title: Natural abundance 15N NMR by dynamic nuclear polarization: fast analysis of binding sites of a novel amine-carboxyl-linked immobilized dirhodium catalyst.
abstract: A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh2(OAc)4) units, which are covalently linked to amine- and carboxyl-bifunctionalized mesoporous silica (SBA-15-NH2-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.
authors.affiliation: Institute of Physical Chemistry, Technical University Darmstadt, Alarich-Weiss-Straße 8, 64287 Darmstadt (Germany). gutmann@chemie.tu-darmstadt.de.
authors.forename: Torsten
authors.initials: T
authors.lastname: Gutmann
authors.forename: Jiquan
authors.initials: J
authors.lastname: Liu
authors.forename: Niels
authors.initials: N
authors.lastname: Rothermel
authors.forename: Yeping
authors.initials: Y
authors.lastname: Xu
authors.forename: Eva
authors.initials: E
authors.lastname: Jaumann
authors.forename: Mayke
authors.initials: M
authors.lastname: Werner
authors.forename: Hergen
authors.initials: H
authors.lastname: Breitzke
authors.forename: Snorri T
authors.initials: ST
authors.lastname: Sigurdsson
authors.forename: Gerd
authors.initials: G
authors.lastname: Buntkowsky
keywords: NMR spectroscopy; dynamic nuclear polarization; heterogeneous catalysis; hyperpolarization; immobilized catalyst