Carbene derivatives of Ir4(CO)12]. Crystal structures of [Ir4(CO)12−x()x] (x=1, 2, 3)

[Ir4(CO)12] reacts with oxirane in the presence of Br− to give [Ir4(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 [Ir4(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 Ir4 clusters, as studied by 2D 13C NMR spectroscopy, is due to CO site exchanges localised on one or on three Ir atoms.