Journal article

Authors list: Pietruschka, DS; Kumari, B; Buntkowsky, G; Gutmann, T; Mollenhauer, D

Publication year: 2021

Pages: 6239-6248

Journal: Inorganic Chemistry

Volume number: 60

Issue number: 9

ISSN: 0020-1669

DOI Link: https://doi.org/10.1021/acs.inorgchem.0c03712

Publisher: American Chemical Society

Abstract: 
Dirhodium(II) complexes such as [Rh-2(TFA)(4)] bound to a functionalized mesoporous SBA-15 carrier material have proven to be valuable candidates for heterogeneous catalysis in the field of pharmaceutical synthesis. However, the mechanistic steps of immobilization by linker molecules containing carboxyl or amine functionalities remain the subject of discussion. Here we present a theoretical study of possible mechanistic binding pathways for the [Rh-2(TFA)(4)] complex through model representations of synthetically investigated linkers, namely n-butylamine and n-butyric acid. Experimentally proposed intermediates of the immobilization process are investigated and analyzed by density functional theory calculations to gain insights into structural properties and the influence of solvation. An evaluation of the thermodynamic data for all identified intermediates allowed distinguishing between two possible reaction pathways that are characterized by a first axial complexation of either n-butyric acid or n-butylamine. In agreement with results from NMR spectroscopy, singly or doubly n-butylamine-fixated complexes were found to present possible immobilization products. Initial binding through a carboxy-functionalized linker is proposed as the most favorable reaction pathway for the formation of the mixed linker pattern [Rh-2(TFA)(3)]center dot(n-butylamine)center dot(n-butyrate). The linkers n-butyric acid and n-butyrate, respectively, are found to exhibit an unaltered binding affinity to the dirhodium complex despite their protonation states, indicating invariance to the acidic environment unlike an immobilization by n-butylamine. These results present a theoretical framework for the rationalization of observed product distributions while also providing inspiration and guidance for the preparation of functionalized heterogeneous SBA-15/dirhodium catalyst systems.

Harvard Citation style: Pietruschka, D., Kumari, B., Buntkowsky, G., Gutmann, T. and Mollenhauer, D. (2021) Mechanism of Heterogenization of Dirhodium Catalysts: Insights from DFT Calculations, Inorganic Chemistry, 60(9), pp. 6239-6248. https://doi.org/10.1021/acs.inorgchem.0c03712

APA Citation style: Pietruschka, D., Kumari, B., Buntkowsky, G., Gutmann, T., & Mollenhauer, D. (2021). Mechanism of Heterogenization of Dirhodium Catalysts: Insights from DFT Calculations. Inorganic Chemistry. 60(9), 6239-6248. https://doi.org/10.1021/acs.inorgchem.0c03712