Synthesis and structural characterization of the isomeric ruthenium-nickel derivatives (η-C₅H₅)NiRu₃(CO)₈(C₆H₉) and related complexes

The synthesis of two isomeric complexes (η-C₅H₅)NiRu₃(CO)₈(C₆H₉) is reported; the structure of one of these derivatives has been determined by X-ray diffraction methods. The two isomers differ for the disposition of the asymmetrical organic ligand with respect to the cluster; this is shown by chemical as well as by ¹H n.m.r. evidence. Crystals of (η-C₅H₅)NiRu₃(CO)₈(C₆H₉) are monoclinic, space P2₁/n, with Z = 4 in a unit cell of dimensions: a = 10.525(9), b = 20.487(13), c = 9.891 (7) Å; β = 92.11(7)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.065 for 2810 independent observed reflections. The complex is characterized by a butterfly arrangement of thre Ru and one Ni atoms with Ni atom occuoying a hinge position; an allylic unit is bound to the four metal atoms, both via MC(σ) and via RuC(π) bonds. The hydride of the starting product is lost during the reaction; some comments on the mechanism of formation of these derivatives are drawn, on the basis of the experimental evidence.