First evidence for two different mu-eta(1)-eta(1)- and mu-eta(1)-eta(2)-co-ordination modes of the P3C2Bu2t ring of [Fe(eta(5)-P3C2Bu2t)(eta(5)-C5H5)] to a same cluster fragment: Synthesis and characterisation of [Ir-4(CO)(10){Fe(eta(5)-P3C2Bu2t)(eta(5)-C5H5)}] and X-ray molecular structure of the mu-eta(1)-eta(2)-isomer

Investigation of the solution structures of [Ir-4(CO)(11)L] (L = [Fe((eta(5 )-P3C2Bu2t)(eta(5)-C5H5)] (1) and [Fe(eta(5)-P3C2Bu2t)(eta(5)-P2C3Bu3t)] (2 ) by C-13 and P-31 NMR spectroscopy showed that, at 163K, 1 exists in the f orm of two isomers with bridged and non-bridged structures, in a 1:0.15 rat io, respectively, whereas 2 exists only in the bridged form. At RT, 1,2 shi ft of the eta(5)-P3C2Bu2t ring was only observed for compound 2. Where as 2 loses CO readily in solution to give [Ir-4(CO)(10){mu-eta(1)-eta(1)-[Fe(et a(5)-P3C2Bu2t)(eta(5)-P2C3Bu3t)}] (3), activation with Me3NO was necessary to produce [Ir-4(CO)(10){[Fe(eta(5)-P3C2Bu2t)(eta(5)-C5H5)}] (4), obtained in the form of two non-interconverting isomers 4a and 4b, which were not ab le to be separated. A single crystal X-ray diffraction study of isomer 4a e stablished that the [Fe(eta(5)-P3C2Bu2t)(eta(5)-C5H5)] ligand bridges one o f the edges of the Ir4 tetrahedron, interacting via the lone electron pair of one of the adjacent P atoms and in an eta(2)- mode via the P-P double bo nd of the eta(5)-P3C2Bu2t ring and that all CO ligands are terminally bonde d. Variable temperature P-31{H-1} NMR spectroscopy evidenced a fluxional pr ocess involving interactions between the Ir-1 and Ir-2 atoms and the lone p air on P-1, the P-1-P-2 bond, and the lone pair on P-2. According to multin uclear NMR, cluster 4b has similar structure to compound 3, with the eta(5) -P3C2Bu2t ring coordinated in a eta(1)-eta(1)-mode via the two adjacent P a toms, and all CO ligands bonded terminally.