Heterogeneous self-supported dirhodium(ii) catalysts with high catalytic efficiency in cyclopropanation - a structural study - Liu, Jiquan; Fasel, Claudia; Braga-Groszewicz, Pedro; Rothermel, Niels; Lilly Thankamony, Aany Sofia; Sauer, Grit; Xu, Yeping; Gutmann, Torsten; Buntkowsky, Gerd (Catalysis Science & Technology, 2016)
Catalytically active dirhodium sheet-like coordination polymers are synthesized from their precursors via ligand exchange. The individual lamellae of the dirhodium-bdc frameworks are stacked as parallel sheets, which are randomly oriented or slightly ordered. As inorganic building blocks Rh2(TFA)4 and Rh2(OAc)4, and as organic linker benzene 1,4-dicarboxylate (bdc) are employed. The successful synthesis of the Rh2-bdc(Tf) and Rh2-bdc(Ac) catalysts is proven by ATR-IR, XPS and 13C CP MAS NMR. Residual trifluoroacetate species are investigated by quantitative 19F MAS NMR which further reflects the configuration of trifluoroacetate in the obtained Rh2-bdc(Tf), and defects in the structure. DR-UV-vis and XPS demonstrate that the oxidation state and the Rh-Rh single bond in the dirhodium node are maintained during the ligand substitution process. The stability and reusability of the catalysts are verified by TG-DTA measurements and leaching tests. The catalysts show similar catalytic efficiency as the homogeneous catalyst in the model cyclopropanation between ethyl diazoacetate (EDA) and styrene.
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