Mechanisms of platinum(II) and palladium(II) catalyzed organic transformations : hydration of alkynes and the cope rearrangement by William Charles Hiscox A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry Montana State University © Copyright by William Charles Hiscox (1993) Abstract: Mechanisms of the platinum (II) catalyzed hydration of alkynes and the palladium (II) catalyzed Cope rearrangement of 2-methy1-3-pheny1-1,5-heptadiene were studied using nuclear magnetic resonance spectrometry (MMR). Kinetic studies were done for both reactions. For both reactions the rate determing steps were found to be ligand substitution reactions of the respective substrates on the active catalysts. The reactions are shown to proceed through metallacycle intermediates. MECHANISMS OF PLATINUM (II) AND PALLADIUM(II) CATALYZED ORGANIC TRANSFORMATIONS: HYDRATION OF ALKYNES AND THE COPE REARRANGEMENT by William Charles Hiscox A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry Montana State University Bozeman, Montana July 1993 MECHANISMS OF PLATINUM (II) AND PALLADIUM(II) CATALYZED ORGANIC TRANSFORMATIONS: HYDRATION OF ALKYNES AND THE COPE REARRANGEMENT William Charles Hiscox Advisor: Reed A. Howald, Ph.D. Montana State University 1993 Abstract Mechanisms of the platinum (II) catalyzed hydration of alkynes and the palladium(II) catalyzed Cope rearrangement of 2-methyl-3-phenyl-I,5-heptadiene were studied using . nuclear magnetic resonance spectrometry (NMR). Kinetic studies were done for both reactions. For both reactions the rate determing steps were found to be ligand substitution reactions of the respective substrates on the active catalysts. The reactions are shown to proceed through metallacycle intermediates. © COPYRIGHT by William Charles Hiscox 1993 All Rights Reserved jyyi? APPROVAL of a thesis submitted by- William Charles Hiscox This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. 7 / 2 0 /f?________ Date Chairperson, Graduate Committee Approved for the Major Department Date Head, Major Department Approved for the College of Graduate Studies 9/ /3 M Date Graduate Dean iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a doctoral degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. I further agree that copying of this thesis is allowable only for scholarly purposes, consistent with "fair use" as prescribed in the U.S . Copyright Law. Requests for extensive copying or reproduction of this thesis should be referred to University Microfilms International, 300 North Zeeb Road, Ann Arbor, Michigan 48106, to whom I have granted "the exclusive right to reproduce and distribute my dissertation for sale in and from microform or electronic format, along with the right to reproduce and distribute my abstract in any format in whole or in part". Date. iv This thesis is dedicated to the memory of Marjorie Nichols, one of the first women ever admitted to a college chemistry course, and the one responsible for my interest in science. V TABLE OF CONTENTS Page 1. INTRODUCTION.......................................... I 2. PLATINUM (II) CATALYZED HYDRATION OF ALKYNES AND RELATED REACTIONS ................................... 3 Background .......................................... 5 Experimental Section ................................ 13 General........................................... 13 Preparation of Zeise1s Dimer .................... 14 di- (4,4 - dime thy I -2 -pentyne) -dichloro-di-JLl- dichloroplatinum (II).............................. 15 General Method for Hydration of Alkynes- Illustrated for I-Hexyne ........................ 16 Recycling of Platinum ........................... 18 Monitoring of Reactions by 1H N M R ................19 Effect of p-toluenesulfonic acid on reaction r a t e ...............................................20 Effect of D2O vs H2O ..............................20 Rate of Reaction with 4,4-dimethyl-2-pentyne dimer vs Zeise1 s D i m e r ........................... 21 Michaelis-Menten kinetics ....................... 22 Reaction of Zeise's Dimer with 4-Octyne in CHCl3 ..............................................23 Dichloroplatinum(II)-tetraalkylyclobutadienes ... 24 Methanol Addition to 1-alkynes .................. 31 Results and Discussion .............................. 36 Mechanistic Studies .............................. 43 Exchange experiments on Zeise's Dimer .......... 48 The Role of the Ethylene Ligand in the Catalyst.......................................... 51 Kinetics Experiments- IH N M R ..................... 56 Michaelis-Menten Catalyst Model ................. 62 Evaluation of Possible Mechanisms ............... 63 Addition of Methanol to I-Alkynes ............... 72 Cyclobutadienes .................................. 78 Summary............................................. 85 3. PALLADIUM CATALYZED COPE REARRANGEMENT OF 2-METHYL-3 -PHENYL-1,5-HEPTADIENE........................ 86 Background........................................... 89 Mechanism of Thermal Cope Rearrangements ....... 91 Palladium(II) Catalyzed Cope Rearrangements .... 98 vi TABLE OF CONTENTS-continued page Experimental Section .................................. 102 General........................................... 102 Synthesis of Starting Materials ................. 103 Thermal Rearrangement of trans-2-methyl-3- phenyl-1,5-heptadiene ........................... 109 Molecular Modeling ................................ 109 bis-Acetonitriledichloropalladium(TI) .......... H O Palladium Catalyzed Cope Rearrangement of trans-2-methyl-3-phenyl-1,5-heptadiene in Tetrahydrofuran .................................. Ill Separation of Cis and Trans Isomers of 2- methyl-3-phenyl-1,5-heptadiene and of their Cope Rearrangement Products, Cis and Trans- 2 ,4-dimethyl-I-phenyl-I,5-hexadiene ............. 112 Characterization of diene I I .................... 113 Kinetics- Monitoring of Reactions by IH NMR .... 114 Reactions of purified Cope Products ............ 116 Data Handling, Analysis ......................... 116 Viability of the Catalyst at Long Reaction T i m e s ............................................ 118 Effect of Added Acetonitrile .................... 118 Double-bond Isomerization of 3-heptene ......... 119 Results............................................. 121 Collecting the Data: Preliminary Results ....... 128 Reactions of Purified Dienes .................... 130 Modeling the Palladium (II) Catalyzed Cope Rearrangement as a Set of Concurrent First Order Reactions.................................. 135 Effect of Added Acetonitrile........ ........... 139 Molecular Modeling Studies ...................... 142 Details of Analysis of the Kinetic Data ........ 143 Kinetic Runs at 308K ............................ 155 Thermodynamic Activation Parameters ............. 155 Discussion.......................................... 159 Summary............................................. 164 4. CONCLUSION.............................................. 166 REFERENCES CITED ........................................ 168 APPENDIX Data From Kinetic Runs in Chapter 3 ........ 17 6 vii LIST OF TABLES Table page 1. Data for Michaelis-Menten Graph .................. 61 2. Thermodynamic Activation Parameters .............. 156 viii LIST OF FIGURES Figure page 1. Hydration of 4-Octyne ............................... 4 2. Chatt-Dewar-Duncanson Model for olefin-metal bonding ........................................... 9 3. Synergistic Bonding of Orthogonal JCy and TUj_* Acetylene Orbitals to Platinum .................. 11 4. Correlation Diagram for Acetylene Backbonding to Platinum........................................... 12 5. Hydration of Dialkylalkynes ........................ 37 6. Explanation for Regioselectivity .................. 38 7. 13C and 1H NMR of 2-Heptanone from Hydration of I-Heptyne.......................................... 40 8 . Structure of Zeise's Dimer ......................... 44 9. NMR Spectra for D20 Monomer of Zeise's Dimer ....... 45 10. 13C and 1H NMR Spectra of Zeise's Dimer in CD30D.... 46 11. Zeise's Dimer in C D 3 C N ...............................47 12. 1H NMR Spectra for Catalytic Reaction in Tetrahydrofuran-dg ................................ 49 13. 1H NMR Spectra for Ethylene Displacement in Chloroform-d ...................................... 50 14. Top: di-(4,4-dimethyl-2-pentyne)-dichloro- di-m-dichlorodiplatinum(II). Bottom: Addition of 4-octyne and water to the complex...... 54 15. Detailed Mechanism of Platinum(II) Catalyzed Hydration of Alkynes Showing the Michaelis Menten Constants .................................. 57 16. First Order Plots at Several Initial Concentrations of Alkyne ......... 58 17. Saturation Kinetics ................................. 59 18. Michaelis-Menten Graph ............................. 60 19. Cis-Addition of Water and Methanol to an Osmium(II)-Alkyne Complex ........................ 67 20. Addition of Protonic Acids to a Platinum(0)- Alkyne Complex .................................... 68 21. Mechanism of Hydroxypalladation .................... 70 ix LIST OF FIGURES-continued Figure page 22. Evidence for External Attack of Water on the