REVERSIBLE CARBONYLATION DECARBONYLATION OF ZEOLITE-ENTRAPPED TETRAIRIDIUM CLUSTERS

Iridium carbonyl clusters in NaY zeolite have been prepared from adsorbed [Ir(CO)2(acad)]. The infrared spectra and the yellow color of the sample are consistent with the formation of Ir4(CO)12] in the zeolite cages, presumably the product of reductive carbonylation of the mononuclear precursor. The iridium carbonyl cluster in the zeolite could be decarbonylated by treatment with flowing H-2 at 300-degrees-C and 1 atm and recarbonylated by treatment with CO at 40-degrees-C and 1 atm. The carbonylation/decarbonylation process is reversible, provided that the temperature of the decarbonylation is low, which suggests that the decarbonylated clusters may be Ir4. Treatment of the sample in H-2 at 425-degrees-C and 1 atm led to the formation of particles or iridium metal outside the zeolite pores.