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Liquid Phase (SILP)-catalyzed gas-phase hydroformylation

Funktionalisierte Aktivkohleträger in der Supported Ionic Liquid Phase (SILP)- katalysierten Gasphasen-Hydroformylierung

Der Technischen Fakultät

der Friedrich-Alexander-Universität Erlangen-Nürnberg zur

Erlangung des Grades

Doktor-Ingenieur

vorgelegt von Alexander Weiß

aus Erlangen

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Als Dissertation genehmigt von der Technischen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg

Tag der mündlichen Prüfung: Freitag, 12. April 2019 Vorsitzender des Promotionsorgans: Prof. Dr.‐Ing. Reinhard Lerch

Gutachter: Prof. Dr. Peter Wasserscheid

Prof. Dr. Nicolas Vogel

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Danksagung

Vorab aller Daten und Ergebnissen aus etwa 4,5 Jahren spannender Promotionszeit möchte ich diesen Abschnitt nutzen, um mich bei einigen Leuten zu bedanken. Ich betrachte es nicht als Selbstverständlichkeit bis zu diesem Punkt in meinem Leben gekommen zu sein, wohlwissend, dass es ohne die Hilfe von Familie und Freunden niemals möglich gewesen wäre. Zu aller erst möchte ich meinen Eltern und meiner Schwester für eine behütete, sorgenfreie Kindheit und die Möglichkeit den akademischen Bildungsweg einschlagen zu können danken. Vor allem meiner Mutter lag immer viel daran mir die bestmöglichste Ausbildung zu garantieren und meinen Ehrgeiz zu wecken. Spätestens jetzt kann ich dankend auf diese treibende, unbeugsame Erziehung zurückblicken.

Neben meinen Eltern gilt mein größter Dank meiner wunderbaren Frau Alexandra. Trotz etwaiger Seitenhiebe wie „das an der Universität nennst du Arbeiten?“, oder „nur am Blödsinn machen und Kaffee trinken!“ konnte und kann ich mich immer zu 100 Prozent auf Dich verlassen. Speziell die Rückendeckung an den vielen Wochenenden, an denen ich an der Rohversion dieser Doktorarbeit feilen musste, und Du dich alleine um Samuel gekümmert hast, kann ich Dir nicht hoch genug anrechnen. An dieser Stelle möchte ich mich außerdem bei meinen Schwiegereltern bedanken, die mich von Anfang an liebend aufgenommen und unterstützt haben - als Untermieter während der Studienzeit bis hin zur Hilfe bei der Erziehung unseres Sohnes. Ich hoffe, dass ich ab sofort wieder mehr Zeit an den Wochenenden mit Dir verbringen kann.

Während meiner Zeit am Lehrstuhl für Chemische Reaktionstechnik durfte ich mit so vielen wunderbaren Menschen zusammenarbeiten, dass es niemals möglich wäre alle aufzuzählen, ohne jemanden zu vergessen. Ich möchte mich an dieser Stelle deswegen bei allen Kollegen für die wunderbaren Jahre bedanken. Die einzigartige Zusammenarbeit und Kollegialität am Lehrstuhl hat in guten wie schlechteren Zeiten immer für eine positive Atmosphäre gesorgt.

Veranstaltungen wie Fußballturniere, Lehrstuhlausflüge, Skifreizeiten, Mittwochsgrillen, Feierabendbiere und vieles mehr, waren allgegenwärtig und lassen mich freudig auf diese Zeit zurückblicken.

Trotz des organisatorisch holprigen Starts in meine Promotion, konnte ich mich zu jeder Zeit auf die wissenschaftliche Unterstützung von Marco Haumann und Peter Wasserscheid in Ihrer Funktion als Gruppenleiter und Lehrstuhlinhaber verlassen. Vielen Dank, dass Ihr mir die Möglichkeit gegeben habt unter diesen wissenschaftlich und menschlich hervorragenden Rahmenbedingungen arbeiten zu dürfen. Durch Euer mir entgegengebrachtes Vertrauen hatte ich die Möglichkeit verschiedenste Konferenzen zu besuchen, wissenschaftliche Themen zu bearbeiten, in wissenschaftlichen Austausch zu treten und somit meinen Horizont zu erweitern.

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Die Tatsache, dass der Titel dieser Arbeit „Funktionalisierung und Anwendung von Kohlenstoffträgern…“ beinhaltet, ist zu einem großen Teil auch Prof. Dr. Bastian Etzold und Dr. Macarena Munoz zu verdanken. Aufgrund der frühen Zusammenarbeit auf dem Gebiet der Kohlenstoffmodifizierung (meinem damaligen wissenschaftlichen Spielbein) wurde der Grundstein für die hier präsentierten Ergebnisse erst gelegt.

Ein weiterer großer Anteil an der erfolgreichen Arbeit am Lehrstuhl geht zurück auf die Unterstützung meiner ehemaligen Studenten. Ohne den Ehrgeiz und die tägliche Motivation am Forschen wäre die Umsetzung von wissenschaftlichen Ansätzen nicht möglich gewesen.

Hierbei gilt mein Dank insbesondere den beiden damaligen Masteranden Matthias Giese und Alexander Hass sowie dem damaligen Bachelorand Andreas Zimmermann.

- Danke -

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Publications

Parts of this work have been previously published in the following journals or presented at the conferences listed below.

Journals:

- A. Weiß, M. Giese, M. Lijewski, R. Franke, P. Wasserscheid, M. Haumann, Catal. Sci.

Technol., 2017, 7, 5562-5571.

- A. Weiß, M. Munoz, A. Haas, F. Rietzler, H-P. Steinrück, M. Haumann, P.

Wasserscheid, B. J. M. Etzold, ACS Catal., 2016, 6, 2280-2286.

Conferences:

- A. Weiß, M. Giese, M. Lijewski, R. Franke, P. Wasserscheid, M. Haumann, Poster, Jahrestreffen Deutscher Katalytiker, 2017, Weimar, Germany.

- A. Weiß, M. Giese, M. Lijewski, R. Franke, P. Wasserscheid, M. Haumann, Poster, Green Solvents for Synthesis, 2016, Kiel, Germany.

- A. Weiß, M. Munoz, A. Haas, F. Rietzler, H-P. Steinrück, M. Haumann, P.

Wasserscheid, B. J. M. Etzold, Poster (awarded), Jahrestreffen Deutscher Katalytiker, 2016, Weimar, Germany.

- A. Weiß, M. Munoz, A. Haas, F. Rietzler, H-P. Steinrück, M. Haumann, P.

Wasserscheid, B. J. M. Etzold, Poster, International Symposium on Homogeneous Catalysis, 2016, Kyoto, Japan.

Further less related publications in journals or conferences:

Journals:

- F. T. U. Kohler, B. Morain, A. Weiß, M. Laurin, J. Libuda, V. Wagner, B. U. Melcher, X. Wang, K. Meyer, P. Wasserscheid, Chem. Phys. Chem., 2011, 12, 3539-3546.

Conferences:

- A. Weiß, J. Haßelberg, Jahrestreffen Reaktionstechnik, 2017, Würzburg, Germany.

- A. Weiß, P. Wolf, P. Wasserscheid, M. Haumann, Poster, CBI Symposium, 2017, Erlangen, Germany.

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List of Contents

1. Introduction ... 2

2. Theory ... 6

2.1 Hydroformylation ... 6

2.1.1 General overview and state of the art processes ... 6

2.1.2 Reaction mechanism of the rhodium catalyzed hydroformylation ... 8

2.1.3 Amines in hydroformylation ...11

2.1.3.1 Hydroaminomethylation ...11

2.1.3.2 Influence of alkaline compounds on the hydroformylation ...13

2.2 Supported Ionic Liquid Phase (SILP) catalysis ...15

2.2.1 An introduction to immobilization concepts ...15

2.2.2 General physical properties of ionic liquids ...17

2.2.2.1 Ionic liquids in hydroformylation ...18

2.2.3 The Supported Ionic Liquid Phase (SILP) concept ...19

2.2.4 Miscibility of SILP components and hydroformylation substrate solubilities ...21

2.2.4.1 Solubility predictions by COSMO-RS simulations ...23

2.2.5 Application of SILP catalysts in the gas-phase hydroformylation ...25

2.2.6 Influence of the SILP support on the catalysis ...28

2.3 Functionalization of carbon materials for the application in SILP catalysis ...29

2.3.1 General physical properties of carbon materials for SILP applications ...29

2.3.2 Functionalized carbons – Advanced properties and applications ...31

2.3.3 Nitrogen-doped carbon supports ...33

2.3.3.1 Oxidative treatment and the resulting surface functionalities ...34

2.3.3.2 Reductive treatment and amination of the oxidized surface ...37

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2.3.3.3 Thermal treatment of functionalized carbon materials ...39

2.4 Starting point and objective of the thesis ...42

3. Experimental ...45

3.1 Materials ...45

3.2 Support functionalization ...48

3.2.1 General carbon functionalization experiments ...48

3.2.2 Optimized functionalization procedure ...48

3.3 SILP catalyst preparation ...50

3.4 Reactor and experimental rig ...51

3.4.1 Continuous gas-phase reactor setup ...51

3.4.2 Experimental procedure ...53

3.4.3 Online GC analysis ...53

3.5 COSMO-RS calculations ...54

3.6 Offline analysis ...54

3.6.1 Nitrogen adsorption measurements ...54

3.6.2 Point of zero charge (PZC) measurements ...54

3.6.3 Water adsorption measurements...55

3.6.4 Elemental analysis ...55

3.6.5 Nuclear magnetic resonance (NMR) spectroscopy ...55

3.6.6 Thermogravimetric mass spectrometry (TG-MS) ...55

3.6.7 Scanning electron microscopy (SEM) ...55

3.7 Calculations...56

3.7.1 Catalyst characteristics ...56

3.7.2 Evaluation of the continuous gas-phase experiments ...56

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4. Results and Discussion ...60 4.1 Extending the substrate scope in the SILP-catalyzed continuous gas-phase hydroaminomethylation ...60 4.1.1 Olefin variation - From ethylene to propylene ...61

4.1.1.1 Catalyst optimization by ionic liquid screening in correlation to COMSO-RS solubility predictions ...62 4.1.2 Amine substrate variation in the SILP-catalyzed continuous gas-phase hydroaminomethylation ...70 4.2 Carbon supports in the SILP-catalyzed continuous gas-phase hydroformylation ....74

4.2.1 Surface functionalization of carbon materials as support material for SILP- catalyzed hydroformylation reactions ...78

4.2.1.1 Surface chemistry and texture of functionalized carbon materials ...78 4.2.1.2 Application of surface-functionalized support materials in the SILP- catalyzed hydroformylation ...84 4.2.2 Urea as reducing agent for surface-modified carbon materials ...88 4.2.2.1 Point of zero charge and nitrogen content of the functionalized carbon materials during the different preparation steps ...89 4.2.2.2 TG-MS characterization of the functionalized carbon materials ...91 4.2.2.3 Nitrogen adsorption measurements of the functionalized carbon materials… ...93 4.2.2.4 Application of urea-functionalized carbon supports in the SILP-catalyzed hydroformylation ...95 4.2.3 Optimized carbon functionalization by the combination of urea and ammonia reduction process ...99 4.2.3.1 Point of zero charge and nitrogen content of the functionalized carbon materials during the different preparation steps ...99 4.2.3.2 TG-MS characterization of the functionalized carbon materials ... 100 4.2.3.3 Nitrogen adsorption characterization ... 101

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4.2.3.4 Application of optimized urea-functionalized carbon supports in the SILP-

catalyzed hydroformylation ... 102

4.2.4 Relation between functionalization, activity and selectivity in the SILP-catalyzed hydroformylation ... 104

4.2.5 Summary of the performance of surface-modified carbon materials in the SILP- catalyzed hydroformylation ... 109

4.2.6 Influence of amines on the catalyst in the SILP-catalyzed hydroformylation .. 111

4.2.6.1 Influence of amines on the carbon support properties ... 111

4.2.6.2 Influence of amines on the gas solubility in ionic liquids of SILP catalysts….. ... 115

4.2.6.3 Influence of amines on the hydroformylation catalyst species ... 116

4.2.7 Ionic liquid screening for carbon-supported SILP catalysts ... 120

4.2.8 Ionic liquid distribution model on carbon surfaces ... 125

4.2.9 Carbon support screening ... 126

4.2.10 Mass transport influences of microporous carbon supports on the SILP- catalyzed gas-phase hydroformylation ... 128

4.2.11 Catalytic performance of different support materials in the SILP catalyzed hydroformylation ... 130

5. Summary / Zusammenfassung ... 134

5.1 Summary ... 134

5.2 Zusammenfassung ... 139

6. Supporting Information ... 144

7. References ... 149

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List of Abbreviations

°C Degree Celcius

α Pore filling degree

AC Activated carbon

AKP Aldol condensation product

n-BDEA N,N-Diethylbutylamine

c concentration

CNT Carbon nanotube

CO Carbon monoxide

COSMO-RS Conductor-like screening model for realistic solvation

DEA Diethylamine

EDX Energy dispersive x-ray spectroscopy EMIM 1-Ethyl-3-methyl-imidazolium

EtNH2 Ethylamine

Et3N Triethylamine

eV Electron volt

FID Flame ionization detector

γ Activity coefficient

g gram

GC Gas chromatograph

H Henry coefficient

h Hour

H2 Hydrogen

He Helium

ICP Inductively coupled plasma

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IL Ionic liquid

K Kelvin

k Rate constant

kg Kilogram

l Liters

M Molar mass

m Mass

MAS Magic angle spinning

MFC Mass flow controller

min Minutes

n Amount of substance

N2 Nitrogen

NMR Nuclear magnetic resonance

NTf2 Bis(trifluoromethylsulfonyl)imide

OAc Acetate

p Pressure

n-PDEA N,N-Diethylpropylamine

ppm Parts per million

PZC Point of zero charge

r Reaction rate

reff Effective reaction rate

RDS Rate determine step

Rh Rhodium

RTIL Room temperature ionic liquid

S Selectivity

s Second

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SAP Supported aqueous phase

SEM Scanning electron microscope

SILP Supported ionic liquid phase

SLP Supported liquid phase

SX Sulfoxantphos

τ Residence time

T Temperature

TG-MS Thermal gravimetric mass spectrometry TPD Temperature programmed desorption

tpp Triphenylphosphine

tppts Trisodium 3-bis(3-sulfonatophenyl)phosphanylbenzenesulfonate

TOF Turnover frequency

TOS Tosylate

V Volume

𝑉̇ Volume flow

ve Valence electrons

wt.-% Weight percentage

x Molar fraction

X Xantphos

X (formula) Conversion

XPS X-ray photoelectron spectroscopy

Y Yield

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List of Figures

Figure 1: Simplified illustration of the Supported Ionic Liquid Phase (SILP) concept. ...20 Figure 2: Schematic illustration of different carbon structures. Graphitic (A) turbostatic (B) and amorphous carbon (C). (Different shades are representing different layers) ...30 Figure 3: Overview of different carbon functionalization strategies. ...31 Figure 4: Continuous gas-phase reactor for the SILP-catalyzed hydroformylation and hydroaminomethylation of ethylene and propylene. ...51 Figure 5: Flow diagram of the continuous gas-phase reactor for the SILP-catalyzed hydroformylation and hydroaminomethylation of ethylene and propylene. ...52 Figure 6: Conversion, yield and selectivity over time diagram of SILP-catalyzed continuous gas-phase hydroaminomethylation with ethylene and diethylamine. ...60 Figure 7: Conversion, yield and selectivity over time diagram in the SILP-catalyzed continuous gas-phase hydroaminomethylation of propylene and diethylamine. ...61 Figure 8: Influence of the propylene and n-BDEA solubility in different ionic liquids on the activity in the SILP-catalyzed hydroaminomethylation. ...65 Figure 9: Influence of the DEA solubility in different ionic liquids on the selectivity in SILP- catalyzed hydroaminomethylation...66 Figure 10: Calculated n-BDEA solubility in correlation to different [MMMIM][NTf2]:DEA ratios.

...67 Figure 11: Activity and selectivity correlation in dependence on the [EMIM][NTf2] pore filling degree in the SILP-catalyzed hydroaminomethylation. ...68 Figure 12: Activity and selectivity correlation in dependence on the AKP pore filling degree in the SLP-catalyzed hydroaminomethylation. ...69 Figure 13: Activity and selectivity of the different primary and secondary amines in the SILP- catalyzed hydroaminomethylation of ethylene. ...70 Figure 14: Exemplary reaction progress of a primary (propylamine, left) and a secondary (diethylamine, right) amine in the SILP-catalyzed hydroaminomethylation. ...72

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Figure 15: 1H-NMR spectrum of the condensed product phase of the SILP-catalyzed hydroaminomethylation of ethylene and isopropylamine. ...73 Figure 16: Conversion, yield and selectivity over time diagram of the SILP-catalyzed sequence of hydroformylation and hydroaminomethylation of ethylene and diethylamine. ...74 Figure 17: Conversion, yield and selectivity over time diagram of the SILP-catalyzed hydroformylation of propylene and triethylamine. ...76 Figure 18: Conversion, yield and selectivity over time diagram of the SILP-catalyzed hydroformylation of ethylene and a urea additive. ...77 Figure 19: DTG-spectra of differently thermally treated AC-AA carbon materials. ...81 Figure 20: TG-MS signals of functionalized carbon materials AC-HNO3 (left) and AC-AA (right) before () and after () ammonia reduction. ...82 Figure 21: N-1s XPS-spectrum of amine functionalized carbon material (AC-AA-800) with deconvoluted data for –NH2 () and –NO2 () surface groups. ...83 Figure 22: Correlation between hydroformylation activity, PZC and nitrogen content of the functionalized carbon supports AC-AA and pristine AC. ...86 Figure 23: Conversion, yield and selectivity over time diagram of functionalized carbon supports (AC-AA-800) in the SILP-catalyzed hydroformylation of propylene. ...87 Figure 24: TG-MS signals of the functionalized carbon materials treated with sulfuric acid (S50/90, left) and nitric acid (N65/90, right) before () and after () urea reduction. ...92 Figure 25: Nitrogen adsorption isotherms of differently functionalized carbon materials. ...94 Figure 26: Pore size distribution of differently functionalized carbon materials...95 Figure 27: Activity versus reaction time of differently sulfuric acid and urea-functionalized carbon materials in the SILP-catalyzed hydroformylation of ethylene. ...96 Figure 28: Activity versus reaction time of differently nitric acid and urea-functionalized carbon materials in the SILP-catalyzed hydroformylation of ethylene. ...97 Figure 29: TG-MS signals of N65/90 carbon material reduced with urea (N65/90-U, left ) or ammonia (N65/90-A, left () and combined oxidation with nitric acid, sulfuric acid and ammonia reduction (N65_S50/90-A, right )... 101 Figure 30: Activity over reaction time of differently functionalized carbon materials in SILP- catalyzed hydroformylation of ethylene. ... 103

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Figure 31: Correlation between activity, selectivity and side product formation of different SILP catalysts with functionalized carbon support in hydroformylation of ethylene. ... 105 Figure 32: Side product formation correlated to the conversion in dependence on the amount of functionalized carbon support (1 g or 2.5 g) in the SILP-catalyzed hydroformylation of ethylene... 106 Figure 33: Difference in byproduct formation over time in SILP-catalyzed hydroformylation of ethylene with functionalized carbon (N65/90-A, left) or urea additive (right). ... 107 Figure 34: Exhaust analysis of a pristine carbon impregnated with ionic liquid ([EMIM][NTf2]) and urea (2:1) after temperature treatment at 120 °C (), 130 °C () and 150 °C () by MS.

... 108 Figure 35: Correlation between nitrogen content and PZC of the functionalized carbon supports and the activity of SILP-catalyzed hydroformylation of ethylene after 15 h reaction time. ... 109 Figure 36: Long term stability of functionalized carbon support (N65/90-A) in SILP-catalyzed hydroformylation of ethylene. ... 110 Figure 37: Water adsorption measurements of differently functionalized carbon materials. 112 Figure 38: Exemplary fluorine EDX cross section scan from center to shell of pristine carbon (top) and functionalized carbon (bottom, N65/90-A) impregnated with [EMIM][NTf2] (α = 0.1).

Exemplary SEM picture of the carbon sphere cross section (right). ... 113 Figure 39: SEM-EDX line scan of silica infiltrated carbon nanotubes impregnated with [EMIM][NTF2]. ... 114 Figure 40: High pressure 31P-NMR results for xantphos (bottom), xantphos and Rh(acac)(CO)2 (middle) and xantphos, Rh(acac)(CO)2 and diethylamine (top) mixtures in toluene-d8. ... 117 Figure 41: High pressure 31P-NMR results for single preparation steps of xantphos and Rh(acac)(CO)2 mixtures with diethylamine additive (left) and without (right) in toluene-d8. . 118 Figure 42: High pressure 31P-NMR results for xantphos, Rh(acac)(CO)2 and ionic liquid mixtures with and without diethylamine additive in toluene-d8. ... 119 Figure 43: Correlation between rhodium () solubility in different ionic liquids and their activity in SILP-catalyzed hydroformylation of ethylene with pristine () and functionalized (, N65/90-A) carbon support material. ... 121

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Figure 44: Correlation of conversion and selectivity in dependence on the differently used ionic liquids in the SILP-catalyzed hydroformylation of ethylene. ... 122 Figure 45: Activation behavior of SILP-catalyzed hydroformylation reaction of ethylene. .... 124 Figure 46: Arrhenius diagram of the SILP-catalyzed hydroformylation of ethylene (), propylene () and 1-butene (). ... 129

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List of Tables

Table 1: Overview on different industrially relevant hydroformylation process technologies.

[34-36] ... 8

Table 2: Henry’s constant (bar) for different gases in ionic liquids at different temperatures (adapted from [125-132] ). ...22

Table 3: Oxygen containing surface groups after functionalization and their respective desorption temperatures. [21, 23, 174] ...35

Table 4: Sulfur containing surface groups after sulfuric acid functionalization and their respective desorption temperatures. [175] ...36

Table 5: Precursor and ligand for the SILP catalyst preparation ...45

Table 6: Ionic liquids for the SILP catalyst preparation. ...45

Table 7: Support materials for the SILP catalyst preparation. ...46

Table 8: Chemicals for the gas-phase hydroformylation and hydroaminomethylation. ...46

Table 9: Chemicals for the carbon functionalization. ...47

Table 10: GC-method for the analysis of the hydroformylation and hydroaminomethylation product feed. ...53

Table 11: COMSO-RS predicted activity coefficients of hydroaminomethylation reactants in different ionic liquids. ...63

Table 12: Activities and selectivities of SILP catalysts with different C2-alkylated imidazolium- based ionic liquids in the hydroaminomethylation of propylene and diethylamine. ...64

Table 13: Activities and selectivities of SILP catalysts with different [EMIM]-based ionic liquids in the hydroaminomethylation of propylene and diethylamine. ...65

Table 14: Nitrogen content and point of zero charge (PZC) of preliminary carbon functionalization experiments. ...79

Table 15: Influence of the thermal treatment on the nitrogen content and the point of zero charge (PZC) of the carbon material AC-AA. ...80

Table 16: Surface area and pore volume of differently functionalized carbon materials. ...83

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Table 17: Activity and selectivity of the SILP-catalyzed hydroformylation with propylene after 4 h reaction time using differently functionalized carbon supports. ...85 Table 18: Nitrogen content and point of zero charge (PZC) of sulfuric acid treated carbon materials during the single preparation steps. ...89 Table 19: Nitrogen content and point of zero charge (PZC) of nitric acid functionalized carbon materials during the single preparation steps. ...90 Table 20: Surface area and pore volume of differently functionalized carbon materials. ...93 Table 21: Correlation between support properties of sulfuric acid and urea functionalized carbon materials and their activity in the SILP-catalyzed hydroformylation of ethylene. ...97 Table 22: Correlation between support properties of nitric acid and urea-functionalized carbon materials and their activity in the SILP-catalyzed hydroformylation of ethylene. ...98 Table 23: Nitrogen content and point of zero charge (PZC) of optimized functionalized carbon materials during preparation progress. ... 100 Table 24: Surface area and pore volume of differently functionalized carbon materials. ... 102 Table 25: Correlation between support properties of functionalized carbon materials and their activity in SILP-catalyzed hydroformylation of ethylene. ... 103 Table 26: Nitrogen adsorption results for pristine and functionalized carbon materials with different ionic liquid [EMIM][NTf2] pore filling degrees. ... 114 Table 27: Gas solubility measurements of ionic liquids supported on pristine or functionalized carbon materials. ... 116 Table 28: Nitrogen adsorption data of different pristine carbon materials tested in SILP- catalyzed hydroformylation. ... 127 Table 29: Activity and selectivity of different pristine carbon supports in SILP-catalyzed hydroformylation of ethylene with two different ionic liquids. ... 127 Table 30: Activity of different support materials in the SILP-catalyzed hydroformylation of ethylene and propylene. ... 130 Table 31: Selectivity and yield of by-products in the SILP-catalyzed hydroformylation of ethylene and propylene with different support materials. ... 131

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List of Schemes

Scheme 1: Exemplary set-up of a SILP catalyst. ... 3 Scheme 2: General hydroformylation reaction scheme. ... 6 Scheme 3: Overview of hydroformylation derived industrial products (adapted from [27] ). ... 7 Scheme 4: Reaction mechanism for the rhodium catalyzed hydroformylation (adapted from [40, 41] ). ... 9 Scheme 5: General reaction scheme of the hydroaminomethylation. ...11 Scheme 6: Relation between typical hydroformylation and hydrogenation catalyst (adapted from [60] ). ...13 Scheme 7: Different immobilization concepts for homogeneous catalysts. ...15 Scheme 8: Typical ionic liquid anion and cation building blocks. ...17 Scheme 9: Schematic illustration of the condensation – evaporation equilibria in the pores of a SILP catalyst. ...27 Scheme 10: Exemplary sulfonation of a carbon surface represented by the electrophilic aromatic substitution of benzene with sulfuric acid. ...35 Scheme 11: Exemplary nitration of a carbon surface represented by the electrophilic aromatic substitution of benzene with nitric acid. ...37 Scheme 12: Exemplary reductive amination of a carbon surface represented by the reduction of nitrobenzene with ammonia and sodium dithionite...37 Scheme 13: Typical carbon surface groups after oxidation (left) and subsequent reductive amination with ammonia and sodium dithionite (right). [21, 172, 180] ...38 Scheme 14: Exemplary reaction of urea with typical oxidized carbon surface groups. [181, 182] ...38 Scheme 15: Exemplary nitrogen insertion into the carbon matrix by the pyrolysis of lactame (A) or imide surface groups (B). [187-189] ...39 Scheme 16: Exemplary activated carbon surface groups after pyrolysis at different temperatures. [21, 172, 180] ...40

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Scheme 17: Exemplary surface rearrangement of urea modified carbons after pyrolysis.

[181, 182] ...41 Scheme 18: Base-catalyzed formation of 2-ethyl-2-hexenal (aldol). ...47 Scheme 19: Summary and labeling of the different optimized carbon functionalization procedures. ...49 Scheme 20: Proposed transalkylation reaction for diethylamine in SILP-catalyzed hydroaminomethylation. ...62 Scheme 21: Hydroaminomethylation reaction scheme with enamine / imine intermediates and side reactions. ...71 Scheme 22: Possible influences of amines on the SILP catalyst building blocks. ... 111 Scheme 23: Structure of the xantphos ligand (1), the monohydride complex (2) and the dimeric species (3). ... 117 Scheme 24: Influence of the surface wettability on the catalytic performance of carbon supported SILP catalysts. ... 122 Scheme 25: Ionic liquid distribution model on carbon surfaces. ... 125 Scheme 26: Schematic summary of the scope of investigation presented in this thesis. .... 134 Scheme 27: Schematischer Überblick über die grundlegenden Forschungsaspekte dieser Arbeit. ... 139

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Chapter 1

Introduction

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1. Introduction

80 years ago, the German chemist Otto Roelen by chance discovered the hydroformylation reaction when he was trying to recycle ethylene generated by the Fischer-Tropsch reaction back into the process. Nowadays, the hydroformylation is one of the most significant reactions in chemical industry with more than 12 million tons hydroformylation products being generated in the year 2012. [1] In hydroformylation, olefins are transformed into their respective aldehyde species in the presence of carbon monoxide and hydrogen, so called synthesis gas, classically catalyzed by homogeneous organometallic catalysts in the liquid phase. The industrial importance of hydroformylation can be explained by the high demand of aldehydes as a raw material for numerous secondary products such as plasticizers, solvents, or synthetic materials.

Amines are among the most important chemical compounds especially in the context of fertilizer production and can also be produced based on hydroformylation oxo-products.

Although, many ways to produce amines are known and realized nowadays (e.g. reductive amination, hydroamination or the nucleophilic substitution of alkyl halides), the hydroaminomethylation, a combination of hydroformylation and reductive amination, offers a highly atom-efficient approach. In this tandem reaction, synthesis gas and olefins are first converted to the respective aldehydes and later converted by reductive amination. Especially the possibility of a one-pot synthesis, where all reaction steps occur at a single catalyst makes the hydroaminomethylation a very attractive synthesis for industrial applications.

Both, hydroformylation and hydroaminomethylation, are classically realized in homogeneously catalyzed liquid phase processes. The biggest advantages of homogeneous compared to heterogeneous catalysis are the higher reaction rates, the high flexibility by choosing different tailored catalyst complexes and the milder reaction conditions. The biggest advantage of heterogeneous catalysis is the simple and cost-efficient catalysts recycling. The recovery of the catalyst after the reaction is of particular importance if precious metal catalysts are being used. In hydroformylation, the expensive rhodium (~ 50 €/g, stock exchange price from 01/2018) catalysts needs to be recycled efficiently to guarantee economic feasibility of the process. Different catalyst immobilization strategies, especially such as biphasic reactions or heterogenization have been intensively investigated over the years. [2] In this thesis, the immobilization concept of supported ionic liquid phase (SILP) catalysis was studied in detail.

SILP catalysis can be described as heterogenization of homogeneous catalysis by immobilizing a liquid catalyst phase onto the surface of a highly porous solid support material. By that, the advantages of homogeneous and heterogeneous catalysis can by combined. Although, on a macroscopic scale the catalyst appears as a solid material with all

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its advantages regarding catalyst recycling, the reaction is occurring at a homogeneous catalyst that is dissolved in a liquid film immobilized on the support surface. The schematic set-up of a SILP catalyst is shown in Scheme 1.

Scheme 1: Exemplary set-up of a SILP catalyst.

Compared to similar immobilization concepts (e.g. supported aqueous phase catalysis), the advantage of the SILP approach is the application of ionic liquids (IL’s) as homogeneous catalyst phase. Ionic liquids are exclusively consisting of ions and feature a melting point below 100 °C per definition. Compared to inorganic salt compounds, their low melting point is caused by the steric complexity and the high degree of charge distribution of the cation and anion building blocks. [3-6] Due to a variety of cation and anion combinations (> 1 million binary systems), ionic liquids are often described as tailor-made solvents, especially designed for a specific application. [4] With respect to the SILP concept, the probably most important characteristic of ionic liquids is their negligible vapor pressure, making them an ideal catalyst solvent for SILP-catalyzed gas-phase applications at high temperatures. Due to the high number of ionic liquid combinations, further properties such as the solubility of the catalyst and the reaction compounds in the ionic liquid that are highly influencing the activity and selectivity of the reaction can be adjusted as desired.

The concept of SILP catalysis is already intensively studied for hydroformylation and was actually introduced for the first time based on this reaction in 2002 by Mehnert et al. [7] Later, mainly the groups of Riisager and Wasserscheid et al. were contributing to the progress in SILP-catalyzed gas-phase hydroformylation. [8-16]

Significant progress could be achieved in this field of research, resulting in highly active and selective hydroformylation systems comparable to industrial standards. Nevertheless,

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commercial application so far suffered from deactivation over time. [17, 18] The formation of high-boiling side products that were accumulating in the catalyst pore system was identified as the main reason for the observed deactivation behavior. Especially, the elimination of acidic surface groups of the primarily used silica supports by thermal treatment could improve the catalyst stability significantly. [19] Support properties such as the pore volume, the surface area or the wettability by the ionic liquids could be further identified as important influencing factors for the performance of SILP catalysts. [12]

So far, practically no publications about the application of different support materials despite the widely used oxidic supports (SiO2 and Al2O3) can be found in the context of SILP- catalyzed hydroformylation, although the enormous influence of this essential element was fairly described. In 2013, Schneider et al. showed the first successful application of activated carbon supports in the SILP-catalyzed gas-phase hydroaminomethylation. A superior performance regarding catalytic activity and especially the reduction of high boiling side products was observed. [20] Compared to oxidic support materials, activated carbons are highly microporous featuring a high surface area and a chemically inert surface making them an ideal support for SILP applications. Although, the impregnation of ionic liquids onto the hydrophobic carbon surface is often described as difficult, surface functionalization can improve the impregnation behavior. [21-26]

In this thesis, the development and further optimization of SILP catalysts for the continuous hydroformylation and hydroaminomethylation was in the focus. Searching for a highly active, selective and stable SILP catalyst for industrial applications, the carbon-supported system reported by Schneider et al. served as a perfect starting point for further investigations.

Especially, the control of aldol formation that is typically responsible for the deactivation of SILP catalysts due to pore flooding seemed highly interesting. As only little knowledge about activated carbons as support material for SILP catalysts was reported so far, a crucial element of this work was to create deeper knowledge about the concept of SILP catalysis regarding the choice of support. Based on a SILP catalyst optimization to further extend the scope of the already successfully tested hydroaminomethylation, the investigation of the hydroformylation reaction using carbon-supported SILP catalysts is also advanced. Due to the surprising performance of these catalysts in hydroformylation, a major part of this work is focusing on the influence of amines on SILP catalysts and on the amine functionalization of the carbon supports used for the SILP-catalyzed hydroformylation.

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Chapter 2

Theory

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2. Theory

2.1 Hydroformylation

The following chapter describes the general theoretical background of hydroformylation. This reaction was mainly used as benchmark for the catalyst systems investigated in this thesis.

The focus is set on the detailed Wilkinson reaction mechanism of the homogeneous rhodium-catalyzed hydroformylation and the known influences of amines on this reaction. In this context, the hydroaminomethylation, which served as a starting point and second reaction of interest in this thesis, will also be described.

2.1.1 General overview and state of the art processes

The hydroformylation reaction also referred to as oxo-synthesis, discovered by Otto Roelen in 1938, has attracted continuous and increasing industrial and academic interest which is well understandable in the light of the fact that the conversion of lower aliphatic olefins into aldehydes and further on into aliphatic alcohols is a million-ton scale industrial production process nowadays. Hydroformylation products are used as important constituents of solvents, plasticizers or specialty chemicals, among others. Scheme 2 shows the general hydroformylation reaction of an olefin and synthesis gas (CO and H2) whereby hydrogen (“hydro”) and a “formyl” group (H-C=O) are added in an atom efficient manner.

Scheme 2: General hydroformylation reaction scheme.

For olefins with more than two carbon atoms (> C2) either branched or the industrially more desired linear aldehydes can be produced. Due to possible internal isomerization of long- chained olefin substrates (e.g. 1-butene to cis/trans-2-butene), multiple, differently branched aldehydes can be produced depending on the applied catalyst system. Furthermore, typical side reactions are, for example, the hydrogenation of the olefin substrate to the respective alkanes or the hydrogenation of the aldehyde products to the respective alcohols. The consecutive reaction of aldehydes into long-chained aldol high boilers is also a critical side reaction. This aspect will be discussed in more detail in Chapter 2.2.3. Hydroformylation is

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among the most important industrially applied homogeneously catalyzed transformations. An overview of several hydroformylation-derived industrial products is shown in Scheme 3.

Scheme 3: Overview of hydroformylation derived industrial products (adapted from [27] ).

A variety of transition metals have been tested in hydroformylation and have been found to promote the reaction in the following order of decreasing catalytic activity: Rh > Co > Ir > Ru

> Os > Pt > Pd > Fe > Ni. [28] A comparison of industrial relevant hydroformylation process technologies is given in Table 1. The first generation of industrially hydroformylation catalysts was based on unmodified cobalt systems (HCo(CO)4). Until now, these cobalt catalysts are used for the production of plasticizers (C4-C10) and detergents (C12-C18) from long-chain or internal olefins. [29] By the application of tertiary phosphine ligands (e.g. tributylphosphine), an increased n/iso-ratio up to 88:12 can be obtained (Shell process). The harsh reaction conditions for the cobalt systems with temperatures up to 200 °C and pressures in the region higher 100 bar led to the replacement with the much more expensive (~ factor of 1000) but highly active rhodium catalysts. Besides the reduction of reaction temperature (85-140 °C) and pressure (15-50 bar), novel rhodium-ligand complexes could further improve the n/iso- selectivity up to a ratio of 95:5. New separation and catalyst regeneration technologies needed to be developed in order to make the more valuable rhodium systems economically profitable. In the “Low-Pressure-Oxo”-process (LPO), the products are recycled from the catalyst phase by vaporization in a gas recycle process licensed by Union Carbide Cooperation (UCC, now Dow Chemical). [30] A different concept is the liquid recycle process (licensed by Union Carbide and Mitsubishi Chemical), where the product separation by distillation is taking place in the downstream independently from the hydroformylation reactor. [31] One major breakthrough was reached by the application of highly water-soluble Rh-complexes using sulfonated triphenylphosphine ligands in the Ruhrchemie/Rhone- Poulenc biphasic process. [32] With this innovative process design, the catalyst/product separation is realized by a liquid-liquid phase separation due to the poor solubility of the feedstock and the products in the aqueous catalyst phase. These rhodium catalysts are

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limited to a C3-C4 feedstock, as the catalytic activity decreases significantly by using less water-soluble higher olefins. [33] Depending on the application, the feedstock, and the infrastructure, different industrial processes are used nowadays.

Table 1: Overview on different industrially relevant hydroformylation process technologies. [34-36]

Parameters Ruhrchemie /

BASF Shell UCC (LPO) Ruhrchemie /

Rhône-Poulenc Typical Feed Also internal, C10+ Also internal, C10+ Only terminal, C3-4 Only terminal, C3-4

Catalyst HCo(CO)4 HCo(CO)3L HRh(CO)L3 HRh(CO)L3

Ligand - tbp1 tpp2 tppts3

Temperature (°C) 110-180 160-200 85-115 110-140

Pressure (bar) 200-300 50-100 15-20 40-50

n/iso-Ratio 80:20 88:12 92:8 95:5

1: tbp = Tributylphosphine 2: tpp = Triphenylphosphine

3: tppts = Tris(m-sulfonatophenyl)phosphine

For C2-C4 feedstocks, mainly the LPO or the Ruhrchemie/Rhône process is applied, whereas in the case of an internal or long-chained olefin feedstock cobalt catalyst-based processes are still used.

Nevertheless, most industrial hydroformylation processes and academic hydroformylation studies use Rh-based catalysts today. [37] For a selective hydroformylation the catalyst must suppress hydrogenation side reactions and iso-aldehyde formation. Therefore, the insertion of carbon monoxide over pure hydrogenation needs to be favored. Although many transition metals tend to form carbonyl complexes, only cobalt and rhodium are sufficiently active for industrial application. The regioselectivity is mainly attributed to the right choice of metal-ligand complexes. For a better understanding, a more detailed reaction mechanism for the rhodium-catalyzed hydroformylation according to Wilkinson, which is also used as basic concept in this thesis, is given in the following chapter.

2.1.2 Reaction mechanism of the rhodium catalyzed hydroformylation

Prior to the first industrial application of unmodified rhodium in hydroformylation in the year 1970 by Mitsubishi, the group of Wilkinson paved the way by postulating a detailed reaction mechanism of the rhodium-catalyzed hydroformylation identifying a hydridorhodiumcarbonyl complex (HRh(CO)2L2) as the active catalyst species. [37, 38] The mechanism was postulated for classical homogeneous liquid-phase reactions and remained valid till nowadays. In Scheme 4 an adapted reaction mechanism for the rhodium-catalyzed hydroformylation is shown. Isomerization and hydrogenation side reactions are indicated but

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will not be discussed in detail. Starting from the dicarbonyl(acetylacetonato) rhodium(I) precursor (Rh(acac)(CO)2), which was also used in this work, the addition of synthesis gas and phosphine ligand leads to the formation of the active hydridorhodiumcarbonyl complex (A) under elimination of acetylacetone. In the case of high carbon monoxide partial pressures, the formation of the Rh-dimer species (A*) can occur, which is inactive in hydroformylation. By the elimination of carbon monoxide, the coordinative saturated complex (A, 18 valence electrons (ve)) turns into the unsaturated resting state (B ,16 ve). After π- complexation of the olefin, a coordinative saturated complex (18 ve) (C) is again formed. This complex also serves as a starting point for an isomerization side reaction pathway. [39] In the case of an olefin insertion into the Rh-H bond, either the linear (D) or the branched (D*) complex can be formed.

Scheme 4: Reaction mechanism for the rhodium catalyzed hydroformylation (adapted from [40, 41] ).

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The regioselectivity of this insertion step is strongly influenced by the steric and electronic properties of the coordinated ligands. Sterically demanding ligands favor the insertion of the less space-consuming linear alkyl chain compared to the branched one. The hydride transfer to either C1 or C2 of the coordinating olefin during Rh-C bond formation is also controlled by the electronic properties of the ligand. A hydrogenation reaction pathway by the oxidative addition of hydrogen to the complex forming the alkane side product is possible at this point.

After the olefin insertion, a carbon monoxide addition to the rhodium center takes place (E).

The same reaction steps would take place for the branched olefin complex (D*) but is not shown in detail here. The following insertion of CO to the Rh-allyl bond is resulting in the acylrhodium(I)-species (F). By the oxidative addition of hydrogen to the metal center, rhodium changes the oxidation state from +1 to +3 forming a coordinative saturated Rh(III)- complex (G). In the final reaction step, the aldehyde product is formed under reductive elimination while the catalyst complex is retransferred into the unsaturated Rh(I) resting state (B).

The reaction step from (F) → (G) was often described as rate-determine due to the change in number of coordination and oxidation state and an observed strong influence of the hydrogen partial pressure on the reaction rate. [42-44] Though, new studies strengthen the insertion steps as rate-determine, as they observed a more dominant influence of the olefin concentration on the reaction rate. [41, 45-47] The conflicting results are probably generated due to the different applied reaction conditions in the different studies. An increased hydrogen partial pressure could, for example, raise the reaction rate by suppressing the dimer formation (A*) resulting in a higher concentration of the hydroformylation active rhodium species. [48] A general rate equation for a rhodium system with tpp ligand is given in Equation 1: [36]

𝑟𝐻𝑦𝑑𝑟𝑜𝑓𝑜𝑟𝑚𝑦𝑙𝑎𝑡𝑖𝑜𝑛 = 𝑘[𝑅ℎ][𝐶𝐻3𝐶𝐻𝐶𝐻2]0.6[𝐻2]0.05[𝐶𝑂]−0.1[𝑃𝑃ℎ3]−0.7 (Eq. 1) Besides the positive reaction order of the olefin and the rhodium catalyst, a negative influence of carbon monoxide and the tpp ligand could be observed. At high carbon monoxide partial pressures, the equilibrium between the fivefold coordinated complex (A) and the resting state (B) is shifted to the side of complex (A) resulting in a decreased reaction rate. Furthermore, a high carbon monoxide concentration is favoring the formation of the inactive Rh-dimer species (A*). The negative influence of CO on the hydroformylation rate has been reported in many different publications. [14, 46, 49, 50] In the case of a high tpp ligand concentration, a HRhCO(tpp)3 complex is formed, which needs to split off one ligand in order to generate the catalytic resting state (B).

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The type of the ligand in hydroformylation has a strong influence on the reaction mechanism regarding reaction rate and selectivity. The different electronic and steric effects of ligands are often described in literature. Besides the widely used phosphine-, or phosphite-type ligands, also amine derivatives were tested as ligands in hydroformylation. [51-53] In this thesis, only the phosphine ligand xantphos was used. For a more detailed overview on ligands in hydroformylation, additional literature is recommended. [27, 54-57]

In the hydroaminomethylation, linear amines can be produced under hydroformylation conditions. The presence of amines is also likely to affect the reaction mechanism of the classical hydroformylation.

2.1.3 Amines in hydroformylation

In the following chapters, a general introduction to the hydroaminomethylation, being a consecutive reaction of hydroformylation and reductive amination, is given. In this thesis, the hydroaminomethylation served as the starting point for the amine functionalization of carbon materials. The few published reports on the influence of amines or alkaline additives on the hydroformylation reaction will be summarized, too.

2.1.3.1 Hydroaminomethylation

Amines range among the most valuable bulk and fine chemicals finding their application in the pharmaceutical and agrochemical industry as fertilizers, dyes, solvents or biologically active molecules. Due to their production in a million ton scale, the selective and cost- efficient synthesis of these chemicals is an attractive target for research. [58] Although many ways for the production of amines are known and realized nowadays (e.g. reductive amination, hydroamination or the nucleophilic substitution of alkyl halides), the hydroaminomethylation offers a highly atom-efficient approach. A general reaction scheme for the hydroaminomethylation is shown in Scheme 5. In this tandem reaction, synthesis gas and olefins are first converted to the respective aldehydes, according to the previously described reaction mechanism of hydroformylation.

Scheme 5: General reaction scheme of the hydroaminomethylation.

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After this reaction step, the amine substrate reacts with the aldehyde under condensation to the respective enamine or imine intermediate that is finally hydrogenated to the desired secondary or tertiary amine product. In the case of primary amines, the imine intermediate is formed, whereas the higher substituted secondary amines are resulting in the enamine intermediate. Especially the possibility of a one-pot synthesis, where all reaction steps are occurring at a single catalyst and with water being the only by-product in the reaction, makes the hydroaminomethylation a very attractive synthesis for industrial applications. [59-63]

In 1943, the group of Reppe et al. at BASF was first to describe the hydroaminomethylation by converting ammonia and acetylenic compounds into the respective amine products under relatively severe reaction conditions (pCO = 170-200 bar, T = 120 - 140 °C) using an iron pentacarbonyl catalyst. Due to the industrial success of hydroformylation, the research on the hydroaminomethylation shifted towards rhodium and cobalt complexes and was further intensified after the successful application of classic hydroformylation catalysts in the reductive amination in 1974. [64] Since the early 1990’s, especially the groups around Kalck, Eilbracht and later Beller and Behr put much effort into the research on hydroaminomethylation by mechanistic studies, catalyst and solvent variations to extend the knowledge regarding this reaction. [59, 61, 62, 65-67]

In the case of sterically demanding amine substrates such as morpholine or diisopropylamine, the hydroaminomethylation was found to rest at the enamine intermediate or directly after the first hydroformylation reaction step. The condensation of aldehyde and bulky amines and the further hydrogenation of the intermediate appeared to be the rate- determine step in this case. [68, 69] It was further observed, that the hydrogenation of the imine intermediates to secondary amines proceeds faster than the enamine hydrogenation. A selective synthesis of secondary amines and therefore the suppression of a consecutive alkylation is possible in the case of an equimolar olefin to amine ratio. [70] Similar to hydroformylation, side reactions such as olefin or aldehyde hydrogenation and aldol formation have the highest impact on the selectivity of the hydroaminomethylation. Although it is possible to use unmodified Rh-catalysts in hydroaminomethylation, higher selectivities are reported for classic Rh-phosphine complexes. [71-73] Especially the balance between the two different reaction steps, namely hydrogenation and hydroformylation, that normally require different reaction conditions, is challenging for the design of a one-pot catalyst system.

In the hydroaminomethylation reaction, the interdependency of amines and hydroformylation is inevitable and needs to be considered carefully. The reaction mechanism for the single steps is assumed to be independent even though certain interplaying effects could be observed. In the following, the influence of amines as additives or ligands on the hydroformylation is pointed out.

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2.1.3.2 Influence of alkaline compounds on the hydroformylation

In hydroformylation, the application of phosphine and phosphite ligands led to significantly improved regioselectivity. Under hydroaminomethylation conditions, the amine substrate will compete with those ligands for the metal center and therefore will influence the regioselectivity of the reaction. In the group of Beller et al. the influence of a triethylamine additive on the hydroformylation of 1-pentene was investigated. [74] It was shown, that an increased amine concentration led to a significantly reduced n/iso-selectivity (from 95:5 to 72:28) using tpp as a ligand, whereas the selectivity of bidentate diphosphine ligands was influenced much less (from 98:2 to 97:3). Generally, the regioselectivity was improved with an increasing bite angle of the different diphosphines. In hydroformylation, a frequently used precursor is the neutral Rh(acac)(CO)2 complex (A), whereas the cationic [Rh(COD)2][BF4] complex (C) is often used in hydrogenation. In Scheme 6, the relation between the active hydrogenation and hydroformylation complex is illustrated. As both reactions steps are necessary in the hydroaminomethylation, the group of Vogt et al. successfully tested the simultaneous application of both complex types. [75] They further observed a strong dependence on the combination of solvent and precursor. If the neutral complex (A) was used, the addition of a protic solvent was necessary for the hydrogenation step to take place.

This role could also be fulfilled by CH-acidity of certain ionic liquids. In the case of the cationic precursor (C) the successful hydroformylation step was attributed to the possible shift towards complex (B) by an amine substrate. Similar observations were also reported be the group of Beller et al. [76]

Scheme 6: Relation between typical hydroformylation and hydrogenation catalyst (adapted from [60] ).

In a detailed study on the formation of the active catalyst species, the group of Kalck et al.

found out that the addition of an amine to a cationic or neutral rhodium precursor led to Rh- amine coordination by CO replacement. [77, 78] They further confirmed the role of amines in the transformation of a cationic rhodium complex into the hydroformylation active monohydride species under reaction conditions. By DFT calculations, an oxidative addition of

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hydrogen and subsequent deprotonation of the dihydride complex by the amine was proposed. In a different study, an increased hydrogenation rate was observed with an increasing tertiary amine additive concentration under hydroformylation conditions. This was attributed to the exclusion of carbon monoxide from the rhodium complex by the amine additive. [53] An increased hydroformylation rate by the addition of amines acting as complexing ligand to a biphasic aqueous system was reported by the group of Beller et al.

[79] The reason for the increased activity and regioselectivity with increasing pH-value was attributed to a faster preformation of the active catalyst species. This is in good agreement to older studies, where an increased reaction rate by a factor up to 10 was achieved by increasing the pH of the aqueous media. [80, 81] An improved dissociation of the hydroformylation inactive Rh-dimer species at basic pH-values was discussed in this context.

All the effects described above show the significant influence of amines on the hydroformylation part. Under hydroaminomethylation conditions, these effects might easily be overlooked as the amines act as the substrate. By the application of tertiary amine additives or other unreactive alkaline compounds those effects can be investigated under comparable reaction conditions.

Besides choosing the right reaction environment for the catalyst in order to realize sufficient activity, the precious rhodium metal (for hydroformylation and hydroaminomethylation) needs to be handled as efficient as possible in order to allow for reasonable process economics.

Besides the already described industrial recycling processes, novel scientific approaches for an improved catalyst immobilization are studied. In the following chapters, the Supported Ionic Liquid Phase (SILP) concept, which was applied as immobilization strategy in this thesis, is explained in more detail.

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2.2 Supported Ionic Liquid Phase (SILP) catalysis

To make hydroformylation more efficient, several different catalyst concepts have been developed in the last decades. In the following chapters, a short introduction to immobilization approaches will be given. Before the SILP concept will be explained in detail, an overview of ionic liquids, their properties and the possibilities for immobilization concepts will be given. A special focus will be put on the solubility of hydroformylation substrates in ionic liquids using COSMO-RS simulations, the miscibility of the SILP building blocks and the choice of support material.

2.2.1 An introduction to immobilization concepts

Homogeneously and heterogeneously catalyzed reactions both offer different advantages and disadvantages. In homogeneous catalysis, the possibility to modify the metal catalyst with specially designed ligands improves reactivity as well as selectivity. Therefore, relatively mild reaction conditions can be applied most of the times. The major drawbacks of homogeneously catalyzed reactions are the complex and hence often expensive catalyst systems. The recycling of the precious metal complexes is of crucial importance for the economic viability of the catalytic process. In heterogeneous catalysis, the recycling of the catalyst is straight forward. Here, the drawbacks are mainly lower activities and selectivities and harsher reaction conditions. The combination of both catalyst operation modes could combine the beneficial effects of homogeneous and heterogeneous catalysis in one system.

Different heterogenization approaches of homogeneous catalysts have been reported. A general overview of immobilization concepts by heterogenization is shown in Scheme 7.

Scheme 7: Different immobilization concepts for homogeneous catalysts.

The immobilization of a catalyst complex by an organic solvent (Supported liquid phase, SLP) or water (supported aqueous phase, SAP) on a support surface represents the simplest immobilization approach. If a thin liquid film is impregnated on the porous structure of a

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catalyst support, a high reactivity due to the large interfacial area can be achieved. More complex immobilization strategies by binding the catalyst covalently onto the support surface or by using spacer molecules were also investigated. [82-85] In hydroformylation, the first immobilization strategies using high boiling organic compounds (benzyl butyl phthalate) as a solvent for the catalyst complex on a support material were carried out in the late 1960s. An optimum loading of the support with the organic solvent with respect to mass transport limitations was already described in this publication. [86] In a different approach, a molten triphenylphosphine ligand was directly used as solvent for the metal precursor and immobilized as a thin film on a silica support. [87] This idea resulted in a detailed engineering of supported liquid phase systems. [88] Similar approaches using a water film on silica were reported by the group of Arhancet et al. [89, 90] The major drawback of the described concepts is the leaching of the catalyst phase by partial miscibility towards hydroformylation substrates or products. By using water as immobilized liquid film, this problem could be suppressed partially. In the gas-phase reaction, the leaching of the catalyst phase can be avoided for the most part. There, the evaporation of the solvent under operation conditions causes a continuous deactivation of the catalyst. To prevent the solvent loss in SAP catalysis, experiments with an additional dosing of vapor were examined. [91] In the gas phase, the substrate scope is limited to volatile compounds to prevent the condensation of compounds that would again lead to a leaching of the catalyst. Additional problems of immobilization concepts are the interaction of support and catalyst phase and reduced activities and selectivities compared to classic homogeneous catalysis.

For a perfect immobilization of a homogeneous catalyst, the solvent phase should feature a sufficiently high miscibility gap towards the reaction compounds, should have a sufficient interaction to the support surface for proper immobilization and should have a negligible vapor pressure to prevent evaporation. A special immobilization technique that was used in this thesis and can fulfil most of these requirements is the SILP concept. The main difference to the previously discussed concepts is the application of ionic liquids that act as a solvent for the homogeneous metal catalyst while being immobilized on a support surface as a thin liquid film. In the following, ionic liquids are discussed in more detail in order to explain their beneficial properties for immobilization techniques.

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2.2.2 General physical properties of ionic liquids

Ionic liquids (IL) represent a special class of salts that feature a melting point below 100 °C by definition. [92] In the case of a liquid state of matter at room temperature, they are sub categorized as so-called room temperature ionic liquids (RTIL). Ionic liquids are exclusively composed of ions (organic cations + organic or inorganic anions) and differ from classic inorganic salts due to their high asymmetry and unorganized crystal structure. The interaction of the molecules is mainly dominated by classic Coulomb forces. The high steric demand of the cations or anions and a highly distributed ionic charge are the main reasons for the reduction of the melting point in ionic liquids. Due to the manifold possibilities of ion combinations, more than 1018 simple organic salts might be possible for the preparation of ionic liquids. [93] Some common ionic liquid cations and anions are shown in Scheme 8.

This large pool of building blocks makes ionic liquids so called “tailor-made” solvents as each combination shows unique properties.

Scheme 8: Typical ionic liquid anion and cation building blocks.

By changing the length of substituted alkyl chains at the cation, the melting point of the ionic liquid can be varied. From methyl to hexyl alkyl substituents, a decrease in the melting point was observed that was again rising when longer alkyl chains were incorporated in the ions.

[94] Further influences on the melting point are the van der Waals interactions, the H- bonding ability and the symmetry and size of the ions. [5] The thermal stability of ionic

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