LongLarf

Fixed: A porous anionic framework was designed to catalyze carboxylative cyclization of propargylic alcohols with CO₂, and the turnover number (TON) can reach to a record value of 14 400 under mild conditions. It represents the first example that noble‐metal‐free MOFs can directly catalyze carboxylative cyclization of propargylic alcohols with CO₂.

Abstract

Cyclization of propargylic alcohols with CO₂ is an important reaction in industry, and noble‐metal catalysts are often employed to ensure the high product yields under environmentally friendly conditions. Herein a porous noble‐metal‐free framework 1 with large 1D channels of 1.66 nm diameter was synthesized for this reaction. Compound 1 exhibits excellent acid/base stability, and is even stable in corrosive triethylamine for one month. Catalytic studies indicate that 1 is an effective catalyst for the cyclization of propargylic alcohols and CO₂ without any solvents under mild conditions, and the turnover number (TON) can reach to a record value of 14 400. Furthermore, this MOF catalyst also has rarely seen catalytic activity when the biological macromolecule ethisterone was used as a substrate. Mechanistic studies reveal that the synergistic catalytic effect between Cu^I and In^III plays a key role in the conversion of CO₂.

Gas‐glue CO₂ : CO₂ can act as a “gas glue” to cross‐link trefoil‐like frustrated Lewis molecular pairs into a new form of molecular network. The CO₂‐bridged cross‐links are dynamically covalent, which endows the gel network with unique gas‐modulated viscoelastic, mechanical, and self‐healing performance.

Abstract

The design of structurally dynamic molecular networks can offer strategies for fabricating stimuli‐responsive adaptive materials. Herein we first report a gas‐responsive dynamic gel system based on frustrated Lewis pair (FLP) chemistry. Two trefoil‐like molecules with bulky triphenylborane and triphenylphosphine groups are synthesized as complementary Lewis acid and base with trivalent sites. They can together bind CO₂ gas molecules and further form a cross‐linked network via the bonding interactions between FLPs and CO₂. Such CO₂‐bridged dative linkages are shown to be dynamic covalent bonds, which endow the frustrated Lewis network with adaptable behaviors and unprecedented gas‐regulated viscoelastic, mechanical, and self‐healing performance. This study is an initial attempt to apply the FLP concept in materials chemistry, but we believe that this strategy will open a promising future for gas‐sensitive smart materials.

Synlett
DOI: 10.1055/s-0037-1611084

Enantiopure α-hydroxy carbonyl compounds are common scaffolds in natural products and pharmaceuticals. Although indirect approaches towards their synthesis are known, direct asymmetric methodologies are scarce. Herein, we report the first direct asymmetric α-hydroxylation of α-branched ketones through enol catalysis, enabling a facile access to valuable α-keto tertiary alcohols. The transformation, characterized by the use of nitrosobenzene as the oxidant and a new chiral phosphoric acid as the catalyst, delivers a good scope and excellent enantioselectivities.
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Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Active catalysts in situ generated from Zn powder, dimethyl formamide and benzyl bromide were designed for fixation of CO₂ to cyclic carbonates at 80 °C and atmospheric pressure of CO₂. Zinc bromide and N,N‐dibenzyl‐N,N‐dimethylammonium bromide, being proved as active catalyst species, were in situ generated and immediately converted various terminal epoxides to the corresponding carbonates efficiently.

Herein, in situ generated efficient catalysts were designed for fixation of CO₂ to cyclic carbonates under mild conditions. Zinc bromide and N,N‐dibenzyl‐N,N‐dimethylammonium bromide, being proved as active catalyst species, were in situ generated from cheap Zn powder, dimethyl formamide and benzyl bromide, and catalyzed the cycloaddition reaction of CO₂ and various terminal epoxides in moderate to excellent yields at 80 °C and atmospheric pressure of CO₂. The protocol circumvents the preparation of active catalysts, simultaneously possesses good catalytic activity under mild conditions.

A combined approach: A simple and general strategy involving the combination of a photo‐organocatalyst (benzaldehyde) and a transition‐metal catalyst (nickel) has been developed for the highly selective photoredox C(sp³)−H alkylation/arylation of ethers. A selective late‐stage modification of (−)‐ambroxide has also been conducted to demonstrate the applicability of the method.

Abstract

Herein we report a highly selective photoredox C(sp³)−H alkylation/arylation of ethers through the combination of a photo‐organocatalyst (benzaldehyde) and a transition‐metal catalyst (nickel). This method provides a simple and general strategy for the C(sp³)−H alkylation/arylation of ethers. A selective late‐stage modification of (−)‐ambroxide has also been conducted to demonstrate the applicability of the method.

In this work a series of bis‐arylselanyl olefins were synthesized using visible white light from common fluorescent lamps as energy source, without catalyst or additives. The products were achieved in a very clean and fast way, yielding E‐olefins with good stereoselectivity, through radical addition‐photoisomerization.

Functionalization of double bonds with arylselenium groups found in the literature, commonly uses high temperatures in the presence of metal catalysts, reducing agents or other additives. In this context, this work presents a series of bis‐arylselanyl olefins synthesized by photoinduced reaction without heating or additives. Since the absorption range of the diselenide comprises the UV/Visible region of spectra, a mixture of arylacetylene and diaryl diselenide in dichloromethane was irradiated with white light from compact (household) fluorescent lamp. The optimized procedure allows preparation of E‐olefins due to radical addition followed by photoisomerization with low cost and low environmental impact.

Abstract

A series of nickel‐aluminium, cobalt‐aluminium and zinc‐aluminum layered double hydroxides were synthesized by urea hydrolysis (UH) and reverse micelle (RM) methods and then applied for the cycloaddition of carbon dioxide to propylene oxide (PO) under solvent‐free and ambient conditions. The most efficient catalyst was zinc‐aluminum layered double hydroxide prepared by RM (denoted as ZnAl‐RM) and it showed, in the presence of a co‐catalyst of tetrabutylammonium bromide, 96% propylene carbonate (PC) yield in 12 h at 25 °C and 1 MPa carbon dioxide. It is noteworthy for the same catalyst system that 74% PC yield was achieved in 24 h at room temperature (about 25 °C) and atmospheric carbon dioxide pressure. The high catalytic performance of the ZnAl‐RM and tetrabutylammonium bromide system should result from cooperative effects between zinc ion and bromine ion. Moreover, the ZnAl‐RM and tetrabutylammonium bromide system showed excellent versatility, which was also an active catalyst to the transformation of carbon dioxide and other epoxides into corresponding cyclic carbonates under mild temperature and pressure conditions.

New structural scaffolds for use in organic electronic materials are in high demand, especially if they possess unique optoelectronic or morphological properties. In this issue of Chem, Dobrovetsky, Baumgartner, and coworkers describe the synthesis of a new “step-conjugated” bi(dithienophosphole) and demonstrate its unique structural and electronic features.

In this issue of Chem, Ma and coworkers meld metal-organic framework (MOF) chemistry with the emerging field of main-group catalysis for the first time. A MOF-supported Lewis pair is prepared, characterized, and shown to be an effective, stable, recyclable, and selective catalyst for hydrogenation.

Bad language in stereochemistry—and elsewhere—can lead to sloppy thinking. In this Essay the history of stereochemical concepts and vocabulary is reviewed in the hope that it may contribute a little to better thinking and communication.

Abstract

Bad language in stereochemistry—and elsewhere—can lead to sloppy thinking. In this Essay I review the history of stereochemical concepts and vocabulary in the hope that it may contribute a little to better thinking and communication.

Superelectrophile: Phosphonium carbenium dications are formed by the protonation of unsaturated phosphine oxides in superacid. The superelectrophilic character of these dications is essential for the syntheses of various novel fluorinated and cyclic phosphine oxides.

Abstract

Unambiguously confirmed by low‐temperature in situ NMR experiments, X‐ray diffraction and vibrational spectroscopy, phosphonium‐carbenium superelectrophiles are shown to be generated in strong acidic conditions. Representing crucial intermediates, their exploitation allows for the synthesis of unprecedented fluorinated (cyclic) phosphine oxides.

The first example of transition‐metal‐free CO₂ hydrogenation to formate catalyzed by BCF/M₂CO₃ (M=Na, K, and Cs) was reported with TON up to 3941. Mechanism studies revealed that BCF reacted with K₂CO₃ to afford a Lewis pair K₂[(BCF)₂‐CO₃] that can react with H₂ and CO₂ to produce formate.

Abstract

Hydrogenation of CO₂ to formate with H₂ in the absence of transition metal is a long‐standing challenge in catalysis. The reactions between tris(pentafluorophenyl)borane (BCF) and K₂CO₃ (or KHCO₃) are found to form a Lewis pair (K₂[(BCF)₂−CO₃]) which can react with both H₂ and CO₂ to produce formate. Based on these stoichiometric reactions, the first catalytic hydrogenation process of CO₂ to formate using transition metal free catalyst (BCF/M₂CO₃, M=Na, K, and Cs) is reported. The highest TON value of this catalytic process is up to 3941. Further research revealed the reaction mechanism in which the Lewis pair enables the splitting of H₂ and the insertion of CO₂ into the B−H bond.

How to design a winning fellowship proposal

How to design a winning fellowship proposal, Published online: 06 November 2018; doi:10.1038/d41586-018-07297-x

Be clear about your training plan and goals to boost your chances of a favourable outcome, say Crystal M. Botham and Tanya M. Evans.

Thar she blows! Whales seen exhaling from space

Thar she blows! Whales seen exhaling from space, Published online: 06 November 2018; doi:10.1038/d41586-018-07284-2

Satellite used by intelligence agencies can identify some large whale species down to the flipper.