1
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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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2
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Schneider JE, Anderson JS. Reconciling Imbalanced and Nonadiabatic Reactivity in Transition Metal-Oxo-Mediated Concerted Proton Electron Transfer (CPET). J Phys Chem Lett 2023; 14:9548-9555. [PMID: 37856336 DOI: 10.1021/acs.jpclett.3c02318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
Recently, there have been several experimental demonstrations of how the rates of concerted proton electron transfer (CPET) are affected by stepwise thermodynamic parameters of only proton (ΔG°PT) or electron (ΔG°ET) transfer. Semiclassical structure-activity relationships have been invoked to rationalize these linear free energy relationships, but it is not clear how they would manifest in a nonadiabatic reaction. Using density functional theory calculations, we demonstrate how a decrease in ΔG°PT can lead to transition state imbalance in a nonadiabatic framework. We then use these calculations to anchor a theoretical model that reproduces experimental trends with ΔG°PT and ΔG°ET. Our results reconcile predictions from semiclassical transition state theory with models that treat proton transfer quantum mechanically in CPET reactivity, make new predictions about the importance of basicity for uphill CPET reactions, and suggest similar treatments may be possible for other nonadiabatic reactions.
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Affiliation(s)
- Joseph E Schneider
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - John S Anderson
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
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3
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Teindl K, Patrick BO, Nichols EM. Linear Free Energy Relationships and Transition State Analysis of CO 2 Reduction Catalysts Bearing Second Coordination Spheres with Tunable Acidity. J Am Chem Soc 2023; 145:17176-17186. [PMID: 37499125 DOI: 10.1021/jacs.3c03919] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
In molecular catalysts, protic functional groups in the secondary coordination sphere (SCS) work in conjunction with an exogenous acid to relay protons to the active site of electrochemical CO2 reduction; however, it is not well understood how the acidity of the SCS and exogenous acid together determine the kinetics of catalytic turnover. To evaluate the relative contributions of proton transfer driving forces, we synthesized a series of modular iron tetraphenylporphyrin electrocatalysts bearing SCS amides of tunable pKa (17.6 to 20.0 in dimethyl sulfoxide (DMSO)) and employed phenols of variable acidity (15.3 to 19.1) as exogenous acids. This system allowed us to (1) evaluate contributions from proton transfer driving forces associated with either the SCS or exogenous acid and (2) obtain mechanistic insights into CO2 reduction as a function of pKa. A series of linear free-energy relationships show that kinetics become increasingly sensitive to variations in SCS pKa when more acidic exogenous acids are used (0.82 ≥ Brønsted α ≥ 0.13), as well as to variations in exogenous acid pKa when SCS acidity is increased (0.62 ≥ Brønsted α ≥ 0.32). An Eyring analysis suggests that the rate-determining transition state becomes more ordered with decreasing SCS acidity, which is consistent with the proposal that SCS acidity modulates charge accumulation and solvation at the rate-limiting transition state. Together, these insights enable the optimization of activation barriers as a function of both SCS and exogenous acid pKa and can further guide the rational design of electrocatalytic systems wherein contributions from all participants in a proton relay are considered.
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Affiliation(s)
- Kaeden Teindl
- Department of Chemistry, The University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Brian O Patrick
- Department of Chemistry, The University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Eva M Nichols
- Department of Chemistry, The University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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4
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Heuer A, Coste SC, Singh G, Mercado BQ, Mayer JM. A Guide to Tris(4-Substituted)-triphenylmethyl Radicals. J Org Chem 2023; 88:9893-9901. [PMID: 37403939 PMCID: PMC10367072 DOI: 10.1021/acs.joc.3c00658] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Indexed: 07/06/2023]
Abstract
Triphenylmethyl (trityl, Ph3C•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph)3C•] have since been used in many ways due to their stability, persistence, and spectroscopic activity. Despite their widespread use, existing synthetic routes toward tris(4-substituted)-trityl radicals are not reproducible and often lead to impure materials. We report here robust syntheses of six electronically varied (4-RPh)3C•, where R = NMe2, OCH3, tBu, Ph, Cl, and CF3. The characterization reported for the radicals and related compounds includes five X-ray crystal structures, electrochemical potentials, and optical spectra. Each radical is best accessed using a stepwise approach from the trityl halide, (RPh)3CCl or (RPh)3CBr, by controllably removing the halide with subsequent 1e- reduction of the trityl cation, (RPh)3C+. These syntheses afford consistently crystalline trityl radicals of high purity for further studies.
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Affiliation(s)
| | | | - Gurjot Singh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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5
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Groff BD, Cattaneo M, Coste SC, Pressley CA, Mercado BQ, Mayer JM. Independent Tuning of the p Ka or the E1/2 in a Family of Ruthenium Pyridine-Imidazole Complexes. Inorg Chem 2023; 62:10031-10038. [PMID: 37326619 PMCID: PMC10734561 DOI: 10.1021/acs.inorgchem.3c01241] [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: 06/17/2023]
Abstract
Two series of RuII(acac)2(py-imH) complexes have been prepared, one with changes to the acac ligands and the other with substitutions to the imidazole. The proton-coupled electron transfer (PCET) thermochemistry of the complexes has been studied in acetonitrile, revealing that the acac substitutions almost exclusively affect the redox potentials of the complex (|ΔE1/2| ≫ |ΔpKa|·0.059 V) while the changes to the imidazole primarily affect its acidity (|ΔpKa|·0.059 V ≫ |ΔE1/2|). This decoupling is supported by DFT calculations, which show that the acac substitutions primarily affect the Ru-centered t2g orbitals, while changes to the py-imH ligand primarily affect the ligand-centered π orbitals. More broadly, the decoupling stems from the physical separation of the electron and proton within the complex and highlights a clear design strategy to separately tune the redox and acid/base properties of H atom donor/acceptor molecules.
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Affiliation(s)
- Benjamin D Groff
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Mauricio Cattaneo
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Scott C Coste
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Chloe A Pressley
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - James M Mayer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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6
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Zhao N, Goetz MK, Schneider JE, Anderson JS. Testing the Limits of Imbalanced CPET Reactivity: Mechanistic Crossover in H-Atom Abstraction by Co(III)-Oxo Complexes. J Am Chem Soc 2023; 145:5664-5673. [PMID: 36867838 PMCID: PMC10023487 DOI: 10.1021/jacs.2c10553] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
Abstract
Transition metal-oxo complexes are key intermediates in a variety of oxidative transformations, notably C-H bond activation. The relative rate of C-H bond activation mediated by transition metal-oxo complexes is typically predicated on substrate bond dissociation free energy in cases with a concerted proton-electron transfer (CPET). However, recent work has demonstrated that alternative stepwise thermodynamic contributions such as acidity/basicity or redox potentials of the substrate/metal-oxo may dominate in some cases. In this context, we have found basicity-governed concerted activation of C-H bonds with the terminal CoIII-oxo complex PhB(tBuIm)3CoIIIO. We have been interested in testing the limits of such basicity-dependent reactivity and have synthesized an analogous, more basic complex, PhB(AdIm)3CoIIIO, and studied its reactivity with H-atom donors. This complex displays a higher degree of imbalanced CPET reactivity than PhB(tBuIm)3CoIIIO with C-H substrates, and O-H activation of phenol substrates displays mechanistic crossover to stepwise proton transfer-electron transfer (PTET) reactivity. Analysis of the thermodynamics of proton transfer (PT) and electron transfer (ET) reveals a distinct thermodynamic crossing point between concerted and stepwise reactivity. Furthermore, the relative rates of stepwise and concerted reactivity suggest that maximally imbalanced systems provide the fastest CPET rates up to the point of mechanistic crossover, which results in slower product formation.
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Affiliation(s)
- Norman Zhao
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | | | - Joseph E. Schneider
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - John S. Anderson
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
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7
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Schreiber E, Brennessel WW, Matson EM. Regioselectivity of concerted proton-electron transfer at the surface of a polyoxovanadate cluster. Chem Sci 2023; 14:1386-1396. [PMID: 36794190 PMCID: PMC9906639 DOI: 10.1039/d2sc05928b] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 12/19/2022] [Indexed: 01/19/2023] Open
Abstract
Proton-coupled electron transfer (PCET) is an important process in the activation and reactivity of metal oxide surfaces. In this work, we study the electronic structure of a reduced polyoxovanadate-alkoxide cluster bearing a single bridging oxide moiety. The structural and electronic implications of the incorporation of bridging oxide sites are revealed, most notably resulting in the quenching of cluster-wide electron delocalization in the most reduced state of the molecule. We correlate this attribute to a change in regioselectivity of PCET to the cluster surface (e.g. reactivity at terminal vs. bridging oxide groups). Reactivity localized at the bridging oxide site enables reversible storage of a single H-atom equivalent, changing the stoichiometry of PCET from a 2e-/2H+ process. Kinetic investigations indicate that the change in site of reactivity translates to an accelerated rate of e-/H+ transfer to the cluster surface. Our work summarizes the role which electronic occupancy and ligand density play in the uptake of e-/H+ pairs at metal oxide surfaces, providing design criteria for functional materials for energy storage and conversion processes.
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Affiliation(s)
- Eric Schreiber
- Department of Chemistry, University of Rochester Rochester NY 14611 USA
| | | | - Ellen M Matson
- Department of Chemistry, University of Rochester Rochester NY 14611 USA
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8
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Bower JK, Reese MS, Mazin IM, Zarnitsa LM, Cypcar AD, Moore CE, Sokolov AY, Zhang S. C(sp 3)-H cyanation by a formal copper(iii) cyanide complex. Chem Sci 2023; 14:1301-1307. [PMID: 36756315 PMCID: PMC9891353 DOI: 10.1039/d2sc06573h] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Accepted: 01/05/2023] [Indexed: 01/18/2023] Open
Abstract
High-valent metal oxo complexes are prototypical intermediates for the activation and hydroxylation of alkyl C-H bonds. Substituting the oxo ligand with other functional groups offers the opportunity for additional C-H functionalization beyond C-O bond formation. However, few species aside from metal oxo complexes have been reported to both activate and functionalize alkyl C-H bonds. We herein report the first example of an isolated copper(iii) cyanide complex (LCuIIICN) and its C-H cyanation reactivity. We found that the redox potential (E ox) of substrates, instead of C-H bond dissociation energy, is a key determinant of the rate of PCET, suggesting an oxidative asynchronous CPET or ETPT mechanism. Among substrates with the same BDEs, those with low redox potentials transfer H atoms up to a million-fold faster. Capitalizing on this mechanistic insight, we found that LCuIIICN is highly selective for cyanation of amines, which is predisposed to oxidative asynchronous or stepwise transfer of H+/e-. Our study demonstrates that the asynchronous effect of PCET is an appealing tool for controlling the selectivity of C-H functionalization.
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Affiliation(s)
- Jamey K. Bower
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Maxwell S. Reese
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Ilia M. Mazin
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Lina M. Zarnitsa
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Andrew D. Cypcar
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Curtis E. Moore
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Alexander Yu. Sokolov
- Department of Chemistry and Biochemistry, The Ohio State University100 W. 18 AveColumbusOH43210USA
| | - Shiyu Zhang
- Department of Chemistry and Biochemistry, The Ohio State University 100 W. 18th Ave Columbus OH 43210 USA
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9
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Hong JE, Yoon J, Baek W, Kim K, Kwak JH, Park Y. Electrochemical C(sp 3)-H Lactonization of 2-Alkylbenzoic Acids toward Phthalides. Org Lett 2023; 25:298-303. [PMID: 36583568 DOI: 10.1021/acs.orglett.2c04211] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Herein, we report direct electrochemical C(sp3)-H lactonization of 2-alkylbenzoic acids toward phthalides. The reaction provides a wide substrate scope of 2-alkylbenzoic acids bearing primary to tertiary C(sp3)-H bonds by utilizing a graphite anode, dichloromethane (DCM) solvent, hexafluoroisopropanol (HFIP) cosolvent, and n-Bu4NClO4 electrolyte. Our synthetic approach offers a simple, intuitive, and atom-economical protocol to synthesize various phthalides (25 examples, up to 92% yield) and obtain other 5- and 6-membered lactones (10 examples, up to 83% yield).
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Affiliation(s)
- Jee Eun Hong
- College of Pharmacy, Inje Institute of Pharmaceutical Sciences and Research, Inje University, 197 Inje-ro, Gimhae, Gyeongnam 50834, Republic of Korea
| | - Jisong Yoon
- College of Pharmacy, Inje Institute of Pharmaceutical Sciences and Research, Inje University, 197 Inje-ro, Gimhae, Gyeongnam 50834, Republic of Korea
| | - Woohyun Baek
- College of Pharmacy, Inje Institute of Pharmaceutical Sciences and Research, Inje University, 197 Inje-ro, Gimhae, Gyeongnam 50834, Republic of Korea
| | - Kyumin Kim
- College of Pharmacy, Inje Institute of Pharmaceutical Sciences and Research, Inje University, 197 Inje-ro, Gimhae, Gyeongnam 50834, Republic of Korea
| | - Jae-Hwan Kwak
- College of Pharmacy, Chungbuk National University, 194-21 Osongsaengmyeong 1-ro, Heungdeok-gu, Cheongju, Chungbuk 28160, Republic of Korea
| | - Yohan Park
- College of Pharmacy, Inje Institute of Pharmaceutical Sciences and Research, Inje University, 197 Inje-ro, Gimhae, Gyeongnam 50834, Republic of Korea
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10
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Zhang J, Lee YM, Seo MS, Nilajakar M, Fukuzumi S, Nam W. A Contrasting Effect of Acid in Electron Transfer, Oxygen Atom Transfer, and Hydrogen Atom Transfer Reactions of a Nickel(III) Complex. Inorg Chem 2022; 61:19735-19747. [PMID: 36445726 DOI: 10.1021/acs.inorgchem.2c02504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
There have been many examples of the accelerating effects of acids in electron transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. Herein, we report a contrasting effect of acids in the ET, OAT, and HAT reactions of a nickel(III) complex, [NiIII(PaPy3*)]2+ (1) in acetone/CH3CN (v/v 19:1). 1 was synthesized by reacting [NiII(PaPy3*)]+ (2) with magic blue or iodosylbenzene in the absence or presence of triflic acid (HOTf), respectively. Sulfoxidation of thioanisole by 1 and H2O occurred in the presence of HOTf, and the reaction rate increased proportionally with increasing concentration of HOTf ([HOTf]). The rate of ET from diacetylferrocene to 1 also increased linearly with increasing [HOTf]. In contrast, HAT from 9,10-dihydroanthracene (DHA) to 1 slowed down with increasing [HOTf], exhibiting an inversely proportional relation to [HOTf]. The accelerating effect of HOTf in the ET and OAT reactions was ascribed to the binding of H+ to the PaPy3* ligand of 2; the one-electron reduction potential (Ered) of 1 was positively shifted with increasing [HOTf]. Such a positive shift in the Ered value resulted in accelerating the ET and OAT reactions that proceeded via the rate-determining ET step. On the other hand, the decelerating effect of HOTf on HAT from DHA to 1 resulted from the inhibition of proton transfer from DHA•+ to 2 due to the binding of H+ to the PaPy3* ligand of 2. The ET reactions of 1 in the absence and presence of HOTf were well analyzed in light of the Marcus theory of ET in comparison with the HAT reactions.
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Affiliation(s)
- Jisheng Zhang
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Mi Sook Seo
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Madhuri Nilajakar
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Shunichi Fukuzumi
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
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11
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Agarwal RG, Mayer JM. Coverage-Dependent Rate-Driving Force Relationships: Hydrogen Transfer from Cerium Oxide Nanoparticle Colloids. J Am Chem Soc 2022; 144:20699-20709. [DOI: 10.1021/jacs.2c07988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Rishi G. Agarwal
- Department of Chemistry, Yale University, New Haven, Connecticut06520-8107, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut06520-8107, United States
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12
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Hybrid bilayer membranes as platforms for biomimicry and catalysis. Nat Rev Chem 2022; 6:862-880. [PMID: 37117701 DOI: 10.1038/s41570-022-00433-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/20/2022] [Indexed: 11/08/2022]
Abstract
Hybrid bilayer membrane (HBM) platforms represent an emerging nanoscale bio-inspired interface that has broad implications in energy catalysis and smart molecular devices. An HBM contains multiple modular components that include an underlying inorganic surface with a biological layer appended on top. The inorganic interface serves as a support with robust mechanical properties that can also be decorated with functional moieties, sensing units and catalytic active sites. The biological layer contains lipids and membrane-bound entities that facilitate or alter the activity and selectivity of the embedded functional motifs. With their structural complexity and functional flexibility, HBMs have been demonstrated to enhance catalytic turnover frequency and regulate product selectivity of the O2 and CO2 reduction reactions, which have applications in fuel cells and electrolysers. HBMs can also steer the mechanistic pathways of proton-coupled electron transfer (PCET) reactions of quinones and metal complexes by tuning electron and proton delivery rates. Beyond energy catalysis, HBMs have been equipped with enzyme mimics and membrane-bound redox agents to recapitulate natural energy transport chains. With channels and carriers incorporated, HBM sensors can quantify transmembrane events. This Review serves to summarize the major accomplishments achieved using HBMs in the past decade.
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13
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Nandy A, Adamji H, Kastner DW, Vennelakanti V, Nazemi A, Liu M, Kulik HJ. Using Computational Chemistry To Reveal Nature’s Blueprints for Single-Site Catalysis of C–H Activation. ACS Catal 2022. [DOI: 10.1021/acscatal.2c02096] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Aditya Nandy
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Husain Adamji
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - David W. Kastner
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Vyshnavi Vennelakanti
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Azadeh Nazemi
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Mingjie Liu
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Heather J. Kulik
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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14
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Wang YF, Zhang MT. Proton-Coupled Electron-Transfer Reduction of Dioxygen: The Importance of Precursor Complex Formation between Electron Donor and Proton Donor. J Am Chem Soc 2022; 144:12459-12468. [PMID: 35776107 DOI: 10.1021/jacs.2c04467] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The proton-coupled electron transfer (PCET) reaction has drawn extensive attention for its widespread occurrence in chemistry, biology, and materials science. The mechanistic studies via model systems such as tyrosine and phenol oxidation have gradually deepened the understanding of PCET reactions, which was widely accepted and applied to bond activation and transformation. However, direct PCET activation of nonpolar bonds such as the C-H bond, O2, and N2 has yet to be explored. Herein, we report that the interaction between electron donor and proton donor could overcome the barrier of direct O2 activation via a concerted electron-proton transfer mechanism. This work provides a new strategy for developing direct PCET activation of nonpolar bonds.
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Affiliation(s)
- Yu-Fan Wang
- Center of Basic Molecular Science, Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Ming-Tian Zhang
- Center of Basic Molecular Science, Department of Chemistry, Tsinghua University, Beijing 100084, China
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15
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Koronkiewicz B, Sayfutyarova ER, Coste SC, Mercado BQ, Hammes-Schiffer S, Mayer JM. Structural and Thermodynamic Effects on the Kinetics of C-H Oxidation by Multisite Proton-Coupled Electron Transfer in Fluorenyl Benzoates. J Org Chem 2022; 87:2997-3006. [PMID: 35113555 DOI: 10.1021/acs.joc.1c02834] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Our recent experimental and theoretical investigations have shown that fluorene C-H bonds can be activated through a mechanism in which the proton and electron are transferred from the C-H bond to a separate base and oxidant in a concerted, elementary step. This multisite proton-coupled electron transfer (MS-PCET) mechanism for C-H bond activation was shown to be facilitated by shorter proton donor-acceptor distances. With the goal of intentionally modulating this donor-acceptor distance, we have now studied C-H MS-PCET in the 3-methyl-substituted fluorenyl benzoate (2-Flr-3-Me-BzO-). This derivative was readily oxidized by ferrocenium oxidants by initial C-H MS-PCET, with rate constants that were 6-21 times larger than those for 2-Flr-BzO- with the same oxidants. Structural comparisons by X-ray crystallography and by computations showed that addition of the 3-methyl group caused the expected steric compression; however, the relevant C···O- proton donor-acceptor distance was longer, due to a twist of the carboxylate group. The structural changes induced by the 3-Me group increased the basicity of the carboxylate, weakened the C-H bond, and reduced the reorganization energy for C-H bond cleavage. Thus, the rate enhancement for 2-Flr-3-Me-BzO- was due to effects on the thermochemistry and kinetic barrier, rather than from compression of the C···O- proton donor-acceptor distance. These results highlight both the challenges of controlling molecules on the 0.1 Å length scale and the variety of parameters that affect PCET rate constants.
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Affiliation(s)
- Brian Koronkiewicz
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Elvira R Sayfutyarova
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Scott C Coste
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - James M Mayer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
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16
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Murray PD, Cox JH, Chiappini ND, Roos CB, McLoughlin EA, Hejna BG, Nguyen ST, Ripberger HH, Ganley JM, Tsui E, Shin NY, Koronkiewicz B, Qiu G, Knowles RR. Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis. Chem Rev 2022; 122:2017-2291. [PMID: 34813277 PMCID: PMC8796287 DOI: 10.1021/acs.chemrev.1c00374] [Citation(s) in RCA: 158] [Impact Index Per Article: 79.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Indexed: 12/16/2022]
Abstract
We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.
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Affiliation(s)
- Philip
R. D. Murray
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - James H. Cox
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Nicholas D. Chiappini
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Casey B. Roos
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | | | - Benjamin G. Hejna
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Suong T. Nguyen
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Hunter H. Ripberger
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Jacob M. Ganley
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Elaine Tsui
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Nick Y. Shin
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Brian Koronkiewicz
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Guanqi Qiu
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Robert R. Knowles
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
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17
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Zhang J, Lee YM, Seo MS, Kim Y, Lee E, Fukuzumi S, Nam W. Oxidative versus basic asynchronous hydrogen atom transfer reactions of Mn(III)-hydroxo and Mn(III)-aqua complexes. Inorg Chem Front 2022. [DOI: 10.1039/d2qi00741j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hydrogen atom transfer (HAT) of metal-oxygen intermediates such as metal-oxo, -hydroxo and -superoxo species have so far been studied extensively. However, HAT reactions of metal-aqua complexes have yet to be...
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18
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Tyburski R, Hammarström L. Strategies for switching the mechanism of proton-coupled electron transfer reactions illustrated by mechanistic zone diagrams. Chem Sci 2022; 13:290-301. [PMID: 35059179 PMCID: PMC8694376 DOI: 10.1039/d1sc05230f] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Accepted: 11/26/2021] [Indexed: 12/19/2022] Open
Abstract
The mechanism by which proton-coupled electron transfer (PCET) occurs is of fundamental importance and has great consequences for applications, e.g. in catalysis. However, determination and tuning of the PCET mechanism is often non-trivial. Here, we apply mechanistic zone diagrams to illustrate the competition between concerted and stepwise PCET-mechanisms in the oxidation of 4-methoxyphenol by Ru(bpy)33+-derivatives in the presence of substituted pyridine bases. These diagrams show the dominating mechanism as a function of driving force for electron and proton transfer (ΔG0ET and ΔG0PT) respectively [Tyburski et al., J. Am. Chem. Soc., 2021, 143, 560]. Within this framework, we demonstrate strategies for mechanistic tuning, namely balancing of ΔG0ET and ΔG0PT, steric hindrance of the proton-transfer coordinate, and isotope substitution. Sterically hindered pyridine bases gave larger reorganization energy for concerted PCET, resulting in a shift towards a step-wise electron first-mechanism in the zone diagrams. For cases when sufficiently strong oxidants are used, substitution of protons for deuterons leads to a switch from concerted electron–proton transfer (CEPT) to an electron transfer limited (ETPTlim) mechanism. We thereby, for the first time, provide direct experimental evidence, that the vibronic coupling strength affects the switching point between CEPT and ETPTlim, i.e. at what driving force one or the other mechanism starts dominating. Implications for solar fuel catalysis are discussed. The mechanism by which proton-coupled electron transfer (PCET) occurs is of fundamental importance and has great consequences for applications, e.g. in catalysis.![]()
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Affiliation(s)
- Robin Tyburski
- Department of Chemistry – Ångström Laboratory, Uppsala University, Box 532, SE75120 Uppsala, Sweden
| | - Leif Hammarström
- Department of Chemistry – Ångström Laboratory, Uppsala University, Box 532, SE75120 Uppsala, Sweden
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19
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Agarwal RG, Coste SC, Groff BD, Heuer AM, Noh H, Parada GA, Wise CF, Nichols EM, Warren JJ, Mayer JM. Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications. Chem Rev 2021; 122:1-49. [PMID: 34928136 DOI: 10.1021/acs.chemrev.1c00521] [Citation(s) in RCA: 134] [Impact Index Per Article: 44.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We present an update and revision to our 2010 review on the topic of proton-coupled electron transfer (PCET) reagent thermochemistry. Over the past decade, the data and thermochemical formalisms presented in that review have been of value to multiple fields. Concurrently, there have been advances in the thermochemical cycles and experimental methods used to measure these values. This Review (i) summarizes those advancements, (ii) corrects systematic errors in our prior review that shifted many of the absolute values in the tabulated data, (iii) provides updated tables of thermochemical values, and (iv) discusses new conclusions and opportunities from the assembled data and associated techniques. We advocate for updated thermochemical cycles that provide greater clarity and reduce experimental barriers to the calculation and measurement of Gibbs free energies for the conversion of X to XHn in PCET reactions. In particular, we demonstrate the utility and generality of reporting potentials of hydrogenation, E°(V vs H2), in almost any solvent and how these values are connected to more widely reported bond dissociation free energies (BDFEs). The tabulated data demonstrate that E°(V vs H2) and BDFEs are generally insensitive to the nature of the solvent and, in some cases, even to the phase (gas versus solution). This Review also presents introductions to several emerging fields in PCET thermochemistry to give readers windows into the diversity of research being performed. Some of the next frontiers in this rapidly growing field are coordination-induced bond weakening, PCET in novel solvent environments, and reactions at material interfaces.
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Affiliation(s)
- Rishi G Agarwal
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Scott C Coste
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Benjamin D Groff
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Abigail M Heuer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Hyunho Noh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Giovanny A Parada
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.,Department of Chemistry, The College of New Jersey, Ewing, New Jersey 08628, United States
| | - Catherine F Wise
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Eva M Nichols
- Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Jeffrey J Warren
- Department of Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
| | - James M Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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20
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Coste SC, Brezny AC, Koronkiewicz B, Mayer JM. C-H oxidation in fluorenyl benzoates does not proceed through a stepwise pathway: revisiting asynchronous proton-coupled electron transfer. Chem Sci 2021; 12:13127-13136. [PMID: 34745543 PMCID: PMC8513817 DOI: 10.1039/d1sc03344a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Accepted: 09/09/2021] [Indexed: 11/21/2022] Open
Abstract
2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant. Kinetic analysis revealed unusual rate-driving force relationships. Our analysis indicated a mechanism of multi-site concerted proton–electron transfer (MS-CPET) for all of these reactions. More recently, an alternative interpretation of the kinetic data was proposed to explain the unusual rate-driving force relationships, invoking a crossover from CPET to a stepwise mechanism with an initial intramolecular proton transfer (PT) (Costentin, Savéant, Chem. Sci., 2020, 11, 1006). Here, we show that this proposed alternative pathway is untenable based on prior and new experimental assessments of the intramolecular PT equilibrium constant and rates. Measurement of the fluorenyl 9-C–H pKa, H/D exchange experiments, and kinetic modelling with COPASI eliminate the possibility of a stepwise mechanism for C–H oxidation in the fluorenyl benzoate series. Implications for asynchronous (imbalanced) MS-CPET mechanisms are discussed with respect to classical Marcus theory and the quantum-mechanical treatment of concerted proton–electron transfer. 2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant.![]()
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Affiliation(s)
- Scott C Coste
- Department of Chemistry, Yale University New Haven CT 06520-8107 USA
| | - Anna C Brezny
- Department of Chemistry, Skidmore College Saratoga Springs New York 12866 USA
| | | | - James M Mayer
- Department of Chemistry, Yale University New Haven CT 06520-8107 USA
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21
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Lee JL, Ross DL, Barman SK, Ziller JW, Borovik AS. C-H Bond Cleavage by Bioinspired Nonheme Metal Complexes. Inorg Chem 2021; 60:13759-13783. [PMID: 34491738 DOI: 10.1021/acs.inorgchem.1c01754] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The functionalization of C-H bonds is one of the most challenging transformations in synthetic chemistry. In biology, these processes are well-known and are achieved with a variety of metalloenzymes, many of which contain a single metal center within their active sites. The most well studied are those with Fe centers, and the emerging experimental data show that high-valent iron oxido species are the intermediates responsible for cleaving the C-H bond. This Forum Article describes the state of this field with an emphasis on nonheme Fe enzymes and current experimental results that provide insights into the properties that make these species capable of C-H bond cleavage. These parameters are also briefly considered in regard to manganese oxido complexes and Cu-containing metalloenzymes. Synthetic iron oxido complexes are discussed to highlight their utility as spectroscopic and mechanistic probes and reagents for C-H bond functionalization. Avenues for future research are also examined.
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Affiliation(s)
- Justin L Lee
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Dolores L Ross
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Suman K Barman
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Joseph W Ziller
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - A S Borovik
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
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22
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Barman SK, Yang MY, Parsell TH, Green MT, Borovik AS. Semiempirical method for examining asynchronicity in metal-oxido-mediated C-H bond activation. Proc Natl Acad Sci U S A 2021; 118:e2108648118. [PMID: 34465626 PMCID: PMC8433561 DOI: 10.1073/pnas.2108648118] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The oxidation of substrates via the cleavage of thermodynamically strong C-H bonds is an essential part of mammalian metabolism. These reactions are predominantly carried out by enzymes that produce high-valent metal-oxido species, which are directly responsible for cleaving the C-H bonds. While much is known about the identity of these transient intermediates, the mechanistic factors that enable metal-oxido species to accomplish such difficult reactions are still incomplete. For synthetic metal-oxido species, C-H bond cleavage is often mechanistically described as synchronous, proton-coupled electron transfer (PCET). However, data have emerged that suggest that the basicity of the M-oxido unit is the key determinant in achieving enzymatic function, thus requiring alternative mechanisms whereby proton transfer (PT) has a more dominant role than electron transfer (ET). To bridge this knowledge gap, the reactivity of a monomeric MnIV-oxido complex with a series of external substrates was studied, resulting in a spread of over 104 in their second-order rate constants that tracked with the acidity of the C-H bonds. Mechanisms that included either synchronous PCET or rate-limiting PT, followed by ET, did not explain our results, which led to a proposed PCET mechanism with asynchronous transition states that are dominated by PT. To support this premise, we report a semiempirical free energy analysis that can predict the relative contributions of PT and ET for a given set of substrates. These findings underscore why the basicity of M-oxido units needs to be considered in C-H functionalization.
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Affiliation(s)
- Suman K Barman
- Department of Chemistry, University of California Irvine, CA 92697;
| | - Meng-Yin Yang
- Department of Chemistry, University of California Irvine, CA 92697
| | | | - Michael T Green
- Department of Chemistry, University of California Irvine, CA 92697;
- Department of Molecular Biosciences and Biochemistry, University of California Irvine, CA 92697
| | - A S Borovik
- Department of Chemistry, University of California Irvine, CA 92697;
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23
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Vartanova AE, Plodukhin AY, Ratmanova NK, Andreev IA, Anisimov MN, Gudimchuk NB, Rybakov VB, Levina II, Ivanova OA, Trushkov IV, Alabugin IV. Expanding Stereoelectronic Limits of endo- tet Cyclizations: Synthesis of Benz[ b]azepines from Donor-Acceptor Cyclopropanes. J Am Chem Soc 2021; 143:13952-13961. [PMID: 34406759 DOI: 10.1021/jacs.1c07088] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The importance of intramolecular constraints in cyclic transition-state geometries is especially pronounced in n-endo-tet cyclizations, where the usual backside approach of a nucleophile to the breaking bond is impossible for the rings containing less than eight atoms. Herein, we expand the limits of endo-tet cyclizations and show that donor-acceptor cyclopropanes can provide a seven-membered ring via a genuine 6-endo-tet process. Substrates containing a N-alkyl-N-arylcarbamoyl moiety as an acceptor group undergo Lewis acid-induced cyclization to form tetrahydrobenz[b]azepin-2-ones in high yields. The reaction proceeds with the inversion of the configuration at the electrophilic carbon. In this process, a formally six-membered transition state yields a seven-membered ring as the pre-existing cycle is merged into the forming ring. The stereochemistry of the products can be controlled by the reaction time and by the nature of Lewis acid, opening access to both diastereomers by tuning of the reaction conditions.
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Affiliation(s)
- Anna E Vartanova
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119334, Russian Federation.,Faculty of Science, RUDN University, Moscow 117198, Russian Federation
| | - Andrey Yu Plodukhin
- Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow 119991, Russian Federation
| | - Nina K Ratmanova
- Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology, and Immunology, Moscow 117997, Russian Federation
| | - Ivan A Andreev
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119334, Russian Federation.,Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology, and Immunology, Moscow 117997, Russian Federation
| | - Mikhail N Anisimov
- Department of Physics, M. V. Lomonosov Moscow State University, Moscow 119991, Russian Federation.,Center for Theoretical Problems of Physicochemical Pharmacology, Moscow 119334, Russian Federation
| | - Nikita B Gudimchuk
- Department of Physics, M. V. Lomonosov Moscow State University, Moscow 119991, Russian Federation.,Center for Theoretical Problems of Physicochemical Pharmacology, Moscow 119334, Russian Federation
| | - Victor B Rybakov
- Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow 119991, Russian Federation
| | - Irina I Levina
- Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russian Federation
| | - Olga A Ivanova
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119334, Russian Federation.,Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow 119991, Russian Federation
| | - Igor V Trushkov
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119334, Russian Federation
| | - Igor V Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390 United States
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24
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Salamone M, Galeotti M, Romero-Montalvo E, van Santen JA, Groff BD, Mayer JM, DiLabio GA, Bietti M. Bimodal Evans-Polanyi Relationships in Hydrogen Atom Transfer from C(sp 3)-H Bonds to the Cumyloxyl Radical. A Combined Time-Resolved Kinetic and Computational Study. J Am Chem Soc 2021; 143:11759-11776. [PMID: 34309387 PMCID: PMC8343544 DOI: 10.1021/jacs.1c05566] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Indexed: 12/11/2022]
Abstract
The applicability of the Evans-Polanyi (EP) relationship to HAT reactions from C(sp3)-H bonds to the cumyloxyl radical (CumO•) has been investigated. A consistent set of rate constants, kH, for HAT from the C-H bonds of 56 substrates to CumO•, spanning a range of more than 4 orders of magnitude, has been measured under identical experimental conditions. A corresponding set of consistent gas-phase C-H bond dissociation enthalpies (BDEs) spanning 27 kcal mol-1 has been calculated using the (RO)CBS-QB3 method. The log kH' vs C-H BDE plot shows two distinct EP relationships, one for substrates bearing benzylic and allylic C-H bonds (unsaturated group) and the other one, with a steeper slope, for saturated hydrocarbons, alcohols, ethers, diols, amines, and carbamates (saturated group), in line with the bimodal behavior observed previously in theoretical studies of reactions promoted by other HAT reagents. The parallel use of BDFEs instead of BDEs allows the transformation of this correlation into a linear free energy relationship, analyzed within the framework of the Marcus theory. The ΔG⧧HAT vs ΔG°HAT plot shows again distinct behaviors for the two groups. A good fit to the Marcus equation is observed only for the saturated group, with λ = 58 kcal mol-1, indicating that with the unsaturated group λ must increase with increasing driving force. Taken together these results provide a qualitative connection between Bernasconi's principle of nonperfect synchronization and Marcus theory and suggest that the observed bimodal behavior is a general feature in the reactions of oxygen-based HAT reagents with C(sp3)-H donors.
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Affiliation(s)
- Michela Salamone
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Marco Galeotti
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Eduardo Romero-Montalvo
- Department
of Chemistry, The University of British
Columbia, 3247 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - Jeffrey A. van Santen
- Department
of Chemistry, The University of British
Columbia, 3247 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - Benjamin D. Groff
- Department
of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, United States
| | - James M. Mayer
- Department
of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, United States
| | - Gino A. DiLabio
- Department
of Chemistry, The University of British
Columbia, 3247 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - Massimo Bietti
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
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25
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Li S, Su M, Sun J, Hu K, Jin J. Visible Light-Promoted Magnesium, Iron, and Nickel Catalysis Enabling C(sp 3)-H Lactonization of 2-Alkylbenzoic Acids. Org Lett 2021; 23:5842-5847. [PMID: 34236198 DOI: 10.1021/acs.orglett.1c01984] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A mild and practical C(sp3)-H lactonization protocol has been achieved by merging photocatalysis and magnesium (iron, nickel) catalysis. A diverse range of 2-alkylbenzoic acids with a variety of substitution patterns could be transformed into the corresponding phthalide products. Based on the mechanistic experimentation and reported prior studies, a possible mechanism for the benzylic oxidative lactonization reaction was proposed with the hypothetic photoactive ternary complex formed between the 2-alkylbenzoic acid substrate, magnesium ion, and bromate anion.
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Affiliation(s)
- Sasa Li
- CAS Key Laboratory of Synthetic Chemistry of Natural Substances, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Mincong Su
- CAS Key Laboratory of Synthetic Chemistry of Natural Substances, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Jie Sun
- CAS Key Laboratory of Synthetic Chemistry of Natural Substances, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Kunjun Hu
- CAS Key Laboratory of Synthetic Chemistry of Natural Substances, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Jian Jin
- CAS Key Laboratory of Synthetic Chemistry of Natural Substances, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
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26
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Chen H, Wang L, Xu S, Liu X, He Q, Song L, Ji H. Selective Functionalization of Hydrocarbons Using a ppm Bioinspired Molecular Tweezer via Proton-Coupled Electron Transfer. ACS Catal 2021. [DOI: 10.1021/acscatal.1c01350] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Hongyu Chen
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
| | - Lingling Wang
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai 519082, China
| | - Sheng Xu
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai 519082, China
| | - Xiaohui Liu
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
| | - Qian He
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
| | - Lijuan Song
- School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055 China
- Shenzhen Bay Laboratory, Shenzhen 518055, China
| | - Hongbing Ji
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
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27
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Costentin C, Limoges B, Robert M, Tard C. A Pioneering Career in Electrochemistry: Jean-Michel Savéant. ACS Catal 2021. [DOI: 10.1021/acscatal.0c05632] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Cyrille Costentin
- Département de Chimie Moléculaire, Université Grenoble-Alpes, CNRS, UMR 5250, 38000 Grenoble, France
- Université de Paris, F-75006 Paris, France
| | - Benoît Limoges
- Université de Paris, Laboratoire d’Electrochimie Moléculaire, CNRS, F-75006 Paris, France
| | - Marc Robert
- Université de Paris, Laboratoire d’Electrochimie Moléculaire, CNRS, F-75006 Paris, France
- Institut Universitaire de France, F-75005 Paris, France
| | - Cédric Tard
- Laboratoire de Chimie Moléculaire (LCM), CNRS, École Polytechnique, Institut Polytechnique de Paris, 91120 Palaiseau, France
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28
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Shada ADR, Miller AJM, Emge TJ, Goldman AS. Catalytic Dehydrogenation of Alkanes by PCP–Pincer Iridium Complexes Using Proton and Electron Acceptors. ACS Catal 2021. [DOI: 10.1021/acscatal.0c05160] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Arun Dixith Reddy Shada
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
| | - Alexander J. M. Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Thomas J. Emge
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
| | - Alan S. Goldman
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
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29
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Schneider JE, Goetz MK, Anderson JS. Statistical analysis of C-H activation by oxo complexes supports diverse thermodynamic control over reactivity. Chem Sci 2021; 12:4173-4183. [PMID: 34163690 PMCID: PMC8179456 DOI: 10.1039/d0sc06058e] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 01/28/2021] [Indexed: 01/29/2023] Open
Abstract
Transition metal oxo species are key intermediates for the activation of strong C-H bonds. As such, there has been interest in understanding which structural or electronic parameters of metal oxo complexes determine their reactivity. Factors such as ground state thermodynamics, spin state, steric environment, oxygen radical character, and asynchronicity have all been cited as key contributors, yet there is no consensus on when each of these parameters is significant or the relative magnitude of their effects. Herein, we present a thorough statistical analysis of parameters that have been proposed to influence transition metal oxo mediated C-H activation. We used density functional theory (DFT) to compute parameters for transition metal oxo complexes and analyzed their ability to explain and predict an extensive data set of experimentally determined reaction barriers. We found that, in general, only thermodynamic parameters play a statistically significant role. Notably, however, there are independent and significant contributions from the oxidation potential and basicity of the oxo complexes which suggest a more complicated thermodynamic picture than what has been shown previously.
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Affiliation(s)
| | - McKenna K Goetz
- Department of Chemistry, University of Chicago Chicago IL 60637 USA
| | - John S Anderson
- Department of Chemistry, University of Chicago Chicago IL 60637 USA
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30
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Tyburski R, Liu T, Glover SD, Hammarström L. Proton-Coupled Electron Transfer Guidelines, Fair and Square. J Am Chem Soc 2021; 143:560-576. [PMID: 33405896 PMCID: PMC7880575 DOI: 10.1021/jacs.0c09106] [Citation(s) in RCA: 196] [Impact Index Per Article: 65.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Indexed: 12/23/2022]
Abstract
Proton-coupled electron transfer (PCET) reactions are fundamental to energy transformation reactions in natural and artificial systems and are increasingly recognized in areas such as catalysis and synthetic chemistry. The interdependence of proton and electron transfer brings a mechanistic richness of reactivity, including various sequential and concerted mechanisms. Delineating between different PCET mechanisms and understanding why a particular mechanism dominates are crucial for the design and optimization of reactions that use PCET. This Perspective provides practical guidelines for how to discern between sequential and concerted mechanisms based on interpretations of thermodynamic data with temperature-, pressure-, and isotope-dependent kinetics. We present new PCET-zone diagrams that show how a mechanism can switch or even be eliminated by varying the thermodynamic (ΔGPT° and ΔGET°) and coupling strengths for a PCET system. We discuss the appropriateness of asynchronous concerted PCET to rationalize observations in organic reactions, and the distinction between hydrogen atom transfer and other concerted PCET reactions. Contemporary issues and future prospects in PCET research are discussed.
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Affiliation(s)
- Robin Tyburski
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
| | - Tianfei Liu
- Department
of Chemistry, University of North Carolina
at Chapel Hill, Chapel
Hill, North Carolina 27599-3290, United States
| | - Starla D. Glover
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
| | - Leif Hammarström
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
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31
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Zhou Z, Kong X, Liu T. Applications of Proton-Coupled Electron Transfer in Organic Synthesis. CHINESE J ORG CHEM 2021. [DOI: 10.6023/cjoc202106001] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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32
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Bím D, Alonso-Gil S, Srnec M. From Synthetic to Biological Fe 4 S 4 Complexes: Redox Properties Correlated to Function of Radical S-Adenosylmethionine Enzymes. Chempluschem 2020; 85:2534-2541. [PMID: 33245201 DOI: 10.1002/cplu.202000663] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 11/02/2020] [Indexed: 11/10/2022]
Abstract
By employing the computational protocol for calculation of reduction potentials of the Fe4 S4 -containing species validated using a representative series of well-defined synthetic complexes, we focused on redox properties of two prototypical radical SAM enzymes to reveal how they transform SAM into the reactive 5'-deoxyadenosyl radical, and how they tune this radical for its proper biological function. We found the reduction potential of SAM is indeed elevated by 0.3-0.4 V upon coordination to Fe4 S4 , which was previously speculated in the literature. This makes a generation of 5'-deoxyadenosyl radical from SAM less endergonic (by ca. 7-9 kcal mol-1 ) and hence more feasible in both enzymes as compared to the identical process in water. Furthermore, our calculations indicate that the enzyme-bound 5'-deoxyadenosyl radical has a significantly lower reduction potential than in referential aqueous solution, which may help the enzymes to suppress potential side redox reactions and simultaneously elevate its proton-philic character, which may, in turn, promote the radical hydrogen-atom abstraction ability.
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Affiliation(s)
- Daniel Bím
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague, 8 182 23, Czech Republic
| | - Santiago Alonso-Gil
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague, 8 182 23, Czech Republic
| | - Martin Srnec
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague, 8 182 23, Czech Republic
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33
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Kotani H, Shimomura H, Ikeda K, Ishizuka T, Shiota Y, Yoshizawa K, Kojima T. Mechanistic Insight into Concerted Proton-Electron Transfer of a Ru(IV)-Oxo Complex: A Possible Oxidative Asynchronicity. J Am Chem Soc 2020; 142:16982-16989. [PMID: 32924508 DOI: 10.1021/jacs.0c05738] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have thoroughly investigated the oxidation of benzyl alcohol (BA) derivatives by a RuIV(O) complex (RuIV(O)) in the absence or presence of Brønsted acids in order to elucidate the proton-coupled electron-transfer (PCET) mechanisms in C-H oxidation on the basis of a kinetic analysis. Oxidation of BA derivatives by RuIV(O) without acids proceeded through concerted proton-electron transfer (CPET) with a large kinetic isotope effect (KIE). In contrast, the oxidation of 3,4,5-trimethoxy-BA ((MeO)3-BA) by RuIV(O) was accelerated by the addition of acids, in which the KIE value reached 1.1 with TFA (550 mM), indicating an alteration of the PCET mechanism from CPET to stepwise electron transfer (ET) followed by proton transfer (PT). Although the oxidized products of BA derivatives were confirmed to be the corresponding benzaldehydes in the range of acid concentrations (0-550 mM), a one-electron-reduction potential of RuIV(O) was positively shifted with increases in the concentrations of acids. The elevated reduction potential of RuIV(O) strongly influenced the PCET mechanisms in the oxidation of (MeO)3-BA, changing the mechanism from CPET to ET/PT, as evidenced by the driving-force dependence of logarithms of reaction rate constants in light of the Marcus theory of ET. In addition, dependence of activation parameters on acid concentrations suggested that an oxidative asynchronous CPET, which is not an admixture of the CPET and ET/PT mechanisms, is probably operative in the boundary region (0 mM < [TFA] < 50 mM) involving a one-proton-interacted RuIV(O)···H+ as a dominant reactive species.
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Affiliation(s)
- Hiroaki Kotani
- Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba and CREST (JST), 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
| | - Hinatsu Shimomura
- Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba and CREST (JST), 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
| | - Kei Ikeda
- Institute for Materials Chemistry and Engineering, Kyushu University and CREST (JST), Motooka, Nishi-Ku, Fukuoka 819-0395, Japan
| | - Tomoya Ishizuka
- Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba and CREST (JST), 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
| | - Yoshihito Shiota
- Institute for Materials Chemistry and Engineering, Kyushu University and CREST (JST), Motooka, Nishi-Ku, Fukuoka 819-0395, Japan
| | - Kazunari Yoshizawa
- Institute for Materials Chemistry and Engineering, Kyushu University and CREST (JST), Motooka, Nishi-Ku, Fukuoka 819-0395, Japan
| | - Takahiko Kojima
- Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba and CREST (JST), 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
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34
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Ghorbani F, Harry SA, Capilato JN, Pitts CR, Joram J, Peters GN, Tovar JD, Smajlagic I, Siegler MA, Dudding T, Lectka T. Carbonyl-Directed Aliphatic Fluorination: A Special Type of Hydrogen Atom Transfer Beats Out Norrish II. J Am Chem Soc 2020; 142:14710-14724. [PMID: 32786786 DOI: 10.1021/jacs.0c07004] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Recently, our group reported that enone and ketone functional groups, upon photoexcitation, can direct site-selective sp3 C-H fluorination in terpenoid derivatives. How this transformation actually occurred remained mysterious, as a significant number of mechanistic possibilities came to mind. Herein, we report a comprehensive study describing the reaction mechanism through kinetic studies, isotope-labeling experiments, 19F NMR, electrochemical studies, synthetic probes, and computational experiments. To our surprise, the mechanism suggests intermolecular hydrogen atom transfer (HAT) chemistry is at play, rather than classical Norrish hydrogen atom abstraction as initially conceived. What is more, we discovered a unique role for photopromoters such as benzil and related compounds that necessitates their chemical transformation through fluorination in order to be effective. Our findings provide documentation of an unusual form of directed HAT and are of crucial importance for defining the necessary parameters for the development of future methods.
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Affiliation(s)
- Fereshte Ghorbani
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Stefan Andrew Harry
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Joseph N Capilato
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Cody Ross Pitts
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Jacob Joram
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Garvin N Peters
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - John D Tovar
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Ivor Smajlagic
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
| | - Maxime A Siegler
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Travis Dudding
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
| | - Thomas Lectka
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
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35
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Kwon YM, Lee Y, Evenson GE, Jackson TA, Wang D. Crystal Structure and C-H Bond-Cleaving Reactivity of a Mononuclear Co IV-Dinitrate Complex. J Am Chem Soc 2020; 142:13435-13441. [PMID: 32639730 PMCID: PMC7429286 DOI: 10.1021/jacs.0c04368] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High-valent FeIV═O intermediates with a terminal metal-oxo moiety are key oxidants in many enzymatic and synthetic C-H bond oxidation reactions. While generating stable metal-oxo species for late transition metals remains synthetically challenging, notably, a number of high-valent non-oxo-metal species of late transition metals have been recently described as strong oxidants that activate C-H bonds. In this work, we obtained an unprecedented mononuclear CoIV-dinitrate complex (2) upon one-electron oxidation of its Co(III) precursor supported by a tridentate dianionic N3 ligand. 2 was structurally characterized by X-ray crystallography, showing a square pyramidal geometry with two coordinated nitrate anions. Furthermore, characterization of 2 using combined spectroscopic and computational methods revealed that 2 is a low-spin (S = 1/2) Co(IV) species with the unpaired electron located on the cobalt dz2 orbital, which is well positioned for substrate oxidations. Indeed, while having a high thermal stability, 2 is able to cleave sp3 C-H bonds up to 87 kcal/mol to afford rate constants and kinetic isotope effects (KIEs) of 2-6 that are comparable to other high-valent metal oxidants. The ability to oxidize strong C-H bonds has yet to be observed for CoIV-O and CoIII═O species previously reported. Therefore, 2 represents the first high-valent Co(IV) species that is both structurally characterized by X-ray crystallography and capable of activating strong C-H bonds.
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Affiliation(s)
- Yubin M. Kwon
- Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, Montana 59803, United States
| | - Yuri Lee
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, The University of Kansas, Kansas 66045, United States
| | - Garrett E. Evenson
- Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, Montana 59803, United States
| | - Timothy A. Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, The University of Kansas, Kansas 66045, United States
| | - Dong Wang
- Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, Montana 59803, United States
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36
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Ener ME, Darcy JW, Menges FS, Mayer JM. Base-Directed Photoredox Activation of C-H Bonds by PCET. J Org Chem 2020; 85:7175-7180. [PMID: 32364382 DOI: 10.1021/acs.joc.0c00333] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Photoredox catalysis using proton-coupled electron transfer (PCET) has emerged as a powerful method for bond transformations. We previously employed traditional chemical oxidants to achieve multiple-site concerted proton-electron transfer (MS-CPET) activation of a C-H bond in a proof-of-concept fluorenyl-benzoate substrate. As described here, photoredox oxidation of the fluorenyl-benzoate follows the same rate constant vs driving force trend determined for thermal MS-CPET. Analogous photoredox catalysis enables C-H activation and H/D exchange in a number of additional substrates with favorably positioned bases. Mechanistic studies support our hypothesis that MS-CPET is a viable pathway for bond activation for substrates in which the C-H bond is weak, while stepwise carboxylate oxidation and hydrogen atom transfer likely predominate for stronger C-H bonds.
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Affiliation(s)
- Maraia E Ener
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Julia W Darcy
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Fabian S Menges
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - James M Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
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37
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Costentin C, Savéant JM. Hydrogen and proton exchange at carbon. Imbalanced transition state and mechanism crossover. Chem Sci 2019; 11:1006-1010. [PMID: 34084355 PMCID: PMC8146334 DOI: 10.1039/c9sc05147c] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A recent remarkable study of the C-H oxidation of substituted fluorenyl-benzoates together with the transfer of a proton to an internal receiving group by means of electron transfer outer-sphere oxidants, in the noteworthy absence of hydrogen-bonding interactions, is taken as an example to uncover the existence of a mechanism crossover, making the reaction pass from a CPET pathway to a PTET pathway as the driving force of the global reaction decreases. This was also the occasion to stress that considerations based on "imbalanced" or "asynchronous" transition states cannot replace activation/driving force models based on the quantum mechanical treatment of both electrons and transferring protons.
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Affiliation(s)
- Cyrille Costentin
- Département de Chimie Moléculaire, Université Grenoble-Alpes, CNRS, UMR 5250 38000 Grenoble France .,Université Paris Diderot, Sorbonne Paris Cité 75205 Paris Cedex 13 France
| | - Jean-Michel Savéant
- Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS No. 7591 Bâtiment Lavoisier, 15 rue Jean de Baïf 75205 Paris Cedex 13 France
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38
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Bruch QJ, Connor GP, Chen CH, Holland PL, Mayer JM, Hasanayn F, Miller AJM. Dinitrogen Reduction to Ammonium at Rhenium Utilizing Light and Proton-Coupled Electron Transfer. J Am Chem Soc 2019; 141:20198-20208. [DOI: 10.1021/jacs.9b10031] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Quinton J. Bruch
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Gannon P. Connor
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Chun-Hsing Chen
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Alexander J. M. Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
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39
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Liu T, Tyburski R, Wang S, Fernández-Terán R, Ott S, Hammarström L. Elucidating Proton-Coupled Electron Transfer Mechanisms of Metal Hydrides with Free Energy- and Pressure-Dependent Kinetics. J Am Chem Soc 2019; 141:17245-17259. [PMID: 31587555 DOI: 10.1021/jacs.9b08189] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Proton-coupled electron transfer (PCET) was studied in a series of tungsten hydride complexes with pendant pyridyl arms ([(PyCH2Cp)WH(CO)3], PyCH2Cp = pyridylmethylcyclopentadienyl), triggered by laser flash-generated RuIII-tris-bipyridine oxidants, in acetonitrile solution. The free energy dependence of the rate constant and the kinetic isotope effects (KIEs) showed that the PCET mechanism could be switched between concerted and the two stepwise PCET mechanisms (electron-first or proton-first) in a predictable fashion. Straightforward and general guidelines for how the relative rates of the different mechanisms depend on oxidant and base are presented. The rate of the concerted reaction should depend symmetrically on changes in oxidant and base strength, that is on the overall ΔG0PCET, and we argue that an "asynchronous" behavior would not be consistent with a model where the electron and proton tunnel from a common transition state. The observed rate constants and KIEs were examined as a function of hydrostatic pressure (1-2000 bar) and were found to exhibit qualitatively different dependence on pressure for different PCET mechanisms. This is discussed in terms of different volume profiles of the PCET mechanisms as well as enhanced proton tunneling for the concerted mechanism. The results allowed for assignment of the main mechanism operating in the different cases, which is one of the critical questions in PCET research. They also show how the rate of a PCET reaction will be affected very differently by changes of oxidant and base strength, depending on which mechanism dominates. This is of fundamental interest as well as of practical importance for rational design of, for example, catalysts for fuel cells and solar fuel formation, which operate in steps of PCET reactions. The mechanistic richness shown by this system illustrates that the specific mechanism is not intrinsic to a specific synthetic catalyst or enzyme active site but depends on the reaction conditions.
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Affiliation(s)
- Tianfei Liu
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Robin Tyburski
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Shihuai Wang
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Ricardo Fernández-Terán
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Sascha Ott
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
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40
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Qiu G, Knowles RR. Understanding Chemoselectivity in Proton-Coupled Electron Transfer: A Kinetic Study of Amide and Thiol Activation. J Am Chem Soc 2019; 141:16574-16578. [PMID: 31573194 DOI: 10.1021/jacs.9b08398] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
While the mechanistic understanding of proton-coupled electron transfer (PCET) has advanced significantly, few reports have sought to elucidate the factors that control chemoselectivity in these reactions. Here we present a kinetic study that provides a quantitative basis for understanding the chemoselectivity in competitive PCET activations of amides and thiols relevant to catalytic olefin hydroamidation reactions. These results demonstrate how the interplay between PCET rate constants, hydrogen-bonding equilibria, and rate-driving force relationships jointly determine PCET chemoselectivity under a given set of conditions. In turn, these findings predict reactivity trends in a model hydroamidation reaction, rationalize the selective activation of amide N-H bonds in the presence of much weaker thiol S-H bonds, and deliver strategies to improve the efficiencies of PCET reactions employing thiol co-catalysts.
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Affiliation(s)
- Guanqi Qiu
- Department of Chemistry , Princeton University , Princeton , New Jersey 08544 , United States
| | - Robert R Knowles
- Department of Chemistry , Princeton University , Princeton , New Jersey 08544 , United States
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41
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Sayfutyarova ER, Lam YC, Hammes-Schiffer S. Strategies for Enhancing the Rate Constant of C-H Bond Cleavage by Concerted Proton-Coupled Electron Transfer. J Am Chem Soc 2019; 141:15183-15189. [PMID: 31464122 DOI: 10.1021/jacs.9b06849] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recently selective C-H bond cleavage under mild conditions with weak oxidants was reported for fluorenyl-benzoates. This mechanism is based on multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an outer-sphere oxidant coupled to intramolecular proton transfer to a well-positioned proton acceptor. The electron transfer driving force depends predominantly on the oxidant, and the proton transfer driving force depends mainly on the basicity of the carboxylate, which is influenced by the substituent on the benzoate fragment. Experiments showed that the rate constants are much more sensitive to the carboxylate basicity than to the redox potential of the oxidant. Herein a vibronically nonadiabatic PCET theory is used to explain how changing the driving force for the electron and proton transfer components of the reaction through varying the oxidant and the substituent, respectively, impacts the PCET rate constant. In addition to increasing the driving force for proton transfer, enhancing the basicity of the carboxylate also decreases the equilibrium proton donor-acceptor distance, thereby facilitating the sampling of shorter proton donor-acceptor distances. This additional effect arising from the strong dependence of proton transfer on the proton donor-acceptor distance provides an explanation for the greater sensitivity of the rate constant to the carboxylate basicity than to the redox potential of the oxidant. These fundamental insights have broad implications for developing new strategies to activate C-H bonds, specifically by designing systems with shorter equilibrium proton donor-acceptor distances.
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Affiliation(s)
- Elvira R Sayfutyarova
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Yan-Choi Lam
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
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