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

The new iridium–gold complex Ir₄(CO)₁₁(Ph)­(μ-AuPPh₃), 1 was obtained from the reaction of the tetrairidium anion [Ir₄(CO)₁₁(Ph)]⁻ with [Au­(PPh₃)]­[NO₃]. Two new iridium–gold complexes Ir₄(CO)₁₀(AuPPh₃)₂, 2, and Ir₄(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 Ir₄(CO)₁₀(PPh₃)­(AuPPh₃)₂, 4, which is structurally similar to 3. Compound 4 loses CO and benzene when heated to form the compound Ir₄(CO)₉(μ₃-PPhC₆H₄)­(AuPPh₃)₂, 5, which contains a triply bridging PPhC₆H₄ ligand.