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Homogeneous and heterogeneous Cp*Ir(III) catalytic systems: Mechanistic studies of redox processes catalyzed by bifunctional iridium complexes, and synthesis of iridium-functionalized MOFs
Stockholm University, Faculty of Science, Department of Organic Chemistry. (Prof. Belén Martín-Matute)ORCID iD: 0000-0002-2856-5295
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of this doctoral thesis is to investigate and develop catalytic processes mediated by iridium(III) complexes. By understanding the mechanisms, the weaknesses of the designed catalysts can be identified and be overcome in the following generation.

The thesis is composed of two general sections dedicated to the synthesis and applications of homogeneous catalysts and to the preparation of heterogeneous catalysts based on metal-organic frameworks (MOFs). After a general introduction (Chapter 1), the first part of the thesis (Chapters 2-4, and Appendix 1) covers the use of several homogeneous bifunctional [Cp*Ir(III)] catalysts in a variety of chemical transformations, as well as mechanistic studies.

Chapter 2 summarizes the studies on the N-alkylation of anilines with benzyl alcohols catalyzed by bifunctional Ir(III) complexes. Mechanistic investigations when the reactions were catalyzed by Ir(III) complexes with a hydroxy-functionalized N-heterocyclic carbene (NHC) ligand are discussed, followed by the design of a new generation of catalysts. The chapter finishes presenting the improved catalytic performance of these new complexes.   

A family of these NHC-iridium complexes was evaluated in the acceptorless dehydrogenation of alcohols, as shown in Chapter 3. The beneficial effect of a co-solvent was investigated too. Under these base-free conditions, a wide scope of alcohols was efficiently dehydrogenated in excellent yields. The unexpected higher activity of the hydroxy-containing bifunctional NHC-Ir(III) catalysts, in comparison to that of the amino-functionalized one, was investigated experimentally.

In the fourth chapter, the catalytic process presented in Chapter 3 was further explored on 1,4- and 1,5-diols, which were transformed into their corresponding tetrahydrofurans and dihydropyrans, respectively. Mechanistic investigations are also discussed.

In the second part of the thesis (Chapter 5), a Cp*Ir(III) complex was immobilized into a MOF. The heterogenization of the metal complex was achieved efficiently, reaching high ratios of functionalization. However, a change in the topology of the MOF was observed. In this chapter, the use of advanced characterization techniques such as X-ray absorption spectroscopy (XAS) and pair distribution function (PDF) analyses enabled to study a phase transformation in these materials.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2017. , 97 p.
Keyword [en]
catalysis, bifunctional, metal-ligand cooperation, amine alkylation, Hammett, kinetics, acceptorless alcohol dehydrogenation, MOF, transition metal, synchrotron
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-143343ISBN: 978-91-7649-876-7 (print)ISBN: 978-91-7649-877-4 (electronic)OAI: oai:DiVA.org:su-143343DiVA: diva2:1098327
Public defence
2017-06-30, Magnéli Hall, Arrhenius Laboratory, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Submitted.

Available from: 2017-06-07 Created: 2017-05-24 Last updated: 2017-08-14Bibliographically approved
List of papers
1. Mechanistic Studies on the Alkylation of Amines with Alcohols Catalyzed by a Bifunctional Iridium Complex
Open this publication in new window or tab >>Mechanistic Studies on the Alkylation of Amines with Alcohols Catalyzed by a Bifunctional Iridium Complex
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2015 (English)In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 6, 3704-3716 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of the N-alkylation of amines with alcohols catalyzed by an iridium complex containing an N-heterocyclic carbene (NHC) ligand with a tethered alcohol/alkoxide functionality was investigated by a combination of experimental and computational methods. The catalyst resting state is an iridium hydride species containing the amine substrate as a ligand, and decoordination of the amine, followed by coordination of the imine intermediate to the iridium center, constitute the rate-determining step (rds) of the catalytic process. The alcohol/alkoxide that is tethered to the NHC participates in every step of the catalytic cycle by accepting or releasing protons and forming hydrogen bonds with the reacting species. Thus, the iridium complex with the alcohol/alkoxide tethered to the N-heterocyclic carbene ligand acts as a bifunctional catalyst.

Keyword
iridium, amine alkylation, Hammett plots, kinetics, DFT calculations
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-119172 (URN)10.1021/acscatal.5b00645 (DOI)000355964300058 ()
Funder
Swedish Research CouncilVINNOVAKnut and Alice Wallenberg FoundationWenner-Gren Foundations
Available from: 2015-08-10 Created: 2015-07-29 Last updated: 2017-08-23Bibliographically approved
2. Acceptorless Alcohol Dehydrogenation: OH vs NH Effect in Bifunctional NHC–Ir(III) Complexes
Open this publication in new window or tab >>Acceptorless Alcohol Dehydrogenation: OH vs NH Effect in Bifunctional NHC–Ir(III) Complexes
2017 (English)In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041Article in journal (Refereed) Epub ahead of print
Abstract [en]

Bifunctional complexes bearing N-heterocyclic carbene (NHC) ligands functionalized with hydroxy or amine groups were synthesized to measure the beneficial effect of different modes of metal–ligand cooperation in the acceptorless dehydrogenation of alcohols. In comparison to complexes with an amine moiety, hydroxy-functionalized iridium catalysts showed superior activity. In contrast to alcohols, 1,4-diols underwent cyclization to give the corresponding tetrahydrofurans without involving dehydrogenation processes. Mechanistic investigations to rationalize the “OH effect” in these types of complexes have been undertaken.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-143339 (URN)10.1021/acs.organomet.7b00220 (DOI)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationVINNOVA
Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-11-10
3. Nonclassical cyclodehydration of diols assisted by metal-ligand cooperation
Open this publication in new window or tab >>Nonclassical cyclodehydration of diols assisted by metal-ligand cooperation
2017 (English)Article in journal (Refereed) Submitted
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-143341 (URN)
Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-05-24Bibliographically approved
4. Topological Transformation of a Metal–Organic Framework Triggered by Ligand Exchange
Open this publication in new window or tab >>Topological Transformation of a Metal–Organic Framework Triggered by Ligand Exchange
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2017 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 8, 4576-4583 p.Article in journal (Refereed) Published
Abstract [en]

Here we describe the topological transformation of the pores of a new framework in the bio-MOF-100 family (dia-c) into the known isomer (lcs) by doubling the pore volume, which occurs during postsynthesis modifications. During this transformation, reassembling of the metal–organic framework (MOF) building blocks into a completely different framework occurs, involving breaking/forming of metal–ligand bonds. MOF crystallinity and local structure are retained, as determined by powder X-ray diffraction (PXRD) and pair distribution function (PDF) analyses, respectively. We exploited the inherent dynamism of bio-MOF-100 by coupling chemical decorations of the framework using solvent-assisted ligand exchange to the topological change. Following this method and starting from the pristine dense dia-c phase, open lcs-bio-MOF-100 was prepared and functionalized in situ with an iridium complex (IrL). Alternatively, the dia-c MOF could be modified with wide-ranging amounts of IrL up to ca. 50 mol %, as determined by solution 1H NMR spectroscopy, by tuning the concentration of the solutions used and with no evidence for isomer transformation. The single-site nature of the iridium complexes within the MOFs was assessed by X-ray absorption spectroscopy (XAS) and PDF analyses. Ligand exchanges occurred quantitatively at room temperature, with no need of excess of the iridium metallolinker.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-143340 (URN)10.1021/acs.inorgchem.7b00149 (DOI)000399625600037 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilVINNOVA
Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-06-30Bibliographically approved

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