In situ spectroscopic of the early events in the rodium mediated pauson khand reaction

IN-SITU SPECTROSCOPY OF THE EARLY EVENTS IN THE RHODIUM MEDIATED PAUSON KHAND REACTION.. Figure 2.1 The suggested mechanism for the Co2CO8 mediated Pauson Khand Figure 2.2 Figure 2.2 Rho

IN-SITU SPECTROSCOPY OF THE EARLY EVENTS IN THE RHODIUM

MEDIATED PAUSON KHAND REACTION

AYMAN DAOUD ALLIAN

NATIONAL UNIVERSITY OF SINGAPORE

2006

IN-SITU SPECTROSCOPY OF THE EARLY EVENTS IN THE RHODIUM

MEDIATED PAUSON KHAND REACTION

AYMAN DAOUD ALLIAN

(B Eng UIUC, M Eng., NUS-UIUC JOINT MS PROGRAM)

A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMICAL & BIOMOLECULAR

ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE

2006

ACKNOWLEDGEMENT

The research carried out in this thesis was a multidisciplinary and required (1)

designing and machining of flow through high/low pressure reactors and spectroscopic cells, (2) using various spectroscopic tools (IR and Raman and NMR) (3) carrying out blind deconvolution of the collected in-situ spectra, (4) a sound understanding of organometallic chemistry in particular coordination chemistry (5) the use of density functional theory to assist in geometrical assignments Such an immense task can not be achieved by a single individual, therefore, I was very fortunate to be part of very competent team at the National University of Singapore and Institute of Chemical and Engineering Sciences (ICES) whom their constant support helped me tremendously overcome many of the obstacles faced while carrying out this diverse project

The first person I would like to thank is my supervisor Marc Garland for making sure that I acquired all the resources needed to carry out my research In addition, I

would like to thank him for all the good conversations on science, politics and life I am very grateful to his understanding of my sense of curiosity which stretched me at times but

it was very satisfying I remember at some point I was working on (i) a thermodynamic project, (ii) analyzing spectra from a heterogeneous system and (iii) writing a MATLAB script to analyze Raman optical activity simultaneously

I would like to thank Prof Mark Saeys and his research group in particular Xu Jing and Sun Wenjie for their help on DFT calculations Our collaboration resulted in a successful project wherein the results were published in the journal of vibrational spectroscopy DFT became an essential tool for the research conducted in this dissertation and I’ll always be grateful to Prof Mark Saeys even for the DFT work carried out beyond the mentioned collaboration because he and his team were the one who got me started In addition, I would like to thank the undergraduate students that I supervised while they were carrying out their final year project Teo Boon Wee and Wang Yezhong as both really made significant contribution to the development of the DFT calculations on Rhodium carbonyl species

I would like to thank Dr Li Chuanzhao, for training me on using in-situ high pressure spectroscopy and valuable remarks/feedback on my work throughout my PHD in particular issues related to organometallics chemistry and reactors design/use I also would

and my experience with chemistry/spectroscopy/DFT were an excellent combination that enabled us to complete four projects successfully Results from two projects were published in good journals and were well received by the scientific community Also, I would like to thank Martin for the wonderful conversation on life and religion

I like to thank Dr Effendi Widjaja, for his valuable support in using Raman spectroscopy and numerical aspects and Dr Chacko Jacob for carrying out the 13C NMR experiment and his help in making sense of the resultant spectra I would like to thank Dr Guo Liangfeng for his resourcefulness in using MATLAB

I also like to thank Dr Gao Feng and Mr Karl Irwin Krummel for enriching conversation on heterogeneous catalysis and rhodium phosphine chemistry I also would like to thank Dr Chew Wee for many of stimulating discussions

I would like to express my thanks all of members in our research group including Ms Cheng Shuying and Mr Zhang Huajun my friends in NUS Jeremy Daniel Lease, N.V.S.N

Murthy Konda and Ng Yew Seng who made my graduate student life interesting

I would like to the technical staff at NUS, in particular Mr Ng Kim Poi and his employee at the workshop their help on machining my designed flow through spectroscopic cells

I would like to thank my family for their moral support through out my PHD I also would like to thank God While I did work hard in the past 10 years of my academic life, but the successful completion of my PHD was just beyond my wildest dreams as young boy growing up in east Jerusalem and would not be possible without his generosity I always felt that I was in the right time and the right place and being part of the right team

Finally this thesis is dedicated to my parents Siham and Daoud Allian

ACKNOWLEDGEMENT ……… … i

SUMMARY ……… x

NOMENCLATURE ……… xii

LIST OF FIGURES ……… xv

LIST OF TABLES ……… … xxiii

1 INTRODUCTION ……… ……… 1

1.1 Problem Statement: Missing Links in the Early Events of Rh4(CO)12 PK Reaction ……… … 2

1.2 Thesis Objective ……… 3

1.3 Thesis Organization ……… … 4

2 LITERATURE REVIEW ……… ……… 6

2.1 Pauson Khand Reaction………….……… … 6

2.1.1 Early Pauson Khand reactions……… ………… ……… … 9

2.1.2 Reaction Mechanism for the Pauson Khand Reaction……… … 10

2.1.3 Cobalt catalyzed Pauson Khand Reaction………….……… 12

2.1.4 Titanocene and Ruthenium catalyzed Pauson Khand Reaction………… 13

2.2 Rhodium Catalyzed Pauson Khand Reaction……… 14

2.2.1 Development of new protocols for the Rhodium catalyzed PK Reaction……… … 16

2.3 Terarhodium dodecacarbonyl……….……… 18

2.3.1 Important transformation of Rh 4 (CO) 12 ……… 21

2.3.2 FTIR spectroscopy to study rhodium carbonyl clusters ……… 21

2.4 Unmodified Cobalt and Rhodium carbonyl cluster reaction with alkynes… 22

2.4.1 Reaction of alkyne with homometallic cobalt carbonyl species ………… 23

2.4.2 Reaction of alkyne with hetrometallics carbonyl species…… … …… 24

2.4.3 Reaction of alkyne with homometallic Rhodium carbonyl species….… 25

3 EXPERIMENTAL APPROACH AND METHODOLOGY……… … 27

3.1 Homogenous Catalysis and in Situ Spectroscopy……… …… … 27

3.2 Experimental Setups.…… ……… 29

3.2.1.1 Advantages of the current in-situ spectroscopic approach ….… 29

3.2.2 High Pressure in-situ FTIR apparatus……… … 30

3.2.3 Low Pressure in-situ FTIR apparatus……… … 32

3.2.4 Spectrometers and Flow through cells……… 33

3.3 General Experimental Procedure……… 34

3.3.1 Schlenk Techniques……… ……… 34

3.3.2 Chemicals and Gases……… 35

3.3.3 Quantitative measurements ……… 35

3.4 Chemometic tools for total algebraic system identification……… 35

3.4.1 Experimental Procedure and Spectra collection ……… 37

3.4.1.1 Lambert-Beer-Bouguer law……… 40

3.4.2 Singular Vale Decomposition (SVD) ……… 41

3.4.3 Pure Component Spectra Reconstruction……… 44

3.4.4 Solvent and background pure Component Spectra; Spectral Substraction……… 48

3.4.5 Relative concentration……….……… 49

3.4.6 Real Molar Concentration……… 52

3.4.6.1 Spectral Renormalization……… 52

3.4.6.2 Real spectral absorptivities and mole numbers……… 56

4 TETRARHODIUM DODECACARBONYLS……… 59

4.1 Experimental Section……… ………… 59

4.1.1 Experimental design……… 60

4.1.2 Experimental Procedure and Spectra collection……… … 61

4.2 Spectral Analysis and preliminary results……… ………… 65

4.2.1 Singular Value Decomposition and spectral reconstruction……… 65

4.2.2 Relative Concentration and Signal Ratio ……… …… 69

4.3 Discussion… ……… ……… ………… 71

4.3.1 Rhodium based Organometallics ……….… … ……….…… 71

4.3.2 Gas impurities Ni(CO) 4 and Fe(CO) 5…….… ……….…… 73

4.3.3 Species X……… …….……… 74

4.4 Real molar concentration and thermodynamics …… …… ………… 77

4.4.1Properly scaled pure component spectra……….… ……….…… 78

4.4.3 Thermodynamics…….……… … ……….……… 81

4.4.3.1 Fluxionally and the discovery of all-terminal Rh4(CO)12……… 81

4.4.3.2 The cluster fragmentation to Rh2(CO)6(μ-CO)8……… 83

4.5 Summary … …… ………… 85

5 Density Functional Theory ……… … 86

5.1 Geometrical assignment based on vibrational spectroscopy……… 87

5.1.1 Traditional approaches for Vibrational assignment ….………… …… 87

5.1.2 DFT assisted structural determination……….……… 87

5.2 Finding the appropriate density functional and basis set….………… …… 88

5.2.1 Widely applied DFT methods for Rhodium based Organometallics…… 89

5.2.2 The HRh(CO) 4 Test……… ……… …….… 90

5.2.2.1 Application to the cobalt hydride HCo(CO)4.……… … 93

5.3 Calculation of Metal Carbonyl Clusters……….……… 94

5.3.1 Dirhodium Octacarbonyl Rh 2 (CO) 6 (μ-CO) 2 …….……… … 94

5.3.1.1 Different Geometries of Rh2(CO)8……… ……… … 96

5.3.1.2 Cobalt dimer Co2(CO)6(μ-CO)2 ……… ……… …… 97

5.3.2 Tetrarhodium Dodecacarbonyl Rh 4 (CO) 9 (μ-CO) 3 ……… … 98

5.3.2.1 Solvent Effect on the Observed Vibrational Spectra …… … 101

5.3.2.2 All-terminal Geometries of Rh4(CO)12……….…… … 102

5.3.3 Hexarhodium Hexacarbonyl Rh 6 (CO) 12 (μ 3 -CO) 4 ……… …… 103

5.3.4 Reliability of the Mid-infrared Predicted Vibrational Spectra………… 105

5.3.4.1 Predicted terminal Carbonyl frequency……….…… … 105

5.3.4.2 Predicted Bridged Carbonyl frequency……….…… … 106

5.4 Calculation of modified Metal Carbonyl Species…… ……… 106

5.4.1 Acylrhodium tetracarbonyl……….… …… 106

5.4.2 Geometry of RCORh(CO) 3 (π-C 2 H 4 )……… 109

5.4.3 The Spectrum of Rh 4 (CO) 11 PPh 3 ……… 111

5.5 Experimental Section…… ……… ……… 113

5.5.1 In-situ Cell For Liquid/Supercritical Gas Measurements……… 113

5.5.2 Experimental Setup and Procedure……… 114

5.6 Summary…… ……… ……… 115

6.1 Preliminary Investigation……… …… 116

6.1.1 Experimental Setup and Procedure ……… 117

6.1.2 Spectra Analysis……… ……… 118

6.2 Mid-Infrared Characterization of the Butterfly Cluster……… 119

6.2.1 High resolution vibrational study of (μ 4 -η 2 -3-hexyne)Rh 4 (CO) 8 (μ-CO) 2 120

6.2.1.1 Experimental Section and procedure……….……… … 120

6.2.1.2 Spectra Analysis and DFT Calculations ……….……… … 121

6.2.2 Low resolution vibrational study of (μ 4 -η 2 -terminal)-Rh 4 (CO) 8 (μ-CO) 2 125

6.2.3 Low resolution vibrational study of (μ 4 -η 2 -asymmetric alkyne)- Rh 4 (CO) 8 (μ-CO) 2 ……… 127

6.2.4 Rates of Formation, Dependence on Substrate ……… 128

6.2.5 Spectra of Various (μ 4 -η 2 -alkyne)Rh 4 (CO) 8 (μ-CO) 2 in d-benzene……… 129

6.2.5.1 Experimental Procedure and BTEM Results.……… … 130

6.2.5.2 Spectra Analysis……….……… … 131

6.3 Raman spectra of (hexyne)Rh4(CO)8(μ-CO)2…….……… ……….… 132

6.3.1 Experimental Section…….……… ……… 133

6.3.1.1 Experimental Setup ……….……… ……… 133

6.3.1.2 Experimental Procedure ……….……… ……… 134

6.3.2 Spectra Analysis.……… ……… ……… ……… 135

6.3.2.1 Mid-Raman Vibrational Spectra ……….……… …… 135

6.3.2.2 Far-Raman Vibrational Spectra ……….……… ……… 140

6.3.2.3 Relative Concentrations……….……… ……… 145

6.4 NMR spectra of (3-hexyne)Rh4(CO)8(μ-CO)2……… 146

6.4.1 Experimental Section- Rh 4 (CO) 9 (µ-CO) 3 Enrichment…….……… 146

6.4.2 Results and Discussion…….……… ……….… 146

6.4.2.1 The 13C NMR Spectrum of Rh4(CO)9(µ-CO)3 ………… … 147

6.4.2.2 The 13C NMR Reaction Spectrum……….……… … 148

6.4.2.3 The 13C NMR Reaction Spectrum of (μ4-η2 -3-hexyne)Rh4(CO)8(μ-CO)2……… ….……… ……… 150

6.5 Kinetics of the formation of (C2H5C2C2H5)Rh4(CO)8(μ-CO)2… ……… 152

6.5.1 Experimental Section……… ….……… ….……… ….……… 152

6.5.1.1 Experimental Design……… ….……… ….……… … 152

6.5.1.2 Experimental Procedure and Spectra Collection……… …… 153

6.5.2 Spectra Analysis……… ….……… ….……… ….……… … 155

6.5.2.2 Real Concentration…… ….……… …… ….……… 156

6.5.3 Alkyne and CO molar concentrations……… …….……… …….…… 157

6.5.4 Kinetic and Mechanism of the Reaction……… …….……… …….… 158

6.5.5 Thermodynamic and Apparent Eyring Activation……… …….……… 163

6.6 Summary……… …….……… …….……… …….……… …….……… 165

7 The Dirhodium Alkyne Species ……… … 166

7.1 Preliminary Analysis ……… ……… 167

7.1.1 Experimental Section ……… ………… … 167

7.1.2 Spectra Analysis……… 168

7.2 High resolution vibrational study of the fragmentation of (μ4-η2 -C2H5C2C2H5)Rh4(CO)8(μ-CO)2……… 169

7.2.1 Experimental Section ……….……… 169

7.2.1.1 Experimental Setup……… ……… … 170

7.2.1.2 Experimental Procedure ……… …… …… 170

7.2.2 Spectral Analysis ……… 171

7.2.2.1 Rh4(CO)9(μ-CO)3 and (μ4-η2- alkyne)Rh4(CO)8(μ-CO)2… … 172

7.2.2.2 Spectra and DFT Analysis of (3-hexyne)Rh2(CO)6 … … … 172

7.2.2.3 Spectra and DFT Analysis of (3-hexyne)Rh2(CO)5 … … … 176

7.2.3 Relative Concentration ……… … … … … …… 179

7.3 Low resolution vibrational study of the fragmentation of (μ4-η2- alkyne)Rh4(CO)8(μ-CO)2, Alkyne= 1-heptyne, Phenyl-1-hexyne…… ……… 180

7.3.1 Experimental Section……… … 181

7.3.3.1 Experimental Design ……….… … 181

7.3.3.2 Experimental Procedure ……….… … 181

7.3.2 Spectra Analysis……… 182

7.3.2.1 Pure Components of the Phenyl-1-hexyne Experiment ……… 182

7.3.2.2 Pure Components of the 1-heptyne Experiment …… ……… 185

7.4 Kinetics of the (1-heptyne)Rh4(CO)8(μ-CO)2 Fragmentation……… 187

7.4.1 Experimental Section……… 187

7.4.1.1 Experimental Design……… 188

7.4.1.2 Experimental Procedure and Spectra Collection……… 188

7.4.2.1 Relative Concentration……… 191

7.4.2.2 Unknown species structural assignments……… 192

7.4.2.3 Organometallics Real Concentration……… 195

7.4.2.4 CO and 1-heptyne molar Concentration.……… 195

7.4.3 Kinetic and Mechanism of the Reaction……… 196

7.4.4 Thermodynamic and Apparent Eyring Activation Parameters………… 199

7.5 Summary……… 201

8 The Reaction of Rh4(CO)9(μ-CO)3 with Enyne……….……… 202

8.1 Reaction of Catalytic Precursor Rh4(CO)9(μ-CO)3 with Equivalent amounts of Enyne……… ……… 202

8.1.1 Experimental Section…….……… 203

8.1.1.1 Experimental Design……… 203

8.1.1.2 Experimental Procedure……… … 203

8.1.2 Spectra Analysis.……… ……… … 204

8.1.3 Unknown Species X……… ……… 207

8.2 Reaction of Catalytic Precursor Rh4(CO)9(μ-CO)3 with Excess Enyne.……… 209

8.2.1 Experimental Section……… …… 209

8.2.1.1 Experimental Design……… 209

8.2.1.1 Experimental Procedure……… 209

8.2.2 Spectra Analysis……… …… 209

8.3 On-line FTIR monitoring of the Effect of Ultrasonic Irradiation on Homogenous Liquids ……….……… 212

8.3.1 Background……….….……… 213

8.3.2 Experimental Setup ……….….…… 214

8.3.3 Preliminary Experimental Results ……… 215

8.3.3.1 Experimental Design ……….… 215

8.3.3.2 Experimental Procedure……… 215

8.3.3.3 Spectra Analysis……… 216

8.4 Summary ……….……… 218

9 Conclusion and Future Work ……… ………… ………… 219

9.1 Results on the Early Event of Pauson Khand Reaction ……… … 219

9.1.1 Experimental Work and Findings …….……… 220

9.1.2 Implication of the Results …….….……… 221

9.2 Methodological Contributions ……… ……… 222

9.2.1 DFT Calculations…….……….…… 222

9.2.2 Raman Spectroscopy.……… ….…… 223

9.2.3 Band Target Entropy Minimization (BTEM).……… 223

REFERENCES ……….……….……….…… 224

APPENDICES ….……….……….……….…… 243

Appendix A: Experimental Setups….……….……… 243

Appendix B: Fluxionality Of Terarhodium Dodecarbonyl Cluster………….……… 247

Appendix C: Applying DFT to (μ4-η2-HC2H)Co4(CO)8(μ-CO)2……….………… 256

Appendix D: Raman Experimental Setup……….………… 258

Appendix E: Butterfly Cluster: Organometallics……….………… 260

Appendix F: On-Line FTIR Sonochemical Reaction Setup….………….………… 267

Appendix G: Preliminary FIR Analysis……… ……… 268

Appendix H: DFT Improvements……… 271

PUBLICATIONS ……….……….……….… 273

SUMMARY

The current dissertation studied the pre-catalytic events involved in the Rh4(CO)9CO)3 mediated Pauson Khand reaction using in-situ spectroscopy In particular, the investigation focused on understanding the (i) catalytic precursor and (ii) its reaction with alkynes

(µ-The study of the catalytic precursor Rh4(CO)12 in chapter 4 allowed the identification of the long-sought all-terminal cluster Rh4(CO)12, an important intermediate that explains the observed fluxionality of the cluster at room temperature In addition, it was observed that the formation of the dimer Rh2(CO)8 was very low even at CO pressure of 70 bar

In chapter 6, the formation of various butterfly clusters (μ4-η2-alkyne)Rh4(CO)8(µ-CO)2

were observed when reacting equimolar amounts of alkyne with Rh4(CO)9(µ-CO)3 The (μ4-η2-3-hexyne)Rh4(CO)8(µ-CO)2 cluster was characterized by mid-infrared, Raman and NMR spectroscopy In addition, both the deconvoluted Raman and mid-infrared spectra of the butterfly cluster were in good agreement with the DFT predicted spectra The rate of formation of the (μ4-η2-3-hexyne)Rh4(CO)8(µ-CO)2 was Kobs[hexyne][Rh4(CO)9(µ-CO)3][CO]-1 indicating inhibition by higher CO partial pressures

Two new species were identified, see chapter 7, namely (alkyne)Rh2(CO)6 and (alkyne)Rh2(CO)5 after reacting excess alkyne with Rh4(CO)9(µ-CO)3 The rate of the fragmentation of the (μ4-η2-1-heptyne)Rh4(CO)8(µ-CO)2 was found to be inhibited by CO

as well with rate= Kobs[(μ4-η2-1-heptyne)Rh4(CO)8(µ-CO)2][heptyne][CO]-1

In chapter 8, a study of the reaction of the catalytic precursor with enyne, C=C, resulted in the identification of a new class of butterfly clusters namely (1-heptenyne)Rh4(CO)7(µ-CO)2 with both the alkyne and the alkene moiety from the same

C≡C-C-C-C-the butterfly cluster and C≡C-C-C-C-the dinuclear rhodium alkyne species were characterized

From computational point view, an appropriate DFT method namely PBE/DGDZVP was found to accurately predict both the geometry and the vibrational spectra, Raman and Infrared, of rhodium carbonyl species The devised DFT method became an important tool

in carrying out geometrical assignments of non-isolatable species based solely on their observed vibrational spectrum

NOMENCLATURE

Abbreviations

BTEM Band-Target Entropy Minimization

CO carbon monoxide (gas or ligand)

DGDZVP Polarized double zeta basis set

Enyne 1,6-Heptenyne

Eq Equation

FTIR Fourier Transformed Infrared

LanL2DZ Los Alamos effective core potential plus double zeta basis set

MCT Mercury cadmium telluride used for infrared detection and they need cooling to temperatures near that of liquid nitrogen NMR Nuclear Magnetic Resonance

SSE Sum of squares error

d Diagonal scaling matrix for transforming normalized spectral estimates into

corresponding estimates with real absorptivity magnitudes

e Number of experiments carried out

Jˆ× Predicted pure component Raman scatter

k Number of spectra taken in each experiment

kobs Observable reaction rate constant

P Saturated vapor pressure of solvent

R Universal gas constant

v Partial molar volume of the dissolved CO gas at infinite dilution

V Total volume of a reaction mixture

E

s×

ν Atomic matrix

V Transposed matrix of the right singular vector

s

x mole fraction of chemical species s

z Number of meaningful right singular vector used to reconstruct the pure component spectra

∈ The prior symbol is an element of

∀ For all elements of

∫ Numerical integration using trapezoid rule

∂ Spectral derivative order (second and fourth)

γ User specified value of the severity of the non-negative constrain on the

estimated pure component spectra

ν total number of wavenumber channels in a FTIR/Raman spectrum

Γ spectral renormalization factor for reaction time t

Ω Objective function

ΔH‡ Enthalpy of activation

ΔS‡ Entropy of activation

ΔrG Equilibrium thermodynamic free energy of reaction

ΔrH Equilibrium thermodynamic enthalpy of reaction

ΔrS Equilibrium thermodynamic entropy of reaction

Figure 2.1 The suggested mechanism for the Co2(CO)8 mediated Pauson Khand

Figure 2.2 Figure 2.2 Rhodium based catalytic precursors capable of mediating PK Reaction 15

Figure 2.3 The proposed structures for Micosahedron; (3) C3v anticubeoctahedron; (4) C4(CO)12: (1) Td cubeoctahedron; (2) T 3v icosahedron; (5) D2d with

four bridging carbonyls (6) Triply Bridged ………

19 Figure 2.4 A schematic structure of the (μ4-η2-CH CH)Co4(CO)8(μ-CO)2.……….… 24 Figure 2.5 A schematic structure of the of (μ4-η

2-PhC2Ph)Co2Rh2(CO)8(μ-CO)2 and (μ4-η2-PhC2Ph)Co3Rh(CO)8(μ-CO)2 based on the reported X-ray by

(Horvath et al., 1986; Tunik et al., 1994).……… 25

Figure 3.1 General experimental setup for in situ spectroscopy approach Legend: 1 Stirrer Tank Reactor (CSTR); 2 Gas supply; 3 Pump; 4 Flow through

cell; 5 Spectrometer (FTIR/Raman) and 6 Data Acquisition.………

29

Figure 3.2

Experimental setup for the high pressure in situ FTIR measurements

Legend: 1 Autoclave; 2 Reservoir; 3 Thermoresisters; 4 Pressure

transducer; 5 Cryostat; 6 FTIR Spectrometer; 6 FTIR Spectrometer; 7

High pressure flow through cell; 8 Membrane pump; 9 Data Acquisition;

10 Deoxy and zeolite columns; 11 Gas tanks

31

Figure 3.3

Experimental setup for in situ FTIR measurements Legend: 1 Argon

tank; 2 Argon purification column; 3 Pressure transducer; 4 Jacketed

Continuous Stirrer Tank Reactor (CSTR); 5 Hermetically sealed Teflon

Pump; 6 FTIR with high pressure flow through cell; 7 Data Acquisition

Figure 3.7 Several right singular vectors (V

T) from the SVD of the experimental data: a) 1st vector, b) 2nd vector, c) 4th vector, d) 6th vector, e) 8th vector and f)

Figure 3.10

Spectra of the (a) solvent of aw mixture date (n-hexane +background),

with the band associated with the background highlighted and (b) The

pure component spectra of n-hexane after using the subtraction

Figure 4.1 Spectra of empty IR compartment which consists of (α) Moisture sharp

bands and (β) rotational of CO2 gas.……… 62 Figure 4.2 Spectra of the hexane (a) under 5 bar, (b) after turning on the pump and the stirrer and (c) under 10 bar of CO.……… 63 Figure 4.3 In-situ raw FTIR of semibatch 1 conducted under CO and temperature of 288 K in the range 1700-2300 cm-1……… 64

Figure 4.4 Several right singular vectors (V

T) from the SVD of the experimental data: a) 1st vector, b) 3rd vector, c) 6th vector, d) 7th vector, e) 12th vector, f) 70th

vector………

66

Figure 4.5 Pure component spectra of (a) n-hexane, (b) background and (c) dissolved CO gas obtained from BTEM analysis ……… 67 Figure 4.6 Pure component spectra obtained from BTEM analysis ……… 69 Figure 4.7 Relative concentrations provided by BTEM analysis for the 7 semibatch reactions………. 70

Figure 4.8

Validation / uniqueness test using TTFA (above) The spectrum of

species X superimposed on that of Rh4(CO)9(μ-CO)3 in the terminal CO

region (middle) Additional comparison to the Td symmetry of Ir4(CO)12

(below)………

75

Figure 4.9

The two possible geometrical isomers In the Td symmetry all -Rh(CO)3

moieties are similar (α) In contrast, the C3v symmetry’s apical -Rh(CO)3

has a different local environment (β)………

76

Figure 4.10 Properly scaled pure component spectra of the Rhodium based organometallics……… 79 Figure 4.11 The calculated equilibrium constants for all-terminal Rh4(CO)12………… 82 Figure 4.12 Estimation of thermodynamic parameters based on Van’t Hoff equation 83

Figure 5.1 Comparison between the theoretically predicted spectrum of HRh(CO)using PBE/DGDZVP and the experimentally observed spectrum after 4

Figure 5.4 DFT optimized geometry of the Rh2(CO)6(μ-CO)2 using

Figure 5.5 Different geometries of the all-terminal Rh2(CO)8 (left) D2d and (right) D3d

Figure 5.6 Comparison between the theoretically predicted spectrum of RhCO)3 plotted using (a) GaussView03 (b) Molden43 and the (c) 4(CO)9

(μ-experimentally obtained spectrum after BTEM deconvolution …………

99

Figure 5.7 Optimized geometry of Rh4(CO)9(μ-CO)3 using PBE/DGDZVP

compared with the X-ray determined structure.……… 100

Figure 5.8 High resolution experimental spectrum of Rhxenon (without deconvolution) and (b) in n-hexane after multi-4(CO)9(μ-CO)3 in (a) liquid

component BTEM deconvolution ………

Figure 5.11 Optimized geometry of Rh6(CO)12(μ3-CO)4 using PBE/DGDZVP and

comparison with the X-ray determined structure parameters ………… 105 Figure 5.12 Optimized geometries of acylrhodium (C2H5CO)Rh(CO)4 using DFT

with PBE/DGDZVP at different dihedral angles……… 107 Figure 5.13 Gibb’s Free energy of the optimized geometries of acylrhodium (C

2H5CO)Rh(CO)4 with different Dihedral angles……… 108 Figure 5.14 The predicted spectra for geometries a-d compared to the experimental spectrum e of acylrhodium (C

2H5CO)Rh(CO)4.……… ……… … 109 Figure 5.15

The optimized geometry along with predicted spectra of three possible

geometries axial, equatorial_1 and equatorial_2 of RCORh(CO)3(π-C2H4)

compared to the experimental spectrum (obtained from Li et al.,

Figure 5.17 Schematic of the newly designed high pressure in-situ IR cell for measurements in liquid xenon 1 Teflon Spacer; 2 KRS-5 windows; 3

Inlet to the stirred compartments of the cell; 4 Cryostat………

Figure 6.2 The spectra of the (a) background, (b) pure hexane (c) Rh4(CO)9(µ-CO)3

and (d) 20 min after alkyne injection.……… 118 Figure 6.3 The spectra of the (a) (μ4-η

2-HC2H)Co4(CO)8(μ-CO)2 (adopted from Gervasio

et al., 1985) and (b) signal of product formed in the current experiment

after preconditioning.………

119

Figure 6.4 DFT predicted spectrum of (μ4-η

2-2-butyne) Rh4(CO)8(μ-CO)2 plotted using (a) GaussView03 and (b) Molden43 and the (c) high resolution

experimental spectrum of (μ4-η2-3-hexyne) Rh4(CO)8(μ-CO)2.…………

122

Figure 6.5 DFT optimized geometry of the (μ4-η2-2-butyne)Rh4(CO)8(μ -CO)2 using

Figure 6.6

DFT predicted spectrum of (μ4-η2-propyne)Rh4(CO)8(μ-CO)2 using (a)

GaussView03 and (b) Molden43 and the low resolution experimental

spectra of (c) (1-heptyne)Rh4(CO)8(μ-CO)2 and (d) (μ4-η2

-phenylacetylene)Rh4(CO)8(μ-CO)2 …… ……

126

Figure 6.7 DFT optimized geometry of the (μ4-η2-propyne)Rh4(CO)8(μ -CO)2 using

Figure 6.8 Low resolution experimental spectra of (a) (μ4-η2

-phenyl-1-hexyne)Rh4(CO)8(μ-CO)2 (b) (μ4-η2-1-phenyl-1-butyne)Rh4(CO)8(μ -CO)2

128 Figure 6.9 The mole fraction of (a) (μ4-η

2-1-heptyne)Rh4(CO)8(μ -CO)2 and (b) (μ4

-η2-3-hexyne)Rh4(CO)8(μ -CO)2 (c) (μ4-η2-3-hexyne)Rh4(CO)8(μ -CO)2as a

function of reaction time.……….………

129

Figure 6.10 Deconvoluted pure component spectra of (a) (μ4-η

2-4-octyne)Rh4(CO)8CO)2 (b) (μ4-η2-1-octyne)Rh4(CO)8(μ-CO)2 (c) (μ4-η2-1-

(μ-heptyne)Rh4(CO)8(μ-CO)2 and (d) (μ4-η2-3-hexyne) Rh4(CO)8(μ-CO)2…… 131

Figure 6.11

Experimental setup for in situ Raman measurements Legend: 1 Stirring

plate; 2 Ten mL Schlenk tube; 3 Argon balloon; 4 Hermetically sealed

Teflon Pump; 5 In-house designed flow through Raman cell; 6 Raman

microscope; 7 Data Acquisition; 8 Cross sectional view of the new flow

through Raman cell.……… ………

134

Figure 6.12 In-situ mid-Raman spectra for the reactions of Rhhexyne at 298.15 K and 0.1 MPa (under argon) in the range 2200-1850 4(CO)9(µ-CO)3 with

136

Figure 6.13 Several right singular vectors (Va) 1st vector, b) 2nd vector, c) 3rd vector and d) 4T) from the SVD of the experimental data: th vector.……… 137

Figure 6.14 Comparison between the theoretically predicted mid-Raman spectrum of Rh4(CO)9(µ-CO)3 plotted using Molden43 and experimentally observed

spectrum.………

139

Figure 6.15 Comparison between the theoretically predicted mid-Raman spectrum of (μ4-η2-3-hexyne)Rh4(CO)10(μ-CO)2 plotted using Molden43 and

experimentally observed spectrum.………

139

Figure 6.16 In-situ far-Raman spectra for the reactions of Rh4(CO)9(µ-CO)3 with 3

hexyne at 298.15 K and 0.1 MPa (under argon) in the range 270-100 cm-1 141

spectrum of Rh4(CO)9(µ-CO)3.………

Figure 6.18

Comparison between (i) the theoretically predicted far-Raman intensities

using Gaussian, (ii) plotted using Molden43 and (iii) deconvoluted

spectrum of (μ4-η2-3-hexyne)Rh4(CO)10(μ-CO)2 3 predominant bands,

designated α, β and γ are highlighted for further discussion ……

13C NMR spectra (a) after adding 6 μL of 3-hexyne at -60 0C, (b) after

injection of an additional 6 μL of 3-hexyne at -60 0C, (c) -80 0C after

shaking NMR tube for 15 min and (d) at room temperature.………

2-C2H5CCC2H5)Rh4(CO)8(μ-CO)2 as a function

of reaction time (a) Rh4(CO)9(μ-CO)3 variation, (b) 3-hexyne variation and (c) CO partial pressure variation………

Figure 6.29 The orders of Rh4(CO)9(μ-CO)3, 3-hexyne and CO estimated using the

method of initial slopes ……… 162 Figure 6.30 The mole fraction of (μ4-η2-C2H5CCC2H5)Rh4(CO)8(μ-CO)2 as a function

of reaction time for 3 isothermal batch reactions ……… 163 Figure 6.31 The regression of rate constants,k obs, for each isothermal batch mole

fraction of (μ4-η2-C2H5CCC2H5)Rh4(CO)8(μ-CO)2 ……… 164 Figure 6.32 Regression of the apparent activation parameters.……… 164

Figure 7.1 The experimental spectrum of (a) Unknown species (b) (3-hexyne) -Rh2(CO)6 obtained from BTEM analysis and (c) (3-hexyne)Co2(CO)6

(adopted from Bitterwolf et al., 2000)………

168 Figure 7.2 Time series of raw reaction spectra for the reaction of 3-hexyne with Rh

Rh4(CO)8(µ-CO)2……….……… ………Figure 7.4 The Optimized geometries of (2-butyne)Rh2(CO)6 with the dihedral angle

Rh3-X2-C5-C4 frozen to (a) 90o, (b) 80o (c) 70o and (d) 50o ……… 173 Figure 7.5 Energy of the optimized geometries of (2-butyne)Rh2(CO)6 with different

Figure 7.8 The geometry of (a) (3-hexyne)Cohexyne)Co2(CO)5 formed after UV irradiation and (c) the 2(CO)6, (b) isomer 1 of

(3-thermodynamically more stable isomer 2 of (3-hexyne)Co2(CO)5.………

177

Figure 7.9 The Optimized geometries of (2-butyne)Rh2(CO)5 with the dihedral angle

C7-Rh2-Rh1-C4 frozen to (a) 0o, (b) 15o (c) 45o and (d) 60o … 178 Figure 7.10 Energy of the optimized geometries of (2-butyne)Rh2(CO)5.……… 178 Figure 7.11 The deconvoluted spectra of (3-hexyne)Rh2(CO)6 along with DFT

predicted spectra of various (2-butyne)Rh2(CO)6 geometries.……… 179 Figure 7.12 The relative metal carbonyl concentrations provided by BTEM analysis.…… ………….……… 180 Figure 7.13 Time series of raw reaction spectra for the reaction of Phenyl-1-hexyne with Rh

4(CO)9(μ-CO)3 ………….……… 182 Figure 7.14 The experimental spectrum of (a) Phenyl-1-hexyne)Rh2(CO)5 (b) butterfly

cluster and (c) Rh4(CO)9(µ-CO)3 obtain after BTEM analysis……… 183 Figure 7.15 The relative metal carbonyl concentrations provided by BTEM analysis 184

Figure 7.16 The experimental spectrum of (a) (1-heptyne)Rhheptyne)Rh2(CO)6 (c) butterfly cluster and (d) Rh2(CO)4(CO)5 (b) (1-9(µ-CO)3 obtain

after BTEM analysis.……….………

185 Figure 7.17 The relative metal carbonyl concentrations provided by BTEM analysis……….……… 187 Figure 7.18 Time series of (a) raw reaction spectra for the reaction of 1-heptyne with (1-heptyne)Rh

4(CO)8(μ-CO)2……… 189 Figure 7.19

Pure component spectra of (a) unknown species i, (b) unknown species ii, (c) unknown species iii, (d) (1-heptyne)Rh2(CO)5, (e) (1-

heptyne)Rh2(CO)6, (f) Rh6(CO)16, (g) (1-heptyne)Rh4(CO)8(µ-CO)2 and (h)

obtained from BTEM analysis.……… ………

Figure 7.23 The (a) pure component spectrum of the 1-heptyne in the C-H vibration region, (b) the raw data of semi-batch experiment 5 along with (c) its time

molar concentration of 1-heptyne ………

196

Figure 7.24 The mole fraction of (1-heptyne)Rhreaction time (a) CO partial pressure variation, (b) 1-heptyne variation and 4(CO)8(µ-CO)2 as a function of

(c) (1-heptyne)Rh4(CO)8(µ -CO)2 variation ………

197

Figure 7.25 The mole fraction of (μ4-η2-C2H5CCC2H5)Rh4(CO)8(µ-CO)2 as a function

of reaction time for 3 isothermal batch reactions ……… 199 Figure 7.26 The regression of rate constants,k obs, for each isothermal batch mole

fraction of (μ4-η2-1-heptyne)Rh4(CO)8(µ-CO)2……… 200 Figure 7.27 Regression of the apparent activation parameters……… 201

Figure 8.1 Time series of raw reaction spectra for the reaction of equivalent amounts enyne with Rh

Figure 8.6 Comparison between the experimentally observed spectra and the DFT predicted spectra for the two proposed geometries for the unknown

species X … ………

208

Figure 8.7 Time series of raw reaction spectra for the reaction of excess enyne with Rh

4(CO)9(μ-CO)3 ……… 210 Figure 8.8 The experimental spectrum of (a) (enyne)Rh2(CO)5 and (b)

(enyne)Rh2(CO)6 ……….… 211 Figure 8.9 The relative metal carbonyl concentrations provided by BTEM analysis… 212

Figure 8.10

Sonochemical apparatus Legend: 1 Ultrasonic power supply; 2 Convertor; 3 Injection port; 4 Sonochemical horn 5 Water bath ; 6 Stirring plate; 7 Membrane pump; 8 High pressure flow through cell 9 FTIR Spectrometer; 10 Data Acquisition; 11 Cryostat; 12 Pressure transducer ………

214

Figure 8.11 Time series of raw reaction spectra for the reaction of 1,6-heptenyne with Rh

4(CO)9(μ-CO)3 in cyclohexane. ……… 216

Figure 8.12 The deconvoluted spectra of (a) (1-6-heptenyne)Rhheptenyne)Rh4(CO)7(μ-CO)2, (c) (1-6-heptenyne)Rh4(CO)2(CO)8(µ-CO)5, (b) (1,6-2 and (d)

(1,6-heptenyne)Rh4(CO)8(µ-CO)2 ………

217

Figure A.2 Low-Pressure Setup……….……… 244 Figure A.3 Vertex 70, Bruker MIR spectrometer……….…… 244

Figure A.4 High Pressure Flow Through IR Cell……….……… 245 Figure A.5 n-hexane Refluxing Setup……….……….… 256

Figure C.1 Optimized geometry of (μ4-η2-HC2H)Co4(CO)8(μ-CO)2 using DFT with

Figure C.2 Comparison between the theoretically predicted spectrum of (μ4-η

2

-HC2H)Co4(CO)8(μ-CO)2 using PBE/DGDZVP and the experimentally

observed spectrum after deconvolution……….………

257

Figure D.1 Experimental setup for in situ Raman measurements Legend: 1 Argon balloon; 2 Ten mL Schlenk tube; 3 Stirring plate; 4 Hermetically sealed

Teflon Pump; 5 In-house designed flow through Raman cell ……… …

258 Figure D.2 Schematic of the flow through Raman cell …… … … … … ……. 258 Figure D.3 Schematic of the Raman microscope …… … … … … ………… 259 Figure D.4 The flow-through Raman cell was placed in a Raman microscope under a

5× microscope objective……….……… 259 Figure F.1 Sonochemical apparatus Legend: 1 Ultrasonic power supply; 2 Converter; 3 Membrane pump; 4 Water bath ……….……… 267

Figure G.1 In-situ raw far-infrared spectra of the hydroformylation of 3,3-dimethyl-1-but-ene in the range 400-700 cm-1………….…….…….…… …….…… 269 Figure G.2 The deconvoluted spectra of (a) Rh4(CO)9(μ-CO)3, (b) RCORh(CO)4, (c)

3,3-dimethyl-1-but-ene, and (c) aldehyde …….…….…….…….…….… 270

Figure H.1 Comparison between the theoretically predicted spectrum of HRh(CO)4 using (a) PBE/DGDZVP, (b) PBE/ DGDZVP [Rh]/6-311g (d,p) [C O]

and (c) the experimentally observed spectrum after deconvolution……… 272

LIST OF TABLES

Table 2.1 Biological activities of various cyclopentenones and their potential

applications.…… ……….…… ……….…… ……….…… 8 Table 2.2 Examples of relevant cobalt catalyzed Pauson Khand reaction…….…… 13 Table 2.3 PK catalytic reactions mediated by titanium and ruthenium based organometallics ……….……….……… 14 Table 2.4 First PK catalytic reactions mediated by rhodium based organometallics… 14 Table 2.5 Examples of PK reactions catalyzed mediated by rhodium based organometallics……… 16 Table 2.6 New protocols for carrying out PK catalytic reactions……….… 17 Table 2.7 List of known un-substituted neutral rhodium carbonyl species relevant to in-situ spectroscopic studies in matrices and hydrocarbon solutions…… 22 Table 3.1 Experiment design for the Rh4(CO)12 coordination reaction.………… 39 Table 3.2 Detailed describtion of the adopted objective function.……… 46 Table 3.3 List of the bands used for BTEM calculations and resultant pure components……… 47 Table 3.4 Pure component spectra recovered by BTEM calculations … ………… 48Table 3.5 Percentage of Reconstructed Integrated Absorbance of each Component compared to the Total original Experimental Data ……….… 52Table 3.6 Calculation of n-hexane molar absorptivity at 1136 cm-1.……… … 55Table 4.1 Experimental design of the 5 semibach experiment conducted under carbon monoxide.……….……… 60Table 4.2 Experimental design of the 2 semibach experiment conducted under helium.……….……… 61Table 4.3 List of the bands used for BTEM calculations and resultant pure components ……… ……… 66Table 4.4 Percentage of Reconstructed Integrated Absorbance of each Component compared to the Total original Experimental Data……… …… 71Table 4.5 Wavenumbers of the deconvoluted pure component spectra of Rhodium carbonyl species ……… ……….… 72Table 5.1 Experimental and calculated vibrational wavenumbers (cmHRh(CO) -1) for

4 and the corresponding deviation percentage (%) in Italic…… 91

Table 5.2 Comparison between predicted and experimental (obtained from McNeil and Scholer, 1977) bond distances (in Å) and angles (in deg) for HCo(CO)

4 93 Table 5.3 Predicted and experimental vibrational (obtained from Li et al., 2002) 93

Table 5.4 Predicted and experimental vibrational wavenumbers (cm

-1) for

Rh2(CO)6(μ-CO)2 and their normalized intensities with respect to the B2

mode.……….…

95

Table 5.5 Comparison between bond distances in Å and angles in degrees between the DFT optimized structures and X-ray structure of the Co2(CO)6

(μ-CO)2 (obtained from Leung and Coppens, 1983).……… ………

98

Table 5.6 Calculated and experimental vibrational wavenumbers (cmCo -1) for

2(CO)6(μ-CO)2 (obtained from Sweany and Brown, 1977).……… 98

Table 5.7 Calculated and experimental vibrational wavenumbers (cmRh -1) for

4(CO)9(μ-CO)3.……… ………… 100 Table 5.8 Predicted vibrational wavenumbers using PBE/DGDZVP and the experimental vibrational wavenumbers (cm-1) for Rh4(CO)9(μ-CO)3.…… 101 Table 5.9 Predicted vibrational spectrum using PBE/DGDZVP and experimental vibrational wavenumbers (cm-1) for Rh6(CO)12(μ3-CO)4…… ………… 104 Table 5.10 Calculated terminal vibrational wavenumbers (cmdeviation in percent from the experimental values ……… …… -1) and their respective 106Table 5.11 Calculated bridging vibrational wavenumbers (cmdeviation in percent from the experimental values……… -1) and their respective 106Table 5.12 Predicted and experimental vibrational wavenumbers (cm(C -1) for

Table 5.13 Calculated and experimental vibrational wavenumbers (cmRh -1) for

4(CO)11PPh3……… 112

Table 6.1 Mid-infrared carbonyl vibrational Spectra (cm-1) of (μ4-η2- Alkyne)-

M4(CO)8(μ-CO)2 butterfly clusters M=Rh, Co…… ……….…… 119

Table 6.2 Predicted and experimental vibrational wavenumbers (cmclusters formed symmetric alkynes and the one experimentally observed -1) for butterfly 123

Table 6.3 Mid-infrared carbonyl vibrational Spectra (cm-1) of (μ4-η2-terminal

Alkyne) -Rh4(CO)8(μ-CO)2 butterfly clusters ……….…… 127 Table 6.4 Experimentally observed wavenumbers (cmcomponent spectra of (μ -1) for the deconvoluted pure

4-η2-Alkyne)Rh4(CO)8(μ-CO)2 in d-benzene…… 132 Table 6.5 Predicted and deconvoluted mid-Raman wavenumbers (cmRh -1) for

4(CO)9(µ-CO)3 ……….…… ……….…… ……… 140

Table 6.6 Predicted and deconvoluted Raman wavenumbers (cm-1) for (μ4-η2

-3-hexyne)Rh4(CO)8(μ-CO)2 ….…… ……….…… ……… 140 Table 6.7 Predicted and experimental vibrational wavenumbers (cmRh -1) for

4(CO)9(µ-CO)3 ….…… ……….…… ……… 143 Table 6.8 Predicted and experimental vibrational wavenumbers (cm-1) for (μ4-η2-3-

hexyne)Rh4(CO)8(μ-CO)2….…… ……….…… ……… 143 Table 6.9 Representation of the DFT predicted vibrational modes in the far-Raman 144

bottom of each representation ……… Table 6.10 Representation of the DFT predicted vibrational modes in the far-Raman for (μ

4-η2-3-hexyne)Rh4(CO)8(μ-CO)2 ……… 144 Table 6.11 The 13C NMR spectra of Rh4(CO)9(µ-CO)3 and (3-hexyne)Rh4(CO)8(µ-

Table 6.12 Experimental Design for Kinetic Experiments… ……… 153 Table 6.13 Initial Rate of Reaction Experimental along with the molar fraction of species of interest … ……… ……… 162 Table 6.14 The estimated values of k as a function of temperature……… obs 164 Table 7.1 Experimental Design for the Preliminary investigation.………….…….… 167 Table 7.2 Comparison between the experimental spectrum of (3-hexyne)Rh2(CO)6

and its analog (3-hexyne)Co2(CO)6 (adopted from Bitterwolf et al., 2000)…… 169

Table 7.3 Experimental Design for the High Resolution Experiment……… 170 Table 7.4 Experimental Design for studying the fragmentation of (alkyne) -Rh

4(CO)8(µ-CO)2, alkyne= Phenyl-1-hexyne, 1-heptyne……… … 181 Table 7.5 Comparison between the experimental spectrum of various (alkyne)Rh

Table 7.6 Experimental Design for Kinetic Experiments.… ……… 188 Table 7.7 Experimental Design for High Pressure Experiment……… 193 Table 7.8 Comparison between the experimental spectrum of Rh2(CO)6{μ−η1-(CO-

HC2C5H11)} ……… … 195

Table 7.9 The estimated values of k as a function of temperature……… obs 200 Table 8.1 Experimental Design for the 1,6-heptyne Experiment……… ………… 203 Table 8.2 Experimental mid-infrared carbonyl vibrational Spectra (cm

-1 ) of (μ 4 -η 2 Alkyne)Rh 4 (CO) 8 (μ -CO) 2 butterfly clusters obtained by BTEM Alkyne=1-heptyne, 1,6-

Table 8.3 Mid-infrared carbonyl vibrational Spectra (cmheptenyne)Rh -1) of

(1,6-4(CO)7(µ-CO)2 butterfly clusters……… ……… 208 Table 8.4 Experimental Design for the excess 1,6-heptyne Experiment……… … 209 Table 8.5 Mid-infrared carbonyl vibrational Spectra (cm-1) of (alkyne)Rh2(CO)5 and

(alkyne)Rh2(CO)6, alkyne=1-heptyne, 1,6-heptenyne……… ……… 211

Table 8.6 Experimental Design for the Sonochemical Experiment………… …… 215 Table 8.7 BTEM reconstructed pure component spectra……… ……… 218

Co4(CO)8(μ-CO)2……… ……… ……… ………

Table C.2 Predicted and experimental vibrational wavenumbers (cm-1) for (μ4-η2

-HC2H)Co4(CO)8(μ-CO)2……… ……… ……… 257

Table H.1 Experimental and calculated vibrational wavenumbers (cmHRh(CO) -1) for

4 and the corresponding deviation percentage (%) in Italic …… 271

Introduction

The Pauson Khand (PK) reaction was discovered in 1971 (Khand, et al., 1971, 1973)

The PK reaction, both the intramolecular and intermolecular, is considered to be the main route to construct the cyclopentenones, see scheme 1.1 The latter is a high value added

commodity (Gibson, et al., 2004) mainly due to its biological activity in particular having

high potency as anti-tumor and anti-bacterial agent

a

O

CO Catalyst

Ph

Catalyst

+ CO

Scheme 1.1 The general form of (a) intramolecular and (b) intermolecular metal

mediated Pauson Khand Reaction

Despite the great economical potential the Pauson Khand (PK) reaction holds, to date it has not been commercialized largely due to harsh condition required or/and low yields

Chapter 1

CHAPTER 1 INTRODUCTION The early generation of PK reactions was mediated by cobalt and these reactions were largely stoichiometric and thus required large quantities of the expensive and toxic metal making the process undesirable The first truly catalyzed version of PK reaction, not

limited to constrained alkenes, was introduced in 1990 (Rautenstrauch et al., 1990) but

required harsh conditions in particular elevated pressure of 140 atm Other metals used to

mediate the PK reaction such as titanium (Hicks et al., 1996) and ruthenium (Kondo, et al., 1997) have been suggested Both metals produce positive results with good yields

under milder conditions, nevertheless, they still required high/higher pressures, circa 15 atm, and temperatures above 90oC

The introduction of a rhodium based catalyst to mediate the PK reaction (Kondo, et al., 1998; Jeong, et al., 1998) marked a new milestone as it (i) abolished the need of high

pressure CO requirements i.e the PK reaction can proceed at atm CO pressure and (ii) lead to drastic improvement in the yields However certain obstacles have not been fully resolved by the introduction of the rhodium based catalytic precursors, in particular the high temperature requirements and the lengthy reaction times which can be as long as 60 hours (Kobayashi, et al., 2001)

1.1 Problem Statement: Missing Links in the Early Events of

Rh4(CO)12 PK Reaction

Although the detailed mechanism of the cobalt mediated PK reaction remains unproven,

at least the early events of this reaction are relatively well documented The catalytic precursor Co2(CO)8 geometry and fluxionality in solution has been extensively investigated Furthermore, kinetic and mechanistic studies of the first step i.e the reaction

of the catalytic precursor Co2(CO)8 with alkyne to form (alkyne)Co2CO6 is well documented In addition, (alkyne)Co2CO6 have been isolated where its (i) X-ray crystal structure and (ii) spectroscopic assignments of its vibrational spectrum have been reported

Unfortunately and to the best of the author’s knowledge, similar studies on the early events of the PK reaction mediated by rhodium based catalytic precursors have not been reported/attempted

The current dissertation will investigate the early events of Rh4(CO)12 mediated PK reaction Rh4(CO)12 was selected partly due to our research group’s expertise in handling and analyzing the latter cluster and to the fact that it has been used to mediate PK reaction

In particular, this study will focus on (i) understanding the catalytic precursor, (ii) the reaction of the precursor with various alkynes where the nature of the intermediates formed and their rate of formation will be investigated using in-situ spectroscopy

For the Rh4(CO)12 mediated PK reaction, two prime candidates are hypothesized to be the active species, namely (I) Rh2(CO)8 and (II) (alkyne)Rh2(CO)6.†Both of these transformations are poorly understood under PK reaction conditions The transformation

of the parent cluster to Rh2(CO)8, was only studied at extreme pressures, therefore, the obvious question is wither (I) it exists at low or even atmospheric pressures i.e typical PK reaction condition? On the other hand, the second dinuclear rhodium species (II) (alkyne)Rh2(CO)6 have not been observed yet despite the fact that its analogue (alkyne)Co2(CO)6 have been identified for more the 50 years (Sly, 1959) All of these

missing links listed above were the main driving force in carrying out most of the research conducted in this thesis

1.2 Thesis Objectives

From the discussion above, one can see that further improvement of the PK reaction conditions is needed in order to bring the idea of “Commercialized PK reaction” closer to reality However, optimization of the reaction and the developing of adequate protocols

CHAPTER 1 INTRODUCTION requires a sound understanding of the reaction mechanism, which to date remains largely due unsupported, due to the absence of mechanistic studies on the reaction

The main objective of the current dissertation is to study the pre-catalytic steps of the

Rh 4 (CO) 12 mediated Pauson Khand reaction which is an important step towards

understanding the entire reaction mechanism and the catalytic cycle of the reaction Consequently, here are the specific targets that the current thesis will be addressing

Target 1: Investigate the catalyst precursor Rh4(CO)12, in particular its geometry and fluxionality in solution along with studying its transformations under various gas partial pressures

characterize the intermediates involved and the mechanism of their formations

1.3 Thesis Organization

The thesis consists of nine chapters Chapter 2 Literature Review presents a brief

historical background of the Pauson Khand Reaction and highlights its significance In addition, basic information on the unmodified rhodium carbonyl precursor Rh4(CO)12

along with the available literature reports on its reaction with alkyne will be described

Chapter 3 In-Situ Spectroscopy and Methodology briefly introduces experimental

setups used to carry out the in-situ flow through spectroscopic measurements In addition,

Band-Target Entropy Minimization (BTEM), the primary numerical tool for decovoluting the collected raw spectra, will be discussed For illustration purposes, the procedure of collecting the spectra data and its analysis using BTEM will be carried out on the relatively simple reaction of Rh4(CO)12 with triphenyl phosphine, PPh3

Chapters 4 to 8 describes the experimental work carried out on Rh4(CO)12 and its

reaction with alkynes Chapter 4 Tetrarhodium Dodecacarbonyls provides the

experimental study of the Rh4(CO)12 under variety of temperatures and under various

pressures of CO and He In Chapter 5 Density Functional Theory the author searches

for an appropriate DFT method to describe rhodium metal carbonyl clusters sufficiently

well so that the good infrared predictability is achieved Chapter 6 The Homometallic

Rhodium Butterfly Cluster describes the study carried out on the formation of various

butterfly clusters (alkyne)Rh4(CO)10 by reacting equimolar amounts of alkyne with

Rh4(CO)12 Chapter 7 The Dirhodium Alkyne Species provides the in-situ spectroscopic

study of the reaction of excess alkyne with Rh4(CO)12 and the formation of (alkyne)Rh2(CO)6 and (alkyne)Rh2(CO)5 Chapter 8 The Reaction of Rh 4 (CO) 12 with Enyne Species Analyze the in-situ spectroscopic data collected from monitoring the

reaction of Rh4(CO)12 with enyne, a substrate used for PK reaction, in an attempt to prove that indeed the identified butterfly and rhodium dimers, observed earlier in chapter 6 and 7 respectively, exist in this system

Chapter 9 Conclusion and Future Work provides a summary of the obtained results

and their implications In addition, recommendation for future experiments will be presented

Literature Review

The current chapter presents a brief background on the Pauson Khand (PK) reaction Furthermore, the importance of the product formed, cyclopentenones, that makes PK reaction a subject of great interest will be highlighted In addition, the advantages of using rhodium based organometallics over the traditional dicobalt octacarbonyl and other metal based organometallics to mediate PK reaction will be described Finally, a review of

Rh4(CO)12, the catalyst precursor used in this thesis and its reactions with alkynes will be presented

2.1 Pauson Khand Reaction

The PK reaction was discovered in 1971 (Khand et al., 1971, 1973) where the

invaluable cyclopentenones were constructed by coupling readily available stocks namely carbon monoxide, alkenes and alkynes The superiority of this reaction lies in the ability to

form three carbon-carbon bonds in a single synthetic step as shown in scheme (2.1) It is

not surprising that the PK reaction was highlighted by Trost in his classical paper on the

Chapter 2

concept of “atom economy” where the PK reaction was listed among various efficient reactions wherein complex products were assembled from simple reactants in a single step (Trost, 1991)

O

CO

Catalyst

Scheme 2.1 The general form of metal mediated Pauson Khand Reaction

To date, metal mediated Pauson Khand Reactions continue to be the main route to

generate high value-added and biologically active cyclopentenones (Gibson et al., 2004)

Before proceeding, the author would like to describe the great value of the product formed, cyclopentenones, by highlighting some of its applications

Substituted cyclopentenones are of considerable interest to the pharmaceutical industry

as they often displayed high potency as anti-tumor and anti-bacterial reagents (Roberts et

al 2002) Table 2.1 provides a few examples of cyclopentenones and their applications in

the pharmaceutical industry

CHAPTER 2 Literature Review

Table 2.1 Biological activities of various cyclopentenones and their potential applications

Cyclopentenone Applications References

O

(CH2)5CO2R

C5H11 HO

Anti-tumor activity (Fukushima et al., 2001)

Anti viral drugs (Gibson et al., 2004)

O

O

Cytotoxic and antimicrobial activities (Srikrishna, 2003)

Furthermore, certain classes of cyclopentenones have been reported to inhibit influenza

and human immunodeficiency virus (HIV) (Gibson et al., 2004) and possess antimalarial

and anticancer activity (Marrero et al 2004) In addition, cyclopentenones derivatives are

important building blocks for the perfume industry (Cornils et al., 2002)

2.1.1 Early Pauson Khand reactions

The very first reported PK reaction (Khand et al., 1971) involved two main steps, see

scheme (2.2) First, the respective alkyne was reacted with dicobalt octacarbonyl

Co2(CO)8 to form the relatively stable (alkyne)Co2(CO)6 complex, step A Then, the latter

was heated in the presence of an alkene to produce substituted cyclopentenone in

stoichiometric amounts, step B

C C C

C

C O O O

O

O O

C

C O

O

O

O

O O

60-700C 4hrs DME

O

R1

R2

Scheme 2.2 Early PK reactions process which proceed as follow, (a) formation of the (alkyne)Co2 (CO) 6 which then

(b) reacts in stoichiometric amounts with alkene to form cyclopenteone

The above reaction was limited to constrained alkenes, such as norbornadiene, and the yields of the reaction with different alkynes were modest with highest conversions of 45

%, achieved when phenyl substituted alkynes were used Almost a decade later, another form of the reaction, coined intramolecular Pauson Khand reaction, was introduced by Schore (Schore, 1981) with the obvious difference that both alkene and alkyne moieties are located on the same molecule, see scheme (2.3)

O

120 o C/heptane

3 days

Co2(CO)8

Scheme 2.3 Intramolecular Pauson Khand reaction using various enynes

While the above reaction extended the utility of the PK reaction to include enyne substrates, the yield was still modest, (58 %), despite the long reaction time

2.1.2 Reaction Mechanism for the Pauson Khand Reaction

Magnus and co-workers proposed a mechanism for the stoichiometric reaction as shown

in Figure 2.1 The first step is the formation of the (alkyne)Co2CO6, complex 2, which to

date, is the only observed intermediate in the proposed mechanism Its X-ray crystal structure has been reported (Sly, 1959) In addition, spectroscopic assignments of its

CHAPTER 2 Literature Review

vibrational spectrum have been well documented (Iwashita et al., 1969) and the kinetics of

its formation has been reported (Ellgen, 1972) The second step involves the dissociation

of one CO ligand, which is presumed to be the rate limiting step as a number of density

functional studies have suggested (Pericas et al., 2002; Yamanaka, 2001) Complex 3, the

unsaturated (alkyne)Co2(CO)5, was not observed under reaction condition but its spectra was reported after irradiation of the (alkyne)Co2(CO)6 with short UV light in Argon

Matrix (Gordon et al., 1998) and more recently in frozen Nujol matrices (Bitterwolf et al.,

2000)

After the dissociation of the CO ligand, the complexation with reacting olefin to occupy

the available coordination site takes place, structure 4 Afterwards, a cobalt metallocycle

is formed with CO coordination to form structure 5 Finally, the reductive elimination step

to produce the cyclopentenones takes place The lack of catalytic activity for Co2CO8 in the PK mediated reaction was blamed on the formation of Co4(CO)12 which was deemed thermally inactive (Jeong, 1998)

C C C

C CC O O O O

O O

O O

C

C C

C C C O O O

O

O O H

O O O

O O

C CC O O O

O O

C

C C

O O O

O O CO

O O O

O

O CO O

Co4(CO)12

1

2

3 4

It is quiet apparent that much of the proposed mechanism remains unproven as none of

the postulated intermediates beyond (alkyne)Co2CO6 have been observed, a remark that has been reiterated repeatedly in virtually all recent reviews of the PK reaction (Blaco-

Urgiti et al., 2004; Gibson et al., 2005) Nevertheless, the author believes that the

proposed mechanism is useful in particular to realize that the CO dissociation is the rate limiting step This lead researchers to use a range of additives/reagents such as N-oxide

(Blanco-Urgoiti et al., 2004) for the purpose of oxidizing one of CO ligand on

(alkyne)Co2CO6, forming CO2, and thus forming a vacant site to allow the coordination of the olefins Indeed, this approach successfully accelerated the stoichiometric PK reaction and it was further exploited where it was the basis for photo-induced catalytic PK reaction,

CHAPTER 2 Literature Review which will be described in the next section, where UV light was used to dissociate the CO ligand (Pagenkopf, 1996)

2.1.3 Cobalt catalyzed Pauson Khand Reaction

The stoichiometric nature of the reaction described above was undesirable as it leads to the consumption of large amounts of toxic and expensive transition metal species making the process uneconomical for industrial application Consequently, there is a constant drive to develop new routes that can mediate the reaction catalytically Some of the historical developments relevant to the catalyzed PK reactions are presented in Table 2.2

It is quite interesting that Pauson and co-workers were the ones who presented the first example of the catalytic PK reaction, entry 1 Table 2.2, shortly after they discovered it

(Khand et al., 1973) While reaction conditions were relatively moderate, the scope of the

reaction was limited to constrained alkenes It took 30 years until Rautenstrauch

(Rautenstrauch et al., 1990) widened the scope of the reaction to simple alkynes,

1-heptyne, and ethane as the olefin source, entry 2 The evident disadvantage of the latter scheme is the high pressure requirements A few years later Livinghouse (Pagenkopf, 1996) introduced the photo-activated reaction proceeding under 1 atm of CO While the

latter process sounds promising, Herrmann (Cornils et al., 2002) indicated that the

photochemistry of metal carbonyls do not have “the slightest chance of an upscaled application” One of the more recent advances in the PK reaction was reported by Jeong,

where the reaction was carried out in supercritical ethylene (Jeong et al., 2000)