Intramolecular dynamics of tetranuclear iridium carbonyl cluster compounds - Part VI - Derivatives with bidentate ligands. Crystal structures of tetrahedro-decacarbonyl{mu-[1,1-bis(methylthio-chi S)ethane]}tetrairidium ([Ir-4(CO)(10)(mu(2)-(MeS)(2))C

摘要

The disubstituted clusters [Ir-4(CO)(10)(mu(2)-L-L)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (L-L = (MeS)(2)CHMe, cluster 1) or with three edge-bridging COs (L-L = (Ph2P)(2)CHMe, cluster 2; L-L = Ph2P(CH2)(3)PPh2, cluster 3) in the solid state and in solution. A comparative C-13-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 triangular 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. [References: 14]