The derivatives of isosilabenzene and isogermabenzene with metal vinylidene bonds have been achieved from phantom species to stable compounds for the first time. The relative stability of these isomers has been elucidated by experimental observations and DFT calculations.

Comprehensive Summary

Metalla-isosilabenzenes and metalla-isogermabenzenes have been successfully synthesized by the formal [5+1]-cycloaddition of diethynylsilane or diethynylgermane with simple metal complexes. This is the first example of a heavier Group 14 metalla-isobenzene isomer bearing a cumulative double bond motif within a metallacycle. These novel complexes were fully characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. The stabilization of the cyclic metal-vinylidene complexes has been analyzed using density functional theory (DFT) calculations. When the metalla-isosilabenzenes bearing Si—H bond were treated with the trityl salt as a hydride scavenger, the formation of silylium cation was observed spectroscopically. Both of metalla-isosilabenzenes and metalla-isogermabenzenes can readily undergo migratory insertion reactions to furnish siloles or germoles.

A facile and robust method to prepare protein α-thioester has been developed. A series of inaccessible protein α-thioesters with limited solubility and internal Cys residues can be efficiently synthesized in one-pot via a SUMO-Protein-Intein sandwich model.

Comprehensive Summary

Expressed protein ligation (EPL) provides a powerful tool to access large-size proteins with precise structures. Existing methods for constructing the critical protein thioester for EPL have predominantly relied on the recombinant intein fusion expressed in Escherichia coli (E. coli). Despite its powerful applications, the expression of thioester derived from eukaryotic protein in E. coli inherently suffers from its limited solubility, the inactivity of intein, premature hydrolysis and low yields. To overcome these obstacles, we present herein the facile one-flask synthesis of inaccessible protein α-thioester via a SUMO-protein-intein (SPI) sandwich model. The utility of SUMO enhances the protein fusion yield and solubility, prevents premature hydrolysis and simplifies the purification process. The inaccessible protein thioester with internal Cys residues can be readily produced and is compatible with the EPL-desulfurization protocol used to prepare complex proteins, which is otherwise difficult to obtain using traditional methods. Its utility has been highlighted through the synthesis of human granulocyte colony-stimulating factor (G-CSF).

A visible-light-enabled, photocatalyst-free hydroacylation reaction of azodicarboxylic acid derivatives was described, which relied on the dual role of 4-acyl-1,4-dihydropyridine (acyl-DHP) reagents.

Comprehensive Summary

A visible-light-enabled, photocatalyst-free hydroacylation reaction of azodicarboxylic acid derivatives was described. This radical conjugate addition (RCA) protocol relied on the dual role of 4-acyl-1,4-dihydropyridine (acyl-DHP) reagents that besides being as radical reservoirs, they also enabled the conversion of radical adducts to anion intermediates via reduction. Under “catalyst-oxidant-additive free” conditions, a wide range of structurally different acyl hydrazide products were readily obtained in 56%—99% yields. The utility of this transformation was further demonstrated by the scale-up synthesis and downstream derivatization.

A twisted organic difluoroboron β-diketonate phosphor possessing intramolecular charge transfer character and flexible molecular structure was doped into different organic matrices to fabricate phosphorescence materials. The twisted phosphor adopts different conformation in different matrices. Consequently, the dopant-matrix systems break T₁ energy conservation and exhibit distinct phosphorescence wavelengths, violating Kasha's exciton model.

Comprehensive Summary

Kasha's exciton model proposes that T₁ energy levels of organic compounds are insensitive to molecular aggregation and microenvironment change because of negligible small transition dipole moments of T₁ states. This model holds true in most organic systems till now. Here we report the fabrication of twisted organic phosphors with intramolecular charge transfer characters and flexible molecular structures. When doped into different organic matrices, the twisted phosphor adopts different conformation, exhibits distinct phosphorescence colors and T₁ energy levels, which violates Kasha's exciton model in organic system. Given that the change of phosphorescence colors and maxima can be readily distinguished by human eyes and conventional instrument, the twisted phosphors would be exploited as a new type of molecular probe, which would exhibit potential application in optical sensing and stimuli-responsive systems.

Comprehensive Summary

As a versatile earth-abundant transition metal, Cu has long been widely applied in the C—C and C—X bond forming reactions. As for now, low-valent Cu(I) is known to reduce the redox active electrophiles via an SET pathway to give the corresponding radical and Cu(II) species. The resulting Cu(II) species can interact with the radical via the out-sphere pathway, affording the coupling product. Alternatively, Cu(II) can trap the radical through the inner-sphere process to generate Cu(III) species and then realize challenging bond formations due to the facile reductive elimination of Cu(III) intermediate. Although copper catalysis has been widely applied in arylations of various nucleophiles, copper-catalyzed enantioconvergent nucleophilic substitutions of racemic alkyl electrophiles have been less explored, likely due to the difficulties in overcoming the reduction potential of alkyl electrophiles, elimination of side reactions, and enantiomeric control. In order to overcome the high reduction potential of alkyl electrophiles, the photo-induced strategy has been developed under mild conditions. An alternative strategy with new anionic tridentate ligands has also been reported in this regard. This review summarizes recent developments in copper-catalyzed enantioconvergent nucleophilic substitutions of alkyl electrophiles by various nucleophiles to realize C—N, C—C, C—B, C—P and C—O bond formations and their brief mechanistic studies.

Key Scientists

In 2016, Fu and Peters et al. reported the first photo-induced Cu-catalyzed enantiocovergent C—N bond formations of tertiary alkyl halides with N-hetereocycles, opening the door for the Cu-catalyzed enantiocovergent nucleophilic substitutions. The photo-induced strategy has been developed that greatly enhances the reducing power of Cu(I). The Cu-catalyzed enantioconvergent cyanation (decarboxylative) and borylation were then successively presented by Liu and Ito in 2017 and 2018, respectively. Other than the photo-induced strategy, Liu et al. in 2019 demonstrated that anionic ligands can also significantly enhance the reducing ability of Cu(I). The cinchona-based chiral anionic tridentate ligands have been utilized for a series of Cu-catalyzed enantiocovergent nucleophilic substitutions. Zhang et al. also developed chiral anionic tridentate ligands containing the oxazoline binding sites in 2020. In 2020, Xiao and Lu et al. reported the Cu-catalyzed enantiocovergent deoxygenative cyanation. Later in 2022, Feng and Liu et al. developed the new guanidine hybrid ligands. This review focuses on the Cu-catalyzed enantioconvergent nucleophilic substitutions that emerged in recent years.

In lead-based perovskite nanocrystals, a fraction of lead is substituted with rare earth elements for the purpose of doping. Given the adverse effects of lead on human health and the environment, the complete substitution of lead with rare earth ions to achieve lead-free characteristics has emerged as a prominent trend.

Comprehensive Summary

Rare earth (RE) ions, with abundant 4f energy level and unique electronic arrangement, are considered as substitutes for Pb²⁺ in perovskite nanocrystals (PNCs), allowing for partial or complete replacement of lead and minimizing environmental impact. This review provides a comprehensive overview of the characteristics of RE-doped PNCs, including up-conversion luminescence, down-conversion luminescence, and quantum confinement effects, etc. Additionally, RE doping has been found to effectively suppress defect formation, reduce nonradiative recombination, enhance photoluminescence quantum yield (PLQY), and even allow for controlling over the morphology of the nanocrystals. The review also highlights the recent advancements in lead-free RE-based perovskites, especially in the case of Eu-based perovskites (CsEuBr₃ and CsEuCl₃). Furthermore, it briefly introduces the applications of PNCs in various fields, such as perovskite solar cells (PSCs), luminescent solar concentrators (LSCs), photodetectors (PDs), and light-emitting diodes (LEDs). A systematic discussion on the luminescence mechanisms of RE-doped PNCs and lead-free RE-based perovskites is provided, along with an outlook on future research directions. The ultimate goal of this review is to provide guidance for the development of RE-based perovskite optoelectronic devices.

Key Scientists

In 2015, Kovalenko et al. pioneered the synthesis of lead-based perovskite nanocrystals using the thermal injection method. Concurrently, Zhong et al. introduced the ligand-assisted reprecipitation method. These methods have become the predominant approaches for fabricating lead-based perovskite nanocrystals. In 2017, Song et al. successfully incorporated various rare earth ions (Ce³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Er³⁺, and Yb³⁺) into CsPbCl₃ perovskite nanocrystals. They also observed the quantum cutting effect induced by defect states, facilitated by the doping of Yb³⁺. Gamelin et al. subsequently proposed that CsPbCl₃:Yb³⁺ nanocrystals exhibit quantum cutting effects due to the introduction of charge-compensating defects (V_Pb), resulting in the formation of Yb³⁺-V_Pb-Yb³⁺ defect complexes with shallow defect levels. In 2020, Zhang et al. successfully doped Nd³⁺ into CsPbBr₃, yielding blue luminescent nanocrystals with a central wavelength of 459 nm and up to 90% photo-luminescence quantum yield (PLQY). In the same year, Yang et al. achieved the synthesis of pure phase CsEuCl₃ perovskite nanocrystals for the first time. In 2022, Paik et al. synthesized Cs₃LnCl₆ (Ln = Y, Ce, Gd, Er, Tm, Yb, Eu, Tb) nanocrystals using the thermal injection method. In 2023, Zhang et al. successfully introduced Ni²⁺ doping into CsEuCl₃, enhancing the PLQY of CsEuCl₃ nanocrystals from 5% to 19.7%. This review focuses on the development history of perovskite nanocrystals, including rare earth-doped lead-based perovskite nanocrystals and rare earth-based lead-free perovskite nanocrystals, as well as their applications.