Amine-borane dehydrogenation : catalyst development, novel materials and mechanistic insight

• Main Author: Robertson, Alasdair P. M.
• Published: University of Bristol 2012
• Subjects: 660.2995
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559079

This Thesis describes investigations into the dehydrogenation of amine-borane adducts and hydrogenation of aminoboranes via metal-catalysed and thermolytic routes. Chapter 1 provides a general introduction to the area of metal-catalysed dehydrocoupling reactions of main-group compounds. Specific emphasis is placed upon amine-borane adducts, for which the physical and chemical properties are also discussed in detail. Chapter 2 describes the identification and application of skeletal Ni as an effective heterogeneous catalyst for the dehydrocoupling of amine-boranes. The optimisations of catalyst formulation and reaction conditions are presented, together with studies of the catalytic dehydrogenation of a series of amine-boranes. Investigations into the mechanism of the catalytic transformation are presented in addition to studies of potential surface poisoning processes. Chapter 3 describes the synthesis of a novel amine-borane / aminoborane pair, iPr2NH'BH(C6F5)2 and iPr2N=B(C6Fs)2. The interconversion of the two species through dehydrogenation and hydrogenation respectively via metal-mediated and thermolytic protocols is described. A DFT study of the thermodynamics of the interconversion is also presented and the thermodynamic parameters for the related phosphine-borane / phosphinoborane pair, iPr2PH'BH(C6F5)2 and iPr2P-B(C6F5)2 are also elucidated. Chapter 4 describes the development of a general route to linear diborazanes, RR'R"N-BH2-NRR' -BH3, with the spectroscopic and crystallographic characterisation of a series of novel compounds presented. The thermal and Ir-catalysed redistributions of these species are investigated in detail, and the formation of transient aminoboranes demonstrated in some cases to result in complex hydrogen transfer reactions. The novel hydrogen transfer reactivity is exemplified by a further study of reactions between amine-boranes and aminoboranes. Chapter 5 describes the development of synthetic routes to amine-thioborane adducts R2NH' BH2SR'. A variety of possible routes to such species are presented, with a broad series of tertiary and secondary amine-thioborane adducts characterised. Studies of the thermal and metal-catalysed dehydrogenation of the secondary amine-thioboranes are also presented. Chapter 6 describes possible future, or indeed ongoing, work based upon the results presented in chapters 2-5.