Crystal and molecular structure of decacarbonyl(cyclododecatrienyl)-tetrahedro-tetraruthenium, Ru4(CO)10(C12H16): a ruthenium cluster with a novel allyl bonding system to the cyclododecatrienyl ligand

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Abstract
The X-ray crystal structure of the title compound has been elucidated from photographic data by symbolic addition and Fourier methods, and has been refined by least-squares to R 0·086 for 1102 independent reflections. Crystals are monoclinic, space group P21/n, Z= 4, with a= 14·51, b= 16·71, c= 10·11 Å, β= 93·0°. An open C12 ring is attached to a ‘butterfly’ Ru4 cluster by means of a unique allyl group which is σ bonded to the cluster ‘hinge’ at both ends and π bonded to the cluster ‘tips’ on both sides. There is a further attachment from the ring to one of the butterfly tips by a second (normal)π-allyl group. In the cluster the Ru–Ru bond lengths are all ca. 2·78 Å except for the hinge distance Ru(1)–Ru(2)(2·85 Å). There is no direct Ru–Ru bonding across the wing-tips of the butterfly (distance 3·67 Å), but three carbon atoms [C(1), C(12), and C(11)] of the C12 ring are held symmetrically between the tips of the cluster Ru(3) and Ru(4), and are coplanar with the hinge Ru atoms. The C12 ring is again bonded to Ru(4) through C(5), C(6), and C(7). Ru(4) carries one terminal carbonyl group in an axial position relative to the Ru(1), Ru(2), Ru(4) plane, while each of the other three ruthenium atoms carries three terminal carbonyl groups, of which two are approximately equatorial and one is axial relative to the Ru(1), Ru(2), Ru(3) plane. The nature of the novel bridging allyl group is discussed. Mean Ru–C and C–O distances for the carbonyl ligands are 1·87 and 1·17 Å. All bond lengths have relatively high standard deviations and the details of the geometry of the C12 ring are not well defined.

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