HETEROGENEOUS CATALYSIS IN PROTODECARBOXYLATION AND C-C BOND FORMATION TOY XIU YI (B Sc (Hons.), National University of Singapore) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2013 DECLARATION I hereby declare that this thesis is my original work and it has been written by me in its entirety, under the supervision of A/P Stephan Jaenicke, Chemistry Department, National University of Singapore, between 01/08/2009 and 01/08/2013 I have duly acknowledged all sources of information which have been used in the thesis This thesis has also not been submitted for any degree in any university previously The content of the thesis has been partly published in: (1) Xiu Yi Toy, Irwan Iskandar Bin Roslan, Gaik Khuan Chuah and Stephan Jaenicke, Catal Sci Technol., 2013, DOI: 10.1039/c3cy00580a Toy  Xiu  Yi   Name   19/11/2013   Signature II     Date       ACKNOWLEDGEMENT This dissertation would not have been possible without the guidance and the help of several individuals who extended their valuable assistance in the preparation and completion of this study The years of Ph.D research study have been a truly memorable learning journey First and foremost, I would like to express my sincere appreciation to my supervisor Associate Professor Dr Stephan Jaenicke for giving me the opportunity to work on the project in his research lab His stimulating suggestions, encouragement and immense knowledge helped me greatly throughout the project I would also like to thank Associate Professor Dr Chuah Gaik Khuan for her help and invaluable advices throughout my research and writing of this thesis I truly appreciate all time she has taken to read and correct my writings and manuscript My sincere thanks also goes to Madam Toh Soh Lian, Madam Tan Lay San and Miss Sabrina Ou from Applied Chemistry lab for all the help they have rendered during my work This thesis would not have been possible without the help and support from my fellow lab mates: Miss Nie Yuntong, Miss Ng Jeck Fei, Mr Do Dong Minh, Mr Fan Ao, Miss Liu Huihui, Mr Wang Jie, Miss Gao Yanxiu, Miss Han Aijuan, Mr Goh Sook Jin, Mr Sun Jiulong, Mr Irwan Iskandar Bin Roslan and Miss Angela Chian I am also grateful to my parents and my family for their unconditional love, encouragement and motivation I would like to give my special thanks to my fiance for believing in me and giving me the moral support when it was most   III         required Last but not least, I am indebted to the National University of Singapore for providing me with a valuable research scholarship and for funding the project   IV           TABLE OF CONTENTS PAGE Declaration II Acknowledgement III Table of contents V Abstract XI List of tables XII List of figures XV List of schemes XXII List of journal publications and conferences paper XXV PAGE Chapter 1: Introduction 1.1 Supported nanosized transition metal catalysts in fine chemical synthesis 1.1.1 Homogeneous catalysts versus heterogeneous catalysts 1.1.2 Heterogeneous catalysts: Supported metal catalysts 1.1.3 Catalyst preparation methods 12 1.1.3.1 12 1.1.3.2 Co-precipitation 15 1.1.3.3 Deposition-precipitation 15 1.1.3.4 1.2 Impregnation Ion exchange 17 Ag, Cu and Pd nanocatalysts in cross coupling reactions 1.2.1   18 21 Suzuki coupling V         1.2.2 Ullmann reaction 23 1.3 Decarboxylative cross-coupling 26 1.4 Aim and outline of the thesis 32 1.5 References 34 Chapter 2: Experimental- Catalyst characterisation techniques 40 2.1 Powder x-ray diffraction 40 2.1.1 41 2.2 Principles of measurement N2 sorption porosimetry 44 2.2.1 Principles of measurement 45 2.2.1.1 2.3 45 2.2.1.2 2.2.2 Brunauer-Emmett-Teller (BET) Theory Barrett-Joyner-Halenda (BJH) method 47 Sample preparation and data measurement 48 Transmission electron microscopy (TEM) 2.3.1 49 53 2.4.1 2.5 Principles of measurement X-ray photoelectron spectroscopy (XPS) 2.4 49 53 Principles of measurement Inductively coupled spectroscopy (ICP-AES) 2.5.1 2.6 plasma atomic Principles of measurement emission 57 57 Temperature programmed reduction (TPR) 2.6.1 2.7 60 60 Principles of measurement References   62 VI           Chapter 3: Homocoupling of aryl halides using palladiumpoly(ethylene glycol) catalysts 64 3.1 Introduction 64 3.1.1 Transition metal-catalysed coupling reactions 64 3.1.2 Polyethylene glycol as reaction medium 64 3.1.3 Examples of coupling reactions carried out in PEG reaction medium 66 Experimental 67 3.2.1 Typical procedure for homocoupling of aryl bromide 68 3.2.2 Recovery and reuse of the catalyst 68 3.2 3.3 Results and discussion 69 3.3.1 Catalyst testing 69 3.3.2 Recycling of the catalyst 77 3.3.3 Scope of reaction 83 3.3.4 Mechanism and characterisation of the Pd-PEG-EG catalyst 84 3.3.5 Proposed mechanism 87 3.4 Conclusion 90 3.5 References 91 3.6 Appendix 95 Chapter Protodecarboxylation of carboxylic acids using heterogeneous silver catalyst 97 4.1 Introduction 97 4.2 Experimental 101 4.2.1 Preparation of supported silver catalysts 101 4.2.2 Procedures for catalytic studies 101   VII         4.3 Results and discussion 102 4.3.1 Catalyst characterisation 102 4.3.2 Catalytic testing 109 4.3.2.1 Optimisation of reaction conditions 109 4.3.2.2 Effect of Ag loading 113 4.3.2.3 Effect of temperature and determination of reaction parameters 117 4.3.2.4 Scope of reaction 119 Study of reaction mechanism 122 4.3.3 4.3.3.1 Role of K2CO3 in the reaction mechanism 122 4.3.3.2 Proposed reaction mechanism 128 4.4 Conclusion 129 4.5 References 130 4.6 Appendix 132 Chapter 5: Alumina supported copper catalyst for protodecarboxylation of aromatic carboxylic acids 135 5.1 Introduction 135 5.2 Experimental 136 5.2.1 Preparation of supported copper catalyst 136 5.2.2 Catalytic studies 137 Results and Discussion 137 5.3.1 Catalyst characterisation 137 5.3.2 Catalyst activity testing and optimisation of reaction conditions 150 5.3.3 154 5.3   Study of catalyst properties VIII           5.3.3.1 Cu weight loading 154 5.3.3.2 Effect of H2 pretreatment of the Cu/Al2O3 WI-SG catalyst 156 5.3.4 Study of reaction mechanism: kinetic rate expression and nature of the reaction 157 5.3.5 Proposed Mechanism 160 5.3.6 Leaching and recycling test 162 5.3.7 Effect of oxidant 166 5.3.7.1 Effect of inert atmosphere and use of oxidant 166 5.3.7.2 Effect of amount of K2S2O8 168 5.3.8 Scope of reaction 170 5.4 Conclusion 171 5.5 References 172 Chapter 6: Heterogeneous catalysts for the decarboxylative cross-coupling of aryl carboxylic acids and aryl halides 174 6.1 Introduction 174 6.2 Experimental 179 6.2.1 Preparation of supported Cu catalyst 179 6.2.2 Catalytic studies 181 Results and discussion 181 6.3.1 Characterisation of catalysts 181 6.3.2 Catalytic testing 191 6.3 6.3.2.1 194 6.3.2.2 Optimisation of reaction conditions 196 6.3.2.3   Effect of moisture-free reaction conditions Effect of amount of iodobenzene 198 IX         6.3.2.4 Effect of Cu loading, amount of catalyst and reaction time 200 6.3.2.5 Cu·Pd/Al2O3-catalysed decarboxylative crosscoupling 201 6.3.2.6 Proposed reaction mechanism 206 6.4 Conclusion 209 6.5 References 210 6.6 Appendix 212 Chapter 7: Final conclusion   213 X           LIST OF TABLES PAGE Table 1.1 A list of PZC of some common oxides in water 17 Table 1.2 Physical properties of Pd, Cu and Ag 19 Table 1.3 Scope of reaction for ligand-free Pd/C catalysed Suzuki coupling 22 Table 3.1 Summary of results for homocoupling bromobenzene using Pd-PEG catalysts of 69 Table 3.2 Homocoupling of bromobenzene carried out using PEG 2000-Pd(OAc)2 with different additives and reaction temperature 71 Table 3.3 Homocoupling of bromobenzene carried out using PEG of different average molecular weight 73 Table 3.4 Homocoupling of bromobenzene carried out using PEG 900 with varying amount of DMA 75 Table 3.5 Homocoupling of bromobenzene carried out in the presence of 4g of PEG 900 and varying amounts of ethylene glycol (EG) 77 Table 3.6 Influence of the halogen atom on the Pd-PEG-EG catalysed homocoupling 83 Table 4.1 BET surface area, pore volume and Ag crystallite size of the supported silver catalysts 102 Table 4.2 XPS results for Ag/Al2O3 107 Table 4.3 Influence of support and active metal 109 Table 4.4 Particle size, total number of surface atoms in the reaction mixture, initial rate and turnover frequency of supported silver catalysts 116 Table 4.5 Protodecarboxylation of various aromatic carboxylic acids using 10 wt % Ag/Al2O3 121 Table 4.6 Protodecarboxylation of 2-nitrobenzoic acid or potassium nitrobenzoate using 10 wt % Ag/Al2O3 under different conditions 124 Table 4.7 Ionic radii of alkali metal ions, Ag+, O2- and Ag-O bond length 126 Table 5.1 Summary of BET surface area and pore volume of γ-Al2O3 (commercial and sol-gel), 10 wt % XII     141         Cu/Al2O3 WI catalyst, WI-SG catalysts with wt % to 15 wt.% Cu weight loadings Table 5.2 Copper (Cu) and aluminium (Al) ratio obtained from ICP measurements 142 Table 5.3 XPS binding energies (BE) for Cu 2p3/2 transitions, Cu LMM kinetic energy (KE) and the modifed Auger parameter, α’ 143 Table 5.4 Reference values for XPS binding energy values (BE) of Cu 2p3/2 transitions, Cu LMM kinetic energy (KE) and the modified Auger parameter, α’ for Cu, Cu2O and CuO 144 Table 5.5 Summary of the copper and aluminium ratio obtained from the XPS measurements 147 Table 5.6 Summary of the results obtained using 10.0 wt % Cu/Al2O3 WI catalyst for the optimisation of reaction conditions The 10.0 wt % Cu/Al2O3 WI catalyst was pretreated under flowing H2 at 300 oC for h before use except for 1a 151 Table 5.7 Reaction conditions used to obtain rate order information 159 Table 5.8 Scope of reaction using optimised reaction conditions 170 Table 6.1 BET surface area, pore volume and average particle size 186 Table 6.2 Elemental analysis results obtained using ICP-AES 186 Table 6.3 XPS binding energies of the electronic transitions of Pd, Cu and Al species 2.5 wt % Cu·1.0 wt % Pd/Al2O3 187 Table 6.4 XPS binding energies and normalised intensity ratios for bimetallic Cu·Pd catalysts prepared by selective adsorption with 1.0 and 5.0 wt % Cu 190 Table 6.5 Preliminary results obtained for decarboxylative cross-coupling of 2-nitrobenzoic acid and iodobenzene using alumina supported metal catalysts 192 Table 6.6 Effect of moisture-free conditions on the decarboxylative cross-coupling of potassium 2–nitrobenzoate and iodobenzene 194 Table 6.7 Summary of results obtained from the solvent screen 196   XIII         Table 6.8 Optimisation of the ratio iodobenzene : potassium nitrobenzoate 199 Table 6.9 Study of Cu loading, amount of Cu catalyst used and reaction time 200 Table 6.10 Summary of results obtained with bimetallic 2.5 wt.% Cu·1.0 wt % Pd/Al2O3 catalysts 204   XIV           LIST OF FIGURES Figure 1.1 A plot of the calculated fraction of Au atoms at the corner (red), edge (blue), and crystal face (green) of a truncated octahedral gold nanoparticle The insert shows the top half of a truncated octahedral gold nanoparticle and the position of the corner, edge and surface atoms Figure 1.2 Furfural hydrogenation pathways on Pt(111) surface Figure 1.3 Examples of reactions of organometallic complexes Figure 1.4 Formation of ammonia on a heterogeneous catalyst surface Figure 1.5 Selective hydrogenation of crotonaldehyde to crotyl alcohol 10 Figure 1.6 The surface-to-volume ratio increasing volume of a particle with 11 Figure 1.7 A schematic representation of the typical features of a metal surface 12 Figure 1.8 Active phase distribution during impregnation, (a) uniform; (b) egg-shell, (c) egg-white and (d) eggyolk 13 Figure 2.1 Schematic diagram of the scattering of x-rays by a crystalline material 42 Figure 2.2 A typical adsorption/desorption isotherm 45 Figure 2.3 Operating modes of TEM: (a) diffraction mode and (b) imaging mode 51 Figure 2.4 The energy levels involved in the emission and detection of the photoelectrons 53 Figure 2.5 (a) Emission of photoelectron and Auger electron; (b) XPS spectrum collected from a silicon wafer 54 Figure 2.6 Wagner plot for B.E.XPS Cu 2p3/2 photoelectron and K.E Cu LMM Auger electron 57 Figure 3.1 Conversion and selectivity of products obtained over consecutive Pd-PEG-EG catalysed homocoupling reaction runs 77 Figure 3.2 Kinetic profile of Pd-PEG-EG catalysed homocoupling reaction carried out in a closed system XV     78   decreases     in the presence of air with addition of fresh bromobenzene after 100 % conversion was achieved Figure 3.3 Pd-PEG-EG catalysed homocoupling of bromobenzene carried out in a closed system in the presence of (♦) no Cs2CO3, (■) mmol Cs2CO3, and (▲) mmol Cs2CO3 79 Figure 3.4 Kinetic profile of recycling test carried out in a closed system in the presence of (□) air and (♦) N2 80 Figure 3.5 Total conversion and selectivities towards benzene, biphenyl and terphenyl obtained in each of the consecutive Pd-PEG-EG catalysed homocoupling reaction runs 81 Figure 3.6 TEM images of Pd nanoparticles formed in PEG-EG (a) before reaction (stir h at 120 oC), (b) after reaction at 120 oC for 24 h using mmol of bromobenzene 82 Figure 3.7 (a) PEG-EG mixture and (b) PEG-EG immediately after addition of Pd(OAc)2 and (c) PEG-EG after stirring with Pd(OAc)2 at 120 oC for mins 86 Figure 3.8 X-ray diffractograms of Pd-EG-PEG carried out at 120 oC taken (a) at every hour for h from Theta = 30-90 o, (b) at h from Theta = 38-42 o 86 Figure 3.9 Typical GC-MS spectrum of the homocoupling of bromobenzene 95 Figure 3.10 GC spectrum of the homocoupling of chlorobenzene 95 Figure 3.11 GC spectrum of homocoupling of iodobenzene 96 Figure 3.12 GC spectrum of homocoupling of 1-chloro-4bromobenzene 96 Figure 4.1 Chelating agents used in protodecarboxylation reactions: 1: 1,10-phenanthroline, 2: 2,2’ bipyridyl 98 Figure 4.2 X–ray diffractograms of 10 wt % Ag supported on (a) SiO2 (b) Al2O3 (c) MgO (d) TiO2 and (e) ZnO The positions of the silver lines are indicated with a star * 103 Figure 4.3 Nitrogen adsorption and desorption isotherms for Al2O3 supported silver catalysts with 10 wt % Ag loading Insert: pore size distribution 104   XVI           Figure 4.4 X-ray diffraction patterns of (a) calcined Al2O3 support, and the catalysts with (b) wt % Ag, (c) 10 wt % Ag, (d) 15 wt % Ag, (e) 20 wt % Ag (traces are offset by 1000 counts) The positions of the silver lines are indicated with a star * 104 Figure 4.5 TEM images of (a) wt %, (b) 10 wt %, (c) 15 wt %, (d) 20 wt % Ag/Al2O3 106 Figure 4.6 XPS spectra for 5-15 wt % Ag/Al2O3 108 Figure 4.7 Kinetic profile of model reaction catalysed by 10 wt % Ag/Al2O3 with different catalyst pretreatment 112 Figure 4.8 Kinetic profile of model reaction catalysed by fresh and recycled 10 wt % Ag/Al2O3 113 Figure 4.9 Kinetic profiles of the model reaction carried out using 5-20 wt % Ag/Al2O3 and AgOAc 114 Figure 4.10 Plot of initial rate against silver loading of the supported silver catalysts 114 Figure 4.11 Kinetic profile of protodecarboxylation 2-nitrobenzoic acid carried out at (u) 100 (n) 110 oC, (▲) 120 oC, (Ÿ) 130 oC 118 Figure 4.12 Arrhenius plot of ln k against 1/T Figure 4.13 Ortho-substituent coordinating to a surface Ag + centre during the decarboxylation process 120 Figure 4.14 Kinetic profiles of 10 wt % Ag/ Al2O3-catalysed protodecarboxylation of (u) 2-nitrobenzoic acid (2 mmol), with K2CO3 (0.3 mmol); (n) 2-nitrobenzoic acid (2 mmol), without K2CO3; (▲) Potassium 2-nitrobenzoate (2 mmol) without AcOH; (Ÿ) Potassium 2-nitrobenzoate (2 mmol) with AcOH (2 mmol) 124 Figure 4.15 Influence of added potassium salts: Kinetic profiles of the protodecarboxylation of 2-nitrobenzoic acid catalysed by 10 wt % Ag/ Al2O3 in the presence of (u) 0.3 mmol of KCl; (n) 0.3 mmol of K2SO4; and (▲) 0.3 mmol of K2CO3; (l) 0.3 mmol of KOH, (×) 0.6 mmol of KOH 125 Figure 4.16 Effect of alkali metal carbonates protodecarboxylation of 2-nitrobenzoic acid 127   o of C, 119 δ XVII     on     Figure 4.17 Plot of initial rate against mol % of K2CO3 used 128 Figure 4.18 N2 adsorption and desorption isotherms of the 5-20 wt % Ag/Al2O3 Insert: Pore size distribution 132 Figure 4.19 XRD pattern of (a) fresh 10 wt % Ag/Al2O3 and (b) recycled 10 wt % Ag/Al2O3 132 Figure 4.20 N2 adsorption and desorption isotherms of (n) fresh and (▲) recycled and recalcined 10 wt % Ag/Al2O3 133 Figure 4.21 Pore size distribution of (n) fresh and (▲) recycled and recalcined 10 wt % Ag/Al2O3 133 Figure 4.22 HPLC spectrum of a typical test reaction carried out using 2-nitrobenzoic acid as substrate, K2CO3 as base, 10 wt % Ag/Al2O3 as catalyst at 120 oC The spectrum was recorded for 30 mins to ensure that no other products are formed 134 Figure 4.23 Kinetic profiles for protodecarboxylation of 2nitrobenzoic acid over (u) 10 wt % Ag/Al2O3, (×) Ag2O (commercial) and (n) Ag powder 134 Figure 5.1 Powder XRD patterns of 10 wt % Cu/Al2O3 : (a) WI catalyst without H2 pretreatment, (b) WI catalyst with H2 pretreatment, (c) WI-SG catalyst with H2 pretreatment ( + : lattice plane of γ-Al2O3; * : lattice plane of metallic Cu, # : lattice plane of CuO) 138 Figure 5.2 N2 adsorption and desorption isotherms of 10 wt % Cu/Al2O3 : (u)WI and (▲) WI-SG catalyst 139 Figure 5.3 Pore size distribution of 10 wt % Cu/Al2O3 : (u)WI and (▲) WI-SG catalyst 139 Figure 5.4 Powder XRD patterns of γ-Al2O3 supported with (a) 1.0 wt % Cu, (b) 2.5 wt % Cu, (c) 5.0 wt % Cu, (d) 10.0 wt % Cu, and (e) 15.0 wt % Cu ( + : lattice plane of γ-Al2O3, * : lattice plane of metallic Cu) 141 Figure 5.5 Cu XPS spectrum of (a) 1.0 wt %, (b) 2.5 wt %, (c) 5.0 wt %, (d) 10.0 wt % and (e) 15.0 wt % Cu/Al2O3 WI-SG catalyst (dotted lines indicate the peak maxima detected) 143 Figure 5.6 The Cu LMM Auger peak of (a) 1.0 wt %, (b) 2.5 wt %, (c) 5.0 wt %, (d) 10.0 wt % and (e) 15.0 wt % Cu/Al2O3 WI-SG catalyst (dotted lines indicate the peak maximum observed.) 146   XVIII           Figure 5.7 TEM images and Cu particle size distribution of (a) 1.0 wt %, (b) 2.5 wt %, (c) 5.0 wt %, (d) 10.0 wt %, (e) 15.0 wt % Cu/Al2O3 148 Figure 5.8 Plot of ion current for CO2 (m/z= 44) against temperature for 2.5 wt % Cu/Al2O3 WI-SG catalyst (a) without pretreatment; (b) after H2 pretreatment for h at 150 oC; (c) after H2 pretreatment for h at 300 oC 149 Figure 5.9 Kinetic profile of protodecarboxylation of 2nitrobenzoic acid carried out in the presence of (♦) Li2CO3, (■) Na2CO3, (▲) K2CO3, (x) Cs2CO3 152 Figure 5.10 Kinetic profile of protodecarboxylation reaction carried using 10 wt % Cu/Al2O3 WI and WI-SG catalyst 153 Figure 5.11 Kinetic profile protodecarboxylation of 2nitrobenzoic acid carried using Cu/Al2O3 WI-SG catalyst with 1.0 wt % to 15.0 wt % Cu loading 154 Figure 5.12 Plot of initial rate of reaction (mmol/mmolcath) against weight loading of copper (%) 154 Figure 5.13 Kinetic profile of protodecarboxylation of 2nitrobenzoic acid using (♦) 2.5 wt % Cu/Al2O3 WISG catalyst without pretreatment; (■) 2.5 wt % Cu/Al2O3 WI-SG catalyst after H2 pretreatment for h at 150 oC; (▲) 2.5 wt % Cu/Al2O3 WI-SG catalyst after H2 pretreatment for h at 300 oC 156 Figure 5.14 Optimised structure of Cu2O (111) and (100) surface: (a) side view of Cu2O (111) and (b) side view of Cu2O (100) The red, brick red and yellow spheres represent oxygen, coordinatively saturated copper (CuCSA) and coordinatively unsaturated copper (CuCUS) atoms The white line defines the uppermost layer 157 Figure 5.15 Leaching test at 165 oC - Kinetic profile for the protodecarboxylation of 2-nitrobenzoic acid carried out (▲) without hot filtration and (■) with hot filtration after 0.5 h 163 Figure 5.16 Leaching test at 150 oC- Kinetic profile of protodecarboxylation of 2-nitrobenzoic acid carried out (▲) without hot filtration and (■) with hot filtration after h 165   XIX         Figure 5.17 Results of multiple reaction runs carried out using recycled 2.5 wt % Cu/Al2O3 WI-SG catalyst 165 Figure 5.18 Kinetic profile of 10.0 wt % Cu/Al2O3 (WI-SG) catalysed protodecarboxylation of 2-nitrobenzoic acid carried out in the presence of air or Ar 166 Figure 5.19 Kinetic profile of 10.0 wt % Cu/Al2O3 (WI-SG) catalysed protodecarboxylation of 2-nitrobenzoic acid carried out under Ar (♦) without oxidant; (▲) with 10 mol % K2S2O8; and (■) with 10 mol % of NH4S2O8 167 Figure 5.20 Leaching test at 150 oC - Kinetic profile for the protodecarboxylation of 2-nitrobenzoic acid carried out in the presence of 10 mol % K2S2O8 (▲) without hot filtration and (■) with hot filtration after h 168 Figure 5.21 Kinetic profiles of 10.0 wt % Cu/Al2O3 (WI-SG) – catalysed protodecarboxylation of 2-nitrobenzoic acid catalysed by (■) 2.5 mol %; (♦) mol %; (▲) 10 mol %; (x) 20 mol %; (□) 100 mol %; and (o) equivalent of TEMPO and 10 mol % K2S2O8 169 Figure 6.1 Continuous flow reactor set-up for decarboxylative cross-coupling 175 Figure 6.2 Proposed mechanism for Pd-catalysed decarboxylative cross-coupling of heteroaromatic carboxylic acids and aryl halide 176 Figure 6.3 XRD pattern of 2.5 wt % Cu · 1.0 wt % Pd/Al2O3 prepared by (a) sequential impregnation; (b) coimpregnation; (c) surface activation (*: lattice plane of CuO, #: lattice plane of γ-Al2O3) 182 Figure 6.4 TEM images and particle size distributions for 2.5 wt % Cu Ÿ1.0 wt % Pd/ Al2O3 prepared via (a) sequential impregnation; (b) co-impregnation; (c) surface activation 184 Figure 6.5 N2 adsorption-desorption isotherm of 2.5 wt % Cu · 1.0 wt % Pd/Al2O3 prepared by (a) sequential impregnation; (b) co-impregnation; (c) surface activation 185 Figure 6.6 Pore size distribution of 2.5 wt % Cu · 1.0 wt % Pd/Al2O3 prepared by (a) sequential impregnation; (b) co-impregnation; (c) surface activation 185   XX           Figure 6.7 Cu 2p3/2 XPS spectra of 2.5 wt % Cu · 1.0 wt % Pd/Al2O3 prepared via (a) sequential impregnation (SI); (b) co-impregnation (CI); and (c) surface activation (SA) 188 Figure 6.8 Pd 3d3/2 XPS spectra of 2.5 wt % Cu · 1.0 wt % Pd/Al2O3 prepared via (a) sequential impregnation (SI); (b) co-impregnation (CI); and (c) surface activation (SA) 189 Figure 6.9 HPLC spectrum of a typical test reaction carried out using potassium 2-nitrobenzoate, iodobenzene, K2CO3, 10 wt % Cu/Al2O3 in DMA at 150 oC, Ar 212 Figure 6.10 HPLC spectrum of a typical test reaction carried out using potassium 2-nitrobenzoate, iodobenzene, K2CO3, 2.5 wt % Cu·1.0 wt % Pd/Al2O3 in DMA at 150 oC, Ar 212   XXI         LIST OF SCHEMES Scheme 1.1 General mechanism of cross-coupling reactions catalysed by Pd catalyst 20 Scheme 1.2 Ligand-free Pd/C-catalysed Suzuki coupling 22 Scheme 1.3 Cu-catalysed Ullmann homocoupling of iodobenzene 24 Scheme 1.4 Pd/C-catalysed Ullmann coupling of aryl chlorides 24 Scheme 1.5 Proposed mechanism for decarboxylative crosscoupling 27 Scheme 1.6 Catalytic transformations of carboxylic acids 28 Scheme 1.7 Protodecarboxylation of ortho-substituted benzoic acids 29 Scheme 1.8 Decarboxylative cross-coupling of ortho-substituted benzoic acids and bromobenzene in the presence of Pd and Cu catalyst 29 Scheme 1.9 Mechanism of decarboxylative Heck reaction 30 Scheme 1.10 Direct arylation of 2,6-dimethoxylbenzoic acid 31 Scheme 3.1 Ullmann coupling of aryl halides 64 Scheme 3.2 Homocoupling of bromobenzene Pd(OAc)2-PEG system by 69 Scheme 3.3 (a) Pd-PEG-EG catalysed homocoupling of bromobenzene; (b) neutralisation reaction of HBr and Cs2CO3 80 Scheme 3.4 Pd-catalysed homocoupling of aryl halides using isopropanol as reductant 85 Scheme 3.5 Reductive homocoupling supported Pd catalyst on 85 Scheme 3.6 Oxidation of hydroxyl functional group of ethylene oxide oligomers to aldehyde functional group 85 Scheme 3.7 Proposed mechanism for the homocoupling of bromobenzenes Pd-catalysed 87 Scheme 3.8 Proposed mechanism for the Pd-catalysed formation of benzene byproduct 88   XXII     of aryl catalysed halides       Scheme 3.9 Proposed mechanism for Pd-PEG-EG catalysed homocoupling of bromobenzene for formation of terphenyls 89 Scheme 3.10 Proposed intermediate structures for the formation of ortho- and para- terphenyls 89 Scheme 4.1 Protodecarboxylation of (1) 2-nitrobenzoic acid and (2) 4-methoxylbenzoic acid using the Cu2O/1,10phenantroline system 99 Scheme 4.2 Protodecarboxylation of 2-nitrobenzoic acid using supported Ag catalyst 100 Scheme 4.3 Delocalisation of electrons in (a) DMSO and (b) DMA 111 Scheme 4.4 Proposed mechanism of protodecarboxylation of ortho-substituted benzoic acids 129 Scheme 5.1 Cu/Al2O3-catalysed 2-nitrobenzoic acid of 136 Scheme 5.2 Possible reaction mechanisms for protodecarboxylation of 2-nitrobenzoic acid via: (a) anionic pathway and (b) radical pathway 158 Scheme 5.3 (a) Trapping of aryl anion using iodobenzene, (b) Trapping of aryl radicals using TEMPO 159 Scheme 5.4 Proposed mechanism of Cu/Al2O3- catalysed protodecarboxylation of 2-nitrobenzoic acid 161 Scheme 6.1 Decarboxylative cross-coupling of 2-nitrobenzoic acid and aryl bromides using Cu·Pd catalytic system 174 Scheme 6.2 Decarboxylative cross-coupling 2-nitrobenzoate and iodobenzene potassium 177 Scheme 6.3 Decarboxylative coupling of 2-nitrobenzoic acid and iodobenzene (main reaction) and protodecarboxylation of 2-nitrobenzoic acids (side reaction) 191 Scheme 6.4 Proposed mechanism for decarboxylative cross-coupling 2-nitrobenzoate and iodobenzene Cu-catalysed of potassium 207 Scheme 6.5 Proposed mechanism for bimetallic Cu·Pd catalysed decarboxylative cross-coupling of potassium 2-nitrobenzoate and iodobenzene 208   protodecarboxylation XXIII     of     Scheme 6.6 Proposed mechanism for formation of 3-NBP 208 Scheme 6.7 Proposed mechanism for formation of DNBP 209   XXIV           LIST OF JOURNAL PUBLICATIONS & CONFERENCE PAPERS Journal publication (1) Protodecarboxylation of carboxylic acids over heterogeneous silver catalysts Xiu Yi Toy, Irwan Iskandar Bin Roslan, Gaik Khuan Chuah and Stephan Jaenicke* Catalysis Science & Technology (Accepted 30 October 2013) Conference paper (1) Novel Catalytic Green Processes for the Syntheses of Conductive Polymer Xiu Yi Toy, Stephan Jaenicke* (Poster Presentation at 6th Singapore International Chemical Conference, 15-18 December 2009, Suntec International Convention and Exhibition centre, Singapore) (2) Novel Catalytic Green Processes for the Syntheses of Conductive Polymer Xiu Yi Toy, Stephan Jaenicke* (Poster Presentation at 6th Asian-European Symposium on metal mediated efficient reactions, 7-9 June 2010, Nanyang Technological University, Singapore)   XXV         (3) Protodecarboxylation of carboxylic acids using heterogenous silver catalyst Xiu Yi Toy, Gaik Khuan Chuah and Stephan Jaenicke* (Poster Presentation at 14th Asian Chemical Congress, 5-8 September 2011, Queen Siriki National Convention Center, Bangkok, Thailand) (4) Protodecarboxylation of carboxylic acids using heterogenous silver catalyst Xiu Yi Toy, Gaik Khuan Chuah and Stephan Jaenicke* (Poster Presentation at 15th International Congress on Catalysis 2012, 1-6 July 2012, Munich Germany) (5) Protodecarboxylation of aromatic carboxylic acids using heterogenous copper catalyst Xiu Yi Toy, Gaik Khuan Chuah and Stephan Jaenicke* (Poster Presentation at 7th Singapore International Chemical Conference, 16-19 December 2012, University Town, National University of Singapore, Singapore) (6) Alumina supported Copper catalyst for protodecarboxylation of aryl carboxylic acids Xiu Yi Toy, Gaik Khuan Chuah and Stephan Jaenicke* (Poster Presentation at 6th Asia-Pacific Congress on Catalysis, 14-17 October 2013, Taipei International Convention Center (TICC), Taiwan)   XXVI           ... Experimental 17 9 6.2 .1 Preparation of supported Cu catalyst 17 9 6.2.2 Catalytic studies 18 1 Results and discussion 18 1 6.3 .1 Characterisation of catalysts 18 1 6.3.2 Catalytic testing 19 1 6.3 6.3.2 .1 194... Deposition-precipitation 15 1. 1.3.4 1. 2 Impregnation Ion exchange 17 Ag, Cu and Pd nanocatalysts in cross coupling reactions 1. 2 .1   18 21 Suzuki coupling V         1. 2.2 Ullmann reaction 23 1. 3 Decarboxylative... reaction 17 0 5.4 Conclusion 17 1 5.5 References 17 2 Chapter 6: Heterogeneous catalysts for the decarboxylative cross-coupling of aryl carboxylic acids and aryl halides 17 4 6 .1 Introduction 17 4 6.2