Biomimetic metal-mediated reactivity

Christina Wegeberg

Biomimetic metal-mediated reactivity

Christina Wegeberg

Institut for Fysik, Kemi og Farmaci

Publikation: Afhandling › Ph.d.-afhandling

Abstract

Denne afhandling fokuserer på aktivering af terminale oxidationsmidler (PhIO, NMO, H2O2,
tBuOOH, cumylOOH, m-CPBA, ClO-) i organiske og vandige opløsninger af det mononukleare nonhæm
jern kompleks [Fe(tpena)]2+ dvs. detektering og karakterisering af transiente [Fe(tpena)]2+-
baserede oxidanter (skema B) samt belysning af mekanismer og reaktivitetsmønstre vigtige for
brugen i oxidation katalyse.

[Fe(tpena)]2+ er et relevant system til bioefterligning af non-hæm jern O2 aktiverende enzymer
grundet tilstedeværelsen af en carboxylat donor i den første koordinationssfære og en base i
den anden koordinationssfære. Carboxylat donoren forårsager et betydelig mindre FeII/FeIII
reduktionspotentiale for [Fe(tpena)]2+ sammenlignet med de mange non-hæm jern komplekser
uden denne funktionelle gruppe rapporteret de sidste tre årtier. En konsekvens deraf er
stabilisering af et jern(III) oxidationstrin til forskel fra et jern(II) oxidationstrin, som herved
skaber en katalysator med en bemærkelsesværdig mangfoldighed: reaktiviteten kontrolleres af
den valgte terminale oxidant, hvilket gør det muligt at skifte mellem paradigmerne af HAT- og
OAT-baserede oxidationer.
Reaktiviteten af jern-tpena systemet tilskrives jern(IV)oxo forbindelsen [FeIVO(Htpena)]2+, som
dannes via homolytisk kløvning af [FeO-X(tpenaH)]2+. Helt afhørende grunde til en mere
aggressiv reaktivitet sammenlignet med andre non-hæm jern model komplekser er
kombinationen af øget labilitet af FeO-X bindingen og større oxyl radikal karakter af
[FeIVO(Htpena)]2+. Dette giver sig til udtryk i hydrogen, alkyl og acylperoxid disproportionation
samt større anden ordens reaktionskonstanter i C-H abstraktion og katalytiske udbytter.
Ulempen ved brugen af peroxider som oxidationsmiddel er dog dannelsen af frie og
promiskuøse radikaler, X•, som dannes samtidig med [FeIVO(Htpena)]2+. Radikalerne kan også
virke som oxidanter, og som konsekvens vil selektiviteten i oxidation af substrater sænkes og
ligand-nedbrydning kan forekomme, hvis ikke det rette eksperimentelle design er blevet
benyttet. Tab i selektivitet kan dog blive forhindret ved at generere jern(IV)oxo forbindelsen direkte med en en-elektron acceptor fra dens jern(III) forgænger. I serien af ethylenediaminbaserede
jern(IV)oxo forbindelser er [FeIVO(Htpena)]2+ og [FeIVO(HtpenO)]2+ overlegne i hhv.
oxidation af C-H (både vandige og organiske opløsninger) og O-H bindinger.
Modsat brugen af peroxider, observeres der ingen radikale kemi, når oxidanten PhIO benyttes.
Selektive og katalytiske oxidationer er derimod demonstreret, hvilket tyder på en OAT
mekanisme katalyseret af en metal-baseret oxidant f.eks. den detekterbare [FeIII(OIPh)(tpena)]2+,
{[FeIII(OIPh)(tpena)]}2
4+ eller en ikke detekterbar jern(V)oxo forbindelse genereret via heterolytisk
kløvning af O-I bindingen. Halogen binding og forskellighederne af FeIIIO-X bindingen for PhIO
sammenlignet med peroxiderne tilordnes en helt afgørende betydning for observationen af de
forskellige reaktionsmønstre (OAT vs. HAT).
[Fe(tpena)]2+ gennemgår under ambiente forhold irreversibel, lys-induceret O2-afhængig Ndeglycinering
under dannelse af et jern(II) kompleks. Denne proces inkluderer et tab svarende til
en glycyl gruppe. Fortløbende C-C og C-N kløvninger er dokumenteret ved kvantitative målinger
samtidig med sekventiel produktion af hhv. CO2 og formaldehyd. Tidsafhængig spektroskopi har
muliggjort spektroskopisk karakterisering af to jern-baserede intermediater på reaktionsvejen til
degenerationsproduktet.

Originalsprog	Engelsk
Bevilgende institution	Syddansk Universitet
Vejledere/rådgivere	Mckenzie, Christine Joy, Vejleder Browne, Wesley R., Vejleder, Ekstern person
Dato for forsvar	11. jan. 2019
Udgivelsessted	Odense
Udgiver	Syddansk Universitet. Det Naturvidenskabelige Fakultet
Status	Udgivet - 11. jan. 2019

Note vedr. afhandling

Grad tildelt 30-01-2019

6 Tidsskriftartikel

Catalytic Alkyl Hydroperoxide and Acyl Hydroperoxide Disproportionation by a Nonheme Iron Complex
Wegeberg, C., Browne, W. R. & McKenzie, C. J., 2018, I: ACS Catalysis. 8, 11, s. 9980-9991
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review

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Directing a Non-Heme Iron(III)-Hydroperoxide Species on a Trifurcated Reactivity Pathway
Wegeberg, C., Lauritsen, F. R., Frandsen, C., Mørup, S., Browne, W. R. & McKenzie, C., 2018, I: Chemistry - A European Journal. 24, 20, s. 5134-5145
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review
Photoinduced O₂-Dependent Stepwise Oxidative Deglycination of a Nonheme Iron(III) Complex
Wegeberg, C., Fernández-Alvarez, V. M., De Aguirre, A., Frandsen, C., Browne, W. R., Maseras, F. & McKenzie, C. J., 2018, I: Journal of the American Chemical Society. 140, 43, s. 14150-14160
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review

Citationsformater

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title = "Biomimetic metal-mediated reactivity",

abstract = "The work presented in this thesis focuses on the activation of terminal oxidants (PhIO, NMO,H2O2, tBuOOH, cumylOOH, m-CPBA, ClO-) in organic and aqueous solutions by the mononuclearnon-heme iron complex [Fe(tpena)]2+, i.e., detection and characterization of transient[Fe(tpena)]2+-based oxidants (scheme A) as well as elucidation of mechanisms and reactivitypatterns important for the use in oxidation catalysis. (tpena = N,N,N{\textquoteright}-tris(2-pyridylmethyl)ethylene diamine-N{\textquoteright}-acetate)[Fe(tpena)]2+ is a germane biomimetic system for iron non-heme O2 activating enzymes due tothe presence of a carboxylate donor in the first coordination sphere and a second coordinationsphere base. The carboxylate donor induces a significantly lower FeII/FeIII reduction potential for[Fe(tpena)]2+ compared to the many non-heme iron complexes without this functional groupreported over the past three decades. As a consequence an iron(III) resting state rather than aniron(II) resting state is stabilized, which creates a catalyst with a remarkable diversity: thereactivity is controlled by the choice of terminal oxidant and can be switched between theparadigms of HAT- and OAT-based oxidations.The HAT-mediated reactivity of the iron-tpena system is ascribed to the iron(IV)oxo species[FeIVO(Htpena)]2+ generated upon homolytic bond cleavage of [FeO-X(tpenaH)]2+. Thecombination of enhanced lability of the FeO-X bond and greater oxyl radical character of[FeIVO(Htpena)]2+ is identified as the key reason for a more aggressive reactivity compared toother non-heme iron model complexes, which is demonstrated through rapid hydrogen, alkyland acylperoxide disproportionation, greater second order constants in C-H abstraction andlarger catalytic product yields. The drawback of using peroxides is that free and promiscuousradicals, X•, are subsequently formed alongside [FeIVO(Htpena)]2+. The radicals can also work asoxidants, and thereby decrease selectivity of the substrate oxidations and cause liganddegradation, if favourable experimental design has not been made. This loss of selectivity canhowever be avoided by the direct generation of the iron(IV)oxo species from its iron(III) precursor with a one electron acceptor in aqueous solutions. Within the series ofethylenediamine based iron(IV)oxo species, [FeIVO(Htpena)]2+ and [FeIVO(HtpenO)]2+ indeedperform best in oxidation of C-H (both in aqueous and organic solutions) and O-H bonds,respectively.In contrast to the use of peroxides, radical chemistry is not observed when the oxidant PhIO isemployed. Rather selective and catalytic oxygenations are demonstrated suggesting an OATmechanism catalysed by a metal-based oxidant, e.g., the detectable [FeIII(OIPh)(tpena)]2+,{[FeIII(OIPh)(tpena)]}24+ or undetected iron(V)oxo species generated through heterolytic O-Ibond cleavage. Halogen bonding and the different nature of the FeIIIO-X bond for PhIO comparedto peroxides are believed to play central roles for the observations of the different reactivitypatterns (OAT vs. HAT).[Fe(tpena)]2+ undergoes irreversible, light-promoted O2-dependent N-deglycination to generatean iron(II) complex under ambient conditions. The transformation includes a mass lossequivalent to a glycyl group involving consecutive C-C and C-N cleavages documented by thequantitative measurement of the sequential production of CO2 and formaldehyde, respectively.Time-resolved spectroscopy has allowed for the spectroscopic characterization of two ironbasedtransients along the reaction pathway.",

author = "Christina Wegeberg",

year = "2019",

month = jan,

day = "11",

language = "English",

publisher = "Syddansk Universitet. Det Naturvidenskabelige Fakultet",

address = "Denmark",

school = "SDU",

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TY - GEN

T1 - Biomimetic metal-mediated reactivity

AU - Wegeberg, Christina

PY - 2019/1/11

Y1 - 2019/1/11

N2 - The work presented in this thesis focuses on the activation of terminal oxidants (PhIO, NMO,H2O2, tBuOOH, cumylOOH, m-CPBA, ClO-) in organic and aqueous solutions by the mononuclearnon-heme iron complex [Fe(tpena)]2+, i.e., detection and characterization of transient[Fe(tpena)]2+-based oxidants (scheme A) as well as elucidation of mechanisms and reactivitypatterns important for the use in oxidation catalysis. (tpena = N,N,N’-tris(2-pyridylmethyl)ethylene diamine-N’-acetate)[Fe(tpena)]2+ is a germane biomimetic system for iron non-heme O2 activating enzymes due tothe presence of a carboxylate donor in the first coordination sphere and a second coordinationsphere base. The carboxylate donor induces a significantly lower FeII/FeIII reduction potential for[Fe(tpena)]2+ compared to the many non-heme iron complexes without this functional groupreported over the past three decades. As a consequence an iron(III) resting state rather than aniron(II) resting state is stabilized, which creates a catalyst with a remarkable diversity: thereactivity is controlled by the choice of terminal oxidant and can be switched between theparadigms of HAT- and OAT-based oxidations.The HAT-mediated reactivity of the iron-tpena system is ascribed to the iron(IV)oxo species[FeIVO(Htpena)]2+ generated upon homolytic bond cleavage of [FeO-X(tpenaH)]2+. Thecombination of enhanced lability of the FeO-X bond and greater oxyl radical character of[FeIVO(Htpena)]2+ is identified as the key reason for a more aggressive reactivity compared toother non-heme iron model complexes, which is demonstrated through rapid hydrogen, alkyland acylperoxide disproportionation, greater second order constants in C-H abstraction andlarger catalytic product yields. The drawback of using peroxides is that free and promiscuousradicals, X•, are subsequently formed alongside [FeIVO(Htpena)]2+. The radicals can also work asoxidants, and thereby decrease selectivity of the substrate oxidations and cause liganddegradation, if favourable experimental design has not been made. This loss of selectivity canhowever be avoided by the direct generation of the iron(IV)oxo species from its iron(III) precursor with a one electron acceptor in aqueous solutions. Within the series ofethylenediamine based iron(IV)oxo species, [FeIVO(Htpena)]2+ and [FeIVO(HtpenO)]2+ indeedperform best in oxidation of C-H (both in aqueous and organic solutions) and O-H bonds,respectively.In contrast to the use of peroxides, radical chemistry is not observed when the oxidant PhIO isemployed. Rather selective and catalytic oxygenations are demonstrated suggesting an OATmechanism catalysed by a metal-based oxidant, e.g., the detectable [FeIII(OIPh)(tpena)]2+,{[FeIII(OIPh)(tpena)]}24+ or undetected iron(V)oxo species generated through heterolytic O-Ibond cleavage. Halogen bonding and the different nature of the FeIIIO-X bond for PhIO comparedto peroxides are believed to play central roles for the observations of the different reactivitypatterns (OAT vs. HAT).[Fe(tpena)]2+ undergoes irreversible, light-promoted O2-dependent N-deglycination to generatean iron(II) complex under ambient conditions. The transformation includes a mass lossequivalent to a glycyl group involving consecutive C-C and C-N cleavages documented by thequantitative measurement of the sequential production of CO2 and formaldehyde, respectively.Time-resolved spectroscopy has allowed for the spectroscopic characterization of two ironbasedtransients along the reaction pathway.

AB - The work presented in this thesis focuses on the activation of terminal oxidants (PhIO, NMO,H2O2, tBuOOH, cumylOOH, m-CPBA, ClO-) in organic and aqueous solutions by the mononuclearnon-heme iron complex [Fe(tpena)]2+, i.e., detection and characterization of transient[Fe(tpena)]2+-based oxidants (scheme A) as well as elucidation of mechanisms and reactivitypatterns important for the use in oxidation catalysis. (tpena = N,N,N’-tris(2-pyridylmethyl)ethylene diamine-N’-acetate)[Fe(tpena)]2+ is a germane biomimetic system for iron non-heme O2 activating enzymes due tothe presence of a carboxylate donor in the first coordination sphere and a second coordinationsphere base. The carboxylate donor induces a significantly lower FeII/FeIII reduction potential for[Fe(tpena)]2+ compared to the many non-heme iron complexes without this functional groupreported over the past three decades. As a consequence an iron(III) resting state rather than aniron(II) resting state is stabilized, which creates a catalyst with a remarkable diversity: thereactivity is controlled by the choice of terminal oxidant and can be switched between theparadigms of HAT- and OAT-based oxidations.The HAT-mediated reactivity of the iron-tpena system is ascribed to the iron(IV)oxo species[FeIVO(Htpena)]2+ generated upon homolytic bond cleavage of [FeO-X(tpenaH)]2+. Thecombination of enhanced lability of the FeO-X bond and greater oxyl radical character of[FeIVO(Htpena)]2+ is identified as the key reason for a more aggressive reactivity compared toother non-heme iron model complexes, which is demonstrated through rapid hydrogen, alkyland acylperoxide disproportionation, greater second order constants in C-H abstraction andlarger catalytic product yields. The drawback of using peroxides is that free and promiscuousradicals, X•, are subsequently formed alongside [FeIVO(Htpena)]2+. The radicals can also work asoxidants, and thereby decrease selectivity of the substrate oxidations and cause liganddegradation, if favourable experimental design has not been made. This loss of selectivity canhowever be avoided by the direct generation of the iron(IV)oxo species from its iron(III) precursor with a one electron acceptor in aqueous solutions. Within the series ofethylenediamine based iron(IV)oxo species, [FeIVO(Htpena)]2+ and [FeIVO(HtpenO)]2+ indeedperform best in oxidation of C-H (both in aqueous and organic solutions) and O-H bonds,respectively.In contrast to the use of peroxides, radical chemistry is not observed when the oxidant PhIO isemployed. Rather selective and catalytic oxygenations are demonstrated suggesting an OATmechanism catalysed by a metal-based oxidant, e.g., the detectable [FeIII(OIPh)(tpena)]2+,{[FeIII(OIPh)(tpena)]}24+ or undetected iron(V)oxo species generated through heterolytic O-Ibond cleavage. Halogen bonding and the different nature of the FeIIIO-X bond for PhIO comparedto peroxides are believed to play central roles for the observations of the different reactivitypatterns (OAT vs. HAT).[Fe(tpena)]2+ undergoes irreversible, light-promoted O2-dependent N-deglycination to generatean iron(II) complex under ambient conditions. The transformation includes a mass lossequivalent to a glycyl group involving consecutive C-C and C-N cleavages documented by thequantitative measurement of the sequential production of CO2 and formaldehyde, respectively.Time-resolved spectroscopy has allowed for the spectroscopic characterization of two ironbasedtransients along the reaction pathway.

M3 - Ph.D. thesis

PB - Syddansk Universitet. Det Naturvidenskabelige Fakultet

CY - Odense

ER -

Biomimetic metal-mediated reactivity

Abstract

Note vedr. afhandling

Fingeraftryk

Relaterede publikationer

Catalytic Alkyl Hydroperoxide and Acyl Hydroperoxide Disproportionation by a Nonheme Iron Complex

Directing a Non-Heme Iron(III)-Hydroperoxide Species on a Trifurcated Reactivity Pathway

Photoinduced O2-Dependent Stepwise Oxidative Deglycination of a Nonheme Iron(III) Complex

Citationsformater

Photoinduced O₂-Dependent Stepwise Oxidative Deglycination of a Nonheme Iron(III) Complex