Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge-bridging bidentate ligands |
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Authors: | Andrs Strawczynski Gianfranco Suardi Renzo Ros Raymond Roulet |
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Institution: | Andrès Strawczynski,Gianfranco Suardi,Renzo Ros,Raymond Roulet |
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Abstract: | The 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. |
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