A metal-free natural dye has been developed to selectively convert methane to methyl trifluoroacetate (CH3TFA) using visible light, probably due to the formation of a chloride-bridged dimer undergoing fast intra-complex charge transfer.
Amine-borane dimers and oligomers with varied steric and electronic profiles were prepared via capping agent-controlled AA/BB polycondensations. They were used for transfer hydrogenations to aldehydes, ketones, imines as well as electron-poor alkene/alkyne moieties. The amine-borane Lewis-paired oligomers and the congested bis(amine-borane)s provided the highest yields. This was likely helped by facilitated dissociation (oligomers) or H-bond assistance. In the case of the oligomers, the second equivalent of H2 present was also engaged in the reaction. Solid-state NMR characterization provides evidence that the Boron-containing materials obtained after transfer dehydrogenation are highly similar to those obtained from thermal dehydrogenation. The oligomers bridge the gap between simple amine-borane molecular reductants and the poly-amine-boranes and provide a full picture of the reactivity changes at the different scales.
The sustainable solution to the environmental problem of polymeric materials calls for efficient and well-controlled ring-opening polymerization catalytic systems. Inspired by the highly reactive and stereospecific bimetallic catalysts, three kinds of bimetallic Salen-Mn catalysts supported by biaryl linking moieties are synthesized and applied to polymerization catalysis of lactide (LA) and ε-caprolactone (ε-CL) in this work. The polymerization is initiated in situ by the ring-opening of epoxide compounds, in which the ionic cocatalyst could accelerate the reaction process. The Mn-Mn coordination effect contributes to the higher activity and iso-selectivity towards LA compared to the mononuclear Salen-Mn catalyst. The reactivity and stereoselectivity are determined by the conformation of catalysts, specifically the Mn-Mn separation and dihedral angle. Finally, the CO2-controlled switchable polymerizations are carried out with LA and ε-CL. The reversibility of the on-off switching operation is influenced by the combination between CO2 molecules and active species. The success in binuclear Salen-Mn catalysts not only expands the range of bimetallic catalyst analogues but also claims the promising potential of Mn-based catalysts in practical and theoretical research.
In Nature, enzymatic reactions proceed through exceptionally ordered transition states giving rise to extraordinary levels of stereoselection. In those reactions, the active site of the enzyme plays crucial roles – through one position, it holds the substrate in the proximity to the reaction epicentre that facilitates both the reactivity and stereoselectivity of the chemical process. Inspired by this natural phenomenon, synthetic chemists have designed bifunctional ligands that not only coordinate to a metal centre but also preassociate with an organic substrate, e.g. aldehyde and ketone, and exerts stereodirecting influence to accelerate the attack of the incoming reacting partner from a particular enantiotopic face. The chief goal of the current review is to give an overview of the recently developed approaches enabled by privileged bio-inspired bifunctional ligands that not only bind to the metal catalyst but also activates carbonyl substrates via organocatalysis, thereby easing in the new bond forming step. As carbonyl a-functionalizations are dominated by enamine and enolate chemistry, the current review primarily focusses on enamine- and enolate-metal catalysis by bifunctional ligands. Thus, developments based on traditional cooperative catalysis occurring through two directly coupled but independent catalytic cycles of an organocatalyst and a metal catalyst are not covered.
We present here a joint experimental and computational study on the formation of benzothiazoles. Our investigation reveals a green protocol for accessing benzothiazoles from acyl chlorides using either water alongside a reducing agent as the reaction medium or in combination with stoichiometric amounts of a weak acid, instead of the harsh conditions and catalysts previously reported. Specifically, we show that a protic solvent, particularly water, enables the formation of 2-substituted benzothiazoles from N-acyl 1,2-aminothiophenols already at room temperature, without the need for strong acids or metal catalysts. DFT Molecular Dynamics simulations coupled with advanced enhanced sampling techniques provide a clear understanding of the catalytic role of water. We demonstrate how bulk water – due to its extended network of hydrogen bonds and an efficient Grotthus mechanism – provides a reaction path that strongly reduces the reaction barriers compared to aprotic environments, namely more than 80 kJ/mol for the first reaction step and 250 kJ/mol for the second. Finally, we discuss the influence of different aliphatic and aromatic substituents with varying electronic properties on chemical reactivity. Besides providing in-depth mechanistic insights, we believe that our findings pave the way for a greener route toward an important class of bioactive molecules.
A convenient three-component tetrafluoroethylation reaction of alkenes induced by visible light has been developed using 1,1,2,2-tetrafluoroethylsulfonyl chloride and quinoxalin-2(1H)-ones. This method provides a facile approach to introduce the HCF2CF2 group into organic molecules under mild conditions, enabling the late-stage modification of biologically active and drug molecules.
1,1,2,2-Tetrafluoroethyl-containing compounds are valuable structures due to their unique physicochemical properties, which have increasing potential application in drug discovery. However, synthetic methods for preparing such compounds are rare. Herein, we report the first use of 1,1,2,2-tetrafluoroethanesulfonyl chloride to introduce the HCF2CF2 group into organic molecules via a three-component, radical tetrafluoroethyl-heteroarylation of alkenes with readily available quinoxalin-2(1H)-ones. This method provides a new and facile approach for late-stage functionalization of potential biologically active molecules.
Gas separation: A novel organic cage with excellent film-forming tendencies was processed into transparent, mechanically robust, self-standing membranes of controllable thickness. Thanks to their peculiar features, the membranes of the neat cage were successfully tested for gas permeation (e.g., with CO2), with behavior similar to that found with stiff glassy polymers such as polymers of intrinsic microporosity or polyimides being reported. More information can be found in the Research Article by J. C. Jansen, V. Amendola and co-workers (DOI: 10.1002/chem.202301437).
With the continuous progress of technology, the research and development of new materials has become a hot topic in today's scientific community. Among them, metal-free perovskite has attracted widespread attention due to its unique photoelectric properties and environmental friendliness. With continuous development, new progress has been made in the growth of metal-free perovskite single crystals and device research, and high-sensitivity metal-free perovskite single crystal X-ray detectors have been prepared. This article will delve into the principles of metal-free perovskite and its application in X-ray imaging.
Metal-free perovskites are a promising class of materials for X-ray detection due to their unique structural, optical, and electrical properties. Here, we first delve into the stoichiometry and geometric argument of metal-free perovskites. Followed, the alternative A/B/X ions and hydrogen-bonding are clearly introduced to further optimize the materials’ stability and properties. Finally, we provide a comprehensive overview of their potential applications for flexible X-ray images and prospects for metal-free perovskite development. In conclusion, metal-free perovskite is a promising material for X-ray detection. Its stoichiometric and geometric parameters, ion, and hydrogen bond selection, and application prospects are worthy of further study.
“Our collaboration started… because of our mutual interest in the photophysical events that occur after photoirradiation of complex systems composed of one (or more) electron-acceptor moieties linked to one (or more) electron-donor systems.” This and more about the story behind the front cover can be found in the article at 10.1002/chem.202301686).
Invited for the cover of this issue are the groups of Fernando Fernández-Lázaro and Ángela Sastre-Santos at the Universidad Miguel Hernández, Elche, Spain, and Francis D'Souza at the University of North Texas at Denton, Texas, USA. The image depicts the structure and properties of bis-styryl BODIPY-perylenediimide donor–acceptor constructs. Read the full text of the article at 10.1002/chem.202301686.