Nitroacetylenes Harnessed by Cobalt By Gary Kenneth Windler, Jr. A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate Division of the University of California, Berkeley Committee in charge: Professor K. Peter C. Vollhardt, chair Dr. Philip F. Pagoria (LLNL) Professor Robert G. Bergman Professor Clayton J. Radke Fall 2011 Nitroacetylenes Harnessed by Cobalt © 2011 by Gary Kenneth Windler, Jr. 1 Abstract Nitroacetylenes Harnessed by Cobalt by Gary Kenneth Windler, Jr. Doctor of Philosophy in Chemistry University of California, Berkeley Professor K. Peter C. Vollhardt, Chair The syntheses and characterization of nitroacetylenes have been studied with respect to their large-scale production, purification, and NMR spectra, respectively. The 13 C NMR spectrum of 1-nitro-2-(trimethylsilyl)ethyne ( 18 ) evidenced 13 C–14 N coupling between the alkynyl carbon and the attached nitrogen, in agreement with the previously reported spectrum of 1-nitroethyne ( 16 ). The multi-gram preparation of high purity 18 is described. A history of previous work with nitroacetylenes is reviewed. The stabilization of nitroacetylenes as hexacarbonyl dicobalt alkyne complexes was investigated. In conjunction with appropriate oxidizers, such complexes were shown to be long-term storage media for free nitroalkynes. The syntheses and complete characterization of the first two nitroalkyne transition metal complexes, [µ-1-nitro-2- (trimethylsilyl)ethyne-1,2-diyl]bis(tricarbonylcobalt)( Co –Co ) ( 25 ) and [µ-1-nitroethyne- 1,2-diyl]bis(tricarbonylcobalt)( Co –Co ) ( 26 ), are described. Phosphine derivatives of 25 were prepared and studied. The synthesis of [µ-1,2-dinitroethyne-1,2- diyl]bis(tricarbonylcobalt)( Co –Co ) ( 24 ) by direct ligation, transformation of functional groups on existing complexes, and nitration of such complexes was unsuccessful. Complexes 25 and 26 were applied to the synthesis of organic molecules. While they did not yield cyclopentenones via the Pauson-Khand cyclization, they rendered benzene derivatives by the [2 + 2 + 2] cobalt-mediated cyclotrimerization. In addition to two nitroindanes and a nitrotetralin, several new trinitrobenzene isomers were made, all potential precursors to energetic materials. The X-ray crystal structure of one of these, 1,3,5-trinitro-2,4,6-tris(trimethylsilyl)benzene ( 325 ), showed a planar, but distorted aromatic ring. i For my mother, Rev. Dr. Diane Earle Windler, who taught me to never, never, never give up. ii Table of Contents Abbreviations and Acronyms ......................................................................................... iv Acknowledgements .......................................................................................................... vi Chapter 1. Introduction: History of Explosives and Goals of this Thesis 1.1 Examples of Explosives .............................................................................. 1 1.1.1 Nitric Esters..................................................................................... 1 1.1.2 Nitroarenes ...................................................................................... 2 1.1.3 Nitroalkanes .................................................................................... 3 1.1.4 Nitramines ....................................................................................... 5 1.1.5 Nitroalkenes .................................................................................... 5 1.2 Nitroacetylenes ........................................................................................... 5 1.3 Goals ........................................................................................................... 7 1.3.1 Production of Nitroacetylenes .........................................................7 1.3.2 Stabilization of Nitroacetylenes as Metal Complexes .................... 7 1.3.3 Preparation of Hexacarbonyldicobalt Dinitroacetylene .................. 8 1.3.4 Nitroacetylene Complexes as Synthons .......................................... 8 Chapter 2. Preparation and Properties of Nitroacetylenes 2.1 Introduction ............................................................................................... 10 2.2 General Properties of Nitroacetylenes ...................................................... 11 2.3 The Synthesis of Nitroacetylenes ............................................................. 14 2.3.1 Unsuccessful Strategies ................................................................ 14 2.3.2 Successful Strategies ..................................................................... 21 2.4 Historical Approaches to Dinitroacetylene (DNA) .................................. 31 2.5 Reactions of Nitroacetylenes .................................................................... 36 2.6 Theoretical Studies of Nitroacetylenes ..................................................... 49 2.7 Results and Discussion ............................................................................. 52 2.7.1 Iodonitroacetylene, (Tributylstannyl)nitroacetylene, and (Trimethylstannyl)nitroacetylene .................................................. 53 2.7.2 Nitroacetylene ............................................................................... 55 2.7.3 (Trimethylsilyl)nitroacetylene ...................................................... 56 2.8 Conclusion ................................................................................................ 63 Chapter 3. Hexacarbonyldicobalt Nitroalkyne Complexes 3.1 Introduction ............................................................................................... 64 3.2 General Properties of Hexacarbonyldicobalt Alkyne Complexes ............ 66 3.3 Results and Discussion ............................................................................. 73 3.3.1 Trapping Strategy ......................................................................... 73 3.3.2 Functional Group Transformation Strategy .................................. 75 3.3.3 Strategy of Nitration of Alkyne[Co2(CO)6] Complexes ............... 82 3.3.4 A Milestone: Hexacarbonyldicobalt (Trimethylsilyl)nitroacetylene ...................................................... 93 3.3.5 Another Milestone: Hexacarbonyldicobalt Nitroacetylene ........ 115 3.4 Conclusion .............................................................................................. 128 Chapter 4. Nitroalkyne Complexes as Precursors to Organic Compounds 4.1 Introduction ............................................................................................. 129 4.2 Attempted Pauson-Khand Reactions ...................................................... 129 4.3 [2 + 2 + 2] Cobalt-mediated Cyclotrimerizations ................................... 135 iii 4.3.1 Reaction of 25 and 26 with α,ω Diynes ..................................... 141 4.3.1.1 Cyclization to Indanes .................................................... 141 4.3.1.2 Cyclization to Tetralins ................................................... 144 4.3.2 All-Intermolecular Cyclization of 25 with Symmetrical and Unsymmetrical Alkynes ............................................................. 147 4.3.2.1 Reaction of 25 with Symmetrical Alkynes 182 and 197 ............................................................................ 147 4.3.2.2 Reaction of 25 with 18 (Trimethylsilylnitroacetylene) .. 149 4.4 Conclusion .............................................................................................. 157 Chapter 5. Experimental ............................................................................................. 158 References ...................................................................................................................... 184 Appendix A: Definitions and Formulae A1 Explosive Terminology .......................................................................... 201 A2 Explosive Detonation Velocities ............................................................ 202 A3 Oxygen Balance ...................................................................................... 203 A4 Explosive Heats of Formation ................................................................ 203 Appendix B: Crystallographic Data B1 [μ-1-Nitro-2-(trimethylsilyl)ethyne-1,2-diyl]bis (tricarbonylcobalt)(Co–Co) (25) ............................................................. 204 B2 [μ-1-Nitroethyne-1,2-diyl]bis(tricarbonylcobalt)(Co–Co) (26) .............. 206 B3 1,3,5-Trinitro-2,4,6-tris(trimethylsilyl)benzene (325) ............................ 208 Appendix C: Numbered List of Compounds .............................................................. 215 iv Abbreviations and Acronyms Ac - Acyl HMDS - Hexamethyldisilizane BDE - Bond Dissociation Energy HMX - High Melting explosive, Boc - N-t-Butoxycarbonyl octahydro-1,3,5,7-tetranitro-1,3,5,7- Bu - Butyl tetrazocine sec-Bu - sec-Butyl HNB - Hexanitrobenzene t-Bu - tert-Butyl IR - Infrared Bz - Benzoyl LAH - Lithium Aluminum Hydride CAN - Ceric Ammonium Nitrate LLNL - Lawrence Livermore National CL-20 - China Lake formulation 20, Laboratory 2,4,6,8,10,12-hexanitro- Me - Methyl 2,4,6,8,10,12-hexaazaisowurtzitane MINDO/3 - Modified Intermediate Cp - Cyclopentadiene Neglect of Differential Overlap m-CPBA - meta-Chloroperoxybenzoic MS - Mass Spectrometry or Mass acid Spectrum CV - Cyclic Voltammetry NMO - N-methylmorphonline-N-oxide DFT - Density Functional Theory NMP - N-methylpyrrolidinone DH50 - Drop hammer