Electronic Structure and Bonding in Pyrrolic Macrocycle-Supported Complexes of Actinides
A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering.
2018
Kieran Thomas Patrick O’Brien
School of Chemistry
Contents
Contents
Section Page number List of tables 5 List of figures 9 Abstract 15 Declaration 16 Copyright Statement 17 Publications 18 Abbreviations 19 Acknowledgements 23
Part I. Introduction
Chapter 1. Theoretical background and methodology 26 1. Aims and objectives 26 2. Quantum chemistry 27 3. Density functional theory 33 4. Mulliken and Hirshfeld population analysis 37 5. Natural bond orbital analysis 39 6. The quantum theory of atoms in molecules 41 7. Energy decomposition analysis 46 8. Nucleus-independent chemical shifts 46 9. References 48
Chapter 2. Organometallic chemistry of the f-elements 52 1. Background and chemistry of organoactinides 52 2. Computational organometallic chemistry of the f- 56 elements 2.1. DFT and orbital-based partition methods 57
1
Contents
2.2. QTAIM analysis of organometallics of the f-block 62 elements 2.3. Non-partition-based methods – EDA and NICS 63 analysis 3. Recent developments in carbocyclic organoactinide 65 chemistry 3.1. The trans-calix[2]benzene[2]pyrrolide ligand 66 4. References 69
Chapter 3. Methodology 77 1. Model complexes 77 2. Computational methodology 80 3. References 82
Part II. Results and Discussion
Chapter 4. Geometry optimisations and electronic 85 structures 1. Geometry optimisations of Th(IV) complexes 86 2. Geometry optimisations of U(III) complexes 91 3. Geometry optimisations of Th(III) complexes 98 4. Partial charge analyses of Th(IV), U(III) and Th(III) 101 complexes 5. QTAIM analysis 107 6. NBO analysis 116 6.1. Transition metal complexes 125 7. Mulliken population analysis of the An-X interaction 138 8. Nucleus-independent chemical shift analysis 143 9. Mulliken population analysis of the An-arene 149 interaction 10. Conclusions and future work 153 11. References 157
2
Contents
Chapter 5. The strength of the An-X interactions 159 1. Introduction 159 2. Methodologies 159 3. Results 162 4. Heterolytic reactions 165 5. Homolytic reactions 170 6. Functional dependence of QTAIM vs bond energies 177 7. QTAIM metrics vs EDA data for [LAnX]n+ complexes 180 7.1. QTAIM metrics vs EDA data for [LAnX’]n+ complexes 184 7.2. QTAIM metrics vs EDA data for [LAnX*]n+ complexes 188 7.3. QTAIM metrics vs EDA data for [LAnX’’]n+ complexes 190 7.4. QTAIM metrics vs EDA data for [LAnX**]n+ 194 complexes 7.5. QTAIM metrics vs EDA data for [LAnX†]n+ complexes 195 8. Conclusions and future work 199 9. References 201
Chapter 6. Bimetallic L2-/4- alkyl and alkynyl complexes 202 1. Introduction 202 2. Computational details 204 3. Results – Complexes 1 and 2 204 4. Complexes 3, 4 and 5 208 5. Complexes 6 and 7 212 5.1 Dipoles of Th6 and Th7 215 5.2 Molecular orbitals of Th6 and Th7 217 5.3 Comparisons with M(IV) and other An(IV) centres 227 for 6 5.4 Comparisons with other An(IV) centres for 7 237 6. Conclusions and future work 245 7. References 248
3
Contents
Chapter 7. Overall conclusions and future work 249 1. Geometry optimisations and electronic structures 249 2. The strength of the An-X interactions 250 3. Bimetallic L2-/4- alkyl and alkynyl complexes 251 4. Concluding remarks 252 5. References 254
Appendix 255 1. PBE0 Cartesian coordinates (Å) and SCF energies 256 (Hartrees) of all complexes studied in chapter 4. 2. PBE0 Cartesian coordinates (Å) and SCF energies 264 (Hartrees) of all complexes studied in chapter 5. 3. PBE0 (unless stated otherwise) Cartesian coordinates 278 (Å) and SCF energies (Hartrees) of all complexes studied in chapter 6.
4
List of tables
List of tables
Chapter 4 Page number
Table
4.1. Key bond lengths of thorium and uranium 88 complexes with experimental data. 4.2 Key bond angles of thorium and uranium 88 complexes with experimental data 4.3 MAD analysis for PBE and PBE0 for N(av) 96 4.4 MAD analysis for PBE and PBE0 for An-Ar1 96 4.5 MAD analysis for PBE and PBE0 for An-Ar2 97 4.6 MAD analysis for PBE and PBE0 for An-X 97 4.7 MAD analysis for PBE and PBE0 for Ar-An-Ar 97 4.8 MAD analysis for PBE and PBE0 for N-An-N 98 4.9 MAD analysis for PBE and PBE0 for interplanar 98 angles 4.10 Key bond lengths and angles for Th(III) complexes 99 4.11 Differences of bond lengths for LUIIIX and [LThIVX]+ 100 4.12 Partial charges for Th(IV) complexes 102 4.13 Partial charges for U(III) complexes 102 4.14 Partial charges for Th(III) complexes 102 4.15 QTAIM metrics for [LAnX]n+ 107 4.16 R2 values from trends in figures 4.21 to 4.23. 112
4.17 QTAIM metrics for [LAnNH2]n+ 113 4.18 R2 values from trends in figures 4.24 to 4.26. 115 4.19 NBO data for Th(IV) and Th(III) 117 4.20 R2 values for figure 4.26. 119 4.21 R2 values for figure 4.27. 120 4.22 R2 values for figures 4.28 to 4.30. 122 4.23 R2 values for figures 4.31 to 4.33 125 4.24 M-X bond lengths for Hf(IV) and W(III) 127
5
List of tables
4.25 QTAIM metrics for [LMX]n+ 129 4.26 NBO data for Hf(IV) and W(III) 133 4.27 Mulliken KS-MO data for [LAnX]n+ An centre 138 4.28 Mulliken KS-MO data for [LAnX]n+ X ligand 139 4.29 R2 values for figures 4.49 to 4.51 142 4.30 NICS data for [LThX]+ 145 4.31 Mulliken KS-MO data for [LAnX]n+ An-arene 150 4.32 HOMO energies for [LAnX]n+ 153
Chapter 5 Page number
Table 5.1 Key bond lengths for [LAnX]n+ 161 5.2 Key bond angles for [LAnX]n+ 161 5.3 SCF energies ZPE and thermal corrections for the 162 [LThIVX]+ 5.4 SCF energies ZPE and thermal corrections for the 162 LThIIIX 5.5 SCF energies ZPE and thermal corrections for the 163 LUIIIX 5.6 Energies of molecular ionic fragments with ZPE 163 and thermal corrections 5.7 Energies of molecular radical fragments with ZPE 164 and thermal corrections 5.8 Heterolytic bond enthalpies and Gibbs free 165 energies for [LThIVX]+ 5.9 Heterolytic bond enthalpies and Gibbs free 165 energies for LThIIIX 5.10 Heterolytic bond enthalpies and Gibbs free energies 166 for LUIIIX 5.11 Homolytic bond enthalpies and Gibbs free energies for 171 IV + [LTh X] 5.12 Homolytic bond enthalpies and Gibbs free 171 energies for LThIIIX
6
List of tables
5.13 Homolytic bond enthalpies and Gibbs free 172 energies for LUIIIX 5.14 QTAIM charge and interaction energies for Th(IV) 176 and Th(III) 5.15 PBE ΔE values for [LAnX]n+ 178 5.16 QTAIM PBE metrics 178 5.17 Th(IV)-X EDA energies 180 5.18 Th(III)-X EDA energies 180 5.19 U-X EDA energies 181 5.20 An-X EDA energies for [LAnX’]n+ 185 5.21 QTAIM metrics for [LAnX’]n+ 185 5.22 R2 values for EDA vs QTAIM for [LAnX’]n+ 186 5.23 R2 values for EDA vs QTAIM for [LThX]+ and 187 [LThX’]+ 5.24 R2 values for EDA vs QTAIM for LThX and LThX’ 187 5.25 R2 values for EDA vs QTAIM for LUX and LUX’ 187 5.26 An-X EDA energies for [LAnX*]n+ 198 5.27 QTAIM metrics for [LAnX*]n+ 198 5.28 R2 values for EDA vs QTAIM for [LAnX*]n+ 199 5.29 R2 values for EDA vs QTAIM for all [LAnX’]n+ and 190 [LAnX*]n+ 5.30 R2 values for EDA vs QTAIM for all [LThX’]n+ and 192 [LThX*]n+ 5.31 An-X EDA energies for [LAnX’’]n+ 193 5.32 QTAIM metrics for [LAnX’’]n+ 193 5.33 R2 values for EDA vs QTAIM for [LAnX’’]n+ 194 5.34 An-X EDA energies for [LAnX**]n+ 194 5.35 QTAIM metrics for [LAnX**]n+ 195 5.36 R2 values for EDA vs QTAIM for [LAnX**]n+ 195 5.37 An-X EDA energies for [LAnX†]n+ 196 5.38 QTAIM metrics for [LAnX†]n+ 196 5.39 R2 values for EDA vs QTAIM for [LAnX†]n+ 197
7
List of tables
Chapter 6 Page number
Table
6.1 M-N separation distances for complex 1 207 6.2 Li-N separation distances for different functionals 208 6.3 Energies of reaction for 1/2 to 3/4/5 209 6.4 Energies of reaction for 1 to 3/4/5 for different 211 methods
6.5 Bond lengths of Th6 for PBE0 and experimental data 213 6.6 SCF, enthalpy and Gibbs free energies of Th6 and Th7 214 6.7 SCF, enthalpy and Gibbs free energies of Th6’ and 214 Th7’ 6.8 ΔE, ΔH and ΔG values between a and b of 6 and 7 215 6.9 Dipole moments of Th6 and Th7 216 6.10 SCF energies in PCM model 216 6.11 Energy differences of a and b forms in PCM model 217 6.12 Selected MO energies for Th6 and Th7 218 6.13 Metal contributions to selected MOs (%, Mulliken 219 analysis) for Th6 and Th7 6.14 Selected MO energies for Th6’ and Th7’ 224 6.15 Metal contributions to selected MOs (%, Mulliken 224 analysis) for Th6’ and Th7’ 6.16 PBE energies for An6 complexes (An = Th-Am) 228 6.17 MO energies for An6 230 6.18 SOMO energies for open-shell An6 234 6.19 Total energy differences between An6a and An6b 235 for various combinations of MOs and SOMOs 6.20 PBE energies for An7 complexes (An = Th-Am) 238 6.21 MO energies for An7 239 6.22 SOMO energies for open-shell An7 242 6.23 Total energy differences between An7a and An7b 243 for various combinations of MOs and SOMOs
8
List of figures
List of figures
Chapter 1 Page number Figure 1.1 Schematic representation of model chemistries 36 according to Pople 1.2 Classification of all types of QTAIM critical points 43 possible in 3D space
Chapter 2 Page number
Figure
2.1 Representations of 5f and 6d-bonding interactions 54 in actinocenes 2.2 Representations of 5f and 6d-bonding interactions 55
in bis-arene and bis-C5H5
2.3 Chemical structure of [N’’2U]2(C6H6) 60 2.4 Chemical structure of TODGA 60 2.5 Neutral form of trans-calix[2]benzene[2]pyrrolide 66 2.6 Different bonding motifs of L2- and L4- with 67 various metal centres
Chapter 3 Page number Figure 3.1 The simplified X ligands 77 3.2 [LAnX]n+ complex with labelled arene and pyrrole 78 rings
3.3 Schematic of M[LAnR] and LAnR’2 79
3.4 Schematic of the [LTh(CCSiMe3)2][NiPR3] 80 complexes (R = Cy, Ph) in the a form and b form
9
List of figures
Chapter 4 Page number
Figure
4.1 The average bond length of the two Th-N(py) 89 bonds vs the Th-X bonds for PBE and PBE0 for [LThIVX]+ complexes 4.2 Bond angles for N(py)-Th-N(py) and Ar-Th-Ar 90 against X ligand for PBE and PBE0 4.3 Interplanar angles against X ligand for PBE and 90 PBE0
4.4 X-ray structure for [LTN(TMS)2]+ and PBE 91
geometry for [LThN(SiH3)2]+ 4.5 The average bond length of the two U-N(py) 92 bonds vs the U-X bonds for PBE and PBE0 for LUIIIX complexes 4.6 X-ray structure for LUDTBP and PBE0 geometry 93 for LUOPh 4.7 Bond angles for N-U-N and Ar-U-Ar against X 94 ligand for PBE and PBE0 for LUIIIX complexes 4.8 Interplanar angles against X ligand for PBE and 95 PBE0 for LUX complexes 4.9 An-X bond distances for [LAnX]n+ complexes 99 4.10 Partial charges of Th(IV) as a function of X ligand 103 4.11 Partial charges of X as a function of X ligand 103 4.12 Hirshfeld An-X charge difference as a function of X 105 ligand 4.13 Mulliken An-X charge difference as a function of X 105 ligand 4.14 Natural An-X charge difference as a function of X 106 ligand 4.15 QTAIM An-X charge difference as a function of X 106 ligand 4.16 δ(An,X) against An-X bond length 108
10
List of figures
4.17 QTAIM ρ against An-X bond length 108 4.18 QTAIM H against An-X bond length 109 4.19 QTAIM ρ against An-X QTAIM charge difference 110 4.20 δ(An,X) against An-X QTAIM charge difference 110 4.21 QTAIM H against An-X QTAIM charge difference 111 4.22 QTAIM ρ against An-X QTAIM charge difference 114
with NH2 4.23 δ(An,X) against An-X QTAIM charge difference 114
with NH2 4.24 QTAIM H against An-X QTAIM charge difference 115
with NH2 4.25 NBOs of An-B and An-O bonds 118 4.26 An-X charge difference against An orbital 119 contribution to An-X NBO 4.27 An-X charge difference against An orbital 120
contribution to An-X NBO (NH2) 4.28 QTAIM ρ against An orbital contribution to An-X 121 NBO 4.29 δ(An,X) against An orbital contribution to An-X 121 NBO 4.30 QTAIM H against An orbital contribution to An-X 122 NBO 4.31 QTAIM ρ against An orbital contribution to An-X 123 NBO at fixed An-X bond length 4.32 δ(An,X) against An orbital contribution to An-X 124 NBO at fixed An-X bond length 4.33 QTAIM H against An orbital contribution to An-X 124 NBO at fixed An-X bond length 4.34 Partial charges of Hf(IV) as a function of X ligand 127 4.35 Partial charges of W(III) as a function of X ligand 128 4.36 QTAIM ρ against M-X bond length 129 4.37 δ(An,X) against M-X bond length 130 4.38 QTAIM H against M-X bond length 130
11
List of figures
4.39 QTAIM ρ against M-X QTAIM charge difference 131 4.40 δ(An,X) against M-X QTAIM charge difference 132 4.41 QTAIM H against M-X QTAIM charge difference 132 4.42 QTAIM ρ against M orbital contribution to M-X NBO 134 4.43 δ(An,X) against M orbital contribution to M-X NBO 134 4.44 QTAIM H against M orbital contribution to M-X NBO 135 4.45 QTAIM ρ against M orbital contribution to M-X 136 NBO at fixed M-X bond length 4.46 δ(An,X) against M orbital contribution to M-X 136 NBO at fixed M-X bond length 4.47 QTAIM H against M orbital contribution to M-X 137 NBO at fixed M-X bond length 4.48 KS-MOs of An-B and An-O bonds 140 4.49 QTAIM ρ against An orbital contribution to An-X 141 KS-MO 4.50 δ(An,X) against An orbital contribution to An-X 141 KS-MO 4.51 QTAIM H against An orbital contribution to An-X 142 KS-MO 4.52 NICS(0), NICS(1) and NICS(2) points in [LThMe]+ 144 4.53 δ(C,C)p values against NICS(0) isotropic values for 145 [LThX]+ complexes on Ar1 4.54 δ(Th,X) values against NICS(0), NICS(1) and 146 NICS(2) isotropic values for [LThX]+ complexes on Ar1 4.55 δ(Th,X) values against δ(C,C)p values for [LThX]+ 147 complexes on Ar1 4.56 δ(Th,X) values against NICS(1) and NICS(2) 148 isotropic values for [LThX]+ complexes on Ar1. [LThBO2C2H4]+ omitted from data set. 4.57 Total Th(IV) orbital contribution to the Th-Ar MO 151 against NICS(1) and NICS(2) isotropies 4.58 HOMO of LThIIIBO2CcH4 and LThIIIOPh 152
12
List of figures
Chapter 5 Page number
Figure
5.1 Heterolytic An-X ΔH298 and ΔG298 against An-X 167 bond length
5.2 Heterolytic An-X ΔH298 and ΔG298 against δ(An,X) 168
5.3 Heterolytic An-X ΔH298 and ΔG298 against QTAIM 168 charge difference
5.4 Heterolytic An-X ΔH298 and ΔG298 against QTAIM ρ 169
5.5 Heterolytic An-X ΔH298 and ΔG298 against QTAIM H 170
5.6 Homolytic An-X ΔH298 and ΔG298 against An-X 174 bond length
5.7 Homolytic An-X ΔH298 and ΔG298 against QTAIM 173 charge difference
5.8 Homolytic An-X ΔH298 and ΔG298 against δ(An,X) 174
5.9 Homolytic An-X ΔH298 and ΔG298 against QTAIM ρ 175
5.10 Homolytic An-X ΔH298 and ΔG298 against QTAIM H 175 5.11 Change in QTAIM charge of An centre from 177 fragment to full complex against An-X interaction energy 5.12 PBE ΔE for An-X reaction energies against QTAIM 179 metrics
5.13 QTAIM metrics vs EDA EB for An-X 182
5.14 QTAIM metrics vs EDA EO for An-X 182
5.15 QTAIM metrics vs EDA EP for An-X 183
5.16 QTAIM metrics vs EDA EE for An-X 183
5.17 QTAIM metrics vs EDA EO for Th-X’ and Th-X* 191
5.18 QTAIM metrics vs EDA EO for Th-X’/X’’/X*/X**/X† 198
Chapter 6 Page number
Figure
6.1 Schematic of the M[LThR] complexes 1 and 2 202
13
List of figures
6.2 Schematic of the LTh(CCR’)2 complexes 3, 4 and 5 203
6.3 Schematic of the [LTh(CCSiMe3)2][NiPR3] 203 complexes Th6 and Th7 6.4 Experimental and PBE0-optimised structure of Li1 205 6.5 Experimental and PBE0-optimised structure of K2 206 6.6 Reaction scheme for 1 going to 3, 4 and 5 208 6.7 Experimental and PBE0-optimised structure of Li1 210 with THF 6.8 Experimental and PBE0-optimised structure of 212 Th6a and Th6b 6.9 Energies of MOs of complexes Th6a and Th6b 213 6.10 Representations of MO 255 in Th6b 220 6.11 Energies of MOs of complexes Th7a and Th7b 221
6.12 MO 256 in Th7a splitting to MO 257 and 243 in Th7b 222 6.13 Energies of MOs of complexes Th6a’ and Th6b’ 225 6.14 Energies of MOs of complexes Th7a’ and Th7b’ 226 6.15 Energy differences between a and b forms of An6 229 as a function of An centre 6.16 Energies of MOs of complexes An6a and An6b 231 6.17 MO energies vs enthalpies for An6 complexes 232 6.18 Key f-orbital SOMOs for open-shell An6 complexes 233 6.19 MO, MO + SOMO and SOMO energies vs enthalpies 236 for open-shell An6 complexes 6.20 Energy differences between a and b forms of An7 238 as a function of An centre 6.21 Energies of MOs of complexes An7a and An7b 241 6.22 MO energies vs enthalpies for An7 complexes 242 6.23 MO, MO + SOMO and SOMO energies vs enthalpies 244 for open-shell An7 complexes
14
Abstract
Abstract
Chemistry of the early actinides has undergone a lot of developments in recent years, and due to the need of specialised laboratories to handle these often highly radioactive complexes, computational chemistry has become a powerful aid in understanding the physical properties of these unique systems.
This thesis describes a systematic computational study of organoactinide and organometallic model complexes of the form [LAnX]n+ where L is the macrocyclic trans- calix[2]benzene[2]pyrrolide ligand using density functional theory (DFT) in conjunction with a variety of partition-based methods – Mulliken populations analysis (MPA), Hirshfield population analysis (HPA), natural population analysis (NPA) and the quantum theory of atoms in molecules (QTAIM) – with the aim of probing the electronic structure of the An-X and An-arene bonds as a function of the X ligand. Natural bond orbital (NBO) analysis was also used to study the nature of the An-X bonds, with these results compared to the QTAIM descriptions of covalency and ionicity in the [LAnX]n+ complexes. Analogous transition metal complexes of the form [LMX]n+ (M = Hf, W) have also been studied with the QTAIM and NBO approaches to compare with the actinide-based systems. Nucleus independent chemical shift (NICS) analysis was carried out to probe the extent of aromaticity of the arene rings of the L2- ligand in the closed- shell [LThX]+ complexes as a function of X ligand, and was compared with QTAIM measurements of aromaticity. The MPA also revealed δ-bonding to the arene rings of the L2- ligand and was compared to the NICS data.
Bond energies and bond energy decomposition analysis (EDA) of An-X were further analysed and compared to the QTAIM data. These same analyses were carried out on complexes where the X-type ligand series was extended to include a larger set of first and second-row p-block based ligands.
Finally, other, bi-metallic actinide-based complexes including the L2-/4- ligand were studied with the aim of understanding the thermal stabilities of these experimentally-characterised complexes, with analogous model complexes modelled to find potential synthetic targets. The Kohn-Sham molecular orbitals (KS-MOs) of some of these complexes were also analysed to try and find a rationale, based on their electronic structure, for the energetic preference for one binding mode of L-An over another.
15
Declaration
Declaration
No portion of the work referred to in this thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning.
16
Copyright statement
Copyright statement
1. The author of this thesis (including any appendices and/or schedules to this thesis) owns certain copyright or related rights in it (the “Copyright”) and s/he has given The University of Manchester certain rights to use such Copyright, including for administrative purposes.
2. Copies of this thesis, either in full or in extracts and whether in hard or electronic copy, may be made only in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under it or, where appropriate, in accordance with licensing agreements which the University has from time to time. This page must form part of any such copies made.
3. The ownership of certain Copyright, patents, designs, trade marks and other intellectual property (the “Intellectual Property”) and any reproductions of copyright works in this thesis, for example graphs and tables (“Reproductions”), which may be described in this thesis, may not be owned by the author and may be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property and/or Reproductions.
4. Further information on the conditions under which disclosure, publication and commercialisation of this thesis, the Copyright and any Intellectual Property University IP Policy (see http://documents.manchester.ac.uk/display.aspx?DocID=24420), in any relevant Thesis restriction declarations deposited in the University Library, The University Library’s regulations (see http://www.library.manchester.ac.uk/about/regulations/) and in The University’s policy on Presentation of Theses.
17
Publications
Publications
K. T. P. O’Brien and N. Kaltsoyannis, “Computational study of An–X bonding (An = Th, U; X = p-block-based ligands) in pyrrolic macrocycle-supported complexes from the quantum theory of atoms in molecules and bond energy decomposition analysis”, Dalton Trans. 2017, 46, 760.
M. Suvova, K. T. P. O’Brien, J. H. Farnaby, J. B. Love, N. Kaltsoyannis and P. L. Arnold, “Thorium(IV) and Uranium(IV) trans-Calix[2]benzene[2]pyrrolide Alkyl and Alkynyl Complexes: Synthesis, Reactivity, and Electronic Structure”, Organometallics, 2017, 36, 4669.
18
Abbreviations
Abbreviations
1 – M[LThMe]
2 – M[LThCH2Ph]
3 – LTh(CCSiH3)2
4 – LTh(CCSiMe3)2
5 – LTh(CCSiiPr3)2
6 – [LAn(CCSiMe3)2][NiPCy3]
6’ – [LTh(CCSiMe3)2][PtPCy3]
7 – [LAn(CCSiMe3)2][NiPPh3]
7’ – [LTh(CCSiMe3)2][PtPPh3]
ADF – Amsterdam density functional
An – actinide
ANO – atomic natural orbital
AO – atomic orbital
Ar – arene
B3 – Becke hybrid exchange functional
B3LYP – Becke-Lee-Yang-Parr hybrid functional
B88 – Becke functional
BCP – bond critical point
BH4 – borohydride
BO – bond order
BO2C2H4 – bis-pinacolato boron without methyl groups
19
Abbreviations
CASSCF – complete active space self-consistent field
CCP – cage critical point
CGTO – contracted Gaussian type orbital
COT – 1,3,5,7-cyclooctatetraene
CP – critical point
DFT – density function theory
DTBP – 2,6-di-tert-butylphenoxide
ECP – effective core potential
EDA – energy decomposition analysis
ESI-MS – electrospray ionisation mass spectrometry
FF – Fukui function
GGA – generalised gradient approximation
GTO – Gaussian type orbital
H – energy density at bond critical point
HF – Hartree-Fock
HOMO – highest occupied molecular orbital
HPA – Hirshfeld population analysis
KS – Kohn-Sham
KS-MO – Kohn-Sham molecular orbital
L – trans-calix[2]benzene[2]pyrrolide
L2- – trans-calix[2]benzene[2]pyrrolide without H on N(py)
L4- – trans-calix[2]benzene[2]pyrrolide without H on N(py) and without one H on each Ar ring
LAnX – full actinide complex with L and X ligands
20
Abbreviations
LCAO – linear combination of atomic orbitals
LDA – local density approximation
LSDA – local spin density approximation
L-type – Lewis type
LUMO – lowest unoccupied molecular orbital
LYP – Lee-Yang-Parr functional
MAD – mean absolute deviation
Me – methyl
MO – molecular orbital
MPA – Mulliken population analysis
N(py) – pyrrolide nitrogen
NAO – natural atomic orbital
NBO – natural bond orbital
NCP – nuclear critical point
NICS – nucleus-independent chemical shift
NL-type –non-Lewis type
NPA – natural population analysis
OPh – phenol
PBE – Perdew-Burke-Ernzerhof functional
PBE0 – Perdew-Burke-Ernzerhof hybrid functional
PP – pseudopotential
PW86/91 – Perdew-Wang exchange-correlation functional
QTAIM – quantum theory of atoms in molecules
RCP – ring critical point
21
Abbreviations
SCF – self-consistent field
SOMO – Singly-occupied molecular orbital
STO – Slater type orbital
TF – Thomas-Fermi model
TFD – Thomas-Fermi-Dirac model
TMS – tetramethylsilane
TODGA – N,N,N’,N’-tetraoctyl-diglycolamide
X – BH4, BO2C2H4, Me, N(SiH3)2 and OPh ligands
X’ – CH3, NH2, OH and F ligands
X’’ – CH2Ph, NHPh and OPh ligands
X* – SiH3, PH2, SH and Cl ligands
X** – SiH2Ph, PHPh and SPh ligands
X† – CPh3, SiPh3, NPh2, PPh2, OPh and SPh ligands
δ(A,B) – delocalisation index between atoms A and B
ηx – haptic bonding to x number of arene carbons
κx – haptic bonding to x number of pyrrole carbons or nitrogens
μ-Hx – bridging bond from x number of hydrogens
ρ – electron density at bond critical point
22
Acknowledgements
Acknowledgements
I would like to thank Prof. Nikolas Kaltsoyannis at the University of Manchester for all his supervision and guidance throughout my postgraduate studies. I would also like to thank Prof. Polly L. Arnold and Dr Marketa Suvova at the University of Edinburgh for providing important experimental data.
Particular thanks to Claire O’Brien for her help and advice regarding my thesis, and my family, Lainey, and friends in room 7.04 for putting up with me for three years!
Also a special thanks to the University of Manchester for funding this PhD, the National Service for Computational Chemistry Software (NSCCS), UCL Researching Computing Platforms Support services, Dr. Jörg Saßmannshausen at UCL Chemistry and of course, the University of Manchester Computational Science Community services, without all of whom the calculations needed for this research would not have been made possible.
23
And you may ask yourself, “well, how did I get here?”
~ David Byrne
24
Part I.
Introduction
25
Theoretical background
Chapter 1. Theoretical background
1.1. Aims and objectives
Computational organoactinide chemistry can be described as the study, using computational chemistry methods, of organoactinide systems in order to describe physical properties such as bonding interactions, bond strength, reaction energies and the electronic structure of such systems. The overall aim of this thesis was to characterise and analyse the electronic structure and bonding of a range of actinide and transition metal complexes incorporating a pyrrolic macrocycle-supported ligand, using a variety of computational methods based on density functional theory (DFT). Some of these complexes have been synthesised and characterised experimentally.
The first objective was to investigate how changing the electronegativity of a second ligand in the macrocycle-metal system affected the bonding and electronic interaction of this metal-ligand bond and the macrocycle-metal bonding. A variety of different bond analysis techniques were used and compared to see how descriptors such as covalency and ionicity were characterised according to the different computational methods, and also how these descriptors related to the bond energies of metal-ligand interactions.
The second objective was to determine reaction energies and thermal stabilities of a range of bimetallic macrocycle-actinide systems synthesised experimentally, and also the reaction and thermal energies of analogous systems having metal centres that have so far eluded experimentalists. The purpose of these studies was to see if potential synthetic targets could be proposed based on the computed reaction energies, and also to determine if computational analysis of the molecular orbitals in these systems can explain the thermal stabilities of certain products found experimentally.
26
Theoretical background
It is hoped that this study will contribute to the large field of computational actinide chemistry and help add to arguments regarding the bonding nature of such systems.
The rest of this chapter first gives a general introduction to quantum chemistry and the mathematical descriptions of electronic wavefunctions and basis sets, before describing the principles of the main method used in this study – density functional theory. Further to this, a range of different electronic structure and bond analysis techniques used in this research, such as natural bond orbital anaylsis, the quantum theory of atoms in molecules, energy decomposition analysis, and nucleus-independent chemical shift analysis, are described.
Chapter 2 is a literature review describing extensively the current status of the fields of actinide and organoactinide chemistry and computational actinide/organoactinide chemistry, with many of the techniques and methodologies mentioned in this chapter discussed in relation to these fields. Specific methodologies for this thesis are given in chapter 3.
The results are presented and discussed in part II where the results for the first aim are given in chapters 4 and 5, and the results for the second aim given in chapter 6.
1.2. Quantum chemistry
Quantum chemistry attempts to define molecular electronic structure by approximating the electron density in the ground state from the wavefunctions of the electrons by solving the time-independent electronic Schrödinger equation: