1
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Garwood JJA, Chen AD, Nagib DA. Radical Polarity. J Am Chem Soc 2024. [PMID: 39363280 DOI: 10.1021/jacs.4c06774] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/05/2024]
Abstract
The polarity of a radical intermediate profoundly impacts its reactivity and selectivity. To quantify this influence and predict its effects, the electrophilicity/nucleophilicity of >500 radicals has been calculated. This database of open-shell species entails frequently encountered synthetic intermediates, including radicals centered at sp3, sp2, and sp hybridized carbon atoms or various heteroatoms (O, N, S, P, B, Si, X). Importantly, these computationally determined polarities have been experimentally validated for electronically diverse sets of >50 C-centered radicals, as well as N- and O- centered radicals. High correlations are measured between calculated polarity and quantified reactivity, as well as within parallel sets of competition experiments (across different radical types and reaction classes). These multipronged analyses show a strong relationship between the computed electrophilicity, ω, of a radical and its relative reactivity (krel vs Δω slopes up to 40; showing mere Δω of 0.1 eV affords up to 4-fold rate enhancement). We expect this experimentally validated database will enable reactivity and selectivity prediction (by harnessing polarity-matched rate enhancement) and assist with troubleshooting in synthetic reaction development.
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Affiliation(s)
- Jacob J A Garwood
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Andrew D Chen
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - David A Nagib
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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2
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An Q, Chang L, Pan H, Zuo Z. Ligand-to-Metal Charge Transfer (LMCT) Catalysis: Harnessing Simple Cerium Catalysts for Selective Functionalization of Inert C-H and C-C Bonds. Acc Chem Res 2024; 57:2915-2927. [PMID: 39291873 DOI: 10.1021/acs.accounts.4c00510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/19/2024]
Abstract
ConspectusChemists have long pursued harnessing light energy and photoexcitation processes for synthetic transformations. Ligand-to-metal charge transfer (LMCT) in high-valent metal complexes often triggers bond homolysis, generating oxidized ligand-centered radicals and reduced metal centers. While photoinduced oxidative activations can be enabled, this process, typically seen as photochemical decomposition, remains underexplored in catalytic applications. To mitigate decomposition during LMCT excitation, we developed a catalytic cycle integrating in situ coordination, LMCT, and ligand homolysis to activate ligated alcohols transiently into alkoxy radicals. This catalytic approach leverages Ce(IV) LMCT excitation and highly reactive alkoxy radical intermediates for selective functionalizations of C(sp3)-H and C(sp3)-C(sp3) bonds under mild conditions. In this Account, we discuss these advancements, highlighting the practical utility of cost-effective cerium salts as catalysts and their potential to develop innovative transformations, addressing long-standing synthetic challenges.Selective functionalization of chemically inert C(sp3)-H bonds has long posed a significant challenge. We first detail our research using LMCT-enabled alkoxy radical-mediated hydrogen atom transfer (HAT) processes for selective C(sp3)-H functionalizations. Using readily available CeCl3, we established a general protocol for employing free alcohols in the Barton reaction. By integrating LMCT and HAT catalysis, we introduced a selective photocatalytic strategy for functionalizing feedstock alkanes, converting gaseous hydrocarbons into valuable products. Employing simple cerium salts like Ce(OTf)3 and CeCl3, we achieved selective C-H amination of methane and ethane at ambient temperature, achieving turnover numbers of 2900 and 9700, respectively. This catalytic manifold has been further exploited to address the site-selectivity challenge in the C-H functionalization of linear alkanes. The use of methanol as a cocatalyst enabled preferential functionalization of the most electron-rich sites, achieving a high intrinsic selectivity over 12:1 of secondary vs primary sites in pentane and hexane.Next, we discuss the catalytic utilization of alkoxy-radical-mediated β-scission, a frequently encountered side reaction in HAT transformations, for selective cleavage and functionalization of C-C bonds. The versatility of the LMCT catalytic platform facilitates the generation of alkoxy radicals from various free alcohols. In our initial demonstration of LMCT-enabled C(sp3)-C(sp3) bond activation, we developed a cerium-catalyzed ring-opening and amination of cycloalkanols, providing an effective protocol for cleaving unstrained C-C bonds. This strategy has been successfully applied to various radical cross-coupling processes, leading to innovative transformations such as ring expansions of cycloalkanols, dehydroxymethylative alkylation, amination, alkenylation, and ring expansions of cyclic ketones. These results highlight the synthetic potential of employing LMCT-mediated β-scission and ubiquitous C-C bonds as unconventional functional handles for generating molecular complexity.Lastly, we delve into our mechanistic investigations. Beyond the catalytic application of Ce(IV) LMCT in various transformations, we have undertaken comprehensive mechanistic studies. These investigations encompass characterization of Ce(IV) alkoxide complexes to elucidate their structures, evaluation of their photoactivity and selectivity in radical generation, and elucidation of kinetic pathways associated with transient LMCT excited states. Our research has revealed ultrafast bond homolysis, back electron transfer, and the selectivity of heteroleptic complexes in homolysis, providing crucial insights for advancing LMCT catalysis.
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Affiliation(s)
- Qing An
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Liang Chang
- School of Pharmacy, Nanjing University of Chinese Medicine, Nanjing 210023, China
| | - Hui Pan
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Zhiwei Zuo
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
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Zhou P, Ding L, Liu Y, Song H, Wang Q. Iron-Catalyzed Electrophotochemical α-Functionalization of a Silylcyclobutanol. Org Lett 2024; 26:7094-7099. [PMID: 39150853 DOI: 10.1021/acs.orglett.4c02279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2024]
Abstract
Four-membered ring structure is important in organic chemistry, and selective cleavage and functionalization of these strained rings are of great interest. However, direct α-functionalization of cyclobutanols is rarely reported because of the high O-H bond dissociation energy and the occurrence of β-scission of C-C bonds in these alcohols. Recently, transition-metal catalysis has facilitated alkoxy radical generation. Herein, we report a method for electrophotochemical α-functionalization of a silylcyclobutanol via visible-light-induced LMCT reactions of M-alkoxy complexes. Introduction of the silyl group into the cyclobutanol structure favored fast [1,2]-silyl transfer over ring opening, thus allowing the generation of α-functionalized products.
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Affiliation(s)
- Pan Zhou
- State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, College of Chemistry, Frontiers Science Center for New Organic Matter, Nankai University, Tianjin 300071, China
| | - Ling Ding
- State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, College of Chemistry, Frontiers Science Center for New Organic Matter, Nankai University, Tianjin 300071, China
| | - Yuxiu Liu
- State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, College of Chemistry, Frontiers Science Center for New Organic Matter, Nankai University, Tianjin 300071, China
| | - Hongjian Song
- State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, College of Chemistry, Frontiers Science Center for New Organic Matter, Nankai University, Tianjin 300071, China
| | - Qingmin Wang
- State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, College of Chemistry, Frontiers Science Center for New Organic Matter, Nankai University, Tianjin 300071, China
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Fernandes AJ, Giri R, Houk KN, Katayev D. Review and Theoretical Analysis of Fluorinated Radicals in Direct C Ar-H Functionalization of (Hetero)arenes. Angew Chem Int Ed Engl 2024; 63:e202318377. [PMID: 38282182 DOI: 10.1002/anie.202318377] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 01/25/2024] [Accepted: 01/26/2024] [Indexed: 01/30/2024]
Abstract
We highlight key contributions in the field of direct radical CAr- H (hetero)aromatic functionalization involving fluorinated radicals. A compilation of Functional Group Transfer Reagents and their diverse activation mechanisms leading to the release of radicals are discussed. The substrate scope for each radical is analyzed and classified into three categories according to the electronic properties of the substrates. Density functional theory computational analysis provides insights into the chemical reactivity of several fluorinated radicals through their electrophilicity and nucleophilicity parameters. Theoretical analysis of their reduction potentials also highlights the remarkable correlation between electrophilicity and oxidizing ability. It is also established that highly fluorinated radicals (e.g. ⋅OCF3) are capable of engaging in single-electron transfer (SET) processes rather than radical addition, which is in good agreement with experimental literature data. A reactivity scale, based on activation barrier of addition of these radicals to benzene is also elaborated using the high accuracy DLPNO-(U)CCSD(T) method.
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Affiliation(s)
- Anthony J Fernandes
- Department für Chemie und Biochemie, Universität Bern, Freiestrasse 3, 3012, Bern, Switzerland
| | - Rahul Giri
- Department für Chemie und Biochemie, Universität Bern, Freiestrasse 3, 3012, Bern, Switzerland
| | - Kendall N Houk
- Department of Chemistry and Biochemistry, University of California, 90095, Los Angeles, California, United States
| | - Dmitry Katayev
- Department für Chemie und Biochemie, Universität Bern, Freiestrasse 3, 3012, Bern, Switzerland
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5
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Zou Y, Yu F, Liu X, Zu L. CH 3O Substitution Effect Revisited in the Vibrationally Resolved Laser-Induced Fluorescence Spectra of Methoxycyclohexoxy Radicals. J Phys Chem A 2024; 128:1025-1031. [PMID: 38301214 DOI: 10.1021/acs.jpca.3c07154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2024]
Abstract
The oxy-substituted alkoxy radicals have attracted wide attention due to the increasing application of oxygenated volatile organic compounds as fuel additives and solvents. Direct detection of these intermediate radicals is desired for measuring the reaction rate and investigating the oxidation mechanism of organic compounds in the atmosphere. A charge-transfer excited state induced by CH3O substitution was identified in our previous study of 3-methoxy-1-propoxy radical [Xue, J. Phys. Chem. Chem. Phys. 2021, 23, 2586]. As the C-C bonds of chain alkoxy radicals can freely rotate, further studies are needed to understand the mechanism of this long-range charge-transfer effect. In this work, vibrational-resolved laser-induced fluorescence (LIF) spectra of 3- and 4-methoxycyclohexoxy radicals were obtained under jet-cooled conditions. A large red-shift of ∼454 cm-1 of the origin band was observed when the CH3O substituent moved from the δ site to the γ site of the cyclohexoxy radical. The LIF spectra are assigned to 3-cis (e, e) and 4-trans (e, e) conformers, respectively, with the assistance of structural optimization and electron excitation studies conducted at the CAM-B3LYP/6-311++G(d,p) level of theory. Natural transition orbital analysis reveals that the intramolecular charge transfer from the C-O-C p orbital to the radical O p orbital in 3-methoxycyclohexoxy has a strong effect on the radical CO σ → O p excitation and hence results in a spectral change. On the other hand, the spectral effect of CH3O substitution almost vanishes at δ carbon. The results propose a through-bond interaction between CH3O and radical CO groups.
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Affiliation(s)
- Yizhen Zou
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Fengming Yu
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Xiaoyu Liu
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Lily Zu
- College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
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Groff BD, Koronkiewicz B, Mayer JM. Polar Effects in Hydrogen Atom Transfer Reactions from a Proton-Coupled Electron Transfer (PCET) Perspective: Abstractions from Toluenes. J Org Chem 2023; 88:16259-16269. [PMID: 37978890 PMCID: PMC10841608 DOI: 10.1021/acs.joc.3c01748] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
Rate constants for hydrogen atom transfer (HAT) reactions of substituted toluenes with tert-butyl, tert-butoxy, and tert-butylperoxyl radicals are reanalyzed here using the free energies of related proton transfer (PT) and electron transfer (ET) reactions, calculated from an extensive set of compiled or estimated pKa and E° values. The Eyring activation energies ΔGHAT‡ do not correlate with the relatively constant ΔG°HAT, but do correlate close-to-linearly with ΔG°PT and ΔG°ET. The slopes of correlations are similar for the three radicals except that the tBu• barriers shift in the opposite direction from the oxyl radical barriers─a clear example of the qualitative "polar effect" in HAT reactions. When cast quantitatively in free energy terms (ΔGHAT‡ vs ΔG°PT/ET), this effect is very small, only 5-10% of the typical Bell-Evans-Polanyi (BEP) effect of changing ΔG°HAT. This analysis also highlights connections between polar effects and the concepts of "asynchronous" or "imbalanced" HAT reactions in which the PT and ET components of ΔG°HAT contribute differently to the barrier. Finally, these observations are discussed in light of the traditional explanations of polar effects and the potential for a rubric that could predict the extent to which contra-thermodynamic selectivity may be achieved in HAT reactions.
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Affiliation(s)
- Benjamin D. Groff
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Brian Koronkiewicz
- Current Address: Johns Hopkins University Applied Physics Laboratory, 11091 Johns Hopkins Rd, Laurel, MD 20723
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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7
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Li Y, Guo S, Li QH, Zheng K. Metal-free photoinduced C(sp 3)-H/C(sp 3)-H cross-coupling to access α‑tertiary amino acid derivatives. Nat Commun 2023; 14:6225. [PMID: 37802984 PMCID: PMC10558569 DOI: 10.1038/s41467-023-41956-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 09/22/2023] [Indexed: 10/08/2023] Open
Abstract
The cross-dehydrogenative coupling (CDC) reaction is the most direct and efficient method for constructing α-tertiary amino acids (ATAAs), which avoids the pre-activation of C(sp3)-H substrates. However, the use of transition metals and harsh reaction conditions are still significant challenges for these reactions that urgently require solutions. This paper presents a mild, metal-free CDC reaction for the construction of ATAAs, which is compatible with various benzyl C-H substrates, functionalized C-H substrates, and alkyl substrates, with good regioselectivity. Notably, our method exhibits excellent functional group tolerance and late-stage applicability. According to mechanistic studies, the one-step synthesized and bench-stable N-alkoxyphtalimide generates a highly electrophilic trifluoro ethoxy radical that serves as a key intermediate in the reaction process and acts as a hydrogen atom transfer reagent. Therefore, our metal-free and additive-free method offers a promising strategy for the synthesis of ATAAs under mild conditions.
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Affiliation(s)
- Yujun Li
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, PR China
| | - Shaopeng Guo
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University, Chengdu, PR China
| | - Qing-Han Li
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University, Chengdu, PR China
| | - Ke Zheng
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, PR China.
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8
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Sun Y, Liu F, Sanders JN, Houk KN. Role of Steric Effects on Rates of Hydrogen Atom Transfer Reactions. J Org Chem 2023; 88:12668-12676. [PMID: 37603684 DOI: 10.1021/acs.joc.3c01361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2023]
Abstract
The influence of steric effects on the rates of hydrogen atom transfer (HAT) reactions between oxyradicals and alkanes is explored computationally. Quantum chemical density functional theory computations of transition states show that activation barriers and reaction enthalpies are both influenced by bulky substituents on the radical but very little by substituents on the alkane. The activation barriers remain roughly correlated with reaction enthalpies via the Evans-Polanyi relationship even when steric repulsion effects become important, although dispersion effects sometimes stabilize transition states. By making comparisons to previously developed Evans-Polanyi and modified Roberts-Steel relationships, we find that HAT reactions between bulky molecules remain well-described by these relationships.
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Affiliation(s)
- Yi Sun
- Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge CB21EW, England
| | - Fengjiao Liu
- College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China
| | - Jacob N Sanders
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
| | - K N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
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9
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Meger FS, Murphy JA. Recent Advances in C-H Functionalisation through Indirect Hydrogen Atom Transfer. Molecules 2023; 28:6127. [PMID: 37630379 PMCID: PMC10459052 DOI: 10.3390/molecules28166127] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Revised: 08/09/2023] [Accepted: 08/15/2023] [Indexed: 08/27/2023] Open
Abstract
The functionalisation of C-H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C-H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann-Löffler-Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C-H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C-H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C-H/Si-H/Ge-H bonds using indirect HAT between 2018-2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols.
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Affiliation(s)
- Filip S. Meger
- Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, 16 Avinguda dels Països Catalans, 43007 Tarragona, Catalonia, Spain
| | - John A. Murphy
- Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK
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10
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Ge J, Zhang XD, Li ZB, Xue BQ, Bai XL. The investigation of the ultrafast excited state deactivation mechanisms for coumarin 307 in different solvents. RSC Adv 2023; 13:21746-21753. [PMID: 37476044 PMCID: PMC10354496 DOI: 10.1039/d3ra03159d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 07/11/2023] [Indexed: 07/22/2023] Open
Abstract
The intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) processes of coumarin 307 (C307) in different solvents were investigated by performing steady-state/time-resolved transient absorption spectroscopic and steady-state photoluminescence spectroscopic characterizations in combination with time-dependent density functional theoretical calculation (TDDFT). The study unveiled the remarkable influence of solvent polarity and the strength of intermolecular hydrogen bonds formed between the solutes and solvents on the relaxation dynamics of the electronic excited state. Significantly, the emergence of the TICT state was observed in polar solvents, specifically dimethylformamide (DMF) and dimethyl sulfoxidemethanol (DMSO), owing to their inherent polarity as well as the enhanced intermolecular hydrogen bonding interactions. Interestingly, even in a weak polar solvent such as methanol (MeOH), the TICT state was also observed due to the intensified hydrogen bonding effects. Conversely, nonpolar solvents, exemplified by 1,4-dioxane (Diox), resulted in the stabilization of the ICT state due to the augmented N-H⋯O hydrogen bonding interactions. The experimental findings were corroborated by the computational calculations, thus ensuring the reliability of the conclusions drawn. Furthermore, schematic diagrams were presented to illustrate the mechanisms underlying the excited-state deactivation. Overall, this investigation contributes valuable mechanistic insights and provides a comprehensive understanding of the photochemical and photophysical properties exhibited by coumarin dyes.
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Affiliation(s)
- Jing Ge
- School of Physics and Information Engineering, Key Laboratory of Spectral Measurement and Analysis of Shanxi Province, Shanxi Normal University Taiyuan 030031 China
| | - Xue-Dong Zhang
- School of Physics and Information Engineering, Key Laboratory of Spectral Measurement and Analysis of Shanxi Province, Shanxi Normal University Taiyuan 030031 China
| | - Zhi-Biao Li
- School of Physics and Information Engineering, Key Laboratory of Spectral Measurement and Analysis of Shanxi Province, Shanxi Normal University Taiyuan 030031 China
| | - Bing-Qian Xue
- School of Physics and Information Engineering, Key Laboratory of Spectral Measurement and Analysis of Shanxi Province, Shanxi Normal University Taiyuan 030031 China
| | - Xi-Lin Bai
- School of Physics and Information Engineering, Key Laboratory of Spectral Measurement and Analysis of Shanxi Province, Shanxi Normal University Taiyuan 030031 China
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11
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Chang L, Wang S, An Q, Liu L, Wang H, Li Y, Feng K, Zuo Z. Resurgence and advancement of photochemical hydrogen atom transfer processes in selective alkane functionalizations. Chem Sci 2023; 14:6841-6859. [PMID: 37389263 PMCID: PMC10306100 DOI: 10.1039/d3sc01118f] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 05/11/2023] [Indexed: 07/01/2023] Open
Abstract
The selective functionalization of alkanes has long been recognized as a prominent challenge and an arduous task in organic synthesis. Hydrogen atom transfer (HAT) processes enable the direct generation of reactive alkyl radicals from feedstock alkanes and have been successfully employed in industrial applications such as the methane chlorination process, etc. Nevertheless, challenges in the regulation of radical generation and reaction pathways have created substantial obstacles in the development of diversified alkane functionalizations. In recent years, the application of photoredox catalysis has provided exciting opportunities for alkane C-H functionalization under extremely mild conditions to trigger HAT processes and achieve radical-mediated functionalizations in a more selective manner. Considerable efforts have been devoted to building more efficient and cost-effective photocatalytic systems for sustainable transformations. In this perspective, we highlight the recent development of photocatalytic systems and provide our views on current challenges and future opportunities in this field.
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Affiliation(s)
- Liang Chang
- School of Pharmacy, Nanjing University of Chinese Medicine Nanjing 210023 China
| | - Shun Wang
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Qing An
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Linxuan Liu
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Hexiang Wang
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Yubo Li
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Kaixuan Feng
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Zhiwei Zuo
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
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12
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An Q, Xing YY, Pu R, Jia M, Chen Y, Hu A, Zhang SQ, Yu N, Du J, Zhang Y, Chen J, Liu W, Hong X, Zuo Z. Identification of Alkoxy Radicals as Hydrogen Atom Transfer Agents in Ce-Catalyzed C-H Functionalization. J Am Chem Soc 2023; 145:359-376. [PMID: 36538367 DOI: 10.1021/jacs.2c10126] [Citation(s) in RCA: 26] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The intermediacy of alkoxy radicals in cerium-catalyzed C-H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)-alkoxide complexes have been synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance and transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified alkoxy radicals as the sole heteroatom-centered radical species generated via ligand-to-metal charge transfer (LMCT) excitation. Alkoxy-radical-mediated hydrogen atom transfer (HAT) has been verified via kinetic analysis, density functional theory (DFT) calculations, and reactions under strictly chloride-free conditions. These experimental findings unambiguously establish the critical role of alkoxy radicals in Ce-LMCT catalysis and definitively preclude the involvement of chlorine radical. This study has also reinforced the necessity of a high relative ratio of alcohol vs Ce for the selective alkoxy-radical-mediated HAT, as seemingly trivial changes in the relative ratio of alcohol vs Ce can lead to drastically different mechanistic pathways. Importantly, the previously proposed chlorine radical-alcohol complex, postulated to explain alkoxy-radical-enabled selectivities in this system, has been examined under scrutiny and ruled out by regioselectivity studies, transient absorption experiments, and high-level calculations. Moreover, the peculiar selectivity of alkoxy radical generation in the LMCT homolysis of Ce(IV) heteroleptic complexes has been analyzed and back-electron transfer (BET) may have regulated the efficiency and selectivity for the formation of ligand-centered radicals.
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Affiliation(s)
- Qing An
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Yang-Yang Xing
- Center of Chemistry for Frontier Technologies, Department of Chemistry, State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310007, China.,Beijing National Laboratory for Molecular Sciences, Zhongguancun North First Street NO. 2, Beijing 100190, China.,Key Laboratory of Precise Synthesis of Functional Molecules of Zhejiang Province, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang, China
| | - Ruihua Pu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Menghui Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yuegang Chen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Anhua Hu
- College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
| | - Shuo-Qing Zhang
- Center of Chemistry for Frontier Technologies, Department of Chemistry, State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310007, China.,Beijing National Laboratory for Molecular Sciences, Zhongguancun North First Street NO. 2, Beijing 100190, China.,Key Laboratory of Precise Synthesis of Functional Molecules of Zhejiang Province, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang, China
| | - Na Yu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Jianbo Du
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Yanxia Zhang
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Weimin Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xin Hong
- Center of Chemistry for Frontier Technologies, Department of Chemistry, State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310007, China.,Beijing National Laboratory for Molecular Sciences, Zhongguancun North First Street NO. 2, Beijing 100190, China.,Key Laboratory of Precise Synthesis of Functional Molecules of Zhejiang Province, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang, China
| | - Zhiwei Zuo
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
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Dherange BD, Yuan M, Kelly CB, Reiher CA, Grosanu C, Berger KJ, Gutierrez O, Levin MD. Direct Deaminative Functionalization. J Am Chem Soc 2023; 145:17-24. [PMID: 36548788 PMCID: PMC10245626 DOI: 10.1021/jacs.2c11453] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Selective functional group interconversions in complex molecular settings underpin many of the challenges facing modern organic synthesis. Currently, a privileged subset of functional groups dominates this landscape, while others, despite their abundance, are sorely underdeveloped. Amines epitomize this dichotomy; they are abundant but otherwise intransigent toward direct interconversion. Here, we report an approach that enables the direct conversion of amines to bromides, chlorides, iodides, phosphates, thioethers, and alcohols, the heart of which is a deaminative carbon-centered radical formation process using an anomeric amide reagent. Experimental and computational mechanistic studies demonstrate that successful deaminative functionalization relies not only on outcompeting the H-atom transfer to the incipient radical but also on the generation of polarity-matched, productive chain-carrying radicals that continue to react efficiently. The overall implications of this technology for interconverting amine libraries were evaluated via high-throughput parallel synthesis and applied in the development of one-pot diversification protocols.
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Affiliation(s)
- Balu D Dherange
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Mingbin Yuan
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
| | - Christopher B Kelly
- Discovery Process Research, Janssen Research & Development LLC, 1400 McKean Road, Spring House, Pennsylvania 19477, United States
| | - Christopher A Reiher
- Parallel Medicinal Chemistry, Janssen Research & Development LLC, 1400 McKean Road, Spring House, Pennsylvania 19477, United States
| | - Cristina Grosanu
- High Throughput Purification, Janssen Research & Development LLC, 1400 McKean Road, Spring House, Pennsylvania 19477, United States
| | - Kathleen J Berger
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Osvaldo Gutierrez
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
| | - Mark D Levin
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
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14
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Lombardi L, Cerveri A, Giovanelli R, Castiñeira Reis M, Silva López C, Bertuzzi G, Bandini M. Direct Synthesis of α-Aryl-α-Trifluoromethyl Alcohols via Nickel Catalyzed Cross-Electrophile Coupling. Angew Chem Int Ed Engl 2022; 61:e202211732. [PMID: 36161744 PMCID: PMC9828748 DOI: 10.1002/anie.202211732] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Indexed: 01/12/2023]
Abstract
A nickel-catalyzed reductive cross-electrophile coupling between the redox-active N-trifluoroethoxyphthalimide and iodoarenes is documented. The protocol reproduces a formal arylation of trifluoroacetaldehyde under mild conditions in high yields (up to 88 %) and with large functional group tolerance (30 examples). A combined computational and experimental investigation revealed a pivotal solvent assisted 1,2-Hydrogen Atom Transfer (HAT) process to generate a nucleophilic α-hydroxy-α-trifluoromethyl C-centered radical for the Csp2 -Csp3 bond forming process.
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Affiliation(s)
- Lorenzo Lombardi
- Dipartimento di Chimica “Giacomo Ciamician”Alma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
- Center for Chemical Catalysis—CAlma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
| | - Alessandro Cerveri
- Dipartimento di Chimica “Giacomo Ciamician”Alma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
| | - Riccardo Giovanelli
- Dipartimento di Chimica “Giacomo Ciamician”Alma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
- Center for Chemical Catalysis—CAlma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
| | | | | | - Giulio Bertuzzi
- Dipartimento di Chimica “Giacomo Ciamician”Alma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
- Center for Chemical Catalysis—CAlma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
| | - Marco Bandini
- Dipartimento di Chimica “Giacomo Ciamician”Alma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
- Center for Chemical Catalysis—CAlma Mater Studiorum—Università di BolognaVia Selmi 240126BolognaItaly
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15
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Ma S, Wang S, Cao J, Liu F. Rapid and Accurate Estimation of Activation Free Energy in Hydrogen Atom Transfer-Based C-H Activation Reactions: From Empirical Model to Artificial Neural Networks. ACS OMEGA 2022; 7:34858-34867. [PMID: 36211072 PMCID: PMC9535641 DOI: 10.1021/acsomega.2c03252] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 09/07/2022] [Indexed: 06/16/2023]
Abstract
A well-performing machine learning (ML) model is obtained by using proper descriptors and artificial neural network (ANN) algorithms, which can quickly and accurately predict activation free energy in hydrogen atom transfer (HAT)-based sp3 C-H activation. Density functional theory calculations (UωB97X-D) are used to establish the reaction system data sets of methoxyl (CH3O·), trifluoroethoxyl (CF3CH2O·), tert-butoxyl (tBuO·), and cumyloxyl (CumO·) radicals. The simplified Roberts' equation proposed in our recent study works here [R 2 = 0.84, mean absolute error (MAE) = 0.85 kcal/mol]. Its performance is comparable with univariate Mulliken-type electronegativity (χ) with the ANN model. The ANN model with bond dissociation free energy, χ, α-unsaturation, and Nolan buried volume (%V buried) successively improves R 2 and MAE to 0.93 and 0.54 kcal/mol, respectively. It reproduces the test sets of trichloroethoxyl (CCl3CH2O·) with R 2 = 0.87 and MAE = 0.89 kcal/mol and accurately predicts the relative experimental barrier of the HAT reactions with CumO· and the site selectivity of CH3O·.
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Affiliation(s)
- Siqi Ma
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
| | - Shipeng Wang
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
| | - Jiawei Cao
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
| | - Fengjiao Liu
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
- Department
of Chemistry and Biochemistry, University
of California, Los Angeles, California 90095, United States
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16
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McKee ML. Exploring the Reaction Mechanism of C-H Oxidation by Copper-Salen Complexes. J Phys Chem A 2022; 126:4969-4980. [PMID: 35861503 DOI: 10.1021/acs.jpca.2c03344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The mechanism of C-H oxidation of propylene (C3H6) and 1-phenyl-1-pentyne (C3H7-C≡C-Ph) by HOOR (R═Me, tBu) and 3O2 by a copper-salen complex was explored by computations. The most noteworthy step is the complexation of two Cu salens to the peroxide to form either the LCuOH/LCuOR pair or an OH-bridged complex LCu(μ-OH)CuL plus OR. The latter pathway involves an avoided crossing of two triplet electronic states. The LCuOH complex can abstract a hydrogen atom from C3H6 and the C3H5 radical plus 3O2 forms the complex LCuOOC3H5. Migration of a hydrogen to the proximal oxygen atom reforms LCuOH and acrolein HC(O)CH═CH2.
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Affiliation(s)
- Michael L McKee
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama36849, United States
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