Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNH Complexes
| Autor: | Joaquín López-Serrano, Laura L. Santos, Andrés Suárez, Isabel Ortega-Lepe, Andrea Rossin, Eleuterio Álvarez, Nuria Rendón, Práxedes Sánchez |
|---|---|
| Přispěvatelé: | Agencia Estatal de Investigación (España), Junta de Andalucía, Universidad de Sevilla. Departamento de Química Inorgánica, Agencia Estatal de Investigación. España |
| Rok vydání: | 2021 |
| Předmět: |
proton-responsive ligands
catalysis Ammonia borane Homogeneous catalysis Nuclear magnetic resonance spectroscopy iridium DFT calculations Medicinal chemistry Article Pincer movement Catalysis Inorganic Chemistry chemistry.chemical_compound Deprotonation chemistry dehydrogenation Dehydrogenation Physical and Theoretical Chemistry ammonia borane Carbene |
| Zdroj: | Inorganic chemistry (Online) 60 (2021): 18490–18502. doi:10.1021/acs.inorgchem.1c03056 info:cnr-pdr/source/autori:Isabel Ortega-Lepe, Andrea Rossin, Praxedes Sanchez, Laura L. Santos, Nuria Rendon, Eleuterio A?lvarez, Joaquin Lopez-Serrano, and Andres Suarez/titolo:Ammonia-Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNH Complexes/doi:10.1021%2Facs.inorgchem.1c03056/rivista:Inorganic chemistry (Online)/anno:2021/pagina_da:18490/pagina_a:18502/intervallo_pagine:18490–18502/volume:60 Digital.CSIC. Repositorio Institucional del CSIC instname Inorganic Chemistry |
| ISSN: | 1520-510X 0020-1669 |
| DOI: | 10.1021/acs.inorgchem.1c03056 |
| Popis: | Metal complexes incorporating proton-responsive ligands have been proved to be superior catalysts in reactions involving the H2 molecule. In this contribution, a series of IrIII complexes based on lutidine-derived CNNH pincers containing N-heterocyclic carbene and secondary amino NHR [R = Ph (4a), tBu (4b), benzyl (4c)] donors as flanking groups have been synthesized and tested in the dehydrogenation of ammonia–borane (NH3BH3, AB) in the presence of substoichiometric amounts (2.5 equiv) of tBuOK. These preactivated derivatives are efficient catalysts in AB dehydrogenation in THF at room temperature, albeit significantly different reaction rates were observed. Thus, by using 0.4 mol % of 4a, 1.0 equiv of H2 per mole of AB was released in 8.5 min (turnover frequency (TOF50%) = 1875 h–1), while complexes 4b and 4c (0.8 mol %) exhibited lower catalytic activities (TOF50% = 55–60 h–1). 4a is currently the best performing IrIII homogeneous catalyst for AB dehydrogenation. Kinetic rate measurements show a zero-order dependence with respect to AB, and first order with the catalyst in the dehydrogenation with 4a (−d[AB]/dt = k[4a]). Conversely, the reaction with 4b is second order in AB and first order in the catalyst (−d[AB]/dt = k[4b][AB]2). Moreover, the reactions of the derivatives 4a and 4b with an excess of tBuOK (2.5 equiv) have been analyzed through NMR spectroscopy. For the former precursor, formation of the iridate 5 was observed as a result of a double deprotonation at the amine and the NHC pincer arm. In marked contrast, in the case of 4b, a monodeprotonated (at the pincer NHC-arm) species 6 is observed upon reaction with tBuOK. Complex 6 is capable of activating H2 reversibly to yield the trihydride derivative 7. Finally, DFT calculations of the first AB dehydrogenation step catalyzed by 5 has been performed at the DFT//MN15 level of theory in order to get information on the predominant metal–ligand cooperation mode. Iridium complexes based on CNNH ligands containing two potential proton-responsive sites—a lutidine scaffold and a secondary amino group—have been tested in the dehydrogenation of ammonia-borane. Upon reaction with base, depending on the amino group acidity, mono- or doubly deprotonated species exhibiting significantly different catalytic activities were observed. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|