LongLarf

Nature Communications, Published online: 29 June 2020; doi:10.1038/s41467-020-17085-9

A radical improvement: Our board member Prof. Yang Li discusses how, by using acridinium photocatalysts with powerful oxidative and reductive ability upon visible‐light excitation, various transformations by visible‐light photoredox catalysis can be expected.

Abstract

In this series of articles, the board members of ChemSusChem discuss recent research articles that they consider of exceptional quality and importance for sustainability. This entry features Prof. Y. Li, who discusses visible‐light photoredox catalysis by acridinium photocatalysts, which show both powerful oxidative and reductive abilities. She also highlights the mechanism for generation of a neutral acridine radical and its application in the reduction of aryl halides.

An approach towards application of heterogenized biocatalysts in continuous synthesis utilizing them embedded in a mobile hydrogel phase for a segmented flow process is presented. The applicability of this concept for biotransformations is exemplified for an alcohol dehydrogenase‐catalyzed ketone reduction, as well as an aldoxime dehydratase‐containing whole‐cell‐catalyzed aldoxime dehydration.

As both, continuous synthesis and (bio‐)catalysis gained increasing interest in research as well as for industrial applications, ways for merging these fields enables novel opportunities for modern sustainable process development. In this contribution, an alternative approach for the application of immobilized enzymes in continuous flow processes is presented utilizing heterogeneous biocatalysts as a mobile phase. Based on superabsorber‐entrapped enzymes and whole cells as a “fluid heterogeneous phase”, a segmented hydrogel/organic solvent system was developed. Its applicability was investigated with two entirely different model reaction systems, namely the alcohol dehydrogenase (ADH)‐catalysed reduction of acetophenone, and the aldoxime dehydratase (Oxd)‐catalysed dehydration of octanal oxime. In particular for solvent labile catalytic systems, this approach offers an alternative for the application of immobilized biocatalysts in a continuously running process beyond the “classic” packed bed and wall coated reactors.

An efficient synthesis of 2‐oxazolidinones from epoxides and isocyanates under solvent‐free conditions, featuring the use of triethylamine hydroiodide as a simple and effective bifunctional organocatalyst is developed.

Among the wide variety of heterocycles, 2‐oxazolidinones are recognized as some of the most important heterocyclic compounds in medicinal chemistry. Therefore, the development of a practical method for their synthesis would be an important development. Herein, we report an efficient method for the synthesis of 2‐oxazolidinones under solvent‐free conditions using triethylamine hydroiodide as a simple and effective bifunctional organocatalyst.

Publication date: 6 August 2020

Source: Chem, Volume 6, Issue 8

Author(s): Zhi Du, Chun Liu, Hualong Song, Peter Scott, Zhenqi Liu, Jinsong Ren, Xiaogang Qu

I mean defunct . Combinations of the boron Lewis acid B(C₆F₅)₃ and hydrosilanes enable the reductive cleavage ofC−N bonds in various, mainly benzylic amines and heterocumulenes. By this, these functionalized substrates can be converted into the corresponding hydrocarbons in moderate to good yields.

Abstract

The strong boron Lewis acid tris(pentafluorophenyl)borane B(C₆F₅)₃ is known to catalyze the dehydrogenative coupling of certain amines and hydrosilanes at elevated temperatures. At higher temperature, the dehydrogenation pathway competes with cleavage of the C−N bond and defunctionalization is obtained. This can be turned into a useful methodology for the transition‐metal‐free reductive deamination of a broad range of amines as well as heterocumulenes such as an isocyanate and an isothiocyanate.

PB&J? Phosphinoboration across a triple bond catalyzed by tributyl phosphine was achieved. The trans‐α‐phosphino‐β‐boryl acrylate products are obtained in moderate to good yield with high regio‐ and Z‐selectivity. This reaction operates under mild conditions and demonstrates good atom economy, requiring only a modest excess of the phosphinoboronate.

Abstract

We report the first trans phosphinoboration of internal alkynes. With an organophosphine catalyst, alkynoate esters and the phosphinoboronate Ph₂P‐Bpin are efficiently converted into the corresponding trans‐α‐phosphino‐β‐boryl acrylate products in moderate to good yield with high regio‐ and Z‐selectivity. This reaction operates under mild conditions and demonstrates good atom economy, requiring only a modest excess of the phosphinoboronate. X‐ray crystallography experiments allowed structural assignment of the unprecedented and densely functionalized (Z )‐α‐phosphino‐β‐boryl acrylate products.

Double transfer : New hypervalent iodine(III) reagents are formed by reactions of difluoroiodotoluene with NH‐sulfoximines. When applied in situ, they photocatalytically react with styrenes by transferring a fluoro and a sulfoximidoyl group onto the olefin with high regioselectivity. The operationally simple process provides a variety of fluorine‐containing N‐functionalized sulfoximines, which are difficult to prepare otherwise. Mechanistic investigations reveal the importance of radical intermediates.

Abstract

Reactions of difluoroiodotoluene with NH‐sulfoximines provide new hypervalent iodine(III) reagents, which photocatalytically transfer a fluoro and a sulfoximidoyl group onto styrenes with high regioselectivity. The substrate scope is broad with respect to both sulfoximines and olefins. Following an operationally simple protocol, a large library of fluorine‐containing N‐functionalized sulfoximines can be accessed. Results from mechanistic investigations revealed the importance of radical intermediates.

Triplet materials are designed by introducing heavy atoms to enhance spin–orbit coupling or constructing donor and acceptor units with a twisted conformation to reduce ΔE _ST. However, the twisted materials have not been applied in solar cells due to weak absorption and low charge‐transport mobilities. Now two nonplanar acceptors with large π‐conjugated core were constructed that achieved over 15 % efficiency.

Abstract

Triplet acceptors have been developed to construct high‐performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T₁) are close to those of charge‐transfer states (³CT). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large π‐conjugated core and D‐A structure, were confirmed to be triplet materials, leading to high‐performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D‐A structures result in large spin–orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T₁ is close to ³CT, facilitating the split of triplet exciton to free charges.

Blown away: Microcellular self‐blown non‐isocyanate polyurethane foams were constructed from reactive formulations by guiding the chemo‐ and regioselective ring‐opening and decarboxylation of cyclic carbonates by amines and thiols. This novel concept is versatile, easily accessible, and scalable.

Abstract

Polyurethane (PU) foams are indisputably daily essential materials found in many applications, notably for comfort (for example, matrasses) or energy saving (for example, thermal insulation). Today, greener routes for their production are intensively searched for to avoid the use of toxic isocyanates. An easily scalable process for the simple construction of self‐blown isocyanate‐free PU foams by exploiting the organocatalyzed chemo‐ and regioselective additions of amines and thiols to easily accessible cyclic carbonates is described. These reactions are first validated on model compounds and rationalized by DFT calculations. Various foams are then prepared and characterized in terms of morphology and mechanical properties, and the scope of the process is illustrated by modulating the composition of the reactive formulation. With impressive diversity and accessibility of the main components of the formulations, this new robust and solvent‐free process could open avenues for construction of more sustainable PU foams, and offers the first realistic alternative to the traditional isocyanate route.

Flexible cyanides : Bulky cations and fast crystallization allowed the isolation and structural characterization of examples of HCN‐cyanide aggregates [CN(HCN)₂)]⁻ and [CN(HCN)₃]⁻ in the solid state. X‐ray structure elucidation revealed hydrogen‐bridged linear [CN(HCN)₂]⁻ and Y‐shaped [CN(HCN)₃]⁻ molecular ions in the crystal.

Abstract

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN⁻), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph₄P, Ph₃PNPPh₃=PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)₂]⁻ and trihydrogen tetracyanide ions [CN(HCN)₃]⁻ from liquid HCN when a fast crystallization was carried out at low temperatures. X‐ray structure elucidation revealed hydrogen‐bridged linear [CN(HCN)₂]⁻ and Y‐shaped [CN(HCN)₃]⁻ molecular ions in the crystal. Both anions can be considered members of highly labile cyanide‐HCN solvates of the type [CN(HCN) _n ]⁻ (n= 1, 2, 3 …) as well as formal polypseudohalide ions.

Nature Catalysis, Published online: 18 June 2020; doi:10.1038/s41929-020-0480-7