Metathesis of functionalized alkanes: understanding the unsolved problem

Dissertation by

Mykyta Tretiakov

In Partial Fulfillment of the Requirements

For the Degree of

Doctor of Philosophy

King Abdullah University of Science and Technology

Thuwal, Kingdom of Saudi Arabia

October, 2019 EXAMINATION COMMITTEE PAGE

The dissertation of Mykyta Tretiakov is approved by the examination committee.

Committee Chairperson: Professor Jean-Marie Basset Committee Members: Professor Kuo-Wei Huang, Professor Osman Bakr, Professor Pascal Saikaly, Professor Didier Astruc

© October 2019

Mykyta Tretiakov

All Rights Reserved ABSTRACT

The aim of this dissertation is to discover the metathesis of functionalized alkane. The first chapter describes an overview of the catalysis field, the role of surface organometallic chemistry

(SOMC) and the history of metathesis.

The second chapter studies the decomposition of the alkane metathesis catalyst precursor based on WMe6 grafted on partially dehydroxylated at 700 °C silica (SiO2-700) [≡Si-O-WMe5] and its activity in the metathesis of non-coordinating substrates. We used thermal programmed desorption (TPD), in situ infrared-mass spectrometry (IRMS) and chemical techniques with nuclear magnetic resonance. We found evidence of decomposition of the catalyst by coordinating substrates (ester and alcohol) and its inactivity in the metathesis of siloxanes and silanes. [≡Si-O-WMe5] catalyzes the disproportionation of n-butyl-ferrocene to ferrocene and dibutylferrocene.

The third chapter is dedicated to the strategy of protection of the catalyst active site by modification of the catalyst support. We modified conventional silica which was partially dehydroxylated at 500 °C, and KCC-1 supports by octyltriethoxysilane as well as 1,1,2,2- tetrahydro-perfluorooctyl-triethoxysilane and grafted the alkane metathesis catalyst precursor –

W(CH3)6. The obtained materials have been thoroughly characterized and studied in catalysis showing the activity towards metathesis of olefins and alkanes, but were inactive in the metathesis of functionalized alkanes.

The fourth chapter provides the strategy with which to design and metathesize a compatible functionalized alkane on well-defined alkane metathesis catalyst. We investigated the weak coordinating pyrrole-based family of substrates. While utilizing [≡Si-O-WMe5] with 1-(alkyl)-2,5- dimethyl-1H-pyrroles, traces of metathesis and isomerization products were observed. With these results, we synthesized a rigid aromatic molecule – 9-hexyl-9H-carbazole and reached 5 % conversion to lower and higher homologs. That result proved to be the first-ever known example of metathesis of a functionalized alkane.

The fifth chapter details the strategy of utilizing the bimetallic catalysts based on supported late

(Ir and Ru) and early (W and Ti) transition metal complexes, as well as a combination of late and early (Ru and Ti). All the systems were thoroughly characterized by FTIR and SS-NMR techniques and showed remarkable activity in the metathesis of alkanes.

The sixth chapter provides conclusions and future outlook.

ACKNOWLEDGMENTS

I would like to sincerely thank everyone who contributed to the work presented in this dissertation. Exceptional thanks go to my supervisor, Professor Jean-Marie Basset. I am extremely honored to be his Ph.D. student and to work in his lab. My Ph.D. has been a very challenging and fantastic experience, and I thank Professor Basset not only for his tremendous academic support but also for giving me so many excellent opportunities to learn and to grow professionally. I thank him for the most challenging research project of my entire chemistry career and for the freedom he gave me to fight against the challenges. I thank him for his guidance and for our long discussions which sparked lots of new ideas and bright thoughts. I will forever remember these moments.

Most enormous gratitude goes to Dr. Manoja Samantaray, who taught me many techniques of surface organometallic chemistry, fruitfully discussed results, improved my scientific writing skills, and taught me to stay motivated during very challenging periods. Special thanks go to my committee members Professor Kuo-Wei Huang, Professor Osman Bakr, Professor Pascal Saikaly, and Professor Didier Astruc.

I want to thank many other people who significantly contributed to my work, Dr. Yury Lebedev for his excellent contribution to our work with ferrocenes, silicon compounds and metathesis of carbazole, Dr. Hicham Idriss and Dr. Shahid Bashir from SABIC for giving me an opportunity to work on an in-situ IR MS instrument and significant intellectual contribution to the work, Prof.

Valentin Rodionov for collaboration in metathesis catalysts on modified hydrophobic supports,

Aya Saidi for our collaboration in hydro-metathesis projects and WMe6 preparations, Dr. Sanjay Lolage for his contribution and help with preparation of bimetallic metathesis-dehydrogenation catalysts, and Dr. Youssef Saih and Dr. Jullian Vittenet for their wonderful training on dynamic flow PID reactors. I thank Dr. Abdelhamid Emwas and Dr. Edy Abou-Hamad for their contribution in many solid-state NMR experiments, and Dr. Anissa Bendjeriou Sedjerari for her guidance and discussions of silica synthesis, Dr. Sergei Lopatin for TEM characterizations and KAUST Core Lab.

Finally, exceptional thanks goes to my wife Elena, and my parents Alina and Sergii for their support and patience while I was doing my Ph.D.

Table of Contents EXAMINATION COMMITTEE PAGE ...... 2 ABSTRACT ...... 4 ACKNOWLEDGMENTS ...... 6 Table of Contents ...... 8 LIST OF ABBREVIATIONS ...... 15 LIST OF FIGURES ...... 18 LIST OF SCHEMES ...... 26 LIST OF TABLES ...... 29 Chapter 1: Bibliography ...... 30 1. Introduction ...... 31 1.1. Introduction to catalysis ...... 31 1.1.1 Homogeneous catalysis ...... 32 1.1.2 Heterogeneous catalysis ...... 33 1.1.3 Advantages and disadvantages of homogeneous and heterogeneous catalysis ...... 34 1.1.4 Surface organometallic chemistry (SOMC) – combining advantages of homogeneous and heterogeneous catalysis ...... 35 1.2. Catalyst Supports ...... 36 1.2.1 Silica ...... 37 1.2.2 Alumina ...... 39 1.2.3 Silica-alumina ...... 41 1.2.4 Other supports ...... 42 1.3. Grafting of metal complexes ...... 43 1.4. Single-site approach ...... 45 1.5. Surface organometallic fragments (SOMF) ...... 46 1.6. The predictive approach of heterogeneous catalysis and catalysis by design ...... 47 1.7. Application of SOMC in catalysis ...... 49 1.7.1 Olefin metathesis ...... 49 1.7.2 Alkane metathesis ...... 50 1.7.3 Olefin hydro-metathesis ...... 52 1.7.4 Imine metathesis ...... 53 1.7.5 Polymerization ...... 54 1.7.6 Alkyne cyclotrimerization ...... 55 1.7.7 Ethylene oligomerization ...... 55

1.7.8 Utilization of CO2 ...... 56 1.8. Metathesis method ...... 57 1.8.1 Discovery of metathesis ...... 59 1.8.2 Metathesis of unsaturated hydrocarbons (olefins and alkynes) ...... 60 1.8.2.1 A general overview ...... 60 1.8.2.2 Mechanistic outlook ...... 64 1.8.3 The development of the functionally tolerant olefin metathesis catalysts ...... 69 1.8.4 SOMC and metathesis of saturated hydrocarbons (alkanes) ...... 74 1.8.4.1 1st generation alkane metathesis catalysts ...... 75 1.8.4.2 2nd generation alkane metathesis catalysts ...... 78 1.8.4.3 3rd generation alkane metathesis catalysts ...... 82 1.8.5 The challenge of functionalized alkane metathesis ...... 84 1.9. References ...... 85 Chapter 2. Understanding the challenge of the metathesis of functionalized alkanes ...... 99 2.1. Introduction ...... 100

2.2. Preparation of silica-supported pentamethyl tungsten [≡Si-O-W(Me)5] ...... 102

2.3. [≡Si-O-W(Me)5] decomposition study ...... 103

2.3.1 Thermal decomposition of [(≡Si-O-)W(Me)5] study by in-situ IR-MS ...... 104

2.3.2 Direct observation of [(≡Si-O-)W(Me)5] decomposition by strongly coordination substrates using solid-state NMR ...... 115

2.3.3 [(≡Si-O-)W(Me)5] poisoning study by ester using in-situ IR-MS ...... 119

2.4. Interaction of [(≡Si-O-)W(Me)5] with Ferrocenes ...... 124 2.4.1 Reaction with n-Butyl-Ferrocene ...... 124 2.4.2 Reaction with trimethylsilyl-ferrocene and tert-butyl-ferrocene ...... 127 2.4.3 Reactions with other Ferrocene-based substrates ...... 128 2.5. Interaction of catalyst with Silicon-based substrates ...... 128 2.5.1 Interaction with siloxanes ...... 129 2.5.2 Interaction with silanes ...... 130

2.5.3 Study of interaction of [≡Si-O-W(Me)5] with triphenyloctyl-silane by in-situ IR-MS . 132 2.5.4 Deactivating of n-butyl-benzene metathesis in the presence of (4- butylphenyl)triisopropyl-silane...... 133 2.6. Conclusions ...... 135 2.7. Experimental section ...... 136 2.8. References ...... 153

Chapter 3. Preparation of WMe5 on modified hydrophobic supports ...... 156 3.1. Introduction ...... 157 3.1.1 Fluorocarbon versus hydrocarbon alkyl chains ...... 158 3.1.2. Applications of the CH- and CF- modified surfaces ...... 159 3.1.2.1. Alkyl and fluoroalkyl modification for the preparation of hydrophobic surfaces .. 159

3.1.2.1.1. Hydrophobic modification of SiO2 surface by aminosilane derivatives ...... 160

3.1.2.1.2. Environmentally benign and durable superhydrophobic coatings based on SiO2 nanoparticles and silanes ...... 160 3.1.2.1.3. Formation of superhydrophobic surfaces by cysteamine-catalyzed co- silicification of (1H,1H,2H,2H-Perfluorooctyl)triethoxysilane (FTES) and tetraethylorthosilicate (TEOS) ...... 161 3.1.2.2. CH- and CF- surface modification for the preparation of polymer semiconductors ...... 162 3.1.2.3 Utilization of hydrophobically modified supports in catalysis ...... 163 3.1.2.3.1 Fluorinated catalyst support in ethylene polymerization ...... 163 3.1.2.3.2 Fluorinated alumina and silica supports in the alkylation of isobutane with olefins ...... 164 3.1.2.3.3 Fluorinated silica catalyst for the preparation of aliphatic/aromatic nitriles .. 165 3.1.2.3.4 Fluorous biphasic catalysis in application to Pd-mediated Suzuki and Sonogashira couplings ...... 166 3.1.2.3.5 A Multifunctional Mesoporous Silica Catalyst for Shifting the Reaction Equilibrium by Removal of Byproduct ...... 167 3.1.2.3.6 Catalytic application of fluorous silica gel in Fries rearrangement ...... 168 3.2. Results and Discussion ...... 170

3.2.1 Modification of SiO2-500 by triethoxyoctylsilane (CH-SiO2-500) ...... 170

3.2.2 Grafting of WMe6 on modified CH-SiO2-500 ...... 176

3.2.3 Modification of SiO2-500 by triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane ...... 181

3.2.4 Grafting of WMe6 on modified CF-SiO2-500 ...... 185

3.2.5 Application of W(CH3)5/CH-SiO2-500 and W(CH3)5/CF-SiO2-500 in catalysis ...... 188 3.2.5.1 Metathesis of n-decene (olefin) ...... 188 3.2.5.2 Metathesis of n-decane (alkane) ...... 189 3.2.5.3 Metathesis of functionalized olefin and alkane ...... 190 3.2.6 Choice of KCC-1 support ...... 190

3.2.6.1 Modification of KCC-1-500 by triethoxy-octylsilane and triethoxy(1H,1H,2H,2H- perfluoro-octyl)silane ...... 191 3.2.6.2 Catalytic applications ...... 196 3.3. Conclusions ...... 198 3.4. Experimental section ...... 199 3.5. References ...... 204 Chapter 4. Metathesis of functionalized alkane. Understanding the unsolved story ...... 207 4.1. Introduction ...... 208 4.2. Results and Discussion ...... 209 4.2.1 Interaction of catalyst with the pyrrole-based family of substrates ...... 209 4.2.2 Metathesis of N-Hexyl-Carbazole ...... 213 4.2.3 Mechanism of the reaction ...... 215 4.3. Conclusions ...... 217 4.4. Experimental Section ...... 218 4.4.1 General remarks ...... 218 4.4.2 Experimental Procedures and Spectroscopic Data ...... 221 4.4.2.1 Synthesis of N-Hexyl-Pyrrole ...... 221 4.4.2.2 Synthesis of N-Hexyl-2,5-dimethyl-pyrrole 2, N-Propyl-2,5-dimethyl-pyrrole 3 and N- Allyl-2,5-dimethyl-pyrrole 4 ...... 221 4.4.2.3 Separation of 1,4-bis(2,5-dimethyl-1-H-pyrrole-1yl)but-2-ene ...... 226

4.4.2.4 Synthesis of 9-hexyl-9H-carbazole 5 ...... 227

4.4.2.5 Synthesis of 9-HEXYL-9H-CARBAZOLE metathesis products ...... 230

4.4.2.6 Synthesis and analysis of 1,10-di-(9H-Carbazole-9yl-)-decane (C34H37N2) ...... 230 4.4.3 Catalytic reactions ...... 232 4.5. References ...... 233 Chapter 5. Exploiting supported bimetallic dehydrogenation-metathesis catalysts based on early and late transition metal complexes ...... 235 5.1. Introduction ...... 236 5.2. Results and Discussion ...... 240 5.2.1 Preparation of heterogeneous metathesis/dehydrogenation catalysts based on late transition metals ...... 240 5.2.1.1 Synthesis and characterization of silica-supported Grubbs-Hoveyda 2nd generation catalyst ...... 240 5.2.1.2 Synthesis and characterization of silica-supported Iridium pincer catalyst ...... 244 5.2.1.3 Synthesis and characterization of silica-supported bimetallic Ru-Ir-based metathesis-dehydrogenation catalyst ...... 245 5.2.1.4 Investigation of catalytic activity of heterogeneous metathesis/dehydrogenation catalysts based on late transition metals ...... 248 5.2.2 Preparation of heterogeneous metathesis/dehydrogenation catalysts based on late and early transition metals ...... 252 5.2.2.1 Synthesis and characterization of Ti-Ru-based metathesis-dehydrogenation catalyst ...... 252 5.2.2.2 Investigation of catalytic activity of Ti-Ru-based metathesis-dehydrogenation catalyst ...... 255 5.2.3 Preparation of heterogeneous metathesis/dehydrogenation catalysts based on early transition metals ...... 257 5.2.3.1 Bimetallic W-Ti-based catalytic system supported on Yolk-Shell Silica ...... 257 5.2.3.1.1 Introducing Yolk-Shell silica ...... 257 5.2.3.1.2 Preparation of suitable yolk-shell silica ...... 259 5.2.3.1.3 Grafting of WMe6 on Yolk-Shell silica and investigation its catalytic activity .. 260 5.2.3.1.3 Preparation of bimetallic W-Ti-based catalytic system on Yolk-Shell silica and investigation its catalytic activity ...... 261 5.2.3.2 Bimetallic W-Ti-based catalytic system supported on KCC-1 ...... 263 5.2.3.2.1 The choice of KCC-1 silica ...... 263 5.2.3.2.2 Preparation of suitable KCC-1 silica ...... 264

5.2.3.2.3 Grafting of WMe6 on KCC-1 silica and investigation its catalytic activity ...... 264 5.2.3.2.4 Preparation of bimetallic W-Ti-based catalytic system on KCC-1 silica and investigation its catalytic activity ...... 266 5.3. Conclusions ...... 267 5.4. Experimental Section ...... 268 5.5. References ...... 281 Chapter 6. Conclusions and outlooks ...... 284 6.1. Achievements ...... 285 6.2. Future outlook ...... 288 APPENDICES ...... 289 Appendix A. Effect of support on hydro-metathesis of propene: A comparative study of

W(CH3)6 anchored to silica vs. silica-alumina ...... 290 1. Introduction ...... 290 2. Results and Discussion ...... 292 2.1. Evolution of hydro-metathesis reaction...... 292 2.2. Mechanistic outlook ...... 297 2.3. Conclusions ...... 298 3. Experimental part ...... 299 3.1. General ...... 299 3.2. GC Analysis ...... 300 3.3. GC-MS Analysis ...... 300 3.4. Hydro-metathesis reaction ...... 300 3.4.1 Reaction A (Silica-supported catalyst, 1:1 ratio of reactants) ...... 300 3.4.2 Reaction B (Silica-supported catalyst, 1:2 ratio of reactants) ...... 301 3.4.3 Reactions C and D (Silica-Alumina-supported catalyst) ...... 301 3.4.4 Reactions with 1:3 ratio of reactants ...... 301 4. References ...... 306 Appendix B. Polymerization of ethylene catalyzed by Ziegler-Natta catalysts. Comparison of homogeneous vs supported catalysts on KCC1-500 and SiO2-500 ...... 308 1. A general procedure for the polymerization...... 309 2. Purification of polyethylene ...... 310 3. Characterization of the PEs obtained ...... 312

LIST OF ABBREVIATIONS Abbreviation / Definition

Ar / Aromatic

BET / Brunauer, Emmett, Teller

CP/MAS / Cross Polarization/ Magic Angle Spinning

DCM / Dichloromethane

DSC / Differential Scanning Calorimetry eq. / equivalent

Et / Ethyl

EtOAc / Ethyl acetate

EXAFS / Extended X-Ray Absorption Fine Structure

FT-IR / Fourier-transform infrared spectroscopy

GC / Gas Chromatography

GC-MS / Gas Chromatography mass spectrometry h / hour(s)

ICP-OES/ Inductively coupled plasma optical emission spectroscopy

IR / Infra-Red

KCC-1 / KAUST Catalysis Center Silica Nanospheres with a Fibrous Morphology

Me / Methyl mg / milligram(s)

MHz / megahertz min / minute(s) mL / milliliter(s) mmol / millimole(s) mol / mole(s)

Mw / molecular weight

NMR / Nuclear Magnetic Resonance

Np / Neopentyl (-CH2C(CH3)3)

PE / polyethylene

Ph / Phenyl ppm / part per million

RT / Room temperature

SBA / Santa Barbara Amorphous

SOMC / Surface Organometallic Chemistry tBu / tertbutyl

T / Temperature

TEM / Transmission Electronic Microscopy

TEOS / TetraEthylOrthoSilicate

THF / Tetrahydrofurane

TOF / Turn over frequency

TON / Turn over number

LIST OF SYMBOLS

° degree δ chemical shift

≡ triple bond

ν IR vibrational frequency

LIST OF FIGURES

Figure 1.1: Energy diagram representing the catalytic effect on a hypothetical chemical reaction A + B  C. Black – activation energy of a non-catalytic reaction, Red – activation energy of a catalytic reaction ...... 32 Figure 1.2: General illustration of the surface organometallic fragment design ...... 36 Figure 1.3: SEM image of silica particles (350 nm)73 ...... 37 Figure 1.4: Surface silanols and siloxane bridges on the silica surface ...... 38 o 103 Figure 1.5: SEM fracture surface of Al2O3 heated at 1050 C for 2 hours ...... 40 Figure 1.6: Structure of Brønsted acid sites; A – with bridging OH group; B – with silanol in the vicinity of Al106 ...... 41 Figure 1.7: SEM micrograph of the fractured surface of the silica-alumina sample (SAPO) with hierarchical pore structure119 ...... 42 Figure 1.8: Surface organometallic fragments (SOMF) evidenced by surface organometallic chemistry (SOMC) ...... 47 Figure 1.9: Schematic representation of hydro-metathesis of propene over silica-alumina- supported WMe5 ...... 53 Figure 1.10: Various types of olefin metathesis reactions ...... 61 209 Figure 1.11: RCM reactions initiated by Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2]2 ...... 70 Figure 1.12: First-generation Grubbs catalyst (D) and second-generation Grubbs catalyst (E) ... 73

Figure 2.1: A – Mass Spectrum of CH4 (electron ionization), B – Mass Spectrum of C2H6 (electron ionization) ...... 105

Figure 2.2: Evolution of methane during the decomposition of [(≡Si-O-)W(Me)5] (3 weight %) by temperature-programmed desorption (TPD). TPD rate 10 °C/min, T range 30-330 °C ...... 105

Figure 2.3: A1 - 16/15 molecular ion ratio in release of CH4 during TPD of [(≡Si-O-)W(Me)5] (1 wt

%), A2 - 16/15 molecular ion ratio in release of CH4 during TPD of [≡Si-O-W(Me)5] (3 wt %), B1 -

16/14 molecular ion ratio in release of CH4 during TPD of [(≡Si-O-)W(Me)5] (1 wt %), B2 - 16/14 molecular ion ratio in release of CH4 during TPD of [(≡Si-O-)W(Me)5] (3 wt %) ...... 106

Figure 2.4: Comparison of CH4 release peak of 1 wt % (blue) and 3 wt % (red) of [(≡Si-O-

)W(Me)5]. TPD rate 10 °C/min, Temperature range 30-330 °C ...... 107 Figure 2.5: Graphical representation of zero-order desorption kinetics ...... 108 Figure 2.6: Graphical representation of first order desorption kinetics ...... 109 Figure 2.7: Graphical representation of second-order desorption kinetics ...... 110

Figure 2.8: FTIR comparison of [(≡Si-O-)W(Me)5] (1 wt %) during the TPD at different temperatures. TPD rate 10 °C/min, T range RT - 300 °C ...... 112

Figure 2.9: FTIR of the [(≡Si-O-)W(Me)5] 1 wt % W (left) and 3 wt % W (right) before and after TPD ...... 113

Figure 2.10: FTIR of the [(≡Si-O-)W(Me)5] 1% and 3 % before and after TPD ...... 113 Figure 2.11: Calibration of methane. GC area as a function of pressure ...... 114 Figure 2.12: Ethyl caprylate (5) and 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol (6) ...... 116

Figure 2.13: Solid-state MAS NMR of [(≡Si-O-)W(Me)5] after interaction with ethyl caprylate 5. A) 1H NMR, B) 13C NMR, C) 1H-13C correlation NMR ...... 116

Figure 2.14: [(≡Si-O-)W(Me)5] after interaction with 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol 6. A) 1H NMR, B) 13C NMR, C) 1H-13C correlation NMR ...... 117

Figure 2.15: FTIR of [≡Si-O-W(Me)5] before (red) and after (blue) adsorption of ethyl caprylate ...... 119

Figure 2.16: FTIR of SiO2-700 before (red) and after (blue) adsorption of ethyl caprylate ...... 120

Figure 2.17: FTIR comparison of the ester 5 adsorbed on SiO2-700 and [(≡Si-O-)W(Me)5]. Red – ester adsorbed on SiO2-700 before TPD. Blue – ester adsorbed on [(≡Si-O-)W(Me)5] before TPD.

Yellow – Ester adsorbed on SiO2-700 after TPD. Green – ester adsorbed on [(≡Si-O-)W(Me)5] after TPD ...... 121

Figure 2.18: FTIR comparison of Ester desorption from SiO2-700 at different temperatures...... 122

Figure 2.19: FTIR comparison of ester desorption from [(≡Si-O-)W(Me)5] at different temperatures ...... 123

Figure 2.20: W(CH3)5/SiO2 decomposition. [(≡Si-O-)W(Me)5] (1 wt %) (Red and Yellow) vs.

[(≡Si-O-)W(Me)5] (1 wt %) treated with ester (Blue and Green) ...... 123 Figure 2.21: 16 - methylene-bisferrocene, 17 - benzyl-ferrocene, 18 - benzoyl-ferrocene, 19 – methylenedimethylamino-ferrocene ...... 128 Figure 2.22: Tert-butyl(cyclooctyl-oxy)dimethylsilane 20, (cyclooctyl-oxy)triisopropylsilane 21 and tert-butyl(hexyloxy)diphenylsilane 22 ...... 129 Figure 2.23: (4-butylphenyl)triisopropyl-silane 23, Octyltriphenylsilane 24 and (4- butylphenyl)triphenylsilane 25 ...... 131

Figure 2.24: Decomposition of [(≡Si-O-)W(Me)5] perturbed by triphenyloctylsilane 24 ...... 133 Figure 2.25: Product distribution in the metathesis of butylbenzene ( – linear alkylbenzenes, – dimers) ...... 134 1 Figure 2.26: H NMR spectrum of WMe6 in CD2Cl2 at 203 K ...... 138 13 Figure 2.27: C NMR spectrum of WMe6 in CD2Cl2 at 203 K ...... 139 Figure 2.28: 2D solution 1H-13C Heteronuclear Single Quantum Correlation (HSQC) NMR spectrum of WMe6 in CD2Cl2 at 203 K ...... 139 1 Figure 2.29: Solid-state NMR spectra of [(≡Si-O-)W(CH3)5] 1. (A) One-dimensional (1D) H MAS solid-state NMR spectrum of 2 acquired at 600 MHz (14.1 T) with a 22 kHz MAS frequency, a repetition delay of 5 s, and 8 scans. (B) Two-dimensional (2D) 1H−1H double-quantum (DQ)/single-quantum (SQ) and (C) 1H−1H triple-quantum (TQ)/SQ NMR spectra of 2 (both acquired with 32 scans per t1 increment, 5 s repetition delay, 32 individual t1 increments). (D) 13 1 C CP/MAS NMR spectrum of 2 acquired at 9.4 T (v0( H) = 400 MHz) with a 10 kHz MAS frequency, 1000 scans, a 4 s repetition delay, and a 2 ms contact time. An exponential line broadening of 80 Hz was applied prior to Fourier transformation. (E) 2D 1H−13C CP/MAS dipolar

HETCOR spectrum of 2 (acquired at 9.4 T with an 8.5 kHz MAS frequency, 2000 scans per t1 increment, A 4 s repetition delay, 64 individual t1 increments, and a 0.2 ms contact time) ..... 140

Figure 2.30: FT-IR spectroscopy of silica partially dehydroxylated at 700 °C and W(CH3)6 grafted on SiO2-700 (1) ...... 141

Figure 2.31: FTIR spectroscopy of [(≡Si-O-)W(Me)5] 1 (1 eq) exposed to ethyl caprylate 5 (4 eq) ...... 141 1 Figure 2.32: H NMR spectrum of Butylferrocene 7 in C6D6 at RT ...... 142 13 Figure 2.33: C NMR spectrum of Butylferrocene 7 in C6D6 at RT ...... 142 1 Figure 2.34: H NMR spectrum of the reaction mixture (Scheme 2.3) in C6D6 at RT ...... 143 13 Figure 2.35: C NMR spectrum of the reaction mixture (Scheme 2.3) in C6D6 at RT ...... 143 Figure 2.36: GC chromatogram of the reaction mixture (Scheme 2.3) in DCM at RT ...... 144 1 Figure 2.37: H NMR spectrum of siloxane 20 in CDCl3 at RT ...... 144 13 Figure 2.38: C NMR spectrum of siloxane 20 in CDCl3 at RT ...... 145 1 Figure 2.39: H NMR spectrum of siloxane 21 in CDCl3 at RT ...... 145 13 Figure 2.40: C NMR spectrum of siloxane 21 in CDCl3 at RT ...... 146 1 Figure 2.41: H NMR spectrum of siloxane 22 in CDCl3 at RT ...... 146 13 Figure 2.42: C NMR spectrum of siloxane 22 in CDCl3 at RT ...... 147 1 Figure 2.43: H NMR spectrum of silane 23 in CDCl3 at RT ...... 147 13 Figure 2.44: C NMR spectrum of silane 23 in CDCl3 at RT ...... 148 1 Figure 2.45: H NMR spectrum of silane 24 in CDCl3 at RT ...... 148 13 Figure 2.46: C NMR spectrum of silane 24 in CDCl3 at RT ...... 149 1 Figure 2.47: H NMR spectrum of silane 25 in CDCl3 at RT ...... 149 13 Figure 2.48: C NMR spectrum of silane 25 in CDCl3 at RT ...... 150 1 Figure 2.49: H solid-state NMR spectrum of [(≡Si-O-)W(Me)5] 1 recovered after the reaction with n-butylferrocene ...... 150 13 Figure 2.50: C solid-state NMR spectrum of [(≡Si-O-)W(Me)5] 1 recovered after the reaction with n-butylferrocene ...... 151 1 13 Figure 2.51: H- C correlation solid-state NMR spectrum of [(≡Si-O-)W(Me)5] 1 recovered after the reaction with n-butylferrocene ...... 151

Figure 2.52: Comparison of ester fragments release from SiO2-700 (E) and from [(≡Si-O-)W(Me)5] 1 (W-E) by fragmentation during TPD ...... 152 Figure 3.1: A hydrophobicity scale. F-carbons are both more hydrophobic and lipophobic than

H-carbons, as reflected by their surface tensions ƴs and their interfacial tensions with water ƴi ...... 159 Figure 3.2: Silica modification by (n-butylamino)-1,1-dimethyl(n-octyl)silane ...... 160 Figure 3.3: a) Chemical structures of FTES and TEOS. b) Representative synthetic procedures for the co-silicification by co-condensation of FTES and TEOS. The total concentration of silica precursors was fixed at 100 mm (40 mm of FTES and 60 mm of TEOS), and the water-to-ethanol ratio was varied from 4:1 to 0.3:1 (v/v) ...... 162

Figure 3.4: Monolithic complementary-like inverter fabricated on Si/SiO2 substrate with two distinct surface regions modified with FDTS- and ODTS-SAMs ...... 163 Figure 3.5: The fluorous solid supports 1 and 2 and Palladium complexes 3 a-c...... 166 Figure 3.6: Representation of a bifunctional PFP/DAT-MSN ...... 168 Figure 3.7: Proposed mechanism for surface interaction of FSG with reactant ...... 170

Figure 3.8: FTIR spectra of bare SiO2-500 (red) and modified CH-SiO2-500 (blue) ...... 172 1 Figure 3.9: H solid-state NMR of CH-SiO2-500 ...... 173 13 Figure 3.10: C cross-polarization magic angle spinning (CP/MAS) NMR spectrum of CH-SiO2-500 ...... 173 1 1 Figure 3.11: 2D single quantum H− H homonuclear dipolar correlation spectrum of CH-SiO2-500 ...... 174 1 13 Figure 3.12: 2D H− C HETCOR NMR spectrum of CH-SiO2-500 ...... 175 29 Figure 3.13: Si CP/MAS NMR spectrum of CH-SiO2-500 ...... 176

Figure 3.14: The structure of CH-SiO2-500 support ...... 176 1 Figure 3.15: Solid-state H MAS NMR spectrum of WMe6 grafted on CH-SiO2-500 ...... 178 13 Figure 3.16: C cross-polarization magic angle spinning (CP/MAS) NMR spectrum of WMe6 grafted on CH-SiO2-500 ...... 179 1 1 Figure 3.17: 2D double quantum H− H homonuclear dipolar correlation spectrum of WMe6 grafted on CH-SiO2-500 ...... 179 1 13 Figure 3.18: 2D H− C HETCOR NMR spectrum of WMe6 grafted on CH-SiO2-500 ...... 180

Figure 3.19: FTIR spectra of bare SiO2-500 (red) and CF-modified SiO2-500 (blue) ...... 182 1 Figure 3.20: Solid-state H MAS NMR spectrum of CF-SiO2-500 ...... 183 13 Figure 3.21: C cross-polarization magic angle spinning (CP/MAS) NMR spectrum of CF-SiO2-500 ...... 183 1 1 Figure 3.22: 2D double quantum H− H homonuclear dipolar correlation spectrum of CF-SiO2-500 ...... 183 29 Figure 3.23: Si CP/MAS NMR spectrum of CF-SiO2-500 ...... 184

Figure 3.24: The structure of CF-SiO2-500 support ...... 185 1 Figure 3.25: H MAS NMR spectrum of WMe5/CF-SiO2-500 ...... 186 13 Figure 3.26: C cross polarization magic angle spinning (CP/MAS) NMR spectrum of WMe5/CF-

SiO2-500 ...... 187 1 1 Figure 3.27: 2D DQ H− H homonuclear dipolar correlation spectrum of W(CH3)5/CF-SiO2-500. 187 Figure 3.28: 5-hexenyl-acetate ...... 190 1 Figure 3.29: H MAS NMR spectra of KCC-1 supported WMe5/CH55 (left), and SiO2 supported

WMe5/CH-SiO2-500 (right)...... 193 13 Figure 3.30: C CP MAS NMR spectra of KCC-1 supported WMe5/CH55 (left) and SiO2 supported

WMe5/CH-SiO2-500 (right)...... 193 29 Figure 3.31: Si MAS NMR spectra of KCC-1 supported WMe5/CH55 (left) and SiO2 supported

WMe5/CH-SiO2-500 (right)...... 194

Figure 3.32: The structure of KCC-1 supported WMe5/CH55 ...... 195 Figure 3.33: A) Scanning transmission electron microscopy, high angle annular dark field (STEM

HAADF) image of WMe5/CH-55. B) High resolution scanning transmission electron microscopy, high angle annular dark field (HR STEM HAADF) image of WMe5/CH-55 ...... 195 1 Figure 3.34: H NMR spectrum of triethoxyoctylsilane (CDCl3) ...... 201 13 Figure 3.35: C NMR spectrum of triethoxyoctylsilane (CDCl3) ...... 201 1 Figure 3.36: H NMR spectrum of triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane (CDCl3) ...... 202 13 Figure 3.37: C NMR spectrum of triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane (CDCl3) ...... 202

Figure 3.38: FTIR spectrum of W(CH3)5/CH-SiO2-500 ...... 203

Figure 3.39: FTIR spectrum of W(CH3)5/CF-SiO2-500 ...... 203

Figure 4.1: Well-defined silica-supported [(≡Si−O−)W(CH3)5] 1 ...... 210 1 Figure 4.2: Exposed [(≡Si−O−)W(CH3)5] to pyrrole 2. A – H MAS solid-state NMR spectrum; B – 13C CP MAS solid-state NMR spectrum; C – 1H-13C MAS correlation solid-state NMR spectrum ...... 211 Figure 4.3: Metathesis of 1-Allyl-2,5-dimethyl-1H-pyrrole, conversion versus time plot. Reaction at RT, Reaction at 150 °C ...... 212 Figure 4.4: Product distribution: functionalized alkane metathesis products, alkane metathesis products and carbazole after 30 days of reaction ...... 214 Figure 4.5: Functionalized alkane metathesis products over time ...... 214 Figure 4.6: Proposed mechanism for functionalized alkane metathesis reaction ...... 216 Figure 4.7: Gradient elution program (Time vs Volume plot) ...... 220 1 Figure 4.8: H NMR spectrum of N-Hexyl-2,5-dimethyl-pyrrole 2 in C6D6 ...... 222 13 Figure 4.9: C NMR spectrum of N-Hexyl-2,5-dimethyl-pyrrole 2 in C6D6 ...... 222 1 Figure 4.10: H NMR spectrum of N-Propyl-2,5-dimethyl-pyrrole 3 in C6D6 ...... 223 13 Figure 4.11: C NMR spectrum of N-Propyl-2,5-dimethyl-pyrrole 3 in C6D6 ...... 224 1 Figure 4.12: H NMR spectrum of N-Allyl-2,5-dimethyl-pyrrole 4 in C6D6 ...... 225 13 Figure 4.13: C NMR spectrum of N-Allyl-2,5-dimethyl-pyrrole 4 in C6D6 ...... 225 1 Figure 4.14: H NMR spectrum of 1,4-bis(2,5-dimethyl 1-H-pyrrole-1yl)but-2-ene in C6D6 ...... 226 13 Figure 4.15: C NMR spectrum of 1,4-bis(2,5-dimethyl 1-H-pyrrole-1yl)but-2-ene in C6D6 ...... 227 1 Figure 4.16: H NMR spectrum of 9-hexyl-9H-carbazole 5 in C6D6 ...... 229 13 Figure 4.17: C NMR spectrum of 9-hexyl-9H-carbazole 5 in C6D6 ...... 229 1 Figure 4.18: H NMR spectrum of 1,10-di(9H-Carbazole-9yl-)decane in C6D6 ...... 231 13 Figure 4.19: C NMR spectrum of 1,10-di(9H-Carbazole-9yl-)decane in C6D6 ...... 231 Figure 4.20: Comparison of the reference 1,10-di-(9H-Carbazole-9yl-)-decane (C34H37N2) with the dimer found in 9-hexyl-9H-carbazole metathesis reaction mixture ...... 232 Figure 5.1: Dehydrogenation catalysts 3 and 4 and Schrock-type metathesis catalyst 5 ...... 239 1 Figure 5.2: H solid-state MAS NMR spectrum of Ru/SiO2-700 (Ru) catalyst. A – Full range spectrum. B – magnified spectrum with a visible Ru=CH carbene proton ...... 242 13 Figure 5.3: C CP/MAS NMR spectrum of Ru/SiO2-700 (Ru) ...... 242 13 1 Figure 5.4: C- H HETCOR correlation of Ru/SiO2-700 (Ru) ...... 243 29 Figure 5.5: Si CP/MAS NMR spectrum of Ru/SiO2-700 (Ru) ...... 244 Figure 5.6: Structure of iridium pincer complex 13 ...... 245 Figure 5.7: 1H MAS NMR spectrum of Ir-Ru ...... 246 Figure 5.8: 13C CP/MAS NMR spectrum of Ir-Ru ...... 247 Figure 5.9: 1H-13C correlation NMR spectrum of Ir-Ru ...... 248 Figure 5.10: Product distribution in metathesis of n-decane catalyzed by Ir-Ru ...... 251 Figure 5.11: Substrates for metathesis of functionalized alkanes used with Ir-Ru catalyst...... 252 Figure 5.12: 1H MAS solid-state NMR spectrum of Ti-Ru catalyst (A – full range spectrum, B – magnified spectrum) ...... 253 Figure 5.13: 13C CP/MAS solid-state NMR spectrum of Ti-Ru catalyst ...... 254 Figure 5.14: 1H-13C 2D HETCOR correlation solid-state NMR spectrum of Ti-Ru catalyst ...... 255 Figure 5.15: Product distribution comparison in metathesis of n-decane catalyzed by Ir-Ru and

Ti-Ru bimetallic systems supported on SiO2-700 ...... 256 Figure 5.16: Graphical representation of RCM of DEDAM on yolk-shell encapsulated metathesis catalyst ...... 258

Figure 5.17: The Ortep plot of WMe6 ...... 259 Figure 5.18: Left – TEM image of yolk-shell silica (current work), Right - TEM image of yolk-shell silica (reported work39) ...... 260

Figure 5.19: Product distribution in the metathesis of n-decane catalyzed by WMe5/YS-200 .... 261

Figure 5.20: Schematic representation of -WMe5 and -TiNp3 system supported on yolk-shell silica ...... 262

Figure 5.21: Product distribution comparison in metathesis of n-decane catalyzed by WMe5/YS-

200 and WMe5-TiNp3/YS-200 ...... 263 Figure 5.22: KCC-1 support with 3.7 nm pore size ...... 264

Figure 5.23: Product distribution in the metathesis of n-decane catalyzed by WMe5/KCC-1-700 ...... 265 Figure 5.24: Product distribution comparison in metathesis of n-decane catalyzed by

WMe5/KCC-1-700 and WMe5-TiNp3/KCC-1-700 ...... 267

Figure 5.25: FTIR spectra of SiO2-700 (red); Ru/SiO2-700 (blue); Ir/SiO2-700 (yellow); Ir-Ru/SiO2-700 (green) ...... 271 Figure 5.26: FTIR spectra of SiO2-700 (red); Ru/SiO2-700 (blue); Ti/SiO2-700 (green); Ti-Ru/SiO2-700 (yellow) ...... 271 Figure 5.27: 1H NMR spectrum of 7 ...... 272 Figure 5.28: 13C NMR spectrum of 7 ...... 272 Figure 5.29: 1H NMR spectrum of 8 ...... 273 Figure 5.30: 13C NMR spectrum of 8 ...... 273 Figure 5.31: 1H NMR spectrum of 9 ...... 274 Figure 5.32: 13C NMR spectrum of 9 ...... 274 Figure 5.33: 1H NMR spectrum of 10 ...... 275 Figure 5.34: 13C NMR spectrum of 10 ...... 275 Figure 5.35: 1H NMR spectrum of 11 ...... 276 Figure 5.36: 13C NMR spectrum of 11 ...... 276 Figure 5.37: 1H NMR spectrum of 13 ...... 277 Figure 5.38: 13C NMR spectrum of 13 ...... 277 Figure 5.39: 1H MAS solid-state NMR spectrum of 14 ...... 278 Figure 5.40: 13C CP/MAS solid-state NMR spectrum of 14 ...... 278 1 Figure 5.41: H MAS solid-state NMR spectrum of WMe5-TiNp3/YS-200 ...... 279 13 Figure 5.42: C MAS solid-state NMR spectrum of WMe5-TiNp3/YS-200 ...... 279 1 Figure 5.43: H MAS solid-state NMR spectrum of WMe5-TiNp3/KCC-1-700...... 280 13 Figure 5.44: C MAS solid-state NMR spectrum of WMe5-TiNp3/KCC-1-700 ...... 280 Figure 1: Well-defined silica supported W-methyl 1 and ...... 292 Figure 2: 2A and 2C represent total conversion (Olefins + Alkanes, red line) and corresponding TON (blue line), 2B and 2D represent conversion of propene to only alkanes except propane (red line) and TON (blue line) in hydro-metathesis reaction of propene (using propene to hydrogen ratio 1:1 for 2A and 2B and 1:2 ratio for 2C and 2D) in a continuous flow reactor at 150 oC in presence of catalyst precursor 1 (106 mg), hydrogen and argon ...... 293 Figure 3: 3A and 3C represent total distribution of products [olefins, alkanes, and propane] when propene to hydrogen ratio 1:1 for 3A and 1:2 for 3C. 3B and 3D represent only alkanes except propane when propene to hydrogen 1:1 for 3B and 1:2 for 3D in a continuous flow reactor for hydro-metathesis reaction catalyzed by catalyst precursor 1 ...... 294 Figure 4: 4A and 4C represent total conversion (Olefins + Alkanes, red line) and corresponding TON (blue line), 4B and 4D represent conversion of propene to only alkanes except propane (red line) and TON (blue line) in hydro-metathesis reaction of propene (using propene to hydrogen ratio 1:1 for 4A and 4B and 1:2 ratio for 4C and 4D) in a continuous flow reactor at 150 oC in presence of catalyst precursor 2 (75 mg), hydrogen and argon ...... 295 Figure 5: 5A and 5C represent total distribution of products [olefins, alkanes, and propane when propene to hydrogen ratio 1:1 for 5A and 1:2 for 5C. 5B and 5D represent only alkanes except propane when propene to hydrogen 1:1 for 5B and 1:2 for 5D in a continuous flow reactor for hydro-metathesis reaction catalyzed by catalyst precursor 2...... 296 Figure 6: The proposed mechanism of propene hydro-metathesis using W catalyst ...... 298 Figure S1: Total conversion (red line) and corresponding turnover numbers (blue lines) were obtained during the hydro-metathesis of propene with a propene to hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon...... 302 Figure S2: Conversion (red line) and corresponding turnover numbers (blue lines) of only alkanes (except propane) were obtained during the hydro-metathesis of propene with propene to a hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon...... 303 Figure S3: Representation of total distribution of products [olefins, alkanes, and propane] when the propene to hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon...... 304 Figure S4: Distribution of products (only alkanes except for propane) was shown during the hydro-metathesis of propene with a propene to hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon...... 305

Figure B1: FT-IR of SiO2/TiMg (2, blue) compared with those of bare SiO2 (grey) ...... 310

Figure B2: FT-IR of SiO2-500/TiMg (red) compared with those of bare SiO2-500 (blue) ...... 311

Figure B3: FT-IR of KCC1-500/TiMg (red) compared with those of bare KCC1-500 (blue) ...... 311

Figure B4: Differential Scanning Calorimetry. Black – SiO2-500/PE (Crystallinity 16.94 %, Integral -

147.37 mJ, Onset 74.77 °C, Peak 109.59 °C, Endset 126.17 °C), Blue – KCC1-500/PE (Crystallinity 18.33 %, Integral -85.91 mJ, Onset 108.10 °C, Peak 123.74 °C, Endset 131.32 °C), red – Homo/PE (Crystallinity 31.02 %, Integral -268.15 mJ, Onset 116.12 °C, Peak 125.98 °C, Endset 132.51 °C) ...... 312

Figure B5: Thermogravimetric analysis of PE. During TGA, HOMO/PE, SiO2-500/PE, KCC-1-500/PE ° (16 mg of each sample) were heated at 2 C/min from 35 to 120 °C, in N2 atmosphere and was stabilized for 1 hour. After that, flow was changed to oxygen and the sample was heated to 600 °C...... 313 Figure B6: 13C solid-state NMR analysis of PE ...... 315 Figure B7: 13C liquid-state NMR analysis of PE ...... 315 Figure B8: GPC analysis of PE ...... 316 Figure B9: GPC analysis of PE (Polymerization 2) ...... 317 Figure B10: GPC analysis of PE (Polymerization 3) ...... 318

LIST OF SCHEMES

Scheme 1.1: Silica dihydroxylation process ...... 39

Scheme 1.2: Grafting of organometallic complex MLn onto the surface of partially dehydroxylated silica ...... 43

Scheme 1.3: Grafting of W(CH3)6 on SiO2-700 ...... 44 Scheme 1.4: Grafting of Zirconium tetraneopentyl (A) and Tantalum pentamethyl (B) on dehydroxylated silica ...... 44

Scheme 1.5: The grafting of WMe6 on partially dehydroxylated SiO2-200 ...... 45 Scheme 1.6: Chauvin’s Reaction Mechanism for Olefin Metathesis136 for the Self-Metathesis of Propylene to Ethylene and 2-Butene ...... 50 Scheme 1.7: Metathesis of alkanes catalyzed by silica-supported tantalum hydride ...... 51 Scheme 1.8: Formation of partially alkylated W-H and its application in the metathesis of propane ...... 51

Scheme 1.9: Metathesis of n-decane catalyzed by silica-supported WMe5 ...... 52 Scheme 1.10: Formation of ethylimido complex B ...... 54 Scheme 1.11: Imine metathesis over silica-supported ethylimido complex B...... 54 Scheme 1.12: Formation of active Ziegler-Natta polymerization catalyst ...... 54 Scheme 1.13: Trimerization of alkyne catalyzed by silica-supported W-carbyne ...... 55

Scheme 1.14: 1) Grafting of NbCl3Me2 onto SiO2-700; 2) Surface alkylation of A to produce supported NbMe4 complex B ...... 56

Scheme 1.15: Catalytic conversion of CO2 to cyclic carbonate catalyzed by Nb complexes at 60 °C and 10 bar CO2 ...... 57

Scheme 1.16: Three-step mechanism for the cycloaddition of CO2 to epoxides catalyzed by a binary system composed of a Lewis acid MLn (M: metal atom, L: ligand) and a nucleophile (Nu). The step of 31 CO2 insertion (II) might be monometallic or bimetallic...... 57 Scheme 1.17: Schematic representation of metathesis reactions ...... 58 Scheme 1.18: Alkyne metathesis reported by Mortreux ...... 62 Scheme 1.19: Early demonstration of the exceptional activity of defined alkylidyne complexes as catalysts for alkyne metathesis ...... 63 Scheme 1.20: Scaleable preparation of the tungsten alkylidyne complex ...... 64 Scheme 1.21: Linear representation of the Chauvin mechanism ...... 66 Scheme 1.22: Cyclic representation of the Chauvin metathesis mechanism ...... 67 Scheme 1.23: Experimental confirmation of Chauvin’s mechanism by Casey and Burkhardt205 68 Scheme 1.24: Accepted mechanism of alkyne metathesis195 ...... 69 Scheme 1.25: Preparation of the first well-defined Ru-carbene catalyst ...... 71 Scheme 1.26: Commercial application of RCM ...... 74 t t Scheme 1.27: The reaction between [Ta(=CHC Bu)(CH2C Bu)3] and SiO2-500 ...... 76 Scheme 1.28: Metathesis of propane pathway catalyzed by supported Ta-H catalyst ...... 77

Scheme 1.29: Preparation of silica-supported [(≡Si-O-)WMe5] and [(≡Si-O-)TaMe3] with their corresponding carbyne and carbene species ...... 79 Scheme 1.30: Evolution of [W]-Me to [W]≡CH on silica-alumina ...... 81 Scheme 1.31: General scheme for the preparation of a bimetallic catalyst system (M = Zr, Ti) . 83

Scheme 2.1: Grafting of WMe6 on silica ...... 103 Scheme 2.2: Formation of W-Methylidyne species upon the thermal transformation of 1 ...... 104

Scheme 2.3: Disproportionation of n-butylferrocene over [(≡Si-O-)W(Me)5] ...... 125

Scheme 2.4: Synproportionation of ferrocene and ethylferrocene over [(≡Si-O-)W(Me)5] ...... 127

Scheme 2.5: Disproportionation of butyl-ferrocene catalyzed by [(≡Si-O-)WCl5] ...... 127 Scheme 2.6: Disproportionation of tert-butylferrocene (E = C) and trimethylsilylferrocene (E =

Si) over [(≡Si-O-)WCl5] ...... 128 Scheme 2.7: Metathesis of butylbezene (A) and Metathesis of butylbenzene in the presence of (4-butylphenyl)triisopropyl-silane (B) ...... 135 Scheme 3.1: Suzuki reactions performed with 3 a-c immobilized on support 1 as catalysts. a)

0.001±1.5 mol % catalyst, DME, 2m aq. Na2CO3, 80 °C ...... 167 Scheme 3.2: General scheme of Fries rearrangement of aryl esters catalyzed by FSG ...... 169

Scheme 3.3: Modification of SiO2-500 with triethoxyoctylsilane...... 171

Scheme 3.4: Grafting of WMe6 onto CH-SiO2-500 ...... 177

Scheme 3.5: Modification of SiO2-500 with triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane ...... 181

Scheme 3.6: Grafting of WMe6 on CF-SiO2-500 ...... 186 Scheme 4.1: Synthesis of N-alkyl pyrroles ...... 210 Scheme 4.2: Synthesis of 9-hexyl-9H-carbazole 5 ...... 213 Scheme 4.3: No functionalized alkane metathesis product was observed using substrates 2 and 3 ...... 224

Scheme 5.1: Synthesis of supported [(≡Si−O−)W(Me)5(≡Si−O−)Ti(Np)3] 2 ...... 238 Scheme 5.2: Alkane metathesis via tandem transfer dehydrogenation–olefin metathesis illustrated with the formation and metathesis of two molecules of 1-alkene. M, active catalyst in the transfer dehydrogenation cycle [e.g., (pincer)Ir] ...... 238 Scheme 5.3: Synthetic route to homogeneous catalyst precursor 11 ...... 240

Scheme 5.4: Grafting of homogeneous catalyst 11 onto the surface of SiO2-700 ...... 241

Scheme 5.5: Grafting of Ir-bis-hydride pincer catalyst to SiO2-700 ...... 245

Scheme 5.6: Grafting of Iridium pincer complex 13 to Ru/SiO2-700 catalyst 12 ...... 246 Scheme 5.7: RCM of DEDAM catalyzed by Ru ...... 249 Scheme 5.8: Dehydrogenation of n-decane over Ir catalyst ...... 249 Scheme 5.9: RCM of DEDAM catalyzed by Ir-Ru...... 250 Scheme 5.10: Metathesis on n-decane catalyzed by supported Ir-Ru bimetallic system ...... 250

Scheme 5.11: Grafting of Titanium tetraneopentyl complex to Ru/SiO2-700 catalyst ...... 253 Scheme 5.12: Process for encapsulating Hoveyda−Grubbs 2nd generation catalyst within a yolk−shell structured silica through silylation ...... 258

Scheme 5.13: Grafting of WMe6 on Yolk-Shell silica (YS-200) ...... 260

Scheme 5.14: Grafting of TiNp4 to WMe5/YS-200 ...... 262

Scheme 5.15: Grafting of WMe6 onto KCC-1-700 silica ...... 265

Scheme 5.16: Grafting of TiNp4 to WMe5/KCC-1-700 ...... 266

LIST OF TABLES

Table 2.1: Quantification of methane by GC-FID ...... 114

Table 2.2: Disproportionation of n-Butyl-Ferrocene over [(≡Si-O-)W(Me)5] ...... 126 Table 2.3: Results on metathesis of siloxanes 20-22 ...... 130

Table 2.4: N-decane metathesis catalyzed by poisoned [(≡Si-O-)W(Me)5] ...... 132

Table 3.1: Preparation of KCC-1-700 supported WMe5 protected by 15-90 % of hydrophobic silanes ...... 192 Table 3.2: Screening of the catalysts CH(CF)15-90 in metathesis of functionalized alkanes. Conditions: 150 °C, 30 days ...... 197 Table 4.1: Gradient elution program (A: 100% Water+0.1% Formic Acid and B: 100% Methanol+0.1% Formic Acid)...... 220

Table A: PE combustion. Ti (start of polymer combustion), T50 (50% combustion of polymer), Tf (complete combustion of polymer)...... 314

Chapter 1: Bibliography

1. Introduction

Catalysis is the chemical process which allows the rate of the chemical reactions to increase by utilizing the catalyst, a substance that interacts with reactants but, in principle, does not undergo any permanent chemical change.1 The catalyst is not consumed during the chemical transformation; instead, it works continuously. Generally, catalyzed reactions occur faster than in the absence of a catalyst and require softer conditions, as they proceed by an alternative reaction pathway with lower activation energy. In such an alternative path, a catalyst forms intermediates or transition states with other substances involved in the reaction. Such intermediates and transition states usually are highly unstable and have a short lifetime, which allows for the transformation of the products and regeneration of an original catalyst that can be involved in the next catalytic cycle. With that, only a tiny amount of the catalyst (catalytic amounts) can be used in a chemical reaction.

1.1. Introduction to catalysis Nowadays, catalysis is an essential tool in chemistry and, primarily, in the chemical and petrochemical industries.2 More than 90 % of industrial chemical processes, including, but not limited to, agrochemicals, pharmaceuticals, polymers, and petrochemicals are catalytic processes.3,4 At the same time, catalysis is not only an artificial phenomenon; a variety of biocatalysts in living organisms are responsible for vital functions and are produced by nature.5

In general, three types of catalysis can be distinguished – homogeneous, heterogeneous, and biocatalysis (enzymatic catalysis). In all three classes, the presence of the catalyst opens a different reaction pathway with a lower activation energy barrier (Figure 1.1).6

Figure 1.1: Energy diagram representing the catalytic effect on a hypothetical chemical reaction A + B  C. Black – activation energy of a non-catalytic reaction, Red – activation energy of a catalytic reaction

This dissertation will cover the classes of homogeneous and heterogeneous catalyses. The focus of the work will be directed towards the surface-supported organometallic species, where the metal center is bonded with the ligands, and the support (which can act as a bulky ligand) and the combination of metal and ligands finally determine the catalytic properties of the supported catalyst. Using the tool of catalysis we will target an unsolved problem in chemistry and discover a new reaction – metathesis of functionalized alkanes.

1.1.1 Homogeneous catalysis In homogeneous catalysis, a catalyst and reactants coexist in the same phase, liquid or gaseous.7

Generally, in organic and organometallic chemistry, a catalyst with substrates (starting materials) are dissolved in a solvent. A variety of reaction conditions can be applied to promote catalyst activity and shift selectivity of a reaction. Homogeneous catalysis is one of the most useful fields of chemistry when it comes to the study of kinetics and mechanisms, molecular causes of reactivity, and of what makes reactions happen. In some particular cases, homogeneous catalysis can be associated with heterogeneous catalysis by anchoring (grafting) the catalytic species onto a solid support. Lastly, an understanding of the molecular effects in homogeneous catalysis can serve as a tool in the development of new metal and metal oxide catalysts and their supports.

1.1.2 Heterogeneous catalysis In heterogeneous catalysis8,9 substrates and a catalyst coexist in different phases. Usually, a heterogeneous catalyst is solid, and the reactants are in the liquid or gaseous phase. A hypothetical heterogeneous catalyst consists of active sites, that is, the atoms or crystal faces where the transformation of starting material to a product occurs. An active site usually represents a planar metal surface, a crystal edge with imperfect metal valence, or a complicated combination of the two, but generally they are composed of ensembles of atoms on the surface of the solid of different sizes and chemical compositions depending on the reaction (nature and size of reactants, reaction mechanism, etc.) and the catalyst structure.10 Thus, most of the surface of a heterogeneous catalyst may be catalytically inactive. Heterogeneous catalysts are

"supported," which means that the catalyst active sites may be dispersed on a second material

(support) that enhances the effectiveness or minimizes the cost. Supports help to reduce agglomeration and sintering of the small catalyst particles, providing a larger surface area; thus, catalysts have a high level of activity per gram of support. Often, the support and the catalyst are covalently bonded; however, in some cases, support can act as a catalyst by itself.

Chemical and petrochemical industries mostly rely on heterogeneous catalysis,11 due to the ease of separating the products of the reaction from the catalyst and regenerating expensive materials

(Ruthenium, Gold, Rhodium, Platinium, etc.). 1.1.3 Advantages and disadvantages of homogeneous and heterogeneous catalysis The two types of catalysts exhibit different characteristics, and both can be applied depending on the particular target and nature of the chemical process. Heterogeneous catalysts show better thermal stability12 and easier catalyst recovery,13-15 but frequently exhibit poor selectivity16 due to the presence of multiple active sites, which are also more challenging to modify.17

Homogeneous catalysts possess extremely high diffusion as compared to heterogeneous, where the diffusion is limited by two different phases.18 This diffusion can affect the activity of the catalyst and conversion of a reaction. Due to the same cause, heat transfer19 is higher in homogeneous catalysis. At the same time, two phases allow for easy recycling20,21 of a catalyst, when in the case of monophasic homogeneous catalysis, the catalyst recycling is often laborious and expensive.22 This results in the creation of continuous chemical processes based on heterogeneous catalysis, and lower operating costs via the re-use of the costly materials. In general, the chemical industry23 usually prefers heterogeneous over homogeneous catalysis.24

However, another critical aspect is understanding the chemical nature of catalysis. In this regard, heterogeneous catalysis displays a non-homogeneous distribution of active sites25,26 frequently making the atomic and molecular understating of its structure extremely challenging. A homogeneous catalyst can be more easily modified and characterized, which makes the identification of catalytic reaction mechanisms easier since the active site of a homogeneous catalyst is well-defined.27 It is more complicated to define an active site of a heterogeneous catalyst,28 but most of the time the sites are different for the same particle. This results in different catalytic properties. It is also more difficult to modify a heterogeneous catalyst29 as it requires control of the particle size and the nature of the active site at the atomic level at the same time. All these varying parameters make it extremely challenging to identify reaction mechanisms in heterogeneous catalysis.30

1.1.4 Surface organometallic chemistry (SOMC) – combining advantages of homogeneous and heterogeneous catalysis Would it be possible to combine the advantages of heterogeneous and homogeneous catalysis and have a well-defined, characterized and molecularly understood catalyst which is, at the same time, thermally stable and easily recovered? The answer is yes, and herewith, the concept of surface organometallic chemistry (SOMC) will be introduced.

SOMC is a new field in catalysis that brings together the concepts of homogeneous and heterogeneous catalysis.31 The idea is based on transferring the instruments from organometallic chemistry to the surface as in the case of heterogeneous catalysis. Molecular organometallic complexes can react with a surface of metal oxides (mainly by interaction with available free –

OH groups on the oxide surface) and lead to new catalytically active materials.32-41 These materials represent surface-supported organometallic complexes (generally, transition metals with ligands) that can be fully characterized by an advanced solid-state characterization technique (NMR, FTIR, etc.). The supported (grafted) molecular-like entity act as a heterogeneous catalyst that can be easily separated from the reaction mixture, and fully structurally characterized – all of which allows for the study of the structure-activity relationships and understanding of reaction mechanisms of heterogeneous catalysis.42

The generally accepted concept behind surface organometallic chemistry is as follows: when a carbon-containing molecule reacts with a surface to form products, bonds are broken, and others are formed. During at least one step of a catalytic process in heterogeneous catalysis, “surface organometallic fragments” (SOMFs) are generated.43 With methods of surface organometallic chemistry (SOMC), SOMFs can be synthesized, and their reactivity can be studied. With this in mind, it becomes possible to transfer most concepts of molecular chemistry to design and rationalize heterogeneous catalysis. As a result, SOMC is bridging the existing gap between heterogeneous and homogeneous catalysis.44 The reactivity follows elementary steps of molecular and organometallic chemistry. To perform any catalytic reaction, a proper surface organometallic fragment should be designed and synthesized. The schematic representation of the design of SOMF is shown in Figure 1.2.43

Figure 1.2: General illustration of the surface organometallic fragment design

1.2. Catalyst Supports Support is a fundamental part of any surface organometallic complex.45 Organometallic complexes can react with, and consequently, become chemically attached (grafted) to the supports. To understand the interactions between an organometallic complex and support, the composition of the support, as well as the structure of the complex, should be established.46 This will provide understanding of how to control the reactivity and structurally determine the composition of the formed surface organometallic fragments. A variety of supports can be used for the organometallic complexes, and among the most commonly used are metal oxides (silica, alumina, silica-alumina, zeolites, mordenites, MOFs, etc.). The choice of support plays a significant role in catalysis47 and can be a primary reason for enhancing/deactivating the catalytic activity of the grafted complex and shifting reaction selectivity,48,49 increasing/decreasing conversion,50,51 affecting TONs of the catalyst and changing the properties of the grafted complex.35,52 Supports can be modified for a particular need, such as conventional, porous, and mesoporous surfaces which can be used for a wide range of applications.53-60 The most commonly used support in this dissertation will be silica; however, some other supports will be utilized.

1.2.1 Silica

Silica, also referred to as silicon dioxide or SiO2 is a colorless, white chemical compound. Silica consists of the most common elements – silicon (Si) and oxygen (O). It is also the most abundant compound in the Earth's crust, representing 59% of its total composition.61 Silica can be found in different forms – silica gel,62 fumed silica,63 quartz,64 mesoporous silica (SBA, MCM-41),65-68 etc.

Silica is neutral support with excellent thermal stability (above 1100 °C)69 which makes it widely useful for supporting organometallic complexes.70-72

Figure 1.1: SEM image of silica particles (350 nm)73 The surface of silica consists of siloxane units (Si-O-Si), which possess low reactivity, and silanol units (Si-OH), which are much more reactive and are often used as covalent grafting sites for organometallic complexes. In turn, three types of available surface silanols can be distinguished: a) isolated silanols; b) vicinal silanols; and c) geminal silanols. The illustration of siloxane units

(siloxane bridges) and available surface silanols are presented in Figure 1.4.

Figure 1.2: Surface silanols and siloxane bridges on the silica surface

The thermal treatment of silica results in dehydration (the removal of physisorbed water from the silica surface).74-76 Upon heating silica under high vacuum, hydrogen-bonded pairs of hydroxyl groups condense, and then the siloxane bridges are formed, and water is released (Scheme 1.1).77

The temperature of silica dehydroxylation controls the density and the nature of the silanols displayed on the surface. After dehydroxylation at 200 °C, the surface hydroxyl groups exist primarily as vicinal pairs. Dehydroxylation at a higher temperature (for example, 500 °C) results in further condensation, and a mixture of vicinal and isolated silanols can be identified; only isolated hydroxyl groups remain on the surface after prolong dehydroxylation of silica at 700 °C

(Scheme 1.1).

Scheme 1.1: Silica dihydroxylation process

FTIR spectroscopy allows for the identification of silanols on the surface. Isolated silanols have stretching vibration at 3745 cm-1, silanols bearing hydrogen bonds vibrate at a lower infrared frequency, down to 3200 cm-1, and geminal silanols have an IR absorption peak close to the isolated silanols, 3745-3736 cm-1. The density78 of silanols decreases with the increase of the applied temperature of dihydroxylation. For example, silica treated at 700 °C has an OH density of 0.7 OH/nm2, which corresponds to approximately 0.3 mmol OH/g of the sample.

1.2.2 Alumina

Alumina is the generic name that is given to aluminum oxide (Al2O3). Alumina most commonly occurs as aluminum (III) oxide. Alumina possesses an amphoteric compound, which means it can react with both acids and bases, such as sulfuric acid and potassium hydroxide; it acts as an acid with a base and a base with an acid, neutralizing the other and forming a salt. Compared to silica or silica-alumina, alumina is a partially ionic solid, consisting of a mixture of interconnected

79,80 tetrahedral AlO4 and AlO6 units that exist with different phases α, δ, γ, η and θ depending on the structural properties. The phase-type γ is the most studied due to its industrial importance81 as support for refining catalyst processes, including reforming82 and hydro-treatment.83 In fact, the alumina surface is very complicated compared to the silica surface. Besides its complex structure, γ -alumina presents different crystallographic facets, mainly (100), (110) and (111). As in the case of silica, the thermal treatment of alumina leads to isolated OH groups.84 Alumina has found a wide application in catalysis, catalyzing a variety of industrially important reactions.81,85-87 Utilization of alumina as a surface, in the SOMC, has been reported in the literature.88-91 Some transition metal complexes were grafted at the surface of alumina,90 such as complexes of W92-96 and Zr.97 The resulting materials were defined as active catalysts and applications were found, such as ethylene to propylene conversion98 and alkane metathesis.99 In this context, the use of alumina can enhance catalytic activity compared to silica. The largest scale application of alumina in catalysis is the Claus process for converting hydrogen sulfide waste gases into elemental sulfur in refineries.100 It is also widely applied for dehydration of alcohols to alkenes.101 At the same time, alumina serves as catalyst support for many industrial catalysts, for instance, in reforming and hydrodesulphurization processes.102

o 103 Figure 1.3: SEM fracture surface of Al2O3 heated at 1050 C for 2 hours

Alumina nanoparticles are also used as a catalysts and carriers of catalysts.104 Due to the very small diameter of the particles/fibers, alumina nanoparticles with high specific surface area and activity associated with its structural defects (the volume and size of pores, degree of crystallinity, phase composition, and composition of the surface) strongly enhance the catalytic properties, and increase the range of massive aluminum oxide as a catalyst. 1.2.3 Silica-alumina

Silica-alumina (SiO2-Al2O3) is an amorphous mixed oxide synthetically prepared and used as a catalyst or catalyst support. It has mixed properties of silica and alumina and, consequently, is a complex material. As such, it has available surface silanols as well as Brønsted acid (protic) and

Lewis acid (aprotic) sites with the coexistence of zeolite-type hydroxyl groups Si-(OH)-Al.105

Brønsted acid sites have an ionizable hydrogen atom, and Lewis acid sites are electron-accepting sites. The material contains both Al and Si atoms in the bulk as well as on the surface, where the surface is mostly dominated by the presence of surface hydroxyls in the vicinity of aluminum atoms (Figure 1.6).

Figure 1.4: Structure of Brønsted acid sites; A – with bridging OH group; B – with silanol in the vicinity of Al106

These different types of acidic sites can be distinguished by how pyridine reacts. On Lewis acid sites it forms π-complexes, and on the Brønsted sites it adsorbs as the pyridinium ion. Silica- alumina is itself an effective catalyst for various reactions.107-113 Silica-alumina is used in combination with zeolites as catalyst components in the FCC process and plays a role as a matrix.114,115 Although the main catalyst for catalytic cracking is zeolite, the activity, and the product selectivity changes depending on the properties of the matrix as well.116-118 One of the important applications of a zeolite combined with silica-alumina is catalytic cracking. It plays a significant role treating heavy oils with boiling points higher than 350 °C which have limited applications. Therefore, these heavey oils should be converted to more valuable petroleum products such as gasoline and kerosene. In the processing, the diffusion rate of these heavy fractions affects the activity and the selectivity of catalysts, and the advantage of the presence of silica-alumina is that large molecules are cracked to smaller molecules. In turn, it helps the diffusion of reactants inside catalyst particles because silica-alumina contains not only acid sites but also larger pores than a zeolite. Therefore, silica-alumina, as well as zeolite, is one of the most important components in FCC catalysts.

Figure 1.5: SEM micrograph of the fractured surface of the silica-alumina sample (SAPO) with hierarchical pore structure119 1.2.4 Other supports 120 Common support materials consist of oxides such as SiO2, Al2O3, or TiO2. These materials exhibit high specific surface areas, high porosities, and high thermal and mechanical stability and come with in a variety of pore sizes. Carbon is also widely used as a catalyst support, while zeolites are often applied in many oil-refining and petrochemical applications. In addition, polymers121 and commercially available resins122 have been used as catalyst supports for different transformations. Recently, a variety of ordered mesoporous materials (SBA, MCM, KCC-1) have been used as model supports.123 Finally, metal-organic frameworks are showing increased use as catalysts or as supports for metal (or metal oxide) nanoparticles.124 To maintain activity and for practical applications, the support requires high mechanical strength and the macroscopic bodies should be resistant to attrition if the catalyst is vigorously agitated, such as in fluid bed or slurry bed reactors. In many cases these materials are covered with a material called “formulation support” to facilitate mechanical properties and preserve diffusion limitations.

1.3. Grafting of metal complexes In SOMC in general, and under the scope of this dissertation, specifically, we will be focusing on transition metal complexes. The choice of transition metal is of primary importance as it changes the characters and properties of the catalyst, which depends on the size of the metal, its oxidation state, coordination sphere, ligands, and many other factors. Impregnation of a suitable organometallic precursor (MLn), something in liquid phase or by sublimation, onto the support

(for example, partially dehydroxylated silica surface [(≡Si-OH)] which leads to the formation of

125 grafted organometallic species, [(≡Si-O-)MLn-1]) (Scheme 1.2). Grafting occurs when it is favored thermodynamically. The quantification of the by-products released during the reaction indicates the stoichiometry of the grafting. Several characterization techniques (IR, UV, EXAFS,

SS MAS NMR, XANES, GC, and others) provide precise structural information of the grafted complexes.

Scheme 1.2: Grafting of organometallic complex MLn onto the surface of partially dehydroxylated silica

For example, group 6 metal alkyls can be grafted to a surface of SiO2-700. In the case of tungsten hexamethyl, it reacts with surface silanols with one of its methyl groups, in which case, the W-C and O-H bonds break with the release of the CH4 molecule, and a W-O bond forms, resulting in the grafting of WMe6 onto a silica surface and the formation of monopodal species (Scheme

1.3).15

Scheme 1.3: Grafting of W(CH3)6 on SiO2-700

In the same way, group 4126 and 517 metal alkyls can be grafted on dehydroxylated silica (Scheme

1.4).

Scheme 1.4: Grafting of Zirconium tetraneopentyl (A) and Tantalum pentamethyl (B) on dehydroxylated silica The ligands on the metal center (in the example above, methyl or neopentyl ligands) and the nature of the metal (d0 early transition metals in their highest oxidation states) affects the reactivity and is responsible for the application of the grafted metal in catalysis. In the case of

Group 4 metal alkyls, grafted Zr and Ti neopentyl complexes can be utilized in the dehydrogenation127 of alkanes due to their ability to activate alkanes by σ-bond metathesis (C-H bond-activation), followed by β-H-elimination and formation of an olefin and a metal-hydride.

Groups 5 (Ta) and 6 (W) grafted methyl complexes are active dehydrogenation-metathesis

11,30 catalysts. The grafting of WMe6 on partially dehydroxylated silica at 200 °C will result in the formation of mostly bipodal species (Scheme 1.5).

Scheme 1.5: The grafting of WMe6 on partially dehydroxylated SiO2-200

Bipodal species possess lower catalytic activity than monopodal systems in the metathesis of alkanes.15 When a mixture of monopodal and bipodal species is formed, the characterization and distinction between these two grafted materials represents an additional challenge.

1.4. Single-site approach Single-site catalysts are the catalysts where most, if not all, of the sites are structurally identical.

This is the best solution for understanding structure-activity relationships in heterogeneous catalysis. When the nature of catalytically active sites differ, and their number is low, their “acid strengths” or “redox properties” are not homogeneous, and the same material displays inactive sites. Within this single-site approach43 and with the right tools, the catalyst structure can be designed and well-defined to reach a molecular understanding and to develop predictable heterogeneous catalysis. This strategy is slowly becoming well-accepted by the scientific community. The single-site approach in heterogeneous catalysis is based on existing mechanistic proposals of molecular chemistry (organic and organometallic) and the rules associated with some concepts of surface sciences. A full characterization of the grafted metal centers can be carried out using tools ranging from molecular organometallic or surface chemistry. With the right choice of metal, its ligand set, and the support (as was shown in the previous section) as X or L ligands, the catalyst can be generated by grafting the organometallic precursor containing the required functional group(s) that are suitable to target a given reaction (surface organometallic fragments (SOMF)).

The selection of these SOMF is based on the elementary steps known in molecular chemistry and applied to the desired particular reaction. The coordination sphere required for any catalytic reaction involving paraffins, olefins, alkynes, or functionalized substrates can also be predicted.

Only the most complete understanding of catalytic reactions can allow for their development with the highest possible selectivity, activity, and lifetime.

1.5. Surface organometallic fragments (SOMF) Homogeneous catalytic systems are better understood regarding both their active sites

(structure) and the elementary steps involved (a mechanism) as compared to heterogeneous systems. Because catalysis fields strongly overlap with molecular and organometallic chemistry, they have benefited from the tools available for structure determination and reactivity studies of organometallic molecules. The concepts of homogeneous and heterogeneous catalysis have much in common, and when the tools of each concept overlap, scientists benefit from that overlap.128 The following is now evident and widely accepted: when a carbon-containing molecule interacts with a surface to form products, bonds are broken, and others are formed. In this way, “surface organometallic fragments” (SOMFs) are generated. Figure 1.8 provides a schematic representation of the most commonly utilized SOMF in SOMC.43

Figure 1.6: Surface organometallic fragments (SOMF) evidenced by surface organometallic chemistry (SOMC)

The critical point in this regard is that the molecular understanding of homogeneous catalysis can be transferred to surfaces and heterogeneous catalysis, taking into account the properties inherent in the surface ligand (such as the bulk, rigidity, and complexity of grafting sites). SOMC covers the rich chemistry of organometallic compounds grafted onto oxides surfaces and nanoparticles of unsupported and supported zerovalent particles.

1.6. The predictive approach of heterogeneous catalysis and catalysis by design “Predictive catalysis” or “catalysis by design” is no longer a utopic dream, but rather a rationalized target to be achieved by recent advances of heterogeneous catalysis and through the use of the conceptual tool of “surface organometallic fragments” (SOMF) to perform and understand a presumed catalytic reaction.129 One or several fragments of the molecule are chemically bonded to a metal atom which is attached to the surface (support), for example, [M]-H, [M]-R, [M]=CR2,

[M]≡CR, etc. in which [M] is a metal atom that is linked to a support by one, two or several sigma or pi bonds. Based on structural determination of surface catalytic sites, it can be understood how a ‘single’ metal atom is linked to ligands and the surface (via covalent, ionic or coordination bonds).128 The concept is a logical continuation of homogeneous catalysis but with a rigid surface as a ligand. Thanks to SOMC, the discovery of many new catalytic reactions has been achieved

(alkane and cycloalkane metathesis).43 Moreover, SOMC has improved the activity, selectivity, or the TONs of known catalysts making possible structural understanding of catalytically active sites and reaction mechanisms, that is, how bonds can be broken and formed.128 In this context, the reactivity of surface organometallic fragments and their sequence in the catalytic cycle are essential to the understanding of catalysis.

SOMC can generate a majority of identical catalytic sites (single-site or close to the single atom) by grafting transition metal atoms onto a highly dehydroxylated metal oxide support under a controlled atmosphere. This strategy is highly advantageous compared to traditional heterogeneous catalysis, where various populations of potentially active metallic sites may coexist. All the steps of catalyst preparation are carefully controlled using the methods of organic, organometallic, and coordination chemistries. Therefore, the coordination sphere of the grafted metal as well as metal loading on the surface can be accurately determined (a well-defined catalytic site) by modern solid/surface characterization techniques (elemental analysis, ICP-

OES, in situ IR, in situ UV, Solid State Nuclear Magnetic Resonance spectroscopy (SS NMR), extended X-ray absorption fine structure (EXAFS), (XANES), etc.).43,128 The surface should be considered as a bulky ligand that prevents undesired interactions between catalytic sites, which could lead to deactivation of these sites. With all these features, the relationship between structure and activity of the catalyst becomes possible to establish; with the addition of the SOMF tools, SOMC is becoming a predictable discipline. The various steps of the catalytic cycle can be monitored, the structure of the catalyst after the reaction can be established and compared to the initial structure to understand deactivation, and increase of activity and/or selectivity can be achieved by changing the support or ligand environment of the ‘active site.’ SOMC serves to bridge the existing gap between heterogeneous catalysis and homogeneous catalysis, and makes the elementary steps of molecular chemistry applicable to ‘single-atom catalysis.’

1.7. Application of SOMC in catalysis

In this section some typical examples will be provided of how the SOMC helps to achieve industrially and academically important chemical transformations. Considering that the focus of this dissertation is metathesis chemistry, and a large number of other transformations have been successfully implemented with SOMC tools, we will limit the scope of examples presented to the most relevant cases.

1.7.1 Olefin metathesis

Olefin metathesis plays a vital role in the creation of carbon-carbon double bonds and is implemented industrially almost exclusively with heterogeneous catalysis (Phillips Triolefin and the Olefin conversion technology,130 Shell higher olefin process (SHOP),131 Neohexene production132). The active catalytic sites of the process are surface carbenes that were first 133 evidenced with niobium ([(≡Si-O)2Nb(=CH)], molybdenum Mo[(≡Si-O-)Mo(=CHCMe3)(=NH)Np]

134 and rhenium [(≡Si-O-)Re(Np) (≡C-CMe3) (=CHCMe3)]). They were eventually successfully employed as catalysts for olefin metathesis. This reactivity is specific to the ([M]=CR2) SOMF, consistently with the metallacyclobutane intermediate proposed by Chauvin135 (Scheme 1.6).

Scheme 1.6: Chauvin’s Reaction Mechanism for Olefin Metathesis136 for the Self-Metathesis of Propylene to Ethylene and 2-Butene

A variety of SOMC catalysts active in the metathesis of olefins have been prepared, and the variation of activity and selectivity has been linked to both the nature of the metal employed and that of the spectator ligands.137

1.7.2 Alkane metathesis

Metal hydrides are active catalytic species for the metathesis of alkanes and the most uncomplicated surface fragments. Alkane metathesis was first reported on silica-supported tantalum hydride.138 In this reaction, saturated hydrocarbons, linear and branched, were rearranged to longer or shorter paraffins (Scheme 1.7). For example, n-propane can be converted into (C1, C2, C4, C5 …) paraffin under mild conditions, which was a chemical breakthrough taking into account the inertness of the sp3 carbon-hydrogen or C–C bonds.

Scheme 1.7: Metathesis of alkanes catalyzed by silica-supported tantalum hydride

[M]-H are mostly generated by hydrogenolysis of metal-alkyls [M]-R and generally promote low- temperature C-H bond activation of alkanes (i.e., methane activation).139 [M]-H and [M]-R can convert into each other by β-hydride elimination of the metal-alkyl and CH insertion by sigma bond metathesis. Another example of alkane metathesis is catalysis by partially alkylated metal hydrides (Scheme 1.8).140

Scheme 1.8: Formation of partially alkylated W-H and its application in the metathesis of propane

By analogy, pure metal alkyls [M]-R as surface organometallic fragments, also represent activity towards metathesis of alkanes (Scheme 1.9).

Scheme 1.9: Metathesis of n-decane catalyzed by silica-supported WMe5

Following the discovery of alkane metathesis using tantalum, tungsten, and then molybdenum hydride141 several catalysts were also reported. Thus, the first multifunctional SOMF fragments

142 [M](H)(=CR2)] were identified.

142 A notable application of [M](H)(=CR2) was cycloalkane (cyclooctane) metathesis to produce both ring contraction and ring dimerization products using [(≡Si-O-)WMe5] as a precursor. The cascade reaction with [M](H)(=CR2) allows ring-opening metathesis (ROM) dimerization or double bond migration followed by a ring-closing metathesis step. Remarkably, so far alkane metathesis can only be achieved by heterogeneous catalysis. A more detailed discussion of alkane metathesis will be further provided in the Introduction chapter (Part 1.8.4).

1.7.3 Olefin hydro-metathesis

Olefin hydro-metathesis was first reported in 2011143 by utilization of bifunctional single‐site tantalum hydride catalyst supported on fibrous silica (KCC‐1) nanospheres and later improved in

35,144 2018 by silica-alumina supported WMe5. In that reaction, the mixture of propylene and hydrogen passed through the batch of the catalyst in continuous flow conditions (Figure 1.9) and the products were analyzed by GC. Formation of petroleum range alkanes (up to n-decane) was found as well as remarkable activity of the catalyst. The details of that study will be given in

Appendix 1 of this dissertation.

Figure 1.7: Schematic representation of hydro-metathesis of propene over silica-alumina-supported WMe5

1.7.4 Imine metathesis

Upon prolonged thermal exposure under vacuum, a distinct single-site surface species

[(≡Si–O)Zr(NEt2)3] (A) evolves into an ethylimido complex [(≡Si–O–)Zr(=NEt)NEt2] (B) (Scheme

1.10).145 Reactions of B with an imine substrate result in imido/imine exchange (metathesis) with the formation of [(≡Si–O–)Zr(=NPh)NEt2] (C) (Scheme 1.11). Compounds B and C effectively catalyze imine/imine cross-metathesis and are thus considered as the first heterogeneous catalysts active for imine metathesis.

Scheme 1.10: Formation of ethylimido complex B

Scheme 1.11: Imine metathesis over silica-supported ethylimido complex B

1.7.5 Polymerization

SOMC based catalysts and, in particular, metal alkyls as surface organometallic fragments have numerous examples as polymerization catalysts.125,146

Scheme 1.12: Formation of active Ziegler-Natta polymerization catalyst The study of ethylene polymerization catalyzed by supported Ziegler-Natta catalysts will be presented in Appendix 2 of this dissertation.

1.7.6 Alkyne cyclotrimerization

An organometallic surface fragment ([M](≡CR)) explains catalytic terminal alkyne cyclotrimerization. Silica-supported tungsten carbyne complexes have shown high turnover numbers (TONs) without generating significant alkyne metathesis products (Scheme 1.13).147

Scheme 1.13: Trimerization of alkyne catalyzed by silica-supported W-carbyne

1.7.7 Ethylene oligomerization

A silica-supported tetramethyl niobium complex [(≡SiO-)NbMe4] B was isolated by the surface

41 alkylation of [(≡SiO-)NbCl3Me] A with dimethyl zinc in pentane. A can be easily synthesized by grafting NbCl3Me2 onto the surface of partially dehydroxylated silica by the SOMC strategy.

Complex A was found to be active in the ethylene oligomerization reaction, producing up to C30, whereas complex B selectively dimerizes ethylene into 1-butene in the absence of a co-catalyst at the same conversion level.

Scheme 1.14: 1) Grafting of NbCl3Me2 onto SiO2-700; 2) Surface alkylation of A to produce supported NbMe4 complex B

1.7.8 Utilization of CO2 Non-reductive processes have emerged as a valuable approach for the sustainable conversion of

148 149 CO2, including CO2 from flue gas. Processes such as the synthesis of polycarbonates, mineral150 or organic carbonates,151 and oxazolidinones152 can proceed under very mild conditions without requiring high energy and potentially hazardous reagents such as hydrogen.

The synthesis of cyclic organic carbonates,153 in particular, represents a way to access commodity chemicals, solvents,154 methanol,155 polycarbonates,156 etc. Unlike bulk chemicals such as urea

(also produced from CO2), cyclic carbonates and their derivatives afford long-term storage of

157 CO2.

A variety of supported catalysts have been prepared by the SOMC strategy for the conversion of

CO2 into valuable chemicals. One of the notable examples is a cycloaddition of CO2 to propylene oxide resulting in cyclic carbonates catalyzed by supported Nb complexes (Scheme 1.15).

Scheme 1.15: Catalytic conversion of CO2 to cyclic carbonate catalyzed by Nb complexes at 60 °C and 10 bar CO2

The general mechanism of CO2 cycloaddition to epoxide is illustrated in Scheme 1.16.

Scheme 1.16: Three-step mechanism for the cycloaddition of CO2 to epoxides catalyzed by a binary system composed of a Lewis acid MLn (M: metal atom, L: ligand) and a nucleophile (Nu). The step of CO2 insertion (II) might be monometallic or bimetallic.31

1.8. Metathesis method Metathesis is one of the most useful methods that has recently changed the synthetic strategies for organic synthesis and polymer science. The semantics of the word metathesis originates from the Greek μεταθεσισ (metathesis) that means “to transpose.” The simplest way to understand metathesis is to imagine a dance. During the Chemistry Nobel prize ceremony on October 5th,

2005, Chauvin’s metathesis mechanism was compared in a video to a dance in which couples exchange partners. The dancing couples represent the two carbene fragments of the olefin.

However, the couples cannot exchange their partner directly; first, they have to unite with a

dance coach (the metal center). The dance coach also has a partner (metallacarbene) and, with

the entering couple (which is the olefin) they both unite to form a circle (transition state). The

coach now can exchange partners within the circle by taking a new partner from the couple; then

with the new partner, he can go to another dancing couple for the following exchange, and so

on.158,159 (The scientific view on the metathesis mechanism will be given in Part 1.3.2.2.) Thus,

metathesis happens when, for example, ions are exchanged in a solution containing two ion pairs

to produce the most stable ion pairs (Scheme 1.17, top).160 In the same way, two carbenes of an

olefin can be exchanged to give, if they are different, another recombination leading to the two

symmetrical olefins (Scheme 1.17, bottom).

A+B- + C+D- ↔ A+D- + C+B-

Scheme 1.17: Schematic representation of metathesis reactions

The hunt for efficient metathesis catalysts is a story full of victories and defeats, and at the end of the day it is a success story that considerably shortens complex synthetic schemes by affording new routes, and therefore this story has changed the way chemists think about synthesis. Starting from organometallic mechanisms followed by the rational design of the active catalysts, the worlds of organic synthesis and polymer science have now benefitted. Using the tools of SOMC, this dissertation aims to discover the last missing brick in the whole fundamental metathesis research – metathesis of functionalized alkanes. The following parts of this chapter will cover the most important historical and scientific breakthroughs in the field of metathesis.

1.8.1 Discovery of metathesis History of olefin metathesis158,159 began in 1931 when Schneider and Frolich observed the

formation of ethylene and 2-butene in the pyrolysis of propylene at 852 °C.161 The first catalyzed

metathesis reactions were discovered in the 1960s when industrial chemists at Du Pont, Standard

Oil, and Phillips Petroleum reported that propene led to ethylene and 2-butenes when it was

162 heated with molybdenum catalyst (in the form of the metal, oxide or [Mo(CO)6]) on alumina.

The first polymerization of norbornene by utilization of bimetallic LiAlBu4 + TiCl4 system was

described by Anderson and Merckling in 1955.163 The term “metathesis” was used for the first

time by Calderon, who applied metathesis to ROMP (ring-opening metathesis polymerization) of

cycloolefins to polyalkenamers.164,165 Bradshaw proposed a metathesis mechanism through a 4-

centered cyclobutanic intermediate.166 Begley and Wilson reported167 first-order kinetic studies

while investigating propylene metathesis in the heterogeneous phase; the same kinetic order on

2-pentene metathesis in the homogeneous phase was reported by Hughes.168 However, the

mechanism through the cyclobutanic intermediate and the results obtained by Begley and Wilson

that indicated a first-order kinetics which contradicted the mechanism through the cyclic

cyclobutanic intermediate, were in contradiction. The real kinetics of the process remained

unclear until the discovery of the Chauvin mechanism. In 1971, Chauvin and Herisson

demonstrated a non-pairwise mechanism for metathesis and ROP (ring-opening polymerization) in the homogeneous phase, through carbenic intermediates.135 In 1976, Chauvin published results showing that WCl6 + CH3Li mixture catalyzes the formation of propylene as a result of the reaction of 2-butene, which was proposed to proceed via methylation of tungsten. This process was then followed by ɑ-elimination in the tungsten carbon bond of W-CH3 to form tungsten

169 carbene hydride W=CH2(H), then metathesis. The carbenic chain mechanism demonstrated by

Chauvin was supported later by new experimental results. A historical account of the most important olefin metathesis breakthroughs was reported by Eleuterio170 and summarized by

Singh171 and Astruc.159

1.8.2 Metathesis of unsaturated hydrocarbons (olefins and alkynes) 1.8.2.1 A general overview Olefin metathesis is an organic reaction that involves the redistribution of fragments of alkenes

(olefins) by the breaking and formation of carbon-carbon double bonds. For that reason, olefin metathesis was initially called olefin disproportionation. Due to the relative simplicity of olefin metathesis, it often creates less undesired by-products and hazardous wastes than alternative organic reactions.

The range of olefin metathesis reactions includes cross-metathesis (CM), ring-closing metathesis

(RCM), acyclic diene metathesis polymerization (ADMEP), ring-opening metathesis polymerization (ROMP), enyne metathesis (EYM), and ring-opening cross-metathesis (ROCM) and schematically illustrated in Figure 1.10.158

Figure 1.8: Various types of olefin metathesis reactions

Metathesis reactions are controlled thermodynamically, which implies inconvenience due to the reactions being equilibriated. This challenge is usually solved using terminal olefins that generate gaseous ethylene as one of the metathesis products, which displaces the reaction toward the metathesis products. Olefin metathesis catalyst systems usually involve a transition metal compound, but often additionally requires a second compound (co-catalyst), and sometimes a third (promoter). The most frequently used systems are based on the chlorides, oxides, or other easily accessible compounds of Mo, Ru, W, Re, Os, Ir, Ti, V, Cr, Co, Nb, Rh, or Ta compounds.

Typical co-catalysts are RAlCl2, R3Al, and R4Sn (R = Ph, Me, Et, Bu), while promoters often contain oxygen as O2, EtOH or PhOH. It has been understood that if reliable and efficient catalysts could be discovered, metathesis could assume great significance for organic synthesis. Thus, olefin metathesis has found numerous applications in pharmaceutical industries,172 renewables,173 and polymer industries.174 The challenge of finding and rationalizing an active catalytic system for the metathesis of olefins will be discussed further. Alkyne metathesis175 relates to the cooperative exchange of the alkylidyne fragments between a pair of (non-terminal) acetylene derivatives. The first effective catalyst described in the literature is a heterogeneous mixture of tungsten oxides and silica that operates only at a high temperature

(ca. 200–450 °C) and is therefore barely relevant for preparative purposes.176 This disclosure was later followed by the work of Mortreux et al. showing that such a scrambling method involves a homogeneous mixture of Mo(CO)6 (or related molybdenum sources) and simple phenol additives heated in solvents with high boiling points, such as decaline (Scheme 1.18).177-182

Scheme 1.18: Alkyne metathesis reported by Mortreux

Because of their ease of application, "Mortreux systems" have gained relatively widespread use; cheap, commercially available and stable "off the shelf" reagents can be used without the need for rigorously purified solvents and inert atmosphere. While, from a practical perspective, these factors make this an appealing protocol, with increasing applications in polymer chemistry (vide infra), the necessity of severe conditions and low activity prevent its use with sensitive moieties.

183 Techniques such as purging the reaction mixture with N2 to remove the released by-products, temperature adjustment and adding chelating 1,2-diphenyloxyethane184 led to somewhat greater yields and reaction rates. Pre-activation of the system by heating the phenol and molybdenum species with185 or without184 sacrificial 3-hexyne before adding the required reaction partners resulted in an expansion of the range and use of reduced temperatures, respectively. Building on Mori's186 and later Bunz's187 developments, Grela identified 2- fluorophenol and 2-fluoro-5-methylphenol as the best additives in a variety of alkyne metatheses.188,189

Although no “Fischer-type” carbyne has been found that allows for sustained alkyne metathesis,

Schrock et al. have demonstrated in a series of elegant investigations that the corresponding high valent metal alkylidyne complexes are catalytically competent and remarkably active (Scheme

1.19).190

Scheme 1.19: Early demonstration of the exceptional activity of defined alkylidyne complexes as catalysts for alkyne metathesis

Astoundingly, they were found to be unreactive towards alkenes191 suggesting that metal alkylidyne complexes allow orthogonal activation of unsaturated C–C bonds despite the apparent mechanistic links between alkene and alkyne metathesis.192 Most applications involving Schrock

193 alkylidyne complexes utilize (tBuO)3W[≡CCMe3] and related species which require mild reaction conditions and, sometimes, ambient temperature, affecting up to several hundred

194 catalytic turnovers per minute. Preparation of 1 by metathesis of (tBuO)3W≡W(OtBu)3 and neoheptyne (Scheme 1.20) is the most useful approach amenable to being carried out on a large scale;190 importantly, complex 1 has been made commercially available. There have been several reviews on the preparation and properties of metal alkylidynes.190,195

Scheme 1.20: Scaleable preparation of the tungsten alkylidyne complex

1.8.2.2 Mechanistic outlook Olefin metathesis is a catalytic reaction, which requires a transition metal catalyst. In 1967

Bradshaw et al.166 proposed the first mechanism to solve the conundrum that included the formation of a four-centered cyclobutane–metal intermediate. The following year, the hypothesis of Bradshaw was supported by Calderon.196 Though cyclobutanes are not produced by metathesis, and they are not metathesis substrates, no other hypothesis appeared for the three years, and Bradshaw’s proposal for the mechanistic puzzle seemed to be adopted by the metathesis community. In 1971, the organometallic chemist Pettit,197 who had generated the

5 first transition-metal methylene species [Fe(η -C5H5)(CO)2(=CH2)][BF4], suggested metallacyclopentane intermediate – the possibility of the formation of a tetra(methylene)metal in which the four methylene units were bonded to the transition metal. However, double oxidative addition to a transition-metal center is not possible, and Grubbs198 proposed rearranging metallacyclopentane intermediates and cyclobutane complexes to a carbene.199

Unfortunately, neither of the mechanisms mentioned above fit the experimental data, and the olefin metathesis mechanism remained rather mysterious until the mid-1970s. In proposing the mechanism of olefin metathesis, Yves Chauvin from the Institut Français du Pétrole had three main findings in mind: the report of Fischer200 on the synthesis of a tungsten–carbene complex, 201 [W(CO)5{C(CH3)(OCH3)}], that of Natta on the polymerization of cyclopentene by ring-opening

162 catalyzed by a mixture of WCl6 and AlEt3, and that of Banks and Bailey on the formation of ethylene and 2-butene from propene catalyzed by [W(CO)6] on alumina. Consequently, Chauvin and his student Hérisson published their proposition of metathesis mechanism in 1971 (Scheme

1.1).135 The Chauvin mechanism includes a metal–carbene species (more precisely, metal– alkylidene), the coordination of the olefin into the metal center of this species, the shift of the coordinated olefin to form the metallocyclobutane intermediate, and lastly, the topologically same shift of the new coordinated olefin in the metallocyclobutane in a direction perpendicular to the initial olefin shift. This forms a metal–alkylidene that is coordinated with the new olefin, then liberated. This new olefin contains two carbene moieties – a carbene from the catalyst and the carbene from the starting olefin. The new metal–alkylidene includes one of the two carbenes of the starting olefin, and it can re-enter the same type of catalytic cycle as the first one (Schemes

1.21 and 1.22). The fresh catalytic cycle may give two distinct metallacyclobutanes, one leading to the symmetrical olefin and the other leading to the starting olefin, based on the coordinated olefin's orientation. It is said that the latter process is degenerate olefin metathesis. Thus, the catalytic cycles involve both metal-alkylidene species arising from the combination of the metal with each of the starting olefin's two carbenes (Scheme 1.21).

Scheme 1.21: Linear representation of the Chauvin mechanism

The metallacyclobutane mechanism was not only suggested by Chauvin and Hérisson, but also several studies have been performed to verify it. As such, they reported that the reaction of a mixture of cyclopentene and 2-pentene led to C9, C10, and C11 dienes in the ratio 1:2:1. Also, the reaction of a mixture of cyclooctene and 2-pentene led almost exclusively to the C13 product. The latter reaction, but not the first one, was compatible with Calderon’s mechanism.

Scheme 1.22: Cyclic representation of the Chauvin metathesis mechanism

169 In 1976, Chauvin published the results indicating that the WCl6 + MeLi mixture catalyzes the formation of propene by the reaction of 2-butene, which was proposed to proceed through methylation of W, followed by the α-elimination in the tungsten–carbon bond of W–CH3 to form a tungsten carbene hydride W(=CH2)(H) species, then metathesis. Let us underline here, at that time, σ-bond metathesis in d0 metal-alkyl complexes that is the only available mechanism to activate α-C–H bonds, was unknown and was discovered only a decade later by the groups of

Watson (Lu),202 Bercaw (Sc),203 and Marks (Th).204 The first recognition of Chauvin’s mechanism together with confirmation came from Casey and Burkhardt205 when they reported that the carbene complex [W(CO)5(=CPh2)] reacted with isobutene to form a new olefin, 1,1- diphenylethene (Scheme 1.23, A), as the major product and that the same complex reacted with

H2C=C(OCH3)Ph to form 1,1-diphenylethene and the metal–carbene complex

[W(CO)5{=C(OCH3)Ph}] (Scheme 1.23, B), just as predicted in the Chauvin mechanism.

Scheme 1.23: Experimental confirmation of Chauvin’s mechanism by Casey and Burkhardt205

Later, labeling experiments by the groups of Grubbs and Katz showed that alkenes were exchanged as required by the Chauvin mechanism in a non-pair manner. In particular, Grubbs206 demonstrated that a mixture of 1,7-octadiene and its analog that was deuterated on both methylene termini underwent metathesis to produce a statistical mixture of d0-, d2-, and d4- ethylene and that d0- and d4-ethylene were not scrambled after their formation. However, at that stage, the real catalytically active species were unknown, because the precatalysts used were 18- electron metal–carbene complexes such as [W(CO)5(=CPh2)] or [W(CO)5{=C(OMe)Ph] or eventually metal precursors which did not contain a carbene ligand.205-208 Such complexes cannot bind olefins because the metal valence electron shell does not rise to 20 electrons; therefore some decomposition of these pre-catalysts had to take place. Contrary to common usage, a double bond between the carbene and the metal should not be used in Fischer-type carbene complexes200 (in the same way as the representation of the metal–carbonyl bond that is not written as M=C=O). Accordingly, the Fisher-type metal–carbene complexes are poor metathesis pre-catalysts, and good tungsten olefin metathesis catalysts systematically have a high oxidation state.209 Katz et al. suggested a plausible mechanism for alkyne metathesis in 1975, where the metal carbynes probably account for the catalytic turnover210 in a series of formal [2+2] cycloaddition and cycloreversion steps as shown in Scheme 1.24.

Scheme 1.24: Accepted mechanism of alkyne metathesis195

Although the known metal carbyne complexes could not cause alkyne metathesis reactions at the time of his proposal,211 Schrock later experimentally established the mechanism using high-valent metal alkylidynes.212 Several metallacyclobutadiene complexes formed by the [2+2] cycloaddition of alkylidynes and alkynes were isolated and characterized213 and have been demonstrated to be catalytically competent intermediates in alkyne metathesis.

1.8.3 The development of the functionally tolerant olefin metathesis catalysts Studies in the Schrock laboratory led to the design and synthesis of several very efficient molybdenum and tungsten metathesis catalysts for olefin metathesis.190 Despite the activity of

Schrock systems, the use of these early-metal catalysts had a significant restriction: the metal center’s oxophilicity provided poor functional group tolerance and required catalyst preparation and handling under an inert atmosphere. Developing new, functional group-tolerant catalysts would be essential to completely exploit the potential of metathesis.214 The first report on metathesis of functionally substituted olefins was published in 1976 by Boelhouwer, where metathesis of unsaturated fatty acid esters was achieved with homogeneous tungsten hexachloride – tetramethyltin catalyst.215 In 1992, Fu and Grubbs published two papers in which they showed how Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2]2 could be used to make cyclic olefins quickly and efficiently that contain functionalities other than a C=C bond),209,216,217 with the only other product being a volatile olefin such as ethylene, propylene, or butene (Figure 1.11).

209 Figure 1.9: RCM reactions initiated by Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2]2

In that way, it is possible to prepare rings of many sizes, and even rings that contain tetrasubstituted olefinic bonds. These reports helped to awaken organic chemists to the utilization of the significant potential of olefin metathesis by well-defined catalysts in organic chemistry.209 The fact that the Mo and W catalysts in this general class are sensitive to air, moisture, and some functionalities, did not restrict their use in organic reactions.

The development of catalysts for metathesis based on ruthenium began with the objective of developing interesting polymeric structures. Polymer chemistry offers an outstanding way to study metathesis catalysts: low catalyst loadings are capable of generating large quantities of polymeric material, the structure of which can provide a historical record of catalyst activity.

Grubbs’ group concentrated on understanding the fundamental concepts of living metathesis polymerization. The group hoped to create novel polymers with interesting structures and physical properties based on this knowledge. From the reports by Michelotti,214,218 it was known that late-transition metal catalysts could be used to polymerize strained olefins in protic media.

It has also been shown that these systems could also effectively promote the formation of poly-

7-oxo-norbornenes. More importantly, it has been found that complexes of ruthenium (II) can serve as very efficient catalysts of polymerization. One of the notable examples is the commercialized technology of producing polynorbornen catalyzed by RuCl3/HCl system in n- butanol, which was marketed in 1976 by CDF Chimie under a trade name of “Norsorex” and clearly indicated that Ru complex can tolerate butanol. As a result of the investigations, a robust catalyst system was developed that tolerated most functional groups and even aqueous media.

In addition to the activity of these ruthenium salt catalysts, only a tiny amount of the ruthenium added to a reaction mixture was found to produce an active catalytic center. However, as the structure of the active catalysts was undefined, it was impossible to make reasonable changes for further improvements.214,219 Nevertheless, the path forward was defined and the potential of

Ru-based systems was shown. A Ru (II) complex and a strained olefin were found to be required to form an active catalyst system. The development of well-defined ruthenium carbene complexes was essential for further catalyst optimization, assuming olefin metathesis had to happen through the formation of metal carbenes. Eventually, the first well-defined and air-stable carbene complex B was prepared as a result of the reaction of ruthenium(II) phosphine complex

A with cyclopropene derivative (Scheme 1.25).

Scheme 1.25: Preparation of the first well-defined Ru-carbene catalyst Interestingly, it was discovered that complex B is an effective catalyst for the polymerization of norbornenes in protic media. Although B was not very active, its structure was well-defined, ultimately providing a scaffold to introduce structural changes for catalyst optimization. While many modifications have been made since then (e.g. ligand exchange using tricyclohexylphosphine to generate the more active catalyst C), the basic structure of catalyst systems is still similar to that of the original catalyst B. This well-defined family of catalysts is distinguished by its incredible oxygen and water tolerance, making it perfect for application to organic synthesis.214,220

As an example, owing to its high air sensitivity and rigorous preparation methods, the overall use of Tebbe reagent with Ti based carbene was limited. In contrast, ruthenium catalysts possess higher stability and tolerance to moisture, which is highly desirable. Eventually, the complex D became commercially available on multikilogram scales.214 With commercial sources, the organic synthetic community found a wide range of creative uses of olefin metathesis catalysts in the synthesis of complex structures, including natural ones. The preference of ruthenium for soft

Lewis-bases and Lewis-acids, such as olefins, over hard bases, such as oxygen-based ligands, is crucial for its high tolerance of air and water. It also makes ruthenium catalysts fundamentally distinct from Ti-, W- and Mo-based systems. Therefore, the rules learned in the development of early-metal catalysts no longer applied. For instance, as ruthenium possesses a metal center rich in d electrons, strong electron-donating ligands are required for high catalyst activity, rather than electron-poor ones. Therefore, detailed mechanistic studies were needed to gain knowledge of the structure/activity relationship of the Ru based catalyst. During such investigations, five- coordinate complexes, such as C and D, were discovered to be catalytic precursors and one of the neutral ligands must be lost to produce the metathesis-active species. The remaining neutral ligand of the resulting 14-electron complex is responsible for the turnover number of the catalyst.

This knowledge was used to understand why bulky, basic tricyclohexylphosphine ligands are more effective than triphenylphosphine ligands in the ruthenium-catalyzed metathesis of cyclooctene.214,221 Further catalyst tuning via the substitution of one of the phosphine ligands on

D with an N-heterocyclic carbene ligand resulted in a series of highly active catalysts (e.g. catalyst

E; Figure 1.12), which were later known as Grubbs second-generation catalysts and also explored by Herrmann.222

Figure 1.10: First-generation Grubbs catalyst (D) and second-generation Grubbs catalyst (E)

This enhancement in metathesis activity was attributed to an increased rate of catalyst turnover due to the favorable electron donation and steric bulk of the NHC ligand as compared to a phosphine ligand. Additional modification of the catalyst by replacing the phosphine in compound 7 with a weaker ligand, such as pyridine, resulted in an increase in activity up to a factor of 104 relative to catalyst D.214 The facile preparation of ruthenium catalysts, coupled with their functional group tolerance and remarkable stability, enabled olefin metathesis to finally realize its broad potential (Scheme 1.26).

Scheme 1.26: Commercial application of RCM

Finally, after more than four decades of extensive scientific research towards the development of active, well-defined and functionally tolerant olefin metathesis catalysts and understanding the mechanism of the reaction, the 2005 Nobel Prize in Chemistry was given to R. Grubbs, R.

Schrock, and Y. Chauvin “for the development of the metathesis method in organic synthesis.”

1.8.4 SOMC and metathesis of saturated hydrocarbons (alkanes) Alkanes are the major constituents of petroleum. Alkane metathesis is a powerful instrument that can be implemented in different chemical and petrochemical areas. Alkane metathesis could provide a solution for the processing of fuels such as crude oil and natural gas; it can also lead from natural gas to ethane through non-oxidative coupling and then metathesis to liquid hydrocarbons.223 The following overall equation describes alkane metathesis:

2CnH2n+2  Cn-iH2(n-i)+2 + Cn+iH2(n+i)+2, where i = 1, 2, ...n-1; with i = 1, 2 favored for n < 4. This reaction was therefore recognized as a method in which an alkyl fragment of one alkane molecule is transferred to another. The methyl group is the smallest fragment of alkyl and the simplest to transfer. It is also possible to transfer ethyl and propyl groups from known cross-metathesis of olefins. Heavier alkanes resulst from either (i) consecutive reactions or (ii) the transfer of a heavier alkyl group. Alkane metathesis and Fisher-Tropsch are the only two processes to produce transportation range fuels. A brief overview of alkane metathesis and catalysts for the aforementioned reaction will be provided next.

Heckelsberg and Banks reported an unprecedented dual-functional catalyst based on silica/chromia-alumina tungsten oxide that could transform propane at 600 °C into heavier olefins and paraffins.224 Different cracking products were formed along with the main product propylene, which was thought to be due to an elevated temperature. In 1973, Burnett and

Hughes reported a dual functional catalytic system for molecular redistribution of alkanes at

400°C, and the process was called ‘‘disproportionation of alkane’’.225 In 1997, Basset et al. reported alkane disproportionation reaction at 150 °C under 1 atm catalyzed by single-site silica- supported [Ta]–H catalyst.138 This new reaction was named ‘‘alkane metathesis’’ due to its similarity with olefin metathesis. Apart from the known metathesis of unsaturated hydrocarbons

(olefins and alkynes), this fundamental discovery makes now possible the metathesis of saturated hydrocarbons as well, and SOMC provides tools for the development of alkane metathesis catalysts.31

1.8.4.1 1st generation alkane metathesis catalysts The catalysts of the first generation are [W] and [Ta] hydrides made from their corresponding neopentyl fragments. The first well-defined surface organometallic catalyst for alkane metathesis is tantalum hydride. The surface organometallic complex, [(≡Si-O-)2TaH], was synthesized by the

t t reaction of [(≡Si-O-)xTa(=CHC Bu)(CH2C Bu)3-x] (x = 1 or 2) by treatment of hydrogen at 150 °C for

15 hours followed by keeping a sample at the constant temperature of 200 °C for 2 hours.226 The parent silica-supported tantalum neopentyl complex was prepared from t t [Ta(=CHC Bu)(CH2C Bu)3] precursor upon grafting to silica dehydroxylated at 500 °C (SiO2-500)

(Scheme 1.27).

t t Scheme 1.27: The reaction between [Ta(=CHC Bu)(CH2C Bu)3] and SiO2-500

t t The reaction between SiO2-500 and the tantalum precursor [Ta(=CHC Bu)(CH2C Bu)3] produces a mixture of monopodal (65%) and bipodal (35%) tantalum surface complexes. It contrasts sharply with group IV metal precursors such as Zr(Np)4 and Ti(Np)4 which form solely monopodal surface

227,228 complexes with SiO2-500. On the other hand, Hf(Np)4 follows the same pattern as [Ta] on

229 SiO2-500 producing a combination of monopodal and bipodal species. The reaction of surface

t t silanol with [Ta(=CHC Bu)(CH2C Bu)3] occurs via the addition of [Si–OH] onto the tantalum carbene bond and formation of monopodal tetra-neopentyl and bipodal tris-neopentyl complexes of tantalum (Scheme 1.27). The monopodal tetraneopentyl and the bipodal tris neopentyl complexes then undergo rearrangement by ɑ-hydrogen transfer with the formation of a neopentylidene moieties followed by elimination of neopentane molecule (by steric compression). It results in the formation of one Ta–carbene bond per tantalum center (Scheme

1.27). This observation was demonstrated by utilizing deuterated silanol.230

The catalysts of the first generation were used in the propane metathesis reaction. Kinetic studies of propane metathesis were conducted in a continuous flow reactor. When tantalum hydride interacted with propane, [Ta]–n-propyl and [Ta]–iso-propyl fragments were formed by σ-bond metathesis (CH-bond activation) with release of hydrogen. Subsequently, by ɑ-H abstraction

[Ta]–n-propylidene hydride or [Ta]–iso-propylidene hydride is formed. In parallel, a propane dehydrogenation product (propene) is formed by b-H elimination from [Ta]–n-propyl or [Ta]–iso- propyl. Once the olefin is formed, it coordinates to tantalum carbene hydride [Ta]=CRH, A or B in two different ways (syn- or anti-) which results in four possible metallacyclobutanes having methyl or ethyl groups in the 1,2- or 1,3-position (C, D, E, F) (Scheme 1.28).

Scheme 1.28: Metathesis of propane pathway catalyzed by supported Ta-H catalyst

Due to steric reasons, the most favorable structures have the substituents at the e-e 1,3-position

(conformer C, E) rather than the 1,2-position (conformer D, F).231 Followed by a cycloreversion and reduction, methane, ethane, butane (n-butane as well as iso-butane) and pentane (n- pentane and iso-pentane) are formed. It was observed that (i) the butanes (n-butane, iso-butane)

C(n+1) formation prevails the formation of pentanes (n-pentane, iso-pentane) C(n+2). Analogously (ii), the formation of ethane C(n-1) is higher than methane C(n-2) when n < 4. Also, linear products were preferred over branched products.232 In general, the path in alkane metathesis is as follows: at first, the initial products are olefins and hydrogen; subsequently, the newly generated olefins involved in olefin metathesis and the metathesis products after reduction with hydrogen are transformed to new alkanes. A mechanism for propane metathesis was suggested based on the product distribution of alkanes and taking into consideration their selectivities (Scheme 1.28).

The suggested reaction mechanism is confirmed by the product selectivities and proves that olefin metathesis is part of alkane metathesis.136

To improve reactivity in alkane metathesis reactions, the focus moved from group V [Ta] to group

VI metals, specifically [W], as tungsten catalysts are well known for their superior activities in olefin metathesis in contrast to their tantalum counterparts.233 Silica-supported [W]–hydrides were prepared and tested in propane metathesis reaction reaching a TON of 129. From the investigations of the alkane metathesis mechanism, it was found that the active species affecting the reaction rate and cumulative TON is a metal carbene hydride. Considering that, the focus shifted towards the formation of metal carbene hydride on the surface utilizing well-defined metal methyl of the active metals (W, Ta). These results open up the door for ‘‘2nd generation catalysts’’ in alkane metathesis.

1.8.4.2 2nd generation alkane metathesis catalysts The first generation catalysts reached the highest TON of 129 in propane metathesis reaction.

The postulated hypothesis was based on the generation of a metal carbene hydride (the active form of the catalyst) from a metal methyl. With that, the silica-supported tungsten pentamethyl

[(≡Si-O-)WMe5] and tantalum trimethyl [(≡Si-O-)TaMe3] catalyst precursors were prepared by the reaction of silica dehydroxylated at 700 °C (SiO2-700) and the corresponding molecular

234,235 counterparts (WMe6 and TaMe4). Upon heating, complexes A and B transform into a mixture of monopodal and bipodal metal carbynes in the case of [(≡Si-O-)WMe5] and carbenes in the case of [(≡Si-O-)TaMe4] (Scheme 1.29).

Scheme 1.29: Preparation of silica-supported [(≡Si-O-)WMe5] and [(≡Si-O-)TaMe3] with their corresponding carbyne and carbene species

The catalysts of the second generation were used in a higher alkane iso-metathesis reaction.

Alkane iso-metathesis derives straight from alkane metathesis. Typically, alkane metathesis is performed in fixed-bed reactors with small molecular gaseous alkanes. The reactions are performed in a batch reactor with higher molecular weight alkanes, which are fluids at low temperature and have low saturation pressure. Accordingly, in the metathesis of n-decane in the batch reactor, catalyzed by the same catalyst precursor [(≡Si-O-)WMe5] a TON of 150 was reached, together with a much higher proportion of lower alkanes.52 The reason for that observation is rather physical: the concentration of a liquid alkane in a batch reactor is higher, making longer the catalyst-to-reactant contact time and, consequently, the rate of metathesis reaction increases. Similarly, butane metathesis forms liquid products up to C8, while n-decane metathesis produces a broad range of alkanes from C2 to C34 instead of C18 and ethane. Such a variety of alkanes can only be observed when isomerization of the alkenes resulting from the alkane occurs by insertion of the olefin into the metal hydride and double bond migration by β-

H elimination/reinsertion. Then olefin metathesis and reduction of the newly formed olefins to new alkanes occurs. At the same time, the newly formed olefins undergo stepwise double bond migration, which further broadens the product distribution.

To further improve the reactivity of this surface organometallic fragment, WMe6 was grafted on a more acidic silica-alumina support (dehydroxylated at 500 °C) to form a mixture of mono- and bipodal complexes.106 The formation of bipodal complexes occurs upon the migration of a [W]– methyl to the alumina center (Scheme 1.30). After heating of the sample at 120 °C for 12 hours, a generation of two sets of [W]–carbyne species has been observed: one comes from the neutral

[W] center and the other from the cationic [W] center (Scheme 1.30). The abstraction of the methyl group from the W center by adjacent Al-center results in the formation of the cationic

[W]-species (Scheme 1.30). A TON of 350 was achieved in n-decane metathesis catalyzed by tungsten hexamethyl supported on silica-alumina.52

Scheme 1.30: Evolution of [W]-Me to [W]≡CH on silica-alumina

Another application of the 2nd generation catalysts has been found in the metathesis of cycloalkanes, which has led to their correspondingly lower and higher cyclic homologs. Similar to a metathesis of linear alkanes, dehydrogenation of a cyclic substrate to an olefin, olefin metathesis, and hydrogenation of the metathesized olefins are the sequential steps in cycloalkane metathesis. Saturated macrocycles (the products of cycloalkane metathesis) are essential building blocks for pharmaceutical intermediates (i.e. macrolides), fragrance (i.e. musk) and as a biomarker for b. Braunii (biotechnology).236,237 After the synthesis of the well-defined

234 W-based catalyst precursor [(≡Si-O-)WMe5] and its successful utilization in propane and n- 52 decane metathesis, [(≡Si-O-)WMe5] was tested for the metathesis of cyclooctane as the model substrate.238 In that case, a TON of 450 was achieved after 190 hours at 150 °C. Interestingly, only cycloalkanes were observed without linear alkanes, olefins, and polymeric byproducts. The overall selectivity of the reaction is restricted to macrocyclic alkanes of carbon numbers cC12– cC40 and ring contracted alkanes (cC5–cC7). By comparison, homogeneous tandem systems showed good selectivity for products with a carbon number of a multiple of 8 but generated considerable quantities of oligomers and polymers that differ significantly from the single-site system.

1.8.4.3 3rd generation alkane metathesis catalysts nd The 2 generation catalyst [(≡Si-O-)WMe5], led to a TON of up to 260 for propane metathesis and even higher for n-decane metathesis (TON=350) and cyclooctane metathesis

(TON=450).52,140,239 To further improve the catalytic system, the study was focused on understanding the elementary steps of alkane metathesis. As the C–H bond activation was assumed to be the rate-determining step,240 the increase of the olefin concentration (alkane dehydrogenation products) will increase the rate of the reaction, its productivity and the lifetime of the catalyst. Based on that, a second surface organometallic fragment (dehydrogenation catalyst precursor) was combined with the monometallic system based on [(≡Si-O-)WMe5]. As a

rd result, by introducing Zr(Np)4 together with WMe6 on silica formed a well-defined 3 generation

240 bi-metallic catalyst [(≡Si-O-)WMe5 / (≡Si-O-)Zr(Np)3] on a silica surface (Scheme 1.31). The concentration of the olefin and its resulting metathesis rate could be improved by combining it with group IV metals that were known to dehydrogenate paraffins (by β-H elimination).

Scheme 1.31: General scheme for the preparation of a bimetallic catalyst system (M = Zr, Ti)

A new method that was developed for the synthesis of bimetallic systems on surfaces keeping

[W] intact and additionally introducing group IV metals was found to be extremely useful in alkane metathesis. The reason lies in the properties of the system: metals of group IV are very active towards σ-bond metathesis of paraffins and the respective hydrides prepared by hydrogen treatment of [(≡Si-O-)WMe5 / (≡Si-O-)Zr(Np)3] proved to be very efficient in alkane metathesis reactions with a TON of 1436 for the n-decane metathesis reaction. When [Ti] was introduced instead of [Zr], the new bimetallic system proved to be better in the hydrogenolysis of alkanes.241

It is known that the first elementary step in hydrogenolysis is C–H bond activation, as it is in the case of dehydrogenation. The new bi-metallic silica-supported catalyst was prepared using [Ti] as the catalyst of dehydrogenating and [W] as the catalyst of metathesis [(≡Si-O-)WMe5 /

(≡Si-O)Ti(Np)3] (Scheme 1.31). This bimetallic system was subjected to the propane metathesis reaction in a continuous flow reactor and resulted in the highest TON (10000) obtained.38 The study also proves that the synergistic effect that comes from the proximity of the two metals is the key for much better results than those of the other catalysts.

1.8.5 The challenge of functionalized alkane metathesis The metathesis field is fundamentally important from both academic and industrial points of view. As we have shown, research dedicated to the development of the robust catalysts for the metathesis of functionalized olefins took almost three decades, and success in this field finally led to the Nobel Prize in Chemistry in 2005. Two decades after the discovery of the metathesis of alkanes in 1997, the third generation catalysts that possess a TON of 10000 were developed.

However, the fundamental science of metathesis is still not complete until the metathesis of functionalized alkanes is developed. In contrast to the metathesis of functionalized olefins, where the catalyst should tolerate the functionalities, but does not perform σ–bond metathesis, in metathesis of functionalized alkanes, the catalyst, apart from being tolerant of a functional group, at the same time, must be active towards CH-activation; however, these two properties are in contradiction to each other. This dissertation aims to understand this unsolved problem and to discover the process of metathesis of functionalized alkanes.

1.9. References 1. Kakaei, K.; Esrafili, M. D.; Ehsani, A., Chapter 1 - Introduction to Catalysis. Interface Science and Technology, 2019, 27, 1-21. 2. Schmidt, F., The Importance of Catalysis in the Chemical and Non-Chemical Industries. In: Baerns, M. (Eds.), Basic Principles in Applied Catalysis. 2004, Springer Series in Chemical Physics, vol 75. Springer, Berlin, Heidelberg, 3-16. 3. Farnetti, E.; Di Monte, R.; Kaspar, J., Homogeneous and Heterogeneous Catalysis. Inorganic and Bioinorganic Chemistry, 2009, Vol. II, 50-87. 4. Fadhel, A. Z.; Pollet, P.; Liotta, C. L.; Eckert, C. A., Combining the Benefits of Homogeneous and Heterogeneous Catalysis with Tunable Solvents and Nearcritical Water. Molecules, 2010, 15, 11, 8400-8424. 5. Bommarius, A. S.; Riebel, B. R., Biocatalysis: fundamentals and applications. Wiley–VCH, 2004. 611 pp; ISBN 3‐527‐30344‐8. 6. Balasanthiran, C.; Hoefelmeyer, J. D. In Chapter 2 Nanocatalysis: Definition and Case Studies, The Royal Society of Chemistry, 2014, 6-29. 7. Bhaduri, S.; Mukesh, D., Homogeneous Catalysis: Mechanisms and Industrial Applications, Second Edition. Wiley, 2014. 276 pp; ISBN 9781118872369. 8. Van Santen, R. A., Modern Heterogeneous Catalysis: An Introduction. Wiley–VCH, 2017. 564 pp; ISBN 9783527810253. 9. Dumesic, J. A.; Huber, G. W.; Boudart, M., Principles of Heterogeneous Catalysis. Part 1. Introduction. 2008, 1-15; In: Handbook of Heterogeneous Catalysis, Wiley–VCH, ISBN 9783527610044. 10. Védrine, J. C., Revisiting active sites in heterogeneous catalysis: Their structure and their dynamic behavior. Applied Catalysis A: General, 2014, 474, 40-50. 11. Lefebvre, F., Synthesis of Well-defined Solid Catalysts by Surface Organometallic Chemistry. 2014, 1-26; in the book Atomically-Precise Methods for Synthesis of Solid Catalysts, Royal Society of Chemistry. 12. Amayuelas, E.; Fidalgo-Marijuán, A.; Bazán, B.; Urtiaga, M. K.; Barandika, G.; Arriortua, M. I., Highly thermally stable heterogeneous catalysts: study of 0D and 3D porphyrinic MOFs. CrystEngComm, 2017, 19, 7244-7252. 13. Parravan, G.; Thomas, J. M., Introduction to Principles of Heterogeneous Catalysis. Ind. Eng. Chem., 1967, 59, 10, 14-21. 14. Austin, J. M.; Groenewald, T.; Spiro, M., Heterogeneous Catalysis in Solution. 18. The Catalysis by Carbons of Oxidation-Reduction Reactions. J. Chem. Soc. Dalton, 1980, 6, 854-859. 15. Takehira, K.; Hayakawa, T.; Ishikawa, T., Heterogeneous Catalysis in the Liquid Phase Oxidation of Olefins. 4. The Activity of a Supported Vanadium or Chromium-Oxide Catalyst in the Decomposition of Tert-Butyl Hydroperoxide. Bull. Chem. Soc. Jpn., 1980, 53, 8, 2103-2110. 16. Leach, B., Applied Industrial Catalysis. Academic Press, 1983. 316 pp; ISBN: 9780323156332. 17. Kalz, K. F.; Kraehnert, R.; Dvoyashkin, M.; Dittmeyer, R.; Gläser, R.; Krewer, U.; Reuter, K.; Grunwaldt, J.-D., Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions. ChemCatChem, 2017, 9, 1, 17-29. 18. Sherwood, T. K., Diffusion phenomena in heterogeneous catalysis. Pure Appl. Chem., 1965, 10, 4, 595-610. 19. Larhed, M.; Moberg, C.; Hallberg, A., Microwave-Accelerated Homogeneous Catalysis in Organic Chemistry. Acc. Chem. Res., 2002, 359, 717-727. 20. Arai, M.; Zhao, F., Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis. Catalysts, 2015, 5, 868-870. 21. Meng, X.; Yua, C.; Zhao, P., An efficient and recyclable heterogeneous catalytic system for the synthesis of 1,2,4-triazoles using air as the oxidant. RSC Adv., 2014, 4, 8612-8616. 22. Cole-Hamilton, D. J., Homogeneous Catalysis--New Approaches to Catalyst Separation, Recovery, and Recycling. Science, 2003, 299, 5613, 1702-1706. 23. Armor, J. N., A history of industrial catalysis. Catal. Today, 2011, 163, 1, 3-9. 24. Hayes, M., Commercial Heterogeneous Catalysis. Handbook of Commercial Catalysts - Heterogeneous Catalysts. Platin. Met. Rev., 2001, 45, 2, 83-83. 25. Wang, Q.; Weng, J. H.; Xu, L. ; Fan, Z. Q.; Feng, L. X., Multiple active sites model of ethylene polymerization with the Cp2ZrCl2–aluminoxanes catalytic system. Polymer, 1999, 40, 1863-1870. 26. Dufaud, V.; Davis, M. E., Design of Heterogeneous Catalysts via Multiple Active Site Positioning in Organic−Inorganic Hybrid Materials. J. Am. Chem. Soc., 2003, 125, 9403-9413. 27. Fairlie, D. P.; Bosnich, B., Homogeneous Catalysis. Mechanism of Catalytic Hydroacylation: The Conversion of 4-Pentenals to Cyclopentanones. Organometallics, 1988, 7, 946-954. 28. Somorjai, G. A., Active Sites in Heterogeneous Catalysis, in: Eley, D. D.; Pines, H.; Weisz, P. B. (Eds.), Advances in Catalysis, Academic Press, 1977, 1-68. 29. Ghiaci, M.; Ghazaie, M., Modification of a heterogeneous catalyst: Sulfonated graphene oxide coated by SiO2 as an efficient catalyst for Beckmann rearrangement. Catalysis Communications, 2016, 87, 70-73. 30. Ertl, G., Mechanisms of Heterogeneous Catalysis. In: Reactions at Solid Surfaces, Ertl. G., Wiley, 2009, 123-157. 31. Samantaray, M. K.; Pump, E.; Bendjeriou-Sedjerari, A.; D’Elia, V.; Pelletier, J. D. A.; Guidotti, M.; Psaroc, R.; Basset, J.-M., Surface organometallic chemistry in heterogeneous catalysis. Chem. Soc. Rev., 2018, 47, 8403-8437. 32. Morlanés, N.; Kavitake, S. G.; Rosenfeld, D. C.; Basset, J.-M., Alkane Cross-Metathesis Reaction between Light and Heavy Linear Alkanes, on a Silica Supported Well-Defined Single-Site Catalyst. ACS Catal., 2019, 92, 1274-1282. 33. Azofra, L. M.; Morlanés, N.; Poater, A.; Samantaray, M. K.; Vidjayacoumar, B.; Albahily, K.; Cavallo, L.; Basset, J.-M., Single‐Site Molybdenum on Solid Support Materials for Catalytic Hydrogenation of N2‐into‐NH3. Angew. Chem. Int. Ed., 2018, 57, 48, 15812-15816. 34. Aljuhani, M. A.; Barman, S.; Abou-Hamad, E.; Gurinov, A.; Ould-Chikh, S.; Guan, E.; Jedidi, A.; Cavallo, L.; Gates, B. C.; Pelletier, J. D. A.; Basset, J.-M., Imine Metathesis Catalyzed by a Silica-Supported Hafnium Imido Complex. ACS Catal., 2018, 810, 9440-9446. 35. Tretiakov, M.; Samantaray, M. K.; Saidi, A.; Basset, J.-M., Effect of support on hydro- metathesis of propene: A comparative study of W(CH3)6 anchored to silica vs. silica- alumina. J. Organomet. Chem., 2018, 863, 102-108. 36. Kelly, M. J.; Barthel, A.; Maheu, C.; Sodpiban, O.; Dega, F.-B.; Vummaleti, S. V. C.; Abou- Hamad, E.; Pelletier, J. D. A.; Cavallo, L.; D’Elia, V.; Basset, J.-M., Conversion of actual flue gas CO2 via cycloaddition to propylene oxide catalyzed by a single-site, recyclable zirconium catalyst. Journal of CO₂ Utilization, 2017, 20, 243-252. 37. Barman, S.; Merle, N.; Minenkov, Y.; De Mallmann, A.; Samantaray, M. K.; Le Quéméner, F.; Szeto, K. C.; Abou-Hamad, E.; Cavallo, L.; Taoufik, M.; Basset, J.-M., Well-Defined Silica Grafted Molybdenum Bis(imido) Catalysts for Imine Metathesis Reactions. Organometallics, 2017, 36, 8, 1550-1556. 38. Samantaray, M. K.; Kavitake, S.; Morlanés, N.; Abou-Hamad, E.; Hamieh, A.; Dey, R.; Basset, J.-M., Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane. J. Am. Chem. Soc., 2017, 139, 9, 3522-3527. 39. Merle, N.; Le Quéméner, F.; Bouhoute, Y.; Szeto, K. C.; De Mallmann, A.; Barman, S.; Samantaray, M. K.; Delevoye, L.; Gauvin, R. M.; Taoufik, M.; Basset, J.-M., Well-Defined Molybdenum Oxo Alkyl Complex Supported on Silica by Surface Organometallic Chemistry: A Highly Active Olefin Metathesis Precatalyst. J. Am. Chem. Soc., 2017, 139, 6, 2144-2147. 40. Qureshi, Z. S.; Hamieh, A.; Barman, S.; Maity, N.; Samantaray, M. K.; Ould-Chikh, S.; Abou- hamad, E.; Falivene, L.; D’Elia, V.; Rothenberger, A.; Llorens, I.; Hazemann, J.- L.; Basset, J.- M., SOMC-Designed Silica Supported Tungsten Oxo Imidazolin-2-iminato Methyl Precatalyst for Olefin Metathesis Reactions. Inorg. Chem., 2017, 56, 2, 861-871. 41. Hamieh, A.; Dey, R.; Nekoueishahraki, B.; Samantaray, M. K.; Chen, Y.; Abou-Hamad, E.; Basset, J.-M., Single site silica supported tetramethyl niobium by the SOMC strategy: synthesis, characterization and structure–activity relationship in the ethylene oligomerization reaction. Chem. Commun., 2017, 53, 7068-7071. 42. Blasco, T., Insights into reaction mechanisms in heterogeneous catalysis revealed by in situ NMR spectroscopy. Chem. Soc. Rev., 2010, 39, 4685-4702. 43. Pelletier, J. D. A.; Basset, J.-M., Catalysis by Design: Well-Defined Single-Site Heterogeneous Catalysts. Acc. Chem. Res., 2016, 49, 664−677. 44. Copéret, C.; Allouche, F.; Chan, K. W.; Conley, M. P.; Delley, M. F.; Fedorov, A.; Moroz, I. B.; Mougel, V.; Pucino, M.; Searles, K.; Yamamoto, K.; Zhizhko, P. A., Bridging the Gap between Industrial and Well‐Defined Supported Catalysts. Angew. Chem. Int. Ed., 2018, 57, 22, 6398-6440. 45. Serna, P.; Gates, B. C., Molecular Metal Catalysts on Supports: Organometallic Chemistry Meets Surface Science. Acc. Chem. Res., 2014, 47, 8, 2612-2620. 46. Basset, J.-M.; Lefebvre, F.; Santini, C., Surface organometallic chemistry: some fundamental features including the coordination effects of the support. Coordination Chemistry Reviews, 1998, 178-180, 1703-1723. 47. Jenness, G. R.; Schmidt, J. R., Unraveling the Role of Metal–Support Interactions in Heterogeneous Catalysis: Oxygenate Selectivity in Fischer–Tropsch Synthesis. ACS Catal., 2013, 3, 12, 2881-2890. 48. Vannice, M. A.; Garten, R. L., Metal-support effects on the activity and selectivity of Ni catalysts in COH2 synthesis reactions. Journal of Catalysis, 1979, 56, 2, 236-248. 49. Babucci, M.; Fang, C.-Y.; Perez-Aguilar, J. E.; Hoffman, A. S.; Boubnov, A.; Guan, E.; Bare, S. R.; Gates, B. C.; Uzun, A., Controlling catalytic activity and selectivity for partial hydrogenation by tuning the environment around active sites in iridium complexes bonded to supports. Chem. Sci., 2019, 10, 2623-2632. 50. Nakagawa, K.; Anzai, K.; Matsui, N.; Ikenaga, N.; Suzuki, T.; Teng, Y.; Kobayashi, T.; Haruta, M., Effect of support on the conversion of methane to synthesis gas over supported iridium catalysts. Catalysis Letters, 1998, 51, 163-167. 51. Owen, R. E.; Plucinski, P.; Mattia, D.; Torrente-Murciano, L.; Ting, V. P.; Jones, M. D., Effect of support of Co-Na-Mo catalysts on the direct conversion of CO2 to hydrocarbons. Journal of CO2 Utilization, 2016, 16, 97-103. 52. Samantaray, M. K.; Dey, R.; Abou‐Hamad, E.; Hamieh, A.; Basset, J.-M., Effect of Support on Metathesis of n‐Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica–Alumina. Chem. Eur. J., 2015, 21, 6100-6106. 53. Burke, A. M.; Hanrahan, J. P.; Healy, D. A.; Sodeau, J. R.; Holmes, J. D.; Morris, M. A., Large pore bi-functionalised mesoporous silica for metal ion pollution treatment. J Haz. Mat., 2009, 164, 229-234. 54. Delaney, P.; McManamon, C.; Hanrahan, J. P.; Copley, M. P.; Holmes, J. D.; Morris, M. A., Development of chemically engineered porous metal oxides for phosphate removal. J Haz. Mat., 2011, 185, 382-391. 55. Delaney, P.; Healy, R. M.; Hanrahan, J. P.; Gibson, L. T.; Wenger, J. C.; Morris, M. A.; Holmes, J. D., Porous silica spheres as indoor air pollutant scavengers. Journal of Environmental Monitoring, 2010, 12, 2244-2251. 56. Barreca, D.; Copley, M. P.; Graham, A. E.; Holmes, J. D.; Morris, M. A.; Seraglia, R.; Spalding, T. R.; Tondello, E., Methanolysis of styrene oxide catalysed by a highly efficient zirconium-doped mesoporous silica. Applied Catalysis A: General, 2006, 304, 14-20. 57. Ahern, R. J.; Hanrahan, J. P.; Tobin, J. M.: Ryan, K. B.; Crean, A. M., Comparison of fenofibrate–mesoporous silica drug-loading processes for enhanced drug delivery. Eur. J. Pharm. Sci., 2013, 50, 400-409. 58. Abdallah, N. H.; Schlumpberger, M.; Gaffney, D. A.; Hanrahan, J. P.; Tobin, J. M.; Magner, E. M., Comparison of mesoporous silicate supports for the immobilisation and activity of cytochrome c and lipase. J. Mol. Cat B: Enzymatic, 2014, 108, 82-88. 59. Flynn, E. J.; Keane, D. A.; Tabari, P. M.; Morris, M. A., Pervaporation performance enhancement through the incorporation of mesoporous silica spheres into PVA membranes. Sep. Purif. Technol., 2013, 118, 73-80. 60. Kumar, A.; Madden, D. G.; Lusi, M.; Chen, K.-J.; Daniels, E. A.; Curtin, T.; Perry, J. J.; Zaworotko, M. J., Direct Air Capture of CO2 by Physisorbent Materials. Angew. Chem. Int. Ed., 2015, 54, 48, 14372-14377. 61. Encyclopaedia Britannica. Encyclopaedia Britannica Online. Encyclopaedia Britannica Inc., 2016. Web: https://www.britannica.com/science/silica 62. Terada, K.; Hayakawa, H.; Sawada, K.; Kiba, T., Silica gel as a support for inorganic ion- exchangers for the determination of caesium-137 in natural waters. Talanta, 1970, 17, 10, 955-693. 63. Kiss, J. T.; Pálinkó, I.; Molnár, A., Surface properties of fumed silica (Cab-O-Sil) and Cab-O- Sil-supported Pt and Cu catalysts, studied by IR spectroscopy. J. Mol. Struct., 1993, 293, 273-278. 64. Vaiano, V.; Iervolino, G.; Sannino, D.; Rizzo, L.; Sarno, G., MoOx/TiO2 immobilized on quartz support as structured catalyst for the photocatalytic oxidation of As(III) to As(V) in aqueous solutions. Chem. Eng. Res. Des., 2016, 109, 190-199. 65. Parlett, C. M. A.; Aydin, A.; Durndell, L. J.; Frattini, L.; Isaacs, M. A.; Lee, A. F.; Liu, X.; Olivi, L.; Trofimovaite, R.; Wilson, K.; Wu, C., Tailored mesoporous silica supports for Ni catalysed hydrogen production from ethanol steam reforming. Catal. Commun., 2017, 91, 76-79. 66. Terra, J. C. S.; Moores, A.; Moura, F. C. C., Amine-Functionalized Mesoporous Silica as a Support for on-Demand Release of Copper in the A3-Coupling Reaction: Ultralow Concentration Catalysis and Confinement Effect. ACS Sustainable Chem. Eng., 2019, 7, 9, 8696-8705. 67. Lee, S.-S.; Park, B.-K.; Byeon, S.-H.; Chang, F.; Kim, H., Mesoporous Silica-Supported Pd Nanoparticles; Highly Selective Catalyst for Hydrogenation of Olefins in Supercritical Carbon Dioxide. Chem. Mater., 2006, 18, 24, 5631-5633. 68. Lim, J.; Lee, S. S.; Ying, J. Y., Mesoporous silica-supported catalysts for metathesis: application to a circulating flow reactor. Chem. Commun., 2010, 46, 806-808. 69. Sneh, O.; George, S. M., Thermal Stability of Hydroxyl Groups on a Well-Defined Silica Surface. J. Phys. Chem., 1995, 99, 4639-4647. 70. Min, B. K.; Santra, A. K.; Goodman, D. W., Understanding silica-supported metal catalysts: Pd/silica as a case study. Catal. Today, 2003, 85, 113-124. 71. Martin, G. A.; Mirodatos, C.; Praliaud, H., Chemistry of silica-supported catalysts: preparation activation and reduction. Appl. Catal., 1981, 1, 6, 367-382. 72. Sermon, P. A.; Sivalingam, J., Mechanisms of preparation of silica supported catalysts. Colloids Surf., 1992, 63, 59-65. 73. Kandpal, D.; Kalele, S.; Kulkarni, S. K., Synthesis and characterization of silica–gold core- shell (SiO2@Au) nanoparticles. Pramana – J. Phys., 2007, 69, 2, 277-283. 74. Shioji, S.; Kawaguchi, M.; Hayashi, Y.; Tokami, K.; Yamamoto, H., Rehydroxylation of dehydrated silica surfaces by water vapor adsorption. Adv. Powder. Technol., 2001, 12, 331-342. 75. Kim, H. N.; Lee, S. K., Atomic structure and dehydration mechanism of amorphous silica: 29 1 Insights from Si and H solid-state MAS NMR study of SiO2 nanoparticles. Geochim. Cosmochim. Acta, 2013, 120, 39-64. 76. Gorlov, Y. I.; Konoplya, M. M.; Chuiko, A. A., Mechanism of the Dehydration and Rehydration of Silica. Theoretical and Experimental Chemistry, 1981, 16, 3, 263-266. 77. Zhuravlev, L. T., The surface chemistry of amorphous silica. Zhuravlev model. Colloids and Surf. A: Physicochemical and Engineering Aspects, 2000, 173, 1-38. 78. Mueller, R.; Kammler, H. K.; Wegner, K.; Pratsinis, S. E., OH Surface Density of SiO2 and TiO2 by Thermogravimetric Analysis. Langmuir, 2003, 19, 1, 160-165. 79. Zecchina, A.; Scarano, D.; Bordiga, S.; Spoto, G.; Lamberti, C., Surface Structures of Oxides and Halides and Their Relationships to Catalytic Properties. Adv. In Catal., 2001, 46, 265-397. 80. Busca, G., The surface of transitional aluminas: A critical review. Catal. Today, 2014, 226, 2- 13. 81. Trueba, M.; Trasatti, S. P., γ‐Alumina as a Support for Catalysts: A Review of Fundamental Aspects. Eur. J. Inorg. Chem., 2005, 2005, 17, 3393-3403. 82. Oh-Shim, J.; Kwang-Deog, J., CH4 Dry Reforming on Alumina-Supported Nickel Catalyst. Bull. Korean Chem. Soc., 2002, 23, 8, 1149-1153. 83. He, S.; Boom, J.; van der Gaast, R.; Seshan, K., Hydro-pyrolysis of lignocellulosic biomass over alumina supported Platinum, Mo2C and WC catalysts. Front. Chem. Sci. Eng., 2018, 12, 1, 155-161. 84. Keysar, S.; Shter, G. E.; de Hazan, Y.; Cohen, Y.; Grader, G. S., Heat Treatment of Alumina Aerogels. Chem. Mater., 1997, 9, 11, 2464-2467. 85. Nahin, P. G.; Huffman, H. C., Alumina and Alumina-Supported Catalysts. Electron Microscope Studies. Ind. Eng. Chem., 1949, 41, 9, 2021-2027. 86. Li, Z.-X.; Shi, F.-B.; Li, L.-L.; Zhang, T.; Yan, C.-H., A facile route to ordered mesoporous- alumina-supported catalysts, and their catalytic activities for CO oxidation. Phys. Chem. Chem. Phys., 2011, 13, 2488-2491. 87. Evangelista, J. P. C.; Gondim, A. D.; Souza, L. D.; Araujo, A. S., Alumina-supported potassium compounds as heterogeneous catalysts for biodiesel production: A review. Renew. Sustain. Energy Rev., 2016, 59, 887-894. 88. Pines, H.; Haag, W. O., Alumina: Catalyst and Support. I. Alumina, its Intrinsic Acidity and Catalytic Activity. J. Am. Chem. Soc., 1960, 82, 10, 2471-2483. 89. Hoang, D. L.; Chan, S. H.; Ding, O. L., Kinetic and modelling study of methane steam reforming over sulfide nickel catalyst on a gamma alumina support. Chem. Eng. J., 2005, 112, 1-11. 90. Bartek, J. P.; Guttmann, A. T.; Brazdil, J. F., Preparation of abrasion resistant alumina-supported vanadium-antimony oxidic catalysts. 1989, US Patent: US4797381A. 91. Kim, P.; Kim, Y.; Kim, H.; Song, I. K.; Yi, J., Synthesis and characterization of mesoporous alumina for use as a catalyst support in the hydrodechlorination of 1,2-dichloropropane: effect of preparation condition of mesoporous alumina. J. Mol. Cat. A: Chemical, 2004, 219, 87-95. 92. Joubert, J.; Delbecq, F.; Sautet, P., Alkane metathesis by a tungsten carbyne complex grafted on gamma alumina: Is there a direct chemical role of the support? Journal of Catalysis, 2007, 251, 507-513. 93. Horsley, J.; Wachs, I.; Brown, J.; Via, G.; Hardcastle, F., Structure of surface tungsten oxide species in the tungsten trioxide/alumina supported oxide system from x-ray absorption near-edge spectroscopy and Raman spectroscopy. J. Phys. Chem., 1987, 91, 15, 4014-4020. 94. Brenner, A.; Hucul, D. A., The synthesis and nature of heterogeneous catalysts of low-valent tungsten supported on alumina. Journal of Catalysis, 1980, 61, 1, 216-222. 95. Taoufik, M.; Le Roux, E.; Thivolle-Cazat, J.; Basset, J.-M., Direct Transformation of Ethylene into Propylene Catalyzed by a Tungsten Hydride Supported on Alumina: Trifunctional Single‐Site Catalysis. Angew. Chem. Int. Ed., 2007, 46, 7202-7205. 96. Le Roux, E.; Taoufik, M.; Copéret, C.; de Mallmann, A.; Thivolle-Cazat, J.; Basset, J.-M.; Maunders, B. M.; Sunley, G. J., Development of Tungsten‐Based Heterogeneous Alkane Metathesis Catalysts Through a Structure–Activity Relationship. Angew. Chem. Int. Ed., 2005, 44, 6755-6758. 97. Joubert, J.; Delbecq, F.; Sautet, P.; Roux, E. L.; Taoufik, M.; Thieuleux, C.; Blanc, F.; Copéret, C.; Thivolle-Cazat, J.; Basset, J.-M., Molecular Understanding of Alumina Supported Single-Site Catalysts by a Combination of Experiment and Theory. J. Am. Chem. Soc., 2006, 128, 9157-9169. 98. Mazoyer, E.; Szeto, K. C.; Merle, N.; Thivolle-Cazat, J.; Boyron, O.; Basset, J.-M.; Nicholas, C. P.; Taoufik, M., Insights into the deactivation mechanism of supported tungsten hydride on alumina (W-H/Al2O3) catalyst for the direct conversion of ethylene to propylene. J. Mol. Cat. A: Chemical, 2014, 385, 125-132. 99. Taoufik, M.; Roux, E. L.; Thivolle-Cazat, J.; Copéret, C.; Basset, J.-M.; Maunders, B.; Sunley, G. J., Alumina supported tungsten hydrides, new efficient catalysts for alkane metathesis. Topics in Catal., 2006, 40, 65-70. 100. Pearson, M. J., Alumina Catalysts in Low-Temperature Claus Process. Product R&D, 1977, 16, 2, 154-158. 101. Roy, S.; Mpourmpakis, G.; Hong, D.-Y.; Vlachos, D. G.; Bhan, A.; Gorte, R. J., Mechanistic Study of Alcohol Dehydration on γ-Al2O3. ACS Catal., 2012, 2, 9, 1846-1853. 102. Escobar, J.; Gutiérrez, A. W.; Barrera, M. C.; Colín, J. A., NiMo/alumina hydrodesulphurization catalyst modified by saccharose: Effect of addition stage of organic modifier. Can. J. Chem. Eng., 2016, 94, 66-74. 103. Scoton, A.; Chinelatto, A.; Pallone, E. M. D. J. A.; de Souza, A. M.; Manosso, M. K.; Chinelatto, A. L.; Tomasi, R., Mechanisms of Microstructure Control in Conventional Sintering. 2012. Mechanisms of Microstructure Control in Conventional Sintering, Sintering of Ceramics - New Emerging Techniques, Dr. Arunachalam Lakshmanan (Ed.), ISBN: 978-953-51-0017-1, InTech, Available from: http://www.intechopen.com/books/sintering-of-ceramics-new-emerging- techniques/mechanisms-ofmicrostructure-control-in-conventional-sintering. 104. Abdulateef, L. T.; Nawaf, A. T.; Mahmood, Q. A.; Dahham, O. S.; Noriman, N. Z.; Shayfull, Z., Preparation, characterization and application of alumina nanoparticles with multiple active component for oxidation desulfurization. AIP Conference Proceedings, 2018, 2030, 1, 020031. DOI: 10.1063/1.5066672. 105. Leydier, F.; Chizallet, C.; Chaumonnot, A.; Digne, M.; Soyer, E.; Quoineaud, A.-A.; Costa, D.; Raybaud, P., Brønsted acidity of amorphous silica–alumina: The molecular rules of proton transfer. Journal of Catalysis, 2011, 284, 2, 215-229. 106. Crépeau, G.; Montouillout, V.; Vimont, A.; Mariey, L.; Cseri, T.; Maugé, F., Nature, Structure and Strength of the Acidic Sites of Amorphous Silica Alumina: An IR and NMR Study. J. Phys. Chem. B, 2006, 110, 31, 15172-15185. 107. Kumar, S. R.; Pillai, P. K.; Warrier, K. G. K., Synthesis of high surface area silica by solvent exchange in alkoxy derived silica gels. Polyhedron, 1998, 17, 1699-1703. 108. Matsumoto, Y.; Mita, K.; Hashimoto, K.; Tokoroyama, T., Preparation of silica-alumina catalyst by the sol-gel method and its activity for the Diels-Alder reaction of isoprene and acrylaldehyde. Appl. Catal. A: General, 1995, 131, L1-L6. 109. Matsumoto, Y.; Mita, K.; Hashimoto, K., Selective cleavage of ethers using silica-alumina gel catalysts prepared by the sol-gel method. Tetrahedron, 1996, 52, 9387-9398. 110. Tamon, H.; Sone, T.; Mikami, M.; Okazaki, M., Preparation and Characterization of Silica–Titania and Silica–Alumina Aerogels. J. Colloid Interface Sci., 1997, 188, 493-500. 111. Carati, A.; Ferraris, G.; Guidotti, M.; Moretti, G.; Psaro, R.; Rizzo, C., Preparation and characterisation of mesoporous silica–alumina and silica–titania with a narrow pore size distribution. Catal. Today, 2003, 77, 315-323. 112. Takahashi, R.; Sato, S.; Sodesawa, T.; Yabuki, M., Effect of diffusion in catalytic dehydration of alcohol over silica–alumina with continuous macropores. J. Catal., 2005, 229, 24-29. 113. Ochoa, R.; Woert, H. V.; Lee, W. H.; Subramanian, R.; Kugler, E.; Eklund, P. C., Catalytic degradation of medium density polyethylene over silica-alumina supports. Fuel Process. Technol., 1996, 49, 119-136. 114. Satou, S.; Morimoto, Y.; Takatsuka, T.; Hashimoto, H., Matrix Pore Structure and Bottom Cracking Capability of Residue FCC Catalysts. J. Jpn. Petrol. Inst., 1986, 29, 1, 60-65. 115. Rajagopalan, K.; Habib Jr., E. T., Understand FCC matrix technology. Hydrocarbon Process, 1992, 9, 43-46. 116. Falco, M.; Morgado, E.; Amadeo, N.; Sedran, U., Accessibility in alumina matrices of FCC catalysts. Appl. Catal. A: Gen., 2006, 315, 29-34. 117. Andreu, P., Development of catalysts for the fluid catalytic cracking process: An example of CYTED-D program. Catal. Lett., 1993, 22, 135-146. 118. Kubicek, N.; Vaudry, F.; Chiche, B. H.; Hudec, P.; Di Renzo, F.; Schulz, P.; Fajula, F., Stabilization of zeolite beta for fcc application by embedding in amorphous matrix. Appl. Catal. A: General, 1998, 175, 159-171. 119. Yabuki, M.; Takahashi, R.; Sato, S.; Sodesawa, T.; Ogura, K., Silica–alumina catalysts prepared in sol–gel process of TEOS with organic additives. Phys. Chem. Chem. Phys., 2002, 4, 4830-4837. 120. Munnik, P.; de Jongh, P. E.; de Jong, K. P., Recent Developments in the Synthesis of Supported Catalysts. Chem. Rev., 2015, 115, 6687-6718. 121. Benaglia, M.; Puglisi, A.; Cozzi, F., Polymer-Supported Organic Catalysts. Chem. Rev., 2003, 103, 9, 3401-3429. 122. Boruah, J. J.; Das, S. P.; Ankireddy, S. R.; Gogoia, S. R.; Islam, N. S., Merrifield resin supported peroxomolybdenum (VI) compounds: recoverable heterogeneous catalysts for the efficient, selective and mild oxidation of organic sulfides with H2O2. Green Chem., 2013, 15, 2944-2959. 123. Werghi, B.; Pump, E.; Tretiakov, M.; Abou-Hamad, E.; Gurinov, A.; Doggali, P.; Anjum, D. H.; Cavallo, L.; Bendjeriou-Sedjerari, A.; Basset, J.-M., Exploiting the interactions between the ruthenium Hoveyda–Grubbs catalyst and Al-modified mesoporous silica: the case of SBA15 vs. KCC-1. Chem. Sci., 2018, 9, 3531-3537. 124. Yang, Q.; Xubc, Q.; Jiang, H.-L., Metal–organic frameworks meet metal nanoparticles: synergistic effect for enhanced catalysis. Chem. Soc. Rev., 2017, 46, 4774-4808. 125. Dufaud, V.; Basset, J.-M., Catalytic Hydrogenolysis at Low Temperature and Pressure of Polyethylene and Polypropylene to Diesels or Lower Alkanes by a Zirconium Hydride Supported on Silica‐Alumina: A Step Toward Polyolefin Degradation by the Microscopic Reverse of Ziegler– Natta Polymerization. Angew. Chem. Int. Ed., 1998, 37, 806-810. 126. Quignard, F.; Lecuyer, C.; Bougault, C.; Lefebvre, F.; Choplin, A.; Olivier, D.; Basset, J.-M., Surface organometallic chemistry: synthesis and characterization of a tris(neopentyl)zirconium(IV) complex grafted to the surface of a partially dehydroxylated silica. Inorg. Chem., 1992, 31, 5, 928- 930. 127. Crestani, M. G.; Hickey, A. K.; Gao, X.; Pinter, B.; Cavaliere, V. N.; Ito, J.-I.; Chen, C.-H.; Mindiola, D. J., Room Temperature Dehydrogenation of Ethane, Propane, Linear Alkanes C4–C8, and Some Cyclic Alkanes by Titanium–Carbon Multiple Bonds. J. Am. Chem. Soc., 2013, 135, 39, 14754- 14767. 128. Basset, J.-M.; Psaro, R.; Roberto, D.; Ugo, R., Modern Surface Organometallic Chemistry. 2009, Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, ISBN: 9783527627097. 129. Basset, J.-M.; Pelletier, J. D. A., Predictive approach of heterogeneous catalysis. National Science Review, 2018, 5, 5, 633-635. 130. Blay, V.; Epelde, E.; Miravalles, R.; Perea, L. A., Converting olefins to propene: Ethene to propene and olefin cracking. Catal. Rev., 2018, 60, 2, 278-335. 131. Lutz, E. F., Shell Higher Olefin Process. J. Chem Educ., 1986, 63, 3, 202-203. 132. Basset, J.-M.; Stoffelbach, F.; Taoufik, M.; Thivolle-Cazat, J., Process for manufacturing neohexene. 2007, US Patent, US8119852B2. 133. Asakura, K.; Nishimura, M.; Iwasawa, Y., Spectroscopic evidence for a surface Nb carbene in a new SiO2-attached Nb catalyst active for propene metathesis. J. Mol. Cat., 1989, 55, 159-169. 134. Herrmann, W. A.; Wagner, W.; Flessner, U. N.; Volkhardt, U.; Komber, H., Methyltrioxorhenium as Catalyst for Olefin Metathesis. Angew. Chem. Int. Ed., 1991, 30, 1636-1638. 135. Herisson, J.-L.; Chauvin, Y., Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques. Makromol. Chem., 1971, 141, 161-176. 136. Lwin, S.; Wachs, I. E., Olefin Metathesis by Supported Metal Oxide Catalysts. ACS Catal., 2014, 4, 8, 2505-2520. 137. Mazoyer, E.; Merle, N.; de Mallmann, A.; Basset, J.-M.; Berrier, E.; Delevoye, L.; Paul, J.-F.; Nicholas, C. P.; Gauvin, R. M.; Taoufik, M., Development of the first well-defined tungsten oxo alkyl derivatives supported on silica by SOMC: towards a model of WO3/SiO2 olefin metathesis catalyst. Chem. Commun., 2010, 46, 8944-8946. 138. Vidal, V.; Théolier, A.; Thivolle-Cazat, J.; Basset, J.-M., Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides. Science, 1997, 276, 5309, 99-102. 139. Tang, P.; Zhu, Q.; Wu, Z.; Ma, D., Methane activation: the past and future. Energy Environ. Sci., 2014, 7, 2580-2591. 140. Maity, N.; Barman, S.; Callens, E.; Samantaray, M. K.; Abou-Hamad, E.; Minenkov, Y.; D’Elia, V.; Hoffman, A. S.; Widdifield, C. M.; Cavallo, L.; Gates, B. C.; Basset, J.-M., Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides. Chem. Sci. 2016, 7, 1558- 1568. 141. Blanc, F.; Coperet, C.; Thivolle-Cazat, J.; Basset, J.-M., Alkane Metathesis Catalyzed by a Well‐

Angew. Chem. Int. Ed., 2006, 45, 6201-6203. 142. Riache, N.; Callens, E.; Samantaray, M. K.; Kharbatia, N. M.; Atiqullah, M., Basset, J.-M., Cyclooctane Metathesis Catalyzed by Silica‐Supported Tungsten Pentamethyl [(≡SiO)W(Me)5]: Distribution of Macrocyclic Alkanes. Chem. Eur. J., 2014, 20, 15089- 15094. 143. Polshettiwar, V.; Thivolle-Cazat, J.; Taoufik, M.; Stoffelbach, F.; Norsic, S.; Basset, J.-M., “Hydro‐ metathesis” of Olefins: A Catalytic Reaction Using a Bifunctional Single‐Site Tantalum Hydride Catalyst Supported on Fibrous Silica (KCC‐1) Nanospheres. Angew. Chem. Int. Ed., 2011, 50, 12, 2747-2751. 144. Saidi, A.; Samantaray, M. K.; Tretiakov, M.; Kavitake, S.; Basset, J.-M., Understanding the Hydro‐ Metathesis Reaction of 1‐Decene By Using Well‐Defined Silica Supported W, Mo, Ta Carbene/Carbyne Complexes. Chem. Cat. Chem., 2017, 10 (8), 1912-1917. 145. Hamzaoui, B.; Pelletier, J. D. A.; Abou-Hamad, E.; Basset, J.-M., Well-defined silica-supported zirconium–imido complexes mediated heterogeneous imine metathesis. Chem. Commun., 2016, 52, 4617-4620. 146. Jezequel, M.; Dufaud, V.; Ruiz-Garcia, M. J.; Carrillo-Hermosilla, F.; Neugebauer, U.; Niccolai, G. P.; Lefebvre, F.; Bayard, F.; Corker, J.; Fiddy, S.; Evans, J.; Broyer, J.-P.; Malinge, J.; Basset, J.-M., Supported Metallocene Catalysts by Surface Organometallic Chemistry. Synthesis, Characterization, and Reactivity in Ethylene Polymerization of Oxide-Supported Mono- and Biscyclopentadienyl Zirconium Alkyl Complexes: Establishment of Structure/Reactivity Relationships. J. Am. Chem. Soc., 2001, 123, 15, 3520-3540. 147. Riache, N.; Dery, A.; Callens, E.; Poater, A.; Samantaray, M. K.; Dey, R.; Hong, J.; Li, K.; Cavallo, L.; Basset, J.-M., Silica-Supported Tungsten Carbynes (≡SiO)xW(≡CH)(Me)y (x = 1, y = 2; x = 2, y = 1): New Efficient Catalysts for Alkyne Cyclotrimerization. Organometallics, 2015, 34, 4, 690-695. 148. Shaikh, R. R.; Pornpraprom, S.; D’Elia, V., Catalytic Strategies for the Cycloaddition of Pure, Diluted, and Waste CO2 to Epoxides under Ambient Conditions. ACS Catal., 2018, 8, 1, 419-450. 149. Poland, S. J.; Darensbourg, D. J., A quest for polycarbonates provided via sustainable epoxide/CO2 copolymerization processes. Green Chem., 2017, 19, 4990-5011. 150. Geerlings, H.; Zevenhoven, R., CO2 Mineralization—Bridge Between Storage and Utilization of CO2. Annu. Rev. Chem. Biomol. Eng., 2013, 4, 103-117. 151. Martin, C.; Fiorani, G.; Kleij, A. W., Recent Advances in the Catalytic Preparation of Cyclic Organic Carbonates. ACS Catal., 2015, 5, 2, 1353-1370. 152. Arayachukiata, S.; Yingcharoena, P.; Vummaleti, S. V. C.; Cavallo, L.; Poater, A.; D’Elia, V., Cycloaddition of CO2 to challenging N-tosyl aziridines using a halogen-free niobium complex: Catalytic activity and mechanistic insights. Mol. Catal., 2017, 443, 280-285. 153. Comerford, J. W.; Ingram, I. D. V.; North, M.; Wu, X., Sustainable metal-based catalysts for the synthesis of cyclic carbonates containing five-membered rings. Green Chem., 2015, 17, 1966- 1987. 154. Schäffner, B.; Schäffner, F.; Verevkin, S. P.; Börner, A., Organic Carbonates as Solvents in Synthesis and Catalysis. Chem. Rev., 2010, 110, 8, 4554-4581. 155. Han, Z.; Rong, L.; Wu, J.; Zhang, L.; Wang, Z.; Ding, K., Catalytic Hydrogenation of Cyclic Carbonates: A Practical Approach from CO2 and Epoxides to Methanol and Diols. Angew. Chem., Int. Ed., 2012, 51, 13041-13045. 156. Fukuoka, S.; Kawamura, M.; Komiya, K.; Tojo, M.; Hachiya, H.; Hasegawa, K.; Aminaka, M.; Okamoto, H.; Fukawa, I.; Konno, S., A novel non-phosgene polycarbonate production process using by-product CO2 as starting material. Green Chem., 2003, 5, 497-507. 157. Kleij, A. W.; North, M.; Urakawa, A., CO2 catalysis. ChemSusChem, 2017, 10, 1036-1038. 158. Astruc, D., Olefin Metathesis Reactions: From a Historical Account to Recent Trends. In: Olefin Metathesis: Theory and Practice, Grela, K., Wiley, 2014, 1-34. 159. Astruc, D., The metathesis reactions: from a historical perspective to recent developments. New J. Chem., 2005, 29, 42-56. 160. Eleuterio, H. S., 1960, German Pat., 1960, 1072811. 161. Schneider, V.; Frolich, P. K., Mechanism of formation of aromatics from lower paraffins. Ind. Eng. Chem., 1931, 23, 1405-1410. 162. Banks, R. L.; Bailey, G. C., Olefin Disproportionation. A New Catalytic Process. Ind. Eng. Chem. Prod. Res. Dev., 1964, 3, 3, 170-173. 163. Anderson, A. W.; Merckling, N. G. Polymeric bicyclo-(2,2,1)-2- heptene. 1955, U.S. Patent 2721189 (A). 164. Fairbanks, A. J.; Ford, P. S.; Watkin, D. J.; Fleet, G. W. J., Synthesis of 1-epihydantocidin from d- ribose. Tetrahedron Lett., 1967, 34 , 3327-3330. 165. Calderon, N., Olefin Metathesis Reaction. Acc. Chem. Res., 1972, 5, 127-132. 166. Bradshaw, C. P. W.; Howmen, E. J.; Turner, L., Olefin dismutaition: Reactions of olefins on cobalt oxidemolybdenum oxide-alumina. J Catalysis, 1967, 7, 269-276. 167. Begley, J. W.; Wilson, R. T., Kinetics of propylene disproportionation, J. Catalysis, 1967, 9, 375- 395. 168. Hughes, W. B., Kinetics and mechanism of the homogeneous olefin disproportionation reaction. J. Am. Chem. Soc., 1970, 92, 532-537. 169. Chauvin, Y.; Commereuc, D.; Cruypelinck, D., Catalysis of olefin transformation by tungsten complexes, 5. Tungsten carbonyl carbenes activated by titanium tetrahalides as catalysts for the ring-opening polymerization of cyclopentene, Makromol. Chem., 1976, 177, 2637-2647. 170. Eleuterio, H. S., Olefin metathesis: chance favors those minds that are best prepared. J. Mol. Catal., 1991, 65, 55-61. 171. Singh, O. M., Metathesis catalysts: Historical perspective, recent developments and practical applications. J. Sci. Ind. Res., 2006, 65, 957-965. 172. Hughes, D.; Wheeler, P.; Ene, D., Olefin Metathesis in Drug Discovery and Development— Examples from Recent Patent Literature. Org. Process Res. Dev., 2017, 21, 12, 1938-1962. 173. Malacea, R.; Dixneuf, P. H., Alkene Metathesis and Renewable Materials: Selective Transformations of Plant Oils. 2010, In: Dragutan V., Demonceau A., Dragutan I., Finkelshtein E.S. (eds) Green Metathesis Chemistry. NATO Science for Peace and Security Series A: Chemistry and Biology. Springer, Dordrecht, ISBN: 978-90-481-3433-5. 174. Slugovc, C., Industrial Applications of Olefin Metathesis Polymerization. In Olefin Metathesis: Theory and Practice; Grela, K., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, 2014; 329-333. 175. Fürstner, A.; Davies, P. W., Alkyne metathesis. Chem. Commun., 2005, 2307-2320. 176. Pennella, F.; Banks, R. L.; Bailey, G. C., Disproportionation of alkynes. J. Chem. Soc. Chem. Commun., 1968, 1548-1549. 177. Mortreux, A.; Blanchard, M., Metathesis of alkynes by a molybdenum hexacarbonyl– resorcinol catalyst. J. Chem. Soc., Chem. Commun., 1974, 786-787. 178. Mortreux, A.; Dy, N.; Blanchard, M., Metathese des hydrocarbures acetyleniques sur des catalyseurs a base de molybdene. J. Mol. Catal., 1976, 1, 101-109. 179. Mortreux, A.; Petit, F.; Blanchard, M., 13C tracer studies of alkynes metathesis. Tetrahedron Lett., 1978, 4967-4968. 180. Bencheick, A.; Petit, M.; Mortreux, A.; Petit, F., New active and selective catalysts for homogeneous metathesis of disubstituted alkynes. J. Mol. Catal., 1982, 15, 93-101. 181. Mortreux, A.; Delgrange, J. C.; Blanchard, M.; Lubochinsky, B., Rôle du phénol dans la métathèse des hydrocarbures acétyléniques sur les catalyseursà base de Mo(CO)6. J. Mol. Catal., 1977, 2, 73-82. 182. Mortreux, A.; Petit, F.; Blanchard, M., Improving selectivity and 13C experiments during metathesis of alkynes on MoO3 2 catalysts. J. Mol. Catal., 1980, 8, 97-106. 183. Kloppenburg, L.; Song, D.; Bunz, U. H. F., Alkyne Metathesis with Simple Catalyst Systems: Poly(p- phenyleneethynylene)s. J. Am. Chem. Soc., 1998, 120, 31, 7973-7974. 184. Huc, V.; Weihofen, R.; Martin-Jimenez, I.; Oulié, P.; Lepetit, C.; Lavigne, G.; Chauvin, R., Ether- induced rate enhancement of Mo-catalyzed alkyne metathesis under mild conditions. New J. Chem., 2003, 27, 1412-1414. 185. Brizius, G.; Bunz, U. H. F., Increased Activity of in Situ Catalysts for Alkyne Metathesis. Org. Lett., 2002, 4, 17, 2829-2831. 186. Naotake, K.; Ken, H.; Shin-ichi, A.; Motokazu, U.; Miwako, M., Novel Synthesis of Disubstituted Alkyne Using Molybdenum Catalyzed Cross-Alkyne Metathesis. Chem. Lett., 1995, 1055-1056. 187. Brizius. G.; Pschirer, N. G.; Steffen, W.; Stitzer, K.; zur Loye, H.-C.; Bunz, U. H. F., Alkyne Metathesis with Simple Catalyst Systems: Efficient Synthesis of Conjugated Polymers Containing Vinyl Groups in Main or Side Chain. J. Am. Chem. Soc., 2000, 122, 50, 12435-12440. 188. Grela, K.; Ignatowska, J., An Improved Catalyst for Ring-Closing Alkyne Metathesis Based on Molybdenum Hexacarbonyl/2-Fluorophenol. Org. Lett., 2002, 4, 21, 3747-3749. 189. Sashuk, V.; Ignatowska, J.; Grela, K., A Fine-Tuned Molybdenum Hexacarbonyl/Phenol Initiator for Alkyne Metathesis. J. Org. Chem., 2004, 69, 22, 7748-7751. 190. Schrock, R. R., High Oxidation State Multiple Metal−Carbon Bonds. Chem. Rev., 2002, 102, 145- 180. 191. Sancho, J.; Schrock, R. R., Acetylene metathesis by tungsten(VI) alkylidyne complexes. J. Mol. Catal., 1982, 15, 75-79. 192. Diver, S. T.; Giessert, A. J., Enyne Metathesis (Enyne Bond Reorganization). Chem. Rev., 2004, 104, 1317-1382. 193. Schrock, R. R.; Clark, D. N.; Sancho, J.; Wengrovius, J. H.; Rocklage, S. M.; Pedersen, S. F., Tungsten(VI) neopentylidyne complexes. Organometallics, 1982, 1, 1645-1651. 194. Akiyama, M.; Chisholm, M. H.; Cotton, F. A.; Extine, M. W.; Haitko, D. A.; Little, D.; Fanwick, P. E., The tungsten-tungsten triple bond. 8. Dinuclear alkoxides of tungsten(III) and structural characterization of hexaisopropoxybis(pyridine)ditungsten, the first compound with four- coordinated tungsten atoms united by a triple bond. Inorg. Chem., 1979, 18, 2266-2270. 195. Schrock, R. R., The alkoxide ligand in olefin and acetylene metathesis reactions. Polyhedron, 1995, 14, 22, 3177-3195. 196. Calderon, N.; Ofstead, E. A.; Ward, J. P.; Judy, W. A.; Scott, K. W., Olefin metathesis. I. Acyclic vinylenic hydrocarbons. J. Am. Chem. Soc., 1968, 90, 15, 4133-4140. 197. Lewandos, G. S.; Pettit, R., Mechanism of the metal-catalyzed disproportionation of olefins. J. Am. Chem. Soc., 1971, 93, 25, 7087-7088. 198. Grubbs, R. H.; Brunck, T. K., Possible intermediate in the tungsten-catalyzed olefin metathesis reaction. J. Am. Chem. Soc., 1972, 94, 7, 2538-2540. 199. Biefeld, C. G.; Eick, H. A.; Grubbs, R. H., Crystal structure of bis(triphenylphosphine)tetramethyleneplatinum(II). Inorg. Chem., 1973, 12, 9, 2166-2170. 200. Fischer, E. O.; Maasböl, A., On the Existence of a Tungsten Carbonyl Carbene Complex. Angew. Chem. Int. Ed., 1964, 3, 8, 580-581. 201. Natta, G.; Dall’Asta, G.; Mazzanti, G., Stereospecific Homopolymerization of Cyclopentene. Angew. Chem. Int. Ed., 1964, 3, 11, 723-729. 202. Watson, P. L.; Methane exchange reactions of lanthanide and early-transition-metal methyl complexes. J. Am. Chem. Soc., 1983, 105, 21, 6491-6493. 203. Thompson, M. E.; Brecaw, J. E., Some aspects of the chemistry of alkyl and hydride derivatives of permethylscandocene. Pure Appl. Chem., 1984, 56, 1-11. 204. Fendrick, C. M.; Marks, T. J., Actinacyclobutanes. Thermochemistry based strategies for the ring- opening stoichiometric activation of saturated and olefinic hydrocarbons. J. Am. Chem. Soc., 1986, 108, 3, 425-437. 205. Casey, C. P.; Burkhardt, T. J., Reactions of (diphenylcarbene)pentacarbonyltungsten(0) with alkenes. Role of metal-carbene complexes in cyclopropanation and olefin metathesis reactions. J. Am. Chem. Soc., 1974, 96, 25, 7808-7809. 206. Grubbs, R. H.; Carr, D. D.; Hoppin, C.; Burk, P. L., Consideration of the mechanism of the metal catalyzed olefin metathesis reaction. J. Am. Chem. Soc., 1976, 98, 12, 3478-3483. 207. McGinnis, J.; Katz, T. J.; Hurwitz, S., Selectivity in the olefin metathesis of unsymmetrically substituted ethylenes. J. Am. Chem. Soc., 1976, 98, 2, 605-606. 208. Katz. T. J., The Olefin Metathesis Reaction. Adv Organomet. Chem., 1977, 16, 283-317. 209. Schrock, R. R., Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture). Angew. Chem. Int. Ed., 2006, 45, 23, 3748-3759. 210. Deraedt, C.; d’Halluin, M.; Astruc, D., Metathesis Reactions: Recent Trends and Challenges. Eur. J. Inorg. Chem., 2013, 2013, 28, 4881-4908. 211. Fischer, E. O.; Kreis, G.; Kreiter, C. G.; Müller, J.; Huttner, G.; Lorenz, H., trans‐ Halogeno[alkyl(aryl)carbyne]tetracarbonyl Complexes of Chromium, Molybdenum, and Tungsten —A New Class of Compounds Having a Transition Metal‐Carbon Triple Bond. Angew. Chem. Int. Ed., 1973, 12, 7, 564-565. 212. Wengrovius, J. H.; Sancho, J.; Schrock. R. R., Metathesis of acetylenes by tungsten(VI)-alkylidyne complexes. J. Am. Chem. Soc., 1981, 103, 13, 3932-3934. 213. Pedersen, S. F.; Schrock, R. R.; Churchill, M. R.; Wasserman, H. J., Reaction of tungsten(VI) alkylidyne complexes with acetylenes to give tungstenacyclobutadiene and cyclopentadienyl complexes. J. Am. Chem. Soc., 1982, 104, 24, 6808-6809. 214. Grubbs, R. H., Olefin-metathesis catalysts for the preparation of molecules and materials (Nobel Lecture). Angew. Chem. Int. Ed., 2006, 45, 23, 3760-3765. 215. Van Dam, P. B.; Mittlemeijer, M. C. Mrs.; Boelhouwer, C., Metathesis of unsaturated fatty esters by a homogeneous tungsten hexachloride – tetramethyltin catalyst. J. Chem. Soc., Chem. Commun., 1972, 1221-1222. 216. Fu, G. C.; Grubbs, R. H., The application of catalytic ring-closing olefin metathesis to the synthesis of unsaturated oxygen heterocycles. J. Am. Chem. Soc., 1992, 114, 13, 5426-5427. 217. Fu, G. C.; Grubbs, R. H., The synthesis of nitrogen heterocycles via catalytic ring-closing metathesis of dienes. J. Am. Chem. Soc., 1992, 114, 18, 7324-7325. 218. Michelotti, F. W.; Keaveney, W. P., Coordinated polymerization of the bicyclo‐[2.2.1]‐heptene‐2 ring system (norbornene) in polar media. J. Poly. Sci., Part A, 1965, 3, 3, 895-905. 219. Novak, B. M.; Grubbs, R. H., The ring opening metathesis polymerization of 7- oxabicyclo[2.2.1]hept-5-ene derivatives: a new acyclic polymeric ionophore. J. Am. Chem. Soc., 1988, 110, 3, 960-961. 220. Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W., Syntheses and activities of new single-component, ruthenium-based olefin metathesis catalysts. J. Am. Chem. Soc., 1993, 115, 21, 9858-9859. 221. Sanford, M. S.; Love, J. A.; Grubbs, R. H., Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts. J. Am. Chem. Soc., 2001, 123, 27, 6543-6554. 222. Weskamp, T.; Kohl, F. J.; Hieringer, W.; Gleich, D.; Herrmann, W. A., Highly Active Ruthenium Catalysts for Olefin Metathesis: The Synergy of N-Heterocyclic Carbenes and Coordinatively Labile Ligands. Angew. Chem. Int. Ed., 1999, 38, 16, 2416-2419. 223. Basset, J.-M.; Taoufik, M.; Thivolle-Cazat, J.; Chakka, S., Process for converting methane into liquid alkane mixtures. Eur. Pat., EP2022772A1, 2009. 224. Heckelsberg, L. F.; Banks, R. L.; Bailey, G. C., Tungsten Oxide on Silica Catalyst for Phillips' Triolefin Process. Ind. Eng. Chem. Prod. Res. Dev., 1968, 7, 1, 29-31. 225. Burnett, R. L.; Hughes, T. R., Mechanism and poisoning of the molecular redistribution reaction of alkanes with a dual-functional catalyst system. J. Catal., 1973, 31, 55-64. 226. Vidal, V.; Théolier, A.; Thivolle-Cazat, J.; Basset, J.-M.; Corker, J., Synthesis, Characterization, and Reactivity, in the C−H Bond Activation of Cycloalkanes, of a Silica-Supported Tantalum(III) III Monohydride Complex: (⋮SiO)2Ta −H. J. Am. Chem. Soc., 1996, 118, 19, 4595-4602. 227. Quignard, F.; Le´cuyer, C.; Choplin, A.; Olivier, D.; Basset, J.-M. Surface organometallic chemistry of zirconium: Application to the stoichiometric activation of the CH bonds of alkanes and to the low-temperature catalytic hydrogenolysis of alkanes. J. Mol. Catal., 1992, 74, 1-3, 353-363. 228. Rosier, C.; Niccolai, G. P.; Basset, J. M., Catalytic Hydrogenolysis and Isomerization of Light Alkanes over the Silica-Supported Titanium Hydride Complex (⋮SiO)3TiH. J. Am. Chem. Soc., 1997, 119, 50, 12408-12409. 229. Le Roux, E.; Chabanas, M.; Baudouin, A.; de Mallmann, A.; Copéret, C.; Quadrelli, E. A.; Thivolle- Cazat, J.; Basset, J.-M.; Lukens, W.; Lesage, A.; Emsley, L.; Sunley, G. J., Detailed Structural Investigation of the Grafting of [Ta(=CHtBu)(CH2tBu)3] and [Cp*TaMe4] on Silica Partially Dehydroxylated at 700 °C and the Activity of the Grafted Complexes toward Alkane Metathesis. J. Am. Chem. Soc., 2004, 126, 41, 13391–13399. 230. Dufaud, V.; Niccolai, G. P.; Thivolle-Cazat, J.; Basset, J.-M., Surface Organometallic Chemistry of Inorganic Oxides: The Synthesis and Characterization of (≡SiO)Ta(:CHC(CH3)3)(CH2C(CH3)3)2 and (≡SiO)2Ta(:CHC(CH3)3)(CH2C(CH3)3). J. Am. Chem. Soc., 1995, 117, 15, 4288–4294. 231. Leconte, M.; Basset, J.-M., Stereoselectivity of metathesis of various acyclic olefins with chromium-, molybdenum-, and tungsten-based catalysts. J. Am. Chem. Soc., 1979, 101, 24, 7296- 7302. 232. Basset, J.-M.; Coperet, C.; Lefort, L.; Maunders, B. M.; Maury, O.; Le Roux, E.; Saggio, G.; Soignier, S.; Soulivong, D.; Sunley, G. J.; Taoufik, M.; Thivolle-Cazat, J., Primary Products and Mechanistic Considerations in Alkane Metathesis. J. Am. Chem. Soc., 2005, 127, 24, 8604-8605. 233. Le Roux, E.; Taoufik, M.; Chabanas, M.; Alcor, D.; Baudouin, A.; Copéret, C.; Thivolle-Cazat, J.; Basset, J.-M.; Lesage, A.; Hediger, S.; Emsley, L., Well-Defined Surface Tungstenocarbyne Complexes through the Reaction of [W(⋮CtBu)(CH2tBu)3] with Silica. Organometallics, 2005, 24, 17, 4274-4279. 234. Samantaray, M. K.; Callens, E.; Abou-Hamad, E.; Rossini, A. J.; Widdifield, C. M.; Dey, R.;

Emsley, L.; Basset, J.-M., WMe6 Tamed by Silica: ≡Si–O–WMe5 as an Efficient, Well- Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W– Methyl/Methylidyne Species. J. Am. Chem. Soc., 2014, 136, 3, 1054-1061. 235. Chen, Y.; Abou-Hamad, E.; Hamieh, A.; Hamzaoui, B.; Emsley, L.; Basset, J.-M., Alkane Metathesis with the Tantalum Methylidene [(≡SiO)Ta(═CH2)Me2]/[(≡SiO)2Ta(═CH2)Me] Generated from Well- V Defined Surface Organometallic Complex [(≡SiO)Ta Me4]. J. Am. Chem. Soc., 2015, 137, 2, 588- 591. 236. You, L.; An, R.; Liang, K.; Cui, B.; Wang, X., Macrocyclic Compounds: Emerging Opportunities for Current Drug Discovery. Curr. Pharm. Des., 2016, 22, 26, 4086-4093. 237. Ogoshi, T.; Yamagishi, T.-A., Pillararenes. The Royal Society of Chemistry, Cambridge, 2016, 1-22. 238. Callens, E.; Abou-Hamad, E.; Riache, N.; Basset, J.-M., Direct observation of supported W bis- methylidene from supported W-methyl/methylidyne species. Chem. Commun., 2014, 50, 3982- 3985. 239. Pump, E.; Cao, Z.; Samantaray, M. K.; Bendjeriou-Sedjerari, A.; Cavallo, L.; Basset, J.-M., Exploiting Confinement Effects to Tune Selectivity in Cyclooctane Metathesis. ACS Catal., 2017, 7, 10, 6581- 6586. 240. Samantaray, M. K.; Dey, R.; Kavitake, S.; Abou-Hamad, E.; Bendjeriou-Sedjerari, A.; Hamieh, A.; Basset, J.-M., Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane. J. Am. Chem. Soc., 2016, 138, 27, 8595-8602. 241. Norsic, S.; Larabi, C.; Delgado, M.; Garron, A.; de Mallmann, A.; Santini, C.; Szeto, K. C.; Basset, J.- M.; Taoufik, M., Low temperature hydrogenolysis of waxes to diesel range gasoline and light alkanes: Comparison of catalytic properties of group 4, 5 and 6 metal hydrides supported on silica–alumina. Catal. Sci. Technol., 2012, 2, 215-219.

Chapter 2. Understanding the challenge of the metathesis of functionalized alkanes

2.1. Introduction Nowadays, the metathesis method is widely used in fundamental research and industrial processes. It allows for the efficient and environmentally-friendly production of a variety of products, such as fuels1, pharmaceuticals2, and organic building blocks.3 After a breakthrough discovery of the olefin metathesis catalyzed by molybdenum on an alumina catalyst by industrial chemists at DuPont, Standard Oil, and Phillips Petroleum,4 demonstrated the conversion of propene to a mixture of ethylene with 2-butenes and ring-opening metathesis polymerization

(ROMP) of norbornene catalyzed by lithium aluminum tetraheptyl and titanium tetrachloride,5,6 organometallic chemists became highly interested in this new method due to its promising potential in synthetic organic and polymer chemistry. A few years later the metathesis of alkynes catalyzed by supported W oxide was first reported by Bailey et al.,7 followed by the development of [Mo(CO)6] with resorcinol system that catalyzes metathesis of aromatic alkynes in inert solvents at 160 °C, though this method represents a narrow functional group tolerance. The new challenge of constructing a catalyst that allows for metathesis and would tolerate the functional groups in typical organic molecules took almost 30 years to overcome. R. Grubbs reported the first molecularly well-defined ruthenium–carbene complex that promoted the ROMP of low- strain olefins as well as the catalytic ring-closing metathesis (RCM) of functionalized dienes8-10 in

1992. In 1997 Basset et al. reported the first metathesis of alkanes catalyzed by single-site silica- supported Ta-hydride, filling the last missing gap in the field of metathesis of hydrocarbons.11

Metathesis of functionally substituted alkanes, despite its ultimate difficulty as well as its significant commercial potential, is the final brick in the wall of fundamental metathesis research.

In this chapter the challenge will be explained and the catalyst deactivation by functionalized substrates will be shown. Furthermore, possible strategies for choosing non-coordinating substrates as well as sterical protection of the coordinating heteroatom that were used in our laboratories to solve this unresolved chemistry problem will be demonstrated.

After the successful discovery of alkane metathesis, the syntheses of active heterogeneous catalysts with higher TONs are of great interest and under constant development. In 2015 our group reported [(≡Si-O-)W(Me)5] efficiently catalyzes metathesis of n-decane with a TON of

142,12 which was far better than that of Ta-H.11 However, d0 early transition metals in their highest oxidation states are extremely sensitive to air, moisture, and any source of free electron

13 pairs. According to Wilkinson’s report, which studied WMe6 chemistry in solution, the formation of adducts with tertiary phosphines clearly shows that WMe6, has the capability of expanding its coordination sphere to form seven-coordinate species. The initial reaction of any ligand L, is presumably one of addition, i.e., WMe6 + L  WMe6L. With the less sterically hindered ligands, eight coordinate species may be formed. Though the silica-supported [(≡Si-O-)W(Me)5] is more thermally stable compared to homogeneous WMe6, the complex remains incompatible with functionalized substrates bearing a lone pair of electrons due to its 12 d-electron configuration, which is far from the stable 18-electron complexes. For that reason, it is not surprising that [(≡Si-O-)W(Me)5] is not active in the metathesis of saturated esters, alcohols, amines, thiols, and other coordinating compounds, where the lone pair(s) of electrons make the metal center more electron-rich and, consequently, not active in CH-activation.

In work presented in this chapter, we chose [(≡Si-O-)W(Me)5] as a model alkane metathesis catalyst precursor and decided to study in detail its deactivation by coordinating substrates to understand the challenge of metathesis of functionalized alkanes. In addition, our attempts to find compatible coordinating and non-coordinating substrates for the metathesis of functionalized alkanes will be demonstrated.

2.2. Preparation of silica-supported pentamethyl tungsten [(≡Si-O-)W(Me)5] 13 The synthesis of WMe6 was first described by Wilkinson in 1973 as a reaction of WCl6 with methyllithium in diethyl ether at –20 °C.

WCl6 + 6 MeLi  WMe6 + 6 LiCl

However, due to the explosive nature of tungsten hexamethyl, the procedure of its synthesis was modified in 1976, where tungsten hexachloride reacted with trimethyl aluminum in isopentane at -70 °C.14

WCl6 + 2 AlMe3  WMe6 + 2 AlCl3

It was reported that hexamethyltungsten reacts explosively with atmospheric oxygen and may also detonate, under certain circumstances, in vacuo or under nitrogen or argon. To handle the compound safely, the procedure was recently improved in our lab.15 We found that the reaction of WCl6 with three equivalents of Zn(Me)2 in DCM at -80 °C for 1 hour followed by the stirring of the reaction mixture at -35 °C for 3 hours leads to WMe6 and ZnCl2.

WCl6 + 3 ZnMe2  WMe6 + 3 ZnCl2

Zink dichloride is removed by precipitation in pentane at -35 °C and WMe6 can be safely stored in the pentane solution at -40 °C in the glove box for years without decomposition.

The grafting of WMe6 on preliminary dehydroxylated SiO2-700 was achieved by the simple addition of WMe6 solution to the cold (-30 °C) slurry of silica-700 in pentane (Scheme 2.1).

Scheme 2.1: Grafting of WMe6 on silica

The reaction mixture was stirred in the fridge of the glove box at -30 °C for 16 h, after that the silica-supported [(≡Si-O-)W(Me)5] 1 was filtered off and dried on HVL. After the grafting, we reached the loading of W between 1 to 3 weight percent on the silica surface. The grafted complex is an active pre-catalyst (catalyst precursor) of the metathesis of olefins,12 alkanes,12 and cycloalkanes.16

2.3. [(≡Si-O-)W(Me)5] decomposition study To start the journey, we decided to study the process of thermal transformation of silica-

15 supported WMe5 [(≡Si-O-)W(Me)5] 1. It was reported by our laboratory that upon the heating of 1, thermal transformation proceeds through the W-methylidene intermediate 2. Thus, the thermal stability of [(≡Si-O-)W(Me)5] was studied by solid-state NMR. Heating the supported sample 1 enriched in 13C (> 95 %) from RT to 72 °C with consequent maintaining of the temperature at 72 °C for 12 h, leads to the conversion of most of the [(≡Si-O-)W(Me)5] 1 to a mixture of unprecedented mono- and bipodal W−methyl/methylidyne species 3 and 4 (Scheme

2.1).

Scheme 2.2: Formation of W-Methylidyne species upon the thermal transformation of 1

These supported W−methylidyne species 3 and 4 were also investigated in catalysis of alkane metathesis and were found active in the metathesis of propane with 50 turnovers after 120 h at

150 °C. However, whether the mechanism of transformation involves the formation of methyl radicals or direct subtraction of the proton by one of the methyl groups (associative mechanism) with in-situ formation of a methane molecule was not investigated in detail.

2.3.1 Thermal decomposition of [(≡Si-O-)W(Me)5] study by in-situ IR-MS To understand the more plausible reaction pathway, we performed the analysis of the reaction using in-situ Infrared-Mass-Spectrometry (IR-MS). Due to the high instability of methyl radicals, the formation of these species during the reaction course will lead to the formation of ethane

(by recombination of ·CH3 radicals). In that case, the ethane can be detected and analyzed by mass spectrometry. Figure 2.1 displays the fragmentation of methane and ethane in electron ionization.

Figure 2.1: A – Mass Spectrum of CH4 (electron ionization), B – Mass Spectrum of C2H6 (electron ionization)

As the characteristic M+ ion for methane is 16 and for ethane is 30, we analyzed its fragments and did not find an evolution of ethane. Instead, the evolution of methane was observed (Figures

2.2, 2.3).

30 44 7.00E-008 28 18 6.00E-008 17 16 5.00E-008 15 14 4.00E-008 29 12 3.00E-008

Offset Y values Offset 2.00E-008

1.00E-008

0.00E+000

50 100 150 200 250 300 350 Temperature (oC)

Figure 2.2: Evolution of methane during the decomposition of [(≡Si-O-)W(Me)5] (3 weight %) by temperature-programmed desorption (TPD). TPD rate 10 °C/min, T range 30-330 °C

Figure 2.3: A1 - 16/15 molecular ion ratio in release of CH4 during TPD of [(≡Si-O-)W(Me)5] (1 wt %), A2 - 16/15 molecular ion ratio in release of CH4 during TPD of [≡Si-O-W(Me)5] (3 wt %), B1 - 16/14 molecular ion ratio in release of CH4 during TPD of [(≡Si-O-)W(Me)5] (1 wt %), B2 - 16/14 molecular ion ratio in release of CH4 during TPD of [(≡Si-O-)W(Me)5] (3 wt %)

Figure 2.3 displays the evolution of methane from 1 during TPD depending on metal coverage

(A1 and B1 – 1 weight %, A2 and B2 – 3 weight %). The increase of the released methane amount with an increase of the W(Me)5 supported on the surface was clearly demonstrated. The methane formation was additionally proved by the simultaneous formation of 15[+] and 14[+] molecular ions together with 16[+], with the ratios of 16[+] : 15[+] : 14[+] = 1: 0.9 : 0.12, which is perfectly consistent with the literature.17

After we proved that only methane was released from the [(≡Si-O-)W(Me)5] during the TPD with no traces of ethane, we decided to compare the methane evolution as a function of the surface coverage (tungsten loading on SiO2-700 support) (Figure 2.4).

1%W-16 3.00E-008 3%W-16

2.50E-008

2.00E-008 150

1.50E-008

1.00E-008 159 5.00E-009

0.00E+000

-5.00E-009

50 100 150 200 250 300 350 o Temperature ( C)

Figure 2.4: Comparison of CH4 release peak of 1 wt % (blue) and 3 wt % (red) of [(≡Si-O-)W(Me)5]. TPD rate 10 °C/min, Temperature range 30-330 °C

As we can see from Figure 2.4, a symmetric peak with shared trailing edge shifts to a lower temperature (from 159 °C to 150 °C) with increasing coverage (from 1 wt % to 3 wt %). According to the theory,18 in thermal desorption, also called flash desorption or temperature-programmed desorption, a sample consisting of a substrate with one or more adsorbates on the surface is heated uniformly with a constant rate. The rate of desorbing particles is monitored with a mass spectrometer as a function of the surface temperature T. Depending on the combination of substrate and adsorbate, at least one pronounced maximum of the desorption rate is observed.

Thermal desorption processes are often distinguished by the formal order “m,” a parameter which characterizes that fraction of particles on the surface which participate in the critical step of the desorption. The value of “m” usually depends on the adsorbate/substrate combination and the coverage. TPD peaks are the convolution of surface coverage and the rate of desorption. Adsorption is an activated process that obeys the Arrhenius equation:

, where A = Pre-exponential factor, Ed = Activation energy for desorption, R = Ideal gas constant. Plugging in kd from the Arrhenius equation gives the Polanyi-Wigner equation:

,

The “m” exponent is the kinetic order of the desorption. Let’s look at the most common cases.

1) m = 0 (zero-order desorption)

In the case of zeroth-order thermal desorption, the evaporation of bulk solid or liquid material takes place, and the desorption rate is independent of coverage.

, with m = 0:

Figure 2.5: Graphical representation of zero-order desorption kinetics

2) m = 1 (first-order desorption) The order of m = 1 corresponds to the desorption of independent particles with no lateral interaction. Consequently, the desorption rate dΘ/dt is directly proportional to the particle density on the surface.

, with m = 1:

Figure 2.6: Graphical representation of first order desorption kinetics

In that case, a) the desorption temperature is independent of coverage, b) asymmetric peaks with an ascending leading edge is observed, and c) first-order desorption occurs when a molecule adsorbs and then desorbs without dissociating.

3) m = 2 (second-order desorption)

The second order of desorption can be observed, for example, if recombination of two species A and B takes place by surface diffusion before molecules of the type AB escape the surface potential, and recombination is the rate-limiting step.

, with m = 2:

Figure 2.7: Graphical representation of second-order desorption kinetics

In that case: a) a symmetric peak with shared trailing edge shifts to a lower temperature with increasing coverage, b) second-order desorption occurs when a molecule adsorbs and, in doing so, dissociates on the surface, and then desorbs, c) at higher coverage, the probability of recombination is greater.

The fragmentation pattern of methane collected during the calibration of the mass spectrometer agrees well with the NIST database mass spectrum, and, at the same time, the shape of the desorption patterns indicates that the desorption order is two, which is also complemented by the shift in the desorption temperature to the lower side with increasing coverage of W(Me5), as we see from Figures 2.4 and 2.7. This confirms the experimental NMR analyses15 and proves that methane forms by association of a methyl group and a proton from a heminal methyl group on

[(≡Si-O-)W(Me)5].

In order to understand the decomposition mechanism, we compared FTIR spectra of the

[(≡Si-O-)W(Me)5] moiety during the temperature-programmed desorption (Figure 2.8). Since the heating rate was only 10 oC/min, this provided an opportunity to scan for and observe the intermediate species during regular intervals. Since these spectra were collected while running the TPD, the spectrum referred to 100 oC is an average of the interval when the temperature varies from 90 to 110 oC. The IR spectra were collected over the range between 700-4000 cm-1.

Since the SiO2 catalyst was used without the dilution of the KBr powder, high signal to noise ratio was observed in the region below 1500 cm-1. In Figure 2.8, the spectral feature at 3745 cm-1 is due to the isolated or free silanol group. The ν (CH) stretching region, between 2800-3100 cm-1,

-1 is dominated mainly by the methyl group, while the peaks at 1800 and 2000 cm are related to the Si and O bond. These latter features are present in the SiO2 sample, which is free of any

-1 tungsten complex. The spectral bands at 3018 and 2990 cm are attributed to the asymmetric

3 and symmetric (CH) stretching due to the CH3 group (sp ) coordinated with tungsten metal. The decay in the intensities of these features is further noticed with an increase in the temperature, with reduction in the signals by 245 oC. The asymmetric and symmetric stretching of the free

3 -1 methyl group with sp carbon bonding appear at 2956 and 2875 cm , for νas (CH3) and νs (CH3) stretching respectively. At room temperature, in addition to the intense vibrational bands at 3018 and 2990 cm-1, the bands at 2956 and 2875 cm-1 are also noticed. Since the starting material only contains the methyl group, these features could not be assigned to carbene or carbyne. In fact, the peaks are more closely related to the CH stretching of the methyl group (free or adsorbed on a polycrystalline surface). On increasing temperature, there is a decline in the methyl feature together with the buildup of species 2858, 2931 and 2963 cm-1.

Figure 2.8: FTIR comparison of [(≡Si-O-)W(Me)5] (1 wt %) during the TPD at different temperatures. TPD rate 10 °C/min, T range RT - 300 °C

Surprisingly, no significant changes in the FTIR were observed at the desorption maximum peak temperature (159 °C) with irreversible disruption of [(≡Si-O-)W(Me)5] starting from 245 °C.

Figure 2.9: FTIR of the [(≡Si-O-)W(Me)5] 1 wt % W (left) and 3 wt % W (right) before and after TPD

Figures 2.9 and 2.10 show the complete disappearance of 3018 cm-1 and 2990 cm-1 bands after the TPD of [(≡Si-O-)W(Me)5] (1 and 3 wt % of tungsten).

3 Before TPD (1%)

3745 After TPD (1%) Before TPD (3%) After TPD (3%) 2

2963 2858

1

Absorbance 2990 2958 2875 3018

0

3500 3000 2500 Wavenumbers (cm-1)

Figure 2.10: FTIR of the [(≡Si-O-)W(Me)5] 1% and 3 % before and after TPD

Additionally, we performed the quantification of the released methane from [(≡Si-O-)W(Me)5]

(Figure 2.11, Table 2.1).

16000

14000

12000

10000

8000

6000

Area in GC (pA·s) in GC Area

4000

2000

0 0.0 0.1 0.2 0.3 0.4 0.5 Pressure of methane (mbar)

Figure 2.11: Calibration of methane. GC area as a function of pressure

Table 2.1: Quantification of methane by GC-FID

Pressure GC Area n, mol n, µmol 1 µmol = (Area) 0.019 651.8 3.88E-07 0.388291 1678.638 0.048 1605.7 9.81E-07 0.980946 1636.89 0.117 3554.8 2.39E-06 2.391055 1486.708 0.176 5289.3 3.6E-06 3.5968 1470.557 0.237 7376.2 4.84E-06 4.843419 1522.933 0.308 9638.1 6.29E-06 6.294401 1531.218 0.369 11849.5 7.54E-06 7.541019 1571.339 0.447 13838.6 9.14E-06 9.135056 1514.889 0.508 15681.5 1.04E-05 10.38167 1510.498

Average: 1547.074497

Quantification of the methane was performed by heating (in a glass reactor) isothermally the

o [(≡Si-O-)W(Me)5] catalyst at 150 C using gas chromatography (GC-TCD). Considering methyl- methylidyne as a final complex formed by the thermal treatment, ideally, two methane molecules should be released per tungsten atom present on the silica surface. As we found from calibration, on average, 1 µmole of methane is equal to the integral of 1547.07 [pA*s] in the GC area. For the quantification experiment, we took 71.7 mg of [(≡Si-O-)W(Me)5] with 3.1 weight % loading of tungsten. The catalyst contains 0.01197 mmol of W, which corresponds to 0.02394 mmol (or 0.5857 mL) of CH4 that can theoretically be released. The sample was placed in the reactor with a known volume (43.64 mL) and heated at 150 °C for 3 hours. From the pV = nRT equation, we calculated the theoretical amount of methane (0.2764 µmole) that can be introduced to the syringe (0.5 mL) if the entire theoretical amount was released from

[(≡Si-O-)W(Me)5], which, by extrapolation, corresponds to the 424.47 [pA*s] area of GC (Table 1).

Experimentally, we found in 321 [pA*s] GC Area of the released methane peak (75% out of the theoretically possible amount), which confirms the formation of two moles of methane from one mole of supported tungsten pentamethyl.

2.3.2 Direct observation of [(≡Si-O-)W(Me)5] decomposition by strongly coordination substrates using solid-state NMR In order to elucidate the poisoning of the catalyst by functionalized alkanes, we treated

[(≡Si-O-)W(Me)5] 1 with two model strongly coordinating substrates: octanoic acid ethyl ester

(ethyl caprylate) 5 and 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol 6 for 1 h at RT in the glove box.

Figure 2.12: Ethyl caprylate (5) and 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol (6)

The reaction with both the ethyl caprylate 5 and the 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol

6 turned the color of the pre-catalyst from yellow to light-yellowish within a few minutes. After

1 h the pre-catalyst was filtered off, thoroughly washed with DCM, dried, and analyzed by solid- state NMR (Figure 2.13). The spectra of pure catalyst precursor 1 are presented on Figure 2.29 in the Experimental Section (Part 2.7).

1 Figure 2.13: Solid-state MAS NMR of [(≡Si-O-)W(Me)5] after interaction with ethyl caprylate 5. A) H NMR, B) 13C NMR, C) 1H-13C correlation NMR

As we can see from 13C solid-state NMR, no peak at 82 ppm was observed. The characteristic peak of the methyl group (See Figure 2.29 in the experimental section) of -W(CH3)5 at 82 ppm completely disappeared (Figure 2.13) after treatment with ester 5. Instead, we observed a

1 13 characteristic peak of (O-CH2-CH3) at 4.2 ppm in H and at 60.4 ppm in C NMR that clearly shows the presence of ethyl caprylate 5 bound to silica surface.

1 Figure 2.14: [(≡Si-O-)W(Me)5] after interaction with 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol 6. A) H NMR, B) 13C NMR, C) 1H-13C correlation NMR

13 As in the case of ester, in C solid-state NMR after the treatment of [(≡Si-O-)W(Me)5] with the alcohol 6, the characteristic peak of the methyl group of -W(CH3)5 at 82 ppm disappeared, indicating the perturbation of -W(Me)5 moiety. Instead, a characteristic peak of (C-CH3) at 2.0

1 13 ppm in H and 47.0 ppm in C NMR appeared (which corresponds to the -CH3 group of the alcohol

6), and shows the presence of 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol 6 on the surface. Remarkably, alcohol 6 does not interact with WMe6 in the solution of pentane at -30 °C. When we heated the mixture of WMe6 with alcohol 6 above -30 °C, we observed the disappearance of the peak at 82 ppm in 13C NMR with no change for the peak at 47 ppm, indicating that the decomposition of WMe6 occurs before its reaction with alcohol 6. It is worth noting that the treatment of [(≡Si-O-)W(Me)5] 1 with ester 5 at RT in the solution of pentane (1:4 molar ratio

W:Ester) with subsequent separation of the perturbed pre-catalyst does not deactivate the latter in the metathesis of n-decane, despite a clear sign of the interaction of the catalyst with the ester

(Figure 2.31 in experimental section). After the exposure to ester, followed by washing of the pre-catalyst in DCM and drying in HVL, the latter (20.2 mg, 3.2 µmol W) was utilized for the metathesis of n-decane (0.25 mL, 400:1 molar ratio to W) for 5 days at 150 °C. After the reaction, the conversion of the starting material was 6.3 % with 25 TON of the catalyst (when the pure catalyst gave 38 % conversion with TON of 142). At the same time, when [(≡Si-O-)W(Me)5] (1 eq) was treated with pure ethyl caprylate (400 eq) at RT for 1 h, the exposed material was completely inactive in the metathesis of n-decane. A detailed study of interaction of [(≡Si-O-)W(Me)5] with the ester is in part 2.1.3. These experiments convey that the ester a) cannot be metathesized, and b) poisons the alkane metathesis catalyst even at RT.

The above experiments represent the incompatibility of the strongly coordinating substrates with the catalysts based on early transition metals, such as [(≡Si-O-)W(Me)5] due to the high electrophilic properties of the metal (tungsten in our case) in its highest oxidation state. With that, esters or alcohols, obviously, cannot be utilized as substrates for the metathesis reaction, at least with the model catalyst precursor used in the study. 2.3.3 [(≡Si-O-)W(Me)5] poisoning study by ester using in-situ IR-MS

To have additional evidence of the perturbation of W-CH3 moiety by strongly coordinating substrates, we compared FTIR spectra of [(≡Si-O-)W(Me)5] before and after adsorption of ethyl caprylate 5 (Figure 2.15).

Figure 2.15: FTIR of [≡Si-O-W(Me)5] before (red) and after (blue) adsorption of ethyl caprylate

For the study, ethyl caprylate (5 µL) (Figure, part 2.1.2) was injected through the septum to the preliminary evacuated IR DRIFT cell containing [(≡Si-O-)W(Me)5] (10 mg, 3 wt % W). The vapors of the ester were allowed to adsorb on the surface for 30 min. Next, the excess of ester was evacuated in a vacuum for 16 h at RT. Figure 2.15 represents the FTIR spectra of [(≡Si-O-)W(Me)5] before injection of the ester and after adsorption of the ester. When the excess of the ester directly interacts with [(≡Si-O-)W(Me)5] (in solution as well as in neat conditions at RT), the FTIR spectrum of the dried catalyst after the ester exposure was found to be identical to the one at

Figure 2.15 (blue). As we can see from FTIR, a strong band at 1710 cm-1 appeared after adsorption of ester and is attributed to the ester carbonyl group. At the same time, carbonyl groups in the adsorbed molecules were involved in the formation of hydrogen bonds with remaining surface silanol groups. The amount of available surface silanols was decreased upon adsorption of ethyl caprylate. The broad maximum due to perturbed silanol groups was found at 3435 cm-1, which is in good agreement with literature data.19 The disappearance of W-CH stretching band at 3018 cm-1 after ester adsorption suggests the perturbation of W moiety by ethyl caprylate, which is also in good agreement with the disappearance of W-CH3 peak observed in solid-state NMR.

These results were compared with a control experiment. As a reference in the control experiment, we exposed the pure surface of SiO2-700 with ethyl caprylate (Figure 2.16).

After Ester adsorption 14 Before Ester adsorption

12

2965 2932 1720 10 3745 3435 2990 2861 8

6

4

Absorbance

2

0

-2

4000 3500 3000 2500 2000 1500 Wavenumbers (cm-1)

Figure 2.16: FTIR of SiO2-700 before (red) and after (blue) adsorption of ethyl caprylate When the ester adsorbs on silica, a maximum at 1720 cm-1 is assigned to the (C=O)-stretching vibrations; maximums at 2861 cm-1, 2932 cm-1, 3965 cm-1, and 2990 cm-1 correspond to the (C-

H)-stretching vibrations; and a maximum at 3435 cm-1 is due to the formation of hydrogen bonds

-1 between silanol groups and carbonyl groups. The small shift of ∆νCO 10 cm in the position of the infrared band was observed between the ester adsorbed on pure SiO2-700 and silica grafted tungsten pentamethyl [(≡Si-O-)W(Me)5]. After that, we compared the FTIR spectra of SiO2-700 and

[(≡Si-O-)W(Me)5] before and after temperature-programmed desorption of the ester (Figure

2.17).

Ester-W-Si/After TPD Ester-Si/After TPD 24 Ester-W-Si/Before TPD 22 Ester-Si/Before TPD 20 3435 18 16 3435 14 1710 12 10 3435 Absorbance 8 6 1720 3435 2965 2932 4 2990 2861 2 0

4000 3500 3000 2500 2000 1500 Wavenumbers (cm-1)

Figure 2.17: FTIR comparison of the ester 5 adsorbed on SiO2-700 and [(≡Si-O-)W(Me)5]. Red – ester adsorbed on SiO2-700 before TPD. Blue – ester adsorbed on [(≡Si-O-)W(Me)5] before TPD. Yellow – Ester adsorbed on SiO2-700 after TPD. Green – ester adsorbed on [(≡Si-O-)W(Me)5] after TPD As a result, no difference in terms of ester desorption was observed. The initial surface silanols on SiO2-700 (0.26 mmol OH per gram of silica) was partially occupied by WMe5, in the sample containing 3.1 wt % of W, 0.17 mmol of OH was occupied by W and 0.09 mmol OH estimated to remain on the surface. This explains why slightly less C=O···HO- hydrogen bonds remained on

[(≡Si-O-)W(Me)5] sample after the TPD compared to SiO2-700 after the desorption of ester (the characteristic band at 3435 cm-1).

Figure 2.18: FTIR comparison of Ester desorption from SiO2-700 at different temperatures

The disappearance of ester carbonyl and CH-stretching bands was observed at 240 °C and above, however, when the sample was cooled down to RT, the remaining ester was still found on the surface (Figure 2.18).

Figure 2.19: FTIR comparison of ester desorption from [(≡Si-O-)W(Me)5] at different temperatures

Figure 2.20: W(CH3)5/SiO2 decomposition. [(≡Si-O-)W(Me)5] (1 wt %) (Red and Yellow) vs. [(≡Si-O- )W(Me)5] (1 wt %) treated with ester (Blue and Green)

In addition, it was observed that the ester fragmentation during the TPD follows different paths when the desorption occurs from a bare silica surface and from [(≡Si-O-)W(Me)5]. The experiment was repeated three times for clarity, which confirms the direct interaction of ester with W moiety.

The obtained data, together with NMR results and control experiments, clearly show that

[(≡Si-O-)W(Me)5] interacts with strongly coordinating substrates. From the collected data we can conclude that in order to perform metathesis of functionalized substrates on an alkane metathesis catalyst, it is important first to study the interaction of the catalyst with non- coordinating substrates and how they will affect the catalyst.

2.4. Interaction of [(≡Si-O-)W(Me)5] with Ferrocenes We chose the alkylated ferrocene family as the typical non-coordinating model substrates where the inorganic Fe heteroatom though cannot be considered as a functional group, but in the same time should not interact and deactivate W-catalyst. Ferrocene is the prototypical metallocene, a type of organometallic compound consisting of two cyclopentadienyl rings bound on inverse sides of a central metal atom, which is also known as a sandwich compound. In terms of bonding, the ferrocene iron center is assigned to the +2 oxidation state. Each cyclopentadienyl (Cp) ring is then allocated a single negative charge, bringing the number of π-electrons on each ring to six, and thus making them aromatic. These twelve electrons (six from each ring) are then shared with the metal via covalent bonding. When combined with the six d-electrons on Fe2+, the complex attains an 18-electron configuration. So, in principle, aromatic rings, or an Fe2+ heteroatom should not coordinate or react with [(≡Si-O-)W(Me)5].

2.4.1 Reaction with n-Butyl-Ferrocene For the detailed study, we chose n-Butyl Ferrocene, expecting the formation of metathesis products by its alkyl chain – lower and higher homologs with respective dimers. However, after heating the [(≡Si-O-)W(Me)5] 1 with n-Butyl-Ferrocene 7 at 150 °C for 5 days, the metathesis products were not detectable by GC-FID. Instead, two new major products were formed – ferrocene 8 and 1,1’-dibutylferrocene 9 (Scheme 2.3).

Scheme 2.3: Disproportionation of n-butylferrocene over [(≡Si-O-)W(Me)5]

Formation of these products out of alkyl-ferrocene is known as disproportionation reaction and

20 can be promoted by strong Lewis acids like AlCl3. To the best of our knowledge, there are no reports of catalytic disproportionation of alkyl-ferrocenes by weak Lewis acids as

21 [(≡Si-O-)W(Me)5]. Remarkably, such disproportionation did not occur on silica-supported TiNp3,

22 23 ZrNp3 and HfNp3, but can be catalyzed by stronger Lewis acids like WCl6. Instead of AlCl3, which catalyzes the reaction at RT in DCM over 2 h, [(≡Si-O-)W(Me)5] is a less strong Lewis acid, therefore the reaction does not proceed at RT and requires more harsh conditions – a temperature of 150°C and several days of reaction time (Table 2.2).

Table 2.2: Disproportionation of n-Butyl-Ferrocene over [(≡Si-O-)W(Me)5]

Entry Reaction time Conversion Product obtained Catalyst TON

(days) (%) (mmol)

1 1 16.3 0.296 35

2 5 24.7 0.475 57

3 10 69.5 1.34 161

4 20 73.4 1.41 169

The equilibrium of the reaction shifts towards the products and, respectively, the conversion of the starting material increases, while the forming ferrocene is sublimed at a high temperature from the reaction mixture. Our attempts to study the catalyst structure by solid-state NMR after reaction were not successful, as we primarily observed the starting material bound to silica even after many washing cycles (Figures 2.49-2.51).

It has been shown that the disproportionation is an equilibrium reaction with

24 synproportionation. So, with the same procedure, [(≡Si-O-)W(Me)5] catalyzes the formation of ethyl ferrocene 11 from the mixture of ferrocene 8 and 1,1’-diethylferrocene 10 with a conversion of 22% after the same period (5 days) (Scheme 2.4).

Scheme 2.4: Synproportionation of ferrocene and ethylferrocene over [(≡Si-O-)W(Me)5]

25 Not surprisingly, such a Lewis acid as silica-supported WCl5 also catalyzes the disproportionation of butyl-ferrocene with conversion of 17.8 % and 23 turnovers of the catalyst after 5 days at 150 °C (Scheme 2.5).

Scheme 2.5: Disproportionation of butyl-ferrocene catalyzed by [(≡Si-O-)WCl5]

2.4.2 Reaction with trimethylsilyl-ferrocene and tert-butyl-ferrocene With more sterically bulky substrates, such as tert-butylferrocene 12 and trimethylsilyl-ferrocene

13, the conversion of disproportionation was expected to be lower than with sterically less pronounced. In 5 days of reaction time, only 1.6 % of initial tert-butylferrocene 12 was converted to its disproportionation products with a catalyst TON of 4, when in the case of trimethylsilylferrocene 13, the conversion was slightly more and reached 3.8 % with 9 turnovers of the catalyst (Scheme 2.6).

Scheme 2.6: Disproportionation of tert-butylferrocene (E = C) and trimethylsilylferrocene (E = Si) over [(≡Si-O-)WCl5]

The influence of the sterically bulky groups on ferrocene disproportionation, synproportionation and ligand exchange reactions has been shown in the literature.24,26

2.4.3 Reactions with other ferrocene-based substrates With methylene-bisferrocene 16, benzylferrocene 17, benzoylferrocene 18, and methylenedimethylaminoferrocene 19 no disproportionation products were detected.

Figure 2.21: 16 - methylene-bisferrocene, 17 - benzyl-ferrocene, 18 - benzoyl-ferrocene, 19 – methylenedimethylamino-ferrocene

2.5. Interaction of catalyst with Silicon-based substrates From the above results, we understood that neither strongly coordinating substrates, nor alkylated ferrocenes (non-coordinating substrates) can be metathesized by an alkane metathesis catalyst. We decided to explore the strategy of protecting the coordinating and non-coordinating heteroatom in a substrate by sterical hindrances to avoid its direct interaction with the metal center. With that, we chose siloxanes (silyl ethers) containing Si-O- group, where the oxygen atom is coordinating one, but at the same time, Si atom, which is next to the oxygen, can be crowded by sterically bulky alkyl or aryl groups.

2.5.1 Interaction with siloxanes We decided to investigate the strategy of preventing the catalyst of being deactivated by using a substrate with sterically hindered functional groups. Since the metathesis of linear12, as well as cyclic16 alkanes, has been well demonstrated, we decided to introduce the bulky siloxo-group into the molecules of hexane and cyclooctane. With that, we prepared tert-butyl(cyclooctyl- oxy)dimethylsilane 20, (cyclooctyl-oxy)triisopropylsilane 21 and tert- butyl(hexyloxy)diphenylsilane 22 according to the methods in the literature (Figure 2.22).27,28 The idea behind this was to protect the coordinating oxygen atom in the molecules by the sterically hindered groups on the silicon atom, since the methyl-, isopropyl-, tert-butyl- or phenyl- groups cannot be dehydrogenated and the oxygen with its two pairs of electrons is crowded. This strategy may potentially allow only alkyl- (hexyl-) or cyclooctyl- groups to interact with W-catalyst by analogy of classical alkane or cycloalkane metathesis.

Figure 2.22: Tert-butyl(cyclooctyl-oxy)dimethylsilane 20, (cyclooctyl-oxy)triisopropylsilane 21 and tert- butyl(hexyloxy)diphenylsilane 22

We heated the substrates 20-22 with [(≡Si-O-)W(Me)5] at 150 °C for 5 days. Unfortunately, metathesis did not occur in neat (when the only substrate is in direct contact with catalyst), nor in the solution of mesitylene (when the substrates were first diluted with mesytilene before the addition to the catalyst).

Table 2.3: Results on metathesis of siloxanes 20-22

Substrates Catalyst and Conditions Result

20, 21, 22 [(≡Si-O-)W(Me)5] 20 mg (3.07 wt %), No reaction

(0.5 mL) 150°C, 5 days

These results suggest that the oxygen atom may still interfere with the catalyst despite the steric hindrances on the functional group. Remarkably, in the control experiment, when the (cyclooctyl- oxy)triisopropylsilane 21 (10 eq) was added to a mixture of [(≡Si-O-)W(Me)5] (1 eq) and n-decane

(400 eq), no metathesis of n-decane was observed, which indicates that the siloxo-substrates deactivate the catalyst.

2.5.2 Interaction with silanes The next step was to synthesize a substrate molecule without an oxygen atom and leave only silicon as the heteroatom. As silicon does not have a free pair of electrons and is not a coordinating heteroatom, silicon-containing substrates (silanes) are assumed to have similar reactivity as alkanes. The motivation to use silicon-containing substrates is as follows: silyl group can be hydrolyzed and a variety of different classes of compounds can be synthesized from silanes, so the metathesis of Si-based substrates is of great interest. We synthesized octyltriphenylsilane 23, (4-butylphenyl)triisopropyl-silane 24 and (4-butylphenyl)triphenylsilane

25 (Figure 2.23) as model compounds according to the method in the literature.29

Figure 2.23: (4-butylphenyl)triisopropyl-silane 23, Octyltriphenylsilane 24 and (4- butylphenyl)triphenylsilane 25

To our surprise, metathesis was not observed with substrates 23-25 at 150°C after 1, 5, 10 and

20 days using [(≡Si-O-)W(Me)5] as a catalyst precursor. An additional experiment with commercially available trimethylsilyloctane showed no alkane metathesis as well. As the reactions were done in strict air and moisture-free conditions using glove box and HVL techniques and repeated several times, the actual reason for why these substrates did not give any traces of metathesis products is still unclear and currently under investigation in our laboratories. In order to understand if Si-based substrates deactivate the catalyst, we did several control experiments.

At first, we did the metathesis of pure butyl benzene on [(≡Si-O-)W(Me)5] and obtained the metathesis products with 33 TON of the catalyst. After that, we repeated the metathesis reaction of butyl benzene (400:1 molar ratio in respect to W active site) in the same conditions with the addition of silane 24 (10:1 molar ratio in respect to W) to the reaction mixture. As a result, no metathesis of butyl benzene was observed in the presence of silane 24. The catalyst after reaction was filtered in the glove box, washed 3 times with the excess of dry DCM, dried and was attempted to be reused in the metathesis of n-decane without success. At the same time, the

[(≡Si-O-)W(Me)5] catalyst was treated with 4:1 molar excess of silane 24 in respect to W in the solution of pentane at RT, then filtered off, washed with the additional pentane, dried and attempted to metathesize n-decane. In that case, the metathesis of n-decane was well demonstrated with the conversion of n-decane of 21 % and TON of 81. The results are consistent with the results obtained in the control experiment of [(≡Si-O-)W(Me)5] poisoning by ethyl caprylate (Part 2.1.2). In the latter case, the metathesis of n-decane in the presence of the ester did not work when the metathesis of n-decane by perturbed [(≡Si-O-)W(Me)5] by 4:1 excess of ethyl caprylate at RT for 1 hour showed the metathesis of n-decane with conversion of 6.3 % and

25 TON. The results show that particular substrates may not be compatible with the metathesis pre-catalyst; however, the poisoning effect is more pronounced with coordinating substrates

(Ethyl caprylate 5 > Silane 24).

Table 2.4: N-decane metathesis catalyzed by poisoned [(≡Si-O-)W(Me)5]

[(≡Si-O- [(≡Si-O- [(≡Si-O- [(≡Si-O- Control )W(Me)5] )W(Me)5] )W(Me)5] )W(Me)5] experiment. poisoned by poisoned by Pure Ethyl Silane 24 in the presence in the Caprylate 5 of Ethyl presence of [(≡Si-O- (1:4 molar Caprylate 5 Silane 24 )W(Me)5] (1:4 molar ratio) ratio) (1:4 molar ratio) (1:4 molar ratio)

Conversion of 6.3 % 21 % 0 % 0 % 38 % n-decane after 5 days at 150 °C

TON of catalyst 25 81 0 0 142

2.5.3 Study of interaction of [(≡Si-O-)W(Me)5] with triphenyloctyl-silane by in-situ IR-MS In order to see whether silane 24 interacts with a metathesis pre-catalyst, we treated

[(≡Si-O-)W(Me)5] with 4 equivalents of silane 24 in pentane at RT for 3 hours, filtered the catalyst, washed with pentane and dried. The perturbed catalyst was analyzed by in-situ IR-MS and TPD

(Figure 2.24).

As we can observe from Figure 2.24, the release of methane peak from [(≡Si-O-)W(Me)5], perturbed by triphenyloctylsilane 24 at 151 °C is very similar to those of pure [(≡Si-O-)W(Me)5]

(150 °C, Figure 2.4). The FTIR spectrum of the perturbed catalyst is the same as the fresh one with no changes observed. These results indicate the inertness of the catalyst to non- coordinating silane 24 at room temperature. At the same time, silanes affect the metathesis of alkanes at 150 °C and can be considered as poison for the alkane metathesis catalyst.

1.00E-007 151

5.00E-008 Offset Y values Offset

0.00E+000

100 200 300 400 500 600 o Temperature ( C)

Figure 2.24: Decomposition of [(≡Si-O-)W(Me)5] perturbed by triphenyloctylsilane 24

2.5.4 Deactivation of n-butyl-benzene metathesis in the presence of (4-butylphenyl)- triisopropyl-silane To better understand the deactivation of the alkane metathesis catalyst in the presence of (4- butylphenyl)triisopropyl-silane 23 in the control experiment, first, we did a metathesis of butyl- benzene catalyzed by supported pentamethyltungten [(≡Si-O-)W(Me)5] (Scheme 2.7, A). As a result, we obtained metathesis products with 33 turnovers of the catalyst. In the reaction mixture, two classes of products were found (Figure 2.25): linear alkylbenzenes and dimeric alkyl- bisbenzenes. The formation of the latter class is understandable as it forms by a self-metathesis of the linear alkylbenzenes. The alkyl-benzenes were formed by dehydrogenation of the butylbenzene by the alkyl chain, followed by the migration of the double bond through the alkyl chain with subsequent metathesis of the formed olefins and hydrogenation to new alkyl- benzenes. At the same time, a small amount of n-alkanes (butane, ethane, propane, and pentane) were formed and detected by GCMS. After we showed a metathesis of butyl-benzene, we decided to determine if the metathesis would still work when silane 23 was added to the reaction mixture (Scheme 2.7, B). In the experiment, we added 10 equivalents of (4-butylphenyl)- triisopropyl-silane 23 to a mixture of butyl-benzene (400 equivalents) and [(≡Si-O-)W(Me)5] (1 equivalent) and ran the reaction at 150 °C for 5 days. As a result, no metathesis of butyl-benzene was observed and the reaction mixture consisted of starting materials only.

14

12

10

8

6

Amount (µmol) 4

2

0

C6H6

C6H5-C1 C6H5-C2 C6H5-C3 C6H5-C5 C6H5-C6 C6H5-C7 C6H5-C8 C6H5-C9

C6H5-C10

Products C6H5-C2-C6H5 C6H5-C3-C6H5 C6H5-C4-C6H5 C6H5-C5-C6H5 C6H5-C6-C6H5 C6H5-C7-C6H5 C6H5-C8-C6H5 C6H5-C9-C6H5 C6H5-C10-C6H5

Figure 2.25: Product distribution in the metathesis of butylbenzene ( – linear alkylbenzenes, – dimers)

Scheme 2.7: Metathesis of butylbezene (A) and Metathesis of butylbenzene in the presence of (4- butylphenyl)triisopropyl-silane (B)

Obviously, the deactivation of the catalyst by functionalized substrates, including silanes, occurs at higher temperatures. The mechanism of catalyst deactivation by silicon-based substrates remains unclear and is under investigation in our laboratories.

2.6. Conclusions In conclusion, using [(≡Si-O-)W(Me)5] as a model alkane metathesis pre-catalyst for our study, we clearly demonstrated the incompatibility of the coordinating substrates with the catalyst. The coordination of the functional carbonyl group (in case of ethyl caprylate) to the metal center causes the disappearance of the characteristic 3018 cm-1 W-CH stretching band in the FTIR, and

13 disappearance of the peak at 82 ppm in C solid-state NMR attributed to W-CH3 group. At the same time, the decomposition pathway of the perturbed catalyst studied by TPD also changes, showing the difference in the methane release peak by 9 °C, proving that the nature of catalyst active sites is affected. Non-coordinating substrates, such as alkyl-ferrocenes do not undergo metathesis and were involved in the disproportionation/synproportionation reaction instead of metathesis; this is an acid-based catalytic reaction which means that this pre-catalyst exhibits some acidic properties.

The bulky alkyl groups on siloxanes do not protect the catalyst from being deactivated, and with that, siloxanes cannot be metathesized by the alkane metathesis catalyst. In the case of expected non-coordinating silanes, the direct decomposition of the catalyst at RT was not observed (in spite of coordinating substrates); however, the silanes remain inert as substrates and moreover, poison the catalyst at a high temperature. In order to perform the metathesis of functionalized alkanes, the bare alkane metathesis catalyst should be protected to avoid its direct interaction with the functional group.

2.7. Experimental section

General

All experiments were carried out using standard Schlenk and glovebox techniques under an inert argon atmosphere. The syntheses and the treatments of the surface species were carried out using high vacuum lines (< 10-5 mbar) and glove-box techniques. Pentane was distilled from a

Na/K alloy under N2 and dichloromethane from CaH2. Both solvents were degassed through freeze-pump-thaw cycles. SiO2-700 was prepared from Aerosil silica from Degussa (specific area of

200 m2/g), which were partly dehydroxylated at 700 °C under high vacuum (< 10-5 mbar) for 24 h to give a white solid having a specific surface area of 190 m2/g and containing around 0.5-0.7

2 OH/nm (0.2-0.3 mmol OH/g). W(CH3)6 and supported pre-catalyst 1 was prepared according to procedures from the literature.15,30 IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF2 windows. The IR samples were prepared under argon within a glove box. Typically, 64 scans were accumulated for each spectrum

(resolution 4 cm−1). Elemental analyses were performed at KAUST Core Lab ACL. NMR spectra were recorded on Bruker Avance III 500 MHz NMR spectrometer (Bruker Biospin AG, Switzerland) equipped with a BBFO CryoProbe. GC measurements were performed with an Agilent 7890A

Series (FID detection). The method for GC analyses: column HP-5; 30 m length × 0.32 mm ID ×

0.25 μm film thickness; flow rate, 1 mL/min (N2); split ratio, 50/1; inlet temperature, 250 °C, detector temperature, 250 °C; temperature program, 40 °C (3 min), 40–250 °C (12 °C/min), 250

°C (3 minutes), 250–300 °C (10 °C/min), 300 °C (3 minutes). GC-MS measurements were performed with an Agilent 7890A Series coupled with an Agilent 5975C Series. A GC-MS, equipped with a capillary column coated with non-polar stationary phase HP-5MS, was used for molecular weight determination and identification, which allowed the separation of chemical compounds according to their boiling point differences. The method for GC-MS analyses: Column

HP-5MS; 30 m length × 0.25 mm ID × 0.25 μm film thickness; flow rate, 1 mL/min (N2); split ratio,

100/1; inlet temperature, 220 °C, detector temperature, 300 °C; temperature program, 150 °C (0 minutes), 150–300 °C (20 °C/min), 300 °C (30 minutes). TPD measurements were carried out in a high vacuum chamber coupled with RGA (residual gas analyzer) mass spectrometer, with a detection mass up to 200 amu (atomic mass units) obtained from Stanford Research Systems

(SRS). The base pressure inside the chamber was maintained at 1 × 10−9 Torr using a turbo molecular pump backed up by a scroll pump. Catalytic reactions: in a typical procedure, a substrate and supported catalyst were mixed in the ampule tube in the glove box; the ampule tube was connected to a high-vacuum line and sealed in a vacuum. The ampule was then heated at 150 °C with stirring (50 rpm). Quenching: the ampule was cooled down in liquid nitrogen, opened, 1 mL of DCM was added, the mixture was filtered through a syringe filter (1 µm), and the sample was analyzed by GC.

1 Figure 2.26: H NMR spectrum of WMe6 in CD2Cl2 at 203 K

13 Figure 2.27: C NMR spectrum of WMe6 in CD2Cl2 at 203 K

Figure 2.28: 2D solution 1H-13C Heteronuclear Single Quantum Correlation (HSQC) NMR spectrum of WMe6 in CD2Cl2 at 203 K

1 Figure 2.29: Solid-state NMR spectra of [(≡Si-O-)W(CH3)5] 1. (A) One-dimensional (1D) H MAS solid-state NMR spectrum of 2 acquired at 600 MHz (14.1 T) with a 22 kHz MAS frequency, a repetition delay of 5 s, and 8 scans. (B) Two-dimensional (2D) 1H−1H double-quantum (DQ)/single-quantum (SQ) and (C) 1H−1H triple-quantum (TQ)/SQ NMR spectra of 2 (both acquired with 32 scans per t1 increment, 5 s repetition 13 1 delay, 32 individual t1 increments). (D) C CP/MAS NMR spectrum of 2 acquired at 9.4 T (v0( H) = 400 MHz) with a 10 kHz MAS frequency, 1000 scans, a 4 s repetition delay, and a 2 ms contact time. An exponential line broadening of 80 Hz was applied prior to Fourier transformation. (E) 2D 1H−13C CP/MAS dipolar HETCOR spectrum of 2 (acquired at 9.4 T with an 8.5 kHz MAS frequency, 2000 scans per t1 increment, A 4 s repetition delay, 64 individual t1 increments, and a 0.2 ms contact time)

8 −1 3747 cm Si 700 W complex (νSi‐OH) 6

1410 cm−1

4 (δC‐H)

% Absorbance % Absorbance

2

0 4000 3500 3000 2500 2000 1500 1 Wavenumber cm

Figure 2.30: FT-IR spectroscopy of silica partially dehydroxylated at 700 °C ( ) and W(CH3)6 grafted on

SiO2-700 (1) ( )

3

2

1710

1 2963 3745 2990 2932 Absorbance 3435 3018 2859

0

4000 3500 3000 2500 2000 1500 Wavenumbers (cm-1)

Figure 2.31: FTIR spectroscopy of [(≡Si-O-)W(Me)5] 1 (1 eq) exposed to ethyl caprylate 5 (4 eq)

1 Figure 2.32: H NMR spectrum of Butylferrocene 7 in C6D6 at RT

13 Figure 2.33: C NMR spectrum of Butylferrocene 7 in C6D6 at RT

1 Figure 2.34: H NMR spectrum of the reaction mixture (Scheme 2.3) in C6D6 at RT

13 Figure 2.35: C NMR spectrum of the reaction mixture (Scheme 2.3) in C6D6 at RT

8000

7000

6000

5000

4000

Area (pA*s) Area 3000

2000

1000

0 0 5 10 15 20 25 30 35 Retention Time (Min)

Figure 2.36: GC chromatogram of the reaction mixture (Scheme 2.3) in DCM at RT

1 Figure 2.37: H NMR spectrum of siloxane 20 in CDCl3 at RT

13 Figure 2.38: C NMR spectrum of siloxane 20 in CDCl3 at RT

1 Figure 2.39: H NMR spectrum of siloxane 21 in CDCl3 at RT

13 Figure 2.40: C NMR spectrum of siloxane 21 in CDCl3 at RT

1 Figure 2.41 H NMR spectrum of siloxane 22 in CDCl3 at RT

13 Figure 2.42: C NMR spectrum of siloxane 22 in CDCl3 at RT

1 Figure 2.43: H NMR spectrum of silane 23 in CDCl3 at RT

13 Figure 2.44: C NMR spectrum of silane 23 in CDCl3 at RT

1 Figure 2.45: H NMR spectrum of silane 24 in CDCl3 at RT

13 Figure 2.46: C NMR spectrum of silane 24 in CDCl3 at RT

1 Figure 2.47: H NMR spectrum of silane 25 in CDCl3 at RT

13 Figure 2.48: C NMR spectrum of silane 25 in CDCl3 at RT

1 Figure 2.49: H solid-state NMR spectrum of [(≡Si-O-)W(Me)5] 1 recovered after the reaction with n- butylferrocene

13 Figure 2.50: C solid-state NMR spectrum of [(≡Si-O-)W(Me)5] 1 recovered after the reaction with n- butylferrocene

1 13 Figure 2.51: H- C correlation solid-state NMR spectrum of [(≡Si-O-)W(Me)5] 1 recovered after the reaction with n-butylferrocene

Figure 2.52: Comparison of ester fragments release from SiO2-700 (E) and from [(≡Si-O-)W(Me)5] 1 (W-E) by fragmentation during TPD

2.8. References 1. Jia, X.; Qin, C.; Friedberger, T.; Guan, Z.; Huang, Z., Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions. Sci. Adv. 2016, 2, 1-7.

2. Hughes, D.; Wheeler, P.; Ene, D., Olefin Metathesis in Drug Discovery and Development—Examples from Recent Patent Literature. Org. Process Res. Dev., 2017, 21, 12, 1938-1962.

3. Sirasani, G.; Paul, T.; Andrade, R. B., Sequencing cross-metathesis and non-metathesis reactions to rapidly access building blocks for synthesis. Tetrahedron, 2011, 67, 12, 2197-2205.

4. Banks, R. L.; Bailey, G. C., Olefin Disproportionation. A New Catalytic Process. Ind. Eng. Chem. Prod. Res. Dev., 1964, 3, 3, 170-173.

5. Truett, W. L.; Johnson, D. R.; Robinson, I. M.; Montague, B. A., Polynorbornene by Coördination Polymerization. J. Am. Chem. Soc., 1960, 82, 9, 2337-2340.

6. Anderson, W. A.; Merckling, G. N., Polymeric bicyclo-(2,2,1)-2-heptene. US Patent 2,721,189, 1955.

7. Pennella, F.; Banks, R. L.; Bailey, G. C., Disproportionation of alkynes. J. Chem. Soc. Chem. Commun., 1968, 1548-1549.

8. Nguyen, T. S.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W., Ring-opening metathesis polymerization (ROMP) of norbornene by a Group VIII carbene complex in protic media. J. Am. Chem. Soc., 1992, 114, 10, 3974-3975.

9. Fu, G. C.; Grubbs, R. H., The application of catalytic ring-closing olefin metathesis to the synthesis of unsaturated oxygen heterocycles. J. Am. Chem. Soc., 1992, 114, 13, 5426-5427.

10. Fu, G. C.; Grubbs, R. H., The synthesis of nitrogen heterocycles via catalytic ring-closing metathesis of dienes. J. Am. Chem. Soc., 1992, 114, 18, 7324-7325.

11. Vidal, V.; Théolier, A.; Thivolle-Cazat, J.; Basset, J.-M., Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides. Science, 1997, 276, 5309, 99-102.

12. Riache, N.; Callens, E.; Espinas, J.; Dery, A.; Samantaray, M. K.; Deya, R.; Basset, J.-M., Striking difference between alkane and olefin metathesis using the well-defined precursor [≡Si– O–WMe5]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride. Catal. Sci. Technol., 2015, 5, 280-285.

13. Shortland, A. J.; Wilkinson, G., Preparation and properties of hexamethyltungsten. J. Chem. Soc., Dalton Trans., 1973, 0, 872-876.

14. Galyer, A. L.; Wilkinson, G., New synthesis of hexamethyltungsten(VI). The octamethyltungstate-(VI) lon. J. Chem. Soc., Dalton Trans., 1976, 0, 2235-2238.

15. Samantaray, M. K.; Callens, E.; Abou-Hamad, E.; Rossini, A. J.; Widdifield, C. M.; Dey, R.;

Emsley, L.; Basset, J.-M., WMe6 Tamed by Silica: ≡Si–O–WMe5 as an Efficient, Well-Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W– Methyl/Methylidyne Species. J. Am. Chem. Soc., 2014, 136, 3, 1054-1061.

16. Riache, N.; Callens, E.; Samantaray, M. K.; Kharbatia, N. M.; Atiqullah, M., Basset, J.-M., Cyclooctane Metathesis Catalyzed by Silica‐Supported Tungsten Pentamethyl [(≡SiO)W(Me)5]: Distribution of Macrocyclic Alkanes. Chem. Eur. J., 2014, 20, 15089-15094.

17. https://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&Mask=200#Mass-Spec

18. Vollmer, M.; Trager, F., Analysis of fractional order thermal desorption. Surface Science, 1987, 187, 445-462.

19. Cross, S. N. W.; Rochester, C. H., Infrared study of the adsorption of aromatic esters on silica immersed in carbon tetrachloride. J. Chem. Soc., Faraday Trans. 1, 1981, 77, 1027-1038.

20. Bublitz, D. E., Ring migration in alkylated ferrocenes. Canadian Journal of Chemistry, 1964, 42, 11, 2385-2392.

21. Larabi, C.; Merle, N.; Norsic, S.; Taoufik, M.; Baudouin, A.; Lucas, C.; Thivolle-Cazat, J.; de Mallmann, A.; Basset, J.-M., Surface Organometallic Chemistry of Titanium on Silica−Alumina and Catalytic Hydrogenolysis of Waxes at Low Temperature. Organometallics, 2009, 28, 19, 5647- 5655.

22. Quignard, F.; Le´cuyer, C.; Choplin, A.; Olivier, D.; Basset, J.-M., Surface organometallic chemistry of zirconium: Application to the stoichiometric activation of the CH bonds of alkanes and to the low-temperature catalytic hydrogenolysis of alkanes. Journal of Molecular Catalysis, 1992, 74, 1-3, 353-363.

23. Tosin, G.; Santini, C. C.; Baudouin, A.; De Mallman, A.; Fiddy, S.; Dablemont, C.; Basset, J.-M., Reactivity of Silica-Supported Hafnium Tris-neopentyl with Dihydrogen: Formation and Characterization of Silica Surface Hafnium Hydrides and Alkyl Hydride. Organometallics, 2007, 26, 17, 4118–4127.

24. Hayashi, T.; Okada, Y.; Shimizu, S., Studies on ferrocene derivatives. Part 12. Substituent effects for the disproportionation, synproportionation and ligand exchange reactions of t- butylferrocenes. Transition Met. Chem., 1996, 21, 418-422.

25. Hamieh, A.; Dey, R.; Samantaray, M. K.; Abdel-Azeim, S.; Abou-Hamad, E.; Chen, Y.; Pelletier, J. D. A.; Cavallo, L.; Basset, J.-M., Investigation of Surface Alkylation Strategy in SOMC: In Situ Generation of a Silica-Supported Tungsten Methyl Catalyst for Cyclooctane Metathesis. Organometallics, 2016, 35, 15, 2524-2531.

26. Okada, Y.; Yoshigami, Y.; Hayashi, T., Studies on ferrocene derivatives. Part XVI*: steric effects on the ligand exchange reactions of alkylferrocenes. Transition Met. Chem., 2003, 28, 794–799.

27. Collins, K. D.; Rühling, A.; Lied, F.; Glorius, F., Rapid Assessment of Protecting‐Group Stability by Using a Robustness Screen. Chem. Eur. J., 2014, 20, 3800-3805. 28. Eliel, E. L.; Satici, H., Conformational Analysis of Cyclohexyl Silyl Ethers. J. Org. Chem., 1994, 59, 3, 688-689.

29. Murakami, K.; Yorimitsu, H.; Oshima, K., Zinc-Catalyzed Nucleophilic Substitution Reaction of Chlorosilanes with Organomagnesium Reagents. J. Org. Chem., 2009, 74, 1415-1417.

30. Samantaray, M. K.; Dey, R.; Abou‐Hamad, E.; Hamieh, A.; Basset, J.-M. Effect of Support on Metathesis of n‐Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica– Alumina. Chem. Eur. J., 2015, 21, 16, 6100-6106.

Chapter 3. Preparation of WMe5 on modified hydrophobic supports

3.1. Introduction As shown in Chapter 2, the model unprotected alkane metathesis catalyst 1 ([(≡Si-O-)W(Me)5]) can be effortlessly deactivated by strongly coordinating substrates, such as esters or alcohols. At the same time, it does not metathesize non-coordinating ferrocene-based compounds, e.g., butylferrocene, though it does catalyze disproportionation/synproportionation equilibrium reactions due to its weak Lewis acidity. The strategy to protect the heteroatom by sterically bulky group proved to be inefficient because even non-coordinating silanes do not undergo metathesis reaction and, even more, deactivate the catalyst at high temperature, which is required for alkane metathesis to occur.

We decided to investigate another strategy which consists of protecting the active site from interaction with coordinating substrates by introducing the sterical hindrances to the catalyst support that will make the surface hydrophobic. As a hydrophobic group, we chose alkyl

(hydrocarbon) and fluoroalkyl (fluorocarbon) chains as modifiers of the silica support. This strategy is based on the physical repelling of hydrophilic functional groups of substrates by hydrophobic linear carbon chains. This modification will hopefully surround the alkane metathesis catalyst and restrict it from interactions with functional groups of functionalized substrates. The modification of the surfaces by carbon chains is not unique; however, the application in catalysis is limited. With that, we decided to investigate the effect of hydrocarbon versus fluorocarbon chains as a protection shield for the catalyst.

3.1.1 Fluorocarbon versus hydrocarbon alkyl chains The fluorine element is larger than hydrogen and has a van der Waals radius of 1.47 Å, when the van der Waals radius of hydrogen is assessed to be 1.20 Å. With that, the size of the fluorine is similar to oxygen (1.52 Å); however, it has lower polarizability.1,2 In the meantime, the fluorine has high electronegativity, electroaffinity as well as ionization potential. Since the fluorine atoms are larger than hydrogens, in this way fluoroalkyl chains (CF-chains) are bulkier and more inflexible than hydrocarbon alkyl chains (CH-chains). CF-chains have a helical structure, as opposed to the planar ‘‘crisscross’’ structure attributed to CH-chains. The mean volumes of -CF2-

3 3 3 3 and -CF3 groups are estimated to be 38 Å and 92 Å versus 27 Å and 54 Å for -CH2- and -CH3, respectively.3,4 In fact, the trifluoromethyl group is larger than isopropyl group and only marginally less bulky than the tertiary butyl group.5 The larger trans/gauche interchange energy of 4.6 versus 2.0 kJ/mol for CF- and CH-chains, respectively, unequivocally lessens the conformational freedom of the former. Consequently, the occurrence of gauche defects at equilibrium is also reduced in CF-chains which, alongside enhanced solidness that supports their arranged stacking.6 On the other hand, the stiffness of CF-chains is a primary driver for slower dissolution and exchange kinetics, as between different types of aggregates or aggregates and monomer.7-9 On a hydrophobicity scale10 (Figure 3.1), CF-alkyl chains are situated on the hydrophobic side, well beyond CH-chains of comparable length and are, therefore, not only more hydrophobic than CH-alkyl chains, but also more lipophobic.

Figure 3.1: A hydrophobicity scale. F-carbons are both more hydrophobic and lipophobic than H- carbons, as reflected by their surface tensions ƴs and their interfacial tensions with water ƴi

Improved hydrophobicity has been related primarily to larger molecular surface area for CF- chains as compared with CH-chains.11,12 These features advance self-aggregation, molecular organization, phase separation, and the exclusion of non-highly fluorinated solutes.13,14 Another important feature of perfluorinated chains is their powerful electron-withdrawing character that can create or intensify an electric dipole, locally increase the polarity of the molecules to which they belong, and change the surface potential of molecules adsorbed on water. CF-alkanoic acids are more extensively dissociated in water than CH-alkanoic acids, and CF-alcohols are substantially more acidic than CH-alcohols, while CF-alkyl diethers and CF-alkyl tertiary amines, for the most part, lose base character in aquaeous media. All these factors may impact catalysis when CF-modified supports or substrates are utilized. Likewise, fluorocarbons and CF-chains have high thermal stability and chemical inertness when contrasted to CH-chains.

3.1.2. Applications of the CH- and CF- modified surfaces 3.1.2.1. Alkyl and fluoroalkyl modification for the preparation of hydrophobic surfaces A variety of hydrophobic heterogeneous materials and surfaces have been prepared by immobilization of CH- or CF- alkyl chains to a surface. In this section, recent examples and applications will be shown. 3.1.2.1.1. Hydrophobic modification of SiO2 surface by aminosilane derivatives Novel aminosilanes with hydrolyzable Si-N bond(s) were prepared by the amination of chlorosilanes and utilized as hydrophobic modifiers of a silica surface.15 It was discovered that the aminosilanes are fairly stable towards hydrolysis in air contrasted with their chlorosilane analogs. The altered SiO2 (Figure 3.2) was applied as an entryway protector of an organic thin- film transistor with a vapor-deposited film of pentacene as the active material. The transistor with the aminosilane-adjusted silica showed double to triple higher hole portability than the device with uncovered SiO2.

Figure 3.2: Silica modification by (n-butylamino)-1,1-dimethyl(n-octyl)silane

3.1.2.1.2. Environmentally benign and durable superhydrophobic coatings based on SiO2 nanoparticles and silanes A straightforward approach was reported for preparation of totally waterborne, fluorine-free, and durable superhydrophobic coatings (SHCs).16 A waterborne suspension of hexadecyl polysiloxane altered SiO2 (SiO2@HD-POS) was prepared via HCl-catalyzed hydrolytic condensation of hexadecyltrimethoxysilane (HDTMS) and tetraethoxysilane with SiO2 nanoparticles. The SHCs with high water contact angles (CA = 163.9 °) and low sliding angles (SA

= 3.7 °) were simply prepared by sequentially spray-coating a polyurethane (PU) waterborne solution and the SiO2@HD-POS waterborne suspension onto glass slides. The impacts of SiO2,

HDTMS, reaction time, and fabrication temperature on superhydrophobicity were also investigated. The coatings additionally show outstanding thermostability in boiling water. The

SHCs showed promising applications in various areas including oil/water separation and preventing scald, as the method is environmentally benign and the coatings are applicable onto different substrates.

3.1.2.1.3. Formation of superhydrophobic surfaces by cysteamine-catalyzed co-silicification of (1H,1H,2H,2H-Perfluorooctyl)triethoxysilane (FTES) and tetraethylorthosilicate (TEOS) Bioinspired silicification attracts a lot of intrigue due to its physiologically pertinent, gentle conditions for hydrolysis and condensation of silica precursors, which makes the bioinspired approach better than the regular sol-gel process, particularly when dealing with biological entities. However, the morphological control of silica structures with the incorporation of functional groups in the bioinspired silicification has been unexplored. The authors of the work,17 co-silicificated (Figure 3.3) FTES and TEOS to examine the morphological advancement of fluorinated silica structures in the cetyltrimethylammonium bromide-mediated, cysteamine- catalyzed silicification. The generated micrometer-long wormlike and spherical silica structures display superhydrophobicity after film arrangement. Interestingly, the measurement of dynamic water contact angles demonstrates that the morphological distinction prompts an alternate wetting state, either the self-cleaning or the pinning state of the superhydrophobic surface.

Figure 3.3: a) Chemical structures of FTES and TEOS. b) Representative synthetic procedures for the co- silicification by co-condensation of FTES and TEOS. The total concentration of silica precursors was fixed at 100 mm (40 mm of FTES and 60 mm of TEOS), and the water-to-ethanol ratio was varied from 4:1 to 0.3:1 (v/v)

3.1.2.2. CH- and CF- surface modification for the preparation of polymer semiconductors A specific unipolarization of ambipolar polymer semiconductor that proceeds by utilizing different self-assembled monolayers (SAMs) has been shown.18 The reported work is the principal case of the control of major carriers in ambipolar polymer semiconductors by SAMs, and the use of the technique to fabricate complementary inverters showed the ideal switching behavior. The obtained SAMs represented in Figure 3.4 is the monolithic complementary-like inverters fabricated on Si/SiO2 substrates with two distinct surface regions modified with

1H,1H,2H,2H-perfluorodecyltriethoxysilane (FDTS) and octadecyltrichlorosilane (ODTS) self- assembled monolayers (SAMs).

Figure 3.4: Monolithic complementary-like inverter fabricated on Si/SiO2 substrate with two distinct surface regions modified with FDTS- and ODTS-SAMs

In the reported work, the mechanistic details of the unipolarization were clarified. It was discovered that the surface potentials were initiated by SAMs and subsequently produced space- charge layers.

3.1.2.3 Utilization of hydrophobically modified supports in catalysis 3.1.2.3.1 Fluorinated catalyst support in ethylene polymerization Various catalyst compositions containing single-site catalysts have been investigated to prepare polyolefins, producing relatively homogeneous copolymers at reasonable polymerization rates.

As opposed to Ziegler-Natta catalyst compositions, single-site catalyst compositions, such as metallocene catalysts, are catalytic compounds in which each catalyst particle contains one or only a few types of polymerization sites. To achieve acceptable and economically viable polymerization activities with single-site catalyst systems, a large amount of activator such as methylaluminoxane ("MAO") is often required. Such activators are often costly, and the large amount of activator needed to produce an active single-site catalyst for polymerization has been a significant obstacle to the commercialization of single-site catalysts for polyolefin production.

The US Patent19 discloses the catalyst system that includes a catalyst compound, fluorinated support, and an aluminoxane compound for the polymerization of ethylene. The fluorinated support is generated by heating catalyst support and a fluoride donor compound at a temperature sufficient to decompose the fluoride donor compound in a fluidized bed reactor while maintaining a ratio of a pressure drop across a distributor plate to a pressure drop across the fluidized bed of greater than about 7 %. The aluminoxane is present in an amount of about

10 mmol or less per gram of the support. The described method shows good productivity of polymerization with a lesser amount of aluminoxane compound used in the reaction mixture.

3.1.2.3.2 Fluorinated alumina and silica supports in the alkylation of isobutane with olefins There are specific targets established to improve the quality of types of gasoline, which in turn must have a direct impact on the quality of air in densely populated areas. For instance, among other actions, the reduction of the olefins and aromatics, especially benzene, a lower Reid vapor pressure (RVP) and elimination of sulfur and lead in gasolines altogether, will help to overcome the most intense ecological issues by, for example, reduction of the ground-level borne ozone,

SOx emissions from internal combustion motors, emission of cancer-causing agent aromatics like benzene, etc. However, to achieve those objectives, a decrease of the severity conditions in reforming reactors might be essential, as well as other adjustments in the composition of heavy ends in FCC gasoline. It implies a further decrease of both the actual octane rates and the absolute volume of accessible gasoline. On the other hand, different processes may be utilized to keep the balance in the pool, as the isobutane alkylation process, which produces high quality alkylate in the Cv-C 9 range, with about 98 % paraffinic character (tri-methyl-pentanes, di-methyl- hexanes), a high octane number, and last, but not least, a minimum of ozone-precursor combustion products.

It was shown20 that fluorinated alumina and silica supports are active catalysts for alkylation of isobutane with mixed olefins, at 0 °C. Among the fluorinating agents tested, di-hydrated trifluoroboride yields a higher acid strength, i.e., for alumina treated with BF3•2H2O the Hammett function H0 is equal to -3.2 or equivalent to 52.5 % H2SO4. At high fluorine concentrations, however, there is substantial leaching, especially on the alumina supports, but silica withstands the leaching process better. The silica modified catalysts were acidic enough to carry out the alkylation reaction without the addition of any acidic agent. However, both series of solid acid catalysts yield more C8 type olefins compared to liquid sulfuric acid, which might be the result of competition between isobutane alkylation and olefin dimerization reactions. In fact, an equivalent acid strength close to or greater than 100 % H2SO4 seems to favor olefin dimerization, rather than alkylation. A low contact time leads to lower olefin dimerization and fewer secondary reactions. Some process variables, for example, temperature and pressure, lead to improvement of the global conversion at a small residence time, without modifying the product distribution.

Also, there is a diminution of the olefin dimerization reactions by changing the residence time and isoparaffin/olefin ratios.

3.1.2.3.3 Fluorinated silica catalyst for the preparation of aliphatic/aromatic nitriles An improved fluorinated siliceous catalyst,21 well adapted for the catalytic synthesis of aromatic/aliphatic nitriles from their corresponding formamides, formanilides or amides, is comprised of a plurality of silica particulates, the specific surface of which ranges from about 200 to about 300 m2/g, having a total pore volume ranging from about 1 to about 1.5 cm/g, with an average pore diameter ranging from about 100 to about 200 Å, having an exchange pH of less than about 3, and with the fluorine content thereof bonded to the silica, expressed in F3, ranging from about 0.05 to about 2 % by weight based upon the silica, and the sodium content (Na2O), being less than about 1 % by weight, also based on the silica. The formation of the resulting silica by the reaction between the sodium silicate and hydrofluoric acid has also been described.

3.1.2.3.4 Fluorous biphasic catalysis in application to Pd-mediated Suzuki and Sonogashira couplings The immobilization of perfluoro-tagged palladium catalysts on fluorous reversed-phase silica gel

(FRPSG) and their use for Suzuki and Sonogashira cross-coupling reactions has been demonstrated.22

Figure 3.5: The fluorous solid supports 1 and 2 and Palladium complexes 3 a-c

To immobilize the complexes, FRPSG was added to the respective complex in diethyl ether and hexafluorobenzene, and the solvent was evaporated. The immobilized precatalyst is an air- stable, free-flowing powder. Silica gels 1-2 (Figure 3.5) were evaluated in the Suzuki cross- coupling reaction of phenylboronic acid and para-nitrobromobenzene and the Sonogashira coupling of phenylacetylene and para-nitrobromobenzene (Scheme 3.1).

Scheme 3.1: Suzuki reactions performed with 3 a-c immobilized on support 1 as catalysts. a) 0.001±1.5 mol % catalyst, DME, 2m aq. Na2CO3, 80 °C

The catalysts possessed activities comparable to those found in liquid-liquid fluorous biphasic catalysis (FBC). The catalysts were separated from the product by decantation. Leaching was as low as 1.9 % and 1.6 % for 1 and 2, respectively, and the recovered catalyst could be reused.22

Due to the dilution of the catalyst with FRPSG, tiny amounts of catalysts could be easily and precisely handled. In contrast to conventional FBC approaches, no fluorous solvent was required for the reaction and the isolation and recovery of the catalyst. An advantage of this strategy compared to covalent catalyst immobilization is that the same support can be used for different catalysts without the need for a separate linker unit.22

3.1.2.3.5 A multifunctional mesoporous silica catalyst for shifting the reaction equilibrium by removal of byproduct Bifunctional mesoporous silica nanoparticle (MSN) catalysts of esterification, containing a

Brønsted acid site of diarylammonium triflate (DAT) and a pentafluorophenyl propyl (PFP) group, were synthesized and thoroughly characterized.23 Their high reactivity is attributed to the formation of a surface-bound hydrophobic layer of PFP molecules, which enhances the extrusion of one of the reaction products (water) from the mesopores by suppressing water adsorption onto the surface, thereby shifting the reaction equilibrium to completion.

Figure 3.6: Representation of a bifunctional PFP/DAT-MSN

It was reported that the bifunctional MSN catalytic system has a superior reactivity in the equilibrium reaction, whose improved yield is the result of a nano environment designed to efficiently remove the byproduct (water) through the incorporation of the secondary functional group (Figure 3.6). The study integrated a novel synthetic approach with state-of-the-art theory, which served as predictive tools in the design of an efficient new catalyst for the esterification reaction.

3.1.2.3.6 Catalytic application of fluorous silica gel in Fries rearrangement Commercially available fluorous silica gel (FSG) with no further post-modification was successfully investigated and applied merely as a catalyst in Fries rearrangement of various aryl esters under solvent-free conditions in 4 h and optimized temperatures (Figure 3.7).24 In addition to good yields and recyclability of the catalyst, toxicity of reaction medium, by-products, and wastes were minimized. Also, low catalyst loading was another advantage of this methodology.

Scheme 3.2: General scheme of Fries rearrangement of aryl esters catalyzed by FSG

According to recent advances in the properties of fluorinated materials such as their solvents and fluorous supports, etc., the present work features the potential catalytic activity of unmodified

FSG in Fries rearrangement (Scheme 3.2). In addition, simplicity, reusability, low cost of preparation, and high efficiency of this catalyst led to a unique catalyst among the other similar catalysts. It can also be concluded that discovering the catalytic activity of FSG may have an impact for further similar organic reactions.

Figure 3.7: Proposed mechanism for surface interaction of FSG with reactant

As shown, the modification of the surface by hydrophobic chains has a variety of applications.

We decided to use this strategy in order to protect the catalyst active sites in metathesis reactions and explore the potential outcomes of this study.

3.2. Results and Discussion

3.2.1 Modification of SiO2-500 by triethoxyoctylsilane (CH-SiO2-500) For a better understanding of the catalyst functions, it is important to investigate the effect of support on the alkane metathesis catalyst by modification of the silica with CH-alkyl chains or CF- fluoroalkyl chains. First, we prepared CH-modified silica (CH-SiO2-500) from preliminarily dehydroxylated conventional silica on a high vacuum line at 500 °C (2 g, 0.8 mmol of available surface hydroxyls) and triethoxyoctylsilane (0.111 g, 0.4 mmol) in toluene at 80 °C overnight in the glovebox. After the reaction, the modified silica product was filtered off, washed with pure toluene (3 x 30 mL) and with pure DCM (3 x 30 mL), and then dried on a high vacuum line at RT for 3 hours. The preparation of CH-SiO2-500 is illustrated in Scheme 3.3.

Scheme 3.3: Modification of SiO2-500 with triethoxyoctylsilane

The initial double excess of available surface silanols in regards to the starting triethoxyctylsilane allows OH groups after grafting of the silane to remain on the surface. The remaining OH groups are necessary for further grafting of the alkane metathesis catalyst and study of its interaction with the CH-chains. 8

(Si-OH) 3743 6

4 (CH)

Absorbance 2927

2 2977 2857

0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumbers (cm-1)

Figure 3.8: FTIR spectra of bare SiO2-500 (red) and modified CH-SiO2-500 (blue)

The FTIR spectroscopy measurements revealed the expected reducing of available surface silanols (the characteristic band at 3743 cm-1), and at the same time the new bands appeared at

2977 cm-1, 2927 cm-1 and 2857 cm-1 that correspond to CH-stretching vibrations of the grafted octyl-triethoxysilane (ν, CH-chains). Remarkably, the properties of the obtained material changed as well, for instance, the hydrophobic CH-SiO2-500 was not miscible with water in spite of non- modified SiO2-500.

In the solid-state 1H MAS NMR spectrum, the strong signal was observed at 1.1 ppm, attributed to methyl groups of the grafted triethoxyoctylsilane (CH-chains), together with two peaks at 3.1 ppm and 3.6 ppm, attributed to -CH2- methylene protons of CH-chains analogous to its homogeneous counterpart (Supporting Information: Figures 3.34, 3.35).

1 Figure 3.9: H solid-state NMR of CH-SiO2-500

In the 13C cross-polarization magic angle spinning (CP/MAS) NMR spectrum, distinct signals at δ

11, 15, 22, 28, 31, and 58 were found (Figure 3.10). The latter peak at 58 ppm is a characteristic peak of methylene carbon of the free non-attached ethoxy- methylene carbon Si-O-CH2-CH3. The presence of the latter excludes the grafting of the triethoxyoctylsilane by T3 structure, in which all (OEt)3-Si- groups are attached to silica. Instead, one or two ethoxy groups did not interact with the silica surface.

13 Figure 3.10: C cross-polarization magic angle spinning (CP/MAS) NMR spectrum of CH-SiO2-500 The signals at 1.1, 3.1, and 3.6 ppm autocorrelate in 2D single quantum 1H−1H homonuclear dipolar correlation spectra and are assigned to different methyl and methylene groups (Figure

3.11).

1 1 Figure 3.11: 2D single quantum H− H homonuclear dipolar correlation spectrum of CH-SiO2-500

The 2D 1H−13C HETCOR NMR spectrum (Figure 3.12) shows a correlation between the methyl protons (1.1 ppm) and carbon atoms (11 and 15 ppm), respectively, and a correlation between the methylene protons centered at 3.1-4.6 ppm with the carbons at 22, 28 and 31 ppm which allows the assignment of the carbon−proton pairs to the individual methylene groups of the grafted CH-chains. Furthermore, the strong correlation between the carbon and proton nuclei signals at 58 and 5.1 ppm, respectively, strongly supports the assignment of a free Si-O-CH2- methylene moiety (Figure 3.12, 3.35).

1 13 Figure 3.12: 2D H− C HETCOR NMR spectrum of CH-SiO2-500

29Si CP/MAS NMR spectrum shows a broad signal at -105 ppm that correspond to Si-O-Si network of SiO2-500 support. At the same time, the signal at -50 ppm corresponds to a silicon atom of the grafted triethoxyoctylsilane. The signal at -50 ppm is characteristic for the T1 type of structure,25 where triethoxyoctylsilane is attached to silica by only one of the available ethoxy groups, with the two other groups remaining unattached (Figure 3.13, 3.14).

29 Figure 3.13: Si CP/MAS NMR spectrum of CH-SiO2-500

Figure 3.14: The structure of CH-SiO2-500 support

3.2.2 Grafting of WMe6 on modified CH-SiO2-500

After the preparation of modified hydrophobic support (CH-SiO2-500), the following step was the grafting of the alkane metathesis catalyst precursor (WMe6) (Scheme 3.4). CH-SiO2-500 and pentane solution of WMe6 were mixed in the glove box at -40 °C and stirred overnight inside the fridge of the glove box, while the temperature of the fridge was kept in the range -35 to -40 °C.

After that, the modified silica with grafted WMe5 was filtered off, washed with pentane and dried in a high vacuum line. The resulting yellowish material contained two weight percent loading of tungsten, based on ICP-OES analysis.

Scheme 3.4: Grafting of WMe6 onto CH-SiO2-500

The solid-state 1H MAS NMR spectrum of the obtained material showed a new strong signal which appeared at 2 ppm, together with a signal at 1.1 ppm that was initially observed and belonged to the CH-alkyl chain on the modified surface. The peak at 2 ppm corresponds to the

26 protons of W-CH3 group and have good accordance with the literature data. A broad signal at

3.9 ppm was also observed and belongs to methylene protons of the CH-chains on the initial modified surface.

1 Figure 3.15: Solid-state H MAS NMR spectrum of WMe6 grafted on CH-SiO2-500

The 13C cross-polarization magic angle spinning (CP/MAS) NMR spectrum is similar to those obtained in the initial surface with a new signal at 82 ppm, corresponding to the carbon of W-

26 CH3 group. It is important to emphasize that the spectrum clearly shows the presence of individual methyl carbons of W-CH3 group (the signal at 82 ppm) and the methylene carbons of free Si-O-CH2-CH3 ethoxy group (the signal at 58 ppm). As a result, the coordinating oxygen atom of Si-O-Et does not coordinate with the W-CH3 moiety on the silica surface, when both species

(CH-chains and WMe5) are grafted to the surface, in contrast to when a silane is used as a substrate. In accordance with the data obtained in Chapter 2 (Part 2.3), silanes and siloxanes poison the alkane metathesis catalyst and deactivate it for further reactions with alkanes. The fact that both moieties are individually present on silica suggests that the oxygen atom is not in close proximity to the tungsten and is not able to coordinate with it.

13 Figure 3.16: C cross-polarization magic angle spinning (CP/MAS) NMR spectrum of WMe6 grafted on CH-SiO2-500

In addition to that, the 2D double quantum 1H−1H homonuclear dipolar correlation spectrum shows a close proximity (Figure 3.17) of the protons of W-CH3 group (2 ppm) with the protons of triethoxyoctylsilane (1.1 and 3.9 ppm) grafted on the surface (CH-chains), which means that the alkane metathesis catalyst precursor is surrounded by protective hydrophobic CH-chains.

1 1 Figure 3.17: 2D double quantum H− H homonuclear dipolar correlation spectrum of WMe6 grafted on CH-SiO2-500

The 2D 1H−13C HETCOR NMR spectrum clearly shows the correlation between the signal at 2 ppm

(protons of W-CH3) and the signal at 82 ppm (carbons of W-CH3), protons at 5 ppm and the carbon atoms at 58 ppm (Si-O-CH2-), protons at 1.1-3.9 ppm and carbons at 11-31 ppm (methyl and methylene groups of the grafted CH-chains).

1 13 Figure 3.18: 2D H− C HETCOR NMR spectrum of WMe6 grafted on CH-SiO2-500

The obtained NMR data suggest that the alkane metathesis catalyst is not perturbed by the grafted CH-chains at room temperature. To understand if the catalyst can be poisoned by itself or by releasing free silanes at higher temperatures, we conducted a series of control experiments.

First, we heated the W(Me)5/CH-SiO2-500 at 150 °C for 3 hours in a vacuum-sealed ampule without a solvent. After that, the ampule was opened, DCM was added to the catalyst, the suspension was stirred, filtered off and analyzed by GC-FID. As a result, no traces of silanes or any other organic molecules were found. Second, we heated a mixture of W(Me)5/CH-SiO2-500 and dry mesitylene at 150 °C overnight in a vacuum-sealed ampule. The ampule then was frozen by liquid nitrogen, opened and mixed with DCM. The suspension was filtered off and analyzed by GC-FID.

As a result, no traces of silanes or any other organic molecules, except a solvent, were detected.

These results show the robustness of the modified surface and its inertness to the catalyst. 3.2.3 Modification of SiO2-500 by triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane

By analogy, we decided to demonstrate the modification of SiO2-500 by triethoxy(1H,1H,2H,2H- perfluoro-octyl)silane (CF-chains) for the further preparation of the alkane metathesis catalyst on CF-modified hydrophobic support. Following the same procedure we used for grafting of triethoxyoctylsilane, we grafted 0.4 mmol of triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane to the surface of SiO2-500 (having 0.8 mmol of available silanols) in toluene at 80 °C for 3 hours (Scheme

3.5).

Scheme 3.5: Modification of SiO2-500 with triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane

The obtained CF-SiO2-500 support is immiscible with water due to its high hydrophobicity and is similar to CH-SiO2-500 in this regard. The FTIR spectrum of CF-SiO2-500 shows the partial reducing of the available surface silanols (IR band at 3743 cm-1) and appearance of the bands at 2901, 2936

-1 and 2980 cm assigned to C-H stretching bands of Si-CH2-CH2- (Figure 3.19). 8

(Si-OH) 3743 6

4

Absorbance

2 (CH) 2980 2936 2901

0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumbers (cm-1)

Figure 3.19: FTIR spectra of bare SiO2-500 (red) and CF-modified SiO2-500 (blue)

1 The solid-state H MAS NMR spectrum of CF-SiO2-500 support has a sharp signal at 1.1 ppm assigned to the protons of the methyl group of one of the free ethoxy groups Si-O-CH2-CH3, and broad signals at 1.9-3.6 ppm were assigned to the available ethoxy methylene protons Si-O-CH2-

CH3 and two methylene groups of the grafted alkyl chain Si-CH2-CH2-(CF2)5-CF3 (Figure 3.20).

1 Figure 3.20: Solid-state H MAS NMR spectrum of CF-SiO2-500

13 Figure 3.21: C cross-polarization magic angle spinning (CP/MAS) NMR spectrum of CF-SiO2-500

In the 13C cross-polarization magic angle spinning (CP/MAS) NMR spectrum signals at δ 15, 24,

31, and 58 were detected (Figure 3.21). The latter peak at 58 ppm has the same chemical shift and nature as was the case of CH-SiO2-500 and is attributed to the methylene carbon of the free ethoxy group Si-O-CH2-CH3. Analogous to CH-SiO2-500, CF-SiO2-500 support excludes the grafting of the triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane by the T3 type of structure.

1 1 Figure 3.22: 2D double quantum H− H homonuclear dipolar correlation spectrum of CF-SiO2-500 The signals at 1.1, 1.9, and 3.6 ppm autocorrelate in 2D double quantum 1H−1H homonuclear dipolar correlation spectra and are assigned to methyl and methylene groups of the grafted triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane (Figure 3.22).

29 Figure 3.23: Si CP/MAS NMR spectrum of CF-SiO2-500

29Si CP/MAS NMR spectrum shows a broad signal at -105 ppm that corresponds to Si-O-Si network of CF-SiO2-500 support. At the same time, we observed two signals at -50 ppm and -59 ppm which correspond to silicon atoms of the grafted triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane.

According to the literature,25 the signal at -50 ppm is characteristic for the T1 type of structure, and the signal at -59 ppm is close to the T2 type. These results suggest that grafted triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane is attached to silica by both one or two of the available ethoxy groups, with the remaining one or two groups unattached (Figure 3.24).

Figure 3.24: The structure of CF-SiO2-500 support

3.2.4 Grafting of WMe6 on modified CF-SiO2-500

Analogous to the procedure of grafting WMe6 on CH-SiO2-500 (section 3.2.2), we grafted WMe6 on

CF-SiO2-500 in the same conditions and obtained the tungsten loading of 3.07 % based on ICP-OES analysis. The higher loading of tungsten on CF-SiO2-500 as compared to CH-SiO2-500 (2 %) despite the fact that fluorocarbon chains are bulkier that hydrocarbon chains can be explained by the fact that CF-chains have a helical structure rather than the planar ‘‘zigzag’’ structure of CH-chains and, therefore, the access to the available surface silanols on the CF-SiO2-500 surface is sterically easier.

Scheme 3.6: Grafting of WMe6 on CF-SiO2-500

After the grafting of the organometallic catalyst precursor, further characterization of the surface species was accomplished by solid-state 1H, 13C CP-MAS and 2D SQ 1H−1H homonuclear dipolar

1 correlation NMR spectroscopy. In the solid-state H MAS NMR spectrum of WMe5/CF-SiO2-500 an

13 intense signal at 2 ppm was observed and attributed to the protons of W-CH3 group. The C cross-polarization magic angle spinning (CP/MAS) NMR spectrum showed a characteristic for the

W-CH3 peak at 81 ppm together with peaks at 15 ppm (methyl carbon of the free ethoxy group

Si-O-CH2-CH3), 20-50 ppm (methylene carbons of the alkyl chain) and 58 ppm (methylene carbon the free ethoxy group Si-O-CH2-CH3) (Figures 3.25, 3.26).

1 Figure 3.25: H MAS NMR spectrum of WMe5/CF-SiO2-500

13 Figure 3.26: C cross polarization magic angle spinning (CP/MAS) NMR spectrum of WMe5/CF-SiO2-500

The signals at 2.0 and 3.8 ppm autocorrelate in 2D double quantum 1H−1H homonuclear dipolar correlation spectra and are assigned to the methyl group of supported -W(CH3)5 and methylene groups of the grafted triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane. The proximity of the organometallic catalyst precursor to the CF-chains is less than that of the CH-chains.

1 1 Figure 3.27: 2D DQ H− H homonuclear dipolar correlation spectrum of W(CH3)5/CF-SiO2-500 Similar to W(CH3)5/CH-SiO2-500, tungsten pentamethyl supported on modified fluorinated silica is not poisoned by the modified surface. Control experiments by heating the catalyst precursor with and without the solvent showed no traces of released silane confirming the robustness of the obtained species W(CH3)5/CF-SiO2-500.

3.2.5 Application of W(CH3)5/CH-SiO2-500 and W(CH3)5/CF-SiO2-500 in catalysis 3.2.5.1 Metathesis of n-decene (olefin)

In order to understand whether W(CH3)5 supported on modified silica by CH-chains (W(CH3)5/CH-

SiO2-500) or CF-chains (W(CH3)5/CF-SiO2-500) will be active in catalysis of metathesis reactions and how the protective chains will affect its performance, first, we tested the catalyst precursors in metathesis of olefin (n-decene). In a typical reaction, 21 mg of supported W(CH3)5 was mixed with

0.5 mL of n-decene and heated at 150 °C for 3 hours in a vacuum-sealed ampule tube. After the reaction, the suspension was cooled down by liquid nitrogen, diluted with 1 mL of DCM, filtered and analyzed by GC-FID. In the case of W(CH3)5/CH-SiO2-500, the conversion of n-decene was

80 % with a cumulative 945 TON of the catalyst (1182 is theoretically possible). However, in the case of W(CH3)5/CF-SiO2-500, the conversion was higher and reached 88 % with a TON of 664 (754 is theoretically possible). In the control experiment, the conversion of n-decene on supported

W(CH3)5/SiO2-500 on non-modified silica was 88 % after 3 hours with TON 896. As we concluded, the protective chains do not affect catalyst activity in olefin metathesis and do not influence the selectivity of metathesis products. (In all cases we observed products ranging from C3 to C20.) The higher conversion of n-decene over the catalyst supported on the fluorinated surface can be explained by more available active sites due to the helical structure of perfluorinated chains compared to the “crisscross” structure of hydrocarbon (alkyl) chains. 3.2.5.2 Metathesis of n-decane (alkane)

In the case of metathesis of n-decane, a drastic difference in the catalytic activity of W(CH3)5/CH-

SiO2-500 and W(CH3)5/CF-SiO2-500 was found. In a typical reaction, 25 mg of the supported catalyst precursor and 0.5 mL of n-decane were mixed and sealed under vacuum. The ampule tube was heated at 150 °C for 5 days and, after that, the ampule was cooled down with liquid nitrogen, opened, and 1 mL of DCM was added. The mixture was filtered off and analyzed by GC-FID. In the case of W(CH3)5/CF-SiO2-500, the conversion of n-decane reached 8 % with 46 cumulative TON of the catalyst. However, in the case of W(CH3)5/CF-SiO2-500, the conversion was 0 %, and only unreacted starting material was observed. Both reactions were repeated under identical conditions with the same result. It is very important to consider the fact that n-decene substrate undergoes metathesis by supported WMe5 on both supports. Considering the aforementioned and unexpected inertness of the tungsten pentamethyl supported on protected silica suggests that 1) the substrate can reach the catalyst active site, 2) hydrocarbon alkyl chains prevent the substrate from interacting with the catalyst with required activation energy, while perfluorinated alkyl chains do not prevent interaction with the catalyst. The last conclusion can be explained by a more rigid (less flexible) structure of perfluorinated alkyl chains in spite of hydrocarbon alkyl chains. For this reason, W(CH3)5/CF-SiO2-500 proved to be a more efficient alkane metathesis catalyst. As in case of olefin metathesis, the selectivity of metathesis was not changed as compared to the control experiment and the range of alkanes from C1 to C32 was observed. It is not surprising that the activity of the catalyst on modified support was decreased in comparison with the control experiment, in which 38 % of n-decane was converted to its metathesis products

27 after 5 days at 150 °C on W(CH3)5/CF-SiO2-700. 3.2.5.3 Metathesis of functionalized olefin and alkane As shown in Chapter 2 (Part 2.1.2), the metathesis of saturated ester, such as ethyl caprylate 5

(Chapter 2), on [(≡Si-O-)W(Me)5] 1 (Chapter 2), does not occur due to the poisoning of the catalyst by the strongly coordinating oxygen atoms of the ester (coordination is more energetically favorable than CH-activation). It is not surprising that the olefinic analog – unsaturated 5-hexenyl- acetate does not undergo metathesis on catalyst 1 as well.

Figure 3.28: 5-hexenyl-acetate

When we tried to utilize W(CH3)5/CH-SiO2-500 and W(CH3)5/CF-SiO2-500 with a hypothesis that the hydrophilic ester group will repel the hydrophobic alkyl and fluoroalkyl chains that will allow only an olefinic double bond of 5-hexenyl-acetate coordinate and insert to W-CH3 bond, we found that no metathesis happened on both catalysts. By introducing more sterical hindrances to a substrate’s heteroatoms, we utilized silyl ethers 20-22 (Chapter 2, Part 2.3.1) and found no metathesis on both W(CH3)5/CH-SiO2-500 and W(CH3)5/CF-SiO2-500. Utilization of non-coordinating silanes 23-25 (Chapter 2, Part 2.3.2) was not successful as well, and we only observed unreacted starting materials in reactions at 150 °C after 1, 5, and 10 days.

3.2.6 Choice of KCC-1 support After we found no metathesis of functionalized olefin and alkanes on conventional hydrophobic silica-modified supported WMe5 catalysts, we decided to apply the same modification to KCC-1 support. It was shown that specific morphology of KCC-1 as compared to normal silica results in a higher surface area and competitive advantages as a support for the catalysts.28-32 KCC-1 with a high surface area and excellent physical and textural properties represents novel fibrous morphologies. Its high surface area is due to its fibers (not pores). Therefore, most of its surface area is accessible, yielding unusually high activity in catalysis. Moreover, KCC-1 has high mechanical and thermal stability that makes KCC-1 extremely useful as a catalyst support, in which there is a need for significant accessibility to active sites. The same approach was implemented in the modification of KCC-1 surface by hydrophobic alkyl and fluoroalkyl chains before grafting of WMe6 as an organometallic alkane metathesis catalyst precursor.

3.2.6.1 Modification of KCC-1-500 by triethoxy-octylsilane and triethoxy(1H,1H,2H,2H-perfluoro- octyl)silane In the previous sections (3.2.1-3.2.4), we mixed conventional silica-500 with triethoxysilanes (in respect to its 50 % by mole of the available surface silanol) and grafted WMe6 on the remaining silanols. Since the approach was not successful, we decided to prepare different ratios of protective chain / WMe6 on the KCC-1 surface. With that, following the same procedures (3.2.1-

3.2.4), and considering the initial amount of OH groups, 1.2 mmol OH/g on KCC-1-700, 100 mg samples of KCC-1-700 (0.12 mmol OH/g) was treated with different amounts of silanes (15-90 %) followed by grafting of WMe6.

Table 3.1: Preparation of KCC-1-700 supported WMe5 protected by 15-90 % of hydrophobic silanes

KCC-1-700 Octyl-triethoxysilane Triethoxy(1H,1H,2H,2H- WMe6 Obtained perfluoro-octyl)silane catalyst (CH-chains) precursor (label) (CF-chains)

0.12 mmol OH/g 0.018 mmol 0 mmol Excess WMe5/CH-15

0.12 mmol OH/g 0.042 mmol 0 mmol Excess WMe5/CH-35

0.12 mmol OH/g 0.066 mmol 0 mmol Excess WMe5/CH-55

0.12 mmol OH/g 0.090 mmol 0 mmol Excess WMe5/CH-75

0.12 mmol OH/g 0.108 mmol 0 mmol Excess WMe5/CH-90

0.12 mmol OH/g 0 mmol 0.018 mmol Excess WMe5/CF-15

0.12 mmol OH/g 0 mmol 0.042 mmol Excess WMe5/CF-35

0.12 mmol OH/g 0 mmol 0.066 mmol Excess WMe5/CF-55

0.12 mmol OH/g 0 mmol 0.090 mmol Excess WMe5/CF-75

0.12 mmol OH/g 0 mmol 0.108 mmol Excess WMe5/CF-90

Since we followed the same procedure for the grafting of the silanes and the WMe6, we chose

WMe5/CH-55 for NMR characterization and compared it to WMe5/CH-SiO2-500.

1 Figure 3.29: H MAS NMR spectra of KCC-1 supported WMe5/CH55 (left), and SiO2 supported WMe5/CH- SiO2-500 (right)

1 As shown from solid-state H MAS NMR spectrum, W-CH3 methyl protons on both silica and KCC-

1 represent a sharp signal at 2 ppm. The grafted hydrocarbon alkyl chains show a broad signal at

1.1 ppm, assigned to its methyl protons, and 3.8-3.9 ppm, assigned to methylene protons. Both

NMR spectra are similar.

13 Figure 3.30: C CP MAS NMR spectra of KCC-1 supported WMe5/CH55 (left) and SiO2 supported WMe5/CH-SiO2-500 (right) 13 The C CP/MAS NMR spectra of KCC-1 (WMe5/CH-55) and SiO2-500 (WMe5/CH-SiO2-500) modified by octyl-triethoxysilane and grafted tungsten pentamethyl have the same signals at 82 ppm (W-

CH3), 58 ppm (Si-O-CH2-), 31-11 ppm (CH2 and CH3 carbons of the grafted alkyl chain) confirming that both the alkyl chain and organometallic catalyst precursor were grafted on the surfaces.

29 Figure 3.31: Si MAS NMR spectra of KCC-1 supported WMe5/CH55 (left) and SiO2 supported WMe5/CH- SiO2-500 (right)

29 The Si solid-state NMR spectrum of WMe5/CH-55 is very similar to the spectrum of CH-modified

SiO2-500 (WMe5/CH-SiO2-500) and consists of the strong broad signal at -105 ppm (Si-O-Si network) and weaker signal at -50 ppm, characteristic of the T1 type of structure of the grafted octyltriethoxysilane and the general structure of the pre-catalyst as indicated in Figure 3.31.

Figure 3.32: The structure of KCC-1 supported WMe5/CH55

In addition, we performed transmission electron microscopy analysis of WMe5/CH-55 to understand the distribution of tungsten atoms on the surface of modified KCC-1 support.

Figure 3.33: A) Scanning transmission electron microscopy, high angle annular dark field (STEM HAADF) image of WMe5/CH-55. B) High resolution scanning transmission electron microscopy, high angle annular dark field (HR STEM HAADF) image of WMe5/CH-55 Figure 3.33 B) clearly demonstrates the bright spots that correspond to clusters and single heavy

W atoms that can be easily distinguished from the lighter silica matrix (KCC-1 support). As we can see, tungsten is well distributed on the surface of KCC-1 support.

3.2.6.2 Catalytic applications After we successfully prepared modified hydrophobic KCC-1 supports and grafted the alkane metathesis catalyst precursor to its surface, we decided to screen the catalysts for the metathesis of functionalized alkanes with 2 model substrates – ester (ethyl caprylate 5, Chapter 2) and silane

(octyltriphenylsilane 24, Chapter 2) at 150°C for 30 days in the conditions listed in the table below. Since we did not obtain a metathesis of functionalized alkanes in neat conditions with modified conventional silica as a support, the screening of KCC-1 supported catalysts was performed in the inert solvents to increase the catalyst/substrate ratio and decrease potential catalyst poisoning.

Table 3.2: Screening of the catalysts CH(CF)15-90 in metathesis of functionalized alkanes. Conditions: 150 °C, 30 days

Entry Catalyst Substrate Solvent (0.5 Stirring, Result mL) rpm

1 CH15 Ester Mesitylene 50 No metathesis

2 CH35 Ester Mesitylene 50 No metathesis

3 CH55 Ester Mesitylene 50 No metathesis

4 CH75 Ester Mesitylene 50 No metathesis

5 CH90 Ester Mesitylene 50 No metathesis

6 CH15 24 Mesitylene 50 No metathesis

7 CH35 24 Mesitylene 50 No metathesis

8 CH55 24 Mesitylene 50 No metathesis

9 CH75 24 Mesitylene 50 No metathesis

10 CH90 24 Mesitylene 50 No metathesis

11 CF15 24 Mesitylene 50 No metathesis

12 CF35 24 Mesitylene 50 No metathesis

13 CF55 24 Mesitylene 50 No metathesis

14 CF75 24 Mesitylene 50 No metathesis

15 CF90 24 Mesitylene 50 No metathesis

16 CF15 Ester Biphenyl 0 No metathesis

17 CF35 Ester Biphenyl 0 No metathesis

18 CF55 Ester Biphenyl 0 No metathesis

19 CF75 Ester Biphenyl 0 No metathesis

20 CF90 Ester Biphenyl 0 No metathesis

However, changing the ratio between the catalyst active site and protective hydrophobic chains surrounding the catalyst, using mesitylene or biphenyl as a solvent, as well as running reactions with or without stirring does not influence the reactivity of functionalized alkanes on the catalyst and none of the 20 reactions show any trace of metathesis products. 3.3. Conclusions

In conclusion, we demonstrated the strategy to protect the catalyst by the grafting of hydrocarbon alkyl as well as perfluorocarbon chains to the catalyst support surface. The grafting of hydrophobic groups has been proved by extensive solid-state NMR characterizations, supplemented by additional FTIR characterizations. We demonstrated that protective groups do not interact with the catalyst and do not deactivate it from metathesis reactions. The CH- modified catalyst proved to be active in olefin metathesis when the CF-modified catalyst was active in olefin and alkane metathesis. Varying the amount of protective chains surrounding the catalyst on different supports (conventional SiO2-500 and KCC-1-500) does not prevent the catalyst from being deactivated by functionalized olefin (5-hexenylacetate) and functionalized alkanes

(ethyl caprilate 5 and silane 24). As a result, the strategy proved to be inefficient in the metathesis of functionalized substrates. Finally, substrates for the metathesis of functionalized alkanes needs to be specifically designed.

3.4. Experimental section

General

All experiments were carried out by using standard Schlenk and glove box techniques under an inert argon atmosphere. The syntheses and the treatments of the surface species were carried out using high vacuum lines (< 10-5 mbar) and glove-box techniques. Pentane was distilled from a Na/K alloy under N2 and dichloromethane from CaH2. Both solvents were degassed through freeze-pump-thaw cycles. SiO2-500 was prepared from Aerosil silica from Degussa (specific area of

200 m2/g), which were partly dehydroxylated at 500 °C under high vacuum (< 10-5 mbar) for 24 hours to give a white solid having a specific surface area of 190 m2/g and containing around 1-

2 1.2 OH/nm (0.4 mmol OH/g). W(CH3)6 and supported pre-catalyst 1 was prepared according to literature procedures.26 IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF2 windows. The IR samples were prepared under argon within a glove box. Typically, 64 scans were accumulated for each spectrum (resolution 4 cm−1). Elemental analyses were performed at KAUST Core Lab ACL. NMR spectra were recorded on Bruker Avance

III 400 MHz NMR spectrometer (Bruker Biospin AG, Switzerland) equipped with a BBFO

CryoProbe. GC measurements were performed with an Agilent 7890A Series (FID detection). The method for GC analyses: Column HP-5; 30 m length × 0.32 mm ID × 0.25 μm film thickness; flow rate, 1 mL/min (N2); split ratio, 50/1; inlet temperature, 250 °C, detector temperature, 250 °C; temperature program, 40 °C (3 min), 40–250 °C (12 °C/min), 250 °C (3 minutes), 250–300 °C (10

°C/min), 300 °C (3 minutes). GC-MS measurements were performed with an Agilent 7890A Series coupled with an Agilent 5975C Series. A GC-MS, equipped with a capillary column coated with non-polar stationary phase HP-5MS, was used for molecular weight determination and identification, which allowed the separation of chemical compounds according to their boiling point differences. The method for GC-MS analyses: Column HP-5MS; 30 m length × 0.25 mm ID

× 0.25 μm film thickness; flow rate, 1 mL/min (N2); split ratio, 100/1; inlet temperature, 220 °C, detector temperature, 300 °C; temperature program, 150 °C (0 minutes), 150–300 °C (20 °C/min),

300 °C (30 minutes).

Catalytic reactions: In a typical procedure, a substrate and supported catalyst were mixed in the ampule tube in the glove box; the ampule tube was connected to a high-vacuum line and sealed in a vacuum. The ampule was then heated at 150 °C with stirring (50 rpm) or without stirring.

Quenching: the ampule was cooled down in liquid nitrogen, opened, 1 mL of DCM was added, the mixture was filtered through a syringe filter (1 µm), and the sample was analyzed by GC.

1 Figure 3.34 H NMR spectrum of triethoxyoctylsilane (CDCl3)

13 Figure 3.35: C NMR spectrum of triethoxyoctylsilane (CDCl3)

1 Figure 3.36: H NMR spectrum of triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane (CDCl3)

13 Figure 3.37: C NMR spectrum of triethoxy(1H,1H,2H,2H-perfluoro-octyl)silane (CDCl3) 6

5

4

3

Absorbance 2 2985 2925 2858 3018 1

0

4000 3500 3000 2500 2000 1500 1000 Wavenumbers (cm-1)

Figure 3.38: FTIR spectrum of W(CH3)5/CH-SiO2-500

1340 6

5

4

3

Absorbance 2 2985 2925 3018 2852 1

0

4000 3500 3000 2500 2000 1500 1000 Wavenumbers (cm-1)

Figure 3.39: FTIR spectrum of W(CH3)5/CF-SiO2-500

3.5. References 1. Bondi, A., van der Waals Volumes and Radii. J. Phys. Chem., 1964, 68, 441-451.

2. Williams, D. E.; Houpt, D. J., Fluorine nonbonded potential parameters derived from crystalline perfluorocarbons. Acta Crystallogr., 1986, B42, 286-295.

3. Tiddy, G. J. T. In Modern Trends of Colloid Science in Chemistry and Biology; Eicke, H. F., Ed.; Birkhäuser Verlag: Basel, 1985; 148-159.

4. Smart, B. E., In Organofluorine Chemistry: Principles and Commercial Applications. Characteristics of C- F systems. R. E. Banks, B. E. Smart, J. C. Tatlow, Eds.; Plenum Press: New York, 1994; 57-88.

5. Schlosser, M.; Michel, D., About the "Physiological Size" of Fluorine Substituents: Comparison of Sensorially Active Compounds with Fluorine and Methyl Substituted Analogues. Tetrahedron, 1996, 52, 99-108.

6. Barton, S. W.; Goudot, A.; Bouloussa, O.; Rondelez, F.; Lin, B.; Novak, F.; Acero, A.; Rice, S. A., Structural transitions in a monolayer of fluorinated amphiphile molecules. J. Chem. Phys., 1992, 96, 1343-1351.

7. Kubo, K.; Moroi, Y.; Nomura, K.; Abe, Y.; Takahahi, T., Study on Molecular Aggregates of N-(1,1- Dihydroperfluoroalkyl)-N,N,N-trimethylammonium Chloride. Langmuir, 2002, 18, 8770-8776.

8. Kondo, Y.; Miyazawa, H.; Sakai, H.; Yoshino, N., First Anionic Micelle with Unusually Long Lifetime: Self- Assembly of Fluorocarbon−Hydrocarbon Hybrid Surfactant. J. Am. Chem. Soc., 2002, 124, 6516-6517.

9. Calvet, D.; Collet, A.; Viguier, M.; Berret, J.-F.; Se´re´ro, Y., Perfluoroalkyl End-Capped Poly(ethylene oxide). Synthesis, Characterization, and Rheological Behavior in Aqueous Solution. Macromolecules, 2003, 36, 449-457.

10. Gladysz, J. A. Handbook of Fluorous Chemistry. Curran, D. P.; Horva´th, I. T. Copyright 8 2004 WILEY- VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 3-527-30617-X.

11. Tanford, C., The Hydrophobic Effect: Formation of Micelles and Biological Membranes, 2nd edn.; Wiley: New York, 1980.

12. Gao, J.; Qiao, S.; Whitesides, G. M., Increasing Binding Constants of Ligands to Carbonic Anhydrase by Using "Greasy Tails". J. Med. Chem., 1995, 38, 2292-2301.

13. Riess, J. G., Fluorous micro- and nanophases with a biomedical perspective. Tetrahedron, 2002, 58, 4113-4131.

14. Krafft, M. P., In Handbook of Fluorous Chemistry, Gladysz, J. A.; Curran, D. P.; Horva´th, I., Eds.; Wiley- VCH: Weinheim, 2003, Chapter 12.

15. Arase, H.; Taniguchi, K.; Kai, T.; Murakami, K.; Adachi, Y.; Ooyama, Y.; Kunugi, Y.; Ohshita, J., Hydrophobic modification of SiO2 surface by aminosilane derivatives. Composite Interfaces, 2019, 26, 1, 15-25.

16. Zhao, X.; Li, Y.; Li, B.; Hu, T.; Yang, Y.; Li, L.; Zhang, J., Environmentally benign and durable superhydrophobic coatings based on SiO2 nanoparticles and silanes. Journal of Colloid and Interface Science, 2019, 542, 8-14. 17. Park, J. H.; Kim, J. Y.; Cho, W. K.; Choi, I. S., Bioinspired, Cysteamine‐Catalyzed Co‐Silicification of (1 H, 1 H, 2 H, 2 H‐Perfluorooctyl)triethoxysilane and Tetraethyl Orthosilicate: Formation of Superhydrophobic Surfaces. Chem. Asian J., 2014, 9, 3, 764-768.

18. Nakano, M.; Osaka, I.; Takimiya, K., Control of Major Carriers in an Ambipolar Polymer Semiconductor by Self‐Assembled Monolayers. Adv. Mater., 2017, 29, 1602893.

19. Moorhouse, J. H.; Cann, K. J.; Cao, P. A.; Goode, M. G.; Harlan, C. J.; Mariott, W. R., Fluorinated catalyst supports and catalyst systems. WO/2016/028278.

20. Mantilla-Ramírez, A.; Ferrat-Torres, G.; Domínguez, J. M.; Aldana-Rivero, C.; Bernal, M., Influence of reaction parameters and comparison of fluorinated alumina and silica supports in the heterogeneous alkylation of isobutane with olefins. Applied Catalysis A: General, 1996, 143, 203-214.

21. Rhone, P.; Jacques, R.; Reppelin, M.; Seigneurin, R., Fluorinated silica catalyst and preparation of aromatic/aliphatic nitriles in the presence thereof. US4822903.

22. Tzschucke, C. C.; Markert, C.; Glatz, H.; Bannwarth, W., Fluorous Biphasic Catalysis without Perfluorinated Solvents: Application to Pd‐Mediated Suzuki and Sonogashira Couplings. Angew. Chem. Int. Ed., 2002, 41, 23, 4500-4503.

23. Tsai, C.-H.; Chen, H.-T.; Althaus, S. M.; Mao, K.; Kobayashi, T.; Pruski, M.; Lin, V. S.-Y., Rational Catalyst Design: A Multifunctional Mesoporous Silica Catalyst for Shifting the Reaction Equilibrium by Removal of Byproduct. ACS Catal., 2011, 1, 729-732.

24. Ghaffarzadeh, M.; Ahmadi, M., Catalytic application of fluorous silica gel in Fries rearrangement. Journal of Fluorine Chemistry, 2014, 160, 77-81.

25. Oubaha M.; Dubois, M.; Murphy, B.; Etienne, P., Structural characterisation of a sol-gel copolymer synthesised from aliphatic and aromatic alkoxysilanes using 29Si-NMR spectroscopy. J. Sol-Gel Sci. Techn., 2006, 38, 111-119.

26. Samantaray, M. K.; Callens, E.; Abou-Hamad, E.; Rossini, A. J.; Widdifield, C. M.; Dey, R.; Emsley, L.;

Basset, J.-M., WMe6 Tamed by Silica: ≡Si–O–WMe5 as an Efficient, Well-Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W–Methyl/Methylidyne Species. J. Am. Chem. Soc., 2014, 136, 3, 1054-1061.

27. Riache, N.; Callens, E.; Espinas, J.; Dery, A.; Samantaray, M. K.; Deya, R.; Basset, J.-M., Striking difference between alkane and olefin metathesis using the well-defined precursor [≡Si–O–WMe5]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride. Catal. Sci. Technol., 2015, 5, 280-285.

28. Bouhrara, M.; Ranga, C.; Fihri, A.; Shaikh, R. R.; Sarawade, P.; Emwas, A.-H.; Hedhili, M. N.; Polshettiwar, V., Nitridated Fibrous Silica (KCC-1) as a Sustainable Solid Base Nanocatalyst. ACS Sustainable Chem. Eng., 2013, 1, 1192-1199.

29. Afzal, S.; Quan, X.; Chen, S.; Wang, J.; Muhammad, D., Synthesis of manganese incorporated hierarchical mesoporous silica nanosphere with fibrous morphology by facile one-pot approach for efficient catalytic ozonation. Journal of Hazardous Materials, 2016, 318, 308-318. 30. Sadeghzadeh, S. M., A multicomponent reaction on a ‘free’ KCC-1 catalyst at room temperature under solvent free conditions by visible light. RSC Adv., 2016, 6, 54236-54240.

31. Ouyang, M.; Wang, Y.; Zhang, J.; Zhao, Y.; Wang, S.; Ma, X., Three dimensional Ag/KCC-1 catalyst with a hierarchical fibrous framework for the hydrogenation of dimethyl oxalate. RSC Adv., 2016, 6, 12788- 12791.

32. Qureshi, Z. S.; Sarawade, P. B.; Albert, M.; D'Elia, V.; Hedhili, M. N.; Köhler, K.; Basset, J.-M., Palladium Nanoparticles Supported on Fibrous‐Structured Silica Nanospheres (KCC‐1): An Efficient and Selective Catalyst for the Transfer Hydrogenation of Alkenes. ChemCatChem, 2015, 7, 635-642.

Chapter 4. Metathesis of functionalized alkane: understanding the unsolved story

4.1. Introduction

Metathesis of functionalized alkanes represents a tremendously difficult challenge in chemistry and is an unsolved problem in the metathesis field. As shown in Chapter 2, substrates with free electron pairs (e.g., esters, silyl ethers, alcohols, etc.) or heteroatoms effortlessly coordinate with and deactivate the alkane metathesis catalyst; non-coordinating substrates (alkylated ferrocenes and silanes), despite their inability to coordinate to early transition metals, remain inert and do not undergo metathesis reaction. The strategy to protect the catalyst active site by introducing hydrophobic alkyl chains to the support of the catalyst (Chapter 3) does not prevent the catalyst from being active in olefin and alkane metathesis. At the same time, this strategy is not efficient in the metathesis of functionalized olefins and alkanes, which still deactivate the catalyst and do not undergo metathesis. Considering our failures to protect the catalyst from functionalized substrates (by both modifying the substrate and catalyst support with sterical hindrances), we decided to approach the problem from a different angle and rationally design a suitable functionalized alkane substrate for the metathesis reaction.

Since the discovery of the alkane metathesis reaction by the well-defined silica-supported [Ta]-H catalyst,1 many groups, including us, have been continuously working on the development of well-defined catalysts for a “functionalized” alkane metathesis reaction or alkyl chains bearing any functionality along with improved reactivity in alkane metathesis reaction.2-8 While significant progress has been achieved in improving the catalyst activity, e.g., by changing the catalyst support and by employing a tandem system (where two catalysts act back-to-back for a cascade reaction), metathesis of a functionalized alkane has remained elusive in the scientific community.7,9-12 To metathesize a functionalized alkane, the reactant should undergo dehydrogenation to a functionalized olefin, then functionalized olefin metathesis, and finally reduction of the newly formed functionalized olefins to newly functionalized alkanes. The main difficulty in the functionalized alkane metathesis reaction is the functional moiety which is expected to poison the catalyst by coordinating with the metal and hence deactivating the system for further reaction. Therefore, it is a tremendous challenge to metathesize an alkane having a functional group.

In this chapter, the first example of functionalized alkane metathesis using silica-supported

[(≡Si-O-)W(Me)5] 1 as a catalyst precursor and 9-hexyl-9H-carbazole 5 as a reactant is presented.

4.2. Results and Discussion 4.2.1 Interaction of catalyst with the pyrrole-based family of substrates From previous publications, it was known that ligands having a lone pair of electrons coordinate with the electron-deficient early transition metals, making them electron-rich and blocking the coordination site for C-H bond activation.13 As metal is more electron-rich and coordinatively more saturated, its affinity towards alkane decreases.14 Considering that alkane metathesis occurs first by sigma-bond metathesis with a d0 system, this becomes increasingly important.15

To avoid this problem while carrying out the functionalized alkane metathesis reaction, our first attempt was to focus on the protection of the functional group. Instead of the sterical protection strategy that has been shown in this dissertation (Chapter 2), to implement this idea we chose

N-Alkyl pyrroles, with the assumption that the lone pair of electrons on the nitrogen atom involved in the formation of an aromatic system is poorly available for coordination. To our disappointment, after many attempts, we only observed a starting material along with its decomposition products. The literature reports that pyrroles interact with Lewis acids to produce pyrrole oligomers through the activation of its α position.16 To avoid this and to carry out the reaction we thought to protect the most reactive α position of the pyrrole ring by methyl groups in order to avoid unwanted reactions of the pyrrole ring while carrying out the metathesis. We synthesized 1-hexyl-2,5-dimethyl-1H-pyrrole 2 and 1-propyl-2,5-dimethyl-1H-pyrrole17,18 3

(Schemes 4.1, 4.3) and carried out the metathesis reaction using [(≡Si−O−)W(CH3)5] 1 as a catalyst precursor (Figure 4.1).

Figure 4.1: Well-defined silica-supported [(≡Si−O−)W(CH3)5] 1

Scheme 4.1: Synthesis of N-alkyl pyrroles

19 We already observed that 1 leads to [(≡Si−O−)W(H)3(=CH2)] during catalyst activation. While testing this family of molecules and expecting the metathesis products of the reactants 2 and 3, we observed unreacted starting material along with traces of decomposition and isomerization of both the substrates without any metathesis products. At the same time, we did a control poisoning experiment by adding a reactant 2 to the catalyst 1 at RT in the glove box, stirred the suspension for 1 hour, filtered the exposed catalyst, washed it 3 times with DCM and analyzed it by solid-state NMR spectroscopy (Figure 4.2).

1 13 Figure 4.2: Exposed [(≡Si−O−)W(CH3)5] to pyrrole 2. A – H MAS solid-state NMR spectrum; B – C CP MAS solid-state NMR spectrum; C – 1H-13C MAS correlation solid-state NMR spectrum

Surprisingly, the catalyst did not change color in spite of the same control experiments with ester

5 and alcohol 6 (Chapter 2, Part 2.1.2). Moreover, in the solid-state NMR spectra, the signals of

W-CH3 group did not disappear and were observed in proton (2 ppm), carbon (81 ppm) and proton-carbon correlation spectra indicating the absence of poisoning at room temperature. The alkane metathesis consists of mainly three subsequent paths – dehydrogenation, olefin metathesis, and hydrogenation. As we did not observe any expected metathesis products from the above two reactants, we decided to investigate if the olefin metathesis step can be performed in our catalytic system. We synthesized 1-allyl-2,5-dimethyl-1H-pyrrole 4, which is the olefinic analog of the 1-propyl-2,5-dimethyl-1H-pyrrole 3 for the olefin metathesis reaction using catalyst 1 (Figure 4.3).

100 90

80

70

60

50

40 Conversion (%) Conversion 30 20 10

0 0 20 40 60 80 100 120 Time (h)

Figure 4.3: Metathesis of 1-Allyl-2,5-dimethyl-1H-pyrrole, conversion versus time plot. ( ) Reaction at

RT, ( ) Reaction at 150 °C

The product was analyzed by GC, GC-MS and NMR spectroscopy confirming the formation of the expected product 1,4-bis-(2,5-dimethyl-1H-pyrrole-1yl)but-2-ene with 85 % conversion and a

TON of 850 (Figure 4.2).20-22 These results clearly indicate that our catalyst is capable of carrying out the olefin metathesis reaction for this particular substrate while in the case of 1-hexyl-2,5- dimethyl-1H-pyrrole 2 or 1-propyl-2,5-dimethyl-1H-pyrrole 3 no metathesis was observed.

During the catalytic reaction, we understood that isomerization of the substrates occurs because of walking of alkyl groups on the ring.23 To avoid this we thought to synthesize 9-hexyl-9H- carbazole (a rigid molecule) to carry out the metathesis reaction.

4.2.2 Metathesis of N-hexyl-carbazole 9-hexyl-9H-carbazole 5 was obtained by the reaction of carbazole and hexyl bromide in the presence of KOH by following a procedure from the literature (Scheme 4.2).24

Scheme 4.2: Synthesis of 9-hexyl-9H-carbazole 5

In a typical reaction, 9-hexyl-9H-carbazole 5 and [(≡Si−O−)W(CH3)5] 1 in 50:1 molar ratio based on loading of W were mixed. The mixture was sealed in an ampoule tube under high vacuum, and the reaction continued at 150 °C. The first sample was quenched with dichloromethane and injected in GC after one day of reaction. To our surprise, neither any considerable amount of product nor decomposition of the starting material (9-hexyl-9H-carbazole) were observed. We continued the reaction for another four days. After five days, the reaction mixture was taken, quenched with dichloromethane, filtered, and analyzed by GC. We could observe a range of alkylated carbazoles starting from cC2 to cC10 with a conversion of starting material of 2.5% and the formation of carbazole itself (Figures 4.4, 4.5).

Figur e 4.4:e

Product distribution: functionalized alkane metathesis products ( Figure4.5: products ( ) and

Amount (µmol)

9

8

7

6

5

4

3

2

1 0 Amount (µmol)

9

8

7

6

5

4

3

2

1

0 Functionalized alkane metathesis products timeover ( ) ( days,5 ( ) 10 days, ) ( 30 days cC2 Carbazole

cC3 cC2 cC3 cC4 c arbazole ( after ) days30 reactionof cC4 cC5 cC5 cC7

cC7

cC8 cC8

Amount (µmol)

1.0

0.8

0.6

0.4

0.2 cC9 cC9 0.0

Alkane metathasis products metathasis Alkane

C3

C4 cC10 cC10

C5

cC11 C6 cC11

C7

cC12 C8

cC12 C9

cC13 C10 cC13

),

a

lkane metathesis

While carrying out the reaction with 1 we anticipated a smoother reaction as the lone pair is delocalized in the carbazole conjugated system and there is no labile group on the ring. To our surprise, we only obtained 5.0 % conversion even after 30 days. While analyzing the reaction mixture, we observed linear alkanes (alkane metathesis products), N-alkyl carbazoles and the dimer of 9-hexyl-9H-carbazole (functionalized alkane metathesis products) (Figures 4.4, 4.6, 4.18-

4.20), along with a considerable amount of carbazole.

4.2.3 Mechanism of the reaction The formation of the dimer [1,10-di(9H-Carbazole-9yl-)decane] is understandable as it is the self- metathesis product of the 9-(hex-5en-1-yl)-9H carbazole (Figures 4.17, 4.18). Initially, 9-(hex-5en-

1-yl)-9H carbazole (dehydrogenation product of 9-hexyl-9H-carbazole) was formed by the reaction of [(≡Si−O−)W(CH3)5] 1 and 9-hexyl-9H-carbazole 5 (Figures 4.15, 4.16). Other N-alkyl carbazoles and alkanes are formed due to chain walking (our active catalyst contains W-H) followed by cross-metathesis with linear olefins, and at the end, reduction of newly formed olefins to new alkanes. Looking at the product distribution, we observed that along with all the metathesis products of the functionalized alkanes a considerable amount of n-alkane metathesis products and carbazole were formed. In n-alkane metathesis products the concentration of the

C6 (hexane) is higher compared to its lower and higher homologs. These products can only form if the catalyst attacks the position 1 of the 9-hexyl-9H-carbazole (Scheme 4.2 and Figure 4.6) forming W-C bond followed by reduction of the N-C bond to generate carbazole and the W-alkyl chain (Figure 4.6).

Figure 4.6: Proposed mechanism for functionalized alkane metathesis reaction

Furthermore, the W−alkyl chain underwent α-H abstraction and β-H elimination generating W- carbene and olefin. Additionally, W-carbene and olefin underwent an olefin metathesis reaction generating a range of n-alkane products (C3-C10) after reduction of the newly formed olefins

(Figure 4.6). The various N-alkyl carbazoles are formed by activation of position 6 (Scheme 4.2) of the alkyl chain of the 9-hexyl-9H-carbazole. Even though we metathesized a functionalized alkane, we could only achieve 5.0 % conversion with a TON of 2. We believe the low conversion was due to the poisoning of the catalyst by the formation of carbazole (Figure 4.6) during the reaction (since the N-H of carbazole is no longer protected, it can attack the catalyst and deactivate it for further reaction).

4.3. Conclusions For the first time, we carried out a functionalized alkane metathesis reaction using a silica- supported catalyst [(≡Si−O−)W(CH3)5] 1 with a conversion of 5.0 %. N-alkane metathesis was also observed due to the reaction course. To avoid catalyst decomposition, we chose 9-hexyl-9H- carbazole, whereby the lone pair is delocalized in the conjugated system.

Our study shows that the catalyst decomposes because of the reaction of the N-H of the carbazole with the catalyst. We believe that our study on functionalized alkane metathesis reaction opens up a perspective for synthetic organic chemistry for the syntheses of new building blocks which are more difficult to synthesize in a classical way. At the same time, the general solution for the metathesis of other functionalized alkanes remain elusive and needs to be addressed.

4.4. Experimental Section 4.4.1 General remarks All experiments were carried out using standard Schlenk and glovebox techniques under an inert argon atmosphere. The syntheses and the treatments of the surface species were carried out using high vacuum lines (< 10-5 mbar) and glove-box techniques. Pentane was distilled from a

Na/K alloy under N2 and dichloromethane from CaH2. Both solvents were degassed through freeze-pump-thaw cycles. SiO2-700 prepared from Aerosil silica from Degussa (specific area of 200 m2/g), which were partly dehydroxylated at 700°C under high vacuum (< 10-5 mbar) for 24 h to give a white solid having a specific surface area of 190 m2/g and containing around 0.5-0.7

2 OH/nm . W(CH3)6 (SI Figures S1-S3) and supported pre-catalyst 1 were prepared according to literature procedures (SI Figures S4).23-25 2,5-hexanedione, hexylbromide, hexylamine, propylamine, allylamine, carbazole, C2-C13-alkylbromides, 1,10-dibromodecane were purchased from Aldrich.

NMR spectra were recorded on Bruker Avance III 500 MHz NMR spectrometer equipped with a

BBFO CryoProbe. IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF2 windows (SI Figures S4). The IR samples were prepared under argon within a glove box. Typically, 64 scans were accumulated for each spectrum (resolution 4 cm−1).

GC measurements were performed with an Agilent 7890A Series (FID detection). Method for GC analyses: Column HP-5; 30 m length x 0.32 mm ID x 0.25 μm film thickness; Flow rate: 1 mL/min

(N2); split ratio: 50/1; Inlet temperature: 250 °C, Detector temperature: 250 °C; Temperature program: 40 °C (3 min), 40-250 °C (12 °C/min), 250 °C (3 min), 250-300 °C (10 °C/min), 300 °C (3 min); 9-hexyl-9H-carbazole retention time: tR = 21.67 min. GC-MS measurements were performed with an Agilent 7890A Series coupled with Agilent 5975C Series. GC/MS equipped with a capillary column coated with non-polar stationary phase HP-5MS was used for molecular weight determination and identification that allowed the separation of chemical compounds according to their boiling point differences. Method for GC-MS analyses: Column HP-5MS; 30 m length x 0.25 mm ID x 0.25 μm film thickness; Flow rate: 1 mL/min (N2); split ratio: 100/1; Inlet temperature: 220 °C, Detector temperature: 300 °C; Temperature program: 150°C (0 min), 150-

300 °C (20 °C/min), 300 °C (30 min);

HPLC-MS analysis was performed at KAUST Core Lab ACL. The separation of the 1,10-di(9H-

Carbazole-9yl-)decane from the metathesis reaction mixture was performed using an Accela

HPLC System and a hypersil gold column 2.1 x 50 mm (Thermo Fisher Scientific). 1 mg of the sample was dissolved in 1 mL (methanol: chloroform), the liquid compound was then diluted x

1000 in 1 mL of methanol. The separation was achieved using a gradient composed of water/methanol. The mobile phase solvents were composed of A: 100% water+0.1% formic acid and B: 100% methanol+0.1% formic acid. The gradient elution program is summarized in Table 1.

The injection volume was 10 μL. The flow rate was 400 μL/min. The data processing was performed using Xclaibur Software (Thermo Fisher Scientific). The mass analysis was performed using a Thermo LTQ Velos Orbitrap mass spectrometer (Thermo Scientific, Pittsburgh, PA, USA) equipped with a heated ESI ion source. The mass scan range was set to 100–1000 m/z, with a resolving power of 100 000. The m/z calibration of the LTQ-Orbitrap analyzer was performed in the positive ESI mode using a solution containing caffeine, MRFA (met-arg-phe-ala) peptide and

Ultramark 1621 according to the manufacturer’s guidelines. The ESI was performed with a heated ion source equipped with a metal needle and operated at 4 kV. The source vaporizer temperature was adjusted to 350 °C, the capillary temperature was set at 250 °C, and the sheath and auxiliary gases were optimized and set to 40 and 20 arbitrary units.

HPLC Gradient 120

100

80

60

%VOLUME 40

20

0 0 5 10 15 20 25 30 TIME (MIN)

A% B%

Figure 4.7: Gradient elution program (Time vs Volume plot)

Table 4.1: Gradient elution program (A: 100% Water+0.1% Formic Acid and B: 100% Methanol+0.1% Formic Acid)

Gradient elution program Time (min) A% B% 0 70 30 1 70 30 15 10 90 22 10 90 24 1 99 28 1 99 28.1 70 30 30 70 30

4.4.2 Experimental procedures and spectroscopic data 4.4.2.1 Synthesis of N-Hexyl-Pyrrole N-Hexyl-Pyrrole was synthesized according to literature procedure.17,18

4.4.2.2 Synthesis of N-Hexyl-2,5-dimethyl-pyrrole 2, N-Propyl-2,5-dimethyl-pyrrole 3 and N- Allyl-2,5-dimethyl-pyrrole 4

Scheme 4.1: Synthesis of N-alkyl pyrroles

Compounds 2, 3, 4 were synthesized according to the Paal-Knorr method of pyrroles synthesis.

General Procedure for 2, 3, 4 (Figures 4.7-4.12):

2,5-hexanedione (10 mmol) was dissolved in MeOH (50 mL), and the respective primary amine

(10 mmol) was added at RT. The reaction is slightly exothermic, and cooling by ice bath is recommended when higher quantities are used for the reaction. RM was stirred for 10 minutes at RT, and evaporated in vacuum. Hexane was added to the RM, and water phase-separated from an organic phase. The organic phase was dried over MgSO4, filtered and evaporated to dryness.

The product was purified by flash column chromatography (Hexane : EtOAc = 4 : 1), distilled over sodium in vacuum and degassed prior to use. The reference N-Alkyl-2,5-dimethyl-Pyrroles (C2-C9) were synthesized with the same procedure and used as standards in GC-MS analysis. Yields are in the range of 60-70%.

1 N-Hexyl-2,5-dimethyl-pyrrole 2. H NMR (C6D6), δ, ppm (J, Hz): 6.04 (2H, s, CH Ar), 3.35–3.32 (2H, t, J = 7.2, N-CH2), 2.09 (6H, s, 2 x Ar CH3), 1.36–1.30 (2H, m, CH2), 1.18–1.14 (2H, m, CH2), 1.07– 13 1.04 (4H, m, 2 x CH2), 0.85–0.82 (3H, t, J = 7.2, CH3). C NMR (C6D6): 126.7, 106.2, 43.5, 31.8,

31.4, 26.8, 22.9, 14.2, 12.7.

1 Figure 4.8: H NMR spectrum of N-Hexyl-2,5-dimethyl-pyrrole 2 in C6D6

13 Figure 4.9: C NMR spectrum of N-Hexyl-2,5-dimethyl-pyrrole 2 in C6D6 1 N-Propyl-2,5-dimethyl-pyrrole 3. H NMR (C6D6), δ, ppm (J, Hz): 6.02 (2H, s, CH Ar), 3.27–3.24 (2H, t, J = 7.5, N-CH2), 2.05 (6H, s, 2 x Ar CH3), 1.34–1.27 (2H, m, J = 7.4, CH2), 0.63–0.60 (3H, t, J = 7.3,

13 CH3). C NMR (C6D6): 126.8, 106.1, 44.9, 24.5, 12.7, 11.2.

1 Figure 4.10: H NMR spectrum of N-Propyl-2,5-dimethyl-pyrrole 3 in C6D6

13 Figure 4.11: C NMR spectrum of N-Propyl-2,5-dimethyl-pyrrole 3 in C6D6

Scheme 4.3: No functionalized alkane metathesis product was observed using substrates 2 and 3

1 N-Allyl-2,5-dimethyl-pyrrole 4. H NMR (C6D6), δ, ppm (J, Hz): 6.03 (2H, s, CH Ar), 5.50–5.43 (1H, m, CH Allyl), 4.85–4.82 (1H, dd, 1J = 10.3, 2J = 1.8 Hz), 4.57–4.53 (1H, dd, 1J = 10.3, 2J = 1.8 Hz),

13 3.82–3.80 (2H, m, CH2), 2.01 (6H, s, 2 x CH3). C NMR (C6D6): 134.8, 127.1, 114.9, 106.1, 45.2,

12.3.

1 Figure 4.12: H NMR spectrum of N-Allyl-2,5-dimethyl-pyrrole 4 in C6D6

13 Figure 4.13: C NMR spectrum of N-Allyl-2,5-dimethyl-pyrrole 4 in C6D6 4.4.2.3 Separation of 1,4-bis(2,5-dimethyl-1-H-pyrrole-1yl)but-2-ene 1,4-bis(2,5-dimethyl 1-H-pyrrole-1yl)but-2-ene was separated from N-Allyl-2,5-dimethyl-pyrrole

4 metathesis reaction mixture as a white solid and characterized by NMR (Figures 4.13 and 4.14).

1 H NMR (C6D6), δ, ppm (J, Hz): 6.04 (4H, s, CH Ar), 4.70–4.69 (2H, t, J = 1.2 Hz, 2 x CH), 3.59 (4H,

13 d, J = 1 Hz, 2 x CH2), 1.95 (12H, s, CH3). C NMR (C6D6): 127.0, 126.9, 106.1, 43.8, 12.3.

1 Figure 4.14: H NMR spectrum of 1,4-bis(2,5-dimethyl 1-H-pyrrole-1yl)but-2-ene in C6D6

13 Figure 4.15: C NMR spectrum of 1,4-bis(2,5-dimethyl 1-H-pyrrole-1yl)but-2-ene in C6D6

4.4.2.4 Synthesis of 9-hexyl-9H-carbazole 5

Scheme 4.2: Synthesis of 9-hexyl-9H-carbazole 5

24 9-hexyl-9H-carbazole 5 was synthesized according to the literature method with modification.

Procedure: Carbazole (37 mmol) was dissolved in DMF (85 mL) under Argon, potassium hydroxide

(232 mmol) was added to a solution, and the mixture was stirred for 40 minutes at RT.

Hexylbromide (37 mmol) was added dropwise, and the RM was stirred for additional 9 hours at RT. After that, RM was poured into water (100 mL). To extract the product from the DMF/Water mixture, 100 mL of n-hexane and 100 mL of EtOAc were added. The resulting 4-component

(DMF/Water/Hexane/EtOAc) mixture was intensively shacked in the separation funnel. The upper organic phase was separated and washed with water (2 x 50 mL). The lower DMF/Water phase was additionally extracted by a mixture of Hexane (100 mL) and EtOAc (100 ml) and the organic phase was washed with water (2 x 50 mL). The combined organic phase (pure from DMF) was dried over Na2SO4 and evaporated in vacuum. The product was purified by column chromatography (Petroleum Ether : DCM = 3 : 1), recrystallized from hexane (-30 °C) and dried on HVL. Yield: 86%, white needle-like crystals. NMR spectra are in accordance with the literature data (Figures 4.15 and 4.16).

1 H NMR (C6D6), δ, ppm (J, Hz): 8.08 (2H, d, J = 7.8 Hz, H Ar), 7.44–7.40 (2H, m, H Ar), 7.25–7.22

(2H, m, H Ar), 7.20–7.18 (2H, m, H Ar), 3.79 (2H, t, J = 7.2 Hz, CH2), 1.51–1.48 (2H, m, CH2), 1.08–

13 1.02 (6H, m, 3 x CH2), 0.79–0.76 (3H, t, J = 7 Hz, CH3). C NMR (C6D6): 140.9, 125.9, 123.5, 120.8,

119.2, 109.0, 42.9, 31.8, 29.0, 27.1, 22.8, 14.2.

1 Figure 4.16: H NMR spectrum of 9-hexyl-9H-carbazole 5 in C6D6

13 Figure 4.17: C NMR spectrum of 9-hexyl-9H-carbazole 5 in C6D6 4.4.2.5 Synthesis of 9-HEXYL-9H-CARBAZOLE metathesis products

The metathesis products (N-Alkyl-Carbazoles, C2-C13) were additionally prepared as reference compounds according to the procedure from section 4.4.2.4 and used for GC-MS analysis without further purification. The retention time and fragmentation of the reference compounds precisely match the products from 9-hexyl-9H-carbazole metathesis reaction proving their linear structure.

Retention times for N-Alkylated Carbazoles: C2 4.73 min, C3 5.11 min, C4 5.55 min, C5 5.98 min, C6

(starting material) 6.51 min, C7 6.87 min, C8 7.27 min, C9 7.67 min, C10 8.13 min, C11 8.63 min, C12

9.20 min, C13 9.86 min.

4.4.2.6 Synthesis and analysis of 1,10-di-(9H-Carbazole-9yl-)-decane (C34H37N2) 1,10-di-(9H-Carbazole-9yl-)-decane was synthesized as a reference compound according to the procedure from section 4.4.2.4 with 1,10-dibromodecane as an alkylation agent and used for

HPLC-MS analysis of the reaction mixture (Figures 4.17, 4.18 and 4.19).

1 H NMR (C6D6), δ, ppm (J, Hz): 8.07 (4H, d, J = 7.7, H Ar), 7.43–7.40 (4H, m, H Ar), 7.24–7.19 (8H,

13 m, H Ar), 3.81 (4H, t, J = 7, 2 x N-CH2), 1.54–1.48 (4H, m, 2 x CH2), 1.05–0.95 (12H, m, 6 x CH2). C

NMR (C6D6): 140.9, 125.9, 123.5, 120.9, 119.3, 109.0, 42.9, 29.6, 29.1, 27.4.

Theoretically predicted isotopic distribution of C34H37N2: 473.29513, 474.29848, 475.30184 (δ =

0 ppm). Experimentally found isotopic distribution of the reference compound: 473.29497,

474.29824, 475.30157 (δ = -0.335 ppm). Experimentally found isotopic distribution of the dimer found in the reaction mixture: 473.29506, 474.29837, 475.30188 (δ = -0.147 ppm).

1 Figure 4.18: H NMR spectrum of 1,10-di(9H-Carbazole-9yl-)decane in C6D6

13 Figure 4.19: C NMR spectrum of 1,10-di(9H-Carbazole-9yl-)decane in C6D6

Figure 4.20: Comparison of the reference 1,10-di-(9H-Carbazole-9yl-)-decane (C34H37N2) with the dimer found in

9-hexyl-9H-carbazole metathesis reaction mixture

4.4.3 Catalytic reactions

9-Hexyl-9H-carbazole 5 (200 mg, 0.8 mmol) and [(≡Si−O−)W(CH3)5] 1 (100 mg, 0.016 mmol W) were mixed in the ampule tube in the glove box; the ampule tube was connected to a high-vacuum line and sealed in a vacuum. The ampule was then heated at 150 °C with stirring (50 rpm). Quenching: the ampule was cooled down in liquid nitrogen, opened, 1 mL of DCM added, the mixture was filtered through a syringe filter (1 µm), and the sample was analyzed by GC. 1-hexyl-2,5-dimethyl-1H-pyrrole 2, 1-propyl-

2,5-dimethyl-1H-pyrrole 3 and 1-allyl-2,5-dimethyl-1H-pyrrole 4 were analyzed with the same procedure.

4.5. References 1. Vidal, V.; Theolier, A.; Thivolle-Cazat, J.; Basset, J.-M., Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides. Science, 1997, 276, 99-102.

2. Samantaray, M. K.; Pump, E.; Bendjeriou-Sedjerari, A.; D’Elia, V.; Pelletier, J. D. A.; Guidotti, M.; Psaro, R.; Basset, J.-M., Surface organometallic chemistry in heterogeneous catalysis. Chem. Soc. Rev., 2018, 47, 8403-8437.

3. Samantaray, M. K.; Callens, E.; Abou-Hamad, E.; Rossini, A. J.; Widdifield, C. M.; Dey, R.; Emsley, L.; Basset, J.- M., WMe6 Tamed by Silica: [≡Si-O-WMe5 ] as an Efficient, Well-Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W–Methyl/Methylidyne Species. J. Am. Chem. Soc., 2014, 136, 1054-1061.

4. Samantaray, M. K.; Dey, R.; Abou-Hamad, E.; Hamieh, A.; Basset, J.-M., Effect of Support on Metathesis of n- Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica–Alumina. Chem. Eur. J., 2015, 21, 6100-6106.

5. Samantaray, M. K.; Dey, R.; Kavitake, S.; Abou-Hamad, E.; Bendjeriou-Sedjerari, A.; Hamieh, A.; Basset, J.-M., Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane. J. Am. Chem. Soc., 2016, 138, 8595-8602.

6. Samantaray, M. K.; Dey, R.; Kavitake, S.; Basset, J.-M., New Concept of C-H and C-C Bond Activation via Surface Organometallic Chemistry. In C-H Bond Activation and Catalytic Functionalization II; Springer: Berlin, Germany, 2016; 155-187.

7. Samantaray, M. K.; Kavitake, S.; Morlanes, N.; Abou-Hamad, E.; Hamieh, A.; Dey, R.; Basset, J.-M., Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane. J. Am. Chem. Soc., 2017, 139, 3522-3527.

8. Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M., Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis. Science, 2006, 312, 257-261.

9. Huang, Z.; Rolfe, E.; Carson, E. C.; Brookhart, M.; Goldman, A. S.; El-Khalafy, S. H.; MacArthur, A. H. R., Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis. Adv. Synth. Catal., 2010, 352, 125-135.

10. Taoufik, M.; Schwab, E.; Schultz, M.; Vanoppen, D.; Walter, M.; Thivolle-Cazat, J.; Basset, J.-M., Cross- metathesis between ethane and toluene catalyzed by [(≡SiO)2TaH]: The first example of a cross-metathesis reaction between an alkane and an aromatic. Chem. Commun., 2004, 12, 1434-1435.

11. Dobereiner, G. E.; Yuan, J.; Schrock, R. R.; Goldman, A. S.; Hackenberg, J. D., Catalytic synthesis of n-alkyl arenes through alkyl group cross-metathesis. J. Am. Chem. Soc., 2013, 135, 12572-12575.

12. Haibach, M. C.; Kundu, S.; Brookhart, M.; Goldman, A. S. Alkane metathesis by tandem alkane- dehydrogenation–olefin-metathesis catalysis and related chemistry. Acc. Chem. Res., 2012, 45, 947-958.

13. Shortland, A. J.; Wilkinson, G. Preparation and properties of hexamethyltungsten. J. Chem. Soc. Dalton Trans., 1973, 872-876.

14. Dudev, M.; Wang, J.; Dudev, T.; Lim, C. Factors Governing the Metal Coordination Number in Metal Complexes from Cambridge Structural Database Analyses. J. Phys. Chem. B, 2006, 110, 1889-1895.

15. Waterman, R. σ-Bond Metathesis: A 30-Year Retrospective. Organometallics, 2013, 32, 7249-7263.

16. Can, M.; Ozaslan, H.; Isildak, O.; Pekmez, N. O.; Yildiz, A., Investigation of catalytic effects of the proton and Lewis acids on oligomerization and chemical polymerization of pyrrole. Polymer, 2004, 45, 7011-7016. 17. Lion, C.; Baudry, R.; Hedayatullah, M.; Da Conceicao, L.; Hocquaux, M.; Genard, S.; Maignan, J., Reaction of pyrroles with naphthoquinones. Synthesis of new pyrrolylnaphthoquinone dyes. Heterocyclic Chem., 2000, 37, 1635-1640.

18. Lanni, E. L.; Locke, J. R.; Gleave, C. M.; McNeil, A. J., Ligand-Based Steric Effects in Ni-Catalyzed Chain-Growth Polymerizations Using Bis(dialkylphosphino)ethanes. Macromolecules, 2011, 44, 5136-5145.

19. Maity, N.; Barman, S.; Callens, E.; Samantaray, M. K.; Abou-Hamad, E.; Minenkov, Y.; D’Elia, V.; Hoffman, A. S.; Widdifield, C. M.; Cavallo, L.; Gates, B. C.; Basset, J.-M., Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides. Chem. Sci., 2016, 7, 1558-1568.

20. Hoveyda, A. H.; Zhugralin, A. R. The remarkable metal-catalysed olefin metathesis reaction. Nature, 2007, 450, 243-251.

21. Ogba, O. M.; Warner, N. C.; O’Leary, D. J.; Grubbs, R. H. Recent advances in ruthenium-based olefin metathesis. Chem. Soc. Rev., 2018, 47, 4510-4544.

22. Connon, S. J.; Blechert, S. Recent Developments in Olefin Cross-Metathesis. Angew. Chem. Int. Ed., 2003, 42, 1900-1923.

23. Jones, R. A. Pyrroles and their Benzo Derivatives: (ii) Reactivity. In Comprehensive Heterocyclic Chemistry, 1st ed.; Katritsky, A.R., Rees, C.W., Eds.; Pergamon Press: Oxford, UK, 1984; 4, 201-312.

24. He, Y.; Yin, J.; Wang, G. New selective “on-off” fluorescence chemosensor based on carbazole Schiff base for Fe3+ detection. Chem. Heterocycl. Comp., 2018, 54, 146-152.

25. Galyer, L.; Mertis, K.; Wilkinson, G. New synthesis of hexamethyltungsten(VI); hexamethylrhenium(VI) and dioxotrimethylrhenium(VII). J. Organomet. Chem., 1975, 85, 37-38.

26. Pfennig, V.; Seppelt, K. Crystal and Molecular Structures of Hexamethyltungsten and Hexamethylrhenium. Science, 1996, 271, 626-628.

− 27. Kleinhenz, S.; Pfennig, V.; Seppelt, K. Preparation and Structures of [W(CH3)6], [Re(CH3)6], [Nb(CH3)6] , and − [Ta(CH3)6] . Chem. Eur. J., 1998, 4, 1687-1691.

Chapter 5. Exploiting supported bimetallic dehydrogenation-metathesis catalysts based on early and late transition metal complexes

5.1. Introduction

As shown in the previous chapter, metathesis of 9H-9-hexyl-carbazole over silica-supported tungsten pentamethyl is the first example of metathesis of an alkane bearing a functionality. That discovery opened a new field of the metathesis of functionalized alkanes; however, the challenge to construct a universal catalyst for the metathesis of functionalized alkanes or particular catalysts for particular classes of functionalized substrates remains an unsolved problem in chemistry.

Since the discovery of a silica-supported tantalum hydride catalyst for the alkane metathesis reaction,1 our group has been researching the development of well-defined single-site supported catalytic systems for the alkane metathesis reaction,2−4 while Brookhart5,6, Burnett, and Hughes7 have been investigating the tandem systems. Several reports were published of group 4 to group 6 oxide-supported catalysts, for various organic transformation reactions involving C−C and C−H bond activation,8-10 low-temperature hydrogenolysis alkanes,11 olefin metathesis,12 and alkane metathesis.13 During the research, we observed primary products and successfully demonstrated that alkane metathesis on Ta-based catalytic systems was a “single-site cascade reaction.” Dehydrogenation of the alkane gives the respective olefin followed by olefin metathesis and finally hydrogenation of these newly formed olefins to new alkanes all occurred on the same metal.14 According to our hypothesis, the reactivity of the catalyst could be improved if a metal possesses sufficient electron-deficiency to achieve C− H bond activation leading to dehydrogenation of alkanes to yield olefins (with subsequent metathesis and hydrogenation of these olefins). To validate our working hypothesis, our first strategy was to support tantalum on a silica support on which we previously grafted a zirconium hydroxyl.9 As expected, this new bimetallic catalyst showed improved activity in the propane metathesis reaction compared to silica-supported tantalum

(the turnover number (TON) increased from 60 to 100).9 Owing to this observation and better understanding of reaction mechanisms, we aimed to design an improved catalyst.15−17 With the concept of catalysis by design, we recently reported a well-defined bimetallic system consisting of W and Zr supported on the same silica support.18 By this route, we were able to increase the TON of the catalyst from 150 to 1400 (9 times) in n-decane metathesis reaction. At the same time, our group also discovered that oxide-supported Ti complexes are better catalysts than Zr complexes for hydrogenolysis of alkanes.11,19 It is worth noting that the first step of this reaction is a C−H bond activation. The effect of cooperation observed in the case of the W/Zr bimetallic system, and the higher reactivity of titanium hydrides compared with zirconium hydrides in low-temperature hydrogenolysis reactions motivated us to combine two metals (Ti and W) and synthesize a well-defined W/Ti bimetallic catalytic system. With that and based on the previous observations, we used the best metals for each of the required elementary steps: Ti for C−H bond activation followed by β-H elimination and W for olefin metathesis.

As a result of that strategy, a recent publication from our group demonstrated a well-defined bimetallic system supported on a single (silica) surface for metathesis of propane,

20 [(≡Si−O−)W(Me)5(≡Si−O−)Ti(Np)3] 2 (Np = neopentyl) (Scheme 5.1). The acquired bimetallic system was defined at the molecular level using modern surface organometallic chemistry (SOMC) characterization methods. The precatalyst 2 was shown to be highly effective in propane metathesis reaction, with a significantly higher TON of 9784 and an initial turnover frequency (TOF) of 900 h−1, compared to the

−1 monometallic system [(≡Si−O−)W(Me)5] 1, which gave a low TON of 98 with an initial TOF of 15 h in the propane metathesis under the same reaction conditions. A comparable approach was used by

Brookhart and co-workers5,6 and earlier by Burnett and Hughes,7 but our strategy was to create the catalyst single site by design starting from mechanistic factors, and we reached the best TON ever observed in propane metathesis reaction.

Scheme 5.1: Synthesis of supported [(≡Si−O−)W(Me)5(≡Si−O−)Ti(Np)3] 2

The representative example of successful utilization of the tandem system was demonstrated by

Brookhart5 using tandem alkane dehydrogenation-olefin metathesis catalysts for the catalytic alkane metathesis. Two systems were reported in which the metathesis of linear alkanes was achieved efficiently and selectively at moderate temperatures via a tandem combination of two independent catalysts, one with activity for alkane dehydrogenation and the other for olefin metathesis. In particular, highly selective and soluble molecular catalysts developed for each of these reactions, as well as solid- phase olefin metathesis catalysts were exploited. The basic tandem catalytic process is outlined in

Scheme 5.2 for metathesis of an alkane of carbon number n (Cn) to give ethane and C(2n–2). A dehydrogenation catalyst, M, reacts with the alkane to give the corresponding Cn terminal alkene and metal-hydride MH2. Olefin metathesis of the 1-alkene generates ethylene and an internal C(2n–2) alkene. The alkenes thus produced serve as acceptors for hydrogen and generate the two new alkanes via reaction with metal-hydride MH2, regenerating M and closing the catalytic cycle.

Scheme 5.2: Alkane metathesis via tandem transfer dehydrogenation–olefin metathesis illustrated with the formation and metathesis of two molecules of 1-alkene. M, active catalyst in the transfer dehydrogenation cycle [e.g., (pincer)Ir]

The investigation was based on the use of Iridium-based pincer complexes; specifically, complex 3, 4a,

4b were used in the study5 (Figure 5.1).

Figure 5.1: Dehydrogenation catalysts 3 and 4 and Schrock-type metathesis catalyst 5

These systems exhibit high stability, but their dehydrogenation activity is inhibited by the buildup of even moderate concentrations of an alkene product. The dual catalytic system (Figure 5.1) would require only a very low steady-state concentration of alkenes during catalysis; thus, inhibition of catalysis by the product could be avoided. Among numerous available olefin metathesis catalysts,

Brookhart examined the Schrock-type catalyst 5 in combination with dehydrogenation catalysts 3-4.

Initial experiments combining 5 with Ir-based dehydrogenation catalysts in solution proved to be successful. For instance, an n-hexane solution containing 10 mM dehydrogenation catalyst precursor

30-C2H4 (0.14 mol % relative to hexane) and 16 mM Schrock catalyst 5 was heated at 125°C under argon in a sealed glass vessel for 24 hours. This process converted 135 equivalents (relative to Ir) of n-hexane to a range of C2 to C15 n-alkanes.

Interestingly, it was determined that the widely used Grubbs-type catalyst21 reacts with and deactivates the iridium-based dehydrogenation catalysts 3-4. With that in mind, we decided to investigate the strategy of grafting both Ru-based Grubbs metathesis catalyst and Ir-based pincer dehydrogenation catalyst on solid support. According to this strategy/hypothesis, two independently grafted metal complexes would possess more stability, and potentially, no deactivation should occur in contrast to the homogeneous system.

5.2. Results and Discussion

5.2.1 Preparation of heterogeneous metathesis/dehydrogenation catalysts based on late transition metals 5.2.1.1 Synthesis and characterization of silica-supported Grubbs-Hoveyda 2nd generation catalyst For the preparation of the metathesis catalyst, we chose the route for the preparation of modified

Hoveyda-Grubbs 2nd generation catalyst22 and optimized the experimental conditions. The general pathway to the homogeneous catalyst precursor 11 is illustrated in Scheme 5.3.

Scheme 5.3: Synthetic route to homogeneous catalyst precursor 11

Mesitylamine 6 reacted with glyoxal in a 1:1 mixture of propanol and water at RT, leading to (1,2)-N,N- dimesitylethane-1,2-diimine 7 as a yellow powder with 90 % yield. Diimine 7 was allylated by Grignard allylmagnesium chloride, and meso-diamine 8 was obtained in 93 % yield after crystallization. The cyclization of 8 using an equimolar amount of ammonium chloride and ethyl orthoformate led to diallyl dihydroimidazolium chloride 9 with 90 % yield. Hydrosilylation of 9 with HSiCl3 and Karstedt’s catalyst followed by treatment with ethanol/triethylamine yielded the bis(triethoxy)silylated imidazolium salt

10 in 65 % yield. Ruthenium complex 11 was prepared by deprotonation of 10 with potassium bis(trimethylsilyl)amide and by treatment of the in situ generated free NHC carbene with commercial

Hoveyda-Grubbs 1st generation complex. The catalyst precursor 11 which was finally obtained was purified by column chromatography and finally grafted onto dehydroxylated SiO2-700 (Scheme 5.4).

Scheme 5.4: Grafting of homogeneous catalyst 11 onto the surface of SiO2-700

The grafted material 12 (later referred to as Ru for clarity) was characterized by solid-state NMR spectroscopy and inductively-coupled plasma optical emission spectroscopy. From a range of experiments, we were able to obtain between 0.08 % and 0.25 % of Ru loading on the surface.

The catalyst was characterized by solid-state NMR spectroscopy (Figures 5.2-5.4). The proton solid-state

NMR spectrum showed a broad signal at 1.76 ppm, which was assigned to a mixture of isopropoxy (-O-

CH(CH3)2 and ethoxy (-Si(OCH2CH3)n) methyl protons and a signal at 2.55 ppm, assigned to mixture of meta-, ortho- and para-methyl protons of the aryls groups. The broad peak at 4.38 ppm was assigned to methylene protons of free ethoxy groups (-Si(OCH2CH3)n). The peak at 7.77 ppm corresponds to aromatic protons of the aryl groups, and the weak broad signal at 17.23 ppm was assigned to Ru-carbene proton (Ru=CH-).

1 Figure 5.2: H solid-state MAS NMR spectrum of Ru/SiO2-700 (Ru) catalyst. A – Full range spectrum. B – magnified spectrum with a visible Ru=CH carbene proton

13 Figure 5.3: C CP/MAS NMR spectrum of Ru/SiO2-700 (Ru) In 13C CP/MAS NMR spectrum the signals at 7.3 and 26.6 ppm were assigned to methylene carbons of

NHC-backbone alkyl chains (-CH2-CH2-CH2-Si), while the strong signal at 17.1 ppm corresponds to a mixture of methyl carbons. The sharp peak at 55.5 ppm belongs to ethoxy methylene carbons (-

Si(OCH2CH3)n). The peaks at 62.8 and 71.5 ppm belong to CH- carbons of imidazole ring (N-CH) and isopropyl group (O-CH(CH3)2), respectively. The signals at 118.8-149.6 ppm correspond to aromatic carbons of the aryl groups, the weak signal at 234.4 ppm belongs to NHC carbene carbon (N-C-N).

13 1 Figure 5.4: C- H HETCOR correlation of Ru/SiO2-700 (Ru) Apparently, we did not observe Ru-carbene peak in the solid state carbon NMR spectrum due to a very weak intensity of the signal. However, the presence of Ru-carbene, essential for the metathesis reaction, was proved while investigating the catalytic activities of the heterogeneous catalyst (See Part 5.2.1.4).

In 29Si CP/MAS NMR spectrum of Ru (0.25 weight % of Ru, based on ICP OES) we observed two major signals. The strong peak at -103.6 ppm corresponds to silicon nuclei of the support (silica matrix). The weaker signal at -52.5 ppm belongs to silicon nuclei of –Si(OEt)n function of the supported modified

nd Hoveyda-Grubbs 2 generation catalyst and is characteristic for T1 type of structure (-Si(OEt)2-).

29 Figure 5.5: Si CP/MAS NMR spectrum of Ru/SiO2-700 (Ru)

5.2.1.2 Synthesis and characterization of silica-supported Iridium pincer catalyst The synthesis of Iridium pincer catalyst 13 (Figure 5.6) was accomplished by following the reported procedure.23

Figure 5.6: Structure of iridium pincer complex 13

The proton and carbon NMR spectra of the obtained Iridium-bishydride 13 (Figures 5.37-5.38, Part 5.4) are identical to those reported23 and a characteristic iridium-bishydride peak at -17 ppm was observed in proton NMR.

Catalyst precursor 13 was successfully grafted to preliminary dehydroxylated SiO2-700, according to the reported protocol (Scheme 5.5).24

Scheme 5.5: Grafting of Ir-bis-hydride pincer catalyst to SiO2-700

The structure of the grafted catalyst 14, later referred to as Ir for clarity, was confirmed by NMR spectroscopy (Figures 5.39-5.40, Part 5.4) and is in good agreement with the reported data. We obtained

1.26 % of Iridium on silica based on ICP-OES analysis.

5.2.1.3 Synthesis and characterization of silica-supported bimetallic Ru-Ir-based metathesis- dehydrogenation catalyst After we successfully grafted and characterized individual Ruthenium Hoveyda-Grubbs catalyst and

Iridium pincer-hydride catalyst to the surface of SiO2-700, we moved towards the association of these two catalysts on the silica support. Additional interest in this regard was due to the fact that catalyst precursors 11 and 13 are entirely incompatible with each other in solution (in the homogeneous phase).5

Since the grafting of Ru-complex by its triethoxy silyl groups release ethanol as a side product that can poison Ir-hydride catalyst, we grafted the Iridium-complex onto the supported Ru catalyst (Scheme 5.6).

Scheme 5.6: Grafting of Iridium pincer complex 13 to Ru/SiO2-700 catalyst 12

The obtained Ir-Ru/SiO2-700 represents the dehydrogenation-metathesis catalytic system, later referred to as Ir-Ru for clarity. To get insight into the structure of the supported bimetallic system, the material was subjected to solid-state NMR analysis.

Figure 5.7: 1H MAS NMR spectrum of Ir-Ru

At first, we did a solid-state 1H MAS NMR experiment and observed three broad signals (Figure 5.7). The most intense signal at 1.9 ppm corresponds to the tertiary butyl groups of Ir-Pincer-hydride complex and is in agreement with 1H MAS NMR spectrum of individually grafted Ir on silica. The broad peak at

4.3 ppm belongs to methylene protons of free Si-ethoxy groups on Ru-Ir catalyst and is the same with Ru. The broader signal at 6.9 ppm is a mixture of aromatic protons from both ruthenium and iridium complexes grafted on silica.

In order to better understand the structure of the bimetallic system and to find out whether grafted complexes had undergone any transformations or decomposition due to the presence of the neighboring complex or if neither of them were perturbed by the presence of each other, we did 13C

CP/MAS NMR spectrum (Figure 5.8).

Figure 5.8: 13C CP/MAS NMR spectrum of Ir-Ru

The carbon spectrum of Ir-Ru catalyst consists of individual signals coming from Ru- and Ir- complexes.

Grafted Ru-complex has intense signals at 16 ppm (CH3 groups), 55 ppm (CH2 groups), 120-135 ppm (a mixture of aromatic carbons) and 234 ppm (NHC carbene peak, N-C-N), and all these peaks are in good agreement with NMR data obtained in individually grafted Ru complex. At the same time, Iridium- complex in Ir-Ru catalyst shows signals at 24 ppm (CH3 groups) and 100-164 ppm (a mixture of aromatic protons), which are in good agreement with data obtained for the individually grafted Ir complex. The obtained results show that the Iridium complex is grafted on the support for the Ru catalyst, and both complexes are attached to the silica surface without decomposition. In addition, we performed the solid-state 1H-13C HETCOR correlation NMR experiment (Figure 5.9). In the correlation spectrum the individual signals from Ru- and Ir- complexes are identified on Ir-Ru heterogeneous system, and the correlation between carbon and proton nuclei was well demonstrated.

Figure 5.9: 1H-13C correlation NMR spectrum of Ir-Ru

Figure 5.25 (Experimental part 5.4) represents an FTIR comparison of the mono (Ir and Ru) grafted complexes with the corresponding Ir-Ru bimetallic system.

5.2.1.4 Investigation of catalytic activity of heterogeneous metathesis/dehydrogenation catalysts based on late transition metals After we synthesized and characterized supported Ru-Hoveyda Grubbs (Ru), Ir-Pincer Hydride (Ir) and bimetallic Ir-Ru catalysts (Ir-Ru), we moved towards the investigation of their catalytic activities in model reactions. As a model reaction to explore the activity of Ru catalyst, we chose the ring-closing metathesis (RCM) of diethyl diallyl malonate (DEDAM) (Scheme 5.7).

Scheme 5.7: RCM of DEDAM catalyzed by Ru

DEDAM was mixed with Ru catalyst in DCM, and the mixture was stirred. After 1 hour of reaction at RT, an aliquot was taken, filtered off and analyzed by GC-FID and GC-MS. As a result, we reached a conversion of 74.4 % and TON of 3346 of the catalyst, which was expectedly less as compared to the homogeneous counterpart in the same reaction conditions, where the conversion was 100 % after 1 hour at RT. However, the heterogeneous catalyst was still active in metathesis and possessed high performance.

To investigate the activity of the Iridium-based catalyst in dehydrogenation, we chose the dehydrogenation of n-decane as a model reaction. Since both dehydrogenations of an alkane and hydrogenation of an olefin may occur on the Iridium catalyst in an equilibrium process, the reaction equilibrium can be shifted towards the olefin (product), if the hydrogen acceptor is introduced to the reaction mixture. The typical hydrogen acceptor in dehydrogenation reactions is tertiary-butyl ethylene

(TBE). At the same time, dehydrogenation, in contrast to hydrogenation, is a thermodynamically unfavorable process, which requires high temperature (due to the high activation energy for the process) to form an olefin from an alkane. As such, we reacted equimolar amounts of n-decane and TBE with Ir catalyst at 150 °C for 5 days (Scheme 5.8).

Scheme 5.8: Dehydrogenation of n-decane over Ir catalyst To our surprise, only unreacted starting material was observed. This result can be explained by the following. First, after the grafting of the homogeneous Iridium pincer catalyst, one out of two hydrides was consumed by a reaction with silica silanols to produce hydrogen, and only one of the hydrides remained available for the reaction with alkane. Second, the remaining Ir-hydride is extensively crowded by four bulky tertiary-butyl groups which limit the access of the substrate molecule.

Notwithstanding the lack of observed activity of the Iridium catalyst, we decided to determine the activity of bimetallic Ir-Ru catalyst in the model metathesis reactions. First, we did ring-closing metathesis of DEDAM on Ir-Ru catalyst and compared the results with supported Ru catalyst (Scheme

5.9).

Scheme 5.9: RCM of DEDAM catalyzed by Ir-Ru

We observed a decrease of activity of Ru on the bimetallic system as compared to monometallic heterogeneous Ru metathesis catalyst. The conversion dropped from 74.4 % to 27.6 % in the same reaction conditions and the TON decreased from 3346 to 1241. However, the catalyst was still active in the metathesis of functionalized olefin (DEDAM). The next step was to investigate the activity of bimetallic system in the metathesis of alkanes. In this case, both catalysts (Ir- and Ru- based complexes) are expected to work back-to-back in a cascade reaction (as in the case of W/Zr18 and W/Ti20 bimetallic systems), where in the case of the formation of an olefin from an alkane on Iridium, a newly formed olefin should immediately undergo metathesis on Ru, which is grafted on the same silica support. Thus, we performed metathesis of n-decane catalyzed by Ru/Ir catalyst (Scheme 5.10).

Scheme 5.10: Metathesis on n-decane catalyzed by supported Ir-Ru bimetallic system We observed alkane metathesis products ranging from n-hexane (C6) to n-heptadecane (C17) (Figure

5.10), however, the conversion of a reaction was less than 1 %, and only 6 cumulative TONs of Ir-Ru catalyst were obtained. Despite very weak activity of Ir-Ru bimetallic system compared to classical

4,16 alkane metathesis catalysts, like W(CH3)5/SiO2-700, this result is the first proof of concept for the metathesis of alkanes catalyzed by supported late transition metal complexes.

1.4

1.2

1.0

0.8

0.6

Quantity (µmol) Quantity 0.4

0.2

0.0 C6 C7 C8 C9 C11 C12 C13 C14 C15 C16 C17 Metathesis products

Figure 5.10: Product distribution in metathesis of n-decane catalyzed by Ir-Ru

The combination of late transition metal complexes (Ir and Ru) on heterogeneous support for the first time resulted in the metathesis of a hydrocarbon. Remarkably, a physical mixture of two catalysts (Ru and Ir) was not active in the metathesis of n-decane, and no conversion was observed.

This result gave us hope to perform a metathesis of functionalized alkanes of Ir-Ru bimetallic catalyst.

Let us emphasize here that any result in the metathesis of functionalized alkanes, where the catalyst will allow for a conversion of a substrate of more than 5 % or a TON of a catalyst of more than 2 (See

Chapter 4), will become a breakthrough discovery.

As our first attempt, we used 9-hexyl-9H-carbazole as a reactant and Ir-Ru catalyst. The substrate is

25 known to be metathesized by W(CH3)5/SiO2-700. We did a reaction for 1, 5 and 10 days at 150 °C and unfortunately, did not observe any trace of metathesis products. On the second try, we chose N-hexyl- 2,5-dimethyl-pyrrole and the reaction was performed under the same conditions. The result was the same with no conversion to metathesis products, and only unreacted substrate was isolated. A third try was attempted with n-octyl-dimethylamine with no result (Figure 5.11).

Figure 5.11: Substrates for metathesis of functionalized alkanes used with Ir-Ru catalyst

As we can see from the results of the study, the ruthenium catalyst shows remarkable activity towards ring-closing metathesis of DEDAM when grafted individually (Ru) or in combination with Iridium catalyst

(Ir-Ru). In the combination of the dehydrogenation catalyst and metathesis catalyst on the same support, the two catalysts do not poison each other and work together for the metathesis of n-decane; however, the metathesis of functionalized substrates was not achieved due to lack of activity of the

26 dehydrogenation catalyst. The more active alkane dehydrogenation catalysts, e.g. TiNp3/SiO2-700, are not functionally tolerant due to their high electron deficiency.

5.2.2 Preparation of heterogeneous metathesis/dehydrogenation catalysts based on late and early transition metals 5.2.2.1 Synthesis and characterization of Ti-Ru-based metathesis-dehydrogenation catalyst After we observed low activity of Ir/Ru based dehydrogenation-metathesis bimetallic catalytic system in metathesis of n-decane and rationalized that the low activity was due to the poor dehydrogenation ability of the supported Ir pincer complex, we decided to associate Ru metathesis catalyst with a more active dehydrogenation Ti catalyst20,26 and prepared the Ti/Ru dehydrogenation-metathesis bimetallic system. In this case we combined late (Ru) and early (Ti) transition metals on the same SiO2-700 support.

With that, we grafted TiNp4 complex to the supported Ru catalyst (Scheme 5.11).

Scheme 5.11: Grafting of Titanium tetraneopentyl complex to Ru/SiO2-700 catalyst

nd The SiO2-700 supported bimetallic Titanium tris-neopentyl - Ruthenium Hoveyda-Grubbs 2 generation catalyst (later referred to as Ti-Ru, for clarity) was characterized by solid-state NMR spectroscopy. In the proton NMR spectrum (Figure 5.12) we observed the signals from TiNp3 moiety (0.81 ppm – CH3 groups,

2.03 ppm – CH2 groups) and protons from Ru-HG-supported catalyst (0.81-2.03 ppm – overlapping mixture of CH3 protons from Ar-CH3, -Si(OCH2CH3)2 and CH(CH3)2 groups; 3.54 ppm – CH2 protons from

NHC-backbone and 4.43 ppm – CH2 protons from -Si(OCH2CH3)2 group; 6.86 ppm – aromatic protons of

Aryl groups). The higher intensity of the TiNp- signals can be explained by the elemental analysis results.

Based on the ICP OES, the loading of Ru is 0.13 weight %, while the loading of Ti is 0.90 weight %.

Figure 5.12: 1H MAS solid-state NMR spectrum of Ti-Ru catalyst (A – full range spectrum, B – magnified spectrum)

In the 13C CP/MAS NMR spectrum (Figure 5.13) of Ti-Ru we observed signals at 17.08 ppm (mixture of

CH3 carbon nuclei of Ru-HG-supported catalyst – Ar-CH3, -Si(OCH2CH3)2 and CH(CH3)2 groups), 30.6 ppm

(CH3 group of TiNp3 moiety), 34.7 ppm ((CH3)3C- of TiNp3 moiety), 56.5 ppm (CH2 methylene carbons of

NHC-backbone of Ru-HG-supported catalyst), 72.3 ppm (CH2 methylene carbons of -Si(OCH2CH3)2 group of Ru-HG-supported catalyst), 99.7 ppm, 127.7 ppm, 136.3 ppm and 144.7 ppm (aromatic carbon nuclei of Aryl groups of Ru-HG-supported catalyst) and 112.3 ppm (CH2 methylene carbon of TiNp3 moiety).

Figure 5.13: 13C CP/MAS solid-state NMR spectrum of Ti-Ru catalyst

In the 1H-13C 2D HETCOR correlation spectrum (Figure 5.14) we observed a correlation of a proton and carbon nuclei of methyls (both from Ti and Ru complexes), methylenes (both from Ti and Ru complexes) as well as aromatic C-H nuclei (from Ru complex).

Figure 5.14: 1H-13C 2D HETCOR correlation solid-state NMR spectrum of Ti-Ru catalyst

Figure 5.26 (Experimental part 5.4) represents an FTIR comparison of the mono (Ti and Ru) grafted complexes with the corresponding bimetallic system.

5.2.2.2 Investigation of catalytic activity of Ti-Ru-based metathesis-dehydrogenation catalyst To demonstrate the enhanced catalytic activity of Ti-Ru catalyst compared to Ir-Ru catalyst (due to better dehydrogenation activity of Ti-complex), we performed metathesis of n-decane under the identical conditions (150 °C, 5 days) with the same amount of catalyst (20 mg, 0.25 µmol of Ru). 20

15

10

Quantity (µmol) Quantity 5

0

C1

C2

C3

C4

C5

C6

C7

C8

C9

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27 Metathesis products

Figure 5.15: Product distribution comparison in metathesis of n-decane catalyzed by Ir-Ru ( ) and Ti-Ru ( ) bimetallic systems supported on SiO2-700

As was expected, we observed an increase in the amount and distribution of metathesis products (Figure

5.15). The conversion of n-decane increased from 0.5 % (Ir-Ru) to 6.4 % (Ti-Ru), and the cumulative TON of the catalyst increased from 6 to 76, respectively. Unfortunately, neither Ir-Ru, nor Ti-Ru catalysts were active in the metathesis of functionalized alkanes and the substrates illustrated in Figure 5.10 were not converted to their metathesis products. At the same time, we understood that a combination of metathesis and dehydrogenation catalysts grafted onto the same support results in the metathesis of hydrocarbon. For that reason, we used bimetallic systems based on two late transition metals (Ru and

Ir) and a combination of late and early transition metals (Ru and Ti). The overall activity of the catalytic system is improved when more active dehydrogenation catalyst is used (Ti). However, for the metathesis of functionalized alkanes, the dehydrogenation of a substrate is the only cornerstone challenge that needs to be solved. The more functionally tolerant Iridium catalyst is not active enough to dehydrogenate a functionalized alkane when Ti catalyst is not functionally tolerant. Based on that we decided to use the more active combination of early transition metals for metathesis and dehydrogenation in confined spaces. 5.2.3 Preparation of heterogeneous metathesis/dehydrogenation catalysts based on early transition metals The strategy to improve the efficiency of alkane metathesis reaction by applying a tandem of two catalysts, one of which is active in dehydrogenation/hydrogenation, while a second one is in charge of metathesis was successfully implemented in our laboratories.18,20 It was shown that the highest activity of bimetallic W-Ti system towards the metathesis of alkanes, as such, silica-supported TiNp3 catalyst possessed better dehydrogenation/hydrogenation activity compared to ZrNp3 catalyst. Obviously, neither W-Zr, nor W-Ti systems showed any activity in dehydrogenation of functionalized alkanes, since the early transition metals in their highest oxidation state are prone to coordinate with any source of free electrons (e.g. functionalized alkanes), which makes the metal center more electron-rich and significantly reduces the activity or completely deactivates the catalyst.

5.2.3.1 Bimetallic W-Ti-based catalytic system supported on yolk-shell silica 5.2.3.1.1 Introducing yolk-shell silica The yolk-shell nanostructures represent a relatively new family of complex nano architectures that have attracted considerable attention, and currently many studies are focusing on investigating its outstanding structures and properties. In these structures a movable core is encapsulated inside a porous shell, and there is a void between the core and the outer shell of this material. It is expected that the void of yolk-shell nanoparticles will be useful for a variety of applications, including chemical storage, confinement of host-guest interactions and providing a unique nano environment for creating concerted actions between the core and shell. Reasonably, over the last few years, the yolk-shell structured nanoparticles have drawn tremendous attention thanks to their excellent performance in catalysis,28-32 medicine,33-36 and lithium batteries.37,38

A recent work39 was dedicated to ring-closing metathesis using yolk-shell encapsulated Hoveyda-Grubbs catalyst. The catalyst was effectively encapsulated in yolk-shell structured silica, resulting in a heterogeneous catalyst for olefin metathesis, which exhibits much higher activity compared to the reported encapsulated catalysts. The metathesis catalyst was introduced through the permeable mesopores in the shells with a void space in the interior, where the pore entrance size was subsequently reduced by grafting dichlorodiphenylsilane to the external surface of the pore, and in that way the catalyst could not leave the interior and was physically trapped inside it (Scheme 5.12).

Scheme 5.12: Process for encapsulating Hoveyda−Grubbs 2nd generation catalyst within a yolk−shell structured silica through silylation

In the result, ring-closing metathesis of functionalized olefin (DEDAM) was achieved by Hoveyda-Grubbs

2nd generation catalyst that was not chemically bonded to silica but encapsulated in the pore (Figure

5.16).

Figure 5.16: Graphical representation of RCM of DEDAM on yolk-shell encapsulated metathesis catalyst

The authors of the paper highlighted the potential variability of pore size in yolk-shell silica and described the procedure for preparing the silica with specific pore sizes.

Considering that, we decided to implement a strategy to graft the metathesis catalyst inside a pore of yolk-shell silica and partially reduce the entry to the pore (with the metathesis catalyst inside).

Accordingly, a substrate having a linear alkyl chain and the bulky functional group might be restricted from entering the pore by its functional group and, consequently, will not deactivate a catalyst located inside the pore.

5.2.3.1.2 Preparation of suitable yolk-shell silica To design yolk-shell silica that would have a suitable pore size for our purpose, we first looked for the size of the catalyst precursor (W(Me)6) that we wanted to encapsulate in the silica. According to the

40 literature, and based on the crystallographic data, the parameters of the WMe6 complex are as follows:

3 a: 0.6309 nm, b: 1.3158 nm, c: 2.0913 nm, Volume: 1.736 nm . The Ortep plot of WMe6 is illustrated in

Figure 5.17.40

Figure 5.17: The Ortep plot of WMe6

Having these data and reproducing the synthesis of yolk-shell silica (See Experimental Section, Part 5.4), potentially suitable to accept WMe6 molecule in its pore, we obtained a material with the following characteristics based on BET analysis: BET Surface area – 1480 m2/g, BJH Adsorption average pore width

(4V/A) – 3.9933 nm, Pore Volume – 0.77 cm3/g. Additionally, we performed TEM analysis and compared it with reported data (Figure 5.18).

Figure 5.18: Left – TEM image of yolk-shell silica (current work), Right - TEM image of yolk-shell silica (reported work39)

Based on the obtained data, the width of the pore was almost two times higher than the largest dimension of WMe6 molecule, which supports the strategy of grafting hexamethyl tungsten on yolk- shell silica and having the grafted complex both inside and outside the pores.

5.2.3.1.3 Grafting of WMe6 on yolk-shell silica and investigation of its catalytic activity Due to the thermal instability of yolk-shell silica at high temperatures (550 °C and above), we performed dehydroxylation of yolk-shell silica at 200 °C for 12 h in high-vacuum line (10-5 mbar) followed by grafting of hexamethyl tungsten (Scheme 5.13). The loading of W on yolk-shell silica is 4.6 weight % based on

ICP-OES analysis.

Scheme 5.13: Grafting of WMe6 on Yolk-Shell silica (YS-200)

The activity of the obtained catalyst was investigated in the metathesis of n-decane. The broad range of alkanes from C1 to C34 were observed in the reaction mixture (Figure 5.19). 14

12

10

8

6

Quantity (µmol) Quantity 4

2

0

C1

C2

C3

C4

C5

C6

C7

C8

C9

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

C28

C29

C30

C31

C32

C33

C34 Metathesis products

Figure 5.19: Product distribution in the metathesis of n-decane catalyzed by WMe5/YS-200

The conversion of the reaction reached 8 % after 5 days of reaction at 150 °C with a cumulative TON of the catalyst of 50. In comparison, WMe5 supported on conventional SiO2-200 has similar reactivity and converts 5 % of propane in 5 days at 150 °C with a TON of 47.20

5.2.3.1.3 Preparation of bimetallic W-Ti-based catalytic system on yolk-shell silica and investigation of its catalytic activity

After we proved the activity of WMe5 supported on yolk-shell silica in the metathesis of an alkane, we moved to the next step of reducing the pore entry. For obvious reasons, dichlorodiphenyl silane cannot be used for this purpose in order to avoid the poisoning of the alkane metathesis catalyst by releasing hydrogen chloride (HCl). Instead, we chose titanium tetraneopentyl for the reasons described below.

Firstly, titanium tetraneopentyl is known to be grafted in tandem with WMe5 without deactivating the latter by releasing neopentane;18,20 secondly, in a cascade reaction of the metathesis of alkanes, the W-

Ti system showed the highest activity and TON ever observed;20 thirdly, three remaining bulky neopentyl groups on titanium may create steric hindrances and protect the WMe5 grafted inside the pores from interaction with functional groups; fourthly, despite the probable inactivity of silica-supported TiNp3 towards dehydrogenation of functionalized alkanes, the titanium as an early transition metal in its highest oxidation state (+4) is electron deficient and potentially may trap the functional group with free pairs of electrons (by coordination) of a functionalized alkane (substrate) prior to its interaction with

WMe5. Accordingly, there will be a greater probability for the tungsten complex to make CH-activation by an alkyl chain of functionalized alkane. With that, we grafted titanium tetraneopentyl to a surface of yolk-shell supported tungsten pentamethyl (WMe5/YS-200) (Scheme 5.14) and obtained 5.6 weight % Ti together with 4.6 weight % of W on the surface according to ICP-OES analysis.

Scheme 5.14: Grafting of TiNp4 to WMe5/YS-200

The graphical illustration of the catalytic system is presented in the Figure 5.20.41

Figure 5.20: Schematic representation of -WMe5 ( ) and -TiNp3 ( ) system supported on yolk-shell silica

In the metathesis of n-decane in the same reaction conditions as listed above (150 °C, 5 days) catalyzed by WMe5-TiNp3/YS-200, the conversion was increased from 8 % (using WMe5/YS-200 as the catalyst) to

70 % and the TON from 50 to 535, respectively. The product distribution is illustrated in Figure 5.21. 200

180

160

140

120

100

80

Quantity (µmol) Quantity 60

40

20

0

C1

C2

C3

C4

C5

C6

C7

C8

C9

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

C28

C29

C30

C31

C32

C33

C34 Metathesis products

Figure 5.21: Product distribution comparison in metathesis of n-decane catalyzed by WMe5/YS-200 ( ) and WMe5-TiNp3/YS-200 ( )

The significant increase of activity of the catalyst after grafting a second metal (Ti) is in good agreement with the reported data.20 These promising results motivated us to explore the catalytic activity of yolk- shell supported W-Ti system in the metathesis of functionalized alkanes. After many a try, to our disappointment, we found that WMe5-TiNp3/YS-200 catalyst is inactive in metathesis of 9-hexyl-9H- carbazole, N-hexyl-2,5-dimethyl-pyrrole, and n-octyl-dimethylamine (N-substituted alkanes), as well as ester (ethyl caprylate) and Si-substituted alkanes (substrates 23-25, Chapter 2).

5.2.3.2 Bimetallic W-Ti-based catalytic system supported on KCC-1 5.2.3.2.1 The choice of KCC-1 silica To further explore the strategy of applying the bimetallic system to specific supports, we decided to support W-Ti system on KCC-1. KCC-1 silica, which was initially introduced in this dissertation in Chapter

3 (Part 3.2.6), which represents a fibrous morphology with the ability to precisely control the structure and pore size of silica particles. Moreover, KCC-1 support with wide walls is thermally stable and can be dehydroxylated at 700 °C without any disruption of the surface morphology. KCC-1-700 will consist of single silanols (with no heminal or vicinal moieties), allowing it to have single-site metal catalysts with higher activity.

5.2.3.2.2 Preparation of suitable KCC-1 silica Considering the pore size (3.99 nm) of yolk-shell silica used in Part 5.2.2.1, the KCC-1 silica was prepared according to the established protocol (See Experimental Section, Part 5.4). After a BET analysis, the following characteristics were found: BJH Pore Size – 3.7 nm; BET surface Area – 636 m2/g; BJH pore volume – 0.6 cm3/g. The size of the pores is similar to those obtained in yolk-shell silica and is larger than the size of WMe6 molecule allowing for its grafting both inside and outside the pores. In addition, the TEM analysis was performed to evaluate the structure of the obtained KCC-1 support (Figure 5.22).

Figure 5.22: KCC-1 support with 3.7 nm pore size

5.2.3.2.3 Grafting of WMe6 on KCC-1 silica and investigation of its catalytic activity After the TEM characterization, we performed dehydroxylation of KCC-1 silica at 700 °C for 12 h in a high-vacuum line (10-5 mbar) followed by grafting hexamethyl tungsten (Scheme 5.15). The loading of

W on KCC-1-700 silica is 2.05 weight % based on ICP-OES analysis. Additionally, the free silanols (Si-OH) remained for further modification.

Scheme 5.15: Grafting of WMe6 onto KCC-1-700 silica

According to BET analysis after grafting of WMe5, the key parameters were found to be as follows: BJH

Pore Size – 3.7 nm (not changed); BET surface Area – 670 m2/g (slightly increased); BJH pore volume –

3 0.1 cm /g (decreased). The decrease of the pore volume after grafting of WMe5 suggests that the complex was grafted both outside and inside the pores.

Nevertheless, we performed a control experiment. The activity of the obtained catalyst

(WMe5/KCC-1-700) was determined in the metathesis of n-decane. The broad range of alkanes from C1 to C34 were observed in the reaction mixture (Figure 5.23).

100

80

60

40

Quantity (µmol) Quantity

20

0

C1

C2

C3

C4

C5

C6

C7

C8

C9

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

C28

C29

C30

C31

C32

C33

C34 Metathesis products

Figure 5.23: Product distribution in the metathesis of n-decane catalyzed by WMe5/KCC-1-700

In spite of WMe5/YS-200, which converted 8 % of n-decane, the KCC-1-supported catalyst converted

56 % of n-decane to its higher and lower homologs after the same reaction time (5 days) at the same temperature (150 °C) with the same amount of catalyst (8 µmol) reaching TON of 834 in respect to W.

The 7-fold increase in the productivity of the reaction can be explained by specific surface morphology of KCC-1 (see discussion in Chapter 3, Part 3.2.6) and the highly dehydroxylated surface with only single silanols which allows for more active monopodal WMe5 species.

5.2.3.2.4 Preparation of bimetallic W-Ti-based catalytic system on KCC-1 silica and investigation of its catalytic activity

The further modification of WMe5/KCC-1-700 with tetraneopentyl titanium led to W-Ti bimetallic system supported on KCC-1-700 (Scheme 5.16).

Scheme 5.16: Grafting of TiNp4 to WMe5/KCC-1-700

The primary activity of W-Ti system on KCC-1 support was established by a model reaction of n-decane metathesis. The reaction was performed under the same conditions as WMe5/KCC-1-700, and a conversion of n-decane of 83 % with 1188 TONs of the catalyst was found. The increase in activity of the tandem system, in which Ti-catalyst dehydrogenates an alkane (and hydrogenates newly formed olefins), and where nearby W-catalyst performs the metathesis reaction, is expected as for W-Ti bimetallic system. 200

180

160

140

120

100

80

Quantity (µmol) Quantity 60

40

20

0

C1

C2

C3

C4

C5

C6

C7

C8

C9

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

C28

C29

C30

C31

C32

C33

C34 Metathesis products

Figure 5.24: Product distribution comparison in metathesis of n-decane catalyzed by WMe5/KCC-1-700 ( ) and WMe5-TiNp3/KCC-1-700 ( )

The metathesis of functionalized alkanes was attempted by utilization of 9-hexyl-9H-carbazole, N-hexyl-

2,5-dimethyl-pyrrole, and n-octyl-dimethylamine (N-substituted alkanes), ethyl caprylate and Si- substituted alkanes (substrates 23-25, Chapter 2). Unfortunately, the WMe5-TiNp3/KCC-1-700 was not active in the metathesis of functionalized alkanes.

5.3. Conclusions

In conclusion, we demonstrated the strategy of preparing dehydrogenation-metathesis bimetallic catalytic systems based on late (iridium and ruthenium), early (tungsten and titanium) and mixture of late and early (ruthenium and titanium) transition metals supported on heterogeneous supports. The systems were characterized by solid-state NMR spectroscopy, inductively-coupled plasma optical emission spectroscopy, Fourier-transform infra-red analysis, and BET analysis. Despite the fact that none of these bimetallic systems were active in the metathesis of functionalized alkanes, all of them showed remarkable activity in alkane metathesis reaction. The iridium-ruthenium based bimetallic catalytic system possessed low conversion and 6 TON, however, became the first reported catalytic system for the metathesis of alkanes based on supported late transition metal complexes. By replacing iridium with the more active titanium dehydrogenation complex, we were able to increase the conversion of n- decane from 0.5 % to 6.5 %. The tungsten-titanium system was developed on two silica surfaces with specific morphology – yolk-shell silica and KCC-1, where W-metathesis catalyst was grafted in the pores and Ti-dehydrogenation/hydrogenation catalyst was grafted further and used as a protection for the tungsten catalyst. Both catalytic systems showed improved activity with higher conversion and TONs in the metathesis of n-decane, however, were not effective in the metathesis of alkanes bearing functional groups.

5.4. Experimental Section

General

All experiments were carried out using standard Schlenk and glove box techniques under an inert argon atmosphere. The syntheses and treatments of the surface species were carried out using high vacuum

-5 lines (< 10 mbar) and glove-box techniques. Pentane was distilled from a Na/K alloy under N2 and dichloromethane from CaH2. Both solvents were degassed through freeze-pump-thaw cycles. Ethanol

(HPLC grade) was purchased from Fisher Scientific and used as received. Tetraethylorthosilicate (TEOS), ammonium hydroxide, dodecyltrimethylammonium bromide (DTAB), and sodium carbonate were purchased from Aldrich and used without further purification. SiO2-700 was prepared from Aerosil silica from Degussa (specific area of 200 m2/g), which was partly dehydroxylated at 700 °C under high vacuum

(< 10-5 mbar) for 24 h to give a white solid having a specific surface area of 190 m2/g and containing around 0.75 OH/nm2 (0.26 mmol OH/g). Yolk-shell and KCC-1 silicas were prepared by the methods described below. IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF2 windows. The IR samples were prepared under argon within a glove box. Typically,

32 scans were accumulated for each spectrum (resolution 4 cm−1). Elemental analyses were performed at KAUST Core Lab ACL. NMR spectra were recorded on Bruker Avance III 400 MHz NMR spectrometer equipped with a BBFO CryoProbe. GC measurements were performed with an Agilent 7890A Series (FID detection). Method for GC analyses: Column HP-5; 30 m length × 0.32 mm ID × 0.25 μm film thickness; flow rate, 1 mL/min (N2); split ratio, 50/1; inlet temperature, 250 °C, detector temperature, 250 °C; temperature program, 40 °C (3 min), 40–250 °C (12 °C/min), 250 °C (3 minutes), 250–300 °C (10 °C/min),

300 °C (3 minutes). GC-MS measurements were performed with an Agilent 7890A Series coupled with an Agilent 5975C Series. A GC-MS, equipped with a capillary column coated with non-polar stationary phase HP-5MS, was used for molecular weight determination and identification, which allowed for the separation of chemical compounds according to their boiling point differences. Method for GC-MS analyses: Column HP-5MS; 30 m length × 0.25 mm ID × 0.25 μm film thickness; flow rate, 1 mL/min (N2); split ratio, 100/1; inlet temperature, 220 °C, detector temperature, 300 °C; temperature program, 150

°C (0 minutes), 150–300 °C (20 °C/min), 300 °C (30 minutes).

Yolk-shell silica preparation procedure: 16 mL of ammonium hydroxide, 200 mL of ethanol and 12.2 mL of deionized water were mixed at RT and intensively stirred at 1500 rpm for 30 minutes. After that, 12.4 mL of TEOS was added dropwise, and the stirring continued for 12 h (RT). The mixture was divided in 6 centrifuge vials and centrifuged (7800 rpm, 15 minutes per cycle) for 1 cycle, then the liquid was decanted, and each vial was washed with deionized water (30 mL) and centrifuged for 6 cycles (with

H2O washing after each cycle). After that, the residue was washed with ethanol (20 mL per vial) for 2 cycles; finally, the liquid was decanted, and the solid residue was dried at 60 °C for 4 hours in air. 3.49 g of silica nanospheres were obtained. 1 gram of silica nanospheres was suspended in 500 mL of deionized water by ultrasonication. DTAB (1.27 g), ethanol (300 mL) and concentrated ammonium hydroxide (5.5 mL) were added to a suspension. The mixture was stirred at 1500 rpm for 30 minutes at RT. Then,

2.35 g of TEOS was added, and the resulting mixture was stirred for additional 7 h. The liquid was decanted, and each vial was washed with deionized water (30 mL) and centrifuged for 6 cycles (with

H2O washing after each cycle). After that, the residue was washed with ethanol (20 mL per vial) for 2 cycles and dried at RT. The obtained solid powder was dispersed in a solution of 4.24 g of Na2CO3 in 200 mL of deionized water by ultrasonication, then stirred for 4 h at 50 °C. The solid was isolated by centrifugation, washed with deionized water (30 mL) and centrifuged for 6 cycles (with H2O washing after each cycle). After that, the residue was washed with ethanol (20 mL per vial) for an additional 2 cycles. The obtained silica was calcined to remove DTAB for 5 h in air (RT to 550 °C, ramp: 1 °C/min). The obtained yolk-shell silica was additionally dehydroxylated at 200 °C in high-vacuum line (10-5 mbar) for

12 hours.

KCC-1 silica preparation procedure:

In order to make KCC-1 with smaller pore size (below 5 nm), the solution containing CTAB (72 g) and urea (86 g) was added to the desired amount of water containing a vessel and was stirred for 20 min at a speed of 500 rpm. In the other flask, 1-Pentanol (1700 mL) and TEOS (360 mL) were added to a solution containing cyclohexane. Water and cyclohexane ratio is maintained at 1:1. Afterward, both solutions were mixed and stirred for 60 min at 4000 rpm. The resulting reaction solution was then transferred to a sealed hydrothermal reactor and heated at 120 °C for 150 minutes. The obtained silica was isolated by centrifugation, washed with distilled water 3 times followed by ethanol and air-dried for 12 hr. The as-synthesized material was then calcined at 550 °C for six hours in air. The desired molar concentration of 1-Pentanol was obtained by optimizing the reagent concentration. 2952 2926 1443 10 2978 1479 2903 3335 2870 3745 3075 8 3745 1443 1479 2948 6 2910 3075 2873

1388 4 2978 1453 2929 3335 1479 Absorbance 3745

2 3745

0

4000 3500 3000 2500 2000 1500 Wavenumbers (cm-1)

Figure 5.25: FTIR spectra of SiO2-700 (red); Ru/SiO2-700 (blue); Ir/SiO2-700 (yellow); Ir-Ru/SiO2-700 (green)

Figure 5.26: FTIR spectra of SiO2-700 (red); Ru/SiO2-700 (blue); Ti/SiO2-700 (green); Ti-Ru/SiO2-700 (yellow)

Figure 5.27: 1H NMR spectrum of 7

Figure 5.28: 13C NMR spectrum of 7

Figure 5.29: 1H NMR spectrum of 8

Figure 5.30: 13C NMR spectrum of 8

Figure 5.31: 1H NMR spectrum of 9

Figure 5.32: 13C NMR spectrum of 9

Figure 5.33: 1H NMR spectrum of 10

Figure 5.34: 13C NMR spectrum of 10

Figure 5.35: 1H NMR spectrum of 11

Figure 5.36: 13C NMR spectrum of 11

Figure 5.37: 1H NMR spectrum of 13

Figure 5.38: 13C NMR spectrum of 13

Figure 5.39: 1H MAS solid-state NMR spectrum of 14

Figure 5.40: 13C CP/MAS solid-state NMR spectrum of 14

1 Figure 5.41: H MAS solid-state NMR spectrum of WMe5-TiNp3/YS-200

13 Figure 5.42: C MAS solid-state NMR spectrum of WMe5-TiNp3/YS-200

1 Figure 5.43: H MAS solid-state NMR spectrum of WMe5-TiNp3/KCC-1-700

13 Figure 5.44: C MAS solid-state NMR spectrum of WMe5-TiNp3/KCC-1-700 5.5. References 1. V. Vidal, A. Theolier, J. ThivolleCazat, J. M. Basset, Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides. Science, 1997, 276, 5309, 99-102.

2. Taoufik, M.; Schwab, E.; Schultz, M.; Vanoppen, D.; Walter, M.; Thivolle-Cazat, J.; Basset, J.-M., Cross- metathesis between ethane and toluene catalyzed by [(≡SiO)2TaH]: The first example of a cross-metathesis reaction between an alkane and an aromatic. Chem. Commun., 2004, 12, 1434-1435.

3. J. D. A. Pelletier, J. M. Basset, Catalysis by Design: Well-Defined Single-Site Heterogeneous Catalysts. Acc. Chem. Res., 2016, 49, 4, 664-677.

4. M. K. Samantaray, R. Dey, E. Abou-Hamad, A. Hamieh, J. M. Basset, Effect of Support on Metathesis of n‐ Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica–Alumina. Chem. Eur. J., 2015, 21, 16, 6100-6106.

5. Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M., Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis. Science, 2006, 312, 257-261.

6. Haibach, M. C.; Kundu, S.; Brookhart, M.; Goldman, A. S., Alkane Metathesis by Tandem Alkane- Dehydrogenation–Olefin-Metathesis Catalysis and Related Chemistry. Acc. Chem. Res., 2012, 45, 6, 947-958.

7. Burnett, R. L.; Hughes, T. R., Mechanism and poisoning of the molecular redistribution reaction of alkanes with a dual-functional catalyst system. J. Catal., 1973, 31, 55-64.

8. Labinger, J. A.; Bercaw, J. E., Understanding and exploiting C–H bond activation. Nature, 2002, 417, 507-514.

9. Rataboul, F.; Coperet, C.; Lefort, L.; de Mallmann, A.; ThivolleCazat, J.; Basset, J.-M., Synthesis, characterization and propane metathesis activity of a tantalum-hydride prepared on high surface area “silica supported zirconium hydroxide”. Dalton Trans., 2007, 923-927.

10. Thieuleux, C.; Maraval, A.; Veyre, L.; Coperet, C.; Soulivong, D.; Basset, J. M.; Sunley, G. J., Homologation of Propane Catalyzed by Oxide‐Supported Zirconium Dihydride and Dialkyl Complexes. Angew. Chem. Int. Ed., 2007, 46, 2288-2290.

11. Larabi, C.; Merle, N.; Norsic, S.; Taoufik, M.; Baudouin, A.; Lucas, C.; Thivolle-Cazat, J.; de Mallmann, A.; Basset, J. M., Surface Organometallic Chemistry of Titanium on Silica−Alumina and Catalytic Hydrogenolysis of Waxes at Low Temperature. Organometallics, 2009, 28, 5647-5655.

12. Rhers, B.; Salameh, A.; Baudouin, A.; Quadrelli, E. A.; Taoufik, M.; Coperet, C.; Lefebvre, F.; Basset, J. M.; Solans-Monfort, X.; Eisenstein, O.; Lukens, W. W.; Lopez, L. P. H.; Sinha, A.; Schrock, R. R., A Well-Defined, Silica- Supported Tungsten Imido Alkylidene Olefin Metathesis Catalyst. Organometallics, 2006, 25, 3554-3557.

13. Le Roux, E.; Taoufik, M.; Baudouin, A.; Coperet, C.; ThivolleCazat, J.; Basset, J. M.; Maunders, B. M.; Sunley, G. J., Silica‐Alumina‐Supported, Tungsten‐Based Heterogeneous Alkane Metathesis Catalyst: Is it Closer to a Silica‐ or an Alumina‐Supported System? Adv. Synth. Catal., 2007, 349, 231-237.

14. Basset, J. M.; Coperet, C.; Lefort, L.; Maunders, B. M.; Maury, O.; Le Roux, E.; Saggio, G.; Soignier, S.; Soulivong, D.; Sunley, G. J.; Taoufik, M.; Thivolle-Cazat, J., Primary Products and Mechanistic Considerations in Alkane Metathesis. J. Am. Chem. Soc., 2005, 127, 8604-8605.

15. Le Roux, E.; Taoufik, M.; Coperet, C.; de Mallmann, A.; Thivolle-Cazat, J.; Basset, J. M.; Maunders, B. M.; Sunley, G. J., Development of Tungsten‐Based Heterogeneous Alkane Metathesis Catalysts Through a Structure–Activity Relationship. Angew. Chem. Int. Ed., 2005, 44, 6755-6758. 16. M. K. Samantaray, E. Callens, E. Abou-Hamad, A. J. Rossini, C. M. Widdifield, R. Dey, L. Emsley, J. M. Basset, WMe6 Tamed by Silica: ≡Si–O–WMe5 as an Efficient, Well-Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W–Methyl/Methylidyne Species. J. Am. Chem. Soc., 2014, 136, 3, 1054-1061.

17. Chen, Y.; Abou-hamad, E.; Hamieh, A.; Hamzaoui, B.; Emsley, L.; Basset, J. M., Alkane Metathesis with the Tantalum Methylidene [(≡SiO)Ta(═CH2)Me2]/[(≡SiO)2Ta(═CH2)Me] Generated from Well-Defined Surface V Organometallic Complex [(≡SiO)Ta Me4]. J. Am. Chem. Soc., 2015, 137, 588-591.

18. M. K. Samantaray, R. Dey, S. Kavitake, E. Abou-Hamad, A. Bendjeriou-Sedjerari, A. Hamieh, J. M. Basset, Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane. J. Am. Chem. Soc., 2016, 138, 27, 8595-8602.

19. Rosier, C.; Niccolai, G. P.; Basset, J. M., Catalytic Hydrogenolysis and Isomerization of Light Alkanes over the Silica-Supported Titanium Hydride Complex (⋮SiO)3TiH. J. Am. Chem. Soc., 1997, 119, 12408-12409.

20. Samantaray, M. K.; Kavitake, S.; Morlanes, N.; Abou-Hamad, E.; Hamieh, A.; Dey, R.; Basset, J. M., Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane. J. Am. Chem. Soc., 2017, 139, 3522-3527.

21. Grubbs, R. H., Olefin metathesis. Tetrahedron, 2004, 60, 34, 7117-7140.

22. Monge-Marcet, A.; Pleixats, R.; Cattoën, X.; Wong Chi Man, M., Sol–gel immobilized Hoveyda–Grubbs complex through the NHC ligand: a recyclable metathesis catalyst. J. Mol. Catal. Chem., 2012, 357, 59-66.

23. Göttker-Schnetmann, I.; White, P. S.; Brookhart, M., Synthesis and Properties of Iridium Bis(phosphinite) Pincer Complexes (p-XPCP)IrH2, (p-XPCP)Ir(CO), (p-XPCP)Ir(H)(aryl), and {(p-XPCP)Ir}2{μ-N2} and Their Relevance in Alkane Transfer Dehydrogenation. Organometallics, 2004, 23, 1766-1776.

24. Rimoldi, M.; Fodor, D.; van Bokhoven, J. A.; Mezzetti, A., A stable 16-electron iridium(III) hydride complex grafted on SBA-15: a single-site catalyst for alkene hydrogenation. Chem. Commun., 2013, 49, 11314-11316.

25. Tretiakov, M.; Lebedev, Y.; Samantaray, M. K.; Saidi, A.; Rueping, M.; Basset, J. M., Metathesis of Functionalized Alkane: Understanding the Unsolved Story. Catalysts, 2019, 9, 3, 238-248.

26. Bini, F.; Rosier, C.; Petroff Saint-Arroman, R.; Neumann, E.; Dablemont, C.; de Mallmann, A.; Lefebvre, F.; Niccolai, G. P.; Basset, J.-M.; Crocker, M.; Buijink, J.-K., Surface Organometallic Chemistry of Titanium: Synthesis, Characterization, and Reactivity of (⋮Si−O)nTi(CH2C(CH3)3)4-n (n = 1, 2) Grafted on Aerosil Silica and MCM-41. Organometallics, 2006, 25, 15, 3743-3760.

27. Wang, X.; He, Y.; Ma, Y.; Liu, J.; Liu, Y.; Qiao, Z.; Huo, Q., Architecture of yolk–shell structured mesoporous silica nanospheres for catalytic applications. Dalton Trans., 2018, 47, 9072-9078.

28. Liu, X.; Qian, G.; Jiao, Z.; Wu, M.; Zhang, H., The Transformation of Hybrid Silica Nanoparticles from Solid to Hollow or Yolk‐Shell Nanostructures. Chem. Eur. J., 2017, 23, 33, 8066-8072.

29. Wu, L.; Li, Y.; Meng, J.; Jin, R.; Lin, J.; Liu, G., Yolk‐Shell‐Mesostructured Silica‐Supported Dual Molecular Catalyst for Enantioselective Tandem Reactions. Angew. Chem., 2018, 83, 9, 861-867.

30. Shi, S.; Wang, M.; Chen, C.; Gao, J.; Ma, H.; Maa, J.; Xu, J., Super-hydrophobic yolk–shell nanostructure with enhanced catalytic performance in the reduction of hydrophobic nitroaromatic compounds. Chem. Commun., 2013, 49, 9591-9593.

31. Lee, I.; Joo, J. B.; Yin, Y.; Zaera, F., A Yolk@Shell Nanoarchitecture for Au/TiO2 Catalysts. Angew. Chem., 2011, 123, 43, 10390-10393. 32. Li, A.; Zhang, P.; Chang, X.; Cai, W.; Wang, T.; Gong, J., Gold Nanorod@TiO2 Yolk‐Shell Nanostructures for Visible‐Light‐Driven Photocatalytic Oxidation of Benzyl Alcohol. Small, 2015, 11, 1892-1899.

33. Dai, L.; Zhang, Q.; Gua, H.; Cai, K., Facile synthesis of yolk–shell silica nanoparticles for targeted tumor therapy. J. Mater. Chem. B, 2015, 3, 8303-8313.

34. Xu, J.; Wang, X.; Teng, Z.; Lu, G.; He, N.; Wang, Z., Multifunctional Yolk–Shell Mesoporous Silica Obtained via Selectively Etching the Shell: A Therapeutic Nanoplatform for Cancer Therapy. ACS Appl. Mater. Interfaces, 2018, 10, 29, 24440-24449.

35. Gao, J.; Liang, G.; Cheung, J. S.; Pan, Y.; Kuang, Y.; Zhao, F.; Zhang, B.; Zhang, X.; Wu, E. X.; Xu, B., Multifunctional Yolk−Shell Nanoparticles: A Potential MRI Contrast and Anticancer Agent. J. Am. Chem. Soc., 2008, 130, 35, 11828-11833.

36. Zhao, L.; Peng, J.; Huang, Q.; Li, C.; Chen, M.; Sun, Y.; Lin, Q.; Zhu, L.; Li, F., Near‐Infrared Photoregulated Drug Release in Living Tumor Tissue via Yolk‐Shell Upconversion Nanocages. Adv. Funct. Mater., 2014, 24, 363-371.

37. Zhang, J.; Wang, K.; Xu, Q.; Zhou, Y.; Cheng, F.; Guo, S., Beyond Yolk–Shell Nanoparticles: Fe3O4@Fe3C Core@Shell Nanoparticles as Yolks and Carbon Nanospindles as Shells for Efficient Lithium Ion Storage. ACS Nano, 2015, 9, 3, 3369-3376.

38. Cai, Z.; Xu, L.; Yan, M.; Han, C.; He, L.; Hercule, K. M.; Niu, C.; Yuan, Z.; Xu, W.; Qu, L.; Zhao, K.; Mai, L., Manganese Oxide/Carbon Yolk–Shell Nanorod Anodes for High Capacity Lithium Batteries. Nano Lett., 2015, 15, 1, 738-744.

39. Li, Q.; Zhou, T.; Yang, H., Encapsulation of Hoveyda–Grubbs2nd Catalyst within Yolk–Shell Structured Silica for Olefin Metathesis. ACS Catal., 2015, 5, 4, 2225-2231.

− 40. Kleinhenz, S.; Pfennig, V.; Seppelt, K., Preparation and Structures of [W(CH3)6], [Re(CH3)6], [Nb(CH3)6] , and − [Ta(CH3)6] . Chem. Eur. J., 1998, 4, 9, 1687-1691.

41. Cheng, X.; Zhao, H.; Huang, W.; Chen, J.; Wang, S.; Dong, J.; Deng, Y., Rational Design of Yolk–Shell CuO/Silicalite-1@mSiO2 Composites for a High-Performance Nonenzymatic Glucose Biosensor. Langmuir, 2018, 34, 26, 7663-7672.

Chapter 6. Conclusions and outlook

6.1. Achievements

The present dissertation represents the first systematic work in the search for a solution to an unsolved chemistry problem – the metathesis of functionalized alkanes. Ever since the accidental discovery of olefin metathesis in the early 1950s, the process became one of the most widely-used methods in the creation of carbon-carbon bonds and nowadays is an everyday tool of both academia and industry. After a breakthrough discovery and understanding of the potential impact of metathesis reaction in hydrocarbons (like olefins and alkynes), scientists have faced a tremendous challenge to metathesize hydrocarbons bearing a functional group. Such a method was expected to significantly widen the area and open new doors for a variety of different applications (e.g. for the pharmaceutical industry).

However, to construct a catalyst that would be tolerant of the presence of functional groups in the metathesis of olefins took almost 30 years of global scientific research. The problem, initially considered as impossible, was finally successfully overcome by R. Grubbs, R. Schrock, and Y. Chauvin and led to the

Nobel Prize in 2005 (“for the development of the metathesis method in organic synthesis”). The impact of the method is great and allows for the simple creation of new C-C bonds in a variety of molecules.

However, saturated hydrocarbons were not known to be metathesized. A breakthrough discovery in metathesis occurred in 1997 by Basset, utilizing transition metal hydrides as catalysts for the metathesis of alkanes. The metathesis of alkanes became the last missing brick in the fundamental science and research of the metathesis of hydrocarbons. The metathesis of functionalized alkanes remained the last gap to be filled in the fundamental science of metathesis. Functionalized alkanes is the last group of substrates that were still unknown in metathesis reaction, and that reaction was not reported by any group in the world until our publication in 2019.

In this work, we successfully proved the concept and showed the first-ever example of the metathesis of functionalized alkane – 9-hexyl-9H-carbazole. After an overview of the history of metathesis given in Chapter 1, starting with Chapter 2, we began our journey by understanding why the process of the metathesis of functionalized alkanes was limited to the established alkane metathesis catalysts. As a model catalyst for the study, we chose pentamethyl tungsten, supported on dehydroxylated SiO2-700

(WMe5/SiO2-700). We clearly showed the deactivation of the catalyst in the presence of functionalized substrates, such as ester and alcohol, and explained the nature of deactivation by coordination of functional groups to early d0 metal (tungsten) in its highest oxidation state (+6). To tackle the problem, we prepared a variety of non-coordinating substrates bearing heteroatoms (such as silicon and iron) and found no activity in the metathesis reaction. Instead, we discovered disproportionation/synproportionation reaction of alkyl-ferrocenes on WMe5/SiO2-700 catalyst.

In Chapter 3, we developed and implemented a strategy to protect the catalyst active site by modification of the catalyst support with hydrophobic chains. We fully characterized the new materials and proved that hydrophobic chains do not deactivate the catalyst in the metathesis of hydrocarbons.

At the same time, we showed that neither the morphology of support, nor different ratios between the catalyst and protective chains allow for the metathesis of functionalized alkanes.

Chapter 4 was dedicated to finding a suitable substrate for the metathesis of functionalized alkanes to prove the concept of the reaction. We investigated a pyrrole-based family of substrates, considering the lower affinity of a delocalized pair of electrons towards coordination and deactivation of the metathesis catalyst. We showed by solid-state NMR spectroscopy that N-propyl-2,5-dimethylpyrrole does not poison WMe5/SiO2-700 at room temperature; however, no metathesis occurs with N-alkyl-2,5- dimethylpyrroles. Instead, we observed traces of isomerization of substrates. Based on the findings, we prepared a rigid molecule – 9-hexyl-9H-carbazole and successfully metathesized it over WMe5/SiO2-700 with a conversion of 5 %. This result became the first-ever observed metathesis of alkane bearing a functionality. In Chapter 5, we attempted to develop a general strategy and synthesize a universal catalyst for the metathesis of functionalized alkanes. In the first part, we combined and supported on silica late transition metals (which are more tolerant to functional groups) for dehydrogenation/hydrogenation

(iridium pincer hydride) and metathesis (ruthenium Grubbs-Hoveyda 2nd generation) catalysts. After the detailed NMR characterization and proving the structures, we found that Ir-Ru catalytic system is slightly active in metathesis of n-decane, however it is not engaged in the metathesis of functionalized alkanes.

By replacing iridium by early transition metal (Ti), we observed an increase in the the activity of the catalytic system towards metathesis of n-decane 12 times, but the system remained inactive in functionalized alkane metathesis. The second part of the chapter aimed to hide the catalyst inside the mesopores of modified yolk-shell and KCC-1 supports and partly reduce the entry of the pores by large steric groups that would limit the entrance of the functional groups of substrates, but not alkyl chains.

We synthesized yolk-shell, and KCC-1 supports with 4 nm pore width, grafted WMe6 inside the pores and partly reduced the entry by grafted TiNp3 moieties. The obtained catalytic systems were well characterized by NMR spectroscopy, BET analysis, and ICP-OES techniques and despite inactivity in metathesis of functionalized alkanes, the systems proved remarkable activity in metathesis of alkanes.

In general, we should underline the following: 1) the metathesis of functionalized alkanes (as well as the metathesis of alkanes) consists of the three following paths: a) dehydrogenation of a functionalized alkane to a functionalized olefin, b) the metathesis of functionalized olefin and c) the hydrogenation of newly formed functionalized olefins to newly functionalized alkanes. 2) Paths b) and c) are well established and a variety of supported heterogeneous catalysts (e.g., Ru HG-II, Chapter 5, Part 5.2) have been developed in this dissertation. 3) The path a) is the most challenging and needs to be addressed and improved in future research. Once a catalyst that selectively dehydrogenates a functionalized alkane by C-C bond is discovered, the general solution for the metathesis of functionalized alkanes will be developed by a combination of that catalyst with the existing Grubbs catalyst supported on the same silica support.

6.2. Future outlook

In our results, we discovered the first example of the metathesis of the functionalized alkane – for that reaction we used 9-hexyl-9H-carbazole as a reactant and WMe5/SiO2-700 as a catalyst and that discovery opened a new field for research. At the same time, we demonstrated a variety of strategies that have been used in order to tackle the problem and clearly demonstrated the ultimate difficulty of the process.

It is worth noting that any improvement in conversion of the substrate, TON of catalyst, discovery of other suitable substrates or new catalysts for the reaction will be breakthroughs in the field. We genuinely believe that scientists from different fields, homogeneous and heterogeneous catalysis and organic and organometallic chemistries, will continue to work on, develop, and improve the field of metathesis of functionalized alkanes. Based on our findings, late transition metals supported on silica are promising candidates for the metathesis reaction. It is likely that a different heterogeneous iridium- based catalyst will be developed with more accessible Ir-hydride groups for better dehydrogenation activity; once combined with supported Ru-systems, the metathesis of functionalized alkanes will be developed for a broader area of substrates and with greater activity. Ultimately, this will lead to the development of robust catalytic systems.

APPENDICES

Appendix A. Effect of support on hydro-metathesis of propene: A comparative study

of W(CH3)6 anchored to silica vs. silica-alumina

The work presented in Appendix A is an additional research project conducted in our laboratories and dedicated to exploring the properties of W(CH3)6 depending on the support of grafting with respect to the hydro-metathesis of propene as a model reaction. The work has been published: Tretiakov, M.;

Samantaray, M. K.; Saidi, A.; Basset, J.-M., Effect of support on hydro-metathesis of propene: A comparative study of W(CH3)6 anchored to silica vs. silica-alumina. J. Organomet. Chem., 2018, 863, 102-

108 (DOI: https://doi.org/10.1016/j.jorganchem.2018.03.018).

1. Introduction

It is well-known that alkanes are the major constituents of petroleum.1 As the global demand for petroleum products is increasing and petroleum reserves are decreasing day by day, there is a growing research interest in the transformation of low molecular weight hydrocarbon feedstock into petroleum range alkanes.2-5 There are two main reactions for conversion of low molecular weight carbon feedstock to petroleum range alkanes: F-T process and alkane metathesis.2,5-11 Though F-T process has wide industrial applications, it suffers from high reaction temperature as well as the formation of wax range alkanes, whereas alkane metathesis suffers from lower reactivity.5,12,13

After the discovery of alkane metathesis in 1997 by a single site Ta-H/silica catalyst, our group reported several catalytic systems for the improvement of conversion as well as TON for this reaction.2,14-16 From the reaction mechanism, we observed that the main steps for the metathesis reaction are the formation of olefins and hydrogen resulting from the C-H bond activation of the paraffin followed by olefin metathesis.16,17 Alkane metathesis is a thermoneutral reaction, meaning that for the reaction to happen, practically no energy is required, but modeling has shown that to form an olefin, which is an intermediate in alkane metathesis reaction, a higher amount of energy is required to overcome this kinetic energy barrier.18,19

Based on the above concepts we believe that by using an olefin in place of an alkane with an extra amount of hydrogen we will be able to carry out the metathesis reaction which is called a “hydro- metathesis” reaction as hydrogen and olefin are used as starting materials with the catalyst. In other words, the hydro-metathesis represents the last step of alkane metathesis. However, in order to be economical, the olefin must be cheap, though propylene is more expensive than n-butene, still we took it as a model molecule.

Another aspect of using olefin for hydro-metathesis reaction is that we expected that we could increase conversion as well as TON in this particular reaction compared to alkane metathesis reaction where the reactivity of alkanes towards the catalyst is comparatively slow, even if we have already considerably increased the TON of alkane metathesis.14,20

Our group first reported the hydro-metathesis reaction in 2011 using Ta-H supported on KCC-121 where we got an impressive result of the conversion of propene to higher and lower alkanes (C2, C4, C5) with a very high TON (786) as compared to the transformation of propane using Ta-H on silica TON (60).2,22

Recently we reported the liquid phase hydro-metathesis reaction of 1-decene with various silica- supported well-defined catalysts with good conversion and TONs.23 With these exciting results, we thought to use W/silica and W/silica-alumina as these new generation catalysts were proven to be very efficient in converting alkanes to their lower and higher homologs.14,20

Herein, we are reporting the hydro-metathesis of propene using well-defined W(CH3)6 supported on silica (1) and silica-alumina (2) in continuous flow reaction conditions.

Figure 1: Well-defined silica supported W-methyl 1 and silica-alumina supported W-methyl 2

2. Results and discussion 2.1. Evolution of hydro-metathesis reaction W(CH3)6 supported silica and silica-alumina catalysts and their application in alkane metathesis reaction were already reported by our group.14,20 During the alkane metathesis reaction, we observed that silica and silica-alumina supported catalysts are very efficient compared to Ta-H supported catalyst for alkane metathesis reaction.22,24,25 Note that W-based catalysts are better metathesis catalysts than the Ta catalysts. The literature data reported above directed us to use an oxide-supported W in hydro- metathesis reaction as olefin metathesis is part of the hydro-metathesis. We used W/silica as well as

W/silica-alumina as we observed that W/silica-alumina is more stable than W/silica and due to the expected increase in acidity on the tungsten center the conversion and TON would be expected to be much better compared to W/silica and Ta/silica.2,20,22

In a typical experiment, 106 mg of silica-supported W catalyst 1 (15 micromoles W) was loaded in a continuous flow reactor, and a mixture of propene 6 mL/min and hydrogen 6 mL/min in the presence of argon was passed through the catalytic bed at 150 oC for 24 hours. The conversion of the reactant was observed every 36 minutes by analyzing the products through gas chromatography (GC).

Initially, we chose catalyst 1, and we observed that the catalyst was stable for 24 hours with the maximum conversion being observed during the initial 6.5 hours of the reaction. The overall conversion of 51 % and a TON of 3532 were achieved at our contact time. To eliminate the percentage of hydrogenation of propene to propane, which is competing with the hydro-metathesis, we subtracted the propane concentration (propane formation is a logical competing reaction) and the concentration of the olefin (coming from olefin metathesis). We observed 25 % conversion and 1635 TON (only higher and lower alkanes) for propene hydro-metathesis, Fig. 2 and 3.

Figure 2: 2A and 2C represent total conversion (Olefins + Alkanes, red line) and corresponding TON (blue line), 2B and 2D represent conversion of propene to only alkanes except propane (red line) and TON (blue line) in hydro-metathesis reaction of propene (using propene to hydrogen ratio 1:1 for 2A and 2B and 1:2 ratio for 2C and 2D) in a continuous flow reactor at 150 oC in presence of catalyst precursor 1 (106 mg), hydrogen and argon

During the reaction, along with alkanes, we also observed a considerable amount of mainly C2, C4, and

C5 olefins (Fig. 3A). We envisioned that we could reduce the formation of olefin only if we could increase the partial pressure of hydrogen. To prove our point, we thought to use a propene to hydrogen ratio of

1:1 to 1:2 and eventually 1:3 and observe the effect of hydrogen.

With this concept, we used 1:2 ratio of propene to hydrogen. As expected, we observed the increase of overall TON to 4328 and TON of only alkanes to 2104 with the decrease of formation of olefins (Fig. 3C and 3D). Furthermore, we thought to increase the propene to hydrogen ratio to 1:3. At the end of the reaction, we observed that the TON was almost equal to that of a 1:2 ratio with the formation of hydrogenolysis products along with other alkanes (SI Fig. S1-S4) which suggests that 1:2 ratio of propene to hydrogen is suitable for our catalyst for hydro-metathesis reaction in our conditions. 30 30

Propene:H2=1:1 Propene:H2=1:2 25 25 3A 3C 20 0.30 20 0.30 0.25 0.25 0.20 0.20 0.15 0.15

mmol mmol 15 0.10 15 0.10

0.05 mmol mmol 0.05 0.00 0.00

CH4

C7H16

C7H14

C8H18

C8H16

10 C9H20 10

C6H12

C7H16

C7H14

C8H18

C8H16 C9H20

iso-C4H10

5 5

0 0 CH4

CH4

C2H6

C2H4

C3H8 C4H8

C2H6

C2H4

C3H8

C4H8

C5H12

C5H10

C6H14

C6H12

C7H16

C7H14

C8H18

C8H16 C9H20

C5H12

C5H10

C6H14

C6H12

C7H16

C7H14

C8H18

C8H16

C9H20

C10H22 n-C4H10

n-C4H10 iso-C4H10

iso-C4H10 30 Product distribution 30 Product distribution

25 25 Propene:H2=1:1 Propene:H2=1:2

0.30 20 0.30 20 3B 3D 0.25 0.25 0.20 0.20 0.15 0.15 mmol 15 mmol 15 0.10 0.10

mmol 0.05 mmol 0.05 0.00 0.00

CH4 10

C7H16

C8H18 C9H20

C7H16

C8H18 10 C9H20

C10H22

iso-C4H10

5 5

0 0 CH4

CH4 C2H6

C2H6

C5H12

C6H14

C7H16

C8H18 C9H20

C5H12

C6H14

C7H16

C8H18

C9H20

C10H22 n-C4H10

n-C4H10 iso-C4H10

iso-C4H10 Alkanes distribution Alkanes distribution

Figure 3: 3A and 3C represent total distribution of products [olefins ( ) alkanes ( ) and propane ( )] when propene to hydrogen ratio 1:1 for 3A and 1:2 for 3C. 3B and 3D represent only alkanes ( ) except propane ( ) when propene to hydrogen 1:1 for 3B and 1:2 for 3D in a continuous flow reactor for hydro-metathesis reaction catalyzed by catalyst precursor 1

We previously showed that W(CH3)6 grafted on silica-alumina catalyst is a much better catalyst for

20 alkane metathesis reaction than the silica counterpart, therefore, we thought to move from W(CH3)6 supported silica catalyst to silica-alumina catalyst. Because the results above showed that a propene to hydrogen 1:2 ratio is better, we chose to use a 1:1 ratio along with a 1:2 ratio of propene to hydrogen for hydro-metathesis reaction.

Figure 4: 4A and 4C represent total conversion (Olefins + Alkanes, red line) and corresponding TON (blue line), 4B and 4D represent conversion of propene to only alkanes except propane (red line) and TON (blue line) in hydro- metathesis reaction of propene (using propene to hydrogen ratio 1:1 for 4A and 4B and 1:2 ratio for 4C and 4D) in a continuous flow reactor at 150 oC in presence of catalyst precursor 2 (75 mg), hydrogen and argon

In a typical reaction, 75 mg of W/silica-alumina (15 micromoles W) catalyst 2 were loaded in a continuous flow reactor, propene 6 mL/min and hydrogen 6 mL/min in the presence of argon were passed on the catalyst bed at 150 oC for 24 hours. The overall conversion of 57 % with a TON of 6402 was obtained. After removing the propane and olefins, we got around 29 % conversion and 3279 TON

(only higher and lower alkanes). Additionally, a 1:2 propene to hydrogen ratio was also tested and, as expected, we observed a higher overall TON of 10736, which contain olefins (except propene), propane and other alkanes, and a TON of 4577 was obtained for only alkanes after excluding olefins and propane from the products. It is worth noting that the results obtained using W/silica-alumina were much better than the results obtained using W/silica and Ta/KCC-1. Comparing the product distribution in both W/silica and W/silica- alumina, we observed that in both cases we could obtain alkanes from C1 to C10 with different quantities.

80 80 70 Propene:H2=1:1 70 Propene:H2=1:2 60 5A 60 5C 0.8 1.4 0.7 1.2 50 0.6 50 0.5 1.0 0.4 0.8

mmol 40 0.3 40 mmol 0.6 0.2 0.4

mmol 0.1 mmol 0.2 0.0 30 30 0.0

CH4 CH4

C6H12

C7H16

C7H14

C8H18

C8H16

C9H20

C10H22

C5H10

C6H14

C6H12

C7H16

C7H14 C8H18

iso-C4H10 iso-C4H10 20 20

10 10

0 0

CH4 CH4

C2H6

C2H4

C3H8

C4H8

C2H6

C2H4

C3H8 C4H8

C5H12

C5H10

C6H14

C6H12

C7H16

C7H14

C8H18

C8H16

C9H20

C5H12

C5H10

C6H14

C6H12

C7H16

C7H14 C8H18

C10H22

n-C4H10 80 n-C4H10

iso-C4H10 80 iso-C4H10 Product distribution Product distribution 70 70 60 Propene:H2=1:1 60 Propene:H2=1:2 0.8 1.4 0.7 1.2 50 0.6 50 1.0 5B 0.5 5D 0.8 0.4

mmol 40 0.3 40 mmol 0.6 0.2 0.4

mmol 0.1 mmol 0.2 30 0.0 30 0.0

CH4 CH4

C7H16

C8H18

C9H20

C6H14

C7H16 C8H18

C10H22

iso-C4H10 iso-C4H10 20 20

10 10

0 0

CH4 CH4

C2H6 C2H6

C5H12

C6H14

C7H16

C8H18

C9H20

C5H12

C6H14

C7H16 C8H18

C10H22

n-C4H10 n-C4H10

iso-C4H10 iso-C4H10 Alkanes distribution Alkanes distribution

Figure 5: 5A and 5C represent total distribution of products [olefins ( ), alkanes ( ) and propane ( ) when propene to hydrogen ratio 1:1 for 5A and 1:2 for 5C. 5B and 5D represent only alkanes ( ) except propane ( ) when propene to hydrogen 1:1 for 5B and 1:2 for 5D in a continuous flow reactor for hydro-metathesis reaction catalyzed by catalyst precursor 2.

In the case of W/silica-alumina, the conversion of propene to higher and lower alkanes was greater, and hence the TON were higher than in the case of W/silica. Both catalysts formed a similar product distribution with the formation of ethane being higher, followed by n-butane, pentane, hexane, heptane, octane, nonane, and decane. The formation of methane, ethane, butane, and pentane is understandable, and it results from the direct addition of hydrogen to olefin metathesis products (Fig.

6). The formation of methane is merely the positive effect of hydrogen on a W-methylidene moiety. 2.2. Mechanistic outlook Interestingly, along with C1 to C5 alkanes, we also observe C6 to C10 alkanes as minor products. Whereas

C1 to C5 alkanes come from the direct metathesis of the starting olefin followed by reduction of the newly formed olefins, higher alkanes are believed to be formed by the competitive cross-metathesis reaction between the newly formed higher olefins resulting in the formation of the higher alkanes after reduction.

Looking at the mechanism (Fig. 6), we could observe that there is very little difference between alkane metathesis and hydro-metathesis reactions.6 In alkane metathesis, the metal-alkyl bond is formed by C-

H bond activation whereas in hydro-metathesis reaction metal-alkyl bond is formed by the insertion of the olefin to a metal hydride bond followed by formation of a metalla-carbene hydride (by α-H elimination). In addition, the mechanism conveys to us that substituents in 1,2-position in the metallacyclobutane intermediate (of the Chauvin mechanism)26 are less favored than the substitution in 1,3-position due to steric reason, which clearly explains why we could observe more ethane and n- butane as compared to methane and other alkanes.26 Furthermore, in the case of branched alkanes, according to the stereo chemical rules of olefin metathesis27, we should observe isobutane rather than isopentane (1,3-di-substituted metallacyclobutane is favored over 1,2-di-substituted metallacyclobutane). We precisely observed that trend in our product distribution curve (Intermediate

4 favored over 5 whereas intermediate 6 favored over 7) and intermediate 8 was more favored over 9.

Figure 6: The proposed mechanism of propene hydro-metathesis using W catalyst

2.3. Conclusions

We employed two well-defined W catalysts for the first time for hydro-metathesis reaction. Our target was to convey a message where lower olefins can be converted to transportation fuel range alkanes. As the literature reports conveyed, W-based catalysts are the better catalysts for olefin metathesis reaction than that of Ta-based catalyst, therefore, we employed W-based catalysts for hydro-metathesis reaction as olefin metathesis reaction is one of the main paths of the hydro-metathesis reaction. As expected, we observed higher range alkanes with very high TON 4577, which is not possible using propane as a reactant. The unprecedented formation of n-decane from propene was observed and opens the way for converting butenes to petroleum range alkanes using hydro-metathesis reaction. We believe this study has much potential in the future for an efficient hydro-metathesis reaction.

3. Experimental part 3.1. General All experiments were carried out using standard Schlenk and glove-box techniques under an inert argon atmosphere. The syntheses and the treatments of the surface species were carried out using high

-5 vacuum lines (< 10 mbar) and glove-box techniques. Pentane was distilled from a Na/K alloy under N2 and dichloromethane from CaH2. Both solvents were degassed through freeze-pump-thaw cycles. SiO2-

o Al2O3-500 was prepared by calcination at 400 C in the presence of air followed by dehydroxylation at

o -5 2 500 C under high vacuum (< 10 mbar) for 24 h containing 0.80-0.90 OH/nm . SiO2-700 prepared from

Aerosil silica from Degussa (specific area of 200 m2/g) was partly dehydroxylated at 700 °C under high vacuum (< 10-5 mbar) for 24 h to give a white solid having a specific surface area of 190 m2/g and containing around 0.5-0.7 OH/nm2. Propylene (99.99 %), hydrogen (99.9999 %), argon (99.999 %) and a calibration mixture (methane, ethane, ethylene, propane, propylene, iso-butane, n-butane, trans-2- butene, 1-butene, iso-butene, cis-2-butene – each component 5000 ppm) gases were purchased from

Specialty Gases Center of Abdullah Hashim Industrial Gases & Equipment Co. Ltd. (Saudi Arabia). A propylene cylinder was connected successively to Agilent Gas Clean Moisture and Agilent Gas Clean

Oxygen filters prior to the mass flow controller of the reactor. Argon and hydrogen cylinders were connected to Thermo Scientific Triple filters (oxygen, moisture, hydrocarbons) prior to the mass flow controllers of the reactor. W(CH3)6 (SI Fig. S5 and S7) and supported pre-catalysts 1 and 2 were prepared according to literature procedures (SI Fig. S8 and S9) [14, 20]. IR spectra were recorded on a Nicolet

6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF2 windows (SI Fig. S8 and S9). The IR samples were prepared under argon within a glove-box. Typically, 64 scans were accumulated for each spectrum (resolution 4 cm−1). Elemental analyses were performed at Mikroanalytisches Labor Pascher

(Germany) and Core Lab ACL KAUST.

3.2. GC analysis The gas products were analyzed every 36 min by on-line gas chromatography using a Varian 450-GC system with a flame-ionization detector (FID) for analysis of hydrocarbons. Column: GS-GASPRO; 30 m length, 0.32 mm diameter (Agilent J&W GC Columns). Method: Front injector setpoint 220 °C, oven: 40

°C hold for 2 minutes followed by 10 °C/min rate up to 220 °C hold for 10 minutes. TCD heater set point

175 °C, filament temperature 225 °C. FID setpoint 250 °C. Split ratio 20. GC was calibrated, and quantification of the products was performed using calibration mixture. Retention times for each component of the calibration mixture were established based on at least 3 independent runs and were used for the calibration curve. The analysis of higher molecular weight products (from n-pentane to n- decane) was confirmed using GC-MS.

3.3. GC-MS analysis For the GC-MS analysis, gaseous products of the reaction were collected to LabPure FEP Gas Bag 6x6

Septum connected to the vent of the reactor and analyzed at KAUST Core Lab.

3.4. Hydro-metathesis reaction Catalytic propylene hydro-metathesis was performed on a micropilot (PID Eng & Tech) equipped with a stainless steel reactor at atmospheric pressure. The catalyst powder was placed in the reactor supported by preliminary dried quartz wool. Conversions were calculated based on carbon mass balance.

3.4.1 Reaction A (silica-supported catalyst, 1:1 ratio of reactants)

[W(Me)6]/SiO2-700 (106 mg , loading 2.60 % of W based on ICP-OES, 15 micromol W) was charged in a glove-box, inside a 0.5-inch diameter stainless steel reactor fitted with a four-channel isolating valve.

After connection to the rack, all the tubing was purged bypassing the reactor by a mixture of helium (80 ml/min), argon (30 mL/min) and hydrogen (20 mL/min) flow for 30 minutes, with argon and hydrogen flow for 20 minutes and with the reaction mixture – 6 mL/min of propylene, 6 mL/min of hydrogen and argon (10 vol %) for an additional 10 minutes. Then, the four-channel valve was switched on, and the reactor was heated at 150 °C and 1 atm. The gas products were analyzed online with a GC. 3.4.2 Reaction B (silica-supported catalyst, 1:2 ratio of reactants)

Reaction B (1:2 ratio of reactants): [W(Me)6]/SiO2-700 (106 mg , loading 2.60 % of W based on ICP-OES,

15 micromol W) was charged in a glove-box, inside a 0.5-inch diameter stainless steel reactor fitted with a four-channel isolating valve. After connection to the rack, all tubing was purged bypassing the reactor by a mixture of helium (80 ml/min), argon (30 mL/min) and hydrogen (20 mL/min) flow for 30 minutes, with argon and hydrogen flow for 20 minutes and with the reaction mixture – 6 mL/min of propylene,

12 mL/min of hydrogen and argon (10 vol %) for an additional 10 minutes. Then, the four-channel valve was switched on, and the reactor was heated at 150 °C and 1 atm. The gas products were analyzed online with a GC.

3.4.3 Reactions C and D (silica-alumina-supported catalyst)

Reaction C (1:1 ratio of reactants) and D (1:2 ratio of reactants): [W(Me)6]/SiO2-Al2O3-500 were done with the same procedure with 75 mg of catalyst (loading 3.65 % of W based on ICP-OES) having the same amount of micromoles of W catalyst in the reactor.

3.4.4 Reactions with a 1:3 ratio of reactants Reactions with a 1:3 ratio of reactants (6 mL/min of propylene, 18 mL/min of hydrogen and argon 10 vol %) were done with the same procedure with 106 mg (15 micromol W) of [W(Me)6]/SiO2-700 and 75 mg of [W(Me)6]/SiO2-Al2O3-500 (15 micromol W).

Conversion (%) TON 100

5000

80 4000

60 3000

TON

40 2000

Conversion (%)

20 1000

0 0 100 200 300 400 500 Time (Min)

Figure S1: Total conversion (red line) and corresponding turnover numbers (blue lines) were obtained during the hydro-metathesis of propene with a propene to hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon.

Conversion (%) TON 2200 40 2000

35 1800

30 1600 1400 25 1200 20

1000 TON

15 800

Conversion (%) 600 10 400 5 200

0 0 100 200 300 400 500 Time (Min)

Figure S2: Conversion (red line) and corresponding turnover numbers (blue lines) of only alkanes (except propane) were obtained during the hydro-metathesis of propene with propene to a hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon.

40

35

30

0.20

25 0.15

0.10

20 mmol 0.05

mmol

15 0.00

C5H10

C6H14

C6H12

C7H16

C7H14

C8H18 10

5

0

CH4

C2H6

C2H4

C3H8

C4H8

C5H12

C5H10

C6H14

C6H12

C7H16

C7H14

C8H18

n-C4H10

iso-C4H10 Product distribution

Figure S3: Representation of total distribution of products [olefins ( ) alkanes ( ) and propane ( )] when the propene to hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon.

40

35

30 0.20

25 0.15

0.10 20 mmol 0.05

mmol 0.00 15

C6H14

C7H16

C8H18 10

5

0

CH4

C2H6

C5H12

C6H14

C7H16

C8H18

n-C4H10

iso-C4H10

Alkanes distribution

Figure S4: Distribution of products (only alkanes except for propane) was shown during the hydro-metathesis of propene with a propene to hydrogen ratio of 1:3 catalyzed by catalyst precursor 1 (106 mg) in a continuous flow reactor at 150 oC in the presence of argon.

4. References

1. Pelletier, J. D. A.; Basset, J.-M., Catalysis by Design: Well-Defined Single-Site Heterogeneous Catalysts. Acc. Chem. Res., 2016, 49, 4, 664-677. 2. Vidal, V.; Theolier, A.; Thivolle-Cazat, J.; Basset, J.-M., Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides. Science, 1997, 276, 5309, 99-102. 3. Coperet, C.; Comas-Vives, A.; Conley, M. P.; Estes, D. P.; Fedorov, A.; Mougel, V.; Nagae, H.; Nunez-Zarur, F.; Zhizhko, P. A., Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities. Chem. Rev., 2016, 116, 2, 323-421. 4. Labinger, J. A.; Bercaw, J. E.; Understanding and exploiting C–H bond activation. Nature, 2002, 417, 507-514. 5. Basset, J.-M.; Coperet, C.; Soulivong, D.; Taoufik, M.; Thivolle-Cazat, J., Metathesis of Alkanes and Related Reactions. Acc. Chem. Res., 2010, 43, 2, 323-334. 6. Basset, J.-M.; Coperet, C.; Lefort, L.; Maunders, B. M.; Maury, O.; Le Roux, E.; Saggio, G.; Soignier, S.; Soulivong, D.; Sunley, G. J.; Taoufik, M.; Thivolle-Cazat, J., Primary Products and Mechanistic Considerations in Alkane Metathesis. J. Am. Chem. Soc., 2005, 127, 24, 8604-8605. 7. Samantaray, M. K.; Dey, R.; Kavitake, S.; Abou-Hamad, E.; Bendjeriou-Sedjerari, A.; Hamieh, A.; Basset, J.-M., Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane. J. Am. Chem. Soc., 2016, 138, 27, 8595-8602. 8. Samantaray, M. K.; Kavitake, S.; Morlanes, N.; Abou-Hamad, E.; Hamieh, A.; Dey, R.; Basset, J.-M., Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane. J. Am. Chem. Soc., 2017, 139, 9, 3522-3527. 9. Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M., Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis. Science, 2006, 312, 5771, 257-261. 10. Ahuja, R.; Kundu, S.; Goldman, A. S.; Brookhart, M.; Vicente, B. C.; Scott, S. L., Catalytic ring expansion, contraction, and metathesis-polymerization of cycloalkanes. Chem. Commun., 2008, 0, 253-255. 11. Huang, Z.; Rolfe, E.; Carson, E. C.; Brookhart, M.; Goldman, A. S.; El-Khalafy, S. H.; MacArthur, A. H. R., Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis. Adv. Synth. Catal., 2010, 352, 1, 125-135. 12. Coperet, C.; Maury, O.; Thivolle-Cazat, J.; Basset, J.-M., σ‐Bond Metathesis of Alkanes on a Silica‐Supported Tantalum(V) Alkyl Alkylidene Complex: First Evidence for Alkane Cross‐Metathesis. Angew. Chem. Int. Ed., 2001, 40, 12, 2331-2334. 13. Coperet, C.; Chabanas, M.; Saint-Arroman, R. P.; Basset, J.-M., Homogeneous and Heterogeneous Catalysis: Bridging the Gap through Surface Organometallic Chemistry. Angew. Chem. Int. Ed., 2003, 42, 2, 156-181. 14. Samantaray, M. K.; Callens, E.; Abou-Hamad, E.; Rossini, A. J.; Widdifield, C. M.; Dey, R.; Emsley, L.; Basset, J.- M., WMe6 Tamed by Silica: ≡Si–O–WMe5 as an Efficient, Well-Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W–Methyl/Methylidyne Species. J. Am. Chem. Soc., 2014, 136, 3, 1054-1061. 15. Chen, Y.; Abou-Hamad, E.; Hamieh, A.; Hamzaoui, B.; Emsley, L.; Basset, J.-M., Alkane Metathesis with the Tantalum Methylidene [(≡SiO)Ta(═CH2)Me2]/[(≡SiO)2Ta(═CH2)Me] Generated from Well-Defined Surface V Organometallic Complex [(≡SiO)Ta Me4]. J. Am. Chem. Soc., 2015, 137, 2, 588-591. 16. Riache, N.; Callens, E.; Samantaray, M. K.; Kharbatia, N. M.; Atiqullah, M.; Basset, J.-M., Corrigendum: Cyclooctane Metathesis Catalyzed by Silica‐Supported Tungsten Pentamethyl [(≡SiO)W(Me)5]: Distribution of Macrocyclic Alkanes. Chem. Eur. J., 2015, 21, 24, 8656-8656. 17. Soulivong, D.; Norsic, S.; Taoufik, M.; Coperet, C.; Thivolle-Cazat, J.; Chakka, S.; Basset, J.-M., Non-Oxidative Coupling Reaction of Methane to Ethane and Hydrogen Catalyzed by the Silica-Supported Tantalum Hydride: (≡SiO)2Ta−H. J. Am. Chem. Soc., 2008, 130, 15, 5044-5045. 18. Basset, J.-M.; Coperet, C.; Soulivong, D.; Taoufik, M.; Thivolle-Cazat, J., From Olefin to Alkane Metathesis: A Historical Point of View. Angew. Chem. Int. Ed., 2006, 45, 37, 6082-6085. 19. Sautet, P.; Delbecq, F., Catalysis and Surface Organometallic Chemistry: A View from Theory and Simulations. Chem. Rev., 2010, 110, 3, 1788-1806. 20. Samantaray, M. K.; Dey, R.; Abou-Hamad, E.; Hamieh, A.; Basset, J.-M., Effect of Support on Metathesis of n‐ Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica–Alumina. Chem. Eur. J., 2015, 21, 16, 6100-6106. 21. Polshettiwar, V.; Thivolle-Cazat, J.; Taoufik, M.; Stoffelbach, F.; Norsic, S.; Basset, J.-M., “Hydro‐metathesis” of Olefins: A Catalytic Reaction Using a Bifunctional Single‐Site Tantalum Hydride Catalyst Supported on Fibrous Silica (KCC‐1) Nanospheres. Angew. Chem. Int. Ed., 2011, 50, 12, 2747-2751. 22. Le Roux, E.; Taoufik, M.; Coperet, C.; de Mallmann, A.; Thivolle-Cazat, J.; Basset, J.-M.; Maunders, B. M.; Sunley, G. J., Development of Tungsten‐Based Heterogeneous Alkane Metathesis Catalysts Through a Structure– Activity Relationship. Angew. Chem. Int. Ed., 2005, 44, 41, 6755-6758. 23. Saidi, A.; Samantaray, M. K.; Tretiakov, M.; Kavitake, S.; Basset, J.-M., Understanding the Hydro‐Metathesis Reaction of 1‐Decene By Using Well‐Defined Silica Supported W, Mo, Ta Carbene/Carbyne Complexes. Chem. Cat. Chem., 2017, 10, 8, 1912-1917. 24. Riache, N.; Callens, E.; Espinas, J.; Dery, A.; Samantaray, M. K.; Dey, R.; Basset, J.-M.; Striking difference between alkane and olefin metathesis using the well-defined precursor [≡Si–O–WMe5]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride. Catal. Sci. Technol., 2015, 5, 280-285. 25. Soignier, S.; Taoufik, M.; Le Roux, E.; Saggio, G.; Dablemont, C.; Baudouin, A.; Lefebvre, F.; de Mallmann, A.; Thivolle-Cazat, J.; Basset, J.-M.; Sunley, G.; Maunders, B. M., Tantalum Hydrides Supported on MCM-41 Mesoporous Silica: Activation of Methane and Thermal Evolution of the Tantalum-Methyl Species. Organometallics, 2006, 25, 7, 1569-1577. 26. Herisson, J. L.; Chauvin, Y.; Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques. Macromol. Chem. Phys., 1971, 141, 1, 161-176. 27. Leconte, M.; Basset, J.-M., Stereoselectivity of metathesis of various acyclic olefins with chromium-, molybdenum-, and tungsten-based catalysts. J. Am. Chem. Soc., 1979, 101, 24, 7296-7302. Appendix B. Polymerization of ethylene catalyzed by Ziegler-Natta catalysts. Comparison of homogeneous vs supported catalysts on KCC1-500

and SiO2-500

The purpose of this work is to understand the effect of carrier/support in the polymerization of ethylene by Ziegler-Natta catalysts.

For this study, we used:

1) Carriers: SiO2-500 and KCC1-500

2) Support: MgCl2·(THF)2 complex

3) Titanium source: TiCl4·(THF)2 complex

4) Activator: Al(Octyl)3

A general procedure for the preparation of Heterogeneous Ziegler-Natta catalysts:

SiO2-500 (or KCC1-500) was treated with a mixture of MgCl2·(THF)2 and TiCl4·(THF)2 complexes

(0.1:0.1:1 = Mg:Ti:Silica by weight, 1.8:1 = TiMg:OH by mmol) in THF at RT for 25 min forming SiO2/TiMg precursor. The precursor was then activated with Al(Octyl)3 (10:1 =

Al:Ti by mmol) forming an active catalyst SiO2/TiMgAl, which was used for ethylene polymerization immediately after preparation. The obtained materials are as follows: 100 mg of SiO2-500/TiMgAl contains 22.6 µmol Ti, 29.6 µmol Mg, 226.1 µmol Al. 100 mg of

KCC1-500/TiMgAl contains 24.65 µmol Ti, 27.98 µmol Mg, 246.5 µmol Al. For the homogeneous catalyst 8.2 mg TiCl4*(THF)2, 6.7 mg MgCl2*(THF)2 and 515 µL Al(Octyl)3 (25 wt% in hexane) were taken.

309

1. A general procedure for the polymerization

Sample A) 109 mg of SiO2-500/TiMg precursor was placed in a vial with a stirring bar, 10 mL of pentane was added, and the mixture was stirred at 700 rpm. After that 515 µL Al(Octyl)3

(25 wt% in hexane) was added, the vial was tightly closed, and the mixture was stirred at

RT for 30 minutes. The initial color of the solution turned dark after a few minutes of stirring.

After 30 minutes of stirring, the vial was taken out of the glove-box and inserted through the septum to a preliminary nitrogen-flushed needle of the high-throughput polymerization apparatus under the flow of nitrogen (the apparatus was preliminarily heated to 309 K). The apparatus was tightly closed; the vial was evacuated in a vacuum, and refilled with ethylene (10 bar). The mixture was stirred for 30 minutes and the system was evacuated in vacuum and flushed with nitrogen (the vacuum-nitrogen cycle was repeated 3 times before the apparatus was opened). The vial containing polyethylene was removed and the PE was separated and dried.

Sample B) Sample B (KCC-1-500) was prepared following the same procedure as for Sample

A), with 100 mg of KCC-1-500/TiMg precursor.

Sample C) Sample C (Homogeneous) was prepared following the same procedure as for

Sample A) with 8.2 mg of TiCl4·(THF)2 complex and 6.7 mg of MgCl2·(THF)2 complex.

1.30 g of PE from sample A, 1.38 g of PE from sample B and 1.04 g of PE was obtained from sample C. 310

2. Purification of polyethylene The polyethylene was purified by first dissolving it in 1,2,4-trichlorobenzene at 150 oC followed by precipitation in MeOH. The precipitated PE was collected by filtration and dried. The PE may have still contained silica particles. To remove silica from PE, the polymer was treated with 48 % HF for 2 days at RT under vigorous stirring. The HF was removed by syringe, PE was washed with water (3 times), DCM (3 times), and MeOH (3 times). Finally, the PE was dried in high-vacuum line and analyzed.

Characterization of the pre-catalyst:

Reference:1

Figure B1: FT-IR of SiO2/TiMg (2, blue) compared with those of bare SiO2 (grey)

311

Sample A:

4000 3500 3000 2500 2000 1500 1000 500

Figure B2: FT-IR of SiO2-500/TiMg (red) compared with those of bare SiO2-500 (blue)

Sample B:

4000 3500 3000 2500 2000 1500 1000 500

Figure B3: FT-IR of KCC1-500/TiMg (red) compared with those of bare KCC1-500 (blue) 312

3. Characterization of the PEs obtained

Figure B4: Differential Scanning Calorimetry. Black – SiO2-500/PE (Crystallinity 16.94 %, Integral -147.37 mJ, Onset 74.77 °C, Peak 109.59 °C, Endset 126.17 °C), Blue – KCC1- 500/PE (Crystallinity 18.33 %, Integral -85.91 mJ, Onset 108.10 °C, Peak 123.74 °C, Endset 131.32 °C), red – Homo/PE (Crystallinity 31.02 %, Integral -268.15 mJ, Onset 116.12 °C, Peak 125.98 °C, Endset 132.51 °C)

313

120

100

80

60 HOMO/PE

40 Weight Weight (%) Loss

20

0 30 80 130 180 230 280 330 380 430 480 530 580 630 Temperature (°C)

100

80 KCC-1 /PE 60 -500

40

20

Weight Weight (%) Loss 0 30 80 130 180 230 280 330 380 430 480 530 580 630 Temeparture (°C)

110 100 90 80 70 60 50 SiO /PE 40 2-500 30 20 Weight Weight (%) loss 10 0 30 80 130 180 230 280 330 380 430 480 530 580 630 Temperature (°C)

Figure B5: Thermogravimetric analysis of PE. During TGA, HOMO/PE, SiO2-500/PE, KCC-1-500/PE (16 ° mg of each sample) were heated at 2 C/min from 35 to 120 °C, in N2 atmosphere and was stabilized for 1 hour. After that, flow was changed to oxygen and the sample was heated to 600 °C.

314

Table A: PE combustion. Ti (start of polymer combustion), T50 (50% combustion of polymer), Tf (complete combustion of polymer). 0 Sample Ti T Tf ( C) 0 0 ( C) 50%( C) HOMO/PE 374 425 475

KCC-1-500/PE 383 440 502

SiO2-500/PE 382 440 487

315

Figure B6: 13C solid-state NMR analysis of PE

Figure B7: 13C liquid-state NMR analysis of PE 316

Figure B8: GPC analysis of PE

In conclusion, no structural difference of PEs was found. Based on NMR analysis, the PEs obtained represent linear PEs with no branches and relatively narrow PDIs. We decided to decrease the high Mw of the PEs obtained by trying to synthesize the PEs using double the amount of catalyst (Polymerization2) and lower ethylene pressure (Polymerization 3).

Polymerization 2:

As pre-catalysts, 218 mg of SiO2-500/TiMg precursor or 200 mg of KCC-1-500/TiMg precursor were chosen followed by the addition of 1030 µL of Al(Octyl)3 25 wt% in hexane. For the preparation of homogeneous catalyst 16.5 mg TiCl4·(THF)2, 13.4 mg MgCl2·(THF)2 and

1030 µL Al(Octyl)3 (25 wt% in hexane) were used. The procedure is the same as

Polymerization 1. As a result, 1.063 g of KCC-1-500/PE, 1.035 g of SiO2-500/PE and 0.135 g of

HOMO/PE were obtained. 317

Characterization of the PEs obtained:

In the DSC, SiO2-500/PE shows crystallinity value of 18.37 % (16.94% in polymerization 1),

Integral -75.90 mJ, Onset 104.16 °C, Peak 121.96 °C (109.59 °C in polymerization 1),

Endset 128.52 °C. KCC1-500/PE shows crystallinity value of 23.91 % (18.33 % in polymerization 1), Integral -240.27 mJ, Onset 109.59 °C, Peak 124.71 °C (123.74 °C in polymerization 1), Endset 132.49 °C. Homo/PE shows crystallinity value of 33.21% (31.02

% in polymerization 1), Integral -156.67 mJ, Onset 106.94 °C, Peak 120.06 °C (125.98 °C in polymerization 1), Endset 132.51 °C.

Figure B9: GPC analysis of PE (Polymerization 2)

318

Polymerization 3:

The procedure is the same as Polymerization 1. The pressure of ethylene was 2.5 bar. As a result, 0.316 g of KCC-1-500/PE, 0.310 g of SiO2-500/PE and 0.043 g of HOMO/PE were obtained.

Characterization of the PEs obtained:

In the DSC, SiO2-500/PE shows crystallinity value of 2.22 % (16.94% in polymerization 1),

Integral -13.83 mJ, Onset 64.67 °C, Peak 99.46 °C (109.59 °C in polymerization 1), Endset

116.37 °C. KCC-1-500/PE shows crystallinity value of 9.48 % (18.33 % in polymerization 1),

Integral -45.56 mJ, Onset 101.67 °C, Peak 120.10 °C (123.74 °C in polymerization 1),

Endset 133.68 °C. Homo/PE shows crystallinity value of 28.72 % (31.02 % in polymerization 1), Integral -126.24 mJ, Onset 108.03 °C, Peak 121.89 °C (125.98 °C in polymerization 1), Endset 128.73 °C.

Figure B10: GPC analysis of PE (Polymerization 3)