Synthesis and characterization of HY zeolite-supported rhodium carbonyl hydride complexes

FTIR and EXAFS measurements, as well as results of isotope labeling experiments were used to characterize the species formed after grafting a Rh(CO)2(acac) precursor on a highly dealuminated HY zeolite and during subsequent ligand exchange reactions. The Rh(CO)2 species initially formed rapidly react with C2H4 to form Rh(CO)(C2H4) complexes. Exposure of the latter to H2 selectively yields Rh(CO)(H)x complexes, characterized by a set of well-defined νCO and νRhH bands in their FTIR spectra. The hydride ligands in these complexes can be displaced by CO and N2 to form Rh(CO)2 and Rh(CO)(N2) complexes, respectively. In contrast, C2H4 reacts with the hydrides, yielding C2H6 and an unstable Rh(CO) intermediate. The latter rapidly reacts with additional gas-phase C2H4 to reform the original Rh(CO)(C2H4) complex. The Rh(CO)(H)x species were stable at room temperature under H2 or He for an extended period of time, but the hydride ligands can be removed at elevated temperatures.