Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge‐bridging bidentate ligands

Abstract

AbstractThe fluxionality of [Ir4(CO)8(μ2‐CO)3L] (L = Br−, I−, SCN−, NO2−, P(4‐ClC6H4)3, PPh3, P(4‐MeOC6H4)3, P(4‐Me2NC6H4)3), as studied by 2D‐13C‐NMR in solution, is due to two successive scrambling processes: the merry‐go‐round of six basal CO's and CO bridging to alternative faces of the Ir4 tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir4(CO)7(μ2‐CO)3(PMePh2)2] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir4(CO)10(μ2‐LL)] with one edge‐bridging ligand have a ground‐state geometry with three edge‐bridging CO's (LL = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (LL = CH3SCH2SCH3). In all cases, the fluxional process of lowest activation energy in the merry‐go‐round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir‐atoms residing on the mirror plane of the unbridged intermediate.