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Lee JL, Ross DL, Barman SK, Ziller JW, Borovik AS. C-H Bond Cleavage by Bioinspired Nonheme Metal Complexes. Inorg Chem 2021; 60:13759-13783. [PMID: 34491738 DOI: 10.1021/acs.inorgchem.1c01754] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The functionalization of C-H bonds is one of the most challenging transformations in synthetic chemistry. In biology, these processes are well-known and are achieved with a variety of metalloenzymes, many of which contain a single metal center within their active sites. The most well studied are those with Fe centers, and the emerging experimental data show that high-valent iron oxido species are the intermediates responsible for cleaving the C-H bond. This Forum Article describes the state of this field with an emphasis on nonheme Fe enzymes and current experimental results that provide insights into the properties that make these species capable of C-H bond cleavage. These parameters are also briefly considered in regard to manganese oxido complexes and Cu-containing metalloenzymes. Synthetic iron oxido complexes are discussed to highlight their utility as spectroscopic and mechanistic probes and reagents for C-H bond functionalization. Avenues for future research are also examined.
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Affiliation(s)
- Justin L Lee
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Dolores L Ross
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Suman K Barman
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Joseph W Ziller
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - A S Borovik
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
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2
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Li S, Zhou R, Zhao W, Du H. Synthesis of novel acyclic and multiple phenyl iron tetraamino ligand catalysts and its catalytic activity for degradation of dye wastewater by H
2
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2. Appl Organomet Chem 2021. [DOI: 10.1002/aoc.6252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Shun‐Lai Li
- College of Chemistry Beijing University of Chemical Technology Beijing China
| | - Run Zhou
- College of Chemistry Beijing University of Chemical Technology Beijing China
| | - Wei‐Jing Zhao
- College of Chemistry Beijing University of Chemical Technology Beijing China
| | - Hong‐Guang Du
- College of Chemistry Beijing University of Chemical Technology Beijing China
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3
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Keshari K, Bera M, Velasco L, Munshi S, Gupta G, Moonshiram D, Paria S. Characterization and reactivity study of non-heme high-valent iron-hydroxo complexes. Chem Sci 2021; 12:4418-4424. [PMID: 34163706 PMCID: PMC8179568 DOI: 10.1039/d0sc07054h] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A terminal FeIIIOH complex, [FeIII(L)(OH)]2− (1), has been synthesized and structurally characterized (H4L = 1,2-bis(2-hydroxy-2-methylpropanamido)benzene). The oxidation reaction of 1 with one equiv. of tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBAH) or ceric ammonium nitrate (CAN) in acetonitrile at −45 °C results in the formation of a FeIIIOH ligand radical complex, [FeIII(L˙)(OH)]− (2), which is hereby characterized by UV-visible, 1H nuclear magnetic resonance, electron paramagnetic resonance, and X-ray absorption spectroscopy techniques. The reaction of 2 with a triphenylcarbon radical further gives triphenylmethanol and mimics the so-called oxygen rebound step of Cpd II of cytochrome P450. Furthermore, the reaction of 2 was explored with different 4-substituted-2,6-di-tert-butylphenols. Based on kinetic analysis, a hydrogen atom transfer (HAT) mechanism has been established. A pKa value of 19.3 and a BDFE value of 78.2 kcal/mol have been estimated for complex 2. One-electron oxidation of an FeIII–OH complex (1) results in the formation of a FeIII–OH ligand radical complex (2). Its reaction with (C6H5)3C˙ results in the formation of (C6H5)3COH, which is a functional mimic of compound II of cytochrome P450.![]()
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Affiliation(s)
- Kritika Keshari
- 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
| | - Lucía Velasco
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia Calle Faraday, 9 28049 Madrid Spain
| | - Sandip Munshi
- School of Chemical Sciences, Indian Association for the Cultivation of Science 2A & 2B Raja S. C. Mullick Road, Jadavpur Kolkata 700032 India
| | - Geetika Gupta
- Department of Chemistry, Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India
| | - Dooshaye Moonshiram
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia Calle Faraday, 9 28049 Madrid Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India
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4
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Kim Y, Kim J, Nguyen LK, Lee YM, Nam W, Kim SH. EPR spectroscopy elucidates the electronic structure of [FeV(O)(TAML)] complexes. Inorg Chem Front 2021. [DOI: 10.1039/d1qi00522g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The complete hyperfine tensor of 17O of the FeV-oxo moeity was probed by ENDOR spectroscopy. The EPR spectroscopic results reported here provide a conclusive experimental basis for elucidating the electronic structure of the FeV-oxo complex.
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Affiliation(s)
- Yujeong Kim
- Western Seoul Center
- Korea Basic Science Institute (KBSI)
- Seoul 03759
- Rep. of Korea
- Department of Chemistry and Nano Science
| | - Jin Kim
- Department of Chemistry
- Sunchon National University
- Suncheon 57922
- Rep. of Korea
| | - Linh K. Nguyen
- Department of Chemistry and Nano Science
- Ewha Womans University
- Seoul 03760
- Rep. of Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science
- Ewha Womans University
- Seoul 03760
- Rep. of Korea
| | - Wonwoo Nam
- Department of Chemistry and Nano Science
- Ewha Womans University
- Seoul 03760
- Rep. of Korea
| | - Sun Hee Kim
- Western Seoul Center
- Korea Basic Science Institute (KBSI)
- Seoul 03759
- Rep. of Korea
- Department of Chemistry and Nano Science
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5
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Somasundar Y, Shen LQ, Hoane AG, Kaaret EZ, Warner GR, Ryabov AD, Collins TJ. Predicting Properties of Iron(III) TAML Activators of Peroxides from Their III/IV and IV/V Reduction Potentials or a Lost Battle to Peroxidase. Chemistry 2020; 26:14738-14744. [DOI: 10.1002/chem.202003535] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 08/27/2020] [Indexed: 12/29/2022]
Affiliation(s)
- Yogesh Somasundar
- Institute for Green Science Department of Chemistry Carnegie Mellon University 4400 Fifth Ave Pittsburgh PA 15213 USA
| | | | - Alexis G. Hoane
- Institute for Green Science Department of Chemistry Carnegie Mellon University 4400 Fifth Ave Pittsburgh PA 15213 USA
| | - Evan Z. Kaaret
- Institute for Green Science Department of Chemistry Carnegie Mellon University 4400 Fifth Ave Pittsburgh PA 15213 USA
| | - Genoa R. Warner
- Institute for Green Science Department of Chemistry Carnegie Mellon University 4400 Fifth Ave Pittsburgh PA 15213 USA
- Present address: Department of Comparative Biosciences University of Illinois 2001 S. Lincoln Avenue Urbana IL 61802 USA
| | - Alexander D. Ryabov
- Institute for Green Science Department of Chemistry Carnegie Mellon University 4400 Fifth Ave Pittsburgh PA 15213 USA
| | - Terrence J. Collins
- Institute for Green Science Department of Chemistry Carnegie Mellon University 4400 Fifth Ave Pittsburgh PA 15213 USA
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6
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Xue SS, Li XX, Lee YM, Seo MS, Kim Y, Yanagisawa S, Kubo M, Jeon YK, Kim WS, Sarangi R, Kim SH, Fukuzumi S, Nam W. Enhanced Redox Reactivity of a Nonheme Iron(V)-Oxo Complex Binding Proton. J Am Chem Soc 2020; 142:15305-15319. [PMID: 32786748 DOI: 10.1021/jacs.0c05108] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Acid effects on the chemical properties of metal-oxygen intermediates have attracted much attention recently, such as the enhanced reactivity of high-valent metal(IV)-oxo species by binding proton(s) or Lewis acidic metal ion(s) in redox reactions. Herein, we report for the first time the proton effects of an iron(V)-oxo complex bearing a negatively charged tetraamido macrocyclic ligand (TAML) in oxygen atom transfer (OAT) and electron-transfer (ET) reactions. First, we synthesized and characterized a mononuclear nonheme Fe(V)-oxo TAML complex (1) and its protonated iron(V)-oxo complexes binding two and three protons, which are denoted as 2 and 3, respectively. The protons were found to bind to the TAML ligand of the Fe(V)-oxo species based on spectroscopic characterization, such as resonance Raman, extended X-ray absorption fine structure (EXAFS), and electron paramagnetic resonance (EPR) measurements, along with density functional theory (DFT) calculations. The two-protons binding constant of 1 to produce 2 and the third protonation constant of 2 to produce 3 were determined to be 8.0(7) × 108 M-2 and 10(1) M-1, respectively. The reactivities of the proton-bound iron(V)-oxo complexes were investigated in OAT and ET reactions, showing a dramatic increase in the rate of sulfoxidation of thioanisole derivatives, such as 107 times increase in reactivity when the oxidation of p-CN-thioanisole by 1 was performed in the presence of HOTf (i.e., 200 mM). The one-electron reduction potential of 2 (Ered vs SCE = 0.97 V) was significantly shifted to the positive direction, compared to that of 1 (Ered vs SCE = 0.33 V). Upon further addition of a proton to a solution of 2, a more positive shift of the Ered value was observed with a slope of 47 mV/log([HOTf]). The sulfoxidation of thioanisole derivatives by 2 was shown to proceed via ET from thioanisoles to 2 or direct OAT from 2 to thioanisoles, depending on the ET driving force.
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Affiliation(s)
- Shan-Shan Xue
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Xiao-Xi Li
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Mi Sook Seo
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Yujeong Kim
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.,Western Seoul Center, Korea Basic Science Institute, Seoul 03759, Korea
| | - Sachiko Yanagisawa
- Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
| | - Minoru Kubo
- Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
| | - Young-Kyo Jeon
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Won-Suk Kim
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Ritimukta Sarangi
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, California 94025, United States
| | - Sun Hee Kim
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.,Western Seoul Center, Korea Basic Science Institute, Seoul 03759, Korea
| | - Shunichi Fukuzumi
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.,School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, P. R. China
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7
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Weitz AC, Biswas S, Rizzolo K, Elliott S, Bominaar EL, Hendrich MP. Electronic State of the His/Tyr-Ligated Heme of BthA by Mössbauer and DFT Analysis. Inorg Chem 2020; 59:10223-10233. [PMID: 32602712 DOI: 10.1021/acs.inorgchem.0c01349] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The BthA protein from the microorganism Burkholderia thailandensis contains two hemes with axial His/OH2 and His/Tyr coordinations separated by the closest interheme distance of 14 Å. BthA has a similar structure and belongs to the same family of multiheme cytochrome c peroxidases as MauG, which performs long-range oxidation of the partner protein methylamine dehydrogenase. Magnetic Mössbauer spectroscopy of the diferric state of BthA corroborates previous structural work identifying a high-spin (His/OH2) peroxidatic heme and a low-spin (His/Tyr) electron transfer heme. Unlike MauG, addition of H2O2 fully converts the diferric form of BthA to a stable 2e- oxidized state, allowing a new assessment of this state. The peroxidatic heme is found to be oxidized to a canonical compound II, S = 1 oxoiron(IV) heme. In contrast, the electronic properties of the oxidized His/Tyr heme are puzzling. The isomer shift of the His/Tyr heme (0.17 mm/s) is close to that of the precursor S = 1/2 Fe3+ heme (0.21 mm/s) which suggests oxidation of the Tyr. However, the spin-dipolar hyperfine coupling constants are found here to be the same as those for the ferryl peroxidatic heme, indicating that the His/Tyr heme is also a compound II, S = 1 Fe4+ heme and ruling out oxidation of the Tyr. DFT calculations indicate that the unusually high isomer shift is not attributable to the rare axial His/Tyr heme coordination. The calculations are only compatible with spectroscopy for an unusually long Fe4+-OTyr distance, which is presumably under the influence of the protein environment of the His/Tyr heme moiety in the H2O2 oxidized state of the protein. The results offer new insights into how high valence intermediates can be tuned by the protein environment for performing long-range oxidation.
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Affiliation(s)
- Andrew C Weitz
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - Saborni Biswas
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Kim Rizzolo
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - Sean Elliott
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
| | - Emile L Bominaar
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Michael P Hendrich
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
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8
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Thapa P, Palacios PM, Tran T, Pierce BS, Foss FW. 1,2-Disubstituted Benzimidazoles by the Iron Catalyzed Cross-Dehydrogenative Coupling of Isomeric o-Phenylenediamine Substrates. J Org Chem 2020; 85:1991-2009. [PMID: 31928002 DOI: 10.1021/acs.joc.9b02714] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and disubstituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O2 and FeCl3·6H2O catalyzed the cross-dehydrogenative coupling and aromatization of diarylmethyl and dialkyl benzimidazole precursors. N,N'-Disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe3+. The reaction also converted N-monosubstituted OPD substrates to 2-substituted benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turnover, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.
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Affiliation(s)
- Pawan Thapa
- Department of Chemistry and Biochemistry , The University of Texas Arlington , Arlington , Texas 76019-0065 , United States
| | - Philip M Palacios
- Department of Chemistry and Biochemistry , The University of Texas Arlington , Arlington , Texas 76019-0065 , United States
| | - Tam Tran
- Department of Chemistry and Biochemistry , The University of Texas Arlington , Arlington , Texas 76019-0065 , United States
| | - Brad S Pierce
- Department of Chemistry and Biochemistry , The University of Alabama , Tuscaloosa , Alabama 35487 , United States
| | - Frank W Foss
- Department of Chemistry and Biochemistry , The University of Texas Arlington , Arlington , Texas 76019-0065 , United States
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9
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Li S, Wang L, Zhou R, Zhou C, Du H. Synthesis of a simplified iron(III) tetraamido macrocyclic ligand (Fe III-TAML) catalyst and its catalytic activity for degradation of dye wastewater by H 2O 2. J COORD CHEM 2020. [DOI: 10.1080/00958972.2019.1710138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Shunlai Li
- College of Chemistry, Beijing University of Chemical Technology, Beijing, China
| | - Liaoyuan Wang
- College of Chemistry, Beijing University of Chemical Technology, Beijing, China
| | - Run Zhou
- College of Chemistry, Beijing University of Chemical Technology, Beijing, China
| | - Cheng Zhou
- College of Chemistry, Beijing University of Chemical Technology, Beijing, China
| | - Hongguang Du
- College of Chemistry, Beijing University of Chemical Technology, Beijing, China
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10
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Zaragoza JPT, Cummins DC, Mubarak MQE, Siegler MA, de Visser SP, Goldberg DP. Hydrogen Atom Abstraction by High-Valent Fe(OH) versus Mn(OH) Porphyrinoid Complexes: Mechanistic Insights from Experimental and Computational Studies. Inorg Chem 2019; 58:16761-16770. [PMID: 31804814 DOI: 10.1021/acs.inorgchem.9b02923] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
High-valent metal-hydroxide species have been implicated as key intermediates in hydroxylation chemistry catalyzed by heme monooxygenases such as the cytochrome P450s. However, in some classes of P450s, a bifurcation from the typical oxygen rebound pathway is observed, wherein the FeIV(OH)(porphyrin) species carries out a net hydrogen atom transfer reaction to form alkene metabolites. In this work, we examine the hydrogen atom transfer (HAT) reactivity of FeIV(OH)(ttppc) (1), ttppc = 5,10,15-tris(2,4,6-triphenyl)-phenyl corrole, toward substituted phenol derivatives. The iron hydroxide complex 1 reacts with a series of para-substituted 2,6-di-tert-butylphenol derivatives (4-X-2,6-DTBP; X = OMe, Me, Et, H, Ac), with second-order rate constants k2 = 3.6(1)-1.21(3) × 104 M-1 s-1 and yielding linear Hammett and Marcus plot correlations. It is concluded that the rate-determining step for O-H cleavage occurs through a concerted HAT mechanism, based on mechanistic analyses that include a KIE = 2.9(1) and DFT calculations. Comparison of the HAT reactivity of 1 to the analogous Mn complex, MnIV(OH)(ttppc), where only the central metal ion is different, indicates a faster HAT reaction and a steeper Hammett slope for 1. The O-H bond dissociation energy (BDE) of the MIII(HO-H) complexes were estimated from a kinetic analysis to be 85 and 89 kcal mol-1 for Mn and Fe, respectively. These estimated BDEs are closely reproduced by DFT calculations and are discussed in the context of how they influence the overall H atom transfer reactivity.
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Affiliation(s)
- Jan Paulo T Zaragoza
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - Daniel C Cummins
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - M Qadri E Mubarak
- The Manchester Institute of Biotechnology and Department of Chemical Engineering and Analytical Science , The University of Manchester , 131 Princess Street , Manchester M1 7DN , United Kingdom
| | - Maxime A Siegler
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - Sam P de Visser
- The Manchester Institute of Biotechnology and Department of Chemical Engineering and Analytical Science , 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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11
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Ehudin MA, Quist DA, Karlin KD. Enhanced Rates of C-H Bond Cleavage by a Hydrogen-Bonded Synthetic Heme High-Valent Iron(IV) Oxo Complex. J Am Chem Soc 2019; 141:12558-12569. [PMID: 31318198 PMCID: PMC6734939 DOI: 10.1021/jacs.9b01253] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Secondary coordination sphere interactions are critical in facilitating the formation, stabilization, and enhanced reactivity of high-valent oxidants required for essential biochemical processes. Herein, we compare the C-H bond oxidizing capabilities of spectroscopically characterized synthetic heme iron(IV) oxo complexes, F8Cmpd-II (F8 = tetrakis(2,6-difluorophenyl)porphyrinate), and a 2,6-lutidinium triflate (LutH+) Lewis acid adduct involving ferryl O-atom hydrogen-bonding, F8Cmpd-II(LutH+). Second-order rate constants utilizing C-H and C-D substrates were obtained by UV-vis spectroscopic monitoring, while products were characterized and quantified by EPR spectroscopy and gas chromatography (GC). With xanthene, F8Cmpd-II(LutH+) reacts 40 times faster (k2 = 14.2 M-1 s-1; -90 °C) than does F8Cmpd-II, giving bixanthene plus xanthone and the heme product [F8FeIIIOH2]+. For substrates with greater C-H bond dissociation energies (BDEs) F8Cmpd-II(LutH+) reacts with the second order rate constants k2(9,10-dihydroanthracene; DHA) = 0.485 M-1 s-1 and k2(fluorene) = 0.102 M-1 s-1 (-90 °C); by contrast, F8Cmpd-II is unreactive toward these substrates. For xanthene vs xanthene-(d2), large, nonclassical deuterium kinetic isotope effects are roughly estimated for both F8Cmpd-II and F8Cmpd-II(LutH+). The deuterated H-bonded analog, F8Cmpd-II(LutD+), was also prepared; for the reaction with DHA, an inverse KIE (compared to F8Cmpd-II(LutH+)) was observed. This work originates/inaugurates experimental investigation of the reactivity of authentic H-bonded heme-based FeIV═O compounds, critically establishing the importance of oxo H-bonding (or protonation) in heme complexes and enzyme active sites.
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Affiliation(s)
- Melanie A. Ehudin
- 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
| | - Kenneth D. Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
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