Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds part VI Derivatives with Bidentate Ligands, Crystal Structures of tetrahedro‐ Decacarbonyl{μ‐[1,1‐bis(methylthio‐χS)ethane]}tetrairidium ([Ir4(CO)10‐(μ2‐(MeS)2CHMe)]), tetrahedro‐Tri‐μ‐carbonylheptacarbonyl{μ‐{ethylidenebis‐ [diphenylphosphine]‐χP:χP'}}tetrairidium ([Ir4(CO)10(μ2‐(Ph2P)2CHMe)]), and tetrahedro‐Tri‐μ‐carbonylheptacarbonyl{μ‐{propane‐1,3‐diylbis[diphenylphosphine]‐χP:χP'}}tetrairidium ([Ir4(CO)10(μ2‐Ph2P(CH2)3PPh2)

Abstract

AbstractThe disubstituted clusters[Ir4(CO)10(μ2‐LL)] with one edge‐bridging ligand have a ground‐state geometry with all COs terminal (LL = (MeS)2CHMe, cluster 1) or with three edge‐bridging COs (LL = (Ph2P)2CHMe, cluste 2; LL =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C‐NMR study of 1–3 shows that their respective ground‐state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry‐go‐round of six COs about a unique trangular face and the rotation of terminal COs about one Ir‐atom. The factors affecting the activation energy of the merry‐go‐round result from the relative bites of the bidentate ligands in the ground‐state geometry, as shown by a comparison of the molecular structures of 2 and 3.