CHEMICAL SCIENCE

Selective carboxylation of inactivated olefins with visible light catalyzed CO2


On September 15, 2022, Beijing time, the team of Professor Yu Dagang of Sichuan University published a research paper entitled “Visible-light photocatalytic di- and hydro-carboxylation of unactivated alkenes with CO2” on Nature Catalysis.

Based on the Continuous Photo-induced Electron Transfer (ConPET), this achievement establishes a strong reductive visible photocatalytic system, reduces CO2 to CO2 radical negative ions, and realizes the selective hydrogen/bicarboxylation reaction of inactivated olefins with the participation of visible photocatalytic CO2 for the first time, which provides a new idea for the high-value utilization of CO2. It also provides a new way for the synthesis of important carboxylic acids such as fatty acids and diacid monomers, which are expected to be applied to medicine, pesticides, food and materials. Yu Dagang is the corresponding author of the paper; Song Lei and Wang Wei are co-first authors.

Carbon dioxide (CO2) is a greenhouse gas with an important impact on climate change, and it is also a rich, inexpensive, non-toxic and renewable carbon resource. The use of CO2 to participate in chemical transformation and the efficient and large-scale preparation of high value-added chemicals and bulk chemicals are important ways to serve the major strategic needs of the country and are of great significance to promoting resource development and sustainable development. Among them, the use of CO2 precision synthesis of carboxylic acids and their derivatives with important applications in the fields of medicine and materials is an important research direction in the field of synthetic chemistry, although there have been gratifying progress, but there are still many problems. On the other hand, solar energy is an inexhaustible clean energy source, and visible light catalysis has the characteristics of green environmental protection, mild conditions and high functional group compatibility, so it has attracted much attention. Considering the wide range of olefin sources, in recent years, people have used visible light to catalyze the reaction of olefins with CO2, realizing a series of carboxylation reactions with different chemical and regional selectivity, and synthesizing a variety of important carboxylic acid products. However, in the examples reported, the substrate is mainly limited to activated olefins (e.g., aryl ethylene and acrylates). In contrast, inactivated olefins are generally more difficult to undergo carboxylation reactions with CO2 than activated olefins due to their lower reactivity. Therefore, it is of great significance to develop a new strategy to achieve visible light-catalyzed carboxylation reactions of inactivated olefins and CO2.

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Different from the common CO2 double electron activation method (nucleophilic reagents directly attack CO2), CO2 single electron activation mode (CO2 single electron reduction to form CO2 radical negative ions) has a unique reaction intermediate and reaction path, which can realize carboxylation reactions of different regions and chemical selectivity, thereby providing a new synthesis method for the synthesis of important carboxylic acid compounds. However, due to CO2 itself reduces the potential[E1/2 (CO2/CO2•−) = -2.21 V vs SCE]Higher, the energy of a single visible photon is limited, and it is difficult to directly reduce it using conventional visible photocatalytic systems, resulting in less reports of visible photocatalytic CO2 single electron activation. In addition, prior to this study, there had been no reports of CO2 radical negative ions attacking ordinary olefins by visible light catalysis.

In view of the above problems, Yu Dagang’s research group of the School of Chemistry of Sichuan University studied the promotion of CO2 transformation by visible light in the early stage (research summary: Acc. Chem. Res. 2021, 54, 2518) successfully realized the hydrogen carboxylation and remote bicarboxylation of visible photocatalytic CO2 involved in inactivated olefins. In this work, the Continuous Photo-induced Electron Transfer (ConPET) strategy was used to reduce CO2 to CO2 radical negative ions and attack inactivated olefins to obtain corresponding alkyl radicals. The alkyl radical can undergo intermolecular hydrogen atom transfer process to obtain selective hydrogen carboxylation products; In a well-designed substrate, the alkyl radical can also occur intramolecular hydrogen atom transfer (HAT), and then occur single electron reduction to form carbon negative ions, attacking another molecule CO2 to obtain the corresponding dibasic acid and its derivatives. The authors also further conducted detailed experimental studies on the novel reaction path, confirmed the existence of related intermediates through mechanism studies, and supported the process of Reducing CO2 by The ConPET mechanism from many aspects. The reaction has the advantages of mild conditions, wide applicability of substrates and good functional group compatibility. A range of alkyl olefins (including propylene and mixed olefins of industrial sources) can participate well in the reaction, with moderate to excellent yields to obtain unary carboxylic acids, dibasic carboxylic acids and unnatural α- amino acid derivatives.

Overall, the study is the first to achieve a selective hydrogen/bicarboxylation reaction of an inactivated olefin involved in visible light catalyzing CO2. The system realizes the activation of CO2 single electrons through continuous photoelectron transfer strategy, which provides a new idea for the high-value utilization of CO2, and also provides a new way for the synthesis of important carboxylic acids such as fatty acids and diacid monomers, which is expected to be applied to medicine, pesticides, food and materials.

The research was supported by the National Natural Science Foundation of China, the Sichuan Provincial Department of Science and Technology, Sichuan University and the Beijing Molecular Science Center. (Source: Science Network)

Related paper information:https://doi.org/10.1038/s41929-022-00841-z



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