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New Grubbs-Mae Catalysts for the Metathesis of Alkenes

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New Grubbs-Mae Catalysts for the Metathesis of Alkenes Emerimental and Theoretical Investigation of New Grubbs-Mae Catalysts for the Metathesis of Alkenes Margaritha Jordaan Experimental and Theoretical investigation of New Grubbs-type Catalysts for the Metathesis of Alkenes Margaritha Jordaan B.Sc, Hons. B.Sc, M.Sc (PU for CHE) Thesis submitted in fulfilment of the requirements for the degree PHILOSOPHUE DOCTOR in CHEMIsrnY of the North-West University (Potchefstroom Campus). Tabl!e of Contents q Table of contents List of abbreviations and catalysts Summary Opsomming Publications 1 Introduction and Aim of study 1.1 Introduction 1.2 Aims and objectives 1.3 References 2 Literature Review: Alkene Metathesis 2.1 Introduction 2.2 Historical overview 2.3 Development of catalytic systems 2.4 Properties of organometallic camysts 2.4.1 Bonding ability of transition metals 2.4.2 Variabitity of the oxidation state 2.4.3 Variability of the coordination number of Me transition metal 2.4.4 Choice of ligands 2.4.5 Ligand effects 2.5 Chelating ligands: hemilability 2.6 Reaction mechanism of alkene metathesis 2.6.1 Patrwise mechanisms 2.6.2 Non-painvise mechanism 2.7 Molecular modelling in catalysis 2.7.1 Computational investigation of alkene metathesis 2.8 Referenas ii TABLEOF CONTENTS 3 Experimental 65 3.1 General 3.1.1 Reagents and solvents 3.1.2. Apparatus 3.1.2.1 General procedure for the remoml of solvents under vacuum 3.1.2.2 General procedure for the filtration of a suspension under inert gas 3.1.2.3 General procedure for pump freezing solvents 3.1.2.4 Detection of oxygen generated from molecular sleves 3.2 Synthesis of the ligand salts 3.2.1 Synthesis of pyridinyl alcoholaio ligands 3.2.1.1 General procedure for the synthesis of L1 - L4 3.2.1.2 Spectroscopic data of the ligands L1 - L4 3.2.2 Synthesis of sodium salts 3.2.3 Synthesis of thallium salts 3.2.4 SynVlesis of lithium salts 3.3 Synthesis of RuCI2(L)(C5H5N),(=CHPh) 3.3.1 RUCI~(PCY,)(C~H~N)~(=CHP~)(Gfl-Py) 3.3.2 RuCI~(HZIM~~)(C~H~N)~(=CHP~)(GR-Py) 3.4 Syntnesis of hemilabile ruthenium carbene complexes 3.4.1 Use of sodium salts 3.4.1 .I RuCli(PCy3)(OAN)(=CHPh)(OAN = L11) 3.4.1.2 RUCI~(PCY~(O"N)(=CHP~)(CPN = L6. L8) 3.4.1.3 RUCI~(PC~,)(O"N)(=CHP~)(O"N = LIZ) 3.4.2 Use of thallium and lithium salts 3.5 Metathesis reactions 3.5.1 General procedures for the metathesis of 3-octene 3.5.1.1 Small-scale reactlon (5 mL reaction viai) 3.5.1.2 Large-scale readon (100 mL reaction flask - ethene liberated) 3.5.1.3 NMR investigation of the 1-octene metathesis reaction 3.6 Analytical methods 3.6.1 Characterisation of hemilabile complexes 3.6.1.1 Nudear Magnetic Resanance (NMR) 3.6.1.2 Infrared spectroscopy (IR) 3.6.1.3 Elemental analysis (CHN analysis) 3.6.2 Progress of the metathesis reaction 3.6.2.1 Gas Chromatography (GC) 3.6.2.2 Gas ChromatographylMass Spectrometry (GCIMS) 3.7 Computational Methods TASLKO?EONYE& 3 7 1 Hardware 3.7.2 Computational details: Software 3.7 3 Model system and notations 3.8 References 4 Synthesis: Hemilabile Ru=C complexes 4.1 Inh'Oduction 4 2 Synthesis of pyridinyl alcoholate ligands 4.3 Synthesis of hemilabile Grubbs mrbene complexes 4.3.1 Unsuccessful syntheses 4.3.2 Characterisation of the successfully synthesised complexes 4.3.2.1 Discussion of the NMR-results of the succesfuliy synthesised complexes 4.4 References 5 Alkene metathesis: Experimental investigation 5.1 lnlroduction 5.2 Metathesisof I-octene with ruthenium carbene complexes 5.2.1 MetaUlesis in the presence of Grl and GR 5.2.1.1 Optimisation of reaction conditions 5.2.1.2 NMR investigation 5.2.2 Metathesis of 1-octene in the presence of GrlCy and GRCy 5.2.2.1 Optimisation of reaction conditions 5.2.2.2 Influence of catalyst concentration 5.2.2.3 NMR investigation 5.2.3 Comparing Gmbbs systems with hemilabile Ru=C complexes 5.2.3.1 Metathesiswith first generation hemilabile Complexes 5.2.3.2 Metathesis with second generation hemilabile complexes 5.3 Referenas 6 Alkene metathesis: Theoretical investigation 6.1 Introduction 6.2 Metathesis of 1-oclene in the presence of Grubbs carbenes 6.2.1 Catalyst initiation 6.2.2 Catalyst activation TABLE OF comm 6.2.2.1 Activation phase: Grl- and GR-mtalysed metathesis reaction 228 6.2.2.2 Activation phase: hemilabile Ru=C-catalysedmetathesis readion 229 6.2.3 Catalytic cycle 247 6.3 References 249 7 Conclusions and Recommendations 7.1 Introduction 7.2 Synthesis d hemilabile complexes 7 3 Catalytic activity 7.4 Mechanistic investigation 7.5 Summary of recommendations 7.6 References Acknowledgements 281 Appendix A References Appendix B References Appendix CI 335 Appendix C2 399 Appendix C3 421 Appendix b 443 Appendix E References Appendix F 455 Appendix 6 473 *List of Abbreviations 8t Catalysts 9 GENERAL c. # indicates Me carbon chain fength e.g. C7 is heptene. & is nonene, etc. =CRR' alkylidene; carbene moiety where R, R' = H, alkyl or aryl groups DFT density functional theory AE change in electronic energy A€: activation energy Em formation energy AG change in Gibbs free energy AH change in enthalpy Ha carbene a-proton HSAB hard and soft acid-base IP isomerisation products knn initiation rate L, ligands mrdinated to a metal M transition metal atom M-H metal hydride M-C metal carbon M-CI metal chloride NHC N-heterocycliccdrbene OAY bidentate ligand coordinated to a metal at 0 and Y where Y = 0, N. S. P, etc. PES potential energy surface PMP primary metathesis products RCM ring-closing metathesis ROMP ringopening metathesis polymerisation RT room temperature Ru=C ruthenium carbene moiety SHOP Shell higher olefins process SMP secondary metathesis products TS or TS's transition state or transition states TLC thin layer chromatography CHEMICALS AND UGANDS Ad : adamantyl CY : cydohexyl l+lMes : ?.3-bis-(2.4.6-trimeVlylphenyl)-2-1madarolidlnyIidene Hx : hexyl Hoqu : 8-quinolinolanion Me : methyl Mes : 1.3-bis-(2.4,6-trirnethytphenyl) Pico : picdinic acid 'Pr : isopropyl PY : pyridine ~CY, : tricydohexylphosphine Pya : picolinic acid anion Ph phenyl Quino : quinoline THF : tetrahydrofuran Ts : tosyl CATALYSTS: (List of catalyst abbreviations IogeLher with structure and name) Benzyliden~ichlom(~s(s(tricyclohexylphosphine))ruthenium Grl -Py BenzylidenPchloro(tricyclohexylphosphine)-[I-(2'-pyridiny1)propan-Zolato] ruthenium Grl Me HZIMes Ju/Aph GRCy Benzyliden~chloro(l.3-bis-(2.4.6himethylphenyl)-2-imidarolidinylidene)-[l-(2'-pyridinyl)-l.l- diphenyCmethanolato]~~thenium zLb>Ph Gri Pica-Py Summary Ekperimental and theoretical investigation of new Grubba-type catalysts for the metathesis of alkenes Despite the high selectivity of Me first generation Grubbs precatalyst (Grl) during the metathes~sof terminal alkenes, it tends to have a limited lifetime at elevated temperatures. The development of the second generation Grubbs precatalyst (GR) has dealt with this problem to some extent. The replacement of one PCy3 ligand with a N-heterocyclic carbene provided a system with improved activity and lifetime. However. GR shows low selectivity at elevated temperatures, due to the formation of secondary metathesis products during the metathesis reactions. In this study, experimental and theoretical studies were combined to gain insight into the mechanism of the metathesis reaction and lo predict structural and reactivrty trends of the catalytic systems. A number of 0,O- 0,N-, 0,s- and 0.P-bidentate ligands were identified as possible hemilabile iigands for incorporation into Grl and Gr2. The steric and etectronic environment of the ligands was Varied to determine the influence of these parameters on the Isctene metathesis activity of the precatalysts. This investigation was motivated by the fa~l'~.'~that hemilabile ligands can release a free coordination site "on demand of an incoming nucleophilic substrate while occupying it otherwise. Th~sis believed to increase the thermal stability and activity of the catalytic systems and therefore prevent decomposition via free coordination sites. This was recently shown to be true for a number of Grubbs carbenes in ring-opening metathesis (ROMP) and ring-closing metathesis (RCM) reactions at elevated temperatures. Molecular modelling was used as a tool to design new Gmbbs-type precatalysts. which were then synthesised and evaluated for I-octene metathesis acttvity. Unfortunately, a number of the ligands could not be successfully incorpomted into the Grubbs carbenes, for which possible reasons are discussed In the thesis. It was generally found that the 0,O-. 0,s- and carboxylic 0.P-ligands resulted in the decomposition of the Gnrbbs carbenes. The yields of these complexes generaliy ranged from 0 - lo%, which made the purification and analysis process difficult. The incorporation of picolinic acid, a 0,Ncarboxylic ligand, into Grl and Gc? resulted in a mixture of carbenes which could not be isolated. However, the 0.N-alcoholate ligands with different steric bulk could be successfully incorporated into Gtl and GR with a yield ranging between 40 - 90% with a 98 - 100% purity. The incorporation of the sterically hindered hemifablle 0.N-ligands into Grl and Or2 improved the thermal stability, activity, selectivity and lifetime of these complexes towards the metathesis of 1-octene. Compared to Grl, a 10 - 30% increase in the primary metathesis products (PMP) formation, together with a 4% decrease in isomerisation products (IP) was observed for the first generation hemilabile Grubbs precatalysts. However, although no signfieant increase in PMP was observed after 7 h for the second generation analogues in comparison to GR, a 4 - 10 % increase was visible after 20 h.
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