Chemistry: A European Journal 2015-08-24

Design of a Heterogeneous Catalyst Based on Cellulose Nanocrystals for Cyclopropanation: Synthesis and Solid-State NMR Characterization.

Jiquan Liu, Andreas Plog, Pedro Groszewicz, Li Zhao, Yeping Xu, Hergen Breitzke, Annegret Stark, Rudolf Hoffmann, Torsten Gutmann, Kai Zhang, Gerd Buntkowsky

Index: Chemistry 21 , 12414-20, (2015)

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Abstract

Heterogeneous dirhodium(II) catalysts based on environmentally benign and biocompatible cellulose nanocrystals (CNC-Rh2) as support material were obtained by ligand exchange between carboxyl groups on the CNC surface and Rh2(OOCCF3)4, as was confirmed by solid-state (19)F and (13)C NMR spectroscopy. On average, two CF3COO(-) groups are replaced during ligand exchange, which is consistent with quantitative analysis by a combination of (19)F NMR spectroscopy and thermogravimetry. CNC-Rh2 catalysts performed well in a model cyclopropanation reaction, in spite of the low dirhodium(II) content on the CNC surface (0.23 mmol g(-1)). The immobilization through covalent bonding combined with the separate locations of binding positions and active sites of CNC-Rh2 guarantees a high stability against leaching and allows the recovery and reuse of the catalyst during the cyclopropanation reaction.© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.