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Wang Y, Zhou Y, Sun W, Wang X, Yao J, Li H. Identifying Radical Pathways for Cu(I)/Cu(II) Relay Catalyzed Oxygenation via Online Coupled EPR/UV-Vis/Near-IR Monitoring. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024:e2402890. [PMID: 38810102 DOI: 10.1002/advs.202402890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 05/11/2024] [Indexed: 05/31/2024]
Abstract
Copper-catalyzed C─H oxygenation has drawn considerable attention in mechanistic studies. However, a comprehensive investigation combining radical pathways with a metal-catalytic cycle is challenged by the intricate organic radicals and metallic intermediates. Herein, an online coupled EPR/UV-vis/near-IR detecting method is developed to simultaneously monitor both reactive radical species and copper complex intermediates during the reaction. Focusing on copper-catalyzed phenol oxygenation with cumene hydroperoxide, the short-lived alkylperoxyl radical (EPR signal at g = 2.0143) as well as the unexpected square planar Cu(II)-alkoxyl radical complex (near-IR signal at 833 nm) are unveiled during the reaction, in addition to the observable phenoxyl radical in EPR, quinone product in UV-vis, and Cu(II) center in EPR. With a comprehensive picture of diverse intermediates evolving over the same timeline, a novel Cu(I)/Cu(II) proposed relay-catalyzed sequential radical pathway. In this sequence, Cu(II) activates hydroperoxide through Cu(II)-OOR into the alkylperoxide radical, while the reaction between Cu(I) and hydroperoxide leads to Cu(II)(•OR)OH with high H-atom abstracting activity. These results provide a thorough understanding of the Cu(I)/Cu(II) relay catalysis for phenol oxygenation, setting the stage for mechanistic investigations into intricate radical reactions promoted by metallic complexes.
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Affiliation(s)
- Yongtao Wang
- Department of Chemistry, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
- Center of Chemistry for Frontier Technologies, ZJU-NHU United R&D Center, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
| | - Yujia Zhou
- Department of Chemistry, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
| | - Wenjing Sun
- Department of Chemistry, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
| | - Xinyu Wang
- Department of Chemistry, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
| | - Jia Yao
- Department of Chemistry, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
- Center of Chemistry for Frontier Technologies, ZJU-NHU United R&D Center, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
| | - Haoran Li
- Department of Chemistry, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
- Center of Chemistry for Frontier Technologies, ZJU-NHU United R&D Center, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
- State Key Laboratory of Chemical Engineering and College of Chemical and Biological Engineering, Zhejiang University, 866 Yuhangtang Rd, Hangzhou, 310058, China
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2
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Thomas J, Mokkawes T, Senft L, Dey A, Gordon JB, Ivanovic-Burmazovic I, de Visser SP, Goldberg DP. Axial Ligation Impedes Proton-Coupled Electron-Transfer Reactivity of a Synthetic Compound-I Analogue. J Am Chem Soc 2024; 146:12338-12354. [PMID: 38669456 DOI: 10.1021/jacs.3c08950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2024]
Abstract
The nature of the axial ligand in high-valent iron-oxo heme enzyme intermediates and related synthetic catalysts is a critical structural element for controlling proton-coupled electron-transfer (PCET) reactivity of these species. Herein, we describe the generation and characterization of three new 6-coordinate, iron(IV)-oxo porphyrinoid-π-cation-radical complexes and report their PCET reactivity together with a previously published 5-coordinate analogue, FeIV(O)(TBP8Cz+•) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato3-) (2) (Cho, K. A high-valent iron-oxo corrolazine activates C-H bonds via hydrogen-atom transfer. J. Am. Chem. Soc. 2012, 134, 7392-7399). The new complexes FeIV(O)(TBP8Cz+•)(L) (L = 1-methyl imidazole (1-MeIm) (4a), 4-dimethylaminopyridine (DMAP) (4b), cyanide (CN-)(4c)) can be generated from either oxidation of the ferric precursors or by addition of L to the Compound-I (Cpd-I) analogue at low temperatures. These complexes were characterized by UV-vis, electron paramagnetic resonance (EPR), and Mössbauer spectroscopies, and cryospray ionization mass spectrometry (CSI-MS). Kinetic studies using 4-OMe-TEMPOH as a test substrate indicate that coordination of a sixth axial ligand dramatically lowers the PCET reactivity of the Cpd-I analogue (rates up to 7000 times slower). Extensive density functional theory (DFT) calculations together with the experimental data show that the trend in reactivity with the axial ligands does not correlate with the thermodynamic driving force for these reactions or the calculated strengths of the O-H bonds being formed in the FeIV(O-H) products, pointing to non-Bell-Evans-Polanyi behavior. However, the PCET reactivity does follow a trend with the bracketed reduction potential of Cpd-I analogues and calculated electron affinities. The combined data suggest a concerted mechanism (a concerted proton electron transfer (CPET)) and an asynchronous movement of the electron/proton pair in the transition state.
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Affiliation(s)
- Jithin Thomas
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Thirakorn Mokkawes
- The Manchester Institute of Biotechnology and Department of Chemical Engineering, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Laura Senft
- Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr., 5-13, Haus D, 81377 München, Germany
| | - Aniruddha Dey
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Jesse B Gordon
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Ivana Ivanovic-Burmazovic
- Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr., 5-13, Haus D, 81377 München, Germany
| | - Sam P de Visser
- The Manchester Institute of Biotechnology and Department of Chemical Engineering, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - David P Goldberg
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
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3
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Kaur L, Mandal D. A density functional theory analysis of the C-H activation reactivity of iron(IV)-oxo complexes with an 'O' substituted tetramethylcyclam macrocycle. Dalton Trans 2024; 53:7527-7535. [PMID: 38597582 DOI: 10.1039/d4dt00063c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
In this article, we present a meticulous computational study to foresee the effect of an oxygen-rich macrocycle on the reactivity for C-H activation. For this study, a widely studied nonheme Fe(IV)O molecule with a TMC (1,4,8,11-tetramethyl 1,4,8,11-tetraazacyclotetradecane) macrocycle that is equatorially attached to four nitrogen atoms (designated as N4) and acetonitrile as an axial ligand has been taken into account. For the goal of hetero-substitution, step-by-step replacement of the N4 framework with O atoms, i.e., N4, N3O1, N2O2, N1O3, and O4 systems, has been considered, and dihydroanthracene (DHA) has been used as the substrate. In order to neutralise the system and prevent the self-interaction error in DFT, triflate counterions have also been included in the calculations. The study of the energetics of these C-H bond activation reactions and the potential energy surfaces mapped therefore reveal that the initial hydrogen abstraction, which is the rate-determining step, follows the two-state reactivity (TSR) pattern, which means that the originally excited quintet state falls lower in the transition state and the product. The reaction follows the hydrogen atom transfer (HAT) mechanism, as indicated by the spin density studies. The results revealed a fascinating reactivity order, in which the reactivity increases with the enrichment of the oxygen atom in the equatorial position, namely the order follows N4 < N3O1 < N2O2 < N1O3 < O4. The impacts of oxygen substitution on quantum mechanical tunneling and the H/D kinetic isotope effect have also been investigated. When analysing the causes of this reactivity pattern, a number of variables have been identified, including the reactant-like transition structure, spin density distribution, distortion energy, and energies of the electron acceptor orbital, i.e., the energy of the LUMO (σ*z2), which validate the obtained outcome. Our results also show very good agreement with earlier combined experimental and theoretical studies considering TMC and TMCO-type complexes. The DFT predictions reported here will undoubtedly encourage experimental research in this biomimetic field, as they provide an alternative with higher reactivity in which heteroatoms can be substituted for the traditional nitrogen atom.
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Affiliation(s)
- Lovleen Kaur
- Department of Chemistry and Biochemistry, Thapar Institute of Engineering and Technology, Patiala-147004, Punjab, India.
| | - Debasish Mandal
- Department of Chemistry and Biochemistry, Thapar Institute of Engineering and Technology, Patiala-147004, Punjab, India.
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4
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Takeyama T, Shimazaki Y. Diversity of oxidation state in copper complexes with phenolate ligands. Dalton Trans 2024; 53:3911-3929. [PMID: 38319292 DOI: 10.1039/d3dt04230h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
The phenoxyl radical binding copper complexes have been widely developed and their detailed geometric and electronic structures have been clarified. While many one-electron oxidized CuII-phenolate complexes have been reported previously, recent studies of the Cu-phenolate complexes proceed toward elucidation of the complexes with other oxidation states, such as the phenoxyl radical binding CuI complexes and CuIV-phenolate complexes in the formal oxidation state. This Perspective focuses on new aspects of the properties and reactivities of various Cu-phenolate and Cu-phenoxyl radical complexes with emphasis on the relationship between geometric and electronic structures.
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Affiliation(s)
- Tomoyuki Takeyama
- Department of Applied Chemistry, Sanyo-Onoda City University, 1-1-1, Daigakudori, Sanyo-Onoda, 756-0884 Yamaguchi, Japan.
| | - Yuichi Shimazaki
- College of Science, Ibaraki University, Bunkyo, Mito 310-8512, Japan.
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5
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Awasthi A, Mallojjala SC, Kumar R, Eerlapally R, Hirschi JS, Draksharapu A. Altering the Localization of an Unpaired Spin in a Formal Ni(V) Species. Chemistry 2024; 30:e202302824. [PMID: 37903027 PMCID: PMC10841873 DOI: 10.1002/chem.202302824] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 10/28/2023] [Accepted: 10/30/2023] [Indexed: 11/01/2023]
Abstract
The participation of both ligand and the metal center in the redox events has been recognized as one of the ways to attain the formal high valent complexes for the late 3d metals, such as Ni and Cu. Such an approach has been employed successfully to stabilize a Ni(III) bisphenoxyl diradical species in which there exist an equilibrium between the ligand and the Ni localized resultant spin. The present work, however, broadens the scope of the previously reported three oxidized equivalent species by conveying the approaches that tend to affect the reported equilibrium in CH3 CN at 233 K. Various spectroscopic characterization revealed that employing exogenous N-donor ligands like 1-methyl imidazole and pyridine favors the formation of the Ni centered localized spin though axial binding. In contrast, due to its steric hinderance, quinoline favors an exclusive ligand localized radical species. DFT studies shed light on the novel intermediates' complex electronic structure. Further, the three oxidized equivalent species with the Ni centered spin was examined for its hydrogen atom abstraction ability stressing their key role in alike reactions.
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Affiliation(s)
- Ayushi Awasthi
- Southern Laboratories-208 A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | | | - Rakesh Kumar
- Southern Laboratories-208 A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Raju Eerlapally
- Southern Laboratories-208 A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Jennifer S Hirschi
- Department of Chemistry, Binghamton University, Binghamton, New York, 13902, USA
| | - Apparao Draksharapu
- Southern Laboratories-208 A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
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6
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Cao E, Sun M. Spectral Physics of Stable Cu(III) Produced by Oxidative Addition of an Alkyl Halide. Int J Mol Sci 2023; 24:15694. [PMID: 37958679 PMCID: PMC10648560 DOI: 10.3390/ijms242115694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Revised: 10/23/2023] [Accepted: 10/26/2023] [Indexed: 11/15/2023] Open
Abstract
In this paper, we theoretically investigated spectral physics on Cu(III) complexes formed by the oxidative addition of α-haloacetonitrile to ionic and neutral Cu(I) complexes, stimulated by recent experimental reports. Firstly, the electronic structures of reactants of α-haloacetonitrile and neutral Cu(I) and two kinds of products of Cu(III) complexes are visualized with the density of state (DOS) and orbital energy levels of HOMO and LUMO. The visually manifested static and dynamic polarizability as well as the first hyperpolarizability are employed to reveal the vibrational modes of the normal and resonance Raman spectra of two Cu(III) complexes. The nuclear magnetic resonance (NMR) spectra are not only used to identify the reactants and products but also to distinguish between two Cu(III) complexes. The charge difference density (CDD) reveals intramolecular charge transfer in electronic transitions in optical absorption spectra. The CDDs in fluorescence visually reveal electron-hole recombination. Our results promote a deeper understanding of the physical mechanism of stable Cu(III) produced by the oxidative addition of an alkyl halide.
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Affiliation(s)
- En Cao
- School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China;
- Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan
| | - Mengtao Sun
- School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China;
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7
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Bera M, Kaur S, Keshari K, Santra A, Moonshiram D, Paria S. Structural and Spectroscopic Characterization of Copper(III) Complexes and Subsequent One-Electron Oxidation Reaction and Reactivity Studies. Inorg Chem 2023; 62:5387-5399. [PMID: 36972560 DOI: 10.1021/acs.inorgchem.2c04168] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
Abstract
The formation of Cu(III) species are often invoked as the key intermediate in Cu-catalyzed organic transformation reactions. In this study, we synthesized Cu(II) (1) and Cu(III) (3) complexes supported by a bisamidate-bisalkoxide ligand consisting of an ortho-phenylenediamine (o-PDA) scaffold and characterized them through an array of spectroscopic techniques, including UV-visible, electron paramagnetic resonance, X-ray crystallography, and 1H nuclear magnetic resonance (NMR) and X-ray absorption spectroscopy. The Cu-N/O bond distances in 3 are ∼0.1 Å reduced compared to 1, implying a significant increase in 3's overall effective nuclear charge. Further, a Cu(III) complex (4) of a bisamidate-bisalkoxide ligand containing a trans-cyclohexane-1,2-diamine moiety exhibits nearly identical Cu-N/O bond distances to that of 3, inferring that the redox-active o-PDA backbone is not oxidized upon one-electron oxidation of the Cu(II) complex (1). In addition, a considerable difference in the 1s → 4p and 1s → 3d transition energy was observed in the X-ray absorption near-edge structure data of 3 vs 1, which is typical for the metal-centered oxidation process. Electrochemical measurements of the Cu(II) complex (1) in acetonitrile exhibited two consecutive redox couples at -0.9 and 0.4 V vs the Fc+/Fc reference electrode. One-electron oxidation reaction of 3 further resulted in the formation of a ligand-oxidized Cu complex (3a), which was characterized in depth. Reactivity studies of species 3 and 3a were explored toward the activation of the C-H/O-H bonds. A bond dissociation free energy (BDFE) value of ∼69 kcal/mol was estimated for the O-H bond of the Cu(II) complex formed upon transfer of hydrogen atom to 3. The study represents a thorough spectroscopic characterization of high-valent Cu complexes and sheds light on the PCET reactivity studies of Cu(III) complexes.
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Affiliation(s)
- Moumita Bera
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Simarjeet Kaur
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Kritika Keshari
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Aakash Santra
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Dooshaye Moonshiram
- Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
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8
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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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9
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Bouchey C, Shopov DY, Gruen AD, Tolman WB. Mimicking the Cu Active Site of Lytic Polysaccharide Monooxygenase Using Monoanionic Tridentate N-Donor Ligands. ACS OMEGA 2022; 7:35217-35232. [PMID: 36211076 PMCID: PMC9535706 DOI: 10.1021/acsomega.2c04432] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 09/02/2022] [Indexed: 06/16/2023]
Abstract
In an effort to prepare small molecule mimics of the active site of lytic polysaccharide monooxygenase (LPMO), three monoanionic tridentate N donor ligands comprising a central deprotonated amide group flanked by two neutral donors were prepared, and their coordination chemistry with Cu(I) and Cu(II) was evaluated. With Cu(I), a dimer formed, which was characterized by X-ray crystallography and NMR spectroscopy. A variety of mononuclear and dinuclear Cu(II) species with a range of auxiliary ligands (MeCN, Cl-, OH-, OAc-, OBz-, CO3 2-) were prepared and characterized by X-ray diffraction and various spectroscopies (UV-vis, EPR). The complexes exhibit structural similarities to the LPMO active site.
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Affiliation(s)
- Caitlin
J. Bouchey
- Department
of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - Dimitar Y. Shopov
- Department
of Chemistry, Washington University in St.
Louis, One Brookings Drive, Campus Box 1134, St.
Louis, Missouri 63130, United States
| | - Aaron D. Gruen
- Department
of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
| | - William B. Tolman
- Department
of Chemistry, Washington University in St.
Louis, One Brookings Drive, Campus Box 1134, St.
Louis, Missouri 63130, United States
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10
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Kaur S, Bera M, Santra A, Munshi S, Sterbinsky GE, Wu T, Moonshiram D, Paria S. Effect of Redox-Inactive Metal Ion-Nickel(III) Interactions on the Redox Properties and Proton-Coupled Electron Transfer Reactivity. Inorg Chem 2022; 61:14252-14266. [PMID: 36041064 DOI: 10.1021/acs.inorgchem.2c01472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mononuclear nickel(II) and nickel(III) complexes of a bisamidate-bisalkoxide ligand, (NMe4)2[NiII(HMPAB)] (1) and (NMe4)[NiIII(HMPAB)] (2), respectively, have been synthesized and characterized by various spectroscopic techniques including X-ray crystallography. The reaction of redox-inactive metal ions (Mn+ = Ca2+, Mg2+, Zn2+, Y3+, and Sc3+) with 2 resulted in 2-Mn+ adducts, which was assessed by an array of spectroscopic techniques including X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and reactivity studies. The X-ray structure of Ca2+ coordinated to Ni(III) complexes, 2-Ca2+T, was determined and exhibited an average Ni-Ca distance of 3.1253 Å, close to the metal ions' covalent radius. XAS analysis of 2-Ca2+ and 2-Y3+ in solution further revealed an additional coordination to Ca and Y in the 2-Mn+ adducts with shortened Ni-M distances of 2.15 and 2.11 Å, respectively, implying direct bonding interactions between Ni and Lewis acids (LAs). Such a short interatomic distance between Ni(III) and M is unprecedented and was not observed before. EPR analysis of 2 and 2-Mn+ species, moreover, displayed rhombic signals with gav > 2.12 for all complexes, supporting the +III oxidation state of Ni. The NiIII/NiII redox potential of 2 and 2-Mn+ species was determined, and a plot of E1/2 of 2-Mn+ versus pKa of [M(H2O)n]m+ exhibited a linear relationship, implying that the NiIII/NiII potential of 2 can be tuned with different redox-inactive metal ions. Reactivity studies of 2 and 2-Mn+ with different 4-X-2,6-ditert-butylphenol (4-X-DTBP) and other phenol derivatives were performed, and based on kinetic studies, we propose the involvement of a proton-coupled electron transfer (PCET) pathway. Analysis of the reaction products after the reaction of 2 with 4-OMe-DTBP showed the formation of a Ni(II) complex (1a) where one of the alkoxide arms of the ligand is protonated. A pKa value of 24.2 was estimated for 1a. The reaction of 2-Mn+ species was examined with 4-OMe-DTBP, and it was observed that the k2 values of 2-Mn+ species increase by increasing the Lewis acidity of redox-inactive metal ions. However, the obtained k2 values for 2-Mn+ species are much lower compared to the k2 value for 2. Such a variation of PCET reactivity between 2 and 2-Mn+ species may be attributed to the interactions between Ni(III) and LAs. Our findings show the significance of the secondary coordination sphere effect on the PCET reactivity of Ni(III) complexes and furnish important insights into the reaction mechanism involving high-valent nickel species, which are frequently invoked as key intermediates in Ni-mediated enzymatic reactions, solar-fuel catalysis, and biomimetic/synthetic transformation reactions.
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Affiliation(s)
- Simarjeet Kaur
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Moumita Bera
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Aakash Santra
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Sandip Munshi
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
| | - George E Sterbinsky
- X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
| | - Tianpin Wu
- X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
| | - Dooshaye Moonshiram
- Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
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11
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Engbers S, Leach IF, Havenith RWA, Klein JEMN. Homolytic X‐H Bond Cleavage at a Gold(III) Hydroxide: Insights into One‐Electron Events at Gold. Chemistry 2022; 28:e202200599. [PMID: 35506505 PMCID: PMC9401072 DOI: 10.1002/chem.202200599] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Indexed: 11/17/2022]
Abstract
C(sp3)‐H and O−H bond breaking steps in the oxidation of 1,4‐cyclohexadiene and phenol by a Au(III)‐OH complex were studied computationally. The analysis reveals that for both types of bonds the initial X−H cleavage step proceeds via concerted proton coupled electron transfer (cPCET), reflecting electron transfer from the substrate directly to the Au(III) centre and proton transfer to the Au‐bound oxygen. This mechanistic picture is distinct from the analogous formal Cu(III)‐OH complexes studied by the Tolman group (J. Am. Chem. Soc. 2019, 141, 17236–17244), which proceed via hydrogen atom transfer (HAT) for C−H bonds and cPCET for O−H bonds. Hence, care should be taken when transferring concepts between Cu−OH and Au−OH species. Furthermore, the ability of Au−OH complexes to perform cPCET suggests further possibilities for one‐electron chemistry at the Au centre, for which only limited examples exist.
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Affiliation(s)
- Silène Engbers
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen (The Netherlands
| | - Isaac F. Leach
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen (The Netherlands
- Zernike Institute for Advanced Materials Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen (The Netherlands
| | - Remco W. A. Havenith
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen (The Netherlands
- Zernike Institute for Advanced Materials Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen (The Netherlands
- Ghent Quantum Chemistry Group Department of Chemistry Ghent University Ghent 9000 Gent Belgium
| | - Johannes E. M. N. Klein
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen (The Netherlands
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12
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Theoretical perspective on mononuclear copper-oxygen mediated C–H and O–H activations: A comparison between biological and synthetic systems. CHINESE JOURNAL OF CATALYSIS 2022. [DOI: 10.1016/s1872-2067(21)63974-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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13
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Bouchey CJ, Tolman WB. Involvement of a Formally Copper(III) Nitrite Complex in Proton-Coupled Electron Transfer and Nitration of Phenols. Inorg Chem 2022; 61:2662-2668. [PMID: 35078314 PMCID: PMC9835712 DOI: 10.1021/acs.inorgchem.1c03790] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
A unique high-valent copper nitrite species, LCuNO2, was accessed via the reversible one-electron oxidation of [M][LCuNO2] (M = NBu4+ or PPN+). The complex LCuNO2 reacts with 2,4,6-tri-tert-butylphenol via a typical proton-coupled electron transfer (PCET) to yield LCuTHF and the 2,4,6-tri-tert-butylphenoxyl radical. The reaction between LCuNO2 and 2,4-di-tert-butylphenol was more complicated. It yielded two products: the coupled bisphenol product expected from a H-atom abstraction and 2,4-di-tert-butyl-6-nitrophenol, the product of an unusual anaerobic nitration. Various mechanisms for the latter transformation were considered.
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Affiliation(s)
- Caitlin J Bouchey
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, Campus Box 1134, St. Louis, Missouri 63130, United States
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - William B Tolman
- Department of Chemistry, Washington University in St. Louis, One Brookings Drive, Campus Box 1134, St. Louis, Missouri 63130, United States
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14
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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: 154] [Impact Index Per Article: 77.0] [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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15
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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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16
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Goetz MK, Schneider JE, Filatov AS, Jesse KA, Anderson JS. Enzyme-Like Hydroxylation of Aliphatic C-H Bonds From an Isolable Co-Oxo Complex. J Am Chem Soc 2021; 143:20849-20862. [PMID: 34856101 DOI: 10.1021/jacs.1c09280] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The selective hydroxylation of aliphatic C-H bonds remains a challenging but broadly useful transformation. Nature has evolved systems that excel at this reaction, exemplified by cytochrome P450 enzymes, which use an iron-oxo intermediate to activate aliphatic C-H bonds with k1 > 1400 s-1 at 4 °C. Many synthetic catalysts have been inspired by these enzymes and are similarly proposed to use transition metal-oxo intermediates. However, most examples of well-characterized transition metal-oxo species are not capable of reacting with strong, aliphatic C-H bonds, resulting in a lack of understanding of what factors facilitate this reactivity. Here, we report the isolation and characterization of a new terminal CoIII-oxo complex, PhB(AdIm)3CoIIIO. Upon oxidation, a transient CoIV-oxo intermediate is generated that is capable of hydroxylating aliphatic C-H bonds with an extrapolated k1 for C-H activation >130 s-1 at 4 °C, comparable to values observed in cytochrome P450 enzymes. Experimental thermodynamic values and DFT analysis demonstrate that, although the initial C-H activation step in this reaction is endergonic, the overall reaction is driven by an extremely exergonic radical rebound step, similar to what has been proposed in cytochrome P450 enzymes. The rapid C-H hydroxylation reactivity displayed in this well-defined system provides insight into how hydroxylation is accomplished by biological systems and similarly potent synthetic oxidants.
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Affiliation(s)
- McKenna K Goetz
- 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
| | - Alexander S Filatov
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Kate A Jesse
- 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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17
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Opalade AA, Hessefort L, Day VW, Jackson TA. Controlling the Reactivity of a Metal-Hydroxo Adduct with a Hydrogen Bond. J Am Chem Soc 2021; 143:15159-15175. [PMID: 34494835 DOI: 10.1021/jacs.1c06199] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The enzymes manganese lipoxygenase (MnLOX) and manganese superoxide dismutase (MnSOD) utilize mononuclear Mn centers to effect their catalytic reactions. In the oxidized MnIII state, the active site of each enzyme contains a hydroxo ligand, and X-ray crystal structures imply a hydrogen bond between this hydroxo ligand and a cis carboxylate ligand. While hydrogen bonding is a common feature of enzyme active sites, the importance of this particular hydroxo-carboxylate interaction is relatively unexplored. In this present study, we examined a pair of MnIII-hydroxo complexes that differ by a single functional group. One of these complexes, [MnIII(OH)(PaPy2N)]+, contains a naphthyridinyl moiety capable of forming an intramolecular hydrogen bond with the hydroxo ligand. The second complex, [MnIII(OH)(PaPy2Q)]+, contains a quinolinyl moiety that does not permit any intramolecular hydrogen bonding. Spectroscopic characterization of these complexes supports a common structure, but with perturbations to [MnIII(OH)(PaPy2N)]+, consistent with a hydrogen bond. Kinetic studies using a variety of substrates with activated O-H bonds, revealed that [MnIII(OH)(PaPy2N)]+ is far more reactive than [MnIII(OH)(PaPy2Q)]+, with rate enhancements of 15-100-fold. A detailed analysis of the thermodynamic contributions to these reactions using DFT computations reveals that the former complex is significantly more basic. This increased basicity counteracts the more negative reduction potential of this complex, leading to a stronger O-H BDFE in the [MnII(OH2)(PaPy2N)]+ product. Thus, the differences in reactivity between [MnIII(OH)(PaPy2Q)]+ and [MnIII(OH)(PaPy2N)]+ can be understood on the basis of thermodynamic considerations, which are strongly influenced by the ability of the latter complex to form an intramolecular hydrogen bond.
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Affiliation(s)
- Adedamola A Opalade
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Logan Hessefort
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Victor W Day
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Timothy A Jackson
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
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18
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Engbers S, Trifonova EA, Hess KM, Vries F, Klein JEMN. Synthesis of a Sterically Encumbered Pincer Au(III)−OH Complex. Eur J Inorg Chem 2021. [DOI: 10.1002/ejic.202100305] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Silène Engbers
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Evgeniya A. Trifonova
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Kristopher M. Hess
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Folkert Vries
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
| | - Johannes E. M. N. Klein
- Molecular Inorganic Chemistry Stratingh Institute for Chemistry Faculty of Science and Engineering University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
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19
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Liu H, Shen Q. Well-defined organometallic Copper(III) complexes: Preparation, characterization and reactivity. Coord Chem Rev 2021. [DOI: 10.1016/j.ccr.2021.213923] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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20
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Wu W, De Hont JT, Parveen R, Vlaisavljevich B, Tolman WB. Sulfur-Containing Analogues of the Reactive [CuOH] 2+ Core. Inorg Chem 2021; 60:5217-5223. [PMID: 33733755 DOI: 10.1021/acs.inorgchem.1c00216] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
With the aim of drawing comparisons to the highly reactive complex LCuOH (L = bis(2,6-diisopropylphenylcarboxamido)pyridine), the complexes [Bu4N][LCuSR] (R = H or Ph) were prepared, characterized by spectroscopy and X-ray crystallography, and oxidized at low temperature to generate the species assigned as LCuSR on the basis of spectroscopy and theory. Consistent with the smaller electronegativity of S versus O, redox potentials for the LCuSR-/0 couples were ∼50 mV lower than for LCuOH-/0, and the rates of the proton-coupled electron transfer reactions of LCuSR with anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine at -80 °C were significantly slower (by more than 100 times) than the same reaction of LCuOH. Density functional theory (DFT) and time-dependent DFT calculations on LCuZ (Z = OH, SH, SPh) revealed subtle differences in structural and UV-visible parameters. Further comparison to complexes with Z = F, Cl, and Br using complete active space (CAS) self-consistent field and localized orbital CAS configuration interaction calculations along with a valence-bond-like interpretation of the wave functions showed differences with previously reported results ( J. Am. Chem. Soc. 2020, 142, 8514), and argue for a consistent electronic structure across the entire series of complexes, rather than a change in the nature of the ligand field arrangement for Z = F.
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Affiliation(s)
- Wen Wu
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
| | - Jacqui Tehranchi De Hont
- Department of Chemistry, University of Minnesota, 207 Pleasant Avenue SE, Minneapolis, Minnesota 55455, United States
| | - Riffat Parveen
- University of South Dakota, 414 E. Clark Street, Vermillion, South Dakota 57069, United States
| | - Bess Vlaisavljevich
- University of South Dakota, 414 E. Clark Street, Vermillion, South Dakota 57069, United States
| | - William B Tolman
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
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21
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Krishnan VM, Shopov DY, Bouchey CJ, Bailey WD, Parveen R, Vlaisavljevich B, Tolman WB. Structural Characterization of the [CuOR] 2+ Core. J Am Chem Soc 2021; 143:3295-3299. [PMID: 33621089 DOI: 10.1021/jacs.0c13470] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Formal Cu(III) complexes bearing an oxygen-based auxiliary ligand ([CuOR]2+, R = H or CH2CF3) were stabilized by modulating the donor character of supporting ligand LY (LY = 4-Y, N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Y = H or OMe) and/or the basicity of the auxiliary ligand, enabling the first characterization of these typically highly reactive cores by NMR spectroscopy and X-ray crystallography. Enhanced lifetimes in solution and slowed rates of PCET with a phenol substrate were observed. NMR spectra corroborate the S = 0 ground states of the complexes, and X-ray structures reveal shortened Cu-ligand bond distances that match well with theory.
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Affiliation(s)
- V Mahesh Krishnan
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
| | - Dimitar Y Shopov
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
| | - Caitlin J Bouchey
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
| | - Wilson D Bailey
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
| | - Riffat Parveen
- University of South Dakota, 414 E. Clark Street, Vermillion, South Dakota 57069, United States
| | - Bess Vlaisavljevich
- University of South Dakota, 414 E. Clark Street, Vermillion, South Dakota 57069, United States
| | - William B Tolman
- Department of Chemistry, Washington University in St. Louis, One Brookings Hall, Campus Box 1134, St. Louis, Missouri 63130-4899, United States
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22
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Brandt A, RanguMagar AB, Szwedo P, Wayland HA, Parnell CM, Munshi P, Ghosh A. Highly economical and direct amination of sp 3 carbon using low-cost nickel pincer catalyst. RSC Adv 2021; 11:1862-1874. [PMID: 35424101 PMCID: PMC8693581 DOI: 10.1039/d0ra09639c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Accepted: 12/07/2020] [Indexed: 11/21/2022] Open
Abstract
Developing more efficient routes to achieve C-N bond coupling is of great importance to industries ranging from products in pharmaceuticals and fertilizers to biomedical technologies and next-generation electroactive materials. Over the past decade, improvements in catalyst design have moved synthesis away from expensive metals to newer inexpensive C-N cross-coupling approaches via direct amine alkylation. For the first time, we report the use of an amide-based nickel pincer catalyst (1) for direct alkylation of amines via activation of sp3 C-H bonds. The reaction was accomplished using a 0.2 mol% catalyst and no additional activating agents other than the base. Upon optimization, it was determined that the ideal reaction conditions involved solvent dimethyl sulfoxide at 110 °C for 3 h. The catalyst demonstrated excellent reactivity in the formation of various imines, intramolecularly cyclized amines, and substituted amines with a turnover number (TON) as high as 183. Depending on the base used for the reaction and the starting amines, the catalyst demonstrated high selectivity towards the product formation. The exploration into the mechanism and kinetics of the reaction pathway suggested the C-H activation as the rate-limiting step, with the reaction second-order overall, holding first-order behavior towards the catalyst and toluene substrate.
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Affiliation(s)
- Andrew Brandt
- Department of Chemistry, University of Arkansas at Little Rock 2801 South University Avenue Little Rock AR 72204 USA +1 501 569 8838 +1 501 569 8827
| | - Ambar B RanguMagar
- Department of Chemistry, University of Arkansas at Little Rock 2801 South University Avenue Little Rock AR 72204 USA +1 501 569 8838 +1 501 569 8827
| | - Peter Szwedo
- Department of Chemistry, University of Arkansas at Little Rock 2801 South University Avenue Little Rock AR 72204 USA +1 501 569 8838 +1 501 569 8827
| | - Hunter A Wayland
- Department of Chemistry, University of Arkansas at Little Rock 2801 South University Avenue Little Rock AR 72204 USA +1 501 569 8838 +1 501 569 8827
| | - Charlette M Parnell
- Department of Chemistry, University of Arkansas at Little Rock 2801 South University Avenue Little Rock AR 72204 USA +1 501 569 8838 +1 501 569 8827
| | - Pradip Munshi
- Research Center, Reliance Industries Limited Vadodara Gujarat 391346 India +91 265 261 6066
| | - Anindya Ghosh
- Department of Chemistry, University of Arkansas at Little Rock 2801 South University Avenue Little Rock AR 72204 USA +1 501 569 8838 +1 501 569 8827
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23
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Li Y, Fan W, Zhang Z, Xie X, Xiang S, Huang D. Copper(II)-hydroxide facilitated C-C bond formation: the carboxamido pyridine system versus the methylimino pyridine system. Dalton Trans 2020; 49:12189-12196. [PMID: 32930687 DOI: 10.1039/d0dt02288h] [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
A copper(ii)-hydroxide-induced carbon-carbon bond formation reaction is explored with the synthesis of an asymmetric carboxamido-methylimino pyridine Cu(i) complex of [CuI(py(N-C[double bond, length as m-dash]O)(N[double bond, length as m-dash]C-C)ph2Me2)2]- (12). Two imine-methyl groups are coupled to form a bridged C-C bond (N[double bond, length as m-dash]C-C-C-C[double bond, length as m-dash]N) at the methyl positions with the reduction of two Cu2+ center ions to Cu+. The reaction is checked with three dicarboxamido pyridine [CuII-OH] complexes, with which dinuclear Cu(i) complexes of [Cu2(py(N-C[double bond, length as m-dash]O)2ph2R2)2]2- (R = methyl (3), methyl and allyl (6)) and trinuclear [CuII-CuI-CuII] complex of [Cu3(⊂20-py(N-C[double bond, length as m-dash]O)2ph2dienMe3)2]+ (9) are obtained. The reactivities of the [CuII-L] (L = DMF, OH-) complexes in dicarboxamido pyridine, carboxamido-methylimino pyridine and dimethylimino pyridine systems are discussed in terms of the electron delocalization properties of ligands. A cooperative metal-ligand (Cu2+ and enamide ligand) interaction is proposed based on the characterization of ligated Cu(ii) intermediates with the techniques of X-ray crystallography, UV-vis spectroscopy, cyclic voltammogram, EPR spectroscopy, and DFT calculations.
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Affiliation(s)
- Yinghua Li
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China.
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24
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VanNatta PE, Ramirez DA, Velarde AR, Ali G, Kieber-Emmons MT. Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof. J Am Chem Soc 2020; 142:16292-16312. [DOI: 10.1021/jacs.0c06425] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Peter E. VanNatta
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, United States
| | - David A. Ramirez
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, United States
| | - Andres R. Velarde
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, United States
| | - Ghazanfar Ali
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, United States
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25
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Mondal P, McDonald AR. Phenol Oxidation by a Nickel(III)-Fluoride Complex: Exploring the Influence of the Proton Accepting Ligand in PCET Oxidation. Chemistry 2020; 26:10083-10089. [PMID: 32567726 DOI: 10.1002/chem.202002135] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 06/15/2020] [Indexed: 11/05/2022]
Abstract
In order to gain insight into the influence of the H+ -accepting terminal ligand in high-valent oxidant mediated proton coupled electron transfer (PCET) reactions, the reactivity of a high valent nickel-fluoride complex [NiIII (F)(L)] (2, L=N,N'-(2,6-dimethylphenyl)-2,6-pyridinecarboxamidate) with substituted phenols was explored. Analysis of kinetic data from these reactions (Evans-Polanyi, Hammett, and Marcus plots, and KIE measurements) and the formed products show that 2 reacted with electron rich phenols through a hydrogen atom transfer (HAT, or concerted PCET) mechanism and with electron poor phenols through a stepwise proton transfer/electron transfer (PT/ET) reaction mechanism. The analogous complexes [NiIII (Z)(L)] (Z=Cl, OCO2 H, O2 CCH3 , ONO2 ) reacted with all phenols through a HAT mechanism. We explore the reason for a change in mechanism with the highly basic fluoride ligand in 2. Complex 2 was also found to react one to two orders of magnitude faster than the corresponding analogous [NiIII (Z)(L)] complexes. This was ascribed to a high bond dissociation free energy value associated with H-F (135 kcal mol-1 ), which is postulated to be the product formed from PCET oxidation by 2 and is believed to be the driving force for the reaction. Our findings show that high-valent metal-fluoride complexes represent a class of highly reactive PCET oxidants.
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Affiliation(s)
- Prasenjit Mondal
- School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin, 2, Ireland
| | - Aidan R McDonald
- School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin, 2, Ireland
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26
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Wu T, MacMillan SN, Rajabimoghadam K, Siegler MA, Lancaster KM, Garcia-Bosch I. Structure, Spectroscopy, and Reactivity of a Mononuclear Copper Hydroxide Complex in Three Molecular Oxidation States. J Am Chem Soc 2020; 142:12265-12276. [PMID: 32531159 DOI: 10.1021/jacs.0c03867] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Structural, spectroscopic, and reactivity studies are presented for an electron transfer series of copper hydroxide complexes supported by a tridentate redox-active ligand. Single crystal X-ray crystallography shows that the mononuclear [CuOH]1+ core is stabilized via intramolecular H-bonds between the H-donors of the ligand and the hydroxide anion when the ligand is in its trianionic form. This complex undergoes two reversible oxidation processes that produce two metastable "high-valent" CuOH species, which can be generated by addition of stoichiometric amounts of 1e- oxidants. These CuOH species are characterized by an array of spectroscopic techniques including UV-vis absorption, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies (XAS), which together indicate that all redox couples are ligand-localized. The reactivity of the complexes in their higher oxidation states toward substrates with modest O-H bond dissociation energies (e.g., 4-substitued-2,6-di-tert-butylphenols) indicates that these complexes act as 2H+/2e- oxidants, differing from the 1H+/1e- reactivity of well-studied [CuOH]2+ systems.
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Affiliation(s)
- Tong Wu
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
| | - Samantha N MacMillan
- Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853, United States
| | | | - Maxime A Siegler
- Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853, United States
| | - Isaac Garcia-Bosch
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
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27
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Muthuramalingam S, Anandababu K, Velusamy M, Mayilmurugan R. Benzene Hydroxylation by Bioinspired Copper(II) Complexes: Coordination Geometry versus Reactivity. Inorg Chem 2020; 59:5918-5928. [DOI: 10.1021/acs.inorgchem.9b03676] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
| | - Karunanithi Anandababu
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
| | - Marappan Velusamy
- Department of Chemistry, North Eastern Hill University, Shillong 793022, India
| | - Ramasamy Mayilmurugan
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
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Fisher KJ, Feuer ML, Lant HMC, Mercado BQ, Crabtree RH, Brudvig GW. Concerted proton-electron transfer oxidation of phenols and hydrocarbons by a high-valent nickel complex. Chem Sci 2020; 11:1683-1690. [PMID: 32206289 PMCID: PMC7069233 DOI: 10.1039/c9sc05565g] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2019] [Accepted: 12/29/2019] [Indexed: 12/21/2022] Open
Abstract
The high-valent nickel(iii) complex Ni(pyalk)2 + (2) was prepared by oxidation of a nickel(ii) complex, Ni(pyalk)2 (1) (pyalk = 2-pyridyl-2-propanoate). 2 and derivatives were fully characterized by mass spectrometry and X-ray crystallography. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy confirm that the oxidation is metal-centered. 2 was found to react with a variety of phenolic and hydrocarbon substrates. A linear correlation between the measured rate constant and the substrate bond dissociation enthalpy (BDE) was found for both phenolic and hydrocarbon substrates. Large H/D kinetic isotope effects were also observed for both sets of substrates. These results suggest that 2 reacts through concerted proton-electron transfer (CPET). Analysis of measured thermodynamic parameters allows us to calculate a bond dissociation free energy (BDFE) of ∼91 kcal mol-1 for the O-H bond of the bound pyalk ligand. These findings may shed light onto CPET steps in oxidative catalysis and have implications for ligand design in catalytic systems.
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Affiliation(s)
- Katherine J Fisher
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA . ;
| | - Margalit L Feuer
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA . ;
| | - Hannah M C Lant
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA . ;
| | - Brandon Q Mercado
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA . ;
| | - Robert H Crabtree
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA . ;
| | - Gary W Brudvig
- Department of Chemistry , Yale University , New Haven , CT 06520 , USA . ;
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29
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Gurjar KK, Sharma RK. Synthetic and computational studies on CuI/ligand pair promoted activation of C(Aryl)-Cl bond in C-N coupling reactions. Heliyon 2020; 6:e03233. [PMID: 32055723 PMCID: PMC7005438 DOI: 10.1016/j.heliyon.2020.e03233] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2019] [Revised: 11/26/2019] [Accepted: 01/13/2020] [Indexed: 11/23/2022] Open
Abstract
Cu/ligand-mediated coupling reactions have been widely investigated in the recent past. However, activation of cheaper aryl chlorides is still a great limitation of these reactions. During the course of present investigations efforts have been made to develop a normal and facile CuI/ligand pair protocol for arylation of phthalimide using aryl chlorides. The protocol has also been extended for arylation of amines. On the basis of experimental and theoretical results, a catalytic cycle has also been proposed and it has been established that these reactions follow oxidative addition-reductive elimination (OA-RE) pathway. These studies have indicated that tetracoordinated [Cu(L1)(L2)]+ complex is active catalytic species in these reactions.
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30
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Unjaroen D, Gericke R, Lovisari M, Nelis D, Mondal P, Pirovano P, Twamley B, Farquhar ER, McDonald AR. High-Valent d 7 Ni III versus d 8 Cu III Oxidants in PCET. Inorg Chem 2019; 58:16838-16848. [PMID: 31804808 DOI: 10.1021/acs.inorgchem.9b03101] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Oxygenases have been postulated to utilize d4 FeIV and d8 CuIII oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal-oxygen adducts, [NiIII(OAc)(L)] (1b) and [CuIII(OAc)(L)] (2b), L = N,N'-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [NiII(OAc)(L)]- (1a) and [CuII(OAc)(L)]- (2a). The complexes 1a/b-2a/b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, X-ray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para-substituted 2,6-di-tert-butylphenols (p-X-2,6-DTBP; X = OCH3, C(CH3)3, CH3, H, Br, CN, NO2) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d8 CuIII oxidant displayed a small increase in the rate constant compared to that of the d7 NiIII oxidant. The d8 CuIII oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDEC-H) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b. It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.
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Affiliation(s)
- Duenpen Unjaroen
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Robert Gericke
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Marta Lovisari
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Daniel Nelis
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Prasenjit Mondal
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Paolo Pirovano
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Brendan Twamley
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
| | - Erik R Farquhar
- Case Western Reserve University Center for Synchrotron Biosciences, National Synchrotron Light Source II , Brookhaven National Laboratory II , Upton , New York 11973 , United States
| | - Aidan R McDonald
- School of Chemistry, Trinity College Dublin , The University of Dublin , College Green , Dublin 2 , Ireland
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31
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Elwell CE, Mandal M, Bouchey CJ, Que L, Cramer CJ, Tolman WB. Carboxylate Structural Effects on the Properties and Proton-Coupled Electron Transfer Reactivity of [CuO 2CR] 2+ Cores. Inorg Chem 2019; 58:15872-15879. [PMID: 31710477 DOI: 10.1021/acs.inorgchem.9b02293] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A series of complexes {[NBu4][LCuII(O2CR)] (R = -C6F5, -C6H4(NO2), -C6H5, -C6H4(OMe), -CH3, and -C6H2(iPr)3)} were characterized (with the complex R = -C6H4(m-Cl) having been published elsewhere ( Mandal et al. J. Am. Chem. Soc. 2019 , 141 , 17236 )). All feature N,N',N″-coordination of the supporting L2- ligand, except for the complex with R = -C6H2(iPr)3, which exhibits N,N',O-coordination. For the N,N',N″-bound complexes, redox properties, UV-vis ligand-to-metal charge transfer (LMCT) features, and rates of hydrogen atom abstraction from 2,4,6,-tri-t-butylphenol using the oxidized, formally Cu(III) compounds LCuIII(O2CR) correlated well with the electron donating nature of R as measured both experimentally and computationally. Specifically, the greater the electron donation, the lower is the energy for LMCT and the slower is the reaction rate. The results are interpreted to support an oxidatively asynchronous proton-coupled electron transfer mechanism that is sensitive to the oxidative power of the [CuIII(O2CR)]2+ core.
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Affiliation(s)
- Courtney E Elwell
- Department of Chemistry, Center for Metals in Biocatalysis, Chemical Theory Center, and Supercomputing Institute , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - Mukunda Mandal
- Department of Chemistry, Center for Metals in Biocatalysis, Chemical Theory Center, and Supercomputing Institute , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - Caitlin J Bouchey
- Department of Chemistry, Center for Metals in Biocatalysis, Chemical Theory Center, and Supercomputing Institute , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States.,Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130 , United States
| | - Lawrence Que
- Department of Chemistry, Center for Metals in Biocatalysis, Chemical Theory Center, and Supercomputing Institute , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - Christopher J Cramer
- Department of Chemistry, Center for Metals in Biocatalysis, Chemical Theory Center, and Supercomputing Institute , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - William B Tolman
- Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130 , United States
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32
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Diaz DE, Bhadra M, Karlin KD. Dimethylanilinic N-Oxides and Their Oxygen Surrogacy Role in the Formation of a Putative High-Valent Copper-Oxygen Species. Inorg Chem 2019; 58:13746-13750. [PMID: 31580063 PMCID: PMC6896993 DOI: 10.1021/acs.inorgchem.9b02066] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The reaction of p-cyano-N,N-dimethylaniline N-oxide, an O-atom donor, with different copper(I) complexes (at room temperature and in acetone) indicates the formation via O-atom transfer of a high-valent copper oxyl species, CuII-O•, a putative key intermediate in the catalytic cycle of copper-containing monooxygenases. The formation of p-cyano-N-hydroxymethyl-N-methylaniline and p-cyano-N-methylaniline as the main products of the reaction highlight the capability of this species to hydroxylate strong C-H bonds (bond dissociation energy ∼ 90 kcal/mol). A plausible mechanism for the reactivity of this catalytic system is proposed.
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Affiliation(s)
- Daniel E. Diaz
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Mayukh Bhadra
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kenneth D. Karlin
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
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33
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Mandal M, Elwell CE, Bouchey CJ, Zerk TJ, Tolman WB, Cramer CJ. Mechanisms for Hydrogen-Atom Abstraction by Mononuclear Copper(III) Cores: Hydrogen-Atom Transfer or Concerted Proton-Coupled Electron Transfer? J Am Chem Soc 2019; 141:17236-17244. [PMID: 31617707 DOI: 10.1021/jacs.9b08109] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In a possibly biomimetic fashion, formally copper(III)-oxygen complexes LCu(III)-OH (1) and LCu(III)-OOCm (2) (L2- = N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Cm = α,α-dimethylbenzyl) have been shown to activate X-H bonds (X = C, O). Herein, we demonstrate similar X-H bond activation by a formally Cu(III) complex supported by the same dicarboxamido ligand, LCu(III)-O2CAr1 (3, Ar1 = meta-chlorophenyl), and we compare its reactivity to that of 1 and 2. Kinetic measurements revealed a second order reaction with distinct differences in the rates: 1 reacts the fastest in the presence of O-H or C-H based substrates, followed by 3, which is followed by (unreactive) 2. The difference in reactivity is attributed to both a varying oxidizing ability of the studied complexes and to a variation in X-H bond functionalization mechanisms, which in these cases are characterized as either a hydrogen-atom transfer (HAT) or a concerted proton-coupled electron transfer (cPCET). Select theoretical tools have been employed to distinguish these two cases, both of which generally focus on whether the electron (e-) and proton (H+) travel "together" as a true H atom, (HAT), or whether the H+ and e- are transferred in concert, but travel between different donor/acceptor centers (cPCET). In this work, we reveal that both mechanisms are active for X-H bond activation by 1-3, with interesting variations as a function of substrate and copper functionality.
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Affiliation(s)
- Mukunda Mandal
- Department of Chemistry, Minnesota Supercomputing Institute, Chemical Theory Center, and Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - Courtney E Elwell
- Department of Chemistry, Minnesota Supercomputing Institute, Chemical Theory Center, and Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - Caitlin J Bouchey
- Department of Chemistry, Minnesota Supercomputing Institute, Chemical Theory Center, and Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States.,Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130 , United States
| | - Timothy J Zerk
- Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130 , United States
| | - William B Tolman
- Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130 , United States
| | - Christopher J Cramer
- Department of Chemistry, Minnesota Supercomputing Institute, Chemical Theory Center, and Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
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34
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Zerk TJ, Saouma CT, Mayer JM, Tolman WB. Low Reorganization Energy for Electron Self-Exchange by a Formally Copper(III,II) Redox Couple. Inorg Chem 2019; 58:14151-14158. [PMID: 31577145 DOI: 10.1021/acs.inorgchem.9b02185] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The rate constant for electron self-exchange (k11) between LCuOH and [LCuOH]- (L = bis-2,6-(2,6-diisopropylphenyl)carboximidopyridine) was determined using the Marcus cross relation. This work involved measurement of the rate of the cross-reaction between [Bu4N][LCuOH] and [Fc][BAr4F] (Fc+ = ferrocenium; BAr4F = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)) by stopped-flow methods at -88 °C in CH2Cl2 and measurement of the equilibrium constant for the redox process by UV-vis titrations under the same conditions. A value of k11 = 3 × 104 M-1 s-1 (-88 °C) led to estimation of a value 9 × 106 M-1 s-1 at 25 °C, which is among the highest values known for copper redox couples. Further Marcus analysis enabled determination of a low reorganization energy, λ = 0.95 ± 0.17 eV, attributed to minimal structural variation between the redox partners. In addition, the reaction entropy (ΔS°) associated with the LCuOH/[LCuOH]- self-exchange was determined from the temperature dependence of the redox potentials, and found to be dependent upon ionic strength. Comparisons to other Cu redox systems and potential new applications for the formally CuIII,II system are discussed.
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Affiliation(s)
- Timothy J Zerk
- Department of Chemistry , Washington University in St. Louis , One Brookings Hall, Campus Box 1134 , St. Louis , Missouri 63130-4899 , United States
| | - Caroline T Saouma
- Department of Chemistry , University of Utah , 315 S 1400 E , Salt Lake City , Utah 84112 , United States
| | - James M Mayer
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520-8107 , United States
| | - William B Tolman
- Department of Chemistry , Washington University in St. Louis , One Brookings Hall, Campus Box 1134 , St. Louis , Missouri 63130-4899 , United States
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35
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Quist DA, Ehudin MA, Schaefer AW, Schneider GL, Solomon EI, Karlin KD. Ligand Identity-Induced Generation of Enhanced Oxidative Hydrogen Atom Transfer Reactivity for a Cu II2(O 2•-) Complex Driven by Formation of a Cu II2( -OOH) Compound with a Strong O-H Bond. J Am Chem Soc 2019; 141:12682-12696. [PMID: 31299154 DOI: 10.1021/jacs.9b05277] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A superoxide-bridged dicopper(II) complex, [CuII2(XYLO)(O2•-)]2+ (1) (XYLO = binucleating m-xylyl derivative with a bridging phenolate ligand donor and two bis(2-{2-pyridyl}ethyl)amine arms), was generated from chemical oxidation of the peroxide-bridged dicopper(II) complex [CuII2(XYLO)(O22-)]+ (2), using ferrocenium (Fc+) derivatives, in 2-methyltetrahydrofuran (MeTHF) at -125 °C. Using Me10Fc+, a 1 ⇆ 2 equilibrium was established, allowing for calculation of the reduction potential of 1 as -0.525 ± 0.01 V vs Fc+/0. Addition of 1 equiv of strong acid to 2 afforded the hydroperoxide-bridged dicopper(II) species [CuII2(XYLO)(OOH)]2+ (3). An acid-base equilibrium between 3 and 2 was achieved through spectral titrations using a derivatized phosphazene base. The pKa of 3 was thus determined to be 24 ± 0.6 in MeTHF at -125 °C. Using a thermodynamic square scheme and the Bordwell relationship, the hydroperoxo complex (3) O-H bond dissociation free energy (BDFE) was calculated as 81.8 ± 1.5 (BDE = 86.8) kcal/mol. The observed oxidizing capability of [CuII2(XYLO)(O2•-)]2+ (1), as demonstrated in H atom abstraction reactions with certain phenolic ArO-H and hydrocarbon C-H substrates, provides direct support for this experimentally determined O-H BDFE. A kinetic study reveals a very fast reaction of TEMPO-H with 1 in MeTHF, with k (-100 °C) = 5.6 M-1 s-1. Density functional theory (DFT) calculations reveal how the structure of 1 may minimize stabilization of the superoxide moiety, resulting in its enhanced reactivity. The thermodynamic insights obtained herein highlight the importance of the interplay between ligand design and the generation and properties of copper (or other metal ion) bound O2-derived reduced species, such as pKa, reduction potential, and BDFE; these may be relevant to the capabilities (i.e., oxidizing power) of reactive oxygen intermediates in metalloenzyme chemical system mediated oxidative processes.
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Affiliation(s)
- David A Quist
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Melanie A Ehudin
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Andrew W Schaefer
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Gregory L Schneider
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Edward I Solomon
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Kenneth D Karlin
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
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36
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Rajpurohit J, Shukla P, Kumar P, Das C, Vaidya S, Sundararajan M, Shanmugam M, Shanmugam M. Stabilizing Terminal Ni(III)-Hydroxide Complex Using NNN-Pincer Ligands: Synthesis and Characterization. Inorg Chem 2019; 58:6257-6267. [PMID: 31009214 DOI: 10.1021/acs.inorgchem.9b00466] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The reaction of [Ni(COD)2] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis(imino)pyridyl (L1) reveals a susceptibility to oxidation in an inert atmosphere ([O2] level <0.5 ppm), resulting in a transient Ni:dioxygen adduct. This reactive intermediate abstracts a hydrogen atom from THF and stabilizes an uncommon Ni(III) complex. The complex is crystallographically characterized by a molecular formula of [NiIII(L1··)2-(OH)] (1). Various isotopically labeled experiments (16O/18O) assertively endorse the origin of terminal oxygen based ligand in 1 due to the activation of molecular dioxygen. The presence of proton bound to the terminal oxygen in 1 is well supported by NMR, IR spectroscopy, DFT calculations, and hydrogen atom transfer (HAT) reactions promoted by 1. The observation of shakeup satellite peaks for the primary photoelectron lines of Ni(2p) in the X-ray photoelectron spectroscopy (XPS) unambiguously confirms the paramagnetic signature associated with the distorted square planar nickel ion, which is consistent with the trivalent oxidation state assigned for the nickel ion in 1. The variable temperature magnetic susceptibility data of 1 shows dominant antiferromagnetic interactions exist among the paramagnetic centers, resulting in an overall S = 1/2 ground state. Variable temperature X-band EPR studies performed on 1 show evidence for the S = 1/2 ground state, which is consistent with magnetic data. The unusual g-tensor extracted for the ground state S = 1/2 is analyzed under a strong exchange limit of spin-coupled centers. The electronic structure predicted for 1 is in good agreement with theoretical calculations.
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Affiliation(s)
- Jitendrasingh Rajpurohit
- Department of Chemistry , Indian Institute of Technology Bombay , Powai - 400076 , Mumbai , Maharashtra , India
| | - Pragya Shukla
- Department of Chemistry , Indian Institute of Technology Bombay , Powai - 400076 , Mumbai , Maharashtra , India
| | - Pardeep Kumar
- Department of Chemistry , Indian Institute of Technology Bombay , Powai - 400076 , Mumbai , Maharashtra , India
| | - Chinmoy Das
- Department of Chemistry , Indian Institute of Technology Bombay , Powai - 400076 , Mumbai , Maharashtra , India
| | - Shefali Vaidya
- Department of Chemistry , Indian Institute of Technology Bombay , Powai - 400076 , Mumbai , Maharashtra , India
| | - Mahesh Sundararajan
- Theoretical Chemistry Section , Bhabha Atomic Research Centre , Mumbai - 400 085 , India
| | - Muralidharan Shanmugam
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princes Street , Manchester - M1 7DN , U.K
| | - Maheswaran Shanmugam
- Department of Chemistry , Indian Institute of Technology Bombay , Powai - 400076 , Mumbai , Maharashtra , India
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37
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Muthuramalingam S, Maheshwaran D, Velusamy M, Mayilmurugan R. Regioselective oxidative carbon-oxygen bond cleavage catalysed by copper(II) complexes: A relevant model study for lytic polysaccharides monooxygenases activity. J Catal 2019. [DOI: 10.1016/j.jcat.2019.03.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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38
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Bailey WD, Dhar D, Cramblitt AC, Tolman WB. Mechanistic Dichotomy in Proton-Coupled Electron-Transfer Reactions of Phenols with a Copper Superoxide Complex. J Am Chem Soc 2019; 141:5470-5480. [PMID: 30907590 DOI: 10.1021/jacs.9b00466] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The kinetics and mechanism(s) of the reactions of [K(Krypt)][LCuO2] (Krypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, L = a bis(arylcarboxamido)pyridine ligand) with 2,2,6,6-tetramethylpiperdine- N-hydroxide (TEMPOH) and the para-substituted phenols XArOH (X = para substituent NO2, CF3, Cl, H, Me, tBu, OMe, or NMe2) at low temperatures were studied. The reaction with TEMPOH occurs rapidly ( k = 35.4 ± 0.3 M-1 s-1) by second-order kinetics to yield TEMPO• and [LCuOOH]- on the basis of electron paramagnetic resonance spectroscopy, the production of H2O2 upon treatment with protic acid, and independent preparation from reaction of [NBu4][LCuOH] with H2O2 ( Keq = 0.022 ± 0.007 for the reverse reaction). The reactions with XArOH also follow second-order kinetics, and analysis of the variation of the k values as a function of phenol properties (Hammett σ parameter, O-H bond dissociation free energy, p Ka, E1/2) revealed a change in mechanism across the series, from proton transfer/electron transfer for X = NO2, CF3, Cl to concerted-proton/electron transfer (or hydrogen-atom transfer) for X = OMe, NMe2 (data for X = H, Me, tBu are intermediate between the extremes). Thermodynamic analysis and comparisons to previous results for LCuOH, a different copper-oxygen intermediate with the same supporting ligand, and literature for other [CuO2]+ complexes reveal significant differences in proton-coupled electron-transfer mechanisms that have implications for understanding oxidation catalysis by copper-containing enzymes and abiological catalysts.
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Affiliation(s)
- Wilson D Bailey
- Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130-4899 , United States
| | - Debanjan Dhar
- Department of Chemistry and Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
| | - Anna C Cramblitt
- Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130-4899 , United States
| | - William B Tolman
- Department of Chemistry , Washington University in St. Louis , One Brookings Drive, Campus Box 1134 , St. Louis , Missouri 63130-4899 , United States.,Department of Chemistry and Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant Street SE , Minneapolis , Minnesota 55455 , United States
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39
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Noh H, Cho J. Synthesis, characterization and reactivity of non-heme 1st row transition metal-superoxo intermediates. Coord Chem Rev 2019. [DOI: 10.1016/j.ccr.2018.12.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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40
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Goetz MK, Anderson JS. Experimental Evidence for p K a-Driven Asynchronicity in C-H Activation by a Terminal Co(III)-Oxo Complex. J Am Chem Soc 2019; 141:4051-4062. [PMID: 30739450 DOI: 10.1021/jacs.8b13490] [Citation(s) in RCA: 84] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
C-H activation by transition metal oxo complexes is a fundamental reaction in oxidative chemistry carried out by both biological and synthetic systems. This centrality has motivated efforts to understand the patterns and mechanisms of such reactivity. We have therefore thoroughly examined the C-H activation reactivity of the recently synthesized and characterized late transition metal oxo complex PhB ( tBuIm)3CoIIIO. Precise values for the p Ka and BDFEO-H of the conjugates of this complex have been experimentally determined and provide insight into the observed reactivity. The activation parameters for the reaction between this complex and 9,10-dihydroanthracene have also been measured and compared to previous literature examples. Evaluation of the rates of reaction of PhB( tBuIm)3CoIIIO with a variety of hydrogen atom donors demonstrates that the reactivity of this complex is dependent on the p Ka of the substrate of interest rather than the BDEC-H. This observation runs counter to the commonly cited reactivity paradigm for many other transition metal oxo complexes. Experimental and computational analysis of C-H activation reactions by PhB( tBuIm)3CoIIIO reveals that the transition state for these processes contains significant proton transfer character. Nevertheless, additional experiments strongly suggest that the reaction does not occur via a stepwise process, leading to the conclusion that C-H activation by this CoIII-oxo complex proceeds by a p Ka-driven "asynchronous" concerted mechanism. This result supports a new pattern of reactivity that may be applicable to other systems and could result in alternative selectivity for C-H activation reactions mediated by transition metal oxo complexes.
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Affiliation(s)
- McKenna K Goetz
- 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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Elwell CE, Neisen BD, Tolman WB. Copper Complexes of Multidentate Carboxamide Ligands. Inorganica Chim Acta 2019; 485:131-139. [PMID: 31105329 DOI: 10.1016/j.ica.2018.10.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The copper coordination chemistry of two multidentate carboxamido ligands derived from HL1 (offering two quinolyl and one carboxamide donor) and H4L2 (with two pyridine(dicarboxamido) units linked by naphthalene spacers) was explored. The former was chosen because upon deprotonation it would provide a monoanionic mer-coordinating N-donor set that would model the putative deprotonated form of the His-brace in copper monooxygenases, while the latter was designed to bind two copper ions and enable comparisons to other systems with different ligand spacers. Upon reaction with Cu(I)-mesityl, HL1 yielded a symmetric dimer (L1Cu)2 in which each bis(quinolyl)amide ligand binds via two N-donors to one Cu(I) ion and via the third to the other Cu(I) center. Monomeric Cu(II) complexes [L 1 Cu(H 2 O) 2 ](OTf) and L 1 2 Cu were also characterized. Treatment of H4L2 with Cu(OTf)2 and excess Me4NOH (in CH3CN, pyridine/H2O, or MeOH) yielded complexes with anions of general formula [L 2 Cu 2 (X)]n-, where X = CH3CONH- (n = 1), CO3 2- (n = 2), or MeO- (n = 1). X-ray structures of these complexes revealed the (L2)4- ligand binding to two Cu(II) ions in an open paddle-wheel geometry, with an additional bridging ligand (X) completing the square planar coordination sphere of each metal ion. The open paddlewheel motif differs from the more 'open' puckered geometry seen with related ligands with different spacer units.
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Affiliation(s)
- Courtney E Elwell
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455
| | - Benjamin D Neisen
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455
| | - William B Tolman
- Department of Chemistry, Washington University in St. Louis, Campus Box 1134, 1 Brookings Drive, St. Louis, MO 63130
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Keown W, Large TAG, Chiang L, Wasinger EC, Stack TDP. Exclusive imidazole ligation to CuIII2O 2 and Cu IIICuII2O 2 cores. Chem Commun (Camb) 2019; 55:7390-7393. [DOI: 10.1039/c9cc02982f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Direct oxygenation of imidazole-ligated Cu(i) generates dinuclear and trinuclear Cu(iii) species with exclusive imidazole ligation.
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Affiliation(s)
- William Keown
- Department of Chemistry
- Stanford University
- Stanford
- USA
| | | | - Linus Chiang
- Department of Chemistry
- Stanford University
- Stanford
- USA
- Department of Chemistry
| | - Erik C. Wasinger
- Department of Chemistry and Biochemistry
- California State University
- Chico
- USA
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Adam SM, Wijeratne GB, Rogler PJ, Diaz DE, Quist DA, Liu JJ, Karlin KD. Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function. Chem Rev 2018; 118:10840-11022. [PMID: 30372042 PMCID: PMC6360144 DOI: 10.1021/acs.chemrev.8b00074] [Citation(s) in RCA: 132] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Heme-copper oxidases (HCOs) are terminal enzymes on the mitochondrial or bacterial respiratory electron transport chain, which utilize a unique heterobinuclear active site to catalyze the 4H+/4e- reduction of dioxygen to water. This process involves a proton-coupled electron transfer (PCET) from a tyrosine (phenolic) residue and additional redox events coupled to transmembrane proton pumping and ATP synthesis. Given that HCOs are large, complex, membrane-bound enzymes, bioinspired synthetic model chemistry is a promising approach to better understand heme-Cu-mediated dioxygen reduction, including the details of proton and electron movements. This review encompasses important aspects of heme-O2 and copper-O2 (bio)chemistries as they relate to the design and interpretation of small molecule model systems and provides perspectives from fundamental coordination chemistry, which can be applied to the understanding of HCO activity. We focus on recent advancements from studies of heme-Cu models, evaluating experimental and computational results, which highlight important fundamental structure-function relationships. Finally, we provide an outlook for future potential contributions from synthetic inorganic chemistry and discuss their implications with relevance to biological O2-reduction.
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Affiliation(s)
- Suzanne M. Adam
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Gayan B. Wijeratne
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Patrick J. Rogler
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Daniel E. Diaz
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David A. Quist
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Jeffrey J. Liu
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kenneth D. Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
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Lymar SV, Ertem MZ, Polyansky DE. Solvent-dependent transition from concerted electron-proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites. Dalton Trans 2018; 47:15917-15928. [PMID: 30375615 DOI: 10.1039/c8dt03858a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The bimolecular rate coefficients (kobsq) for quenching the metal-to-ligand charge transfer excited states of two Ru polypyridine complexes containing H-bond accepting sites by six p-substituted phenols exhibit abrupt deviations from the expected linear correlations of log kobsq with phenol's Hammett σp constant. This pattern is attributed to a transition of the quenching mechanism from a concerted electron-proton transfer (EPT) to a proton transfer (PT); the latter becomes predominant for the most acidic phenols in acetonitrile, but not in dichloromethane. This assertion is supported by a detailed thermochemical analysis, which also excludes the quenching pathways involving electron transfer from phenols with or without deprotonation of phenols to the solvent, either concerted or sequential. The transition from EPT to PT upon the σp increase is consistent/supported by the magnitudes of the measured and computed PhOH/OD kinetic isotope effects and by the observed reduction of the EPT product yields upon replacing the low σp methoxyphenol by the high σp nitrophenol. In addition to modulating the relative contribution of the EPT and PT quenching pathways, the solvent strongly affects the bimolecular rate coefficients for the EPT quenching proper. Unlike with H-atom transfer reactions, this kinetic solvent effect could not be quantitatively accounted for by the phenol-solvent H-bonding alone, which suggests a solvent effect on the H-bonding constants in the phenol-Ru complex precursor exciplexes and/or on the unimolecular EPT rate coefficients within these exciplexes.
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Affiliation(s)
- Sergei V Lymar
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
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Nam W, Lee YM, Fukuzumi S. Hydrogen Atom Transfer Reactions of Mononuclear Nonheme Metal-Oxygen Intermediates. Acc Chem Res 2018; 51:2014-2022. [PMID: 30179459 DOI: 10.1021/acs.accounts.8b00299] [Citation(s) in RCA: 84] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Molecular oxygen (O2), the greenest oxidant, is kinetically stable in the oxidation of organic substrates due to its triplet ground state. In nature, O2 is reduced by two electrons with two protons to produce hydrogen peroxide (H2O2) and by four electrons with four protons to produce water (H2O) by oxidase and oxygenase metalloenzymes. In the process of the two-electron/two-proton and four-electron/four-proton reduction of O2 by metalloenzymes and their model compounds, metal-oxygen intermediates, such as metal-superoxido, -peroxido, -hydroperoxido, and -oxido species, are generated depending on the numbers of electrons and protons involved in the O2 activation reactions. The one-electron reduction of metal-oxygen intermediates is coupled with the binding of one proton. Such a hydrogen atom transfer (HAT) is defined as proton-coupled electron transfer (PCET), and there is a mechanistic dichotomy whether HAT occurs via a concerted PCET pathway or stepwise pathways [i.e., electron transfer followed by proton transfer (ET/PT) or proton transfer followed by electron transfer (PT/ET)]. The metal-oxygen intermediates formed are oxidants that can abstract a hydrogen atom (H-atom) from substrate C-H bonds. The H-atom abstraction from substrate C-H bonds by the metal-oxygen intermediates can also occur via a concerted PCET or stepwise PCET pathways. In the PCET reactions, a proton can be provided not only by the substrate itself but also by an acid that is added to a reaction solution. This Account describes the reactivities of metal-oxygen intermediates, such as metal-superoxido, -peroxido, -hydroperoxido, and -oxido complexes, in HAT reactions, focusing on the mechanisms of PCET reactions of metal-oxygen intermediates and on the mechanistic dichotomy of concerted versus stepwise pathways. Recent developments in the reactivity studies of Cr-, Fe-, and Cu-superoxido complexes in H-atom and hydride transfer reactions are discussed. Reactivities of an iron(III)-hydroperoxido complex and an iron(III)-peroxido complex binding redox-inactive metal ions are also summarized briefly. Mononuclear nonheme iron(IV)- and manganese(IV)-oxido complexes have shown high reactivities in HAT reactions, and their chemistry in PCET reactions is discussed intensively. Acid-catalyzed HAT reactions of metal-oxygen intermediates are also discussed to demonstrate a unified driving force dependence of logarithm of the rate constants of acid-catalyzed oxidation of various substrates by an iron(IV)-oxido complex and that of PCET from one-electron donors to the iron(IV)-oxido complex. PCET reactions of metal-oxygen intermediates are shown to proceed via a concerted pathway (one-step HAT) or a stepwise ET/PT pathway depending on the ET and PCET driving forces (-Δ G). The boundary conditions between concerted versus stepwise PCET pathways are clarified to demonstrate a switchover of the mechanisms only by changing the reaction temperature in the boundary conditions. This Account summarizes recent developments in the HAT reactions by synthetic mononuclear nonheme metal-oxygen intermediates over the past 10 years.
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Affiliation(s)
- Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
- School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Yong-Min Lee
- 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
- Graduate School of Science and Engineering, Meijo University, Nagoya, Aichi 468-8502, Japan
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Dhar D, Yee GM, Tolman WB. Effects of Charged Ligand Substituents on the Properties of the Formally Copper(III)-Hydroxide ([CuOH] 2+) Unit. Inorg Chem 2018; 57:9794-9806. [PMID: 30070473 PMCID: PMC6653640 DOI: 10.1021/acs.inorgchem.8b01529] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
With the goal of understanding how distal charge influences the properties and hydrogen atom transfer (HAT) reactivity of the [CuOH]2+ core proposed to be important in oxidation catalysis, the complexes [M]3[SO3LCuOH] (M = [K(18-crown-6)]+ or [K(crypt-222)]+) and [NMe3LCuOH]X (X = BArF4- or ClO4-) were prepared, in which SO3- or NMe3+ substituents occupy the para positions of the flanking aryl rings of the supporting bis(carboxamide)pyridine ligands. Structural and spectroscopic characterization showed that the [CuOH]+ cores in the corresponding complexes were similar, but cyclic voltammetry revealed the E1/2 value for the [CuOH]2+/[CuOH]+ couple to be nearly 0.3 V more oxidizing for the [NMe3LCuOH]2+ than the [SO3LCuOH]- species, with the latter influenced by interactions between the distal -SO3- substituents and K+ or Na+ counterions. Chemical oxidations of the complexes generated the corresponding [CuOH]2+ species as evinced by UV-vis spectroscopy. The rates of HAT reactions of these species with 9,10-dihydroanthracene to yield the corresponding [Cu(OH2)]2+ complexes and anthracene were measured, and the thermodynamics of the processes were evaluated via determination of the bond dissociation enthalpies (BDEs) of the product O-H bonds. The HAT rate for [SO3LCuOH]- was found to be ∼150 times faster than that for [NMe3LCuOH]2+, despite finding approximately the same BDEs for the product O-H bonds. Rationales for these observations and new insights into the roles of supporting ligand attributes on the properties of the [CuOH]2+ unit are presented.
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Affiliation(s)
| | | | - William B. Tolman
- Department of Chemistry, Washington University in St. Louis, Campus Box 1134, 1 Brookings Drive, St. Louis, Missouri 63130, United States
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48
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Bhadra M, Lee JYC, Cowley RE, Kim S, Siegler MA, Solomon EI, Karlin KD. Intramolecular Hydrogen Bonding Enhances Stability and Reactivity of Mononuclear Cupric Superoxide Complexes. J Am Chem Soc 2018; 140:9042-9045. [PMID: 29957998 PMCID: PMC6217813 DOI: 10.1021/jacs.8b04671] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
[(L)CuII(O2•-)]+ (i.e., cupric-superoxo) complexes, as the first and/or key reactive intermediates in (bio)chemical Cu-oxidative processes, including in the monooxygenases PHM and DβM, have been systematically stabilized by intramolecular hydrogen bonding within a TMPA ligand-based framework. Also, gradual strengthening of ligand-derived H-bonding dramatically enhances the [(L)CuII(O2•-)]+ reactivity toward hydrogen-atom abstraction (HAA) of phenolic O-H bonds. Spectroscopic properties of the superoxo complexes and their azido analogues, [(L)CuII(N3-)]+, also systematically change as a function of ligand H-bonding capability.
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Affiliation(s)
- Mayukh Bhadra
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Jung Yoon C. Lee
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Ryan E. Cowley
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Sunghee Kim
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Maxime A. Siegler
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Kenneth D. Karlin
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
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49
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Meier KK, Jones SM, Kaper T, Hansson H, Koetsier MJ, Karkehabadi S, Solomon EI, Sandgren M, Kelemen B. Oxygen Activation by Cu LPMOs in Recalcitrant Carbohydrate Polysaccharide Conversion to Monomer Sugars. Chem Rev 2018; 118:2593-2635. [PMID: 29155571 PMCID: PMC5982588 DOI: 10.1021/acs.chemrev.7b00421] [Citation(s) in RCA: 114] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Natural carbohydrate polymers such as starch, cellulose, and chitin provide renewable alternatives to fossil fuels as a source for fuels and materials. As such, there is considerable interest in their conversion for industrial purposes, which is evidenced by the established and emerging markets for products derived from these natural polymers. In many cases, this is achieved via industrial processes that use enzymes to break down carbohydrates to monomer sugars. One of the major challenges facing large-scale industrial applications utilizing natural carbohydrate polymers is rooted in the fact that naturally occurring forms of starch, cellulose, and chitin can have tightly packed organizations of polymer chains with low hydration levels, giving rise to crystalline structures that are highly recalcitrant to enzymatic degradation. The topic of this review is oxidative cleavage of carbohydrate polymers by lytic polysaccharide mono-oxygenases (LPMOs). LPMOs are copper-dependent enzymes (EC 1.14.99.53-56) that, with glycoside hydrolases, participate in the degradation of recalcitrant carbohydrate polymers. Their activity and structural underpinnings provide insights into biological mechanisms of polysaccharide degradation.
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Affiliation(s)
- Katlyn K. Meier
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Stephen M. Jones
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Thijs Kaper
- DuPont Industrial Biosciences, 925 Page Mill Road, Palo Alto, California 94304, United States
| | - Henrik Hansson
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden
| | - Martijn J. Koetsier
- DuPont Industrial Biosciences, Netherlands, Nieuwe Kanaal 7-S, 6709 PA Wageningen, The Netherlands
| | - Saeid Karkehabadi
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Mats Sandgren
- Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden
| | - Bradley Kelemen
- DuPont Industrial Biosciences, 925 Page Mill Road, Palo Alto, California 94304, United States
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Ho WC, Chung K, Ingram AJ, Waymouth RM. Pd-Catalyzed Aerobic Oxidation Reactions: Strategies To Increase Catalyst Lifetimes. J Am Chem Soc 2018; 140:748-757. [PMID: 29244945 DOI: 10.1021/jacs.7b11372] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.
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Affiliation(s)
- Wilson C Ho
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Kevin Chung
- Department of Chemistry, Stanford University , Stanford, California 94305, United States.,Formosa Plastics Corporation , 201 Formosa Drive, Point Comfort, Texas 77978, United States
| | - Andrew J Ingram
- Department of Chemistry, Stanford University , Stanford, California 94305, United States.,James R. Randall Research Center, Archer Daniels Midland Company , Decatur, Illinois 62521, United States
| | - Robert M Waymouth
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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