Yuya Hu

You shall know our viscosity: Functionalized ethylenediamines are applied as water‐lean CO₂ absorbents with high capacity and low viscosity. The success of these single‐component absorbents can be attributed to a concise two‐step molecular design strategy that involves the introduction of alkoxyethyl and the replacement of unnecessary N−H bonds by N−Me, to prevent the viscosity increase of CO₂‐bonded ethylenediamines.

Abstract

The exponentially increasing viscosity of water‐lean CO₂ absorbents during carbon capture processes is a critical problem for practical application, owing to its strong correlation with systems’ mass transfer properties, as well as convenience of transportation. In this work, a concise strategy based on structure–viscosity relationships is proposed and applied to construct a series of functionalized ethylenediamines as single‐component absorbents for post‐combustion CO₂ capture. These nonaqueous absorbents have outstanding viscosities (50–200 cP, 25 °C) at their maximal CO₂ capacities (up to 22 wt % or 4.92 mol kg⁻¹, 1 bar), and are readily regenerated at low temperatures (50–80 °C) under ambient pressure. Additional capture of CO₂ through physisorption could also be achieved by operating at high pressures. The CO₂ capture and release process is systematically investigated by means of ¹³C NMR spectroscopy, differential scanning calorimetry (DSC), in situ FTIR analysis, and density functional theory (DFT) calculations, which could provide sufficient spectroscopic details to reveal the ease of reversibility and enable rational interpretation of the absorption mechanism.

Publication date: 12 December 2019

Source: Chem, Volume 5, Issue 12

Author(s): Saravanan Subramanian, Julius Oppenheim, Doyun Kim, Thien S. Nguyen, Wahyu M.H. Silo, Byoungkook Kim, William A. Goddard, Cafer T. Yavuz

The Bigger Picture

Summary

Graphical Abstract

Photocatalysis: Reproducibility for photocatalytic CO₂ reduction has been evaluated on the example of [FeFe] hydrogenase mimics in combination with a heteroleptic Cu photosensitizer. Based on these results, we highlight the importance of testing reproducibility for new photocatalytic reaction protocols. Furthermore, we provide suggestions on how to ensure reproducibility of those transformations.

Abstract

Reproducibility of photocatalytic reactions, especially when conducted on small scale for improved turnover numbers with in situ formed catalysts can prove challenging. Herein, we showcase the problematic reproducibility on the example of attractive photocatalytic CO₂ reduction utilizing [FeFe] hydrogenase mimics. These Fe complexes, well‐known for their application in proton reduction reactions, were combined with a heteroleptic Cu photosensitizer and produced CO/H₂/HCO₂H mixtures of variable constitution. However, the reactions indicated a poor reproducibility, even when conducted with well‐defined complexes. Based on our experience, we make suggestions for scientists working in the field of photocatalysis on how to address and report the reproducibility of novel photocatalytic reaction protocols. In addition, we would like to highlight the importance of studying reproducibility of novel reaction protocols, especially in the fields of photocatalytic water splitting and CO₂ reduction, where TONs are widely used as the comparable measure for catalytic activity.

Nature, Published online: 08 October 2019; doi:10.1038/d41586-019-03020-6

Direct vinylogous Michael addition of the remote γ‐carbon atoms of α,β‐unsaturated imines to enals is realized through iminium organic catalysis, providing a quick access to enantiopure cyclic amino acids.

Abstract

Disclosed herein is a new catalytic approach for an efficient access to cyclic β‐amino acids widely found in bioactive small molecules and peptidic foldamers. Our method involves addition of the remote γ‐carbon atoms of α,β‐unsaturated imines to enals by iminium organic catalysis. This highly chemo‐ and stereo‐selective reaction affords cyclic β‐amino aldehydes that can be converted to amino acids bearing quaternary stereocenters with exceptional optical purities. Our study demonstrates the unique power of organic catalytic remote carbon reactions in rapid synthesis of functional molecules.

Tamed: A new catalytic asymmetric approach for the synthesis of chiral tetrahydrothiophenes and tetrahydroselenophenes bearing all‐carbon quaternary stereocenters is disclosed. This reaction employs a chiral acid to promote efficient desymmetrization of the oxetanes by either a well‐positioned internal sulfur or selenium nucleophile with excellent enantioselectivities. Key to success is the taming of the sulfur and selenium reactivities in the form of a thioester and selenoester, respectively.

Abstract

Chiral tetrahydrothiophenes and tetrahydroselenophenes are highly useful structural units. Described here is a new catalytic asymmetric approach for their synthesis. With a suitable chiral Brønsted acid catalyst, an oxetane desymmetrization by a well‐positioned internal sulfur or selenium nucleophile proceeded efficiently to generate all‐carbon quaternary stereocenters with excellent enantioselectivities. Taming the sulfur and selenium nucleophile in the form of a thioester and selenoester, respectively, is crucial to the success of this work. This approach also allows the facile synthesis of chiral tetrahydrothiopyrans. Mechanistic studies, including DFT calculations, suggested an intramolecular acyl‐transfer pathway. Utilities of the chiral products are also demonstrated.

Nature Communications, Published online: 25 September 2019; doi:10.1038/s41467-019-12414-z