Query: Organic catalysis

Candidate papers:

abstract: A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single electron transfer (SET) processes with organic substrates upon photoexcitation with visible light. Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2' bipyridine) ruthenium(II) or Ru(bpy)32+ (Figure 1) These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+ that it may engage in bimolecular electron transfer reactions in competition with deactivation pathways.3 Although these species are poor single electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single electron transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes. Figure 1 Ruthenium polypyridyl complexes: versatile visible light photocatalysts. The ability of Ru(bpy)32+ and related complexes to function as visible light photocatalysts has been recognized and extensively investigated for applications in inorganic and materials chemistry. In particular, photoredox catalysts have been utilized to accomplish the splitting of water into hydrogen and oxygen4 and the reduction of carbon dioxide to methane.5 Ru(bpy)32+ and its analogues have been used (i) as components of dye sensitized solar cells6 and organic light emitting diodes,7 (ii) to initiate polymerization reactions,8 and (iii) in photo dynamic therapy.9 Until recently, however, these complexes had been only sporadically employed as photocatalysts in the area of organic synthesis. The limited exploration of this area is perhaps surprising, as single electron, radical processes have long been employed in C C bond construction and often provide access to reactivity that is complementary to that of closed shell, two electron pathways.10 In 2008, concurrent reports from the Yoon group and our own lab detailed the use of Ru(bpy)32+ as a visible light photoredox catalyst to perform a [2 2] cycloaddition11 and an a alkylation of aldehydes,12 respectively. Shortly thereafter, Stephenson and co workers disclosed a photoredox reductive dehalogenation of activated alkyl halides mediated by the same catalyst.13 The combined efforts of these three research groups have helped to initiate a renewed interest in this field, prompting a diversity of studies into the utility of photoredox catalysis as a conceptually novel approach to synthetic organic reaction development. Much of the promise of visible light photoredox catalysis hinges on its ability to achieve unique, if not exotic bond constructions that are not possible using established protocols. For instance, photoredox catalysis may be employed to perform overall redox neutral reactions. As both oxidants and reductants may be transiently generated in the same reaction vessel, photoredox approaches may be used to develop reactions requiring both the donation and the reception of electrons at disparate points in the reaction mechanism. This approach stands in contrast to methods requiring stoichiometric chemical oxidants and reductants, which are often incompatible with each other, as well as to electrochemical approaches, which are not amenable to redox neutral transformations. Furthermore, single electron transfer events often provide access to radical ion intermediates having reactivity patterns fundamentally different from those of their ground electronic or excited states.14 Access to these intermediates using other means of activation is often challenging or requires conditions under which their unique reactivity cannot be productively harnessed. At the same time, photoredox catalysts such as Ru(bpy)32+ may also be employed to generate radicals for use in a diverse range of established radical chemistries. Photoredox reactions occur under extremely mild conditions, with most reactions proceeding at room temperature without the need for highly reactive radical initiators. The irradiation source is typically a commercial household light bulb, a significant advantage over the specialized equipment required for processes employing high energy ultraviolet (UV) light. Additionally, because organic molecules generally do not absorb visible light, there is little potential for deleterious side reactions that might arise from photoexcitation of the substrate itself. Finally, photoredox catalysts may be employed at very low loadings, with 1 mole or less being typical. This Review will highlight the early work on the use of transition metal complexes as photoredox catalysts to promote reactions of organic compounds (prior to 2008) as well as cover the surge of work that has appeared since 2008. We have for the most part grouped reactions according to whether the organic substrate undergoes reduction, oxidation, or a redox neutral reaction and throughout have sought to highlight the variety of reactive intermediates that may be accessed via this general reaction manifold.15 Studies on the use of transition metal complexes as visible light photocatalysts for organic synthesis have benefited tremendously from advances in the related fields of organic and semiconductor photocatalysis. Many organic molecules may function as visible light photocatalysts; analogous to metal complexes such as Ru(bpy)32+ organic dyes such as eosin Y, 9,10 dicyanoanthracene, and triphenylpyrylium salts absorb light in the visible region to give excited states capable of single electron transfer. These catalysts have been employed to achieve a vast range of bond forming reactions of broad utility in organic synthesis.16 Visible light photocatalysis has also been carried out with heterogeneous semiconductors such as mesoporous carbon nitride17 and various metal oxides and sulfides.18 These approaches are often complementary to photoredox catalysis with transition metal polypyridyl complexes, and we have referred to work in these areas when it is similar to the chemistry under discussion. However, an in depth discussion of the extensive literature in these fields is outside the scope of this Review, and readers are directed to existing reviews on these topics.16 18
author_names: Christopher K Prier

Danica A Rankic

David W C MacMillan
title: Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis.
venue: Chemical reviews
year: 2013

abstract: More than 95% (in volume) of all of today's chemical products are manufactured through catalytic processes, making research into more efficient catalytic materials a thrilling and very dynamic research field. In this regard, metal organic frameworks (MOFs) offer great opportunities for the rational design of new catalytic solids, as highlighted by the unprecedented number of publications appearing over the past decade. In this review, the recent advances in the application of MOFs in heterogeneous catalysis are discussed. MOFs with intrinsic thermocatalytic activity, as hosts for the incorporation of metal nanoparticles, as precursors for the manufacture of composite catalysts and those active in photo and electrocatalytic processes are critically reviewed. The review is wrapped up with our personal view on future research directions.
author_names: Anastasiya Bavykina

Nikita Kolobov

Il Son Khan

Jeremy A Bau

Adrian Ramirez

Jorge Gascon
title: Metal Organic Frameworks in Heterogeneous Catalysis: Recent Progress, New Trends, and Future Perspectives.
venue: Chemical reviews
year: 2020

abstract: Organodiselenides are an important class of compounds characterized by the presence of two adjacent covalently bonded selenium nuclei. Among them, diaryldiselenides and their parent compound diphenyl diselenide attract continuing interest in chemistry as well as in close disciplines like medicinal chemistry, pharmacology and biochemistry. A search in SCOPUS database has revealed that in the last three years 105 papers have been published on the archetypal diphenyl diselenide and its use in organic catalysis and drug tests. The reactivity of the Se Se bond and the redox properties of selenium make diselenides efficient catalysts for numerous organic reactions, such as Bayer Villiger oxidations of aldehydes/ketones, epoxidations of alkenes, oxidations of alcohols and nitrogen containing compounds. In addition, organodiselenides might find application as mimics of glutathione peroxidase (GPx) a family of enzymes, which, besides performing other functions, regulate the peroxide tone in the cells and control the oxidative stress level. In this review, the essential synthetic and reactivity aspects of organoselenides are collected and rationalized using the results of accurate computational studies, which have been carried out mainly in the last two decades. The results obtained in silico provide a clear explanation of the anti oxidant activity of organodiselenides and more in general of their ability to reduce hydroperoxides. At the same time, they are useful to gain insight into some aspects of the enzymatic activity of the GPx, inspiring novel elements for rational catalyst and drug design.
author_names: Marco Dalla Tiezza

Giovanni Ribaudo

Laura Orian
title: Organodiselenides: Organic Catalysis and Drug Design Learning from Glutathione Peroxidase
venue: Current Organic Chemistry
year: 2019

author_names: Benjamin List

Oleg Grossmann
title: Cinchona Alkaloids in Organic Catalysis
venue: Synfacts
year: 2019

abstract: To meet the ever increasing global demand for energy, conversion of solar energy to chemical/thermal energy is very promising. Light mediated catalysis, including photocatalysis (organic transformations, water splitting, CO2 reduction, etc. and photothermal catalysis play key roles in solar to chemical/thermal energy conversion via the light matter interaction. The major challenges in traditional semiconductor photocatalysts include insufficient sunlight utilization, charge carrier recombination, limited exposure of active sites, and particularly the difficulty of understanding the structure activity relationship. Metal organic frameworks (MOFs) featuring semiconductor like behavior, have recently captured broad interest toward photocatalysis and photothermal catalysis because of their well defined and tailorable porous structures, high surface areas, etc. These advantages are beneficial for rational structural modulation for improved light harvesting and charge separation as well as other effects, greatly helping to address the aforementioned challenges and especially facilitating the establishment of the structure activity relationship. Therefore, it is increasingly important to summarize this research field and provide in depth insight into MOF based photocatalysis and photothermal catalysis to accelerate the future development. In this Account, we have summarized the recent advances in these two directly relevant applications, photocatalysis and photothermal catalysis, mainly focusing on the results in our lab. Given the unique structural features of MOFs, we have put an emphasis on rational material design to optimize the components and performance and to understand related mechanisms behind the enhanced activity. This Account starts by presenting an overview of solar energy conversion by catalysis. We explain why MOFs can be promising photocatalysts and exemplify the semiconductor like behavior of MOFs. More importantly, we show that MOFs provide a powerful platform to study photocatalysis, in which the involved three key processes, namely, light harvesting, electron hole separation, and surface redox reactions, can be rationally improved. Meanwhile, the structure activity relationship and charge separation dynamics are illustrated in this part. In addition, MOFs for photothermal catalysis have been introduced that are based on the photothermal effect of plasmonic metals and/or MOFs, together with light driven electronic state optimization of active sites, toward enhanced heterogeneous organic reactions. Finally, our brief outlooks on the current challenges and future development of MOF photocatalysis and photothermal catalysis are provided. It is believed that this Account will afford significant understanding and inspirations toward solar energy conversion over MOF based catalysts.
author_names: Juan-Ding Xiao

Hai-Long Jiang
title: Metal Organic Frameworks for Photocatalysis and Photothermal Catalysis.
venue: Accounts of chemical research
year: 2019

abstract: Metal organic frameworks (MOFs) have drawn wide attention as potential catalysts, offering high densities of catalytic sites in high area porous solids, some with stabilities at high temperatures. The field is at an early stage, characterized by numerous discoveries and novel demonstrations of catalytic properties associated with the crystalline structures of MOFs, but applications of MOFs as catalysts are still lacking. In this perspective we summarize advantages and limitations of MOFs as catalysts and fundamental issues to be addressed about their potential applications. MOF framework compositions and pore structures can strongly influence catalytic performance, allowing, for example, shape selective and bifunctional catalysis, but research is needed to quantify reaction/transport processes in MOFs, identify catalytic sites, and determine intrinsic catalytic reaction rates. Progress is hindered by the lack of understanding of the heterogeneity of MOFs, with catalytic sites sometimes being in structures.
author_names: D S Yang

Bruce C Gates
title: Catalysis by Metal Organic Frameworks: Perspective and Suggestions for Future Research
year: 2019

abstract: Abstract Metal organic frameworks (MOFs) also known as porous coordination polymers (PCPs) are a unique class of porous crystalline materials that are constructed by metal ions/clusters and organic ligands. The intriguing, numerous and tailorable structures as well as permanent porosity of MOFs make them very promising for a variety of potential applications, especially in catalysis. In this review, we systematically summarize the recent progress of MOF based materials (including pristine MOFs, MOF composites, and MOF derivatives) for heterogeneous catalysis, photocatalysis and electrocatalysis, according to the category of active site origin. We clearly indicate the significant strengths (and also weaknesses) of the MOF based materials, in reference to traditional catalysts, in catalytic studies. The challenges and opportunities in regard to the MOF based materials for catalysis have also been critically discussed.
author_names: Dandan Li

Hai-Qun Xu

Long Jiao

Hailong Jiang
title: Metal organic frameworks for catalysis: State of the art, challenges, and opportunities
venue: EnergyChem
year: 2019

author_names: Benny K G Theng
title: Organic Catalysis by Clay Supported Reagents
year: 2018

abstract: Organic catalysis in ring opening polymerization (ROP) has become a powerful alternative to more traditional metal based catalysts. The field has developed to a point at which there are not only excellent low cost and easy to use organocatalysts for day to day polymerizations, but the ability to precisely control the synthesis of advanced polymer architectures and ROP monomers that are extremely challenging to polymerize with other catalysts now exists. This viewpoint article will highlight the key advances in organocatalyst design with the aim of encouraging the wider application of organic catalysts in ROP.
author_names: Andrew P Dove
title: Organic Catalysis for Ring Opening Polymerization
year: 2012

abstract: Metal organic frameworks (MOFs) have emerged as a promising class of materials with several unique properties, such as high porosity, diverse composition, tunable pore structures, and versatile functionality. These characteristics enable MOFs to show potential in the field of heterogeneous catalysis. To satisfy the practical applications of MOFs, controllable integration of MOFs and functional materials (e.g. metal nanoparticles, quantum dots, polyoxometalates, molecular species, enzymes, silica, and polymers) can enhance the characteristics of MOFs through activity improvement and framework stabilization. In MOF composites/hybrids, functional materials can cooperatively work with MOFs to show enhanced catalytic activity, selectivity, and stability in a variety of chemical transformations. This review provides an overview of the significant advances in the development of diverse MOF composites/hybrids with special emphases on the preparation and catalytic applications.
author_names: Liyu Chen

Qiang Xu
title: Metal Organic Framework Composites for Catalysis
venue: Matter
year: 2019