Carbene derivatives of Ir 4 (CO) 12 ]. Crystal structures of [Ir 4 (CO) 12−x (COCH2CH2O) x ] ( x =1, 2, 3)

[Ir 4 (CO) 12 ] reacts with oxirane in the presence of Br − to give [Ir 4 (CO) 12− x ( ) x ] ( x =1, 2, 3). The structures of three products were established by X-ray diffraction studies. All ligands are in terminal positions in [Ir 4 (CO) 11 ( )]. The di- and tri-substituted cluster compounds have 3 edge-bridging COs and dioxycarbene ligands in axial positions. The fluxional behaviour of these Ir 4 clusters, as studied by 2D 13 C NMR spectroscopy, is due to CO site exchanges localised on one or on three Ir atoms.