First evidence for two different mu-eta1-eta1- and mu-eta1-eta2- co-ordination modes of the P3C2Bu t2 ring of [Fe(eta5-P3C2Bu t2)(eta5-C5H5)] to a same cluster fragment: synthesis and characterisation of [Ir4(CO)10{[Fe(eta5-P3C2Bu t2)(eta5-C5H5)}] and x-ray molecular structure of the mu-eta1-eta2- isomer

investigation of the solution structures of [ir4(co)11l] (l = [fe(h5-p3c2bu t2)(h5-c5h 5)] (1) and [fe(h5-p3c2bu t2)(h5-p2c 3but3)] (2) by 13c and 31p nmr spectroscopy showed that, at 163k, 1 exists in the form of two isomers with bridged and non-bridged structures, in a 1:0.15 ratio, respectively, whereas 2 exists only in the bridged form. at rt, 1,2 shift of the h5-p3c2but 2 ring was only observed for compound 2. where as 2 loses co readily in solution to give [ir4(co)10{m-h1-h 1-[fe(h5-p3c2 but2)(h5-p2 c3but3)}] (3), activation with me3no was necessary to produce [ir4(co)10{[fe(h5-p 3c2but2)(h5-c5h5)}] (4), obtained in the form of two non-interconverting isomers 4a and 4b, which were not able to be separated. a single crystal x-ray diffraction study of isomer 4a established that the [fe(h5-p3c2bu t2)(h5-c5h 5)] ligand bridges one of the edges of the ir4 tetrahedron, interacting via the lone electron pair of one of the adjacent p atoms and in an h2- mode via the p-p double bond of the h5-p3c2but 2 ring and that all co ligands are terminally bonded. variable temperature 31p{1h} nmr spectroscopy evidenced a fluxional process involving interactions between the ir1 and ir2 atoms and the lone pair on p1, the p1-p2 bond, and the lone pair on p2. according to multinuclear nmr, cluster 4b has similar structure to compound 3, with the h5-p3c2but 2 ring co-ordinated in a h1-h1- mode via the two adjacent p atoms, and all co ligands bonded terminally.