American Chemical Society
jp100673y_si_001.pdf (365.13 kB)

Reactions of Highly Uniform Zeolite H-β-Supported Rhodium Complexes: Transient Characterization by Infrared and X-ray Absorption Spectroscopies

Download (365.13 kB)
journal contribution
posted on 2010-05-13, 00:00 authored by Isao Ogino, Bruce C. Gates
A zeolite H-β-supported mononuclear rhodium diethene complex (Rh(C2H4)2{O2Al}, where the braces indicate a part of the zeolite) was formed by the reaction of Rh(acac)(η2-C2H4)2 (acac = acetylacetonate, C5H7O2) with the zeolite. Transient characterization of the sample by X-ray absorption near edge structure (XANES) and infrared (IR) spectroscopies (combined with mass spectrometry of the effluent gas) while the sample was in contact with flowing CO indicates a simple stoichiometric conversion of the supported metal complex into another species, identified by the spectra as the zeolite-supported rhodium gem-dicarbonyl (Rh(CO)2{O2Al}). The sharpness of the νCO bands in the IR spectrum indicates a high degree of uniformity of the supported rhodium gem-dicarbonyl, and isosbestic points in the XANES spectra as the transformation was occurring imply that the rhodium diethene complex was also highly uniform. Spectra similarly show that treatment of the supported rhodium gem-dicarbonyl with flowing C2H4 resulted in another stoichiometrically simple transformation, giving a species suggested to be Rh(C2H4)(CO)2{O2Al}. The intermediate was ultimately transformed when the sample was purged with helium into another highly uniform supported species, inferred on the basis of IR spectra to be Rh(C2H4)(CO){O2Al}. Extended X-ray absorption fine structure spectra characterizing the supported rhodium diethene complex and the species formed from it show how the Rh−O bond distance at the Rh-support interface varied in response to the changes in the ligands bonded to the rhodium.