The Chemistry of Β-Diketiminate-Supported Boron, Aluminum
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Copyright By Dragoslav Vidović 2007 The Dissertation Committee for Dragoslav Vidović certifies that this is the approved version of the following dissertation: The Chemistry of β-Diketiminate-Supported Boron, Aluminum, Gallium and Phosphorus Compounds Committee: ___________________________ Alan H. Cowley, Supervisor ___________________________ Richard A. Jones ___________________________ Bradley J. Holliday ___________________________ Ben A. Shoulders ___________________________ Jason A. C. Clyburne 3 The Chemistry of β-Diketiminate-Supported Boron, Aluminum, Gallium and Phosphorus Compounds by Dragoslav Vidović, B.S. Dissertation Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy The University of Texas at Austin May 2007 2 Dedicated to: my Father, mother and brother for endless love and support Посвећено: мом Оцу, мајци и брату на бескрајној љубави и подршци 4 Acknowledgements First and foremost, I would like to thank Professor Alan H. Cowley for not hesitating even for a moment to accept me as a part of his research group. His endless knowledge, insights, instructions and enthusiasm are truly inspirational. All of the Cowley group members with whom I had the privilege to work certainly played an important role in my achievement. Thus, I would like to thank Dr. Jeffery Pietryga, Silvia Filliponi, Lucille Mullins, Zheng Lu, Dr. Christopher Entwisltle, Dr. Leonardo Apostolico, Kalyan Vasudevan, Clint Hoberg and Adam Powell. The toughest times are usually at the beginning but Dr. Piyush Shukla’s help and guidance eased lots of those first jitters and concerns when I joined the Cowley group. Special thanks go to Dr. Jamie Jones, Dr. Jennifer Moore, Dr. Nick Hill, Dr. Gregor Reeske and Michael Findlater for sacrificing their valuable time for the X-ray crystallographic analyses of the compounds included in this work. I also greatly appreciate the time Jamie, Jennifer and Michael invested to perform computational studies of several compounds included in this work. Even though Jamie was understandably “uptight” when she was finishing her PhD, I arguably had the best times dancing down on 6th Street during her numerous visits from South Carolina. I am thankful to Jennifer not only for insightful chemistry related discussions but also for all of the delicious home-made cooking I loved so much. Pete Webber, a member of the Krische group, performed an organic transformation reaction involving one of the compounds described in this work. He was also probably one of the subconscious reasons I kept showing up at the Gregory gym at v 6 am every morning. I really did enjoy our time working out together but I had much more fun watching the Longhorns-Buckeyes clashes over the years. Dr. Kenneth Matthews and I met thanks to the common passion that is The Sacramento Kings. However, we later discovered that we had much more in common than just being die-hard Kings fans. He did allow me to be his wing-man when he was rebuilding a car engine which I treasure as invaluable experience. He was also instrumental for the introduction of many US specific events/experiences such as trips to the Texas State Fair and Rodeo and NHRA Drag Racing. Finally, I want to thank my family for helping me become the man I am today. For various life lessons and more importantly for emphasizing the importance of education, I would like to thank my father. For infinite love and encouragement, I would like to thank my mother. To my brother, I am thankful for simply being an exceptional brother. vi The Chemistry of β-Diketiminate-Supported Boron, Aluminum, Gallium and Phosphorus Compounds Publication No.____________ Dragoslav Vidović, Ph.D. The University of Texas at Austin, 2007 Supervisor: Alan H. Cowley Six synthetic methods have been explored for the preparation of several boron, aluminum, gallium and phosphorus compounds supported by the C6F5-substituted β- diketiminate ligand. The most significant advance was achieved in the synthesis of β- diketiminato boron dihalide complexes (LBX2, L = β-diketiminate ligand, X = halide) because only a handful of compounds with this general formula were known. These syntheses were carried out in virtually quantitative yields by treatment of an N- trimethylsilyl aminoimine intermediate with the appropriate boron trihalides. The synthesis and characterization of the elusive monomeric oxoborane, a compound with formal double bond between boron and oxygen, was also achieved by vii employing the C6F5-substituted β-diketiminate ligand. The overall stability of the resulting monomeric oxoborane was enhanced by complexation of the Lewis acid AlCl3 to the oxoborane oxygen atom. Successful synthetic approaches to the boron, aluminum and gallium bistriflate complexes of the general formula LE(OTf)2, where E = B, Al or Ga, were also developed and preliminary studies involving the use of these compounds as catalysts in organic transformations gave promising results. These bistriflate group 13 compounds also proved to be effective reagents for the synthesis of the first examples of boron, aluminum and gallium dications. The boron and aluminum dications were characterized by single-crystal X-ray diffraction. Finally, the use of the pentamethylcyclopentadienyl group as the boron substituent has allowed the synthesis and structural characterization of a new cationic terminal borylene complex. This complex, together with the two previously reported cationic terminal borylene complexes, demonstrate that the boron-metal bond order is sensitive to the electronic properties of the boron substituents and can vary from 1 to 2. viii Table of Contents: List of Figures……………………………………………………………………….....xi List of Schemes…………………………………………………………………..…...xix List of Tables………………………………………………………………………….xxi Index of Compounds………………………………………………………………..xxvii CHAPTER 1: Synthetic Approaches to C6F5-Substituted β-Diketiminate Complexes of Boron, Aluminum, Gallium and Phosphorus………..……………….1 INTRODUCTION……………………….………………………………………………….1 Results and Discussion…………………….………………………………………..…14 Section 1.1. Methane Elimination Method……………………….……………14 Section 1.2. Dehydrohalogenation Method……………..……...….…………..16 Section 1.3. Salt Metathesis Methods……………………..……….…………..18 Section 1.4. Trimethylsilyl Halide Elimination Method………………….……24 Section 1.5. Discussion of X-Ray Crystallographic Data ………………....….28 CONCLUSIONS……………………….………………………………………………….42 CHAPTER 2, Part I: Synthesis and Characterization of a Coordinated Oxoborane. Lewis Acid Stabilization of a Boron-Oxygen Double Bond………….44 INTRODUCTION…………………………….…………………………………………...44 Results and Discussion…………………………………….…………………………..49 CHAPTER 2, Part II: A Single-Bonded Cationic Terminal Borylene Complex....59 INTRODUCTION…………….…………………………………………………………...59 Results and Discussion………….……………………………………………………..65 ix CONCLUSIONS………….……………………………………………………………….71 CHAPTER 3: Synthesis, Characterization, and Reactivity of β-Diketiminate- Supported Boron, Aluminum and Gallium Bistriflate Complexes…….………….72 INTRODUCTION….……………………………………………………………………...72 Results and Discussion……….………………………………………………………..80 Section 3.1. Boron Triflates……………….…………………………………...80 Section 3.2. Aluminum Triflates.……………………….…..………………….88 Section 3.3. Gallium Triflates……………………….…………………………96 Section 3.4. Hydrolysis products………………….………………………….101 Section 3.5. Organic Transformation……………….………………………..104 CONCLUSIONS………………….……………………………………………………...106 CHAPTER 4: Experimental…………………….……………...………………..…108 Section 4.1. General Procedures…………….……………………………….108 Section 4.2. Physical Measurements…………………………….…………...108 Section 4.3. X-Ray Crystallography………………………….………………109 Section 4.4. DFT calculations…………………………….………………….110 Section 4.5. Experimental Procedures and Spectroscopic Data……….…….111 Section 4.6. Figures and Tables of X-ray Crystallographic Data…………....134 References ..………….…………………………………………………………..…..221 Vita………………….………………………………………………………………..228 x List of Figures Figure 1.1. General structure for a β-diketiminate ligand…………………...…….…..1 Figure 1.2. Different binding modes of β-diketiminate ligands.…….……….………..2 Figure 1.3. (a) Structure of the Dipp-substituted β-diketiminate ligand. (b) General structure of the group 13 carbene analogues……………………….………...…….…...5 Figure 1.4. Structure of the C6F5-substituted β-diketiminate ligand……………....…...7 Figure 1.5. Examples of β-diketiminate-supported boron difluoride complexes….…...8 Figure 1.6. (a) Phosphanyl-substituted β-diketiminate complexes (b) Dipp-substituted β-diketiminate ligand incorporating different phosphorus moieties……..…………….10 Figure 1.7. General structure of the targeted compounds………………….………….12 Figure 1.8. Molecular structure of (CH(CMe2)2(NC6F5)2)H, 1.1 ……………...……..28 Figure 1.9. Molecular structure of (CH(CMe2)2(NC6F5)2)BCl2, 1.6. All hydrogen atoms have been omitted for clarity……………………………………………….………….29 Figure 1.10. Molecular structure of (CH(CMe2)2(NC6F5)2)BBr2, 1.7. All hydrogen atoms have been omitted for clarity…………………………………………………....31 Figure 1.11. Molecular structure of (CH(CMe2)2(NC6F5)2)BI2, 1.8. All hydrogen atoms have been omitted for clarity…………………………………………………….…….32 Figure 1.12. Molecular structure of (CH(CMe2)2(NC6F5)2)AlMe2, 1.9. All hydrogen atoms have been omitted for clarity………………………….………………………...33 Figure 1.13. Molecular structure of (CH(CMe2)2(NC6F5)2)AlCl2, 1.11. All hydrogen atoms have been omitted for clarity……………………….…………………………...34 Figure 1.14. Molecular structure of (CH(CMe2)2(NC6F5)2)AlI2,