FTIR STUDY OF NOVEL PALLADIUM TRIMETHYLPHOSPHINECARBONYL CLUSTERS ENCAGED IN ZEOLITE-Y

Green palladium trimethylphosphinecarbonyl (TMPC) clusters in zeolite Y have been prepared using a "ship-in-a-bottle" method. Trimethylphosphine (TMP) ligands stabilize palladium clusters of small nuclearity; they preferentially coordinate to the corner palladium atoms. Absorption bands of triply-bonded carbonyl (1886 cm-1) are observed only for samples with initially large palladium nuclearity (n > 4). Bands at 1960 and 1950 cm-1, attributed to doubly-bonded carbonyl in a butterfly configuration, dominate the IR spectra. The palladium core in palladium TMPC clusters is electron-rich, in comparison to palladium single crystals, due to electron donation from phosphorus to the palladium. The spectra of the zeolite encaged clusters differ from those reported for Pd TAPC (A = alkyl such as ethyl and butyl) clusters in solution with nuclearity varying from 4 to 38. Zeolite encaged Pd TMPC clusters are stable at 200-degrees-C in a flow of H2 + CO. At 300-degrees-C, the TMP ligands decompose and poison the palladium particles.