© Copyright 2019 Braden A. Zahora i Synthesis and Reactivity of PtII Complexes with Secondary Sphere N-H Moieties Braden A. Zahora A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2019 Reading Committee: Karen I. Goldberg, Chair D. Michael Heinekey Forrest E. Michael Program Authorized to Offer Degree: Department of Chemistry ii University of Washington Abstract Synthesis and Reactivity of PtII Complexes with Secondary Sphere N-H Moieties Braden A. Zahora Chairperson of the Supervisory Committee: Professor Karen I. Goldberg Department of Chemistry Direct transformations of abundant hydrocarbons into higher valued products would circumvent energy intensive processes, reforming the chemical industry. Late transition metals, particularly platinum, are known to selectively convert alkanes into functionalized products. However, a practical method with an economically viable oxidant has yet to be discovered. New methods for alkane activation may yield further advances towards this goal. This dissertation focuses on how platinum methyl complexes with ligand-based protons can form methane, the microscopic reverse of methane activation. Chapter 1 provides an introduction on the need to develop new methods to functionalize hydrocarbons. Furthermore, a survey of the literature with respect to how late metal complexes can undergo productive reactivity with substrates which are deemed necessary for practical alkane partial oxidation is presented. Chapter 2 focuses on the synthesis and reactivity of 5-(6-methyl-2-pyridyl)-3-tert- butylpyrazolate (NNMe) and 2-(5-tert-butylpyrazol-3-yl)-6 (diethylaminomethyl)pyridine (NNNEt) ligated PtII complexes. Once formed, conditions necessary for methane formation were found and iii it was determined that the ligand-based N-H was not involved in methane formation. Chapter 3 explores synthesis and reactivity of 5-tert-butyl-1,3-bis(pyrazol-3-yl)pyridine (NNN) and 5-tert- butyl-1,3-bis(pyrazol-3-yl)benzene (NCN) ligated PtII-alkyl complexes with electrophilic reagents. It was found that tridentate ligated pyrazolate PtII-R systems can undergo protonation at the ligand if there is a weak pyridine trans donor (vs strong phenyl trans donor) to the PtII-R moiety. However, reactivity with methyl iodide occurred at the metal first, with further ligand methylation spectroscopically observed for the NNN ligated Pt-CH3 complex. Chapter 4 discusses the synthesis and characterization of bis(phosphino)amine ligated PtII complexes, which contained a ligand-based N-H. Taking advantage of unfavorable steric congestion of bulky Ph groups on the ligand, methane formation was observed from thermolysis reactions of a bis(phosphino)amine ligated Pt(CH3)2. Although additional characterization of the resulting metal-containing product is required, it appears that methane was formed through cooperation of the ligand-based N-H moiety and the Pt-CH3 ligand. iv v Table of Contents List of Figures ......................................................................................................... ix List of Schemes ..................................................................................................... xiii List of Tables ........................................................................................................ xiv Glossary ................................................................................................................... xv Compound Numbering Scheme ......................................................................... xvii Acknowledgements ............................................................................................. xxii Chapter Contributions ...................................................................................... xxiv Chapter 1 Introduction............................................................................................ 1 1.1 A Need to Reduce Hydrocarbon Flaring ............................................................................... 1 1.2 Homogeneous Partial Oxidation of Methane, an Overview ................................................. 4 1.3 Designing A New System for Alkane Functionalization ...................................................... 8 1.4 Dissertation Summary ......................................................................................................... 14 1.5 Notes for Chapter 1 ............................................................................................................. 16 Chapter 2 Synthesis and Reactivity of Bidentate and Hemilabile Pyrazolate Ligated Pt Complexes ............................................................................................22 2.1 Introduction ......................................................................................................................... 22 2.2 Results and Discussion ........................................................................................................ 28 II 2.21 Synthesis of Bidentate Ligand Supported Pyrazolate Pt -Complexes .......................... 28 Et II 2.22 Preparation of (NNN) Ligated Pt Complexes ........................................................... 31 2.23 The Reactivity of B2a/B2b and 4a with Acid............................................................... 32 2.24 Release of methane from B4a under acidic conditions ................................................. 35 2.25 Release of methane from B7 and B4a by thermolysis ................................................... 36 2.26 Reactivity of Pt(*NNN)EtX Under Basic Conditions and in the Presence of Exogeneous Ligands .............................................................................................................. 41 2.3 Conclusion ........................................................................................................................... 45 2.4 Experimental ....................................................................................................................... 46 2.41 General Experimental .................................................................................................... 46 2.42 Synthesis, Characterization and Spectroscopic Data ..................................................... 48 2.43 X-ray Crystallography General Information ................................................................. 71 vi 2.5 Notes to Chapter 2 ............................................................................................................... 73 Chapter 3 Synthesis of Pyrazolate Supported Tridentate PtII Alkyl Complexes and Reactivity with Electrophiles ......................................................................... 77 3.1 Introduction ......................................................................................................................... 77 3.2 Results and Discussion ........................................................................................................ 82 H H 3.21 Preparation of NNN Ligated Complexes .................................................................. 82 H H 3.22 Preparation of NCN Ligated Complexes .................................................................. 84 3.23 Synthesis of *NNN* Ligated Pt-Alkyl Species ............................................................. 88 3.24 Synthesis of *NCN* Ligated Pt-Alkyl Species ............................................................. 92 + + II 3.25 Electrophile (H and CH3 ) Addition to Pyrazolate Supported Pt -alkyl Compounds . 94 II 3.25.1 Proton Addition to (*NNN*) ligated Pt -alkyl (C6, C7, C8) Compounds ............ 95 3.25.2 Proton Addition to Pt(*NCN*)CH3 (C11, C12) and Pt(*NCN*)C6H5 (C13) ....... 101 II 3.25.3 Reactivity of *NCN* ligated (C11) and *NNN* ligated (C8) Pt -CH3 complexes with CH3I ......................................................................................................................... 103 3.3 Conclusion ......................................................................................................................... 106 3.4 Experimental and NMR Data ............................................................................................ 108 3.41 General Experimental .................................................................................................. 108 3.42 Synthesis, Characterization and Spectroscopic Data ................................................... 109 3.43 X-ray Crystallography General Information ............................................................... 136 3.5 References to Chapter 3 .................................................................................................... 140 Chapter 4 Synthesis of Bis(phosphino)amine Ligated PtII Species and Investigations Towards C-H coupling ................................................................144 4.1 Introduction ....................................................................................................................... 144 4.2 Results and Discussion ...................................................................................................... 148 II 4.21 Ligation of Protic Amino(bisphosphines) to Pt ......................................................... 148 4.22 Reactivity of Pt(*N(P(C6H5)2)2)2 (D3) towards X-H Activation................................. 153 H H t 4.23 Towards C-H coupling from Pt( N(P(C6H5)2)2(CH3)2 (D1a) and Pt( N(P( Bu)2)2(CH3)2 (D1b) ..................................................................................................................................