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Advances in organophosphorus chemistrySynthesis, reactivity and recyclingKrachko, T.

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Citation for published version (APA):Krachko, T. (2018). Advances in organophosphorus chemistry: Synthesis, reactivity andrecycling.

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Summary

Phosphorus is an essential element for agriculture, farm production, industry,

organic synthesis and for survival of living organisms. Being a non-renewable

resource, phosphate rock – the industrial source of phosphorus – will be depleted

within 50–400 years with the current mining rate. Since in contrast to oil, gas and

other non-renewable minerals, phosphorus has no other alternatives, the

sustainable use of phosphorus is highly desirable. This thesis, entitled “Advances

in Organophosphorus Chemistry: Synthesis, Reactivity and Recycling”, describes

possible solutions for the more sustainable use of phosphorus, including efficient

approaches towards an atom-economical production, smart use, and recycling of

organophosphorus compounds.

Convenient synthons for the synthesis of a wide variety of organophosphorus

compounds are low-valent phosphinidenes [P–R]. Since most “free”

phosphinidenes exist in the triplet ground state, suitable substitution is required to

stabilize the singlet species to provide non-radical, selective reactivity. Typically,

transition metal-complexed species are used which after phosphinidene transfer

require a demetallation step to provide the free ligand. Alternatively,

phosphinidenes can be stabilized by carbenes, forming carbene-phosphinidene

adducts, which can be represented by the three canonical structures A-C (Scheme

1). These cyclic C-amino substituted phosphaalkenes differ significantly from the

classical phosphaalkenes and feature high nucleophilicity at the phosphorus atom,

which mostly defines their reactivity. A complete overview of the synthesis,

properties and reactivity of NHC-phosphinidene adducts is provided in Chapter 1.

Scheme 1. Resonance forms of NHC-phosphinidene adducts, X = CR2, NR or S.

Summary

174

In Chapter 2, we describe a simple one-pot synthesis of the sterically

accessible carbene-phosphinidene adduct MeNHC=PPh (1), its coordination

chemistry towards ZnCl2 and the use of the resulting zinc(II) complex (2) as a

phosphinidene transfer agent (Scheme 2). ZnCl2 as a Lewis acid of choice allows

controlled phosphinidene transfer, which is driven by formation of an insoluble

polymeric NHC-zinc complex. The applicability of this method was demonstrated by

phenylphosphinidene transfer to 9,10-phenanthrenequinone, diphenylketene and

trans-chalcone, affording uncomplexed phosphorus heterocycles. The isolation of

an intermediate in the reaction with diphenylketene allowed to study the

mechanism of this transfer in more detail, which was supported by DFT calculations

at the wB97X-D/6-31G(d,p) level of theory.

Scheme 2. Synthesis and coordination chemistry of the carbene-phosphinidene complex 1 and phenylphosphinidene transfer reactions of 2.

In Chapter 3, to access the phosphorus analogues of tricyclopentanone,

cyclopentadienone, and housene we utilize sodium phosphaethynolate (NaOCP)

Advances in Organophosphorus Chemistry

175

as a source of phosphide together with a cyclopropenium cation. The salt

metathesis reaction of 1,2,3-tris-tert-butylcyclopropenium tetrafluoroborate with

sodium phosphaethynolate leads to bis(cyclopropenyl)diphosphetanedione 3.

Photolytic decarbonylation of 3 affords bis(cyclopropenyl)diphosphene 4 and after

rearrangement diphosphahousene 5, while its thermolysis provides access to

phosphatricyclo[2.1.0.0]pentanone 6 and, after Rh(I)-mediated valence

isomerization of 6, phosphacyclopentadienone 7 (Scheme 3). We also study these

pericyclic rearrangements by a detailed DFT analysis.

Scheme 3. Synthesis of the phosphorus analogues of cyclopentadienone, tricyclopentadienone and housene.

Chapter 4 deals with the detailed investigation of the reactivity of frustrated

P/B Lewis pairs 8 and 9,the methylene- and o-phenylene-bridged combinations of

sterically encumbered phosphines and boranes, with mono-substituted epoxides

resulting in epoxide ring-opening (Scheme 4). We study these reactions with DFT

Summary

176

calculations at wB97X-D/6-31G(d,p) as well as kinetic analyses and show that they

proceed via activation of the epoxide by the Lewis acidic borane moiety, followed

by intermolecular nucleophilic attack of the phosphine of a second FLP molecule.

The resulting chain-like intermediates afford the final cyclic products by ring-closure

and concurrent release of the second equivalent of FLP that behaves as a catalyst

in these reactions.

Scheme 4. Ring-opening of epoxides mediated by frustrated Lewis pairs.

Finally, Chapter 5 describes the efficient reduction of tertiary phosphine

oxides to phosphines via the simultaneous action of Brønsted acids and readily

available hydrosiloxanes (Scheme 5).

Scheme 5. Brønsted acid promoted reduction of tertiary phosphine oxides

Aiming at better understanding the reaction mechanism, we first investigate

the stoichiometric protonation of triphenylphosphine oxide and subsequently,

perform the reduction of the protonated phosphine oxide with hydrosiloxanes. We

Advances in Organophosphorus Chemistry

177

find that reduction of the HOTf adduct of triphenylphosphine oxide (10) with PMHS

or TMDS at 100 °C results in the formation of triphenylphosphine. Under the same

reaction conditions, also the Me2SiHOTf adduct of TPPO (11) gives TPP

demonstrating its possible intermediary nature in this reduction (Scheme 5).

The research described in this thesis provides advances in the three aspects

of organophosphorus chemistry: synthesis, reactivity and recycling. The

development of convenient and high yielding methodologies towards the synthesis

of uncomplexed phosphorus heterocycles opens an avenue for their application as

ligands in homogeneous catalysis. In addition, the detailed mechanistic analysis of

these reactions at the molecular level enables better understanding of the systems

allowing their rational application in future processes. Furthermore, we believe that

the development of the efficient method for phosphine oxide recycling is of great

importance for the sustainable use of phosphorus in industrial chemistry.

179

Samenvatting

Fosfor is cruciaal voor alle levende organismes en speelt een essentiele rol

binnen de landbouw, industrie en de organische synthese. Industrieel wordt fosfor

gewonnen vanuit fosfaaterts, dit is echter een eindige grondstof en met de huidige

consumptie zal het over 50-400 jaar op zijn. In tegenstelling tot olie, gas en andere

meer bekende niet-hernieuwbare grondstoffen, is er voor fosfor geen alternatief

waardoor het zeer belangrijk is om er duurzaam mee om te gaan. Dit proefschrift,

met als titel “Advances in Organophosphorus Chemistry: Synthesis, Reactivity and

Recycling”, beschrijft verschillende mogelijkheden voor duurzamer gebruik van

fosfor door te kijken naar atoom-economische productie, ‘smart use’, en hergebruik

van organofosforverbindingen.

Laag-valente fosfinidenen [P-R] zijn zeer handige bouwstenen voor de

efficiënte synthese van een groot aantal organofosforverbindingen. Aangezien de

meeste ‘vrije’ fosfinidenen zich in een triplet grondtoestand bevinden, moet er eerst

een substitutie plaatsvinden om de singlet toestand te stabiliseren om zo

selectieve, niet-radicale reactiviteit te verkrijgen. Zulke substitutie wordt meestal

bewerkstelligd met behulp van een overgangsmetaalcomplex waardoor er na de

fosfinideenoverdracht een extra stap nodig is om het overgangsmetaal weer te

verwijderen. Een alternatief is het gebruik van carbenen om het fosfinideen te

stabiliseren. Hierbij worden carbeen-fosfinideen adducten gevormd die kunnen

worden weergegeven met de drie canonische structuren A–C (Schema 1). Deze

cyclische C-amino gesubstitueerde fosfaalkenen hebben zeer verschillende

eigenschappen in vergelijking met klassieke fosfaalkenen door een hoge

nucleofiliciteit van het fosforatoom die zeer bepalend is voor hun reactiviteit. Een

compleet overzicht van de synthese, eigenschappen en reactiviteit van NHC-

fosfinideen adducten is beschreven in Hoofdstuk 1.

Samenvatting

180

Schema 1. Resonantiestructuren van NHC-fosfinideen adducten, X = CR2, NR or S.

Hoofdstuk 2 beschrijft een simpele één-pot synthese van het sterisch

toegankelijke carbeen-fosfinideen adduct MeNHC=PPh (1), de bijbehorende

coordinatiechemie met ZnCl2 en het gebruik van het gevormde zink(II) complex (2)

voor de overdracht van het fosfinideen (Schema 2).

Schema 2. Synthese en coordinatiechemie van het carbeen-fosfinideen complex 1 en fenylfosfinideenoverdrachtreacties van 2.

ZnCl2 is geselecteerd als Lewiszuur daar dit leidt tot gecontrolleerde

fosfinideenoverdracht en tegelijk is ZnCl2 de drijvende kracht achter de reactie: de

vorming van een onoplosbaar NHC-zink polymeer. Om de toepasbaarheid van

Advances in Organophosphorus Chemistry

181

deze methode te demonstreren werd fenylfosfinideen succesvol overgedragen

naar 9,10-fenantreenquinoon, difenylketeen en trans-chalcoon om zo de

bijbehorende niet-gecomplexeerde heterocyclische fosforverbindingen te vormen.

Het isoleren van een intermediair uit de fosfinideenoverdrachtsreactie naar

difenylketeen leidde tot belangrijke inzichten in het mechanisme welke verder

werden ondersteund door DFT berekeningen (wB97X-D/6-31G(d,p)).

Hoofstuk 3 bespreekt het gebruik van natriumfosfaethynolaat (NaOCP) in

combinatie met een cyclopropeniumcation om zo fosforanalogen van

tricyclopentanon, cyclopentadienon en ‘housene’ te maken (Schema 3).

Schema 3. Synthese van de fosfineanalogen van cyclopentadienon, tricyclopentadienon en ‘housene’.

De zoutmetathesereactie van 1,2,3-tri-tert-butylcyclopropeniumtetrafluoroboraat

met natriumfosfaethynolaat leidt tot de vorming van

bis(cyclopropenyl)difosfetaandion 3. Fotokatalytische decarbonylatie van 3 geeft

bis(cyclopropenyl)difosfeen 4 dat na omlegging difosfahousene 5 vormt.

Samenvatting

182

Thermolyse van 3 leidt echter tot fosfatricyclo[2.1.0.0]pentanon 6, waarna een

Rh(I)-geinduceerde valentieisomerisatie uitgevoerd kan worden om

fosfacyclopentadienon 7 te verkrijgen. Deze pericyclische omleggingen werden ook

uitgebreid bestudeerd met behulp van DFT berekeningen.

Hoofdstuk 4 beschrijft een gedetailleerd onderzoek naar de reactiviteit van

‘frustrated P/B Lewis pairs’ 8 en 9, de methyleen- en o-fenyleen gebrugde

combinaties van sterisch gehinderde fosfines en boranen, met mono-

gesubtitueerde epoxides. Dit resulteert in het openen van de epoxide ring (Schema

4). Deze reacties zijn onderzocht door middel van een DFT studie (wB97X-D/6-

31G(d,p)) en een kinetische analyse om aan te tonen dat deze verlopen via

activatie van het epoxide door het Lewiszure boraan, waarna er vervolgens een

intermoleculaire, nucleofiele aanval plaatsvindt waarbij een fosfine van een ander

FLP molecuul aanvalt om zo kettingachtige intermediairen te vormen. Deze

reageren vervolgens verder via een ringsluitingsreactie waarbij het tweede FLP

molecuul weer vrijkomt waardoor het tweede FLP molecuul in deze reactie zich dus

gedraagt als katalysator.

Schema 4. De ringopening van epoxides door frustrated Lewis pairs.

Ten slotte wordt er in Hoofdstuk 5 gekeken naar een efficiënte reductie van

tertiaire fosfineoxides tot fosfines door gebruik te maken van Brønstedzuren en

makkelijk te verkrijgen hydrosiloxanen (Schema 5). Om het mechanisme beter te

kunnen begrijpen, wordt allereerst de stoichometrische protonatie van

trifenylfosfineoxide onderzocht, waarna vervolgens de reductie van het

geprotoneerde fosfineoxide door hydrosiloxanen wordt bestudeerd. Dit wees uit dat

Advances in Organophosphorus Chemistry

183

de reductie van het HOTf adduct van trifenylfosfineoxide (10) met PMHS of TMDS

bij 100 °C leidt tot de vorming van trifenylfosfine. Dezelfde reactieconditites kunnen

ook gebruikt worden om het Me2SiHOTf adduct van TPPO (11) om te zetten naar

TPP wat er op wijst dat 11 waarschijnlijk een intermediair is.

Schema 5. Door Brønstedzuur bevorderde reductie van tertiaire fosfineoxides

Het onderzoek in dit proefschrift heeft geresulteerd in vooruitgang op drie

vlakken binnen de fosforchemie: synthese, reactiviteit en hergebruik. De

ontwikkeling van een makkelijke en efficiënte methode voor de synthese van niet-

gecomplexeerde heterocyclische fosforverbindingen maakt het mogelijk om dit

soort verbindingen in de toekomst toe te passen als liganden binnen de homogene

katalyse. Daarbij zorgt de uitgebreide mechanistische analyse van deze reacties

voor belangrijke inzichten voor het begrijpen van de chemie van dit soort systemen

waardoor er efficiënter kan worden gekeken naar mogelijke toepassingen. Verder

geloven wij dat het ontwikkelen van een efficiënte methode voor het hergebruiken

van fosfineoxides zeer belangrijk is voor het duurzaam gebruik van fosfor binnen

de chemische industrie.

185

Acknowledgements

What made this challenging PhD possible was the support in many ways of

my supervisor, colleagues, family and friends to whom I am greatly indebted.

Firstly, I would like to address my sincere gratitude to my supervisor Chris.

Thank you deeply for your help in all the time of research and writing of the papers;

for your supervision, patience, unbounded support and faith in me. I highly

appreciated your attention to details and special talent in writing, I learned a lot

from you. I was very fortunate to work with you and I am proud of the results that

we got together. Thank you also for building up SusPhos, which besides funding

gave me an opportunity to meet and collaborate with amazing people all over the

world. I would also like to acknowledge my co-supervisor Andreas. Thank you for

sharing your knowledge in DFT calculations, helping with NMR measurements and

for valuable comments on our papers; also thanks for motivating and challenging

me, you made me try harder to refine and communicate my arguments and ideas.

I am grateful to Prof. Dr. Koop Lammertsma. Thank you for your scientific and

personal support, critical suggestions or appreciation regarding my research and

for being a referee of this thesis. Prof. Dr. Jan van Maarseveen, thank you for your

boundless enthusiasm, positivity and endless encouragement. You contributed

greatly to my good results obtained after the move to the UvA. Thank you also for

agreeing to be in my Doctorate cometee. My sincere thanks also go to Prof. Dr.

Hansjörg Grützmacher, who provided me an opportunity to join his team for three

months at ETH Zürich. I truly enjoyed the time spent in your friendly research

group. Thank you for our fruitful co-operation, for your enthusiasm about my first

results and for taking your time to read this thesis. I would also like to thank Prof.

Dr. Paul G. Pringle, Prof. Dr. Bas de Bruin and Dr. Steen Ingemann Jorgensen for

kindly accepting to be the referees of this thesis and for providing valuable advice

for the final version of my thesis.

Acknowledgements

186

I would like to thank my students Anouk, Consuela and Kinga for their hard

work and contribution to this research. Kinga, thank you also for your enthusiasm,

moral support and friendship over all these years.

Next, I would like to express my gratitude to all the colleagues, who have

helped me during these years. Bas de Jong, thanks a lot for your passion to new

glassware and lab equipment. You have built the labs really nicely, which makes

them such a pleasure to work. Many thanks for your help with special setups to

work with gazes and vacuum distillations. Dr. Martin Nieger and Dr. Martin Lutz,

thank you for your precious X-ray crystal structure determinations, without your

work this thesis would lose a lot. Ed and Dorette, thank you greatly for your help

with mass measurements. You did a great job to make my sensitive substances to

survive the analysis. Jan-Meine, thank you for all the help with NMR.

Special thanks to my former colleagues from the VU. Mark, Jaap, Jeroen,

Leon (inspiring singing), Tom, Jos, Emmanuel, Max, Yann, Vova, thanks for all the

fun times, for your support and advice, and importantly for your natural erudition

and high achievements which served as a good example for me. Additional thanks

to Emmanuel for teaching me to perform DFT calculations and for your valuable

advice in experiments. Mark, also thanks for your persistence in teaching me

Dutch, you diversified my vocabulary.

Further thanks to my VU colleagues who experienced together with me all the

fun of the move to another university (UvA) during doctoral studies. Devin, my

permanent lab- and officemate, thank you for hating dirty unorganized labs as

much as I do and for your support and advice throughout the PhD. Marissa, I know

you since my first day in Amsterdam and am very grateful for all your help over

these years – for organising, facilitating, communicating and other tireless

administrative things you helped me with. Also thanks to you and Evi for your

support and friendship, our “xco” team was great. Laurian, you know I did not share

your preferences in music, but I liked a lot your preferences in wine. Thank you for

organizing our wine tasting events, for the trip to Charly’s wedding, and for being

always friendly and helpful to me. Particular thanks to Flip for translating my

Acknowledgements

187

summary into Dutch, for attentive proof-reading of all my papers and for the

valuable feedback. Thank you sincerely for being always cheerful, helpful and

super friendly.

Chère Feriel, thank you for all the nice time we had together drinking coffee or

wine, chatting, discussing chemistry or work-family balance. I am truly happy you

joined our group on my last year, you supported and inspired me greatly and you

brought a nice lovely atmosphere in the group. Thank you for being so much of my

kind of person and for being a good caring friend.

A huge thanks to all the SOC colleagues for warm welcoming in your group at

the UvA and for making me feel so at home. Henk, Tati and Francesco, thank you

for the useful feedback and suggestions during the group meetings, for

your support and intellectual inspiration. Gaston, Roel, Yolanda, Jan, Maria and

Vasilis, thanks for all the good times, support, your uniqueness and

friendship. I truly enjoyed our trip to Prague, Friday-drinks, recording the video

and simply our every chat. Roel and Luuk, thanks also for your help with

administrative part of the PhD. Dieuwertje, Arnout, Hans, Kananat, Wen-Liang,

Martin, Nick, Piotr, Wesley, Marie and Wowa, thanks for all the good times.

I would also like to thank every and each colleague at my new workplace

HomKat, especially Sandra, Catriona, Tiddo, Tessel, Marianne, Eddy, Charles,

Julien, Zohar, Sander and Pim. Particular thanks to Prof. Dr. Joost Reek for the

opportunity to start the new challenging work while not being a PhD yet. Thank you

deeply for your understanding, kindness and unforgettable jokes.

All the SusPhos members, thank you for the unforgettable memories and

productive collaborations. Special thanks to Mark Bispinghoff for the good time in

Zürich and for all the help and support in the lab. Massimo and Prof. Dr. Christian

Müller, thank you for the fruitful co-operation, hopefully our joint research project

would result in a nice publication. Charly, thank you for your friendship, support and

good times in Toulouse, Amsterdam, Kazan, Ferme du Couvent and so much

more.

Acknowledgements

188

Crucial to this doctoral journey was the support from my family and friends. A

huge thanks to my Russian-speaking friends Anna, Yaroslav, Sasha, Dima, Alina,

Igor, Veronika and Beso. Thank you for making my time so far away from home so

wonderful, for your emotional support and encouragement, and even for being my

practice audience the day before a research presentation.

Sasha Badiya, I can’t thank you enough. It is you who six years ago have

motivated me to leave my home country and do my master studies in France. This

was a first step, which grew up into this challenging PhD in Amsterdam. Thank you

deeply for your friendship, loyalty and support, and for making all the fantastic

covers for my papers and this thesis.

A sincerest thanks to my family for supporting me in so many ways – from

being such proud parents and a supportive sister, to the adorable smiles of my

nephew in daily messages helping to put everything in perspective. Without you I

would never become who I am. Любимые мамочка и папочка, я вам бесконечно

благодарна за вашу заботу, поддержку, терпение и безусловную любовь.

Finally, I want to thank my beloved Mitya. All these years you believed in me

so much more than I did myself. You are the reason I finished this PhD. Thank you

for listening, motivating and infinitely supporting me. Пока ты рядом, мне ничего

не страшно.

189

List of Publications

[1] T. Krachko,1-5 E. Nicolas,1,6 A. W. Ehlers,6,8 M. Nieger,7 J. C.

Slootweg,1,8,9 “Ring-opening of epoxides mediated by frustrated Lewis pairs”,

submitted (Full Paper).

[2] T. Krachko,1,3 J. C. Slootweg,1,8,9 “N-heterocyclic carbene-

phosphinidene adducts: synthesis, properties and applications”, Eur. J. Inorg.

Chem. 2018, DOI 10.1002/ejic.201800459.

[3] T. Krachko,1-5 A. W. Ehlers,6,8 M. Nieger,7 M. Lutz,7 J. C. Slootweg,1,8,9

“Synthesis and reactivity of the phosphorus analogues of cyclopentadienone,

tricyclopentanone, and housene”, Angew. Chem. Int. Ed. 2018, 57, 1683–1687;

Angew. Chem. 2018, 130, 1699–1703.

[4] T. Krachko,1-3,5 V. Lyaskovskyy,1-3,5 M. Lutz,7 K. Lammertsma,9 J. C.

Slootweg,1,8,9 “Brønsted acid promoted reduction of tertiary phosphine oxides”, Z.

Anorg. Allg. Chem. 2017, 643, 916–921.

(Cover Picture)

[5] T. Krachko,1-5 M. Bispinghoff,1,8 A. M. Tondreau,1,2,5 D. Stein,2,5 M.

Baker,5 A. W. Ehlers,6,8 J. C. Slootweg,1,8,9 H. Grützmacher,1,8,9 “Facile

phenylphosphinidene transfer reactions from carbene-phosphinidene zinc

complexes”, Angew. Chem. Int. Ed. 2017, 56, 7948–7951; Angew. Chem. 2017,

129, 8056–8059.

190

1 Conceptual ideas 2 Experimental work 3 Preparation of the manuscript 4 Computational studies 5 Spectroscopic studies 6 Supervision of computational studies 7 X-ray analysis

8 Feedback on the manuscript 9 Project supervision