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Application of Ammonia Borane and Metal View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by ScholarBank@NUS APPLICATION OF AMMONIA BORANE AND METAL AMIDOBORANES IN ORGANIC REDUCTION XU WEILIANG (B.Sci., Soochow University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2012 ACKNOWLEDGEMENTS I would like to express my sincere gratitude to Prof. Chen Ping. As my Ph.D. supervisor, Prof. Chen taught me both basic and advanced techniques in chemistry with great patience. She also led me to the right direction with her experience and knowledge at every critical point of this thesis. Her assistance and supervision are great treasures to me and this thesis work. I also appreciate the help from my co-supervisor, Asst. Prof. Wu Jishan. Dr Wu gave me great suggestions on my research work and inspired me in every discussion with him. In addition, I need to warmly acknowledge Prof. Fan Hongjun and Prof. Zhou Yonggui from Dalian Institute of Chemical Physics, Chinese Academy of Sciences. The help from Prof. Fan in theoretical calculation improves the understanding of my research topic. The discussion with Prof. Zhou on research topic helps me achieve several additional insights into this topic. A very special recognition needs to be given to my research group members such as Prof. Xiong Zhitao and Prof. Wu Guotao for their extensive help and support during research. Finally, a special thanks to my family for their uncontional love and support in every way possible throughout the process of my Ph.D. course. i THESIS DECLARATION The work in this thesis is the original work of Xu Weiliang, performed independently under the supervision of Assoc Prof. Chen Ping, Chemistry Department, National University of Singapore, between 2007 and 2011. The content of the thesis has been published in: 1. Xu, W.; Zhou, Y.; Wang, R.; Wu, G.; Chen, P., Lithium amidoborane, highly chemoselective reagent for reduction of -unsaturated ketones to allylic alcohols. Organic & Biomolecular Chemistry, 2012,10, 367-371. 2. Xu, W.; Wang, R.; Wu, G.; Chen, P. Calcium amidoborane, a new chemoselective reagent for reduction of ,-unsaturated aldehydes and ketones to allylic alcohols. RSC Advances, DOI: 10.1039/C2RA01291J. 3. Xu, W.; Zheng, X; Wu, G.; Chen, P. Reductive amination of aldehydes and ketones with primary amines by using lithium amidoborane. Chinese Journal of Chemistry, DOI: 10.1002/cjoc.201200132. 4. Xu, W.; Fan, H.; Wu, G.; Chen, P., Comparative study on reducing aromatic aldehydes by using ammonia borane and lithium amidoborane as reducing reagents. New Journal of Chemistry, DOI: 10.1039/c2nj40227k. Name Signature Date ii Table of contents Acknowledgements………………………………………………………….. i Publication list…………………………………………………….................. viii Summary………………………………………………………………………. ix List of Tables………………………………………………………………….. xi List of Figures…………………………………………………………………. xii Abbreviation List…………………………………………………………….. xiv Chapter 1. Introduction 1.1 Review on methods for organic reduction……………………………….. 2 1.1.1 Catalytic hydrogenation………………………………………………. 2 1.1.2 Electroreduction and reduction with metals………………………….. 4 1.1.3 Transfer hydrogenation……………………………………………..... 6 1.1.4 Reduction with hydrides and complex hydrides……………………… 9 1.2 Reducing reactivity of some typical borohydride compounds………… 10 1.2.1 Sodium borohydride (NaBH4)……………………………………… 10 1.2.2 Diborane (B2H6), tetrahydrofuran-borane complex (BH3-THF) and dimethyl sulfide Borane (BMS) ………………………………………………. 13 1.2.3 Amine borane ………………………………………………………… 19 1.2.4 Sodium aminoborohydrides (NaNRR’BH3) ………………………… 25 1.2.5 Lithium aminoborohydrides (LiNRR’BH3, LAB) …………………... 28 1.3 Mechanistic interpretations on borohydride reduction……………………. 31 1.4 Review on ammonia borane and metal amidoboranes for hydrogen iii storage ………………………………………………………………..... 35 1.4.1 Ammonia borane (AB)……………………………………………….. 35 1.4.2 Metal amidoborane (MAB)………………………………………….. 38 1.5 Research gaps and aims…………………………………………………… 39 1.5.1 Research gaps………………………………………………………… 39 1.5.2 Research aims………………………………………………………… 40 Chapter 2. Methodology 2.1 Synthesis of metal amidoboranes…………………………………………. 42 2.1.1 Introduction………………………………………………………….. 42 2.1.2 Synthetic procedure of metal amidoboranes. ……………………… 43 2.2 Synthesis of deuterated ammonia borane and deuterated metal amidoboranes.......................................................................................... 45 2.2.1 Introduction…………………………………………………………. 46 2.2.2 Synthetic procedure of deuterated ammonia borane and deuterated metal amidoboranes……………………………………………………….. 46 2.3 Characterization methods………………………………………………. 47 Chapter 3. Reducing aldehydes and ketones by ammonia boranes 3.1 Introduction……………………………………………………………….. 48 3.2 Results and discussion ……………………………………………………. 49 3.2.1 Reaction process and reactivity study………………………………... 49 3.2.2 Kinetic study………………………………………………………….. 53 3.2.3 Theoretical study……………………………………………………. 55 iv 3.3 Conclusion……………………………………………………………… 58 3.4 Experimental section………………………………………………………. 58 3.4.1 General Remarks…………………………………………………..... 58 3.4.2 General experimental procedure for reducing aldehydes and ketones with AB........................................................................................................ 59 3.4.3 Products characterization..................................................................... 60 Chapter 4. Reducing aldehydes, ketones and imines by metal amidoboranes 4.1 Introduction………………………………………………………………… 64 4.2 Results and discussion ……………………………………………………. 65 4.2.1 Reducing ketones by MAB………………………………………..... 65 4.2.2 Reducing imines with MAB………………………………………..... 71 4.2.3 Theoretical Study…………………………………………………...... 77 4.2.4 Reducing aromatic aldehydes with MAB…………………………… 79 4.3 Conclusion………………………………………………………………. 82 4.4 Experimental section……………………………………………………….. 83 4.4.1 General Remarks…………………………………………………….. 83 4.4.2 Synthesis of imines............................................................................... 83 4.4.3 General experimental procedure for reducing ketones with LiAB, NaAB or CaAB................................................................................................... 84 4.4.4 General experimental procedure for reducing imines with LiAB, NaAB or CaAB.................................................................................................... 84 4.4.5 Products characterization...................................................................... 85 v Chapter 5. Chemoselectively reducing -unsaturated aldehydes and ketones into allyic alcohols by metal amidoboranes 5.1 Introduction……………………………………………………………….. 92 5.2 Results and discussion …………………………………………………….. 94 5.2.1 Reactivity study………………………………………………............ 94 5.2.2 Mechanism study…………………………………………………...... 97 5.2.3 Reducing -unsaturated aldehydes with MAB…………………..... 98 5.2.4 Explanation on 1,2-reduction property of MAB…………………...... 100 5.3 Conclusion………………………………………………………………… 100 5.4 Experimental section……………………………………………………….. 101 5.4.1 General remarks…………………………………………………... 101 5.4.2 Synthesis of -unsaturated ketones…………………………......... 101 5.4.3 General experimental procedure for reducing -unsaturated ketones or aldehydes with CaAB………………………………………………………. 102 5.4.4 Products characterization……………………………………….... 103 Chapter 6. Reductive amination of aldehydes and ketones with primary amines by using lithium amidoborane 6.1 Introduction………………………………………………………………. 109 6.2 Results and discussion ……………………………………………………. 111 6.2.1 Choice of Lewis acid……………………………………………..... 111 6.2.2 Reactivity study………………………………………………….... 112 vi 6.3 Conclusion………………………………………………………………… 114 6.4 Experimental section………………………………………………………. 115 6.4.1 General remarks…………………………………………………….. 115 6.4.2 General experimental procedure for reducing amination by LiAB.. 115 6.4.3 Products characterization………………………………………....... 116 Chapter 7. Conclusion and Future work 7.1 Conclusion ……………………………………………………………… 121 7.2 Future work……………………………………………………………… 124 Reference……………………………………………………………………… 125 vii PUBLICATION LIST 1. Xu, W.; Zhou, Y.; Wang, R.; Wu, G.; Chen, P., Lithium amidoborane, highly chemoselective reagent for reduction of ,-unsaturated ketones to allylic alcohols. Organic & Biomolecular Chemistry, 2012,10, 367-371. 2. Xu, W.; Wang, R.; Wu, G.; Chen, P. Calcium amidoborane, a new chemoselective reagent for reduction of ,-unsaturated aldehydes and ketones to allylic alcohols. RSC Advances, DOI: 10.1039/C2RA01291J. 3. Xu, W.; Zheng, X.; Wu, G.; Chen, P. Reductive amination of aldehydes and ketones with primary amines by using lithium amidoborane. Chinese Journal of Chemistry, DOI: 10.1002/cjoc.201200132. 4. Xu, W.; Fan, H.; Wu, G.; Chen, P., Comparative study on reducing aromatic aldehydes by using ammonia borane and lithium amidoborane as reducing reagents. New Journal of Chemistry, DOI: 10.1039/c2nj40227k 5. Xu, W.; Fan, H.; Wu, G.; Wu, J.; Chen, P., Metal Amidoboranes, Superior Double Hydrogen Transfer Agents in Reducing Ketones and Imines. Chemistry- a European Journal, under revision. 6. Zheng, X.; Xu, W.; Xiong, Z.; Chua, Y.; Wu, G.; Qin, S.; Chen, H.; Chen, P., Ambient temperature hydrogen desorption from LiAlH4-LiNH2 mediated by HMPA. Journal of Material Chemistry. 2009, 19 (44), 8426-8431. 7. Xiong, Z.; Wu, G.; Chua, Y. S.; Hu, J.; He, T.; Xu, W.; Chen, P., Synthesis of sodium amidoborane (NaNH2BH3) for hydrogen production. Energy & Environmental Science 2008, 1 (3), 360-363. 8. Xiong, Z. T.; Chua, Y. S.;
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