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

Abstract

Abstract The fluxionality of [Ir 4 (CO) 8 (μ 2 ‐CO) 3 L] (L = Br − , I − , SCN − , NO 2 − , P(4‐ClC 6 H 4 ) 3 , PPh 3 , P(4‐MeOC 6 H 4 ) 3 , P(4‐Me 2 NC 6 H 4 ) 3 ), as studied by 2D‐ 13 C‐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 Ir 4 tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir 4 (CO) 7 (μ 2 ‐CO) 3 (PMePh 2 ) 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 [Ir 4 (CO) 10 (μ 2 ‐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 = CH 3 SCH 2 SCH 3 ). 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.