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Natural Abundance 15 N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine‐Carboxyl‐Linked Immobilized Dirhodium Catalyst
Author(s) -
Gutmann Torsten,
Liu Jiquan,
Rothermel Niels,
Xu Yeping,
Jaumann Eva,
Werner Mayke,
Breitzke Hergen,
Sigurdsson Snorri T.,
Buntkowsky Gerd
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201405043
Subject(s) - chemistry , catalysis , ethyl diazoacetate , heteronuclear molecule , amine gas treating , dimer , styrene , covalent bond , chemical shift , cyclopropanation , mesoporous material , mesoporous silica , nuclear magnetic resonance spectroscopy , stereochemistry , organic chemistry , polymer , copolymer
A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh 2 (OAc) 4 ) units, which are covalently linked to amine‐ and carboxyl‐bifunctionalized mesoporous silica (SBA‐15NH 2 COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis ‐ and trans ‐1‐ethoxycarbonyl‐2‐phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid‐state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal‐enhanced 13 C CP MAS and 15 N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes.