. Accepted by IEEE/CIC International Conference on Communications in China, Dalian, China, 202

AI/ML for Beam Management in 5G-Advanced

In beamformed wireless cellular systems such as 5G New Radio (NR) networks, beam management (BM) is a crucial operation. In the second phase of 5G NR standardization, known as 5G-Advanced, which is being vigorously promoted, the key component is the use of artificial intelligence (AI) based on machine learning (ML) techniques. AI/ML for BM is selected as a representative use case. This article provides an overview of the AI/ML for BM in 5G-Advanced. The legacy non-AI and prime AI-enabled BM frameworks are first introduced and compared. Then, the main scope of AI/ML for BM is presented, including improving accuracy, reducing overhead and latency. Finally, the key challenges and open issues in the standardization of AI/ML for BM are discussed, especially the design of new protocols for AI-enabled BM. This article provides a guideline for the study of AI/ML-based BM standardization.Comment: 4 figure

我国医疗保健的城乡分割问题研究

Based on the definition of health care disparities in international health economic academia, the paper adopts the method of counterfactual analysis, using cross-section data of CHNS2009, to make a precise calculation of the inequity section of the urban-rural differences in health care, which refers to urban-rural disparities. According to research, 88.1%of urban-rural differences are inequity, mere 11.9% are supposed to legitimatable. In addition, the larger amounts of expenditures on healthcare, the more conspicuous urban-rural disparities become

我国医疗保健的城乡分割问题研究

Based on the definition of health care disparities in international health economic academia, the paper adopts the method of counterfactual analysis, using cross-section data of CHNS2009, to make a precise calculation of the inequity section of the urban-rural differences in health care, which refers to urban-rural disparities. According to research, 88.1%of urban-rural differences are inequity, mere 11.9% are supposed to legitimatable. In addition, the larger amounts of expenditures on healthcare, the more conspicuous urban-rural disparities become

The legacy of bacterial invasions on soil native communities

Soil microbial communities are often not resistant to the impact caused by microbial invasions, both in terms of structure and functionality, but it remains unclear whether these changes persist over time. Here, we used three strains of Escherichia coli O157:H7 (E. coli O157:H7), a species used for modelling bacterial invasions, to evaluate the resilience of the bacterial communities from four Chinese soils to invasion. The impact of E. coli O157:H7 strains on soil native communities was tracked for 120 days by analysing bacterial community composition as well as their metabolic potential. We showed that soil native communities were not resistant to invasion, as demonstrated by a decline in bacterial diversity and shifts in bacterial composition in all treatments. The resilience of native bacterial communities (diversity and composition) was inversely correlated with invader's persistence in soils (R2 = 0.487, p < 0.001). Microbial invasions also impacted the functionality of the soil communities (niche breadth and community niche), the degree of resilience being dependent on soil or native community diversity. Collectively, our results indicate that bacteria invasions can potentially leave a footprint in the structure and functionality of soil communities, indicating the need of assessing the legacy of introducing exotic species in soil environments