Iridium-Gold Cluster Compounds: Syntheses, Structures, and an Unusual Ligand-Induced Skeletal Rearrangement

The new iridium-gold complex Ir-4(CO)(11),(Ph)(mu-AuPPh3), 1 was obtained from the reaction of the tetrairidium anion [Ir-4(CO)(11)(Ph)](-) with [Au(PPh3)][NO3]. Two new iridium-gold complexes Ir-4(CO)(10)(AuPPh3)(2), 2, and Ir-4(CO)(11)(AuPPh3)(2), 3, were obtained from the reaction of [HIr4(CO)(11)](-) with [Au(PPh3)][NO3]. Compounds 1-3 were structurally characterized by single crystal X-ray diffraction analyses. Compound 2 adds CO reversibly to form compound 3. In this process, the octahedral Ir4Au2 cluster of 2 is converted into the Au(PPh3)-capped Ir4Au trigonal bipyramidal cluster found in 3. Compounds 2 and 3 have been investigated by DFT computational analyses in order to understand the metal-metal bonding and the mechanism of their interconversion by CO addition and elimination. Compound 2 adds PPh3 to form the compound Ir-4(CO)(10)(PPh3)-(AuPPh3)(2), 4, which is structurally similar to 3. Compound 4 loses CO and benzene when heated to form the compound Ir-4(CO)(9)(mu(3)-PPhC6H4)(AuPPh3)(2), 5, which contains a triply bridging PPhC6H4 ligand.