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The Photochemical Properties of Arene Metal Carbonyl Complexes of Group 6 and 7 Elements

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The Photochemical Properties of Arene Metal Carbonyl Complexes of Group 6 and 7 Elements THE PHOTOCHEMICAL PROPERTIES OF ARENE METAL CARBONYL COMPLEXES OF GROUP 6 AND 7 ELEMENTS DCU THIS THESIS IS PRESENTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY AT DUBLIN CITY UNIVERSITY BY Peter Brennan B.Sc. UNDER THE SUPERVISION OF DR. MARY PRYCE AND PROF. CONOR LONG SCHOOL OF CHEMICAL SCIENCES FEBRUARY-2003 DECLARATION I hereby certify that this thesis, which I now submit for assessment on the programme of study leading to the award of Doctor of Philosophy is entirely my own work and has not been taken from the work of others save and to the extent that such work has been cited and acknowledged within the text of my work Signed :________________________ Date :_________________________ Peter Brennan Student ID No. 97970646 Table of contents Page Title i Declaration ii Table of contents iii Acknowledgements ix Abstract x Chapter 1 Literature survey 1.1 Introduction to the chemistry of organometallic complexes 2 1.2 UV/vis monitored flash photolysis 8 1.3 Time Resolved InfraRed (TRIR) Spectroscopy 10 1.3.1 Step scan TRIR spectroscopy 10 1.3.2 Point by point TRIR 12 1.4 Matrix isolation 14 1.5 Bonding in M-CO complexes 19 1.6 Metal - Arene bonding 24 1.7 The electronic absorption spectra of (fi6-arene)Cr(CO)3 complexes 26 1.8 Photochemistry of (ri6-arene)M(CO)3 complexes 27 1.9 Photochemistry of (r|S-CsHs)Mn(CO)3 complexes 32 1.10 Arene exchange reactions 35 1.11 Ring slippage reactions 41 1.12 The Indenyl ligand effect 43 1.13 References 46 Chapter 2 The photochemistry of substituted arene metal carbonyls 2.1 Introduction to the photochemistry of (r|6-arene)Cr(CO)3 complexes 51 2.2 Spectroscopic properties of (r|6-C6H6)Cr(CO)3, (r|6-C6HsNH2)Cr(CO)3, (Ti6-C6HsOCH3)Cr(CO)3, (Ti6-C6HsC02CH3)Cr(C0)3 and (r|6-C6H5COH)Cr(CO)3 52 Page 2.3 X-ray crystallography of substituted (ri6-arene)Cr(CO)3 complexes 56 2.4 Steady state photolysis of (r|6-arene)Cr(CO)3 complexes in CO saturated cyclohexane and 1,1,2 trifluorotrichloroethane 59 2.5 UV/vis flash photolysis of the substituted (r)6-C6HsX)Cr(CO)3 systems (X = NH2, OCH3, C(CO)OCH3, C(O)H) at A,exc = 355 nm in CO / argon saturated cyclohexane 66 2.5.1 UV/vis flash photolysis of the substituted (ri6-C6HsX)Cr(CO)3 systems ( X = NH2, OCH3, C(CO)OCH3, C(O)H) at K xc = 355 nm in CO saturated cyclohexane, the primary photoproduct 66 2.5.2 UV/vis flash photolysis of the substituted (r|6-C6HsX)Cr(CO)3 systems ( X = NH2, OCH3, C(CO)OCH3, C(O)H) at A,cxc = 355 nm in CO saturated cyclohexane, the secondary photoproduct 76 2.6 UV /vis flash photolysis of the substituted (r|6-C6HsX)Cr(CO)3 systems ( X = NH2, OCH3, C(CO)OCH3, C(O)CH) at ^exc = 355 nm in 1,1,2 trichlorotrifluoroethane 84 2.7 Discussion 86 2.8 Conclusions 92 2.9 References 93 Chapter 3 The photochemistry of (Tis-C4H4S)Cr(CO)3 and (r|5-C4H4Se)Cr(CO)3 3.1 Introduction to the use of transition metal complexes as models for hydrodesulphurisation 96 3.1.1 Thiophene complexes as model compounds for the hydrodesulphurisation process 96 3.1.2 Selenophene complexes as model compounds for the hydrodesulphurisation process 103 3.2 Bonding and reactivity in Cn5-C4H4S)Cr(CO)3 complexes 105 3.3 Photoinduced ring slippage in cyclopentadienyl metal carbonyl systems 110 Page 3.4. Organometallic complexes in modelling the hydrodesulphurisation process 111 3.5 Spectroscopic parameters for (r|S-C4H4S)Cr(CO)3 112 3.6 UV/vis, IR and NMR monitored steady state photolysis of (Tis-C4H4S)Cr(CO)3 114 3.7 Photochemical Investigations of (r|S-C4H4S)Cr(CO)3 using both step scan and point by point TRIR techniques 121 3.8 Matrix isolation experiments on (r|S-C4H4S)Cr(CO)3 with IR detection 128 3.9 UV/vis flash photolysis of (r|s-C4H4S)Cr(CO)3 at A,exc = 266 nm and 355 nm 131 3.10 Spectroscopic parameters for (r|S-C4H4Se)Cr(CO)3 134 3.11 UV/vis, IR and NMR monitored steady state photolysis of (Tis-C4H4Se)Cr(CO)3 136 3.12 TRIR spectroscopy experiments on (r|5-C4H4Se)Cr(CO)3 142 3.13 Matrix isolation experiments on (r|S-C4H4Se)Cr(CO)3 with IR detection 146 3.14 UV/vis flash photolysis of (ri5-C4H4Se)Cr(CO)3 at A,exc = 266 nm and 355 nm 150 3.15 Discussion 153 3.14 Conclusions 162 3.15 References 163 Chapter 4 The photochemistry of (r|6-C8H6S)Cr(CO)3 and (r|6-Ci2H8S)Cr(CO)3 4.1 Introduction to the photochemistry of polyaromatic (r|6-arene)Cr(CO)3 complexes 166 4.2 Benzothiophene and dibenzothiophene complexes as model compounds for the hydrodesulphurisation process 166 4.3 TRIR experiments on (ri6-C8H6S)Cr(CO)3 175 v Page 4.4 Matrix isolation studies of (r|6-C8H6S)Cr(CO)3 in nitrogen and argon matrices 177 4.5.1 UV/vis monitored laser flash photolysis of (r|6-C8H6S)Cr(CO)3 in CO saturated cyclohexane, the primary photoproduct 183 4.5.2 UV/vis monitored laser flash photolysis of (r|6-C8H6S)Cr(CO)3 in argon saturated cyclohexane, the secondary photoproduct 192 4.6 UV/vis monitored laser flash photolysis of (r|6-Ci2H8S)Cr(CO)3 in CO saturated cyclohexane, the primary photoproduct 195 4.6.1 The secondary photoproduct UV/vis monitored laser flash photolysis of (r|6-Ci2H8S)Cr(CO)3 in argon saturated cyclohexane, the secondary photoproduct 201 4.7 Discussion 204 4.8 Conclusion 211 4.9 References 212 Chapter 5 The photochemistry of (r|5-C4H4N)Mn(CO)3 5.1 Introduction to the photochemistry of (r|5-CsH5)Mn(CO)3 215 5.2 Bonding in (rjS-C5Hs)Mn(CO)3 complexes 215 5.3 Haptotropic shifts in (r|S-CsHs)Mn(CO)3 complexes 216 5.4 Haptotropic shifts in (t|5-C4H4N)Mn(CO)3 complexes 220 5.5 Thermal CO substitution reactions of (r)5-C4H4N)Mn(CO)3 Complex 221 5.6 Spectroscopic properties of (r]S-C4H4N)Mn(CO)3 223 5.7 IR and UV/vis steady state monitored photolysis of (r|5-C4H4N)Mn(CO)3 224 5.8 TRIR spectroscopy of (ri5-C4H4N)Mn(CO)3 227 5.9 Matrix isolation studies of (r|5-C4H4N)Mn(CO)3 229 5.10 UV/vis monitored laser flash photolysis of (r|5-C4H4N)Mn(CO)3 in CO saturated cyclohexane, the primary photoproduct 234 vi Page 5.11 UV/vis monitored laser flash photolysis of (ris-C4H4N)Mn(CO)3 in argon saturated cyclohexane, the secondary photoproduct 241 5.12 Discussion 245 5.13 Conclusions 248 5.14 References 249 Chapter 6 Experimental 6.1 Materials 252 6.2 Equipment 252 6. 3 The synthesis of (r|6-arene)Cr(CO)3 252 6. 3. 1 The reaction of chromium hexacarbonyl with arene, for the synthesis of(ri6-arene)Cr(CO)3 252 6.3.2 The synthesis of (r)6-C6HsOCH3)Cr(CO)3 253 6.3.3 The synthesis of (r]6-C6HsNH2)Cr(CO)3 253 6.3.4 The synthesis of (r|6-C8H6S)Cr(CO)3 254 6.3.5 The synthesis of (ri6-Ci2H8S)Cr(CO)3 255 6.3.6 The synthesis of (r|6-Ci4Hio)Cr(CO)3 255 6.3.7 The synthesis of (r|S-C4H4N)Mn(CO)3 256 6.4 The arene exchange reaction 256 6.4.1 The arene exchange reaction of (r|6-Ci4Hio)Cr(CO)3 with C4H4S to yield (r|5-C4H4S)Cr(CO)3 257 6.4.2 The arene exchange reaction of (r|6-Ci4Hio)Cr(CO)3 with C4H4Se to yield (t|5-C4H4Se)Cr(CO)3 258 6.5 Attempted preperative photochemical synthesis of (Ti4-C4H4Se)Cr(CO)4 259 6.5.1 Procedure for the synthesis of (r|4-C4H4Se)Cr(CO)3 260 6.6 Determination of molar absorbtivity values 262 6.7 Determination of solubility of CO in alkane solution 262 vii Page 6.8 Determination of quantum yields for the photo displacement of the arene ring in the (ri6-C6HsX)Cr(CO)3 systems (X = NH2, OCH3, C(0)0CH3 and C(O)H) 263 6.8.1 Preperation of the actinometry solution 263 6.8.2 Determination of the light intensity of the source 263 6.8.3 Calculation of light intensity of source 264 6.9 Laser flash photolysis with UV/vis monitoring 264 6.10 T.R.I.R spectroscopy 265 6.11 References 266 Appendix A Data for determination of quantum yields for arene displacement of the substituted (r|6-arene)Cr(CO)3 systems (X = NH2, OCH3, C 02CH3, C(O)H) at 298 K 267 Appendix B Data for determination of molar absorbtivity values at 298 K 280 Appendix C Data for determination of second order rate constants at 298 K 295 viii Acknowledgements I would like to say a most heartfelt thanks to all the following people; Prof. Conor Long and Dr. Mary Pryce for all their support, help and advice over the past few years. All members past and present of the research group, Bronagh, Carl, Ciaran, Davnat, Jennifer and Kevin. All members of the chemistry department, especially the technicians, who were always at hand to help when a problem arose.
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