Rhodium Complex with Ethylene Ligands Supported on Highly Dehydroxylated MgO:  Synthesis, Characterization, and Reactivity

Mononuclear rhodium complexes with reactive olefin ligands, supported on MgO powder, were synthesized by chemisorption of Rh(C2H4)2(C5H7O2) and characterized by infrared (IR), 13C MAS NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. IR spectra show that the precursor adsorbe...

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Bibliographic Details
Published in:Langmuir 2006-01, Vol.22 (1), p.490-496
Main Authors: Bhirud, Vinesh A, Ehresmann, Justin O, Kletnieks, Philip W, Haw, James F, Gates, Bruce C
Format: Article
Language:English
Subjects:
ADSORPTION
CARBON MONOXIDE
CARBONYLS
Catalysis
CHEMICAL BONDS
CHEMISORPTION
Chemistry
DISSOCIATION
ETHANE
ETHYLENE
Exact sciences and technology
General and physical chemistry
HYDROGENATION
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
MAGNESIUM OXIDES
national synchrotron light source
RHODIUM COMPLEXES
SUBSTRATES
SYNTHESIS
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
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Summary:Mononuclear rhodium complexes with reactive olefin ligands, supported on MgO powder, were synthesized by chemisorption of Rh(C2H4)2(C5H7O2) and characterized by infrared (IR), 13C MAS NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. IR spectra show that the precursor adsorbed on MgO with dissociation of acetylacetonate ligand from rhodium, with the ethylene ligands remaining bound to the rhodium, as confirmed by the NMR spectra. EXAFS spectra give no evidence of Rh−Rh contributions, indicating that site-isolated mononuclear rhodium species formed on the support. The EXAFS data also show that the mononuclear complex was bonded to the support by two Rh−O bonds, at a distance of 2.18 Å, which is typical of group 8 metals bonded to oxide supports. This is the first simple and nearly uniform supported mononuclear rhodium−olefin complex, and it appears to be a close analogue of molecular catalysts for olefin hydrogenation in solution. Correspondingly, the ethylene ligands bonded to rhodium in the supported complex were observed to react with H2 to form ethane, and the supported complex was catalytically active for the ethylene hydrogenation at 298 K. The ethylene ligands also underwent facile exchange with C2D4, and exposure of the sample to carbon monoxide led to the formation of rhodium gem dicarbonyls.
ISSN:0743-7463
1520-5827
DOI:10.1021/la052268f