Semibridging Phenyl Ligands in Iridium–Copper and Iridium–Silver Cluster Compounds: Synthesis, Structures, and Bonding

Abstract

Reactions of the tetrairidium anion [Ir4(CO)11(Ph)]– (1) with [Cu(NCMe)4][BF4] and Ag[NO3] have yielded the new iridium–copper and iridium–silver complexes Ir4(CO)11(μ-η1-Ph)[μ3-Cu(NCMe)] (2) and [Et4N][{Ir4(CO)11Ph}2(μ4-Ag)] (3), respectively. Compound 2 consists of a tetrahedral Ir4 cluster with a Cu(NCMe) group bridging one of the Ir3 triangular faces of the cluster and a semibridging η1-phenyl ligand that is σ–π-coordinated as a bridge across one of the Ir–Cu bonds. The complex anion of 3 contains two Ir4(CO)11Ph anions linked by a single quadruply bridging silver atom that has adopted a bow-tie geometry between the four iridium atoms. It contains two terminally coordinated σ-phenyl ligands. Compound 3 reacts with a second equivalent of Ag[NO3] to yield the uncharged complex [Ir4(CO)11]2(μ4-Ag)(μ-Ag)(μ3-Ph)(μ-Ph) (4), which contains two Ir4(CO)11 clusters linked by a quadruply bridging silver atom and one triply bridging Ph ligand. The second Ag atom in 4 is an edge bridge on one of the Ir4 clusters, and the second Ph ligand bridges an Ir–Ag bond to it. When it is dissolved in NCMe, compound 4 is split in two and adds 1 equiv of NCMe to the Ag atom in each half to form the compound Ir4(CO)11(η1-Ph)[μ3-Ag(NCMe)] (5; 73% yield). Unlike 2, the phenyl ligand in 5 is terminally coordinated. The NCMe ligand is coordinated to the Ag atom. When 4 was treated with PPh3, the complex Ir4(CO)11(μ-η1-Ph)[μ3-Ag(PPh3)] (6) was obtained in 87% yield. The cluster of 6 is structurally similar to that of 5 except that the phenyl ligand has adopted a semibridging coordination to the silver atom, similar to that found between the phenyl ligand and the copper atom in 2. All of the new products were characterized by single-crystal X-ray diffraction analyses. The bonding of the bridging phenyl ligands to the clusters in 2 and 4 was analyzed by DFT computational methods.