Quantum dots enable direct alkylation and arylation of allylic C(sp3)–H bonds with hydrogen evolution by solar energy
TL;DR: The protocol bypasses stoichiometric oxidant or reductant and pre-functionalization of both the coupling partners and produces hydrogen (H2) as the byproduct and represents the first direct alkylation and arylation of allylic C(sp3)–H bonds with hydrogen evolution powered by solar energy.
About: This article is published in Chem.The article was published on 2021-05-13. It has received 43 citations till now. The article focuses on the topics: Allylic rearrangement.
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TL;DR: In this paper, the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H2 production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal are discussed.
Abstract: Merging hydrogen (H2) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H2 fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H2 can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H2 production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H2 production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H2 production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.
251 citations
TL;DR: In this article, a comprehensive review highlights the recent advances in CO2 photoreduction, including critical challenges such as light-harvesting, charge separation, and activation of CO2 molecules.
Abstract: Photocatalytic production of solar fuels from CO2 is a promising strategy for addressing global environmental problems and securing future energy supplies. Although extensive research has been conducted to date, numerous impediments to realizing efficient, selective, and stable CO2 reduction have yet to be overcome. This comprehensive review highlights the recent advances in CO2 photoreduction, including critical challenges such as light-harvesting, charge separation, and the activation of CO2 molecules. We present promising strategies for enhancing the photocatalytic activities and discuss theoretical insights and equations for quantifying photocatalytic performance, which are expected to afford a fundamental understanding of CO2 photoreduction. We then provide a thorough overview of both traditional photocatalysts such as metal oxides and state-of-the-art catalysts such as metal–organic frameworks and 2D materials, followed by a discussion of the origin of carbon in CO2 photoreduction as a means to further understand the reaction mechanism. Finally, we discuss the economic viability of photocatalytic CO2 reduction before concluding the review with proposed future research directions.
165 citations
TL;DR: In this article , the authors propose fundamentals, challenges, strategies, and prospects for photocatalytic CO 2 conversion research and propose a review of the current state of the art.
Abstract: Photocatalytic CO 2 conversion is vital technology to realize global carbon neutrality and generate future energy supplies. This review proposes fundamentals, challenges, strategies, and prospects for photocatalytic CO 2 conversion research.
165 citations
TL;DR: The cross-dehydrogenative coupling (CDC) reaction has been widely developed as one of the most sustainable and efficient synthesis strategies for constructing C-C bonds as mentioned in this paper, and a review summarizes the development of this field over the past 20 years, with a discussion on future trends and directions.
88 citations
TL;DR: In this article, a semiconductor quantum dot (QD) conjugate of tetrahydrofuran (THF) was demonstrated to activate α-C-H bond of THF via forming QDs/THF conjugates.
Abstract: As one of the most ubiquitous bulk reagents available, the intrinsic chemical inertness of tetrahydrofuran (THF) makes direct and site-selective C(sp 3 )-H bond activation difficult, especially under redox neutral condition. Here, we demonstrate that semiconductor quantum dots (QDs) can activate α-C-H bond of THF via forming QDs/THF conjugates. Under visible light irradiation, the resultant alkoxyalkyl radical directly engages in radical cross-coupling with α-amino radical from amino C-H bonds or radical addition with alkene or phenylacetylene, respectively. In contrast to stoichiometric oxidant or hydrogen atom transfer reagents required in previous studies, the scalable benchtop approach can execute α-C-H bond functionalization of THF only by a QD photocatalyst under redox-neutral condition, thus providing a broad of value added chemicals starting from bulk THFs reagent. The high step- and atom-economy, high efficiency and broad substrate scope make the photocatalysis with QDs and visible light promising in both academic and industrial setting.
30 citations
References
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TL;DR: 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.
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.
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Figure 1
Ruthenium polypyridyl complexes: versatile visible light photocatalysts.
6,252 citations
TL;DR: An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.
Abstract: In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.
3,550 citations
3,322 citations
TL;DR: This Review highlights the recent progress in the field of cross-dehydrogenative C sp 3C formations and provides a comprehensive overview on existing procedures and employed methodologies.
Abstract: Over the last decade, substantial research has led to the introduction of an impressive number of efficient procedures which allow the selective construction of CC bonds by directly connecting two different CH bonds under oxidative conditions. Common to these methodologies is the generation of the reactive intermediates in situ by activation of both CH bonds. This strategy was introduced by the group of Li as cross-dehydrogenative coupling (CDC) and discloses waste-minimized synthetic alternatives to classic coupling procedures which rely on the use of prefunctionalized starting materials. This Review highlights the recent progress in the field of cross-dehydrogenative C sp 3C formations and provides a comprehensive overview on existing procedures and employed methodologies.
1,528 citations
TL;DR: In this article, the electron spin resonance hyperfine splitting constants of spin adducts of interest in this area are tabulated and a brief comment on the source of the radical trapped is given.
1,487 citations