Iron Catalysis in Organic Synthesis

Imines as valuable intermediates are widely applied in pharmaceutical syntheses and organic transformation. However, the traditional imine synthesis involves unstable aldehydes, dehydrating agents, and Lewis acid catalysts. The topic of this review is focused on three new approaches, namely, the cross-coupling of alcohols with amines, the self-coupling of primary amines, and the oxidative dehydrogenation of secondary amines, utilizing much more readily available starting materials and green oxidant (O2/air) to furnish the imine products. The related catalysts are classified into metal, metal-free, photo-, and bioinspired catalysts. Particular emphasis is placed on the high-activity, low-cost, and versatile catalysts; key factors that affect the catalytic activity and reaction mechanisms are also highlighted.

Recent Advances in Aerobic Oxidation of Alcohols and Amines to Imines

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Porous aromatic frameworks (PAFs) represent an important category of porous solids. PAFs possess rigid frameworks and exceptionally high surface areas, and, uniquely, they are constructed from carbon-carbon-bond-linked aromatic-based building units. Various functionalities can either originate from the intrinsic chemistry of their building units or are achieved by postmodification of the aromatic motifs using established reactions. Specially, the strong carbon-carbon bonding renders PAFs stable under harsh chemical treatments. Therefore, PAFs exhibit specificity in their chemistry and functionalities compared with conventional porous materials such as zeolites and metal organic frameworks. The unique features of PAFs render them being tolerant of severe environments and readily functionalized by harsh chemical treatments. The research field of PAFs has experienced rapid expansion over the past decade, and it is necessary to provide a comprehensive guide to the essential development of the field at this stage. Regarding research into PAFs, the synthesis, functionalization, and applications are the three most important topics. In this thematic review, the three topics are comprehensively explained and aptly exemplified to shed light on developments in the field. Current questions and a perspective outlook will be summarized.

Porous Aromatic Frameworks (PAFs)

In recent years, radical C–C bond cleavage reactions have been increasingly understood and used to perform transformations that complement traditional ionic processes. However, to date radical C–C bond cleavage/functionalization reactions have not been the subject of a dedicated review. Herein we summarize the most recent and significant developments in the radical activation and functionalization of carbon–carbon bonds, with an emphasis on both synthetic outcomes and reaction mechanisms, and highlight how these radical C–C bond cleavage reactions enable challenging transformations.

Cleavage of carbon-carbon bonds by radical reactions.

We report an efficient, reusable, and selective 6-aminothiouracil (ATA)-modified Zr(IV)-based adsorbent (defined as UiO-66-ATA(Zr)) for lead ion removal in water. The adsorption equilibrium time an...

Efficient Selective Removal of Pb(II) by Using 6-Aminothiouracil-Modified Zr-Based Organic Frameworks: From Experiments to Mechanisms

Photocatalytic Properties and Mechanistic Insights into Visible Light-Promoted Aerobic Oxidation of Sulfides to Sulfoxides via Tin Porphyrin-Based Porous Aromatic Frameworks

An imidazolium-based ionic liquid (IL) functionalized zinc porphyrin catalyst was successfully synthesized for the first time, and was employed as an efficient catalyst for CO2 transformation including both the chemoselective synthesis of cyclic carbonates from various epoxides and the regioselective synthesis of 5-aryl-2-oxazolidinones from N-substituted aziridines. Detailed studies demonstrated that the intramolecular cooperative effect between the coordinated zinc center (electrophile) and flexible bromine anions (nucleophile) could mediate these reactions effectively under solvent-free and mild conditions. More importantly, the IL-based catalyst could be readily recovered by solvent precipitation and reused with retention of high activity and selectivity more than ten times based on the concept of “one-phase catalytic coupling with two-phase separation”.

Imidazolium-based ionic liquid decorated zinc porphyrin catalyst for converting CO2 into five-membered heterocyclic molecules

Herein, CuO/Bi2MoO6 hybrid nanosheets were prepared as a surface multifunctional photocatalyst for gas-phase toluene oxidation with high conversion (>99%). Aberration-corrected scanning transmission electron microscopy suggested that CuO species were highly dispersed on the nanosheets. X-ray absorption fine structure spectra indicated that the distorted and stretched Cu-O coordination structures in CuO/Bi2MoO6 nanosheets would provide open active sites. In situ Fourier transform infrared and density functional theory results showed that toluene molecules could be chemisorbed and activated on the active sites of CuO/Bi2MoO6 nanosheets by the C-H group forming CuO/Bi2MoO6···Ph-CH3 surface complex compounds. These would induce electron-hole transfer and initiate photocatalytic reactions under visible light irradiation. The corresponding intermediates of benzaldehyde and benzoic acid would be detected by in situ diffuse reflectance infrared Fourier transform spectroscopy. Furthermore, the synergistic effect of CuO and Bi2MoO6 nanosheets could monitor charge dynamics to facilitate their respective transmission from photoexcitation sites to active centers. This work provides new insights into the essence of visible-light-driven surface photocatalysis and is expected to promote the design of novel and more effective photocatalysts at the molecular level.

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation.

Graphitic carbon nitride (g ­ C3N4, CN) has been widely used as a photocatalyst due to its high stability and suitable band gap. However, its further development is limited due to inefficient light harvesting and rapid recombination of photogenerated carriers. In this study, a visible-light-responsive zinc porphyrin (ZnP)/CN heterojunction photocatalyst was synthesized by the combination of CN and a zinc-porphyrin-conjugated microporous polymer (ZnP-CMP). ZnP/CN exhibited excellent photocatalytic activity for the oxidative coupling of amines to imines under visible-light irradiation. The efficiency of the as-developed photocatalyst was 25 times greater than that of CN and about 2 times greater than that of ZnP-CMP. The significantly enhanced catalytic efficiency was attributed to the promotion of visible-light harvesting and photogenerated charge mobility via the introduction of ZnP-CMP. The ZnP/CN heterojunction photocatalyst also exhibited excellent broad substrate scope, stability, and reusability.

Enhancement of the visible-light absorption and charge mobility in a zinc porphyrin polymer/g-C3N4 heterojunction for promoting the oxidative coupling of amines

Xiantai Zhou

Papers

Efficient Selective Removal of Pb(II) by Using 6-Aminothiouracil-Modified Zr-Based Organic Frameworks: From Experiments to Mechanisms

Photocatalytic Properties and Mechanistic Insights into Visible Light-Promoted Aerobic Oxidation of Sulfides to Sulfoxides via Tin Porphyrin-Based Porous Aromatic Frameworks

Imidazolium-based ionic liquid decorated zinc porphyrin catalyst for converting CO2 into five-membered heterocyclic molecules

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation.

Enhancement of the visible-light absorption and charge mobility in a zinc porphyrin polymer/g-C3N4 heterojunction for promoting the oxidative coupling of amines