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A Computational Study of Ruthenium Metal Vinylidene Complexes: Novel Mechanisms and Catalysis

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A Computational Study of Ruthenium Metal Vinylidene Complexes: Novel Mechanisms and Catalysis A Computational Study of Ruthenium Metal Vinylidene Complexes: Novel Mechanisms and Catalysis David G. Johnson PhD University of York, Department of Chemistry September 2013 Scientist: How much time do we have professor? Professor Frink: Well according to my calculations, the robots won't go berserk for at least 24 hours. (The robots go berserk.) Professor Frink: Oh, I forgot to er, carry the one. - The Simpsons: Itchy and Scratchy land Abstract A theoretical investigation into several reactions is reported, centred around the chemistry, formation, and reactivity of ruthenium vinylidene complexes. The first reaction discussed involves the formation of a vinylidene ligand through non-innocent ligand-mediated alkyne- vinylidene tautomerization (via the LAPS mechanism), where the coordinated acetate group acts as a proton shuttle allowing rapid formation of vinylidene under mild conditions. The reaction of hydroxy-vinylidene complexes is also studied, where formation of a carbonyl complex and free ethene was shown to involve nucleophilic attack of the vinylidene Cα by an acetate ligand, which then fragments to form the coordinated carbonyl ligand. Several mechanisms are compared for this reaction, such as transesterification, and through allenylidene and cationic intermediates. The CO-LAPS mechanism is also examined, where differing reactivity is observed with the LAPS mechanism upon coordination of a carbonyl ligand to the metal centre. The system is investigated in terms of not only the differing outcomes to the LAPS-type mechanism, but also with respect to observed experimental Markovnikov and anti-Markovnikov selectivity, showing a good agreement with experiment. Finally pyridine-alkenylation to form 2-styrylpyridine through a half-sandwich ruthenium complex is also investigated. The mechanism for this process is elucidated, along with a description of the formation of the unexpected experimental deactivation product. Additionally the chemistry and bonding of pyridylidene complexes is also studied. 5 Contents Abstract ........................................................................................................................................ 5 List of Figures ............................................................................................................................ 11 List of Tables ............................................................................................................................. 25 List of Accompanying Material ................................................................................................... 26 Acknowledgements ................................................................................................................... 27 Authors Declaration ................................................................................................................... 28 1. Introduction ........................................................................................................................ 29 1.1 Computational Methods ................................................................................................... 30 1.1.1 Introduction ............................................................................................................... 30 1.1.2 Particles, Waves and Quanta ................................................................................... 30 1.1.3 The Schrödinger Equation – Introduction, Description and Limits ........................... 35 1.1.4 Many Electron Wavefunctions – Hartree Theory ..................................................... 40 1.1.5 Many Electron Wavefunctions - Accounting for Spin ............................................... 44 1.1.6 Many Electron Wavefunctions – Orbitals and Basis Sets ........................................ 46 1.1.7 Many Electron Wavefunctions –Hartree-Fock Theory ............................................. 51 1.1.8 Density Functional Theory – Beginnings and Hohenberg-Kohn Theory .................. 53 1.1.9 Density Functional Theory – Kohn-Sham Theory .................................................... 57 1.1.10 Exchange-Correlation Functionals ......................................................................... 58 1.1.11 General DFT Procedure ......................................................................................... 61 1.1.12 Vibrational Spectrum, Zero Point Energy, Thermodynamic and Entropic Corrections ........................................................................................................................ 65 1.1.13 Solvation Models with the Conductor-Like Screening Model (COSMO) ................ 68 1.1.14 Applicability of Theoretical Methods ....................................................................... 70 1.1.15 The Natural Bond Orbital (NBO) Program ............................................................. 73 1.1.16 Computational Summary ........................................................................................ 75 1.2 Modelling Reaction Mechanisms ..................................................................................... 76 1.2.1 Transition State Theory ............................................................................................ 76 1.2.2 The Energetic Span Model ....................................................................................... 78 6 1.3 General Organometallic Introduction – C-H Activation ................................................... 82 1.3.1 Transition Metal Mediated C-H Activation ............................................................... 82 1.3.2 Ligand-Mediated C-H Activation and Proton Transfer ............................................. 84 1.4 General Organometallic Introduction – Vinylidenes and Allenylidenes .......................... 91 1.4.1 Vinylidenes – General Background.......................................................................... 91 1.4.2 Alkyne-Vinylidene Tautomerization.......................................................................... 95 1.4.3 Vinylidenes – Role in Catalysis and Oxygen-based Nucleophilic Attack ................ 99 1.4.4 Allenylidenes: Chemistry and Formation ............................................................... 103 2. Investigation into a Ruthenium bis-Acetate Mediated Alkyne-Vinylidene Tautomerization: Elucidation of the Ligand Assisted Proton Shuttle (LAPS) Mechanism .................................. 107 2.1 Introduction ................................................................................................................... 107 2.1.1 Experimental Observations .................................................................................... 108 2.2 Results and Discussion ................................................................................................. 115 2.2.1 Computational Preamble ....................................................................................... 115 2.2.2 Classical Alkyne-Vinylidene Tautomerization ........................................................ 116 2.2.3 Acetate-Ligand Assisted Mechanism ..................................................................... 124 2.2.4 Investigation of Metallo-Enol Ester Complexes ..................................................... 132 2.2.5 Effects of a Smaller Model System ........................................................................ 135 2.2.6 Investigation into Phosphine Cis/Trans Isomerisation During the LAPS Mechanism in Ruthenium Complexes of 1,2-bis(diphenylphosphino)butane .................................... 138 2.2.7 Assessment of the Location of cis/trans Phosphine Isomerisation during the LAPS Mechanism ...................................................................................................................... 140 2.2.8 Summary ................................................................................................................ 142 3. Further Reactions of Hydroxy-Vinylidenes – Alkene Formation from Propargyl Alcohols 143 3.1 Introduction .............................................................................................................. 143 3.1.1 Experimental Observations .................................................................................... 144 3.2 Results and Discussion ................................................................................................. 152 3.2.1 Computational Preamble ....................................................................................... 152 3.2.2 Initial Mechanistic Search via an Intramolecular Transition State ......................... 153 7 3.2.3 Investigations Involving an Allenylidene Intermediate ............................................ 162 3.2.4 Investigation into the Formation of 302 and Ethene via Water Addition ................ 166 3.2.5 Investigation of Formation of 302 and Ethene via a Cationic Intermediate............ 167 3.2.6 Summary and Current Conclusions on the Mechanism of Ethene Formation ....... 170 4. Investigation of the Ligand Assisted Proton Shuttle Mechanism in the Presence of a CO Ligand: The CO-LAPS Mechanism ......................................................................................... 173 4.1 Introduction .................................................................................................................... 173 4.1.1 Initial Experimental Observations ........................................................................... 174 4.1.2 Substituent Effects .................................................................................................
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