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University of Groningen
Biomimetic metal-mediated reactivityWegeberg, Christina
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BIOMIMETIC METAL-MEDIATED
REACTIVITY
Christina Wegeberg
Design, synthesis and characterization (NMR, IR, UV/vis, EPR, MS, SCXRD, CV) of the iron
compounds described in this thesis together with reactivity studies and catalysis were
performed at the Department of Physics, Chemistry and Pharmacy, University of Southern
Denmark, Denmark. Head-space gas detection and additional characterization (rRaman,
UV/vis) were completed at the Molecular Inorganic Chemistry Department of the Stratingh
Institute for Chemistry, University of Groningen, The Netherlands.
The work reported in this thesis was supported financially by The
Danish Council for Independent Research | Natural Sciences
(grant 4181-00329).
Printed by: Ipskamp Printing, The Netherlands
Cover artwork made by Mie Thorborg Pedersen. Enzyme: Taurine/α-ketoglutarate
dioxygenase from Escherichia coli. PDB ID: 1GQW. Crystal structure:
[Fe(tpena)](ClO4)2(MeCN)1.5. CCDC reference code: CUXPAO.
ISBN: 978-94-034-1166-8 (printed version)
ISBN: 978-94-034-1165-1 (electronic version)
BIOMIMETIC METAL-MEDIATED REACTIVITY
PhD thesis
to obtain the degree of PhD at the University of Groningen on the authority of the
Rector Magnificus Prof. E. Sterken and in accordance with
the decision by the College of Deans
and
to obtain the degree of PhD at the University of Southern Denmark
on the authority of the Dean Prof. Martin Zachariasen
Double PhD degree
This thesis will be defended in public on
Friday January 11th 2019 at 16.15 hours
and
Monday January 14th 2019 at 14.00 hours
by
Christina Wegeberg
born on the 18th of February 1989
in Middelfart, Denmark
Supervisors
Prof. C. J. McKenzie
Prof. W. R. Browne
Assessment Committee
Prof. V. McKee
Prof. E. Otten
Prof. T. D. Waite
Prof. M. Swart
Table of Contents
List of Publication .............................................................................................................................. i
Abbreviations ................................................................................................................................... ii
Abstract ........................................................................................................................................... iv
Resumé ............................................................................................................................................ vi
Samenvatting ................................................................................................................................. viii
Acknowledgements .......................................................................................................................... x
1. Introduction
1.1 Inspiration from Nature ...................................................................................................... 1
1.2 Mononuclear Non-Heme Systems ...................................................................................... 5
1.3 Generation of Mononuclear Iron(III) Peroxo Species ......................................................... 6
1.4 Generation of Mononuclear Iron(IV)oxo Species ............................................................. 11
1.5 The Hunt for a Mononuclear Iron(V)oxo Species ............................................................. 16
1.6 The Nature of the Active Oxidant ..................................................................................... 19
1.7 Conclusions ....................................................................................................................... 22
2. Summary ................................................................................................................................. 23
Bibliography .................................................................................................................................... 28
3. Paper I: Halogen-Bonding-Assisted Iodosylbenzene Activation by a Homogenous Iron
Catalyst ................................................................................................................................... 37
4. Paper II: Reduction of Hypervalent Iodine by Coordination to Iron(III) and the Crystal
Structures of PhIO and PhIO2 .................................................................................................. 49
5. Paper III: Noncovalent Halogen Bonding as a Mechanism for Gas-Phase Clustering ............ 59
6. Paper IV: Directing a Non-Heme Iron(III)-Hydroperoxide Species on a Trifurcated Reactivity
Pathway .................................................................................................................................. 69
7. Paper V: Catalytic Alkyl Hydroperoxide and Acylperoxide Disproportionation by a Nonheme
Iron Complex ........................................................................................................................... 83
8. Paper VI: Photoinduced O2-dependent Stepwise Oxidative-Deglycination of a Nonheme
Iron(III) Complex ................................................................................................................... 109
9. Paper VII: The Reactivities of Non-heme Iron(III)peroxo and Iron(IV)oxo Complexes are
Tuned by Presence of a Cis Carboxylato, Alkoxido or Pyridine Donor ................................. 137
10. Paper VIII: The Oxidizing Power of Iron(IV)oxo Complexes of a Series of Rtpen Ligands in
Water Correlates with the Increasing Energy of the LMCT .................................................. 151
Appendix A ................................................................................................................................... 176
Appendix B .................................................................................................................................... 177
Appendix C .................................................................................................................................... 178
i
List of Publication
This thesis is based on the following publications:
I. D. P. de Sousa, C. Wegeberg, M. S. Vad, S. Mørup, C. Frandsen, W. A. Donald and C. J.
McKenzie. Halogen-Bonding Assisted Iodosylbenzene Activation by a Homogenous Iron
Catalyst. Chem., Eur. J. 2016, 22, 3810-3820. DOI: 10.1002/chem.201503112
II. C. Wegeberg, C. G. Frankær, C. J. McKenzie. Reduction of Hypervalent Iodine by
Coordination to Iron(III) and the Crystal Structures of PhIO and PhIO2. Dalton Trans.
2016, 45, 17714 – 17722. DOI: 10.1039/C6DT02937J
III. C. Wegeberg, W. A. Donald, C. J. McKenzie, Non-Covalent Halogen Bonding as a
Mechanism for Gas Phase Clustering. J. Am. Soc. Mass Spectr. 2017, 28, 2209-2216. DOI:
10.1007/s13361-017-1722-z
IV. C. Wegeberg, F. R. Lauritsen, C. Frandsen, S. Mørup, W. R. Browne, C. J. McKenzie.
Directing a Non-Heme Iron(III)-Hydroperoxide Species on a Trifurcated Reactivity
Pathway. Chem. Eur. J. 2018. DOI: 10.1002/chem.201704615
V. C. Wegeberg, W. R. Browne, C. J. McKenzie. Catalytic Alkyl Hydroperoxide and
Acylperoxide Disproportionation by a Nonheme Iron Complex. ACS Catalysis 2018, 8,
9980-9991. DOI: 10.1021/acscatal.8b02882
VI. C. Wegeberg, V. M. Fernández-Alvarez, A. de Aguirre, C. Frandsen, W. R. Browne, F.
Maseras, C. J. McKenzie. Photoinduced O2-dependent Stepwise Oxidative-Deglycination
of a Nonheme Iron(III) Complex. J. Am. Chem. Soc. 2018, 140, 14150-14160 DOI:
10.1021/jacs.8b07455
VII. C. Wegeberg, W. R. Browne, C. J. McKenzie. The Reactivities of Non-heme Iron(III)peroxo
and Iron(IV)oxo Complexes are Tuned by Presence of a Cis Carboxylato, Alkoxido or
Pyridine Donor, in preparation
VIII. C. Wegeberg, A. L. Gonzalez, W. R. Browne, C. J. McKenzie. The Oxidizing Power of
Iron(IV)oxo complexes of a Series of Rtpen Ligands in Water Correlates with the
Increasing Energy of the LMCT, in preparation
List of publications not included in this thesis:
IX. C. Wegeberg, V. McKee, C. J. McKenzie, A Coordinatively Flexible Hexadentate Ligand
Gives Structural Isomeric Complexes M2(L)X3 (M = Cu, Zn; X = Br, Cl). Acta Cryst. 2016,
C72, 68-74. DOI: 10.1107/S2053229615023773
X. C. Henriksen, C. Wegeberg, D. Ravnsbæk, Phase Transformation Mechanism of Li-ion
Storage in Iron(III) Hydroxide Phosphates. J. Phys. Chem. C 2018, 122, 1930-1938. DOI:
10.1021/acs.jpcc.7b10352
XI. K. Vejlegaard, C. Wegeberg, V. McKee, J. Wengel, Novel Conformationally Constrained 2’-
C-Methylribonucleosides: Synthesis and Incorporation into Oligonucleotides. Org.
Biomol. Chem. 2018, 16, 1312-1321. DOI: 10.1039/C7OB02663C
ii
Abbreviations Ac acetate BLM Bleomycin BPMCN N,N’-bis(2-pyridylmethyl)-N,N’-dimethyltrans-1,2-diaminocyclohexane bppa bis(6-pivalamido-2-pyridylmethyl)(2-pyridylmethyl)amine bpy 2,2'-bipyridine H3buea tris[(N’-tert-butylureaylato)-N-ethyl]aminato Bz benzyl bzbpena N-benzyl-N,N’-bis(2-pyridylmethyl)ethylenediamine-N’-acetate bztpen N-benzyl-N,N’,N’-tris(2-pyridylmethyl)-1,2-diaminoethane CAN ceric ammonium nitrate CCDC The Cambridge Crystallographic Data Centre CID collision-induced dissociation cryptand 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane DFT density functional theory DNA deoxyribonucleic acid EPR electron paramagnetic resonance ESI-MS electrospray ionization mass spectrometry Et ethyl EXAFS extended X-ray absorption fine structure HAT hydrogen atom transfer IR infrared m-CPBA meta-chloro peroxy benzoic acid Me methyl MeN4Py 1,1-di(pyridin-2-yl)N,N-bis(pyridin-2-ylmethyl)ethan-1-amine metpen N-methyl-N,N’,N’-tris(2-pyridylmethyl)-1,2-diaminoethane MIMS membrane inlet mass spectrometry N4Py N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine NMO N-Methylmorpholine N-oxide NMR nuclear magnetic resonance NIR near infrared OAT oxygen atom transfer OTf triflate phen phenanthroline PhIO iodosylbenzene Py pyridyl PyNMe3 3,6,9-trimethyl-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane Hqn quinaldic acid rRaman resonance Raman TACNPy2 1-di(2-pyridyl)methyl-4,7-dimethyl-1,4,7-triazacyclononane TAML 3,4,8,9-tetrahydro-3,3,6,6,9,9-hexamethyl-1H-1,4,7,10-benzotetraazacyclo- tridocane-2,5,7,10-(6H,11H)tetrone TAML* substituted TAML derivative TLA tris[(6-methyl-2-pyridyl)methyl]amine TMC 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane TMCO 4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane TMG3tren 1,1,1-tris{2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl}amine TPA tris(2-pyridylmethyl)amine tpen N,N,N’,N’-tetrakis(2-pyridylmethyl)ethane-1,2-diamine tpena N,N,N’-tris(2-pyridylmethyl)ethylenediamine-N’-acetate)
iii
H3TPAPh tris-(5-phenyl-1H-pyrrol-2-ylmethyl)-amine UV/vis ultraviolet/visible XAS X-ray absorption spectroscopy XANES X-ray absorption near edge structure
iv
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 mononuclear
non-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 reactivity
patterns important for the use in oxidation catalysis. (tpena = N,N,N’-tris(2-
pyridylmethyl)ethylene diamine-N’-acetate)
Scheme A. Simplified and unified schematic illustration of the iron chemistry presented in this PhD thesis. Changes of
the oxidant (XO- or PhIO) and/or the ligand (L) around the iron centre in non-heme iron complexes control the
formation of the possible iron-based oxidants and hence the catalytic activity. X = OH, OtBu, Ocumyl, m-CBA, Cl,
NM(O). L = ethylenediamine backboned ligand: N-R-N,N’,N’-tris(2-pyridylmethyl)ethane-1,2-diamine, (R = CH3
(metpen), CH2CH3 (ettpen), CH2C6H5 (bztpen), CH2C6H4N (tpen), CH2CH2OH (tpenOH) and CH2COOH (tpenaH)).
[Fe(tpena)]2+ is a germane biomimetic system for iron non-heme O2 activating enzymes due to
the presence of a carboxylate donor in the first coordination sphere and a second coordination
sphere 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 group
reported over the past three decades. As a consequence an iron(III) resting state rather than an
iron(II) resting state is stabilized, which creates a catalyst with a remarkable diversity: the
reactivity is controlled by the choice of terminal oxidant and can be switched between the
paradigms 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+. The
combination 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 to
other non-heme iron model complexes, which is demonstrated through rapid hydrogen, alkyl
and acylperoxide disproportionation, greater second order constants in C-H abstraction and
larger catalytic product yields. The drawback of using peroxides is that free and promiscuous
radicals, X•, are subsequently formed alongside [FeIVO(Htpena)]2+. The radicals can also work as
oxidants, and thereby decrease selectivity of the substrate oxidations and cause ligand
degradation, if favourable experimental design has not been made. This loss of selectivity can
however be avoided by the direct generation of the iron(IV)oxo species from its iron(III)
v
precursor with a one electron acceptor in aqueous solutions. Within the series of
ethylenediamine based iron(IV)oxo species, [FeIVO(Htpena)]2+ and [FeIVO(HtpenO)]2+ indeed
perform 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 is
employed. Rather selective and catalytic oxygenations are demonstrated suggesting an OAT
mechanism 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-I
bond cleavage. Halogen bonding and the different nature of the FeIIIO-X bond for PhIO compared
to peroxides are believed to play central roles for the observations of the different reactivity
patterns (OAT vs. HAT).
[Fe(tpena)]2+ undergoes irreversible, light-promoted O2-dependent N-deglycination to generate
an iron(II) complex under ambient conditions. The transformation includes a mass loss
equivalent to a glycyl group involving consecutive C-C and C-N cleavages documented by the
quantitative measurement of the sequential production of CO2 and formaldehyde, respectively.
Time-resolved spectroscopy has allowed for the spectroscopic characterization of two iron-
based transients along the reaction pathway.
vi
Resumé
Denne afhandling fokuserer på aktivering af terminale oxidationsmidler (PhIO, NMO, H2O2, tBuOOH, cumylOOH, m-CPBA, ClO-) i organiske og vandige opløsninger af det mononukleare non-
hæm 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.
Skema B. Forenklet skematisk illustration af jern-kemien rapporteret i denne ph.d.-afhandling. Ændringer af
oxidationsmidlet (XO- eller PhIO) og/eller liganden (L) omkring jern centeret i non-hæm komplekser kontrollerer
dannelsen af de mulige jern-baserede oxidanter og som konsekvens den katalytiske aktivitet. X = OH, OtBu, Ocumyl,
m-CBA, Cl, NM(O). L = ethylenediamin-baseret ligand: N-R-N,N’,N’-tris(2-pyridylmethyl)ethan-1,2-diamin, (R = CH3
(metpen), CH2CH3 (ettpen), CH2C6H5 (bztpen), CH2C6H4N (tpen), CH2CH2OH (tpenOH) and CH2COOH (tpenaH)).
[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
vii
direkte med en en-elektron acceptor fra dens jern(III) forgænger. I serien af ethylenediamin-
baserede 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)]}24+ 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 N-
deglycinering under dannelse af et jern(II) kompleks. Denne proces inkluderer et masse 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 nedbrydningsproduktet.
viii
Samenvatting
Het werk gepresenteerd in dit proefschrift richt zich primair op de activatie van terminale
oxidanten (PhIO, NMO, H2O2, tBuOOH, cumylOOH, m-CPBA, ClO-) in organische oplossingen en in
water door het mononucleaire niet-heem ijzer complex [Fe(tpena)]2+ (tpena = N,N,N’-tris(2-
pyridylmethyl)ethylene diamine-N’-acetate), bijvoorbeeld voor de detectie en karakterizatie van
kortlevende op [Fe(tpena)]2+ gebaseerde oxidanten (Schema C) zowel als de verheldering van
mechanismen en patronen in reactiviteit die belangrijk zijn voor gebruik in katalytische oxidaties.
Schema C. Versimpeld schematisch overzicht van de reactiviteit van het ijzercomplex dat centraal staat in dit
proefschrift. Veranderingen in de oxidant (XO- or PhIO) en/of het ligand (L) rond het ijzer-centrum in niet-heem ijzer
complexen beïnvloeden de formatie van mogelijke op ijzer gebaseerde oxidanten, en daarmee de katalytische functie.
X = OH, OtBu, Ocumyl, m-CBA, Cl, NM(O). L = op ethyleendiamine gebaseerde ligand (R = CH3 (metpen), CH2CH3
(ettpen), CH2C6H5 (bztpen), CH2C6H4N (tpen), CH2CH2OH (tpenOH) and CH2COOH (tpenaH)).
[Fe(tpena)]2+ is een bloedeigen biomimetisch systeem voor ijzer niet-heem O2 activerende
enzymen dankzij de aanwezigheid van een carboxylaat donor in de eerste coördinatiesfeer en
een tweede coördinatiesfeer base. De carboxylaat donor brengt een significant lager FeII/FeIII
reductiepotentiaal teweeg voor [Fe(tpena)]2+ vergeleken met de meeste niet-heem ijzer
complexen van de afgelopen tientallen jaren zonder deze functionele groep. Hierdoor is een
ijzer(III) ruststaat in plaats van een ijzer(II) ruststaat gestabiliseerd, wat een katalytisch systeem
met uitzonderlijke eigenschappen creëert: de reactiviteit is beïnvloed door de keuze van
terminale oxidant en kan verwisseld worden tussen het paradigma van HAT- en OAT-bemiddelde
oxidaties.
De HAT-bemiddelde reactiviteit van het ijzer-tpena systeem is toegeschreven aan het
ijzer(IV)oxo soort [FeIVO(Htpena)]2+ dat ontstaat onder homolytische dissociatie van de bond in
[FeO-X(tpenaH)]2+. De combinatie van verlaagde stabiliteit van de FeO-X bond en het verhoogde
radicaal-karakter van het oxyl van [FeIVO(Htpena)]2+ is geïdentificeerd als de primaire reden voor
een versterkte reactiviteit in vergelijking tot de andere niet-heem complexen, wat is
gedemonstreerd met snelle waterstof, alkyl en acylperoxide disproportionering, hogere
tweedegraads constanten in C-H abstractie en grotere katalytische opbrengsten. Het nadeel van
het gebruik van peroxiden is dat vrije radicalen, X•, vervolgens naast [FeIVO(Htpena)]2+
gegenereerd worden. De radicalen kunnen ook als oxidanten fungeren, en verlagen daarmee de
selectiviteit van de oxidaties op de substraten en veroorzaken tevens degradatie van de
ix
liganden, wanneer de experimentele condities hier niet op zijn aangepast. Het verlies in
selectiviteit kan echter vermeden worden door het direct creëren van het ijzer(IV)oxo soort van
zijn ijzer(III) voorganger met een één elektron acceptor in water. Binnen de series van de op
ethyleendiamine gebaseerde ijzer(IV)oxo soorten vertonen [FeIVO(Htpena)]2+ en
[FeIVO(HtpenO)]2+ inderdaad verbeterde oxidatie van respectievelijk C-H bonden (zowel in water
als in organische oplosmiddelen) en O-H bonden.
In tegenstelling tot bij het gebruik van peroxide is radicaal-chemie niet geobserveerd wanneer
de oxidant PhIO is gebruikt. In plaats daarvan wordt selectieve en katalytische oxygenatie
waargenomen, wat suggereert dat een OAT-mechanisme wordt gekatalyseerd door een op
metaal gebaseerde oxidant, namelijk de geobserveerde [FeIII(OIPh)(tpena)]2+,
{[FeIII(OIPh)(tpena)]}24+ of het niet geobserveerde ijzer(IV)oxo soort dat gecreëerd wordt door
heterolytische O-I bond dissociatie. Halogeen binding en de afwijkende aard van de FeIIIO-X bond
voor PhIO vergeleken met peroxides worden geacht een centrale rol te spelen in de observaties
van afwijkende reactiviteit (OAT versus HAT).
[Fe(tpena)]2+ ondergaat onomkeerbare, licht-gestimuleerde O2-afhankelijke N-deglycinatie om
een ijzer(III) complex te genereren onder atmosferische omstandigheden. De verandering omvat
een verlies in massa equivalent aan de glycyl groep, wat betekent dat successieve C-C en C-N
dissociaties voorvallen, verder ondersteund door de kwantitatieve detectie van respectievelijk
de daaruit volgende productie van CO2 en formaldehyde. Tijd-afhankelijke spectroscopie maakte
bovendien de spectroscopische karakterizatie van twee op ijzer gebaseerde kortlevende
intermediaire soorten mogelijk tijdens het reactieverloop.
x
Acknowledgements
As this thesis marks the end of my PhD studies, there are several people I would like to thank.
First and foremost I would like to thank my supervisor Prof. Christine McKenzie: I still think back
to the day when I entered your office in 2012 and told you that I wanted to go to Australia, and if
you could basically help me skipping the dark Danish winter in return for an Australian summer
with a scuba diving tank on my back. You laughed and told me that everyone wants to go to
Australia; I felt like a fool, but an adventure certainly started! Jeg har haft det som blommen i et
æg the past several years, and I deeply value the professional and personal relationship we have
developed. I admire your optimistic attitude to science and life in general, and you have certainly
taught me the importance of small details. I will miss our marathon meetings in front of your
computer discussing a sentence word for word or tiny aesthetics in a picture, while a “duck” or
two occasionally interfere. In the beginning your mad ChemBioDraw schemes were a mystery to
me; but now, several years later, I realize that I actually also enjoy the puzzle of drawing a
catalytic cycle, which somehow is rather scary! I appreciate the friendly and humorous
atmosphere during our many(!) discussions, and I have loved that it is not all about science; so,
whenever you need a fashion advice for a talk in the future – just send a picture beforehand, I
will be happy to comment. I also want to thank you for letting me develop on my own and
inviting me into your network all over the world, which leads me to thank my supervisor Prof.
Wesley Browne. It is funny that it all started with just one visit, which turned into numerous
visits and now years later I in fact feel at home in Groningen. Wes, thank you for improving my
skills with spectroscopy and experimental setups, your hospitality and many great discussions
over the past years. The combination of both of you as supervisors has been perfect for me: you
have very different mindsets, approaches and forces, which have challenged me to make up my
own opinion and become my own boss. I have no doubt that the double degree agreement has
made me a stronger and more independent researcher – thank you!
My sincere gratitude goes out to the reading committee Prof. Vickie McKee, Prof. Edwin Otten,
Prof. Marcel Swart and Prof. T. David Waite for approving this thesis and(!) for taking the time
out of your schedules to come to both Groningen and Odense for evaluation of my PhD thesis.
Also, I want to thank Vickie for your enormous patience while teaching me crystallography – I
still remember the day, where we spent several hours going through a cif-file line for line! It has
been great having you visiting Odense so often, and I have enjoyed our many walks with ice
cream.
Prof. Feliu Maseras and his group are thanked for performing DFT calculations on the light-
promoted O2-activation presented in Paper VI, Prof. Cathrine Frandsen for assistance with
collection of Mössbauer data in Paper IV and Paper VI, Dr. Christian G. Frankær for assistance
with PXRD and XAS experiments in Paper II, Dr. W. Alex Donald for calculations on the gas-phase
clusters in Paper III, Andrea L. Gonzalez for the initial characterization on the iron(IV)oxo species
in Paper VIII and of course Nina Stiesdal and Mie Thorborg Pedersen are thanked for their
graphical expertise making the inside cover of Chem. Eur. J. for Paper IV and the front cover of
this thesis, respectively.
xi
I would like to thank my administrative helpers Tanja Løvgren and Cristina D’Arrigo for taking
care of all of the extra work with legal details in connection with the double degree doctorate.
Without your willingness and persistency, I am not sure a contract would ever have formed.
Also, the Head of the PhD school at SDU Prof. Jacob Kongsted is specially thanked for being so
helpful and calming in the entire process.
Former and present members of the McKenzie Group are thanked for a great working
environment over the years. Especially I want to thank David de Sousa for discussions on the
iron-tpena system, Claire Deville for proofreading parts of this thesis and Morten Liljedahl for
assisting with ligand synthesis. Charlotte Damsgaard is thanked for all of her assistance in the
lab. At SDU I also must thank the entire TAP group for always being so helpful! A special thanks
to Danny Kyrping for assistance with the X-ray diffractometer and the EPR spectrometer – the
fact that you are always ready to help whenever an instrument is not working is highly
appreciated. Pia Haussmann is thanked for being so helpful with my many MS samples and Lars
Duelund for teaching me the EPR spectrometer.
Huge thanks to all previous and current Brownies! Whenever I have left my so-called holiday in
Denmark to spend time Groningen, I have never felt like a visitor, but rather as a full-time
member of the group, so basically: thanks for adopting me in your family! A special thanks to
Sandeep Padamati for babysitting me during my first visits at RUG. Also, I want to thank the
Otten group for introducing me to the Borrel and always being up for a fun Friday evening.
Particularly, I want to thank Francesca Milocco. I am so happy that I happened to place myself
next to you at that CARISMA meeting in Ljubljana back in 2015. I have indeed enjoyed our many
talks, fits of laughter and beers all over Europe. Francesca and Jorn Steen are specially thanked
for doing me the honour of being my paranymphs.
During the past years at SDU, I have always enjoyed the friendly atmosphere during lunch breaks
under the chandelier. Thanks to former and present members of the groups of TUG, DBR, UGN,
theoretical chemistry as well as experimental physics for making these friendly links among the
research groups possible.
I am probably what one could call “a child of the ECOSTBio action”, and neither can I imagine my
PhD time without being involved in both this COST action and the CARISMA COST action, hence I
want to thank both actions for financial support to attend conferences, scientific short-term
missions and summer schools. Involvement in these COST actions has certainly expanded my
scientific network and I have now great friends and colleagues all over Europe. Furthermore, I
would like to specially thank Dr. Eckhard Bill for agreeing on organizing a scientific school with
me on EPR and Mössbauer spectroscopy. It was 10 wonderful days in Mülheim and I must admit:
I still deeply admire how d-orbitals seem to simply just split up for your inner eye.
Finally, I want to thank my family for all of your support over the past years. Constantly you are
trying to understand what I am doing; I am well aware that it is not an easy task. I highly
appreciate that you are still trying so hard. The fact that you have learned buzzwords such as
diffractometer, synchrotron and catalysis means the world to me – af hjertet tak!