The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡
The σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ,...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal article |
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Royal Society of Chemistry
2019
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| _version_ | 1797073778347343872 |
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| author | Spearing-Ewyn, E Beattie, N Colebatch, A Martinez-Martinez, A Docker, A Boyd, T Baillie, G Reed, R Macgregor, S Weller, A |
| author_facet | Spearing-Ewyn, E Beattie, N Colebatch, A Martinez-Martinez, A Docker, A Boyd, T Baillie, G Reed, R Macgregor, S Weller, A |
| author_sort | Spearing-Ewyn, E |
| collection | OXFORD |
| description | The σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ, but this undergoes dehydrocoupling to reform 1 and give the aminoborane dimer [H2BNMe2]2. NMR studies on this system reveal an intermediate neutral hydride forms, Rh(PONOP)H, 4, that has been prepared independently. 1 is a competent catalyst (2 mol%, ∼30 min) for the dehydrocoupling of H3B·Me2H. Kinetic, mechanistic and computational studies point to the role of NMe2H in both forming the neutral hydride, via deprotonation of a σ-amine-borane complex and formation of aminoborane, and closing the catalytic cycle by reprotonation of the hydride by the thus-formed dimethyl ammonium [NMe2H2]+. Competitive processes involving the generation of boronium [H2B(NMe2H)2]+ are also discussed, but shown to be higher in energy. Off-cycle adducts between [NMe2H2]+ or [H2B(NMe2H)2]+ and amine-boranes are also discussed that act to modify the kinetics of dehydrocoupling. |
| first_indexed | 2024-03-06T23:26:55Z |
| format | Journal article |
| id | oxford-uuid:6aaf519f-ea3d-4a4a-8a43-f7f42f3c04dd |
| institution | University of Oxford |
| last_indexed | 2024-03-06T23:26:55Z |
| publishDate | 2019 |
| publisher | Royal Society of Chemistry |
| record_format | dspace |
| spelling | oxford-uuid:6aaf519f-ea3d-4a4a-8a43-f7f42f3c04dd2022-03-26T18:59:03ZThe role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:6aaf519f-ea3d-4a4a-8a43-f7f42f3c04ddSymplectic Elements at OxfordRoyal Society of Chemistry2019Spearing-Ewyn, EBeattie, NColebatch, AMartinez-Martinez, ADocker, ABoyd, TBaillie, GReed, RMacgregor, SWeller, AThe σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ, but this undergoes dehydrocoupling to reform 1 and give the aminoborane dimer [H2BNMe2]2. NMR studies on this system reveal an intermediate neutral hydride forms, Rh(PONOP)H, 4, that has been prepared independently. 1 is a competent catalyst (2 mol%, ∼30 min) for the dehydrocoupling of H3B·Me2H. Kinetic, mechanistic and computational studies point to the role of NMe2H in both forming the neutral hydride, via deprotonation of a σ-amine-borane complex and formation of aminoborane, and closing the catalytic cycle by reprotonation of the hydride by the thus-formed dimethyl ammonium [NMe2H2]+. Competitive processes involving the generation of boronium [H2B(NMe2H)2]+ are also discussed, but shown to be higher in energy. Off-cycle adducts between [NMe2H2]+ or [H2B(NMe2H)2]+ and amine-boranes are also discussed that act to modify the kinetics of dehydrocoupling. |
| spellingShingle | Spearing-Ewyn, E Beattie, N Colebatch, A Martinez-Martinez, A Docker, A Boyd, T Baillie, G Reed, R Macgregor, S Weller, A The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡ |
| title | The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡ |
| title_full | The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡ |
| title_fullStr | The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡ |
| title_full_unstemmed | The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡ |
| title_short | The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst†‡ |
| title_sort | role of neutral rh ponop h free nme2h boronium and ammonium salts in the dehydrocoupling of dimethylamine borane using the cationic pincer rh ponop η2 h2 catalyst†‡ |
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