skip to main content


Title: Asymmetric Photocatalysis Enabled by Chiral Organocatalysts
Abstract

Visible‐light photocatalysis has advanced as a versatile tool in organic synthesis. However, attaining precise stereocontrol in photocatalytic reactions has been a longstanding challenge due to undesired photochemical background reactions and the involvement of highly reactive radicals or radical ion intermediates generated under photocatalytic conditions. To address this problem and expand the synthetic utility of photocatalytic reactions, a number of innovative strategies, including mono‐ and dual‐catalytic approaches, have recently emerged. Of these, exploiting chiral organocatalysis, such as enamine catalysis, iminium‐ion catalysis, Brønsted acid/base catalysis, andN‐heterocyclic carbene catalysis, to induce chirality transfer of photocatalytic reactions has been widely explored. This Review aims to provide a current, comprehensive overview of asymmetric photocatalytic reactions enabled by chiral organocatalysts published through June 2021. The substrate scope, advantages, limitations, and proposed reaction mechanisms of each reaction are discussed. This review should serve as a reference for the development of visible‐light‐induced asymmetric photocatalysis and promote the improvement of the chemical reactivity and stereoselectivity of these reactions.

 
more » « less
Award ID(s):
1848463
NSF-PAR ID:
10303411
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
ChemCatChem
Volume:
14
Issue:
1
ISSN:
1867-3880
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Hybrid plasmonic nanostructures are built on plasmonic metalnanostructures surrounded by catalytic metals or metal oxides. Recent studies have shown that hybrid plasmonic nanocatalysts can concurrently utilize thermal energy and photon stimuli and exhibit high catalytic activity, selectivity, and stability that are not attainable in conventional purely thermally activated catalytic processes. The hybrid plasmonic photocatalytic approach has recently emerged as an attractive concept for the conversion of solar energy into chemical energy, the distributed synthesis of valuable chemicals such as ammonia with little to no requirement of external heating, and the development of coke‐resistant and selective catalytic processes. The field of hybrid plasmonic photocatalysis has grown tremendously in the last decade. In this review article, the advantages of visible‐light‐augmented hybrid plasmonic photocatalysis over conventional pure thermally activated heterogeneous catalysis are discussed. Fundamental insights are provided into photocatalytic mechanisms by which the photoexcited charge carriers (electrons and holes) are formed and transferred to adsorbates triggering chemical transformations on the surface of hybrid plasmonic nanocatalysts. Computational modeling used for predicting and understanding the photocatalytic activity and selectivity on hybrid plasmonic nanostructures is also reviewed. The review closes with a discussion of the current challenges, new opportunities, and future outlook for hybrid plasmonic photocatalysis.

     
    more » « less
  2. Abstract

    This personal account concerns novel recent discoveries in the area of mesoporous materials. Most of the papers discussed have been published within the last two to three years. A major emphasis of most of these papers is the synthesis of unique mesoporous materials by a variety of synthetic methods. Many of these articles focus on the control of the pore sizes and shapes of mesoporous materials. Synthetic methods of various types have been used for such control of porosity including soft templating, hard templating, nano‐casting, electrochemical methods, surface functionalization, and trapping of species in pores. The types of mesoporous materials range from carbon materials, metal oxides, metal sulfides, metal nitrides, carbonitriles, metal organic frameworks (MOFs), and composite materials. The vast majority of recent publications have centered around biological applications with a majority dealing with drug delivery systems. Several other bio‐based articles on mesoporous systems concern biomass conversion and biofuels, magnetic resonance imaging (MRI) studies, ultrasound therapy, enzyme immobilization, antigen targeting, biodegradation of inorganic materials, applications for improved digestion, and antitumor activity. Numerous nonbiological applications of mesoporous materials have been pursued recently. Some specific examples are photocatalysis, photo‐electrocatalysis, lithium ion batteries, heterogeneous catalysis, extraction of metals, extraction of lanthanide and actinide species, chiral separations and catalysis, capturing and the mode of binding of carbon dioxide (CO2), optical devices, and magneto‐optical devices. Of this latter class of applications, heterogeneous catalysis is predominant. Some of the types of catalytic reactions being pursued include hydrogen generation, selective oxidations, aminolysis, Suzuki coupling and other coupling reactions, oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and bifunctional catalysis. For perspective, there have been over 40,000 articles on mesoporous materials published in the last 4 years and about 1388 reviews. By no means is this personal account thorough or all inclusive. One objective has been to choose a variety of articles of different types to obtain a flavor of the breadth of diversity involved in the area of mesoporous materials.

     
    more » « less
  3. Abstract

    The effect of rare earth (RE) single atoms on photocatalytic activity is very complex due to its special electronic configuration, which leads to few reports on the RE single atoms. Here, Dy3+single atom composite photocatalysts are successfully constructed based on both the special role of Dy3+and the special advantages of CdS/g‐C3N4heterojunction in the field of photocatalysis. The results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO2molecular activation of rare‐earth single atom and 4flevels as electron transport bridge are fully exploited. It is exciting that under visible‐light irradiation, the catalytic performance of CdS:Dy3+/g‐C3N4is6.9 times higher than that of pure g‐C3N4. The catalytic performance of CdS:Dy3+and CdS:Dy3+/g‐C3N4are7 and13.7 times higher than those of pure CdS, respectively. Besides, not all RE ions are suitable for charge transfer bridges, which is not only related to the 4flevels of RE ions but also related to the bandgap structure of CdS and g‐C3N4. The pattern of combining single‐atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.

     
    more » « less
  4. CuBiW 2 O 8 (CBTO), with a band gap of 1.9–2.0 eV, responds to a wide region of the electromagnetic spectrum, which makes it a good candidate for solar-driven photocatalytic energy conversion and water treatment. We have previously demonstrated a Cu-rich solid state approach that enables the synthesis of CBTO accompanied by thermodynamically stable Bi 2 WO 6 impurity. Here, we describe an improved synthesis protocol with decreased impurity and synthesis time, and the first demonstration of CBTO as a functional material using photocatalytic Cr( vi ) photoreduction as a probe reaction. Transient absorption spectroscopy (TAS) was performed to investigate the ultrafast dynamics of the charge carriers after photoexcitation. The presence of two populations of photoexcited carriers was found, including short-lived free carriers with ∼10 ps lifetime and long-lived shallowly-trapped carriers with ∼1 ns lifetime. Together with carrier mobilities measured in our previous study, the new TAS results indicate that the long-lived charges have diffusion lengths similar to the CBTO particle size and were likely responsible for the majority of the photocatalytic activity. High activity of CBTO for Cr( vi ) photoreduction (∼100% reduction of 5 mg L −1 of Cr( vi ) in 15 minutes) was demonstrated, which clearly establishes the promise of this novel oxide for visible light-driven photocatalytic applications. Radical quenching experiments indicate that both ˙OH radicals and O 2 ˙ − radicals are produced by CBTO and are involved in the photoreduction of Cr( vi ). Repeated photocatalysis tests and analysis of the surface after the reaction show that CBTO is a stable and potentially reusable catalyst. Insights gained from correlating the synthesis conditions, carrier dynamics, and reactive species suggests that CBTO prepared with the improved protocol would be a favorable choice for photocatalytic reactions such as water decontamination from organic pollutants, water splitting, and solar fuel generation using visible light. 
    more » « less
  5. Abstract

    Efficient utilization of sunlight in photocatalysis is widely recognized as a promising solution for addressing the growing energy demand and environmental issues resulting from fossil fuel consumption. Recently, there have been significant developments in various near‐infrared (NIR) light‐harvesting systems for artificial photosynthesis and photocatalytic environmental remediation. This review provides an overview of the most recent advancements in the utilization of NIR light through the creation of novel nanostructured materials and molecular photosensitizers, as well as modulating strategies to enhance the photocatalytic processes. A special focus is given to the emerging two‐photon excitation NIR photocatalysis. The unique features and limitations of different systems are critically evaluated. In particular, it highlights the advantages of utilizing NIR light and two‐photon excitation compared to UV–visible irradiation and one‐photon excitation. Ongoing challenges and potential solutions for the future exploration of NIR light‐responsive materials are also discussed.

     
    more » « less