Design and characterization of novel dirhodium coordination polymers - the impact of ligand size on selectivity in asymmetric cyclopropanation

Three chiral dirhodium coordination polymers Rh 2 -L n ( n = 1-3) have been synthesized via ligand exchange between dirhodium trifluoroacetate Rh 2 (TFA) 4 and differently sized chiral dicarboxylic acids derived from l - tert -leucine. SEM images indicate that the Rh 2 -L n ( n = 1-3) polymers have...

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Bibliographic Details
Published in:Catalysis science & technology 2021-05, Vol.11 (1), p.3481-3492
Main Authors: Li, Zhenzhong, Rösler, Lorenz, Wissel, Till, Breitzke, Hergen, Hofmann, Kathrin, Limbach, Hans-Heinrich, Gutmann, Torsten, Buntkowsky, Gerd
Format: Article
Language:English
Subjects:
Asymmetry
Chemical synthesis
Coordination polymers
Dicarboxylic acids
Enantiomers
Lamellar structure
Leucine
Ligands
NMR spectroscopy
Oxidation
Phenylalanine
Polymers
Rhodium
Selectivity
Spectrum analysis
Substitution reactions
Valence
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Summary:Three chiral dirhodium coordination polymers Rh 2 -L n ( n = 1-3) have been synthesized via ligand exchange between dirhodium trifluoroacetate Rh 2 (TFA) 4 and differently sized chiral dicarboxylic acids derived from l - tert -leucine. SEM images indicate that the Rh 2 -L n ( n = 1-3) polymers have a lamellar structure. XPS data demonstrate that the oxidation state of rhodium in the dirhodium nodes is maintained during the synthesis of the polymers. The coordination polymers have been further characterized by FTIR, 1 H → 13 C CP MAS NMR and 19 F MAS NMR spectroscopy to prove the formation of polymers via ligand exchange. Although the quantitative 19 F MAS NMR spectra reveal incomplete ligand substitution in the coordination polymers, these catalysts show excellent activity and selectivity in the asymmetric cyclopropanation reaction between styrene and diazooxindole. In particular, the enantioselectivity has been significantly improved compared with previously designed dirhodium coordination polymers, which were synthesized from aromatic dicarboxylic acids derived from l - phenylalanine. Meanwhile, the dirhodium polymers can be easily recycled five times without significant reduction in their catalytic efficiency. Novel dirhodium coordination polymers are synthesized and characterized by various spectroscopic techniques. The catalysts exhibit good stability and excellent catalytic performance and selectivity in the cyclopropanation of diazooxindoles.
ISSN:2044-4753
2044-4761
DOI:10.1039/d1cy00109d