Robby Vroemans

A visible light driven nickel carbonylation catalyst has been develop. This offers a method for carbonylative coupling reactions with an earth abundant metal at ambient temperature for the conversion of alkyl halides into synthetically versatile acid chlorides. The acid chlorides can then be transformed into an array of challenging ester, thioester and amide products.

Abstract

We describe here the development of a visible light driven nickel carbonylation catalyst. The combination of the large bite-angle Xantphos ligand with nickel(0) generates a catalyst capable of activating alkyl halides toward carbonylation at ambient temperature in the presence of blue light irradiation, and the reductive elimination of high energy acid chloride products. Unlike classical carbonylations, where the coordination of carbon monoxide inhibits the reactivity of earth abundant nickel catalysts, a CO-associated nickel is found to be the active catalyst in the reaction. Coupling the build-up of acid chlorides with nucleophile addition can be used to access various amides, esters and thioesters, including those of sterically encumbered substrates or with metal-reactive functionalities.

Beilstein J. Org. Chem. 2023, 19, 89–90. doi:10.3762/bjoc.19.8

Photocatalytic Synthesis: Sulfur dioxide is incorporated into organic compounds using visible light and sensitizers made from earth-abundant chromium(III) ions giving sulfones and sulfonamides. Detailed mechanistic studies including electrochemical, luminescence quenching, photolysis, laser flash photolysis and catalytic experiments identify key reaction steps of the photocatalytic cycles including quenching, cage escape and photocatalyst regeneration.

Abstract

Incorporation of sulfur dioxide into organic compounds is achieved by a photocatalytic approach using sensitizers made from earth-abundant chromium(III) ions and visible light leading to sulfones and sulfonamides. We employed three different chromium(III) sensitizers [Cr(ddpd)₂]³⁺ , [Cr(bpmp)₂]³⁺ and [Cr(tpe)₂]³⁺ with long excited state lifetimes and different ground and excited state redox potentials as well as varying stability under the reaction conditions (ddpd=N,N’-dimethyl-N,N’-dipyridin-2-yl-pyridine-2,6-diamine; bpmp=2,6-bis(2-pyridylmethyl)pyridine; tpe=1,1,1-tris(pyrid-2-yl)ethane). Key reaction steps of the catalytic cycles are identified by electrochemical, luminescence quenching, photolysis, laser flash photolysis and catalytic experiments delivering a detailed picture of the challenges in these transformations. The reactivity of the reduced chromium complex was identified as a key property to explain the reaction outcomes. Initial cage escape yield determinations with [Cr(tpe)₂]³⁺ revealed that desired photoreactions occur with unusually high quantum efficiencies, whereas side reactions are almost unproductive.

Nature, Published online: 20 January 2023; doi:10.1038/d41586-023-00157-3

A photocatalytic carboxylation of C−N bonds in cyclic amines with CO₂ is realized by consecutive photo-induced electron transfer (ConPET). This mild and transition-metal-free protocol provides a general and practical route to valuable β-, γ-, δ- and ϵ-amino acids.

Abstract

Visible-light photocatalytic carboxylation with CO₂ is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C−N bonds in cyclic amines with CO₂ via consecutive photo-induced electron transfer (ConPET). It is also the first photocatalytic reductive ring-opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β-, γ-, δ- and ϵ-amino acids in moderate-to-excellent yields. Moreover, the method also features mild and transition-metal-free conditions, high selectivity, good functional-group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.

Zr oxo cluster bifunctional catalyst: The Zr oxo cluster [Zr₆O₄(OH)₄ (HSCH₂CH₂COO)₁₂]₂ has been developed, and then the molecular catalyst with Lewis acid and Brönsted acid sites were attained by the oxidation of the sulfhydryl group of the Zr oxo cluster with H₂O₂. The resulting bifunctional catalyst showed a superior catalytic activity for alcoholysis of furfural to alkyl levulinates.

Abstract

A novel dodecanuclear Zr oxo cluster [Zr₆O₄(OH)₄ (HSCH₂CH₂COO)₁₂]₂ (ZrO-SH-10) has been constructed under the room temperature, followed by oxidation of the sulfhydryl group with H₂O₂ to achieve a bifunctional catalyst with Lewis acid and Brönsted acid sites. The characterization of catalysts indicated that {Zr₆O₄} cluster core can be stabilized with a shell of carboxylate ligands, and the resulting ZrO-SO₃H was formed as a discrete molecular catalyst, exhibiting superior activity and recyclability for the cascade conversion of furfural to alkyl levulinate by the integration of transfer hydrogenation and alcoholysis in n-butanol. The yield of n-butyl levulinate can achieve as high as 91 % under the optimum conditions. Meanwhile, no leaching of the active species was found, which confirmed the structure of the Zr oxo cluster was air and moisture-stable. On the basis of the studies on the reaction kinetics and isotope tracking, the reaction mechanism was proposed accordingly.

Nature, Published online: 17 January 2023; doi:10.1038/d41586-023-00085-2

Synthesis
DOI: 10.1055/a-2004-1006

A mild and transition-metal-free arylsulfonylation reaction of arynes has been developed. Arynes generated in situ from 2-(trimethylsilyl)aryl triflates undergo nucleophilic addition with thiosulfonates to produce diaryl sulfones in 41–99% yield. The reaction can be scaled easily to gram-scale with the high yield maintained. Finally, mechanistic experiments showed that acetonitrile acted as a proton source.
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Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Ionic liquids (ILs) are distinctive organic salts that can dissolve lignocellulosic biomass and can also act as organocatalysts for homogeneous chemical modification reactions. IL catalysis varies depending on the designable structures of the cation and the anion, while the non-distillable nature and viscosity of ILs can be exploited as ingenious synthetic strategy for the sustainable and scalable production of lignocellulosic materials. The recent advances in our group are summarized in this Personal Account.

Abstract

Ionic liquids (ILs) are the only media that can allow the homogeneous organocatalytic reactions of lignocellulosic biomass (lignocellulose), since the designability of their cations and anions offers the dual functions of solubility and catalytic activity. This review provides an account of our recent achievements in the organocatalytic approaches for converting lignocellulose into polymer materials based on the principles of IL design that we have originally established. These methodologies include the simple and mild chemical modification of cellulose and lignin under high conversions, with high selectivity, and/or with efficient atom economy. Similar reactions and subsequent fractionation processes are applied to lignocellulose, and a highly productive reaction system is developed using a twin-screw extruder that is specific to the IL media.

In recent years, significant progress has been made in the design of recyclable polymers, enabling the regulation of the “polymerization-depolymerization” equilibrium and closed-loop recycling under mild conditions. This review summarizes the closed-loop recycling of poly(sulfur) esters, polycarbonates, polyacetals, polyolefins, and poly(disulfide) polymers, illustrates the challenges in this area, and provides an outlook on future directions.

Abstract

The development of modern society is closely related to polymer materials. However, the accumulation of polymer materials and their evolution in the environment causes not only serious environmental problems, but also waste of resources. Although physical processing can be used to reuse polymers, the properties of the resulting polymers are significantly degraded. Chemically recyclable polymers, a type of polymer that degrades into monomers, can be an effective solution to the degradation of polymer properties caused by physical recycling of polymers. The ideal chemical recycling of polymers, i. e., quantitative conversion of the polymer to monomers at low energy consumption and repolymerization of the formed monomers into polymers with comparable properties to the original, is an attractive research goal. In recent years, significant progress has been made in the design of recyclable polymers, enabling the regulation of the “polymerization-depolymerization” equilibrium and closed-loop recycling under mild conditions. This review will focus on the following aspects of closed-loop recycling of poly(sulfur) esters, polycarbonates, polyacetals, polyolefins, and poly(disulfide) polymer, illustrate the challenges in this area, and provide an outlook on future directions.

Nature Synthesis, Published online: 09 January 2023; doi:10.1038/s44160-022-00207-0

Publication date: February 2023

Source: Trends in Chemistry, Volume 5, Issue 2

Author(s): Jingxiang Low, Chao Zhang, Jun Ma, Dmitry Yu. Murzin, Yujie Xiong