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

摘要

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 C_2H_4 to form Rh(CO)(C_2H_4) complexes. Exposure of the latter to H_2 selectively yields Rh(CO)(H)_x complexes, characterized by a set of well-defined mCO and mRhH bands in their FTIR spectra. The hydride ligands in these complexes can be displaced by CO and N_2 to form Rh(CO)_2 and Rh(CO)(N_2) complexes, respectively. In contrast, C_2H_4 reacts with the hydrides, yielding C_2H_6 and an unstable Rh(CO) intermediate. The latter rapidly reacts with additional gas-phase C_2H_4 to reform the original Rh(CO)(C_2H_4) complex. The Rh(CO)(H)_x species were stable at room temperature under H_2 or He for an extended period of time, but the hydride ligands can be removed at elevated temperatures.