Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes
<p>This thesis details the synthesis of novel Rh(I) and Rh(III) bis-phosphine fragments, and their use, along with other known rhodium species, to investigate the reactivity of amine-boranes, with a particular focus on the dehydrocoupling of the secondary amine-borane H3B.NMe2H (DMAB).</p&g...
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
2013
|
| Subjects: |
| _version_ | 1817932223156846592 |
|---|---|
| author | Sewell, LJ |
| author2 | Weller, A |
| author_facet | Weller, A Sewell, LJ |
| author_sort | Sewell, LJ |
| collection | OXFORD |
| description | <p>This thesis details the synthesis of novel Rh(I) and Rh(III) bis-phosphine fragments, and their use, along with other known rhodium species, to investigate the reactivity of amine-boranes, with a particular focus on the dehydrocoupling of the secondary amine-borane H3B.NMe2H (DMAB).</p> <p>Chapter 2 utilises the new mixed phosphine, PtBuiBu2, to investigate the role of the phosphine with regard to the corresponding low-coordinate organometallic species isolated. Their coordination and reactivity with amine-boranes is studied, leading to the development of a mechanism for an alkene hydroboration catalyst that employs H3B.NMe3 (TMAB). The final section of the chapter studies several fluxional processes pertinent to rhodium and iridium complexes of the model amine-borane TMAB using H/D exchange and low temperature NMR experiments.</p> <p>In Chapter 3, the mechanism of dehydrocoupling of DMAB is investigated in detail, employing catalysts based on the cationic bis¬-phosphine Rh fragment, {Rh(PCy3)2Ln}+. A series of stoichiometric and catalytic reactions are probed using NMR spectroscopy and mass spectrometry, revealing a complex mechanistic landscape. Subtleties include: the product of dehydrocoupling, [H2BNMe2]2, acting in an autocatalytic role; and parallel dehydrogenation of DMAB by a neutral catalyst present in a low but constant concentration. The mechanism was additionally interrogated through kinetic simulations conducted by Prof. Guy C. Lloyd-Jones (University of Bristol). From this, a generic mechanistic scheme has been suggested, aspects of which can be applied to transition metal and main group systems reported to catalyse the dehydrocoupling of DMAB.</p> <p>The final chapter moves on from cationic rhodium fragments to investigate the reactivity of the neutral rhodium species, Rh(H)2(PCy3)2Cl and [Rh(PCy3)2Cl]2, with amine-boranes. The mechanism by which Rh(H)2(PCy3)2Cl catalyses the dehydrogenation of DMAB has been investigated through initial rate and H/D exchange experiments, leading to the proposal of a reaction scheme. Additionally, the formation and characterisation of a base-stabilised boryl species has been reported resulting from the reactivity of an amino-borane with [Rh(PCy3)2Cl]2.</p> |
| first_indexed | 2024-03-06T19:44:13Z |
| format | Thesis |
| id | oxford-uuid:21b883f1-9ffd-4589-ad82-1243b988af91 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-12-09T03:34:30Z |
| publishDate | 2013 |
| record_format | dspace |
| spelling | oxford-uuid:21b883f1-9ffd-4589-ad82-1243b988af912024-12-01T18:04:11ZExploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranesThesishttp://purl.org/coar/resource_type/c_db06uuid:21b883f1-9ffd-4589-ad82-1243b988af91Inorganic chemistryCatalysisOrganometallic ChemistryEnglishOxford University Research Archive - Valet2013Sewell, LJWeller, A<p>This thesis details the synthesis of novel Rh(I) and Rh(III) bis-phosphine fragments, and their use, along with other known rhodium species, to investigate the reactivity of amine-boranes, with a particular focus on the dehydrocoupling of the secondary amine-borane H3B.NMe2H (DMAB).</p> <p>Chapter 2 utilises the new mixed phosphine, PtBuiBu2, to investigate the role of the phosphine with regard to the corresponding low-coordinate organometallic species isolated. Their coordination and reactivity with amine-boranes is studied, leading to the development of a mechanism for an alkene hydroboration catalyst that employs H3B.NMe3 (TMAB). The final section of the chapter studies several fluxional processes pertinent to rhodium and iridium complexes of the model amine-borane TMAB using H/D exchange and low temperature NMR experiments.</p> <p>In Chapter 3, the mechanism of dehydrocoupling of DMAB is investigated in detail, employing catalysts based on the cationic bis¬-phosphine Rh fragment, {Rh(PCy3)2Ln}+. A series of stoichiometric and catalytic reactions are probed using NMR spectroscopy and mass spectrometry, revealing a complex mechanistic landscape. Subtleties include: the product of dehydrocoupling, [H2BNMe2]2, acting in an autocatalytic role; and parallel dehydrogenation of DMAB by a neutral catalyst present in a low but constant concentration. The mechanism was additionally interrogated through kinetic simulations conducted by Prof. Guy C. Lloyd-Jones (University of Bristol). From this, a generic mechanistic scheme has been suggested, aspects of which can be applied to transition metal and main group systems reported to catalyse the dehydrocoupling of DMAB.</p> <p>The final chapter moves on from cationic rhodium fragments to investigate the reactivity of the neutral rhodium species, Rh(H)2(PCy3)2Cl and [Rh(PCy3)2Cl]2, with amine-boranes. The mechanism by which Rh(H)2(PCy3)2Cl catalyses the dehydrogenation of DMAB has been investigated through initial rate and H/D exchange experiments, leading to the proposal of a reaction scheme. Additionally, the formation and characterisation of a base-stabilised boryl species has been reported resulting from the reactivity of an amino-borane with [Rh(PCy3)2Cl]2.</p> |
| spellingShingle | Inorganic chemistry Catalysis Organometallic Chemistry Sewell, LJ Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes |
| title | Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes |
| title_full | Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes |
| title_fullStr | Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes |
| title_full_unstemmed | Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes |
| title_short | Exploring the reactivity patterns of cationic and neutral rhodium bis-phosphine species with amine-boranes |
| title_sort | exploring the reactivity patterns of cationic and neutral rhodium bis phosphine species with amine boranes |
| topic | Inorganic chemistry Catalysis Organometallic Chemistry |
| work_keys_str_mv | AT sewelllj exploringthereactivitypatternsofcationicandneutralrhodiumbisphosphinespecieswithamineboranes |