TETRANUCLEAR AND HEXANUCLEAR IRIDIUM CLUSTERS IN NAY ZEOLITE - CHARACTERIZATION BY INFRARED-SPECTROSCOPY

Molecular iridium carbonyl clusters, [Ir4(CO)12] and [Ir6(CO)16], Were synthesized from [Ir(CO)2(acac)] in the cages of NaY zeolite in the presence of CO. The clusters and their reversible decarbonylation and recarbonylation were characterized by infrared spectroscopy at temperatures ranging from -196 to 300-degrees-C. [Ir4(CO)12] in the zeolite was decarbonylated by treatment in H-2 at 300-degrees-C. CO was adsorbed on the decarbonylated clusters at -196-degrees-C, and as the temperature was raised with the sample in the presence of CO, iridium subcarbonyls were formed at about 30-degrees-C. At about 50-degrees-C, the iridium subcarbonyls were converted into [Ir4(CO)12], which was converted at about 125-degrees-C into the isomer of (Ir6(CO)16] with edge-bridging and terminal CO ligands. Each of the isomers of [Ir6(CO)16] was decarbonylated and then recarbonylated as the temperature was increased from -196-degrees-C. The spectra show that the structures formed were the same as those formed by recarbonylation of decarbonylated [Ir4(CO)12]. These results are the first evidence of intermediates in a reversible metal carbonyl cluster formation and indicate the potential for application of zeolite cages as microreactors for chemical synthesis, whereby the chemistry can be characterized in the absence of solvents over wide ranges of temperature.