POP-type rhodium complexes in amine borane dehydropolymerisation
<p>This thesis explores the catalytic dehydropolymerisation of N-methylamine borane, H3B·NMeH2, to form N-methylpolyaminoborane, (H<sub>2</sub>BNMeH)<sub>n</sub>, using POP-type rhodium complexes based upon the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</s...
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| Formato: | Thesis |
| Idioma: | English |
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2018
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| _version_ | 1826306623936659456 |
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| author | Adams, G |
| author2 | Weller, A |
| author_facet | Weller, A Adams, G |
| author_sort | Adams, G |
| collection | OXFORD |
| description | <p>This thesis explores the catalytic dehydropolymerisation of N-methylamine borane, H3B·NMeH2, to form N-methylpolyaminoborane, (H<sub>2</sub>BNMeH)<sub>n</sub>, using POP-type rhodium complexes based upon the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> and {Rh(DPEphos)}<sup>+</sup> fragments. A comparison of these metal-ligand frameworks provides a structure/activity relationship in order to gain mechanistic insight into the H3B·NMeH2 dehydropolymerisation process.</p> <p>Chapter 2 describes the synthesis of a suitable {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> precatalyst for H<sub>3</sub>B·NMeH<sub>2</sub> dehydropolymerisation. Its reactivity with H<sub>3</sub>B·NMeH<sub>2</sub> is examined by NMR spectroscopy, and independent synthetic routes to the complexes observed are described. From this, a dimetalloborylene is isolated and crystallographically characterised. The kinetics of H3B·NMeH2 dehydrogenation and (H<sub>2</sub>BNMeH)<sub>n</sub> growth using the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> fragment are reported in Chapter 3, which combined with the speciation studies in Chapter 2, allows for a mechanistic proposal for dehydropolymerisation. The formation and subsequent deprotonation of a boronium cation is postulated to lead to the monomer, H<sub>2</sub>B=NMeH, which forms (H<sub>2</sub>BNMeH)<sub>n</sub> via an on-metal end-chain propagation mechanism.</p> <p>In Chapter 4 the focus shifts to synthesise a suitable {Rh(DPEphos)}<sup>+</sup> precatalyst for H3B·NMeH2 dehydropolymerisation. Here, speciation studies of the {Rh(DPEphos)}<sup>+</sup> fragment with H<sub>3</sub>B·NMeH<sub>2</sub> enables the observation of bimetallic complexes, one of which is considered an amidodiboryl complex. An in-depth dehydropolymerisation kinetic study using the {Rh(DPEphos)}<sup>+</sup> system is undertaken in Chapter 5, and strong dependence of (H<sub>2</sub>BNMeH)<sub>n</sub> molecular weight on H<sub>2</sub> pressure and catalyst loading indicates that an on-metal coordination/dehydrogenation/insertion mechanism operates, contrasting that proposed for the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> system. The bimetallic amidodiboryl complex described in Chapter 4 and NMeH<sub>2</sub>-derived {Rh(DPEphos)}<sup>+</sup> species are also tested in catalysis, and appear close in identity to the true active catalytic species, due to the lack of induction period observed prior to H<sub>2</sub> evolution.</p> |
| first_indexed | 2024-03-07T06:50:46Z |
| format | Thesis |
| id | oxford-uuid:fc7ce845-62be-41ea-a2f2-c898b21f2f47 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T06:50:46Z |
| publishDate | 2018 |
| record_format | dspace |
| spelling | oxford-uuid:fc7ce845-62be-41ea-a2f2-c898b21f2f472022-03-27T13:21:09ZPOP-type rhodium complexes in amine borane dehydropolymerisationThesishttp://purl.org/coar/resource_type/c_db06uuid:fc7ce845-62be-41ea-a2f2-c898b21f2f47Organometallic ChemistryChemistryInorganic ChemistryEnglishORA Deposit2018Adams, GWeller, A<p>This thesis explores the catalytic dehydropolymerisation of N-methylamine borane, H3B·NMeH2, to form N-methylpolyaminoborane, (H<sub>2</sub>BNMeH)<sub>n</sub>, using POP-type rhodium complexes based upon the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> and {Rh(DPEphos)}<sup>+</sup> fragments. A comparison of these metal-ligand frameworks provides a structure/activity relationship in order to gain mechanistic insight into the H3B·NMeH2 dehydropolymerisation process.</p> <p>Chapter 2 describes the synthesis of a suitable {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> precatalyst for H<sub>3</sub>B·NMeH<sub>2</sub> dehydropolymerisation. Its reactivity with H<sub>3</sub>B·NMeH<sub>2</sub> is examined by NMR spectroscopy, and independent synthetic routes to the complexes observed are described. From this, a dimetalloborylene is isolated and crystallographically characterised. The kinetics of H3B·NMeH2 dehydrogenation and (H<sub>2</sub>BNMeH)<sub>n</sub> growth using the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> fragment are reported in Chapter 3, which combined with the speciation studies in Chapter 2, allows for a mechanistic proposal for dehydropolymerisation. The formation and subsequent deprotonation of a boronium cation is postulated to lead to the monomer, H<sub>2</sub>B=NMeH, which forms (H<sub>2</sub>BNMeH)<sub>n</sub> via an on-metal end-chain propagation mechanism.</p> <p>In Chapter 4 the focus shifts to synthesise a suitable {Rh(DPEphos)}<sup>+</sup> precatalyst for H3B·NMeH2 dehydropolymerisation. Here, speciation studies of the {Rh(DPEphos)}<sup>+</sup> fragment with H<sub>3</sub>B·NMeH<sub>2</sub> enables the observation of bimetallic complexes, one of which is considered an amidodiboryl complex. An in-depth dehydropolymerisation kinetic study using the {Rh(DPEphos)}<sup>+</sup> system is undertaken in Chapter 5, and strong dependence of (H<sub>2</sub>BNMeH)<sub>n</sub> molecular weight on H<sub>2</sub> pressure and catalyst loading indicates that an on-metal coordination/dehydrogenation/insertion mechanism operates, contrasting that proposed for the {Rh(Xantphos-<sup>i</sup>Pr)}<sup>+</sup> system. The bimetallic amidodiboryl complex described in Chapter 4 and NMeH<sub>2</sub>-derived {Rh(DPEphos)}<sup>+</sup> species are also tested in catalysis, and appear close in identity to the true active catalytic species, due to the lack of induction period observed prior to H<sub>2</sub> evolution.</p> |
| spellingShingle | Organometallic Chemistry Chemistry Inorganic Chemistry Adams, G POP-type rhodium complexes in amine borane dehydropolymerisation |
| title | POP-type rhodium complexes in amine borane dehydropolymerisation |
| title_full | POP-type rhodium complexes in amine borane dehydropolymerisation |
| title_fullStr | POP-type rhodium complexes in amine borane dehydropolymerisation |
| title_full_unstemmed | POP-type rhodium complexes in amine borane dehydropolymerisation |
| title_short | POP-type rhodium complexes in amine borane dehydropolymerisation |
| title_sort | pop type rhodium complexes in amine borane dehydropolymerisation |
| topic | Organometallic Chemistry Chemistry Inorganic Chemistry |
| work_keys_str_mv | AT adamsg poptyperhodiumcomplexesinamineboranedehydropolymerisation |