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

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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.